Inter-detector scattering in BGO crystal arrays for PET

Positron Emission Tomography instrumentation has been directed towards improving detector spatial resolution with an emphasis on reduction of detector size. From the early days better resolution has meant ability to easily visualize and delineate regions in brain images in addition to improved accuracy in the measurement of smaller volumes of radionuclide concentration. The major difficulty in achieving both high resolution and high detection efficiency is the requirement for a small detector to fully absorb the 511 keV photon within its volume, thus minimising Compton scattered photons and also escape into neighbouring detector crystals. The latter could be recorded as true events and accepted as part of the data thus leading to mispositioning and consequently loss in spatial resolution. In addition, under certain conditions, identifying the correct pair of detectors in coincidence is ambiguous and an event can be rejected, causing a loss in the efficiency and an increase in the dead time. As individual detector crystals are becoming smaller the contribution of inter-detector scattering needs to be addressed.