A novel diffusion MRI acquisition scheme for optimal orientation sampling and susceptibility distortion correction at 7T

Motivation: 7T provides higher SNR compared to clinical field strengths, but susceptibility-induced distortion compromises diffusion imaging at 7T. Current methods to accurately correct distortion require doubling of scan time. Goal(s): Develop an efficient acquisition scheme to enable distortion correction of multi-direction diffusion images without increased scan time. Approach: Two ‘half-density’ acquisitions with opposing phase-encoding directions are collected, such that their gradient orientations uniformly sub-sample the sphere in a complementary manner. Spherical harmonics are used to interpolate image pairs for distortion correction. Results: The proposed method provides distortion correction comparable to the full blip-up/blip-down approach, in half the acquisition time, while retaining the orientation density. Impact: As the clinical benefits of 7T become established, it is crucial for all sequence types to be available for use. The methods proposed here enable advanced distortion-corrected diffusion imaging to be routinely and efficiently included in 7T imaging protocols.