Glutamine Metabolism and Metabolic Profiling Using 7 T CRT-FID MRSI in Focal Epilepsy

BACKGROUND: 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 (EZ) which proves especially challenging in the 20% of PWE that remain MRI-negative. 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 EZ.

METHODS: Fifty-six people with focal epilepsy were prospectively measured using 7 T 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 15 lesional and 14 MRI-negative PWE.

RESULTS: In the lesional group, metabolic alterations in the suspected EZ were present in 86.7% of maps normalized to N-acetyl-aspartate, whereas this was reduced to 80% in creatine ratios. Metabolites with the highest consistency in the lesional group included myo-inositol and choline, showing increases in 92.3% of PWE. In MRI-negative patients, changes were heterogeneous, with a detection rate of 57.1%. We also observed a tendency toward an inverse relationship of glutamate to glutamine in the EZ, with increases of glutamine in PWE with lower seizure frequencies, contrasting glutamate increases in higher seizure frequencies.

CONCLUSION: Our preliminary analysis suggests that 7 T CRT-FID MRSI shows promise not only in identifying metabolic alterations in focal epilepsy but may also provide insights into disease pathomechanisms.