Optimization of diffusion spectrum imaging and q-ball imaging on clinical MRI system.

Mapping complex crossing fibers using diffusion MRI techniques requires adequate angular precision and accuracy. Beyond diffusion tensor imaging (DTI), high angular resolution sampling schemes such as diffusion spectrum imaging (DSI) and q-ball imaging (QBI) were proposed to resolve crossing fibers. These schemes require hundreds of data approximately five to ten times more than DTI, offsetting their clinical feasibility. To facilitate its clinical application, optimum values of highest diffusion sensitivity (bmax) must be investigated under the constraint of scan time and gradient performance. In this study, simulation of human data sets and a following verification experiment were performed to investigate the optimum bmax of DSI and QBI. Four sampling schemes, two with high sampling number, i.e., DSI515 and QBI493, and two with low sampling number, i.e., DSI203 and QBI253, were compared. Deviation angle and angular dispersion were used to evaluate the precision and accuracy among different bmax of each scheme. The results indicated that the optimum bmax was a trade-off between SNR and angular resolution. At their own optimum bmax, the reduced sampling schemes yielded angular precision and accuracy comparable to the high sampling schemes. On our current 3 T system, the optimum bmax (s/mm2) were 6500 for DSI515, 4000 for DSI203, 3000 for QBI493 and 2500 for QBI253. DSI was incrementally more accurate than QBI, but required a greater demand for gradient performance. In conclusion, our systematic study of optimum bmax in different sampling schemes and the consideration derived wherein could be helpful to determine optimum sampling schemes in other MRI systems.