A comparison of fast spin echo and gradient field echo sequences.

Abstract

Optimal angle, fast repeat time, gradient field echo imaging techniques such as FISP (Fast Imaging with Steady Precession) and FLASH (Fast Low Angle Shot) often fail to discriminate disease from healthy tissue for two main reasons. First, T1 and T2 of the affected tissue may increase such that the ratio of T1 to T2 remains nearly unchanged, hence there is no contrast change with FISP. Second, T2 weighted gradient field echo images suffer severely from T2* signal and resolution loss leading to a reduction in C/N. Although FLASH imaging with two separate angles can, in principle, extract the longer T1 tumors, contrast is often not good. To overcome the inhomogeneity and contrast problems, we have implemented a FAst optimal angle spin-echo sequence with a short TE(FATE). For the first echo, FATE has the same contrast properties as FLASH with a slight decrease in signal intensity. The advantage is that the intensity of the signal does not suffer from T2* signal decay, hence improved contrast and disease detection via T2 weighted FATE images is possible. Contrast-to-noise in lesion detection is also considered for CE FAST (Contrast Enhanced Fast), a T2-weighted version of FISP, and HYBRID.