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Title: Multi-parametric quantification of white matter microstructure in the human brain
Author: Bells, Sonya
ISNI:       0000 0004 2733 7690
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2012
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To date the majority of MRI studies of white matter (WM) microstructure have used diffusion tensor MRI (DT-MRI), comparing groups on a voxel-by-voxel basis. There are limitations to this approach. Firstly, the analysis approach treats each voxel independently, ignoring the fact that adjacent voxels may come from the same tract (or may come from completely separate tracts). Secondly, DT-MRI is sensitive to both interesting properties of WM (e.g., myelination, axon density), and less interesting properties (e.g., intra-voxel orientational dispersion). In contrast, other imaging approaches, based on different contrast mechanisms, can provide increased specificity and therefore sensitivity to differences in one particular attribute of tissue microstructure (e.g., myelin content or axonal density). Both quantitative magnetization transfer (qMT) imaging and multicomponent relaxometry provide proxy estimates of myelin content while the combined hindered and restricted model of diffusion (CHARMED) provides a proxy estimate of axon density. We present a novel imaging method called tractometry, which permits simultaneous quantitative assessment of these different microstructural attributes along specific pathways.Crucially, the metrics were only weakly correlated, suggesting that tractometry provides complementary WM microstructural information to DT-MRI. In developing the tractometry pipeline, we also performed a detailed examination of the qMT pipeline, identifying and reducing sources of variance to provide optimized results. We also identify a number of issues with the current state-of-the art, including the stability of tract based spatial statistics (TBSS). We show that conducting a structure-function correlation TBSS study may lead to vastly different conclusions, based simply on the participants recruited into the study. We also address microstructural asymmetry, including the degree of partial-volume effects (PVEs) from free water, which impact on WM metrics. The observed spatial heterogeneity of PVEs can potentially confound interpretation in studies where contralateral hemispheres are used as internal controls, and could either exacerbate or possibly negate tissue differences
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: BF Psychology ; QH301 Biology