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Nuclear Medicine: Introduction to U.S. & International Regulations and Clinical Practice Resources: What is Nuclear Medicine?

Overview of Nuclear Medicine

Nuclear Medicine is the medical specialty that uses unsealed sources of radiation (liquids and gases) for diagnosis and therapy. These unsealed sources are known as radiopharmaceuticals, drugs that emit radiation.  The Society of Nuclear Medicine has brochures available that provide educational information for the general public and patients.  Another nice source of information for patients is

If Nuclear Medicine terminology is unfamiliar, consulting a glossary may be helpful.

Diagnostic nuclear medicine includes imaging studies as well as in vitro studies of body fluids using radioisotopes in the laboratory. In general, Nuclear Medicine imaging is based on physiologic processes, in contrast to most other radiology procedures, which are based on anatomic changes.  Diagnostic nuclear medicine is typically available in medium to large hospitals as well as some out-patient imaging centers. Therapeutic nuclear medicine is also available at some facilities, including virtually all major medical centers.  The most common diagnostic imaging procedures today are myocardial perfusion scans to determine the function of the heart muscle at rest and during stress, PET (Positron Emission Tomography) scans for cancer and other conditions, and bone scans for cancer, injuries, infections, and other causes of skeletal abnormalities.  

In the U.S., most nuclear medicine procedures are performed under the supervision of radiologists; however, there are also Nuclear Medicine Physicians who specialize in performing these procedures.  Outside of the United States, radiology and nuclear medicine are considered separate specialties.  Nuclear cardiologists may perform nuclear medicine procedures related to the heart and some endocrinologists perform nuclear medicine procedures related to the thyroid gland. The physician is responsible for the performance of the nuclear medicine procedure by the nuclear medicine technologist. The physician also interprets the diagnostic images and issues a report to the referring health care provider. Some physicians also perform therapeutic nuclear medicine procedures.

Radiation Oncology, also known as Radiation Therapy, is different from Nuclear Medicine.  Radiation Oncologists study the use of sealed sources of radiation to treat a wide range of cancers as well as a few non-cancerous conditions.  Sealed sources may be in the form of seeds and wires that may be implanted in the body.  Other sealed sources are located inside radiation producing devices that are designed to control the administration of powerful radiation from outside the body to treat conditions on or inside the body.  Radiation Oncology is focused on treatment, rather than diagnosis.

Diagnostic Nuclear Medicine


The image above shows a PET (Positron Emission Tomography) scan of the upper body using a form of sugar (glucose) with a radioactive tracer attached (fluorine-18).  The more intense the color, the more sugar is being processed by the cells in that area. Notice the intense, though normal, uptake in the brain (in red at the top of the image), and in the heart muscle (the red crescent near the middle of the image). The other two red spots in the upper mid chest are not normal. These scans are often used to detect cancer or to study brain activity.

A nuclear medicine bone scan uses a phosphate compound that is labeled with technetium-99m, a radioactive tracer.  The dark black spots on the bones are areas in which the bone cells are working harder (metabolizing more of the phosphate) in response to cancer that has invaded that area.

Nuclear Medicine Imaging is used for diagnosis of a wide range of diseases and conditions.  Nuclear imaging involves the administration of a small amount of a radiopharmaceutical to the patient. The radiopharmaceutical may be injected into the blood stream, other tissues, or into a body cavity.  The radiopharmaceutical might instead be ingested or inhaled.  The route of administration depends upon the type of procedure being performed. Different radiopharmaceuticals go to different locations in the body depending upon the chemical or physical properties of the radiopharmaceutical. During and/or after the administration of the radiopharmaceutical, special images of the patient are obtained using a gamma camera A gamma camera detects the gamma radiation emitted by the radiopharmaceutical.    The images are displayed on a computer screen and are interpreted by the imaging physician.  The interpreting physician issues a report to the referring health care provider.  The most common diagnostic nuclear medicine procedures are for evaluation of the heart to determine the risk or presence of a heart attack; of the skeleton to look for cancer, injury, or other source of skeletal pain; and of the likelihood of the presence or changes in the distribution of certain types of cancer.

A smaller part of diagnostic nuclear medicine involves in vitro studies. In vitro nuclear medicine uses laboratory equipment, such as test tubes, to study body fluids outside of the body using radiopharmaceuticals. Today the most common in vitro study is to determine red blood cell mass.

Therapeutic Nuclear Medicine

Therapeutic Nuclear Medicine, also known as radionuclide or radioisotope therapy, uses radiopharmaceuticals that emit alpha or beta radiation.  Alpha and beta radiation are more powerful types of radiation than the gamma radiation used for diagnostic imaging, but these types of radiation do not travel as far, so the energy is deposited very close to the location where the radiopharmaceutical localizes in the body.  These radiopharmaceuticals are also administered via injection or ingestion, depending on the type of treatment.  The most common therapy uses Iodine-131, a beta-emitter, to treat certain thyroid problems. 

For More Information

If you prefer to get information via videos, You Tube as a good selection of videos on various nuclear medicine topics, PET scans, understanding radioactivity, and radiation effects.

Radiation Exposure

A special part of the practice of nuclear medicine is constant vigilance to minimize the radiation exposure for patients, staff, and the general public while still performing effective medical procedures.  Nuclear Medicine uses the ALARA principle: radiation exposure should always be As Low As Reasonably Achievable.   To implement ALARA effectively, the physician and other staff must understand radiation, radiopharmaceuticals, radiation detection equipment, and radioisotope handling. More about radiation exposure and radiation effects can be found on the "Radiation Exposure" page of this guide.

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