A qualitative analysis of the relationship of glutamate and glutamine and metabolic profiling in focal epilepsy using 7T CRT-FID-MRSI

Epilepsy, a debilitating illness characterized by seizures, often proves resistant to medication necessitating surgical intervention. Advanced MRI techniques, notably 7T MRI, can offer improved lesion detection. However, patients without structural abnormalities pose a particular challenge. In such cases, 7T Magnetic Resonance Spectroscopy Imaging (MRSI) may prove beneficial in identifying subtle metabolic alterations though higher spectral resolution, allowing the separation of metabolites with overlapping resonance frequencies such as glutamate and glutamine, key metabolites in excitatory processes. This study aimed to elucidate metabolic profiles of glutamate (Glu), glutamine (Gln), myo-inositol (Ins), choline (tCho), creatine (tCr) and N-acetylaspartate (NAA), normalized to NAA and tCr in epileptic zones using 7T MRSI. Furthermore, concentration estimates of Glu and Gln were qualitatively assessed.Forty-two focal epilepsy patients underwent 7T MRI with a specialized MRSI protocol. Data processing involved spectral quantification and ratio mapping. Though we could find no consistent metabolic pattern throughout pathologies, ratio-maps showed high sensitivity, identifying alterations in seizure onset zones (SOZ) in all patients when normalized to NAA. Sensitivity was only marginally reduced normalizing to tCr (86%).Furthermore, we found a relative increase of Gln over Glu in patients with lower seizure frequencies, whereas this relationship was inversed with high seizure burden, indicating a potential alteration of the glutamate/glutamine cycle in SOZ. Overall, 7T CRT-FID-MRSI presents high sensitivity in detecting metabolic alterations in focal epilepsy, particularly when normalized to NAA, offering potential insights into the disease's pathophysiology and prognosis. However, studies with larger cohorts and quantitative analyses are necessary for further validation.