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Ionizing Radiation and Diagnostic Examinations

Every day, in hospitals and in doctor’s offices, people have tests to diagnose diseases and injuries. Some of these tests (x-rays, for example) involve exposure to ionizing radiation. Also, some tests expose patients to much more radiation than what occurs naturally in everyday life. Scientists call this daily, non-medical exposure to ionizing radiation, background radiation.

What are some examples of medical tests that use ionizing radiation?

Most people have had one or more medical tests that use ionizing radiation. Doctors use these tests to help diagnose disease and injury. Examples include:
  • X-rays (including dental x-rays, chest x-rays, spine x-rays)
  • CT or CAT (computed tomography) scans
  • PET (positron emission tomography) scans
  • Fluoroscopy

Magnetic resonance imaging (MRI) and ultrasound are two other commonly used diagnostic tests. MRI and ultrasound do not involve exposure to ionizing radiation.

What is an x-ray?

An x-ray is an image created using photographic film to diagnose illness and injury. During a medical testing procedure an x-ray machine is used to take pictures of the body. The x-rays pass through objects and various parts of the body to produce images of tissues, organs, and bones.

Various types of medical uses of x-rays are described below.

What is a CT scan?

Doctors use computed tomography (CT) scans, also known as computerized tomography or computerized axial tomography (CAT) scans, to diagnose disease or injuries of the head and brain, the chest, the abdomen, and the pelvis.

In a CT scan:

  • Special x-ray equipment is used to take pictures of the body. Patients must lie very still as a table moves slowly through a large x-ray machine. Sometimes doctors give patients special chemicals (called contrast) before the CT scan. Contrast helps doctors better see certain parts of the body in the scan.
  • A computer organizes the x-ray information to show organs, bones, and other tissues.

Some doctors now use CT to take pictures of the large intestine (colon) to find cancer and other diseases. This procedure is called virtual colonoscopy. In virtual colonoscopy, the computer creates an animated, 3-D view of the inside of the colon. This is different from traditional colonoscopy, where doctors place a camera into the colon and rectum.

What is a PET scan?

A positron emission tomography (PET) scan is one example of a diagnostic nuclear medicine test. Doctors use nuclear medicine tests to diagnose diseases in many different organs, including the heart, liver, bones, lungs, kidneys, and thyroid.

In a PET scan:

  • Doctors give patients small amounts of radioactive isotopes (radionuclides). These radionuclides may be inhaled (breathed in), injected, or swallowed. The radionuclides leave the body within hours or days.
  • A special camera is used to track, record, and measure the radionuclide once it enters the body.
  • The pictures from the special camera show doctors the organs of the body and tell how well these organs are working.

PET scans can help diagnose cancer, heart problems, brain disorders, and central nervous system conditions. Sometimes doctors use CT and PET scans together to create more detailed pictures of the body.

What is Fluoroscopy?

Patients who have a fluoroscopy examination are placed between an x-ray source and a fluorescent screen. The x-ray images on the screen are shown on a video monitor. Fluoroscopy allows doctors to watch internal organs move in real time.

Doctors can use fluoroscopy to:

  • Check to make sure that broken bones are aligned properly while the bones are being set.
  • Check to make sure that catheters, wires, and tubes are being put in the right place within the body. Doctors performing coronary angiograms and angioplasty use fluoroscopy to find and treat blockages in the arteries of the heart.

Fluoroscopy involves continuous exposure to ionizing radiation. For this reason, doctors need to remember to keep the machine on for as brief a time as necessary.

What are the risks of medical tests that use ionizing radiation?

All medical tests have risks and benefits. Usually, the benefits of a medical test outweigh its risks. Two different types of medical tests, and their risks and benefits are listed in the table below:

Blood testsPain
Diagnose a disease or medical condition
X-rays and other tests involving ionizing radiationExposure to radiationDiagnose a disease or injury

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How can I reduce my exposure to diagnostic ionizing radiation?

The risk of harm from exposure to radiation from diagnostic procedures is, for the most part, small. However, exposures to ionizing radiation should be only as long as is necessary to perform the test.

In the case of x-rays or other tests involving exposure to ionizing radiation, doctors and radiation experts can help reduce your exposure to and risk of harm from diagnostic ionizing radiation by:

  • Checking to see if you have had a similar test done recently that can provide them with the background information they need.
  • Checking to see if a test that does not use ionizing radiation can provide similar information.
  • Estimating in advance the typical radiation dose for the test.
  • Estimating your exposure to radiation from the test.
  • Making certain the least possible amount of radiation is used for your procedure.

Radiation experts include the following:

  • Hospital radiation safety officer
  • Radiation physicist
  • Diagnostic medical physicist