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Using a field-map to undistort EPIs
Background
Improvement in power!
Acquiring fieldmaps
Download
What you'll need to undistort an EPI data series
Guide and reference
Step-by-step example
Batch mode

Improvement in power in RFX analysis

What you really care about is probably power to detect functional activation. Here are the results of a random effects analysis (N=12) of a motor cortex localiser task. Subjects were asked to press a button either with a finger of their left hand (left column) or their right (right column). The data were analysed with or without undistortion.

http://imaging.mrc-cbu.cam.ac.uk/images/motortask.gif

Functional images (thresholded at 0.001 uncorrected) are shown superimposed on the SPM T1 template. The numbers in the top left of each image indicate peak t values over the whole volume. After the application of undistortion, clear activation can be seen in motor cortex (BA 4) on each side.