Hybrid Monte Carlo simulation in Positron Emission Tomography

Positron Emission Tomography (PET) offers the possibility to measure quantitatively the radiotracer distribution in tissues of interest. However, a number of physical issues must be accurately addressed in order to fully achieve this potential. The scattered radiation is one of the most challenging tasks among these issues. Up to now, Monte Carlo simulation (MC) is the ideal technique to evaluate and correct for the scattered photons. Nevertheless, these simulations are often complex and CPU time consuming. In this work, we have developed a combined MC simulations and analytical calculations for the small animal PET imaging systems. As a first step, MC simulation was performed only for the photon interactions within the studied object. The detection efficiency was analytically calculated as the energy deposited by the photons in the crystals and their attenuation in the surrounded crystal packages. The inter-crystal scatter was modeled by convolving the simulated data with the detector scatter kernels that were experimentally assessed from the line source measurements. The results showed good agreements between the measured and the simulated images. This technique, which allowed to substantially reduce the execution time without losing accuracy, can be easily implemented for the scatter and attenuation correction in PET imaging.