Influence of contamination from scattered and emission photons in singles-mode transmission data for small-animal PET

We investigate the influence of scatter correction (SC) and emission-contamination corrections (EC) for singles- mode transmission data in small animal PET. In a previous work, we described and validated a scatter correction for singles-mode transmission data using experimental pre-injection data acquired with the microPET Focus 120 dedicated rodent PET scanner. In this work, we test the general validity of our SC by applying it to pre-injection transmission data from a different imaging system (the larger microPET Focus 220 dedicated primate scanner). We acquired transmission data for a large water cylinder (50 mm radius) and for a nemestrina monkey and found that, for the scatter corrected (SC) attenuation-maps, the average reconstructed mu-values were within 3% of the expected values for water and soft-tissue, while uncorrected values were 19% to 26% lower than their expected values. We also tested our attenuation-map reconstruction and scatter correction procedure for post-injection transmission data acquired with the Focus 120 dedicated rodent scanner. For these data, we also investigated the quantitative accuracy of reconstructed emission images which use attenuation corrections derived from post-injection transmission data. For these studies, we saw how important emission contamination corrections are singles-mode transmission data acquired using a ⁶⁸Ge source (a positron emitter). Lower-noise, higher-quality attenuation-maps were obtained using ⁵⁷Co, a 122 keV gamma-emitter, due to the lower amounts of emission contamination and better contrast between mu-values at lower energy. In spite of these differences, correct average mu-values and consistent reconstructed activity concentrations for the emission data could be obtained when both emission-contamination (EC) and scatter corrections (SC) were applied to post-injection transmission data.