Comparison of multi-echo and single-echo gradient-recalled echo sequences for SPIO-enhanced Liver MRI at 3 T

International Nuclear Information System (INIS)

Choi, J.S.; Kim, M.-J.; Kim, J.H.; Choi, J.-Y.; Chung, Y.E.; Park, M.-S.; Kim, K.W.

2010-01-01

Aim: To assess the utility of a T2*-weighted, multi-echo data imaging combination sequenced on superparamagnetic iron oxide (SPIO)-enhanced liver magnetic resonance imaging (MRI) using a 3 T system. Materials and methods: Fifty patients underwent SPIO-enhanced MRI at 3 T using T2*-weighted, single-echo, gradient-recalled echo (GRE) sequences [fast imaging with steady precession; repetition time (TR)/echo time (TE), 126 ms/9 ms; flip angle, 30 o ] and multi-echo GRE (multi-echo data image combination) sequences (TR/TE, 186 ms/9 ms; flip angle, 30 o ). Three radiologists independently reviewed the images in a random order. The sensitivity and accuracy for the detection of focal hepatic lesions (a total of 76 lesions in 33 patients; 48 solid lesions, 28 non-solid lesions) were compared by analysing the area under the receiver operating characteristic curves. Image artefacts (flow artefacts, susceptibility artefacts, dielectric artefacts, and motion artefacts), lesion conspicuity, and overall image quality were evaluated according to a four-point scale: 1, poor; 2, fair; 3, good; 4, excellent. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the lesions were compared. Results: Image artefacts were more frequent with single-echo GRE (p < 0.05). The mean scale of image quality assessment for flow, susceptibility, dielectric, and motion artefacts were 2.76, 3.13, 3.42, and 2.89 with singe-echo, respectively, compared with 3.47, 3.43, 3.47, and 3.39, respectively, with multi-echo GRE. There was no significant difference in lesion conspicuity between single-echo (3.15) and multi-echo (3.30) GRE sequences. The overall image quality was significantly (p < 0.05) better with multi-echo (3.37) than with single-echo GRE (2.89). The mean SNR and CNR of the lesions were significantly (p < 0.05) higher on multi-echo (79 ± 23 and 128 ± 59, respectively) images than on single-echo (38 ± 11 and 102 ± 44, respectively) images. Lesion detection accuracy and

Contrast-enhanced dynamic MR imaging of parasellar tumor using fast spin-echo sequence

International Nuclear Information System (INIS)

Kusunoki, Katsusuke; Ohue, Shiro; Ichikawa, Haruhisa; Saito, Masahiro; Sadamoto, Kazuhiko; Sakaki, Saburo; Miki, Hitoshi.

1995-01-01

We have applied a new dynamic MRI technique that uses a fast spin-echo sequence to parasellar tumors. This sequence has less susceptible effect and better spatial resolution than a gradient echo sequence, providing faster images than a short spin-echo sequence does. Image was obtained in the coronal or sagittal plane using a 1.5T clinical MRI system, and then, dynamic MR images were acquired every 10 to 20 sec after administration of Gd-DTPA (0.1 mmol/kg). The subjects were 12 patients (5 microadenomas, 5 macroadenomas and 2 Rathke's cleft cysts) and 5 normal volunteers. As for volunteers, the cavernous sinus, pituitary stalk and posterior pituitary gland were contrasted on the first image, followed by visualization of the proximal portion adjacent to the junction of the infundibulum and the anterior pituitary gland, and finally by contrasting the distal portion of the anterior pituitary gland. There was a difference with respect to tumor contrast between microadenomas and macroadenomas. In the case of the macroadenomas, the tumor was contrasted at the same time as, or faster than the anterior pituitary gland, while with the microadenomas the tumor was enhanced later than the anterior pituitary gland. No enhancement with contrast medium was seen in Rathke's cleft cysts. In addition, it was possible to differentiate a recurrent tumor from a piece of muscle placed at surgery since the images obtained by the fast spin-echo sequence were clearer than those obtained by gradient echo sequence. (author)

Characteristics of spondylotic myelopathy on 3D driven-equilibrium fast spin echo and 2D fast spin echo magnetic resonance imaging: a retrospective cross-sectional study.

Science.gov (United States)

Abdulhadi, Mike A; Perno, Joseph R; Melhem, Elias R; Nucifora, Paolo G P

2014-01-01

In patients with spinal stenosis, magnetic resonance imaging of the cervical spine can be improved by using 3D driven-equilibrium fast spin echo sequences to provide a high-resolution assessment of osseous and ligamentous structures. However, it is not yet clear whether 3D driven-equilibrium fast spin echo sequences adequately evaluate the spinal cord itself. As a result, they are generally supplemented by additional 2D fast spin echo sequences, adding time to the examination and potential discomfort to the patient. Here we investigate the hypothesis that in patients with spinal stenosis and spondylotic myelopathy, 3D driven-equilibrium fast spin echo sequences can characterize cord lesions equally well as 2D fast spin echo sequences. We performed a retrospective analysis of 30 adult patients with spondylotic myelopathy who had been examined with both 3D driven-equilibrium fast spin echo sequences and 2D fast spin echo sequences at the same scanning session. The two sequences were inspected separately for each patient, and visible cord lesions were manually traced. We found no significant differences between 3D driven-equilibrium fast spin echo and 2D fast spin echo sequences in the mean number, mean area, or mean transverse dimensions of spondylotic cord lesions. Nevertheless, the mean contrast-to-noise ratio of cord lesions was decreased on 3D driven-equilibrium fast spin echo sequences compared to 2D fast spin echo sequences. These findings suggest that 3D driven-equilibrium fast spin echo sequences do not need supplemental 2D fast spin echo sequences for the diagnosis of spondylotic myelopathy, but they may be less well suited for quantitative signal measurements in the spinal cord.

Inaudible functional MRI using a truly mute gradient echo sequence

International Nuclear Information System (INIS)

Marcar, V.L.; Girard, F.; Rinkel, Y.; Schneider, J.F.; Martin, E.

2002-01-01

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.)

Application of velocity imaging and gradient-recalled echo in neuroimaging

International Nuclear Information System (INIS)

Boyko, O.B.; Pelc, N.J.; Shimakawa, A.

1990-01-01

This paper describes the initial clinical experience with imaging blood flow at 1.5 T by means of a phase-sensitive gradient refocused pulse sequence. A spin-echo flow-encoding technique was modified to a gradient recalled acquisition in a steady state sequence, producing a velocity imaging and gradient recalled echo (VIGRE) sequence (TR = 24 msec, TE = 13 msec, flip angle = 45 degrees, 24-cm field of view, 7 mm contiguous sections). Two views per phase-encoding step are acquired; one using the first-moment flow-compensation gradient waveform and the second having a (selectable) nonzero first moment. A phase subtraction image is obtained where the signal is dependent on the direction and velocity of flow. The sequence was done following routine spin-echo imaging in 35 patients

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.)

Liver iron content determined by MRI. Spin-echo vs. gradient-echo

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Juchems, M.S.; Wunderlich, A.P. [Universitaetskliniken Ulm (Germany). Klinik fuer Diagnostische und Interventionelle Radiologie; Cario, H. [Universitaetskliniken Ulm (Germany). Klinik fuer Kinder- und Jugendmedizin; Schmid, M. [Stadtspital Triemli, Zuerich (Switzerland). Medizinische Onkologie und Haematologie

2012-05-15

Purpose: Liver iron content (LIC) measurement plays a central role in the management of patients with transfusional iron overload. Calculating the LIC with data obtained from standardized MRI sequences represents an attractive alternative diagnostic possibility. The purpose of this study was to compare the LIC measurement obtained with gradient-echo (GRE) sequences to the mean liver proton transverse relaxation (R2) acquired with SE sequences. Materials and Methods: 68 patients with iron overload (median age: 24, range: 3 - 88) underwent 1.5 T MRI for liver iron content measurement. All patients received spin-echo (SE) and gradient-echo (GRE) sequences. Results: The two MRI methods revealed different liver iron content results although a significant correlation was found (r = 0.85, p < 0.001). Values evaluated using GRE sequences (median: 260 {mu}mol/g dry weight [d.w.], range: 6 - 732) were generally higher than those obtained by SE examinations (median: 161 {mu}mol /g d.w., range: 5 - 830). Conclusion: In conclusion, our study revealed different results for both MRI measurements, which could lead to different decisions concerning the management of chelation therapy in individual patients. (orig.)

Exact algebraization of the signal equation of spoiled gradient echo MRI

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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.

Fast spine echo and fast fluid attenuated inversion recovery sequences in multiple sclerosis

International Nuclear Information System (INIS)

Paolillo, Andrea; Giugni, Elisabetta; Bozzao, Alessandro; Bastianello, Stefano

1997-01-01

Fast spin echo (FSE) and fast fluid attenuated inversion recovery (fast-FLAIR) sequences, were compared with conventional spin echo (CSE) in quantitating multiple sclerosis (MS) lesion burden. For each sequence, the total number and volume of MS lesions were calculated in 38 remitting multiple sclerosis patients using a semiautomated lesion detection program. Conventional spin echo, fast spin echo, and fast fluid attenuated inversion recovery image were reported on randomly and at different times by two expert observers. Interobserver differences, the time needed to quantitative multiple sclerosis lesions and lesion signal intensity (contrast-to-noise ratio and overall contrast) were considered. The lesions were classified by site into infratentorial, white matter and cortical/subcortical. A total of 2970 lesions with a volume of 961.7 cm 3 was calculated on conventional spin echo images. Fast spin echo images depicted fewer (16.6%; p < .005) and smaller (24.9%; p < .0001) lesions and the differences were statistically significant. Despite an overall nonsignificant reduction for fast-FLAIR images (-5% and 4.8% for lesion number and volume, respectively), significantly lower values (lesion number: p < 0.1; volume: p < .04)were observed for infratentorial lesions, while significantly higher values were seen for cortical/subcortical lesions (lesion number: p < .01; volume: p < .02). A higher lesion/white matter contrast (p < .002), a significant time saving for lesion burden quantitation (p < .05) and very low interobserver variability were found in favor of fast-FLAIR. Our data suggest that, despite the limitations regarding infratentorial lesions, fast-FLAIR sequences are indicated in R studies because of their good identification of cortical/subcortical lesions, almost complete interobserver agreement, higher contrast-to-noise ratio and limited time needed for semiautomated quantitation

Increased flow sensitivity from gradient recalled echoes and short TRs

International Nuclear Information System (INIS)

Hearshen, D.O.; Froelich, J.W.; Wehrli, F.W.; Haggar, A.M.; Shimakawa, A.

1986-01-01

Time-of-flight effects from flow have been characterized in spin-echo images. ''Paradoxical'' enhancement and flow void are observed. Similar enhancement is seen on GRASS images. With no flow void and gradients existing throughout the volume, spins experiencing radio-frequency pulses will give rise to signals even for fast flow, providing a greater velocity sensitivity. GRASS images were obtained from a volunteer with a blood pressure cuff placed over the right thigh. With the cuff inflated, flow in the popliteal vein results in signal saturation. Increasing TR increases intensity in the popliteal vein relative to other vessels. This suggests a clinical role for the technique in assessment of slow flow

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.

Clinical characteristics in normal healthy adults with microbleeds on echo-planar gradient-echo T2*-weighted MRI

International Nuclear Information System (INIS)

Takahashi, Wakoh; Ide, Michiru; Ohnuki, Tomohide; Takagi, Shigeharu; Shinohara, Yukito

2004-01-01

The gradient-echo T 2 * -weighted sequence in magnetic resonance imaging is known to be useful for detecting microbleeds (MBs) in patients with intracranial hemorrhage or lacunar stroke. We investigated the characteristics of apparently healthy adults with MBs but without stroke, employing echo-planar gradient-echo T 2 * -weighted MRI. The subjects were recruited from among 3,537 participants who underwent brain check-ups at the HIMEDIC Imaging Center. Of the 3,537 participants, 3,296 (mean age, 55±11 years) without any history of cerebrovascular disease or apparent focal neurological manifestations were selected for the present study. MBs on echo-planar gradient-echo T 2 * -weighted MRI were observed in 74 (2.2%) of the 3,296 subjects. Of a total of 133 lesions found in these 74 persons, 31 were located in the basal ganglia or cortico-subcortical regions. Thirty were in the deep white matter, 19 in the thalamus, 16 in the cerebellum, and 6 in the brain stem. The subjects with MBs were significantly older than the subjects without MBs, and the mean values for their systolic and diastolic blood pressures were higher than those in the subjects without MBs. Asymptomatic cerebral infarction, periventricular hyperintensity, and deep and subcortical white matter hyperintensity on T 1 - and T 2 -weighted MRI were more frequent in the subjects with MBs, as compared with those without MBs. Asymptomatic cerebral infarction, periventricular hyperintensity, and deep and subcortical white matter hyperintensity on T 1 - and T 2 -weighted MRI were more frequent in the subjects with MBs of the basal ganglia or thalamus than in those with MBs in other regions. MBs on echo-planar gradient-echo T 2 * -weighted MRI were thus relatively rare in apparently healthy adults. However, MBs in the basal ganglia or thalamus are suggested to be closely related to intracerebral microangiopathy. Persons with MBs in such regions should therefore be carefully checked for cerebrovascular risk

[3D FSPGR (fast spoiled gradient echo) magnetic resonance imaging in the diagnosis of focal cortical dysplasia in children].

Science.gov (United States)

Alikhanov, A A; Sinitsyn, V E; Perepelova, E M; Mukhin, K Iu; Demushkina, A A; Omarova, M O; Piliia, S V

2001-01-01

Small dysplastic lesions of the cerebral cortex are often missed by conventional MRI methods. The identification of subtle structural abnormalities by traditional multiplanar rectilinear slices is often limited by the complex convolutional pattern of the brain. We used a method of FSPGR (fast spoiled gradient-echo) of three-dimensional MRI data that improves the anatomical display of the sulcal structure of the hemispheric convexities. It also reduces the asymmetric sampling of gray-white matter that may lead to false-positive results. We present 5 from 12 patients with dysplastic cortical lesions in whom conventional two-dimensional and three-dimensional MRI with multiplanar reformatting was initially considered normal. Subsequent studies using 3D FSPGR identified various types of focal cortical dysplasia in all. These results indicate that an increase in the detection of subtle focal dysplastic lesions may be accomplished when one improves the anatomical display of the brain sulcal structure by performing 3D FSPGR.

Comparison between two.magnetic resonance sequences (spin-echo and gradient-echo) in the analysis of lesions of the knee joint meniscus

International Nuclear Information System (INIS)

Marti-Bonati, L.; Casillas, C.

1999-01-01

To compare the diagnostic reliability, the proportion of common diagnoses and the degree of agreement between the results of two magnetic resonance (MR) sequences in the diagnosis of lesions of the meniscus of the knee. One hundred consecutive patients were studied prospectively by MR (1,5 Teslas). All of them underwent T1-weighted spin-echo and T1 and T2-weighted gradient-echo sequences. The final diagnosis was based on the combined results of four imaging sequences. The sensitivity, specificity, positive predictive value (PPV) and negative predictive (NPV) in terms of the final diagnosis were calculated for each meniscus and MR technique. The chi.squared test and kappa test were employed for the statistical analysis. There were discrepancies between the final diagnosis and the spin-echo sequence in 4 cases and between the final diagnosis and the gradient-echo sequences in 5 Both spin-echo and gradient-echo sequences showed the same diagnostic reliabilities: sensitivity of 0.98, specificity of 0.99, PPV of 0.98 and NPV of 0.99. The correlation between the two sequences was highly significant (chi-squared, p < 0.001) with a very high rate of agreement (kappa=0.84). The two sequences can be considered equally reliable in the study of meniscal lesions. (Author) 7 refs

A new technique for MR elastography of the supraspinatus muscle: A gradient-echo type multi-echo sequence.

Science.gov (United States)

Ito, Daiki; Numano, Tomokazu; Mizuhara, Kazuyuki; Takamoto, Koichi; Onishi, Takaaki; Nishijo, Hisao

2016-10-01

Magnetic resonance elastography (MRE) can measure tissue stiffness quantitatively and noninvasively. Supraspinatus muscle injury is a significant problem among throwing athletes. The purpose of this study was to develop an MRE technique for application to the supraspinatus muscle by using a conventional magnetic resonance imaging (MRI). MRE acquisitions were performed with a gradient-echo type multi-echo MR sequence at 100Hz pneumatic vibration. A custom-designed vibration pad was used as a pneumatic transducer in order to adapt to individual shoulder shapes. In a gradient-echo type multi-echo MR sequence, without motion encoding gradient (MEG) that synchronizes with vibrations, bipolar readout gradient lobes achieved a similar function to MEG (MEG-like effect). In other words, a dedicated MRE sequence (built-in MEG) is not always necessary for MRE. In this study, 7 healthy volunteers underwent MRE. We investigated the effects of direction of the MEG-like effect and selected imaging planes on the patterns of wave propagation (wave image). The results indicated that wave images showed clear wave propagation on a condition that the direction of the MEG-like effect was nearly perpendicular to the long axis of the supraspinatus muscle, and that the imaging plane was superior to the proximal supraspinatus muscle. This limited condition might be ascribed to specific features of fibers in the supraspinatus muscle and wave reflection from the boundaries of the supraspinous fossa. The mean stiffness of the supraspinatus muscle was 10.6±3.17kPa. Our results demonstrated that using MRE, our method can be applied to the supraspinatus muscle by using conventional MRI. Copyright © 2016 Elsevier Inc. All rights reserved.

Diagnosis of partial and complete rotator cuff tears using combined gradient echo and spin echo imaging

International Nuclear Information System (INIS)

Tuite, M.J.; Yandow, D.R.; DeSmet, A.A.; Orwin, J.F.; Quintana, F.A.

1994-01-01

Most magnetic resonance (MR) studies evaluating the rotator cuff for tears have used T2-weighted imaging in the coronal oblique and sagittal oblique planes. T2 * -weighted gradient echo imaging, however, has advantages over spin echo imaging, including contiguous slices without cross-talk, high contrast around the cuff, and intrinsically shorter imaging times which can be used to increase the number of signals averaged and thus improve the signal-to-noise ratio. We reviewed the shoulder MR scans of 87 consecutive patients who underwent both a MR scan and a shoulder arthroscopy during which the size of tears, if present, was graded. The reviewers were blinded as to the history and arthroscopic results. The MR scans included oblique coronal T2 * -weighted gradient echo and oblique sagittal T2-weighted spin echo images. MR cuff grades were correlated with arthroscopic findings. For complete tears, the sensitivity of MR was 0.91 and the specificity 0.95. For partial tears, the sensitivity was 0.74 and the specificity 0.87. This accuracy is similar to two-plane T2-weighted imaging as previously reported in the literature. There was a statistically significant correlation (p < 0.0005) between the cuff grade as determined by MR and the arthroscopic findings. (orig.)

Diagnosis of partial and complete rotator cuff tears using combined gradient echo and spin echo imaging

Energy Technology Data Exchange (ETDEWEB)

Tuite, M J [Dept. of Radiology, Univ. of Wisconsin, Madison, WI (United States); Yandow, D R [Dept. of Radiology, Univ. of Wisconsin, Madison, WI (United States); DeSmet, A A [Dept. of Radiology, Univ. of Wisconsin, Madison, WI (United States); Orwin, J F [Div. of Orthopedic Surgery, Univ. of Wisconsin, Madison, WI (United States); Quintana, F A [Dept. of Biostatistics, Univ. of Wisconsin, Madison, WI (United States)

1994-10-01

Most magnetic resonance (MR) studies evaluating the rotator cuff for tears have used T2-weighted imaging in the coronal oblique and sagittal oblique planes. T2{sup *}-weighted gradient echo imaging, however, has advantages over spin echo imaging, including contiguous slices without cross-talk, high contrast around the cuff, and intrinsically shorter imaging times which can be used to increase the number of signals averaged and thus improve the signal-to-noise ratio. We reviewed the shoulder MR scans of 87 consecutive patients who underwent both a MR scan and a shoulder arthroscopy during which the size of tears, if present, was graded. The reviewers were blinded as to the history and arthroscopic results. The MR scans included oblique coronal T2{sup *}-weighted gradient echo and oblique sagittal T2-weighted spin echo images. MR cuff grades were correlated with arthroscopic findings. For complete tears, the sensitivity of MR was 0.91 and the specificity 0.95. For partial tears, the sensitivity was 0.74 and the specificity 0.87. This accuracy is similar to two-plane T2-weighted imaging as previously reported in the literature. There was a statistically significant correlation (p < 0.0005) between the cuff grade as determined by MR and the arthroscopic findings. (orig.)

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.

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

MR imaging of articular cartilage : comparison of magnetization transfer contrast and fat-suppression in multiplanar and 3D gradient-echo, spin-echo, turbo spin-echo techniques

International Nuclear Information System (INIS)

Lee, Young Joon; Joo, Eun Young; Eun, Choong Ki

1999-01-01

The purpose of this study was to evaluate the effects of magnetization transfer contrast(MTC) and fat-suppression(FS) in variable spin-echo and gradient-echo sequences for articular cartilage imaging and to determine the optimal pulse sequences. Using variable 7-pulse sequences, the knees of 15 pigs were imaged Axial images were obtained using proton density and T2-weighted spin-echo (PDWSE and T2WSE), turbo spin-echo (TSE), multiplanar gradient-echo (MPGR), and 3D steady-state gradient-echo (3DGRE) sequences, and the same pulse sequences were then repeated using MTC. Also T1-weighted spin-echo(T1WSE) and 3D spoiled gradient-echo(3DSPGR) images of knees were also acquired, and the procedure was repeated using FS. For each knee, a total of 14 axial images were acquired, and using a 6-band scoring system, the visibility of and the visibilities of the the articular cartilage was analyzed. The visual effect of MTC and FS was scored using a 4-band scale. For each image, the signal intensities of articular cartilage, subchondral bone, muscles, and saline were measured, and signal-to-noise ratios(SNR) and contrast-to-noise ratios(CNR) were also calculated. Visibility of the cartilage was best when 3DSPGR and T1WSE sequences were used. MTC imaging increased the negative contrast between cartilage and saline, but FS imaging provided more positive contrast. CNR between cartilage and saline was highest when using TSE with FS(-351.1±15.3), though CNR between cartilage and bone then fell to -14.7±10.8. In MTC imaging using MPGR showed the greatest increase of negative contrast between cartilage and saline(CNR change=-74.7); the next highest was when 3DGRE was used(CNR change=-34.3). CNR between cartilage and bone was highest with MPGR(161.9±17.7), but with MTC, the greatest CNR decrease(-81.8) was observed. The greatest CNR increase between cartilage and bone was noted in T1WSE with FS. In all scans, FS provided a cartilage-only positive contrast image, though the absolute

Fast spin echo MRI techniques. Contrast characteristics and clinical potential. Techniques d'IRM en fast spin echo. Caracteristiques de contraste et potentiels cliniques

Energy Technology Data Exchange (ETDEWEB)

Melki, P.; Mulkern, R.V.; Dacher, J.N.; Helenon, O.; Higuchi, N. (Harvard Medical School, Boston, MA (United States)); Oshio, K.; Jolesz, F. (Keio Univ., Tokyo (Japan)); Pourcelot, L. (Hopital Bretonneau, 37 - Tours (France)); Einstein, S. (General Electric Medical System, Milwaukee, WI (United States))

1993-03-01

Based on partial RF echo planar principles, Fast Spin Echo techniques (FSE) were implemented on high field systems. These methods produce image quality and contrast which resemble to conventional spin echo (SE) techniques. By reducing acquisition times by factors between 1.4 and 16 over SE methods, FSE allows for several imaging options usually prohibitive with conventional spin echo (SE) sequences. These include fast scans (especially breathold acquisitions); improved T2 contrast with longer TR intervals; increased spatial resolution with the use of larger image matrices and/or smaller fields of view; and 3D volume imaging with a 3D multislab FSE technique. Contrast features of FSE techniques are directly comparable to those of multiple echo SE sequences using the same echo spacing than FSE methods. However, essential contrast differences existing between the FSE sequences and their routine asymmetric dual SE counterpart can be identified. Decreased magnetic susceptibility effects and increased fat signal present within T2 weighted images compared to conventional dual SE images are due to the use of shorter echo spacings employed in FSE sequences. Off-resonance irradiation inherent to the use of a large number of radio frequency pulses in shown to results in dramatic magnetization contrast transfer effects in FSE images acquired in multislice mode.

A short TE gradient-echo sequence using asymmetric sampling

International Nuclear Information System (INIS)

Fujita, Norihiko; Harada, Kohshi; Sakurai, Kosuke; Nakanishi, Katsuyuki; Kim, Shyogen; Kozuka, Takahiro

1990-01-01

We have developed a gradient-echo pulse sequence with a short TE less than 4 msec using a data set of asymmetric off-center sampling with a broad bandwidth. The use of such a short TE significantly reduces T 2 * dephasing effect even in a two-dimensional mode, and by collecting an off-center echo, motion-induced phase dispersion is also considerably decreased. High immunity of this sequence to these dephasing effects permits clear visualization of anatomical details near the skull base where large local field inhomogeneities and rapid blood flow such as in the internal carotid artery are present. (author)

Fast spin echo MRI techniques. Contrast characteristics and clinical potential

International Nuclear Information System (INIS)

Melki, P.; Mulkern, R.V.; Dacher, J.N.; Helenon, O.; Higuchi, N.; Oshio, K.; Jolesz, F.; Pourcelot, L.; Einstein, S.

1993-01-01

Based on partial RF echo planar principles, Fast Spin Echo techniques (FSE) were implemented on high field systems. These methods produce image quality and contrast which resemble to conventional spin echo (SE) techniques. By reducing acquisition times by factors between 1.4 and 16 over SE methods, FSE allows for several imaging options usually prohibitive with conventional spin echo (SE) sequences. These include fast scans (especially breathold acquisitions); improved T2 contrast with longer TR intervals; increased spatial resolution with the use of larger image matrices and/or smaller fields of view; and 3D volume imaging with a 3D multislab FSE technique. Contrast features of FSE techniques are directly comparable to those of multiple echo SE sequences using the same echo spacing than FSE methods. However, essential contrast differences existing between the FSE sequences and their routine asymmetric dual SE counterpart can be identified. Decreased magnetic susceptibility effects and increased fat signal present within T2 weighted images compared to conventional dual SE images are due to the use of shorter echo spacings employed in FSE sequences. Off-resonance irradiation inherent to the use of a large number of radio frequency pulses in shown to results in dramatic magnetization contrast transfer effects in FSE images acquired in multislice mode

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.)

Cartilage destruction in small joints by rheumatoid arthritis: assessment of fat-suppressed three-dimensional gradient-echo MR pulse sequences in vitro

International Nuclear Information System (INIS)

Uhl, M.; Allmann, K.H.; Hauer, M.P.; Langer, M.; Ihling, C.; Conca, W.

1998-01-01

Purpose. To assess the accuracy of different MR sequences for the detection of articular cartilage abnormalities in rheumatoid arthritis. Design and patients. Ten metacarpophalangeal joints and 10 metatarsophalangeal joints (specimens from arthritis patients undergoing ablative joint surgery) were examined with a fat-suppressed (FS) 3D FLASH, a FS 3D FISP, a FS 2D fast spin-echo T2-weighted, and a 2D FS spin-echo T1-weighted sequence. Each cartilage lesion and each cortical lesion was graded from 0 to 4 (modified Outerbridge staging system). Subsequently, the results of each sequence were compared with the macroscopic findings and statistically tested against each other. Results. The study shows that 3D gradient-echo sequences with fat suppression were best for imaging and grading of cartilage lesions in arthritis of the small joints of the hands and feet. Using 3D techniques, all grade 2, grade 3, and grade 4 lesions of cartilage or cortical bone were detected. Conclusion. FS 3D gradient-echo techniques were best for the detection and grading of hyaline cartilage and subchondral bone lesions in rheumatoid arthritis. MRI has a great potential as an objective method of evaluating cartilage damage and bone erosions in rheumatoid arthritis. (orig.)

Cartilage destruction in small joints by rheumatoid arthritis: assessment of fat-suppressed three-dimensional gradient-echo MR pulse sequences in vitro

Energy Technology Data Exchange (ETDEWEB)

Uhl, M.; Allmann, K.H.; Hauer, M.P.; Langer, M. [Department of Diagnostic Radiology, University Hospital Freiburg (Germany); Ihling, C. [Department of Pathology, University Hospital Freiburg, Freiburg (Germany); Conca, W. [Department of Rheumatology, University Hospital Freiburg (Germany)

1998-12-01

Purpose. To assess the accuracy of different MR sequences for the detection of articular cartilage abnormalities in rheumatoid arthritis. Design and patients. Ten metacarpophalangeal joints and 10 metatarsophalangeal joints (specimens from arthritis patients undergoing ablative joint surgery) were examined with a fat-suppressed (FS) 3D FLASH, a FS 3D FISP, a FS 2D fast spin-echo T2-weighted, and a 2D FS spin-echo T1-weighted sequence. Each cartilage lesion and each cortical lesion was graded from 0 to 4 (modified Outerbridge staging system). Subsequently, the results of each sequence were compared with the macroscopic findings and statistically tested against each other. Results. The study shows that 3D gradient-echo sequences with fat suppression were best for imaging and grading of cartilage lesions in arthritis of the small joints of the hands and feet. Using 3D techniques, all grade 2, grade 3, and grade 4 lesions of cartilage or cortical bone were detected. Conclusion. FS 3D gradient-echo techniques were best for the detection and grading of hyaline cartilage and subchondral bone lesions in rheumatoid arthritis. MRI has a great potential as an objective method of evaluating cartilage damage and bone erosions in rheumatoid arthritis. (orig.) With 5 figs., 19 refs.

Simultaneous pH-sensitive and oxygen-sensitive MRI of human gliomas at 3 T using multi-echo amine proton chemical exchange saturation transfer spin-and-gradient echo echo-planar imaging (CEST-SAGE-EPI).

Science.gov (United States)

Harris, Robert J; Yao, Jingwen; Chakhoyan, Ararat; Raymond, Catalina; Leu, Kevin; Liau, Linda M; Nghiemphu, Phioanh L; Lai, Albert; Salamon, Noriko; Pope, Whitney B; Cloughesy, Timothy F; Ellingson, Benjamin M

2018-04-06

To introduce a new pH-sensitive and oxygen-sensitive MRI technique using amine proton CEST echo spin-and-gradient echo (SAGE) EPI (CEST-SAGE-EPI). pH-weighting was obtained using CEST estimations of magnetization transfer ratio asymmetry (MTR asym ) at 3 ppm, and oxygen-weighting was obtained using R2' measurements. Glutamine concentration, pH, and relaxation rates were varied in phantoms to validate simulations and estimate relaxation rates. The values of MTR asym and R2' in normal-appearing white matter, T 2 hyperintensity, contrast enhancement, and macroscopic necrosis were measured in 47 gliomas. Simulation and phantom results confirmed an increase in MTR asym with decreasing pH. The CEST-SAGE-EPI estimates of R 2 , R2*, and R2' varied linearly with gadolinium diethylenetriamine penta-acetic acid concentration (R 2  = 6.2 mM -1 ·sec -1 and R2* = 6.9 mM -1 ·sec -1 ). The CEST-SAGE-EPI and Carr-Purcell-Meiboom-Gill estimates of R 2 (R 2  = 0.9943) and multi-echo gradient-echo estimates of R2* (R 2  = 0.9727) were highly correlated. T 2 lesions had lower R2' and higher MTR asym compared with normal-appearing white matter, suggesting lower hypoxia and high acidity, whereas contrast-enhancement tumor regions had elevated R2' and MTR asym , indicating high hypoxia and acidity. The CEST-SAGE-EPI technique provides simultaneous pH-sensitive and oxygen-sensitive image contrasts for evaluation of the brain tumor microenvironment. Advantages include fast whole-brain acquisition, in-line B 0 correction, and simultaneous estimation of CEST effects, R 2 , R2*, and R2' at 3 T. © 2018 International Society for Magnetic Resonance in Medicine.

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

Evaluation of the chondromalacia patella using a microscopy coil: comparison of the two-dimensional fast spin echo techniques and the three-dimensional fast field echo techniques.

Science.gov (United States)

Kim, Hyun-joo; Lee, Sang Hoon; Kang, Chang Ho; Ryu, Jeong Ah; Shin, Myung Jin; Cho, Kyung-Ja; Cho, Woo Shin

2011-01-01

We wanted to compare the two-dimensional (2D) fast spin echo (FSE) techniques and the three-dimensional (3D) fast field echo techniques for the evaluation of the chondromalacia patella using a microscopy coil. Twenty five patients who underwent total knee arthroplasty were included in this study. Preoperative MRI evaluation of the patella was performed using a microscopy coil (47 mm). The proton density-weighted fast spin echo images (PD), the fat-suppressed PD images (FS-PD), the intermediate weighted-fat suppressed fast spin echo images (iw-FS-FSE), the 3D balanced-fast field echo images (B-FFE), the 3D water selective cartilage scan (WATS-c) and the 3D water selective fluid scan (WATS-f) were obtained on a 1.5T MRI scanner. The patellar cartilage was evaluated in nine areas: the superior, middle and the inferior portions that were subdivided into the medial, central and lateral facets in a total of 215 areas. Employing the Noyes grading system, the MRI grade 0-I, II and III lesions were compared using the gross and microscopic findings. The sensitivity, specificity and accuracy were evaluated for each sequence. The significance of the differences for the individual sequences was calculated using the McNemar test. The gross and microscopic findings demonstrated 167 grade 0-I lesions, 40 grade II lesions and eight grade III lesions. Iw-FS-FSE had the highest accuracy (sensitivity/specificity/accuracy = 88%/98%/96%), followed by FS-PD (78%/98%/93%, respectively), PD (76%/98%/93%, respectively), B-FFE (71%/100%/93%, respectively), WATS-c (67%/100%/92%, respectively) and WATS-f (58%/99%/89%, respectively). There were statistically significant differences for the iw-FS-FSE and WATS-f and for the PD-FS and WATS-f (p chondromalacia patella.

Myocardial viability: comparison of free-breathing navigator-echo-gated three-dimensional inversion-recovery gradient-echo MR and standard multiple breath-hold two-dimensional inversion-recovery gradient-echo MR

International Nuclear Information System (INIS)

Kim, Jin Hee; Seo, Joon Beom; Do, Kyung Hyun; Yang, Dong Hyun; Lee, Soo Hyun; Ko, Sung Min; Heo, Jeong Nam; Lim, Tae Hwan

2004-01-01

To compare a free-breathing, navigator-echo-gated, three-dimensional, inversion-recovery, gradient-echo, MR pulse sequence (3D-MRI) with standard, multiple breath-hold, two-dimensional, inversion-recovery, gradient-echo MR (2D-MRI) for the evaluation of delayed hyperenhancement of nonviable myocardium in patients with chronic ischemic heart disease. Ten patients with chronic ischemic heart disease were enrolled in this study. MRI was performed on a 1.5-T system. 3D-MRI was obtained in the short axis plane at 10 minutes after the administration of Gd-DTPA (0.2 mmol/kg, 4 cc/sec). Prospective gating of the acquisition based on the navigator echo was applied. 2D-MRI was performed immediately after finishing 3D-MRI. The area of total and hyperenhanced myocardium measured on both image sets was compared with paired Student t-test and Bland-Altman method. By using a 60-segment model, the transmural extent and segment width of the hyperenhanced area were recorded by 3-scale grading method. The agreement between the two sequences was evaluated with kappa statistics. We also evaluated the agreement of hyperenhancement among the three portions (apical, middle and basal portion) of the left ventricle with kappa statistics. The two sequences showed good agreement for the measured area of total and hyperenhanced myocardium on paired t-test (ρ = 0.11 and ρ = 0.34, respectively). No systematic bias was shown on Bland-Altman analysis. Good agreement was found for the segmental width (Κ = 0.674) and transmural extent (Κ = 0.615) of hyperenhancement on the segmented analysis. However, the agreement of the transmural extent of hyperenhancement in the apical segments was relatively poor compared with that in the middle or basal portions. This study showed good agreement between 3D-MRI and 2D-MRI in evaluation of non-viable myocardium. Therefore, 3D-MRI may be useful in the assessment of myocardial viability in patients with dyspnea and children because it allows free

Evaluation of the Chondromalacia Patella Using a Microscopy Coil: Comparison of the Two-Dimensional Fast Spin Echo Techniques and the Three-Dimensional Fast Field Echo Techniques

International Nuclear Information System (INIS)

Kim, Hyun Joo; Lee, Sang Hoon; Kang, Chang Ho; Ryu, Jeong Ah; Shin, Myung Jin; Cho, Kyung Ja; Cho, Woo Shin

2011-01-01

We wanted to compare the two-dimensional (2D) fast spin echo (FSE) techniques and the three-dimensional (3D) fast field echo techniques for the evaluation of the chondromalacia patella using a microscopy coil. Twenty five patients who underwent total knee arthroplasty were included in this study. Preoperative MRI evaluation of the patella was performed using a microscopy coil (47 mm). The proton density-weighted fast spin echo images (PD), the fat-suppressed PD images (FS-PD), the intermediate weighted-fat suppressed fast spin echo images (iw-FS-FSE), the 3D balanced-fast fi eld echo images (B-FFE), the 3D water selective cartilage scan (WATS-c) and the 3D water selective fluid scan (WATS-f) were obtained on a 1.5T MRI scanner. The patellar cartilage was evaluated in nine areas: the superior, middle and the inferior portions that were subdivided into the medial, central and lateral facets in a total of 215 areas. Employing the Noyes grading system, the MRI grade 0-I, II and III lesions were compared using the gross and microscopic findings. The sensitivity, specificity and accuracy were evaluated for each sequence. The significance of the differences for the individual sequences was calculated using the McNemar test. The gross and microscopic findings demonstrated 167 grade 0-I lesions, 40 grade II lesions and eight grade III lesions. Iw-FS-FSE had the highest accuracy (sensitivity/specificity/accuracy = 88%/98%/96%), followed by FSPD (78%/98%/93%, respectively), PD (76%/98%/93%, respectively), B-FFE (71%/100%/93%, respectively), WATS-c (67%/100%/92%, respectively) and WATS-f (58%/99%/89%, respectively). There were statistically significant differences for the iw-FS-FSE and WATS-f and for the PD-FS and WATS-f (p < 0.01). The iw-FS-FSE images obtained with a microscopy coil show best diagnostic performance among the 2D and 3D GRE images for evaluating the chondromalacia patella

Evaluation of the Chondromalacia Patella Using a Microscopy Coil: Comparison of the Two-Dimensional Fast Spin Echo Techniques and the Three-Dimensional Fast Field Echo Techniques

Energy Technology Data Exchange (ETDEWEB)

Kim, Hyun Joo; Lee, Sang Hoon; Kang, Chang Ho; Ryu, Jeong Ah; Shin, Myung Jin; Cho, Kyung Ja; Cho, Woo Shin [University of Ulsan College of Medicine, Asan Medical Center, Seoul (Korea, Republic of)

2011-02-15

We wanted to compare the two-dimensional (2D) fast spin echo (FSE) techniques and the three-dimensional (3D) fast field echo techniques for the evaluation of the chondromalacia patella using a microscopy coil. Twenty five patients who underwent total knee arthroplasty were included in this study. Preoperative MRI evaluation of the patella was performed using a microscopy coil (47 mm). The proton density-weighted fast spin echo images (PD), the fat-suppressed PD images (FS-PD), the intermediate weighted-fat suppressed fast spin echo images (iw-FS-FSE), the 3D balanced-fast fi eld echo images (B-FFE), the 3D water selective cartilage scan (WATS-c) and the 3D water selective fluid scan (WATS-f) were obtained on a 1.5T MRI scanner. The patellar cartilage was evaluated in nine areas: the superior, middle and the inferior portions that were subdivided into the medial, central and lateral facets in a total of 215 areas. Employing the Noyes grading system, the MRI grade 0-I, II and III lesions were compared using the gross and microscopic findings. The sensitivity, specificity and accuracy were evaluated for each sequence. The significance of the differences for the individual sequences was calculated using the McNemar test. The gross and microscopic findings demonstrated 167 grade 0-I lesions, 40 grade II lesions and eight grade III lesions. Iw-FS-FSE had the highest accuracy (sensitivity/specificity/accuracy = 88%/98%/96%), followed by FSPD (78%/98%/93%, respectively), PD (76%/98%/93%, respectively), B-FFE (71%/100%/93%, respectively), WATS-c (67%/100%/92%, respectively) and WATS-f (58%/99%/89%, respectively). There were statistically significant differences for the iw-FS-FSE and WATS-f and for the PD-FS and WATS-f (p < 0.01). The iw-FS-FSE images obtained with a microscopy coil show best diagnostic performance among the 2D and 3D GRE images for evaluating the chondromalacia patella

Spin echoes of nuclear magnetization diffusing in a constant magnetic field gradient and in a restricted geometry

International Nuclear Information System (INIS)

Sen, P.N.; Andre, A.; Axelrod, S.

1999-01-01

We study the influence of restriction on Carr - Purcell - Meiboom - Gill spin echoes response of magnetization of spins diffusing in a bounded region in the presence of a constant magnetic field gradient. Depending on three main length scales: L S pore size, L G dephasing length and L D diffusion length during half-echo time, three main regimes of decay have been identified: free, localization and motionally averaging regime. In localization regime, the decay exponent depends on a fractional power (2/3) of the gradient, denoting a strong breakdown of the second cumulant or the Gaussian phase approximation (GPA). In the other two regimes, the exponent depends on the gradient squared, and the GPA holds. We find that the transition from the localization to the motionally averaging regime happens when the magnetic field gradients approach special values, corresponding to branch points of the eigenvalues. Transition from one regime to another as a function of echo number for a certain range of parameters is discussed. In this transition region, the signal shows large oscillations with echo number. For large n, asymptotic behavior sets in as a function of n for the decay exponent per echo. This is true for all values of the parameters L S , L G , and L D . copyright 1999 American Institute of Physics

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...... were 10 and 20 ms, respectively. Good quality proton spectra with practically no eddy current artefacts were acquired allowing observation of strongly coupled compounds, and compounds with short T2 relaxation times. The gradient head coil thus permits further studies of compounds such as glutamine....../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....

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.

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.

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

International Nuclear Information System (INIS)

Fellner, Franz A.; Fellner, Claudia; Aichner, Franz T.; Moelzer, Guenther

2005-01-01

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 μs, 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

Isotropic three-dimensional fast spin-echo Cube magnetic resonance dacryocystography: comparison with the three-dimensional fast-recovery fast spin-echo technique

Energy Technology Data Exchange (ETDEWEB)

Zhang, Jing; Chen, Lang; Wang, Qiu-Xia; Zhu, Wen-Zhen; Luo, Xin; Peng, Li [Huazhong University of Science and Technology, Department of Radiology, Tongji Hospital, Wuhan (China); Liu, Rong [Huazhong University of Science and Technology, Department of Ophthalmology, Tongji Hospital, Wuhan (China); Xiong, Wei [GE Healthcare China Wuhan Office, Wuhan (China)

2015-04-01

Three-dimensional fast spin-echo Cube (3D-FSE-Cube) uses modulated refocusing flip angles and autocalibrates two dimensional (2D)-accelerated parallel and nonlinear view ordering to produce high-quality volumetric image sets with high-spatial resolution. Furthermore, 3D-FSE-Cube with topical instillation of fluid can also be used for magnetic resonance dacryocystography (MRD) with good soft tissue contrast. The purpose of this study was to evaluate the technical quality and visualization of the lacrimal drainage system (LDS) when using the 3D-FSE-Cube sequence and the 3D fast-recovery fast spin-echo (FRFSE) sequence. In total, 75 patients with primary LDS outflow impairment or postsurgical recurrent epiphora underwent 3D-FSE-Cube MRD and 3D-FRFSE MRD at 3.0 T after topical administration of compound sodium chloride eye drops. Two radiologists graded the images from either of the two sequences in a blinded fashion, and appropriate statistical tests were used to assess differences in technical quality, visibility of ductal segments, and number of segments visualized per LDS. Obstructions were confirmed in 90 of the 150 LDSs assessed. The technical quality of 3D-FSE-Cube MRD and 3D-FRFSE MRD was statistically equivalent (P = 0.871). However, compared with 3D-FRFSE MRD, 3D-FSE-Cube MRD improved the overall visibility and the visibility of the upper drainage segments in normal and obstructed LDSs (P < 0.001). There was a corresponding increase in the number of segments visualized per LDS in both groups (P < 0.001). Compared with 3D-FRFSE MRD, 3D-FSE-Cube MRD potentially improves the visibility of the LDS. (orig.)

High incidence of microbleeds in hemodialysis patients detected by T2*-weighted gradient-echo magnetic resonance imaging

International Nuclear Information System (INIS)

Yokoyama, Shunichi; Uomizu, Kenji; Kajiya, Yoriko; Tajitsu, Kenichiro; Kusumoto, Kazuhiro; Hirano, Hirofumi

2005-01-01

The incidence and characteristics of microbleeds in hemodialysis (HD) patients were investigated to elucidate the clinical significance with T 2 * -weighted gradient-echo magnetic resonance (MR) imaging. The 57 patients with chronic renal failure maintained by HD had no previous history of stroke. The control group consisted of 53 patients without previous history of stroke or chronic renal failure. The incidence and the number of microbleeds were assessed in the HD and control groups. The findings of microbleeds with T 2 * -weighted gradient-echo MR imaging were compared with those of T 1 - and T 2 -weighted MR imaging in HD patients. The incidence of microbleeds was significantly greater in the HD patients compared with the control patients. T 2 * -weighted gradient-echo imaging revealed a total of 44 microbleeds in 11 HD patients. T 2 -weighted imaging demonstrated 13 of 44 microbleeds as hyperintensity, whereas T 1 -weighted imaging demonstrated 12 lesions as hypointensity. T 2 - and T 1 -weighted imagings did not demonstrate any findings in 31 and 32 lesions, respectively. T 2 * -weighted gradient-echo MR imaging is effective to detect microbleeds which may be a predictor of intracerebral hemorrhage in HD patients and should be included in the protocol for the study of cerebrovascular disease, because T 2 - and T 1 -weighted MR imaging recognizes microbleeds as lacunar infarction. (author)

Fast spin-echo MR imaging of the eye

International Nuclear Information System (INIS)

Hosten, N.; Lemke, A.J.; Bornfeld, N.; Wassmuth, R.; Schweiger, U.; Terstegge, K.; Felix, R.

1996-01-01

Magnetic resonance imaging of the eye usually includes T2-weighted images both for screening purposes and for characterization of melanoma. Conventional T2-weighted spin-echo (SE) imaging suffers both from long acquisition times and incomplete recovery of the virteous' signal. A fast SE sequence was therefore compared prospectively with conventional sequences in 29 consecutive patients with lesions of the eye. Fast SE images delineated melanoma and other lesions of the eye from vitreous better than conventional T2-weighted images. Image quality and lesion conspicuity were improved on the fast sequence. Whereas melanoma appeared hypointense to vitreous on both types of images, subretinal effusion was hypointense on fast images and hyperintense on conventional T2-weighted images. Ghosting of the globe, which, however, did not decrease diagnostic value, was more pronounced on fast images. Conventional T2-weighted images may be replaced by fast SE images in MR studies of the eye with a gain in lesion conspicuity and significant time saving. (orig.)

Turbo-Proton Echo Planar Spectroscopic Imaging (t-PEPSI) MR technique in the detection of diffuse axonal damage in brain injury. Comparison with Gradient-Recalled Echo (GRE) sequence.

Science.gov (United States)

Giugni, E; Sabatini, U; Hagberg, G E; Formisano, R; Castriota-Scanderbeg, A

2005-01-01

Diffuse axonal injury (DAI) is a common type of primary neuronal injury in patients with severe traumatic brain injury, and is frequently accompanied by tissue tear haemorrhage. The T2*-weighted gradient-recalled echo (GRE) sequences are more sensitive than T2-weighted spin-echo images for detection of haemorrhage. This study was undertaken to determine whether turbo-PEPSI, an extremely fast multi-echo-planar-imaging sequence, can be used as an alternative to the GRE sequence for detection of DAI. Nineteen patients (mean age 24,5 year) with severe traumatic brain injury (TBI), occurred at least 3 months earlier, underwent a brain MRI study on a 1.5-Tesla scanner. A qualitative evaluation of the turbo-PEPSI sequences was performed by identifying the optimal echo time and in-plane resolution. The number and size of DAI lesions, as well as the signal intensity contrast ratio (SI CR), were computed for each set of GRE and turbo-PEPSI images, and divided according to their anatomic location into lobar and/or deep brain. There was no significant difference between GRE and turbo-PEPSI sequences in the total number of DAI lesions detected (283 vs 225 lesions, respectively). The GRE sequence identified a greater number of hypointense lesions in the temporal lobe compared to the t-PEPSI sequence (72 vs 35, pPEPSI than for the GRE sequence (pPEPSI sequence can be used as an alternative to the GRE to assess brain DAI in severe TBI patients, especially if uncooperative and medically unstable.

The Usefulness of Fast-Spin-Echo T2-Weighted MR Imaging in Nutcracker Syndrome: a Case Report

Energy Technology Data Exchange (ETDEWEB)

Wong, Heong Leng; Chen, Matt Chiung Yu; Wu, Cgek Siung; Fu, Kuo An; Lin, Cheng Hao [Yuan' s General Hospital, Kaohsiung (China); Weng, Mei Jui; Liang, Huei Lung; Pan, Huay Ben [National Yang-Ming University, Taipei (Korea, Republic of)

2010-06-15

Nutcracker syndrome occurs when the left renal vein (LRV) is compressed between the superior mesenteric artery and the aorta, and this syndrome is often characterized by venous hypertension and related pathologies. However, invasive studies such as phlebography and measuring the reno-caval pressure gradient should be performed to identify venous hypertension. Here we present a case of Nutcracker syndrome where the LRV and intra-renal varicosities appeared homogeneously hyperintense on magnetic resonance (MR) fast-spin-echo T2- weighted imaging, which suggested markedly stagnant intravenous blood flow and the presence of venous hypertension. The patient was diagnosed and treated without obtaining the reno-caval pressure gradient. The discomfort of the patient lessened after treatment. Furthermore, on follow-up evaluation, the LRV displayed a signal void, and this was suggestive of a restoration of the normal LRV flow and a decrease in LRV pressure.

Comparison of gradient-recalled echo and spin-echo echo-planar imaging MR elastography in staging liver fibrosis. A meta-analysis

International Nuclear Information System (INIS)

Kim, Yong Seek; Jang, Yu Na; Song, Ji Soo

2018-01-01

To compare the diagnostic performance of gradient-recalled echo-based magnetic resonance elastography (GRE-MRE) and spin-echo echo-planar imaging-based MRE (SE-EPI-MRE) in liver fibrosis staging. A systematic literature search was performed to identify studies involving the performance of MRE for the diagnosis of liver fibrosis. Pooled sensitivity, specificity, positive and negative likelihood ratios, the diagnostic odds ratio, and a summary receiver operating characteristic (ROC) curve were estimated by using a bivariate random effects model. Subgroup analyses were performed between different study characteristics. Twenty-six studies with a total of 3,200 patients were included in the meta-analysis. Pooled sensitivity and specificity of GRE-MRE and SE-EPI-MRE did not differ significantly. The area under the summary ROC curve for stage diagnosis of any (F ≥ 1), significant (F ≥ 2), advanced (F ≥ 3), and cirrhosis (F = 4) on GRE-MRE and SE-EPI-MRE were 0.93 versus 0.94, 0.95 versus 0.94, 0.94 versus 0.95, and 0.92 versus 0.93, respectively. Substantial heterogeneity was detected for both sequences. Both GRE and SE-EPI-MRE show high sensitivity and specificity for detection of each stage of liver fibrosis, without significant differences. Magnetic resonance elastography (MRE) may be useful for noninvasive evaluation of liver fibrosis in chronic liver disease. (orig.)

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.)

Assessment of the image quality and tumor detectability of breath-hold T2-weighted imaging of liver tumors using a fast gradient MR system

International Nuclear Information System (INIS)

Yoshida, Kotaro; Suto, Yuji; Sugihara, Shuji; Tokuda, Yukiko

1996-01-01

Fourteen patients with various types of focal liver tumors were imaged with turbo spin-echo (TSE), breath-hold TSE (BH-TSE) and half-Fourier single-shot TSE (HASTE) pulse sequences using a fast gradient magnetic resonance imaging (MRI) system. We compared the T2-weighted images of the liver with the TSE, BH-TSE, HASTE and conventional spin-echo (SE) pulse sequences in order to determine whether those fast T2-weighted images, including fat suppressed images, could replace SE images. In quantitative and qualitative analysis, the fast T2-weighted images were slightly superior to the SE images, but they were inferior in the conspicuousness of liver tumor to the SE images. These findings suggest that the fast T2-weighted images can shorten the examination time of the liver MRI, but cannot replace the T2-weighted SE images because of the low conspicuousness. (author)

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

2018-04-01

It is highly desirable in clinical abdominal MR scans to accelerate single-shot fast spin echo (SSFSE) imaging and reduce blurring due to T 2 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 2018;47:954-966. © 2017 International Society for Magnetic Resonance in Medicine.

Fast method of NMR imaging based on trains of spin echoes

International Nuclear Information System (INIS)

Hennel, F.

1993-01-01

A theoretical introduction to Fourier NMR imaging and a discussion of fast methods are presented. Then an application of the method of echo-planar imaging (EPI) with spin echoes in a micro-imaging system is described together with introduced modifications of the sequence. A new technique for the measurement of flow profiles in liquids which results from a modification of x-pulsed EPI is presented. The development of new software for a NMR micro-imaging system is described, too. 51 refs, 29 refs

Detection of renal arteries with fast spin-echo magnetic resonance imaging

Energy Technology Data Exchange (ETDEWEB)

Tello, R.; Mitchell, P.J.; Witte, D.J.; Thomson, K.R. [University of Melbourne, Parkville, VIC (Australia). Department of Radiology

1998-08-01

With the increasing use of non-invasive imaging with MR and volumetric CT to evaluate renal arteries, the ability to accurately detect the number and state of native renal arteries becomes critical if conventional angiography is to be supplanted in these settings. The present study evaluated the utility of a fast spin-echo (FSE) T2-weighted sequence to detect the number and course of renal arteries and their ostia compared to conventional angiography. Ten patients underwent conventional catheter angiography either for renal artery stenosis evaluation or as potential renal donors. Each patient then had an MR study of the renal arteries and kidneys with FSE MR (TR = 4000 ms, TE = 102 ms, eight- echo train length, 5-mm-thick interleaved 128 phase encodes, superior and inferior saturation pulses, number of excitations (NEX) = 4, on a 1.5-T superconducting magnet). Images were reviewed by two `blinded` radiologists and renal arteries were counted and their ostia were evaluated. Results were compared with angiography and inter- and intra-observer statistics were calculated. All 10 patients underwent MR successfully, nine for renal artery stenosis (RAS) evaluation and one was a renal donor. A total of 24 renal arteries were imaged in 19 kidneys. Fast spin-echo MR is 95% accurate (95%CI: 88-100%) in detection of renal arteries, with no statistical difference between FSE MR and catheter angiography (McNemar P = 0.0). Inter- and intra-observer statistics demonstrate good-to-excellent agreement in renal artery detection (kappa: 0.63-0.90). In one case of RAS evaluation an incidental adrenal mass was detected as the aetiology of the patient`s hypertension. Fast spin-echo MR can be a useful adjunct as part of the imaging for renal arteries with MRI. Copyright (1998) Blackwell Science Pty Ltd 16 refs., 1 fig.

Detection of renal arteries with fast spin-echo magnetic resonance imaging

International Nuclear Information System (INIS)

Tello, R.; Mitchell, P.J.; Witte, D.J.; Thomson, K.R.

1998-01-01

With the increasing use of non-invasive imaging with MR and volumetric CT to evaluate renal arteries, the ability to accurately detect the number and state of native renal arteries becomes critical if conventional angiography is to be supplanted in these settings. The present study evaluated the utility of a fast spin-echo (FSE) T2-weighted sequence to detect the number and course of renal arteries and their ostia compared to conventional angiography. Ten patients underwent conventional catheter angiography either for renal artery stenosis evaluation or as potential renal donors. Each patient then had an MR study of the renal arteries and kidneys with FSE MR (TR = 4000 ms, TE = 102 ms, eight- echo train length, 5-mm-thick interleaved 128 phase encodes, superior and inferior saturation pulses, number of excitations (NEX) = 4, on a 1.5-T superconducting magnet. Images were reviewed by two 'blinded' radiologists and renal arteries were counted and their ostia were evaluated. Results were compared with angiography and inter- and intra-observer statistics were calculated. All 10 patients underwent MR successfully, nine for renal artery stenosis (RAS) evaluation and one was a renal donor. A total of 24 renal arteries were imaged in 19 kidneys. Fast spin-echo MR is 95% accurate (95%CI: 88-100%) in detection of renal arteries, with no statistical difference between FSE MR and catheter angiography (McNemar P = 0.0). Inter- and intra-observer statistics demonstrate good-to-excellent agreement in renal artery detection (kappa: 0.63-0.90). In one case of RAS evaluation an incidental adrenal mass was detected as the aetiology of the patient's hypertension. Fast spin-echo MR can be a useful adjunct as part of the imaging for renal arteries with MRI. Copyright (1998) Blackwell Science Pty Ltd

MRI of the breast with 2D spin-echo and gradient echo sequences in diagnostically difficult cases

International Nuclear Information System (INIS)

Allgayer, B.; Lukas, P.; Loos, W.; Kersting-Sommerhoff, B.

1993-01-01

One or both breasts of 296 patients with equivocal clinical or mammographical findings were examined with MRI. T 1 weighted spinecho (SE) and gradient echo (FFE) sequences were acquired before and after i.v. application of Gadolinium DTPA. 50 lesions with enhancement after Gd-DTPA were biopsied -26 carcinomas, 17 proliferating mastopathic tissues, 5 fibroadenomas and 1 abscess were found. Contrast enhanced MRI with 2D-SE and FFE sequences is an effective technqiue for evaluating suspicious breast lesions with high diagnostic acurracy. (orig.) [de

MR cholangiography using a fast spin-echo technique: prospective evaluation in 20 patients

International Nuclear Information System (INIS)

Rondeau, Y.; Meduri, B.; Spelle, L.; Gouhiri, M.; Aubert, A.; Scherrer, A.; Soyer, Ph.; Rymer, R.

1998-01-01

To evaluate a MR cholangiographic technique using a non breath-hold fast spin-echo technique in patients with suspected bile duct obstruction. Twenty patients with suspected bile duct obstruction were prospectively investigated with MR cholangiography using a T2-weighted non breath-hold fast spin-echo technique (TR 8000-9000 msec, effective TE 120-266 msec, ETL = 16-32, acquisition time = 1-3 min) with a body coil. Results of MR cholangiography were compared to those obtained with endoscopic retrograde cholangiography (n = 20 patients) and endoscopic sonography (n 12 patients) that were considered as reference. MR cholangiography provided high-quality images in 19 out of 20 cases (95 %). MR cholangiography had 100 % sensitivity, 100 % specificity and 73 % accuracy in the diagnosis of bile duct obstruction. MR cholangiography failed to depict small stones (< 3 mm) of the main bile duct in 4 cases in which no bile duct dilation was found. MR cholangiography using a non breath-hold fast spin-echo technique depicts bile duct dilatation with a degree of accuracy comparable to that achieved with endoscopic examination. In the absence of bile duct dilatation, small stones of the main bile duct may be undetected with MR cholangiography. (author)

Direct magnetic field estimation based on echo planar raw data.

Science.gov (United States)

Testud, Frederik; Splitthoff, Daniel Nicolas; Speck, Oliver; Hennig, Jürgen; Zaitsev, Maxim

2010-07-01

Gradient recalled echo echo planar imaging is widely used in functional magnetic resonance imaging. The fast data acquisition is, however, very sensitive to field inhomogeneities which manifest themselves as artifacts in the images. Typically used correction methods have the common deficit that the data for the correction are acquired only once at the beginning of the experiment, assuming the field inhomogeneity distribution B(0) does not change over the course of the experiment. In this paper, methods to extract the magnetic field distribution from the acquired k-space data or from the reconstructed phase image of a gradient echo planar sequence are compared and extended. A common derivation for the presented approaches provides a solid theoretical basis, enables a fair comparison and demonstrates the equivalence of the k-space and the image phase based approaches. The image phase analysis is extended here to calculate the local gradient in the readout direction and improvements are introduced to the echo shift analysis, referred to here as "k-space filtering analysis." The described methods are compared to experimentally acquired B(0) maps in phantoms and in vivo. The k-space filtering analysis presented in this work demonstrated to be the most sensitive method to detect field inhomogeneities.

In-phase and out-of-phase gradient-echo imaging in abdominal studies: intra-individual comparison of three different techniques

Energy Technology Data Exchange (ETDEWEB)

Ramalho, Miguel; Heredia, Vasco; Campos, Rafael O. P. de; Azevedo, Rafael M.; Semelka, Richard C. (Dept. of Radiology, Univ. of North Carolina at Chapel Hill (United States)); Dale, Brian M. (Siemens Medical Systems, Morrisville (United States)), email: richsem@med.unc.edu

2012-05-15

Background: T1-weighted gradient-echo in-phase and out-of-phase imaging is an essential component of comprehensive abdominal MR exams. It is useful for the study of fat-containing lesions and to identify various disease states related to the presence of fat in the liver. Purpose: To compare three T1-weighted in-phase and out-of-phase (IP/OP) gradient-echo imaging sequences in an intra-individual fashion, and to determine whether advantages exist for each of these sequences for various patient types. Material and Methods: One hundred and eighteen consecutive subjects (74 men, 44 women; mean age 53.9 +- 13.8 years) who had MRI examinations containing all three different IP/OP sequences (two-dimensional spoiled gradient-echo [2D-GRE], three-dimensional gradient-echo [3D-GRE], and magnetization-prepared gradient-recall echo [MP-GRE]) were included. Two different reviewers independently and blindly qualitatively evaluated IP/OP sequences to determine image quality, extent of artifacts, lesion detectability and conspicuity, and subjective grading of liver steatosis for the various sequences. Quantitative analysis was also performed. Qualitative and quantitative data were subjected to statistical analysis. Results: Respiratory ghosting, parallel imaging, and truncation artifacts as well as shading and blurring were more pronounced with 3D-GRE IP/OP imaging. Overall image quality was higher with 2D-GRE (P < 0.05). Detectability of low-fluid content lesions was lower with IP/OP MP-GRE sequences. MP-GRE sequences had the lowest SNRs (P < 0.001). Liver-to-spleen and liver-to-lesion CNRs were significantly lower with 3D-GRE and MP-GR, respectively (P < 0.001). Fat liver indexes showed strongly positive correlation between all sequences. Conclusion: Currently, 2D-GRE remains the best approach for clinical IP/OP imaging. The good image quality of MP-GRE sequences acquired in a free-breathing manner should recommend its use in patients unable to suspend breathing

In-phase and out-of-phase gradient-echo imaging in abdominal studies: intra-individual comparison of three different techniques

International Nuclear Information System (INIS)

Ramalho, Miguel; Heredia, Vasco; Campos, Rafael O. P. de; Azevedo, Rafael M.; Semelka, Richard C.; Dale, Brian M.

2012-01-01

Background: T1-weighted gradient-echo in-phase and out-of-phase imaging is an essential component of comprehensive abdominal MR exams. It is useful for the study of fat-containing lesions and to identify various disease states related to the presence of fat in the liver. Purpose: To compare three T1-weighted in-phase and out-of-phase (IP/OP) gradient-echo imaging sequences in an intra-individual fashion, and to determine whether advantages exist for each of these sequences for various patient types. Material and Methods: One hundred and eighteen consecutive subjects (74 men, 44 women; mean age 53.9 ± 13.8 years) who had MRI examinations containing all three different IP/OP sequences (two-dimensional spoiled gradient-echo [2D-GRE], three-dimensional gradient-echo [3D-GRE], and magnetization-prepared gradient-recall echo [MP-GRE]) were included. Two different reviewers independently and blindly qualitatively evaluated IP/OP sequences to determine image quality, extent of artifacts, lesion detectability and conspicuity, and subjective grading of liver steatosis for the various sequences. Quantitative analysis was also performed. Qualitative and quantitative data were subjected to statistical analysis. Results: Respiratory ghosting, parallel imaging, and truncation artifacts as well as shading and blurring were more pronounced with 3D-GRE IP/OP imaging. Overall image quality was higher with 2D-GRE (P < 0.05). Detectability of low-fluid content lesions was lower with IP/OP MP-GRE sequences. MP-GRE sequences had the lowest SNRs (P < 0.001). Liver-to-spleen and liver-to-lesion CNRs were significantly lower with 3D-GRE and MP-GR, respectively (P < 0.001). Fat liver indexes showed strongly positive correlation between all sequences. Conclusion: Currently, 2D-GRE remains the best approach for clinical IP/OP imaging. The good image quality of MP-GRE sequences acquired in a free-breathing manner should recommend its use in patients unable to suspend breathing

MUSIC. a fast T2* - sensitive MRI technique with enhanced volume coverage

International Nuclear Information System (INIS)

Loenneker, Thomas; Hennig, Juergen

1994-01-01

A fast imaging method based on gradient-recalled echoes and echo time inter-leaved multi-slice excitation is presented. This method maintains the sensitivity of T 2 * by using a long echo time of at least 35 milliseconds. Bipolar gradients are used to shift the gradient echoes in order to ensure constant TE for each slab and prevent ghost-artefacts within the images caused by spin- or stimulated echoes. This method enhances the total imaging time of a conventional multi-slice gradient echo technique, while maintaining the high volume coverage. Thus, stimulated human cortical activation maps can be detected on standard clinical MR instruments at several planes within measuring times of a few seconds. The efficiency of the technique is demonstrated in the detection of temporary changes in T 2 * in functional MRI experiments of the human visual cortex at a magnetic field strength of 2 tesla. (author). 18 refs., 6 figs

Differentiation between grade 3 and grade 4 articular cartilage defects of the knee: Fat-suppressed proton density-weighted versus fat-suppressed three-dimensional gradient-echo MRI

Energy Technology Data Exchange (ETDEWEB)

Lee, So Yeon; Jee, Won-Hee; Kim, Sun Ki (Dept. of Radiology, Seoul St Mary' s Hospital, Catholic Univ. of Korea, Seoul (Korea)), e-mail: whjee@catholic.ac.kr; Koh, In-Jun (Dept. of Joint Reconstruction Center, Seoul National Univ. Bundang Hospital, Seoul (Korea)); Kim, Jung-Man (Dept. of Orthopedic Surgery, Seoul St Mary' s Hospital, Catholic Univ. of Korea, Seoul (Korea))

2010-05-15

Background: Fat-suppressed (FS) proton density (PD)-weighted magnetic resonance imaging (MRI) and FS three-dimensional (3D) gradient-echo imaging such as spoiled gradient-recalled (SPGR) sequence have been established as accurate methods for detecting articular cartilage defects. Purpose: To retrospectively compare the diagnostic efficacy between FS PD-weighted and FS 3D gradient-echo MRI for differentiating between grade 3 and grade 4 cartilage defects of the knee with arthroscopy as the standard of reference. Material and Methods: Twenty-one patients who had grade 3 or 4 cartilage defects in medial femoral condyle at arthroscopy and knee MRI were included in this study: grade 3, >50% cartilage defects; grade 4, full thickness cartilage defects exposed to the bone. Sagittal FS PD-weighted MR images and FS 3D gradient-echo images with 1.5 T MR images were independently graded for the cartilage abnormalities of medial femoral condyle by two musculoskeletal radiologists. Statistical analysis was performed by Fisher's exact test. Inter-observer agreement in grading of cartilage was assessed using ? coefficients. Results: Arthroscopy revealed grade 3 defects in 17 patients and grade 4 defects in 4 patients in medial femoral condyles. For FS 3D gradient-echo images grade 3 defects were graded as grade 3 (n=15) and grade 4 (n=2), and all grade 4 defects (n=4) were correctly graded. However, for FS PD-weighted MR images all grade 3 defects were misinterpreted as grade 1 (n=1) and grade 4 (n=16), whereas all grade 4 defects (n=4) were correctly graded. FS 3D gradient-echo MRI could differentiate grade 3 from grade 4 defects (P=0.003), whereas FS PD-weighted imaging could not (P=1.0). Inter-observer agreement was substantial (?=0.70) for grading of cartilage using FS PD-weighted imaging, whereas it was moderate (?=0.46) using FS 3D gradient-echo imaging. Conclusion: FS 3D gradient-echo MRI is more helpful for differentiating between grade 3 and grade 4 cartilage

Comparison of a conventional cardiac-triggered dual spin-echo and a fast STIR sequence in detection of spinal cord lesions in multiple sclerosis

International Nuclear Information System (INIS)

Bot, J.C.J.; Barkhof, F.; Lycklama a Nijeholt, G.J.; Bergers, E.; Castelijns, J.A.; Polman, C.H.; Ader, H.J.

2000-01-01

The current optimal imaging protocol in spinal cord MR imaging in patients with multiple sclerosis includes a long TR conventional spin-echo (CSE) sequence, requiring long acquisition times. Using short tau inversion recovery fast spin-echo (fast STIR) sequences both acquisition time can be shortened and sensitivity in the detection of multiple sclerosis (MS) abnormalities can be increased. This study compares both sequences for the potential to detect both focal and diffuse spinal abnormalities. Spinal cords of 5 volunteers and 20 MS patients were studied at 1.0 T. Magnetic resonance imaging included cardiac-gated sagittal dual-echo CSE and a cardiac-gated fast STIR sequence. Images were scored regarding number, size, and location of focal lesions, diffuse abnormalities and presence/hindrance of artifacts by two experienced radiologists. Examinations were scored as being definitely normal, indeterminate, or definitely abnormal. Interobserver agreement regarding focal lesions was higher for CSE (κ=0.67) than for fast STIR (κ=0.57) but did not differ significantly. Of all focal lesions scored in consensus, 47 % were scored on both sequences, 31 % were only detected by fast STIR, and 22 % only by dual-echo CSE (n. s.). Interobserver agreement for diffuse abnormalities was lower with fast STIR (κ=0.48) than dual-echo CSE (κ=0.65; n. s.). After consensus, fast STIR showed in 10 patients diffuse abnormalities and dual-echo CSE in 3. After consensus, in 19 of 20 patients dual-echo CSE scans were considered as definitely abnormal compared with 17 for fast STIR. The fast STIR sequence is a useful adjunct to dual-echo CSE in detecting focal abnormalities and is helpful in detecting diffuse MS abnormalities in the spinal cord. Due to the frequent occurrence of artifacts and the lower observer concordance, fast STIR cannot be used alone. (orig.)

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.

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

of this study was to design a robust and accurate quantitative measurement method based on NMR imaging combined with contrast agent (CA) for mapping and quantifying water transport in growing cherry tomato fruits. A multiple flip-angle Spoiled Gradient Echo (SGE) imaging sequence was used to evaluate...

Usefulness of enhanced breathhold 3D spoiled gradient-echo MRA for intrathoracic mass

International Nuclear Information System (INIS)

Kobayashi, Takeshi; Kadoya, Masumi; Kamimura, Ryoichi; Takashima, Tsutomu

1999-01-01

Enhanced Breathhold 3D Spoiled Gradient-echo MRA was very attractive method for not only evaluating relationship between intrathoracic mass and intrathoracic vessels, but also visualizing small pulmonary vessels that could not be detected conventional MRA methods. Moreover, this methods could be applied for evaluating vascularity of the lesions. This method will be accepted as routine pulse sequence for evaluating intrathoracic mass especially malignant tumors. (author)

Three-dimensional fast recovery fast spin-echo imaging of the inner ear and the vestibulocochlear nerve

Energy Technology Data Exchange (ETDEWEB)

Nakashima, K.; Morikawa, M.; Ishimaru, H.; Ochi, M.; Hayashi, K. [Department of Radiology, Nagasaki University School of Medicine, 1-7-1 Sakamoto, Nagasaki 852-8501 (Japan); Kabasawa, H. [GE Yokogawa Medical Systems, Tokyo (Japan)

2002-11-01

The aim of this study was to assess the performance of three-dimensional fast recovery fast spin-echo (3DFRFSE) for imaging of the inner ear as well as the facial and vestibulocochlear nerves. We evaluated 3DFRFSE sequences, comparing it with 3D fast spin-echo (3DFSE) in a water phantom and in 12 normal volunteers. We also examined 66 patients using 3DFRFSE sequence and assessed the visualization of their pathologies. In a water phantom study, signal intensity (SI) on 3DFRFSE was higher than that on 3DFSE at the same TR ranging from 1500 to 6000 ms. In normal volunteers, 3DFRFSE with TR of 2800 ms showed comparable SI, and signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) superior to those on 3DFSE with TR of 5000 ms. In clinical setting, 3DFRFSE was useful in demonstrating anatomic details in the labyrinth and pathologic findings of inner ear. The 3DFRFSE can provide high-resolution heavily T2-weighted images (T2WI) with shorter scan time than 3DFSE without significant disadvantage. The 3DFRFSE is a beneficial technique for evaluation of lesions in the inner ear as well as the facial and vestibulocochlear nerves. (orig.)

Application of fast spin-echo T2-weighted imaging for examination of the neurocranium. Comparison with the conventional T2-weighted spin-echo sequence

International Nuclear Information System (INIS)

Siewert, C.; Hosten, N.; Felix, R.

1994-01-01

T 2 -weighted spin-echo imaging is the standard screening procedure in MR imaging of the neutrocranium. We evaluated fast spin-echo T 2 -weighted imaging (TT 2 ) of the neurocranium in comparison to conventional spin-echo T 2 -weighted imaging (T 2 ). Signal-to-noise and contrast-to-noise ratio of normal brain tissues (basal ganglia, grey and white matter, CSF fluid) and different pathologies were calculated. Signal-to-noise ratio and contrast-to-noise ratio were significantly higher than TT 2 than in T 2 (with the exception of grey-to-white matter contrast). Tissues with increased content of water protons (mobile protons) showed the highest contrast to surrounding tissues. The increased signal intensity of fat must be given due attention in fatty lesions. Because the contrast-to-noise ratio between white matter and basal ganglia is less in TT 2 , Parkinson patients have to be examined by conventional T 2 . If these limitations are taken into account, fast spin-echo T 2 -weighted imaging is well appropriate for MR imaging of the neurocranium, resulting in heavy T 2 -weighting achieved in a short acquisition time. (orig.) [de

The evaluation of fat saturation fast spin-echo T2W1 for patients with acute spinal trauma

International Nuclear Information System (INIS)

Kim, Sung Gyu; Lee, Chang Jun; Lee, Myung Joon; Kang, Ik Won; Yoo, Jeong Hyun

2002-01-01

To determine the usefulness of fat saturation fast spin-echo T2W1 for patients with mild acute trauma of the spine. Between July 1998 and June 2002, 36 patients with acute spinal trauma underwent MRI within four months of injury. One, whose clinal symptoms indicated neurological paralysis, was excluded form our study. A superconductive 1.0-T MRI scanner was used, and conventional T1W1, T2W1, and additional fat-saturation fast spin-echo T2W1 were performed. Two radiologists compared conventional T2-weighted sagittal imaging and fat-saturation T2-weighted sagittal imaging in terms of the extension of increased high signal intensities in soft tissue and vertebral bodies, bone marrow signal change, disk herniation, and signal change of the disk. The detection rate of focal high signal intensities in soft tissue and bone marrow was significantly higher at fat-saturation fast spin-echo T2W1 than at conventional T2W1. Fat-saturation fast spin-echo T2W1 is useful for the evaluation of patients with mild acute spinal trauma without neurological impairment

Diagnostic equivalence of conventional and fast spin echo magnetic resonance imaging of the anterior cruciate ligament of the knee

International Nuclear Information System (INIS)

Munk, P.L.; Hilborn, M.D.; Vellet, A.D.; University of Calgary, Calgary, Alberta,; Romano, C.C.; University of Calgary, Calgary, Alberta,

1997-01-01

Many techniques and pulse sequences have been devised for the assessment of the anterior cruciate ligament. The present study compares fast spin echo (FSE) imaging to conventional spin echo imaging at a field strength of 1.5 T in an effort to determine if these sequences are diagnostically equivalent. Where available, arthroscopy was also done. A total of 52 patients were imaged using both FSE and conventional spin echo sequences. Eight volunteers were used as controls. Arthroscopy was performed on 10 patients. The anterior cruciate ligament was assessed in a blinded fashion by three radiologists. The Kappa statistic was then used to determine the percentage agreement between FSE and conventional spin echo imaging. Fast spin echo sequencing demonstrated a sensitivity of 100%, a specificity of 94.8% and an accuracy of 96.3% when compared to arthroscopy. Conventional spin echo imaging and arthroscopy had a sensitivity of 100%, specificity of 84.6% and an accuracy of 88.9%. The remaining 34 patients who did not undergo arthroscopy were followed clinically because clinical and imaging findings were not suggestive of ACL tears. These demonstrated 72% agreement between FSE and conventional spin echo imaging using the Kappa statistic, with regards to calling ACL normal or having only a low-grade partial tear. Fast spin echo imaging produces images of the anterior cruciate ligament that have similar diagnostic accuracy to conventional spin echo images (P<0.05) within a much shorter scan time. These results however, require further validation in a larger group, preferably with arthroscopic correlation. (author)

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...... loss or inaccurate R2* estimates. If the strong field gradients are measured, their influence can be removed by postprocessing. METHODS: Conventional corrections usually assume a linear phase evolution with time. For high macroscopic gradient inhomogeneities near the edge of the brain...

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

International Nuclear Information System (INIS)

Lee, Marc J.; Motamedi, Kambiz; Chow, Kira; Seeger, Leanne L.

2008-01-01

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 0.7). 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.)

Magnetic resonance imaging of lumbar spine. Comparison of multiple spin echo and low flip angle gradient echo imaging

Energy Technology Data Exchange (ETDEWEB)

Murakami, Takamichi; Fujita, Norihiko; Harada, Koushi; Kozuka, Takahiro (Osaka Univ. (Japan). Faculty of Medicine)

1989-07-01

Sixteen patients including 13 cases with disk herniation and 3 cases with spondylosis of lumbar spine were examined on a resistive MRI system operating at 0.1 T. All lesions were studied with both multiple spin echo (MSE) and low flip angle gradient echo (LF) techniques to evaluate which technique is more effective in detecting the disk degeneration and the indentation on subarachnoid space. MSE images were obtained with repetition time (TR) of 1100-1500 ms or cardiac gating, an echo time (TE) of 30, 60, 90, 120, 150, and 180 ms symmetrical 6 echoes, and total acquisition time of more than 281 sec. LF images were obtained with TR of 500, 250, and 100 ms, TE of 18 ms, a flip angle of 30 degree, and total acquisition time of 128 sec. Eleven lesions of spinal disk degeneration and 12 of indentation on subarachnoid space were detected with LF. On the other hand, 26 lesions of spinal disk degeneration and 38 of indentation on subarachnoid space were detected with MSE. Although the parameters of LF employed in this study were relatively effective to emphasize T2{sup *}-based contrast, the ability of LF in detection of spinal disk degeneration and indentation on subarachnoid space is less than that of MSE. Signal contrast to noise ratios for normal disk and degenerative disk, epidural-fat and disk herniated material, CSF and disk herniated material, and epidural-fat and CSF were less than 4 with LF, but more than 4 with MSE. This difference of contrast to noise ratio between MSE and LF was one of the main causes of the difference of the detection rate of spinal disk degeneration and indentation on subarachnoid space. (author).

Quantification of liver iron concentration with magnetic resonance imaging by combining T1-, T2-weighted spin echo sequences and a gradient echo sequence

NARCIS (Netherlands)

Kreeftenberg, HG; Mooyaart, EL; Sluiter, WJ; Kreeftenberg, HG; Huizenga, Reint

Background: The aim of the study was to quantify hepatic iron by MRI for practical use. Methods: In twenty-three patients with various degrees of iron overload, measurements were carried out with a 1.5 Tesla MR unit. A combination of pulse sequences (T1, T2 and gradient echo) enabled us to quantify

Inner ear malformations in patients with sensorineural heating loss: detection with gradient-echo (3DFT-CISS) MRI

Energy Technology Data Exchange (ETDEWEB)

Casselman, J.W. [Dept. of Radiology, A.Z. St.-Jan Brugge, Bruges (Belgium); Kuhweide, R. [Dept. of Otorhinolaryngology, A.Z. St.-Jan Brugge, Bruges (Belgium); Ampe, W. [Dept. of Otorhinolaryngology, A.Z. St.-Jan Brugge, Bruges (Belgium); D`Hont, G.D. [Dept. of Otorhinolaryngology, A.Z. St.-Jan Brugge, Bruges (Belgium); Offeciers, E.F. [ENT Dept., Sint-Augustinus Medical Inst., Univ. of Antwerp (Belgium); Faes, W.K. [Dept. of Radiology, A.Z. St.-Jan Brugge, Bruges (Belgium); Pattyn, G. [Dept. of Radiology, A.Z. St.-Jan Brugge, Bruges (Belgium)

1996-04-01

The sensitivity of different MRI sequences in the detection of inner ear malformations in patients presenting with sensorineural hearing loss (SNHL) and/or vertigo was evaluated. We studied 650 patients presenting with SNHL and/or vertigo, clinically not suspected of having inner ear malformations. The sensitivity of T1-weigted, Gd-enhanced T1-weighted and (when available) T2-weighted spin-echo images, and three-dimensional Fourier transformation-constructive interference in steady state (3DFT-CISS) gradient-echo images, to unexpected malformations was assessed. Inner ear malformations were found in 15 (2.3%) of these patients. Enlargement of the endolymphatic duct and sac was the most frequent malformation, found in 11 patients. The 3DFT-CISS images showed all lesions; the other sequences were less sensitive and the pathology was missed, partially or only retrospectively seen in 11 of the 15 patients. Therefore, in addition to the routine unenhanced and Gd-enhanced T1-weighted and T2-weighted images, thin gradient-echo (3DFT-CISS) images are necessary to detect all clinically unexpected inner ear malformations in patients presenting with vertigo and/or SNHL. (orig.)

Inner ear malformations in patients with sensorineural heating loss: detection with gradient-echo (3DFT-CISS) MRI

International Nuclear Information System (INIS)

Casselman, J.W.; Kuhweide, R.; Ampe, W.; D'Hont, G.D.; Offeciers, E.F.; Faes, W.K.; Pattyn, G.

1996-01-01

The sensitivity of different MRI sequences in the detection of inner ear malformations in patients presenting with sensorineural hearing loss (SNHL) and/or vertigo was evaluated. We studied 650 patients presenting with SNHL and/or vertigo, clinically not suspected of having inner ear malformations. The sensitivity of T1-weigted, Gd-enhanced T1-weighted and (when available) T2-weighted spin-echo images, and three-dimensional Fourier transformation-constructive interference in steady state (3DFT-CISS) gradient-echo images, to unexpected malformations was assessed. Inner ear malformations were found in 15 (2.3%) of these patients. Enlargement of the endolymphatic duct and sac was the most frequent malformation, found in 11 patients. The 3DFT-CISS images showed all lesions; the other sequences were less sensitive and the pathology was missed, partially or only retrospectively seen in 11 of the 15 patients. Therefore, in addition to the routine unenhanced and Gd-enhanced T1-weighted and T2-weighted images, thin gradient-echo (3DFT-CISS) images are necessary to detect all clinically unexpected inner ear malformations in patients presenting with vertigo and/or SNHL. (orig.)

Magnetic resonance cisternography using the fast spin echo method for the evaluation of vestibular schwannoma

Energy Technology Data Exchange (ETDEWEB)

Nishizawa, Shigeru; Yokoyama, Tetsuo; Uemura, Kenichi [Hamamatsu Univ. School of Medicine, Shizuoka (Japan)

1999-04-01

Neuroimaging of vestibular schwannoma was performed with the fat-suppression spoiled gradient recalled acquisition in the steady state (SPGR) method and magnetic resonance (MR) cisternography, which is a fast spin echo method using a long echo train length, for the preoperative evaluation of the lateral extension of the tumor in the internal auditory canal, and the anatomical identification of the posterior semicircular canal and the nerves in the canal distal to the tumor. The SPGR method overestimated the lateral extension in eight cases, probably because of enhancement of the nerves adjacent to the tumor in the canal. The posterior semicircular canal could not be clearly identified, and the cranial nerves in the canal were shown only as a nerve bundle. In contrast, MR cisternography showed clear images of the lateral extension of the tumor and the facial and cochlear nerves adjacent to the tumor in the internal auditory canal. The anatomical location of the posterior semicircular canal was also clearly shown. These preoperative findings are very useful to plan the extent to which the internal auditory canal can be opened, and for intraoperative identification of the nerves in the canal. MR cisternography is less invasive since no contrast material or radiation is required, as with thin-slice high-resolution computed tomography (CT). MR cisternography should replace high-resolution CT for the preoperative neuroradiological evaluation of vestibular schwannoma. (author)

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.)

Observations of fast magnetospheric echoes of artificially injected electrons above an auroral arc

International Nuclear Information System (INIS)

Wilhelm, K.; Becker, C.; Schmidt, R.

1984-04-01

Electron beam experiments using rocket-borne instrumentation have confirmed earlier observations of fast magnetospheric echoes of artificially injected energetic electrons. These experiments were jointly carried out by the University of Minnesota, the National Research Council of Canada and the Max-Planck-Institut fuer Aeronomie. A total of 234 echoes have been observed in a pitch angle range from 0 0 to 110 0 at energies of 1.87 and 3.90 keV. Out of this number, 95 echoes could unambiguously be identified with known accelerator operations at 2, 4 or 8 keV energy and highest current levels resulting in the determination of transit times of typically 400 ms. In most cases, when echoes were present in both energy channels, the higher energy electrons led the lower energy ones by approximately 50 ms. No echoes have been found in the 7.9 keV-detector channels. Adiabatic theory applied to these observations yields a reflection height of 3000 to 4000 km. The injection process is briefly discussed as the strong beam-plasma interaction that occurred near the electron accelerator appears to be instrumental in generating the source of heated electrons required for successful echo detection. Two consequences of this interaction, namely, strong energy and pitch angle diffusion and electron acceleration are illustrated with several examples. (orig.) [de

A comparison between fast and conventional spin-echo in the detection of multiple sclerosis lesions

International Nuclear Information System (INIS)

Thorpe, J.W.; Halpin, S.F.; MacManus, D.G.; Barker, G.J.; Kendall, B.E.; Miller, D.H.

1994-01-01

Long repetition time (TR) spin-echo (SE) with T 2 - or proton density weighting is the sequence of choice to detect the brain lesions of multiple sclerosis (MS). Fast spin-echo (FSE) permits the generation of T 2 -weighted images with similar contrast to SE but in a fraction of the time. We compared the sensitivity of FSE and SE in the detection of the brain lesions of MS. Six patients with clinically definite MS underwent brain imaging with both dual echo (long TR, long and short echo time (TE) SE and dual echo FSE. The SE and FSE images were first reviewed independently and then compared. A total of 404 lesions was detected on SE and 398 on FSE. Slightly more periventricular lesions were detected using SE than FSE (145 vs 127), whereas more posterior cranial fossa lesions were detected by FSE (77 vs 57). With both SE and FSE the short TE images revealed more lesions than the long echo. These results suggest that FSE could replace SE as the long TR sequence of choice in the investigation of MS. (orig.)

The evaluation of fat saturation fast spin-echo T2WI for patients with acute spinal trauma

International Nuclear Information System (INIS)

Kim, Sung Gyu; Lee, Chang Jun; Lee, Myung Joon; Kang, Ik Won; Yoo, Jeong Hyun

2002-01-01

To determine the usefulness of fat saturation fast spin-echo T2WI for patients with mild acute trauma of the spine. Between July 1998 and June 2002, 36 patients with acute spinal trauma underwent MRI within four months of injury. One, whose clinal symptoms indicated neurological paralysis, was excluded form our study. A superconductive 1.0-T MRI scanner was used, and conventional T1W1, T2W1, and additional fat-saturation fast spin-echo T2W1 were performed. Two radiologists compared conventional T2-weighted sagittal imaging and fat-saturation T2-weighted sagittal imaging in terms of the extension of increased high signal intensities in soft tissue and vertebral bodies, bone marrow signal change, disk herniation, and signal change of the disk. The detection rate of focal high signal intensities in soft tissue and bone marrow was significantly higher at fat-saturation fast spin-echo T2W1 is useful the evaluation of patients with mild acute spinal trauma without neurological impairment

Proton T2 Relaxation effect of superparamagnetic iron oxide on fast spin echo sequence. Influence of echo number (even or odd) of effective TE

International Nuclear Information System (INIS)

Tsuchihashi, Toshio; Maki, Toshio; Kitagawa, Matsuo; Suzuki, Takeshi; Fujita, Isao

1999-01-01

The T 2 relaxation effect of the fast spin echo sequence (FSE) was investigated using superparamagnetic iron oxide (SPIO) particles. When even echoes were used as the effective TE of FSE, the signal intensity ratio [signal intensity of FSE/signal intensity of conventional spin echo sequence (CSE)] of FSE and CSE increased, whereas the T 2 relaxation effect of SPIO with FSE was reduced. However, when odd echoes were used, neither signal intensity changed, and weakening of the T 2 relaxation effect, considered a problem with FSE, was reduced. This phenomenon was not observed when the refocusing flip angle was changed to 30 and 60 degrees. However, it was observed when the refocusing flip angle was 120 and 150 degrees. Thus, this phenomenon can be considered to be related to oscillation in longitudinal magnetization when using the Carr-Purcell-Meiboom-Gill (CPMG) technique. (author)

Fast fluid-attenuated inversion-recovery MR image in the intracranial tumors: comparison with fast spin-echo image

International Nuclear Information System (INIS)

Choi, Hye Young; Kwang, Hyoen Joo; Baek, Seoung Yeon; Lee, Sun Wha

1997-01-01

To evaluate the significance of fluid-attenuated inversion recovery(FLAIR) magnetic resonance(MR) images for the diagnosis of intracranial tumors. MR imaging was used to study 15 patients with various intracranial tumors and were compared the findings according to fast spin echo and fast FLAIR images. In 12 of 15 patients, tumor signal intensities on FLAIR images were consistent with those shown on T2-weighted(T2W) images. In seven of eight patients who had cystic or necrotic components within the mass, FLAIR images showed isosignal intensity and in the other patient, high signal intensity was seen. There was variation in the signal intensity from cerebrospinal fluid(CSF). In 12 of 13 patients in whom edema was associated with tumor, FLAIR images were clearer than T2W images as their signal intensity was brighter. In eight patients, however, FLAIR and T2W images provided a similar definition of the margin between edema and tumor. In six patients with intratumoral hemorrhage except the chronic cystic stage. We concluded that in the diagnosis of intracranial tumors, FLAIR images can supplement conventional spin-echo images

Contrast-enhanced MR imaging of metastatic brain tumor at 3 Tesla. Utility of T1-weighted SPACE compared with 2D spin echo and 3D gradient echo sequence

International Nuclear Information System (INIS)

Komada, Tomohiro; Naganawa, Shinji; Ogawa, Hiroshi

2008-01-01

We evaluated the newly developed whole-brain, isotropic, 3-dimensional turbo spin-echo imaging with variable flip angle echo train (SPACE) for contrast-enhanced T 1 -weighted imaging in detecting brain metastases at 3 tesla (T). Twenty-two patients with suspected brain metastases underwent postcontrast study with SPACE, magnetization-prepared rapid gradient-echo (MP-RAGE), and 2-dimensional T 1 -weighted spin echo (2D-SE) imaging at 3 T. We quantitatively compared SPACE, MP-RAGE, and 2D-SE images by using signal-to-noise ratios (SNRs) for gray matter (GM) and white matter (WM) and contrast-to-noise ratios (CNRs) for GM-to-WM, lesion-to-GM, and lesion-to-WM. Two blinded radiologists evaluated the detection of brain metastases by segment-by-segment analysis and continuously-distributed test. The CNR between GM and WM was significantly higher on MP-RAGE images than on SPACE images (P 1 -weighted imaging. (author)

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......, GE-EPI under the present condition was superior to SE-EPI in monitoring cerebral vascular changes...

MR imaging characteristics of intracranial hemorrhage using gradient-echo signal acquisition at 1.5 T: Comparison with spin-echo imaging and clinical applications

International Nuclear Information System (INIS)

Atlas, S.W.; Grossman, R.I.; Gomori, J.M.; Hackney, D.B.; Goldberg, H.I.; Bilaniuk, L.T.; Zimmerman, R.A.

1987-01-01

Evolving paramagnetic blood-breakdown products create static local magnetic susceptibility gradients, which induce rapid phase dispersion on the basis of T2/sup */ shortening. The authors evaluated 30 patients with 50 separate hemorrhagic intracranial lesions with both spin-echo (SE) and gradient echo signal acquisition (GESA) MR imaging at 1.5 T. GESA sequences used repetition time (TR) of 200-750 msec, echo time (TE) of 50-80 msec, and flip angles of 10 0 to 15 0 to emphasize T2/sup */-based contributions to contrast. SE sequences in all cases utilized both short and long TR (600 and 2,500-3,000 msec), with TE of 20-120 msec. Advantages of GESA imaging with Long TE and short flip angles in the evaluation of intracranial hemorrhage include (1) increased sensitivity to susceptibility-induced phase loss from T2/sup */ shortening, resulting in detection of hemorrhagic lesions not seen on conventional long TR/long TE SE images, and (2) very rapid acquisition of images with T2/sup */-based contrast. Limitations of this sequence include (1) severe diamagnetic susceptibility-induced artifacts, especially near air-brain interfaces, which often obscure large portions of the brain and occasionally simulate serious pathology, (2) characteristic internal signal intensity patterns demonstrated by SE imaging, such as in evolving hematomas, occult vascular malformations, and hemorrhagic malignancies, are often obscured by marked hypointensity on GESA images, and (3) reduced signal-noise ratio. The authors conclude that, although images with marked sensitivity to T2/sup */ effects can be rapidly generated by GESA, there is only a limited role for this sequence when evaluating intracranial hemorrhage at 1.5 T, and, in fact, significant information is lost when compared to SE images

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.)

Analysis of artefacts and detail resolution of lung MRI with breath-hold T1-weighted gradient-echo and T2-weighted fast spin-echo sequences with respiratory triggering

International Nuclear Information System (INIS)

Biederer, J.; Reuter, M.; Both, M.; Grimm, J.; Heller, M.; Muhle, C.; Graessner, J.

2002-01-01

The aim of this study was to evaluate feasibility and limitations of two MR sequences for imaging of the lung using a semi-quantitative rating scale. Ten healthy volunteers were assessed with a breath-hold T1-weighted gradient-recalled-echo (TR/TE=129/2.2 ms, matrix 173 x 256) and a T2-weighted turbo spin-echo (TSE) sequence with respiratory triggering (TR/TE=3000-5000/120 ms, matrix 270 x 512) in axial 6-mm slices. The T1-weighted GRE protocol included a pre-saturation pulse over the mediastinal structures. Artefacts and resolution of vessel/airway structures in each lung segment were evaluated by two observers (10 volunteers, 180 segments). Cardiac and vessel pulsation artefacts predominated on T1-weighted GRE, respiration artefacts on T2-weighted TSE (lingula and middle lobe). Pre-saturation of the mediastinum reduced pulsation artefacts on T1-weighted GRE. T1-weighted GRE images were improved by bright flow signal of vessels, whereas image quality of T2-weighted TSE was reduced by black-blood effects in central parts of the lung. Delineation of lung periphery and the mediastinum was superior with T2-weighted TSE. Segmental/sub-segmental vessels (up to fourth/fifth order) and bronchi (up to third order) were identified. All 180 lung segments were imaged in diagnostic quality with at least one of the two sequences (T1-weighted GRE not diagnostic in 9 of 180, T2-weighted TSE in 4 of 180). Both sequences were found to be complementary: superior identification of gross lung anatomy with T1-weighted GRE and higher detail resolution in the periphery and the mediastinum with T2-weighted TSE. (orig.)

Proton T2 relaxation effect of superparamagnetic iron oxide. Comparison between fast spin echo and conventional spin echo sequence

International Nuclear Information System (INIS)

Tanimoto, Akihiro; Satoh, Yoshinori; Higuchi, Nobuya; Izutsu, Mutsumu; Yuasa, Yuji; Hiramatsu, Kyoichi

1995-01-01

Superparamagnetic iron oxide (SPIO) particles have been known to show a great T 2 relaxation effect in the liver, which contributes to significant liver signal decrease and detection of hepatic neoplasms. Recently, fast spin echo (FSE) sequence with less scanning time than conventional spin echo (SE) sequence has been rapidly introduced in clinical MR imaging. To investigate whether SPIO would show decreased T 2 relaxation effect on FSE, we obtained T 2 relaxivity (R2) of SPIO in vitro and liver signal decrease caused by SPIO in vivo. SPIO showed 20% less R2 on Carr-Purcell-Meiboom-Gill (CPMG) sequence than on SE. Relative liver signal-to-noise ratio (SNR) decrease caused by SPIO was significantly smaller (p 2 relaxation effect on FSE than on SE. However, further studies will be required to assess the diagnostic capability of SPIO on FSE, in the detection of hepatic neoplasms. (author)

Comparison of respiratory-triggered 3-D fast spin-echo and single-shot fast spin-echo radial slab MR cholangiopancreatography images in children

Energy Technology Data Exchange (ETDEWEB)

Chavhan, Govind B.; Almehdar, Abeer; Gupta, Sumeet [The Hospital for Sick Children and University of Toronto, Department of Diagnostic Imaging, Toronto (Canada); Moineddin, Rahim [University of Toronto, Department of Family and Community Medicine, Toronto (Canada); Babyn, Paul S. [Royal University Hospital, Department of Medical Imaging, Saskatoon (Canada)

2013-09-15

The two most commonly performed magnetic resonance cholangiopancreatography (MRCP) sequences, 3-D fast spin-echo (3-D FSE) and single-shot fast spin-echo radial slabs (radial slabs), have not been compared in children. The purpose of this study was to compare 3-D FSE and radial slabs MRCP sequences on a 3-T scanner to determine their ability to show various segments of pancreaticobiliary tree and presence of artifacts in children. We reviewed 79 consecutive MRCPs performed in 74 children on a 3-T scanner. We noted visibility of major ducts on 3-D FSE and radial slabs. We noted the order of branching of ducts in the right and left hepatic ducts and the degree of visibility of the pancreatic duct. Statistical analysis was performed using McNemar and signed rank tests. There was no significant difference in the visibility of major bile ducts and the order of branching in the right hepatic lobe between sequences. A higher order of branching in the left lobe was seen on radial slabs than 3-D FSE (mean order of branching 2.82 versus 2.27; P-value = 0.0002). The visibility of pancreatic duct was better on radial slabs as compared to 3-D FSE (mean value of 1.53 vs. 0.90; P-value < 0.0001). 3-D FSE sequence was artifact-free in 25/79 (31.6%) MRCP exams as compared to radial slabs, which were artifact-free in 18/79 (22.8%) MRCP exams (P-value = 0.0001). There is no significant difference in the visibility of major bile ducts between 3-D FSE and radial slab MRCP sequences at 3-T in children. However, radial slab MRCP shows a higher order of branching in the left hepatic lobe and superior visibility of the pancreatic duct than 3-D FSE. (orig.)

Fast MR imaging for evaluating the pancreaticobiliary system

International Nuclear Information System (INIS)

Takehara, Yasuo

1999-01-01

Due to physiological movement clinical MR applications for abdominal organs got off to a very slow start compared to MR imaging of other organs. However, with recent cutting-edge hardware technologies such as high performance gradient systems and phased-array capability, as well as software innovations including short TR fast spoiled gradient recalled acquisition in the steady state (GRASS), snapshot imaging such as single shot fast spin echo sequence (SSFSE) and echo planar imaging (EPI), scan times have been further reduced to make breath-hold imaging clinically viable and to enable semi-fluoroscopic, kinematic imaging recognition. The elimination of physiological motion has contributed to the significant improvement in image quality, or more specifically, the physiological motion that had long been problematic has been turned into a source of physiological information about pancreaticobiliary pathologies. In this article, the author reviewed the current status of fast MR technologies for examining pancreaticobiliary pathologies, stressing the functional and physiological aspects of the corresponding anatomy. The technologies included secretin MRCP, which became a powerful tool when combined with kinematic imaging

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.

Fast triple-spin-echo Dixon (FTSED) sequence for water and fat imaging

Czech Academy of Sciences Publication Activity Database

Kořínek, Radim; Bartušek, Karel; Starčuk jr., Zenon

2017-01-01

Roč. 37, APR (2017), s. 164-170 ISSN 0730-725X R&D Projects: GA MŠk ED0017/01/01; GA MŠk(CZ) LO1212 Institutional support: RVO:68081731 Keywords : fast triple-spin-echo Dixon * sequence * MRI * fat fraction * water-fat * ultra-high field * 9.4 T * FTSED Subject RIV: BH - Optics, Masers, Lasers OBOR OECD: Radiology, nuclear medicine and medical imaging Impact factor: 2.225, year: 2016

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.......e., it performs as well as the full discrete Fourier transform for band limited signals while allowing for use of the fast Fourier transform. The method is demonstrated for reconstruction of data that are partially undersampled in the time domain. The advantages of undersampling are lower hardware requirements...

Storage and manipulation of light using a Raman gradient-echo process

International Nuclear Information System (INIS)

Hosseini, M; Sparkes, B M; Campbell, G T; Lam, P K; Buchler, B C

2012-01-01

The gradient-echo memory (GEM) scheme has potential to be a suitable protocol for storage and retrieval of optical quantum information. In this paper, we review the properties of the Λ-GEM method that stores information in the ground states of three-level atomic ensembles via Raman coupling. The scheme is versatile in that it can store and re-sequence multiple pulses of light. To date, this scheme has been implemented using warm rubidium gas cells. There are different phenomena that can influence the performance of these atomic systems. We investigate the impact of atomic motion and four-wave mixing and present experiments that show how parasitic four-wave mixing can be mitigated. We also use the memory to demonstrate preservation of pulse shape and the backward retrieval of pulses. (paper)

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

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...... 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...... degrees the values of delta R2* for cortical grey matter, central grey matter, white matter and the sagittal sinus were 0.79, 0.41, 0.26 and 3.00/s; with a flip angle of 10 degrees the corresponding values were 0.70, 0.37, 0.24 and 3.15/s. The total cerebral blood flow increased by 41% during inhalation...

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...... perfusion metrics was investigated for the gradient echo pulse sequence at 1.5 T and 3.0 T. It is shown that the tissue contribution broadens and introduces fluctuations in the AIF. Furthermore, partial volume effects bias perfusion metrics in a nonlinear fashion, compromising quantitative perfusion...

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...

Dual-echo, chemical shift gradient-echo magnetic resonance imaging to quantify hepatic steatosis: Implications for living liver donation.

Science.gov (United States)

Rinella, Mary E; McCarthy, Richard; Thakrar, Kiran; Finn, John Paul; Rao, Sambasiva M; Koffron, Alan J; Abecassis, Michael; Blei, Andres T

2003-08-01

In living liver donation, a fatty liver poses risks for both recipient and donor. Currently, liver biopsy is the standard for assessing the presence and extent of steatosis. The goals of this study were to correlate a steatosis index derived from magnetic resonance imaging (MRI) to the histologic grade on biopsy as well as to determine the topographic distribution of steatosis within the liver. We examined the ability of dual-echo, chemical shift gradient-echo MRI to predict the degree of steatosis on liver biopsy. A total of 22 subjects received both a liver biopsy and detailed MRI evaluation. These individuals included 15 potential living donors and 7 patients with nonalcoholic fatty liver disease. MRI steatosis index was then compared with histologic grade on liver biopsy. The topographic distribution of hepatic steatosis was determined from those subjects in whom MRI detected hepatic steatosis. The steatosis index had a positive correlation with grade of steatosis on liver biopsy (correlation coefficient, 0.84). There was no significant variation in the degree of steatosis among segments. A steatosis index of >0.2 had good positive and negative predictive value for the presence of significant steatosis (>15%) on biopsy. Our quantitative MRI protocol can predict the degree of hepatic steatosis when it is minimal to moderate, and may obviate the need for liver biopsy for the purpose of quantification of steatosis in living donors. Fat saturation added to the MRI protocol may further improve diagnostic accuracy. This technique may be applicable to the larger population with hepatic steatosis.

Spin-echo Echo-planar Imaging MR Elastography versus Gradient-echo MR Elastography for Assessment of Liver Stiffness in Children and Young Adults Suspected of Having Liver Disease.

Science.gov (United States)

Serai, Suraj D; Dillman, Jonathan R; Trout, Andrew T

2017-03-01

Purpose To compare two-dimensional (2D) gradient-recalled echo (GRE) and 2D spin-echo (SE) echo-planar imaging (EPI) magnetic resonance (MR) elastography for measurement of hepatic stiffness in pediatric and young adult patients suspected of having liver disease. Materials and Methods In this institutional review board-approved, HIPAA-compliant study, 58 patients underwent both 2D GRE and 2D SE-EPI MR elastography at 1.5 T during separate breath holds. Liver stiffness (mean of means; in kilopascals) was measured by five blinded reviewers. Pooled mean liver stiffness and region-of-interest (ROI) size were compared by using paired t tests. Intraclass correlation coefficients (ICCs) were used to assess agreement between techniques. Respiratory motion artifacts were compared across sequences by using the Fisher exact test. Results Mean patient age was 14.7 years ± 5.2 (standard deviation; age range, 0.7-20.5 years), and 55.2% (32 of 58) of patients were male. Mean liver stiffness was 2.92 kPa ± 1.29 measured at GRE MR elastography and 2.76 kPa ± 1.39 at SE-EPI MR elastography (n = 290; P = .15). Mean ROI sizes were 8495 mm 2 ± 4482 for 2D GRE MR elastography and 15 176 mm 2 ± 7609 for 2D SE-EPI MR elastography (n = 290; P range, 0.91-0.95). Moderate or severe breathing artifacts were observed on 27.5% (16 of 58) of 2D GRE images versus 0% 2D SE-EPI images (P < .001). Conclusion There is excellent agreement on measured hepatic stiffness between 2D GRE and 2D SE-EPI MR elastography across multiple reviewers. SE-EPI MR elastography allowed for stiffness measurement across larger areas of the liver and can be performed in a single breath hold. © RSNA, 2016.

Fast FLAIR MR imaging finidngs of cerebral infarction : comparison with T2-weighted spin echo imaging

International Nuclear Information System (INIS)

Kong, Keun Young; Choi, Woo Suk; Kim, Eui Jong

1997-01-01

To evaluate the utility of FLAIR(Fluid Attenuated Inversion Recovery) MR imaging in cerebral infarction by comparing its results with those of T2-weighted spin-echo imaging. We retrospectively evaluated fast FLAIR images and conventional spin echo images of 82 patients (47 men and 20 women ; median age 60.9 years) with cerebral infarction. MR imaging used a 1.5T MR unit with conventional T2(TR 3900, TE 90) and fast FLAIR sequence (TR 8000, TE 105, TI 2400). We analysed the size of the main lesion and number of lesions, and discrimination between old and new lesions and between small infarction and perivascular space. When T2-weighted and FLAIR imaging were compared, the latter showed that the main lesion was larger in 38 cases (46%), similar in 38 (46%), and smaller in six (7%). The number of lesions was greater in 23 cases(28%), similar in 52 (63%), and fewer in seven (9%). FLAIR images discriminated between old and new lesions in 31 cases ; perivascular space and small infarotion were differentiated in eight cases, and CSF inflowing artifact was observed in 66 (80%). In the diagnosis of cerebral infaretion, fast FLAIR provides images that are equal or superior to T2-weighted images. The fast FLAIR sequence may therefore be used as a part of routine MR brain study in the diagnosis of cerebral infarction

Application of fast spin-echo T[sub 2]-weighted imaging for examination of the neurocranium. Comparison with the conventional T[sub 2]-weighted spin-echo sequence. Die Anwendung der T[sub 2]-gewichteten Turbo-Spin-Echo-Sequenz zur Untersuchung des Neurokraniums. Vergleich mit der konventionellen T[sub 2]-gewichteten Spin-Echo-Sequenz

Energy Technology Data Exchange (ETDEWEB)

Siewert, C. (Strahlenklinik und Poliklinik, Universitaets-Klinikum Rudolf Virchow, Standort Wedding, Freie Univ. Berlin (Germany)); Hosten, N. (Strahlenklinik und Poliklinik, Universitaets-Klinikum Rudolf Virchow, Standort Wedding, Freie Univ. Berlin (Germany)); Felix, R. (Strahlenklinik und Poliklinik, Universitaets-Klinikum Rudolf Virchow, Standort Wedding, Freie Univ. Berlin (Germany))

1994-07-01

T[sub 2]-weighted spin-echo imaging is the standard screening procedure in MR imaging of the neutrocranium. We evaluated fast spin-echo T[sub 2]-weighted imaging (TT[sub 2]) of the neurocranium in comparison to conventional spin-echo T[sub 2]-weighted imaging (T[sub 2]). Signal-to-noise and contrast-to-noise ratio of normal brain tissues (basal ganglia, grey and white matter, CSF fluid) and different pathologies were calculated. Signal-to-noise ratio and contrast-to-noise ratio were significantly higher than TT[sub 2] than in T[sub 2] (with the exception of grey-to-white matter contrast). Tissues with increased content of water protons (mobile protons) showed the highest contrast to surrounding tissues. The increased signal intensity of fat must be given due attention in fatty lesions. Because the contrast-to-noise ratio between white matter and basal ganglia is less in TT[sub 2], Parkinson patients have to be examined by conventional T[sub 2]. If these limitations are taken into account, fast spin-echo T[sub 2]-weighted imaging is well appropriate for MR imaging of the neurocranium, resulting in heavy T[sub 2]-weighting achieved in a short acquisition time. (orig.)

Fast MR imaging and ultrafast MR imaging of fetal central nervous system abnormalities

Energy Technology Data Exchange (ETDEWEB)

Shakudo, Miyuki; Manabe, Takao; Murata, Katsuko; Matsuo, Ryoichi; Oda, Junro [Osaka City General Hospital (Japan); Inoue, Yuichi; Mochizuki, Kunizo; Yamada, Ryusaku

2001-12-01

The aims of this study were two: to compare the efficacy of fast MRI (breath-hold fast spin-echo T2-weighted and fast gradient-echo T1-weighted sequence) and ultrafast MRI (half-Fourier acquisition single-shot turbo spin-echo sequence) in evaluation of fetal central nervous system (CNS) abnormalities at late gestational age, and to compare the capability of fast MRI and ultrafast MRI to assess fetal CNS abnormalities with that of prenatal ultrasonography (US). Forty-nine women with fetuses at gestational ages of 26-39 weeks underwent fast MRI (29 patients) or ultrafast MRI (20 patients). In detection of motion artifact, visualization of the lateral and 4th ventricles, and differentiation between gray and white matter in cerebral hemispheres, ultrafast MRI was significantly superior to fast MRI (p<0.0001, Mann-Whitney U test). In 25 of 43 cases, US and MR diagnoses were the same and consistent with postnatal diagnosis. In 10 of 43 cases, MRI demonstrated findings additional to or different from those of US, and MR findings were confirmed postnatally. MRI, particularly ultrafast MRI, is useful for demonstrating CNS abnormalities in situations in which US is suggestive but not definitive. (author)

Diffusional behavior of n-paraffins with various chain lengths in urea adduct channels by pulsed field-gradient spin-echo NMR spectroscopy

International Nuclear Information System (INIS)

Kim, Sunmi; Kuroki, Shigeki; Ando, Isao

2006-01-01

The diffusion coefficients (D) of n-paraffin molecules (n-C n H 2n+2 ) with various chain-lengths (n = 8, 12, 21, 26, 28 and 32) in the long channels of a deuterated urea-d 4 adduct have been measured at 25 deg. C by means of pulsed field-gradient spin-echo 1 H NMR method. The aim is to clarify diffusional behavior of the n-paraffin molecules in the urea adduct channels. From the experimental results, it is found that n-paraffin molecules are diffusing in the long channels and have two kinds of diffusion components, namely a fast (D ∼ 10 -10 m 2 /s) and a slow diffusion component (D ∼ 10 -11 m 2 /s). The diffusing-time (Δ) dependence of the diffusion coefficients of the n-paraffins shows some likely evidence of restricted diffusion since the n-paraffin molecules are confined in the urea channel. The diffusion coefficients (D) decrease as the carbon number increases from 8 to 28, and very slowly decreases as the carbon number increases from 28 to 32

Evaluation of MR cisternography of the cerebellopontine angle using a balanced fast-field-echo sequence: preliminary findings

Energy Technology Data Exchange (ETDEWEB)

Tsuchiya, Kazuhiro; Aoki, Chinatsu; Hachiya, Junichi [Department of Radiology, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka, 181-8611, Tokyo (Japan)

2004-02-01

We evaluated the feasibility of MR cisternography by the balanced fast-field-echo (bFFE) sequence, comparing with that by a turbo-spin-echo (TSE) sequence, for cerebellopontine angle lesions on a 1.5-T imager (Gyroscan Intera, Philips, Best, The Netherlands). The bFFE MR cisternograms depicted target cranial nerves with less cerebrospinal fluid pulsation artifacts than TSE cisternograms and visualized an acoustic schwannoma in 6 of 44 patients with suspicion and a causative vessel of hemifacial spasm in all of 3 patients in a short scanning time (1 min 53 s). The bFFE sequence can be promising for MR cisternography in the diagnosis of cerebellopontine angle lesions. (orig.)

Magnetization transfer contrast on gradient echo MR imaging of the temporomandibular joint

International Nuclear Information System (INIS)

Niitsu, M.; Hirohata, H.; Yoshioka, H.; Anno, I.; Campeau, N.G.; Itai, Y.

1995-01-01

Thirty-nine temporomandibular joints (TMJ) from 20 patients with suspected internal derangements were imaged by a 1.5 T MR imager. The on-resonance binomial magnetization transfer contrast (MTC) pulse was applied to gradient echo images with a dual receiver coil (9 s/section). With the use of an opening device, a series of sequential images were obtained at increments of mouth opening and closing. The tissue signal intensities with (Ms) and without (Mo) MTC were measured and subjective image analysis was performed. Compared with the standard images, MTC technique provided selective signal suppression of disks. The average of Ms/Mo ratio of the disks (0.56) was lower than that of the retrodiskal pad (0.79) and of the effusion (0.89). With MTC technique, fluid conspicuity was superior to standard image. However, no significant superiority was found in disk definition subjectively. (orig.)

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.

Magnetic resonance in cartilaginous lesions of the knee joint with three-dimensional gradient-echo imaging

International Nuclear Information System (INIS)

Reiser, M.F.; Bongartz, G.; Erlemann, R.; Gaebert, K.; Stoeber, U.; Peters, P.E.; Strobel, M.; Pauly, T.

1988-01-01

Diagnosis of chondromalacia of the patellofemoral joint using three-dimensional gradient-echo sequences was investigated in 41 patients, with arthroscopic verification in 25 patients. In vitro examinations in human caderveric patellae were performed in order to determine optimal imaging parameters. FLASH (T R =40 ms, T E =10 ms, flip angle=30 0 ) and FISP (T R =40 ms, T E =10 ms, flip angle=40 0 ) were used in clinical studies. The therapeutically relevant differentiation of major and minor degrees of chondromalacia seems to be possible. 30 0 FLASH-images in the axial plane proved to be the most efficacious technique for the diagnosis of chondromalacia. (orig./GDG)

Self-normalizing multiple-echo technique for measuring the in vivo apparent diffusion coefficient

International Nuclear Information System (INIS)

Perman, W.H.; Gado, M.; Sandstrom, J.C.

1989-01-01

This paper presents work to develop a new technique for quantitating the in vivo apparent diffusion/perfusion coefficient (ADC) by obtaining multiple data points from only two images with the capability to normalize the data from consecutive images, thus minimizing the effect of interimage variation. Two multiple-echo (six-to eight-echo) cardiac-gated images are obtained, one without and one with additional diffusion/perfusion encoding gradients placed about the 180 RF pulses of all but the first echo. Since the first echoes of both images have identical pulse sequence parameters, variations in signal intensity-between the first echoes represent image-to-image variation. The signal intensities of the subsequent echoes with additional diffusion/perfusion encoding gradients are then normalized by using the ratio of the first-echo signal intensities

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.)

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.

Moderately T2-weighted images obtained with the single-shot fast spin-echo technique. Differentiating between malignant and benign urinary obstructions

International Nuclear Information System (INIS)

Obuchi, Masao; Sugimoto, Hideharu; Kubota, Hayato; Yamamoto, Wakako; Kinebuchi, Yuko; Honda, Minoru; Takahara, Taro

2002-01-01

The purpose of this study was to determine whether a distinction could be made between benign and malignant urinary obstructions in moderately T 2 -weighted images obtained with the single-shot fast spin-echo technique. Forty-four lesions in 39 patients with urinary obstruction were evaluated with the single-shot fast spin-echo (SSFSE) technique with an effective TE of 90-100 ms and without fat saturation. Benign and malignant lesions were compared for the presence of ureteral wall thickening and a signal intensity relative to the proximal ureteral wall. Statistically significant differences were found between benign and malignant lesions in both morphologic change (P 2 -weighted SSFSE technique without fat saturation can accurately distinguish between benign and malignant urinary obstructions. (author)

A 3D T1-weighted gradient-echo sequence for routine use in 3D radiosurgical treatment planning of brain metastases: first clinical results

International Nuclear Information System (INIS)

Hawighorst, H.; Schad, L.R.; Gademann, G.; Knopp, M.V.; Wenz, F.; Kaick, G. van

1995-01-01

The authors report on a 3D sequence for MRI of the brain and its application in radiosurgical treatment planning of 35 brain metastases. The measuring sequence, called magnetization - prepared rapid gradient echo (MPRAGE), was compared with 2D T1-weighted spin-echo (SE) sequences following intravenous contrast-medium application in 19 patients with brain metastases. The average diameter of all lesions was similar in both sequences, with 16.8 and 17.0 mm for SE and MPRAGE, respectively. Target point definition was equal in 29 metastases, and in 6 cases superior on MPRAGE, due to better gray-white matter contrast and increased contrast enhancement. In cases of bleeding metastases there was improved depiction of internal structures in 3D MRI. Postprocessing of 3D MPRAGE data created multiplanar reconstruction along any chosen plane with isotropic spatial resolution, which helped to improve radiosurgical isodose distribution in 4 cases when compared to 2D SE. However, sensitivity of 3D MPRAGE to detect small lesions (< 3 mm) was decreased in one patient with more than 50 metastases. We conclude that 3D gradient-echo (GE) imaging might be of great value for radiosurgical treatment planning, but does not replace 2D SE with its current parameters. (orig.)

Magnetic resonance in cartilaginous lesions of the knee joint with three-dimensional gradient-echo imaging

Energy Technology Data Exchange (ETDEWEB)

Reiser, M.F.; Bongartz, G.; Erlemann, R.; Gaebert, K.; Stoeber, U.; Peters, P.E.; Strobel, M.; Pauly, T.

1988-10-01

Diagnosis of chondromalacia of the patellofemoral joint using three-dimensional gradient-echo sequences was investigated in 41 patients, with arthroscopic verification in 25 patients. In vitro examinations in human caderveric patellae were performed in order to determine optimal imaging parameters. FLASH (T/sub R/=40 ms, T/sub E/=10 ms, flip angle=30/sup 0/) and FISP (T/sub R/=40 ms, T/sub E/=10 ms, flip angle=40/sup 0/) were used in clinical studies. The therapeutically relevant differentiation of major and minor degrees of chondromalacia seems to be possible. 30/sup 0/ FLASH-images in the axial plane proved to be the most efficacious technique for the diagnosis of chondromalacia. (orig./GDG).

MR Imaging of the Spine at 3.0T with T2-Weighted IDEAL Fast Recovery Fast Spin-Echo Technique

International Nuclear Information System (INIS)

Ren, Ai Jun; Guo, Yong; Tian, Shu Ping; Shi, Li Jing; Huang, Min Hua

2012-01-01

To compare the iterative decomposition of water and fat with echo asymmetry and the least-squares estimation (IDEAL) method with a fat-saturated T2-weighted (T2W) fast recovery fast spin-echo (FRFSE) imaging of the spine. Images acquired at 3.0 Tesla (T) in 35 patients with different spine lesions using fat-saturated T2W FRFSE imaging were compared with T2W IDEAL FRFSE images. Signal-to-noise ratio (SNR)-efficiencies measurements were made in the vertebral bodies and spinal cord in the mid-sagittal plane or nearest to the mid-sagittal plane. Images were scored with the consensus of two experienced radiologists on a four-point grading scale for fat suppression and overall image quality. Statistical analysis of SNR-efficiency, fat suppression and image quality scores was performed with a paired Student's t test and Wilcoxon's signed rank test. Signal-to-noise ratio-efficiency for both vertebral body and spinal cord was higher with T2W IDEAL FRFSE imaging (p < 0.05) than with T2W FRFSE imaging. T2W IDEAL FRFSE demonstrated superior fat suppression (p < 0.01) and image quality (p < 0.01) compared to fat-saturated T2W FRFSE. As compared with fat-saturated T2W FRFSE, IDEAL can provide a higher image quality, higher SNR-efficiency, and consistent, robust and uniform fat suppression. T2W IDEAL FRFSE is a promising technique for MR imaging of the spine at 3.0T.

Optimization image of magnetic resonance imaging (MRI) T2 fast spin echo (FSE) with variation echo train length (ETL) on the rupture tendon achilles case

International Nuclear Information System (INIS)

Muzamil, Akhmad; Firmansyah, Achmad Haries

2017-01-01

The research was done the optimization image of Magnetic Resonance Imaging (MRI) T2 Fast Spin Echo (FSE) with variation Echo Train Length (ETL) on the Rupture Tendon Achilles case. This study aims to find the variations Echo Train Length (ETL) from the results of ankle’s MRI image and find out how the value of Echo Train Length (ETL) works on the MRI ankle to produce optimal image. In this research, the used ETL variations were 12 and 20 with the interval 2 on weighting T2 FSE sagittal. The study obtained the influence of Echo Train Length (ETL) on the quality of ankle MRI image sagittal using T2 FSE weighting and analyzed in 25 images of five patients. The data analysis has done quantitatively with the Region of Interest (ROI) directly on computer MRI image planes which conducted statistical tests Signal to Noise Ratio (SNR) and Contras to Noise Ratio (CNR). The Signal to Noise Ratio (SNR) was the highest finding on fat tissue, while the Contras to Noise Ratio (CNR) on the Tendon-Fat tissue with ETL 12 found in two patients. The statistics test showed the significant SNR value of the 0.007 (p<0.05) of Tendon tissue, 0.364 (p>0.05) of the Fat, 0.912 (p>0.05) of the Fibula, and 0.436 (p>0.05) of the Heel Bone. For the contrast to noise ratio (CNR) of the Tendon-FAT tissue was about 0.041 (p>0.05). The results of the study showed that ETL variation with T2 FSE sagittal weighting had difference at Tendon tissue and Tendon-Fat tissue for MRI imaging quality. SNR and CNR were an important aspect on imaging optimization process to give the diagnose information. (paper)

Lesion discrimination in optic neuritis using high-resolution fat-suppressed fast spin-echo MRI

International Nuclear Information System (INIS)

Gass, A.; Moseley, I.F.; Barker, G.J.; Jones, S.; MacManus, D.; McDonald, W.I.; Miller, D.H.

1996-01-01

Fast spin-echo (FSE) is a new sequence with acquisition times currently down to one-sixteenth of those obtained with conventional spin-echo sequences, which allows high-resolution (512 x 512 matrix) images to be acquired in an acceptable time. We compared the higher resolution of FSE with the medium resolution of a short inversion-time inversion-recovery (STIR) sequence in depicting the optic nerves of healthy controls and patients with optic neuritis. Optic nerve MRI examinations were performed in 18 patients with optic neuritis and 10 normal controls. Two sequences were obtained coronally: fat-suppressed FSE (FSE TR 3250 ms/TEef 68 ms, echo-train length 16, 4 excitations, 24 cm rectangular field of view, 3 mm interleaved contiguous slices, in-plane resolution 0.5 x 0.5 mm) and STIR (TR 2000 ms/TE 50 ms/TI 175 ms, in-plane resolution 0.8 x 0.8 mm, slice thickness 5 mm). FSE demonstrated much more anatomical detail than STIR, e. g. distinction of optic nerve and sheath. Lesions were seen in 20 of 21 symptomatic nerves using FSE and in 18 of 21 using STIR. Nerve swelling or partial cross-sectional lesions of the optic nerve were each seen only on FSE in 3 cases. Fat-suppressed FSE imaging of the optic nerve improves anatomical definition and increases lesion detection in optic neuritis. (orig.). With 5 figs

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

International Nuclear Information System (INIS)

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

2014-01-01

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 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.)

Evaluation of short repetition time, partial flip angle, gradient recalled echo pulse sequences in cervical spine imaging

International Nuclear Information System (INIS)

Enzmann, D.; Rubin, J.B.

1987-01-01

A short repetition time (TR), partial flip angle, gradient recalled echo pulse sequence (GRASS) was prospectively studied to optimize it for the diagnosis of cervical disk and cord disease in 98 patients. Changes in signal-to-noise ratio (SNR) and contrast were measured as the following parameters were varied: flip angle (3 0 to 18 0 ), TR (22-60 msec), and echo time (TE) (12.5-25 msec). Flip angle was the single most important parameter. For disk disease, cerebrospinal fluid (CSF) SNR peaked at an 8 0 flip angle in the axial view but at a 4 0 flip angle in the sagittal view. In the sagittal view, disk-CSF contrast decreased progressively from a flip angle of 3 0 , while in the axial view it peaked at 10 0 . For cord lesions the findings were similar except that lesion-cord contrast could be increased by lengthening both TR and TE. No one combination of parameters proved greatly superior for either disk disease or cord disease. The selection of parameters required balancing of several factors that often had opposing effects

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

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Noam Shemesh

Full Text Available Objects making up complex porous systems in Nature usually span a range of sizes. 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 to Central Nervous System diseases. Accurate and noninvasive measurements of size distributions in opaque, three-dimensional objects, have thus remained long-standing and important challenges. Herein we describe how a recently introduced diffusion-based magnetic resonance methodology, Non-Uniform-Oscillating-Gradient-Spin-Echo (NOGSE, can determine such distributions noninvasively. The method relies on its ability to probe confining lengths with a (length6 parametric sensitivity, in a constant-time, constant-number-of-gradients fashion; combined, these attributes provide sufficient sensitivity for characterizing the underlying distributions in μm-scaled cellular systems. Theoretical derivations and simulations are presented to verify NOGSE's ability to faithfully reconstruct size distributions through suitable modeling of their distribution parameters. Experiments in yeast cell suspensions - where the ground truth can be determined from ancillary microscopy - corroborate these trends experimentally. Finally, by appending to the NOGSE protocol an imaging acquisition, novel MRI maps of cellular size distributions were collected from a mouse brain. The ensuing micro-architectural contrasts successfully delineated distinctive hallmark anatomical sub-structures, in both white matter and gray matter tissues, in a non-invasive manner. Such findings highlight NOGSE's potential for characterizing aberrations in cellular size distributions upon disease, or during normal processes such as development.

Optimizing the magnetization-prepared rapid gradient-echo (MP-RAGE sequence.

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Jinghua Wang

Full Text Available The three-dimension (3D magnetization-prepared rapid gradient-echo (MP-RAGE sequence is one of the most popular sequences for structural brain imaging in clinical and research settings. The sequence captures high tissue contrast and provides high spatial resolution with whole brain coverage in a short scan time. In this paper, we first computed the optimal k-space sampling by optimizing the contrast of simulated images acquired with the MP-RAGE sequence at 3.0 Tesla using computer simulations. Because the software of our scanner has only limited settings for k-space sampling, we then determined the optimal k-space sampling for settings that can be realized on our scanner. Subsequently we optimized several major imaging parameters to maximize normal brain tissue contrasts under the optimal k-space sampling. The optimal parameters are flip angle of 12°, effective inversion time within 900 to 1100 ms, and delay time of 0 ms. In vivo experiments showed that the quality of images acquired with our optimal protocol was significantly higher than that of images obtained using recommended protocols in prior publications. The optimization of k-spacing sampling and imaging parameters significantly improved the quality and detection sensitivity of brain images acquired with MP-RAGE.

High signal intensity of fat on fast spin echo imaging

International Nuclear Information System (INIS)

Ogura, Akio; Yamazaki, Masaru; Hongoh, Takaharu; Inoue, Hiroshi; Ishikuro, Akihiro

2000-01-01

The fast spin echo (FSE) technique of producing T 2 -weighted images in greatly reduced imaging times has recently been used for routine clinical study. FSE images show contrast that is very similar in most tissues to that of conventional SE images. However, fat shows a high signal intensity that is influenced by j-coupling and the magnetization transfer effect. The purpose of this study was to assess whether the higher signal intensity of fat is different among MRI systems and to examine the effects of j-coupling and magnetization transfer on the high signal intensity of fat on FSE. The contrast in signal intensity between fat and water was measured for various echo train lengths (ETL) with and without multislicing on FSE using a contrast phantom. Measurements were obtained with four different MRI systems. In addition, the effective T 2 values of fat were calculated for the above conditions. Results indicated that contrast for fat and water was reduced with increased ETL and by using multislicing and was different among the four MRI systems. The effective T 2 values of fat were extended for increased ETL and were not dependent on multislicing. They also differed among the four MRI systems. The extent of effective T 2 values was affected by j-coupling. In this study, it was indicated that the degree of the high signal intensity of fat on FSE differed for different MRI systems. In addition, the reasons for the high signal intensity of fat on FSE were related to the effects of j-coupling and magnetization transfer. (author)

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

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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.)

3D isotropic T2-weighted fast spin echo (VISTA) versus 2D T2-weighted fast spin echo in evaluation of the calcaneofibular ligament in the oblique coronal plane.

Science.gov (United States)

Park, H J; Lee, S Y; Choi, Y J; Hong, H P; Park, S J; Park, J H; Kim, E

2017-02-01

To investigate whether the image quality of three-dimensional (3D) volume isotropic fast spin echo acquisition (VISTA) magnetic resonance imaging (MRI) of the calcaneofibular ligament (CFL) view is comparable to that of 2D fast spin echo T2-weighted images (2D T2 FSE) for the evaluation of the CFL, and whether 3D VISTA can replace 2D T2 FSE for the evaluation of CFL injuries. This retrospective study included 76 patients who underwent ankle MRI with CFL views of both 2D T2 FSE MRI and 3D VISTA. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of both techniques were measured. The anatomical identification score and diagnostic performances were evaluated by two readers independently. The diagnostic performances of 3D VISTA and 2D T2 FSE were analysed by sensitivity, specificity, and accuracy for diagnosing CFL injury with reference standards of surgically or clinically confirmed diagnoses. Surgical correlation was performed in 29% of the patients, and clinical examination was used in those who did not have surgery (71%). The SNRs and CNRs of 3D VISTA were significantly higher than those of 2D T2 FSE. The anatomical identification scores on 3D VISTA were inferior to those on 2D T2 FSE, and the differences were statistically significant (pT2 FSE for the anatomical evaluation of CFL, 3D VISTA has a diagnostic performance comparable to that of 2D T2 FSE for the diagnosis of CFL injuries. Copyright © 2016 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

Characteristics of magnetic resonance imaging with partial flip angle and gradient field echo

International Nuclear Information System (INIS)

Hamada, Tatsumi; Uto, Tatsurou; Okafuji, Tatsumasa; Ookusa, Akihiko; Oonishi, Takuya; Mabuchi, Nobuhisa; Fujii, Kouichi; Yoshioka, Hiroyasu; Ishida, Osamu

1988-01-01

Characteristics of a magnetic resonance (MR) imaging pulse sequence with short repetition time (Tr), short echo time (Te), partial flip angle and gradient field echo, at 0.5 T, were studied. A series of sagittal images of the cerebrospinal region was obtained with varied Tr, Te and flip angle, signal intensities were measured by means of a region of interest (ROI) function, and optimal parameters to achieve maximum tissue contrast were found. Of the parameters flip angle had the greatest effect on tissue contrast. Flip angles less than 20 or more than 60 degrees were necessary to discriminate between spinal cord and cerebrospinal fluid. So called MR myelography was obtained with the flip angle of 15 degrees. Opposed and inphase images were obtained at the Te levels of 21 and 28 ms, respectively. Likewise, a series of transverse images of the abdomen with short Tr, short Te and varied flip angles was obtained in a breath-holding interval, and signal intensities of ROIs were measured. Maximum intensities of the liver, the spleen and perirenal fat were obtained at the flip angles of 40, 30 and 60 degrees, respectively. Although maximum intensity was found at the flip angle of 30 degrees for both of the renal cortex and medulla, the maximum contrast between the two tissues was obtained at the flip angles of 50-60 degrees. The image contrast obtained by these pulse sequences was also theoretically predictable, and so it is thought possible that flip angle, Tr and Te are manipulated to yield a desired contrast. (author)

Radar observations of density gradients, electric fields, and plasma irregularities near polar cap patches in the context of the gradient-drift instability

Science.gov (United States)

Lamarche, Leslie J.; Makarevich, Roman A.

2017-03-01

We present observations of plasma density gradients, electric fields, and small-scale plasma irregularities near a polar cap patch made by the Super Dual Auroral Radar Network radar at Rankin Inlet (RKN) and the northern face of Resolute Bay Incoherent Scatter Radar (RISR-N). RKN echo power and occurrence are analyzed in the context of gradient-drift instability (GDI) theory, with a particular focus on the previously uninvestigated 2-D dependencies on wave propagation, electric field, and gradient vectors, with the latter two quantities evaluated directly from RISR-N measurements. It is shown that higher gradient and electric field components along the wave vector generally lead to the higher observed echo occurrence, which is consistent with the expected higher GDI growth rate, but the relationship with echo power is far less straightforward. The RKN echo power increases monotonically as the predicted linear growth rate approaches zero from negative values but does not continue this trend into positive growth rate values, in contrast with GDI predictions. The observed greater consistency of echo occurrence with GDI predictions suggests that GDI operating in the linear regime can control basic plasma structuring, but measured echo strength may be affected by other processes and factors, such as multistep or nonlinear processes or a shear-driven instability.

MRI of the breast with 2D spin-echo and gradient echo sequences in diagnostically difficult cases. MRT der Mamma mit 2D-Spinecho- und Gradientenecho-Sequenzen in diagnostischen Problemfaellen

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Allgayer, B. (Technische Univ. Muenchen (Germany). Inst. fuer Roentgendiagnostik); Lukas, P. (Technische Univ. Muenchen (Germany). Inst. und Poliklinik fuer Strahlentherapie und Radiologische Onkologie); Loos, W. (Technische Univ. Muenchen (Germany). Frauenklinik und Poliklinik); Kersting-Sommerhoff, B. (Technische Univ. Muenchen (Germany). Inst. fuer Roentgendiagnostik)

1993-05-01

One or both breasts of 296 patients with equivocal clinical or mammographical findings were examined with MRI. T[sub 1] weighted spinecho (SE) and gradient echo (FFE) sequences were acquired before and after i.v. application of Gadolinium DTPA. 50 lesions with enhancement after Gd-DTPA were biopsied - 26 carcinomas, 17 proliferating mastopathic tissues, 5 fibroadenomas and 1 abscess were found. Contrast enhanced MRI with 2D-SE and FFE sequences is an effective technqiue for evaluating suspicious breast lesions with high diagnostic acurracy. (orig.)

Spatial resolution properties in 3D fast spin-echo using variable refocusing flip angles

International Nuclear Information System (INIS)

Ozaki, Masanori; Mizukami, Shinya; Hata, Hirofumi; Sato, Mayumi; Komi, Syotaro; Miyati, Tosiaki; Nozaki, Atsushi

2011-01-01

A new 3-dimensional fast spin-echo (3D FSE) method that uses a variable refocusing flip angle technique has recently been applied to imaging. The imaging pulse sequence can inhibit T 2 decay by varying the refocusing flip angle. Use of a long echo train length allows acquisition of 3D T 2 -weighted images with less blurring in a short scan time. The smaller refocusing flip angle in the new 3D FSE method than in the conventional method can reduce the specific absorption rate. However, T 2 decay differs between the new and conventional 3D FSE methods, so the resolution properties of the 2 methods may differ. We investigated the resolution properties of the new 3D FSE method using a variable refocusing flip angle technique. Varying the refocusing flip angle resulted in different resolution properties for the new 3D FSE method compared to the conventional method, a difference particularly noticeable when the imaging parameters were set for obtaining proton density weighted images. (author)

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

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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.

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

Parameter Optimization for Quantitative Signal-Concentration Mapping Using Spoiled Gradient Echo MRI

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Gasser Hathout

2012-01-01

Full Text Available Rationale and Objectives. Accurate signal to tracer concentration maps are critical to quantitative MRI. The purpose of this study was to evaluate and optimize spoiled gradient echo (SPGR MR sequences for the use of gadolinium (Gd-DTPA as a kinetic tracer. Methods. Water-gadolinium phantoms were constructed for a physiologic range of gadolinium concentrations. Observed and calculated SPGR signal to concentration curves were generated. Using a percentage error determination, optimal pulse parameters for signal to concentration mapping were obtained. Results. The accuracy of the SPGR equation is a function of the chosen MR pulse parameters, particularly the time to repetition (TR and the flip angle (FA. At all experimental values of TR, increasing FA decreases the ratio between observed and calculated signals. Conversely, for a constant FA, increasing TR increases this ratio. Using optimized pulse parameter sets, it is possible to achieve excellent accuracy (approximately 5% over a physiologic range of concentration tracer concentrations. Conclusion. Optimal pulse parameter sets exist and their use is essential for deriving accurate signal to concentration curves in quantitative MRI.

Comparison of spin-echo and gradient recalled echo T1 weighted MR images for quantitative voxel-based clinical brain research

International Nuclear Information System (INIS)

Barnden, L.R.; Crouch, B.

2010-01-01

Full text: New methods to normalise inter-subject global variations in T 1 -weighted MR (T I w) signal levels have permitted their use in voxel based population studies of brain dysfunction. Here we address the question of whether a spin-echo (SE) or a gradient recalled echo (GRE) T I w sequence is better for this purpose. GRE images are commonly referred to as 3D MRL SE has superior signal/noise properties to GRE but is slower to acquire so that typical slice thicknesses are 3-5 mm compared to 1-2 mm for GRE. GRE has better grey/white matter contrast which should permit better spatial normalization. However, unlike SE, GRE is affected by subject-specific magnetic field inhomogeneities that distort the images. We acquired T I brain images for 25 chronic fatigue syndrome (CFS) patients and 25 normal controls (NC) with TRITE/flip-angle of 600 ms/l5 ms/90 deg for SE and 5.76 ms/1.9 ms/9 deg for GRE. For GRE, the magnetic field inhomogeneity related signal level distortions could be corrected, but not the spatial distortions. After spatial normalization we subjected them to voxel-based statistical analysis with adjustment for global signal level using the SPM5 package. Initially, the same spatial normalization deformations were applied to both SE and GRE after coregistering them. Although the SPM regressions of SE and GRE yielded similar spatial distributions of significance, the SE regressions were consistently statistically stronger. For example, in one strong regression, the corrected cluster P value was twenty times stronger (I.Oe-5 versus I.Oe-3). T I w SE have proved better than T I GRE images in quantitative analysis in a clinical research study. (author)

Evaluation of grades 3 and 4 chondromalacia of the knee using T2*-weighted 3D gradient-echo articular cartilage imaging.

Science.gov (United States)

Murphy, B J

2001-06-01

To determine the accuracy of T2*-weighted three-dimensional (3D) gradient-echo articular cartilage imaging in the identification of grades 3 and 4 chondromalacia of the knee. A retrospective evaluation of 80 patients who underwent both arthroscopic and MRI evaluation was performed. The 3D images were interpreted by one observer without knowledge of the surgical results. The medial and lateral femoral condyles, the medial and lateral tibial plateau, the patellar cartilage and trochlear groove were evaluated. MR cartilage images were considered positive if focal reduction of cartilage thickness was present (grade 3 chondromalacia) or if complete loss of cartilage was present (grade 4 chondromalacia). Comparison of the 3D MR results with the arthroscopic findings was performed. Eighty patients were included in the study group. A total of 480 articular cartilage sites were evaluated with MRI and arthroscopy. Results of MR identification of grades 3 and 4 chondromalacia, all sites combined, were: sensitivity 83%, specificity 97%, false negative rate 17%, false positive rate 3%, positive predictive value 87%, negative predictive value 95%, overall accuracy 93%. The results demonstrate that T2*-weighted 3D gradient-echo articular cartilage imaging can identify grades 3 and 4 chondromalacia of the knee.

Evaluation of grades 3 and 4 chondromalacia of the knee using T2*-weighted 3D gradient-echo articular cartilage imaging

International Nuclear Information System (INIS)

Murphy, B.J.

2001-01-01

Objective. To determine the accuracy of T2*-weighted three-dimensional (3D) gradient-echo articular cartilage imaging in the identification of grades 3 and 4 chondromalacia of the knee.Design and patients. A retrospective evaluation of 80 patients who underwent both arthroscopic and MRI evaluation was performed. The 3D images were interpreted by one observer without knowledge of the surgical results. The medial and lateral femoral condyles, the medial and lateral tibial plateau, the patellar cartilage and trochlear groove were evaluated. MR cartilage images were considered positive if focal reduction of cartilage thickness was present (grade 3 chondromalacia) or if complete loss of cartilage was present (grade 4 chondromalacia). Comparison of the 3D MR results with the arthroscopic findings was performed.Results. Eighty patients were included in the study group. A total of 480 articular cartilage sites were evaluated with MRI and arthroscopy. Results of MR identification of grades 3 and 4 chondromalacia, all sites combined, were: sensitivity 83%, specificity 97%, false negative rate 17%, false positive rate 3%, positive predictive value 87%, negative predictive value 95%, overall accuracy 93%.Conclusion. The results demonstrate that T2*-weighted 3D gradient-echo articular cartilage imaging can identify grades 3 and 4 chondromalacia of the knee. (orig.)

Evaluation of grades 3 and 4 chondromalacia of the knee using T2*-weighted 3D gradient-echo articular cartilage imaging

Energy Technology Data Exchange (ETDEWEB)

Murphy, B.J. [Dept. of Radiology, Univ. of Miami School of Medicine, FL (United States)

2001-06-01

Objective. To determine the accuracy of T2*-weighted three-dimensional (3D) gradient-echo articular cartilage imaging in the identification of grades 3 and 4 chondromalacia of the knee.Design and patients. A retrospective evaluation of 80 patients who underwent both arthroscopic and MRI evaluation was performed. The 3D images were interpreted by one observer without knowledge of the surgical results. The medial and lateral femoral condyles, the medial and lateral tibial plateau, the patellar cartilage and trochlear groove were evaluated. MR cartilage images were considered positive if focal reduction of cartilage thickness was present (grade 3 chondromalacia) or if complete loss of cartilage was present (grade 4 chondromalacia). Comparison of the 3D MR results with the arthroscopic findings was performed.Results. Eighty patients were included in the study group. A total of 480 articular cartilage sites were evaluated with MRI and arthroscopy. Results of MR identification of grades 3 and 4 chondromalacia, all sites combined, were: sensitivity 83%, specificity 97%, false negative rate 17%, false positive rate 3%, positive predictive value 87%, negative predictive value 95%, overall accuracy 93%.Conclusion. The results demonstrate that T2*-weighted 3D gradient-echo articular cartilage imaging can identify grades 3 and 4 chondromalacia of the knee. (orig.)

The role of T2*-weighted gradient echo in the diagnosis of tumefactive intrahepatic extramedullary hematopoiesis in myelodysplastic syndrome and diffuse hepatic iron overload: a case report and review of the literature.

Science.gov (United States)

Belay, Abel A; Bellizzi, Andrew M; Stolpen, Alan H

2018-01-15

Extramedullary hematopoiesis is the proliferation of hematopoietic cells outside bone marrow secondary to marrow hematopoiesis failure. Extramedullary hematopoiesis rarely presents as a mass-forming hepatic lesion; in this case, imaging-based differentiation from primary and metastatic hepatic neoplasms is difficult, often leading to biopsy for definitive diagnosis. We report a case of tumefactive hepatic extramedullary hematopoiesis in the setting of myelodysplastic syndrome with concurrent hepatic iron overload, and the role of T2*-weighted gradient-echo magnetic resonance imaging in differentiating extramedullary hematopoiesis from primary and metastatic hepatic lesions. To the best of our knowledge, T2*-weighted gradient-echo evaluation of extramedullary hematopoiesis in the setting of diffuse hepatic hemochromatosis has not been previously described. A 52-year-old white man with myelodysplastic syndrome and marrow fibrosis was found to have a 4 cm hepatic lesion on ultrasound during workup for bone marrow transplantation. Magnetic resonance imaging revealed diffuse hepatic iron overload and non-visualization of the lesion on T2* gradient-echo sequence suggesting the presence of iron deposition within the lesion similar to that in background hepatic parenchyma. Subsequent ultrasound-guided biopsy of the lesion revealed extramedullary hematopoiesis. Six months later, while still being evaluated for bone marrow transplant, our patient was found to have poor pulmonary function tests. Follow-up computed tomography angiogram showed a mass within his right main pulmonary artery. Bronchoscopic biopsy of this mass once again revealed extramedullary hematopoiesis. He received radiation therapy to his chest. However, 2 weeks later, he developed mediastinal hematoma and died shortly afterward, secondary to respiratory arrest. Mass-forming extramedullary hematopoiesis is rare; however, our report emphasizes that it needs to be considered in the initial differential

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.)

Spin echo SPI methods for quantitative analysis of fluids in porous media.

Science.gov (United States)

Li, Linqing; Han, Hui; Balcom, Bruce J

2009-06-01

Fluid density imaging is highly desirable in a wide variety of porous media measurements. The SPRITE class of MRI methods has proven to be robust and general in their ability to generate density images in porous media, however the short encoding times required, with correspondingly high magnetic field gradient strengths and filter widths, and low flip angle RF pulses, yield sub-optimal S/N images, especially at low static field strength. This paper explores two implementations of pure phase encode spin echo 1D imaging, with application to a proposed new petroleum reservoir core analysis measurement. In the first implementation of the pulse sequence, we modify the spin echo single point imaging (SE-SPI) technique to acquire the k-space origin data point, with a near zero evolution time, from the free induction decay (FID) following a 90 degrees excitation pulse. Subsequent k-space data points are acquired by separately phase encoding individual echoes in a multi-echo acquisition. T(2) attenuation of the echo train yields an image convolution which causes blurring. The T(2) blur effect is moderate for porous media with T(2) lifetime distributions longer than 5 ms. As a robust, high S/N, and fast 1D imaging method, this method will be highly complementary to SPRITE techniques for the quantitative analysis of fluid content in porous media. In the second implementation of the SE-SPI pulse sequence, modification of the basic measurement permits fast determination of spatially resolved T(2) distributions in porous media through separately phase encoding each echo in a multi-echo CPMG pulse train. An individual T(2) weighted image may be acquired from each echo. The echo time (TE) of each T(2) weighted image may be reduced to 500 micros or less. These profiles can be fit to extract a T(2) distribution from each pixel employing a variety of standard inverse Laplace transform methods. Fluid content 1D images are produced as an essential by product of determining the

Utility of echo-planar gradient-echo T2*-weighted MR images in patients with primary intracerebral hemorrhage

International Nuclear Information System (INIS)

Yokoe, Toshio; Yoshida, Tazuka; Kobayashi, Nozomu; Nakamura, Yukihiro; Kubota, Kazuyuki

2005-01-01

Magnetic resonance imaging (MRI) has the potential to reveal residues of intracerabral hemorrhage (ICH) throughout life because of the high sensitivity for iron-containing compounds. Gradient-echo T2 * -weighted MR imaging (T2 * MRI) requiring short times for complete acquisition is known to detect small areas of signal loss without surrounding edema representing microbleeds (MBs). MBs in the basal ganglia including the thalami are suggested to be closely related to intracerebral atherosclerotic microangiopathy. We looked for more than 3 MBs in basal ganglia or thalamus of patients with and without episodes of previous ICH. Twelve patients with previous hemorrhagic stroke and 82 without were studied. Multiple MBs in those regions were significantly more frequent in patients with recurrent ICH. In addition, a 76-year-old woman with a history of hypertension was transferred to our hospital for treatment of head injury. She had multiple incidental old basal ganglionic and thalamic MBs. The patient had an asymptomatic primary ICH on computed tomography (CT) 3 months later. In conclusion, MR evidence of multiple MBs in the basal ganglia and thalamus might identify patients at a risk for new and recurrent ICH. Therefore, patients with multiple MBs in those regions should be treated for cerebrovascular risk factors, especially hypertension. Our results appear to confirm the utility of T2 * MRI in hemorrhagic stroke. (author)

Numerical calculation of spin echo amplitude in pulsed NMR: effects of quadrupole interaction

International Nuclear Information System (INIS)

Sobral, R.R.

1986-01-01

The spin echo obtained by nuclear magnetic resonance, in systems which atomic nuclei interact with magnetic fields and electric field gradients, present oscillations in function of the time interval between two excitations pulses. Using the density matrix formalism, the amplitudes of these echo is calculated, analytically. In this work, echo amplitudes obtained under different excitation conditions for nuclei of different nuclear spin values are calculated. The numerical results are compared with disposable analytical solutions. Applications of this method to the case of electric field gradient without axial symmetry were studied. Within the used approximation limits, an expression for attnuation of oscillatory behaviour of echo amplitude in function of the time interval between experimentally observed pulses was obtained. (M.C.K.) [pt

High-spatial-resolution isotropic three-dimensional fast-recovery fast spin-echo magnetic resonance dacryocystography combined with topical administration of sterile saline solution

International Nuclear Information System (INIS)

Jing, Zhang; Lang, Chen; Qiu-Xia, Wang; Rong, Liu; Xin, Luo; Wen-Zhen, Zhu; Li-Ming, Xia; Jian-Pin, Qi; He, Wang

2013-01-01

Objective: This study aims to investigate the clinical performance of three-dimensional (3D) fast-recovery fast spin-echo (FRFSE) magnetic resonance dacryocystography (MRD) with topical administration of sterile saline solution for the assessment of the lacrimal drainage system (LDS). Methods: A total of 13 healthy volunteers underwent both 3D-FRFSE MRD and two-dimensional (2D)-impulse recovery (IR)-single-shot fast spin-echo (SSFSE) MRD after topical administration of sterile saline solution, and 31 patients affected by primary LDS outflow impairment or postsurgical recurrent epiphora underwent 3D-FRFSE MRD and conventional T1- and T2-weighted sequences. All patients underwent lacrimal endoscopy or surgery, which served as a standard of reference for confirming the MRD findings. Results: 3D-FRFSE MRD detected more visualized superior and inferior canaliculi and nasolacrimal duct than 2D-IR-SSFSE MRD. Compared with 2D-IR-SSFSE MRD, 3D-FRFSE MRD showed more visualized segments per LDS, although the difference was not statistically significant. Significant improvements in the inferior canaliculus and nasolacrimal duct visibility grades were achieved using 3D-FRFSE MRD. 3D-FRFSE MRD had 100% sensitivity and 63.6% specificity for detecting LDS obstruction. In 51 out of the 62 LDSs that were assessed, a 90% agreement was noted between the findings of 3D-FRFSE MRD and lacrimal endoscopy in detecting the obstruction level. Conclusion: 3D-FRFSE MRD combined with topical administration of sterile saline solution is a simple and noninvasive method of obtaining detailed morphological and functional information on the LDS. Overall, 3D-FRFSE MRD could be used as a reliable diagnostic method in many patients with epiphora prior to surgery

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

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...... 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......-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 we here used in a simple model for the microstructure – and that, for axons parallel to the main magnetic field...

A fast, preconditioned conjugate gradient Toeplitz solver

Science.gov (United States)

Pan, Victor; Schrieber, Robert

1989-01-01

A simple factorization is given of an arbitrary hermitian, positive definite matrix in which the factors are well-conditioned, hermitian, and positive definite. In fact, given knowledge of the extreme eigenvalues of the original matrix A, an optimal improvement can be achieved, making the condition numbers of each of the two factors equal to the square root of the condition number of A. This technique is to applied to the solution of hermitian, positive definite Toeplitz systems. Large linear systems with hermitian, positive definite Toeplitz matrices arise in some signal processing applications. A stable fast algorithm is given for solving these systems that is based on the preconditioned conjugate gradient method. The algorithm exploits Toeplitz structure to reduce the cost of an iteration to O(n log n) by applying the fast Fourier Transform to compute matrix-vector products. Matrix factorization is used as a preconditioner.

Magnetic resonance, especially spin echo, in spinor Bose-Einstein condensates

International Nuclear Information System (INIS)

Yasunaga, Masashi; Tsubota, Makoto

2009-01-01

Magnetic resonance, especially NMR and ESR, has been studied in magnetic materials for a long time, having been used in various fields. Spin echo is typical phenomenon in magnetic resonance. The magnetic resonance should be applied to spinor Bose-Einstein condensates (BECs). We numerically study spin echo of a spinor BEC in a gradient magnetic field by calculating the spin-1 two-dimensional Gross-Pitaevskii equations, obtaining the recovery of the signal of the spins, which is called spin echo. We will discuss the relation between the spin echo and the Stern-Gelrach separation in the system.

Gradient field echo imaging and Gd-DTPA for the assessment of renal function in humans

International Nuclear Information System (INIS)

Von Schulthess, G.K.; Kikinis, R.; Durr, R.; Bino, M.; Jager, P.; Kubler, O.

1986-01-01

To evaluate renal parenchymal function, 1.5 T gradient field echo imaging using a sequence of repetitive 10-second scans was performed in apneic patients after injection of Gd-DTPA (0.1 mmol/kg body weight). During the 10-second pauses the patients were allowed to breathe. Angled coronal images (TR=40 msec, TE =20 msec, flip angle = 40 0 ) were obtained in four volunteers and four patients with hydronephrosis. Image quality was excellent, suggesting unprecedented spatial resolution for renal function studies. Initially, cortical perfusion was observed. Then the papilae became isointense; after 70 seconds they became hypointense; and finally the renal pelvic signal dropped. No papillary signal drop was seen in hydronephrosis, as confirmed by region-of-interest analysis. These results strongly suggest that in MR renal ''function'' studies with Gd-DTPA, T1 and T2 paramagnetic effects are operative

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.

Evaluation of renal function with dynamic MRI-T2-weighted gradient echo technique

International Nuclear Information System (INIS)

Kato, Katsuya

1995-01-01

To evaluate the usefulness of dynamic MRI of kidneys in healthy volunteers and patients with different 24-hour creatinine clearance (Ccr) levels, a dynamic study that employed the T2 weighted gradient echo technique (FLASH: TR/TE=34/25 msec, flip angle= 20 degrees) with single images during breathhold was performed on 10 healthy volunteers and 35 patients, all examined for the Ccr and suspected of having renal parenchymal disease after a phantom study. T1-weighted and dynamic MR imagings were obtained with a 1.5T imager. I analyzed the time-intensity curve of renal cortex and medulla, and defined a cortex decreased ratio (CDR) and medulla decreased ratio (MDR) in comparison with the Ccr. The cortico-medullary difference ratio (CMDR) of T1WI was also compared with the Ccr. The parameters of the T2 dynamic MRI study (CDR, MDR) better correlated with the Ccr than CMDR. Renal function can be quantitatively evaluated with the T2 dynamic MRI and there is a possibility that we can qualitatively evaluate the renal dysfunction and estimate its cause. (author)

MR Imaging of the Internal Auditory Canal and Inner Ear at 3T: Comparison between 3D Driven Equilibrium and 3D Balanced Fast Field Echo Sequences

Energy Technology Data Exchange (ETDEWEB)

Byun, Jun Soo; Kim, Hyung Jin; Yim, Yoo Jeong; Kim, Sung Tae; Jeon, Pyoung; Kim, Keon Ha [Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul (Korea, Republic of); Kim, Sam Soo; Jeon, Yong Hwan; Lee, Ji Won [Kangwon National University College of Medicine, Chuncheon (Korea, Republic of)

2008-06-15

To compare the use of 3D driven equilibrium (DRIVE) imaging with 3D balanced fast field echo (bFFE) imaging in the assessment of the anatomic structures of the internal auditory canal (IAC) and inner ear at 3 Tesla (T). Thirty ears of 15 subjects (7 men and 8 women; age range, 22 71 years; average age, 50 years) without evidence of ear problems were examined on a whole-body 3T MR scanner with both 3D DRIVE and 3D bFFE sequences by using an 8-channel sensitivity encoding (SENSE) head coil. Two neuroradiologists reviewed both MR images with particular attention to the visibility of the anatomic structures, including four branches of the cranial nerves within the IAC, anatomic structures of the cochlea, vestibule, and three semicircular canals. Although both techniques provided images of relatively good quality, the 3D DRIVE sequence was somewhat superior to the 3D bFFE sequence. The discrepancies were more prominent for the basal turn of the cochlea, vestibule, and all semicircular canals, and were thought to be attributed to the presence of greater magnetic susceptibility artifacts inherent to gradient-echo techniques such as bFFE. Because of higher image quality and less susceptibility artifacts, we highly recommend the employment of 3D DRIVE imaging as the MR imaging choice for the IAC and inner ear

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

International Nuclear Information System (INIS)

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 ( 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. (orig.) [de

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.

High-resolution T2-weighted MR imaging of the inner ear using a long echo-train-length 3D fast spin-echo sequence

International Nuclear Information System (INIS)

Naganawa, S.; Yamakawa, K.; Fukatsu, H.; Ishigaki, T.; Nakashima, T.; Sugimoto, H.; Aoki, I.; Miyazaki, M.; Takai, H.

1996-01-01

The purpose of this study was to assess the value of a long echo-train-length 3D fast spin-echo (3D-FSE) sequence in visualizing the inner ear structures. Ten normal ears and 50 patient ears were imaged on a 1.5T MR unit using a head coil. Axial high-resolution T2-weighted images of the inner ear and the internal auditory canal (IAC) were obtained in 15 min. In normal ears the reliability of the visualization for the inner ear structures was evaluated on original images and the targeted maximum intensity projection (MIP) images of the labyrinth. In ten normal ears, 3D surface display (3D) images were also created and compared with MIP images. On the original images the cochlear aqueduct, the vessels in the vicinity of the IAC, and more than three branches of the cranial nerves were visualized in the IAC in all the ears. The visibility of the endolympathic duct was 80%. On the MIP images the visibility of the three semicircular canals, anterior and posterior ampulla, and of more than two turns of the cochlea was 100%. The MIP images and 3D images were almost comparable. The visibility of the endolymphatic duct was 80% in normal ears and 0% in the affected ears of the patients with Meniere's disease (p<0.001). In one patient ear a small intracanalicular tumor was depicted clearly. In conclusion, the long echo train length T2-weighted 3D-FSE sequence enables the detailed visualization of the tiny structures of the inner ear and the IAC within a clinically acceptable scan time. Furthermore, obtaining a high contrast between the soft/bony tissue and the cerebrospinal/endolymph/perilymph fluid would be of significant value in the diagnosis of the pathologic conditions around the labyrinth and the IAC. (orig.)

Value of MR cisternography using three-dimensional half-fourier single-shot fast spin-echo sequences in the diagnosis of diseases related to cranial nerves VII and VIII

Energy Technology Data Exchange (ETDEWEB)

Yamakami, Norio [Kyorin Univ., Mitaka, Tokyo (Japan). School of Medicine

1999-05-01

The purpose of this study was to evaluate the value of MR cisternography using three-dimensional half-Fourier single-shot fast spin-echo sequences in the diagnosis of diseasea related to cranial nerves VII and VIII. With a 0.5-T imager, the most appropriate setting of echo time and section thickness was first assessed in five volunteers. This resulted in echo time of 250 msec and section thickness of 2 mm as the most effective parameters. Second, using echo time of 120 msec and section thickness of 1.5 mm that were available from the beginning of this study, the demonstration of four nerves within the audistory canal was assessed in seven volunteers. In all of the volunteers, the facial, cochlear, and vestibular nerves were determined with demonstration of each of superior and inferior vestibular nerves in four of them. Next, MR cisternography using the same echo time and section thickness was applied in 368 patients with suspicion of acoustic neurinoma and 14 with hemifacial spasm. In 28 of the 368 patients, MR cisternograms depicted an acoustic neurinoma that was confirmed on postcontrast T1-weighted images. Meanwhile, in five of the 14 patients with hemifacial spasm, MR cisternograms revealed a vessel compressing the root exit zone of the affected facial nerve. It is concluded that MR cisternography using three-dimensional half-Fourier single-shot fast spin-echo sequences can be a useful means for demonstrating nerves within the auditory nerve as well as for the screening of acoustic neurionoma. (author)

Value of MR cisternography using three-dimensional half-fourier single-shot fast spin-echo sequences in the diagnosis of diseases related to cranial nerves VII and VIII

International Nuclear Information System (INIS)

Yamakami, Norio

1999-01-01

The purpose of this study was to evaluate the value of MR cisternography using three-dimensional half-Fourier single-shot fast spin-echo sequences in the diagnosis of diseasea related to cranial nerves VII and VIII. With a 0.5-T imager, the most appropriate setting of echo time and section thickness was first assessed in five volunteers. This resulted in echo time of 250 msec and section thickness of 2 mm as the most effective parameters. Second, using echo time of 120 msec and section thickness of 1.5 mm that were available from the beginning of this study, the demonstration of four nerves within the audistory canal was assessed in seven volunteers. In all of the volunteers, the facial, cochlear, and vestibular nerves were determined with demonstration of each of superior and inferior vestibular nerves in four of them. Next, MR cisternography using the same echo time and section thickness was applied in 368 patients with suspicion of acoustic neurinoma and 14 with hemifacial spasm. In 28 of the 368 patients, MR cisternograms depicted an acoustic neurinoma that was confirmed on postcontrast T1-weighted images. Meanwhile, in five of the 14 patients with hemifacial spasm, MR cisternograms revealed a vessel compressing the root exit zone of the affected facial nerve. It is concluded that MR cisternography using three-dimensional half-Fourier single-shot fast spin-echo sequences can be a useful means for demonstrating nerves within the auditory nerve as well as for the screening of acoustic neurionoma. (author)

FAST (Four chamber view And Swing Technique) Echo: a Novel and Simple Algorithm to Visualize Standard Fetal Echocardiographic Planes

Science.gov (United States)

Yeo, Lami; Romero, Roberto; Jodicke, Cristiano; Oggè, Giovanna; Lee, Wesley; Kusanovic, Juan Pedro; Vaisbuch, Edi; Hassan, Sonia S.

2010-01-01

Objective To describe a novel and simple algorithm (FAST Echo: Four chamber view And Swing Technique) to visualize standard diagnostic planes of fetal echocardiography from dataset volumes obtained with spatiotemporal image correlation (STIC) and applying a new display technology (OmniView). Methods We developed an algorithm to image standard fetal echocardiographic planes by drawing four dissecting lines through the longitudinal view of the ductal arch contained in a STIC volume dataset. Three of the lines are locked to provide simultaneous visualization of targeted planes, and the fourth line (unlocked) “swings” through the ductal arch image (“swing technique”), providing an infinite number of cardiac planes in sequence. Each line generated the following plane(s): 1) Line 1: three-vessels and trachea view; 2) Line 2: five-chamber view and long axis view of the aorta (obtained by rotation of the five-chamber view on the y-axis); 3) Line 3: four-chamber view; and 4) “Swing” line: three-vessels and trachea view, five-chamber view and/or long axis view of the aorta, four-chamber view, and stomach. The algorithm was then tested in 50 normal hearts (15.3 – 40 weeks of gestation) and visualization rates for cardiac diagnostic planes were calculated. To determine if the algorithm could identify planes that departed from the normal images, we tested the algorithm in 5 cases with proven congenital heart defects. Results In normal cases, the FAST Echo algorithm (3 locked lines and rotation of the five-chamber view on the y-axis) was able to generate the intended planes (longitudinal view of the ductal arch, pulmonary artery, three-vessels and trachea view, five-chamber view, long axis view of the aorta, four-chamber view): 1) individually in 100% of cases [except for the three-vessel and trachea view, which was seen in 98% (49/50)]; and 2) simultaneously in 98% (49/50). The “swing technique” was able to generate the three-vessels and trachea view, five

Four-chamber view and 'swing technique' (FAST) echo: a novel and simple algorithm to visualize standard fetal echocardiographic planes.

Science.gov (United States)

Yeo, L; Romero, R; Jodicke, C; Oggè, G; Lee, W; Kusanovic, J P; Vaisbuch, E; Hassan, S

2011-04-01

To describe a novel and simple algorithm (four-chamber view and 'swing technique' (FAST) echo) for visualization of standard diagnostic planes of fetal echocardiography from dataset volumes obtained with spatiotemporal image correlation (STIC) and applying a new display technology (OmniView). We developed an algorithm to image standard fetal echocardiographic planes by drawing four dissecting lines through the longitudinal view of the ductal arch contained in a STIC volume dataset. Three of the lines are locked to provide simultaneous visualization of targeted planes, and the fourth line (unlocked) 'swings' through the ductal arch image (swing technique), providing an infinite number of cardiac planes in sequence. Each line generates the following plane(s): (a) Line 1: three-vessels and trachea view; (b) Line 2: five-chamber view and long-axis view of the aorta (obtained by rotation of the five-chamber view on the y-axis); (c) Line 3: four-chamber view; and (d) 'swing line': three-vessels and trachea view, five-chamber view and/or long-axis view of the aorta, four-chamber view and stomach. The algorithm was then tested in 50 normal hearts in fetuses at 15.3-40 weeks' gestation and visualization rates for cardiac diagnostic planes were calculated. To determine whether the algorithm could identify planes that departed from the normal images, we tested the algorithm in five cases with proven congenital heart defects. In normal cases, the FAST echo algorithm (three locked lines and rotation of the five-chamber view on the y-axis) was able to generate the intended planes (longitudinal view of the ductal arch, pulmonary artery, three-vessels and trachea view, five-chamber view, long-axis view of the aorta, four-chamber view) individually in 100% of cases (except for the three-vessels and trachea view, which was seen in 98% (49/50)) and simultaneously in 98% (49/50). The swing technique was able to generate the three-vessels and trachea view, five-chamber view and/or long

Magnetic resonance imaging of the sacroiliac joints in patients with suspected spondyloarthritis. Comparison of turbo spin-echo and gradient-echo sequences for the detection of structural alterations

International Nuclear Information System (INIS)

Dornia, C.; Hoffstetter, P.; Asklepios Klinikum, Bad Abbach; Fleck, M.; Asklepios Klinikum, Bad Abbach; Hartung, W.; Niessen, C.; Stroszczynski, C.

2015-01-01

Magnetic resonance imaging (MRI) is the method of choice for the evaluation of spondyloarthritis (SpA). According to the guidelines of the Assessment of Spondyloarthritis International Society (ASAS) and Outcome Measures in Rheumatology (OMERACT), MRI findings in SpA of the spine and the sacroiliac joints (SIJ) are classified as inflammatory and structural alterations. Modern gradient-echo sequences (GRE) are recommended for optimized detection of structural alterations of the SIJ. We assess the benefit of GRE in the detection of structural alterations of the SIJ in comparison to conventional turbo spin-echo sequences (TSE). Retrospective study of 114 patients who received MRI of the SIJ for the evaluation of SpA. Structural alterations of the SIJ were assessed by two blinded readers separately for T1 TSE and T2 * GRE. The findings were classified according to a previously published chronicity score separately for both sides and sequences. Interobserver reliability was calculated with Cohen's Kappa, and the significance of findings was assessed with the Wilcoxon test. P-values * GRE showed a high interobserver reliability in the detection of structural alterations in patients with SpA. However, T2 * GRE detected significantly more structural alterations than T1 TSE and should be an integral part of a modern MRI protocol for the diagnostic workup of patients with suspected SpA.

Echo-Interleaved-Spiral MR Imaging

International Nuclear Information System (INIS)

Rosenthal, Shirrie; Azhari, Haim; Montag, Avram

1998-01-01

Interleaved-Spiral imaging is an efficient method for MRI fast scans. However, images suffer from blurring and artifacts due to field inhomogeneities and the long readout times. In this paper, we combine interleaved-spirals with spin-echo for 3D scans. The refocusing RF-pulses (echoes) refocus off-resonance spins, thus allowing longer acquisition times per excitation, by limiting inhomogeneity effects. The total number of excitations for a 3D scan is reduced by half. The 3D Fourier transform of an object is divided into pairs of slices, one slice is scanned in an outgoing interleaved-spiral, initiated after a 90 degree pulse has been applied. The second slice is scanned in an ingoing interleaved-spiral, after a 180 degree pulse has been applied, thus reaching the slice origin at the echo time. (authors)

Laser pulse propagation and enhanced energy coupling to fast electrons in dense plasma gradients

International Nuclear Information System (INIS)

Gray, R J; Carroll, D C; Yuan, X H; Brenner, C M; Coury, M; Quinn, M N; Tresca, O; McKenna, P; Burza, M; Wahlström, C-G; Lancaster, K L; Neely, D; Lin, X X; Li, Y T

2014-01-01

Laser energy absorption to fast electrons during the interaction of an ultra-intense (10 20 W cm −2 ), picosecond laser pulse with a solid is investigated, experimentally and numerically, as a function of the plasma density scale length at the irradiated surface. It is shown that there is an optimum density gradient for efficient energy coupling to electrons and that this arises due to strong self-focusing and channeling driving energy absorption over an extended length in the preformed plasma. At longer density gradients the laser filaments, resulting in significantly lower overall energy coupling. As the scale length is further increased, a transition to a second laser energy absorption process is observed experimentally via multiple diagnostics. The results demonstrate that it is possible to significantly enhance laser energy absorption and coupling to fast electrons by dynamically controlling the plasma density gradient. (paper)

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

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

International Nuclear Information System (INIS)

Dupuy, Sheena L.; Tauhid, Shahamat; Kim, Gloria; Chu, Renxin; Tummala, Subhash; Hurwitz, Shelley; Bakshi, Rohit

2015-01-01

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

MR cisternography with three-dimensional fast advanced spin-echo (FASE)

International Nuclear Information System (INIS)

Ohgi, Kazuyuki; Yamamoto, Hidefumi; Yokote, Hiroyuki

2000-01-01

To evaluate the usefulness of MR cisternography (MRC) combined with various postprocessing techniques and three-dimensional (3D) time-of-flight (TOF) MR angiography, MR cisternograms in 212 patients with various cranial nerve symptoms were retrospectively evaluated. MR examinations were performed with a 1.5 T MR imager using a 3D fast advanced spin-echo (FASE) sequence. Maximum intensity projection (MIP) had the advantage of demonstrating fluid-filled structures such as cerebrospinal fluid (CSF)-internal auditory canal (IAC) and Meckel's cave. Minimum intensity projection (Min IP) was especially useful in delineating neurovascular structures (NVS) in wide CSF space. Addition provided the most well-balanced images of NVS, and was superior to Min IP in the depiction of NVS in narrow CSF space. Virtual endoscopy and volume rendering had the potential to provide additional information in the evaluation of the three-dimensional relationships of NVS. Combination of 3D TOF MRA with MRC was helpful in differentiating arteries, veins, and nerves. With the judicious use of various postprocessing techniques and combined MRA, the value of MRC in the evaluation of patients with various cranial nerve symptoms can be further strengthened. (author)

MR cisternography with three-dimensional fast advanced spin-echo (FASE)

Energy Technology Data Exchange (ETDEWEB)

Ohgi, Kazuyuki; Yamamoto, Hidefumi; Yokote, Hiroyuki [Japanese Red-Cross Medical Center, Tokyo (Japan)] [and others

2000-06-01

To evaluate the usefulness of MR cisternography (MRC) combined with various postprocessing techniques and three-dimensional (3D) time-of-flight (TOF) MR angiography, MR cisternograms in 212 patients with various cranial nerve symptoms were retrospectively evaluated. MR examinations were performed with a 1.5 T MR imager using a 3D fast advanced spin-echo (FASE) sequence. Maximum intensity projection (MIP) had the advantage of demonstrating fluid-filled structures such as cerebrospinal fluid (CSF)-internal auditory canal (IAC) and Meckel's cave. Minimum intensity projection (Min IP) was especially useful in delineating neurovascular structures (NVS) in wide CSF space. Addition provided the most well-balanced images of NVS, and was superior to Min IP in the depiction of NVS in narrow CSF space. Virtual endoscopy and volume rendering had the potential to provide additional information in the evaluation of the three-dimensional relationships of NVS. Combination of 3D TOF MRA with MRC was helpful in differentiating arteries, veins, and nerves. With the judicious use of various postprocessing techniques and combined MRA, the value of MRC in the evaluation of patients with various cranial nerve symptoms can be further strengthened. (author)

Diagnositc value of 3D-gradient echo dynamic contrast enhanced MRI in breast cancer

Energy Technology Data Exchange (ETDEWEB)

Yang, Ik; Chung, Soo Young; Park, Hai Jung; Lee, Yul; Chung, Bong Wha; Shim, Jeong Won [Hallym Univ. College of Medicine, Seoul (Korea, Republic of)

1997-10-01

To assess the usefulness of 3D-gradient echo dynamic contrast enhanced MRI (3D-DMRI) in the diagnosis of breast cancer and to determine the most useful parameter for this diagnosis. Using a 1.0T MR unit, (Magnetom, Siemens, Erlaugen, Germany), 3D-DMRI (TR/TE=3D30/12) with Gd-DTPA was performed in 38 cases of breast cancer, 22 of fibroadenoma, and in three normal volunteers. We retrospectively evaluated the findings according to the speed on dynamic study and maximal amount of contrast enhancement during the delayed phase;we calculated the contrast index and morphology of the cancers and compared diagnostic accuracy among these three diagnostic parameters. On conventional spin-echo T1-and T2-weighted images, there was no significant difference of signal intensity between benign fibroadenoma and breast carcinoma. Rapid contrast enhancement (within one minute) was noted in 35 breast cancer lesions (92.1%), but relatively low and slow contrast enhancement (after five minutes) was noted in three such lesions (7.9%). Gradual contrast enhancement was noted in 21 lesions of fibroadenoma(95.5%), but a moderate degree of rapid contrast enhancement (from three to five minutes) was noted in the other case (7.9%). of On the delayed enhanced phase of 3D-DMRI, the maximal amount of contrast enhancement showed no significant difference between fibroadenoma and cancer. On 3D-DMRI, an irregular, spiculated border, with high contrast enhancement was noted in all cases of breast cancer, in particular, irregular thick peripheral contrast enhancement with central necrosis was noted 11cases(28.9%). For the diagnosis of breast cancer, 3D-DMRI is a useful technique. Among the diagnostic criteria of speed, maximal amount of contrast enhancement and morphology, morphologic change after contrast enhancement study was the most useful diagnostic parameter.=20.

Diagnositc value of 3D-gradient echo dynamic contrast enhanced MRI in breast cancer

International Nuclear Information System (INIS)

Yang, Ik; Chung, Soo Young; Park, Hai Jung; Lee, Yul; Chung, Bong Wha; Shim, Jeong Won

1997-01-01

To assess the usefulness of 3D-gradient echo dynamic contrast enhanced MRI (3D-DMRI) in the diagnosis of breast cancer and to determine the most useful parameter for this diagnosis. Using a 1.0T MR unit, (Magnetom, Siemens, Erlaugen, Germany), 3D-DMRI (TR/TE=3D30/12) with Gd-DTPA was performed in 38 cases of breast cancer, 22 of fibroadenoma, and in three normal volunteers. We retrospectively evaluated the findings according to the speed on dynamic study and maximal amount of contrast enhancement during the delayed phase;we calculated the contrast index and morphology of the cancers and compared diagnostic accuracy among these three diagnostic parameters. On conventional spin-echo T1-and T2-weighted images, there was no significant difference of signal intensity between benign fibroadenoma and breast carcinoma. Rapid contrast enhancement (within one minute) was noted in 35 breast cancer lesions (92.1%), but relatively low and slow contrast enhancement (after five minutes) was noted in three such lesions (7.9%). Gradual contrast enhancement was noted in 21 lesions of fibroadenoma(95.5%), but a moderate degree of rapid contrast enhancement (from three to five minutes) was noted in the other case (7.9%). of On the delayed enhanced phase of 3D-DMRI, the maximal amount of contrast enhancement showed no significant difference between fibroadenoma and cancer. On 3D-DMRI, an irregular, spiculated border, with high contrast enhancement was noted in all cases of breast cancer, in particular, irregular thick peripheral contrast enhancement with central necrosis was noted 11cases(28.9%). For the diagnosis of breast cancer, 3D-DMRI is a useful technique. Among the diagnostic criteria of speed, maximal amount of contrast enhancement and morphology, morphologic change after contrast enhancement study was the most useful diagnostic parameter.=20

31P NMR imaging of solid bone with solid echoes combined with refocused gradients

International Nuclear Information System (INIS)

Li, L.; Utah Univ., Salt Lake City, UT; Kruger, R.A.

1990-01-01

This note on 31 p NMR imaging presents some observations of the solid echoes acquired from solid bone and how the proposed solid echo imaging method can be employed to obtain the 31 images of solid bone. (UK)

Gadolinium-Enhanced Three-Dimensional Magnetization - Prepared Rapid Gradient-Echo (3D MP-RAGE) Imaging is Superior to Spin-Echo Imaging in Delineating Brain Metastases

International Nuclear Information System (INIS)

Takeda, T.; Takeda, A.; Nagaoka, T.; Kunieda, E.; Takemasa, K.; Watanabe, M.; Hatou, T.; Oguro, S.; Katayama, M.

2008-01-01

Background: Precisely defining the number and location of brain metastases is very important for establishing a treatment strategy for malignancies. Although magnetic resonance imaging (MRI) is now considered the best modality, various improvements in sequences are still being made. Purpose: To prospectively compare the diagnostic ability of three-dimensional, magnetization-prepared rapid gradient-echo (3D MP-RAGE) imaging in detecting metastatic brain tumors, with that of two-dimensional spin-echo (2D SE) T1-weighted imaging. Material and Methods: A total of 123 examinations were included in this study, and 119 examinations from 88 patients with known malignancies were analyzed. All patients underwent T1- and T2-weighted 2D SE transverse imaging, followed by gadolinium-enhanced T1-weighted transverse and coronal 2D SE imaging and 3D MP-RAGE transverse imaging. Four radiologists interpreted the images to compare the accuracy and the time required for interpretation for each imaging. Results: 3D MP-RAGE imaging was significantly better than 2D SE imaging for detecting metastatic brain lesions, regardless of the readers' experience. The sensitivities of the 3D MP-RAGE and 2D SE imaging for all observers were 0.81 vs. 0.80 (P>0.05), specificities were 0.93 vs. 0.87 (P 0.05), and accuracies were 0.84 vs. 0.78 (P<0.05), respectively. There was no significant difference in the time required for image interpretation between the two modalities (15.6±4.0 vs. 15.4±4.1 min). Conclusion: 3D MP-RAGE imaging proved superior to 2D SE imaging in the detection of brain metastases

Comparison of single-shot fast spin-echo sequence and T2-weighted fast spin-echo sequence in MR imaging of the brain

International Nuclear Information System (INIS)

Cha, Sung Ho; Seo, Jeong Jin; Jeong, Gwang Woo; Kim, Jae Kyu; Kim, Yun Hyeon; Jeong, Yong Yeon; Kang, Heoung Keun; Oh, Hee Yeon; Yoon, Jong Hoon

1998-01-01

The purpose of this study was to evaluate the usefulness of the single-shot fast spinecho (SS-FSE) sequence in comparison with the T2-weighted fast spin-echo (T2-FSE) sequence in brain MR imaging. In 41 patients aged 15-75 years with intracranial lesion, both SS-FSE and T2-FES images were obtained using a 1.5-T MR system. Lesions included cerebral ischemia or infarcts (n=3D23), tumors (n=3D10), hemorrhages (n=3D3), inflammatory diseases (n=3D2), arachnoid cysts(n=3D2), and vascular disease (n=3D1), and the MR images were retrospectively evaluated. To calculate contrast-to-noise ratio (CNR), percentage contrast, and signal-to-noise ratio (SNR)-and thus make a quantitative comparison-the mean signal intensities of lesions, normal brain tissue, and noise out-side the patient were measured. For qualitative comparison, the visibility, margin, and extent of the lesions were rated using a five-grade system, and the degree of MR artifacts was also evaluated. Wilcoxon's signed ranks test was used for statistical analysis. The mean CNR of lesions was significantly higher on SS-FSE (31.3) than on T2-FSE images (27.5) (p=3D0.0131). Mean percentage contrast was also higher on SS-FSE (159.0) than on T2-FSE images (108.5) (p=3D0.0222), but mean SNR was higher on T2-FSE (80.3) than on SS-FSE images (53.5) (p=3D0.0000). No significant differences in lesion visibility were observed between the two imaging sequences, though margin and extent of the lesion were worse on SS-FSE images. For MR artifacts, no significant differences were demonstrated. For the evaluation of most intracranial lesions, MR imaging using the SS-FSE sequence appears to be slightly inferior to the T2-FSE sequence, but may be useful where patients are ill or uncooperative, or where children require sedation.=20

Echo-Interleaved-Spiral MR Imaging

Energy Technology Data Exchange (ETDEWEB)

Rosenthal, Shirrie; Azhari, Haim [Department of Biomedical Engineering, Technion, Israel Institute of Technology, Haifa 32000 (Israel); Montag, Avram [Elscint Ltd., MRI division, Haifa (Israel)

1999-12-31

Interleaved-Spiral imaging is an efficient method for MRI fast scans. However, images suffer from blurring and artifacts due to field inhomogeneities and the long readout times. In this paper, we combine interleaved-spirals with spin-echo for 3D scans. The refocusing RF-pulses (echoes) refocus off-resonance spins, thus allowing longer acquisition times per excitation, by limiting inhomogeneity effects. The total number of excitations for a 3D scan is reduced by half. The 3D Fourier transform of an object is divided into pairs of slices, one slice is scanned in an outgoing interleaved-spiral, initiated after a 90 degree pulse has been applied. The second slice is scanned in an ingoing interleaved-spiral, after a 180 degree pulse has been applied, thus reaching the slice origin at the echo time. (authors) 4 refs., 3 figs.

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.)

Echo III: The study of electric and magnetic fields with conjugate echoes from artificial electron beams injected into the auroral zone ionosphere

International Nuclear Information System (INIS)

Hendrickson, R.A.; Winckler, J.R.; Arnoldy, R.L.

1976-01-01

The third in a series of rocket flights carrying large electron guns for electron beam-plasma analysis and magnetosphere probing has been carried out from the Poker Flat rocket range near Fairbanks, Alaska at L=6. Echoes from the injected electrons mirroring at the southern hemisphere conjugate point were observed on the rocket by particle detectors and in the nearby ionosphere by photometers on board the rocket. The bounce time and drift velocities of the echoes were measured using the known trajectory and aspect of the rocket. Ionospheric electric fields near the rocket were inferred from drift motion of the ambient ion population measured by two techniques, electrostatic analyzers on board the rocket and incoherent backscatter radar from the ground. Using model magnetic fields, gradient and curvature drift and bound times have been computed under the conditions appropriate for this experiment. Assuming that field lines are equipotentials, the addition of the observed ionospheric electric field drift to the model-independent gradient and curvature drifts predicts a net echo drift velocity that is in agreement with the observations, provided the Mead-Fairfield 1972--73 model is used. The observed bounce time constitutes an independent model check and is in better agreement with the Olson-Pfitzer model. Echo spatial and temporal fluctuations reflected the turbulence associated with the diffuse aurora into which the rocket was launched

New spoiled spin-echo technique for three-dimensional MR imaging

International Nuclear Information System (INIS)

Darrasse, L.; Mao, L.; Saint-Jalmes, H.

1989-01-01

For 3D MR imaging within a convenient scanning time, the authors propose an improved spin-echo technique that permits the use of TRs shorter than 100 msec. They use a two-pulse RF sequence (α-π echo). The echo is read with conventional 3DFT encoding. To avoid steady-state signal refocusing before either α or (imperfect) π pulses, we apply randomized gradient spoilers both before each α pulse and on each side of the π pulse. So the sequence works like standard spin- echo sequences, with the z-magnetization recovery being adjusted by means of α rather than TR. The authors have investigated the method on a new 0.1-T Magnetom system dedicated for 3D MR imaging

The pelvis after surgery and radio-chemotherapy for rectal cancer studied with Gd-DTPA-enhanced fast dynamic MR imaging

International Nuclear Information System (INIS)

Blomqvist, L.; Fransson, P.; Hindmarsh, T.

1998-01-01

The aim of this work was to study the gadolinium-enhancement of malignant and benign pathology in the pelvis after surgery for rectal cancer. Thirty patients with either local recurrence (n = 17) or benign changes related to treatment for rectal cancer (n = 13) were studied with pelvic MR imaging. T2-weighted fast spin-echo as well as T1-weighted spin- or gradient-echo imaging before and after intravenous contrast was performed and referred to as contrast-enhanced MRI (CEMRI). In addition, between the pre- and postcontrast images, dynamic contrast-enhanced MRI (DCEMRI) was performed using a single-slice, multi-phase, contrast-enhanced T1-weighted fast spoiled gradient-echo sequence. The time between the start of contrast injection to the beginning of enhancement, the duration and rate of enhancement as well as enhancement amplitude were recorded. The data were compared with the clinical diagnosis according to biopsy in 8 patients and surgery in 6 patients. In the remaining 16 patients, the clinical diagnosis was obtained by clinical or radiological follow-up. DCEMRI did not improve the diagnostic information compared with CEMRI. None of the examined parameters were found to help discriminating malignant from benign changes. Characterisation of lesions in the pelvis after rectal cancer surgery was not improved by a dynamic gadolinium-enhanced sequence. (orig.)

Fast high-resolution MR imaging using the snapshot-FLASH MR sequence

International Nuclear Information System (INIS)

Matthaei, D.; Haase, A.; Henrich, D.; Duhmke, E.

1990-01-01

Snapshot, fast low-angle short (FLASH) MR imaging using an accelerated FLASH-MR sequence provides MR images with measuring times far below 1 second. The short TE of this sequence prevents susceptibility artifacts in gradient-echo imaging. In this paper variations of the sequence are shown that provide high resolution images with T1-weighted IR, T2-weighted SE, and chemical shift (CHESS) contrast sequences. METHODS AND MATERIALS: A whole-body 2-T system (Bruker-Medizintechnik) were used in combination with a 60-cm gradient system (providing gradient strength of 5 mT/m) to study healthy volunteers. The measuring time for a 256 x 256 image matrix was 800 msec. This sequence has been used in combination with T1-weighted IR, T2-weighted SE, and CHESS variations

NMR multiple-echo phase-contrast blood flow imaging

International Nuclear Information System (INIS)

O'Donnell, M.

1986-01-01

A method is described for magnetic resonance imaging of fluid flow in a sample, comprising the steps of: (a) immersing the sample in a static magnetic field disposed in a first direction; (b) applying a first sequence of magnetic field gradients and radio-frequency signals to the sample to both define a slab, of the sample to be imaged, in a plane substantially orthogonal to a selected direction for which flow velocity is to be measured, and to obtain a plurality N of spin-echo response signals form that slab; (c) processing the plurality of first sequence spin-echo signals to obtain a complex value A/sub 1/(X,Y,Z) relating both the spin density rho'(X,Y,Z),... and the phase rotation phi(X,Y,Z), induced by the first sequence, for each of a selected number of sequential locations (X,Y,Z) in the sample slab; (d) applying a second sequence of magnetic field gradient and radio-frequency signals to both define the same sample slab as in step (b) and to obtain another plurality N of spin-echo response signals from that slab; (e) including a waveform in at least one of the magnetic field gradient and radio-frequency signals applied in step (d) for imparting to each of the spin-echo signal components from each slab location having a flowing material therein a phase rotation dependent upon the magnitude of the flow velocity therein in the selected direction; (f) processing the plurality of second sequence spin-echo signals to obtain a complex value A/sub 2/(X,Y,Z) relating the spin density rho'(X,Y,Z) and the imparted phase rotation of the sample material along the selected flow measurement direction for each of the sequential locations (X,Y,Z) in the sample slab; and (g) processing the complex values A/sub 1/(X,Y,Z) and A/sub 2/(X,Y,Z) for each sample location to obtain a differential phase-contrast value related to the velocity of the flowing material therein in the selected measurement direction

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

International Nuclear Information System (INIS)

Hodgson, R.J.; Emery, P.; Grainger, A.J.; O'Connor, P.J.; Evans, R.; Coates, L.; Marzo-Ortega, H.; Helliwell, P.; McGonagle, D.; Robson, M.D.

2011-01-01

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.)

Correction of echo shift in reconstruction processing for ultra-short TE pulse sequence

International Nuclear Information System (INIS)

Takizawa, Masahiro; Ootsuka, Takehiro; Abe, Takayuki; Takahashi, Tetsuhiko

2010-01-01

An ultra-short echo time (TE) pulse sequence is composed of a radial sampling that acquires echo signals radially in the K-space and a half-echo acquisition that acquires only half of the echo signal. The shift in the position of the echo signal (echo shift) caused by the timing errors in the gradient magnetic field pulses affects the image quality in the radial sampling with the half-echo acquisition. To improve image quality, we have developed a signal correction algorithm that detects and eliminates this echo shift during reconstruction by performing a pre-scan within 10 seconds. The results showed that image quality is improved under oblique and/or off-centering conditions that frequently cause image distortion due to hardware error. In conclusion, we have developed a robust ultra-short TE pulse sequence that allows wide latitude in the scan parameters, including oblique and off-centering conditions. (author)

A paradoxical signal intensity increase in fatty livers using opposed-phase gradient echo imaging with fat-suppression pulses

International Nuclear Information System (INIS)

Mulkern, Robert V.; Voss, Stephan; Loeb Salsberg, Sandra; Krauel, Marta Ramon; Ludwig, David S.

2008-01-01

With the increase in obese and overweight children, nonalcoholic fatty liver disease has become more prevalent in the pediatric population. Appreciating subtleties of magnetic resonance (MR) signal intensity behavior from fatty livers under different imaging conditions thus becomes important to pediatric radiologists. We report an initially confusing signal behavior - increased signal from fatty livers when fat-suppression pulses are applied in an opposed-phase gradient echo imaging sequence - and seek to explain the physical mechanisms for this paradoxical signal intensity behavior. Abdominal MR imaging at 3 T with a 3-D volumetric interpolated breath-hold (VIBE) sequence in the opposed-phase condition (TR/TE 3.3/1.3 ms) was performed in five obese boys (14±2 years of age, body mass index >95th percentile for age and sex) with spectroscopically confirmed fatty livers. Two VIBE acquisitions were performed, one with and one without the use of chemical shift selective (CHESS) pulse fat suppression. The ratios of fat-suppressed over non-fat-suppressed signal intensities were assessed in regions-of-interest (ROIs) in five tissues: subcutaneous fat, liver, vertebral marrow, muscle and spleen. The boys had spectroscopically estimated hepatic fat levels between 17% and 48%. CHESS pulse fat suppression decreased subcutaneous fat signals dramatically, by more than 85% within regions of optimal fat suppression. Fatty liver signals, in contrast, were elevated by an average of 87% with CHESS pulse fat suppression. Vertebral marrow signal was also significantly elevated with CHESS pulse fat suppression, while spleen and muscle signals demonstrated only small signal increases on the order of 10%. We demonstrated that CHESS pulse fat suppression actually increases the signal intensity from fatty livers in opposed-phase gradient echo imaging conditions. The increase can be attributed to suppression of one partner of the opposed-phase pair that normally contributes to the

A paradoxical signal intensity increase in fatty livers using opposed-phase gradient echo imaging with fat-suppression pulses

Energy Technology Data Exchange (ETDEWEB)

Mulkern, Robert V.; Voss, Stephan [Harvard Medical School, Department of Radiology, Children' s Hospital Boston, Boston, MA (United States); Loeb Salsberg, Sandra; Krauel, Marta Ramon; Ludwig, David S. [Harvard Medical School, Department of Medicine, Children' s Hospital Boston, Boston, MA (United States)

2008-10-15

With the increase in obese and overweight children, nonalcoholic fatty liver disease has become more prevalent in the pediatric population. Appreciating subtleties of magnetic resonance (MR) signal intensity behavior from fatty livers under different imaging conditions thus becomes important to pediatric radiologists. We report an initially confusing signal behavior - increased signal from fatty livers when fat-suppression pulses are applied in an opposed-phase gradient echo imaging sequence - and seek to explain the physical mechanisms for this paradoxical signal intensity behavior. Abdominal MR imaging at 3 T with a 3-D volumetric interpolated breath-hold (VIBE) sequence in the opposed-phase condition (TR/TE 3.3/1.3 ms) was performed in five obese boys (14{+-}2 years of age, body mass index >95th percentile for age and sex) with spectroscopically confirmed fatty livers. Two VIBE acquisitions were performed, one with and one without the use of chemical shift selective (CHESS) pulse fat suppression. The ratios of fat-suppressed over non-fat-suppressed signal intensities were assessed in regions-of-interest (ROIs) in five tissues: subcutaneous fat, liver, vertebral marrow, muscle and spleen. The boys had spectroscopically estimated hepatic fat levels between 17% and 48%. CHESS pulse fat suppression decreased subcutaneous fat signals dramatically, by more than 85% within regions of optimal fat suppression. Fatty liver signals, in contrast, were elevated by an average of 87% with CHESS pulse fat suppression. Vertebral marrow signal was also significantly elevated with CHESS pulse fat suppression, while spleen and muscle signals demonstrated only small signal increases on the order of 10%. We demonstrated that CHESS pulse fat suppression actually increases the signal intensity from fatty livers in opposed-phase gradient echo imaging conditions. The increase can be attributed to suppression of one partner of the opposed-phase pair that normally contributes to the

Fast mapping of the T2 relaxation time of cerebral metabolites using proton echo-planar spectroscopic imaging (PEPSI).

Science.gov (United States)

Tsai, Shang-Yueh; Posse, Stefan; Lin, Yi-Ru; Ko, Cheng-Wen; Otazo, Ricardo; Chung, Hsiao-Wen; Lin, Fa-Hsuan

2007-05-01

Metabolite T2 is necessary for accurate quantification of the absolute concentration of metabolites using long-echo-time (TE) acquisition schemes. However, lengthy data acquisition times pose a major challenge to mapping metabolite T2. In this study we used proton echo-planar spectroscopic imaging (PEPSI) at 3T to obtain fast T2 maps of three major cerebral metabolites: N-acetyl-aspartate (NAA), creatine (Cre), and choline (Cho). We showed that PEPSI spectra matched T2 values obtained using single-voxel spectroscopy (SVS). Data acquisition for 2D metabolite maps with a voxel volume of 0.95 ml (32 x 32 image matrix) can be completed in 25 min using five TEs and eight averages. A sufficient spectral signal-to-noise ratio (SNR) for T2 estimation was validated by high Pearson's correlation coefficients between logarithmic MR signals and TEs (R2 = 0.98, 0.97, and 0.95 for NAA, Cre, and Cho, respectively). In agreement with previous studies, we found that the T2 values of NAA, but not Cre and Cho, were significantly different between gray matter (GM) and white matter (WM; P PEPSI and SVS scans was less than 9%. Consistent spatial distributions of T2 were found in six healthy subjects, and disagreement among subjects was less than 10%. In summary, the PEPSI technique is a robust method to obtain fast mapping of metabolite T2. (c) 2007 Wiley-Liss, Inc.

Sensitivity-encoded (SENSE) proton echo-planar spectroscopic imaging (PEPSI) in the human brain.

Science.gov (United States)

Lin, Fa-Hsuan; Tsai, Shang-Yueh; Otazo, Ricardo; Caprihan, Arvind; Wald, Lawrence L; Belliveau, John W; Posse, Stefan

2007-02-01

Magnetic resonance spectroscopic imaging (MRSI) provides spatially resolved metabolite information that is invaluable for both neuroscience studies and clinical applications. However, lengthy data acquisition times, which are a result of time-consuming phase encoding, represent a major challenge for MRSI. Fast MRSI pulse sequences that use echo-planar readout gradients, such as proton echo-planar spectroscopic imaging (PEPSI), are capable of fast spectral-spatial encoding and thus enable acceleration of image acquisition times. Combining PEPSI with recent advances in parallel MRI utilizing RF coil arrays can further accelerate MRSI data acquisition. Here we investigate the feasibility of ultrafast spectroscopic imaging at high field (3T and 4T) by combining PEPSI with sensitivity-encoded (SENSE) MRI using eight-channel head coil arrays. We show that the acquisition of single-average SENSE-PEPSI data at a short TE (15 ms) can be accelerated to 32 s or less, depending on the field strength, to obtain metabolic images of choline (Cho), creatine (Cre), N-acetyl-aspartate (NAA), and J-coupled metabolites (e.g., glutamate (Glu) and inositol (Ino)) with acceptable spectral quality and localization. The experimentally measured reductions in signal-to-noise ratio (SNR) and Cramer-Rao lower bounds (CRLBs) of metabolite resonances were well explained by both the g-factor and reduced measurement times. Thus, this technology is a promising means of reducing the scan times of 3D acquisitions and time-resolved 2D measurements. Copyright (c) 2007 Wiley-Liss, Inc.

Fast, three-dimensional, MR Imaging for polymer gel dosimetric applications involving high dose and steep dose gradients

International Nuclear Information System (INIS)

Sandilos, Panagiotis; Baras, Panagiotis; Georgiou, Evangelos; Dardoufas, Konstantinos; Karaiskos, Pantelis; Papagiannis, Panagiotis; Paschalis, Theodoros; Tatsis, Elias; Torrens, Michael; Vlahos, Lampros

2006-01-01

Polymer gels constitute water equivalent integrating detectors, which, combined with magnetic resonance imaging (MRI), can provide accurate three dimensional (3D) dose distributions in contemporary radiotherapy applications where the small field dimensions and steep dose gradients induce limitations to conventional dosimeters. One of the main obstacles for adapting the method for routine use in the clinical setting is the cost effectiveness of the MRI readout method. Currently, optimized Carr-Purcell-Meiboom-Gill (CPMG) multiple spin echo imaging pulse sequences are commonly used which however result in long imaging times. This work evaluates the efficiency of 3D, dual-echo, k-space segmented turbo spin echo (TSE) scanning sequences for accurate dosimetry with sub-millimetre spatial resolution in strenuous radiation therapy applications. PABIG polymer gel dosimeters were irradiated with an 192 Ir High Dose Rate brachytherapy source, the 4 mm and 8 mm collimator helmets of a gamma knife unit and a custom made x-knife collimator of 1 cm diameter. Profile and dose distribution measurements using TSE are benchmarked against corresponding findings obtained by the commonly used, but time consuming, CPMG sequence as well as treatment planning calculations, Monte Carlo (MC) simulations and film measurements. The implementation of a high Turbo factor was found to provide comparable accuracy, allowing a 64-fold MRI scan acceleration compared to conventional multi-echo sequences. The availability of TSE sequences in typical MRI installations greatly facilitates the introduction of polymer gel dosimetry in the clinical environment as a practicable tool for the determination of full 3D dose distributions in contemporary radiotherapy applications

Fast, three-dimensional, MR Imaging for polymer gel dosimetric applications involving high dose and steep dose gradients

Energy Technology Data Exchange (ETDEWEB)

Sandilos, Panagiotis [Department of Radiology, Medical School, University of Athens, Areteion Hospital, 76 Vas. Sofias Ave., 115 28 Athens (Greece); Baras, Panagiotis [Philips Hellas Medical Systems, 44 Kifissias Ave., Maroussi 151 25, Athens (Greece); Georgiou, Evangelos [Medical Physics Department, University of Athens, 75 Mikras Asias, 115 27 Athens (Greece); Dardoufas, Konstantinos [Department of Radiology, Medical School, University of Athens, Areteion Hospital, 76 Vas. Sofias Ave., 115 28 Athens (Greece): Hygeia Hospital, Kiffisias Avenue and 4 Erythrou Stavrou, Marousi, 151 23 Athens (Greece); Karaiskos, Pantelis [Medical Physics Department, University of Athens, 75 Mikras Asias, 115 27 Athens (Greece): Hygeia Hospital, Kiffisias Avenue and 4 Erythrou Stavrou, Marousi, 151 23 Athens (Greece)]. E-mail: p.karaiskos@hygeia.gr; Papagiannis, Panagiotis [Physics Department, Nuclear and Particle Physics Section, University of Athens, Panepistimioupolis, Ilisia, 157 71 Athens (Greece); Paschalis, Theodoros [Department of Radiology, Medical School, University of Athens, Areteion Hospital, 76 Vas. Sofias Ave., 115 28 Athens (Greece); Tatsis, Elias [Department of Radiology, Medical School, University of Athens, Areteion Hospital, 76 Vas. Sofias Ave., 115 28 Athens (Greece); Torrens, Michael [Hygeia Hospital, Kiffisias Avenue and 4 Erythrou Stavrou, Marousi, 151 23 Athens (Greece); Vlahos, Lampros [Department of Radiology, Medical School, University of Athens, Areteion Hospital, 76 Vas. Sofias Ave., 115 28 Athens (Greece)

2006-12-20

Polymer gels constitute water equivalent integrating detectors, which, combined with magnetic resonance imaging (MRI), can provide accurate three dimensional (3D) dose distributions in contemporary radiotherapy applications where the small field dimensions and steep dose gradients induce limitations to conventional dosimeters. One of the main obstacles for adapting the method for routine use in the clinical setting is the cost effectiveness of the MRI readout method. Currently, optimized Carr-Purcell-Meiboom-Gill (CPMG) multiple spin echo imaging pulse sequences are commonly used which however result in long imaging times. This work evaluates the efficiency of 3D, dual-echo, k-space segmented turbo spin echo (TSE) scanning sequences for accurate dosimetry with sub-millimetre spatial resolution in strenuous radiation therapy applications. PABIG polymer gel dosimeters were irradiated with an {sup 192}Ir High Dose Rate brachytherapy source, the 4 mm and 8 mm collimator helmets of a gamma knife unit and a custom made x-knife collimator of 1 cm diameter. Profile and dose distribution measurements using TSE are benchmarked against corresponding findings obtained by the commonly used, but time consuming, CPMG sequence as well as treatment planning calculations, Monte Carlo (MC) simulations and film measurements. The implementation of a high Turbo factor was found to provide comparable accuracy, allowing a 64-fold MRI scan acceleration compared to conventional multi-echo sequences. The availability of TSE sequences in typical MRI installations greatly facilitates the introduction of polymer gel dosimetry in the clinical environment as a practicable tool for the determination of full 3D dose distributions in contemporary radiotherapy applications.

Diagnostic performance of the three-dimensional fast spin echo-Cube sequence in comparison with a conventional imaging protocol in evaluation of the lachrymal drainage system

International Nuclear Information System (INIS)

Zhang, Jing; Chen, Lang; Wang, Qiu-Xia; Zhu, Wen-Zhen; Luo, Xin; Peng, Li; Liu, Rong; Xiong, Wei

2015-01-01

To compare the three-dimensional (3D)-fast spin-echo (FSE)-Cube with a conventional imaging protocol in evaluation of dacryostenosis. Thirty-three patients with epiphora underwent examinations using Cube magnetic resonance dacryocystography (MRD) and a conventional protocol, which included 3D fast-recovery fast spin-echo (FRFSE) MRD and two-dimensional (2D)-FSE sequences at 3.0 T. Using lachrymal endoscopic findings as the reference standard, we calculated the sensitivity and specificity of both protocols for detecting lachrymal drainage system (LDS) obstruction and their accuracies in depicting the level of obstruction. Comparable coronal and axial images were selected for bot sequences. Two neuroradiologists graded paired images for blurring, artefacts, anatomic details, and overall image quality. The two methods showed no significant difference in sensitivity (89.5 % vs. 94.7 %; p =0.674), specificity (64.3 %; p =1) or accuracy (86.8 %; p =1) in detecting or depicting LDS obstruction. Blurring and artefacts were significantly better on 2D-FSE images (p 0.05). In comparison with the conventional protocol, Cube MRD demonstrates satisfactory image quality and similar diagnostic capability for cases of possible LDS disease. (orig.)

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

International Nuclear Information System (INIS)

Kim, Yong Pyo; Kim, Sung Jun; Chung, Tae Sub; Yoo, Yeon Hwa; Yoon, Choon Sik; Kanneengiesser, Stephan; Paek, Moon Young; 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.

MRI of acute cerebral infarction: a comparison of FLAIR and T2-weighted fast spin-echo imaging

International Nuclear Information System (INIS)

Noguchi, K.; Ogawa, T.; Inugami, A.; Fujita, H.; Hatazawa, J.; Shimosegawa, E.; Okudera, T.; Uemura, K.; Seto, H.

1997-01-01

Fluid-attenuated inversion-recovery (FLAIR) sequences have been reported to provide high sensitivity to a wide range of central nervous system diseases. To our knowledge, however, FLAIR sequences have not been used to study patients with acute cerebral infarcts. We evaluated the usefulness of FLAIR sequences in this context. FLAIR sequences were acquired on a 0.5 T superconducting unit within 8 h of the onset in 19 patients (aged 26-80 years) with a total of 23 ischaemic lesions. The images were reviewed retrospectively by three neuroradiologists, and the FLAIR images were compared with T2-weighted fast spin-echo images. All but one of the ischaemic lesions involving grey matter was clearly demonstrated on FLAIR images as increased signal intensity in cortical or central grey matter. FLAIR images were particularly useful for detecting the hyperacute cortical infarcts within 3 h of onset, which were not readily detected on the spin-echo images. In 9 of 11 patients with complete proximal occlusion, the distal portion of the cerebral artery was visible as an area of high signal intensity on FLAIR images. (orig.). With 4 figs., 1 tab

Comparison of a T1-weighted inversion-recovery-, gradient-echo- and spin-echo sequence for imaging of the brain at 3.0 Tesla

International Nuclear Information System (INIS)

Stehling, C.; Niederstadt, T.; Kraemer, S.; Kugel, H.; Schwindt, W.; Heindel, W.; Bachmann, R.

2005-01-01

Purpose: The increased T1 relaxation times at 3.0 Tesla lead to a reduced T1 contrast, requiring adaptation of imaging protocols for high magnetic fields. This prospective study assesses the performance of three techniques for T1-weighted imaging (T1w) at 3.0 T with regard to gray-white differentiation and contrast-to-noise-ratio (CNR). Materials and Methods: Thirty-one patients were examined at a 3.0 T system with axial T1 w inversion recovery (IR), spin-echo (SE) and gradient echo (GE) sequences and after contrast enhancement (CE) with CE-SE and CE-GE sequences. For qualitative analysis, the images were ranked with regard to artifacts, gray-white differentiation, image noise and overall diagnostic quality. For quantitative analysis, the CNR was calculated, and cortex and basal ganglia were compared with the white matter. Results: In the qualitative analysis, IR was judged superior to SE and GE for gray-white differentiation, image noise and overall diagnostic quality, but inferior to the GE sequence with regard to artifacts. CE-GE proved superior to CE-SE in all categories. In the quantitative analysis, CNR of the based ganglia was highest for IR, followed by GE and SE. For the CNR of the cortex, no significant difference was found between IR (16.9) and GE (15.4) but both were superior to the SE (9.4). The CNR of the cortex was significantly higher for CE-GE compared to CE-SE (12.7 vs. 7.6, p<0.001), but the CNR of the basal ganglia was not significantly different. Conclusion: For unenhanced T1w imaging at 3.0 T, the IR technique is, despite increased artifacts, the method of choice due to its superior gray-white differentiation and best overall image quality. For CE-studies, GE sequences are recommended. For cerebral imaging, SE sequences give unsatisfactory results at 3.0 T. (orig.)

A fast nonlinear conjugate gradient based method for 3D frictional contact problems

NARCIS (Netherlands)

Zhao, J.; Vollebregt, E.A.H.; Oosterlee, C.W.

2014-01-01

This paper presents a fast numerical solver for a nonlinear constrained optimization problem, arising from a 3D frictional contact problem. It incorporates an active set strategy with a nonlinear conjugate gradient method. One novelty is to consider the tractions of each slip element in a polar

MRI of bone marrow: opposed-phase gradient-echo sequences with long repetition time

International Nuclear Information System (INIS)

Seiderer, M.; Staebler, A.; Wagner, H.

1999-01-01

Signal intensity for opposed-phase gradient-echo (GE) sequences of tissues composed of fat- and water-equivalent cells such as red bone marrow is extremely sensitive to variation of the ratio of both cell populations (fat-to-water ratio Q F/W ). Because most bone marrow pathology results in variation of Q F/W , GE sequences are characterized by high-contrast imaging of pathology. The aim of this study was to evaluate the influence of TR, TE, FA, Q F/W and histology on signal intensity. Signal intensity of opposed-phase GE sequences as a function of TR, TE, FA, and Q F/W was measured for a fat-water phantom and cadaver specimens of normal bone marrow (red and yellow) and pathological bone marrow (tumors). All specimens were correlated to histology. Opposed-phase GE imaging of red bone marrow pathology results in low-signal-intensity imaging of intact red bone marrow and high-signal-intensity positive contrast imaging of pathology associated with a change in Q F/W . In first-order approximation the signal intensity of pathology is linearly correlated to the change in Q F/W . Opposed-phase GE imaging is a sensitive imaging technique for red bone marrow pathology. Relative contrast of red bone marrow pathology is similar to fat-suppressed imaging techniques. Acquisition time is identical to T1-weighted SE sequences. (orig.)

Evaluation of chondromalacia of the patella with axial inversion recovery-fast spin-echo imaging.

Science.gov (United States)

Lee, S H; Suh, J S; Cho, J; Kim, S J; Kim, S J

2001-03-01

The purpose of our study was to assess the accuracy of inversion recovery-fast spin-echo (IR-FSE) imaging for the evaluation of chondromalacia of the patella. Eighty-six patients were included, they underwent magnetic resonance (MR) examination and subsequent knee arthroscopy. Medial and lateral facets of the patella were evaluated separately. Axial images were obtained by using IR-FSE (TR/TE/TI = 3000/25/150 msec; echo train length, 8; 4-mm thickness; 12-cm field of view; 512 x 256 matrix; two, number of excitations) with a 1.5-T MR machine. MR interpretation of chondromalacia was made on the basis of the arthroscopic grading system. Of a total of 172 facets graded, arthroscopy revealed chondromalacia in 14 facets with various grades (G0, 158; G1, 1; G2, 3; G3, 6; G4, 4). Sensitivity, specificity, and accuracy in the chondromalacia grades were 57.1%, 93.0%, and 90.1%, respectively. There was one false-negative case (G4) and 11 false-positive cases (G1, eight; G2, two; G3, one). Sensitivity and specificity corrected by one grade difference were improved to 85.7% and 98.1%, respectively. When cartilage changes were grouped into early (corresponding to grade 1 and 2) and advanced (grade 3 and 4) diseases, sensitivity and specificity of the early and advanced diseases were 75% and 94% and 80% and 99%, respectively. IR-FSE imaging of the knee revealed high specificity but low sensitivity for the evaluation of chondromalacia of the patella.

E-region echo characteristics governed by auroral arc electrodynamics

Directory of Open Access Journals (Sweden)

S. E. Milan

2003-07-01

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

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

Clinical utility of partial flip angle T2-weighted spin-echo imaging of the brain

International Nuclear Information System (INIS)

Chang, K.H.; Yi, J.G.; Han, M.H.; Han, M.C.; Kim, C.W.; Cho, M.H.; Cho, Z.H.

1990-01-01

To assess the clinical usefulness of partial flip angle (PFA) spin-echo (SE) brain imaging, a total of eighty patients were examined with both conventional double echo T2-weighted SE (2500/30, 80/90deg/one excitation) and PFA double echo SE (1200/30, 70/45deg/two excitations) on 2.0T system. Two comparative studies were performed: (1) In 65 patients PFA SE technique was compared with conventional SE without flow compensating gradients, and (2) in 15 patients the former was compared with the latter with flow compensating gradients. Imaging time was nearly identical in each sequence. In both studies we found that PFA T2-weighted SE images were almost identical to those obtained with the conventional SE technique in the contrast characteristics and the detection rate of the abnormalities (100%, 85/85 lesions), and more importantly, PFA SE revealed few flow artifacts in the brain stem, temporal lobes and basal ganglia which were frequently seen on conventional SE without flow compensating gradients. Additionally, PFA SE images demonstrated no suppression of CSF flow void in the aqueduct which was commonly seen on conventional SE with flow compensating gradients. In overall image quality, the PFA SE images, particularly the second echo images, were almost comparable with those of conventional SE with flow compensating gradients. A flip angle of 45deg seems to be close to Ernst angle, the angle at which maximum signal occurs, for a given TR of 1200 msec for CSF and most of the abnormalities containing higher water content. In conclusion, PFA SE sequence (i.e. 1200/30, 70/45deg/2) appears to be useful as a primary or an adjunctive technique in certain clinical circumstances, particularly in imaging of hydrocephalic patients for assessing aqueductal patency. (orig.)

[The use of the T2-weighted turbo-spin-echo sequence in studying the neurocranium. A comparison with the conventional T2-weighted spin-echo sequence].

Science.gov (United States)

Siewert, C; Hosten, N; Felix, R

1994-07-01

T2-weighted spin-echo imaging is the standard screening procedure in MR imaging of the neurocranium. We evaluated fast spin-echo T2-weighted imaging (TT2) of the neurocranium in comparison to conventional spin-echo T2-weighted imaging (T2). Signal-to-noise and contrast-to-noise ratio of normal brain tissues (basal ganglia, grey and white matter, CSF fluid) and different pathologies were calculated. Signal-to-noise ratio and contrast-to-noise ratio were significantly higher in TT2 than in T2 (with the exception of gray-to-white matter contrast). Tissues with increased content of water protons (mobile protons) showed the highest contrast to surrounding tissues. The increased signal intensity of fat must be given due attention in fatty lesions. Because the contrast-to-noise ratio between white matter and basal ganglia is less in TT2, Parkinson patients have to be examined by conventional T2. If these limitations are taken into account, fast spin-echo T2-weighted imaging is well appropriate for MR imaging of the neurocranium, resulting in heavy T2-weighting achieved in a short acquisition time.

A fast nonlinear conjugate gradient based method for 3D concentrated frictional contact problems

NARCIS (Netherlands)

J. Zhao (Jing); E.A.H. Vollebregt (Edwin); C.W. Oosterlee (Cornelis)

2015-01-01

htmlabstractThis paper presents a fast numerical solver for a nonlinear constrained optimization problem, arising from 3D concentrated frictional shift and rolling contact problems with dry Coulomb friction. The solver combines an active set strategy with a nonlinear conjugate gradient method. One

Fast alternating projected gradient descent algorithms for recovering spectrally sparse signals

KAUST Repository

Cho, Myung

2016-06-24

We propose fast algorithms that speed up or improve the performance of recovering spectrally sparse signals from un-derdetermined measurements. Our algorithms are based on a non-convex approach of using alternating projected gradient descent for structured matrix recovery. We apply this approach to two formulations of structured matrix recovery: Hankel and Toeplitz mosaic structured matrix, and Hankel structured matrix. Our methods provide better recovery performance, and faster signal recovery than existing algorithms, including atomic norm minimization.

Fast alternating projected gradient descent algorithms for recovering spectrally sparse signals

KAUST Repository

Cho, Myung; Cai, Jian-Feng; Liu, Suhui; Eldar, Yonina C.; Xu, Weiyu

2016-01-01

We propose fast algorithms that speed up or improve the performance of recovering spectrally sparse signals from un-derdetermined measurements. Our algorithms are based on a non-convex approach of using alternating projected gradient descent for structured matrix recovery. We apply this approach to two formulations of structured matrix recovery: Hankel and Toeplitz mosaic structured matrix, and Hankel structured matrix. Our methods provide better recovery performance, and faster signal recovery than existing algorithms, including atomic norm minimization.

Kinematic MRI using short TR single shot fast spin echo (SSFSE) in evaluating swallowing

Energy Technology Data Exchange (ETDEWEB)

Isogai, Satoshi; Takehara, Yasuo; Isoda, Haruo; Kodaira, Nami; Masunaga, Hatsuko; Ozawa, Fukujirou; Kaneko, Masao [Hamamatsu Univ. School of Medicine, Shizuoka (Japan); Nozaki, Atsushi; Kabasawa, Hiroyuki

1999-03-01

The utility of short TR single shot fast spin echo (SSFSE) MR imaging for evaluating swallowing was determined. Five healthy volunteers underwent kinematic MR imaging of swallowing with a 1.5 T MR scanner using the short TR (300 ms) SSFSE sequence. Twenty phases of sagittal sections were acquired within 6 sec, where the temporal resolution was 300 ms. For oral contrast medium, we used prune yogurt juice with Fe added. The image contrast of short TR SSFSE was found to be somewhere like that of T1-weighted images. In all cases, both the buccal and pharyngeal stages of swallowing were successfully depicted. The Fe-added prune yogurt juice performed as a positive contrast medium and helped determine anatomical structures in the buccal stage. Short TR (300 ms) SSFSE was useful in evaluating swallowing. The combined use of Fe-added prune yogurt juice was helpful in enhancing the surface of the oropharynx. (author)

Kinematic MRI using short TR single shot fast spin echo (SSFSE) in evaluating swallowing

International Nuclear Information System (INIS)

Isogai, Satoshi; Takehara, Yasuo; Isoda, Haruo; Kodaira, Nami; Masunaga, Hatsuko; Ozawa, Fukujirou; Kaneko, Masao; Nozaki, Atsushi; Kabasawa, Hiroyuki

1999-01-01

The utility of short TR single shot fast spin echo (SSFSE) MR imaging for evaluating swallowing was determined. Five healthy volunteers underwent kinematic MR imaging of swallowing with a 1.5 T MR scanner using the short TR (300 ms) SSFSE sequence. Twenty phases of sagittal sections were acquired within 6 sec, where the temporal resolution was 300 ms. For oral contrast medium, we used prune yogurt juice with Fe added. The image contrast of short TR SSFSE was found to be somewhere like that of T1-weighted images. In all cases, both the buccal and pharyngeal stages of swallowing were successfully depicted. The Fe-added prune yogurt juice performed as a positive contrast medium and helped determine anatomical structures in the buccal stage. Short TR (300 ms) SSFSE was useful in evaluating swallowing. The combined use of Fe-added prune yogurt juice was helpful in enhancing the surface of the oropharynx. (author)

Modified echo peak correction for radial acquisition regime (RADAR).

Science.gov (United States)

Takizawa, Masahiro; Ito, Taeko; Itagaki, Hiroyuki; Takahashi, Tetsuhiko; Shimizu, Kanichirou; Harada, Junta

2009-01-01

Because radial sampling imposes many limitations on magnetic resonance (MR) imaging hardware, such as on the accuracy of the gradient magnetic field or the homogeneity of B(0), some correction of the echo signal is usually needed before image reconstruction. In our previous study, we developed an echo-peak-shift correction (EPSC) algorithm not easily affected by hardware performance. However, some artifacts remained in lung imaging, where tissue is almost absent, or in cardiac imaging, which is affected by blood flow. In this study, we modified the EPSC algorithm to improve the image quality of the radial aquisition regime (RADAR) and expand its application sequences. We assumed the artifacts were mainly caused by errors in the phase map for EPSC and used a phantom on a 1.5-tesla (T) MR scanner to investigate whether to modify the EPSC algorithm. To evaluate the effectiveness of EPSC, we compared results from T(1)- and T(2)-weighted images of a volunteer's lung region using the current and modified EPSC. We then applied the modified EPSC to RADAR spin echo (SE) and RADAR balanced steady-state acquisition with rewound gradient echo (BASG) sequence. The modified EPSC reduced phase discontinuity in the reference data used for EPSC and improved visualization of blood vessels in the lungs. Motion and blood flow caused no visible artifacts in the resulting images in either RADAR SE or RADAR BASG sequence. Use of the modified EPSC eliminated artifacts caused by signal loss in the reference data for EPSC. In addition, the modified EPSC was applied to RADAR SE and RADAR BASG sequences.

Modified echo peak correction for radial acquisition regime (RADAR)

International Nuclear Information System (INIS)

Takizawa, Masahiro; Ito, Taeko; Itagaki, Hiroyuki; Takahashi, Tetsuhiko; Shimizu, Kanichirou; Harada, Junta

2009-01-01

Because radial sampling imposes many limitations on magnetic resonance (MR) imaging hardware, such as on the accuracy of the gradient magnetic field or the homogeneity of B 0 , some correction of the echo signal is usually needed before image reconstruction. In our previous study, we developed an echo-peak-shift correction (EPSC) algorithm not easily affected by hardware performance. However, some artifacts remained in lung imaging, where tissue is almost absent, or in cardiac imaging, which is affected by blood flow. In this study, we modified the EPSC algorithm to improve the image quality of the radial acquisition regime (RADAR) and expand its application sequences. We assumed the artifacts were mainly caused by errors in the phase map for EPSC and used a phantom on a 1.5-tesla (T) MR scanner to investigate whether to modify the EPSC algorithm. To evaluate the effectiveness of EPSC, we compared results from T 1 -and T 2 -weighted images of a volunteer's lung region using the current and modified EPSC. We then applied the modified EPSC to RADAR spin echo (SE) and RADAR balanced steady-state acquisition with rewound gradient echo (BASG) sequence. The modified EPSC reduced phase discontinuity in the reference data used for EPSC and improved visualization of blood vessels in the lungs. Motion and blood flow caused no visible artifacts in the resulting images in either RADAR SE or RADAR BASG sequence. Use of the modified EPSC eliminated artifacts caused by signal loss in the reference data for EPSC. In addition, the modified EPSC was applied to RADAR SE and RADAR BASG sequences. (author)

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

Screening for skeletal metastases of the spine and pelvis: gradient echo opposed-phase MRI compared with bone scintigraphy

International Nuclear Information System (INIS)

Neumann, K.; Hosten, N.; Venz, S.

1995-01-01

Opposed-phase gradient echo (GRE) MRI at 0.5 T was compared with T1-weighted GRE MRI and bone scintigraphy regarding the detection of malignant bone marrow infiltrates of the spine and pelvis. Seventeen control patients and 41 patients with suspected skeletal metastases were studied with plain and gadolinium-enhanced MRI. In the control group only a vertebral haemangioma showed contrast enhancement, while all metastases (confirmed histologically or by follow-up) were enhancing. Opposed-phase surface coil MRI showed a significantly higher contrast-to-noise ratio of 56 metastases than T1-weighted images. In 28 patients body coil opposed-phase MRI detected more metastatic foci of the spine and pelvis than did bone scintigraphy (84 vs 56). No scintigraphically visualised lesion was missed by MRI. In conclusion, body coil gadolinium-enhanced opposed-phase GRE MRI may be applied as a screening method for skeletal metastases of the spine and pelvis at intermediate field strengths. (orig.)

Screening for skeletal metastases of the spine and pelvis: gradient echo opposed-phase MRI compared with bone scintigraphy

Energy Technology Data Exchange (ETDEWEB)

Neumann, K. [Zentralinstitut fuer Roentgendiagnostik, Universitaetsklinikum Essen, Gesamthochschule Essen (Germany); Hosten, N. [Strahlenklinik und Poliklinik, Universitaetsklinikum Rudolf Virchow, Freie Univ. Berlin (Germany); Venz, S. [Strahlenklinik und Poliklinik, Universitaetsklinikum Rudolf Virchow, Freie Univ. Berlin (Germany)

1995-11-01

Opposed-phase gradient echo (GRE) MRI at 0.5 T was compared with T1-weighted GRE MRI and bone scintigraphy regarding the detection of malignant bone marrow infiltrates of the spine and pelvis. Seventeen control patients and 41 patients with suspected skeletal metastases were studied with plain and gadolinium-enhanced MRI. In the control group only a vertebral haemangioma showed contrast enhancement, while all metastases (confirmed histologically or by follow-up) were enhancing. Opposed-phase surface coil MRI showed a significantly higher contrast-to-noise ratio of 56 metastases than T1-weighted images. In 28 patients body coil opposed-phase MRI detected more metastatic foci of the spine and pelvis than did bone scintigraphy (84 vs 56). No scintigraphically visualised lesion was missed by MRI. In conclusion, body coil gadolinium-enhanced opposed-phase GRE MRI may be applied as a screening method for skeletal metastases of the spine and pelvis at intermediate field strengths. (orig.)

Detection of fast oscillating magnetic fields using dynamic multiple TR imaging and Fourier analysis.

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Ki Hwan Kim

Full Text Available Neuronal oscillations produce oscillating magnetic fields. There have been trials to detect neuronal oscillations using MRI, but the detectability in in vivo is still in debate. Major obstacles to detecting neuronal oscillations are (i weak amplitudes, (ii fast oscillations, which are faster than MRI temporal resolution, and (iii random frequencies and on/off intervals. In this study, we proposed a new approach for direct detection of weak and fast oscillating magnetic fields. The approach consists of (i dynamic acquisitions using multiple times to repeats (TRs and (ii an expanded frequency spectral analysis. Gradient echo echo-planar imaging was used to test the feasibility of the proposed approach with a phantom generating oscillating magnetic fields with various frequencies and amplitudes and random on/off intervals. The results showed that the proposed approach could precisely detect the weak and fast oscillating magnetic fields with random frequencies and on/off intervals. Complex and phase spectra showed reliable signals, while no meaningful signals were observed in magnitude spectra. A two-TR approach provided an absolute frequency spectrum above Nyquist sampling frequency pixel by pixel with no a priori target frequency information. The proposed dynamic multiple-TR imaging and Fourier analysis are promising for direct detection of neuronal oscillations and potentially applicable to any pulse sequences.

Occupational exposure measurements of static and pulsed gradient magnetic fields in the vicinity of MRI scanners

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Kaennaelae, Sami; Toivo, Tim; Jokela, Kari [STUK-Radiation and Nuclear Safety Authority, PO Box 14, 00881 Helsinki (Finland); Alanko, Tommi [Finnish Institute of Occupational Health, New Technologies and Risks, Topeliuksenkatu 41a A, 00250 Helsinki (Finland)], E-mail: sami.kannala@stuk.fi

2009-04-07

Recent advances in magnetic resonance imaging (MRI) have increased occupational exposure to magnetic fields. In this study, we examined the assessment of occupational exposure to gradient magnetic fields and time-varying magnetic fields generated by motion in non-homogeneous static magnetic fields of MRI scanners. These magnetic field components can be measured simultaneously with an induction coil setup that detects the time rate of change of magnetic flux density (dB/dt). The setup developed was used to measure the field components around two MRI units (1 T open and 3 T conventional). The measured values can be compared with dB/dt reference levels derived from magnetic flux density reference levels given by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The measured motion-induced dB/dt values were above the dB/dt reference levels for both MRI units. The measured values for the gradient fields (echo planar imaging (EPI) and fast field echo (FFE) sequences) also exceeded the dB/dt reference levels in positions where the medical staff may have access during interventional procedures. The highest motion-induced dB/dt values were 0.7 T s{sup -1} for the 1 T scanner and 3 T s{sup -1} for the 3 T scanner when only the static field was present. Even higher values (6.5 T s{sup -1}) were measured for simultaneous exposure to motion-induced and gradient fields in the vicinity of the 3 T scanner.

Minimum TE gradient-recalled phosphorus imaging sequence on a whole-body imager

International Nuclear Information System (INIS)

Listerud, J.; Lenkinski, R.E.; Axel, L.

1989-01-01

To define the lower limits of spatial resolution in gradient-recalled echo phosphorus studies at 1.5 T, the authors have implemented a phosphorus gradient-recalled imaging sequence on the Signa imager. All gradient ramps for the section-selective rephasing lobe, the phase-encoding pulse, and the dephasing pulse of the frequency-encoding gradient are slowed at the maximal rate. Consequently, with a field of view of 24 cm, an in-plane resolution of 3 cm, an echo appropriately offset, an RF bandwidth of 1.2 KHz, and a section thickness of 5 cm, the echo time may be reduced to 1.35 msec. The reconstruction algorithm has been modified to support oversampled data of low spatial resolution appropriate for phosphorus imaging. The sequence will acquire H-1 images and supports the automatic and manual prescan features of the commercial instrument. To facilitate setup in the phosphorus imaging mode the sequence supports the product spectroscopic mode with a DRESS (depth recalled surface coil spectroscopy) sequence and a section profile sequence for appropriate shimming, receiver characteristics, and averaging requirements. The suitability for adaptation of this sequence to three-dimensional chemical shift imaging is discussed

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

International Nuclear Information System (INIS)

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

2015-01-01

Aim: 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. Methods: 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. Results: 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). Conclusion: 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. -- Highlights: •We investigate the potential of 3D FFE sequence to distinguish the grey-white of the cervical spinal cord at 3T MRI system. •We optimized The 3D FFE sequence was optimized to increase the grey-white contrast. •Utilizing medium TE for T2W and the shortest TR for reduction of susceptibility related artifacts and motion artefacts. •This technique may increase the confidence in the diagnosis of disease with the improved delineation of cord anatomy

Comparison of spin echo T1-weighted sequences versus fast spin-echo proton density-weighted sequences for evaluation of meniscal tears at 1.5 T

International Nuclear Information System (INIS)

Wolff, Andrew B.; Pesce, Lorenzo L.; Wu, Jim S.; Smart, L.R.; Medvecky, Michael J.; Haims, Andrew H.

2009-01-01

At our institution, fast spin-echo (FSE) proton density (PD) imaging is used to evaluate articular cartilage, while conventional spin-echo (CSE) T1-weighted sequences have been traditionally used to characterize meniscal pathology. We sought to determine if FSE PD-weighted sequences are equivalent to CSE T1-weighted sequences in the detection of meniscal tears, obviating the need to perform both sequences. We retrospectively reviewed the records of knee arthroscopies performed by two arthroscopy-focused surgeons from an academic medical center over a 2-year period. The preoperative MRI images were interpreted independently by two fellowship-trained musculoskeletal radiologists who graded the sagittal CSE T1 and FSE PD sequences at different sittings with grades 1-5, where 1 = normal meniscus, 2 = probable normal meniscus, 3 indeterminate, 4 = probable torn meniscus, and 5 = torn meniscus. Each meniscus was divided into an anterior and posterior half, and these halves were graded separately. Operative findings provided the gold standard. Receiver operating characteristic (ROC) analysis was performed to compare the two sequences. There were 131 tears in 504 meniscal halves. Using ROC analysis, the reader 1 area under curve for FSE PD was significantly better than CSE T1 (0.939 vs. 0.902, >95% confidence). For reader 2, the difference met good criteria for statistical non-inferiority but not superiority (0.913 for FSE PD and 0.908 for CSE T1; >95% non-inferiority for difference at most of -0.027). FSE PD-weighted sequences, using our institutional protocol, are not inferior to CSE T1-weighted sequences for the detection of meniscal tears and may be superior. (orig.)

Fast spin-echo MR assessment of patients with poor outcome following spinal cervical surgery

International Nuclear Information System (INIS)

Wu, W.; Thuomas, K.AA.; Hedlund, R.; Leszniewski, W.; Vavruch, L.

1996-01-01

The aim of the investigation was to evaluate poor outcome following spinal cervical surgery. A total of 146 consecutive patients operated with anterior discectomy and fusion (ADF) with the Cloward technique were investigated. Clinical notes, plain radiography, CT, and fast spin-echo (FSE) images were retrospectively evaluated. Some 30% of the patients had unsatisfactory clinical results within 12 months after surgery; 13% had initial improvement followed by deterioration of the preoperative symptoms, while 14.4% were not improved or worsened. Disc herniation and bony stenosis above, below, or at the fused level were the most common findings. In 45% of patients, surgery failed to decompress the spinal canal. In only 4 patients was no cause of remaining myelopathy and/or radiculopathy found. FSE demonstrated a large variety of pathological findings in the patients with poor clinical outcome after ADF. Postoperatively, patients with good clinical outcome had a lower incidence of pathological changes. FSE is considered the primary imaging modality for the cervical spine. However, CT is a useful complement in the axial projection to visualize bone changes. (orig.)

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.

Mapping brain activity in gradient-echo functional MRI using principal component analysis

Science.gov (United States)

Khosla, Deepak; Singh, Manbir; Don, Manuel

1997-05-01

The detection of sites of brain activation in functional MRI has been a topic of immense research interest and many technique shave been proposed to this end. Recently, principal component analysis (PCA) has been applied to extract the activated regions and their time course of activation. This method is based on the assumption that the activation is orthogonal to other signal variations such as brain motion, physiological oscillations and other uncorrelated noises. A distinct advantage of this method is that it does not require any knowledge of the time course of the true stimulus paradigm. This technique is well suited to EPI image sequences where the sampling rate is high enough to capture the effects of physiological oscillations. In this work, we propose and apply tow methods that are based on PCA to conventional gradient-echo images and investigate their usefulness as tools to extract reliable information on brain activation. The first method is a conventional technique where a single image sequence with alternating on and off stages is subject to a principal component analysis. The second method is a PCA-based approach called the common spatial factor analysis technique (CSF). As the name suggests, this method relies on common spatial factors between the above fMRI image sequence and a background fMRI. We have applied these methods to identify active brain ares during visual stimulation and motor tasks. The results from these methods are compared to those obtained by using the standard cross-correlation technique. We found good agreement in the areas identified as active across all three techniques. The results suggest that PCA and CSF methods have good potential in detecting the true stimulus correlated changes in the presence of other interfering signals.

Correction of inhomogeneous RF field using multiple SPGR signals for high-field spin-echo MRI

International Nuclear Information System (INIS)

Ishimori, Yoshiyuki; Monma, Masahiko; Yamada, Kazuhiro; Kimura, Hirohiko; Uematsu, Hidemasa; Fujiwara, Yasuhiro; Yamaguchi, Isao

2007-01-01

The purpose of this study was to propose a simple and useful method for correcting nonuniformity of high-field (3 Tesla) T 1 -weighted spin-echo (SE) images based on a B1 field map estimated from gradient recalled echo (GRE) signals. The method of this study was to estimate B1 inhomogeneity, spoiled gradient recalled echo (SPGR) images were collected using a fixed repetition time of 70 ms, flip angles of 45 and 90 degrees, and echo times of 4.8 and 10.4 ms. Selection of flip angles was based on the observation that the relative intensity changes in SPGR signals were very similar among different tissues at larger flip angles than the Ernst angle. Accordingly, spatial irregularity that was observed on a signal ratio map of the SPGR images acquired with these 2 flip angles was ascribed to inhomogeneity of the B1 field. Dual echo time was used to eliminate T 2 * effects. The ratio map that was acquired was scaled to provide an intensity correction map for SE images. Both phantom and volunteer studies were performed using a 3T magnetic resonance scanner to validate the method. In the phantom study, the uniformity of the T 1 -weighted SE image improved by 23%. Images of human heads also showed practically sufficient improvement in the image uniformity. The present method improves the image uniformity of high-field T 1 -weighted SE images. (author)

Can a single-shot black-blood T2-weighted spin-echo echo-planar imaging sequence with sensitivity encoding replace the respiratory-triggered turbo spin-echo sequence for the liver? An optimization and feasibility study.

Science.gov (United States)

Hussain, Shahid M; De Becker, Jan; Hop, Wim C J; Dwarkasing, Soendersing; Wielopolski, Piotr A

2005-03-01

To optimize and assess the feasibility of a single-shot black-blood T2-weighted spin-echo echo-planar imaging (SSBB-EPI) sequence for MRI of the liver using sensitivity encoding (SENSE), and compare the results with those obtained with a T2-weighted turbo spin-echo (TSE) sequence. Six volunteers and 16 patients were scanned at 1.5T (Philips Intera). In the volunteer study, we optimized the SSBB-EPI sequence by interactively changing the parameters (i.e., the resolution, echo time (TE), diffusion weighting with low b-values, and polarity of the phase-encoding gradient) with regard to distortion, suppression of the blood signal, and sensitivity to motion. The influence of each change was assessed. The optimized SSBB-EPI sequence was applied in patients (N = 16). A number of items, including the overall image quality (on a scale of 1-5), were used for graded evaluation. In addition, the signal-to-noise ratio (SNR) of the liver was calculated. Statistical analysis was carried out with the use of Wilcoxon's signed rank test for comparison of the SSBB-EPI and TSE sequences, with P = 0.05 considered the limit for significance. The SSBB-EPI sequence was improved by the following steps: 1) less frequency points than phase-encoding steps, 2) a b-factor of 20, and 3) a reversed polarity of the phase-encoding gradient. In patients, the mean overall image quality score for the optimized SSBB-EPI (3.5 (range: 1-4)) and TSE (3.6 (range: 3-4)), and the SNR of the liver on SSBB-EPI (mean +/- SD = 7.6 +/- 4.0) and TSE (8.9 +/- 4.6) were not significantly different (P > .05). Optimized SSBB-EPI with SENSE proved to be feasible in patients, and the overall image quality and SNR of the liver were comparable to those achieved with the standard respiratory-triggered T2-weighted TSE sequence. (c) 2005 Wiley-Liss, Inc.

Chondromalacia patellae: an in vitro study. Comparison of MR criteria with histologic and macroscopic findings.

Science.gov (United States)

van Leersum, M; Schweitzer, M E; Gannon, F; Finkel, G; Vinitski, S; Mitchell, D G

1996-11-01

To develop MR criteria for grades of chondromalacia patellae and to assess the accuracy of these grades. Fat-suppressed T2-weighted double-echo, fat-suppressed T2-weighted fast spin echo, fat-suppressed T1-weighted, and gradient echo sequences were performed at 1.5 T for the evaluation of chondromalacia. A total of 1000 MR, 200 histologic, and 200 surface locations were graded for chondromalacia and statistically compared. Compared with gross inspection as well as with histology the most accurate sequences were fat-suppressed T2-weighted conventional spin echo and fat suppressed T2-weighted fast spin echo, although the T1-weighted and proton density images also correlated well. The most accurate MR criteria applied to the severe grades of chondromalacia, with less accurate results for lesser grades. This study demonstrates that fat-suppressed routine T2-weighted and fast spin echo T2-weighted sequences seem to be more accurate than proton density, T1-weighted, and gradient echo sequences in grading chondromalacia. Good histologic and macroscopic correlation was seen in more severe grades of chondromalacia, but problems remain for the early grades in all sequences studied.

Comparison of 3D vs. 2D fast spin echo imaging for evaluation of articular cartilage in the knee on a 3 T system scientific research

International Nuclear Information System (INIS)

Milewski, Matthew D.; Smitaman, Edward; Moukaddam, Hicham; Katz, Lee D.; Essig, David A.; Medvecky, Michael J.; Haims, Andrew H.

2012-01-01

Highlights: ► Compared 3D to 2D MR sequences for articular cartilage in the knee. ► 3D imaging acquired in a single plane, 2D acquired in 3 separate planes. ► No significant difference in accuracy between 3D and 2D sequences. - Abstract: Purpose: We sought to retrospectively compare the accuracy of a three-dimensional fat-suppressed, fast spin-echo sequences acquired in the sagittal plane, with multiplanar reconstructions to that of two-dimensional fat-suppressed, fast spin echo sequences acquired in three planes on a 3 T MR system for the evaluation of articular cartilage in the knee. Materials and methods: Our study group consisted of all patients (N = 34) that underwent 3 T MR imaging of the knee at our institution with subsequent arthroscopy over an 18-month period. There were 21 males and 13 females with an average age of 36 years. MR images were reviewed by 3 musculoskeletal radiologists, blinded to operative results. 3D and 2D sequences were reviewed at different sittings separated by 4 weeks to prevent bias. Six cartilage surfaces were evaluated both with MR imaging and arthroscopically with a modified Noyes scoring system and arthroscopic results were used as the gold standard. Sensitivity, specificity, and accuracy were calculated for each reader along with Fleiss Kappa assessment agreement between the readers. Accuracies for each articular surface were compared using a difference in proportions test with a 95% confidence interval and statistical significance was calculated using a Fisher's Exact Test. Results: Two hundred and four articular surfaces were evaluated and 49 articular cartilage lesions were present at arthroscopy. For the patellofemoral surfaces, the sensitivity, specificity, and accuracy were 76.5%, 83%, and 78.2% for the 3D sequences and were 82.3%, 76%, and 82% respectively for the 2D sequences. For the medial compartment surfaces, the sensitivity, specificity, and accuracy were 81.1%, 65.1%, and 78.5% for the 3D sequences and were

Meniscal tear evaluation. Comparison of a conventional spin-echo proton density sequence with a fast spin-echo sequence utilizing a 512x358 matrix size

International Nuclear Information System (INIS)

Hopper, M.A.; Robinson, P.; Grainger, A.J.

2011-01-01

Aim: To determine the sensitivities, specificities, and receiver-operating characteristics (ROCs) for sagittal conventional spin-echo proton density (SE-PD) and fast spin-echo proton density (FSE-PD) sequences in the diagnosis of meniscal tears when compared to arthroscopic findings utilizing increased FSE matrix acquisition size. Method and materials: Magnetic resonance imaging (MRI) studies of 97 knees (194 menisci) were independently and prospectively interpreted by two experienced musculoskeletal radiologists over four separate readings at least 3 weeks apart. Readings 1 and 2 included images in all three planes in accordance with the standard protocol with either a SE or FSE sagittal PD, at readings 3 and 4 just the SE or FSE sagittal PD sequences were reported. The FSE sequence was acquired with an increased matrix size, compared to the SE sequence, to provide increased resolution. Menisci were graded for the presence of a tear and statistical analysis to calculate sensitivity and specificity was performed comparing to arthroscopy as the reference standard. ROC analysis for the diagnosis of meniscal tears on the SE and FSE sagittal sequences was also evaluated. Reader concordance for the SE and FSE sequences was calculated. Results: Sixty-seven tears were noted at arthroscopy; 60 were detected on SE and 56 on FSE. The sensitivity and specificity for SE was 90 and 90%, and for FSE was 84 and 94%, respectively, with no significant difference. ROC analysis showed no significant difference between the two sequences and kappa values demonstrated a higher level of reader agreement for the FSE than for the SE reading. Conclusion: Use of a FSE sagittal PD sequence with an increased matrix size provides comparable performance to conventional SE sagittal PD when evaluating meniscal disease with a modern system. The present study indicates an increased level of concordance between readers for the FSE sagittal sequence compared to the conventional SE.

Meniscal tear evaluation. Comparison of a conventional spin-echo proton density sequence with a fast spin-echo sequence utilizing a 512x358 matrix size

Energy Technology Data Exchange (ETDEWEB)

Hopper, M.A.; Robinson, P. [Leeds Teaching Hospitals NHS Trust, Leeds (United Kingdom); Grainger, A.J., E-mail: andrew.grainger@leedsth.nhs.u [Leeds Teaching Hospitals NHS Trust, Leeds (United Kingdom)

2011-04-15

Aim: To determine the sensitivities, specificities, and receiver-operating characteristics (ROCs) for sagittal conventional spin-echo proton density (SE-PD) and fast spin-echo proton density (FSE-PD) sequences in the diagnosis of meniscal tears when compared to arthroscopic findings utilizing increased FSE matrix acquisition size. Method and materials: Magnetic resonance imaging (MRI) studies of 97 knees (194 menisci) were independently and prospectively interpreted by two experienced musculoskeletal radiologists over four separate readings at least 3 weeks apart. Readings 1 and 2 included images in all three planes in accordance with the standard protocol with either a SE or FSE sagittal PD, at readings 3 and 4 just the SE or FSE sagittal PD sequences were reported. The FSE sequence was acquired with an increased matrix size, compared to the SE sequence, to provide increased resolution. Menisci were graded for the presence of a tear and statistical analysis to calculate sensitivity and specificity was performed comparing to arthroscopy as the reference standard. ROC analysis for the diagnosis of meniscal tears on the SE and FSE sagittal sequences was also evaluated. Reader concordance for the SE and FSE sequences was calculated. Results: Sixty-seven tears were noted at arthroscopy; 60 were detected on SE and 56 on FSE. The sensitivity and specificity for SE was 90 and 90%, and for FSE was 84 and 94%, respectively, with no significant difference. ROC analysis showed no significant difference between the two sequences and kappa values demonstrated a higher level of reader agreement for the FSE than for the SE reading. Conclusion: Use of a FSE sagittal PD sequence with an increased matrix size provides comparable performance to conventional SE sagittal PD when evaluating meniscal disease with a modern system. The present study indicates an increased level of concordance between readers for the FSE sagittal sequence compared to the conventional SE.

SNR-optimized phase-sensitive dual-acquisition turbo spin echo imaging: a fast alternative to FLAIR.

Science.gov (United States)

Lee, Hyunyeol; Park, Jaeseok

2013-07-01

Phase-sensitive dual-acquisition single-slab three-dimensional turbo spin echo imaging was recently introduced, producing high-resolution isotropic cerebrospinal fluid attenuated brain images without long inversion recovery preparation. Despite the advantages, the weighted-averaging-based technique suffers from noise amplification resulting from different levels of cerebrospinal fluid signal modulations over the two acquisitions. The purpose of this work is to develop a signal-to-noise ratio-optimized version of the phase-sensitive dual-acquisition single-slab three-dimensional turbo spin echo. Variable refocusing flip angles in the first acquisition are calculated using a three-step prescribed signal evolution while those in the second acquisition are calculated using a two-step pseudo-steady state signal transition with a high flip-angle pseudo-steady state at a later portion of the echo train, balancing the levels of cerebrospinal fluid signals in both the acquisitions. Low spatial frequency signals are sampled during the high flip-angle pseudo-steady state to further suppress noise. Numerical simulations of the Bloch equations were performed to evaluate signal evolutions of brain tissues along the echo train and optimize imaging parameters. In vivo studies demonstrate that compared with conventional phase-sensitive dual-acquisition single-slab three-dimensional turbo spin echo, the proposed optimization yields 74% increase in apparent signal-to-noise ratio for gray matter and 32% decrease in imaging time. The proposed method can be a potential alternative to conventional fluid-attenuated imaging. Copyright © 2012 Wiley Periodicals, Inc.

Diffusion-weighted echo-planar MRI of lacunar infarcts

International Nuclear Information System (INIS)

Noguchi, K.; Nagayoshi, T.; Watanabe, N.; Kanazawa, T.; Toyoshima, S.; Morijiri, M.; Shojaku, H.; Shimizu, M.; Seto, H.

1998-01-01

We studied 35 patients with lacunar infarcts, using diffusion-weighted echo-planar imaging (DW-EPI) at 1.5 T. The relative apparent diffusion coefficient ratio (ADCR) of each lesion was calculated and lesion conspicuity on DW-EPI was compared to that on images aquired with fast fluid-attenuated inversion recovery and T2-weighted fast spin-echo sequences. Acute small infarcts (within 3 days) were identified with DW-EPI as an area of decreased ADCR (range 0.33-0.87; mean 0.67) and high signal, subacute small infarcts (4-30 days) as a high-signal or isointense areas of decreased or nearly normal ADCR (0.54-0.98; 0.73), and chronic small infarcts (> 30 days) as low- or high-signal areas of nearly normal or increased ADCR (0.97-1.92; 1.32). In three patients, small infarcts of the brain stem in the hyperacute phase (within 6 h) were seen only with DW-EPI. In five patients, fresh small infarcts adjacent to multiple old infarcts could be distinguished only with DW-EPI. (orig.)

On the factors controlling occurrence of F-region coherent echoes

Directory of Open Access Journals (Sweden)

D. W. Danskin

2002-09-01

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

Large Airborne Full Tensor Gradient Data Inversion Based on a Non-Monotone Gradient Method

Science.gov (United States)

Sun, Yong; Meng, Zhaohai; Li, Fengting

2018-03-01

Following the development of gravity gradiometer instrument technology, the full tensor gravity (FTG) data can be acquired on airborne and marine platforms. Large-scale geophysical data can be obtained using these methods, making such data sets a number of the "big data" category. Therefore, a fast and effective inversion method is developed to solve the large-scale FTG data inversion problem. Many algorithms are available to accelerate the FTG data inversion, such as conjugate gradient method. However, the conventional conjugate gradient method takes a long time to complete data processing. Thus, a fast and effective iterative algorithm is necessary to improve the utilization of FTG data. Generally, inversion processing is formulated by incorporating regularizing constraints, followed by the introduction of a non-monotone gradient-descent method to accelerate the convergence rate of FTG data inversion. Compared with the conventional gradient method, the steepest descent gradient algorithm, and the conjugate gradient algorithm, there are clear advantages of the non-monotone iterative gradient-descent algorithm. Simulated and field FTG data were applied to show the application value of this new fast inversion method.

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.

Dynamic MR imaging of cavernous hemangioma with Gd-DTPA

International Nuclear Information System (INIS)

Luning, M.; Wolf, K.J.; Hamm, B.; Dewey, C.; Koch, M.; Taupitz, M.; Schnackenburg, B.; Schneider, T.; Petersein, J.; Muhler, A.; Haustein, J.

1990-01-01

This paper evaluates the use of gradient-echo, fast-field-echo (FFE), breathhold MR imaging in The characterization of liver tumors. The authors examined 32 hepatic hemangiomas with a 1.5-T imager using T1-weighted (500/15) and T2-weighted (2,480/100) spin-echo sequences, and multi-echo sequences (2,000/30,60,90...240); also, after intravenous administration of Gd-DTPA (0.2 mmol/kg), gradient-echo, FFE, breathhold images (27/13/60 degrees) were obtained. We evaluated the relationship of peripheral and central enhancement to the size of the lesion in 22 hemangiomas

Bilateral mesial temporal sclerosis: MRI with high-resolution fast spin-echo and fluid-attenuated inversion-recovery sequences

Energy Technology Data Exchange (ETDEWEB)

Oppenheim, C.; Dormont, D.; Lehericy, S.; Marsault, C. [Dept. of Neuroradiology, Groupe Hospitalier Pite-Salpetriere, Paris (France); Hasboun, D. [Dept. of Neuroradiology, Groupe Hospitalier Pite-Salpetriere, Paris (France)]|[Dept. of Neurology, Paris VI Univ. (France); Bazin, B.; Samson, S.; Baulac, M. [Dept. of Neurology, Paris VI Univ. (France)

1999-07-01

We report a retrospective analysis of MRI in 206 patients with intractable seizures and describe the findings in bilateral mesial temporal sclerosis (MTS) on fast spin-echo (FSE) and fast fluid-attenuated inversion-recovery (fFLAIR) sequences. Criteria for MTS were atrophy, signal change and loss of the digitations of the head of the hippocampus. In patients with bilateral MRI signs of MTS, correlation with clinical electro, volumetric MRI data and neuropsychological tests, when available, was performed. Bilateral MTS was observed in seven patients. Bilateral loss of the digitations and signal change of fFLAIR was seen in all seven. In three, bilateral atrophy was obvious. In two patients, mild bilateral atrophy was observed and in two others, the hippocampi were: asymmetrical, with obvious atrophy on only one side. Volumetric data confirmed bilateral symmetrical atrophy in five patients, and volumes were at the lowest of the normal range in other two. The EEG showed temporal abnormalities in all patients, unilateral in five and bilateral in two. All patients had memory impairment and neuropsychological data confirmed visual and verbal memory deficits; two patients failed the Wada test on both sides. High-resolution T2-weighted FSE and fFLAIR sequences allow diagnosis of bilateral MTS, which has important therapeutic and prognostic implications. (orig.)

Bilateral mesial temporal sclerosis: MRI with high-resolution fast spin-echo and fluid-attenuated inversion-recovery sequences

International Nuclear Information System (INIS)

Oppenheim, C.; Dormont, D.; Lehericy, S.; Marsault, C.; Hasboun, D.; Bazin, B.; Samson, S.; Baulac, M.

1999-01-01

We report a retrospective analysis of MRI in 206 patients with intractable seizures and describe the findings in bilateral mesial temporal sclerosis (MTS) on fast spin-echo (FSE) and fast fluid-attenuated inversion-recovery (fFLAIR) sequences. Criteria for MTS were atrophy, signal change and loss of the digitations of the head of the hippocampus. In patients with bilateral MRI signs of MTS, correlation with clinical electro, volumetric MRI data and neuropsychological tests, when available, was performed. Bilateral MTS was observed in seven patients. Bilateral loss of the digitations and signal change of fFLAIR was seen in all seven. In three, bilateral atrophy was obvious. In two patients, mild bilateral atrophy was observed and in two others, the hippocampi were: asymmetrical, with obvious atrophy on only one side. Volumetric data confirmed bilateral symmetrical atrophy in five patients, and volumes were at the lowest of the normal range in other two. The EEG showed temporal abnormalities in all patients, unilateral in five and bilateral in two. All patients had memory impairment and neuropsychological data confirmed visual and verbal memory deficits; two patients failed the Wada test on both sides. High-resolution T2-weighted FSE and fFLAIR sequences allow diagnosis of bilateral MTS, which has important therapeutic and prognostic implications. (orig.)

Contrast-enhanced MR venography of the head using magnetization prepared rapid gradient echo imaging. Comparison between head and body radiofrequency transmitter coil systems

International Nuclear Information System (INIS)

Matsunobu, Satosi; Amanuma, Makoto; Tsukuda, Shunji

2004-01-01

The purpose of this study was to evaluate the image quality and vascular selectivity of MR venography of the head using an magnetization prepared rapid gradient echo (MP-RAGE) technique when obtained with a body radiofrequency transmitter coil system. A total of 24 patients were imaged with a head or body radiofrequency (RF) transmission system. Subtraction MR angiography (MRA) was processed with 0.1 mmol Gd-DTPA administration, and signal-to-noise ratios of the vascular system were measured. Venous demonstration and selectivity were also assessed. MP-RAGE MR venography with a body transmission system showed almost the same signal intensity for the venous and arterial systems, resulting in nonspecific vascular demonstration, while the head transmission system showed semi-selective venograms owing to inflow-induced high signal on precontrast images. However, MRA with a body transmission system provided a 1.5- to 2.5-fold higher signal-to-noise ratios based on higher gradient performance and excellent demonstration of the head veins, especially those below the skull base. Although selective venography was difficult, MRA with a body transmission coil provided excellent vascular images of the brain. (author)

Evaluation of iron colloid-enhanced T{sub 2}-weighted fast MR imaging of hepatocellular carcinoma. Comparison of SE, TSE and TGSE sequences

Energy Technology Data Exchange (ETDEWEB)

Sugihara, Shuji; Suto, Yuji; Kamba, Masayuki; Yoshida, Kotarou; Ohta, Yoshio [Tottori Univ., Yonago (Japan). Faculty of Medicine

1996-06-01

We have applied chondroitin sulfate iron colloid (CSIC) as a contrast agent for MRI in detecting hepatocellular carcinoma (HCC) on conventional spin-echo sequences (SE). In this report, we evaluated CSIC-enhanced T{sub 2}-weighted fast MR imaging of HCC. MR imaging were performed before and after i.v. administration of CSIC in 15 patients with 46 HCCs. T{sub 2}-weighted SE (1800/80/2, 210 x 256 matrix), T{sub 2}-weighted turbo spin-echo (TSE1800) (1800/90/5, echo train length=7, 252 x 256 matrix), TSE (3500/90/5, echo train length=7, 252 x 256 matrix) (TSE7), TSE (3500/99/5, echo train length=11, 242 x 256 matrix) (TSE11) and T{sub 2}-weighted turbo-gradient spine-echo (TGSE) (4500/108/4, echo train length=33, 252 x 256 matrix) images were compared quantitatively and qualitatively. In all sequences, liver signal-to-noise ratio (SNR) was significantly decreased and lesion-to-liver contrast-to-noise ratio (CNR) was significantly increased after CSIC administration. Although decreased ratio in liver and tumor SNR caused by CSIC was smaller on TSE sequences compared with SE and TGSE, increased ratio in lesion-to-liver CNR was largest on TSE7. Either before or after i.v. administration of CSIC, the number of detectable lesions was largest on TSE7. TSE with used longer TR, TE and decreased echo factor was useful method for CSIC-enhanced abdominal MR imaging. (author)

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.

Differential diagnosis of pituitary adenomas and Rathke's cleft cysts by diffusion-weighted MRI using single-shot fast spin echo technique

International Nuclear Information System (INIS)

Abe, Takumi; Izumiyama, Hitoshi; Fukuda, Ataru; Tanioka, Daisuke; Kunii, Norihiko; Komatsu, Daisuke; Fujita, Shogo; Ukisu, Ryutaro; Moritani, Toshio

2002-01-01

The purpose of the present study was to prospectively evaluate the diagnostic ability of diffusion-weighted magnetic resonance imaging (DWI) using single-shot fast spin echo (SSFSE) technique to discriminate pituitary adenomas from Rathke's cleft cysts. DWIs were obtained from 40 patients with pathologically proven pituitary macroadenomas and 15 patients with proven Rathke's cleft cysts. Pituitary adenomas were divided into 27 cases with solid components alone, five with non-hemorrhagic large cysts, and eight with intratumoral hemorrhage. On SSFSE DWI, solid components of pituitary adenomas revealed iso or slightly increased intensity and intratumoral hemorrhage showed higher intensity than normal brain parenchyma, whereas Rathke's cleft cysts and intratumoral cysts demonstrated very low intensity. SSFSE DWI did not display the susceptibility artifacts that are seen close to the skull base and sinonasal cavities on echo planar diffusion imaging. On the basis of our preliminary findings, DWI may enable us to differentiate pituitary adenomas with only solid components and hemorrhagic pituitary adenomas appearing hyperintense on T1-weighted images from Rathke's cleft cysts without administration of gadolinium-DTPA. SSFSE DWI appears to be a useful technique for characterizing pituitary diseases without the susceptibility artifacts. Our study is the first report to demonstrate the identification of pituitary disorders on SSFSE DWI. (author)

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

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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.)

Chondromalacia patellae: an in vitro study. Comparison of MR criteria with histologic and macroscopic findings

International Nuclear Information System (INIS)

Leersum, M. van; Schweitzer, M.E.; Gannon, F.; Finkel, G.; Vinitski, S.; Mitchell, D.G.

1996-01-01

Objective. To develop MR criteria for grades of chondromalacia patellae and to assess the accuracy of these grades. Design. Fat-suppressed T2-weighted double-echo, fat-suppressed T2-weighted fast spin echo, fat-suppressed T1-weighted, and gradient echo sequences were performed at 1.5 T for the evaluation of chondromalacia. A total of 1000 MR, 200 histologic, and 200 surface locations were graded for chondromalacia and statistically compared. Results. Compared with gross inspection as well as with histology the most accurate sequences were fat-suppressed T2-weighted conventional spin echo and fat suppressed T2-weighted fast spin echo, although the T1-weighted and proton density images also correlated well. The most accurate MR criteria applied to the severe grades of chondromalacia, with less accurate results for lesser grades. Conclusions. This study demonstrates that fat-suppressed routine T2-weighted and fast spin echo T2-weighted sequences seem to be more accurate than proton density, T1-weighted, and gradient echo sequences in grading chondromalacia. Good histologic and macroscopic correlation was seen in more severe grades of chondromalacia, but problems remain for the early grades in all sequences studied. (orig.). With 2 figs., 3 tabs

Chondromalacia patellae: an in vitro study. Comparison of MR criteria with histologic and macroscopic findings

Energy Technology Data Exchange (ETDEWEB)

Leersum, M. van [Department of Radiology, Thomas Jefferson University Hospital, Philadelphia, PA (United States); Schweitzer, M.E. [Department of Radiology, Thomas Jefferson University Hospital, Philadelphia, PA (United States); Gannon, F. [Department of Pathology, Thomas Jefferson University Hospital, Philadelphia, PA (United States); Finkel, G. [Department of Pathology, Thomas Jefferson University Hospital, Philadelphia, PA (United States); Vinitski, S. [Department of Radiology, Thomas Jefferson University Hospital, Philadelphia, PA (United States); Mitchell, D.G. [Department of Radiology, Thomas Jefferson University Hospital, Philadelphia, PA (United States)

1996-11-01

Objective. To develop MR criteria for grades of chondromalacia patellae and to assess the accuracy of these grades. Design. Fat-suppressed T2-weighted double-echo, fat-suppressed T2-weighted fast spin echo, fat-suppressed T1-weighted, and gradient echo sequences were performed at 1.5 T for the evaluation of chondromalacia. A total of 1000 MR, 200 histologic, and 200 surface locations were graded for chondromalacia and statistically compared. Results. Compared with gross inspection as well as with histology the most accurate sequences were fat-suppressed T2-weighted conventional spin echo and fat suppressed T2-weighted fast spin echo, although the T1-weighted and proton density images also correlated well. The most accurate MR criteria applied to the severe grades of chondromalacia, with less accurate results for lesser grades. Conclusions. This study demonstrates that fat-suppressed routine T2-weighted and fast spin echo T2-weighted sequences seem to be more accurate than proton density, T1-weighted, and gradient echo sequences in grading chondromalacia. Good histologic and macroscopic correlation was seen in more severe grades of chondromalacia, but problems remain for the early grades in all sequences studied. (orig.). With 2 figs., 3 tabs.

Rotation commensurate echo of asymmetric molecules—Molecular fingerprints in the time domain

Energy Technology Data Exchange (ETDEWEB)

Chesnokov, E. N., E-mail: chesnok@kinetics.nsc.ru [Institute of Chemical Kinetics and Combustion, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Kubarev, V. V. [Budker Institute of Nuclear Physics, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Koshlyakov, P. V. [Institute of Chemical Kinetics and Combustion, Novosibirsk 630090 (Russian Federation)

2014-12-29

Using the pulses of terahertz free electron laser and ultra-fast Schottky diode detectors, we observed the coherent transients within a free induction decay of gaseous nitrogen dioxide NO{sub 2}. The laser excited different sub-bands of rotation spectra of NO{sub 2} containing about 50–70 lines. The free induction signal continued more than 30 ns and consisted of many echo-like bursts duration about 0.2 ns. Unlike the similar effect observed previously for linear and symmetric top molecules, the sequence of echo bursts is not periodic. The values for delay of individual echo are stable, and the set of these delays can be considered as a “molecular fingerprint” in the time domain.

Initial study of stability and repeatability of measuring R2' and oxygen extraction fraction values in the healthy brain with gradient-echo sampling of spin-echo sequence

International Nuclear Information System (INIS)

Hui Lihong; Zhang Xiaodong; He Chao; Xie Sheng; Xiao Jiangxi; Zhang jue; Wang Xiaoying; Jiang Xuexiang

2010-01-01

Objective: To evaluate the stability and repeatability of gradient-echo sampling of spin- echo (GESSE) sequence in measuring the R 2 ' value in volunteers, by comparison with traditional GRE sequence (T 2 * ]nap and T 2 map). Methods: Eight normal healthy volunteers were enrolled in this study and written informed consents were obtained from all subjects. MR scanning including sequences of GESSE, T 2 map and T 2 * map were performed in these subjects at resting status. The same protocol was repeated one day later. Raw data from GESSE sequence were transferred to PC to conduct postprocessing with the software built in house. R 2 ' map and OEF map were got consequently. To obtain quantitative R 2 ' and OEF values in the brain parenchyma, six ROIs were equally placed in the anterior, middle and posterior part of bilateral hemispheres. Both mean and standard deviation of R 2 ' and OEF were recorded. All images from T 2 * map and T 2 map were transferred to the Workstation for postprocessing. The ROIs were put at the same areas as those for GESSE sequence. R 2 ' is defined as R 2 ' = R 2 * - R 2 , R 2 * = 1/T 2 * . The R 2 ' value of GESSE sequence were compared with that of GRE sequence. Results: The mean R 2 ' values of GESSE at the first and second scan and those of the GRE were (4.21±0.92), (4.45±0.94) Hz and (7.37±1.47), (6.42±2.33) Hz respectively. The mean OEF values of GESSE at the first and second scan is 0.327±0.036 and 0.336± 0.035 respectively. The R 2 ' value and OEF value obtained from GESSE were not significantly different between the first and second scan (t=-0.83, -1.48, P>0.05). The R 2 ' value of first GRE imaging had significantly statistical difference from that of second GRE imaging (t=1.80, P 2 ' value of GESSE sequence was less than that of GRE sequence, and there was significantly statistical difference between them (t=1.71, P<0.05). Conclusion: The GESSE sequence has good stability and repeatability with promising clinical practicability

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

International Nuclear Information System (INIS)

Drejer, J.; Thomsen, H.S.; Tanttu, J.

1995-01-01

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)

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).

MRI in multiple sclerosis of the spinal cord: evaluation of fast short-tan inversion-recovery and spin-echo sequences

International Nuclear Information System (INIS)

Dietemann, J.L.; Thibaut-Menard, A.; Neugroschl, C.; Gillis, C.; Abu Eid, M.; Bogorin, A.; Warter, J.M.; Tranchant, C.

2000-01-01

We compared the sensitivity of T2-weighted spin-echo (FSE) and fast short-tau inversion-recovery (fSTIR) sequences in detection of multiple sclerosis of the spinal cord in 100 consecutive patients with clinically confirmed multiple sclerosis (MS); 86 patients underwent also brain MRI. In all, 310 focal lesions were detected on fSTIR and 212 on T2-weighted FSE, spinal cord lesions were seen better on fSTIR images, with a higher contrast between the lesion and the normal spinal cord. In 24 patients in whom cord plaques were shown with both sequences, the cranial study was normal or inconclusive. Assessment of spinal plaques can be particularly important when MRI of the brain is inconclusive, and in there situations fSTIR can be helpful. (orig.)

Free-breathing black-blood CINE fast-spin echo imaging for measuring abdominal aortic wall distensibility: a feasibility study

Science.gov (United States)

Lin, Jyh-Miin; Patterson, Andrew J.; Chao, Tzu-Cheng; Zhu, Chengcheng; Chang, Hing-Chiu; Mendes, Jason; Chung, Hsiao-Wen; Gillard, Jonathan H.; Graves, Martin J.

2017-05-01

The paper reports a free-breathing black-blood CINE fast-spin echo (FSE) technique for measuring abdominal aortic wall motion. The free-breathing CINE FSE includes the following MR techniques: (1) variable-density sampling with fast iterative reconstruction; (2) inner-volume imaging; and (3) a blood-suppression preparation pulse. The proposed technique was evaluated in eight healthy subjects. The inner-volume imaging significantly reduced the intraluminal artifacts of respiratory motion (p  =  0.015). The quantitative measurements were a diameter of 16.3  ±  2.8 mm and wall distensibility of 2.0  ±  0.4 mm (12.5  ±  3.4%) and 0.7  ±  0.3 mm (4.1  ±  1.0%) for the anterior and posterior walls, respectively. The cyclic cross-sectional distensibility was 35  ±  15% greater in the systolic phase than in the diastolic phase. In conclusion, we developed a feasible CINE FSE method to measure the motion of the abdominal aortic wall, which will enable clinical scientists to study the elasticity of the abdominal aorta.

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: FS - Medical Facilities ; Equipment OBOR OECD: Medical engineering Impact factor: 2.225, year: 2016

Evaluation with fat-suppression fast spin-echo T2-weighted images for bone and soft tissue disorders

International Nuclear Information System (INIS)

Kakitsubata, Yousuke; Watanabe, Katsushi; Kakitsubata, Sachiko; Shimizu, Tokiyoshi.

1997-01-01

One hundred and sixty-four magnetic resonance (MR) studies of bone or soft tissue disorders were evaluated with T2-weighted fast spin echo (FSE) imaging and T2-weighted fat-suppressed FSE (FS-FSE) imaging. Fifty-two patients with bone contusion of the knee were also evaluated with conventional T2-weighted SE imaging and T2-weighted FS-FSE imaging. In 50 of 71 patients (70.4%), areas of high signal intensity in bone marrow were more clearly demonstrated on T2-weighted FS-FSE images than on T2-weighted FSE image. Edema or inflammation of soft tissues were also clearly revealed on T2-weighted FS-FSE images. In 27 of 32 patients (84%), bone contusions were more apparently shown on T2-weighted FS-FSE images than on conventional T2-weighted SE image. T2-weighted FS-FSE imaging is a sensitive method of evaluating the long T2 lesions of bone or soft tissue disorders. (author)

Accelerated whole brain intracranial vessel wall imaging using black blood fast spin echo with compressed sensing (CS-SPACE).

Science.gov (United States)

Zhu, Chengcheng; Tian, Bing; Chen, Luguang; Eisenmenger, Laura; Raithel, Esther; Forman, Christoph; Ahn, Sinyeob; Laub, Gerhard; Liu, Qi; Lu, Jianping; Liu, Jing; Hess, Christopher; Saloner, David

2018-06-01

Develop and optimize an accelerated, high-resolution (0.5 mm isotropic) 3D black blood MRI technique to reduce scan time for whole-brain intracranial vessel wall imaging. A 3D accelerated T 1 -weighted fast-spin-echo prototype sequence using compressed sensing (CS-SPACE) was developed at 3T. Both the acquisition [echo train length (ETL), under-sampling factor] and reconstruction parameters (regularization parameter, number of iterations) were first optimized in 5 healthy volunteers. Ten patients with a variety of intracranial vascular disease presentations (aneurysm, atherosclerosis, dissection, vasculitis) were imaged with SPACE and optimized CS-SPACE, pre and post Gd contrast. Lumen/wall area, wall-to-lumen contrast ratio (CR), enhancement ratio (ER), sharpness, and qualitative scores (1-4) by two radiologists were recorded. The optimized CS-SPACE protocol has ETL 60, 20% k-space under-sampling, 0.002 regularization factor with 20 iterations. In patient studies, CS-SPACE and conventional SPACE had comparable image scores both pre- (3.35 ± 0.85 vs. 3.54 ± 0.65, p = 0.13) and post-contrast (3.72 ± 0.58 vs. 3.53 ± 0.57, p = 0.15), but the CS-SPACE acquisition was 37% faster (6:48 vs. 10:50). CS-SPACE agreed with SPACE for lumen/wall area, ER measurements and sharpness, but marginally reduced the CR. In the evaluation of intracranial vascular disease, CS-SPACE provides a substantial reduction in scan time compared to conventional T 1 -weighted SPACE while maintaining good image quality.

Time efficient whole-brain coverage with MR Fingerprinting using slice-interleaved echo-planar-imaging.

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Rieger, Benedikt; Akçakaya, Mehmet; Pariente, José C; Llufriu, Sara; Martinez-Heras, Eloy; Weingärtner, Sebastian; Schad, Lothar R

2018-04-27

Magnetic resonance fingerprinting (MRF) is a promising method for fast simultaneous quantification of multiple tissue parameters. The objective of this study is to improve the coverage of MRF based on echo-planar imaging (MRF-EPI) by using a slice-interleaved acquisition scheme. For this, the MRF-EPI is modified to acquire several slices in a randomized interleaved manner, increasing the effective repetition time of the spoiled gradient echo readout acquisition in each slice. Per-slice matching of the signal-trace to a precomputed dictionary allows the generation of T 1 and T 2 * maps with integrated B 1 + correction. Subsequent compensation for the coil sensitivity profile and normalization to the cerebrospinal fluid additionally allows for quantitative proton density (PD) mapping. Numerical simulations are performed to optimize the number of interleaved slices. Quantification accuracy is validated in phantom scans and feasibility is demonstrated in-vivo. Numerical simulations suggest the acquisition of four slices as a trade-off between quantification precision and scan-time. Phantom results indicate good agreement with reference measurements (Difference T 1 : -2.4 ± 1.1%, T 2 *: -0.5 ± 2.5%, PD: -0.5 ± 7.2%). In-vivo whole-brain coverage of T 1 , T 2 * and PD with 32 slices was acquired within 3:36 minutes, resulting in parameter maps of high visual quality and comparable performance with single-slice MRF-EPI at 4-fold scan-time reduction.

ECHO Gov Login | 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.

Comparison of third-order plasma wave echoes with ballistic second-order plasma wave echoes

International Nuclear Information System (INIS)

Leppert, H.D.; Schuelter, H.; Wiesemann, K.

1982-01-01

The apparent dispersion of third-order plasma wave echoes observed in a high frequency plasma is compared with that of simultaneously observed ballistic second-order echoes. Amplitude and wavelength of third-order echoes are found to be always smaller than those of second-order echoes, however, the dispersion curves of both types of echoes are very similar. These observations are in qualitative agreement with calculations of special ballistic third-order echoes. The ballistic nature of the observed third-order echoes may, therefore, be concluded from these measurements. (author)

Gradient pre-emphasis to counteract first-order concomitant fields on asymmetric MRI gradient systems.

Science.gov (United States)

Tao, Shengzhen; Weavers, Paul T; Trzasko, Joshua D; Shu, Yunhong; Huston, John; Lee, Seung-Kyun; Frigo, Louis M; Bernstein, Matt A

2017-06-01

To develop a gradient pre-emphasis scheme that prospectively counteracts the effects of the first-order concomitant fields for any arbitrary gradient waveform played on asymmetric gradient systems, and to demonstrate the effectiveness of this approach using a real-time implementation on a compact gradient system. After reviewing the first-order concomitant fields that are present on asymmetric gradients, we developed a generalized gradient pre-emphasis model assuming arbitrary gradient waveforms to counteract their effects. A numerically straightforward, easily implemented approximate solution to this pre-emphasis problem was derived that was compatible with the current hardware infrastructure of conventional MRI scanners for eddy current compensation. The proposed method was implemented on the gradient driver subsystem, and its real-time use was tested using a series of phantom and in vivo data acquired from two-dimensional Cartesian phase-difference, echo-planar imaging, and spiral acquisitions. The phantom and in vivo results demonstrated that unless accounted for, first-order concomitant fields introduce considerable phase estimation error into the measured data and result in images with spatially dependent blurring/distortion. The resulting artifacts were effectively prevented using the proposed gradient pre-emphasis. We have developed an efficient and effective gradient pre-emphasis framework to counteract the effects of first-order concomitant fields of asymmetric gradient systems. Magn Reson Med 77:2250-2262, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

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

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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.

Application of diffusion-weighted echo planar imaging for diagnosis of small acute and subacute brain ischemic lesions

International Nuclear Information System (INIS)

Enomoto, Kyoko; Watanabe, Tsuneya; Amanuma, Makoto; Heshiki, Atsuko

1997-01-01

The aim of this study was to determine the utility of diffusion-weighted echo planar imaging (DW-EPI) for detecting acute and subacute brain ischemic foci less than 2 cm in size. Thirty patients underwent DW-EPI on a 1.5 T super-conducting unit using a SE-EPI sequence with an arbitrary pair of Stejskal-Tanner gradients applied along the imaging axes. DW-EPI demonstrated all the mast recent ischemic lesions as areas of decreased diffusion, providing greater conspicuity and larger size than conventional spin-echo imaging. DW-EPI is a promising method to detect within a subsecond early ischemia and reversible ischemic changes that are not demonstrate on routine spin-echo images. (author)

Slow flow and mural thrombus in aortic diseases: Spin-echo MR findings and their differentiation

International Nuclear Information System (INIS)

Chung, Jin Wook; Park, Jae Hyung; Han, Man Chung

1993-01-01

In order to evaluate the ability of spin-echo MR imaging to differentiate slow flow from mural thrombus in aortic diseases, we reviewed the spin-echo MR images of 13 patients with intraaortic thrombus documented by CT (N=11) or aortography (N=2). Six patients had aortic aneurysms and seven had aortic dissections. Intraaortic mural thrombi were accompanied by flow-related intraluminal signal of various pattern and extents in all 13 patients. On 10 gated MR studies, slow flow regions showed ever-echo rephasing phenomenon (N=8), interslice variation of signal intensities of the intraluminal signal (N=7) and flow-related ghost artifact (N=2). However, these MR flow phenomena were obscured on two of three non-gated studies. Seven of 13 intraaortic thrombi remained hyperintense on T2-weighted second-echo images. In these circumstance, a hypointense boundary layer between slow flow and mural thrombus, which was caused by either ' boundary layer dephasing phenomenon' of slow flow or 'paramagnetic T2 shortening' of fresh clot at the edge of mural thrombus, was very useful in discriminating the area of slow flow from that of mural thrombus. Proper interpretation of spin-echo MR images may obviate the need for phase display imaging or gradient-echo imaging in differentiating slow flow and mural thrombus

ECHO virus

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... 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 ...

Comparative study between the Spin-echo and 3-D fast imaging techniques in the Knee evaluation with magnetic resonance

International Nuclear Information System (INIS)

Oleaga Zufiria, L.; Ibanez Zubiarrain, A.; Grande Icaran, J.; Vela Martin, A.C.; Cintora Leon, E.; Grau Garcia, M.; Grande Icaran, D.

1993-01-01

We have carried out a retrospective analysis of the results of magnetic resonance (MR) studies in 20 patients, comparing two different sequences. We compared a 2-D spin-echo (SE2D) sequence with a 3-D fast imaging with steady-state precession (FISP3D) sequence in the attempt to compare the reliability of each in the detection of knee injuries. Arthroscopy was employed as a control technique. Our study revealed no statistically significant difference between the two sequences, although the overall sensitivity for the detection of meniscal lesions was slightly greater with the FISP3D sequence; however, the reliability in the detection of ruptures of the posterior cruciate ligament is less with this sequence than with the SE2D sequence. Both sequences showed very low sensitivity in the detection of hyaline cartilage injuries. (Author) 14 refs

Qualitative and quantitative assessment of wrist MRI at 3.0T - Comparison between isotropic 3D turbo spin echo and isotropic 3D fast field echo and 2D turbo spin echo

International Nuclear Information System (INIS)

Jung, Jee Young; Yoon, Young Cheol; Jung, Jin Young; Choe, Bong-Keun

2013-01-01

Background: Isotropic three-dimensional (3D) magnetic resonance imaging (MRI) has been applied to various joints. However, comparison for image quality between isotropic 3D MRI and two-dimensional (2D) turbo spin echo (TSE) sequence of the wrist at a 3T MR system has not been investigated. Purpose: To compare the image quality of isotropic 3D MRI including TSE intermediate-weighted (VISTA) sequence and fast field echo (FFE) sequence with 2D TSE intermediate-weighted sequence of the wrist joint at 3.0 T. Material and Methods: MRI was performed in 10 wrists of 10 healthy volunteers with isotropic 3D sequences (VISTA and FFE) and 2D TSE intermediate-weighted sequences at 3.0 T. The signal-to-noise ratio (SNR) was obtained by imaging phantom and noise-only image. Contrast ratios (CRs) were calculated between fluid and cartilage, triangular fibrocartilage complex (TFCC), and the scapholunate ligament. Two radiologists independently assessed the visibility of TFCC, carpal ligaments, cartilage, tendons and nerves with a four-point grading scale. Statistical analysis to compare CRs (one way ANOVA with a Tukey test) and grades of visibility (Kruskal-Wallis test) between three sequences and those for inter-observer agreement (kappa analysis) were performed. Results: The SNR of 2D TSE (46.26) was higher than those of VISTA (23.34) and 3D FFE (19.41). CRs were superior in 2D TSE than VISTA (P = 0.02) for fluid-cartilage and in 2D TSE than 3D FFE (P < 0.01) for fluid-TFCC. The visibility was best in 2D TSE (P < 0.01) for TFCC and in VISTA (P = 0.01) for scapholunate ligament. The visibility was better in 2D TSE and 3D FFE (P 0.04) for cartilage and in VISTA than 3D FFE (P < 0.01) for TFCC. The inter-observer agreement for the visibility of anatomic structures was moderate or substantial. Conclusion: Image quality of 2D TSE was superior to isotropic 3D MR imaging for cartilage, and TFCC. 3D FFE has better visibility for cartilage than VISTA and VISTA has superior visibility for

Qualitative and quantitative assessment of wrist MRI at 3.0T - Comparison between isotropic 3D turbo spin echo and isotropic 3D fast field echo and 2D turbo spin echo

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Jung, Jee Young [Dept. of Radiology, Chungang Univ. Hospital, School of Medicine, Chungang Univ. (Korea, Republic of); Yoon, Young Cheol [Dept. of Radiology, Samsung Medical Center, School of Medicine, Sungkyunkwan Univ. (Korea, Republic of)], e-mail: ycyoon@skku.edu; Jung, Jin Young [Dept. of Radiology, Saint Paul' s Hospital, The Catholic Univ. (Korea, Republic of); Choe, Bong-Keun [Dept. of Preventive Medicine, School of Medicine, Kyung Hee Univ., Seoul (Korea, Republic of)

2013-04-15

Background: Isotropic three-dimensional (3D) magnetic resonance imaging (MRI) has been applied to various joints. However, comparison for image quality between isotropic 3D MRI and two-dimensional (2D) turbo spin echo (TSE) sequence of the wrist at a 3T MR system has not been investigated. Purpose: To compare the image quality of isotropic 3D MRI including TSE intermediate-weighted (VISTA) sequence and fast field echo (FFE) sequence with 2D TSE intermediate-weighted sequence of the wrist joint at 3.0 T. Material and Methods: MRI was performed in 10 wrists of 10 healthy volunteers with isotropic 3D sequences (VISTA and FFE) and 2D TSE intermediate-weighted sequences at 3.0 T. The signal-to-noise ratio (SNR) was obtained by imaging phantom and noise-only image. Contrast ratios (CRs) were calculated between fluid and cartilage, triangular fibrocartilage complex (TFCC), and the scapholunate ligament. Two radiologists independently assessed the visibility of TFCC, carpal ligaments, cartilage, tendons and nerves with a four-point grading scale. Statistical analysis to compare CRs (one way ANOVA with a Tukey test) and grades of visibility (Kruskal-Wallis test) between three sequences and those for inter-observer agreement (kappa analysis) were performed. Results: The SNR of 2D TSE (46.26) was higher than those of VISTA (23.34) and 3D FFE (19.41). CRs were superior in 2D TSE than VISTA (P = 0.02) for fluid-cartilage and in 2D TSE than 3D FFE (P < 0.01) for fluid-TFCC. The visibility was best in 2D TSE (P < 0.01) for TFCC and in VISTA (P = 0.01) for scapholunate ligament. The visibility was better in 2D TSE and 3D FFE (P 0.04) for cartilage and in VISTA than 3D FFE (P < 0.01) for TFCC. The inter-observer agreement for the visibility of anatomic structures was moderate or substantial. Conclusion: Image quality of 2D TSE was superior to isotropic 3D MR imaging for cartilage, and TFCC. 3D FFE has better visibility for cartilage than VISTA and VISTA has superior visibility for

Detection and Elimination of Oncogenic Signaling Networks in Premalignant and Malignant Cells with Magnetic Resonance Imaging

Science.gov (United States)

2015-10-01

proton resonance frequency TR- relaxation time GRE- gradient echo MT- magnetization transfer 6 FSE- fast spin echo 7 3. Overall Progress Summary...support project. – SBA certified 8(a)/Small Disadvantaged Business, HUBZone, and 8(m)/Economically Disadvantaged Woman owned, technology services

Detection and Elimination of Oncogenic Signalling Networks in Premalignant and Malignant Cells with Magnetic Resonance Imaging

Science.gov (United States)

2015-10-01

proton resonance frequency TR- relaxation time GRE- gradient echo MT- magnetization transfer 6 FSE- fast spin echo 7 3. Overall Progress Summary...support project. – SBA certified 8(a)/Small Disadvantaged Business, HUBZone, and 8(m)/Economically Disadvantaged Woman owned, technology services

3D hybrid profile order technique in a single breath-hold 3D T2-weighted fast spin-echo sequence: Usefulness in diagnosis of small liver lesions.

Science.gov (United States)

Hirata, Kenichiro; Nakaura, Takeshi; Okuaki, Tomoyuki; Tsuda, Noriko; Taguchi, Narumi; Oda, Seitaro; Utsunomiya, Daisuke; Yamashita, Yasuyuki

2018-01-01

We compared the efficacy of three-dimensional (3D) isotropic T2-weighted fast spin-echo imaging using a 3D hybrid profile order technique with a single-breath-hold (3D-Hybrid BH) with a two-dimensional (2D) T2-weighted fast spin-echo conventional respiratory-gated (2D-Conventional RG) technique for visualising small liver lesions. This study was approved by our institutional review board. The requirement to obtain written informed consent was waived. Fifty patients with small (≤15mm) hepatocellular carcinomas (HCC) (n=26), or benign cysts (n=24), had undergone hepatic MRI including both 2D-Conventional RG and 3D-Hybrid BH. We calculated the signal-to-noise ratio (SNR) and tumour-to-liver contrast (TLC). The diagnostic performance of the two protocols was analysed. The image acquisition time was 89% shorter with the 3D-Hybrid BH than with 2D-Conventional RG. There was no significant difference in the SNR between the two protocols. The area under the curve (AUC) of the TLC was significantly higher on 3D-Hybrid BH than on 2D-Conventional RG. The 3D-Hybrid BH sequence significantly improved diagnostic performance for small liver lesions with a shorter image acquisition time without sacrificing accuracy. Copyright © 2017. Published by Elsevier B.V.

Measurement of gradient magnetic field temporal characteristics

International Nuclear Information System (INIS)

Bartusek, K.; Jflek, B.

1994-01-01

We describe a technique of measuring the time dependence and field distortions of magnetic fields due to eddy currents (EC) produced by time-dependent magnetic field gradients. The EC measuring technique makes use of a large volume sample and selective RF excitation pulses and free induction decay (FID) (or a spin or gradient echo) to measure the out-of-phase component of the FID, which is proportional to γδB, i.e. the amount the signal is off resonance. The measuring technique is sensitive, easy to implement and interpret, and used for determining pre-emphasis compensation parameters

MR imaging of the gastrointestinal tract with half-fourier single-shot fast spin echo (SSFSE)

International Nuclear Information System (INIS)

Boku, Houjun; Takehara, Yasuo; Isoda, Haruo; Isogai, Satoshi; Kaneko, Masao

1999-01-01

Our objective was to implement a non-invasive magnetic resonance imaging (MRI) technique combined with concentrated milk ingestion for depicting the gastrointestinal (GI) tract and detecting gastrointestinal motility and transit. The half-Fourier SSFSE (single-shot fast spin echo) sequence was optimized on the basis of a phantom study. In order to determine the feasibility of milk ingestion as a substitute for contrast medium, ten human volunteers were examined with SSFSE after two types of liquid ingestion (i.e., milk and water). The snapshot images provided subsecond data acquisition for each coronal plane, allowing visualization of peristalsis in the gastrointestinal tract in an almost real-time fashion, without motion-related image degradation, as would normally be seen using conventional MRI. There was no significant difference between concentrated milk and water in terms of depiction of the upper gastrointestinal tract; however, 10 min and 30 min after ingestion, concentrated milk showed better delineation of the intestine than that observed after water ingestion (p<0.01). MR gastrointestinal imaging is a non-invasive method that allows gastrointestinal depiction as well as analysis of motility and passage. Especially with concentrated milk ingestion, the distal intestines were well depicted with adequate contrast filling and distention. (author)

Grating stimulated echo

International Nuclear Information System (INIS)

Dubetsky, B.; Berman, P.R.; Sleator, T.

1992-01-01

A theory of a grating simulated echo (GTE) is developed. The GSE involves the sequential excitation of atoms by two counterpropagating traveling waves, a standing wave, and a third traveling wave. It is shown that the echo signal is very sensitive to small changes in atomic velocity, much more sensitive than the normal stimulated echo. Use of the GSE as a collisional probe or accelerometer is discussed

Fast spin-echo T2-weighted MR imaging of tongue cancer; the value of fat-suppression

International Nuclear Information System (INIS)

Kim, Zu Byoung; Na, Dong Gyu; Ryoo, Jae Wook; Kim, Kyeong Ah; Byun, Hong Sik; Baek, Chung Whan; Son, Yong Ik

2000-01-01

To compare the diagnostic efficacy of fast spin-echo (FSE) T2-weighted MR imaging with and without fat suppression. Twelve patients (7 men and 5 women; mean age, 48 years) with pathologically proven cancer of the tongue were included in this study. In all of these, FSE T2-weighted MR images with and without fat suppression were obtained in the same imaging planes before surgery or biopsy. Two radiologists visually compared the images thus obtained in terms of detection, extent, and conspicuity of the tumor, and the contrast-to-noise ratio (CNR) of each tumor was also calculated. In all patients, both imaging modalities were equal in terms of tumor detection. In 4 of 12(33%), the extent of the tumor was greater with fat suppression, while in eight (67%), it was almost the same both with and without. In ten patients (83%), the tumor was more conspicuous with fat suppression, and percentage CNRs were significantly higher with fat suppression than without (180±70% and 113±61%, respectively; p=0.02). For the evaluation of patients with tongue cancer, fat-suppressed FSE T2-weighted MR imaging is superior to its conventional equivalent

Monte Carlo Simulation of the Echo Signals from Low-Flying Targets for Airborne Radar

Directory of Open Access Journals (Sweden)

Mingyuan Man

2014-01-01

Full Text Available A demonstrated hybrid method based on the combination of half-space physical optics method (PO, graphical-electromagnetic computing (GRECO, and Monte Carlo method on echo signals from low-flying targets based on actual environment for airborne radar is presented in this paper. The half-space physical optics method , combined with the graphical-electromagnetic computing (GRECO method to eliminate the shadow regions quickly and rebuild the target automatically, is employed to calculate the radar cross section (RCS of the conductive targets in half space fast and accurately. The direct echo is computed based on the radar equation. The reflected paths from sea or ground surface cause multipath effects. In order to accurately obtain the echo signals, the phase factors are modified for fluctuations in multipath, and the statistical average value of the echo signals is obtained using the Monte Carlo method. A typical simulation is performed, and the numerical results show the accuracy of the proposed method.

Larmor labeling by time-gradient magnetic fields

International Nuclear Information System (INIS)

Ioffe, Alexander; Bodnarchuk, Victor; Bussmann, Klaus; Mueller, Robert

2007-01-01

The Larmor labeling of neutrons, due to the Larmor precession of neutron spin in a magnetic field, opens the unique possibility for the development of neutron spin-echo (NSE) based on neutron scattering techniques, featuring an extremely high energy (momentum) resolution. Here, we present the experimental proof of a new method of the Larmor labeling using time-gradient magnetic fields

B1 gradient coherence selection using a tapered stripline.

Science.gov (United States)

van Meerten, S G J; Tijssen, K C H; van Bentum, P J M; Kentgens, A P M

2018-01-01

Pulsed-field gradients are common in modern liquid state NMR pulse sequences. They are often used instead of phase cycles for the selection of coherence pathways, thereby decreasing the time required for the NMR experiment. Soft off-resonance pulses with a B 1 gradient result in a spatial encoding similar to that created by pulsed-field (B 0 ) gradients. In this manuscript we show that pulse sequences with pulsed-field gradients can easily be converted to one which uses off-resonance B 1 field gradient (OFFBEAT) pulses. The advantage of B 1 gradient pulses for coherence selection is that the chemical shift evolution during the pulses is (partially) suppressed. Therefore no refocusing echos are required to correct for evolution during the gradient pulses. A tapered stripline is shown to be a convenient tool for creating a well-defined gradient in the B 1 field strength. B 1 gradient coherence selection using a tapered stripline is a simple and cheap alternative to B 0 pulsed-field gradients. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

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

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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

Mono-Exponential Fitting in T2-Relaxometry: Relevance of Offset and First Echo.

Directory of Open Access Journals (Sweden)

David Milford

Full Text Available T2 relaxometry has become an important tool in quantitative MRI. Little focus has been put on the effect of the refocusing flip angle upon the offset parameter, which was introduced to account for a signal floor due to noise or to long T2 components. The aim of this study was to show that B1 imperfections contribute significantly to the offset. We further introduce a simple method to reduce the systematic error in T2 by discarding the first echo and using the offset fitting approach.Signal curves of T2 relaxometry were simulated based on extended phase graph theory and evaluated for 4 different methods (inclusion and exclusion of the first echo, while fitting with and without the offset. We further performed T2 relaxometry in a phantom at 9.4T magnetic resonance imaging scanner and used the same methods for post-processing as in the extended phase graph simulated data. Single spin echo sequences were used to determine the correct T2 time.The simulation data showed that the systematic error in T2 and the offset depends on the refocusing pulse, the echo spacing and the echo train length. The systematic error could be reduced by discarding the first echo. Further reduction of the systematic T2 error was reached by using the offset as fitting parameter. The phantom experiments confirmed these findings.The fitted offset parameter in T2 relaxometry is influenced by imperfect refocusing pulses. Using the offset as a fitting parameter and discarding the first echo is a fast and easy method to minimize the error in T2, particularly for low to intermediate echo train length.

Normal range of hepatic fat fraction on dual- and triple-echo fat quantification MR in children.

Science.gov (United States)

Shin, Hyun Joo; Kim, Hyun Gi; Kim, Myung-Joon; Koh, Hong; Kim, Ha Yan; Roh, Yun Ho; Lee, Mi-Jung

2015-01-01

To evaluate hepatic fat fraction on dual- and triple-echo gradient-recalled echo MRI sequences in healthy children. We retrospectively reviewed the records of children in a medical check-up clinic from May 2012 to November 2013. We excluded children with abnormal laboratory findings or those who were overweight. Hepatic fat fraction was measured on dual- and triple-echo sequences using 3T MRI. We compared fat fractions using the Wilcoxon signed rank test and the Bland-Altman 95% limits of agreement. The correlation between fat fractions and clinical and laboratory findings was evaluated using Spearman's correlation test, and the cut-off values of fat fractions for diagnosing fatty liver were obtained from reference intervals. In 54 children (M:F = 26:28; 5-15 years; mean 9 years), the dual fat fraction (0.1-8.0%; median 1.6%) was not different from the triple fat fraction (0.4-6.5%; median 2.7%) (p = 0.010). The dual- and triple-echo fat fractions showed good agreement using a Bland-Altman plot (-0.6 ± 2.8%). Eight children (14.8%) on dual-echo sequences and six (11.1%) on triple-echo sequences had greater than 5% fat fraction. From these children, six out of eight children on dual-echo sequences and four out of six children on triple-echo sequences had a 5-6% hepatic fat fraction. When using a cut-off value of a 6% fat fraction derived from a reference interval, only 3.7% of children were diagnosed with fatty liver. There was no significant correlation between clinical and laboratory findings with dual and triple-echo fat fractions. Dual fat fraction was not different from triple fat fraction. We suggest a cut-off value of a 6% fat fraction is more appropriate for diagnosing fatty liver on both dual- and triple-echo sequences in children.

Differential diagnosis of pituitary adenomas and Rathke's cleft cysts by diffusion-weighted MRI using single-shot fast spin echo technique

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Abe, Takumi; Izumiyama, Hitoshi; Fukuda, Ataru; Tanioka, Daisuke; Kunii, Norihiko; Komatsu, Daisuke; Fujita, Shogo; Ukisu, Ryutaro; Moritani, Toshio [Showa Univ., Tokyo (Japan). School of Medicine

2002-09-01

The purpose of the present study was to prospectively evaluate the diagnostic ability of diffusion-weighted magnetic resonance imaging (DWI) using single-shot fast spin echo (SSFSE) technique to discriminate pituitary adenomas from Rathke's cleft cysts. DWIs were obtained from 40 patients with pathologically proven pituitary macroadenomas and 15 patients with proven Rathke's cleft cysts. Pituitary adenomas were divided into 27 cases with solid components alone, five with non-hemorrhagic large cysts, and eight with intratumoral hemorrhage. On SSFSE DWI, solid components of pituitary adenomas revealed iso or slightly increased intensity and intratumoral hemorrhage showed higher intensity than normal brain parenchyma, whereas Rathke's cleft cysts and intratumoral cysts demonstrated very low intensity. SSFSE DWI did not display the susceptibility artifacts that are seen close to the skull base and sinonasal cavities on echo planar diffusion imaging. On the basis of our preliminary findings, DWI may enable us to differentiate pituitary adenomas with only solid components and hemorrhagic pituitary adenomas appearing hyperintense on T1-weighted images from Rathke's cleft cysts without administration of gadolinium-DTPA. SSFSE DWI appears to be a useful technique for characterizing pituitary diseases without the susceptibility artifacts. Our study is the first report to demonstrate the identification of pituitary disorders on SSFSE DWI. (author)

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.

ECHO-UseFY17.png | 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.

Help Content for ECHO Reports | 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.

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.

A Fast Gradient Method for Nonnegative Sparse Regression With Self-Dictionary

Science.gov (United States)

Gillis, Nicolas; Luce, Robert

2018-01-01

A nonnegative matrix factorization (NMF) can be computed efficiently under the separability assumption, which asserts that all the columns of the given input data matrix belong to the cone generated by a (small) subset of them. The provably most robust methods to identify these conic basis columns are based on nonnegative sparse regression and self dictionaries, and require the solution of large-scale convex optimization problems. In this paper we study a particular nonnegative sparse regression model with self dictionary. As opposed to previously proposed models, this model yields a smooth optimization problem where the sparsity is enforced through linear constraints. We show that the Euclidean projection on the polyhedron defined by these constraints can be computed efficiently, and propose a fast gradient method to solve our model. We compare our algorithm with several state-of-the-art methods on synthetic data sets and real-world hyperspectral images.

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

International Nuclear Information System (INIS)

Cai, B; Rao, Y; Tsien, C; Huang, J; Green, O; Mutic, S; Gach, H; Wen, J; Yablonskiy, D

2016-01-01

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

Rotary spin echoes

Energy Technology Data Exchange (ETDEWEB)

Solomon, I. [Commissariat a l' energie atomique et aux energies alternatives - CEA, Centre d' Etudes Nucleaires de Saclay, BP2, Gif-sur-Yvette (France)

1959-07-01

Torrey has observed the free precession of nuclear spins around an r-f field H{sub 1}, fixed in a frame rotating at the Larmor frequency ω{sub 0} = γH{sub 0} around a large d-c magnetic field H{sub 0}. He showed that for an H{sub 1}, much larger than inhomogeneity of H{sub 0}, the latter has a negligible effect on the decay of the spin magnetization which is mainly due to the inhomogeneity of H{sub 1}. We report here on a method of overcoming the inhomogeneity of H{sub 1}, by production of echoes in the rotating frame ('rotary echoes'). These echoes are obtained by a 180 deg. phase shift at t = τ on the r-f field so that H{sub 1}, is suddenly reversed, producing a re-focussing of the magnetization vectors at the time t = 2 τ. The rotary echoes so obtained are very similar to the usual spin-echoes with, however some specific features that make them particularly suitable for the measurement of long relaxation times. Reprint of a paper published in Physical Review Letters, vol. 2, no. 7, Apr 1959, p. 301-302.

Rotary spin echoes

International Nuclear Information System (INIS)

Solomon, I.

1959-01-01

Torrey has observed the free precession of nuclear spins around an r-f field H 1 , fixed in a frame rotating at the Larmor frequency ω 0 = γH 0 around a large d-c magnetic field H 0 . He showed that for an H 1 , much larger than inhomogeneity of H 0 , the latter has a negligible effect on the decay of the spin magnetization which is mainly due to the inhomogeneity of H 1 . We report here on a method of overcoming the inhomogeneity of H 1 , by production of echoes in the rotating frame ('rotary echoes'). These echoes are obtained by a 180 deg. phase shift at t = τ on the r-f field so that H 1 , is suddenly reversed, producing a re-focussing of the magnetization vectors at the time t = 2 τ. The rotary echoes so obtained are very similar to the usual spin-echoes with, however some specific features that make them particularly suitable for the measurement of long relaxation times. Reprint of a paper published in Physical Review Letters, vol. 2, no. 7, Apr 1959, p. 301-302

The time window of MRI of murine atherosclerotic plaques after administration of CB2 receptor targeted micelles: inter-scan variability and relation between plaque signal intensity increase and gadolinium content of inversion recovery prepared versus non-prepared fast spin echo

NARCIS (Netherlands)

te Boekhorst, B. C. M.; Bovens, S. M.; van de Kolk, C. W. A.; Cramer, M. J. M.; Doevendans, P. A. F. M.; ten Hove, M.; van der Weerd, L.; Poelmann, R.; Strijkers, G. J.; Pasterkamp, G.; van Echteld, C. J. A.

2010-01-01

Single fast spin echo scans covering limited time frames are mostly used for contrast-enhanced MRI of atherosclerotic plaque biomarkers. Knowledge on inter-scan variability of the normalized enhancement ratio of plaque (NER(plaque)) and relation between NER(plaque) and gadolinium content for

Reticuloendothelial negative contrast media for hepatocellular carcinoma. Initial comparison of chondroitin sulfate iron colloid and Ferrixan in fast T2-weighted MR imaging

International Nuclear Information System (INIS)

Sugihara, Shuji; Suto, Yuji; Kamba, Masayuki; Yoshida, Kotaro

1996-01-01

Chondroitin sulfate iron colloid (CSIC), a paramagnetic substance, and Ferrixan (SHU555A), a superparamagnetic substance, were administered to 20 patients with 26 nodules of hepatocellular carcinoma, and the visualization of the lesions by fast T2-weighted magnetic resonance imaging (MRI) was quantitatively evaluated. Conventional spin-echo (CSE), turbo spin-echo (TSE), and turbo gradient spin-echo (TGSE) sequences were performed in all patients before and after the administration of the iron colloid preparations. The signal-to-noise ratio (SNR) in the liver decreased significantly after administration of iron colloid preparations by all sequences and at all doses. A reduction in SNR in the liver similar to that obtained with SHU555A could be obtained by increasing the dose of CSIC, which has a weaker T2-shortening effect. In the TSE sequence with a weaker susceptibility effect, the decrease in SNR in the liver tended to be equalized to those in the CSE or TGSE sequences by high dose administration of the iron colloid preparation. We think perhaps that the imaging ability for hepatocellular carcinoma, similar to that of superparamagnetic contrast media, can be obtained with paramagnetic CSIC by administering it at a higher dose. (author)

Reticuloendothelial negative contrast media for hepatocellular carcinoma. Initial comparison of chondroitin sulfate iron colloid and Ferrixan in fast T2-weighted MR imaging

Energy Technology Data Exchange (ETDEWEB)

Sugihara, Shuji; Suto, Yuji; Kamba, Masayuki; Yoshida, Kotaro [Tottori Univ., Yonago (Japan). Faculty of Medicine

1996-11-01

Chondroitin sulfate iron colloid (CSIC), a paramagnetic substance, and Ferrixan (SHU555A), a superparamagnetic substance, were administered to 20 patients with 26 nodules of hepatocellular carcinoma, and the visualization of the lesions by fast T2-weighted magnetic resonance imaging (MRI) was quantitatively evaluated. Conventional spin-echo (CSE), turbo spin-echo (TSE), and turbo gradient spin-echo (TGSE) sequences were performed in all patients before and after the administration of the iron colloid preparations. The signal-to-noise ratio (SNR) in the liver decreased significantly after administration of iron colloid preparations by all sequences and at all doses. A reduction in SNR in the liver similar to that obtained with SHU555A could be obtained by increasing the dose of CSIC, which has a weaker T2-shortening effect. In the TSE sequence with a weaker susceptibility effect, the decrease in SNR in the liver tended to be equalized to those in the CSE or TGSE sequences by high dose administration of the iron colloid preparation. We think perhaps that the imaging ability for hepatocellular carcinoma, similar to that of superparamagnetic contrast media, can be obtained with paramagnetic CSIC by administering it at a higher dose. (author)

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.

Bending of fuel fast reactor fuel elements under action of non-uniform temperature gradients and radiation-induced swelling

International Nuclear Information System (INIS)

Kulikov, I.S.; Tverkovkin, B.E.; Karasik, E.A.

1984-01-01

The bending of rod fuel elements in gas-cooled fast reactors under the action of temperature gradients radiation-induced swelling non-uniform over the perimeter of fuel cans is evaluated. It is pointed out that the radiation-induced swelling gives the main contribution to the bending of fuel elements. Calculated data on the bending of the corner fuel element in the assembly of the fast reactor with dissociating gas coolant are given. With the growth of temperature difference over the perimeter, the bending moment and deformation increase, resulting in the increase of axial stresses. The obtained data give the basis for accounting the stresses connected with thermal and radiation bending when estimating serviceability of fuel elements in gas cooled fast reactors. Fuel element bending must be also taken into account when estimating the thermal hydrualic properties

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.

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.

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.

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; Haacke, E Mark

2018-02-01

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 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 across the ten subjects compared to the single echo result of 17.5ms 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. Published by Elsevier Inc.

Wind yield forecast with Echo State Networks; Windertragsprognose mit Echo State Networks

Energy Technology Data Exchange (ETDEWEB)

Kobialka, Hans-Ulrich [Fraunhofer IAIS, Sankt Augustin (Germany)

2012-07-01

Statistical methods are able to create models of complex system dynamics which are difficult to capture analytically. This paper describes a wind energy prediction system based on a machine learning method, called Echo State Networks. Echo State Networks enable the training of large recurrent neural networks which are able to model and predict highly non-linear system dynamics. This paper gives a short description of Echo State Networks and the realization of the wind energy prediction system. (orig.)

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.)

Ultra-high-speed inversion recovery echo planar MR imaging

International Nuclear Information System (INIS)

Stehling, M.K.; Ordidge, R.J.; Coxon, R.; Chapman, B.; Houseman, A.M.; Guifoyle, D.; Blamire, A.; Gibbs, P.; Mansfield, P.

1988-01-01

Fast two-dimensional FT MR imaging techniques such as fast low-angle shot do not allow inversion recovery (IR). Rapid repetition of low-angle pulses is incompatible with a 180 0 inversion pulse. Echo planar imaging (EPI) can be applied in conjunction with IR, because after preparation of the spin system, a complete image is acquired. Data acquisition in less than 100 msec and real-time display allows interactive optimization of inversion time (4.0-9,000 msec) with little time penalty. The authors have applied IR EPI to the study of the brain, liver, and kidneys in normal volunteers and patients. Technical details are presented, and the applications of this first ultra-high-speed IR technique will be shown

Happy birthday Echo!

CERN Document Server

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...

Technical Assessment of Artifact Production from Neuro Endovascular Coil At 3 Tesla MRI: An In Vitro Study

International Nuclear Information System (INIS)

Kampaengtip, A.; Krisanachinda, A.; Singhara Na Ayudya, S.; Asavaphatiboon, S.

2012-01-01

Introduction: Magnetic resonance imaging (MRI) is an essential part of the diagnostic procedures in radiology. MRI 3 Tesla becomes more widespread due to high signal to noise ratio (SNR). The use of the neuro endovascular coil to overcome the neuro aneurysm can introduce the artifact in magnetic resonance imaging. Susceptibility artifacts and geometric distortions caused by magnetic field inhomogeneity- related signal loss is used to refer to an artifact in magnetic resonance images. It consists of a region of signal void with a surrounding area of an increased signal intensity that appears to be considerably larger than the actual size of the device causing the artifact. The objective of the study is to compare the size of the artifact on the MR image to the actual size of endovascular coils using a 3 Tesla magnetic resonance imaging system, in vitro study. Methods: The endovascular coils were made from detachable platinum and aneurysm models were constructed by using silicone tube. MRI 3 Tesla Philips Model Achieva with pulse sequence selections were: spin echo, fast spin echo, inversion recovery, fast gradient echo while additional parameters were echo time and turbo factor. Results: Improved visualization of perianeurysmal soft tissues is best accomplished by spin echo for fast spin echo sequences, even better suited to reduce metal artifact. Furthermore, shorter turbo factor and shorter effective TE in the latter sequences are beneficial for the same reason as sequences having shorter TE. Sequences with a shorter TE are preferred because of less time for dephasing and frequency shifting. Imaging at gradient echo series increases susceptibility artifacts. In this in vitro study, some of the major characteristics related to MRI imaging of coil packs have been defined. Discussion: Pulse sequence spin echo is the best sequence reducing the susceptibility artifact. Reducing the TE is the main factor in improving endovascular coil visualization on MRI images. The

Measurement of short transverse relaxation times by pseudo-echo nutation experiments

Science.gov (United States)

Ferrari, Maude; Moyne, Christian; Canet, Daniel

2018-07-01

Very short NMR transverse relaxation times may be difficult to measure by conventional methods. Nutation experiments constitute an alternative approach. Nutation is, in the rotating frame, the equivalent of precession in the laboratory frame. It consists in monitoring the rotation of magnetization around the radio-frequency (rf) field when on-resonance conditions are fulfilled. Depending on the amplitude of the rf field, nutation may be sensitive to the two relaxation rates R1 and R2. A full theoretical development has been worked out for demonstrating how these two relaxation rates could be deduced from a simple nutation experiment, noticing however that inhomogeneity of the rf field may lead to erroneous results. This has led us to devise new experiments which are the equivalent of echo techniques in the rotating frame (pseudo spin-echo nutation experiment and pseudo gradient-echo experiment). Full equations of motion have been derived. Although complicated, they indicate that the sum of the two relaxation rates can be obtained very accurately and not altered by rf field inhomogeneity. This implies however an appropriate data processing accounting for the oscillations which are superposed to the echo decays and, anyway, theoretically predicted. A series of experiments has been carried out for different values of the rf field amplitude on samples of water doped with a paramagnetic compound at different concentrations. Pragmatically, as R1 can be easily measured by conventional methods, its value is entered in the data processing algorithm which then returns exclusively the value of the transverse relaxation time. Very consistent results are obtained that way.

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

International Nuclear Information System (INIS)

Juras, Vladimir; Szomolanyi, Pavol; Bohndorf, Klaus; Kronnerwetter, Claudia; Hager, Benedikt; Zbyn, Stefan; Heule, Rahel; Bieri, Oliver; Trattnig, Siegfried

2016-01-01

To assess the clinical relevance of T 2 relaxation times, measured by 3D triple-echo steady-state (3D-TESS), in knee articular cartilage compared to conventional multi-echo spin-echo T 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 2 mapping, and 3D TESS with the same geometry settings, but variable acquisition times: standard (TESSs 4:35min) and quick (TESSq 2:05min). T 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 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 1 and B 0 changes. (orig.)

Fast Gradient Elution Reversed-Phase HPLC with Diode-Array Detection as a High Throughput Screening Method for Drugs of Abuse

Energy Technology Data Exchange (ETDEWEB)

Peter W. Carr; K.M. Fuller; D.R. Stoll; L.D. Steinkraus; M.S. Pasha; Glenn G. Hardin

2005-12-30

A new approach has been developed by modifying a conventional gradient elution liquid chromatograph for the high throughput screening of biological samples to detect the presence of regulated intoxicants. The goal of this work was to improve the speed of a gradient elution screening method over current approaches by optimizing the operational parameters of both the column and the instrument without compromising the reproducibility of the retention times, which are the basis for the identification. Most importantly, the novel instrument configuration substantially reduces the time needed to re-equilibrate the column between gradient runs, thereby reducing the total time for each analysis. The total analysis time for each gradient elution run is only 2.8 minutes, including 0.3 minutes for column reequilibration between analyses. Retention times standard calibration solutes are reproducible to better than 0.002 minutes in consecutive runs. A corrected retention index was adopted to account for day-to-day and column-to-column variations in retention time. The discriminating power and mean list length were calculated for a library of 47 intoxicants and compared with previous work from other laboratories to evaluate fast gradient elution HPLC as a screening tool.

Dynamic studies of cardiac valvular disease using a new fast multiphase MR imaging technique

International Nuclear Information System (INIS)

Pettigrew, R.; Churchwell, A.; Parks, W.J.; Dannels, W.; Smith, H. III; Baron, M.G.

1986-01-01

To determine the potential utility of fast multiphase (FM) imaging for the assessment of cardiac valvular disease, ten healthy volunteers and 18 patients were studied. The FM technique employed gradient echoes with TE -- 15 msec and small exitation angles with TR -- 50 msec. Cine display of the electrocardiographically gated FM images allowed clear visualization of regurgitant blood flow in each of 15 patients with tricuspid or mitral insufficiency. Magnetic field distortions in two patients with Bjork-Shiley aortic prostheses and regurgitation prevented definitive visualization of the flow patterns. An equivocal flow pattern was seen in one case of mitral stenosis. Thus, FM imaging may have significant utility as an adjunctive procedure for the assessment of atrioventricular valve insufficiently, without requiring a contrast agent. Difficulties may exist with some prosthetic valves

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.)

An analysis of the uncertainty and bias in DCE-MRI measurements using the spoiled gradient-recalled echo pulse sequence

International Nuclear Information System (INIS)

Subashi, Ergys; Choudhury, Kingshuk R.; Johnson, G. Allan

2014-01-01

Purpose: The pharmacokinetic parameters derived from dynamic contrast-enhanced (DCE) MRI have been used in more than 100 phase I trials and investigator led studies. A comparison of the absolute values of these quantities requires an estimation of their respective probability distribution function (PDF). The statistical variation of the DCE-MRI measurement is analyzed by considering the fundamental sources of error in the MR signal intensity acquired with the spoiled gradient-echo (SPGR) pulse sequence. Methods: The variance in the SPGR signal intensity arises from quadrature detection and excitation flip angle inconsistency. The noise power was measured in 11 phantoms of contrast agent concentration in the range [0–1] mM (in steps of 0.1 mM) and in onein vivo acquisition of a tumor-bearing mouse. The distribution of the flip angle was determined in a uniform 10 mM CuSO 4 phantom using the spin echo double angle method. The PDF of a wide range of T1 values measured with the varying flip angle (VFA) technique was estimated through numerical simulations of the SPGR equation. The resultant uncertainty in contrast agent concentration was incorporated in the most common model of tracer exchange kinetics and the PDF of the derived pharmacokinetic parameters was studied numerically. Results: The VFA method is an unbiased technique for measuringT1 only in the absence of bias in excitation flip angle. The time-dependent concentration of the contrast agent measured in vivo is within the theoretically predicted uncertainty. The uncertainty in measuring K trans with SPGR pulse sequences is of the same order, but always higher than, the uncertainty in measuring the pre-injection longitudinal relaxation time (T1 0 ). The lowest achievable bias/uncertainty in estimating this parameter is approximately 20%–70% higher than the bias/uncertainty in the measurement of the pre-injection T1 map. The fractional volume parameters derived from the extended Tofts model were found to be

THIRTY YEARS OF SN 1980K: EVIDENCE FOR LIGHT ECHOES

Energy Technology Data Exchange (ETDEWEB)

Sugerman, Ben E. K. [Department of Physics and Astronomy, Goucher College, 1021 Dulaney Valley Road, Baltimore, MD 21208 (United States); Andrews, Jennifer E. [Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States); Barlow, Michael J. [Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT (United Kingdom); Clayton, Geoffrey C. [Department of Physics and Astronomy, Lousiana State University, 202 Nicholson Hall, Baton Roughe, LA 70803 (United States); Ercolano, Barbara [Excellence Cluster ' Universe' , Universitaets-Sternwarte Muenchen, Scheinerstr. 1, 81679 Muenchen (Germany); Ghavamian, Parviz [Department of Physics, Astronomy and Geosciences, Towson University, Smith Hall, Towson, MD 21252 (United States); Kennicutt, Robert C. Jr. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CM3 0HA (United Kingdom); Krause, Oliver [Max Planck Institute for Astronomy, Koenigstuhl 17, 69117 Heidelberg (Germany); Meixner, Margaret [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Otsuka, Masaaki, E-mail: ben.sugerman@goucher.edu [Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan (China)

2012-04-20

We report optical and mid-infrared photometry of SN 1980K between 2004 and 2010, which shows slow monotonic fading consistent with previous spectroscopic and photometric observations made 8-17 yr after outburst. The slow rate of change over two decades suggests that this evolution may result from scattered and thermal light echoes off of extended circumstellar material. We present a semi-analytic dust radiative-transfer model that uses an empirically corrected effective optical depth to provide a fast and robust alternative to full Monte Carlo radiative-transfer modeling for homogenous dust at low to intermediate optical depths. We find that unresolved echoes from a thin circumstellar shell 14-15 lt-yr from the progenitor, and containing {approx}< 0.02 M{sub Sun} of carbon-rich dust, can explain the broadband spectral and temporal evolution. The size, mass, and dust composition are in good agreement with the contact discontinuity observed in scattered echoes around SN 1987A. The origin of slowly changing high-velocity [O I] and H{alpha} lines is also considered. We propose an origin in shocked high-velocity metal-rich clumps of ejecta, rather than arising in the impact of ejecta on slowly moving circumstellar material, as is the case with hot spots in SN 1987A.

Ultrasonic particle image velocimetry for improved flow gradient imaging: algorithms, methodology and validation

International Nuclear Information System (INIS)

Niu Lili; Qian Ming; Yu Wentao; Jin Qiaofeng; Ling Tao; Zheng Hairong; Wan Kun; Gao Shen

2010-01-01

This paper presents a new algorithm for ultrasonic particle image velocimetry (Echo PIV) for improving the flow velocity measurement accuracy and efficiency in regions with high velocity gradients. The conventional Echo PIV algorithm has been modified by incorporating a multiple iterative algorithm, sub-pixel method, filter and interpolation method, and spurious vector elimination algorithm. The new algorithms' performance is assessed by analyzing simulated images with known displacements, and ultrasonic B-mode images of in vitro laminar pipe flow, rotational flow and in vivo rat carotid arterial flow. Results of the simulated images show that the new algorithm produces much smaller bias from the known displacements. For laminar flow, the new algorithm results in 1.1% deviation from the analytically derived value, and 8.8% for the conventional algorithm. The vector quality evaluation for the rotational flow imaging shows that the new algorithm produces better velocity vectors. For in vivo rat carotid arterial flow imaging, the results from the new algorithm deviate 6.6% from the Doppler-measured peak velocities averagely compared to 15% of that from the conventional algorithm. The new Echo PIV algorithm is able to effectively improve the measurement accuracy in imaging flow fields with high velocity gradients.

Liver Lobe Based Multi-Echo Gradient Recalled Echo T2*-Weighted Imaging in Chronic Hepatitis B-Related Cirrhosis: Association with the Presence and Child-Pugh Class of Cirrhosis.

Directory of Open Access Journals (Sweden)

Dan Wang

Full Text Available To investigate whether liver lobe based T2* values measured on gradient recalled echo T2*-weighted imaging are associated with the presence and Child-Pugh class of hepatitis B-related cirrhosis.Fifty-six patients with hepatitis B-related cirrhosis and 23 healthy control individuals were enrolled in this study and underwent upper abdominal T2*-weighted magnetic resonance imaging. T2* values of the left lateral lobe (LLL, left medial lobe (LML, right lobe (RL and caudate lobe (CL were measured on T2*-weighted imaging. Statistical analyses were performed to determine the association between liver lobe based T2* values and the presence and Child-Pugh class of cirrhosis.The T2* values of the LLL, LML and RL decreased with the progression of cirrhosis from Child-Pugh class A to C (r = -0.231, -0.223, and -0.395, respectively; all P 0.05. To a certain extent, Mann-Whitney U tests with Bonferroni correction for multigroup comparisons showed that the T2* values of the LLL, LML and RL could distinguish cirrhotic liver from healthy liver (all P 0.05. Receiver operating characteristic analysis demonstrated that the T2* value of the RL could best distinguish cirrhosis from healthy liver, with an area under the receiver operating characteristic curve (AUC of 0.713 among T2* values of the liver lobes, and that only the T2* value of the RL could distinguish Child-Pugh class C from A-B, with an AUC of 0.697 (all P < 0.05.The T2* value of the RL can be associated with the presence and Child-Pugh class of hepatitis B-related cirrhosis.

Cardiovascular magnetic resonance physics for clinicians: part I.

Science.gov (United States)

Ridgway, John P

2010-11-30

There are many excellent specialised texts and articles that describe the physical principles of cardiovascular magnetic resonance (CMR) techniques. There are also many texts written with the clinician in mind that provide an understandable, more general introduction to the basic physical principles of magnetic resonance (MR) techniques and applications. There are however very few texts or articles that attempt to provide a basic MR physics introduction that is tailored for clinicians using CMR in their daily practice. This is the first of two reviews that are intended to cover the essential aspects of CMR physics in a way that is understandable and relevant to this group. It begins by explaining the basic physical principles of MR, including a description of the main components of an MR imaging system and the three types of magnetic field that they generate. The origin and method of production of the MR signal in biological systems are explained, focusing in particular on the two tissue magnetisation relaxation properties (T1 and T2) that give rise to signal differences from tissues, showing how they can be exploited to generate image contrast for tissue characterisation. The method most commonly used to localise and encode MR signal echoes to form a cross sectional image is described, introducing the concept of k-space and showing how the MR signal data stored within it relates to properties within the reconstructed image. Before describing the CMR acquisition methods in detail, the basic spin echo and gradient pulse sequences are introduced, identifying the key parameters that influence image contrast, including appearances in the presence of flowing blood, resolution and image acquisition time. The main derivatives of these two pulse sequences used for cardiac imaging are then described in more detail. Two of the key requirements for CMR are the need for data acquisition first to be to be synchronised with the subject's ECG and to be fast enough for the subject

Classification of radar echoes using fractal geometry

International Nuclear Information System (INIS)

Azzaz, Nafissa; Haddad, Boualem

2017-01-01

Highlights: • Implementation of two concepts of fractal geometry to classify two types of meteorological radar echoes. • A new approach, called a multi-scale fractal dimension is used for classification between fixed echoes and rain echoes. • An Automatic identification system of meteorological radar echoes was proposed using fractal geometry. - Abstract: This paper deals with the discrimination between the precipitation echoes and the ground echoes in meteorological radar images using fractal geometry. This study aims to improve the measurement of precipitations by weather radars. For this, we considered three radar sites: Bordeaux (France), Dakar (Senegal) and Me lbourne (USA). We showed that the fractal dimension based on contourlet and the fractal lacunarity are pertinent to discriminate between ground and precipitation echoes. We also demonstrated that the ground echoes have a multifractal structure but the precipitations are more homogeneous than ground echoes whatever the prevailing climate. Thereby, we developed an automatic classification system of radar using a graphic interface. This interface, based on the fractal geometry makes possible the identification of radar echoes type in real time. This system can be inserted in weather radar for the improvement of precipitation estimations.

WE-DE-206-04: MRI Pulse Sequences - Spin Echo, Gradient Echo, EPI, Non-Cartesia

Energy Technology Data Exchange (ETDEWEB)

Pooley, R. [Mayo Clinic (United States)

2016-06-15

Magnetic resonance imaging (MRI) has become an essential part of clinical imaging due to its ability to render high soft tissue contrast. Instead of ionizing radiation, MRI use strong magnetic field, radio frequency waves and field gradients to create diagnostic useful images. It can be used to image the anatomy and also functional and physiological activities within the human body. Knowledge of the basic physical principles underlying MRI acquisition is vitally important to successful image production and proper image interpretation. This lecture will give an overview of the spin physics, imaging principle of MRI, the hardware of the MRI scanner, and various pulse sequences and their applications. It aims to provide a conceptual foundation to understand the image formation process of a clinical MRI scanner. Learning Objectives: Understand the origin of the MR signal and contrast from the spin physics level. Understand the main hardware components of a MRI scanner and their purposes Understand steps for MR image formation including spatial encoding and image reconstruction Understand the main kinds of MR pulse sequences and their characteristics.

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

Science.gov (United States)

Juras, Vladimir; Bohndorf, Klaus; Heule, Rahel; Kronnerwetter, Claudia; Szomolanyi, Pavol; Hager, Benedikt; Bieri, Oliver; Zbyn, Stefan; Trattnig, Siegfried

2016-06-01

To assess the clinical relevance of T2 relaxation times, measured by 3D triple-echo steady-state (3D-TESS), in knee articular cartilage compared to conventional multi-echo spin-echo T2-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 T2 mapping, and 3D TESS with the same geometry settings, but variable acquisition times: standard (TESSs 4:35min) and quick (TESSq 2:05min). T2 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 T2 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 B1 and B0 changes. • 3D-TESS T 2 mapping provides clinically comparable results to CPMG in shorter scan-time. • Clinical and investigational studies may benefit from high temporal resolution of 3D-TESS. • 3D-TESS T 2 values are able to differentiate between healthy and damaged cartilage.

Lithium ion diffusion measurements on a garnet-type solid conductor Li6.6La3Zr1.6Ta0.4O12 by using a pulsed-gradient spin-echo NMR method.

Science.gov (United States)

Hayamizu, Kikuko; Matsuda, Yasuaki; Matsui, Masaki; Imanishi, Nobuyuki

2015-09-01

The garnet-type solid conductor Li7-xLa3Zr2-xTaxO12 is known to have high ionic conductivity. We synthesized a series of compositions of this conductor and found that cubic Li6.6La3Zr1.6Ta0.4O12 (LLZO-Ta) has a high ionic conductivity of 3.7×10(-4)Scm(-1) at room temperature. The (7)Li NMR spectrum of LLZO-Ta was composed of narrow and broad components, and the linewidth of the narrow component varied from 0.69kHz (300K) to 0.32kHz (400K). We carried out lithium ion diffusion measurements using pulsed-field spin-echo (PGSE) NMR spectroscopy and found that echo signals were observed at T≥313K with reasonable sensitivity. The lithium diffusion behavior was measured by varying the observation time and pulsed-field gradient (PFG) strength between 313 and 384K. We found that lithium diffusion depended significantly on the observation time and strength of the PFG, which is quite different from lithium ion diffusion in liquids. It was shown that lithium ion migration in the solid conductor was distributed widely in both time and space. Copyright © 2015 Elsevier Inc. All rights reserved.

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.

Self-diffusion imaging by spin echo in Earth's magnetic field.

Science.gov (United States)

Mohoric, A; Stepisnik, J; Kos, M; Planinsi

1999-01-01

The NMR of the Earth's magnetic field is used for diffusion-weighted imaging of phantoms. Due to a weak Larmor field, care needs to be taken regarding the use of the usual high field assumption in calculating the effect of the applied inhomogeneous magnetic field. The usual definition of the magnetic field gradient must be replaced by a generalized formula valid when the strength of a nonuniform magnetic field and a Larmor field are comparable (J. Stepisnik, Z. Phys. Chem. 190, 51-62 (1995)). It turns out that the expression for spin echo attenuation is identical to the well-known Torrey formula only when the applied nonuniform field has a proper symmetry. This kind of problem may occur in a strong Larmor field as well as when the slow diffusion rate of particles needs an extremely strong gradient to be applied. The measurements of the geomagnetic field NMR demonstrate the usefulness of the method for diffusion and flow-weighted imaging. Copyright 1999 Academic Press.

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

Myocardial T1 mapping at 3.0 tesla using an inversion recovery spoiled gradient echo readout and bloch equation simulation with slice profile correction (BLESSPC) T1 estimation algorithm.

Science.gov (United States)

Shao, Jiaxin; Rapacchi, Stanislas; Nguyen, Kim-Lien; Hu, Peng

2016-02-01

To develop an accurate and precise myocardial T1 mapping technique using an inversion recovery spoiled gradient echo readout at 3.0 Tesla (T). The modified Look-Locker inversion-recovery (MOLLI) sequence was modified to use fast low angle shot (FLASH) readout, incorporating a BLESSPC (Bloch Equation Simulation with Slice Profile Correction) T1 estimation algorithm, for accurate myocardial T1 mapping. The FLASH-MOLLI with BLESSPC fitting was compared with different approaches and sequences with regards to T1 estimation accuracy, precision and image artifact based on simulation, phantom studies, and in vivo studies of 10 healthy volunteers and three patients at 3.0 Tesla. The FLASH-MOLLI with BLESSPC fitting yields accurate T1 estimation (average error = -5.4 ± 15.1 ms, percentage error = -0.5% ± 1.2%) for T1 from 236-1852 ms and heart rate from 40-100 bpm in phantom studies. The FLASH-MOLLI sequence prevented off-resonance artifacts in all 10 healthy volunteers at 3.0T. In vivo, there was no significant difference between FLASH-MOLLI-derived myocardial T1 values and "ShMOLLI+IE" derived values (1458.9 ± 20.9 ms versus 1464.1 ± 6.8 ms, P = 0.50); However, the average precision by FLASH-MOLLI was significantly better than that generated by "ShMOLLI+IE" (1.84 ± 0.36% variance versus 3.57 ± 0.94%, P < 0.001). The FLASH-MOLLI with BLESSPC fitting yields accurate and precise T1 estimation, and eliminates banding artifacts associated with bSSFP at 3.0T. © 2015 Wiley Periodicals, Inc.

Performance of a fast and high-resolution multi-echo spin-echo sequence for prostate T2 mapping across multiple systems.

Science.gov (United States)

van Houdt, Petra J; Agarwal, Harsh K; van Buuren, Laurens D; Heijmink, Stijn W T P J; Haack, Søren; van der Poel, Henk G; Ghobadi, Ghazaleh; Pos, Floris J; Peeters, Johannes M; Choyke, Peter L; van der Heide, Uulke A

2018-03-01

To evaluate the performance of a multi-echo spin-echo sequence with k-t undersampling scheme (k-t T 2 ) in prostate cancer. Phantom experiments were performed at five systems to estimate the bias, short-term repeatability, and reproducibility across all systems expressed with the within-subject coefficient of variation (wCV). Monthly measurements were performed on two systems for long-term repeatability estimation. To evaluate clinical repeatability, two T 2 maps (voxel size 0.8 × 0.8 × 3 mm 3 ; 5 min) were acquired at separate visits on one system for 13 prostate cancer patients. Repeatability was assessed per patient in relation to spatial resolution. T 2 values were compared for tumor, peripheral zone, and transition zone. Phantom measurements showed a small bias (median = -0.9 ms) and good short-term repeatability (median wCV = 0.5%). Long-term repeatability was 0.9 and 1.1% and reproducibility between systems was 1.7%. The median bias observed in patients was -1.1 ms. At voxel level, the median wCV was 15%, dropping to 4% for structures of 0.5 cm 3 . The median tumor T 2 values (79 ms) were significantly lower (P < 0.001) than in the peripheral zone (149 ms), but overlapped with the transition zone (91 ms). Reproducible T 2 mapping of the prostate is feasible with good spatial resolution in a clinically reasonable scan time, allowing reliable measurement of T 2 in structures as small as 0.5 cm 3 . Magn Reson Med 79:1586-1594, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Theory of single-photon echo (SP-echo) and the possibility of its experimental study in the gamma-region

International Nuclear Information System (INIS)

Moiseev, S.A.

1997-01-01

The single-photon echo (SP-echo) effect is predicted to appear in the case of three-level medium excitation by means of a single photon propagating to the medium along two optical paths with a mutual time delay surpassing the temporal duration of the photon wave packet. The quantum electrodynamical theory describing this interaction is presented and the S-matrix of the field is shown for infinite time (t=∞). Using the S-matrix approach, physical properties of the scattering field are studied. Hence, it is shown that the field has an echo signal at the ω 32 0 carrier frequency. It has been shown that the echo signal exists only in the field amplitude while being absent in its intensity behaviour. Thus, SP-echo is an interference effect and is not influenced by the energy irradiation. The problems of SP-echo detection in the gamma-region (where special generation difficulties appear) are discussed. The influence of the additional detection of theω 21 0 frequency field on the echo signal has been shown. A special case is the EPR-paradox which can appear within the echo phenomenon

Theory of single-photon echo (SP-echo) and the possibility of its experimental study in the gamma-region

Energy Technology Data Exchange (ETDEWEB)

Moiseev, S.A

1997-05-15

The single-photon echo (SP-echo) effect is predicted to appear in the case of three-level medium excitation by means of a single photon propagating to the medium along two optical paths with a mutual time delay surpassing the temporal duration of the photon wave packet. The quantum electrodynamical theory describing this interaction is presented and the S-matrix of the field is shown for infinite time (t={infinity}). Using the S-matrix approach, physical properties of the scattering field are studied. Hence, it is shown that the field has an echo signal at the {omega}{sub 32}{sup 0} carrier frequency. It has been shown that the echo signal exists only in the field amplitude while being absent in its intensity behaviour. Thus, SP-echo is an interference effect and is not influenced by the energy irradiation. The problems of SP-echo detection in the gamma-region (where special generation difficulties appear) are discussed. The influence of the additional detection of the{omega}{sub 21}{sup 0} frequency field on the echo signal has been shown. A special case is the EPR-paradox which can appear within the echo phenomenon.

A radar-echo model for Mars

International Nuclear Information System (INIS)

Thompson, T.W.; Moore, H.J.

1990-01-01

Researchers developed a radar-echo model for Mars based on 12.6 cm continuous wave radio transmissions backscattered from the planet. The model broadly matches the variations in depolarized and polarized total radar cross sections with longitude observed by Goldstone in 1986 along 7 degrees S. and yields echo spectra that are generally similiar to the observed spectra. Radar map units in the model include an extensive cratered uplands unit with weak depolarized echo cross sections, average thermal inertias, moderate normal refelectivities, and moderate rms slopes; the volcanic units of Tharsis, Elysium, and Amazonis regions with strong depolarized echo cross sections, low thermal inertia, low normal reflectivities, and large rms slopes; and the northern planes units with moderate to strong depolarized echo cross sections, moderate to very high thermal inertias, moderate to large normal reflectivities, and moderate rms slopes. The relevance of the model to the interpretation of radar echoes from Mars is discussed

The acoustics of the echo cornet

Science.gov (United States)

Pyle, Robert W., Jr.; Klaus, Sabine K.

2002-11-01

The echo cornet was an instrument produced by a number of makers in several countries from about the middle of the nineteenth to the early twentieth centuries. It consists of an ordinary three-valve cornet to which a fourth valve has been added, downstream of the three normal valves. The extra valve diverts the airstream from the normal bell to an ''echo'' bell that gives a muted tone quality. Although the air column through the echo bell is typically 15 cm longer than the path through the normal bell, there is no appreciable change of playing pitch when the echo bell is in use. Acoustic input impedance and impulse response measurements and consideration of the standing-wave pattern within the echo bell show how this can be so. Acoustically, the echo bell is more closely related to hand-stopping on the French horn than to the mutes commonly used on the trumpet and cornet.

Study of optimal flip angle for inversion-recovery gradient echo method in delayed contrast-enhanced cardiac magnetic resonance imaging

International Nuclear Information System (INIS)

Ogawa, Masashi; Matsumura, Yoshio; Tsuchihashi, Toshio

2013-01-01

Delayed contrast-enhanced cardiac magnetic resonance imaging (MRI) is a valuable tool for detecting myocardial infarction and assessing myocardial viability. The standard viability MRI technique is the inversion-recovery gradient echo (IR-GRE) method. Several previous studies have demonstrated that this imaging technique provides superior image quality at high magnetic field strengths, e.g., 3.0 T. However, there are numerous possible flip angles. We investigated the optimal flip angle of IR-GRE in delayed contrast-enhanced cardiac MRI. Phantoms were made that modeled infarcted myocardium and normal myocardium after administration of contrast agent. To determine optimal flip angle, we compared the contrast-to-noise ratio (CNR) among these phantoms and evaluated the degree of artifacts induced by increased flip angle. The flip angle that showed the highest CNR for 2D IR-GRE and 3D IR-GRE was 30deg/15deg at 1.5 T and 25deg/15deg at 3.0 T. The flip angle that showed the highest CNR was independent of R-R interval. Streak artifacts induced by increased flip angle tended to occur more readily at 3.0 T than 1.5 T. The optimal flip angle for 2D IR-GRE and 3D IR-GRE at 1.5 T was 30deg and 15deg, respectively. At 3.0 T, taking into account the results for both CNR and streak artifacts, we concluded the optimal flip angle of 2D IR-GRE to be 15-20deg. (author)

Fast T1-weighted imaging using GRASE sequence for the female pelvis

International Nuclear Information System (INIS)

Dohke, Masako; Watanabe, Yuji; Kumashiro, Masayuki; Amoh, Yoshiki; Ishimori, Takayoshi; Oda, Kazushige; Okumura, Akira; Koike, Shinji; Dodo, Yoshihiro

1998-01-01

GRASE sequence, a combination of TSE and gradient echo, has been developed as a fast T 2 -weighted imaging technique. We have modified the GRASE sequence to be used for fast T 1 -weighted imaging of the female pelvis. In this article, we compared image quality and incidence of artifacts between T 1 -weighted GRASE images and conventional T 1 -weighted SE images. In a phantom study, signal-to-noise ratio was inferior in the GRASE images relative to corresponding on SE images. Susceptibility and chemical shift artifacts seen in GRASE images were seen with almost equal incidence in SE and TSE images. In a clinical study, we compared GRASE images with SE images in six patients with endometrial cysts and four patients with dermoid cysts. The overall image quality obtained with GRASE sequence was satisfactory in all patients and was almost identical with that obtained with SE sequence. GRASE images demonstrated endometrial cysts and dermoid cysts as clearly as did SE images. T 1 -weighted GRASE imaging, however, has a relatively long TE (35 ms) for T 1 -weighted images, which makes the signal intensity of urine and uterine endometrium with long T 2 values higher than in SE images. In conclusion, GRASE sequence can be used for fast T 1 -weighted imaging of the female pelvis because of short imaging time. (author)

Physiological noise in murine solid tumours using T2*-weighted gradient-echo imaging: a marker of tumour acute hypoxia?

International Nuclear Information System (INIS)

Baudelet, Christine; Ansiaux, Reginald; Jordan, Benedicte F; Havaux, Xavier; Macq, Benoit; Gallez, Bernard

2004-01-01

T2*-weighted gradient-echo magnetic resonance imaging (T2*-weighted GRE MRI) was used to investigate spontaneous fluctuations in tumour vasculature non-invasively. FSa fibrosarcomas, implanted intramuscularly (i.m.) in the legs of mice, were imaged at 4.7 T, over a 30 min or 1 h sampling period. On a voxel-by-voxel basis, time courses of signal intensity were analysed using a power spectrum density (PSD) analysis to isolate voxels for which signal changes did not originate from Gaussian white noise or linear drift. Under baseline conditions, the tumours exhibited spontaneous signal fluctuations showing spatial and temporal heterogeneity over the tumour. Statistically significant fluctuations occurred at frequencies ranging from 1 cycle/3 min to 1 cycle/h. The fluctuations were independent of the scanner instabilities. Two categories of signal fluctuations were reported: (i) true fluctuations (TFV), i.e., sequential signal increase and decrease, and (ii) profound drop in signal intensity with no apparent signal recovery (SDV). No temporal correlation between tumour and contralateral muscle fluctuations was observed. Furthermore, treatments aimed at decreasing perfusion-limited hypoxia, such as carbogen combined with nicotinamide and flunarizine, decreased the incidence of tumour T2*-weighted GRE fluctuations. We also tracked dynamic changes in T2* using multiple GRE imaging. Fluctuations of T2* were observed; however, fluctuation maps using PSD analysis could not be generated reliably. An echo-time dependency of the signal fluctuations was observed, which is typical to physiological noise. Finally, at the end of T2*-weighted GRE MRI acquisition, a dynamic contrast-enhanced MRI was performed to characterize the microenvironment in which tumour signal fluctuations occurred in terms of vessel functionality, vascularity and microvascular permeability. Our data showed that TFV were predominantly located in regions with functional vessels, whereas SDV occurred in regions

A high-performance gradient insert for rapid and short-T2 imaging at full duty cycle.

Science.gov (United States)

Weiger, Markus; Overweg, Johan; Rösler, Manuela Barbara; Froidevaux, Romain; Hennel, Franciszek; Wilm, Bertram Jakob; Penn, Alexander; Sturzenegger, Urs; Schuth, Wout; Mathlener, Menno; Borgo, Martino; Börnert, Peter; Leussler, Christoph; Luechinger, Roger; Dietrich, Benjamin Emanuel; Reber, Jonas; Brunner, David Otto; Schmid, Thomas; Vionnet, Laetitia; Pruessmann, Klaas P

2018-06-01

The goal of this study was to devise a gradient system for MRI in humans that reconciles cutting-edge gradient strength with rapid switching and brings up the duty cycle to 100% at full continuous amplitude. Aiming to advance neuroimaging and short-T 2 techniques, the hardware design focused on the head and the extremities as target anatomies. A boundary element method with minimization of power dissipation and stored magnetic energy was used to design anatomy-targeted gradient coils with maximally relaxed geometry constraints. The design relies on hollow conductors for high-performance cooling and split coils to enable dual-mode gradient amplifier operation. With this approach, strength and slew rate specifications of either 100 mT/m with 1200 mT/m/ms or 200 mT/m with 600 mT/m/ms were reached at 100% duty cycle, assuming a standard gradient amplifier and cooling unit. After manufacturing, the specified values for maximum gradient strength, maximum switching rate, and field geometry were verified experimentally. In temperature measurements, maximum local values of 63°C were observed, confirming that the device can be operated continuously at full amplitude. Testing for peripheral nerve stimulation showed nearly unrestricted applicability in humans at full gradient performance. In measurements of acoustic noise, a maximum average sound pressure level of 132 dB(A) was determined. In vivo capability was demonstrated by head and knee imaging. Full gradient performance was employed with echo planar and zero echo time readouts. Combining extreme gradient strength and switching speed without duty cycle limitations, the described system offers unprecedented options for rapid and short-T 2 imaging. Magn Reson Med 79:3256-3266, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

MR fingerprinting using fast imaging with steady state precession (FISP) with spiral readout.

Science.gov (United States)

Jiang, Yun; Ma, Dan; Seiberlich, Nicole; Gulani, Vikas; Griswold, Mark A

2015-12-01

This study explores the possibility of using gradient echo-based sequences other than balanced steady-state free precession (bSSFP) in the magnetic resonance fingerprinting (MRF) framework to quantify the relaxation parameters . An MRF method based on a fast imaging with steady-state precession (FISP) sequence structure is presented. A dictionary containing possible signal evolutions with physiological range of T1 and T2 was created using the extended phase graph formalism according to the acquisition parameters. The proposed method was evaluated in a phantom and a human brain. T1 , T2 , and proton density were quantified directly from the undersampled data by the pattern recognition algorithm. T1 and T2 values from the phantom demonstrate that the results of MRF FISP are in good agreement with the traditional gold-standard methods. T1 and T2 values in brain are within the range of previously reported values. MRF-FISP enables a fast and accurate quantification of the relaxation parameters. It is immune to the banding artifact of bSSFP due to B0 inhomogeneities, which could improve the ability to use MRF for applications beyond brain imaging. © 2014 Wiley Periodicals, Inc.

Fast-electron self-collimation in a plasma density gradient

International Nuclear Information System (INIS)

Yang, X. H.; Borghesi, M.; Robinson, A. P. L.

2012-01-01

A theoretical and numerical study of fast electron transport in solid and compressed fast ignition relevant targets is presented. The principal aim of the study is to assess how localized increases in the target density (e.g., by engineering of the density profile) can enhance magnetic field generation and thus pinching of the fast electron beam through reducing the rate of temperature rise. The extent to which this might benefit fast ignition is discussed.

Dynamic multi-coil technique (DYNAMITE) shimming for echo-planar imaging of the human brain at 7 Tesla.

Science.gov (United States)

Juchem, Christoph; Umesh Rudrapatna, S; Nixon, Terence W; de Graaf, Robin A

2015-01-15

Gradient-echo echo-planar imaging (EPI) is the primary method of choice in functional MRI and other methods relying on fast MRI to image brain activation and connectivity. However, the high susceptibility of EPI towards B0 magnetic field inhomogeneity poses serious challenges. Conventional magnetic field shimming with low-order spherical harmonic (SH) functions is capable of compensating shallow field distortions, but performs poorly for global brain shimming or on specific areas with strong susceptibility-induced B0 distortions such as the prefrontal cortex (PFC). Excellent B0 homogeneity has been demonstrated recently in the human brain at 7 Tesla with the DYNAmic Multi-coIl TEchnique (DYNAMITE) for magnetic field shimming (J Magn Reson (2011) 212:280-288). Here, we report the benefits of DYNAMITE shimming for multi-slice EPI and T2* mapping. A standard deviation of 13Hz was achieved for the residual B0 distribution in the human brain at 7 Tesla with DYNAMITE shimming and was 60% lower compared to conventional shimming that employs static zero through third order SH shapes. The residual field inhomogeneity with SH shimming led to an average 8mm shift at acquisition parameters commonly used for fMRI and was reduced to 1.5-3mm with DYNAMITE shimming. T2* values obtained from the prefrontal and temporal cortices with DYNAMITE shimming were 10-50% longer than those measured with SH shimming. The reduction of the confounding macroscopic B0 field gradients with DYNAMITE shimming thereby promises improved access to the relevant microscopic T2* effects. The combination of high spatial resolution and DYNAMITE shimming allows largely artifact-free EPI and T2* mapping throughout the brain, including prefrontal and temporal lobe areas. DYNAMITE shimming is expected to critically benefit a wide range of MRI applications that rely on excellent B0 magnetic field conditions including EPI-based fMRI to study various cognitive processes and assessing large-scale brain connectivity

Dynamic Multi-Coil Technique (DYNAMITE) Shimming for Echo-Planar Imaging of the Human Brain at 7 Tesla

Science.gov (United States)

Juchem, Christoph; Rudrapatna, S. Umesh; Nixon, Terence W.; de Graaf, Robin A.

2014-01-01

Gradient-echo echo-planar imaging (EPI) is the primary method of choice in functional MRI and other methods relying on fast MRI to image brain activation and connectivity. However, the high susceptibility of EPI towards B0 magnetic field inhomogeneity poses serious challenges. Conventional magnetic field shimming with low-order spherical harmonic (SH) functions is capable of compensating shallow field distortions, but performs poorly for global brain shimming or on specific areas with strong susceptibility-induced B0 distortions such as the prefrontal cortex (PFC). Excellent B0 homogeneity has been demonstrated recently in the human brain at 7 Tesla with the DYNAmic Multi-coIl TEchnique (DYNAMITE) for magnetic field shimming (Juchem et al., J Magn Reson (2011) 212:280-288). Here, we report the benefits of DYNAMITE shimming for multi-slice EPI and T2* mapping. A standard deviation of 13 Hz was achieved for the residual B0 distribution in the human brain at 7 Tesla with DYNAMITE shimming and was 60% lower compared to conventional shimming that employs static zero through third order SH shapes. The residual field inhomogeneity with SH shimming led to an average 8 mm shift at acquisition parameters commonly used for fMRI and was reduced to 1.5-3 mm with DYNAMITE shimming. T2* values obtained from the prefrontal and temporal cortices with DYNAMITE shimming were 10-50% longer than those measured with SH shimming. The reduction of the confounding macroscopic B0 field gradients with DYNAMITE shimming thereby promises improved access to the relevant microscopic T2* effects. The combination of high spatial resolution and DYNAMITE shimming allows largely artifact-free EPI and T2* mapping throughout the brain, including prefrontal and temporal lobe areas. DYNAMITE shimming is expected to critically benefit a wide range of MRI applications that rely on excellent B0 magnetic field conditions including EPI-based fMRI to study various cognitive processes and assessing large

A multi-slice gradient sequence for contrast enhanced MR diagnosis of intracranial tumours

International Nuclear Information System (INIS)

Schoerner, W.; Sander, B.; Kornmesser, W.; Laniado, M.; Nakamura, T.; Felix, R.

1988-01-01

A multi-slice gradient echo sequence (FLASH) was compared with a conventional spin-echo (SE) technique with regard to its value for contrast enhanced MR diagnosis. In 28 patients with cerebral tumours, SE images (SE 400/30; four images/3.4 minutes) and FLASH images (FLASH 315/14; 15 images/1.4 minutes) were obtained before and after gadolinium DTPA. After gadolinium-DTPA results were comparable for both techniques with respect to contrast enhancement, tumor contrast and delineation. Because of the higher efficiency of the FLASH 315/14 technique, this sequence is the method of choice for contrast enhanced cerebral MR imaging. (orig.) [de

Echo-lucency of computerized ultrasound images of carotid atherosclerotic plaques are associated with increased levels of triglyceride-rich lipoproteins as well as increased plaque lipid content

DEFF Research Database (Denmark)

Grønholdt, Marie-Louise Moes; Nordestgaard, Børge G.; Weibe, Brit M.

1998-01-01

carotid plaque echo-lucency and that echo-lucency predicts a high plaque lipid content. Methods and Results-The study included 137 patients with neurological symptoms and greater than or equal to 50% stenosis of the relevant carotid artery, High-resolution B-mode ultrasound images of carotid plaques were......Background-Echo-lucency of carotid atherosclerotic plaques on computerized ultrasound B-mode images has been associated with a high incidence of brain infarcts as evaluated on CT scans. We tested the hypotheses that triglyceride-rich lipoproteins in the fasting and postprandial state predict...

Suppressing magnetization exchange effects in stimulated-echo diffusion experiments.

Science.gov (United States)

Pagès, Guilhem; Dvinskikh, Sergey V; Furó, István

2013-09-01

Exchange of nuclear magnetization between spin pools, either by chemical exchange or by cross-relaxation or both, has a significant influence on the signal attenuation in stimulated-echo-type pulsed field gradient experiments. Hence, in such cases the obtained molecular self-diffusion coefficients can carry a large systematic error. We propose a modified stimulated echo pulse sequence that contains T2-filters during the z-magnetization store period. We demonstrate, using a common theoretical description for chemical exchange and cross-relaxation, that these filters suppress the effects of exchange on the diffusional decay in that frequent case where one of the participating spin pools is immobile and exhibits a short T2. We demonstrate the performance of this experiment in an agarose/water gel. We posit that this new experiment has advantages over other approaches hitherto used, such as that consisting of measuring separately the magnetization exchange rate, if suitable by Goldman-Shen type experiments, and then correcting for exchange effects within the framework of a two-site exchange model. We also propose experiments based on selective decoupling and applicable in systems with no large T2 difference between the different spin pools. Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.

Experimental separation of a frequency spin echo signal

International Nuclear Information System (INIS)

Bun'kov, Yu.M.; Dmitriev, V.V.

1981-01-01

To study systems with bound nuclear-electron precession CsMnF 2 antiferromagnetic light-plane monocrystal was investigated. Crystal orientation was carried out by roentgenoscopy. Measurements were performed at helium temperatures in the 500-700 MHz frequency range. A NMR pulsed spectrometer with generators of both resonance and doubled frequency was used to produce an echo signal (to study by the parametric echo method). It was shown that the theory of the formation of a frequency modulated echo (FM echo) did not fully describe the properties of the echo signals in systems with dynamic frequency shift (DFS). An intense spin echo signal, which formation was apparently connected with other nonlinear properties of the systems with nuclear-electron precession, was observed. The spin echo signal in magnetics with DFS, which properties correspond to notions of the frequency mechanism of echo formation, was experimentally separated. As a result of the investigations it had been possible to settle contradictions between the theory of FM echo formation and the experimental results for the last 9 years. It turned out that the mechanism of FM echo formation in the magnetics with bound nuclear-electron precession was effective only at large delay times between the pulses. In the range of small delays the FM echo is ''jammed'' by a gigantic echo signal of a nature different from that of the traditional FM signal. The constant of gigantic echo intensity drop at increasing delay between the pulses weakly depends on spin-spin relaxation time [ru

Single-shot echo-planar imaging of multiple sclerosis: effects of varying echo time

International Nuclear Information System (INIS)

Wolansky, L.J.; Chong, S.; Liu, W.C.; Kang, E.; Simpson, S.W.; Karimi, S.; Akbari, H.

1999-01-01

Our aim was to determine the relative merits of short and long echo times (TE) with single-shot echo-planar imaging for imaging cerebral lesions such as multiple sclerosis. We examined seven patients with clinically definite multiple sclerosis were imaged at 1.5 T. Patients were scanned with spin-echo, single-shot echo-planar imaging, using TEs of 45, 75, 105, and 135 ms. Region of interest (ROI) measurements were performed on 36 lesions at or above the level of the corona radiata. The mean image contrast (IC) was highest (231.1) for a TE of 45 ms, followed by 75 ms (218.9), 105 ms (217.9), and 135 ms (191.6). When mean contrast-to-noise ratios (C/N) were compared, the value was again highest (29.7) for TE 45 ms, followed by 75 ms (28.9), 105 ms (28.5), and 135 ms (26.3). In a lesion-by-lesion comparison, TE 45 ms had the highest IC and C/N in the largest number of cases (50 % and 47.2 %, respectively). IC and C/N for TE 45 ms were superior to those of 75 ms in 64 % and 58 %, respectively. These results support the use of relatively short TEs for single-shot echo-planar imaging in the setting of cerebral lesions such as multiple sclerosis. (orig.) (orig.)

Comparing an accelerated 3D fast spin-echo sequence (CS-SPACE) for knee 3-T magnetic resonance imaging with traditional 3D fast spin-echo (SPACE) and routine 2D sequences

Energy Technology Data Exchange (ETDEWEB)

Altahawi, Faysal F.; Blount, Kevin J.; Omar, Imran M. [Northwestern University Feinberg School of Medicine, Department of Radiology, Chicago, IL (United States); Morley, Nicholas P. [Marshfield Clinic, Department of Radiology, Marshfield, WI (United States); Raithel, Esther [Siemens Healthcare GmbH, Erlangen (Germany)

2017-01-15

To compare a faster, new, high-resolution accelerated 3D-fast-spin-echo (3D-FSE) acquisition sequence (CS-SPACE) to traditional 2D and high-resolution 3D sequences for knee 3-T magnetic resonance imaging (MRI). Twenty patients received knee MRIs that included routine 2D (T1, PD ± FS, T2-FS; 0.5 x 0.5 x 3 mm{sup 3}; ∝10 min), traditional 3D FSE (SPACE-PD-FS; 0.5 x 0.5 x 0.5 mm{sup 3}; ∝7.5 min), and accelerated 3D-FSE prototype (CS-SPACE-PD-FS; 0.5 x 0.5 x 0.5 mm{sup 3}; ∝5 min) acquisitions on a 3-T MRI system (Siemens MAGNETOM Skyra). Three musculoskeletal radiologists (MSKRs) prospectively and independently reviewed the studies with graded surveys comparing image and diagnostic quality. Tissue-specific signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were also compared. MSKR-perceived diagnostic quality of cartilage was significantly higher for CS-SPACE than for SPACE and 2D sequences (p < 0.001). Assessment of diagnostic quality of menisci and synovial fluid was higher for CS-SPACE than for SPACE (p < 0.001). CS-SPACE was not significantly different from SPACE but had lower assessments than 2D sequences for evaluation of bones, ligaments, muscles, and fat (p ≤ 0.004). 3D sequences had higher spatial resolution, but lower overall assessed contrast (p < 0.001). Overall image quality from CS-SPACE was assessed as higher than SPACE (p = 0.007), but lower than 2D sequences (p < 0.001). Compared to SPACE, CS-SPACE had higher fluid SNR and CNR against all other tissues (all p < 0.001). The CS-SPACE prototype allows for faster isotropic acquisitions of knee MRIs over currently used protocols. High fluid-to-cartilage CNR and higher spatial resolution over routine 2D sequences may present a valuable role for CS-SPACE in the evaluation of cartilage and menisci. (orig.)

Wavelet-LMS algorithm-based echo cancellers

Science.gov (United States)

Seetharaman, Lalith K.; Rao, Sathyanarayana S.

2002-12-01

This paper presents Echo Cancellers based on the Wavelet-LMS Algorithm. The performance of the Least Mean Square Algorithm in Wavelet transform domain is observed and its application in Echo cancellation is analyzed. The Widrow-Hoff Least Mean Square Algorithm is most widely used algorithm for Adaptive filters that function as Echo Cancellers. The present day communication signals are widely non-stationary in nature and some errors crop up when Least Mean Square Algorithm is used for the Echo Cancellers handling such signals. The analysis of non-stationary signals often involves a compromise between how well transitions or discontinuities can be located. The multi-scale or multi-resolution of signal analysis, which is the essence of wavelet transform, makes Wavelets popular in non-stationary signal analysis. In this paper, we present a Wavelet-LMS algorithm wherein the wavelet coefficients of a signal are modified adaptively using the Least Mean Square Algorithm and then reconstructed to give an Echo-free signal. The Echo Canceller based on this Algorithm is found to have a better convergence and a comparatively lesser MSE (Mean Square error).

Non-invasive quantification of hepatic fat fraction by fast 1.0, 1.5 and 3.0 T MR imaging

International Nuclear Information System (INIS)

Schuchmann, Sebastian; Weigel, Christiane; Albrecht, Lothar; Kirsch, Michael; Lemke, Arne; Lorenz, Gerd; Warzok, Rolf; Hosten, Norbert

2007-01-01

Introduction: Even mild hepatic steatosis in a split liver donor may cause general liver failure and death in the donor. So far, CT density measurements or percutaneous biopsy is used to determine the presence of hepatic steatosis. Magnetic resonance imaging (MRI) may be an elegant method of non-invasive and non-radiation quantification of hepatic fat content. Methods: Fast gradient echo (GRE) technique was used to discriminate between fat and water spins. Echo time (TE) was adjusted for field strength dependent in-phase and out-of-phase states at 1.0, 1.5 and 3.0 T. Continuous MR signal transition from 100% water to 100% fat was investigated using a wedge water-oil phantom, which was positioned in such a way, that no spatial resolution occurred, thereby combining water and fat in one slice. Results: Using the phantom, a significant difference for a 5% difference in fat content was demonstrated in the range from 20 to 80% fat content (p 2 = 0.93 for TE 6 ms and r 2 = 0.91 for TE 10 ms). Conclusion: The described method can be used to determine the presence of hepatic steatosis of >10% with p < 0.05

Fast ion stabilization of the ion temperature gradient driven modes in the Joint European Torus hybrid-scenario plasmas: a trigger mechanism for internal transport barrier formation

Energy Technology Data Exchange (ETDEWEB)

Romanelli, M; Zocco, A [Euratom/CCFE Fusion Association, Culham Science Centre, Abingdon, Oxon, OX14 3DB (United Kingdom); Crisanti, F, E-mail: Michele.Romanelli@ccfe.ac.u [Associazione Euratom-ENEA sulla Fusione, C.R. Frascati, Frascati (Italy)

2010-04-15

Understanding and modelling turbulent transport in thermonuclear fusion plasmas are crucial for designing and optimizing the operational scenarios of future fusion reactors. In this context, plasmas exhibiting state transitions, such as the formation of an internal transport barrier (ITB), are particularly interesting since they can shed light on transport physics and offer the opportunity to test different turbulence suppression models. In this paper, we focus on the modelling of ITB formation in the Joint European Torus (JET) [1] hybrid-scenario plasmas, where, due to the monotonic safety factor profile, magnetic shear stabilization cannot be invoked to explain the transition. The turbulence suppression mechanism investigated here relies on the increase in the plasma pressure gradient in the presence of a minority of energetic ions. Microstability analysis of the ion temperature gradient driven modes (ITG) in the presence of a fast-hydrogen minority shows that energetic ions accelerated by the ion cyclotron resonance heating (ICRH) system (hydrogen, n{sub H,fast}/n{sub D,thermal} up to 10%, T{sub H,fast}/T{sub D,thermal} up to 30) can increase the pressure gradient enough to stabilize the ITG modes driven by the gradient of the thermal ions (deuterium). Numerical analysis shows that, by increasing the temperature of the energetic ions, electrostatic ITG modes are gradually replaced by nearly electrostatic modes with tearing parity at progressively longer wavelengths. The growth rate of the microtearing modes is found to be lower than that of the ITG modes and comparable to the local E x B-velocity shearing rate. The above mechanism is proposed as a possible trigger for the formation of ITBs in this type of discharges.

MR imaging studies of multiple myeloma in the vertebral column

International Nuclear Information System (INIS)

Albert, S.; Leeds, N.E.

1990-01-01

This paper studies the sensitivity and characteristics of MR imaging in the diagnosis of myeloma in the vertebral column. The cervical, thoracic, and lumbar spines of 12 patients with known multiple myeloma were imaged with small flip angle, fast gradient-echo, proton-density (FPD) as well as spin-echo T1-weighted, T2-weighted, and intermediate (SE 2,000/20-30) imaging. The FPD images were acquired with pulse sequence gradient recalled acquisition in a steady state at a magnetic field strength of 1.5T with use of a license-plate and a circular surface coil

Hemodynamic analysis of bladder tumors using T1-dynamic contrast-enhanced fast spin-echo MRI

International Nuclear Information System (INIS)

Kanazawa, Yuki; Miyati, Tosiaki; Sato, Osamu

2012-01-01

Objectives: To evaluate the hemodynamics of bladder tumors, we developed a method to calculate change in R 1 value (ΔR 1 ) from T 1 -dynamic contrast-enhanced fast spin-echo magnetic resonance imaging (T 1 DCE-FSE-MRI). Materials and methods: On a 1.5-T MR system, T 1 DCE-FSE-MRI was performed. This study was applied to 12 patients with urinary bladder tumor, i.e. urothelial carcinoma. We compared ΔR 1 –time and ΔSI–time between a peak in the ΔR 1 –time and ΔSI–time curve occurred during the first pass within 60 s. Next, we assessed the slope of increase for 180 s after CA injection (Slope 0–180 ). Results: The mean slope of the first pass was significantly higher for bladder tumors on both the ΔR 1 –time and the ΔSI–time curve compared with normal bladder walls. Moreover, a significant difference was apparent between bladder tumors and normal bladder walls on the mean Slope 0–180 in the ΔR 1 -time curve. However, no significant difference in the mean Slope 0–180 was observed on the ΔSI-time curve between bladder tumors and normal bladder walls. Conclusion: T 1 DCE-FSE-MRI offers three advantages: quantitative analysis; high-quality (i.e., artifact-free) images; and high temporal resolution even for SE images. Use of ΔR 1 analysis with T 1 DCE-FSE-MRI allows more detailed information on the hemodynamics of bladder tumors to be obtained and assists in differentiation between bladder tumors and the normal bladder wall.

Quantitative comparison between a multiecho sequence and a single-echo sequence for susceptibility-weighted phase imaging.

Science.gov (United States)

Gilbert, Guillaume; Savard, Geneviève; Bard, Céline; Beaudoin, Gilles

2012-06-01

The aim of this study was to investigate the benefits arising from the use of a multiecho sequence for susceptibility-weighted phase imaging using a quantitative comparison with a standard single-echo acquisition. Four healthy adult volunteers were imaged on a clinical 3-T system using a protocol comprising two different three-dimensional susceptibility-weighted gradient-echo sequences: a standard single-echo sequence and a multiecho sequence. Both sequences were repeated twice in order to evaluate the local noise contribution by a subtraction of the two acquisitions. For the multiecho sequence, the phase information from each echo was independently unwrapped, and the background field contribution was removed using either homodyne filtering or the projection onto dipole fields method. The phase information from all echoes was then combined using a weighted linear regression. R2 maps were also calculated from the multiecho acquisitions. The noise standard deviation in the reconstructed phase images was evaluated for six manually segmented regions of interest (frontal white matter, posterior white matter, globus pallidus, putamen, caudate nucleus and lateral ventricle). The use of the multiecho sequence for susceptibility-weighted phase imaging led to a reduction of the noise standard deviation for all subjects and all regions of interest investigated in comparison to the reference single-echo acquisition. On average, the noise reduction ranged from 18.4% for the globus pallidus to 47.9% for the lateral ventricle. In addition, the amount of noise reduction was found to be strongly inversely correlated to the estimated R2 value (R=-0.92). In conclusion, the use of a multiecho sequence is an effective way to decrease the noise contribution in susceptibility-weighted phase images, while preserving both contrast and acquisition time. The proposed approach additionally permits the calculation of R2 maps. Copyright © 2012 Elsevier Inc. All rights reserved.

Degenerative disc disease of the lumbar spine: a prospective comparison of fast T1-weighted fluid-attenuated inversion recovery and T1-weighted turbo spin echo MR imaging

International Nuclear Information System (INIS)

Erdem, L. Oktay; Erdem, C. Zuhal; Acikgoz, Bektas; Gundogdu, Sadi

2005-01-01

Objective: To compare fast T1-weighted fluid-attenuated inversion recovery (FLAIR) and T1-weighted turbo spin-echo (TSE) imaging of the degenerative disc disease of the lumbar spine. Materials and methods: Thirty-five consecutive patients (19 females, 16 males; mean age 41 years, range 31-67 years) with suspected degenerative disc disease of the lumbar spine were prospectively evaluated. Sagittal images of the lumbar spine were obtained using T1-weighted TSE and fast T1-weighted FLAIR sequences. Two radiologists compared these sequences both qualitatively and quantitatively. Results: On qualitative evaluation, CSF nulling, contrast at the disc-CSF interface, the disc-spinal cord (cauda equina) interface, and the spinal cord (cauda equina)-CSF interface of fast T1-weighted FLAIR images were significantly higher than those for T1-weighted TSE images (P < 0.001). On quantitative evaluation of the first 15 patients, signal-to-noise ratios of cerebrospinal fluid of fast T1-weighted FLAIR imaging were significantly lower than those for T1-weighted TSE images (P < 0.05). Contrast-to-noise ratios of spinal cord/CSF and normal bone marrow/disc for fast T1-weighted FLAIR images were significantly higher than those for T1-weighted TSE images (P < 0.05). Conclusion: Results in our study have shown that fast T1-weighted FLAIR imaging may be a valuable imaging modality in the armamentarium of lumbar spinal T1-weighted MR imaging, because the former technique has definite superior advantages such as CSF nulling, conspicuousness of the normal anatomic structures and changes in the lumbar spinal discogenic disease and image contrast and also almost equally acquisition times

Degenerative disc disease of the lumbar spine: a prospective comparison of fast T1-weighted fluid-attenuated inversion recovery and T1-weighted turbo spin echo MR imaging

Energy Technology Data Exchange (ETDEWEB)

Erdem, L. Oktay [Department of Radiology, Zonguldak Karaelmas University, School of Medicine, 6700 Kozlu, Zonguldak (Turkey)]. E-mail: sunarerdem@yahoo.com; Erdem, C. Zuhal [Department of Radiology, Zonguldak Karaelmas University, School of Medicine, 6700 Kozlu, Zonguldak (Turkey); Acikgoz, Bektas [Department of Neurosurgery, Zonguldak Karaelmas University, School of Medicine, Zonguldak (Turkey); Gundogdu, Sadi [Department of Radiology, Zonguldak Karaelmas University, School of Medicine, 6700 Kozlu, Zonguldak (Turkey)

2005-08-01

Objective: To compare fast T1-weighted fluid-attenuated inversion recovery (FLAIR) and T1-weighted turbo spin-echo (TSE) imaging of the degenerative disc disease of the lumbar spine. Materials and methods: Thirty-five consecutive patients (19 females, 16 males; mean age 41 years, range 31-67 years) with suspected degenerative disc disease of the lumbar spine were prospectively evaluated. Sagittal images of the lumbar spine were obtained using T1-weighted TSE and fast T1-weighted FLAIR sequences. Two radiologists compared these sequences both qualitatively and quantitatively. Results: On qualitative evaluation, CSF nulling, contrast at the disc-CSF interface, the disc-spinal cord (cauda equina) interface, and the spinal cord (cauda equina)-CSF interface of fast T1-weighted FLAIR images were significantly higher than those for T1-weighted TSE images (P < 0.001). On quantitative evaluation of the first 15 patients, signal-to-noise ratios of cerebrospinal fluid of fast T1-weighted FLAIR imaging were significantly lower than those for T1-weighted TSE images (P < 0.05). Contrast-to-noise ratios of spinal cord/CSF and normal bone marrow/disc for fast T1-weighted FLAIR images were significantly higher than those for T1-weighted TSE images (P < 0.05). Conclusion: Results in our study have shown that fast T1-weighted FLAIR imaging may be a valuable imaging modality in the armamentarium of lumbar spinal T1-weighted MR imaging, because the former technique has definite superior advantages such as CSF nulling, conspicuousness of the normal anatomic structures and changes in the lumbar spinal discogenic disease and image contrast and also almost equally acquisition times.

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.

Triple echo steady-state (TESS) relaxometry.

Science.gov (United States)

Heule, Rahel; Ganter, Carl; Bieri, Oliver

2014-01-01

Rapid imaging techniques have attracted increased interest for relaxometry, but none are perfect: they are prone to static (B0 ) and transmit (B1 ) field heterogeneities, and commonly biased by T2 /T1 . The purpose of this study is the development of a rapid T1 and T2 relaxometry method that is completely (T2 ) or partly (T1 ) bias-free. A new method is introduced to simultaneously quantify T1 and T2 within one single scan based on a triple echo steady-state (TESS) approach in combination with an iterative golden section search. TESS relaxometry is optimized and evaluated from simulations, in vitro studies, and in vivo experiments. It is found that relaxometry with TESS is not biased by T2 /T1 , insensitive to B0 heterogeneities, and, surprisingly, that TESS-T2 is not affected by B1 field errors. Consequently, excellent correspondence between TESS and reference spin echo data is observed for T2 in vitro at 1.5 T and in vivo at 3 T. TESS offers rapid T1 and T2 quantification within one single scan, and in particular B1 -insensitive T2 estimation. As a result, the new proposed method is of high interest for fast and reliable high-resolution T2 mapping, especially of the musculoskeletal system at high to ultra-high fields. Copyright © 2013 Wiley Periodicals, Inc.

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 T 1 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 T 1 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 T 1 and T2∗ parameter maps acquired with MRF-EPI in phantoms are in good agreement with reference measurements, showing deviations under 5% and 4% for T 1 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 T 1 : 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 T 1 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.

Detection of cerebrospinal fluid leakage: initial experience with three-dimensional fast spin-echo magnetic resonance myelography.

Science.gov (United States)

Tomoda, Y; Korogi, Y; Aoki, T; Morioka, T; Takahashi, H; Ohno, M; Takeshita, I

2008-03-01

The pathogenesis of cerebrospinal fluid (CSF) hypovolemia is supposed to be caused by CSF leakage through small dural defects. To compare source three-dimensional (3D) fast spin-echo (FSE) images of magnetic resonance (MR) myelography with radionuclide cisternography findings, and to evaluate the feasibility of MR myelography in the detection of CSF leakage. A total of 67 patients who were clinically suspected of CSF hypovolemia underwent indium-111 radionuclide cisternography, and 27 of those who had direct findings of CSF leakage were selected for evaluation. MR myelography with 3D FSE sequences (TR/TE 6000/203 ms) was performed at the lumbar spine for all patients. We evaluated source images and maximum intensity projection (MIP) images of MR myelography, and the findings were correlated with radionuclide cisternography findings. MR myelography of five healthy volunteers was used as a reference. The MR visibility of the CSF leakage was graded as definite (leakage clearly visible), possible (leakage poorly seen), or absent (not shown). CSF leakage was identified with source 3D FSE images in 22 (81.5%) of 27 patients. Of the 22 patients, 16 were graded as definite and six were graded as possible. For the definite cases, 3D FSE images clearly showed the extent of the leaked CSF in the paraspinal structures. In the remaining five patients with absent findings, radionuclide cisternography showed only slight radionuclide activity out of the arachnoid space. Source 3D FSE images of MR myelography seem useful in the detection of CSF leakage. Invasive radionuclide cisternography may be reserved for equivocal cases only.

Fast conjugate phase image reconstruction based on a Chebyshev approximation to correct for B0 field inhomogeneity and concomitant gradients.

Science.gov (United States)

Chen, Weitian; Sica, Christopher T; Meyer, Craig H

2008-11-01

Off-resonance effects can cause image blurring in spiral scanning and various forms of image degradation in other MRI methods. Off-resonance effects can be caused by both B0 inhomogeneity and concomitant gradient fields. Previously developed off-resonance correction methods focus on the correction of a single source of off-resonance. This work introduces a computationally efficient method of correcting for B0 inhomogeneity and concomitant gradients simultaneously. The method is a fast alternative to conjugate phase reconstruction, with the off-resonance phase term approximated by Chebyshev polynomials. The proposed algorithm is well suited for semiautomatic off-resonance correction, which works well even with an inaccurate or low-resolution field map. The proposed algorithm is demonstrated using phantom and in vivo data sets acquired by spiral scanning. Semiautomatic off-resonance correction alone is shown to provide a moderate amount of correction for concomitant gradient field effects, in addition to B0 imhomogeneity effects. However, better correction is provided by the proposed combined method. The best results were produced using the semiautomatic version of the proposed combined method.

Electric Dipole Echoes and Noise-Induced Coherence

International Nuclear Information System (INIS)

Mestayer, J.J.; Zhao, W.; Lancaster, J.C.; Dunning, F.B.; Yoshida, S.; Reinhold, Carlos O.; Burgdorfer, J.

2007-01-01

The generation of echoes in the electric dipole moment of a Rydberg wavepacket precessing in an external electric field by reversal of the field is described. When the wavepacket experiences reversible dephasing, large echoes are observed pointing to strong refocusing of the wavepacket. The presence of irreversible dephasing leads to a reduction in the size of the echoes. The effect of irreversible dynamics on echoes is investigated using artificially synthesized noise. Methods to determine the decoherence rate are discussed

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.

Plane wave fast color flow mode imaging

DEFF Research Database (Denmark)

Bolic, Ibrahim; Udesen, Jesper; Gran, Fredrik

2006-01-01

A new Plane wave fast color flow imaging method (PWM) has been investigated, and performance evaluation of the PWM based on experimental measurements has been made. The results show that it is possible to obtain a CFM image using only 8 echo-pulse emissions for beam to flow angles between 45...... degrees and 75 degrees. Compared to the conventional ultrasound imaging the frame rate is similar to 30 - 60 times higher. The bias, B-est of the velocity profile estimate, based on 8 pulse-echo emissions, is between 3.3% and 6.1% for beam to flow angles between 45 degrees and 75 degrees, and the standard...

Evaluation of Chondrocalcinosis and Associated Knee Joint Degeneration Using MR Imaging: Data from the Osteoarthritis Initiative.

Science.gov (United States)

Gersing, Alexandra S; Schwaiger, Benedikt J; Heilmeier, Ursula; Joseph, Gabby B; Facchetti, Luca; Kretzschmar, Martin; Lynch, John A; McCulloch, Charles E; Nevitt, Michael C; Steinbach, Lynne S; Link, Thomas M

2017-06-01

To evaluate the ability of different MRI sequences to detect chondrocalcinosis within knee cartilage and menisci, and to analyze the association with joint degeneration. Subjects with radiographic knee chondrocalcinosis (n = 90, age 67.7 ± 7.3 years, 50 women) were selected from the Osteoarthritis Initiative and matched to controls without radiographic chondrocalcinosis (n = 90). Visualization of calcium-containing crystals (CaC) was compared between 3D T1-weighted gradient-echo (T1GE), 3D dual echo steady-state (DESS), 2D intermediate-weighted (IW), and proton density (PD)-weighted fast spin-echo (FSE) sequences obtained with 3T MRI and correlated with a semiquantitative CaC score obtained from radiographs. Structural abnormalities were assessed using Whole-Organ MRI Score (WORMS) and logistic regression models were used to compare cartilage compartments with and without CaC. Correlations between CaC counts of MRI sequences and degree of radiographic calcifications were highest for GE (r T1GE  = 0.73, P  0.05). Meniscus WORMS was significantly higher in subjects with chondrocalcinosis compared to controls (P = 0.005). Cartilage defects were significantly more frequent in compartments with CaC than without (patella: P = 0.006; lateral tibia: P < 0.001; lateral femur condyle: P = 0.017). Gradient-echo sequences were most useful for the detection of chondrocalcinosis and presence of CaC was associated with higher prevalence of cartilage and meniscal damage. • Magnetic resonance imaging is useful for assessing burden of calcium-containing crystals (CaC). • Gradient-echo sequences are superior to fast spin echo sequences for CaC imaging. • Presence of CaC is associated with meniscus and cartilage degradation.

Effectiveness of dynamic MRI for diagnosing pericicatricial minimal residual breast cancer following excisional biopsy

International Nuclear Information System (INIS)

Kawashima, Hiroko; Tawara, Mari; Suzuki, Masayuki; Matsui, Osamu; Kadoya, Masumi

2001-01-01

The purpose of this study was to investigate the effectiveness of dynamic MRI for diagnosing pericicatricial minimal residual breast cancer following excisional biopsy. Twenty-six patients who underwent excisional biopsy of a tumor or calcified lesion of the breast underwent gadolinium-enhanced dynamic MRI by the fat-saturated 2D fast spoiled gradient echo (SPGR) sequence (group 1), 24 patients by the spectral IR enhanced 3D fast gradient echo (Efgre3d) sequence (group 2). Pericicatricial residual cancer was confirmed histologically in 29 of the 50 patients. The overall sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of MRI for residual cancer diagnosis was 66, 81, 72, 83 and 63%. A nodular, thick and discontinuous enhanced rim around the scar is indicative of a residual tumor. However, false-positive findings due to granulation or proliferative fibrocystic change remain limitations

Effectiveness of dynamic MRI for diagnosing pericicatricial minimal residual breast cancer following excisional biopsy

Energy Technology Data Exchange (ETDEWEB)

Kawashima, Hiroko E-mail: hirokok@med.kanazawa-u.ac.jp; Tawara, Mari; Suzuki, Masayuki; Matsui, Osamu; Kadoya, Masumi

2001-10-01

The purpose of this study was to investigate the effectiveness of dynamic MRI for diagnosing pericicatricial minimal residual breast cancer following excisional biopsy. Twenty-six patients who underwent excisional biopsy of a tumor or calcified lesion of the breast underwent gadolinium-enhanced dynamic MRI by the fat-saturated 2D fast spoiled gradient echo (SPGR) sequence (group 1), 24 patients by the spectral IR enhanced 3D fast gradient echo (Efgre3d) sequence (group 2). Pericicatricial residual cancer was confirmed histologically in 29 of the 50 patients. The overall sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of MRI for residual cancer diagnosis was 66, 81, 72, 83 and 63%. A nodular, thick and discontinuous enhanced rim around the scar is indicative of a residual tumor. However, false-positive findings due to granulation or proliferative fibrocystic change remain limitations.

Multi-Rate Acquisition for Dead Time Reduction in Magnetic Resonance Receivers: Application to Imaging With Zero Echo Time.

Science.gov (United States)

Marjanovic, Josip; Weiger, Markus; Reber, Jonas; Brunner, David O; Dietrich, Benjamin E; Wilm, Bertram J; Froidevaux, Romain; Pruessmann, Klaas P

2018-02-01

For magnetic resonance imaging of tissues with very short transverse relaxation times, radio-frequency excitation must be immediately followed by data acquisition with fast spatial encoding. In zero-echo-time (ZTE) imaging, excitation is performed while the readout gradient is already on, causing data loss due to an initial dead time. One major dead time contribution is the settling time of the filters involved in signal down-conversion. In this paper, a multi-rate acquisition scheme is proposed to minimize dead time due to filtering. Short filters and high output bandwidth are used initially to minimize settling time. With increasing time since the signal onset, longer filters with better frequency selectivity enable stronger signal decimation. In this way, significant dead time reduction is accomplished at only a slight increase in the overall amount of output data. Multi-rate acquisition was implemented with a two-stage filter cascade in a digital receiver based on a field-programmable gate array. In ZTE imaging in a phantom and in vivo, dead time reduction by multi-rate acquisition is shown to improve image quality and expand the feasible bandwidth while increasing the amount of data collected by only a few percent.

X-ray echoes from gamma-ray bursts

International Nuclear Information System (INIS)

Dermer, C.D.; Hurley, K.C.; Hartmann, D.H.

1991-01-01

The identification of an echo of reflected radiation in time histories of gamma-ray burst spectra can provide important information about the existence of binary companions or accretion disks in gamma-ray burst systems. Because of the nature of Compton scattering, the spectrum of the echo will be attenuated at gamma-ray energies compared with the spectrum of the primary burst emission. The expected temporal and spectral signatures of the echo and a search for such echoes are described, and implications for gamma-ray burst models are discussed. 35 refs

Nanosecond time-resolved EPR in pulse radiolysis via the spin echo method

International Nuclear Information System (INIS)

Trifunac, A.D.; Norris, J.R.; Lawler, R.G.

1979-01-01

The design and operation of a time-resolved electron spin echo spectrometer suitable for detecting transient radicals produced by 3 MeV electron radiolysis is described. Two modes of operation are available: Field swept mode which generates a normal EPR spectrum and kinetic mode in which the time dependence of a single EPR line is monitored. Techniques which may be used to minimize the effects of nonideal microwave pulses and overlapping sample tube signals are described. The principal advantages of the spin echo method over other time-resolved EPR methods are: (1) Improved time resolution (presently approx.30--50 nsec) allows monitoring of fast changes in EPR signals of transient radicals, (2) Lower susceptibility to interference between the EPR signal and the electron beam pulse at short times, and (3) Lack of dependence of transient signals on microwave field amplitude or static field inhomogeneity at short times. The performance of the instrument is illustrated using CIDEP from acetate radical formed in pulsed radiolysis of aqueous solutions of potassium acetate. The relaxation time and CIDEP enhancement factor obtained for this radical using the spin echo method compare favorably with previous determinations using direct detection EPR. Radical decay rates yield estimates of initial radical concentrations of 10 -4 10 -3 M per electron pulse. The Bloch equations are solved to give an expression for the echo signal for samples exhibiting CIDEP using arbitrary microwave pulse widths and distributions of Larmor frequencies. Conditions are discussed under which the time-dependent signal would be distorted by deviations from an ideal nonselective 90 0 --tau--180 0 pulse sequence

Reduction of vascular artifact on T1-weighted images of the brain by using three-dimensional double IR fast spoiled gradient echo recalled acquisition in the steady state (FSPGR) at 3.0 Tesla

International Nuclear Information System (INIS)

Fujiwara, Yasuhiro; Yamaguchi, Isao; Ookoshi, Yusuke; Ootani, Yuriko; Matsuda, Tsuyoshi; Ishimori, Yoshiyuki; Hayashi, Hiroyuki; Miyati, Tosiaki; Kimura, Hirohiko

2007-01-01

The purpose of this study was to decrease vascular artifacts caused by the in-flow effect in three-dimensional inversion recovery prepared fast spoiled gradient recalled acquisition in the steady state (3D IR FSPGR) at 3.0 Tesla. We developed 3D double IR FSPGR and investigated the signal characteristics of the new sequence. The 3D double IR FSPGR sequence uses two inversion pulses, the first for obtaining tissue contrast and the second for nulling vascular signal, which is applied at the time of the first IR period at the neck region. We have optimized scan parameters based on both phantom and in-vivo study. As a result, optimized parameters (1st TI=700 ms, 2nd TI=400 ms) successfully have produced much less vessel signal at reduction than conventional 3D IR FSPGR over a wide imaging range, while preserving the signal-to-noise ratio (SNR) and gray/white matter contrast. Moreover, the decreased artifact was also confirmed by visual inspection of the images obtained in vivo using those parameters. Thus, 3D double IR FSPGR was a useful sequence for the acquisition of T1-weighted images at 3.0 Tesla. (author)

Implications of oxidative stress in the brain plasticity originated by fasting: a BOLD-fMRI study.

Science.gov (United States)

Belaïch, Rachida; Boujraf, Saïd; Benzagmout, Mohammed; Magoul, Rabia; Maaroufi, Mustapha; Tizniti, Siham

2017-11-01

The goal of this study was assessing the intermittent fasting effect on brain plasticity and oxidative stress (OS) using blood-oxygenation-level dependent (BOLD)-functional magnetic resonance image (fMRI) approach. Evidences of physiological and molecular phenomena involved in this process are discussed and compared to reported literature. Six fully healthy male non-smokers volunteered in this study. All volunteers were right handed, and have an equilibrated, consistent and healthy daily nutritional habit, and a healthy lifestyle. Participants were allowed consuming food during evening and night time while fasting with self-prohibiting food and liquids during 14 hours/day from sunrise to sunset. All participants underwent identical brain BOLD-fMRI protocol. The images were acquired in the Department of Radiology and Clinical Imaging of the University Hospital of Fez, Fez, Morocco. The anatomical brain and BOLD-fMRIs were acquired using a 1.5-Tesla scanner (Signa, General Electric, Milwaukee, United States). BOLD-fMRI image acquisition was done using single-shot gradient echo echo-planer imaging sequence. BOLD-fMRI paradigm consisted of the motor task where volunteers were asked to perform finger taping of the right hand. Two BOLD-fMRI scan sessions were performed, the first one between the 5th and 10th days preceding the start of fasting and the second between days 25th and 28th of the fasting month. All sessions were performed between 3:30 PM and 5:30 PM. Although individual maps were originated from different individual participants, they cover the same anatomic area in each case. Image processing and statistical analysis were conducted with Statistical Parameter Mapping version 8 (2008, Welcome Department of Cognitive Neurology, London UK). The maximal BOLD signal changes were calculated for each subject in the motor area M1; Activation maps were calculated and overlaid on the anatomical images. Group analysis of the data was performed, and the average volume

Comparison of T1-weighted fast spin-echo and T1-weighted fluid-attenuated inversion recovery images of the lumbar spine at 3.0 Tesla

International Nuclear Information System (INIS)

Lavdas, Eleftherios; Vlychou, Marianna; Arikidis, Nikos; Kapsalaki, Eftychia; Roka, Violetta; Fezoulidis, Ioannis V.

2010-01-01

Background: T1-weighted fluid-attenuated inversion recovery (FLAIR) sequence has been reported to provide improved contrast between lesions and normal anatomical structures compared to T1-weighted fast spin-echo (FSE) imaging at 1.5T regarding imaging of the lumbar spine. Purpose: To compare T1-weighted FSE and fast T1-weighted FLAIR imaging in normal anatomic structures and degenerative and metastatic lesions of the lumbar spine at 3.0T. Material and Methods: Thirty-two consecutive patients (19 females, 13 males; mean age 44 years, range 30-67 years) with lesions of the lumbar spine were prospectively evaluated. Sagittal images of the lumbar spine were obtained using T1-weighted FSE and fast T1-weighted FLAIR sequences. Both qualitative and quantitative analyses measuring the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and relative contrast (ReCon) between degenerative and metastatic lesions and normal anatomic structures were conducted, comparing these sequences. Results: On quantitative evaluation, SNRs of cerebrospinal fluid (CSF), nerve root, and fat around the root of fast T1-weighted FLAIR imaging were significantly lower than those of T1-weighted FSE images (P<0.001). CNRs of normal spinal cord/CSF and disc herniation/ CSF for fast T1-weighted FLAIR images were significantly higher than those for T1-weighted FSE images (P<0.001). ReCon of normal spinal cord/CSF, disc herniation/CSF, and vertebral lesions/CSF for fast T1-weighted FLAIR images were significantly higher than those for T1-weighted FSE images (P<0.001). On qualitative evaluation, it was found that CSF nulling and contrast at the spinal cord (cauda equina)/CSF interface for T1-weighted FLAIR images were significantly superior compared to those for T1-weighted FSE images (P<0.001), and the disc/spinal cord (cauda equina) interface was better for T1-weighted FLAIR images (P<0.05). Conclusion: The T1-weighted FLAIR sequence may be considered as the preferred lumbar spine imaging

Application of three-dimensional fast spin-echo T2-weighted image in lesions of the inner ear

International Nuclear Information System (INIS)

Xian Junfang; Wang Zhenchang; Yan Fei; Niu Yantao; Zhu Ye; Wang Yan; Tian Qichang; Lan Baosen

1999-01-01

Objective: To investigate the advantage of three-dimensional fast spin-echo T 2 -weighted image (3D FSE T 2 WI) in depicting normal structures and lesions of the inner ear. Methods: 3D FSE T 2 WI and 2D FSE T 2 WI were performed in 10 healthy volunteers and 20 cases with inner ear diseases. Advantages and disadvantages of the two techniques were compared. CT was performed in 6 cases with enlarged endo-lymphatic sac and 1 cases of Mondini malformation. Results: 3D FSE T 2 WI enabled visualization of detailed anatomic structures. Enlarged endo-lymphatic sacs were clearly revealed in 9 cases on 16 sides by 3D FSE T 2 WI, while only a part but not the whole of the enlarged endo-lymphatic sac could be shown on 2D FSE T 2 WI. In 6 cases, 3D FSE T 2 WI displayed enlarged endo-lymphatic sac on 11 sides and normal on 1 side; however, CT revealed enlarged vestibular aqueduct on all 12 sides. One case with small acoustic neuroma (only 4 mm in diameter) was clearly demonstrated on 3D FSE T 2 WI but not well shown on 2D FSE T 2 WI. One case with cochlear Mondini malformation associated with dysplasia of vestibule and semicircular canals was displayed more clearly on 3D FSE T 2 WI than on 2D FSE T 2 WI. Conclusions: 3D FSE T 2 WI can clearly display normal structures and lesions of the inner ear

Cerebral staging of lung cancer: is one single contrast-enhanced T1-weighted three-dimensional gradient-echo sequence sufficient?

Energy Technology Data Exchange (ETDEWEB)

Ohana, Mickael; Jeung, Mi-Young; Roy, Catherine [Nouvel Hopital Civil-Hopitaux Universitaires de Strasbourg, Service de Radiologie B/Radiology Department, Strasbourg (France); Bazille, Gauthier [Clinique Saint Anne-Groupe Radiologique MIM, Strasbourg (France)

2014-08-15

Gadolinium-enhanced magnetic resonance imaging (MRI) is the gold standard for cerebral staging in thoracic oncology. We hypothesize that a minimalist examination, consisting of a single contrast-enhanced T1-weighted three-dimensional gradient-echo sequence (CE 3D-GRE), would be sufficient for the cerebral staging of nonsymptomatic lung cancer patients. Seventy nonsymptomatic patients (50 % men; 62 years ± 10.2) referred for cerebral staging of a lung cancer were retrospectively included. All underwent a standard 3 T MRI examination with T1, FLAIR, T2* GRE, diffusion, and CE 3D-GRE sequences, for a total examination time of 20 min. The sole CE 3D-GRE (acquisition time: 6 min) was extracted and blindly interpreted by two radiologists in search of brain metastases. Hemorrhagic features of potential lesions and relevant incidental findings were also noted. Discrepant cases were reviewed by a third reader. The full MRI examination and follow-up studies were used as a reference to calculate sensitivity and specificity of the sole CE 3D-GRE. Thirty-eight point six percent (27 out of 70) of the patients had brain metastases. Performances and reader's agreement with the sole CE 3D-GRE sequence were excellent for the diagnosis of brain metastases (sensitivity = 96.3 %, specificity = 100 %, κ = 0.91) and incidental findings (sensitivity = 85.7 %, specificity = 100 %, κ = 0.62) but insufficient for the identification of hemorrhages within the metastases (sensitivity = 33.3 %, specificity = 85.7 %, κ = 0.47). In the specific case of lung cancer, cerebral staging in nonsymptomatic patients can be efficiently achieved with a minimalistic protocol consisting of a single CE 3D-GRE sequence, completed if positive with a T2* sequence for hemorrhagic assessment, thus halving appointment delays. (orig.)

Magnetic resonance imaging of the sacroiliac joints in patients with suspected spondyloarthritis. Comparison of turbo spin-echo and gradient-echo sequences for the detection of structural alterations; MRT-Bildgebung der Sakroiliakalgelenke bei Verdacht auf Spondyloarthritis. Vergleich von Turbospinecho- und Gradientenechosequenzen zum Nachweis struktureller Veraenderungen

Energy Technology Data Exchange (ETDEWEB)

Dornia, C.; Hoffstetter, P. [Universitaetsklinikum Regensburg (Germany). Inst. fuer Roentgendiagnostik; Asklepios Klinikum, Bad Abbach (Germany). Inst. fuer Roentgendiagnostik; Fleck, M. [Universitaetsklinikum Regensburg (Germany). Klinik fuer Innere Medizin I; Asklepios Klinikum, Bad Abbach (Germany). Klinik fuer Rheumatologie und Klinische Immunologie; Hartung, W. [Asklepios Klinikum, Bad Abbach (Germany). Klinik fuer Rheumatologie und Klinische Immunologie; Niessen, C.; Stroszczynski, C. [Universitaetsklinikum Regensburg (Germany). Inst. fuer Roentgendiagnostik

2015-02-15

Magnetic resonance imaging (MRI) is the method of choice for the evaluation of spondyloarthritis (SpA). According to the guidelines of the Assessment of Spondyloarthritis International Society (ASAS) and Outcome Measures in Rheumatology (OMERACT), MRI findings in SpA of the spine and the sacroiliac joints (SIJ) are classified as inflammatory and structural alterations. Modern gradient-echo sequences (GRE) are recommended for optimized detection of structural alterations of the SIJ. We assess the benefit of GRE in the detection of structural alterations of the SIJ in comparison to conventional turbo spin-echo sequences (TSE). Retrospective study of 114 patients who received MRI of the SIJ for the evaluation of SpA. Structural alterations of the SIJ were assessed by two blinded readers separately for T1 TSE and T2{sup *} GRE. The findings were classified according to a previously published chronicity score separately for both sides and sequences. Interobserver reliability was calculated with Cohen's Kappa, and the significance of findings was assessed with the Wilcoxon test. P-values < 0.05 were required for statistical significance. 68 of 114 (60%) patients showed SpA-typical findings of the SIJ. The average chronicity score for GRE (score 3.3) was significantly higher than for TSE (score 2.6), p=0.001. The Kappa-values for the interobserver reliability were 0.86-0.90 without any statistically significant differences between both sides and sequences. Both T1 TSE and T2{sup *} GRE showed a high interobserver reliability in the detection of structural alterations in patients with SpA. However, T2{sup *} GRE detected significantly more structural alterations than T1 TSE and should be an integral part of a modern MRI protocol for the diagnostic workup of patients with suspected SpA.

A magnetic gradient induced force in NMR restricted diffusion experiments

International Nuclear Information System (INIS)

Ghadirian, Bahman; Stait-Gardner, Tim; Castillo, Reynaldo; Price, William S.

2014-01-01

We predict that the phase cancellation of a precessing magnetisation field carried by a diffusing species in a bounded geometry under certain nuclear magnetic resonance pulsed magnetic field gradient sequences results in a small force over typically micrometre length scales. Our calculations reveal that the total magnetisation energy in a pore under the influence of a pulsed gradient will be distance-dependent thus resulting in a force acting on the boundary. It is shown that this effect of the magnetisation of diffusing particles will appear as either an attractive or repulsive force depending on the geometry of the pore and magnetic properties of the material. A detailed analysis is performed for the case of a pulsed gradient spin-echo experiment on parallel planes. It is shown that the force decays exponentially in terms of the spin-spin relaxation. The proof is based on classical electrodynamics. An application of this effect to soft matter is suggested

MEASUREMENT OF TRANSVERSE ECHOES IN RHIC

International Nuclear Information System (INIS)

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

2005-01-01

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 τ after the dipole kick, the beam re-cohered at time 2τ 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

Time-resolved Femtosecond Photon Echo Probes Bimodal Solvent Dynamics

NARCIS (Netherlands)

Pshenichnikov, M.S; Duppen, K.; Wiersma, D. A.

1995-01-01

We report on time-resolved femtosecond photon echo experiments of a dye molecule in a polar solution. The photon echo is time resolved by mixing the echo with a femtosecond gate pulse in a nonlinear crystal. It is shown that the temporal profile of the photon echo allows separation of the

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.

Gravitational wave sources: reflections and echoes

International Nuclear Information System (INIS)

Price, Richard H; Khanna, Gaurav

2017-01-01

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. (paper)

Sparse adaptive filters for echo cancellation

CERN Document Server

Paleologu, Constantin

2011-01-01

Adaptive filters with a large number of coefficients are usually involved in both network and acoustic echo cancellation. Consequently, it is important to improve the convergence rate and tracking of the conventional algorithms used for these applications. This can be achieved by exploiting the sparseness character of the echo paths. Identification of sparse impulse responses was addressed mainly in the last decade with the development of the so-called ``proportionate''-type algorithms. The goal of this book is to present the most important sparse adaptive filters developed for echo cancellati

Vertical structure of the vhf backscattering region in the equatorial electrojet and the gradient drift instability

International Nuclear Information System (INIS)

Fejer, B.G.; Farley, D.T.; Balsley, B.B.; Woodman, R.F.

1974-01-01

Radar measurements made with high spatial resolution and large dynamic range at the Jicamarca Radar Observatory near the time of reversal of the electrojet current provide further proof that the gradient drift instability is in fact responsible for the type-2 irregularities. Echoes are received over a much wider range of altitudes at night than during the day, partly because of the change in character of the background electron density profile and partly because of recombination effects, which can be important during the day. One must be cautious, particularly at night, in associating the mean Doppler shift of oblique radar echoes with the maximum east--west electron drift velocity

Mock ECHO: A Simulation-Based Medical Education Method.

Science.gov (United States)

Fowler, Rebecca C; Katzman, Joanna G; Comerci, George D; Shelley, Brian M; Duhigg, Daniel; Olivas, Cynthia; Arnold, Thomas; Kalishman, Summers; Monnette, Rebecca; Arora, Sanjeev

2018-04-16

This study was designed to develop a deeper understanding of the learning and social processes that take place during the simulation-based medical education for practicing providers as part of the Project ECHO® model, known as Mock ECHO training. The ECHO model is utilized to expand access to care of common and complex diseases by supporting the education of primary care providers with an interprofessional team of specialists via videoconferencing networks. Mock ECHO trainings are conducted through a train the trainer model targeted at leaders replicating the ECHO model at their organizations. Trainers conduct simulated teleECHO clinics while participants gain skills to improve communication and self-efficacy. Three focus groups, conducted between May 2015 and January 2016 with a total of 26 participants, were deductively analyzed to identify common themes related to simulation-based medical education and interdisciplinary education. Principal themes generated from the analysis included (a) the role of empathy in community development, (b) the value of training tools as guides for learning, (c) Mock ECHO design components to optimize learning, (d) the role of interdisciplinary education to build community and improve care delivery, (e) improving care integration through collaboration, and (f) development of soft skills to facilitate learning. Mock ECHO trainings offer clinicians the freedom to learn in a noncritical environment while emphasizing real-time multidirectional feedback and encouraging knowledge and skill transfer. The success of the ECHO model depends on training interprofessional healthcare providers in behaviors needed to lead a teleECHO clinic and to collaborate in the educational process. While building a community of practice, Mock ECHO provides a safe opportunity for a diverse group of clinician experts to practice learned skills and receive feedback from coparticipants and facilitators.

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.

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...... model and in colored non-stationary noise....

The effect of strong pitch angle scattering on the use of artificial auroral streaks for echo detection - Echo 5

International Nuclear Information System (INIS)

Swanson, R.L.; Steffen, J.E.; Winckler, J.R.

1986-01-01

During the Echo 5 experiment launched 13 November 1979 from the Poker Flat Research Range (Fairbanks, Alaska), a 0.75 A, 37 keV electron beam was injected both up and down the field line to test the use of optical and X-ray methods to detect the beam as it interacted with the atmosphere below the rocket for both the downward injections (markers) and the upward injected electrons which mirrored at the Southern Hemisphere and returned echoes. The artificial auroral streaks created by the markers were easily visible on the ground TV system but the large intensity of photons produced around the rocket masked any response to the markers by the on-board photometers and X-ray detectors. No echoes were detected with any of the detection systems although the power in some of the upward injections was 7.6 times the power in a detected downward injection thus setting an upper limit on the loss-cone echo flux. The magnitude of the bounce averaged pitch angle diffusion coefficient necessary to explain the lack of observable echoes was found to be 4 x 10 -4 S -1 . It was found that an equatorial wave electric field of 11 mVm -1 would account for the lack of echoes. Such fields should cause strong pitch angle scattering of up to 10 keV natural electrons and thus be consistent with the presence of diffuse aurora on the Echo 5 trajectory. (author)

Catheter visualisation in MR tomography: first animal experimental experiences with field inhomogeneity catheters

International Nuclear Information System (INIS)

Adam, G.; Glowinski, A.; Neuerburg, J.; Buecker, A.; Vaals, J.J. van; Hurtak, W.; Guenther, R.W.

1997-01-01

Purpose: To assess the feasibility of a new developed field inhomogeneity catheter for interventional MR imaging in vivo. Materials and methods: Three different prototypes of a field inhomogeneity catheter were investigated in 6 pigs. The catheters were introduced in Seldinger technique via the femoral vessels over a guide wire on an interventional MR system (Philips Gyroscan NT combined with a C-arm fluoroscopy unit [Philips BV 212[). Catheters were placed in veins and arteries. The catheter position was controlled by a fast gradient echo sequence (Turbo Field Echo [TEF[). Results: Catheters were introduced over a guide wire without complications in all cases. Using the field inhomogeneity concept, catheters were easily visualised in the inferior vena cava and the aorta by the fast gradient echo technique on MR in all cases. Although aortic branches were successfully cannulated, the catheters were not displayed by the TFE technique due to the complex and tortuous anatomy. All animals survived the experiments without complications. Conclusion: MR guided visualisation of a field inhomogeneity catheter is a simple concept which can be realised on each MR scanner and may allow intravascular MR guided interventions in future. (orig.) [de

Manifold regularized discriminative nonnegative matrix factorization with fast gradient descent.

Science.gov (United States)

Guan, Naiyang; Tao, Dacheng; Luo, Zhigang; Yuan, Bo

2011-07-01

Nonnegative matrix factorization (NMF) has become a popular data-representation method and has been widely used in image processing and pattern-recognition problems. This is because the learned bases can be interpreted as a natural parts-based representation of data and this interpretation is consistent with the psychological intuition of combining parts to form a whole. For practical classification tasks, however, NMF ignores both the local geometry of data and the discriminative information of different classes. In addition, existing research results show that the learned basis is unnecessarily parts-based because there is neither explicit nor implicit constraint to ensure the representation parts-based. In this paper, we introduce the manifold regularization and the margin maximization to NMF and obtain the manifold regularized discriminative NMF (MD-NMF) to overcome the aforementioned problems. The multiplicative update rule (MUR) can be applied to optimizing MD-NMF, but it converges slowly. In this paper, we propose a fast gradient descent (FGD) to optimize MD-NMF. FGD contains a Newton method that searches the optimal step length, and thus, FGD converges much faster than MUR. In addition, FGD includes MUR as a special case and can be applied to optimizing NMF and its variants. For a problem with 165 samples in R(1600), FGD converges in 28 s, while MUR requires 282 s. We also apply FGD in a variant of MD-NMF and experimental results confirm its efficiency. Experimental results on several face image datasets suggest the effectiveness of MD-NMF.

CONTRIBUTION OF VELOCITY VORTICES AND FAST SHOCK REFLECTION AND REFRACTION TO THE FORMATION OF EUV WAVES IN SOLAR ERUPTIONS

Energy Technology Data Exchange (ETDEWEB)

Wang, Hongjuan; Liu, Siqing; Gong, Jiancun [Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); Wu, Ning [School of Tourism and Geography, Yunnan Normal University, Kunming, Yunnan 650031 (China); Lin, Jun [Yunnan Observatories, Chinese Academy of Sciences, Kunming, Yunnan 650011 (China)

2015-06-01

We numerically study the detailed evolutionary features of the wave-like disturbance and its propagation in the eruption. This work is a follow-up to Wang et al., using significantly upgraded new simulations. We focus on the contribution of the velocity vortices and the fast shock reflection and refraction in the solar corona to the formation of the EUV waves. Following the loss of equilibrium in the coronal magnetic structure, the flux rope exhibits rapid motions and invokes the fast-mode shock at the front of the rope, which then produces a type II radio burst. The expansion of the fast shock, which is associated with outward motion, takes place in various directions, and the downward expansion shows the reflection and the refraction as a result of the non-uniform background plasma. The reflected component of the fast shock propagates upward and the refracted component propagates downward. As the refracted component reaches the boundary surface, a weak echo is excited. The Moreton wave is invoked as the fast shock touches the bottom boundary, so the Moreton wave lags the type II burst. A secondary echo occurs in the area where reflection of the fast shock encounters the slow-mode shock, and the nearby magnetic field lines are further distorted because of the interaction between the secondary echo and the velocity vortices. Our results indicate that the EUV wave may arise from various processes that are revealed in the new simulations.

Image correction during large and rapid B(0) variations in an open MRI system with permanent magnets using navigator echoes and phase compensation.

Science.gov (United States)

Li, Jianqi; Wang, Yi; Jiang, Yu; Xie, Haibin; Li, Gengying

2009-09-01

An open permanent magnet system with vertical B(0) field and without self-shielding can be quite susceptible to perturbations from external magnetic sources. B(0) variation in such a system located close to a subway station was measured to be greater than 0.7 microT by both MRI and a fluxgate magnetometer. This B(0) variation caused image artifacts. A navigator echo approach that monitored and compensated the view-to-view variation in magnetic resonance signal phase was developed to correct for image artifacts. Human brain imaging experiments using a multislice gradient-echo sequence demonstrated that the ghosting and blurring artifacts associated with B(0) variations were effectively removed using the navigator method.

The multigrid preconditioned conjugate gradient method

Science.gov (United States)

Tatebe, Osamu

1993-01-01

A multigrid preconditioned conjugate gradient method (MGCG method), which uses the multigrid method as a preconditioner of the PCG method, is proposed. The multigrid method has inherent high parallelism and improves convergence of long wavelength components, which is important in iterative methods. By using this method as a preconditioner of the PCG method, an efficient method with high parallelism and fast convergence is obtained. First, it is considered a necessary condition of the multigrid preconditioner in order to satisfy requirements of a preconditioner of the PCG method. Next numerical experiments show a behavior of the MGCG method and that the MGCG method is superior to both the ICCG method and the multigrid method in point of fast convergence and high parallelism. This fast convergence is understood in terms of the eigenvalue analysis of the preconditioned matrix. From this observation of the multigrid preconditioner, it is realized that the MGCG method converges in very few iterations and the multigrid preconditioner is a desirable preconditioner of the conjugate gradient method.

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.

Time Delay Estimation Algoritms for Echo Cancellation

Directory of Open Access Journals (Sweden)

Kirill Sakhnov

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.

Faster pediatric 3-T abdominal magnetic resonance imaging: comparison between conventional and variable refocusing flip-angle single-shot fast spin-echo sequences

Energy Technology Data Exchange (ETDEWEB)

Ruangwattanapaisarn, Nichanan [Mahidol University, Department of Diagnostic and Therapeutic Radiology, Ramathibodi Hospital, Bangkok (Thailand); Stanford University, LPCH Department of Radiology, Stanford, CA (United States); Loening, Andreas M.; Saranathan, Manojkumar; Vasanawala, Shreyas S. [Stanford University, LPCH Department of Radiology, Stanford, CA (United States); Litwiller, Daniel V. [GE Healthcare, Rochester, MN (United States)

2015-06-15

Single-shot fast spin echo (SSFSE) is particularly appealing in pediatric patients because of its motion robustness. However radiofrequency energy deposition at 3 tesla forces long pauses between slices, leading to longer scans, longer breath-holds and more between-slice motion. We sought to learn whether modulation of the SSFSE refocusing flip-angle train could reduce radiofrequency energy deposition without degrading image quality, thereby reducing inter-slice pauses and overall scan times. We modulated the refocusing flip-angle train for SSFSE to minimize energy deposition while minimizing blurring and motion-related signal loss. In a cohort of 50 consecutive patients (25 boys, mean age 5.5 years, range 1 month to 17 years) referred for abdominal MRI we obtained standard SSFSE and variable refocusing flip-angle (vrfSSFSE) images and recorded sequence scan times. Two readers independently scored the images in blinded, randomized order for noise, tissue contrast, sharpness, artifacts and left lobe hepatic signal uniformity on a four-point scale. The null hypothesis of no difference between SSFSE and vrfSSFSE image-quality was assessed with a Mann-Whitney U test, and the null hypothesis of no scan time difference was assessed with the paired t-test. SSFSE and vrfSSFSE mean acquisition times were 54.3 and 26.2 s, respectively (P-value <0.0001). For each reader, SSFSE and vrfSSFSE noise, tissue contrast, sharpness and artifacts were not significantly different (P-values 0.18-0.86). However, SSFSE had better left lobe hepatic signal uniformity (P < 0.01, both readers). vrfSSFSE is twice as fast as SSFSE, with equivalent image quality with the exception of left hepatic lobe signal heterogeneity. (orig.)

summarytable.PNG | 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.

Resources.PNG | 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.

Custom Search | 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.

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.

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 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

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.

Myocardial first pass perfusion imaging with gadobutrol: impact of parallel imaging algorithms on image quality and signal behavior.

Science.gov (United States)

Theisen, Daniel; Wintersperger, Bernd J; Huber, Armin; Dietrich, Olaf; Reiser, Maximilian F; Schönberg, Stefan O

2007-07-01

To implement parallel imaging algorithms in fast gradient recalled echo sequences for myocardial perfusion imaging and evaluate image quality, signal-to-noise ratio (SNR), contrast-enhancement ratio (CER), and semiquantitative perfusion parameters. In 20 volunteers, myocardial perfusion imaging with gadobutrol was performed at rest using an accelerated TurboFLASH sequence (TR 2.3 milliseconds, TE 0.93 milliseconds, flip angle [FA] 15 degrees) with GRAPPA, R=2. A nonaccelerated TurboFLASH sequence with similar scan parameters served as standard of reference. Artifacts were assessed qualitatively. SNR, CER, and CNR were calculated and semiquantitative perfusion parameters were determined from fitted SI-time curves. Phantom measurements yielded significant higher SNR for nonaccelerated images (Pimages (Pimages for artifacts by 2 board-certified radiologists yielded a significant reduction in dark rim artifacts with GRAPPA, R=2 (P<0.001). The application of GRAPPA with an acceleration factor of R=2 leads to a significant reduction of dark rim artifacts in fast gradient recalled echo sequences.

Theory and optical design of x-ray echo spectrometers

Science.gov (United States)

Shvyd'ko, Yuri

2017-08-01

X-ray echo spectroscopy, a space-domain counterpart of neutron spin echo, is a recently proposed inelastic x-ray scattering (IXS) technique. X-ray echo spectroscopy relies on imaging IXS spectra and does not require x-ray monochromatization. Due to this, the echo-type IXS spectrometers are broadband, and thus have a potential to simultaneously provide dramatically increased signal strength, reduced measurement times, and higher resolution compared to the traditional narrow-band scanning-type IXS spectrometers. The theory of x-ray echo spectrometers presented earlier [Yu. Shvyd'ko, Phys. Rev. Lett. 116, 080801 (2016), 10.1103/PhysRevLett.116.080801] is developed here further with a focus on questions of practical importance, which could facilitate optical design and assessment of the feasibility and performance of the echo spectrometers. Among others, the following questions are addressed: spectral resolution, refocusing condition, echo spectrometer tolerances, refocusing condition adjustment, effective beam size on the sample, spectral window of imaging and scanning range, impact of the secondary source size on the spectral resolution, angular dispersive optics, focusing and collimating optics, and detector's spatial resolution. Examples of optical designs and characteristics of echo spectrometers with 1-meV and 0.1-meV resolutions are presented.

Echo phenomena in a plasma

International Nuclear Information System (INIS)

Pavlenko, V.N.

1983-01-01

The mechanism of echo phenomenon in different plasma media: laboratory and cosmic plasma, metals and semiconductors is analyzed to get a more comprehensive idea on collective processes in a plasma and for practical applications in radiophysics and plasma diagnostics. The echo phenomenon permitted to confirm a reversible nature of the Landau damping, to prove the fact that the information on perturbation is conserved in a plasma (as non-damping oscillations of the distribution function) even after disappearing of the macroscopic field. The dependence of the diffusion coefficient on the velocity is measured, microturbulences in a plasma are investigated. New ways of the plasma wave conversion are suggested, as well as ''lightning'' of super-critical plasma layers and regions of plasma non-transparency. Prospective advantages of using echo for studying the mechanisms of charged particle interaction with the surface bounding a plasma are revealed

Vertical structure of the VHF backscattering region in the equatorial electrojet and the gradient drift instability

International Nuclear Information System (INIS)

Fejer, B.G.; Farley, D.T.; Balsley, B.B.; Woodman, R.F.

1975-01-01

Radar measurements made with high spatial resolution and large dynamic range at the Jicamarca Radar Observatory near the time of reversal of the electrojet current provide further proof that the gradient drift instability is in fact responsible for the type 2 irregularities. Echoes are received over a much wider range of altitudes at night than during the day partly because of the change in character of the background electron density profile and partly because of recombination effects, which can be important during the day. It is also shown that one must be cautious, particularly at night, in associating the mean Doppler shift of oblique radar echoes with the maximum east-west electron drift velocity

Multi-site study of diffusion metric variability: effects of site, vendor, field strength, and echo time on regions-of-interest and histogram-bin analyses.

Science.gov (United States)

Helmer, K G; Chou, M-C; Preciado, R I; Gimi, B; Rollins, N K; Song, A; Turner, J; Mori, S

2016-02-27

It is now common for magnetic-resonance-imaging (MRI) based multi-site trials to include diffusion-weighted imaging (DWI) as part of the protocol. It is also common for these sites to possess MR scanners of different manufacturers, different software and hardware, and different software licenses. These differences mean that scanners may not be able to acquire data with the same number of gradient amplitude values and number of available gradient directions. Variability can also occur in achievable b-values and minimum echo times. The challenge of a multi-site study then, is to create a common protocol by understanding and then minimizing the effects of scanner variability and identifying reliable and accurate diffusion metrics. This study describes the effect of site, scanner vendor, field strength, and TE on two diffusion metrics: the first moment of the diffusion tensor field (mean diffusivity, MD), and the fractional anisotropy (FA) using two common analyses (region-of-interest and mean-bin value of whole brain histograms). The goal of the study was to identify sources of variability in diffusion-sensitized imaging and their influence on commonly reported metrics. The results demonstrate that the site, vendor, field strength, and echo time all contribute to variability in FA and MD, though to different extent. We conclude that characterization of the variability of DTI metrics due to site, vendor, field strength, and echo time is a worthwhile step in the construction of multi-center trials.

Fast FLAIR MR images of intracranial hemorrhage

International Nuclear Information System (INIS)

Chun, Eun Ju; Choi, Hye Young; Cho, Young A; Kim, Wha Young

1998-01-01

The purpose of this study is to evaluate the signal characteristics of intracranial hemorrhage, as seen on fluid attenuated inversion recovery (FLAIR) MR imaging according to various stages, and to compare FLAIR imaging with spin-echo T1- and T2-weighted MR imaging. We retrospectively evaluated fast FLAIR images along with spin-echo T1- and T2 weighted MR images of 32 lesions in 25 patients (12 males and 14 females, aged 3 - 84 yrs) with intracranial hemorrhagic lesions. For imaging, 1.5 T unit was used, and the nature of the lesions was found to be as follows : intracranial hemorrhage (n=15); tumor (n=9); infarction (n=4); arteriovenous malformation (n=3); and arachnoid cyst with hemorrhage (n=1). On the basis of spin-echo MR imaging, lesions were classified as acute, early subacute, late subacute, early chronic, or late chronic stage. The signal characteristics of intracranial hemorrhage were analysed in accordance with each staging, as seen on MR FLAIR imaging, and compared to the staging seen on spin-echo T1- and T-2 weighted MR imaging. The signal intensity of intracranial hemorrhage, as seen on FLAIR imaging, was not characteristic; it was similar to that of T2WI during the acute and subacute stages, and similiar to that of T1WI during the chronic stage. When used together with spin-echo T1- and T2-weighted MR imaging, however, FLAIR imaging may be useful for the classification of chronic intracranial hemorrhage as either early or late stage. (author). 20 refs., 2 tabs., 6 figs

Comparison of two-dimensional fast spin echo T2 weighted sequences and three-dimensional volume isotropic T2 weighted fast spin echo (VISTA) MRI in the evaluation of triangular fibrocartilage of the wrist.

Science.gov (United States)

Park, Hee Jin; Lee, So Yeon; Kang, Kyung A; Kim, Eun Young; Shin, Hun Kyu; Park, Se Jin; Park, Jai Hyung; Kim, Eugene

2018-04-01

To compare image quality of three-dimensional volume isotropic T 2 weighted fast spin echo (3D VISTA) and two-dimensional (2D) T 2 weighted images (T2WI) for evaluation of triangular fibrocartilage (TFC) and to investigate whether 3D VISTA can replace 2D T 2 WI in evaluating TFC injury. This retrospective study included 69 patients who received wrist MRIs using both 2D T 2 WI and 3D VISTA techniques for assessment of wrist pathology, including TFC injury. Two radiologists measured the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR) of the two sequences. The anatomical identification score and diagnostic performance were independently assessed by two interpreters. The diagnostic abilities of 3D VISTA and 2D T 2 WI were analysed by sensitivity, specificity and accuracy for diagnosing TFC injury using surgically or clinically confirmed diagnostic reference standards. 17 cases (25%) were classified as having TFC injury. 2 cases (12%) were diagnosed surgically, and 15 cases (88%) were diagnosed by physical examination. 52 cases (75%) were diagnosed as having intact TFC. 8 of these cases (15%) were surgically confirmed, while the others were diagnosed by physical examination and clinical findings. The 3D VISTA images had significantly higher SNR and CNR values for the TFC than 2D T 2 WI images. The scores of 3D VISTA's total length, full width and sharpness were similar to those of 2D T 2 WI. We were unable to find a significant difference between 3D VISTA and 2D T 2 WI in the ability to diagnose TFC injury. 3D VISTA image quality is similar to that of 2D T 2 WI for TFC evaluation and is also excellent for tissue contrast. 3D VISTA can replace 2D images in TFC injury assessment. Advances in knowledge: 3D VISTA image quality is similar to that of 2D T 2 WI for TFC evaluation and is also excellent for tissue contrast. 3D VISTA can replace 2D images in TFC injury assessment.

Method of T2 spectrum inversion with conjugate gradient algorithm from NMR data

International Nuclear Information System (INIS)

Li Pengju; Shi Shangming; Song Yanjie

2010-01-01

Based on the optimization techniques, the T 2 spectrum inversion method of conjugate gradient that is easy to realize non-negativity constraint of T2 spectrum is proposed. The method transforms the linear mixed-determined problem of T2 spectrum inversion into the typical optimization problem of searching the minimum of objective function by building up the objective function according to the basic idea of geophysics modeling. The optimization problem above is solved with the conjugate gradient algorithm that has quick convergence rate and quadratic termination. The method has been applied to the inversion of noise free echo train generated from artificial spectrum, artificial echo train with signal-to-noise ratio (SNR)=25 and NMR experimental data of drilling core. The comparison between the inversion results of this paper and artificial spectrum or the result of software imported in NMR laboratory shows that the method can correctly invert T 2 spectrum from artificial NMR relaxation data even though SNR=25 and that inversion T 2 spectrum with good continuity and smoothness from core NMR experimental data accords perfectly with that of laboratory software imported, and moreover,the absolute error between the NMR porosity computed from T 2 spectrum and helium (He) porosity in laboratory is 0.65%. (authors)

Practical aspects of MR image interpretation

International Nuclear Information System (INIS)

Bradley, W.G.

1987-01-01

This is a practical course designed for those already reading CT scans who will be interpreting MR images. The course focuses on the unique information available from MR imaging that distinguishes it from CT. The following questions in specific subject areas are addressed: (1) What determines the proton density and T1 and T2 times of a particular tissue? How and why do these parameters change in certain disease states? (2) How does the protein content affect signal intensity through the mechanism of ''hydration layer water''? Why does hemorrhage sometimes appear dark and sometimes bright? Why do some paramagnetic substances (e.g., methemoglobin and Gd-DTPA) increase signal intensity and others (e.g., deoxyhemoglobin, hemosiderin, and ferritin) decrease signal intensity? How do the magnetic susceptibility effects depend on field strength and imaging technique (e.g., traditional Hahn spin echo versus gradient echo)? (3) What determines T1, T2, and proton density contrast in the traditional spin-echo and inversion-recovery images and in the new fast partial saturation techniques that use gradient echoes and reduced flip angles? (4) Why do flowing blood and CSF sometimes appear dark and sometimes bright? Exactly how do time-of-flight effects, turbulence, and odd-echo dephasing decrease signal intensity while flow-related enhancement, even-echo rephasing, and diastolic pseudogating increase signal intensity? How does one distinguish intraluminal pathology from high-intensity flow effects? How does one utilize the information in these flow phenomena and turn these ''artifacts'' to clinical advantage? Why do flowing blood and CSF generally appear bright on the new fast scan (e.g., FLASH and GRASS) images?

Magnetic resonance findings in amyotrophic lateral sclerosis using a spin echo magnetization transfer sequence: preliminary report

Directory of Open Access Journals (Sweden)

ROCHA ANTÔNIO JOSÉ DA

1999-01-01

Full Text Available We present the magnetic resonance (MR findings of five patients with amyotrophic lateral sclerosis (ALS using a spin-echo sequence with an additional magnetization transfer (MT pulse on T1-weighted images (T1 SE/MT. These findings were absent in the control group and consisted of hyperintensity of the corticospinal tract. Moreover we discuss the principles and the use of this fast but simple MR technique in the diagnosis of ALS

Meteor head echoes - observations and models

Directory of Open Access Journals (Sweden)

A. Pellinen-Wannberg

2005-01-01

Full Text Available Meteor head echoes - instantaneous echoes moving with the velocities of the meteors - have been recorded since 1947. Despite many attempts, this phenomenon did not receive a comprehensive theory for over 4 decades. The High Power and Large Aperture (HPLA features, combined with present signal processing and data storage capabilities of incoherent scatter radars, may give an explanation for the old riddle. The meteoroid passage through the radar beam can be followed with simultaneous spatial-time resolution of about 100m-ms class. The current views of the meteor head echo process will be presented and discussed. These will be related to various EISCAT observations, such as dual-frequency target sizes, altitude distributions and vector velocities.

MR diagnosis of temporomandibular arthrosis

Energy Technology Data Exchange (ETDEWEB)

Suenaga, Shigeaki [Kagoshima Univ. (Japan). Faculty of Dentistry

1996-09-01

This review described lesions of articular disk and its surrounding tissues revealed by MR examination in temporomandibular arthrosis, and problems and limits of the examination. Apparatus and imaging methods: Spin echo method was generally used and gradient echo method was alternatively used. Author`s apparatus was 1.5 tesla Signa, Advantage type, equipped with surface coil for temporomandibular joint. Imaging conditions were T1-weighted spin echo method, T2-weighted fast spin echo method, spoiled GRASS (gradient recalled acquisition in the steady state) method and GRASS method. MR findings of articular disk: MR images of normal and abnormal temporomandibular joint were presented together with computed radiographic findings. The role of dynamic imaging was described for evaluation and analysis of the joint functioning. MR findings of surrounding tissues of the disk: Dynamic MRI of the tissues was found useful to see whether the cause of pain was present inside or outside of the articular capsule. Joint effusion could not be fully imaged in T2-weighted conditions. (K.H.)

MR diagnosis of temporomandibular arthrosis

International Nuclear Information System (INIS)

Suenaga, Shigeaki

1996-01-01

This review described lesions of articular disk and its surrounding tissues revealed by MR examination in temporomandibular arthrosis, and problems and limits of the examination. Apparatus and imaging methods: Spin echo method was generally used and gradient echo method was alternatively used. Author's apparatus was 1.5 tesla Signa, Advantage type, equipped with surface coil for temporomandibular joint. Imaging conditions were T1-weighted spin echo method, T2-weighted fast spin echo method, spoiled GRASS (gradient recalled acquisition in the steady state) method and GRASS method. MR findings of articular disk: MR images of normal and abnormal temporomandibular joint were presented together with computed radiographic findings. The role of dynamic imaging was described for evaluation and analysis of the joint functioning. MR findings of surrounding tissues of the disk: Dynamic MRI of the tissues was found useful to see whether the cause of pain was present inside or outside of the articular capsule. Joint effusion could not be fully imaged in T2-weighted conditions. (K.H.)

Microchip capillary gel electrophoresis using programmed field strength gradients for the ultra-fast analysis of genetically modified organisms in soybeans.

Science.gov (United States)

Kim, Yun-Jeong; Chae, Joon-Seok; Chang, Jun Keun; Kang, Seong Ho

2005-08-12

We have developed a novel method for the ultra-fast analysis of genetically modified organisms (GMOs) in soybeans by microchip capillary gel electrophoresis (MCGE) using programmed field strength gradients (PFSG) in a conventional glass double-T microchip. Under the programmed electric field strength and 0.3% poly(ethylene oxide) sieving matrix, the GMO in soybeans was analyzed within only 11 s of the microchip. The MCGE-PFSG method was a program that changes the electric field strength during GMO analysis, and was also applied to the ultra-fast analysis of PCR products. Compared to MCGE using a conventional and constantly applied electric field, the MCGE-PFSG analysis generated faster results without the loss of resolving power and reproducibility for specific DNA fragments (100- and 250-bp DNA) of GM-soybeans. The MCGE-PFSG technique may prove to be a new tool in the GMO analysis due to its speed, simplicity, and high efficiency.

ECHO Data Partners Join Forces to Federate Access to Resources

Science.gov (United States)

Kendall, J.; Macie, M.

2003-12-01

During the past year the NASA's Earth Science Data and Information System (ESDIS) project has been collaborating with various Earth science data and client providers to design and implement the EOS Clearinghouse (ECHO). ECHO is an open, interoperable metadata clearinghouse and order broker system. ECHO functions as a repository of information intended to streamline access to digital data and services provided by NASA's Earth Science Enterprise and the extended Earth science community. In a unique partnership, ECHO data providers are working to extend their services in the digital era, to reflect current trends in scientific and educational communications. The multi-organization, inter-disciplinary content of ECHO provides a valuable new service to a growing number of Earth science applications and interdisciplinary research efforts. As such, ECHO is expected to attract a wide audience. In this poster, we highlight the contributions of current ECHO data partners and provide information for prospective data partners on how the project supports the incorporation of new collections and effective long-term asset management that is directly under the control of the organizations who contribute resources to ECHO.

Ultrafast bold fMRI using single-shot spin-echo echo planar imaging

Directory of Open Access Journals (Sweden)

Boujraf Said

2009-01-01

Full Text Available The choice of imaging parameters for functional MRI can have an impact on the accuracy of functional localization by affecting the image quality and the degree of blood oxygenation-dependent (BOLD contrast achieved. By improving sampling efficiency, parallel acquisition techniques such as sensitivity encoding (SENSE have been used to shorten readout trains in single-shot (SS echo planar imaging (EPI. This has been applied to susceptibility artifact reduction and improving spatial resolution. SENSE together with single-shot spin-echo (SS-SE imaging may also reduce off-resonance artifacts. The goal of this work was to investigate the BOLD response of a SENSE-adapted SE-EPI on a three Tesla scanner. Whole-brain fMRI studies of seven healthy right hand-dominant volunteers were carried out in a three Tesla scanner. fMRI was performed using an SS-SE EPI sequence with SENSE. The data was processed using statistical parametric mapping. Both, group and individual subject data analyses were performed. Individual average percentage and maximal percentage signal changes attributed to the BOLD effect in M1 were calculated for all the subjects as a function of echo time. Corresponding activation maps and the sizes of the activated clusters were also calculated. Our results show that susceptibility artifacts were reduced with the use of SENSE; and the acquired BOLD images were free of the typical quadrature artifacts of SS-EPI. Such measures are crucial at high field strengths. SS SE-EPI with SENSE offers further benefits in this regard and is more specific for oxygenation changes in the microvasculature bed. Functional brain activity can be investigated with the help of single-shot spin echo EPI using SENSE at high magnetic fields.

Nonlinear conjugate gradient methods in micromagnetics

Directory of Open Access Journals (Sweden)

J. Fischbacher

2017-04-01

Full Text Available Conjugate gradient methods for energy minimization in micromagnetics are compared. The comparison of analytic results with numerical simulation shows that standard conjugate gradient method may fail to produce correct results. A method that restricts the step length in the line search is introduced, in order to avoid this problem. When the step length in the line search is controlled, conjugate gradient techniques are a fast and reliable way to compute the hysteresis properties of permanent magnets. The method is applied to investigate demagnetizing effects in NdFe12 based permanent magnets. The reduction of the coercive field by demagnetizing effects is μ0ΔH = 1.4 T at 450 K.

Comparative study of interventricular phase difference and pressure gradient in cases of isolated ventricular septal defect

Energy Technology Data Exchange (ETDEWEB)

Elhaddad, SH; Moustafa, H; Ziada, G; Seleem, Z; Elsabban, KH; Mahmoud, F [Nuclear medicine department and pediatric cardiology department Faculty of medicine, Cairo university, Cairo, (Egypt)

1995-10-01

One hundred and fifty patients with isolated VSD were evaluated by radionuclide MUGA study and Echo-Doppler. Difference between phase angle of the right and left ventricles as detected by MUGA had been divided into main four groups according to pressure gradient between the two ventricles : group I (with pressure gradient {<=}30 mmHg and phase difference 80.10 degree{+-}34.1), group III (with pressure gradient > 70 mmHg and phase difference -0.5 degree {+-} 8.4). It has been found that there was a significant difference between the 4 groups as regards right - to - left ventricular phase difference (P<0.0001). There was significant delay in emptying of right ventricle in groups with pressure gradient < 50 mmHg. Regression analysis revealed inverse correlation between right -to- left ventricular phase difference with changes in pressure gradient (r= 0.81). Similarly, significant correlation had been found between right -to-left ventricular phase difference in relation Qp/Qs (r=0.85); conclusion: interventricular phase difference can be used to evaluate interventricular pressure gradient in cases of isolated VSD. 4 figs., 2 tabs.

Intracellular chemical gradients: morphing principle in bacteria

Directory of Open Access Journals (Sweden)

Endres Robert G

2012-09-01

Full Text Available Abstract Advances in computational biology allow systematic investigations to ascertain whether internal chemical gradients can be maintained in bacteria – an open question at the resolution limit of fluorescence microscopy. While it was previously believed that the small bacterial cell size and fast diffusion in the cytoplasm effectively remove any such gradient, a new computational study published in BMC Biophysics supports the emerging view that gradients can exist. The study arose from the recent observation that phosphorylated CtrA forms a gradient prior to cell division in Caulobacter crescentus, a bacterium known for its complicated cell cycle. Tropini et al. (2012 postulate that such gradients can provide an internal chemical compass, directing protein localization, cell division and cell development. More specifically, they describe biochemical and physical constraints on the formation of such gradients and explore a number of existing bacterial cell morphologies. These chemical gradients may limit in vitro analyses, and may ensure timing control and robustness to fluctuations during critical stages in cell development.

Rapid line scan MR angiography

International Nuclear Information System (INIS)

Frahm, J.; Merboldt, K.D.; Hanicke, W.; Bruhn, H.

1987-01-01

Direct MR angiography may be performed using line scan imaging techniques combined with presaturation of stationary spins. Thus, a single line scan echo yields a projection of vessels due to the signal from reflowing unsaturated spins. Reconstruction of an angiographic image is performed line by line at slightly incremented positions. In particular, line scan angiography is direct and fast without a sensitivity to artifacts even for high flow rates. Image resolution and field of view may be chosen without restrictions, and zoom images using enhanced gradients may be recorded without aliasing artifacts. The method is robust with respect to eddy currents and pulsatile flow. Line scan MR angiograms of phantoms, animals, and human volunteers have been recorded using 90 0 radio frequency pulses and gradient-recalled echoes

Utility of dual echo T2-weighted turbo spin echo MR imaging for differentiation of solid, malignant hepatic lesions from nonsolid, benign hepatic lesions

International Nuclear Information System (INIS)

Yang, Dal Mo; Yoon, Myung Hwan; Kim, Hak Soo; Lee, Eun Joo; Kim, Jong Ho; Kim, Hyung Sik; Chung, Jin Woo

1999-01-01

To evaluate the additive value of multiphasic contrast-enhanced dynamic MR imaging as a supplement to dual-echo T2-weighted TSE MR imaging for the differentiation of solid, malignant hepatic lesions from nonsolid, benign hepatic lesions. Two radiologists retrospectively reviewed dual-echo T2-weighted TSE MR images and gadolinium-enhanced MR images in 51 patients with hepatic lesions (28 malignant, 69 benign). For the differentiation of malignant from benign lesions, as seen on dual-echo T2-weighted TSE MR images, we evaluated sensitivity, specificity, and accuracy, and compared with the results with those for dual echo T2-weighted MR images plus multiphasic contrast-enhanced dynamic MR images. In addition, Az values for dual echo T2-weighted MR images were compared with those for dual echo T2-weighted MR images plus multiphasic contrast-enhanced dynamic MR images. For the differentiation of malignant from benign hepatic lesions, as seen on dual-echo T2-weighted TSE images, sensitivity, specificity, and accuracy were 80.0%, 97.5%, and 93.9%, respectively, for lesions less than 3cm in diameter, and 92.3%, 95.0%, and 93.5%, respectively, for those that were 3cm or larger. The results for dual-echo T2-weighted MR imaging plus multiphasic contrast-enhanced dynamic MR imaging were 86.7%, 100.0%, and 97.3%, respectively, for lesions less than 3cm, and 92.3%, 100.0%, and 95.7%, respectively for those that were 3cm or larger. There were no significant differences in sensitivity, specificity, or accuracy between the results obtained using dual-echo T2-weighted MR imaging and those obtained with dual-echo T2-weighted MR imaging plus multiphasic contrast-enhanced dynamic MR imaging. Nor were these statistically significant differences in Az values between the two groups. For the differentiation of solid, malignant hepatic lesions from nonsolid, benign hepatic lesions, there is no difference in accuracy between dual-echo T2-weighted TSE MR imaging and the additional use of

Effect of pressure on the fast motions in ordered phase phospholipid bilayers

Energy Technology Data Exchange (ETDEWEB)

Singh, H

2005-07-01

Application of hydrostatic pressure to phospholipid bilayers increases acyl chain order and raises the main transition temperature. {sup 2}H NMR spectra and quadrupole echo decay times were obtained at ambient pressure and pressures of 85 MPa and 196.1 MPa for ordered phase bilayers of a zwitterionic phospholipid : 16:0-16:0 PC-d{sub 62} (DPPC-d{sub 62}) and an anionic phospholipid : 16:0-16:0 PG-d{sub 62} (DPPG-d{sub 62}). The extent to which deuterium magnetization following an RF pulse is refocused in the echo after a second pulse is limited by the motions that modulate the orientation-dependent quadrupole interaction. The q-CPMG pulse sequence is used to separate the contribution of slow and fast motions to the echo decay rate. This work provides insight into how chain packing affects local motion.

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

International Nuclear Information System (INIS)

Cain, Peter A; Ahl, Ragnhild; Hedstrom, Erik; Ugander, Martin; Allansdotter-Johnsson, Ase; Friberg, Peter; Arheden, Hakan

2009-01-01

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. 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). 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 < 0.001), similar SV (p = 0.51) and lower EF (p = 0.014). No gender differences were seen in the youngest, 11–15 year, age range. 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

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

International Nuclear Information System (INIS)

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

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-naive 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. (orig.)

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

Energy Technology Data Exchange (ETDEWEB)

Morana, Giovanni; Tortora, Domenico; Severino, Mariasavina; Rossi, Andrea [Istituto Giannina Gaslini, Neuroradiology Unit, Genoa (Italy); Alves, Cesar Augusto [Hospital Das Clinicas, Radiology Department, Sao Paulo (Brazil); Finlay, Jonathan L. [Nationwide Children' s Hospital and The Ohio State University, Division of Hematology, Oncology and BMT, Columbus, OH (United States); Nozza, Paolo [Istituto Giannina Gaslini, Pathology Unit, Genoa (Italy); Ravegnani, Marcello; Pavanello, Marco [Istituto Giannina Gaslini, Neurosurgery Unit, Genoa (Italy); Milanaccio, Claudia; Garre, Maria Luisa [Istituto Giannina Gaslini, Neuro-oncology Unit, Genoa (Italy); Maghnie, Mohamad [Istituto Giannina Gaslini, University of Genova, Pediatric Endocrine Unit, Genoa (Italy)

2018-01-15

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-naive 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. (orig.)

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.

Frequency-Domain Adaptive Algorithm for Network Echo Cancellation in VoIP

Directory of Open Access Journals (Sweden)

Patrick A. Naylor

2008-05-01

Full Text Available We propose a new low complexity, low delay, and fast converging frequency-domain adaptive algorithm for network echo cancellation in VoIP exploiting MMax and sparse partial (SP tap-selection criteria in the frequency domain. We incorporate these tap-selection techniques into the multidelay filtering (MDF algorithm in order to mitigate the delay inherent in frequency-domain algorithms. We illustrate two such approaches and discuss their tradeoff between convergence performance and computational complexity. Simulation results show an improvement in convergence rate for the proposed algorithm over MDF and significantly reduced complexity. The proposed algorithm achieves a convergence performance close to that of the recently proposed, but substantially more complex improved proportionate MDF (IPMDF algorithm.

Multi-site Study of Diffusion Metric Variability: Characterizing the Effects of Site, Vendor, Field Strength, and Echo Time using the Histogram Distance

Science.gov (United States)

Helmer, K. G.; Chou, M-C.; Preciado, R. I.; Gimi, B.; Rollins, N. K.; Song, A.; Turner, J.; Mori, S.

2016-01-01

MRI-based multi-site trials now routinely include some form of diffusion-weighted imaging (DWI) in their protocol. These studies can include data originating from scanners built by different vendors, each with their own set of unique protocol restrictions, including restrictions on the number of available gradient directions, whether an externally-generated list of gradient directions can be used, and restrictions on the echo time (TE). One challenge of multi-site studies is to create a common imaging protocol that will result in a reliable and accurate set of diffusion metrics. The present study describes the effect of site, scanner vendor, field strength, and TE on two common metrics: the first moment of the diffusion tensor field (mean diffusivity, MD), and the fractional anisotropy (FA). We have shown in earlier work that ROI metrics and the mean of MD and FA histograms are not sufficiently sensitive for use in site characterization. Here we use the distance between whole brain histograms of FA and MD to investigate within- and between-site effects. We concluded that the variability of DTI metrics due to site, vendor, field strength, and echo time could influence the results in multi-center trials and that histogram distance is sensitive metrics for each of these variables. PMID:27350723

Multi-site Study of Diffusion Metric Variability: Characterizing the Effects of Site, Vendor, Field Strength, and Echo Time using the Histogram Distance.

Science.gov (United States)

Helmer, K G; Chou, M-C; Preciado, R I; Gimi, B; Rollins, N K; Song, A; Turner, J; Mori, S

2016-02-27

MRI-based multi-site trials now routinely include some form of diffusion-weighted imaging (DWI) in their protocol. These studies can include data originating from scanners built by different vendors, each with their own set of unique protocol restrictions, including restrictions on the number of available gradient directions, whether an externally-generated list of gradient directions can be used, and restrictions on the echo time (TE). One challenge of multi-site studies is to create a common imaging protocol that will result in a reliable and accurate set of diffusion metrics. The present study describes the effect of site, scanner vendor, field strength, and TE on two common metrics: the first moment of the diffusion tensor field (mean diffusivity, MD), and the fractional anisotropy (FA). We have shown in earlier work that ROI metrics and the mean of MD and FA histograms are not sufficiently sensitive for use in site characterization. Here we use the distance between whole brain histograms of FA and MD to investigate within- and between-site effects. We concluded that the variability of DTI metrics due to site, vendor, field strength, and echo time could influence the results in multi-center trials and that histogram distance is sensitive metrics for each of these variables.

Mobile Bay.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.

Report Environmental Violations | 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.

DWDashboard_Year.png | 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.

dashboard_3.PNG | 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.

ExampleDFR.PNG | 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.

monperload_1.PNG | 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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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.

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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.

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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.

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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.

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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.

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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.

Custom Search 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.

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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.

Water Pollution Search | 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.

Duel frequency echo data acquisition system for sea-floor classification

Digital Repository Service at National Institute of Oceanography (India)

Navelkar, G.S.; Desai, R.G.P.; Chakraborty, B.

An echo data acquisition system is designed to digitize echo signal from a single beam shipboard echo-sounder for use in sea-floor classification studies using a 12 bit analog to digital (A/D) card with a maximum sampling frequency of 1 MHz. Both 33...

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.

Fat-suppressed fast spin-echo mid-TE (TE[effective]=34) MR images: comparison with fast spin-echo T2-weighted images for the diagnosis of tears and anatomic variants of the glenoid labrum

Energy Technology Data Exchange (ETDEWEB)

Tuite, M J [Dept. of Radiology, Univ. of Wisconsin School of Medicine, Madison (United States); University of Wisconsin Hospital and Clinics, Dept. of Radiology, Madison, WI (United States); Shinners, T J; Hollister, M C [Dept. of Radiology, Univ. of Wisconsin School of Medicine, Madison (United States); Orwin, J F [Dept. of Orthopedic Surgery, University of Wisconsin School of Medicine, Madison (United States)

1999-12-01

Objective. To compare the sensitivity, specificity, and accuracy of fat-suppressed fast spin-echo (FSE) mid-TE (TE[effective]=34) images with fat-suppressed FSE T2-weighted images for the diagnosis of labral abnormalities.Design and patients. The study included 27 consecutive patients who had axial fat-suppressed FSE T2-weighted and fat-suppressed FSE mid-TE MR images, and had labral abnormalities diagnosed at arthroscopy. The acquisition time was about 5 min for each sequence, but the mid-TE sequence allowed a higher spatial resolution than the T2-weighted images (256 x 256 versus 256 x 192). Twenty-eight age-matched patients with arthroscopically normal labra were included as a control group. The labrum was graded on the MR images as normal or abnormal separately by two musculoskeletal radiologists who were masked to the history and arthroscopic results. The surgical findings were used as the gold standard for calculating the sensitivity, specificity, and accuracy for interpreting the correct location of a labral abnormality. The sensitivity, specificity, and accuracy for the two sequences were compared with a McNemar test, and significance defined as P<0.05.Results. For observer 1, the sensitivity for labral abnormalities was 0.59 on the T2-weighted images, and 0.78 on the mid-TE images (P=0.12). The specificity was 0.54 for the T2-weighted, and 0.64 for the mid-TE images (P=0.51). The accuracy was 0.56 for the T2-weighted, and 0.71 for the mid-TE images (P=0.08). For observer 2, the sensitivity/specificity/accuracy was 0.67/0.93/0.80 for the T2-weighted, and 0.70/0.86/0.78 for the mid-TE images (all P>0.5).Conclusion. In this small study there is no statistically significant difference for demonstrating labral abnormalities between FSE T2-weighted images, and higher-resolution fat-suppressed FSE mid-TE (TE[effective]=34) images obtained with a similar acquisition time. Although there was a general trend toward higher sensitivity and accuracy with the mid

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.)

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

International Nuclear Information System (INIS)

Fishbein, M.H.; Stevens, W.R.

2001-01-01

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.)

Feasibility of Imaging Tissue Electrical Conductivity by Switching Field Gradients with MRI.

Science.gov (United States)

Gibbs, Eric; Liu, Chunlei

2015-12-01

Tissue conductivity is a biophysical marker of tissue structure and physiology. Present methods of measuring tissue conductivity are limited. Electrical impedance tomography, and magnetic resonance electrical impedance tomography rely on passing external current through the object being imaged, which prevents its use in most human imaging. Recently, the RF field used for MR excitation has been used to non-invasively measure tissue conductivity. This technique is promising, but conductivity at higher frequencies is less sensitive to tissue structure. Measuring tissue conductivity non-invasively at low frequencies remains elusive. It has been proposed that eddy currents generated during the rise and decay of gradient pulses could act as a current source to map low-frequency conductivity. This work centers on a gradient echo pulse sequence that uses large gradients prior to excitation to create eddy currents. The electric and magnetic fields during a gradient pulse are simulated by a finite-difference time-domain simulation. The sequence is also tested with a phantom and an animal MRI scanner equipped with gradients of high gradient strengths and slew rate. The simulation demonstrates that eddy currents in materials with conductivity similar to biological tissue decay with a half-life on the order of nanoseconds and any eddy currents generated prior to excitation decay completely before influencing the RF signal. Gradient-induced eddy currents can influence phase accumulation after excitation but the effect is too small to image. The animal scanner images show no measurable phase accumulation. Measuring low-frequency conductivity by gradient-induced eddy currents is presently unfeasible.

Robust water fat separated dual-echo MRI by phase-sensitive reconstruction.

Science.gov (United States)

Romu, Thobias; Dahlström, Nils; Leinhard, Olof Dahlqvist; Borga, Magnus

2017-09-01

The purpose of this work was to develop and evaluate a robust water-fat separation method for T1-weighted symmetric two-point Dixon data. A method for water-fat separation by phase unwrapping of the opposite-phase images by phase-sensitive reconstruction (PSR) is introduced. PSR consists of three steps; (1), identification of clusters of tissue voxels; (2), unwrapping of the phase in each cluster by solving Poisson's equation; and (3), finding the correct sign of each unwrapped opposite-phase cluster, so that the water-fat images are assigned the correct identities. Robustness was evaluated by counting the number of water-fat swap artifacts in a total of 733 image volumes. The method was also compared to commercial software. In the water-fat separated image volumes, the PSR method failed to unwrap the phase of one cluster and misclassified 10. One swap was observed in areas affected by motion and was constricted to the affected area. Twenty swaps were observed surrounding susceptibility artifacts, none of which spread outside the artifact affected regions. The PSR method had fewer swaps when compared to commercial software. The PSR method can robustly produce water-fat separated whole-body images based on symmetric two-echo spoiled gradient echo images, under both ideal conditions and in the presence of common artifacts. Magn Reson Med 78:1208-1216, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

Cinematic study of temporomandibular joint motion using ultra-fast magnetic resonance imaging.

Science.gov (United States)

Manière-Ezvan, A; Havet, T; Franconi, J M; Quémar, J C; de Certaines, J D

1999-10-01

Magnetic Resonance Images (MRI) of the temporomandibular joint (TMJ) are usually performed to study the opening/closing movements of the mandible and have up to now been pseudodynamic step-by-step images simulating condylar motion by post-processing reconstruction. The aim of this study was: 1. to optimize a TMJ cine-imaging method to give a better clinical result than the step-by-step methods; 2. to develop an ultra-fast MRI Gradient Echo (GE) sequence for this purpose; and 3. to analyze condylar movements in the sagittal, coronal and para-axial planes during border mandibular displacements and chewing. Both TM joints were studied in six asymptomatic volunteers. The method involved a compromise between in-plane resolution, slice thickness, signal-to-noise ratio and time resolution. Routine clinical use was found to be a GE pulse sequence providing three images per second with an isometric voxel resolution of approximately two millimeters in ridge. This did not allow visualization of the disk. Using this sequence enabled real and simultaneous condylar displacement observation in the three planes of space and therefore contributed to a better functional diagnosis of pathologic TMJ motions.

Automated two-point dixon screening for the evaluation of hepatic steatosis and siderosis: comparison with R2-relaxometry and chemical shift-based sequences.

Science.gov (United States)

Henninger, B; Zoller, H; Rauch, S; Schocke, M; Kannengiesser, S; Zhong, X; Reiter, G; Jaschke, W; Kremser, C

2015-05-01

To evaluate the automated two-point Dixon screening sequence for the detection and estimated quantification of hepatic iron and fat compared with standard sequences as a reference. One hundred and two patients with suspected diffuse liver disease were included in this prospective study. The following MRI protocol was used: 3D-T1-weighted opposed- and in-phase gradient echo with two-point Dixon reconstruction and dual-ratio signal discrimination algorithm ("screening" sequence); fat-saturated, multi-gradient-echo sequence with 12 echoes; gradient-echo T1 FLASH opposed- and in-phase. Bland-Altman plots were generated and correlation coefficients were calculated to compare the sequences. The screening sequence diagnosed fat in 33, iron in 35 and a combination of both in 4 patients. Correlation between R2* values of the screening sequence and the standard relaxometry was excellent (r = 0.988). A slightly lower correlation (r = 0.978) was found between the fat fraction of the screening sequence and the standard sequence. Bland-Altman revealed systematically lower R2* values obtained from the screening sequence and higher fat fraction values obtained with the standard sequence with a rather high variability in agreement. The screening sequence is a promising method with fast diagnosis of the predominant liver disease. It is capable of estimating the amount of hepatic fat and iron comparable to standard methods. • MRI plays a major role in the clarification of diffuse liver disease. • The screening sequence was introduced for the assessment of diffuse liver disease. • It is a fast and automated algorithm for the evaluation of hepatic iron and fat. • It is capable of estimating the amount of hepatic fat and iron.

Highly transparent, stable, and superhydrophobic coatings based on gradient structure design and fast regeneration from physical damage

International Nuclear Information System (INIS)

Chen, Zao; Liu, Xiaojiang; Wang, Yan; Li, Jun; Guan, Zisheng

2015-01-01

Graphical abstract: - Highlights: • Highly transparent, stable, and superhydrophobic PET film was fabricated by dip-coating way. • The gradient structure is beneficial to both hydrophobicity and transparency. • The superhydrophobic PET film after physical damage can quickly regain by one-step spary. • The fabrication method is available for various substrates and large-scale production. - Abstract: Optical transparency, mechanical flexibility, and fast regeneration are important factors to expand the application of superhydrophobic surfaces. Herein, we fabricated highly transparent, stable, and superhydrophobic coatings through a novel gradient structure design by versatile dip-coating of silica colloid particles (SCPs) and diethoxydimethysiliane cross-linked silica nanoparticles (DDS-SNPs) on polyethylene terephthalate (PET) film and glass, followed by the modification of octadecyltrichlorosiliane (OTCS). When the DDS concentration reached 5 wt%, the modified SCPs/DDS-SNPs coating exhibited a water contact angle (WCA) of 153° and a sliding angle (SA) <5°. Besides, the average transmittance of this superhydrophobic coating on PET film and glass was increased by 2.7% and 1% in the visible wavelength, respectively. This superhydrophobic coating also showed good robustness and stability against water dropping impact, ultrasonic damage, and acid solution. Moreover, the superhydrophobic PET film after physical damage can quickly regain the superhydrophobicity by one-step spray regenerative solution of dodecyltrichlorosilane (DTCS) modified silica nanoparticles at room temperature. The demonstrated method for the preparation and regeneration of superhydrophobic coating is available for different substrates and large-scale production at room temperature.

Ultrasound pulse-echo measurements on rough surfaces with linear array transducers

DEFF Research Database (Denmark)

Sjøj, Sidsel M. N.; Blanco, Esther N.; Wilhjelm, Jens E.

2012-01-01

The echo from planar surfaces with rms roughness, Rq, in the range from 0-155 μm was measured with a clinical linear array transducer at different angles of incidence at 6 MHz and 12 MHz. The echo-pulse from the surfaces was isolated with an equal sized window and the power of the echo-pulse was ......The echo from planar surfaces with rms roughness, Rq, in the range from 0-155 μm was measured with a clinical linear array transducer at different angles of incidence at 6 MHz and 12 MHz. The echo-pulse from the surfaces was isolated with an equal sized window and the power of the echo......-pulse was calculated. The power of the echo from the smooth surface (Rq = 0) is highly angle-dependent due to a high degree of specular reflection. Within the angular range considered here, -10° to 10°, the variation spans a range of 18 dB at both 6 MHz and 12 MHz. When roughness increases, the angle......-dependence decreases, as the echo process gradually changes from pure reflection to being predominantly governed by backscattering. The power of the echoes from the two roughest surfaces (Rq = 115 μm and 155 μm) are largely independent of angle at both 6 MHz and 12 MHz with a variation of 2 dB in the angular range...

Automated two-point dixon screening for the evaluation of hepatic steatosis and siderosis: comparison with R2*-relaxometry and chemical shift-based sequences

Energy Technology Data Exchange (ETDEWEB)

Henninger, B.; Rauch, S.; Schocke, M.; Jaschke, W.; Kremser, C. [Medical University of Innsbruck, Department of Radiology, Innsbruck (Austria); Zoller, H. [Medical University of Innsbruck, Department of Internal Medicine, Innsbruck (Austria); Kannengiesser, S. [Siemens AG, Healthcare Sector, MR Applications Development, Erlangen (Germany); Zhong, X. [Siemens Healthcare, MR R and D Collaborations, Atlanta, GA (United States); Reiter, G. [Siemens AG, Healthcare Sector, MR R and D Collaborations, Graz (Austria)

2015-05-01

To evaluate the automated two-point Dixon screening sequence for the detection and estimated quantification of hepatic iron and fat compared with standard sequences as a reference. One hundred and two patients with suspected diffuse liver disease were included in this prospective study. The following MRI protocol was used: 3D-T1-weighted opposed- and in-phase gradient echo with two-point Dixon reconstruction and dual-ratio signal discrimination algorithm (''screening'' sequence); fat-saturated, multi-gradient-echo sequence with 12 echoes; gradient-echo T1 FLASH opposed- and in-phase. Bland-Altman plots were generated and correlation coefficients were calculated to compare the sequences. The screening sequence diagnosed fat in 33, iron in 35 and a combination of both in 4 patients. Correlation between R2* values of the screening sequence and the standard relaxometry was excellent (r = 0.988). A slightly lower correlation (r = 0.978) was found between the fat fraction of the screening sequence and the standard sequence. Bland-Altman revealed systematically lower R2* values obtained from the screening sequence and higher fat fraction values obtained with the standard sequence with a rather high variability in agreement. The screening sequence is a promising method with fast diagnosis of the predominant liver disease. It is capable of estimating the amount of hepatic fat and iron comparable to standard methods. (orig.)

Automated two-point dixon screening for the evaluation of hepatic steatosis and siderosis: comparison with R2*-relaxometry and chemical shift-based sequences

International Nuclear Information System (INIS)

Henninger, B.; Rauch, S.; Schocke, M.; Jaschke, W.; Kremser, C.; Zoller, H.; Kannengiesser, S.; Zhong, X.; Reiter, G.

2015-01-01

To evaluate the automated two-point Dixon screening sequence for the detection and estimated quantification of hepatic iron and fat compared with standard sequences as a reference. One hundred and two patients with suspected diffuse liver disease were included in this prospective study. The following MRI protocol was used: 3D-T1-weighted opposed- and in-phase gradient echo with two-point Dixon reconstruction and dual-ratio signal discrimination algorithm (''screening'' sequence); fat-saturated, multi-gradient-echo sequence with 12 echoes; gradient-echo T1 FLASH opposed- and in-phase. Bland-Altman plots were generated and correlation coefficients were calculated to compare the sequences. The screening sequence diagnosed fat in 33, iron in 35 and a combination of both in 4 patients. Correlation between R2* values of the screening sequence and the standard relaxometry was excellent (r = 0.988). A slightly lower correlation (r = 0.978) was found between the fat fraction of the screening sequence and the standard sequence. Bland-Altman revealed systematically lower R2* values obtained from the screening sequence and higher fat fraction values obtained with the standard sequence with a rather high variability in agreement. The screening sequence is a promising method with fast diagnosis of the predominant liver disease. It is capable of estimating the amount of hepatic fat and iron comparable to standard methods. (orig.)

The architecture of dynamic reservoir in the echo state network

Science.gov (United States)

Cui, Hongyan; Liu, Xiang; Li, Lixiang

2012-09-01

Echo state network (ESN) has recently attracted increasing interests because of its superior capability in modeling nonlinear dynamic systems. In the conventional echo state network model, its dynamic reservoir (DR) has a random and sparse topology, which is far from the real biological neural networks from both structural and functional perspectives. We hereby propose three novel types of echo state networks with new dynamic reservoir topologies based on complex network theory, i.e., with a small-world topology, a scale-free topology, and a mixture of small-world and scale-free topologies, respectively. We then analyze the relationship between the dynamic reservoir structure and its prediction capability. We utilize two commonly used time series to evaluate the prediction performance of the three proposed echo state networks and compare them to the conventional model. We also use independent and identically distributed time series to analyze the short-term memory and prediction precision of these echo state networks. Furthermore, we study the ratio of scale-free topology and the small-world topology in the mixed-topology network, and examine its influence on the performance of the echo state networks. Our simulation results show that the proposed echo state network models have better prediction capabilities, a wider spectral radius, but retain almost the same short-term memory capacity as compared to the conventional echo state network model. We also find that the smaller the ratio of the scale-free topology over the small-world topology, the better the memory capacities.

Can T1 w/T2 w ratio be used as a myelin-specific measure in subcortical structures? Comparisons between FSE-based T1 w/T2 w ratios, GRASE-based T1 w/T2 w ratios and multi-echo GRASE-based myelin water fractions.

Science.gov (United States)

Uddin, Md Nasir; Figley, Teresa D; Marrie, Ruth Ann; Figley, Chase R

2018-03-01

Given the growing popularity of T 1 -weighted/T 2 -weighted (T 1 w/T 2 w) ratio measurements, the objective of the current study was to evaluate the concordance between T 1 w/T 2 w ratios obtained using conventional fast spin echo (FSE) versus combined gradient and spin echo (GRASE) sequences for T 2 w image acquisition, and to compare the resulting T 1 w/T 2 w ratios with histologically validated myelin water fraction (MWF) measurements in several subcortical brain structures. In order to compare these measurements across a relatively wide range of myelin concentrations, whole-brain T 1 w magnetization prepared rapid acquisition gradient echo (MPRAGE), T 2 w FSE and three-dimensional multi-echo GRASE data were acquired from 10 participants with multiple sclerosis at 3 T. Then, after high-dimensional, non-linear warping, region of interest (ROI) analyses were performed to compare T 1 w/T 2 w ratios and MWF estimates (across participants and brain regions) in 11 bilateral white matter (WM) and four bilateral subcortical grey matter (SGM) structures extracted from the JHU_MNI_SS 'Eve' atlas. Although the GRASE sequence systematically underestimated T 1 w/T 2 w values compared to the FSE sequence (revealed by Bland-Altman and mountain plots), linear regressions across participants and ROIs revealed consistently high correlations between the two methods (r 2 = 0.62 for all ROIs, r 2 = 0.62 for WM structures and r 2 = 0.73 for SGM structures). However, correlations between either FSE-based or GRASE-based T 1 w/T 2 w ratios and MWFs were extremely low in WM structures (FSE-based, r 2 = 0.000020; GRASE-based, r 2 = 0.0014), low across all ROIs (FSE-based, r 2 = 0.053; GRASE-based, r 2 = 0.029) and moderate in SGM structures (FSE-based, r 2 = 0.20; GRASE-based, r 2 = 0.17). Overall, our findings indicated a high degree of correlation (but not equivalence) between FSE-based and GRASE-based T 1 w/T 2 w ratios, and low correlations between T 1 w/T 2 w ratios and MWFs. This

Electric Dipole Echoes in Rydberg Atoms

International Nuclear Information System (INIS)

Yoshida, S.; Reinhold, C. O.; Burgdoerfer, J.; Zhao, W.; Mestayer, J. J.; Lancaster, J. C.; Dunning, F. B.

2007-01-01

We report the first observation of echoes in the electric dipole moment of an ensemble of Rydberg atoms precessing in an external electric field F. Rapid reversal of the field direction is shown to play a role similar to that of a π pulse in NMR in rephasing a dephased ensemble of electric dipoles resulting in the buildup of an echo. The mechanisms responsible for this are discussed with the aid of classical trajectory Monte Carlo simulations

Quantifying Fast and Slow Responses of Terrestrial Carbon Exchange across a Water Availability Gradient in North American Flux Sites

Science.gov (United States)

Biederman, J. A.; Scott, R. L.; Goulden, M.

2014-12-01

prediction of terrestrial carbon balance. We will also present results of ongoing work to quantify fast and slow contributions to the relationship between evapotranspiration and precipitation across a precipitation gradient.

No counterpart of visual perceptual echoes in the auditory system.

Directory of Open Access Journals (Sweden)

Barkın İlhan

Full Text Available It has been previously demonstrated by our group that a visual stimulus made of dynamically changing luminance evokes an echo or reverberation at ~10 Hz, lasting up to a second. In this study we aimed to reveal whether similar echoes also exist in the auditory modality. A dynamically changing auditory stimulus equivalent to the visual stimulus was designed and employed in two separate series of experiments, and the presence of reverberations was analyzed based on reverse correlations between stimulus sequences and EEG epochs. The first experiment directly compared visual and auditory stimuli: while previous findings of ~10 Hz visual echoes were verified, no similar echo was found in the auditory modality regardless of frequency. In the second experiment, we tested if auditory sequences would influence the visual echoes when they were congruent or incongruent with the visual sequences. However, the results in that case similarly did not reveal any auditory echoes, nor any change in the characteristics of visual echoes as a function of audio-visual congruence. The negative findings from these experiments suggest that brain oscillations do not equivalently affect early sensory processes in the visual and auditory modalities, and that alpha (8-13 Hz oscillations play a special role in vision.

Echo project

DEFF Research Database (Denmark)

Gfader, Verina; Carson, Rebecca; Kraus, Chris

2016-01-01

team to both present the printed matter in the format of running a book stall, and stage a discursive event at the Classroom. Echo reverberates some of the encounters and debates there, with new commissioned chapters propelling a ongoing correspondence across urban environs: An essay on the General...... mothers and demonology (Kathy Acker’s property deals in the UK), and more; and future materials formalized as poster texts . . ....

T2-Weighted Dixon Turbo Spin Echo for Accelerated Simultaneous Grading of Whole-Body Skeletal Muscle Fat Infiltration and Edema in Patients With Neuromuscular Diseases.

Science.gov (United States)

Schlaeger, Sarah; Klupp, Elisabeth; Weidlich, Dominik; Cervantes, Barbara; Foreman, Sarah C; Deschauer, Marcus; Schoser, Benedikt; Katemann, Christoph; Kooijman, Hendrik; Rummeny, Ernst J; Zimmer, Claus; Kirschke, Jan S; Karampinos, Dimitrios C

2018-04-02

The assessment of fatty infiltration and edema in the musculature of patients with neuromuscular diseases (NMDs) typically requires the separate performance of T1-weighted and fat-suppressed T2-weighted sequences. T2-weighted Dixon turbo spin echo (TSE) enables the generation of T2-weighted fat- and water-separated images, which can be used to assess both pathologies simultaneously. The present study examines the diagnostic performance of T2-weighted Dixon TSE compared with the standard sequences in 10 patients with NMDs and 10 healthy subjects. Whole-body magnetic resonance imaging was performed including T1-weighted Dixon fast field echo, T2-weighted short-tau inversion recovery, and T2-weighted Dixon TSE. Fatty infiltration and intramuscular edema were rated by 2 radiologists using visual semiquantitative rating scales. To assess intermethod and interrater agreement, weighted Cohen's κ coefficients were calculated. The ratings of fatty infiltration showed high intermethod and high interrater agreement (T1-weighted Dixon fast field echo vs T2-weighted Dixon TSE fat image). The evaluation of edematous changes showed high intermethod and good interrater agreement (T2-weighted short-tau inversion recovery vs T2-weighted Dixon TSE water image). T2-weighted Dixon TSE imaging is an alternative for accelerated simultaneous grading of whole-body skeletal muscle fat infiltration and edema in patients with NMDs.

Time-resolved echo-shared parallel MRA of the lung: observer preference study of image quality in comparison with non-echo-shared sequences

International Nuclear Information System (INIS)

Fink, C.; Puderbach, M.; Zaporozhan, J.; Plathow, C.; Kauczor, H.-U.; Ley, S.

2005-01-01

The aim of this study was to evaluate the image quality of time-resolved echo-shared parallel MRA of the lung. The pulmonary vasculature of nine patients (seven females, two males; median age: 44 years) with pulmonary disease was examined using a time-resolved MRA sequence combining echo sharing with parallel imaging (time-resolved echo-shared angiography technique, or TREAT). The sharpness of the vessel borders, conspicuousness of peripheral lung vessels, artifact level, and overall image quality of TREAT was assessed independently by four readers in a side-by-side comparison with non-echo-shared time-resolved parallel MRA data (pMRA) previously acquired in the same patients. Furthermore, the SNR of pulmonary arteries (PA) and veins (PV) achieved with both pulse sequences was compared. The mean voxel size of TREAT MRA was decreased by 24% compared with the non-echo-shared MRA. Regarding the sharpness of the vessel borders, conspicuousness of peripheral lung vessels, and overall image quality the TREAT sequence was rated superior in 75-76% of all cases. If the TREAT images were preferred over the pMRA images, the advantage was rated as major in 61-71% of all cases. The level of artifacts was not increased with the TREAT sequence. The mean interobserver agreement for all categories ranged between fair (artifact level) and good (overall image quality). The maximum SNR of TREAT did not differ from non-echo-shared parallel MRA (PA: TREAT: 273±45; pMRA: 280±71; PV: TREAT: 273±33; pMRA: 258±62). TREAT achieves a higher spatial resolution than non-echo-shared parallel MRA which is also perceived as an improved image quality. (orig.)

Role of resistivity gradient in laser-driven ion acceleration

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