High-angular-resolution diffusion-weighted imaging (HARDI) MRI acquisitions have become common for use with
higher order models of diffusion. Despite successes in resolving complex fiber configurations and probing
microstructural properties of brain tissue, there is no common consensus on the optimal b-value and number of
diffusion directions to use for these HARDI methods. While this question has been addressed by analysis of the
diffusion-weighted signal directly, it is unclear how this translates to the information and metrics derived from the
HARDI models themselves. Using a high angular resolution data set acquired at a range of b-values, and repeated 11
times on a single subject, we study how the b-value and number of diffusion directions impacts the reproducibility
and precision of metrics derived from Q-ball imaging, a popular HARDI technique. We find that Q-ball metrics
associated with tissue microstructure and white matter fiber orientation are sensitive to both the number of diffusion
directions and the spherical harmonic representation of the Q-ball, and often are biased when under sampled. These
results can advise researchers on appropriate acquisition and processing schemes, particularly when it comes to
optimizing the number of diffusion directions needed for metrics derived from Q-ball imaging.
Kurt G. Schilling, Vishwesh Nath, Justin Blaber, Robert L. Harrigan, Zhaohua Ding, Adam W. Anderson, and Bennett A. Landman, "Effects of b-value and number of gradient directions on diffusion MRI measures obtained with Q-ball imaging," Proc. SPIE 10133, Medical Imaging 2017: Image Processing, 101330N (Presented at SPIE Medical Imaging: February 13, 2017; Published: 24 February 2017); https://doi.org/10.1117/12.2254545.
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