Statistical 3D image reconstruction for the RatCAP PET tomograph using a physically accurate, Monte Carlo based system matrix

This work describes a fully 3D statistical image reconstruction for the RatCAP (Rat Conscious Animal PET) using a Monte Carlo based system matrix. The RatCAP consists of 12 Iutetium oxyorthosilicate (LSO)-avalanche photodiode (APD) detector blocks arranged in a ring of 41.2 mm diameter. Due to the small ring diameter and low number of total lines of response (LORs), the size of a complete system matrix is small in comparison to a typical small animal scanner. This allows incorporation of an accurate, RatCAP-specific physical model with the inclusion of crystal penetration, Compton scattering in both rat´s brain and detector, attenuation and the realistic event positioning errors. The trade off between the statistical accuracy and the matrix computational time as it relates to the accuracy of image reconstruction will also be discussed.