This chapter provides background material essential for understanding the scientific and technical underpinnings of the image-formation process in positron emission tomography (PET). X-ray computed tomography (CT) will also be briefly discussed, though in much less detail. Instead, we will emphasize, later in this chapter, the ways in which the CT acquisition and resulting images influence reconstructed PET images. Because the terminology used to describe the most important nuclear physics and PET instrumentation concepts may be unfamiliar to some readers, we have highlighted certain key words and expressions in bold font when these terms are first introduced. For more advanced treatments of selected topics related to PET instrumentation and imaging, readers are referred to physics texts, such as those by Cherry et al. (1) and Wernick and Aarsvold (2).

Radioactive decay: positron emission, annihilation, and detection

In this section, we discuss the basic nuclear physics concepts on which PET imaging is based. We begin by presenting some information and terminology related to the decay of radioactive atoms, in general, as well as more detailed and specific descriptions of positron decay. Along the way, we will discuss several key characteristics of radioactive nuclei that emit positrons; these will later be shown to influence the quality of PET images.