Uses In Medicine
Looking Inside the Human Body
Instead of relying on x-rays, doctors can use the radiation given off by certain radioisotopes to take pictures of the internal workings of the body. To do this, a radioisotope is concentrated in an organ, such as the heart or the brain, and an external camera, sensitive to the emitted radiation, produces an image of the organ. One method of imaging an organ with a radioisotope is called single photon emission computed tomography (SPECT), and the process is called a SPECT scan.
Some elements concentrate naturally in certain parts of the body-iodine in the thyroid, potassium in the muscles, and so one. For this reason, doctors can use radioisotopes of these elements for certain types of procedures. If the required radioisotope does not concentrate naturally in the organ under study, a radioisotope can be chemically attached to a compound that will carry it to the organ so that a picture can be taken. This process is called labeling, and the procedure has greatly expanded how radioisotopes can be used to diagnose disease.
With technetium-99m, now the most widely used radioisotope for diagnosis, doctors examine the brain, heart, blood, lungs, liver, kidneys, thyroid, spleen, and bone. For example, the loss of calcium in older people-especially women-can lead to weakened bones and a condition called osteoporosis. To diagnose the condition, doctors can view a patient's skeleton by injecting technetium-99m into the blood in a chemical form that concentrates in the bones. From pictures taken by a sensitive camera, doctors diagnose the condition of the bones and prescribe treatment.
Heart Disease and Other Diagnoses
Doctors currently use two radioisotopes to detect the risk of heart disease: thallium-201 and technetium-99m. Doctors inject one of the radioisotopes into the patient's blood while the patient exercises on a treadmill. The radioisotope concentrates in the heart and allows doctors to follow the blood flow. Looking at an image of the heart, doctors can see whether there is reduced blood flow through the arteries leading to the heart, which can signal heart disease.
Radioisotopes such as carbon-11 or fluoroine-18 provide another method of looking at internal organs. These radioisotopes emit positively charged beta particles-called positrons-and pairs of gamma rays traveling in opposite directions. Moveable cameras can detect the rays and create a three-dimensional image on a computer. The technique is called positron emission tomography (PET).
Doctors also use these scanning methods to study the circulatory system and examine brain activity, adding to our understanding of epilepsy, schizophrenia, Parkinson's disease, strokes, Down's syndrome, and Huntington's chorea.
Cancer Treatment
The property of radiation that makes it dangerous also makes it useful in healing. When radiation's energy is deposited in living tissue, cells can be damaged or destroyed. For this very reason, radioisotopes play an important role in cancer therapy. Large doses of radiation focused directly on a cancer can destroy it with little damage to surrounding tissue.
An important advance in the radiation treatment of cancer involves artificial antibodies labeled with radioisotopes. Our bodies naturally produce antibodies that attack foreign matter to eliminate it from the body. Recent advances in biotechnology have enabled scientists to manufacture artificial antibodies. Artificial antibodies can be genetically engineered to bind to a type of molecule found primarily in a cancerous tumor in order to prevent the cancer from growing.
Surgical Tools
In addition to their importance in the diagnosis and treatment of diseases, radioisotopes play an important role in the sterilization of medical supplies. Syringes, surgical gloves, and pharmaceuticals like ointments and powders, which might be damaged by conventional methods of sterilization, are routinely treated by radiation from radioisotopes. Other supplies, such as petri dishes, test tubes, and surgical instruments, are also sterilized with radiation.
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