Investigation of 90 degrees dual-camera half-fanbeam collimation for myocardial SPECT imaging

This study investigated several aspects of the use of half-fanbeam collimat ion with a 90 degrees dual-camera system for myocardial single photon emiss ion computed tomography (SPECT) imaging. The detection efficiency, relative to parallel-hole collimation, was evaluated for a range of focal lengths a nd radii of rotation (ROR) to determine if there was an optimum focal lengt h, which maximized the detection efficiency. In addition, sinograms were co nstructed and a simulation study was performed to determine if there was an optimal camera system rotation that maximized the total acquired myocardia l counts while providing sufficient angular sampling for the myocardial reg ion. Finally, artifacts in images reconstructed fi-om data acquired over va rious system rotations were evaluated using simulated and experimental data . There existed an optimal collimator focal length for a given ROR; but it varied with ROR. Relative to parallel-hole collimation, the detection effic iency for half-fanbeam collimation was roughly 20% greater, for cast collim ators constructed using the same pins and thickness. The theoretical minimu m system rotation for sufficient sampling of the myocardial region ranged f rom 124 degrees to 148 degrees for RORs ranging from 13 to 25 cm, respectiv ely. The total number of acquired myocardial counts was relatively constant for system rotations of 90 degrees to 360 degrees. Myocardial SPECT images reconstructed iteratively with attenuation compensation from half-fanbeam data collected over system rotations ranging from 135 degrees to 360 degree s showed no artifacts in the myocardial region. Based on these results, we concluded that there was no single optimum system rotation, but that a syst em rotation of 180 degrees centered at 45 degrees left anterior oblique was a good, practical minimum rotation. Half-fanbeam collimation is a useful a lternative system configuration for myocardial SPECT imaging.