Image tests provide pictures of bones, organs (such as the liver, pancreas, or intestines), tissues, and other structures (such as blood vessels) inside the body. These tests are used to help diagnose medical conditions.

Image tests include:

• X-rays, which use a radiation beam to detect bone injuries or abnormal growths or changes in bone structure or size.
• Ultrasound, which uses reflected sound waves to produce an image. Ultrasound is most useful for looking at organs and structures that are either uniform and solid (like the liver) or that contain water (like the gallbladder). Mineralized structures (like bones) or air-filled organs (like the lungs) do not show up well. Echocardiography is a type of ultrasound that produces an image of the heart. It is used in heart conditions.
• Computed tomography (CT or CAT), which uses a series of X-ray pulses through the body to obtain information about almost any body organ, blood vessels, the abdominal cavity, bones, and the spinal canal.
• Magnetic resonance image (MRI), which uses a magnetic field and pulses of radio-wave energy to detect changes in the normal structure and characteristics of organs or tissues. An MRI can provide information that cannot be obtained from an X-ray, ultrasound, or CT scan. MRI is most effective at providing pictures of tissues that contain water, such as ligaments and muscles. An MRI is not as useful in looking at structures that do not contain water, such as bones.
• Nuclear medicine scans, which use a camera to take pictures of certain tissues in the body after a radioactive tracer (radionuclide or radioisotope) is put into the body. The radioactive tracer helps make the tissues visible on the scanning pictures. Each type of tissue that may be scanned (including bones, organs, glands, and blood vessels) uses a different radioactive compound as a tracer.
• Positron emission tomography (PET), which combines computed tomography and nuclear scanning. PET has been used primarily in heart and brain conditions and cancer.

By	Healthwise Staff
Primary Medical Reviewer	William H. Blahd, Jr., MD, FACEP - Emergency Medicine
Specialist Medical Reviewer	Robert B. Keller, MD - Orthopedics
Last Revised	August 2, 2010