Optimization of a mixed block and event-related fMRS acquisition protocol for a working-memory task at 7T

Motivation: The temporal response of metabolites during cognitive tasks is not well understood. Goal(s): Optimize the timings and acquisition of an fMRS protocol at 7T within a working memory (WM) paradigm to allow for block and event analyses. Approach: Compare glutamate (Glu) and GABA detection semi-LASER localisation at TE=30 ms and TE=80 ms across five volunteers to inform timings when designing a mixed 'block and event-related' protocol. Perform preliminary analysis of Glu concentrations using this approach. Results: TE=80 ms improved GABA detection and led to reliable Glu detection with averages ≥4. Glu differences were observed across four subjects when comparing control vs. rest trials. Impact: This study validates that TE=80ms semi-LASER improves GABA and Glu detection and offers a mixed-design fMRS protocol for cognitive studies. This opens the possibility to study temporal dynamics of glutamate during a working memory task.