Recent publications have suggested the use of 11C-acetate as another PET tracer for tumor imaging. The accumulation of 11C-acetate in tumor cells is related to the highly active lipid metabolism in the cell membrane associated with tumor growth. 11C-acetate is channeled into the tricarboxylic acid cycle via acetyl coenzyme A and then incorporated via phosphatidylcholine into the cell membrane's phopholipids. Possible biochemical paths of acetate incorporation or accumulation include (a) entering the Krebs cycle from acetyl coenzyme A (acetyl CoA) or as an intermediate metabolite, (b) esterification to form acetyl CoA as a major precursor in ß-oxidation for fatty acid synthesis, (c) combining with glycine in heme synthesis, and (d) through citrate for cholesterol synthesis. Of all of these possible metabolic pathways, participation in free fatty acid (lipid) synthesis is believed to be the dominant method of incorporation in tumors.