Backprojection-space 3D scatter correction for the PETRRA positron camera

Positron volume images have been produced by the new large-area positron camera PETRRA directly from list-mode data acquisition then reconstruction using backprojection then filter methods (BPF). These images have been corrected for scatter and attenuation using backprojection space methods. Two methods have been developed to provide scatter distributions. The first method uses a spatially-invariant scatter response function derived from measured point spread functions in a water-filled phantom. The second uses the scatter distributions measured at various points in the same phantom to allow for the spatial variance of the scatter. The correction methods have been tested using a uniformly-filled radioactive elliptical phantom (major and minor axes of 29.5 cm and 19.6 cm). Preliminary results show that both methods can improve the quantitative nature of the reconstructed images but that the use of spatially variant scatter distribution is superior. The methods could be applied to any large-area, rotating positron camera system which acquires data in list mode.