Fundamentals of PET-radiochemistry

Positron emission tomography (PET) is a powerful imaging technique using compounds labeled with short-lived positron emitting radioisotopes for the in-vivo study of molecular interactions and molecular pathways in the human body. The unique sensitivity and specificity of PET make the methodology also a very attractive scientific tool in drug development and evaluation. In combination with appropriately labeled radiotracer, PET offers exceptional possibilities to study physiology, metabolism, pharmacokinetics and modes of action of novel drugs. The key element in PET is the PET-radiotracer, a compound labeled with a short-lived positron emitter. The most useful positron-emitters carbon-11 and fluorine-18 have half-lives measured in minutes, being 20.4 min and 109.8 min. respectively. Consequently, times dominates all aspects of PET, and the radiotracer must be synthesized within a time frame compatible with the half-life of the radioisotope. Thus, the extensive development of the radiochemistry of positron-emitters carbon-11 and fluorine-18 is fundamental but also a special challenge. In this context, the recent developments of organic PET radiochemistry and its potential impact on drug development and evaluation will be discussed.