CT Scan (Computed Tomography Scan)

Photo is CT scan in process

A CT scan stands for Computed Tomography scan. It is also known as a CAT (Computer Axial Tomography) scan. It is a medical imaging method that employs tomography. Tomography is the process of generating a two-dimensional image of a slice or section through a 3-dimensional object (a tomogram). The medical device (the machine) is called a CTG scanner; it is a large machine and uses X-rays. It used to be called an EMI scan, because it was developed by the company EMI. Undergoing a CT scan is a painless procedure. 

The CT scanner uses digital geometry processing to generate a 3-dimensional (3-D) image of the inside of an object. The 3-D image is made after many 2-dimensional (2-D) X-ray images are taken around a single axis of rotation - in other words, many pictures of the same area are taken from many angles and then placed together to produce a 3-D image. The Greek wordtomos means "slice", and the Greek word graphein means "write".

How does a CT scan work?

A CT scanner emits a series of narrow beams through the human body as it moves through an arc, unlike an X-ray machine which sends just one radiation beam. The final picture is far more detailed than an X-ray one. 

Inside the CT scanner there is an X-ray detector which can see hundreds of different levels of density. It can see tissues inside 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 shows up much more clearly on the screen. 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 vessels are the target images the barium will be injected. 

The accuracy and speed of CT scans may be improved with the application of spiral CT. The X-ray beam takes a spiral path during the scanning - it gathers continuous data with no gaps between images. For a spiral scan of the chest, for example, the patient will be asked to hold his/her breath for a few seconds.

What is a CT scan like for the patient?

Most places will provide the patient with a gown. He/she will need to undress, usually down to their underwear, and put the gown on. If the place does not provide a gown the patient should wear loose-fitting clothes. 

Any woman who suspects she may be pregnant should tell her doctor beforehand. 

Doctors may ask the patient to fast (eat nothing) and even refrain from consuming liquids for a specific period before the scan. 

The patient will be asked to lie down on a motorized examination table, which then goes into the giant doughnut-like machine. The couch with the patient goes into the doughnut hole. 

Some patients may be given a contrast dye or substance which is either swallowed, given as an enema, or injected. This improves the picture of some blood vessels or tissues. If a patient is allergic to contrast material he/she should tell the doctor beforehand. There are some medications that reduce allergic reactions to contrast materials.