Monte Carlo simulation of single photon emission computed tomography

A Monte Carlo code was used to simulate the scatter processes which occur in single photon emission computer tomography. The transport of photons from their emission by the radioactive source within the phantom to their detection by the nuclear medicine camera was modeled. The simulation was tested by comparing qualitatively and quantitatively the theoretical with the experimental energy spectra. Also, experimental and theoretical scatter fractions and detector efficiencies were compared. In addition, two phenomenological correction algorithms, the Gaussian Subtraction and Least Squares Fit methods, were studied for their ability to correct for scatter. Eighteen cases involving phantoms containing uniform and nonuniform biological media along with a point or distributed source were studied. Cylindrical symmetry of the phantom and source was assumed in order to reduce the computer runtime. The theoretical energy spectra generated by the Monte Carlo code agreed with the experimental spectra to within one standard deviation. The exceptions involved regions in the energy spectrum below 120 keV for a radioactive source in air and the nonscattered peak region for the modeling of bone. The energy spectra were found to be dependent on the medium and radioactive source distribution within the phantom