The Value Of ¹³N-NH₃ Combined With ¹⁸F-FDG PET Imaging In Localizing Epileptogenic Zone In Presurgical Epilepsy

Objective More than 50%of the refractory epilepsy could benefit from neurosurgical management.If the neurosurgical method was used for the patients with refractory epilepsy,the key point was the accuracy in localizing epileptogenic zone.For purpose of this,¹⁸F-FDG PET have been widely studied and well established,which show high sensitivity but low specificity.At present,there are fewer studies about ¹³N-NH₃ PET in localizing epileptogenic zone.The aim of this study is to explore the characteristic appearance of blood perfusion and glucose metabolism in epileptogenic zone using interictal PET imaging,to evaluate the value and reliability of ¹³N-NH₃ perfusion imaging and the value of the combination of the two agents in diagnosing epileptogenic zone and to study the value of Statistical Parametric Mapping in localizing epileptogenic zone.Materials and Methods 31 patients(19 male,12 female,aged 12-52 years,mean age 28.6 years) with medically refractory epilepsy were examined with ¹³N-NH₃ and ¹⁸F-FDG PET imaging sequentially.The images were interpreted independently by two experienced nuclear medicine physicians who were unware of any clinical information.Coronal,sagittal,and transaxial images were visually assessed.Any two contiguous images showed focally increased or decreased intensity should be considered abnormal.Then the asymmetric index(AI) was calculated by drawing region of interest(ROI) in the region of abnormality.Both the visual analysis and the asymmetric index were taken into account.18 cases with ¹⁸F-FDG imaging were analyzed with SPM2 software using two-sample t test.The largest cluster which showed significantly hyper- or hypo-metabolism revealed by SPM analysis was considered as epileptogenic zone.Results According to the electrocorticography and depth electroencephalography performed in the surgery,as well as the outcome of the surgery,15 cases(48.4%) were localized in temporal lobe,8 cases(25.8%) were in frontal lobe,2 cases(6.5%) in parietal lobe and 6 cases(19.4%) in multi brain lobes.The localization sensitivity is 58.1%for ¹³N-NH₃ PET and 71.0%for ¹⁸F-FDG PET.The diagnostic performance of the two agents were in moderate concordance by Kappa test(K=0.515,p=0.000). About 25.8%of the cases which were not correctly localized by one agent could get correct localization by the combination of the two agents.The localization sensitivity approached 77.4%.There was statistically significant difference in the AI values between ¹³N-NH₃ and ¹⁸F-FDG.The AI values of ¹⁸F-FDG group were higher than that of ¹³N-NH₃ group.Based on the examination of MRI,the patients were divided into 2 groups:lesional group and non-lesional group.No statistical significance were found in the diagnostic performance between the two agents in each group.The localization sensitivity of SPM is 83.3%,which showed no statistical difference with visual analysis using McNemar test.Conclusion The characteristic appearance of epileptogenic zone depicted by interictal PET imaging is not only hypoperfusion and hypometabolism,but also hyperperfusion and hypometabolism.Interictal ¹³N-NH₃ PET showed relatively good sensitivity (58.1%) of localization and the diagnostic performance was in moderate concordance with ¹⁸F-FDG.We can get an excellent sensitivity of 77.4%by combination of the two examinations.SPM analysis yielded equivalent results to visual analysis and did not significantly improve the localization sensitivity despite it's objective and quantitative interpretation.