<qa>  What is FDG injected into?18F-Fluorodeoxyglucose FDG is the most commonly used tracer for PET imaging; its use and safety are well established world wide. The 18F-FDG is injected intravenously and is transported from blood to tissues in a manner similar to glucose. It has been understood for over 5o years, that cancer cells, in general, have increased glucose uptake and anaerobic metabolism compared to normal tissues. Like glucose, FDG is taken up into cells through glucose transport proteins GLUT and then phosphorylated by hexokinase to FDG-6-phosphate. However, since FDG-6-phosphate is not a substrate for subsequent glucose metabolic pathways and has a very low membrane permeability, the FDG-6-phosphate becomes trapped in tissue in proportion to the rate of glycolysis. This accumulation of 18F-FDG-6-phosphate forms the basis of tumor metabolic imaging with PET. 