DIM: A diffusion instability measure for MRI quality assurance.

The aim of the presented work is to develop a diffusion instability measure (DIM) that can be used in quality assurance. 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. 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/mm2 on the Philips Achieva and for b-value = 500 s/mm2 on the Siemens Cima.X without concurrent field monitoring, respectively. 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.