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What Is the Difference Between a Cat Scan & a Bone Scan?

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 2.

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 2.

How Scans Are Performed

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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 2.

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
  • metastases


Side Effects of a Bone Scan

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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 2.


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