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Proton Density (proton + density)
Selected AbstractsWhite matter lesions in euthymic patients with bipolar disorderACTA PSYCHIATRICA SCANDINAVICA, Issue 6 2009A. J. Lloyd Objective:, We aimed to quantify both load and regional distributions of hyperintensities on magnetic resonance imaging (MRI) in prospectively verified euthymic bipolar patients and matched controls. Method:, Cerebral hyperintensities on T2, proton density and fluid-attenuated inversion recovery (FLAIR) MRI were compared between 48 bipolar and 47 control subjects using semi-quantitative rating scales. Results:, Bipolar subjects had more severe frontal deep white matter lesions (DWML). Hyperintensity load was independent of age in bipolar patients but increased with age in controls. Global prevalence and severity of hyperintensities did not differ between groups. Exploratory analysis showed DWML in excess in the left hemisphere in bipolar subjects but not in controls. Conclusion:, Findings are consistent with clinical, particularly some neurocognitive, features of bipolar disorder and implicate fronto-subcortical circuits in its neurobiology. They more probably reflect a trait abnormality or illness scar rather than a mood state-dependent finding. Processes other than ageing and vascular factors may underlie their development. [source] MR imaging of the brain in patients with hepatic form of Wilson's diseaseEUROPEAN JOURNAL OF NEUROLOGY, Issue 5 2003D. Kozi The aim of this study was to detect the sites and frequency of possible lesions by brain magnetic resonance imaging (MRI; 1,5T) in a group of 16 neurologically asymptomatic patients with hepatic form of Wilson's disease (WD; seven untreated and nine under treatment). Abnormal MR findings of the brain were found in 75% of patients. Lesions in brain parenchyma were detected in all untreated, drug-naive patients and in 44% of treated patients. Abnormal signal in globus pallidus, putamen, and caudate nucleus was revealed in 86, 71 and 71% of treated and in 33, 33 and 22% of untreated patients, respectively. In five of eight patients with putaminal pathology (62.5%) and in four of seven patients with caudate nuclei involvement (57%), only proton density 2-weighted sequence (PDW) exhibited sensitivity for lesion detection, with both T1W and long echo T2W sequences being insensitive. This superiority of PDW sequence was even more pronounced in the group of untreated patients in whom 80% of putaminal pathology was visible exclusively on this sequence. The lower frequency of lesions in the group of treated in comparison with untreated patients indicated that they might be reversible in the course of chronic chelating therapy. [source] The human hippocampus at 7 T,In vivo MRIHIPPOCAMPUS, Issue 1 2009Jens M. Theysohn Abstract The human hippocampus plays a central role in various neuropsychiatric disorders, such as temporal lobe epilepsy (TLE), Alzheimer's dementia, mild cognitive impairment, and schizophrenia. Its volume, morphology, inner structure, and function are of scientific and clinical interest. Magnetic resonance (MR) imaging is a widely employed tool in neuroradiological workup regarding changes in brain anatomy, (sub-) volumes, and cerebral function including the hippocampus. Gain in intrinsic MR signal provided by higher field strength scanners and concomitant improvements in spatial resolution seem highly valuable. An examination protocol permitting complete, high-resolution imaging of the human hippocampus at 7 T was implemented. Coronal proton density, T2, T2*, and fluid-attenuated inversion recovery contrasts were acquired as well as an isotropic 3D magnetization-prepared rapid acquisition gradient-echo (500 ,m isotropic voxel dimension, noninterpolated). Observance of energy deposition restrictions within acceptable scan times remained challenging in the acquisition of thin, spin-echo-based sections. At the higher resolution enabled by 7 T, demarcation of the hippocampus and some internal features including gray/white matter differentiation and depiction of the hippocampal mantle becomes much more viable when compared with 1.5 T; thus, in the future, this imaging technology might help in the diagnosis of subtle hippocampal changes. © 2008 Wiley-Liss, Inc. [source] Cognitive correlates of brain MRI subcortical signal hyperintensities in non-demented elderlyINTERNATIONAL JOURNAL OF GERIATRIC PSYCHIATRY, Issue 1 2006Gad A. Marshall Abstract Objective To investigate the relationship between magnetic resonance imaging (MRI) subcortical gray and capsular (SGCH) and white matter hyperintensities (WMH) and cognitive functions in non-demented community dwelling elderly. Methods The severity of SGCH and WMH on proton density and T2 MR images in 16 subjects was scored using the semi-quantitative rating scale of Scheltens et al. (1993). A limited series of cognitive tests selected a priori were then correlated with severity of SGCH and WMH. Results Analysis demonstrated that severity of SGCH was inversely related to performance on the Digit Span (R,=,,0.64, p,<,0.01) and the Stroop Color Word Tests (R,=,,0.64, p,<,0.01). Severity of WMH was related to worsening performance on the Trail Making Test (R,=,0.67, p,<,0.005). Conclusions These findings indicate that severity of WMH is negatively related to more pure executive cognitive functions, specifically set shifting, while severity of SGCH is inversely related to more basic functions of attention and working memory. Copyright © 2005 John Wiley & Sons, Ltd. [source] Conspicuity of zones of ablation after radiofrequency ablation in porcine livers: Comparison of an extracellular and an SPIO contrast agentJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 1 2008Christopher Bangard MD Abstract Purpose To compare conspicuity of zones of ablation on nonenhanced, gadopentetate dimeglumine-(Gd-DTPA) and ferucarbotran-(SPIO)-enhanced magnetic resonance (MR) images. Materials and Methods In all, 33 radiofrequency ablations (RFA) were performed in 17 healthy porcine livers at 1.5T MR imaging 1 day and 2 and 4 weeks after RFA: T2-weighted (w) ultra turbo spin echo (UTSE), proton density (PD)-w UTSE, T1-w gradient echo (GRE) pre- and 5 minutes postcontrast administration, dynamic T1-w GRE during Gd-DTPA (Magnevist) or SPIO (Resovist) administration, T2-w UTSE, and PD-w UTSE sequences 10 minutes after SPIO administration. Regions of interest (ROIs) for contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) were drawn in consensus by two radiologists. Results PD-w SPIO-enhanced images (23.5 ± 5.5) showed higher liver-to-lesion CNR than T1-w GRE Gd-DTPA-enhanced images (13.5 ± 6.1) 1 day after RFA (P , 0.05). At all other timepoints, liver-to-lesion CNR of PD-w and T2-w SPIO-enhanced images did not differ significantly from T1-w GRE Gd-DTPA-enhanced images (P , 0.05). Nonenhanced T2-w images revealed lower liver-to-lesion CNR (7.0 ± 7.5/6.5 ± 5.9/6.8 ± 5.0, 1 day/2 weeks/4 weeks, respectively) than T2-w SPIO-enhanced (17.4 ± 4.8/15.3 ± 4.5/14.2 ± 5.7), PD-w SPIO-enhanced (23.5 ± 5.5/16.9 ± 3.6, 1 day/2 weeks), and T1-w Gd-DTPA-enhanced (15.3 ± 3.6/12.7 ± 3.5, 2/4 weeks) images (P , 0.05). Liver-to-lesion CNR of SPIO-enhanced dynamic T1-w GRE images after 30, 80, 150, and 240 seconds did not change significantly over time (P , 0.05). Conclusion One day after RFA lesion conspicuity on PD-w ferucarbotran-enhanced images is better than on T1-w GRE Gd-DTPA-enhanced images. At all other timepoints, ferucarbotran is not superior to gadolinium. Ferucarbotran- and gadolinium-enhanced images improve lesion conspicuity compared with nonenhanced T2-w images at all timepoints. J. Magn. Reson. Imaging 2008;28:263,270. © 2008 Wiley-Liss, Inc. [source] Multicontrast black-blood MRI of carotid arteries: Comparison between 1.5 and 3 tesla magnetic field strengthsJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 5 2006Vasily L. Yarnykh PhD Abstract Purpose To compare black-blood multicontrast carotid imaging at 3T and 1.5T and assess compatibility between morphological measurements of carotid arteries at 1.5T and 3T. Materials and Methods Five healthy subjects and two atherosclerosis patients were scanned in 1.5T and 3T scanners with a similar protocol providing transverse T1 -, T2 -, and proton density (PD)-weighted black-blood images using a fast spin-echo sequence with single- (T1 -weighted) or multislice (PD-/T2 -weighted) double inversion recovery (DIR) preparation. Wall and lumen signal-to-noise ratio (SNR) and wall/lumen contrast-to-noise ratio (CNR) were compared in 44 artery cross-sections by paired t -test. Interscanner variability of the lumen area (LA), wall area (WA), and mean wall thickness (MWT) was assessed using Bland-Altman analysis. Results Wall SNR and lumen/wall CNR significantly increased (P < 0.0001) at 3T with a 1.5-fold gain for T1 -weighted images and a 1.7/1.8-fold gain for PD-/T2 -weighted images. Lumen SNR did not differ for single-slice DIR T1 -weighted images (P = 0.2), but was larger at 3T for multislice DIR PD-/T2 -weighted images (P = 0.01/0.03). The LA, WA, and MWT demonstrated good agreement with no significant bias (P 0.5), a coefficient of variation (CV) of <10%, and intraclass correlation coefficient (ICC) of >0.95. Conclusion This study demonstrated significant improvement in SNR, CNR, and image quality for high- resolution black-blood imaging of carotid arteries at 3T. Morphologic measurements are compatible between 1.5T and 3T. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Investigation of proton density for measuring tissue temperature,JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2006Jing Chen MS Abstract Purpose To examine the temperature dependence of the proton density (PD) in both adipose and muscle tissues, and the application of the PD as a thermometry parameter in breast tissues. Materials and Methods Porcine fat samples and bovine muscle samples were successively heated to temperatures ranging from 30°C to 76°C and then cooled. They were then imaged with a dual-echo spin-echo sequence. T1 and T2 effects were carefully corrected from the images. The apparent PD (APD) in regions of interest (ROIs) and the sum of the APD in all pixels (Sum_APD) were measured and analyzed by linear regression. Results APD in adipose tissue is linear and reversible, and changes with a 0.3%/°C to 0.45%/°C temperature variation. The temperature coefficient of Sum_APD in adipose tissue is approximately 0.29%/°C, as predicted from the Boltzmann distribution. However, the results in muscle tissue are more variable. There is an offset in both APD and Sum_APD between heating and cooling phases, as well as different temperature coefficients between these two phases. Conclusion The Sum_APD in adipose tissue validates the 1/T dependence on temperature. The APD is a potentially useful parameter for fat thermometry; however, its application in muscle tissue requires further investigation. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Cranial magnetic resonance imaging of Wolfram (DIDMOAD) syndromeJOURNAL OF MEDICAL IMAGING AND RADIATION ONCOLOGY, Issue 2 2005E Pakdemirli Summary Wolfram syndrome is a rare neurodegenerative disorder characterized by diabetes insipidus, diabetes mellitus, optic atrophy and deafness (DIDMOAD). A wide spectrum of abnormalities of the central nervous system, urinary tract and endocrine glands is also observed. We report cranial MRI findings in a 32-year-old female patient with Wolfram syndrome. In addition to the classical features, including absence of the normal high signal of the neurohypophysis, atrophy of visual pathways, the brainstem, cerebellum and cerebral cortex, we observed bilateral hyperintensity on proton density- and T2- weighted images related to the optic radiations in the periventricular white matter of the temporal and parieto-occipital lobes, which may reflect gliosis pathologically. [source] A Magnetization Transfer MRI Study of Deep Gray Matter Involvement in Multiple SclerosisJOURNAL OF NEUROIMAGING, Issue 4 2006Jitendra Sharma MD ABSTRACT Background/Purpose: Gray matter involvement in multiple sclerosis (MS) is of growing interest with respect to disease pathogenesis. Magnetization transfer imaging (MTI), an advanced MRI technique, is sensitive to disease in normal appearing white matter (NAWM) in patients with MS. Design/Methods: We tested if MTI detected subcortical (deep) gray matter abnormalities in patients with MS (n= 60) vs. age-matched normal controls (NL, n= 20). Magnetization transfer ratio (MTR) maps were produced from axial proton density, conventional spin-echo, 5 mm gapless slices covering the whole brain. Region-of-interest,derived MTR histograms for the caudate, putamen, globus pallidus, thalamus, and NAWM were obtained. Whole brain MTR was also measured. Results: Mean whole brain MTR and the peak position of the NAWM MTR histogram were lower in patients with MS than NL (P < .001) and mean whole brain MTR was lower in secondary progressive (SP, n= 10) than relapsing-remitting (RR, n= 50, P < .001) patients. However, none of the subcortical gray matter nuclei showed MTR differences in MS vs. NL, RR vs. SP, or SP vs. NL. Conclusions: The MTI technique used in this cohort was relatively insensitive to disease in the deep gray matter nuclei despite showing sensitivity for whole brain disease in MS. It remains to be determined if other MRI techniques are more sensitive than MTI for detecting pathology in these areas. [source] Measurement of Spin Diffusion Coefficients in Glassy Polymers: Failure of a Simple Scaling LawMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2008Bernard Meurer Abstract For a series of polymers, the spin diffusion coefficients D do not scale as predicted from a simple expression based on regularly spaced nuclei. We compare D for PVA and polystyrene with their side group either protonated or deuterated. For polystyrene, D is considerably reduced from 600,800 to 65 nm2,·,s,1. For PVA, D is already small for the fully protonated chain and is only slightly reduced from 170 to 130 nm2,·,s,1. This indicates that the rapidly rotating methyl group does not contribute appreciably to spin diffusion between neighboring chains and confirms that the mean proton density is not the pertinent parameter to control D. [source] Rapid magnetic resonance quantification on the brain: Optimization for clinical usageMAGNETIC RESONANCE IN MEDICINE, Issue 2 2008J.B.M. Warntjes Abstract A method is presented for rapid simultaneous quantification of the longitudinal T1 relaxation, the transverse T2 relaxation, the proton density (PD), and the amplitude of the local radio frequency B1 field. All four parameters are measured in one single scan by means of a multislice, multiecho, and multidelay acquisition. It is based on a previously reported method, which was substantially improved for routine clinical usage. The improvements comprise of the use of a multislice spin-echo technique, a background phase correction, and a spin system simulation to compensate for the slice-selective RF pulse profile effects. The aim of the optimization was to achieve the optimal result for the quantification of magnetic resonance parameters within a clinically acceptable time. One benchmark was high-resolution coverage of the brain within 5 min. In this scan time the measured intersubject standard deviation (SD) in a group of volunteers was 2% to 8%, depending on the tissue (voxel size = 0.8 × 0.8 × 5 mm). As an example, the method was applied to a patient with multiple sclerosis in whom the diseased tissue could clearly be distinguished from healthy reference values. Additionally it was shown that, using the approach of synthetic MRI, both accurate conventional contrast images as well as quantification maps can be generated based on the same scan. Magn Reson Med 60:320,329, 2008. © 2008 Wiley-Liss, Inc. [source] Method for quantitative imaging of the macromolecular 1H fraction in tissuesMAGNETIC RESONANCE IN MEDICINE, Issue 5 2003Stefan Ropele Abstract A new method was developed for mapping the relative density of the macromolecular protons involved in magnetization transfer (MT). This method employs a stimulated echo preparation scheme in order to modulate the phase distribution within a spin ensemble. This labeled spin ensemble is then used as an intrinsic indicator, which is diluted due to magnetization exchange with macromolecular protons. A pulse sequence is presented which compensates for longitudinal relaxation, allows observation of the dilution effect only, and provides for calculation of parameter maps using indicator dilution theory. Compared to other quantitative MT techniques, neither additional relaxation time measurements nor knowledge regarding the lineshape of the macromolecular proton pool are required. Moreover, the inherent low specific absorption rate and the low sensitivity for B1 errors make this method favorable in a clinical setting. This sequence was used to measure the macromolecular proton density in cross-linked bovine serum albumin. Using a navigated echo planar readout, the sequence was also employed to visualize the macromolecular content of human brain in vivo. Magn Reson Med 49:864,871, 2003. © 2003 Wiley-Liss, Inc. [source] On the transient phase of balanced SSFP sequencesMAGNETIC RESONANCE IN MEDICINE, Issue 4 2003Klaus Scheffler Abstract The signal intensity of balanced steady-state free precession (SSFP) imaging is a function of the proton density, T1, T2, flip angle (,), and repetition time (TR). The steady-state signal intensity that is established after about 5*T1/TR can be described analytically. The transient phase or the approach of the echo amplitudes to the steady state is an exponential decay from the initial amplitude after the first excitation pulse to the steady-state signal. An analytical expression of the decay rate of this transient phase is presented that is based on a simple analysis derived from the Bloch equations. The decay rate is a weighted average of the T1 and T2 relaxation times, where the weighting is determined by the flip angle of the excitation pulses. Thus, balanced SSFP imaging during the transient phase can provide various contrasts depending on the flip angle and the number of excitation pulses applied before the acquisition of the central k -space line. In addition, transient imaging of hyperpolarized nuclei, such as 3He, 129Xe, or 13C, can be optimized according to their T1 and T2 relaxation times. Magn Reson Med 49:781,783, 2003. © 2003 Wiley-Liss, Inc. [source] Trabecular bone volume fraction mapping by low-resolution MRIMAGNETIC RESONANCE IN MEDICINE, Issue 1 2001M.A. Fernández-Seara Abstract Trabecular bone volume fraction (TBVF) is highly associated with the mechanical competence of trabecular bone. TBVF is ordinarily measured by histomorphometry from bone biopsies or, noninvasively, by means of high-resolution microcomputed tomography and, more recently, by micro-MRI. The latter methods require spatial resolution sufficient to resolve trabeculae, along with segmentation techniques that allow unambiguous assignment of the signal to bone or bone marrow. In this article it is shown that TBVF can be measured under low-resolution conditions by exploiting the attenuation of the MR signal resulting from fractional occupancy of the imaging voxel by bone and bone marrow, provided that a reference signal is available from a marrow volume devoid of trabeculation. The method requires accurate measurement of apparent proton density, which entails correction for various sources of error. Key among these are the spatial nonuniformity in the RF field amplitude and effects of the slice profile, which are determined by B1 field mapping and numerical integration of the Bloch equations, respectively. By contrast, errors from variations in bone marrow composition (hematopoietic vs. fatty) between trabecular and reference site are predicted to be small and usually negligible. The method was evaluated in phantoms and in vivo in the distal radius and found to be accurate to 1% in marrow volume fraction. Finally, in a group of 12 patients of varying skeletal status, TBVF in the calcaneus was found to strongly correlate with integral bone mineral density of the lumbar vertebrae (r2 = 0.83, p < 0.0001). The method may fail in large imaging objects such as the human trunk at high magnetic field where standing wave and RF penetration effects cause intensity variations that cannot be corrected. Magn Reson Med 46:103,113, 2001. © 2001 Wiley-Liss, Inc. [source] Stem cell implantation in ischemic mouse heart: a high-resolution magnetic resonance imaging investigation,NMR IN BIOMEDICINE, Issue 6 2005Ekkehard Küstermann Abstract Advances in the biology of stem cells have evoked great interest in cell replacement therapies for the regeneration of heart tissue after myocardial infarction. However, results from human trials are controversial, since the destination of the injected cells, their engraftment and their long-term fate have remained unclear. Here we investigate whether transplanted cells can be identified in the intact and lesioned murine myocardium employing high-resolution MRI. Cardiac progenitor cells, expressing the enhanced green fluorescent protein (EGFP), were labeled with ultra-small paramagnetic iron-oxide (USPIO) nanoparticles and transplanted into the intact or injured myocardium of mice. Their precise location was determined with high-resolution MRI and compared with histological tissue sections, stained with Prussian blue for iron content. These experiments showed that iron nanoparticle-loaded cells could be identified at high resolution in the mouse heart. However, ischemic myocardium (after cryoinjury or left coronary artery ligation) was characterized by a signal attenuation similar to that induced by USPIO-labeled cells in T -weighted MR images, making detection of labeled stem cells in this area by T -sensitive contrast rather difficult. In animals with myocardial injury only, the signal attenuated areas were of the same size in proton density- and T -weighted MR images. In injured animals also receiving labeled cells the lesioned area appeared larger in T - than in proton density-weighted MR images. This sequence-dependent lesion size change is due to the increased signal loss caused by the iron oxide nanoparticles, most sensitively detectable in the T -sensitive images. Thus, using the novel combination of these two parameter weightings, USPIO-labeled cells can be detected at high resolution in ischemic myocardium. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||