Objective: We sought to investigate the contribution of delayed 18F-FDG imaging data to epileptogenic zone (EZ) identification using a hybrid positron emission tomography/magnetic resonance imaging (PET/MRI) system.
Methods: Forty-one patients with epilepsy underwent a brain dual time point 18F-FDG PET/MRI examination. All early imaging was acquired at approximately 40 min. Late imaging was classified as short delay (150.1 ± 20.2 min) or long delay (247.8 ± 24.6 min). Visual evaluation and scoring of 18F-FDG uptake at dual time points were performed. An SUVmean asymmetry index (AI) was calculated representing the difference in uptake between the EZ and the contralateral side. The EZ location was defined by a multidisciplinary team based on findings on video electroencephalography, 18F-FDG, and MRI. EZ location was classified as extratemporal lobe epilepsy (extra-TLE) or temporal lobe epilepsy (TLE). MRI findings were classified as positive if there were signal/structural abnormalities, or negative. AI of dual time points was compared between MRI-positive and MRI-negative, between extra-TLE and TLE, and between short delay and long delay of the late imaging time point.
Results: The AI at the delayed time points was increased by a mean of 3.7 over the early time point in all patients (P < 0.01). The biggest AIs were found in the MRI-positive group. The ΔAI between two imaging points were 3.71 ± 3.50 and 4.67 ± 7.94 for MRI-positive and MRI-negative; 4.52 ± 6.70 and 2.51 ± 2.42 for extra-TLE and TLE; and 4.24 ± 6.52 and 3.46 ± 2.90 for short delay and long delay groups, respectively. There were more patients with increased AI at the delayed time with MRI-positive (95.8%, 23/24), with extra-TLE (96.8%, 30/31), and with short delay time (93.7%, 30/32). Two observers who had no knowledge of the images chose 85.4% and 82.9% of the delay-time point images as the more obvious asymmetry from all images. The kappa value between the two observers was 0.66 with good agreement.
Conclusion: Delayed 18F-FDG PET imaging can be used to better identify EZs with relatively greater metabolic asymmetry between the EZ and contralateral regions.
Keywords: 18F-FDG; Asymmetry index; Delayed imaging; Epilepsy; Hybrid PET/MRI.