A doctor might order a type of scan to help diagnose an internal problem. As described by the American College of Radiology and the Radiologic Society of North America, Computerized Axial Tomography, also known as a CAT or CT scan, combines X-rays and computer analysis to generate detailed images of the body. By contrast, a bone scan produces images of a radiotracer administered into the body via a specialized camera.

How They Work

A CAT scan takes multiple, focused X-ray images of the body and sends them to a computer, which assembles them into multiple, cross-sectional images–apparent "slices" of the body.

A bone scan camera detects a small amount of radioactive material injected into the body that collects in abnormal areas of bone.

How Scans Are Performed

For a CAT scan, the patient lies on a platform that slowly moves through a large, often doughnut-like, X-ray machine. Intravenous and/or oral contrast may be administered prior to the exam.

For a bone scan, the patient is injected with a radio tracer and then approximately two hours later lies on a table under a specialized camera for up to an hour.

How Scans Are Used

Doctors use CAT scans to diagnose a wide variety of diseases in all parts of the body. Bone scans, however, are limited to diagnosing diseases specific to the skeletal system, such as infection, fractures, tumors and metastases.

Radiation

CAT scans subject the patient to more radiation than bone scans. A single CAT scan generally equals a similar amount of background radiation exposure that humans normally acquire over three to five years. Radiation exposure from a bone scan is negligible.

Interpretation

Both CAT and bone scans are interpreted by doctors specialty trained as radiologists.