The Effect Of ¹⁸F-FDG PET Delayed Imaging On The Identification Of Epileptogenic Zone In Temporal Lobe Epilepsy

BACKGROUND:Epilepsy is the second most common neurological disorder,second only to stroke,and is a chronic state of brain disease with recurrent seizures that affect the normal function of the brain.The pathophysiology of epilepsy is based on an imbalance of excitation and inhibition of neuronal cells,resulting in abnormal synchronous firing of neuronal populations.There are currently about 70 million people with epilepsy worldwide,and the number of new epilepsy patients in China is about 400,000 per year.Epilepsy affects the mental health and social life of patients and increases the economic burden on families,which has a serious impact on the quality of life of patients.Temporal lobe epilepsy（TLE）accounts for 60%to 70%of epilepsy.Most patients are able to control their seizures with the use of anti-seizure medicines（ASMs）.Despite the development of next-generation ASMs,30-40%of patients continue to develop drug-refractory epilepsy after drug treatment.Temporal lobe epilepsy（TLE）is the most common type of drug-refractory epilepsy.Surgical removal of the epileptogenic zone（EZ）is the most effective treatment for refractory epilepsy.Temporal lobe epilepsy（TLE）can be divided into three types of epileptogenic foci:lateral temporal lobe epilepsy（LTLE）,medial temporal lobe epilepsy（MTLE）,and mesio-lateral temporal lobe epilepsy（M-L TLE）.Different types of temporal lobe epilepsy need to be treated with different surgical approaches.Precise localization of the epileptogenic focus is the key to successful surgical resection for temporal lobe epilepsy.Therefore,how to accurately localize the epileptogenic focus has become an important direction of clinical epileptology research.At present,the effective localization of epileptogenic foci is still a major challenge.Some studies have shown that PET can provide lateralization or localization information in 60-90%of TLE patients.¹⁸F-FDG PET dual time point imaging has been of great help in tumor benign and malignant identification,brain tumor classification,and tumor recurrence detection.Although this technique is well established for clinical use,however,it has not been performed in epilepsy diagnosis,and there is only one study in epileptogenic focus diagnosis.In 2020,Liu et al.performed PET/MR dual time point scans in 41 epileptic patients,including 10 cases of temporal lobe epilepsy,and showed that delayed imaging would be better than early imaging for epileptogenic focus identification.Since PET/CT is more widely used in clinical applications than PET/MR,it has the advantages of low price and low noise;in the present study,we used PET/CT dual time point imaging for the first time to enable the study of epileptogenic zone for the diagnosis of epilepsy.OBJECTIVETo investigate the effect of ¹⁸F-FDG PET delayed imaging on the identification of epileptogenic zone in temporal lobe epilepsy using PET/CT dual time point imaging.METHODSFifty-two patients with temporal lobe epilepsy who underwent ¹⁸F-FDG PET/CT dual time point examination in our outpatient clinic or ward were prospectively included.All early imaging of patients was obtained at approximately 40 minutes（43.44±18.04 minutes）after ¹⁸F-FDG injection,and delayed imaging was obtained at approximately 2 to 3 hours（160.46±28.70 minutes）after ¹⁸F-FDG injection.The localization of the epileptic focus was determined by a multidisciplinary team based on patient symptomatology,video electroencephalogram（VEEG）results,magnetic resonance imaging（MRI）and PET/CT findings.PET images of 52 TLE patients were analyzed after identification of the epileptogenic focus.Visual and semiquantitative analyses of ¹⁸F-FDG uptake at dual time points in the epileptogenic zones（EZs）and contralateral symmetric regions were performed separately.Two observers with unknown PET images acquired at early or delayed visual analysis comparing which image the epileptogenic zones was more pronounced in were divided into three cases:1)early effect was better than delayed effect,2)early effect was the same as delayed effect,and 3)delayed effect was better than early effect.The kappa test was used to evaluate the visual assessment of two radiologists for consistency.The mean standardized uptake value（SUVmean）of the epileptogenic zone（EZ）and the contralateral symmetric region in the patient’s PET images were extracted to determine the asymmetry index（AI）of the early and delayed images.Patients were divided into MRI-positive and negative groups based on the presence or absence of signal/structural abnormalities on MRI.For patients with temporal lobe epilepsy,MRI-positive group,and MRI-negative group,paired t-tests were used to compare patients’early and delayed AIs,respectively.RESULTSSemiquantitative analysis of dual time point ¹⁸F-FDG PET/CT images of 52 TLE patients showed that the SUVmean of the epileptogenic zone was 5.21±1.29 and 5.61±1.52 in early and delayed imaging,respectively,and the SUVmean of the contralateral symmetrical region was 5.94±1.42 in early imaging and 6.58±1.63 in delayed imaging.In delayed imaging,both the epileptogenic focus and the contralateral regional SUVmean were increased.The AI values for early and delayed PET images were 13.47±6.10 and16.43±6.66,respectively.52 TLE patients had aΔAI of 2.95±3.05 between the two time points.The AI of delayed imaging of the epileptogenic zones（EZs）was significantly higher compared with early imaging（P<0.001）.The AI of delayed imaging was also significantly higher in the MRI-positive group（ΔAI=2.81±2.54,P<0.001）and MRI-negative group（ΔAI=3.21±3.91,P<0.003）compared with early imaging,with theΔAIs in the MRI-negative group was slightly greater in the MRI-negative group than in the MRI-positive group.Delayed time patient AI did not all rise,44（88.61%）patients had greater delayed AI than earlier,and 8（15.38%）patients had decreased AI at the delayed time point.One of the neuroradiologists considered that the delayed images were visually superior to the early effect in 45（86.54%）patients with TLE,with the early effect being the same as the delayed effect in 5 patients,and the early effect being superior to the delayed effect in 2 patients;another neuroradiologist concluded that the delayed images were visually superior to the early effect in 43 patients（82.69%）with temporal lobe epilepsy,with the early effect being the same as the delayed effect in 7 patients,and the early effect was superior to the delayed effect in 2 patients.In general,two observers considered the delayed images to be better for EZ identification,with a good agreement between the two observers with a kappa value of 0.71.CONCLUSIONDelayed ¹⁸F-FDG PET imaging provides better identification of temporal lobe epileptogenic zone（EZ）compared to standard early imaging,which could be an important tool for preoperative evaluation of epilepsy in TLE patients.