rubidium-82

rubidium-82 is a radioactive isotope of the alkali metal rubidium, widely utilized as a positron emission tomography tracer in nuclear cardiology. It is a generator-produced nuclide with a short half-life, decaying to stable krypton-82. Its primary clinical use is in myocardial perfusion imaging for the diagnosis of coronary artery disease.

Properties

Rubidium-82 is an artificial isotope with no natural abundance, possessing a nuclear spin of 1⁺ and a mass excess of approximately −76 keV. Its most critical physical property is a half-life of 1.273 minutes, which necessitates on-site production via a radioisotope generator. It decays almost exclusively by positron emission (β⁺), with a minor branch for electron capture, both pathways yielding the stable daughter nuclide krypton-82. The emitted positrons have a maximum energy of 3.379 MeV, resulting in an average positron range in tissue of about 5.9 mm, which influences the spatial resolution of PET scan images.

Production

Commercial production of rubidium-82 relies on the decay chain of its longer-lived parent isotope, strontium-82, which has a half-life of 25.36 days. Strontium-82 is typically produced by proton irradiation of a molybdenum target at a particle accelerator facility like TRIUMF or the Los Alamos Neutron Science Center. The purified strontium-82 is then adsorbed onto a tin dioxide or stannic oxide column to create a rubidium-82 generator, often referred to by the trade name CardioGen-82. Through elution with a sterile sodium chloride solution, the short-lived rubidium-82 is washed from the column as the strontium-82 decays, providing a sterile, pyrogen-free solution for intravenous injection.

Medical applications

The principal application of rubidium-82 is in myocardial perfusion imaging (MPI) using positron emission tomography. It is administered to patients to assess blood flow to the myocardium both at rest and under pharmacological stress, typically induced by agents like adenosine or dipyridamole. This technique is a cornerstone of nuclear cardiology for diagnosing coronary artery disease, evaluating the significance of coronary stenosis, and assessing myocardial viability after events like myocardial infarction. Its rapid uptake and clearance kinetics, coupled with the high image quality of PET-CT, offer advantages over traditional SPECT imaging with technetium-99m or thallium-201.

Decay

Rubidium-82 decays with a half-life of 1.273 minutes primarily via positron emission (96.2% probability) to the ground state of stable krypton-82. The remaining 3.8% of decays occur through electron capture to the same product. Each positron emission event is followed by annihilation with an electron, producing two coincident 511 keV gamma ray photons detected in coincidence by the PET scanner. The decay scheme is simple, with no significant gamma emissions from excited states of the daughter nucleus, making it an ideal pure positron emitter for medical imaging.

Safety and handling

Handling of rubidium-82 is governed by strict radiopharmacy protocols and regulations from bodies like the Nuclear Regulatory Commission and the International Atomic Energy Agency. The primary radiation safety concern is not rubidium-82 itself, but potential breakthrough of the parent strontium-82 or its granddaughter strontium-85 from the generator, which have longer half-lives and different biodistribution. Generators must be tested frequently for such breakthrough as mandated by the U.S. Food and Drug Administration. Patient doses are kept as low as reasonably achievable (ALARA principle), and all procedures follow guidelines from the Society of Nuclear Medicine and Molecular Imaging.

Category:Rubidium Category:Medical isotopes Category:Positron emission tomography