DIM: A diffusion instability measure for MRI quality assurance.

Purpose: The aim of the presented work is to develop a diffusion instability measure (DIM) that can be used in quality assurance.

Methods: Single-shot, spin-echo, echo-planar imaging HARDI diffusion data sets were collected on a spherical silicone oil phantom with 64 different diffusion directions on a 3T Philips Achieva and a 3T Siemens Cima.X scanner with similar acquisition protocols. A few data sets on the Philips Achieva included concurrent magnetic field monitoring. A correlation coefficient matrix among the diffusion directions for each data set was calculated, and subsequently, one minus its eigenratio was defined as the DIM.

Results: The DIM values ranged between about 5000 and 280 000 ppm across the data sets. The worst and best image quality-and hence the highest and lowest DIM values-were observed for b-value = 4000 s/mm on the Philips Achieva and for b-value = 500 s/mm on the Siemens Cima.X without concurrent field monitoring, respectively.

Conclusion: DIM is a sensitive tool for evaluating image quality in HARDI scans on a quantitative basis. It is simple to implement without the need for hardware or software modifications.