Room: AAPM ePoster Library
Purpose: To develop a clinically viable MRI protocol to image microscopic fractional anisotropy (µFA), a measure of water diffusion anisotropy that is insensitive to crossing neuron fiber errors. Anisotropy is high in white matter (WM) brain regions due to the coherent shape of neurons but is likely reduced in patients with neurodegenerative diseases; thus, µFA may be a robust surrogate measure of neuron integrity in WM.
Methods: A simple method to approximate µFA using linear (unidirectional) and isotropic (omnidirectional) diffusion-weighted MRI (dMRI) acquisitions was developed. To maximize µFA image quality, the signal-to-noise ratio (SNR) was derived using standard error propagation. Data were acquired from 4 healthy volunteers (2 male, 2 female) at a field strength of 3T over b-values from 0 to 3500 s/mm² in increments of 500 s/mm² to determine the optimal ratio of linear to isotropic acquisitions and b-value. Note that the b-value is a parameter that sets the magnitude of diffusion weighting. A clinically-viable MRI protocol was developed using the optimal parameters and tested on 1 healthy volunteer.
Results: The optimal b-value and ratio of linear to isotropic acquisitions were found to be 2000 s/mm² and 1:1.6, respectively. Images from the healthy volunteer were high quality and showed the expected contrast: µFA was highest in WM regions, reduced in grey matter, and lowest in cerebrospinal fluid. The scan time of the optimized protocol was under 4 minutes total.
Conclusion: This work demonstrates the potential for clinical implementation of µFA imaging as contrast and SNR were high at 3T despite the short scan time. We expect µFA to negatively correlate with neuron damage and provide an indication of WM integrity in patients with neurodegenerative diseases. The optimized protocol will be used in future studies to investigate neuronal integrity in patients with multiple sclerosis.
Funding Support, Disclosures, and Conflict of Interest: Canada First Research Excellence Fund to BrainsCAN, NSERC, Ontario Graduate Scholarships, Queen Elizabeth II Graduate Scholarship in Science and Technology