The relationship of glutamate and glutamine and metabolic profiling in focal epilepsy using 7T CRT-FID-MRSI

Approximately one-third of people with epilepsy (PWE) remain drug-resistant. In these cases, surgical resection of the epileptogenic zone may significantly reduce or eliminate seizures. Surgery necessitates precise delineation of the epileptogenic zone which proves especially challenging in the 20% of PWE that remain MRI-negative. To this end, the purpose of this study was to analyze the feasibility and robustness of ultra-high-field MRSI in identifying and characterizing pathologies in focal epilepsy. In addition, the relationship of glutamate and glutamine was evaluated in the epileptogenic zone (EZ) Fifty-six people with focal epilepsy were prospectively measured using 7T concentric ring trajectory direct acquisition of free-induction-decay MRSI which generated whole-brain metabolic maps with an isotropic resolution of 3.4mm3. After exclusion criteria were applied, we assessed metabolite ratios in 29 lesional- and MRI-negative PWE. In the lesional group, metabolic alterations in the suspected EZ were present in 86.7% of maps normalized to NAA, whereas this was reduced to 80% in creatine ratios. Metabolites with the highest stability in the lesional group included myo-inositol and choline, increased in 92.3%. In MRI-negative patients, changes were heterogeneous and less circumscribed, with a detection rate of 57.1%. We also observed a tendency towards an inverse relationship of glutamate to glutamine in the EZ, with relative increases of glutamine in PWE with lower seizure frequencies, contrasting relative glutamate increases in higher seizure frequencies. Our preliminary analysis suggests that 7T CRT-FID MRSI shows promise not only in identifying metabolic alterations in focal epilepsy but may also provide insights into disease pathomechanisms.