Use of Fluorine 18 in Nuclear Medicine Fluorine 18 is a positron emitter with a half life of 109.77 minutes. It is used in PET scans.
Decay mode: 9F18 8O18 + +1e0 (1.656 MeV). Oxygen 18 is stable. The positron travels only a few millimetres in the human body before it meets an electron, when both are annihilated producing two gamma ray photons. The energy of each gamma ray photon is 511 MeV, the rest mass of the electron, so presumably the positron looses some energy prior to annihilation. The typical exposure from a PET scan is about 7 mSv.
Production: Irradiation of the stable oxygen 18 isotope with high energy protons (18 MeV) from a cyclotron. 8O18 + +1p1 9F18 + 0n1. The target is either normal or enriched water.
Half life: 109.77 minutes, which means that the radioisotope must be transported post haste. Ideally a nuclear medicine facility at a hospital would have its own cyclotron.
Fluorine is used as a radioactive tracer in PET Scans mostly as Fluorodeoxyglucose (more precisely 2-Deoxy-2-fluoro-D-glucose or FDG for short), which is a glucose analogue and is taken up by body cells that are high users of glucose such as brain and cancer cells. The presence of Fluorine in the molecule inhibits the body metabolising it as a normal glucose molecule. Once the Fluorine has decayed to Oxygen 18 the normal metabolic process proceeds. A typical dose is 5 - 10 millicuries or 200 to 400 MBq administered by saline drip. The patient is scanned an hour later during which the patient should avoid activity so that the FDG does not go to active muscles.
When one of the carbon atoms is replaced with a Carbon 11 atom, flumazenil becomes a radiopharmaceutical as Carbon 11 is a positron emitter. The PET scan reveals the distribution of the receptor sites for both the benzodiazepines and for the flumazenil. However the half life of Carbon 11 is 20.38 min with a positron with energy of 0.45 MeV
The Cooperative Research Centre for Biomedical Imaging Development (CRCBID) based at ANSTO has produced flumazenil with a Fluorine 18 atom (18FMZ). The longer half life of Fluorine 18 will enhance this diagnostic tool. The press release and the article in The Age discuss the benefits to epilepsy sufferers.