Ammonia is thought to play a significant role in the development of hepatic encephalopathy
(HE) in patients with liver failure. Some of the key questions have been whether there is an abnormal
permeability surface-area product across the blood-brain barrier (PSBBB) for ammonia in patients with
cirrhosis and whether the cerebral metabolic rate of ammonia is altered. In this chapter, we discuss how
functional molecular imaging using positron emission tomography (PET) can be utilized for in vivo
studies of cerebral ammonia kinetics and what the studies so far have shown.
Keywords: Hepatic encephalopathy; Blood-brain barrier; Permeability surface-area product.
