Objective evaluation of dynamic imaging protocols needs a realistic simulation tool to model the data acquisition and image reconstruction of a PET system. Availability of the correlated functional and anatomical images in many centers allows the creation of highly realistic objects to represent brain activity and attenuation distribution for each study. The authors have developed a fast analytical model that incorporates key physical factors inherent in coincidence detection along with spatially variant 3-D detection efficiency and deadtime. Here, they use MR and PET data of a 3-D Hoffman brain phantom to demonstrate and validate their computational methods. The simulated total projection, attenuation factor: and scatter profiles are in very good agreement with the experimental data. The corresponding regional activity values in the gray matter and white matter have a discrepancy of /spl les/8.5%. The authors also show typical emission and transmission images generated from MR brain scans. This tool is particularly useful in evaluating projection data processing and image reconstruction algorithms.