Nuclear Medicine

Nuclear Medicine, medical specialty that uses radioactive substances, or radiopharmaceuticals, combined with imaging techniques to diagnose and treat injury or disease, such as sports injuries, heart disease, cancer, and Alzheimer's disease (see Radiology). When used for diagnosis, nuclear imaging lets doctors study bodily functions as they are occurring. In treatment applications, which are less common, substantially larger doses of radiation are used to destroy diseased tissues. Although some doctors practice nuclear medicine as a full-time specialty, many more physicians in such fields as radiology, pathology, and internal medicine use aspects of nuclear medicine in their work.

At the most basic level, nuclear imaging examines the chemical reactions that occur in the human body. To produce an image, a patient is given (by mouth or injection) a radioactive substance that is chemically drawn to the site of the problem—a specific organ, bony structure, or tissue. Once the substance finds its target, it produces an emission that is transformed into a visible image through the use of a camera-like detector or scanner. The resulting image gives a picture of the structure and function of the target site. Because the substance contains only trace amounts of radioactivity that decay rapidly in the body, this process poses no danger to the patient. As treatment for disease, nuclear medicine is noted for being pain-free as well as safer and more cost-effective than many other treatments, such as surgery or chemotherapy.

Diagnostic tests are typically performed within a patient's body, or in vivo. In some cases, nuclear medicine tests are used to analyze blood or urine specimens in the laboratory, or in vitro. Positron emission tomography (PET) or magnetic resonance imaging (MRI) scanners portray the movement and distribution of the radioactive materials within a patient's body. This approach enables doctors to detect disorders in the earliest stages—often before significant organ or joint damage has occurred. Patients can then start treatment sooner, which ultimately can yield better results.

The applications of nuclear medicine are numerous. Nuclear imaging can detect the narrowing of blood vessels—an early warning sign of possible heart disease or stroke. It can show the rapid absorption of iodine that characterizes hyperthyroidism (a disease of the thyroid gland); the spread of cancer cells to bone; and the function of the nervous system in a patient with a degenerative brain disorder, such as Alzheimer's disease. Similar techniques permit doctors to monitor these and other bodily functions after surgery, after drug treatment, and during radiation therapy.

In treatment applications, a high dose of a radioactive substance is administered to kill diseased cells. For instance, therapy with a form of radioactive iodine can successfully treat hyperthyroidism in some patients by destroying an overactive thyroid gland. In many cancer patients, radiation therapy is used to kill malignant tissue. Researchers are currently working on new applications, including the use of radiopharmaceuticals to clear scarred arteries after heart surgery, and to painlessly remove inflamed tissue from arthritic joints.

The field of nuclear medicine emerged in the 1930s, when researchers began producing radioactive phosphorus in a machine called a cyclotron and using it to treat patients with blood disorders. The invention of the nuclear reactor in 1940 enabled scientists to generate nuclear substances (including those used in medicine) with far greater ease. A significant step in nuclear medicine occurred in 1946, when treatment with radioactive iodine completely stopped the spread of thyroid cancer in a patient. The earliest imaging devices were invented in the 1950s, but complex diagnostic applications were not possible until computers were integrated with these systems in the 1960s. The advent of PET and MRI technology in the 1970s transformed the field, enabling physicians to record the structure and function of virtually every organ in the body—including the brain and spleen, the gastrointestinal tract, and even developing tumors. Radiopharmaceuticals emerged as a specialized field in the 1980s, yielding the development of new radioactive compounds for both diagnostic and therapeutic applications.

In order to obtain board certification in nuclear medicine, physicians must complete a one-year general clinical internship followed by a two-year residency in the specialty. Subspecialties in the field—such as pediatric nuclear medicine, which focuses on the diagnosis and treatment of disease in children—are emerging. In addition to physicians, other health care professionals in the field include certified technologists who administer dosages of radiopharmaceuticals and operate the imaging devices and computer applications; specially trained pharmacists who deal exclusively with radiopharmaceuticals; and physicists who perform instrument testing and development.