Variations in T1 and T2 relaxation times of normal appearing white matter and lesions in multiple sclerosis

Stevenson, Valerie; Parker, Geoffrey; Barker, Gareth J.; Birnie, K; Tofts, Paul S.; Miller, David H.; Thompson, Alan J.

doi:10.1016/s0022-510x(00)00339-7

Cited by 117 publications

(102 citation statements)

References 19 publications

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“…Myelin water is virtually invisible in diffusion MRI due to very short T2 45. When myelin is lost, the local T2 increases,46 effectively increasing the amount of MRI‐visible water and causing NDI to decrease 26…”

Section: Discussionmentioning

confidence: 99%

Neurite dispersion: a new marker of multiple sclerosis spinal cord pathology?

Grussu

Schneider

Tur

et al. 2017

Ann Clin Transl Neurol

267

243

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ObjectiveConventional magnetic resonance imaging (MRI) of the multiple sclerosis spinal cord is limited by low specificity regarding the underlying pathological processes, and new MRI metrics assessing microscopic damage are required. We aim to show for the first time that neurite orientation dispersion (i.e., variability in axon/dendrite orientations) is a new biomarker that uncovers previously undetected layers of complexity of multiple sclerosis spinal cord pathology. Also, we validate against histology a clinically viable MRI technique for dispersion measurement (neurite orientation dispersion and density imaging, NODDI), to demonstrate the strong potential of the new marker.MethodsWe related quantitative metrics from histology and MRI in four post mortem spinal cord specimens (two controls; two progressive multiple sclerosis cases). The samples were scanned at high field, obtaining maps of neurite density and orientation dispersion from NODDI and routine diffusion tensor imaging (DTI) indices. Histological procedures provided markers of astrocyte, microglia, myelin and neurofilament density, as well as neurite dispersion.ResultsWe report from both NODDI and histology a trend toward lower neurite dispersion in demyelinated lesions, indicative of reduced neurite architecture complexity. Also, we provide unequivocal evidence that NODDI‐derived dispersion matches its histological counterpart (P < 0.001), while DTI metrics are less specific and influenced by several biophysical substrates.InterpretationNeurite orientation dispersion detects a previously undescribed and potentially relevant layer of microstructural complexity of multiple sclerosis spinal cord pathology. Clinically feasible techniques such as NODDI may play a key role in clinical trial and practice settings, as they provide histologically meaningful dispersion indices.

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Section: Discussionmentioning

confidence: 99%

Neurite dispersion: a new marker of multiple sclerosis spinal cord pathology?

Grussu

Schneider

Tur

et al. 2017

Ann Clin Transl Neurol

267

243

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“…À3 mm 2 /sec (estimated from 1.5-T data (26,27), assuming $30% increase in T 1 and no changes in T 2 and D); and cerebrospinal fluid (CSF):…”

Section: Simulationsmentioning

confidence: 99%

Optimal radiofrequency and gradient spoiling for improved accuracy of T₁ and B₁ measurements using fast steady‐state techniques

Yarnykh¹

2010

Magnetic Resonance in Med

148

227

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Variable flip angle T 1 mapping and actual flip-angle imaging B 1 mapping are widely used quantitative MRI methods employing radiofrequency spoiled gradient-echo pulse sequences. Incomplete elimination of the transverse magnetization in these sequences has been found to be a critical source of T 1 and B 1 measurement errors. In this study, comprehensive theoretical analysis of spoiling-related errors in variable flip angle and actual flip-angle imaging methods was performed using the combined isochromat summation and diffusion propagator model and validated by phantom experiments. The key theoretical conclusion is that correct interpretation of spoiling phenomena in fast gradient-echo sequences requires accurate consideration of the diffusion effect. A general strategy for improvement of T 1 and B 1 measurement accuracy was proposed based on the strong spoiling regimen, where diffusion-modulated spatial averaging of isochromats becomes a dominant factor determining magnetization evolution. Practical implementation of strongly spoiled variable flip angle and actual flip-angle imaging techniques requires sufficiently large spoiling gradient areas (A G ) in combination with optimal radiofrequency phase increments (f 0 ). Optimal regimens providing <2% relative T 1 and B 1 measurement errors in a variety of tissues were theoretically derived for prospective in vivo variable flip angle (pulse repetition time 5 (1) is a widely used method allowing generation of T 1 -weighted contrast in gradient echo (GRE) sequences with short pulse repetition time (TR). Technically, RF spoiling is achieved by linearly incrementing the phase of an RF pulse between successive TR with a specific value of the phase increment. After the initial publication (1) suggested optimal phase increments of 117 or 123 , several other values were proposed (2-4). Default settings of the RF phase increment also vary between MRI equipment manufacturers (5). While all these approaches generally allow acquisition of heavily T 1 -weighted GRE images in the steady state, special attention should be given to the role of RF spoiling in quantitative imaging methods.One of most widely used quantitative applications of the RF spoiled GRE sequence is the variable flip angle (VFA) method for T 1 mapping (6,7). In modern implementations, the VFA method takes advantage of a very short TR achievable due to RF spoiling, which allows time-efficient three-dimensional implementation with large anatomic coverage (8-10). Accuracy of VFA T 1 measurements was extensively studied in aspects of optimal flip-angle sampling (7-10) and correction of amplitude of RF field (B 1 ) nonuniformities (4,9,10). Recently, incomplete spoiling was identified as a critical source of errors in the VFA method (4,5,11). While data processing in this method relies on the ideally spoiled signal equation (12), the use of fast RF spoiled sequences may result in partial preservation of transverse coherences and, therefore, deviation of the signal behavior from the idealized theoretical model. Techn...

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“…This could be a coincidental finding due to the limited number of patients. However, it has been stated before that FLAIR sequences might not be ideally suited for the detection of infratentorial lesions as a result of lower lesion-white matter contrast compared to supratentorial regions [21,22]. Cortical and juxtacortical MS lesions have recently received more attention in pathological and imaging studies as they occur more frequently and seem to affect clinical disability to a larger extent than primarily assumed [23 -25].…”

mentioning

confidence: 99%

Comparison of 3D Cube FLAIR with 2D FLAIR for Multiple Sclerosis Imaging at 3 Tesla

Patzig

Burke

Brückmann

et al. 2013

Fortschr Röntgenstr

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Variations in T1 and T2 relaxation times of normal appearing white matter and lesions in multiple sclerosis

Cited by 117 publications

References 19 publications

Neurite dispersion: a new marker of multiple sclerosis spinal cord pathology?

Neurite dispersion: a new marker of multiple sclerosis spinal cord pathology?

Optimal radiofrequency and gradient spoiling for improved accuracy of T₁ and B₁ measurements using fast steady‐state techniques

Comparison of 3D Cube FLAIR with 2D FLAIR for Multiple Sclerosis Imaging at 3 Tesla

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Variations in T1 and T2 relaxation times of normal appearing white matter and lesions in multiple sclerosis

Cited by 117 publications

References 19 publications

Neurite dispersion: a new marker of multiple sclerosis spinal cord pathology?

Neurite dispersion: a new marker of multiple sclerosis spinal cord pathology?

Optimal radiofrequency and gradient spoiling for improved accuracy of T1 and B1 measurements using fast steady‐state techniques

Comparison of 3D Cube FLAIR with 2D FLAIR for Multiple Sclerosis Imaging at 3 Tesla

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Optimal radiofrequency and gradient spoiling for improved accuracy of T₁ and B₁ measurements using fast steady‐state techniques