Transient RF Spoiling for 3D Look-Locker Acquisitions

Introduction: In spoiled gradient-recalled echo pulse sequences, the standard RF spoiling scheme uses an ever increasing phase angle of the RF pulse and crusher gradients to spoil the transverse magnetization [1]: φn=φn-1+nφseed. Optimal ideal seed values have been arrived at either from experimentation or simulation for a particular set of imaging parameters or cost function [2,3]. The parameter space has been investigated for both steady state and transient cases, and optimum values of 117 and 84 [2], respectively, were found based on minimizing the sum of the squared differences between ideally spoiled and RF-spoiled pulse trains for different values of φseed. These values, and in particular the transient case (84) value, were optimized for fairly short T1 values and fairly long TR times, and therefore may not be ideal for fast sequences such as the accelerated 3D Look-Locker (3DLL) sequence [4], where TR values can be very short, or for very high field strengths, where T1 values can be very long. Here, we investigate optimal RF spoiling for the transient magnetization case over a broad range of parameters that includes very short-TR, very long-T1 regime.