Positron Emission Tomographic (PET) Scanning

Positron emission tomography (PET) is a nuclear-medicine imaging technique, and like CT it produces a computerised image, but unlike CT it images function rather than just structure. It works by measuring positrons emitted from a radiolabelled tracer molecule that has been introduced into the body. PET uses positron-emitting radioisotopes such as carbon-11, nitrogen-13, oxygen-15 and fluorine-18, which are produced in a cyclotron; the most widely used tracer is 18F-fluorodeoxyglucose (18F-FDG), a radioactively labelled form of glucose. These labelled atoms are chemically incorporated into biological molecules such as glucose, amino acids or ammonia, and the resulting tracer compound is then injected in a very small amount into, or inhaled by, the subject. As the tracer distributes through the body, powerful PET cameras detect the three-dimensional pattern of radioactive decay, and a computer reconstructs this into an image; because the amount of tracer taken up in a given region reflects how metabolically active that tissue is, PET imaging gives quantitative regional information about metabolic and physiological processes, interpreted using mathematical models of tracer uptake and metabolism. Clinically, PET is especially useful for …