Data completeness in multiplexing multi-pinhole SPECT

Multi-pinhole collimators are often used in preclinical SPECT systems because of their high resolution and reasonable sensitivity. Most multi-pinhole collimators are designed to allow only a limited amount of overlap between the different pinholes´ projections (also called multiplexing) because it has been shown that the ambiguity introduced by multiplexing pinholes can result in artifacts. We investigate the origin of these artifacts and simulate phantom data for different multiplexing systems to developed a theory that can predict whether a multi-pinhole system will show multiplexing artifacts or not. This resulted in a theory based on data completeness. In most multiplexing systems, the projections overlap only partially, so that both multiplexed and non-multiplexed data is available. We show that a certain activity distribution can be successfully reconstructed when the nonmultiplexed data is complete (using Orlov´s theory) or when the overlap can be sufficiently de-multiplexed. The computer simulated phantom data agrees well with the simulation results. In conclusion, more multiplexing does not necessarily result in more artifacts. Systems with a high amount of multiplexing can still result in artifact-free images if data sufficiency is achieved.