As regards Alzheimer's Disease (AD), SPM allows to determine significant hypofunctional areas in subjects affected by AD. Such hypofunctional areas are identified through the statistical comparison of the functional images (SPECT or PET) of the suspected patient with functionally normal images from a control group including healthy subjects comparable to the patient under examination.

The main steps of an SPM procedure are:

• spatial normalization of the images of the patient suspected AD to a stereotactic space described by a standard reference brain atlas (e.g. the Talairach atlas). This function is carried out through the geometric transform (coregistration) of the tomographic study of the patient into the atlas space and allows the direct spatial comparison with the corresponding images from the set of normal subjects already normalized to the same atlas. This way the statistical comparison between different studies (subject suspected AD versus subjects form the control group) is made possible as well as the localization of statistical significant brain areas through the spatial coordinates of the stereotactic space of the standard atlas.
• image filtering by means of convolution methods able to smooth the intensity differences among nearby voxels due to the discrete representation of the spatial distribution of radioactivity. SPM can be applied only to data showing features typical of gaussian fields. Among these features the continuity of the signal is very important. The image filtering process make therefore the functional data more suitable for SPM.
• statistical analysis with the goal of comparing, voxel by voxel, the images of the subject suspected AD with those coming from the control group in the same conditions and in the same space. The analysis takes into account both relevant variables as age and sex of the patient and global statistical parameters as the medium cerebral blood flow. By means of a cluster analysis of voxels with statistically reduced functionality, hypoperfusion areas are determined and spatially mapped on the reference atlas and on the original images of the subject.