Characterization of Compton scattering in emission tomography

Characterization of the scatter background in positron emission tomography and in single photon emission tomography is necessary for the development of scatter correction algorithms and for the optimization of tomograph design parameters. Computer programs using Monte Carlo methods have been used to obtain event distributions which conform to the scattering cross sections of Klein and Nishina. Scattering is simulated in an attenuating medium of arbitrary complexity and the number of scatters undergone by each photon is not artificially limited. Early work has emphasized the simulation and detection of positron-annihilation photons. The results from these simulations agree very closely with results from scattering experiments using the Donner 280-Crystal Positron Tomograph. A large number of simulations have been performed to determine the scatter impulse response as a function of source position, attenuator size, photo-peak energy discrimination, and shielding geometry. Although the shape of the scatter background depends on the position of the source, these simulations show that it is only a very weak function of attenuator radius. They also show that the amplitude, but not the spatial extent of the scatter background can be effectively reduced with a reduction in shielding gap, and that a photo-peak energy discrimination of two percent or better is required to reduce the FWHM of the scatter point-spread function to less than 10 cm