Broadband RF Pulses with Polynomial-Phase Response

Introduction Broad-bandwidth radio-frequency (RF) pulses are important for various kinds of MR experiments. The achievable RF field strength B1 of the transmitting system is limited on whole-body scanners, leading to small bandwidths of regular amplitude-modulated RF pulses. In order to increase the bandwidth, pulses with inherently reduced maximum B1 amplitude (B1max) are necessary. Overlaying a quadratic phase in the frequency domain leads to frequencymodulated pulses, which are near optimal in terms of minimising B1max [1]. Some further reduction of B1max has been achieved by complementing a quadratic phase with a single higher-order phase term [2]. In this work, we generalise this concept towards combining multiple higher-order terms with a direct search algorithm, hence providing considerably improved bandwidth and selectivity.