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.

15 thoughts on “What Does a CT Scan Look At?”

  1. Avatar jerry hyslop says:

    what if you have a pace maker/ defibrilator can you still get a cat can? thanks Jerry hyslop

    1. Inogen Inogen says:

      Hi Jerry, Please consult your primary care doctor. You may or may not be able too depending on the maker of your pace maker/defibrillator and other health conditions.

  2. Avatar Joseph says:

    The question by Jerry caught my attention. I have had a monitor/generator Pacemaker (on the 3rd one now) and was never held back from a CT Scan of which I have had many in my 90 years. The answer by Inogen, however, caused me to look into my Pacemaker User's Manual and I discovered that ablation, which I was considering to reduce an edema problem, is not recommended. However, I will check further with the doctor. It may be that using it on the lower leg is far enough away from the device.

  3. Avatar frank belot says:

    I have had 3 or 4 ct scans in the month of may
    my right lung has been drained twice of a litre of water
    they have not found any cancer but cannot figure out
    where the water is coming from. How many of these ct scans do I dare have going forword?

    1. Inogen Inogen says:

      Hi Frank, We're sorry to hear you've had so many recent medical procedures. We know how hard it can be to be in and out of the doctor's office without getting a proper diagnosis. It sounds like your doctors are working hard on your behalf and they are trying to diagnosis your condition. Since we are not your primary care doctor and we do not have access to your full medical history we are not able to give you a diagnosis or offer advice on how many more CT Scans you have going forward. Please work with your primary care doctor as he or she is working on your treatment plan.

  4. Avatar Everette Dale Deweese says:

    I am preparing for a CT scan at the end of this month. I have been diagnosed with pulmonary fibrosis.
    How definitive is a CT scan for pulmonary fibrosis? To what purpose will the scan serve? I use an INOGEN G4. It seems to reduce the time of hard breathing when I exercise, walk, …

    1. Inogen Inogen says:

      Hi Everette, One of the reasons a doctor may order multiple CT scans is so they can compare CT scans over time to evaluate the efficacy of certain treatments. If you were recently put on oxygen therapy, your doctor likely wants to compare a CT scan of your lungs prior to starting oxygen therapy to a CT scan of your lungs now that you are using oxygen therapy.

  5. Avatar Pamm says:

    can a doctor see if I smoke cigarettes in the ct scan

    1. Inogen Inogen says:

      Hi Pamm, When looking at CT scans, it is hard to determine a single source that caused lung damage. If your doctor sees lung damage, in order to determine what caused it he or she needs to know your full health history so if you do smoke, do not leave that out. In order for your doctor to determine the best treatment plan for you, he or she needs to know if you are smoking. For more information on what smoker's lungs look like and if you are at risk for COPD, please visit: https://www.inogen.com/blog/smokers-lungs/ and https://www.inogen.com/resources/living-with-copd/are-you-at-risk-for-copd/

  6. Avatar Greensboro Imaging says:

    Great article! We know it can cause people some anxiety to get imaging procedures, like the CT scan. You guys do a really good job explaining the different aspects of the scan and what to expect.

    Here at Greensboro Imaging, we recently published a blog post called "CT and MRI: Reducing Concerns with Common Imaging Procedures" where we delve into the two different imaging procedure and what patients can expect. For people who may be struggling to understand the difference, the article can be found at this link: https://www.greensboroimaging.com/2018/06/04/ct-mri-reducing-concerns-common-imaging-procedures/

  7. Avatar Sarah Cummings says:

    Great post! This has been an informative article. This surely gives background on the process itself. Thumbs up!

    1. Inogen Inogen says:

      Thank you Sarah!

  8. Avatar Ben Spock says:

    Thank you for such an informative article. It very well explains about how a CT scan is done as well as how we can prepare for one. I have been recently advised to undergo a CT Scan after I experienced severe recurring headaches for the past 10 to 15 days. I was constantly worried as to how this test would go and what would be the result. But after reading your article, many of my doubts have been answered and I am much more educated about a CT Scan. Again, thank you for helping out people like me who are totally unaware of these tests, in such a simple and easy way. Also, I found some online sites like econolabs, LabFinder which allow you to book these tests with just a click.

    1. Inogen Inogen says:

      Dear Ben, Thank you so much for your feedback. We are pleased to hear that the information we publish has helped you out. Take care and be well!

  9. Avatar Kate Hansen says:

    I never knew that you would need to remove any metal objects you're wearing because it could interfere with the machine. My sister's jaw has been hurting for a couple of months now and she was wondering if she would need to get a CT scan to check it out. I'll make sure to pass this information along to her in case she does end up getting a CT scan. https://hobokenradiology.com/services/petct/

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