Computerized Tomography Scan (CT or CAT scan): Purpose, Preparation, Procedure, Results and Risks Associated with a CT Scan

CT scans are special X-ray tests that produce cross-sectional images of your organs, bones, and other tissues using X-rays and a computer.

Updated: June 16, 2022

CT scans are special X-ray tests that produce cross-sectional images of your organs, bones, and other tissues using X-rays and a computer. It shows more detail images than a regular X-ray.
The higher-resolution images produced in CT scan help assist the doctor in making a diagnosis of small nodules or tumors, which is not possible with a plain film X-ray.
A CT scan can be done on any part of your body. This include the brain, neck, spine, chest, abdomen, knee, pelvis, and sinuses. The procedure doesn't take very long, and it is painless.

Purpose of CT Scan:

As CT is noninvasive, safe, and well-tolerated, it is a commonly performed for diagnosing diseases and evaluating injuries. The imaging technique can

  • detect bone and joint problems, like complex bone fractures and tumors
  • diagnose the condition like cancer, heart disease, emphysema, or liver masses.
  • show internal injuries and bleeding, such as those caused by a car accident.
  • can locate a tumor, blood clot, excess fluid, or infection.
  • guide the doctors for treatment plans and procedures, such as biopsies, surgeries, and radiation therapy.
  • be used as a comparison to find out if certain treatments are working. For example, scans of a tumor over time can show whether it’s responding to chemotherapy or radiation.
  • monitor the effectiveness of treatments for certain medical conditions, including cancer and heart disease.

CT is mostly done to evaluate soft tissues such as the brain, liver, and abdominal organs, as well as to visualize subtle abnormalities that may not be apparent on regular X-ray tests.This can be done to further evaluate an abnormality seen on another test such as an X-ray or an ultrasound. People with cancer may have a CT to evaluate the spread of disease.

  • CT of a head or brain is used to evaluate the various structures of the brain to look for a mass, stroke, area of bleeding, or blood vessel abnormality. It is also sometimes used to look at the skull.
  • A neck CT checks the soft tissues of the neck and is frequently used to study a lump or mass in the neck or to look for enlarged lymph nodes or glands.
  • CT of the chest is frequently used to further study an abnormality on a plain chest X-ray. It is also often used to look for enlarged lymph nodes.
  • An abdominal and pelvic CT can detect the cause of pain in the gastrointestinal tract and abdominal and pelvic organs, such as the liver, spleen, kidneys, pancreas, and adrenal glands. Sometimes to follow up on an abnormality seen on another test such as an ultrasound, these scans are done.
  • A sinus CT scan is used to diagnose sinus disease and also to detect a narrowing or obstruction in the sinus drainage pathway.
  • A spine CT test is most commonly used to detect a herniated disc or narrowing of the spinal canal (spinal stenosis) in people with neck, arm, back, and leg pain. It is also used to detect a fracture or break in the spine.

Preparation of CT Scan:

You will have to fast for four to six hours before your CT scan, if you are going to have a contrast injection. This is because the injection may cause stomach upset. An IV is inserted into the arm just prior to the scan to receive the contrast injection. The contrast then enters the body through the IV.
Prior to most CT scans of the abdomen and pelvis, the patient will be asked to drink an oral contrast agent that contains dilute barium. This contrast agent helps the radiologist identify the gastrointestinal tract, detect abnormalities of these organs, and to separate these structures from other structures within the abdomen. Just before the procedure, you will be asked to change into a hospital gown and to remove any metal objects as these can interfere with the CT scan results. These items include jewelry, glasses, and dentures.

Procedure of CT Scan:

During the procedure your doctor will ask you to lie face up on a table that slides into the CT scanner. They will leave the exam room and go into the control room where they can see you and hear you. You will be able to communicate with them via an intercom. The table will then slowly moves you into the scanner and the X-ray machine will rotate around you. Each rotation produces numerous images of thin slices of your body. During scan, you may hear clicking, buzzing, and whirring noises. The table will move a few millimeters at a time until the exam is finished. The entire procedure may take 20 minutes to one hour.
As movement can result in blurry pictures, it is very important for you to lie still while CT images are being taken. Your doctor may ask you to hold your breath for a short period during the test to prevent your chest from moving up and down. In case of CT scan of a young child, the doctor may recommend a sedative to keep the child from moving.
The images are sent to a radiologist for examination once the CT scan is over. A radiologist is a doctor who specializes in diagnosing and treating conditions using imaging techniques, such as CT scans and X-rays. Your doctor will follow-up with you to explain the results. The IV is removed from the arm before going home if the patient received a contrast injection. Generally there is no ill effects from the scan or the contrast injection.

Results of CT Scan:

CT scan results are considered normal if the radiologist did not see any tumors, blood clots, fractures, or other abnormalities in the images. If any abnormalities are detected during the CT scan, you may need further tests or treatments, depending on the type of abnormality found.

Risks Associated with a CT Scan:

There are very few risks associated with a CT scan. Although you are more exposed to radiation than typical X-rays, the risk of cancer caused by radiation is very small if you only have one scan. However, if you have multiple X-rays or CT scans, your risk for cancer may increase over time. However the risk of cancer increases in children receiving CT scans, especially to the chest and abdomen. 
Some people have an allergic reaction to the contrast material. Most contrast material contains iodine, so if you have had an adverse reaction to iodine in the past, make sure to notify your doctor. Your doctor may give you allergy medication or steroids to counteract any potential side effects if you are allergic to iodine but must be given contrast. The intravenous dye can damage the kidneys, particularly if an individual already has marginal kidney disease. In such cases, the patient is advised to drink plenty of fluids to help flush the dye out of their system.
It is also important to notify your doctor if you are pregnant. Although the radiation from a CT scan does not harm your baby, your doctor may recommend an ultrasound or MRI scan, to minimize risk.

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