Fluorine-18 (¹⁸F, also called radiofluorine) is a

fluorine Fluorine is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...

radioisotope which is an important source of

positron The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...

s. It has a mass of 18.0009380(6) u and its

half-life Half-life is a mathematical and scientific description of exponential or gradual decay. Half-life, half life or halflife may also refer to: Film * Half-Life (film), ''Half-Life'' (film), a 2008 independent film by Jennifer Phang * ''Half Life: ...

is 109.771(20) minutes. It decays by

positron emission Positron emission, beta plus decay, or β+ decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (). Positron emi ...

96.7% of the time and

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Th ...

3.3% of the time. Both modes of decay yield stable oxygen-18.

Natural occurrence

is a natural trace radioisotope produced by cosmic ray spallation of atmospheric argon as well as by reaction of protons with natural oxygen: ¹⁸O + p → ¹⁸F + n.SCOPE 50 - Radioecology after Chernobyl
, the Scientific Committee on Problems of the Environment (SCOPE), 1993. See table 1.9 in Section 1.4.5.2.

Synthesis

In the radiopharmaceutical industry, fluorine-18 is made using either a

cyclotron A cyclotron is a type of particle accelerator invented by Ernest Lawrence in 1929–1930 at the University of California, Berkeley, and patented in 1932. Lawrence, Ernest O. ''Method and apparatus for the acceleration of ions'', filed: Januar ...

linear particle accelerator A linear particle accelerator (often shortened to linac) is a type of particle accelerator that accelerates charged subatomic particles or ions to a high speed by subjecting them to a series of Oscillation, oscillating electric potentials along ...

to bombard a target, usually of natural or enriched sup>18Oater with high energy

protons A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' ( elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an electron (the pro ...

(typically ~18 MeV). The fluorine produced is in the form of a water solution of sup>18F luoride, which is then used in a rapid chemical synthesis of various radio pharmaceuticals. The organic oxygen-18 pharmaceutical molecule is not made before the production of the radiopharmaceutical, as high energy protons destroy such molecules ( radiolysis). Radiopharmaceuticals using fluorine must therefore be synthesized after the fluorine-18 has been produced.

History

First published synthesis and report of properties of fluorine-18 were in 1937 by Arthur H. Snell, produced by the nuclear reaction of ²⁰Ne(d,α)¹⁸F in the cyclotron laboratories of Ernest O. Lawrence.

Chemistry

Fluorine-18 is often substituted for a

hydroxyl group In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydroxy ...

in a radiotracer parent molecule, due to similar steric and electrostatic properties. This may however be problematic in certain applications due to possible changes in the molecule polarity.

Applications

Fluorine-18 is one of the early tracers used in

positron emission tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, r ...

(PET), having been in use since the 1960s. Its significance is due to both its short half-life and the emission of positrons when decaying. A major medical use of fluorine-18 is: in positron emission tomography (PET) to image the brain and heart; to image the thyroid gland; as a radiotracer to image bones and seeking cancers that have metastasized from other locations in the body and in radiation therapy treating internal tumors. Tracers include sodium fluoride which can be useful for skeletal imaging as it displays high and rapid bone uptake accompanied by very rapid blood clearance, which results in a high bone-to-background ratio in a short time and fluorodeoxyglucose (FDG), where the ¹⁸F substitutes a hydroxyl. New dioxaborolane chemistry enables radioactive fluoride (¹⁸F) labeling of

antibodies An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as bacteria and viruses, including those that caus ...

, which allows for

(PET) imaging of

cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

. A Human-Derived, Genetic, Positron-emitting and Fluorescent (HD-GPF) reporter system uses a human protein, PSMA and non-immunogenic, and a small molecule that is positron-emitting (¹⁸F) and fluorescent for dual modality PET and fluorescence imaging of genome modified cells, e.g.

, CRISPR/Cas9, or CAR T-cells, in an entire mouse. The dual-modality small molecule targeting PSMA was tested in humans and found the location of primary and metastatic

prostate cancer Prostate cancer is the neoplasm, uncontrolled growth of cells in the prostate, a gland in the male reproductive system below the bladder. Abnormal growth of the prostate tissue is usually detected through Screening (medicine), screening tests, ...

, fluorescence-guided removal of cancer, and detects single cancer cells in tissue margins.

References

{{Isotope sequence , element=fluorine , lighter= fluorine-17 , heavier= fluorine-19 , before= neon-18 , after= oxygen-18 Isotopes of fluorine Medicinal radiochemistry Positron emitters Medical isotopes