CT Scan

Medically Reviewed By William C. Lloyd III, MD, FACS

What is a CT scan?

A CT scan is an imaging test that uses X-rays and a computer to take cross-sectional pictures of the body. A CT scan, also called a CAT (computed axial tomography) scan, makes layered images of an entire body area. The images are similar to slices of a loaf of bread. CT scans are more detailed than regular X-rays They help doctors diagnose and treat many diseases, disorders and conditions. 

A CT scan is a painless, noninvasive medical test. It makes images of any organ or body part. A CT scan is only one method of diagnosing and monitoring many diseases, disorders and conditions. Discuss all your diagnostic and monitoring options with your doctor to understand which options are best for you.

Types of CT scans

Standard CT scans can make pictures of almost any body structure using only the CT scan machine. Your doctor may add a contrast agent or dye or use specialized CT scan machines and techniques to make clearer or more detailed images. Specialized CT scans include:

  • Cardiac CT makes detailed images of the heart and often involves injecting a contrast dye into a vein.

  • Coronary calcium scan looks for calcium deposits in the coronary (heart) arteries. A coronary calcium scan uses medication to slow your heart and an EKG machine to record your heart’s electrical activity during the scan.

  • CT angiography makes detailed images of blood vessels and tissues by injecting a dye through a small tube (catheter) inserted into a vein.

  • CT enterography makes detailed pictures of the small intestine using a contrast dye that you drink.

  • CT colonography (virtual colonoscopy) makes detailed pictures of the inside of the large intestine. It involves pumping carbon dioxide gas through a tube in the rectum to expand the large intestine for better viewing.

  • Multislice CT or multidetector CT makes thinner imaging slices in a shorter period than a traditional CT scan. This creates images with more detail.

  • SPECT (single-photon emission computed tomography) shows the function of organs. A SPECT scan is a type of nuclear imaging test that uses a radioactive substance and a special camera combined with CT scanning to create 3-D pictures.

  • PET/CT (positron emission tomography/computed tomography) is used to diagnose or determine the severity of many diseases, such as cancer. PET/CT is a type of nuclear imaging test that makes images using a radioactive substance and a special camera combined with CT to create detailed pictures.

Why is a CT scan performed?

Your doctor may recommend a CT scan to screen, diagnose, and monitor the progress of many diseases, disorders and conditions in almost any part of the body. Examples include:

  • Aneurysms including brain aneurysms and aortic aneurysms in the abdomen or chest

  • Atherosclerotic disease including coronary artery disease and peripheral artery disease

  • Blood clots including clots that cause pulmonary embolisms and ischemic stroke

  • Chronic diseases including osteoporosis and arthritis

  • Congenital malformations including birth defects of the heart, kidneys, brain, and blood vessels

  • Infections including abscesses and acute appendicitis

  • Inflammatory bowel disease including Crohn’s disease and ulcerative colitis

  • Injuries and trauma including broken bones and organ injury such as a ruptured pancreas or brain hematoma

  • Internal bleeding including hemorrhagic stroke and bleeding due to trauma

  • Tumors and cancer including benign masses, lymphomas, and cancers of organs such as the kidney, brain, liver, pancreas and colon

CT scans are also used to:

  • Confirm a diagnosis of symptoms including facial drooping, slurred speech, changes in vision, and abdominal and pelvic pain

  • Guide procedures including biopsies and drainages of abscesses

  • Monitor treatments including the results of surgery, chemotherapy, and radiation therapy

  • Plan surgery and other treatments including chemotherapy, radiation therapy, and cancer, tumor, and organ transplant surgeries

Who performs a CT scan?

A radiologic technologist supervised by a radiologist will perform your CT scan. A radiologic technologist is a healthcare provider who performs imaging procedures and takes care of patients during procedures. A radiologist, also called a diagnostic radiologist, is a doctor who specializes in medical imaging. Your radiologist will look at your ultrasound images and provide your doctor with the results.

How is a CT scan performed?

Your CT scan will be performed in a hospital or outpatient imaging setting. The procedure takes less than 30 minutes and generally includes these steps:

  1. You will undress and put on a patient gown. You will remove all jewelry and metal objects.

  2. You may have an IV inserted in your arm to administer IV contrast.

  3. You will lie on a padded CT table. Your radiologic technologist will position you in a way that makes the best images for your specific type of CT scan. This may be flat on your back, or on your side or stomach. A strap or soft wedge may be used to keep you from moving a body part, such as your head.

  4. Children and people who are very anxious may have a light sedative to help them relax and stay still.

  5. You may have a contrast agent or dye by IV, as an enema, or as a drink depending on the type of CT scan.

  6. The radiologic technologist will leave the room to start the CT scan, but will see you at all times through a window and hear you through a speaker system.

  7. The CT table will move through the hole in a large doughnut-shaped scanner. It may move back and forth several times as it takes pictures, depending on the type of CT scan.

  8. The radiologic technologist may ask you to hold your breath briefly, depending on the type of CT scan.

  9. You will wait briefly after the CT scan while the radiologic technologist checks the images to make sure they are clear. Your IV is removed once the radiologic technologist has verified image clarity.

  10. If the CT scan is an outpatient procedure, you will likely go home right away.

  11. Your doctor will discuss the results with you at a later time. Your doctor will interpret your CT scan in relation to your physical exam, medical history, and other tests.

Will I feel pain?

Your comfort and relaxation is important to you and your care team. The CT scanning machine never touches you and is not painful. Your positioning on the table should be comfortable. Tell your radiologic technologist if you are uncomfortable.

You may feel a brief stick or pinch during IV insertion if you need IV contrast. You may also feel a fleeting warm sensation when the contrast is injected. Take a few long, deep breaths to help yourself relax. Tell your radiologic technologist if any discomfort does not pass quickly.

If you need to take your contrast by enema, you may feel brief rectal pressure as the enema tube is inserted. Take a few long, deep breaths to help yourself relax. The enema should not cause pain. If it does, tell your radiologic technologist.

What are the risks and potential complications of a CT scan?

There is a small increase in the risk of cancer due to radiation exposure during a CT scan. CT scans use slightly more radiation than regular X-rays, but the benefit of more detailed images generally outweighs the minimal risk. Your care team follows strict standards for X-ray techniques and will use the smallest amount of radiation possible to produce the best images. 

Your doctor will generally not order a CT scan if you are pregnant due to the danger of radiation to an unborn child. It is very important to tell your doctor or radiologic technologist if there is any chance that you are pregnant.

Allergic reactions to contrast materials are rare, but can occur. CT scan teams are well prepared to handle allergic reactions. 

How do I prepare for my CT scan?

You are an important member of your own healthcare team. The steps you take before your test can improve your comfort and help obtain the most accurate results. 

You can prepare for a CT scan by:

  • Answering all questions about your medical history and medications. This includes prescriptions, over-the-counter drugs, herbal treatments, and vitamins. It is a good idea to carry a current list of your medical conditions, medications, and allergies at all times.

  • Leaving all jewelry and metal objects at home

  • Telling your doctor or radiologic technologist if you are breastfeeding or there is any possibility of pregnancy

  • Telling your doctor and your radiologic technologist if you are nervous or anxious about lying still or having the CT

  • Telling all members of your care team if you have any allergies

Questions to ask your doctor

Having a CT scan can be stressful. It is common for patients to forget some of their questions during a doctor’s office visit. You may also think of other questions after your appointment. Contact your doctor with concerns and questions before a CT scan and between appointments. 

It is also a good idea to bring a list of questions to your appointments. Questions can include:

  • Why do I need a CT scan? Are there any other options for diagnosing or screening my condition?

  • Will I need contrast for my CT scan? How will I receive the contrast?

  • How long will the procedure take? When can I go home?

  • When and how will I receive the results of my test?

  • What other tests or treatments might I need?

  • When should I follow up with you?

  • How should I contact you? Ask for numbers to call during and after regular hours.

What can I expect after my CT scan?

Knowing what to expect after a CT scan can help you get back to your everyday life as soon as possible.

How will I feel after the CT scan?

You will return to all your normal activities right away after an outpatient CT scan or as advised by your doctor, depending on your condition. If you had a contrast enema, you may experience some loose stools that contain contrast for a day or two. Call your doctor if unusual stools last longer or you have any pain or discomfort after a CT scan. 

When can I go home?

Most people go home right away after an outpatient CT scan. You will likely stay in the hospital for further evaluation and treatment If you are hospitalized.

When should I call my doctor?

It is important to keep your follow-up appointments after a CT scan. Contact your doctor for questions and concerns between appointments.  

Was this helpful?
  1. Cardiac CT for Calcium Scoring. Radiological Society of North America. http://www.radiologyinfo.org/en/info.cfm?pg=ct_calscoring.
  2. Computed Tomography (CT): Questions and Answers. National Cancer Institute. http://www.cancer.gov/cancertopics/factsheet/Detection/CT.
  3. CT Angiography. Radiological Society of North America. http://www.radiologyinfo.org/en/info.cfm?pg=angioct.
  4. CT – Body. American College of Radiology. http://www.radiologyinfo.org/en/info.cfm?pg=bodyct.
  5. CT Colonography. American College of Radiology. http://www.radiologyinfo.org/en/info.cfm?pg=ct_colo.
  6. CT Scans. United States Environmental Agency. http://www.epa.gov/radtown/ct_scans.html.
  7. Positron Emission Tomography - Computed Tomography (PET/CT). Radiological Society of North America. http://www.radiologyinfo.org/en/info.cfm?pg=pet.
  8. What is Computed Tomography? U.S. Food and Drug Administration. http://www.fda.gov/Radiation-EmittingProducts/RadiationEmittingProductsandProcedures/MedicalImaging/....
Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Nov 15
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