According to the American Association of Physicists in Medicine (AAPM), "Medical Nuclear physics pertains to:

• the therapeutic and diagnostic applications of radionuclides (except those used in sealed sources for therapeutic purposes)
• the equipment associated with their production, use, measurement and evaluation
• the quality of images resulting form their production and use
• medical health physics associated with this subfield."

Medical physicists in this field employ radionuclides in diagnosis and therapy. It is their responsibility to maintain extensive knowledge of the equipment used in these methods for the purposes of clinical work, scientific research, and teaching services.

A certified medical physicist can specialize in one or more subfields of medical physics.