Novel application of the 8 π gamma-ray spectrometer for 3 γ positron emission tomography

In tissue, approximately 0.5% of positron annihilations emit three γ rays instead of the usual two. Although these events are not currently used for imaging in Positron Emission Tomography (PET) scans, they can provide valuable diagnostic information on tissue properties such as porosity and hypoxia. The present work demonstrates an approach for imaging 3 γ positron annihilations from β + decays of 18 F. The isotope is produced through a novel method of neutron activation of a polytetrafluoroethylene (Teflon) disk. Measurements were performed using the 8 π gamma-ray spectrometer, a highly efficient and selective ball array of 72 Bismuth Germanium Oxide (BGO) detectors arranged in an icosahedron geometry with ∼ 95% solid-angle coverage. Coupled with a digital data acquisition system, the 8 π spectrometer provides waveform digitization and online multiplicity filtering capabilities, enabling efficient and selective measurement of rare 3 γ positron annihilations. An energy-based reconstruction method was applied to produce three-dimensional 3 γ PET images with a FWHM point spread of 4.0 cm at the center of the array.