# Lateralization of FDG-PET Hypometabolism Using Resting-State fMRI in Temporal Lobe Epilepsy: A Simultaneous PET-MRI Study

## TL;DR

This study explores whether resting-state fMRI can identify brain regions with reduced metabolism in epilepsy patients, using PET scans as a reference.

## Contribution

The study demonstrates that fALFF from resting-state fMRI correlates with FDG-PET hypometabolism in temporal lobe epilepsy.

## Key findings

- fALFF asymmetry indices were significantly reduced in hypometabolic zones identified by FDG-PET.
- A significant negative correlation was found between FDG-PET and slow-3 band fALFF (r = −0.62, p < 0.05).
- Conventional and slow-3 band fALFF may replicate FDG-PET findings for epileptogenic zone localization.

## Abstract

This study investigated whether resting-state fMRI (rs-fMRI) can localize the epileptogenic onset zone in temporal lobe epilepsy (TLE) using FDG-PET as ground truth. Twelve patients with drug-resistant TLE underwent simultaneous PET-MR scanning at 3T. Hypometabolic regions identified on FDG-PET were compared with rs-fMRI metrics including regional homogeneity (ReHo), amplitude of low-frequency fluctuations (ALFF), and fractional ALFF (fALFF) calculated in conventional and slow-3 frequency bands. Results showed that fALFF asymmetry indices were significantly reduced in hypometabolic zones, with a significant negative correlation between FDG-PET and slow-3 fALFF (r = −0.62, p < 0.05). These findings suggest fALFF may replicate FDG-PET findings for epileptogenic zone localization.

Background: In temporal lobe epilepsy (TLE), locally reduced glucose metabolism (i.e., hypometabolism) is indicative of the epileptogenic onset zone (EZ). Here, we investigate the potential value of resting-state fMRI (rs-fMRI) for localizing the EZ with fluorodeoxyglucose positron emission tomography (FDG-PET) as ground truth. Methods: Twelve PET-positive patients (34.1 ± 13.1 y; 5 females) with unilateral drug-resistant TLE were included. FDG-PET and rs-fMRI were acquired simultaneously at a hybrid 3T PET-MR scanner. Hypometabolic regions were identified on the FDG-PET images by a nuclear medicine expert. The FDG-PET images were compared with a clinical FDG-PET control dataset with normal glucose uptake distribution. The output z-score maps were thresholded at z < −2 to produce a binary mask of the significantly hypometabolic regions. The hypometabolism masks were mirrored onto the contralateral hemisphere for the asymmetry comparison. Regional homogeneity (ReHo), amplitude of low-frequency fluctuations (ALFF), and fractional ALFF (fALFF) were calculated from the rs-fMRI in conventional (0.01–0.1 Hz) and slow-3 (0.073–0.198 Hz) frequency bands. Asymmetry indices (AIs) were calculated using the ipsilateral and contralateral hypometabolic masks in the PET-positive subjects and assessed via the one-sample Wilcoxon test and Spearman correlation coefficients. Results: The AIs of conventional fALFF were significantly lower in the hypometabolic zone (p < 0.05). A significant negative correlation was found between the AIs of FDG-PET and fALFF in the slow-3 band (r = −0.62; p < 0.05). Conclusions: Conventional and slow-3 band fALFF showed a potential to mimic the FDG-PET findings in terms of EZ localization. Further research with extended cohorts and histopathological validation is required to determine the clinical value.