Balanced Binomial-Pulse Steady-State Free Precession (BP-SSFP) for fast, inherently fat suppressed, non-contrast enhanced angiography

Introduction: In balanced SSFP for angiography, blood and muscle are inherently differentiated via the T2/T1 contrast. Fat signal suppression, however, relies on contrast preparation or chemical shift manipulation. The disadvantages of the former include regular interruption of the steady state MR signal, and fat signal regrowth during data acquisition. The latter can be divided into multiple versus single echo methods. Multiple echoes, while offering superior fat and water signal separation by iterative estimation, may significantly increase scan time [1]. A conventional single echo strategy places a 1/TR null band at the chemical shift frequency of fat and is inflexible in terms of TR and stopband width. A more flexible alternative, called Water-Excitation SSFP, was introduced by Lin et al. [2]. This technique leaves the fat magnetization on the longitudinal axis after each steady state excitation by using a binomial spectral-spatial RF pulse [3]. While the fat signal suppression is independent of the choice of TR, there is a minimum TR related to the fat/water chemical shift, which can be longer than desired especially for the 1-2-1 binomial pulse at 1.5T. In this work, we present a generalized design of the 1-2-1 binomial pulse SSFP sequence, and the trade-off between TR reduction, water SNR, and water/fat CNR. We apply our method to obtain fast, non-contrast enhanced MR angiograms of the popliteal artery. Design: The behaviour of the generalized 1-2-1 binomial pulse is explained in Figure 1.