A CT scanner emits a series of narrow beams through the human body as it moves through an arc. This is different from an X-ray machine, which sends just one radiation beam. The CT scan produces a more detailed final picture than an X-ray image. The CT scanner s X-ray detector can see hundreds of different levels of density. It can see tissues within a solid organ.
This data is transmitted to a computer, which builds up a 3-D cross-sectional picture of the part of the body and displays it on the screen. Sometimes, a contrast dye is used because it can help show certain structures more clearly.
For instance, if a 3-D image of the abdomen is required, the patient may have to drink a barium meal. The barium appears white on the scan as it travels through the digestive system.
If images lower down the body are required, such as the rectum, the patient may be given a barium enema. If blood vessel images are the target, a contrast agent will be injected into the veins.
The accuracy and speed of CT scans may be improved with the application of spiral CT, a relatively new technology. The beam takes a spiral path during the scanning, so it gathers continuous data with no gaps between images.
CT is a useful tool for assisting diagnosis in medicine, but it is a source of ionizing radiation, and it can potentially cause cancer. The National Cancer Institute advise patients to discuss the risks and benefits of CT scans with their doctors.