How is thallium 201 used in medicine

Basics and technology

In nuclear medicine, functional examinations of various organs can be carried out, with which diseases and functional disorders of the affected organs can be detected at a very early stage.

In nuclear medicine, special radionuclides, i.e. radioactive substances, are administered which, depending on their nature and chemical composition, take part in various metabolic processes in the body or accumulate in the metabolism of the organ or tissue to be examined.

Examples of radionuclides used in diagnostics are:
99m-Tc-pertechnetate (Tc = technetium) for thyroid examination,
99m-Tc-phosphates for skeletal scintigraphy,
201 thallium for studying myocardial blood flow.

These short-lived radionuclides emit radiation through radioactive decay. The most commonly used nuclide, 99m-Tc, has a short half-life of only 6 hours. The term half-life means that after just 6 hours only half of the radiation dose is still present. Since one does not want to expose the body to radiation exposure for an unnecessarily long time, short-lived nuclides are used in medical diagnostics. In addition, pure gamma emitters are mainly used. In principle, however, nuclides can also contain other radiation components, e.g. ß-radiation. However, this cannot be measured for gamma cameras. Because ß-radiation can also have a harmful effect on organs, it is rather undesirable in diagnostic medicine. The situation is different with therapy with radionuclides. Here ß-emitters are often used.

Gamma camera, SPECT
The activity distribution of the gamma radiation released from the body is measured with so-called gamma cameras. These receive the radiation with special crystal faces (e.g. cesium iodide). Flashes of light are generated in the crystals, which are converted into an electrical signal by detectors. This is how you get a digital image that is further processed with a computer. Color images can then be generated on the basis of the measured values. Here the computer assigns different colors for areas of different activity; For example, the color red stands for a lot of activity, blue for little.

For a better assessment of individual examination regions, slices can be taken without additional radiation exposure, similar to computed tomography. The so-called “Single-Photon-Emission-Computed-Tomography” (SPECT) allows an overlay-free representation of selected areas.