A CT (Computed Tomography) or CAT scan is a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce images (often called slices) of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, organs and blood vessels. CT scans are more detailed than standard x-rays, especially with the three-dimensional (3-D) images possible through advanced technology.

CT scans may be done with or without contrast – a substance taken by mouth or injected into an intravenous (IV) line that causes the particular organ or tissue under study to be seen more clearly. Contrast exams may require you to fast for a certain period of time before the procedure. Your doctor will notify you of this prior to the procedure.

If you are pregnant or suspect that you may be pregnant, you should notify your doctor. If you are claustrophobic or tend to become anxious easily, tell your doctor ahead of time, as he or she may prescribe a mild sedative for you before the procedure to make you more comfortable. It will be necessary for you to remain still and quiet during the procedure, which may last 10 to 20 minutes, on average.

Advances in CT scan technology include the following:

  • High-resolution computed tomography. This type of CT scan uses very thin slices (less than one-tenth of an inch), which are effective in providing greater detail in certain conditions such as lung disease.
  • Helical or spiral computed tomography. During this type of CT scan, both the patient and the x-ray beam move continuously, with the x-ray beam circling the patient. The images are obtained much more quickly than with standard CT scans. The resulting images have greater resolution and contrast, thus providing more detailed information.
  • Ultrafast computed tomography (also called electron beam computed tomography). This type of CT scan produces images very rapidly, thus creating a type of “movie” of moving parts of the body, such as the chambers and valves of the heart. This scan may be used to obtain information about calcium build-up inside the coronary arteries of the heart.
  • Computed tomographic angiography (CTA). Angiography (or arteriography) is an x-ray image of the blood vessels. A CT angiogram uses CT technology rather than standard x-rays or fluoroscopy to obtain images of blood vessels, for example, the coronary arteries of the heart.
  • Combined computed tomography and positron emission tomography (PET/CT). The combination of computed tomography and positron emission tomography technologies into a single machine is referred to as PET/CT. PET/CT combines the ability of CT to provide detailed anatomy with the ability of PET to show cell function and metabolism to offer greater accuracy in the diagnosis and treatment of certain types of diseases, particularly cancer. PET/CT may also be used to evaluate epilepsy, Alzheimer’s disease, and coronary artery disease.