Estimating axon radius using diffusion-relaxation MRI: calibrating a surface-based relaxation model with histology

Muhamed Barakovic, Marco Pizzolato, Chantal M.W. Tax, Umesh Rudrapatna, Stefano Magon, Tim B. Dyrby, Cristina Granziera, Jean Philippe Thiran, Derek K. Jones, Erick J. Canales-Rodríguez*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

26 Downloads (Pure)

Abstract

Axon radius is a potential biomarker for brain diseases and a crucial tissue microstructure parameter that determines the speed of action potentials. Diffusion MRI (dMRI) allows non-invasive estimation of axon radius, but accurately estimating the radius of axons in the human brain is challenging. Most axons in the brain have a radius below one micrometer, which falls below the sensitivity limit of dMRI signals even when using the most advanced human MRI scanners. Therefore, new MRI methods that are sensitive to small axon radii are needed. In this proof-of-concept investigation, we examine whether a surface-based axonal relaxation process could mediate a relationship between intra-axonal T2 and T1 times and inner axon radius, as measured using postmortem histology. A unique in vivo human diffusion-T1-T2 relaxation dataset was acquired on a 3T MRI scanner with ultra-strong diffusion gradients, using a strong diffusion-weighting (i.e., b = 6,000 s/mm2) and multiple inversion and echo times. A second reduced diffusion-T2 dataset was collected at various echo times to evaluate the model further. The intra-axonal relaxation times were estimated by fitting a diffusion-relaxation model to the orientation-averaged spherical mean signals. Our analysis revealed that the proposed surface-based relaxation model effectively explains the relationship between the estimated relaxation times and the histological axon radius measured in various corpus callosum regions. Using these histological values, we developed a novel calibration approach to predict axon radius in other areas of the corpus callosum. Notably, the predicted radii and those determined from histological measurements were in close agreement.

Original languageEnglish
Article number1209521
JournalFrontiers in Neuroscience
Volume17
DOIs
Publication statusPublished - 11 Aug 2023

Keywords

  • axon radius
  • brain
  • diffusion MRI
  • histology
  • T relaxation

Fingerprint

Dive into the research topics of 'Estimating axon radius using diffusion-relaxation MRI: calibrating a surface-based relaxation model with histology'. Together they form a unique fingerprint.

Cite this