Efficacy of delayed ¹⁸F-FDG hybrid PET/MRI for epileptic focus identification: a prospective cohort study

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.

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 SUV_mean 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.

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.

Delayed ¹⁸F-FDG PET imaging can be used to better identify EZs with relatively greater metabolic asymmetry between the EZ and contralateral regions.