CT Scan: Computed Tomography

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.

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.

client1

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.

WHEN IS A CT SCAN USED?

CT scanning is useful to get a very detailed 3-D image of certain parts of the body, such as soft tissues, the pelvis, blood vessels, the lungs, the brain, abdomen, and bones.

It is often the preferred method of diagnosing many cancers, such as liver, lung, and pancreatic cancers. The image allows a doctor to confirm the presence of a tumor. The tumor’s size can be measured, plus its exact location, as well as to determine how much the tumor has affected nearby tissue.

A scan of the head can provide the doctor with important information about the brain – he/she may want to know whether there is any bleeding, swelling of the arteries, or tumors.

A CT scan will tell the doctor whether the patient has a tumor in his/her abdomen, and whether any internal organs in that area are swollen or inflamed. It will reveal whether there are lacerations of the spleen, kidneys or liver.

As a CT Scan can detect abnormal tissue it is a useful device for planning areas for radiotherapy and biopsies.

A CT Scan can also provide valuable data on the patient’s vascular condition. Vascular refers to blood flow. Many vascular conditions can lead to stroke, kidney failure, and even death. It can help a doctor assess bone diseases, bone density, and the state of the patient’s spine.

TYPES OF CT SCAN MACHINES

  •  
    Old axial scanners – not used any more.
  •  
    Spiral CT scanners – single slice per rotation to upto 128 slice level.

PREPARING FOR CT SCAN

  •  Some CT exams require an injection called an “Iodinated contrast.” Please tell your doctor if you have ever had a reaction to an X-Ray dye or to a  topical antiseptic iodine, such as betadine. If you are sensitive to iodine, you will have to take medicine beginning few hours before your exam

  •  Wear comfortable clothing without zippers, metal buttons, or snaps.

  •  If you plan to receive any sedation, arrange for someone to drive you home after your scan.

  •  You can expect to resume your normal activities the same day as your test.

BEFORE YOUR TEST

  • You will put on a hospital gown

  • Remove all metal objects that might interfere with the scan.

  • If a contrast enhancing agent is used, you’ll either receive it by:

  • Drinking it

  • An enema (Inserted through the rectum)

  • An intravenous (IV) line in your arm

The IV enhancing agent may give you a brief sensation that moves up your arm and cause:

  • 1A warm, flushed feeling
  • 2A taste of salt in your mouth
  • 3Nausea for a few minutes

The CT scanner has a very large ring, like a donut standing upright. A narrow table moves through the center hole.
CT scans require you to remain very still. You will be asked to lie flat for your CT scan.
Next:

  • The technologist will help you onto the table and then go into a room behind a large window.

  • Through the intercom, the technologist will ask you to hold your breath for a short time and give you other directions. You can talk to the technologist through this intercom as well.

  • You will hear whirring sounds and the table will move.

  • When your scan is over, the technologist will help you off the table.