Phase stabilization with motion compensated diffusion weighted imaging

Diffusion encoding gradient waveforms can impart intra-voxel and inter-voxel dephasing owing to bulk motion, limiting achievable signal-to-noise and complicating multishot acquisitions. In this study, we characterize improvements in phase consistency via gradient moment nulling of diffusion encoding waveforms.

Healthy volunteers received neuro ( $N=10$ ) and cardiac ( $N=10$ ) MRI. Three gradient moment nulling levels were evaluated: compensation for position ( $M_0$ ), position + velocity ( $M_1$ ), and position + velocity + acceleration ( $M_1+M_2$ ). Three experiments were completed: (Exp-1) Fixed Trigger Delay Neuro DWI; (Exp-2) Mixed Trigger Delay Neuro DWI; and (Exp-3) Fixed Trigger Delay Cardiac DWI. Significant differences ( ) of the temporal phase SD between repeated acquisitions and the spatial phase gradient across a given image were assessed.

$M_0$ moment nulling was a reference for all measures. In Exp-1, temporal phase SD for $G_z$ diffusion encoding was significantly reduced with $M_1$ (35% of t-tests) and $M_1+M_2$ (68% of t-tests). The spatial phase gradient was reduced in 23% of t-tests for $M_1$ and 2% of cases for $M_1+M_2$ . In Exp-2, temporal phase SD significantly decreased with $M_1+M_2$ gradient moment nulling only for $G_z$ (83% of t-tests), but spatial phase gradient significantly decreased with only $M_1$ (50% of t-tests). In Exp-3, $M_1+M_2$ gradient moment nulling significantly reduced temporal phase SD and spatial phase gradients (100% of t-tests), resulting in less signal attenuation and more accurate ADCs.

We characterized gradient moment nulling phase consistency for DWI. Using M₁ for neuroimaging and M₁ + M₂ for cardiac imaging minimized temporal phase SDs and spatial phase gradients.