Optimization of quasi-diffusion magnetic resonance imaging for quantitative accuracy and time-efficient acquisition
Catherine A. Spilling, Franklyn A. Howe, Thomas R. Barrick
Abstract
Purpose
Quasi-diffusion MRI (QDI) is a novel quantitative technique based on the continuous time random walk model of diffusion dynamics. QDI provides estimates of the diffusion coefficient, D1,2 in mm2s-1 and a fractional exponent, α, defining the non-Gaussianity of the diffusion signal decay. Here, the b-value selection for rapid clinical acquisition of QDI tensor imaging (QDTI) data is optimized.
Methods
Clinically appropriate QDTI acquisitions were optimized in healthy volunteers with respect to a multi-b-value reference (MbR) dataset comprising 29 diffusion-sensitized images arrayed between b=0 and 5000 s mm−2. The effects of varying maximum b-value (bmax ), number of b-value shells, and the effects of Rician noise were investigated.
Results
QDTI measures showed bmax dependence, most significantly for α in white matter, which monotonically decreased with higher bmax leading to improved tissue contrast. Optimized 2 b-value shell acquisitions showed small systematic differences in QDTI measures relative to MbR values, with overestimation of D1,2 and underestimation of α in white matter, and overestimation of D1,2 and α anisotropies in gray and white matter. Additional shells improved the accuracy, precision, and reliability of QDTI estimates with 3 and 4 shells at bmax=5000 s mm−2, and 4 b-value shells at bmax=3960 s mm−2, providing minimal bias in D1,2 compared to the MbR.
Conclusion
A highly detailed optimization of non-Gaussian dMRI for in vivo brain imaging was performed. QDI provided robust parameterization of non-Gaussian diffusion signal decay in clinically feasible imaging times with high reliability, accuracy, and precision of QDTI measures.