Before having a positron emission tomography/computerized tomography (PET/CT) scan, the patient has an intravenous injection of FDG. FDG is a low-level radioactive tracer, which is a form of glucose. After the injection, the patient is asked to relax and wait quietly for 45-60 minutes while the glucose distributes throughout his or her body.
Cancer cells tend to grow faster than normal cells and utilize glucose as a primary source of energy. The faster that cells grow and multiply, the more glucose is taken up for energy. The FDG molecules are absorbed at a greater rate in fast-growing cancer cells than in normal cells, resulting in higher concentrations of FDG in areas of cancer.
For assessing cancer, the PET/CT scanner detects levels of the radiopharmaceutical within the patient and provides images that map the locations of abnormally high concentrations of FDG.
In the case of brain disorders and cardiac viability imaging, the PET/CT scanner is able to detect areas of lower-than-normal FDG concentration. This would indicate to the physician that the tissue being evaluated is not functioning normally and may no longer be viable.
PET FDG mapping is combined with CT imaging, which provides structural detail. Combined PET/CT imaging can identify both the presence of disease and its precise location.