FUNCTIONAL NMR IMAGING USING FAST SPIN-ECHO AT 1.5 T

Functional NMR imaging of the brains response to a simple visual task has been performed using a fast spin echo (FSE) imaging sequence at 1. 5 T. The FSE method refocuses dephasing effects induced by large-scale susceptibility variations, and permits imaging in regions where macro scopic field gradients produce artifacts in gradient echo sequences. A t 1.5 T, gradient echo (GRE) sequences are sensitive to the effects of brain activation, but relatively large effects may arise from large v essels and veins, and these may dominate the effects produced by small er capillaries. Spin echo (SE) sequences with short echo times are rel atively immune to large vessel effects and emphasize the susceptibilit y induced losses from small capillaries, but the imaging time for thes e sequences is prohibitive for most functional brain studies. We demon strate that multislice functional brain imaging may be performed in re asonable imaging times at 1.5 T using an FSE imaging sequence. The FSE sequence with short echo spacing but long effective TE is sensitive t o susceptibility induced effects at the capillary level. It is not sen sitive to larger scale inhomogeneities such as those found in veins an d can be used in regions near tissue/air boundaries. Results are shown comparing conventional GRE and FSE images in activation of the visual cortex and these are supported by theoretical calculations and phanto m experiments.