Redesigning Parallel-transmit Pulses in Runtime to Correct for the Effect of Patient Motion on B1+-maps for Ultrahigh-field MRI.

Motivation: Low-field motion-tracking methods are insufficient at ultrahigh-field as motion also affects flip-angle . Goal(s): Our goal was to develop a method that can redesign pulses for ultrahigh-field MRI within 1 second. Approach: We implemented a method to rapidly recalculate the post-motion basis-functions needed for pulse design and complemented it with dictionary matching to reduce pulse computation times a of small-tip-angle multi-spoke multi-slice parallel-transmit pulse design method. Results: With basis-functions recalculated in 0.13 seconds/slice and pulses reoptimized in 0.18 seconds/slice, multi-slice multi-spoke parallel-transmit pulses can be redesigned in runtime using the proposed method. Redesigned pulses significantly reduce motion-induced error, yielding consistent excitation with pre-motion excitation. Impact: A pulse design method is developed that can redesign practical parallel-transmit pulses in under a second. It can correct for motion-related flip angle distortions at ultrahigh-field and will help facilitate scanning of patients who cannot remain still (e.g., paediatric, dementia).