Colon cancer, coloured frontal PET scan. The cancer is the green region at lower left. A PET (positron emission tomography) scan uses a radioactive tracer to image body tissues. The tracer is a molecule, usually glucose, that is taken up preferentially by active areas. Cancers use far more glucose than normal body tissues, and thus show up brightly. The brain (red, top) also uses a high proportion of the body's glucose. Colon cancer is a very common cancer that usually arises from glandular tissue. If it is caught early the prognosis is good, but it has often reached an advanced stage by the time it is diagnosed.
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