Ethylcholine labeled with fluorine F 18, a positron-emitting isotope. Fluorine F 18 fluoroethylcholine incorporates into tumor cells through an active, carrier-mediated transport mechanism for choline and then is phosphorylated intracellularly by choline kinase, yielding a phosphoryl derivative, and finally is integrated into cellular phospholipids, probably primarily into a phosphatidyl derivative; concentration of this agent in tumor cells as various fluorine F 18 fluoroethylcholine derivatives enables tumor imaging using positron emission tomography (PET). Choline kinase, the enzyme responsible for the phosphorylation of choline, is frequently up-regulated in human tumor cell lines. or A radioactive substance being studied in PET imaging to detect certain types of cancer. Fluorine F 18 fluoromethylcholine gets taken up by cells in the body and more of it is taken up by tumor cells than by normal cells. A PET scanner is used to detect which cells in the body have taken up fluorine F 18 fluoromethylcholine. It is a type of radioimaging agent. Also called 18F-choline, 18F-fluoromethylcholine, and 18F-FMCH.