RatCAP: miniaturized head-mounted PET for conscious rodent brain imaging

Anesthesia is currently required for PET studies of the animal brain in order to eliminate motion artifacts. However, anesthesia profoundly affects the neurological state of the animal, complicating the interpretation of PET results. Furthermore, it precludes the use of PET to study the brain during natural behavior. The RatCAP tomograph (rat conscious animal PET) is designed to eliminate the need for anesthesia in rat brain studies. It is a miniaturized full-ring PET scanner which is attached directly to the head, covering nearly the entire brain. RatCAP utilizes arrays of 2 mm × 2 mm LSO crystals coupled to matching avalanche photodiode arrays, which are in turn read out by full custom integrated circuits. Principal challenges have been addressed considering the physical constraints on size, weight, and heat generation in addition to the usual requirements of small-animal PET such as high spatial resolution in the presence of parallax error. A partial prototype has been constructed and preliminary measurements and optimization completed. Realistic Monte Carlo simulations have also been carried out to optimize system performance, which is predicted to be competitive with existing microPET systems.