Imaging (Radiology) Tests

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What are imaging tests?

An imaging test is a way to let doctors see what’s going on inside your body. These tests send forms of energy (x-rays, sound waves, radioactive particles, or magnetic fields) through your body. The changes in energy patterns made by body tissues create an image or picture. These pictures can show normal body structures and functions as well as abnormal ones caused by diseases like cancer.

Imaging tests are different from endoscopy (like a colonoscopy or bronchoscopy), which puts a flexible, lighted tube with a lens or a video camera inside your body. Endoscopy lets doctors see inside parts of the body as if they were looking with the naked eye – more like real pictures. (For more information on this, see our document called Endoscopy.) These pictures are very different from the images that are made with imaging tests.

What are imaging tests used for?

Imaging tests are used for cancer in many ways:

  • They are sometimes used to look for cancer in its early stages (when it’s small and has not spread), even though a person has no symptoms. When used this way, it is called cancer screening. A mammogram is an example of an imaging test used for cancer screening.
  • They can be used to look for a mass or lump (tumor) if a person has symptoms. They can also help find out if the symptoms are caused by a tumor or by some other type of disease.
  • They can sometimes help predict whether a tumor is likely to be cancer. This can help doctors decide if a biopsy is needed. (In a biopsy, a tissue sample is removed and looked at under the microscope.) A biopsy is almost always needed to know for sure that a tumor is cancer.
  • They can show exactly where the tumor is, even deep inside the body. This helps if a sample (biopsy) of the tumor is needed for further study.
  • They can help find out the stage of the cancer (figure out how far the cancer has spread).
  • They can be used to plan treatment, such as when pinpointing where the beams should be focused in radiation therapy.
  • They can show if a tumor has gotten smaller, stayed the same, or grown after treatment. This can give a doctor an idea of how well treatment is working.
  • They can help find out if a cancer has come back (recurred) after treatment.

Imaging tests are only part of the process of cancer diagnosis and treatment. A complete cancer work-up also includes your doctor getting your medical history (asking questions about your symptoms and risk factors), a physical exam, and blood work or other lab tests.

Many doctors ask that x-rays or other imaging tests be done before treatment starts so they can then track changes during treatment. These are called baseline studies because they show how things looked at the start. Doctors can compare them with later images to see the results of treatment over time. They can also be used later on to find out if the cancer has progressed.

Limitations of imaging tests

Imaging tests can find large collections of cancer cells, but no imaging test can show a single cancer cell or even a few. In fact, it takes millions of cells to make a tumor big enough for an area to look abnormal on an imaging test. This is why doctors sometimes recommend treatment even when cancer cells can no longer be seen on an imaging test. Even one surviving cancer cell can grow and, over time, become a tumor that will again be big enough to cause problems and/or show up on an imaging test.


Last Medical Review: 01/11/2013
Last Revised: 08/09/2013