Pupil-PET: a novel PET camera with adjustable FOV, AFOV and sensitivity

The conventional PET cameras, consisting of rings of gamma detectors which may block the paths of radiation beams, are not ideal for in-beam monitoring. In this paper, we presented a novel PET design with adjustable field-of-view (FOV), axial field-of-view (AFOV) and sensitivity, like the pupil of the human eye. Thus, we named it Pupil-PET. The sensitivity of a Pupil-PET is no fixed and depends on the system configuration. We designed a 16-module prototypic pupil-PET system which has two planes with Archimedean spiral tracks on both of them. Four step motors are used to adjust the aperture and the AFOV automatically with a precision of 1 mm per step. The system can automatically transform into a two-ring system with a 100 mm aperture and a 72 mm AFOV, a two-ring system with an aperture ranged from 100 mm to 200 mm and an AFOV ranged from 72 mm to 100 mm, or a two-ring system with a 200 mm aperture and a 38 mm AFOV. The sensitivity of the smallaperture two-ring configuration is about 8 times higher than that in a large-aperture one-ring configuration. Sixteen detector modules have been fabricated and tested for the prototypic PupilPET system. The detector module consists of a 10 x 10 LYSO crystal array (3 mm x 3 mm x 20 mm), a 10 x 10 SiPM array (3 mm), and a high performance readout board (call Pico-PET electronics) which are able to read out all 100 SiPMs in parallel. In conclusion, our Pupil-PET has two unique features: (1) It is able to transform to adapt objects with different sizes. The largeaperture one-ring configuration can be adapted to achieve a large FOV for objects large in size, such as big animal and whole-body human. Small-aperture two-ring configuration can be adapted to achieve an 8 times higher sensitivity for objects small in size, such as small animal, human brain or breast. (2) The gaps between the detectors and between the rings in a Pupil-PET system provide omnidirectional paths for radiation beams.