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Sample records for relaxation time t1

  1. Determination of T1- and T2-relaxation times in the spleen of patients with splenomegaly

    DEFF Research Database (Denmark)

    Thomsen, C; Josephsen, P; Karle, H

    1990-01-01

    Twenty-nine patients with known splenomegaly and seven healthy volunteers were examined. The T1 and T2 relaxation times were read out from a region of interest centrally in the spleen. Even though different mean T1 and T2 relaxation times were found between the groups, the great scatter and the c......Twenty-nine patients with known splenomegaly and seven healthy volunteers were examined. The T1 and T2 relaxation times were read out from a region of interest centrally in the spleen. Even though different mean T1 and T2 relaxation times were found between the groups, the great scatter...

  2. Local tissue properties of human osteoarthritic cartilage correlate with magnetic resonance T(1) rho relaxation times.

    Science.gov (United States)

    Tang, Simon Y; Souza, Richard B; Ries, Michael; Hansma, Paul K; Alliston, Tamara; Li, Xiaojuan

    2011-09-01

    The objective of this study is to examine the local relationship between T(1ρ) relaxation times and the mechanical behavior of human osteoarthritic articular cartilage using high-resolution magnetic resonance imaging (MRI) and local in situ microindentation. Seven human tibial plateaus were obtained from patients who underwent total knee arthroplasty due to severe osteoarthritis (OA). Three to six sites were selected from each sample for visual classification using the ICRS Outerbridge scale (a total of 36 sites). Samples were imaged by MR, and the local distribution of T(1ρ) relaxation times were obtained at these selected sites. The elastic and viscoelastic characteristics of the tissue were quantified nondestructively using dynamic microindentation to measure peak dynamic modulus, energy dissipation, and phase angle. Measured Outerbridge scores, MR T(1ρ) relaxation times, and mechanical properties were highly heterogeneous across each cartilage surface. Site-specific measures of T(1ρ) relaxation times correlated significantly with the phase angle (p properties in highly heterogeneous OA cartilage. These findings suggest that MRI T(1ρ) can provide a functional assessment of articular cartilage. Copyright © 2011 Orthopaedic Research Society.

  3. Normal-appearing brain t1 relaxation time predicts disability in early primary progressive multiple sclerosis.

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    Manfredonia, Francesco; Ciccarelli, Olga; Khaleeli, Zhaleh; Tozer, Daniel J; Sastre-Garriga, Jaume; Miller, David H; Thompson, Alan J

    2007-03-01

    To investigate whether patients with early primary progressive multiple sclerosis show changes in T1 relaxation time (T1-RT) in normal-appearing white matter (NAWM) and normal-appearing gray matter (NAGM) during 2 years and whether T1-RT at baseline predicts disability. Twenty-one patients and 12 control subjects were studied at baseline and after 2 years. Expanded Disability Status Scale (EDSS) and Multiple Sclerosis Functional Composite (MSFC) scores were assessed. T1 relaxation time histograms of NAWM and NAGM were obtained in all subjects, and mean, peak height, and peak location of the histograms were measured. Paired t tests were used to compare baseline and 2-year histogram values in patients and control subjects. To investigate whether T1-RT predicted clinical changes, multiple linear regression analysis was used. Patients showed increases in NAWM and NAGM T1-RT mean and peak location during follow-up, and significant decreases in NAWM and NAGM peak height. Baseline NAWM T1-RT mean values and peak height predicted disability at 2 years, as measured with the Multiple Sclerosis Functional Composite score. T1 relaxometry is a good marker of disease progression and has prognostic potential in primary progressive multiple sclerosis.

  4. Influence of spatial resolution and contrast agent dosage on myocardial T1 relaxation times.

    Science.gov (United States)

    Blaszczyk, Edyta; Töpper, Agnieszka; Schmacht, Luisa; Wanke, Felix; Greiser, Andreas; Schulz-Menger, Jeanette; von Knobelsdorff-Brenkenhoff, Florian

    2017-02-01

    Our aim was to study the influence of small variations in spatial resolution and contrast agent dosage on myocardial T1 relaxation time. Twenty-nine healthy volunteers underwent cardiovascular magnetic resonance at 3T twice, including a modified look-locker inversion recovery (MOLLI) technique-3(3)3(3)5-for T1 mapping. Native T1 was assessed in three spatial resolutions (voxel size 1.4 × 1.4 × 6, 1.6 × 1.6 × 6, 1.7 × 1.7 × 6 mm(3)), and postcontrast T1 after 0.1 and 0.2 mmol/kg gadobutrol. Partition coefficient was calculated based on myocardial and blood T1. T1 analysis was done per segment, per slice, and for the whole heart. Native T1 values did not differ with varying spatial resolution per segment (p = 0.116-0.980), per slice (basal: p = 0.772; middle: p = 0.639; apex: p = 0.276), and globally (p = 0.191). Postcontrast T1 values were significantly lower with higher contrast agent dosage (p 3T, very small variations in spatial resolution (voxel sizes between 1.4 × 1.4 × 6 and 1.7 × 1.7 × 6 mm(3)) remained without effect on the native T1 relaxation times. Postcontrast T1 values were naturally shorter with higher contrast agent dosage while the partition coefficient remained constant. Further studies are necessary to test whether these conclusions hold true for larger matrix sizes and in larger cohorts.

  5. In vivo measurements of T1 relaxation times of 31P-metabolites in human skeletal muscle

    DEFF Research Database (Denmark)

    Thomsen, C; Jensen, K E; Henriksen, O

    1989-01-01

    The T1 relaxation times were estimated for 31P-metabolites in human skeletal muscle. Five healthy volunteers were examined in a 1.5 Tesla wholebody imaging system using an inversion recovery pulse sequence. The calculated T1 relaxation times ranged from 5.517 sec for phosphocreatine to 3.603 sec...

  6. Knee Cartilage Thickness, T1ρ and T2 Relaxation Time Are Related to Articular Cartilage Loading in Healthy Adults.

    Directory of Open Access Journals (Sweden)

    Sam Van Rossom

    Full Text Available Cartilage is responsive to the loading imposed during cyclic routine activities. However, the local relation between cartilage in terms of thickness distribution and biochemical composition and the local contact pressure during walking has not been established. The objective of this study was to evaluate the relation between cartilage thickness, proteoglycan and collagen concentration in the knee joint and knee loading in terms of contact forces and pressure during walking. 3D gait analysis and MRI (3D-FSE, T1ρ relaxation time and T2 relaxation time sequence of fifteen healthy subjects were acquired. Experimental gait data was processed using musculoskeletal modeling to calculate the contact forces, impulses and pressure distribution in the tibiofemoral joint. Correlates to local cartilage thickness and mean T1ρ and T2 relaxation times of the weight-bearing area of the femoral condyles were examined. Local thickness was significantly correlated with local pressure: medial thickness was correlated with medial condyle contact pressure and contact force, and lateral condyle thickness was correlated with lateral condyle contact pressure and contact force during stance. Furthermore, average T1ρ and T2 relaxation time correlated significantly with the peak contact forces and impulses. Increased T1ρ relaxation time correlated with increased shear loading, decreased T1ρ and T2 relaxation time correlated with increased compressive forces and pressures. Thicker cartilage was correlated with higher condylar loading during walking, suggesting that cartilage thickness is increased in those areas experiencing higher loading during a cyclic activity such as gait. Furthermore, the proteoglycan and collagen concentration and orientation derived from T1ρ and T2 relaxation measures were related to loading.

  7. Relationship between aging and T1relaxation time in deep gray matter: A voxel-based analysis.

    Science.gov (United States)

    Okubo, Gosuke; Okada, Tomohisa; Yamamoto, Akira; Fushimi, Yasutaka; Okada, Tsutomu; Murata, Katsutoshi; Togashi, Kaori

    2017-09-01

    To investigate age-related changes in T 1 relaxation time in deep gray matter structures in healthy volunteers using magnetization-prepared 2 rapid acquisition gradient echoes (MP2RAGE). In all, 70 healthy volunteers (aged 20-76, mean age 42.6 years) were scanned at 3T magnetic resonance imaging (MRI). A MP2RAGE sequence was employed to quantify T 1 relaxation times. After the spatial normalization of T 1 maps with the diffeomorphic anatomical registration using the exponentiated Lie algebra algorithm, voxel-based regression analysis was conducted. In addition, linear and quadratic regression analyses of regions of interest (ROIs) were also performed. With aging, voxel-based analysis (VBA) revealed significant T 1 value decreases in the ventral-inferior putamen, nucleus accumbens, and amygdala, whereas T 1 values significantly increased in the thalamus and white matter as well (P VBA result. T 1 values in the thalamus (P < 0.0001), substantia nigra (P = 0.0003), and globus pallidus (P < 0.0001) had a best fit to quadratic curves, with the minimum T 1 values observed between 30 and 50 years of age. Age-related changes in T 1 relaxation time vary by location in deep gray matter. 2 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:724-731. © 2017 International Society for Magnetic Resonance in Medicine.

  8. Intraindividual comparison of T1 relaxation times after gadobutrol and Gd-DTPA administration for cardiac late enhancement imaging

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    Doeblin, Patrick, E-mail: Patrick.doeblin@charite.de [Department of Cardiology, Charité – Universitätsmedizin Berlin, Charité Campus Benjamin Franklin, Berlin (Germany); Schilling, Rene, E-mail: rene.schilling@charite.de [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); Wagner, Moritz, E-mail: moritz.wagner@charite.de [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); Luhur, Reny, E-mail: renyluhur@yahoo.com [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); Huppertz, Alexander, E-mail: alexander.huppertz@charite.de [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); Imaging Science Institute, Charité, Berlin (Germany); Hamm, Bernd, E-mail: bernd.hamm@charite.de [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); Taupitz, Matthias, E-mail: matthias.taupitz@harite.de [Department of Radiology, Charité – Universitätsmedizin Berlin, Charité Campus Mitte, Berlin (Germany); and others

    2014-04-15

    Purpose: To evaluate T1-relaxation times of chronic myocardial infarction (CMI) using gadobutrol and gadopentetate dimeglumine (Gd-DTPA) over time and to determine the optimal imaging window for late enhancement imaging with both contrast agents. Material and methods: Twelve patients with CMI were prospectively included and examined on a 1.5 T magnetic resonance (MR) system using relaxivity-adjusted doses of gadobutrol (0.15 mmol/kg) and Gd-DTPA (0.2 mmol/kg) in random order. T1-relaxation times of remote myocardium (RM), infarcted myocardium (IM), and left ventricular cavity (LVC) were assessed from short-axis TI scout imaging using the Look–Locker approach and compared intraindividually using a Wilcoxon paired signed-rank test (α < 0.05). Results: Within 3 min of contrast agent administration (CA), IM showed significantly lower T1-relaxation times than RM with both contrast agents, indicating beginning cardiac late enhancement. Differences between gadobutrol and Gd-DTPA in T1-relaxation times of IM and RM were statistically not significant through all time points. However, gadobutrol led to significantly higher T1-relaxation times of LVC than Gd-DTPA from 6 to 9 min (220 ± 15 ms vs. 195 ± 30 ms p < 0.01) onwards, resulting in a significantly greater ΔT1 of IM to LVC at 9–12 min (−20 ± 35 ms vs. 0 ± 35 ms, p < 0.05) and 12–15 min (−25 ± 45 ms vs. −10 ± 60 ms, p < 0.05). Using Gd-DTPA, comparable ΔT1 values were reached only after 25–35 min. Conclusion: This study indicates good delineation of IM to RM with both contrast agents as early as 3 min after administration. However, we found significant differences in T1 relaxation times with greater ΔT1 IM–LVC using 0.15 mmol/kg gadobutrol compared to 0.20 mmol/kg Gd-DTPA after 9–15 min post-CA suggesting earlier differentiability of IM and LVC using gadobutrol.

  9. Magnetic resonance imaging of spinal cord lesions in multiple sclerosis. Detection of lesions and serial T1 relaxation time values

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    Kojima, S.; Yagishita, T.; Fukutake, T.; Hirayama, K.; Fukuda, N.

    1987-05-01

    Magnetic resonance imaging (MRI) was used in three patients with multiple sclerosis (MS) to demonstrate the longitudinal distribution of demyelinating plaques in the spinal cord and to measure their T1 relaxation time values in these disease processes. Neurological examination allowed the detection of the superior limit of the spinal cord lesions in the three patients, but did not permit detection of the inferior limit in two of the patients. With MRI, however, it was possible to demonstrate the longitudinal distribution of demyelinating plaques in all three patients from coronal or sagittal images using spin echo and inversion recovery pulse sequences. In two patients treated with prednisolone, serial T1 relaxation time values of MS spinal cord lesions were measured from T1 calculated images. In one patient with transverse myelopathy, the T1 relaxation time values of MS spinal cord lesions were significantly increased at a stage of acute exacerbation. This is apparently in contrast with the values at the stage of remission. In the patient with localized cervical myelopathy, the increase in T1 relaxation time values of MS spinal cord lesions at the acute stage was small and significantly different from the values at the remission stage. Several recent reports have indicated that MRI is extremely sensitive in the detection of MS plaques, but most efforts to use MRI in the diagnosis of MS have been concentrated on brain lesions in spite of their frequent associations with spinal cord involvements. It is concluded from our case studies that MRI coronal or sagittal image is useful in demonstrating the longitudinal distribution of MS spinal cord lesions. In addition, serial observations of T1 relaxation time values of MS plaques may be important in assessing the activity of MS plaques and evaluation of the steroid therapy in MS processes.

  10. Tumor T1 Relaxation Time for Assessing Response to Bevacizumab Anti-Angiogenic Therapy in a Mouse Ovarian Cancer Model.

    Directory of Open Access Journals (Sweden)

    Murali K Ravoori

    Full Text Available To assess whether T1 relaxation time of tumors may be used to assess response to bevacizumab anti-angiogenic therapy.12 female nude mice bearing subcutaneous SKOV3ip1-LC ovarian tumors were administered bevacizumab (6.25ug/g, n=6 or PBS (control, n=6 therapy twice a week for two weeks. T1 maps of tumors were generated before, two days, and 2 weeks after initiating therapy. Tumor weight was assessed by MR and at necropsy. Histology for microvessel density, proliferation, and apoptosis was performed.Bevacizumab treatment resulted in tumor growth inhibition (p<0.04, n=6, confirming therapeutic efficacy. Tumor T1 relaxation times increased in bevacizumab treated mice 2 days and 2 weeks after initiating therapy (p<.05, n=6. Microvessel density decreased 59% and cell proliferation (Ki67+ decreased 50% in the bevacizumab treatment group (p<.001, n=6, but not apoptosis.Findings suggest that increased tumor T1 relaxation time is associated with response to bevacizumab therapy in ovarian cancer model and might serve as an early indicator of response.

  11. The effects of proteoglycan and type II collagen on T1rho relaxation time of articular cartilage

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    Choi, Won Seok; Yoo, Hye Jin; Hong, Sung Hwan; Choi, Ja Young [Dept. of Radiology and Institute of Radiation Medicine, Seoul National University Hospital, Seoul National University College of Medicine, Seoul (Korea, Republic of)

    2015-02-15

    To evaluate the effects of proteoglycan and type II collagen within articular cartilage on T1rho relaxation time of articular cartilage. This study was exempted by the institutional and animal review boards, and informed consent was not required. Twelve porcine patellae were assigned to three groups of control, trypsin-treated (proteoglycan-degraded), or collagenase-treated (collagen-degraded). The T1rho images were obtained with a 3 tesla magnetic resonance imaging scanner with a single loop coil. Statistical differences were detected by analysis of variance to evaluate the effects of the enzyme on T1rho relaxation time. Safranin-O was used to stain proteoglycan in the articular cartilage and immunohistochemical staining was performed for type II collagen. Mean T1rho values of the control, trypsin-treated, and collagenase-treated groups were 37.72 +/- 5.82, 57.53 +/- 8.24, and 45.08 +/- 5.31 msec, respectively (p < 0.001). Histology confirmed a loss of proteoglycan and type II collagen in the trypsin- and collagenase-treated groups. Degradation of proteoglycans and collagen fibers in the articular cartilage increased the articular cartilage T1rho value.

  12. Comparison of different pulse sequences for in vivo determination of T1 relaxation times in the human brain

    DEFF Research Database (Denmark)

    Kjaer, L; Henriksen, O

    1988-01-01

    ). T1 measurements were performed on the human brain using a whole body MR scanner operating at 1.5 tesla. Three different pulse sequences were compared including two 6-points inversion recovery (IR) sequences with TR = 2.0 s and 4.0, respectively, and a 12-points partial saturation inversion recovery...... (PSIR) sequence with TR varying between 0.24 and 8.0 s. The median T1 relaxation times obtained in cortical grey matter and cerebrospinal fluid were significantly shorter in the IR experiments at TR = 2 s than in those carried out at TR = 4 s. Concerning white matter the discrepancy was much less...

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

    Science.gov (United States)

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

    2017-11-01

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

  14. Fully Automatic Analysis of the Knee Articular Cartilage T1ρ relaxation time using Voxel Based Relaxometry

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    Pedoia, Valentina; Li, Xiaojuan; Su, Favian; Calixto, Nathaniel; Majumdar, Sharmila

    2016-01-01

    Purpose To develop and compare with classical ROI-based approach, a fully-automatic, local and unbiased way of studying the knee T1ρ relaxation time by creating an atlas and using Voxel Based Relaxometry (VBR) in OA and ACL subjects Materials and Methods In this study 110 subjects from 2 cohorts: (i) Mild OA 40 patients with mild-OA KL ≤ 2 and 15 controls KL ≤ 1; (ii) ACL cohort (a model for early OA): 40 ACL-injured patients imaged prior to ACL reconstruction and 1-year post-surgery and 15 controls are analyzed. All the subjects were acquired at 3T with a protocol that includes: 3D-FSE (CUBE) and 3D-T1ρ. A Non-rigid registration technique was applied to align all the images on a single template. This allows for performing VBR to assess local statistical differences of T1ρ values using z-score analysis. VBR results are compared with those obtained with classical ROI-based technique Results ROI-based results from atlas-based segmentation were consistent with classical ROI-based method (CV = 3.83%). Voxel-based group analysis revealed local patterns that were overlooked by ROI-based approach; e.g. VBR showed posterior lateral femur and posterior lateral tibia significant T1ρ elevations in ACL injured patients (sample mean z-score=9.7 and 10.3). Those elevations were overlooked by the classical ROI-based approach (sample mean z-score =1.87, and −1.73) Conclusion VBR is a feasible and accurate tool for the local evaluation of the biochemical composition of knee articular cartilage. VBR is capable of detecting specific local patterns on T1ρ maps in OA and ACL subjects PMID:26443990

  15. The application of T1 and T2 relaxation time and magnetization transfer ratios to the early diagnosis of patellar cartilage osteoarthritis

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    Yao, Weiwu; Qu, Nan; Lu, Zhihua; Yang, Shixun [Shanghai Jiaotong University, Department of Radiology, Shanghai (China)

    2009-11-15

    We compare the T1 and T2 relaxation times and magnetization transfer ratios (MTRs) of normal subjects and patients with osteoarthritis (OA) to evaluate the ability of these techniques to aid in the early diagnosis and treatment of OA. The knee joints in 11 normal volunteers and 40 patients with OA were prospectively evaluated using T1 relaxation times as measured using delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T2 relaxation times (multiple spin-echo sequence, T2 mapping), and MTRs. The OA patients were further categorized into mild, moderate, and severe OA. The mean T1 relaxation times of the four groups (normal, mild OA, moderate OA, and severe OA) were: 487.3{+-}27.7, 458.0{+-}55.9, 405.9{+-}57.3, and 357.9{+-}36.7 respectively (p<0.001). The mean T2 relaxation times of the four groups were: 37.8{+-}3.3, 44.0{+-}8.5, 50.9{+-}9.5, and 57.4{+-}4.8 respectively (p<0.001). T1 relaxation time decreased and T2 relaxation time increased with worsening degeneration of patellar cartilage. The result of the covariance analysis showed that the covariate age had a significant influence on T2 relaxation time (p<0.001). No significant differences between the normal and OA groups using MTR were noted. T1 and T2 relaxation times are relatively sensitive to early degenerative changes in the patellar cartilage, whereas the MTR may have some limitations with regard to early detection of OA. In addition, The T1 and T2 relaxation times negatively correlate with each other, which is a novel finding. (orig.)

  16. Native T1 Relaxation Time and Extracellular Volume Fraction as Accurate Markers of Diffuse Myocardial Fibrosis in Heart Valve Disease - Comparison With Targeted Left Ventricular Myocardial Biopsy.

    Science.gov (United States)

    Kockova, Radka; Kacer, Petr; Pirk, Jan; Maly, Jiri; Sukupova, Lucie; Sikula, Viktor; Kotrc, Martin; Barciakova, Lucia; Honsova, Eva; Maly, Marek; Kautzner, Josef; Sedmera, David; Penicka, Martin

    2016-04-25

    The aim of our study was to investigate the relationship between the cardiac magnetic resonance (CMR)-derived native T1 relaxation time and myocardial extracellular volume (ECV) fraction and the extent of diffuse myocardial fibrosis (DMF) on targeted myocardial left ventricular (LV) biopsy. The study population consisted of 40 patients (age 63±8 years, 65% male) undergoing valve and/or ascending aorta surgery for severe aortic stenosis (77.5%), root dilatation (7.5%) or valve regurgitation (15%). The T1 relaxation time was assessed in the basal interventricular septum pre- and 10-min post-contrast administration using the modified Look-Locker Inversion recovery sequence prior to surgery. LV myocardial biopsy specimen was obtained during surgery from the basal interventricular septal segment matched with the T1 mapping assessment. The percentage of myocardial collagen was quantified using picrosirius red staining. The average percentage of myocardial collagen was 22.0±14.8%. Both native T1 relaxation time with cutoff value ≥1,010 ms (sensitivity=90%, specificity=73%, area under the curve=0.82) and ECV with cutoff value ≥0.32 (sensitivity=80%, specificity=90%, area under the curve=0.85) showed high accuracy to identify severe (>30%) DMF. The native T1 relaxation time showed significant correlation with LV mass (Pmarkers of DMF. (Circ J 2016; 80: 1202-1209).

  17. (31) P MR spectroscopic imaging of the human prostate at 7 T: T1 relaxation times, Nuclear Overhauser Effect, and spectral characterization

    NARCIS (Netherlands)

    Lagemaat, M.W.; Maas, M.C.; Vos, E.K.; Bitz, A.K.; Orzada, S.; Weiland, E.; Uden, M.J. van; Kobus, T.; Heerschap, A.; Scheenen, T.W.J.

    2015-01-01

    Optimization of phosphorus ((31) P) MR spectroscopic imaging (MRSI) of the human prostate at 7 T by the evaluation of T1 relaxation times and the Nuclear Overhauser Effect (NOE) of phosphorus-containing metabolites.Twelve patients with prostate cancer and one healthy volunteer were scanned on a 7 T

  18. Reproducibility of myocardial T1 and T2 relaxation time measurement using slice-interleaved T1 and T2 mapping sequences.

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    Bellm, Steven; Basha, Tamer A; Shah, Ravi V; Murthy, Venkatesh L; Liew, Charlene; Tang, Maxine; Ngo, Long H; Manning, Warren J; Nezafat, Reza

    2016-11-01

    To assess measurement reproducibility and image quality of myocardial T1 and T2 maps using free-breathing slice-interleaved T1 and T2 mapping sequences at 1.5 Tesla (T). Eleven healthy subjects (33 ± 16 years; 6 males) underwent a slice-interleaved T1 and T2 mapping test/retest cardiac MR study at 1.5T on 2 days. For each day, subjects were imaged in two sessions with removal out of the magnet and repositioning before the subsequent session. We studied measurement reproducibility as well as the required sample size for sufficient statistical power to detect a predefined change in T1 and T2 . In a separate prospective study, we assessed T1 and T2 map image quality in 241 patients (54 ± 15 years; 73 women) with known/suspected cardiovascular disease referred for clinical cardiac MR. A subjective quality score was used to assess a segment-based image quality. In the healthy cohort, the slice-interleaved T1 measurements were highly reproducible, with global coefficients of variation (CVs) of 2.4% between subjects, 2.1% between days, and 1.7% between sessions. Slice-interleaved T2 mapping sequences provided similar reproducibility with global CVs of 7.2% between subjects, 6.3% between days, and 5.0 between sessions. A lower variability resulted in a reduction of the required number of subjects to achieve a certain statistical power when compared with other T1 mapping sequences. In the subjective image quality assessment, >80% of myocardial segments had interpretable data. Slice-interleaved T1 and T2 mapping sequences yield highly reproducible T1 and T2 measurements with >80% of interpretable myocardial segments. J. Magn. Reson. Imaging 2016;44:1159-1167. © 2016 International Society for Magnetic Resonance in Medicine.

  19. Combined Fat Imaging/Look Locker for mapping of lipid spin-lattice (T1) relaxation time

    Science.gov (United States)

    Jihyun Park, Annie; Yung, Andrew; Kozlowski, Piotr; Reinsberg, Stefan

    2012-10-01

    Tumor hypoxia is a main problem arising in the treatment of cancer due to its resistance to cytotoxic therapy such as radiation and chemotherapy, and selection for more aggressive tumor phenotypes. Attempts to improve and quantify tumor oxygenation are in development and tools to assess the success of such schemes are required. Monitoring oxygen level with MRI using T1 based method (where oxygen acts as T1 shortening agent) is a dynamic and noninvasive way to study tumor characteristics. The method's sensitivity to oxygen is higher in lipids than in water due to higher oxygen solubility in lipid. Our study aims to develop a time-efficient method to spatially map T1 of fat inside the tumor. We are combining two techniques: Fat/Water imaging and Look Locker (a rapid T1 measurement technique). Fat/Water Imaging is done with either Dixon or Direct Phase Encoding (DPE) method. The combination of these techniques poses new challenges that are tackled using spin dynamics simulations as well as experiments in vitro and in vivo.

  20. Effects of unloading on knee articular cartilage T1rho and T2 magnetic resonance imaging relaxation times: a case series.

    Science.gov (United States)

    Souza, Richard B; Baum, Thomas; Wu, Samuel; Feeley, Brian T; Kadel, Nancy; Li, Xiaojuan; Link, Thomas M; Majumdar, Sharmila

    2012-06-01

    Case series. It has been shown in rodent and canine models that cartilage composition is significantly altered in response to long-term unloading. To date, however, no in vivo human studies have investigated this topic. The objective of this case series was to determine the influence of unloading and reloading on T1rho and T2 relaxation times of articular cartilage in healthy young joints. Ten patients who required 6 to 8 weeks of non-weight bearing (NWB) for injuries affecting the distal lower extremity participated in the study. Quantitative T1rho and T2 imaging of the ipsilateral knee joint was performed at 3 time points: (1) prior to surgery (baseline), (2) immediately after a period of NWB (post-NWB), and (3) after 4 weeks of full weight bearing (post-FWB). Cartilage regions of interest were segmented and overlaid on T1rho and T2 relaxation time maps for quantification. Descriptive statistics are provided for all changes. Increases of 5% to 10% in T1rho times of all femoral and tibial compartments were noted post-NWB. All values returned to near-baseline levels post-FWB. Increases in medial tibia T2 times were noted post-NWB and remained elevated post-FWB. The load-bearing regions showed the most significant changes in response to unloading, with increases of up to 12%. The observation of a transient shift in relaxation times confirms that cartilage composition is subject to alterations based on loading conditions. These changes appear to be mostly related to proteoglycan content and more localized to the load-bearing regions. However, following 4 weeks of full weight bearing, relaxation times of nearly all regions had returned to baseline levels, demonstrating reversibility in compositional fluctuations. Therapy, level 4.

  1. [Relaxation times T1, T2, and T2* of apples, pears, citrus fruits, and potatoes with a comparison to human tissues].

    Science.gov (United States)

    Werz, Karin; Braun, Hans; Vitha, Dominik; Bruno, Graziano; Martirosian, Petros; Steidle, Günter; Schick, Fritz

    2011-09-01

    The aim of the project was a systematic assessment of relaxation times of different fruits and vegetables and a comparison to values of human tissues. Results provide an improved basis for selection of plant phantoms for development of new MR techniques and sequences. Vessels filled with agar gel are mostly used for this purpose, preparation of which is effortful and time-consuming. In the presented study apples, (malus, 8 species), pears, (pyrus, 2 species), citrus fruits (citrus, 5 species) and uncooked potatoes (solanum tuberosum, 8 species) from the supermarket were examined which are easily available nearly all-the-year. T1, T2 and T2* relaxation times of these nature products were measured on a 1.5 Tesla MR system with adapted examination protocols and mono-exponential fitting, and compared to literature data of human parenchyma tissues, fatty tissue and body fluid (cerebrospinal fluid). Resulting values were as follows: apples: T1: 1486-1874 ms, T2: 163-281 ms, T2*: 2.3-3.2 ms; pears: T1: 1631-1969 ms, T2: 119-133 ms, T2* : 10.1-10.6 ms, citrus fruits (pulp) T1: 2055-2632 ms, T2: 497-998 ms, T2* : 151-182 ms; citrus fruits (skin) T1: 561-1669 ms, T2: 93-119 ms; potatoes: T1: 1011-1459 ms, T2: 166 - 210 ms, T2* : 20 - 30 ms. All T1-values of the examined objects (except for potatoes and skins of citrus fruits) were longer than T1 values of human tissues. Also T2 values (except for pears and skins of citrus fruits) of the fruits and the potatoes tended to be longer. T2* values of apples, pears and potatoes were shorter than in healthy human tissue. Results show relaxation values of many fruits to be not exactly fitting to human tissue, but with suitable selection of the fruits and optionally with an adaption of measurement parameters one can achieve suitable contrast and signal characteristics for some purposes. Copyright © 2011. Published by Elsevier GmbH.

  2. Comparison of different pulse sequences for in vivo determination of T1 relaxation times in the human brain

    DEFF Research Database (Denmark)

    Kjaer, L; Henriksen, O

    1988-01-01

    ). T1 measurements were performed on the human brain using a whole body MR scanner operating at 1.5 tesla. Three different pulse sequences were compared including two 6-points inversion recovery (IR) sequences with TR = 2.0 s and 4.0, respectively, and a 12-points partial saturation inversion recovery...

  3. High-field 1H T1 and T2 NMR relaxation time measurements of H2O in homeopathic preparations of quartz, sulfur, and copper sulfate

    Science.gov (United States)

    Baumgartner, Stephan; Wolf, Martin; Skrabal, Peter; Bangerter, Felix; Heusser, Peter; Thurneysen, André; Wolf, Ursula

    2009-09-01

    Quantitative meta-analyses of randomized clinical trials investigating the specific therapeutic efficacy of homeopathic remedies yielded statistically significant differences compared to placebo. Since the remedies used contained mostly only very low concentrations of pharmacologically active compounds, these effects cannot be accounted for within the framework of current pharmacology. Theories to explain clinical effects of homeopathic remedies are partially based upon changes in diluent structure. To investigate the latter, we measured for the first time high-field (600/500 MHz) 1H T1 and T2 nuclear magnetic resonance relaxation times of H2O in homeopathic preparations with concurrent contamination control by inductively coupled plasma mass spectrometry (ICP-MS). Homeopathic preparations of quartz (10 c-30 c, n = 21, corresponding to iterative dilutions of 100-10-100-30), sulfur (13 x-30 x, n = 18, 10-13-10-30), and copper sulfate (11 c-30 c, n = 20, 100-11-100-30) were compared to n = 10 independent controls each (analogously agitated dilution medium) in randomized and blinded experiments. In none of the samples, the concentration of any element analyzed by ICP-MS exceeded 10 ppb. In the first measurement series (600 MHz), there was a significant increase in T1 for all samples as a function of time, and there were no significant differences between homeopathic potencies and controls. In the second measurement series (500 MHz) 1 year after preparation, we observed statistically significant increased T1 relaxation times for homeopathic sulfur preparations compared to controls. Fifteen out of 18 correlations between sample triplicates were higher for controls than for homeopathic preparations. No conclusive explanation for these phenomena can be given at present. Possible hypotheses involve differential leaching from the measurement vessel walls or a change in water molecule dynamics, i.e., in rotational correlation time and/or diffusion. Homeopathic preparations

  4. INVESTIGATION OF MOLECULAR INTERACTION BETWEEN PHENYLACETYLENE AND HEXAMETHYLPHOSPHORIC TRIAMIDE BY 13C NMR T1 RELAXATION TIME STUDIES AND AB INITIO QM CALCULATIONS

    Directory of Open Access Journals (Sweden)

    Parsaoran Siahaan

    2010-06-01

    Full Text Available Intermolecular interactions and molecular translational and rotational mobility are key factors in molecular material sciences, e.g. liquid crystals. One of the important substructures is given by phenylacetylene, Ph-CºCH. Its rotational behavior in its pure form and in high dilution in hexamethylphosphoric triamide OP[N(CH32]3 (HMPA has been studied by means 13C NMR T1 relaxation times at ambient temperature as measured by the inversion recovery method. HMPA is an exceptional solvent in that is has a quite large dipole moment but comparatively low relative dielectricity constant. From the molecular shape Ph-CºCH is expected to exhibit anisotropic rotational diffusion which in fact can be deduced from the measured set of T1 values of the ortho, meta and para carbon nuclei in the neat liquid as well as in the HMPA solution. This expected result rules the dominance of a linearly molecules pair Ph-CºCH...HMPA along their dipole moment axes as anticipated in view of the large HMPA dipole moment. In order to conform with the T1 data, a linear arrangement of Ph-CºCH via the interaction between its weakly acidic H-atom with negatively charge O-atom of HMPA molecules seems to lead to such an anisotropic rotational motion. This hypothesis is supported by ab initio QM calculations which come out with higher interaction energy for linear orientation than other geometries. These ab initio calculations were performed with the basis set of RHF/6-31G(d for the single molecules of Ph-CºCH and HMPA as well as for their various geometries of the molecules pair. Molecular dynamics simulations need to be performed for further confirmation.   Keywords: Relaxation Times, HMPA, pheylacetylene, ab initio, intermolecular interaction, rotational diffusion

  5. Interrelations of Epicardial Fat Volume, Left Ventricular T1-Relaxation Times and Myocardial Strain in Hypertensive Patients: A Cardiac Magnetic Resonance Study.

    Science.gov (United States)

    Homsi, Rami; Kuetting, Daniel; Sprinkart, Alois; Steinfeld, Nina; Meier-Schroers, Michael; Luetkens, Julian; Nadal, Jennifer; Dabir, Darius; Fischer, Stefan; Gieseke, Juergen; Schild, Hans; Thomas, Daniel

    2017-05-01

    This cardiac magnetic resonance study was performed to assess myocardial fibrosis by evaluating T1-relaxation time (T1), to measure left ventricular (LV) strain, and to determine epicardial fat volume (EFV) in hypertensive patients with no history of cardiovascular (CV) events and to relate the results to the presence of coronary atherosclerotic artery disease (CAD) in these patients. A total of 123 subjects were examined at 1.5 T. Of them, 98 were hypertensive patients (58 men; mean age, 62.9±10.7 y; body mass index, 29.0±5.6 kg/m) and 25 were controls without CV risk factors or disease (13 men; 60.1±10.7 y; 28.1±5.4 kg/m). All patients had a well-treated blood pressure. In the hypertensive group, 56 patients had no CAD, whereas 42 patients had CAD. T1 was assessed by a modified Look-Locker inversion recovery sequence. Longitudinal and circumferential peak systolic strain (LS; CS) was determined with dedicated cardiac magnetic resonance software (feature tracking). EFV (normalized to the body surface area) was assessed by a 3D Dixon sequence. T1 (ms) and EFV (mL/m) were higher and CS and LS (%) were lower in hypertensive patients compared with those in nonhypertensive controls (PEFV=58.2±21.1; hypertensive patients overall: T1=991.3±45.5, LS=-21.0±4.5, CS=-25.0±5.9, EFV=71.1±25.3; hypertensive patients without CAD: T1=991.6±48.4, LS=-21.0±4.7, CS=-24.6±6.3, EFV=71.3±26.6; hypertensive patients with CAD: T1=986.7±39.2, LS=-21.1±4.3, CS=-25.5±5.4, EFV=70.9±23.6). There were no significant differences between hypertensive patients with and those without CAD and between patients grouped according to the number of vessels affected (0-vessel disease, 1-vessel disease, 2-vessel disease, or 3-vessel disease). Hypertension is associated with signs of myocardial fibrosis and an impaired LV contractility despite a normal LV ejection fraction, as well as with an increased EFV. However, CAD, in the absence of previous pathologies with consecutive myocardial

  6. Hybrid approaches to magnetic resonance thermometry using the proton resonance frequency shift and the spin-lattice relaxation time T1

    Science.gov (United States)

    Diakite, Mahamadou

    Minimally invasive thermal therapy under Magnetic Resonance Imaging (MRI) guidance is becoming popular with several applications in the process of getting FDA approval. The ability to determine in near real-time the temperature map of a tumor and its surrounding tissue makes MR thermometry very attractive and well suited for thermal treatment. The proton resonance frequency shift (PRF) is currently the gold standard method for temperature monitoring using MRI. However, its incapacity to measure temperature in fatty tissue limits the scope of its applicability. The spin lattice relaxation time T1, on the other hand, has shown good temperature sensitivity and works well in all types of tissues. In this dissertation, we have addressed a number of challenges currently affecting MRI thermometry. A non-CPMG Turbo Spin Echo (TSE) sequence has been implemented to monitor the temperature rise due to the high RF power deposition inherent to this sequence at high field (3T and higher). This new implementation allows TSE sequences to be used safely without altering their high contrast properties which make them appealing in clinical settings. Tissue damage assessment during thermal therapy is critical for the safety of the patient. We have developed a new hybrid PRF-T1 sequence that has the capability to provide simultaneously in near real-time the temperature map and T1 information, which is a good indication of the state of the tissue. The simplicity and the real-time capability of the newly developed sequence make it an ideal tool for tissue damage assessment. Temperature monitoring during thermal therapy in organs with large fat content have been hindered by the lack of an MRI thermometry method that can provide simultaneous temperature in fat and aqueous tissue. A new sequence and acquisition scheme have been developed to address this issue. In sum, this dissertation proposed several pulse sequence implementation techniques and an acquisition scheme to overcome some of

  7. Rapid Parametric Mapping of the Longitudinal Relaxation Time T1 Using Two-Dimensional Variable Flip Angle Magnetic Resonance Imaging at 1.5 Tesla, 3 Tesla, and 7 Tesla

    Science.gov (United States)

    Dieringer, Matthias A.; Deimling, Michael; Santoro, Davide; Wuerfel, Jens; Madai, Vince I.; Sobesky, Jan; von Knobelsdorff-Brenkenhoff, Florian; Schulz-Menger, Jeanette; Niendorf, Thoralf

    2014-01-01

    Introduction Visual but subjective reading of longitudinal relaxation time (T1) weighted magnetic resonance images is commonly used for the detection of brain pathologies. For this non-quantitative measure, diagnostic quality depends on hardware configuration, imaging parameters, radio frequency transmission field (B1+) uniformity, as well as observer experience. Parametric quantification of the tissue T1 relaxation parameter offsets the propensity for these effects, but is typically time consuming. For this reason, this study examines the feasibility of rapid 2D T1 quantification using a variable flip angles (VFA) approach at magnetic field strengths of 1.5 Tesla, 3 Tesla, and 7 Tesla. These efforts include validation in phantom experiments and application for brain T1 mapping. Methods T1 quantification included simulations of the Bloch equations to correct for slice profile imperfections, and a correction for B1+. Fast gradient echo acquisitions were conducted using three adjusted flip angles for the proposed T1 quantification approach that was benchmarked against slice profile uncorrected 2D VFA and an inversion-recovery spin-echo based reference method. Brain T1 mapping was performed in six healthy subjects, one multiple sclerosis patient, and one stroke patient. Results Phantom experiments showed a mean T1 estimation error of (-63±1.5)% for slice profile uncorrected 2D VFA and (0.2±1.4)% for the proposed approach compared to the reference method. Scan time for single slice T1 mapping including B1+ mapping could be reduced to 5 seconds using an in-plane resolution of (2×2) mm2, which equals a scan time reduction of more than 99% compared to the reference method. Conclusion Our results demonstrate that rapid 2D T1 quantification using a variable flip angle approach is feasible at 1.5T/3T/7T. It represents a valuable alternative for rapid T1 mapping due to the gain in speed versus conventional approaches. This progress may serve to enhance the capabilities of

  8. Rapid parametric mapping of the longitudinal relaxation time T1 using two-dimensional variable flip angle magnetic resonance imaging at 1.5 Tesla, 3 Tesla, and 7 Tesla.

    Directory of Open Access Journals (Sweden)

    Matthias A Dieringer

    Full Text Available INTRODUCTION: Visual but subjective reading of longitudinal relaxation time (T1 weighted magnetic resonance images is commonly used for the detection of brain pathologies. For this non-quantitative measure, diagnostic quality depends on hardware configuration, imaging parameters, radio frequency transmission field (B1+ uniformity, as well as observer experience. Parametric quantification of the tissue T1 relaxation parameter offsets the propensity for these effects, but is typically time consuming. For this reason, this study examines the feasibility of rapid 2D T1 quantification using a variable flip angles (VFA approach at magnetic field strengths of 1.5 Tesla, 3 Tesla, and 7 Tesla. These efforts include validation in phantom experiments and application for brain T1 mapping. METHODS: T1 quantification included simulations of the Bloch equations to correct for slice profile imperfections, and a correction for B1+. Fast gradient echo acquisitions were conducted using three adjusted flip angles for the proposed T1 quantification approach that was benchmarked against slice profile uncorrected 2D VFA and an inversion-recovery spin-echo based reference method. Brain T1 mapping was performed in six healthy subjects, one multiple sclerosis patient, and one stroke patient. RESULTS: Phantom experiments showed a mean T1 estimation error of (-63±1.5% for slice profile uncorrected 2D VFA and (0.2±1.4% for the proposed approach compared to the reference method. Scan time for single slice T1 mapping including B1+ mapping could be reduced to 5 seconds using an in-plane resolution of (2×2 mm2, which equals a scan time reduction of more than 99% compared to the reference method. CONCLUSION: Our results demonstrate that rapid 2D T1 quantification using a variable flip angle approach is feasible at 1.5T/3T/7T. It represents a valuable alternative for rapid T1 mapping due to the gain in speed versus conventional approaches. This progress may serve to enhance

  9. Rapid parametric mapping of the longitudinal relaxation time T1 using two-dimensional variable flip angle magnetic resonance imaging at 1.5 Tesla, 3 Tesla, and 7 Tesla.

    Science.gov (United States)

    Dieringer, Matthias A; Deimling, Michael; Santoro, Davide; Wuerfel, Jens; Madai, Vince I; Sobesky, Jan; von Knobelsdorff-Brenkenhoff, Florian; Schulz-Menger, Jeanette; Niendorf, Thoralf

    2014-01-01

    Visual but subjective reading of longitudinal relaxation time (T1) weighted magnetic resonance images is commonly used for the detection of brain pathologies. For this non-quantitative measure, diagnostic quality depends on hardware configuration, imaging parameters, radio frequency transmission field (B1+) uniformity, as well as observer experience. Parametric quantification of the tissue T1 relaxation parameter offsets the propensity for these effects, but is typically time consuming. For this reason, this study examines the feasibility of rapid 2D T1 quantification using a variable flip angles (VFA) approach at magnetic field strengths of 1.5 Tesla, 3 Tesla, and 7 Tesla. These efforts include validation in phantom experiments and application for brain T1 mapping. T1 quantification included simulations of the Bloch equations to correct for slice profile imperfections, and a correction for B1+. Fast gradient echo acquisitions were conducted using three adjusted flip angles for the proposed T1 quantification approach that was benchmarked against slice profile uncorrected 2D VFA and an inversion-recovery spin-echo based reference method. Brain T1 mapping was performed in six healthy subjects, one multiple sclerosis patient, and one stroke patient. Phantom experiments showed a mean T1 estimation error of (-63±1.5)% for slice profile uncorrected 2D VFA and (0.2±1.4)% for the proposed approach compared to the reference method. Scan time for single slice T1 mapping including B1+ mapping could be reduced to 5 seconds using an in-plane resolution of (2×2) mm2, which equals a scan time reduction of more than 99% compared to the reference method. Our results demonstrate that rapid 2D T1 quantification using a variable flip angle approach is feasible at 1.5T/3T/7T. It represents a valuable alternative for rapid T1 mapping due to the gain in speed versus conventional approaches. This progress may serve to enhance the capabilities of parametric MR based lesion detection and

  10. Prolonged bone marrow T1-relaxation in patients with polycythemia vera

    DEFF Research Database (Denmark)

    Jensen, K E; Grube, T; Thomsen, C

    1988-01-01

    In vitro as well as in vivo studies have shown prolonged T1 relaxation times in patients with acute leukemia. The mechanism behind this finding is not known. In order to evaluate if this was specific for leukemia we examined eight patients with polycythemia vera, representing a condition with a r......In vitro as well as in vivo studies have shown prolonged T1 relaxation times in patients with acute leukemia. The mechanism behind this finding is not known. In order to evaluate if this was specific for leukemia we examined eight patients with polycythemia vera, representing a condition...

  11. Reproducibility of in vivo magnetic resonance imaging T1 rho and T2 relaxation time measurements of hip cartilage at 3.0T in healthy volunteers.

    Science.gov (United States)

    Nemeth, Angeline; Di Marco, Lucy; Boutitie, Florent; Sdika, Michael; Grenier, Denis; Rabilloud, Muriel; Beuf, Olivier; Pialat, Jean-Baptiste

    2017-06-26

    To assess the T1 ρ and T2 values in the hip cartilage of healthy volunteers and to evaluate the reproducibility of these measurements. The right hip joint of 30 asymptomatic volunteers was explored with 3T magnetic resonance imaging (MRI). Quantitative 3D T1 ρ- and T2 -maps sequences were repeated twice with a 30-minute delay (immediate reproducibility). The same protocol was repeated 14 days later (short-term reproducibility). Immediate and short-term reproducibility were estimated using coefficients of variation and correlation concordance coefficients (CCC). The precisions of the measurements were estimated by the ratio of the standard deviations. A mixed linear model was used to analyze the effect of patient's characteristics on T1 ρ and T2 values. Immediate reproducibility was significantly better than short-term reproducibility for T1 ρ (CCC of 0.75 versus 0.55; P = 0.007) and T2 (CCC 0.65 versus 0.32; P measurements were estimated between 5.5% and 9.1%. Median T1 ρ values were 6.0 msec higher in women than in men (P = 0.006), with no significant influence of age, body mass index (BMI), or sports activity. Median T2 values were not significantly different between men and women (0.4 msec lower in women; P = 0.76). There was no significant influence of age, BMI, or sports activity. T1 ρ and T2 values were lower in lateral regions than in medial regions (4.9 msec and 2.5 msec lower respectively; P < 0.0001). Immediate reproducibility of T1 ρ and T2 values is better than short-term, with limited effect of 30 minutes decubitus. T1 ρ values are significantly higher in women. 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2017. © 2017 International Society for Magnetic Resonance in Medicine.

  12. Relaxation times T1, T2, and T2{sup *} of apples, pears, citrus fruits, and potatoes with a comparison to human tissues; T1-, T2- und T2{sup *}-Relaxationswerte von Aepfeln, Birnen, Zitrusfruechten und Kartoffeln im Vergleich zu menschlichen Geweben

    Energy Technology Data Exchange (ETDEWEB)

    Werz, Karin; Braun, Hans; Vitha, Dominik; Bruno, Graziano; Martirosian, Petros; Steidle, Guenter; Schick, Fritz [Tuebingen Univ. (Germany). Sektion fuer Experimentelle Radiologie

    2011-07-01

    The aim of the project was a systematic assessment of relaxation times of different fruits and vegetables and a comparison to values of human tissues. Results provide an improved basis for selection of plant phantoms for development of new MR techniques and sequences. Vessels filled with agar gel are mostly used for this purpose, preparation of which is effortful and time-consuming. In the presented study apples, (malus, 8 species), pears, (pyrus, 2 species), citrus fruits (citrus, 5 species) and uncooked potatoes (solanum tuberosum, 8 species) from the supermarket were examined which are easily available nearly all-the-year. T1, T2 and T2{sup *} relaxation times of these nature products were measured on a 1.5 Tesla MR system with adapted examination protocols and mono-exponential fitting, and compared to literature data of human parenchyma tissues, fatty tissue and body fluid (cerebrospinal fluid). Resulting values were as follows: apples: T1: 1486 - 1874 ms, T2: 163 - 281 ms, T2{sup *}: 2,3 - 3,2 ms; pears: T1: 1631 - 1969 ms, T2: 119 - 133 ms, T2{sup *}: 10,1 - 10,6 ms, citrus fruits (pulp) T1: 2055 - 2632 ms, T2: 497 - 998 ms, T2{sup *}: 151 - 182 ms; citrus fruits (skin) T1: 561 - 1669 ms, T2: 93 - 119 ms; potatoes: T1: 1011 - 1459 ms, T2: 166 - 210 ms, T2{sup *}: 20 - 30 ms. All T1-values of the examined objects (except for potatoes and skins of citrus fruits) were longer than T1 values of human tissues. Also T2 values (except for pears and skins of citrus fruits) of the fruits and the potatoes tended to be longer. T2{sup *} values of apples, pears and potatoes were shorter than in healthy human tissue. Results show relaxation values of many fruits to be not exactly fitting to human tissue, but with suitable selection of the fruits and optionally with an adaption of measurement parameters one can achieve suitable contrast and signal characteristics for some purposes. (orig.)

  13. Prolonged T1 relaxation of the hemopoietic bone marrow in patients with chronic leukemia

    DEFF Research Database (Denmark)

    Jensen, K E; Sørensen, P G; Thomsen, C

    1990-01-01

    Eleven patients with chronic leukemia (7 with chronic lymphocytic leukemia and 4 with chronic myeloid leukemia) were evaluated with magnetic resonance (MR) imaging and T1 relaxation time measurements by use of a 1.5 tesla whole body MR scanner. Bone marrow biopsies were obtained from the posterior...

  14. Gd-DTPA bolus tracking in the myocardium using T1 fast acquisition relaxation mapping (T1 FARM).

    Science.gov (United States)

    Bellamy, D D; Pereira, R S; McKenzie, C A; Prato, F S; Drost, D J; Sykes, J; Wisenberg, G

    2001-09-01

    MRI methods currently used for bolus tracking in the myocardium, such as saturation recovery turbo-fast low-angle shot (FLASH) (srTFL), are limited by signal intensity (SI) saturation at high contrast agent (CA) concentrations. By using T1 fast acquisition relaxation mapping (T1 FARM), a Gd-DTPA bolus (0.075 vs. 0.025 mmol/kg) may be injected without causing saturation. This study tested the feasibility of in vivo T1 FARM bolus tracking under rest/stress conditions in seven beagles with multiple permanently occluded branches of the left anterior descending (LAD) coronary artery. Although it underestimated the myocardial perfusion reserve (MPR) measured ex vivo using radioactive microspheres (mean +/- SEM; 3.60 +/- 0.26), the MPR determined upon application of the modified Kety model (1.86 +/- 0.10) enabled distinction between normal and infarcted tissue. The partition coefficient (lambda) estimated at rest and stress using the modified Kety model underestimated ex vivo radioactive measurements in infarcted tissue (0.25 +/- 0.01 vs. 0.26 +/- 0.01 vs. 0.79 +/- 0.08 ml/g, P T1 FARM bolus tracking shows potential for assessment of myocardial perfusion. Copyright 2001 Wiley-Liss, Inc.

  15. Relaxation times estimation in MRI

    Science.gov (United States)

    Baselice, Fabio; Caivano, Rocchina; Cammarota, Aldo; Ferraioli, Giampaolo; Pascazio, Vito

    2014-03-01

    Magnetic Resonance Imaging is a very powerful techniques for soft tissue diagnosis. At the present, the clinical evaluation is mainly conducted exploiting the amplitude of the recorded MR image which, in some specific cases, is modified by using contrast enhancements. Nevertheless, spin-lattice (T1) and spin-spin (T2) relaxation times can play an important role in many pathology diagnosis, such as cancer, Alzheimer or Parkinson diseases. Different algorithms for relaxation time estimation have been proposed in literature. In particular, the two most adopted approaches are based on Least Squares (LS) and on Maximum Likelihood (ML) techniques. As the amplitude noise is not zero mean, the first one produces a biased estimator, while the ML is unbiased but at the cost of high computational effort. Recently the attention has been focused on the estimation in the complex, instead of the amplitude, domain. The advantage of working with real and imaginary decomposition of the available data is mainly the possibility of achieving higher quality estimations. Moreover, the zero mean complex noise makes the Least Square estimation unbiased, achieving low computational times. First results of complex domain relaxation times estimation on real datasets are presented. In particular, a patient with an occipital lesion has been imaged on a 3.0T scanner. Globally, the evaluation of relaxation times allow us to establish a more precise topography of biologically active foci, also with respect to contrast enhanced images.

  16. T1(Gd) gives comparable information as Delta T1 relaxation rate in dGEMRIC evaluation of cartilage repair tissue.

    Science.gov (United States)

    Trattnig, Siegfried; Burstein, Dehorah; Szomolanyi, Pavol; Pinker, Katja; Welsch, Goetz H; Mamisch, Tallal C

    2009-09-01

    To evaluate the relationship between T1 after intravenous contrast administration (T1Gd) and Delta relaxation rate (DeltaR1) = (1/T1(Gd) - 1/T1o) in the delayed Gadolinium-Enhanced MRI of cartilage (dGEMRIC) evaluation of cartilage repair tissue. Thirty single MR examinations from 30 patients after matrix-associated autologous chondrocyte transplantations of the knee joint with different postoperative intervals were examined using an 8-channel knee-coil at 3T. T1 mapping using a 3D GRE sequence with a 35/10 degrees flip angle excitation pulse combination was performed before and after contrast administration (dGEMRIC technique). T1 postcontrast (T1(Gd)) and the DeltaR1 (relative index of pre- and postcontrast R1 value) were calculated for repair tissue and the weight-bearing normal appearing control cartilage. For evaluation of the different postoperative intervals, MR exams were subdivided into 3 groups (up to 12 months, 12-24 months, more than 24 months). For statistical analysis Spearman correlation coefficients were calculated. The mean value for T1 postcontrast was 427 +/- 159 ms, for DeltaR1 1.85 +/- 1.0; in reference cartilage 636 +/- 181 ms for T1 postcontrast and 0.83 +/- 0.5 for DeltaR1.The correlation coefficients were highly significant between T1 (Gd) and DeltaR1 for repair tissue (0.969) as well as normal reference cartilage (0.928) in total, and for the reparative cartilage in the early, middle postoperative, and late postoperative interval after surgery (R values: -0.986, -0.970, and -0.978, respectively). Using either T1(Gd) or DeltaR1, the 2 metrics resulted in similar conclusions regarding the time course of change of repair tissue and control tissue, namely that highly significant (P > 0.01) differences between cartilage repair tissue and reference cartilage were found for all follow-up groups. Additionally, for both metrics highly significant differences (P T1 (Gd) or DeltaR1. The high correlation between T1 (Gd) and DeltaR1 and the comparable

  17. Quantitative analysis of 17O exchange and T1 relaxation data: application to zirconium tungstate.

    Science.gov (United States)

    Hodgkinson, Paul; Hampson, Matthew R

    2006-09-01

    The theoretical basis behind a recent quantitative analysis of 17O exchange in ZrW2O8 [M.R. Hampson, J.S.O. Evans, P. Hodgkinson, J. Am. Chem. Soc. 127 (2005) 15175-15181] is set out. Despite the complexities of combining the multi-exponential relaxation of half-integer quadrupolar nuclei with chemical exchange, it is shown how magnetisation transfer experiments can be analysed to obtain estimates of absolute exchange rates. The multi-exponential relaxation is best modelled using a magnetic mechanism, i.e. the rapid T1 relaxation observed, particularly at high temperatures, can be directly related to the relatively high degree of 17O labelling employed. The combination of the 1D EXSY results with T1 values as a function of temperature provides exchange rates and activation barriers over a wide temperature range (40-226 degrees C).

  18. Gadolinium-based magnetic resonance contrast agents at 7 Tesla: in vitro T1 relaxivities in human blood plasma.

    Science.gov (United States)

    Noebauer-Huhmann, Iris M; Szomolanyi, Pavol; Juras, Vladimír; Kraff, Oliver; Ladd, Mark E; Trattnig, Siegfried

    2010-09-01

    PURPOSE/INTRODUCTION: The aim of this study was to determine the T1 relaxivities (r1) of 8 gadolinium (Gd)-based MR contrast agents in human blood plasma at 7 Tesla, compared with 3 Tesla. Eight commercially available Gd-based MR contrast agents were diluted in human blood plasma to concentrations of 0, 0.25, 0.5, 1, and 2 mmol/L. In vitro measurements were performed at 37 degrees C, on a 7 Tesla and on a 3 Tesla whole-body magnetic resonance imaging scanner. For the determination of T1 relaxation times, Inversion Recovery Sequences with inversion times from 0 to 3500 ms were used. The relaxivities were calculated. The r1 relaxivities of all agents, diluted in human blood plasma at body temperature, were lower at 7 Tesla than at 3 Tesla. The values at 3 Tesla were comparable to those published earlier. Notably, in some agents, a minor negative correlation of r1 with a concentration of up to 2 mmol/L could be observed. This was most pronounced in the agents with the highest protein-binding capacity. At 7 Tesla, the in vitro r1 relaxivities of Gd-based contrast agents in human blood plasma are lower than those at 3 Tesla. This work may serve as a basis for the application of Gd-based MR contrast agents at 7 Tesla. Further studies are required to optimize the contrast agent dose in vivo.

  19. Effect of Lanthanide Ions on Dynamic Nuclear Polarization Enhancement and Liquid State T1 Relaxation

    Science.gov (United States)

    Gordon, Jeremy; Fain, Sean B.; Rowland, Ian J

    2012-01-01

    In the dynamic nuclear polarization process, microwave irradiation facilitates exchange of polarization from a radical’s unpaired electron to nuclear spins at cryogenic temperatures, increasing polarization by >10000. Doping samples with Gd3+ ions further increases the achievable solid-state polarization. However, upon dissolution, paramagnetic lanthanide metals can be potent relaxation agents, decreasing liquid-state polarization. Here, the effects of lanthanide metals on the solid and liquid-state magnetic properties of [1-13C]pyruvate are studied. The results show that in addition to gadolinium, holmium not only increases the achievable polarization but also the rate of polarization. Liquid-state relaxation studies found that unlike gadolinium, holmium minimally affects T1. Additionally, results reveal that linear contrast agents dissociate in pyruvic acid, greatly reducing liquid-state T1. While macrocyclic agents do not readily dissociate, they yield lower solid-state polarization. Results indicate that polarization with free lanthanides and subsequent chelation during dissolution produces the highest polarization enhancement while minimizing liquid-state relaxation. PMID:22367680

  20. Biexponential longitudinal relaxation in white matter: Characterization and impact on T1 mapping with IR-FSE and MP2RAGE.

    Science.gov (United States)

    Rioux, James A; Levesque, Ives R; Rutt, Brian K

    2016-06-01

    Magnetization transfer in white matter (WM) causes biexponential relaxation, but most quantitative T1 measurements fit data assuming monoexponential relaxation. The resulting monoexponential T1 estimate varies based on scan parameters and represents a source of variation between studies, especially at high fields. In this study, we characterized WM T1 relaxation and performed simulations to determine how to minimize this deviation. To characterize biexponential relaxation, four volunteers were scanned at 3T and 7T using inversion recovery fast spin echo (IR-FSE) with 13 inversion times (TIs). Three volunteers were scanned with IR-FSE using TIs chosen by simulations to reduce T1 deviation, and with MP2RAGE. At 3T, the biexponential relaxation has a short component of T1  = 48 ms (9%) and a long component of T1  = 939 ms. At 7T the short component is T1  = 57 ms (11%) and the long component is 1349 ms (89%). For IR-FSE, acquiring four TIs with a minimum of 150 ms (3T) or 200 ms (7T) yielded monoexponential T1 estimates that match the long component to within 10 ms. For MP2RAGE, significant differences (90 ms at 3T, 125 ms at 7T) remain at all parameter values. Many T1 mapping sequences yield robust estimates of the long T1 component with suitable choice of TIs, allowing reproducible, sequence-independent T1 values to be measured. However, this is not true of MP2RAGE in its current implementation. Magn Reson Med 75:2265-2277, 2016. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.

  1. TU-EF-BRA-02: Longitudinal Proton Spin Relaxation and T1-Imaging

    Energy Technology Data Exchange (ETDEWEB)

    Lemen, L. [Univ Cincinnati (United States)

    2015-06-15

    NMR, and Proton Density MRI of the 1D Patient - Anthony Wolbarst Net Voxel Magnetization, m(x,t). T1-MRI; The MRI Device - Lisa Lemen ‘Classical’ NMR; FID Imaging in 1D via k-Space - Nathan Yanasak Spin-Echo; S-E/Spin Warp in a 2D Slice - Ronald Price Magnetic resonance imaging not only reveals the structural, anatomic details of the body, as does CT, but also it can provide information on the physiological status and pathologies of its tissues, like nuclear medicine. It can display high-quality slice and 3D images of organs and vessels viewed from any perspective, with resolution better than 1 mm. MRI is perhaps most extraordinary and notable for the plethora of ways in which it can create unique forms of image contrast, reflective of fundamentally different biophysical phenomena. As with ultrasound, there is no risk from ionizing radiation to the patient or staff, since no X-rays or radioactive nuclei are involved. Instead, MRI harnesses magnetic fields and radio waves to probe the stable nuclei of the ordinary hydrogen atoms (isolated protons) occurring in water and lipid molecules within and around cells. MRI consists, in essence, of creating spatial maps of the electromagnetic environments around these hydrogen nuclei. Spatial variations in the proton milieus can be related to clinical differences in the biochemical and physiological properties and conditions of the associated tissues. Imaging of proton density (PD), and of the tissue proton spin relaxation times known as T1 and T2, all can reveal important clinical information, but they do so with approaches so dissimilar from one another that each is chosen for only certain clinical situations. T1 and T2 in a voxel are determined by different aspects of the rotations and other motions of the water and lipid molecules involved, as constrained by the local biophysical surroundings within and between its cells – and they, in turn, depend on the type of tissue and its state of health. Three other common

  2. Quantitative Study of Longitudinal Relaxation (T 1) Contrast Mechanisms in Brain MRI

    Science.gov (United States)

    Jiang, Xu

    Longitudinal relaxation (T1) contrast in MRI is important for studying brain morphology and is widely used in clinical applications. Although MRI only detects signals from water hydrogen ( 1H) protons (WPs), T1 contrast is known to be influenced by other species of 1H protons, including those in macromolecules (MPs), such as lipids and proteins, through magnetization transfer (MT) between WPs and MPs. This complicates the use and quantification of T1 contrast for studying the underlying tissue composition and the physiology of the brain. MT contributes to T1 contrast to an extent that is generally dependent on MT kinetics, as well as the concentration and NMR spectral properties of MPs. However, the MP spectral properties and MT kinetics are both difficult to measure directly, as the signal from MPs is generally invisible to MRI. Therefore, to investigate MT kinetics and further quantify T1 contrast, we first developed a reliable way to indirectly measure the MP fraction and their exchange rate with WPs, with minimal dependence on the spectral properties of MPs. For this purpose, we used brief, highpower radiofrequency (RF) NMR excitation pulses to almost completely saturate the magnetization of MPs. Based on this, both MT kinetics and the contribution of MPs to T1 contrast through MT were studied. The thus obtained knowledge allowed us to subsequently infer the spectral properties of MPs by applying low-power, frequencyselective off-resonance RF pulses and measuring the offset-frequency dependent effect of MPs on the WP MRI signal. A two-pool exchange model was used in both cases to account for direct effects of the RF pulse on WP magnetization. Consistent with earlier works using MRI at low-field and post-mortem analysis of brain tissue, our novel measurement approach found that MPs constitute an up to 27% fraction of the total 1H protons in human brain white matter, and their spectrum follows a super-Lorentzian line with a T2 of 9.6+/-0.6 mus and a resonance

  3. In vivo measurements of the T1 relaxation processes in the bone marrow in patients with myelodysplastic syndrome. A magnetic resonance imaging study

    DEFF Research Database (Denmark)

    Jensen, K E; Nielsen, H; Thomsen, C

    1989-01-01

    Nine patients with myelodysplastic syndrome (MDS) were examined with magnetic resonance imaging and in vivo T1 relaxation time measurements of the vertebral bone marrow in a 1.5 tesla whole body scanner. Two patients underwent transformation to acute myeloid leukemia and were evaluated at follow-...... not differ from patients with polycythemia vera....

  4. In vivo measurements of the T1 relaxation processes in the bone marrow in patients with myelodysplastic syndrome. A magnetic resonance imaging study

    DEFF Research Database (Denmark)

    Jensen, K E; Nielsen, H; Thomsen, C

    1989-01-01

    Nine patients with myelodysplastic syndrome (MDS) were examined with magnetic resonance imaging and in vivo T1 relaxation time measurements of the vertebral bone marrow in a 1.5 tesla whole body scanner. Two patients underwent transformation to acute myeloid leukemia and were evaluated at follow...

  5. Changes in T1 relaxation processes in the bone marrow following treatment in children with acute lymphoblastic leukemia. A magnetic resonance imaging study

    DEFF Research Database (Denmark)

    Jensen, K E; Thomsen, C; Henriksen, O

    1990-01-01

    data from bone marrow biopsies obtained in close association to the MR examinations. Ten age matched children were examined as a control group. A 1.5 Tesla whole body scanner was used for the measurements. The pretreatment T1 relaxation times of the bone marrow were significantly prolonged, compared...

  6. Prolonged bone marrow T1-relaxation in acute leukaemia. In vivo tissue characterization by magnetic resonance imaging

    DEFF Research Database (Denmark)

    Thomsen, C; Sørensen, P G; Karle, H

    1987-01-01

    osseous tissue. Nine patients with acute leukaemia, one patient with myelodysplastic syndrome, and ten normal volunteers were included in the study. The T1- and T2-relaxation processes were measured in the lumbar spine bone marrow using a wholebody superconductive MR-scanner operating at 1.5 Tesla...

  7. Quantification of T(1ρ) relaxation by using rotary echo spin-lock pulses in the presence of B(0) inhomogeneity.

    Science.gov (United States)

    Yuan, Jing; Li, Yujia; Zhao, Feng; Chan, Queenie; Ahuja, Anil T; Wang, Yi-Xiang j

    2012-08-07

    T(1ρ) relaxation is traditionally described as a mono-exponential signal decay with spin-lock time. However, T(1ρ) quantification by fitting to the mono-exponential model can be substantially compromised in the presence of field inhomogeneities, especially for low spin-lock frequencies. The normal approach to address this issue involves the development of dedicated composite spin-lock pulses for artifact reduction while still using the mono-exponential model for T(1ρ) fitting. In this work, we propose an alternative approach for improved T(1ρ) quantification with the widely-used rotary echo spin-lock pulses in the presence of B(0) inhomogeneities by fitting to a modified theoretical model which is derived to reveal the dependence of T(1ρ)-prepared magnetization on T(1ρ), T(2ρ), spin-lock time, spin-lock frequency and off-resonance, without involving complicated spin-lock pulse design. It has potentials for T(1ρ) quantification improvement at low spin-lock frequencies. Improved T(1ρ) mapping was demonstrated on phantom and in vivo rat spin-lock imaging at 3 T compared to the mapping using the mono-exponential model.

  8. Medial meniscal posterior root/horn radial tears correlate with cartilage degeneration detected by T1ρ relaxation mapping

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Kenji, E-mail: Kenji-am@nms.ac.jp [Department of Orthopaedic Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603 (Japan); Hashimoto, Sanshiro, E-mail: info@msorc.jp [Minami-Shinjuku Orthopaedic Rehabilitation Clinic, 2-16-7 Yoyogi, Shibuya-ku, Tokyo 151-0053 (Japan); Nakamura, Hiroshi, E-mail: nakamura@nms.ac.jp [Department of Orthopaedic Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603 (Japan); Mori, Atsushi, E-mail: atsu@nms.ac.jp [Department of Orthopaedic Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603 (Japan); Sato, Akiko, E-mail: akiko-sato@nms.ac.jp [Department of Orthopaedic Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603 (Japan); Majima, Tokifumi, E-mail: tkmajima@iuhw.ac.jp [Department of Orthopaedic Surgery, International University of Health and Welfare Hospital, 537-3 Iguchi, Nasu-shiobara, Tochigi 329-2763 (Japan); Takai, Shinro, E-mail: takai-snr@nms.ac.jp [Department of Orthopaedic Surgery, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603 (Japan)

    2015-06-15

    Highlights: • Posterior radial tears in medial meniscus associate T1ρ values of cartilage. • Posterior radial tears relate to cartilage degeneration even in early-stage osteoarthritis. • Abnormalities in meniscus on MRI are useful for screening early-stage osteoarthritis. - Abstract: Objective: This study aimed to identify factors on routine pulse sequence MRI associated with cartilage degeneration observed on T1ρ relaxation mapping. Materials and methods: This study included 137 subjects with knee pain. T1ρ values were measured in the regions of interest on the surface layer of the cartilage on mid-coronal images of the femorotibial joint. Assessment of cartilage, subchondral bone, meniscus and ligaments was performed using routine pulse sequence MRI. Radiographic evaluation for osteoarthritis was also performed. Results: Multiple regression analysis revealed posterior root/horn tears to be independent factors increasing the T1ρ values of the cartilage in the medial compartment of the femorotibial joint. Even when adjusted for radiographically defined early-stage osteoarthritis, medial posterior meniscal radial tears significantly increased the T1ρ values. Conclusions: This study showed that posterior root/horn radial tears in the medial meniscus are particularly important MRI findings associated with cartilage degeneration observed on T1ρ relaxation mapping. Morphological factors of the medial meniscus on MRI provide findings useful for screening early-stage osteoarthritis.

  9. A method for longitudinal relaxation time measurement in inhomogeneous fields

    Science.gov (United States)

    Chen, Hao; Cai, Shuhui; Chen, Zhong

    2017-08-01

    The spin-lattice relaxation time (T1) plays a crucial role in the study of spin dynamics, signal optimization and data quantification. However, the measurement of chemical shift-specific T1 constants is hampered by the magnetic field inhomogeneity due to poorly shimmed external magnetic fields or intrinsic magnetic susceptibility heterogeneity in samples. In this study, we present a new protocol to determine chemical shift-specific T1 constants in inhomogeneous fields. Based on intermolecular double-quantum coherences, the new method can resolve overlapped peaks in inhomogeneous fields. The measurement results are in consistent with the measurements in homogeneous fields using the conventional method. Since spatial encoding technique is involved, the experimental time for the new method is very close to that for the conventional method. With the aid of T1 knowledge, some concealed information can be exploited by T1 weighting experiments.

  10. Experimental evidence for the role of cross-relaxation in proton nuclear magnetic resonance spin lattice relaxation time measurements in proteins.

    Science.gov (United States)

    Sykes, B D; Hull, W E; Snyder, G H

    1978-02-01

    Proton nuclear magnetic resonance (NMR) spin lattice relaxation time (T1) and spin-spin relaxation time (T2) measurements are presented for a number of proteins with molecular weights spanning the range of 6,500-150,000 daltons. These measurements provide experimental evidence for the role of cross-relaxation in 1H NMR T1 measurements in proteins. The relationship between these measurements and the theory recently presented by Kalk and Berendsen is discussed. The results indicate that cross-relaxation dominates the T1 measurements for the larger proteins, even at relatively low resonance frequencies such as 100 MHz.

  11. Enhancement of T1 and T2 relaxation by paramagnetic silica-coated nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Gerion, D; Herberg, J; Gjersing, E; Ramon, E; Maxwell, R; Gray, J W; Budinger, T F; Chen, F F

    2006-08-28

    We present the first comprehensive investigation on water-soluble nanoparticles embedded into a paramagnetic shell and their properties as an MRI contrast agent. The nanoprobes are constructed with an inorganic core embedded into an ultra-thin silica shell covalently linked to chelated Gd{sup 3+} paramagnetic ions that act as an MRI contrast agent. The chelator contains the molecule DOTA and the inorganic core contains a fluorescent CdSe/ZnS qdots in Au nanoparticles. Optical properties of the cores (fluorescence emission or plasmon position) are not affected by the neither the silica shell nor the presence of the chelated paramagnetic ions. The resulting complex is a MRI/fluorescence probe with a diameter of 8 to 15 nm. This probe is highly soluble in high ionic strength buffers at pH ranging from {approx}4 to 11. In MRI experiments at clinical field strengths of 60 MHz, the QDs probes posses spin-lattice (T{sub 1}) and a spin-spin (T{sub 2}) relaxivities of 1018.6 +/- 19.4 mM{sup -1} s{sup -1} and 2438.1 +/- 46.3 mM{sup -1} s{sup -1} respectively for probes having {approx}8 nm. This increase in relaxivity has been correlated to the number of paramagnetic ions covalently linked to the silica shell, ranging from approximately 45 to over 320. We found that each bound chelated paramagnetic species contributes by over 23 mM{sup -1} s{sup -1} to the total T{sub 1} and by over 54 mM{sup -1} s{sup -1} to the total T{sub 2} relaxivity respectively. The contrast power is modulated by the number of paramagnetic moieties linked to the silica shell and is only limited by the number of chelated paramagnetic species that can be packed on the surface. So far, the sensitivity of our probes is in the 100 nM range for 8-10 nm particles and reaches 10 nM for particles with approximately 15-18 nm in diameter. The sensitivities values in solutions are equivalent of those obtained with small superparamagnetic iron oxide nanoparticles of 7 nm diameter clustered into a 100 nm polymeric

  12. Coherence transfer and electron T1-, T2-relaxation in nitroxide spin labels

    Science.gov (United States)

    Marsh, Derek

    2017-04-01

    Abragam's double-commutator spin operator method is used to analyse: 1) electron coherence transfer by intermolecular dipolar interaction between spin-label radicals, and 2) longitudinal and transverse electron spin relaxation by rotational modulation of the Zeeman and nitrogen-hyperfine anisotropies of isolated nitroxide spin labels. Results compatible with earlier treatments by Redfield theory are obtained without specifically evaluating matrix elements. Extension to single-transition operators for isolated nitroxides predicts electron coherence transfer by pseudosecular electron-nuclear dipolar interaction, in the absence of intermolecular dipolar coupling. This explains earlier experimental findings that coherence transfer (specifically dispersion-like distortion of the EPR absorption line shape) does not extrapolate to zero at low concentrations of nitroxide spin labels.

  13. Coherence transfer and electron T1-, T2-relaxation in nitroxide spin labels

    DEFF Research Database (Denmark)

    Marsh, Derek

    2017-01-01

    Abragam's double-commutator spin operator method is used to analyse: 1) electron coherence transfer by intermolecular dipolar interaction between spin-label radicals, and 2) longitudinal and transverse electron spin relaxation by rotational modulation of the Zeeman and nitrogen......-hyperfine anisotropies of isolated nitroxide spin labels. Results compatible with earlier treatments by Redfield theory are obtained without specifically evaluating matrix elements. Extension to single-transition operators for isolated nitroxides predicts electron coherence transfer by pseudosecular electron......-nuclear dipolar interaction, in the absence of intermolecular dipolar coupling. This explains earlier experimental findings that coherence transfer (specifically dispersion-like distortion of the EPR absorption line shape) does not extrapolate to zero at low concentrations of nitroxide spin labels....

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

    Science.gov (United States)

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

    2017-08-09

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

  15. T1 mapping of the myocardium: intra-individual assessment of post-contrast T1 time evolution and extracellular volume fraction at 3T for Gd-DTPA and Gd-BOPTA.

    Science.gov (United States)

    Kawel, Nadine; Nacif, Marcelo; Zavodni, Anna; Jones, Jacquin; Liu, Songtao; Sibley, Christopher T; Bluemke, David A

    2012-04-28

    Myocardial T1 relaxation time (T1 time) and extracellular volume fraction (ECV) are altered in patients with diffuse myocardial fibrosis. The purpose of this study was to perform an intra-individual assessment of normal T1 time and ECV for two different contrast agents. A modified Look-Locker Inversion Recovery (MOLLI) sequence was acquired at 3 T in 24 healthy subjects (8 men; 28 ± 6 years) at mid-ventricular short axis pre-contrast and every 5 min between 5-45 min after injection of a bolus of 0.15 mmol/kg gadopentetate dimeglumine (Gd-DTPA; Magnevist®) (exam 1) and 0.1 mmol/kg gadobenate dimeglumine (Gd-BOPTA; Multihance®) (exam 2) during two separate scanning sessions. T1 times were measured in myocardium and blood on generated T1 maps. ECVs were calculated as ΔR1 myocardium/ΔR1 blood*1-hematocrit. Mean pre-contrast T1 relaxation times for myocardium and blood were similar for both the first and second CMR exam (p > 0.5). Overall mean post-contrast myocardial T1 time was 15 ± 2 ms (2.5 ± 0.7%) shorter for Gd-DTPA at 0.15 mmol/kg compared to Gd-BOPTA at 0.1 mmol/kg (p T1 time of blood pool (p > 0.05). Between 5 and 45 minutes after contrast injection, mean ECV values increased linearly with time for both contrast agents from 0.27 ± 0.03 to 0.30 ± 0.03 (p T1 relaxation time (CV 4.5% [exam 1] and 3.0% [exam 2], respectively). ECV with Gd-DTPA was highly correlated to ECV by Gd-BOPTA (r = 0.803; p T1 relaxation time, variation in ECV values of normal subjects is larger. However, absolute differences in ECV between Gd-DTPA and Gd-BOPTA were small and rank correlation was high. There is a small and linear increase in ECV over time, therefore ideally images should be acquired at the same delay after contrast injection.

  16. Biologically aggressive regions within glioblastoma identified by spin-lock contrast T1 relaxation in the rotating frame (T1ρ MRI

    Directory of Open Access Journals (Sweden)

    Ramon Francisco Barajas, Jr., MD

    2017-12-01

    Full Text Available Spin-lattice relaxation in the rotating frame magnetic resonance imaging allows for the quantitative assessment of spin-lock contrast within tissues. We describe the utility of spin-lattice relaxation in the rotating frame metrics in characterizing glioblastoma biological heterogeneity. A 84-year-old man presented to our institution with a right frontal temporal mass. Prior tissue sampling from a peripheral nonenhancing lesion was nondiagnostic. Stereotactic image-guided tissue sampling of the nonenhancing T2-fluid-attenuated inversion recovery hyperintense region involving the anterior cingulate gyrus with elevated spin-lattice relaxation in the rotating frame metrics provided a pathologic diagnosis of glioblastoma. This case illustrates the utility of spin-lattice relaxation in the rotating frame magnetic resonance imaging in identifying biologically aggressive regions within glioblastoma.

  17. Evaluation of relaxation time measurements by magnetic resonance imaging. A phantom study

    DEFF Research Database (Denmark)

    Kjaer, L; Thomsen, C; Henriksen, O

    1987-01-01

    Several circumstances may explain the great variation in reported proton T1 and T2 relaxation times usually seen. This study was designed to evaluate the accuracy of relaxation time measurements by magnetic resonance imaging (MRI) operating at 1.5 tesla. Using a phantom of nine boxes with different...

  18. Time-Dependent Changes in T1 during Fracture Healing in Juvenile Rats: A Quantitative MR Approach.

    Directory of Open Access Journals (Sweden)

    Katharina Baron

    Full Text Available Quantitative magnetic resonance imaging (qMRI offers several advantages in imaging and determination of soft tissue alterations when compared to qualitative imaging techniques. Although applications in brain and muscle tissues are well studied, its suitability to quantify relaxation times of intact and injured bone tissue, especially in children, is widely unknown. The objective observation of a fracture including its age determination can become of legal interest in cases of child abuse or maltreatment. Therefore, the aim of this study is the determination of time dependent changes in intact and corresponding injured bones in immature rats via qMRI, to provide the basis for an objective and radiation-free approach for fracture dating. Thirty-five MR scans of 7 Sprague-Dawley rats (male, 4 weeks old, 100 ± 5 g were acquired on a 3T MRI scanner (TimTrio, Siemens AG, Erlangen, Germany after the surgical infliction of an epiphyseal fracture in the tibia. The images were taken at days 1, 3, 7, 14, 28, 42 and 82 post-surgery. A proton density-weighted and a T1-weighted 3D FLASH sequence were acquired to calculate the longitudinal relaxation time T1 of the fractured region and the surrounding tissues. The calculation of T1 in intact and injured bone resulted in a quantitative observation of bone development in intact juvenile tibiae as well as the bone healing process in the injured tibiae. In both areas, T1 decreased over time. To evaluate the differences in T1 behaviour between the intact and injured bone, the relative T1 values (bone-fracture were calculated, showing clear detectable alterations of T1 after fracture occurrence. These results indicate that qMRI has a high potential not only for clinically relevant applications to detect growth defects or developmental alterations in juvenile bones, but also for forensically relevant applications such as the dating of fractures in cases of child abuse or maltreatment.

  19. T1 mapping of the myocardium: intra-individual assessment of post-contrast T1 time evolution and extracellular volume fraction at 3T for Gd-DTPA and Gd-BOPTA

    Directory of Open Access Journals (Sweden)

    Kawel Nadine

    2012-04-01

    Full Text Available Abstract Purpose Myocardial T1 relaxation time (T1 time and extracellular volume fraction (ECV are altered in patients with diffuse myocardial fibrosis. The purpose of this study was to perform an intra-individual assessment of normal T1 time and ECV for two different contrast agents. Methods A modified Look-Locker Inversion Recovery (MOLLI sequence was acquired at 3 T in 24 healthy subjects (8 men; 28 ± 6 years at mid-ventricular short axis pre-contrast and every 5 min between 5-45 min after injection of a bolus of 0.15 mmol/kg gadopentetate dimeglumine (Gd-DTPA; Magnevist® (exam 1 and 0.1 mmol/kg gadobenate dimeglumine (Gd-BOPTA; Multihance® (exam 2 during two separate scanning sessions. T1 times were measured in myocardium and blood on generated T1 maps. ECVs were calculated as ΔR1myocardium/ΔR1blood*1−hematocrit. Results Mean pre-contrast T1 relaxation times for myocardium and blood were similar for both the first and second CMR exam (p > 0.5. Overall mean post-contrast myocardial T1 time was 15 ± 2 ms (2.5 ± 0.7% shorter for Gd-DTPA at 0.15 mmol/kg compared to Gd-BOPTA at 0.1 mmol/kg (p  0.05. Between 5 and 45 minutes after contrast injection, mean ECV values increased linearly with time for both contrast agents from 0.27 ± 0.03 to 0.30 ± 0.03 (p pre-contrast myocardial T1 relaxation time (CV 4.5% [exam 1] and 3.0% [exam 2], respectively. ECV with Gd-DTPA was highly correlated to ECV by Gd-BOPTA (r = 0.803; p  Conclusion In comparison to pre-contrast myocardial T1 relaxation time, variation in ECV values of normal subjects is larger. However, absolute differences in ECV between Gd-DTPA and Gd-BOPTA were small and rank correlation was high. There is a small and linear increase in ECV over time, therefore ideally images should be acquired at the same delay after contrast injection.

  20. Vibrational and rotational relaxation times of solvated molecular ions

    Science.gov (United States)

    Li, M.; Owrutsky, J.; Sarisky, M.; Culver, J. P.; Yodh, A.; Hochstrasser, R. M.

    1993-04-01

    Infrared pump-probe and infrared polarization spectroscopy have been used to measure the vibrational relaxation times (T1) of the antisymmetric stretching mode and the reorientation times (TR) for N3-, NCS-, and NCO- in D2O and/or methanol. For N3-, experiments were also conducted in H2O and hexamethyl-phosphamide (HPMA) solutions. The rapid vibrational relaxation and slow reorientation observed demonstrate strong coupling between the ions and the solvents. Longer vibrational relaxation and shorter reorientation times measured for NCS- reveal weaker solvent interactions that may be due to the importance of the charge distribution and the form of the normal coordinate. A comparison of the T1 and TR times in different solvents permits a determination of the relative interaction strengths for the solvents investigated. The relatively weaker coupling of N3- in the aprotic solvent HMPA demonstrates the importance of hydrogen bonding in strong solvent interactions in ionic solutions. The experimental results are compared with recent molecular dynamics simulations of ionic solutions.

  1. The follow-up of progressive hypertrophic cardiomyopathy using magnetic resonance rotating frame relaxation times.

    Science.gov (United States)

    Khan, Muhammad Arsalan; Laakso, Hanne; Laidinen, Svetlana; Kettunen, Sanna; Heikura, Tommi; Ylä-Herttuala, Seppo; Liimatainen, Timo

    2017-12-15

    Magnetic resonance rotating frame relaxation times are an alternative non-contrast agent choice for the diagnosis of chronic myocardial infarct. Fibrosis typically occurs in progressive hypertrophic cardiomyopathy. Fibrosis has been imaged in myocardial infarcted tissue using rotating frame relaxation times, which provides the possibility to follow up progressive cardiomyopathy without contrast agents. Mild and severe left ventricular hypertrophy were induced in mice by transverse aortic constriction, and the longitudinal rotating frame relaxation times (T1ρ ) and relaxation along the fictitious field (TRAFF2 , TRAFF3 ) were measured at 5, 10, 24, 62 and 89 days after transverse aortic constriction in vivo. Myocardial fibrosis was verified using Masson's trichrome staining. Increases in the relative relaxation time differences of T1ρ , together with TRAFF2 and TRAFF3 , between fibrotic and remote tissues over time were observed. Furthermore, TRAFF2 and TRAFF3 showed higher relaxation times overall in fibrotic tissue than T1ρ . Relaxation time differences were highly correlated with an excess of histologically verified fibrosis. We found that TRAFF2 and TRAFF3 are more sensitive than T1ρ to hypertrophic cardiomyopathy-related tissue changes and can serve as non-invasive diagnostic magnetic resonance imaging markers to follow up the mouse model of progressive hypertrophic cardiomyopathy. Copyright © 2017 John Wiley & Sons, Ltd.

  2. A unified Maximum Likelihood framework for simultaneous motion and T1 estimation in quantitative MR T1 mapping

    NARCIS (Netherlands)

    Ramos-Llorden, Gabriel; den Dekker, A.J.; Van Steenkiste, G.; Jeurissen, Ben; Vanhevel, Floris; Audekerke, Johan Van; Verhoye, Marleen; Sijbers, Jan

    2017-01-01

    In quantitative MR T1 mapping, the spin-lattice relaxation time T1 of tissues is estimated from a series of T1-weighted images. As the T1 estimation is a voxel-wise estimation procedure, correct spatial alignment of the T1-weighted images is crucial. Conventionally, the T1-weighted images are

  3. Quantifying Temperature-Dependent T1 Changes in Cortical Bone Using Ultrashort Echo-Time MRI

    Science.gov (United States)

    Han, Misung; Rieke, Viola; Scott, Serena J; Ozhinsky, Eugene; Salgaonkar, Vasant A; Jones, Peter D; Larson, Peder E Z; Diederich, Chris J; Krug, Roland

    2015-01-01

    Purpose To demonstrate the feasibility of using ultrashort echo-time (UTE) MRI to quantify T1 changes in cortical bone due to heating. Methods Variable flip-angle T1 mapping combined with 3D UTE imaging was used to measure T1 in cortical bone. A calibration experiment was performed to detect T1 changes with temperature in ex vivo cortical bone samples from a bovine femur. Ultrasound heating experiments were performed using an interstitial applicator in ex vivo bovine femur specimens, and heat-induced T1 changes were quantified. Results The calibration experiment demonstrated that T1 increases with temperature in cortical bone. We observed a linear relationship between temperature and T1 with a linear coefficient of 0.67–0.84 ms/°C over a range of 25–70°C. The ultrasound heating experiments showed increased T1 changes in the heated regions, and the relationship between the temperature changes and T1 changes was similar to that of the calibration. Conclusion We demonstrated a temperature dependence of T1 in ex vivo cortical bone using a variable flip-angle UTE T1 mapping method. PMID:26390357

  4. Development of rapid methods for relaxation time mapping and motion estimation using magnetic resonance imaging

    OpenAIRE

    Gilani, Syed Irtiza Ali

    2008-01-01

    Recent technological developments in the field of magnetic resonance imaging have resulted in advanced techniques that can reduce the total time to acquire images. For applications such as relaxation time mapping, which enables improved visualisation of in vivo structures, rapid imaging techniques are highly desirable. TAPIR is a Look- Locker-based sequence for high-resolution, multislice T1 relaxation time mapping. Despite the high accuracy and precision of TAPIR, an improveme...

  5. Relaxation time estimation in surface NMR

    Energy Technology Data Exchange (ETDEWEB)

    Grunewald, Elliot D.; Walsh, David O.

    2017-03-21

    NMR relaxation time estimation methods and corresponding apparatus generate two or more alternating current transmit pulses with arbitrary amplitudes, time delays, and relative phases; apply a surface NMR acquisition scheme in which initial preparatory pulses, the properties of which may be fixed across a set of multiple acquisition sequence, are transmitted at the start of each acquisition sequence and are followed by one or more depth sensitive pulses, the pulse moments of which are varied across the set of multiple acquisition sequences; and apply processing techniques in which recorded NMR response data are used to estimate NMR properties and the relaxation times T.sub.1 and T.sub.2* as a function of position as well as one-dimensional and two-dimension distributions of T.sub.1 versus T.sub.2* as a function of subsurface position.

  6. Probing relaxation times in graphene quantum dots

    Science.gov (United States)

    Volk, Christian; Neumann, Christoph; Kazarski, Sebastian; Fringes, Stefan; Engels, Stephan; Haupt, Federica; Müller, André; Stampfer, Christoph

    2013-01-01

    Graphene quantum dots are attractive candidates for solid-state quantum bits. In fact, the predicted weak spin-orbit and hyperfine interaction promise spin qubits with long coherence times. Graphene quantum dots have been extensively investigated with respect to their excitation spectrum, spin-filling sequence and electron-hole crossover. However, their relaxation dynamics remain largely unexplored. This is mainly due to challenges in device fabrication, in particular concerning the control of carrier confinement and the tunability of the tunnelling barriers, both crucial to experimentally investigate decoherence times. Here we report pulsed-gate transient current spectroscopy and relaxation time measurements of excited states in graphene quantum dots. This is achieved by an advanced device design that allows to individually tune the tunnelling barriers down to the low megahertz regime, while monitoring their asymmetry. Measuring transient currents through electronic excited states, we estimate a lower bound for charge relaxation times on the order of 60–100 ns. PMID:23612294

  7. Evaluation of relaxation time measurements by magnetic resonance imaging. A phantom study

    DEFF Research Database (Denmark)

    Kjaer, L; Thomsen, C; Henriksen, O

    1987-01-01

    Several circumstances may explain the great variation in reported proton T1 and T2 relaxation times usually seen. This study was designed to evaluate the accuracy of relaxation time measurements by magnetic resonance imaging (MRI) operating at 1.5 tesla. Using a phantom of nine boxes with different...... concentrations of CuSO4 and correlating the calculated T1 and T2 values with reference values obtained by two spectrometers (corrected to MRI-proton frequency = 64 MHz) we found a maximum deviation of about 10 per cent. Measurements performed on a large water phantom in order to evaluate the homogeneity...

  8. T1 mapping of the myocardium: intra-individual assessment of post-contrast T1 time evolution and extracellular volume fraction at 3T for Gd-DTPA and Gd-BOPTA

    Science.gov (United States)

    2012-01-01

    Purpose Myocardial T1 relaxation time (T1 time) and extracellular volume fraction (ECV) are altered in patients with diffuse myocardial fibrosis. The purpose of this study was to perform an intra-individual assessment of normal T1 time and ECV for two different contrast agents. Methods A modified Look-Locker Inversion Recovery (MOLLI) sequence was acquired at 3 T in 24 healthy subjects (8 men; 28 ± 6 years) at mid-ventricular short axis pre-contrast and every 5 min between 5-45 min after injection of a bolus of 0.15 mmol/kg gadopentetate dimeglumine (Gd-DTPA; Magnevist®) (exam 1) and 0.1 mmol/kg gadobenate dimeglumine (Gd-BOPTA; Multihance®) (exam 2) during two separate scanning sessions. T1 times were measured in myocardium and blood on generated T1 maps. ECVs were calculated as ΔR1myocardium/ΔR1blood*1−hematocrit. Results Mean pre-contrast T1 relaxation times for myocardium and blood were similar for both the first and second CMR exam (p > 0.5). Overall mean post-contrast myocardial T1 time was 15 ± 2 ms (2.5 ± 0.7%) shorter for Gd-DTPA at 0.15 mmol/kg compared to Gd-BOPTA at 0.1 mmol/kg (p  0.05). Between 5 and 45 minutes after contrast injection, mean ECV values increased linearly with time for both contrast agents from 0.27 ± 0.03 to 0.30 ± 0.03 (p < 0.0001). Mean ECV values were slightly higher (by 0.01, p < 0.05) for Gd-DTPA compared to Gd-BOPTA. Inter-individual variation of ECV was higher (CV 8.7% [exam 1, Gd-DTPA] and 9.4% [exam 2, Gd-BOPTA], respectively) compared to variation of pre-contrast myocardial T1 relaxation time (CV 4.5% [exam 1] and 3.0% [exam 2], respectively). ECV with Gd-DTPA was highly correlated to ECV by Gd-BOPTA (r = 0.803; p < 0.0001). Conclusion In comparison to pre-contrast myocardial T1 relaxation time, variation in ECV values of normal subjects is larger. However, absolute differences in ECV between Gd-DTPA and Gd-BOPTA were small and rank correlation was high. There is a small

  9. First Passage Times, Lifetimes, and Relaxation Times of Unfolded Proteins.

    Science.gov (United States)

    Dai, Wei; Sengupta, Anirvan M; Levy, Ronald M

    2015-07-24

    The dynamics of proteins in the unfolded state can be quantified in computer simulations by calculating a spectrum of relaxation times which describes the time scales over which the population fluctuations decay to equilibrium. If the unfolded state space is discretized, we can evaluate the relaxation time of each state. We derive a simple relation that shows the mean first passage time to any state is equal to the relaxation time of that state divided by the equilibrium population. This explains why mean first passage times from state to state within the unfolded ensemble can be very long but the energy landscape can still be smooth (minimally frustrated). In fact, when the folding kinetics is two-state, all of the unfolded state relaxation times within the unfolded free energy basin are faster than the folding time. This result supports the well-established funnel energy landscape picture and resolves an apparent contradiction between this model and the recently proposed kinetic hub model of protein folding. We validate these concepts by analyzing a Markov state model of the kinetics in the unfolded state and folding of the miniprotein NTL9 (where NTL9 is the N-terminal domain of the ribosomal protein L9), constructed from a 2.9 ms simulation provided by D. E. Shaw Research.

  10. Effects of Stress and Relaxation on Time Perception

    Science.gov (United States)

    2003-01-01

    1998). Common relaxation methods include progressive muscle relaxation, meditation, imaging, autogenic training (self- hypnosis ), listening to 14 music...2001). Menstrual and circadian rythms in time perception in healthy women and women with premenstrual syndrome. Neuroscience Research, 41(4), 339

  11. T1ρ magnetic resonance: basic physics principles and applications in knee and intervertebral disc imaging

    NARCIS (Netherlands)

    Wáng, Yì-Xiáng J.; Zhang, Qinwei; Li, Xiaojuan; Chen, Weitian; Ahuja, Anil; Yuan, Jing

    2015-01-01

    T1ρ relaxation time provides a new contrast mechanism that differs from T1- and T2-weighted contrast, and is useful to study low-frequency motional processes and chemical exchange in biological tissues. T1ρ imaging can be performed in the forms of T1ρ-weighted image, T1ρ mapping and T1ρ dispersion.

  12. Immersed boundary lattice Boltzmann model based on multiple relaxation times

    Science.gov (United States)

    Lu, Jianhua; Han, Haifeng; Shi, Baochang; Guo, Zhaoli

    2012-01-01

    As an alterative version of the lattice Boltzmann models, the multiple relaxation time (MRT) lattice Boltzmann model introduces much less numerical boundary slip than the single relaxation time (SRT) lattice Boltzmann model if some special relationship between the relaxation time parameters is chosen. On the other hand, most current versions of the immersed boundary lattice Boltzmann method, which was first introduced by Feng and improved by many other authors, suffer from numerical boundary slip as has been investigated by Le and Zhang. To reduce such a numerical boundary slip, an immerse boundary lattice Boltzmann model based on multiple relaxation times is proposed in this paper. A special formula is given between two relaxation time parameters in the model. A rigorous analysis and the numerical experiments carried out show that the numerical boundary slip reduces dramatically by using the present model compared to the single-relaxation-time-based model.

  13. Stroke Onset Time Determination Using MRI Relaxation Times without Non-Ischaemic Reference in A Rat Stroke Model.

    Science.gov (United States)

    Norton, Terence J T; Pereyra, Marcelo; Knight, Michael J; McGarry, Bryony M; Jokivarsi, Kimmo T; Gröhn, Olli H J; Kauppinen, Risto A

    2017-06-20

    Objective timing of stroke in emergency departments is expected to improve patient stratification. Magnetic resonance imaging (MRI) relaxations times, T2 and T1ρ , in abnormal diffusion delineated ischaemic tissue were used as proxies of stroke time in a rat model. Both 'non-ischaemic reference'-dependent and -independent estimators were generated. Apparent diffusion coefficient (ADC), T2 and T1ρ , were sequentially quantified for up to 6 hours of stroke in rats (n = 8) at 4.7T. The ischaemic lesion was identified as a contiguous collection of voxels with low ADC. T2 and T1ρ in the ischaemic lesion and in the contralateral non-ischaemic brain tissue were determined. Differences in mean MRI relaxation times between ischaemic and non-ischaemic volumes were used to create reference-dependent estimator. For the reference-independent procedure, only the parameters associated with log-logistic fits to the T2 and T1ρ distributions within the ADC-delineated lesions were used for the onset time estimation. The reference-independent estimators from T2 and T1ρ data provided stroke onset time with precisions of ±32 and ±27 minutes, respectively. The reference-dependent estimators yielded respective precisions of ±47 and ±54 minutes. A 'non-ischaemic anatomical reference'-independent estimator for stroke onset time from relaxometric MRI data is shown to yield greater timing precision than previously obtained through reference-dependent procedures.

  14. Time scales of relaxation dynamics during transient conditions in two-phase flow: RELAXATION DYNAMICS

    Energy Technology Data Exchange (ETDEWEB)

    Schlüter, Steffen [School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis Oregon USA; Department Soil Physics, Helmholtz-Centre for Environmental Research-UFZ, Halle Germany; Berg, Steffen [Shell Global Solutions International B.V., Rijswijk Netherlands; Li, Tianyi [School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis Oregon USA; Vogel, Hans-Jörg [Department Soil Physics, Helmholtz-Centre for Environmental Research-UFZ, Halle Germany; Institut für Agrar- und Ernährungswissenschaften, Martin-Luther-Universität Halle-Wittenberg, Halle Germany; Wildenschild, Dorthe [School of Chemical, Biological and Environmental Engineering, Oregon State University, Corvallis Oregon USA

    2017-06-01

    The relaxation dynamics toward a hydrostatic equilibrium after a change in phase saturation in porous media is governed by fluid reconfiguration at the pore scale. Little is known whether a hydrostatic equilibrium in which all interfaces come to rest is ever reached and which microscopic processes govern the time scales of relaxation. Here we apply fast synchrotron-based X-ray tomography (X-ray CT) to measure the slow relaxation dynamics of fluid interfaces in a glass bead pack after fast drainage of the sample. The relaxation of interfaces triggers internal redistribution of fluids, reduces the surface energy stored in the fluid interfaces, and relaxes the contact angle toward the equilibrium value while the fluid topology remains unchanged. The equilibration of capillary pressures occurs in two stages: (i) a quick relaxation within seconds in which most of the pressure drop that built up during drainage is dissipated, a process that is to fast to be captured with fast X-ray CT, and (ii) a slow relaxation with characteristic time scales of 1–4 h which manifests itself as a spontaneous imbibition process that is well described by the Washburn equation for capillary rise in porous media. The slow relaxation implies that a hydrostatic equilibrium is hardly ever attained in practice when conducting two-phase experiments in which a flux boundary condition is changed from flow to no-flow. Implications for experiments with pressure boundary conditions are discussed.

  15. TIME-COURSE OF ACTION AND ENDOTRACHEAL INTUBATING CONDITIONS OF ORG-9487, A NEW SHORT-ACTING STEROIDAL MUSCLE-RELAXANT - A COMPARISON WITH SUCCINYLCHOLINE

    NARCIS (Netherlands)

    WIERDA, JMKH; VANDENBROEK, L; PROOST, JH; VERBAAN, BW; HENNIS, PJ

    In a randomized study, we evaluated lag time (time from the end of injection of muscle relaxant until the first depression of the train-of-four response [TOF]), onset time (time from the end of injection of muscle relaxant until the maximum depression of the first twitch of the TOF [T1]),

  16. Regional cerebral relaxation times measured by magnetic ...

    African Journals Online (AJOL)

    However, regional T1 was found to vary significantly (p < 0.01) while regional T2 did not vary significantly (p = 0.07) by one-way ANOVA. These findings are consistent with theory and published data for the ROIs studied. The results could thus serve as a reference data set for brain MRI pulse sequence optimisation at 3.0 T ...

  17. The comparative influence of anesthetics on the in vitro proton NMR relaxation times in rat liver.

    Science.gov (United States)

    Scheindlin, B; Jacobs, D O; Settle, R G; Wolf, G L; Rombeau, J L

    1985-01-01

    To determine the effect of anesthetics on liver relaxation times in rat, two experiments were performed. In the first experiment, normal and protein-depleted rats underwent total hepatectomy under ether anesthesia or following decapitation. In the second experiment, livers were excised from normal rats under ketamine or pentobarbital anesthesia, or following decapitation. Hepatic T1 and T2 were measured for all animals using a RADX 10 MHz spin analyzer. Ketamine produced T1 values significantly different from decapitation. Ketamine, pentobarbital, and ether in normal animals all produced T2 values significantly different from decapitation. It is apparent that anesthetization of rats prior to in vitro measurement of hepatic relaxation times is not equivalent to decapitation; nor are the anesthetics examined equivalent to one another.

  18. A fast method for the quantification of fat fraction and relaxation times: Comparison of five sites of bone marrow.

    Science.gov (United States)

    Le Ster, Caroline; Lasbleiz, Jérémy; Kannengiesser, Stephan; Guillin, Raphaël; Gambarota, Giulio; Saint-Jalmes, Hervé

    2017-06-01

    Bone marrow is found either as red bone marrow, which mainly contains haematopoietic cells, or yellow bone marrow, which mainly contains adipocytes. In adults, red bone marrow is principally located in the axial skeleton. A recent study has introduced a method to simultaneously estimate the fat fraction (FF), the T1 and T2* relaxation times of water (T1w, T2*w) and fat (T1f and T2*f) in the vertebral bone marrow. The aim of the current study was to measure FF, T1w, T1f, T2*w and T2*f in five sites of bone marrow, and to assess the presence of regional variations. MRI experiments were performed at 1.5T on five healthy volunteers (31.6±15.6years) using a prototype chemical-shift-encoded 3D multi-gradient-echo sequence (VIBE) acquired with two flip angles. Acquisitions were performed in the shoulders, lumbar spine and pelvis, with acquisition times of fat fraction and relaxation times were observed in these sites, with higher fat fraction and longer T1w in the epiphyses of long bones. A high correlation between FF and T1w was measured in these bones (R=0.84 in the humerus and R=0.84 in the femur). In most sites, there was a significant difference between water and fat relaxation times, attesting the relevance of measuring these parameters separately. The method proposed in the current study allowed for measurements of FF, T1w, T1f, T2*w and T2*f in five sites of bone marrow. Regional variations of these parameters were observed and a strong negative correlation between the T1 of water and the fat fraction in bones with high fat fractions was found. Copyright © 2017 Elsevier Inc. All rights reserved.

  19. Temperature dependence of relaxation times and temperature mapping in ultra-low-field MRI.

    Science.gov (United States)

    Vesanen, Panu T; Zevenhoven, Koos C J; Nieminen, Jaakko O; Dabek, Juhani; Parkkonen, Lauri T; Ilmoniemi, Risto J

    2013-10-01

    Ultra-low-field MRI is an emerging technology that allows MRI and NMR measurements in microtesla-range fields. In this work, the possibilities of relaxation-based temperature measurements with ultra-low-field MRI were investigated by measuring T1 and T2 relaxation times of agarose gel at 50 μT-52 mT and at temperatures 5-45°C. Measurements with a 3T scanner were made for comparison. The Bloembergen-Purcell-Pound relaxation theory was combined with a two-state model to explain the field-strength and temperature dependence of the data. The results show that the temperature dependencies of agarose gel T1 and T2 in the microtesla range differ drastically from those at 3T; the effect of temperature on T1 is reversed at approximately 5 mT. The obtained results were used to reconstruct temperature maps from ultra-low-field scans. These time-dependent temperature maps measured from an agarose gel phantom at 50 μT reproduced the temperature gradient with good contrast. Copyright © 2013 Elsevier Inc. All rights reserved.

  20. In vivo field dependence of proton relaxation times in human brain, liver and skeletal muscle: a multicenter study

    DEFF Research Database (Denmark)

    Henriksen, O; de Certaines, J D; Spisni, A

    1993-01-01

    and MRS, the in vivo field dispersion of T1 and T2 has been measured in order to evaluate whether ex vivo data are representative for the in vivo situation. Brain, skeletal muscle, and liver of healthy human volunteers were studied. Fifteen MR units with a field strength ranging from 0.08 T to 1.5 T took......T1 and T2 relaxation times are fundamental parameters for signal contrast behaviour in MRI. A number of ex vivo relaxometry studies have dealt with the magnetic field dispersion of T1. By means of multicenter study within the frame of the COMAC BME Concerted Action on Tissue Characterization by MRI...... part in the trial, which comprised 218 volunteers. All the MR systems were tested for measurement accuracy using the Eurospin TO5 test object. The measured relaxation data were subsequently corrected according to the obtained calibration curves. The results showed a clear field dispersion of T1...

  1. Multiple-Relaxation-Time Lattice Boltzmann Models in 3D

    Science.gov (United States)

    dHumieres, Dominique; Ginzburg, Irina; Krafczyk, Manfred; Lallemand, Pierre; Luo, Li-Shi; Bushnell, Dennis M. (Technical Monitor)

    2002-01-01

    This article provides a concise exposition of the multiple-relaxation-time lattice Boltzmann equation, with examples of fifteen-velocity and nineteen-velocity models in three dimensions. Simulation of a diagonally lid-driven cavity flow in three dimensions at Re=500 and 2000 is performed. The results clearly demonstrate the superior numerical stability of the multiple-relaxation-time lattice Boltzmann equation over the popular lattice Bhatnagar-Gross-Krook equation.

  2. Immersed Boundary-Lattice Boltzmann Method Using Two Relaxation Times

    Directory of Open Access Journals (Sweden)

    Kosuke Hayashi

    2012-06-01

    Full Text Available An immersed boundary-lattice Boltzmann method (IB-LBM using a two-relaxation time model (TRT is proposed. The collision operator in the lattice Boltzmann equation is modeled using two relaxation times. One of them is used to set the fluid viscosity and the other is for numerical stability and accuracy. A direct-forcing method is utilized for treatment of immersed boundary. A multi-direct forcing method is also implemented to precisely satisfy the boundary conditions at the immersed boundary. Circular Couette flows between a stationary cylinder and a rotating cylinder are simulated for validation of the proposed method. The method is also validated through simulations of circular and spherical falling particles. Effects of the functional forms of the direct-forcing term and the smoothed-delta function, which interpolates the fluid velocity to the immersed boundary and distributes the forcing term to fixed Eulerian grid points, are also examined. As a result, the following conclusions are obtained: (1 the proposed method does not cause non-physical velocity distribution in circular Couette flows even at high relaxation times, whereas the single-relaxation time (SRT model causes a large non-physical velocity distortion at a high relaxation time, (2 the multi-direct forcing reduces the errors in the velocity profile of a circular Couette flow at a high relaxation time, (3 the two-point delta function is better than the four-point delta function at low relaxation times, but worse at high relaxation times, (4 the functional form of the direct-forcing term does not affect predictions, and (5 circular and spherical particles falling in liquids are well predicted by using the proposed method both for two-dimensional and three-dimensional cases.

  3. In-vivo T2-relaxation times of asymptomatic cervical intervertebral discs

    Energy Technology Data Exchange (ETDEWEB)

    Driscoll, Sean J.; Mao, Haiqing; Li, Guoan [Massachusetts General Hospital/Harvard Medical School, Bioengineering Laboratory, Department of Orthopaedic Surgery, Boston, MA (United States); Zhong, Weiye [Massachusetts General Hospital/Harvard Medical School, Bioengineering Laboratory, Department of Orthopaedic Surgery, Boston, MA (United States); Second Xiangya Hospital and Central South University, Department of Spinal Surgery, Changsha, Hunan (China); Torriani, Martin [Massachusetts General Hospital/Harvard Medical School, Musculoskeletal Imaging and Intervention, Department of Radiology, Boston, MA (United States); Wood, Kirkham B.; Cha, Thomas D. [Massachusetts General Hospital/Harvard Medical School, Spine Service, Department of Orthopaedic Surgery, Boston, MA (United States)

    2016-03-15

    Limited research exists on T2-mapping techniques for cervical intervertebral discs and its potential clinical utility. The objective of this research was to investigate the in-vivo T2-relaxation times of cervical discs, including C2-C3 through C7-T1. Ten asymptomatic subjects were imaged using a 3.0 T MR scanner and a sagittal multi-slice multi-echo sequence. Using the mid-sagittal image, intervertebral discs were divided into five regions-of-interest (ROIs), centered along the mid-line of the disc. Average T2 relaxation time values were calculated for each ROI using a mono-exponential fit. Differences in T2 values between disc levels and across ROIs of the same disc were examined. For a given ROI, the results showed a trend of increasing relaxation times moving down the spinal column, particularly in the middle regions (ROIs 2, 3 and 4). The C6-C7 and C7-T1 discs had significantly greater T2 values compared to superior discs (discs between C2 and C6). The results also showed spatial homogeneity of T2 values in the C3-C4, C4-C5, and C5-C6 discs, while C2-C3, C6-C7, and C7-T1 showed significant differences between ROIs. The findings indicate there may be inherent differences in T2-relaxation time properties between different cervical discs. Clinical evaluations utilizing T2-mapping techniques in the cervical spine may need to be level-dependent. (orig.)

  4. DCE-PWI 3D T1-measurement as function of time or flip angle

    DEFF Research Database (Denmark)

    Mikkelsen, Irene Klærke; Peters, David Alberg; Tietze, Anna

    Dynamic Contrast Enhanced Perfusion Weighted Imaging (DCE-PWI) and the preceding T1 measurement is usually performed with a FLASH sequence. For the sake of speed, the 3D T1 measurement is often performed by measuring the signal for a range of flip angles instead of as a function the inversion (or...

  5. Rapid volumetric T1 mapping of the abdomen using three-dimensional through-time spiral GRAPPA.

    Science.gov (United States)

    Chen, Yong; Lee, Gregory R; Aandal, Gunhild; Badve, Chaitra; Wright, Katherine L; Griswold, Mark A; Seiberlich, Nicole; Gulani, Vikas

    2016-04-01

    To develop an ultrafast T1 mapping method for high-resolution, volumetric T1 measurements in the abdomen. The Look-Locker method was combined with a stack-of-spirals acquisition accelerated using three-dimensional (3D) through-time spiral GRAPPA reconstruction for fast data acquisition. A segmented k-space acquisition scheme was proposed and the time delay between segments for the recovery of longitudinal magnetization was optimized using Bloch equation simulations. The accuracy of this method was validated in a phantom experiment and in vivo T1 measurements were performed with 35 asymptomatic subjects on both 1.5 Tesla (T) and 3T MRI systems. Phantom experiments yielded close agreement between the proposed method and gold standard measurements for a large range of T1 values (200 to 1600 ms). The in vivo results further demonstrate that high-resolution T1 maps (2 × 2 × 4 mm(3)) for 32 slices can be achieved in a single clinically feasible breath-hold of approximately 20 s. The T1 values for multiple organs and tissues in the abdomen are in agreement with the published literature. A high-resolution 3D abdominal T1 mapping technique was developed, which allows fast and accurate T1 mapping of multiple abdominal organs and tissues in a single breath-hold. © 2015 Wiley Periodicals, Inc.

  6. Ice sheet growth with laterally varying bedrock relaxation time

    Science.gov (United States)

    van der Wal, Wouter; Vizcaino Rubio, Pablo; De Boer, Bas; van de Wal, Roderik

    2017-04-01

    Isostatic response of the bedrock, or glacial isostatic adjustment (GIA) in included in most ice sheet models. This is important because the surface elevation determines the mass balance and thereby implicitly also the strength of the mass balance feedback where higher surface elevation yields lower temperatures implying less melt and vice versa. Usually a single relaxation time or a set of relaxation times is used to model the response everywhere on Earth or at least for an entire ice sheet. In reality the viscosity in the Earth's mantle, and hence the relaxation time experienced by the ice, varies with location. Seismic studies indicate that several regions that were covered by ice during the last glacial cycle are underlain by mantle in which viscosity varies with orders of magnitude, such as Antarctica and North America. The question is whether such a variation of viscosity influences ice evolution. Several GIA models exist that can deal with 3D viscosity, but their large computation times make it nearly impossible to couple them to ice sheet models. Here we use the ANICE ice-sheet model (de Boer et al. 2013) with a simple bedrock-relaxation model in which a different relaxation time is used for separate regions. A temperature anomaly is applied to grow a schematic ice sheet on a flat earth, with other forcing mechanisms neglected. It is shown that in locations with a fast relaxation time of 300 years the equilibrium ice sheet is significantly thinner and narrower but also ice thickness in neighbouring regions (with the more standard relaxation time of 3000 years) is affected.

  7. Optimal Configuration for Relaxation Times Estimation in Complex Spin Echo Imaging

    Directory of Open Access Journals (Sweden)

    Fabio Baselice

    2014-01-01

    Full Text Available Many pathologies can be identified by evaluating differences raised in the physical parameters of involved tissues. In a Magnetic Resonance Imaging (MRI framework, spin-lattice T1 and spin-spin T2 relaxation time parameters play a major role in such an identification. In this manuscript, a theoretical study related to the evaluation of the achievable performances in the estimation of relaxation times in MRI is proposed. After a discussion about the considered acquisition model, an analysis on the ideal imaging acquisition parameters in the case of spin echo sequences, i.e., echo and repetition times, is conducted. In particular, the aim of the manuscript consists in providing an empirical rule for optimal imaging parameter identification with respect to the tissues under investigation. Theoretical results are validated on different datasets in order to show the effectiveness of the presented study and of the proposed methodology.

  8. Parameterization of NMR relaxation curves in terms of logarithmic moments of the relaxation time distribution

    Science.gov (United States)

    Petrov, Oleg V.; Stapf, Siegfried

    2017-06-01

    This work addresses the problem of a compact and easily comparable representation of multi-exponential relaxation data. It is often convenient to describe such data in a few parameters, all being of physical significance and easy to interpret, and in such a way that enables a model-free comparison between different groups of samples. Logarithmic moments (LMs) of the relaxation time constitute a set of parameters which are related to the characteristic relaxation time on the log-scale, the width and the asymmetry of an underlying distribution of exponentials. On the other hand, the calculation of LMs does not require knowing the actual distribution function and is reduced to a numerical integration of original data. The performance of this method has been tested on both synthetic and experimental NMR relaxation data which differ in a signal-to-noise ratio, the sampling range and the sampling rate. The calculation of two lower-order LMs, the log-mean time and the log-variance, has proved robust against deficiencies of the experiment such as scattered data point and incomplete sampling. One may consider using them as such to monitor formation of a heterogeneous structure, e.g., in phase separation, vitrification, polymerization, hydration, aging, contrast agent propagation processes. It may also assist in interpreting frequency and temperature dependences of relaxation, revealing a crossover from slow to fast exchange between populations. The third LM was found to be a less reliable quantity due to its susceptibility to the noise and must be used with caution.

  9. Experimental study on relaxation time in direction changing movement

    Science.gov (United States)

    Liu, Chi; Song, Weiguo; Fu, Libi; Lian, Liping; Lo, Siuming

    2017-02-01

    Controlled experiments were conducted to clarify the movement characteristics of pedestrians in direction changing processes. We track pedestrians' trajectories and map them into real space coordinates by the direct linear transformation method. In the acceleration process, the relaxation time and free moving speed in our experiments respectively equal 0.659 s and 1.540 m/s, which are consistent with those for Chinese participants in other experiments. Meanwhile, the values of relaxation time in the direction changing process are calculated by a derived equation from the concept of the social force model. It is observed that the relaxation time is not an invariable parameter, and tends to increase with an increase in the angular difference. Furthermore, results show that pedestrians are insensitive to a tiny angular difference between instantaneous velocity and desired velocity. These experimental results presented in this work can be applied in model development and validation.

  10. Optically-detected spin-echo method for relaxation times measurements in a Rb atomic vapor

    Science.gov (United States)

    Gharavipour, M.; Affolderbach, C.; Gruet, F.; Radojičić, I. S.; Krmpot, A. J.; Jelenković, B. M.; Mileti, G.

    2017-06-01

    We introduce and demonstrate an experimental method, optically-detected spin-echo (ODSE), to measure ground-state relaxation times of a rubidium (Rb) atomic vapor held in a glass cell with buffer-gas. The work is motivated by our studies on high-performance Rb atomic clocks, where both population and coherence relaxation times (T 1 and T 2, respectively) of the ‘clock transition’ (52S1/2 | {F}g = 1,{m}F=0> ≤ftrightarrow | {F}g=2,{m}F=0> ) are relevant. Our ODSE method is inspired by classical nuclear magnetic resonance spin-echo method, combined with optical detection. In contrast to other existing methods, like continuous-wave double-resonance (CW-DR) and Ramsey-DR, principles of the ODSE method allow suppression of decoherence arising from the inhomogeneity of the static magnetic field across the vapor cell, thus enabling measurements of intrinsic relaxation rates, as properties of the cell alone. Our experimental result for the coherence relaxation time, specific for the clock transition, measured with the ODSE method is in good agreement with the theoretical prediction, and the ODSE results are validated by comparison to those obtained with Franzen, CW-DR and Ramsey-DR methods. The method is of interest for a wide variety of quantum optics experiments with optical signal readout.

  11. T1 mapping for diagnosis of mild chronic pancreatitis.

    Science.gov (United States)

    Tirkes, Temel; Lin, Chen; Fogel, Evan L; Sherman, Stuart S; Wang, Qiushi; Sandrasegaran, Kumaresan

    2017-04-01

    To determine if the T1 relaxation time of the pancreas can detect parenchymal changes in mild chronic pancreatitis (CP). This Institutional Review Board (IRB)-approved, Health Insurance Portability and Accountability Act (HIPAA)-compliant retrospective study analyzed 98 patients with suspected mild CP. Patients were grouped as normal (n = 53) or mild CP (n = 45) based on history, presenting symptomatology, and concordant findings on both the secretin-enhanced magnetic resonance cholangiopancreatography (S-MRCP) and endoscopic retrograde cholangiopancreatography (ERCP). T1 maps were obtained in all patients using the same 3D gradient echo technique on the same 3T scanner. T1 relaxation times, fat signal fraction (FSF), and anterior-posterior (AP) diameter were correlated with the clinical diagnosis of CP. There was a significant difference (P T1 relaxation times between the control (mean = 797 msec, 95% confidence interval [CI]: 730, 865) and mild CP group (mean = 1099 msec, 95% CI: 1032, 1166). A T1 relaxation time threshold value of 900 msec was 80% sensitive (95% CI: 65, 90) and 69% specific (95% CI: 56, 82) for the diagnosis of mild CP (area under the curve [AUC]: 0.81). Multiple regression analysis showed that T1 relaxation time was the only statistically significant variable correlating with the diagnosis of CP (P T1 relaxation times showed a weak positive correlation with the pancreatic FSF (ρ = 0.33, P = 0.01) in the control group, but not in the mild CP group. The T1 relaxation time of the pancreatic parenchyma was significantly increased in patients with mild CP. Therefore, T1 mapping might be used as a practical quantitative imaging technique for the evaluation of suspected mild CP. 3 J. Magn. Reson. Imaging 2017;45:1171-1176. © 2016 International Society for Magnetic Resonance in Medicine.

  12. High resolution NMR study of T1 magnetic relaxation dispersion. III. Influence of spin 1/2 hetero-nuclei on spin relaxation and polarization transfer among strongly coupled protons.

    Science.gov (United States)

    Korchak, Sergey E; Ivanov, Konstantin L; Pravdivtsev, Andrey N; Yurkovskaya, Alexandra V; Kaptein, Robert; Vieth, Hans-Martin

    2012-09-07

    Effects of spin-spin interactions on the nuclear magnetic relaxation dispersion (NMRD) of protons were studied in a situation where spin ½ hetero-nuclei are present in the molecule. As in earlier works [K. L. Ivanov, A. V. Yurkovskaya, and H.-M. Vieth, J. Chem. Phys. 129, 234513 (2008); S. E. Korchak, K. L. Ivanov, A. V. Yurkovskaya, and H.-M. Vieth, ibid. 133, 194502 (2010)], spin-spin interactions have a pronounced effect on the relaxivity tending to equalize the longitudinal relaxation times once the spins become strongly coupled at a sufficiently low magnetic field. In addition, we have found influence of (19)F nuclei on the proton NMRD, although in the whole field range, studied protons and fluorine spins were only weakly coupled. In particular, pronounced features in the proton NMRD were found; but each feature was predominantly observed only for particular spin states of the hetero-nuclei. The features are explained theoretically; it is shown that hetero-nuclei can affect the proton NMRD even in the limit of weak coupling when (i) protons are coupled strongly and (ii) have spin-spin interactions of different strengths with the hetero-nuclei. We also show that by choosing the proper magnetic field strength, one can selectively transfer proton spin magnetization between spectral components of choice.

  13. Relaxation Characteristics of 828 DGEBA Epoxy Over Long Time Periods

    Science.gov (United States)

    Hoo, Jasmine; Reprogle, Riley C.; Wisler, Brian; Arechederra, Gabriel K.; McCoy, John D.; Kropka, Jamie M.; Long, Kevin N.

    The mechanical relaxation response in uniaxial compression of a diglycidyl ether of bisphenol-A epoxy was studied over long time periods. The epoxy, 828DEA, was Epon 828 cured with diethanolamine (DEA). A sample was compressed at constant strain rate and held at various strain levels for days to allow the sample to relax. The sample was then compressed further and held once more. The relaxation curves were fit with a stretched exponential function. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  14. The influence of microvascular injury on native T1 and T2* relaxation values after acute myocardial infarction: implications for non-contrast-enhanced infarct assessment.

    Science.gov (United States)

    Robbers, Lourens F H J; Nijveldt, Robin; Beek, Aernout M; Teunissen, Paul F A; Hollander, Maurits R; Biesbroek, P Stefan; Everaars, Henk; van de Ven, Peter M; Hofman, Mark B M; van Royen, Niels; van Rossum, Albert C

    2018-02-01

    Native T1 mapping and late gadolinium enhancement (LGE) imaging offer detailed characterisation of the myocardium after acute myocardial infarction (AMI). We evaluated the effects of microvascular injury (MVI) and intramyocardial haemorrhage on local T1 and T2* values in patients with a reperfused AMI. Forty-three patients after reperfused AMI underwent cardiovascular magnetic resonance imaging (CMR) at 4 [3-5] days, including native MOLLI T1 and T2* mapping, STIR, cine imaging and LGE. T1 and T2* values were determined in LGE-defined regions of interest: the MI core incorporating MVI when present, the core-adjacent MI border zone (without any areas of MVI), and remote myocardium. Average T1 in the MI core was higher than in the MI border zone and remote myocardium. However, in the 20 (47%) patients with MVI, MI core T1 was lower than in patients without MVI (MVI 1048±78ms, no MVI 1111±89ms, p=0.02). MI core T2* was significantly lower in patients with MVI than in those without (MVI 20 [18-23]ms, no MVI 31 [26-39]ms, pvalues. T2* mapping suggested that this may be the result of intramyocardial haemorrhage. These findings have important implications for the interpretation of native T1 values shortly after AMI. • Microvascular injury after acute myocardial infarction affects local T1 and T2* values. • Infarct zone T1 values are lower if microvascular injury is present. • T2* mapping suggests that low infarct T1 values are likely haemorrhage. • T1 and T2* values are complimentary for correctly assessing post-infarct myocardium.

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

    Science.gov (United States)

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

    2008-09-01

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

  16. Effects of Liver Fibrosis Progression on Tissue Relaxation Times in Different Mouse Models Assessed by Ultrahigh Field Magnetic Resonance Imaging

    Directory of Open Access Journals (Sweden)

    Andreas Müller

    2017-01-01

    Full Text Available Recently, clinical studies demonstrated that magnetic resonance relaxometry with determination of relaxation times T1 and T2⁎ may aid in staging and management of liver fibrosis in patients suffering from viral hepatitis and steatohepatitis. In the present study we investigated T1 and T2⁎ in different models of liver fibrosis to compare alternate pathophysiologies in their effects on relaxation times and to further develop noninvasive quantification methods of liver fibrosis. MRI was performed with a fast spin echo sequence for measurement of T1 and a multigradient echo sequence for determination of T2⁎. Toxic liver fibrosis was induced by injections of carbon tetrachloride (1.4 mL CCl4 per kg bodyweight and week, for 3 or 6 weeks in BALB/cJ mice. Chronic sclerosing cholangitis was mimicked using the ATP-binding cassette transporter B4 knockout (Abcb4 -/- mouse model. Untreated BALB/cJ mice served as controls. To assess hepatic fibrosis, we ascertained collagen contents and fibrosis scores after Sirius red staining. T1 and T2⁎ correlate differently to disease severity and etiology of liver fibrosis. T2⁎ shows significant decrease correlating with fibrosis in CCl4 treated animals, while demonstrating significant increase with disease severity in Abcb4 -/- mice. Measurements of T1 and T2⁎ may therefore facilitate discrimination between different stages and causes of liver fibrosis.

  17. Effects of Liver Fibrosis Progression on Tissue Relaxation Times in Different Mouse Models Assessed by Ultrahigh Field Magnetic Resonance Imaging.

    Science.gov (United States)

    Müller, Andreas; Hochrath, Katrin; Stroeder, Jonas; Hittatiya, Kanishka; Schneider, Günther; Lammert, Frank; Buecker, Arno; Fries, Peter

    2017-01-01

    Recently, clinical studies demonstrated that magnetic resonance relaxometry with determination of relaxation times T1 and T2⁎ may aid in staging and management of liver fibrosis in patients suffering from viral hepatitis and steatohepatitis. In the present study we investigated T1 and T2⁎ in different models of liver fibrosis to compare alternate pathophysiologies in their effects on relaxation times and to further develop noninvasive quantification methods of liver fibrosis. MRI was performed with a fast spin echo sequence for measurement of T1 and a multigradient echo sequence for determination of T2⁎. Toxic liver fibrosis was induced by injections of carbon tetrachloride (1.4 mL CCl4 per kg bodyweight and week, for 3 or 6 weeks) in BALB/cJ mice. Chronic sclerosing cholangitis was mimicked using the ATP-binding cassette transporter B4 knockout (Abcb4 -/-) mouse model. Untreated BALB/cJ mice served as controls. To assess hepatic fibrosis, we ascertained collagen contents and fibrosis scores after Sirius red staining. T1 and T2⁎ correlate differently to disease severity and etiology of liver fibrosis. T2⁎ shows significant decrease correlating with fibrosis in CCl4 treated animals, while demonstrating significant increase with disease severity in Abcb4 -/- mice. Measurements of T1 and T2⁎ may therefore facilitate discrimination between different stages and causes of liver fibrosis.

  18. An open-source software tool for the generation of relaxation time maps in magnetic resonance imaging

    Directory of Open Access Journals (Sweden)

    Kühne Titus

    2010-07-01

    Full Text Available Abstract Background In magnetic resonance (MR imaging, T1, T2 and T2* relaxation times represent characteristic tissue properties that can be quantified with the help of specific imaging strategies. While there are basic software tools for specific pulse sequences, until now there is no universal software program available to automate pixel-wise mapping of relaxation times from various types of images or MR systems. Such a software program would allow researchers to test and compare new imaging strategies and thus would significantly facilitate research in the area of quantitative tissue characterization. Results After defining requirements for a universal MR mapping tool, a software program named MRmap was created using a high-level graphics language. Additional features include a manual registration tool for source images with motion artifacts and a tabular DICOM viewer to examine pulse sequence parameters. MRmap was successfully tested on three different computer platforms with image data from three different MR system manufacturers and five different sorts of pulse sequences: multi-image inversion recovery T1; Look-Locker/TOMROP T1; modified Look-Locker (MOLLI T1; single-echo T2/T2*; and multi-echo T2/T2*. Computing times varied between 2 and 113 seconds. Estimates of relaxation times compared favorably to those obtained from non-automated curve fitting. Completed maps were exported in DICOM format and could be read in standard software packages used for analysis of clinical and research MR data. Conclusions MRmap is a flexible cross-platform research tool that enables accurate mapping of relaxation times from various pulse sequences. The software allows researchers to optimize quantitative MR strategies in a manufacturer-independent fashion. The program and its source code were made available as open-source software on the internet.

  19. Krylov-subspace acceleration of time periodic waveform relaxation

    Energy Technology Data Exchange (ETDEWEB)

    Lumsdaine, A. [Univ. of Notre Dame, IN (United States)

    1994-12-31

    In this paper the author uses Krylov-subspace techniques to accelerate the convergence of waveform relaxation applied to solving systems of first order time periodic ordinary differential equations. He considers the problem in the frequency domain and presents frequency dependent waveform GMRES (FDWGMRES), a member of a new class of frequency dependent Krylov-subspace techniques. FDWGMRES exhibits many desirable properties, including finite termination independent of the number of timesteps and, for certain problems, a convergence rate which is bounded from above by the convergence rate of GMRES applied to the static matrix problem corresponding to the linear time-invariant ODE.

  20. Viscous hydrodynamics relaxation time from AdS/CFT correspondence

    Science.gov (United States)

    Heller, Michał P.; Janik, Romuald A.

    2007-07-01

    We consider an expanding boost-invariant plasma at strong coupling using the AdS/CFT correspondence for N=4 super Yang-Mills theory. We determine the relaxation time in second order viscous hydrodynamics and find that it is around 30 times shorter than weak coupling expectations. We find that the nonsingularity of the dual geometry in the string frame necessitates turning on the dilaton which leads to a nonvanishing expectation value for trF2 behaving like τ-10/3.

  1. Diffusion MRI/NMR magnetization equations with relaxation times

    Science.gov (United States)

    de, Dilip; Daniel, Simon

    2012-10-01

    Bloch-Torrey diffusion magnetization equation ignores relaxation effects of magnetization. Relaxation times are important in any diffusion magnetization studies of perfusion in tissues(Brain and heart specially). Bloch-Torrey equation cannot therefore describe diffusion magnetization in a real-life situation where relaxation effects play a key role, characteristics of tissues under examination. This paper describes derivations of two equations for each of the y and z component diffusion NMR/MRI magnetization (separately) in a rotating frame of reference, where rf B1 field is applied along x direction and bias magnetic field(Bo) is along z direction. The two equations are expected to further advance the science & technology of Diffusion MRI(DMRI) and diffusion functional MRI(DFMRI). These two techniques are becoming increasingly important in the study and treatment of neurological disorders, especially for the management of patients with acute stroke. It is rapidly becoming a standard for white matter disorders, as diffusion tensor imaging (DTI) can reveal abnormalities in white matter fibre structure and provide models of brain connectivity.

  2. Clustered continuous-time random walks: diffusion and relaxation consequences.

    Science.gov (United States)

    Weron, Karina; Stanislavsky, Aleksander; Jurlewicz, Agnieszka; Meerschaert, Mark M; Scheffler, Hans-Peter

    2012-06-08

    We present a class of continuous-time random walks (CTRWs), in which random jumps are separated by random waiting times. The novel feature of these CTRWs is that the jumps are clustered. This introduces a coupled effect, with longer waiting times separating larger jump clusters. We show that the CTRW scaling limits are time-changed processes. Their densities solve two different fractional diffusion equations, depending on whether the waiting time is coupled to the preceding jump, or the following one. These fractional diffusion equations can be used to model all types of experimentally observed two power-law relaxation patterns. The parameters of the scaling limit process determine the power-law exponents and loss peak frequencies.

  3. Critical Slowing Down of Relaxation Time in VCSEL's Polarization Switching

    Science.gov (United States)

    Li, Yueh-Chen; Kuo, Wang-Chuang; Wu, Yu-Heng; Yen, Tsu-Chiang

    2013-03-01

    This study investigates the polarization switching (PS) of vertical-cavity surface-emitting lasers (VCSELs) approaching to criticality. The dynamical bifurcation of VCSEL's PS (VPS) which was researched in earlier investigations essentially differs from the static cases typically presented in thermodynamics. Therefore, a VCSEL is driven by quasi-increasing step current and quasi-decreasing step current instead of alternating current in this study. The results show a critical slowing down nearing PS, a power law and scaling law of the relaxation time which are the characteristics of second order phase transition. This investigation has potential for connecting the phase transition characteristics of VPS and quantum phase transitions (QPTs).

  4. Effective rotational correlation times of proteins from NMR relaxation interference

    Science.gov (United States)

    Lee, Donghan; Hilty, Christian; Wider, Gerhard; Wüthrich, Kurt

    2006-01-01

    Knowledge of the effective rotational correlation times, τc, for the modulation of anisotropic spin-spin interactions in macromolecules subject to Brownian motion in solution is of key interest for the practice of NMR spectroscopy in structural biology. The value of τc enables an estimate of the NMR spin relaxation rates, and indicates possible aggregation of the macromolecular species. This paper reports a novel NMR pulse scheme, [ 15N, 1H]-TRACT, which is based on transverse relaxation-optimized spectroscopy and permits to determine τc for 15N- 1H bonds without interference from dipole-dipole coupling of the amide proton with remote protons. [ 15N, 1H]-TRACT is highly efficient since only a series of one-dimensional NMR spectra need to be recorded. Its use is suggested for a quick estimate of the rotational correlation time, to monitor sample quality and to determine optimal parameters for complex multidimensional NMR experiments. Practical applications are illustrated with the 110 kDa 7,8-dihydroneopterin aldolase from Staphylococcus aureus, the uniformly 15N-labeled Escherichia coli outer membrane protein X (OmpX) in 60 kDa mixed OmpX/DHPC micelles with approximately 90 molecules of unlabeled 1,2-dihexanoyl- sn-glycero-3-phosphocholine (DHPC), and the 16 kDa pheromone-binding protein from Bombyx mori, which cover a wide range of correlation times.

  5. Quantitative evaluation of Gd-EOB-DTPA uptake in focal liver lesions by using T1 mapping: differences between hepatocellular carcinoma, hepatic focal nodular hyperplasia and cavernous hemangioma.

    Science.gov (United States)

    Peng, Zhenpeng; Li, Chang; Chan, Tao; Cai, Huasong; Luo, Yanji; Dong, Zhi; Li, Zi-Ping; Feng, Shi-Ting

    2017-09-12

    To investigate the difference of T1 relaxation time on Gd-EOB-DTPA-enhanced MRI in hepatocellular carcinoma (HCC), hepatic focal nodular hyperplasia (FNH) and cavernous hemangioma of liver (CHL), and to quantitatively evaluate the uptake of Gd-EOB-DTPA in these three focal liver lesions (FLLs). The T1P of CHL was significantly higher than those of HCC and FNH (P T1 relaxation time on hepatobiliary phase could be observed in all three types of lesions. There were significant differences of T1P, T1E, T1D and T1D% between FNH, CHL and HCC (P T1 mapping were enrolled, consisting of 51 HCCs, 10 FNHs, and 13 CHLs. T1 relaxation times of these lesions were measured on pre-contrast (T1P) and on hepatobiliary phase images at 20 minute after contrast (T1E). The reduction of T1 relaxation time on hepatobiliary (T1D) and the percentage reduction (T1D%) was calculated. The differences of T1P, T1E, T1D and T1D% in these FLLs were analyzed. The usefulness of these parameters for classification of FLLs was evaluated. Uptake of Gd-EOB-DTPA is different between in HCC, FNH and CHL. These three lesions can be distinguished using T1 mapping.

  6. Time course of corticospinal excitability and intracortical inhibition just before muscle relaxation

    Directory of Open Access Journals (Sweden)

    Tomotaka eSuzuki

    2016-01-01

    Full Text Available Using transcranial magnetic stimulation (TMS, we investigated how short-interval intracortical inhibition (SICI was involved with transient motor cortex excitability changes observed just before the transition from muscle contraction to muscle relaxation. Ten healthy participants performed a simultaneous relaxation task of the ipsilateral finger and foot, relaxing from 10% of their maximal voluntary contraction force after the go signal. In the simple reaction time paradigm, single or paired TMS pulses were randomly delivered after the go signal, and motor evoked potentials were recorded from the right first dorsal interosseous muscle. We analyzed the time course prior to the estimated relaxation reaction time, defined here as the onset of voluntary relaxation. SICI decreased in the 80–100 ms before relaxation reaction time, and motor evoked potentials were significantly greater in amplitude in the 60–80 ms period before relaxation reaction time than in the other intervals in single-pulse trials. TMS pulses did not effectively increase relaxation reaction time. These results show that cortical excitability in the early stage, before muscle relaxation, plays an important role in muscle relaxation control. SICI circuits may vary between decreased and increased activation to continuously maintain muscle relaxation during or after a relaxation response. With regard to motor cortex excitability dynamics, we suggest that SICI also dynamically changes throughout the muscle relaxation process.

  7. Theory of the short time mechanical relaxation in articular cartilage.

    Science.gov (United States)

    Ruberti, J W; Sokoloff, J B

    2011-10-01

    Articular cartilage is comprised of macromolecules, proteoglycans, with (charged) chondroitin sulfate side-chains attached to them. The proteoglycans are attached to longer hyaluronic acid chains, trapped within a network of type II collagen fibrils. As a consequence of their relatively long persistence lengths, the number of persistence lengths along the chondroitin sulfate and proteoglycan chains is relatively small, and consequently, the retraction times for these side chains are also quite short. We argue that, as a consequence of this, they will not significantly inhibit the reptation of the hyaluronic acid chains. Scaling arguments applied to this model allow us to show that the shortest of the mechanical relaxation times of cartilage, that have been determined by Fyhrie and Barone to be due to reptation of the hyaluronic acid polymers, should have a dependence on the load, i.e., force per unit interface area P, carried by the cartilage, proportional to P(3/2).

  8. Metastable States, Relaxation Times and Free-energy Barriers in Finite Dimensional Glassy Systems

    OpenAIRE

    Franz, Silvio

    2005-01-01

    In this note we discuss metastability in a long-but-finite range disordered model for the glass transition. We show that relaxation is dominated by configuration belonging to metastable states and associate an in principle computable free-energy barrier to the equilibrium relaxation time. Adam-Gibbs like relaxation times appear naturally in this approach.

  9. Assessment of liver fibrosis by variable flip angle T1 mapping at 3.0T.

    Science.gov (United States)

    Li, Zhiming; Sun, Jihong; Hu, Xi; Huang, Ning; Han, Guocan; Chen, Lumin; Zhou, Yurong; Bai, Weixian; Yang, Xiaoming

    2016-03-01

    To evaluate the possibility of using a variable flip angle (VFA) T1 mapping technique to diagnose liver fibrosis. Liver fibrosis was induced in rabbits by repetitive administration of carbon tetrachloride (CCl4 ). T1 -weighted magnetic resonance imaging (MRI) was performed in 29 animals (liver fibrosis, n = 18; control, n = 11) using a series of nonenhanced liver acquisition volume acceleration (LAVA) with VFAs at 3.0T. Hepatic T1 relaxation times were measured via regions of interest, which were correlated with subsequent histologic confirmation. The results of T1 mapping in assessment of liver fibrosis were compared with that of apparent diffusion coefficient (ADC) values. The mean T1 relaxation time of the control group was the lowest (250.07 ± 88.12 msec), followed by the nonadvanced fibrosis group (387.83 ± 166.58 msec) and the advanced fibrosis group (496.90 ± 291.24 msec). T1 relaxation time measurements differed significantly between the liver fibrosis group and control group (P T1 relaxation times as the fibrotic stage increased. Statistically significant differences were observed between the control group and the nonadvanced fibrosis group (P T1 relaxation times and ADC values in assessment of liver fibrosis in our study. VFA T1 mapping may become a noninvasive imaging tool for the diagnosis of liver fibrosis. © 2015 Wiley Periodicals, Inc.

  10. High resolution NMR study of T1 magnetic relaxation dispersion. III. Influence of spin 1/2 hetero-nuclei on spin relaxation and polarization transfer among strongly coupled protons

    NARCIS (Netherlands)

    Korchak, S.E.; Ivanov, K.L.; Pravdivtsev, A.N.; Yurkovskaya, A.V.; Kaptein, R.|info:eu-repo/dai/nl/074334603; Vieth, H.-M.

    2012-01-01

    Effects of spin-spin interactions on the nuclear magnetic relaxation dispersion (NMRD) of protons were studied in a situation where spin ½ hetero-nuclei are present in the molecule. As in earlier works [K. L. Ivanov, A. V. Yurkovskaya, and H.-M. Vieth, J. Chem. Phys. 129, 234513

  11. Evaluation of PHB/Clay nanocomposite by spin-lattice relaxation time

    Directory of Open Access Journals (Sweden)

    Mariana Bruno

    2008-12-01

    Full Text Available Poly(3-hydroxybutyrate (PHB based on nanocomposites containing different amounts of a commercial organically modified clay (viscogel B7 were prepared employing solution intercalation method. Three solvents, such as: CHCl3, dimethylchloride (DMC and tetrahydrofuran (THF were used. The relationship among the processing conditions; molecular structure and intermolecular interaction, between both nanocomposite components, were investigated using a nuclear magnetic resonance (NMR, as a part of characterization methodology, which has been used by Tavares et al. It involves the hydrogen spin-lattice relaxation time, T1H, by solid state nuclear magnetic resonance, employing low field NMR. X ray diffraction was also employed because it is a conventional technique, generally used to obtain the first information on nanocomposite formation. Changes in PHB crystallinity were observed after the organophilic nanoclay had been incorporated in the polymer matrix. These changes, in the microstructure, were detected by the variation of hydrogen nuclear relaxation time values and by X ray, which showed an increase in the clay interlamelar space due to the intercalation of the polymer in the clay between lamellae. It was also observed, for both techniques, that the solvents affect directly the organization of the crystalline region, promoting a better intercalation, considering that they behave like a plasticizer.

  12. Dependence of Brownian and Néel relaxation times on magnetic field strength.

    Science.gov (United States)

    Deissler, Robert J; Wu, Yong; Martens, Michael A

    2014-01-01

    In magnetic particle imaging (MPI) and magnetic particle spectroscopy (MPS) the relaxation time of the magnetization in response to externally applied magnetic fields is determined by the Brownian and Néel relaxation mechanisms. Here the authors investigate the dependence of the relaxation times on the magnetic field strength and the implications for MPI and MPS. The Fokker-Planck equation with Brownian relaxation and the Fokker-Planck equation with Néel relaxation are solved numerically for a time-varying externally applied magnetic field, including a step-function, a sinusoidally varying, and a linearly ramped magnetic field. For magnetic fields that are applied as a step function, an eigenvalue approach is used to directly calculate both the Brownian and Néel relaxation times for a range of magnetic field strengths. For Néel relaxation, the eigenvalue calculations are compared to Brown's high-barrier approximation formula. The relaxation times due to the Brownian or Néel mechanisms depend on the magnitude of the applied magnetic field. In particular, the Néel relaxation time is sensitive to the magnetic field strength, and varies by many orders of magnitude for nanoparticle properties and magnetic field strengths relevant for MPI and MPS. Therefore, the well-known zero-field relaxation times underestimate the actual relaxation times and, in particular, can underestimate the Néel relaxation time by many orders of magnitude. When only Néel relaxation is present--if the particles are embedded in a solid for instance--the authors found that there can be a strong magnetization response to a sinusoidal driving field, even if the period is much less than the zero-field relaxation time. For a ferrofluid in which both Brownian and Néel relaxation are present, only one relaxation mechanism may dominate depending on the magnetic field strength, the driving frequency (or ramp time), and the phase of the magnetization relative to the applied magnetic field. A simple

  13. Changes in MR Relaxation Times of the Meniscus With Acute Loading: An In Vivo Pilot Study in Knee Osteoarthritis

    Science.gov (United States)

    Subburaj, Karupppasamy; Souza, Richard B.; Wyman, Bradley T.; Le Graverand-Gastineau, Marie-Pierre Hellio; Li, Xiaojuan; Link, Thomas M.; Majumdar, Sharmila

    2014-01-01

    Purpose To prospectively evaluate changes in T1ρ and T2 relaxation times in the meniscal body with acute loading using MRI in osteoarthritic knees and to compare these findings with those of age-matched healthy controls. Materials and Methods Female subjects above 40 years of age with (N1 = 20) and without osteoarthritis (OA) (N2 = 10) were imaged on a 3 Tesla MR scanner using a custom made loading device. MR images were acquired, with the knee flexed at 20°, with and without a compressive load of 50% of the subject's bodyweight. The subjects were categorized based on the radiographic evidence of OA. Three different zones (outer, middle, and inner) of meniscus body were defined (each occupying 1/3rd the width). After adjusting for age and body mass index in the general linear regression model, repeated measures analysis of variance was used to detect significant differences in T1ρ and T2 with and without loading. Results In the unloaded condition, the average T1ρ and T2 times were elevated in the outer and middle zones of the medial meniscus in OA subjects compared with the controls. In the loaded condition, T1ρ and T2 times of the outer zone of the medial meniscus was significantly elevated in OA subjects compared with controls. Finally the change (from unloaded to loaded) was significantly higher in controls than OA subjects (15.1% versus 8.3%; P = 0.039 for ΔT1ρ, and 11.5% versus 6.9%, P = 0.049 for ΔT2). Conclusion These findings suggest that while the OA process appears to affect the relaxation times of all regions within the meniscus, it may affect some regions sooner or to a greater degree. Furthermore, the differences in the change in relaxation times between unloaded and loaded conditions may reveal evidence about load transmission failure of the outer zone of the medial meniscus in subjects with knee OA. It is possible that these metrics (ΔT1ρ and ΔT2) may be valuable as an early biomechanical biomarker, which could be used to predict load

  14. T1 mapping in patients with acute myocardial infarction.

    Science.gov (United States)

    Messroghli, Daniel R; Niendorf, Thoralf; Schulz-Menger, Jeanette; Dietz, Rainer; Friedrich, Matthias G

    2003-01-01

    Pixel-by-pixel calculation of T1 values (T1 mapping) has been used in different tissues to focus on T1 changes in a quantitative fashion. The aim of this study was to establish T1 mapping of human myocardium on a 1.5 Tesla system and to examine its diagnostic potential in patients with acute myocardial infarction (AMI). 8 patients with reperfused AMI (day 3 +/- 1) underwent multi-breath-hold MRI in a 1.5 Tesla system. Sets of five images with varying T1 weighting were acquired prior to and after the administration of contrast agent to generate images from calculated T1 values (T1 mapping). Prior to the contrast agent administration, all patients showed T1 prolongation in the area of infarction, which was identified in separate measurements using the delayed enhancement approach. Compared to noninfarcted areas, T1 values in the infarcted areas were increased by 18 +/- 7% (SE, p T1 prolongation was larger than that of the hyper-enhanced areas in conventional contrast-enhanced images. T1 maps obtained after the application of Gadolinium-DTPA revealed a T1 reduction of 27 +/- 4% in infarcted tissue compared to noninfarcted areas (p T1 reduction were in agreement with the hyper-enhanced regions in conventional T1-weighted images. T1 mapping visualizes changes in the longitudinal relaxation time induced by AMI. T1 mapping can detect myocardial necrosis without the use of contrast media. Information that can be extracted from a combination of pre- and postcontrast T1 maps exceeds that from conventional contrast studies.

  15. Measurements of T1 and T2 relaxation times of colon cancer metastases in rat liver at 7 T

    NARCIS (Netherlands)

    Gambarota, G.; Veltien, A.; van Laarhoven, H.; Philippens, M.; Jonker, A.; Mook, O. R.; Frederiks, W. M.; Heerschap, A.

    2004-01-01

    The purpose of this study was to investigate the magnetic resonance imaging (MRI) characteristics of colon cancer metastases in rat liver at 7 T. A dedicated RF microstrip coil of novel design was built in order to increase the signal-to-noise ratio and, in combination with respiratory triggering,

  16. Super-resolution T1 estimation: Quantitative high resolution T1 mapping from a set of low resolution T1 -weighted images with different slice orientations.

    Science.gov (United States)

    Van Steenkiste, Gwendolyn; Poot, Dirk H J; Jeurissen, Ben; den Dekker, Arnold J; Vanhevel, Floris; Parizel, Paul M; Sijbers, Jan

    2017-05-01

    Quantitative T1 mapping is a magnetic resonance imaging technique that estimates the spin-lattice relaxation time of tissues. Even though T1 mapping has a broad range of potential applications, it is not routinely used in clinical practice as accurate and precise high resolution T1 mapping requires infeasibly long acquisition times. To improve the trade-off between the acquisition time, signal-to-noise ratio and spatial resolution, we acquire a set of low resolution T1 -weighted images and directly estimate a high resolution T1 map by means of super-resolution reconstruction. Simulation and in vivo experiments show an increased spatial resolution of the T1 map, while preserving a high signal-to-noise ratio and short scan time. Moreover, the proposed method outperforms conventional estimation in terms of root-mean-square error. Super resolution T1 estimation enables resolution enhancement in T1 mapping with the use of standard (inversion recovery) T1 acquisition sequences. Magn Reson Med 77:1818-1830, 2017. © 2016 International Society for Magnetic Resonance in Medicine. © 2016 International Society for Magnetic Resonance in Medicine.

  17. The search for negative amplitude components in quasi-continuous distributions of relaxation times: the example of 1H magnetization exchange in articular cartilage and hydrated collagen

    Science.gov (United States)

    Fantazzini, Paola; Galassi, Francesca; Bortolotti, Villiam; Brown, Robert J. S.; Vittur, Franco

    2011-06-01

    When inverting nuclear magnetic resonance relaxation data in order to obtain quasi-continuous distributions of relaxation times for fluids in porous media, it is common practice to impose a non-negative (NN) constraint on the distributions. While this approach can be useful in reducing the effects of data distortion and/or preventing wild oscillations in the distributions, it may give misleading results in the presence of real negative amplitude components. Here, some examples of valid negative components for articular cartilage and hydrated collagen are given. Articular cartilage is a connective tissue, consisting mainly of collagen, proteoglycans and water, which can be considered, in many aspects, as a porous medium. Separate T1 relaxation data are obtained for low-mobility ('solid') macromolecular 1H and for higher-mobility ('liquid') 1H by the separation of these components in free induction decays, with α denoting the solid/liquid 1H ratio. When quasi-continuous distributions of relaxation times (T1) of the solid and liquid signal components of cartilage or collagen are computed from experimental relaxation data without imposing the usual NN constraint, valid negative peaks may appear. The features of the distributions, in particular negative peaks, and the fact that peaks at longer times for macromolecular and water protons are at essentially the same T1, are interpreted as the result of a magnetization exchange between these two spin pools. For the only-slightly-hydrated collagen samples, with α>1, the exchange leads to small negative peaks at short T1 times for the macromolecular component. However, for the cartilage, with substantial hydration or for a strongly hydrated collagen sample, both with αLt1, the behavior is reversed, with a negative peak for water at short times. The validity of a negative peak may be accepted (dismissed) by a high (low) cost of NN in error of fit. Computed distributions for simulated data using observed signal

  18. Whole brain MP2RAGE-based mapping of the longitudinal relaxation time at 9.4T.

    Science.gov (United States)

    Hagberg, G E; Bause, J; Ethofer, T; Ehses, P; Dresler, T; Herbert, C; Pohmann, R; Shajan, G; Fallgatter, A; Pavlova, M A; Scheffler, K

    2017-01-01

    Mapping of the longitudinal relaxation time (T1) with high accuracy and precision is central for neuroscientific and clinical research, since it opens up the possibility to obtain accurate brain tissue segmentation and gain myelin-related information. An ideal, quantitative method should enable whole brain coverage within a limited scan time yet allow for detailed sampling with sub-millimeter voxel sizes. The use of ultra-high magnetic fields is well suited for this purpose, however the inhomogeneous transmit field potentially hampers its use. In the present work, we conducted whole brain T1 mapping based on the MP2RAGE sequence at 9.4T and explored potential pitfalls for automated tissue classification compared with 3T. Data accuracy and T2-dependent variation of the adiabatic inversion efficiency were investigated by single slice T1 mapping with inversion recovery EPI measurements, quantitative T2 mapping using multi-echo techniques and simulations of the Bloch equations. We found that the prominent spatial variation of the transmit field at 9.4T (yielding flip angles between 20% and 180% of nominal values) profoundly affected the result of image segmentation and T1 mapping. These effects could be mitigated by correcting for both flip angle and inversion efficiency deviations. Based on the corrected T1 maps, new, 'flattened', MP2RAGE contrast images were generated, that were no longer affected by variations of the transmit field. Unlike the uncorrected MP2RAGE contrast images acquired at 9.4T, these flattened images yielded image segmentations comparable to 3T, making bias-field correction prior to image segmentation and tissue classification unnecessary. In terms of the T1 estimates at high field, the proposed correction methods resulted in an improved precision, with test-retest variability below 1% and a coefficient-of-variation across 25 subjects below 3%. Copyright © 2016 Elsevier Inc. All rights reserved.

  19. Early Time Spinodal Decomposition in a Relaxational Tricritical Model

    Science.gov (United States)

    Dee, G.; Gunton, J. D.; Kawasaki, K.

    1981-01-01

    We present a Langer, Bar-on, Miller type theory far early stage tricritical spinodal decomposition of a model with relaxational dynamics, based on an adiabatic elimination of the nonconserved order parameter. The structure factor for the conserved variable exhibits an interesting asymmetry with respect to the quench position.

  20. Early Time Spinodal Decomposition in a Relaxational Tricritical Model

    OpenAIRE

    Gregory, DEE; James D., GUNTON; Kyoji, KAWASAKI; Physics Department, Temple University; Physics Department, Kyushu University

    1981-01-01

    We present a Langer, Bar-on, Miller type theory for early stage tricritical spinodal decomposition of a model with relaxational dynamics, based on an adiabatic elimination of the nonconserved order parameter. The structure factor for the conserved variable exhibits an interesting asymmetry with respect to the quench position.

  1. PANDA-T1ρ: Integrating principal component analysis and dictionary learning for fast T1ρ mapping.

    Science.gov (United States)

    Zhu, Yanjie; Zhang, Qinwei; Liu, Qiegen; Wang, Yi-Xiang J; Liu, Xin; Zheng, Hairong; Liang, Dong; Yuan, Jing

    2015-01-01

    Long scanning time greatly hinders the widespread application of spin-lattice relaxation in rotating frame (T1ρ) in clinics. In this study, a novel method is proposed to reconstruct the T1ρ-weighted images from undersampled k-space data and hence accelerate the acquisition of T1ρ imaging. The proposed approach (PANDA-T1ρ) combined the benefit of PCA and dictionary learning when reconstructing image from undersampled data. Specifically, the PCA transform was first used to sparsify the image series along the parameter direction and then the sparsified images were reconstructed by means of dictionary learning and finally solved the images. A variation of PANDA-T1ρ was also developed for the heavy noise case. Numerical simulation and in vivo experiments were carried out with the accelerating factor from 2 to 4 to verify the performance of PANDA-T1ρ. The reconstructed T1ρ maps using the PANDA-T1ρ method were found to be comparable to the reference at all verified acceleration factors. Moreover, the variation exhibited better performance than the original version when the k-space data were contaminated by heavy noise. PANDA-T1ρ can significantly reduce the scanning time of T1ρ by integrating PCA and dictionary learning and provides better parameter estimation than the state-of-art methods for a fixed acceleration factor. © 2014 Wiley Periodicals, Inc.

  2. Probing the Nuclear Spin-Lattice Relaxation Time at the Nanoscale

    NARCIS (Netherlands)

    Wagenaar, J.C.; Den Haan, A. M J; de Voogd, J.M.; Bossoni, L; de Jong, T.A.; de Wit, M.; Bastiaans, K. M.; Thoen, D.J.; Endo, A.; Klapwijk, T.M.; Zaanen, J.; Oosterkamp, TH

    2016-01-01

    Nuclear spin-lattice relaxation times are measured on copper using magnetic-resonance force microscopy performed at temperatures down to 42 mK. The low temperature is verified by comparison with the Korringa relation. Measuring spin-lattice relaxation times locally at very low temperatures opens up

  3. T1 mapping in ischaemic heart disease.

    Science.gov (United States)

    h-Ici, Darach O; Jeuthe, Sarah; Al-Wakeel, Nadya; Berger, Felix; Kuehne, Titus; Kozerke, Sebastian; Messroghli, Daniel R

    2014-06-01

    A unique feature of cardiac magnetic resonance is its ability to characterize myocardium. Proton relaxation times, T1, T2, and T2* are a reflection of the composition of individual tissues, and change in the presence of disease. Research into T1 mapping has largely been focused in the study of cardiomyopathies, but T1 mapping also shows huge potential in the study of ischaemic heart disease. In fact, the first cardiac T1 maps were used to characterize myocardial infarction. Robust high-resolution myocardial T1 mapping is now available for use as a clinical tool. This quantitative technique is simple to perform and analyse, minimally subjective, and highly reproducible. This review aims to summarize the present state of research on the topic, and to show the clinical potential of this method to aid the diagnosis and treatment of patients with ischaemic heart disease. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2014. For permissions please email: journals.permissions@oup.com.

  4. Wettability of Chalk and Argillaceous Sandstones Assessed from T1/T2 Ratio

    OpenAIRE

    Katika, Konstantina; Saidian, M.; Fabricius, Ida Lykke

    2016-01-01

    Low-field NMR relaxation of the fluids inside the porous rock is the result of bulk and surface relaxation of the protons inside the pore fluid. Bulk relaxation is a fluid property when the solid-fluid interaction is minimized. Surface relaxation is the result of the solid-fluid interaction related to mineral properties. Thus, longitudinal, T1, and transverse, T2, relaxation times should in principle be similar. However, microscopic magnetic gradients related to minerals can shorten T2 as com...

  5. Accurate prediction of spectral phonon relaxation time and thermal conductivity of intrinsic and perturbed materials

    Science.gov (United States)

    Feng, Tianli

    The prediction of spectral phonon relaxation time, mean-free-path, and thermal conductivity can provide significant insights into the thermal conductivity of bulk and nanomaterials, which are important for thermal management and thermoelectric applications. We perform frequency-domain normal mode analysis (NMA) on pure bulk argon and pure bulk germanium. Spectral phonon properties, including the phonon dispersion, relaxation time, mean free path, and thermal conductivity of argon and germanium at different temperatures have been calculated. We find the dependence of phonon relaxation time tau on frequency o and temperature T vary from ~o-1.3 to ~o -1.8 and ~T-0.8 to ~T-1.8 for argon, and from ~o-0.6 to ~o-2.8 and ~T -0.4 to ~T-2.5 for germanium. The predicted thermal conductivities are in reasonable agreement with those obtained from the Green-Kubo method. We show, using both analytical derivations and numerical simulations, that the eigenvectors are necessary in time-domain NMA but unnecessary in frequency-domain NMA. The function of eigenvectors in frequency-domain NMA is to distinguish each phonon branch. Furthermore, it is found in solids not only the phonon frequency but also the phonon eigenvector can shift from harmonic lattice profile at finite temperature, due to thermal expansion and anharmonicity of interatomic potential. The anharmonicity of phonon eigenvector, different with that of frequency, only exists in the materials which contain at least two types of atoms and two different interatomic forces. Introducing anharmonic eigenvectors makes it easier to distinguish phonon branches in frequency-domain NMA although does not influence the results. For time-domain NMA, anharmonic eigenvectors make the results more accurate than harmonic eigenvectors. In addition, the phonon spectral relaxation time of defective silicon is calculated from frequency-domain NMA based on molecular dynamics. We show that the thermal conductivity k predicted from this approach

  6. T1 and T2 temperature dependence of female human breast adipose tissue at 1.5 T : groundwork for monitoring thermal therapies in the breast

    NARCIS (Netherlands)

    Baron, Paul; Deckers, RHR; Knuttel, Floor M.; Bartels, LW

    2015-01-01

    The T-1 and T-2 temperature dependence of female breast adipose tissue was investigated at 1.5 T in order to evaluate the applicability of relaxation-based MR thermometry in fat for the monitoring of thermal therapies in the breast. Relaxation times T-1, T-2 and T-2TSE (the apparent T-2 measured

  7. Time-parallel iterative methods for parabolic PDES: Multigrid waveform relaxation and time-parallel multigrid

    Energy Technology Data Exchange (ETDEWEB)

    Vandewalle, S. [Caltech, Pasadena, CA (United States)

    1994-12-31

    Time-stepping methods for parabolic partial differential equations are essentially sequential. This prohibits the use of massively parallel computers unless the problem on each time-level is very large. This observation has led to the development of algorithms that operate on more than one time-level simultaneously; that is to say, on grids extending in space and in time. The so-called parabolic multigrid methods solve the time-dependent parabolic PDE as if it were a stationary PDE discretized on a space-time grid. The author has investigated the use of multigrid waveform relaxation, an algorithm developed by Lubich and Ostermann. The algorithm is based on a multigrid acceleration of waveform relaxation, a highly concurrent technique for solving large systems of ordinary differential equations. Another method of this class is the time-parallel multigrid method. This method was developed by Hackbusch and was recently subject of further study by Horton. It extends the elliptic multigrid idea to the set of equations that is derived by discretizing a parabolic problem in space and in time.

  8. Effect of off-resonance on T1 saturation recovery measurement in inhomogeneous fields

    Science.gov (United States)

    Duan, Chong; Ryan, Colm; Utsuzawa, Shin; Song, Yi-Qiao; Hürlimann, Martin D.

    2017-08-01

    Saturation-recovery measurements with Carr-Purcell-Meiboom-Gill sequences are commonly employed to measure the longitudinal relaxation time constant, T1 , in grossly inhomogeneous fields. We show that in general the off-resonant effect generates unexpected extra signals in the T1 measurement. In the present study, we derive a modified T1 kernel that accounts for this off-resonance effect quantitatively. The new kernel has been tested with numerical simulations and experiments, and excellent agreement is found.

  9. Improved differentiation between knees with cartilage lesions and controls using 7T relaxation time mapping

    Directory of Open Access Journals (Sweden)

    Cory Wyatt

    2015-10-01

    Conclusion: T1ρ imaging at 7T has been established as a viable imaging method for the differentiation of degenerated cartilage despite previous concerns over specific absorption rate and imaging time. The potential increased sensitivity of T1ρ and T2 imaging at 7T may be useful for future studies in the development of OA.

  10. The relaxation time of processes in a FitzHugh-Nagumo neural system with time delay

    Energy Technology Data Exchange (ETDEWEB)

    Gong Ailing; Zeng Chunhua [Faculty of Science, Kunming University of Science and Technology, Kunming 650093 (China); Wang Hua, E-mail: zchh2009@126.com [Province Engineering Research Center of Industrial Energy Conservation and New Technology, Kunming University of Science and Technology, Kunming, Yunnan 650093 (China)

    2011-08-01

    In this paper, we study the relaxation time (RT) of the steady-state correlation function in a FitzHugh-Nagumo neural system under the presence of multiplicative and additive white noises and time delay. The noise correlation parameter {lambda} can produce a critical behavior in the RT as functions of the multiplicative noise intensity D, the additive noise intensity Q and the time delay {tau}. That is, the RT decreases as the noise intensities D and Q increase, and increases as the time delay {tau} increases below the critical value of {lambda}. However, above the critical value, the RT first increases, reaches a maximum, and then decreases as D, Q and {tau} increase, i.e. a noise intensity D or Q and a time delay {tau} exist, at which the time scales of the relaxation process are at their largest. In addition, the additive noise intensity Q can also produce a critical behavior in the RT as a function of {lambda}. The noise correlation parameter {lambda} first increases the RT of processes, then decreases it below the critical value of Q. Above the critical value, {lambda} increases it.

  11. Uncertainty estimations for quantitative in vivo MRI T1 mapping

    Science.gov (United States)

    Polders, Daniel L.; Leemans, Alexander; Luijten, Peter R.; Hoogduin, Hans

    2012-11-01

    Mapping the longitudinal relaxation time (T1) of brain tissue is of great interest for both clinical research and MRI sequence development. For an unambiguous interpretation of in vivo variations in T1 images, it is important to understand the degree of variability that is associated with the quantitative T1 parameter. This paper presents a general framework for estimating the uncertainty in quantitative T1 mapping by combining a slice-shifted multi-slice inversion recovery EPI technique with the statistical wild-bootstrap approach. Both simulations and experimental analyses were performed to validate this novel approach and to evaluate the estimated T1 uncertainty in several brain regions across four healthy volunteers. By estimating the T1 uncertainty, it is shown that the variation in T1 within anatomic regions for similar tissue types is larger than the uncertainty in the measurement. This indicates that heterogeneity of the inspected tissue and/or partial volume effects can be the main determinants for the observed variability in the estimated T1 values. The proposed approach to estimate T1 and its uncertainty without the need for repeated measurements may also prove to be useful for calculating effect sizes that are deemed significant when comparing group differences.

  12. Myocardial T1 Mapping: Techniques and Potential Applications

    Science.gov (United States)

    Burt, Jeremy R.; Zimmerman, Stefan L.; Kamel, Ihab R.; Halushka, Marc

    2014-01-01

    Myocardial fibrosis is a common endpoint in a variety of cardiac diseases and a major independent predictor of adverse cardiac outcomes. Short of histopathologic analysis, which is limited by sampling bias, most diagnostic modalities are limited in their depiction of myocardial fibrosis. Cardiac magnetic resonance (MR) imaging has the advantage of providing detailed soft-tissue characterization, and a variety of novel quantification methods have further improved its usefulness. Contrast material–enhanced cardiac MR imaging depends on differences in signal intensity between regions of scarring and adjacent normal myocardium. Diffuse myocardial fibrosis lacks these differences in signal intensity. Measurement of myocardial T1 times (T1 mapping) with gadolinium-enhanced inversion recovery–prepared sequences may depict diffuse myocardial fibrosis and has good correlation with ex vivo fibrosis content. T1 mapping calculates myocardial T1 relaxation times with image-based signal intensities and may be performed with standard cardiac MR imagers and radiologic workstations. Myocardium with diffuse fibrosis has greater retention of contrast material, resulting in T1 times that are shorter than those in normal myocardium. Early studies have suggested that diffuse myocardial fibrosis may be distinguished from normal myocardium with T1 mapping. Large multicenter studies are needed to define the role of T1 mapping in developing prognoses and therapeutic assessments. However, given its strengths as a noninvasive method for direct quantification of myocardial fibrosis, T1 mapping may eventually play an important role in the management of cardiac disease. © RSNA, 2014 PMID:24617686

  13. Landauer’s formula with finite-time relaxation: Kramers’ crossover in electronic transport

    Science.gov (United States)

    Gruss, Daniel; Velizhanin, Kirill A.; Zwolak, Michael

    2016-04-01

    Landauer’s formula is the standard theoretical tool to examine ballistic transport in nano- and meso-scale junctions, but it necessitates that any variation of the junction with time must be slow compared to characteristic times of the system, e.g., the relaxation time of local excitations. Transport through structurally dynamic junctions is, however, increasingly of interest for sensing, harnessing fluctuations, and real-time control. Here, we calculate the steady-state current when relaxation of electrons in the reservoirs is present and demonstrate that it gives rise to three regimes of behavior: weak relaxation gives a contact-limited current; strong relaxation localizes electrons, distorting their natural dynamics and reducing the current; and in an intermediate regime the Landauer view of the system only is recovered. We also demonstrate that a simple equation of motion emerges, which is suitable for efficiently simulating time-dependent transport.

  14. Evolvement law of a macroscopic traffic model accounting for density-dependent relaxation time

    Science.gov (United States)

    Wang, Yu-Qing; Chu, Xing-Jian; Zhou, Chao-Fan; Jia, Bin; Lin, Sen; Wu, Zi-Han; Zhu, Hua-Bing; Gao, Zi-You

    2017-11-01

    In this paper, a modified macroscopic traffic flow model is presented. The term of the density-dependent relaxation time is introduced here. The relation between the relaxation time and the density in traffic flow is presented quantitatively. Besides, a factor R depicting varied properties of traffic flow in different traffic states is also introduced in the formulation of the model. Furthermore, the evolvement law of traffic flow with distinctly initial density distribution and boundary perturbations is emphasized.

  15. Measurement of the Water Relaxation Time of ɛ-Polylysine Aqueous Solutions

    Science.gov (United States)

    Shirakashi, Ryo; Amano, Yuki; Yamada, Jun

    2017-05-01

    ɛ-Polylysine is an effective food preservative. In this paper, the β-relaxation time of ɛ-polylysine aqueous solutions, which represents the rotational speed of a single water molecule, was measured by broadband dielectric spectroscopy at various temperatures and concentrations. The broadband dielectric spectrum of each sample containing water ranging from 35 wt% to 75 wt% at temperatures ranging from 0°C to 25°C was measured using a co-axial semirigid cable probe. The measured dielectric spectra of the samples were composed of several Debye relaxation peaks, including a shortest single molecular rotational relaxation time of water, the β-relaxation time, longer than that of pure water. This result represents that ɛ-polylysine suppresses the molecular kinetics of water. It is also found that the β-relaxation time of an ɛ-polylysine solution that contained more than 35 wt% water showed a typical Arrhenius plot in the temperature range from 0°C to 25°C. The activation energy of each sample depends on the water content ratio of the sample. As indicated by its long β-relaxation time, ɛ-polylysine is expected to possess high abilities of suppressing freezing and ice coarsening.

  16. The relationships between half-life (t1/2) and mean residence time (MRT) in the two-compartment open body model.

    Science.gov (United States)

    Sobol, Eyal; Bialer, Meir

    2004-05-01

    In the one-compartment model following i.v. administration the mean residence time (MRT) of a drug is always greater than its half-life (t(1/2)). However, following i.v. administration, drug plasma concentration (C) versus time (t) is best described by a two-compartment model or a two exponential equation:C=Ae(-alpha t)+Be(-beta t), where A and B are concentration unit-coefficients and alpha and beta are exponential coefficients. The relationships between t(1/2) and MRT in the two-compartment model have not been explored and it is not clear whether in this model too MRT is always greater than t(1/2). In the current paper new equations have been developed that describe the relationships between the terminal t(1/2) (or t(1/2 beta)) and MRT in the two-compartment model following administration of i.v. bolus, i.v. infusion (zero order input) and oral administration (first order input). A critical value (CV) equals to the quotient of (1-ln2) and (1-beta/alpha) (CV=(1-ln2)/(1-beta/alpha)=0.307/(1-beta/alpha)) has been derived and was compared with the fraction (f(1)) of drug elimination or AUC (AUC-area under C vs t curve) associated with the first exponential term of the two-compartment equation (f(1)=A/alpha/AUC). Following i.v. bolus, CV ranges between a minimal value of 0.307 (1-ln2) and infinity. As long as f(1)MRT>t(1/2) and vice versa, and when f(1)=CV, then MRT=t(1/2). Following i.v. infusion and oral administration the denominator of the CV equation does not change but its numerator increases to (0.307+beta T/2) (T-infusion duration) and (0.307+beta/ka) (ka-absorption rate constant), respectively. Examples of various drugs are provided. For every drug that after i.v. bolus shows two-compartment disposition kinetics the following conclusions can be drawn (a) When f(1)MRT>t(1/2). (b) When beta/alpha>ln2, then CV>1>f(1) and thus(,) MRT>t(1/2). (c) When ln2>beta/alpha>(ln4-1), then 1>CV>0.5 and thus, in order for t(1/2)>MRT, f(1) has to be greater than its

  17. A model-based reconstruction technique for fast dynamic T1 mapping.

    Science.gov (United States)

    Tran-Gia, Johannes; Bisdas, Sotirios; Köstler, Herbert; Klose, Uwe

    2016-04-01

    To present a technique for dynamic T1 mapping. A recently proposed model-based reconstruction entitled IR-MAP allows T1 mapping of a single slice from a single radial inversion recovery Look-Locker FLASH acquisition. To enable dynamic T1 mapping, multiple of these acquisitions are consecutively performed, each followed by a waiting period of 3s for relaxation. Next, IR-MAP is used to reconstruct an individual T1 map for each of these acquisitions. Finally, T1 errors caused by insufficient relaxation between subsequent IR pulses are iteratively corrected. The functionality of the proposed setup was validated in a phantom and in seven healthy volunteers. Systematic deviations between subsequent T1 maps originating from insufficient relaxation periods were effectively corrected. Additionally, the approach was successfully applied to monitor the T1 dynamic in a patient with primary lymphoma after the intravenous injection of contrast agent. The proposed setup enables dynamic T1 mapping of a single slice with a spatial resolution of 1.6 mm × 1.6 mm × 3 mm and a temporal resolution of one parameter map every 9 s. It therefore represents a new opportunity to track changes in T1 over time, as it is desirable in many applications such as dynamic contrast-enhanced MRI. Copyright © 2015 Elsevier Inc. All rights reserved.

  18. T1-mapping in the heart: accuracy and precision

    Science.gov (United States)

    2014-01-01

    The longitudinal relaxation time constant (T1) of the myocardium is altered in various disease states due to increased water content or other changes to the local molecular environment. Changes in both native T1 and T1 following administration of gadolinium (Gd) based contrast agents are considered important biomarkers and multiple methods have been suggested for quantifying myocardial T1 in vivo. Characterization of the native T1 of myocardial tissue may be used to detect and assess various cardiomyopathies while measurement of T1 with extracellular Gd based contrast agents provides additional information about the extracellular volume (ECV) fraction. The latter is particularly valuable for more diffuse diseases that are more challenging to detect using conventional late gadolinium enhancement (LGE). Both T1 and ECV measures have been shown to have important prognostic significance. T1-mapping has the potential to detect and quantify diffuse fibrosis at an early stage provided that the measurements have adequate reproducibility. Inversion recovery methods such as MOLLI have excellent precision and are highly reproducible when using tightly controlled protocols. The MOLLI method is widely available and is relatively mature. The accuracy of inversion recovery techniques is affected significantly by magnetization transfer (MT). Despite this, the estimate of apparent T1 using inversion recovery is a sensitive measure, which has been demonstrated to be a useful tool in characterizing tissue and discriminating disease. Saturation recovery methods have the potential to provide a more accurate measurement of T1 that is less sensitive to MT as well as other factors. Saturation recovery techniques are, however, noisier and somewhat more artifact prone and have not demonstrated the same level of reproducibility at this point in time. This review article focuses on the technical aspects of key T1-mapping methods and imaging protocols and describes their limitations including

  19. Three-dimensional T1 and T2* mapping of human lung parenchyma using interleaved saturation recovery with dual echo ultrashort echo time imaging (ITSR-DUTE).

    Science.gov (United States)

    Gai, Neville D; Malayeri, Ashkan A; Bluemke, David A

    2017-04-01

    To develop and assess a new technique for three-dimensional (3D) full lung T1 and T2* mapping using a single free breathing scan during a clinically feasible time. A 3D stack of dual-echo ultrashort echo time (UTE) radial acquisition interleaved with and without a WET (water suppression enhanced through T1 effects) saturation pulse was used to map T1 and T2* simultaneously in a single scan. Correction for modulation due to multiple views per segment was derived. Bloch simulations were performed to study saturation pulse excitation profile on lung tissue. Optimization of the saturation delay time (for T1 mapping) and echo time (for T2* mapping) was performed. Monte Carlo simulation was done to predict accuracy and precision of the sequence with signal-to-noise ratio of in vivo images used in the simulation. A phantom study was carried out using the 3D interleaved saturation recovery with dual echo ultrashort echo time imaging (ITSR-DUTE) sequence and reference standard inversion recovery spin echo sequence (IR-SE) to compare accuracy of the sequence. Nine healthy volunteers were imaged and mean (SD) of T1 and T2* in lung parenchyma at 3T were estimated through manually assisted segmentation. 3D lung coverage with a resolution of 2.5 × 2.5 × 6 mm(3) was performed and nominal scan time was recorded for the scans. Repeatability was assessed in three of the volunteers. Regional differences in T1/T2* values were also assessed. The phantom study showed accuracy of T1 values to be within 2.3% of values obtained from IR-SE. Mean T1 value in lung parenchyma was 1002 ± 82 ms while T2* was 0.85 ± 0.1 ms. Scan time was ∼10 min for volunteer scans. Mean coefficient of variation (CV) across slices was 0.057 and 0.09, respectively. Regional variation along the gravitational direction and between right and left lung were not significant (P = 0.25 and P = 0.06, respectively) for T1. T2* showed significant variation (P = 0.03) along the

  20. Investigation of microenvironmental factors influencing the longitudinal relaxation times of drugs and other compounds

    DEFF Research Database (Denmark)

    Dzik-Jurasz, A.S.K.; Leach, M.O.; Rowland, Ian John

    2004-01-01

    The aim of this study was to investigate the microenvironmental factors likely to influence the longitudinal relaxation time of MR visible drugs or compounds in vivo at 1.5 T. The relative influence that viscosity, albumin and paramagnetic contrast agent concentrations have on the observed...... longitudinal relaxation times of three 19F MR detectable drugs and compounds have been investigated. Our data show that for 5-fluorouracil, flucloxacillin and tetrafluorosuccinic acid-containing phantoms, the presence of albumin at normal physiological concentrations will have relaxation effects of the same...... order of magnitude as that of a commonly clinically administered contrast agent, gadolinium diethylenetriamine pentaacetic acid. The contribution of viscosity is shown, in the examples studied here, to be of minor importance, contributing less than 6.5% to the observed relaxation effects. It is also...

  1. Transient transport in III-nitrides: interplay of momentum and energy relaxation times

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigues, Cloves G [Nucleo de Pesquisa em Fisica, Departamento de Fisica, Universidade Catolica de Goias, 74605-010, Goiania, Goias (Brazil); Vasconcellos, Aurea R [Instituto de Fisica ' Gleb Wataghin' , Universidade Estadual de Campinas, UNICAMP, 13083-970, Campinas, Sao Paulo (Brazil); Luzzi, Roberto [Instituto de Fisica ' Gleb Wataghin' , Universidade Estadual de Campinas, UNICAMP, 13083-970, Campinas, Sao Paulo (Brazil); Freire, Valder N [Departamento de Fisica, Universidade Federal do Ceara, Campus do Pici, 60455-760 Fortaleza, Ceara (Brazil)

    2007-08-29

    The ultrafast transient transport in wide-gap polar III-nitride semiconductors in electric fields is considered. A nonlinear and time-dependent (on the evolution of the nonequilibrium-irreversible thermodynamic state of the system) Drude-like law is derived, with the conductivity related to a so-called transport time (or current characteristic time which is related to a memory-dependent momentum relaxation time). From the collision operators, present in the evolution equations for the carriers' energy and momentum, are obtained quantities playing the role of time-dependent energy and momentum relaxation times. The electron drift velocity overshoot at intermediate-intensity fields in GaN, AlN and InN is evidenced, and its onset is explained as a result of the interplay of momentum and energy relaxation times.

  2. Evaluation of MRI sequences for quantitative T1 brain mapping

    Science.gov (United States)

    Tsialios, P.; Thrippleton, M.; Glatz, A.; Pernet, C.

    2017-11-01

    T1 mapping constitutes a quantitative MRI technique finding significant application in brain imaging. It allows evaluation of contrast uptake, blood perfusion, volume, providing a more specific biomarker of disease progression compared to conventional T1-weighted images. While there are many techniques for T1-mapping there is a wide range of reported T1-values in tissues, raising the issue of protocols reproducibility and standardization. The gold standard for obtaining T1-maps is based on acquiring IR-SE sequence. Widely used alternative sequences are IR-SE-EPI, VFA (DESPOT), DESPOT-HIFI and MP2RAGE that speed up scanning and fitting procedures. A custom MRI phantom was used to assess the reproducibility and accuracy of the different methods. All scans were performed using a 3T Siemens Prisma scanner. The acquired data processed using two different codes. The main difference was observed for VFA (DESPOT) which grossly overestimated T1 relaxation time by 214 ms [126 270] compared to the IR-SE sequence. MP2RAGE and DESPOT-HIFI sequences gave slightly shorter time than IR-SE (~20 to 30ms) and can be considered as alternative and time-efficient methods for acquiring accurate T1 maps of the human brain, while IR-SE-EPI gave identical result, at a cost of a lower image quality.

  3. Giant deviation of a relaxation time from generalized Newtonian theory in discontinuous shear thickening suspensions

    Science.gov (United States)

    Maharjan, Rijan; Brown, Eric

    2017-12-01

    We investigated the transient relaxation of a discontinuous shear thickening (DST) suspension of cornstarch in water. We performed two types of relaxation experiments starting from a steady shear in a parallel-plate rheometer, followed either by stopping the top plate rotation and measuring the transient torque relaxation or by removing the torque on the plate and measuring the transient rotation of the tool. We found that at low effective weight fraction ϕeff<58.8 ±0.4 % , the suspensions exhibited a relaxation behavior consistent with a generalized Newtonian fluid in which the relaxation is determined by the steady-state relationship between shear stress and shear rate. However, for larger weight fraction 58.8 %<ϕeff<61.0 % , near the liquid-solid transition ϕc=61.0 ±0.7 % , we found relaxation behaviors qualitatively and quantitatively different from the generalized Newtonian model. The regime where the relaxation was inconsistent with the generalized Newtonian model was the same where we found positive normal stress during relaxation, and in some cases we found an oscillatory response, suggestive of a solidlike structure consisting of a system-spanning contact network of particles. This regime also corresponds to the same packing fraction range where we consistently found discontinuous shear thickening in rate-controlled, steady-state measurements. The relaxation time in this range scales with the inverse of the critical shear rate at the onset of shear thickening, which may correspond to a contact relaxation time for nearby particles in the structure to flow away from each other. In this range, the relaxation time was the same in both stress- and rate-controlled relaxation experiments, indicating the relaxation time is more intrinsic than an effective viscosity in this range and is needed in addition to the steady-state viscosity function to describe transient flows. The discrepancy between the measured relaxation times and the generalized Newtonian

  4. [MR relaxation time measurements with and without selective fat suppression (SPIR) in endocrine orbitopathy].

    Science.gov (United States)

    Pauleit, D; Schüller, H; Textor, J; Leutner, C; Keller, E; Sommer, T; Träber, F; Block, W; Boldt, I; Schild, H

    1997-12-01

    To determine the value and utility of relaxation time measurements with magnetic resonance (MR) imaging in patients with Graves' ophthalmopathy (G.O.). 20 orbits were studied in control subjects and 58 orbits in patients with G.O. T2 relaxation times of extraocular muscles and retrobulbar fat tissue were calculated. The thickness of the eye muscles was correlated with the calculated T2 times. 18 orbits were measured before and after retro-orbital radiation therapy. Upper limits of determined normal T2 values were 60 ms in extraocular eye muscles and 40 ms in retrobulbar fat tissue. 89% (17/19) of the patients with G.O. had prolonged T2 times in extraocular eye muscles. The retrobulbar fat tissue in 5 of 38 orbits revealed minimal edema with the use of fat saturated sequences. T2 relaxation times decreased significantly (p < 10(-4)) after 10 Gy radiation therapy. No correlation was found between enlargement and T2 relaxation times in extraocular eye muscles (r = 0.44 in patients before radiation therapy). In patients with G.O. the determination of the enlargement of extraocular eye muscles in computed tomography is not a sufficient parameter for an antiinflammatory therapy, since CT cannot visualise eye muscle edema. T2 relaxation time measurements with MR imaging allow differentiation between edematous and fibrotic changes. This is the diagnostic method of choice in patients with Graves' ophthalmopathy.

  5. Long valley relaxation time of free carriers in monolayer WSe2

    Science.gov (United States)

    Yan, Tengfei; Yang, Siyuan; Li, Dian; Cui, Xiaodong

    2017-06-01

    Monolayer transition metal dichalcogenides (TMDs) feature a valley degree of freedom, giant spin-orbit coupling, and spin-valley locking. These exotic natures have stimulated efforts of exploring potential applications in conceptual spintronics, valleytronics, and quantum computing. Among all the exotic directions, a long relaxation time of spin and/or valley polarization is critical. The present valley dynamics studies concentrate on the band edge excitons which predominate the optical response due to an enhanced Coulomb interaction in two dimensions. The valley relaxation time of free carriers remains ambiguous. In this Rapid Communication, we use time-resolved Kerr rotation spectroscopy to probe the valley dynamics of excitons and free carriers in monolayer tungsten diselenide. The valley relaxation time of free carriers is found around 2 ns at 70 K, about three orders of magnitude longer than the excitons of about 2 ps, and 15 times larger than that of trions (130 ps). The extended valley relaxation time of free carriers evidences that an exchange interaction dominates the valley relaxation in optical excitations. The pump-probe spectroscopy also reveals an exciton binding energy of 0.60 eV in monolayer WSe2.

  6. Torque and mechanomyogram correlations during muscle relaxation: effects of fatigue and time-course of recovery.

    Science.gov (United States)

    Cè, Emiliano; Rampichini, Susanna; Limonta, Eloisa; Esposito, Fabio

    2013-12-01

    To assess the validity and reliability of the mechanomyogram (MMG) as a tool to investigate the fatigue-induced changes in the muscle during relaxation, the torque and MMG signals from the gastrocnemius medialis muscle of 23 participants were recorded during tetanic electrically-elicited contractions before and immediately after fatigue, as well as at min 2 and 7 of recovery. The peak torque (pT), contraction time (CT) and relaxation time (RT), and the acceleration of force development (d2RFD) and relaxation (d2RFR) were calculated. The slope and τ of force relaxation were also determined. MMG peak-to-peak was assessed during contraction (MMG p-p) and relaxation (R-MMG p-p). After fatigue, pT, d2RFD, d2RFR, slope, MMG p-p and R-MMG p-p decreased significantly, while CT, RT and τ increased (P muscle mechanical behavior, and could be therefore considered an effective alternative to the force signal, also during relaxation. Copyright © 2013 Elsevier Ltd. All rights reserved.

  7. Space and time dynamical heterogeneity in glassy relaxation. The role of democratic clusters

    Energy Technology Data Exchange (ETDEWEB)

    Appignanesi, G A; Rodriguez Fris, J A [Fisicoquimica, Departamento de Quimica, Universidad Nacional del Sur, Avenida Alem 1253, 8000 BahIa Blanca (Argentina); Seccion de Fisicoquimica, Instituto de Quimica de la Universidad Nacional del Sur, INQUISUR-UNS-CONICET, Universidad Nacional del Sur, Avenida Alem 1253, 8000 BahIa Blanca (Argentina)], E-mail: appignan@criba.edu.ar

    2009-05-20

    In this work we review recent computational advances in the understanding of the relaxation dynamics of supercooled glass-forming liquids. In such a supercooled regime these systems experience a striking dynamical slowing down which can be rationalized in terms of the picture of dynamical heterogeneities, wherein the dynamics can vary by orders of magnitude from one region of the sample to another and where the sizes and timescales of such slowly relaxing regions are expected to increase considerably as the temperature is decreased. We shall focus on the relaxation events at a microscopic level and describe the finding of the collective motions of particles responsible for the dynamical heterogeneities. In so doing, we shall demonstrate that the dynamics in different regions of the system is not only heterogeneous in space but also in time. In particular, we shall be interested in the events relevant to the long-time structural relaxation or {alpha} relaxation. In this regard, we shall focus on the discovery of cooperatively relaxing units involving the collective motion of relatively compact clusters of particles, called 'democratic clusters' or d-clusters. These events have been shown to trigger transitions between metabasins of the potential energy landscape (collections of similar configurations or structures) and to consist of the main steps in the {alpha} relaxation. Such events emerge in systems quite different in nature such as simple model glass formers and supercooled amorphous water. Additionally, another relevant issue in this context consists in the determination of a link between structure and dynamics. In this context, we describe the relationship between the d-cluster events and the constraints that the local structure poses on the relaxation dynamics, thus revealing their role in reformulating structural constraints. (topical review)

  8. Time and Temperature Dependence of Viscoelastic Stress Relaxation in Gold and Gold Alloy Thin Films

    Science.gov (United States)

    Mongkolsuttirat, Kittisun

    Radio frequency (RF) switches based on capacitive MicroElectroMechanical System (MEMS) devices have been proposed as replacements for traditional solid-state field effect transistor (FET) devices. However, one of the limitations of the existing capacitive switch designs is long-term reliability. Failure is generally attributed to electrical charging in the capacitor's dielectric layer that creates an attractive electrostatic force between a moving upper capacitor plate (a metal membrane) and the dielectric. This acts as an attractive stiction force between them that may cause the switch to stay permanently in the closed state. The force that is responsible for opening the switch is the elastic restoring force due to stress in the film membrane. If the restoring force decreases over time due to stress relaxation, the tendency for stiction failure behavior will increase. Au films have been shown to exhibit stress relaxation even at room temperature. The stress relaxation observed is a type of viscoelastic behavior that is more significant in thin metal films than in bulk materials. Metal films with a high relaxation resistance would have a lower probability of device failure due to stress relaxation. It has been shown that solid solution and oxide dispersion can strengthen a material without unacceptable decreases in electrical conductivity. In this study, the viscoelastic behavior of Au, AuV solid solution and AuV2O5 dispersion created by DC magnetron sputtering are investigated using the gas pressure bulge testing technique in the temperature range from 20 to 80°C. The effectiveness of the two strengthening approaches is compared with the pure Au in terms of relaxation modulus and 3 hour modulus decay. The time dependent relaxation curves can be fitted very well with a four-term Prony series model. From the temperature dependence of the terms of the series, activation energies have been deduced to identify the possible dominant relaxation mechanism. The measured

  9. Impact and relationship of anterior commissure and time-dose factor on the local control of T1N0 glottic cancer treated by 6 MV photons

    Directory of Open Access Journals (Sweden)

    Fu Yiu-Tung

    2011-05-01

    Full Text Available Abstract Background To evaluate prognostic factors that may influence local control (LC of T1N0 glottic cancer treated by primary radiotherapy (RT with 6 MV photons. Methods We retrospectively reviewed the medical records of 433 consecutive patients with T1N0 glottic cancer treated between 1983 and 2005 by RT in our institution. All patients were treated with 6 MV photons. One hundred and seventy seven (41% patients received 52.5 Gy in 23 fractions with 2.5 Gy/fraction, and 256 (59% patients received 66 Gy in 33 fractions with 2 Gy/fraction. Results The median follow-up time was 10.5 years. The 10-year LC rates were 91% and 87% for T1a and T1b respectively. Multivariate analysis showed LC rate was adversely affected by poorly differentiated histology (Hazard Ratio [HR]: 7.5, p = 0.035; involvement of anterior commissure (HR: 2.34, p = 0.011; fraction size of 2.0 Gy (HR: 2.17, p = 0.035 and tumor biologically effective dose (BED 15 (HR: 3.38, p = 0.017. Conclusions The negative impact of anterior commissure involvement could be overcome by delivering a higher tumor BED through using fraction size of > 2.0 Gy. We recommend that fraction size > 2.0 Gy should be utilized, for radiation schedules with five daily fractions each week.

  10. Caffeine intake inverts the effect of adenosine on myocardial perfusion during stress as measured by T1 mapping

    NARCIS (Netherlands)

    Kuijpers, Dirkjan; Prakken, Niek H.; Vliegenthart, Rozemarijn; van Dijkman, Paul R. M.; van der Harst, Pim; Oudkerk, Matthijs

    2016-01-01

    Caffeine intake before adenosine stress myocardial perfusion imaging may cause false negative findings. We hypothesized that the antagonistic effect of caffeine can be measured by T1 relaxation times in rest and adenosine stress cardiac magnetic resonance imaging (CMR), as T1 mapping techniques are

  11. T2 relaxation time mapping of the cartilage cap of osteochondromas

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hee Kyung; Horn, Paul; Laor, Tal [Cincinnati Children' s Hospital Medical Center, Cincinnati (United States); Daedzinski, Bernard J. [Dept. of Radiology, Children' s Hospital of Philadelphia, University of Pennsylvania, Philadelphia (United States); Kim, Dong Hoon [Dept. of Radiology, Pharmacology, Korea University College of Medicine, Seoul (Korea, Republic of)

    2016-02-15

    Our aim was to evaluate the cartilage cap of osteochondromas using T2 maps and to compare these values to those of normal patellar cartilage, from age and gender matched controls. This study was approved by the Institutional Review Board and request for informed consent was waived. Eleven children (ages 5-17 years) with osteochondromas underwent MR imaging, which included T2-weighted fat suppressed and T2 relaxation time mapping (echo time = 9-99/repetition time = 1500 msec) sequences. Lesion origins were femur (n = 5), tibia (n = 3), fibula (n = 2), and scapula (n = 1). Signal intensity of the cartilage cap, thickness, mean T2 relaxation times, and T2 spatial variation (mean T2 relaxation times as a function of distance) were evaluated. Findings were compared to those of patellar cartilage from a group of age and gender matched subjects. The cartilage caps showed a fluid-like high T2 signal, with mean thickness of 4.8 mm. The mean value of mean T2 relaxation times of the osteochondromas was 264.0 ± 80.4 msec (range, 151.0-366.0 msec). Mean T2 relaxation times were significantly longer than the values from patellar cartilage (39.0 msec) (p < 0.0001). These findings were observed with T2 spatial variation plots across the entire distance of the cartilage cap, with the most pronounced difference in the middle section of the cartilage. Longer T2 relaxation times of the cartilage caps of osteochondromas should be considered as normal, and likely to reflect an increased water content, different microstructure and component.

  12. Myocardial T1 mapping: application to patients with acute and chronic myocardial infarction.

    Science.gov (United States)

    Messroghli, Daniel R; Walters, Kevin; Plein, Sven; Sparrow, Patrick; Friedrich, Matthias G; Ridgway, John P; Sivananthan, Mohan U

    2007-07-01

    T(1) maps obtained with modified Look-Locker inversion recovery (MOLLI) can be used to measure myocardial T(1). We aimed to evaluate the potential of MOLLI T(1) mapping for the assessment of acute and chronic myocardial infarction (MI). A total of 24 patients with a first MI underwent MRI within 8 days and after 6 months. T(1) mapping was performed at baseline and at selected intervals between 2-20 min following administration of gadopentetate dimeglumine (Gd-DTPA). Delayed-enhancement (DE) imaging served as the reference standard for delineation of the infarct zone. On T(1) maps the myocardial T(1) relaxation time was assessed in hyperenhanced areas, hypoenhanced infarct cores, and remote myocardium. The planimetric size of myocardial areas with standardized T(1) threshold values was measured. Acute and chronic MI exhibited different T(1) changes. Precontrast threshold T(1) maps detected segmental abnormalities caused by acute MI with 96% sensitivity and 91% specificity. Agreement between measurements of infarct size from T(1) mapping and DE imaging was higher in chronic than in acute infarcts. Precontrast T(1) maps enable the detection of acute MI. Acute and chronic MI show different patterns of T(1) changes. Standardized T(1) thresholds provide the potential to dichotomously identify areas of infarction. (c) 2007 Wiley-Liss, Inc.

  13. Multigrid waveform relaxation for the time-fractional heat equation

    NARCIS (Netherlands)

    F.J. Gaspar Lorenz (Franscisco); C. Rodrigo (Carmen)

    2017-01-01

    textabstractIn this work, we propose an efficient and robust multigrid method for solving the time-fractional heat equation. Due to the nonlocal property of fractional differential operators, numerical methods usually generate systems of equations for which the coefficient matrix is dense.

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

    Science.gov (United States)

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

    2014-05-01

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

  15. Spin-relaxation time in the impurity band of wurtzite semiconductors

    Science.gov (United States)

    Tamborenea, Pablo I.; Wellens, Thomas; Weinmann, Dietmar; Jalabert, Rodolfo A.

    2017-09-01

    The spin-relaxation time for electrons in the impurity band of semiconductors with wurtzite crystal structure is determined. The effective Dresselhaus spin-orbit interaction Hamiltonian is taken as the source of the spin relaxation at low temperature and for doping densities corresponding to the metallic side of the metal-insulator transition. The spin-flip hopping matrix elements between impurity states are calculated and used to set up a tight-binding Hamiltonian that incorporates the symmetries of wurtzite semiconductors. The spin-relaxation time is obtained from a semiclassical model of spin diffusion, as well as from a microscopic self-consistent diagrammatic theory of spin and charge diffusion in doped semiconductors. Estimates are provided for particularly important materials. The theoretical spin-relaxation times compare favorably with the corresponding low-temperature measurements in GaN and ZnO. For InN and AlN we predict that tuning of the spin-orbit coupling constant induced by an external potential leads to a potentially dramatic increase of the spin-relaxation time related to the mechanism under study.

  16. Time Resolved Broadband Terahertz Relaxation Dynamics of Electron in Water

    DEFF Research Database (Denmark)

    Wang, Tianwu; Iwaszczuk, Krzysztof; Cooke, David G.

    We investigated the transient response of the solvated electron in water ejected by photodetachment from potassium ferrocyanide using time resolved terahertz spectroscopy (TSTS). Ultrabroadband THz transients are generated and detected by a two-color femtosecond-induced air plasma and air biased...... coherent detection, respectively. We find that the measured frequency dependent conductivity can be well described by a Drude-Smith model, supplemented by a Lorentz model oscillating near 5 THz....

  17. T2 relaxation times are increased in Skeletal muscle of DMD but not BMD patients.

    Science.gov (United States)

    Wokke, Beatrijs H; Van Den Bergen, Janneke C; Hooijmans, Melissa T; Verschuuren, Jan J; Niks, Erik H; Kan, Hermien E

    2016-01-01

    Exon-skipping drugs in Duchenne muscular dystrophy (DMD) aim to restore truncated dystrophin expression, which is present in the milder Becker muscular dystrophy (BMD). MRI skeletal muscle T2 relaxation times as a representation of edema/inflammation could be quantitative outcome parameters for such trials. We studied T2 relaxation times, adjusted for muscle fat fraction using Dixon MRI, in lower leg muscles of DMD and BMD patients and healthy controls. T2 relaxation times correlated significantly with fat fractions in patients only (P DMD patients (P DMD but are influenced by fat despite fat suppression. This should be accounted for when using quantitative T2 mapping to investigate edema/inflammation. © 2015 Wiley Periodicals, Inc.

  18. Photoacoustic Determination of Non-radiative Relaxation Time of Absorbing Centers in Maize Seeds

    Science.gov (United States)

    Domínguez-Pacheco, A.; Hernández-Aguilar, C.; Cruz-Orea, A.

    2017-07-01

    Using non-destructive photothermal techniques, it is possible to characterize non-homogenous materials to obtain its optical and thermal properties through photoacoustic spectroscopy (PAS). In photoacoustic (PA) phenomena, there are transient states of thermal excitation, when samples absorb the incident light; these states manifest an excitation process that generates the PA signal, being in direct relation with the non-radiative relaxation times with the sample absorbent centers. The objective of this study was to determine the non-radiative relaxation times associated with different absorbent centers of corn seeds ( Zea mays L.), by using PAS. A frequency scan was done at different wavelengths (350 nm, 470 nm and 650 nm) in order to obtain the non-radiative relaxation times with different types of maize seeds.

  19. Only through perturbation can relaxation times be estimated

    DEFF Research Database (Denmark)

    Ditlevsen, Susanne; Lansky, Petr

    2012-01-01

    from finite sample sizes and especially the estimator of the time constant of the system is degraded. Therefore an alternative solution is of paramount importance. We present such a solution based on perturbation of the system, observing trajectories far from equilibrium. The results are illustrated...... on computer experiments based on applications in neuroscience and pharmacokinetics, which show a striking improvement of the quality of estimation. The results are important for judicious designs of experiments to obtain maximal information from each data point, especially when samples are expensive...

  20. On-chip Brownian relaxation measurements of magnetic nanobeads in the time domain

    DEFF Research Database (Denmark)

    Østerberg, Frederik Westergaard; Rizzi, Giovanni; Hansen, Mikkel Fougt

    2013-01-01

    the time and frequency domain methods on Brownian relaxation detection of clustering of streptavidin coated magnetic beads in the presence of different concentrations of biotin-conjugated bovine serum albumin and obtain comparable results. In the time domain, a measurement is carried out in less than 30 s...

  1. Option pricing during post-crash relaxation times

    Science.gov (United States)

    Dibeh, Ghassan; Harmanani, Haidar M.

    2007-07-01

    This paper presents a model for option pricing in markets that experience financial crashes. The stochastic differential equation (SDE) of stock price dynamics is coupled to a post-crash market index. The resultant SDE is shown to have stock price and time dependent volatility. The partial differential equation (PDE) for call prices is derived using risk-neutral pricing. European call prices are then estimated using Monte Carlo and finite difference methods. Results of the model show that call option prices after the crash are systematically less than those predicted by the Black-Scholes model. This is a result of the effect of non-constant volatility of the model that causes a volatility skew.

  2. NMR relaxation time measurements of Xenon-129 dissolved in tissue and blood: Toward MR imaging of laser-polarized Xenon-129 in tissue

    Science.gov (United States)

    Wilson, Gregory J.

    Nuclear magnetic resonance relaxation measurements of 129Xe in tissue homogenates and blood were performed to explore the feasibility of magnetic resonance (MR) imaging of laser-polarized (LP) 129Xe in tissues. Laser polarization of 129Xe by optical pumping and spin exchange increases the signal obtained from 129Xe to a sufficient level that, after inhalation of LP 129Xe, it may be detected by MR throughout the body. Image signal-to-noise ratio (SNR) will depend on longitudinal (T1) and transverse (T2) relaxation times of 129Xe in tissues and blood. 129Xe T1 and T2 were measured at 9.4 T and 10°C in rat whole blood and homogenates of rat liver, brain, kidney, and lung at varying oxygenation levels. T1 values ranged from 4.4 +/- 0.4 to 22 +/- 2 s. T2 values ranged from 1.4 +/- 1.0 to 7.00 +/- 0.09 ms. Oxygenation dependence of the relaxation times varied between tissues. The observed oxygen dependence suggests relaxation due to paramagnetic deoxyhemoglobin dominates that due to free oxygen in tissues with sufficiently high fractions of blood. In addition, T1 and T2 of 129Xe in separated blood plasma were measured at both 9.4 and 1.89 T to explore the dependence on field strength. T1 of 129Xe in plasma decreased from 46 +/- 8 to 20 +/- 3 s and T2 increased from 11 +/- 2 to 127 +/- 8 ms when the field strength decreased from 9.4 to 1.89 T. When an inhalation model of gas delivery to tissue is used, the expected intrinsic SNR for LP 129Xe in gray matter at 9.4 T is approximately 3% of the conventional proton intrinsic SNR at 1.5 T. Short 129Xe T2 values (at 9.4 T) and the finite amount of magnetization available for imaging LP 129Xe further reduce the expected image SNR compared to conventional proton imaging. Several common pulse sequences were modeled to predict their relative effectiveness for imaging LP 129Xe at both 9.4 and 1.89 T. Each modeled sequence predicted higher SNR at 1.89 that at 9.4 T.

  3. MR pulse sequences for selective relaxation time measurements: a phantom study

    DEFF Research Database (Denmark)

    Thomsen, C; Jensen, K E; Jensen, M

    1990-01-01

    The accuracy of relaxation time measurements of spectroscopic inversion recovery and CPMG multi-echo pulse sequences together with ISIS and stimulated echo-pulse methods have been tested on a reference phantom (test object no. 5, of the EEC Concerted Research Project). For the measurements...... a Siemens Magnetom wholebody magnetic resonance scanner operating at 1.5 Tesla was used. For comparison six imaging pulse sequences for relaxation time measurements were tested on the same phantom. The spectroscopic pulse sequences all had an accuracy better than 10% of the reference values....

  4. A medical device-grade T1 and ECV phantom for global T1 mapping quality assurance-the T1 Mapping and ECV Standardization in cardiovascular magnetic resonance (T1MES) program.

    Science.gov (United States)

    Captur, Gabriella; Gatehouse, Peter; Keenan, Kathryn E; Heslinga, Friso G; Bruehl, Ruediger; Prothmann, Marcel; Graves, Martin J; Eames, Richard J; Torlasco, Camilla; Benedetti, Giulia; Donovan, Jacqueline; Ittermann, Bernd; Boubertakh, Redha; Bathgate, Andrew; Royet, Celine; Pang, Wenjie; Nezafat, Reza; Salerno, Michael; Kellman, Peter; Moon, James C

    2016-09-22

    T1 mapping and extracellular volume (ECV) have the potential to guide patient care and serve as surrogate end-points in clinical trials, but measurements differ between cardiovascular magnetic resonance (CMR) scanners and pulse sequences. To help deliver T1 mapping to global clinical care, we developed a phantom-based quality assurance (QA) system for verification of measurement stability over time at individual sites, with further aims of generalization of results across sites, vendor systems, software versions and imaging sequences. We thus created T1MES: The T1 Mapping and ECV Standardization Program. A design collaboration consisting of a specialist MRI small-medium enterprise, clinicians, physicists and national metrology institutes was formed. A phantom was designed covering clinically relevant ranges of T1 and T2 in blood and myocardium, pre and post-contrast, for 1.5 T and 3 T. Reproducible mass manufacture was established. The device received regulatory clearance by the Food and Drug Administration (FDA) and Conformité Européene (CE) marking. The T1MES phantom is an agarose gel-based phantom using nickel chloride as the paramagnetic relaxation modifier. It was reproducibly specified and mass-produced with a rigorously repeatable process. Each phantom contains nine differently-doped agarose gel tubes embedded in a gel/beads matrix. Phantoms were free of air bubbles and susceptibility artifacts at both field strengths and T1 maps were free from off-resonance artifacts. The incorporation of high-density polyethylene beads in the main gel fill was effective at flattening the B 1 field. T1 and T2 values measured in T1MES showed coefficients of variation of 1 % or less between repeat scans indicating good short-term reproducibility. Temperature dependency experiments confirmed that over the range 15-30 °C the short-T1 tubes were more stable with temperature than the long-T1 tubes. A batch of 69 phantoms was mass-produced with random sampling of ten of

  5. Nonradiative Relaxation in Real-Time Electronic Dynamics OSCF2: Organolead Triiodide Perovskite.

    Science.gov (United States)

    Nguyen, Triet S; Parkhill, John

    2016-09-01

    We apply our recently developed nonequilibrium real-time time-dependent density functional theory (OSCF2) to investigate the transient spectrum and relaxation dynamics of the tetragonal structure of methylammonium lead triiodide perovskite (MAPbI3). We obtain an estimate of the interband relaxation kinetics and identify multiple ultrafast cooling channels for hot electrons and hot holes that largely corroborate the dual valence-dual conduction model. The computed relaxation rates and absorption spectra are in good agreement with the existing experimental data. We present the first ab initio simulations of the perovskite transient absorption (TA) spectrum, substantiating the assignment of induced bleaches and absorptions including a Pauli-bleach signal. This paper validates both OSCF2 as a good qualitative model of electronic dynamics, and the dominant interpretation of the TA spectrum of this material.

  6. Estimating mean first passage time of biased random walks with short relaxation time on complex networks.

    Directory of Open Access Journals (Sweden)

    Zhuo Qi Lee

    Full Text Available Biased random walk has been studied extensively over the past decade especially in the transport and communication networks communities. The mean first passage time (MFPT of a biased random walk is an important performance indicator in those domains. While the fundamental matrix approach gives precise solution to MFPT, the computation is expensive and the solution lacks interpretability. Other approaches based on the Mean Field Theory relate MFPT to the node degree alone. However, nodes with the same degree may have very different local weight distribution, which may result in vastly different MFPT. We derive an approximate bound to the MFPT of biased random walk with short relaxation time on complex network where the biases are controlled by arbitrarily assigned node weights. We show that the MFPT of a node in this general case is closely related to not only its node degree, but also its local weight distribution. The MFPTs obtained from computer simulations also agree with the new theoretical analysis. Our result enables fast estimation of MFPT, which is useful especially to differentiate between nodes that have very different local node weight distribution even though they share the same node degrees.

  7. Caffeine intake inverts the effect of adenosine on myocardial perfusion during stress as measured by T1 mapping

    OpenAIRE

    Kuijpers, Dirkjan; Prakken, Niek H.; Vliegenthart, Rozemarijn; van Dijkman, Paul R. M.; Van der Harst, Pim; Oudkerk, Matthijs

    2016-01-01

    Caffeine intake before adenosine stress myocardial perfusion imaging may cause false negative findings. We hypothesized that the antagonistic effect of caffeine can be measured by T1 relaxation times in rest and adenosine stress cardiac magnetic resonance imaging (CMR), as T1 mapping techniques are sensitive to changes in myocardial blood volume. We prospectively analyzed 105 consecutive patients with adenosine stress perfusion CMR on a 1.5-T MRI system. Rest and stress T1 mapping was perform...

  8. Evaluating segmental liver function using T1 mapping on Gd-EOB-DTPA-enhanced MRI with a 3.0 Tesla.

    Science.gov (United States)

    Zhou, Zhi-Peng; Long, Li-Ling; Qiu, Wei-Jia; Cheng, Ge; Huang, Li-Juan; Yang, Teng-Fei; Huang, Zhong-Kui

    2017-03-01

    Assessing the liver function provides valuable information to evaluate surgical risk and plan accordingly. Current studies focus on whole liver function evaluation. However, assessment of segmental liver function is equally important in the clinical practice. The purpose of this study was to investigate whether Gd-EOB-DTPA-enhanced MRI can evaluate the liver function of each segment by using T1 mapping at 3 Tesla MRI. One hundred three patients were classified into one of 4 groups: a normal liver function (NLF) group (n = 38), a liver cirrhosis with Child-Pugh A (LCA) group (n = 33), a liver cirrhosis with Child-Pugh B (LCB) group (n = 21), and a liver cirrhosis with Child-Pugh C (LCC) group (n = 11). All patients underwent Gd-EOB-DTPA-enhanced MRI scans. T1 relaxation times were measured on the liver superimposing T1 mapping images. Reduction rate (△%) of T1 relaxation time of the liver parenchyma were calculated. After 20 min of Gd-EOB-DTPA enhancement, the T1 relaxation time of all liver segments in the LCC group were different from those in all the other groups, and more liver segments from the LCB and LCA groups different from the NLF group (p T1 relaxation time, and 0.709-0.905 on △%. For the LCC group, the AUCs of different liver segments for HBP were 0.842-0.997 on T1 relaxation time, and 0.887-0.990 on △%. For LCB patients, segmental liver function evaluation is possible using Gd-EOB-DTPA-enhanced MRI T1 mapping. For LCC patients, all liver segments can be used to evaluate liver function and both T1 relaxation time and the △% of T1 relaxation time have good diagnostic performance.

  9. T1 measurements in the human myocardium: the effects of magnetization transfer on the SASHA and MOLLI sequences.

    Science.gov (United States)

    Robson, Matthew D; Piechnik, Stefan K; Tunnicliffe, Elizabeth M; Neubauer, Stefan

    2013-09-01

    Quantitative mapping of the native T1 of the heart using the modified look-locker inversion recovery (MOLLI) technique provides high quality diagnostic information without requiring contrast agents. Previous work has considered the effects of T2 relaxation on MOLLI T1 measurements, finding that the T1 measured by MOLLI is biased, and that Saturation-recovery single-Shot Acquisition generates a more precise T1. However, despite detailed experiments and simulation the exact relaxation times observed in vivo remain unexplained, but might be due to magnetization transfer (MT). We used an MT simulation based on the Bloch-McConnell equations to evaluate the most common MOLLI and saturation-recovery single-shot acquisition sequence variants. For myocardial tissue we find that the T1 measured by saturation-recovery single-shot acquisition is insensitive to MT and T2, whereas MT reduces the T1 measured by MOLLI (>10%) in addition to the effects due to T2 relaxation. The consequences of this T1 underestimation by MOLLI are relevant. Increases in the actual T1 and T2 and decreases in MT will all result in an increase in T1 measured by MOLLI. Myocardial infarction demonstrates increased native T1 and T2 and decreased MT, indicating that these biases enhance the sensitivity of MOLLI to detect this and possibly other cardiovascular disease states. Copyright © 2013 Wiley Periodicals, Inc.

  10. Source of non-arrhenius average relaxation time in glass-forming liquids

    DEFF Research Database (Denmark)

    Dyre, Jeppe

    1998-01-01

    A major mystery of glass-forming liquids is the non-Arrhenius temperature-dependence of the average relaxation time. This paper briefly reviews the classical phenomenological models for non-Arrhenius behavior – the free volume model and the entropy model – and critiques against these models. We t...

  11. Assessment of clinical signs of liver cirrhosis using T1 mapping on Gd-EOB-DTPA-enhanced 3T MRI.

    Science.gov (United States)

    Haimerl, Michael; Verloh, Niklas; Zeman, Florian; Fellner, Claudia; Müller-Wille, René; Schreyer, Andreas G; Stroszczynski, Christian; Wiggermann, Philipp

    2013-01-01

    To assess the differences between normal and cirrhotic livers by means of T1 mapping of liver parenchyma on gadoxetic acid (Gd-EOB-DTPA)-enhanced 3 Tesla (3T) MR imaging (MRI). 162 patients with normal (n = 96) and cirrhotic livers (n = 66; Child-Pugh class A, n = 30; B, n = 28; C, n = 8) underwent Gd-EOB-DTPA-enhanced 3T MRI. To obtain T1 maps, two TurboFLASH sequences (TI = 400 ms and 1000 ms) before and 20 min after Gd-EOB-DTPA administration were acquired. T1 relaxation times of the liver and the reduction rate between pre- and post-contrast enhancement images were measured. The T1 relaxation times for Gd-EOB-DTPA-enhanced MRI showed significant differences between patients with normal liver function and patients with Child-Pugh class A, B, and C (p T1 relaxation times showed a constant significant increase from Child-Pugh class A up to class C (Child-Pugh class A, 335 ms ± 80 ms; B, 431 ms ± 75 ms; C, 557 ms ± 99 ms; Child-Pugh A to B, p T1 relaxation times (Child-Pugh class A, 57.1% ± 8.8%; B, 44.3% ± 10.2%, C, 29.9% ± 6.9%; Child-Pugh A to B, p T1 mapping of the liver parenchyma may present a useful method for determining severity of liver cirrhosis.

  12. Simultaneous T(1) and B(1) (+) mapping using reference region variable flip angle imaging.

    Science.gov (United States)

    Sung, Kyunghyun; Saranathan, Manojkumar; Daniel, Bruce L; Hargreaves, Brian A

    2013-10-01

    To present a new method that can simultaneously and efficiently measure T1 and B1 (+) maps using reference region variable flip angle (RR-VFA) imaging. Assuming T1 relaxation time in a reference region such as fat is well characterized, and the reference region sufficiently covers smoothly varying B1 (+) field inhomogeneity, B1 (+) maps can be measured from VFA images, conventionally used for T1 measurements. Fat-only images from two-point Dixon acquisitions were used to compute B1 (+) maps, and the B1 (+) maps were compared with ones using the double-angle method (DAM) in 22 breast MRI patients at 3T. Additionally, high spatial resolution VFA images were acquired to show T1 measurements with and without the RR-VFA B1 (+) correction in six patients. RR-VFA is able to generate reliable B1 (+) maps, similar to those using the conventional DAM. This simultaneous T1 and B1 (+) mapping can also be used to reduce T1 estimation errors, where T1 maps have more uniform fibroglandular tissue T1 and better depiction of heterogeneous T1 of breast masses. A new method that can measure both T1 and B1 (+) maps based on Dixon VFA images is described, offering improved T1 quantification with no scan time penalty. Copyright © 2013 Wiley Periodicals, Inc.

  13. Simultaneous T1 and B1+ Mapping using Reference Region Variable Flip Angle Imaging

    Science.gov (United States)

    Sung, Kyunghyun; Saranathan, Manojkumar; Daniel, Bruce L.; Hargreaves, Brian A.

    2013-01-01

    Purpose To present a new method that can simultaneously and efficiently measure T1 and B1+ maps using reference region variable flip angle (RR-VFA) imaging. Methods Assuming T1 relaxation time in a reference region such as fat is well characterized, and the reference region sufficiently covers smoothly varying B1+ field inhomogeneity, B1+ maps can be measured from VFA images, conventionally used for T1 measurements. Fat-only images from 2-point Dixon acquisitions were used to compute B1+ maps, and the B1+ maps were compared with ones using the double angle method (DAM) in 22 breast MRI patients at 3T. Additionally, high spatial resolution VFA images were acquired to show T1 measurements with and without the RR-VFA B1+ correction in six patients. Results RR-VFA is able to generate reliable B1+ maps, similar those using the conventional DAM. This simultaneous T1 and B1+ mapping can also be used to reduce T1 estimation errors, where T1 maps have more uniform fibroglandular tissue T1 and better depiction of heterogeneous T1 of breast masses. Conclusion A new method that can measure both T1 and B1+ maps based on Dixon VFA images is described, offering improved T1 quantification with no scan time penalty. PMID:23943610

  14. Estimation of T2 relaxation time of breast cancer: Correlation with clinical, imaging and pathological features

    Energy Technology Data Exchange (ETDEWEB)

    Seo, Mirinae; Sohn, Yu Mee [Dept. of Radiology, Kyung Hee University Hospital, College of Medicine, Kyung Hee University, Seoul (Korea, Republic of); Ryu, Jung Kyu; Jahng, Geon Ho; Rhee, Sun Jung; Oh, Jang Hoon; Won, Kyu Yeoun [Kyung Hee University Hospital at Gangdong, College of Medicine, Kyung Hee University, Seoul (Korea, Republic of)

    2017-01-15

    The purpose of this study was to estimate the T2* relaxation time in breast cancer, and to evaluate the association between the T2* value with clinical-imaging-pathological features of breast cancer. Between January 2011 and July 2013, 107 consecutive women with 107 breast cancers underwent multi-echo T2*-weighted imaging on a 3T clinical magnetic resonance imaging system. The Student's t test and one-way analysis of variance were used to compare the T2* values of cancer for different groups, based on the clinical-imaging-pathological features. In addition, multiple linear regression analysis was performed to find independent predictive factors associated with the T2* values. Of the 107 breast cancers, 92 were invasive and 15 were ductal carcinoma in situ (DCIS). The mean T2* value of invasive cancers was significantly longer than that of DCIS (p = 0.029). Signal intensity on T2-weighted imaging (T2WI) and histologic grade of invasive breast cancers showed significant correlation with T2* relaxation time in univariate and multivariate analysis. Breast cancer groups with higher signal intensity on T2WI showed longer T2* relaxation time (p = 0.005). Cancer groups with higher histologic grade showed longer T2* relaxation time (p = 0.017). The T2* value is significantly longer in invasive cancer than in DCIS. In invasive cancers, T2* relaxation time is significantly longer in higher histologic grades and high signal intensity on T2WI. Based on these preliminary data, quantitative T2* mapping has the potential to be useful in the characterization of breast cancer.

  15. Assessment of acute kidney injury with T1 mapping MRI following solid organ transplantation.

    Science.gov (United States)

    Peperhove, Matti; Vo Chieu, Van Dai; Jang, Mi-Sun; Gutberlet, Marcel; Hartung, Dagmar; Tewes, Susanne; Warnecke, Gregor; Fegbeutel, Christiane; Haverich, Axel; Gwinner, Wilfried; Lehner, Frank; Bräsen, Jan Hinrich; Haller, Hermann; Wacker, Frank; Gueler, Faikah; Hueper, Katja

    2017-07-14

    To evaluate T1 mapping as a non-invasive, functional MRI biomarker in patients shortly after solid organ transplantation to detect acute postsurgical kidney damage and to correlate T1 times with renal function. 101 patients within 2 weeks after solid organ transplantation (49 kidney transplantation, 52 lung transplantation) and 14 healthy volunteers were examined by MRI between July 2012 and April 2015 using the modified Look-Locker inversion recovery (MOLLI) sequence. T1 times in renal cortex and medulla and the corticomedullary difference were compared between groups using one-way ANOVA adjusted for multiple comparison with the Tukey test, and T1 times were correlated with renal function using Pearson's correlation. Compared to healthy volunteers T1 times were significantly increased after solid organ transplantation in the renal cortex (healthy volunteers 987 ± 102 ms; kidney transplantation 1299 ± 101 ms, p T1 changes were more pronounced following kidney compared to lung transplantation, were associated with the stage of renal impairment and significantly correlated with renal function. T1 mapping may be helpful for early non-invasive assessment of acute kidney injury and renal pathology following major surgery such as solid organ transplantation. • Renal cortical T1 relaxation times are prolonged after solid organ transplantation. • Cortical T1 values increase with higher stages of renal function impairment. • Corticomedullary difference decreases with higher stages of renal function impairment. • Renal cortical T1 relaxation time and corticomedullary difference correlate with renal function. • T1 mapping may be helpful for non-invasive assessment of post-operative renal pathology.

  16. Hemoglobin A1c (HbA1c) changes over time among adolescent and young adult participants in the T1D exchange clinic registry.

    Science.gov (United States)

    Clements, Mark A; Foster, Nicole C; Maahs, David M; Schatz, Desmond A; Olson, Beth A; Tsalikian, Eva; Lee, Joyce M; Burt-Solorzano, Christine M; Tamborlane, William V; Chen, Vincent; Miller, Kellee M; Beck, Roy W

    2016-08-01

    Hemoglobin A1c (HbA1c) levels among individuals with type 1 diabetes (T1D) influence the longitudinal risk for diabetes-related complications. Few studies have examined HbA1c trends across time in children, adolescents, and young adults with T1D. This study examines changes in glycemic control across the specific transition periods of pre-adolescence-to-adolescence and adolescence-to-young adulthood, and the demographic and clinical factors associated with these changes. Available HbA1c lab results for up to 10 yr were collected from medical records at 67 T1D Exchange clinics. Two retrospective cohorts were evaluated: the pre-adolescent-to-adolescent cohort consisting of 85 016 HbA1c measurements from 6574 participants collected when the participants were 8-18 yr old and the adolescent-to-young adult cohort, 2200 participants who were 16-26 yr old at the time of 17 279 HbA1c measurements. HbA1c in the 8-18 cohort increased over time after age 10 yr until ages 16-17; followed by a plateau. HbA1c levels in the 16-26 cohort remained steady from 16-18, and then gradually declined. For both cohorts, race/ethnicity, income, health insurance, and pump use were all significant in explaining individual variations in age-centered HbA1c (p adulthood. Focused interventions to prevent deterioration in glucose control in pre-adolescence, adolescence, and early adulthood are needed. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

  17. Rapid T1 quantification based on 3D phase sensitive inversion recovery.

    Science.gov (United States)

    Warntjes, Marcel J B; Kihlberg, Johan; Engvall, Jan

    2010-08-17

    In Contrast Enhanced Magnetic Resonance Imaging fibrotic myocardium can be distinguished from healthy tissue using the difference in the longitudinal T1 relaxation after administration of Gadolinium, the so-called Late Gd Enhancement. The purpose of this work was to measure the myocardial absolute T1 post-Gd from a single breath-hold 3D Phase Sensitivity Inversion Recovery sequence (PSIR). Equations were derived to take the acquisition and saturation effects on the magnetization into account. The accuracy of the method was investigated on phantoms and using simulations. The method was applied to a group of patients with suspected myocardial infarction where the absolute difference in relaxation of healthy and fibrotic myocardium was measured at about 15 minutes post-contrast. The evolution of the absolute R1 relaxation rate (1/T1) over time after contrast injection was followed for one patient and compared to T1 mapping using Look-Locker. Based on the T1 maps synthetic LGE images were reconstructed and compared to the conventional LGE images. The fitting algorithm is robust against variation in acquisition flip angle, the inversion delay time and cardiac arrhythmia. The observed relaxation rate of the myocardium is 1.2 s-1, increasing to 6 - 7 s-1 after contrast injection and decreasing to 2 - 2.5 s-1 for healthy myocardium and to 3.5 - 4 s-1 for fibrotic myocardium. Synthesized images based on the T1 maps correspond very well to actual LGE images. The method provides a robust quantification of post-Gd T1 relaxation for a complete cardiac volume within a single breath-hold.

  18. Relaxation times of the two-phonon processes with spin-flip and spin-conserving in quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zi-Wu, E-mail: zwwang@semi.ac.cn [Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Department of Physics, Tianjin University, Tianjin 300072 (China); Liu, Lei [Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215125 (China); Li, Shu-Shen [Institute of Semiconductor, CAS, Beijing 100083 (China)

    2014-04-07

    We perform a theoretical investigation on the two-phonon processes of the spin-flip and spin-conserving relaxation in quantum dots in the frame of the Huang-Rhys' lattice relaxation model. We find that the relaxation time of the spin-flip is two orders of magnitude longer than that of the spin-conserving, which is in agreement with previous experimental measurements. Moreover, the opposite variational trends of the relaxation time as a function of the energy separation for two-phonon processes are obtained in different temperature regime. The relaxation times display the oscillatory behaviors at the demarcation point with increasing magnetic field, where the energy separation matches the optical phonon energy and results in the optical phonon resonance. These results are useful in understanding the intraband levels' relaxation in quantum dots and could be helpful in designing photoelectric and spin-memory devices.

  19. Isothermal structural relaxation of Fe40Ni40B20 metallic glass in the relaxation times spectrum model

    NARCIS (Netherlands)

    Csach, K; Haruyama, O; Kasardova, A; Ocelik, Vaclav

    1997-01-01

    The structural relaxation of amorphous as-quenched Fe40Ni40B20 sample was investigated during isothermal annealing at temperatures close to 400 degrees C by: (i) the residual electrical resistance measured at liquid N-2 temperature; (ii) the in-situ electrical resistance; and (iii) the length

  20. Endogenous assessment of diffuse myocardial fibrosis in patients with T1ρ -mapping.

    Science.gov (United States)

    van Oorschot, Joep W M; Güçlü, Fatih; de Jong, Sanne; Chamuleau, Steven A J; Luijten, Peter R; Leiner, Tim; Zwanenburg, Jaco J M

    2017-01-01

    Recently, it was shown that a significantly higher T1ρ is found in compact myocardial fibrosis after chronic myocardial infarction. In this study, we investigated the feasibility of native T1ρ -mapping for the detection of diffuse myocardial fibrosis in patients with dilated cardiomyopathy (DCM). T1ρ -mapping was performed on three explanted hearts from DCM patients at 3 Tesla (T). Histological fibrosis quantification was performed, and compared with the T1ρ -relaxation times in the heart. Furthermore, twenty DCM patients underwent an MRI at 1.5T. Native T1ρ -maps, native T1 -maps, and extracellular volume (ECV)-maps were acquired. Additionally, eight healthy volunteers were scanned for reference values. A significant correlation (Pearson r = 0.49; P = 0.005) was found between ex vivo T1ρ -values and fibrosis fraction from histology. Additionally, a significantly higher T1ρ -relaxation time (55.2 ± 2.7 ms) was found in DCM patients compared with healthy control subjects (51.5 ± 1.2 ms) (P = 0.0024). The relation between in vivo T1ρ -values and ECV-values was significant (Pearson r = 0.66). No significant relation was found between native T1 - and ECV-values in this study (P = 0.89). This study showed proof of principle for the endogenous detection of diffuse myocardial fibrosis with T1ρ -MRI. Ex vivo and in vivo experiments showed promising results that T1ρ -MRI can be used to measure the extent of diffuse myocardial fibrosis in the myocardium. 2 J. Magn. Reson. Imaging 2017;45:132-138. © 2016 International Society for Magnetic Resonance in Medicine.

  1. Determination of relaxation modulus of time-dependent materials using neural networks

    Science.gov (United States)

    Aulova, Alexandra; Govekar, Edvard; Emri, Igor

    2017-08-01

    Health monitoring systems for plastic based structures require the capability of real time tracking of changes in response to the time-dependent behavior of polymer based structures. The paper proposes artificial neural networks as a tool of solving inverse problem appearing within time-dependent material characterization, since the conventional methods are computationally demanding and cannot operate in the real time mode. Abilities of a Multilayer Perceptron (MLP) and a Radial Basis Function Neural Network (RBFN) to solve ill-posed inverse problems on an example of determination of a time-dependent relaxation modulus curve segment from constant strain rate tensile test data are investigated. The required modeling data composed of strain rate, tensile and related relaxation modulus were generated using existing closed-form solution. Several neural networks topologies were tested with respect to the structure of input data, and their performance was compared to an exponential fitting technique. Selected optimal topologies of MLP and RBFN were tested for generalization and robustness on noisy data; performance of all the modeling methods with respect to the number of data points in the input vector was analyzed as well. It was shown that MLP and RBFN are capable of solving inverse problems related to the determination of a time dependent relaxation modulus curve segment. Particular topologies demonstrate good generalization and robustness capabilities, where the topology of RBFN with data provided in parallel proved to be superior compared to other methods.

  2. Investigation of dielectric relaxation in systems with hierarchical organization: From time to frequency domain and back again

    Energy Technology Data Exchange (ETDEWEB)

    Yokoi, Koki [Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI (United States); Raicu, Valerică, E-mail: vraicu@uwm.edu [Department of Physics, University of Wisconsin-Milwaukee, Milwaukee, WI (United States); Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI (United States)

    2017-06-28

    Relaxation in fractal structures was investigated theoretically starting from a simple model of a Cantorian tree and kinetic equations linking the change in the number of particles (e.g., electrical charges) populating each branch of the tree and their transfer to other branches or to the ground state. We numerically solved the system of differential equations obtained and determined the so-called cumulative distribution function of particles, which, in dielectric or mechanical relaxation parlance, is the same as the relaxation function of the system. As a physical application, we studied the relationship between the dielectric relaxation in time-domain and the dielectric dispersion in the frequency-domain. Upon choosing appropriate rate constants, our model described accurately well-known non-exponential and non-Debye time- and frequency-domain functions, such as stretched exponentials, Havrilliak–Negami, and frequency power law. Our approach opens the door to applying kinetic models to describe a wide array of relaxation processes, which traditionally have posed great challenges to theoretical modeling based on first principles. - Highlights: • Relaxation was investigated for a system of particles flowing through a Cantorian tree. • A set of kinetic equations was formulated and used to compute the relaxation function of the system. • The dispersion function of the system was computed from the relaxation function. • An analytical method was used to recover the original relaxation function from the dispersion function. • This formalism was used to study dielectric relaxation and dispersion in fractal structures.

  3. Slice selection and T1 contrast in FLASH NMR imaging

    Science.gov (United States)

    Hänicke, Wolfgang; Merboldt, Klaus-Dietmar; Frahm, Jens

    This paper describes the signal intensity in rapid FLASH NMR imaging as a function of the repetition time, the NMR relaxation times, the flip angle, and the shape of the tailored RF pulses used for slice selection. In the absence or after elimination of signal contributions from transverse coherences the theoretical treatment may be confined to a steady state of the longitudinal magnetization. It turns out that deviations from a rectangular excitation profile due to imperfect pulse shapes strongly alter both the dynamic approach to steady-state conditions and the resulting saturation behavior as expected from theoretical expressions. As a consequence the signal-to-noise and image contrast become dependent on the actual slice profile. In T1 images calculated from series of FLASH images with different flip angles or repetition times qualitative relations between tissues with different T1 values are borne out correctly, whereas the accuracy of T1 relaxation times may not be satisfactory. No restrictions are expected for 3D imaging using a spatially homogeneous RF excitation. Experiments have been carried out on phantoms and human volunteers using a Bruker 2.35 T 40 cm NMR system.

  4. A new approach for calculation of relaxation time and magnetic anisotropy of ferrofluids containing superparmagnetic nanoparticles

    Directory of Open Access Journals (Sweden)

    Ahmadi R.

    2012-01-01

    Full Text Available In this work, a new approach is described for the calculation of the relaxation time and magnetic anisotropy energy of magnetic nanoparticles. Ferrofluids containing monodispersed magnetite nanoparticles were synthesized via hydrothermal method and then heated using the 10 kA/m external AC magnetic fields in three different frequencies: 10, 50 and 100 kHz. By measuring the temperature variations during the application of the magnetic field, the total magnetic time constant including both Brownian and Neel relaxation times can be calculated. By measuring the magnetic core size and hydrodynamic size of particles, the magnetic anisotropy can be calculated too. Synthesized ferrofluids were characterized via TEM, XRD, VSM and PCS techniques and the results were used for the mentioned calculations.

  5. Correlation and relaxation times for a stochastic process with a fat-tailed steady-state distribution

    Science.gov (United States)

    Liu, Z.; Serota, R. A.

    2017-05-01

    We study a stochastic process defined by the interaction strength for the return to the mean and a stochastic term proportional to the magnitude of the variable. Its steady-state distribution is the Inverse Gamma distribution, whose power-law tail exponent is determined by the ratio of the interaction strength to stochasticity. Its time-dependence is characterized by a set of discrete times describing relaxation of respective cumulants to their steady-state values. We show that as the progressively lower cumulants diverge with the increase of stochasticity, so do their relaxation times. We analytically evaluate the correlation function and show that it is determined by the longest of these times, namely the inverse interaction strength, which is also the relaxation time of the mean. We also investigate relaxation of the entire distribution to the steady state and the distribution of relaxation times, which we argue to be Inverse Gaussian.

  6. Rate variation and estimation of divergence times using strict and relaxed clocks

    Directory of Open Access Journals (Sweden)

    Yang Ziheng

    2011-09-01

    Full Text Available Abstract Background Understanding causes of biological diversity may be greatly enhanced by knowledge of divergence times. Strict and relaxed clock models are used in Bayesian estimation of divergence times. We examined whether: i strict clock models are generally more appropriate in shallow phylogenies where rate variation is expected to be low, ii the likelihood ratio test of the clock (LRT reliably informs which model is appropriate for dating divergence times. Strict and relaxed models were used to analyse sequences simulated under different levels of rate variation. Published shallow phylogenies (Black bass, Primate-sucking lice, Podarcis lizards, Gallotiinae lizards, and Caprinae mammals were also analysed to determine natural levels of rate variation relative to the performance of the different models. Results Strict clock analyses performed well on data simulated under the independent rates model when the standard deviation of log rate on branches, σ, was low (≤0.1, but were inappropriate when σ>0.1 (95% of rates fall within 0.0082-0.0121 subs/site/Ma when σ = 0.1, for a mean rate of 0.01. The independent rates relaxed clock model performed well at all levels of rate variation, although posterior intervals on times were significantly wider than for the strict clock. The strict clock is therefore superior when rate variation is low. The performance of a correlated rates relaxed clock model was similar to the strict clock. Increased numbers of independent loci led to slightly narrower posteriors under the relaxed clock while older root ages provided proportionately narrower posteriors. The LRT had low power for σ = 0.01-0.1, but high power for σ = 0.5-2.0. Posterior means of σ2 were useful for assessing rate variation in published datasets. Estimates of natural levels of rate variation ranged from 0.05-3.38 for different partitions. Differences in divergence times between relaxed and strict clock analyses were greater in two

  7. Menstrual variation of breast volume and T{sub 2} relaxation times in cyclical mastalgia

    Energy Technology Data Exchange (ETDEWEB)

    Hussain, Zainab [Department of Medical Imaging, University of Liverpool, Johnstone Building, Brownlow Hill, P.O. Box 147, Liverpool, Merseyside L69 3GB (United Kingdom); Magnetic Resonance and Image Analysis Research Centre, University of Liverpool, Johnstone Building, Brownlow Hill, P.O. Box 147, Liverpool, Merseyside L69 3GB (United Kingdom)], E-mail: zay@liverpool.ac.uk; Brooks, Jonathan [Magnetic Resonance and Image Analysis Research Centre, University of Liverpool, Johnstone Building, Brownlow Hill, P.O. Box 147, Liverpool, Merseyside L69 3GB (United Kingdom); Department of Human Anatomy and Genetics, University of Oxford, Oxford (United Kingdom); Percy, Dave [Centre for Operational Research and Applied Statistics, University of Salford, Salford, Greater Manchester M5 4WT (United Kingdom)

    2008-02-15

    Purpose: Hormonal activity causes breast volume to change during the menstrual cycle. One possible cause of this volume change is thought to be due to water retention or oedema within the tissues. We used magnetic resonance imaging (MRI) to study the variation in breast volume and {sup 1}H Magnetic Resonance Spectroscopy (MRS) to measure T{sub 2} relaxation times which are known to increase with increasing tissue water content. We hypothesised that an increase in breast volume will elevate T{sub 2} relaxation due to the presence of an increased water content within the breast. T{sub 2} Relaxation time and volume were studied in fifteen control subjects and in a cohort of eight patients with cyclical mastalgia in order to determine whether changes in breast volume and T{sub 2} relaxation times differed in controls and patients during menses, ovulation and premenses. Method: Breast volume was determined by the Cavalieri method in combination with point counting techniques on MR images and T{sub 2} relaxation times of the water and fat in a voxel of breast tissue were obtained using {sup 1}H Magnetic Resonance Spectroscopy (MRS). Results: Statistical analysis (ANOVA) demonstrated highly significant differences in breast volume between the three stages of the cycle (p < 0.0005) with breast volume being greatest premenstrually. Patients did not exhibit an increase in volume premenstrually, significantly above controls. T{sub 2} of fat or water did not depend on stage of cycle. T-tests demonstrated no significant differences in T{sub 2} of water or fat between patient and control groups. The average T{sub 2} relaxation time of water was lowest in the patient and control groups during ovulation and highest in the patient group during premenses. Conclusion: We have performed the first combined volumetric and spectroscopic study of women with cyclical mastalgia and demonstrated that the global changes in volumes and T{sub 2} were not significantly different from normal

  8. T1 mapping of the ischemic myocardium: Review of potential clinical use

    Energy Technology Data Exchange (ETDEWEB)

    Baxa, Jan, E-mail: baxaj@fnplzen.cz [Department of Imaging Methods, Faculty of Medicine in Pilsen, Charles University in Prague and University Hospital Pilsen (Czech Republic); Ferda, Jiří [Department of Imaging Methods, Faculty of Medicine in Pilsen, Charles University in Prague and University Hospital Pilsen (Czech Republic); Hromádka, Milan [Department of Cardiology, University Hospital Pilsen (Czech Republic)

    2016-10-15

    Highlights: • T1 mapping is a feasible method for detailed characterization of the myocardium. • Non-contrast T1 mapping has potential for precise quantification of myocardial edema in acute infarction. • Evaluation of non-contrast T1 maps and extracellular volume improve detection of the area at risk and final infarct size. • T1 mapping could be beneficial in the quantification of chronic fibrous scar of the myocardium. - Abstract: Cardiac magnetic resonance imaging (CMR) is an indispensable part of the diagnostic algorithm in cardiology. CMR has become a gold standard in various disorders; moreover, it is well established also as a surrogate end-point in experimental and clinical studies. Particularly, the ability to directly display myocardial injury is a unique feature in comparison with other methods. The mapping of magnetic relaxation properties (T1, T2 and T2* relaxation times) are still relatively new techniques, but promising to improve the robustness of CMR and add new appropriate indications. The high potential of T1 mapping in the diagnostic of myocardial ischemic involvement has been highlighted in several experimental and clinical studies, but the use in clinical routine was limited due to the shortcomings in scanning and image evaluation. However, the quantitative technique of T1 mapping is now commercially available and its simple use, good reproducibility and limited subjectivity allow its incorporation into routine CMR protocols. This review article is aimed to summarise existing results and clinical experience with T1 mapping in patients with ischemic cardiac disease.

  9. Prolonged T1 in patients with liver cirrhosis: an in vivo MRI study

    DEFF Research Database (Denmark)

    Thomsen, C; Christoffersen, P; Henriksen, O

    1990-01-01

    Fifteen patients with liver cirrhosis and two control groups were examined. The first control group consisted of 7 healthy volunteers, and the second group of 17 patients with nonfocal liver diseases. The T1 and T2 relaxation times were calculated from signal intensities read out from a region...

  10. Dielectric Relaxation Studies of 2-Butoxyethanol with Aniline and Substituted Anilines Using Time Domain Reflectometry

    Directory of Open Access Journals (Sweden)

    P. Jeevanandham

    2014-01-01

    Full Text Available The complex dielectric spectra of 2-butoxyethanol with aniline and substituted anilines like aniline, o-chloroaniline, m-chloroaniline, o-anisidine and m-anisidine binary mixtures in the composition of different volumes of percent (0%, 25%, 50%, 75%, and 100% have been measured as a function of frequency between 10 MHz and 30 GHz at 298.15 K. The dielectric parameters like static dielectric constant ε0 and relaxation time τ have been obtained by using least square fit method. By using these parameters ε0,τ, effective Kirkwood correlation factor geff, corrective Kirkwood correlation factor gf, Bruggeman factor fB, excess dielectric constant εE, and excess inverse relaxation time 1/τE values are calculated and discussed to yield information on the dipolar alignment and molecular rotation of the binary liquid mixtures. From all the derived dielectric parameters, molecular interactions are interpreted through hydrogen bonding.

  11. Enthalpy Relaxation of a DGEBA Epoxy as a function of Time, Temperature, and Cooling Rate

    Science.gov (United States)

    Clarkson, Caitlyn M.; McCoy, John D.; Kropka, Jamie M.

    2015-03-01

    Enthalpy relaxation resulting from physical aging of a DGEBA epoxy, Epon 828, cross-linked with an amine curative, Jeffamine T-403, was studied for two isothermal aging temperatures at sequential aging times up to two weeks. Results were analyzed using the peak shift method to obtain the relaxation parameters β, δ (H*), and χ. The individual effects of cooling rate from the equilibrated state, aging time, and aging temperature were isolated to understand the initial state of the glassy epoxy and its evolution during physical aging. [Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  12. Transport coefficients in the Polyakov quark meson coupling model: A relaxation time approximation

    Science.gov (United States)

    Abhishek, Aman; Mishra, Hiranmaya; Ghosh, Sabyasachi

    2018-01-01

    We compute the transport coefficients, namely, the coefficients of shear and bulk viscosities, as well as thermal conductivity for hot and dense matter. The calculations are performed within the Polyakov quark meson model. The estimation of the transport coefficients is made using the Boltzmann kinetic equation within the relaxation time approximation. The energy-dependent relaxation time is estimated from meson-meson scattering, quark-meson scattering, and quark-quark scattering within the model. In our calculations, the shear viscosity to entropy ratio and the coefficient of thermal conductivity show a minimum at the critical temperature, while the ratio of bulk viscosity to entropy density exhibits a peak at this transition point. The effect of confinement modeled through a Polyakov loop potential plays an important role both below and above the critical temperature.

  13. Accuracy and Numerical Stabilty Analysis of Lattice Boltzmann Method with Multiple Relaxation Time for Incompressible Flows

    Science.gov (United States)

    Pradipto; Purqon, Acep

    2017-07-01

    Lattice Boltzmann Method (LBM) is the novel method for simulating fluid dynamics. Nowadays, the application of LBM ranges from the incompressible flow, flow in the porous medium, until microflows. The common collision model of LBM is the BGK with a constant single relaxation time τ. However, BGK suffers from numerical instabilities. These instabilities could be eliminated by implementing LBM with multiple relaxation time. Both of those scheme have implemented for incompressible 2 dimensions lid-driven cavity. The stability analysis has done by finding the maximum Reynolds number and velocity for converged simulations. The accuracy analysis is done by comparing the velocity profile with the benchmark results from Ghia, et al and calculating the net velocity flux. The tests concluded that LBM with MRT are more stable than BGK, and have a similar accuracy. The maximum Reynolds number that converges for BGK is 3200 and 7500 for MRT respectively.

  14. Single-shot T1 mapping of the corpus callosum: A rapid characterization of fiber bundle anatomy

    Directory of Open Access Journals (Sweden)

    Sabine eHofer

    2015-05-01

    Full Text Available Using diffusion-tensor MRI and fiber tractography the topographic organization of the corpus callosum (CC has been described to comprise 5 segments with fibers projecting into prefrontal (I, premotor and supplementary motor (II, primary motor (III, and primary sensory areas (IV, as well as into parietal, temporal, and occipital cortical areas (V. In order to more rapidly characterize the underlying anatomy of these segments, this study used a novel single-shot T1 mapping method to quantitatively determine T1 relaxation times in the human CC. A region-of-interest analysis revealed a tendency for the lowest T1 relaxation times in the genu and the highest T1 relaxation times in the somatomotor region of the CC. This observation separates regions dominated by myelinated fibers with large diameters (somatomotor area from densely packed smaller axonal bundles (genu with less myelin. The results indicate that characteristic T1 relaxation times in callosal profiles provide an additional means to monitor differences in fiber anatomy, fiber density, and gray matter in respective neocortical areas. In conclusion, rapid T1 mapping allows for a characterization of the axonal architecture in an individual CC in less than 10 s. The approach emerges as a valuable means for studying neocortical brain anatomy with possible implications for the diagnosis of neurodegenerative processes.

  15. Influence of Polymer Relaxation Time on the Electrospinning Process: Numerical Investigation

    Directory of Open Access Journals (Sweden)

    Siddharth Gadkari

    2017-10-01

    Full Text Available “Electrospinnability”, or the ease with which a solution can be used to obtain bead-free uniform fibers, depends on a large number of parameters, including solution properties, process parameters and ambient conditions. In this study, the effect of the polymer relaxation time on electrospinning of dilute polymer solutions is investigated numerically. It is shown that elastic stresses (ES increase exponentially with the Deborah number ( D e . For each polymer concentration there exists a critical D e below which the ES are insufficient to overcome capillary stresses (CS and lead to the formation of beaded fibers. However, above the critical D e , there is a higher probability of the ES overcoming the CS and leading to the formation of uniform fibers. This analysis suggests the possibility of improved electrospinnability even with dilute polymer solutions, provided the relaxation time is sufficiently large. It is also found that changes in the drag coefficient due to change in the polymer conformation and self-concentration of polymer molecules would become significant for the electrospinning of polymer solutions with a longer relaxation time and high conductivity.

  16. Viscosity, relaxation time, and dynamics within a model asphalt of larger molecules

    Energy Technology Data Exchange (ETDEWEB)

    Li, Derek D.; Greenfield, Michael L., E-mail: greenfield@egr.uri.edu [Department of Chemical Engineering, University of Rhode Island, Kingston, Rhode Island 02881 (United States)

    2014-01-21

    The dynamics properties of a new “next generation” model asphalt system that represents SHRP AAA-1 asphalt using larger molecules than past models is studied using molecular simulation. The system contains 72 molecules distributed over 12 molecule types that range from nonpolar branched alkanes to polar resins and asphaltenes. Molecular weights range from 290 to 890 g/mol. All-atom molecular dynamics simulations conducted at six temperatures from 298.15 to 533.15 K provide a wealth of correlation data. The modified Kohlrausch-Williams-Watts equation was regressed to reorientation time correlation functions and extrapolated to calculate average rotational relaxation times for individual molecules. The rotational relaxation rate of molecules decreased significantly with increasing size and decreasing temperature. Translational self-diffusion coefficients followed an Arrhenius dependence. Similar activation energies of ∼42 kJ/mol were found for all 12 molecules in the model system, while diffusion prefactors spanned an order of magnitude. Viscosities calculated directly at 533.15 K and estimated at lower temperatures using the Debye-Stokes-Einstein relationship were consistent with experimental data for asphalts. The product of diffusion coefficient and rotational relaxation time showed only small changes with temperature above 358.15 K, indicating rotation and translation that couple self-consistently with viscosity. At lower temperatures, rotation slowed more than diffusion.

  17. Two-relaxation-time lattice Boltzmann method and its application to advective-diffusive-reactive transport

    Science.gov (United States)

    Yan, Zhifeng; Yang, Xiaofan; Li, Siliang; Hilpert, Markus

    2017-11-01

    The lattice Boltzmann method (LBM) based on single-relaxation-time (SRT) or multiple-relaxation-time (MRT) collision operators is widely used in simulating flow and transport phenomena. The LBM based on two-relaxation-time (TRT) collision operators possesses strengths from the SRT and MRT LBMs, such as its simple implementation and good numerical stability, although tedious mathematical derivations and presentations of the TRT LBM hinder its application to a broad range of flow and transport phenomena. This paper describes the TRT LBM clearly and provides a pseudocode for easy implementation. Various transport phenomena were simulated using the TRT LBM to illustrate its applications in subsurface environments. These phenomena include advection-diffusion in uniform flow, Taylor dispersion in a pipe, solute transport in a packed column, reactive transport in uniform flow, and bacterial chemotaxis in porous media. The TRT LBM demonstrated good numerical performance in terms of accuracy and stability in predicting these transport phenomena. Therefore, the TRT LBM is a powerful tool to simulate various geophysical and biogeochemical processes in subsurface environments.

  18. Generalized Mittag-Leffler relaxation: clustering-jump continuous-time random walk approach.

    Science.gov (United States)

    Jurlewicz, Agnieszka; Weron, Karina; Teuerle, Marek

    2008-07-01

    A stochastic generalization of renormalization-group transformation for continuous-time random walk processes is proposed. The renormalization consists in replacing the jump events from a randomly sized cluster by a single renormalized (i.e., overall) jump. The clustering of the jumps, followed by the corresponding transformation of the interjump time intervals, yields a new class of coupled continuous-time random walks which, applied to modeling of relaxation, lead to the general power-law properties usually fitted with the empirical Havriliak-Negami function.

  19. Comparative study of acoustic relaxation time of cholesteric liquid crystal and mixtures

    Science.gov (United States)

    Bhave, Manisha G.; Gharde, Rita; Radha, S.

    2016-09-01

    The present study focuses on the relaxation processes in Cholesteric Liquid Crystal and mixtures. We have dispersed two different monomers in CLC to form Polymer dispersed liquid crystals (PDCLCs). PDLC films have a remarkable electro-optical behavior since they can be switched from highly light scattering state (OFF) to transparent state (ON) simply by application of an electric field. We have also doped ferroelectric nano - powder (NP) in CLC. The phase transitions occurred at temperatures lower than those exhibited by the mesogenic component before doping. The viscosity, ultrasonic velocity and density show variation with change in the material as well as temperature. The acoustic relaxation time and ultrasonic attenuation decrease with increase in temperature for CLC and CLC+NP. The parameters of PDCLC2 in comparison with PDCLC1 are more linear in isotropic and anisotropic regions. For PDCLC2 the values reach maximum value at the Cholesteric-isotropic transition.

  20. Relaxation dynamics and thermophysical properties of vegetable oils using time-domain reflectometry.

    Science.gov (United States)

    Sonkamble, Anil A; Sonsale, Rahul P; Kanshette, Mahesh S; Kabara, Komal B; Wananje, Kunal H; Kumbharkhane, Ashok C; Sarode, Arvind V

    2017-04-01

    Dielectric relaxation studies of vegetable oils are important for insights into their hydrogen bonding and intermolecular dynamics. The dielectric relaxation and thermo physical properties of triglycerides present in some vegetable oils have been measured over the frequency range of 10 MHz to 7 GHz in the temperature region 25 to 10 °C using a time-domain reflectometry approach. The frequency and temperature dependence of dielectric constants and dielectric loss factors were determined for coconut, peanut, soya bean, sunflower, palm, and olive oils. The dielectric permittivity spectra for each of the studied vegetable oils are explained using the Debye model with their complex dielectric permittivity analyzed using the Havriliak-Negami equation. The dielectric parameters static permittivity (ε 0), high-frequency limiting static permittivity (ε ∞), average relaxation time (τ 0), and thermodynamic parameters such as free energy (∆F τ), enthalpy (∆H τ), and entropy of activation (∆S τ) were also measured. Calculation and analysis of these thermodynamic parameters agrees with the determined dielectric parameters, giving insights into the temperature dependence of the molecular dynamics of these systems.

  1. Mapping myocardial viability using interleaved T1-T2* weighted imaging.

    Science.gov (United States)

    Li, Gang; Dai, Guangping; Xiang, Bo; Mark, John; Tomanek, Boguslaw; Liu, Hongyu; Deslauriers, Roxanne; Tian, Ganghong

    2004-04-01

    The present study was to evaluate the efficacy of our interleaved T1-T2* weighted imaging for assessing myocardial viability. The left anterior descending coronary artery (LAD) of pig hearts (n = 7) were occluded for 2 h, followed by 1 h reperfusion. After removed from animals, the hearts were perfused in a Langendorff apparatus with a mixture of pig blood and crystalloid solution in 1:1 ratio. T1 relaxation times of the myocardium were measured with a TurboFLASH inversion-recovery sequence. Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) (0.05 mmol/kg body wt) was then injected as a bolus into the aortic perfusion line. The first pass of the contrast agent through the heart was followed using the interleaved T1-T2* imaging sequence. Once the concentration of the contrast agent was in an equilibrium state, T1 relaxation times were measured again. It was found that the percentage recovery of T2* intensity (PRT2*) at the maximum T1 intensity measured during the first pass of the contrast agent with the interleaved T1-T2* imaging was significantly higher in infarcted myocardium than in normal myocardium. Moreover, the regions showing a high T2* percentage recovery on PRT2* maps matched well with the infarcted myocardium demarcated with triphenyl tetrazolium chloride (TTC) staining. We therefore conclude that infarcted myocardium can be delineated using the interleaved T1-T2* imaging method.

  2. New Insight into Time-Temperature Correlation for Polymer Relaxations Ranging from Secondary Relaxation to Terminal Flow: Application of a Universal and Developed WLF Equation

    Directory of Open Access Journals (Sweden)

    Yonggang Shangguan

    2017-11-01

    Full Text Available The three equations involved in the time-temperature superposition (TTS of a polymer, i.e., Williams–Landel–Ferry (WLF, Vogel–Fulcher–Tammann–Hesse (VFTH and the Arrhenius equation, were re-examined, and the mathematical equivalence of the WLF form to the Arrhenius form was revealed. As a result, a developed WLF (DWLF equation was established to describe the temperature dependence of relaxation property for the polymer ranging from secondary relaxation to terminal flow, and its necessary criteria for universal application were proposed. TTS results of viscoelastic behavior for different polymers including isotactic polypropylene (iPP, high density polyethylene (HDPE, low density polyethylene (LDPE and ethylene-propylene rubber (EPR were well achieved by the DWLF equation at high temperatures. Through investigating the phase-separation behavior of poly(methyl methacrylate/poly(styrene-co-maleic anhydride (PMMA/SMA and iPP/EPR blends, it was found that the DWLF equation can describe the phase separation behavior of the amorphous/amorphous blend well, while the nucleation process leads to a smaller shift factor for the crystalline/amorphous blend in the melting temperature region. Either the TTS of polystyrene (PS and PMMA or the secondary relaxations of PMMA and polyvinyl chloride (PVC confirmed that the Arrhenius equation can be valid only in the high temperature region and invalid in the vicinity of glass transition due to the strong dependence of apparent activation energy on temperature; while the DWLF equation can be employed in the whole temperature region including secondary relaxation and from glass transition to terminal relaxation. The theoretical explanation for the universal application of the DWLF equation was also revealed through discussing the influences of free volume and chemical structure on the activation energy of polymer relaxations.

  3. Assaying Biomarkers via Real-Time Measurements of the Effective Relaxation Time of Biofunctionalized Magnetic Nanoparticles Associated with Biotargets

    Directory of Open Access Journals (Sweden)

    Shu-Hsien Liao

    2015-01-01

    Full Text Available An assay of biomarkers consisting of alpha-fetoprotein (AFP is reported. Real-time measurements of the effective relaxation time τeff, when the biofunctionalized magnetic nanoparticles (BMNs were conjugating with biotargets, were made. The BMNs are anti-alpha-fetoprotein (antiAFP coated onto dextran-coated iron oxide nanoparticles labeled as Fe3O4-antiAFP. It was found that the effective relaxation time, τeff, increases as the association of AFP and Fe3O4-antiAFP evolves. We attribute this to the enhanced Brownian motion of BMNs when magnetic clusters are present during the conjugation. We found that saturation magnetization, Ms, increases when the concentration of AFP increases. This is due to the fact that more magnetic clusters are associated in the reagent, and therefore the Ms increases when the concentration of AFP increases. The change of effective relaxation time and saturation magnetization shows a behavior of logistic function, which provides a foundation for assaying an unknown amount of biomolecules. Thus, we demonstrate sensitive platforms for detecting AFP by characterizing τeff. The detection platform is robust and easy to use and shows promise for further use in assaying a broad number of biomarkers.

  4. NMR relaxation times of trabecular bone—reproducibility, relationships to tissue structure and effects of sample freezing

    Science.gov (United States)

    Prantner, Viktória; Isaksson, Hanna; Närväinen, Johanna; Lammentausta, Eveliina; Nissi, Mikko J.; Avela, Janne; Gröhn, Olli H. J.; Jurvelin, Jukka S.

    2010-12-01

    Nuclear magnetic resonance (NMR) spectroscopy provides a potential tool for non-invasive evaluation of the trabecular bone structure. The objective of this study was to determine the reproducibility of the NMR relaxation parameters (T2, Carr-Purcel-T2, T1ρ) for fat and water and relate those to the structural parameters obtained by micro-computed tomography (μCT). Especially, we aimed to evaluate the effect of freezing on the relaxation parameters. For storing bone samples, freezing is the standard procedure during which the biochemical and cellular organization of the bone marrow may be affected. Bovine trabecular bone samples were stored at -20 °C for 7 days and measured by NMR spectroscopy before and after freezing. The reproducibility of NMR relaxation parameters, as expressed by the coefficient of variation, ranged from 3.1% to 27.9%. In fresh samples, some correlations between NMR and structural parameters (Tb.N, Tb.Sp) were significant (e.g. the relaxation rate for T2 of fat versus Tb.Sp: r = -0.716, p bone samples for NMR relaxation studies may provide inferior information about the trabecular bone structure.

  5. Two-step relaxation mode analysis with multiple evolution times applied to all-atom molecular dynamics protein simulation

    Science.gov (United States)

    Karasawa, N.; Mitsutake, A.; Takano, H.

    2017-12-01

    Proteins implement their functionalities when folded into specific three-dimensional structures, and their functions are related to the protein structures and dynamics. Previously, we applied a relaxation mode analysis (RMA) method to protein systems; this method approximately estimates the slow relaxation modes and times via simulation and enables investigation of the dynamic properties underlying the protein structural fluctuations. Recently, two-step RMA with multiple evolution times has been proposed and applied to a slightly complex homopolymer system, i.e., a single [n ] polycatenane. This method can be applied to more complex heteropolymer systems, i.e., protein systems, to estimate the relaxation modes and times more accurately. In two-step RMA, we first perform RMA and obtain rough estimates of the relaxation modes and times. Then, we apply RMA with multiple evolution times to a small number of the slowest relaxation modes obtained in the previous calculation. Herein, we apply this method to the results of principal component analysis (PCA). First, PCA is applied to a 2-μ s molecular dynamics simulation of hen egg-white lysozyme in aqueous solution. Then, the two-step RMA method with multiple evolution times is applied to the obtained principal components. The slow relaxation modes and corresponding relaxation times for the principal components are much improved by the second RMA.

  6. Model-Based Acceleration of Look-Locker T1 Mapping

    Science.gov (United States)

    Tran-Gia, Johannes; Wech, Tobias; Bley, Thorsten; Köstler, Herbert

    2015-01-01

    Mapping the longitudinal relaxation time T1 has widespread applications in clinical MRI as it promises a quantitative comparison of tissue properties across subjects and scanners. Due to the long scan times of conventional methods, however, the use of quantitative MRI in clinical routine is still very limited. In this work, an acceleration of Inversion-Recovery Look-Locker (IR-LL) T1 mapping is presented. A model-based algorithm is used to iteratively enforce an exponential relaxation model to a highly undersampled radially acquired IR-LL dataset obtained after the application of a single global inversion pulse. Using the proposed technique, a T1 map of a single slice with 1.6mm in-plane resolution and 4mm slice thickness can be reconstructed from data acquired in only 6s. A time-consuming segmented IR experiment was used as gold standard for T1 mapping in this work. In the subsequent validation study, the model-based reconstruction of a single-inversion IR-LL dataset exhibited a T1 difference of less than 2.6% compared to the segmented IR-LL reference in a phantom consisting of vials with T1 values between 200ms and 3000ms. In vivo, the T1 difference was smaller than 5.5% in WM and GM of seven healthy volunteers. Additionally, the T1 values are comparable to standard literature values. Despite the high acceleration, all model-based reconstructions were of a visual quality comparable to fully sampled references. Finally, the reproducibility of the T1 mapping method was demonstrated in repeated acquisitions. In conclusion, the presented approach represents a promising way for fast and accurate T1 mapping using radial IR-LL acquisitions without the need of any segmentation. PMID:25860381

  7. Relaxation times and symmetries in the nonlinear optical properties of a two-level system

    Science.gov (United States)

    Paz, J. L.; León-Torres, J. R.; Lascano, Luis; Vera, César Costa

    2017-12-01

    In this work we introduce a methodology for the determination of the longitudinal and transversal relaxation times in a two-level system using symmetry properties of the optical responses in the frequency space ε(Δ1 ,Δ2). Employing the density matrix formalism and a perturbative scheme for the incident field amplitudes in the Four-wave mixing spectroscopy, the nonlinear macroscopic polarization is determined. The collective effects of the thermal reservoir are modeled as a time dependent frequency, whose manifestation is the broadening of the upper level according to a prescribed random function.

  8. Electron spin relaxation time in (110) InGaAs/InAlAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Yokota, Nobuhide; Yasuda, Yusuke; Ikeda, Kazuhiro; Kawaguchi, Hitoshi, E-mail: khitoshi@ms.naist.jp [Graduate School of Materials Science, Nara Institute of Science and Technology 8916-5 Takayama, Ikoma, Nara 630-0192 (Japan)

    2014-07-14

    Electron spin relaxation time τ{sub s} in InGaAs/InAlAs quantum wells (QWs) grown on (110) and (100) InP substrates was investigated by pump-probe transmission measurements. Similar τ{sub s} of 0.83–1.0 ns were measured at room temperature for all the measured (110) and (100) QWs, indicating suppression of the D'yakonov-Perel' spin relaxation mechanism in (110) QWs is not effective in InGaAs/InAlAs QWs as opposed to GaAs/AlGaAs QWs. Contribution of the Bir-Aronov-Pikus mechanism dominant in (110) GaAs/AlGaAs QWs was found to be small in both the (110) and (100) InGaAs/InAlAs QWs from the weak dependences of τ{sub s} on pump intensity at room temperature. These results suggest that the spin relaxation mechanism dominant in InGaAs/InAlAs QWs at a temperature higher than 200 K is the Elliott-Yafet mechanism independent of the crystal orientation among the above three major mechanisms.

  9. Electron spin relaxation time in (110) InGaAs/InAlAs quantum wells

    Science.gov (United States)

    Yokota, Nobuhide; Yasuda, Yusuke; Ikeda, Kazuhiro; Kawaguchi, Hitoshi

    2014-07-01

    Electron spin relaxation time τs in InGaAs/InAlAs quantum wells (QWs) grown on (110) and (100) InP substrates was investigated by pump-probe transmission measurements. Similar τs of 0.83-1.0 ns were measured at room temperature for all the measured (110) and (100) QWs, indicating suppression of the D'yakonov-Perel' spin relaxation mechanism in (110) QWs is not effective in InGaAs/InAlAs QWs as opposed to GaAs/AlGaAs QWs. Contribution of the Bir-Aronov-Pikus mechanism dominant in (110) GaAs/AlGaAs QWs was found to be small in both the (110) and (100) InGaAs/InAlAs QWs from the weak dependences of τs on pump intensity at room temperature. These results suggest that the spin relaxation mechanism dominant in InGaAs/InAlAs QWs at a temperature higher than 200 K is the Elliott-Yafet mechanism independent of the crystal orientation among the above three major mechanisms.

  10. T1 difficulty modulates the attentional blink only when T1 is unmasked

    DEFF Research Database (Denmark)

    Nielsen, Simon; Andersen, Tobias S

    with contrast and exposure. We suggested that the use of pattern masks might have compromised ours, and similar studies. In a new set of experiments we test this hypothesis and vary T1 difficulty with contrast, only this time we omit T1's mask. We find significant AB interference from manipulating T1....... We hypothesize that the rapid onset of T1 induces an attentional capture effect, which increases with contrast. This challenges the use of contrast to manipulate T1 in studies examining how an easy T1 affects the AB – any positive effects may be compromised by the increased capture effect....... processing resources being occupied by T1 when T2 is presented. If so, it is expected that varying T1 difficulty should modulate the AB magnitude. Previous findings however are inconsistent: Christmann & Leuthold (2004) manipulated T1 difficulty by contrast and found that an easy T1 (high contrast) decreased...

  11. Hyperpolarized (129)Xe T (1) in oxygenated and deoxygenated blood

    Science.gov (United States)

    Albert, M. S.; Balamore, D.; Kacher, D. F.; Venkatesh, A. K.; Jolesz, F. A.

    2000-01-01

    The viability of the new technique of hyperpolarized (129)Xe MRI (HypX-MRI) for imaging organs other than the lungs depends on whether the spin-lattice relaxation time, T(1), of (129)Xe is sufficiently long in the blood. In previous experiments by the authors, the T(1) was found to be strongly dependent upon the oxygenation of the blood, with T(1) increasing from about 3 s in deoxygenated samples to about 10 s in oxygenated samples. Contrarily, Tseng et al. (J. Magn. Reson. 1997; 126: 79-86) reported extremely long T(1) values deduced from an indirect experiment in which hyperpolarized (129)Xe was used to create a 'blood-foam'. They found that oxygenation decreased T(1). Pivotal to their experiment is the continual and rapid exchange of hyperpolarized (129)Xe between the gas phase (within blood-foam bubbles) and the dissolved phase (in the skin of the bubbles); this necessitated a complicated analysis to extract the T(1) of (129)Xe in blood. In the present study, the experimental design minimizes gas exchange after the initial bolus of hyperpolarized (129)Xe has been bubbled through the sample. This study confirms that oxygenation increases the T(1) of (129)Xe in blood, from about 4 s in freshly drawn venous blood, to about 13 s in blood oxygenated to arterial levels, and also shifts the red blood cell resonance to higher frequency. Copyright 2000 John Wiley & Sons, Ltd. Abbreviations used BOLD blood oxygen level dependent NOE nuclear overhouses effect PO(2) oxygen partial pressure RBC red blood cells RF radio frequency SNR signal-to-noise ratio.

  12. Caffeine intake inverts the effect of adenosine on myocardial perfusion during stress as measured by T1 mapping.

    Science.gov (United States)

    Kuijpers, Dirkjan; Prakken, Niek H; Vliegenthart, Rozemarijn; van Dijkman, Paul R M; van der Harst, Pim; Oudkerk, Matthijs

    2016-10-01

    Caffeine intake before adenosine stress myocardial perfusion imaging may cause false negative findings. We hypothesized that the antagonistic effect of caffeine can be measured by T1 relaxation times in rest and adenosine stress cardiac magnetic resonance imaging (CMR), as T1 mapping techniques are sensitive to changes in myocardial blood volume. We prospectively analyzed 105 consecutive patients with adenosine stress perfusion CMR on a 1.5-T MRI system. Rest and stress T1 mapping was performed using Modified Look-Locker Inversion recovery. T1 reactivity was defined as difference in T1rest and T1stress (∆T1). Fifteen patients drank coffee within 4 h of CMR (8H caffeine group). Comparison was made to patients without self-reported coffee intake: 50 with normal CMR (control group), 18 with myocardial ischemia, and 12 with myocardial infarction. The national review board approved the study; all patients gave written informed consent. The T1 of -7.8 % (T1rest 975 ± 42 ms, T1stress 898 ± 51 ms, p 8H caffeine group showed reduced T1 reactivity (1.8 %; T1rest 979 ms, T1stress 997 ms) compared to the controls (4.3 %; T1rest 977 ± 40 ms, T1stress 1018 ± 40 ms), p infarcted myocardium showed minimal T1 reactivity (0.2 and 0.3 %, respectively). Caffeine intake inverts the adenosine effect during stress perfusion CMR as measured by T1 mapping. T1 reactivity can assess the adequacy of adenosine-induced stress in perfusion CMR.

  13. Quantitative T1 and T2 mapping in recurrent glioblastomas under bevacizumab: earlier detection of tumor progression compared to conventional MRI

    Energy Technology Data Exchange (ETDEWEB)

    Lescher, Stephanie; Jurcoane, Alina; Veit, Andreas [Hospital of Goethe University, Institute of Neuroradiology, Frankfurt am Main (Germany); Baehr, Oliver [Hospital of Goethe University, Department of Neurology, Dr. Senckenberg Institute of Neurooncology, Frankfurt am Main (Germany); Deichmann, Ralf [Brain Imaging Center, Center for Imaging in Neuroscience, Frankfurt am Main (Germany); Hattingen, Elke [Hospital of Goethe University, Institute of Neuroradiology, Frankfurt am Main (Germany); Hospital of University Bonn, Instiute of Neuroradiology, Bonn (Germany)

    2014-10-07

    Treatment with the humanized anti-vascular endothelial growth factor (VEGF) antibody bevacizumab in glioblastoma patients suppresses contrast enhancement via the reduction of vascular permeability, which does not necessarily indicate real reduction of tumor cell mass. Therefore, other imaging criteria are needed to recognize tumor growth under bevacizumab more reliably. It is still unknown, whether quantitative T1 mapping is useful to monitor the effects of anti-angiogenic therapy or to indicate a tumor progression earlier and more reliable compared to conventional magnetic resonance imaging (MRI) sequences. This raised the question whether quantitative T1 mapping is more suitable to monitor treatment effects of bevacizumab. Conventional and quantitative MRI was performed on six consecutive patients with recurrent glioblastoma before treatment with bevacizumab and every 8 weeks thereafter until further tumor progression. Quantitative T1 maps before and after intravenous application of contrast agent and quantitative T2 maps were performed to calculate serial differential maps and subtraction maps from one time point, subtracting contrast-enhanced T1 maps from non-contrast T1 maps. In five illustrative cases, tumor progression was documented earlier in differential T1 relaxation time (DiffT1) and T2 relaxation time (DiffT2) maps before changes in the conventional MRI studies were obvious. Four patients showed previous prolongation of T1 relaxation time in the DiffT1 maps, suggesting tumor progression, and subtraction maps revealed faint contrast enhancement matching with the areas of T1 prolongation. Our results emphasize that quantitative relaxation time mapping could be a promising method for tumor monitoring in glioblastoma patients under anti-angiogenic therapy. Quantitative T1 mapping seems to detect enhancing tumor earlier than conventional contrast-enhanced T1-weighted images. (orig.)

  14. Quantitative evaluation of Gd-EOB-DTPA uptake in focal liver lesions by using T1 mapping: differences between hepatocellular carcinoma, hepatic focal nodular hyperplasia and cavernous hemangioma

    OpenAIRE

    Peng, Zhenpeng; Li, Chang; Chan, Tao; Cai, Huasong; Luo, Yanji; Dong, Zhi; Li, Zi-Ping; Feng, Shi-Ting

    2017-01-01

    Objectives To investigate the difference of T1 relaxation time on Gd-EOB-DTPA-enhanced MRI in hepatocellular carcinoma (HCC), hepatic focal nodular hyperplasia (FNH) and cavernous hemangioma of liver (CHL), and to quantitatively evaluate the uptake of Gd-EOB-DTPA in these three focal liver lesions (FLLs). Results The T1P of CHL was significantly higher than those of HCC and FNH (P < 0.05). Reduction of T1 relaxation time on hepatobiliary phase could be observed in all three types of lesions. ...

  15. Cardiac T1 Imaging

    OpenAIRE

    Jerosch-Herold, Michael; Kwong, Raymond Y.

    2014-01-01

    T1 mapping of the heart has evolved into a valuable tool to evaluate myocardial tissue properties, with or without contrast injection, including assessment of myocardial edema and free water content, extra-cellular volume (expansion), and most recently cardiomyocyte hypertrophy. The MRI pulse sequence techniques developed for these applications have had to address at least two important considerations for cardiac applications: measure magnetization inversion recoveries during cardiac motion w...

  16. Quantitative evaluation of ischemic myocardial scar tissue by unenhanced T1 mapping using 3.0 Tesla MR scanner.

    Science.gov (United States)

    Okur, Aylin; Kantarcı, Mecit; Kızrak, Yeşim; Yıldız, Sema; Pirimoğlu, Berhan; Karaca, Leyla; Oğul, Hayri; Sevimli, Serdar

    2014-01-01

    We aimed to use a noninvasive method for quantifying T1 values of chronic myocardial infarction scar by cardiac magnetic resonance imaging (MRI), and determine its diagnostic performance. We performed cardiac MRI on 29 consecutive patients with known coronary artery disease (CAD) on 3.0 Tesla MRI scanner. An unenhanced T1 mapping technique was used to calculate T1 relaxation time of myocardial scar tissue, and its diagnostic performance was evaluated. Chronic scar tissue was identified by delayed contrast-enhancement (DE) MRI and T2-weighted images. Sensitivity, specificity, and accuracy values were calculated for T1 mapping using DE images as the gold standard. Four hundred and forty-two segments were analyzed in 26 patients. While myocardial chronic scar was demonstrated in 45 segments on DE images, T1 mapping MRI showed a chronic scar area in 54 segments. T1 relaxation time was higher in chronic scar tissue, compared with remote areas (1314±98 ms vs. 1099±90 ms, P T1 values were shown in areas of myocardium colocalized with areas of DE and normal signal on T2-weighted images. There was a significant correlation between T1 mapping and DE images in evaluation of myocardial wall injury extent (P T1 mapping MRI combined with T2-weighted images might be a feasible imaging modality for detecting chronic myocardial infarction scar tissue.

  17. Application of Generalized Fractional Thermoelasticity Theory with Two Relaxation Times to an Electromagnetothermoelastic Thick Plate

    Directory of Open Access Journals (Sweden)

    A. M. Abd El-Latief

    2016-01-01

    Full Text Available The fractional mathematical model of Maxwell’s equations in an electromagnetic field and the fractional generalized thermoelastic theory associated with two relaxation times are applied to a 1D problem for a thick plate. Laplace transform is used. The solution in Laplace transform domain has been obtained using a direct method and its inversion is calculated numerically using a method based on Fourier series expansion technique. Finally, the effects of the two fractional parameters (thermo and magneto on variable fields distributions are made. Numerical results are represented graphically.

  18. One-Dimensional Problem of a Conducting Viscous Fluid with One Relaxation Time

    Directory of Open Access Journals (Sweden)

    Angail A. Samaan

    2011-01-01

    Full Text Available We introduce a magnetohydrodynamic model of boundary-layer equations for conducting viscous fluids. This model is applied to study the effects of free convection currents with thermal relaxation time on the flow of a viscous conducting fluid. The method of the matrix exponential formulation for these equations is introduced. The resulting formulation together with the Laplace transform technique is applied to a variety problems. The effects of a plane distribution of heat sources on the whole and semispace are studied. Numerical results are given and illustrated graphically for the problem.

  19. Native T1 Relaxation Time and Extracellular Volume Fraction as Accurate Markers of Diffuse Myocardial Fibrosis in Heart Valve Disease - Comparison With Targeted Left Ventricular Myocardial Biopsy -

    Czech Academy of Sciences Publication Activity Database

    Kočková, Radka; Kačer, P.; Pirk, J.; Malý, J.; Sukupová, L.; Sikula, V.; Kotrc, M.; Barciaková, L.; Honsová, E.; Malý, M.; Kautzner, J.; Sedmera, David; Penicka, M.

    2016-01-01

    Roč. 80, č. 5 (2016), s. 1202-1209 ISSN 1346-9843 R&D Projects: GA ČR(CZ) GAP302/11/1308 Institutional support: RVO:67985823 Keywords : cardiac magnetic resonance imaging * echocardiography * fibrosis * speckle tracking * valvular disease Subject RIV: EA - Cell Biology Impact factor: 3.544, year: 2016

  20. Functional lung MRI in chronic obstructive pulmonary disease: comparison of T1 mapping, oxygen-enhanced T1 mapping and dynamic contrast enhanced perfusion.

    Directory of Open Access Journals (Sweden)

    Bertram J Jobst

    Full Text Available Monitoring of regional lung function in interventional COPD trials requires alternative endpoints beyond global parameters such as FEV1. T1 relaxation times of the lung might allow to draw conclusions on tissue composition, blood volume and oxygen fraction. The aim of this study was to evaluate the potential value of lung Magnetic resonance imaging (MRI with native and oxygen-enhanced T1 mapping for the assessment of COPD patients in comparison with contrast enhanced perfusion MRI.20 COPD patients (GOLD I-IV underwent a coronal 2-dimensional inversion recovery snapshot flash sequence (8 slices/lung at room air and during inhalation of pure oxygen, as well as dynamic contrast-enhanced first-pass perfusion imaging. Regional distribution of T1 at room air (T1, oxygen-induced T1 shortening (ΔT1 and peak enhancement were rated by 2 chest radiologists in consensus using a semi-quantitative 3-point scale in a zone-based approach.Abnormal T1 and ΔT1 were highly prevalent in the patient cohort. T1 and ΔT1 correlated positively with perfusion abnormalities (r = 0.81 and r = 0.80; p&0.001, and with each other (r = 0.80; p<0.001. In GOLD stages I and II ΔT1 was normal in 16/29 lung zones with mildly abnormal perfusion (15/16 with abnormal T1. The extent of T1 (r = 0.45; p<0.05, ΔT1 (r = 0.52; p<0.05 and perfusion abnormalities (r = 0.52; p<0.05 showed a moderate correlation with GOLD stage.Native and oxygen-enhanced T1 mapping correlated with lung perfusion deficits and severity of COPD. Under the assumption that T1 at room air correlates with the regional pulmonary blood pool and that oxygen-enhanced T1 reflects lung ventilation, both techniques in combination are principally suitable to characterize ventilation-perfusion imbalance. This appears valuable for the assessment of regional lung characteristics in COPD trials without administration of i.v. contrast.

  1. Dielectric relaxation processes in ethanol/water mixtures measured with attenuated total reflection terahertz time-domain spectroscopy

    DEFF Research Database (Denmark)

    Møller, Uffe; Yada, Hiriyuki; Arikawa, Takashi

    We use attenuated total reflection terahertz time-domain spectroscopy (THz-ATR) to characterize the dielectric relaxation processes of 10 different ethanol/water mixtures at 25°C with ethanol mole fractions of 0-100%.......We use attenuated total reflection terahertz time-domain spectroscopy (THz-ATR) to characterize the dielectric relaxation processes of 10 different ethanol/water mixtures at 25°C with ethanol mole fractions of 0-100%....

  2. Experimental issues in the measurement of multi-component relaxation times in articular cartilage by microscopic MRI

    Science.gov (United States)

    Wang, Nian; Xia, Yang

    2013-10-01

    A number of experimental issues in the measurement of multi-component T2 and T1ρ relaxations in native and enzymatically digested articular cartilage were investigated by microscopic MRI (μMRI). The issues included the bath solutions (physiological saline and phosphate buffered saline (PBS)), the imaging resolution (35-140 μm), the specimen orientations (0° and 55°), and the strength of spin-lock frequencies (0.5-2 kHz) in the T1ρ experiments. In addition to cartilage, the samples of agar gel and doped water solution were also used in the investigation. Two imaging sequences were used: CPMG-SE and MSME. All raw data were analyzed by the non-negative least square (NNLS) method. The MSME sequence was shown to result in the observation of multi-component T2, even in the gel and liquid samples, demonstrating the artificial uncleanness of this sequence in the multi-component measurements. The soaking of cartilage in PBS reduced the observable T2 components to one at both 0° and 55°, suggesting the effect of phosphate ions on proton exchange between different pools of water molecules. The cartilage orientation with respect to the external magnetic field and the spin-lock strengths in the T1ρ experiment both affected the quantification of the multi-component relaxation. The transitions between a mono-component and multi-components in cartilage under various experimental conditions call for the extra caution in interpreting the relaxation results.

  3. Kubo formulas for the shear and bulk viscosity relaxation times and the scalar field theory shear τπ calculation

    Science.gov (United States)

    Czajka, Alina; Jeon, Sangyong

    2017-06-01

    In this paper we provide a quantum field theoretical study on the shear and bulk relaxation times. First, we find Kubo formulas for the shear and the bulk relaxation times, respectively. They are found by examining response functions of the stress-energy tensor. We use general properties of correlation functions and the gravitational Ward identity to parametrize analytical structures of the Green functions describing both sound and diffusion mode. We find that the hydrodynamic limits of the real parts of the respective energy-momentum tensor correlation functions provide us with the method of computing both the shear and bulk viscosity relaxation times. Next, we calculate the shear viscosity relaxation time using the diagrammatic approach in the Keldysh basis for the massless λ ϕ4 theory. We derive a respective integral equation which enables us to compute η τπ and then we extract the shear relaxation time. The relaxation time is shown to be inversely related to the thermal width as it should be.

  4. Effects of aging on muscle T2 relaxation time: difference between fast- and slow-twitch muscles.

    Science.gov (United States)

    Hatakenaka, M; Ueda, M; Ishigami, K; Otsuka, M; Masuda, K

    2001-12-01

    To determine whether the T2 relaxation time of skeletal muscle is affected by aging and to compare the effects of aging between fast- and slow-twitch muscles in a human study. To investigate the mechanisms of age-related changes in T2 relaxation time in an animal (mouse) study. T2 relaxation times of the soleus (slow-twitch, rich in type I fiber) and gastrocnemius (fast-twitch, rich in type II fiber) muscles were examined in 59 healthy human subjects, 22 to 76 years of age, by clinical magnetic resonance imaging. In mice, T2 relaxation times, fat ratios, and extracellular space ratios (extracellular space/intracellular plus extracellular space) of the spinalis (fast-twitch, rich in type II fiber) muscles were also examined (group of 7 old mice, 24-26 months; group of 7 young mice, 8-10 weeks). In the human study, the T2 relaxation time of the gastrocnemius muscle increased significantly with aging (r = 0.53, P muscle did not. In the animal study, the T2 relaxation time of the spinalis muscle was significantly longer (P spinalis muscle significantly wider (P muscle increases with aging, due mainly to increased extracellular space, reflecting age-related type II fiber atrophy.

  5. Measuring hepatic functional reserve using T1 mapping of Gd-EOB-DTPA enhanced 3T MR imaging: A preliminary study comparing with (99m)Tc GSA scintigraphy and signal intensity based parameters.

    Science.gov (United States)

    Nakagawa, Masataka; Namimoto, Tomohiro; Shimizu, Kie; Morita, Kosuke; Sakamoto, Fumi; Oda, Seitaro; Nakaura, Takeshi; Utsunomiya, Daisuke; Shiraishi, Shinya; Yamashita, Yasuyuki

    2017-07-01

    To determine the utility of liver T1-mapping on gadolinium-ethoxybenzyl-diethylenetriamine-pentaacetic acid (Gd-EOB-DTPA) enhanced magnetic resonance (MR) imaging for the measurement of liver functional reserve compared with the signal intensity (SI) based parameters, technetium-99m-galactosyl serum albumin ((99m)Tc-GSA) scintigraphy and indocyanine green (ICG) clearance. This retrospective study included 111 patients (Child-Pugh-A 90; -B 21) performed with both Gd-EOB-DTPA enhanced liver MR imaging and (99m)Tc-GSA (76 patients with ICG). Receiver operating characteristic (ROC) curve analysis was performed to compare diagnostic performances of T1-relaxation-time parameters [pre-(T1pre) and post-contrast (T1hb) Gd-EOB-DTPA], SI based parameters [relative enhancement (RE), liver-to-muscle-ratio (LMR), liver-to-spleen-ratio (LSR)] and (99m)Tc-GSA scintigraphy blood clearance index (HH15)] for Child-Pugh classification. Pearson's correlation was used for comparisons among T1-relaxation-time parameters, SI-based parameters, HH15 and ICG. A significant difference was obtained for Child-Pugh classification with T1hb, ΔT1, all SI based parameters and HH15. T1hb had the highest AUC followed by RE, LMR, LSR, ΔT1, HH15 and T1pre. The correlation coefficients with HH15 were T1pre 0.22, T1hb 0.53, ΔT1 -0.38 of T1 relaxation parameters; RE -0.44, LMR -0.45, LSR -0.43 of SI-based parameters. T1hb was highest for correlation with HH15. The correlation coefficients with ICG were T1pre 0.29, T1hb 0.64, ΔT1 -0.42 of T1 relaxation parameters; RE -0.50, LMR -0.61, LSR -0.58 of SI-based parameters; 0.64 of HH15. Both T1hb and HH15 were highest for correlation with ICG. T1 relaxation time at post-contrast of Gd-EOB-DTPA (T1hb) was strongly correlated with ICG clearance and moderately correlated HH15 with (99m)Tc-GSA. T1hb has the potential to provide robust parameter of liver functional reserve. Copyright © 2017 Elsevier B.V. All rights reserved.

  6. Investigation of the effect of the uranyl ion on proton-spin-relaxation times in aqueous solutions

    Energy Technology Data Exchange (ETDEWEB)

    Renshaw, A.W.

    1983-01-01

    The purpose of this project was to determine the effect of the uranyl ion on the spin-lattice relaxation time of protons in aqueous solutions. A flowmeter using nuclear magnetic resonance (NMR) techniques is being designed for monitoring the flow rate of aqueous solutions which are acidic, contain plutonium and uranium ions, chemical waste, and radioactive waste materials. The spin-lattice relaxation time is critical to the design of a flowmeter using nuclear magnetic resonance techniques. Experimental studies showed that spin-lattice relaxation time did not change for different molar concentrations of sample solutions of uranyl nitrate and uranyl acetate prepared from pure laboratory chemicals dissolved in distilled water. Therefore, it was concluded that the uranyl ion does not contribute to the relaxation process for protons in water.

  7. Phase-field-based multiple-relaxation-time lattice Boltzmann model for incompressible multiphase flows.

    Science.gov (United States)

    Liang, H; Shi, B C; Guo, Z L; Chai, Z H

    2014-05-01

    In this paper, a phase-field-based multiple-relaxation-time lattice Boltzmann (LB) model is proposed for incompressible multiphase flow systems. In this model, one distribution function is used to solve the Chan-Hilliard equation and the other is adopted to solve the Navier-Stokes equations. Unlike previous phase-field-based LB models, a proper source term is incorporated in the interfacial evolution equation such that the Chan-Hilliard equation can be derived exactly and also a pressure distribution is designed to recover the correct hydrodynamic equations. Furthermore, the pressure and velocity fields can be calculated explicitly. A series of numerical tests, including Zalesak's disk rotation, a single vortex, a deformation field, and a static droplet, have been performed to test the accuracy and stability of the present model. The results show that, compared with the previous models, the present model is more stable and achieves an overall improvement in the accuracy of the capturing interface. In addition, compared to the single-relaxation-time LB model, the present model can effectively reduce the spurious velocity and fluctuation of the kinetic energy. Finally, as an application, the Rayleigh-Taylor instability at high Reynolds numbers is investigated.

  8. Enhancing Web applications in radiology with Java: estimating MR imaging relaxation times.

    Science.gov (United States)

    Dagher, A P; Fitzpatrick, M; Flanders, A E; Eng, J

    1998-01-01

    Java is a relatively new programming language that has been used to develop a World Wide Web-based tool for estimating magnetic resonance (MR) imaging relaxation times, thereby demonstrating how Java may be used for Web-based radiology applications beyond improving the user interface of teaching files. A standard processing algorithm coded with Java is downloaded along with the hypertext markup language (HTML) document. The user (client) selects the desired pulse sequence and inputs data obtained from a region of interest on the MR images. The algorithm is used to modify selected MR imaging parameters in an equation that models the phenomenon being evaluated. MR imaging relaxation times are estimated, and confidence intervals and a P value expressing the accuracy of the final results are calculated. Design features such as simplicity, object-oriented programming, and security restrictions allow Java to expand the capabilities of HTML by offering a more versatile user interface that includes dynamic annotations and graphics. Java also allows the client to perform more sophisticated information processing and computation than is usually associated with Web applications. Java is likely to become a standard programming option, and the development of stand-alone Java applications may become more common as Java is integrated into future versions of computer operating systems.

  9. Nuclear magnetic resonance water relaxation time changes in bananas during ripening: a new mechanism.

    Science.gov (United States)

    Ribeiro, Fayene Zeferino; Marconcini, Lucinéia Vizzotto; de Toledo, Ingrid Bertoni; de Vasconcellos Azeredo, Rodrigo Bagueira; Barbosa, Lucio Leonel; Colnago, Luiz Alberto

    2010-09-01

    Nuclear magnetic resonance studies of banana fragments during ripening show an increase on the water transverse relaxation time (T2) and a decrease in water self-diffusion coefficient (D). As T(2) and D are normally directly correlated, we studied these two properties in intact bananas during ripening, in an attempt to rule out the effect of injury on the apparent discrepancies in the behavior of T(2) and D. The results show that injury in bananas causes a decrease in T2 of the water in vacuoles (T(2vac)). They also show that T(2vac) increased and D decreased during ripening, ruling out the injury effect. To explain the apparent discrepancies, we propose a new hypothesis for the increase in T2 values, based on the reduction of Fe3+ ions to Fe2+ by galacturonic acid, produced by the hydrolysis of pectin and a decrease in internal oxygen concentration during ripening. As injury alters T2 values it is necessary to use intact bananas to study relaxation times during ripening. The novel interpretation for the increase in T(2vac) based on reduction of Fe+3 and O2 concentration is an alternative mechanism to that based on the hydrolysis of starch in amyloplasts. Copyright 2010 Society of Chemical Industry.

  10. Simultaneous measurements of T1 and T2 during fast polymerization reaction using continuous wave-free precession NMR method.

    Science.gov (United States)

    Venâncio, Tiago; Colnago, Luiz Alberto

    2012-08-01

    Continuous wave-free precession (CWFP) pulse sequence employing time domain nuclear magnetic resonance spectroscopy (TD-NMR) was used to measure longitudinal (T(1)) and transverse relaxation times (T(2)), during the cure of a commercial epoxy resin (Araldite(TM)) with a 10-min solidification time. The intensity of the NMR signal after the first pulse and in the CWFP regime were used to monitor the concentration of the monomers, and the relaxation times were used to monitor the chain mobility. The main advantage of CWFP over the standard methods to measure relaxation times, inversion recovery (inv-rec) for T(1) and Carr-Purcell-Meiboom-Gill (CPMG) for T(2), is that the measurement of both relaxation times can be performed in a fast and single NMR experiment and, therefore, using a single reaction batch. CWFP is also as fast as the CPMG measurement but at least fivefold faster than the method to obtain T(1) using null point approximation in the inv-rec method. Therefore, the CWFP sequence can be used as a fast and general method to measure relaxation times in polymerization reactions, even with fast solidification time. As a TD-NMR technique, CWFP can be employed in any low-cost bench top TD-NMR equipment commonly used in an academic or industrial laboratory. Copyright © 2012 John Wiley & Sons, Ltd.

  11. Reduced Right Ventricular Native Myocardial T1 in Anderson-Fabry Disease: Comparison to Pulmonary Hypertension and Healthy Controls.

    Directory of Open Access Journals (Sweden)

    Joseph J Pagano

    Full Text Available Anderson-Fabry disease (AFD is characterized by progressive multiorgan accumulation of intracellular sphingolipids due to α-galactosidase A enzyme deficiency, resulting in progressive ventricular hypertrophy, heart failure, arrhythmias, and death. Decreased native (non-contrast left ventricular (LV T1 (longitudinal relaxation time with MRI discriminates AFD from healthy controls or other presentations of concentric hypertrophy, but the right ventricle (RV has not been studied. The aims of the current study were to evaluate native RV T1 values in AFD, with a goal of better understanding the pathophysiology of RV involvement.Native T1 values were measured in the inferior RV wall (RVI, interventricular septum (IVS, and inferior LV (LVI in patients with AFD, patients with pulmonary hypertension, who provided an alternative RV pathological process for comparison, and healthy controls. A minimum wall thickness of 4 mm was selected to minimize partial volume errors in tissue T1 analysis. T1 analysis was performed in 6 subjects with AFD, 6 subjects with PH, and 21 controls. Native T1 values were shorter (adjusted p<0.05 for all comparisons, independent of location, in subjects with AFD (RVI-T1 = 1096±49 ms, IVS-T1 = 1053±41 ms, LVI-T1 = 1072±44 ms compared to both PH (RVI-T1 = 1239±41 ms, IVS-T1 = 1280±123 ms, LVI-T1 = 1274±57 ms and HC (IVS-T1 = 1180±60 ms, LVI-T1 = 1183±45 ms. RVI measurements were not possible in controls due to insufficient wall thickness.Native T1 values appear similarly reduced in the left and right ventricles of individuals with AFD and RV wall thickening, suggesting a common pathology. In contrast, individuals with PH and thickened RVs showed increased native T1 values in both ventricles, suggestive of fibrosis.

  12. Quantitative T1-mapping detects cloudy-enhancing tumor compartments predicting outcome of patients with glioblastoma.

    Science.gov (United States)

    Müller, Andreas; Jurcoane, Alina; Kebir, Sied; Ditter, Philip; Schrader, Felix; Herrlinger, Ulrich; Tzaridis, Theophilos; Mädler, Burkhard; Schild, Hans H; Glas, Martin; Hattingen, Elke

    2017-01-01

    Contrast enhancement of glioblastomas (GBM) is caused by the decrease in relaxation time, T1. Here, we demonstrate that the quantitative measurement of T1 (qT1) discovers a subtle enhancement in GBM patients that is invisible in standard MRI. We assessed the volume change of this "cloudy" enhancement during radio-chemotherapy and its impact on patients' progression-free survival (PFS). We enrolled 18 GBM patients in this observational, prospective cohort study and measured 3T-MRI pre- and post contrast agent with standard T1-weighted (T1w) and with sequences to quantify T1 before radiation, and at 6-week intervals during radio-chemotherapy. We measured contrast enhancement by subtracting pre from post contrast contrast images, yielding relative signal increase ∆T1w and relative T1 shortening ∆qT1. On ∆qT1, we identified a solid and a cloudy-enhancing compartment and evaluated the impact of their therapy-related volume change upon PFS. In ∆qT1 maps cloudy-enhancing compartments were found in all but two patients at baseline and in all patients during therapy. The qT1 decrease in the cloudy-enhancing compartment post contrast was 21.64% versus 1.96% in the contralateral control tissue (P mapping and may represent tumor infiltration. Its early volume decrease predicts a longer PFS in GBM patients during standard radio-chemotherapy. © 2016 The Authors. Cancer Medicine published by John Wiley & Sons Ltd.

  13. Time-dependent alteration in cromakalim-induced relaxation of corpus cavernosum from streptozocin-induced diabetic rats.

    Science.gov (United States)

    Ghasemi, Mehdi; Sadeghipour, Hamed; Asadi, Shahrzad; Dehpour, Ahmad Reza

    2007-09-01

    The purpose of the present study was to investigate the relaxant responses to the ATP-sensitive potassium (K(ATP)) channel opener cromakalim in corpus cavernosum strips from 1-, 2-, 4-, 6-, and 8-week streptozocin-induced diabetic rats. Cromakalim (1 nM-0.1 mM) produced concentration-dependent relaxation in phenylephrine (7.5 microM)-precontracted isolated rat corporal strips. Compared with age-matched control animals, a significant enhancement in cromakalim-induced relaxation of corpus cavernosum was observed in 2-week diabetic animals, whereas the relaxant responses to cromakalim were decreased in 6-and 8-week diabetic animals. However, the cromakalim-induced relaxation was not altered in either 1-week or 4-week rat corporal strips in comparison with corresponding age-matched non-diabetic groups. Preincubation with the K(ATP) channel blocker glibenclamide (10 microM) significantly inhibited the cromakalim-induced relaxation in both non-diabetic and diabetic rat corpus cavernosum, but neither the voltage-dependent K(+) channel (K(V)) antagonist 4-aminopyridine (1 mM) nor the calcium-activated K(+) channel (K(Ca)) antagonist charybdotoxin (0.1 microM) had significant effect on cromakalim-induced relaxation in both control and diabetic rat corporal strips. Relaxation responses to the nitric oxide donor sodium nitroprusside (1 nM-0.1 mM) in diabetic rat corpus cavernosum were similar to that of age-matched controls. These data demonstrated that the relaxant responses to cromakalim were altered in diabetic cavernosal strips in a time dependent manner, suggesting that the period of diabetes mellitus may play a key role in the K(ATP) channels function in rat corpus cavernosum.

  14. The impact of gender difference on operative time in laparoscopic partial nephrectomy for T1 renal tumor and the utility of retroperitoneal fat thickness as a predictor of operative time.

    Science.gov (United States)

    Ito, Hiroki; Makiyama, Kazuhide; Kawahara, Takashi; Osaka, Kimito; Izumi, Koji; Yokomizo, Yumiko; Nakaigawa, Noboru; Yao, Masahiro

    2016-12-12

    To investigate the impact of biological gender on operative parameters, especially operative time, in laparoscopic partial nephrectomy (LPN) for T1 renal tumor. One hundred and eleven (28 female and 83 male) patients and 64 (20 female and 44 male) patients with renal tumors suspected to be RCC cT1aN0M0 who underwent retroperitoneal and transperitoneal LPN, respectively, were analyzed. The influence of sex on operative factors including retroperitoneal fat tissue thickness, determined on CT, was analyzed. The correlation between operative time and gender was evaluated by unpaired t-test and linear logistic regression model. In both retroperitoneal and transperitoneal LPN, the retroperitoneal fat tissue thickness was greater in men than in women. In retroperitoneal LPN, the operative time was significantly longer in men than in women. In contrast, in transperitoneal LPN, no gender difference was observed in regard to the operative time. In retroperitoneal LPN, linear logistic regression assessment showed that gender, retroperitoneal fat tissue thickness, and tumor size were significantly associated with operative time. Coefficient of determination of the prediction model was 0.317. The operative time of retroperitoneal LPN is significantly correlated with gender, maximum tumor diameter, and retroperitoneal fat tissue thickness. We have developed a prediction model for the operative time of retroperitoneal LPN based on preoperative parameters. Interestingly, in transperitoneal LPN, a gender difference in operative time was not apparent, and also predicting operative time might be difficult.

  15. Characterization of the uncertainty of divergence time estimation under relaxed molecular clock models using multiple loci.

    Science.gov (United States)

    Zhu, Tianqi; Dos Reis, Mario; Yang, Ziheng

    2015-03-01

    Genetic sequence data provide information about the distances between species or branch lengths in a phylogeny, but not about the absolute divergence times or the evolutionary rates directly. Bayesian methods for dating species divergences estimate times and rates by assigning priors on them. In particular, the prior on times (node ages on the phylogeny) incorporates information in the fossil record to calibrate the molecular tree. Because times and rates are confounded, our posterior time estimates will not approach point values even if an infinite amount of sequence data are used in the analysis. In a previous study we developed a finite-sites theory to characterize the uncertainty in Bayesian divergence time estimation in analysis of large but finite sequence data sets under a strict molecular clock. As most modern clock dating analyses use more than one locus and are conducted under relaxed clock models, here we extend the theory to the case of relaxed clock analysis of data from multiple loci (site partitions). Uncertainty in posterior time estimates is partitioned into three sources: Sampling errors in the estimates of branch lengths in the tree for each locus due to limited sequence length, variation of substitution rates among lineages and among loci, and uncertainty in fossil calibrations. Using a simple but analogous estimation problem involving the multivariate normal distribution, we predict that as the number of loci ([Formula: see text]) goes to infinity, the variance in posterior time estimates decreases and approaches the infinite-data limit at the rate of 1/[Formula: see text], and the limit is independent of the number of sites in the sequence alignment. We then confirmed the predictions by using computer simulation on phylogenies of two or three species, and by analyzing a real genomic data set for six primate species. Our results suggest that with the fossil calibrations fixed, analyzing multiple loci or site partitions is the most effective way

  16. T1 difficulty modulates the attentional blink only when T1 is unmasked

    DEFF Research Database (Denmark)

    Nielsen, Simon; Andersen, Tobias

    processing resources being occupied by T1 when T2 is presented. If so, it is expected that varying T1 difficulty should modulate the AB magnitude. Previous findings however are inconsistent: Christmann & Leuthold (2004) manipulated T1 difficulty by contrast and found that an easy T1 (high contrast) decreased...... with contrast and exposure. We suggested that the use of pattern masks might have compromised ours, and similar studies. In a new set of experiments we test this hypothesis and vary T1 difficulty with contrast, only this time we omit T1's mask. We find significant AB interference from manipulating T1....... In the easy condition (high contrast) we observe an increase in AB magnitude for SOA's of 200 ms. These findings supports the hypothesis that visual masking has an antagonistic influence on the AB effects of T1 difficulty. The result however, is the opposite of what we should expect from the two stage theory...

  17. Nuclear transfer and anisotropic motional spin phenomena: relaxation time temperature dependence studies of water adsorbed on silica gel. Part IV

    Energy Technology Data Exchange (ETDEWEB)

    Woessner, D.E.; Zimmerman, J.R.

    1962-12-15

    An experimental investigation of the temperature dependence of the nuclear magnetic resonance relaxation phenomena of water vapor adsorbed on silica gel is described. Two-component relaxation data are observed. With temperature increase, the longer T/sub 2/ value decreases while its fractional population increases. These data are shown to be consistent with nuclear transfers between two state environments possessing distinct relaxation characteristics. and a comparison with theory is made. Evidence of a change of surface characteristics is presented; for early experiments, two-component longitudinal relaxation occurs below a transition temperature; in later experiments, only one-component T/sub 1/ behavior is found. A theory for an anisotropic motional model for nuclear magnetic dipole-dipole relaxation on surfaces is presented. The motional model is random reorientation of the interproton vector about an axis normal to the surface that occurs much faster than the time dependence of the angle between the vector and this axis. The relaxation processes are thus related to multiple nuclear correlation times. Consequences of an anisotropic model agree with experimental observations. (auth)

  18. A multiple relaxation time extension of the constant speed kinetic model

    Science.gov (United States)

    Zadehgol, Abed; Ashrafizaadeh, Mahmud

    2016-02-01

    In this work, a multiple relaxation time (MRT) extension of the recently introduced constant speed kinetic model (CSKM) is proposed. The CSKM, which is an entropic kinetic model and based on unconventional entropies of Burg and Tssalis, was introduced in [A. Zadehgol and M. Ashrafizaadeh, J. Comput. Phys. 274, 803 (2014)]; [A. Zadehgol Phys. Rev. E 91, 063311 (2015)] as an extension of the model of Boghosian et al. [Phys. Rev. E 68, 025103 (2003)] in the limit of fixed speed continuous velocities. The present extension improves the stability of the previous models at very high Reynolds numbers, while allowing for a more convenient orthogonal lattice. The model is verified by solving the following benchmark problems: (i) the lid driven square cavity and (ii) the Kelvin-Helmholtz instability of thin shear layers in a doubly periodic square domain.

  19. Intracerebral pH affects the T2 relaxation time of brain tissue

    Energy Technology Data Exchange (ETDEWEB)

    Schilling, A.M.; Blankenburg, F.B.; Bernarding, J.; Heidenreich, J.O.; Wolf, K.J. [Department of Radiology, University Hospital Benjamin Franklin, Free University Berlin, Hindenburgdamm 30, 12200 Berlin (Germany)

    2002-12-01

    Signal changes in activated brain areas are detectable by MRI and MR spectroscopy (MRS). Shifts in pH occur during brain activation. Our aim was to investigate the relationship between changes in pH and T2 relaxation times. T2 was determined in vitro at 24 MHz in various liquids at different pH using a Carr-Purcell-Meiboom-Gill (CPMG) spin-echo sequence. We also studied five Fisher rats were studied at 2.4 tesla with a double-tuneable surface coil. After baseline measurements, potassium cyanide was injected, producing intracerebral acidosis. Alternating series of 1H CPMG spin-echo sequences and 31P spectra were acquired. True T2 relaxation times were calculated from a CPMG multi-echo train. Changes in intracellular pH determined from 31P spectra. In vitro measurements demonstrated a correlation between T2 and pH that could be described by a quadratic fit curve. Depending on the initial pH, changes of 0.2 induced changes in T2 of up to 150 ms. In vivo measurements confirmed these findings. After intraperitoneal injection of a sublethal dose of cyanide, T2 decreased by about 5% in four cases, followed by recovery after 2 h. The in vitro measurements demonstrated that changes in pH can lead to significant signal change on T2- or T2*- weighted images. The dependence of T2 on pH in vitro was confirmed in vivo; it may contribute to signal change in activated brain areas. (orig.)

  20. Relaxation time: a proton NMR-based approach as a metric to measure reactivity of engineered nanomaterials

    Science.gov (United States)

    Paruthi, Archini; Misra, Superb K.

    2017-08-01

    The toxicological impact of engineered nanoparticles in environmental or biological milieu is very difficult to predict and control because of the complexity of interactions of nanoparticles with the varied constituents in the suspended media. Nanoparticles are different from their bulk counterparts due to their high surface area-to-volume ratio per unit mass, which plays a vital role in bioavailability of these nanoparticles to its surroundings. This study explores how changes in the spin-spin nuclear relaxation time can be used to gauge the availability of surface area and suspension stability of selected nanoparticles (CuO, ZnO, and SiO2), in a range of simulated media. Spin-spin nuclear relaxation time can be mathematically correlated to wetted surface area, which is well backed up by the data of hydrodynamic size measurements and suspension stability. We monitored the change in spin-spin relaxation time for all the nanoparticles, over a range of concentrations (2.5 -100 ppm) in deionized water and artificial seawater. Selective concentrations of nanoparticle suspensions were subjected for temporal studies over a period of 48 hrs to understand the concept of spin-spin nuclear relaxation time-based reactivity of nanoparticle suspension. The nanoparticles showed high degree of agglomeration, when suspended in artificial seawater. This was captured by a decrease in spin-spin nuclear relaxation time and also an increment in the hydrodynamic size of the nanoparticles.

  1. Temperature Dependence of Spin Relaxation Time in InAs Columnar Quantum Dots at 10 to 150 K

    Science.gov (United States)

    Nakanishi, Sota; Sasayama, Kazutoshi; Oyanagi, Yoshitsugu; Yamaguchi, Ryo; Lu, Shulong; Li, Lianhe; Fiore, Andrea; Tackeuchi, Atsushi

    2012-04-01

    We have investigated carrier spin relaxation in InAs columnar quantum dots (CQDs) using time-resolved photoluminescence measurement. The CQDs were formed by depositing a 1.8 monolayer InAs seed dot layer and a short-period GaAs/InAs superlattice (SL). The spin relaxations of the 3- and 35-period SL CQDs show double exponential decay up to 50 and 130 K, respectively. The spin relaxation times of the fast component, whose amplitudes are 4-11 times larger than that of the slow component, are around 100 ps for the two samples. For the 3-period SL CQDs, the fast spin relaxation time shows no temperature dependence up to around 50 K, indicating the relevance of the Bir-Aronov-Pikus process. The slow spin relaxation time of the 35-period SL CQDs was found to decrease from 3.42 ns at 10 K to 0.849 ns at 130 K. This large change may be explained by the Elliott-Yafet process considering acoustic phonon scattering.

  2. Development of rapid methods for relaxation time mapping and motion estimation using magnetic resonance imaging

    Energy Technology Data Exchange (ETDEWEB)

    Gilani, Syed Irtiza Ali

    2008-09-15

    Recent technological developments in the field of magnetic resonance imaging have resulted in advanced techniques that can reduce the total time to acquire images. For applications such as relaxation time mapping, which enables improved visualisation of in vivo structures, rapid imaging techniques are highly desirable. TAPIR is a Look- Locker-based sequence for high-resolution, multislice T{sub 1} relaxation time mapping. Despite the high accuracy and precision of TAPIR, an improvement in the k-space sampling trajectory is desired to acquire data in clinically acceptable times. In this thesis, a new trajectory, termed line-sharing, is introduced for TAPIR that can potentially reduce the acquisition time by 40 %. Additionally, the line-sharing method was compared with the GRAPPA parallel imaging method. These methods were employed to reconstruct time-point images from the data acquired on a 4T high-field MR research scanner. Multislice, multipoint in vivo results obtained using these methods are presented. Despite improvement in acquisition speed, through line-sharing, for example, motion remains a problem and artefact-free data cannot always be obtained. Therefore, in this thesis, a rapid technique is introduced to estimate in-plane motion. The presented technique is based on calculating the in-plane motion parameters, i.e., translation and rotation, by registering the low-resolution MR images. The rotation estimation method is based on the pseudo-polar FFT, where the Fourier domain is composed of frequencies that reside in an oversampled set of non-angularly, equispaced points. The essence of the method is that unlike other Fourier-based registration schemes, the employed approach does not require any interpolation to calculate the pseudo-polar FFT grid coordinates. Translation parameters are estimated by the phase correlation method. However, instead of two-dimensional analysis of the phase correlation matrix, a low complexity subspace identification of the phase

  3. Assessment of clinical signs of liver cirrhosis using T1 mapping on Gd-EOB-DTPA-enhanced 3T MRI.

    Directory of Open Access Journals (Sweden)

    Michael Haimerl

    Full Text Available OBJECTIVES: To assess the differences between normal and cirrhotic livers by means of T1 mapping of liver parenchyma on gadoxetic acid (Gd-EOB-DTPA-enhanced 3 Tesla (3T MR imaging (MRI. METHODS: 162 patients with normal (n = 96 and cirrhotic livers (n = 66; Child-Pugh class A, n = 30; B, n = 28; C, n = 8 underwent Gd-EOB-DTPA-enhanced 3T MRI. To obtain T1 maps, two TurboFLASH sequences (TI = 400 ms and 1000 ms before and 20 min after Gd-EOB-DTPA administration were acquired. T1 relaxation times of the liver and the reduction rate between pre- and post-contrast enhancement images were measured. RESULTS: The T1 relaxation times for Gd-EOB-DTPA-enhanced MRI showed significant differences between patients with normal liver function and patients with Child-Pugh class A, B, and C (p < 0.001. The T1 relaxation times showed a constant significant increase from Child-Pugh class A up to class C (Child-Pugh class A, 335 ms ± 80 ms; B, 431 ms ± 75 ms; C, 557 ms ± 99 ms; Child-Pugh A to B, p < 0.001; Child-Pugh A to C, p < 0.001; Child-Pugh B to C, p < 0.001 and a constant decrease of the reduction rate of T1 relaxation times (Child-Pugh class A, 57.1% ± 8.8%; B, 44.3% ± 10.2%, C, 29.9% ± 6.9%; Child-Pugh A to B, p < 0.001; Child-Pugh A to C,p < 0.001; Child-Pugh B to C, p < 0.001. CONCLUSION: Gd-EOB-DTPA-enhanced T1 mapping of the liver parenchyma may present a useful method for determining severity of liver cirrhosis.

  4. An anisotropic linear thermo-viscoelastic constitutive law - Elastic relaxation and thermal expansion creep in the time domain

    Science.gov (United States)

    Pettermann, Heinz E.; DeSimone, Antonio

    2017-09-01

    A constitutive material law for linear thermo-viscoelasticity in the time domain is presented. The time-dependent relaxation formulation is given for full anisotropy, i.e., both the elastic and the viscous properties are anisotropic. Thereby, each element of the relaxation tensor is described by its own and independent Prony series expansion. Exceeding common viscoelasticity, time-dependent thermal expansion relaxation/creep is treated as inherent material behavior. The pertinent equations are derived and an incremental, implicit time integration scheme is presented. The developments are implemented into an implicit FEM software for orthotropic material symmetry under plane stress assumption. Even if this is a reduced problem, all essential features are present and allow for the entire verification and validation of the approach. Various simulations on isotropic and orthotropic problems are carried out to demonstrate the material behavior under investigation.

  5. Characteristics of Viscoelastic Crustal Deformation Following a Megathrust Earthquake: Discrepancy Between the Apparent and Intrinsic Relaxation Time Constants

    Science.gov (United States)

    Fukahata, Yukitoshi; Matsu'ura, Mitsuhiro

    2017-12-01

    The viscoelastic deformation of an elastic-viscoelastic composite system is significantly different from that of a simple viscoelastic medium. Here, we show that complicated transient deformation due to viscoelastic stress relaxation after a megathrust earthquake can occur even in a very simple situation, in which an elastic surface layer (lithosphere) is underlain by a viscoelastic substratum (asthenosphere) under gravity. Although the overall decay rate of the system is controlled by the intrinsic relaxation time constant of the asthenosphere, the apparent decay time constant at each observation point is significantly different from place to place and generally much longer than the intrinsic relaxation time constant of the asthenosphere. It is also not rare that the sense of displacement rate is reversed during the viscoelastic relaxation. If we do not bear these points in mind, we may draw false conclusions from observed deformation data. Such complicated transient behavior can be explained mathematically from the characteristics of viscoelastic solution: for an elastic-viscoelastic layered half-space, the viscoelastic solution is expressed as superposition of three decaying components with different relaxation time constants that depend on wavelength.

  6. Understanding generalized inversions of nuclear magnetic resonance transverse relaxation time in porous media

    Science.gov (United States)

    Mitchell, J.; Chandrasekera, T. C.

    2014-12-01

    The nuclear magnetic resonance transverse relaxation time T2, measured using the Carr-Purcell-Meiboom-Gill (CPMG) experiment, is a powerful method for obtaining unique information on liquids confined in porous media. Furthermore, T2 provides structural information on the porous material itself and has many applications in petrophysics, biophysics, and chemical engineering. Robust interpretation of T2 distributions demands appropriate processing of the measured data since T2 is influenced by diffusion through magnetic field inhomogeneities occurring at the pore scale, caused by the liquid/solid susceptibility contrast. Previously, we introduced a generic model for the diffusion exponent of the form -ant_e^k (where n is the number and te the temporal separation of spin echoes, and a is a composite diffusion parameter) in order to distinguish the influence of relaxation and diffusion in CPMG data. Here, we improve the analysis by introducing an automatic search for the optimum power k that best describes the diffusion behavior. This automated method is more efficient than the manual trial-and-error grid search adopted previously, and avoids variability through subjective judgments of experimentalists. Although our method does not avoid the inherent assumption that the diffusion exponent depends on a single k value, we show through simulation and experiment that it is robust in measurements of heterogeneous systems that violate this assumption. In this way, we obtain quantitative T2 distributions from complicated porous structures and demonstrate the analysis with examples of ceramics used for filtration and catalysis, and limestone of relevance to the construction and petroleum industries.

  7. Nonadiabatic dynamics of electron transfer in solution: explicit and implicit solvent treatments that include multiple relaxation time scales.

    Science.gov (United States)

    Schwerdtfeger, Christine A; Soudackov, Alexander V; Hammes-Schiffer, Sharon

    2014-01-21

    The development of efficient theoretical methods for describing electron transfer (ET) reactions in condensed phases is important for a variety of chemical and biological applications. Previously, dynamical dielectric continuum theory was used to derive Langevin equations for a single collective solvent coordinate describing ET in a polar solvent. In this theory, the parameters are directly related to the physical properties of the system and can be determined from experimental data or explicit molecular dynamics simulations. Herein, we combine these Langevin equations with surface hopping nonadiabatic dynamics methods to calculate the rate constants for thermal ET reactions in polar solvents for a wide range of electronic couplings and reaction free energies. Comparison of explicit and implicit solvent calculations illustrates that the mapping from explicit to implicit solvent models is valid even for solvents exhibiting complex relaxation behavior with multiple relaxation time scales and a short-time inertial response. The rate constants calculated for implicit solvent models with a single solvent relaxation time scale corresponding to water, acetonitrile, and methanol agree well with analytical theories in the Golden rule and solvent-controlled regimes, as well as in the intermediate regime. The implicit solvent models with two relaxation time scales are in qualitative agreement with the analytical theories but quantitatively overestimate the rate constants compared to these theories. Analysis of these simulations elucidates the importance of multiple relaxation time scales and the inertial component of the solvent response, as well as potential shortcomings of the analytical theories based on single time scale solvent relaxation models. This implicit solvent approach will enable the simulation of a wide range of ET reactions via the stochastic dynamics of a single collective solvent coordinate with parameters that are relevant to experimentally accessible

  8. PP084. Magnetic resonance imaging measurements of T2 relaxation times within contrasting regions of murine placenta is dependent upon blood flow.

    Science.gov (United States)

    Bobek, G; Stait-Gardner, T; Surmon, L; Makris, A; Price, W S; Hennessy, A

    2012-07-01

    It has been postulated that reduced placental perfusion as a result of abnormal placental implantation is the initiating event that leads to the maternal symptoms of preeclampsia. To be able to directly measure blood flow and perfusion in the placenta in experimental models of preeclampsia would provide valuable insight into the structural abnormalities of this syndrome. Magnetic resonance imaging (MRI) offers visualization of anatomy and analysis of changes in tissue morphology and function including blood flow and perfusion. The major source of image contrast in MRI comes from the variation in relaxation times between tissues. Previously, human placenta has appeared as fairly homogeneous in studies of T1 and T2 relaxation times, with no internal morphology apparent. The aim of this study was to investigate, using much higher field strengths (11.7Tesla) and much higher resolution than have been used previously, whether structural inhomogeneities in the placenta can be discerned by T2 mapping and whether T2 mapping is capable of detecting structural abnormalities that may affect blood flow in a preeclamptic placenta. Magnetic resonance images were acquired on an anaesthetised C57BL/6JArc mouse placed in a vertical animal probe using a Bruker Avance 11.7Tesla wide-bore spectrometer with micro-imaging probe capable of generating gradients of 0.45T/m. T2 measurements were acquired using an MSME sequence protocol (Bruker MSME-T2-map) with an in-plane resolution of 0.1-0.2mm. Matlab was used to generate R2 (i.e., 1/T2) maps from the acquired data with the T2 values being calculated from selected regions of interest within 5 individual placenta. Additional T2 measurements were acquired on the same slices immediately after blood flow was reduced to zero. Three distinct regions of T2 contrast were discerned in the mouse placenta, likely correlating to the labrynthine, junctional and decidual zones. The contrast between the inner two regions was substantially abrogated when

  9. Myocardial T1 and T2 mapping at 3 T: reference values, influencing factors and implications

    Science.gov (United States)

    2013-01-01

    Background Myocardial T1 and T2 mapping using cardiovascular magnetic resonance (CMR) are promising to improve tissue characterization and early disease detection. This study aimed at analyzing the feasibility of T1 and T2 mapping at 3 T and providing reference values. Methods Sixty healthy volunteers (30 males/females, each 20 from 20–39 years, 40–59 years, 60–80 years) underwent left-ventricular T1 and T2 mapping in 3 short-axis slices at 3 T. For T2 mapping, 3 single-shot steady-state free precession (SSFP) images with different T2 preparation times were acquired. For T1 mapping, modified Look-Locker inversion recovery technique with 11 single shot SSFP images was used before and after injection of gadolinium contrast. T1 and T2 relaxation times were quantified for each slice and each myocardial segment. Results Mean T2 and T1 (pre-/post-contrast) times were: 44.1 ms/1157.1 ms/427.3 ms (base), 45.1 ms/1158.7 ms/411.2 ms (middle), 46.9 ms/1180.6 ms/399.7 ms (apex). T2 and pre-contrast T1 increased from base to apex, post-contrast T1 decreased. Relevant inter-subject variability was apparent (scatter factor 1.08/1.05/1.11 for T2/pre-contrast T1/post-contrast T1). T2 and post-contrast T1 were influenced by heart rate (p T1 by age (p T1 (r = 0.91; r = 0.93) were high. T2 maps: 97.7% of all segments were diagnostic and 2.3% were excluded (susceptibility artifact). T1 maps (pre-/post-contrast): 91.6%/93.9% were diagnostic, 8.4%/6.1% were excluded (predominantly susceptibility artifact 7.7%/3.2%). Conclusions Myocardial T2 and T1 reference values for the specific CMR setting are provided. The diagnostic impact of the high inter-subject variability of T2 and T1 relaxation times requires further investigation. PMID:23777327

  10. Light-induced refractive-index modifications in dielectric thin films: experimental determination of relaxation time and amplitude.

    Science.gov (United States)

    Monneret, S; Tisserand, S; Flory, F; Rigneault, H

    1996-09-01

    A two-beam setup based on the totally reflecting prism coupler is shown to be a powerful means of characterizing light-induced refractive-index modifications in dielectric thin films. Rise and relaxation times and amplitudes of thin-film refractive-index variations can be measured. Some developments of the electromagnetic theory of prism coupling are presented for Gaussian incident beams. Measurements made on a single Ta(2)O(5) layer deposited on a silica glass are presented. Relaxation times of a few milliseconds reveal the thermal origin of the phenomena. The thermal nonlinear coefficient of this Ta(2)O(5) layer is nearly 10(-15) m(2)/W.

  11. Current T1 and T2 mapping techniques applied with simple thresholds cannot discriminate acute from chronic myocadial infarction on an individual patient basis: a pilot study

    OpenAIRE

    von Knobelsdorff-Brenkenhoff, F.; Prothmann, M.; Dieringer, M.A.; WASSMUTH, R.; Rudolph, A. (Anja); Utz, W.; Traber, J.; Greiser, A; Niendorf, T.; Schulz-Menger, J.

    2016-01-01

    BACKGROUND: Studying T1- and T2-mapping for discrimination of acute from chronic myocardial infarction (AMI, CMI). METHODS: Eight patients with AMI underwent CMR at 3 T acutely and after >3 months. Imaging techniques included: T2-weighted imaging, late enhancement (LGE), T2-mapping, native and post-contrast T1-mapping. Myocardial T2- and T1-relaxation times were determined for every voxel. Abnormal voxels as defined by having T2- and T1-values beyond a predefined threshold (T2 > 50 ms, native...

  12. Real-Time Observation of Ultrafast Intraband Relaxation and Exciton Multiplication in PbS Quantum Dots

    KAUST Repository

    El-Ballouli, Ala’a O.

    2014-03-19

    We examine ultrafast intraconduction band relaxation and multiple-exciton generation (MEG) in PbS quantum dots (QDs) using transient absorption spectroscopy with 120 fs temporal resolution. The intraconduction band relaxation can be directly and excellently resolved spectrally and temporally by applying broadband pump-probe spectroscopy to excite and detect the wavelengths around the exciton absorption peak, which is located in the near-infrared region. The time-resolved data unambiguously demonstrate that the intraband relaxation time progressively increases as the pump-photon energy increases. Moreover, the relaxation time becomes much shorter as the size of the QDs decreases, indicating the crucial role of spatial confinement in the intraband relaxation process. Additionally, our results reveal the systematic scaling of the intraband relaxation time with both excess energy above the effective energy band gap and QD size. We also assess MEG in different sizes of the QDs. Under the condition of high-energy photon excitation, which is well above the MEG energy threshold, ultrafast bleach recovery due to the nonradiative Auger recombination of the multiple electron-hole pairs provides conclusive experimental evidence for the presence of MEG. For instance, we achieved quantum efficiencies of 159, 129 and 106% per single-absorbed photon at pump photoexcition of three times the band gap for QDs with band gaps of 880 nm (1.41 eV), 1000 nm (1.24 eV) and 1210 nm (1.0 eV), respectively. These findings demonstrate clearly that the efficiency of transferring excess photon energy to carrier multiplication is significantly increased in smaller QDs compared with larger ones. Finally, we discuss the Auger recombination dynamics of the multiple electron-hole pairs as a function of QD size.

  13. Two-relaxation-time lattice Boltzmann method for the anisotropic dispersive Henry problem

    Science.gov (United States)

    Servan-Camas, Borja; Tsai, Frank T.-C.

    2010-02-01

    This study develops a lattice Boltzmann method (LBM) with a two-relaxation-time collision operator (TRT) to cope with anisotropic heterogeneous hydraulic conductivity and anisotropic velocity-dependent hydrodynamic dispersion in the saltwater intrusion problem. The directional-speed-of-sound technique is further developed to address anisotropic hydraulic conductivity and dispersion tensors. Forcing terms are introduced in the LBM to correct numerical errors that arise during the recovery procedure and to describe the sink/source terms in the flow and transport equations. In order to facilitate the LBM implementation, the forcing terms are combined with the equilibrium distribution functions (EDFs) to create pseudo-EDFs. This study performs linear stability analysis and derives LBM stability domains to solve the anisotropic advection-dispersion equation. The stability domains are used to select the time step at which the lattice Boltzmann method provides stable solutions to the numerical examples. The LBM was implemented for the anisotropic dispersive Henry problem with high ratios of longitudinal to transverse dispersivities, and the results compared well to the solutions in the work of Abarca et al. (2007).

  14. Multiple-relaxation-time lattice Boltzmann simulation for flow, mass transfer, and adsorption in porous media

    Science.gov (United States)

    Ma, Qiang; Chen, Zhenqian; Liu, Hao

    2017-07-01

    In this paper, to predict the dynamics behaviors of flow and mass transfer with adsorption phenomena in porous media at the representative elementary volume (REV) scale, a multiple-relaxation-time (MRT) lattice Boltzmann (LB) model for the convection-diffusion equation is developed to solve the transfer problem with an unsteady source term in porous media. Utilizing the Chapman-Enskog analysis, the modified MRT-LB model can recover the macroscopic governing equations at the REV scale. The coupled MRT-LB model for momentum and mass transfer is validated by comparing with the finite-difference method and the analytical solution. Moreover, using the MRT-LB method coupled with the linear driving force model, the fluid transfer and adsorption behaviors of the carbon dioxide in a porous fixed bed are explored. The breakthrough curve of adsorption from MRT-LB simulation is compared with the experimental data and the finite-element solution, and the transient concentration distributions of the carbon dioxide along the porous fixed bed are elaborated upon in detail. In addition, the MRT-LB simulation results show that the appearance time of the breakthrough point in the breakthrough curve is advanced as the mass transfer resistance in the linear driving force model increases; however, the saturation point is prolonged inversely.

  15. 7 Tesla quantitative hip MRI: T1, T2 and T2* mapping of hip cartilage in healthy volunteers

    Energy Technology Data Exchange (ETDEWEB)

    Lazik, Andrea; Theysohn, Jens M.; Geis, Christina [University Hospital Essen, Department of Diagnostic and Interventional Radiology and Neuroradiology, Essen (Germany); Johst, Soeren; Kraff, Oliver [University of Duisburg-Essen, Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen (Germany); Ladd, Mark E. [University Hospital Essen, Department of Diagnostic and Interventional Radiology and Neuroradiology, Essen (Germany); University of Duisburg-Essen, Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen (Germany); German Cancer Research Center (DKFZ), Medical Physics in Radiology, Heidelberg (Germany); Quick, Harald H. [University of Duisburg-Essen, Erwin L. Hahn Institute for Magnetic Resonance Imaging, Essen (Germany); University Hospital Essen, High Field and Hybrid MR Imaging, Essen (Germany)

    2016-05-15

    To evaluate the technical feasibility and applicability of quantitative MR techniques (delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T2 mapping, T2* mapping) at 7 T MRI for assessing hip cartilage. Hips of 11 healthy volunteers were examined at 7 T MRI with an 8-channel radiofrequency transmit/receive body coil using multi-echo sequences for T2 and T2* mapping and a dual flip angle gradient-echo sequence before (T1{sub 0}) and after intravenous contrast agent administration (T1{sub Gd}; 0.2 mmol/kg Gd-DTPA{sup 2-} followed by 0.5 h of walking and 0.5 h of rest) for dGEMRIC. Relaxation times of cartilage were measured manually in 10 regions of interest. Pearson's correlations between R1{sub delta} = 1/T1{sub Gd} - 1/T1{sub 0} and T1{sub Gd} and between T2 and T2* were calculated. Image quality and the delineation of acetabular and femoral cartilage in the relaxation time maps were evaluated using discrete rating scales. High correlations were found between R1{sub delta} and T1{sub Gd} and between T2 and T2* relaxation times (all p < 0.01). All techniques delivered diagnostic image quality, with best delineation of femoral and acetabular cartilage in the T2* maps (mean 3.2 out of a maximum of 4 points). T1, T2 and T2* mapping of hip cartilage with diagnostic image quality is feasible at 7 T. To perform dGEMRIC at 7 T, pre-contrast T1 mapping can be omitted. (orig.)

  16. Characteristics and effectiveness of vasodilatory and pressor compensation for reduced relaxation time during rhythmic forearm contractions.

    Science.gov (United States)

    Bentley, Robert F; Poitras, Veronica J; Hong, Terrence; Tschakovsky, Michael E

    2017-06-01

    What is the central question of this study? Reduced relaxation time between contractions in exercise requires increased vasodilatation and/or pressor response to prevent hypoperfusion and potential compromise to exercise tolerance. However, it remains unknown whether and to what extent local vasodilatation and/or systemic pressor compensation occurs and whether the efficacy of compensation is exercise intensity dependent. What is the main finding and its importance? We demonstrate that in a forearm exercise model vasodilatory but not pressor compensation occurs and is adequate to prevent hypoperfusion below but not above ∼40% peak work rate. Inadequate compensation occurs with exercise still well inside the submaximal domain, despite a vasodilatory reserve, and compromises exercise performance. During muscle contraction in rhythmic exercise, muscle blood flow is significantly impeded by microvascular compression. The purpose of this study was to establish the nature and magnitude of vasodilatory and/or pressor compensatory responses during forearm exercise in the face of an increased duration of mechanical microvascular compression, and whether the effectiveness of such compensation was exercise intensity dependent. Seven healthy males (21.0 ± 1.8 years old) completed progressive forearm exercise (24.5 N every 3 min; 2 s contraction-4 s relaxation duty cycle) in two conditions: control (CON), 2 s 100 mmHg forearm cuff inflation during contraction; and impedance (IMP), extension of cuff inflation 2 s beyond contraction. Forearm blood flow (in millilitres per minute); brachial artery Doppler and echo ultrasound), mean arterial blood pressure (in millimetres of mercury; finger photoplethysmography) and exercising forearm venous effluent (antecubital vein catheter) measurements revealed an exercise intensity-dependent compensatory vasodilatation effectiveness whereby increased vasodilatation fully protected forearm blood flow up to the 30% exercise

  17. New Techniques for Cartilage Magnetic Resonance Imaging Relaxation Time Analysis: Texture Analysis of Flattened Cartilage and Localized Intra- and Inter-subject Comparisons

    OpenAIRE

    Carballido-Gamio, Julio; Link, Thomas M.; Majumdar, Sharmila

    2008-01-01

    MR relaxation time measurements of knee cartilage have shown potential to characterize knee osteoarthritis (OA). In this work, techniques that allow localized intra- and inter-subject comparisons of cartilage relaxation times, as well as cartilage flattening for texture analysis parallel and perpendicular to the natural cartilage layers, are presented. The localized comparisons are based on the registration of bone structures and the assignment of relaxation time feature vectors to each point...

  18. On a two-relaxation-time D2Q9 lattice Boltzmann model for the Navier-Stokes equations

    Science.gov (United States)

    Zhao, Weifeng; Wang, Liang; Yong, Wen-An

    2018-02-01

    In this paper, we are concerned with the stability of some lattice kinetic schemes. First, we show that a recently proposed lattice kinetic scheme is a two-relaxation-time model different from those in the literature. Second, we analyze the stability of the model by verifying the Onsager-like relation. In addition, a necessary stability criterion for hyperbolic relaxation systems is adapted to the lattice Boltzmann method. As an application of this criterion, we find some necessary stability conditions for a previously proposed lattice kinetic scheme. Numerical experiments are conducted to validate the necessary stability conditions.

  19. Diffusion relaxation times of nonequilibrium isolated small bodies and their solid phase ensembles to equilibrium states

    Science.gov (United States)

    Tovbin, Yu. K.

    2017-08-01

    The possibility of obtaining analytical estimates in a diffusion approximation of the times needed by nonequilibrium small bodies to relax to their equilibrium states based on knowledge of the mass transfer coefficient is considered. This coefficient is expressed as the product of the self-diffusion coefficient and the thermodynamic factor. A set of equations for the diffusion transport of mixture components is formulated, characteristic scales of the size of microheterogeneous phases are identified, and effective mass transfer coefficients are constructed for them. Allowing for the developed interface of coexisting and immiscible phases along with the porosity of solid phases is discussed. This approach can be applied to the diffusion equalization of concentrations of solid mixture components in many physicochemical systems: the mutual diffusion of components in multicomponent systems (alloys, semiconductors, solid mixtures of inert gases) and the mass transfer of an absorbed mobile component in the voids of a matrix consisting of slow components or a mixed composition of mobile and slow components (e.g., hydrogen in metals, oxygen in oxides, and the transfer of molecules through membranes of different natures, including polymeric).

  20. Determination of proton transverse relaxation times in homonuclear-coupled Spin Systems

    Science.gov (United States)

    Gochin, Miriam

    A new method is described for obtaining proton transverse relaxation times in homonuclear-coupled systems. The oscillatory effect of the coupling on the T2 decay was removed by using the attached heteronucleus as a filter. A BIRD pulse (J. R. Garbow, D. P. Weitekamp, and A. Pines, Chem. Phys. Lett.93, 504, 1982) was applied in the center of the T2 decay period, causing protons directly and remotely connected to the heteronucleus to be decoupled from each other. Protons directly bound to the heteronucleus were inverted, leaving remote protons unaffected. Thus the method works well in natural-abundance 13C and 15N systems or for 15N-enriched biological materials, where no NN connectivities exist. The importance of obtaining proton T2 values pertains to their usefulness and sensitivity in quantitating structure and mobility in molecules. Sequences for obtaining proton T2 values were described and demonstrated on formate, alcohol, and gramicidin S. The accuracy of the measured T2 as a function of X-nucleus offset and heteronuclear coupling constant was assessed.

  1. Sensitivity of the simulated precipitation to changes in convective relaxation time scale

    Directory of Open Access Journals (Sweden)

    S. K. Mishra

    2010-10-01

    Full Text Available The paper describes the sensitivity of the simulated precipitation to changes in convective relaxation time scale (TAU of Zhang and McFarlane (ZM cumulus parameterization, in NCAR-Community Atmosphere Model version 3 (CAM3. In the default configuration of the model, the prescribed value of TAU, a characteristic time scale with which convective available potential energy (CAPE is removed at an exponential rate by convection, is assumed to be 1 h. However, some recent observational findings suggest that, it is larger by around one order of magnitude. In order to explore the sensitivity of the model simulation to TAU, two model frameworks have been used, namely, aqua-planet and actual-planet configurations. Numerical integrations have been carried out by using different values of TAU, and its effect on simulated precipitation has been analyzed. The aqua-planet simulations reveal that when TAU increases, rate of deep convective precipitation (DCP decreases and this leads to an accumulation of convective instability in the atmosphere. Consequently, the moisture content in the lower- and mid- troposphere increases. On the other hand, the shallow convective precipitation (SCP and large-scale precipitation (LSP intensify, predominantly the SCP, and thus capping the accumulation of convective instability in the atmosphere. The total precipitation (TP remains approximately constant, but the proportion of the three components changes significantly, which in turn alters the vertical distribution of total precipitation production. The vertical structure of moist heating changes from a vertically extended profile to a bottom heavy profile, with the increase of TAU. Altitude of the maximum vertical velocity shifts from upper troposphere to lower troposphere. Similar response was seen in the actual-planet simulations. With an increase in TAU from 1 h to 8 h, there was a significant improvement in the simulation of the seasonal mean precipitation. The fraction

  2. MRI of bone marrow in the distal radius: in vivo precision of effective transverse relaxation times

    Energy Technology Data Exchange (ETDEWEB)

    Grampp, S. [California Univ., San Francisco, CA (United States). Musculoskeletal Section and Magnetic Resonance Science Center; Majumdar, S. [California Univ., San Francisco, CA (United States). Musculoskeletal Section and Magnetic Resonance Science Center; Jergas, M. [California Univ., San Francisco, CA (United States). Musculoskeletal Section and Magnetic Resonance Science Center; Lang, P. [California Univ., San Francisco, CA (United States). Musculoskeletal Section and Magnetic Resonance Science Center; Gies, A. [California Univ., San Francisco, CA (United States). Musculoskeletal Section and Magnetic Resonance Science Center; Genant, H.K. [California Univ., San Francisco, CA (United States). Musculoskeletal Section and Magnetic Resonance Science Center

    1995-02-01

    The effective transverse relaxation time T2{sup *} is influenced by the presence of trabecular bone, and can potentially provide a measure of bone density as well as bone structure. We determined the in vivo precision of T2{sup *} in repeated bone marrow measurements. The T2{sup *} measurements of the bone marrow of the distal radius were performed twice within 2 weeks in six healthy young volunteers using a modified water-presaturated 3D Gradient-Recalled Acquisition at Steady State (GRASS) sequence with TE 7, 10, 12, 20, and 30; TR 67; flip angle (FA) 90 . An axial volume covering a length of 5.6 cm in the distal radius was measured. Regions of interest (ROIs) were determined manually and consisted of the entire trabecular bone cross-section extending proximally from the radial subchondral endplate. Reproducibility of T2{sup *} and area measurements was expressed as the absolute precision error (standard deviation [SD] in ms or mm{sup 2}) or as the relative precision error (SD/mean x 100, or coefficient of variation [CV] in %) between the two-point measurements. Short-term precision of T2{sup *} and area measurements varied depending on section thickness and location of the ROI in the distal radius. Absolute precision errors for T2{sup *} times were between 1.3 and 2.9 ms (relative precision errors 3.8-9.5 %) and for area measurements between 20 and 55 mm{sup 2} (relative precision errors 5.1-16.4%). This MR technique for quantitative assessment of trabecular bone density showed reasonable reproducibility in vivo and is a promising future tool for the assessment of osteoporosis. (orig.)

  3. Measurement of the relaxation time of hot electrons in laser-solid interaction at relativistic laser intensities

    Energy Technology Data Exchange (ETDEWEB)

    Chen, H; Shepherd, R; Chung, H K; Dyer, G; Faenov, A; Fournier, K B; Hansen, S B; Hunter, J; Kemp, A; Pikuz, T; Ping, Y; Widmann, K; Wilks, S C; Beiersdorfer, P

    2006-08-22

    The authors have measured the relaxation time of hot electrons in short pulse laser-solid interactions using a picosecond time-resolved x-ray spectrometer and a time-integrated electron spectrometer. Employing laser intensities of 10{sup 17}, 10{sup 18}, and 10{sup 19} W/cm{sup 2}, they find increased laser coupling to hot electrons as the laser intensity becomes relativistic and thermalization of hot electrons at timescales on the order of 10 ps at all laser intensities. They propose a simple model based on collisional coupling and plasma expansion to describe the rapid relaxation of hot electrons. The agreement between the resulting K{sub {alpha}} time-history from this model with the experiments is best at highest laser intensity and less satisfactory at the two lower laser intensities.

  4. Harsh corporal punishment is associated with increased T2 relaxation time in dopamine-rich regions.

    Science.gov (United States)

    Sheu, Yi-Shin; Polcari, Ann; Anderson, Carl M; Teicher, Martin H

    2010-11-01

    Harsh corporal punishment (HCP) was defined as frequent parental administration of corporal punishment (CP) for discipline, with occasional use of objects such as straps, or paddles. CP is linked to increased risk for depression and substance abuse. We examine whether long-term exposure to HCP acts as sub-traumatic stressor that contributes to brain alterations, particularly in dopaminergic pathways, which may mediate their increased vulnerability to drug and alcohol abuse. Nineteen young adults who experienced early HCP but no other forms of maltreatment and twenty-three comparable controls were studied. T2 relaxation time (T2-RT) measurements were performed with an echo planar imaging TE stepping technique and T2 maps were calculated and analyzed voxel-by-voxel to locate regional T2-RT differences between groups. Previous studies indicated that T2-RT provides an indirect index of resting cerebral blood volume. Region of interest (ROI) analyses were also conducted in caudate, putamen, nucleus accumbens, anterior cingulate cortex, dorsolateral prefrontal cortex, thalamus, globus pallidus and cerebellar hemispheres. Voxel-based relaxometry showed that HCP was associated with increased T2-RT in right caudate and putamen. ROI analyses also revealed increased T2-RT in dorsolateral prefrontal cortex, substantia nigra, thalamus and accumbens but not globus pallidus or cerebellum. There were significant associations between T2-RT measures in dopamine target regions and use of drugs and alcohol, and memory performance. Alteration in the paramagnetic or hemodynamic properties of dopaminergic cell body and projection regions were observed in subjects with HCP, and these findings may relate to their increased risk for drug and alcohol abuse. Copyright 2010 Elsevier Inc. All rights reserved.

  5. Acute changes in knee cartilage transverse relaxation time after running and bicycling.

    Science.gov (United States)

    Gatti, Anthony A; Noseworthy, Michael D; Stratford, Paul W; Brenneman, Elora C; Totterman, Saara; Tamez-Peña, José; Maly, Monica R

    2017-02-28

    To compare the acute effect of running and bicycling of an equivalent cumulative load on knee cartilage composition and morphometry in healthy young men. A secondary analysis investigated the relationship between activity history and the change in cartilage composition after activity. In fifteen men (25.8±4.2 years), the vertical ground reaction force was measured to determine the cumulative load exposure of a 15-min run. The vertical pedal reaction force was recorded during bicycling to define the bicycling duration of an equivalent cumulative load. On separate visits that were spaced on average 17 days apart, participants completed these running and bicycling bouts. Mean cartilage transverse relaxation times (T 2 ) were determined for cartilage on the tibia and weight-bearing femur before and after each exercise. T 2 was measured using a multi-echo spin-echo sequence and 3T MRI. Cartilage of the weight bearing femur and tibia was segmented using a highly-automated segmentation algorithm. Activity history was captured using the International Physical Activity Questionnaire. The response of T 2 to bicycling and running was different (p=0.019; mean T 2 : pre-running=34.27ms, pre-bicycling=32.93ms, post-running=31.82ms, post-bicycling=32.36ms). While bicycling produced no change (-1.7%, p=0.300), running shortened T 2 (-7.1%, prunning. Activity history was inversely related to tibial T 2 , suggesting cartilage conditioning. Copyright © 2017 Elsevier Ltd. All rights reserved.

  6. Breakdown of the Korringa law of nuclear spin relaxation in metallic GaAs.

    Science.gov (United States)

    Kölbl, Dominikus; Zumbühl, Dominik M; Fuhrer, Andreas; Salis, Gian; Alvarado, Santos F

    2012-08-24

    We present nuclear spin relaxation measurements in GaAs epilayers using a new pump-probe technique in all-electrical, lateral spin-valve devices. The measured T(1) times agree very well with NMR data available for T>1 K. However, the nuclear spin relaxation rate clearly deviates from the well-established Korringa law expected in metallic samples and follows a sublinear temperature dependence T(1)(-1) is proportional to T(0.6) for 0.1 K≤T≤10 K. Further, we investigate nuclear spin inhomogeneities.

  7. Quantitative assessment of hepatic function: modified look-locker inversion recovery (MOLLI) sequence for T1 mapping on Gd-EOB-DTPA-enhanced liver MR imaging

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Jeong Hee [Seoul National University Hospital, Department of Radiology, Seoul (Korea, Republic of); Lee, Jeong Min; Han, Joon Koo; Choi, Byung Ihn [Seoul National University Hospital, Department of Radiology, Seoul (Korea, Republic of); Seoul National University College of Medicine, Institute of Radiation Medicine, Jongno-gu, Seoul (Korea, Republic of); Paek, Munyoung [Siemens Healthcare, Seoul (Korea, Republic of)

    2016-06-15

    To determine whether multislice T1 mapping of the liver using a modified look-locker inversion recovery (MOLLI) sequence on gadoxetic acid-enhanced magnetic resonance imaging (MRI) can be used as a quantitative tool to estimate liver function and predict the presence of oesophageal or gastric varices. Phantoms filled with gadoxetic acid were scanned three times using MOLLI sequence to test repeatability. Patients with chronic liver disease or liver cirrhosis who underwent gadoxetic acid-enhanced liver MRI including MOLLI sequence at 3 T were included (n = 343). Pre- and postcontrast T1 relaxation times of the liver (T1liver), changes between pre- and postcontrast T1liver (ΔT1liver), and adjusted postcontrast T1liver (postcontrast T1liver-T1spleen/T1spleen) were compared among Child-Pugh classes. In 62 patients who underwent endoscopy, all T1 parameters and spleen sizes were correlated with varices. Phantom study showed excellent repeatability of MOLLI sequence. As Child-Pugh scores increased, pre- and postcontrast T1liver were significantly prolonged (P < 0.001), and ΔT1liver and adjusted postcontrast T1liver decreased (P< 0.001). Adjusted postcontrast T1liver and spleen size were independently associated with varices (R{sup 2} = 0.29, P < 0.001). T1 mapping of the liver using MOLLI sequence on gadoxetic acid-enhanced MRI demonstrated potential in quantitatively estimating liver function, and adjusted postcontrast T1liver was significantly associated with varices. (orig.)

  8. SU-F-I-63: Relaxation Times of Lipid Resonances in NAFLD Animal Model Using Enhanced Curve Fitting

    Energy Technology Data Exchange (ETDEWEB)

    Song, K-H; Yoo, C-H; Lim, S-I; Choe, B-Y [Department of Biomedical Engineering, and Research Institute of Biomedical Engineering, The Catholic University of Korea College of Medicine, Seoul (Korea, Republic of)

    2016-06-15

    Purpose: The objective of this study is to evaluate the relaxation time of methylene resonance in comparison with other lipid resonances. Methods: The examinations were performed on a 3.0T MRI scanner using a four-channel animal coil. Eight more Sprague-Dawley rats in the same baseline weight range were housed with ad libitum access to water and a high-fat (HF) diet (60% fat, 20% protein, and 20% carbohydrate). In order to avoid large blood vessels, a voxel (0.8×0.8×0.8 cm{sup 3}) was placed in a homogeneous area of the liver parenchyma during free breathing. Lipid relaxations in NC and HF diet rats were estimated at a fixed repetition time (TR) of 6000 msec, and multi echo time (TEs) of 40–220 msec. All spectra for data measurement were processed using the Advanced Method for Accurate, Robust, and Efficient Spectral (AMARES) fitting algorithm of the Java-based Magnetic Resonance User Interface (jMRUI) package. Results: The mean T2 relaxation time of the methylene resonance in normal-chow diet was 37.1 msec (M{sub 0}, 2.9±0.5), with a standard deviation of 4.3 msec. The mean T2 relaxation time of the methylene resonance was 31.4 msec (M{sub 0}, 3.7±0.3), with a standard deviation of 1.8 msec. The T2 relaxation times of methylene protons were higher in normal-chow diet rats than in HF rats (p<0.05), and the extrapolated M{sub 0} values were higher in HF rats than in NC rats (p<0.005). The excellent linear fit with R{sup 2}>0.9971 and R{sup 2}>0.9987 indicates T2 relaxation decay curves with mono-exponential function. Conclusion: In in vivo, a sufficient spectral resolution and a sufficiently high signal-to-noise ratio (SNR) can be achieved, so that the data measured over short TE values can be extrapolated back to TE = 0 to produce better estimates of the relative weights of the spectral components. In the short term, treating the effective decay rate as exponential is an adequate approximation.

  9. T1- Thresholds in Black Holes Increase Clinical-Radiological Correlation in Multiple Sclerosis Patients.

    Science.gov (United States)

    Thaler, Christian; Faizy, Tobias; Sedlacik, Jan; Holst, Brigitte; Stellmann, Jan-Patrick; Young, Kim Lea; Heesen, Christoph; Fiehler, Jens; Siemonsen, Susanne

    2015-01-01

    Magnetic Resonance Imaging (MRI) is an established tool in diagnosing and evaluating disease activity in Multiple Sclerosis (MS). While clinical-radiological correlations are limited in general, hypointense T1 lesions (also known as Black Holes (BH)) have shown some promising results. The definition of BHs is very heterogeneous and depends on subjective visual evaluation. We aimed to improve clinical-radiological correlations by defining BHs using T1 relaxation time (T1-RT) thresholds to achieve best possible correlation between BH lesion volume and clinical disability. 40 patients with mainly relapsing-remitting MS underwent MRI including 3-dimensional fluid attenuated inversion recovery (FLAIR), magnetization-prepared rapid gradient echo (MPRAGE) before and after Gadolinium (GD) injection and double inversion-contrast magnetization-prepared rapid gradient echo (MP2RAGE) sequences. BHs (BHvis) were marked by two raters on native T1-weighted (T1w)-MPRAGE, contrast-enhancing lesions (CE lesions) on T1w-MPRAGE after GD and FLAIR lesions (total-FLAIR lesions) were detected separately. BHvis and total-FLAIR lesion maps were registered to MP2RAGE images, and the mean T1-RT were calculated for all lesion ROIs. Mean T1 values of the cortex (CTX) were calculated for each patient. Subsequently, Spearman rank correlations between clinical scores (Expanded Disability Status Scale and Multiple Sclerosis Functional Composite) and lesion volume were determined for different T1-RT thresholds. Significant differences in T1-RT were obtained between all different lesion types with highest T1 values in visually marked BHs (BHvis: 1453.3±213.4 ms, total-FLAIR lesions: 1394.33±187.38 ms, CTX: 1305.6±35.8 ms; p1500 ms (Expanded Disability Status Scale vs. lesion volume: rBHvis = 0.442 and rtotal-FLAIR = 0.497, p<0.05; Multiple Sclerosis Functional Composite vs. lesion volume: rBHvis = -0.53 and rtotal-FLAIR = -0.627, p<0.05). Clinical-radiological correlations in MS patients are

  10. Low-Field NMR Spectrometry of Chalk and Argillaceous Sandstones: Rock-Fluid Affinity Assessed from T-1/T-2 Ratio

    DEFF Research Database (Denmark)

    Katika, Konstantina; Saidian, Milad; Prasad, Manika

    2017-01-01

    Nuclear magnetic resonance (NMR) procedure typically minimizes the effects of external magnetic field gradients on the transverse relaxation. Thus, longitudinal, and transverse, T-2, relaxation times should in principle be similar. However, internal magnetic field gradients related to minerals can...... shorten T-2, as compared to provided the saturating fluid has high affinity to the solid. Consequently, the T-1/T-2 ratio should quantify the affinity between the mineral and wetting pore fluid, so we estimate wettability from logging data by comparing the T-1/T-2 ratio of oil and water peaks...

  11. Assessment of liver fibrosis using T1 mapping on Gd-EOB-DTPA-enhanced magnetic resonance.

    Science.gov (United States)

    Sheng, Ruo Fan; Wang, He Qing; Yang, Li; Jin, Kai Pu; Xie, Yan Hong; Fu, Cai Xia; Zeng, Meng Su

    2017-07-01

    Few studies have investigated the value of Gd-EOB-DTPA-enhanced T1 mapping in exact fibrosis staging, especially its correlation with hepatic molecular transporters. To investigate the diagnostic value of Gd-EOB-DTPA-enhanced T1 mapping in staging liver fibrosis and its relationship with hepatic molecular transporters. Thirty rats were divided into the carbon tetrachloride-induced fibrosis groups and a control group. T1-mapping was performed before and 20min after administration of Gd-EOB-DTPA. The T1 relaxation time and reduction rate (Δ%) were calculated, and their correlations with the degree of fibrosis, necroinflammatory activity, iron load and hepatic molecular transporters were assessed and compared. Hepatobiliary phase T1 relaxation time (HBP) and Δ% were different between each adjacent fibrosis subgroups(P=0.000-0.042). Very strong correlations existed between fibrosis and both HBP and Δ% (r=0.960/-0.952), and multivariate analyses revealed that fibrosis was the only factor independently predicted by HBP (P=0.000) and Δ% (P=0.001), comparing to necroinflammatory activity and iron load. The expression of the organic anion transporting polypeptide1a1 (Oatp1a1) was significantly correlated with HBP and Δ% at both mRNA (r=-0.741/0.697) and protein (r=-0.577/0.602) levels. Weaker correlations were found for multidrug resistance associated protein2 (Mrp2). Generally, both transporters showed decreasing levels with increasing degrees of fibrosis. Gd-EOB-DTPA-enhanced T1 mapping may provide a reliable diagnostic tool in staging liver fibrosis, and can be regarded as a useful imaging biomarker of hepatocyte transporter function. Copyright © 2017 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved.

  12. Quantitative T1 mapping under precisely controlled graded hyperoxia at 7T

    NARCIS (Netherlands)

    Bhogal, Alex A; Siero, JCW; Zwanenburg, Jaco; Luijten, Peter R; Philippens, Marielle EP; Hoogduin, Hans

    2017-01-01

    Increasing the concentration of oxygen dissolved in water is known to increase the recovery rate (R1 = 1/T1) of longitudinal magnetization (T1 relaxation). Direct T1 changes in response to precise hyperoxic gas challenges have not yet been quantified and the actual effect of increasing arterial

  13. In vivo relaxation of N-acetyl-aspartate, creatine plus phosphocreatine, and choline containing compounds during the course of brain infarction: a proton MRS study

    DEFF Research Database (Denmark)

    Gideon, P; Henriksen, O

    1992-01-01

    the course of infarction can be explained by changes in T1 and T2 relaxation times, eight patients with acute stroke were studied. STEAM sequences with varying echo delay times and repetition times were used to measure T1 and T2 of N-acetyl-aspartate (NAA), creatine plus phosphocreatine (Cr+PCr) and choline...

  14. Evaluation of MR imaging with T1 and T2* mapping for the determination of hepatic iron overload

    Energy Technology Data Exchange (ETDEWEB)

    Henninger, B.; Kremser, C.; Rauch, S.; Eder, R.; Schocke, M. [Innsbruck Medical University, Department of Radiology, Innsbruck (Austria); Zoller, H.; Finkenstedt, A. [Innsbruck Medical University, Department of Internal Medicine, Innsbruck (Austria); Michaely, H.J. [Medical Faculty Mannheim - Heidelberg University, Institute of Clinical Radiology and Nuclear Medicine, University Medical Center Mannheim, Mannheim (Germany)

    2012-11-15

    To evaluate MRI using T1 and T2* mapping sequences in patients with suspected hepatic iron overload (HIO). Twenty-five consecutive patients with clinically suspected HIO were retrospectively studied. All underwent MRI and liver biopsy. For the quantification of liver T2* values we used a fat-saturated multi-echo gradient echo sequence with 12 echoes (TR = 200 ms, TE = 0.99 ms + n x 1.41 ms, flip angle 20 ). T1 values were obtained using a fast T1 mapping sequence based on an inversion recovery snapshot FLASH sequence. Parameter maps were analysed using regions of interest. ROC analysis calculated cut-off points at 10.07 ms and 15.47 ms for T2* in the determination of HIO with accuracy 88 %/88 %, sensitivity 84 %/89.5 % and specificity 100 %/83 %. MRI correctly classified 20 patients (80 %). All patients with HIO only had decreased T1 and T2* relaxation times. There was a significant difference in T1 between patients with HIO only and patients with HIO and steatohepatitis (P = 0.018). MRI-based T2* relaxation diagnoses HIO very accurately, even at low iron concentrations. Important additional information may be obtained by the combination of T1 and T2* mapping. It is a rapid, non-invasive, accurate and reproducible technique for validating the evidence of even low hepatic iron concentrations. (orig.)

  15. Intraband relaxation time in wurtzite InGaN quantum-well lasers and comparison with experiment

    CERN Document Server

    Park, S H

    1999-01-01

    The intraband relaxation time for wurtzite (WZ) 3.5-nm In sub 0 sub . sub 1 sub 5 Ga sub 0 sub . sub 8 sub 5 N/In sub 0 sub . sub 0 sub 2 Ga sub 0 sub . sub 9 sub 8 N quantum well (QW) lasers is investigated theoretically. The results are also compared with those obtained from fitting the experimental data with a non-Markovian gain model with many-body effects. An intraband relaxation time of 25 fs is obtained from the comparison with experiment, which is in reasonably good agreement with the calculated value of 20 fs at the subband edge. These values are significantly shorter than those (40 - 100 sf) reported for zinc-blende crystals, such as InP and GaAs. This is because the hole effective masses of GaN are larger than those of GaAs and InP.

  16. Effect of the off-diagonal Onsager rate coefficient on the relaxation times in a spin-1 Ising system

    Science.gov (United States)

    Keskin, Mustafa; Erdem, Rıza

    2002-05-01

    As a continuation of our previously published works, we used the lowest approximation of the cluster variation method that is identical to the mean-field approximation and linearized equations of motions which are obtained by the Onsager reciprocity theorem to study the effect of the off-diagonal Onsager rate coefficient ( γ) on the relaxation times τ1 and τ2 near the critical point of the spin-1 Ising system. The temperature variations of the relaxation times have been studied for different values of the kinetic coefficient ( γ) which couples the dipolar and quadrupolar order currents in the system. Below and above the critical temperature ( TC), a maximum of τ2 is observed according to the values of off-diagonal coefficient ( γ).

  17. The effect of guided relaxation and exercise imagery on self-reported leisure-time exercise behaviors in older adults.

    Science.gov (United States)

    Kim, Bang Hyun; Newton, Roberta A; Sachs, Michael L; Giacobbi, Peter R; Glutting, Joseph J

    2011-04-01

    The purpose of this study was to examine the effects of a 6-wk intervention that used guided relaxation and exercise imagery (GREI) to increase self-reported leisure-time exercise behavior among older adults. A total of 93 community-dwelling healthy older adults (age 70.38 ± 8.15 yr, 66 female) were randomly placed in either a placebo control group or an intervention group. The intervention group received instructions to listen to an audio compact disk (CD) containing a GREI program, and the placebo control group received an audio CD that contained 2 relaxation tracks and instructions to listen to music of their choice for 6 wk. Results revealed that listening to a GREI CD for 6 wk significantly increased self-reported leisure-time exercise behaviors (p = .03). Further exploration of GREI and its effects on other psychological variables related to perceived exercise behaviors may substantiate its effectiveness.

  18. Magnetic resonance spin-spin relaxation time estimation in a rat model of fatty liver disease.

    Science.gov (United States)

    Alghamdi, Sami; Sinclair, Benjamin; Cowin, Gary; Brereton, Ian; Tesiram, Yasvir A

    2017-06-22

    To compare mono- and bi-exponential relaxation model equations to discriminate between normal and fatty liver disease. Six rats on a choline deficient amino acid modified (CDAA) diet and six on normal chow were studied. Multiple spin echo images with increasing echo times (TEs) were collected at 9.4T. Pixel-wise T2 maps were generated using mono-exponential decay function to calculate T2M , and a bi-exponential to calculate, short T2 component (T2S ), long T2 component (T2L ), and fractions of these components (ρS , ρL ), respectively. Statistical F-tests and Akaike's information criterion (AIC) were used to assess the relative performance of the two models. F-test and AIC showed that in the CDAA group, T2 bi-exponential model described the signal of T2 weighted imaging of the liver better than the mono-exponential model. Controls were best described by the mono-exponential model. Mean values for T2M , T2L , T2S , ρS , ρL were 31.2 ± 0.7 ms, 72.8 ± 3.3 ms, 8.2 ± 0.6 ms,71.2 ± 2.1%, 30.4 ± 1.3%, respectively, in CDAA rats, compared with 18.8 ± 0.5 ms, 32.3 ± 0.7 ms, 9.2 ± 1.8 ms, 79 ± 2%, 21.0 ± 1.1% in controls. In the fatty liver of CDAA rats we have shown that T2 weighted images fit the bi-exponential model better than mono-exponential decays thus providing a better description of the data. 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2017. © 2017 International Society for Magnetic Resonance in Medicine.

  19. SU-E-I-64: Transverse Relaxation Time in Methylene Protons of Non-Alcoholic Fatty Liver Disease Rats

    Energy Technology Data Exchange (ETDEWEB)

    Song, K-H; Lee, D-W; Choe, B-Y [Department of Biomedical Engineering, Research Institute of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul, Seoul (Korea, Republic of)

    2015-06-15

    Purpose: The aim of this study was to evaluate transverse relaxation time of methylene resonance compared to other lipid resonances. Methods: The examinations were performed using a 3.0 T scanner with a point — resolved spectroscopy (PRESS) sequence. Lipid relaxation time in a lipid phantom filled with canola oil was estimated considering repetition time (TR) as 6000 msec and echo time (TE) as 40 — 550 msec. For in vivo proton magnetic resonance spectroscopy ({sup 1}H — MRS), eight male Sprague — Dawley rats were given free access to a normal - chow (NC) and eight other male Sprague-Dawley rats were given free access to a high — fat (HF) diet. Both groups drank water ad libitum. T{sub 2} measurements in the rats’ livers were conducted at a fixed TR of 6000 msec and TE of 40 – 220 msec. Exponential curve fitting quality was calculated through the coefficients of determination (R{sup 2}). Results: A chemical analysis of phantom and liver was not performed but a T{sub 2} decay curve was acquired. The T{sub 2} relaxation time of methylene resonance was estimated as follows: NC rats, 37.07 ± 4.32 msec; HF rats, 31.43 ± 1.81 msec (p < 0.05). The extrapolated M0 values were higher in HF rats than in NC rats (p < 0.005). Conclusion: This study of {sup 1}H-MRS led to sufficient spectral resolution and signal — to — noise ratio differences to characterize all observable resonances for yielding T{sub 2} relaxation times of methylene resonance. {sup 1}H — MRS relaxation times may be useful for quantitative characterization of various liver diseases, including fatty liver disease. This study was supported by grant (2012-007883 and 2014R1A2A1A10050270) from the Mid-career Researcher Program through the NRF funded by Ministry of Science. In addition, this study was supported by the Industrial R&D of MOTIE/KEIT (10048997, Development of the core technology for integrated therapy devices based on real-time MRI-guided tumor tracking)

  20. T1 slope and degenerative cervical spondylolisthesis.

    Science.gov (United States)

    Jun, Hyo Sub; Kim, Ji Hee; Ahn, Jun Hyong; Chang, In Bok; Song, Joon Ho; Kim, Tae Hwan; Park, Moon Soo; Kim, Yong Chan; Kim, Seok Woo; Oh, Jae Keun

    2015-02-15

    Retrospective analysis. The main objectives of this study were to analyze and compare cervical sagittal parameters, including the T1 slope, in a population of 45 patients with degenerative cervical spondylolisthesis (DCS) and to compare these patients with a control group of asymptomatic population. Sagittal balance in the cervical spine is as important as the pelvic incidence and is related to the concept of T1 slope. Compared with degenerative lumbar spondylolisthesis, there are few studies evaluating DCS, and characteristic changes of the cervical sagittal parameters (including T1 slope) in patients with DCS are not well studied. We identified 45 patients with DCS (5.8%) from a database of 767 patients, using cervical radiograph in a standing position. All had radiograph and computed tomographic scan at the same time. Cervical sagittal parameters were analyzed on computed tomographic scan in a standardized supine position. The following cervical sagittal parameters were measured: T1 slope, neck tilt, thoracic inlet angle, and cervical lordosis (C2-C7 angle). The DCS group was compared with a control group of 45 asymptomatic age- and sex-matched adults to the DCS group, who were studied in a recently published study. Of our initial group of 767 patients, 45 with anterolisthesis (5.8%) were included for this study. The T1 slope was significantly greater for DCS (26.06° ± 7.3°) compared with the control group (22.32° ± 7.0°). No significant difference of the neck tilt, thoracic inlet angle, and C2-C7 angle was seen between the DSC group and the control group. Therefore, the T1 slope of the DSC group was significantly greater than that of the control group (P < 0.005). The DCS group was characterized by a greater T1 slope than the control group; therefore, we suggest that a high T1 slope may be a predisposing factor in developing DCS. 3.

  1. Measurement of electron spin-lattice relaxation times in radical doped butanol samples at 1 K using the NEDOR method

    Energy Technology Data Exchange (ETDEWEB)

    Hess, C., E-mail: hess@ep1.rub.de [Ruhr-Universitaet Bochum, Experimentalphysik I, Universitaetsstr. 150, 44801 Bochum (Germany); Herick, J.; Berlin, A.; Meyer, W.; Reicherz, G. [Ruhr-Universitaet Bochum, Experimentalphysik I, Universitaetsstr. 150, 44801 Bochum (Germany)

    2012-12-01

    The electron spin-lattice relaxation time (T{sub 1e}) of TEMPO- and trityl-doped butanol samples at 2.5 T and temperatures between 0.95 K and 2.17 K was studied by pulsed nuclear magnetic resonance (NMR) using the nuclear-electron double resonance (NEDOR) method. This method is based on the idea to measure the NMR lineshift produced by the local field of paramagnetic impurities, whose polarization can be manipulated. This is of technical advantage as measurements can be performed under conditions typically used for the dynamic nuclear polarization (DNP) process - in our case 2.5 T and temperatures around 1 K - where a direct measurement on the electronic spins would be far more complicated to perform. As T{sub 1e} is a crucial parameter determining the overall efficiency of DNP, the effect of the radical type, its spin concentration, the temperature and the oxygen content on T{sub 1e} has been investigated. For radical concentrations as used in DNP (several 10{sup 19} spins/cm{sup 3}) the relaxation rate (T{sub 1e}{sup -1}) has shown a linear dependence on the paramagnetic electron concentration for both radicals investigated. Experiments with perdeuterated and ordinary butanol have given no indication for any influence of the host materials isotopes. The measured temperature dependence has shown an exponential characteristic. It is further observed that the oxygen content in the butanol samples has a considerable effect on the electron relaxation time and thus influences the nuclear relaxation time and polarization rate during the DNP. The experiments also show a variation in the NMR linewidth, leading to comparable time constants as determined by the lineshift. NEDOR measurements were also performed on irradiated, crystal grains of {sup 6}LiD. These samples exhibited a linewidth behavior similar to that of the cylindrically shaped butanol samples.

  2. Algorithmic developments of the kinetic activation-relaxation technique: Accessing long-time kinetics of larger and more complex systems

    Science.gov (United States)

    Trochet, Mickaël; Sauvé-Lacoursière, Alecsandre; Mousseau, Normand

    2017-10-01

    In spite of the considerable computer speed increase of the last decades, long-time atomic simulations remain a challenge and most molecular dynamical simulations are limited to 1 μ s at the very best in condensed matter and materials science. There is a need, therefore, for accelerated methods that can bridge the gap between the full dynamical description of molecular dynamics and experimentally relevant time scales. This is the goal of the kinetic Activation-Relaxation Technique (k-ART), an off-lattice kinetic Monte-Carlo method with on-the-fly catalog building capabilities based on the topological tool NAUTY and the open-ended search method Activation-Relaxation Technique (ART nouveau) that has been applied with success to the study of long-time kinetics of complex materials, including grain boundaries, alloys, and amorphous materials. We present a number of recent algorithmic additions, including the use of local force calculation, two-level parallelization, improved topological description, and biased sampling and show how they perform on two applications linked to defect diffusion and relaxation after ion bombardement in Si.

  3. T2* relaxation time of acetabular and femoral cartilage with and without intraarticular gadopentetate dimeglumine in patients with femoroacetabular impingement.

    Science.gov (United States)

    Nissi, Mikko J; Mortazavi, Shabnam; Hughes, John; Morgan, Patrick; Ellermann, Jutta

    2015-06-01

    The purpose of this study was to assess whether the presence of intraarticular gadopentetate dimeglumine during clinical MR arthrography significantly alters the T2* relaxation time of hip articular cartilage in patients with femoroacetabular impingement. T2* mapping of 10 patient volunteers (seven female patients, three male patients; age range, 14-49 years; mean, 33.0 ± 12.2 [SD] years) with symptomatic femoroacetabular impingement was performed before and after intraarticular administration of gadopentetate dimeglumine. Overall 323 ROIs were defined in each acetabular and femoral cartilage before and after gadolinium injection. Agreement of the T2* relaxation times before and after gadolinium injection was assessed with the Krippendorff alpha coefficient and linear regression through the origin. T2* relaxation times before and after gadolinium injection in both acetabular and femoral cartilage were found to agree strongly. Specifically, estimated Krippendorff alpha values were greater than 0.8 for both acetabular and femoral cartilage, linear regressions through the origin yielded estimated slopes very close to 1, and R(2) values were greater than 0.98. The results indicate that intraarticular injection of gadopentetate dimeglumine according to the protocol described in this study has little effect on the T2* of femoral and acetabular cartilage. The results suggest that T2* mapping can be safely performed as an addition to a standard clinical hip imaging protocol that includes gadopentetate dimeglumine administration.

  4. High-resolution T1 mapping of the brain at 3T with driven equilibrium single pulse observation of T1 with high-speed incorporation of RF field inhomogeneities (DESPOT1-HIFI).

    Science.gov (United States)

    Deoni, Sean C L

    2007-10-01

    To investigate an alternative approach to correct for flip angle inaccuracies in the driven equilibrium single pulse observation of T1 (DESPOT1) T1 mapping method. While DESPOT1 is a robust method for rapid whole-brain voxelwise mapping of the longitudinal relaxation time, the approach is inherently sensitive to inaccuracies in the transmitted flip angle, defined by the B1 field, which become more severe with increased field. Here we propose an extension of the DESPOT1 technique, involving the additional acquisition of an inversion-prepared SPGR image alongside the conventional multiangle DESPOT1 data. From these combined data both B1 and T1 may be determined with high accuracy and precision. The method is evaluated at 3T with phantom and in vivo imaging experiments, with derived T1 estimates compared with values calculated from multiple inversion time inversion recovery data. The method provides robust correction of flip angle variations, with less than 5% error compared with reference values for T1 between 300 msec and 2500 msec. The described approach, dubbed DESPOT1-HIFI, permits whole-brain T1 mapping at 3T, with 1 mm(3) isotropic voxels, in a clinically feasible time (approximately 10 minutes) with T1 accuracy greater than 5% and with high precision. (c) 2007 Wiley-Liss, Inc.

  5. Using the Relaxation Test to Study Variation in the Time-Dependent Property of Rock and the Consequent Effect on Time-Dependent Roof Failure

    Science.gov (United States)

    Xue, Yuting; Mishra, Brijes; Gao, Danqing

    2017-09-01

    Field observations have demonstrated that roof failure occurs spatially in a mine from the time of excavation. It is suspected that time-dependent deformation propagates failure in the rock mass. In this paper, the relaxation test is used to study variation in the time-dependent property of rock and the consequent effect on time-dependent roof failure. This investigation uses a numerical simulation in 3DEC. The relaxation equation is developed from Burgers model. Variations in the time-dependent property in the post-failure region show negligible variation and, therefore, are averaged to represent the time-dependent property of the failed rock. Finally, these parameters are used in the numerical simulation of underground excavations. Two groups of parameters are used to represent the time-dependent property for pre- and post-failure conditions. FISH functions within 3DEC are used to monitor the state of each zone. Once failure is detected, the parameters are changed to the values corresponding to failed rock. The results show that the new relaxation model accurately predicts the time-dependent propagation of the failure zone. The variation of the time-dependent parameters significantly affects the rock mass behavior and roof convergence.

  6. Predicting How Nanoconfinement Changes the Relaxation Time of a Supercooled Liquid

    DEFF Research Database (Denmark)

    Ingebrigtsen, Trond; Errington, Jeff; Truskett, Tom

    2013-01-01

    The properties of nanoconfined fluids can be strikingly different from those of bulk liquids. A basic unanswered question is whether the equilibrium and dynamic consequences of confinement are related to each other in a simple way. We study this question by simulation of a liquid comprising...... asymmetric dumbbell-shaped molecules, which can be deeply supercooled without crystallizing. We find that the dimensionless structural relaxation times—spanning six decades as a function of temperature, density, and degree of confinement—collapse when plotted versus excess entropy. The data also collapse...

  7. Comparison of the T2 relaxation time of the temporomandibular joint articular disk between patients with temporomandibular disorders and asymptomatic volunteers.

    Science.gov (United States)

    Kakimoto, N; Shimamoto, H; Chindasombatjaroen, J; Tsujimoto, T; Tomita, S; Hasegawa, Y; Murakami, S; Furukawa, S

    2014-07-01

    T2 relaxation time is a quantitative MR imaging parameter used to detect degenerated cartilage in the knee and lumbar intervertebral disks. We measured the T2 relaxation time of the articular disk of the temporomandibular joint in patients with temporomandibular disorders and asymptomatic volunteers to demonstrate an association between T2 relaxation time and temporomandibular disorder MR imaging findings. One hundred forty-four patients with temporomandibular disorders and 17 volunteers were enrolled in this study. An 8-echo spin-echo sequence for measuring the T2 relaxation times was performed in the closed mouth position, and the T2 relaxation time of the entire articular disk was measured. Patients were classified according to the articular disk location and function, articular disk configuration, presence of joint effusion, osteoarthritis, and bone marrow abnormalities. The T2 relaxation time of the entire articular disk was 29.3 ± 3.8 ms in the volunteer group and 30.7 ± 5.1 ms in the patient group (P = .177). When subgroups were analyzed, however, the T2 relaxation times of the entire articular disk in the anterior disk displacement without reduction group, the marked or extensive joint effusion group, the osteoarthritis-positive group, and the bone marrow abnormality-positive group were significantly longer than those in the volunteer group (P temporomandibular joint in patients with progressive temporomandibular disorders were longer than those of healthy volunteers. © 2014 by American Journal of Neuroradiology.

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

    Science.gov (United States)

    Pavuluri, KowsalyaDevi; Ramanathan, K V

    2016-02-01

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

  9. Regional contrast agent quantification in a mouse model of myocardial infarction using 3D cardiac T1 mapping.

    Science.gov (United States)

    Coolen, Bram F; Geelen, Tessa; Paulis, Leonie E M; Nicolay, Klaas; Strijkers, Gustav J

    2011-10-05

    Quantitative relaxation time measurements by cardiovascular magnetic resonance (CMR) are of paramount importance in contrast-enhanced studies of experimental myocardial infarction. First, compared to qualitative measurements based on signal intensity changes, they are less sensitive to specific parameter choices, thereby allowing for better comparison between different studies or during longitudinal studies. Secondly, T1 measurements may allow for quantification of local contrast agent concentrations. In this study, a recently developed 3D T1 mapping technique was applied in a mouse model of myocardial infarction to measure differences in myocardial T1 before and after injection of a liposomal contrast agent. This was then used to assess the concentration of accumulated contrast agent. Myocardial ischemia/reperfusion injury was induced in 8 mice by transient ligation of the LAD coronary artery. Baseline quantitative T1 maps were made at day 1 after surgery, followed by injection of a Gd-based liposomal contrast agent. Five mice served as control group, which followed the same protocol without initial surgery. Twenty-four hours post-injection, a second T1 measurement was performed. Local ΔR1 values were compared with regional wall thickening determined by functional cine CMR and correlated to ex vivo Gd concentrations determined by ICP-MS. Compared to control values, pre-contrast T1 of infarcted myocardium was slightly elevated, whereas T1 of remote myocardium did not significantly differ. Twenty-four hours post-contrast injection, high ΔR1 values were found in regions with low wall thickening values. However, compared to remote tissue (wall thickening > 45%), ΔR1 was only significantly higher in severe infarcted tissue (wall thickening T1 mapping by CMR can be used to monitor the accumulation of contrast agents in contrast-enhanced studies of murine myocardial infarction. The contrast agent relaxivity was decreased under in vivo conditions compared to in vitro

  10. Cardiac MOLLI T1 mapping at 3.0 T: comparison of patient-adaptive dual-source RF and conventional RF transmission.

    Science.gov (United States)

    Rasper, Michael; Nadjiri, Jonathan; Sträter, Alexandra S; Settles, Marcus; Laugwitz, Karl-Ludwig; Rummeny, Ernst J; Huber, Armin M

    2017-06-01

    To prospectively compare image quality and myocardial T1 relaxation times of modified Look-Locker inversion recovery (MOLLI) imaging at 3.0 T (T) acquired with patient-adaptive dual-source (DS) and conventional single-source (SS) radiofrequency (RF) transmission. Pre- and post-contrast MOLLI T1 mapping using SS and DS was acquired in 27 patients. Patient wise and segment wise analysis of T1 times was performed. The correlation of DS MOLLI measurements with a reference spin echo sequence was analysed in phantom experiments. DS MOLLI imaging reduced T1 standard deviation in 14 out of 16 myocardial segments (87.5%). Significant reduction of T1 variance could be obtained in 7 segments (43.8%). DS significantly reduced myocardial T1 variance in 16 out of 25 patients (64.0%). With conventional RF transmission, dielectric shading artefacts occurred in six patients causing diagnostic uncertainty. No according artefacts were found on DS images. DS image findings were in accordance with conventional T1 mapping and late gadolinium enhancement (LGE) imaging. Phantom experiments demonstrated good correlation of myocardial T1 time between DS MOLLI and spin echo imaging. Dual-source RF transmission enhances myocardial T1 homogeneity in MOLLI imaging at 3.0 T. The reduction of signal inhomogeneities and artefacts due to dielectric shading is likely to enhance diagnostic confidence.

  11. Assessment of the two relaxation time Lattice-Boltzmann scheme to simulate Stokes flow in porous media

    Science.gov (United States)

    Talon, L.; Bauer, D.; Gland, N.; Youssef, S.; Auradou, H.; Ginzburg, I.

    2012-04-01

    The recent advances in 3-D imaging of porous structures have generated a tremendous interest in the simulation of complex single and two-phase flows. Lattice-Boltzmann (LB) schemes present a powerful tool to solve the flow field directly from the binarized 3-D images. However, as viscosity often plays an important role, the LB scheme should correctly treat viscosity effects. This is the case using a LB scheme with two relaxation times (TRT) unlike the broadly used, the single-relaxation rate, BGK, where the velocity of the modeled fluid does not vary as the inverse of the viscosity applying the bounce-back (no-slip) boundary rule. The aim of this work is to apply the LB-TRT approach to different types of porous media (straight channels, 2-D model porous media, sandstone) to solve for the flow field and to evaluate the approach in terms of parameter dependence, error and convergence time on the basis of permeability. We show that the variation of permeability with the free relaxation parameter Λ of the TRT scheme depends on the heterogeneity of the sample and on the numerical resolution. The convergence time depends on the applied viscosity and the parameter standing for the speed of sound, thus the computation time can be reduced by choosing appropriate values of those parameters. Two approaches to calculate permeability (Darcy's law and viscous energy dissipation) are proposed and investigated. We recommend to use Darcy's law, as dependence on Λ is less important. Periodic (in the presence of a driving body force) and pressure boundary conditions are evaluated in terms of the results.

  12. Spin relaxation and dephasing mechanism in (Ga,Mn)As studied by time-resolved Kerr rotation

    Science.gov (United States)

    Zhu, Yonggang; Zhang, Xinhui; Li, Tao; Chen, Lin; Lu, Jun; Zhao, Jianhua

    2009-04-01

    Spin dynamics in (Ga,Mn)As films grown on GaAs(001) was investigated by Time-resolved magneto-optical Kerr effect. The Kerr signal decay time of (Ga,Mn)As without external magnetic field applied was found to be several hundreds picoseconds, which suggested that photogenerated polarized holes and magnetic ions are coupled as a ferromagnetic system. Nonmonotonic temperature dependence of relaxation and dephasing (R&D) time and Larmor frequency manifests that Bir-Aronov-Pikus mechanism dominates the spin R&D time at low temperature, while D'yakonov-Perel mechanism dominates the spin R&D time at high temperature, and the crossover between the two regimes is Curie temperature.

  13. Relaxed clocks and inferences of heterogeneous patterns of nucleotide substitution and divergence time estimates across whales and dolphins (Mammalia: Cetacea).

    Science.gov (United States)

    Dornburg, Alex; Brandley, Matthew C; McGowen, Michael R; Near, Thomas J

    2012-02-01

    Various nucleotide substitution models have been developed to accommodate among lineage rate heterogeneity, thereby relaxing the assumptions of the strict molecular clock. Recently developed "uncorrelated relaxed clock" and "random local clock" (RLC) models allow decoupling of nucleotide substitution rates between descendant lineages and are thus predicted to perform better in the presence of lineage-specific rate heterogeneity. However, it is uncertain how these models perform in the presence of punctuated shifts in substitution rate, especially between closely related clades. Using cetaceans (whales and dolphins) as a case study, we test the performance of these two substitution models in estimating both molecular rates and divergence times in the presence of substantial lineage-specific rate heterogeneity. Our RLC analyses of whole mitochondrial genome alignments find evidence for up to ten clade-specific nucleotide substitution rate shifts in cetaceans. We provide evidence that in the uncorrelated relaxed clock framework, a punctuated shift in the rate of molecular evolution within a subclade results in posterior rate estimates that are either misled or intermediate between the disparate rate classes present in baleen and toothed whales. Using simulations, we demonstrate abrupt changes in rate isolated to one or a few lineages in the phylogeny can mislead rate and age estimation, even when the node of interest is calibrated. We further demonstrate how increasing prior age uncertainty can bias rate and age estimates, even while the 95% highest posterior density around age estimates decreases; in other words, increased precision for an inaccurate estimate. We interpret the use of external calibrations in divergence time studies in light of these results, suggesting that rate shifts at deep time scales may mislead inferences of absolute molecular rates and ages.

  14. The effect of timing of intravenous muscle relaxant on the quality of double-contrast barium enema

    Energy Technology Data Exchange (ETDEWEB)

    Elson, E.M.; Campbell, D.M.; Halligan, S.; Shaikh, I.; Davitt, S.; Bartram, C.I

    2000-05-01

    AIM: To determine whether the timing of buscopan administration during double-contrast barium enema examination (DCBE) affects diagnostic quality. MATERIALS AND METHODS: In a prospective setting, 100 consecutive adult out-patients referred for DCBE received 20 mg buscopan (hyoscine-N-butylbromide) intravenously, either before infusion of barium suspension (Group A) or after barium infusion and gas insufflation (Group B). A subjective assessment of ease of contrast medium infusion was made at the time of examination and the films subsequently analysed by two radiologists unaware of the mode of relaxant administration, who noted the quality of mucosal coating and made subjective and objective measurements of segmental distension. RESULTS: There was no significant difference in screening times, infusion difficulty or colonic contrast medium coating between the two groups. Subjective assessment of distension of the caecum, ascending colon, transverse colon and rectum were not significantly different. Patients receiving intravenous relaxant after barium and gas infusion had less subjective descending (P = 0.05) and sigmoid (P = 0.04) colon distension, but there was no significant difference with respect to maximal bowel diameter in any of the segments measured. CONCLUSION: The timing of intravenous administration during DCBE is likely to have no significant effect on the diagnostic quality of the study. Elson, E.M. (2000)

  15. Simplex-TSDC spectroscopy: An efficient tool to measure the relaxation time of the isothermal transient depolarization current in organic dielectrics

    Energy Technology Data Exchange (ETDEWEB)

    Benchenane-Mehor, Halima, E-mail: halima_mehor_2000@yahoo.fr [Laboratoire CaSiCCE, Département de Génie Electrique, ENSET-Oran, B.P. 1523, El M’Naouer, 31000 Oran (Algeria); Laboratoire de Microphysique et de Nanophysique (LaMiN), Département de Physique-Chimie, ENSET-Oran, B.P. 1523 EL M’Naouer, 31000 Oran (Algeria); Soufi, Manil M.; Saiter, Jean-Marc; Benzohra, Mohamed [Laboratoire LECAP-AMME, EA 4528, Université de Rouen, Faculté des Sciences, Avenue de l' Université BP 12, 76801 Saint Etienne du Rouvray (France)

    2013-03-01

    The temporal technique analysis by a simplex optimization method of isothermal transient depolarization current measurements (Simplex-TSDC) is presented for the study of the glass transition domain of different polymers. The advantage of the present method compared to the classical TSDC is that it gives direct results comparable to the experiment and allows a good estimate of the relaxation time close to the glass transition temperature in dielectric thin films. The present method also allows a direct determination of two relaxation times corresponding to a fast and a slow dynamics; and then confirms the heterogeneous character of the molecular relaxation dynamics.

  16. Noncontrast Myocardial T1 Mapping by Cardiac Magnetic Resonance Predicts Outcome in Patients With Aortic Stenosis.

    Science.gov (United States)

    Lee, Heesun; Park, Jun-Bean; Yoon, Yeonyee E; Park, Eun-Ah; Kim, Hyung-Kwan; Lee, Whal; Kim, Yong-Jin; Cho, Goo-Yeong; Sohn, Dae-Won; Greiser, Andreas; Lee, Seung-Pyo

    2017-11-10

    The aim of this study was to evaluate whether native T1 value of the myocardium on cardiac magnetic resonance (CMR) could predict clinical events in patients with significant aortic stenosis (AS). Although previous studies have demonstrated the prognostic value of focal fibrosis using late gadolinium enhancement (LGE) by CMR in AS patients, the prognostic implication of diffuse myocardial fibrosis by noninvasive imaging remains unknown. A prospective observational longitudinal study was performed in 127 consecutive patients with moderate or severe AS (68.8 ± 9.2 years of age, 49.6% male) and 33 age- and sex-matched controls who underwent 3-T CMR. The degree of diffuse myocardial fibrosis was assessed by noncontrast mapping of T1 relaxation time using modified Look-Locker inversion-recovery sequence, and the presence and extent of LGE were also evaluated. The AS patients were divided into 3 groups by the native T1 value. Primary endpoint was a composite of all-cause death and hospitalization for heart failure. Native T1 value was higher in AS patients, compared with control subjects (1,232 ± 53 ms vs. 1,185 ± 37 ms; p = 0.008). During follow-up (median 27.9 months), there were 24 clinical events including 9 deaths (6 pre-operative and 3 post-operative), the majority of which occurred in the patients in the highest T1 tertile group (2.4% vs. 11.6% vs. 42.9% for lowest, mid-, and highest tertile groups; p T1 tertile group. EuroSCORE II, the presence and/or extent of LGE, and the native T1 value were predictors of poor prognosis (adjusted hazard ratio for every 20-ms increase of native T1: 1.28; p = 0.003). In particular, the highest native T1 value provided further risk stratification regardless of the presence of LGE. High native T1 value on noncontrast T1 mapping CMR is a novel, independent predictor of adverse outcome in patients with significant AS. Copyright © 2017 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.

  17. Comparison of different cardiovascular magnetic resonance sequences for native myocardial T1 mapping at 3T.

    Science.gov (United States)

    Teixeira, Tiago; Hafyane, Tarik; Stikov, Nikola; Akdeniz, Cansu; Greiser, Andreas; Friedrich, Matthias G

    2016-10-04

    T1 mapping based on cardiovascular magnetic resonance (CMR) is a novel approach using the magnetic relaxation T1 time as a quantitative marker for myocardial tissue composition. Various T1 mapping sequences are being used, with different strengths and weaknesses. Data comparing different sequences head to head however are sparse. We compared three T1 mapping sequences, ShMOLLI, MOLLI and SASHA in phantoms and in a mid-ventricular slice of 40 healthy individuals (mean age 59 ± 7 years, 45 % male) with low (68 %) or moderate cardiovascular risk. We calculated global and segmental T1 in vivo through exponential curve fitting and subsequent parametric mapping. We also analyzed image quality and inter-observer reproducibility. There was no association of T1 with cardiovascular risk groups. T1 however differed significantly depending on the sequence, with SASHA providing consistently higher mean values than ShMOLLI and MOLLI (1487 ± 36 ms vs. 1174 ± 37 ms and 1199 ± 28 ms, respectively; p maps. On multivariate regression analysis, a longer T1 measured by MOLLI was correlated with lower ejection fraction and female gender. Inter-observer variability as assessed by intra-class correlation coefficients was excellent for all sequences (ShMOLLI: 0.995; MOLLI: 0.991; SASHA: 0.961; all p T1 mapping results between inversion-recovery vs. saturation-recovery sequences in vivo, which were less evident in phantom images, despite a small interobserver variability. Thus, physiological factors, most likely related to B1 inhomogeneities, and tissue-specific properties, like magnetization transfer, that impact T1 values in vivo, render phantom validation insufficient, and have to be further investigated for a better understanding of the clinical utility of different T1 mapping approaches. "Canadian Alliance For Healthy Hearts and Minds" - ClinicalTrials.gov NCT02220582 ; registered August 18, 2014.

  18. Relaxation and Dephasing in a Two-Electron 13C Nanotube Double Quantum Dot

    DEFF Research Database (Denmark)

    Churchill, H O H; Kuemmeth, Ferdinand; Harlow, J W

    2009-01-01

    We use charge sensing of Pauli blockade (including spin and isospin) in a two-electron 13C nanotube double quantum dot to measure relaxation and dephasing times. The relaxation time T1 first decreases with a parallel magnetic field and then goes through a minimum in a field of 1.4 T. We attribute...... both results to the spin-orbit-modified electronic spectrum of carbon nanotubes, which at high field enhances relaxation due to bending-mode phonons. The inhomogeneous dephasing time T2* is consistent with previous data on hyperfine coupling strength in 13C nanotubes....

  19. Synthesis of Long-T1 Silicon Nanoparticles for Hyperpolarized 29Si Magnetic Resonance Imaging

    Science.gov (United States)

    Atkins, Tonya M.; Cassidy, Maja C.; Lee, Menyoung; Ganguly, Shreyashi; Marcus, Charles M.; Kauzlarich, Susan M.

    2013-01-01

    We describe the synthesis, materials characterization and dynamic nuclear polarization (DNP) of amorphous and crystalline silicon nanoparticles for use as hyperpolarized magnetic resonance imaging (MRI) agents. The particles were synthesized by means of a metathesis reaction between sodium silicide (Na4Si4) and silicon tetrachloride (SiCl4) and were surface functionalized with a variety of passivating ligands. The synthesis scheme results in particles of diameter ~10 nm with long size-adjusted 29Si spin lattice relaxation (T1) times (> 600 s), which are retained after hyperpolarization by low temperature DNP. PMID:23350651

  20. Resonance phonon approach to phonon relaxation time and mean free path in one-dimensional nonlinear lattices

    Science.gov (United States)

    Xu, Lubo; Wang, Lei

    2017-04-01

    We extend a previously proposed resonance phonon approach that is based on the linear response theory. By studying the complex response function in depth, we work out the phonon relaxation time besides the oscillating frequency of the phonons in a few one-dimensional nonlinear lattices. The results in the large wave-number-k regime agree with the expectations of the effective phonon theory. However, in the small-k limit they follow different scaling laws. The phonon mean free path can also be calculated indirectly. It coincides well with that derived from the anharmonic phonon approach. A power-law divergent heat conduction, i.e., the heat conductivity κ depends on lattice length N by κ ˜Nβ with β >0 , then is supported for the momentum-conserving lattices. Furthermore, this approach can be applied to diatomic lattices. So obtained relaxation time quantitatively agrees with that from the effective phonon theory. As for the mean free path, the resonance phonon approach can detect both the acoustic and the optical branches, whereas the anharmonic phonon approach can only detect a combined branch, i.e., the acoustic branch for small k and the optical branch for large k .

  1. Evaluation of the kinetic and relaxation time of gentamicin sulfate released from hybrid biomaterial Bioglass-chitosan scaffolds

    Science.gov (United States)

    Wers, E.; Oudadesse, H.; Lefeuvre, B.; Merdrignac-Conanec, O.; Barroug, A.

    2015-10-01

    Chitosan scaffolds, combined with bioactive glass 46S6, were prepared to serve as gentamicin sulfate delivery in situ systems for bone biomaterials. This work presents a study about the effect of the ratio chitosan/bioactive glass (CH/BG) on the release of gentamicin sulfate and on the bioactivity during in vitro experiments. SEM observations allowed understanding the bond between the glass grains and the chitosan matrix. In vitro results showed that scaffolds form a hydroxyapatite (HA) Ca10(PO4)6(OH)2 after 15 days of immersion in a simulated body fluid (SBF).The interest of this study is to see that the increase of the content of bioactive glass in the chitosan matrix slows the release of gentamicin sulfate in the liquid medium. Starting concentration of gentamicin sulfate has an influence on the relaxation time of the scaffolds. Indeed, an increasing concentration delays the return to a new equilibrium. Contents of chitosan and bioactive glass do not affect the relaxation time. Synthesized scaffolds could be adapted to a clinical situation: severity and type of infection, weight and age of the patient.

  2. Assessment of demyelination, edema, and gliosis by in vivo determination of T1 and T2 in the brain of patients with acute attack of multiple sclerosis

    DEFF Research Database (Denmark)

    Larsson, H B; Frederiksen, J; Petersen, J

    1989-01-01

    -body superconductive MR-scanner, operating at 1.5 T. The measurements were repeated several times, from onset of the disease and during remission by use of six-point partial saturation inversion recovery and 32-echo multiple spin-echo sequences, giving T1 and T2, respectively. We also focused on the issue, whether T1...... followed a monoexponential course. The T2 relaxation process was a monoexponential function in the acute plaques, when measured within 20 days from onset of disease. After an average of 78 days, however, the T2 relaxation process clearly became biexponential in all but two patients. Later some...... of the relaxation curves changed back toward monoexponentiality. Thus, the study shows that it is possible to detect significant changes in MR parameters during the evolution of the disease, and these changes are discussed in relation to knowledge of pathoanatomical events in MS....

  3. Acoustic Properties of Crystals with Jahn-Teller Impurities: Elastic Moduli and Relaxation Time. Application to SrF2:Cr2+

    Science.gov (United States)

    Averkiev, Nikita S.; Bersuker, Isaac B.; Gudkov, Vladimir V.; Zhevstovskikh, Irina V.; Sarychev, Maksim N.; Zherlitsyn, Sergei; Yasin, Shadi; Shakurov, Gilman S.; Ulanov, Vladimir A.; Surikov, Vladimir T.

    2017-11-01

    A new approach to evaluate the relaxation contribution to the total elastic moduli for crystals with Jahn-Teller (JT) impurities is worked out and applied to the analysis of the experimentally measured ultrasound velocity and attenuation in SrF2:Cr2+. Distinguished from previous work, the background adiabatic contribution to the moduli, important for revealing the impurity relaxation contribution, is taken into account. The temperature dependence of the relaxation time for transitions between the equivalent configurations of the JT centers has been obtained, and the activation energy for the latter in SrF2:Cr2+, as well as the linear vibronic coupling constant have been evaluated.

  4. [Evaluation of imaging parameters for T1 dynamic contrast enhanced MRI with fast spin-echo].

    Science.gov (United States)

    Kanazawa, Yuuki; Miyati, Tosiaki; Inoue, Yusuke; Sato, Osamu

    2007-10-20

    For the purpose of continual measurement of the T1 value using the FSE (fast spin-echo) sequence and evaluation of the hemodynamics, we assessed T1 values when the imaging parameters were changed. Moreover, with the imaging parameters derived from this study, dynamic contrast-enhanced MR imaging (MRI) was examined in prostatic disease. First, the T1 value before contrast agent injection was measured with imaging parameters that had different TR and fixed TE. Next, dynamic contrast-enhanced imaging data were acquired for the imaging parameters using TE and TR in the same way as before contrast agent injection, and the T1 value of the tissue at contrast enhancement was measured. In the phantom studies, the TSE imaging parameters with short TE, long TR, and few ETL were connected with the mixed sequence. In dynamic study of the prostate, the difference between normal prostate and prostate cancer became clearer with the time-relaxation rate curve than the time-signal curve. This method using TSE is able to evaluate in greater detail information on hemodynamics and to perform dynamic study with the spin-echo sequence in extensive tissues.

  5. T1-mapping for assessment of ischemia-induced acute kidney injury and prediction of chronic kidney disease in mice

    Energy Technology Data Exchange (ETDEWEB)

    Hueper, Katja; Gutberlet, Marcel; Wacker, Frank; Hartung, Dagmar [Hannover Medical School, Department of Radiology, Hannover (Germany); Hannover Medical School, REBIRTH Cluster of Excellence, Hannover (Germany); Peperhove, Matti; Tewes, Susanne; Barrmeyer, Amelie [Hannover Medical School, Department of Radiology, Hannover (Germany); Rong, Song [Hannover Medical School, Department of Nephrology, Hannover (Germany); Zunyi Medical College, Laboratory of Organ Transplantation, Zunyi (China); Gerstenberg, Jessica; Haller, Herman; Gueler, Faikah [Hannover Medical School, Department of Nephrology, Hannover (Germany); Mengel, Michael [University of Alberta, Department of Laboratory Medicine and Pathology, Edmonton (Canada); Meier, Martin [Hannover Medical School, REBIRTH Cluster of Excellence, Hannover (Germany); Hannover Medical School, Institute for Animal Science, Hannover (Germany); Chen, Rongjun [Hannover Medical School, Department of Nephrology, Hannover (Germany); Zhejiang University, The Kidney Disease Center of the First Affiliated Hospital, Hangzhou (China)

    2014-09-15

    To investigate whether T1-mapping allows assessment of acute kidney injury (AKI) and prediction of chronic kidney disease (CKD) in mice. AKI was induced in C57Bl/6N mice by clamping of the right renal pedicle for 35 min (moderate AKI, n = 26) or 45 min (severe AKI, n = 23). Sham animals served as controls (n = 9). Renal histology was assessed in the acute (day 1 + day 7; d1 + d7) and chronic phase (d28) after AKI. Furthermore, longitudinal MRI-examinations (prior to until d28 after surgery) were performed using a 7-Tesla magnet. T1-maps were calculated from a fat-saturated echoplanar inversion recovery sequence, and mean and relative T1-relaxation times were determined. Renal histology showed severe tubular injury at d1 + d7 in both AKI groups, whereas, at d28, only animals with prolonged 45-min ischemia showed persistent signs of AKI. Following both AKI severities T1-values significantly increased and peaked at d7. T1-times in the contralateral kidney without AKI remained stable. At d7 relative T1-values in the outer stripe of the outer medulla were significantly higher after severe than after moderate AKI (138 ± 2 % vs. 121 ± 3 %, p = 0.001). T1-elevation persisted until d28 only after severe AKI. Already at d7 T1 in the outer stripe of the outer medulla correlated with kidney volume loss indicating CKD (r = 0.83). T1-mapping non-invasively detects AKI severity in mice and predicts further outcome. (orig.)

  6. Exciton spin relaxation dynamics in InGaAs /InP quantum wells

    Science.gov (United States)

    Akasaka, Shunsuke; Miyata, Shogo; Kuroda, Takamasa; Tackeuchi, Atsushi

    2004-09-01

    We have investigated the exciton spin relaxation mechanism between 13 and 300K in InGaAs /InP quantum wells using time-resolved spin-dependent pump and probe absorption measurements. The exciton spin relaxation time, τs above 40K was found to depend on temperature, T, according to τs∝T-1.1, although the spin relaxation time is constant below 40K. The clear carrier density dependence of the exciton spin relaxation time was observed below 40K, although the carrier density dependence is weak above 40K. These results imply that the main spin relaxation mechanism above and below 40K are the D'yakonov-Perel' process and the Bir-Aronov-Pikus process, respectively.

  7. Measurement of Myocardial T1ρ with a Motion Corrected, Parametric Mapping Sequence in Humans.

    Directory of Open Access Journals (Sweden)

    Sebastian Berisha

    Full Text Available To develop a robust T1ρ magnetic resonance imaging (MRI sequence for assessment of myocardial disease in humans.We developed a breath-held T1ρ mapping method using a single-shot, T1ρ-prepared balanced steady-state free-precession (bSSFP sequence. The magnetization trajectory was simulated to identify sources of T1ρ error. To limit motion artifacts, an optical flow-based image registration method was used to align T1ρ images. The reproducibility and accuracy of these methods was assessed in phantoms and 10 healthy subjects. Results are shown in 1 patient with pre-ventricular contractions (PVCs, 1 patient with chronic myocardial infarction (MI and 2 patients with hypertrophic cardiomyopathy (HCM.In phantoms, the mean bias was 1.0 ± 2.7 msec (100 msec phantom and 0.9 ± 0.9 msec (60 msec phantom at 60 bpm and 2.2 ± 3.2 msec (100 msec and 1.4 ± 0.9 msec (60 msec at 80 bpm. The coefficient of variation (COV was 2.2 (100 msec and 1.3 (60 msec at 60 bpm and 2.6 (100 msec and 1.4 (60 msec at 80 bpm. Motion correction improved the alignment of T1ρ images in subjects, as determined by the increase in Dice Score Coefficient (DSC from 0.76 to 0.88. T1ρ reproducibility was high (COV < 0.05, intra-class correlation coefficient (ICC = 0.85-0.97. Mean myocardial T1ρ value in healthy subjects was 63.5 ± 4.6 msec. There was good correspondence between late-gadolinium enhanced (LGE MRI and increased T1ρ relaxation times in patients.Single-shot, motion corrected, spin echo, spin lock MRI permits 2D T1ρ mapping in a breath-hold with good accuracy and precision.

  8. Characterization of the Uncertainty of Divergence Time Estimation under Relaxed Molecular Clock Models Using Multiple Loci

    OpenAIRE

    2014-01-01

    Genetic sequence data provide information about the distances between species or branch lengths in a phylogeny, but not about the absolute divergence times or the evolutionary rates directly. Bayesian methods for dating species divergences estimate times and rates by assigning priors on them. In particular, the prior on times (node ages on the phylogeny) incorporates information in the fossil record to calibrate the molecular tree. Because times and rates are confounded, our posterior time es...

  9. Assessment of the evaluation of liver T1 mapping imaging applying virtual ECG gating on a modified look-locker inversion recovery (MOLLI) pulse sequence

    Science.gov (United States)

    Yu, Seung-Man; Goo, Eun-Hoe; Lee, Suk-Jun; Choe, Bo-Young

    2014-10-01

    A T1 mapping calculation error may occur in a physicochemical environment with large relaxivity. We evaluated through a simulated electrocardiogram (ECG) the administration of a contrast with high relaxivity and its effect on the heart rate by using a modified Look-Locker inversion recovery (MOLLI) pulse sequence. The agarose 2% phantom of high relaxivity environment was developed by diluting gadoxetic acid magnetic resonance imaging (MRI) T1 contrast media. The gold standard T1 determination was based on coronal single section imaging with a 2D inversion-recovery turbo spin echo sequence (2D-IRTSE) in a 3T MR unit. Using the identical 3T MR scanner, we acquired T1 mapping for the MOLLI pulse sequence with various virtual heart rates. T1 mapping data of the two different pulse sequences ( i.e., 2D-IRTSE and MOLLI) were measured to investigate the accuracy and the specificity. An in vivo study was conducted in the same manner as the phantom experiments for liver T1 mapping imaging in three healthy volunteers. The MOLLI pulse sequence showed an error rate of less than 10% at a contrast agent concentration of 0.4 mmol/L, and significant error, compared with the reference value, was observed at 0.6 mmol/L or higher. The percentage error of the T1 value did not correlated with the RR ( i.e., the time between heart beats) change that was observed (P =.270). Based on the in-vivo liver test, T1 mapping imaging of an abdominal organ as the liver can be successfully achieved using the applied virtual ECG gating on the MOLLI sequence.

  10. Dielectric dispersion, relaxation dynamics and thermodynamic studies of Beta-Alanine in aqueous solutions using picoseconds time domain reflectometry

    Science.gov (United States)

    Vinoth, K.; Ganesh, T.; Senthilkumar, P.; Sylvester, M. Maria; Karunakaran, D. J. S. Anand; Hudge, Praveen; Kumbharkhane, A. C.

    2017-09-01

    The aqueous solution of beta-alanine characterised and studied by their dispersive dielectric properties and relaxation process in the frequency domain of 10×106 Hz to 30×109 Hz with varying concentration in mole fractions and temperatures. The molecular interaction and dielectric parameters are discussed in terms of counter-ion concentration theory. The static permittivity (ε0), high frequency dielectric permittivity (ε∞) and excess dielectric parameters are accomplished by frequency depended physical properties and relaxation time (τ). Molecular orientation, ordering and correlation factors are reported as confirmation of intermolecular interactions. Ionic conductivity and thermo dynamical properties are concluded with the behaviour of the mixture constituents. Solute-solvent, solute-solute interaction, structure making and breaking abilities of the solute in aqueous medium are interpreted. Fourier Transform Infrared (FTIR) spectra of beta- alanine single crystal and liquid state have been studied. The 13C Nuclear Magnetic Resonance (NMR) spectral studies give the signature for resonating frequencies and chemical shifts of beta-alanine.

  11. Concentration regimes of biopolymers xanthan, tara, and clairana, comparing dynamic light scattering and distribution of relaxation time.

    Directory of Open Access Journals (Sweden)

    Patrícia D Oliveira

    Full Text Available The aim of this work was to evaluate the utilization of analysis of the distribution of relaxation time (DRT using a dynamic light back-scattering technique as alternative method for the determination of the concentration regimes in aqueous solutions of biopolymers (xanthan, clairana and tara gums by an analysis of the overlap (c* and aggregation (c** concentrations. The diffusion coefficients were obtained over a range of concentrations for each biopolymer using two methods. The first method analysed the behaviour of the diffusion coefficient as a function of the concentration of the gum solution. This method is based on the analysis of the diffusion coefficient versus the concentration curve. Using the slope of the curves, it was possible to determine the c* and c** for xanthan and tara gum. However, it was not possible to determine the concentration regimes for clairana using this method. The second method was based on an analysis of the DRTs, which showed different numbers of relaxation modes. It was observed that the concentrations at which the number of modes changed corresponded to the c* and c**. Thus, the DRT technique provided an alternative method for the determination of the critical concentrations of biopolymers.

  12. Engineering estimation of time-dependent deformation characteristics as bending moment relaxation and released unfolding motion of creased paperboard

    Science.gov (United States)

    Nagasawa, Sh

    2017-02-01

    Paperboards are recognized to be important raw materials for packaging industry due to their advantages such as high strength-to-weight ratio, recyclability. Regarding the development of advanced packaging materials and the requirement of smart formed products, a study of sheet’s response behaviour is necessary for expanding the advanced converting industry. After introducing a couple of past research works concerned crease technologies, a fundamental mechanisms of crease deformation is reviewed using the scoring depth and the folding angle of a paperboard. Since one of important forming characteristics is a time-dependent stress relaxation or time-delayed strain during a fold/unfold process, the author’s experimental approaches for estimating a short term (less than 10 seconds) dynamic deformation behaviour of creased paperboard are discussed.

  13. Effects of magnetic field strength and particle aggregation on relaxivity of ultra-small dual contrast iron oxide nanoparticles

    Science.gov (United States)

    Ta, Hang T.; Li, Zhen; Wu, Yuao; Cowin, Gary; Zhang, Shaohua; Yago, Anya; Whittaker, Andrew K.; Xu, Zhi Ping

    2017-11-01

    This study aims to compare the relaxivities of ultra-small dual positive and negative contrast iron oxide nanoparticles (DCION) at different magnetic field strengths ranging from 4.7 to 16.4 T at physiological temperatures; and to investigate the effect of particle aggregation on relaxivities. Relaxivities of DCIONs were determined by magnetic resonance imaging scanners at 4.7, 7, 9.4, and 16.4 T. Both longitudinal (T 1) and transverse relaxation times (T 2) were measured by appropriate spin-echo sequences. It has been found that both longitudinal and transverse relaxivities are significantly dependent on the magnetic field strength. Particle aggregation also strongly affects the relaxivities. Awareness of the field strength and particle colloid stability is crucial for the comparison and evaluation of relaxivity values of these ultra-small iron oxide nanoparticles, and also for their medical applications as contrast agents.

  14. Using Bio-Functionalized Magnetic Nanoparticles and Dynamic Nuclear Magnetic Resonance to Characterize the Time-Dependent Spin-Spin Relaxation Time for Sensitive Bio-Detection

    Directory of Open Access Journals (Sweden)

    Shu-Hsien Liao

    2014-11-01

    Full Text Available In this work, we report the use of bio-functionalized magnetic nanoparticles (BMNs and dynamic magnetic resonance (DMR to characterize the time-dependent spin-spin relaxation time for sensitive bio-detection. The biomarkers are the human C-reactive protein (CRP while the BMNs are the anti-CRP bound onto dextran-coated Fe3O4 particles labeled as Fe3O4-antiCRP. It was found the time-dependent spin-spin relaxation time, T2, of protons decreases as time evolves. Additionally, the ΔT2 of of protons in BMNs increases as the concentration of CRP increases. We attribute these to the formation of the magnetic clusters that deteriorate the field homogeneity of nearby protons. A sensitivity better than 0.1 μg/mL for assaying CRP is achieved, which is much higher than that required by the clinical criteria (0.5 mg/dL. The present MR-detection platform shows promise for further use in detecting tumors, viruses, and proteins.

  15. Correlation between right ventricular T1 mapping and right ventricular dysfunction in non-ischemic cardiomyopathy.

    Science.gov (United States)

    Jellis, Christine L; Yingchoncharoen, Teerapat; Gai, Neville; Kusunose, Kenya; Popović, Zoran B; Flamm, Scott; Kwon, Deborah

    2017-03-29

    Right ventricular (RV) fibrosis is increasingly recognized as the underlying pathological substrate in a variety of clinical conditions. We sought to employ cardiac magnetic resonance (CMR) techniques of strain imaging and longitudinal relaxation time (T1) mapping to better examine the relationship between RV function and structure. Our aim was to initially evaluate the feasibility of these techniques to evaluate the right ventricle. We then sought to explore the relationship between RV function and underlying fibrosis, along with examining the evolution of RV remodeling according to the amount of baseline fibrosis. Echocardiography was performed in 102 subjects with non-ischemic cardiomyopathy. Right ventricular parameters were assessed including: fractional area change (FAC) and longitudinal strain. The same cohort underwent CMR. Post-contrast T1 mapping was performed as a marker of fibrosis with a Look-Locker technique using inversion recovery imaging. Mid-ventricular post-contrast T1 values of the RV free wall, RV septum and lateral LV were calculated using prototype analysis software. Biventricular volumetric data including ejection fraction was measured by CMR using a cine short axis stack. CMR strain analysis was also performed to assess 2D RV longitudinal and radial strain. Simultaneous biochemical and anthropometric data were recorded. Subjects were followed over a median time of 29 months (IQR 20-37 months) with echocardiography to evaluate temporal change in RV FAC according to baseline post-contrast T1 values. Longitudinal data analysis was performed to adjust for patient loss during follow-up. Subjects (62% men, 51 ± 15 years) had mild to moderately impaired global RV systolic function (RVEF = 39 ± 15%; RVEDV = 187 ± 69 ml; RVESV = 119 ± 68 ml) and moderate left ventricular dysfunction at baseline (LVEF 30 ± 17%). Good correlation was observed between mean LV and RV post-contrast T1 values (r = 0.652, p T1

  16. Novel cardiac magnetic resonance biomarkers: native T1 and extracellular volume myocardial mapping

    Science.gov (United States)

    Cannaò, Paola Maria; Altabella, Luisa; Petrini, Marcello; Alì, Marco; Secchi, Francesco; Sardanelli, Francesco

    2016-01-01

    Cardiac magnetic resonance (CMR) is a non-invasive diagnostic tool playing a key role in the assessment of cardiac morphology and function as well as in tissue characterization. Late gadolinium enhancement is a fundamental CMR technique for detecting focal or regional abnormalities such as scar tissue, replacement fibrosis, or inflammation using qualitative, semi-quantitative, or quantitative methods, but not allowing for evaluating the whole myocardium in the presence of diffuse disease. The novel T1 mapping approach permits a quantitative assessment of the entire myocardium providing a voxel-by-voxel map of native T1 relaxation time, obtained before the intravenous administration of gadolinium-based contrast material. Combining T1 data obtained before and after contrast injection, it is also possible to calculate the voxel-by-voxel extracellular volume (ECV), resulting in another myocardial parametric map. This article describes technical challenges and clinical perspectives of these two novel CMR biomarkers: myocardial native T1 and ECV mapping. PMID:28533719

  17. Myocardial tissue characterization using magnetic resonance noncontrast t1 mapping in hypertrophic and dilated cardiomyopathy.

    Science.gov (United States)

    Dass, Sairia; Suttie, Joseph J; Piechnik, Stefan K; Ferreira, Vanessa M; Holloway, Cameron J; Banerjee, Rajarshi; Mahmod, Masliza; Cochlin, Lowri; Karamitsos, Theodoros D; Robson, Matthew D; Watkins, Hugh; Neubauer, Stefan

    2012-11-01

    Noncontrast magnetic resonance T1 mapping reflects a composite of both intra- and extracellular signal. We hypothesized that noncontrast T1 mapping can characterize the myocardium beyond that achieved by the well-established late gadolinium enhancement (LGE) technique (which detects focal fibrosis) in both hypertrophic (HCM) and dilated (DCM) cardiomyopathy, by detecting both diffuse and focal fibrosis. Subjects underwent Cardiovascular Magnetic Resonance imaging at 3T (28 HCM, 18 DCM, and 12 normals). Matching short-axis slices were acquired for cine, T1 mapping, and LGE imaging (0.1 mmol/kg). Circumferential strain was measured in the midventricular slice, and (31)P magnetic resonance spectroscopy was acquired for the septum of the midventricular slice. Mean T1 relaxation time was increased in HCM and DCM (HCM 1209±28 ms, DCM 1225±42 ms, normal 1178±13 ms, PT1 and LGE (r=0.32, PT1 values were higher in segments with LGE than in those without (HCM with LGE 1228±41 ms versus no LGE 1192±79 ms, PT1 values were significantly higher than normal (PT1 values correlated with disease severity, being increased as wall thickness increased in HCM; conversely, in DCM, T1 values were highest in the thinnest myocardial segments. T1 values also correlated significantly with circumferential strain (r=0.42, PT1 values and phosphocreatine/adenosine triphosphate ratios (r=-0.59, PT1 mapping detects underlying disease processes beyond those assessed by LGE in relatively low-risk individuals.

  18. 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.

  19. Role of T1 Mapping in Inherited Cardiomyopathies.

    Science.gov (United States)

    Swoboda, Peter P; McDiarmid, Adam K; Page, Stephen P; Greenwood, John P; Plein, Sven

    2016-01-01

    T1 mapping by cardiovascular magnetic resonance is a rapidly evolving method for the quantitative assessment of tissue characteristics in cardiac disease. The myocardial T1 time can be measured without contrast (native T1) or following the administration of intravenous gadolinium-based contrast agent (post-contrast T1). By combining both of these measures, the myocardial extracellular volume fraction can be approximated. This value has been validated histologically in various inherited cardiomyopathies. Due to overlapping phenotypes, the diagnosis of inherited cardiomyopathy can at times be challenging. In this article we discuss when T1 mapping may be a useful tool in the differential diagnosis of cardiomyopathy. We also present evidence of when T1 mapping provides incremental risk stratification over other biomarkers.

  20. T1 Recovery Is Predominantly Found in Black Holes and Is Associated with Clinical Improvement in Patients with Multiple Sclerosis.

    Science.gov (United States)

    Thaler, C; Faizy, T D; Sedlacik, J; Holst, B; Stürner, K; Heesen, C; Stellmann, J-P; Fiehler, J; Siemonsen, S

    2017-02-01

    Quantitative MR imaging parameters help to evaluate disease progression in multiple sclerosis and increase correlation with clinical disability. We therefore hypothesized that T1 values might be a marker for ongoing tissue damage or even remyelination and may help increase clinical correlation. MR imaging was performed in 17 patients with relapsing-remitting MS at baseline and after 12 months of starting immunotherapy with dimethyl fumarate. On baseline images, lesion segmentation was performed for normal-appearing white matter, T2 hyperintense (FLAIR lesions), T1 hypointense (black holes), and contrast-enhancing lesions, and T1 relaxation times were obtained at baseline and after 12 months. Changes in clinical status were assessed by using the Expanded Disability Status Scale and Symbol Digit Modalities Test at both dates (Expanded Disability Status Scale-difference/Symbol Digit Modalities Test-diff). The highest T1 relaxation time at baseline was measured in black holes (1460.2 ± 209.46 ms) followed by FLAIR lesions (1400.38 ± 189.1 ms), pure FLAIR lesions (1327.5 ± 210.04 ms), contrast-enhancing lesions (1205.59 ± 199.95 ms), and normal-appearing white matter (851.34 ± 30.61 ms). After 12 months, T1 values had decreased significantly in black holes (1369.4 ± 267.81 ms), contrast-enhancing lesions (1079.57 ± 183.36 ms) (both P black holes (P black holes. Additionally, decreasing T1 values in black holes were associated with clinical improvement. © 2017 by American Journal of Neuroradiology.

  1. Multi-relaxation-time Lattice Boltzman model for uniform-shear flow over a rotating circular cylinder

    Directory of Open Access Journals (Sweden)

    Nemati Hasan

    2011-01-01

    Full Text Available A numerical investigation of the two-dimensional laminar flow and heat transfer a rotating circular cylinder with uniform planar shear, where the free-stream velocity varies linearly across the cylinder using Multi-Relaxation-Time Lattice Boltzmann method is conducted. The effects of variation of Reynolds number, rotational speed ratio at shear rate 0.1, blockage ratio 0.1 and Prandtl number 0.71 are studied. The Reynolds number changing from 50 to 160 for three rotational speed ratios of 0, 0.5, 1 is investigated. Results show that flow and heat transfer depends significantly on the rotational speed ratio as well as the Reynolds number. The effect of Reynolds number on the vortex-shedding frequency and period-surface Nusselt numbers is overall very strong compared with rotational speed ratio. Flow and heat conditions characteristics such as lift and drag coefficients, Strouhal number and Nusselt numbers are studied.

  2. A weighted multiple-relaxation-time lattice Boltzmann method for multiphase flows and its application to partial coalescence cascades

    Science.gov (United States)

    Fakhari, Abbas; Bolster, Diogo; Luo, Li-Shi

    2017-07-01

    We present a lattice Boltzmann method (LBM) with a weighted multiple-relaxation-time (WMRT) collision model and an adaptive mesh refinement (AMR) algorithm for direct numerical simulation of two-phase flows in three dimensions. The proposed WMRT model enhances the numerical stability of the LBM for immiscible fluids at high density ratios, particularly on the D3Q27 lattice. The effectiveness and efficiency of the proposed WMRT-LBM-AMR is validated through simulations of (a) buoyancy-driven motion and deformation of a gas bubble rising in a viscous liquid; (b) the bag-breakup mechanism of a falling drop; (c) crown splashing of a droplet on a wet surface; and (d) the partial coalescence mechanism of a liquid drop at a liquid-liquid interface. The numerical simulations agree well with available experimental data and theoretical approximations where applicable.

  3. Electron-ion relaxation time dependent signal enhancement in ultrafast double-pulse laser-induced breakdown spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Harilal, S. S.; Diwakar, P. K.; Hassanein, A. [Center for Materials Under Extreme Environment, School of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)

    2013-07-22

    We investigated the emission properties of collinear double-pulse compared to single-pulse ultrafast laser induced breakdown spectroscopy. Our results showed that the significant signal enhancement noticed in the double pulse scheme is strongly correlated to the characteristic electron-ion relaxation time and hence to the inter-pulse delays. Spectroscopic excitation temperature analysis showed that the improvement in signal enhancement is caused by the delayed pulse efficient reheating of the pre-plume. The signal enhancement is also found to be related to the upper excitation energy of the selected lines, i.e., more enhancement noticed for lines originating from higher excitation energy levels, indicating reheating is the major mechanism behind the signal improvement.

  4. Electron-ion relaxation time dependent signal enhancement in ultrafast double-pulse laser-induced breakdown spectroscopy

    Science.gov (United States)

    Harilal, S. S.; Diwakar, P. K.; Hassanein, A.

    2013-07-01

    We investigated the emission properties of collinear double-pulse compared to single-pulse ultrafast laser induced breakdown spectroscopy. Our results showed that the significant signal enhancement noticed in the double pulse scheme is strongly correlated to the characteristic electron-ion relaxation time and hence to the inter-pulse delays. Spectroscopic excitation temperature analysis showed that the improvement in signal enhancement is caused by the delayed pulse efficient reheating of the pre-plume. The signal enhancement is also found to be related to the upper excitation energy of the selected lines, i.e., more enhancement noticed for lines originating from higher excitation energy levels, indicating reheating is the major mechanism behind the signal improvement.

  5. Native T1-mapping for non-contrast assessment of myocardial fibrosis in patients with hypertrophic cardiomyopathy--comparison with late enhancement quantification.

    Science.gov (United States)

    Małek, Łukasz A; Werys, Konrad; Kłopotowski, Mariusz; Śpiewak, Mateusz; Miłosz-Wieczorek, Barbara; Mazurkiewicz, Łukasz; Petryka-Mazurkiewicz, Joanna; Marczak, Magdalena; Witkowski, Adam

    2015-07-01

    Myocardial fibrosis was shown to influence prognosis in hypertrophic cardiomyopathy (HCM). It is typically assessed by late gadolinium enhancement (LGE) on cardiac magnetic resonance. Native T1-mapping has been proposed, as a contrast-free method of fibrosis assessment. The aim of the study was to define a cut-off value for native T1 relaxation time that best reflects LGE quantification of myocardial fibrosis. In 25 patients with HCM and 20 controls we performed T1-mapping pre-contrast using ShMOLLI technique. This was followed by LGE assessment in the studied group 10 minutes after gadolinium contrast injection. Relative myocardial fibrosis size was calculated for varying T1 time thresholds (940-1100 ms) and compared with 6 standard deviations (6SD) method for LGE. Median fibrosis size calculated with T1-mapping was insignificantly different from LGE only for native T1 time threshold of 1060 ms (p = 0.62). Using this threshold, Bland-Altman plots demonstrated very good agreement between fibrosis sizes from the two methods (slightly better only for 1080 ms threshold). For threshold of 1060 ms we also observed good correlation (rho = 0.73) with LGE 6SD method (insignificantly better for lower thresholds, best for threshold of 980 ms-rho = 0.88). In control group with no diagnosis of HCM, fibrosis size T1-mapping can be used for non-contrast assessment of myocardial fibrosis in HCM. The 1060 ms threshold of the native T1 relaxation time is characterized by the best balance between agreement and correlation with fibrosis assessed by LGE 6SD method. Copyright © 2015 Elsevier Inc. All rights reserved.

  6. Quantitative Assessment of the T2 Relaxation Time of the Gluteus Muscles in Children with Duchenne Muscular Dystrophy: a Comparative Study Before and After Steroid Treatment

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hee Kyung; Laor, Tal; Wong, Brenda [Cincinnati Children' s Hospital Medical Center, Cincinnati (United States); Horn, Paul S. [University of Cincinnati, Cincinnati (United States)

    2010-06-15

    To determine the feasibility of using T2 mapping as a quantitative method to longitudinally follow the disease activity in children with Duchenne muscular dystrophy (DMD) who are treated with steroids. Eleven boys with DMD (age range: 5-14 years) underwent evaluation with the clinical functional score (CFS), and conventional pelvic MRI and T2 mapping before and during steroid therapy. The gluteus muscle inflammation and fatty infiltration were evaluated on conventional MRI. The histograms and mean T2 relaxation times were obtained from the T2 maps. The CFS, the conventional MRI findings and the T2 values were compared before and during steroid therapy. None of the patients showed interval change of their CFSs. On conventional MRI, none of the images showed muscle inflammation. During steroid treatment, two boys showed increased fatty infiltration on conventional MRI, and both had an increase of the mean T2 relaxation time (p < 0.05). The remaining nine boys had no increase in fatty infiltration. Of these, three showed an increased mean T2 relaxation time (p < 0.05), two showed no change and four showed a decreased mean T2 relaxation time (p < 0.05). T2 mapping is a feasible technique to evaluate the longitudinal muscle changes in those children who receive steroid therapy for DMD. The differences of the mean T2 relaxation time may reflect alterations in disease activity, and even when the conventional MRI and CFS remain stable.

  7. Theoretical study of built-in-polarization effect on relaxation time and ...

    Indian Academy of Sciences (India)

    61

    time is enhanced due to built-in-polarization effect and makes phonon mean free path longer which is required .... The interaction between the phonons and the built-in-polarization field; and their effect on phonon ...... AlxGa1-xN for electric energy generation from waste heat energy through Seebeck effect, can be achieved ...

  8. Numerical simulation of ( T 2, T 1) 2D NMR and fluid responses

    Science.gov (United States)

    Tan, Mao-Jin; Zou, You-Long; Zhang, Jin-Yan; Zhao, Xin

    2012-12-01

    One-dimensional nuclear magnetic resonance (1D NMR) logging technology is limited for fluid typing, while two-dimensional nuclear magnetic resonance (2D NMR) logging can provide more parameters including longitudinal relaxation time ( T 1) and transverse relaxation time ( T 2) relative to fluid types in porous media. Based on the 2D NMR relaxation mechanism in a gradient magnetic field, echo train simulation and 2D NMR inversion are discussed in detail. For 2D NMR inversion, a hybrid inversion method is proposed based on the damping least squares method (LSQR) and an improved truncated singular value decomposition (TSVD) algorithm. A series of spin echoes are first simulated with multiple waiting times ( T W s) in a gradient magnetic field for given fluid models and these synthesized echo trains are inverted by the hybrid method. The inversion results are consistent with given models. Moreover, the numerical simulation of various fluid models such as the gas-water, light oil-water, and vicious oil-water models were carried out with different echo spacings ( T E s) and T W s by this hybrid method. Finally, the influences of different signal-to-noise ratios (SNRs) on inversion results in various fluid models are studied. The numerical simulations show that the hybrid method and optimized observation parameters are applicable to fluid typing of gas-water and oil-water models.

  9. Effect of glatiramer acetate three-times weekly on the evolution of new, active multiple sclerosis lesions into T1-hypointense "black holes": a post hoc magnetic resonance imaging analysis.

    Science.gov (United States)

    Zivadinov, Robert; Dwyer, Michael; Barkay, Hadas; Steinerman, Joshua R; Knappertz, Volker; Khan, Omar

    2015-03-01

    Conversion of active lesions to black holes has been associated with disability progression in subjects with relapsing-remitting multiple sclerosis (RRMS) and represents a complementary approach to evaluating clinical efficacy. The objective of this study was to assess the conversion of new active magnetic resonance imaging (MRI) lesions, identified 6 months after initiating treatment with glatiramer acetate 40 mg/mL three-times weekly (GA40) or placebo, to T1-hypointense black holes in subjects with RRMS. Subjects received GA40 (n = 943) or placebo (n = 461) for 12 months. MRI was obtained at baseline and Months 6 and 12. New lesions were defined as either gadolinium-enhancing T1 or new T2 lesions at Month 6 that were not present at baseline. The adjusted mean numbers of new active lesions at Month 6 converting to black holes at Month 12 were analyzed using a negative binomial model; adjusted proportions of new active lesions at Month 6 converting to black holes at Month 12 were analyzed using a logistic regression model. Of 1,292 subjects with complete MRI data, 433 (50.3 %) GA-treated and 247 (57.2 %) placebo-treated subjects developed new lesions at Month 6. Compared with placebo, GA40 significantly reduced the mean number (0.31 versus 0.45; P = .0258) and proportion (15.8 versus 19.6 %; P = .006) of new lesions converting to black holes. GA significantly reduced conversion of new active lesions to black holes, highlighting the ability of GA40 to prevent tissue damage in RRMS.

  10. Analysis of proton-density bias corrections based on T1 measurement for robust quantification of water content in the brain at 3 Tesla.

    Science.gov (United States)

    Abbas, Zaheer; Gras, Vincent; Möllenhoff, Klaus; Keil, Fabian; Oros-Peusquens, Ana-Maria; Shah, Nadim J

    2014-12-01

    Estimating tissue water content using high field MRI, such as 3 Tesla (T), is challenging due to the difficulty in dissociating the radio frequency inhomogeneity pattern from the signal arising from tissue intrinsic proton density (PD) variations. To overcome this problem the longitudinal relaxation time T1 can be combined with an initial guess of the PD to yield the desired PD bias correction. However, it is necessary to know whether T1 effects, i.e., any effect contributing to T1 while being independent of tissue hydration, influence the estimated correction. Twenty-five healthy subjects underwent a quantitative 3T MRI protocol enabling acquisition of 64 slices with 1 mm in-plane resolution and 2 mm slice thickness in 14 min. Influence of T1 effects on the estimated water content map is evaluated using a dedicated method including T1 and T2 * information and region of interest-based water content values are compared with the literature. Our analysis indicates that the PD bias correction based on T1 is largely insensitive to T1 effects. Besides, water content results are in good agreement with literature values obtained at 1.5T. This study demonstrates the applicability of a PD bias correction based on T1 to yield tissue water content at 3T. © 2014 Wiley Periodicals, Inc.

  11. Test-retest reliability and concurrent validity of in vivo myelin content indices: Myelin water fraction and calibrated T1 w/T2 w image ratio.

    Science.gov (United States)

    Arshad, Muzamil; Stanley, Jeffrey A; Raz, Naftali

    2017-04-01

    In an age-heterogeneous sample of healthy adults, we examined test-retest reliability (with and without participant repositioning) of two popular MRI methods of estimating myelin content: modeling the short spin-spin (T2 ) relaxation component of multi-echo imaging data and computing the ratio of T1 -weighted and T2 -weighted images (T1 w/T2 w). Taking the myelin water fraction (MWF) index of myelin content derived from the multi-component T2 relaxation data as a standard, we evaluate the concurrent and differential validity of T1 w/T2 w ratio images. The results revealed high reliability of MWF and T1 w/T2 w ratio. However, we found significant correlations of low to moderate magnitude between MWF and the T1 w/T2 w ratio in only two of six examined regions of the cerebral white matter. Notably, significant correlations of the same or greater magnitude were observed for T1 w/T2 w ratio and the intermediate T2 relaxation time constant, which is believed to reflect differences in the mobility of water between the intracellular and extracellular compartments. We conclude that although both methods are highly reliable and thus well-suited for longitudinal studies, T1 w/T2 w ratio has low criterion validity and may be not an optimal index of subcortical myelin content. Hum Brain Mapp 38:1780-1790, 2017. © 2017 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  12. Abbreviated Upright Behavioral Relaxation Training for Test Anxiety among College Students: Initial Results

    Science.gov (United States)

    Tatum, Teresa; Lundervold, Duane A.; Ament, Patrick

    2006-01-01

    Effect of abbreviated upright Behavioral Relaxation Training (BRT) on two self-report measures of test anxiety was examined using a quasi-experimental pre-post between groups (N = 20) research design with self-referred college students. At time 1 (T1) assessment, all participants completed the Abbreviated Test Anxiety Scale (ATAS) and were trained…

  13. Broadband ultrafast nonlinear absorption and ultra-long exciton relaxation time of black phosphorus quantum dots.

    Science.gov (United States)

    Chen, Runze; Zheng, Xin; Jiang, Tian

    2017-04-03

    Black phosphorus (BP) has recently attracted significant attention for its brilliant physical and chemical features. The remarkable strong light-matter interaction and tunable direct wide range band-gap make it an ideal candidate in various application regions, especially saturable absorbers. In this paper, ultrasmall black phosphorus quantum dots (BPQDs), a unique form of phosphorus nanostructures, with average size of 5.7 ± 0.8 nm are synthesized. Compared with BP nanosheets (BPNs) with similar thickness, the ultrafast nonlinear optical (NLO) absorption properties and excited carrier dynamics are investigated in wide spectra. Beyond the saturation absorption (SA), giant two photon absorption (TPA) is observed in BPQDs. BPQDs exhibit quite different excitation intensity and wavelength dependent nonlinear optical (NLO) response from BPNs, which is attributed to the quantum confinement and edge effects. The BPQDs show broadband photon-induced absorption (PIA) under the probe wavelength from 470 nm to 850 nm and a fast and a slow decay time are obtained as long as 92 ± 10 ps and 1100 ± 100 ps, respectively. The substantial independence for ultra-long time scales of pump intensity and temperature reveals that the carrier recombination mechanism may be attributed to a defect-assisted Auger capture process. These findings will help to develop optoelectronic and photonic devices operating in the infrared and visible wavelength region.

  14. Time-domain quanification of amplitude, chemical shift, apparent relaxation time T2, and phase by wavelet-transform analysis. Application to biomedical magnetic resonance spectroscopy.

    Science.gov (United States)

    Serrai, H; Senhadji, L; de Certaines, J D; Coatrieux, J L

    1997-01-01

    The wavelet-transform method is used to quantify the magnetic resonance spectroscopy (MRS) parameters: chemical shift, apparent relaxation time T2, resonance amplitude, and phase. Wavelet transformation is a time-frequency representation which separates each component from the FID, then successively quantifies it and subtracts it from the raw signal. Two iterative procedures have been developed. They have been combined with a nonlinear regression analysis method and tested on both simulated and real sets of biomedical MRS data selected with respect to the main problems usually encountered in quantifying biomedical MRS, specifically "chemical noise," resulting from overlapping resonances, and baseline distortion. The results indicate that the wavelet-transform method can provide efficient and accurate quantification of MRS data.

  15. Assessment of demyelination, edema, and gliosis by in vivo determination of T1 and T2 in the brain of patients with acute attack of multiple sclerosis

    DEFF Research Database (Denmark)

    Larsson, H B; Frederiksen, J; Petersen, J

    1989-01-01

    -body superconductive MR-scanner, operating at 1.5 T. The measurements were repeated several times, from onset of the disease and during remission by use of six-point partial saturation inversion recovery and 32-echo multiple spin-echo sequences, giving T1 and T2, respectively. We also focused on the issue, whether T1...... of the relaxation curves changed back toward monoexponentiality. Thus, the study shows that it is possible to detect significant changes in MR parameters during the evolution of the disease, and these changes are discussed in relation to knowledge of pathoanatomical events in MS....

  16. MR T1{rho} as an imaging biomarker for monitoring liver injury progression and regression: an experimental study in rats with carbon tetrachloride intoxication

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Feng; Wang, Yi-Xiang J.; Yuan, Jing; Deng, Min; Ahuja, Anil T. [Chinese University of Hong Kong, Department of Imaging and Interventional Radiology, Prince of Wales Hospital, Hong Kong SAR (China); Wong, Hing Lok [School of Public Health and Primary Care, Prince of Wales Hospital, The Chinese University of Hong Kong, Jockey Club Centre for Osteoporosis Care and Control, Hong Kong SAR (China); Chu, Eagle S.H.; Go, Minnie Y.Y.; Yu, Jun [Chinese University of Hong Kong, Institute of Digestive Disease and Department of Medicine and Therapeutics, Li Ka Shing Institute of Health Sciences, Hong Kong SAR (China); Teng, Gao-Jun [Southeast University, Department of Radiology, Zhongda Hospital, Nanjing (China)

    2012-08-15

    Recently it was shown that the magnetic resonance imaging (MRI) T1{rho} value increased with the severity of liver fibrosis in rats with bile duct ligation. Using a rat carbon tetrachloride (CCl{sub 4}) liver injury model, this study further investigated the merit of T1{rho} relaxation for liver fibrosis evaluation. Male Sprague-Dawley rats received intraperitoneal injection of 2 ml/kg CCl{sub 4} twice weekly for up to 6 weeks. Then CCl{sub 4} was withdrawn and the animals were allowed to recover. Liver T1{rho} MRI and conventional T2-weighted images were acquired. Animals underwent MRI at baseline and at 2 days, 2 weeks, 4 weeks and 6 weeks post CCl{sub 4} injection, and they were also examined at 1 week and 4 weeks post CCl{sub 4} withdrawal. Liver histology was also sampled at these time points. Liver T1{rho} values increased slightly, though significantly, on day 2, and then increased further and were highest at week 6 post CCl{sub 4} insults. The relative liver signal intensity change on T2-weighted images followed a different time course compared with that of T1{rho}. Liver T1{rho} values decreased upon the withdrawal of the CCl{sub 4} insult. Histology confirmed the animals had typical CCl{sub 4} liver injury and fibrosis progression and regression processes. MR T1{rho} imaging can monitor CCl{sub 4}-induced liver injury and fibrosis. (orig.)

  17. T1, T2 Mapping and Extracellular Volume Fraction (ECV): Application, Value and Further Perspectives in Myocardial Inflammation and Cardiomyopathies.

    Science.gov (United States)

    Roller, F C; Harth, S; Schneider, C; Krombach, G A

    2015-09-01

    Cardiac magnetic resonance imaging (CMRI) is a versatile diagnostic tool. One of its main advantages is the possibility of tissue characterization. T1-weighted images for scar and T2-weighted images for edema visualization are key methods for tissue characterization. Otherwise these sequences are strongly limited for the detection of diffuse myocardial pathologies. Recently, rapid technical innovations have generated new techniques. T1, T2 mapping and evaluation of the extracellular volume fraction (ECV) allow quantification of diffuse myocardial pathologies and showed great potential in the visualization of fibrosis, edema, amyloid, iron overload and lipid. In the future these techniques might enable the detection of early cardiac involvement, even act as a prognosticator. Moreover, therapy monitoring and follow-up might be possible due to versatile parameter quantification with these new techniques. CMR allows for tissue characterization via T1- and T2-weighted sequences. In cases of diffuse, global myocardial pathologies, correct image interpretation with traditional CMR sequences might be difficult. T1, T2 mapping and ECV can quantify diffuse, global myocardial pathologies. Alterations of myocardial T1 and T2 relaxation times occur in various myocardial diseases (e.g. acute myocarditis). In the future mapping might act as a prognosticator or therapy monitoring tool. © Georg Thieme Verlag KG Stuttgart · New York.

  18. T1 Mapping by CMR Imaging

    National Research Council Canada - National Science Library

    Kammerlander, Andreas A; Marzluf, Beatrice A; Zotter-Tufaro, Caroline; Aschauer, Stefan; Duca, Franz; Bachmann, Alina; Knechtelsdorfer, Klaus; Wiesinger, Matthias; Pfaffenberger, Stefan; Greiser, Andreas; Lang, Irene M; Bonderman, Diana; Mascherbauer, Julia

    2016-01-01

    ..., native T1 mapping and the calculation of ECV by use of native and post-contrast T1 maps have been described as the most promising measures of extracellular matrix expansion (11) . Native T1 mapping identifies pathological changes affecting the intracellular or extracellular space, such as myocardial edema in acute myocardial infarction or in myoc...

  19. In vivo proton magnetic resonance spectroscopy of liver metabolites in non-alcoholic fatty liver disease in rats: T2 relaxation times in methylene protons.

    Science.gov (United States)

    Song, Kyu-Ho; Baek, Hyeon-Man; Lee, Do-Wan; Choe, Bo-Young

    2015-10-01

    The aim of this study was to evaluate the transverse relaxation time of methylene resonance as compared to other lipid resonances. The examinations were performed using a 3.0 T scanner with a point-resolved spectroscopy (PRESS) sequence. Lipid relaxation time in a lipid phantom filled with canola oil was estimated with a repetition time (TR) of 6000ms and echo time (TE) of 40-550ms. For in vivo proton magnetic resonance spectroscopy ((1)H-MRS), eight male Sprague-Dawley rats were given free access to a normal-chow (NC) and another eight male Sprague-Dawley rats were given free access to a high-fat (HF) diet. Both groups drank water ad libitum. T2 measurements in the rats' livers were conducted at a fixed TR of 6000ms and TE of 40-220ms. Exponential curve fitting quality was calculated through the coefficients of determination (R(2)). Chemical analyses of the phantom and livers were not performed, but T2 decay curves were acquired. The T2 relaxation time of methylene resonance was estimated as follows: NC rats, 37.1±4.3ms; HF rats, 31.4±1.8ms (p<0.05). The extrapolated M0 values were higher in HF rats than in NC rats (p<0.005). This study of (1)H MRS led to sufficient spectral resolution and signal-to-noise ratio differences to characterize the T2 relaxation times of methylene resonance. (1)H MRS relaxation times may be useful for quantitative characterization of various liver diseases, including fatty liver disease. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  20. Activation of the umami taste receptor (T1R1/T1R3) initiates the peristaltic reflex and pellet propulsion in the distal colon

    Science.gov (United States)

    Kendig, Derek M.; Hurst, Norman R.; Bradley, Zachary L.; Mahavadi, Sunila; Kuemmerle, John F.; Lyall, Vijay; DeSimone, John; Murthy, Karnam S.

    2014-01-01

    Intraluminal nutrients in the gut affect the peristaltic reflex, although the mechanism is not well defined. Recent evidence supports the presence of taste receptors and their signaling components in enteroendocrine cells, although their function is unclear. This study aimed to determine if nutrients modify colonic motility through activation of taste receptors. Colonic sections were immunostained for the umami taste receptor T1R1/T1R3, which mediates the response to umami ligands, such as monosodium glutamate (MSG), in taste cells. Ascending contraction, descending relaxation, and calcitonin gene-related peptide release were measured in three-chamber flat-sheet preparations of rat colon in response to MSG alone or with inosine 5′-monophosphate (IMP). Velocity of artificial fecal pellet propulsion was measured by video recording in guinea pig distal colon. T1R1/T1R3 receptors were present in enteroendocrine cells of colonic sections from human, rat, mouse, and guinea pig. MSG initiated ascending contraction and descending relaxation components of the peristaltic reflex and calcitonin gene-related peptide release in flat-sheet preparations. IMP augmented the MSG-induced effects, suggesting activation of T1R1/T1R3 receptors. In T1R1−/− mice, mucosal stroking, but not MSG, elicited a peristaltic reflex. Intraluminal perfusion of MSG enhanced the velocity of artificial fecal pellet propulsion, which was also augmented by IMP. Propulsion was also increased by l-cysteine, but not l-tryptophan, supporting a role of T1R1/T1R3 receptors. We conclude that T1R1/T1R3 activation by luminal MSG or l-cysteine elicits a peristaltic reflex and CGRP release and increases the velocity of pellet propulsion in distal colon. This mechanism may explain how nutrients regulate colonic propulsion. PMID:25324508

  1. Laboratory observations of time-dependent frictional strengthening and stress relaxation in natural and synthetic fault gouges

    Science.gov (United States)

    Carpenter, B. M.; Ikari, M. J.; Marone, C.

    2016-02-01

    Interseismic recovery of fault strength (healing) following earthquake failure is a fundamental requirement of the seismic cycle and likely plays a key role in determining the stability and slip behavior of tectonic faults. We report on laboratory measurements of time- and slip-dependent frictional strengthening for natural and synthetic gouges to evaluate the role of mineralogy in frictional strengthening. We performed slide-hold-slide (SHS) shearing experiments on nine natural fault gouges and eight synthetic gouges at conditions of 20 MPa normal stress, 100% relative humidity (RH), large shear strain (~15), and room temperature. Phyllosilicate-rich rocks show the lowest rates of frictional strengthening. Samples rich in quartz and feldspar exhibit intermediate rates of frictional strengthening, and calcite-rich gouges show the largest values. Our results show that (1) the rates of frictional strengthening and creep relaxation scale with frictional strength, (2) phyllosilicate-rich fault gouges have low strength and healing characteristics that promote stable, aseismic creep, (3) most natural fault gouges exhibit intermediate rates of frictional strengthening, consistent with a broad range of fault slip behaviors, and (4) calcite-rich fault rocks show the highest rates of frictional strengthening, low values of dilation upon reshear, and high frictional strengths, all of which would promote seismogenic behavior.

  2. Numerical simulation of convection and heat transfer in Czochralski crystal growth by multiple-relaxation-time LBM

    Science.gov (United States)

    Liu, Ding; Huang, Weichao; Zhang, Ni

    2017-07-01

    A two-dimensional axisymmetric swirling model based on the lattice Boltzmann method (LBM) in a pseudo Cartesian coordinate system is posited to simulate Czochralski (Cz) crystal growth in this paper. Specifically, the multiple-relaxation-time LBM (MRT-LBM) combined with the finite difference method (FDM) is used to analyze the melt convection and heat transfer in the process of Cz crystal growth. An incompressible axisymmetric swirling MRT-LB D2Q9 model is applied to solve for the axial and radial velocities by inserting thermal buoyancy and rotational inertial force into the two-dimensional lattice Boltzmann equation. In addition, the melt temperature and the azimuthal velocity are solved by MRT-LB D2Q5 models, and the crystal temperature is solved by FDM. The comparison results of stream functions values of different methods demonstrate that our hybrid model can be used to simulate the fluid-thermal coupling in the axisymmetric swirling model correctly and effectively. Furthermore, numerical simulations of melt convection and heat transfer are conducted under the conditions of high Grashof (Gr) numbers, within the range of 105 ˜ 107, and different high Reynolds (Re) numbers. The experimental results show our hybrid model can obtain the exact solution of complex crystal-growth models and analyze the fluid-thermal coupling effectively under the combined action of natural convection and forced convection.

  3. A multiphase three-dimensional multi-relaxation time (MRT) lattice Boltzmann model with surface tension adjustment

    Science.gov (United States)

    Ammar, Sami; Pernaudat, Guillaume; Trépanier, Jean-Yves

    2017-08-01

    The interdependence of surface tension and density ratio is a weakness of pseudo-potential based lattice Boltzmann models (LB). In this paper, we propose a 3D multi-relaxation time (MRT) model for multiphase flows at large density ratios. The proposed model is capable of adjusting the surface tension independently of the density ratio. We also present the 3D macroscopic equations recovered by the proposed forcing scheme. A high order of isotropy for the interaction force is used to reduce the amplitude of spurious currents. The proposed 3D-MRT model is validated by verifying Laplace's law and by analyzing its thermodynamic consistency and the oscillation period of a deformed droplet. The model is then applied to the simulation of the impact of a droplet on a dry surface. Impact dynamics are determined and the maximum spread factor calculated for different Reynolds and Weber numbers. The numerical results are in agreement with data published in the literature. The influence of surface wettability on the spread factor is also investigated. Finally, our 3D-MRT model is applied to the simulation of the impact of a droplet on a wet surface. The propagation of transverse waves is observed on the liquid surface.

  4. Field dependence of T1 for hyperpolarized [1-13C]pyruvate

    DEFF Research Database (Denmark)

    Chattergoon, N.; Martnez-Santiesteban, F.; Handler, W. B.

    2013-01-01

    conformation and properties of the dissolution media such as buffer composition, solution pH, temperature and magnetic field. We have measured the magnetic field dependence of the spin–lattice relaxation time of hyperpolarized [1-13C]pyruvate using field-cycled relaxometry. [1-13C]pyruvate was hyperpolarized.......75 T. The magnetic field of the relaxometer was rapidly varied between relaxation and acquisition fields where the sample magnetization was periodically measured using a small flip angle. Data were recorded for relaxation fields varying between 0.237 mT and 0.705 T to map the T1 dispersion of the C-1...... using dynamic nuclear polarization and then rapidly thawed and dissolved in a buffered solution to a concentration of 80 mmol l−1 and a pH of ~7.8. The hyperpolarized liquid was transferred within 8 s to a fast field-cycling relaxometer with a probe tuned for detection of 13C at a field strength of ~0...

  5. T2, Carr Purcell T2 and T1ρ of fat and water as surrogate markers of trabecular bone structure

    Science.gov (United States)

    Lammentausta, E.; Silvast, T. S.; Närväinen, J.; Jurvelin, J. S.; Nieminen, M. T.; Gröhn, O. H. J.

    2008-02-01

    Magnetic resonance imaging (MRI) techniques have been developed for non-invasive assessment of the structural properties of trabecular bone. These measurements, however, suffer from relatively long acquisition times and low resolution compared to the trabecular size. Spectroscopic measurement of relaxation times could be applied for more detailed and faster assessment of relaxation properties of bone marrow and also provide surrogate information on trabecular structure. In the present study, bovine trabecular bone was investigated with spectroscopic NMR (nuclear magnetic resonance) methods to determine the relationship between structural parameters as measured with micro-CT and T2, Carr-Purcell T2 and T1ρ relaxation times of fat and water. To compare bone with a sample matrix with magnetic susceptibility interfaces, phantoms consisting of glass beads with different diameters in oil or water were used. The behavior of T2 measured with different sequences and T1ρ at different magnitudes of spin-lock fields were characterized, and relaxation times were correlated with structural parameters. T2 and T1ρ showed significant associations with structural bone parameters. Strongest linear correlations (r = 0.81, p fat component and structural model index. For glass beads, the behavior of T2 and T1ρ was similar to that of the water compartment of bone marrow. The present results suggest feasibility of spectroscopic NMR measurements to assess trabecular structure. However, further studies are required to determine the sensitivity of this approach to fat content of bone marrow and to lower the field strengths used in clinical devices.

  6. T2, Carr-Purcell T2 and T1rho of fat and water as surrogate markers of trabecular bone structure.

    Science.gov (United States)

    Lammentausta, E; Silvast, T S; Närväinen, J; Jurvelin, J S; Nieminen, M T; Gröhn, O H J

    2008-02-07

    Magnetic resonance imaging (MRI) techniques have been developed for non-invasive assessment of the structural properties of trabecular bone. These measurements, however, suffer from relatively long acquisition times and low resolution compared to the trabecular size. Spectroscopic measurement of relaxation times could be applied for more detailed and faster assessment of relaxation properties of bone marrow and also provide surrogate information on trabecular structure. In the present study, bovine trabecular bone was investigated with spectroscopic NMR (nuclear magnetic resonance) methods to determine the relationship between structural parameters as measured with micro-CT and T(2), Carr-Purcell T(2) and T(1rho) relaxation times of fat and water. To compare bone with a sample matrix with magnetic susceptibility interfaces, phantoms consisting of glass beads with different diameters in oil or water were used. The behavior of T(2) measured with different sequences and T(1rho) at different magnitudes of spin-lock fields were characterized, and relaxation times were correlated with structural parameters. T(2) and T(1rho) showed significant associations with structural bone parameters. Strongest linear correlations (r = 0.81, p fat component and structural model index. For glass beads, the behavior of T(2) and T(1rho) was similar to that of the water compartment of bone marrow. The present results suggest feasibility of spectroscopic NMR measurements to assess trabecular structure. However, further studies are required to determine the sensitivity of this approach to fat content of bone marrow and to lower the field strengths used in clinical devices.

  7. A robust method for calculating geometric mean times from multiexponential relaxation data, using only a few data points and only a few elementary operations.

    Science.gov (United States)

    Borgia, G C; Bortolotti, V; Brown, R J; Fantazzini, P

    1996-01-01

    A method is presented to compute values of geometric mean time Tg that uses only a few data points equispaced in the logarithm of time (or equispaced in time and weighted by 1/t) and a few elementary operations for the computation. The method has been tested on a large number of synthetic relaxation data and on actual NMR relaxation measurements in porous samples, using as few as four points (including the two points needed to normalize the relaxation for decay from 1.0 to 0) on each relaxation curve. This computation of the geometric-mean rate very adequately matches the synthetic data and the results of multiexponential inversion of many (or only a few) data points from NMR measurements. When many computations are needed in short times, as for voxel-by-voxel computations in magnetic resonance imaging (MRI) or for depth-by-depth computation in nuclear magnetism logging (NML) of oilwells, a very quickly computed estimate of Tg should be useful.

  8. Perturbative harmonic modulation of longitudinal electron-spin magnetization for short T1 determination

    Science.gov (United States)

    Suzuki, Takayuki

    2015-10-01

    Longitudinally detected T1 measurement scheme (LOD-T1) is studied in detail. In contrast to the original work on LOD-T1 , using high power microwave pulses, this work deals with general and practically frequent cases in which perfect inversion of the electron-spin magnetization is not feasible due to the effect of relaxation during microwave pulses. Theoretical studies, numerical simulations, and experiments reveal a pair of separate contributions of the dynamics of the longitudinal magnetization to the LOD signal, namely, the periodic modulation and the relaxation contributions. The latter alone which is of interest can be extracted to give relaxation curves. In addition, it is shown that T1 information can be obtained even when the available microwave power is so low that the electron magnetization can only be perturbatively modulated, at the cost of reduced sensitivity. To overcome this, a modified pulse sequence is proposed. In this new method, the pulse excitations are repeated during half a period of the resonance of the longitudinal detection circuit. The method is called the perturbative harmonic modulation method for longitudinally detected T1 measurement (HM-LOD-T1). HM-LOD-T1 experiments are demonstrated in 2,2-diphenyl-1-picrylhydrazyl (DPPH).

  9. Perturbative harmonic modulation of longitudinal electron-spin magnetization for short T(1) determination.

    Science.gov (United States)

    Suzuki, Takayuki

    2015-10-01

    Longitudinally detected T1 measurement scheme (LOD-T1) is studied in detail. In contrast to the original work on LOD-T1, using high power microwave pulses, this work deals with general and practically frequent cases in which perfect inversion of the electron-spin magnetization is not feasible due to the effect of relaxation during microwave pulses. Theoretical studies, numerical simulations, and experiments reveal a pair of separate contributions of the dynamics of the longitudinal magnetization to the LOD signal, namely, the periodic modulation and the relaxation contributions. The latter alone which is of interest can be extracted to give relaxation curves. In addition, it is shown that T1 information can be obtained even when the available microwave power is so low that the electron magnetization can only be perturbatively modulated, at the cost of reduced sensitivity. To overcome this, a modified pulse sequence is proposed. In this new method, the pulse excitations are repeated during half a period of the resonance of the longitudinal detection circuit. The method is called the perturbative harmonic modulation method for longitudinally detected T1 measurement (HM-LOD-T1). HM-LOD-T1 experiments are demonstrated in 2,2-diphenyl-1-picrylhydrazyl (DPPH). Copyright © 2015 Elsevier Inc. All rights reserved.

  10. T1ρ Magnetic Resonance Imaging to Assess Cartilage Damage After Primary Shoulder Dislocation.

    Science.gov (United States)

    Saxena, Vishal; D'Aquilla, Kevin; Marcoon, Shannon; Krishnamoorthy, Guruprasad; Gordon, Joshua A; Carey, James L; Borthakur, Ari; Kneeland, J Bruce; Kelly, John D; Reddy, Ravinder; Sennett, Brian J

    2016-11-01

    Patients who suffer anterior shoulder dislocations are at higher risk of developing glenohumeral arthropathy, but little is known about the initial cartilage damage after a primary shoulder dislocation. T1ρ is a magnetic resonance imaging (MRI) technique that allows quantification of cartilage proteoglycan content and can detect physiologic changes in articular cartilage. This study aimed to establish baseline T1ρ MRI values for glenoid and humeral head cartilage, determine whether T1ρ MRI can detect glenohumeral cartilage damage after traumatic primary shoulder dislocation, and assess for patterns in cartilage damage in anterior shoulder dislocation. Cross-sectional study; Level of evidence, 3. Nine male patients (mean age, 32.0 years; range, 20-59 years) who sustained first-time anterior shoulder dislocations underwent 3T T1ρ MRI. Five healthy controls (mean age, 27.4 years; range, 24-30 years) without prior dislocation or glenohumeral arthritis also underwent 3T T1ρ MRI. The T1ρ relaxation constant was determined for the entire glenoid and humeral head for patients with a dislocation and for healthy controls. The glenoid and humeral head were divided into 9 zones, and T1ρ values were determined for each zone in dislocated and control shoulders to identify patterns in cartilage damage in dislocated shoulders. Average overall T1ρ values for humeral head cartilage in dislocated shoulders were significantly greater than in controls (41.7 ± 3.9 ms vs 38.4 ± 0.6 ms, respectively; P = .03). However, average overall T1ρ values for glenoid cartilage were not significantly different in dislocated shoulders compared with controls (44.0 ± 3.3 ms vs 44.6 ± 2.4 ms, respectively; P = .40), suggesting worse damage to humeral head cartilage. T1ρ values in the posterior-middle humeral head were higher in patients with a dislocation compared with controls (41.5 ± 3.8 ms vs 38.2 ± 2.2 ms, respectively; P = .021) and trended toward significance in the posterior

  11. Dynamic Quantitative T1 Mapping in Orthotopic Brain Tumor Xenografts

    Directory of Open Access Journals (Sweden)

    Kelsey Herrmann

    2016-04-01

    Full Text Available Human brain tumors such as glioblastomas are typically detected using conventional, nonquantitative magnetic resonance imaging (MRI techniques, such as T2-weighted and contrast enhanced T1-weighted MRI. In this manuscript, we tested whether dynamic quantitative T1 mapping by MRI can localize orthotopic glioma tumors in an objective manner. Quantitative T1 mapping was performed by MRI over multiple time points using the conventional contrast agent Optimark. We compared signal differences to determine the gadolinium concentration in tissues over time. The T1 parametric maps made it easy to identify the regions of contrast enhancement and thus tumor location. Doubling the typical human dose of contrast agent resulted in a clearer demarcation of these tumors. Therefore, T1 mapping of brain tumors is gadolinium dose dependent and improves detection of tumors by MRI. The use of T1 maps provides a quantitative means to evaluate tumor detection by gadolinium-based contrast agents over time. This dynamic quantitative T1 mapping technique will also enable future quantitative evaluation of various targeted MRI contrast agents.

  12. Discrete effect on the halfway bounce-back boundary condition of multiple-relaxation-time lattice Boltzmann model for convection-diffusion equations

    Science.gov (United States)

    Cui, Shuqi; Hong, Ning; Shi, Baochang; Chai, Zhenhua

    2016-04-01

    In this paper, we will focus on the multiple-relaxation-time (MRT) lattice Boltzmann model for two-dimensional convection-diffusion equations (CDEs), and analyze the discrete effect on the halfway bounce-back (HBB) boundary condition (or sometimes called bounce-back boundary condition) of the MRT model where three different discrete velocity models are considered. We first present a theoretical analysis on the discrete effect of the HBB boundary condition for the simple problems with a parabolic distribution in the x or y direction, and a numerical slip proportional to the second-order of lattice spacing is observed at the boundary, which means that the MRT model has a second-order convergence rate in space. The theoretical analysis also shows that the numerical slip can be eliminated in the MRT model through tuning the free relaxation parameter corresponding to the second-order moment, while it cannot be removed in the single-relaxation-time model or the Bhatnagar-Gross-Krook model unless the relaxation parameter related to the diffusion coefficient is set to be a special value. We then perform some simulations to confirm our theoretical results, and find that the numerical results are consistent with our theoretical analysis. Finally, we would also like to point out the present analysis can be extended to other boundary conditions of lattice Boltzmann models for CDEs.

  13. The effect of the polymer relaxation time on the nonlinear energy cas- cade and dissipation of statistically steady and decaying homogeneous isotropic turbulence

    Science.gov (United States)

    Valente, Pedro C.; da Silva, Carlos B.; Pinho, Fernando T.

    2013-11-01

    We report a numerical study of statistically steady and decaying turbulence of FENE-P fluids for varying polymer relaxation times ranging from the Kolmogorov dissipation time-scale to the eddy turnover time. The total turbulent kinetic energy dissipation is shown to increase with the polymer relaxation time in both steady and decaying turbulence, implying a ``drag increase.'' If the total power input in the statistically steady case is kept equal in the Newtonian and the viscoelastic simulations the increase in the turbulence-polymer energy transfer naturally lead to the previously reported depletion of the Newtonian, but not the overall, kinetic energy dissipation. The modifications to the nonlinear energy cascade with varying Deborah/Weissenberg numbers are quantified and their origins investigated. The authors acknowledge the financial support from Fundação para a Ciência e a Tecnologia under grant PTDC/EME-MFE/113589/2009.

  14. Electron spin relaxation in graphene nanoribbon quantum dots

    Science.gov (United States)

    Droth, Matthias; Burkard, Guido

    2013-05-01

    Graphene is promising as a host material for electron spin qubits because of its predicted potential for long coherence times. In armchair graphene nanoribbons (aGNRs) a small band gap is opened, allowing for electrically gated quantum dots, and furthermore the valley degeneracy is lifted. The spin lifetime T1 is limited by spin relaxation, where the Zeeman energy is absorbed by lattice vibrations, mediated by spin-orbit and electron-phonon coupling. We have calculated T1 by treating all couplings analytically and find that T1 can be in the range of seconds for several reasons: (i) low phonon density of states away from Van Hove singularities; (ii) destructive interference between two relaxation mechanisms; (iii) Van Vleck cancellation at low magnetic fields; (iv) vanishing coupling to out-of-plane modes in lowest order due to the electronic structure of aGNRs. Owing to the vanishing nuclear spin of 12C, T1 may be a good measure for overall coherence. These results and recent advances in the controlled production of graphene nanoribbons make this system interesting for spintronics applications.

  15. Anomalous NMR Relaxation in Cartilage Matrix Components and Native Cartilage: Fractional-Order Models

    Science.gov (United States)

    Magin, Richard L.; Li, Weiguo; Velasco, M. Pilar; Trujillo, Juan; Reiter, David A.; Morgenstern, Ashley; Spencer, Richard G.

    2011-01-01

    We present a fractional-order extension of the Bloch equations to describe anomalous NMR relaxation phenomena (T1 and T2). The model has solutions in the form of Mittag-Leffler and stretched exponential functions that generalize conventional exponential relaxation. Such functions have been shown by others to be useful for describing dielectric and viscoelastic relaxation in complex, heterogeneous materials. Here, we apply these fractional-order T1 and T2 relaxation models to experiments performed at 9.4 and 11.7 Tesla on type I collagen gels, chondroitin sulfate mixtures, and to bovine nasal cartilage (BNC), a largely isotropic and homogeneous form of cartilage. The results show that the fractional-order analysis captures important features of NMR relaxation that are typically described by multi-exponential decay models. We find that the T2 relaxation of BNC can be described in a unique way by a single fractional-order parameter (α), in contrast to the lack of uniqueness of multi-exponential fits in the realistic setting of a finite signal-to-noise ratio. No anomalous behavior of T1 was observed in BNC. In the single-component gels, for T2 measurements, increasing the concentration of the largest components of cartilage matrix, collagen and chondroitin sulfate, results in a decrease in α, reflecting a more restricted aqueous environment. The quality of the curve fits obtained using Mittag-Leffler and stretched exponential functions are in some cases superior to those obtained using mono- and bi-exponential models. In both gels and BNC, α appears to account for microstructural complexity in the setting of an altered distribution of relaxation times. This work suggests the utility of fractional-order models to describe T2 NMR relaxation processes in biological tissues. PMID:21498095

  16. Rapid Simultaneous Mapping of Total and Myelin Water Content, T1 and T2* in Multiple Sclerosis

    CERN Document Server

    Arhelger, Volker; Gliedstein, Detlef; Lafontaine, Marie-Sofie; Tonkova, Vyara; Holz, Dietrich; Böer, Andreas; Schenk, Jochen; Neeb, Heiko; (,; Koblenz, University of Applied Sciences; Koblenz, Radiologisches Institut Hohenzollernstrasse; Engineering, Institute for Medical; Koblenz, Information Processing; Boeer, Neurologie Dr; Koblenz,

    2010-01-01

    Quantitative magnetic resonance imaging might provide a more specific insight into disease process, progression and therapeutic response of multiple sclerosis. We present an extension of a previously published approach for the simultaneous mapping of brain T1, T2* and total water content. In addition to those three parameters, the method presented in the current work allows for the measurement of myelin bound water content, a surrogate marker of tissue myelination. Myelin water was measured based on its distinct relaxation with reduced T2*, resulting in a multiexponential decay signal. However, only 10 points could be acquired on the relaxation curve within a maximum echo time of <40ms as the quantitative protocol has been adapted previously for fast acquisitions with whole brain coverage. The sparse sampling required an adaption of the optimisation approach with additional constraints necessary in order to obtain reliable results. Therefore, the corresponding pool fractions were determined using linear op...

  17. 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.

  18. Analytical representation of time correlation functions and application to relaxation problems; Representation analytique des fonctions de correlation temporelle et application a des problemes de relaxation

    Energy Technology Data Exchange (ETDEWEB)

    Dupuis, M. [Commissariat a l' Energie Atomique, 91 - Saclay (France). Centre d' Etudes Nucleaires, departement de physico-chimie, services des isotopes stables

    1971-07-01

    Two analytical representations of the Laplace transform of the time autocorrelation of a dynamical variable, namely the moment expansion and Mori's continued fraction expansion, are investigated from the point of view of structure and convergence properties, and the relation between them is established. The general theory is applied first to a dynamical model exactly solvable, the isotopic impurity in a linear chain of coupled harmonic oscillators, and then to two stochastic models recently introduced by Gordon for the rotational diffusion of molecules. In the latter case, the continued fraction expansion yields simple analytical expressions for the infrared absorption band shapes, showing that these models contain all the features of observed shapes in compressed gases, liquids and solutions. (author) [French] Deux representations analytiques de la transformee de Laplace de la fonction d'autocorrelation temporelle d'une variable dynamique, le developpement en moments et le developpement en fraction continue recemment introduit par Mori, sont etudiees du point de vue de leurs proprietes de structure et de convergence, en meme temps que la relation qui existe entre elles est etablie. La theorie generale est appliquee, d'une part, a un modele dynamique exactement soluble, celui d'une particule isotopique dans une chaine lineaire d'oscillateurs harmoniques couples, et, d'autre part, a deux modeles stochastiques recemment proposes par Gordon pour la diffusion rotationnelle des molecules. Dans ce dernier cas, la voie de la fraction continue fournit des expressions analytiques simples pour les formes de bande d'absorption infrarouge, montrant que ces modeles possedent les caracteristiques des formes observees dans les gaz comprimes, les liquides ou les solutions. (auteur)

  19. The Arrow of Time in the Collapse of Collisionless Self-gravitating Systems: Non-validity of the Vlasov-Poisson Equation during Violent Relaxation

    Science.gov (United States)

    Beraldo e Silva, Leandro; de Siqueira Pedra, Walter; Sodré, Laerte; Perico, Eder L. D.; Lima, Marcos

    2017-09-01

    The collapse of a collisionless self-gravitating system, with the fast achievement of a quasi-stationary state, is driven by violent relaxation, with a typical particle interacting with the time-changing collective potential. It is traditionally assumed that this evolution is governed by the Vlasov-Poisson equation, in which case entropy must be conserved. We run N-body simulations of isolated self-gravitating systems, using three simulation codes, NBODY-6 (direct summation without softening), NBODY-2 (direct summation with softening), and GADGET-2 (tree code with softening), for different numbers of particles and initial conditions. At each snapshot, we estimate the Shannon entropy of the distribution function with three different techniques: Kernel, Nearest Neighbor, and EnBiD. For all simulation codes and estimators, the entropy evolution converges to the same limit as N increases. During violent relaxation, the entropy has a fast increase followed by damping oscillations, indicating that violent relaxation must be described by a kinetic equation other than the Vlasov-Poisson equation, even for N as large as that of astronomical structures. This indicates that violent relaxation cannot be described by a time-reversible equation, shedding some light on the so-called “fundamental paradox of stellar dynamics.” The long-term evolution is well-described by the orbit-averaged Fokker-Planck model, with Coulomb logarithm values in the expected range 10{--}12. By means of NBODY-2, we also study the dependence of the two-body relaxation timescale on the softening length. The approach presented in the current work can potentially provide a general method for testing any kinetic equation intended to describe the macroscopic evolution of N-body systems.

  20. The contrasting roles of creep and stress relaxation in the time-dependent deformation during in-situ cooling of a nickel-base single crystal superalloy.

    Science.gov (United States)

    Panwisawas, Chinnapat; D'Souza, Neil; Collins, David M; Bhowmik, Ayan

    2017-09-11

    Time dependent plastic deformation in a single crystal nickel-base superalloy during cooling from casting relevant temperatures has been studied using a combination of in-situ neutron diffraction, transmission electron microscopy and modelling. Visco-plastic deformation during cooling was found to be dependent on the stress and constraints imposed to component contraction during cooling, which mechanistically comprises creep and stress relaxation. Creep results in progressive work hardening with dislocations shearing the γ' precipitates, a high dislocation density in the γ channels and near the γ/γ' interface and precipitate shearing. When macroscopic contraction is restricted, relaxation dominates. This leads to work softening from a decreased dislocation density and the presence of long segment stacking faults in γ phase. Changes in lattice strains occur to a similar magnitude in both the γ and γ' phases during stress relaxation, while in creep there is no clear monotonic trend in lattice strain in the γ phase, but only a marginal increase in the γ' precipitates. Using a visco-plastic law derived from in-situ experiments, the experimentally measured and calculated stresses during cooling show a good agreement when creep predominates. However, when stress relaxation dominates accounting for the decrease in dislocation density during cooling is essential.

  1. Assessment of T1, T1ρ, and T2 values of the ulnocarpal disc in healthy subjects at 3 tesla.

    Science.gov (United States)

    Rauscher, Isabel; Bender, Benjamin; Grözinger, Gerd; Luz, Oliver; Pohmann, Rolf; Erb, Michael; Schick, Fritz; Martirosian, Petros

    2014-11-01

    The purpose of this study was to implement clinically feasible imaging techniques for determination of T1, T1ρ, and T2 values of the ulnocarpal disc and to assess those values in a cohort of asymptomatic subjects at 3 tesla. Resulting values were compared between different age groups, since former histological findings of the ulnocarpal disc indicated frequent early degenerative changes of this tissue starting in the third decade of life, even in asymptomatic subjects. Twenty-seven healthy subjects were included in this study. T1 measurements were performed using 3D spoiled gradient-echo (GRE) sequence with variable flip angle. A series of T1ρ and T2-weighted images was acquired by a 3D GRE sequence after suitable magnetization preparation. T1,T1ρ, and T2 maps of the ulnocarpal disc were calculated pixel-wise. Representative mean values from extended regions were analysed. Mean T1 values of the ulnocarpal disc ranged from 722 ms in a 39 year-old subject to 1264 ms in a 65 year-old subject, T1ρ ranged from 9.2 ms (26 year-old subject) to 25.9 ms (65 year-old subject). Calculated T2 values showed a large range from 4.1 ms to 22.3 ms. T1ρ and T1 values tended to increase with age (p<0.05), whereas T2 did not. MR relaxometry of the ulnocarpal disc is feasible, and T1,T1ρ, and T2 values show modest variance in asymptomatic subjects. The potential of relaxation mapping to reveal relevant structural changes in patients has to be investigated in further studies. Copyright © 2014 Elsevier Inc. All rights reserved.

  2. Clinical feasibility of 3D-QALAS - Single breath-hold 3D myocardial T1- and T2-mapping.

    Science.gov (United States)

    Kvernby, Sofia; Warntjes, Marcel; Engvall, Jan; Carlhäll, Carl-Johan; Ebbers, Tino

    2017-05-01

    To investigate the in-vivo precision and clinical feasibility of 3D-QALAS - a novel method for simultaneous three-dimensional myocardial T1- and T2-mapping. Ten healthy subjects and 23 patients with different cardiac pathologies underwent cardiovascular 3T MRI examinations including 3D-QALAS, MOLLI and T2-GraSE acquisitions. Precision was investigated in the healthy subjects between independent scans, between dependent scans and as standard deviation of consecutive scans. Clinical feasibility of 3D-QALAS was investigated for native and contrast enhanced myocardium in patients. Data were analyzed using mean value and 95% confidence interval, Pearson correlation, Paired t-tests, intraclass correlation and Bland-Altman analysis. Average myocardial relaxation time values and SD from eight repeated acquisitions within the group of healthy subjects were 1178±18.5ms (1.6%) for T1 with 3D-QALAS, 52.7±1.2ms (2.3%) for T2 with 3D-QALAS, 1145±10.0ms (0.9%) for T1 with MOLLI and 49.2±0.8ms (1.6%) for T2 with GraSE. Myocardial T1 and T2 relaxation times obtained with 3D-QALAS correlated very well with reference methods; MOLLI for T1 (r=0.994) and T2-GraSE for T2 (r=0.818) in the 23 patients. Average native/post-contrast myocardial T1 values from the patients were 1166.2ms/411.8ms for 3D-QALAS and 1174.4ms/438.9ms for MOLLI. Average native myocardial T2 values from the patients were 53.2ms for 3D-QALAS and 54.4ms for T2-GraSE. Repeated independent and dependent scans together with the intra-scan repeatability, demonstrated all a very good precision for the 3D-QALAS method in healthy volunteers. This study shows that 3D T1 and T2 mapping in the left ventricle is feasible in one breath hold for patients with different cardiac pathologies using 3D-QALAS. Copyright © 2016 Elsevier Inc. All rights reserved.

  3. Determination of intra-axial brain tumors cellularity through the analysis of T2 Relaxation time of brain tumors before surgery using MATLAB software.

    Science.gov (United States)

    Abdolmohammadi, Jamil; Shafiee, Mohsen; Faeghi, Fariborz; Arefan, Douman; Zali, Alireza; Motiei-Langroudi, Rouzbeh; Farshidfar, Zahra; Nazarlou, Ali Kiani; Tavakkoli, Ali; Yarham, Mohammad

    2016-08-01

    Timely diagnosis of brain tumors could considerably affect the process of patient treatment. To do so, para-clinical methods, particularly MRI, cannot be ignored. MRI has so far answered significant questions regarding tumor characteristics, as well as helping neurosurgeons. In order to detect the tumor cellularity, neuro-surgeons currently have to sample specimens by biopsy and then send them to the pathology unit. The aim of this study is to determine the tumor cellularity in the brain. In this cross-sectional study, 32 patients (18 males and 14 females from 18-77 y/o) were admitted to the neurosurgery department of Shohada-E Tajrish Hospital in Tehran, Iran from April 2012 to February 2014. In addition to routine pulse sequences, T2W Multi echo pulse sequences were taken and the images were analyzed using the MATLAB software to determine the brain tumor cellularity, compared with the biopsy. These findings illustrate the need for more T2 relaxation time decreases, the higher classes of tumors will stand out in the designed table. In this study, the results show T2 relaxation time with a 85% diagnostic weight, compared with the biopsy, to determine the brain tumor cellularity (p<0.05). Our results indicate that the T2 relaxation time feature is the best method to distinguish and present the degree of intra-axial brain tumors cellularity (85% accuracy compared to biopsy). The use of more data is recommended in order to increase the percent accuracy of this techniques.

  4. Free-breathing post-contrast three-dimensional T1 mapping: Volumetric assessment of myocardial T1 values.

    Science.gov (United States)

    Weingärtner, Sebastian; Akçakaya, Mehmet; Roujol, Sébastien; Basha, Tamer; Stehning, Christian; Kissinger, Kraig V; Goddu, Beth; Berg, Sophie; Manning, Warren J; Nezafat, Reza

    2015-01-01

    To develop a three-dimensional (3D) free-breathing myocardial T1 mapping sequence for assessment of left ventricle diffuse fibrosis after contrast administration. In the proposed sequence, multiple 3D inversion recovery images are acquired in an interleaved manner. A mixed prospective/retrospective navigator scheme is used to obtain the 3D Cartesian k-space data with fully sampled center and randomly undersampled outer k-space. The resulting undersampled 3D k-space data are then reconstructed using compressed sensing. Subsequently, T1 maps are generated by voxel-wise curve fitting of the individual interleaved images. In a phantom study, the accuracy of the 3D sequence was evaluated against two-dimensional (2D) modified Look-Locker inversion recovery (MOLLI) and spin-echo sequences. In vivo T1 times of the proposed method were compared with 2D multislice MOLLI T1 mapping. Subsequently, the feasibility of high-resolution 3D T1 mapping with spatial resolution of 1.7 × 1.7 × 4 mm(3) was demonstrated. The proposed method shows good agreement with 2D MOLLI and the spin-echo reference in phantom. No significant difference was found in the in vivo T1 times estimated using the proposed sequence and the 2D MOLLI technique (myocardium, 330 ± 66 ms versus 319 ± 93 ms; blood pools, 211 ± 68 ms versus 210 ± 98 ms). However, improved homogeneity, as measured using standard deviation of the T1 signal, was observed in the 3D T1 maps. The proposed sequence enables high-resolution 3D T1 mapping after contrast injection during free-breathing with volumetric left ventricle coverage. © 2014 Wiley Periodicals, Inc.

  5. Acoustic multipole sources for the regularized lattice Boltzmann method: Comparison with multiple-relaxation-time models in the inviscid limit

    Science.gov (United States)

    Zhuo, Congshan; Sagaut, Pierre

    2017-06-01

    In this paper, a variant of the acoustic multipole source (AMS) method is proposed within the framework of the lattice Boltzmann method. A quadrupole term is directly included in the stress system (equilibrium momentum flux), and the dependency of the quadrupole source in the inviscid limit upon the fortuitous discretization error reported in the works of E. M. Viggen [Phys. Rev. E 87, 023306 (2013), 10.1103/PhysRevE.87.023306] is removed. The regularized lattice Boltzmann (RLB) method with this variant AMS method is presented for the 2D and 3D acoustic problems in the inviscid limit, and without loss of generality, the D3Q19 model is considered in this work. To assess the accuracy and the advantage of the RLB scheme with this AMS for acoustic point sources, the numerical investigations and comparisons with the multiple-relaxation-time (MRT) models and the analytical solutions are performed on the 2D and 3D acoustic multipole point sources in the inviscid limit, including monopoles, x dipoles, and x x quadrupoles. From the present results, the good precision of this AMS method is validated, and the RLB scheme exhibits some superconvergence properties for the monopole sources compared with the MRT models, and both the RLB and MRT models have the same accuracy for the simulations of acoustic dipole and quadrupole sources. To further validate the capability of the RLB scheme with AMS, another basic acoustic problem, the acoustic scattering from a solid cylinder presented at the Second Computational Aeroacoustics Workshop on Benchmark Problems, is numerically considered. The directivity pattern of the acoustic field is computed at r =7.5 ; the present results agree well with the exact solutions. Also, the effects of slip and no-slip wall treatments within the regularized boundary condition on this pure acoustic scattering problem are tested, and compared with the exact solution, the slip wall treatment can present a better result. All simulations demonstrate that the

  6. The contrasting roles of creep and stress relaxation in the time-dependent deformation during in-situ cooling of a nickel-base single crystal superalloy

    OpenAIRE

    Panwisawas, Chinnapat; D?Souza, Neil; David M. Collins; Bhowmik, Ayan

    2017-01-01

    Time dependent plastic deformation in a single crystal nickel-base superalloy during cooling from casting relevant temperatures has been studied using a combination of in-situ neutron diffraction, transmission electron microscopy and modelling. Visco-plastic deformation during cooling was found to be dependent on the stress and constraints imposed to component contraction during cooling, which mechanistically comprises creep and stress relaxation. Creep results in progressive work hardening w...

  7. T1 Shortening in the Globus Pallidus after Multiple Administrations of Gadobutrol: Assessment with a Multidynamic Multiecho Sequence.

    Science.gov (United States)

    Kang, Koung Mi; Choi, Seung Hong; Hwang, Moonjung; Yun, Tae Jin; Kim, Ji-Hoon; Sohn, Chul-Ho

    2017-11-01

    Purpose To determine the association between the administration of the macrocyclic contrast medium gadobutrol and T1 relaxation time in the brains of patients with normal renal function by using multidynamic multiecho (MDME) magnetic resonance (MR) imaging sequences. Materials and Methods The institutional review board approved this retrospective study, and the need to obtain written informed consent was waived. This study included 46 patients (revealed by an electronic medical record search) who had received one or more gadobutrol injections and a maximum of one MR imaging contrast medium injection other than gadobutrol before MDME sequence acquisition. One radiologist performed quantitative analyses of regions of interest on quantitative T1 maps twice to cover the normal-appearing globus pallidus (GP), frontal white matter, frontal cortex, and thalamus. The number of administrations and the cumulative dose of gadobutrol, age, intervals between administrations, sex, and treatment were investigated. Univariable and multivariable linear regression analyses of the T1 values in four brain regions and the GP-to-thalamus signal intensity (SI) ratio were performed. P values of less than the Bonferroni-corrected value of .01 were considered to indicate significant differences. Results Intraobserver reproducibility was good to excellent (intraclass correlation coefficients, 0.62-0.81). Because of high multicollinearity between the number of gadobutrol administrations and accumulated dose (r = 0.96, P .01). Conclusion Multiple exposures to gadobutrol are associated with T1 shortening in the GP. (©) RSNA, 2017 Online supplemental material is available for this article.

  8. Hydration of surfactant-modified and PEGylated cationic cholesterol-based liposomes and corresponding lipoplexes by monitoring a fluorescent probe and the dielectric relaxation time.

    Science.gov (United States)

    Maitani, Yoshie; Nakamura, Ayako; Tanaka, Takumi; Aso, Yukio

    2012-05-10

    For the optimization of plasmid DNA (pDNA)-cationic lipid complexes and lipoplex delivery, proper indexes of the physicochemical properties of lipoplexes are required. In general, the characteristics of lipoplexes are defined by particle size and zeta-potential at various mixing ratios of cationic liposomes and pDNA. In this study, we characterized the hydration level of surfactant-modified and PEGylated cationic cholesterol-based (OH-Chol) liposomes and their lipoplexes by monitoring both the fluorescent probe laurdan and the dielectric relaxation time. Fluorescence measurement using laurdan detected hydration of the headgroup of lipids in surfactant-modified liposomes and PEGylated DOTAP-liposomes, but hardly any fluorescence was detected in PEGylated OH-Chol-liposomes because the PEG layers may extend and cover the fluorescent maker. On the other hand, the measurement of dielectric relaxation time of water molecules revealed total hydration, including hydration of the PEG layer and the headgroup of cationic lipids. Furthermore, we found an inverse correlation between hydration level and cellular uptake of PEGylated lipoplexes (R=0.946). This finding indicated that the dielectric relaxation time of water molecules provides an important indicator of hydration of liposome and lipoplexes along with the fluorescence intensity of laurdan. Copyright © 2012 Elsevier B.V. All rights reserved.

  9. Improved T1 mapping by motion correction and template based B1 correction in 3T MRI brain studies

    Science.gov (United States)

    Castro, Marcelo A.; Yao, Jianhua; Lee, Christabel; Pang, Yuxi; Baker, Eva; Butman, John; Thomasson, David

    2009-02-01

    Accurate estimation of relaxation time T1 from MRI images is increasingly important for some clinical applications. Low noise, high resolution, fast and accurate T1 maps from MRI images of the brain can be performed using a dual flip angle method. However, accuracy is limited by the scanners ability to deliver the prescribed flip angle due to the B1 inhomogeneity, particularly at high field strengths (e.g. 3T). One of the most accurate methods to correct that inhomogeneity is to acquire a subject-specific B1 map. However, since B1 map acquisition takes up precious scanning time and most retrospective studies do not have B1 map, it would be desirable to perform that correction from a template. For this work a dual repetition time method was used for B1 map acquisition in five normal subjects. Inaccuracies due to misregistration of acquired T1-weighted images were corrected by rigid registration, and the effects of misalignment were compared to those of B1 inhomogeneity. T1-intensity histograms were produced and three-Gaussian curves were fitted for every fully-, partially- and non-corrected histogram in order to estimate and compare the white and gray matter peaks. In addition, in order to reduce the scanning time we designed a template based correction strategy. Images from different subjects were aligned using a twelve-parameter affine registration, and B1 maps were aligned according to that transformation. Recomputed T1 maps showed a significant improvement with respect to non-corrected ones. These results are very promising and have the potential for clinical application.

  10. Sodium and T1rho MRI for molecular and diagnostic imaging of articular cartilage.

    Science.gov (United States)

    Borthakur, Arijitt; Mellon, Eric; Niyogi, Sampreet; Witschey, Walter; Kneeland, J Bruce; Reddy, Ravinder

    2006-11-01

    In this article, both sodium magnetic resonance (MR) and T1rho relaxation mapping aimed at measuring molecular changes in cartilage for the diagnostic imaging of osteoarthritis are reviewed. First, an introduction to structure of cartilage, its degeneration in osteoarthritis (OA) and an outline of diagnostic imaging methods in quantifying molecular changes and early diagnostic aspects of cartilage degeneration are described. The sodium MRI section begins with a brief overview of the theory of sodium NMR of biological tissues and is followed by a section on multiple quantum filters that can be used to quantify both bi-exponential relaxation and residual quadrupolar interaction. Specifically, (i) the rationale behind the use of sodium MRI in quantifying proteoglycan (PG) changes, (ii) validation studies using biochemical assays, (iii) studies on human OA specimens, (iv) results on animal models and (v) clinical imaging protocols are reviewed. Results demonstrating the feasibility of quantifying PG in OA patients and comparison with that in healthy subjects are also presented. The section concludes with the discussion of advantages and potential issues with sodium MRI and the impact of new technological advancements (e.g. ultra-high field scanners and parallel imaging methods). In the theory section on T1rho, a brief description of (i) principles of measuring T1rho relaxation, (ii) pulse sequences for computing T1rho relaxation maps, (iii) issues regarding radio frequency power deposition, (iv) mechanisms that contribute to T1rho in biological tissues and (v) effects of exchange and dipolar interaction on T1rho dispersion are discussed. Correlation of T1rho relaxation rate with macromolecular content and biomechanical properties in cartilage specimens subjected to trypsin and cytokine-induced glycosaminoglycan depletion and validation against biochemical assay and histopathology are presented. Experimental T1rho data from osteoarthritic specimens, animal models

  11. Molecular Relaxation in Liquids

    CERN Document Server

    Bagchi, Biman

    2012-01-01

    This book brings together many different relaxation phenomena in liquids under a common umbrella and provides a unified view of apparently diverse phenomena. It aligns recent experimental results obtained with modern techniques with recent theoretical developments. Such close interaction between experiment and theory in this area goes back to the works of Einstein, Smoluchowski, Kramers' and de Gennes. Development of ultrafast laser spectroscopy recently allowed study of various relaxation processes directly in the time domain, with time scales going down to picosecond (ps) and femtosecond (fs

  12. Influence of aging time of oleate precursor on the magnetic relaxation of cobalt ferrite nanoparticles synthesized by the thermal decomposition method

    Energy Technology Data Exchange (ETDEWEB)

    Herrera, Adriana P.; Polo-Corrales, Liliana [Department of Chemical Engineering, University of Puerto Rico, Mayagueez, Puerto Rico, PR 00681-9000 (United States); Chavez, Ermides; Cabarcas-Bolivar, Jari [Department of Physics, University of Puerto Rico, Mayagueez, Puerto Rico, PR 00681-9000 (United States); Uwakweh, Oswald N.C. [Department of General Engineering, University of Puerto Rico, Mayagueez, Puerto Rico, PR 00681-9000 (United States); Rinaldi, Carlos, E-mail: crinaldi@uprm.edu [Department of Chemical Engineering, University of Puerto Rico, Mayagueez, Puerto Rico, PR 00681-9000 (United States)

    2013-02-15

    Cobalt ferrite nanoparticles are of interest because of their room temperature coercivity and high magnetic anisotropy constant, which make them attractive in applications such as sensors based on the Brownian relaxation mechanism and probes to determine the mechanical properties of complex fluids at the nanoscale. These nanoparticles can be synthesized with a narrow size distribution by the thermal decomposition of an iron-cobalt oleate precursor in a high boiling point solvent. We studied the influence of aging time of the iron-cobalt oleate precursor on the structure, chemical composition, size, and magnetic relaxation of cobalt ferrite nanoparticles synthesized by the thermal decomposition method. The structure and thermal behavior of the iron-cobalt oleate was studied during the aging process. Infrared spectra indicated a shift in the coordination state of the oleate and iron/cobalt ions from bidentate to bridging coordination. Aging seemed to influence the thermal decomposition of the iron-cobalt oleate as determined from thermogravimmetric analysis and differential scanning calorimetry, where shifts in the temperatures corresponding to decomposition events and a narrowing of the endotherms associated with these events were observed. Aging promoted formation of the spinel crystal structure, as determined from X-ray diffraction, and influenced the nanoparticle magnetic properties, resulting in an increase in blocking temperature and magnetocrystalline anisotropy. Mossbauer spectra also indicated changes in the magnetic properties resulting from aging of the precursor oleate. Although all samples exhibited some degree of Brownian relaxation, as determined from complex susceptibility measurements in a liquid medium, aging of the iron-cobalt oleate precursor resulted in crossing of the in-phase {chi} Prime and out-of-phase {chi} Double-Prime components of the complex susceptibility at the frequency of the Brownian magnetic relaxation peak, as expected for

  13. T1 mapping of the myocardium: Intra-individual assessment of the effect of field strength, cardiac cycle and variation by myocardial region

    Directory of Open Access Journals (Sweden)

    Kawel Nadine

    2012-05-01

    Full Text Available Abstract Background Myocardial T1 relaxation time (T1 time and extracellular volume fraction (ECV are altered in the presence of myocardial fibrosis. The purpose of this study was to evaluate acquisition factors that may result in variation of measured T1 time and ECV including magnetic field strength, cardiac phase and myocardial region. Methods 31 study subjects were enrolled and underwent one cardiovascular MR exam at 1.5 T and two exams at 3 T, each on separate days. A Modified Look-Locker Inversion Recovery (MOLLI sequence was acquired before and 5, 10, 12, 20, 25 and 30 min after administration of 0.15 mmol/kg gadopentetate dimeglumine (Gd-DTPA; Magnevist at 1.5 T (exam 1. For exam 2, MOLLI sequences were acquired at 3 T both during diastole and systole, before and after administration of Gd-DTPA (0.15 mmol/kg Magnevist.Exam 3 was identical to exam 2 except gadobenate dimeglumine was administered (Gd-BOPTA; 0.1 mmol/kg Multihance. T1 times were measured in myocardium and blood. ECV was calculated by (ΔR1myocardium/ΔR1blood*(1-hematocrit. Results Before gadolinium, T1 times of myocardium and blood were significantly greater at 3 T versus 1.5 T (28% and 31% greater, respectively, p  Conclusion ECV is similar at field strengths of 1.5 T and 3 T. Due to minor variations in T1 time and ECV during the cardiac cycle and in different myocardial regions, T1 measurements should be obtained at the same cardiac phase and myocardial region in order to obtain consistent results.

  14. T1 mapping of the myocardium: intra-individual assessment of the effect of field strength, cardiac cycle and variation by myocardial region.

    Science.gov (United States)

    Kawel, Nadine; Nacif, Marcelo; Zavodni, Anna; Jones, Jacquin; Liu, Songtao; Sibley, Christopher T; Bluemke, David A

    2012-05-01

    Myocardial T1 relaxation time (T1 time) and extracellular volume fraction (ECV) are altered in the presence of myocardial fibrosis. The purpose of this study was to evaluate acquisition factors that may result in variation of measured T1 time and ECV including magnetic field strength, cardiac phase and myocardial region. 31 study subjects were enrolled and underwent one cardiovascular MR exam at 1.5 T and two exams at 3 T, each on separate days. A Modified Look-Locker Inversion Recovery (MOLLI) sequence was acquired before and 5, 10, 12, 20, 25 and 30 min after administration of 0.15 mmol/kg gadopentetate dimeglumine (Gd-DTPA; Magnevist) at 1.5 T (exam 1). For exam 2, MOLLI sequences were acquired at 3 T both during diastole and systole, before and after administration of Gd-DTPA (0.15 mmol/kg Magnevist).Exam 3 was identical to exam 2 except gadobenate dimeglumine was administered (Gd-BOPTA; 0.1 mmol/kg Multihance). T1 times were measured in myocardium and blood. ECV was calculated by (ΔR1myocardium/ΔR1blood)*(1-hematocrit). Before gadolinium, T1 times of myocardium and blood were significantly greater at 3 T versus 1.5 T (28% and 31% greater, respectively, p Myocardial T1 time was 1% shorter at systole compared to diastole pre-contrast and 2% shorter at diastole compared to systole post-contrast (p myocardial regions, T1 measurements should be obtained at the same cardiac phase and myocardial region in order to obtain consistent results.

  15. Native myocardial T1 mapping in pulmonary hypertension: correlations with cardiac function and hemodynamics.

    Science.gov (United States)

    Reiter, Ursula; Reiter, Gert; Kovacs, Gabor; Adelsmayr, Gabriel; Greiser, Andreas; Olschewski, Horst; Fuchsjäger, Michael

    2017-01-01

    To analyze alterations in left ventricular (LV) myocardial T1 times in patients with pulmonary hypertension (PH) and to investigate their associations with ventricular function, mass, geometry and hemodynamics. Fifty-eight patients with suspected PH underwent right heart catheterization (RHC) and 3T cardiac magnetic resonance imaging. Ventricular function, geometry and mass were derived from cine real-time short-axis images. Myocardial T1 maps were acquired by a prototype modified Look-Locker inversion-recovery sequence in short-axis orientations. LV global, segmental and ventricular insertion point (VIP) T1 times were evaluated manually and corrected for blood T1. Septal, lateral, global and VIP T1 times were significantly higher in PH than in non-PH subjects (septal, 1249 ± 58 ms vs. 1186 ± 33 ms, p T1 (r = 0.72). Septal, lateral and global T1 showed strong correlations with VIP T1 (r = 0.81, r = 0.59 and r = 0.75, respectively). In patients with PH, T1 times in VIPs and in the entire LV myocardium are elevated. LV eccentricity strongly correlates with VIP T1 time, which in turn is strongly associated with T1 time changes in the entire LV myocardium. • Native T1 mapping detects left ventricular myocardial alterations in pulmonary hypertension • In pulmonary hypertension, native T1 times at ventricular insertion points are increased • These T1 times correlate strongly with left ventricular eccentricity • In pulmonary hypertension, global and segmental myocardial T1 times are increased • Global, segmental and ventricular insertion point T1 times are strongly correlated.

  16. Robust determination of surface relaxivity from nuclear magnetic resonance DT(2) measurements.

    Science.gov (United States)

    Luo, Zhi-Xiang; Paulsen, Jeffrey; Song, Yi-Qiao

    2015-10-01

    Nuclear magnetic resonance (NMR) is a powerful tool to probe into geological materials such as hydrocarbon reservoir rocks and groundwater aquifers. It is unique in its ability to obtain in situ the fluid type and the pore size distributions (PSD). The T1 and T2 relaxation times are closely related to the pore geometry through the parameter called surface relaxivity. This parameter is critical for converting the relaxation time distribution into the PSD and so is key to accurately predicting permeability. The conventional way to determine the surface relaxivity ρ2 had required independent laboratory measurements of the pore size. Recently Zielinski et al. proposed a restricted diffusion model to extract the surface relaxivity from the NMR diffusion-T2 relaxation (DT2) measurement. Although this method significantly improved the ability to directly extract surface relaxivity from a pure NMR measurement, there are inconsistencies with their model and it relies on a number of preset parameters. Here we propose an improved signal model to incorporate a scalable LT and extend their method to extract the surface relaxivity based on analyzing multiple DT2 maps with varied diffusion observation time. With multiple diffusion observation times, the apparent diffusion coefficient correctly describes the restricted diffusion behavior in samples with wide PSDs, and the new method does not require predetermined parameters, such as the bulk diffusion coefficient and tortuosity. Laboratory experiments on glass beads packs with the beads diameter ranging from 50 μm to 500 μm are used to validate the new method. The extracted diffusion parameters are consistent with their known values and the determined surface relaxivity ρ2 agrees with the expected value within ±7%. This method is further successfully applied on a Berea sandstone core and yields surface relaxivity ρ2 consistent with the literature. Copyright © 2015 Elsevier Inc. All rights reserved.

  17. UN H and SH H cross-relaxation in hydrated proteins

    Energy Technology Data Exchange (ETDEWEB)

    Winter, F.; Kimmich, R.

    1985-08-01

    The frequency dependence of the proton spin-lattice relaxation time T1 of solid hydrated bovine serum albumin and alpha-chymotrypsin has been measured over 4.5 decades in the range 10(4) to 3 X 10(8) Hz mainly by the aid of the field-cycling technique. The comparison between H2O- and D2O-hydrated samples permitted the distinction of exchangeable and unexchangeable protons. In all cases the UN H cross-relaxation dips due mainly to the amide groups have been observed. In addition, in the case of the deuterium exchanged proteins a SH H quadrupole dip appears. The amide groups act as relaxation sinks due to the coupling of the amide proton to UN and adjacent protons. Outside of the dip regions the proton-proton coupling dominates. The fluctuations of the UN H and H H interactions are of a different type. The unexchangeable protons show a T1 dispersion outside of the quadrupole dip regions given by the exceptional power law T1 approximately v0.75 +/- 0.05. It is shown that apart from structural information of the UN spectra, UN H cross-relaxation spectroscopy permits the determination of correlation times in the range 10(-7) s less than tau less than 10(-4)S.

  18. Assessment of T2 Relaxation Times for Normal Canine Knee Articular Cartilage by T2 Mapping Using 1.5-T Magnetic Resonance Imaging.

    Science.gov (United States)

    Matsui, Asami; Shimizu, Miki; Beale, Brian; Takahashi, Fumitaka; Yamaguchi, Sinya

    2017-11-01

    Objectives  This study aims to assess and compare the T2 relaxation times for articular cartilage of normal canine stifle joints in four regions by T2 mapping using a 1.5-T magnetic resonance imaging (MRI). Methods   In vivo prospective study: 20 hindlimbs (left and right) from 10 normal healthy beagle dogs ( n  = 20). The region of interest (ROI) was subdivided into medial and lateral condyles of femoral cartilage (MF and LF, respectively) and medial and lateral condyles of tibial cartilage (MT and LT, respectively). The T2 relaxation times were assessed in regions where the cartilage thickness was greater than 0.5 mm. Results  The median maximum cartilage thickness (mm) of the four ROI were 0.7 (range: 0.9-0.6), 0.6 (range: 0.7-0.5), 0.7 (range: 0.9-0.5) and 0.6 (range: 0.8-0.5) at MF, LF, MT and LT, respectively. The errors in the measurement (%) of the four ROI were 64.3 (range: 50.0-75.0), 75.0 (range: 64.3-90.0), 64.3 (range: 20.0-90.0) and 75.0 (range: 56.3-90.0) at MF, LF, MT and LT, respectively. The median T2 relaxation times (ms) for the articular cartilage of the four ROI were 70.2 (range: 57.9-87.9), 57.5 (range: 46.8-66.9), 65.0 (range: 52.0-92.0) and 57.0 (range: 49.0-66.2) at MF, LF, MT and LT, respectively. The inter-observer correlation coefficient (ICC, 2.1) for the T2 relaxation times of MF was 0.644. Clinical Significance  This study offers useful information on T2 relaxation times for articular cartilage of the stifle joint using a 1.5-T MRI in normal dogs. Schattauer GmbH Stuttgart.

  19. Effects of heat input rates on T-1 and T-1A steel welds

    Science.gov (United States)

    Davis, R. A.; Olsen, M. G.; Worden, S. W.

    1967-01-01

    Technology of T-1 and T-1A steels is emphasized in investigation of their weld-fabrication. Welding heat input rate, production weldment circumstances, and standards of welding control are considered.

  20. Wettability of Chalk and Argillaceous Sandstones Assessed from T1/T2 Ratio

    DEFF Research Database (Denmark)

    Katika, Konstantina; Saidian, M.; Fabricius, Ida Lykke

    Low-field NMR relaxation of the fluids inside the porous rock is the result of bulk and surface relaxation of the protons inside the pore fluid. Bulk relaxation is a fluid property when the solid-fluid interaction is minimized. Surface relaxation is the result of the solid-fluid interaction related...... with water, oil or oil/water at irreducible water saturation. The T1/T2 ratio obtained from T1-T2 maps reflects the T2-shortening. We compare the T1/T2 ratio for the same type of rock, saturated with different fluids. The chalk shows high affinity for water, Berea sandstone has no clear preference for oil...... ratio can quantify the affinity between the rock and wetting pore fluid. The affinity is a measure directly linked to wettability. In order to investigate the T2-shortening, we performed T1-T2 NMR experiments on different samples of chalk, Berea sandstone, and chloritic greensand, saturated either...

  1. Effect of Relaxation and Attachment Behaviors Training on Anxiety in First-time Mothers in Shiraz City, 2010: A Randomized Clinical Trial

    Directory of Open Access Journals (Sweden)

    Akbarzadeh M

    2013-01-01

    Full Text Available Background and Objectives: Anxiety of mother, as the first personality influencing child’s mental health, is of great importance. Use of anxiety-reducing techniques for pregnant mothers plays an important role in decreasing maternal and child psychological problems. This study aimed to determine the effect of relaxation and attachment behaviors training on anxiety in first-time mothers.Methods: The present study was done as a clinical trial on 126 primigravida women (42 subjects as relaxation group, 42 subjects as attachment group and 42 subjects as control group referred to Hafiz and Shushtari hospitals in Shiraz (2010. Data were collected using personal data form and Spielberger Anxiety Inventory questionnaire. In addition to routine pregnancy care, four 90 minute sessions of attachment behaviors and relaxation training courses were held during 4 weeks (once a week. The control group only received routine pregnancy care. Anxiety score before the intervention and at the end of the intervention were analyzed in all three groups. Data analysis was done using chi-square, Anova and paired t-test analysis, p<0.05 was considered statistically significant.Results: In this study, the mean anxiety scores were not significantly different in the three groups before the intervention, but there were significant differences among three groups after the intervention (p<0.004. There was a decrease in the mean anxiety score in the two experimental groups after the intervention, whereas there was an increase in the control group. Conclusion: The results of this study indicated that relaxation and attachment behaviors training could reduce anxiety in pregnant mothers.

  2. Fast and robust 3D T1 mapping using spiral encoding and steady RF excitation at 7 T: application to cardiac manganese enhanced MRI (MEMRI) in mice.

    Science.gov (United States)

    Castets, Charles R; Ribot, Emeline J; Lefrançois, William; Trotier, Aurélien J; Thiaudière, Eric; Franconi, Jean-Michel; Miraux, Sylvain

    2015-07-01

    Mapping longitudinal relaxation times in 3D is a promising quantitative and non-invasive imaging tool to assess cardiac remodeling. Few methods are proposed in the literature allowing us to perform 3D T1 mapping. These methods often require long scan times and use a low number of 3D images to calculate T1 . In this project, a fast 3D T1 mapping method using a stack-of-spirals sampling scheme and regular RF pulse excitation at 7 T is presented. This sequence, combined with a newly developed fitting procedure, allowed us to quantify T1 of the whole mouse heart with a high spatial resolution of 208 × 208 × 315 µm(3) in 10-12 min acquisition time. The sensitivity of this method for measuring T1 variations was demonstrated on mouse hearts after several injections of manganese chloride (doses from 25 to 150 µmol kg(-1) ). T1 values were measured in vivo in both pre- and post-contrast experiments. This protocol was also validated on ischemic mice to demonstrate its efficiency to visualize tissue damage induced by a myocardial infarction. This study showed that combining spiral gradient shape and steady RF excitation enabled fast and robust 3D T1 mapping of the entire heart with a high spatial resolution. Copyright © 2015 John Wiley & Sons, Ltd.

  3. The contribution of time-dependent stress relaxation in protein gels to the recoverable energy that is used as a tool to describe food texture

    Science.gov (United States)

    de Jong, Saskia; van Vliet, Ton; de Jongh, Harmen H. J.

    2015-11-01

    The recoverable energy (RE), defined as the ratio of the work exerted on a test specimen during compression and recovered upon subsequent decompression, has been shown to correlate to sensory profiling of protein-based food products. Understanding the mechanism determining the time-dependency of RE is primordial. This work aims to identify the protein-specific impact on the recoverable energy by stress dissipation via relaxation of (micro)structural rearrangements within protein gels. To this end, caseinate and gelatin gels are studied for their response to time-dependent mechanical deformation as they are known to develop structurally distinct network morphologies. This work shows that in gelatin gels no significant stress relaxation occurs on the seconds timescale, and consequently no time-dependency of the amount of energy stored in this material is observed. In caseinate gels, however, the energy dissipation via relaxation processes does contribute significantly to the time-dependency of reversible stored energy in the network. This can explain the obtained RE as a function of applied deformation at slow deformation rates. At faster deformation, an additional contribution to the dissipated energy is apparent, that increases with the deformation rate, which might point to the role of energy dissipation related to friction of the serum entrapped by the protein-network. This work shows that engineering strategies focused on controlling viscous flow in protein gels could be more effective to dictate the ability to elastically store energy in protein gels than routes that direct protein-specific aggregation and/or network-assembly.

  4. Associations of three-dimensional T1 rho MR mapping and three-dimensional T2 mapping with macroscopic and histologic grading as a biomarker for early articular degeneration of knee cartilage.

    Science.gov (United States)

    Sasho, T; Katsuragi, J; Yamaguchi, S; Haneishi, H; Aizimu, T; Tanaka, T; Watanabe, A; Sato, Y; Akagi, R; Matsumoto, K; Uno, T; Motoori, K

    2017-04-29

    T1 rho and T2 mapping are magnetic resonance imaging (MRI) techniques to detect early degenerative changes in cartilage. Recent advancements have enabled 3D acquisition for both techniques. The objective of the present study was to examine the correlation of 3D T1 rho and 3D T2 mapping with macroscopic and histological characteristics of knee cartilage. Twenty-one patients who underwent total knee arthroplasty due to osteoarthritis with involvement of the medial compartment but with minimum involvement of the lateral compartment were enrolled. Prior to surgery, five series of MRI were acquired with a 3-T scanner. 3D T1 rho/T2 analyses were performed following determination of regions to be assessed using in-house software that incorporated three series of MRI acquisitions data (3D-MERGE, 3D-SPGR, and 3D-CUBE). During surgery, the cartilage of the lateral compartment was macroscopically assessed with the International Cartilage Research Society (ICRS) articular classification system. The extracted specimens were histologically assessed using the OARSI histology score. Three regions of interest (ROI) were assessed for each slice (two slices per knee): the central lateral femoral condyle (cLFC), the posterior portion of the lateral femoral condyle (pLFC), and the lateral tibia plateau (LTP). For each ROI, the mean T1 rho and T2 relaxation time, the ICRS grade, and the OARSI score were compared. Neither the T1 rho nor the T2 reflected the macroscopic grading. The T1 rho could discriminate between histological grades 1 and 2. However, the T2 could not. The T1 rho relaxation time was higher in the pLFC than in the cLFC even in the same grade. Compared to T2 mapping, T1 rho mapping may have an advantage in differentiating grades I and II cartilage degeneration on OARSI histological grading system.

  5. Density relaxation and particle motion characteristics in a non-ionic deep eutectic solvent (acetamide + urea): Time-resolved fluorescence measurements and all-atom molecular dynamics simulations

    Energy Technology Data Exchange (ETDEWEB)

    Das, Anuradha; Das, Suman; Biswas, Ranjit, E-mail: ranjit@bose.res.in [Chemical, Biological and Macromolecular Sciences, S. N. Bose National Centre for Basic Sciences, Block-JD, Sector-III, Salt Lake, Kolkata, West Bengal 700098 (India)

    2015-01-21

    Temperature dependent relaxation dynamics, particle motion characteristics, and heterogeneity aspects of deep eutectic solvents (DESs) made of acetamide (CH{sub 3}CONH{sub 2}) and urea (NH{sub 2}CONH{sub 2}) have been investigated by employing time-resolved fluorescence measurements and all-atom molecular dynamics simulations. Three different compositions (f) for the mixture [fCH{sub 3}CONH{sub 2} + (1 − f)NH{sub 2}CONH{sub 2}] have been studied in a temperature range of 328-353 K which is ∼120-145 K above the measured glass transition temperatures (∼207 K) of these DESs but much lower than the individual melting temperature of either of the constituents. Steady state fluorescence emission measurements using probe solutes with sharply different lifetimes do not indicate any dependence on excitation wavelength in these metastable molten systems. Time-resolved fluorescence anisotropy measurements reveal near-hydrodynamic coupling between medium viscosity and rotation of a dissolved dipolar solute. Stokes shift dynamics have been found to be too fast to be detected by the time-resolution (∼70 ps) employed, suggesting extremely rapid medium polarization relaxation. All-atom simulations reveal Gaussian distribution for particle displacements and van Hove correlations, and significant overlap between non-Gaussian (α{sub 2}) and new non-Gaussian (γ) heterogeneity parameters. In addition, no stretched exponential relaxations have been detected in the simulated wavenumber dependent acetamide dynamic structure factors. All these results are in sharp contrast to earlier observations for ionic deep eutectics with acetamide [Guchhait et al., J. Chem. Phys. 140, 104514 (2014)] and suggest a fundamental difference in interaction and dynamics between ionic and non-ionic deep eutectic solvent systems.

  6. Interaction between umami peptide and taste receptor T1R1/T1R3.

    Science.gov (United States)

    Dang, Yali; Gao, Xinchang; Xie, Aiying; Wu, Xueqian; Ma, Fumin

    2014-12-01

    The umami taste receptor is a heterodimer composed of two members of the T1R taste receptor family: T1R1 and T1R3. The homology models of the ligand binding domains of the human umami receptor have been constructed based on crystallographic structures of the taste receptor of the central nervous system. Furthermore, the molecular simulations of the ligand binding domain show that the likely conformation was that T1R1 protein exists in the closed conformation, and T1R3 in the open conformation in the heterodimer. The molecular docking study of T1R1 and T1R3 in complex with four peptides, including Lys-Gly-Asp-Glu-Ser-Leu-Leu-Ala, Ser-Glu-Glu, G1u-Ser, and Asp-Glu-Ser, displayed that the amino acid residue of SER146 and Glu277 in T1R3 may play great roles in the synergism of umami taste. This docking result further validated the robustness of the model. In the paper, binding of umami peptide and the T1R1/T1R3 receptor was first described and the interaction is the base of umami activity theory.

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

    Science.gov (United States)

    Lee, DongKyu; Han, Sohyun; Cho, HyungJoon

    2017-01-01

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

  8. EEG-based time and spatial interpretation of activation areas for relaxation and words writing between poor and capable dyslexic children.

    Science.gov (United States)

    Mohamad, N B; Lee, Khuan Y; Mansor, W; Mahmoodin, Z; Fadzal, C W N F C W; Amirin, S

    2015-01-01

    Symptoms of dyslexia such as difficulties with accurate and/or fluent word recognition, and/or poor spelling as well as decoding abilities, are easily misinterpreted as laziness and defiance amongst school children. Indeed, 37.9% of 699 school dropouts and failures are diagnosed as dyslexic. Currently, Screening for dyslexia relies heavily on therapists, whom are few and subjective, yet objective methods are still unavailable. EEG has long been a popular method to study the cognitive processes in human such as language processing and motor activity. However, its interpretation is limited to time and frequency domain, without visual information, which is still useful. Here, our research intends to illustrate an EEG-based time and spatial interpretation of activated brain areas for the poor and capable dyslexic during the state of relaxation and words writing, being the first attempt ever reported. From the 2D distribution of EEG spectral at the activation areas and its progress with time, it is observed that capable dyslexics are able to relax compared to poor dyslexics. During the state of words writing, neural activities are found higher on the right hemisphere than the left hemisphere of the capable dyslexics, which suggests a neurobiological compensation pathway in the right hemisphere, during reading and writing, which is not observed in the poor dyslexics.

  9. A New Method to Identify Reservoirs in Tight Sandstones Based on the New Model of Transverse Relaxation Time and Relative Permeability

    Directory of Open Access Journals (Sweden)

    Yuhang Guo

    2017-01-01

    Full Text Available Relative permeability and transverse relaxation time are both important physical parameters of rock physics. In this paper, a new transformation model between the transverse relaxation time and the wetting phase’s relative permeability is established. The data shows that the cores in the northwest of China have continuous fractal dimension characteristics, and great differences existed in the different pore size scales. Therefore, a piece-wise method is used to calculate the fractal dimension in our transformation model. The transformation results are found to be quite consistent with the relative permeability curve of the laboratory measurements. Based on this new model, we put forward a new method to identify reservoir in tight sandstone reservoir. We focus on the Well M in the northwestern China. Nuclear magnetic resonance (NMR logging is used to obtain the point-by-point relative permeability curve. In addition, we identify the gas and water layers based on new T2-Kr model and the results showed our new method is feasible. In the case of the price of crude oil being low, this method can save time and reduce the cost.

  10. Segment-by-segment assessment of left ventricular myocardial affection in Anderson-Fabry disease by non-enhanced T1-mapping.

    Science.gov (United States)

    Walter, Thula C; Knobloch, Gesine; Canaan-Kuehl, Sima; Greiser, Andreas; Sandek, Anja; Blaschke, Daniela; Denecke, Timm; Hamm, Bernd; Makowski, Marcus R

    2017-08-01

    Background Anderson-Fabry disease (AFD) is an X-linked lysosomal enzyme disorder associated with an intracellular accumulation of sphingolipids, which shorten myocardial T1 relaxation times. Myocardial affection, however, varies between different segments. Purpose To evaluate the specific segmental distribution and degree of segmental affection in AFD patients. Material and Methods Twenty-five patients with AFD, 14 patients with hypertrophic cardiomyopathy (HCM), and 21 controls were included. A Modified Look-Locker Inversion Recovery sequence (MOLLI) was used for non-enhanced T1 mapping at 1.5 T in addition to standard cardiac imaging in 10-12 short axis views. T1 values were evaluated with a mixed model ANOVA and regression analysis to determine the best diagnostic cutoff values for T1 for each myocardial segment. Results Regression analysis showed the best diagnostic cutoff compared to controls in cardiac segments 1-4, 8-9, and 14. Mean differences between T1 for AFD versus HCM were greatest in segment 3, 4, and 9 (99 ms, 103 ms, 86 ms, respectively). Overall T1 times were 888 ± 70 ms and 903 ± 14 ms (AFD with and without LVH); 1014 ± 17 ms and 1001 ± 22 ms (HCM and controls, P T1 shortening in AFD patients. Segment-specific cutoff values allow the most specific detection and quantification of the extent of myocardial affection.

  11. T2* and T1 assessment of abdominal tissue response to graded hypoxia and hypercapnia using a controlled gas mixing circuit for small animals.

    Science.gov (United States)

    Ganesh, Tameshwar; Estrada, Marvin; Duffin, James; Cheng, Hai Ling

    2016-08-01

    To characterize T2* and T1 relaxation time response to a wide spectrum of gas challenges in extracranial tissues of healthy rats. A range of graded gas mixtures (hyperoxia, hypercapnia, hypoxia, and hypercapnic hypoxia) were delivered through a controlled gas-mixing circuit to mechanically ventilated and intubated rats. Quantitative magnetic resonance imaging (MRI) was performed on a 3T clinical scanner; T2* and T1 maps were computed to determine tissue response in the liver, kidney cortex, and paraspinal muscles. Heart rate and blood oxygen saturation (SaO2 ) were measured through a rodent oximeter and physiological monitor. T2* decreases consistent with lowered SaO2 measurements were observed for hypercapnia and hypoxia, but decreases were significant only in liver and kidney cortex (P 10% CO2 and gas stimulus, hypercapnic hypoxia, producing the greatest T2* decrease. Hyperoxia-related T2* increases were accompanied by negligible increases in SaO2 . T1 generally increased, if at all, in the liver and decreased in the kidney. Significance was observed (P 90% O2 and >5% CO2 . T2* and T1 provide complementary roles for evaluating extracranial tissue response to a broad range of gas challenges. Based on both measured and known physiological responses, our results are consistent with T2* as a sensitive marker of blood oxygen saturation and T1 as a weak marker of blood volume changes. J. Magn. Reson. Imaging 2016;44:305-316. © 2016 Wiley Periodicals, Inc.

  12. Orientational mobility and relaxation spectra of dendrimers: Theory and computer simulation.

    Science.gov (United States)

    Markelov, Denis A; Lyulin, Sergey V; Gotlib, Yuli Y; Lyulin, Alexey V; Matveev, Vladimir V; Lahderanta, Erkki; Darinskii, Anatolij A

    2009-01-28

    The developed theory of the orientational mobility of individual segments of a perfectly branched dendrimer is used to calculate the relaxation spectrum of a dendrimer. Frequency dependences of NMR relaxation 1/T(1) and of the nuclear Overhauser effect have been theoretically calculated from the Brownian dynamics simulation data. The dendrimer segmental orientational mobility is governed by three main relaxation processes: (i) the rotation of the dendrimer as a whole, (ii) the rotation of the dendrimer's branch originated from a given segment, and (iii) the local reorientation of the segment. The internal orientational mobility of an individual dendrimer segment depends only on the topological distance between this segment and the terminal shell of the dendrimer. Characteristic relaxation times of all processes and their contributions to the segmental mobility have been calculated. The influence of the number of generations and the number of the generation shell on the relaxation times has been studied. The correlation between the characteristic times and the calculated relaxation spectrum of the dendrimer has been established.

  13. MR relaxation time measurements with and without fat saturation (SPIR) in Graves` ophthalmopathy; MR-Relaxometriemessung mit und ohne frequenzselektive Fettunterdrueckung (SPIR) bei endokriner Orbitopathie

    Energy Technology Data Exchange (ETDEWEB)

    Pauleit, D.; Schueller, H.; Textor, J.; Leutner, C.; Keller, E.; Sommer, T.; Traeber, F.; Block, W.; Boldt, I.; Schild, H. [Bonn Univ. (Germany). Radiologische Klinik

    1997-12-01

    Purpose: To determine the value and utility of relaxation time measurements with magnetic resonance (MR) imaging in patients with Graves` ophthalmopathy (G.O.). Materials and methods: 20 rrbits were studied in control subjects and 58 orbits in patients with G.O. T{sub 2} relaxation times of extraocular muscles and retrobulbar fat tissue were calculated. The thickness of the eye muscles was correlated with the calculated T{sub 2} times. 18 orbits were measured before and after retroorbital radiation therapy. Results: Upper limits of determined normal T{sub 2} values were 60 ms in extraocular eye muscles and 40 ms in retrobulbar fat tissue. 89% (17/19) of the patients with G.O. had prolonged T{sub 2} times in extraocular eye muscles. The retrobulbar fat tissue in 5 of 38 orbits revealed minimal edema with the use of fat saturated sequences. T{sub 2} relaxation times decreased significantly (p<10{sup -4}) after 10 Gy radiation therapy. No correlation was found between enlargement and T{sub 2} relaxation times in extraocular eye muscles (r=0.44 in patients before radiation therapy). Conclusion: In patients with G.O. the determination of the enlargement of extraocular eye muscles in computed tomography is not a sufficient parameter for an antiinflammatory therapy, since CT cannot visualise eye muscle edema. T{sub 2} relaxation time measurements with MR imaging allow differentiation between edematous and fibrotic changes. This is the diagnostic method of choice in patients with Graves` ophthalmopathy. (orig.) [Deutsch] Ziel: Pruefung der Wertigkeit der MR-Relaxometrie bei Patienten mit endokriner Orbitopathie. Material und Methode: 20 Orbitae von Probanden und 58 Orbitae von Patienten mit endokriner Orbitopathie wurden ausgewertet. Die T{sub 2}-Zeiten der extraokulaeren Augenmuskeln und des retrobulbaeren Fettkoerpers wurden bestimmt. Die Dicke der Augenmuskeln wurde mit den T{sub 2}-Zeiten korreliert. Bei 18 Orbitae wurden der Verlauf unter Strahlentherapie beobachtet

  14. Utility of real-time prospective motion correction (PROMO) for segmentation of cerebral cortex on 3D T1-weighted imaging: Voxel-based morphometry analysis for uncooperative patients

    Energy Technology Data Exchange (ETDEWEB)

    Igata, Natsuki; Kakeda, Shingo; Watanabe, Keita; Narimatsu, Hidekuni; Ide, Satoru; Korogi, Yukunori [University of Occupational and Environmental Health School of Medicine, Department of Radiology, Kitakyushu (Japan); Nozaki, Atsushi [MR Applications and Workflow Asia Pacific GE Healthcare Japan, Tokyo (Japan); Rettmann, Dan [MR Applications and Workflow GE Healthcare, Rochester, MN (United States); Abe, Osamu [University of Tokyo, Department of Radiology, Graduate School of Medicine, Tokyo (Japan)

    2017-08-15

    To assess the utility of the motion correction method with prospective motion correction (PROMO) in a voxel-based morphometry (VBM) analysis for 'uncooperative' patient populations. High-resolution 3D T1-weighted imaging both with and without PROMO were performed in 33 uncooperative patients with Parkinson's disease (n = 11) or dementia (n = 22). We compared the grey matter (GM) volumes and cortical thickness between the scans with and without PROMO. For the mean total GM volume with the VBM analysis, the scan without PROMO showed a significantly smaller volume than that with PROMO (p < 0.05), which was caused by segmentation problems due to motion during acquisition. The whole-brain VBM analysis showed significant GM volume reductions in some regions in the scans without PROMO (familywise error corrected p < 0.05). In the cortical thickness analysis, the scans without PROMO also showed decreased cortical thickness compared to the scan with PROMO (p < 0.05). Our results with the uncooperative patients indicate that the use of PROMO can reduce misclassification during segmentation of the VBM analyses, although it may not prevent GM volume reduction. (orig.)

  15. Advanced Colloids Experiment (ACE-T1)

    Science.gov (United States)

    Meyer, William V.; Sicker, Ron; Brown, Dan; Eustace, John

    2015-01-01

    Increment 45 - 46 Science Symposium presentation of Advanced Colloids Experiment (ACE-T1) to RPO. The purpose of this event is for Principal Investigators to present their science objectives, testing approach, and measurement methods to agency scientists, managers, and other investigators.

  16. Comparison of T2* relaxation times of articular cartilage of the knee in elite professional football players and age-and BMI-matched amateur athletes.

    Science.gov (United States)

    Behzadi, C; Welsch, G H; Laqmani, A; Henes, F O; Kaul, M G; Schoen, G; Adam, G; Regier, M

    2017-01-01

    Recent investigation has underlined the potential of quantitative MR imaging to be used as a complementary tool for the diagnosis of cartilage degeneration at an early state. The presented study analyses T2* relaxation times of articular cartilage of the knee in professional athletes and compares the results to age- and BMI (Body Mass Index)-matched healthy amateur athletes. 22 professional football players and 22 age- and BMI-matched individuals were underwent knee Magnetic Resonance Imaging (MRI) at 3T including qualitative and quantitative analysis. Qualitative analysis included e.g. meniscal tears, joint effusion and bone edema. For quantitative analysis T2* (22 ET: 4.6-53.6ms) measurements in 3D data acquisition were performed. Deep and superficial layers of 22 predefined cartilage segments were analysed. All data sets were postprocessed using a dedicated software tool. Statistical analysis included Student t-test, confidence intervals and a random effects model. In both groups, T2* relaxation times were significantly higher in the superficial compared to the deep layers (pweight-bearing segments of the lateral superficial femoral condyle (p<0.001). Elevated T2* values in cartilage layers of professional football players compared to amateur athletes were noted. The effects seem to predominate in superficial cartilage layers. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  17. Phosphorus Taste Involves T1R2 and T1R3.

    Science.gov (United States)

    Tordoff, Michael G

    2017-06-01

    Rodents consume solutions of phosphates and pyrophosphates in preference to water. Recently, we found that the preference for trisodium pyrophosphate (Na3HP2O7) was greater in T1R3 knockout (KO) mice than wild-type (WT) controls, suggesting that T1R3 is a pyrophosphate detector. We now show that this heightened Na3HP2O7 preference of T1R3 KO mice extends to disodium phosphate (Na2HPO4), disodium and tetrasodium pyrophosphate (Na2H2PO4 and Na4H2PO4), a tripolyphosphate (Na5P3O10), a non-sodium phosphate [(NH4)2HPO4], and a non-sodium pyrophosphate (K4P2O7) but not to non-P salts with large anions (sodium gluconate, acetate, or propionate). Licking rates for Na3HP2O7 are higher in T1R2 KO mice than WT controls; Na3HP2O7 preference scores are increased even more in T1R2 KO mice and T1R2+T1R3 double KO mice than in T1R3 KO mice; preference scores for Na3HP2O7 are normal in T1R1 KO mice. These results implicate each subunit of the T1R2+T1R3 dimer in the behavioral response to P-containing taste compounds. © The Author 2017. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  18. T1 and T2 mapping for early diagnosis of dilated non-ischaemic cardiomyopathy in middle-aged patients and differentiation from normal physiological adaptation.

    Science.gov (United States)

    Mordi, Ify; Carrick, David; Bezerra, Hiram; Tzemos, Nikolaos

    2016-07-01

    The differential diagnosis of patients with early non-ischaemic dilated cardiomyopathy (DCM) and those with physiological adaptation to exercise ('athlete's heart') may be difficult as many of the morphological adaptations are shared in the two conditions. Increased physical fitness is becoming more common in later adulthood, a group in whom there may be even more diagnostic difficulty. We hypothesized that tissue characterization using cardiovascular magnetic resonance (CMR) T1 and T2 mapping would be able to differentiate between patients with left ventricular (LV) dilatation due to early DCM and exercisers. Fifty-eight middle-aged males [21 healthy controls, 21 males with a history of aerobic exercise and LV ejection fraction (LVEF) 45-55%, and 16 patients with DCM and LVEF 45-55%] underwent a CMR protocol including T1 and T2 mapping and calculation of extracellular volume (ECV) using a 1.5 T MRI scanner. Native T1, ECV, and T2 relaxation times were significantly increased in DCM patients compared with controls (native T1 1017 ± 42 vs. 952 ± 31 ms, P T1 957 ± 32 ms, P T1 gave the best differentiation between exercisers and sedentary patients with early DCM (area under the curve 0.91). T1 and T2 mapping are potentially useful tools for differentiating between athlete's heart and patients with early DCM, and could be used whenever differentiation between these two phenotypes is inconclusive using standard imaging techniques. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2015. For permissions please email: journals.permissions@oup.com.

  19. Protein conformational relaxation and ligand migration in myoglobin: a nanosecond to millisecond molecular movie from time-resolved Laue X-ray diffraction.

    Science.gov (United States)

    Srajer, V; Ren, Z; Teng, T Y; Schmidt, M; Ursby, T; Bourgeois, D; Pradervand, C; Schildkamp, W; Wulff, M; Moffat, K

    2001-11-20

    A time-resolved Laue X-ray diffraction technique has been used to explore protein relaxation and ligand migration at room temperature following photolysis of a single crystal of carbon monoxymyoglobin. The CO ligand is photodissociated by a 7.5 ns laser pulse, and the subsequent structural changes are probed by 150 ps or 1 micros X-ray pulses at 14 laser/X-ray delay times, ranging from 1 ns to 1.9 ms. Very fast heme and protein relaxation involving the E and F helices is evident from the data at a 1 ns time delay. The photodissociated CO molecules are detected at two locations: at a distal pocket docking site and at the Xe 1 binding site in the proximal pocket. The population by CO of the primary, distal site peaks at a 1 ns time delay and decays to half the peak value in 70 ns. The secondary, proximal docking site reaches its highest occupancy of 20% at approximately 100 ns and has a half-life of approximately 10 micros. At approximately 100 ns, all CO molecules are accounted for within the protein: in one of these two docking sites or bound to the heme. Thereafter, the CO molecules migrate to the solvent from which they rebind to deoxymyoglobin in a bimolecular process with a second-order rate coefficient of 4.5 x 10(5) M(-1) s(-1). Our results also demonstrate that structural changes as small as 0.2 A and populations of CO docking sites of 10% can be detected by time-resolved X-ray diffraction.

  20. Is T1ρ Mapping an Alternative to Delayed Gadolinium-enhanced MR Imaging of Cartilage in the Assessment of Sulphated Glycosaminoglycan Content in Human Osteoarthritic Knees? An in Vivo Validation Study.

    Science.gov (United States)

    van Tiel, Jasper; Kotek, Gyula; Reijman, Max; Bos, Pieter K; Bron, Esther E; Klein, Stefan; Nasserinejad, Kazem; van Osch, Gerjo J V M; Verhaar, Jan A N; Krestin, Gabriel P; Weinans, Harrie; Oei, Edwin H G

    2016-05-01

    To determine if T1ρ mapping can be used as an alternative to delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) in the quantification of cartilage biochemical composition in vivo in human knees with osteoarthritis. This study was approved by the institutional review board. Written informed consent was obtained from all participants. Twelve patients with knee osteoarthritis underwent dGEMRIC and T1ρ mapping at 3.0 T before undergoing total knee replacement. Outcomes of dGEMRIC and T1ρ mapping were calculated in six cartilage regions of interest. Femoral and tibial cartilages were harvested during total knee replacement. Cartilage sulphated glycosaminoglycan (sGAG) and collagen content were assessed with dimethylmethylene blue and hydroxyproline assays, respectively. A four-dimensional multivariate mixed-effects model was used to simultaneously assess the correlation between outcomes of dGEMRIC and T1ρ mapping and the sGAG and collagen content of the articular cartilage. T1 relaxation times at dGEMRIC showed strong correlation with cartilage sGAG content (r = 0.73; 95% credibility interval [CI] = 0.60, 0.83) and weak correlation with cartilage collagen content (r = 0.40; 95% CI: 0.18, 0.58). T1ρ relaxation times did not correlate with cartilage sGAG content (r = 0.04; 95% CI: -0.21, 0.28) or collagen content (r = -0.05; 95% CI = -0.31, 0.20). dGEMRIC can help accurately measure cartilage sGAG content in vivo in patients with knee osteoarthritis, whereas T1ρ mapping does not appear suitable for this purpose. Although the technique is not completely sGAG specific and requires a contrast agent, dGEMRIC is a validated and robust method for quantifying cartilage sGAG content in human osteoarthritis subjects in clinical research. (©) RSNA, 2015.

  1. Structural Dependence of the Ising-type Magnetic Anisotropy and of the Relaxation Time in Mononuclear Trigonal Bipyramidal Co(II) Single Molecule Magnets.

    Science.gov (United States)

    Shao, Feng; Cahier, Benjamin; Rivière, Eric; Guillot, Régis; Guihéry, Nathalie; Campbell, Victoria E; Mallah, Talal

    2017-02-06

    This paper describes the correlation between Ising-type magnetic anisotropy and structure in trigonal bipyramidal Co(II) complexes. Three sulfur-containing trigonal bipyramidal Co(II) complexes were synthesized and characterized. It was shown that we can engineer the magnitude of the Ising anisotropy using ligand field theory arguments in conjunction with structural parameters. To prepare this series of compounds, we used, on the one hand, a tetradentate ligand containing three sulfur atoms and one amine (NS3tBu) and on the other hand three different axial ligands, namely, Cl-, Br-, and NCS-. The organic ligand imposes a trigonal bipyramidal arrangement with the three sulfur atoms lying in the trigonal plane with long Co-S bond distances. The magnetic properties of the compounds were measured, and ab initio calculations were used to analyze the anisotropy parameters and perform magneto-structural correlations. We demonstrate that a smaller axial zero-field splitting parameter leads to slower relaxation time when the symmetry is strictly axial, while the presence of very weak rhombicity decreases the energy barrier and speeds the relaxation of the magnetization.

  2. Measurement of 15N longitudinal relaxation rates in 15NH4+ spin systems to characterise rotational correlation times and chemical exchange

    Science.gov (United States)

    Hansen, D. Flemming

    2017-06-01

    Many chemical and biological processes rely on the movement of monovalent cations and an understanding of such processes can therefore only be achieved by characterising the dynamics of the involved ions. It has recently been shown that 15N-ammonium can be used as a proxy for potassium to probe potassium binding in bio-molecules such as DNA quadruplexes and enzymes. Moreover, equations have been derived to describe the time-evolution of 15N-based spin density operator elements of 15NH4+ spin systems. Herein NMR pulse sequences are derived to select specific spin density matrix elements of the 15NH4+ spin system and to measure their longitudinal relaxation in order to characterise the rotational correlation time of the 15NH4+ ion as well as report on chemical exchange events of the 15NH4+ ion. Applications to 15NH4+ in acidic aqueous solutions are used to cross-validate the developed pulse sequence while measurements of spin-relaxation rates of 15NH4+ bound to a 41 kDa domain of the bacterial Hsp70 homologue DnaK are presented to show the general applicability of the derived pulse sequence. The rotational correlation time obtained for 15N-ammonium bound to DnaK is similar to the correlation time that describes the rotation about the threefold axis of a methyl group. The methodology presented here provides, together with the previous theoretical framework, an important step towards characterising the motional properties of cations in macromolecular systems.

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

    Science.gov (United States)

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

    2017-01-01

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

  4. Influence of Free Radicals on the Intrinsic MRI Relaxation Properties.

    Science.gov (United States)

    Tain, Rong-Wen; Scotti, Alessandro M; Li, Weiguo; Zhou, Xiaohong Joe; Cai, Kejia

    2017-01-01

    Free radicals are critical contributors in various conditions including normal aging, Alzheimer's disease, cancer, and diabetes. Currently there is no non-invasive approach to image tissue free radicals based on endogenous contrast due to their extremely short lifetimes and low in vivo concentrations. In this study we aim at characterizing the influence of free radicals on the MRI relaxation properties. Phantoms containing free radicals were created by treating egg white with various H 2 O 2 concentrations and scanned on a 9.4 T MRI scanner at room temperature. T1 and T2 relaxation maps were generated from data acquired with an inversion recovery sequence with varied inversion times and a multi-echo spin echo sequence with varied echo times (TEs), respectively. Results demonstrated that free radicals express a strong shortening effect on T1, which was proportional to the H 2 O 2 concentration, and a relatively small reduction in T2 (free radicals was estimated to be in the pM range that is within the physiological range of in vivo free radical expression. In conclusion, the free radicals show a strong paramagnetic effect that may be utilized as an endogenous MRI contrast for its non-invasive in vivo imaging.

  5. Spin relaxation of electrons in bulk CdTe

    Science.gov (United States)

    Sprinzl, Daniel; Nahalkova, Petra; Kunc, Jan; Maly, Petr; Horodysky, Petr; Grill, Roman; Belas, Eduard; Franc, Jan; Nemec, Petr

    2007-03-01

    We report on the measurements of the spin relaxation time T1 of photo-excited electrons in bulk CdTe. The carrier dynamics were investigated by transient absorption experiments using 80 fs circularly polarized laser pulses at sample temperatures from 20 to 300 K. We studied both p and n type doped CdTe samples, which were prepared in the form of thin platelets from the crystals grown by the modified Bridgman method. The obtained results are compared with the spin relaxation times reported for other semiconductors with the same crystal structure (e.g., GaAs [1]). Finally, the relative contributions of the D'yakonov-Perel, Elliott-Yafet, Bir-Aronov-Pikus, and other mechanisms to the measured spin relaxation times in CdTe are discussed. This work was supported by the Grant Agency of the Czech Republic (grant 202/03/H003), by the Ministry of Education of the Czech Republic in the framework of the research centre LC510 and the research plan MSM 0021620834. [1] J. M. Kikkawa and D. D. Awschalom, Phys. Rev. Lett. 80, 4313 (1998).

  6. Unconventional Superconductivity in La(7)Ir(3) Revealed by Muon Spin Relaxation: Introducing a New Family of Noncentrosymmetric Superconductor That Breaks Time-Reversal Symmetry.

    Science.gov (United States)

    Barker, J A T; Singh, D; Thamizhavel, A; Hillier, A D; Lees, M R; Balakrishnan, G; Paul, D McK; Singh, R P

    2015-12-31

    The superconductivity of the noncentrosymmetric compound La(7)Ir(3) is investigated using muon spin rotation and relaxation. Zero-field measurements reveal the presence of spontaneous static or quasistatic magnetic fields below the superconducting transition temperature T(c)=2.25  K-a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic and that the pairing symmetry of the superconducting electrons is predominantly s wave with an enhanced binding strength. The results indicate that the superconductivity in La(7)Ir(3) may be unconventional and paves the way for further studies of this family of materials.

  7. Determination of correlation times from selective and non-selective spin-lattice relaxation rates and their use in drug-drug and drug-albumin interaction studies

    Directory of Open Access Journals (Sweden)

    Tinoco Luzineide Wanderley

    1999-01-01

    Full Text Available The effects of the changes in sample concentration on the NMR chemical shifts and on the selective and non-selective spin-lattice relaxation rates (R1S and R1NS of the three isomers of nitrobenzaldeyde guanyl hydrazone (NBGH pure and with bovine serum albumin (BSA were measured in solution. The results wereused to determine the correlation times (tauc, showing that the degree of intermolecular drug-drug association varies with the nitro group position on the ring and that this degree of association interferes with the interaction of these drugs with BSA. The results suggest that the degree of drug-drug and drug-BSA association are related to the in vitro anti-Trypanosoma cruzi activity of these compounds.

  8. Role of threading dislocations in strain relaxation during GaInN growth monitored by real-time X-ray reflectivity

    Science.gov (United States)

    Ju, Guangxu; Tabuchi, Masao; Takeda, Yoshikazu; Amano, Hiroshi

    2017-06-01

    Ga1-xInxN epilayers (x = 0.09 or 0.14) grown on c-plane GaN layers with different densities of threading dislocations have been investigated by real-time x-ray reflectivity during metal-organic vapor phase epitaxial growth. We found that the density of pre-existing threading dislocations in GaN plays an important role in the strain relaxation of Ga1-xInxN. Critical thicknesses were obtained and compared with theoretical predictions using the mechanical equilibrium model and the energy balance model. The critical thickness of GaInN varies inversely with dislocation density in the GaN sublayer. When the threading dislocation density in the sublayer was reduced by three orders of magnitude, the photoluminescence intensity of the Ga0.86In0.14N epilayer was improved by a factor of ten.

  9. In vivo tumor lactate relaxation measurements by selective multiple-quantum-coherence (Sel-MQC) transfer.

    Science.gov (United States)

    Muruganandham, Manickam; Koutcher, Jason A; Pizzorno, Giuseppe; He, Qiuhong

    2004-10-01

    The frequency-selective multiple-quantum-coherence (Sel-MQC) lactate (Lac) filter offers complete lipid and water suppression in a single scan for robust in vivo detection of tumor Lac, even in the presence of abundant lipids. Conversion of the detected signal into accurate tissue concentrations of Lac requires knowledge of in vivo Lac T1 and T2 relaxation times. This work reports modifications to the Sel-MQC pulse sequence, T1- and T2-Sel-MQC, that facilitate relaxation measurements of Lac. The T1-Sel-MQC sequence combines an inversion prepulse with the Sel-MQC filter. The T2-Sel-MQC sequence incorporates a CH3-selective 180 degrees pulse during the MQ preparation period to overcome the J-modulation effects and allow the insertion of variable echo delays. The performance of these sequences was evaluated with the use of phantoms and subcutaneous murine tumor models in vivo. The present approach will allow investigators to correct for the relaxation-induced Lac signal loss in Sel-MQC experiments for the quantitative mapping of in vivo tumor Lac distribution.

  10. Distinct human and mouse membrane trafficking systems for sweet taste receptors T1r2 and T1r3.

    Science.gov (United States)

    Shimizu, Madoka; Goto, Masao; Kawai, Takayuki; Yamashita, Atsuko; Kusakabe, Yuko

    2014-01-01

    The sweet taste receptors T1r2 and T1r3 are included in the T1r taste receptor family that belongs to class C of the G protein-coupled receptors. Heterodimerization of T1r2 and T1r3 is required for the perception of sweet substances, but little is known about the mechanisms underlying this heterodimerization, including membrane trafficking. We developed tagged mouse T1r2 and T1r3, and human T1R2 and T1R3 and evaluated membrane trafficking in human embryonic kidney 293 (HEK293) cells. We found that human T1R3 surface expression was only observed when human T1R3 was coexpressed with human T1R2, whereas mouse T1r3 was expressed without mouse T1r2 expression. A domain-swapped chimera and truncated human T1R3 mutant showed that the Venus flytrap module and cysteine-rich domain (CRD) of human T1R3 contain a region related to the inhibition of human T1R3 membrane trafficking and coordinated regulation of human T1R3 membrane trafficking. We also found that the Venus flytrap module of both human T1R2 and T1R3 are needed for membrane trafficking, suggesting that the coexpression of human T1R2 and T1R3 is required for this event. These results suggest that the Venus flytrap module and CRD receive taste substances and play roles in membrane trafficking of human T1R2 and T1R3. These features are different from those of mouse receptors, indicating that human T1R2 and T1R3 are likely to have a novel membrane trafficking system.

  11. Negative magnetic relaxation in superconductors

    Directory of Open Access Journals (Sweden)

    Krasnoperov E.P.

    2013-01-01

    Full Text Available It was observed that the trapped magnetic moment of HTS tablets or annuli increases in time (negative relaxation if they are not completely magnetized by a pulsed magnetic field. It is shown, in the framework of the Bean critical-state model, that the radial temperature gradient appearing in tablets or annuli during a pulsed field magnetization can explain the negative magnetic relaxation in the superconductor.

  12. Butyrate transcriptionally enhances peptide transporter PepT1 expression and activity.

    Directory of Open Access Journals (Sweden)

    Guillaume Dalmasso

    Full Text Available BACKGROUND: PepT1, an intestinal epithelial apical di/tripeptide transporter, is normally expressed in the small intestine and induced in colon during chronic inflammation. This study aimed at investigating PepT1 regulation by butyrate, a short-chain fatty acid produced by commensal bacteria and accumulated inside inflamed colonocyte. RESULTS: We found that butyrate treatment of human intestinal epithelial Caco2-BBE cells increased human PepT1 (hPepT1 promoter activity in a dose- and time-dependent manner, with maximal activity observed in cells treated with 5 mM butyrate for 24 h. Under this condition, hPepT1 promoter activity, mRNA and protein expression levels were increased as assessed by luciferase assay, real-time RT-PCR and Western blot, respectively. hPepT1 transport activity was accordingly increased by approximately 2.5-fold. Butyrate did not alter hPepT1 mRNA half-life indicating that butyrate acts at the transcriptional level. Molecular analyses revealed that Cdx2 is the most important transcription factor for butyrate-induced increase of hPepT1 expression and activity in Caco2-BBE cells. Butyrate-activated Cdx2 binding to hPepT1 promoter was confirmed by gel shift and chromatin immunoprecipitation. Moreover, Caco2-BBE cells overexpressing Cdx2 exhibited greater hPepT1 expression level than wild-type cells. Finally, treatment of mice with 5 mM butyrate added to drinking water for 24 h increased colonic PepT1 mRNA and protein expression levels, as well as enhanced PepT1 transport activity in colonic apical membranes vesicles. CONCLUSIONS: Collectively, our results demonstrate that butyrate increases PepT1 expression and activity in colonic epithelial cells, which provides a new understanding of PepT1 regulation during chronic inflammation.

  13. Accelerated and navigator-gated look-locker imaging for cardiac T1 estimation (ANGIE): Development and application to T1 mapping of the right ventricle.

    Science.gov (United States)

    Mehta, Bhairav B; Chen, Xiao; Bilchick, Kenneth C; Salerno, Michael; Epstein, Frederick H

    2015-01-01

    To develop a method for high-resolution cardiac T1 mapping. A new method, accelerated and navigator-gated look-locker imaging for cardiac T1 estimation (ANGIE), was developed. An adaptive acquisition algorithm that accounts for the interplay between navigator gating and undersampling patterns well-suited for compressed sensing was used to minimize scan time. Computer simulations, phantom experiments, and imaging of the left ventricle (LV) were used to optimize and evaluate ANGIE. ANGIE's high spatial resolution was demonstrated by T1 mapping of the right ventricle (RV). Comparisons were made to modified Look-Locker imaging (MOLLI). Retrospective reconstruction of fully sampled datasets demonstrated the advantages of the adaptive algorithm. For the LV, ANGIE measurements of T1 were in good agreement with MOLLI. For the RV, ANGIE achieved a spatial resolution of 1.2 × 1.2 mm(2) with a scan time of 157 ± 53 s per slice, and measured RV T1 values of 980 ± 96 ms versus 1076 ± 157 ms for lower-resolution MOLLI. ANGIE provided lower intrascan variation in the RV T1 estimate compared with MOLLI (P T1 mapping in clinically reasonable scan times. ANGIE opens the prospect of quantitative T1 mapping of thin cardiovascular structures such as the RV wall. © 2014 Wiley Periodicals, Inc.

  14. Twitch potentiation influences the time course of twitch depression in muscle relaxant studies : A pharmacokinetic-pharmacodynamic explanation

    NARCIS (Netherlands)

    Eleveld, Douglas J.; Proost, Johannes H.; Wierda, J. Mark K. H.

    2006-01-01

    The time course of twitch depression following neuromuscular blocking agent (NMBA) administration is influenced by the duration of control neuromuscular monitoring (twitch stabilization). The physiological mechanism for this interaction is not known. During twitch stabilization twitch response often

  15. A longitudinal qualitative study examining the factors impacting on the ability of persons with T1DM to assimilate the Dose Adjustment For Normal Eating (DAFNE) principles into daily living and how these factors change over time

    LENUS (Irish Health Repository)

    Casey, Dympna

    2011-08-30

    Abstract Background The literature reveals that structured education programmes, such as DAFNE, result in many positive outcomes for people with Type 1 diabetes including a decrease in HbA1c levels and reductions in hypoglycaemia. While there is evidence that some of these outcomes are maintained we do not know at present what factors are most important over time. The study aim was to identify the key factors impacting on persons with Type 1 diabetes ability to assimilate the Dose Adjustment For Normal Eating (DAFNE) DAFNE principles into their daily lives and how these factors change over time. Methods This is a longitudinal descriptive qualitative study. Interviews were undertaken with 40 participants who had attended DAFNE in one of 5 study sites across the Island of Ireland, at 6 weeks, 6 and 12 months after completion of the programme. The interviews lasted from 30 to 60 minutes and were transcribed verbatim. Data were analysed in three ways, a within time analysis, a cross sectional analysis for each participant and a thematic analysis which focused on examining changes over time Results Four themes that influenced participants\\' ability to assimilate DAFNE into their daily lives over time were identified. These were: embedded knowledge, continued responsive support, enduring motivation and being empowered. Support at the 6 month period was found to be crucial to continued motivation. Conclusions Understanding the factors that influence people\\'s ability to assimilate DAFNE principles over time into their daily lives can help health professionals give focused responsive support that helps people with diabetes become more empowered. Understanding that continued support matters, particularly around 6 months, is important as health professionals can influence good management by providing appropriate support and enhancing motivation. Trial registration ISRCTN79759174

  16. A longitudinal qualitative study examining the factors impacting on the ability of persons with T1DM to assimilate the Dose Adjustment for Normal Eating (DAFNE principles into daily living and how these factors change over time

    Directory of Open Access Journals (Sweden)

    White Florence

    2011-08-01

    Full Text Available Abstract Background The literature reveals that structured education programmes, such as DAFNE, result in many positive outcomes for people with Type 1 diabetes including a decrease in HbA1c levels and reductions in hypoglycaemia. While there is evidence that some of these outcomes are maintained we do not know at present what factors are most important over time. The study aim was to identify the key factors impacting on persons with Type 1 diabetes ability to assimilate the Dose Adjustment For Normal Eating (DAFNE DAFNE principles into their daily lives and how these factors change over time. Methods This is a longitudinal descriptive qualitative study. Interviews were undertaken with 40 participants who had attended DAFNE in one of 5 study sites across the Island of Ireland, at 6 weeks, 6 and 12 months after completion of the programme. The interviews lasted from 30 to 60 minutes and were transcribed verbatim. Data were analysed in three ways, a within time analysis, a cross sectional analysis for each participant and a thematic analysis which focused on examining changes over time Results Four themes that influenced participants' ability to assimilate DAFNE into their daily lives over time were identified. These were: embedded knowledge, continued responsive support, enduring motivation and being empowered. Support at the 6 month period was found to be crucial to continued motivation. Conclusions Understanding the factors that influence people's ability to assimilate DAFNE principles over time into their daily lives can help health professionals give focused responsive support that helps people with diabetes become more empowered. Understanding that continued support matters, particularly around 6 months, is important as health professionals can influence good management by providing appropriate support and enhancing motivation. Trial registration ISRCTN79759174

  17. Connexin 43-targeted T1 contrast agent for MRI diagnosis of glioma.

    Science.gov (United States)

    Abakumova, Tatiana; Abakumov, Maxim; Shein, Sergey; Chelushkin, Pavel; Bychkov, Dmitry; Mukhin, Vladimir; Yusubalieva, Gaukhar; Grinenko, Nadezhda; Kabanov, Alexander; Nukolova, Natalia; Chekhonin, Vladimir

    2016-01-01

    Glioblastoma multiforme is the most aggressive form of brain tumor. Early and accurate diagnosis of glioma and its borders is an important step for its successful treatment. One of the promising targets for selective visualization of glioma and its margins is connexin 43 (Cx43), which is highly expressed in reactive astrocytes and migrating glioma cells. The purpose of this study was to synthesize a Gd-based contrast agent conjugated with specific antibodies to Cx43 for efficient visualization of glioma C6 in vivo. We have prepared stable nontoxic conjugates of monoclonal antibody to Cx43 and polylysine-DTPA ligands complexed with Gd(III), which are characterized by higher T1 relaxivity (6.5 mM(-1) s(-1) at 7 T) than the commercial agent Magnevist® (3.4 mM(-1) s(-1)). Cellular uptake of Cx43-specific T1 contrast agent in glioma C6 cells was more than four times higher than the nonspecific IgG-contrast agent, as detected by flow cytometry and confocal analysis. MRI experiments showed that the obtained agents could markedly enhance visualization of glioma C6 in vivo after their intravenous administration. Significant accumulation of Cx43-targeted contrast agents in glioma and the peritumoral zone led not only to enhanced contrast but also to improved detection of the tumor periphery. Fluorescence imaging confirmed notable accumulation of Cx43-specific conjugates in the peritumoral zone compared with nonspecific IgG conjugates at 24 h after intravenous injection. All these features of Cx43-targeted contrast agents might be useful for more precise diagnosis of glioma and its borders by MRI. Copyright © 2015 John Wiley & Sons, Ltd.

  18. Relaxation time of the global order parameter on multiplex networks: The role of interlayer coupling in Kuramoto oscillators

    Science.gov (United States)

    Allen-Perkins, Alfonso; de Assis, Thiago Albuquerque; Pastor, Juan Manuel; Andrade, Roberto F. S.

    2017-10-01

    This work considers the time scales associated with the global order parameter and the interlayer synchronization of coupled Kuramoto oscillators on multiplexes. For two-layer multiplexes with an initially high degree of synchronization in each layer, the difference between the average phases in each layer is analyzed from two different perspectives: the spectral analysis and the nonlinear Kuramoto model. Both viewpoints confirm that the prior time scales are inversely proportional to the interlayer coupling strength. Thus, increasing the interlayer coupling always shortens the transient regimes of both the global order parameter and the interlayer synchronization. Surprisingly, the analytical results show that the convergence of the global order parameter is faster than the interlayer synchronization, and the latter is generally faster than the global synchronization of the multiplex. The formalism also outlines the effects of frequencies on the difference between the average phases of each layer, and it identifies the conditions for an oscillatory behavior. Computer simulations are in fairly good agreement with the analytical findings, and they reveal that the time scale of the global order parameter is half the size of the time scale of the multiplex, if not smaller.

  19. Characterization of structural relaxation in inorganic glasses using length dilatometry

    Science.gov (United States)

    Koontz, Erick

    characterization technique is comprised of three main components: experimental measurements, fitting of configurational length change, and description of glass behavior by analysis of fitting parameters. N-BK7 optical glass from Schott was used as the proof of concept glass but the main scientific interest was in three chalcogenide glasses: As40Se 60, As20Se80, and Ge17.9As19.7 Se62.4. The dilatometric experiments were carried out using a thermomechanical analyzer (TMA) on glass sample that were synthesized by the author, in all cases except N-BK7. Isothermal structural relaxation measurements were done on (12 mm tall x 3 mm x 3 mm) beams placed vertically in the TMA. The samples were equilibrated at a starting temperature (T 0) until structural equilibrium was reached then a temperature down step was initiated to the final temperature (T 1) and held isothermally until relaxation concluded. The configurational aspect of length relaxation, and therefore volume relaxation was extracted and fit with a Prony series. The Prony series parameters indicated a number of relaxation events occurring within the glass on timescales typically an order of magnitude apart in time. The data analysis showed as many as 4 discrete relaxation times at lower temperatures. The number of discrete relaxation decreased as the temperature increased until just one single relaxation was left in the temperature range just at or above Tg. In the case of N-BK7 these trends were utilized to construct a simple model that could be applied to glass manufacturing in the areas of annealing or PGM. A future development of a rather simple finite element model (FEM) would easily be able to use this model to predict the exponential-like, temperature and time dependent relaxation behaviors of the glass. The predictive model was not extended to the chalcogenide glass studied here, but could easily be applied to them in the future. The relaxation time trends versus temperature showed a definite region of transition between a

  20. MOLLI and AIR T1 mapping pulse sequences yield different myocardial T1 and ECV measurements.

    Science.gov (United States)

    Hong, KyungPyo; Kim, Daniel

    2014-11-01

    Both post-contrast myocardial T1 and extracellular volume (ECV) have been reported to be associated with diffuse interstitial fibrosis. Recently, the cardiovascular magnetic resonance (CMR) field is recognizing that post-contrast myocardial T1 is sensitive to several confounders and migrating towards ECV as a measure of collagen volume fraction. Several recent studies using widely available Modified Look-Locker Inversion-recovery (MOLLI) have reported ECV cutoff values to distinguish between normal and diseased myocardium. It is unclear if these cutoff values are translatable to different T1 mapping pulse sequences such as arrhythmia-insensitive-rapid (AIR) cardiac T1 mapping, which was recently developed to rapidly image patients with cardiac rhythm disorders. We sought to evaluate, in well-controlled canine and pig experiments, the relative accuracy and precision, as well as intra- and inter-observer variability in data analysis, of ECV measured with AIR as compared with MOLLI. In 16 dogs, as expected, the mean T1 was significantly different (p ECV between MOLLI (21.8 ± 2.1%) and AIR (19.6 ± 2.4%) was also significantly different (p ECV calculations were similar between MOLLI and AIR. In six pigs, the coefficient of repeatability (CR), as defined by the Bland-Altman analysis, in T1 calculation was considerably lower for MOLLI (32.5 ms) than AIR (82.3 ms), and the CR in ECV calculation was also lower for MOLLI (1.8%) than AIR (4.5%). In conclusion, this study shows that MOLLI and AIR yield significantly different T1 and ECV values in large animals and that MOLLI yields higher precision than AIR. Findings from this study suggest that CMR researchers must consider the specific pulse sequence when translating published ECV cutoff values into their own studies. Copyright © 2014 John Wiley & Sons, Ltd.

  1. ANALISIS PERBEDAAN CITRA MRI BRAIN PADA SEKUENT1SE DAN T1FLAIR

    Directory of Open Access Journals (Sweden)

    Nursama Heru Apriantoro

    2015-10-01

    Full Text Available MRI adalah bagian dari ilmu kedokteran untuk mediagnosa kelainan organ dengan memanfaatkan medan magnet dan pergerakan proton atom hidrogen. Salah satu pemeriksaan MRI adalah pemeriksaan brain. Pemeriksaan MRI brain dapat dilakukan T1 weighted image Spin Echo (T1 SE atau T1 Fluid Attenuated Inversion Recovery (T1 FLAIR. Kajian dilakukan untuk menentukan perbedaan T1 SE dan T1 FLAIR dari segi citra berdasarkan nilai Rasio Signal terhadap Noise (SNR dengan MRI GE Type Signa HD xt 1.5 Tesla. Penelitian menggunakan pendekatan kuantitatif.  20 pasien  telah diambil pada pemeriksaan MRI brain pada potongan axial, dengan parameter T1 SE potongan axial dengan parameter Time Repetition (TR 700 ms, Time Echo (TE 20 ms, Field of View (FOV 240 mm, Slice Thickness 5,0 mm, Spacing 1,0 mm, Number of Excitations (NEX 1, Phase 224, dan total slice 20. T1 FLAIR  parameter TR 3000 ms, TE 13,9 ms, TI 920 ms, FOV 240 mm, slice thickness 5,0 mm, spacing 1,0 mm,   NEX 1, phase 224, dan total slice 20. SNR dihitung pada anatomi brain meliputi CSF (Cerebro Spinal Fluid, White Matter dan Gray Matter. Hasil penelitian kedua sequence tersebut menunjukkan bahwa sequence T1 SE lebih baik daripada sequence T1 FLAIR.

  2. Relaxation Pathways in Metallic Glasses

    Science.gov (United States)

    Gallino, Isabella; Busch, Ralf

    2017-11-01

    At temperatures below the glass transition temperature, physical properties of metallic glasses, such as density, viscosity, electrical resistivity or enthalpy, slowly evolve with time. This is the process of physical aging that occurs among all types of glasses and leads to structural changes at the microscopic level. Even though the relaxation pathways are ruled by thermodynamics as the glass attempts to re-attain thermodynamic equilibrium, they are steered by sluggish kinetics at the microscopic level. Understanding the structural and dynamic pathways of the relaxing glassy state is still one of the grand challenges in materials physics. We review some of the recent experimental advances made in understanding the nature of the relaxation phenomenon in metallic glasses and its implications to the macroscopic and microscopic properties changes of the relaxing glass.

  3. Electron spin-lattice relaxation of the S0 state of the oxygen-evolving complex in photosystem II and of dinuclear manganese model complexes.

    Science.gov (United States)

    Kulik, L V; Lubitz, W; Messinger, J

    2005-07-05

    The temperature dependence of the electron spin-lattice relaxation time T1 was measured for the S0 state of the oxygen-evolving complex (OEC) in photosystem II and for two dinuclear manganese model complexes by pulse EPR using the inversion-recovery method. For [Mn(III)Mn(IV)(mu-O)2 bipy4]ClO4, the Raman relaxation process dominates at temperatures below 50 K. In contrast, Orbach type relaxation was found for [Mn(II)Mn(III)(mu-OH)(mu-piv)2(Me3 tacn)2](ClO4)2 between 4.3 and 9 K. For the latter complex, an energy separation of 24.7-28.0 cm(-1) between the ground and the first excited electronic state was determined. In the S0 state of photosystem II, the T1 relaxation times were measured in the range of 4.3-6.5 K. A comparison with the relaxation data (rate and pre-exponential factor) of the two model complexes and of the S2 state of photosystem II indicates that the Orbach relaxation process is dominant for the S0 state and that its first excited state lies 21.7 +/- 0.4 cm(-1) above its ground state. The results are discussed with respect to the structure of the OEC in photosystem II.

  4. Reliability of 7T (1) H-MRS measured human prefrontal cortex glutamate, glutamine, and glutathione signals using an adapted echo time optimized PRESS sequence: A between- and within-sessions investigation.

    Science.gov (United States)

    Lally, Níall; An, Li; Banerjee, Dipavo; Niciu, Mark J; Luckenbaugh, David A; Richards, Erica M; Roiser, Jonathan P; Shen, Jun; Zarate, Carlos A; Nugent, Allison C

    2016-01-01

    To ascertain the mechanisms of neuropsychiatric illnesses and their treatment, accurate and reliable imaging techniques are required; proton magnetic resonance spectroscopy ((1) H-MRS) can noninvasively measure glutamatergic function. Evidence suggests that aberrant glutamatergic signaling plays a role in numerous psychopathologies. Until recently, overlapping glutamatergic signals (glutamate, glutamine, and glutathione) could not easily be separated. However, the advent of novel pulse sequences and higher field magnetic resonance imaging (MRI) allows more precise resolution of overlapping glutamatergic signals, although the question of signal reliability remains undetermined. At 7T MR, we acquired (1) H-MRS data from the medial pregenual anterior cingulate cortex of healthy volunteers (n = 26) twice on two separate days. An adapted echo time optimized point-resolved spectroscopy sequence, modified with the addition of a J-suppression pulse to attenuate N-acetyl-aspartate multiplet signals at 2.49 ppm, was used to excite and acquire the spectra. In-house software was used to model glutamate, glutamine, and glutathione, among other metabolites, referenced to creatine. Intraclass correlation coefficients (ICCs) were computed for within- and between-session measurements. Within-session measurements of glutamate, glutamine, and glutathione were on average reliable (ICCs ≥0.7). As anticipated, ICCs for between-session values of glutamate, glutamine, and glutathione were slightly lower but nevertheless reliable (ICC >0.62). A negative correlation was observed between glutathione concentration and age (r(24)  = -0.37; P signals. © 2015 Wiley Periodicals, Inc.

  5. Relaxation Dynamics in Photoexcited Chiral Molecules Studied by Time-Resolved Photoelectron Circular Dichroism: Toward Chiral Femtochemistry

    CERN Document Server

    Comby, Antoine; Boggio-Pasqua, Martial; Descamps, Dominique; Légaré, Francois; Nahon, Laurent; Petit, Stéphane; Pons, Bernard; Fabre, Baptiste; Mairesse, Yann; Blanchet, Valérie

    2016-01-01

    Unravelling the main initial dynamics responsible for chiral recognition is a key stepin the understanding of many biological processes. However this challenging task requires a sensitive enantiospecic probe to investigate molecular dynamics on their natural femtosecond timescale. Here we show that, in the gas phase, the ultrafast relaxationdynamics of photoexcited chiral molecules can be tracked by recording Time-ResolvedPhotoElectron Circular Dichroism (TR-PECD) resulting from the photoionisation bya circularly polarized probe pulse. A large forward/backward asymmetry along theprobe propagation axis is observed in the photoelectron angular distribution. Its evolution with pump-probe delay reveals ultrafast dynamics that are inaccessible in theangle-integrated photoelectron spectrum nor via the usual electron emission anisotropyparameter ($\\beta$). PECD, which originates from the electron scattering in the chiral molecular potential, appears as a new sensitive observable for ultrafast molecular dynamicsin ch...

  6. Shoreline relaxation at pocket beaches

    Science.gov (United States)

    Turki, Imen; Medina, Raul; Kakeh, Nabil; González, Mauricio

    2015-09-01

    A new physical concept of relaxation time is introduced in this research as the time required for the beach to dissipate its initial perturbation. This concept is investigated using a simple beach-evolution model of shoreline rotation at pocket beaches, based on the assumption that the instantaneous change of the shoreline plan-view shape depends on the long-term equilibrium plan-view shape. The expression of relaxation time is developed function of the energy conditions and the physical characteristics of the beach; it increases at longer beaches having coarse sediments and experiencing low-energy conditions. The relaxation time, calculated by the developed model, is validated by the shoreline observations extracted from video images at two artificially embayed beaches of Barcelona (NW Mediterranean) suffering from perturbations of sand movement and a nourishment project. This finding is promising to estimate the shoreline response and useful to improve our understanding of the dynamic of pocket beaches and their stability.

  7. OS044. Morphological differences in murine placenta detected by magneticresonance imaging measurements of T2 relaxation times in mouse models ofpreeclampsia.

    Science.gov (United States)

    Bobek, G; Stait-Gardner, T; Surmon, L; Makris, A; Price, W S; Hennessy, A

    2012-07-01

    We have demonstrated that morphologically distinct regions of the murine placenta can be detected by magnetic resonance imaging (MRI), with image contrast arising from the variation in T2 relaxation times between regions and dependent upon blood flow. Previous studies of human placenta by other groups have shown a homogeneous tissue with correlation of relaxation times with gestational age and a trend for shorter relaxation times in pregnancies complicated by preeclampsia and fetal growth restriction. The ability to detect morphological changes and alterations in blood flow in experimental models of preeclampsia would be a significant boost in understanding the relationship between abnormal placental implantation, reduced placental perfusion, inflammatory cytokines, angiogenic molecules and other factors that may play a role in the syndrome. The aim of this study was to investigate whether morphological changes or abnormalities can be detected by T2 mapping in the placenta of mice subject to two experimental models of preeclampsia (reduced uterine perfusion pressure (RUPP) model and TNF-α induced model). Pregnant C57BL/6JArc mice were, on day 13.5 of gestation, either subject to a unilateral ligation of the right uterine artery (RUPP) (n=2) or given an infusion of TNF-α by subcutaneous insertion of a mini-osmotic pump primed to deliver 500ng/kg/day for 4days (n=2). Controls were normal pregnant (n=2), sham-operated (n=1) or saline infused animals(n=1). MRI images were acquired on anaesthetised mice on day 17.5 of gestation using a Bruker Avance 11.7 Tesla wide-bore spectrometer with micro-imaging probe capable of generating gradients of 0.45T/m. T2 measurements were acquired using an MSME sequence protocol (Bruker MSME-T2-map) with an in-plane resolution of 0.1-0.2mm. Matlab was used to generate R2 (i.e.,1/T2) maps from the acquired data with the T2 values being calculated from selected regions of interest from 2-6 individual placenta from each mouse. Differences

  8. Under which conditions does T1 difficulty affect T2 performance in the attentional blink?

    DEFF Research Database (Denmark)

    Nielsen, Simon; Petersen, Anders; Andersen, Tobias Søren

    When two visual targets (T1 & T2) are presented in rapid succession, performance of T2 suffers up to 900 ms. One theory of this attentional blink (Raymond, Shapiro, & Arnell, 1992) propose that T1 and T2 compete for limited processing resources (Chun & Potter, 1995), and predict that prolonging...... processing time for T1 by increasing its perceptual difficulty will induce a larger blink. Several studies have tested this prediction without reaching a consistent answer. McLaughlin, Shore, & Klein (2001) found no effect of the exposure duration of T1 on the attentional blink. Christmann & Leuthold (2004......) found that increasing the contrast of T1 decreased the attentional blink but Chua (2005) found the opposite effect. In the current study, we varied the perceptual difficulty of T1 in the two-target paradigm (Duncan, Ward, & Shapiro, 1994) both by changing the contrast and by changing the exposure...

  9. Two Distinct Determinants of Ligand Specificity in T1R1/T1R3 (the Umami Taste Receptor)*

    OpenAIRE

    Toda, Yasuka; Nakagita, Tomoya; Hayakawa, Takashi; Okada, Shinji; Narukawa, Masataka; Imai, Hiroo; Ishimaru, Yoshiro; Misaka, Takumi

    2013-01-01

    Umami taste perception in mammals is mediated by a heteromeric complex of two G-protein-coupled receptors, T1R1 and T1R3. T1R1/T1R3 exhibits species-dependent differences in ligand specificity; human T1R1/T1R3 specifically responds to l-Glu, whereas mouse T1R1/T1R3 responds more strongly to other l-amino acids than to l-Glu. The mechanism underlying this species difference remains unknown. In this study we analyzed chimeric human-mouse receptors and point mutants of T1R1/T1R3 and identified 1...

  10. Masking T1 Difficulty: Processing Time and the Attentional Blink

    Science.gov (United States)

    Visser, Troy A. W.

    2007-01-01

    When observers are presented with 2 targets in rapid succession, identification of the 1st is highly accurate, whereas identification of the 2nd is impaired at brief intertarget intervals (i.e., 200-500 ms). This 2nd-target deficit is known as the attentional blink (AB). According to bottleneck models, the AB arises because attending to the 1st…

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

    Science.gov (United States)

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

    2017-01-01

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

  12. Fast T1 and T2 mapping methods: the zoomed U-FLARE sequence compared with EPI and snapshot-FLASH for abdominal imaging at 11.7 Tesla.

    Science.gov (United States)

    Pastor, Géraldine; Jiménez-González, María; Plaza-García, Sandra; Beraza, Marta; Reese, Torsten

    2017-06-01

    A newly adapted zoomed ultrafast low-angle RARE (U-FLARE) sequence is described for abdominal imaging applications at 11.7 Tesla and compared with the standard echo-plannar imaging (EPI) and snapshot fast low angle shot (FLASH) methods. Ultrafast EPI and snapshot-FLASH protocols were evaluated to determine relaxation times in phantoms and in the mouse kidney in vivo. Owing to their apparent shortcomings, imaging artefacts, signal-to-noise ratio (SNR), and variability in the determination of relaxation times, these methods are compared with the newly implemented zoomed U-FLARE sequence. Snapshot-FLASH has a lower SNR when compared with the zoomed U-FLARE sequence and EPI. The variability in the measurement of relaxation times is higher in the Look-Locker sequences than in inversion recovery experiments. Respectively, the average T1 and T2 values at 11.7 Tesla are as follows: kidney cortex, 1810 and 29 ms; kidney medulla, 2100 and 25 ms; subcutaneous tumour, 2365 and 28 ms. This study demonstrates that the zoomed U-FLARE sequence yields single-shot single-slice images with good anatomical resolution and high SNR at 11.7 Tesla. Thus, it offers a viable alternative to standard protocols for mapping very fast parameters, such as T1 and T2, or dynamic processes in vivo at high field.

  13. Correction with blood T1 is essential when measuring post-contrast myocardial T1 value in patients with acute myocardial infarction.

    Science.gov (United States)

    Choi, Eui-Young; Hwang, Sung Ho; Yoon, Young Won; Park, Chul Hwan; Paek, Mun Young; Greiser, Andreas; Chung, Hyemoon; Yoon, Ji-Hyun; Kim, Jong-Youn; Min, Pil-Ki; Lee, Byoung Kwon; Hong, Bum-Kee; Rim, Se-Joong; Kwon, Hyuck Moon; Kim, Tae Hoon

    2013-01-19

    Post-contrast T1 mapping by modified Look-Locker inversion recovery (MOLLI) sequence has been introduced as a promising means to assess an expansion of the extra-cellular space. However, T1 value in the myocardium can be affected by scanning time after bolus contrast injection. In this study, we investigated the changes of the T1 values according to multiple slicing over scanning time at 15 minutes after contrast injection and usefulness of blood T1 correction. Eighteen reperfused acute myocardial infarction (AMI) patients, 13 cardiomyopathy patients and 8 healthy volunteers underwent cardiovascular magnetic resonance with 15 minute-post contrast MOLLI to generate T1 maps. In 10 cardiomyopathy cases, pre- and post-contrast MOLLI techniques were performed to generate extracellular volume fraction (Ve). Six slices of T1 maps according to the left ventricular (LV) short axis, from apex to base, were consecutively obtained. Each T1 value was measured in the whole myocardium, infarcted myocardium, non-infarcted myocardium and LV blood cavity. The mean T1 value of infarcted myocardium was significantly lower than that of non-infarcted myocardium (425.4 ± 68.1 ms vs. 540.5 ± 88.0 ms, respectively, p infarcted myocardium increased significantly from apex to base (from 523.1 ± 99.5 ms to 561.1 ± 81.1 ms, p = 0.001), and were accompanied by a similar increase in blood T1 value in LV cavity (from 442.1 ± 120.7 ms to 456.8 ± 97.5 ms, p myocardial T1 values, however, were adjusted by the blood T1 values, they were consistent throughout the slices from apex to base (from 1.17 ± 0.18 to 1.25 ± 0.13, p > 0.05). The Ve did not show significant differences from apical to basal slices. Post-contrast myocardial T1 corrected by blood T1 or Ve, provide more stable measurement of degree of fibrosis in non-infarcted myocardium in short- axis multiple slicing.

  14. Superparamagnetic relaxation of weakly interacting particles

    DEFF Research Database (Denmark)

    Mørup, Steen; Tronc, Elisabeth

    1994-01-01

    The influence of particle interactions on the superparamagnetic relaxation time has been studied by Mossbauer spectroscopy in samples of maghemite (gamma-Fe2O3) particles with different particle sizes and particle separations. It is found that the relaxation time decreases with decreasing particl...