Single-shot T2(*) measurement to establish optimum echo time for fMRI: studies of the visual, motor, and auditory cortices at 3.0 T.

The signal change in fMRI is dependent on the echo time and the rate of decay of transverse magnetization. The latter factor may vary across regions of the brain as a result of variations in field homogeneity. Previous measurements of the signal change with echo time have generally employed relatively slow multi-echo techniques, which may be sensitive to movement and habituation effects. Here a fast T(2)(*) measurement technique, involving the generation of six low-resolution echo planar images from a single FID, is described, and its use in the evaluation of the optimum echo time for visual, motor, and auditory fMRI experiments at 3.0 T is outlined.