Medical Imaging

CT (CAT) Scan

Frequently Asked Questions


What is a CT Scan?

CT stands for Computed Tomography. It is a computerized X-ray machine that examines the body. The scanner is comprised of a table and a gantry. The gantry is the donut shape part that houses the X-ray source. The X-ray source rotates inside the gantry as the patient moves through. Data is obtained and processed by a computer to produce a two dimensional image.

What are Contrast Agents?

Contrast agents are used to image tissues and structures that are not normally seen, or not seen very well. Intravenous contrast agents are used to enhance organs and visualize blood vessels. Oral contrast agents are used to visualize the digestive tract.

How do CT scans differ from MRI scans?

CT and MRI images sometimes look very similar, but the equipment used to perform the scans is different. CT uses ionizing radiation just as with a routine X-ray, while MRI uses a magnetic field. Depending on the clinical indications, one may be preferred over the other, or both may be desirable. CT scanners are faster and as a result, claustrophobia and movement are not as problematic as with the MRI scanner.

Who performs the CT scan?

Medical radiation technologists specially trained in the operation of CT scanners perform the procedure. All technologists must be members of the College of Medical Radiation Technologists of Ontario, and have passed qualifying examinations. The technologist also administers oral and intravenous contrast.

What will I feel during the scan?

CT scanning causes no pain, just as a routine X-ray is painless. If intravenous contrast is used, you may feel warm and flush and get a metallic taste in your mouth. These sensations normally disappear after a few minutes.

How long will the scan take?

The time required will depend upon the type of scan. If oral contrast is required, about 45 to 60 minutes is needed for the contrast to move through your digestive tract. Actual scan times vary from a few seconds to several minutes. If no oral contrast is required, the examination will take about 15 to 30 minutes, including the time for intravenous preparation and interview. In some cases additional scanning is required as scans are tailored to suit individual diagnostic needs.

Will I need to drink anything?

Most abdominal scans require the patient to drink a barium sulfate oral contrast mixture. This mixture is flavoured and not at all unpleasant. Oral contrast highlights the stomach and upper intestine providing the radiologist with a detailed image for review. If you are scheduled for a CT scan requiring oral contrast, you will be asked to arrive one hour before the scan time.

Should I arrive early to see if I can get in earlier?

No. You should arrive at the designated booking time, and check in at the Medical Imaging Reception desk. Appointment times are given in 15 minute increments. Very rarely are there openings in the schedule to permit you being scanned earlier than your appointment time.

How long will I have to wait after I arrive?

Every attempt is made to keep procedures and scan appointments on schedule. However there may be fluctuations in appointment times due to emergency patient needs. Trauma patients, and patients whose lives are in jeopardy will take precedence over booked outpatient appointments. We appreciate your understanding and patience when we must attend to these life and death situations.

Can my spouse/friend stay in the room with me?

No. CT scanners use ionizing radiation and only the patient requiring the scan is permitted in the room.

Why does the technologist leave the room?

The technologist must operate the computer system to complete the scanning procedure.

Can I see the images after my scan?

No. In order to stay on schedule, time will not permit a review with the patient. In addition, the technologists are restricted from discussing images with you. While we understand your curiosity and anxiousness, it is in your best interest to discuss the results of your examination with your doctor.

Will I get the results after the scan?

No. In most cases several hundred images are created during the scan, all of which will be reviewed by the radiologist. Previous examinations will also be reviewed and compared if applicable. The radiologist completes an in-depth review of all images and may at times consult with other physicians to provide an accurate report of your examination to your physician. The final report may take several days to complete. Upon completion it will be sent to your referring physician

Should I have a CT scan if I am pregnant?

No. If you are pregnant or suspect that you may be, you should not have a CT scan or any type of X-ray examination. You should inform the technologist if you suspect you may be pregnant. Alternative arrangements may be made to meet your medical needs.

Will I see the X-ray dye in my urine?

No. X-ray dye or intravenous contrast is a colorless compound that is excreted unnoticed in the urine.

Why do some patients need X-ray dye and others not?

Depending upon your condition and the images required to diagnose or rule out pathology, X-ray dye or intravenous contrast may or may not be needed. The radiologist reviews the information sent to us by your physician and decides what contrast is needed to provide the best images.

Are there any instructions I need to follow after the scan?

If no contrast was used, there are no instructions and you may continue with your normal activities. If intravenous contrast or oral contrast is used, you will be instructed to drink water for the rest of the day to help eliminate the contrast.

Will I have to hold my breath?

Depending upon the body part being scanned, you may be required to hold your breath several times during the scan. It is important that you not move during the scan. The technologist will instruct you on breathing prior to the start of the scan.

Can I breastfeed after an injection of intravenous contrast?

You should not breastfeed for 48 hours after an injection of intravenous contrast.

Does the radiation stay in my body?

No. CT uses a thin beam of radiation that is captured by detectors as it exits your body.