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Imaging tests are also used to screen for and detect colorectal cancer. These
tests use technologies that visualize your bodily organs and present them like a
picture. Imaging tests are also used to determine how far the cancer has spread
or how well it is responding, or has responded to treatment. While some tests
still use X-rays, newer technologies use radioactivity (in very tiny doses),
ultrasound, or magnetic fields to obtain the pictures.
Imaging tests you may be given include:
Computed tomography. Commonly called CT scan, in this test multiple
X-rays of the body are taken from different angles in a very short period of
time. These images are collected by a computer to give a series of
"slices" of the body, which can help doctors determine if the cancer
has spread to other parts of the body.
Virtual colonoscopy. New technology has made it possible for a computer
to take CT images of the colon and reconstruct a three-dimensional model of your
colon. The inside of this model can be inspected, obviously without causing any
pain to you, while searching for abnormalities. The test involves distension of
the colon with air. Early results show promise for screening the colon and
detecting small polyps or asymptomatic cancers. The main disadvantage of virtual
colonoscopy is that any abnormalities have to be evaluated and treated by real
colonoscopy. However, it is likely to have a place in screening for colorectal
cancer.
Magnetic resonance imaging. Commonly called MRI, this test produces very
clear pictures, or images, of the human body without the use of X-rays. MRI uses
a large magnet, radio waves, and a computer to produce these images. The MRI
examination poses no risk to the average person if appropriate safety guidelines
are followed.
Ultrasound. When ultrasound is performed high-frequency sound waves
bounce back off the organs in the body, and are caught by a receiver, which
translates the sound into pictures. In this way, the person doing the ultrasound
can see your internal organs. Ultrasound may be used in colon cancer to
determine if the cancer has spread to the liver.
Angiography. This is a special type of test used to look at blood
vessels. This test is done when the doctor suspects a blockage in or around a
blood vessel, or a blood vessel that may be bleeding, or to visualize where
blood vessels are located. A blockage interferes with blood flow, which can
result in belly pain or bleeding from the digestive tract.
In the case of colorectal cancer, it can be used to exclude other diagnoses,
or in the case the cancer has spread to the liver, it can show surgeons the
location of blood vessels so that they can remove the tumor in the liver without
causing a lot of bleeding.
Radionuclide scanning. Also called nuclear medicine scanning, this is a
test that produces pictures of internal parts of the body using small amounts of
radioactive material. This test is used to provide images of organs and areas of
the body that cannot be seen well with standard X-rays. Many abnormal tissue
growths, or tumors, are particularly visible using radionuclide scanning.
In addition to showing the structure of an organ, radionuclide scanning
allows the doctor to see how the organ is functioning. A diseased or poorly
working organ will appear differently on the scan than will a healthy organ.
The information from this test is valuable in diagnosing many diseases,
including cancer. Because this test shows internal areas that are not visible on
standard X-rays, radionuclide scanning can also help identify problems very
early in the progression of a disease.
Although radiation is used in this scanning technique, the test is very safe.
The actual dose of radiation you receive is quite low and stays in your body
only for a short time. Drinking plenty of fluids after your scan will help to
eliminate any radioactive material from your system.
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