Effect of Overlapping Projections on Reconstruction Image Quality in Multipinhole SPECT

Multipinhole imaging has a lot of advantages over single pinhole, such as an increased sensitivity and an improved sampling. However, the quest for a good design is tedious, due to the large number of design parameters. One of these, the amount of overlap in the projection images, and its effect on the reconstruction image quality, is examined in this paper. The evaluation of the quality is based on efficient approximations for the linearized local impulse response and the covariance in a voxel. Two (theoretical) methods for overlap removal and two measures to quantify the overlap are proposed. First, the approximate method is validated with standard iterative reconstructions. Second, designs with different amounts of overlap are evaluated before and after overlap removal to verify the effect of multiplexing. Third, the results are interpreted with the overlap quantification measures. We can conclude that overlap removal improves image quality: the loss of information due to multiplexing is not compensated by the increase in sensitivity.