A fast projector backprojector pair for use in iterative reconstruction of SPECT images

Reconstructed SPECT images suffer from decreased image quality due to photon attenuation within the patient and distance-dependent blurring introduced by the collimated gamma camera. Several iterative reconstruction algorithms have been proposed to compensate for these degradations, as well as to suppress noise. These methods require the use of a realistic projector and back-projector pair which can accurately model the physics of photon transport. Here, the authors describe a projector/backprojector pair which accurately models both photon attenuation and the distance-dependent detector response, and provides a substantial decrease in computational complexity over previous methods. The computational savings are obtained by using the frequency distance principle (FDP) to incorporate distance-dependent blurring into the projector/back-projector pair. Since this procedure can be implemented using FFT methods, distance-dependent blurring can be modeled with a substantial reduction in the number of computations required. Simulation studies using a paint source object and the Hoffman bit-map brain phantom have shown that use of the FDP based projector-backprojector pair can reduce the computation time required for iterative reconstruction, with minimal loss of accuracy