Visualization

The final result of fMRI data analysis will often be visualized as a map in standard space. The background for the map will generally be a grey-scale image of cerebral anatomy. This image could be simply the fMRI data averaged over time at each slice. Alternatively, one might wish to use a structural MRI dataset with superior spatial resolution or tissue contrast between grey and white matter. In this case, one should beware of the potential discrepancy in geometric distortion between images of the same brain acquired using different sequences.

The background image will often be combined with, or substituted by, a rectangular grid allowing any feature of interest to be referred directly to the appropriate atlas of standard anatomical space. If the image is displayed as a series of two-dimensional slices, the z co-ordinate for each slice in standard space should also be displayed. Images are often rendered so that the right side of the brain is represented by the left side of each slice.

Voxels or clusters that demonstrate a significant effect are generally coloured against the grey-scale background image ( PlateJJ.). A range of colours can be used to encode additional information. For example, the haemodynamic delay of response at each generically activated voxel may be colour coded by a continuous spectrum. Other strategies for visualization include use of three-dimensional rendering to show foci of activation in the context of the sulcogyral anatomy of a whole hemisphere, and 'flat mapping' whereby the template image is deformed to a smooth sphere and then mapped to a plane before activation foci are superimposed on it. (1..3>

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