Effects of truncation of transmission projections on cardiac SPECT images acquired by a right-angle dual-camera with half-fan-beam collimators

Right-angle dual-head SPECT systems equipped with half-fan-beam collimators have some advantages compared to right-angle dual-head systems with parallel-hole collimators. A potential drawback of the half-fan-beam system in cardiac studies is that it potentially truncates the transmission data and therefore yields attenuation maps containing inaccuracies in an area to the dorso-lateral region of the torso. The objective of this study is to investigate whether the transmission projection truncation introduces artifacts into iteratively reconstructed emission images of the heart. To this end, a combined cardiac emission transmission study was simulated, modeling 514 mm wide detectors and collimators with focal line distances of 890 mm. Emission images were reconstructed iteratively on the basis of truncated and untruncated attenuation maps. The iterative reconstruction methods include the detector response, and compensate for attenuation and scatter in media with non-uniform density. The results indicate that attenuation- and scatter-corrected cardiac studies are not significantly influenced by the truncation of dorso-lateral region of the patient in the transmission projections, even if the patient is extremely large.