Consistent fat suppression with compensated spectral-spatial pulses

Reliable fat suppression is especially important with fast imaging techniques such as echo-planar (EPI), spiral, and fast spin-echo (FSE) T₂-weighted imaging. Spectral-spatial excitation has a number of advantages over spectrally selective presaturation techniques, including better resilience to B₀ and B₁, inhomogeneity. In this paper, a FSE sequence using a spectral-spatial excitation pulse for superior fat suppression is presented. Previous problems maintaining the CPMG condition are solved using simple methods to accurately program radio-frequency (RF) phase. Next an analysis shows how B₀ eddy currents can reduce fat suppression effectiveness for spectral-spatial pulses designed for conventional gradient systems. Three methods to compensate for the degradation are provided. Both the causes of the degradation and the compensation techniques apply equally to gradient-recalled applications using these pulses. These problems do not apply to pulses designed for high-speed gradient systems. The spectral-spatial FSE sequence delivers clinically lower fat signal with better uniformity than spectrally selective pre-saturation techniques.