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Impact of b-value on estimates of apparent fibre density

Genc, Sila, Tax, Chantal M. W., Raven, Erika P., Chamberland, Maxime, Parker, Greg D. and Jones, Derek K. 2020. Impact of b-value on estimates of apparent fibre density. Human Brain Mapping 10.1002/hbm.24964
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Recent advances in diffusion magnetic resonance imaging (dMRI) analysis techniques have improved our understanding of fibre-specific variations in white matter microstructure. Increasingly, studies are adopting multi-shell dMRI acquisitions to improve the robustness of dMRI-based inferences. However, the impact of b-value choice on the estimation of dMRI measures such as apparent fibre density (AFD) derived from spherical deconvolution is not known. Here, we investigate the impact of b-value sampling scheme on estimates of AFD. First, we performed simulations to assess the correspondence between AFD and simulated intra-axonal signal fraction across multiple b-value sampling schemes. We then studied the impact of sampling scheme on the relationship between AFD and age in a developmental population (n=78) aged 8-18 (mean=12.4, SD=2.9 years) using hierarchical clustering and whole brain fixel-based analyses. Multi-shell dMRI data were collected at 3.0T using ultra-strong gradients (300 mT/m), using 6 diffusion-weighted shells ranging from 0 – 6000 s/mm2. Simulations revealed that the correspondence between estimated AFD and simulated intra-axonal signal fraction was improved with high b-value shells due to increased suppression of the extra-axonal signal. These results were supported by in vivo data, as sensitivity to developmental age-relationships was improved with increasing b-value (b=6000 s/mm2, median R2 = .34; b=4000 s/mm2, median R2 = .29; b=2400 s/mm2, median R2 = .21; b=1200 s/mm2, median R2 = .17) in a tract-specific fashion. Overall, estimates of AFD and age-related microstructural development were better characterised at high diffusion-weightings due to improved correspondence with intra-axonal properties.

Item Type: Article
Date Type: Published Online
Status: In Press
Schools: Psychology
Cardiff University Brain Research Imaging Centre (CUBRIC)
Publisher: Wiley
ISSN: 1065-9471
Funders: Wellcome Trust
Date of First Compliant Deposit: 18 February 2020
Date of Acceptance: 13 February 2020
Last Modified: 31 Mar 2020 17:13

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