nitrogen13

Nitrogen-13 (13N) is a radioactive isotope of nitrogen with a mass number of 13. It contains seven protons and six neutrons. 13N is not stable and is used primarily in medical imaging due to its positron emission pathway.

13N decays by positron emission to carbon-13 (13C) with a half-life of about 9.97 minutes. The emitted positrons quickly annihilate with electrons, producing two 511 keV gamma photons. This radiative signature enables the tracing of metabolic processes in positron emission tomography (PET). The short half-life means that radiosynthesis and imaging must be performed close to the point of use.

Production and availability

13N is produced in cyclotrons through proton irradiation of oxygen-16 targets. A common reaction is 16O(p, α)13N, typically using water enriched in 16O as the target. The short half-life requires on-site or nearby radiochemical facilities to prepare usable radiopharmaceuticals and to minimize decay losses during transport. The radiolabeled products are then formulated for rapid administration to patients.

Medical applications

The most widely used 13N-labeled tracer is ammonia, [13N]ammonia, employed in PET imaging to assess myocardial perfusion and cerebral blood flow. Its rapid uptake and clearance make it suitable for dynamic imaging studies. Beyond ammonia, other 13N-labeled compounds have been investigated, but they remain less common in routine clinical practice due to the logistics of near-site production.

Safety and handling

As a radiopharmaceutical, 13N requires controlled production, sterile formulation, and appropriate shielding and monitoring. Its short half-life limits long-term radiation exposure and enables rapid decay once administration is complete, but it also imposes stringent infrastructure requirements for safe use in clinical settings.