TC means computed tomography. Virtual colonoscopy uses a CT scanner to produce detailed images of the colon and rectum. This test can be used in place of a colonoscopy to help detect bowel cancer and other conditions. Note: The following information is a general guide only. The agreements and the way tests are performed, may vary between different hospitals. Always follow the instructions of your doctor or local hospital.
On this page
- What is virtual colonoscopy?
- What is virtual colonoscopy uses?
- How does the CT colonography work?
- What happens during a CT colonography?
- What should I do to prepare for CT colonography?
- What I can expect after CT colonography?
- Are there any side effects or complications of CT colonography?
What is virtual colonoscopy?
Virtual colonoscopy, known in full as CT colonography is a test that uses a CT scanner to produce images of the inside of the colon and rectum (colon is the last part of the bowel or intestines, rectum is the step between the colon and anus). For further information on this, see separate leaflet called computed tomography.
Virtual colonoscopy can provide information about the colon which would usually only obtainable by colonoscopy. A colonoscopy is a test in which a flexible tube is inserted into the rectum and through the colon (see separate leaflet called colonoscopy). Virtual colonoscopy is less invasive than colonoscopy because the test involves inserting a tube all the way around the colon.
Virtual colonoscopy is sometimes referred to as virtual colonoscopy.
What is virtual colonoscopy uses?
The main reason for virtual colonoscopy is to find polyps or cancer in the colon or rectum. Polyps are small growths inside your gut. They are usually harmless, but some polyps can turn into cancer.
Virtual colonoscopy can be used if you have symptoms such as changes in bowel habits, weight loss or blood in the stool (bowel movement). Can also be used to detect people who are at risk of developing bowel cancer.
Virtual colonoscopy is often used in people who are too weak to have a colonoscopy, or there are other reasons why a colonoscopy would not be appropriate.
How does the CT colonography work?
The CT scanner looks like a giant ring thickness. Within the wall of the scanner is no X-ray source Opposite the X-ray source on the other side of the ring, X-ray detectors are You lie on a table that slides into the center of the ring until the body part to be scanned is within the ring. The X-ray machine in the ring rotates around its body. As you turn around, the X-ray machine emits X-ray thin beams through the body, which are detected by the X-ray detectors.
The detectors detect the intensity of X-ray beam that has passed through the body. The denser the tissue, less X-rays pass through. X-ray detectors feed this information into a computer. The different kinds of fabric with different densities are displayed as an image on the computer monitor in different colors or shades of gray. Thus, in effect, an image is created by the computer on a slice (cross section) of a thin section of the body.
As the couch moves slowly through the ring X-ray beam passes through the next section of your body. Thus, several cross-sectional images (slices) of the body part under investigation are made by the team. Newer scanners can even produce 3-D images of the data received from the different cuts of the body part being scanned.
What happens during a CT colonography?
The way this test is carried out varies between different hospitals and can also vary according to what is taking the test.
You may receive an injection of a muscle relaxant to help relax the muscles of the bowel wall. May also be given an injection of contrast agent at the same time, depending on the reason for the test.
The test begins by positioning you on the CT examination table, usually lying flat on your back or possibly on your side or stomach. Straps and pillows may be used to help maintain the correct position during imaging.
A very small flexible tube is passed a little way into the rectum to enable the gas is pumped into the colon gently. Sometimes, an electronic pump is used to put gas in the colon. The gas helps dilate (open) the colon as much as possible to get rid of creases or wrinkles that can hide polyps or tumors.
When this happens, you may briefly feel pains similar to trapped wind. You may also have the need to go to the bathroom, but, because their colon is empty, this will not happen. Spend the wind, but no need to be embarrassed, as the wait staff that this can happen.
Then, the table will move through the scanner. You may be asked to hold your breath for about 15 seconds before turning over and lie on your back or sideways. As you go through the scanner photos will be taken.
Once the scan is complete, remove the tube and allowed to get off the table.
The CT scan itself is painless. You can not see or feel the radiographs. You will be asked to remain as still as possible, because otherwise the scanned images may be blurred. The scanning may take about 5-30 minutes, depending on which part (or parts) of the body being scanned.
What should I do to prepare for CT colonography?
You should be given instructions by the CT department detailing what to do. As a general rule, so that your doctor can clearly see your gut, you may need to follow a special diet for a few days before the procedure and take a laxative to empty your bowel.
You may be asked to swallow a liquid called contrast (dye) around two days before the test. This fluid will help your intestines show more precisely in the analysis. If you need an injection of contrast medium, may be necessary to stop taking certain medications before procedure.This can apply to people taking metformin, a drug used to treat diabetes. If you are taking this medicine, your doctor will give you instructions on what to do.
You may be asked not to eat or drink for several hours before the scan.
What I can expect after CT colonography?
Generally, you can return to your normal activities as soon as the scan is finished. You may experience some swelling or find the wind passes for a while after the test. This has to be resolved fairly quickly.
If you have had muscle relaxants or injection of contrast medium, you may have to wait a short time before driving. You can arrange for someone to drive you home after the test.
If you are breastfeeding, you may need to express and discard milk for 24 hours after the scan. Ask your doctor or radiologist for specific advice.
Are there any side effects or complications of CT colonography?
Pregnant women, if possible, should not have CT colonography, as there is a small risk that X-rays can cause an abnormality in the fetus. Tell your doctor if you are pregnant, or think you may be pregnant.
Laxatives are used to prepare the bowel can cause diarrhea and can make you feel sick and bloated. Sometimes, some people feel a warm sensation or get a metallic taste in the mouth after having an injection of contrast. This usually lasts only a minute or two. If you have had muscle relaxants, these can distort your vision temporarily or make you feel dizzy.
Rarely, some people have an allergic reaction to the dye that is sometimes used. This can be treated immediately. Rarely, the dye may cause some kidney damage, most often in people who already have kidney problems.
There is a small possibility that the colon can be damaged during the procedure. This can lead to bleeding and infection, which may require treatment with medication or surgery.
Risks of X-ray radiation used in CT scans
Used X-ray CT, which are a type of radiation. Exposure to large doses of radiation is linked with the development of cancer or leukemia – often many years later.
The dose of X-ray radiation necessary for a CT scan is much more than one X-ray image, but still quite a dose is generally lower. The risk of damage from the radiation dose used in CT scanning is thought to be very small, but not completely without risk. As a rule, the higher the radiation dose, the greater the risk. For example, most of the body of scanning, the higher the radiation dose. And, repeat CT eventually cause an overall increase in dose. Also, the younger you are when you have a TC, the greater the risk of developing life cancer or leukemia.
Several studies have attempted to estimate the risk of developing cancer or leukemia after a CT scan. Some are listed below. In general, the risk is small.