SPM Papers

Statistical Parametric Mapping


Written by members of the Wellcome Department of Imaging Neuroscience

Movement-Related Effects in fMRI Time-Series

Friston KJ, Williams SR, Howard R, Frackowiak RSJ & Turner R (1996)
Magnetic Resonance in Medicine 35:346-355


This paper concerns the spatial and intensity transformations that are required to adjust for the confounding effects of subject movement during fMRI activation studies. We present an approach that models, and removes, movement-related artifacts from fMRI time-series. This approach is predicated on the observation that movement-related effects are extant even after perfect realignment. These effects can be divided into those that are some function of position of the object in the frame of reference of the scanner, and a component that is due to movement in previous scans. This second component depends on the history of excitation experienced by spins in a small volume and consequent differences in local saturation. The spin excitation history will itself be a function of previous positions. This suggests an autoregression-moving average model for the effects of previous displacements on the current signal. We describe such a model and the adjustments for movement-related components that ensue. Our empirical analyses suggest that (in extreme situations) over 90% of fMRI signal can be attributed to movement, and that this artifactual component can be successfully removed.

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