  The receive field of MRI imparts an image contrast which is spatially fixed
relative to the receive coil. If motion correction is used to correct subject
motion occurring during an EPI time series then the receiver contrast will
effectively move relative to the subject and produce temporal modulations in
the image amplitude. This effect, which we will call the RFC-MoCo effect, may
have consequences in the analysis and interpretation of fMRI results. There are
many potential causes of motion-related noise and systematic error in EPI time
series and isolating the RFC-MoCo effect would be difficult. Therefore, we have
undertaken a simulation of this effect to better understand its severity. The
simulations examine this effect for a receive-only single-channel 16-leg
birdcage coil and a receive-only 12-channel phased array. In particular we
study: (1) The effect size; (2) Its consequences to the temporal correlations
between signals arising at different spatial locations (spatial-temporal
correlations) as is often calculated in resting state fMRI analyses; and (3)
Its impact on the temporal signal-to-noise ratio of an EPI time series. We find
that signal changes arising from the RFC-MoCo effect are likely to compete with
BOLD (blood-oxygen-level-dependent) signal changes in the presence of
significant motion, even under the assumption of perfect motion correction.
Consequently, we find that the RFC-MoCo effect may lead to spurious temporal
correlations across the image space, and that temporal SNR may be degraded with
increasing motion.
