Efficacy of delayed18F-FDG hybrid PET/MRI for epileptic focus identification: a prospective cohort study

Objective We sought to investigate the contribution of delayed(18)F-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(18)F-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(18)F-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,F-18-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 Delta AI 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(18)F-FDG PET imaging can be used to better identify EZs with relatively greater metabolic asymmetry between the EZ and contralateral regions.

Automated summary

The study demonstrates that delayed (18)F-FDG PET imaging can effectively assist in identifying epileptogenic zones (EZs) with significant metabolic asymmetry in patients with epilepsy, especially in those with positive MRI results, extratemporal lobe epilepsy (extra-TLE), and shorter delay time points.