Computed tomography or CT scan may be used to tell if the anal cancer has spread into the liver or other organs. This is an x-ray procedure that produces detailed cross-sectional images of your body parts.
Unlike a standard x-ray, a CT scanner will not take one picture but will take many pictures as it rotates around you. A computer then combines these “sliced images” into a complete image of the part of your body being studied.
Before a scan, you may be asked to drink 1 to 2 pints of a liquid called “oral contrast” to help “coat” the intestine so that certain areas are not mistaken for tumors.
You may also receive an IV (intravenous) line through which a different kind of contrast dye (IV contrast) is injected to help produce a better outline of your body structures.
This injection can cause some “flushing” or redness and a warm feeling that may last hours to days. A few people may even be allergic to the dye and will get hives. More serious allergic reactions, like trouble breathing and low blood pressure, do happen, but rarely.
Be sure to tell the doctor if you have ever had a reaction to any contrast material used for x-rays. Medicine can be given to prevent and treat allergic reactions. Because CT scans take longer than regular x-rays and you need to lie still on a table while these are being done, you might feel a bit confined.
Magnetic resonance imaging or MRI scans use radio waves and strong magnets instead of x-rays to make images. Radio waves is absorbed by the body and then released in a specific pattern, which a computer translates into a detailed image of body parts being examined.
Like a CT scanner, MRI scanners produces cross-sectional slices of the body. A contrast material might be used, but it is not needed as often.
Because you have to be placed inside tube-like equipment, MRI scans are more uncomfortable than CT scans and take longer to complete—often up to an hour. They are confining and can upset people who suffer from claustrophobia.
If you have trouble with closed spaces, medication can be given just before the scan to reduce anxiety or a special “open” MRI machine that is less confining can be used.
The MRI machine also makes a buzzing or clanging noise that some people may find disturbing. Some hospitals and clinics will provide headphones with music to block this sound.
When your doctor thinks the cancer has spread, but doesn’t know where, a positron emission tomography or PET scan can be done to determine the spread accurately, since this type of machine scans your entire body. Instead of taking several different x-rays, a single PET scan can be done.
PET scans use glucose that contains a low-level radioactive atom to identify cancer cells. Because they are very active, cancer cells absorb larger amounts of the sugar than normal cells and display more radioactivity. A special camera can be used to detect this radioactivity.