PET radiotracer is a type of radioligand that is used for the diagnostic purposes via positron emission tomography imaging technique

MECHANISM

PET is a functional imaging technique that produces a three-dimensional image of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide (tracer), which is introduced into the body on a biologically active molecule.

APPLICATION

In in vivo systems it is often used to quantify the binding of a test molecule to the binding site of radioligand. The higher the affinity of the molecule the more radioligand is displaced from the binding site and the increasing radioactive decay can be measured by scintillography. This assay is commonly used to calculate binding constant of molecules to receptors. Due to the probable injuries of PET-radiotracers, they could not be administrated in the normal doses of the medications. Therefore, the binding affinity (P_KD) of the PET-tracers must be high. In addition, since via the PET imaging technique is desired to investigate a function accurately, the selectivity of bindings to the specific targets is very important.

PET scanning is a non-invasive imaging method that differs from others because it observes "in vivo" metabolic activity using radio-isotopes with specific tissutal tropism. More in detail PET scans necessitate the injection of a small quantity of biologically important material like glucose or oxygen which have labelled with radio-nuclides such as carbon-11, nitrogen-13, oxygen-15 and fluoride-18.

All the used isotopes are radioactive with a rapid time of decaying by positron emission: carbon-11 or 11C is a radioactive isotope of carbon with a half-life in the order of twenty minutes. Nitrogen-13 or 13N is an isotope of nitrogen with a half life of approximately ten minutes. Oxygen-15 or 15O is an isotope of oxygen having a half life of about two minutes.

The most commonly used isotope in PET scans is fluorine-18. It is a fluorine isotope with a half life of approximately 110 minutes. This tracer is very useful because of its long half life and because it decays by emitting positrons having the lowest positron energy which contributes to a high-resolution imaging acquire.