Franciszek Hennel

Purpose To evaluate the utility of up to second‐order motion‐compensated diffusion encoding in multi‐shot human brain acquisitions. Methods Experiments were performed with high‐performance gradients using three forms of diffusion encoding motion‐compensated through different orders: conventional zeroth‐order–compensated pulsed gradients (PG), first‐order–compensated gradients (MC1), and second‐order–compensated gradients (MC2). Single‐shot acquisitions were conducted to correlate the order of motion compensation with resultant phase variability. Then, multi‐shot acquisitions were performed at varying interleaving factors. Multi‐shot images were reconstructed using three levels of shot‐to‐shot phase correction: no correction, channel‐wise phase correction based on FID navigation, and correction based on explicit phase mapping (MUSE). Results In single‐shot acquisitions, MC2 diffusion encoding most effectively suppressed phase variability and sensitivity to brain pulsation, yielding residual variations of about 10° and of low spatial order. Consequently, multi‐shot MC2 images were largely satisfactory without phase correction and consistently improved with the navigator correction, which yielded repeatable high‐quality images; contrarily, PG and MC1 images were inadequately corrected using the navigator approach. With respect to MUSE reconstructions, the MC2 navigator‐corrected images were in close agreement for a standard interleaving factor and considerably more reliable for higher interleaving factors, for which MUSE images were corrupted. Finally, owing to the advanced gradient hardware, the relative SNR penalty of motion‐compensated diffusion sensitization was substantially more tolerable than that faced previously. Conclusion Second‐order motion‐compensated diffusion encoding mitigates and simplifies shot‐to‐shot phase variability in the human brain, rendering the multi‐shot acquisition strategy an effective means to circumvent limitations of retrospective phase correction methods.