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MRI Parameters (mri + parameter)
Selected AbstractsVisualizing feedback-enhanced contrast in magnetic resonance imagingCONCEPTS IN MAGNETIC RESONANCE, Issue 6 2007Susie Y. Huang Abstract A new approach to magnetic resonance imaging (MRI) contrast enhancement has recently been developed that exploits nonlinear feedback interactions to amplify contrast arising from small variations in the underlying MRI parameters. A unified framework for understanding feedback-enhanced contrast is presented here based on the concepts of instability and positive feedback. The specific mechanisms governing contrast enhancement under the feedback interactions of radiation damping, the distant dipolar field, and their joint effect are elucidated through numerical simulations illustrating the involved spin dynamics. Experimental demonstrations of feedback-enhanced contrast are shown on samples of in vitro human brain tissue, and applications to improving lesion detection in disease states such as epilepsy and cancer are discussed. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 378,393, 2007. [source] Three-dimensional MRI mapping of minimum temperatures achieved in microwave and conventional food processingINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 3 2001John R. Bows Microbiological assurance protocols for food preservation are based on the ,worst-case' slowest heating point within the food product. For conduction-limited processing, this leads to well-known overheating near surface regions of products, with resultant quality loss. For volumetric heating processes such as microwave heating, it is practically impossible to guarantee where the slowest heating point will be. Consequently, microwave heating regimes are generally excessive and product quality is often similar to conventional conduction-limited heating processes. It is well known that Magnetic Resonance Imaging (MRI) can provide three-dimensional (3D) images which quantify the spatial distribution of water in foods, and also that the MRI parameters of water are temperature dependent. The present study demonstrates that a combination of these two concepts has led to a new approach for the validation of thermal processing in food manufacture. The potential for on-line assurance of minimum and maximum temperatures for manufacture of microbiologically assured, minimally processed, high quality food is discussed. [source] In Vivo Determination of Bone Structure in Postmenopausal Women: A Comparison of HR-pQCT and High-Field MR Imaging,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 4 2008Galateia J Kazakia PhD Abstract Bone structural measures obtained by two noninvasive imaging tools,3T MRI and HR-pQCT,were compared. Significant but moderate correlations and 2- to 4-fold discrepancies in parameter values were detected, suggesting that differences in acquisition and analysis must be considered when interpreting data from these imaging modalities. Introduction: High-field MRI and high resolution (HR)-pQCT are currently being used in longitudinal bone structure studies. Substantial differences in acquisition and analysis between these modalities may influence the quantitative data produced and could potentially influence clinical decisions based on their results. Our goal was to compare trabecular and cortical bone structural measures obtained in vivo by 3T MRI and HR-pQCT. Materials and Methods: Postmenopausal osteopenic women (n = 52) were recruited for this study. HR-pQCT imaging of the radius and tibia was performed using the XtremeCT scanner, with a voxel size of 82 × 82 × 82 ,m3. MR imaging was performed on a 3T Signa scanner using SSFP imaging sequences, with a pixel size of 156 × 156 ,m2 and slice thickness of 500 ,m. Structure parameters were calculated using standard HR-pQCT and MRI analysis techniques. Relationships between measures derived from HR-pQCT, MRI, and DXA were studied. Results: Significant correlations between HR-pQCT and MRI parameters were found (p < 0.0001) and were strongest for Tb.N (r2 = 0.52), Ct.Th (r2 = 0.59), and site-specific Tb.Sp (r2 = 0.54,0.60). MRI and HR-pQCT provided statistically different values of structure parameters (p < 0.0001), with BV/TV and Tb.Th exhibiting the largest discrepancies (MR/HR-pQCT = 3,4). Although differences in the Tb.N values were statistically significant, the mean differences were on the order of our reproducibility measurements. Systematic differences between MRI and HR-pQCT analysis procedures leading to discrepancies in cortical thickness values were observed, with MRI values consistently higher. Minimal correlations were found between MRI or HR-pQCT parameters and DXA BMD or T-score, except between HR-pQCT measures at the radius and the ultradistal radius T-scores, where moderate correlations were found (r2 = 0.19,0.58). Conclusions: This study provides unique insight into two emerging noninvasive tools for bone structure evaluation. Our findings highlight the significant influence of analysis technique on results of in vivo assessment and underscore the importance of accounting for these differences when interpreting results from these modalities. [source] Three-dimensional MRI assessment of regional wall stress after acute myocardial infarction predicts postdischarge cardiac eventsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2008Fabrice Prunier MD Abstract Purpose To determine the prognostic significance of systolic wall stress (SWS) after reperfused acute myocardial infarction (AMI) using MRI. Materials and Methods A total of 105 patients underwent MRI 7.8 ± 4.2 days after AMI reperfusion. SWS was calculated by using a three-dimensional (3D) MRI approach to left ventricular (LV) wall thickness and to the radius of curvature. Between hospital discharge and the end of follow-up, an average of 4.1 ± 1.7 years after AMI, 19 patients experienced a major cardiac event, including cardiac death, nonfatal reinfarction or heart failure (18.3%). Results The results were mainly driven by heart failure outcome. In univariate analysis the following factors were predictive of postdischarge major adverse cardiac events: 1) at the time of AMI: higher heart rate, previous calcium antagonist treatment, in-hospital congestive heart failure, proximal left anterior descending artery (LAD) occlusion, a lower ejection fraction, higher maximal ST segment elevation before reperfusion, and ST segment reduction lower than 50% after reperfusion; 2) MRI parameters: higher LV end-systolic volume, lower ejection fraction, higher global SWS, higher SWS in the infarcted area (SWS MI) and higher SWS in the remote myocardium (SWS remote). In the final multivariate model, only SWS MI (odds ratio [OR]: 1.62; 95% confidence interval [CI]: 1.01,2.60; P = 0.046) and SWS remote (OR: 2.17; 95% CI: 1.02,4.65; P = 0.046) were independent predictors. Conclusion Regional SWS assessed by means of MRI a few days after AMI appears to be strong predictor of postdischarge cardiac events, identifying a subset of at risk patients who could qualify for more aggressive management. J. Magn. Reson. Imaging 2008. © 2008 Wiley-Liss, Inc. [source] Comparison of relative forced expiratory volume of one second with dynamic magnetic resonance imaging parameters in healthy subjects and patients with lung cancer,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2005Christian Plathow MD Abstract Purpose To assess relative forced expiratory volume in one second (FEV1/vital capacity (VC)) in healthy subjects and patients with a lung tumor using dynamic magnetic resonance imaging (dMRI) parameters. Materials and Methods In 15 healthy volunteers and 31 patients with a non-small-cell lung carcinoma stage I (NSCLC I), diaphragmatic length change (LE1) and craniocaudal (CC) intrathoracic distance change within one second from maximal inspiration (DE1) were divided by total length change (LEtotal, DEtotal) as a surrogate of spirometric FEV1/VC using a true fast imaging with steady-state precession (trueFISP) sequence (TE/TR = 1.7/37.3 msec, temporal resolution = 3 images/second). Influence of tumor localization was examined. Results In healthy volunteers FEV1/VC showed a highly significant correlation with LE1/LEtotal and DE1/DEtotal (r > 0.9, P < 0.01). In stage IB tumor patients, comparing tumor-bearing with the non-tumor-bearing hemithorax, there was a significant difference in tumors of the middle (LE1/LEtotal = 0.63 ± 0.05 vs. 0.73 ± 0.04, DE1/DEtotal = 0.66 ± 0.05 vs. 0.72 ± 0.04; P < 0.05) and lower (P < 0.05) lung region. Stage IA tumor patients showed no significant differences with regard to healthy subjects. Conclusion dMRI is a simple noninvasive method to locally determine LE1/LEtotal and DE1/DEtotal as a surrogate of FEV1/VC in volunteers and patients. Tumors of the middle and lower lung regions have a significant influence on these MRI parameters. J. Magn. Reson. Imaging 2005;21:212,218. © 2005 Wiley-Liss, Inc. [source] Manganese-guided cellular MRI of human embryonic stem cell and human bone marrow stromal cell viabilityMAGNETIC RESONANCE IN MEDICINE, Issue 4 2009Mayumi Yamada Abstract This study investigated the ability of MnCl2 as a cellular MRI contrast agent to determine the in vitro viability of human embryonic stem cells (hESC) and human bone marrow stromal cells (hBMSC). Basic MRI parameters including T1 and T2 values of MnCl2 -labeled hESC and hBMSC were measured and viability signal of manganese (Mn2+)-labeled cells was validated. Furthermore, the biological activity of Ca2+ -channels was modulated utilizing both Ca2+ -channel agonist and antagonist to evaluate concomitant signal changes. Metabolic effects of MnCl2 -labeling were also assessed using assays for cell viability, proliferation, and apoptosis. Finally, in vivo Mn2+ -guided MRI of the transplanted hESC was successfully achieved and validated by bioluminescence imaging. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [source] Quantitative MRI-pathology correlations of brain white matter lesions developing in a non-human primate model of multiple sclerosisNMR IN BIOMEDICINE, Issue 2 2007Erwin L. A. Blezer Abstract Experimental autoimmune encephalomyelitis (EAE) induced with recombinant human myelin/oligodendrocyte glycoprotein in the common marmoset is a useful preclinical model of multiple sclerosis in which white matter lesions can be well visualized with MRI. In this study we characterized lesion progression with quantitative in vivo MRI (4.7,T; T1 relaxation time,±,Gd-DTPA; T2 relaxation time; magnetization transfer ratio, MTR, imaging) and correlated end stage MRI presentation with quantitative ex vivo MRI (formaldehyde fixed brains; T1 and T2 relaxation times; MTR) and histology. The histopathological characterization included axonal density measurements and the numeric quantification of infiltrated macrophages expressing markers for early active [luxol fast blue (LFB) or migration inhibition factor-related protein-14 positive] or late active/inactive [periodic acid Schiff (PAS) positive] demyelinating lesion. MRI experiments were done every two weeks until the monkeys were sacrificed with severe EAE-related motor deficits. Compared with the normal appearing white matter, lesions showed an initial increase in T1 relaxation times, leakage of Gd-DTPA and decrease in MTR values. The progressive enlargement of lesions was associated with stabilized T1 values, while T2 initially increased and stabilized thereafter and MTR remained decreased. Gd-DTPA leakage was highly variable throughout the experiment. MRI characteristics of the cortex and (normal appearing) white matter did not change during the experiment. We observed that in vivo MTR values correlated positively with the number of early active (LFB+) and negatively with late active (PAS+) macrophages. Ex vivo MTR and relaxation times correlated positively with the number of PAS-positive macrophages. None of the investigated MRI parameters correlated with axonal density. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||