Motion-compensated diffusion encoding gradients for segmented thick-slab 3D magnetic resonance diffusion-weighted imaging of the brain.

backgroundRoutine clinical magnetic resonance diffusion-weighted imaging (DWI) is generally performed with 2D echo planar sequences. A single thick-slab 3D approach could offer higher signal-to-noise ratio and better slice resolution. This has not been adopted due to the difficulty to avoid motion-induced phase error that interfere with multi-shot spatial encoding. PURPOSE: To introduce a new approach for 3D brain DWI: rather than relying on navigator echoes for phase correction, moment-nulled diffusion encoding gradients are used to minimize phase variations at the source.

methodsA standard 2D echo planar imaging sequence was modified to incorporate moment-nulled diffusion encoding gradients and a second phase encoding gradient for spatial multi-shot encoding along the slice select direction. The single thick-slab 3D diffusion-weighted imaging sequence was evaluated with brain scans in healthy volunteers on a 3 Tesla scanner.

resultsIncorporation of both first and second order moment nulling achieved substantial, albeit not comprehensive, reduction of motion-related ghosting artifacts. Without such motion compensation or with first order moment nulling only, motion-related artifacts were consistently more severe. Even though the approach comes with a penalty in echo time-at a diffusion weighting of 1000 s/mm

conclusionsThis proof-of-concept shows that first and second order moment nulling may be a viable avenue for enabling 3D diffusion imaging. At higher slice numbers the SNR