Gantry design with accurate crystal positioning for a high-resolution transformable PET camera

A PET camera capable of transforming its geometric configuration is being developed. This high-resolution oncologic transformable PET (HOTPET) can be modified from a large detector ring of 83 cm to a small diameter ring of 54 cm. The system consists of 12 rectangular detector modules arranged in a polygon. The detector gap between modules remains constant in both configurations because each module is rotated around its own axis and displaced radialy, bringing together adjacent modules. HOTPET's detectors are highly pixilated (crystal pitch 2.6 mm), requiring accurate placement of the modules relative to each other to ensure alignment of crystals within the same detector ring. We have designed a precise detector bank holder with keyways and complementary keys built onto its sides to allow interlocking with each other to form a polygon and maintain crystal co-planarity. Consequently we were able to design the gantry supporting the modules using wider tolerances and so reduce its construction cost. The module provides support for 77 PMT, the analog front-end electronics, and an automated PMT-gain control, all enclosed within a controlled environment. By having only 2 departing surfaces throughout the module's box we minimize light leaks, and with air ducts inside the walls, its temperature can be controlled. Removal of just a back cover and a motherboard gives access to any part of the electronic components or a PMT with minimal disturbance to other components.