Page "Functional magnetic resonance imaging" Paragraph 39

In general, fMRI studies acquire both many functional images with fMRI and a structural image with MRI.

The structural image is usually of a higher resolution and depends on a different signal, the T1 magnetic field decay after excitation.

To demarcate regions of interest in the functional image, one needs to align it with the structural one.

Even when whole-brain analysis is done, to interpret the final results, that is to figure out which regions the active voxels fall in, one has to align the functional image to the structural one.

This is done with a coregistration algorithm that works similar to the motion-correction one, except that here the resolutions are different, and the intensity values cannot be directly compared since the generating signal is different.