Computer tomography (CT) scan
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.
CT scan is used to detect abnormalities e.g., blood clots, cysts, fractures, infections and tumors in internal structures (e.g., bones, muscles, organs and soft tissue). The procedure 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 and reproductive organs), in the chest (e.g., heart, aorta and lungs) and in the head (e.g., brain, skull and sinuses). It can be used to detect abnormalities in the neck and spine (e.g., vertebrae, intervertebral discs and spinal cord) and in nerves and blood vessels.
CT scan is a non-invasive procedure and is usually performed in an outpatient basis (e.g., does not require overnight hospitalization). The amount of radiation used in a CT scan is low and 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 or 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 are usually 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 the CT scan is given 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 or 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 and zippers) and may be required to change into a hospital gown that does 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 takes from 30-90 minutes to perform.
To provide clear images, patients must remain as still as possible during the CT scan. The technician is able to see the patient and communicate through an intercom system throughout the procedure. At certain points during the 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 used in cases of severe trauma and injury.