In PET imaging, [F]FDG is primarily used for imaging tumors in oncology, where a static [F]FDG PET scan is performed and the tumor [F]FDG uptake is analyzed in terms of Standardized Uptake Value (SUV). FDG PET/CT can be used for the assessment of glucose metabolism in the heart and the brain. [F]FDG is taken up by cells, and subsequently phosphorylated by hexokinase (whose mitochondrial form is greatly elevated in rapidly growing malignant tumours). Phosphorylated [F]FDG cannot be further metabolised and is thus retained by tissues with high metabolic activity, such as most types of malignant tumours.  As a result, FDG-PET can be used for diagnosis, staging, and monitoring treatment of cancers, particularly in Hodgkins disease, non-Hodgkin lymphoma, colorectal cancer, breast cancer, melanoma, and lung cancer. It has also been approved for use in diagnosing Alzheimers disease.
In body-scanning applications in searching for tumor or metastatic disease, a dose of [F]-FDG in solution (typically 5 to 10 millicuries or 200 to 400 MBq) is typically injected rapidly into a saline drip running into a vein, in a patient who has been fasting for at least six hours, and who has a suitably low blood sugar. (This is a problem for some diabetics; usually PET scanning centers will not administer the isotope to patients with blood glucose levels over about 180 mg/dL = 10 mmol/L, and such patients must be rescheduled). The patient must then wait about an hour for the sugar to distribute and be taken up into organs which use glucose – a time during which physical activity must be kept to a minimum, in order to minimize uptake of the radioactive sugar into muscles (this causes unwanted artifacts in the scan, interfering with reading especially when the organs of interest are inside the body vs. inside the skull). Then, the patient is placed in the PET scanner for a series of one or more scans which may take from 20 minutes to as long as an hour (often, only about one-quarter of the body length may be imaged at a time).