Patient education: CT scan (The Basics)

What is a CT scan? — CT stands for "computed tomography." It is a type of imaging test that creates pictures of the inside of the body.

With a CT scan, the machine's X-ray beam moves around you to quickly to make pictures from many angles around your body (figure 1). Then, a computer uses the pictures to make cross-sectional images, or "slices," of your body. The slices can be combined or stacked together to create 3-D images on the computer.

There are different types of CT scans:

●Standard CT scan – This type uses fan-shaped or spiral X-rays to make images. Each slice is combined with others to create a good image. During a standard CT scan, you lie down and hold your breath for short periods. Doctors can also use a special dye, or "contrast," to make the area being studied clearer. Sometimes, you drink the contrast. Other times, the contrast material is given through an "IV" (a thin tube that goes into a vein).

●Cone beam CT scan – This type uses cone-shaped X-rays to make images. It gives a different quality of pictures and is most often used for looking at the teeth, mouth, jaw, head, and neck. Cone beam CT scans use less radiation than a standard CT scan. They are also faster than a standard CT scan and can be done while you sit up.

CT scans are quick and painless. They can look for problems like tumors, injuries, and blood clots in any part of the body.

Do CT scans use radiation? — Yes. X-rays work by giving you a very small amount of radiation. Since a CT scan is a series of many X-rays, it gives you more radiation than a single X-ray. Cone beam CT scans give off less radiation than a standard CT scan.

How do I prepare for a CT scan? — The doctor or nurse will tell you if you need to do anything special to prepare.

They will also ask you about your "health history." This involves asking you questions about any health problems you have or had in the past, past surgeries, and any medicines you take. Tell them about:

●Any medicines you are taking – This includes any prescription or "over-the-counter" medicines you use, plus any herbal supplements you take. It helps to write down and bring a list of any medicines you take, or bring a bag with all of your medicines with you.

●Any allergies you have

●Whether you could be pregnant – An CT scan can be done during pregnancy if needed. But your doctor might want to delay the test until after your baby is born.

●If you get nervous in small spaces – Some CT machines are narrow. If small spaces make you feel nervous or anxious, tell your doctor. If needed, they can prescribe medicine to help you stay calm during the procedure. If there is concern that you will not be able to lie still for the entire test, your doctor will talk to you about other options, such as sedation.

Ask the doctor or nurse if you have questions or if there is anything that you do not understand.

What happens during a CT scan? — When it is time for the procedure:

●You will change into a hospital gown and remove any metal objects from your body. These include jewelry, glasses, dentures, and hearing aids.

●You might get an "IV," which is a thin tube that goes into a vein.

●If your doctor prescribed medicine to help you stay calm during the CT scan, you will take this before the procedure starts.

●The person doing the CT scan (called a "technician") will use your IV to inject the contrast dye into your vein, if you are getting it.

●You will lie on the narrow table of the CT machine. The table slides into the scanner. The technician will not be in the room with you, but they will be nearby and able to see you and talk to you.

●You will need to lie very still during the CT scan, so the images are clear. Sometimes, young children need medicine to help them lie still.

●During the scan, the table might move. You might also be asked to do things, like hold your breath for a few seconds. The machine does not touch you, and it does not hurt.

●A CT scan usually takes only a few minutes. This depends on how many pictures your doctor wants to see.

●When the procedure is over, the table will slide back out of the machine.

What happens after a CT scan? — If you had an IV, it will be removed. In most cases, you can go home right away after a CT scan.

If you got medicine to help you stay calm during the test, someone will need to take you home afterward.

What are the risks of a CT scan? — Your doctor will talk to you about all of the possible risks, and answer your questions. Possible risks include:

●A minor or serious allergic reaction to the dye

●Kidney damage from the dye

●Radiation exposure – A CT scan exposes you to some radiation. In general, exposure to radiation very slightly raises a person's risk of developing cancer later in life. But the amount of radiation during a CT scan is very small. The overall risk increases if you have to get many imaging tests over time.

What else should I know? — You might get your results the same day, or it might take a little longer for them to be read by an expert. Your doctor or nurse will let you know when to expect your results.

If your CT scan shows any abnormal results, your doctor or nurse will talk to you about what to do next.

More on this topic

Patient education: X-ray (The Basics)
Patient education: MRI scan (The Basics)