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Progress is reported in several areas of design of a positron volume imaging tomograph. As a means of increasing the volume imaged and the detector packing fraction, a lens system of detector light coupling is considered. A prototype layered scintillator detector demonstrates improved spatial resolution due to a unique Compton rejection capability. The conceptual design of a novel mechanism for measuring scattered radiation during emission scans has been tested by Monte Carlo simulation. The problem of how to use effectively the resulting sampled scattered radiation projections is discussed.<>

Three different computing algorithms for performing positron emission image reconstruction have been compared using Monte Carlo phantom simulations. The work was motivated by the recent announcement of the commercial availability of a positron volume imaging camera, the Siemens-CTI 953 B/31, which has improved axial (slice) resolution and retractable interslice septa. The simulations demonstrate the importance of developing a complete three-dimensional reconstruction algorithm to deal with the increased gamma detection solid angle and the increased scatter fraction that result when the interslice septa are removed from a ring tomograph. The 3-D algorithm has a lower noise level than either the conventional 2-D algorithm (appropriate to tomographs with interslice septa) or the modified 2-D algorithm (proposed to implement positron volume imaging on the new scanner). The new 3-D algorithm is free of a serious artifact that affects the modified 2-D algorithm, caused by spillover of activity from one slice to another.<>