Tomographic systems employing truncated projections have been developed for parallel and fan beam collimation but the idea has not been extensively explored in pinhole SPECT. In this paper, we explore the sampling requirements and system performance of pinhole SPECT systems with truncated projections. We demonstrate that complete 3D sampling can be achieved by using multiple detectors with axially displaced pinholes and a spiral orbit. This can be exploited in the design of pinhole SPECT systems by moving the pinholes closer to the subject, resulting in increased sensitivity and improved spatial resolution. Truncated and untruncated pinhole systems were evaluated using contrast to noise ratio (CNR) calculated from the linearized local impulse response as a figure of merit. CNR for the truncated pinhole system is up to 40% greater than the untruncated system at matched resolution. We also found that when multi-pinhole projections contain a truncated but complete partition, the reconstruction may be modified to follow a different and potentially more efficient convergence path. We conclude that an object can be reconstructed from truncated pinhole projections, which leads to potentially important applications in single and multi-pinhole SPECT.
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