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| When we tried to coregister a T2 structural image to a | T2* functional image, the resulting coregistration seemed | reasonable in the xy plane. However, the coregistration in | the z axis was off by approximately 1 slice (slice | thickness=8 mm) in a majority of the subjects' data. | | Does anyone know why this might be happening ? There are any number of things that could go wrong, particularly because of the large dropouts and distortions that are present in fMRI data. The default coregistration method makes a number of assumptions, many of which are violated by many datasets. As an alternative, you may like to try the mutual information registration approach (set by the <Defaults> button). This makes much fewer assumptions, so may prove to be better for your data. The distortions present in fMRI data mean that a really good match can never be achieved using a rigid body transformation. Ideally, some kind of nonlinear warping should be used, but this is not currently available within SPM. Best regards, -John