The University of Arizona Medical Center -- Academic Medicine is Smart Medicine

CT Scan

What is Computed Tomography?

CT (computed tomography), also called a CAT scan, uses x-ray and computer equipment to produce cross-sectional images from of body issues and organs. CT imaging is useful because it can show several types of tissue, such as lung, bone, soft tissue and blood vessels.

What are some common uses of CT?

  • Studying the chest and abdomen.
  • Diagnosing cancer. CT examinations are often used to:
    • Plan and properly administer radiation treatments for tumors.
    • Guide biopsies and other minimally invasive procedures.
    • Plan surgery.
    • Determine surgical resectability.
  • Diagnosing and treating spinal problems and injuries to the hands, feet and other skeletal structures.
  • Measuring bone mineral density for the detection of osteoporosis.
  • Identifying injuries to the liver, spleen, kidneys, or other internal organs.
  • Detecting, diagnosing and treating vascular diseases that can lead to stroke, kidney failure, or even death.

How should I prepare for a CAT scan?

  • On the day of your exam, wear comfortable, loose-fitting clothing.
  • Avoid clothing with zippers and snaps as metal objects can affect the image.
  • Depending on the part of the body that is being scanned, you may also be asked to remove hair pins, jewelry, eyeglasses, hearing aids and any dentures.
  • You may be asked not to eat or drink anything for one or more hours before the exam.
  • Women should inform their doctor or x-ray tech if there is any possibility that they are pregnant.

What can I expect during this procedure?

A CT examination usually takes five minutes to half an hour.

  • The technologist positions you on the CT table and pillows are used to help keep you still and in the proper position during the scan. The table will move slowly into the CT scanner opening. Depending on the area of the body being examined, the increments of movement may be very small and almost undetectable, or large enough to feel the motion.
  • To enhance the visibility of certain tissues or blood vessels, use of different contrast materials may be required. Depending on the type of examination, contrast material may be injected through an IV, swallowed or administered by enema. Before administering the contrast material, you should inform the radiologist or technologist of the following:
    • Any allergies, especially to medications or iodine,
    • Whether you have a history of diabetes, asthma, kidney problems, heart or thyroid conditions. These conditions may indicate a higher risk of reaction to the contrast material or potential problems eliminating the material from the patient's system after the exam.
  • You will be alone in the room during your scan however your technologist can see, hear and speak with you at all times. If necessary, many centers allow a friend or family member to stay in the room with you during the exam. To prevent radiation exposure, the friend or family member will be required to wear a lead apron.
  • To determine if more images are needed, you may be asked to wait until the images are reviewed.

What will I experience during the procedure?

CT scanning is painless. Depending on the type of scan you are having, your preparation may differ. To enhance the visibility of body tissue or blood vessels, use of different contrast materials may be administered by:

  • Mouth: You may be asked to swallow water or contrast material, a liquid that allows the radiologist to better see the stomach, small bowel and colon. Some patients find the taste of the contrast material slightly unpleasant, but tolerable.
  • Enema: For a study of the colon, your exam may require the administration of the contrast material by enema. You will experience a sense of abdominal fullness and may feel an increasing need to expel the liquid. The discomfort is generally mild.
  • IV injection: To accentuate the appearance between normal and abnormal tissue in organs like the liver and spleen and to better define the blood vessels and kidneys, a contrast material is commonly injected into a vein. You might feel:
    • Flushed or have a metallic taste in your mouth. These are common reactions which disappear in a minute or two.
    • A mild itching sensation. If the itching persists or is accompanied by hives, it can be easily treated with medication.
    • In very rare cases, you may experience shortness of breath or swelling in the throat or other parts of the body. These can be indications of a more serious reaction to the contrast material. Your technologist should be notified immediately.

Dual-Energy CT

What is Dual-Energy CT ?

Dual-Energy Computed Tomography (CT) scans utilize two x-ray tubes with two different x-ray energies to acquire two sets of data/information during a CT scan. Double the amount of information is obtained during one dual-energy CT scan when compared to conventional CT scans. Utilizing this advanced technology, dual-energy CT aids radiologists in the diagnosis of some diseases.

What is Dual-Energy CT used for?

One application of dual-energy CT is in the diagnosis and treatment of gout. Gout is the most common crystalline arthropathy in the United States. Dual-energy CT can detect subtle uric acid crystals (gout crystals) in joints and soft tissues. Conventional CT scans and radiographs are unable to detect uric acid crystals.

How can Dual-Energy CT help the patient or clinician?

Sometimes the diagnosis of gout is not as straightforward as a simple blood test. Dual-energy CT scans can help clinicians make the diagnosis of gout when such blood tests are inconclusive. Once the diagnosis of gout is established, the appropriate medical therapy can be initiated. Dual-energy CT can also help clinician monitor patient response to therapy.

Conventional radiographs fail to demonstrate uric acid crystals in joints. These crystals are imperceptible.

Dual-energy CT scans very easily detect uric acid crystals (gout crystals) in joints. Affected joints will appear green on imaging.

Conventional Radiographs cannot detect uric acid crystals in soft tissues. These crystals are virtually invisible on radiographs.

Dual-energy CT can also detect uric acid crystals (gout crystals) in soft tissues, such as tendons, which appear yellow on dual-energy CT scans when present.