Diffusion imaging of the brain at 3T and 7T: a comparison of metrics and reproducibility using a matched acquisition scheme

Motivation: The SNR benefits of diffusion weighted imaging (DWI) at 7T are unclear. Previous studies comparing across field strengths involved varying scanner hardware and acquisition protocols. Goal(s): To characterise the spatial SNR differences of brain DWI at 3T and 7T. Approach: Participants were scanned back-to-back on 3T and 7T scanners with well-matched hardware and acquisition protocols. SNR and DTI metrics were compared between field strengths in white and grey matter regions. Results: SNR is higher at 7T in WM but comparable or lower in GM. DTI metrics also vary between field strengths, and fitting error is lower at 7T. Impact: This study indicates that there is tangible SNR benefit to studying white matter using diffusion-weighted imaging at 7T in humans. However, we caution researchers when studying grey matter structures, especially in the pallidum and close to the air-tissue interfaces.