USE OF RADIO ISOTOPE IN DIAGNOSIS
Nuclear medicine uses radiation to provide diagnostic information about the functioning of a person's specific organs, or to treat them. Diagnostic procedures are now routine.
· Radiotherapy can be used to treat some medical conditions, especially cancer, using radiation to weaken or destroy particular targeted cells.
· Tens of millions of nuclear medicine procedures are performed each year, and demand for radioisotopes is increasing rapidly.
Radiation is used to both detect and treat abnormalities in the body. We've already discussed the use of iodine-131 therapy for hyperthyroidism. Iodine-131 can also be used in a diagnostic procedure to monitor the function of the thyroid.
The rate at which the thyroid rakes up the iodine-131 can be monitored with a scanning device to see if it is functioning properly.What makes radioisotopes so useful in diagnostic procedures is that the body treats the tagged isotope in the same way that it treats the nonradioactive element.
Therefore, the tagged isotope goes right to the area of the body where you want it to go. For example, iodine, whether it's radioactive or not, goes right to the thyroid, where it is incorporated into the amino acid thyroxine (the only molecule in the body that contains iodine). Therefore, iodine-131 is perfect for monitoring the thyroid gland.
Chromium, in the form of sodium chromate, attaches strongly to the hemoglobin of red blood cells. This makes radioactive chromium-151 an excellent isotope for determining the flow of blood through the heart. This isotope is also useful for determining the lifetime of red blood cells, which can be of great importance in the diagnoses of anemias.
Radioactive cobalt (cobalt-59 or cobalt-60) is used to study defects in vitamin B12 absorption. Cobalt is the metallic atom at the center of the B12 molecule. By injecting a patient with vitamin B12, labeled with radioactive cobalt, the physician can study the path of the vitamin through the body and discover any irregularities.
One method is teletherapy, in which a high-energy beam of radiation is aimed at the cancerous tissues. A second method is brachytherapy, in which a radioactive isotope is placed into the area to be treated. This is usually done by means of a seed, which could be a glass bead containing the isotope. In this way the isotope delivers a constant beam of radiation to the affected area.
The third method is called radiopharmaceutical therapy. This method involves oral or intravenous administration of the isotope. The isotope then uses the normal body pathway to seek its target. This is the method that is used to get iodine-131 to the thyroid gland.
A synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. Examples include technetium-95 and promethium-146. Many of these are found in, and harvested from, spent nuclear fuel assemblies. Some must be manufactured in particle accelerators.
Some synthetic radioisotope are extracted from spent nuclear reactor fuel rods, which contain various fission products. For example, it is estimated that up to 1994, about 49,000 TBq (78 metric ton) of technetium was produced in nuclear reactors, which is by far the dominant source of terrestrial technetium. However, only a fraction of the production is used commercially. Other synthetic isotopes are produced in significant quantities by fission but are not yet being reclaimed. Other isotopes are manufactured by neutron irradiation of parent isotopes in a nuclear reactor (for example, Tc-97 can be made by neutron irradiation of Ru-96) or by bombarding parent isotopes with high energy particles from a particle accelerator.
Most synthetic radioisotopes are extremely radioactive and have a short half life. Though a health hazard, radioactive materials have many medical and industrial uses.
The general field of nuclear medicine covers any use of radioisotopes for diagnosis or treatment.
Radioactive tracer compounds are used to observe the function of various organs and body systems. These compounds use a chemical tracer which is attracted to or concentrated by the activity which is being studied. That chemical tracer incorporates a short lived radioactive isotope, usually one which emits a gamma ray which is energetic enough to travel through the body and be captured outside by a gamma camera to map the concentrations. Gamma cameras and other similar detectors are highly efficient, and the tracer compounds are generally very effective at concentrating at the areas of interest, so the total amounts of radioactive material needed are very small.The metastable nuclear isomer Tc-99m is a Gamma-emitter widely used for medical diagnostics because it has a short half-life of 6 hours, but can be easily made in the hospital using a "technetium-cow".
Radiopharmaceuticals are any of a number of compounds using a radioisotope for medical treatment, usually by bringing the radioactive isotope to a high concentration in the body near a particular organ. For example, iodine-131 is used for treating some disorders and tumors of the thyroid gland.
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