Technetium-99m
The single most widely used medical radioisotope: a metastable metal with a six-hour lifetime, milked on demand from a bedside generator (a 'moly cow') and attached to a cold kit to image bone, heart, kidneys or lymph nodes.
Overview
Technetium-99m decays with a 6.0067-hour half-life, almost entirely by isomeric transition, emitting a 140.5 keV gamma ray that sits close to the energy of diagnostic X-ray equipment and is close to ideal for gamma-camera and SPECT imaging. It underpins on the order of tens of millions of scans a year worldwide (bone scans, myocardial perfusion, sentinel lymph node mapping, renal and hepatobiliary studies), each prepared on site by adding the eluted pertechnetate to a lyophilised cold kit.
It is the daughter of molybdenum-99 (65.94-hour half-life), which is shipped to hospital and radiopharmacy radiopharmacies worldwide as a 99Mo/99mTc generator; the longer-lived parent decays continuously and the daughter is eluted, typically once or twice a day, for use within hours before it decays away. This generator relationship is what makes just-in-time global distribution of a six-hour isotope possible at all.
Because supply of 99mTc is entirely downstream of 99Mo production, its reliability tracks the well-documented fragility of that upstream reactor supply chain (see mo-99): unplanned reactor outages, most recently the October 2024 shutdown of the High Flux Reactor in the Netherlands, have repeatedly caused short-notice shortages of Tc-99m-based scans.
- γ 140.5 keV (89%)
- internal conversion electrons (~11% of decays)
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.
A radioactive form of fluoride that collects in areas of bone rebuilding. A PET scan after the injection shows those hot spots, which can be cancer that has spread to bone or something harmless like a healed fracture.
A puff of radioactive carbon particles so fine they travel with the breath into the depths of the lung, where they stick. A gamma camera then photographs which parts of the lung are getting air, which is compared with a second scan showing which parts are getting blood.
A Chinese-invented injection that makes tumours visible on the cheap, widely available type of scanner (SPECT) rather than the expensive one (PET). It was approved in China in April 2026 to check whether lung cancer has spread to the lymph nodes.
Tiny clumps of albumin, a normal blood protein, tagged with a radioactive marker and injected into a vein. They wedge briefly in the smallest blood vessels of the lung wherever blood is flowing, so the scan maps the lung's blood supply; the clumps then break up and clear.
The standard, decades-old bone scan: a radioactive tracer that sticks to areas of bone rebuilding, so a gamma-camera picture afterwards shows where cancer may have spread to bone, or where a fracture or infection is healing.
A version of the PSMA prostate cancer scan that uses the same cheap, widely available radioactive tag as a standard bone scan instead of the PET tracers. Surgeons can also carry a small radiation detector into the operating room to help find and remove cancerous lymph nodes. It has not been through formal drug approval; it is used as an academic, in-house preparation.
A bone-scanning radioactive tracer that also sticks to stray protein deposits that build up in a stiffened heart in transthyretin amyloidosis. Comparing how brightly the heart lights up against the ribs on the same scan tells doctors whether this specific, now-treatable type of heart disease is present, usually without needing a heart biopsy.
A radioactive tracer injected into a vein that lodges inside heart muscle cells in proportion to blood flow, so a gamma camera picture taken after exercise or a stress drug shows which parts of the heart are not getting enough blood.
Technetium sulfur colloid is the radioactive tracer injected around a breast cancer or melanoma before surgery so the surgeon can find the first lymph node the tumour drains to and remove only that node instead of the whole basin.
A radioactive tracer, chemically similar to Cardiolite, injected into a vein and taken up by heart muscle in proportion to blood flow; a gamma camera scan after rest and after exercise or a stress drug shows areas with reduced blood supply.
A cold-kit radioactive tracer that maps blood flow inside the brain on a SPECT scan, used mainly to look for the effects of stroke and, off-label in practice, to help support a diagnosis of brain death.
The purpose-built tracer for sentinel lymph node mapping in breast cancer, melanoma and oral cancer, replacing off-label sulfur colloid.
The original heart-blood-flow tracer: a radioactive form of the metal thallium that heart muscle cells pull in almost like potassium, so a scan straight after exercise and a second scan hours later can tell a starved-but-alive muscle from permanently dead muscle without a second injection.
Tiny radioactive beads are injected through a small tube into the artery that feeds the liver. They lodge in the tumour and give it radiation from the inside, mostly sparing the rest of the liver.
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