CT Scan

A computerized axial tomographic (CT) scan is a painless test that displays 2-dimensional images of internal structures of the body on a computer monitor. Neurologists primarily use CT scans of the head, neck, and spine. A computer can also create lifelike 3-dimensional images of the body from CT images. Sometimes a contrast dye is given to a patient intravenously during a CT scan to emphasize hollow or fluid-filled structures such as blood vessels.

CT scans help diagnose the following:

Stroke;
Brain tumors;
Aneurysms;
Arteriovenous malformations; and
Degenerative nerve diseases such as multiple sclerosis.

PRE-TEST GUIDELINES

Before a CT scan, the patient changes into a hospital gown and removes objects that may interfere with x rays, such as:

Jewelry;
Wig or hairpiece;
Hairpins; or
Partial dentures.

RISK FACTORS

Because CT scanning uses x rays, it exposes the body to radiation. These radiation doses are small, but they can damage cells, which can increase a person's risk for cancer.

Patients that may be unsuited for a CT scan include patients who:

Are pregnant (fetuses are vulnerable to x ray radiation);
Have an allergy to contrast dye (rare);
Weigh more than 300 pounds;
Have unstable vital signs; or
Are claustrophobic.

Patients who are nursing should stop breast feeding for 24 hours after having a CT scan if a contrast medium or dye was used.

WHAT TO EXPECT

Patients may receive a CT scan on an outpatient basis or as part of a hospital stay. The patient lies on a table, which slides into the gantry, a donut-shaped device that houses the scanning equipment.

If the physician chooses to perform CT scanning with x ray dye (contrast material), it will be injected through an IV into a vein in the patient's arm or hand. If the patient is mildly claustrophobic, a sedative can be given.

When the procedure starts, an x ray tube passes a narrow beam of x rays through the brain. The gantry rotates slightly, another x ray is taken, and the procedure is repeated until the x ray beams have passed through a 180-degree arc. The gantry rotates slightly, another x ray is taken, and the procedure is repeated until the x ray beams have passed through a 180-degree arc. After one arc, the scanning table moves forward a short distance and the tube transmits another arc of x rays. To retrieve images from different angles, the technician may adjust the position of the gantry. An x ray detector transmits the x ray energy to a computer, which transforms the information about the reflected energy into an image. The patient will be asked to hold his or her breath and remain still while each scan is taken to ensure that the images are clear.

The full procedure usually takes less than 60 minutes to perform. The use of contrast material during CT scanning doubles procedure time. The use of contrast material during CT scanning increases the procedure time since commonly the first scan is done without contrast and the second is done with the dye.

CT scans are recorded and stored by the computer as a digital image that can be passed throughout a confidential computer network. After a radiologist (a medical doctor who specializes in images of the body) interprets the scans, a report will be sent to the physician requesting the examination. The patient will usually receive the results from the physician who requested the CT exam.

POST-TEST GUIDELINES

Patients can resume normal activities immediately. However, patients who received sedation should arrange for a ride home. If patients have been given a contrast agent, they are asked to drink fluids following the test for hydration and to speed the body's excretion of the contrast.

POSSIBLE COMPLICATIONS

Complications are rare but include allergic reaction to the contrast dye, kidney failure from contrast, and tissue damage, which can result if a significant amount of dye leaks under the skin at the point of insertion.

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