RASEE: a rapid spin-echo pulse sequence

Most fast-imaging sequences use gradient echoes and a low flip-angle excitation. The low flip angle is used because it gives increased signal when TR less than T1. However, spin-echo sequences are less productive of certain artifacts, among them flow and magnetic susceptibility artifacts. We present a modification of the spin-echo pulse sequence designed to optimize the signal-to-noise ratio for repetition times (TR) less than 100 msec while preserving good image quality. Our implementation performs a 128 x 128 image in under 7 sec (TR = 50 msec) and has been used to follow the dynamics of Gd-DTPA in the rat kidneys.