Contrast-to-noise ratios for indices of anisotropy obtained from diffusion MRI: A study with standard clinical b-values at 3T

Correia, Marta; Newcombe, Virginia; Williams, Guy B.

doi:10.1016/j.neuroimage.2011.03.004

Cited by 6 publications

(16 citation statements)

References 64 publications

(86 reference statements)

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“…The use of multiple b values for equivalent number of gradient directions has been shown to improve contrast to noise ratio in diffusion‐weighted white matter imaging (Correia et al. 2011). The field of view was 19.2 cm, and the acquisition matrix size was 96 × 96, giving a voxel size of 2 × 2 × 2 mm.…”

Section: Methodsmentioning

confidence: 99%

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Dominant hemisphere functional networks compensate for structural connectivity loss to preserve phonological retrieval with aging

Agarwal

Stamatakis

Geva³

et al. 2016

Brain and Behavior

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IntroductionLoss of hemispheric asymmetry during cognitive tasks has been previously demonstrated in the literature. In the context of language, increased right hemisphere activation is observed with aging. Whether this relates to compensation to preserve cognitive function or dedifferentiation implying loss of hemispheric specificity without functional consequence, remains unclear.MethodsWith a multifaceted approach, integrating structural and functional imaging data during a word retrieval task, in a group of younger and older adults with equivalent cognitive performance, we aimed to establish whether interactions between hemispheres or reorganization of dominant hemisphere networks preserve function. We examined functional and structural connectivity on data from our previously published functional activation study. Functional connectivity was measured using psychophysiological interactions analysis from the left inferior frontal gyrus (LIFG) and the left insula (LINS), based on published literature, and the right inferior frontal gyrus (RIFG) based on our previous study.ResultsAlthough RIFG showed increased activation, its connectivity decreased with age. Meanwhile, LIFG and LINS connected more bilaterally in the older adults. White matter integrity, measured by fractional anisotropy (FA) from diffusion tensor imaging, decreased significantly in the older group. Importantly, LINS functional connectivity to LIFG correlated inversely with FA.ConclusionsWe demonstrate that left hemispheric language areas show higher functional connectivity in older adults with intact behavioral performance, and thus, may have a role in preserving function. The inverse correlation of functional and structural connectivity with age is in keeping with emerging literature and merits further investigation with tractography studies and in other cognitive domains.

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Section: Methodsmentioning

confidence: 99%

“…2011). However, given that the number of directions of gradients applied was only 12, the data acquired cannot be meaningfully used for tractography (Correia et al.…”

Section: Methodsmentioning

confidence: 99%

Dominant hemisphere functional networks compensate for structural connectivity loss to preserve phonological retrieval with aging

Agarwal

Stamatakis

Geva³

et al. 2016

Brain and Behavior

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“…As demonstrated in previous studies, FA has excellent potential for the assessment of white matter remodeling after TBI [6], [11], [49], [50], [51], [52]. However, when white matter fiber tracts cross, conventional DTI produces an anomalous result, showing inability to resolve more than one fiber direction and an overall lowering of FA despite the presence of highly-oriented tissue [18], [19], [29], [33], [35], [53]. The inability of conventional DTI to resolve multiple fiber directions and low FA derive from the assumption of Gaussian diffusion inherent to the tensor model, and different q-space DTI (qDTI)methodologies have been developed to address these issues [18], [19], [29], [33], [35], [53].…”

Section: Discussionmentioning

confidence: 78%

Characterizing Brain Structures and Remodeling after TBI Based on Information Content, Diffusion Entropy

et al. 2013

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BackgroundTo overcome the limitations of conventional diffusion tensor magnetic resonance imaging resulting from the assumption of a Gaussian diffusion model for characterizing voxels containing multiple axonal orientations, Shannon's entropy was employed to evaluate white matter structure in human brain and in brain remodeling after traumatic brain injury (TBI) in a rat.MethodsThirteen healthy subjects were investigated using a Q-ball based DTI data sampling scheme. FA and entropy values were measured in white matter bundles, white matter fiber crossing areas, different gray matter (GM) regions and cerebrospinal fluid (CSF). Axonal densities' from the same regions of interest (ROIs) were evaluated in Bielschowsky and Luxol fast blue stained autopsy (n = 30) brain sections by light microscopy. As a case demonstration, a Wistar rat subjected to TBI and treated with bone marrow stromal cells (MSC) 1 week after TBI was employed to illustrate the superior ability of entropy over FA in detecting reorganized crossing axonal bundles as confirmed by histological analysis with Bielschowsky and Luxol fast blue staining.ResultsUnlike FA, entropy was less affected by axonal orientation and more affected by axonal density. A significant agreement (r = 0.91) was detected between entropy values from in vivo human brain and histologically measured axonal density from post mortum from the same brain structures. The MSC treated TBI rat demonstrated that the entropy approach is superior to FA in detecting axonal remodeling after injury. Compared with FA, entropy detected new axonal remodeling regions with crossing axons, confirmed with immunohistological staining.ConclusionsEntropy measurement is more effective in distinguishing axonal remodeling after injury, when compared with FA. Entropy is also more sensitive to axonal density than axonal orientation, and thus may provide a more accurate reflection of axonal changes that occur in neurological injury and disease.

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“…Currently, investigation of neuronal remodeling after brain injury has been dominated by traditional DTI such as FA and fiber tracking [50]–[55]. However, conventional DTI produces an anomalous result, showing an overall lowering of FA despite the presence of highly-oriented tissue [3], [44], [56]–[60]. Currently, there are few published studies to target the issue related to low FA in areas with highly-oriented tissue [44], [57], [58], [60], [61] and no investigation has been published in white matter remodeling after brain injury, such as TBI, using MRI axonal permeability and diameter.…”

Section: Resultsmentioning

confidence: 99%

“…However, conventional DTI produces an anomalous result, showing an overall lowering of FA despite the presence of highly-oriented tissue [3], [44], [56]–[60]. Currently, there are few published studies to target the issue related to low FA in areas with highly-oriented tissue [44], [57], [58], [60], [61] and no investigation has been published in white matter remodeling after brain injury, such as TBI, using MRI axonal permeability and diameter. Our data demonstrated that physiological measurable parameters, MRI axonal permeability, diameter, and density are sensitive in detecting axonal changes after TBI and could be very useful in the evaluation of axonal damage and remodeling after neurological diseases, such as TBI, stroke, and MS.…”

Section: Resultsmentioning

confidence: 99%

An Analytical Model for Estimating Water Exchange Rate in White Matter Using Diffusion MRI

et al. 2014

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Substantial effort is being expended on using micro-structural modeling of the white matter, with the goal of relating diffusion weighted magnetic resonance imaging (DWMRI) to the underlying structure of the tissue, such as axonal density. However, one of the important parameters affecting diffusion is the water exchange rate between the intra- and extra-axonal space, which has not been fully investigated and is a crucial marker of brain injury such as multiple sclerosis (MS), stroke, and traumatic brain injury (TBI). To our knowledge, there is no diffusion analytical model which includes the Water eXchange Rate (WXR) without the requirement of short gradient pulse (SGP) approximation. We therefore propose a new analytical model by deriving the diffusion signal for a permeable cylinder, assuming a clinically feasible pulse gradient spin echo (PGSE) sequence. Simulations based on Markov Random Walk confirm that the exchange parameter included in our model has a linear correlation (R2>0.88) with the actual WXR. Moreover, increasing WXR causes the estimated values of diameter and volume fraction of the cylinders to increase and decrease, respectively, which is consistent with our findings from histology measurements in tissues near TBI regions. This model was also applied to the diffusion signal acquired from ex vivo brains of 14 male (10 TBI and 4 normal) rats using hybrid diffusion imaging. The estimated values of axon diameter and axonal volume fraction are in agreement with their corresponding histological measurements in normal brains, with 0.96 intra-class correlation coefficient value resulting from consistency analysis. Moreover, a significant increase (p = 0.001) in WXR and diameter and decrease in axonal volume fraction in the TBI boundary were detected in the TBI rats compared with the normal rats.

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Contrast-to-noise ratios for indices of anisotropy obtained from diffusion MRI: A study with standard clinical b-values at 3T

Cited by 6 publications

References 64 publications

Dominant hemisphere functional networks compensate for structural connectivity loss to preserve phonological retrieval with aging

Dominant hemisphere functional networks compensate for structural connectivity loss to preserve phonological retrieval with aging

Characterizing Brain Structures and Remodeling after TBI Based on Information Content, Diffusion Entropy

An Analytical Model for Estimating Water Exchange Rate in White Matter Using Diffusion MRI

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