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

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Abstract
The dependence of functional magnetic resonance imaging (MRI) contrast on the 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 electrical forepaw stimulation in α‐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 T*2, was assessed by the calculation of quantitative T*2 and quantitative STE=0 maps, the latter representing the back‐extrapolated signal intensity for TE = 0. The subsequently determined T*2 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 T*2 map is recommended as minimum further information to judge the intensity and the regional pattern of the resulting activation maps. Magn Reson Med 42:118–126, 1999.