A CT (computed tomography) scan, also called a CAT (computed axial tomography) scan, is a diagnostic exam used to detect tumors, determine the stage and location of a cancer, check the effectiveness of cancer treatment, or guide a biopsy (the removal of a small amount of tissue for examination). It takes multiple cross-sectional images using special x-rays and computer enhancement. CT scans can take images of body parts that cannot be seen on regular x-rays.
The examination will generally last up to an hour, though the scanning itself takes only 10 to 15 minutes. When the scan is finished, you may be asked to remain on the exam table while a radiologist reviews the images to determine if additional images are needed.
Preparing for your CT scan
- Tell the doctor if you previously had an allergic reaction to intravenous (IV) dye or any other allergies.
- If you become uncomfortable lying still for a long time or if you are uncomfortable with close spaces, talk to your doctor beforehand. He or she may make arrangements for you to receive a sedative before your scan.
- When your doctor schedules a CT scan, let him or her know if you have diabetes (sugar in the blood) and take a drug called Glucophage (metformin). You may be asked not to take it the day before your CT scan, the day of your CT scan, and the day after your CT scan. Check with your doctor for your specific instructions.
- Tell your doctor/nurse about all your medications, including over-the-counter products, vitamins, and herbal supplements.
- Check with your doctor/nurse if you should take your regular medications that day.
- Women: tell your doctor if you may be pregnant or breast-feeding.
- Do not eat anything for 4-6 hours before your scan.
- Do not drink anything for 2 hours before your scan.
- For some scans, there are no restrictions on eating or drinking.
The day of your CT scan
- If you take other medications, you may take them with a sip of water.
- Wear loose, comfortable clothing to your appointment. When you arrive for your CT scan, you may need to change into a gown.
- You will be asked to remove any item that contains metal (including jewelry, eyeglasses, dentures and hairpins) because metal objects may affect the CT images. You may also be asked to remove hearing aids and removable dental work. Women may be asked to remove their bra due to metallic clasps.
- Tell the technologist if you have any allergies to IV dye or asthma, multiple myeloma, or any disorder of the heart, kidneys or thyroid gland, or if you have diabetes.
- You may receive a contrast agent before the scan, which may be a drink or an intravenous (IV) injection. The contrast helps create a clearer picture of the parts of the body being scanned.
- Intravenous contrast may cause you to feel hot or get a metallic taste in your mouth; both sensations should disappear after a few minutes. If you experience a more serious reaction, tell the technologist immediately.
- A technologist will help position you on the table and then monitor the procedure from an adjoining control room. You can communicate through an intercom system.
- The CT scan resembles a large donut. You will hear whirring or clicking sounds from the machine; some machines are noisier than others.
- CT scans are not painful. You will need to lie still for the entire scan, which may become uncomfortable. You may be asked to hold your breath during part of the scan because the motion created by breathing can blur the images. The exam table may be raised, lowered, or tilted to create the correct angle for the x-rays; ask the technologist performing the scan to tell you when the table will move.
After the scan
- You can expect to resume your normal activities immediately after your CT scan, including driving. If you received a contrast agent for the scan, you are encouraged to drink a lot of water to help flush it out of your body.