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Diffusion Magnetic Resonance Imaging (diffusion + magnetic_resonance_imaging)
Selected AbstractsDiffusion Magnetic Resonance Imaging in Intermediate Form of Maple Syrup Urine DiseaseJOURNAL OF NEUROIMAGING, Issue 4 2002R. N. Sener ABSTRACT An 8-year-old boy with the intermediate variant of maple syrup urine disease is reported. On b= 1000 s/mm2 (heavily diffusion weighted) images of diffusion magnetic resonance imaging, there was symmetric high signal in the globus pallidus, mesencephalon, dorsal pons, and nucleus dentatus, consistent with restriction of the mobility of water molecules. Apparent diffusion coefficient (ADC) maps revealed low ADC values ranging from 0.42 to 0.56 ?10,3mm2/s in these regions, compared to those of apparently unaffected regions in the brain parenchyma ranging from 0.63 to 0.97 ?10,3 mm 2/s. It is suggested that the areas of increased signal (and low ADC values) are the result of dysmyelination as a reflection of disorganized tissue integrity. [source] Physical foundations, models, and methods of diffusion magnetic resonance imaging of the brain: A reviewCONCEPTS IN MAGNETIC RESONANCE, Issue 5 2007Ludovico Minati Abstract The foundations and characteristics of models and methods used in diffusion magnetic resonance imaging, with particular reference to in vivo brain imaging, are reviewed. The first section introduces Fick's laws, propagators, and the relationship between tissue microstructure and the statistical properties of diffusion of water molecules. The second section introduces the diffusion-weighted signal in terms of diffusion of magnetization (Bloch,Torrey equation) and of spin-bearing particles (cumulant expansion). The third section is dedicated to the rank-2 tensor model, the bb -matrix, and the derivation of indexes of anisotropy and shape. The fourth section introduces diffusion in multiple compartments: Gaussian mixture models, relationship between fiber layout, displacement probability and diffusivity, and effect of the b -value. The fifth section is devoted to higher-order generalizations of the tensor model: singular value decompositions (SVD), representation of angular diffusivity patterns and derivation of generalized anisotropy (GA) and scaled entropy (SE), and modeling of non-Gaussian diffusion by means of series expansion of Fick's laws. The sixth section covers spherical harmonic decomposition (SHD) and determination of fiber orientation by means of spherical deconvolution. The seventh section presents the Fourier relationship between signal and displacement probability (Q -space imaging, QSI, or diffusion-spectrum imaging, DSI), and reconstruction of orientation-distribution functions (ODF) by means of the Funk,Radon transform (Q -ball imaging, QBI). © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 278,307, 2007. [source] Optic radiation changes after optic neuritis detected by tractography-based group mappingHUMAN BRAIN MAPPING, Issue 3 2005Olga Ciccarelli Abstract Postmortem data suggest that trans-synaptic degeneration occurs in the lateral geniculate nucleus after optic nerve injury. This study investigated in vivo the optic radiations in patients affected by optic neuritis using fast marching tractography (FMT), a diffusion magnetic resonance imaging (MRI) fiber tracking method, and group mapping techniques, which allow statistical comparisons between subjects. Seven patients, 1 year after isolated unilateral optic neuritis, and ten age and gender-matched controls underwent whole-brain diffusion tensor MR imaging. The FMT algorithm was used to generate voxel-scale connectivity (VSC) maps in the optic radiations in each subject in native space. Group maps of the left and right optic radiations were created in the patient and control group in a standardized reference frame using statistical parametric mapping (SPM99). The reconstructed optic radiations in the patient group were localized more laterally in the posterior part of the tracts and more inferiorly than in the control group. Patients showed reduced VSC values in both tracts compared with controls. These findings suggest that the group mapping techniques might be used to assess changes in the optic radiations in patients after an episode of optic neuritis. The changes we have observed may be secondary to the optic nerve damage. Hum Brain Mapp, 2005. © 2005 Wiley-Liss, Inc. [source] Water diffusion in a rat glioma during ganciclovir-thymidine kinase gene therapy-induced programmed cell death in vivo: Correlation with cell densityJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2004Piia K. Valonen MSc Abstract Purpose To study the characteristics of diffusion magnetic resonance imaging (MRI) contrast in a rat brain BT4C glioma during progression of ganciclovir (GCV)-thymidine kinase gene therapy-induced programmed cell death (PCD) in vivo. Materials and Methods The trace of the diffusion tensor (Dav = 1/3Trace ), T2, and spin density were determined by MRI and the apparent diffusion coefficient (ADC) of water by diffusion nuclear MR (NMR) spectroscopy using largely varying b values and diffusion times (tD) at 4.7 T. Cell count and apoptotic cells were quantified by histological means. Results Decline in cell count was strongly associated with increase in both Dav and T2. Spin density ratio between tumor and contralateral parietal cortex increased with a very similar time course as Dav and T2, indicating net water gain into the eradicating tumor. Diffusion spectroscopy showed a nonmonoexponential signal decay at all tD values ranging from 14,192 msec. During PCD, the ADC of the component yielding fast diffusion coefficient (D1), as acquired with tD , 47 msec, increased with kinetics similar to those of Dav (tD = 4.8 msec). The fractional size of D1 increased by 10% to 15% throughout the entire tD range. Apparent water residence time of the slow diffusion component, D2, shortened from a value of 38.3 ± 1.7 msec on day 0 to 33.4 ± 0.5 msec by day 8. Conclusion The present results show that reduced cell density and increased water content, leading to altered water microenvironment, are associated with increased water diffusion coefficient in eradicating gliomas as a result of PCD. J. Magn. Reson. Imaging 2004;19:389,396. © 2004 Wiley-Liss, Inc. [source] Water Apparent Diffusion Coefficient and T2 Changes in the Acute Stage of Maple Syrup Urine Disease: Evidence of Intramyelinic and Vasogenic-Interstitial EdemaJOURNAL OF NEUROIMAGING, Issue 2 2003Andrea Righini MD ABSTRACT Background. The acute phase of the neonatal classical form of maple syrup urine disease (MSUD) is usually associated with generalized brain edema. Methods and Results. The authors present the case of a newborn infant in the acute stage of the classical form of MSUD in whom a remarkable decrease in the water apparent diffusion coefficient (ADC) in advanced myelinating white matter areas was associated with an increase in the T2 signal. This diffusion magnetic resonance imaging (MRI) pattern appears to be compatible with a rare kind of cytotoxic edema, the so-called intramyelinic edema. At the same time, an increase in the ADC was seen in unmyelinated areas together with an increase in the T2 signal, a sign of a coexistent vasogenic-interstitial edema. Conclusions. ADC measurements in MSUD provide more specific information than conventional MRI about the pathophysiology of white matter changes. [source] Diffusion Magnetic Resonance Imaging in Intermediate Form of Maple Syrup Urine DiseaseJOURNAL OF NEUROIMAGING, Issue 4 2002R. N. Sener ABSTRACT An 8-year-old boy with the intermediate variant of maple syrup urine disease is reported. On b= 1000 s/mm2 (heavily diffusion weighted) images of diffusion magnetic resonance imaging, there was symmetric high signal in the globus pallidus, mesencephalon, dorsal pons, and nucleus dentatus, consistent with restriction of the mobility of water molecules. Apparent diffusion coefficient (ADC) maps revealed low ADC values ranging from 0.42 to 0.56 ?10,3mm2/s in these regions, compared to those of apparently unaffected regions in the brain parenchyma ranging from 0.63 to 0.97 ?10,3 mm 2/s. It is suggested that the areas of increased signal (and low ADC values) are the result of dysmyelination as a reflection of disorganized tissue integrity. [source] Water diffusion in the different microenvironments of breast cancerNMR IN BIOMEDICINE, Issue 4 2004Yael Paran Abstract The parameters that characterize the intricate water diffusion in tumors may serve to reveal their distinct pathology. Specifically, the application of diffusion magnetic resonance imaging (MRI) can aid in characterizing breast cancer, as well as monitoring response to therapy. We present here a non-invasive, quantitative MRI investigation, at high spatial resolution, of water diffusion in hormonal dependent MCF7 breast tumors implanted orthotopically in immunodeficient mice. Distinctive MRI protocols were designed in this study, utilizing a broad range of diffusion times and diffusion gradient strengths. Application of these protocols allowed water diffusion in the tissue extracellular and intracellular compartments to be distinguished, and the effect of restricted diffusion and water exchange on the water diffusion in these compartments to be evaluated. Pixel-by-pixel analysis yielded parametric maps of the estimated volume fraction and apparent diffusion coefficient of each compartment. The diffusion of the water in the extracellular microenvironment was approximately two fold slower than that of free water, and in the intracellular compartment was about one order of magnitude slower than that of free water and demonstrated restriction of water diffusion at long diffusion times. Mapping of the water fraction in each compartment was further employed to monitor changes during tumor progression and to assess tumor response to hormonal manipulation with a new antiestrogenic drug, tamoxifen methiodide (TMI). It was found that, in parallel to the growth arrest by this drug, the volume fraction of the slowly diffusing water increased, suggesting a TMI-induced cell swelling. This study can serve as a basis for extending diffusion breast MRI in the clinical setting. Copyright © 2004 John Wiley & Sons, Ltd. [source] Monitoring cytotoxic tumour treatment response by diffusion magnetic resonance imaging and proton spectroscopyNMR IN BIOMEDICINE, Issue 1 2002Risto A. Kauppinen Abstract Exposure of tumours to anti-cancer drugs, gene or radiation therapy consistently leads to an increase in water diffusion in the cases expressing favourable treatment response. The diffusion change coincides cytotoxic cell eradication and precedes volume reduction in drug or gene therapy-treated experimental tumours. Interestingly, the recent studies from human brain tumour patients undergoing chemotherapy show similar behaviour of diffusion, suggesting important application for MRI in patient management. In this review observations from diffusion MRI and MRS in the tumours during cytotoxic treatment are summarized and the cellular mechanisms affecting molecular mobility are discussed in the light of tissue microenvironmental and microdynamic changes. Copyright © 2002 John Wiley & Sons, Ltd. 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