Which isotopes are used in nuclear medicine?

Answer 1

Radioisotopes give doctors the ability to "look" inside the body and observe soft tissues and organs, in a manner similar to the way x-rays provide images of bones. Radioisotopes carried in the blood also allow doctors to detect clogged arteries or check the functioning of the circulatory system. Some chemical compounds concentrate naturally in specific organs or tissues in the body. For example, iodine collects in the thyroid while various compounds of technetium-99m* (Tc-99m) collect in the bones, heart, and other organs. Taking advantage of this proclivity, doctors can use radioisotopes of these elements as tracers. A radioactive tracer is chemically attached to a compound that will concentrate naturally in an organ or tissue so that a picture can be taken. The process of attaching a radioisotope to a chemical compound is called labeling. To detect problems within a body organ, doctors use radio-pharmaceuticals or radioactive drugs. Radioisotopes that have short half-lives are preferred for use in these drugs to minimize the radiation dose to the patient. In most cases, these short-lived radioisotopes decay to stable elements within minutes, hours, or days, allowing patients to be released from the hospital in a relatively short time. The radioisotope used in about 80 percent of nuclear diagnostic procedures is Tc-99m. The penetrating properties of its gamma rays and its short (6-hour) half-life help reduce risk to the patient from more prolonged radiation exposure. Because of their short half-lives, certain radio-pharmaceuticals must be produced, shipped to the hospital, and then used within a couple of weeks. Short-lived radionuclides such as Tc-99m, gallium-67, and thallium-201 are often used to diagnose the functioning of the heart, brain, lung, kidney, or liver. For example, Tc-99m is used to diagnose osteoporosis, a condition caused by calcium deficiency in older people, especially women. To evaluate the presence of Heart disease, a radioisotope is injected into a patient's bloodstream while he or she is exercising on a treadmill. The radioisotope travels toward the heart, allowing doctors to follow the blood flow on a screen. While looking at the image, doctors can check for reduced blood flow through the arteries, a possible signal of heart disease. Nuclear imaging is also used to evaluate brain function. Organic radio-chemicals are labeled with F-18 and then injected into the bloodstream. A device called a gamma camera detects radiation emitted from the organ, displaying an image that can enable the physician to detect blockages or other dysfunctional activity. For some diagnostic tests, the patient need not come into contact with radioactivity at all. The tests are performed on blood or other fluids taken from the patient, using a procedure called radio-immunoassay. These tests can detect some diseases by identifying and measuring the amounts of hormones, vitamins, enzymes, or drugs in the body. The same property that makes radiation hazardous can also make it useful in helping the body heal. When living tissue is exposed to high levels of radiation, cells can be destroyed or damaged so they can neither reproduce nor continue their normal functions. For this reason radioisotopes are used in the treatment of cancer (which amounts to uncontrolled cell division). Although some healthy tissue surrounding a tumor may be damaged during the treatment, mostly cancerous tissue can be targeted for destruction. A device called a teletherapy unit destroys malignant tumors with gamma radiation from a radioisotope such as cobalt-60 (Co-60). Teletherapy units use a high-energy beam of gamma rays to reduce or eradicate tumors deep within the body. These units are licensed by the NRC because they use byproduct material that is produced only by a nuclear reactor. Another treatment, called brachytherapy, destroys cells by-placing the radioisotope (in the form of a seated source) directly into the tumor. Generally, two techniques are used for this type of treatment: (1) direct, manual implantation of a radiation source by a physician or (2) automated implantation using a device called a remote afterloader. The NRC as well as Agreement States license these brachytherapy devices. Using these devices, a small, thin wire or sealed needle containing radioactive material, such as iridium-192 (Ir-192) or iodine-125 (1-125), is inserted directly into the cancerous tissue. The radiation from the isotope attacks the tumor as long as the device is in place. When the treatment is complete, long-lived material (Ir- 1 92) is removed, but short-lived radioisotopes (1-125) may be left permanently. This technique is used frequently to treat mouth, breast, lung, and uterine cancer. Brachytherapy and teletherapy procedures are performed only in hospitals or clinics by trained medical personnel. Strict controls and safety requirements set by the NRC or the Agreement States must be followed. For example, treatment rooms must have adequate shielding to prevent scattered radiation from penetrating into an adjacent room. Radiation monitors must be used and patients carefully observed at all times during treatment. Many types of cancer, such as Hodgkin's disease (cancer of the lymph glands) and cancers of the cervix, larynx, and skin, can be treated by radiation alone. Boron capture neutron therapy has been used on a trial basis recently to treat potentially fatal brain cancer. In this procedure, the diseased brain tissue incorporates a neutron-absorbing isotope and then is exposed to neutron radiation originating from a nuclear research reactor. The energy and radiation emitted as a result of the neutron activation slow down the growth of cancer cells and, in some cases, completely kill them. The overall objectives of NRC's safety rules for radiation medicine are to ensure that patients receive only the exposure medically prescribed and that the radiation is delivered in accordance with the physician's instructions. NRC regulations require that physicians and physicists have special training and experience to practice radiation medicine. The training emphasizes safe operation of' nuclear-related equipment and accurate record-keeping. When using radiation as a medical treatment, the physician weighs the potential benefits against the risk of side effects. Intense radiation exposure often destroys tumors that would prove fatal, but side effects such as hair loss, reduced white blood cell count, and nausea can be sever and must be monitored carefully.

Answer 2

They are normally used as tracers. A small amount (Non lethal!!!!!) of a radioactive substance is put into the patient and by monitoring the radioactivity emitted it can be traced where the radioactive substance has moved to.

It is also used in PET scans (Positron emission tomography) and MRI scans )magnetic resonance Imaging) possibly also used in CAT scans, I don't know how they work though.

Answer 3

There are a variety, depending on the type of imaging being performed. The most common by far is Tc-99m.

Answer 4

Iodine-131, phosphorus-32 are commonly used in radiotherapy.