A computerized brain atlas, adjustable to the patient's anatomy, has been developed. It is primarily intended for use in positron emission tomography (PET), but may also be employed in other fields utilizing neuro-imaging, such as stereotactic surgery. The atlas is based on anatomic information obtained from digitized cryosectioned cadaver brains. It can be adjusted to fit a wide range of individual brains with reasonable accuracy. The corresponding transformation is chosen so that the modified atlas agrees with a set of CT or MR images of the patient. The computerized atlas can be used to facilitate and improve the quantification and evaluation of PET data by: enabling the merging and comparison of results from different individuals or groups of individuals; serving as a vehicle in the comparison of different examinations of the same patient, thus reducing the need of reproducible fixation systems; supplying external information to be used in the image reconstruction, such as proper three-dimensional regions of interest; improving the attenuation and scatter corrections; helping to select suitable patient orientation during the PET study. By applying the inverse atlas transformation to the PET data volume it is possible to relate the PET information to the anatomy of the reference atlas. Reformatted PET data from different patients can thus be averaged, and averages from different categories of patients can be compared. The method will facilitate the identification of statistically significant differences in the PET information from different groups of patients.