Abstract
Blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) indirectly measures brain activity based on neurovascular coupling, a reporter that limits both the spatial and temporal resolution of the technique as well as the cellular and metabolic specificity. Emerging methods using functional spectroscopy (fMRS) and diffusion-weighted fMRI suggest that metabolic and structural modifications are also taking place in the activated cells. This paper explores an alternative metabolic imaging approach based on Chemical Exchange Saturation Transfer (CEST) to assess potential metabolic changes induced by neuronal stimulation in rat brains at 17.2 T. An optimized CEST-fMRI data acquisition and processing protocol was developed and used to experimentally assess the feasibility of glucoCEST-based fMRI. Images acquired under glucose-sensitizing conditions showed a substantial negative contrast that highlighted the same brain regions as those activated with BOLD-fMRI. We ascribe this novel fMRI contrast to CEST’s ability to monitor changes in the local concentration of glucose, a metabolite closely coupled to neuronal activity. Our findings are in good agreement with literature employing other modalities. The use of CEST-based techniques for fMRI is not limited to glucose detection; other metabolic pathways involved in neuronal activation could be potentially probed. Moreover, being non invasive, it is conceivable that the same approach can be used for human studies.
Highlights
Blood Oxygenation Level Dependent functional imaging (BOLD functional magnetic resonance imaging (fMRI)) is one of the keystones of modern neuroimaging[1,2,3]
This paper presents the implementation of a Chemical Exchange Saturation Transfer (CEST)-based fMRI method, adapted to investigate neuronal activation
On such basis this study introduces functional CEST-based measurements and explores their potential for real-time glucose metabolism detection
Summary
Blood Oxygenation Level Dependent functional imaging (BOLD fMRI) is one of the keystones of modern neuroimaging[1,2,3]. BOLD imaging allows the indirect measurement of brain activity by detecting changes in the blood oxygenation level and relying on the neurovascular coupling as a reporter[4]. Emerging methods such as functional MR spectroscopy (fMRS), vascular-space occupancy fMRI, and diffusion-weighted fMRI, are opening alternative ways of studying neuronal activation by detecting changes in metabolism[5], blood volume[6] and water diffusion properties. We detect a substantial change in the CEST properties of glucose, which could be related to a decrease in its accessibility The latter can be linked to the consumption and the drop in its local concentration during neuronal activation.
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