Positron Emission Tomography (PET Scanning)

Positron emission tomography (PET) has provided the capability of obtaining in vivo regional biochemical and physiologic information about the human brain in health and disease. This capability, not long ago considered an unattainable fantasy, is the product of four major developments in the necessary technology: (1) the apparatus for nuclear bombardment, ie, the cyclotron, to produce positronemitting isotopes, (2) techniques for rapid synthesis of radiopharaceuticals necessary for biochemical and physiologic studies, (3) the mathematical models and practical algorithms to obtain the critical information from the data, and (4) the PET instrumentation to detect safely the radiopharmaceuticals in vivo in a regional and quantitative manner. In this presentation, I will review briefly the basic principles of PET, the principal measurements afforded by the technique, and the major clinical applications; a brief review of recent work in pediatric patients will also be presented. BASIC PRINCIPLES OF PET The principle of PET is based on the events provoked by the emission of a positron within the tissue from the active isotope. The positron-emitting isotopes most suitable for in vivo measurements, oxygen-15 (15O), nitrogen-13 (13N), carbon-11 (11C), and fluorine-18 (18F), are incorporated into a chemical compound with desired biologic activity or distribution. The positron emitted from the isotope into the tissue is a low-energy particle which travels only a few millimeters before combining with an electron (Fig 1).