Properties of Technetium-99m
Technetium-99m is used because of its properties which have ideal characteristics for medical scanning:
- it has a very short half-life of 6 hours which is long enough to examine metabolic processes, yet short enough to minimise the radiation dose to the patient.
- it emits low energy gamma radiation that minimises damage to tissues but can still be detected in a person's body by a gamma ray sensitive camera
- it is quickly eliminated from the body
- technetium is reasonably reactive; it can be reacted to form a compound with chemical properties that leads to concentration in the organ of interest such as the heart, liver, lungs, bones or thyroid
- Technetium-99m decays by a process called "isomeric"; which emits gamma rays and low energy electrons. Since there is no high-energy beta emission the radiation dose to the patient is low.
- The low energy gamma rays it emits easily escape the human body and are accurately detected by a gamma camera.
- The chemistry of technetium is so versatile it can form tracers by being incorporated into a range of biologically-active substances to ensure that it concentrates in the tissue or organ of interest.
- Tc-99m can be changed to a number of oxidation states. This enables production of a wide range of biologically active chemicals. The Tc-99m is attached to a biological molecule that concentrates in the organ to be investigated.
- The short half-life of the isotope allows for scanning procedures that collect data rapidly.
- The fact that both its physical half-life and its biological half-life are very short leads to very fast clearing from the body after an imaging process.
- A further advantage is that the gamma is a single energy, not accompanied by beta emission, and that permits more precise alignment of imaging detectors.