Introduction

Functional brain imaging refers to the use of techniques to obtain images of the brain that are related to its physiology or biochemistry, rather than its structural anatomy. Two nuclear medicine-based approaches to functional brain imaging can be used to study the pediatric population, positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Both will be reviewed in this chapter.

PET is a nuclear medicine technique for performing physiologic measurements in vivo. The PET scanner provides tomographic images of the distribution of positronemitting radiopharmaceuticals in the body. From these images, measurements such as regional cerebral blood flow (rCBF) and glucose metabolism can be obtained. PET has been widely used as a research tool to study normal brain function and the pathophysiology of neurologic and psychiatric disease in adults (Grafton and Mazziotta, 1992;Volkow and Fowler, 1992). Its role in the management of patients with brain disorders is at an earlier stage (Powers et al., 1991) and its use in children has been limited. Conceptually, PET consists of three components: (i) tracer compounds labeled with radioactive atoms that emit positrons; (ii) scanners that provide tomographic images of the concentration of positron-emitting radioactivity in the body; and (iii) mathematical models that describe the in vivo behavior of radiotracers and allow the physiologic process under study to be quantified from the images. The first tomographs for quantitative PET imaging were developed in the mid-1970s (Ter-Pogossian, 1992). Subsequently, instrument design has become more sophisticated, with improved spatial resolution and sensitivity.