Uses of Technetium-99m
Technetium-99m (Tc-99m) is used in a wide range of medical applications, such as distinguishing brain tumours. Over 10,000 hospitals worldwide use radioisotopes in medicine, and about 90% of the procedures are for diagnosis. The most common radioisotope used in diagnosis is technetium-99, with some 30 million procedures per year, accounting for 80% of all nuclear medicine procedures worldwide.
Technetium-99m is used to image the skeleton and heart muscle in particular, but also for brain, thyroid, lungs, liver, spleen, kidney, gall bladder, bone marrow, salivary and lacrimal glands, heart blood pool, infection and numerous specialised medical studies. This diagnostic imaging uses Technetium-99m as a radioactive tracer which can be detected in the body by medical equipment, such as gamma cameras.
When using technetium-99m, the radioisotope is given to the patient and the escaping gamma rays are shown upon a moving gamma camera which computes and processes the image. To acquire images, the gamma camera is rotated around the patient. Projections are collected at defined points during the rotation, normally every three to six degrees. In most cases, a full 360° rotation is used to collect an optimal reconstruction. The time taken to collect each projection is also variable, but 15–20 seconds are usual. This gives a total scan time of around 15–20 minutes.
The technetium-99m radioisotope is used predominantly in bone and brain scans. For bone scans, it is used directly, as they attempt to heal a skeletal injury, or in some cases as a reaction of these cells to a tumor in the bone. In brain scanning, it is useful for the detection of strokes and dementing illnesses.
The radioactive properties of 99mTc can be used to identify the predominant lymph nodes draining a cancer, such as breast cancer or melanoma. This is usually performed at the time of the medical check up. Immunoscintigraphy (finding cancer cells) includes it into an immune system protein capable of binding to cancer cells. A few hours after injection, medical equipment is used to detect the gamma rays emitted by the Technetium-99m; higher concentrations show where the tumor is. This technique is particularly useful for detecting hard-to-find cancers.
^ (Above Left) Thyroid scan
A shows the healthy result
A shows the healthy result