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This chapter describes PET systems for imaging of small animals. It also discusses the opportunities for bringing together high-resolution PET imaging systems with the techniques of modern molecular biology, functional genomics, and drug development. Important factors considered in the design of dedicated small animal PET scanners are identified and the geometry and performance of several first-generation systems are reviewed. This chapter also describes newer small animal PET systems that are under development. Last section illustrates some of the early applications of PET for studying small laboratory animals and identifies the challenges, opportunities, and ultimate limitations in applying PET to small animal imaging. The role of PET in modern biology has yet to be defined, but, if some of the challenges identified in this chapter can be overcome, then it is likely to play a significant role in the study of animal models of disease.

MicroPET is a prototype high-resolution positron emission tomography (PET) scanner designed for imaging small laboratory animals. It is the first PET system to make use of the new scintillator lutetium oxyorthosilicate and also the first system to employ fiber-optic coupling as a means for reading out very small scintillator elements with minimal deadspace. MicroPET consists of a total of thirty, 8 × 8 element detectors in a ring of diameter 17.1 cm. The animal port is 16 cm in diameter, and the useful field of view measures 11 cm transaxially by 1.8 cm axially. There are no interplane septa and data are acquired exclusively in three-dimensional mode. The system also includes a computer-controlled animal bed with built-in wobble motion. MicroPET produces images with a spatial resolution of 2 mm in all three axes and has sufficient sensitivity to realize this resolution for many applications. For studying biological systems that are easy to saturate, improved sensitivity could be realized by the addition of a second or third detector ring, which would also serve to increase the axial coverage of the system. The use of microPET to image the brain of several species of animals is presented. Based on the success of this first prototype system, a second, higher resolution, higher sensitivity system is now being developed exclusively for use in mice and rats.