The dependence of functional magnetic resonance imaging (MRI) contrast on the gradient echo time TE in T2*-weighted blood oxygenation level-dependent (BOLD) fast low-angle shot (FLASH) imaging has been studied at 7 T for electrical forepaw stimulation in alpha-chloralose anesthetized rats. The observed variation of both the activation signal intensity and spatial pattern with echo time TE, resulting from the regional heterogeneity of T2*, was assessed by the calculation of quantitative T2* and quantitative STE = 0 maps, the latter representing the back-extrapolated signal intensity for TE = 0. The subsequently determined T2* and STE = 0 activation maps allowed a pixelwise separation of true BOLD from inflow contributions to forepaw stimulation-induced signal change in the somatosensory cortex of rat brain. For functional activation experiments performed with one single echo time the prior measurement of a quantitative T2* map is recommended as minimum further information to judge the intensity and the regional pattern of the resulting activation maps.
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