Medical Uses
In 1970, Exckelman and Richards presented in 1970 the first "kit" containing all the ingredients required to release the Tc-99m, "milked" from the generator, in the chemical form to be administered to the patient.
Technetium-99m is used in 20 million diagnostic nuclear medical procedures every year. Approximately 85% of diagnostic imaging procedures in nuclear medicine use this isotope as radioactive tracer. It conveniently dissolves in aqua regia, nitric acid, and concentrated sulfuric acid, but it is not soluble in hydrochloric acid of any strength. Klaus Schwochau's book Technetium lists 31 radiopharmaceuticals based on 99mTc for imaging and functional studies of the brain, myocardium, thyroid, lungs, liver, gallbladder, kidneys, skeleton, blood, and tumors. Depending on the procedure, the 99mTc is tagged (or bound to) a pharmaceutical that transports it to its required location. For example, when 99mTc is chemically bound to exametazime, the drug is able to cross the blood–brain barrier and flow through the vessels in the brain for cerebral blood-flow imaging. This combination is also used for labeling white blood cells to visualize sites of infection. 99mTc sestamibi is used for myocardial perfusion imaging, which shows how well the blood flows through the heart. Imaging to measure renal function is done by attaching 99mTc to mercaptoacetyl triglycine (MAG3); this procedure is known as a MAG3 scan.
Technetium-99m can be readily detected in the body by medical equipment because it emits 140.5 keV gamma rays (these are about the same wavelength as emitted by conventional X-ray diagnostic equipment), and its half-life for gamma emission is six hours (meaning 94% of it decays to 99Tc in 24 hours). The "short" physical half-life of the isotope and its biological half-life of 1 day (in terms of human activity and metabolism) allows for scanning procedures which collect data rapidly, but keep total patient radiation exposure low.
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