Gradient echo time dependence and quantitative parameter maps for somatosensory activation in rats at 7 T

The dependence of functional magnetic resonance imaging (MRI) contrast on t he gradient echo time TE in T-2*-weighted blood oxygenation level-dependent (BOLD) fast low-angle shot (FLASH) imaging has been studied at 7 T for ele ctrical forepaw stimulation in alpha-chloralose anesthetized rats. The obse rved variation of both the activation signal intensity and spatial pattern with echo time TE, resulting from the regional heterogeneity of T-2*, was a ssessed by the calculation of quantitative T-2* and quantitative S-TE = 0 m aps, the latter representing the back-extrapolated signal intensity for TE = 0, The subsequently determined T-2* and S-TE = 0 activation maps allowed a pixelwise separation of true BOLD from inflow contributions to forepaw st imulation-induced signal change in the somatosensory cortex of rat brain. F or functional activation experiments performed with one single echo time th e prior measurement of a quantitative T2* map is recommended as minimum fur ther information to judge the intensity and the regional pattern of the res ulting activation maps. Magn Reson Med 42:118-126, 1999. (C) 1999 Wiley-Lis s, Inc.