CT Scan Overview
Computed tomography (CT) scan, also called computerized axial tomography (CAT) scan, is used to create cross-sectional images of structures in the body. In this procedure, x-rays are taken from many different angles and processed through a computer to produce a three-dimensional (3-D) image called a tomogram.
Computed tomography is used to detect abnormalities such as blood clots, cysts, fractures, infections, and tumors in internal structures (e.g., bones, muscles, organs, soft tissue). The procedure also may be used to guide the placement of instruments within the body (e.g., to perform a biopsy).
CT scan may be used to examine structures in the abdomen and pelvis (e.g., liver, gallbladder, pancreas, spleen, intestines, reproductive organs), in the chest (e.g., heart, aorta, lungs), and in the head (e.g., brain, skull, sinuses). It also can be used to detect abnormalities in the neck and spine (e.g., vertebrae, intervertebral discs, spinal cord) and in nerves and blood vessels.
CT scan is a noninvasive procedure and is usually performed on an outpatient basis (i.e., does not require overnight hospitalization). The amount of radiation used in a CT scan is low, and the procedure is considered to be safe. However, CT scans should be used with caution in women who are pregnant, especially during the first trimester. Other diagnostic tests (e.g., ultrasound) may be used during pregnancy.
A contrast agent (e.g., iodine-based dye, barium solution) may be administered prior to CT scan to allow organs and structures to be seen more easily. Contrast agents can be administered through a vein (IV), by injection, or taken orally. Patients usually are instructed not to eat or drink for a few hours prior to contrast injection or IV because the dye may cause stomach upset. Patients may be required to drink an oral contrast solution 1–2 hours before CT scan of the abdomen or pelvis.
Contrast dye may cause a rash, itching, or a feeling of warmth throughout the body. Usually, these side effects are brief and resolve without treatment. Antihistamines may be administered to help relieve symptoms.
A severe anaphylactic reaction (e.g., hives, difficulty breathing) to the contrast dye may occur. This reaction, which is rare, is life threatening and requires immediate treatment. Patients with a prior allergic reaction to contrast dye or medication and patients who have asthma, emphysema, or heart disease are at increased risk for anaphylactic reaction. Epinephrine, corticosteroids, and antihistamines are used to treat this condition.
Rarely, contrast dye may cause kidney failure. Patients with diabetes, impaired kidney function, and patients who are dehydrated are at higher risk for kidney failure.
Before undergoing a CT scan, patients must remove all metallic materials (e.g., jewelry, clothing with snaps, zippers) and may be required to change into a hospital gown that will not interfere with the x-ray images. Patients lie on a movable table, which is slipped into a doughnut-shaped computed tomography scanner. The procedure usually takes from 30 to 90 minutes to perform.
To provide clear images, patients must remain as still as possible during CT scan. The technician is able to see the patient and communicate through an intercom system throughout the procedure. At certain points during a CT scan of the chest or abdomen, the technician may ask the patient not to breathe for a few seconds. Spiral or helical scanners are newer machines that provide faster and more accurate CT scans. These machines often are used in cases of severe trauma and injury.
A radiologist (physician who specializes in imaging procedures) interprets the results of a CT scan.