Optimized glutamate detection at 3T.

PURPOSE: To identify the pulse sequence and acquisition parameters that result in the most accurate and repeatable measurements of glutamate (Glu) concentration in the brain at 3T.
MATERIALS AND METHODS: Simulations were performed to compare the accuracy and repeatability of 11 pulse sequences and acquisition parameters, within four general classes (PRESS, STEAM, Carr-Purcell PRESS [CPRESS] and TE averaged PRESS [JPRESS]), the majority of which were previously suggested as optimal for Glu detection. Three of the simulated acquisitions were implemented in a clinical scanner and measures of repeatability in vivo were compared to their simulated values.
RESULTS: Good agreement was demonstrated between simulated and experimentally determined measures of repeatability. Among the acquisitions considered, a CPRESS sequence with minimal echo time, together with, possibly, a short TE PRESS sequence, result in the most repeatable within session Glu measurements, while slightly overestimating the Glu concentration. Excellent accuracy is demonstrated by the simulations for a JPRESS sequence, at the expense of lower repeatability than optimal PRESS or CPRESS sequences.
CONCLUSION: Further proof of concept is presented toward validation of a simulation approach to understand pulse sequence performance in measuring the concentration of a given metabolite. Improved within session Glu measurement repeatability is predicted for CPRESS and demonstrated in vivo.