Ratio‐Images Calculated From Interictal Positron Emission Tomography and Single‐Photon Emission Computed Tomography for Quantification of the Uncoupling of Brain Metabolism and Perfusion in Epilepsy

Abstract

Summary:Purpose: Image processing techniques were applied to interictal positron emission tomography (PET) and single-photon emission computed tomography (SPECT) brain images to aid in the localization of epileptogenic foci by calculating a functional image that represents the degree of coupling between perfusion and metabolism. Uncoupling of these two functions has been demonstrated to be a characteristic of epileptogenic tissue in temporal lobe epilepsy and has the potential to serve as a diagnostic measure for localization in other areas as well.Methods: Interictal PET ( 18 F-FDG) and interictal SPECT ( 99m Tc-HMPAO) scans were acquired from 11 epilepsy patients. The metabolism and perfusion images were threedimensionally spatially registered, and a functional ratio-image was computed. These functional maps are overlaid onto a threedimensional rendering of the same patient's magnetic resonance imaging anatomy.Results: In all patients, an average uniform perfusion-tometabolism ratio showed approximately constant values throughout most of the whole brain. However, the epileptogenic area (confirmed on surgery) demonstrated an area of elevated perfusion/metabolism in the grey matter.Conclusions: Although hypometabolism in the PET image was observed in most of these patients, the calculation of a functional ratio-image demonstrated localized foci that in some cases could not be observed on the PET image alone. The ratio-image also yields a quantitative measure of the uncoupling phenomenon.