Computing and visualising intra-voxel orientation-specific relaxation–diffusion features in the human brain

Research output: Contribution to journalArticle

Abstract

Diffusion MRI techniques are used widely to study the characteristics of the human brain connectome in vivo. However, to resolve and characterise white matter (WM) fibres in heterogeneous MRI voxels remains a challenging problem typically approached with signal models that rely on prior information and constraints. We have recently introduced a 5D relaxation–diffusion correlation framework wherein multidimensional diffusion encoding strategies are used to acquire data at multiple echo-times to increase the amount of information encoded into the signal and ease the constraints needed for signal inversion. Nonparametric Monte Carlo inversion of the resulting datasets yields 5D relaxation–diffusion distributions where contributions from different sub-voxel tissue environments are separated with minimal assumptions on their microscopic properties. Here, we build on the 5D correlation approach to derive fibre-specific metrics that can be mapped throughout the imaged brain volume. Distribution components ascribed to fibrous tissues are resolved, and subsequently mapped to a dense mesh of overlapping orientation bins to define a smooth orientation distribution function (ODF). Moreover, relaxation and diffusion measures are correlated to each independent ODF coordinate, thereby allowing the estimation of orientation-specific relaxation rates and diffusivities. The proposed method is tested on a healthy volunteer, where the estimated ODFs were observed to capture major WM tracts, resolve fibre crossings, and, more importantly, inform on the relaxation and diffusion features along with distinct fibre bundles. If combined with fibre-tracking algorithms, the methodology presented in this work has potential for increasing the depth of characterisation of microstructural properties along individual WM pathways.

Details

Authors
Organisations
External organisations
  • Cardiff University
  • University Medical Center Utrecht
  • Harvard Medical School
  • Brigham and Women's Hospital, Boston
  • Australian Catholic University
  • Random Walk Imaging AB
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Radiology, Nuclear Medicine and Medical Imaging
  • Medical Image Processing

Keywords

  • diffusion MRI, fibre ODF, fibre-specific metrics, partial volume effects, tensor-valued diffusion encoding, white matter
Original languageEnglish
Pages (from-to)310-328
JournalHuman Brain Mapping
Volume42
Issue number2
Early online date2020
Publication statusPublished - 2021
Publication categoryResearch
Peer-reviewedYes