Rationale:
18F-fluorodeoxyglucose positron emission tomography-computed tomography (18F-FDG PET-CT) measures neuronal metabolic activities, reflecting the regional brain functions. Metabolic connectivity explores the functional interactions among the brain regions.
Temporal lobe epilepsy (TLE) demonstrated alterations of the brain connectivity by functional magnetic resonance imaging (MRI) studies, especially default mode network (DMN) impairments. However, brain functions might fluctuate as the time. In this study, we used dynamic PET imaging to identify how the DMN reorganized in metabolic aspects and their relationship with the cognitive functions.
Methods:
We enrolled 24 patients with pharmaco-resistant, temporal lobe epilepsy (TLE) from the neurological ward from December 2021 to June 2023 who had received epilepsy surgery evaluation in Taichung Veteran Hospital. Their brain PET imaging was collected for 30 minutes, and then divided into six frames to the successive five minute segment images. Then, the images were registered to the MRI images based on the normalized mutual information method. The standard uptake values (SUVs) of pons were used as the reference for intensity normalization of the gray matter signals. Six volumes of interest (VOIs) were selected: bilateral superior frontal and medial gyrus, angular gyrus, and precuneus, whose signals of the six frames were set as the vector. Their correlation with the other two ipsilateral regions were calculated to generate the three values of coefficient (R) on each side. These correlations were compared on the contralateral side with Wilcoxon signed rank test. Their relationship with the four main intelligence quotients (IQs) were calculated by partial correlation coefficient, with adjusting education years, age, and gender.
Results:
There were 15 Left-TLE and 9-TLE enrolled. The intra-hemispheric correlations of the normalized SUVs among the six VOIs were calculated. They showed almost synchronously metabolic activity of the six DMN regions based on the phase lag measurement. Their correlation coefficients presented higher R values between the regional pairs (0.550-0.794), which neither showed differences between the correlations of the corresponding regions on the contralateral side. The dynamic, intra-hemispheric, metabolic connectivity was associated with the verbal IQ (VIQ) scores. The connectivity between left precuneus and left angular gyrus was positively related to VIQ (r = 0.673, p = 0.033) in left-TLE. The metabolic connectivity between right precuneus and right superior-medial frontal region was negatively related to VIQ (r = -0.933, p = 0.007) in right-TLE.
Conclusions:
The ipsilateral DMN regions seemed to present grossly synchronous metabolic activities in TLE. However, the connectivity of the ipsilateral precuneus region played the role in cognitive functions, especially verbal IQ.
Funding:
The study was financially supported of the Higher Education Sprout Project by the Ministry of Education (MOE) in Taiwan.