The present invention relates to a novel methodology for the field of brain images from Positron Emission Tomography (PET), likewise applicable to brain images from Single-Photon Emission Computer Tomography (SPECT) or another technique that makes it possible to generate images of brain metabolism, function or blood flow. This methodology arises from the need to improve the medical diagnosis of neurological disorders and from the need for objective, unbiased quantification of brain metabolism. The method is based on the spatial symmetry of the metabolism of the healthy human brain. Under this assumption, the entire healthy brain metabolism can be deduced from the metabolism of a single hemisphere of the brain.