3D diffusion MRI at 7T with Universal Pulses for improved image uniformity

Motivation: 2D multi-slice diffusion-weighted MRI (dMRI) suffers from severe signal non-uniformity caused by B1+ inhomogeneity at ultra-high fields. Goal(s): To design a 3D dMRI sequence with Universal parallel transmission radio-frequency Pulses (UPs) to improve image uniformity across the brain at 7T without lengthening workflow. Approach: We propose a 3D spin-echo sequence with an inversion pulse before excitation to enhance SNR. 3D UPs were designed for inversion, excitation, and refocussing and implemented in a sequence with a stack-of-EPI readout. Results: Diffusion-weighted image uniformity was significantly improved using the 3D sequence with UPs in comparison to 2D dMRI at 7T. Impact: We propose a 3D dMRI sequence that includes UPs to improve image uniformity across the brain at 7T, including the temporal lobes and cerebellum. This improvement in image quality is critical for precision mapping of whole brain structural connectivity.