A CT or CAT scan is a diagnostic imaging procedure that uses a combination of x-rays and computer technology to produce cross-sectional images (often called slices), both horizontally and vertically, 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.
CT scans may be done with or without contrast. "Contrast" refers to 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 examinations may require you to fast for a certain period of time before the procedure. Your physician will notify you of this prior to the procedure.
CT scans may be performed to help diagnose tumors, investigate internal bleeding, or check for other internal injuries or damage.
You may want to ask your physician about the amount of radiation used during the CT procedure and the risks related to your particular situation. It is a good idea to keep a record of your past history of radiation exposure, such as previous CT scans and other types of x-rays, so that you can inform your physician. Risks associated with radiation exposure may be related to the cumulative number of x-ray examinations and/or treatments over a long period of time. If you are pregnant or suspect that you may be pregnant, you should notify your doctor.
Advances in computed tomography 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.
Studies show that eighty-five percent of the population will not experience an adverse reaction from iodinated contrast; however, you will need to let your physician know if you have ever had a reaction to any contrast dye, and/or any kidney problems. A reported seafood allergy is not considered to be a contraindication for iodinated contrast. If you have any medical conditions or recent illnesses, inform your physician. The effects of kidney disease and contrast agents have attracted increased attention over the last decade, as patients with kidney disease are more prone to kidney damage after contrast exposure. If you are pregnant or think you may be pregnant, you should notify your physician. If you are claustrophobic or tend to become anxious easily, tell your physician ahead of time, as he/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.