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MRI Methods (mri + methods)
Selected AbstractsVariable-field relaxometry of iron-containing human tissues: a preliminary studyCONTRAST MEDIA & MOLECULAR IMAGING, Issue 4 2009Aline Hocq Abstract Excess iron is found in brain nuclei from neurodegenerative patients (with Parkinson's, Alzheimer's and Huntington's diseases) and also in the liver and spleen of cirrhosis, hemochromatosis and thalassaemia patients. Ferritin, the iron-storing protein of mammals, is known to darken T2 -weighted MR images. Understanding NMR tissue behavior may make it possible to detect those diseases, to follow their evolution and finally to establish a protocol for non-invasive measurement of an organ's iron content using MRI methods. In this preliminary work, the MR relaxation properties of embalmed iron-containing tissues were studied as well as their potential correlation with the iron content of these tissues. Relaxometric measurements (T1 and T2) of embalmed samples of brain nuclei (caudate nucleus, dentate nucleus, globus pallidus, putamen, red nucleus and substantia nigra), liver and spleen from six donors were made at different magnetic fields (0.00023,14 T). The influence of the inter-echo time on transverse relaxation was also studied. Moreover, iron content of tissues was determined by inductively coupled plasma atomic emission spectroscopy. In brain nuclei, 1/T2 increases quadratically with the field and depends on the inter-echo time in CPMG sequences at high fields, both features compatible with an outer sphere relaxation theory. In liver and spleen, 1/T2 increases linearly with the field and depends on the inter-echo time at all fields. In our study, a correlation between 1/T2 and iron concentration is observed. Explaining the relaxation mechanism for these tissues is likely to require a combination of several models. The value of 1/T2 at high field could be used to evaluate iron accumulation in vivo. In the future, confirmation of those features is expected to be achieved from measurements of fresh (not embalmed) human tissues. Copyright © 2009 John Wiley & Sons, Ltd. [source] Increased gyrification in Williams syndrome: evidence using 3D MRI methodsDEVELOPMENTAL MEDICINE & CHILD NEUROLOGY, Issue 5 2002J Eric Schmitt BABS Understanding patterns of gyrification in neurogenetic disorders helps to uncover the neurodevelopmental etiology underlying behavioral phenotypes. This is particularly true in Williams syndrome (WS), a condition caused by de novo deletion of approximately 1 to 2Mb in the 7q11.23 region. Individuals with WS characteristically possess an unusual dissociation between deficits in visual-spatial ability and relative preservations in language, music, and social drive. A preliminary postmortem study reported anomalous gyri and sulci in individuals with WS. The present study examined gyrification patterns in 17 participants with WS (10 females, 7 males; mean age 28 years 11 months, SD 8 years 6 months) and 17 age- and sex-matched typically developing control participants (mean age 29 years 1 month, SD 8 years 1 month) using new automated techniques in MRI. Significantly increased cortical gyrification was found globally with abnormalities being more marked in the right parietal (p=0.0227), right occipital (p=0.0249), and left frontal (p=0.0086) regions. These results suggest that one or more genes in the 7q11.23 region are involved during the critical period when cortical folding occurs, and may be related to the hypothesized dorsal/ventral dissociation in this condition. [source] Resting state sensorimotor functional connectivity in multiple sclerosis inversely correlates with transcallosal motor pathway transverse diffusivityHUMAN BRAIN MAPPING, Issue 7 2008Mark J. Lowe Abstract Recent studies indicate that functional connectivity using low-frequency BOLD fluctuations (LFBFs) is reduced between the bilateral primary sensorimotor regions in multiple sclerosis. In addition, it has been shown that pathway-dependent measures of the transverse diffusivity of water in white matter correlate with related clinical measures of functional deficit in multiple sclerosis. Taken together, these methods suggest that MRI methods can be used to probe both functional connectivity and anatomic connectivity in subjects with known white matter impairment. We report the results of a study comparing anatomic connectivity of the transcallosal motor pathway, as measured with diffusion tensor imaging (DTI) and functional connectivity of the bilateral primary sensorimotor cortices (SMC), as measured with LFBFs in the resting state. High angular resolution diffusion imaging was combined with functional MRI to define the transcallosal white matter pathway connecting the bilateral primary SMC. Maps were generated from the probabilistic tracking employed and these maps were used to calculate the mean pathway diffusion measures fractional anisotropy ,FA,, mean diffusivity ,MD,, longitudinal diffusivity ,,1,, and transverse diffusivity ,,2,. These were compared with LFBF-based functional connectivity measures (Fc) obtained at rest in a cohort of 11 multiple sclerosis patients and ,10 age- and gender-matched control subjects. The correlation between ,FA, and Fc for MS patients was r = ,0.63, P < 0.04. The correlation between all subjects ,,2, and Fc was r = 0.42, P < 0.05. The correlation between all subjects ,,2, and Fc was r = ,0.50, P < 0.02. None of the control subject correlations were significant, nor were ,FA,, ,,1,, or ,MD, significantly correlated with Fc for MS patients. This constitutes the first in vivo observation of a correlation between measures of anatomic connectivity and functional connectivity using spontaneous LFBFs. Hum Brain Mapp, 2008. © 2008 Wiley-Liss, Inc. [source] Magnetic resonance imaging near metal implantsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2010K.M. Koch PhD Abstract The desire to apply magnetic resonance imaging (MRI) techniques in the vicinity of embedded metallic hardware is increasing. The soft-tissue contrast available with MR techniques is advantageous in diagnosing complications near an increasing variety of MR-safe metallic hardware. Near such hardware, the spatial encoding mechanisms utilized in conventional MRI methods are often severely compromised. Mitigating these encoding difficulties has been the focus of numerous research investigations over the past two decades. Such approaches include view-angle tilting, short echo-time projection reconstruction acquisitions, single-point imaging, prepolarized MRI, and postprocessing image correction. Various technical advances have also enabled the recent development of two alternative approaches that have shown promising clinical potential. Here, the physical principals and proposed solutions to the problem of MRI near embedded metal are discussed. J. Magn. Reson. Imaging 2010;32:773,787. © 2010 Wiley-Liss, Inc. [source] The Alzheimer's disease neuroimaging initiative (ADNI): MRI methodsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2008Clifford R. Jack Jr. MD Abstract The Alzheimer's Disease Neuroimaging Initiative (ADNI) is a longitudinal multisite observational study of healthy elders, mild cognitive impairment (MCI), and Alzheimer's disease. Magnetic resonance imaging (MRI), (18F)-fluorodeoxyglucose positron emission tomography (FDG PET), urine serum, and cerebrospinal fluid (CSF) biomarkers, as well as clinical/psychometric assessments are acquiredat multiple time points. All data will be cross-linked and made available to the general scientific community. The purpose of this report is to describe the MRI methods employed in ADNI. The ADNI MRI core established specifications thatguided protocol development. A major effort was devoted toevaluating 3D T1 -weighted sequences for morphometric analyses. Several options for this sequence were optimized for the relevant manufacturer platforms and then compared in a reduced-scale clinical trial. The protocol selected for the ADNI study includes: back-to-back 3D magnetization prepared rapid gradient echo (MP-RAGE) scans; B1 -calibration scans when applicable; and an axial proton density-T2 dual contrast (i.e., echo) fast spin echo/turbo spin echo (FSE/TSE) for pathology detection. ADNI MRI methods seek to maximize scientific utility while minimizing the burden placed on participants. The approach taken in ADNI to standardization across sites and platforms of the MRI protocol, postacquisition corrections, and phantom-based monitoring of all scanners could be used as a model for other multisite trials. J. Magn. Reson. Imaging 2008. © 2008 Wiley-Liss, Inc. [source] Simulation of phase contrast MRI of turbulent flowMAGNETIC RESONANCE IN MEDICINE, Issue 4 2010Sven Petersson Abstract Phase contrast MRI is a powerful tool for the assessment of blood flow. However, especially in the highly complex and turbulent flow that accompanies many cardiovascular diseases, phase contrast MRI may suffer from artifacts. Simulation of phase contrast MRI of turbulent flow could increase our understanding of phase contrast MRI artifacts in turbulent flows and facilitate the development of phase contrast MRI methods for the assessment of turbulent blood flow. We present a method for the simulation of phase contrast MRI measurements of turbulent flow. The method uses an Eulerian-Lagrangian approach, in which spin particle trajectories are computed from time-resolved large eddy simulations. The Bloch equations are solved for each spin for a frame of reference moving along the spins trajectory. The method was validated by comparison with phase contrast MRI measurements of velocity and intravoxel velocity standard deviation (IVSD) on a flow phantom consisting of a straight rigid pipe with a stenosis. Turbulence related artifacts, such as signal drop and ghosting, could be recognized in the measurements as well as in the simulations. The velocity and the IVSD obtained from the magnitude of the phase contrast MRI simulations agreed well with the measurements. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source] Early detection of radiation therapy response in non-Hodgkin's lymphoma xenografts by in vivo1H magnetic resonance spectroscopy and imagingNMR IN BIOMEDICINE, Issue 6 2010Seung-Cheol Lee Abstract The purpose of the study was to investigate the capability of 1H MRS and MRI methods for detecting early response to radiation therapy in non-Hodgkin's lymphoma (NHL). Studies were performed on the WSU-DLCL2 xenograft model in nude mice of human diffuse large B-cell lymphoma, the most common form of NHL. Radiation treatment was applied as a single 15,Gy dose to the tumor. Tumor lactate, lipids, total choline, T2 and apparent diffusion coefficients (ADC) were measured before treatment and at 24,h and 72,h after radiation. A Hadamard-encoded slice-selective multiple quantum coherence spectroscopy sequence was used for detecting lactate (Lac) while a stimulated echo acquisition mode sequence was used for detection of total choline (tCho) and lipids. T2 - and diffusion-weighted imaging sequences were used for measuring T2 and ADC. Within 24,h after radiation, significant changes were observed in the normalized integrated resonance intensities of Lac and the methylenes of lipids. Lac/H2O decreased by 38,±,15% (p,=,0.03), and lipid (1.3,ppm, CH2)/H2O increased by 57,±,14% (p,=,0.01). At 72,h after radiation, tCho/H2O decreased by 45,±,14% (p,=,0.01), and lipid (2.8,ppm, polyunsaturated fatty acid)/H2O increased by 970,±,36% (p,=,0.001). ADC increased by 14,±,2% (p,=,0.003), and T2 did not change significantly. Tumor growth delay and regression were observed thereafter. This study enabled comparison of the relative sensitivities of various 1H MRS and MRI indices to radiation and suggests that 1H MRS/MRI measurements detect early responses to radiation that precede tumor volume changes. Copyright © 2010 John Wiley & Sons, Ltd. [source] Assessment of blood volume, vessel size, and the expression of angiogenic factors in two rat glioma models: a longitudinal in vivo and ex vivo studyNMR IN BIOMEDICINE, Issue 10 2008Samuel Valable Abstract Assessment of angiogenesis may help to determine tumor grade and therapy follow-up. In vivo imaging methods for non-invasively monitoring microvasculature evolution are therefore of major interest for tumor management. MRI evaluation of blood volume fraction (BVf) and vessel size index (VSI) was applied to assess the evolution of tumor microvasculature in two rat models of glioma (C6 and RG2). The results show that repeated MRI of BVf and VSI , which involves repeated injection of an iron-based MR contrast agent , does not affect either the physiological status of the animals or the accuracy of the MR estimates of the microvascular parameters. The MR measurements were found to correlate well with those obtained from histology. They indicate that microvascular evolution differs significantly between the two glioma models, in good agreement with expression of angiogenic factors (vascular endothelial growth factor, angiopoietin-2) and with activities of matrix metalloproteinases, also assessed in this study. These MRI methods thus provide considerable potential for assessing the response of gliomas to anti-angiogenic and anti-vascular agents, in preclinical studies as well as in the clinic. Furthermore, as differences between the fate of tumor microvasculature may underlie differences in therapeutic response, there is a need for preclinical study of several tumor models. Copyright © 2008 John Wiley & Sons, Ltd. [source] In-vivo visualization of phagocytotic cells in rat brains after transient ischemia by USPIONMR IN BIOMEDICINE, Issue 4 2002M. Rausch Abstract Cerebral ischemia provokes tissue damage by two major patho-physiological mechanisms. Direct cell necrosis is induced by diminished access of neurons and glia to essential nutrients such as glucose and oxygen leading to energy failure. A second factor of cellular loss is related to the activation of immune-competent cells within and around the primary infarct. While granulocytes and presumably monocytes are linked to the no-reflow phenomenon, activated microglia cells and monocytes can release cytotoxic substrates, which cause delayed cell death. As a consequence the infarct volume will increase, despite restoration of cerebral perfusion. In the past, visualization of immune competent cells was only possible by histological analysis of post-mortem tissue. However, contrast agents based on small particles of iron oxide are known to accumulate in organs rich in cells with phagocytotic function. These particles can be tracked in vivo by MRI methods based on their relaxation properties. In the present study, the spatio-temporal distribution of USPIO particles was monitored in a rat model of transient cerebral infarction using T1 - and T2 -weighted MRI sequences. USPIO were detected in vessels at 24,h after administration. At later time points specific accumulation of USPIO was observed within the infarcted hemisphere, with maximal signal enhancement on day 2. Their detectability based on T1 -contrast disappeared between day 4 and day 7. Immuno-histochemically (IHC) stains confirmed the presence of macrophages, presumably blood-derived monocytes within areas of T1 signal enhancement. Direct visualization of iron-burdened macrophages by IHC was only possible later than day 3 after occlusion. Copyright © 2002 John Wiley & Sons, Ltd. [source] Arterial spin-labeled perfusion combined with segmentation techniques to evaluate cerebral blood flow in white and gray matter of children with sickle cell anemia,PEDIATRIC BLOOD & CANCER, Issue 1 2009Kathleen J. Helton MD Abstract Background Changes in cerebral perfusion are an important feature of the pathophysiology of sickle cell anemia (SCA); cerebrovascular ischemia occurs frequently and leads to neurocognitive deficits, silent infarcts, and overt stroke. Non-invasive MRI methods to measure cerebral blood flow (CBF) by arterial spin labeling (ASL) afford new opportunities to characterize disease- and therapy-induced changes in cerebral hemodynamics in patients with SCA. Recent studies have documented elevated gray matter (GM) CBF in untreated children with SCA, but no measurements of white matter (WM) CBF have been reported. Procedures Pulsed ASL with automated brain image segmentation-classification techniques were used to determine the CBF in GM, WM, and abnormal white matter (ABWM) of 21 children with SCA, 18 of whom were receiving hydroxyurea therapy. Results GM and WM CBF were highly associated (R2,=,0.76, P,<,0.0001) and the GM to WM CBF ratio was 1.6 (95% confidence interval: 1.43,1.83). Global GM CBF in our treated cohort was 87,±,24 mL/min/100 g, a value lower than previously reported in untreated patients with SCA. CBF was elevated in normal appearing WM (43,±,14 mL/min/100 g) but decreased in ABWM (6,±,12 mL/min/100 g), compared to published normal pediatric controls. Hemispheric asymmetry in CBF was noted in most patients. Conclusions These perfusion measurements suggest that hydroxyurea may normalize GM CBF in children with SCA, but altered perfusion in WM may persist. This novel combined approach for CBF quantification will facilitate prospective studies of cerebral vasculopathy in SCA, particularly regarding the effects of treatments such as hydroxyurea. Pediatr Blood Cancer 2009;52:85,91. © 2008 Wiley-Liss, Inc. [source] Grey matter pathology in multiple sclerosisACTA NEUROLOGICA SCANDINAVICA, Issue 2006L. Bö Although multiple sclerosis (MS) has been considered a white matter disease, MS lesions are known to occur in grey matter. Recent immunohistochemical studies have demonstrated extensive grey matter demyelination in chronic MS. The most common lesion type consists of purely cortical lesions extending inward from the surface of the brain, this lesion subgroup is grossly underestimated by standard histochemical myelin staining methods. Some MS patients have subpial demyelination in all cortical areas of the brain; this pattern has been termed ,,general cortical subpial demyelination''. Extensive cortical demyelination is associated with the progressive phases of disease, as less cortical demyelination has been detected in relapsing-remitting MS. The pathology of grey matter lesions differs from that of white matter lesions; grey matter lesions are less inflammatory, with less macrophage and lymphocyte infiltration. In purely cortical lesions there is no significant increase in lymphocytes compared with non-demyelinated adjacent cortical areas in MS patients or cerebral cortex in control patients. Significant axonal transection and neuronal loss have been demonstrated in grey matter MS lesions. Current magnetic resonance imaging (MRI) methods are not sensitive for purely cortical MS lesions. The clinical significance of cortical MS lesions may not be characterised until more sensitive MRI methods are developed. [source] | ||||||||||||||||||||||