Multiple point sources collimated with transaxial septa for high energy gamma camera transmission scanning

The axial imaging properties of the transmission scanning system for attenuation correction of gamma camera coincidence imaging are evaluated. This system uses multiple Cs-137 point sources collimated by transaxial septa already in place for emission imaging. Both the spacing and the degree of collimation of the sources can be controlled. Axial image quality was evaluated with three levels of collimation (4 mm, 7 mm, and 10 mm slot, all 6 cm deep) and two source spacing distances (1.3 cm and 2.6 cm). A multiple disk phantom with adjustable spacing was imaged, as well as a thorax phantom. The 4 mm collimation and 1.3 cm source spacing provided well-resolved images of the disks with 2.9 cm center-to-center spacing. The best collimation/spacing combinations come with substantial overlap of flux from difference sources in the detector. Axial resolution can be adequately controlled with extra lead collimation of the sources.