A Monte Carlo correction for the effect of Compton scattering in 3-D PET brain imaging

A Monte Carlo simulation has been developed to simulate and correct for the effect of Compton scatter in 3-D acquired PET brain scans. The method utilizes the 3-D reconstructed image volume as the source intensity distribution for a photon-tracking Monte Carlo simulation. It is assumed that the number of events in each pixel of the image represents the isotope concentration at that location in the brain. The history of each annihilation photon's interactions in the scattering medium is followed, and the sinograms for the scattered and unscattered photon pairs are generated in a simulated 3-D PET acquisition. The calculated scatter contribution is used to correct the original data set. The method is general and can be applied to any scanner configuration or geometry. In its current form the simulation requires 25 hours on a single Sparc10 CPU when every pixel in a 15-plane, 128x128 pixel image volume is sampled, and less than 2 hours when 16 pixels (4x4) are grouped as a single pixel. Results of the correction applied to 3-D human and phantom studies are presented.