Fluorine-18

Fluorine-18 (18F) is a fluorine radioisotope which is an important source of positrons. It has a mass of 18.0009380(6) u and its half-life is 109.771(20) minutes. It decays by positron emission 96.7% of the time and electron capture 3.3% of the time. Both modes of decay yield stable oxygen-18.

Fluorine-18, 18F
Decay over 24 hours
General
Symbol18F
Namesfluorine-18, 18F, F-18,
Fluorine-18
Protons (Z)9
Neutrons (N)9
Nuclide data
Natural abundanceRadioisotope
Half-life (t1/2)109.771(20) min
Isotope mass18.0009380(6) Da
Spin1+
Excess energy873.431±0.593 keV
Binding energy137369.199±0.593 keV
Decay products18O
Decay modes
Decay modeDecay energy (MeV)
Positron emission (97%)0.6335
Electron capture (3%)1.6555
Isotopes of fluorine
Complete table of nuclides

Natural occurrence

18
F 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.[1]

Synthesis

In the radiopharmaceutical industry, fluorine-18 is made using either a cyclotron or linear particle accelerator to bombard a target, usually of natural or enriched [18O]water[2] with high energy protons (typically ~18 MeV). The fluorine produced is in the form of a water solution of [18F]fluoride, 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.[3]

Chemistry

Fluorine-18 is often substituted for a hydroxyl group (–OH) 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 (PET), having been in use since the 1960s.[4] 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[5] and fluorodeoxyglucose (FDG), where the 18F substitutes a hydroxyl. New dioxaborolane chemistry enables radioactive fluoride (18F) labeling of antibodies, which allows for positron emission tomography (PET) imaging of cancer.[6] 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. cancer, CRISPR/Cas9, or CAR T-cells, in an entire mouse.[7] The dual-modality small molecule targeting PSMA was tested in humans and found the location of primary and metastatic prostate cancer, fluorescence-guided removal of cancer, and detects single cancer cells in tissue margins.[8]

References
  1. SCOPE 50 - Radioecology after Chernobyl Archived 2014-05-13 at the Wayback Machine, the Scientific Committee on Problems of the Environment (SCOPE), 1993. See table 1.9 in Section 1.4.5.2.
  2. Fowler J. S. and Wolf A. P. (1982). The synthesis of carbon-11, fluorine-18 and nitrogen-13 labeled radiotracers for biomedical applications. Nucl. Sci. Ser. Natl Acad. Sci. Natl Res. Council Monogr. 1982.
  3. Anonymous (1937-01-15). "Minutes of the Pasadena Meeting, December 18 and 19, 1936". Physical Review. 51 (2). #5 shows the abstract of Arthur H. Snell about the discovery of the first produced fluorine-18.: 142–150. Bibcode:1937PhRv...51..142.. doi:10.1103/PhysRev.51.142. ISSN 0031-899X.
  4. Blau, Monte; Ganatra, Ramanik; Bender, Merrill A. (January 1972). "18F-fluoride for bone imaging". Seminars in Nuclear Medicine. 2 (1): 31–37. doi:10.1016/S0001-2998(72)80005-9. PMID 5059349.
  5. Ordonez, A. A.; DeMarco, V. P.; Klunk, M. H.; Pokkali, S.; Jain, S.K. (October 2015). "Imaging Chronic Tuberculous Lesions Using Sodium [18F]Fluoride Positron Emission Tomography in Mice". Molecular Imaging and Biology. 17 (5): 609–614. doi:10.1007/s11307-015-0836-6. PMC 4561601. PMID 25750032.
  6. Rodriguez, Erik A.; Wang, Ye; Crisp, Jessica L.; Vera, David R.; Tsien, Roger Y.; Ting, Richard (2016-04-27). "New Dioxaborolane Chemistry Enables [18F]-Positron-Emitting, Fluorescent [18F]-Multimodality Biomolecule Generation from the Solid Phase". Bioconjugate Chemistry. 27 (5): 1390–1399. doi:10.1021/acs.bioconjchem.6b00164. PMC 4916912. PMID 27064381.
  7. Guo, Hua; Harikrishna, Kommidi; Vedvyas, Yogindra; McCloskey, Jaclyn E; Zhang, Weiqi; Chen, Nandi; Nurili, Fuad; Wu, Amy P; Sayman, Haluk B. (2019-05-23). "A fluorescent, [ 18 F]-positron-emitting agent for imaging PMSA allows genetic reporting in adoptively-transferred, genetically-modified cells". ACS Chemical Biology. 14 (7): 1449–1459. doi:10.1021/acschembio.9b00160. ISSN 1554-8929. PMC 6775626. PMID 31120734.
  8. Aras, Omer; Demirdag, Cetin; Kommidi, Harikrishna; Guo, Hua; Pavlova, Ina; Aygun, Aslan; Karayel, Emre; Pehlivanoglu, Hüseyin; Yeyin, Nami; Kyprianou, Natasha; Chen, Nandi (March 2021). "Small Molecule, Multimodal [18F]-PET and Fluorescence Imaging Agent Targeting Prostate Specific Membrane Antigen: First-in-Human Study". Clinical Genitourinary Cancer. 19 (5): 405–416. doi:10.1016/j.clgc.2021.03.011. PMC 8449790. PMID 33879400.
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