Cerebral metabolism and perfusion in MR-negative individuals with refractory focal epilepsy assessed by simultaneous acquisition of (18)F-FDG PET and arterial spin labeling

Abstract

The major challenge in pre-surgical epileptic patient evaluation is the correct identification of the seizure onset area, especially in MR-negative patients. In this study, we aimed to: (1) assess the concordance between perfusion, from ASL, and metabolism, from (18)F-FDG, acquired simultaneously on PET/MR; (2) verify the utility of a statistical approach as supportive diagnostic tool for clinical readers. Secondarily, we compared (18)F-FDG PET data from the hybrid PET/MR system with those acquired with PET/CT, with the purpose of validate the reliability of (18)F-FDG PET/MR data. Twenty patients with refractory focal epilepsy, negative MR and a defined electro-clinical diagnosis underwent PET/MR, immediately followed by PET/CT. Standardized uptake value ratio (SUVr) and cerebral blood flow (CBF) maps were calculated for PET/CT-PET/MR and ASL, respectively. For all techniques, z-score of the asymmetry index (zAI) was applied for depicting significant Right/Left differences. SUVr and CBF images were firstly visually assessed by two neuroimaging readers, who then re-assessed them considering zAI for reaching a final diagnosis. High agreement between (18)F-FDG PET/MR and ASL was found, showing hypometabolism and hypoperfusion in the same hemisphere in 18/20 patients, while the remaining were normal. They were completely concordant in 14/18, concordant in at least one lobe in the remaining. zAI maps improved readers' confidence in 12/20 and 15/20 patients for (18)F-FDG PET/MR and ASL, respectively. (18)F-FDG PET/CT-PET/MR showed high agreement, especially when zAI was considered. The simultaneous metabolism-perfusion acquisition provides excellent concordance on focus lateralisation and good concordance on localisation, determining useful complementary information.

Keywords: Arterial spin labeling; Cerebral blood flow; Epilepsy; Glucose; Positron emission tomography; Simultaneous PET/MR.

Fig. 1

¹⁸F-FDG PET/CT, ¹⁸F-FDG PET/MR, ASL and the corresponding z_AI statistical maps for some representative patients with a Right hemisphere focal localisation (normalized data). SUVr and CBF maps for two slices of interest encompassing the presumed focus are reported for ¹⁸F-FDG PET and ASL, respectively.

Fig. 2

¹⁸F-FDG PET/CT, ¹⁸F-FDG PET/MR, ASL and the corresponding z_AI statistical maps for some representative patients with a Left hemisphere focal localisation (normalized data). SUVr and CBF maps for two slices of interest encompassing the presumed focus are reported for ¹⁸F-FDG PET and ASL, respectively.

Fig. 3

Regional comparison across the twenty patients for ten regions of interest. A) ¹⁸F-FDG PET/CT vs ¹⁸F-FDG PET/MR; B) ASL vs ¹⁸F-FDG PET/MR.