Combining frequency navigator and optical prospective motion correction for functional MRS during motor activation at 3 T: A feasibility study

Abstract

Background

Functional magnetic resonance spectroscopy (fMRS) is a powerful tool for investigating neurometabolic dynamics in response to physiological stimuli in vivo. However, fMRS is challenging due to the low SNR of the spectrum and small neurochemical changes. Many existing studies were conducted at ultrahigh field strength (7 T). To translate fMRS studies to the more common 3 T clinical field strength, averaging more transients can improve SNR. However, this results in a long scan time compounds physiological motion which incurs degradations in spectrum quality and consistency.

Purpose

Investigate the feasibility of PRESS fMRS studies at 3 T assisted by the combination of prospective motion correction (PMC) system and frequency navigator.

Methods

A combination of markerless PMC system and frequency navigator was applied to an fMRS study during motor activation with a clinical PRESS protocol at 3 T. Twenty-one volunteers were involved in the study. The functional task paradigm consisted of three blocks REST-TASK-REST. During the TASK period, the volunteer was asked to squeeze a hand-hold balloon according to a red rectangle flashing at 2 Hz shown centered in a black background. The same motor task was repeated twice, once with PMC ON and once with PMC OFF. The data were processed and quantified by in-house VDI software. The following two analyses were performed: a motion pattern analysis and a metabolite dynamics analysis. The motion analysis was used to compare the motion states when PMC was ON and OFF. The metabolite dynamic change was a key assessment for the fMRS study. It was estimated via $\Delta =\frac{{\mu }_{task}-{\mu }_{rest}}{{\mu }_{rest}}\equiv \frac{\Delta \mu }{{\mu }_{rest}}$. p-values < 0.05 were considered significant.

Results

A statistically significant increase in Glx of 5.73% when the PMC was switched on was observed. No statistically significant increase in any of the metabolites with PMC OFF was observed. The major singlets (tCho, tCr, and tNAA) for both PMC ON and OFF keep constant.

Conclusions

With a markerless PMC system and frequency navigator, PRESS fMRS at 3 T is capable of detecting small changes of a few percent in Glx concentration during functional activation.