You will be asked to lie on a narrow table (gantry) that slides into the center of the scanner. Depending on what is being scanned, you may lie on your stomach, back, or side. If contrast media (dye) is to be given, an IV (intravenous needle or tube) will be placed in a small vein in your hand or arm.
As with standard photography, if you move while the CT image is being taken, it will blur. Because of this, the operator of the scanner will tell you when to hold your breath and not move.
As the exam takes place, the gantry will advance small intervals through the scanner. Modern spiral scanners can perform the examination in one continuous motion of the gantry. Generally, complete scans will only take a few minutes. However, additional contrast-enhanced or higher-resolution scans will add to the scan time. The newest multi-detector scanners can image the entire body, head-to-toe, in less than 30 seconds.
The health care provider may advise you to avoid eating or drinking for 4 - 6 hours prior to the scan, if contrast dye is to be used. You may need to have your kidney function checked with a blood test (creatinine level) prior to the scan.
The CT scanner has a weight limit to prevent damage to the mechanized gantry. Have the health care provider contact the scanner operator if you weigh more than 300 pounds.
Metal interferes with the x-rays, so you may be asked to remove jewelry and wear a hospital gown during the study.
The x-rays are painless. The primary discomfort may be from the need to lie still on the table.
If intravenous contrast dye is given, you may feel a slight burning sensation in the injected arm, a metallic taste in the mouth, and a warm flushing of the body. These sensations are normal and usually go away within a few seconds.
Thoracic CT may be recommended when there is a need for examination of the structures inside the chest. It is noninvasive and poses less risk than invasive procedures (such as angiography or exploratory surgery).
Common reasons for having a thoracic CT include:
- When there is a chest injury
- When a tumor or mass (clump of cells) is suspected
- To determine the size, shape, and position of internal organs
- To look for bleeding or fluid collections in the lungs or other areas
Thoracic CT may show many disorders of the heart, lungs, or chest area, including:
Additional conditions under which the test may be performed:
CT scans and other x-rays are regulated to provide the minimum amount of radiation exposure needed to produce the image. During pregnancy, a thoracic CT scan is not recommended unless the benefits outweigh the risk of radiation exposure to the fetus. CT scans provide low levels of radiation.
The most common dye used is iodine-based. A person who is allergic to iodine may experience nausea, vomiting, sneezing, itching, or hives, and occasionally anaphylaxis (life-threatening allergic response). In people with kidney problems, the dye may have toxic effects on the kidneys.
The benefits of a CT scan usually far outweigh the risks. A CT scan is one of the best ways of looking at soft tissues such as the heart and lungs.