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By Mayo Clinic staff
During a CT scan, you lie on a table inside a doughnut-shaped machine called a gantry. An X-ray tube inside the machine rotates around your body and sends small doses of radiation through it at various angles. As X-rays pass through your body, different tissues absorb different amounts of radiation.
Detectors inside the gantry measure the radiation that passed through your body and converts it into electrical signals. A computer gathers these signals and assigns them a color ranging from black to white, depending on signal intensity. The computer then assembles the images and displays them on a computer monitor.
You can have a CT scan in a hospital or an outpatient facility. Expect the exam to last no longer than an hour, depending on the preparation needed and whether it includes the use of a contrast medium. The scan itself may take less than a minute on the newest machines. Most scans take just a few minutes to complete.
During the CT scan, you lie on a narrow table that slides through the opening of the gantry. You may lie on your back, side or stomach, depending on the area to be scanned. The table can be raised or lowered. Straps and pillows may help you stay in position. During a CT scan of the head, the table may be fitted with a special cradle that holds your head still.
What the device does
As the X-ray tube rotates around your body, the table slowly moves through the gantry. While the table is moving you may need to hold your breath to avoid blurring the images. You may hear clicking and whirring noises. Each rotation yields several images of thin slices of your body.
During this time, a technologist in a shielded room supervises the CT scan and monitors the images as they appear on the computer screen. The technologist can see and hear you, and you can communicate via intercom.
CT scans are painless. If your exam involves use of an intravenous contrast medium, you may feel a brief sensation of heat or experience a metallic taste in your mouth. If you receive the contrast medium through an enema — to help highlight your lower gastrointestinal region — you may feel a sense of fullness or cramping.
After the exam you can return to your normal routine. If you were given a contrast medium, your doctor, a nurse or the CT technologist performing the scan may give you special instructions. You may be asked to wait for a short time in the radiology department to ensure that you feel well after the exam. After the scan, you'll likely be told to drink lots of fluids to help your kidneys remove the medium from your body.
During your small child's exam
If an infant or small child is having the CT scan, you may be allowed to stay with your child during the test. If so, you may be asked to wear a lead apron to shield you from X-ray exposure.
