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- What is the test?
- How do I prepare for the test?
- What happens when the test is performed?
- What risks are there from the test?
- Must I do anything special after the test is over?
- How long is it before the result of the test is known?
What is the test?
CT scans are pictures taken by a specialized x-ray machine. The machine circles your body and scans an area from every angle within that circle. The machine measures how much the x-ray beams change as they pass through your body. It then relays that information to a computer, which generates a collection of black-and-white pictures, each showing a slightly different “slice” or cross-section of your internal organs. Because these “slices” are spaced only about a quarter-inch apart, they give a very good representation of your internal organs and other structures. Doctors use CT scans to evaluate all major parts of the body, including the abdomen, back, chest, and head.
A CT scan is not a very common test to have done for back problems. It does a better job showing the abdominal internal organs than showing details of the bones in the spine. But some back pain is caused by problems in these internal organs, such as the pancreas or the kidney. The CT scan is an excellent way to examine these organs. Also, the CT scan can be combined with a test called a "myelogram" (discussed separately) to give a clear view of the spinal cord and places where the vertebral bones might be pinching it.
How do I prepare for the test?
If you are having an abdominal CT scan, you might have to fast 2–4 hours before your test. You also may have to drink a large quantity of oral contrast, a fluid that will show up on the CT scan and help define the lining of some internal organs. Tell your doctor if you’re allergic to x-ray contrast dyes, may be pregnant, or have diabetes and take insulin. Insulin can cause hypoglycemia after missing a meal.
What happens when the test is performed?
The test is done in the radiology department of a hospital or in a diagnostic clinic. You wear a hospital gown and lie on your back on a table that can slide back and forth through the donut-shaped CT machine. A technician or other health care professional inserts an IV and injects more contrast dye through it. This dye outlines blood vessels and soft tissue to help them show up clearly on the pictures.
The technologist moves the table with a remote control to enable the CT machine to scan your body from all of the desired angles. You will be asked to hold your breath for a few seconds each time a new level is scanned. The technologist usually works the controls from an adjoining room, watching through a window and sometimes speaking to you through a microphone. A CT scan takes about 30–45 minutes. Although it’s not painful, you might find it uncomfortable if you don’t like to lie still for extended periods.
What risks are there from the test?
There are a few small risks. The contrast dye used in the test can damage your kidneys, especially if they are already impaired by disease.However, some newer dyes are less likely to cause kidney injuries. If kidney damage does occur, this is usually temporary, although in some rare cases it becomes permanent. If you are allergic to the dye used in the procedure, you may get a rash or your blood pressure may drop enough to make you feel faint until you get treatment. As with x-rays, there is a small exposure to radiation. The amount of radiation from a CT scan is greater than that from regular x-rays, but it’s still too small to be likely to cause harm unless you’re pregnant.
Must I do anything special after the test is over?
No.
How long is it before the result of the test is known?
The radiologist can probably give you preliminary results within a day. The formal reading of your CT scan might take another day.