Impact of signal-to-noise on functional MRI

Functional magnetic resonance imaging (fMRI) has recently been adopted as a n investigational toot in the field of neuroscience. The signal changes ind uced by brain activations are small (similar to1-2%) at 1.5T. Therefore, th e signal-to-noise ratio (SNR) of the time series used to calculate the func tional maps is critical. In this study, the minimum SNR required to detect an expected MR signal change is determined using computer simulations for t ypical fMRI experimental designs. These SNR results are independent of manu facturer, site environment, field strength, coil type, or type of cognitive task used. Sensitivity maps depicting the minimum detectable signal change can be constructed. These sensitivity maps can be used as a mask of the ac tivation map to help remove false positive activations as well as identify regions of the brain where it is not possible to confidently reject the nul l hypothesis due to a low SNR, (C) 2000 Wiley-Liss, Inc.