Single shot fast spin echo diffusion imaging with correction for non-linear phase errors using tailored RF pulses

The use of tailored RF excitation pulses for prospective correction of non-linear motion-induced phase patterns is shown to enable diffusion-weighted (DW) fast spin echo (FSE) imaging in vivo. Echo-planar imaging (EPI) remains the most used sequence for DW imaging. Despite being highly sensitive to field inhomogeneities, EPI is robust to motion-induced phase shifts. FSE sequences are much less sensitive to field inhomogeneities, but require precise control of the transverse magnetization phase, which is hard to achieve with DW. Real time measurements and correction of phase ramps due to rigid-body motion had been proposed, but performance remained unsatisfactory because of non-linear phase patterns related to pulsatile motion.

Reproducible non-linear phase components are calibrated using 2D-EPI navigators and tailored RF excitation pulses designed. Real time correction of rigid-body motion was not yet implemented.

Phase correction was confirmed with full signal DW-FSE images obtained on co-operative subjects. Full diffusion tensor acquisitions were obtained and color-coded maps displaying principal fiber directionality calculated. Results were consistent with corresponding EPI acquisitions except for absence of spatial distortions.

Combining the proposed method with real time compensation of rigid-body motion has the potential to allow high quality, distortion free diffusion imaging throughout the brain.