Demonstration of small animal Compton imaging by a whole gamma imaging (WGI) prototype

[Purpose] We have proposed the whole gamma imaging (WGI) concept, which enables tomographic imaging of various types of gamma-ray emissions by a combination of PET and Compton imaging. To realize the WGI concept, we have developed a proof-of-concept prototype by inserting a scatterer ring into a PET ring, in which the PET ring works as an absorber ring for Compton event detection. In this study, we demonstrated the Compton imaging performance of the WGI with small animal experiment. [Method] The WGI prototype consists of a scatterer ring with 10x2 (transverse x axial) detectors (94 mm diameter, 24x24x1 GAGG 0.9x0.9x6 mm3, MPPC) and a PET (absorber) ring with 40x4 detectors (660 mm diameter, 16x16x4 GSOZ, 2.8x2.8x7.5 mm3, PMT). We measured a mouse for 1 hour long, 22 hours after injection of 9.8 MBq 89Zr oxalate. 89Zr emits 909-keV single gamma rays as well as positrons at different timing. Therefore, we can directly compare the PET image and Compton image. For normalization, we measured an annulus phantom filled with 89Zr solution. Singles events without energy window were recorded. PET events and Compton events were extracted from singles data after the measurement by a software coincidence method. For image reconstruction, we implemented the list-mode OSEM method for the both modes.[Results] The number of extracted list-mode events were 25 M counts for the Compton imaging mode and 125 M counts for the PET mode. As the 89Zr oxalate is assimilated in bone, PET image depicted the bone structure of the mouse clearly. Although the spatial resolution of the Compton imaging mode was lower than the PET mode, we could observe the bone structure even in the Compton image.[Conclusion] We demonstrated the performance of WGI for 3D single gamma imaging with the Compton imaging mode. The image reconstructed with a full-ring geometry of the WGI prototype incorporating the normalization method showed the capability of WGI for high quality Compton imaging.第119回日本医学物理学会学術大