[Positron emission tomography: basic principle and radionuclides/probes for metabolic/functional analysis]

Abstract

Positron emission tomography (PET) is a functional imaging modality that can non-invasively visualize the distribution and dynamic movement of injected PET probes. In this article, the basic principle of PET technique is briefly explained followed by the introduction of various positron-emitters and PET probes used in clinical and research settings. With the coincidence detection of a pair of annihilation radiation emitted from positron emitters and the attenuation correction technique, PET can afford highly sensitive and quantitative data for analysis. However, spatial resolution of PET is limited and not suitable for detecting small lesions. In addition, PET image lacks anatomical information, and correct anatomical localization of the detected uptake is sometimes difficult. Most positron emitters are produced by cyclotrons and have very short half-lives. Therefore, PET institution should be equipped with an in-house cyclotron to produce positron emitters as well as the facility to prepare PET probes. Using positron emitters such as C-11, N-13 and O-15, functional/physiological molecules such as water, oxygen gas, carbon dioxide gas and ammonia, can be radiolabeled without modifying the structure or behavior, which makes these molecules suitable for the precise evaluation of physiological function and its deviation under pathological conditions. Although 18F-fluorodeoxyglucose (FDG), a marker of glucose metabolism, is the most commonly used PET probe especially in the field of oncology, many PET probes are available to evaluate various important characteristics such as blood flow, metabolism, tumor hypoxia, and neurotransmitter and receptor conditions, and are applied in the fields of oncology, neurology/psychiatry and cardiology.