Design of pTx pulses with free RF and gradient waveforms for cardiac MRI at 7T: Initial results and comparison to kT-point pulses

Motivation: Parallel transmission (pTx) pulses with fixed gradient trajectory such as kT-points have successfully demonstrated to benefit cardiac imaging at 7T. However, it is possible to optimize pTx pulses without restrictions regarding RF and gradient waveforms. Goal(s): Our aim was to optimize first pTx pulses with free RF and gradient trajectory for cardiac imaging. Approach: We designed tailored free pulses for 35 heart subjects and compared them in terms of flip angle (FA) homogeneity and applied energy dose to kT-point pulses. Results: Comparable performance in FA homogeneity was obtained for both pulse types, but the free pulses additionally achieved a reduction of SED. Impact: Generating homogeneous excitation while complying with RF power deposition regulations is a challenge for cardiac imaging at 7T. Designing pTx pulses with free RF and gradient waveforms allows for reduced SED and similar homogeneity compared to kT-point pulses.