Medical scans at a glance

A look at different types of advanced medical imaging scans:

PET SCAN, or positron emission tomography. Creates images by detecting subatomic particles emitted from a radioactive substance given to the patient. Used to detect abnormal function, usually in the brain and heart.

CT SCAN, or computed tomography; sometimes called a CAT scan, for computerized axial tomography. Takes multiple X-rays from different directions, and a computer instantly assembles a high-clarity image allowing two-dimensional and three-dimensional views. Used to look for structural abnormalities in bone, organs, muscles and tumors, for diagnosis and during surgery and radiation therapy treatment.

MRI, or magnetic resonance imaging. Uses a powerful magnetic field, radio waves and a computer to produce detailed images of organs, soft tissues, bone and virtually all other internal body structures. Enables doctors to evaluate some body areas and certain diseases or injuries better than X-rays, ultrasound or CT scans.

Nuclear cardiology, a segment within nuclear medicine. Uses radioactive material called a radiotracer that's injected, swallowed or inhaled and gives off gamma rays, which are detected by a special gamma camera or other probe. A computer measures how much radiotracer is absorbed by the body and produces detailed pictures of the structure and function of the heart. Nuclear medicine can also be used on other organs and internal body parts.

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Sources: American College of Radiology, Radiological Society of North America, Merck Manual of Medical Information.

Patient information: http://www.radiologyinfo.org