Spin-echo versus gradient-echo fMRI with short echo times

Blood-oxygen level dependent signal changes in the visual cortex were inves tigated as a function of echo time with spin-echo and gradient-echo EPI at 1.5 T and 3 T. The linear relationship between the fractional signal change and the echo time was apparent in all cases. Relaxation rate changes deter mined from the slope of this linear relation agree with published values, i ntercept values extrapolated to an echo time of zero, however, were 0.66% t o 1.0% with spin-echo EPI, and 0.11% to 0.35% with gradient-echo EPI. Spin- echo and gradient-echo EPI can therefore yield similar signal changes at su fficiently short echo times. (C) 2001 Elsevier Science Inc. All rights rese rved.