A CT scan makes use of computer-processed combinations of many X-ray images taken from different angles to produce cross-sectional (tomographic) images (virtual “slices”) of specific areas of a scanned object, allowing the user to see inside the object without cutting.
Since its introduction in the 1970s, CT has become an important tool in medical imaging to supplement X-rays and medical ultrasonography. It has more recently been used for preventive medicine or screening for disease, for example CT colonography for people with a high risk of colon cancer, or full-motion heart scans for people with high risk of heart disease.
Your CT scan will be performed with you lying on a narrow, motorized table that slides through the short donut-shaped scanner. An X-ray tube and several detectors will move around the table as it moves the table in or out. You may hear buzzing, whirring, or clicking noises during the scan.
The CT technologist will first do a “scout” view to determine the range of images needed to include the area of interest your physician has requested. The table will move in or out then there will be a brief pause as the technologist prepares the scanner for the exam. She/he is always within view of you from the scan console in the window behind you. You can be heard and attended to within moments if you should need anything.
If your exam includes an area that moves during breathing (chest, abdomen, pelvis), you will be asked to hold your breath during the scans. For every exam, it is extremely important that you hold still and do not reposition on the table.
Depending on the type of CT scan your physician has ordered, you may be asked to:
Change clothing or remove clothing in the area being scanned. You will be given a gown or other means of being covered during the scan.
Remove metal objects such as a belt, jewelry, dentures and glasses, if they are within the area being scanned. Metals cause streak artifacts on CT scans and greatly decrease the scan quality.
Refrain from eating or drinking for a few hours prior to the scan.
There are two different types of contrast typically used for CT scans. The first is oral contrast – a contrast that you drink. This type of contrast is used for most esophageal, abdomen and pelvis CT scans. It is used to define the esophagus, stomach, colon and loops of bowel.
A second type of contrast is called IV contrast. This contrast is used to define vascular structures and vascular supply. This is injected into a vein and timed to capture the contrast as it goes through the vessels into particular organs or areas. You may experience a feeling of warmth during the injection or a metallic taste in your mouth. This is normal.
Not every scan requires the use of contrast, and some require only one or both. The use of contrast is determined by your physician’s order and the area being examined.