In vivo measurement of inter-hemispheric axon diameters on a clinical scanner using multiple pulsed-field gradient (mPFG) diffusion MRI

Thursday, October 11, 2012 — Poster Session III
10:00 a.m. – Noon	Natcher Conference Center, Building 45	NICHD	IMAG-2

* FARE Award Winner

Authors

• A.V. Avram
• E. Ozarslan
• J.E. Sarlls
• M.E. Komlosh
• P.J. Basser

Abstract

Quantifying microanatomical features of neurons, e.g. axon diameters, provides valuable neuropathological and functional information. Multiple pulsed-field gradient (mPFG) diffusion MR has been proposed as a non-invasive full-brain alternative to biopsy-driven histology. This technique exclusively characterizes diffusion of water trapped in microscopic compartments, providing measures of average cell geometry. Nevertheless, its translation to bedside requires efficient use of limited gradient strength and a suitable theoretical framework. We implemented novel mPFG MRI pulse sequences on a standard clinical scanner. Following validation in calibrated phantoms, we acquired sagittal mPFG images through the medial corpus callosum (CC) in healthy volunteers. CC fiber orientations, measured using high-resolution diffusion tensor imaging (DTI), were incorporated in our numerical model for myelinated axons, approximated as parallel impermeable cylinders. Average axon diameters were fit using our recently-proposed mathematical framework. Inter-hemispheric axon diameter maps provide information complementary to DTI, revealing an anterior-posterior CC topography which is not detectable with DTI-derived metrics. Average axon diameters measured in fiber pathways connecting specialized brain regions are in remarkable topographical agreement with ex vivo studies. Our results establish the clinical feasibility of acquiring mPFG MRIs in vivo. This technique could have a transformative impact on our ability to diagnose and investigate numerous neurodegenerative pathologies.

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