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Sample records for rapid gradient echo

  1. Shuffled magnetization-prepared multicontrast rapid gradient-echo imaging.

    Science.gov (United States)

    Cao, Peng; Zhu, Xucheng; Tang, Shuyu; Leynes, Andrew; Jakary, Angela; Larson, Peder E Z

    2018-01-01

    To develop a novel acquisition and reconstruction method for magnetization-prepared 3-dimensional multicontrast rapid gradient-echo imaging, using Hankel matrix completion in combination with compressed sensing and parallel imaging. A random k-space shuffling strategy was implemented in simulation and in vivo human experiments at 7 T for 3-dimensional inversion recovery, T2 /diffusion preparation, and magnetization transfer imaging. We combined compressed sensing, based on total variation and spatial-temporal low-rank regularizations, and parallel imaging with pixel-wise Hankel matrix completion, allowing the reconstruction of tens of multicontrast 3-dimensional images from 3- or 6-min scans. The simulation result showed that the proposed method can reconstruct signal-recovery curves in each voxel and was robust for typical in vivo signal-to-noise ratio with 16-times acceleration. In vivo studies achieved 4 to 24 times accelerations for inversion recovery, T2 /diffusion preparation, and magnetization transfer imaging. Furthermore, the contrast was improved by resolving pixel-wise signal-recovery curves after magnetization preparation. The proposed method can improve acquisition efficiencies for magnetization-prepared MRI and tens of multicontrast 3-dimensional images could be recovered from a single scan. Furthermore, it was robust against noise, applicable for recovering multi-exponential signals, and did not require any previous knowledge of model parameters. Magn Reson Med 79:62-70, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  2. T1rho-prepared balanced gradient echo for rapid 3D T1rho MRI.

    Science.gov (United States)

    Witschey, Walter R T; Borthakur, Arijitt; Elliott, Mark A; Fenty, Matthew; Sochor, Matthew A; Wang, Chenyang; Reddy, Ravinder

    2008-09-01

    To develop a T1rho-prepared, balanced gradient echo (b-GRE) pulse sequence for rapid three-dimensional (3D) T1rho relaxation mapping within the time constraints of a clinical exam (prepared, fat saturation, T1rho-preparation, and b-GRE image acquisition was used to obtain 3D volume coverage of the patellofemoral and tibiofemoral cartilage and lower lumbar spine. Multiple T1rho-weighted images at various contrast times (spin-lock pulse duration [TSL]) were used to construct a T1rho relaxation map in both phantoms and in the knee joint and spine in vivo. The transient signal decay during b-GRE image acquisition was corrected using a k-space filter. The T1rho-prepared b-GRE sequence was compared to a standard T1rho-prepared spin echo (SE) sequence and pulse sequence parameters were optimized numerically using the Bloch equations. The b-GRE transient signal decay was found to depend on the initial T1rho-preparation and the corresponding T1rho map was altered by variations in the point spread function with TSL. In a two compartment phantom, the steady state response was found to elevate T1rho from 91.4+/-6.5 to 293.8+/-31 and 66.9+/-3.5 to 661+/-207 with no change in the goodness-of-fit parameter R2. Phase encoding along the longest cartilage dimension and a transient signal decay k-space filter retained T1rho contrast. Measurement of T1rho using the T1rho-prepared b-GRE sequence matches standard T1rho-prepared SE in the medial patellar and lateral patellar cartilage compartments. T1rho-preparedb-GRE T1rho was found to have low interscan variability between four separate scans. Mean patellar cartilage T1rho was elevated compared to femoral and tibial cartilage T1rho. The T1rho-prepared b-GRE acquisition rapidly and reliably accelerates T1rho quantification of tissues offset partially by a TSL-dependent point spread function. Copyright (c) 2008 Wiley-Liss, Inc.

  3. First results in rapid MR imaging of focal liver and spleen lesions using field echos and small angle excitation (gradient echo sequences)

    Energy Technology Data Exchange (ETDEWEB)

    Griebel, J.; Hess, C.F.; Kurtz, B.; Klose, U.; Kueper, K.

    1987-01-01

    15 healthy subjects and 39 patients with focal liver and spleen lesions were examined via MR tomography at 1.5 tesla. Gradient field echos at small angle excitation (< 90/sup 0/) were employed. The imaging time per layer was 10 seconds so that rapid imaging could be carried out at respiratory standstill. This enabled visualisation of liver and spleen without interference by breathing artifacts and with accurate localisation. Focal lesions can be imaged best at low flip-angle pulses (liver) or low to medium-angle pulses (spleen). The primary liver cell carcinoma is visualised as an inhomogeneous structure with similar signal intensity as the surrounding tissue. All other examined liver lesions (metastases, haemangiomas, lymphatic infiltrates, echinococcus cysts, FNH, gummae) showed greater signal intensity than the remaining organ at small angle excitation. Furthermore, contrast reversals were seen at medium-angle pulses. Contrariwise, with the exception of the light-coloured spleen infarcts, spleen lesions (lymphatic infiltrate, Boeck's disease or sarcoidosis) appeared darker at all excitation angles than the surrounding tissue.

  4. Microscopic imaging of slow flow and diffusion: a pulsed field gradient stimulated echo sequence combined with turbo spin echo imaging

    NARCIS (Netherlands)

    Scheenen, T.W.J.; Vergeldt, F.J.; Windt, C.W.; Jager, de P.A.; As, van H.

    2001-01-01

    In this paper we present a pulse sequence that combines a displacement-encoded stimulated echo with rapid sampling of k-space by means of turbo spin echo imaging. The stimulated echo enables the use of long observation times between the two pulsed field gradients that sample q-space completely.

  5. Rapid high-resolution three-dimensional mapping of T1 and age-dependent variations in the non-human primate brain using magnetization-prepared rapid gradient-echo (MPRAGE) sequence

    Science.gov (United States)

    Liu, Junjie V.; Bock, Nicholas A.; Silva, Afonso C.

    2011-01-01

    The use of quantitative T1 mapping in neuroscience and neurology has raised strong interest in the development of T1-mapping techniques that can measure T1 in the whole brain, with high accuracy and precision and within short imaging and computation times. Here, we present a new inversion-recovery (IR) based T1-mapping method using a standard 3D magnetization-prepared rapid gradient-echo (MPRAGE) sequence. By varying only the inversion time (TI), but keeping other parameters constant, MPRAGE image signals become linear to exp(−TI/T1), allowing for accurate T1 estimation without flip angle correction. We also show that acquiring data at just 3 TIs, with the three different TI values optimized, gives maximum T1 precision per unit time, allowing for new efficient approaches to measure and compute T1. We demonstrate the use of our method at 7 Tesla to obtain 3D T1 maps of the whole brain in common marmosets at 0.60 mm resolution and within 11 minutes. T1 maps from the same individuals were highly reproducible across different days. Across subjects, the peak of cerebral gray matter T1 distribution was 1735±52 ms, and the lower edge of cerebral white matter T1 distribution was 1270±43 ms. We found a significant decrease of T1 in both gray and white matter of the marmoset brain with age over a span of 14 years, in agreement with previous human studies. This application illustrates that MPRAGE-based 3D T1 mapping is rapid, accurate and precise, and can facilitate high-resolution anatomical studies in neuroscience and neurological diseases. PMID:21376814

  6. Hematoma volume measurement in gradient echo MRI using quantitative susceptibility mapping.

    Science.gov (United States)

    Wang, Shuo; Lou, Min; Liu, Tian; Cui, Deqi; Chen, Xiaomei; Wang, Yi

    2013-08-01

    A novel quantitative susceptibility mapping (QSM) processing technology has been developed to map tissue susceptibility property without blooming artifacts. We hypothesize that hematoma volume measurement on QSM is independent of imaging parameters, eliminating its echo time dependence on gradient echo MRI. Gradient echo MRI of 16 patients with intracerebral hemorrhage was processed with susceptibility-weighted imaging, R2* (=1/T2*) mapping, and QSM at various echo times. Hematoma volumes were measured from these images. Linear regression of hematoma volume versus echo time showed substantial slopes for gradient echo magnitude (0.45±0.31 L/s), susceptibility-weighted imaging (0.52±0.46), and R2* (0.39±0.30) but nearly zero slope for QSM (0.01±0.05). At echo time=20 ms, hematoma volume on QSM was 0.80× that on gradient echo magnitude image (R2=0.99). QSM can provide reliable measurement of hematoma volume, which can be performed rapidly and accurately using a semiautomated segmentation tool.

  7. Gradient Based Adaptive Algorithm for Echo Cancellation from Recorded Echo Corrupted Speech

    Directory of Open Access Journals (Sweden)

    Upal Mahbub

    2014-01-01

    Full Text Available An offline single channel acoustic echo cancellation (AEC scheme is proposed based on gradient based adaptive least mean squares (LMS algorithm considering a major practical application of echo cancellation system for enhancing recorded echo corrupted speech data. The unavailability of a reference signal makes the problem of single channel adaptive echo cancellation to be extremely difficult to handle. Moreover, continuous feedback of the echo corrupted signal to the input microphone can significantly degrade the quality of the original speech signal and may even result in howling. In order to overcome these problems, in the proposed scheme, the delayed version of the echo corrupted speech signal is considered as a reference. An objective function is thus formulated and thereby a modified LMS update equation is derived, which is shown to converge to the optimum Wiener-Hopf solution. The performance of the proposed method is evaluated in terms of both subjective and objective measures via extensive experimentation on several real-life echo corrupted signals and very satisfactory performance is obtained.

  8. Compensation of Slice Profile Mismatch in Combined Spin- And Gradient-Echo EPI Pulse Sequences

    OpenAIRE

    Schmiedeskamp, Heiko; Straka, Matus; Bammer, Roland

    2011-01-01

    Combined acquisition of gradient-echo and spin-echo signals in MRI time series reveals additional information for perfusion-weighted imaging and functional magnetic resonance imaging due to differences in the sensitivity of gradient-echo and spin-echo measurements to the properties of the underlying vascular architecture. The acquisition of multiple echo trains within one time frame facilitates the simultaneous estimation of the transversal relaxation parameters R2 and R2*. However, the simul...

  9. Inaudible functional MRI using a truly mute gradient echo sequence

    Energy Technology Data Exchange (ETDEWEB)

    Marcar, V.L. [University of Zurich, Department of Psychology, Neuropsychology, Treichlerstrasse 10, 8032 Zurich (Switzerland); Girard, F. [GE Medical Systems SA, 283, rue de la Miniere B.P. 34, 78533 Buc Cedex (France); Rinkel, Y.; Schneider, J.F.; Martin, E. [University Children' s Hospital, Neuroradiology and Magnetic Resonance, Department of Diagnostic Imaging, Steinwiesstrasse 75, 8032 Zurich (Switzerland)

    2002-11-01

    We performed functional MRI experiments using a mute version of a gradient echo sequence on adult volunteers using either a simple visual stimulus (flicker goggles: 4 subjects) or an auditory stimulus (music: 4 subjects). Because the mute sequence delivers fewer images per unit time than a fast echo planar imaging (EPI) sequence, we explored our data using a parametric ANOVA test and a non-parametric Wilcoxon-Mann-Whitney test in addition to performing a cross-correlation analysis. All three methods were in close agreement regarding the location of the BOLD contrast signal change. We demonstrated that, using appropriate statistical analysis, functional MRI using an MR sequence that is acoustically inaudible to the subject is feasible. Furthermore compared with the ''silent'' event-related procedures involving an EPI protocol, our mGE protocol compares favourably with respect to experiment time and the BOLD signal. (orig.)

  10. Simultaneous perfusion and permeability measurements using combined spin- and gradient-echo MRI

    OpenAIRE

    Schmiedeskamp, Heiko; Andre, Jalal B; Straka, Matus; Christen, Thomas; Nagpal, Seema; Recht, Lawrence; Thomas, Reena P; Zaharchuk, Greg; Bammer, Roland

    2013-01-01

    The purpose of this study was to estimate magnetic resonance imaging-based brain perfusion parameters from combined multiecho spin-echo and gradient-echo acquisitions, to correct them for T1-, T2-, and -related contrast agent (CA) extravasation effects, and to simultaneously determine vascular permeability. Perfusion data were acquired using a combined multiecho spin- and gradient-echo (SAGE) echo-planar imaging sequence, which was corrected for CA extravasation effects using pharmacokinetic ...

  11. Functional MRI in human subjects with gradient-echo and spin-echo EPI at 9.4 T.

    Science.gov (United States)

    Budde, Juliane; Shajan, G; Zaitsev, Maxim; Scheffler, Klaus; Pohmann, Rolf

    2014-01-01

    The increased signal-to-noise ratio and blood oxygen level dependent signal at ultra-high field can only help to boost the resolution in functional MRI studies if the spatial specificity of the activation signal is improved. At a field strength of 9.4 T, both gradient-echo and spin-echo based echo-planar imaging were implemented and applied to investigate the specificity of human functional MRI. A finger tapping paradigm was used to acquire functional MRI data with scan parameters similar to standard neuroscientific applications. Spatial resolution, echo, and readout times were varied to determine their influence on the distribution of the blood oxygen level dependent signal. High-resolution co-localized images were used to classify the signal according to its origin in veins or tissue. High-quality activation maps were obtained with both sequences. Signal contributions from tissue were found to be smaller or slightly larger than from veins. Gradient-echo echo-planar imaging yielded lower ratios of micro-/macro-vascular signals of around 0.6 than spin-echo based functional MRI, where this ratio varied between 0.75 and 1.02, with higher values for larger echo and shorter readout time. This study demonstrates the feasibility of human functional MRI at 9.4 T with high spatial specificity. Although venous contributions could not be entirely suppressed, venous effects in spin-echo echo-planar imaging are significantly reduced compared with gradient-echo echo-planar imaging. Copyright © 2013 Wiley Periodicals, Inc.

  12. Improved T2* imaging without increase in scan time: SWI processing of 2D gradient echo.

    Science.gov (United States)

    Soman, S; Holdsworth, S J; Barnes, P D; Rosenberg, J; Andre, J B; Bammer, R; Yeom, K W

    2013-01-01

    2D gradient-echo imaging is sensitive to T2* lesions (hemorrhages, mineralization, and vascular lesions), and susceptibility-weighted imaging is even more sensitive, but at the cost of additional scan time (SWI: 5-10 minutes; 2D gradient-echo: 2 minutes). The long acquisition time of SWI may pose challenges in motion-prone patients. We hypothesized that 2D SWI/phase unwrapped images processed from 2D gradient-echo imaging could improve T2* lesion detection. 2D gradient-echo brain images of 50 consecutive pediatric patients (mean age, 8 years) acquired at 3T were retrospectively processed to generate 2D SWI/phase unwrapped images. The 2D gradient-echo and 2D SWI/phase unwrapped images were compared for various imaging parameters and were scored in a blinded fashion. Of 50 patients, 2D gradient-echo imaging detected T2* lesions in 29 patients and had normal findings in 21 patients. 2D SWI was more sensitive than standard 2D gradient-echo imaging in detecting T2* lesions (P echo images were more sensitive in detecting T2* lesions and delineating normal venous structures and nonpathologic mineralization, and they also helped distinguish calcification at no additional scan time. SWI processing of 2D gradient-echo images may be a useful adjunct in cases in which longer scan times of 3D SWI are difficult to implement.

  13. A simplified spin and gradient echo approach for brain tumor perfusion imaging.

    Science.gov (United States)

    Stokes, Ashley M; Quarles, C Chad

    2016-01-01

    In this study, we propose a simplified acquisition and analysis approach for spin and gradient echo (SAGE)-based dynamic susceptibility-contrast MRI (DSC-MRI) data that is free of contrast agent T1 leakage effects. A five-echo SAGE sequence was used to acquire DSC-MRI data in rat C6 tumors (n = 7). Nonlinear fitting of all echoes was performed to obtain T1-insensitive ΔR2* and ΔR2 time series. The simplified approach, which includes two gradient echoes and one spin echo, was also used to analytically compute T1-insensitive ΔR2* using the two gradient echoes and ΔR2 using all three echoes. The blood flow, blood volume, and vessel size values derived from each method were compared. In all cases, the five-echo and simplified SAGE ΔR2* and ΔR2 were in excellent agreement and demonstrated significant T1 leakage correction compared with the uncorrected single-echo data. The derived hemodynamic parameters for blood volume, blood flow, and vessel size were not significantly different between the two methods. The proposed simplified SAGE technique enables the acquisition of gradient and spin echo DSC-MRI data corrected for T1 leakage effects yields parameters that are in agreement with the five-echo SAGE approach and does not require nonlinear fitting to extract ΔR2* and ΔR2 time series. © 2015 Wiley Periodicals, Inc.

  14. A Simplified Spin and Gradient Echo (SAGE) Approach for Brain Tumor Perfusion Imaging

    Science.gov (United States)

    Stokes, Ashley M.; Quarles, C. Chad

    2014-01-01

    Purpose A simplified acquisition and analysis approach for spin- and gradient-echo (SAGE) based DSC-MRI data that is free of contrast agent T1 leakage effects is proposed. Methods A five-echo SAGE sequence was used to acquire DSC-MRI data in rat C6 tumors (n=7). Non-linear fitting of all echoes was performed to obtain T1-insensitive ΔR2* and ΔR2 time series. The simplified approach, which includes two gradient echoes and one spin echo, was also used to analytically compute T1-insensitive ΔR2*, using the two gradient echoes, and ΔR2, using all three echoes. The blood flow, blood volume and vessel size values derived from each method were compared. Results In all cases, the five-echo and simplified SAGE ΔR2* and ΔR2 were in excellent agreement and demonstrated significant T1-leakage correction compared to the uncorrected single-echo data. The derived hemodynamic parameters for blood volume, blood flow and vessel size were not significantly different between the two methods. Conclusions The proposed simplified SAGE technique enables the acquisition of gradient and spin echo DSC-MRI data corrected for T1 leakage effects, yields parameters that are in agreement with the five echo SAGE, and does not require non-linear fitting to extract ΔR2* and ΔR2 time series. PMID:25753958

  15. Imaging of the brain using the fast-spin-echo and gradient-spin-echo techniques

    Energy Technology Data Exchange (ETDEWEB)

    Umek, W.; Ba-Ssalamah, A.; Prokesch, R. [Department of Radiology, University of Vienna (Austria); Mallek, R.; Heimberger, K. [Division of Neuroradiology, University of Vienna (Austria); Hittmair, K. [Department of Radiology, University of Vienna (Austria)]|[Department of Radiology, AKH Linz (Austria)

    1998-03-27

    The aim of our study was to compare gradient-spin-echo (GRASE) to fast-spin-echo (FSE) sequences for fast T2-weighted MR imaging of the brain. Thirty-one patients with high-signal-intensity lesions on T2-weighted images were examined on a 1.5-T MR system. The FSE and GRASE sequences with identical sequence parameters were obtained and compared side by side. Image assessment criteria included lesion conspicuity, contrast between different types of normal tissue, and image artifacts. In addition, signal-to-noise, contrast-to-noise, and contrast ratios and were determined. The FSE technique demonstrated more lesions than GRASE and with generally better conspicuity. Smaller lesions in particular were better demonstrated on FSE because of lower image noise and slightly weaker image artifacts. Gray-white differentiation was better on FSE. Ferritin and hemosiderin depositions appeared darker on GRASE, which resulted in better contrast. Fatty tissue was less bright on GRASE. With current standard hardware equipment, the FSE technique seems preferable to GRASE for fast T2-weighted routine MR imaging of the brain. For the assessment of hemosiderin or ferritin depositions, GRASE might be considered. (orig.) With 3 figs., 4 tabs., 29 refs.

  16. Compensation of slice profile mismatch in combined spin- and gradient-echo echo-planar imaging pulse sequences.

    Science.gov (United States)

    Schmiedeskamp, Heiko; Straka, Matus; Bammer, Roland

    2012-02-01

    Combined acquisition of gradient-echo and spin-echo signals in MRI time series reveals additional information for perfusion-weighted imaging and functional MRI because of differences in the sensitivity of gradient-echo and spin-echo measurements to the properties of the underlying vascular architecture. The acquisition of multiple echo trains within one time frame facilitates the simultaneous estimation of the transversal relaxation parameters R2 and R2*. However, the simultaneous estimation of these parameters tends to be incorrect in the presence of slice profile mismatches between signal excitation and subsequent refocusing pulses. It is shown here that improvements in pulse design reduced R2 and R2* estimation errors. Further improvements were achieved by augmented parameter estimation through the introduction of an additional parameter δ to correct for discordances in slice profiles to facilitate more quantitative measurements. Moreover, the analysis of time-resolved acquisitions revealed that the temporal stability of R2 estimates could be increased with improved pulse design, counteracting low contrast-to-noise ratios in spin-echo-based perfusion and functional MRI. Copyright © 2011 Wiley Periodicals, Inc.

  17. Volume T1-weighted gradient echo MRI in multiple sclerosis patients.

    Science.gov (United States)

    Shah, M; Ross, J S; VanDyke, C; Rudick, R A; Goodkin, D E; Obuchowski, N; Modic, M T

    1992-01-01

    Three-dimensional (3D) volume turbo fast low angle shot (FLASH) techniques have become available which produce heavily T1-weighted images, similar to inversion recovery scans, utilizing the appropriate flip angle and inversion time. The purpose of this study was to compare the sensitivity of a rapid volume gradient echo technique [3D magnetization prepared rapid acquisition gradient echo (MP RAGE)] in identifying multiple sclerosis (MS) plaques with a conventional T2-weighted spin echo (SE) sequence. Ten patients with clinical MS were evaluated. Patients underwent a routine examination consisting of an axial T2-weighted SE sequence (2,500,22/90) and a coronal 3D MP RAGE, 10/4/10, acquired as 128 two mm partitions. In six patients, area measurements of 22 plaques were determined on both the axial T2-weighted SE examinations and the axial reformatted MP RAGE examinations. The overall number of plaques utilizing each technique was approximately the same. One hundred twenty-two plaques were visualized for the 3D MP RAGE sequence, and 128 plaques for the T2-weighted SE sequence. There were differences in detection of plaques in different regions, with plaques in gray matter better demonstrated utilizing the conventional T2-weighted SE sequence. Plaques in the corpus callosum, pons, and brachia pontis were better demonstrated utilizing 3D MP RAGE. No significant difference was found between the areas measured on the MP RAGE sequence and on the T2-weighted SE sequence. Three-dimensional MP RAGE provides a sensitive and complementary method to conventional T2-weighted SE sequences in the evaluation of patients with MS.

  18. Signal changes in gradient echo images of human brain induced by hypo- and hyperoxia

    DEFF Research Database (Denmark)

    Rostrup, Egill; Larsson, H B; Toft, P B

    1995-01-01

    The effect of hypoxia (inspired oxygen fraction, FiO2 of 10% and 16%) and hyperoxia (FiO2) of 100%) on gradient echo images of the brain using long echo times was investigated in six healthy volunteers (age 24-28 years). Different flip angles were used with an FiO2 of 10% to assess the importance...

  19. A rapid and robust gradient measurement technique using dynamic single-point imaging.

    Science.gov (United States)

    Jang, Hyungseok; McMillan, Alan B

    2017-09-01

    We propose a new gradient measurement technique based on dynamic single-point imaging (SPI), which allows simple, rapid, and robust measurement of k-space trajectory. To enable gradient measurement, we utilize the variable field-of-view (FOV) property of dynamic SPI, which is dependent on gradient shape. First, one-dimensional (1D) dynamic SPI data are acquired from a targeted gradient axis, and then relative FOV scaling factors between 1D images or k-spaces at varying encoding times are found. These relative scaling factors are the relative k-space position that can be used for image reconstruction. The gradient measurement technique also can be used to estimate the gradient impulse response function for reproducible gradient estimation as a linear time invariant system. The proposed measurement technique was used to improve reconstructed image quality in 3D ultrashort echo, 2D spiral, and multi-echo bipolar gradient-echo imaging. In multi-echo bipolar gradient-echo imaging, measurement of the k-space trajectory allowed the use of a ramp-sampled trajectory for improved acquisition speed (approximately 30%) and more accurate quantitative fat and water separation in a phantom. The proposed dynamic SPI-based method allows fast k-space trajectory measurement with a simple implementation and no additional hardware for improved image quality. Magn Reson Med 78:950-962, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  20. Combined Spin-And Gradient-Echo Perfusion-Weighted Imaging

    Science.gov (United States)

    Schmiedeskamp, Heiko; Straka, Matus; Newbould, Rexford D.; Zaharchuk, Greg; Andre, Jalal B.; Olivot, Jean-Marc; Moseley, Michael E.; Albers, Gregory W.; Bammer, Roland

    2011-01-01

    In this study, a spin- and gradient-echo echo-planar imaging (SAGE EPI) MRI pulse sequence is presented that allows simultaneous measurements of gradient-echo and spin-echo dynamic susceptibility-contrast perfusion-weighted imaging (DSC-PWI) data. Following signal excitation, five EPI readout trains were acquired using SAGE EPI, all of them with echo times of less than 100 ms. Contrast agent concentrations in brain tissue were determined based on absolute R2* and R2 estimates rather than relative changes in the signals of individual echo trains, producing T1-independent DSC-PWI data. Moreover, this acquisition technique enabled vessel size imaging through the simultaneous quantification of R2* and R2, without an increase in acquisition time. In this work, the concepts of the SAGE EPI pulse sequence and results in stroke and tumor imaging are presented. Overall, SAGE EPI combined the advantages of higher sensitivity of gradient-echo DSC-PWI acquisitions to the contrast agent passage with the better selectivity of spin-echo DSC-PWI measurements to the microvasculature. PMID:22114040

  1. Gradient-echo MR imaging of the cervical spine: evaluation of extradural disease.

    Science.gov (United States)

    VanDyke, C; Ross, J S; Tkach, J; Masaryk, T J; Modic, M T

    1989-08-01

    A prospective study was undertaken on 204 consecutive patients comparing low flip angle gradient-echo and T1-weighted spin-echo techniques in the MR evaluation of cervical extradural disease. Four patient groups were studied with varying gradient-echo TEs (6 or 13 msec) and flip angles (10 degrees or 60 degrees). Images were evaluated independently for contrast behavior and anatomy, then directly compared for conspicuity of lesions. The FLASH sequences (especially with a 10 degrees flip angle) produced better conspicuity of disease in half the imaging time. T1-weighted spin-echo sequences were more sensitive to marrow changes and intradural disease. The short TE sequence (6 msec) did not produce any diagnostic advantage over the longer TE sequence (13 msec). A fast and sensitive MR examination for cervical extradural disease combines a sagittal T1-weighted spin-echo acquisition with sagittal and axial FLASH 10 degrees sequences.

  2. Gradient echo single scan inversion recovery: application to proton and fluorine relaxation studies.

    Science.gov (United States)

    Pavuluri, KowsalyaDevi; Ramanathan, K V

    2016-02-01

    Single scan longitudinal relaxation measurement experiments enable rapid estimation of the spin-lattice relaxation time (T1 ) as the time series of spin relaxation is encoded spatially in the sample at different slices resulting in an order of magnitude saving in time. We consider here a single scan inversion recovery pulse sequence that incorporates a gradient echo sequence. The proposed pulse sequence provides spectra with significantly enhanced signal to noise ratio leading to an accurate estimation of T1 values. The method is applicable for measuring a range of T1 values, thus indicating the possibility of routine use of the method for several systems. A comparative study of different single scan methods currently available is presented, and the advantage of the proposed sequence is highlighted. The possibility of the use of the method for the study of cross-correlation effects for the case of fluorine in a single shot is also demonstrated. Copyright © 2015 John Wiley & Sons, Ltd.

  3. Simultaneous perfusion and permeability measurements using combined spin- and gradient-echo MRI.

    Science.gov (United States)

    Schmiedeskamp, Heiko; Andre, Jalal B; Straka, Matus; Christen, Thomas; Nagpal, Seema; Recht, Lawrence; Thomas, Reena P; Zaharchuk, Greg; Bammer, Roland

    2013-05-01

    The purpose of this study was to estimate magnetic resonance imaging-based brain perfusion parameters from combined multiecho spin-echo and gradient-echo acquisitions, to correct them for T₁₋, T₂₋, and T₂₋*-related contrast agent (CA) extravasation effects, and to simultaneously determine vascular permeability. Perfusion data were acquired using a combined multiecho spin- and gradient-echo (SAGE) echo-planar imaging sequence, which was corrected for CA extravasation effects using pharmacokinetic modeling. The presented method was validated in simulations and brain tumor patients, and compared with uncorrected single-echo and multiecho data. In the presence of CA extravasation, uncorrected single-echo data resulted in underestimated CA concentrations, leading to underestimated single-echo cerebral blood volume (CBV) and mean transit time (MTT). In contrast, uncorrected multiecho data resulted in overestimations of CA concentrations, CBV, and MTT. The correction of CA extravasation effects resulted in CBV and MTT estimates that were more consistent with the underlying tissue characteristics. Spin-echo perfusion data showed reduced large-vessel blooming effects, facilitating better distinction between increased CBV due to active tumor progression and elevated CBV due to the presence of cortical vessels in tumor proximity. Furthermore, extracted permeability parameters were in good agreement with elevated T1-weighted postcontrast signal values.

  4. Phase alterations of spin echoes by motion along magnetic field gradients.

    Science.gov (United States)

    Wendt, R E; Murphy, P H; Ford, J J; Bryan, R N; Burdine, J A

    1985-12-01

    Using a Taylor series expansion of the phase shift of a moving isochromatic spin group in the presence of a magnetic field gradient, the refocusing effects of the Carr-Purcell-Meiboom-Gill pulse sequence on stationary nuclei and those with constant, rectilinear velocity are readily demonstrated. Continuing the analysis to higher orders of motion reveals that nuclei with a constant, rectilinear acceleration have a phase shift at the spin echoes which increases linearly with echo number. Constant, rectilinear jerk (the time rate of change of acceleration) leads to an increase in phase shift from echo to echo which is quadratic in nature with an overlying reduction of the odd-numbered echoes by a constant amount. Motion parameters may be measured by parameter identification techniques. These principles may be applied to phase-sensitive NMR imaging.

  5. The effect of echo-sampling strategy on the accuracy of out-of-phase and in-phase multi-echo gradient-echo magnetic resonance imaging hepatic fat fraction estimation

    Science.gov (United States)

    Levin, Yakir S.; Yokoo, Takeshi; Wolfson, Tanya; Gamst, Anthony C.; Collins, Julie; Achmad, Emil A.; Hamilton, Gavin; Middleton, Michael S.; Loomba, Rohit; Sirlin, Claude B.

    2013-01-01

    Purpose To assess the effect of echo-sampling strategy on the accuracy of out-of-phase (OP) and in-phase (IP) multi-echo gradient-echo magnetic resonance imaging (MRI) hepatic fat fraction (FF) estimation, using MR spectroscopy (MRS) proton density FF (PDFF) as a reference standard. Materials and Methods In this IRB-approved, HIPAA-compliant prospective study, 84 subjects underwent proton MRS and non-T1-weighted gradient-echo imaging of the liver at 3T. Imaging data were collected at 16 nominally OP and IP echo times (TEs). MRI-FF was estimated while varying two echo-sampling parameters (number of consecutive echoes, starting echo number). For each combination of these parameters, MRI-FF estimation accuracy was assessed with slope, intercept, average bias and R2 from a linear regression of MRS-PDFF on MRI-FF. The relationship between accuracy metrics and echo-sampling parameters was assessed by Spearman rank correlation. Results For FF calculations using 3-16 echoes and a starting echo number of 1, the intercept ranged from 0.0046 to 0.0124, slope from 0.941 to 0.96, average bias from 0.0034 to 0.0078, and R2 from 0.968 to 0.976. All four accuracy metrics were the best with the 3- and 4- echo calculations and worsened progressively with increasing number of echoes. For a given number of echoes, there was an overall trend toward decreasing accuracy as starting echo number increased. Spearman correlation coefficients between starting echo number and intercept, slope, average bias and R2 were 0.911, -.64, -.889 and -.954, respectively, indicating progressive loss of accuracy in each case. Conclusion Multi-echo OP and IP imaging provided high FF estimation accuracy. Accuracy was highest using the earliest 3 or 4 echoes. Incorporation of additional echoes or delaying the starting echo number progressively reduced accuracy. PMID:23720420

  6. Designing hyperbolic secant excitation pulses to reduce signal dropout in gradient-echo echo-planar imaging.

    Science.gov (United States)

    Wastling, Stephen J; Barker, Gareth J

    2015-09-01

    To design hyperbolic secant (HS) excitation pulses to reduce signal dropout in the orbitofrontal and inferior temporal regions in gradient-echo echo-planar imaging (GE-EPI) for functional MRI (fMRI) applications. An algorithm based on Bloch simulations optimizes the HS pulse parameters needed to give the desired signal response across the range of susceptibility gradients observed in the human head (approximately ±250 μT·m(-1) ). The impact of the HS pulse on the signal, temporal signal-to-noise ratio, blood oxygen level-dependent (BOLD) sensitivity, and ability to detect resting state BOLD signal changes was assessed in six healthy male volunteers at 3T. The optimized HS pulse (μ = 4.25, β = 3040 Hz, A0 = 12.3 μT, Δf = 4598 Hz) had a near uniform signal response for through-plane susceptibility gradients in the range ±250 μT·m(-1) . Signal, temporal signal-to-noise ratio, BOLD sensitivity, and the detectability of resting state networks were all partially recovered in the orbitofrontal and inferior temporal regions; however, there were signal losses of up to 50% in regions of homogeneous field (and signal loss from in-plane susceptibility gradients remained). The HS pulse reduced signal dropout and could be used to acquire task and resting state fMRI data without loss of spatial coverage or temporal resolution. © 2014 Wiley Periodicals, Inc.

  7. Diuretic-enhanced gadolinium excretory MR urography: comparison of conventional gradient-echo sequences and echo-planar imaging.

    Science.gov (United States)

    Nolte-Ernsting, C C; Tacke, J; Adam, G B; Haage, P; Jung, P; Jakse, G; Günther, R W

    2001-01-01

    The aim of this study was to investigate the utility of different gadolinium-enhanced T1-weighted gradient-echo techniques in excretory MR urography. In 74 urologic patients, excretory MR urography was performed using various T1-weighted gradient-echo (GRE) sequences after injection of gadolinium-DTPA and low-dose furosemide. The examinations included conventional GRE sequences and echo-planar imaging (GRE EPI), both obtained with 3D data sets and 2D projection images. Breath-hold acquisition was used primarily. In 20 of 74 examinations, we compared breath-hold imaging with respiratory gating. Breath-hold imaging was significantly superior to respiratory gating for the visualization of pelvicaliceal systems, but not for the ureters. Complete MR urograms were obtained within 14-20 s using 3D GRE EPI sequences and in 20-30 s with conventional 3D GRE sequences. Ghost artefacts caused by ureteral peristalsis often occurred with conventional 3D GRE imaging and were almost completely suppressed in EPI sequences (p urography, the entire pelvicaliceal system was imaged by acquisition of a fast single-slice sequence and the conventional 2D GRE technique provided superior morphological accuracy than 2D GRE EPI projection images (p excretory MR urography especially in old or critically ill patients unable to suspend breathing for more than 20 s. Conventional GRE sequences are superior to EPI in high-resolution detail MR urograms and in projection imaging.

  8. Diuretic-enhanced gadolinium excretory MR urography: comparison of conventional gradient-echo sequences and echo-planar imaging

    Energy Technology Data Exchange (ETDEWEB)

    Nolte-Ernsting, C.C.A.; Tacke, J.; Adam, G.B.; Haage, P.; Guenther, R.W. [Univ. of Technology, Aachen (Germany). Dept. of Diagnostic Radiology; Jung, P.; Jakse, G. [Univ. of Technology, Aachen (Germany). Dept. of Urology

    2001-01-01

    The aim of this study was to investigate the utility of different gadolinium-enhanced T1-weighted gradient-echo techniques in excretory MR urography. In 74 urologic patients, excretory MR urography was performed using various T1-weighted gradient-echo (GRE) sequences after injection of gadolinium-DTPA and low-dose furosemide. The examinations included conventional GRE sequences and echo-planar imaging (GRE EPI), both obtained with 3D data sets and 2D projection images. Breath-hold acquisition was used primarily. In 20 of 74 examinations, we compared breath-hold imaging with respiratory gating. Breath-hold imaging was significantly superior to respiratory gating for the visualization of pelvicaliceal systems, but not for the ureters. Complete MR urograms were obtained within 14-20 s using 3D GRE EPI sequences and in 20-30 s with conventional 3D GRE sequences. Ghost artefacts caused by ureteral peristalsis often occurred with conventional 3D GRE imaging and were almost completely suppressed in EPI sequences (p < 0.0001). Susceptibility effects were more pronounced on GRE EPI MR urograms and calculi measured 0.8-21.7% greater in diameter compared with conventional GRE sequences. Increased spatial resolution degraded the image quality only in GRE-EPI urograms. (orig.)

  9. Microscopic Displacement Imaging with Pulsed Field Gradient Turbo Spin-Echo NMR

    NARCIS (Netherlands)

    Scheenen, T.W.J.; Dusschoten, van D.; Jager, de P.A.; As, van H.

    2000-01-01

    We present a pulse sequence that enables the accurate and spatially resolved measurements of the displacements of spins in a variety of (biological) systems. The pulse sequence combines pulsed field gradient (PFG) NMR with turbo spin–echo (TSE) imaging. It is shown here that by ensuring that the

  10. MRI appearances of the asymptomatic patellar tendon on gradient echo imaging

    Energy Technology Data Exchange (ETDEWEB)

    Reiff, D.B. [Dept. of Diagnostic Radiology, St. George`s Hospital, London (United Kingdom); Heenan, S.D. [Dept. of Diagnostic Radiology, St. George`s Hospital, London (United Kingdom); Heron, C.W. [Dept. of Diagnostic Radiology, St. George`s Hospital, London (United Kingdom)

    1995-02-01

    Thickening of the patellar tendon and foci of increased signal intensity have been described as characteristic features of ``jumper`s knee`` (chronic patellar tendinitis) on magnetic resonance imaging (MRI). It was our impression that such appearances may be seen in the patellar tendons of patients without symptoms referable to the anterior part of the knee when using gradient echo images. The appearances of the asymptomatic patellar tendon on three-dimensional gradient echo sequences were studied by retrospectively reviewing the images of 60 patients, none of whom had symptoms related to the anterior part of the knee. The anteroposterior width of the patellar tendon was measured at three levels (superior, middle and inferior) on the central sagittal image of a gradient echo sequence. The relative signal intensities at the same levels were recorded. In 97% of subjects the superior part of the tendon was wider than the midpoint, and in 97% the inferior part was wider than the midpoint. The range of widths was wide, and there was no significant difference between sexes. Focal increased signal intensity in the superior part was shown in 75%, and in the inferior part in 43%. The asymptomatic patellar tendon shows uniform thickness throughout most of its length, but there are focal expansions at the proximal and distal ends. It usually demonstrates low signal on MRI, but may contain foci of increased signal intensity at either or both ends when imaged on gradient-echo sequences. (orig.)

  11. Effect of echo-sampling strategy on the accuracy of out-of-phase and in-phase multiecho gradient-echo MRI hepatic fat fraction estimation.

    Science.gov (United States)

    Levin, Yakir S; Yokoo, Takeshi; Wolfson, Tanya; Gamst, Anthony C; Collins, Julie; Achmad, Emil A; Hamilton, Gavin; Middleton, Michael S; Loomba, Rohit; Sirlin, Claude B

    2014-03-01

    To assess the effect of echo-sampling strategy on the accuracy of out-of-phase (OP) and in-phase (IP) multiecho gradient-echo magnetic resonance imaging (MRI) hepatic fat fraction (FF) estimation, using MR spectroscopy (MRS) proton density FF (PDFF) as a reference standard. In this Institutional Review Board (IRB)-approved, Health Insurance Portability and Accountability Act (HIPAA)-compliant prospective study, 84 subjects underwent proton MRS and non-T1 -weighted gradient-echo imaging of the liver at 3T. Imaging data were collected at 16 nominally OP and IP echo times (TEs). MRI-FF was estimated while varying two echo-sampling parameters (number of consecutive echoes, starting echo number). For each combination of these parameters, MRI-FF estimation accuracy was assessed with slope, intercept, average bias, and R2 from a linear regression of MRS-PDFF on MRI-FF. The relationship between accuracy metrics and echo-sampling parameters was assessed by Spearman rank correlation. For FF calculations using 3-16 echoes and a starting echo number of 1, the intercept ranged from 0.0046 to 0.0124, slope from 0.941 to 0.96, average bias from 0.0034 to 0.0078, and R2 from 0.968 to 0.976. All four accuracy metrics were the best with the 3- and 4-echo calculations and worsened progressively with an increasing number of echoes. For a given number of echoes, there was an overall trend toward decreasing accuracy as starting echo number increased. Spearman correlation coefficients between starting echo number and intercept, slope, average bias, and R2 were 0.911, -0.64, -0.889, and -0.954, respectively, indicating progressive loss of accuracy in each case. Multiecho OP and IP imaging provided high FF estimation accuracy. Accuracy was highest using the earliest 3 or 4 echoes. Incorporation of additional echoes or delaying the starting echo number progressively reduced accuracy. Copyright © 2013 Wiley Periodicals, Inc.

  12. Echo

    Energy Technology Data Exchange (ETDEWEB)

    Harvey, Dustin Yewell [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-01-25

    This document is a white paper marketing proposal for Echo™ is a data analysis platform designed for efficient, robust, and scalable creation and execution of complex workflows. Echo’s analysis management system refers to the ability to track, understand, and reproduce workflows used for arriving at results and decisions. Echo improves on traditional scripted data analysis in MATLAB, Python, R, and other languages to allow analysts to make better use of their time. Additionally, the Echo platform provides a powerful data management and curation solution allowing analysts to quickly find, access, and consume datasets. After two years of development and a first release in early 2016, Echo is now available for use with many data types in a wide range of application domains. Echo provides tools that allow users to focus on data analysis and decisions with confidence that results are reported accurately.

  13. Accelerated Parameter Mapping of Multiple-Echo Gradient-Echo Data Using Model-Based Iterative Reconstruction.

    Science.gov (United States)

    Zimmermann, Markus; Abbas, Zaheer; Dzieciol, Krzysztof; Shah, N Jon

    2018-02-01

    A new reconstruction method, coined MIRAGE, is presented for accurate, fast, and robust parameter mapping of multiple-echo gradient-echo (MEGE) imaging, the basis sequence of novel quantitative magnetic resonance imaging techniques such as water content and susceptibility mapping. Assuming that the temporal signal can be modeled as a sum of damped complex exponentials, MIRAGE performs model-based reconstruction of undersampled data by minimizing the rank of local Hankel matrices. It further incorporates multi-channel information and spatial prior knowledge. Finally, the parameter maps are estimated using nonlinear regression. Simulations and retrospective undersampling of phantom and in vivo data affirm robustness, e.g., to strong inhomogeneity of the static magnetic field and partial volume effects. MIRAGE is compared with a state-of-the-art compressed sensing method, -ESPIRiT. Parameter maps estimated from reconstructed data using MIRAGE are shown to be accurate, with the mean absolute error reduced by up to 50% for in vivo results. The proposed method has the potential to improve the diagnostic utility of quantitative imaging techniques that rely on MEGE data.

  14. Importance of T2*-weighted gradient-echo MRI for diagnosis of cortical vein thrombosis

    Energy Technology Data Exchange (ETDEWEB)

    Fellner, Franz A. [Institut fuer Radiologie, Landes-Nervenklinik Wagner Jauregg, Linz (Austria) and Zentrales Radiologie Institut, Allgemeines Krankenhaus der Stadt Linz, Krankenhausstr. 9, 4020 Linz (Austria)]. E-mail: franz.fellner@akh.linz.at; Fellner, Claudia [Institut fuer Radiologie, Landes-Nervenklinik Wagner Jauregg, Linz (Austria); Aichner, Franz T. [Abteilung fuer Neurologie, Landes-Nervenklinik Wagner-Jauregg, Linz (Austria); Moelzer, Guenther [Institut fuer Radiologie, Landes-Nervenklinik Wagner Jauregg, Linz (Austria)

    2005-11-01

    We examined six patients with isolated venous thrombosis (n = 2), or venous thrombosis combined with sinus thrombosis (n = 4) (CVT). The clinical symptoms were non-specific (acute cephalea, paresis, epileptic seizure, progressive speech disorder). All examinations were performed on a 1.5 T system (Magnetom Symphony, Siemens, Erlangen, Germany), maximum gradient field strength 30 mT/m, minimal gradient rise time 450 {mu}s, according to the following protocol: Transverse T2-weighted turbo spin-echo (TSE), fluid attenuated inversion recovery (FLAIR), T1-weighted spin-echo (SE), before and after administration of contrast medium, T2*-weighted conventional gradient-echo (GRE), T2*-weighted spin-echo echo planar imaging (SE EPI), both without and with diffusion weighting as well as two-dimensional (2D) venous time-of-flight (TOF) MRA. The venous thromboses were best detectable in the T2*-weighted conventional GRE sequence in all patients. In two patients, the CVT was discernible only in this sequence. The sinus thrombosis was well discernible only in the T2*-weighted GRE sequence in only one case; in the remaining cases it was detectable only with difficulty. For these cases, other sequences such as SE, diffusion-weighted, or 2D-TOF-MRA sequence were superior. The T2*-weighted conventional GRE sequence was superior to the T2*-weighted SE EPI sequence in all patients. To sum up, it can be concluded, that T2*-weighted conventional GRE sequences are possibly the best method of detection of acute cortical vein thromboses. Therefore, it seems to be of benefit to integrate a T2*-weighted conventional GRE sequence into the MR-protocol for the diagnosis of isolated cortical vein thrombosis.

  15. MR contrast of ferritin and hemosiderin in the brain: comparison among gradient-echo, conventional spin-echo and fast spin-echo sequences

    Energy Technology Data Exchange (ETDEWEB)

    Haque, Tabassum Laz; Miki, Yukio E-mail: mikiy@kuhp.kyoto-u.ac.jp; Kanagaki, Mitsunori; Takahashi, Takahiro; Yamamoto, Akira; Konishi, Junya; Nozaki, Kazuhiko; Hashimoto, Nobuo; Konishi, Junji

    2003-12-01

    Objective: To compare the magnetic resonance image contrasts due to ferritin and hemosiderin in the brain tissue among different pulse sequences. Materials and methods: Fourteen patients with cavernous hemangioma in the brain prospectively underwent MR imaging with T2*-weighted gradient-echo (GRE), T2-weighted conventional spin-echo (SE) and fast spin-echo (FSE) sequences. The relative contrast ratios (CRs) of the hypointense part of cavernous hemangioma, globus pallidus and putamen to the deep frontal white matter were measured on each pulse sequence and statistically analyzed using analysis of variance followed by paired t-test. Results: In the hypointense part of cavernous hemangioma, relative CRs were significantly lower on T2*-weighted GRE than on T2-weighted SE images (P=0.0001), and on T2-weighted SE than on T2-weighted FSE images (P=0.0001). In the globus pallidus, relative CRs were significantly lower on T2-weighted SE than on T2*-weighted GRE images (P=0.002), and on T2*-weighted GRE than on T2-weighted FSE images (P=0.0002). In the putamen, relative CRs were significantly lower on T2-weighted SE than on T2*-weighted GRE images (P=0.001), and there was no significant difference between CRs on T2-weighted FSE and T2*-weighted GRE images (P=0.90). Conclusion: Hemosiderin showed best image contrast on T2*-weighted GRE images but ferritin showed more prominent image contrast on T2-weighted SE than on T2*-weighted GRE images, which may help to determine an appropriate pulse sequence in neurological diseases associated with excessive ferritin accumulation.

  16. MR contrast of ferritin and hemosiderin in the brain: comparison among gradient-echo, conventional spin-echo and fast spin-echo sequences.

    Science.gov (United States)

    Haque, Tabassum Laz; Miki, Yukio; Kanagaki, Mitsunori; Takahashi, Takahiro; Yamamoto, Akira; Konishi, Junya; Nozaki, Kazuhiko; Hashimoto, Nobuo; Konishi, Junji

    2003-12-01

    To compare the magnetic resonance image contrasts due to ferritin and hemosiderin in the brain tissue among different pulse sequences. Fourteen patients with cavernous hemangioma in the brain prospectively underwent MR imaging with T2*-weighted gradient-echo (GRE), T2-weighted conventional spin-echo (SE) and fast spin-echo (FSE) sequences. The relative contrast ratios (CRs) of the hypointense part of cavernous hemangioma, globus pallidus and putamen to the deep frontal white matter were measured on each pulse sequence and statistically analyzed using analysis of variance followed by paired t-test. In the hypointense part of cavernous hemangioma, relative CRs were significantly lower on T2*-weighted GRE than on T2-weighted SE images (P=0.0001), and on T2-weighted SE than on T2-weighted FSE images (P=0.0001). In the globus pallidus, relative CRs were significantly lower on T2-weighted SE than on T2*-weighted GRE images (P=0.002), and on T2*-weighted GRE than on T2-weighted FSE images (P=0.0002). In the putamen, relative CRs were significantly lower on T2-weighted SE than on T2*-weighted GRE images (P=0.001), and there was no significant difference between CRs on T2-weighted FSE and T2*-weighted GRE images (P=0.90). Hemosiderin showed best image contrast on T2*-weighted GRE images but ferritin showed more prominent image contrast on T2-weighted SE than on T2*-weighted GRE images, which may help to determine an appropriate pulse sequence in neurological diseases associated with excessive ferritin accumulation.

  17. Mixed model phase evolution for correction of magnetic field inhomogeneity effects in 3D quantitative gradient echo-based MRI

    DEFF Research Database (Denmark)

    Fatnassi, Chemseddine; Boucenna, Rachid; Zaidi, Habib

    2017-01-01

    PURPOSE: In 3D gradient echo magnetic resonance imaging (MRI), strong field gradients B0macro are visually observed at air/tissue interfaces. At low spatial resolution in particular, the respective field gradients lead to an apparent increase in intravoxel dephasing, and subsequently, to signal l......), but appearing more robust in regions with low SNR (SNR research applications still require further investigation....

  18. Diagnostic accuracy of dual-echo (in- and opposed-phase) T1-weighted gradient recalled echo for detection and grading of hepatic iron using quantitative and visual assessment

    Energy Technology Data Exchange (ETDEWEB)

    Schieda, Nicola; Ramanathan, Subramaniyan; Ryan, John; Khanna, Maneesh; Virmani, Vivek; Avruch, Leonard [The University of Ottawa, The Ottawa Hospital, Ottawa, Ontario (Canada)

    2014-07-15

    Detection and quantification of hepatic iron with dual-echo gradient recalled echo (GRE) has been proposed as a rapid alternative to other magnetic resonance imaging (MRI) techniques. Co-existing steatosis and T1 weighting are limitations. This study assesses the accuracy of routine dual-echo GRE. Between 2010 and 2013, 109 consecutive patients underwent multi-echo (ME) MRI and dual-echo GRE for quantification of hepatic iron. Liver iron concentration (LIC) was calculated from ME-MRI. Relative signal intensity (RSI) and fat signal fraction (FSF) were calculated from dual-echo GRE. Four radiologists subjectively evaluated dual-echo GRE (±subtraction). Diagnostic accuracy was compared between techniques and correlated with biopsy using Fisher's exact test, Spearman correlation and regression. The sensitivity of visual detection of iron ranged from 48 to 55 %. Subtraction did not increase sensitivity (p < 0.001). Inter-observer variability was substantial (κ = 0.72). The specificity of visual detection of iron approached 100 % with false-positive diagnoses observed using subtraction. LIC showed a higher correlation with histopathological iron grade (r = 0.94, p < 0.001) compared with RSI (r = 0.65, p = 0.02). Univariate regression showed an association between RSI and LIC (B = 0.98, p < 0.001, CI 0.73-1.23); however, the association was not significant with multi-variate regression including FSF (p = 0.28). Dual-echo GRE has low sensitivity for hepatic iron. Subtraction imaging can result in false-positive diagnoses. (orig.)

  19. Prognostic value of gradient echo T2* sequences for brain MR imaging in preterm infants

    Energy Technology Data Exchange (ETDEWEB)

    Bruine, Francisca T. de; Berg-Huysmans, Annette A. van den; Buchem, Mark A. van; Grond, Jeroen van der [Leiden University Medical Center, Department of Radiology, PO Box 9600, Leiden (Netherlands); Steggerda, Sylke J.; Leijser, Lara M.; Rijken, Monique [Leiden University Medical Center, Department of Pediatrics, subdivision of Neonatology, Leiden (Netherlands); Wezel-Meijler, Gerda van [Leiden University Medical Center, Department of Pediatrics, subdivision of Neonatology, Leiden (Netherlands); Isala Hospital, Department of Neonatology, Zwolle (Netherlands)

    2014-03-15

    Gradient echo T2*-W sequences are more sensitive than T2-W spin-echo sequences for detecting hemorrhages in the brain. The aim of this study is to correlate presence of hemosiderin deposits in the brain of very preterm infants (gestational age <32 weeks) detected by T2*-W gradient echo MRI to white matter injury and neurodevelopmental outcome at 2 years. In 101 preterm infants, presence and location of hemosiderin were assessed on T2*-W gradient echo MRI performed around term-equivalent age (range: 40-60 weeks). White matter injury was defined as the presence of >6 non-hemorrhagic punctate white matter lesions (PWML), cysts and/or ventricular dilatation. Six infants with post-hemorrhagic ventricular dilatation detected by US in the neonatal period were excluded. Infants were seen for follow-up at 2 years. Univariate and regression analysis assessed the relation between presence and location of hemosiderin, white matter injury and neurodevelopmental outcome. In 38/95 (40%) of the infants, hemosiderin was detected. Twenty percent (19/95) of the infants were lost to follow-up. There was a correlation between hemosiderin in the ventricular wall with >6 PWML (P < 0.001) and cysts (P < 0.001) at term-equivalent age, and with a lower psychomotor development index (PDI) (P=0.02) at 2 years. After correcting for known confounders (gestational age, gender, intrauterine growth retardation and white matter injury), the correlation with PDI was no longer significant. The clinical importance of detecting small hemosiderin deposits is limited as there is no independent association with neurodevelopmental outcome. (orig.)

  20. Prognostic value of gradient echo T2* sequences for brain MR imaging in preterm infants.

    Science.gov (United States)

    de Bruïne, Francisca T; Steggerda, Sylke J; van den Berg-Huysmans, Annette A; Leijser, Lara M; Rijken, Monique; van Buchem, Mark A; van Wezel-Meijler, Gerda; van der Grond, Jeroen

    2014-03-01

    Gradient echo T2*-W sequences are more sensitive than T2-W spin-echo sequences for detecting hemorrhages in the brain. The aim of this study is to correlate presence of hemosiderin deposits in the brain of very preterm infants (gestational age hemosiderin were assessed on T2*-W gradient echo MRI performed around term-equivalent age (range: 40-60 weeks). White matter injury was defined as the presence of >6 non-hemorrhagic punctate white matter lesions (PWML), cysts and/or ventricular dilatation. Six infants with post-hemorrhagic ventricular dilatation detected by US in the neonatal period were excluded. Infants were seen for follow-up at 2 years. Univariate and regression analysis assessed the relation between presence and location of hemosiderin, white matter injury and neurodevelopmental outcome. In 38/95 (40%) of the infants, hemosiderin was detected. Twenty percent (19/95) of the infants were lost to follow-up. There was a correlation between hemosiderin in the ventricular wall with >6 PWML (P hemosiderin deposits is limited as there is no independent association with neurodevelopmental outcome.

  1. Short echo time proton spectroscopy of the brain in healthy volunteers using an insert gradient head coil

    DEFF Research Database (Denmark)

    Gideon, P; Danielsen, E R; Schneider, M

    1995-01-01

    An insert gradient head coil with built-in X, Y, and Z gradients was used for localized proton spectroscopy in the brain of healthy volunteers, using short echo time stimulated echo acquisition mode (STEAM) sequences. Volume of interest size was 3.4 ml, repetition time was 6.0 s, and echo times w....../glutamate and myo-inositols. These compounds were more prominent within grey matter than within white matter. Rough estimations of metabolite concentrations using water as an internal standard were in good agreement with previous reports....

  2. MRI detection of hypointense brain lesions in patients with multiple sclerosis: T1 spin-echo vs. gradient-echo

    Energy Technology Data Exchange (ETDEWEB)

    Dupuy, Sheena L.; Tauhid, Shahamat; Kim, Gloria; Chu, Renxin; Tummala, Subhash [Departments of Neurology, Brigham and Women' s Hospital, Laboratory for Neuroimaging Research, Partners MS Center, Harvard Medical School, Boston, MA (United States); Hurwitz, Shelley [Departments of Medicine, Brigham and Women' s Hospital, Harvard Medical School, Boston, MA (United States); Bakshi, Rohit, E-mail: rbakshi@bwh.harvard.edu [Departments of Neurology, Brigham and Women' s Hospital, Laboratory for Neuroimaging Research, Partners MS Center, Harvard Medical School, Boston, MA (United States); Departments of Radiology, Brigham and Women' s Hospital, Harvard Medical School, Boston, MA (United States)

    2015-08-15

    Highlights: • Compared T1SE and T1GE in detecting hypointense brain lesions in MS patients. • T1GE detected a higher cerebral lesion volume and number than T1SE. • T1SE correlated significantly with disability, while T1GE did not. • Hypointense lesions on T1SE and T1GE are not interchangeable in patients with MS. - Abstract: Objective: Compare T1 spin-echo (T1SE) and T1 gradient-echo (T1GE) sequences in detecting hypointense brain lesions in multiple sclerosis (MS). Background: Chronic hypointense lesions on T1SE MRI scans are a surrogate of severe demyelination and axonal loss in MS. The role of T1GE images in the detection of such lesions has not been clarified. Design/methods: In 45 patients with MS [Expanded Disability Status Scale (EDSS) score (mean ± SD) 3.5 ± 2.0; 37 relapsing-remitting (RR); 8 secondary progressive (SP)], cerebral T1SE, T1GE, and T2-weighted fluid-attenuated inversion-recovery (FLAIR) images were acquired on a 1.5 T MRI scanner. Images were re-sampled to axial 5 mm slices before directly comparing lesion detectability using Jim (v.7, Xinapse Systems). Statistical methods included Wilcoxon signed rank tests to compare sequences and Spearman correlations to test associations. Results: Considering the entire cohort, T1GE detected a higher lesion volume (5.90 ± 6.21 vs. 4.17 ± 4.84 ml, p < 0.0001) and higher lesion number (27.82 ± 20.66 vs. 25.20 ± 20.43, p < 0.05) than T1SE. Lesion volume differences persisted when considering RR and SP patients separately (both p < 0.01). A higher lesion number by T1GE was seen only in the RR group (p < 0.05). When comparing correlations between lesion volume and overall neurologic disability (EDSS score), T1SE correlated with EDSS (Spearman r = 0.29, p < 0.05) while T1GE (r = 0.23, p = 0.13) and FLAIR (r = 0.24, p = 0.12) did not. Conclusion: Our data suggest that hypointense lesions on T1SE and T1GE are not interchangeable in patients with MS. Based on these results, we hypothesize that T1GE

  3. Whole brain, high resolution multiband spin-echo EPI fMRI at 7 T: a comparison with gradient-echo EPI using a color-word Stroop task

    NARCIS (Netherlands)

    Boyacioglu, R.; Schulz, J.; Müller, N.C.J.; Koopmans, P.J.; Barth, M.; Norris, D.G.

    2014-01-01

    A whole brain, multiband spin-echo (SE) echo planar imaging (EPI) sequence employing a high spatial (1.5 mm isotropic) and temporal (TR of 2 s) resolution was implemented at 7 T. Its overall performance (tSNR, sensitivity and CNR) was assessed and compared to a geometrically matched gradient-echo

  4. Whole brain, high resolution multiband spin-echo EPI fMRI at 7 T: A comparison with gradient-echo EPI using a color-word Stroop task

    NARCIS (Netherlands)

    Boyacioglu, R.; Schulz, J.; Müller, N.C.J.; Koopmans, P.J.; Barth, M.; Norris, David Gordon

    2014-01-01

    A whole brain, multiband spin-echo (SE) echo planar imaging (EPI) sequence employing a high spatial (1.5 mm isotropic) and temporal (TR of 2 s) resolution was implemented at 7 T. Its overall performance (tSNR, sensitivity and CNR) was assessed and compared to a geometrically matched gradient-echo

  5. Gradient-recalled echo sequences in direct shoulder MR arthrography for evaluating the labrum

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Marc J.; Motamedi, Kambiz; Chow, Kira; Seeger, Leanne L. [David Geffen School of Medicine at UCLA, Department of Radiology, 200 UCLA Medical Plaza, Suite 165-59, Box 956952, Los Angeles, CA (United States)

    2008-01-15

    The purpose of this study was to determine the utility of fat-suppressed gradient-recalled echo (GRE) compared with conventional spin echo T1-weighted (T1W) sequences in direct shoulder MR arthrography for evaluating labral tears. Three musculoskeletal radiologists retrospectively reviewed MR arthrograms performed over a 12-month period for which surgical correlation was available. Of 180 serial arthrograms, 31 patients had surgery with a mean of 48 days following imaging. Paired coronal oblique and axial T1W or GRE sequences were analyzed by consensus for labral tear (coronal oblique two-dimensional multi-echo data image combination, 2D MEDIC; and axial three-dimensional double-echo steady-state, 3D DESS; Siemens MAGNETOM Sonata 1.5-T MR system). Interpretations were correlated with operative reports. Of 31 shoulders, 25 had labral tears at surgery. The GRE sequences depicted labral tears in 22, while T1W images depicted tears in 16 (sensitivity 88% versus 64%; p < 0.05). Subdividing the labrum, GRE was significantly more sensitive for the posterior labrum (75% versus 25%; p < 0.05) with a trend toward greater sensitivity at the anterior labrum (78% versus 56%; p = 0.157) but not significantly different for the superior labrum (50% versus 57%; p > 0.7). Specificities were somewhat lower for GRE. Thin section GRE sequences are more sensitive than T1W for the detection of anterior and posterior labral tears. As the specificity of GRE was lower, it should be considered as an adjunctive imaging sequence that may improve depiction of labral tears, particularly smaller tears, in routine MR arthrography protocols. (orig.)

  6. Exact algebraization of the signal equation of spoiled gradient echo MRI

    Energy Technology Data Exchange (ETDEWEB)

    Dathe, Henning [Department of Orthodontics, Biomechanics Group, University Medical Centre, Goettingen (Germany); Helms, Gunther, E-mail: ghelms@gwdg.d [MR-Research in Neurology and Psychiatry, University Medical Centre, Goettingen (Germany)

    2010-08-07

    The Ernst equation for Fourier transform nuclear magnetic resonance (MR) describes the spoiled steady-state signal created by periodic partial excitation. In MR imaging (MRI), it is commonly applied to spoiled gradient-echo acquisition in the steady state, created by a small flip angle {alpha} at a repetition time TR much shorter than the longitudinal relaxation time T{sub 1}. We describe two parameter transformations of {alpha} and TR/T{sub 1}, which render the Ernst equation as a low-order rational function. Computer algebra can be readily applied for analytically solving protocol optimization, as shown for the dual flip angle experiment. These transformations are based on the half-angle tangent substitution and its hyperbolic analogue. They are monotonic and approach identity for small {alpha} and small TR/T{sub 1} with a third-order error. Thus, the exact algebraization can be readily applied to fast gradient echo MRI to yield a rational approximation in {alpha} and TR/T{sub 1}. This reveals a fundamental relationship between the square of the flip angle and TR/T{sub 1} which characterizes the Ernst angle, constant degree of T{sub 1}-weighting and the influence of the local radio-frequency field.

  7. Assessment of a combined spin- and gradient-echo (SAGE) DSC-MRI method for preclinical neuroimaging.

    Science.gov (United States)

    Stokes, Ashley M; Skinner, Jack T; Quarles, C Chad

    2014-12-01

    The goal of this study was to optimize and validate a combined spin- and gradient-echo (SAGE) sequence for dynamic susceptibility-contrast magnetic resonance imaging to obtain hemodynamic parameters in a preclinical setting. The SAGE EPI sequence was applied in phantoms and in vivo rat brain (normal, tumor, and stroke tissue). Partial and full Fourier encoding schemes were implemented and characterized. Maps of cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), vessel size index (VSI), volume transfer constant (K(trans)), and volume fraction of the extravascular extracellular space (ve) were obtained. Partial Fourier encoding provided shortened echo times with acceptable signal-to-noise ratio and temporal stability, thus enabling reliable characterization of T2, T2(*) and T1 in both phantoms and rat brain. The hemodynamic parameters CBV, CBF, and MTT for gradient-echo and spin-echo contrast were determined in tumor and stroke; VSI, K(trans), and ve were also computed in tumor tissue. The SAGE EPI sequence allows the acquisition of multiple gradient- and spin-echoes, from which measures of perfusion, permeability, and vessel size can be obtained in a preclinical setting. Partial Fourier encoding can be used to minimize SAGE echo times and reliably quantify dynamic T2 and T2(*) changes. This acquisition provides a more comprehensive assessment of hemodynamic status in brain tissue with vascular and perfusion abnormalities. Copyright © 2014 Elsevier Inc. All rights reserved.

  8. Gaussian phase distribution approximations for oscillating gradient spin echo diffusion MRI.

    Science.gov (United States)

    Ianuş, Andrada; Siow, Bernard; Drobnjak, Ivana; Zhang, Hui; Alexander, Daniel C

    2013-02-01

    Oscillating gradients provide an optimal probe of small pore sizes in diffusion MRI. While sinusoidal oscillations have been popular for some time, recent work suggests additional benefits of square or trapezoidal oscillating waveforms. This paper presents analytical expressions of the free and restricted diffusion signal for trapezoidal and square oscillating gradient spin echo (OGSE) sequences using the Gaussian phase distribution (GPD) approximation and generalises existing similar expressions for sinusoidal OGSE. Accurate analytical models are necessary for exploitation of these pulse sequences in imaging studies, as they allow model fitting and parameter estimation in reasonable computation times. We evaluate the accuracy of the approximation against synthesised data from the Monte Carlo (MC) diffusion simulator in Camino and Callaghan's matrix method and we show that the accuracy of the approximation is within a few percent of the signal, while providing several orders of magnitude faster computation. Moreover, since the expressions for trapezoidal wave are complex, we test sine and square wave approximations to the trapezoidal OGSE signal. The best approximations depend on the gradient amplitude and the oscillation frequency and are accurate to within a few percent. Finally, we explore broader applications of trapezoidal OGSE, in particular for non-model based applications, such as apparent diffusion coefficient estimation, where only sinusoidal waveforms have been considered previously. We show that with the right apodisation, trapezoidal waves also have benefits by virtue of the higher diffusion weighting they provide compared to sinusoidal gradients. Copyright © 2012 Elsevier Inc. All rights reserved.

  9. Gradient Spin Echo (GraSE) imaging for fast myocardial T2 mapping.

    Science.gov (United States)

    Sprinkart, Alois M; Luetkens, Julian A; Träber, Frank; Doerner, Jonas; Gieseke, Jürgen; Schnackenburg, Bernhard; Schmitz, Georg; Thomas, Daniel; Homsi, Rami; Block, Wolfgang; Schild, Hans; Naehle, Claas P

    2015-02-12

    Quantitative Cardiovascular Magnetic Resonance (CMR) techniques have gained high interest in CMR research. Myocardial T2 mapping is thought to be helpful in diagnosis of acute myocardial conditions associated with myocardial edema. In this study we aimed to establish a technique for myocardial T2 mapping based on gradient-spin-echo (GraSE) imaging. The local ethics committee approved this prospective study. Written informed consent was obtained from all subjects prior to CMR. A modified GraSE sequence allowing for myocardial T2 mapping in a single breath-hold per slice using ECG-triggered acquisition of a black blood multi-echo series was developed at 1.5 Tesla. Myocardial T2 relaxation time (T2-RT) was determined by maximum likelihood estimation from magnitude phased-array multi-echo data. Four GraSE sequence variants with varying number of acquired echoes and resolution were evaluated in-vitro and in 20 healthy volunteers. Inter-study reproducibility was assessed in a subset of five volunteers. The sequence with the best overall performance was further evaluated by assessment of intra- and inter-observer agreement in all volunteers, and then implemented into the clinical CMR protocol of five patients with acute myocardial injury (myocarditis, takotsubo cardiomyopathy and myocardial infarction). In-vitro studies revealed the need for well defined sequence settings to obtain accurate T2-RT measurements with GraSE. An optimized 6-echo GraSE sequence yielded an excellent agreement with the gold standard Carr-Purcell-Meiboom-Gill sequence. Global myocardial T2 relaxation times in healthy volunteers was 52.2 ± 2.0 ms (mean ± standard deviation). Mean difference between repeated examinations (n = 5) was -0.02 ms with 95% limits of agreement (LoA) of [-4.7; 4.7] ms. Intra-reader and inter-reader agreement was excellent with mean differences of -0.1 ms, 95% LoA = [-1.3; 1.2] ms and 0.1 ms, 95% LoA = [-1.5; 1.6] ms, respectively (n = 20). In

  10. Visual Perceptual Echo Reflects Learning of Regularities in Rapid Luminance Sequences.

    Science.gov (United States)

    Chang, Acer Y-C; Schwartzman, David J; VanRullen, Rufin; Kanai, Ryota; Seth, Anil K

    2017-08-30

    A novel neural signature of active visual processing has recently been described in the form of the "perceptual echo", in which the cross-correlation between a sequence of randomly fluctuating luminance values and occipital electrophysiological signals exhibits a long-lasting periodic (∼100 ms cycle) reverberation of the input stimulus (VanRullen and Macdonald, 2012). As yet, however, the mechanisms underlying the perceptual echo and its function remain unknown. Reasoning that natural visual signals often contain temporally predictable, though nonperiodic features, we hypothesized that the perceptual echo may reflect a periodic process associated with regularity learning. To test this hypothesis, we presented subjects with successive repetitions of a rapid nonperiodic luminance sequence, and examined the effects on the perceptual echo, finding that echo amplitude linearly increased with the number of presentations of a given luminance sequence. These data suggest that the perceptual echo reflects a neural signature of regularity learning.Furthermore, when a set of repeated sequences was followed by a sequence with inverted luminance polarities, the echo amplitude decreased to the same level evoked by a novel stimulus sequence. Crucially, when the original stimulus sequence was re-presented, the echo amplitude returned to a level consistent with the number of presentations of this sequence, indicating that the visual system retained sequence-specific information, for many seconds, even in the presence of intervening visual input. Altogether, our results reveal a previously undiscovered regularity learning mechanism within the human visual system, reflected by the perceptual echo.SIGNIFICANCE STATEMENT How the brain encodes and learns fast-changing but nonperiodic visual input remains unknown, even though such visual input characterizes natural scenes. We investigated whether the phenomenon of "perceptual echo" might index such learning. The perceptual echo is a

  11. Voxel spread function method for correction of magnetic field inhomogeneity effects in quantitative gradient-echo-based MRI.

    Science.gov (United States)

    Yablonskiy, Dmitriy A; Sukstanskii, Alexander L; Luo, Jie; Wang, Xiaoqi

    2013-11-01

    Macroscopic magnetic field inhomogeneities adversely affect different aspects of MRI images. In quantitative MRI when the goal is to quantify biological tissue parameters, they bias and often corrupt such measurements. The goal of this article is to develop a method for correction of macroscopic field inhomogeneities that can be applied to a variety of quantitative gradient-echo-based MRI techniques. We have reanalyzed a basic theory of gradient echo MRI signal formation in the presence of background field inhomogeneities and derived equations that allow for correction of magnetic field inhomogeneity effects based on the phase and magnitude of gradient echo data. We verified our theory by mapping effective transverse relaxation rate in computer simulated, phantom, and in vivo human data collected with multi-gradient echo sequences. The proposed technique takes into account voxel spread function effects and allowed obtaining virtually free from artifacts effective transverse relaxation rate maps for all simulated, phantom and in vivo data except of the edge areas with very steep field gradients. The voxel spread function method, allowing quantification of tissue specific effective transverse relaxation rate-related tissue properties, has a potential to breed new MRI biomarkers serving as surrogates for tissue biological properties similar to longitudinal and transverse relaxation rate constants widely used in clinical and research MRI. Copyright © 2012 Wiley Periodicals, Inc.

  12. Compressed sensing fMRI using gradient-recalled echo and EPI sequences.

    Science.gov (United States)

    Zong, Xiaopeng; Lee, Juyoung; John Poplawsky, Alexander; Kim, Seong-Gi; Ye, Jong Chul

    2014-05-15

    Compressed sensing (CS) may be useful for accelerating data acquisitions in high-resolution fMRI. However, due to the inherent slow temporal dynamics of the hemodynamic signals and concerns of potential statistical power loss, the CS approach for fMRI (CS-fMRI) has not been extensively investigated. To evaluate the utility of CS in fMRI application, we systematically investigated the properties of CS-fMRI using computer simulations and in vivo experiments of rat forepaw sensory and odor stimulations with gradient-recalled echo (GRE) and echo planar imaging (EPI) sequences. Various undersampling patterns along the phase-encoding direction were studied and k-t FOCUSS was used as the CS reconstruction algorithm, which exploits the temporal redundancy of images. Functional sensitivity, specificity, and time courses were compared between fully-sampled and CS-fMRI with reduction factors of 2 and 4. CS-fMRI with GRE, but not with EPI, improves the statistical sensitivity for activation detection over the fully sampled data when the ratio of the fMRI signal change to noise is low. CS improves the temporal resolution and reduces temporal noise correlations. While CS reduces the functional response amplitudes, the noise variance is also reduced to make the overall activation detection more sensitive. Consequently, CS is a valuable fMRI acceleration approach, especially for GRE fMRI studies. Copyright © 2014 Elsevier Inc. All rights reserved.

  13. MRI of the cervical spine with 3D gradient echo sequence at 3 T: initial experience.

    Science.gov (United States)

    Xiao, L; Siu, C W J; Yeung, K; Leung, A; Yuen, M K; Wong, Y C

    2015-09-01

    The aim of this study was to compare three-dimensional (3D) high resolution T2*-weighted gradient echo (3D FFE) magnetic resonance (MR) sequence with conventional 2D T2-weighted turbo spin echo (TSE) MR sequence for imaging of the cervical spine, especially to assess the detectability of the internal anatomy of the cervical spinal cord, i.e. to distinguish the grey and white matter. Fifteen volunteers were examined at 3.0T MR unit. Signal-to-noise (SNR), contrast-to-noise (CNR) and image homogeneity were evaluated. In the visual analysis, the visibility of anatomical structures of the cervical spine and artifacts were assessed. The nonparametric method of paired sample t-test was adopted to evaluate the differences between the sequences. The 3D FFE sequence provided better results for CNR, cerebrospinal fluid (CSF) versus white matter, grey matter, disk and bone. Moreover, it yielded good results for the CNR grey matter versus white matter. The butterfly-shaped "H" is clearly displayed in the 3D FFE sequence. The statistical analysis revealed the statistically significant difference between the 2D TSE and 3D FFE sequences for the contrast of CSF versus spinal cord (both grey matter and white matter). The 3D FFE sequence in MR imaging of the cervical spinal cord is superior in delineation of spinal cord anatomical structures compared to 2D TSE sequence. Copyright © 2015 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

  14. Detection and quantification of regional cortical gray matter damage in multiple sclerosis utilizing gradient echo MRI

    Directory of Open Access Journals (Sweden)

    Jie Wen

    2015-01-01

    Full Text Available Cortical gray matter (GM damage is now widely recognized in multiple sclerosis (MS. The standard MRI does not reliably detect cortical GM lesions, although cortical volume loss can be measured. In this study, we demonstrate that the gradient echo MRI can reliably and quantitatively assess cortical GM damage in MS patients using standard clinical scanners. High resolution multi-gradient echo MRI was used for regional mapping of tissue-specific MRI signal transverse relaxation rate values (R2* in 10 each relapsing–remitting, primary-progressive and secondary-progressive MS subjects. A voxel spread function method was used to correct artifacts induced by background field gradients. R2* values from healthy controls (HCs of varying ages were obtained to establish baseline data and calculate ΔR2* values – age-adjusted differences between MS patients and HC. Thickness of cortical regions was also measured in all subjects. In cortical regions, ΔR2* values of MS patients were also adjusted for changes in cortical thickness. Symbol digit modalities (SDMT and paced auditory serial addition (PASAT neurocognitive tests, as well as Expanded Disability Status Score, 25-foot timed walk and nine-hole peg test results were also obtained on all MS subjects. We found that ΔR2* values were lower in multiple cortical GM and normal appearing white matter (NAWM regions in MS compared with HC. ΔR2* values of global cortical GM and several specific cortical regions showed significant (p < 0.05 correlations with SDMT and PASAT scores, and showed better correlations than volumetric measures of the same regions. Neurological tests not focused on cognition (Expanded Disability Status Score, 25-foot timed walk and nine-hole peg tests showed no correlation with cortical GM ΔR2* values. The technique presented here is robust and reproducible. It requires less than 10 min and can be implemented on any MRI scanner. Our results show that quantitative tissue-specific R2

  15. Correction of gradient echo images for first and second order macroscopic signal dephasing using phase derivative mapping.

    Science.gov (United States)

    de Leeuw, H; Bakker, C J G

    2012-03-01

    Gradient echo techniques are often hampered by signal dephasing due to macroscopic phase perturbations because of system imperfections (shimming) or object induced perturbations of the magnetic field (hemorrhagic lesions, calcified tissue, air-tissue interfaces). Many techniques have been proposed to reduce the effects of macroscopic phase variations. Among these techniques are tuned pulse sequences, fitting techniques and reconstruction algorithms. These methods, however, suffer from one or more of the following drawbacks: they require longer acquisition times, require additional acquisitions, compensate only locally, can only be applied to multi-gradient echo data or may result in inaccurate results. In this work a generally applicable post-processing technique is presented to evaluate and compensate signal alterations invoked by first and second order macroscopic phase incoherences. In this technique, the derivatives of the signal phase are determined by applying the Fourier derivative theorem on the complex data. As a result, the phase derivatives are obtained without phase unwrapping and without compromising the resolution. The method is validated for single and multi-echo acquisitions by experiments on a co-axial cylinder phantom with known macroscopic field disturbances. The potential of the method is demonstrated on a multi-gradient echo acquisition on the head of a human volunteer. In general a first order correction is shown to be sufficient, however higher order correction is found to be beneficial near sharp transitions of the magnetic field. Copyright © 2011 Elsevier Inc. All rights reserved.

  16. Effect of magnetic susceptibility contrast medium on myocardial signal intensity with fast gradient-recalled echo and spin-echo MR imaging: initial experience in humans.

    Science.gov (United States)

    Sakuma, H; O'Sullivan, M; Lucas, J; Wendland, M F; Saeed, M; Dulce, M C; Watson, A; Bleyl, K L; LaFrance, N D; Higgins, C B

    1994-01-01

    To show the effect of dysprosium diethylenetriaminepentaacetic acid bis-methylamine injection on the images of normal human myocardium. T2-sensitive fast gradient-recalled echo (GRE) (repetition time [TR], 10.8 msec; echo time [TE], 4.2 msec) and spin-echo (SE) (TR, three RR intervals; TE, 60 msec) magnetic resonance (MR) imaging with driven equilibrium-preparation pulse was used to produce T2 contrast material enhancement. The contrast agent was injected into 12 healthy subjects at doses of 0.05, 0.1, 0.2, 0.4, and 0.6 mmol/kg. Driven equilibrium-prepared GRE images showed a transient decrease of myocardial signal intensity at doses of 0.2-0.6 mmol/kg. Postcontrast T2-weighted SE images showed a myocardial signal attenuation (30%-45% decrease) at a dose of 0.4 mmol/kg or higher. Dynamic MR imaging with a magnetic susceptibility contrast medium can be used to monitor the first pass of contrast media through human myocardium with a conventional MR imager and a fast GRE sequence.

  17. Noise analysis in fast magnetic resonance electrical impedance tomography (MREIT) based on spoiled multi gradient echo (SPMGE) pulse sequence.

    Science.gov (United States)

    Oh, Tong In; Jeong, Woo Chul; Kim, Ji Eun; Sajib, Saurav Z K; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je

    2014-08-21

    Magnetic resonance electrical impedance tomography (MREIT) is a promising non-invasive method to visualize a static cross-sectional conductivity and/or current density image by injecting low frequency currents. MREIT measures one component of the magnetic flux density caused by the injected current using a magnetic resonance (MR) scanner. For practical in vivo implementations of MREIT, especially for soft biological tissues where the MR signal rapidly decays, it is crucial to develop a technique for optimizing the magnetic flux density signal by the injected current while maintaining spatial-resolution and contrast. We design an MREIT pulse sequence by applying a spoiled multi-gradient-echo pulse sequence (SPMGE) to the injected current nonlinear encoding (ICNE), which fully injects the current at the end of the read-out gradient. The applied ICNE-SPMGE pulse sequence maximizes the duration of injected current almost up to a repetition time by measuring multiple magnetic flux density data. We analyze the noise level of measured magnetic flux density with respect to the pulse width of injection current and T*(2) relaxation time. In due consideration of the ICNE-SPMGE pulse sequence, using a reference information of T*(2) values in a local region of interest by a short pre-scan data, we predict the noise level of magnetic flux density to be measured for arbitrary repetition time TR. Results from phantom experiment demonstrate that the proposed method can predict the noise level of magnetic flux density for an appropriate TR = 40 ms using a reference scan for TR = 75 ms. The predicted noise level was compared with the noise level of directly measured magnetic flux density data.

  18. Mixed model phase evolution for correction of magnetic field inhomogeneity effects in 3D quantitative gradient echo-based MRI.

    Science.gov (United States)

    Fatnassi, Chemseddine; Boucenna, Rachid; Zaidi, Habib

    2017-07-01

    In 3D gradient echo magnetic resonance imaging (MRI), strong field gradients B0macro are visually observed at air/tissue interfaces. At low spatial resolution in particular, the respective field gradients lead to an apparent increase in intravoxel dephasing, and subsequently, to signal loss or inaccurate R2* estimates. If the strong field gradients are measured, their influence can be removed by postprocessing. Conventional corrections usually assume a linear phase evolution with time. For high macroscopic gradient inhomogeneities near the edge of the brain and at the paranasal sinuses, however, this assumption is often broken. Herein, we explored a novel model that considers both linear and stochastic dependences of the phase evolution with echo time in the presence of weak and strong macroscopic field inhomogeneities. We tested the performance of the model at large field gradients using simulation, phantom, and human in vivo studies. The performance of the proposed approach was markedly better than the standard correction method, providing a correction equivalent to that of the conventional approach in regions with high signal to noise ratio (SNR > 10), but appearing more robust in regions with low SNR (SNR < 4). The proposed technique shows promise to improve R2* measurements in regions of large susceptibilities. The clinical and research applications still require further investigation. © 2017 American Association of Physicists in Medicine.

  19. Simultaneous assessment of vessel size index, relative blood volume, and vessel permeability in a mouse brain tumor model using a combined spin echo gradient echo echo-planar imaging sequence and viable tumor analysis.

    Science.gov (United States)

    Kording, Fabian; Weidensteiner, Claudia; Zwick, Stefan; Osterberg, Nadja; Weyerbrock, Astrid; Staszewski, Ori; von Elverfeldt, Dominik; Reichardt, Wilfried

    2014-12-01

    Combining multiple imaging biomarkers in one magnetic resonance imaging (MRI) session would be beneficial to gain more data pertaining to tumor vasculature under therapy. Therefore, simultaneous measurement of perfusion, permeability, and vessel size imaging (VSI) using a gradient echo spin echo (GE-SE) sequence with injection of a clinically approved gadolinium (Gd)-based contrast agent was assessed in an orthotopic glioma model. A combined spin echo gradient echo echo-planar imaging sequence was implemented using a single contrast agent Gd diethylenetriaminepentaacetic acid (Gd-DTPA). This sequence was tested in a mouse brain tumor model (U87_MG), also under treatment with an antiangiogenic agent (bevacizumab). T2 maps and the apparent diffusion coefficient (ADC) were used to differentiate regions of cell death and viable tumor tissue. In viable tumor tissue regional blood volume was 5.7 ± 0.6% in controls and 5.2 ± 0.3% in treated mice. Vessel size was 18.1 ± 2.4 μm in controls and 12.8 ± 2.0 μm in treated mice, which correlated with results from immunohistochemistry. Permeability (K(trans) ) was close to zero in treated viable tumor tissue and 0.062 ± 0.024 min(-1) in controls. Our MRI method allows simultaneous assessment of several physiological and morphological parameters and extraction of MRI biomarkers for vasculature. These could be used for treatment monitoring of novel therapeutic agents such as antiangiogenic drugs. © 2014 Wiley Periodicals, Inc.

  20. Single-scan z-shim method for reducing susceptibility artifacts in gradient echo myelin water imaging.

    Science.gov (United States)

    Lee, Doohee; Lee, Jingu; Lee, Jongho; Nam, Yoonho

    2018-02-25

    Myelin water imaging (MWI) reportedly corresponds closely to the myelin content in the brain. An MWI technique based on multi-echo gradient echo (mGRE) has recently been proposed as an alternative to the conventional spin-echo-based MWI. However, the mGRE signal is vulnerable to macroscopic field inhomogeneity, which makes MWI unreliable. In the present study, a z-shim-based single-scan correction method is proposed to overcome this limitation. Z-shim gradients in the slice-selection direction were added to an mGRE sequence after an echo time of 12 ms. A 3-pool model corresponding to the proposed sequence was suggested for fitting the acquired signal. The method was evaluated through a comparison with methods without a correction and with post-processing only from non-z-shimmed data. To do this, numerical simulations and in vivo experiments were conducted. The simulation and in vivo experiment results indicated that post-processing alone was not sufficient to offset the macroscopic field inhomogeneity, particularly in inferior regions of the brain. On the other hand, the proposed method compensated the field inhomogeneity in most brain areas. The estimated in vivo myelin water fraction values were in good agreement with literature values obtained by previously proposed field inhomogeneity correction method. The proposed method showed reliable myelin water fraction in most regions of the brain in vivo, including those with severe field inhomogeneity. © 2018 International Society for Magnetic Resonance in Medicine.

  1. Self-calibrated multiple-echo acquisition with radial trajectories using the conjugate gradient method (SMART-CG).

    Science.gov (United States)

    Jung, Youngkyoo; Samsonov, Alexey A; Bydder, Mark; Block, Walter F

    2011-04-01

    To remove phase inconsistencies between multiple echoes, an algorithm using a radial acquisition to provide inherent phase and magnitude information for self correction was developed. The information also allows simultaneous support for parallel imaging for multiple coil acquisitions. Without a separate field map acquisition, a phase estimate from each echo in multiple echo train was generated. When using a multiple channel coil, magnitude and phase estimates from each echo provide in vivo coil sensitivities. An algorithm based on the conjugate gradient method uses these estimates to simultaneously remove phase inconsistencies between echoes, and in the case of multiple coil acquisition, simultaneously provides parallel imaging benefits. The algorithm is demonstrated on single channel, multiple channel, and undersampled data. Substantial image quality improvements were demonstrated. Signal dropouts were completely removed and undersampling artifacts were well suppressed. The suggested algorithm is able to remove phase cancellation and undersampling artifacts simultaneously and to improve image quality of multiecho radial imaging, the important technique for fast three-dimensional MRI data acquisition. Copyright © 2011 Wiley-Liss, Inc.

  2. Assessment of microstructural signal compartments across the corpus callosum using multi-echo gradient recalled echo at 7 T.

    Science.gov (United States)

    Thapaliya, Kiran; Vegh, Viktor; Bollmann, Steffen; Barth, Markus

    2017-11-26

    Quantitative assessment of tissue microstructure is important in studying human brain diseases and disorders in which white matter is implicated, as it has been linked to demyelination, re-myelination, and axonal damage in clinical conditions. Ultra-high field magnetic resonance imaging data obtained using a multi-echo gradient echo sequence has been shown to contain information on myelin, axonal and extracellular compartments in white matter. In this study, we aimed to assess the sensitivity of a three-compartment model to estimate the variation of corresponding compartment parameters (water fraction, relaxation time and frequency shift) of the corpus callosum sub-regions, which are known to have different tissue structure. Additionally, we computed the g-ratio using myelin and axonal water fractions and performed a voxel-by-voxel analysis in the corpus callosum. Based on data acquired for ten participants, we show that the myelin compartment water fraction and T 2 ∗ is consistent across the corpus callosum sub-regions, whilst myelin frequency shift varies. The results show that the variation in water fraction, T 2 ∗ and frequency shift for the myelin signal compartment across the corpus callosum is smaller than for the axonal and extracellular signal compartments. The computed g-ratio was comparable to previously published studies in the corpus callosum. Our study suggests that a multi-echo GRE approach in vivo combined with a complex three-compartment model is sensitive to microstructural parameter variations across the human corpus callosum. Copyright © 2017 Elsevier Inc. All rights reserved.

  3. Characterization of high-resolution Gradient Echo and Spin Echo EPI for fMRI in the human visual cortex at 7T.

    Science.gov (United States)

    Rua, Catarina; Costagli, Mauro; Symms, Mark R; Biagi, Laura; Donatelli, Graziella; Cosottini, Mirco; Del Guerra, Alberto; Tosetti, Michela

    2017-07-01

    The increased signal-to-noise ratio (SNR) offered by functional Magnetic Resonance Imaging (fMRI) at 7T allows the acquisition of functional data at sub-millimetric spatial resolutions. However, simply reducing partial volume effects is not sufficient to precisely localize task-induced activation due to the indirect mechanisms that relate brain function and the changes in the measured signal. In this work T2* and T2 weighted Echo Planar Imaging (EPI) schemes based on Gradient Recalled Echo (GRE) and Spin Echo (SE) were evaluated in terms of temporal SNR, percent signal change, contrast to noise ratio (CNR), activation volume, and sensitivity and specificity to gray matter. Datasets were acquired during visual stimulation at in-plane resolutions ranging between 1.5×1.5mm(2) and 0.75×0.75mm(2) targeting the early visual cortex. While similar activation foci were obtained in all acquisitions, at in-plane resolutions of 1.0×1.0mm(2) and larger voxel sizes the T2 weighted contrast of SE-EPI allowed the identification of the activation site with better spatial accuracy. However, at sub-millimetric resolutions the decrease in temporal SNR significantly hampered the sensitivity and the extent of the activation site. On the other hand, high resolution T2* weighted data collected with GRE-EPI provided higher CNR and sensitivity, benefiting from the decreased physiological and partial volume effects. However, spurious activations originating from regions of blood drainage were still present in GRE data, and simple thresholding techniques were found to be inadequate for the removal of such contributions. The combination of 2-class and 3-class automated segmentations, performed directly in EPI space, allowed the selection of active voxels in gray matter. This approach could enable GRE-EPI to accurately map functional activity with satisfactory CNR and specificity to the true site of activation. Copyright © 2017 Elsevier Inc. All rights reserved.

  4. Slice-accelerated gradient-echo echo planar imaging dynamic susceptibility contrast-enhanced MRI with blipped CAIPI: effect of increasing temporal resolution.

    Science.gov (United States)

    Takamura, Tomohiro; Hori, Masaaki; Kamagata, Koji; Kumamaru, Kanako K; Irie, Ryusuke; Hagiwara, Akifumi; Hamasaki, Nozomi; Aoki, Shigeki

    2018-01-01

    To assess the influence of high temporal resolution on the perfusion measurements and image quality of perfusion maps, by applying simultaneous-multi-slice acquisition (SMS) dynamic susceptibility contrast-enhanced (DSC) magnetic resonance imaging (MRI). DSC-MRI data using SMS gradient-echo echo planar imaging sequences in 10 subjects with no intracranial abnormalities were retrospectively analyzed. Three additional data sets with temporal resolution of 1.0, 1.5, and 2.0 s were created from the raw data sets of 0.5 s. Cerebral blood flow (CBF), cerebral blood volume, mean transit time (MTT), time to peak (TTP), and time to maximum tissue residue function (T max ) measurements were performed, as was visual perfusion map analysis. The perfusion parameter for temporal resolution of 0.5 s (reference) was compared with each synthesized perfusion parameter. CBF, MTT, and TTP values at temporal resolutions of 1.5 and 2.0 s differed significantly from the reference. The image quality of MTT, TTP, and T max maps deteriorated with decreasing temporal resolution. The temporal resolution of DSC-MRI influences perfusion parameters and SMS DSC-MRI provides better image quality for MTT, TTP, and T max maps.

  5. Three-dimensional gradient echo versus spin echo sequence in contrast-enhanced imaging of the pituitary gland at 3 T

    Energy Technology Data Exchange (ETDEWEB)

    Kakite, Suguru, E-mail: sugkaki@med.tottori-u.ac.jp [Division of Radiology, Department of Pathophysiological and Therapeutic Science, Faculty of Medicine, Tottori University, 36-1, Nishicho, Yonago 683-8503 (Japan); Fujii, Shinya [Division of Radiology, Department of Pathophysiological and Therapeutic Science, Faculty of Medicine, Tottori University, 36-1, Nishicho, Yonago 683-8503 (Japan); Kurosaki, Masamichi [Department of Neurosurgery, Faculty of Medicine, Tottori University, 36-1, Nishicho, Yonago 683-8503 (Japan); Kanasaki, Yoshiko; Matsusue, Eiji; Kaminou, Toshio; Ogawa, Toshihide [Division of Radiology, Department of Pathophysiological and Therapeutic Science, Faculty of Medicine, Tottori University, 36-1, Nishicho, Yonago 683-8503 (Japan)

    2011-07-15

    Introduction: To clarify whether a three-dimensional-gradient echo (3D-GRE) or spin echo (SE) sequence is more useful for evaluating sellar lesions on contrast-enhanced T1-weighted MR imaging at 3.0 Tesla (T). Methods: We retrospectively assessed contrast-enhanced T1-weighted images using 3D-GRE and SE sequences at 3.0 T obtained from 33 consecutive patients with clinically suspected sellar lesions. Two experienced neuroradiologists evaluated the images qualitatively in terms of the following criteria: boundary edge of the cavernous sinus and pituitary gland, border of sellar lesions, delineation of the optic nerve and cranial nerves within the cavernous sinus, susceptibility and flow artifacts, and overall image quality. Results: At 3.0 T, 3D-GRE provided significantly better images than the SE sequence in terms of the border of sellar lesions, delineation of cranial nerves, and overall image quality; there was no significant difference regarding the boundary edge of the cavernous sinus and pituitary gland. In addition, the 3D-GRE sequence showed fewer pulsation artifacts but more susceptibility artifacts. Conclusion: Our results indicate that 3D-GRE is the more suitable sequence for evaluating sellar lesions on contrast-enhanced T1-weighted imaging at 3.0 T.

  6. Retrospective comparison of gradient recalled echo R2* and spin-echo R2 magnetic resonance analysis methods for estimating liver iron content in children and adolescents

    Energy Technology Data Exchange (ETDEWEB)

    Serai, Suraj D.; Fleck, Robert J. [Cincinnati Children' s Hospital Medical Center, Department of Radiology, MLC 5031, Cincinnati, OH (United States); Quinn, Charles T. [Cincinnati Children' s Hospital Medical Center, Division of Hematology, Cincinnati, OH (United States); Zhang, Bin [Cincinnati Children' s Hospital Medical Center, Division of Biostatistics and Epidemiology, Cincinnati, OH (United States); Podberesky, Daniel J. [Nemours Children' s Health System Nemours Children' s Hospital, Department of Radiology, Orlando, FL (United States)

    2015-10-15

    Serial surveillance of liver iron concentration (LIC) provides guidance for chelation therapy in patients with iron overload. The diagnosis of iron overload traditionally relies on core liver biopsy, which is limited by invasiveness, sampling error, cost and general poor acceptance by pediatric patients and parents. Thus noninvasive diagnostic methods such as MRI are highly attractive for quantification of liver iron concentration. To compare two MRI-based methods for liver iron quantification in children. 64 studies on 48 children and young adults (age range 4-21 years) were examined by gradient recalled echo (GRE) R2* and spin-echo R2 MRI at 1.5T to evaluate liver iron concentration. Scatter plots and Bland-Altman difference plots were generated to display and assess the relationship between the methods. With the protocols used in this investigation, Bland-Altman agreement between the methods is best when LIC is <20 mg/g dry tissue. Scatter plots show that all values with LIC <20 mg/g dry tissue fall within the 95% prediction limits. Liver iron concentration as determined by the R2* and R2 MR methods is statistically comparable, with no statistical difference between these methods for LIC <20 mg/g. (orig.)

  7. Internal derangements of the temporomandibular joint: comparison of assessment with three-dimensional gradient-echo and spin-echo MRI

    Energy Technology Data Exchange (ETDEWEB)

    Yamada, I. [Department of Radiology, Faculty of Medicine, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113 (Japan); Murata, Y. [Department of Radiology, Faculty of Medicine, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113 (Japan); Shibuya, H. [Department of Radiology, Faculty of Medicine, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113 (Japan); Suzuki, S. [Department of Radiology, Faculty of Medicine, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113 (Japan)

    1997-09-01

    Our purpose was to assess the diagnostic accuracy of three-dimensional (3D) gradient-echo (GRE) MRI in the diagnosis of internal derangements of the temporomandibular joint (TMJ). We studied 140 joints in 70 patients with TMJ internal derangements. We obtained 3D-GRE and spin-echo (SE) images in the closed-mouth position; the images were reviewed for disc displacement as well as bone and cartilage abnormalities. The 3D-GRE and SE images were interpreted independently by different radiologists. The sensitivity and specificity of 3D-GRE imaging for assessing mediolateral disc displacement was 100 %, whereas the sensitivity and specificity of sagittal SE images were 82 % and 72 %, respectively (P < 0.001). The 3D-GRE images also demonstrated more bone abnormalities (in 112 condyles or 80 %) than did SE images (in 79 condyles or 56 %) (P < 0.001). Furthermore, 3D-GRE imaging revealed articular cartilage abnormalities in 46 condyles (33 %) that were not visible on SE images. The frequency of pain was significantly higher in joints with bone and cartilage abnormalities (P < 0.05 and P < 0.001, respectively). For assessment of disc displacement, 3D-GRE images were superior to sagittal SE images alone, and comparable to combined sagittal and coronal SE images, while for bone and cartilage abnormalities, they were superior to sagittal and coronal SE images. (orig.). With 5 figs., 2 tabs.

  8. Echo-Planar Imaging for a 9.4 Tesla Vertical-Bore Superconducting Magnet Using an Unshielded Gradient Coil.

    Science.gov (United States)

    Kodama, Nao; Kose, Katsumi

    2016-10-11

    Echo-planar imaging (EPI) sequences were developed for a 9.4 Tesla vertical standard bore (~54 mm) superconducting magnet using an unshielded gradient coil optimized for live mice imaging and a data correction technique with reference scans. Because EPI requires fast switching of intense magnetic field gradients, eddy currents were induced in the surrounding metallic materials, e.g., the room temperature bore, and this produced serious artifacts on the EPI images. We solved the problem using an unshielded gradient coil set of proper size (outer diameter = 39 mm, inner diameter = 32 mm) with time control of the current rise and reference scans. The obtained EPI images of a phantom and a plant sample were almost artifact-free and demonstrated the promise of our approach.

  9. Echo-Planar Imaging for a 9.4 Tesla Vertical-Bore Superconducting Magnet Using an Unshielded Gradient Coil

    Science.gov (United States)

    KODAMA, Nao; KOSE, Katsumi

    2016-01-01

    Echo-planar imaging (EPI) sequences were developed for a 9.4 Tesla vertical standard bore (∼54 mm) superconducting magnet using an unshielded gradient coil optimized for live mice imaging and a data correction technique with reference scans. Because EPI requires fast switching of intense magnetic field gradients, eddy currents were induced in the surrounding metallic materials, e.g., the room temperature bore, and this produced serious artifacts on the EPI images. We solved the problem using an unshielded gradient coil set of proper size (outer diameter = 39 mm, inner diameter = 32 mm) with time control of the current rise and reference scans. The obtained EPI images of a phantom and a plant sample were almost artifact-free and demonstrated the promise of our approach. PMID:27001398

  10. A single-shot T2mapping protocol based on echo-split gradient-spin-echo acquisition and parametric multiplexed sensitivity encoding based on projection onto convex sets reconstruction.

    Science.gov (United States)

    Chu, Mei-Lan; Chang, Hing-Chiu; Oshio, Koichi; Chen, Nan-Kuei

    2018-01-01

    To develop a high-speed T 2 mapping protocol that is capable of accurately measuring T 2 relaxation time constants from a single-shot acquisition. A new echo-split single-shot gradient-spin-echo (GRASE) pulse sequence is developed to acquire multicontrast data while suppressing signals from most nonprimary echo pathways in Carr-Purcell-Meiboom-Gill (CPMG) echoes. Residual nonprimary pathway signals are taken into consideration when performing T 2 mapping using a parametric multiplexed sensitivity encoding based on projection onto convex sets (parametric-POCSMUSE) reconstruction method that incorporates extended phase graph modeling of GRASE signals. The single-shot echo-split GRASE-based T 2 mapping procedure was evaluated in human studies at 3 Tesla. The acquired data were compared with reference data obtained with a more time-consuming interleaved spin-echo echo planar imaging protocol. T 2 maps derived from conventional single-shot GRASE scans, in which nonprimary echo pathways were not appropriately addressed, were also evaluated. Using the developed single-shot T 2 mapping protocol, quantitatively accurate T 2 maps can be obtained with a short scan time (parametric-POCSMUSE reconstruction. Magn Reson Med 79:383-393, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  11. Hippocampal Microbleed on a Post-Mortem T2*-Weighted Gradient-Echo 7.0-Tesla Magnetic Resonance Imaging

    Directory of Open Access Journals (Sweden)

    J. De Reuck

    2011-09-01

    Full Text Available The present post-mortem study of a brain from an Alzheimer patient showed on a T2*-weighted gradient-echo 7.0-T MRI of a coronal brain section a hyposignal in the hippocampus, suggesting a microbleed. On the corresponding histological examination, only iron deposits around the granular cellular layer and in blood vessel walls of the hippocampus were observed without evidence of a bleeding. This case report illustrates that the detection of microbleeds on MRI has to be interpreted with caution.

  12. Transmit and receive RF fields determination from a single low-tip-angle gradient-echo scan by scaling of SVD data.

    Science.gov (United States)

    Sbrizzi, Alessandro; Raaijmakers, Alexander J E; Hoogduin, Hans; Lagendijk, Jan J W; Luijten, Peter R; van den Berg, Cornelis A T

    2014-07-01

    A new method, called Transmit and Receive Patterns from Low-Tip-angle gradient-Echo Images (TRIPLET), is described which simultaneously maps the B1+ and B1- fields of a transmit/receive radiofrequency coil array. The input data are low-tip-angle gradient-echo images, which can be acquired in a relatively short scanning time. For each voxel in the field of view, a matrix can be assembled with the low-tip-angle gradient-echo image values of the radiofrequency coil array. Applying the singular value decomposition to those matrices, datasets are obtained which show a high resemblance with the true B1+ and B1- fields. These datasets are a voxel-wise scaled version of the true radiofrequency maps. The channel independent scaling parameters can be found by implicitly forcing the reconstructed fields to be solutions of the Maxwell equations. This is achieved by introducing a multipole expansion consisting of Bessel/Fourier functions. Two FDTD simulated radiofrequency fields for two coil array combinations at 7 T and a measured, in vivo dataset at 7 T are investigated to illustrate the singular value decomposition analysis of the low-tip-angle gradient-echo images and to show how the B1+ and B1- fields can be reconstructed by Transmit and Receive Patterns from Low-Tip-angle gradient-Echo Images. The Transmit and Receive Patterns from Low-Tip-angle gradient-Echo Images algorithm can convert the datasets from singular value decomposition analysis of low-tip-angle gradient-echo images to true B1+ and B1- fields. Copyright © 2013 Wiley Periodicals, Inc.

  13. Comparison of spin-echo echoplanar imaging and gradient recalled echo-based MR elastography at 3 Tesla with and without gadoxetic acid administration

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Yong Seek [Chonbuk National University Medical School and Hospital, Department of Radiology, Jeonju, Chonbuk (Korea, Republic of); Song, Ji Soo [Chonbuk National University Medical School and Hospital, Department of Radiology, Jeonju, Chonbuk (Korea, Republic of); Research Institute of Clinical Medicine of Chonbuk National University, Jeonju, Chonbuk (Korea, Republic of); Biomedical Research Institute of Chonbuk National University Hospital, Jeonju, Chonbuk (Korea, Republic of); Kannengiesser, Stephan [Siemens Healthcare, MR Applications Development, Erlangen (Germany); Seo, Seung Young [Research Institute of Clinical Medicine of Chonbuk National University, Jeonju, Chonbuk (Korea, Republic of); Biomedical Research Institute of Chonbuk National University Hospital, Jeonju, Chonbuk (Korea, Republic of); Chonbuk National University Medical School and Hospital, Department of Internal Medicine, Jeonju (Korea, Republic of)

    2017-10-15

    To compare spin-echo echoplanar imaging (SE-EPI) and gradient recalled echo (GRE) MR elastography (MRE) at 3 T with and without gadoxetic acid administration. We included 84 patients who underwent MRE before and after gadoxetic acid administration, each time using SE-EPI and GRE sequences. Diagnostic performance for predicting clinical liver cirrhosis and high-risk oesophageal varices was assessed using the area under the receiver-operating characteristic curve (AUC). The relationships between T2* and success of MRE, and correlations of liver stiffness (LS) values between the two sequences or before and after gadoxetic acid administration, were investigated. SE-EPI-MRE resulted in a significantly lower failure rate than GRE-MRE (1.19% vs. 10.71%, P = 0.018). Increased T2* was related to higher probability of successful LS measurement (odds ratio, 1.426; P = 0.004). The AUC of SE-EPI-MRE was comparable to that of GRE-MRE for the detection of clinical liver cirrhosis (0.938 vs. 0.948, P = 0.235) and high-risk oesophageal varices (0.839 vs. 0.752, P = 0.354). LS values were not significantly different before and after gadoxetic acid administration. SE-EPI-MRE can substitute for GRE-MRE for the detection of clinical liver cirrhosis and high-risk oesophageal varices. SE-EPI-MRE is particularly useful in patients with iron deposition, with lower failure rates than GRE-MRE. (orig.)

  14. Cerebral hemodynamic changes measured by gradient-echo or spin-echo bolus tracking and its correlation to changes in ICA blood flow measured by phase-mapping MRI

    DEFF Research Database (Denmark)

    Marstrand, J.R.; Rostrup, Egill; Garde, Ellen

    2001-01-01

    Changes in cerebral blood flow (CBF) induced by Acetazolamide (ACZ) were measured using dynamic susceptibility contrast MRI (DSC-MRI) with both spin echo (SE) EPI and gradient echo (GE) EPI, and related to changes in internal carotid artery (ICA) flow measured by phase-mapping. Also examined...... increase in CBF and CBV in response to ACZ, while SE-EPI measured a significant increase in CBV and MTT. CBV and MTT change measured by SE-EPI was sensitive to previous bolus injections. There was a significant linear relation between change in CBF measured by GE-EPI and change in ICA flow. In conclusion...

  15. Dobutamine stress tagging and gradient-echo imaging for detection of coronary heart disease at 3 T.

    Science.gov (United States)

    Thomas, D; Meyer, C; Strach, K; Naehle, C P; Mazraeh, J; Gampert, T; Schild, H H; Sommer, T

    2011-01-01

    The purpose of this study was to evaluate the feasibility and diagnostic accuracy of a combined spoiled gradient-echo (sGRE) and tagged gradient-echo (SPAMM-GRE) protocol for detection of coronary artery disease (CAD) during high-dose dobutamine stress at 3 T. The study protocol was approved by the local ethics committee. For stress testing, a standard high-dose dobutamine protocol was employed. Image quality at the highest stress level and diagnostic accuracy of the sGRE and SPAMM-GRE sequences were compared. The final study population consisted of 37 patients. The mean image quality score was 2.6±0.6 for the sGRE sequence and 2.4±0.6 for the SPAMM-GRE sequence (p>0.05). Sensitivity, specificity and diagnostic accuracy were 0.81, 0.86, 0.84 and 0.88, 0.86, 0.86 for the sGRE and SPAMM-GRE, respectively. In three cases with new wall motion abnormalities (WMAs), detected by sGRE and SPAMM-GRE, WMAs were detected at a lower stress level by tagging. The combined sGRE and SPAMM-GRE high-dose dobutamine protocol at 3 T is feasible and delivers good diagnostic accuracy. Tagging increases the sensitivity of high-dose dobutamine stress testing for detection of CAD and may allow for detection of new WMAs at lower stress levels compared with sGRE alone.

  16. Mapping axonal density and average diameter using non-monotonic time-dependent gradient-echo MRI.

    Science.gov (United States)

    Nunes, Daniel; Cruz, Tomás L; Jespersen, Sune N; Shemesh, Noam

    2017-04-01

    White Matter (WM) microstructures, such as axonal density and average diameter, are crucial to the normal function of the Central Nervous System (CNS) as they are closely related with axonal conduction velocities. Conversely, disruptions of these microstructural features may result in severe neurological deficits, suggesting that their noninvasive mapping could be an important step towards diagnosing and following pathophysiology. Whereas diffusion based MRI methods have been proposed to map these features, they typically entail the application of powerful gradients, which are rarely available in the clinic, or extremely long acquisition schemes to extract information from parameter-intensive models. In this study, we suggest that simple and time-efficient multi-gradient-echo (MGE) MRI can be used to extract the axon density from susceptibility-driven non-monotonic decay in the time-dependent signal. We show, both theoretically and with simulations, that a non-monotonic signal decay will occur for multi-compartmental microstructures - such as axons and extra-axonal spaces, which were here used as a simple model for the microstructure - and that, for axons parallel to the main magnetic field, the axonal density can be extracted. We then experimentally demonstrate in ex-vivo rat spinal cords that its different tracts - characterized by different microstructures - can be clearly contrasted using the MGE-derived maps. When the quantitative results are compared against ground-truth histology, they reflect the axonal fraction (though with a bias, as evident from Bland-Altman analysis). As well, the extra-axonal fraction can be estimated. The results suggest that our model is oversimplified, yet at the same time evidencing a potential and usefulness of the approach to map underlying microstructures using a simple and time-efficient MRI sequence. We further show that a simple general-linear-model can predict the average axonal diameters from the four model parameters, and

  17. Mapping axonal density and average diameter using non-monotonic time-dependent gradient-echo MRI

    Science.gov (United States)

    Nunes, Daniel; Cruz, Tomás L.; Jespersen, Sune N.; Shemesh, Noam

    2017-04-01

    White Matter (WM) microstructures, such as axonal density and average diameter, are crucial to the normal function of the Central Nervous System (CNS) as they are closely related with axonal conduction velocities. Conversely, disruptions of these microstructural features may result in severe neurological deficits, suggesting that their noninvasive mapping could be an important step towards diagnosing and following pathophysiology. Whereas diffusion based MRI methods have been proposed to map these features, they typically entail the application of powerful gradients, which are rarely available in the clinic, or extremely long acquisition schemes to extract information from parameter-intensive models. In this study, we suggest that simple and time-efficient multi-gradient-echo (MGE) MRI can be used to extract the axon density from susceptibility-driven non-monotonic decay in the time-dependent signal. We show, both theoretically and with simulations, that a non-monotonic signal decay will occur for multi-compartmental microstructures - such as axons and extra-axonal spaces, which were here used as a simple model for the microstructure - and that, for axons parallel to the main magnetic field, the axonal density can be extracted. We then experimentally demonstrate in ex-vivo rat spinal cords that its different tracts - characterized by different microstructures - can be clearly contrasted using the MGE-derived maps. When the quantitative results are compared against ground-truth histology, they reflect the axonal fraction (though with a bias, as evident from Bland-Altman analysis). As well, the extra-axonal fraction can be estimated. The results suggest that our model is oversimplified, yet at the same time evidencing a potential and usefulness of the approach to map underlying microstructures using a simple and time-efficient MRI sequence. We further show that a simple general-linear-model can predict the average axonal diameters from the four model parameters, and

  18. Whole brain, high resolution multiband spin-echo EPI fMRI at 7 T: a comparison with gradient-echo EPI using a color-word Stroop task.

    Science.gov (United States)

    Boyacioğlu, Rasim; Schulz, Jenni; Müller, Nils C J; Koopmans, Peter J; Barth, Markus; Norris, David G

    2014-08-15

    A whole brain, multiband spin-echo (SE) echo planar imaging (EPI) sequence employing a high spatial (1.5 mm isotropic) and temporal (TR of 2 s) resolution was implemented at 7 T. Its overall performance (tSNR, sensitivity and CNR) was assessed and compared to a geometrically matched gradient-echo (GE) EPI multiband sequence (TR of 1.4 s) using a color-word Stroop task. PINS RF pulses were used for refocusing to reduce RF amplitude requirements and SAR, summed and phase-optimized standard pulses were used for excitation enabling a transverse or oblique slice orientation. The distortions were minimized with the use of parallel imaging in the phase encoding direction and a post-acquisition distortion correction. In general, GE-EPI shows higher efficiency and higher CNR in most brain areas except in some parts of the visual cortex and superior frontal pole at both the group and individual-subject levels. Gradient-echo EPI was able to detect robust activation near the air/tissue interfaces such as the orbito-frontal and subcortical regions due to reduced intra-voxel dephasing because of the thin slices used and high in-plane resolution. Copyright © 2014 Elsevier Inc. All rights reserved.

  19. Familial form of cerebral cavernous malformations: evaluation of gradient-spin-echo (GRASE) imaging in lesion detection and characterization at 1.5 T

    Energy Technology Data Exchange (ETDEWEB)

    Brunereau, L. [Service de Radiologie Adultes Bretonneau, CHRU Tours (France); INSERM Faculte de Medecine, Tours (France); Leveque, C.; Cordoliani, Y. [Service de Radiologie et d' Imagerie Medicale, HIA Val de Grace, Paris (France); Bertrand, P.; Rouleau, P. [Service de Radiologie Adultes Bretonneau, CHRU Tours (France); Tranquart, F. [INSERM Faculte de Medecine, Tours (France); Labauge, P. [INSERM EPI Faculte de Medecine Lariboisiere-Saint-Louis, Paris (France)

    2001-11-01

    The purpose of this study was to evaluate the turbo gradient-spin-echo sequence (GRASE) in the MR assessment of the familial form of cerebral cavernous malformations (CCM). Twenty-one patients (15 male, six female) aged from 21 to 68 years (mean = 42.2 years) were prospectively examined with cerebral MR imaging, including T2-weighted turbo gradient-spin-echo (TGSE), turbo spin-echo (TSE) and gradient-echo (GRE) sequences. All sequences were performed in the same plane, the same matrix and the same field of view and were analyzed for signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), susceptibility effects, number of CCM, size of CCM and signal of CCM. It was found that SNR and CNR in the TGSE sequence were significantly inferior to those in both TSE and GRE sequences. TGSE and TSE sequences were significantly less prone to susceptibility effects than the GRE sequence. The sensitivity of TGSE and TSE sequences in detecting CCM was significantly lower than that of the GRE sequence. TGSE and TSE sequences provided comparable information about CCM size and signal. It was concluded that GRASE imaging was less sensitive than the GRE sequence in the detection of CCM and provided information similar to that yielded by the TSE sequence in the characterization of lesions, but with a higher number of artifacts. GRASE imaging cannot therefore replace TSE or GRE sequences in the MR evaluation of the familial form of CCM. (orig.)

  20. A Magnetic Resonance Measurement Technique for Rapidly Switched Gradient Magnetic Fields in a Magnetic Resonance Tomograph

    Directory of Open Access Journals (Sweden)

    K. Bartušek

    2003-01-01

    Full Text Available This paper describes a method for measuring of the gradient magnetic field in Nuclear Magnetic Resonance (NMR tomography, which is one of the modern medical diagnostic methods. A very important prerequisite for high quality imaging is a gradient magnetic field in the instrument with exactly defined properties. Nuclear magnetic resonance enables us to measure the pulse gradient magnetic field characteristics with high accuracy. These interesting precise methods were designed, realised, and tested at the Institute of Scientific Instruments (ISI of the Academy of Sciences of the Czech Republic. The first of them was the Instantaneous Frequency (IF method, which was developed into the Instantaneous Frequency of Spin Echo (IFSE and the Instantaneous Frequency of Spin Echo Series (IFSES methods. The above named methods are described in this paper and their a comparison is also presented.

  1. Age and gender specific normal values of left ventricular mass, volume and function for gradient echo magnetic resonance imaging: a cross sectional study

    Directory of Open Access Journals (Sweden)

    Allansdotter-Johnsson Ase

    2009-01-01

    Full Text Available Abstract Background Knowledge about age-specific normal values for left ventricular mass (LVM, end-diastolic volume (EDV, end-systolic volume (ESV, stroke volume (SV and ejection fraction (EF by cardiac magnetic resonance imaging (CMR is of importance to differentiate between health and disease and to assess the severity of disease. The aims of the study were to determine age and gender specific normal reference values and to explore the normal physiological variation of these parameters from adolescence to late adulthood, in a cross sectional study. Methods Gradient echo CMR was performed at 1.5 T in 96 healthy volunteers (11–81 years, 50 male. Gender-specific analysis of parameters was undertaken in both absolute values and adjusted for body surface area (BSA. Results Age and gender specific normal ranges for LV volumes, mass and function are presented from the second through the eighth decade of life. LVM, ESV and EDV rose during adolescence and declined in adulthood. SV and EF decreased with age. Compared to adult females, adult males had higher BSA-adjusted values of EDV (p = 0.006 and ESV (p Conclusion LV volumes, mass and function vary over a broad age range in healthy individuals. LV volumes and mass both rise in adolescence and decline with age. EF showed a rapid decline in adolescence compared to changes throughout adulthood. These findings demonstrate the need for age and gender specific normal ranges for clinical use.

  2. Low frequency oscillating gradient spin-echo sequences improve sensitivity to axon diameter: An experimental study in viable nerve tissue.

    Science.gov (United States)

    Kakkar, Lebina S; Bennett, Oscar F; Siow, Bernard; Richardson, Simon; Ianuş, Andrada; Quick, Tom; Atkinson, David; Phillips, James B; Drobnjak, Ivana

    2017-08-01

    Mapping axon diameters within the central and peripheral nervous system could play an important role in our understanding of nerve pathways, and help diagnose and monitor an array of neurological disorders. Numerous diffusion MRI methods have been proposed for imaging axon diameters, most of which use conventional single diffusion encoding (SDE) spin echo sequences. However, a growing number of studies show that oscillating gradient spin echo (OGSE) sequences can provide additional advantages over conventional SDE sequences. Recent theoretical results suggest that this is especially the case in realistic scenarios, such as when fibres have unknown or dispersed orientation. In the present study, we adopt the ActiveAx approach to experimentally investigate the extent of these advantages by comparing the performances of SDE and trapezoidal OGSE in viable nerve tissue. We optimise SDE and OGSE ActiveAx protocols for a rat peripheral nerve tissue and test their performance using Monte Carlo simulations and a 800 mT/m gradient strength pre-clinical imaging experiment. The imaging experiment uses excised sciatic nerve from a rat's leg placed in a MRI compatible viable isolated tissue (VIT) maintenance chamber, which keeps the tissue in a viable physiological state that preserves the structural complexity of the nerve and enables lengthy scan times. We compare model estimates to histology, which we perform on the nerve post scanning. Optimisation produces a three-shell SDE and OGSE ActiveAx protocol, with the OGSE protocol consisting of one SDE sequence and two low-frequency oscillating gradient waveform sequences. Both simulation and imaging results show that the OGSE ActiveAx estimates of the axon diameter index have a higher accuracy and a higher precision compared to those from SDE. Histology estimates of the axon diameter index in our nerve tissue samples are 4-5.8 μm and these are excellently matched with the OGSE estimates 4.2-6.5 μm, while SDE overestimates at

  3. Efficacy of T2*-Weighted Gradient-Echo MRI in Early Diagnosis of Cerebral Venous Thrombosis with Unilateral Thalamic Lesion

    Directory of Open Access Journals (Sweden)

    Shingo Mitaki

    2013-01-01

    Full Text Available Cerebral venous thrombosis (CVT is an uncommon cause of stroke with diverse etiologies and varied clinical presentations. Because of variability in clinical presentation and neuroimaging, CVT remains a diagnostic challenge. Recently, some studies have highlighted the value of T2*-weighted gradient-echo MRI (T2*WI in the diagnosis of CVT. We report the case of a 79-year-old woman with CVT due to a hypercoagulable state associated with cancer. On the initial T2-weighted image (T2WI, there was a diffuse high-intensity lesion in the right thalamus, extending into the posterior limb of the internal capsule and midbrain. T2*WI showed diminished signal and enlargement of the right basilar vein and the vein of Galen. Even though there is a wide range of differential diagnoses in unilateral thalamic lesions, and a single thalamus lesion is a rare entity of CVT, based on T2*WI findings we could make an early diagnosis and perform treatment. Our case report suggests that T2*WI could detect thrombosed veins and be a useful method of early diagnosis in CVT.

  4. Relationship between the trochlear groove angle and patellar cartilage morphology defined by 3D spoiled gradient-echo imaging

    Energy Technology Data Exchange (ETDEWEB)

    Harada, Yuko; Tokuda, Osamu; Matsunaga, Naofumi [Yamaguchi University Graduate School of Medicine, Department of Radiology, Yamaguchi (Japan); Fukuda, Kouji [Shunan Memorial Hospital, Division of Radiological Technology, Yamaguchi (Japan); Shiraishi, Gen; Motomura, Tetsuhisa [Shunan Memorial Hospital, Department of Orthopedics Surgery, Yamaguchi (Japan); Kimura, Motoichi [Customer Application Gr., GE Healthcare MR Sales and Marketing Department, Osaka (Japan)

    2012-05-15

    To examine whether the femoral trochlear groove angle (TGA) is a determinant of the patellar cartilage volume and patellar cartilage damage. Patellar cartilage was evaluated by MR imaging in 66 patients (22 males and 44 females) with knee pain. Fat-suppressed 3D spoiled gradient-echo images were used to calculate the cartilage volume and to grade the cartilage damage. The proximal and distal TGAs were measured from axial PD-weighted FSE MR images with fat suppression. For every increase in the TGA at the distal femur, the patellar cartilage volume was significantly increased by 6.07 x 10{sup -3} cm{sup 3} (95% CI: 1.27 x 10{sup -3}, 10.9 x 10{sup -3}) after adjustment for age, gender, and patellar bone volume (P < 0.05). The MR grade of medial patellar cartilage damage progressed as the distal TGA became narrower, although there was no significant correlation between the distal TGA and the MR grading of patellar cartilage damage. A more flattened distal TGA was associated with increased patellar cartilage volume. However, there was no association between TGA and patellar cartilage defects. (orig.)

  5. Detection of intratumoral susceptibility signals using T2*-weighted gradient echo MRI in patients with clear cell renal cell carcinoma.

    Directory of Open Access Journals (Sweden)

    Shengnan Yu

    Full Text Available OBJECTIVE: To retrospectively evaluate whether T2*-weighted imaging can be used to grade clear cell renal cell carcinomas (ccRCC based on intratumoral susceptibility signals (ISSs. MATERIALS AND METHODS: MR imaging from 37 patients with pathologically-proven ccRCCs was evaluated. ISSs on T2*WI were classified as linear or conglomerated linear structures (type I and dot-like or patchy foci (type II. Two radiologists assessed the likelihood of the presence of ISS, dominant structure of ISS and ratio of ISS area to tumor area. Results were analyzed by nonparametric Mann-Whitney test. RESULTS: ISSs were seen in all patients except for four patients with low-grade ccRCCs and two patients with high-grade ccRCCs. There was no significant difference of the likelihood of the presence of ISS between low- and high-grade ccRCCs. More type I ISSs and less type II ISSs were predictive of low-grade tumors, whereas more conspicuity type II ISSs correlated with higher occurrence of high-grade tumors (P<0.05. The ratio of ISS area to tumor area was also significantly higher for the high-grade group (1.27±0.79 than that for the low-grade group (0.81±0.40 (P<0.05. CONCLUSION: ISSs on T2*-weighted gradient-echo MR images can help grade ccRCCs before operations.

  6. Detection of intratumoral susceptibility signals using T2*-weighted gradient echo MRI in patients with clear cell renal cell carcinoma.

    Science.gov (United States)

    Yu, Shengnan; Qiu, Jianguo; Zhang, Jinggang; Pan, Liang; Xing, Shijun; Zhang, Lijun

    2013-01-01

    To retrospectively evaluate whether T2*-weighted imaging can be used to grade clear cell renal cell carcinomas (ccRCC) based on intratumoral susceptibility signals (ISSs). MR imaging from 37 patients with pathologically-proven ccRCCs was evaluated. ISSs on T2*WI were classified as linear or conglomerated linear structures (type I) and dot-like or patchy foci (type II). Two radiologists assessed the likelihood of the presence of ISS, dominant structure of ISS and ratio of ISS area to tumor area. Results were analyzed by nonparametric Mann-Whitney test. ISSs were seen in all patients except for four patients with low-grade ccRCCs and two patients with high-grade ccRCCs. There was no significant difference of the likelihood of the presence of ISS between low- and high-grade ccRCCs. More type I ISSs and less type II ISSs were predictive of low-grade tumors, whereas more conspicuity type II ISSs correlated with higher occurrence of high-grade tumors (PISSs on T2*-weighted gradient-echo MR images can help grade ccRCCs before operations.

  7. Enhancement of respiratory navigator-gated three-dimensional spoiled gradient-recalled echo sequence with variable flip angle scheme.

    Science.gov (United States)

    Iwadate, Yuji; Brau, Anja C S; Vasanawala, Shreyas S; Kabasawa, Hiroyuki

    2014-07-01

    To develop and demonstrate the feasibility of a new technique for respiratory-gated, fat-suppressed, three-dimensional spoiled gradient-recalled echo (3D-SPGR) with navigator gating for more accurate and robust motion detection. A navigator-gated 3D-SPGR technique was modified to include a wait period immediately prior to the navigator sequence for magnetization recovery. Furthermore, a variable flip angle scheme was realized by a combination of ramp-up, ramp-down, and attenuation strategies for optimizing point spread functions. Phantom and human experiments were conducted with our technique on 1.5T scanners. Using the method, T1-weighted 3D images with improved signal homogeneity were acquired with a maximum flip angle of 30° in phantom and human tests. Also, compared with the conventional navigator-gated 3D-SPGR, accurate respiratory motion detection of free-breathing subjects was provided, leading to reduced motion artifacts. The combination of wait insertion and the variable flip angle method improved both motion detection accuracy and image homogeneity in a navigator-gated 3D-SPGR study. Copyright © 2013 Wiley Periodicals, Inc.

  8. Lateral diffusion of PEG-Lipid in magnetically aligned bicelles measured using stimulated echo pulsed field gradient 1H NMR.

    Science.gov (United States)

    Soong, Ronald; Macdonald, Peter M

    2005-01-01

    Lateral diffusion measurements of PEG-lipid incorporated into magnetically aligned bicelles are demonstrated using stimulated echo (STE) pulsed field gradient (PFG) proton (1H) nuclear magnetic resonance (NMR) spectroscopy. Bicelles were composed of dimyristoyl phosphatidylcholine (DMPC) plus dihexanoyl phosphatidylcholine (DHPC) (q = DMPC/DHPC molar ratio = 4.5) plus 1 mol % (relative to DMPC) dimyristoyl phosphatidylethanolamine-N-[methoxy(polyethylene glycol)-2000] (DMPE-PEG 2000) at 25 wt % lipid. 1H NMR STE spectra of perpendicular aligned bicelles contained only resonances assigned to residual HDO and to overlapping contributions from a DMPE-PEG 2000 ethoxy headgroup plus DHPC choline methyl protons. Decay of the latter's STE intensity in the STE PFG 1H NMR experiment (g(z) = 244 G cm(-1)) yielded a DMPE-PEG 2000 (1 mol %, 35 degrees C) lateral diffusion coefficient D = 1.35 x 10(-11) m2 s(-1). Hence, below the "mushroom-to-brush" transition, DMPE-PEG 2000 lateral diffusion is dictated by its DMPE hydrophobic anchor. D was independent of the diffusion time, indicating unrestricted lateral diffusion over root mean-square diffusion distances of microns, supporting the "perforated lamellae" model of bicelle structure under these conditions. Overall, the results demonstrate the feasibility of lateral diffusion measurements in magnetically aligned bicelles using the STE PFG NMR technique.

  9. [The MRT of focal liver lesions: the value of gadolinium-enhanced dynamic studies of the whole organ with a fast 3D-turbo-gradient echo sequence].

    Science.gov (United States)

    Pauleit, D; Textor, J; Conrad, R; Flacke, S; Gieseke, J; Born, M; Bachmann, R; Kreft, B; Schild, H

    1999-04-01

    To determine the value of a dynamic Gd-enhanced ultrafast T1-weighted 3D-turbo-gradient-echo sequence (3D-TFE) in the detection and characterization of focal liver lesions. 51 patients with 124 focal liver lesions (35 hemangiomas, 30 HCC, 24 metastases, 22 cysts, 5 FNH/adenoma, 8 other lesions) were examined using a 1.5 T system. The dynamic 3D-TFE sequence, achieving 40 slices with a thickness of 4.5 mm in a 17-s breath-hold, was compared with a fat-suppressed T2-weighted fast-spin-echo sequence (TSE SPIR), unenhanced and Gd-enhanced T1-weighted spin-echo sequences (SE), and a T1-weighted gradient-echo sequence (FFE). On 3D-TFE images more lesions (107/124) were identified than on T1-weighted SE (101/124) and T1-weighted FFE images (106/124), but less compared to T2-weighted TSE SPIR images (115/124). The 3D-TFE-sequence provided additional information in 65/107 (61%) detected lesions by delineating the dynamic enhancement pattern, most valuable in patients with HCCs in 90%. On dynamic 3D-TFE images more lesions could be depicted than on conventional T1-weighted SE and T1-weighted FFE images. Visualization of the dynamic enhancement pattern provided additional information for tumor characterization in 61% of the detected lesions on the 3D-TFE images.

  10. Study of intracardiac blood flow by MRI using gradient echo method

    Energy Technology Data Exchange (ETDEWEB)

    Ohnishi, Shusaku; Fukui, Sugao; Atsumi, Chisato; Morita, Ruriko; Kusuoka, Hideo; Fujii, Kenshi; Kitabatake, Akira; Takizawa, Osamu.

    1988-06-01

    In order to investigate the possibility of MR imaging for the evaluation of intracardiac blood flow especially valvular regurgitant flow, we obtained MR images using a 1.5 tesla superconductive magnet system (Siemens Medical) in 3 healthy volunteers, 3 patients with hypertrophic cardiomyopathy and 8 patients with valvular heart disease. Rapid FLASH (Fast Low-Angle Shot) imaging technique was applied to collect 11 time frames per section throughout one cardiac cycle in axial, coronal, saggital and oblique sections. Then these sequential frames were displayed in a cine mode on CRT. (1) Intracardiac and intravascular blood flow were visualized with high signal intensity in each frame and cardiac structures such as atria, ventricles, and aorta were also identified in all subjects. (2) Ventricular ejection flow was easily visualized in coronal section as the signal loss in the ascending aorta. Ventricularfilling was visualized in axial and oblique sections as the high signal influx of atrial blood into the ventricle. (3) In 3 patients with aortic regurgitation, regurgitant flow was detected during diastole as the teardrop shaped signal loss originating from aortic valve cusps. (4) Both mitral and tricuspid regurgitant flow were detected during systole as the signal loss in atrium in axial and oblique sections in 2 patients with MR and 2 patients with TR. (5) Pulmonary regurgitant flow was observed in oblique section along the long axis of right ventricular outflow tract. These results indicate that intracardiac forward and regurgitant flow could be identified with rapid FLASH imaging in normal subjects and in patients with valvular heart diseases, and cine mode MR imaging is a useful tool for the evaluation of intracardiac blood flow.

  11. Cerebral hemodynamic changes measured by gradient-echo or spin-echo bolus tracking and its correlation to changes in ICA blood flow measured by phase-mapping MRI

    DEFF Research Database (Denmark)

    Marstrand, J.R.; Rostrup, Egill; Garde, Ellen

    2001-01-01

    Changes in cerebral blood flow (CBF) induced by Acetazolamide (ACZ) were measured using dynamic susceptibility contrast MRI (DSC-MRI) with both spin echo (SE) EPI and gradient echo (GE) EPI, and related to changes in internal carotid artery (ICA) flow measured by phase-mapping. Also examined...... was the effect of repeated bolus injections. CBF, cerebral blood volume (CBV), and mean transit time (MTT) were calculated by singular value decomposition (SVD) and by deconvolution using an exponential function as kernel. The results showed no dependency on calculation method. GE-EPI measured a significant...... increase in CBF and CBV in response to ACZ, while SE-EPI measured a significant increase in CBV and MTT. CBV and MTT change measured by SE-EPI was sensitive to previous bolus injections. There was a significant linear relation between change in CBF measured by GE-EPI and change in ICA flow. In conclusion...

  12. Gradient-echo magnetic resonance imaging study of pancreatic iron overload in young Egyptian beta-thalassemia major patients and effect of splenectomy

    Directory of Open Access Journals (Sweden)

    Matter Randa M

    2010-04-01

    Full Text Available Abstract Background Thalassemic patients suffer from diabetes mellitus secondary to hemosiderosis. Aims The study aimed to evaluate pancreatic iron overload by T2*-weighted Gradient-echo magnetic resonance imaging (MRI in young beta-thalassemia major patients and to correlate it with glucose disturbances, hepatic hemosiderosis, serum ferritin and splenectomy. Methods Forty thalassemic patients (20 non diabetic, 10 diabetic, and 10 with impaired glucose tolerance were recruited from Pediatric Hematology Clinic, in addition to 20 healthy controls. All patients underwent clinical assessment and laboratory investigations included complete blood count, liver function tests, serum ferritin and oral glucose tolerance test (OGTT. A T2*-weighted gradient-echo sequence MRI was performed with 1.5 T scanner and signal intensity ratio (SIR of the liver and the pancreas to noise were calculated. Results Significant reduction in signal intensity ratio (SIR of the liver and the pancreas was shown in thalassemic patients compared to controls (P Conclusions pancreatic siderosis can be detected by T2* gradient-echo MRI since childhood in thalassemic patients, and is more evident in patients with abnormal glucose tolerance. After splenectomy, iron deposition may be accelerated in the pancreas. Follow up of thalassemic patients using pancreatic MRI together with intensive chelation therapy may help to prevent the development of overt diabetes.

  13. MR imaging of iliofemoral peripheral vascular calcifications using proton density-weighted, in-phase three-dimensional stack-of-stars gradient echo.

    Science.gov (United States)

    Ferreira Botelho, Marcos P; Koktzoglou, Ioannis; Collins, Jeremy D; Giri, Shivraman; Carr, James C; Gupta, NavYash; Edelman, Robert R

    2017-06-01

    The presence of vascular calcifications helps to determine percutaneous access for interventional vascular procedures and has prognostic value for future cardiovascular events. Unlike CT, standard MRI techniques are insensitive to vascular calcifications. In this prospective study, we tested a proton density-weighted, in-phase (PDIP) three-dimensional (3D) stack-of-stars gradient-echo pulse sequence with approximately 1 mm 3 isotropic spatial resolution at 1.5 Tesla (T) and 3T to detect iliofemoral peripheral vascular calcifications and correlated MR-determined lesion volumes with CT angiography (CTA). The study was approved by the Institutional Review Board. The prototype PDIP stack-of-stars pulse sequence was applied in 12 patients with iliofemoral peripheral vascular calcifications who had undergone CTA. Vascular calcifications were well visualized in all subjects, excluding segments near prostheses or stents. The location, size, and shape of the calcifications were similar to CTA. Quantitative analysis showed excellent correlation (r 2  = 0.84; P stars outperformed cartesian 3D gradient-echo and point-wise encoding time reduction with radial acquisition (PETRA). In this pilot study, a PDIP 3D stack-of-stars gradient-echo pulse sequence with high spatial resolution provided excellent image quality and accurately depicted the location and volume of iliofemoral vascular calcifications. Magn Reson Med 77:2146-2152, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  14. Flip angle optimization for dynamic contrast-enhanced MRI-studies with spoiled gradient echo pulse sequences

    Science.gov (United States)

    De Naeyer, D.; Verhulst, J.; Ceelen, W.; Segers, P.; De Deene, Y.; Verdonck, P.

    2011-08-01

    Spoiled gradient echo pulse (SPGRE) sequences are commonly used in dynamic contrast-enhanced MRI (DCE-MRI) studies to measure the contrast agent concentration in a tissue of interest over time. However, due to improper tuning of the SPGRE parameters, concentration uncertainty can be very high, even at high signal-to-noise ratio in the MR measurement. In this work, an optimization procedure is proposed for selecting the optimal value of the SPGRE-flip angle FAopt, given the expected concentration range. The optimization condition ensures that every concentration in the assumed range has the lowest possible uncertainty. By decoupling the R1- and R*2-effects caused by the presence of the contrast agent, a contour plot has been generated from which FAopt can be read off for any study design. Investigation of ten recent DCE-MRI studies showed that improper flip angle selection unnecessarily increases the concentration uncertainty, up to 742% and 72% on average for the typical physiological concentration ranges of 0-2 mM in tumour tissue and 0-10 mM in blood, respectively. Simulations show that the reduced noise levels on the concentration curves, observed at the optimal flip angle, effectively increase the precision of the kinetic parameters estimates (up to 82% for Ktrans, 82% for νe and 92% for νp in the case of an individually measured arterial input function (AIF), up to 53% for Ktrans, 59% for νe and 67% for νp in the case of a standard AIF). In vivo experiments confirm the potential of flip angle optimization to increase the reproducibility of the kinetic parameter estimates.

  15. Typical MR intensity distribution patterns in different knee joint diseases using a gradient echo sequence. Typische kernspintomographische Intensitaets-Verteilungsmuster bei unterschiedlichen Kniegelenkerkrankungen unter Anwendungen einer Gradienten-Echo-Sequenz

    Energy Technology Data Exchange (ETDEWEB)

    Tuerkay, S. (Radiologische Klinik und Poliklinik, Klinikum Steglitz, Freie Univ. Berlin (Germany)); Koenig, H. (Radiologische Klinik und Poliklinik, Klinikum Steglitz, Freie Univ. Berlin (Germany)); Wolf, K.J. (Radiologische Klinik und Poliklinik, Klinikum Steglitz, Freie Univ. Berlin (Germany))

    1993-07-01

    The knee joints of 31 patients and 3 volunteers were examined with a 1.5 T Magnetom using 3D-gradient echo sequences. We measured for the most widespread diseases: The gonarthrosis (n=23) and rheumatoid arthritis (n=8) the signal intensities in all joint parts and the typical signal plots were worked out. In case of minimal changes at the articular cartilage, the method developed and tried out by us can facilitate diagnosis. A special aspect of this method is also the patient follow-up which is now possible quantitatively and objectively. (orig.)

  16. Validation of surface-to-volume ratio measurements derived from oscillating gradient spin echo on a clinical scanner using anisotropic fiber phantoms.

    Science.gov (United States)

    Lemberskiy, Gregory; Baete, Steven H; Cloos, Martijn A; Novikov, Dmitry S; Fieremans, Els

    2017-05-01

    A diffusion measurement in the short-time surface-to-volume ratio (S/V) limit (Mitra et al., Phys Rev Lett. 1992;68:3555) can disentangle the free diffusion coefficient from geometric restrictions to diffusion. Biophysical parameters, such as the S/V of tissue membranes, can be used to estimate microscopic length scales non-invasively. However, due to gradient strength limitations on clinical MRI scanners, pulsed gradient spin echo (PGSE) measurements are impractical for probing the S/V limit. To achieve this limit on clinical systems, an oscillating gradient spin echo (OGSE) sequence was developed. Two phantoms containing 10 fiber bundles, each consisting of impermeable aligned fibers with different packing densities, were constructed to achieve a range of S/V values. The frequency-dependent diffusion coefficient, D(ω), was measured in each fiber bundle using OGSE with different gradient waveforms (cosine, stretched cosine, and trapezoidal), while D(t) was measured from PGSE and stimulated-echo measurements. The S/V values derived from the universal high-frequency behavior of D(ω) were compared against those derived from quantitative proton density measurements using single spin echo (SE) with varying echo times, and from magnetic resonance fingerprinting (MRF). S/V estimates derived from different OGSE waveforms were similar and demonstrated excellent correlation with both SE- and MRF-derived S/V measures (ρ  ≥  0.99). Furthermore, there was a smoother transition between OGSE frequency f and PGSE diffusion time when using teffS/V=9/64f, rather than the commonly used t eff  = 1/(4f), validating the specific frequency/diffusion time conversion for this regime. Our well-characterized fiber phantom can be used for the calibration of OGSE and diffusion modeling techniques, as the S/V ratio can be measured independently using other MR modalities. Moreover, our calibration experiment offers an exciting perspective of mapping tissue S/V on clinical

  17. Differentiation between focal malignant marrow-replacing lesions and benign red marrow deposition of the spine with T2*-corrected fat-signal fraction map using a three-echo volume interpolated breath-hold gradient echo Dixon sequence.

    Science.gov (United States)

    Kim, Yong Pyo; Kannengiesser, Stephan; Paek, Mun-Young; Kim, Sungjun; Chung, Tae-Sub; Yoo, Yeon Hwa; Yoon, Choon-Sik; Song, Ho-Taek; Lee, Young Han; Suh, Jin-Suck

    2014-01-01

    To assess the feasibility of T2*-corrected fat-signal fraction (FF) map by using the three-echo volume interpolated breath-hold gradient echo (VIBE) Dixon sequence to differentiate between malignant marrow-replacing lesions and benign red marrow deposition of vertebrae. We assessed 32 lesions from 32 patients who underwent magnetic resonance imaging after being referred for assessment of a known or possible vertebral marrow abnormality. The lesions were divided into 21 malignant marrow-replacing lesions and 11 benign red marrow depositions. Three sequences for the parameter measurements were obtained by using a 1.5-T MR imaging scanner as follows: three-echo VIBE Dixon sequence for FF; conventional T1-weighted imaging for the lesion-disc ratio (LDR); pre- and post-gadolinium enhanced fat-suppressed T1-weighted images for the contrast-enhancement ratio (CER). A region of interest was drawn for each lesion for parameter measurements. The areas under the curve (AUC) of the parameters and their sensitivities and specificities at the most ideal cutoff values from receiver operating characteristic curve analysis were obtained. AUC, sensitivity, and specificity were respectively compared between FF and CER. The AUCs of FF, LDR, and CER were 0.96, 0.80, and 0.72, respectively. In the comparison of diagnostic performance between the FF and CER, the FF showed a significantly larger AUC as compared to the CER (p = 0.030), although the difference of sensitivity (p = 0.157) and specificity (p = 0.157) were not significant. Fat-signal fraction measurement using T2*-corrected three-echo VIBE Dixon sequence is feasible and has a more accurate diagnostic performance, than the CER, in distinguishing benign red marrow deposition from malignant bone marrow-replacing lesions.

  18. Three-dimensional gradient-echo imaging for percutaneous MR-guided laser therapy of liver metastasis.

    Science.gov (United States)

    Puls, Ralf; Stroszczynski, Christian; Rosenberg, Christian; Kuehn, Jens-Peter; Hegenscheid, Katrin; Speck, Ulrich; Stier, Albrecht; Hosten, Norbert

    2007-06-01

    To evaluate the use of three-dimensional (3D) gradient-echo (GRE) magnetic resonance imaging (MRI) for percutaneous MR-guided catheter placement for laser therapy of liver metastases. Thirty-four patients were included. A total of 122 MR-guided percutaneous punctures of 67 liver metastases were performed on a 1.5T scanner (Symphony and Sonata; Siemens, Erlangen, Germany) using a 5.5F microcatheter system and titanium needle (Monocath; MeoMedical, Augsburg, Germany). In 88 of 122 procedures, a 2D fast low-angle shot (FLASH) T1-weighted GRE breath-hold sequence was acquired in the axial plane and if necessary in a second plane. Sequences were acquired and reviewed using the panel in the control room. In 34 of 122 procedures a 3D FLASH T1-weighted fat-saturated GRE (volume-interpolated breath-hold examination (VIBE)) sequence was acquired in the axial plane only. Acquisition and 3D review were controlled under sterile conditions with a panel inside the examination room (Syngo; Siemens). The 3D FLASH sequence significantly decreased the mean number of acquisitions needed to place the microcatheter with the titanium needle in the metastasis compared to interventions with the 2D FLASH sequence (2.9 +/- 0.83 vs. 4.4 +/- 1.63). With 2D FLASH imaging, acquisition in a second plane was necessary in 78 instances (20% of acquired 2D sequences) to ensure adequate positioning of the device during the procedure. The artifact caused by the titanium needle was smaller with the 3D FLASH sequence. The conspicuity of liver metastases and morphology (liver edge and vessels) was acceptable with both sequences. The 3D FLASH sequence improved differentiation when two to four titanium needles were inserted, due to smaller susceptibility artifacts caused by the needles. 3D GRE imaging with the capability to perform multiplanar reconstruction (MPR) shortens the procedure by reducing the number of sequences needed. Improved visibility of the titanium needles allows more precise insertion of

  19. SNR efficiency of combined bipolar gradient echoes: Comparison of three-dimensional FLASH, MPRAGE, and multiparameter mapping with VFA-FLASH and MP2RAGE.

    Science.gov (United States)

    Jutras, Jean-David; Wachowicz, Keith; Gilbert, Guillaume; De Zanche, Nicola

    2017-06-01

    High-bandwidth bipolar multiecho gradient echo sequences are increasingly popular in structural brain imaging because of reduced water-fat shifts, lower susceptibility effects, and improved signal-to-noise ratio (SNR) efficiency. In this study, we investigated the performance of three three-dimensional multiecho sequences (MPRAGE, MP2RAGE, and FLASH) with scan times 3T. We also compared the performance of multiparameter mapping (PD, T1 , and T2*) with bipolar multiecho MP2RAGE versus the variable flip angle technique with multiecho FLASH (VFA-FLASH). Multiecho sequences were optimized to yield equivalent contrast and improved SNR compared with their single-echo counterparts. Theoretical SNR gains were verified with measurements in a multilayered phantom. Robust image processing pipelines extracted PD, T1 , and T2* maps from MP2RAGE or VFA-FLASH, and the corresponding SNR was measured with varying SENSE accelerations (R = 1-5) and number of echoes (N = 1-12). All sequences were tested on four healthy volunteers. Multiecho sequences achieved SNR gains of 1.3-1.6 over single-echo sequences. MP2RAGE yielded comparable T1 -to-noise ratio to VFA-FLASH, but significantly lower SNR (maps. Measured SNR gains agreed with the theoretical predictions for SENSE accelerations ≤3. Multiecho sequences achieve higher SNR efficiency over conventional single-echo sequences, despite three-fold higher sampling bandwidths. VFA-FLASH surpasses MP2RAGE in its ability to map three parameters with high SNR and 1-mm isotropic resolution in a clinically relevant scan time (∼8:30 min), whereas MP2RAGE yields lower intersubject variability in T1 . Magn Reson Med 77:2186-2202, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  20. Optimizing contrast agent concentration and spoiled gradient echo pulse sequence parameters for catheter visualization in MR-guided interventional procedures: an analytic solution.

    Science.gov (United States)

    Sussman, Marshall S; Lindner, Uri; Haider, Masoom; Kucharczyk, Walter; Hlasny, Eugen; Trachtenberg, John

    2013-08-01

    A critical requirement of MR-guided interventions is the visualization of an instrument (e.g., catheter, needle) during the procedure. One approach is to fill the instrument with a contrast agent. Previously, the optimization of contrast agent visualization was performed only empirically. In the present study, an analytic optimization of contrast agent SNR efficiency was performed for a spoiled gradient echo pulse sequence. Optimal flip angle, repetition time, echo time, and contrast agent concentration were derived analytically. The solution is valid for any contrast agent, provided the relationship between T1 , T2 , and doping concentration is known. Phantom experiments validated the analytic optimization for Gd- and MnCl2 -based contrast agents. Results showed excellent agreement between experimentally predicted and theoretically observed magnetization behavior. In vivo experiments demonstrated optimized contrast agent visualization in brain, heart, and prostate applications. The results demonstrated the large SNR that can be achieved with analytic optimization. As a practical guideline, an 11% dilution of 500 mMol/L Gd-DTPA solution, repetition time ≈ 4 ms, echo time ≈ 1 ms, and θ ≈ 65° was found to provide a large SNR. This study derived and validated a method for analytically optimizing contrast agent SNR efficiency. This information may be useful for visualizing instruments during MR-guided interventions. © 2013 Wiley Periodicals, Inc.

  1. Evaluation of a multiple spin- and gradient-echo (SAGE) EPI acquisition with SENSE acceleration: applications for perfusion imaging in and outside the brain.

    Science.gov (United States)

    Skinner, Jack T; Robison, Ryan K; Elder, Christopher P; Newton, Allen T; Damon, Bruce M; Quarles, C Chad

    2014-12-01

    Perfusion-based changes in MR signal intensity can occur in response to the introduction of exogenous contrast agents and endogenous tissue properties (e.g. blood oxygenation). MR measurements aimed at capturing these changes often implement single-shot echo planar imaging (ssEPI). In recent years ssEPI readouts have been combined with parallel imaging (PI) to allow fast dynamic multi-slice imaging as well as the incorporation of multiple echoes. A multiple spin- and gradient-echo (SAGE) EPI acquisition has recently been developed to allow measurement of transverse relaxation rate (R2 and R2(*)) changes in dynamic susceptibility contrast (DSC)-MRI experiments in the brain. With SAGE EPI, the use of PI can influence image quality, temporal resolution, and achievable echo times. The effect of PI on dynamic SAGE measurements, however, has not been evaluated. In this work, a SAGE EPI acquisition utilizing SENSE PI and partial Fourier (PF) acceleration was developed and evaluated. Voxel-wise measures of R2 and R2(*) in healthy brain were compared using SAGE EPI and conventional non-EPI multiple echo acquisitions with varying SENSE and PF acceleration. A conservative SENSE factor of 2 with PF factor of 0.73 was found to provide accurate measures of R2 and R2(*) in white (WM) (rR2=[0.55-0.79], rR2*=[0.47-0.71]) and gray (GM) matter (rR2=[0.26-0.59], rR2*=[0.39-0.74]) across subjects. The combined use of SENSE and PF allowed the first dynamic SAGE EPI measurements in muscle, with a SENSE factor of 3 and PF factor of 0.6 providing reliable relaxation rate estimates when compared to multi-echo methods. Application of the optimized SAGE protocol in DSC-MRI of high-grade glioma patients provided T1 leakage-corrected estimates of CBV and CBF as well as mean vessel diameter (mVD) and simultaneous measures of DCE-MRI parameters K(trans) and ve. Likewise, application of SAGE in a muscle reperfusion model allowed dynamic measures of R2', a parameter that has been shown to correlate

  2. Comparison between gadolinium-enhanced 2D T1-weighted gradient-echo and spin-echo sequences in the detection of active multiple sclerosis lesions on 3.0T MRI

    Energy Technology Data Exchange (ETDEWEB)

    Aymerich, F.X. [Hospital Universitari Vall d' Hebron, Universitat Autonoma de Barcelona, MR Unit. Department of Radiology (IDI), Barcelona (Spain); Universitat Politecnica de Catalunya - Barcelona Tech (UPC), Department of Automatic Control (ESAII), Barcelona (Spain); Auger, C.; Alcaide-Leon, P.; Pareto, D.; Huerga, E.; Corral, J.F.; Mitjana, R.; Rovira, A. [Hospital Universitari Vall d' Hebron, Universitat Autonoma de Barcelona, MR Unit. Department of Radiology (IDI), Barcelona (Spain); Sastre-Garriga, J.; Montalban, X. [Hospital Universitari Vall d' Hebron, Universitat Autonoma de Barcelona, Centre d' Esclerosi Multiple de Catalunya (Cemcat), Department of Neurology/Neuroimmunology, Barcelona (Spain)

    2017-04-15

    To compare the sensitivity of enhancing multiple sclerosis (MS) lesions in gadolinium-enhanced 2D T1-weighted gradient-echo (GRE) and spin-echo (SE) sequences, and to assess the influence of visual conspicuity and laterality on detection of these lesions. One hundred MS patients underwent 3.0T brain MRI including gadolinium-enhanced 2D T1-weighted GRE and SE sequences. The two sets of contrast-enhanced scans were evaluated in random fashion by three experienced readers. Lesion conspicuity was assessed by the image contrast ratio (CR) and contrast-to-noise ratio (CNR). The intracranial region was divided into four quadrants and the impact of lesion location on detection was assessed in each slice. Six hundred and seven gadolinium-enhancing MS lesions were identified. GRE images were more sensitive for lesion detection (0.828) than SE images (0.767). Lesions showed a higher CR in SE than in GRE images, whereas the CNR was higher in GRE than SE. Most misclassifications occurred in the right posterior quadrant. The gadolinium-enhanced 2D T1-weighted GRE sequence at 3.0T MRI enables detection of enhancing MS lesions with higher sensitivity and better lesion conspicuity than 2D T1-weighted SE. Hence, we propose the use of gadolinium-enhanced GRE sequences rather than SE sequences for routine scanning of MS patients at 3.0T. (orig.)

  3. Single-Breath-Hold Whole-heart Unenhanced Coronary MRA Using Multi-shot Gradient Echo EPI at 3T: Comparison with Free-breathing Turbo-field-echo Coronary MRA on Healthy Volunteers.

    Science.gov (United States)

    Iyama, Yuji; Nakaura, Takeshi; Nagayama, Yasunori; Oda, Seitaro; Utsunomiya, Daisuke; Kidoh, Masafumi; Yuki, Hideaki; Hirata, Kenichiro; Namimoto, Tomohiro; Kitajima, Mika; Morita, Kosuke; Funama, Yoshinori; Takemura, Atsushi; Okuaki, Tomoyuki; Yamashita, Yasuyuki

    2017-06-26

    We investigated the feasibility of single breath hold unenhanced coronary magnetic resonance angiography (MRA) using multi-shot gradient echo planar imaging (MSG-EPI) on a 3T-scanner. Fourteen volunteers underwent single breath hold coronary MRA with a MSG-EPI and free-breathing turbo field echo (TFE) coronary MRA at 3T. The acquisition time, signal to noise ratio (SNR), and the contrast of the sequences were compared with the paired t-test. Readers evaluated the image contrast, noise, sharpness, artifacts, and the overall image quality. The acquisition time was 88.1% shorter for MSG-EPI than TFE (24.7 ± 2.5 vs 206.4 ± 23.1 sec, P EPI than TFE scans (P EPI and TFE scans (1.8 ± 0.3 vs 1.9 ± 0.3, P = 0.24). There was no significant difference in image contrast, image sharpness, and overall image quality between two scan techniques. The score of image noise and artifact were significantly higher on MSG-EPI than TFE scans (P EPI sequence is a promising technique for shortening the scan time and for preserving the image quality of unenhanced whole heart coronary MRA on a 3T scanner.

  4. MR renography using a dynamic gradient-echo sequence and low-dose gadopentetate dimeglumine as an alternative to radionuclide renography.

    Science.gov (United States)

    Teh, Hui Seong; Ang, Ee Sin; Wong, Weng Cheong; Tan, Say Beng; Tan, Andrew Gee Seng; Chng, Soke Miang; Lin, Michael Beng Kiang; Goh, Jeffery Seow Kuang

    2003-08-01

    Our aim was to evaluate the feasibility of acquiring an MR signal intensity-time renographic curve and dynamic serial images in a way similar to that of acquiring radionuclide renograms, with a dynamic gradient-echo sequence and a low-dose gadopentetate dimeglumine technique, using a commonly available 1.5-T MR scanner. SUBJECTS AND METHODS. Patients who underwent both radionuclide and MR renographic studies within a 3-month period were included in the analysis. This yielded 21 studies from 19 patients. Nineteen of the 21 studies were available for analysis. Two studies were excluded because of technical errors during MR renographic acquisition. Serial MR renograms were obtained using a dynamic two-dimensional spoiled gradient-echo fast low-angle shot T1-weighted sequence. Low-dose IV furosemide and gadopentetate dimeglumine (0.025 mmol/kg of body weight) were administered. Intensity-time curves were obtained from the manually selected regions of interest over the renal parenchyma and whole kidney for calculation of split renal function and assessment of urinary excretion, respectively. Results were compared with those obtained with radionuclide renography. Good correlation (Pearson's correlation coefficient, r = 0.97, p gadopentetate dimeglumine technique can produce an intensity-time curve and serial dynamic images of the urinary system, in a way similar to that of radionuclide renography. This technique allows assessment of split renal function and urinary excretory status and is a feasible alternative to radionuclide renography.

  5. Free-breathing contrast-enhanced T1-weighted gradient-echo imaging with radial k-space sampling for paediatric abdominopelvic MRI

    Energy Technology Data Exchange (ETDEWEB)

    Chandarana, Hersh; Block, Kai T.; Winfeld, Matthew J.; Lala, Shailee V.; Mazori, Daniel; Giuffrida, Emalyn; Babb, James S.; Milla, Sarah S. [New York University Langone Medical Center, Department of Radiology, New York, NY (United States)

    2014-02-15

    To compare the image quality of contrast-enhanced abdominopelvic 3D fat-suppressed T1-weighted gradient-echo imaging with radial and conventional Cartesian k-space acquisition schemes in paediatric patients. Seventy-three consecutive paediatric patients were imaged at 1.5 T with sequential contrast-enhanced T1-weighted Cartesian (VIBE) and radial gradient echo (GRE) acquisition schemes with matching parameters when possible. Cartesian VIBE was acquired as a breath-hold or as free breathing in patients who could not suspend respiration, followed by free-breathing radial GRE in all patients. Two paediatric radiologists blinded to the acquisition schemes evaluated multiple parameters of image quality on a five-point scale, with higher score indicating a more optimal examination. Lesion presence or absence, conspicuity and edge sharpness were also evaluated. Mixed-model analysis of variance was performed to compare radial GRE and Cartesian VIBE. Radial GRE had significantly (all P < 0.001) higher scores for overall image quality, hepatic edge sharpness, hepatic vessel clarity and respiratory motion robustness than Cartesian VIBE. More lesions were detected on radial GRE by both readers than on Cartesian VIBE, with significantly higher scores for lesion conspicuity and edge sharpness (all P < 0.001). Radial GRE has better image quality and lesion conspicuity than conventional Cartesian VIBE in paediatric patients undergoing contrast-enhanced abdominopelvic MRI. (orig.)

  6. Validity of gradient-echo three-dimensional delayed gadolinium-enhanced magnetic resonance imaging of hip joint cartilage: A histologically controlled study

    Energy Technology Data Exchange (ETDEWEB)

    Zilkens, Christoph, E-mail: christoph.zilkens@med.uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Orthopaedic Surgery, Moorenstraße 5, D-40225 Dusseldorf (Germany); Miese, Falk, E-mail: falk.miese@med.uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Moorenstraße 5, D-40225 Dusseldorf (Germany); Herten, Monika, E-mail: Moherten@web.de [Univ Dusseldorf, Medical Faculty, Department of Orthopaedic Surgery, Moorenstraße 5, D-40225 Dusseldorf (Germany); Kurzidem, Sabine, E-mail: sabine.kurzidem@uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Orthopaedic Surgery, Moorenstraße 5, D-40225 Dusseldorf (Germany); Jäger, Marcus [Univ Essen, Medical Faculty, Department of Orthopaedic Surgery, D-45147 Essen (Germany); König, Dietmar, E-mail: Dietmarpierre.koenig@lvr.de [LVR Clinic for Orthopedic Surgery, D-41749 Viersen (Germany); Antoch, Gerald, E-mail: antoch@med.uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Diagnostic and Interventional Radiology, Moorenstraße 5, D-40225 Dusseldorf (Germany); Krauspe, Rüdiger, E-mail: krauspe@med.uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Orthopaedic Surgery, Moorenstraße 5, D-40225 Dusseldorf (Germany); Bittersohl, Bernd, E-mail: bernd.bittersohl@med.uni-duesseldorf.de [Univ Dusseldorf, Medical Faculty, Department of Orthopaedic Surgery, Moorenstraße 5, D-40225 Dusseldorf (Germany)

    2013-02-15

    Objective: To validate gradient-echo three-dimensional (3D) delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) by means of histological analyses in the assessment of hip joint cartilage. Materials and methods: Twenty-one femoral head specimens collected from 21 patients (7 males, 14 females, mean age: 60.9 ± 9.6 years; range: 37.6–77.3 years), who underwent total hip replacement for symptomatic hip joint osteoarthritis, underwent MRI and histological assessment. A region of 2 cm{sup 2} at the weight-bearing area was marked with four pins to enable multi-planar MRI reformatting to be matched with histological sections. MRI was performed at 3 T with a 3D double-echo steady-state (DESS) sequence for morphological cartilage assessment and 3D Volumetric Interpolated Breathhold Examination (VIBE) for T1{sub Gd} mapping. Histological sections were evaluated according to the Mankin score system. Total Mankin score, grade of toluidine staining (sensitive for glycosaminoglycan content) and a modified Mankin score classification system with four sub-groups of cartilage damage were correlated with MRI data. Results: Spearman's rho correlation analyses revealed a statistically significant correlation between T1{sub Gd} mapping and histological analyses in all categories including total Mankin score (r = −0.658, p-value ≤ 0.001), toluidine staining (r = −0.802, p-value < 0.001) and modified Mankin score (r = −0.716, p-value < 0.001). The correlation between morphological MRI and histological cartilage assessment was statistically significant but inferior to the biochemical cartilage MRI (r-values ranging from −0.411 to 0.525, p-values < 0.001). Conclusions: Gradient-echo dGEMRIC is reliable while offering the unique features of high image resolution and 3D biochemically sensitive MRI for the assessment of early cartilage degeneration.

  7. Enhancing acoustic signal quality by rapidly switching between pulse-echo and through-transmission using diplexers

    Science.gov (United States)

    Valencia, Juan D.; Diaz, Aaron A.; Tucker, Brian J.

    2008-03-01

    The increase of terrorism and its global impact has made the screening of the contents of liquid-filled containers a necessity. The ability to evaluate the contents of a container rapidly and accurately is a critical tool in maintaining global safety and security. Due to the immense quantities and large variety of containers shipped worldwide, there is a need for a technology that enables rapid and effective ways of conducting non-intrusive container inspections. Such inspections can be performed utilizing "through-transmission" or "pulse-echo" acoustic techniques, in combination with multiple frequency excitation pulses or waveforms. The challenge is combining and switching between the different acoustic techniques without distorting the excitation pulse or waveform, degrading or adding noise to the receive signal; while maintaining a portable, low-power, low-cost, and easy to use system. The Pacific Northwest National Laboratory (PNNL) has developed a methodology and prototype device focused on this challenge. The prototype relies on an advanced diplexer circuit capable of rapidly switching between both "through-transmission" and "pulse-echo" detection modes. This type of detection requires the prototype to isolate the pulsing circuitry from the receiving circuitry to prevent damage and reduce noise. The results of this work demonstrate that an advanced diplexer circuit can be effective; however, some bandwidth issues exist. This paper focuses on laboratory measurements and test results acquired with the PNNL prototype device as applied to several types of liquid-filled containers. Results of work conducted in the laboratory will be presented and future measurement platform enhancements will be discussed.

  8. Rapid quantitative T2 mapping of the prostate using three-dimensional dual echo steady state MRI at 3T.

    Science.gov (United States)

    Dregely, Isabel; Margolis, Daniel A J; Sung, Kyunghyun; Zhou, Ziwu; Rangwala, Novena; Raman, Steven S; Wu, Holden H

    2016-12-01

    To develop and evaluate a rapid three-dimensional (3D) quantitative T2 mapping method for prostate cancer imaging using dual echo steady state (DESS) MRI at 3T. In simulations, DESS-T2 mapping in the presence of T1 and B1+ variations was evaluated. In a phantom and in healthy volunteers (n = 4), 3D DESS-T2 mapping was compared with a two-dimensional turbo spin echo (TSE) approach. In volunteers and a pilot patient study (n = 29), quantitative T2 in normal prostate anatomical zones and in suspected cancerous lesions was evaluated. The simulated bias for DESS-T2 was T1 ( B1+) variations. In phantoms and in vivo, high correlation of DESS-T2 and TSE-T2 (r(2)  = 0.98 and 0.88, P mapping in the entire prostate can be performed in 1 min using DESS MRI. Magn Reson Med 76:1720-1729, 2016. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  9. Rapid estimation of cartilage T2 with reduced T1 sensitivity using double echo steady state imaging.

    Science.gov (United States)

    Heule, Rahel; Ganter, Carl; Bieri, Oliver

    2014-03-01

    In principle, double echo steady state (DESS) offers morphological and quantitative T2 imaging of cartilage within one single scan. However, accurate T2 estimation is hampered by its prominent T1 dependency in the limit of low flip angles, generally used to image cartilage morphology, as for the osteoarthritis initiative. A new postprocessing approach is introduced to overcome this T1-related bias for rapid DESS-based T2 quantification in the low flip angle regime. Based on a rough global T1 estimator and a golden section search, T2 is extracted from the ratio of the two echoes acquired with DESS. The new relaxometry method is evaluated from simulations and in vivo 3D measurements of the knee joint at 3T. A pronounced reduction in the T1-related bias of DESS-T2 estimation and increased zonal variation in T2 between deep and superficial cartilage layers are observed. The improvement becomes particularly evident in the range of low flip angles (α estimate, the reliability of DESS-T2 quantification can be considerably increased. The results emphasize the potential of DESS to fuse accurate quantitative T2 and morphological imaging of the musculoskeletal system within one single scan. Copyright © 2013 Wiley Periodicals, Inc.

  10. Simultaneous Quantitative MRI Mapping of T1, T2 and Magnetic Susceptibility with Multi-Echo MP2RAGE

    National Research Council Canada - National Science Library

    Riccardo Metere; Tobias Kober; Harald E Möller; Andreas Schäfer

    2017-01-01

    ...) Magnetization-Prepared 2 RApid Gradient Echoes (MP2RAGE) sequence. T1 maps can be obtained using the MP2RAGE sequence, which is relatively insensitive to inhomogeneities of the radio-frequency transmit field...

  11. Accuracy of SWI sequences compared to T2*-weighted gradient echo sequences in the detection of cerebral cavernous malformations in the familial form.

    Science.gov (United States)

    Sparacia, Gianvincenzo; Speciale, Claudia; Banco, Aurelia; Bencivinni, Francesco; Midiri, Massimo

    2016-10-01

    The purpose of this study was to assess the accuracy of susceptibility-weighted imaging (SWI), compared with T2*-weighted gradient echo (GRE) imaging in assessing cerebral cavernous malformations. We retrospectively evaluated 21 patients with a familial form of cavernous malformation. Magnetic resonance (MR) protocol included non-enhanced and contrast-enhanced fast-spin echo (FSE) T1-weighted sequences, FSE T2-weighted sequences, fluid-attenuated inversion-recovery (FLAIR), GRE T2*-weighted and SWI sequences. Images were reviewed in consensus by two expert neuroradiologists to assess the location, number, size and conspicuity of the lesions on T2*-weighted GRE and SWI sequences. Statistical differences in the number, size and conspicuity of the lesions seen on the SWI images and the T2*-weighted GRE images were assessed with the nonparametric Wilcoxon signed rank test. The number of cavernous malformations was significantly higher (p cavernous malformation that was demonstrated only on the SWI images in the previous MR examination. The SWI sequence, being more sensitive to substances which distort the local magnetic field than the GRE T2*W sequence, showed a higher sensitivity in identifying cerebral cavernous malformations. Thus, routine clinical neuroimaging protocol should contain SWI sequences to evaluate patients with (or suspected) cerebral cavernous malformations. © The Author(s) 2016.

  12. Low-field MR imaging of the spine. A comparative study of a traditional and a new, completely balanced gradient-echo sequence

    Energy Technology Data Exchange (ETDEWEB)

    Drejer, J. [Dept. of Diagnostic Radiology, Herlev Hospital, Univ. Copenhagen (Denmark); Thomsen, H.S. [Dept. of Diagnostic Radiology, Herlev Hospital, Univ. Copenhagen (Denmark); Tanttu, J. [Picker Nordstar, Helsinki (Finland)

    1995-09-01

    49 patients underwent 53 examinations with both a traditional T1-weighted gradient-echo (PS) sequence and a new completely balanced steady-state 3-D (CBASS3D) sequence; 20 examinations included the cervical spine, 8 the thoracic spine and 25 the lumbar spine. All 106 examinations were reviewed twice regarding visibility of selected structures in the spinal region and diagnostic usefulness. The CBASS3D sequence delineated the medulla, nerve roots, CSF, the intervertebral discs and the posterior longitudinal ligament significantly better than the PS sequence. Disc hernia was also better visualised (p<0.01). There were significantly more artefacts on images obtained with the CBASS3D sequence, but they were usually outside the region of interest and occurred less frequently over time due to increased experience of the staff. Both reviewers found the diagnostic usefulness of CBASS3D to be superior compared to that of PS and excellent for diagnostic purposes. (orig./MG).

  13. A study of MRI gradient echo signals from discrete magnetic particles with considerations of several parameters in simulations.

    Science.gov (United States)

    Kokeny, Paul; Cheng, Yu-Chung N; Xie, He

    2017-12-26

    Modeling MRI signal behaviors in the presence of discrete magnetic particles is important, as magnetic particles appear in nanoparticle labeled cells, contrast agents, and other biological forms of iron. Currently, many models that take into account the discrete particle nature in a system have been used to predict magnitude signal decays in the form of R2* or R2' from one single voxel. Little work has been done for predicting phase signals. In addition, most calculations of phase signals rely on the assumption that a system containing discrete particles behaves as a continuous medium. In this work, numerical simulations are used to investigate MRI magnitude and phase signals from discrete particles, without diffusion effects. Factors such as particle size, number density, susceptibility, volume fraction, particle arrangements for their randomness, and field of view have been considered in simulations. The results are compared to either a ground truth model, theoretical work based on continuous mediums, or previous literature. Suitable parameters used to model particles in several voxels that lead to acceptable magnetic field distributions around particle surfaces and accurate MR signals are identified. The phase values as a function of echo time from a central voxel filled by particles can be significantly different from those of a continuous cubic medium. However, a completely random distribution of particles can lead to an R2' value which agrees with the prediction from the static dephasing theory. A sphere with a radius of at least 4 grid points used in simulations is found to be acceptable to generate MR signals equivalent from a larger sphere. Increasing number of particles with a fixed volume fraction in simulations reduces the resulting variance in the phase behavior, and converges to almost the same phase value for different particle numbers at each echo time. The variance of phase values is also reduced when increasing the number of particles in a fixed

  14. SU-D-207A-04: Use of Gradient Echo Plural Contrast Imaging (GEPCI) in MR-Guided Radiation Therapy: A Feasibility Study Targeting Brain Treatment

    Energy Technology Data Exchange (ETDEWEB)

    Cai, B; Rao, Y; Tsien, C; Huang, J; Green, O; Mutic, S; Gach, H [Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO (United States); Wen, J; Yablonskiy, D [Department of Radiology, Washington University School of Medicine, St Louis, MO (United States)

    2016-06-15

    Purpose: To implement the Gradient Echo Plural Contrast Imaging(GEPCI) technique in MRI-simulation for radiation therapy and assess the feasibility of using GEPCI images with advanced inhomogeneity correction in MRI-guided radiotherapy for brain treatment. Methods: An optimized multigradient-echo GRE sequence (TR=50ms;TE1=4ms;delta-TE=4ms;flip angle=300,11 Echoes) was developed to generate both structural (T1w and T2*w) and functional MRIs (field and susceptibility maps) from a single acquisition. One healthy subject (Subject1) and one post-surgical brain cancer patient (Subject2) were scanned on a Philips Ingenia 1.5T MRI used for radiation therapy simulation. Another healthy subject (Subject3) was scanned on a 0.35T MRI-guided radiotherapy (MR-IGRT) system (ViewRay). A voxel spread function (VSF) was used to correct the B0 inhomogeneities caused by surgical cavities and edema for Subject2. GEPCI images and standard radiotherapy planning MRIs for this patient were compared focusing the delineation of radiotherapy target region. Results: GEPCI brain images were successfully derived from all three subjects with scan times of <7 minutes. The images derived for Subjects1&2 demonstrated that GEPCI can be applied and combined into radiotherapy MRI simulation. Despite low field, T1-weighted and R2* images were successfully reconstructed for Subject3 and were satisfactory for contour and target delineation. The R2* distribution of grey matter (center=12,FWHM=4.5) and white matter (center=14.6, FWHM=2) demonstrated the feasibility for tissue segmentation and quantification. The voxel spread function(VSF) corrected surgical site related inhomogeneities for Subject2. R2* and quantitative susceptibility map(QSM) images for Subject2 can be used to quantitatively assess the brain structure response to radiation over the treatment course. Conclusion: We implemented the GEPCI technique in MRI-simulation and in MR-IGRT system for radiation therapy. The images demonstrated that it

  15. Two-Dimensional Spoiled Gradient-Recalled Echo Magnetic Resonance Imaging of the Liver Using Respiratory Navigator-Gating Techniques.

    Science.gov (United States)

    Inoue, Yusuke; Hata, Hirofumi; Matsunaga, Keiji; Nakajima, Ai; Komi, Shotaro; Abe, Yutaka; Miyatake, Hiroki

    We assessed the feasibility of T1-weighted 2-dimensional spoiled gradient-recalled (2D SPGR) acquisition in steady-state imaging of the liver with various respiratory navigator gating techniques. A total of 12 healthy volunteers underwent in-phase and out-of-phase 2D SPGR imaging of the liver during breath-holding and free-breathing. Four techniques for respiratory navigation, 2 conventional navigator techniques and 2 self-navigator techniques, were used for free-breathing imaging. Good navigator waveforms were obtained in conventional navigation, whereas fluctuations were evident in self navigation. All of the 4 navigator-based methods provided better images in terms of background signals and visual image quality compared with images obtained with no respiratory control. However, differences remained in comparison with breath-holding. Superiority of self-navigation to conventional navigation was not shown. Navigator-gating techniques improved 2D SPGR images of the liver acquired during free-breathing, suggesting feasibility and beneficial effects, although navigator-based images were still inferior to breath-hold images.

  16. Feasibility of dual gradient-echo in-phase and opposed-phase magnetic resonance imaging for the evaluation of epicardial fat

    Energy Technology Data Exchange (ETDEWEB)

    Okayama, Satoshi; Ayako, Seno; Somekawa, Satoshi; Uemura, Shiro; Saito, Yoshihiko (First Dept. of Internal Medicine, Nara Medical Univ., Nara (Japan)), email: satosi01@naramed-u.ac.jp; Kubota, Yasushi (Radiology, Hirai Hospital, Nara (Japan))

    2011-09-15

    Background: Dual gradient-echo in-phase (IP) and opposed-phase (OP) magnetic resonance imaging (MRI) can evaluate small amounts of fat, and is widely used for imaging abdominal organs. Epicardial fat has recently been revealed as having an important role in the development of heart disease, but IPOP-MRI has not been widely applied in this field, probably because of cardiac motion artifacts. Purpose: To demonstrate the feasibility of IPOP-MRI with electrocardiography (ECG)-gating for evaluation of epicardial fat in the normal human heart, compared to black-blood T1-weighted imaging (T1WI). Material and Methods: Ten healthy volunteers were studied. Epicardial fat volume was quantitatively evaluated on OP-from-IP subtraction images and T1-weighted images. Results: Epicardial fat was clearly visualized on the subtraction images as hyperintense areas that corresponded to regions identified as epicardial fat on the T1-weighted images. Epicardial fat volume correlated well between the two methods (r = 0.93, P <0.0001), and tended to be larger on the subtraction images than on the T1-weighted images (91.4 +- 30.1 vs. 84.1 +- 30.5 mL, P = 0.07). Conclusion: IPOP-MRI with ECG-gating may be a useful alternative method to black-blood T1WI for evaluation of epicardial fat

  17. Hematoma size in deep intracerebral hemorrhage and its correlation with dot-like hemosiderin spots on gradient echo T2*-weighted MRI.

    Science.gov (United States)

    Imaizumi, Toshio; Honma, Toshimi; Horita, Yoshifumi; Kohama, Ikuhide; Miyata, Kei; Kawamura, Maiko; Niwa, Jun

    2006-07-01

    Dot-like low intensity spots (dot-like hemosiderin spots: dotHSs) on gradient echo T2*-weighted MRI have been histologically diagnosed to represent old cerebral microbleeds associated with microangiopathies. They have also been correlated to the fragility of small vessels and the tendency to bleed. Therefore, a substantial number of dotHSs might be associated with a large-sized, deep intracerebral hematoma (ICH). On the other hand, dotHSs may reflect old microbleeds that did not enlarge to symptomatic size. To investigate how dotHSs are related to the size (maximal diameter) of primary deep ICH, we analyzed the diameter and the number of dotHSs in 151 patients with deep ICH not associated with subarachnoid hemorrhage or intraventricular hemorrhage (75 males and 76 females, age ranged from 37 to 90 [65.7 +/- 11.3 years old] who were consecutively admitted to Hakodate Municipal Hospital. The hazard ratio (HR) for a maximal diameter of deep ICH or =2 cm (4.7 +/- 7.0, P= .012). Multivariate analysis revealed that a maximal diameter of deep ICH of < or =2 cm was found in patients with dotHS (HR, 3.7; 95% confidence interval [CI], 1.4-10.1; P= .009). Though small sample size limited the power of our analyses, these findings suggest that the number of dotHSs may be associated with a small diameter of deep ICH.

  18. Multi-gradient echo MR thermometry for monitoring of the near-field area during MR-guided high intensity focused ultrasound heating.

    Science.gov (United States)

    Lam, Mie K; de Greef, Martijn; Bouwman, Job G; Moonen, Chrit T W; Viergever, Max A; Bartels, Lambertus W

    2015-10-07

    The multi-gradient echo MR thermometry (MGE MRT) method is proposed to use at the interface of the muscle and fat layers found in the abdominal wall, to monitor MR-HIFU heating. As MGE MRT uses fat as a reference, it is field-drift corrected. Relative temperature maps were reconstructed by subtracting absolute temperature maps. Because the absolute temperature maps are reconstructed of individual scans, MGE MRT provides the flexibility of interleaved mapping of temperature changes between two arbitrary time points. The method's performance was assessed in an ex vivo water bath experiment. An ex vivo HIFU experiment was performed to show the method's ability to monitor heating of consecutive HIFU sonications and to estimate cooling time constants, in the presence of field drift. The interleaved use between scans of a clinical protocol was demonstrated in vivo in a patient during a clinical uterine fibroid treatment. The relative temperature measurements were accurate (mean absolute error 0.3 °C) and provided excellent visualization of the heating of consecutive HIFU sonications. Maps were reconstructed of estimated cooling time constants and mean ROI values could be well explained by the applied heating pattern. Heating upon HIFU sonication and subsequent cooling could be observed in the in vivo demonstration.

  19. ECHO virus

    Science.gov (United States)

    ... page: //medlineplus.gov/ency/article/001340.htm ECHO virus To use the sharing features on this page, please enable JavaScript. Enteric cytopathic human orphan (ECHO) viruses are a group of viruses that can lead ...

  20. Evaluation of multi-echo ICA denoising for task based fMRI studies: Block designs, rapid event-related designs, and cardiac-gated fMRI.

    Science.gov (United States)

    Gonzalez-Castillo, Javier; Panwar, Puja; Buchanan, Laura C; Caballero-Gaudes, Cesar; Handwerker, Daniel A; Jangraw, David C; Zachariou, Valentinos; Inati, Souheil; Roopchansingh, Vinai; Derbyshire, John A; Bandettini, Peter A

    2016-11-01

    Multi-echo fMRI, particularly the multi-echo independent component analysis (ME-ICA) algorithm, has previously proven useful for increasing the sensitivity and reducing false positives for functional MRI (fMRI) based resting state connectivity studies. Less is known about its efficacy for task-based fMRI, especially at the single subject level. This work, which focuses exclusively on individual subject results, compares ME-ICA to single-echo fMRI and a voxel-wise T2(⁎) weighted combination of multi-echo data for task-based fMRI under the following scenarios: cardiac-gated block designs, constant repetition time (TR) block designs, and constant TR rapid event-related designs. Performance is evaluated primarily in terms of sensitivity (i.e., activation extent, activation magnitude, percent detected trials and effect size estimates) using five different tasks expected to evoke neuronal activity in a distributed set of regions. The ME-ICA algorithm significantly outperformed all other evaluated processing alternatives in all scenarios. Largest improvements were observed for the cardiac-gated dataset, where ME-ICA was able to reliably detect and remove non-neural T1 signal fluctuations caused by non-constant repetition times. Although ME-ICA also outperformed the other options in terms of percent detection of individual trials for rapid event-related experiments, only 46% of all events were detected after ME-ICA; suggesting additional improvements in sensitivity are required to reliably detect individual short event occurrences. We conclude the manuscript with a detailed evaluation of ME-ICA outcomes and a discussion of how the ME-ICA algorithm could be further improved. Overall, our results suggest that ME-ICA constitutes a versatile, powerful approach for advanced denoising of task-based fMRI, not just resting-state data. Published by Elsevier Inc.

  1. Comparison of Spoiled Gradient Echo and Steady-State Free-Precession Imaging for Native Myocardial T1 Mapping Using the Slice Interleaved T1 mapping (STONE) Sequence

    Science.gov (United States)

    Jang, Jihye; Bellm, Steven; Roujol, Sébastien; Basha, Tamer A.; Nezafat, Maryam; Kato, Shingo; Weingärtner, Sebastian; Nezafat, Reza

    2017-01-01

    Cardiac T1 mapping allows non-invasive imaging of interstitial diffuse fibrosis. Myocardial T1 is commonly calculated by voxel-wise fitting of the images acquired using balanced steady-state free precession (SSFP) after an inversion pulse. However, SSFP imaging is sensitive to B1 and B0 imperfection, which may result in additional artifacts. Gradient echo (GRE) imaging sequence has been used for myocardial T1 mapping, however its use has been limited to higher magnetic field to compensate for lower signal-to-noise ratio (SNR) of GRE vs. SSFP imaging. A slice-interleaved T1 mapping (STONE) sequence with SSFP readout (STONE-SSFP) has been recently proposed for native myocardial T1 mapping, which allows longer recovery of magnetization (>8 R-R) after each inversion pulse. In this study, we hypothesize that a longer recovery allows higher SNR and enables native myocardial T1 mapping using STONE with GRE imaging readout (STONE-GRE) at 1.5T. Numerical simulations, phantom and in-vivo imaging were performed to compare the performance of STONE-GRE and STONE-SSFP for native myocardial T1 mapping at 1.5T. In numerical simulations, STONE-SSFP shows sensitivity to both T2 and off-resonance. Despite insensitivity of GRE imaging to T2, STONE-GRE remains sensitive to T2 due to the dependence of the inversion pulse performance on T2. In the phantom study, STONE-GRE had inferior accuracy, precision, and similar repeatability as compared to STONE-SSFP. In in-vivo studies, STONE-GRE and STONE-SSFP had similar myocardial native T1 times, precision, repeatability and subjective T1 map quality. Despite lower SNR of GRE imaging readout compared to SSFP, STONE-GRE provides similar native myocardial T1 measurements, precision, repeatability and subjective image quality when compared to STONE-SSFP at 1.5T. PMID:27658506

  2. T2*-based MR imaging (gradient echo or susceptibility-weighted imaging) in midline and off-midline intracranial germ cell tumors: a pilot study.

    Science.gov (United States)

    Morana, Giovanni; Alves, Cesar Augusto; Tortora, Domenico; Finlay, Jonathan L; Severino, Mariasavina; Nozza, Paolo; Ravegnani, Marcello; Pavanello, Marco; Milanaccio, Claudia; Maghnie, Mohamad; Rossi, Andrea; Garrè, Maria Luisa

    2018-01-01

    The role of T2*-based MR imaging in intracranial germ cell tumors (GCTs) has not been fully elucidated. The aim of this study was to evaluate the susceptibility-weighted imaging (SWI) or T2* gradient echo (GRE) features of germinomas and non-germinomatous germ cell tumors (NGGCTs) in midline and off-midline locations. We retrospectively evaluated all consecutive pediatric patients referred to our institution between 2005 and 2016, for newly diagnosed, treatment-naïve intracranial GCT, who underwent MRI, including T2*-based MR imaging (T2* GRE sequences or SWI). Standard pre- and post-contrast T1- and T2-weighted imaging characteristics along with T2*-based MR imaging features of all lesions were evaluated. Diagnosis was performed in accordance with the SIOP CNS GCT protocol criteria. Twenty-four subjects met the inclusion criteria (17 males and 7 females). There were 17 patients with germinomas, including 5 basal ganglia primaries, and 7 patients with secreting NGGCT. All off-midline germinomas presented with SWI or GRE hypointensity; among midline GCT, all NGGCTs showed SWI or GRE hypointensity whereas all but one pure germinoma were isointense or hyperintense to normal parenchyma. A significant difference emerged on T2*-based MR imaging among midline germinomas, NGGCTs, and off-midline germinomas (p < 0.001). Assessment of the SWI or GRE characteristics of intracranial GCT may potentially assist in differentiating pure germinomas from NGGCT and in the characterization of basal ganglia involvement. T2*-based MR imaging is recommended in case of suspected intracranial GCT.

  3. A tissue-scale gradient of hydrogen peroxide mediates rapid wound detection in zebrafish.

    Science.gov (United States)

    Niethammer, Philipp; Grabher, Clemens; Look, A Thomas; Mitchison, Timothy J

    2009-06-18

    Barrier structures (for example, epithelia around tissues and plasma membranes around cells) are required for internal homeostasis and protection from pathogens. Wound detection and healing represent a dormant morphogenetic program that can be rapidly executed to restore barrier integrity and tissue homeostasis. In animals, initial steps include recruitment of leukocytes to the site of injury across distances of hundreds of micrometres within minutes of wounding. The spatial signals that direct this immediate tissue response are unknown. Owing to their fast diffusion and versatile biological activities, reactive oxygen species, including hydrogen peroxide (H(2)O(2)), are interesting candidates for wound-to-leukocyte signalling. Here we probe the role of H(2)O(2) during the early events of wound responses in zebrafish larvae expressing a genetically encoded H(2)O(2) sensor. This reporter revealed a sustained rise in H(2)O(2) concentration at the wound margin, starting approximately 3 min after wounding and peaking at approximately 20 min, which extended approximately 100-200 microm into the tail-fin epithelium as a decreasing concentration gradient. Using pharmacological and genetic inhibition, we show that this gradient is created by dual oxidase (Duox), and that it is required for rapid recruitment of leukocytes to the wound. This is the first observation, to our knowledge, of a tissue-scale H(2)O(2) pattern, and the first evidence that H(2)O(2) signals to leukocytes in tissues, in addition to its known antiseptic role.

  4. Comparison of multi-echo dixon methods with volume interpolated breath-hold gradient magnetic resonance imaging in fat-signal fraction quantification of paravaertebral muscle

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Yeon Hwa; Kim, Hak Sun; Lee, Young Han [Dept. of Radiology, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul (Korea, Republic of); and others

    2015-10-15

    To assess whether multi-echo Dixon magnetic resonance (MR) imaging with simultaneous T2{sup *} estimation and correction yields more accurate fat-signal fraction (FF) measurement of the lumbar paravertebral muscles, in comparison with non-T2{sup *}-corrected two-echo Dixon or T2{sup *}-corrected three-echo Dixon, using the FF measurements from single-voxel MR spectroscopy as the reference standard. Sixty patients with low back pain underwent MR imaging with a 1.5T scanner. FF mapping images automatically obtained using T2{sup *}-corrected Dixon technique with two (non-T2{sup *}-corrected), three, and six echoes, were compared with images from single-voxel MR spectroscopy at the paravertebral muscles on levels L4 through L5. FFs were measured directly by two radiologists, who independently drew the region of interest on the mapping images from the three sequences. A total of 117 spectroscopic measurements were performed either bilaterally (57 of 60 subjects) or unilaterally (3 of 60 subjects). The mean spectroscopic FF was 14.3 ± 11.7% (range, 1.9-63.7%). Interobserver agreement was excellent between the two radiologists. Lin's concordance correlation between the spectroscopic findings and all the imaging-based FFs were statistically significant (p < 0.001). FFs obtained from the T2*-corrected six-echo Dixon sequences showed a significantly better concordance with the spectroscopic data, with its concordance correlation coefficient being 0.99 and 0.98 (p < 0.001), as compared with two- or three-echo methods. T2{sup *}-corrected six-echo Dixon sequence would be a better option than two- or three-echo methods for noninvasive quantification of lumbar muscle fat quantification.

  5. Rapid 3D imaging of the lower airway by MRI in patients with congenital heart disease: A retrospective comparison of delayed volume interpolated breath-hold examination (VIBE) to turbo spin echo (TSE).

    Science.gov (United States)

    Goot, Benjamin H; Patel, Sonali; Fonseca, Brian

    2017-01-01

    When imaging the lower airway by MRI, the traditional technique turbo spin echo (TSE) results in high quality 2D images, however planning and acquisition times are lengthy. An alternative, delayed volume interpolated breath-holds examination (VIBE), is a 3D gradient echo technique that produces high spatial resolution imaging of the airway in one breath-hold. The objective of this study is to retrospectively evaluate the accuracy of lower airway measurements obtained by delayed VIBE when compared to TSE. Patients with congenital heart disease who underwent a cardiac MRI (CMR) that included a delayed VIBE sequence from 5/2008 to 9/2013 were included. Standard TSE imaging was performed and delayed VIBE was acquired 5 min after gadolinium contrast administration. Airway measurements were made on both sequences by two observers in a blinded fashion to the other observer and other technique. Intraclass correlations (ICC) were calculated to assess for agreement between both techniques and the observers. 29 studies met inclusion criteria with a mean patient age of 8.8 years (2 months to 63 years) and mean patient weight of 30.2 kg (3.5-110). All delayed VIBE and TSE sequences were found to be of diagnostic quality. Mean acquisition time was shorter for the delayed VIBE (13.1 seconds) than TSE (949.9 seconds). Overall there was very good agreement between the delayed VIBE and TSE measurements for both observers (ICC 0.78-0.94) with the exception of the distal right bronchus (ICC 0.67) The interobserver agreement was also excellent for both TSE (ICC 0.78-0.96) and VIBE (ICC 0.85-0.96). Delayed VIBE is rapid and at least as accurate as the alternative TSE imaging for assessment of the lower airway by MRI across a wide spectrum of patients. © 2016 Wiley Periodicals, Inc.

  6. The value of 3D T1-weighted gradient-echo MR imaging for evaluation of the appendix during pregnancy: preliminary results

    Energy Technology Data Exchange (ETDEWEB)

    Jang, Kyung Mi; Kim, Seong Hyun; Choi, Dongil; Lee, Soon Jin; Rhim, Hyunchul; Park, Min Jung (Depts. of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan Univ. School of Medicine, Seoul (Korea, Republic of)), email: kshyun@skku.edu

    2011-10-15

    Background The use of oral contrast has been essential for the identification of a normal appendix on MR imaging during pregnancy. However, stool could be used as a positive oral contrast as it is characterized by a relatively high signal on T1-weighted imaging, and 3D T1-weighted gradient-echo (T1W-GRE) MR imaging has been used to evaluate 3 mm diameter intestines in fetuses. Purpose To evaluate the added value of 3D T1W-GRE MR imaging in combination with T2-weighted imaging (T2WI) compared to T2WI alone for evaluating the appendix during pregnancy. Material and Methods Eighteen consecutive pregnant patients who were clinically suspected of having acute appendicitis underwent appendix MR imaging which included T2WI with or without spectral presaturation attenuated inversion-recovery (SPAIR) fat suppression, and 3D T1W-GRE with SPAIR fat suppression. Two radiologists reviewed the two image sets (the T2WI set and the combined set of T2WI and 3D T1W-GRE images). Pathologic and clinical results served as the reference standard. The differences in the degree of visibility of the appendix and confidence scale for diagnosing acute appendicitis between two image sets were compared by using the paired Wilcoxon signed rank test. Results For both reviewers, the degree of visibility of the appendix using the combined T2WI and 3D T1W-GRE images was significantly higher than using T2WI alone (P < 0.01), and the confidence levels for acute appendicitis using combined T2WI and 3D T1W-GRE images were significantly different from those using T2WI alone (P < 0.01). In the 13 patients with a normal appendix, both reviewers showed improved confidence levels for appendicitis using combined T2WI and 3D T1W-GRE images than T2WI alone. Conclusion Adding 3D T1W-GRE images to T2WI is helpful for identification of the appendix, as compared to T2WI alone in pregnant women without ingestion of oral contrast material. This may improve diagnostic confidence for acute appendicitis in pregnant

  7. [In-phase and out-of-phase single-shot magnetization-prepared gradient recalled echo: description and optimization of technique at 1.5 T].

    Science.gov (United States)

    Ramalho, M; Herédia, V; de Campos, R O P; de Toni, M; Dale, B M; Semelka, R C

    2014-01-01

    To implement in-phase and out-of-phase (IP/OP) techniques with Magnetization-Prepared Gradient Recalled Echo (MP-GRE) and to evaluate the feasibility and diagnostic image quality among pre and post-optimized MP-GRE sequences, including patients unable to cooperate with breath-hold requirements. Institutional review board approval with waiver of informed consent was obtained for this HIPAA-compliant retrospective study. Two groups of patients were included in the study, before and after optimization of MP-GRE parameters, with seventy-three (24 noncooperative/49 cooperative) and sixty-four (22 noncooperative/42 cooperative) consecutive patients, respectively. The motion-insensitive sequence used in this study was a single-shot 2D MP-GRE. Two radiologists qualitatively evaluated the sequences to identify the presence of phase cancellation artifact in OP images and to determine image quality, extent of artifacts (respiratory ghosting, bounce-point artifact, spatial misregistration and pixel graininess) and lesion conspicuity on the various sequences. The ability to visually detect liver steatosis and fatty adrenal adenomas was evaluated. Qualitative analyses were compared using the Wilcoxon and Mann-Whitney tests. There were statistically significant differences between all MP-GRE sequences concerning phase cancellation artifact (P<.0001) which was present in MP-GRE OP sequences and negligible to absent in the pre (IP1) and post-optimized (IP2) MP-GRE IP sequences, respectively, in all patients. Bounce point artifacts were significantly more pronounced in MP-GRE IP1 (P<.0001). Spatial misregistration was slightly more prominent in noncooperative patients with MP-GRE IP2 (P=.0027). MP-GRE OP and MP-GRE IP2 showed significantly higher overall image quality (P<.0001). MP-GRE sequences subjectively identified hepatic steatosis (n=20) and adrenal adenomas (n=5) based on signal loss from IP to OP sequence. Single shot IP/OP MP-GRE is feasible and allows motion resistant

  8. Comparison of T1rho measurements in agarose phantoms and human patellar cartilage using 2D multislice spiral and 3D magnetization prepared partitioned k-space spoiled gradient-echo snapshot techniques at 3 T.

    Science.gov (United States)

    Buck, Florian M; Bae, Won C; Diaz, Eric; Du, Jiang; Statum, Sheronda; Han, Eric T; Chung, Christine B

    2011-02-01

    The purpose of this article is to compare in vitro T1rho measurements in agarose phantoms and articular cartilage specimens using 2D multislice spiral and 3D magnetization prepared partitioned k-space spoiled gradient-echo snapshot MRI sequences. Six phantoms (agarose concentration, 2%, 3%, and 4%; n = 2 each) and 10 axially sliced patellar specimens from five cadaveric donors were scanned at 3 T. T1rho-weighted images were acquired using 2D spiral and 3D magnetization prepared partitioned k-space spoiled gradient-echo snapshot sequences. Regions of interest were analyzed to measure T1rho values centrally within phantoms, to evaluate effects of pulse sequence and agarose concentration. In patellar specimens, regions of interest were analyzed to measure T1rho values with respect to anatomic location (the medial and lateral facets and the median ridge in deep and superficial halves of the cartilage) as well as location that exhibited magic angle effect in proton density-weighted images, to evaluate the effects of pulse sequence, anatomic location, and magic angle. In phantoms, T1rho values were similar (p = 0.9) between sequences but decreased significantly (p measurements of human patellar cartilage specimens and agarose phantoms using 2D spiral and 3D magnetization prepared partitioned k-space spoiled gradient-echo snapshot sequences gave similar values. Lower T1rho values for phantoms with higher agarose concentrations and proteoglycan concentrations that are higher in deeper layers of cartilage than in superficial layers suggest that our method is sensitive to concentration of macromolecules in biologic tissues.

  9. Strategically acquired gradient Echo (STAGE) imaging, part I: Creating enhanced T1 contrast and standardized susceptibility weighted imaging and quantitative susceptibility mapping.

    Science.gov (United States)

    Chen, Yongsheng; Liu, Saifeng; Wang, Yu; Kang, Yan; Mark Haacke, E

    2017-10-19

    To provide whole brain grey matter (GM) to white matter (WM) contrast enhanced T1W (T1WE) images, multi-echo quantitative susceptibility mapping (QSM), proton density (PD) weighted images, T1 maps, PD maps, susceptibility weighted imaging (SWI), and R2* maps with minimal misregistration in scanning times 3T) were used for both T1 mapping with radio frequency (RF) transmit field correction and creating enhanced GM/WM contrast (the T1WE). The proposed T1WE image was created from a combination of the proton density weighted (6°, PDW) and T1W (24°) images and corrected for RF transmit field variations. Prior to the QSM calculation, a multi-echo phase unwrapping strategy was implemented using the unwrapped short echo to unwrap the longer echo to speed up computation. R2* maps were used to mask deep grey matter and veins during the iterative QSM calculation. A weighted-average sum of susceptibility maps was generated to increase the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR). The proposed T1WE image has a significantly improved CNR both for WM to deep GM and WM to cortical GM compared to the acquired T1W image (the first echo of 24° scan) and the T1MPRAGE image. The weighted-average susceptibility maps have 80±26%, 55±22%, 108±33% SNR increases for the ten datasets compared to the single echo result of 17.5ms, and 80±36%, 59±29% and 108±37% CNR increases for the putamen, caudate nucleus, and globus pallidus, respectively. STAGE imaging offers the potential to create a standardized brain imaging protocol providing four pieces of quantitative tissue property information and multiple types of qualitative information in just 5min. Copyright © 2017. Published by Elsevier Inc.

  10. Miniaturized Antimicrobial Susceptibility Test by Combining Concentration Gradient Generation and Rapid Cell Culturing

    Directory of Open Access Journals (Sweden)

    Samuel C. Kim

    2015-10-01

    Full Text Available Effective treatment of bacterial infection relies on timely diagnosis and proper prescription of antibiotic drugs. The antimicrobial susceptibility test (AST is one of the most crucial experimental procedures, providing the baseline information for choosing effective antibiotic agents and their dosages. Conventional methods, however, require long incubation times or significant instrumentation costs to obtain test results. We propose a lab-on-a-chip approach to perform AST in a simple, economic, and rapid manner. Our assay platform miniaturizes the standard broth microdilution method on a microfluidic device (20 × 20 mm that generates an antibiotic concentration gradient and delivers antibiotic-containing culture media to eight 30-nL chambers for cell culture. When tested with 20 μL samples of a model bacterial strain (E. coli ATCC 25922 treated with ampicillin or streptomycin, our method allows for the determination of minimum inhibitory concentrations consistent with the microdilution test in three hours, which is almost a factor of ten more rapid than the standard method.

  11. Spin echo magnetic resonance imaging.

    Science.gov (United States)

    Jung, Bernd André; Weigel, Matthias

    2013-04-01

    The spin echo sequence is a fundamental pulse sequence in MRI. Many of today's applications in routine clinical use are based on this elementary sequence. In this review article, the principles of the spin echo formation are demonstrated on which the generation of the fundamental image contrasts T1, T2, and proton density is based. The basic imaging parameters repetition time (TR) and echo time (TE) and their influence on the image contrast are explained. Important properties such as the behavior in multi-slice imaging or in the presence of flow are depicted and the basic differences with gradient echo imaging are illustrated. The characteristics of the spin echo sequence for different magnetic field strengths with respect to clinical applications are discussed. Copyright © 2013 Wiley Periodicals, Inc.

  12. Graffiti echoes

    National Research Council Canada - National Science Library

    Purcell, John

    2014-01-01

      Graffiti and street art are a kind of "voice" of the city. From the street-tagged neighborhoods to the grand billboards high in the air, graffiti seems to always echo what is happening in Los Angeles...

  13. Validation of Perfusion Quantification with 3D Gradient Echo Dynamic Contrast-Enhanced Magnetic Resonance Imaging Using a Blood Pool Contrast Agent in Skeletal Swine Muscle.

    Directory of Open Access Journals (Sweden)

    Stefan Hindel

    Full Text Available The purpose of our study was to validate perfusion quantification in a low-perfused tissue by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI with shared k-space sampling using a blood pool contrast agent. Perfusion measurements were performed in a total of seven female pigs. An ultrasonic Doppler probe was attached to the right femoral artery to determine total flow in the hind leg musculature. The femoral artery was catheterized for continuous local administration of adenosine to increase blood flow up to four times the baseline level. Three different stable perfusion levels were induced. The MR protocol included a 3D gradient-echo sequence with a temporal resolution of approximately 1.5 seconds. Before each dynamic sequence, static MR images were acquired with flip angles of 5°, 10°, 20°, and 30°. Both static and dynamic images were used to generate relaxation rate and baseline magnetization maps with a flip angle method. 0.1 mL/kg body weight of blood pool contrast medium was injected via a central venous catheter at a flow rate of 5 mL/s. The right hind leg was segmented in 3D into medial, cranial, lateral, and pelvic thigh muscles, lower leg, bones, skin, and fat. The arterial input function (AIF was measured in the aorta. Perfusion of the different anatomic regions was calculated using a one- and a two-compartment model with delay- and dispersion-corrected AIFs. The F-test for model comparison was used to decide whether to use the results of the one- or two-compartment model fit. Total flow was calculated by integrating volume-weighted perfusion values over the whole measured region. The resulting values of delay, dispersion, blood volume, mean transit time, and flow were all in physiologically and physically reasonable ranges. In 107 of 160 ROIs, the blood signal was separated, using a two-compartment model, into a capillary and an arteriolar signal contribution, decided by the F-test. Overall flow in hind leg muscles

  14. MR Measurement Technique of Rapidly Switched Gradient Magnetic Fields in MR Tomography

    Czech Academy of Sciences Publication Activity Database

    Bartušek, Karel; Gescheidtová, E.

    2005-01-01

    Roč. 29, č. 4 (2005), s. 675-686 ISSN 0937-9347 Institutional research plan: CEZ:AV0Z20650511 Keywords : MR tomography * gradiernt magnet ic field * IF method * IFSE method * IFSES method * spin echo Subject RIV: JA - Electronics ; Optoelectronics, Electrical Engineering Impact factor: 0.743, year: 2005

  15. Rapid Time-Resolved Magnetic Resonance Angiography via a multi-echo radial trajectory and GraDeS reconstruction

    Science.gov (United States)

    Lee, Gregory R.; Seiberlich, Nicole; Sunshine, Jeffrey L.; Carroll, Timothy J.; Griswold, Mark A.

    2012-01-01

    Contrast enhanced magnetic resonance angiography (CE-MRA) is challenging due to the need for both high spatial and temporal resolution. A multi-shot trajectory composed of pseudo-random rotations of a single multi-echo radial readout was developed. The trajectory is designed to give incoherent aliasing artifacts and a relatively uniform distribution of projections over all time scales. A field map (computed from the same data set) is used to avoid signal dropout in regions of substantial field inhomogeneity. A compressed sensing reconstruction using the GraDeS algorithm was employed. Whole brain angiograms were reconstructed at 1 mm isotropic resolution and a 1.1 s frame rate (corresponding to an acceleration factor > 100). The only parameter which must be chosen is the number of iterations of the GraDeS algorithm. A larger number of iterations improves the temporal behavior at cost of decreased image signal to noise ratio. The resulting images provide a good depiction of the cerebral vasculature and have excellent arterial/venous separation. PMID:22473742

  16. Development of a symmetric echo planar imaging framework for clinical translation of rapid dynamic hyperpolarized 13 C imaging.

    Science.gov (United States)

    Gordon, Jeremy W; Vigneron, Daniel B; Larson, Peder E Z

    2017-02-01

    To develop symmetric echo planar imaging (EPI) and a reference scan framework for hyperpolarized 13 C metabolic imaging. Symmetric, ramp-sampled EPI with partial Fourier reconstruction was implemented on a 3T scanner. The framework for acquiring a reference scan on the 1 H channel and applied to 13 C data was described and validated in both phantoms and in vivo metabolism of [1-13 C]pyruvate. Ramp-sampled, symmetric EPI provided a substantial increase in the signal-to-noise ratio of the phantom experiments. The reference scan acquired on the 1 H channel yielded 13 C phantom images that varied in mean signal intensity Ramp-sampled, symmetric EPI with spectral-spatial excitation of a single metabolite provides a fast, robust, and clinically efficacious approach to acquire hyperpolarized 13 C dynamic molecular imaging data. The gains of this efficient sampling, combined with partial Fourier methods, enables large matrix sizes required for human studies. Magn Reson Med 77:826-832, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  17. Wiener variable step size and gradient spectral variance smoothing for double-talk-robust acoustic echo cancellation and acoustic feedback cancellation

    DEFF Research Database (Denmark)

    Gil-Cacho, Jose M.; Van Waterschoot, Toon; Moonen, Marc

    2014-01-01

    Double-talk (DT)-robust acoustic echo cancellation (AEC) and acoustic feedback cancellation (AFC) are needed in speech communication systems, e.g., in hands-free communication systems and hearing aids. In this paper, we derive a practical and computationally efficient algorithm based......-GSVS-FDAF-PEM-AFROW algorithm obtains outstanding robustness and smooth adaptation in highly adverse scenarios such as in bursting DT at high levels, and in a change of acoustic path during continuous DT. Similarly, in AFC simulations, the algorithm outperforms state-of-the-art algorithms when using a low-order near-end speech...

  18. Ultrashort Echo Time and Zero Echo Time MRI at 7T

    Science.gov (United States)

    Larson, Peder E. Z.; Han, Misung; Krug, Roland; Jakary, Angela; Nelson, Sarah J.; Vigneron, Daniel B.; Henry, Roland G.; McKinnon, Graeme; Kelley, Douglas A. C.

    2016-01-01

    Object Zero echo time (ZTE) and ultrashort echo time (UTE) pulse sequences for MRI offer unique advantages of being able to detect signal from rapidly decaying short-T2 tissue components. In this paper, we applied 3D zero echo time (ZTE) and ultrashort echo time (UTE) pulse sequences at 7T to assess differences between these methods. Materials and Methods We matched the ZTE and UTE pulse sequences closely in terms of readout trajectories and image contrast. Our ZTE used the Water- and fat-suppressed solid-state proton projection imaging (WASPI) method to fill the center of k-space. Images from healthy volunteers obtained at 7T were compared qualitatively as well as with SNR and CNR measurements for various ultrashort, short, and long-T2 tissues. Results We measured nearly identical contrast-to-noise and signal-to-noise ratios (CNR/SNR) in similar scan times between the two approaches for ultrashort, short, and long-T2 components in the brain, knee and ankle. In our protocol, we observed gradient fidelity artifacts in UTE, and our chosen flip angle and readout also resulted as well as shading artifacts in ZTE due to inadvertent spatial selectivity. These can be corrected by advanced reconstruction methods or with different chosen protocol parameters. Conclusion The applied ZTE and UTE pulse sequences achieved similar contrast and SNR efficiency for volumetric imaging of ultrashort-T2 components. Several key differences are that ZTE is limited to volumetric imaging but has substantially reduced acoustic noise levels during the scan. Meanwhile, UTE has higher acoustic noise levels and greater sensitivity to gradient fidelity, but offers more flexibility in image contrast and volume selection. PMID:26702940

  19. MR-Imaging optimisation of the articular hip cartilage by using a T{sub 1}-weighted 3-dimensional gradient-echo sequence and the application of a hip joint traction; Magnetresonanztomographische Optimierung der Hueftknorpeldarstellung durch die Wahl einer T{sub 1}-Volumen-Gradienten-Echo-Sequenz und die Anwendung einer Hueftgelenkstraktion

    Energy Technology Data Exchange (ETDEWEB)

    Rosenberg, R. [Heidelberg Univ. (Germany). Orthopaedische Klinik und Poliklinik; Bernd, L. [Heidelberg Univ. (Germany). Orthopaedische Klinik und Poliklinik; Wrazidlo, W. [ATOS-Praxisklinik, Heidelberg (Germany). Radiologische Gemeinschaftspraxis Drs. Lederer, Schneider und Wrazidlo; Lederer, W. [ATOS-Praxisklinik, Heidelberg (Germany). Radiologische Gemeinschaftspraxis Drs. Lederer, Schneider und Wrazidlo; Schneider, S. [ATOS-Praxisklinik, Heidelberg (Germany). Radiologische Gemeinschaftspraxis Drs. Lederer, Schneider und Wrazidlo

    1995-10-01

    Images of three animal cadaver hips, 8 dissected patient femoral heads and 18 hip joints of human corpses, all either with arthrosis stage I-III or artificial cartilage defects, were compared with their corresponding anatomic sections. Additional histomorphologic examinations of the arthrotic cartilages were conducted, and MR-Imaging of 20 healthy and 21 arthrotic patient hips was performed using a specific traction method. Using a T{sub 1}-weighted 3-dimensional gradient-echo sequence and a traction of the hip joint, it was possible due to the low-signal imaging of the joint space to separate in vivo the high-signal femoral head cartilage from the high-signal acetabular cartilage. In horizontal position of the phase-encoding parameter, minimisation of the chemical-shift artifact, mainly in the ventro-lateral areas, was accomplished. MRI measurements of the articular cartilage widths showed significant correlations (p < 0.001) with the corresponding anatomic sections. At the same time the T{sub 1} 3-dimensional gradient-echo sequence of the lateral femoral head with r = 0.94 showed the lowest deviations of the measurements. It was possible with MR-Imaging to distinguish four cartilage qualities. (orig./MG) [Deutsch] Im experimentellen Teil der Studie wurden den MRT-Bildern von drei Kadavertierhueften, 8 resezierten Patientenhueftkoepfen und 18 Leichenhueftgelenken, an denen entweder artifizielle Knorpeldefekte gesetzt wurden oder die ein Koxarthrose-Stadium I-III aufwiesen, die korrespondierenden makroskopischen Kryomikrotomschnitte zugeordnet. Bei den Koxarthrosen erfolgten zusaetzliche histomorphologische Knorpeluntersuchungen. Im klinischen Teil der Studie wurden 20 gesunde und 21 arthrotische Probandenhueftgelenke mit einem speziellen Traktionsverfahren untersucht. Unter Anwendung einer T{sub 1}-Volumen-Gradienten-Echo-Sequenz und einer Traktion am zu untersuchenden Hueftgelenk konnte in vivo durch die signalarme Darstellung des Gelenkspaltes der

  20. Echo project

    DEFF Research Database (Denmark)

    Gfader, Verina; Carson, Rebecca; Kraus, Chris

    2016-01-01

    Echo project (ed. by Verina Gfader and Ruth Höflich) is an online publication and community board that developed from a visit to the Los Angeles Art Book fair in January 2014. It was on the occasion of a prior book project, titled Prospectus, that the editorial team had been invited by the LAABF...... Intellect and Financialization sets a conceptual ground for rethinking subjective freedom; an encounter with Another LA opens out a multitude of cartographies - revealing more discreet and politically dynamic movements in the urban grid; there are glimpses of Machine Project’s events, a visual story around...

  1. Rapid manufacturing of polyethylene parts with controlled pore size gradients using selective laser sintering

    Directory of Open Access Journals (Sweden)

    Gean Vitor Salmoria

    2007-06-01

    Full Text Available In this study HDPE specimens were fabricated by selective laser sintering using different particle sizes to obtain controlled variations in the porosity. Electron microscopy, density measurements and mechanical analyses were conducted for the characterization of the specimens. Parts with controlled pore gradients were also manufactured and characterized. The specimens with larger particle sizes had a high sintering degree and a significant level of close pores, as shown by microscopy and density analyses. However, the mechanical properties of specimens prepared with large particles had low values due to the limited density of union points, i.e., low neck number/area. HDPE parts with pore gradients were prepared by selective laser sintering demonstrating that this technique can be used to easily control the structure and the properties of the parts manufactured. This technology may have applications in areas such as drug delivery devices and scaffolds for tissue engineering.

  2. Differentiation between simple cyst and hepatic hemangioma utilizing T2-weighted magnetic resonance imaging with gradient-echo (b-FFE) technique

    Energy Technology Data Exchange (ETDEWEB)

    Burim, Carolina Valente; D' Ippolito, Giuseppe [Universidade Federal de Sao Paulo (UNIFESP/EPM), SP (Brazil). Dept. de Diagnostico por Imagem]. E-mail: scoposl@uol.com.br; Pecci Neto, Luiz; Torlai, Fabiola Goda; Tiferes, Dario Ariel [Laboratorio Fleury, Sao Paulo, SP (Brazil). Centro de Medicina Diagnostica

    2008-11-15

    Objective: to establish the role of MRI T2-weighted sequences in the differentiation between simple cysts and hepatic hemangiomas. Materials and methods: a double-blinded, prospective, observational, cross sectional study evaluated 52 patients with 91 hepatic lesions (34 simple cysts and 57 hemangiomas) submitted to abdominal magnetic resonance imaging. The combined analysis of all sequences was considered as the golden-standard. TSE sequences with long echo trains and b-FFE sequences were subjectively analyzed by two independent observers for differentiating cysts from hemangiomas. The kappa test ({kappa}) was utilized in the analysis of the methods accuracy and inter- and intra-observer agreement (p < 0.05{sup *}). Results: cysts and hemangiomas dimensions ranged respectively between 0.5 and 6.5 cm (mean 1.89 cm), and 0.8 and 11 cm (mean = 2.62 cm). The analysis of the sequences with long-TE and the golden-standard demonstrated a non-statistically significant agreement (k: 0.00-0.10). The agreement between the evaluation of the b-FFE sequence and the golden-standard ranged from substantial ({kappa}: 0.62-0.71) to almost perfect ({kappa}: 0.86) for both observers. The inter- and intra-observer agreement for the b-FFE sequence ranged from substantial ({kappa}: 0.62-0.70) to almost perfect ({kappa}: 0.85-0.91). Conclusion: T2-weighted images acquired with the b-FFE technique present a high accuracy and reproducibility in the differentiation between cysts and hepatic hemangiomas. (author)

  3. Multiband echo-shifted echo planar imaging

    NARCIS (Netherlands)

    Boyacioǧlu, R.; Schulz, J.; Norris, David Gordon

    2016-01-01

    Purpose To propose the technique multiband echo-shifted (MESH) echo planar imaging (EPI), which combines the principles of echo-shifted acquisition for two-dimensional multislice EPI, with both in-plane and multiband acceleration by means of partial parallel imaging techniques. Methods MESH EPI is

  4. An analytical model which determines the apparent T1for Modified Look-Locker Inversion Recovery - Analysis of the longitudinal relaxation under the influence of discontinuous balanced (classical MOLLI) and spoiled gradient echo readouts.

    Science.gov (United States)

    Kampf, Thomas; Reiter, Theresa; Bauer, Wolfgang Rudolf

    2017-08-09

    Quantitative nuclear magnetic resonance imaging (MRI) shifts more and more into the focus of clinical research. Especially determination of relaxation times without/and with contrast agents becomes the foundation of tissue characterization, e.g. in cardiac MRI for myocardial fibrosis. Techniques which assess longitudinal relaxation times rely on repetitive application of readout modules, which are interrupted by free relaxation periods, e.g. the Modified Look-Locker Inversion Recovery = MOLLI sequence. These discontinuous sequences reveal an apparent relaxation time, and, by techniques extrapolated from continuous readout sequences, a putative real T 1 is determined. What is missing is a rigorous analysis of the dependence of the apparent relaxation time on its real partner, readout sequence parameters and biological parameters as heart rate. This is provided in this paper for the discontinuous balanced steady state free precession (bSSFP) and spoiled gradient echo readouts. It turns out that the apparent longitudinal relaxation rate is the time average of the relaxation rates during the readout module, and free relaxation period. Knowing the heart rate our results vice versa allow to determine the real T 1 from its measured apparent partner. Copyright © 2017. Published by Elsevier GmbH.

  5. Superficial siderosis of the central nervous system induced by a single-episode of traumatic subarachnoid hemorrhage: a study using MRI-enhanced gradient echo T2 star-weighted angiography.

    Directory of Open Access Journals (Sweden)

    Hongwei Zhao

    Full Text Available The purpose of this study was to examine whether a single episode of traumatic subarachnoid hemorrhage (tSAH could cause superficial siderosis of the central nervous system (SS-CNS.This study was approved by the local ethics committee. Thirty-two patients with a history of a single episode of tSAH were enrolled in the study. An episode of tSAH was confirmed in patients based on a CT scan or a lumbar puncture, and a follow-up examination was conducted at least six weeks after the brain trauma. A follow-up MRI examination was performed, using enhanced gradient echo T2 star-weighted angiography (ESWAN to detect hemosiderin deposition on the cortical surface. The extent to which hemosiderin deposition was associated with several clinical factors was investigated. Various degrees of hemosiderin deposition were detected in 31 of 32 (96.9% single-episode tSAH patients. Analysis of contingency tables revealed an association between the regions of subarachnoid bleeding based on CT images and the regions of hemosiderin deposition based on ESWAN images (χ2 = 17.73, P<0.05. SS-CNS was determined to be a common consequence after a single episode of tSAH. The extent of hemosiderin deposition is closely correlated with the initial bleeding sites and bleeding volume.

  6. Rapid adaptive evolution of photoperiodic response during invasion and range expansion across a climatic gradient.

    Science.gov (United States)

    Urbanski, Jennifer; Mogi, Motoyoshi; O'Donnell, Deborah; DeCotiis, Mark; Toma, Takako; Armbruster, Peter

    2012-04-01

    Abstract Understanding the mechanisms of adaptation to spatiotemporal environmental variation is a fundamental goal of evolutionary biology. This issue also has important implications for anticipating biological responses to contemporary climate warming and determining the processes by which invasive species are able to spread rapidly across broad geographic ranges. Here, we compare data from a historical study of latitudinal variation in photoperiodic response among Japanese and U.S. populations of the invasive Asian tiger mosquito Aedes albopictus with contemporary data obtained using comparable methods. Our results demonstrated rapid adaptive evolution of the photoperiodic response during invasion and range expansion across ∼15° of latitude in the United States. In contrast to the photoperiodic response, size-based morphological traits implicated in climatic adaptation in a wide range of other insects did not show evidence of adaptive variation in Ae. albopictus across either the U.S. (invasive) or Japanese (native) range. These results show that photoperiodism has been an important adaptation to climatic variation across the U.S. range of Ae. albopictus and, in conjunction with previous studies, strongly implicate the photoperiodic control of seasonal development as a critical evolutionary response to ongoing contemporary climate change. These results also emphasize that photoperiodism warrants increased attention in studies of the evolution of invasive species.

  7. MR imaging of focal liver lesions: value of Gadolinium-enhanced dynamic imaging of the whole liver using an ultra-fast 3D-turbo-gradient-echo sequence; MRT fokaler Leberlaesionen: Stellenwert Gadolinium-verstaerkter dynamischer Untersuchungen des gesamten Organs mit einer schnellen 3D-Turbo-Gradienten-Echo-Sequenz

    Energy Technology Data Exchange (ETDEWEB)

    Pauleit, D.; Textor, J.; Conrad, R.; Flacke, S.; Born, M.; Bachmann, R.; Kreft, B.; Schild, H. [Bonn Univ. (Germany). Radiologische Klinik; Gieseke, J. [Philips Medizin Systeme (Germany)

    1999-04-01

    Purpose: To determine the value of a dynamic Gd-enhanced ultrafast T{sub 1}-weighted 3D-turbo-gradient-echo sequence (3D-TFE) in the detection and characterization of focal liver lesions. Results: On 3D-TFE images more lesions (107/124) were identified than on T{sub 1}-weighted SE (101/124) and T{sub 1}-weighted FFE images (106/124), but less compared to T{sub 2}-weighted TSE SPIR images (115/124). The 3D-TFE-sequence provided additional information in 65/107 (61%) detected lesions by delineating the dynamic enhancement pattern, most valuable in patients with HCCs in 90%. Conclusions: On dynamic 3D-TFE images more lesions could be depicted than on conventional T{sub 1}-weighted SE and T{sub 1}-weighted FFE images. Visualization of the dynamic enhancement pattern provided additional information for tumor characterization in 61% of the detected lesions on the 3D-TFE images. (orig./AJ) [Deutsch] Ziel: Bestimmung des Stellenwerts einer dynamischen Gd-DTPA-verstaerkten schnellen T{sub 1}-gewsichteten 3D-Turbo-Gradienten-Echo-Sequenz (3D-TFE) fuer die Detektion und Charakterisierung fokaler Leberlaesionen. Ergebnisse: Von den 124 Leberlaesionen wurden mit der 3D-FFE-Sequenz 107, mit der T{sub 1}-gewichteten SE 101 und mit der T{sub 1}-gewichteten FFE-Sequenz 106 nachgewiesen. In der T{sub 2}-gewichteten TSE-SPIR-Sequenz konnten 115 Laesionen detektiert werden. Bei 65/107 in der 3D-TFE-Sequenz nachgewiesenen Tumoren ergaben sich aus der Beruecksichtigung des dynamischen Anreicherungsverhaltens gegenueber den anderen Sequenzen wichtige Zusatzinformationen, die bei den hepatozellulaeren Karzinomen mit 90% die groesste Bedeutung hatten. Schlussfolgerung: Die dynamische 3D-TFE-Sequenz ist den nicht dynamischen T{sub 1}-gewichteten SE- und FFE-Sequenzen in der Detektion ueberlegen und erbringt bei 61% der Herde wichtige Zusatzinformationen fuer die Tumorcharakterisierung. (orig./AJ)

  8. Prospective intraindividual comparison between respiratory-triggered balanced steady-state free precession and breath-hold gradient-echo and time-of-flight magnetic resonance imaging for assessment of portal and hepatic veins

    Energy Technology Data Exchange (ETDEWEB)

    Willmann, Juergen K.; Goepfert, Kerstin; Lutz, Amelie M.; Marincek, Borut; Weishaupt, Dominik [University Hospital Zurich, Institute of Diagnostic Radiology, Zurich (Switzerland); Nanz, Daniel [University Hospital Zurich, Department of Medical Radiology, Zurich (Switzerland); McCormack, Lucas; Petrowsky, Henrik [University Hospital Zurich, Department of Visceral and Transplantation Surgery, Zurich (Switzerland); Seifert, Burkhardt [University of Zurich, Department of Biostatistics, Zurich (Switzerland); Hervo, Patrice [GE Healthcare, Buc Cedex (France)

    2007-01-15

    The purpose of this study was to compare respiratory-triggered balanced steady-state free precession (bSSFP) with breath-hold contrast-enhanced dynamic two-dimensional (2D) gradient-echo (GRE) and time-of-flight (TOF) magnetic resonance imaging (MRI) for portal and hepatic vein visualization and assessment of portal and hepatic venous variants. Sixty patients with liver disease underwent nonenhanced bSSFP and contrast-enhanced GRE, bSSFP, and TOF imaging. Contrast-to-noise ratios (CNRs) for portal and hepatic veins were measured. Two readers rated the quality of portal and hepatic vein visualization on a 5-point Likert scale. The diagnostic performance of each MRI series in the detection of portal and hepatic venous variants was assessed in 40/60 patients who also underwent contrast-enhanced multidetector-row computed tomography (MDCT). CNRs for portal and hepatic veins were highest on contrast-enhanced bSSFP images. Image quality of portal and hepatic veins was rated higher for nonenhanced bSSFP than for contrast-enhanced GRE (p<0.03) and TOF (p<0.003) and higher for contrast-enhanced than for nonenhanced bSSFP (p<0.003). Compared with MDCT, portal and hepatic venous variants were identified with an accuracy of 99% on bSSFP images, with an excellent interobserver agreement ({kappa}=0.97). Compared with MDCT, presence of surgically important portal and hepatic venous anatomical variants can be predicted with high accuracy on bSSFP images. (orig.)

  9. BREATHING FIRE: HOW STELLAR FEEDBACK DRIVES RADIAL MIGRATION, RAPID SIZE FLUCTUATIONS, AND POPULATION GRADIENTS IN LOW-MASS GALAXIES

    Energy Technology Data Exchange (ETDEWEB)

    El-Badry, Kareem; Geha, Marla [Department of Astronomy, Yale University, New Haven, CT (United States); Wetzel, Andrew; Hopkins, Philip F. [TAPIR, California Institute of Technology, Pasadena, CA USA (United States); Kereš, Dusan; Chan, T. K. [Department of Physics, Center for Astrophysics and Space Sciences, University of California at San Diego, La Jolla (United States); Faucher-Giguère, Claude-André, E-mail: kareem.el-badry@yale.edu [Department of Physics and Astronomy and CIERA, Northwestern University, Evanston, IL (United States)

    2016-04-01

    We examine the effects of stellar feedback and bursty star formation on low-mass galaxies (M{sub star} = 2 × 10{sup 6} − 5 × 10{sup 10} M{sub ⊙}) using the Feedback in Realistic Environments (FIRE) simulations. While previous studies emphasized the impact of feedback on dark matter profiles, we investigate the impact on the stellar component: kinematics, radial migration, size evolution, and population gradients. Feedback-driven outflows/inflows drive significant radial stellar migration over both short and long timescales via two processes: (1) outflowing/infalling gas can remain star-forming, producing young stars that migrate ∼1 kpc within their first 100 Myr, and (2) gas outflows/inflows drive strong fluctuations in the global potential, transferring energy to all stars. These processes produce several dramatic effects. First, galaxies’ effective radii can fluctuate by factors of >2 over ∼200 Myr, and these rapid size fluctuations can account for much of the observed scatter in the radius at fixed M{sub star}. Second, the cumulative effects of many outflow/infall episodes steadily heat stellar orbits, causing old stars to migrate outward most strongly. This age-dependent radial migration mixes—and even inverts—intrinsic age and metallicity gradients. Thus, the galactic-archaeology approach of calculating radial star formation histories from stellar populations at z = 0 can be severely biased. These effects are strongest at M{sub star} ≈ 10{sup 7–9.6} M{sub ⊙}, the same regime where feedback most efficiently cores galaxies. Thus, detailed measurements of stellar kinematics in low-mass galaxies can strongly constrain feedback models and test baryonic solutions to small-scale problems in ΛCDM.

  10. Gravitational wave sources: reflections and echoes

    Science.gov (United States)

    Price, Richard H.; Khanna, Gaurav

    2017-11-01

    The recent detection of gravitational waves has generated interest in alternatives to the black hole interpretation of sources. A subset of such alternatives involves a prediction of gravitational wave ‘echoes’. We consider two aspects of possible echoes: first, general features of echoes coming from spacetime reflecting conditions. We find that the detailed nature of such echoes does not bear any clear relationship to quasi-normal frequencies. Second, we point out the pitfalls in the analysis of local reflecting ‘walls’ near the horizon of rapidly rotating black holes.

  11. Comparison of spoiled gradient echo and steady-state free-precession imaging for native myocardial T1 mapping using the slice-interleaved T1 mapping (STONE) sequence.

    Science.gov (United States)

    Jang, Jihye; Bellm, Steven; Roujol, Sébastien; Basha, Tamer A; Nezafat, Maryam; Kato, Shingo; Weingärtner, Sebastian; Nezafat, Reza

    2016-10-01

    Cardiac T1 mapping allows non-invasive imaging of interstitial diffuse fibrosis. Myocardial T1 is commonly calculated by voxel-wise fitting of the images acquired using balanced steady-state free precession (SSFP) after an inversion pulse. However, SSFP imaging is sensitive to B1 and B0 imperfection, which may result in additional artifacts. A gradient echo (GRE) imaging sequence has been used for myocardial T1 mapping; however, its use has been limited to higher magnetic field to compensate for the lower signal-to-noise ratio (SNR) of GRE versus SSFP imaging. A slice-interleaved T1 mapping (STONE) sequence with SSFP readout (STONE-SSFP) has been recently proposed for native myocardial T1 mapping, which allows longer recovery of magnetization (>8 R-R) after each inversion pulse. In this study, we hypothesize that a longer recovery allows higher SNR and enables native myocardial T1 mapping using STONE with GRE imaging readout (STONE-GRE) at 1.5T. Numerical simulations and phantom and in vivo imaging were performed to compare the performance of STONE-GRE and STONE-SSFP for native myocardial T1 mapping at 1.5T. In numerical simulations, STONE-SSFP shows sensitivity to both T2 and off resonance. Despite the insensitivity of GRE imaging to T2 , STONE-GRE remains sensitive to T2 due to the dependence of the inversion pulse performance on T2 . In the phantom study, STONE-GRE had inferior accuracy and precision and similar repeatability as compared with STONE-SSFP. In in vivo studies, STONE-GRE and STONE-SSFP had similar myocardial native T1 times, precisions, repeatabilities and subjective T1 map qualities. Despite the lower SNR of the GRE imaging readout compared with SSFP, STONE-GRE provides similar native myocardial T1 measurements, precision, repeatability, and subjective image quality when compared with STONE-SSFP at 1.5T. Copyright © 2016 John Wiley & Sons, Ltd.

  12. Rapid chemical shift encoding with single-acquisition single-slab 3D GRASE.

    Science.gov (United States)

    Kim, Hahnsung; Kim, Dong-Hyun; Sohn, Chul-Ho; Park, Jaeseok

    2017-11-01

    To investigate the feasibility of chemical shift encoded, single-slab 3D GRASE for rapid fat-water separation within a single acquisition. The proposed method incorporates signal-to-noise-ratio-optimal chemical shift encoding into single-slab 3D GRASE with variable flip angles. Chemical shift induced phase information was encoded in succession to different positions in k-space by inserting phase encoding blips between adjacent lobes of the oscillating readout gradients. To enhance imaging efficiency, signal prescription-based variable flip angles were used in the long refocusing pulse train. After echo-independent phase correction, missing signals in k-echo space were interpolated using convolution kernels that span over all echoes. Fat-water separation in a single acquisition was performed using both multi-echo fast spin echo and GRASE as compared to conventional multiacquisition fast spin echo with echo shifts. The proposed single-slab 3D GRASE shows superior performance in accurately delineating cartilage structures compared to its counterpart, multi-echo 3D fast spin echo. Compared with multiacquisition fast spin echo with three echo shifts (63 min), the proposed method substantially speeds up imaging time (7 min), and achieves 0.6 mm isotropic resolution in knee imaging with reduced artifacts and noise. We successfully demonstrated the feasibility of rapid chemical shift encoding and separation using the proposed, single-acquisition single-slab 3D GRASE for high resolution isotropic imaging within clinically acceptable time. Magn Reson Med 78:1852-1861, 2017. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  13. Multishot echo-planar MREIT for fast imaging of conductivity, current density, and electric field distributions.

    Science.gov (United States)

    Chauhan, Munish; Vidya Shankar, Rohini; Ashok Kumar, Neeta; Kodibagkar, Vikram D; Sadleir, Rosalind

    2018-01-01

    Magnetic resonance electrical impedance tomography (MREIT) sequences typically use conventional spin or gradient echo-based acquisition methods for reconstruction of conductivity and current density maps. Use of MREIT in functional and electroporation studies requires higher temporal resolution and faster sequences. Here, single and multishot echo planar imaging (EPI) based MREIT sequences were evaluated to see whether high-quality MREIT phase data could be obtained for rapid reconstruction of current density, conductivity, and electric fields. A gel phantom with an insulating inclusion was used as a test object. Ghost artifact, geometric distortion, and MREIT correction algorithms were applied to the data. The EPI-MREIT-derived phase-projected current density and conductivity images were compared with simulations and spin-echo images as a function of EPI shot number. Good agreement among measures in simulated, spin echo, and EPI data was achieved. Current density errors were stable and below 9% as the shot number decreased from 64 to 2, but increased for single-shot images. Conductivity reconstruction relative contrast ratios were stable as the shot number decreased. The derived electric fields also agreed with the simulated data. The EPI methods can be combined successfully with MREIT reconstruction algorithms to achieve fast imaging of current density, conductivity, and electric field. Magn Reson Med 79:71-82, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  14. High angular resolution diffusion imaging with stimulated echoes

    DEFF Research Database (Denmark)

    Lundell, Henrik; Alexander, Daniel C; Dyrby, Tim B

    2014-01-01

    Stimulated echo acquisition mode (STEAM) diffusion MRI can be advantageous over pulsed-gradient spin-echo (PGSE) for diffusion times that are long compared with T2 . It therefore has potential for biomedical diffusion imaging applications at 7T and above where T2 is short. However, gradient pulses...... angular resolution diffusion imaging (HARDI) data were acquired with and without the proposed compensation. The data were processed to derive standard diffusion tensor imaging (DTI) maps, which highlight the need for the compensation. Ignoring the other gradient pulses, a bias in DTI parameters from STEAM...

  15. Happy birthday Echo!

    CERN Multimedia

    Staff Association

    2010-01-01

    You are reading the number hundred and one (no. 101) edition of our bulletin Echo. Just over four years ago, on 27th March 2006, the first untitled edition was published (Fig. 1 on the left). The title Echo appeared on the second edition on 10th April 2006 (Fig. 1 in the centre). Today (see Fig. 1 on the right), the layout is slightly different, but the structure of each edition has remained more or less the same: an editorial informing you of the important issues, followed by articles on club life, cultural activities (exhibitions and conferences), information from GAC-EPA, and special offers for our members.     Fig. 1 : Nos. 1, 2 and 100 of our twice-monthly publication Echo Echo was created in March 2006 when, much to our regret, CERN official communication and that of your representatives were separated. November 2009 saw a return to normal practice, and since then the CERN st...

  16. Echo 11 conjunctivitis.

    OpenAIRE

    Spalton, D J; Palmer, S; Logan, L C

    1980-01-01

    We describe a case of Echo 11 virus infection producing a moderately severe conjunctivitis in a laboratory worker who had handled infected material. This virus has previously been known to cause systemic disease, sometimes fatal, in children.

  17. Maps | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  18. Trends | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  19. A rapid fabrication of C/C composites by a thermal gradient chemical vapor infiltration method with vaporized kerosene as a precursor

    Energy Technology Data Exchange (ETDEWEB)

    Wang Jiping [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China)]. E-mail: buickwang@hotmail.com; Qian Junmin [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China); Qiao Guanjun [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China); Jin Zhihao [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China)

    2007-01-15

    A thermal gradient, atmospheric pressure chemical vapor infiltration method with simultaneous vaporized kerosene as a precursor for rapid fabrication of C/C composites was studied. By this method, carbon felts (bulk density {approx}0.2 g cm{sup -3}) were densified to C/C composites with density of 1.67 and 1.71 g cm{sup -3} when prepared at 1050 and 1150 deg. C for 6 h, respectively. X-ray diffraction result indicates that the composites have a strong ability to graphitize and the higher deposition temperature leads to the increased graphitization degree. Polarized light microscope and scanning electron microscope images reveal that fibers of the composites prepared for 6 h are surrounded by ring-shaped pyrocarbon matrix with a thickness of {approx}20 {mu}m, and that the matrix is delaminated to 4-6 layer-like regions. The deposition process is analyzed by dividing the reactor into four regions associated with specific functions and the reasons for the rapid fabrication are proposed as the short convection and diffusion path for the precursor and the existing of thermal gradient across the preform.

  20. The thermal and dynamical state of the atmosphere during polar mesosphere winter echoes

    Directory of Open Access Journals (Sweden)

    F.-J. Lübken

    2006-01-01

    Full Text Available In January 2005, a total of 18 rockets were launched from the Andøya Rocket Range in Northern Norway (69° N into strong VHF radar echoes called 'Polar Mesosphere Winter Echoes' (PMWE. The echoes were observed in the lower and middle mesosphere during large solar proton fluxes. In general, PMWE occur much more seldom compared to their summer counterparts PMSE (typical occurrence rates at 69° N are 1–3% vs. 80%, respectively. Our in-situ measurements by falling sphere, chaff, and instrumented payloads provide detailed information about the thermal and dynamical state of the atmosphere and therefore allow an unprecedented study of the background atmosphere during PMWE. There are a number of independent observations indicating that neutral air turbulence has caused PMWE. Ion density fluctuations show a turbulence spectrum within PMWE and no fluctuations outside. Temperature lapse rates close to the adiabatic gradient are observed in the vicinity of PMWE indicating persistent turbulent mixing. The spectral broadening of radar echoes is consistent with turbulent velocity fluctuations. Turbulence also explains the mean occurrence height of PMWE (~68–75 km: viscosity increases rapidly with altitude and destroys any small scale fluctuations in the upper mesosphere, whereas electron densities are usually too low in the lower mesosphere to cause significant backscatter. The seasonal variation of echoes in the lower mesosphere is in agreement with a turbulence climatology derived from earlier sounding rocket flights. We have performed model calculations to study the radar backscatter from plasma fluctuations caused by neutral air turbulence. We find that volume reflectivities observed during PMWE are in quantitative agreement with theory. Apart from turbulence the most crucial requirement for PMWE is a sufficiently large number of electrons, for example produced by solar proton events. We have studied the sensitivity of the radar echo strength on

  1. Minimum complexity echo state network.

    Science.gov (United States)

    Rodan, Ali; Tino, Peter

    2011-01-01

    Reservoir computing (RC) refers to a new class of state-space models with a fixed state transition structure (the reservoir) and an adaptable readout form the state space. The reservoir is supposed to be sufficiently complex so as to capture a large number of features of the input stream that can be exploited by the reservoir-to-output readout mapping. The field of RC has been growing rapidly with many successful applications. However, RC has been criticized for not being principled enough. Reservoir construction is largely driven by a series of randomized model-building stages, with both researchers and practitioners having to rely on a series of trials and errors. To initialize a systematic study of the field, we concentrate on one of the most popular classes of RC methods, namely echo state network, and ask: What is the minimal complexity of reservoir construction for obtaining competitive models and what is the memory capacity (MC) of such simplified reservoirs? On a number of widely used time series benchmarks of different origin and characteristics, as well as by conducting a theoretical analysis we show that a simple deterministically constructed cycle reservoir is comparable to the standard echo state network methodology. The (short-term) MC of linear cyclic reservoirs can be made arbitrarily close to the proved optimal value.

  2. Echo Boom Impact

    Science.gov (United States)

    Dordai, Phillipe; Rizzo, Joseph

    2006-01-01

    Like their baby-boomer parents, the echo-boom generation is reshaping the college and university landscape. At 80 million strong, this group of children and young adults born between 1980 and 1995 now is flooding the college and university system, spurring a college building boom. According to Campus Space Crunch, a Hillier Architecture survey of…

  3. Noncontrast peripheral MRA with spiral echo train imaging.

    Science.gov (United States)

    Fielden, Samuel W; Mugler, John P; Hagspiel, Klaus D; Norton, Patrick T; Kramer, Christopher M; Meyer, Craig H

    2015-03-01

    To develop a spin echo train sequence with spiral readout gradients with improved artery-vein contrast for noncontrast angiography. Venous T2 becomes shorter as the echo spacing is increased in echo train sequences, improving contrast. Spiral acquisitions, due to their data collection efficiency, facilitate long echo spacings without increasing scan times. Bloch equation simulations were performed to determine optimal sequence parameters, and the sequence was applied in five volunteers. In two volunteers, the sequence was performed with a range of echo times and echo spacings to compare with the theoretical contrast behavior. A Cartesian version of the sequence was used to compare contrast appearance with the spiral sequence. Additionally, spiral parallel imaging was optionally used to improve image resolution. In vivo, artery-vein contrast properties followed the general shape predicted by simulations, and good results were obtained in all stations. Compared with a Cartesian implementation, the spiral sequence had superior artery-vein contrast, better spatial resolution (1.2 mm(2) versus 1.5 mm(2) ), and was acquired in less time (1.4 min versus 7.5 min). The spiral spin echo train sequence can be used for flow-independent angiography to generate three-dimensional angiograms of the periphery quickly and without the use of contrast agents. © 2014 Wiley Periodicals, Inc.

  4. Inducing magnetic anisotropy and optimized microstructure in rapidly solidified Nd-Fe-B based magnets by thermal gradient, magnetic field and hot deformation

    Science.gov (United States)

    Zhao, L. Z.; Li, W.; Wu, X. H.; Hussain, M.; Liu, Z. W.; Zhang, G. Q.; Greneche, J. M.

    2016-10-01

    Direct preparation of Nd-Fe-B alloys by rapid solidification of copper mold casting is a very simple and low cost process for mini-magnets, but these magnets are generally magnetically isotropic. In this work, high coercivity Nd24Co20Fe41B11Al4 rods were produced by injection casting. To induce magnetic anisotropy, temperature gradient, assisted magnetic field, and hot deformation (HD) procedures were employed. As-cast samples showed non-uniform microstructure due to the melt convection. The thermal gradient during solidification led to the formation of radially distributed acicular hard magnetic grains, which gives the magnetic anisotropy. The growth of the oriented grains was confirmed by phase field simulation. A magnetic field up to 1 T applied along the casting direction could not induce significant magnetic anisotropy, but it improved the magnetic properties by reducing the non-uniformity and forming a uniform microstructure. The annealed alloys exhibited high intrinsic coercivity but disappeared anisotropy. HD was demonstrated to be a good approach for inducing magnetic anisotropy and enhanced coercivity by deforming and refining the grains. This work provides an alternative approach for preparing fully dense Nd-rich anisotropic bulk Nd-Fe-B magnets.

  5. Echo-Spacing Optimization for the Simultaneous Measurement of Reversible (R2′) and Irreversible (R2) Transverse Relaxation Rates

    OpenAIRE

    Song, Ruitian; Song, Hee Kwon

    2006-01-01

    Accurate measurement of reversible (R2′) and irreversible (R2) transverse relaxation rates plays a key role in various MRI research and applications. Although optimizing the echo spacing for a multi-echo pulse sequence measuring a single exponential decay has been investigated, optimization in sequences such as GESFIDE (Gradient-Echo Sampling of Free Induction Decay and Echo), in which two echo trains are simultaneously measured to obtain both R2 and R2′, has not been reported. In this work, ...

  6. Simultaneous Quantitative MRI Mapping of T1, T2* and Magnetic Susceptibility with Multi-Echo MP2RAGE

    Science.gov (United States)

    Kober, Tobias; Möller, Harald E.; Schäfer, Andreas

    2017-01-01

    The knowledge of relaxation times is essential for understanding the biophysical mechanisms underlying contrast in magnetic resonance imaging. Quantitative experiments, while offering major advantages in terms of reproducibility, may benefit from simultaneous acquisitions. In this work, we demonstrate the possibility of simultaneously recording relaxation-time and susceptibility maps with a prototype Multi-Echo (ME) Magnetization-Prepared 2 RApid Gradient Echoes (MP2RAGE) sequence. T1 maps can be obtained using the MP2RAGE sequence, which is relatively insensitive to inhomogeneities of the radio-frequency transmit field, B1+. As an extension, multiple gradient echoes can be acquired in each of the MP2RAGE readout blocks, which permits the calculation of T2* and susceptibility maps. We used computer simulations to explore the effects of the parameters on the precision and accuracy of the mapping. In vivo parameter maps up to 0.6 mm nominal resolution were acquired at 7 T in 19 healthy volunteers. Voxel-by-voxel correlations and the test-retest reproducibility were used to assess the reliability of the results. When using optimized paramenters, T1 maps obtained with ME-MP2RAGE and standard MP2RAGE showed excellent agreement for the whole range of values found in brain tissues. Simultaneously obtained T2* and susceptibility maps were of comparable quality as Fast Low-Angle SHot (FLASH) results. The acquisition times were more favorable for the ME-MP2RAGE (≈ 19 min) sequence as opposed to the sum of MP2RAGE (≈ 12 min) and FLASH (≈ 10 min) acquisitions. Without relevant sacrifice in accuracy, precision or flexibility, the multi-echo version may yield advantages in terms of reduced acquisition time and intrinsic co-registration, provided that an appropriate optimization of the acquisition parameters is performed. PMID:28081157

  7. Application of stepwise gradients in counter-current chromatography: a rapid and economical strategy for the one-step separation of eight coumarins from Seseli resinosum.

    Science.gov (United States)

    Shehzad, Omer; Khan, Salman; Ha, In Jin; Park, Youmie; Tosun, Alev; Kim, Yeong Shik

    2013-10-04

    The targeted purification of compounds with a broad polarity range from traditional medicinal plants is a big challenge for counter-current chromatography (CCC). Gradient elution was introduced in CCC to address this problem. However, once a suitable solvent system is selected, the separation process requires optimization of operational parameters. The present study was conducted to optimize various operational parameters to integrate the flow rate and solvent gradients for the rapid isolation of eight coumarins from Seseli resinosum in a single run. An increase in the system temperature from 15°C to 35°C increased the stationary phase retention and solubility of the sample, whereas the operation time and viscosity of the system were decreased. The high purity of each compound was ensured by collecting the fractions from the main peaks while all the shoulder peaks were mixed and separated under the same conditions with semi-preparative CCC. GC-FID was used to analyze the components of each phase, which was prepared without presaturation to save the time and solvent consumption. Finally, eight coumarins were purified, including (1) d-laserpitin, (2) (3'S,4'S)-3'-angeloyloxy-4'-hydroxy-3',4'-dihydroseselin, (3) (+)-samidin, (4) (3'S,4'S)-3'-acetoxy-4'-angeloyloxy-3',4'-dihydroseselin, (5) deltoin (6), calipteryxin, (7) (3'S,4'S)-3',4'-disenecioyloxy-3',4'-dihydroseselin, and (8) (-)-anomalin. The present technique has successfully accomplished the goal of one-step separation of these compounds with high purity and recovery in an economic and time efficient manner. Copyright © 2013 Elsevier B.V. All rights reserved.

  8. Magnetization-prepared shells trajectory with automated gradient waveform design.

    Science.gov (United States)

    Shu, Yunhong; Tao, Shengzhen; Trzasko, Joshua D; Huston, John; Weavers, Paul T; Bernstein, Matt A

    2017-08-21

    To develop a fully automated trajectory and gradient waveform design for the non-Cartesian shells acquisition, and to develop a magnetization-prepared (MP) shells acquisition to achieve an efficient three-dimensional acquisition with improved gray-to-white brain matter contrast. After reviewing the shells k-space trajectory, a novel, fully automated trajectory design is developed that allows for gradient waveforms to be automatically generated for specified acquisition parameters. Designs for two types of shells are introduced, including fully sampled and undersampled/accelerated shells. Using those designs, an MP-Shells acquisition is developed by adjusting the acquisition order of shells interleaves to synchronize the center of k-space sampling with the peak of desired gray-to-white matter contrast. The feasibility of the proposed design and MP-Shells is demonstrated using simulation, phantom, and volunteer subject experiments, and the performance of MP-Shells is compared with a clinical Cartesian magnetization-prepared rapid gradient echo acquisition. Initial experiments show that MP-Shells produces excellent image quality with higher data acquisition efficiency and improved gray-to-white matter contrast-to-noise ratio (by 36%) compared with the conventional Cartesian magnetization-prepared rapid gradient echo acquisition. We demonstrated the feasibility of a three-dimensional MP-Shells acquisition and an automated trajectory design to achieve an efficient acquisition with improved gray-to-white matter contrast. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  9. Isotropic 3-D T2-weighted spin-echo for abdominal and pelvic MRI in children.

    Science.gov (United States)

    Dias, Sílvia Costa; Ølsen, Oystein E

    2012-11-01

    MRI has a fundamental role in paediatric imaging. The T2-weighted fast/turbo spin-echo sequence is important because it has high signal-to-noise ratio compared to gradient-echo sequences. It is usually acquired as 2-D sections in one or more planes. Volumetric spin-echo has until recently only been possible with very long echo times due to blurring of the soft-tissue contrast with long echo trains. A new 3-D spin-echo sequence uses variable flip angles to overcome this problem. It may reproduce useful soft-tissue contrast, with improved spatial resolution. Its isotropic capability allows subsequent reconstruction in standard, curved or arbitrary planes. It may be particularly useful for visualisation of small lesions, or if large lesions distort the usual anatomical relations. We present clinical examples, describe the technical parameters and discuss some potential artefacts and optimisation of image quality.

  10. View Angle Tilting Echo Planar Imaging for Distortion Correction

    OpenAIRE

    Ahn, Sinyeob; Hu, Xiaoping

    2011-01-01

    Geometric distortion caused by field inhomogeneity along the phase-encode (PE) direction is one of the most prominent artifacts due to a relatively low effective bandwidth along that direction in magnetic resonance echo planar imaging (EPI). This work describes a method for correcting in-plane image distortion along the PE direction using a view angle tilting (VAT) imaging technique in spin-echo EPI (SE-EPI). SE-EPI with VAT (SE-EPI-VAT) utilizes the addition of gradient blips along the slice...

  11. Quiet echo planar imaging for functional and diffusion MRI.

    Science.gov (United States)

    Hutter, Jana; Price, Anthony N; Cordero-Grande, Lucilio; Malik, Shaihan; Ferrazzi, Giulio; Gaspar, Andreia; Hughes, Emer J; Christiaens, Daan; McCabe, Laura; Schneider, Torben; Rutherford, Mary A; Hajnal, Joseph V

    2018-03-01

    To develop a purpose-built quiet echo planar imaging capability for fetal functional and diffusion scans, for which acoustic considerations often compromise efficiency and resolution as well as angular/temporal coverage. The gradient waveforms in multiband-accelerated single-shot echo planar imaging sequences have been redesigned to minimize spectral content. This includes a sinusoidal read-out with a single fundamental frequency, a constant phase encoding gradient, overlapping smoothed CAIPIRINHA blips, and a novel strategy to merge the crushers in diffusion MRI. These changes are then tuned in conjunction with the gradient system frequency response function. Maintained image quality, SNR, and quantitative diffusion values while reducing acoustic noise up to 12 dB (A) is illustrated in two adult experiments. Fetal experiments in 10 subjects covering a range of parameters depict the adaptability and increased efficiency of quiet echo planar imaging. Purpose-built for highly efficient multiband fetal echo planar imaging studies, the presented framework reduces acoustic noise for all echo planar imaging-based sequences. Full optimization by tuning to the gradient frequency response functions allows for a maximally time-efficient scan within safe limits. This allows ambitious in-utero studies such as functional brain imaging with high spatial/temporal resolution and diffusion scans with high angular/spatial resolution to be run in a highly efficient manner at acceptable sound levels. Magn Reson Med 79:1447-1459, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. © 2017 The Authors Magnetic Resonance in

  12. Properties of echo spectra observed by MST radars

    Science.gov (United States)

    Wakasugi, K.

    1983-01-01

    Turbulent scatter and Fresnel reflection are the fundamental echoing mechanisms to interpret the signals observed by Mesosphere-stratosphere-troposphere (MST) radars. Turbulent scattered echoes provide information about the turbulence structure and mean flow of the atmosphere. Observational results with VHF MST radars, however, show the importance of Fresnel reflection due to the infinite gradient of reflectivity at the edges of a scattering layer. This condition is excluded for the weak fluctuation models but it is still possible to include the observed aspect sensitivity by assuming an anisotropic structure of fluctuations. Another explanation of the aspect sensitivity observed by MST radars is advanced. Spectral estimates by the widely used periodogram were related to a four-dimensional spectrum of atmospheric fluctuations with anisotropic structure. Effects of the radar system such as antenna beam width, beam direction and Fast Fourier Transformations (FFT) data length were discussed for the anisotropic turbulent atmosphere. Echo parameters were also estimated.

  13. Rapid MRI using a modified Dixon technique: a non-invasive and effective method for detection and monitoring of fatty metamorphosis of the liver

    Energy Technology Data Exchange (ETDEWEB)

    Fishbein, M.H. [Pediatric Gastroenterology, Dept. of Pediatrics, Springfield, IL (United States); Stevens, W.R. [St. John' s Hospital, Department of Radiology, Springfield, IL (United States)

    2001-11-01

    Fatty liver and non-alcoholic steatohepatitis are frequently associated with obesity. Weight loss is the mainstay of therapy for these conditions. In this case report, we used a modification of the Dixon method to demonstrate normalization of hepatic fat content in an obese individual with fatty liver following weight reduction. This technique involves fast gradient echo instead of spin echo, which has been utilized previously, as the former provides an accurate and more rapid means of assessing hepatic fat content. This technique is recommended for the assessment of hepatic steatosis in at-risk subjects. (orig.)

  14. E-region echo characteristics governed by auroral arc electrodynamics

    Directory of Open Access Journals (Sweden)

    S. E. Milan

    Full Text Available Observations of a pair of auroral arc features by two imagers, one ground- and one space-based, allows the associated field-aligned current (FAC and electric field structure to be inferred. Simultaneous observations of HF radar echoes provide an insight into the irregularity-generating mechanisms. This is especially interesting for the E-region echoes observed, which form the focus of our analysis, and from which several conclusions can be drawn, summarized as follows. Latitudinal variations in echo characteristics are governed by the FAC and electric field background. Particularly sharp boundaries are found at the edges of auroral arcs. Within regions of auroral luminosity, echoes have Doppler shifts below the ion-acoustic speed and are proportional to the electric field, suggesting scatter from gradient drift waves. Regions of downward FAC are associated with mixed high and low Doppler shift echoes. The high Doppler shift component is greatly in excess of the ion-acoustic speed, but seems to be commensurate with the driving electric field. The low Doppler shift component appears to be much depressed below expectations.

    Key words. Ionosphere (ionospheric irregularities; electric fields and currents

  15. Respiration impacts phase difference-based field maps in echo planar imaging.

    Science.gov (United States)

    Zeller, Mario; Kraus, Philip; Müller, Alexander; Bley, Thorsten A; Köstler, Herbert

    2014-08-01

    To investigate the influence of respiration on field maps for geometric distortion correction derived from two rapidly acquired consecutive echo planar images. Displacement maps of the brains of seven healthy volunteers were acquired under breath hold and free breathing for a 64 × 64 pixel image matrix using phase labeling for additional coordinate encoding (PLACE). The maps were transformed into undistorted gradient echo space and analyzed with regard to standard deviation and absolute deviation from an accurate reference field map derived from a multiecho reference scan. Standard deviations between PLACE field maps and absolute difference from the reference field map are a factor of about 3 higher under free breathing than under breath hold. The mean deviation decreases from 3 pixels in the slice closest to the lung to 1 pixel in the most superior slice under free breathing and from 1 to field map and thus corrupt the geometric distortion correction. The effect can be greatly reduced by acquiring the field map data under breath hold. Data acquired under free breathing can be improved with retrospective phase correction or by averaging several field maps. Copyright © 2013 Wiley Periodicals, Inc.

  16. State Statistics | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  17. Watershed Statistics | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  18. Nonlinear theory of transverse beam echoes

    OpenAIRE

    Sen, Tanaji; Li, Yuan Shen

    2017-01-01

    Transverse beam echoes can be excited with a single dipole kick followed by a single quadrupole kick. They have been used to measure diffusion in hadron beams and have other diagnostic capabilities. Here we develop theories of the transverse echo nonlinear in both the dipole and quadrupole kick strengths. The theories predict the maximum echo amplitudes and the optimum strength parameters. We find that the echo amplitude increases with smaller beam emittance and the asymptotic echo amplitude ...

  19. Stellar Echo Imaging of Exoplanets

    Science.gov (United States)

    Mann, Chris; Lerch, Kieran; Lucente, Mark; Meza-Galvan, Jesus; Mitchell, Dan; Ruedin, Josh; Williams, Spencer; Zollars, Byron

    2016-01-01

    All stars exhibit intensity fluctuations over several timescales, from nanoseconds to years. These intensity fluctuations echo off bodies and structures in the star system. We posit that it is possible to take advantage of these echoes to detect, and possibly image, Earth-scale exoplanets. Unlike direct imaging techniques, temporal measurements do not require fringe tracking, maintaining an optically-perfect baseline, or utilizing ultra-contrast coronagraphs. Unlike transit or radial velocity techniques, stellar echo detection is not constrained to any specific orbital inclination. Current results suggest that existing and emerging technology can already enable stellar echo techniques at flare stars, such as Proxima Centauri, including detection, spectroscopic interrogation, and possibly even continent-level imaging of exoplanets in a variety of orbits. Detection of Earth-like planets around Sun-like stars appears to be extremely challenging, but cannot be fully quantified without additional data on micro- and millisecond-scale intensity fluctuations of the Sun. We consider survey missions in the mold of Kepler and place preliminary constraints on the feasibility of producing 3D tomographic maps of other structures in star systems, such as accretion disks. In this report we discuss the theory, limitations, models, and future opportunities for stellar echo imaging.

  20. Current-induced alternating reversed dual-echo-steady-state for joint estimation of tissue relaxation and electrical properties.

    Science.gov (United States)

    Lee, Hyunyeol; Sohn, Chul-Ho; Park, Jaeseok

    2017-07-01

    To develop a current-induced, alternating reversed dual-echo-steady-state-based magnetic resonance electrical impedance tomography for joint estimation of tissue relaxation and electrical properties. The proposed method reverses the readout gradient configuration of conventional, in which steady-state-free-precession (SSFP)-ECHO is produced earlier than SSFP-free-induction-decay (FID) while alternating current pulses are applied in between the two SSFPs to secure high sensitivity of SSFP-FID to injection current. Additionally, alternating reversed dual-echo-steady-state signals are modulated by employing variable flip angles over two orthogonal injections of current pulses. Ratiometric signal models are analytically constructed, from which T 1 , T 2 , and current-induced B z are jointly estimated by solving a nonlinear inverse problem for conductivity reconstruction. Numerical simulations and experimental studies are performed to investigate the feasibility of the proposed method in estimating relaxation parameters and conductivity. The proposed method, if compared with conventional magnetic resonance electrical impedance tomography, enables rapid data acquisition and simultaneous estimation of T 1 , T 2 , and current-induced B z , yielding a comparable level of signal-to-noise ratio in the parameter estimates while retaining a relative conductivity contrast. We successfully demonstrated the feasibility of the proposed method in jointly estimating tissue relaxation parameters as well as conductivity distributions. It can be a promising, rapid imaging strategy for quantitative conductivity estimation. Magn Reson Med 78:107-120, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  1. The EChO science case

    Science.gov (United States)

    Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul; Hartogh, Paul; Isaak, Kate; Linder, Martin; Lovis, Christophe; Micela, Giusi; Ollivier, Marc; Puig, Ludovic; Ribas, Ignasi; Snellen, Ignas; Swinyard, Bruce; Allard, France; Barstow, Joanna; Cho, James; Coustenis, Athena; Cockell, Charles; Correia, Alexandre; Decin, Leen; de Kok, Remco; Deroo, Pieter; Encrenaz, Therese; Forget, Francois; Glasse, Alistair; Griffith, Caitlin; Guillot, Tristan; Koskinen, Tommi; Lammer, Helmut; Leconte, Jeremy; Maxted, Pierre; Mueller-Wodarg, Ingo; Nelson, Richard; North, Chris; Pallé, Enric; Pagano, Isabella; Piccioni, Guseppe; Pinfield, David; Selsis, Franck; Sozzetti, Alessandro; Stixrude, Lars; Tennyson, Jonathan; Turrini, Diego; Zapatero-Osorio, Mariarosa; Beaulieu, Jean-Philippe; Grodent, Denis; Guedel, Manuel; Luz, David; Nørgaard-Nielsen, Hans Ulrik; Ray, Tom; Rickman, Hans; Selig, Avri; Swain, Mark; Banaszkiewicz, Marek; Barlow, Mike; Bowles, Neil; Branduardi-Raymont, Graziella; du Foresto, Vincent Coudé; Gerard, Jean-Claude; Gizon, Laurent; Hornstrup, Allan; Jarchow, Christopher; Kerschbaum, Franz; Kovacs, Géza; Lagage, Pierre-Olivier; Lim, Tanya; Lopez-Morales, Mercedes; Malaguti, Giuseppe; Pace, Emanuele; Pascale, Enzo; Vandenbussche, Bart; Wright, Gillian; Ramos Zapata, Gonzalo; Adriani, Alberto; Azzollini, Ruymán; Balado, Ana; Bryson, Ian; Burston, Raymond; Colomé, Josep; Crook, Martin; Di Giorgio, Anna; Griffin, Matt; Hoogeveen, Ruud; Ottensamer, Roland; Irshad, Ranah; Middleton, Kevin; Morgante, Gianluca; Pinsard, Frederic; Rataj, Mirek; Reess, Jean-Michel; Savini, Giorgio; Schrader, Jan-Rutger; Stamper, Richard; Winter, Berend; Abe, L.; Abreu, M.; Achilleos, N.; Ade, P.; Adybekian, V.; Affer, L.; Agnor, C.; Agundez, M.; Alard, C.; Alcala, J.; Allende Prieto, C.; Alonso Floriano, F. J.; Altieri, F.; Alvarez Iglesias, C. A.; Amado, P.; Andersen, A.; Aylward, A.; Baffa, C.; Bakos, G.; Ballerini, P.; Banaszkiewicz, M.; Barber, R. J.; Barrado, D.; Barton, E. J.; Batista, V.; Bellucci, G.; Belmonte Avilés, J. A.; Berry, D.; Bézard, B.; Biondi, D.; Błęcka, M.; Boisse, I.; Bonfond, B.; Bordé, P.; Börner, P.; Bouy, H.; Brown, L.; Buchhave, L.; Budaj, J.; Bulgarelli, A.; Burleigh, M.; Cabral, A.; Capria, M. T.; Cassan, A.; Cavarroc, C.; Cecchi-Pestellini, C.; Cerulli, R.; Chadney, J.; Chamberlain, S.; Charnoz, S.; Christian Jessen, N.; Ciaravella, A.; Claret, A.; Claudi, R.; Coates, A.; Cole, R.; Collura, A.; Cordier, D.; Covino, E.; Danielski, C.; Damasso, M.; Deeg, H. J.; Delgado-Mena, E.; Del Vecchio, C.; Demangeon, O.; De Sio, A.; De Wit, J.; Dobrijévic, M.; Doel, P.; Dominic, C.; Dorfi, E.; Eales, S.; Eiroa, C.; Espinoza Contreras, M.; Esposito, M.; Eymet, V.; Fabrizio, N.; Fernández, M.; Femenía Castella, B.; Figueira, P.; Filacchione, G.; Fletcher, L.; Focardi, M.; Fossey, S.; Fouqué, P.; Frith, J.; Galand, M.; Gambicorti, L.; Gaulme, P.; García López, R. J.; Garcia-Piquer, A.; Gear, W.; Gerard, J.-C.; Gesa, L.; Giani, E.; Gianotti, F.; Gillon, M.; Giro, E.; Giuranna, M.; Gomez, H.; Gomez-Leal, I.; Gonzalez Hernandez, J.; González Merino, B.; Graczyk, R.; Grassi, D.; Guardia, J.; Guio, P.; Gustin, J.; Hargrave, P.; Haigh, J.; Hébrard, E.; Heiter, U.; Heredero, R. L.; Herrero, E.; Hersant, F.; Heyrovsky, D.; Hollis, M.; Hubert, B.; Hueso, R.; Israelian, G.; Iro, N.; Irwin, P.; Jacquemoud, S.; Jones, G.; Jones, H.; Justtanont, K.; Kehoe, T.; Kerschbaum, F.; Kerins, E.; Kervella, P.; Kipping, D.; Koskinen, T.; Krupp, N.; Lahav, O.; Laken, B.; Lanza, N.; Lellouch, E.; Leto, G.; Licandro Goldaracena, J.; Lithgow-Bertelloni, C.; Liu, S. J.; Lo Cicero, U.; Lodieu, N.; Lognonné, P.; Lopez-Puertas, M.; Lopez-Valverde, M. A.; Lundgaard Rasmussen, I.; Luntzer, A.; Machado, P.; MacTavish, C.; Maggio, A.; Maillard, J.-P.; Magnes, W.; Maldonado, J.; Mall, U.; Marquette, J.-B.; Mauskopf, P.; Massi, F.; Maurin, A.-S.; Medvedev, A.; Michaut, C.; Miles-Paez, P.; Montalto, M.; Montañés Rodríguez, P.; Monteiro, M.; Montes, D.; Morais, H.; Morales, J. C.; Morales-Calderón, M.; Morello, G.; Moro Martín, A.; Moses, J.; Moya Bedon, A.; Murgas Alcaino, F.; Oliva, E.; Orton, G.; Palla, F.; Pancrazzi, M.; Pantin, E.; Parmentier, V.; Parviainen, H.; Peña Ramírez, K. Y.; Peralta, J.; Perez-Hoyos, S.; Petrov, R.; Pezzuto, S.; Pietrzak, R.; Pilat-Lohinger, E.; Piskunov, N.; Prinja, R.; Prisinzano, L.; Polichtchouk, I.; Poretti, E.; Radioti, A.; Ramos, A. A.; Rank-Lüftinger, T.; Read, P.; Readorn, K.; Rebolo López, R.; Rebordão, J.; Rengel, M.; Rezac, L.; Rocchetto, M.; Rodler, F.; Sánchez Béjar, V. J.; Sanchez Lavega, A.; Sanromá, E.; Santos, N.; Sanz Forcada, J.; Scandariato, G.; Schmider, F.-X.; Scholz, A.; Scuderi, S.; Sethenadh, J.; Shore, S.; Showman, A.; Sicardy, B.; Sitek, P.; Smith, A.; Soret, L.; Sousa, S.; Stiepen, A.; Stolarski, M.; Strazzulla, G.; Tabernero, H. M.; Tanga, P.; Tecsa, M.; Temple, J.; Terenzi, L.; Tessenyi, M.; Testi, L.; Thompson, S.; Thrastarson, H.; Tingley, B. W.; Trifoglio, M.; Martín Torres, J.; Tozzi, A.; Turrini, D.; Varley, R.; Vakili, F.; de Val-Borro, M.; Valdivieso, M. L.; Venot, O.; Villaver, E.; Vinatier, S.; Viti, S.; Waldmann, I.; Waltham, D.; Ward-Thompson, D.; Waters, R.; Watkins, C.; Watson, D.; Wawer, P.; Wawrzaszk, A.; White, G.; Widemann, T.; Winek, W.; Wiśniowski, T.; Yelle, R.; Yung, Y.; Yurchenko, S. N.

    2015-12-01

    allows us to explore the spectroscopic and chemical diversity of the exoplanet population as a whole. The EChO Origin: This is a deep survey of a subsample of tens of exoplanets for which significantly higher signal to noise and spectral resolution spectra can be obtained to explain the origin of the exoplanet diversity (such as formation mechanisms, chemical processes, atmospheric escape). The EChO Rosetta Stones: This is an ultra-high accuracy survey targeting a subsample of select exoplanets. These will be the bright "benchmark" cases for which a large number of measurements would be taken to explore temporal variations, and to obtain two and three dimensional spatial information on the atmospheric conditions through eclipse-mapping techniques. If EChO were launched today, the exoplanets currently observed are sufficient to provide a large and diverse sample. The Chemical Census survey would consist of > 160 exoplanets with a range of planetary sizes, temperatures, orbital parameters and stellar host properties. Additionally, over the next 10 years, several new ground- and space-based transit photometric surveys and missions will come on-line (e.g. NGTS, CHEOPS, TESS, PLATO), which will specifically focus on finding bright, nearby systems. The current rapid rate of discovery would allow the target list to be further optimised in the years prior to EChO's launch and enable the atmospheric characterisation of hundreds of planets.

  2. Application of spin echoes in the regime of weak dephasing to T1 -mapping of the lung.

    Science.gov (United States)

    Assländer, Jakob; Glaser, Steffen J; Hennig, Jürgen

    2017-04-17

    This work presents an approach to mapping the entire lung's proton density and T1 within a single breath-hold and analyzes the apparent T1 when exciting with a spin echo generating pulse in comparison to a standard gradient echo acquisition. An inversion-recovery SNAPSHOT-FLASH sequence with a stack-of-stars k-space readout with a golden angle increment was modified to use a spin echo generating radiofrequency-pulse for excitation. Data of five volunteers were acquired on a 3T scanner and image reconstruction was performed by an iterative algorithm adopted from MR-Fingerprinting. The feasibility of acquiring quantitative maps of the entire lung with a resolution of 5 × 5 × 10 mm within 7.5 s is demonstrated. It is shown that the proposed spin echo forming radiofrequency-pulse increases the apparent proton density compared to a rectangular pulse. Further, the apparent T1 is reduced in the spin echo case compared to the gradient echo sequence. The proposed spin echo based method results in T1 maps that are comparable to the ones that were acquired with ultra-short echo time sequences elsewhere. The T1 shortening is believed to originate from increased signal contributions of the extra vascular compartment, which has a short T2∗ and T1 . Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  3. Implementation of spin-echo blood oxygen level-dependent (BOLD) functional MRI in birds.

    Science.gov (United States)

    Poirier, Colline; Verhoye, Marleen; Boumans, Tiny; Van der Linden, Annemie

    2010-11-01

    The advent of high-field MRI systems has allowed the implementation of blood oxygen level-dependent functional MRI (BOLD fMRI) on small animals. An increased magnetic field improves the signal-to-noise ratio and thus allows an improvement in the spatial resolution. However, it also increases susceptibility artefacts in the commonly acquired gradient-echo images. This problem is particularly prominent in songbird MRI because of the presence of numerous air cavities in the skull of birds. These T(2)*-related image artefacts can be circumvented using spin-echo BOLD fMRI. In this article, we describe the implementation of spin-echo BOLD fMRI in zebra finches, a small songbird of 15-25 g, extensively studied in the behavioural neurosciences of birdsong. Because the main topics in this research domain are song perception and song learning, the protocol implemented used auditory stimuli. Despite the auditory nature of the stimuli and the weak contrast-to-noise ratio of spin-echo BOLD fMRI compared with gradient-echo BOLD fMRI, we succeeded in detecting statistically significant differences in BOLD responses triggered by different stimuli. This study shows that spin-echo BOLD fMRI is a viable approach for the investigation of auditory processing in the whole brain of small songbirds. It can also be applied to study auditory processing in other small animals, as well as other sensory modalities.

  4. Imaging of the Achilles tendon in spondyloarthritis: a comparison of ultrasound and conventional, short and ultrashort echo time MRI with and without intravenous contrast

    Energy Technology Data Exchange (ETDEWEB)

    Hodgson, R.J.; Emery, P. [University of Leeds, Chapel Allerton Hospital, Leeds Musculoskeletal Biomedical Research Centre, Leeds (United Kingdom); Grainger, A.J.; O' Connor, P.J.; Evans, R. [Chapel Allerton Hospital, Leeds Musculoskeletal Biomedical Research Centre, Leeds (United Kingdom); Coates, L.; Marzo-Ortega, H.; Helliwell, P.; McGonagle, D. [University of Leeds, Leeds Institute for Molecular Medicine, Leeds (United Kingdom); Robson, M.D. [University of Oxford, Oxford Centre for Clinical Magnetic Resonance Research, Oxford (United Kingdom)

    2011-06-15

    To compare conventional MRI, ultrashort echo time MRI and ultrasound for assessing the extent of tendon abnormalities in spondyloarthritis. 25 patients with spondyloarthritis and Achilles symptoms were studied with MRI and ultrasound. MR images of the Achilles tendon were acquired using T1-weighted spin echo, gradient echo and ultrashort echo time (UTE) sequences with echo times (TE) between 0.07 and 16 ms, before and after intravenous contrast medium. Greyscale and power Doppler ultrasound were also performed. The craniocaudal extent of imaging abnormalities measured by a consultant musculoskeletal radiologist was compared between the different techniques. Abnormalities were most extensive on spoiled gradient echo images with TE=2 ms. Contrast enhancement after intravenous gadolinium was greatest on the UTE images (TE=0.07 ms). Fewer abnormalities were demonstrated using unenhanced UTE. Abnormalities were more extensive on MRI than ultrasound. Contrast enhancement was more extensive than power Doppler signal. 3D spoiled gradient echo images with an echo time of 2 ms demonstrate more extensive tendon abnormalities than the other techniques in spondyloarthritis. Abnormalities of vascularity are best demonstrated on enhanced ultrashort echo time images. (orig.)

  5. Superluminal light echoes in astronomy

    Energy Technology Data Exchange (ETDEWEB)

    Falla, D F; Floyd, M J; Potter, A G [Department of Physics, University of Wales, Aberystwyth, SY23 3BZ (United Kingdom)

    2003-03-01

    The echo produced when a light 'pulse' from a stellar source (e.g. a nova or supernova) is reflected by circumstellar or interstellar material can appear as a luminous ring expanding at a rate that can be superluminal, i.e. having an apparent motion within the source, transverse to the observer's line of sight, at a speed greater than that of light. 'Light-echo optics' applied to the star RS Puppis and its nebula suggests that when nebular features in peripheral regions of circumstellar-shell images are observed, superluminal effects are not evident; however, such observations can give the stellar distance from the observer. Light-echo optics for an interstellar plane sheet, inclined to the observer's line of sight, can be applied to Nova GK Persei 1901 and SN 1987A, which show superluminal effects. For SN 1987A, an intense thermal x-ray source should be produced in AD 2003, when the advancing supernova ejecta interact with a circumstellar ring, 250 light days in radius: the arc-shaped x-ray image, while not actually a 'radiation echo', should expand at a superluminal rate for about 75 days from the time of its first appearance, and also for the same time before the completion of its 'circuit' around the ring.

  6. Dance of the Light Echoes

    Science.gov (United States)

    2008-01-01

    [figure removed for brevity, see original site] Click on image for larger poster version This composite image from NASA's Spitzer Space Telescope shows the remnant of a star that exploded, called Cassiopeia A (center) and its surrounding 'light echoes' -- dances of light through dusty clouds, created when stars blast apart. The light echoes are colored and the surrounding clouds of dust are gray. In figure 1, dramatic changes are highlighted in phenomena referred to as light echoes (colored areas) around the Cassiopeia A supernova remnant (center). Cassiopeia A is the remnant of a once massive star that died in a violent supernova explosion. It consists of a dead star, called a neutron star, and a surrounding shell of material that was blasted off as the star died. A light echo occurs when a star explodes, acting like a cosmic flashbulb. The light from this explosion zips through nearby dust clumps, illuminating and heating them up slightly. This brief period of warming causes them to glow in infrared, like a chain of Christmas bulbs lighting up one by one. The result is an optical illusion, in which the dust appears to be flying outward at the speed of light. In figure 1, this apparent motion can be seen here by the shift in colored dust clumps Cassiopeia A is the remnant of a once massive star that died in a violent supernova explosion. It consists of a dead star, called a neutron star, and a surrounding shell of material that was blasted off as the star died. This remnant is located 11,000 light-years away in the northern constellation Cassiopeia. This composite consists of six processed images taken over a time span of three years. Dust features that have not changed over time appear gray, while those that have changed are colored blue or orange. Bluer colors represent an earlier time and redder ones, a later time. The progression of the light echo through the dust can be seen here by the shift in colored dust clumps. This light echo is the largest ever seen

  7. A modified multi-echo AFI for simultaneous B1(+) magnitude and phase mapping.

    Science.gov (United States)

    Choi, Narae; Lee, Joonsung; Kim, Min-Oh; Shin, Jaewook; Kim, Dong-Hyun

    2014-05-01

    To simultaneously acquire the B1(+) magnitude and B1(+) phase, a modified multi-echo actual flip-angle imaging (AFI) sequence is proposed. A multi-echo gradient echo sequence was integrated into every even TR of AFI to measure both magnitude and phase of B1(+). In addition, to increase the signal-to-noise ratio of the B1(+) phase, a double-angle multi-echo AFI sequence, in which the flip-angle of the RF pulses is α at the odd TR and 2α at the even TR is proposed. Images were simulated to evaluate the performance of this method under various imaging and physical parameters. The performance was compared to the spin echo based B1(+) mapping method in phantom and in vivo studies. In the simulation, the estimation error decreased as TR1/T1 decreased and TR2/TR1 increased. For double-angle AFI, flip-angle ranges that could estimate B1(+) magnitude and phase better than the original AFI were identified. Using the proposed method, B1(+) phase estimation was similar to spin echo phase. In the phantom study, correlation coefficient between the estimated B1(+) phases using the spin echo and the proposed method was 0.9998. The results show that the B1(+) magnitude and B1(+) phase can be simultaneously acquired and accurately estimated using the proposed double-angle AFI method. Copyright © 2014 Elsevier Inc. All rights reserved.

  8. Multi-echo GRE imaging of knee cartilage.

    Science.gov (United States)

    Yuen, Joanna; Hung, Jachin; Wiggermann, Vanessa; Robinson, Simon D; McCormack, Robert; d'Entremont, Agnes G; Rauscher, Alexander

    2017-05-01

    To visualize healthy and abnormal articular cartilage, we investigated the potential of using the 3D multi-echo gradient echo (GRE) signal's magnitude and frequency and maps of T2* relaxation. After optimizing imaging parameters in five healthy volunteers, 3D multi-echo GRE magnetic resonance (MR) images were acquired at 3T in four patients with chondral damage prior to their arthroscopic surgery. Average magnitude and frequency information was extracted from the GRE images, and T2* maps were generated. Cartilage abnormalities were confirmed after arthroscopy and were graded using the Outerbridge classification scheme. Regions of interest were identified on average magnitude GRE images and compared to arthroscopy. All four patients presented with regions of Outerbridge Grade I and II cartilage damage on arthroscopy. One patient had Grade III changes. Grade I, II, and III changes were detectable on average magnitude and T2* maps, while Grade II and higher changes were also observable on MR frequency maps. For average magnitude images of healthy volunteers, the signal-to-noise ratio of the magnitude image averaged over three echoes was 4.26 ± 0.32, 12.26 ± 1.09, 14.31 ± 1.93, and 13.36 ± 1.13 in bone, femoral, tibial, and patellar cartilage, respectively. This proof-of-principle study demonstrates the feasibility of using different imaging contrasts from the 3D multi-echo GRE scan to visualize abnormalities of the articular cartilage. © 2016 International Society for Magnetic Resonance in Medicine Level of Evidence: 1 J. MAGN. RESON. IMAGING 2017;45:1502-1513. © 2016 International Society for Magnetic Resonance in Medicine.

  9. Echo-free and relatively echo-free 'renal sinus lipomatosis'

    Energy Technology Data Exchange (ETDEWEB)

    Suramo, I.; Paeivaensalo, M.; Myllylae, V.

    1983-05-01

    Eleven echo-free and 37 relatively echo-free peripelvic lesions, primarily interpreted as sinus lipomatosis by experienced sonologists, were examined using CT. Eight echo-free lesions proved to be cysts and only three ''fibrous fat''. Hypodense peripelvic fat accumulations were not totally echo-free in any of the cases, but tended to show up weak echos.

  10. K-space trajectory mapping and its application for ultrashort Echo time imaging

    Czech Academy of Sciences Publication Activity Database

    Latta, P.; Starčuk jr., Zenon; Gruwel, M. L. H.; Weber, M.H.; Tomanek, B.

    2017-01-01

    Roč. 36, February (2017), s. 68-76 ISSN 0730-725X R&D Projects: GA ČR(CZ) GA15-12607S Institutional support: RVO:68081731 Keywords : gradient imperfections * K-space deviation * trajectrory estaimation * ultrashort echo time Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.225, year: 2016

  11. Reconstruction strategy for echo planar spectroscopy and its application to partially undersampled imaging

    DEFF Research Database (Denmark)

    Hanson, Lars Peter Grüner; Schaumburg, K; Paulson, O B

    2000-01-01

    The most commonly encountered form of echo planar spectroscopy involves oscillating gradients in one spatial dimension during readout. Data are consequently not sampled on a Cartesian grid. A fast gridding algorithm applicable to this particular situation is presented. The method is optimal, i...

  12. Longitudinal collective echoes in coasting particle beams

    Directory of Open Access Journals (Sweden)

    Ahmed Al-Khateeb

    2003-01-01

    Full Text Available Longitudinal ballistic and collective beam echoes with diffusion effects are investigated theoretically. In the presence of the space-charge impedance, the collective echo amplitude is obtained as a closed form expression. In contrast to the ballistic case, the collective echo amplitude consists of one maximum at time t_{echo}. The echo amplitude grows up and damps down with a rate proportional to the Landau damping rate of space-charge waves. The effect of weak diffusion is found to modify the ballistic and the collective echo amplitudes in the same manner. This effect of diffusion was confirmed using a “noiseless,” grid-based simulation code. As a first application the amount of numerical diffusion in our simulation code was determined using the echo effect.

  13. Nonlinear theory of transverse beam echoes

    Energy Technology Data Exchange (ETDEWEB)

    Sen, Tanaji; Li, Yuan Shen

    2017-10-04

    Transverse beam echoes can be excited with a single dipole kick followed by a single quadrupole kick. They have been used to measure diffusion in hadron beams and have other diagnostic capabilities. Here we develop theories of the transverse echo nonlinear in both the dipole and quadrupole kick strengths. The theories predict the maximum echo amplitudes and the optimum strength parameters. We find that the echo amplitude increases with smaller beam emittance and the asymptotic echo amplitude can exceed half the initial dipole kick amplitude. We show that multiple echoes can be observed provided the dipole kick is large enough. The spectrum of the echo pulse can be used to determine the nonlinear detuning parameter with small amplitude dipole kicks. Simulations are performed to check the theoretical predictions. In the useful ranges of dipole and quadrupole strengths, they are shown to be in reasonable agreement.

  14. Neutron resonance spin echo spectroscopy on split modes

    Energy Technology Data Exchange (ETDEWEB)

    Habicht, K [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Lise-Meitner-Campus, Hahn-Meitner Platz 1, D-14109 Berlin (Germany); Enderle, M [Institut Laue-Langevin, BP 156-38042 Grenoble Cedex 9 (France); Faak, B [Commissariat a l' Energie Atomique, INAC, SPSMS, 38054 Grenoble (France); Hradil, K [Institut fuer Physikalische Chemie, Georg-August-Universitaet Goettingen, Aussenstelle am FRM II, Lichtenbergstrasse 1, D-85747 Garching (Germany); Boeni, P [Physik-Department E21, Technische Universitaet Muenchen, D-85747 Garching (Germany); Keller, T, E-mail: habicht@helmholtz-berlin.d [ZWE FRMII, TU Munich, Lichtenbergstrasse 1, D-85747 Garching (Germany)

    2010-02-01

    We present an analytical formalism investigating effects of multiple excitations with different dispersion parameters in the context of neutron resonance spin echo spectroscopy. This allows identifying conditions to obtain high-resolution information on the energy split of two dispersive modes which may differ or not in their local energy gradient. Comparison to experimental data is provided by recent measurements on magnon excitations in RbMnF{sub 3}. Potential future applications are investigations of hybridized phonon or magnon modes or mixed excitations.

  15. ECHO parameters of diastolic dysfunction.

    Science.gov (United States)

    Schumacher, A; Khojeini, Ev; Larson, Df

    2008-09-01

    Most patients with cardiac disease have diastolic dysfunction which is characterized by impaired diastolic filling and/or abnormal diastolic relaxation. The trans-esophageal echocardiography (TEE) used routinely during open-heart surgical procedures has exceptional resolution that may permit the identification and grading of diastolic dysfunction. The goal of this study was to determine which echocardiography (ECHO) parameters can best describe diastolic dysfunction due to myocardial remodeling and fibrosis. Baseline transthoracic ECHO was performed on 3-month-old C57BL/6J female mice followed by administration of isoproterenol (2 microg/g/d) for 6 days. On day 7, transthoracic ECHO was performed to determine the change of left ventricular (LV) inflow parameters due to isoproterenol-mediated cardiac remodeling. The mid-LV region was stained with picrosirius red to quantify myocardial fibrosis and demonstrated a 5-fold increase in cardiac fibrosis (p = 0.002). LV mass was increased by 36% (p = 0.0016). Mitral valve flow Doppler peak velocities E and A were measured from a 4-chamber view. The E/A ratio did not change, but the E deceleration time, velocity time integral of the E-A complex (E-A VTI), E/E-A VTI ratio, isovolumic relaxation time (IVRT), and diastolic time all significantly increased. The corresponding tissue Doppler parameter, Ea/Aa ratio, decreased by 25% (p = 0.035). The left atrial dimension and the ECHO index of left atrial pressure (E/Ea) significantly increased (p < 0.02). These data suggest that, with a long-axis and a 4-chamber view, the clinician can adequately determine diastolic function in the open-heart surgical patient.

  16. Independence of echo-threshold and echo-delay in the barn owl.

    Directory of Open Access Journals (Sweden)

    Brian S Nelson

    Full Text Available Despite their prevalence in nature, echoes are not perceived as events separate from the sounds arriving directly from an active source, until the echo's delay is long. We measured the head-saccades of barn owls and the responses of neurons in their auditory space-maps while presenting a long duration noise-burst and a simulated echo. Under this paradigm, there were two possible stimulus segments that could potentially signal the location of the echo. One was at the onset of the echo; the other, after the offset of the direct (leading sound, when only the echo was present. By lengthening the echo's duration, independently of its delay, spikes and saccades were evoked by the source of the echo even at delays that normally evoked saccades to only the direct source. An echo's location thus appears to be signaled by the neural response evoked after the offset of the direct sound.

  17. Independence of echo-threshold and echo-delay in the barn owl.

    Science.gov (United States)

    Nelson, Brian S; Takahashi, Terry T

    2008-01-01

    Despite their prevalence in nature, echoes are not perceived as events separate from the sounds arriving directly from an active source, until the echo's delay is long. We measured the head-saccades of barn owls and the responses of neurons in their auditory space-maps while presenting a long duration noise-burst and a simulated echo. Under this paradigm, there were two possible stimulus segments that could potentially signal the location of the echo. One was at the onset of the echo; the other, after the offset of the direct (leading) sound, when only the echo was present. By lengthening the echo's duration, independently of its delay, spikes and saccades were evoked by the source of the echo even at delays that normally evoked saccades to only the direct source. An echo's location thus appears to be signaled by the neural response evoked after the offset of the direct sound.

  18. Superluminal light echoes in astronomy

    CERN Document Server

    Falla, D F; Potter, A G

    2003-01-01

    The echo produced when a light 'pulse' from a stellar source (e.g. a nova or supernova) is reflected by circumstellar or interstellar material can appear as a luminous ring expanding at a rate that can be superluminal, i.e. having an apparent motion within the source, transverse to the observer's line of sight, at a speed greater than that of light. 'Light-echo optics' applied to the star RS Puppis and its nebula suggests that when nebular features in peripheral regions of circumstellar-shell images are observed, superluminal effects are not evident; however, such observations can give the stellar distance from the observer. Light-echo optics for an interstellar plane sheet, inclined to the observer's line of sight, can be applied to Nova GK Persei 1901 and SN 1987A, which show superluminal effects. For SN 1987A, an intense thermal x-ray source should be produced in AD 2003, when the advancing supernova ejecta interact with a circumstellar ring, 250 light days in radius: the arc-shaped x-ray image, while not ...

  19. The HET Echo Mapping Project

    Science.gov (United States)

    Welsh, W.; Robinson, E. L.; Hill, G.; Shields, G.; Wills, B.; Brandt, N.; Eracleous, M.; Kollatschny, W.; Horne, K.; Gallo, L.

    2000-12-01

    The ``HET Echo Mapping Project'' is a new research program that is using the echo mapping technique to probe supermassive black holes and their environments in AGN. Its primary goals are to: (1) Map the size, geometry, and the flow of the BLR gas; (2) Make direct dynamical estimates of the mass of the black hole using the measured geometry and kinematics of the BLR; (3) Map higher luminosity AGN (at redshifts z ~2.3--2.8), probing accretion onto black holes that are 10--100 times more massive than could previously be studied; (4) Measure the temporal evolution of BLR structure. The Project relies on two key elements: (1) We are using the new, queue--scheduled, 9--m ``HET'' telescope to obtain superb data. Previous projects were limited by the noisy and non--uniform data produced by the small telescopes (1--2.5 m) that were used. (2) We will carry out full 2--dimensional (velocity--resolved) echo mapping. Most previous attempts have only been able to produce 1--D maps. Details and initial results from the Project will be presented. This project is supported in part by the NSF.

  20. Quaternion-valued echo state networks.

    Science.gov (United States)

    Xia, Yili; Jahanchahi, Cyrus; Mandic, Danilo P

    2015-04-01

    Quaternion-valued echo state networks (QESNs) are introduced to cater for 3-D and 4-D processes, such as those observed in the context of renewable energy (3-D wind modeling) and human centered computing (3-D inertial body sensors). The introduction of QESNs is made possible by the recent emergence of quaternion nonlinear activation functions with local analytic properties, required by nonlinear gradient descent training algorithms. To make QENSs second-order optimal for the generality of quaternion signals (both circular and noncircular), we employ augmented quaternion statistics to introduce widely linear QESNs. To that end, the standard widely linear model is modified so as to suit the properties of dynamical reservoir, typically realized by recurrent neural networks. This allows for a full exploitation of second-order information in the data, contained both in the covariance and pseudocovariances, and a rigorous account of second-order noncircularity (improperness), and the corresponding power mismatch and coupling between the data components. Simulations in the prediction setting on both benchmark circular and noncircular signals and on noncircular real-world 3-D body motion data support the analysis.

  1. [Extra echo spaces: what do they represent?].

    Science.gov (United States)

    Wada, T

    1984-01-01

    The echocardiographic diagnosis of pericardial effusion is based on the assumption that "echo-free spaces" observed behind the posterior wall of the left ventricle are surrounded by epicardium and pericardial echoes. However, inexplicable extra echo spaces (EES) which may either be echo-dense or echo-free are observed in many asymptomatic patients. These EES often show no changes in their sizes or contours during lengthy follow-up studies. Therefore, we propose a hypothesis that subepicardial fat rather than effusions may be the cause of such EES. According to this hypothesis, a border zone of myocardium and subepicardial fat produces a linear echo which has been misinterpreted as an epicardial echo. Furthermore, a dense, broad band-like echo behind the posterior wall of the left ventricle believed to be a pericardial echo is a fusion echo caused by epicardium, pericardium and pleura. Differentiating EES as due either to subepicardial fat or pericardial effusion is difficult echocardiographically; however, CT scans can differentiate them due to their differing CT values. The echocardiographic diagnosis of pericardial effusion is more easily made among young patients who do not have appreciable subepicardial fat, or massive pericardial effusions causing pendulum-like movements of the heart.

  2. Dung beetle community and functions along a habitat-disturbance gradient in the Amazon: a rapid assessment of ecological functions associated to biodiversity.

    Directory of Open Access Journals (Sweden)

    Rodrigo F Braga

    Full Text Available Although there is increasing interest in the effects of habitat disturbance on community attributes and the potential consequences for ecosystem functioning, objective approaches linking biodiversity loss to functional loss are uncommon. The objectives of this study were to implement simultaneous assessment of community attributes (richness, abundance and biomass, each calculated for total-beetle assemblages as well as small- and large-beetle assemblages and three ecological functions of dung beetles (dung removal, soil perturbation and secondary seed dispersal, to compare the effects of habitat disturbance on both sets of response variables, and their relations. We studied dung beetle community attributes and functions in five land-use systems representing a disturbance gradient in the Brazilian Amazon: primary forest, secondary forest, agroforestry, agriculture and pasture. All response variables were affected negatively by the intensification of habitat disturbance regimes, but community attributes and ecological functions did not follow the same pattern of decline. A hierarchical partitioning analysis showed that, although all community attributes had a significant effect on the three ecological functions (except the abundance of small beetles on all three ecological functions and the biomass of small beetles on secondary dispersal of large seed mimics, species richness and abundance of large beetles were the community attributes with the highest explanatory value. Our results show the importance of measuring ecological function empirically instead of deducing it from community metrics.

  3. Dung beetle community and functions along a habitat-disturbance gradient in the Amazon: a rapid assessment of ecological functions associated to biodiversity.

    Science.gov (United States)

    Braga, Rodrigo F; Korasaki, Vanesca; Andresen, Ellen; Louzada, Julio

    2013-01-01

    Although there is increasing interest in the effects of habitat disturbance on community attributes and the potential consequences for ecosystem functioning, objective approaches linking biodiversity loss to functional loss are uncommon. The objectives of this study were to implement simultaneous assessment of community attributes (richness, abundance and biomass, each calculated for total-beetle assemblages as well as small- and large-beetle assemblages) and three ecological functions of dung beetles (dung removal, soil perturbation and secondary seed dispersal), to compare the effects of habitat disturbance on both sets of response variables, and their relations. We studied dung beetle community attributes and functions in five land-use systems representing a disturbance gradient in the Brazilian Amazon: primary forest, secondary forest, agroforestry, agriculture and pasture. All response variables were affected negatively by the intensification of habitat disturbance regimes, but community attributes and ecological functions did not follow the same pattern of decline. A hierarchical partitioning analysis showed that, although all community attributes had a significant effect on the three ecological functions (except the abundance of small beetles on all three ecological functions and the biomass of small beetles on secondary dispersal of large seed mimics), species richness and abundance of large beetles were the community attributes with the highest explanatory value. Our results show the importance of measuring ecological function empirically instead of deducing it from community metrics.

  4. Beam echoes in the presence of coupling

    Energy Technology Data Exchange (ETDEWEB)

    Gross, Axel [Case Western Reserve U.

    2017-10-03

    Transverse beam echoes could provide a new technique of measuring diusion characteristics orders of magnitude faster than the current methods; however, their interaction with many accelerator parameters is poorly understood. Using a program written in C, we explored the relationship between coupling and echo strength. We found that echoes could be generated in both dimensions, even with a dipole kick in only one dimension. We found that the echo eects are not destroyed even when there is strong coupling, falling o only at extremely high coupling values. We found that at intermediate values of skew quadrupole strength, the decoherence time of the beam is greatly increased, causing a destruction of the echo eects. We found that this is caused by a narrowing of the tune width of the particles. Results from this study will help to provide recommendations to IOTA (Integrable Optics Test Accelerator) for their upcoming echo experiment.

  5. View Angle Tilting Echo Planar Imaging for Distortion Correction

    Science.gov (United States)

    Ahn, Sinyeob; Hu, Xiaoping

    2011-01-01

    Geometric distortion caused by field inhomogeneity along the phase-encode (PE) direction is one of the most prominent artifacts due to a relatively low effective bandwidth along that direction in magnetic resonance echo planar imaging (EPI). This work describes a method for correcting in-plane image distortion along the PE direction using a view angle tilting (VAT) imaging technique in spin-echo EPI (SE-EPI). SE-EPI with VAT (SE-EPI-VAT) utilizes the addition of gradient blips along the slice-select (SS) direction, concurrently applied with the PE gradient blips, producing an additional phase. This phase effectively offsets an unwanted phase accumulation caused by field inhomogeneity, resulting in the removal of image distortion along the PE direction. The proposed method is simple and straightforward both in implementation and application with no scan time penalty. Therefore, it is readily applicable on commercial scanners without having any customized post-processing. The efficacy of the SE-EPI-VAT technique in the correction of image distortion is demonstrated in phantom and in vivo brain imaging. PMID:22213567

  6. How to misuse echo contrast

    Directory of Open Access Journals (Sweden)

    Missios Anna

    2009-01-01

    Full Text Available Abstract Background Primary intracardiac tumours are rare, there are however several entities that can mimic tumours. Contrast echocardiography has been suggested to aid the differentiation of various suspected masses. We present a case where transthoracic echocardiography completely misdiagnosed a left atrial mass, partly due to use of echo contrast. Case presentation An 80 year-old woman was referred for transthoracic echocardiography because of one-month duration of worsening of dyspnoea. Transthoracic echocardiography displayed a large echodense mass in the left atrium. Intravenous injection of contrast (SonoVue, Bracco Inc., It indicated contrast-enhancement of the structure, suggesting tumour. Transesophageal echocardiography revealed, however, a completely normal finding in the left atrium. Subsequent gastroscopy examination showed a hiatal hernia. Conclusion It is noteworthy that the transthoracic echocardiographic exam completely misdiagnosed what seemed like a left atrial mass, which in part was an effect of the use of echo contrast. This example highlights that liberal use of transoesophageal echocardiography is often warranted if optimal display of cardiac structures is desired.

  7. FM echolocating bats shift frequencies to avoid broadcast-echo ambiguity in clutter.

    Science.gov (United States)

    Hiryu, Shizuko; Bates, Mary E; Simmons, James A; Riquimaroux, Hiroshi

    2010-04-13

    Sonar broadcasts are followed by echoes at different delays from objects at different distances. When broadcasts are emitted rapidly in cluttered surroundings, echo streams from successive broadcasts overlap and cause ambiguity in matching echoes to corresponding broadcasts. To identify reactions to ambiguity in clutter, echolocating bats that emit multiple-harmonic FM sounds were trained to fly into a dense, extended array of obstacles (multiple rows of vertically hanging chains) while the sonar sounds the bat emitted were recorded with a miniature radio microphone carried by the bat. Flight paths were reconstructed from thermal-infrared video recordings. Successive rows of chains extended more than 6 m in depth, so each broadcast was followed by a series of echoes from multiple rows of chains that lasted up to 40 ms. Bats emitted sounds in pairs ("strobe groups") at short (20-40 ms) interpulse intervals (IPIs) alternating with longer IPIs (>50 ms). For many short IPIs, the stream of echoes from the first broadcast was still arriving when the second broadcast was emitted. This overlap caused ambiguity about matching echoes with broadcasts. Bats shifted frequencies of the first sound in each strobe group upward and the second sound downward by 3-6 kHz. When overlap and ambiguity ceased, frequency shifts ceased also. Frequency differences were small compared with the total broadcast band, which was 75-80 kHz wide, but the harmonic structure of echoes enhances the differences in spectrograms. Bats could use time-frequency comparisons of echoes with broadcasts to assign echoes to the corresponding broadcasts and thus avoid ambiguity.

  8. Magnetic resonance fingerprinting using echo-planar imaging: Joint quantification of T1 and T2∗ relaxation times.

    Science.gov (United States)

    Rieger, Benedikt; Zimmer, Fabian; Zapp, Jascha; Weingärtner, Sebastian; Schad, Lothar R

    2017-11-01

    To develop an implementation of the magnetic resonance fingerprinting (MRF) paradigm for quantitative imaging using echo-planar imaging (EPI) for simultaneous assessment of T1 and T2∗. The proposed MRF method (MRF-EPI) is based on the acquisition of 160 gradient-spoiled EPI images with rapid, parallel-imaging accelerated, Cartesian readout and a measurement time of 10 s per slice. Contrast variation is induced using an initial inversion pulse, and varying the flip angles, echo times, and repetition times throughout the sequence. Joint quantification of T1 and T2∗ is performed using dictionary matching with integrated B1+ correction. The quantification accuracy of the method was validated in phantom scans and in vivo in 6 healthy subjects. Joint T1 and T2∗ parameter maps acquired with MRF-EPI in phantoms are in good agreement with reference measurements, showing deviations under 5% and 4% for T1 and T2∗, respectively. In vivo baseline images were visually free of artifacts. In vivo relaxation times are in good agreement with gold-standard techniques (deviation T1 : 4 ± 2%, T2∗: 4 ± 5%). The visual quality was comparable to the in vivo gold standard, despite substantially shortened scan times. The proposed MRF-EPI method provides fast and accurate T1 and T2∗ quantification. This approach offers a rapid supplement to the non-Cartesian MRF portfolio, with potentially increased usability and robustness. Magn Reson Med 78:1724-1733, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  9. Study on diffusion anisotropy of cerebral ischemia using diffusion weighted echo-planar MRI

    Energy Technology Data Exchange (ETDEWEB)

    Kajima, Toshio [Hiroshima Univ. (Japan). School of Medicine

    1997-08-01

    Focal cerebral ischemia was produced by occlusion of the intracranial main cerebral artery with a silicone cylinder in Wistar rats. Diffusion-weighted echo-planar images (DW-EPls) using the motion-probing gradient (MPG) method were acquired at 1-3 hours and 24-48 hours after occlusion. Apparent diffusion coefficients (ADCs) were calculated from these images in ischemic lesions and in normal unoccluded regions. Results were as follows. Ischemic lesions could be detected on the DW-EPIs at 1 hour after occlusion. The ADC of water in the brain tissue was smaller than that of free water as a result of restricted diffusion. Anisotropic diffusion that probably can be attributed to the myelin sheath was observed in the normal white matter. In the ischemic lesions, the ADC decreased rapidly within 1-3 hours after occlusion and then decreased gradually after 24-48 hours. In the ischemic white matter, diffusion anisotropy disappeared at 24-48 hours after occlusion. Diffusion-weighted imaging may have applications in the examination of pathophysiological mechanisms in cerebral ischemia by means of evaluation of ADC and diffusion anisotropy. (author)

  10. Gradient waveform pre-emphasis based on the gradient system transfer function.

    Science.gov (United States)

    Stich, Manuel; Wech, Tobias; Slawig, Anne; Ringler, Ralf; Dewdney, Andrew; Greiser, Andreas; Ruyters, Gudrun; Bley, Thorsten A; Köstler, Herbert

    2018-02-25

    The gradient system transfer function (GSTF) has been used to describe the distorted k-space trajectory for image reconstruction. The purpose of this work was to use the GSTF to determine the pre-emphasis for an undistorted gradient output and intended k-space trajectory. The GSTF of the MR system was determined using only standard MR hardware without special equipment such as field probes or a field camera. The GSTF was used for trajectory prediction in image reconstruction and for a gradient waveform pre-emphasis. As test sequences, a gradient-echo sequence with phase-encoding gradient modulation and a gradient-echo sequence with a spiral read-out trajectory were implemented and subsequently applied on a structural phantom and in vivo head measurements. Image artifacts were successfully suppressed by applying the GSTF-based pre-emphasis. Equivalent results are achieved with images acquired using GSTF-based post-correction of the trajectory as a part of image reconstruction. In contrast, the pre-emphasis approach allows reconstruction using the initially intended trajectory. The artifact suppression shown for two sequences demonstrates that the GSTF can serve for a novel pre-emphasis. A pre-emphasis based on the GSTF information can be applied to any arbitrary sequence type. © 2018 International Society for Magnetic Resonance in Medicine.

  11. Photon echo relaxation in molecular mixed crystals

    NARCIS (Netherlands)

    Aartsma, Thijs Jitse

    1978-01-01

    In dit proefschrift worden foton-echo experimenten beschreven, toegepast op molekulaire mengkristallen. De primaire doelstelling van het onderzoek was om met behulp van foton-echo experimenten nieuwe informatie te verkrijgen over de relaxatie processen die optreden in molekulaire mengkristallen bij

  12. MRI of the temporomandibular joint using flip back spin echo technique

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Eun Ha; Kim, Yun Ju; Kim, Chang Soo; Chung, Chun Phil; Kim, Yang Sook [Maryknoll Hospital, Pusan (Korea, Republic of)

    1993-07-15

    The authors introduced flip back spin echo (FBSE) technique for MR imaging of the temporomandibular joint (TMI) instead of conventional spin echo (SE) technique, and evaluated whether FBSE technique in MRI of TMJ is adequate for the diagnosis of the disorders or not. FBSE T1 parasagital images in closed mouth state and sequential opening and closing mouth states using patient's own finger(s) were obtained, and then FBSE T1 paracoronal images in closed mouth state and STAGE (short tip angle gradient echo) parasagital T2WI were followed. All 30 images of the symptomatic TMJs using FBSE technique were excellent in the visualization of articular discs and their displacement, and we could easily diagnosis the internal derangement. FBSE technique was adequate for the diagnosis of internal derangement of the TMJ, and the modified cine display from images using FBSE technique was advantageous in the diagnosis of the disorders by visualization of the dynamic motion of the TMJ.

  13. Rapid measurement of transient velocity evolution using GERVAIS.

    Science.gov (United States)

    Davies, Colin J; Sederman, Andrew J; Pipe, Chris J; McKinley, Gareth H; Gladden, Lynn F; Johns, Mike L

    2010-01-01

    Rapid velocity measurements using GERVAIS (Gradient Echo Rapid Velocity and Acceleration Imaging Sequence), an EPI (Echo Planar Imaging) based technique capable of measuring velocity over an observation time of several milliseconds, are performed on a wide-gap Couette Rheo-NMR cell for the first time. A variable delay time between a control signal to initiate a transition in flow and the start of the measurement sequence is incorporated to allow investigation of the transient evolution of the velocity field following a step change in rotation rate. Both the commencement and the cessation of imposed shear stress are investigated for (i) a shear banding micellar solution of CPyCl (cetylpyridiniumchloride)/NaSal (sodium salicylate) in brine and (ii) a low molecular weight PDMS (polydimethylsiloxane) oil. With respect to the micellar solution, an elastic shear wave is seen to propagate across the cell following the commencement of shear stress whilst an oscillatory 'recoil' is observed following the cessation of shear stress; neither of these phenomena were observed for the PDMS oil which exhibited a purely viscous response as expected for an incompressible Newtonian fluid. This technique has potential applications across a wide range of transient rheological investigations, particularly with respect to optically opaque materials. Copyright 2009 Elsevier Inc. All rights reserved.

  14. Hematite Abundance Map at Echo

    Science.gov (United States)

    2004-01-01

    This image shows the hematite abundance map for a portion of the Meridiani Planum rock outcrop near where the Mars Exploration Rover Opportunity landed. It was acquired by the rover's miniature thermal emission spectrometer instrument from a spot called 'Echo.' Portions of the inner crater wall in this region appear rich in hematite (red). The sharp boundary from hematite-rich to hematite-poor (yellow and green) surfaces corresponds to a change in the surface texture and color. The hematite-rich surfaces have ripple-like forms suggesting wind transported hematite to these surfaces. The bounce marks produced during landing at the base of the slope on the left are low in hematite (blue). The hematite grains that originally covered the surface were pushed below the surface by the lander, exposing a soil that has less hematite.

  15. [Optimization of Three-dimensional Ultrashort Echo Time Magnetic Resonance Imaging at a Low Field].

    Science.gov (United States)

    Huang, Yuli; Du, Yiping

    2015-12-01

    Conventional magnetic resonance (MR) pulse sequences typically have an echo time (TE) of 1 ms or longer, providing an excellent contrast between different soft tissues. However, some short T2 tissues appear dark in conventional MR images because the signal from these tissues has decayed to nearly zero before the center of k-space is acquired. Because of the ability of directly imaging short T2 tissues, ultrashort echo time technique has been widely studied in recent years. An overwhelming majority of the studies were carried out at high fields, while many low- field scanner systems are still used in developing countries. To investigate the effects of the delay between analog-to-digital converter sampling and the readout gradient, the TE of the second echo used to calculate the R2 * map, and the undersampling ratio on the results of three-dimensional (3D) ultrashort echo time imaging at a low field, we implemented a 3D ultrashort echo time sequence on a 0. 35T scanner. Different parameters were used and the reconstructed images and R2 * maps were compared. Images reconstructed with slightly varying delays appeared quite different. Different contrast between short and long T2 tissues were found in R2 * maps calculated with different echoes. The result of undersampling study indicated that excessive undersampling could cause unwanted blurring, making it difficult to better visualize the short T2 tissues in the R2 * map. The results suggested that cautions should be taken in the choice of these parameters in 3D ultrashort echo time imaging. Short T2 tissues can be visualized with appropriate imaging parameters at this low field.

  16. On the factors controlling occurrence of F-region coherent echoes

    Directory of Open Access Journals (Sweden)

    D. W. Danskin

    Full Text Available Several factors are known to control the HF echo occurrence rate, including electron density distribution in the ionosphere (affecting the propagation path of the radar wave, D-region radio wave absorption, and ionospheric irregularity intensity. In this study, we consider 4 days of CUTLASS Finland radar observations over an area where the EISCAT incoherent scatter radar has continuously monitored ionospheric parameters. We illustrate that for the event under consideration, the D-region absorption was not the major factor affecting the echo appearance. We show that the electron density distribution and the radar frequency selection were much more significant factors. The electron density magnitude affects the echo occurrence in two different ways. For small F-region densities, a minimum value of 1 × 1011 m-3 is required to have sufficient radio wave refraction so that the orthogonality (with the magnetic field lines condition is met. For too large densities, radio wave strong "over-refraction" leads to the ionospheric echo disappearance. We estimate that the over-refraction is important for densities greater than 4 × 1011 m-3. We also investigated the backscatter power and the electric field magnitude relationship and found no obvious relationship contrary to the expectation that the gradient-drift plasma instability would lead to stronger irregularity intensity/echo power for larger electric fields.

    Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; auroral ionosphere

  17. Photon Echoes from Retinal Proteins

    Science.gov (United States)

    Johnson, Philip James Maddigan

    This thesis focuses on the ultrafast isomerization reaction of retinal in both rhodopsin and bacteriorhodopsin, examples of sensory and energy transduction proteins that exploit the same photoactive chromophore for two very different functions. In bacteriorhodopsin, retinal isomerizes from an all-trans to 13-cis conformation as the primary event in light- driven proton pumping. In the visual pigment rhodopsin, the retinal chromophore isomerizes from an 11-cis to all-trans geometry as the primary step leading to our sense of vision. This diversity of function for nominally identical systems raises the question as to just how optimized are these proteins to arrive at such drastically different functions? Previous work has employed transient absorption spectroscopy to probe retinal protein photochemistry, but many of the relevant electronic and nuclear dynamics of isomerization are masked by inhomogeneous broadening effects and strong spectral overlap between reactant and photoproduct states. This work exploits the unique properties of two-dimensional photon echo spectroscopy to deconvolve inhomogeneous broadening and spectral overlap effects and fully reveal the dynamics that direct retinal isomerization in proteins. In bacteriorhodopsin, vibrational coupling to the reaction coordinate results in a surface crossing event prior to the conventional conical intersection associated with isomerization to the J intermediate. In rhodopsin, however, a similarly early vibrationally-mediated barrier crossing event is observed, resulting in spectral signals consistent with the known photoproduct state appearing an order of magnitude faster than determined from conventional transient absorption measurements. The competing overlapping spectral signals that obscured the initial dynamics when probed with transient absorption spectroscopy are now clearly resolved with two-dimensional photon echo spectroscopy. These experiments illustrate the critical role of the protein in directing

  18. MEASUREMENT OF TRANSVERSE ECHOES IN RHIC.

    Energy Technology Data Exchange (ETDEWEB)

    FISCHER, W.; SATOGATA, T.; TOMAS. R.

    2005-05-16

    Beam echoes are a very sensitive method to measure diffusion, and longitudinal echo measurements were performed in a number of machines. In RHIC, for the first time, a transverse beam echo was observed after applying a dipole kick followed by a quadrupole .kick. After application of the dipole kick, the dipole moment decohered completely due to lattice nonlinearities. When a quadrupole kick is applied at time {tau} after the dipole kick, the beam re-cohered at time 2{tau} thus showing an echo response. We describe the experimental setup and measurement results. In the measurements the dipole and quadrupole kick amplitudes, amplitude dependent tune shift, and the time between dipole and quadrupole kick were varied. In addition, measurements were taken with gold bunches of different intensities. These should exhibit different transverse diffusion rates due to intra-beam scattering.

  19. Geometric spin echo under zero field

    Science.gov (United States)

    Sekiguchi, Yuhei; Komura, Yusuke; Mishima, Shota; Tanaka, Touta; Niikura, Naeko; Kosaka, Hideo

    2016-05-01

    Spin echo is a fundamental tool for quantum registers and biomedical imaging. It is believed that a strong magnetic field is needed for the spin echo to provide long memory and high resolution, since a degenerate spin cannot be controlled or addressed under a zero magnetic field. While a degenerate spin is never subject to dynamic control, it is still subject to geometric control. Here we show the spin echo of a degenerate spin subsystem, which is geometrically controlled via a mediating state split by the crystal field, in a nitrogen vacancy centre in diamond. The demonstration reveals that the degenerate spin is protected by inherent symmetry breaking called zero-field splitting. The geometric spin echo under zero field provides an ideal way to maintain the coherence without any dynamics, thus opening the way to pseudo-static quantum random access memory and non-invasive biosensors.

  20. Enforcement and Compliance History Online (ECHO) Facilities

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    U.S. Environmental Protection Agency — ECHO provides integrated compliance and enforcement information for about 800,000 regulated facilities nationwide. Its features range from simple to advanced,...

  1. Echoes of Kerr-like wormholes

    Science.gov (United States)

    Bueno, Pablo; Cano, Pablo A.; Goelen, Frederik; Hertog, Thomas; Vercnocke, Bert

    2018-01-01

    Structure at the horizon scale of black holes would give rise to echoes of the gravitational wave signal associated with the postmerger ringdown phase in binary coalescences. We study the waveform of echoes in static and stationary, traversable wormholes in which perturbations are governed by a symmetric effective potential. We argue that echoes are dominated by the wormhole quasinormal frequency nearest to the fundamental black hole frequency that controls the primary signal. We put forward an accurate method to construct the echoes' waveform(s) from the primary signal and the quasinormal frequencies of the wormhole, which we characterize. We illustrate this in the static Damour-Solodukhin wormhole and in a new, rotating generalization that approximates a Kerr black hole outside the throat. Rotation gives rise to a potential with an intermediate plateau region that breaks the degeneracy of the quasinormal frequencies. Rotation also leads to late-time instabilities that, however, fade away for small angular momentum.

  2. Time Delay Estimation Algoritms for Echo Cancellation

    Directory of Open Access Journals (Sweden)

    Boris Simak

    2011-01-01

    Full Text Available The following case study describes how to eliminate echo in a VoIP network using delay estimation algorithms. It is known that echo with long transmission delays becomes more noticeable to users. Thus, time delay estimation, as a part of echo cancellation, is an important topic during transmission of voice signals over packetswitching telecommunication systems. An echo delay problem associated with IP-based transport networks is discussed in the following text. The paper introduces the comparative study of time delay estimation algorithm, used for estimation of the true time delay between two speech signals. Experimental results of MATLab simulations that describe the performance of several methods based on cross-correlation, normalized crosscorrelation and generalized cross-correlation are also presented in the paper.

  3. TRISP: Three axes spin echo spectrometer

    Directory of Open Access Journals (Sweden)

    Thomas Keller

    2015-12-01

    Full Text Available TRISP, operated by the Max-Planck-Institute for Solid State Research, is a high-resolution neutron spectrometer combining the three axes and neutron resonance spin echo (NRSE techniques.

  4. Water Dashboard Help | ECHO | US EPA

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    The dashboards found on the Enforcement and Compliance History Online (ECHO) website are specialized to track both facility and agency performance as they relate to compliance with and enforcement of environmental standards under the Clean Water Act (CWA).

  5. Radar cross sections for mesospheric echoes at Jicamarca

    Directory of Open Access Journals (Sweden)

    G. A. Lehmacher

    2009-07-01

    Full Text Available Radar cross sections (RCS of mesospheric layers at 50 MHz observed at Jicamarca, Peru, range from 10−18 to 10−16 m−1, three orders of magnitudes smaller than cross sections reported for polar mesospheric winter echoes during solar proton events and six orders of magnitude smaller than polar mesospheric summer echoes. Large RCS are found in thick layers around 70 km that also show wide radar spectra, which is interpreted as turbulent broadening. For typical atmospheric and ionospheric conditions, volume scattering RCS for stationary, homogeneous, isotropic turbulence at 3 m are also in the range 10−18 to 10−16 m−1, in reasonable agreement with measurements. Moreover, theory predicts maximum cross sections around 70 km, also in agreement with observations. Theoretical values are still a matter of order-of-magnitude estimation, since the Bragg scale of 3 m is near or inside the viscous subrange, where the form of the turbulence spectrum is not well known. In addition, steep electron density gradients can increase cross-sections significantly. For thin layers with large RCS and narrow spectra, isotropic turbulence theory fails and scattering or reflection from anisotropic irregularities may gain relevance.

  6. BLIPPED (BLIpped Pure Phase EncoDing) high resolution MRI with low amplitude gradients

    Science.gov (United States)

    Xiao, Dan; Balcom, Bruce J.

    2017-12-01

    MRI image resolution is proportional to the maximum k-space value, i.e. the temporal integral of the magnetic field gradient. High resolution imaging usually requires high gradient amplitudes and/or long spatial encoding times. Special gradient hardware is often required for high amplitudes and fast switching. We propose a high resolution imaging sequence that employs low amplitude gradients. This method was inspired by the previously proposed PEPI (π Echo Planar Imaging) sequence, which replaced EPI gradient reversals with multiple RF refocusing pulses. It has been shown that when the refocusing RF pulse is of high quality, i.e. sufficiently close to 180°, the magnetization phase introduced by the spatial encoding magnetic field gradient can be preserved and transferred to the following echo signal without phase rewinding. This phase encoding scheme requires blipped gradients that are identical for each echo, with low and constant amplitude, providing opportunities for high resolution imaging. We now extend the sequence to 3D pure phase encoding with low amplitude gradients. The method is compared with the Hybrid-SESPI (Spin Echo Single Point Imaging) technique to demonstrate the advantages in terms of low gradient duty cycle, compensation of concomitant magnetic field effects and minimal echo spacing, which lead to superior image quality and high resolution. The 3D imaging method was then applied with a parallel plate resonator RF probe, achieving a nominal spatial resolution of 17 μm in one dimension in the 3D image, requiring a maximum gradient amplitude of only 5.8 Gauss/cm.

  7. Optimal Echo Spacing for Multi-Echo Imaging measurements of Bi-exponential T2 relaxation

    OpenAIRE

    Dula, Adrienne N.; Gochberg, Daniel F.; Does, Mark D.

    2008-01-01

    Calculations, analytical solutions, and simulations were used to investigate the trade-off of echo spacing and receiver bandwidth for the characterization of bi-exponential transverse relaxation using a multi-echo imaging pulse sequence. The Cramer-Rao lower bound of the standard deviation of the four parameters of a two-pool model were computed for a wide range of component T2 values and echo spacing. The results demonstrate that optimal echo spacing (TEopt) is not generally the minimal avai...

  8. Reconstruction strategy for echo planar spectroscopy and its application to partially undersampled imaging

    DEFF Research Database (Denmark)

    Hanson, L G; Schaumburg, K; Paulson, O B

    2000-01-01

    The most commonly encountered form of echo planar spectroscopy involves oscillating gradients in one spatial dimension during readout. Data are consequently not sampled on a Cartesian grid. A fast gridding algorithm applicable to this particular situation is presented. The method is optimal, i...... or fewer interleaves per acquisition. The method is of particular interest when large bandwidths are needed (e.g., for high field scanning) and for scanners with limited gradient performance. The unavoidable artifacts resulting from undersampling are demonstrated to be acceptable for spectroscopy with long...

  9. Search Results Help - Air | ECHO | US EPA

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    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  10. Water Pollution Search | ECHO | US EPA

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    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  11. Detailed Facility Report | ECHO | US EPA

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    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

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    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

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  15. Mobile Bay.pdf | ECHO | US EPA

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    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

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    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  17. Technical Users Background Document | ECHO | US EPA

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    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  18. Exoplanetary Characterisation Observatory (EChO)

    Science.gov (United States)

    Waldmann, Ingo; Tinetti, Giovanna

    2013-04-01

    The science of extrasolar planets is one of the most rapidly changing areas of astrophysics and since 1995 the number of planets known has increased by almost two orders of magnitude. A combination of ground-based surveys and dedicated space missions has resulted in 800-plus planets being detected, and over 2000 that await confirmation. NASA's Kepler mission has opened up the possibility of discovering Earth-like planets in the habitable zone around some of the 100,000 stars it is surveying during its 3 to 4-year lifetime. The new ESA's Gaia mission is expected to discover thousands of new planets around stars within 200 parsecs of the Sun. The key challenge now is moving on from discovery, important though that remains, to characterisation: what are these planets actually like, and why are they as they are? The Exoplanet Characterisation Observatory (EChO) is a space mission dedicated to undertaking spectroscopy of transiting exoplanets over the widest range possible and is currently being studied by ESA in the context of a medium class mission within the Cosmic Vision programme for launch post 2020. The mission is based around a highly stable space platform with a 1.2 m class telescope at L2, hosting a suit of spectrographs providing continuous spectral coverage from 0.5 to 16 microns. Such a broad and simultaneous wavelength coverage allows the unique insight into the atmospheric make up of these foreign worlds and allows us to study their planetary and atmospheric compositions and evolutions.

  19. Diferenciação entre cisto simples e hemangioma hepático utilizando seqüência de ressonância magnética ponderada em T2 com técnica gradiente-eco (B-FFE Differentiation between simple cyst and hepatic hemangioma utilizing T2-weighted magnetic resonance imaging with gradient-echo (b-FFE technique

    Directory of Open Access Journals (Sweden)

    Carolina Valente Burim

    2008-12-01

    Full Text Available OBJETIVO: Estabelecer o valor das seqüências ponderadas em T2 para diferenciar cistos simples de hemangiomas hepáticos. MATERIAIS E MÉTODOS: Estudo prospectivo, observacional, transversal e duplo-cego em 52 pacientes com 91 lesões hepáticas (34 cistos simples e 57 hemangiomas submetidos a ressonância magnética de abdome. A análise conjunta de todas as seqüências realizadas foi considerada o padrão-ouro. Dois observadores independentes avaliaram, subjetivamente, as seqüências TSE com TE longo e B-FFE, procurando diferenciar cistos de hemangiomas. Foram calculadas a eficácia das seqüências e a concordância interobservador e intra-observador por meio do teste kappa (κ (p OBJECTIVE: To establish the role of MRI T2-weighted sequences in the differentiation between simple cysts and hepatic hemangiomas. MATERIALS AND METHODS: A double-blinded, prospective, observational, cross-sectional study evaluated 52 patients with 91 hepatic lesions (34 simple cysts and 57 hemangiomas submitted to abdominal magnetic resonance imaging. The combined analysis of all sequences was considered as the golden-standard. TSE sequences with long echo trains and b-FFE sequences were subjectively analyzed by two independent observers for differentiating cysts from hemangiomas. The kappa test (κ was utilized in the analysis of the methods accuracy and inter- and intra-observer agreement (p < 0.05*. RESULTS: Cysts and hemangiomas dimensions ranged respectively between 0.5 and 6.5 cm (mean = 1.89 cm, and 0.8 and 11 cm (mean = 2.62 cm. The analysis of the sequences with long-TE and the golden-standard demonstrated a non-statistically significant agreement (κ: 0.00-0.10. The agreement between the evaluation of the b-FFE sequence and the golden-standard ranged from substantial (κ: 0.62-0.71 to almost perfect (κ: 0.86 for both observers. The inter- and intra-observer agreement for the b-FFE sequence ranged from substantial (κ: 0.62-0.70 to almost perfect (κ

  20. Echoes from a Dying Star

    Science.gov (United States)

    Kohler, Susanna

    2017-06-01

    When a passing star is torn apart by a supermassive black hole, it emits a flare of X-ray, ultraviolet, and optical light. What can we learn from the infrared echo of a violent disruption like this one?Stellar DestructionOptical (black triangles) and infrared (blue circles and red squares) observations of F010042237. Day 0 marks the day the optical emission peaked. The infrared emission rises steadily through the end of the data. [Dou et al. 2017]Tidal disruption events occur when a star passes within the tidal radius of a supermassive black hole. After tidal forces pull the star apart, much of the stellar matter falls onto the black hole, radiating briefly in X-ray, ultraviolet and optical as it accretes. This signature rise and gradual fall of emission has allowed us to detect dozens of tidal disruption events thus far.One of the recently discovered candidate events is a little puzzling. Not only does the candidate in ultraluminous infrared galaxy F010042237 have an unusual host most disruptions occur in galaxies that are no longer star-forming, in contrast to this one but its optical light curve also shows an unusually long decay time.Now mid-infrared observations of this event have beenpresented by a team of scientists led by Liming Dou (Guangzhou University and Department of Education, Guangdong Province, China), revealing why this disruption is behaving unusually.Schematic of a convex dusty ring (red bows) that absorbs UV photons and re-emits in the infrared. It simultaneously scatters UV and optical photons into our line of sight. The dashed lines illustrate the delays at lags of 60 days, 1, 2, 3, 4, and 5 years. [Adapted from Dou et al. 2017]A Dusty Solution?The optical flare from F010042237s nucleus peaked in 2010, so Dou and collaborators obtained archival mid-infrared data from the WISE and NEOWISE missions from 2010 to 2016. The data show that the galaxy is quiescent in mid-infrared in 2010 but in data from three years later, the infrared emission has

  1. Ringing effects eliminated spin echo in solids

    Science.gov (United States)

    Ma, Chao; Li, Peng; Chen, Qun; Zhang, Shanmin

    2013-08-01

    Two types of ringing effects eliminated spin echo sequences have been introduced. To achieve the task, two additional 90° pulses with proper phase cycles are placed at the beginning of the pulse sequences. The spin echo time is calculated with the perturbation method to the first order, i.e. taking into account only the dipolar secular term. The non-secular term causes an imaginary part of the FID, leading to an unsymmetrical NMR spectrum. This effect, according to a symmetry of NMR sequences under phase inversion, can be compensated by inverting all the x and -x or y and -y phases. The properties of the symmetry are derived based on the theory of density matrix. In addition, the non-secular term also results in a small drop (several per cent) of the echo amplitude, but it nearly does not affect the echo time. With these pulse sequences we are able to get a spectrum with an echo delay only 1.1 μs without distortion using a Bruker AVANCE III NMR instrument.

  2. Iterative Decomposition of Water and Fat with Echo Asymmetric and Least—Squares Estimation (IDEAL (Reeder et al. 2005 Automated Spine Survey Iterative Scan Technique (ASSIST (Weiss et al. 2006

    Directory of Open Access Journals (Sweden)

    Kenneth L. Weiss

    2008-01-01

    Full Text Available Background and Purpose: Multi-parametric MRI of the entire spine is technologist-dependent, time consuming, and often limited by inhomogeneous fat suppression. We tested a technique to provide rapid automated total spine MRI screening with improved tissue contrast through optimized fat-water separation.Methods: The entire spine was auto-imaged in two contiguous 35 cm field of view (FOV sagittal stations, utilizing out-of-phase fast gradient echo (FGRE and T1 and/or T2 weighted fast spin echo (FSE IDEAL (Iterative Decomposition of Water and Fat with Echo Asymmetric and Least-squares Estimation sequences. 18 subjects were studied, one twice at 3.0T (pre and post contrast and one at both 1.5 T and 3.0T for a total of 20 spine examinations (8 at 1.5 T and 12 at 3.0T. Images were independently evaluated by two neuroradiologists and run through Automated Spine Survey Iterative Scan Technique (ASSIST analysis software for automated vertebral numbering.Results: In all 20 total spine studies, neuroradiologist and computer ASSIST labeling were concordant. In all cases, IDEAL provided uniform fat and water separation throughout the entire 70 cm FOV imaged. Two subjects demonstrated breast metastases and one had a large presumptive schwannoma. 14 subjects demonstrated degenerative disc disease with associated Modic Type I or II changes at one or more levels. FGRE ASSIST afforded subminute submillimeter in-plane resolution of the entire spine with high contrast between discs and vertebrae at both 1.5 and 3.0T. Marrow signal abnormalities could be particularly well characterized with IDEAL derived images and parametric maps.Conclusion: IDEAL ASSIST is a promising MRI technique affording a rapid automated high resolution, high contrast survey of the entire spine with optimized tissue characterization.

  3. Ultrafast 3D spin-echo acquisition improves Gadolinium-enhanced MRI signal contrast enhancement

    Science.gov (United States)

    Han, S. H.; Cho, F. H.; Song, Y. K.; Paulsen, J.; Song, Y. Q.; Kim, Y. R.; Kim, J. K.; Cho, G.; Cho, H.

    2014-01-01

    Long scan times of 3D volumetric MR acquisitions usually necessitate ultrafast in vivo gradient-echo acquisitions, which are intrinsically susceptible to magnetic field inhomogeneities. This is especially problematic for contrast-enhanced (CE)-MRI applications, where non-negligible T2* effect of contrast agent deteriorates the positive signal contrast and limits the available range of MR acquisition parameters and injection doses. To overcome these shortcomings without degrading temporal resolution, ultrafast spin-echo acquisitions were implemented. Specifically, a multiplicative acceleration factor from multiple spin echoes (×32) and compressed sensing (CS) sampling (×8) allowed highly-accelerated 3D Multiple-Modulation-Multiple-Echo (MMME) acquisition. At the same time, the CE-MRI of kidney with Gd-DOTA showed significantly improved signal enhancement for CS-MMME acquisitions (×7) over that of corresponding FLASH acquisitions (×2). Increased positive contrast enhancement and highly accelerated acquisition of extended volume with reduced RF irradiations will be beneficial for oncological and nephrological applications, in which the accurate in vivo 3D quantification of contrast agent concentration is necessary with high temporal resolution. PMID:24863102

  4. Theoretical model of the single spin-echo relaxation time for spherical magnetic perturbers.

    Science.gov (United States)

    Kurz, Felix T; Kampf, Thomas; Heiland, Sabine; Bendszus, Martin; Schlemmer, Heinz-Peter; Ziener, Christian H

    2014-05-01

    Magnetically labeled cells and tissue iron deposits provide qualitative means to detect and monitor cardiovascular and cerebrovascular diseases with magnetic resonance imaging. However, to quantitatively examine the extent of pathological micromorphological changes, detailed knowledge about microstructural parameters and relaxation times is required. The complex geometrical arrangement of spherical magnetic perturbers is considered in an external magnetic field. They create a magnetic dipole field, whose corresponding spin-echo formation is investigated by analyzing the diffusion process in the dephasing volume. Quantitative predictions of the present analysis are compared with experimental data and empirical models. Single spin-echo relaxation times can be characterized by morphological parameters such as magnetic particle concentration and size as well as tissue diffusion coefficient and local magnetic susceptibility properties. As expected, no formation of a static dephasing plateau is observed in contrast to the gradient-echo relaxation time. Instead, the relaxation rate drops for large particle sizes and exhibits a prominent maximal value at intermediate sizes. These findings agree well with experimental data and previous theoretical results. Obtained results for the single spin-echo relaxation time allow to accurately quantify pathological processes in neurodegenerative disease and migration dynamics of magnetically labeled cells with the help of magnetic resonance imaging. Copyright © 2014 Wiley Periodicals, Inc.

  5. How can dolphins recognize fish according to their echoes? A statistical analysis of fish echoes.

    Directory of Open Access Journals (Sweden)

    Yossi Yovel

    Full Text Available Echo-based object classification is a fundamental task of animals that use a biosonar system. Dolphins and porpoises should be able to rely on echoes to discriminate a predator from a prey or to select a desired prey from an undesired object. Many studies have shown that dolphins and porpoises can discriminate between objects according to their echoes. All of these studies however, used unnatural objects that can be easily characterized in human terminologies (e.g., metallic spheres, disks, cylinders. In this work, we collected real fish echoes from many angles of acquisition using a sonar system that mimics the emission properties of dolphins and porpoises. We then tested two alternative statistical approaches in classifying these echoes. Our results suggest that fish species can be classified according to echoes returning from porpoise- and dolphin-like signals. These results suggest how dolphins and porpoises can classify fish based on their echoes and provide some insight as to which features might enable the classification.

  6. Quantitative comparison of cortical surface reconstructions from MP2RAGE and multi-echo MPRAGE data at 3 and 7 T.

    Science.gov (United States)

    Fujimoto, Kyoko; Polimeni, Jonathan R; van der Kouwe, André J W; Reuter, Martin; Kober, Tobias; Benner, Thomas; Fischl, Bruce; Wald, Lawrence L

    2014-04-15

    The Magnetization-Prepared 2 Rapid Acquisition Gradient Echo (MP2RAGE) method achieves spatially uniform contrast across the entire brain between gray matter and surrounding white matter tissue and cerebrospinal fluid by rapidly acquiring data at two points during an inversion recovery, and then combining the two volumes so as to cancel out sources of intensity and contrast bias, making it useful for neuroimaging studies at ultrahigh field strengths (≥7T). To quantify the effectiveness of the MP2RAGE method for quantitative morphometric neuroimaging, we performed tissue segmentation and cerebral cortical surface reconstruction of the MP2RAGE data and compared the results with those generated from conventional multi-echo MPRAGE (MEMPRAGE) data across a group of healthy subjects. To do so, we developed a preprocessing scheme for the MP2RAGE image data to allow for automatic cortical segmentation and surface reconstruction using FreeSurfer and analysis methods to compare the positioning of the surface meshes. Using image volumes with 1mm isotropic voxels we found a scan-rescan reproducibility of cortical thickness estimates to be 0.15 mm (or 6%) for the MEMPRAGE data and a slightly lower reproducibility of 0.19 mm (or 8%) for the MP2RAGE data. We also found that the thickness estimates were systematically smaller in the MP2RAGE data, and that both the interior and exterior cortical boundaries estimated from the MP2RAGE data were consistently positioned within the corresponding boundaries estimated from the MEMPRAGE data. Therefore several measureable differences exist in the appearance of cortical gray matter and its effect on automatic segmentation methods that must be considered when choosing an acquisition or segmentation method for studies requiring cortical surface reconstructions. We propose potential extensions to the MP2RAGE method that may help to reduce or eliminate these discrepancies. Copyright © 2013 Elsevier Inc. All rights reserved.

  7. Search Results Help - Water | ECHO | US EPA

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    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available. Search Results Help explains how to navigate the search results page and describes the data presented.

  8. Characterization of adrenal lesions using chemical shift MRI: comparison between 1.5 Tesla and two echo time pair selection at 3.0 Tesla MRI.

    Science.gov (United States)

    Nakamura, Shinichi; Namimoto, Tomohiro; Morita, Kosuke; Utsunomiya, Daisuke; Oda, Seitaro; Nakaura, Takeshi; Hirai, Toshinori; Yamashita, Yasuyuki

    2012-01-01

    To compare chemical shift MRI obtained at 1.5 Tesla (T) and two pairs of echo time (TE) in-phase and opposed-phase 3.0T MRI to assess their usefulness for the differentiation between adrenal adenomas and non-adenomas. We evaluated 91 adrenal masses (75 adenomas, 16 non-adenomas) in 85 patients. The MR imaging parameters were: T1-dual-gradient-echo(GRE) [echo times (TEs) = 1.1/2.3 ms (first-echo-pair) or 3.5/4.6 ms (second-echo-pair)] at 3.0T, and T1-dual-GRE (TEs = 2.4/4.8 ms) at 1.5T. Scans were quantitatively assessed for the signal intensity (SI) index, calculated as [(SIin-phase-SIopposed-phase)/(SIin-phase)] × 100(%). To test for differences between adenomas and non-adenomas, we performed quantitative analysis and analysis of variance. For all images, the SI index differed significantly between adenomas and non-adenomas. The sensitivity /specificity of SI index at the first-echo-pair of 3.0T was 100%/ 100%, that of 95.6%/ 100% at the second-echo-pair of 3.0T, and 91.7%/ 88.9% at 1.5T, respectively. At intra-individual comparisons, the SI indices obtained with the second-echo-pair at 3.0T were significantly lower than on the first-echo-pair at 3.0T and 1.5T. Chemical shift MRI at 3.0T provides more accurate differentiation between adenomas and non-adenomas than at 1.5T. The SI index of the first-echo-pair at 3.0T is the most reliable evaluation method for differentiating adrenal adenomas from non-adenomas. Copyright © 2011 Wiley Periodicals, Inc.

  9. Quantification of early fatty infiltration of the rotator cuff muscles: comparison of multi-echo Dixon with single-voxel MR spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Agten, Christoph A.; Rosskopf, Andrea B.; Pfirrmann, Christian W.A. [Balgrist University Hospital, Radiology, Zurich (Switzerland); University of Zurich, Faculty of Medicine, Zurich (Switzerland); Gerber, Christian [Balgrist University Hospital, Orthopaedic Surgery, Zurich (Switzerland); University of Zurich, Faculty of Medicine, Zurich (Switzerland)

    2016-10-15

    To evaluate quantification of early fatty infiltration in supraspinatus muscles with magnetic resonance (MR) imaging using a T2*-corrected multi-echo 3D-gradient-echo Dixon-based sequence (multi-echo Dixon) and compare it to proton-MR-spectroscopy. Sixty subjects (mean age 46 years, 41 men) with good supraspinatus muscle quality on 1.5 T MR imaging were included. Fat percentage (FP) in the supraspinatus muscle was quantified using a multi-echo Dixon compared to single-voxel MR spectroscopy as reference standard. In 18 subjects the multi-echo Dixon was repeated to assess test-retest reliability. Measurements based on multi-echo Dixon were performed by two independent readers by placing regions-of-interest (ROIs) in the supraspinatus muscle corresponding to the MR-spectroscopy voxel. Intraclass and concordance correlation coefficients (ICC/CCC) were used for statistical analysis. Test-retest reliability was substantial for reader 1 (ICC = 0.757) and almost perfect for reader 2 (ICC = 0.873). Inter-reader reliability for multi-echo Dixon was almost perfect (ICC = 0.893, P <.0005). Mean FP in all 60 subjects with multi-echo Dixon was 3.5 ± 1.6 for reader 1, 3.7 ± 1.8 for reader 2, and 2.8 ± 1.4 with MR spectroscopy. Correlation between multi-echo Dixon and MR spectroscopy was moderate (CCC = 0.641). The multi-echo Dixon sequence is a reliable method and comparable to MR-spectroscopy for quantification of low levels of fatty infiltration in the supraspinatus muscle. (orig.)

  10. The Educational Gradient in Health in China

    Science.gov (United States)

    Chen, Qiulin; Eggleston, Karen; Zhang, Wei; Zhao, Jiaying; Zhou, Sen

    2017-01-01

    It has been well established that better educated individuals enjoy better health and longevity. In theory, the educational gradients in health could be flattening if diminishing returns to improved average education levels and the influence of earlier population health interventions outweigh the gradient-steepening effects of new medical and health technologies. This paper documents how the gradients are evolving in China, a rapidly developing country, about which little is known on this topic. Based on recent mortality data and nationally representative health surveys, we find large and, in some cases, steepening educational gradients. We also find that the gradients vary by cohort, gender and region. Further, we find that the gradients can only partially be accounted for by economic factors. These patterns highlight the double disadvantage of those with low education, and suggest the importance of policy interventions that foster both aspects of human capital for them. PMID:29056815

  11. Dictionary for Sparse Representation of Chirp Echo in Broadband Radar

    OpenAIRE

    Gao, Lei

    2010-01-01

    A new dictionary for sparse representation of chirp echo in broadband radar is put forward in this paper. Different with chirplet decomposition which decomposes echo in time-frequency plane, the dictionary transforms the sparsity of target observed by radar in distance range to the sparsity in frequency domain by stretch processing and the sparse representation of echo is realized. Using strict deduction with mathematics, the sparsity of echo in dictionary is proved and the dictionary is orth...

  12. Calculations on resonance spin-echo coils

    CERN Document Server

    Prokudaylo, S B; Keller, T; Bleuel, M; Axtner, M; Selvachev, A

    2002-01-01

    The performance of the coils used for a resonance spin-echo spectrometer is simulated to obtain the optimum parameters. The possibility to use a round wire instead of a flat band for coil production is explored. The parameters of the static bootstrap coils were varied in a 2D approach and a better configuration than one actually uses was found. (orig.)

  13. Pesticide Dashboard Help | ECHO | US EPA

    Science.gov (United States)

    The dashboards found on the Enforcement and Compliance History Online (ECHO) website are specialized to track both facility and agency performance as they relate to compliance with and enforcement of environmental standards under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA).

  14. State Comparative Maps Help | ECHO | US EPA

    Science.gov (United States)

    Comparative Maps in ECHO focus on environmental compliance and enforcement trends at a state and national level. Comparative maps provide a quick cross-country look at key environmental compliance and enforcement indicators. The maps link to dashboards that provide details by state/territory.

  15. Looking for Dust-Scattering Light Echoes

    Science.gov (United States)

    Mills, Brianna; Heinz, Sebastian; Corrales, Lia

    2018-01-01

    Galactic X-ray transient sources such as neutron stars or black holes sometimes undergo an outburst in X-rays. Ring structures have been observed around three such sources, produced by the X-ray photons being scattered by interstellar dust grains along our line of sight. These dust-scattering light echoes have proven to be a useful tool for measuring and constraining Galactic distances, mapping the dust structure of the Milky Way, and determining the dust composition in the clouds producing the echo. Detectable light echoes require a sufficient quantity of dust along our line of sight, as well as bright, short-lived Galactic X-ray flares. Using data from the Monitor of All-Sky X-ray Image (MAXI) on-board the International Space Station, we ran a peak finding algorithm in Python to look for characteristic flare events. Each flare was characterized by its fluence, the integrated flux of the flare over time. We measured the distribution of flare fluences to show how many observably bright flares were recorded by MAXI. This work provides a parent set for dust echo searches in archival X-ray data and will inform observing strategies with current and future X-ray missions such as Athena and Lynx.

  16. Asymmetric radar echo patterns from insects

    Science.gov (United States)

    Radar echoes from insects, birds, and bats in the atmosphere exhibit both symmetry and asymmetry in polarimetric patterns. Symmetry refers to similar magnitudes of polarimetric variables at opposite azimuths, and asymmetry relegates to differences in these magnitudes. Asymmetry can be due to diffe...

  17. Evaluating and overcoming the impact of second echo in Brillouin echoes distributed sensing.

    Science.gov (United States)

    Yang, Zhisheng; Hong, Xiaobin; Lin, Wenqiao; Wu, Jian

    2016-01-25

    The detrimental impact of the second echo phenomenon that commonly exists in Brillouin echoes distributed sensing (BEDS) methods is thoroughly investigated by further developing the analytical model of the Brillouin gain on the probe wave. The presented analysis not only points out that the most severe impact imposed by the second echo occurs when the length of the heated/stressed fiber section is exactly equal to the spatial resolution, but also quantifies the systematic error on the estimated Brillouin frequency shift, the maximum of which could reach up to 8.5 MHz. A novel parabolic-amplitude four-section pulse is proposed, which can compensate the impact of the second echo optically, without using extra measurement time and post-processing. The key parameters of the proposed pulse are optimized by combining an upgraded mathematical model and the iterative algorithm. The experimental results show a good agreement with the analysis about the behavior of the second echo, and demonstrate that the proposed technique is capable of providing sub-meter spatial resolution and the natural linewidth of Brillouin gain spectrum simultaneously, while completely eliminating the impact of the second echo.

  18. Diffusion weighted imaging with circularly polarized oscillating gradients

    DEFF Research Database (Denmark)

    Lundell, Henrik; Sønderby, Casper Kaae; Dyrby, Tim B

    2015-01-01

    PURPOSE: The short diffusion time regime provides an interesting probe for tissue microstructure and can be investigated with oscillating gradient spin echo (OGSE) experiments. Several studies report new contrasts in preclinical settings and the first in vivo human experiments have recently been...... and CP-OGSE. RESULTS: Simulations and experiments show that CP-OGSE provides the same microstructural information as OGSE but provides more robust parameter estimates with limited gradient strength. CONCLUSIONS: CP-OGSE can be an important contribution for making OGSE imaging more effective in clinical...

  19. Robust MR assessment of cerebral blood volume and mean vessel size using SPION-enhanced ultrashort echo acquisition.

    Science.gov (United States)

    Han, S H; Cho, J H; Jung, H S; Suh, J Y; Kim, J K; Kim, Y R; Cho, G; Cho, H

    2015-05-15

    Intravascular superparamagnetic iron oxide nanoparticles (SPION)-enhanced MR transverse relaxation rates (∆R2(⁎) and ∆R2) are widely used to investigate in vivo vascular parameters, such as the cerebral blood volume (CBV), microvascular volume (MVV), and mean vessel size index (mVSI, ∆R2(⁎)/∆R2). Although highly efficient, regional comparison of vascular parameters acquired using gradient-echo based ∆R2(⁎) is hampered by its high sensitivity to magnetic field perturbations arising from air-tissue interfaces and large vessels. To minimize such demerits, we took advantage of the dual contrast property of SPION and both theoretically and experimentally verified the direct benefit of replacing gradient-echo based ∆R2(⁎) measurement with ultra-short echo time (UTE)-based ∆R1 contrast to generate the robust CBV and mVSI maps. The UTE acquisition minimized the local measurement errors from susceptibility perturbations and enabled dose-independent CBV measurement using the vessel/tissue ∆R1 ratio, while independent spin-echo acquisition enabled simultaneous ∆R2 measurement and mVSI calculation of the cortex, cerebellum, and olfactory bulb, which are animal brain regions typified by significant susceptibility-associated measurement errors. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. Sensitive J-coupled metabolite mapping using Sel-MQC with selective multi-spin-echo readout.

    Science.gov (United States)

    Melkus, Gerd; Mörchel, Philipp; Behr, Volker C; Kotas, Markus; Flentje, Michael; Jakob, Peter M

    2009-10-01

    The selective multiple quantum coherence technique is combined with a read gradient to accelerate the measurement of a specific scalar-coupled metabolite. The sensitivities of the localization using pure phase encoding and localization with the read gradient are compared in experiments at high magnetic field strength (17.6 T). Multiple spin-echoes of the selective multiple quantum coherence edited metabolite are acquired using frequency-selective refocusing of the specified molecule group. The frequency-selective refocusing does not affect the J-modulation of a coupled spin system, and the echo time is not limited to a multiple of 1/J to acquire pure in-phase or antiphase signal. The multiple echoes can be used to accelerate the metabolite imaging experiment or to measure the apparent transverse relaxation T(2). A simple phase-shifting scheme is presented, which enables the suppression of editing artifacts resulting from the multiple spin-echoes of the water resonance. The experiments are carried out on phantoms, in which lactate and polyunsaturated fatty acids are edited, and in vivo on tumors, in which lactate content and T(2) are imaged. The method is of particular interest when a fast and sensitive selective multiple quantum coherence editing is necessary, e.g., for spatial three dimensional experiments. (c) 2009 Wiley-Liss, Inc.

  1. The relationship between fireballs and HRO Long Echos

    Science.gov (United States)

    Yanagida, E.; Amikura, S.

    Ham-band Radio Observation (HRO) is one of the major methods used to observe meteor activity in Japan. We receive certain types of meteor echoes. One of the types is the long-lasting echo called a ``Long Echo''. We have the impression that Long Echoes correspond to fireballs. The present research found this relation and tried to identify fireball data from visual observations with Long Echo data of the 2002 Leonids, Geminids, and Quadrantids. From these data, we found that the identification percentage tended to be higher for fainter magnitudes, but that the percentage is small, the percentages of each meteor stream being less than 30 %. From these results, this research found that we could not simply say that brighter meteors were received as Long Echoes. It depends on the geocentric velocity of the meteor stream, with a possibility that Long Echoes correspond to darker as well as brighter fireballs.

  2. The EChO science case

    DEFF Research Database (Denmark)

    Tinetti, Giovanna; Drossart, Pierre; Eccleston, Paul

    2015-01-01

    in the Solar System. Observations to date have shown that our Solar System is certainly not representative of the general population of planets in our Milky Way. The key science questions that urgently need addressing are therefore: What are exoplanets made of? Why are planets as they are? How do planetary....... The mission can target super-Earths, Neptune-like, and Jupiter-like planets, in the very hot to temperate zones (planet temperatures of 300–3000 K) of F to M-type host stars. The EChO core science would be delivered by a three-tier survey. The EChO Chemical Census: This is a broad survey of a few...

  3. Workshop on neutron spin-echo

    Energy Technology Data Exchange (ETDEWEB)

    Aynajian, P.; Habicht, K.; Keller, Th.; Keimer, B.; Mezei, F.; Monkenbusch, M.; Allgaier, J.; Richter, D.; Fetters, L.J.; Muller, K.; Kreiling, S.; Dehnicke, K.; Greiner, A.; Ehlers, G.; Arbe, A.; Colmenero, J.; Richter, D.; Farago, B.; Monkenbusch, M.; Ohl, M.; Butzek, M.; Kozielewski, T.; Monkenbusch, M.; Richter, D.; Pappas, C.; Hillier, A.; Manuel, P.; Cywinski, R.; Bentley, P.; Alba, M.; Mezei, F.; Campbell, I.A.; Zimmermann, U.; Ellis, J.; Jobic, H.; Pickup, R.M.; Pappas, C.; Farago, B.; Cywinski, R.; Haussler, W.; Holderer, O.; Frielinghaus, H.; Byelov, D.; Monkenbusch, M.; Allgaier, J.; Richter, D.; Egger, H.; Hellweg, Th.; Malikova, N.; Cadene, A.; Marry, V.; Dubois, E.; Turq, P.; Gardner, J.S.; Ehlers, G.; Bramwell, St.S.; Grigoriev, S.; Kraan, W.; Rekveldt, T.; Bouwman, W.; Van Dijk, N.; Falus, P.; Vorobiev, A.; Major, J.; Felcher, G.P.; Te-velthuis, S.; Dosch, H.; Vorobiev, A.; Dridi, M.H.; Major, J.; Dosch, H.; Falus, P.; Felcher, G.P.; Te Velthuis, S.G.E.; Bleuel, M.; Broell, M.; Lang, E.; Littrell, K.; Gahler, R.; Lal, J.; Lauter, H.; Toperverg, B.; Lauter, V.; Jernenkov, M.; Stueber, S.; Enderle, M.; Janoschek, M.; Keller, Th.; Klimko, S.; Boeni, P.; Nagao, M.; Yamada, N.; Kawabata, Y.; Seto, H.; Takeda, T.; Yoshizawa, H.; Yoshida, K.; Yamaguchi, T.; Bellissent-Funel, M.C.; Longeville, St

    2005-07-01

    This document gathers the abstracts of most papers presented at the workshop. Neutron spin-echo (NSE) spectroscopy is a well established technique with a growing expert user community, the aim of the meeting was to discuss the latest achievements in neutron spin-echo science and instrumentation. One of the applications presented is the investigation on the microscopic scale of the dynamics of water in montmorillonite clays with Na{sup +} and Cs{sup +} ions in monolayer and bilayer states. The NSE technique has been used in the normal and resonance modes. NSE results show consistently slower dynamics (higher relaxation times) than both time-of-flight technique (TOF) and classical molecular dynamics simulations (MD). In the present TOF and NSE experiments, anisotropy of the water motion in the interlayer is almost impossible to detect, due to the use of powder samples and insufficient resolution. (A.C.)

  4. A TEMPORAL MAP IN GEOSTATIONARY ORBIT: THE COVER ETCHING ON THE EchoStar XVI ARTIFACT

    Energy Technology Data Exchange (ETDEWEB)

    Weisberg, Joel M., E-mail: jweisber@carleton.edu [Department of Physics and Astronomy, Carleton College, Northfield, MN 55057 (United States); Paglen, Trevor, E-mail: trevor@paglen.com

    2012-10-01

    Geostationary satellites are unique among orbital spacecraft in that they experience no appreciable atmospheric drag. After concluding their respective missions, geostationary spacecraft remain in orbit virtually in perpetuity. As such, they represent some of human civilization's longest lasting artifacts. With this in mind, the EchoStar XVI satellite, to be launched in fall 2012, will play host to a time capsule intended as a message for the deep future. Inspired in part by the Pioneer Plaque and Voyager Golden Records, the EchoStar XVI Artifact is a pair of gold-plated aluminum jackets housing a small silicon disk containing 100 photographs. The Cover Etching, the subject of this paper, is etched onto one of the two jackets. It is a temporal map consisting of a star chart, pulsar timings, and other information describing the epoch from which EchoStar XVI came. The pulsar sample consists of 13 rapidly rotating objects, 5 of which are especially stable, having spin periods <10 ms and extremely small spin-down rates. In this paper, we discuss our approach to the time map etched onto the cover and the scientific data shown on it, and we speculate on the uses that future scientists may have for its data. The other portions of the EchoStar XVI Artifact will be discussed elsewhere.

  5. GESTATIONAL ECHO BIOMETRY IN BRACHYCEPHALIC PREGNANT BITCHES

    Directory of Open Access Journals (Sweden)

    Marcus Antônio Rossi Feliciano

    2015-07-01

    Full Text Available Ultrasonography is an accurate pregnancy diagnostic method, besides being completely innocuous for female and fetuses evaluation. The objective of this paper was to determine the reference values for gestational echo biometry of different breeds of bitches. A total of 25 multiparous females were included in the experiment, five English Bulldog bitches, five Pugs and 15 Shih Tzu, weighing 4-25 kg and aged 4-6 years. The echo biometric assessments were performed during the 2nd, 5th, 6th, 7th and 8th weeks of pregnancy, including gestational vesicle diameter, femur length, placenta thickness, parietal diameter, liver, heart and abdominal diameter and area. Early echo biometric study started at the second week of gestation. Measurements like fetal heart and liver diameter and area are still poorly studied, but can provide useful information for early detection of congenital anomalies that may reduce the viability of pregnancy. The significant results (P < 0.001 obtained for biometrics (P < 0.001 of the parietal (r2 = 81% and abdominal diameter (r2 = 86%, abdominal area (r2 = 80%, femur length (r2 = 84%, cardiac length (r2 = 79%, width (r2 = 79%, area (r2 = 82% and volume (r2 = 72% and liver area (r2 = 71% in brachycephalic conceptus may help to assess the development of fetuses, complementing the conventional gestational ultrasound of bitches and become a model for the study in other breeds of dogs and alternative animal species.

  6. Light Echoes of Galactic Explosions and Eruptions

    Science.gov (United States)

    Rest, Armin; Bianco, Federica; Chornock, Ryan; Clocchiatti, Alejandro; Foley, Ryan; James, David; Matheson, Thomas; Narayan, Gautham; Olsen, Knut; Points, Sean; Prieto, Jose Luis; Smith, Chris; Smith, Nathan; Suntzeff, Nick; Welch, Doug; Zenteno, Alfredo

    2014-08-01

    We propose to search for light echoes (LEs) from the historical brightening of the Luminous Blue Variable (LBV) P Cygni using the KPNO 4m Mosaic 1.1 imager. We also propose to us DECam to continue our search for LEs from the the Crab supernova SN 1054. In addition, we continue to monitor the LEs from the Cas A and Tycho supernovae in order to identify suitable LE candidates for 3D-spectroscopy and spectral time series. In previously granted NOAO time, we have discovered light echoes of three ancient SNe in the LMC as well as from the historic SN events of Cas A and Tycho [2, 3], which allowed their spectroscopic classification [6, 7, 10] and 3D spectroscopy [8, 9]. Most recently, we discovered light echoes of the mid-19th-century Great Eruption of η Carinae using CTIO 4m Mosaic images [11]. Subsequent spectroscopic follow-up of Eta Carinae revealed that its outburst spectral type was most similar to those of G-type supergiants, rather than reported LBV outburst spectral types of F-type (or earlier) [11]. Our extension of LE techniques to LBV outbursts promises to extend our ability to record outburst activity hundreds of years into the past - a timescale which is likely a significant fraction of the brief final phases of these probable core- collapse supernova precursors.

  7. Echo amplitude sensitivity of bat auditory neurons improves with decreasing pulse-echo gap.

    Science.gov (United States)

    Jen, Philip H-S; Wu, Chung Hsin

    2015-01-07

    During hunting, insectivorous bats systematically vary the parameters of emitted pulses and analyze the returning echoes to extract prey features. As such, the duration of the pulse (P) and echo (E), the P-E gap, and the P-E amplitude difference progressively decrease throughout the prey-approach sequence. Our previous studies have shown that most inferior collicular neurons of bats discharge maximally to a best duration, and they have the sharpest echo frequency and amplitude sensitivity when stimulated with P-E pairs with duration the same as the best duration. Furthermore, their echo duration and frequency sensitivity improves with decreasing P-E duration and P-E gap. The present study shows that this is also true in the amplitude domain. Thus, all these data indicate that bats can better extract multiple parameters of expected rather than unexpected echo after pulse emission. They also support the hypothesis that a bat's inferior collicular neurons improve the response sensitivity in multiple parametric domains as the prey is approached to increase the success of hunting.

  8. Non-inflammatory cerebral amyloid angiopathy as a cause of rapidly progressive dementia: A case study

    Directory of Open Access Journals (Sweden)

    Leonel Tadao Takada

    Full Text Available Abstract A 77 year-old men developed a subacute-onset, rapidly progressive cognitive decline. After 6 months of evolution, he scored 6 on the Mini-Mental State Examination and had left hemiparesis and hemineglect. The patient died 11 months after the onset of cognitive symptoms. Brain MRI showed microhemorrhages on gradient-echo sequence and confluent areas of white matter hyperintensities on T2-weighted images. Brain biopsy revealed amyloid-b peptide deposition in vessel walls, some of them surrounded by micro-bleeds. In this case report, we discuss the role of cerebral amyloid angiopathy (CAA in cognitive decline, due to structural lesions associated with hemorrhages and infarcts, white matter lesions and co-morbidity of Alzheimer's disease, as well as the most recently described amyloid angiopathy-related inflammation.

  9. Temperature sheets and aspect sensitive radar echoes

    Directory of Open Access Journals (Sweden)

    H. Luce

    Full Text Available here have been years of discussion and controversy about the existence of very thin and stable temperature sheets and their relationship to the VHF radar aspect sensitivity. It is only recently that very high-resolution in situ temperature observations have brought credence to the reality and ubiquity of these structures in the free atmosphere and to their contribution to radar echo enhancements along the vertical. Indeed, measurements with very high-resolution sensors are still extremely rare and rather difficult to obtain outside of the planetary boundary layer. They have only been carried out up to the lower stratosphere by Service d’A´ eronomie (CNRS, France for about 10 years. The controversy also persisted due to the volume resolution of the (Mesosphere-Stratosphere-Troposphere VHF radars which is coarse with respect to sheet thickness, although widely sufficient for meteorological or mesoscale investigations. The contribution within the range gate of many of these structures, which are advected by the wind, and decay and grow at different instants and could be distorted either by internal gravity waves or turbulence fields, could lead to radar echoes with statistical properties similar to those produced by anisotropic turbulence. Some questions thus remain regarding the manner in which temperature sheets contribute to VHF radar echoes. In particular, the zenithal and azimuthal angular dependence of the echo power may not only be produced by diffuse reflection on stable distorted or corrugated sheets, but also by extra contributions from anisotropic turbulence occurring in the stratified atmosphere. Thus, for several years, efforts have been put forth to improve the radar height resolution in order to better describe thin structures. Frequency interferometric techniques are widely used and have been recently further developed with the implementation of high-resolution data processings. We begin by reviewing briefly some characteristics

  10. Temperature sheets and aspect sensitive radar echoes

    Directory of Open Access Journals (Sweden)

    H. Luce

    2001-08-01

    Full Text Available here have been years of discussion and controversy about the existence of very thin and stable temperature sheets and their relationship to the VHF radar aspect sensitivity. It is only recently that very high-resolution in situ temperature observations have brought credence to the reality and ubiquity of these structures in the free atmosphere and to their contribution to radar echo enhancements along the vertical. Indeed, measurements with very high-resolution sensors are still extremely rare and rather difficult to obtain outside of the planetary boundary layer. They have only been carried out up to the lower stratosphere by Service d’A´ eronomie (CNRS, France for about 10 years. The controversy also persisted due to the volume resolution of the (Mesosphere-Stratosphere-Troposphere VHF radars which is coarse with respect to sheet thickness, although widely sufficient for meteorological or mesoscale investigations. The contribution within the range gate of many of these structures, which are advected by the wind, and decay and grow at different instants and could be distorted either by internal gravity waves or turbulence fields, could lead to radar echoes with statistical properties similar to those produced by anisotropic turbulence. Some questions thus remain regarding the manner in which temperature sheets contribute to VHF radar echoes. In particular, the zenithal and azimuthal angular dependence of the echo power may not only be produced by diffuse reflection on stable distorted or corrugated sheets, but also by extra contributions from anisotropic turbulence occurring in the stratified atmosphere. Thus, for several years, efforts have been put forth to improve the radar height resolution in order to better describe thin structures. Frequency interferometric techniques are widely used and have been recently further developed with the implementation of high-resolution data processings. We begin by reviewing briefly some characteristics

  11. Diffusion-prepared stimulated-echo turbo spin echo (DPsti-TSE): An eddy current-insensitive sequence for three-dimensional high-resolution and undistorted diffusion-weighted imaging.

    Science.gov (United States)

    Zhang, Qinwei; Coolen, Bram F; Versluis, Maarten J; Strijkers, Gustav J; Nederveen, Aart J

    2017-07-01

    In this study, we present a new three-dimensional (3D), diffusion-prepared turbo spin echo sequence based on a stimulated-echo read-out (DPsti-TSE) enabling high-resolution and undistorted diffusion-weighted imaging (DWI). A dephasing gradient in the diffusion preparation module and rephasing gradients in the turbo spin echo module create stimulated echoes, which prevent signal loss caused by eddy currents. Near to perfect agreement of apparent diffusion coefficient (ADC) values between DPsti-TSE and diffusion-weighted echo planar imaging (DW-EPI) was demonstrated in both phantom transient signal experiments and phantom imaging experiments. High-resolution and undistorted DPsti-TSE was demonstrated in vivo in prostate and carotid vessel wall. 3D whole-prostate DWI was achieved with four b values in only 6 min. Undistorted ADC maps of the prostate peripheral zone were obtained at low and high imaging resolutions with no change in mean ADC values [(1.60 ± 0.10) × 10-3 versus (1.60 ± 0.02) × 10-3  mm2 /s]. High-resolution 3D DWI of the carotid vessel wall was achieved in 12 min, with consistent ADC values [(1.40 ± 0.23) × 10-3  mm2 /s] across different subjects, as well as slice locations through the imaging volume. This study shows that DPsti-TSE can serve as a robust 3D diffusion-weighted sequence and is an attractive alternative to the traditional two-dimensional DW-EPI approaches. Copyright © 2017 John Wiley & Sons, Ltd.

  12. Acoustic noise reduction in T 1- and proton-density-weighted turbo spin-echo imaging.

    Science.gov (United States)

    Ott, Martin; Blaimer, Martin; Breuer, Felix; Grodzki, David; Heismann, Björn; Jakob, Peter

    2016-02-01

    To reduce acoustic noise levels in T 1-weighted and proton-density-weighted turbo spin-echo (TSE) sequences, which typically reach acoustic noise levels up to 100 dB(A) in clinical practice. Five acoustic noise reduction strategies were combined: (1) gradient ramps and shapes were changed from trapezoidal to triangular, (2) variable-encoding-time imaging was implemented to relax the phase-encoding gradient timing, (3) RF pulses were adapted to avoid the need for reversing the polarity of the slice-rewinding gradient, (4) readout bandwidth was increased to provide more time for gradient activity on other axes, (5) the number of slices per TR was reduced to limit the total gradient activity per unit time. We evaluated the influence of each measure on the acoustic noise level, and conducted in vivo measurements on a healthy volunteer. Sound recordings were taken for comparison. An overall acoustic noise reduction of up to 16.8 dB(A) was obtained by the proposed strategies (1-4) and the acquisition of half the number of slices per TR only. Image quality in terms of SNR and CNR was found to be preserved. The proposed measures in this study allowed a threefold reduction in the acoustic perception of T 1-weighted and proton-density-weighted TSE sequences compared to a standard TSE-acquisition. This could be achieved without visible degradation of image quality, showing the potential to improve patient comfort and scan acceptability.

  13. 3D printed phantoms mimicking cortical bone for the assessment of ultrashort echo time magnetic resonance imaging.

    Science.gov (United States)

    Rai, Robba; Manton, David; Jameson, Michael G; Josan, Sonal; Barton, Michael B; Holloway, Lois C; Liney, Gary P

    2018-02-01

    Human cortical bone has a rapid T2∗ decay, and it can be visualized using ultrashort echo time (UTE) techniques in magnetic resonance imaging (MRI). These sequences operate at the limits of gradient and transmit-receive signal performance. Development of multicompartment anthropomorphic phantoms that can mimic human cortical bone can assist with quality assurance and optimization of UTE sequences. The aims of this study were to (a) characterize the MRI signal properties of a photopolymer resin that can be 3D printed, (b) develop multicompartment phantoms based on the resin, and (c) demonstrate the feasibility of using these phantoms to mimic human anatomy in the assessment of UTE sequences. A photopolymer resin (Prismlab China Ltd, Shanghai, China) was imaged on a 3 Tesla MRI system (Siemens Skyra) to characterize its MRI properties with emphasis on T2∗ signal and longevity. Two anthropomorphic phantoms, using the 3D printed resin to simulate skeletal anatomy, were developed and imaged using UTE sequences. A skull phantom was developed and used to assess the feasibility of using the resin to develop a complex model with realistic morphological human characteristics. A tibia model was also developed to assess the suitability of the resin at mimicking a simple multicompartment anatomical model and imaged using a three-dimensional UTE sequence (PETRA). Image quality measurements of signal-to-noise ratio (SNR) and contrast factor were calculated and these were compared to in vivo values. The T2∗ and T1 (mean ± standard deviation) of the photopolymer resin was found to be 411 ± 19 μs and 74.39 ± 13.88 ms, respectively, and demonstrated no statistically significant change during 4 months of monitoring. The resin had a similar T2∗ decay to human cortical bone; however, had lower T1 properties. The bone water concentration of the resin was 59% relative to an external water reference phantom, and this was higher than in vivo values reported for human cortical

  14. A method for the dynamic correction of B0-related distortions in single-echo EPI at 7T.

    Science.gov (United States)

    Dymerska, Barbara; Poser, Benedikt A; Barth, Markus; Trattnig, Siegfried; Robinson, Simon D

    2016-07-07

    We propose a method to calculate field maps from the phase of each EPI in an fMRI time series. These field maps can be used to correct the corresponding magnitude images for distortion caused by inhomogeneity in the static magnetic field. In contrast to conventional static distortion correction, in which one 'snapshot' field map is applied to all subsequent fMRI time points, our method also captures dynamic changes to B0 which arise due to motion and respiration. The approach is based on the assumption that the non-B0-related contribution to the phase measured by each radio-frequency coil, which is dominated by the coil sensitivity, is stable over time and can therefore be removed to yield a field map from EPI. Our solution addresses imaging with multi-channel coils at ultra-high field (7T), where phase offsets vary rapidly in space, phase processing is non-trivial and distortions are comparatively large. We propose using dual-echo gradient echo reference scan for the phase offset calculation, which yields estimates with high signal-to-noise ratio. An extrapolation method is proposed which yields reliable estimates for phase offsets even where motion is large and a tailored phase unwrapping procedure for EPI is suggested which gives robust results in regions with disconnected tissue or strong signal decay. Phase offsets are shown to be stable during long measurements (40min) and for large head motions. The dynamic distortion correction proposed here is found to work accurately in the presence of large motion (up to 8.1°), whereas a conventional method based on single field map fails to correct or even introduces distortions (up to 11.2mm). Finally, we show that dynamic unwarping increases the temporal stability of EPI in the presence of motion. Our approach can be applied to any EPI measurements without the need for sequence modification. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

  15. We Three (My echo, my shadow and me)

    OpenAIRE

    Veator, Valerie E.

    2015-01-01

    We Three (My echo, my shadow and me) presents a tripartite work that exercises forms of tracing, imbedding, concealing and revealing across painting, video, and installation. Inspired by Jacques Rivette’s 1974 film Celine and Julie Go Boating, We Three examines perception and subjectivity in today’s screenic culture. We Three draws out modes transference in the form of an echoed, displaced transmission as it exists within and between specific artworks. The three parts are installed as echoes ...

  16. An Acoustic Echo Cancellation System based on Adaptive Algorithm

    OpenAIRE

    Garre, Veeratej; Mannem, Sailesh Kumar

    2012-01-01

    Adaptive filtering technique is one of the core technologies in digital signal processing and finds numerous application areas in science as well as in industry. Adaptive filtering technique is widely used in many applications, including echo cancellation, adaptive noise cancellation, adaptive beam forming and adaptive equalization. Acoustic echo is a common occurrence in today’s telecommunication systems. The distraction caused by the acoustic echo, reduces the speech quality in the communic...

  17. Differentiation of breast cancer from fibroadenoma with dual-echo dynamic contrast-enhanced MRI.

    Science.gov (United States)

    Wang, Shiwei; Delproposto, Zachary; Wang, Haoyu; Ding, Xuewei; Ji, Conghua; Wang, Bei; Xu, Maosheng

    2013-01-01

    Dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) of the breast is a routinely used imaging method which is highly sensitive for detecting breast malignancy. Specificity, though, remains suboptimal. Dynamic susceptibility contrast magnetic resonance imaging (DSC MRI), an alternative dynamic contrast imaging technique, evaluates perfusion-related parameters unique from DCE MRI. Previous work has shown that the combination of DSC MRI with DCE MRI can improve diagnostic specificity, though an additional administration of intravenous contrast is required. Dual-echo MRI can measure both T1W DCE MRI and T2*W DSC MRI parameters with a single contrast bolus, but has not been previously implemented in breast imaging. We have developed a dual-echo gradient-echo sequence to perform such simultaneous measurements in the breast, and use it to calculate the semi-quantitative T1W and T2*W related parameters such as peak enhancement ratio, time of maximal enhancement, regional blood flow, and regional blood volume in 20 malignant lesions and 10 benign fibroadenomas in 38 patients. Imaging parameters were compared to surgical or biopsy obtained tissue samples. Receiver operating characteristic (ROC) curves and area under the ROC curves were calculated for each parameter and combination of parameters. The time of maximal enhancement derived from DCE MRI had a 90% sensitivity and 69% specificity for predicting malignancy. When combined with DSC MRI derived regional blood flow and volume parameters, sensitivity remained unchanged at 90% but specificity increased to 80%. In conclusion, we show that dual-echo MRI with a single administration of contrast agent can simultaneously measure both T1W and T2*W related perfusion and kinetic parameters in the breast and the combination of DCE MRI and DSC MRI parameters improves the diagnostic performance of breast MRI to differentiate breast cancer from benign fibroadenomas.

  18. Echo Shaping Using Sums of Damped Complex Sinusoids

    DEFF Research Database (Denmark)

    Putnam, Lance Jonathan

    2015-01-01

    Feedback delay lines are the basis of myriad audio effects and reverberation schemes. The feedback delay line, by itself, is limited to producing an infinite sequence of exponentially decaying echoes. We introduce a new type of linear time-invariant echo effect whose impulse response is a general......Feedback delay lines are the basis of myriad audio effects and reverberation schemes. The feedback delay line, by itself, is limited to producing an infinite sequence of exponentially decaying echoes. We introduce a new type of linear time-invariant echo effect whose impulse response...

  19. Optimization of sparse phase encodings for variable repetition-delay turbo-spin echo (TSE) T1 measurements for preclinical applications

    Science.gov (United States)

    Lee, DongKyu; Han, Sohyun; Cho, HyungJoon

    2017-01-01

    A variable repetition-delay (TR) spin echo sequence with repeated refocusing pulses, i.e., a variable TR turbo-spin echo (TSE), provides an attractive means of acquiring an accurate T1 map information that is free from gradient echo based artifacts such as magnetic field inhomogeneities particularly for ultra-high field (at 7T and above) preclinical applications. However, the applicability of multi-slice TSE sequences is often limited by signal distortion from T2 relaxation due to echo-train acquisitions for short T2 tissues, inter-slice cross talks and magnetization transfer (MT) from repetitive slice-selective 180° pulse, and extended scan times with multiple TR excitations. These TSE shortcomings are difficult to remedy for preclinical applications, where small sizes of target organs usually limit the slice-gap control with restricted parallel imaging capabilities. In this study, compressed-sensing-assisted turbo-spin echo (CS-TSE) acquisitions for variable TR T1 measurements at 7T preclinical scanner were implemented to reduce the echo-trains by sparse phase encodings. Following the sparse signal simulation and sampling scheme optimization, the measured T1 values from CS-TSE and TSE were compared for phantoms, ex vivo, and in vivo subjects. The phantom T1 values from CS-TSE and TSE were identical to those from the inversion recovery spin echo. For both ex vivo and in vivo multi-slice T1 mapping, the shortened echo-trains of CS-TSE relieved the T2 relaxation, reduced the inter-slice interferences of multi-slice acquisition, and made room for additional slice encodings while maintaining a shorter scan time than the conventional TSE at the expense of local image smoothness from CS regularizations.

  20. Universal gradient descent

    OpenAIRE

    Gasnikov, Alexander

    2017-01-01

    In this small book we collect many different and useful facts around gradient descent method. First of all we consider gradient descent with inexact oracle. We build a general model of optimized function that include composite optimization approach, level's methods, proximal methods etc. Then we investigate primal-dual properties of the gradient descent in general model set-up. At the end we generalize method to universal one.

  1. 3 Echo: concept of operations for early care and evacuation of victims of mass violence.

    Science.gov (United States)

    Autrey, Allen W; Hick, John L; Bramer, Kurtis; Berndt, Jeremy; Bundt, Jonathan

    2014-08-01

    This report describes the successful use of a simple 3-phase approach that guides the initial 30 minutes of a response to blast and active shooter events with casualties: Enter, Evaluate, and Evacuate (3 Echo) in a mass-shooting event occurring in Minneapolis, Minnesota USA, on September 27, 2012. Early coordination between law enforcement (LE) and rescue was emphasized, including establishment of unified command, a common operating picture, determination of evacuation corridors, swift victim evaluation, basic treatment, and rapid evacuation utilizing an approach developed collaboratively over the four years prior to the event. Field implementation of 3 Echo requires multi-disciplinary (Emergency Medical Services (EMS), fire and LE) training to optimize performance. This report details the mass-shooting event, the framework created to support the response, and also describes important aspects of the concepts of operation and curriculum evolved through years of collaboration between multiple disciplines to arrive at unprecedented EMS transport times in response to the event.

  2. Correcting dynamic distortions in 7T echo planar imaging using a jittered echo time sequence

    Science.gov (United States)

    Dymerska, Barbara; Poser, Benedikt A.; Bogner, Wolfgang; Visser, Eelke; Eckstein, Korbinian; Cardoso, Pedro; Barth, Markus; Trattnig, Siegfried

    2015-01-01

    Purpose To develop a distortion correction method for echo planar imaging (EPI) that is able to measure dynamic changes in B0. Theory and Methods The approach we propose is based on single‐echo EPI with a jittering of the echo time between two values for alternate time points. Field maps are calculated between phase images from adjacent volumes and are used to remove distortion from corresponding magnitude images. The performance of our approach was optimized using an analytical model and by comparison with field maps from dual‐echo EPI. The method was tested in functional MRI experiments at 7T with motor tasks and compared with the conventional static approach. Results Unwarping using our method was accurate even for head rotations up to 8.2°, where the static approach introduced errors up to 8.2 mm. Jittering the echo time between 19 and 25 ms had no measurable effect on blood oxygenation level–dependent (BOLD) sensitivity. Our approach reduced the distortions in activated regions to distortion correction in the presence of motion. No reduction in BOLD sensitivity was observed. As such, it is suitable for application in a wide range of functional MRI experiments. Magn Reson Med 76:1388–1399, 2016. © 2015 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. PMID:26584148

  3. Rapid MRI evaluation of acute intracranial hemorrhage in pediatric head trauma

    Energy Technology Data Exchange (ETDEWEB)

    Ryan, Maura E.; Jaju, Alok [Northwestern University Feinberg School of Medicine, Department of Radiology, Chicago, IL (United States); Ann and Robert H. Lurie Children' s Hospital of Chicago, Department of Medical Imaging, Chicago, IL (United States); Ciolino, Jody D. [Northwestern University, Biostatistics Collaboration Center, Department of Preventive Medicine Feinberg School of Medicine, Chicago, IL (United States); Alden, Tord [Northwestern University Feinberg School of Medicine, Department of Neurological Surgery, Chicago, IL (United States); Ann and Robert H. Lurie Children' s Hospital of Chicago, Department of Neurosurgery, Chicago, IL (United States)

    2016-08-15

    Rapid MRI with ultrafast T2 sequences can be performed without sedation and is often used in place of computed tomography (CT) to evaluate pediatric patients for indications such as hydrocephalus. This study investigated the sensitivity of rapid magnetic resonance imaging (MRI) for detection and follow-up of acute intracranial hemorrhage in comparison to CT, which is commonly the first-line imaging. Patients presenting to a pediatric hospital with acute intracranial hemorrhage on CT and follow-up rapid MRI within 48 h were included. Rapid MRI studies consisted of three plane ultrafast T2 sequences either with or without axial gradient echo (GRE) sequences. Identification of hemorrhage on rapid MRI was assessed by readers both blinded and unblinded to prior CT results. One hundred two acute hemorrhages in 61 patients were identified by CT. Rapid MRI detection of subdural and epidural hemorrhages was modest in the absence of prior CT for comparison (sensitivity 61-74 %), but increased with review of the prior CT (sensitivity 80-86 %). Hemorrhage size was a significant predictor of detection (p < 0.0001). Three plane fast T2 images alone without GRE sequences were poor at detecting subarachnoid hemorrhage (sensitivity 10-25 %); rapid MRI with GRE sequences identified the majority of subarachnoid hemorrhage (sensitivity 71-93 %). GRE modestly increased detection of other extra-axial hemorrhages. Rapid MRI with GRE sequences is sensitive for most acute intracranial hemorrhages only when a prior CT is available for review. Rapid MRI is not adequate to replace CT in initial evaluation of intracranial hemorrhages but may be helpful in follow-up of known hemorrhages. (orig.)

  4. Spin-echo echo-planar perfusion prior to chemoradiation is a strong independent predictor of progression-free and overall survival in newly diagnosed glioblastoma.

    Science.gov (United States)

    Akgoz, Ayca; Rahman, Rifaquat; You, Hui; Qu, Jinrong; Hamdan, Alhafidz; Seethamraju, Ravi T; Wen, Patrick Y; Young, Geoffrey S

    2014-08-01

    Spin-echo echo planar (EP) perfusion weighted imaging (SE-PWI) has been demonstrated to be more selective than gradient-echo EP PWI for blood volume in microvessels the size of glioma neocapillaries, but it has not been comprehensively studied in human clinical use. We assessed whether SE-PWI before and after initiating chemoradiation can stratify patients with respect to progression free survival (PFS) and overall survival (OS). Sixty-eight patients with newly diagnosed glioblastoma (mean age 58.3, 36 males) were included in analysis. SE EP cerebral blood volumes (SE-CBVs) in enhancing and nonenhancing tumor, normalized to contralateral normal appearing white matter (SE-nCBV), were assessed at baseline and after initial chemoradiation. SE-nCBV parameters predictive of PFS and OS were identified in univariate and multivariate Cox proportional hazards models. Multivariate analysis demonstrated that baseline tumor mean SE-nCBV was predictive of PFS (p = 0.038) and OS (p = 0.004). Within the patient sample, baseline tumor mean SE-nCBV 2.0 (median PFS 25.3, median OS 56.0 weeks). Exploratory multi-group stratification demonstrated that very high (>4.0) tumor SE-nCBV was associated with worse patient OS than intermediate high (>2.0, <4.0) SE-nCBV (p = 0.025). Baseline mean SE-nCBV can stratify patients for PFS and OS prior to initiation of chemoradiation, which may help select patients who require closer surveillance. Our exploratory analysis indicates a magnitude-dependent relationship between baseline SE-nCBV and OS.

  5. Caustic echoes from a Schwarzschild black hole

    CERN Document Server

    Zenginoğlu, Anıl

    2012-01-01

    We present the first numerical construction of the scalar Schwarzschild Green function in the time-domain, which reveals several universal features of wave propagation in black hole spacetimes. We demonstrate the trapping of energy near the photon sphere and confirm its exponential decay. The trapped wavefront propagates through caustics resulting in echoes that propagate to infinity. The arrival times and the decay rate of these caustic echoes are consistent with propagation along null geodesics and the large l-limit of quasinormal modes. We show that the four-fold singularity structure of the retarded Green function is due to the well-known action of a Hilbert transform on the trapped wavefront at caustics. A two-fold cycle is obtained for degenerate source-observer configurations along the caustic line, where the energy amplification increases with an inverse power of the scale of the source. Finally, we discuss the tail piece of the solution due to propagation within the light cone, up to and including nu...

  6. On Stellar Flash Echoes from Circular Rings

    Science.gov (United States)

    Nemiroff, Robert; Mukherjee, Oindabi

    2018-01-01

    A flash -- or any episode of variability -- that occurs in the vicinity of a circular ring might be seen several times later, simultaneously, as echoes on the ring. Effective images of the flash are created and annihilated in pairs, with as many as four flash images visible concurrently. Videos detailing sequences of image pair creation, tandem motion, and subsequent image annihilation are shown, given simple opacity and scattering assumptions. It is proven that, surprisingly, images from a second pair creation event always annihilate with images from the first. Caustic surfaces between flash locations yielding two and four images are computed. Although such ring echos surely occur, their practical detection might be difficult as it could require dedicated observing programs involving sensitive photometry of extended objects. Potential flash sources include planetary and interstellar gas and dust rings near and around variable stars, flare stars, novae, supernovae, and GRBs. Potentially recoverable information includes size, distance, temporal history, and angular isotropy of both the ring and flash.

  7. Gradient and vorticity banding

    NARCIS (Netherlands)

    Dhont, Jan K.G.; Briels, Willem J.

    2008-01-01

    "Banded structures" of macroscopic dimensions can be induced by simple shear flow in many different types of soft matter systems. Depending on whether these bands extend along the gradient or vorticity direction, the banding transition is referred to as "gradient banding" or "vorticity banding,"

  8. Ultrashort echo time imaging with acquisition trajectory mapping for correction of gradient imperfections

    Czech Academy of Sciences Publication Activity Database

    Latta, P.; Starčuk jr., Zenon; Gruwel, M. L. H.; Tománek, B.

    2015-01-01

    Roč. 28, S1 (2015), S102 ISSN 0968-5243. [ESMRMB 2015. Annual Scientific Meeting /32./. 01.09.2015-03.09.2015, Edinburgh] R&D Projects: GA ČR(CZ) GA15-12607S Institutional support: RVO:68081731 Keywords : UTE MRI * radial sampling * image reconstructio Subject RIV: FS - Medical Facilities ; Equipment

  9. Size Distribution Imaging by Non-Uniform Oscillating-Gradient Spin Echo (NOGSE) MRI

    National Research Council Canada - National Science Library

    Shemesh, Noam; Álvarez, Gonzalo A; Frydman, Lucio

    2015-01-01

    .... These size distributions play fundamental roles in defining the physicochemical, biophysical and physiological properties of a wide variety of systems - ranging from advanced catalytic materials...

  10. In vivo quantitative NMR imaging of fruit tissues during growth using Spoiled Gradient Echo sequence

    DEFF Research Database (Denmark)

    Kenouche, S.; Perrier, M.; Bertin, N.

    2014-01-01

    Nondestructive studies of physiological processes in agronomic products require increasingly higher spatial and temporal resolutions. Nuclear Magnetic Resonance (NMR) imaging is a non-invasive technique providing physiological and morphological information on biological tissues. The aim of this s......Nondestructive studies of physiological processes in agronomic products require increasingly higher spatial and temporal resolutions. Nuclear Magnetic Resonance (NMR) imaging is a non-invasive technique providing physiological and morphological information on biological tissues. The aim...... of columella and in the seed envelopes. The total quantities and the average volume flow of water estimated are: 198 mg, 1.76 mm 3/h for the columella and 326 mg, 2.91 mm 3/h for the seed envelopes. We demonstrate in this paper that the NMR imaging technique coupled with efficient and biocompatible CA...

  11. Analysis of Partial Volume Effects on Arterial Input Functions Using Gradient Echo: A Simulation Study

    DEFF Research Database (Denmark)

    Kjølby, Birgitte Fuglsang; Mikkelsen, Irene Klærke; Pedersen, Michael

    2009-01-01

    of an AIF voxel including the relaxation properties of blood and tissue. Artery orientations parallel and perpendicular to the main magnetic field were investigated and AIF voxels were modeled to either include or be situated close to a large artery. The impact of partial volume effects on quantitative...

  12. Signal changes in gradient echo images of human brain induced by hypo- and hyperoxia

    DEFF Research Database (Denmark)

    Rostrup, Egill; Larsson, H B; Toft, P B

    1995-01-01

    of saturation effects. The total cerebral blood flow was measured by a phase mapping technique during normoxia as well as hypoxia (FiO2 of 10% and 16%) and hyperoxia (FiO2 of 50% and 100%). High relative signal changes were found, independently of the flip angle, with FiO2 of 10%. With a flip angle of 40...

  13. Conjugate Gradient Algorithms For Manipulator Simulation

    Science.gov (United States)

    Fijany, Amir; Scheid, Robert E.

    1991-01-01

    Report discusses applicability of conjugate-gradient algorithms to computation of forward dynamics of robotic manipulators. Rapid computation of forward dynamics essential to teleoperation and other advanced robotic applications. Part of continuing effort to find algorithms meeting requirements for increased computational efficiency and speed. Method used for iterative solution of systems of linear equations.

  14. Effects of room impulse responses to stereophonic acoustic echo cancellation

    Science.gov (United States)

    Kim, Jeonghee

    2000-09-01

    Teleconferencing provides people the ability to hold meetings in different locations without traveling. Currently, most teleconferencing systems use full duplex single channel for voice communication. These systems use an acoustic echo canceller to reduce echoes resulting from the coupling between the microphone and the speaker. To provide a more realistic presence and spatial realism that one-channel systems cannot offer, future teleconferencing systems are expected to have at least two channels (stereophonic sound) of full duplex voice communication. However stereophonic acoustic echo cancellation (AEC) is fundamentally different from monophonic AEC. In this work, we review some of adaptive filters used for the AEC systems and develop exponentially weighted step size for two-channel normalized least mean square (2C- NLMS) and generalized normalized least mean square (2C- GNLMS or APA: affine projection algorithm) adaptive algorithms based on the statistics of room impulse response. In one-channel AEC systems, there is only one acoustic echo path to identify. However, there are four acoustic echo paths to identify in two-channel AEC systems, so non-uniqueness problems exist. These problems are presented and some approaches done by researchers are shown with simulations. Finally, effects of room impulse responses, transmission room and receiving room impulse responses, and returning echoes into the transmission room to the performance of adaptive filters are simulated. A comparison of error performance with echoes and without echoes is presented.

  15. Mean grain size mapping with single-beam echo sounders

    NARCIS (Netherlands)

    Walree, P.A. van; Ainslie, M.A.; Simons, D.G.

    2006-01-01

    Echo energies of single-beam echo sounders are inverted for the sediment mean grain size via a combination of theoretical and empirical relationships. In situ measurements of the seafloor mass density have revealed the presence of a thin transition layer between the water and the sediment. Within

  16. Revival of silenced echo and quantum memory for light

    Energy Technology Data Exchange (ETDEWEB)

    Damon, V; Bonarota, M; Louchet-Chauvet, A; Chaneliere, T; Le Gouet, J-L, E-mail: jean-louis.legouet@lac.u-psud.fr [Laboratoire Aime Cotton, CNRS-UPR 3321, Univ. Paris-Sud, Bat. 505, 91405 Orsay cedex (France)

    2011-09-15

    We propose an original quantum memory protocol. It belongs to the class of rephasing processes and is closely related to two-pulse photon echo. It is known that the strong population inversion produced by the rephasing pulse prevents the plain two-pulse photon echo from serving as a quantum memory scheme. Indeed, gain and spontaneous emission generate prohibitive noise. A second {pi}-pulse can be used to simultaneously reverse the atomic phase and bring the atoms back into the ground state. Then a secondary echo is radiated from a non-inverted medium, avoiding contamination by gain and spontaneous emission noise. However, one must kill the primary echo, in order to preserve all the information for the secondary signal. In the present work, spatial phase mismatching is used to silence the standard two-pulse echo. An experimental demonstration is presented.

  17. Revival of silenced echo and quantum memory for light

    Science.gov (United States)

    Damon, V.; Bonarota, M.; Louchet-Chauvet, A.; Chanelière, T.; Le Gouët, J.-L.

    2011-09-01

    We propose an original quantum memory protocol. It belongs to the class of rephasing processes and is closely related to two-pulse photon echo. It is known that the strong population inversion produced by the rephasing pulse prevents the plain two-pulse photon echo from serving as a quantum memory scheme. Indeed, gain and spontaneous emission generate prohibitive noise. A second π-pulse can be used to simultaneously reverse the atomic phase and bring the atoms back into the ground state. Then a secondary echo is radiated from a non-inverted medium, avoiding contamination by gain and spontaneous emission noise. However, one must kill the primary echo, in order to preserve all the information for the secondary signal. In the present work, spatial phase mismatching is used to silence the standard two-pulse echo. An experimental demonstration is presented.

  18. Theory of electron spin echoes in solids

    CERN Document Server

    Asadullina, N Y; Asadullin, Y Y

    2002-01-01

    We propose modified Bloch equations (MBEs) with specific power-dependent relaxation and dispersion parameters characteristic for two-pulse excitation and when the magnetic dipole-dipole interactions in the electron spin system control the dephasing. We discriminate between the 'active' (excited by both pulses) and 'passive' (excited by the second pulse only) spins: it is shown that the 'active' spins participate in a new effect, an active spin frequency modulation effect giving rise to the power-dependent dispersion and multiple electron spin echoes (ESEs); the 'passive' spins contribute to the power-dependent relaxation. The MBEs are solved and a general expression for the two-pulse ESEs is obtained. Detailed numerical analysis of this expression gives results in good quantitative agreement with the recent experiments on the two-pulse ESEs at conventional low applied fields. The developed theory is applied also to high field ESEs, which are promising for future investigations. On the basis of published resul...

  19. Image domain propeller fast spin echo.

    Science.gov (United States)

    Skare, Stefan; Holdsworth, Samantha J; Lilja, Anders; Bammer, Roland

    2013-04-01

    A new pulse sequence for high-resolution T2-weighted (T2-w) imaging is proposed - image domain propeller fast spin echo (iProp-FSE). Similar to the T2-w PROPELLER sequence, iProp-FSE acquires data in a segmented fashion, as blades that are acquired in multiple TRs. However, the iProp-FSE blades are formed in the image domain instead of in the k-space domain. Each iProp-FSE blade resembles a single-shot fast spin echo (SSFSE) sequence with a very narrow phase-encoding field of view (FOV), after which N rotated blade replicas yield the final full circular FOV. Our method of combining the image domain blade data to a full FOV image is detailed, and optimal choices of phase-encoding FOVs and receiver bandwidths were evaluated on phantom and volunteers. The results suggest that a phase FOV of 15-20%, a receiver bandwidth of ±32-63 kHz and a subsequent readout time of about 300 ms provide a good tradeoff between signal-to-noise ratio (SNR) efficiency and T2 blurring. Comparisons between iProp-FSE, Cartesian FSE and PROPELLER were made on single-slice axial brain data, showing similar T2-w tissue contrast and SNR with great anatomical conspicuity at similar scan times - without colored noise or streaks from motion. A new slice interleaving order is also proposed to improve the multislice capabilities of iProp-FSE. Copyright © 2013 Elsevier Inc. All rights reserved.

  20. How accurate is MOLLI T1 mapping in vivo? Validation by spin echo methods.

    Directory of Open Access Journals (Sweden)

    Mitchell A Cooper

    Full Text Available T1 mapping is a promising quantitative tool for assessing diffuse cardiomyopathies. The purpose of this study is to quantify in vivo accuracy of the Modified Look-Locker Inversion Recovery (MOLLI cardiac T1 mapping sequence against the spin echo gold standard, which has not been done previously. T1 accuracy of MOLLI was determined by comparing with the gold standard inversion recovery spin echo sequence in the calf muscle, and with a rapid inversion recovery fast spin echo sequence in the heart. T1 values were obtained with both conventional MOLLI fitting and MOLLI fitting with inversion efficiency correction. In the calf (n = 6, conventional MOLLI fitting produced inconsistent T1 values with error ranging from 8.0% at 90° to 17.3% at 30°. Modified MOLLI fitting with inversion efficiency correction improved error to under 7.4% at all flip angles. In the heart (n = 5, modified MOLLI fitting with inversion correction reduced T1 error to 5.5% from 14.0% by conventional MOLLI fitting. This study shows that conventional MOLLI fitting can lead to significant in vivo T1 errors when not accounting for the lower adiabatic inversion efficiency often experienced in vivo.

  1. Characterization of anomalous relaxation using the time-fractional Bloch equation and multiple echo T2*-weighted magnetic resonance imaging at 7 T.

    Science.gov (United States)

    Qin, Shanlin; Liu, Fawang; Turner, Ian W; Yu, Qiang; Yang, Qianqian; Vegh, Viktor

    2017-04-01

    To study the utility of fractional calculus in modeling gradient-recalled echo MRI signal decay in the normal human brain. We solved analytically the extended time-fractional Bloch equations resulting in five model parameters, namely, the amplitude, relaxation rate, order of the time-fractional derivative, frequency shift, and constant offset. Voxel-level temporal fitting of the MRI signal was performed using the classical monoexponential model, a previously developed anomalous relaxation model, and using our extended time-fractional relaxation model. Nine brain regions segmented from multiple echo gradient-recalled echo 7 Tesla MRI data acquired from five participants were then used to investigate the characteristics of the extended time-fractional model parameters. We found that the extended time-fractional model is able to fit the experimental data with smaller mean squared error than the classical monoexponential relaxation model and the anomalous relaxation model, which do not account for frequency shift. We were able to fit multiple echo time MRI data with high accuracy using the developed model. Parameters of the model likely capture information on microstructural and susceptibility-induced changes in the human brain. Magn Reson Med 77:1485-1494, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  2. Fast T2 Mapping with Improved Accuracy Using Undersampled Spin-echo MRI and Model-based Reconstructions with a Generating Function

    CERN Document Server

    Sumpf, Tilman J; Uecker, Martin; Knoll, Florian; Frahm, Jens

    2014-01-01

    A model-based reconstruction technique for accelerated T2 mapping with improved accuracy is proposed using undersampled Cartesian spin-echo MRI data. The technique employs an advanced signal model for T2 relaxation that accounts for contributions from indirect echoes in a train of multiple spin echoes. An iterative solution of the nonlinear inverse reconstruction problem directly estimates spin-density and T2 maps from undersampled raw data. The algorithm is validated for simulated data as well as phantom and human brain MRI at 3 T. The performance of the advanced model is compared to conventional pixel-based fitting of echo-time images from fully sampled data. The proposed method yields more accurate T2 values than the mono-exponential model and allows for undersampling factors of at least 6. Although limitations are observed for very long T2 relaxation times, respective reconstruction problems may be overcome by a gradient dampening approach. The analytical gradient of the utilized cost function is included...

  3. Second gradient poromechanics

    CERN Document Server

    Sciarra, Giulio; Coussy, Olivier

    2010-01-01

    Second gradient theories have been developed in mechanics for treating different phenomena as capillarity in fluids, plasticity and friction in granular materials or shear band deformations. Here, there is an attempt of formulating a second gradient Biot like model for porous materials. In particular the interest is focused in describing the local dilatant behaviour of a porous material induced by pore opening elastic and capillary interaction phenomena among neighbouring pores and related micro-filtration phenomena by means of a continuum microstructured model. The main idea is to extend the classical macroscopic Biot model by including in the description second gradient effects. This is done by assuming that the surface contribution to the external work rate functional depends on the normal derivative of the velocity or equivalently assuming that the strain work rate functional depends on the porosity and strain gradients. According to classical thermodynamics suitable restrictions for stresses and second g...

  4. A comparison of multi-echo spin-echo and triple-echo steady-state T2 mapping for in vivo evaluation of articular cartilage

    Energy Technology Data Exchange (ETDEWEB)

    Juras, Vladimir; Szomolanyi, Pavol [Medical University of Vienna, High Field MR Centre, Department of Biomedical Imaging and Image-Guided Therapy, Vienna (Austria); Institute of Measurement Science, Department of Imaging Methods, Bratislava (Slovakia); Bohndorf, Klaus; Kronnerwetter, Claudia; Hager, Benedikt; Zbyn, Stefan [Medical University of Vienna, High Field MR Centre, Department of Biomedical Imaging and Image-Guided Therapy, Vienna (Austria); Heule, Rahel; Bieri, Oliver [University of Basel Hospital, Division of Radiological Physics, Department of Radiology, Basel (Switzerland); Trattnig, Siegfried [Medical University of Vienna, High Field MR Centre, Department of Biomedical Imaging and Image-Guided Therapy, Vienna (Austria); Christian Doppler Laboratory for Clinical Molecular MR Imaging, Vienna (Austria); Ludwig Boltzmann Institute for Experimental and Clinical Traumatology, Austrian Cluster for Tissue Regeneration, Vienna (Austria)

    2016-06-15

    To assess the clinical relevance of T{sub 2} relaxation times, measured by 3D triple-echo steady-state (3D-TESS), in knee articular cartilage compared to conventional multi-echo spin-echo T{sub 2}-mapping. Thirteen volunteers and ten patients with focal cartilage lesions were included in this prospective study. All subjects underwent 3-Tesla MRI consisting of a multi-echo multi-slice spin-echo sequence (CPMG) as a reference method for T{sub 2} mapping, and 3D TESS with the same geometry settings, but variable acquisition times: standard (TESSs 4:35min) and quick (TESSq 2:05min). T{sub 2} values were compared in six different regions in the femoral and tibial cartilage using a Wilcoxon signed ranks test and the Pearson correlation coefficient (r). The local ethics committee approved this study, and all participants gave written informed consent. The mean quantitative T{sub 2} values measured by CPMG (mean: 46±9ms) in volunteers were significantly higher compared to those measured with TESS (mean: 31±5ms) in all regions. Both methods performed similarly in patients, but CPMG provided a slightly higher difference between lesions and native cartilage (CPMG: 90ms→61ms [31%],p=0.0125;TESS 32ms→24ms [24%],p=0.0839). 3D-TESS provides results similar to those of a conventional multi-echo spin-echo sequence with many benefits, such as shortening of total acquisition time and insensitivity to B{sub 1} and B{sub 0} changes. (orig.)

  5. Retrospective correction of B0-field-induced geometric distortions in multislice echo planar images: a 3D solution

    Science.gov (United States)

    McColl, Roderick W.; Coburn, Edward A.

    2000-04-01

    A method has been developed to utilize a 3D B0 fieldmap, with a multi-volume-of-interest segmentation map, to quantify and correct geometric distortions in echo-planar images. The purpose is to provide accurate co-registration of anatomical MRI to functional MRI time course sequences. A data structure capable of extracting and reporting the necessary information forms a central part of the solution. Images were obtained from a 1.5 Tesla scanner with an experimental y-gradient insert coil. Two 3D-gradient echo sequences supply the data needed to calculate the B0 map across the volume. Segmentation of the volume into brain/background produces the data needed for the phase unwrapping and volume(s) of interest generation, from which the global B0 variation map is obtained. Subsequent EPI acquisition yields the fMRI time- course information. Tests were carried out on a phantom and a human volunteer engaged in a motor task (finger-tapping). Strong distortions were measured, and subsequently corrected, particularly near the petrous bone/mastoid air cells and in the frontal and maxillary sinuses. Additionally, a strong eddy current resulting from the unshielded y-gradient was detected. The method facilitates geometric distortion correction through an imaging volume, containing multiple regions of interest within a slice, starting from a single starting point.

  6. Echo spectroscopy and quantum stability of trapped atoms

    OpenAIRE

    Andersen, M. F.; Kaplan, A.; Davidson, N.

    2002-01-01

    We investigate the dephasing of ultra cold ^{85}Rb atoms trapped in an optical dipole trap and prepared in a coherent superposition of their two hyperfine ground states by interaction with a microwave pulse. We demonstrate that the dephasing, measured as the Ramsey fringe contrast, can be reversed by stimulating a coherence echo with a pi-pulse between the two pi/2 pulses, in analogy to the photon echo. We also demonstrate that the failure of the echo for certain trap parameters is due to dyn...

  7. First HF radar measurements of summer mesopause echoes at SURA

    Directory of Open Access Journals (Sweden)

    A. N. Karashtin

    Full Text Available HF sounding of the mesosphere was first carried out at SURA in summer 1994 at frequencies in the range 8–9 MHz using one of the sub-arrays of the SURA heating facility. The observations had a range resolution of 3 km. Almost all measurements indicated the presence of strong radar returns from altitudes between 83 and 90 km with features very similar to VHF measurements of mesopause summer echoes at mid-latitudes and polar mesopause summer echoes. In contrast to VHF observations, HF mesopause echoes are almost always present.

  8. Ultrasound attenuation estimation using backscattered echoes from multiple sources

    OpenAIRE

    Bigelow, Timothy A.

    2008-01-01

    The objective of this study was to devise an algorithm that can accurately estimate the attenuation along the propagation path (i.e., the total attenuation) from backscattered echoes. It was shown that the downshift in the center frequency of the backscattered ultrasound echoes compared to echoes obtained in a water bath was calculated to have the form Δf=mfo+b after normalizing with respect to the source bandwidth where m depends on the correlation length, b depends on the total attenuation,...

  9. Multiple-echo diffusion tensor acquisition technique (MEDITATE) on a 3T clinical scanner.

    Science.gov (United States)

    Baete, Steven H; Cho, Gene; Sigmund, Eric E

    2013-11-01

    This article describes the concepts and implementation of an MRI method, the multiple-echo diffusion tensor acquisition technique (MEDITATE), which is capable of acquiring apparent diffusion tensor maps in two scans on a 3T clinical scanner. In each MEDITATE scan, a set of RF pulses generates multiple echoes, the amplitudes of which are diffusion weighted in both magnitude and direction by a pattern of diffusion gradients. As a result, two scans acquired with different diffusion weighting strengths suffice for accurate estimation of diffusion tensor imaging (DTI) parameters. The MEDITATE variation presented here expands previous MEDITATE approaches to adapt to the clinical scanner platform, such as exploiting longitudinal magnetization storage to reduce T2 weighting. Fully segmented multi-shot Cartesian encoding is used for image encoding. MEDITATE was tested on isotropic (agar gel), anisotropic diffusion phantoms (asparagus) and in vivo skeletal muscle in healthy volunteers with cardiac gating. Comparisons of accuracy were performed with standard twice-refocused spin echo (TRSE) DTI in each case and good quantitative agreement was found between diffusion eigenvalues, mean diffusivity and fractional anisotropy derived from TRSE DTI and from the MEDITATE sequence. Orientation patterns were correctly reproduced in both isotropic and anisotropic phantoms, and approximately for in vivo imaging. This illustrates that the MEDITATE method of compressed diffusion encoding is feasible on the clinical scanner platform. With future development and employment of appropriate view-sharing image encoding, this technique may be used in clinical applications requiring time-sensitive acquisition of DTI parameters such as dynamical DTI in muscle. Copyright © 2013 John Wiley & Sons, Ltd.

  10. Comparison of GRASE and turbo spin echo sequences in brain MR imaging

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Jong Youk; Lee, Young Joon; Eun, Choong Ki; Jeon, Young Seup; Kim, Ig Dae; Cha, Seong Sook [Inje Univ., Pusan (Korea, Republic of). Coll. of Medicine

    1998-04-01

    The purpose of this study was to evaluate the utility of GRASE images of the brain, which combine gradient echo-EPI and turbo spin echo, and to compare the results with those of the turbo spin echo (TSE) technique. We analyzed and compared brain MR images obtained in 25 patients between October, 1996 and January, 1997, both TSE and GRASE techniques. Diagnosis was normal (n=5), infarct or ischemia (n=10), intracerebral hemorrhage (n=6), and neoplasm (n=4). TSE and GRASE MR images were obtained using a 1.5 T Gyroscan ACS-NT (Philips, Netherlands). For qualitative assessment, overall image quality, discrimination between cortical gray-white matter and basal ganglia-white matter, lesion conspicuity, and MR artifact were evaluated using a subjective grading system ranging from 1 to 5 (1=TSE better than GRASE, 5=GRASE better than TSE). For quantitative assessment, signal-to-noise ratios (SNRs) were calculated for cortical gray matter, white matter, basal ganglia, and lesions, and contrast-to-noise ratios (CNRs) were calculated for cortical gray-white matter, basal ganglia-white matter and lesions-white matter. We measured image acquisition time and RF specific absorption rate (SAR) on TSE and GRASE. With regard to MR artifact, GRASE is more sensitive than TSE, but as regards image quality and lesion distinction, the two modalities show no distinct difference. Since GRASE is superior to TSE for the detection of hemosiderin, and image acquisition time is three times shorter using GRASE, GRASE might usefully be applied during the evaluation by MR imaging of certain brain conditions. (author). 17 refs., 3 tabs., 5 figs.

  11. Variability at Multiple Scales: Using an Array of Current and Pressure Sensor Equipped Inverted Echo Sounders to Measure the Ocean

    Science.gov (United States)

    2016-11-29

    and listens for each ping’s first echo. In typical applications, twenty-four pings are emitted each hour in bursts of 4 at ten-minute interval with 6...Moored instruments from the FLEAT array comprising: 4 CPIESs (green circles , WHOI/this project), which fall under repeated glider tracks (D. Rudnick...which run meridionally from Palau towards the north (tracks not shown); 3 PlESs (blue circles , University of Rhode Island/MIT, T. Peacock); 2 rapid

  12. Rapid Formation of Cerebral Microbleeds after Carotid Artery Stenting

    Directory of Open Access Journals (Sweden)

    Kousuke Kakumoto

    2012-03-01

    Full Text Available Background: Recent studies reported that cerebral microbleeds (CMBs, i.e. small areas of signal loss on T2*-weighted gradient-echo (GE imaging, could develop rapidly after acute ischemic stroke. We hypothesized that CMBs rapidly emerge after carotid artery stenting (CAS. Objective: We investigated the frequency of and predisposing factors for CMBs after CAS. Methods: We retrospectively examined MRI before and after CAS in 88 consecutive patients (average age: 71.7 ± 7.2 years, average rates of carotid stenosis: 72.6 ± 12.8% who underwent CAS for carotid artery stenosis between March 1, 2009, and September 30, 2010. We defined new CMBs as signal losses that newly appeared on the follow-up GE. We examined the association of new CMBs with demographics, risk factors, and baseline MBs. Results: Among 88 patients, 18 (20.5% had CMBs initially, and 7 (8.0% developed new CMBs right after CAS. New CMBs appeared on the same side of CAS in all of the 7 patients. New CMBs appeared significantly more frequently in the CMB-positive group than in the CMB-negative one (22% vs. 4%, p = 0.03 on the pre-CAS MRI. Multivariate analysis also revealed that the presence of CMBs before CAS was an independent predictor of new development of CMBs after CAS (odds ratio: 8.09, 95% confidence interval: 1.39–47.1. Conclusion: CMBs can develop rapidly after CAS, especially in patients with pre-existing CMBs. Since the existence of CMBs prior to CAS suggests a latent vascular damage which is vulnerable to hemodynamic stress following CAS, particular attention should be paid to the prevention of intracerebral hemorrhage due to hyperperfusion after CAS.

  13. Echoes from Angicos: freirean Themes and the today's pedagogy

    National Research Council Canada - National Science Library

    Danilo R Streck

    2014-01-01

    ...) dialogue as a methodological principle; e) the liberation of pedagogy. The "echoes" of Angicos help to articulate different positions, not renouncing to work in the frontiers of different fields of knowledge and epistemological perspectives...

  14. Acoustic Proximity Ranging in the Presence of Secondary Echoes

    National Research Council Canada - National Science Library

    Li, Xi; Wu, Renbiao; Rasmi, Srihari; Li, Jian; Cattafesta, III, Louis N; Sheplak, Mark

    2003-01-01

    .... However, in the presence of strong and closely spaced secondary echoes, the aforementioned matched filter based algorithms tend to fail or suffer from severe performance degradations due to their poor resolutions...

  15. [Stress echo and valvular heart disease].

    Science.gov (United States)

    Monin, J L

    2005-06-01

    Stress echo has already been validated in some forms of valvular heart disease, especially in calcific aortic stenosis with low cardiac output and dynamic mitral regurgitation (MR) of valvular heart disease. Stress Doppler haemodynamics is a term used to differentiate these new indications from that of segmental wall analysis of the left atrium in ischaemic heart disease. In calcific aortic stenosis with low output, the haemodynamics with low dose dobutamine allows assessment of the real severity of the aortic stenosis and identification of the rare cases with mild stenosis: the principal indication remains the assessment of operative risk and long-term prognosis by the study of left ventricular contractile reserve. In cases of ischaemic left ventricular systolic dysfunction, the presence of mild mitral regurgitation (regurgitant surface area >20 mm2 at rest) is a poor prognostic factor. The dynamic character of mitral regurgitation is related to left ventricular remodelling which leads to deformation of the valvular apparatus (mitral tenting). Dynamic mitral regurgitation (regurgitant orifice area >13 mm2 on exercise) is a powerful prognostic factor, the role of which has recently been demonstrated in the genesis of acute pulmonary oedema. the other indications of stress haemodynamics are under validation, mainly the assessment of exercise capacity and valvular compliance in mitral stenosis or asymptomatic aortic stenosis.

  16. Geomagnetic control of polar mesosphere summer echoes

    Directory of Open Access Journals (Sweden)

    J. Bremer

    2000-02-01

    Full Text Available Using observations with the ALOMAR SOUSY radar near Andenes (69.3°N, 16.0°E from 1994 until 1997 polar mesosphere summer echoes (PMSE have been investigated in dependence on geomagnetic K indices derived at the Auroral Observatory Tromsø (69.66°N, 18.94°E. During night-time and morning hours a significant correlation between the signal-to-noise ratio (SNR of the radar results and the geomagnetic K indices could be detected with a maximum correlation near midnight. The correlation becomes markedly smaller in the afternoon and early evening hours with a minimum near 17 UT. This diurnal variation is in reasonable agreement with riometer absorption at Ivalo (68.55°N, 27.28°E and can be explained by the diurnal variation of ionization due to precipitating high energetic particles. Therefore, a part of the diurnal PMSE variation is caused by this particle precipitation. The variability of the solar EUV variation, however, has no significant influence on the PMSE during the observation period.Keywords: Ionosphere (auroral ionosphere - Magnetospheric physics (energetic particles, precipitating - Radio science (remote sensing

  17. Geomagnetic control of polar mesosphere summer echoes

    Directory of Open Access Journals (Sweden)

    J. Bremer

    Full Text Available Using observations with the ALOMAR SOUSY radar near Andenes (69.3°N, 16.0°E from 1994 until 1997 polar mesosphere summer echoes (PMSE have been investigated in dependence on geomagnetic K indices derived at the Auroral Observatory Tromsø (69.66°N, 18.94°E. During night-time and morning hours a significant correlation between the signal-to-noise ratio (SNR of the radar results and the geomagnetic K indices could be detected with a maximum correlation near midnight. The correlation becomes markedly smaller in the afternoon and early evening hours with a minimum near 17 UT. This diurnal variation is in reasonable agreement with riometer absorption at Ivalo (68.55°N, 27.28°E and can be explained by the diurnal variation of ionization due to precipitating high energetic particles. Therefore, a part of the diurnal PMSE variation is caused by this particle precipitation. The variability of the solar EUV variation, however, has no significant influence on the PMSE during the observation period.

    Keywords: Ionosphere (auroral ionosphere - Magnetospheric physics (energetic particles, precipitating - Radio science (remote sensing

  18. Digital Signal Processing Methods for Ultrasonic Echoes.

    Science.gov (United States)

    Sinding, Kyle; Drapaca, Corina; Tittmann, Bernhard

    2016-04-28

    Digital signal processing has become an important component of data analysis needed in industrial applications. In particular, for ultrasonic thickness measurements the signal to noise ratio plays a major role in the accurate calculation of the arrival time. For this application a band pass filter is not sufficient since the noise level cannot be significantly decreased such that a reliable thickness measurement can be performed. This paper demonstrates the abilities of two regularization methods - total variation and Tikhonov - to filter acoustic and ultrasonic signals. Both of these methods are compared to a frequency based filtering for digitally produced signals as well as signals produced by ultrasonic transducers. This paper demonstrates the ability of the total variation and Tikhonov filters to accurately recover signals from noisy acoustic signals faster than a band pass filter. Furthermore, the total variation filter has been shown to reduce the noise of a signal significantly for signals with clear ultrasonic echoes. Signal to noise ratios have been increased over 400% by using a simple parameter optimization. While frequency based filtering is efficient for specific applications, this paper shows that the reduction of noise in ultrasonic systems can be much more efficient with regularization methods.

  19. High Gradient Accelerator Research

    Energy Technology Data Exchange (ETDEWEB)

    Temkin, Richard [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States). Dept. of Physics. Plasma Science and Fusion Center

    2016-07-12

    The goal of the MIT program of research on high gradient acceleration is the development of advanced acceleration concepts that lead to a practical and affordable next generation linear collider at the TeV energy level. Other applications, which are more near-term, include accelerators for materials processing; medicine; defense; mining; security; and inspection. The specific goals of the MIT program are: • Pioneering theoretical research on advanced structures for high gradient acceleration, including photonic structures and metamaterial structures; evaluation of the wakefields in these advanced structures • Experimental research to demonstrate the properties of advanced structures both in low-power microwave cold test and high-power, high-gradient test at megawatt power levels • Experimental research on microwave breakdown at high gradient including studies of breakdown phenomena induced by RF electric fields and RF magnetic fields; development of new diagnostics of the breakdown process • Theoretical research on the physics and engineering features of RF vacuum breakdown • Maintaining and improving the Haimson / MIT 17 GHz accelerator, the highest frequency operational accelerator in the world, a unique facility for accelerator research • Providing the Haimson / MIT 17 GHz accelerator facility as a facility for outside users • Active participation in the US DOE program of High Gradient Collaboration, including joint work with SLAC and with Los Alamos National Laboratory; participation of MIT students in research at the national laboratories • Training the next generation of Ph. D. students in the field of accelerator physics.

  20. Preconditioned Stochastic Gradient Descent.

    Science.gov (United States)

    Li, Xi-Lin

    2017-03-09

    Stochastic gradient descent (SGD) still is the workhorse for many practical problems. However, it converges slow, and can be difficult to tune. It is possible to precondition SGD to accelerate its convergence remarkably. But many attempts in this direction either aim at solving specialized problems, or result in significantly more complicated methods than SGD. This paper proposes a new method to adaptively estimate a preconditioner, such that the amplitudes of perturbations of preconditioned stochastic gradient match that of the perturbations of parameters to be optimized in a way comparable to Newton method for deterministic optimization. Unlike the preconditioners based on secant equation fitting as done in deterministic quasi-Newton methods, which assume positive definite Hessian and approximate its inverse, the new preconditioner works equally well for both convex and nonconvex optimizations with exact or noisy gradients. When stochastic gradient is used, it can naturally damp the gradient noise to stabilize SGD. Efficient preconditioner estimation methods are developed, and with reasonable simplifications, they are applicable to large-scale problems. Experimental results demonstrate that equipped with the new preconditioner, without any tuning effort, preconditioned SGD can efficiently solve many challenging problems like the training of a deep neural network or a recurrent neural network requiring extremely long-term memories.

  1. Non-magnetic aspect sensitive auroral echoes from the lower E region observed at 50 MHz

    Directory of Open Access Journals (Sweden)

    R. Rüster

    1999-10-01

    Full Text Available Backscatter from E-region irregularities was observed at aspect angles close to 90° (almost parallel to the direction of the magnetic field using the ALOMAR SOUSY radar at Andoya/Norway. Strong electric fields and increased E-region electron temperatures simultaneously measured with the incoherent scatter facility EISCAT proved that the Farley-Buneman plasma instability was excited. In addition, strong particle precipitation was present as inferred from EISCAT electron densities indicating that the gradient drift instability may have been active, too. Backscatter at such large aspect angles was not expected and has not been observed before. The characteristics of the observed echoes, however, are in many aspects completely different from usual auroral radar results: the Doppler velocities are only of the order of 10 m/s, the half-width of the spectra is around 5 m/s, the echoes originate at altitudes well below 100 km, and they seem to be not aspect-sensitive with respect to the magnetic field direction. We, therefore, conclude that the corresponding irregularities are not caused by the mentioned instabilities and that other mechanism have to be invoked.Key words. Ionosphere (plasma waves and instabilities; ionosphere irregularities; particle precipitaion · Meteorology and atmospheric dynamics (middle atmosphere dynamics

  2. Observation of Gravitationally Induced Vertical Striation of Polarized Ultracold Neutrons by Spin-Echo Spectroscopy.

    Science.gov (United States)

    Afach, S; Ayres, N J; Ban, G; Bison, G; Bodek, K; Chowdhuri, Z; Daum, M; Fertl, M; Franke, B; Griffith, W C; Grujić, Z D; Harris, P G; Heil, W; Hélaine, V; Kasprzak, M; Kermaidic, Y; Kirch, K; Knowles, P; Koch, H-C; Komposch, S; Kozela, A; Krempel, J; Lauss, B; Lefort, T; Lemière, Y; Mtchedlishvili, A; Musgrave, M; Naviliat-Cuncic, O; Pendlebury, J M; Piegsa, F M; Pignol, G; Plonka-Spehr, C; Prashanth, P N; Quéméner, G; Rawlik, M; Rebreyend, D; Ries, D; Roccia, S; Rozpedzik, D; Schmidt-Wellenburg, P; Severijns, N; Thorne, J A; Weis, A; Wursten, E; Wyszynski, G; Zejma, J; Zenner, J; Zsigmond, G

    2015-10-16

    We describe a spin-echo method for ultracold neutrons (UCNs) confined in a precession chamber and exposed to a |B0|=1  μT magnetic field. We have demonstrated that the analysis of UCN spin-echo resonance signals in combination with knowledge of the ambient magnetic field provides an excellent method by which to reconstruct the energy spectrum of a confined ensemble of neutrons. The method takes advantage of the relative dephasing of spins arising from a gravitationally induced striation of stored UCNs of different energies, and also permits an improved determination of the vertical magnetic-field gradient with an exceptional accuracy of 1.1  pT/cm. This novel combination of a well-known nuclear resonance method and gravitationally induced vertical striation is unique in the realm of nuclear and particle physics and should prove to be invaluable for the assessment of systematic effects in precision experiments such as searches for an electric dipole moment of the neutron or the measurement of the neutron lifetime.

  3. Water Pollution Search Results Help - TRI | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  4. Water Pollution Search Criteria Help | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  5. Water Quality Indicators Data Review | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  6. How New National Air Data System Affects ECHO Data ...

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  7. Water Pollution Search Results Help - DMR | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  8. Ohio River Basin.pdf | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  9. Puget Sound Watershed.pdf | ECHO | US EPA

    Science.gov (United States)

    ECHO, Enforcement and Compliance History Online, provides compliance and enforcement information for approximately 800,000 EPA-regulated facilities nationwide. ECHO includes permit, inspection, violation, enforcement action, and penalty information about facilities regulated under the Clean Air Act (CAA) Stationary Source Program, Clean Water Act (CWA) National Pollutant Elimination Discharge System (NPDES), and/or Resource Conservation and Recovery Act (RCRA). Information also is provided on surrounding demographics when available.

  10. Phase incremented echo train acquisition applied to magnetic resonance pore imaging

    Science.gov (United States)

    Hertel, S. A.; Galvosas, P.

    2017-02-01

    Efficient phase cycling schemes remain a challenge for NMR techniques if the pulse sequences involve a large number of rf-pulses. Especially complex is the Carr Purcell Meiboom Gill (CPMG) pulse sequence where the number of rf-pulses can range from hundreds to several thousands. Our recent implementation of Magnetic Resonance Pore Imaging (MRPI) is based on a CPMG rf-pulse sequence in order to refocus the effect of internal gradients inherent in porous media. While the spin dynamics for spin- 1 / 2 systems in CPMG like experiments are well understood it is still not straight forward to separate the desired pathway from the spectrum of unwanted coherence pathways. In this contribution we apply Phase Incremented Echo Train Acquisition (PIETA) to MRPI. We show how PIETA offers a convenient way to implement a working phase cycling scheme and how it allows one to gain deeper insights into the amplitudes of undesired pathways.

  11. Significance-aware filtering for nonlinear acoustic echo cancellation

    Science.gov (United States)

    Hofmann, Christian; Huemmer, Christian; Guenther, Michael; Kellermann, Walter

    2016-12-01

    This article summarizes and extends the recently proposed concept of Significance-Aware (SA) filtering for nonlinear acoustic echo cancellation. The core idea of SA filtering is to decompose the estimation of the nonlinear echo path into beneficially interacting subsystems, each of which can be adapted with high computational efficiency. The previously proposed SA Hammerstein Group Models (SA-HGMs) decompose the nonlinear acoustic echo path into a direct-path part, modeled by a Hammerstein Group Model (HGM) and a complementary part, modeled by a very efficient Hammerstein model. In this article, we furthermore propose a novel Equalization-based SA (ESA) structure, where the echo path is equalized by a linear filter to allow for an estimation of the loudspeaker nonlinearities by very small and efficient models. Additionally, we provide a novel in-depth analysis of the computational complexity of the previously proposed SA and the novel ESA filters and compare both SA filtering approaches to each other, to adaptive HGMs, and to linear filters, where fast partitioned-block frequency-domain realizations of the competing filter structures are considered. Finally, the echo reduction performance of the proposed SA filtering approaches is verified using real recordings from a commercially available smartphone. Beyond the scope of previous publications on SA-HGMs, the ability of the SA filters to generalize for double-talk situations is explicitly considered as well. The low complexity as well as the good echo reduction performance of both SA filters illustrate the potential of SA filtering in practice.

  12. Uniform gradient expansions

    Directory of Open Access Journals (Sweden)

    Massimo Giovannini

    2015-06-01

    Full Text Available Cosmological singularities are often discussed by means of a gradient expansion that can also describe, during a quasi-de Sitter phase, the progressive suppression of curvature inhomogeneities. While the inflationary event horizon is being formed the two mentioned regimes coexist and a uniform expansion can be conceived and applied to the evolution of spatial gradients across the protoinflationary boundary. It is argued that conventional arguments addressing the preinflationary initial conditions are necessary but generally not sufficient to guarantee a homogeneous onset of the conventional inflationary stage.

  13. Correction for Eddy Current-Induced Echo-Shifting Effect in Partial-Fourier Diffusion Tensor Imaging.

    Science.gov (United States)

    Truong, Trong-Kha; Song, Allen W; Chen, Nan-Kuei

    2015-01-01

    In most diffusion tensor imaging (DTI) studies, images are acquired with either a partial-Fourier or a parallel partial-Fourier echo-planar imaging (EPI) sequence, in order to shorten the echo time and increase the signal-to-noise ratio (SNR). However, eddy currents induced by the diffusion-sensitizing gradients can often lead to a shift of the echo in k-space, resulting in three distinct types of artifacts in partial-Fourier DTI. Here, we present an improved DTI acquisition and reconstruction scheme, capable of generating high-quality and high-SNR DTI data without eddy current-induced artifacts. This new scheme consists of three components, respectively, addressing the three distinct types of artifacts. First, a k-space energy-anchored DTI sequence is designed to recover eddy current-induced signal loss (i.e., Type 1 artifact). Second, a multischeme partial-Fourier reconstruction is used to eliminate artificial signal elevation (i.e., Type 2 artifact) associated with the conventional partial-Fourier reconstruction. Third, a signal intensity correction is applied to remove artificial signal modulations due to eddy current-induced erroneous T2(∗) -weighting (i.e., Type 3 artifact). These systematic improvements will greatly increase the consistency and accuracy of DTI measurements, expanding the utility of DTI in translational applications where quantitative robustness is much needed.

  14. Correction for Eddy Current-Induced Echo-Shifting Effect in Partial-Fourier Diffusion Tensor Imaging

    Directory of Open Access Journals (Sweden)

    Trong-Kha Truong

    2015-01-01

    Full Text Available In most diffusion tensor imaging (DTI studies, images are acquired with either a partial-Fourier or a parallel partial-Fourier echo-planar imaging (EPI sequence, in order to shorten the echo time and increase the signal-to-noise ratio (SNR. However, eddy currents induced by the diffusion-sensitizing gradients can often lead to a shift of the echo in k-space, resulting in three distinct types of artifacts in partial-Fourier DTI. Here, we present an improved DTI acquisition and reconstruction scheme, capable of generating high-quality and high-SNR DTI data without eddy current-induced artifacts. This new scheme consists of three components, respectively, addressing the three distinct types of artifacts. First, a k-space energy-anchored DTI sequence is designed to recover eddy current-induced signal loss (i.e., Type 1 artifact. Second, a multischeme partial-Fourier reconstruction is used to eliminate artificial signal elevation (i.e., Type 2 artifact associated with the conventional partial-Fourier reconstruction. Third, a signal intensity correction is applied to remove artificial signal modulations due to eddy current-induced erroneous T2*-weighting (i.e., Type 3 artifact. These systematic improvements will greatly increase the consistency and accuracy of DTI measurements, expanding the utility of DTI in translational applications where quantitative robustness is much needed.

  15. Measuring light echoes in NGC 4051

    Science.gov (United States)

    Turner, T. J.; Miller, L.; Reeves, J. N.; Braito, V.

    2017-06-01

    Five archived X-ray observations of NGC 4051, taken using the NuSTAR observatory, have been analysed, revealing lags between flux variations in bands covering a wide range of X-ray photon energy. In all pairs of bands compared, the harder band consistently lags the softer band by at least 1000 s, at temporal frequencies ˜5 × 10-5 Hz. In addition, soft-band lags up to 400 s are measured at frequencies ˜2 × 10-4 Hz. Light echoes from an excess of soft band emission in the inner accretion disc cannot explain the lags in these data, as they are seen in cross-correlations with energy bands where the softer band is expected to have no contribution from reflection. The basic properties of the time delays have been parametrized by fitting a top-hat response function that varies with photon energy, taking fully into account the covariance between measured time lag values. The low-frequency hard-band lags and the transition to soft-band lags are consistent with time lags arising as reverberation delays from circumnuclear scattering of X-rays, although greater model complexity is required to explain the entire spectrum of lags. The scattered fraction increases with increasing photon energy as expected, and the scattered fraction is high, indicating the reprocessor to have a global covering fraction ˜50 per cent around the continuum source. Circumnuclear material, possibly associated with a disc wind at a few hundred gravitational radii from the primary X-ray source, may provide suitable reprocessing.

  16. The impact of spin coupling signal loss on fat content characterization in multi-echo acquisitions with different echo spacing.

    Science.gov (United States)

    Nikiforaki, K; Manikis, G C; Boursianis, T; Marias, K; Karantanas, A; Maris, T G

    2017-05-01

    This study aimed to assess the effect of echo spacing in transverse magnetization (T2) signal decay of gel and fat (oil) samples. Additionally, we assess the feasibility of using spin coupling as a determinant of fat content. Phantoms of known T2 values, as well as vegetable oil phantoms, were scanned at 1.5T scanner with a multi echo FSE sequence of variable echo spacing above and below the empirical threshold of 20ms for echo train signal modulation (6.7, 13.6, 26.8, and 40ms). T2 values were calculated from monoexponential fitting of the data. Relative signal loss between the four acquisitions of different echo spacing was calculated. Agreement in the T2 values of water gel phantom was observed in all acquisitions as opposed to fat phantom (oil) samples. Relative differences in signal intensity between two successive sequences of different echo spacing on composite fat/water regions of interest was found to be linearly correlated to fat fraction of the ROI. The sample specific degree of signal loss that was observed between different fat samples (vegetable oils) can be attributed to the composition of each sample in J coupled fat components. Hence, spin coupling may be used as a determinant of fat content. Copyright © 2016 Elsevier Inc. All rights reserved.

  17. Scan parameters and the diffusion emphasis effect in diffusion-weighted imaging using a motion-probing gradient preparation pulse.

    Science.gov (United States)

    Takahashi, Daisuke; Tanji, Hajime; Yamaki, Tomoya; Obara, Makoto; Machida, Yoshio

    2014-07-01

    Diffusion-sensitized driven equilibrium preparation (DSDE) is a gradient echo (GRE) diffusion-weighted imaging (DWI) sequence that employs a motion-probing gradient (MPG) preparation pulse and phase cycling. In DSDE, several scan parameters of the MPG preparation pulse and the GRE sequence affect diffusion sensitivity. Our investigation of the relationship between these scan parameters and the diffusion emphasis effect revealed the importance of "prep.TE" in the MPG preparation pulse and "TFE shot interval" in the gradient echo sequence. Appropriate choice of these parameters allows DSDE to provide a similar DWI to that of conventional single-shot SEEPI DWI. We therefore concluded DSDE to be a useful DWI method.

  18. Probabilistic Multileave Gradient Descent

    NARCIS (Netherlands)

    Oosterhuis, H.; Schuth, A.; de Rijke, M.; Ferro, N.; Crestani, F.; Moens, M.-F.; Mothe, J.; Silvestri, F.; Di Nunzio, G.M.; Hauff, C.; Silvello, G.

    2016-01-01

    Online learning to rank methods aim to optimize ranking models based on user interactions. The dueling bandit gradient descent (DBGD) algorithm is able to effectively optimize linear ranking models solely from user interactions. We propose an extension of DBGD, called probabilistic multileave

  19. Project ECHO (Extension for Community Healthcare Outcomes): A new model for educating primary care providers about treatment of substance use disorders

    Science.gov (United States)

    Komaromy, Miriam; Duhigg, Dan; Metcalf, Adam; Carlson, Cristina; Kalishman, Summers; Hayes, Leslie; Burke, Tom; Thornton, Karla; Arora, Sanjeev

    2016-01-01

    ABSTRACT Background: Project ECHO (Extension for Community Healthcare Outcomes) trains and mentors primary care providers (PCPs) in the care of patients with complex conditions. ECHO is a distance education model that connects specialists with numerous PCPs via simultaneous video link for the purpose of facilitating case-based learning. This article describes a teleECHO clinic based at the University of New Mexico Health Sciences Center that is focused on treatment of substance use disorders (SUDs) and behavioral health disorders. Methods: Since 2005, specialists in treatment of SUDs and behavioral health disorders at Project ECHO have offered a weekly 2-hour Integrated Addictions and Psychiatry (IAP) TeleECHO Clinic focused on supporting PCP evaluation and treatment of SUDs and behavioral health disorders. We tabulate the number of teleECHO clinic sessions, participants, and CME/CEU (continuing medical education/continuing education unit) credits provided annually. This teleECHO clinic has also been used to recruit physicians to participate in DATA-2000 buprenorphine waiver trainings. Using a database of the practice location of physicians who received the buprenorphine waiver since 2002, the number of waivered physicians per capita in US states was calculated. The increase in waivered physicians practicing in underserved areas in New Mexico was evaluated and compared with the rest of the United States. Results: Since 2008, approximately 950 patient cases have been presented during the teleECHO clinic, and more than 9000 hours of CME/CEU have been awarded. Opioids are the substances discussed most commonly (31%), followed by alcohol (21%) and cannabis (12%). New Mexico is near the top among US states in DATA-2000 buprenorphine-waivered physicians per capita, and it has had much more rapid growth in waivered physicians practicing in traditionally underserved areas compared with the rest of the United States since the initiation of the teleECHO clinic focused on

  20. In situ pulsed-field gradient NMR determination of the size of oil bodies in vegetable seeds. Analysis of the effect of the gradient pulse length.

    Science.gov (United States)

    Guillermo, Armel; Bardet, Michel

    2007-09-01

    We report a pulsed-field gradient NMR study of the size of the oil bodies in lettuce seeds. The pulsed-field gradient spin-echo method (PFGSE) was applied to measure the self-diffusion coefficient of triacylglycerol molecules (TAG) inside the oil bodies. The confined nature of TAG diffusion is used to determine the size dispersion of the oil bodies. At long diffusion time, we measure a spin-echo attenuation that is related to the form factor of the confining volumes in the reciprocal q space, where q is proportional to the product of the gradient intensity and the length of the pulse gradient. Specific care was taken in analyzing the influence of the gradient pulse length delta on the shape of the PFGSE decay in order to construct the function corresponding to the short gradient pulse approximation (SGP). The SGP model gives an analytical framework for the PFGSE signal that enables the size distribution of the oil bodies to be determined. The SGP function was unambiguously obtained by varying the gradient pulse length delta in order to linearly extrapolate at delta = 0 the SGP limit. In this work, we also consider the Gaussian phase distribution (GPD) assumption that is often used to analyze confined diffusion experiments. Although the GPD assumption is known to be inaccurate in predicting the fine structure of the PFGSE function in q space, we point out that in the present case it can be used to take into account the finite value of delta. A log-normal distribution of the radius values was assumed in simulating the PFGNMR experiments since this type of distribution is observed in vegetable seeds by transmission electronic microscopy. From a practical and experimental standpoint, the NMR measurements reported here require no specific treatment of the seeds and the size of oil bodies is determined "in situ" on seeds poured into the NMR tube.

  1. Parotid fat contents in healthy subjects evaluated with iterative decomposition with echo asymmetry and least squares fat-water separation.

    Science.gov (United States)

    Chang, Hing-Chiu; Juan, Chun-Jung; Chiu, Hui-Chu; Liu, Yi-Jui; Cheng, Cheng-Chieh; Chiu, Su-Chin; Chen, Cheng-Yu; Huang, Guo-Shu; Chung, Hsiao-Wen

    2013-06-01

    To evaluate the effectiveness of three fat measurement methods for parotid glands in healthy subjects, with or without metallic dental implants. The institutional review board approved this study, with informed consent obtained from 114 volunteers undergoing magnetic resonance (MR) imaging at 1.5 T. Fat-saturated (FS) and non-fat-saturated (NFS) fast spin-echo T1-weighted imaging (T1 method), FS and NFS T2-weighted periodically rotated overlapping parallel lines with enhanced reconstruction fast spin-echo imaging (T2 method), and gradient-echo imaging with fat-water separation using iterative decomposition with echo asymmetry and least squares (IDEAL) method were used to derive parotid fat contents. Two raters examined the homogeneity of fat saturation to determine whether parotid fat quantification was successful, with the success rate in the 114 subjects recorded for each protocol. In subjects whose fat quantification was successful with all three imaging methods, linear regression was used to analyze the correlation between any pair of the three parotid fat content measurement methods. Success rates in parotid fat measurements by using T1, T2, and IDEAL methods were 87.7% (100 of 114), 87.7% (100 of 114), and 100% (114 of 114), respectively. The means of measured parotid fat contents revealed significant differences (P measurement methods. The parotid fat contents measured with the three methods were significantly correlated with each other between any pair of combinations. The IDEAL method provided a high success rate for parotid fat measurements, even in subjects with metallic dental implants.

  2. Bone quantitative susceptibility mapping using a chemical species-specific R2* signal model with ultrashort and conventional echo data.

    Science.gov (United States)

    Dimov, Alexey V; Liu, Zhe; Spincemaille, Pascal; Prince, Martin R; Du, Jiang; Wang, Yi

    2017-03-05

    To develop quantitative susceptibility mapping (QSM) of bone using an ultrashort echo time (UTE) gradient echo (GRE) sequence for signal acquisition and a bone-specific effective transverse relaxation rate ( R2*) to model water-fat MR signals for field mapping. Three-dimensional radial UTE data (echo times ≥ 40 μs) was acquired on a 3 Tesla scanner and fitted with a bone-specific signal model to map the chemical species and susceptibility field. Experiments were performed ex vivo on a porcine hoof and in vivo on healthy human subjects (n = 7). For water-fat separation, a bone-specific model assigning R2* decay mostly to water was compared with the standard models that assigned the same decay for both fat and water. In the ex vivo experiment, bone QSM was correlated with CT. Compared with standard models, the bone-specific R2* method significantly reduced errors in the fat fraction within the cortical bone in all tested data sets, leading to reduced artifacts in QSM. Good correlation was found between bone CT and QSM values in the porcine hoof (R(2)  = 0.77). Bone QSM was successfully generated in all subjects. The QSM of bone is feasible using UTE with a conventional echo time GRE acquisition and a bone-specific R2* signal model. Magn Reson Med 000:000-000, 2017. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

  3. X-ray shout echoing through space

    Science.gov (United States)

    2004-01-01

    a flash of X-rays hi-res Size hi-res: 3991 Kb Credits: ESA, S. Vaughan (University of Leicester) EPIC camera shows the expanding rings caused by a flash of X-rays XMM-Newton's X-ray EPIC camera shows the expanding rings caused by a flash of X-rays scattered by dust in our Galaxy. The X-rays were produced by a powerful gamma-ray burst that took place on 3 December 2003. The slowly fading afterglow of the gamma-ray burst is at the centre of the expanding rings. Other, unrelated, X-ray sources can also be seen. The time since the gamma-ray explosion is shown in each panel in hours. At their largest size, the rings would appear in the sky about five times smaller than the full moon. a flash of X-rays hi-res Size hi-res: 2153 Kb Credits: ESA, S. Vaughan (University of Leicester) EPIC camera shows the expanding rings caused by a flash of X-rays (Please choose "hi-res" version for animation) XMM-Newton's X-ray EPIC camera shows the expanding rings caused by a flash of X-rays scattered by dust in our Galaxy. The X-rays were produced by a powerful gamma-ray burst that took place on 3 December 2003. The slowly fading afterglow of the gamma-ray burst is at the centre of the expanding rings. Other, unrelated, X-ray sources can also be seen. The time since the gamma-ray explosion is shown in each panel in seconds. At their largest size, the rings would appear in the sky about five times smaller than the full moon. This echo forms when the powerful radiation of a gamma-ray burst, coming from far away, crosses a slab of dust in our Galaxy and is scattered by it, like the beam of a lighthouse in clouds. Using the expanding rings to precisely pin-point the location of this dust, astronomers can identify places where new stars and planets are likely to form. On 3 December 2003 ESA's observatory, Integral, detected a burst of gamma rays, lasting about 30 seconds, from the direction of a distant galaxy. Within minutes of the detection, thanks to a sophisticated alert network, many

  4. A recipe for echoes from exotic compact objects

    Science.gov (United States)

    Mark, Zachary; Zimmerman, Aaron; Du, Song Ming; Chen, Yanbei

    2017-10-01

    Gravitational wave astronomy provides an unprecedented opportunity to test the nature of black holes and search for exotic, compact alternatives. Recent studies have shown that exotic compact objects (ECOs) can ring down in a manner similar to black holes, but can also produce a sequence of distinct pulses resembling the initial ringdown. These "echoes" would provide definite evidence for the existence of ECOs. In this work we study the generation of these echoes in a generic, parametrized model for the ECO, using Green's functions. We show how to reprocess radiation in the near-horizon region of a Schwarzschild black hole into the asymptotic radiation from the corresponding source in an ECO spacetime. Our methods allow us to understand the connection between distinct echoes and ringing at the resonant frequencies of the compact object. We find that the quasinormal mode ringing in the black hole spacetime plays a central role in determining the shape of the first few echoes. We use this observation to develop a simple template for echo waveforms. This template preforms well over a variety of ECO parameters, and with improvements may prove useful in the analysis of gravitational waves.

  5. Echo Meadows Project Winter Artificial Recharge.

    Energy Technology Data Exchange (ETDEWEB)

    Ziari, Fred

    2002-12-19

    This report discusses the findings of the Echo Meadows Project (BPA Project 2001-015-00). The main purpose of this project is to artificially recharge an alluvial aquifer, WITH water from Umatilla River during the winter high flow period. In turn, this recharged aquifer will discharge an increased flow of cool groundwater back to the river, thereby improving Umatilla River water quality and temperature. A considerable side benefit is that the Umatilla River should improve as a habitat for migration, spanning, and rearing of anadromous and resident fish. The scope of this project is to provide critical baseline information about the Echo Meadows and the associated reach of the Umatilla River. Key elements of information that has been gathered include: (1) Annual and seasonal groundwater levels in the aquifer with an emphasis on the irrigation season, (2) Groundwater hydraulic properties, particularly hydraulic conductivity and specific yield, and (3) Groundwater and Umatilla River water quality including temperature, nutrients and other indicator parameters. One of the major purposes of this data gathering was to develop input to a groundwater model of the area. The purpose of the model is to estimate our ability to recharge this aquifer using water that is only available outside of the irrigation season (December through the end of February) and to estimate the timing of groundwater return flow back to the river. We have found through the data collection and modeling efforts that this reach of the river had historically returned as much as 45 cubic feet per second (cfs) of water to the Umatilla River during the summer and early fall. However, this return flow was reduced to as low as 10 cfs primarily due to reduced quantities of irrigation application, gain in irrigation efficiencies and increased groundwater pumping. Our modeling indicated that it is possible to restore these critical return flows using applied water outside of the irrigation season. We further

  6. Increasing SLEDed Linac Gradient

    Energy Technology Data Exchange (ETDEWEB)

    Farkas, Zoltan D

    2001-11-08

    This note will show how to increase the SLED [1] gradient by varying Q{sub e}, the external Q of the SLED cavity, by increasing its Q{sub 0} and by increasing the compression ratio. If varying the external Q is to be effective, then the copper losses should be small so that Q{sub 0} >> Q{sub e}. Methods of varying Q{sub e} will be indicated but no experimental data will be presented. If we increase the klystron pulse width from 3.5 to 5 {micro}S and increase Q{sub 0} from the present 100000 to 300000, then the gradient increases by 19% and the beam energy increases from 50 to 60 GeV. This note will also discuss SLED operation at 11424 MHz, the NLC frequency. Without Q{sub e} switching, using SLED at 11424 MHz increases the SLAC gradient from 21 MV/m to 34 MV/m, and at the same repetition rate, uses about 1/5 of rf average power. If we also double the compression ratio, we reach 47 MV/m and over 100 GeV beam energy.

  7. Design And Simulation Of An Acoustic Echo Cancellation System For Hand-Free Telecommunication

    Directory of Open Access Journals (Sweden)

    Ein Gyin Pwint

    2015-06-01

    Full Text Available Abstract Acoustic echo cancellation is a common occurrence in todays telecommunication systems. The signal interference caused by acoustic echo is distracting to users and causes a reduction in the quality of the communication. This paper is implementing the overall system of acoustic echo cancellation system using LMS and NLMS algorithms for adaptive filter normalized cross correlation NCC algorithm double talk detector. The result of echo return loss enhancement ERLE and mean squared error MSE which show that how much the amount of echo signal cancelled and the amount of residual error signal for cancelling acoustic echo cancellation on a PC with the help of the MATLAB software.

  8. Geometry of Superluminal Light-Echo Pair Events

    Science.gov (United States)

    Nemiroff, Robert J.

    2017-01-01

    Light echoes, shadows, and ionization fronts can and do move faster than light, both in the lab and out in the cosmos. In general, though, a single observer cannot tell the speed of such echoes without distance information -- unless a very specific geometry arises: the radial component crosses c. The observer then sees this crossing location as the site where a pair of bright light echoes is created or annihilated. This pair event tells the observer that a precise speed occurs, a speed that does not scale with distance and so can potentially be leveraged to reveal geometry and distance information. A few simple scattering surface geometries are shown illuminated by a point flash, including linear and circular filaments. In practice, useful astronomical flash sources include novae and supernovae, although in theory any uniquely varying source of stellar variability could be sufficient.

  9. A computational model for biosonar echoes from foliage.

    Directory of Open Access Journals (Sweden)

    Chen Ming

    Full Text Available Since many bat species thrive in densely vegetated habitats, echoes from foliage are likely to be of prime importance to the animals' sensory ecology, be it as clutter that masks prey echoes or as sources of information about the environment. To better understand the characteristics of foliage echoes, a new model for the process that generates these signals has been developed. This model takes leaf size and orientation into account by representing the leaves as circular disks of varying diameter. The two added leaf parameters are of potential importance to the sensory ecology of bats, e.g., with respect to landmark recognition and flight guidance along vegetation contours. The full model is specified by a total of three parameters: leaf density, average leaf size, and average leaf orientation. It assumes that all leaf parameters are independently and identically distributed. Leaf positions were drawn from a uniform probability density function, sizes and orientations each from a Gaussian probability function. The model was found to reproduce the first-order amplitude statistics of measured example echoes and showed time-variant echo properties that depended on foliage parameters. Parameter estimation experiments using lasso regression have demonstrated that a single foliage parameter can be estimated with high accuracy if the other two parameters are known a priori. If only one parameter is known a priori, the other two can still be estimated, but with a reduced accuracy. Lasso regression did not support simultaneous estimation of all three parameters. Nevertheless, these results demonstrate that foliage echoes contain accessible information on foliage type and orientation that could play a role in supporting sensory tasks such as landmark identification and contour following in echolocating bats.

  10. Echo intensity of the rectus femoris in stable COPD patients

    Directory of Open Access Journals (Sweden)

    Ye X

    2017-10-01

    Full Text Available Xiong Ye,1 Mingjie Wang,2 Hui Xiao2 1College of Clinical Medicine, Shanghai University of Medicine & Health Sciences, 2Department of Respiratory Medicine, Shanghai General Hospital, Shanghai Jiaotong University, Shanghai, China Objective: The aim of this study was to investigate whether echo intensity of the rectus femoris when measured using ultrasound can distinguish muscles affected by COPD compared with healthy non-COPD affected muscles and whether the severity of ultrasonic abnormalities was associated with health-related quality of life (HRQoL. Methods: Echo intensity, areas of the rectus femoris, and the thickness of quadriceps muscles were measured using ultrasound in 50 COPD outpatients and 21 age-matched non-COPD controls. The results of the 8-Item Short-Form Health Survey and the functional assessment of chronic illness therapy fatigue scales were used to evaluate HRQoL. Results: There was a significantly higher echo intensity of the rectus femoris in all stages of COPD patients than in age-matched non-COPD subjects; the quadriceps muscle thickness and cross-sectional area of the rectus femoris significantly decreased in COPD GOLD III–IV only. Furthermore, in our stable COPD patients, echo intensity of the rectus femoris was associated with HRQoL independently. Conclusion: Quantitative ultrasound distinguishes healthy muscles from those affected by COPD grade I–IV, and quality and quantity of muscles are associated with HRQoL and forced expiratory volume in 1 second. Ultrasonic echo intensity of the rectus femoris may be a useful instrument for assessing disease severity and monitoring the changes of skeletal muscle resulting from disease progression or clinical intervention in patients with COPD. Keywords: echo intensity, ultrasound, rectus femoris, chronic obstructive pulmonary disease

  11. Functional localization in the human brain: Gradient-echo, spin-echo, and arterial spin-labeling fMRI compared with neuronavigated TMS.

    NARCIS (Netherlands)

    Diekhoff, S.; Uludag, K.; Sparing, R.; Tittgemeyer, M.; von Cramon, D.Y.; Grefkes, C.

    2010-01-01

    A spatial mismatch of up to 14 mm between optimal transcranial magnetic stimulation (TMS) site and functional magnetic resonance imaging (fMRI) signal has consistently been reported for the primary motor cortex. The underlying cause might be the effect of magnetic susceptibility around large

  12. A record "longest echo" within the Inchindown oil despository.

    Science.gov (United States)

    Cox, Trevor J; Kilpatrick, Allan

    2015-03-01

    In 2013, Guinness World Records awarded tank number 1 at the Inchindown oil despository, Ross-shire, Scotland, the record for the "longest echo" at 75 s. Guinness World Records calls it the longest echo because that was the name of the record that was broken, however, the correct name for the phenomenon measured is reverberation. This Letter has been written to document this unique acoustic space where the reverberation time is 112 s at 125 Hz, to detail the methodology for those who wish to attempt to break the record, and to discuss why the tank is so uniquely reverberant.

  13. Piston cylinder cell for high pressure ultrasonic pulse echo measurements

    Energy Technology Data Exchange (ETDEWEB)

    Kepa, M. W., E-mail: mkepa@staffmail.ed.ac.uk; Huxley, A. D. [SUPA, Centre for Science at Extreme Conditions and School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ (United Kingdom); Ridley, C. J.; Kamenev, K. V. [Centre for Science at Extreme Conditions and School of Engineering, University of Edinburgh, Edinburgh EH9 3FD (United Kingdom)

    2016-08-15

    Ultrasonic techniques such as pulse echo, vibrating reed, or resonant ultrasound spectroscopy are powerful probes not only for studying elasticity but also for investigating electronic and magnetic properties. Here, we report on the design of a high pressure ultrasonic pulse echo apparatus, based on a piston cylinder cell, with a simplified electronic setup that operates with a single coaxial cable and requires sample lengths of mm only. The design allows simultaneous measurements of ultrasonic velocities and attenuation coefficients up to a pressure of 1.5 GPa. We illustrate the performance of the cell by probing the phase diagram of a single crystal of the ferromagnetic superconductor UGe{sub 2}.

  14. Radio echo sounding data analysis of the Shackleton Ice Shelf

    Directory of Open Access Journals (Sweden)

    James A. Baskaradas

    2010-05-01

    Full Text Available In this study, our initial results are presented for the interpretation of the radio echo sounding data collected over the Shackleton Ice Shelf and adjacent ice sheet (East Antarctica during the 2003/2004 Australian-Italian expedition. The Shackleton Ice Shelf is one of the larger ice shelves of the East Antarctic Ice Sheet. The radar survey provided data relating to ice thickness and bed morphology of the outlet glaciers, and thickness of their floating portions. The glacier grounding lines were determined by assessment of the basal echo characters. The information derived is compared with data from the BEDMAP database and from other sources.

  15. Logical Operation of Set Intersection for Images in Optical Echo Holography

    Science.gov (United States)

    Sakhbieva, A. R.; Nefed'ev, L. A.; Garnaeva, G. I.

    2017-07-01

    We use a stimulated echo hologram to consider performing logical operations on sets represented in the form of images. We show that a stimulated echo hologram can be used to perform the logical operation of set intersection.

  16. Pre-IceBridge MCoRDS L1B Geolocated Radar Echo Strength Profiles

    Data.gov (United States)

    National Aeronautics and Space Administration — The Pre-IceBridge MCoRDS L1B Geolocated Radar Echo Strength Profiles (BRMCR1B) data set contains Arctic and Antarctic radio echo-sounding measurements taken from the...

  17. Numerical experiment with modelled return echo of a satellite

    Indian Academy of Sciences (India)

    Abstract. We have simulated the return echo of a satellite altimeter from a rough ocean surface using an analytical formula and have studied its sensitivity with respect to various oceanic and altimeter parameters. Our numerical expcriment shows that for normally observed significant wave heights (SWFI) the effect of ...

  18. Echo structures and Target Strength modelling for a synthetic submarine

    NARCIS (Netherlands)

    Schippers, P.; Beerens, S.P.

    2007-01-01

    Since the early nineties, performance modelling of active sonars has been developed at TNO in the ALMOST model, including propagation and sonar processing, based on point targets of given Target Strength. Recently, the modelling was extended with a computation module for target echo structure,

  19. Long-term changes of (polar) mesosphere summer echoes

    Science.gov (United States)

    Bremer, J.; Hoffmann, P.; Latteck, R.; Singer, W.; Zecha, M.

    2009-10-01

    Strong VHF radar echoes have been observed not only during summer months at polar latitudes (polar mesosphere summer echoes, PMSE) but also at middle latitudes (mesosphere summer echoes, MSE). These echoes are closely connected with small ice particles, thus containing information about mesospheric temperature and water vapour content. But the (P)MSE also depend on the ionisation due to solar wave radiation and precipitating high energetic particles. Observations with VHF radars at Andenes (69.3°N; 16.0°E) since 1994 and at Kühlungsborn (54.6°N; 11.8°E) since 1998 are used for investigations of the solar and geomagnetic control of the (P)MSE as well as of possible long-term changes. The (P)MSE are positively correlated with the solar Lyman [alpha] radiation and the geomagnetic activity and have slightly positive trends. Due to the limited measuring period, the significance levels of the detected (P)MSE trends are small. Positive trends in noctilucent clouds (NLC) and polar mesospheric clouds (PMC) are in general agreement with (P)MSE trends.

  20. A simple prescan calibration procedure for Ultrashort echo time imaging

    Czech Academy of Sciences Publication Activity Database

    Latta, P.; Starčuk jr., Zenon; Gruwel, M.; Tománek, B.

    2016-01-01

    Roč. 29, S1 (2016), S42 E-ISSN 1352-8661. [ESMRMB 2016 Congress. 29.09.2016-01.10.2016, Vienna] R&D Projects: GA ČR(CZ) GA15-12607S Institutional support: RVO:68081731 Keywords : ultrashort echo time * calibration * prescan procedure Subject RIV: FS - Medical Facilities ; Equipment

  1. Inserting digital watermark by method on delaying echo

    Directory of Open Access Journals (Sweden)

    Vitaliy Grigorievich Ivanenko

    2016-03-01

    Full Text Available The questions of the fight against piracy in media, using digital watermarks have considered. Main requirements have been formulated, which integration method have to satisfy. Method of inserting digital watermark, founded on delay echo. Principal characteristics of applications of chosen method have been listed.

  2. Infrasound - the cause of strong Polar Mesosphere Winter Echoes?

    Directory of Open Access Journals (Sweden)

    S. Kirkwood

    2006-03-01

    Full Text Available The ESRAD 52-MHz and the EISCAT 224-MHz radars in northern Scandinavia observed thin layers of strongly enhanced radar echoes from the mesosphere (Polar Mesosphere Winter Echoes - PMWE during a solar proton event in November 2004. Using the interferometric capabilities of ESRAD it was found that the scatterers responsible for PMWE show very high horizontal travel speeds, up to 500 ms-1 or more, and high aspect sensitivity, with echo arrival angles spread over as little as 0.3°. ESRAD also detected, on some occasions, discrete scattering regions moving across the field of view with periodicities of a few seconds. The very narrow, vertically directed beam of the more powerful EISCAT radar allowed measurements of the spectral widths of the radar echoes both inside the PMWE and from the background plasma above and below the PMWE. Spectral widths inside the PMWE were found to be indistinguishable from those from the background plasma. We propose that scatter from highly-damped ion-acoustic waves generated by partial reflection of infrasonic waves provides a reasonable explanation of the characteristics of the very strong PMWE reported here.

  3. Infrasound - the cause of strong Polar Mesosphere Winter Echoes?

    Directory of Open Access Journals (Sweden)

    S. Kirkwood

    2006-03-01

    Full Text Available The ESRAD 52-MHz and the EISCAT 224-MHz radars in northern Scandinavia observed thin layers of strongly enhanced radar echoes from the mesosphere (Polar Mesosphere Winter Echoes - PMWE during a solar proton event in November 2004. Using the interferometric capabilities of ESRAD it was found that the scatterers responsible for PMWE show very high horizontal travel speeds, up to 500 ms-1 or more, and high aspect sensitivity, with echo arrival angles spread over as little as 0.3°. ESRAD also detected, on some occasions, discrete scattering regions moving across the field of view with periodicities of a few seconds. The very narrow, vertically directed beam of the more powerful EISCAT radar allowed measurements of the spectral widths of the radar echoes both inside the PMWE and from the background plasma above and below the PMWE. Spectral widths inside the PMWE were found to be indistinguishable from those from the background plasma. We propose that scatter from highly-damped ion-acoustic waves generated by partial reflection of infrasonic waves provides a reasonable explanation of the characteristics of the very strong PMWE reported here.

  4. Echos, Doubles, and Delusions : Capgras Syndrome in Science and Literature

    NARCIS (Netherlands)

    Draaisma, Douwe

    2009-01-01

    Mark Schluter, the main protagonist in Richard Powers's The Echo Maker (2006), suffers from Capgras Syndrome, a disorder characterized by the patient's delusional belief that his near ones are replaced by doubles. Since its initial identification in 1923, Capgras Syndrome has had a two-stage

  5. Spin-Echo Small-Angle Neutron Scattering Development

    NARCIS (Netherlands)

    Uca, O.

    2003-01-01

    Spin-Echo Small-Angle Neutron Scattering (SESANS) instrument is a novel SANS technique which enables one to characterize distances from a few nanometers up to the micron range. The most striking difference between normal SANS and SESANS is that in SESANS one gets information in real space, whereas

  6. Echo width of foam supports used in scattering measurements

    DEFF Research Database (Denmark)

    Appel-Hansen, Jørgen; Solodukhov, V. V.

    1979-01-01

    Theoretically and experimentally determined echo widths of dielectric cylinders having circular, triangular, and quadratic cross sections have been compared. The cylinders were made of foam material having a relative dielectric constant of about 1.035. The purpose of the investigation was to find...

  7. Polarization optimization of spin-echo small angle scattering instruments

    NARCIS (Netherlands)

    Rekveldt, M.T.; Duif, C.P.; Kraan, W.H.; Plomp, J.; Bouwman, W.G.

    2008-01-01

    The polarization optimization in a small angle scattering spin-echo setup is considered, under the depolarization and phase errors that occur in field transition regions by improper adjustment of inclined magnetized foils as n-flippers. Various correction procedures are discussed. In these setups

  8. Subband Affine Projection Algorithm for Acoustic Echo Cancellation System

    Directory of Open Access Journals (Sweden)

    Choi Hun

    2007-01-01

    Full Text Available We present a new subband affine projection (SAP algorithm for the adaptive acoustic echo cancellation with long echo path delay. Generally, the acoustic echo canceller suffers from the long echo path and large computational complexity. To solve this problem, the proposed algorithm combines merits of the affine projection (AP algorithm and the subband filtering. Convergence speed of the proposed algorithm is improved by the signal-decorrelating property of the orthogonal subband filtering and the weight updating with the prewhitened input signal of the AP algorithm. Moreover, in the proposed algorithms, as applying the polyphase decomposition, the noble identity, and the critical decimation to subband the adaptive filter, the sufficiently decomposed SAP updates the weights of adaptive subfilters without a matrix inversion. Therefore, computational complexity of the proposed method is considerably reduced. In the SAP, the derived weight updating formula for the subband adaptive filter has a simple form as ever compared with the normalized least-mean-square (NLMS algorithm. The efficiency of the proposed algorithm for the colored signal and speech signal was evaluated experimentally.

  9. Characterization of trehalose aqueous solutions by neutron spin echo

    CERN Document Server

    Branca, C; Magazù, S; Maisano, G; Mangione, A; Pappas, C; Triolo, A

    2002-01-01

    The present work reports neutron spin-echo (NSE) results on aqueous mixtures of trehalose, a naturally occurring disaccharide of glucose, which shows an extraordinary bioprotective effectiveness against dehydration and freezing. The aim of the work is to furnish new results on the dynamics of the trehalose/water system on the nano- and picosecond scales. (orig.)

  10. Probability distribution functions of echo signals from meteorological targets

    Science.gov (United States)

    Vasilyev, G. V.

    1975-01-01

    Simple expressions are obtained for the laws and moments of the probability distributions of averaged echo signals from meteorological targets at the output of a logarithmic radar receiver. Here, the distribution function is assumed to be represented in the form of an Edgeworth series.

  11. Vibrational echo spectral observables and frequency fluctuations of ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 129; Issue 7. Vibrational echo spectral observables and frequency fluctuations of hydration shell water around a fluoride ion from first principles simulations. DEEPAK OJHA AMALENDU CHANDRA. REGULAR ARTICLE Volume 129 Issue 7 July 2017 pp 1069-1080 ...

  12. Vibrational echo spectral observables and frequency fluctuations of ...

    Indian Academy of Sciences (India)

    Deepak Ojha

    Vibrational echo; frequency fluctuations; hydration shell water; fluoride ion; ab initio molecular dynamics. 1. Introduction. Ions dissolved in liquid water play important roles in several chemical and biological processes.1,2 Simi- larly, water molecules in aqueous ionic solutions exhibit different dynamics in comparison to pure ...

  13. Echoing Hylas: A Study in Hellenistic and Roman Metapoetics

    NARCIS (Netherlands)

    Heerink, M.

    2015-01-01

    In Echoing Hylas, Mark Heerink argues that the story of Hylas—a famous episode of the Argonauts’ voyage—was used by poets throughout classical antiquity to reflect symbolically on the position of their poetry in the literary tradition. Certain elements of the story, including the characters of Hylas

  14. Fast high resolution whole brain T2* weighted imaging using echo planar imaging at 7T.

    Science.gov (United States)

    Zwanenburg, Jaco J M; Versluis, Maarten J; Luijten, Peter R; Petridou, Natalia

    2011-06-15

    Magnetic susceptibility based (T(2)* weighted) contrast in MRI at high magnetic field strength is of great value in research on brain structure and cortical architecture, but its use is hampered by the low signal-to-noise ratio (SNR) efficiency of the conventional spoiled gradient echo sequence (GRE) leading to long scan times even for a limited number of slices. In this work, we show that high resolution (0.5mm isotropic) T(2)* weighted images of the whole brain can be obtained in 6min by utilizing the high SNR efficiency of echo-planar imaging (EPI). A volumetric (3D) EPI protocol is presented and compared to conventional 3D GRE images acquired with the same resolution, amount of T(2)* weighting, and imaging duration. Spatial coverage in 3D EPI was increased by a factor of 4.5 compared to 3D GRE, while also the SNR was increased by a factor of 2. Image contrast for both magnitude and phase between gray and white matter was similar for both sequences, with enhanced conspicuity of anatomic details in the 3D EPI images due to the increased SNR. Even at 7T, image blurring and distortion is limited if the EPI train length remains short (not longer than the T(2)* of the imaged tissue). 3D EPI provides steps (speed, whole brain coverage, and high isotropic resolution) that are necessary to utilize the benefits of high field MRI in research that employs T(2)* weighted imaging. Copyright © 2011 Elsevier Inc. All rights reserved.

  15. Self-Calibrating Wave-Encoded Variable-Density Single-Shot Fast Spin Echo Imaging.

    Science.gov (United States)

    Chen, Feiyu; Taviani, Valentina; Tamir, Jonathan I; Cheng, Joseph Y; Zhang, Tao; Song, Qiong; Hargreaves, Brian A; Pauly, John M; Vasanawala, Shreyas S

    2017-09-14

    It is highly desirable in clinical abdominal MR scans to accelerate single-shot fast spin echo (SSFSE) imaging and reduce blurring due to T2 decay and partial-Fourier acquisition. To develop and investigate the clinical feasibility of wave-encoded variable-density SSFSE imaging for improved image quality and scan time reduction. Prospective controlled clinical trial. With Institutional Review Board approval and informed consent, the proposed method was assessed on 20 consecutive adult patients (10 male, 10 female, range, 24-84 years). A wave-encoded variable-density SSFSE sequence was developed for clinical 3.0T abdominal scans to enable high acceleration (3.5×) with full-Fourier acquisitions by: 1) introducing wave encoding with self-refocusing gradient waveforms to improve acquisition efficiency; 2) developing self-calibrated estimation of wave-encoding point-spread function and coil sensitivity to improve motion robustness; and 3) incorporating a parallel imaging and compressed sensing reconstruction to reconstruct highly accelerated datasets. Image quality was compared pairwise with standard Cartesian acquisition independently and blindly by two radiologists on a scale from -2 to 2 for noise, contrast, confidence, sharpness, and artifacts. The average ratio of scan time between these two approaches was also compared. A Wilcoxon signed-rank tests with a P value under 0.05 considered statistically significant. Wave-encoded variable-density SSFSE significantly reduced the perceived noise level and improved the sharpness of the abdominal wall and the kidneys compared with standard acquisition (mean scores 0.8, 1.2, and 0.8, respectively, P variable-density sampling SSFSE achieves improved image quality with clinically relevant echo time and reduced scan time, thus providing a fast and robust approach for clinical SSFSE imaging. 1 TECHNICAL EFFICACY: Stage 6 J. Magn. Reson. Imaging 2017. © 2017 International Society for Magnetic Resonance in Medicine.

  16. Diverse Evill Persons: Echoes in the Landscape, Echoes in the Archives

    Directory of Open Access Journals (Sweden)

    Martin Bashforth

    2011-12-01

    Full Text Available This is an account of a process, the working together of cross-disciplinary insights between an artist and a historian, to create a means by which members of the public might encounter the past on their own terms. In the summer of 2009, the historian [MB] and the conceptual artist [PB] decided to collaborate on a project based around events at Cannon Hall, Cawthorne in the West Riding of Yorkshire, 1673-74. The events are located in the B family genealogy but carry in them echoes of deeper social and economic forces in the past, as well as relevance to modern debates about crime, welfare and justice. The aim of the project is to create an exhibition/installation within which members of the public can experience what it means to make sense of the past through the prism of the present. The project is intended to challenge normative approaches in museology and the interpretation of heritage objects, places and documents. The article explores the foundational processes and concepts.

  17. Edward Albee’s The Zoo Story: Echo/es of Contemporary Subversive Culture

    Directory of Open Access Journals (Sweden)

    Naqibun Nabi

    2016-02-01

    Full Text Available The post-world war II American social and cultural setting was ambiguously featured with enforced conformity in the name of prosperity and Americanization of the nation. Despite of this fact, American writers, especially, dramatists conveyed their message against this fixation through variety and intellectuality. Edward Albee’s The Zoo Story is one of those literary assets which dedicatedly cut through the illusions of contemporary American social and cultural ethos. Here, his characters are seen struggling constantly with their insecurities and existential angst in the society. He presents America, the so-called ‘Land of Free and Home of Braves’ (note 1, in such a portrayal that unveils the traps of cages and confinement underneath. The target of this paper is to trace Edward Albee’s heightened awareness about the post-war American socio-cultural reality evident in The Zoo Story. It also looks for the voice in which the text echoes out the anti-communist, materialistic, gender-coded boundaries, coupled with paradoxical media representations, religious bordering and how Albee challenges these issues with an anti-establishment tone. Keywords: subversive culture, anti-communism, media, religion and homosexuality

  18. Near-surface temperature gradient in a coastal upwelling regime

    Science.gov (United States)

    Maske, H.; Ochoa, J.; Almeda-Jauregui, C. O.; Ruiz-de la Torre, M. C.; Cruz-López, R.; Villegas-Mendoza, J. R.

    2014-08-01

    In oceanography, a near homogeneous mixed layer extending from the surface to a seasonal thermocline is a common conceptual basis in physics, chemistry, and biology. In a coastal upwelling region 3 km off the coast in the Mexican Pacific, we measured vertical density gradients with a free-rising CTD and temperature gradients with thermographs at 1, 3, and 5 m depths logging every 5 min during more than a year. No significant salinity gradient was observed down to 10 m depth, and the CTD temperature and density gradients showed no pronounced discontinuity that would suggest a near-surface mixed layer. Thermographs generally logged decreasing temperature with depth with gradients higher than 0.2 K m-1 more than half of the time in the summer between 1 and 3 m, 3 and 5 m and in the winter between 1 and 3 m. Some negative temperature gradients were present and gradients were generally highly variable in time with high peaks lasting fractions of hours to hours. These temporal changes were too rapid to be explained by local heating or cooling. The pattern of positive and negative peaks might be explained by vertical stacks of water layers of different temperatures and different horizontal drift vectors. The observed near-surface gradient has implications for turbulent wind energy transfer, vertical exchange of dissolved and particulate water constituents, the interpretation of remotely sensed SST, and horizontal wind-induced transport.

  19. Distortion Correction in EPI Using an Extended PSF Method with a Reversed Phase Gradient Approach

    Science.gov (United States)

    In, Myung-Ho; Posnansky, Oleg; Beall, Erik B.; Lowe, Mark J.; Speck, Oliver

    2015-01-01

    In echo-planar imaging (EPI), such as commonly used for functional MRI (fMRI) and diffusion-tensor imaging (DTI), compressed distortion is a more difficult challenge than local stretching as spatial information can be lost in strongly compressed areas. In addition, the effects are more severe at ultra-high field (UHF) such as 7T due to increased field inhomogeneity. To resolve this problem, two EPIs with opposite phase-encoding (PE) polarity were acquired and combined after distortion correction. For distortion correction, a point spread function (PSF) mapping method was chosen due to its high correction accuracy and extended to perform distortion correction of both EPIs with opposite PE polarity thus reducing the PSF reference scan time. Because the amount of spatial information differs between the opposite PE datasets, the method was further extended to incorporate a weighted combination of the two distortion-corrected images to maximize the spatial information content of a final corrected image. The correction accuracy of the proposed method was evaluated in distortion-corrected data using both forward and reverse phase-encoded PSF reference data and compared with the reversed gradient approaches suggested previously. Further we demonstrate that the extended PSF method with an improved weighted combination can recover local distortions and spatial information loss and be applied successfully not only to spin-echo EPI, but also to gradient-echo EPIs acquired with both PE directions to perform geometrically accurate image reconstruction. PMID:25707006

  20. Ultraviolet Echoes of Quasar Accretion Disks

    Science.gov (United States)

    Trump, Jonathan

    2017-08-01

    We propose a novel ultraviolet monitoring campaign with WFC3/UVIS to measure quasar accretion disk structure. The bulk of supermassive black hole growth occurs in luminous quasar phases of rapid accretion, yet the governing physics remains poorly understood. Continuum reverberation mapping (RM) measures the accretion disk size via the time lag between short- and long-wavelength emission: the proposed UV monitoring forms the foundation for simultaneous optical observations (expected to continue for our quasars through 2019). Currently only 4 Seyfert AGNs have UV/optical RM accretion-disk sizes, all low-luminosity and at z<0.02. We propose to monitor 5 new quasars, spanning an order of magnitude higher accretion rate and out to z 1. The 5 quasar targets are drawn from SDSS-RM, a pioneering multi-object spectroscopic RM campaign, and have been monitored with optical photometry and spectroscopy since 2014. The higher luminosity and accurate RM masses of our sample enable the first measurements of accretion-rate effects on accretion-disk size, with UV monitoring directly probing changes in the inner disk suggested by theory and previous indirect observations. Our proposed HST monitoring campaign is unusually efficient, targeting 5 quasars per orbit using the DASH method with UVIS subarray readouts. We use simulations to demonstrate that our 2-day cadence over 32 epochs will accurately measure continuum lags and accretion-disk structure. Ultraviolet monitoring of these 5 quasars will enable critical new measurements of accretion-disk structure during the rapid accretion mode that dominates black hole growth.

  1. ECHO: health care performance assessment in several European health systems.

    Science.gov (United States)

    Bernal-Delgado, E; Christiansen, T; Bloor, K; Mateus, C; Yazbeck, A M; Munck, J; Bremner, J

    2015-02-01

    Strengthening health-care effectiveness, increasing accessibility and improving resilience are key goals in the upcoming European Union health-care agenda. European Collaboration for Health-Care Optimization (ECHO), an international research project on health-care performance assessment funded by the seventh framework programme, has provided evidence and methodology to allow the attainment of those goals. This article aims at describing ECHO, analysing its main instruments and discussing some of the ECHO policy implications. Using patient-level administrative data, a series of observational studies (ecological and cross-section with associated time-series analyses) were conducted to analyze population and patients' exposure to health care. Operationally, several performance dimensions such as health-care inequalities, quality, safety and efficiency were analyzed using a set of validated indicators. The main instruments in ECHO were: (i) building a homogeneous data infrastructure; (ii) constructing coding crosswalks to allow comparisons between countries; (iii) making geographical units of analysis comparable; and (iv) allowing comparisons through the use of common benchmarks. ECHO has provided some innovations in international comparisons of health-care performance, mainly derived from the massive pooling of patient-level data and thus: (i) has expanded the usual approach based on average figures, providing insight into within and across country variation at various meaningful policy levels, (ii) the important effort made on data homogenization has increased comparability, increasing stakeholders' reliance on data and improving the acceptance of findings and (iii) has been able to provide more flexible and reliable benchmarking, allowing stakeholders to make critical use of the evidence. © The Author 2015. Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved.

  2. Neutron resonance spin echo with longitudinal DC fields

    Science.gov (United States)

    Krautloher, Maximilian; Kindervater, Jonas; Keller, Thomas; Häußler, Wolfgang

    2016-12-01

    We report on the design, construction, and performance of a neutron resonance spin echo (NRSE) instrument employing radio frequency (RF) spin flippers combining RF fields with DC fields, the latter oriented parallel (longitudinal) to the neutron propagation direction (longitudinal NRSE (LNRSE)). The advantage of the longitudinal configuration is the inherent homogeneity of the effective magnetic path integrals. In the center of the RF coils, the sign of the spin precession phase is inverted by a π flip of the neutron spins, such that non-uniform spin precession at the boundaries of the RF flippers is canceled. The residual inhomogeneity can be reduced by Fresnel- or Pythagoras-coils as in the case of conventional spin echo instruments (neutron spin echo (NSE)). Due to the good intrinsic homogeneity of the B0 coils, the current densities required for the correction coils are at least a factor of three less than in conventional NSE. As the precision and the current density of the correction coils are the limiting factors for the resolution of both NSE and LNRSE, the latter has the intrinsic potential to surpass the energy resolution of present NSE instruments. Our prototype LNRSE spectrometer described here was implemented at the resonance spin echo for diverse applications (RESEDA) beamline at the MLZ in Garching, Germany. The DC fields are generated by B0 coils, based on resistive split-pair solenoids with an active shielding for low stray fields along the beam path. One pair of RF flippers at a distance of 2 m generates a field integral of ˜0.5 Tm. The LNRSE technique is a future alternative for high-resolution spectroscopy of quasi-elastic excitations. In addition, it also incorporates the MIEZE technique, which allows to achieve spin echo resolution for spin depolarizing samples and sample environments. Here we present the results of numerical optimization of the coil geometry and first data from the prototype instrument.

  3. Innovative telementoring for pain management: project ECHO pain.

    Science.gov (United States)

    Katzman, Joanna G; Comerci, George; Boyle, Jeannie F; Duhigg, Daniel; Shelley, Brian; Olivas, Cynthia; Daitz, Benson; Carroll, Christie; Som, Dara; Monette, Rebecca; Kalishman, Summers; Arora, Sanjeev

    2014-01-01

    Project ECHO Pain, the innovative telementoring program for health professionals, was developed in 2009 at the University Of New Mexico Health Sciences Center to fill considerable gaps in pain management expertise. Substantive continuing education for clinicians who practice in rural and underserved communities convenes weekly by means of telehealth technology. Case-based learning, demonstrations, and didactics are incorporated into the interprofessional program that helps to improve pain management in the primary care setting. Three different approaches were used to evaluate the program over a 3-year period: (1) evaluation of all weekly continuing medical education surveys; (2) aggregation of annual clinic data; and (3) assessment of practice change in clinicians who joined Project ECHO Pain for at least 1 year. Between January 2010 and December 2012, 136 Project ECHO Pain clinics were held, with 3835 total instances of participation, representing 763 unique individuals from 191 different sites. Sixty percent self-identified as advanced practice or other nonphysician health professional. Statistically significant improvements in participant self-reported knowledge, skills, and practice were demonstrated. Focus group analyses of 9 subjects detailed specific practice improvements. Project ECHO Pain is a successful continuing professional development program. The telementoring model closes the large knowledge gap in pain education seen in primary care and other settings. Expertise is delivered by implementing effective, evidence-based, and work-based education for diverse health professionals. Project ECHO Pain serves as a model for interprofessional collaborative practice. © 2014 The Alliance for Continuing Education in the Health Professions, the Society for Academic Continuing Medical Education, and the Council on Continuing Medical Education, Association for Hospital Medical Education.

  4. A Year in the Life of an Infrared Echo

    Science.gov (United States)

    2005-01-01

    [figure removed for brevity, see original site] Figure 1: Supernova Remnant Cassiopeia A One Year Apart These Spitzer Space Telescope images, taken one year apart, show the supernova remnant Cassiopeia A (yellow ball) and surrounding clouds of dust (reddish orange). The pictures illustrate that a blast of light from Cassiopeia A is waltzing outward through the dusty skies. This dance, called an 'infrared echo,' began when the remnant erupted about 50 years ago. Cassiopeia A is the remnant of a once massive star that died in a violent supernova explosion 325 years ago. It consists of a dead star, called a neutron star, and a surrounding shell of material that was blasted off as the star died. This remnant is located 10,000 light-years away in the northern constellation Cassiopeia. Infrared echoes are created when a star explodes or erupts, flashing light into surrounding clumps of dust. As the light zips through the dust clumps, it heats them up, causing them to glow successively in infrared, like a chain of Christmas bulbs lighting up one by one. The result is an optical illusion, in which the dust appears to be flying outward at the speed of light. Echoes are distinct from supernova shockwaves, which are made up material that is swept up and hurled outward by exploding stars. This infrared echo is the largest ever seen, stretching more than 50 light-years away from Cassiopeia A. If viewed from Earth, the entire movie frame would take up the same amount of space as two full moons. Hints of an older infrared echo from Cassiopeia A's supernova explosion hundreds of years ago can also be seen. The top Spitzer image was taken on November 30, 2003, and the bottom, on December 2, 2004.

  5. Generalized conjugate gradient squared

    Energy Technology Data Exchange (ETDEWEB)

    Fokkema, D.R.; Sleijpen, G.L.G. [Utrecht Univ. (Netherlands)

    1994-12-31

    In order to solve non-symmetric linear systems of equations, the Conjugate Gradient Squared (CGS) is a well-known and widely used iterative method. In practice the method converges fast, often twice as fast as the Bi-Conjugate Gradient method. This is what you may expect, since CGS uses the square of the BiCG polynomial. However, CGS may suffer from its erratic convergence behavior. The method may diverge or the approximate solution may be inaccurate. BiCGSTAB uses the BiCG polynomial and a product of linear factors in an attempt to smoothen the convergence. In many cases, this has proven to be very effective. Unfortunately, the convergence of BiCGSTAB may stall when a linear factor (nearly) degenerates. BiCGstab({ell}) is designed to overcome this degeneration of linear factors. It generalizes BiCGSTAB and uses both the BiCG polynomial and a product of higher order factors. Still, CGS may converge faster than BiCGSTAB or BiCGstab({ell}). So instead of using a product of linear or higher order factors, it may be worthwhile to look for other polynomials. Since the BiCG polynomial is based on a three term recursion, a natural choice would be a polynomial based on another three term recursion. Possibly, a suitable choice of recursion coefficients would result in method that converges faster or as fast as CGS, but less erratic. It turns out that an algorithm for such a method can easily be formulated. One particular choice for the recursion coefficients leads to CGS. Therefore one could call this algorithm generalized CGS. Another choice for the recursion coefficients leads to BiCGSTAB. It is therefore possible to mix linear factors and some polynomial based on a three term recursion. This way one may get the best of both worlds. The authors will report on their findings.

  6. Liver fat quantification: Comparison of dual-echo and triple-echo chemical shift MRI to MR spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Satkunasingham, Janakan; Besa, Cecilia [Department of Radiology, Body MRI, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, New York, NY 10029 (United States); Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, New York, NY 10029 (United States); Bane, Octavia [Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, New York, NY 10029 (United States); Shah, Ami [Department of Radiology, Body MRI, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, New York, NY 10029 (United States); Oliveira, André de; Gilson, Wesley D.; Kannengiesser, Stephan [Siemens AG, Healthcare Sector, Erlangen (Germany); Taouli, Bachir, E-mail: bachir.taouli@mountsinai.org [Department of Radiology, Body MRI, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, New York, NY 10029 (United States); Translational and Molecular Imaging Institute, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, New York, NY 10029 (United States)

    2015-08-15

    Highlights: • We present a large cohort of patients who underwent dual and triple echo chemical shift imaging against multi-echo T{sub 2} corrected MR spectroscopy (MRS) for liver fat quantification. • Our data suggests that a triple-echo sequence is highly accurate for detection of liver fat, even in the presence of T{sub 2}{sup *} shortening, with minor discrepancies when compared with the advanced fat quantification method. - Abstract: Purpose: To assess the diagnostic value of MRI using dual-echo (2PD) and triple-echo (3PD) chemical shift imaging for liver fat quantification against multi-echo T{sub 2} corrected MR spectroscopy (MRS) used as the reference standard, and examine the effect of T{sub 2}{sup *} imaging on accuracy of MRI for fat quantification. Materials and methods: Patients who underwent 1.5 T liver MRI that incorporated 2PD, 3PD, multi-echo T{sub 2}{sup *} and MRS were included in this IRB approved prospective study. Regions of interest were placed in the liver to measure fat fraction (FF) with 2PD and 3PD and compared with MRS-FF. A random subset of 25 patients with a wide range of MRS-FF was analyzed with an advanced FF calculation method, to prove concordance with the 3PD. The statistical analysis included correlation stratified according to T{sub 2}{sup *}, Bland-Altman analysis, and calculation of diagnostic accuracy for detection of MRS-FF > 6.25%. Results: 220 MRI studies were identified in 217 patients (mean BMI 28.0 ± 5.6). 57/217 (26.2%) patients demonstrated liver steatosis (MRS-FF > 6.25%). Bland-Altman analysis revealed strong agreement between 3PD and MRS (mean ± 1.96 SD: −0.5% ± 4.6%) and weaker agreement between 2PD and MRS (4.7% ± 16.0%). Sensitivity of 3PD for diagnosing FF> 6.25% was higher than that of 2PD. 3PD-FF showed minor discrepancies (coefficient of variation <10%) from FF measured with the advanced method. Conclusion: Our large series study validates the use of 3PD chemical shift sequence for detection of

  7. Study of translational dynamics in molten polymer by variation of gradient pulse-width of PGSE.

    Science.gov (United States)

    Stepišnik, Janez; Lahajnar, Gojmir; Zupančič, Ivan; Mohorič, Aleš

    2013-11-01

    Pulsed gradient spin echo is a method of measuring molecular translation. Changing Δ makes it sensitive to diffusion spectrum. Spin translation effects the buildup of phase structure during the application of gradient pulses as well. The time scale of the self-diffusion measurement shortens if this is taken into account. The method of diffusion spectrometry with variable δ is also less sensitive to artifacts caused by spin relaxation and internal gradient fields. Here the method is demonstrated in the case of diffusion spectrometry of molten polyethylene. The results confirm a model of constraint release in a system of entangled polymer chains as a sort of tube Rouse motion. Copyright © 2013 Elsevier Inc. All rights reserved.

  8. Gradient Boosting Machines, A Tutorial

    Directory of Open Access Journals (Sweden)

    Alexey eNatekin

    2013-12-01

    Full Text Available Gradient boosting machines are a family of powerful machine-learning techniques that have shown considerable success in a wide range of practical applications. They are highly customizable to the particular needs of the application, like being learned with respect to different loss functions. This article gives a tutorial introduction into the methodology of gradient boosting methods. A theoretical information is complemented with many descriptive examples and illustrations which cover all the stages of the gradient boosting model design. Considerations on handling the model complexity are discussed. A set of practical examples of gradient boosting applications are presented and comprehensively analyzed.

  9. Reproducibility of rapid short echo time CSI at 3 tesla for clinical applications.

    Science.gov (United States)

    Van Cauter, Sofie; Sima, Diana M; Luts, Jan; ter Beek, Leon; Ribbens, Annemie; Peeters, Ronald R; Osorio Garcia, Maria I; Li, Yuquan; Sunaert, Stefan; Van Gool, Stefaan W; Van Huffel, Sabine; Himmelreich, Uwe

    2013-02-01

    To validate the reproducibility of a chemical shift imaging (CSI) acquisition protocol with parallel imaging, using automated repositioning software. Ten volunteers were imaged three times on two different 3 Tesla (T) MRI scanners, receiving anatomical imaging and two identical CSI measurements, using automated repositioning software for consistent repositioning of the CSI grid. Offcenter parameters of the CSI plane were analyzed. Coefficients of variation (CoV), Cramér-Rao lower bounds (CRLB), intraclass correlation coefficients (ICC), and coefficients of repeatability (CoR) for immediate repetition and between scanners were calculated for N-acetylaspartate, total choline, creatine, myo-inositol (Myo) and glutamine+glutamate (Glx). Proportions of variance reflecting the effect of voxel location, volunteer, repetition, time instance and scanner were calculated from an analysis of variance analysis. The offcenter vector and angulations of the CSI grid differed less than 1 mm and 2° between all measurements. The mean CoV and CRLB were less than 30% for all metabolites, except for Myo. The variance due to voxel location in the volume of interest and the error represent the largest contributions in variability. The ICC is the lowest for Myo and Glx. CoR for immediate repetition and between scanners display values between 22 and 83%. We propose a CSI protocol with acceptable reproducibility, applicable in clinical routine. Copyright © 2012 Wiley Periodicals, Inc.

  10. Reproducibility of rapid short echo time CSI at 3 tesla for clinical applications

    National Research Council Canada - National Science Library

    Van Cauter, Sofie; Sima, Diana M; Luts, Jan; ter Beek, Leon; Ribbens, Annemie; Peeters, Ronald R; Osorio Garcia, Maria I; Li, Yuquan; Sunaert, Stefan; Van Gool, Stefaan W; Van Huffel, Sabine; Himmelreich, Uwe

    2013-01-01

    .... Ten volunteers were imaged three times on two different 3 Tesla (T) MRI scanners, receiving anatomical imaging and two identical CSI measurements, using automated repositioning software for consistent repositioning of the CSI grid...

  11. MRI-based attenuation correction for hybrid PET/MRI systems: a 4-class tissue segmentation technique using a combined ultrashort-echo-time/Dixon MRI sequence.

    Science.gov (United States)

    Berker, Yannick; Franke, Jochen; Salomon, André; Palmowski, Moritz; Donker, Henk C W; Temur, Yavuz; Mottaghy, Felix M; Kuhl, Christiane; Izquierdo-Garcia, David; Fayad, Zahi A; Kiessling, Fabian; Schulz, Volkmar

    2012-05-01

    Accurate γ-photon attenuation correction (AC) is essential for quantitative PET/MRI as there is no simple relation between MR image intensity and attenuation coefficients. Attenuation maps (μ-maps) can be derived by segmenting MR images and assigning attenuation coefficients to the compartments. Ultrashort-echo-time (UTE) sequences have been used to separate cortical bone and air, and the Dixon technique has enabled differentiation between soft and adipose tissues. Unfortunately, sequential application of these sequences is time-consuming and complicates image registration. A UTE triple-echo (UTILE) MRI sequence is proposed, combining UTE sampling for bone detection and gradient echoes for Dixon water-fat separation in a radial 3-dimensional acquisition (repetition time, 4.1 ms; echo times, 0.09/1.09/2.09 ms; field strength, 3 T). Air masks are derived mainly from the phase information of the first echo; cortical bone is segmented using a dual-echo technique. Soft-tissue and adipose-tissue decomposition is achieved using a 3-point Dixon-like decomposition. Predefined linear attenuation coefficients are assigned to classified voxels to generate MRI-based μ-maps. The results of 6 patients are obtained by comparing μ-maps, reciprocal sensitivity maps, reconstructed PET images, and brain region PET activities based on either CT AC, two 3-class MRI AC techniques, or the proposed 4-class UTILE AC. Using the UTILE MRI sequence, an acquisition time of 214 s was achieved for the head-and-neck region with 1.75-mm isotropic resolution, compared with 164 s for a single-echo UTE scan. MRI-based reciprocal sensitivity maps show a high correlation with those derived from CT scans (R(2) = 0.9920). The same is true for PET activities (R(2) = 0.9958). An overall voxel classification accuracy (compared with CT) of 81.1% was reached. Bone segmentation is inaccurate in complex regions such as the paranasal sinuses, but brain region activities in 48 regions across 6 patients show a

  12. BOLD contrast and noise characteristics of densely sampled multi-echo fMRI data.

    Science.gov (United States)

    Chiew, Mark; Graham, Simon J

    2011-09-01

    Blood oxygenation level dependent (BOLD) contrast in functional magnetic resonance imaging (fMRI) can be enhanced using multi-echo imaging and postprocessing techniques that combine the echoes in weighted summation. Here, existing echo-weighting methods are reassessed in the context of an explicit physiological noise model, and a new method is introduced: weights that scale linearly with echo time. Additionally, a method using data-driven weights defined using principal component analysis (PCA) is included for comparison. Differences in BOLD contrast enhancement between methods were compared analytically where possible, and using Monte Carlo simulations for different noise conditions and different combinations of acquisition parameters. The comparisons were also validated through densely sampled (256-echo) multi-echo fMRI experimental data acquired at 1.5T and 3.0T. Results indicated that the contrast-to-noise ratio (CNR) of the studied weighting methods have a strong dependence on the physiological noise, echo spacing and the width of the sampling window. With low noise correlations between echoes, contrast gain for all weighting methods was shown to have a square root dependence on the echo sampling density, and in typical experimental noise conditions, increasing the sampling window beyond 3·T2* produced marginal additional benefit. Simulations and experiments also emphasized that noise correlations between echoes are likely the main factor limiting the potential CNR gains achievable by densely sampled multi-echo fMRI.

  13. Accelerated 3D echo-planar imaging with compressed sensing for time-resolved hyperpolarized 13 C studies.

    Science.gov (United States)

    Geraghty, Benjamin J; Lau, Justin Y C; Chen, Albert P; Cunningham, Charles H

    2017-02-01

    To enable large field-of-view, time-resolved volumetric coverage in hyperpolarized 13 C metabolic imaging by implementing a novel data acquisition and image reconstruction method based on the compressed sensing framework. A spectral-spatial pulse for single-resonance excitation followed by a symmetric echo-planar imaging (EPI) readout was implemented for encoding a 72 × 18 cm2 field of view at 5 × 5 mm2 resolution. Random undersampling was achieved with blipped z-gradients during the ramp portion of the echo-planar imaging readout. The sequence and reconstruction were tested with phantom studies and consecutive in vivo hyperpolarized 13 C scans in rats. Retrospectively and prospectively undersampled data were compared on the basis of structural similarity in the reconstructed images and the quantification of the lactate-to-pyruvate ratio in rat kidneys. No artifacts or loss of resolution are evident in the compressed sensing reconstructed images acquired with the proposed sequence. Structural similarity analysis indicate that compressed sensing reconstructions can accurately recover spatial features in the metabolic images evaluated. A novel z-blip acquisition sequence for compressed sensing accelerated hyperpolarized 13 C 3D echo-planar imaging was developed and demonstrated. The close agreement in lactate-to-pyruvate ratios from both retrospectively and prospectively undersampled data from rats shows that metabolic information is preserved with acceleration factors up to 3-fold with the developed method. Magn Reson Med 77:538-546, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  14. Fast susceptibility-weighted imaging with three-dimensional short-axis propeller (SAP)-echo-planar imaging.

    Science.gov (United States)

    Holdsworth, Samantha J; Yeom, Kristen W; Moseley, Michael E; Skare, S

    2015-05-01

    Susceptibility-weighted imaging (SWI) in neuroimaging can be challenging due to long scan times of three-dimensional (3D) gradient recalled echo (GRE), while faster techniques such as 3D interleaved echo-planar imaging (iEPI) are prone to motion artifacts. Here we outline and implement a 3D short-axis propeller echo-planar imaging (SAP-EPI) trajectory as a faster, motion-correctable approach for SWI. Experiments were conducted on a 3T MRI system. The 3D SAP-EPI, 3D iEPI, and 3D GRE SWI scans were acquired on two volunteers. Controlled motion experiments were conducted to test the motion-correction capability of 3D SAP-EPI. The 3D SAP-EPI SWI data were acquired on two pediatric patients as a potential alternative to 2D GRE used clinically. The 3D GRE images had a better target resolution (0.47 × 0.94 × 2 mm, scan time = 5 min), iEPI and SAP-EPI images (resolution = 0.94 × 0.94 × 2 mm) were acquired in a faster scan time (1:52 min) with twice the brain coverage. SAP-EPI showed motion-correction capability and some immunity to undersampling from rejected data. While 3D SAP-EPI suffers from some geometric distortion, its short scan time and motion-correction capability suggest that SAP-EPI may be a useful alternative to GRE and iEPI for use in SWI, particularly in uncooperative patients. © 2014 Wiley Periodicals, Inc.

  15. Variability at Multiple Scales: Using an Array of Current- and Pressure-Sensor Equipped Inverted Echo Sounders to Measure the Ocean

    Science.gov (United States)

    2016-11-29

    and listens for each ping’s first echo. In typical applications, twenty-four pings are emitted each hour in bursts of 4 at ten-minute interval with 6...Moored instruments from the FLEAT array comprising: 4 CPIESs (green circles , WHOI/this project), which fall under repeated glider tracks (D. Rudnick...which run meridionally from Palau towards the north (tracks not shown); 3 PlESs (blue circles , University of Rhode Island/MIT, T. Peacock); 2 rapid

  16. Spatially resolved solid-state 1H NMR for evaluation of gradient-composition polymeric libraries.

    Science.gov (United States)

    Leisen, Johannes; Gomez, Ismael J; Roper, John A; Meredith, J Carson; Beckham, Haskell W

    2012-07-09

    Polyurethane libraries consisting of films with composition gradients of aliphatic polyisocyanate and hydroxy-terminated polyacrylate resin were characterized using methods of (1)H NMR microimaging (i.e., magnetic resonance imaging, (MRI)) and solid-state NMR. Molecular mobilities and underlying structural information were extracted as a function of the relative content of each of the two components. Routine NMR microimaging using the spin-echo sequence only allows investigations of transverse relaxation of magnetization at echo times >2 ms. A single-exponential decay was found, which is likely due to free, noncross-linked polymer chains. The mobility of these chains decreases with increasing content of the aliphatic polyisocyanate. The concept of a 1D NMR profiler is introduced as a novel modality for library screening, which allows the convenient measurement of static solid-state NMR spectra as a function of spatial location along a library sample that is repositioned in the rf coil between experiments. With this setup the complete transverse relaxation function was measured using Bloch decays and spin echoes. For all positions within the gradient-composition film, relaxation data consisted of at least three components that were attributed to a rigid highly cross-linked resin, an intermediate cross-linked but mobile constituent, and the highly mobile free polymer chains (the latter is also detectable by MRI). Analysis of this overall relaxation function measured via Bloch decays and spin echoes revealed only minor changes in the mobilities of the individual fractions. Findings with respect to the most mobile components are consistent with the results obtained by NMR microimaging. The major effect is the significant increase in the rigid-component fraction with the addition of the hydroxy-terminated polyacrylate resin.

  17. Analysis of Gradient Waveform in Magnetic Resonance Imaging

    Directory of Open Access Journals (Sweden)

    OU-YANG Shan-mei

    2017-12-01

    Full Text Available The accuracy of gradient pulse waveform affects image quality significantly in magnetic resonance imaging (MRI. Recording and analyzing the waveform of gradient pulse helps to make rapid and accurate diagnosis of spectrometer gradient hardware and/or pulse sequence. Using the virtual instrument software LabVIEW to control the high speed data acquisition card DAQ-2005, a multi-channel acquisition scheme was designed to collect the gradient outputs from a custom-made spectrometer. The collected waveforms were post-processed (i.e., histogram statistical analysis, data filtering and difference calculation to obtain feature points containing time and amplitude information. Experiments were carried out to validate the method, which is an auxiliary test method for the development of spectrometer and pulses sequence.

  18. CUTLASS HF radar observations of high-velocity E-region echoes

    Directory of Open Access Journals (Sweden)

    M. V. Uspensky

    2001-04-01

    Full Text Available A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magnetic L-shell direction. Two echo groups were identified: one group corresponded to the classical type 1 echoes with velocities close to the nominal ion-acoustic speed of 400 ms–1 , while the other group had significantly larger velocities, of the order of 700 ms–1 . The mutual relationship between the echo power, Doppler velocity, spectral width and elevation angles for these two groups was studied. Plotting of echo parameters versus slant range showed that all ~700 ms–1 echoes originated from larger heights and distances of 500–700 km, while all ~400 ms–1 echoes came from lower heights and from farther distances; 700–1000 km. We argue that both observed groups of echoes occurred due to the Farley-Buneman plasma instability excited by strong ( ~70 mVm–1 and uniformly distributed electric fields. We show that the echo velocities for the two groups were different because the echoes were received from different heights. Such a separation of echo heights occurred due to the differing amounts of ionospheric refraction at short and large ranges. Thus, the ionospheric refraction and related altitude modulation of ionospheric parameters are the most important factors to consider, when various characteristics of E-region decametre irregularities are derived from HF radar measurements.Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; polar ionosphere

  19. Efficient Multichannel NLMS Implementation for Acoustic Echo Cancellation

    Directory of Open Access Journals (Sweden)

    Schüldt Christian

    2007-01-01

    Full Text Available An acoustic echo cancellation structure with a single loudspeaker and multiple microphones is, from a system identification perspective, generally modelled as a single-input multiple-output system. Such a system thus implies specific echo-path models (adaptive filter for every loudspeaker to microphone path. Due to the often large dimensionality of the filters, which is required to model rooms with standard reverberation time, the adaptation process can be computationally demanding. This paper presents a selective updating normalized least mean square (NLMS-based method which reduces complexity to nearly half in practical situations, while showing superior convergence speed performance as compared to conventional complexity reduction schemes. Moreover, the method concentrates the filter adaptation to the filter which is most misadjusted, which is a typically desired feature.

  20. Stochastic Maximum Likelihood (SML parametric estimation of overlapped Doppler echoes

    Directory of Open Access Journals (Sweden)

    E. Boyer

    2004-11-01

    Full Text Available This paper investigates the area of overlapped echo data processing. In such cases, classical methods, such as Fourier-like techniques or pulse pair methods, fail to estimate the first three spectral moments of the echoes because of their lack of resolution. A promising method, based on a modelization of the covariance matrix of the time series and on a Stochastic Maximum Likelihood (SML estimation of the parameters of interest, has been recently introduced in literature. This method has been tested on simulations and on few spectra from actual data but no exhaustive investigation of the SML algorithm has been conducted on actual data: this paper fills this gap. The radar data came from the thunderstorm campaign that took place at the National Astronomy and Ionospheric Center (NAIC in Arecibo, Puerto Rico, in 1998.

  1. Efficient Multichannel NLMS Implementation for Acoustic Echo Cancellation

    Directory of Open Access Journals (Sweden)

    Fredric Lindstrom

    2007-02-01

    Full Text Available An acoustic echo cancellation structure with a single loudspeaker and multiple microphones is, from a system identification perspective, generally modelled as a single-input multiple-output system. Such a system thus implies specific echo-path models (adaptive filter for every loudspeaker to microphone path. Due to the often large dimensionality of the filters, which is required to model rooms with standard reverberation time, the adaptation process can be computationally demanding. This paper presents a selective updating normalized least mean square (NLMS-based method which reduces complexity to nearly half in practical situations, while showing superior convergence speed performance as compared to conventional complexity reduction schemes. Moreover, the method concentrates the filter adaptation to the filter which is most misadjusted, which is a typically desired feature.

  2. Echo movement and evolution from real-time processing.

    Science.gov (United States)

    Schaffner, M. R.

    1972-01-01

    Preliminary experimental data on the effectiveness of conventional radars in measuring the movement and evolution of meteorological echoes when the radar is connected to a programmable real-time processor are examined. In the processor programming is accomplished by conceiving abstract machines which constitute the actual programs used in the methods employed. An analysis of these methods, such as the center of gravity method, the contour-displacement method, the method of slope, the cross-section method, the contour crosscorrelation method, the method of echo evolution at each point, and three-dimensional measurements, shows that the motions deduced from them may differ notably (since each method determines different quantities) but the plurality of measurement may give additional information on the characteristics of the precipitation.

  3. Emergence of metapopulations and echo chambers in mobile agents

    CERN Document Server

    Starnini, Michele; Baronchelli, Andrea

    2016-01-01

    Multi-agent models often describe populations segregated either in the physical space, i.e. subdivided in metapopulations, or in the ecology of opinions, i.e. partitioned in echo chambers. Here we show how the interplay between homophily and social influence controls the emergence of both kinds of segregation in a simple model of mobile agents, endowed with a continuous opinion variable. In the model, physical proximity determines a progressive convergence of opinions but differing opinions result in agents moving away from each others. This feedback between mobility and social dynamics determines to the onset of a stable dynamical metapopulation scenario where physically separated groups of like-minded individuals interact with each other through the exchange of agents. The further introduction of confirmation bias in social interactions, defined as the tendency of an individual to favor opinions that match his own, leads to the emergence of echo chambers where different opinions can coexist also within the ...

  4. Benefits of the Multiple Echo Technique for Ultrasonic Thickness Testing

    Energy Technology Data Exchange (ETDEWEB)

    Elder, J.; Vandekamp, R.

    2011-02-10

    Much effort has been put into determining methods to make accurate thickness measurements, especially at elevated temperatures. An accuracy of +/- 0.001 inches is typically noted for commercial ultrasonic thickness gauges and ultrasonic thickness techniques. Codes and standards put limitations on many inspection factors including equipment, calibration tolerance and temperature variations. These factors are important and should be controlled, but unfortunately do not guarantee accurate and repeatable measurements in the field. Most technicians long for a single technique that is best for every situation, unfortunately, there are no 'silver bullets' when it comes to nondestructive testing. This paper will describe and discuss some of the major contributors to measurement error as well as some advantages and limitations of multiple echo techniques and why multiple echo techniques should be more widely utilized for ultrasonic thickness measurements.

  5. Photon-echo-based quantum memory for optical squeezed states

    Science.gov (United States)

    Wu, Miao-Xin; Wang, Ming-Feng; Zheng, Yi-Zhuang

    2015-08-01

    The ability to efficiently realize storage and readout of optical squeezed states plays a key roll in continuous-variables quantum information processing. Here we study the quantum memory for squeezed state of propagating light in atoms based on the hybrid photon echo re-phasing. The optical quantum state is recorded in two sublevels of the ground state of an atomic ensemble to realize long-lived quantum memory. Taking into account the noise effect due to atomic decay, our estimation indicates that high fidelities larger than the classical fidelity threshold 81.5% are obtainable even with currently available techniques. Moreover, our result shows that the decay rate of atoms restricts the maximal fidelity. Our work provides some practical guidance for the realization of efficient and faithful photon-echo-based memory for squeezed light.

  6. Multilayered Echo State Machine: A Novel Architecture and Algorithm.

    Science.gov (United States)

    Malik, Zeeshan Khawar; Hussain, Amir; Wu, Qingming Jonathan

    2017-04-01

    In this paper, we present a novel architecture and learning algorithm for a multilayered echo state machine (ML-ESM). Traditional echo state networks (ESNs) refer to a particular type of reservoir computing (RC) architecture. They constitute an effective approach to recurrent neural network (RNN) training, with the (RNN-based) reservoir generated randomly, and only the readout trained using a simple computationally efficient algorithm. ESNs have greatly facilitated the real-time application of RNN, and have been shown to outperform classical approaches in a number of benchmark tasks. In this paper, we introduce a novel criteria for integrating multiple layers of reservoirs within the ML-ESM. The addition of multiple layers of reservoirs are shown to provide a more robust alternative to conventional RC networks. We demonstrate the comparative merits of this approach in a number of applications, considering both benchmark datasets and real world applications.

  7. Prospects for Precise Measurements with Echo Atom Interferometry

    Science.gov (United States)

    Barrett, Brynle; Carew, Adam; Beica, Hermina; Vorozcovs, Andrejs; Pouliot, Alexander; Kumarakrishnan, A.

    2016-06-01

    Echo atom interferometers have emerged as interesting alternatives to Raman interferometers for the realization of precise measurements of the gravitational acceleration $g$ and the determination of the atomic fine structure through measurements of the atomic recoil frequency $\\omega_q$. Here we review the development of different configurations of echo interferometers that are best suited to achieve these goals. We describe experiments that utilize near-resonant excitation of laser-cooled rubidium atoms by a sequence of standing wave pulses to measure $\\omega_q$ with a statistical uncertainty of 37 parts per billion (ppb) on a time scale of $\\sim 50$ ms and $g$ with a statistical precision of 75 ppb. Related coherent transient techniques that have achieved the most statistically precise measurements of atomic g-factor ratios are also outlined. We discuss the reduction of prominent systematic effects in these experiments using off-resonant excitation by low-cost, high-power lasers.

  8. Prospects for Precise Measurements with Echo Atom Interferometry

    Directory of Open Access Journals (Sweden)

    Brynle Barrett

    2016-06-01

    Full Text Available Echo atom interferometers have emerged as interesting alternatives to Raman interferometers for the realization of precise measurements of the gravitational acceleration g and the determination of the atomic fine structure through measurements of the atomic recoil frequency ω q . Here we review the development of different configurations of echo interferometers that are best suited to achieve these goals. We describe experiments that utilize near-resonant excitation of laser-cooled rubidium atoms by a sequence of standing wave pulses to measure ω q with a statistical uncertainty of 37 parts per billion (ppb on a time scale of ∼50 ms and g with a statistical precision of 75 ppb. Related coherent transient techniques that have achieved the most statistically precise measurements of atomic g-factor ratios are also outlined. We discuss the reduction of prominent systematic effects in these experiments using off-resonant excitation by low-cost, high-power lasers.

  9. Echo Chambers: Emotional Contagion and Group Polarization on Facebook

    CERN Document Server

    Del Vicario, Michela; Bessi, Alessandro; Zollo, Fabiana; Scala, Antonio; Caldarelli, Guido; Quattrociocchi, Walter

    2016-01-01

    Recent findings showed that users on Facebook tend to select information that adhere to their system of beliefs and to form polarized groups -- i.e., echo chambers. Such a tendency dominates information cascades and might affect public debates on social relevant issues. In this work we explore the structural evolution of communities of interest by accounting for users emotions and engagement. Focusing on the Facebook pages reporting on scientific and conspiracy content, we characterize the evolution of the size of the two communities by fitting daily resolution data with three growth models -- i.e. the Gompertz model, the Logistic model, and the Log-logistic model. Then, we explore the interplay between emotional state and engagement of users in the group dynamics. Our findings show that communities' emotional behavior is affected by the users' involvement inside the echo chamber. Indeed, to an higher involvement corresponds a more negative approach. Moreover, we observe that, on average, more active users sh...

  10. Echo pattern of lymph nodes in colorectal cancer

    DEFF Research Database (Denmark)

    Rafaelsen, Søren Rafael; Kronborg, Ole; Fenger, Claus

    1992-01-01

    in vivo. The pathologist examined each node without knowledge of the sonographic finding. Malignant nodes were larger than benign nodes. Of 21 nodes less than 5 mm in diameter, 20 were benign. Round nodes were malignant more often (45/78) than ovoid nodes (6/61). A homogeneous echo pattern was associated......Surgical specimens from 75 patients with colorectal cancer were examined within 15 min of removal with a 7.5 MHz linear-array transducer. The echo pattern of 139 lymph nodes was analysed to evaluate previous criteria of malignancy and to establish other possible criteria, which could be tested...... with malignancy in 39 of 82 nodes in contrast to 12 of 57 with a heterogeneous pattern. Thirty-one nodes were ovoid as well as heterogeneous and all of these were benign. A hyperechoic centre was found in 14 nodes of which two were malignant. The highest predictive value for malignancy (59%) was obtained...

  11. Strain gradients in epitaxial ferroelectrics

    NARCIS (Netherlands)

    Catalan, G; Noheda, Beatriz; McAneney, J; Sinnamon, LJ; Gregg, JM

    2005-01-01

    X-ray analysis of ferroelectric thin layers of Ba1/2Sr1/2TiO3 with different thicknesses reveals the presence of strain gradients across the films and allows us to propose a functional form for the internal strain profile. We use this to calculate the influence of strain gradient, through

  12. Computational Strain Gradient Crystal Plasticity

    DEFF Research Database (Denmark)

    Niordson, Christian Frithiof; Kysar, Jeffrey W.

    2011-01-01

    A model for strain gradient crystal visco-plasticity is formulated along the lines proposed by Fleck andWillis (2009) for isotropic plasticity. Size-effects are included in the model due to the addition of gradient terms in both the free energy as well as through a dissipation potential. A finite...

  13. Sobolev gradients and differential equations

    CERN Document Server

    Neuberger, J W

    2010-01-01

    A Sobolev gradient of a real-valued functional on a Hilbert space is a gradient of that functional taken relative to an underlying Sobolev norm. This book shows how descent methods using such gradients allow a unified treatment of a wide variety of problems in differential equations. For discrete versions of partial differential equations, corresponding Sobolev gradients are seen to be vastly more efficient than ordinary gradients. In fact, descent methods with these gradients generally scale linearly with the number of grid points, in sharp contrast with the use of ordinary gradients. Aside from the first edition of this work, this is the only known account of Sobolev gradients in book form. Most of the applications in this book have emerged since the first edition was published some twelve years ago. What remains of the first edition has been extensively revised. There are a number of plots of results from calculations and a sample MatLab code is included for a simple problem. Those working through a fair p...

  14. The application of polymerase chain reaction-denaturing gradient ...

    African Journals Online (AJOL)

    A rapid microbial screening method was developed based on denaturing gradient gel electrophoresis (DGGE). To evaluate the repeatability and reliability of this system, three DGGE markers were used. Then, the feasibility of DGGE method was verified by microbial screenings in viili (a traditional fermented dairy product ...

  15. Low-Complexity Adaptive Filtering Implementation for Acoustic Echo Cancellation

    OpenAIRE

    Schüldt, Christian; Lindström, Fredric; Claesson, Ingvar

    2006-01-01

    Acoustic echo cancellation is generally achieved with adaptive FIR filters. Due to the often large dimensionality of the adaptive filters, required to model rooms with standard reverberation time, the adaptation process can be computationally demanding. This paper presents a block based selective updating method which reduces the complexity with nearly a half in practical situations, while showing superior convergence speed performance as compared to conventional partial update complexity red...

  16. Deep Echo State Network (DeepESN): A Brief Survey

    OpenAIRE

    Gallicchio, Claudio; Micheli, Alessio

    2017-01-01

    The study of deep recurrent neural networks (RNNs) and, in particular, of deep Reservoir Computing (RC) is gaining an increasing research attention in the neural networks community. The recently introduced deep Echo State Network (deepESN) model opened the way to an extremely efficient approach for designing deep neural networks for temporal data. At the same time, the study of deepESNs allowed to shed light on the intrinsic properties of state dynamics developed by hierarchical compositions ...

  17. NovoPen Echo® insulin delivery device

    Directory of Open Access Journals (Sweden)

    Hyllested-Winge J

    2016-01-01

    Full Text Available Jacob Hyllested-Winge,1 Thomas Sparre,2 Line Kynemund Pedersen2 1Novo Nordisk Pharma Ltd, Tokyo, Japan; 2Novo Nordisk A/S, Søborg, Denmark Abstract: The introduction of insulin pen devices has provided easier, well-tolerated, and more convenient treatment regimens for patients with diabetes mellitus. When compared with vial and syringe regimens, insulin pens offer a greater clinical efficacy, improved quality of life, and increased dosing accuracy, particularly at low doses. The portable and discreet nature of pen devices reduces the burden on the patient, facilitates adherence, and subsequently contributes to the improvement in glycemic control. NovoPen Echo® is one of the latest members of the NovoPen® family that has been specifically designed for the pediatric population and is the first to combine half-unit increment (=0.5 U of insulin dosing with a simple memory function. The half-unit increment dosing amendments and accurate injection of 0.5 U of insulin are particularly beneficial for children (and insulin-sensitive adults/elders, who often require small insulin doses. The memory function can be used to record the time and amount of the last dose, reducing the fear of double dosing or missing a dose. The memory function also provides parents with extra confidence and security that their child is taking insulin at the correct doses and times. NovoPen Echo is a lightweight, durable insulin delivery pen; it is available in two different colors, which may help to distinguish between different types of insulin, providing more confidence for both users and caregivers. Studies have demonstrated a high level of patient satisfaction, with 80% of users preferring NovoPen Echo to other pediatric insulin pens. Keywords: NovoPen Echo®, memory function, half-unit increment dosing, adherence, children, adolescents 

  18. Polarization optimization of spin-echo small angle scattering instruments.

    Science.gov (United States)

    Rekveldt, M Theo; Duif, Chris P; Kraan, Wicher H; Plomp, Jeroen; Bouwman, Wim G

    2008-01-01

    The polarization optimization in a small angle scattering spin-echo setup is considered, under the depolarization and phase errors that occur in field transition regions by improper adjustment of inclined magnetized foils as pi-flippers. Various correction procedures are discussed. In these setups with precession fields perpendicular to the beam directions, corrections can be reduced strongly by the use of pi-flippers, and for the remaining errors, correction coils can be constructed.

  19. RESPECT: Neutron resonance spin-echo spectrometer for extreme studies

    Energy Technology Data Exchange (ETDEWEB)

    Georgii, R., E-mail: Robert.Georgii@frm2.tum.de [Physik-Department, Technische Universität München, James-Franck-Str. 1, D-85748 Garching (Germany); Heinz Maier-Leibnitz Zentrum, Technische Universität München, Lichtenbergstr. 1, D-85748 Garching (Germany); Kindervater, J. [Physik-Department, Technische Universität München, James-Franck-Str. 1, D-85748 Garching (Germany); Institute for Quantum Matter and Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street Baltimore, MD 21218 (United States); Pfleiderer, C.; Böni, P. [Physik-Department, Technische Universität München, James-Franck-Str. 1, D-85748 Garching (Germany)

    2016-11-21

    We propose the design of a REsonance SPin-echo spECtrometer for exTreme studies, RESPECT, that is ideally suited for the exploration of non-dispersive processes such as diffusion, crystallization, slow dynamics, tunneling processes, crystal electric field excitations, and spin fluctuations. It is a variant of the conventional neutron spin-echo technique (NSE) by (i) replacing the long precession coils by pairs of longitudinal neutron spin-echo coils combined with RF-spin flippers and (ii) by stabilizing the neutron polarization with small longitudinal guide fields that can in addition be used as field subtraction coils thus allowing to adjust the field integrals over a range of 8 orders of magnitude. Therefore, the dynamic range of RESPECT can in principle be varied over 8 orders of magnitude in time, if neutrons with the required energy are made available. Similarly as for existing NSE-spectrometers, spin echo times of up to approximately 1 μs can be reached if the divergence and the correction elements are properly adjusted. Thanks to the optional use of neutron guides and the fact that the currents for the correction coils are much smaller than in standard NSE, intensity gains of at least one order of magnitude are expected, making the concept of RESPECT also competitive for operation at medium flux neutron sources. RESPECT can also be operated in a MIEZE configuration allowing the investigation of relaxation processes in depolarizing environments as they occur when magnetic fields are applied at the sample position, i.e. for the investigation of the dynamics of flux lines in superconductors, magnetic fluctuations in ferromagnetic materials, and samples containing hydrogen.

  20. Lawrencian Echoes in Freud’s Civilization and its Discontents

    OpenAIRE

    Macadré-Nguyên, Brigitte

    2015-01-01

    Trying to find Freudian echoes in Lawrence may appear somewhat contrived insofar as Freud published his book after D.H. Lawrence’s death. However, as Freud often quotes from writers, Twain, Goethe, Shakespeare, Rousseau and Rolland, he may also have been inspired by other literary sources which he did not explicitly quote from. These unacknowledged sources could include the writings of Lawrence. It is furthermore obvious that discontents with civilization were quite common among artists and w...

  1. Structural-communicative types of the perplexed echo question

    OpenAIRE

    VOROBYOVA ELENA N.

    2015-01-01

    Modern linguistics has shown us that the language is not limited to questions with the standard semantics of interrogation. Among the interrogative sentences used in the secondary functions one can find inquiries with additional emotional colourings. Perplexity is the closest emotional evaluative meaning, accompanying the interrogative semantics of a question. In the paper, one of the structural-communicative types of the perplexed question (an echo question) is considered. Two structural typ...

  2. Charge gradient microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Roelofs, Andreas; Hong, Seungbum

    2018-02-06

    A method for rapid imaging of a material specimen includes positioning a tip to contact the material specimen, and applying a force to a surface of the material specimen via the tip. In addition, the method includes moving the tip across the surface of the material specimen while removing electrical charge therefrom, generating a signal produced by contact between the tip and the surface, and detecting, based on the data, the removed electrical charge induced through the tip during movement of the tip across the surface. The method further includes measuring the detected electrical charge.

  3. Polar mesosphere winter echoes during MaCWAVE

    Directory of Open Access Journals (Sweden)

    S. Kirkwood

    2006-07-01

    Full Text Available During the MaCWAVE winter campaign in January 2003, layers of enhanced echo power known as PMWE (Polar Mesosphere Winter Echoes were detected by the ESRAD 52 MHz radar on several occasions. The cause of these echoes is unclear and here we use observations by meteorological and sounding rockets and by lidar to test whether neutral turbulence or aerosol layers might be responsible. PMWE were detected within 30 min of meteorological rocket soundings (falling spheres on 5 separate days. The observations from the meteorological rockets show that, in most cases, conditions likely to be associated with neutral atmospheric turbulence are not observed at the heights of the PMWE. Observations by instrumented sounding rockets confirm low levels of turbulence and indicate considerable small-scale structure in charge density profiles. Comparison of falling sphere and lidar data, on the other hand, show that any contribution of aerosol scatter to the lidar signal at PMWE heights is less than the detection threshold of about 10%.

  4. Gradient elution in capillary electrochromatography

    Energy Technology Data Exchange (ETDEWEB)

    Anex, D.; Rakestraw, D.J. [Sandia National Labs., Livermore, CA (United States); Yan, Chao; Dadoo, R.; Zare, R.N. [Stanford Univ., CA (United States). Dept. of Chemistry

    1997-08-01

    In analogy to pressure-driven gradient techniques in high-performance liquid chromatography, a system has been developed for delivering electroosmotically-driven solvent gradients for capillary electrochromatography (CEC). Dynamic gradients with sub-mL/min flow rates are generated by merging two electroosmotic flows that are regulated by computer-controlled voltages. These flows are delivered by two fused-silica capillary arms attached to a T-connector, where they mix and then flow into a capillary column that has been electrokinetically packed with 3-mm reversed-phase particles. The inlet of one capillary arm is placed in a solution reservoir containing one mobile phase and the inlet of the other is placed in a second reservoir containing a second mobile phase. Two independent computer-controlled programmable high-voltage power supplies (0-50 kV)--one providing an increasing ramp and the other providing a decreasing ramp--are used to apply variable high-voltage potentials to the mobile phase reservoirs to regulate the electroosmotic flow in each arm. The ratio of the electroosmotic flow rates between the two arms is changed with time according to the computer-controlled voltages to deliver the required gradient profile to the separation column. Experiments were performed to confirm the composition of the mobile phase during a gradient run and to determine the change of the composition in response to the programmed voltage profile. To demonstrate the performance of electroosmotically-driven gradient elution in CEC, a mixture of 16 polycyclic aromatic hydrocarbons (PAHs) was separated in less than 90 minutes. This gradient technique is expected to be well-suited for generating not only solvent gradients in CEC, but also other types of gradients such as pH- and ionic-strength gradients in capillary electrokinetic separations and analyses.

  5. Magnetic resonance imaging of the cervical spine: comparison of 2D T2-weighted turbo spin echo, 2D T2*weighted gradient-recalled echo and 3D T2-weighted variable flip-angle turbo spin echo sequences

    Energy Technology Data Exchange (ETDEWEB)

    Meindl, T.; Wirth, S.; Dietrich, O.; Reiser, M. [University Hospitals Munich, Department of Clinical Radiology, Munich (Germany); Weckbach, S.; Schoenberg, S.O. [University Hospital Mannheim, Medical Faculty Mannheim-University of Heidelberg, Department of Clinical Radiology, Mannheim (Germany)

    2009-03-15

    To compare an isotropic three-dimensional (3D) high-resolution T2-weighted (w) MR sequence and its reformations with conventional sequences for imaging of the cervical spine. Fifteen volunteers were examined at 1.5 T using sagittal and axial 3D T2-w, sagittal and axial 2D T2w, and axial 2D T2*w MR sequences. Axial reformations of the sagittal 3D dataset were generated (3D MPR T2w). Signal-to-noise and image homogeneity were evaluated in a phantom and in vivo. Visibility of ten anatomical structures of the cervical spine was evaluated. Artifacts were assessed. For statistical analysis, Cohen's kappa, Wilcoxon matched pairs, and t-testing were utilized. There were no significant differences in homogeneity between the sequences. Sagittal 3D T2w enabled better delineation of nerve roots, neural foramina, and intraforaminal structures compared to sagittal 2D T2w. Axial 3D T2w and axial 3D MPR T2w resulted in superior visibility of most anatomical structures compared to axial 2D T2w and comparable results to 2D T2*w concerning the spinal cord, nerve roots, intraforaminal structures, and fat. Artifacts were most pronounced in axial 2D T2w and axial 3D T2w. Acquisition of a 3D T2w data set is feasible in the cervical spine with superior delineation of anatomical structures compared to 2D sequences. (orig.)

  6. Gradient zone boundary control in salt gradient solar ponds

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R. (Downers Grove, IL)

    1984-01-01

    A method and apparatus for suppressing zone boundary migration in a salt gradient solar pond includes extending perforated membranes across the pond at the boundaries, between the convective and non-convective zones, the perforations being small enough in size to prevent individual turbulence disturbances from penetrating the hole, but being large enough to allow easy molecular diffusion of salt thereby preventing the formation of convective zones in the gradient layer. The total area of the perforations is a sizable fraction of the membrane area to allow sufficient salt diffusion while preventing turbulent entrainment into the gradient zone.

  7. Improved sensitivity and specificity for resting state and task fMRI with multiband multi-echo EPI compared to multi-echo EPI at 7T.

    NARCIS (Netherlands)

    Boyacioglu, R.; Schulz, J.; Koopmans, P.J.; Barth, M.; Norris, David Gordon

    2015-01-01

    A multiband multi-echo (MBME) sequence is implemented and compared to a matched standard multi-echo (ME) protocol to investigate the potential improvement in sensitivity and spatial specificity at 7 T for resting state and task fMRI. ME acquisition is attractive because BOLD sensitivity is less

  8. Wave influence on polar mesosphere summer echoes above Wasa. Experimental and model studies

    Energy Technology Data Exchange (ETDEWEB)

    Dalin, P.; Kirkwood, S.; Mihalikova, M.; Mikhaylova, D.; Wolf, I. [Swedish Institute of Space Physics, Kiruna (Sweden); Hervig, M. [GATS Inc., Driggs, ID (United States); Osepian, A. [Polar Geophysical Institute, Murmansk (Russian Federation)

    2012-11-01

    Comprehensive analysis of the wave activity in the Antarctic summer mesopause is performed using polar mesospheric summer echoes (PMSE) measurements for December 2010-January 2011. The 2-day planetary wave is a statistically significant periodic oscillation in the power spectrum density of PMSE power. The strongest periodic oscillation in the power spectrum belongs to the diurnal solar tide; the semi-diurnal solar tide is found to be a highly significant harmonic oscillation as well. The inertial-gravity waves are extensively studied by means of PMSE power and wind components. The strongest gravity waves are observed at periods of about 1, 1.4, 2.5 and 4 h, with characteristic horizontal wavelengths of 28, 36, 157 and 252 km, respectively. The gravity waves propagate approximately in the west-east direction over Wasa (Antarctica). A detailed comparison between theoretical and experimental volume reflectivity of PMSE, measured at Wasa, is made. It is demonstrated that a new expression for PMSE reflectivity derived by Varney et al. (2011) is able to adequately describe PMSE profiles both in the magnitude and in height variations. The best agreement, within 30 %, is achieved when mean values of neutral atmospheric parameters are utilized. The largest contribution to the formation and variability of the PMSE layer is explained by the ice number density and its height gradient, followed by waveinduced perturbations in buoyancy period and the turbulent energy dissipation rate. (orig.)

  9. Spatio-temporal learning with the online finite and infinite echo-state Gaussian processes.

    Science.gov (United States)

    Soh, Harold; Demiris, Yiannis

    2015-03-01

    Successful biological systems adapt to change. In this paper, we are principally concerned with adaptive systems that operate in environments where data arrives sequentially and is multivariate in nature, for example, sensory streams in robotic systems. We contribute two reservoir inspired methods: 1) the online echostate Gaussian process (OESGP) and 2) its infinite variant, the online infinite echostate Gaussian process (OIESGP) Both algorithms are iterative fixed-budget methods that learn from noisy time series. In particular, the OESGP combines the echo-state network with Bayesian online learning for Gaussian processes. Extending this to infinite reservoirs yields the OIESGP, which uses a novel recursive kernel with automatic relevance determination that enables spatial and temporal feature weighting. When fused with stochastic natural gradient descent, the kernel hyperparameters are iteratively adapted to better model the target system. Furthermore, insights into the underlying system can be gleamed from inspection of the resulting hyperparameters. Experiments on noisy benchmark problems (one-step prediction and system identification) demonstrate that our methods yield high accuracies relative to state-of-the-art methods, and standard kernels with sliding windows, particularly on problems with irrelevant dimensions. In addition, we describe two case studies in robotic learning-by-demonstration involving the Nao humanoid robot and the Assistive Robot Transport for Youngsters (ARTY) smart wheelchair.

  10. Wave influence on polar mesosphere summer echoes above Wasa: experimental and model studies

    Directory of Open Access Journals (Sweden)

    P. Dalin

    2012-08-01

    Full Text Available Comprehensive analysis of the wave activity in the Antarctic summer mesopause is performed using polar mesospheric summer echoes (PMSE measurements for December 2010–January 2011. The 2-day planetary wave is a statistically significant periodic oscillation in the power spectrum density of PMSE power. The strongest periodic oscillation in the power spectrum belongs to the diurnal solar tide; the semi-diurnal solar tide is found to be a highly significant harmonic oscillation as well. The inertial-gravity waves are extensively studied by means of PMSE power and wind components. The strongest gravity waves are observed at periods of about 1, 1.4, 2.5 and 4 h, with characteristic horizontal wavelengths of 28, 36, 157 and 252 km, respectively. The gravity waves propagate approximately in the west-east direction over Wasa (Antarctica. A detailed comparison between theoretical and experimental volume reflectivity of PMSE, measured at Wasa, is made. It is demonstrated that a new expression for PMSE reflectivity derived by Varney et al. (2011 is able to adequately describe PMSE profiles both in the magnitude and in height variations. The best agreement, within 30%, is achieved when mean values of neutral atmospheric parameters are utilized. The largest contribution to the formation and variability of the PMSE layer is explained by the ice number density and its height gradient, followed by wave-induced perturbations in buoyancy period and the turbulent energy dissipation rate.

  11. Wave influence on polar mesosphere summer echoes above Wasa: experimental and model studies

    Science.gov (United States)

    Dalin, P.; Kirkwood, S.; Hervig, M.; Mihalikova, M.; Mikhaylova, D.; Wolf, I.; Osepian, A.

    2012-08-01

    Comprehensive analysis of the wave activity in the Antarctic summer mesopause is performed using polar mesospheric summer echoes (PMSE) measurements for December 2010-January 2011. The 2-day planetary wave is a statistically significant periodic oscillation in the power spectrum density of PMSE power. The strongest periodic oscillation in the power spectrum belongs to the diurnal solar tide; the semi-diurnal solar tide is found to be a highly significant harmonic oscillation as well. The inertial-gravity waves are extensively studied by means of PMSE power and wind components. The strongest gravity waves are observed at periods of about 1, 1.4, 2.5 and 4 h, with characteristic horizontal wavelengths of 28, 36, 157 and 252 km, respectively. The gravity waves propagate approximately in the west-east direction over Wasa (Antarctica). A detailed comparison between theoretical and experimental volume reflectivity of PMSE, measured at Wasa, is made. It is demonstrated that a new expression for PMSE reflectivity derived by Varney et al. (2011) is able to adequately describe PMSE profiles both in the magnitude and in height variations. The best agreement, within 30%, is achieved when mean values of neutral atmospheric parameters are utilized. The largest contribution to the formation and variability of the PMSE layer is explained by the ice number density and its height gradient, followed by wave-induced perturbations in buoyancy period and the turbulent energy dissipation rate.

  12. MODIFIED ARMIJO RULE ON GRADIENT DESCENT AND CONJUGATE GRADIENT

    Directory of Open Access Journals (Sweden)

    ZURAIDAH FITRIAH

    2017-10-01

    Full Text Available Armijo rule is an inexact line search method to determine step size in some descent method to solve unconstrained local optimization. Modified Armijo was introduced to increase the numerical performance of several descent algorithms that applying this method. The basic difference of Armijo and its modified are in existence of a parameter and estimating the parameter that is updated in every iteration. This article is comparing numerical solution and time of computation of gradient descent and conjugate gradient hybrid Gilbert-Nocedal (CGHGN that applying modified Armijo rule. From program implementation in Matlab 6, it's known that gradient descent was applying modified Armijo more effectively than CGHGN from one side: iteration needed to reach some norm of the gradient  (input by the user. The amount of iteration was representing how long the step size of each algorithm in each iteration. In another side, time of computation has the same conclusion.

  13. The geomagnetic field gradient tensor

    DEFF Research Database (Denmark)

    Kotsiaros, Stavros; Olsen, Nils

    2012-01-01

    of the magnetic gradient tensor and provide explicit expressions of its elements in terms of spherical harmonics. Finally we discuss the benefit of using gradient measurements for exploring the Earth’s magnetic field from space, in particular the advantage of the various tensor elements for a better determination......We develop the general mathematical basis for space magnetic gradiometry in spherical coordinates. The magnetic gradient tensor is a second rank tensor consisting of 3 × 3 = 9 spatial derivatives. Since the geomagnetic field vector B is always solenoidal (∇ · B = 0) there are only eight independent...

  14. Circumstellar Light Echo as a Possible Origin of the Polarization of Type IIP Supernovae

    Science.gov (United States)

    Nagao, Takashi; Maeda, Keiichi; Tanaka, Masaomi

    2017-10-01

    Type IIP supernovae (SNe IIP) are the most common class of core-collapse SNe. They often show a rapid increase of polarization degree in the late phase. This time evolution is generally believed to originate from the emergence of an inner aspherical core, while the effect of polarized-scattered echoes by circumstellar (CS) dust around the SN may also substantially contribute to this polarization feature. In this study, we examine the effects of the scattered echoes on the SN polarization through radiative transfer simulations for various geometries and amounts of CS dust. It is found that asymmetrically distributed CS dust, which is generally inferred for red supergiants, can reproduce the observed polarization features. We have applied our results to SNe 2004dj and 2006ov, deriving the geometry and amount of CS dust to explain their observed polarization features in this scenario. For both SNe, the blob-like or bipolar distribution of CS dust rather than the disk-like distribution is favored. The derived dust masses {M}{dust} in the blob model (the bipolar CS dust model) for SNe 2004dj and 2006ov are ˜ 7.5× {10}-4 {M}⊙ (˜ 8.5× {10}-4 {M}⊙ ) and ˜ 5.2× {10}-4 {M}⊙ (˜ 1.3× {10}-3 {M}⊙ ), respectively. Even in the case where this process would not play a dominant role in the observed polarization signals, this effect should in principle contribute to it, the strength of which depends on the nature of the CS dust. Therefore, this effect must be taken into account in discussing the multi-dimensional structure of an SN explosion through polarimetric observations.

  15. Sobolev gradients and differential equations

    CERN Document Server

    Neuberger, John William

    1997-01-01

    A Sobolev gradient of a real-valued functional is a gradient of that functional taken relative to the underlying Sobolev norm. This book shows how descent methods using such gradients allow a unified treatment of a wide variety of problems in differential equations. Equal emphasis is placed on numerical and theoretical matters. Several concrete applications are made to illustrate the method. These applications include (1) Ginzburg-Landau functionals of superconductivity, (2) problems of transonic flow in which type depends locally on nonlinearities, and (3) minimal surface problems. Sobolev gradient constructions rely on a study of orthogonal projections onto graphs of closed densely defined linear transformations from one Hilbert space to another. These developments use work of Weyl, von Neumann and Beurling.

  16. Mixed-Methods Study of Uptake of the Extension for Community Health Outcomes (ECHO) Telemedicine Model for Rural Veterans With HIV.

    Science.gov (United States)

    Moeckli, Jane; Stewart, Kenda R; Ono, Sarah; Alexander, Bruce; Goss, Tyler; Maier, Marissa; Tien, Phyllis C; Howren, M Bryant; Ohl, Michael E

    2017-06-01

    Extension for Community Health Outcomes (ECHO) is a provider-level telemedicine model successfully applied to hepatitis C care, but little is known about its application to Human Immunodeficiency Virus (HIV) care. We performed a mixed-methods evaluation of 3 HIV ECHO programs in the Veterans Health Administration, focusing on uptake by primary care clinics and veterans. Administrative data were used to assess program uptake, including adoption (ie, proportion of primary care clinics participating) and reach (ie, proportion of eligible veterans participating). Veterans were considered eligible if they had an HIV diagnosis and lived nearer to a primary care clinic than to the HIV specialty clinic. We interviewed 31 HIV specialists, primary care providers (PCPs), and administrators engaged in HIV ECHO, and we analyzed interview transcripts to identify factors that influenced program adoption and reach. Nine (43%) of 21 primary care clinics adopted HIV ECHO (range 33%-67% across sites). Program reach was limited, with 47 (6.1%) of 776 eligible veterans participating. Reach was similar among rural and urban veterans (5.3% vs 6.3%). In interviews, limited adoption and reach were attributed partly to: (1) a sense of "HIV exceptionalism" that complicated shifting ownership of care from HIV specialists to PCPs, and (2) low HIV prevalence and long treatment cycles that prevented rapid learning loops for PCPs. There was limited uptake of HIV ECHO telemedicine programs in settings where veterans historically traveled to distant specialty clinics. Other telemedicine models should be considered for HIV care. © 2016 National Rural Health Association.

  17. Characteristic analysis of underwater acoustic scattering echoes in the wavelet transform domain

    Science.gov (United States)

    Yang, Mei; Li, Xiukun; Yang, Yang; Meng, Xiangxia

    2017-03-01

    Underwater acoustic scattering echoes have time-space structures and are aliasing in time and frequency domains. Different series of echoes properties are not identified when incident angle is unknown. This article investigates variations in target echoes of monostatic sonar to address this problem. The mother wavelet with similar structures has been proposed on the basis of preprocessing signal waveform using matched filter, and the theoretical expressions between delay factor and incident angle are derived in the wavelet domain. Analysis of simulation data and experimental results in free-field pool show that this method can effectively separate geometrical scattering components of target echoes. The time delay estimation obtained from geometrical echoes at a single angle is consistent with target geometrical features, which provides a basis for object recognition without angle information. The findings provide valuable insights for analyzing elastic scattering echoes in actual ocean environment.

  18. Research on adaptive acoustic echo cancellation algorithm in digital hearing aids

    Science.gov (United States)

    Ma, Min; Wang, Mingjiang; Hu, Jiebin

    2017-08-01

    At present, the study of acoustic echo cancellation (AEC) is mainly based on the adaptive acoustic echo cancellation algorithm. It is proved that the echo signal of the near-end microphone must be compensated by the time delay to achieve the purpose of echo cancellation, and the accuracy of the delay estimation affecting the final effect of echo cancellation. This paper proposes a combination of the normalized minimum mean square algorithm (NLMS) and the time delay estimation model to solve the echo problem in hearing aids. In this paper, using generalized cross correlation (GCC) to estimate time delay. In addition, using the energy, Teager-Kaiser Energy Operator (TKEO) and the signal correlation coefficient as the threshold value to detect the howling signal in digital hearing aids. Finally, the simulation and experimental results are given. The experiment proves that the method has good effect.

  19. Mapping axonal density and average diameter using non-monotonic time-dependent gradient-echo MRI

    DEFF Research Database (Denmark)

    Nunes, Daniel; Cruz, Tomás L; Jespersen, Sune N

    2017-01-01

    the quantitative results are compared against ground-truth histology, they seem to reflect the axonal fraction (though with a bias, as evident from Bland-Altman analysis). As well, the extra-axonal fraction can be estimated. The results suggest that our model is oversimplified, yet at the same time evidencing...

  20. Molecular weight prediction in polystyrene blends. Unprecedented use of a genetic algorithm in pulse field gradient spin echo (PGSE) NMR.

    Science.gov (United States)

    Arrabal-Campos, Francisco M; Álvarez, José D; García-Sancho, Amador; Fernández, Ignacio

    2017-09-27

    A genetic algorithm that uses boxcar functions (diffGA) has been applied for the first time in PGSE NMR. It reconstructs accurate diffusion coefficients for all the components of the mixture, and therefore predicts correct weight-average molecular weights for all of them. The results reported herein complement those obtained with established methods such as ITAMeD, CONTIN and TRAIn algorithms, and provide a detailed solution picture. Its robustness and limits have been stretched in order to ascertain the minimum separation within diffusion coefficients or relative proportion between components. In addition, the new genetic algorithm has been also applied to a mixture of small molecules, providing excellent results at very low computational times.

  1. Graded/Gradient Porous Biomaterials

    Directory of Open Access Journals (Sweden)

    Xigeng Miao

    2009-12-01

    Full Text Available Biomaterials include bioceramics, biometals, biopolymers and biocomposites and they play important roles in the replacement and regeneration of human tissues. However, dense bioceramics and dense biometals pose the problem of stress shielding due to their high Young’s moduli compared to those of bones. On the other hand, porous biomaterials exhibit the potential of bone ingrowth, which will depend on porous parameters such as pore size, pore interconnectivity, and porosity. Unfortunately, a highly porous biomaterial results in poor mechanical properties. To optimise the mechanical and the biological properties, porous biomaterials with graded/gradient porosity, pores size, and/or composition have been developed. Graded/gradient porous biomaterials have many advantages over graded/gradient dense biomaterials and uniform or homogenous porous biomaterials. The internal pore surfaces of graded/gradient porous biomaterials can be modified with organic, inorganic, or biological coatings and the internal pores themselves can also be filled with biocompatible and biodegradable materials or living cells. However, graded/gradient porous biomaterials are generally more difficult to fabricate than uniform or homogenous porous biomaterials. With the development of cost-effective processing techniques, graded/gradient porous biomaterials can find wide applications in bone defect filling, implant fixation, bone replacement, drug delivery, and tissue engineering.

  2. Multifractal Modelling of Aircraft Echoes from Low-resolution Radars Based on Structural Functions

    OpenAIRE

    Qiu Sheng Li; Wei Xin Xie

    2013-01-01

    As a kind of complex targets, the nonrigid vibration and attitude change of an aircraft as well as the rotation of its rotating parts will induce complex nonlinear modulation on its echo from low-resolution radars. If one performs the multifractal analysis of measures on an aircraft echo, it may offer a fine description of the dynamic characteristics which induce the echo structure. On basis of introducing multifractal theory based on structural functions, the paper models real recorded aircr...

  3. Prostate treatments, 1MRT o RapidArc; Tratamiento de prostata, IMART o RapidArc?

    Energy Technology Data Exchange (ETDEWEB)

    Castro novais, J.; Ruiz Maqueda, S.; Pardo Perez, E.; Molina Lopez, M. Y.; Cerro Penalver, E.

    2015-07-01

    Techniques that modulate the dose (as IMRT or RapidArcTM) improve dose homogeneity within the target volume decreasing the dose in healthy organs. The aim of this work is to study the dosimetric differences in prostate radiotherapy treatments with IMRT and RapidArcTM. The results of the 109 patients studied show that plans to RapidArcTM have better coverage, compliance and dose gradient outside the target volume. (Author)

  4. First Demonstration of ECHO: an External Calibrator for Hydrogen Observatories

    Science.gov (United States)

    Jacobs, Daniel C.; Burba, Jacob; Bowman, Judd D.; Neben, Abraham R.; Stinnett, Benjamin; Turner, Lauren; Johnson, Kali; Busch, Michael; Allison, Jay; Leatham, Marc; Serrano Rodriguez, Victoria; Denney, Mason; Nelson, David

    2017-03-01

    Multiple instruments are pursuing constraints on dark energy, observing reionization and opening a window on the dark ages through the detection and characterization of the 21 cm hydrogen line for redshifts ranging from ˜1 to 25. These instruments, including CHIME in the sub-meter and HERA in the meter bands, are wide-field arrays with multiple-degree beams, typically operating in transit mode. Accurate knowledge of their primary beams is critical for separation of bright foregrounds from the desired cosmological signals, but difficult to achieve through astronomical observations alone. Previous beam calibration work at low frequencies has focused on model verification and does not address the need of 21 cm experiments for routine beam mapping, to the horizon, of the as-built array. We describe the design and methodology of a drone-mounted calibrator, the External Calibrator for Hydrogen Observatories (ECHO), that aims to address this need. We report on a first set of trials to calibrate low-frequency dipoles at 137 MHz and compare ECHO measurements to an established beam-mapping system based on transmissions from the Orbcomm satellite constellation. We create beam maps of two dipoles at a 9° resolution and find sample noise ranging from 1% at the zenith to 100% in the far sidelobes. Assuming this sample noise represents the error in the measurement, the higher end of this range is not yet consistent with the desired requirement but is an improvement on Orbcomm. The overall performance of ECHO suggests that the desired precision and angular coverage is achievable in practice with modest improvements. We identify the main sources of systematic error and uncertainty in our measurements and describe the steps needed to overcome them.

  5. Using the Echo Nest's automatically extracted music features for a musicological purpose

    DEFF Research Database (Denmark)

    Andersen, Jesper Steen

    2014-01-01

    This paper sums up the preliminary observations and challenges encountered during my first engaging with the music intelligence company Echo Nest's automatically derived data of more than 35 million songs. The overall purpose is to investigate whether musicologists can draw benefit from Echo Nest......'s API, and to explore what practical and analytical considerations one should take into account when engaging with the numbers derived from the Echo Nest API. This paper suggests that the Echo Nest API hold a large potential of doing new types of analyses and visualizing the results. But it concurrently...... argues that a careful and critical approach is requisite, when interpreting the results....

  6. Extraction of scattering echo time by surf noise background subtracted autocorrelation.

    Science.gov (United States)

    Li, Xiaolei; Chi, Jing; Gao, Dazhi; Li, Jie; Wang, Ning

    2017-07-01

    Extracting echo time is an important step in scatterer detection by ambient noise, while in general the scattered signal is weak and submerged in the background. An experiment of a Polyvinyl chloride pipe in a coastline surf noise environment is designed to extract the pipe's echo time by noise autocorrelation. As expected, the scattered wave of the pipe is submerged in an autocorrelation signal. A method called background subtracted autocorrelation is proposed in this paper, which can retrieve scattered echo time from autocorrelation signal effectively. And the biggest relative error of extracted echo time is less than 2% in the experiment.

  7. Finland HF and Esrange MST radar observations of polar mesosphere summer echoes

    Directory of Open Access Journals (Sweden)

    T. Ogawa

    2003-04-01

    Full Text Available Peculiar near range echoes observed in summer with the SuperDARN HF radar in Finland are presented. The echoes were detected at four frequencies of 9, 11, 13 and 15 MHz at slant ranges of 105–250 km for about 100 min. Interferometer measurements indicate that the echoes are returned from 80–100 km altitudes with elevation angles of 20°–60°. Echo power (< 16 dB, Doppler velocity (between –30 and + 30 ms-1 and spectral width (< 60 ms-1 fluctuate with periods of several to 20 min, perhaps due to short–period atmospheric gravity waves. When the HF radar detected the echoes, a vertical incidence MST radar, located at Esrange in Sweden (650 km north of the HF radar site, observed polar mesosphere summer echoes (PMSE at altitudes of 80–90 km. This fact suggests that the near range HF echoes are PMSE at HF band, although both radars did not probe a common volume. With increasing radar frequency, HF echo ranges are closer to the radar site and echo power becomes weaker. Possible mechanisms to explain these features are discussed.Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; thermospheric dynamics; waves and tides; instruments and techniques

  8. Finland HF and Esrange MST radar observations of polar mesosphere summer echoes

    Directory of Open Access Journals (Sweden)

    T. Ogawa

    Full Text Available Peculiar near range echoes observed in summer with the SuperDARN HF radar in Finland are presented. The echoes were detected at four frequencies of 9, 11, 13 and 15 MHz at slant ranges of 105–250 km for about 100 min. Interferometer measurements indicate that the echoes are returned from 80–100 km altitudes with elevation angles of 20°–60°. Echo power (< 16 dB, Doppler velocity (between –30 and + 30 ms-1 and spectral width (< 60 ms-1 fluctuate with periods of several to 20 min, perhaps due to short–period atmospheric gravity waves. When the HF radar detected the echoes, a vertical incidence MST radar, located at Esrange in Sweden (650 km north of the HF radar site, observed polar mesosphere summer echoes (PMSE at altitudes of 80–90 km. This fact suggests that the near range HF echoes are PMSE at HF band, although both radars did not probe a common volume. With increasing radar frequency, HF echo ranges are closer to the radar site and echo power becomes weaker. Possible mechanisms to explain these features are discussed.

    Key words. Meteorology and atmospheric dynamics (middle atmosphere dynamics; thermospheric dynamics; waves and tides; instruments and techniques

  9. Identification of pulse echo impulse responses for multi source transmission

    DEFF Research Database (Denmark)

    Gran, Fredrik; Jensen, Jørgen Arendt

    2004-01-01

    is a mixture of the information corresponding to several transmitters. There is, thus, no direct way of determining which information corresponds to which transmitter, preventing proper focusing. In this paper we decode the received signal by estimating the pulse echo impulse responses between every....... The method is evaluated using the simulation tool Field II. Three point spread functions are simulated where axial movement of 1 m/s is present. The axial resolution for the moving scatterer is 0.249 mm (-3dB) and 0.291 mm (-6dB), which is compared to a standard STA transmission scheme with sequential...

  10. CFAR Detection from Noncoherent Radar Echoes Using Bayesian Theory

    Directory of Open Access Journals (Sweden)

    Wataru Suganuma

    2010-01-01

    Full Text Available We propose a new constant false alarm rate (CFAR detection method from noncoherent radar echoes, considering heterogeneous sea clutter. It applies the Bayesian theory for adaptive estimation of the local clutter statistical distribution in the cell under test. The detection technique can be readily implemented in existing noncoherent marine radar systems, which makes it particularly attractive for economical CFAR detection systems. Monte Carlo simulations were used to investigate the detection performance and demonstrated that the proposed technique provides a higher probability of detection than conventional techniques, such as cell averaging CFAR (CA-CFAR, especially with a small number of reference cells.

  11. CFAR Detection from Noncoherent Radar Echoes Using Bayesian Theory

    Directory of Open Access Journals (Sweden)

    Yamaguchi Hiroyuki

    2010-01-01

    Full Text Available Abstract We propose a new constant false alarm rate (CFAR detection method from noncoherent radar echoes, considering heterogeneous sea clutter. It applies the Bayesian theory for adaptive estimation of the local clutter statistical distribution in the cell under test. The detection technique can be readily implemented in existing noncoherent marine radar systems, which makes it particularly attractive for economical CFAR detection systems. Monte Carlo simulations were used to investigate the detection performance and demonstrated that the proposed technique provides a higher probability of detection than conventional techniques, such as cell averaging CFAR (CA-CFAR, especially with a small number of reference cells.

  12. The echo-enabled harmonic generation options for FLASH II

    Energy Technology Data Exchange (ETDEWEB)

    Deng, Haixiao [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Shanghai Inst. of Applied Physics (China); Decking, Winfried; Faatz, Bart [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany)

    2011-03-15

    FLASH II is an upgrade to the existing free electron laser (FEL) FLASH. The echo-enabled harmonic generation (EEHG) scheme is proposed to be a potential seeding option of FLASH II. In this paper, the possibility of EEHG operation of FLASH II is investigated for the first time. With a combination of existing numerical codes, i.e. a laser-beam interaction code in an undulator (LBICU), a beam tracking code in a chicane (ELEGANT) and an universal FEL simulating code (GENESIS), the effects of beam energy chirp and coherent synchrotron radiation (CSR) on EEHG operation are studied as well. In addition, several interesting issues concerning EEHG simulation are discussed. (orig.)

  13. Automatic speech recognition using a predictive echo state network classifier.

    Science.gov (United States)

    Skowronski, Mark D; Harris, John G

    2007-04-01

    We have combined an echo state network (ESN) with a competitive state machine framework to create a classification engine called the predictive ESN classifier. We derive the expressions for training the predictive ESN classifier and show that the model was significantly more noise robust compared to a hidden Markov model in noisy speech classification experiments by 8+/-1 dB signal-to-noise ratio. The simple training algorithm and noise robustness of the predictive ESN classifier make it an attractive classification engine for automatic speech recognition.

  14. Rapid Prototyping

    Science.gov (United States)

    1999-01-01

    Javelin, a Lone Peak Engineering Inc. Company has introduced the SteamRoller(TM) System as a commercial product. The system was designed by Javelin during a Phase II NASA funded small commercial product. The purpose of the invention was to allow automated-feed of flexible ceramic tapes to the Laminated Object Manufacturing rapid prototyping equipment. The ceramic material that Javelin was working with during the Phase II project is silicon nitride. This engineered ceramic material is of interest for space-based component.

  15. Parameter estimation of gravitational wave echoes from exotic compact objects

    Science.gov (United States)

    Maselli, Andrea; Völkel, Sebastian H.; Kokkotas, Kostas D.

    2017-09-01

    Relativistic ultracompact objects without an event horizon may be able to form in nature and merge as binary systems, mimicking the coalescence of ordinary black holes. The postmerger phase of such processes presents characteristic signatures, which appear as repeated pulses within the emitted gravitational waveform, i.e., echoes with variable amplitudes and frequencies. Future detections of these signals can shed new light on the existence of horizonless geometries and provide new information on the nature of gravity in a genuine strong-field regime. In this work we analyze phenomenological templates used to characterize echolike structures produced by exotic compact objects, and we investigate for the first time the ability of current and future interferometers to constrain their parameters. Using different models with an increasing level of accuracy, we determine the features that can be measured with the largest precision, and we span the parameter space to find the most favorable configurations to be detected. Our analysis shows that current detectors may already be able to extract all the parameters of the echoes with good accuracy, and that multiple interferometers can measure frequencies and damping factors of the signals at the level of percent.

  16. Range imaging results from polar mesosphere summer echoes

    Science.gov (United States)

    Zecha, Marius; Hoffmann, Peter; Rapp, Markus; Chen, Jenn-Shyong

    The range resolution of pulsed radars is usually limited by the transmitting pulse length and the sampling time. The so-called range imaging (RIM) has been developed to reduce these lim-itations. To apply this method the radar operates alternately over a set of distinct frequencies. Then the phase differences of the receiving signals can be used for optimization methods to generate high-resolution maps of reflections as function of range insight the pulse length. The technique has been implemented on the ALWIN VHF radar in Andenes (69) and the OSWIN VHF radar in Kühlungsborn (54N). Here we present results of the RIM method from measurements in polar mesosphere summer echoes -PMSE. These strong radar echoes are linked to ice particle clouds in the mesopause region. The dynamic of the PMSE can be reflected very well by RIM. The movement of PMSE and the edges of the extension can be tracked with a high altitude resolution. Comparisons between simultaneous measurements by RIM and by standard radar techniques demonstrate the advan-tages of RIM. Wave structures can be identified with RIM whereas they are not detectable with the lesser resolution of the standard measurements. Gravity wave parameter associated with these variations are estimated using the simultaneous measured velocity field.

  17. The Effect of Weak Collisions on the Plasma Wave Echo

    Science.gov (United States)

    Black, Carrie; Germaschewski, Kai; Ng, C. S.; Bhattacharjee, Amitava

    2008-11-01

    It has been shown recently that weak collisions, which are a singular perturbation on the collisionless Vlasov equation, have a profound effect on the underlying spectrum for linear plasma waves by eliminating the Case-Van Kampen continuous spectrum and replacing it with a complete class of discrete eigenmodes [C.S. Ng, A. Bhattacharjee, F. Skiff, Phys. Rev. Lett. 83, 1974 (1999); 92, 065002 (2004).]. This discovery has important consequences for the regime of validity of C. H. Su and C. Oberman's classical theory [Phys. Rev. Lett. 20, 427 (1968)] on the collisional decay of plasma wave echoes. Using a fully nonlinear one-dimensional Vlasov-Poisson system solver including the Lenard-Bernstein collision operator, we have studied the effects of collisions on the echoes. We have identified the Su-Oberman regime on intermediate time scales. The long-time asymptotics of the system and its relation to the complete set of discrete eigenmodes found by Ng, Bhattacharjee and Skiff will be discussed.

  18. First observations of polar mesosphere summer echoes in Antarctica

    Science.gov (United States)

    Woodman, Ronald F.; Balsley, Ben B.; Aquino, Fredy; Flores, Luis; Vazquez, Edilberto; Sarango, Martin; Huaman, Mercedes M.; Soldi, Hector

    1999-10-01

    A 25-kW peak power 50-MHz radar was installed at the Peruvian base on King George Island, Antarctica (62°S), in early 1993. A search for polar mesospheric summer echoes (PMSEs) was made during late January and early February of the first year of operation with negative results. These results have been reported in the literature [Balsley et al., 1993; 1995]. We report here results obtained during the austral summer of the second year (1994) of operation. Observations during the second year were begun earlier, i.e., closer to the austral summer solstice. PMSEs were observed during this period, albeit the echoes were much weaker than what one would expect based on earlier Poker Flat radar results at a comparable latitude (65°N) in the Northern Hemisphere. A large and measurable asymmetry in PMSE strength in the two hemispheres therefore exists. We explain this asymmetry by postulating a difference in summer mesopause temperatures between the two hemispheres of ~7.5 K. This difference has been estimated using an empirical relationship between the variations of the Poker Flat PMSE power as a function of temperature given by the mass spectrometer incoherent scatter extended (MSISE-90) model.

  19. Echo Chambers: Emotional Contagion and Group Polarization on Facebook

    Science.gov (United States)

    Del Vicario, Michela; Vivaldo, Gianna; Bessi, Alessandro; Zollo, Fabiana; Scala, Antonio; Caldarelli, Guido; Quattrociocchi, Walter

    2016-12-01

    Recent findings showed that users on Facebook tend to select information that adhere to their system of beliefs and to form polarized groups - i.e., echo chambers. Such a tendency dominates information cascades and might affect public debates on social relevant issues. In this work we explore the structural evolution of communities of interest by accounting for users emotions and engagement. Focusing on the Facebook pages reporting on scientific and conspiracy content, we characterize the evolution of the size of the two communities by fitting daily resolution data with three growth models - i.e. the Gompertz model, the Logistic model, and the Log-logistic model. Although all the models appropriately describe the data structure, the Logistic one shows the best fit. Then, we explore the interplay between emotional state and engagement of users in the group dynamics. Our findings show that communities’ emotional behavior is affected by the users’ involvement inside the echo chamber. Indeed, to an higher involvement corresponds a more negative approach. Moreover, we observe that, on average, more active users show a faster shift towards the negativity than less active ones.

  20. Sum-frequency generation echo and grating from interface.

    Science.gov (United States)

    Volkov, Victor

    2014-10-14

    The work addresses spectroscopy of fourth-order Sum Frequency Generation Echo and Grating responses as an experimental tool to study structure and dynamics at interfaces. First, it addresses experimental geometry to extract background-free fourth-order Echo and Grating responses. Further, the article provides the analytical expressions of the response functions for these nonlinearities. The derived expressions are used to model the χ((4)) two-dimensional spectral responses of a hydrated methyl acetate, which resembles a hydrated carbonyl moiety at the polar outer side of a phospholipid membrane. Orientation, transition dipole moments, and Raman tensors are obtained from the results of classical and quantum calculations, respectively. The numerical studies for the nonlinear responses under different polarization schemes and timings suggest the possibility of securely factoring of spectral contributions of χ(YYYZX) and χ(YYYZY) macroscopic susceptibilities. As such, the nonlinearities provide an experimental perspective on orientation of a generic (low-symmetry) molecular system at interfaces. Besides, the spectral properties of the tensors may reflect correlations of the in-plane and out-of-plane field components specific to the interface. For the case of a phospholipid membrane, the experiment would address in-plane and out-of-plane anisotropy of hydrogen bonding and related dynamics.

  1. Bipartite fidelity and Loschmidt echo of the bosonic conformal interface

    Science.gov (United States)

    Zhou, Tianci; Lin, Mao

    2017-12-01

    We study the quantum quench problem for a class of bosonic conformal interfaces by computing the Loschmidt echo and the bipartite fidelity. The quench can be viewed as a sudden change of boundary conditions parametrized by θ when connecting two one-dimensional critical systems. They are classified by S (θ ) matrices associated with the current scattering processes on the interface. The resulting Loschmidt echo of the quench has long time algebraic decay t-α, whose exponent also appears in the finite size bipartite fidelity as L-α/2. We perform analytic and numerical calculations of the exponent α , and find that it has a quadratic dependence on the change of θ if the prior and post-quench boundary conditions are of the same type of S , while remaining 1/4 otherwise. Possible physical realizations of these interfaces include, for instance, connecting different quantum wires (Luttinger liquids), quench of the topological phase edge states, etc., and the exponent can be detected in an x-ray edge singularity-type experiment.

  2. Spin-echo length calibration of OffSpec

    Science.gov (United States)

    Plomp, J.; de Haan, V. O.; Dalgliesh, R. M.; Langridge, S.; van Well, A. A.

    2011-06-01

    OffSpec is one of the seven new spectrometers operational from day one in the second Target Station (TS2) at the pulsed spallation neutron source ISIS. OffSpec is a time-of-flight, low-background reflectometer specialized in off-specular scattering. It is unique because in addition to conventional reflectivity techniques, it is capable of using the neutron spin-echo angle labelling technique. One of the many possibilities of using this technique is measuring structures on a surface with the length scale of 20 nm-15 μm. Up to now the calibration of this length scale was made on the prototype instrument in Delft by measuring magnetic line integrals. This showed that the pole shoe design, an essential part of the spin-echo encoding, was not perfect, resulting in a different effective magnetic encoding angle from the physical angle. Recent reflection measurements on gold gratings not only confirmed this but also resulted in a reliable calibration.

  3. Sum-frequency generation echo and grating from interface

    Energy Technology Data Exchange (ETDEWEB)

    Volkov, Victor [Bereozovaya 2A, Konstantinovo, Moscow Region 140207 (Russian Federation)

    2014-10-14

    The work addresses spectroscopy of fourth-order Sum Frequency Generation Echo and Grating responses as an experimental tool to study structure and dynamics at interfaces. First, it addresses experimental geometry to extract background-free fourth-order Echo and Grating responses. Further, the article provides the analytical expressions of the response functions for these nonlinearities. The derived expressions are used to model the χ{sup (4)} two-dimensional spectral responses of a hydrated methyl acetate, which resembles a hydrated carbonyl moiety at the polar outer side of a phospholipid membrane. Orientation, transition dipole moments, and Raman tensors are obtained from the results of classical and quantum calculations, respectively. The numerical studies for the nonlinear responses under different polarization schemes and timings suggest the possibility of securely factoring of spectral contributions of χ{sub YYYZX} and χ{sub YYYZY} macroscopic susceptibilities. As such, the nonlinearities provide an experimental perspective on orientation of a generic (low-symmetry) molecular system at interfaces. Besides, the spectral properties of the tensors may reflect correlations of the in-plane and out-of-plane field components specific to the interface. For the case of a phospholipid membrane, the experiment would address in-plane and out-of-plane anisotropy of hydrogen bonding and related dynamics.

  4. Quantum and classical correlations in electron-nuclear spin echo

    Energy Technology Data Exchange (ETDEWEB)

    Zobov, V. E., E-mail: rsa@iph.krasn.ru [Russian Academy of Sciences, Kirensky Institute of Physics, Siberian Branch (Russian Federation)

    2014-11-15

    The quantum properties of dynamic correlations in a system of an electron spin surrounded by nuclear spins under the conditions of free induction decay and electron spin echo have been studied. Analytical results for the time evolution of mutual information, classical part of correlations, and quantum part characterized by quantum discord have been obtained within the central-spin model in the high-temperature approximation. The same formulas describe discord in both free induction decay and spin echo although the time and magnetic field dependences are different because of difference in the parameters entering into the formulas. Changes in discord in the presence of the nuclear polarization β{sub I} in addition to the electron polarization β{sub S} have been calculated. It has been shown that the method of reduction of the density matrix to a two-spin electron-nuclear system provides a qualitatively correct description of pair correlations playing the main role at β{sub S} ≈ β{sub I} and small times. At large times, such correlations decay and multispin correlations ensuring nonzero mutual information and zero quantum discord become dominant.

  5. Full-waveform LiDAR echo decomposition based on wavelet decomposition and particle swarm optimization

    Science.gov (United States)

    Li, Duan; Xu, Lijun; Li, Xiaolu

    2017-04-01

    To measure the distances and properties of the objects within a laser footprint, a decomposition method for full-waveform light detection and ranging (LiDAR) echoes is proposed. In this method, firstly, wavelet decomposition is used to filter the noise and estimate the noise level in a full-waveform echo. Secondly, peak and inflection points of the filtered full-waveform echo are used to detect the echo components in the filtered full-waveform echo. Lastly, particle swarm optimization (PSO) is used to remove the noise-caused echo components and optimize the parameters of the most probable echo components. Simulation results show that the wavelet-decomposition-based filter is of the best improvement of SNR and decomposition success rates than Wiener and Gaussian smoothing filters. In addition, the noise level estimated using wavelet-decomposition-based filter is more accurate than those estimated using other two commonly used methods. Experiments were carried out to evaluate the proposed method that was compared with our previous method (called GS-LM for short). In experiments, a lab-build full-waveform LiDAR system was utilized to provide eight types of full-waveform echoes scattered from three objects at different distances. Experimental results show that the proposed method has higher success rates for decomposition of full-waveform echoes and more accurate parameters estimation for echo components than those of GS-LM. The proposed method based on wavelet decomposition and PSO is valid to decompose the more complicated full-waveform echoes for estimating the multi-level distances of the objects and measuring the properties of the objects in a laser footprint.

  6. Investigating the Group-Level Impact of Advanced Dual-Echo fMRI Combinations

    Directory of Open Access Journals (Sweden)

    Adam Kettinger

    2016-12-01

    Full Text Available Multi-echo fMRI data acquisition has been widely investigated and suggested to optimize sensitivity for detecting the BOLD signal. Several methods have also been proposed for the combination of data with different echo times. The aim of the present study was to investigate how these advance echo combination methods provide advantages over the simple averaging of echoes when state-of-the-art group-level random-effect analyses are performed. Both resting-state and task-based dual-echo fMRI data were collected from 27 healthy adult individuals (14 male, mean age = 25.75 years using standard echo-planar acquisition methods at 3T. Both resting-state and task-based data were subjected to a standard image pre-processing pipeline. Subsequently the two echoes were combined as a weighted average, using four different strategies for calculating the weights: (1 simple arithmetic averaging, (2 BOLD sensitivity weighting, (3 temporal-signal-to-noise ratio weighting and (4 temporal BOLD sensitivity weighting. Our results clearly show that the simple averaging of data with the different echoes is sufficient. Advanced echo combination methods may provide advantages on a single-subject level but when considering random-effects group level statistics they provide no benefit regarding sensitivity (i.e. group-level t-values compared to the simple echo-averaging approach. One possible reason for the lack of clear advantages may be that apart from increasing the average BOLD sensitivity at the single-subject level, the advanced weighted averaging methods also inflate the inter-subject variance. As the echo combination methods provide very similar results, the recommendation is to choose between them depending on the availability of time for collecting additional resting-state data or whether subject-level or group-level analyses are planned.

  7. Diffusion tensor cardiovascular magnetic resonance with a spiral trajectory: An in vivo comparison of echo planar and spiral stimulated echo sequences.

    Science.gov (United States)

    Gorodezky, Margarita; Scott, Andrew D; Ferreira, Pedro F; Nielles-Vallespin, Sonia; Pennell, Dudley J; Firmin, David N

    2017-12-19

    Diffusion tensor cardiovascular MR (DT-CMR) using stimulated echo acquisition mode (STEAM) with echo-planar-imaging (EPI) readouts is a low signal-to-noise-ratio (SNR) technique and therefore typically has a low spatial resolution. Spiral trajectories are more efficient than EPI, and could increase the SNR. The purpose of this study was to compare the performance of a novel STEAM spiral DT-CMR sequence with an equivalent established EPI technique. A STEAM DT-CMR sequence was implemented with a spiral readout and a reduced field of view. An in vivo comparison of DT-CMR parameters and data quality between EPI and spiral was performed in 11 healthy volunteers imaged in peak systole and diastasis at 3 T. The SNR was compared in a phantom and in vivo. There was a greater than 49% increase in the SNR in vivo and in the phantom measurements (in vivo septum, systole: SNR EPI  = 8.0 ± 2.2, SNR spiral  = 12.0 ± 2.7; diastasis: SNR EPI  = 8.1 ± 1.6, SNR spiral  = 12.0 ± 3.7). There were no significant differences in helix angle gradient (HAG) (systole: HAG EPI  = -0.79 ± 0.07 °/%; HAG spiral  = -0.74 ± 0.16 °/%; P = 0.11; diastasis: HAG EPI  = -0.63 ± 0.05 °/%; HAG spiral  = -0.56 ± 0.14 °/%; P = 0.20), mean diffusivity (MD) in systole (MD EPI  = 0.99 ± 0.06 × 10 -3 mm 2 /s, MD spiral  = 1.00 ± 0.09 × 10 -3 mm 2 /s, P = 0.23) and secondary eigenvector angulation (E2A) (systole: E2A EPI  = 61 ± 10 °; E2A spiral  = 63 ± 10 °; P = 0.77; diastasis: E2A EPI  = 18 ± 11 °; E2A spiral  = 15 ± 8 °; P = 0.20) between the sequences. There was a small difference (≈ 20%) in fractional anisotropy (FA) (systole: FA EPI  = 0.49 ± 0.03, FA spiral  = 0.41 ± 0.04; P parameters were largely similar between the two sequences. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in

  8. Photon echoes stimulated from an accumulated grating : Theory of generation and detection

    NARCIS (Netherlands)

    Hesselink, W.H.; Wiersma, Douwe A.

    1981-01-01

    We present a theoretical description of the generation and detection of photon echoes, stimulated from an accumulated frequency grating in the inhomogeneous distribution. We show that detection of the echoes takes place via interference in the sample between a properly phased and directed probe

  9. Technology of obtaining fine textured films for femtosecond instrumentation based on photon echo

    Science.gov (United States)

    Belyaev, R. W.; Bakhadurov, A. U.; Vashourin, N. S.; Gazizov, K. Sh.; Musanov, A. N.; Nikitin, D. A.; Popov, I. I.; Moroz, A. V.; Stepanov, S. A.; Sushentsov, N. I.

    2017-10-01

    This paper presents the technological approaches to the creation of thin textured films by the method of magnetron sputtering with parameters ensuring excitation of detected photon echo signals in them and the adjusted metrological characteristics of devices on a photon echo.

  10. Technology of obtaining fine textured films for femtosecond instrumentation based on photon echo

    Directory of Open Access Journals (Sweden)

    Belyaev R.W.

    2017-01-01

    Full Text Available This paper presents the technological approaches to the creation of thin textured films by the method of magnetron sputtering with parameters ensuring excitation of detected photon echo signals in them and the adjusted metrological characteristics of devices on a photon echo.

  11. Manifestation of the geometric phase in neutron spin-echo experiments

    NARCIS (Netherlands)

    Kraan, W.H.; Grigoriev, S.V.; Rekveldt, M.T.

    2010-01-01

    We show how the geometric (Berry’s) phase becomes manifest on adiabatic rotation of the polarization vector in the magnetic field configuration in the arms in a neutron spin echo (NSE) experiment.When the neutron beam used is monochromatic, a geometric phase collected in one spin-echo arm can be

  12. Echo and reverberation in a Pekeris waveguide by convolution and by the product rule

    NARCIS (Netherlands)

    Ainslie, M.A.

    2013-01-01

    The detection performance of an active sonar depends on the intensity of the signal (target echo) relative to that of a background of reverberation plus noise. The echo is calculated for a standard test problem by convolving the time-domain impulse response at the target position with itself. The

  13. Variations in the occurrence of SuperDARN F region echoes

    Directory of Open Access Journals (Sweden)

    M. Ghezelbash

    2014-02-01

    Full Text Available The occurrence of F region ionospheric echoes observed by a number of SuperDARN HF radars is analyzed statistically in order to infer solar cycle, seasonal, and diurnal trends. The major focus is on Saskatoon radar data for 1994–2012. The distribution of the echo occurrence rate is presented in terms of month of observation and magnetic local time. Clear repetitive patterns are identified during periods of solar maximum and solar minimum. For years near solar maximum, echoes are most frequent near midnight during winter. For years near solar minimum, echoes occur more frequently near noon during winter, near dusk and dawn during equinoxes and near midnight during summer. Similar features are identified for the Hankasalmi and Prince George radars in the northern hemisphere and the Bruny Island TIGER radar in the southern hemisphere. Echo occurrence for the entire SuperDARN network demonstrates patterns similar to patterns in the echo occurrence for the Saskatoon radar and for other radars considered individually. In terms of the solar cycle, the occurrence rate of nightside echoes is shown to increase by a factor of at least 3 toward solar maximum while occurrence of the near-noon echoes does not significantly change with the exception of a clear depression during the declining phase of the solar cycle.

  14. Mode suppression in the non-Markovian limit by time-gated stimulated photon echo

    NARCIS (Netherlands)

    de Boeij, W.P.; Pshenichnikov, M.S; Wiersma, D. A.

    1996-01-01

    It is demonstrated that enhanced mode suppression in stimulated photon echo experiments can be obtained by diagonal time gating of the echo. This technique is especially important when the optical dynamics of the system is non-Markovian. A two-mode Brownian oscillator model is used to analyze the

  15. CUTLASS HF radar observations of high-velocity E-region echoes

    Directory of Open Access Journals (Sweden)

    M. V. Uspensky

    Full Text Available A short event of high-velocity E-region echo observations by the Pykkvibaer HF radar is analysed to study echo parameters and the echo relation to the Farley-Buneman plasma instability. The echoes were detected in several beams aligned closely to the magnetic L-shell direction. Two echo groups were identified: one group corresponded to the classical type 1 echoes with velocities close to the nominal ion-acoustic speed of 400 ms1 , while the other group had significantly larger velocities, of the order of 700 ms1 . The mutual relationship between the echo power, Doppler velocity, spectral width and elevation angles for these two groups was studied. Plotting of echo parameters versus slant range showed that all ~700 ms1 echoes originated from larger heights and distances of 500–700 km, while all ~400 ms1 echoes came from lower heights and from farther distances; 700–1000 km. We argue that both observed groups of echoes occurred due to the Farley-Buneman plasma instability excited by strong ( ~70 mVm1 and uniformly distributed electric fields. We show that the echo velocities for the two groups were different because the echoes were received from different heights. Such a separation of echo heights occurred due to the differing amounts of ionospheric refraction at short and large ranges. Thus, the ionospheric refraction and related altitude modulation of ionospheric parameters are the most important factors to consider, when various characteristics of E-region decametre irregularities are derived from HF radar measurements.

    Key words. Ionosphere (ionospheric irregularities; plasma waves and instabilities; polar ionosphere

  16. The influence of geomagnetic activity on mesospheric summer echoes in middle and polar latitudes

    Directory of Open Access Journals (Sweden)

    O. Zeller

    2009-02-01

    Full Text Available The dependence of mesospheric VHF radar echoes during summer months on geomagnetic activity has been investigated with observation data of the OSWIN radar in Kühlungsborn (54° N and of the ALWIN radar in Andenes (69° N. Using daily mean values of VHF radar echoes and of geomagnetic activity indices in superimposed epoch analyses, the comparison of both data sets shows in general stronger radar echoes on the day of the maximum geomagnetic activity, the maximum value one day after the geomagnetic disturbance, and enhanced radar echoes also on the following 2–3 days. This phenomenon is observed at middle and polar latitudes and can be explained by precipitating particle fluxes during the ionospheric post storm effect. At polar latitudes, the radar echoes decrease however during and one day after very strong geomagnetic disturbances. The possible reason of this surprising effect is discussed.

  17. The influence of geomagnetic activity on mesospheric summer echoes in middle and polar latitudes

    Science.gov (United States)

    Zeller, O.; Bremer, J.

    2009-02-01

    The dependence of mesospheric VHF radar echoes during summer months on geomagnetic activity has been investigated with observation data of the OSWIN radar in Kühlungsborn (54° N) and of the ALWIN radar in Andenes (69° N). Using daily mean values of VHF radar echoes and of geomagnetic activity indices in superimposed epoch analyses, the comparison of both data sets shows in general stronger radar echoes on the day of the maximum geomagnetic activity, the maximum value one day after the geomagnetic disturbance, and enhanced radar echoes also on the following 2-3 days. This phenomenon is observed at middle and polar latitudes and can be explained by precipitating particle fluxes during the ionospheric post storm effect. At polar latitudes, the radar echoes decrease however during and one day after very strong geomagnetic disturbances. The possible reason of this surprising effect is discussed.

  18. De-noising methods for NMR logging echo signals based on wavelet transform

    Science.gov (United States)

    Xie, Ranhong; Wu, Youbin; Liu, Kang; Liu, Mi; Xiao, Lizhi

    2014-06-01

    The signal-to-noise ratio (SNR) of the echo signals in nuclear magnetic resonance (NMR) is one of the most important factors that affect the effective application of NMR logging. Wavelet transform can be used to remove the noise and improve the SNR of echo signals in NMR logging. This paper uses three de-noising methods to treat the NMR echo signals: modulus maxima, spatial correlation and wavelet threshold based on wavelet transform. The effects of the three methods in the noise reduction of NMR echo signals were compared by numerical simulation, core experiment and NMR logging data. The results show that while these three methods can all effectively improve the SNR of NMR echo signals and the NMR T2 inversion results, the most effective among them is the wavelet threshold method, which can obtain a higher SNR and provides more accurate formation porosity.

  19. Characteristics of C-band meteorological radar echoes at Petrolina, Northeast Brazil

    Science.gov (United States)

    da Silva Aragão, Maria Regina; Correia, Magaly De Fatima; Alves de Araújo, Heráclio

    2000-03-01

    A unique set of C-band meteorological radar echoes is analyzed. The data were obtained in Petrolina (9°24S, 40°30W), located in the semi-arid region of Northeast Brazil, from January to June 1985. The characteristics analyzed are echo areas, types and patterns.As in other tropical areas of the world, echoes with an area100 km2 dominated, making up 53% of the total number of echoes while echoes with 100 km2Petrolina surface and upper air data enable speculation that a system of frontal origin penetrating the radar area provided the dynamical forcing to form the bands in June. All five distinct patterns were more frequent in the southeast quadrant of the radar coverage. It is hypothesized that this preferential location may be explained, among other factors, by the interaction between the smooth relief and moisture advection by the southeasterly trade winds.

  20. A theory of gradient analysis

    NARCIS (Netherlands)

    Braak, ter C.J.F.

    1988-01-01

    The theory of gradient analysis is presented in this chapter, in which the heuristic techniques are integrated with regression, calibration, ordination and constrained ordination as distinct, well-defined statistical problems. The various techniques used for each type of problem are classified into

  1. Orderings for conjugate gradient preconditionings

    Science.gov (United States)

    Ortega, James M.

    1991-01-01

    The effect of orderings on the rate of convergence of the conjugate gradient method with SSOR or incomplete Cholesky preconditioning is examined. Some results also are presented that help to explain why red/black ordering gives an inferior rate of convergence.

  2. Compositional gradients in Gramineae genes

    DEFF Research Database (Denmark)

    Wong, Gane Ka-Shu; Wang, Jun; Tao, Lin

    2002-01-01

    In this study, we describe a property of Gramineae genes, and perhaps all monocot genes, that is not observed in eudicot genes. Along the direction of transcription, beginning at the junction of the 5'-UTR and the coding region, there are gradients in GC content, codon usage, and amino-acid usage...

  3. Imaging tooth enamel using zero echo time (ZTE) magnetic resonance imaging

    Science.gov (United States)

    Rychert, Kevin M.; Zhu, Gang; Kmiec, Maciej M.; Nemani, Venkata K.; Williams, Benjamin B.; Flood, Ann B.; Swartz, Harold M.; Gimi, Barjor

    2015-03-01

    In an event where many thousands of people may have been exposed to levels of radiation that are sufficient to cause the acute radiation syndrome, we need technology that can estimate the absorbed dose on an individual basis for triage and meaningful medical decision making. Such dose estimates may be achieved using in vivo electron paramagnetic resonance (EPR) tooth biodosimetry, which measures the number of persistent free radicals that are generated in tooth enamel following irradiation. However, the accuracy of dose estimates may be impacted by individual variations in teeth, especially the amount and distribution of enamel in the inhomogeneous sensitive volume of the resonator used to detect the radicals. In order to study the relationship between interpersonal variations in enamel and EPR-based dose estimates, it is desirable to estimate these parameters nondestructively and without adding radiation to the teeth. Magnetic Resonance Imaging (MRI) is capable of acquiring structural and biochemical information without imparting additional radiation, which may be beneficial for many EPR dosimetry studies. However, the extremely short T2 relaxation time in tooth structures precludes tooth imaging using conventional MRI methods. Therefore, we used zero echo time (ZTE) MRI to image teeth ex vivo to assess enamel volumes and spatial distributions. Using these data in combination with the data on the distribution of the transverse radio frequency magnetic field from electromagnetic simulations, we then can identify possible sources of variations in radiation-induced signals detectable by EPR. Unlike conventional MRI, ZTE applies spatial encoding gradients during the RF excitation pulse, thereby facilitating signal acquisition almost immediately after excitation, minimizing signal loss from short T2 relaxation times. ZTE successfully provided volumetric measures of tooth enamel that may be related to variations that impact EPR dosimetry and facilitate the development

  4. RARE/turbo spin echo imaging with Simultaneous Multislice Wave-CAIPI.

    Science.gov (United States)

    Gagoski, Borjan A; Bilgic, Berkin; Eichner, Cornelius; Bhat, Himanshu; Grant, P Ellen; Wald, Lawrence L; Setsompop, Kawin

    2015-03-01

    To enable highly accelerated RARE/Turbo Spin Echo (TSE) imaging using Simultaneous MultiSlice (SMS) Wave-CAIPI acquisition with reduced g-factor penalty. SMS Wave-CAIPI incurs slice shifts across simultaneously excited slices while playing sinusoidal gradient waveforms during the readout of each encoding line. This results in an efficient k-space coverage that spreads aliasing in all three dimensions to fully harness the encoding power of coil sensitivities. The novel MultiPINS radiofrequency (RF) pulses dramatically reduce the power deposition of multiband (MB) refocusing pulse, thus allowing high MB factors within the Specific Absorption Rate (SAR) limit. Wave-CAIPI acquisition with MultiPINS permits whole brain coverage with 1 mm isotropic resolution in 70 s at effective MB factor 13, with maximum and average g-factor penalties of gmax  = 1.34 and gavg  = 1.12, and without √R penalty. With blipped-CAIPI, the g-factor performance was degraded to gmax  = 3.24 and gavg  = 1.42; a 2.4-fold increase in gmax relative to Wave-CAIPI. At this MB factor, the SAR of the MultiBand and PINS pulses are 4.2 and 1.9 times that of the MultiPINS pulse, while the peak RF power are 19.4 and 3.9 times higher. Combination of the two technologies, Wave-CAIPI and MultiPINS pulse, enables highly accelerated RARE/TSE imaging with low SNR penalty at reduced SAR. © 2015 Wiley Periodicals, Inc.

  5. Echo decorrelation imaging of ex vivo HIFU and bulk ultrasound ablation using image-treat arrays

    Science.gov (United States)

    Fosnight, Tyler R.; Hooi, Fong Ming; Colbert, Sadie B.; Keil, Ryan D.; Barthe, Peter G.; Mast, T. Douglas

    2017-03-01

    In this study, the ability of ultrasound echo decorrelation imaging to map and predict heat-induced cell death was tested using bulk ultrasound thermal ablation, high intensity focused ultrasound (HIFU) thermal ablation, and pulse-echo imaging of ex vivo liver tissue by a custom image-treat array. Tissue was sonicated at 5.0 MHz using either pulses of unfocused ultrasound (N=12) (7.5 s, 50.9-101.8 W/cm2 in situ spatial-peak, temporal-peak intensity) for bulk ablation or focused ultrasound (N=21) (1 s, 284-769 W/cm2 in situ spatial-peak, temporal-peak intensity and focus depth of 10 mm) for HIFU ablation. Echo decorrelation and integrated backscatter (IBS) maps were formed from radiofrequency pulse-echo images captured at 118 frames per second during 5.0 s rest periods, beginning 1.1 s after each sonication pulse. Tissue samples were frozen at -80˚C, sectioned, vitally stained, imaged, and semi-automatically segmented for receiver operating characteristic (ROC) analysis. ROC curves were constructed to assess prediction performance for echo decorrelation and IBS. Logarithmically scaled mean echo decorrelation in non-ablated and ablated tissue regions before and after electronic noise and motion correction were compared. Ablation prediction by echo decorrelation and IBS was significant for both focused and bulk ultrasound ablation. The log10-scaled mean echo decorrelation was significantly greater in regions of ablation for both HIFU and bulk ultrasound ablation. Echo decorrelation due to electronic noise and motion was significantly reduced by correction. These results suggest that ultrasound echo decorrelation imaging is a promising approach for real-time prediction of heat-induced cell death for guidance and monitoring of clinical thermal ablation, including radiofrequency ablation and HIFU.

  6. Energy cables: defects pre-localization by echo-metry; Cables d'energie: prelocalisation des defauts par echometrie

    Energy Technology Data Exchange (ETDEWEB)

    Kuzyk, H. [Electricite de France (EDF), 75 - Paris (France)

    2006-05-15

    Echo-metric methods, based on the analysis of a cable response to an electromagnetic pulse, allow the pre-localization of defects. The precise localization is performed with a shock wave generator. This article describes the different echo-metric methods: 1 - low voltage pulse echo-metric methods: classical method, arc reflection method; 2 - current pulse echo-metric methods: direct voltage method, comparison methods, direct shock method, differential comparison method. (J.S.)

  7. Extending stability through hierarchical clusters in Echo State Networks

    Directory of Open Access Journals (Sweden)

    Sarah Jarvis

    2010-07-01

    Full Text Available Echo State Networks (ESN are reservoir networks that satisfy well-established criteria for stability when constructed as feedforward networks. Recent evidence suggests that stability criteria are altered in the presence of reservoir substructures, such as clusters. Understanding how the reservoir architecture affects stability is thus important for the appropriate design of any ESN. To quantitatively determine the influence of the most relevant network parameters, we analysed the impact of reservoir substructures on stability in hierarchically clustered ESNs (HESN, as they allow a smooth transition from highly structured to increasingly homogeneous reservoirs. Previous studies used the largest eigenvalue of the reservoir connectivity matrix (spectral radius as a predictor for stable network dynamics. Here, we evaluate the impact of clusters, hierarchy and intercluster connectivity on the predictive power of the spectral radius for stability. Both hierarchy and low relative cluster sizes extend the range of spectral radius values, leading to stable networks, while increasing intercluster connectivity decreased maximal spectral radius.

  8. Spin echo and nuclear orientation study of metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Pavlovsky, J.; Rotter, M.; Sedlak, B.; Lestak, L.; Bartos, M.; Prochazka, I.; Finger, M.

    Hyperfine fields on Co nuclei in amorphous as-quenched and heat-treated Co/sub 75/Fe/sub 5/B/sub 20/ samples were studied by conventional NMR and by very low temperature nuclear orientation techniques. The /sup 59/Co spin echo measurement at 1.4 K yielded broad spectra between 130 - 260 MHz, with narrow maxima at 145.5 MHz and 155.1 MHz for as-quenched sample and with a broad maximum at 227 MHz for heat-treated sample well below the recrystallization point. The /sup 60/Co nuclear orientation measurements gave the mean value of the hyperfine field 15 T nearly independent of the sample heat-treatment. The spin-lattice relaxation was studied by pulse NMR and also by nuclear orientation thermal cycling technique.

  9. Heavy ion collision evolution modeling with ECHO-QGP

    Science.gov (United States)

    Rolando, V.; Inghirami, G.; Beraudo, A.; Del Zanna, L.; Becattini, F.; Chandra, V.; De Pace, A.; Nardi, M.

    2014-11-01

    We present a numerical code modeling the evolution of the medium formed in relativistic heavy ion collisions, ECHO-QGP. The code solves relativistic hydrodynamics in (3 + 1)D, with dissipative terms included within the framework of Israel-Stewart theory; it can work both in Minkowskian and in Bjorken coordinates. Initial conditions are provided through an implementation of the Glauber model (both Optical and Monte Carlo), while freezeout and particle generation are based on the Cooper-Frye prescription. The code is validated against several test problems and shows remarkable stability and accuracy with the combination of a conservative (shock-capturing) approach and the high-order methods employed. In particular it beautifully agrees with the semi-analytic solution known as Gubser flow, both in the ideal and in the viscous Israel-Stewart case, up to very large times and without any ad hoc tuning of the algorithm.

  10. Charged questions concerning noctilucent clouds and polar mesospheric summer echoes

    Science.gov (United States)

    Gumbel, J.

    2012-12-01

    Noctilucent clouds (NLC) and polar mesosphere summer echoes (PMSE) are prominent phenomena related to ice layers in the Earth's atmosphere at 80-90 km. These phenomena have been recognized as important tracers for interactions and variability in this part of the atmosphere. In order to draw proper conclusions from global observations, a better understanding of the microphysics of mesospheric ice grains is needed. This presentation provides an overview of current research topics concerning NLC and PMSE, with an emphasis is on charging pocesses. NLC and PMSE coincide with the ionospheric D-region, thus constituting a weakly ionized dusty plasma. Prominent open questions concern the efficiency of charge capture and photoionization, the role of charges in ice nucleation, charge diffusion, and interactions between ice and meteoric material.

  11. EChO payload electronics architecture and SW design

    Science.gov (United States)

    Focardi, M.; Di Giorgio, A. M.; Farina, M.; Pancrazzi, M.; Ottensamer, R.; Lim, T. L.; Pezzuto, S.; Micela, G.; Pace, E.

    2015-12-01

    EChO is a three-modules (VNIR, SWIR, MWIR), highly integrated spectrometer, covering the wavelength range from 0.55 μ m to 11.0 μ m. The baseline design includes the goal wavelength extension to 0.4 μ m while an optional LWIR module extends the range to the goal wavelength of 16.0 μ m. An Instrument Control Unit (ICU) is foreseen as the main electronic subsystem interfacing the spacecraft and collecting data from all the payload spectrometers modules. ICU is in charge of two main tasks: the overall payload control ( Instrument Control Function) and the housekeepings and scientific data digital processing ( Data Processing Function), including the lossless compression prior to store the science data to the Solid State Mass Memory of the Spacecraft. These two main tasks are accomplished thanks to the Payload On Board Software (P-OBSW) running on the ICU CPUs.

  12. 3D spatially encoded and accelerated TE-averaged echo planar spectroscopic imaging in healthy human brain.

    Science.gov (United States)

    Iqbal, Zohaib; Wilson, Neil E; Thomas, M Albert

    2016-03-01

    Several different pathologies, including many neurodegenerative disorders, affect the energy metabolism of the brain. Glutamate, a neurotransmitter in the brain, can be used as a biomarker to monitor these metabolic processes. One method that is capable of quantifying glutamate concentration reliably in several regions of the brain is TE-averaged (1) H spectroscopic imaging. However, this type of method requires the acquisition of multiple TE lines, resulting in long scan durations. The goal of this experiment was to use non-uniform sampling, compressed sensing reconstruction and an echo planar readout gradient to reduce the scan time by a factor of eight to acquire TE-averaged spectra in three spatial dimensions. Simulation of glutamate and glutamine showed that the 2.2-2.4 ppm spectral region contained 95% glutamate signal using the TE-averaged method. Peak integration of this spectral range and home-developed, prior-knowledge-based fitting were used for quantitation. Gray matter brain phantom measurements were acquired on a Siemens 3 T Trio scanner. Non-uniform sampling was applied retrospectively to these phantom measurements and quantitative results of glutamate with respect to creatine 3.0 (Glu/Cr) ratios showed a coefficient of variance of 16% for peak integration and 9% for peak fitting using eight-fold acceleration. In vivo scans of the human brain were acquired as well and five different brain regions were quantified using the prior-knowledge-based algorithm. Glu/Cr ratios from these regions agreed with previously reported results in the literature. The method described here, called accelerated TE-averaged echo planar spectroscopic imaging (TEA-EPSI), is a significant methodological advancement and may be a useful tool for categorizing glutamate changes in pathologies where affected brain regions are not known a priori. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

  13. Research on Marine Photovoltaic Power Forecasting Based on Wavelet Transform and Echo State Network

    Directory of Open Access Journals (Sweden)

    Xinhui Du

    2017-08-01

    Full Text Available With the rapid development of photovoltaic power generation technology, photovoltaic power generation system has gradually become an important component of the integrated energy system of marine. High precision short-term photovoltaic power generation forecasting is becoming one of the key technologies in ship energy saving and ship energy efficiency improving. Aiming at the characteristics of marine photovoltaic power generation system, we designed a highprecision power forecasting model (WT+ESN for marine photovoltaic power generation system with anti-marine environmental interference. In this model, the information mining of the photovoltaic system in marine environment is carried out based on wavelet theory, then the forecasting model basing on echo state network is construct ed. Lastly, three kinds of error metrics are compared with the three traditional models by Matlab, the result shows that the model has high forecasting accuracy and strong robustness to marine environmental factors, which is of great significance to save fuel for ships, improve the energy utilization rate and assist the power dispatching and fuel dispatching of the marine power generation system.

  14. Tissue electrical property mapping from zero echo-time magnetic resonance imaging.

    Science.gov (United States)

    Lee, Seung-Kyun; Bulumulla, Selaka; Wiesinger, Florian; Sacolick, Laura; Sun, Wei; Hancu, Ileana

    2015-02-01

    The capability of magnetic resonance imaging (MRI) to produce spatially resolved estimation of tissue electrical properties (EPs) in vivo has been a subject of much recent interest. In this work we introduce a method to map tissue EPs from low-flip-angle, zero-echo-time (ZTE) imaging. It is based on a new theoretical formalism that allows calculation of EPs from the product of transmit and receive radio-frequency (RF) field maps. Compared to conventional methods requiring separation of the transmit RF field (B(1)(+)) from acquired MR images, the proposed method has such advantages as: 1) reduced theoretical error, 2) higher acquisition speed, and 3) flexibility in choice of different transmit and receive RF coils. The method is demonstrated in electrical conductivity and relative permittivity mapping in a salt water phantom, as well as in vivo measurement of brain conductivity in healthy volunteers. The phantom results show the validity and scan-time efficiency of the proposed method applied to a piece-wise homogeneous object. Quality of in vivo EP results was limited by reconstruction errors near tissue boundaries, which highlights need for image segmentation in EP mapping in a heterogeneous medium. Our results show the feasibility of rapid EP mapping from MRI without B(1)(+) mapping.

  15. Quantitative visualization of coherent flow structures in alluvial channels using multibeam echo-sounding

    Science.gov (United States)

    Parsons, D. R.; Simmons, S.; Best, J.

    2010-12-01

    Multibeam Echo-Sounder systems have developed rapidly over recent decades and are routinely deployed to provide high-resolution bathymetric details in range of aquatic environments. Modern data handling and storage technologies now facilitate the logging of the raw acoustic back-scatter information that was previously discarded by these systems. This paper describes methodologies that exploit this logging capability to quantify the concentration and dynamics of suspended sediment within the water column and presents a novel method that also allows for quantification of 2D flow velocities. This development provides a multi-purpose tool for the holistic surveying of the process linkages between flow, sediment transport and bed morphology. The application of this new technique is illustrated with reference to flow over alluvial sand dunes, which allows, for the first time in a field study, quantitative visualization of larg-scale, whole flow field, turbulent coherent flow structures, associated with the dune leeside, that are responsible for suspending bed sediment. This methodology holds great potential for use in a wide range of aqueous geophysical flows. CFS captured by MBES in the lee of an alluvial dune. Contours of suspended sediment concentration and superimposed 2D flow velocity vectors

  16. Seasonal variations of long period oscillations in the mesosphere at high- and mid-latitudes and their relation to mesospheric summer echoes

    Science.gov (United States)

    Zeller, Olof; Hoffmann, Peter; Bremer, Juergen; Singer, Werner

    Continuous MF and meteor radar observations allow detailed studies of the wind field in the mesosphere and lower thermosphere, which is characterized by a high variability due to the presence of gravity and tidal waves as well as planetary waves. Here the seasonal variation of long period oscillations (periods of few days) is used to indicate the presence of transient planetary waves in the mesosphere at high and mid-latitudes. Our studies are based on wind measurements from meteor and MF radars at Andenes (69° N, 16° E) and Juliusruh (55° N, 13° E). These measurements are supplemented by mesospheric temperatures derived from meteor decay times. For investigations of wind and temperature oscillations wavelet analyses have been performed showing the seasonal varations of their preferred periods and amplitudes. The activity of oscillations with a period in the range 2 - 4 d have their maximum during summer while the long period ones (˜10 d) occur preferably in winter. Oscillations with periods of 4 - 7 d occur in every season. Such periods are not only observed in wind and temperature variations, but also in variations of (polar) mesosphere summer echos (P)MSE observed by VHF radars in Kuehlungsborn (54° N, 12° E) and Andenes. (P)MSE are connected with very cold temperatures where ice particles can exist. Due to an equatorward directed meridional temperature gradient variations of meridional wind and temperature are positively correlated. Generally radar echoes at mid latitudes are strongly affected by meridional wind variations due to a mean temperature around the frost point of water vapour. In contrast there is mostly no significant impact of the meridional wind on radar echoes at polar latitudes. A mean temperature well below the frost point and a weaker meridional temperature gradient than at mid latitudes are reasons for this reduced impact. But because of higher temperatures in 2002 long period temperature and meridional wind variations impact the PMSE

  17. Toppling analysis of the Echo Cliffs precariously balanced rock

    Science.gov (United States)

    Veeraraghavan, Swetha; Hudnut, Kenneth W.; Krishnan, Swaminathan

    2017-01-01

    Toppling analysis of a precariously balanced rock (PBR) can provide insight into the nature of ground motion that has not occurred at that location in the past and, by extension, can constrain peak ground motions for use in engineering design. Earlier approaches have targeted 2D models of the rock or modeled the rock–pedestal contact using spring‐damper assemblies that require recalibration for each rock. Here, a method to model PBRs in 3D is presented through a case study of the Echo Cliffs PBR. The 3D model is created from a point cloud of the rock, the pedestal, and their interface, obtained using terrestrial laser scanning. The dynamic response of the model under earthquake excitation is simulated using a rigid‐body dynamics algorithm. The veracity of this approach is demonstrated through comparisons against data from shake‐table experiments. Fragility maps for toppling probability of the Echo Cliffs PBR as a function of various ground‐motion parameters, rock–pedestal interface friction coefficient, and excitation direction are presented. These fragility maps indicate that the toppling probability of this rock is low (less than 0.2) for peak ground acceleration (PGA) and peak ground velocity (PGV) lower than 3  m/s2 and 0.75  m/s, respectively, suggesting that the ground‐motion intensities at this location from earthquakes on nearby faults have most probably not exceeded the above‐mentioned PGA and PGV during the age of the PBR. Additionally, the fragility maps generated from this methodology can also be directly coupled with existing probabilistic frameworks to obtain direct constraints on unexceeded ground motion at a PBR’s location.

  18. Artificial intelligence for the EChO mission planning tool

    Science.gov (United States)

    Garcia-Piquer, Alvaro; Ribas, Ignasi; Colomé, Josep

    2015-12-01

    The Exoplanet Characterisation Observatory (EChO) has as its main goal the measurement of atmospheres of transiting planets. This requires the observation of two types of events: primary and secondary eclipses. In order to yield measurements of sufficient Signal-to-Noise Ratio to fulfil the mission objectives, the events of each exoplanet have to be observed several times. In addition, several criteria have to be considered to carry out each observation, such as the exoplanet visibility, its event duration, and no overlapping with other tasks. It is expected that a suitable mission plan increases the efficiency of telescope operation, which will represent an important benefit in terms of scientific return and operational costs. Nevertheless, to obtain a long term mission plan becomes unaffordable for human planners due to the complexity of computing the huge number of possible combinations for finding an optimum solution. In this contribution we present a long term mission planning tool based on Genetic Algorithms, which are focused on solving optimization problems such as the planning of several tasks. Specifically, the proposed tool finds a solution that highly optimizes the defined objectives, which are based on the maximization of the time spent on scientific observations and the scientific return (e.g., the coverage of the mission survey). The results obtained on the large experimental set up support that the proposed scheduler technology is robust and can function in a variety of scenarios, offering a competitive performance which does not depend on the collection of exoplanets to be observed. Specifically, the results show that, with the proposed tool, EChO uses 94% of the available time of the mission, so the amount of downtime is small, and it completes 98% of the targets.

  19. T2{sup *} mapping from multi-echo dixon sequence on gadoxetic acid-enhanced magnetic resonance imaging for the hepatic fat quantification: Can it be used for hepatic function assessment?

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, Hyun Suk; Lee, Jeong Min; Yoon, Jeong Hee; Kang, Hyo Jin; Lee, Sang Min; Yang, Hyun Kyung; Han, Joon Koo [Dept. of Radiology, Seoul National University Hospital, Seoul (Korea, Republic of)

    2017-08-01

    To evaluate the diagnostic value of T2{sup *} mapping using 3D multi-echo Dixon gradient echo acquisition on gadoxetic acid-enhanced liver magnetic resonance imaging (MRI) as a tool to evaluate hepatic function. This retrospective study was approved by the IRB and the requirement of informed consent was waived. 242 patients who underwent liver MRIs, including 3D multi-echo Dixon fast gradient-recalled echo (GRE) sequence at 3T, before and after administration of gadoxetic acid, were included. Based on clinico-laboratory manifestation, the patients were classified as having normal liver function (NLF, n = 50), mild liver damage (MLD, n = 143), or severe liver damage (SLD, n = 30). The 3D multi-echo Dixon GRE sequence was obtained before, and 10 minutes after, gadoxetic acid administration. Pre- and post-contrast T2{sup *} values, as well as T2{sup *} reduction rates, were measured from T2{sup *} maps, and compared among the three groups. There was a significant difference in T2{sup *} reduction rates between the NLF and SLD groups (−0.2 ± 4.9% vs. 5.0 ± 6.9%, p = 0.002), and between the MLD and SLD groups (3.2 ± 6.0% vs. 5.0 ± 6.9%, p = 0.003). However, there was no significant difference in both the pre- and post-contrast T2{sup *} values among different liver function groups (p = 0.735 and 0.131, respectively). A receiver operating characteristic (ROC) curve analysis showed that the area under the ROC curve for using T2{sup *} reduction rates to differentiate the SLD group from the NLF group was 0.74 (95% confidence interval: 0.63–0.83). Incorporation of T2{sup *} mapping using 3D multi-echo Dixon GRE sequence in gadoxetic acid-enhanced liver MRI protocol may provide supplemental information for liver function deterioration in patients with SLD.

  20. Controlling Photon Echo in a Quantum-Dot Semiconductor Optical Amplifier Using Shaped Excitation

    Science.gov (United States)

    Mishra, A. K.; Karni, O.; Khanonkin, I.; Eisenstein, G.

    2017-05-01

    Two-pulse photon-echo-based quantum-memory applications require a precise control over the echo strength and appearance time. We describe a numerical investigation of observation and control of photon echo in a room-temperature InAs /InP -based quantum-dot (QD) semiconductor optical amplifier (SOA). We address an important case where the spectral excitation is narrower than the inhomogeneous broadening of the SOA. It is revealed that, in such a QD SOA, the amplitude of the echo pulse depends not only on the excitation-to-rephasing pulse temporal separation but also on the interference among the rephrasing pulse and the echo pulses generated during the propagation along the amplifier. More importantly, the appearance time and amplitude of the echo pulse can be precisely controlled by shaping the first (excitation) pulse. We also assert that deviations in the echo pulse stemming from the SOA gain inhomogeneity can be compensated for so as to be utilized in quantum coherent information processing.