Nitrogen-13
A radioactive gas-forming isotope with a ten-minute lifetime, turned into ammonia and injected to map blood flow to the heart muscle on a PET scan.
Overview
Nitrogen-13 decays by pure positron emission with a 9.97-minute half-life. Its main clinical use is as ammonia N-13 injection, an FDA-approved PET myocardial perfusion agent (initial US approval 2007) used at rest and under pharmacological stress to evaluate suspected or existing coronary artery disease; it clears the blood with a biological half-life of under three minutes and is trapped in viable myocardium as glutamine.
It is made on a cyclotron via the 16O(p,α)13N reaction, typically by irradiating a dilute ethanol-in-water target, with the proton beam degraded to avoid co-producing oxygen-15 by the competing 16O(p,pn)15O channel. Because the ten-minute half-life is even shorter than fluorine-18's, N-13 ammonia must be made on site or very close to the scanner, which historically limited it to centres with an in-house cyclotron; compact superconducting mini-cyclotrons introduced in the 2010s and 2020s have made single-site N-13 ammonia production more practical for community cardiac PET programmes.
Alongside 82Rb and 15O-water, 13N-ammonia is one of only a small number of PET perfusion tracers, and one of only two (with 82Rb) that carry FDA approval for that indication in the United States.
- β+ 100% (max 1.19 MeV)
- annihilation γ 511 keV
A radioactive form of ammonia gas, made fresh on site in a cyclotron and injected into a vein; heart muscle cells trap it in proportion to how much blood is flowing through, so a PET scan maps blood flow to the heart very precisely.
The newest heart PET tracer, approved in the US in September 2024. It sticks tightly to a protein inside heart-muscle mitochondria in proportion to blood flow, lasts long enough to be made off site and shipped like a hospital's regular PET drug, and is the first cardiac PET tracer practical to pair with a treadmill exercise test.
A generator-produced radioactive form of the metal rubidium, chemically similar to potassium, given as a fast intravenous infusion; because it decays away in about a minute and a half it can be produced on site without a cyclotron, letting a PET scan of heart blood flow be done in around half an hour.
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