Computed Tomography Test 
What is a computed tomography scan? Computed tomography (CT), sometimes called a CAT scan, is a diagnostic procedure in which cross-sectional pictures or "tomographic slides" of the body are made by special x-ray equipment. Doctors use a CT scan to study internal parts of the body, such as the abdomen, brain or chest, in greater detail than they could using conventional x-rays. CT offers some advantages over other x-ray techniques in diagnosing diseases, particularly because it clearly shows the shape and exact location of organs, soft tissues, and bones. Why would I need a CT scan? A CT scan is used to help identify problems such as cancers, blood clots, cardiovascular disease, infectious disease, trauma and musculoskeletal disorders. A CT scan may be ordered if you have had a traumatic injury (such as abdominal trauma or skull fractures), infection, tumor or other abnormal structures of the body. At times, a CT scan is ordered in an attempt to explain the cause of certain symptoms that you might have. For example, a CT scan of the brain might be done to help find out why you are having headaches, and also to check the brain's structure, to find tumors and to detect possible internal bleeding after a head injury. A scan of the spine can be done to diagnose spinal lesions or tissue damage, or to monitor effects of spinal surgery or therapy. How is a CT scan performed? The procedure is painless. A patient lies very still on a table that passes through a doughnut-shaped x-ray machine. The machine, which is linked to a computer, rotates around the patient, taking pictures of one thin slice of tissue after another. To obtain a clearer picture, the patient may be given a solution of an x-ray dye to drink, or get an injection into a vein in the arm before the CT is done. The length of the procedure can take from seconds to 15 minutes, depending on the scanner or size of the area to be x-rayed. Images from these x-rays are then processed by the computer. The final image, called a "computed tomogram" or "CT slice," is displayed on a monitor. This image can be recorded permanently on film. In addition, a CT scan can be stored on magnetic tape or optical disk. How can I prepare for the test? A radiologist or technologist will check your medical history to see if you have had any allergies to shellfish, iodine, or certain dyes, and whether you have a history of diabetes, asthma, a heart condition, kidney problems, or thyroid conditions. These conditions may indicate a higher risk of reaction to contrast dye, which is sometimes given. If you believe that you may be pregnant, inform the radiologist before undergoing any CT scan. If an oral contrast dye will be used during the test, you might be asked to fast for four hours before a non emergency scan. During the test, you'll be asked to remove all metal objects, jewelry, and any removable dental work, depending on the part of the body that is being scanned. Are there risks in receiving a CT scan? A CT scan is a low-risk, noninvasive procedure. A CT does involve exposure to radiation, which is higher than the exposure from a regular x-ray. While the benefit of an accurate diagnosis usually outweighs the risk associated with radiation exposure, doctors should not order a CT scan without a good reason. The typical radiation dose from a CT exam is equivalent to the amount of natural background radiation received over a year's time. Some patients may have an adverse reaction to the contrast dye that may be used. You may feel flushed and warm and may experience a brief headache, a salty taste, or nausea and vomiting after the dye is injected. The risk of serious allergic reaction to contrast dye-containing iodine is rare, and radiology departments are well equipped to deal with them. If you have diabetes, there is also a risk of worsening kidney function, especially if you are taking the drug, glucophage. Your kidneys might also be adversely affected from the contrast dye used in the scan if you have pre-existing renal disease. Preventive measures are available to avoid these side effects, however. Ask your doctor about this. Also, if you are pregnant, an abdominal CT scan is not recommended due to possible risks to the fetus. Who interprets the results, and how do I get them? A radiologist will analyze the images and send a signed report with an interpretation to the patient's personal physician. At other times a specialist will review the films like a surgeon or neurologist. The personal physician's office will inform the patient on how to obtain the results. Sources: National Cancer Institute Radiological Society of North America
This article was reviewed and updated June 2007.
| 