11C-Acetate PET/CT Imaging Physiologic Uptake, Variants, and Pitfalls

KEY POINTS � 11C-acetate is a biomarker for cell membrane lipid synthesis and may increase in various malignancies. � Enhanced uptake is observed in salivary glands, tonsils, meningeal tuberculoma, meningiomas, macroadenomas of pituitary gland, and benign thyroid nodes. � Reactive lymphadenopathy in mediastinum and hilum shows mild to moderate 11C-acetate accumulation. � Pancreas, spleen, and liver show an increased uptake of 11C-acetate; however, pancreatitis is related with reduced tracer accumulation. � Proliferative or granulomatous cystitis may be present with enhanced 11C-acetate tracer accumulation. This article describes the physiologic distribution of 11C-acetate and discusses regions that occasionally may present increased activity not related to tumor tissue or owing to other nononcologic findings. The short half-life of 11C-acetate (20 min) warrants an onsite cyclotron. Hence, there are less data available comparing 18F-labeled PET tracers. 11C-acetate PET has been used to measure myocardial oxygen consumption and to study prostate cancer (PCa), hepatocellular carcinoma (HCC), renal cell carcinoma (RCC), bladder carcinoma, and brain tumors.1 There are also rare conditions that have been incidentally depicted by 11C-acetate PET, such as thymoma,2 cerebellopontine angle schwannoma,3 angiomyolipoma of the kidney,4 and encephalitis.5 Assessment ofmultiple myeloma has also been studied by this tracer.6 Acetate is a molecule quickly picked up by cells and converted into acetyl-CoA by acetyl-CoA synthetase. 1 It is used to synthesize cholesterol and fatty acids, thus forming cell membrane (anabolic pathway), or is oxidized (catabolic pathway) in mitochondria by the tricarboxylic acid (TCA) cycle to CO2 and H2O, thus producing energy. The predominant pathway is strictly linked with the type of cell; in myocardial tissue, acetate is mainly metabolized to CO2 via the TCA cycle,7 whereas tumor cells overexpress the enzyme fatty acid synthetase, thus converting most of the acetate into fatty acids and incorporating them into intracellular phosphatidylcholine membrane microdomains that are important for tumor growth and metastasis. 8 For nuclear medicine purposes, acetate is labeled with 11C, and the derived compound is called 11C-acetate.