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Diffusion MRI (diffusion + mri)
Selected AbstractsEFNS guideline on neuroimaging in acute stroke.EUROPEAN JOURNAL OF NEUROLOGY, Issue 12 2006Report of an EFNS task force Neuroimaging techniques are necessary for the evaluation of stroke, one of the leading causes of death and neurological impairment in developed countries. The multiplicity of techniques available has increased the complexity of decision making for physicians. We performed a comprehensive review of the literature in English for the period 1965,2005 and critically assessed the relevant publications. The members of the panel reviewed and corrected an initial draft, until a consensus was reached on recommendations stratified according to the European Federation of Neurological Societies (EFNS) criteria. Non-contrast computed tomography (CT) scan is the established imaging procedure for the initial evaluation of stroke patients. However, magnetic resonance imaging (MRI) has a higher sensitivity than CT for the demonstration of infarcted or ischemic areas and depicts well acute and chronic intracerebral hemorrhage. Perfusion and diffusion MRI together with MR angiography (MRA) are very helpful for the acute evaluation of patients with ischemic stroke. MRI and MRA are the recommended techniques for screening cerebral aneurysms and for the diagnosis of cerebral venous thrombosis and arterial dissection. For the non-invasive study of extracranial vessels, MRA is less portable and more expensive than ultrasonography but it has higher sensitivity and specificity for carotid stenosis. Transcranial Doppler is very useful for monitoring arterial reperfusion after thrombolysis, for the diagnosis of intracranial stenosis and of right-to-left shunts, and for monitoring vasospasm after subarachnoid hemorrhage. Currently, single photon emission computed tomography and positron emission tomography have a more limited role in the evaluation of the acute stroke patient. [source] Cardiac diffusion MRI without motion effectsMAGNETIC RESONANCE IN MEDICINE, Issue 1 2002Jiangang Dou Abstract We present a method for diffusion tensor MRI in the beating heart that is insensitive to cardiac motion and strain. Using a stimulated echo pulse sequence with two electrocardiogram (ECG) triggers, diffusion-encoding bipolar gradient pulses are applied at identical phases in consecutive cardiac cycles. In this experiment, diffusion is encoded at a single phase in the cardiac cycle of less than 30 ms in duration. This encoding produces no phase shifts for periodic motion and is independent of intervening strains. Studies in a gel phantom with cyclic deformation confirm that by using this sequence we can map the diffusion tensor free of effects of cyclic motion. In normal human subjects, myocardial diffusion eigenvalues measured with the present method showed no significant change between acquisitions encoded at maximum contractile velocity (peak) vs. at myocardial standstill (end-systole), demonstrating motion independence of in vivo diffusion measurements. Diffusion tensor images acquired with the present method agree with registered data acquired with a previous cardiac diffusion MRI method that was shown to be valid in the normal heart, strongly supporting the validity of MRI diffusion measurement in the beating heart. Myocardial sheet and fiber dynamics measured during systole showed that normal human myocardial sheet orientations tilt toward the radial during systole, and fiber orientations tilt toward the longitudinal, in qualitative agreement with previous invasive studies in canines. These results demonstrate the technique's ability to measure myocardial diffusion accurately at any point in the cardiac cycle free of measurable motion effect, as if the heart were frozen at the point of acquisition. Magn Reson Med 48:105,114, 2002. © 2002 Wiley-Liss, Inc. [source] Twenty-five pitfalls in the analysis of diffusion MRI data,NMR IN BIOMEDICINE, Issue 7 2010Derek K. Jones Abstract Obtaining reliable data and drawing meaningful and robust inferences from diffusion MRI can be challenging and is subject to many pitfalls. The process of quantifying diffusion indices and eventually comparing them between groups of subjects and/or correlating them with other parameters starts at the acquisition of the raw data, followed by a long pipeline of image processing steps. Each one of these steps is susceptible to sources of bias, which may not only limit the accuracy and precision, but can lead to substantial errors. This article provides a detailed review of the steps along the analysis pipeline and their associated pitfalls. These are grouped into 1 pre-processing of data; 2 estimation of the tensor; 3 derivation of voxelwise quantitative parameters; 4 strategies for extracting quantitative parameters; and finally 5 intra-subject and inter-subject comparison, including region of interest, histogram, tract-specific and voxel-based analyses. The article covers important aspects of diffusion MRI analysis, such as motion correction, susceptibility and eddy current distortion correction, model fitting, region of interest placement, histogram and voxel-based analysis. We have assembled 25 pitfalls (several previously unreported) into a single article, which should serve as a useful reference for those embarking on new diffusion MRI-based studies, and as a check for those who may already be running studies but may have overlooked some important confounds. While some of these problems are well known to diffusion experts, they might not be to other researchers wishing to undertake a clinical study based on diffusion MRI. Copyright © 2010 John Wiley & Sons, Ltd. [source] Assessing optic nerve pathology with diffusion MRI: from mouse to humanNMR IN BIOMEDICINE, Issue 9 2008Junqian Xu Abstract The optic nerve is often affected in patients with glaucoma and multiple sclerosis. Conventional MRI can detect nerve damage, but it does not accurately assess the underlying pathologies. Mean diffusivity and diffusion anisotropy indices derived from diffusion tensor imaging have been shown to be sensitive to a variety of central nervous system white matter pathologies. Despite being sensitive, the lack of specificity limits the ability of these measures to differentiate the underlying pathology. Directional (axial and radial) diffusivities, measuring water diffusion parallel and perpendicular to the axonal tracts, have been shown to be specific to axonal and myelin damage in mouse models of optic nerve injury, including retinal ischemia and experimental autoimmune encephalomyelitis. The progression of Wallerian degeneration has also been detected using directional diffusivities after retinal ischemia. However, translating these findings to human optic nerve is technically challenging. The current status of diffusion MRI of human optic nerve, including imaging sequences and protocols, is summarized herein. Despite the lack of a consensus among different groups on the optimal sequence or protocol, increased mean diffusivity and decreased diffusion anisotropy have been observed in injured optic nerve from patients with chronic optic neuritis. From different mouse models of optic nerve injuries to the emerging studies on patients with optic neuritis, directional diffusivities show great potential to be specific biomarkers for axonal and myelin injury. Copyright © 2008 John Wiley & Sons, Ltd. [source] Applications of diffusion-weighted and diffusion tensor MRI to white matter diseases , a reviewNMR IN BIOMEDICINE, Issue 7-8 2002Mark A. Horsfield Abstract This paper reviews the current applications of diffusion-weighted and diffusion tensor MRI in diseases of the brain white matter. The contribution that diffusion-weighted imaging has made to our understanding of white matter diseases is critically appraised. The quantitative nature of diffusion MRI is one of its major attractions; however, this is offset by the more advanced hardware required to collect diffusion-weighted images reliably, and the more complex processing to produce quantitative parametric diffusion images. With the now common availability of scanners equipped to perform echo-planar imaging, the acquisition of diffusion tensor images is sure to become more widespread and routine. Copyright © 2002 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. [source] Can we use diffusion MRI as a bio-marker of neurodegenerative processes?BIOESSAYS, Issue 11-12 2008Yaniv Assaf Magnetic resonance imaging (MRI) is an imaging technique with a rapidly expanding application range. This methodology, which relies on quantum physics and substance magnetic properties, is now being routinely used in the clinics and medical research. With the advent of measuring functional brain activity with MRI (functional MRI), this methodology has reached a larger section of the neuroscience community (e.g. psychologists, neurobiologists). In the past, the use of MRI as a biomarker or as an assay to probe tissue pathophysiological condition was limited. However, with the new applications of MRI: molecular imaging, contrast-enhanced imaging and diffusion imaging, MRI is turning into a powerful tool for in vivo characterization of tissue pathophysiology. This review focuses on the diffusion MRI. Although it only measures the averaged Brownian translational motion of water molecules, using different analysis schemes, one can extract a wide range of quantitative indices that represent tissue morphology and compartmentalization. Statistical and visualization routines help to relate these indices to biologically relevant measures such as cell density, water content and size distribution. The aim of this review is to shed light on the potential of this methodology to be used in biological research. To that end, this review is intended for the non-MRI specialists who wish to pursue biological research with this methodology. We will overview the current applications of diffusion MRI and its relation to cellular biology of brain tissue. BioEssays 30:1235,1245, 2008. © 2008 Wiley Periodicals, Inc. [source] Using diffusion MRI for measuring the temperature of cerebrospinal fluid within the lateral ventriclesACTA PAEDIATRICA, Issue 2 2010LR Kozak Abstract Aim:, Hypothermia is often induced to reduce brain injury in newborns, following perinatal hypoxic,ischaemic events, and in adults following traumatic brain injury, stroke or cardiac arrest. We aimed to devise a method, based on diffusion-weighted MRI, to measure non-invasively the temperature of the cerebrospinal fluid in the lateral ventricles. Methods:, The well-known temperature dependence of the water diffusion constant was used for the estimation of temperature. We carried out diffusion MRI measurements on a 3T Philips Achieva Scanner involving phantoms (filled with water or artificial cerebrospinal fluid while slowly cooling from 41 to 32°C) and healthy adult volunteers. Results:, The estimated temperature of water phantoms followed that measured using a mercury thermometer, but the estimates for artificial cerebrospinal fluid were 1.04°C lower. After correcting for this systematic difference, the estimated temperature within the lateral ventricles of volunteers was 39.9°C. Using diffusion directions less sensitive to cerebrospinal fluid flow, it was 37.7°C, which was in agreement with the literature. Conclusion:, Although further improvements are needed, measuring the temperature within the lateral ventricles using diffusion MRI is a viable method that may be useful for clinical applications. We introduced the method, identified sources of error and offered remedies for each. [source] | ||||||||||