Monte Carlo investigation of scatter in dual head coincidence imaging

Scatter is a major problem in dual head coincidence imaging using 3D acquisition. We investigated the scatter response in an ADAC Vertex MCD camera using Monte Carlo simulations. Simulations of different cylindrical phantoms were done to compare with measured values. These show agreement in the relative scatter fraction distribution but underestimate the magnitude of the scatter. The simulation bins by number of scatters to allow the relative contribution from single and multiple scatter to be determined. Results for the NEMA scatter phantom yield global multiple scatter fractions (multiple over total scatter) of 16% in p-p mode and 29% in p-C mode, which do not vary axially. Simulations of a digital anthropomorphic phantom were then done to assess scatter in clinical situations. These showed global scatter fractions 37% to 48% in p-C acquisition for different activity distributions and positioning, significantly higher than from cylindrical phantoms. The global multiple scatter fractions were also higher for the anthropomorphic phantom with values from 31% to 48% in p-C mode. The distributions from the anthropomorphic phantom also showed that the scatter fractions and multiple scatter fractions varied axially and with source distribution and positioning. The characterization of scatter is valuable in guiding scatter correction strategies