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Purpose: To study the anisotropic characteristics of both multi-component T2 and T1ρ relaxation times in tendon. Materials and Methods: T2 and T1ρ were measured in tendon by NMR spectroscopy at different orientations and by microscopic MRI at the magic angle. Several experimental issues in the multi-component relaxation measurements were investigated, including the effects of echo spacing, the resolution of MRI experiments, the influence of the specimen orientations, and the strengths of different spin-lock frequencies in T1ρ experiments. Results: Both the values and fractions of T2 in tendon showed significant orientational dependence. The values and fractions of T1ρ strongly depended on both the specimen orientation and the spin-lock strength. The imaging resolution (35-280 μm) had little influence in the T2 experiments. Both the echo spacings (0.6-3.0 ms) in the T2 experiment and the spin-lock strengths (0.5-5 kHz) in the T1ρ experiment affected the quantification of the multi-component relaxation. Up to three T2 and T1ρ components were resolved in tendon. Conclusion: Multi-component relaxations could be attributed to different populations of water in the tissue. The transitions between a mono-component and multi-component result call for the caution in interpreting the relaxation results. J. Magn. Reson. Imaging 2013;38:625-633. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Estimation of multiple T2 components within single imaging voxels typically proceeds in one of two ways; a nonparametric grid approximation to a continuous distribution is made and a regularized nonnegative least squares algorithm is employed to perform the parameter estimation, or a parametric multicomponent model is assumed with a maximum likelihood estimator for the component estimation. In this work, we present a Bayesian algorithm based on the principle of progressive correction for the latter choice of a discrete multicomponent model. We demonstrate in application to simulated data and two experimental datasets that our Bayesian approach provides robust and accurate estimates of both the T2 model parameters and nonideal flip angles. The second contribution of the paper is to present a Cramér-Rao analysis of T2 component width estimators. To this end, we introduce a parsimonious parametric and continuous model based on a mixture of inverse-gamma distributions. This analysis supports the notion that T2 spread is difficult, if not infeasible, to estimate from relaxometry data acquired with a typical clinical paradigm. These results justify the use of the discrete distribution model. [ABSTRACT FROM AUTHOR]

Aim X-ray contrast media ( CM) can cause acute kidney injury ( AKI). Medullary hypoxia is pivotal in CM-induced AKI, as indicated by invasively and pin-point measured tissue oxygenation. MRI provides spatially resolved blood oxygenation level-dependent data using T2* and T2 mapping. We studied CM effects on renal T2*/T2 and benchmarked them against short periods of hyperoxia, hypoxia and aortic occlusion ( AO). Methods Rats were equipped with carotid artery catheters (tip towards aorta) and supra-renal aortic occluders. T2*/T2 mapping was performed using a 9.4-T animal scanner. CM (1.5 mL iodixanol) was injected into the thoracic aorta with the animal in the scanner followed by 2 h of T2*/T2 mapping. For T2*/T2 assessment, regions of interest in the cortex ( C), outer medulla ( OM), inner medulla ( IM) and papilla ( P) were determined according to morphological features. Results Hyperoxia increased T2* in C (by 17%) and all medullary layers (25-35%). Hypoxia decreased T2* in C (40%) and all medullary layers (55-60%). AO decreased T2* in C (18%) and all medullary layers (30-40%). Upon injection of CM, T2* increased transiently, then decreased, reaching values 10-20% below baseline in C and OM and 30-40% below baseline in IM and P. Conclusion T2* mapping corroborates data previously obtained with invasive methods and demonstrates that CM injection affects renal medullary oxygenation. CM-induced T2* decrease in OM was small vs. hypoxia and aortic occlusion. T2* decrease obtained for hypoxia was more pronounced than for AO. This indicates that T2* may not accurately reflect blood oxygenation under certain conditions. [ABSTRACT FROM AUTHOR]

Lower back pain is a common problem frequently encountered without specific biomarkers that correlate well with an individual patient's pain generators. MRI quantification of diffusion and T2 relaxation properties may provide novel insight into the mechanical and inflammatory changes that occur in the lumbosacral nerve roots in patients with lower back pain. Accurate imaging of the spinal nerve roots is difficult because of their small caliber and oblique course in all three planes. Two-dimensional in-plane imaging of the lumbosacral nerve roots requires oblique coronal imaging with large field of view (FOV) in both dimensions, resulting in severe geometric distortions using single-shot echo planar imaging (EPI) techniques. The present work describes initial success using a reduced-FOV single-shot spin-echo EPI acquisition to obtain in-plane diffusion tensor imaging (DTI) and T2 mapping of the bilateral lumbar nerve roots at the L4 level of healthy subjects, minimizing partial volume effects, breathing artifacts and geometric distortions. A significant variation in DTI and T2 mapping metrics is also reported along the course of the normal nerve root. The fractional anisotropy is statistically significantly lower in the dorsal root ganglia (0.287 ± 0.068) than in more distal regions in the spinal nerve (0.402 ± 0.040) ( p < 10-5). The T2 relaxation value is statistically significantly higher in the dorsal root ganglia (78.0 ± 11.9 ms) than in more distal regions in the spinal nerve (59.5 ± 7.4 ms) ( p < 10-5). The quantification of nerve root DTI and T2 properties using the proposed methodology may identify the specific site of any degenerative and inflammatory changes along the nerve roots of patients with lower back pain. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the impact of T2 relaxation of the carotid wall on measurements of its thickness. Materials and Methods: The common carotid artery wall was imaged using a spin echo sequence acquired at four echo times (17 ms to 68 ms) in 65 participants as part of VALIDATE study. Images were acquired transverse to the artery 1.5 cm proximal to the flow divider. Mean wall thickness, mean wall signal intensity, lumen area, and outer wall area were measured for each echo. Contours were also traced on the image from the fourth echo and then propagated to the images from the preceding echoes. This was repeated using the image from the first echo. Mean wall signal intensity measurements at the four echo times were fit to a mono-exponential decay curve to derive the mean T2 relaxation time for each set of contours. Results: Mean wall thickness decreased with increasing echo time, with an average thickness reduction of 8.6% between images acquired at the first and last echo times (TE) (0.93 mm at TE 17 ms versus 0.85 mm at TE 68 ms, P < 0.001). Average T2 relaxation time of the carotid wall decreased by 3% when the smaller contours from the last echo were used, which excluded the outer-most layer (54.3 ± 7.6 ms versus 52.7 ± 6.6 ms, P = 0.03). Conclusion: Carotid wall thickness measurements decrease with echo time as expected by the fast T2 relaxation time of the outer-most layer, namely the adventitia. A short echo time is needed for thickness measurements to include adventitia, which plays an important role in plaque development. J. Magn. Reson. Imaging 2013;37:1493-1498. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Purpose: (i) To develop an MRS technique to measure 7Li levels in human brain in a reasonable scan time, (ii) to develop a technique to quantify 7Li T2 relaxation times as measured from human brain in patients taking lithium for the treatment of their bipolar disorder, and (iii) to confirm or refute the presence of bi-exponential 7Li T2 relaxation in human brain. Materials and Methods: We modified a spin-echo MRS pulse sequence to decrease its minimum echo time. With IRB approval, we performed lithium MRS with the modified pulse sequence on 13 euthymic bipolar patients stable on long-term lithium to treat their disease. Results: We were able to achieve a total scan time per sample of 8:20; total scan time including imaging, calibration and MRS was approximately 1 h 15 min. We observed bi-exponential T2 relaxation in the majority of patients, with an average short decay time of 5.3 ± 1.4 ms and an average long decay time of 68.2 ± 10.2 ms. However, in two patients we observed strongly mono-exponential T2 relaxation with an average decay time of 47.4 ± 1.3 ms. Conclusion: 7Li relaxation patterns may prove useful to distinguish between lithium-responsive and lithium nonresponsive bipolar patients. J. Magn. Reson. Imaging 2013;37:1451-1459. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Crosslinking reaction of hydroxyl-terminated polybutadiene (HTPB)/isophorone di-isocyanate (IPDI) was monitored by infrared spectroscopy, dynamic mechanical analysis (DMA), swelling measurements, and by relaxation time ( T2) measurements obtained by low-field NMR technique. Chemical reaction monitored by FTIR shows that urethane bonds were predominantly formed throughout the whole reaction period while DMA and swelling became only effective once the three-dimensional network was formed. NMR results allow differentiating between relaxation-processes associated with different fractions of the reactants in the mixture prior to the network formation. The most important finding in this study is that two of the relaxation processes were found to decline whereas a new fraction with a short relaxation time which emerged specifically at an early stage of reaction and progressed along with advancement of the reaction. All results pointed out to a change in the mixture behavior around 30 h of crosslinking reaction at 60°C, reflecting an important restriction in molecules diffusion and mobilities which were attributed to the gel point formation. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Abstract: The corticospinal tract (CST) appears hyperintense on both T2-weighted images and myelin water maps. Here, an extended multiecho T2 relaxation sequence with echoes out to 1120 ms was used to characterize the longer T2 times present in the CST. The T2 distribution from the CST was compared to other white matter structures in 14 healthy subjects. The intra-/extracellular T2 peak of the CST was broadened relative to other white matter structures and often split into two distinct peaks. In the CST, it appeared that the intracellular and extracellular water environments had unique T2 times, causing the intracellular water peak to be pushed down into the myelin water T2 regime and the extracellular peak to be pushed up to longer T2 times. The conventional myelin water T2 limits of 5-40 ms resulted in an artificial increase in myelin water fraction (MWF), causing the CST to be bright on myelin water images. When the upper limit for MWF was decreased to 25 ms, the CST regions exhibited MWF values similar to those found for adjacent anterior and posterior regions. The CST has unique magnetic resonance characteristics, which should be taken into consideration when being examined, especially when compared to pathological tissue. [Copyright &y& Elsevier]

Abstract: Myelin water imaging, a magnetic resonance imaging technique capable of resolving the fraction of water molecules which are located between the layers of myelin, is a valuable tool for investigating both normal and pathological brain structure in vivo. There is a strong need for pulse sequences which improve the quality and applicability of myelin water imaging in a clinical setting. In this study, we validated the use of a fast multi echo T2 relaxation sequence for myelin water imaging. Using a multiple combined gradient and spin echo (GRASE) technique, we attain whole cerebrum myelin water images in under 15minutes. Region of interest analysis indicates that this fast GRASE imaging sequence produces results which are in good agreement with pure spin echo measurements (R 2 =0.95, p <0.0001). This drastic improvement in speed and brain coverage compared to current spin echo standards will allow increased inclusion of myelin water imaging in neurological research protocols and opens up the possibility of applications in a clinical setting. [Copyright &y& Elsevier]

Conventional MR images are qualitative, and their signal intensity is dependent on several complementary contrast mechanisms that are manipulated by the MR hardware and software. In the absence of a quantitative metric for absolute interpretation of pixel signal intensities, one that is independent of scanner hardware and sequences, it is difficult to perform comparisons of MR images across subjects or longitudinally in the same subject. Quantitative relaxometry isolates the contributions of individual MR contrast mechanisms (T1, T2, T2*) and provides maps, which are independent of the MR protocol and have a physical interpretation often expressed in absolute units. In addition to providing an unbiased metric for comparing MR scans, quantitative relaxometry uses the relationship between MR maps and physiology to provide a noninvasive surrogate for biopsy and histology. This study provides an overview of some promising clinical applications of quantitative relaxometry, followed by a description of the methods and challenges of acquiring accurate and precise quantitative MR maps. It concludes with three case studies of quantitative relaxometry applied to studying multiple sclerosis, liver iron, and acute myocardial infarction. J. Magn. Reson. Imaging 2012;36:805-824. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: This invited personal story, covering the period from 1979 to 2010, describes the discovery of the dependence of the transverse relaxation time of water in blood on the oxygenation state of hemoglobin in the erythrocytes. The underlying mechanism of the compartmentation of the different magnetic susceptibilities of hemoglobin in its different oxygenation states also explains the mechanism that underlies blood oxygenation level dependent contrast used in fMRI. The story begins with the initial observation of line broadening during ischemia in small rodents detected by in vivo 31P NMR spectroscopy at high field. This spectroscopic line broadening or T2* relaxation effect was demonstrated to be related to the oxygenation state of blood. The effect was quantified more accurately using T2 values measured by the Carr–Purcell–Meiboom–Gill method. The effect was dependent on the integrity of the erythrocytes to compartmentalize the different magnetic susceptibilities produced by the changing spin state of the ferrous iron of hemoglobin in its different oxygenation states between the erythrocytes and the suspending solution. The hematocrit and magnetic field dependence, the requirement for erythrocyte integrity and lack of T1 dependence confirmed that the magnetic susceptibility effect explained the oxygenation state dependence of T2* and T2. This T2/T2* effect was combined with T1 based measurements of blood flow to measure oxygen consumption in animals. This blood oxygenation assay and its underlying magnetic susceptibility gradient mechanism was published in the biochemistry literature in 1982 and largely forgotten. The observation was revived to explain evolving imaging features of cerebral hematoma as MR imaging of humans increased in field strength to 1.5T by the mid 1980s. Although the imaging version of this assay was used to measure a global metabolic rate of cerebral oxygen consumption in humans at 1.5-T by 1991, the global measurement had little clinical value. By contrast, a decade after the spectroscopic observation, imaging experiments performed on rodents at 7T by Ogawa and colleagues identified the extravascular T2* imaging characteristics of the blood oxygenation effect and, most importantly, associated that change with brain functional states. Ogawa appropriately branded this blood oxygenation level dependent mechanism as BOLD contrast. This mechanism was subsequently shown to be the basis of localized MR signal changes associated with local brain function. This connection led to the fMRI revolution in human brain mapping. [Copyright &y& Elsevier]

We propose a multicomponent fitting algorithm for multiecho T2 data which allows for correction of T2 distributions in the presence of stimulated echoes. Tracking the population of spins in many coherence pathways via the iterated method of the Extended Phase Graph algorithm allows for accurate quantification of echo magnitudes. The resulting decay curves allow for correction of errors due to nonideal refocusing pulses as a result of inhomogeneities in the B1 transmit field. Non-Negative Least Squares fitting is used to quantify the magnitude of T2 components at various T2 values. This method, allowing calculation of the T2 distribution with simultaneous extraction of the refocusing pulse flip angle, requires no change to image acquisition procedures and no extra data input. Validation by means of both simulations and in vivo data shows excellent interscan reproducibility while vastly improving the accuracy of extracted T2 parameters in voxels where poor B1 homogeneity leads to refocusing pulse flip angles significantly less than 180°. Most notably, myelin water fraction values in these regions are found to have increased consistency and accuracy. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the utility of multimodal quantitative MRI (qMRI) and atlas-based methods to identify characteristics of lesion-driven injury and neurodegeneration in relapsing remitting multiple sclerosis (RRMS). Materials and Methods: This work is health insurance portability and accountability act compliant. High resolution T1-weighted, dual echo, and fluid-attenuated inversion recovery and diffusion tensor MRI images were prospectively acquired on 68 RRMS patients (range, 25-58 years) and 68 age-matched controls. The data were analyzed using standardized human brain atlas-based tissue segmentation procedures to obtain regional volumes and their corresponding T2 relaxation times and DTI maps. Results: Group-averaged brain atlas-based qMRI maps of T2, fractional anisotropy and diffusivities are visually presented and compared between controls and RRMS. The analysis shows a widespread injury in RRMS. Atrophy of the corpus callosum (CC) was substantial in RRMS. The qMRI attributes of the neocortex in combination with the CC such as T2 and diffusivities were elevated and correlated with disability. Conclusion: Using a standardized multimodal qMRI acquisition and analyses that accounted for lesion distribution we demonstrate that cerebral pathology is widespread in RRMS. Our analysis of CC and neocortex qMRI metrics in relation to disability points to a neurodegenerative injury component that is independent from lesions. J. Magn. Reson. Imaging 2012;. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Abstract: Multiple sclerosis (MS) is the most common immune-mediated disabling neurological disease of the central nervous system. The pathogenesis of MS is not fully understood. Histopathology implicates both demyelination and axonal degeneration as the major contributors to the accumulation of disability. The application of several in vivo quantitative magnetic resonance imaging (MRI) methods to both lesioned and normal-appearing brain tissue has not yet provided a solid conclusive support of the hypothesis that MS might be a diffuse disease. In this work, we adopted FreeSurfer to provide standardized macrostructure or volumetry of lesion free normal-appearing brain tissue in combination with multiple quantitative MRI metrics (T2 relaxation time, diffusion tensor anisotropy and diffusivities) that characterize tissue microstructural integrity. By incorporating a large number of healthy controls, we have attempted to separate the natural age-related change from the disease-induced effects. Our work shows elevation in diffusivity and relaxation times and reduction in volume in a number of normal-appearing white matter and gray matter structures in relapsing–remitting multiple sclerosis patients. These changes were related in part with the spatial distribution of lesions. The whole brain lesion load and age-adjusted expanded disability status score showed strongest correlations in regions such as corpus callosum with qMRI metrics that are believed to be specific markers of axonal dysfunction, consistent with histologic data of others indicating axonal loss that is independent of focal lesions. Our results support that MS at least in part has a neurodegenerative component. [Copyright &y& Elsevier]

Abstract: Multiecho T2 relaxation measurements offer specific information about myelin content through the myelin water fraction (MWF), as well as about the water environments through the intra- and extra-cellular (IE), and global, geometric mean T2 (GMT2) times. While these measurements have yielded new insights into brain development and pathologies, they have yet to be thoroughly investigated in the spinal cord. The goals of this study were: (1) to apply a new 3D multiecho T2 relaxation measurement in the cervical spine with sufficient axial resolution to distinguish grey and white matter; (2) to perform a pilot reliability assessment of the resulting MWF and GMT2 measures in a target population; and (3) to detect differences in these measures between a younger cohort (20–30years of age) and an older cohort (50–75years of age) of healthy adults. The results demonstrated that the MWF in younger healthy adults follows the known pattern of lower myelin content in grey matter (mean (95% confidence interval)) (0.049 (0.030–0.067)) as compared to white matter (0.296 (0.275–0.317), p<0.001). The reliability coefficients were 0.65 and 0.82 for the MWF in the dorsal (DC) and lateral column (LC) white matter, respectively; 0.79 and 0.52 for the IE GMT2; and 0.74 and 0.73 for the global GMT2. Significantly lower MWF were found in the older adults than in the younger adults (DC p=0.014; LC p=0.012), as well as lower IE GMT2 times (DC p=0.008; LC p=0.042), however, the global GMT2 times did not show any differences. These changes in MWF and IE GMT2 times, but not in global GMT2 times, indicate that multiecho T2 relaxation measures are sensitive to changes in myelin integrity and cell morphology that may not be apparent on conventional T2 weighted images. [ABSTRACT FROM AUTHOR]

A major difference between arterial-spin-labeling MRI and gold-standard radiotracer blood flow methods is that the compartment localization of the labeled spins in the arterial-spin-labeling image is often ambiguous, which may affect the quantification of cerebral blood flow. In this study, we aim to probe whether the spins are located in the vascular system or tissue by using T2 of the arterial-spin-labeling signal as a marker. We combined two recently developed techniques, pseudo-continuous arterial spin labeling and T2-Relaxation-Under-Spin-Tagging, to determine the T2 of the labeled spins at multiple postlabeling delay times. Our data suggest that the labeled spins first showed the T2 of arterial blood followed by gradually approaching and stabilizing at the tissue T2. The T2 values did not decrease further toward the venous T2. By fitting the experimental data to a two-compartment model, we estimated gray matter cerebral blood flow, arterial transit time, and tissue transit time to be 74.0 ± 10.7 mL/100g/min (mean ± SD, N = 10), 938 ± 156 msec, and 1901 ± 181 msec, respectively. The arterial blood volume was calculated to be 1.18 ± 0.21 mL/100 g. A postlabeling delay time of 2 s is sufficient to allow the spins to completely enter the tissue space for gray matter but not for white matter. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Abstract: White matter disorders can involve injury to myelin or axons but the respective contribution of each to clinical course is difficult to evaluate non-invasively. Here, to develop a paradigm for further investigations of axonal pathology by MRI, we compared two genetic mouse models exhibiting relatively selective axonal or myelin deficits using quantitative MRI relaxography of the transverse relaxation times (T2) in vivo and ultrastructural morphometry. In HM-DKO mice, which lack genes encoding the heavy (NF-H) and medium (NF-M) subunits of neurofilaments, neurofilament content of large myelinated axons of the central nervous system (CNS) is markedly reduced in the absence of changes in myelin thickness and volume. In shiverer mutant mice, which lack functional myelin basic protein, CNS myelin sheath formation is markedly reduced but neurofilament content is normal. We observed increases in T2 in nearly all white matter in shiverer mice compared to their wild type, while more subtle increases in T2 were observed in HM-DKO in the corpus callosum. White matter T2 was generally greater in shiverer mice than HM-DKO mice. Ultrastructural morphometry of the corpus callosum, which exhibited the greatest T2 differences, confirmed that total cross-sectional area occupied by axons was similar in the two mouse models and that the major ultrastructural differences, determined by morphometry, were an absence of myelin and larger unmyelinated axons in shiverer mice and absence of neurofilaments in HM-DKO mice. Our findings indicate that T2 is strongly influenced by myelination state and axonal volume, while neurofilament structure within the intra-axonal compartment has a lesser effect upon single compartment T2 estimates. [Copyright &y& Elsevier]

Abstract: A low-field (LF) 1H NMR T2 relaxation and 23Na/1H MRI study was performed on Atlantic salmon to study the effect of ante-mortem handling stress and rigor mortis on muscle water properties and subsequent post-rigor salting. Compared to rested fish, exhausted fish exhibited a more rapid and stronger development of rigor mortis. This resulted in significant differences in post-rigor water-holding capacity and salt uptake. By LF NMR T2 relaxation analysis significant differences in water distribution according to (1) ante-mortem handling, (2) fillet location, and (3) brine salting were detected. Furthermore, 23Na MRI revealed differences between the two treatments in fillet salt distribution, where the salt penetration in exhausted fillets was more pronounced. By combining 1H and 23Na MR images, the salt diffusion and distribution seemed to be highly affected by the distribution of fat. [Copyright &y& Elsevier]

Abstract: Localized tissue transverse relaxation time (T 2) is obtained by fitting a decaying exponential to the signals from several spin-echo experiments at different echo times (TE). Unfortunately, time constraints in magnetic resonance spectroscopy (MRS) often mandate in vivo acquisition schemes at short repetition times (TR), that is, comparable with the longitudinal relaxation constant (T 1). This leads to different T 1-weighting of the signals at each TE. Unaccounted for, this varying weighting causes systematic underestimation of the T 2''s, sometimes by as mush as 30%. In this article, we (i) analyze the phenomenon for common MRS spin-echo T 2 acquisition schemes; (ii) propose a general post hoc T 1-bias correction for any (TR, TE) combination; (iii) show that approximate knowledge of T 1 is sufficient, since a 20% uncertainty in T 1 leads to under 3% bias in T 2; and consequently, (iv) efficient, precision-optimized short TR spin-echo T 2 measurement protocols can be designed and used without risk of accuracy loss. Tables of correction for single-refocusing (conventional) spin-echo and double refocusing, such as, PRESS acquisitions, are provided. [Copyright &y& Elsevier]

Summary: Objective: To assess the normal topographical variation of T2 relaxation time of articular cartilage in different compartments of the knee joint and at different tissue depths in young healthy adults. Methods: Twenty asymptomatic young adult volunteers (age range, 21–27 years; mean age, 22.5 years), were studied at 1.5T. Both axial and sagittal multi-slice multi-echo spin echo measurements were performed to determine the T2 relaxation time of cartilage in the femoral, tibial and patellar compartments. The cartilage surfaces were divided into 24 segments and each segment was divided into deep and superficial regions-of-interest (ROIs) of equal thickness. The reproducibility for ROI analysis was assessed for five patients by determining the interclass correlation coefficient (ICC) and the root-mean-square coefficient of variation (CVRMS). Results: Cartilage T2 was significantly dependent on joint topography, compartment and tissue depth. For all joint surfaces, superficial T2 values were systematically higher as compared to deep tissue. The data showed a trend toward higher T2 values at the load bearing area of the femoral condyles. The interobserver error varied significantly among different locations and showed mostly good reproducibility with mean ICC of 0.70 and a CVRMS of 5.0%. Conclusion: The normal variation in cartilage T2 within a joint is significant and should be acknowledged when pathology-related T2 changes are investigated. The knowledge on normal variation can be used for power and sample size calculations in further studies, and the T2 values as control data in future patient studies. [Copyright &y& Elsevier]

We hypothesized that magnetic resonance magnetization transfer (MT) imaging would be sensitive for detecting cerebral ischemic injury in white matter of neonatal brain. We compared the progression of changes in T2 and the MT ratio (MTR) after cerebral hypoxic–ischemic insults of differing severity in neonatal rats. Magnetization transfer imaging parameters were first optimized, and then MTR and T2 maps were acquired at various times after a mild (rather selective white matter) or substantial insult produced by unilateral cerebral hypoxia–ischemia. Depending on insult severity, time after insult, and region (e.g., subcortical white matter or cortex), cerebral hypoxia–ischemia produced reductions in MTR and an increase in T2. The exception was acutely at 1 to 5 h at which time points MTR was reduced ipsilaterally in white matter, whereas T2 was not affected significantly. Progression of imaging changes differed in rats grouped according to whether gross damage was present after chronic recovery. Behavioral changes were generally associated with chronic reductions in MTR and gross brain damage. Magnetization transfer imaging was capable of early detection of hypoxic–ischemic injury and particularly sensitive for identifying the progression of cerebral injury in white matter. Magnetization transfer ratio has potential for assisting with early diagnosis and treatment assessment for infants affected by perinatal hypoxia–ischemia.Journal of Cerebral Blood Flow & Metabolism (2008) 28, 1613–1623; doi:10.1038/jcbfm.2008.49; published online 28 May 2008 [ABSTRACT FROM AUTHOR]

Abstract: The depth-wise variation of T2 relaxation time is known to reflect the collagen network architecture in cartilage, while the delayed Gadolinium Enhanced MRI of Cartilage (dGEMRIC) technique is sensitive to tissue proteoglycan (PG) concentration. As the cartilage PG content varies along the tissue depth, the depth-dependent accumulation of the contrast agent may affect the inherent T2 of cartilage in a nonconstant manner. Therefore, T2 and dGEMRIC are typically measured in separate MRI sessions. In the present in vitro MRI study at 9.4 T, depth-wise T2 profiles and collagenous zone thicknesses as determined from T2 maps in the absence and presence of Gd-DTPA2− (T2 and T2Gd, respectively) were compared in samples of intact human articular cartilage (n=65). These T2 measures were further correlated with birefringence (BF) of polarized light microscopy (PLM) to quantify the ability of MRI to predict the properties of the collagen fibril network. The reproducibility of the T2 measurement in the current setup was also studied. Typical tri-laminar collagen network architecture was observed both with and without Gd-DTPA2−. The inverse of BF (1/BF) correlated significantly with both T2 and T2Gd (r=0.91, slope=0.56 and r=0.90, slope=0.63), respectively. The statistically significant linear correlations between zone thicknesses as determined from T2 and T2Gd were r=0.55 (slope=0.49), r=0.74 (slope=0.71) and r=0.95 (slope=0.94) for superficial, middle and deep tissue zones, respectively. Reproducibility of the T2 measurement was worst for superficial cartilage. Consistent with PLM, T2 and T2Gd measurements reveal highly similar depth-dependent information on collagen network in intact human cartilage. Thus, dGEMRIC and T2 measurements in one MRI session are feasible for intact articular cartilage in vitro. [Copyright &y& Elsevier]

Aims: Magnetic nanoparticles have been studied widely as MRI contrast agents to increase the sensitivity of this technique. This work describes the synthesis and characterization of magnetic nanotubes (MNTs) as a novel MRI contrast agent. Methods: MNTs with high saturation magnetization were fabricated by the synthesis of superparamagnetic iron oxide nanoparticles (SPIONs) directly in the pores of silica nanotubes (SNTs). The MNTs were characterized by electron microscopy, superconducting quantum interference device and MRI. Preliminary studies on in vitro cytotoxicity and cell labeling were carried out. Results: The MNTs retained the superparamagnetic characteristics in bulk solutions with a considerably high saturation magnetization of 95 emu/gFe. The nuclear magnetic resonance (NMR) relaxivities for MNTs of 500 nm in length and of 60 nm in diameter were r1 = 1.6 ± 0.3 mM-1s-1 and r2 = 264 ± 56 mM-1s-1 and, for the MNTs of 2 µm in length and 70 nm in diameter, the r1 and r2 were 3.0 ± 1.3 and 358 ± 65 mM-1s-1, respectively. In vitro cell labeling showed promising results with excellent labeling efficiency. No cellular toxicity was observed in vitro. Conclusions: The integration of SPIONs with SNTs imparts the superparamagnetic characteristics of SPIONs onto the SNTs, creating unique magnetic nanoparticles with multifunctionality. The MNTs showed promising results as a MRI contrast agent with high NMR relaxivities, little cytotoxicity and high cell-labeling efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Huntington''s disease (HD) is an autosomal dominant inherited neurodegenerative disease. It has been hypothesized that changes of iron content in the brain may be involved in the pathogenesis of HD. To ascertain the hypothesis, we investigated the relationship between T2 relaxation time (T2), the number of cytosine–adenine–guanine triplet repeats (CAG) and clinical status in patients suffering from HD. 34 HD patients (mean age 50.1±11.8 standard deviation (SD) years) and 34 control subjects (49.6±13.3) were scanned using a 1.5 tesla magnetic resonance (MR) scanner and the patients underwent clinical and genetic testing. A multiple echo sequence was employed for T2 measurements. T2 from healthy volunteers matched previous studies. A T2 shortening was found in the pallidum of HD patients compared to controls (65.4±6.4 ms vs. 71.8±3.6 ms, P <0.00001). A correlation between the number of CAG and T2 was found for the left pallidum (decrease in T2, P <0.05) and an inverse correlation for the left caudate (increase in T2, P <0.05). In HD patients, alterations in iron levels may be caused by an alteration in its axonal transport. The observed T2/CAG covariations may reflect changes in levels and forms of iron: this suggests that HD patients with a higher genetic load have more ferritin-bound (“safe form”) iron in the pallidum and/or more low-molecular (“toxic”) iron in the caudate. An increase in “toxic” iron in the caudate may enable oxidative stress and thus underlie progression of the disease. [Copyright &y& Elsevier]

Multi-echo T2 measurements are invaluable in studying brain pathology in multiple sclerosis (MS). In addition to information about myelin water and total water content, the T2 distribution has the potential to detect additional water reservoirs arising from other sources such as inflammation or edema. The purpose of this study was to better define the T2 distribution in MS lesions and normal appearing white matter (NAWM) with particular emphasis on the characterisation of longer T2 components.Magnetisation transfer (MT), T1 and 48-echo T2 relaxation data were acquired in 20 MS subjects and regions of interest were drawn in lesions and NAWM. Twenty-seven out of 107 lesions exhibited signal with a markedly prolonged T2 (200–800 ms). Lesions with a Long-T2 signal also exhibited a longer geometric mean T2 (GMT2), increased water content (WC), higher T1, reduced magnetisation transfer ratio (MTR) and decreased myelin water fraction (MWF) than lesions without a Long-T2 signal. Those subjects with Long-T2 lesions had a significantly longer disease duration than subjects without this lesion subtype. A strong correlation was observed between T1 and Long-T2 fraction, while a slightly weaker relationship was found for GMT2, MTR and MWF with Long-T2 fraction. A potential source of the Long-T2 signal is an increase in extracellular water. This study supports the usefulness of increasing the data acquisition window of the multi-echo T2 relaxation sequence to better characterise the T2 decay in MS. [ABSTRACT FROM AUTHOR]

The changes in water distribution in maturing lupin (Lupinus luteus L.) seeds were visualized with magnetic resonance imaging (MRI). MRI data showed local inhomogeneities of water distribution inside the seed. At the late seed-filling stage the most intense signal was detected in the seed coat and the outer parts of cotyledons in the hilum area, but during maturation drying the decline in MR image intensity was faster in the outer part of the seed than in the central part. The changes in water status were characterized by NMR spectroscopy. Analyses of T2 relaxation times revealed a three-component water proton system in maturing lupin seeds. Three populations of protons found during seed maturation, each with a different magnetic environment causing a different relaxation rate, were correlated with three fractions of water (structural, intracellular, and extracellular) that were observed during seed germination. This study provides evidence that lupin seeds have similar states of the different water components with regard to seed moisture content at two distinct physiological stages, seed maturation and germination. The unique feature of maturing lupin seeds is the presence of the high 1H-NMR signal in areas corresponding to the vascular bundles. Tissue localization of dehydrins showed the presence of dehydrin protein in the area of vascular tissue. An anti-dehydrin antibody detected three polypeptides in lupin embryos with molecular masses of 73, 43 and 28 kDa, respectively. The temporal pattern of dehydrin protein accumulation correlates well with seed desiccation. [ABSTRACT FROM PUBLISHER]

Consumers’ awareness of food quality has never been more pronounced. Meat forms a substantial part of the food consumption, and accordingly techniques to control the quality of meat are needed. In addition, a better understanding of how basic biochemical and biophysical factors influence the final meat quality is also required for optimization of the quality. Water-holding capacity (WHC) is a major quality attribute of fresh meat. However, the exact mechanisms determining the WHC of meat are not fully understood. Especially, characteristics about proposed water populations in the meat and how they are interrelated with drip loss need to be studied further. Moreover, the distribution and mobility of water in muscle during its conversion to meat and how they are affected by intrinsic and extrinsic factors are poorly elucidated. Nuclear magnetic resonance (NMR) has during recent years gained increasing use within different areas of muscle physiology and meat science. NMR 1H relaxation methodologies enable detection of the mobility of protons in heterogeneous materials and thereby provide possibilities for a characterization of the properties of water. The objective of this presentation is to give an overview of the use of NMR relaxation measurements to characterize the proposed water populations in meat and investigate how the distribution and mobility of the water changes postmortem. In addition, applications of NMR spectroscopy in metabolic studies will be considered. [ABSTRACT FROM AUTHOR]

This study introduces the use of nuclear magnetic resonance (NMR) relaxometry in the elucidation of the curing-induced water mobility and distribution within pork. Fresh meat samples of three different meat qualities [normal; pale, soft and exudative (PSE); dark, firm and dry (DFD)] were cured by using different curing conditions (0.9–9% NaCl and 6% NaCl + 10 mm Na4P2O7). Distributed NMR T2 relaxation data revealed the presence of three distinct water populations ( T2 b, T21, T22), with the T21 population being most influenced by the curing conditions, which was reflected by strong correlations between the salt-induced swelling and the mean relaxation time of the T21 population. Consequently, the T21 population reflects the myofibrillar swelling, and is an excellent indicator of myofibrillar geometry upon curing. Both the NMR data and the salt-induced swelling capacity were highly dependent on fresh meat quality. Independent of brine composition, the DFD meat had a significantly higher swelling capacity than the two other meat qualities. A higher response to NaCl concentration on the swelling capacity was observed for PSE and normal meat than for DFD meat, which suggests interactions between the pH of the meat and NaCl-induced swelling. [ABSTRACT FROM AUTHOR]

Water content and hydraulic conductivity, including transport within cells, over membranes, cell-to-cell, and long-distance xylem and phloem transport, are strongly affected by plant water stress. By being able to measure these transport processes non-invasely in the intact plant situation in relation to the plant (cell) water balance, it will be possible explicitly or implicitly to examine many aspects of plant function, plant performance, and stress responses. Nuclear magnetic resonance imaging (MRI) techniques are now available that allow studying plant hydraulics on different length scales within intact plants. The information within MRI images can be manipulated in such a way that cell compartment size, water membrane permeability, water cell-to-cell transport, and xylem and phloem flow hydraulics are obtained in addition to anatomical information. These techniques are non-destructive and non-invasive and can be used to study the dynamics of plant water relations and water transport, for example, as a function of environmental (stress) conditions. An overview of NMR and MRI methods to measure such information is presented and hardware solutions for minimal invasive intact plant MRI are discussed. [ABSTRACT FROM PUBLISHER]

Abstract: The effects of fresh meat quality (PSE versus DFD), freezing temperature (−20°C versus −80C°) and duration of freezer storage on changes in water mobility and distribution were followed at intervals of 1–2 months during 10-month freezer storage of pork using low-field NMR T2 relaxometry. Fresh meat quality was found to have a strong significant effect (P <0.0001) on the amount of loosely bound water (relaxation time >100ms) also after freezing, which was reflected in a significantly lower cooking yield in PSE meat compared with DFD meat (P <0.0001). While no significant changes in the cooking yield were observed with increasing length of freezer storage, NMR T2 relaxation measurements revealed a significant increase in the amount of loosely bound water in PSE meat with increasing length of freezer storage. This finding indicates that NMR T2 relaxation measurements are quite sensitive to freezing-induced changes in the meat structure, causing a shift in the distribution of water and possibly capable of detecting these before they are reflected in a reduced cooking yield. In addition, an interaction between fresh meat quality and effect of length of freezer storage on the amount of very mobile water easily lost as drip was observed, implying that PSE meat is more susceptible to freezer storage-induced deteriorative changes in the meat structure, causing a shift in the distribution of water, than DFD meat. [Copyright &y& Elsevier]

Various magnetic resonance (MR) techniques are used to study the pathological evolution of demyelinating diseases, such as multiple sclerosis (MS). However, few studies have validated MR derived measurements with histopathology. Here, we determine the correlation of myelin water imaging, an MR measure of myelin content, with quantitative histopathologic measures of myelin density. The multi-component T2 distribution of water was determined from 25 formalin-fixed MS brain samples using a multi-echo T2 relaxation MR experiment. The myelin water fraction (MWF), defined as T2 signal below 30 milliseconds divided by the total signal, was determined for various regions of interest and compared to Luxol fast blue (myelin stain) mean optical density (OD) for each sample. MWF had a strong correlation with myelin stain [mean (range) R2 = 0.67 (0.45–0.92)], validating MWF as a measure of myelin density. This quantitative technique has many practical applications for the in vivo monitoring of demyelination and remyelination in a variety of disorders of myelin. [ABSTRACT FROM AUTHOR]

We describe a family of calcium indicators for magnetic resonance imaging (MRI), formed by combining a powerful iron oxide nanoparticle-based contrast mechanism with the versatile calcium-sensing protein calmodulin and its targets. Calcium-dependent protein-protein interactions drive particle clustering and produce up to 5-fold changes in T2 relaxivity, an indication of the sensors' potency. A variant based on conjugates of wild-type calmodulin and the peptide M13 reports concentration changes near 1 μM Ca2+, suitable for detection of elevated intracellular calcium levels. The midpoint and cooperativity of the response can be tuned by mutating the protein domains that actuate the sensor. Robust MRI signal changes are achieved even at nanomolar particle concentrations (<1 μM in calmodulin) that are unlikely to buffer calcium levels. When combined with technologies for cellular delivery of nanoparticulate agents, these sensors and their derivatives may be useful for functional molecular imaging of biological signaling networks in live, opaque specimens. [ABSTRACT FROM AUTHOR]

T2 relaxation can augment delayed-enhancement viability imaging because it is sensitive to tissue edema and microcirculatory oxygen state. We demonstrate the T2 'signatures' of sub-lethal ischemia and stunning in porcine myocardium perfused by the distal left anterior descending artery, by imaging during percutaneous balloon occlusion for 25 minutes and subsequent reperfusion (n = 9). Muscle displayed ischemic dysfunction and partial post-ischemic functional recovery (p ≤ 0.0004), concommitant with an elevated post-ischemic T2 (Δ T2 = 27 ± 18%, p = 0.005). TTC staining verified muscle viability. The T2 fluctuations may reflect hyperemia and tissue cellular edema in accord with the known pathophysiology of ischemic and post-ischemic yet viable muscle. [ABSTRACT FROM AUTHOR]

Abstract: The study of rotational and translational diffusion requires the measurement of both T2 and apparent diffusion coefficient (ADC), quantities that are typically measured in separate experiments. The exploitation of echoes generated via multiple coherence transfer pathways offers an opportunity for measuring T2 and ADC values simultaneously in a single experiment. A series of RF pulses can generate multiple echoes via different coherence pathways with each one being uniquely encoded. Here, we demonstrate one pulse sequence that uses an initial θ RF pulse to generate three coherence orders (C=0, −1, +1). In the particular version of the method discussed here only two are used (C=0, +1). Each order is encoded with a different b value from which the ADC is derived. The coherence order echo C=0 is refocused to quantify T2. The performance of the method—dubbed simultaneous measurement of ADC and relaxation time (SMART)—is demonstrated on a set of samples differing in T2 and ADC achieved by varying the relative volume fractions in mixtures of gadolinium-doped H2O and D2O. The regional SMART derived T2 and ADC agree well with those obtained with conventional double-spin–echo and pulsed gradient spin–echo methods. [Copyright &y& Elsevier]