What is CT?
The CT (Computed Tomography or CAT) scan uses X-rays to obtain detailed, cross-sectional views of internal organs, blood vessels, soft tissues and bone. It can diagnose disorders of the lungs, digestive system, heart and vascular system, as well as infectious disease. Beyond its diagnostic value, CT can be used to guide biopsies and administer radiation treatment.
How does it work?
CT resembles conventional X-rays in that a low dose of radiation is passed through the body and its absorption is measured. But the X-rays are administered from a gantry that can move around the patient, emitting the beam in a fan shape. A detector on the other side of the patient's body receives the image.
Each time the X-ray passes through the body, a "slice" of image is acquired and stored. When the scanner's computer reunites the slices, it produces a precise, multidimensional view of the organ being imaged.
What does the equipment look like?
The CT scanner is a square unit with a large hole in the middle, though which the patient table slides and can be raised or lowered. The gantry moves around the patient.
How should I prepare for the CT scan?
Your doctor may instruct you not to eat or drink anything for a period of time before the exam. Wear loose, comfortable clothing without metal buttons or fittings. You may asked to remove jewelry, eyeglasses, hearing aids or removable dental work. As with any test, tell the technician if there is a possibility you may be pregnant. Nursing mothers should wait 24 hours to breast feed if a contrast material has been used during the scan.
What will I experience during the CT scan?
The CT scan is painless, fast (5-30 minutes) and non-invasive. You will be asked to remain still as the table slides slowly through the scanner. A sensation of motion as the table moves may or may not be discernable.
Contrast materials are often used to enhance visibility of organs or blood vessels. If the contrast material is injected, you may experience a momentary sensation of warmth, a metallic taste or mild itching. Shortness of breath or swelling of the throat or other parts of the body are more serious reactions that should be reported to the technician immediately.
If the contrast material is to be swallowed, some people will find the taste unpleasant. If it is administered by enema, there will be a feeling of abdominal fullness.
As it passes over the body, the scanner emits clicking and whirring noises.
How will I get the results?
A radiologist, a physician who is trained to interpret medical images, reviews test results before sending them, along with a written report, to your personal physician. Results are usually available from your physician's office within a few days.
What are the benefits and risks of CT scans?
CT scanning can identify both healthy and diseased tissue, making it useful to not only diagnose, but also treat, illness. It is less expensive than MRI and some other diagnostic procedures.
The effective radiation delivered is 10 mSv, equal to the amount of "background" radiation a person would receive in about three years. If not being studied, the abdomen and pelvis are protected with a lead apron. A small risk of allergic reaction to iodine (used as a contrast material) exists, but imaging centers are equipped to deal with it.
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