Fluoroethylcholine ion F-18 is ethylcholine labeled with fluorine F 18, a positron-emitting isotope. Fluorine F18 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. F18-fluoroethylcholine is used for imaging of prostate cancer and brain tumors, mainly in Europe and Japan.