Open-Field Mouse Brain PET: Design Considerations and Detector Development

'Open-field' PET imaging offers the key capability of correlating functional changes in the brain of an awake animal with its behavioral response to environmental or pharmacologic challenges. Previously we have demonstrated the feasibility of this concept for rats using motion compensation techniques. That system, however, is not suitable for imaging the mouse brain due to limitations imposed by the use of a commercial PET scanner. Therefore, we are designing a purpose-built PET scanner which optimizes the geometry, motion tracking and imaging performance for open-field imaging of the mouse brain. We simulated the sensitivity and spatial resolution performance of four candidate scanner designs: ring, parallel plate, and two box designs. The block detector was a 23x23 array comprising 0.785 x 0.785 x 20 mm(3) LSO crystals. A ML-EM reconstruction with DoI capability was used to determine the DoI resolution necessary to achieve approximately uniform and isotropic sub-millimeter spatial resolution throughout the FoV. The results showed that 3 mm DoI resolution was sufficient to achieve the required spatial resolution performance for all scanners except the parallel-plate design. However, the sensitivity advantage of the overlapping box design (peak absolute sensitivity of 16% and 36% improvement over the ring design) suggested this unconventional design is favored for imaging the mouse brain. We also designed a dual-ended readout DoI-encoding detector module based on a 6x6 array of through-silicon-via SiPM arrays to meet the DoI requirement. The next stage of work is to characterize the performance of this detector module and use it to build a prototype bench-top scanner for initial testing of the scanner concept. For the final scanner design we propose to slide the scanner axially on rails according to the animal's motion, rather than move the animal (as in our previous design). This will allow faster motion without disturbing the animal's behavior, and also achieve a large axial FoV for animal movement at minimal cost.