CHAPTER 15 – Positron-emission Tomography in Epilepsy

This chapter discusses the role of positron emission tomography (PET) in epilepsy. PET is a noninvasive functional imaging method for representation of various aspects of brain activity. PET can be used to measure baseline functional activity, as well as physiologic or pathologic changes and responses in cerebral activity. The most widely available PET tracer is 2-deoxy-2[ 18 F]-fluoro-D-glucose (FDG) for the measurement of glucose metabolism of various organs. Although several other tracers have been used or proposed to image an epileptic brain, FDG is the most commonly used tracer for epilepsy studies. The chapter focuses on the clinical uses of FDG PET studies in epilepsy. FDG is transported to tissues and phosphorylated to FDG-6-phosphate in the same manner glucose is transported. However, FDG-6-phosphate is not a substrate for the next reaction step of glycolysis and not a significant substrate for glycogen synthesis or for pentose shunt. Because of this, FDG cannot immediately leave the cell. Phosphorylated FDG gets trapped without further metabolism. Its location and amount can be measured by PET as the 18 F decays. FDG is similar to glucose in its plasma-to-tissue transport and phosphorylation. Thus, under steady-state conditions, FDG uptake reflects the utilization rate of exogenous glucose. In the brain, this rate is highly related to the synaptic and functional density and functional activity of the brain tissues.