What Does a CT Scan Look At?

ct scan, computed tomography, ct lung scan, ct scan or lungsA computed tomography (CT) scan uses a combination of X-ray images taken from different angles and computer processing to create cross-sectional images, or slices, of the bone, blood vessels and soft tissues within your body. Compared to a standard X-ray, CT scan images show much more detail.[1]

When is a CT Scan Necessary?

There are a number of reasons your doctor may order a CT scan, for example, to:[2]

  • Detect bone or joint problems, such as complex bone fractures or tumors.
  • Identify and/or monitor changes in conditions such as cancer, heart disease, emphysema or liver masses.
  • Visualize internal injuries and bleeding, such as those caused by an automobile accident.
  • Locate a tumor, blood clot, excess fluid or infection.
  • Guide treatment plans or procedures, such as biopsies, surgeries and radiation therapy.
  • Compare CT scans over time to evaluate the efficacy of certain treatments.

Why Might a Doctor Order a CT Scan of Your Lungs?

Sometimes, a CT scan of the chest (lungs) may be ordered to follow up on a previous, abnormal chest X-ray. Your doctor may also order a chest CT to help assess the reason behind abnormal symptoms such as shortness of breath or chest pain. Other reasons for a CT scan of your lungs may include:[3]

  • A lung tumor
  • Pleural effusion (excess fluid around the lungs)
  • Pulmonary embolism (blood clot in the lungs)
  • Emphysema
  • Tuberculosis
  • Pneumonia

Are There Any Risks?

The X-rays generated during a CT scan produce ionizing radiation, a type of radiation that has been found to increase your risk of cancer. Research shows, however, that this risk is very small and your chances of developing a terminal cancer from a CT scan are approximately 1 in 2000.2

What about Side Effects?

In certain cases, your doctor may order a special dye called contrast to be injected into your vein prior to your CT scan. This helps highlight blood vessels and enhance the tissue structure of various organs allowing for better visualization. Some people experience complications or allergic reactions from intravenous contrast dye. Most of the time, these reactions are mild and only result in a rash or itchiness. In rare cases, however, a serious, life-threatening allergic reaction can occur. Prior to a CT scan, be sure to inform your doctor if you’ve ever had an adverse reaction to contrast.1

Preparing for a CT Scan

Preparation for a CT scan depends upon which part of your body is being studied and whether your doctor ordered contrast. Once you arrive at the imaging center, you may be asked to:1

  • Remove some or all of your clothes and don a hospital gown.
  • Remove jewelry, eyeglasses, hair clips, belts and other metal objects that may interfere with test results.
  • Abstain from eating or drinking for a certain amount of time prior to the scan.
  • Swallow a liquid that contains contrast material that may taste unpleasant (if your esophagus or stomach is being scanned).

During the Scan

A radiology technician will perform the scan. During the scan, the technician will be in a separate room but will be able to see and hear you. An intercom will allow for mutual communication. You’ll be asked to lie on a table that protrudes from a large, doughnut-shaped CT machine. Once on the table, it will slowly move through the scanner while the X-rays rotate around your body. You may hear loud whirring or buzzing noises while the CT machine is carrying out the scan.1

It’s important to keep very still, as movement can blur the images making them unreadable. At certain times, you may be asked to hold your breath for a few seconds to help avoid blurry images.1

After the Scan

Once the scan is complete, you may resume your normal routine. Special instructions may be given if you received contrast dye, which may include drinking plenty of fluids to help your kidneys flush the dye from your system. The CT scan images are stored as electronic data files which are forwarded to a radiologist for review. Once the radiologist interprets the test, results are sent to your doctor who will discuss them with you at your follow-up appointment.1

For more information about getting a CT scan, contact your primary care provider.


[1] Mayo Clinic. CT Scan. March 25, 2015.

[2] WebMD. What is a CT Scan? December 23, 2016.

[3] National Heart, Lung and Blood Institute. Chest CT Scan. Accessed April 30, 2018.


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