Broadband RF Pulses with Polynomial-Phase Response
Schulte R, Boesiger P, Pruessmann K, Tsao J
University and ETH Zurich
The bandwidth of common linear-phase RF pulses is tightly limited by the maximal feasible B1 amplitude. For reducing B1 requirements and hence increasing the achievable bandwidth, targeting a quadratic-phase response can be argued to be nearly optimal. Nevertheless, as shown in this work significant further B1 reduction can be accomplished with higher-order polynomial corrections to the quadratic phase. A non-linear optimisation scheme is introduced, using a direct search algorithm for approximating the optimal polynomial phase adjustment. For fixed pulse duration and B1 limit, this approach enables increases in bandwidth and selectivity by factors of two and more.