A DOI-dependent extended energy window method to control balance of scatter and true events

In a conventional PET scanner, coincidence events are limited by the energy window for detection of photoelectric events. In contrast, Compton scatter events occur both in a patient and detector crystals. Scatter events within the patient cause scatter coincidence, but scatter events within crystal have useful information for an activity distribution. The PET scanner with an extended energy window has higher sensitivity but higher scatter fraction than the PET scanner with a default energy window. In this work, we develop a scatter reduction method using a depth-of-interaction (DOI) detector. The DOI detector can make an upper layer act as an absorber of patient scatter for a lower layer. Therefore, crystal scatter with an interacting lower layer has a potential to discriminate patient scatter. Our method has a different energy window for each layer. The energy window of the upper layer is limited to the region of photoelectric events. The energy window of the lower layer is extended to the region of crystal scatter and photoelectric events. We applied our proposal technique for a whole-body PET scanner using GATE simulation. The DOI- PET scanner can provide more true events while keeping a low scatter fraction using this scatter reduction method. Based on simulation results, this method is judged to be promising for obtaining high image quality using DOI information and energy information.