TechniqueApplication of multichannel near-infrared spectroscopic topography to physiological monitoring of the cortex during cortical mapping: technical case report
Introduction
Preoperative direct cortical stimulation via a SGE provides the most reliable and precise method currently available that allows the identification of eloquent areas including motor and language areas. The threshold responses at each electrode vary from one stimulation session to the next [3]; however, the physiological conditions and neuronal activities during cortical stimulation cannot be accurately monitored electrophysiologically because of electrical artifacts. In the present case, we used multichannel NIRS topography [4], [7], [8], a noninvasive optical imaging technique, to monitor the (CBO) changes occurring during cortical stimulation.
Section snippets
Presentation
The patient was a previously healthy 27-year-old right-handed man who presented with seizures. Conventional MRI revealed a nonenhancing mass within the left frontal lobe (Fig. 1A). To clarify the relation between the tumor and adjacent functional areas, 3 SGEs were implanted chronically over the left motor cortex as well as Broca's area before resection of the tumor (Fig. 1B). Histological analysis after removal of the tumor revealed a grade II astrocytoma.
Methods
We used an OMM 2000 (Shimadzu, Japan)
Discussion
Near-infrared spectroscopy topography is a noninvasive optical technique that can image activated cortices by measuring evoked CBO changes, and has been applied to the diagnosis of epileptic foci [8] or language hemispheric dominance [7]. These findings demonstrate that NIRS topography can be used to obtain evoked CBO maps during electrical stimulation via an SGE. Although NIR light cannot pass through the metal electrodes in the SGE, the results indicate that NIR light did pass through the
Conclusion
Near-infrared spectroscopy topography is considered applicable for the monitoring of evoked CBO changes during cortical mapping. Near-infrared spectroscopy topography may represent a useful method for evaluating the degree and extent of the physiological effects of electrical stimulation on the cortex, and permits safe and accurate cortical mapping.
Acknowledgments
This work was supported by Grants-in-Aid from the Ministry of Education, Culture, Sports, Sciences and Technology of Japan (A12307029, A15209047, C15591553, and a grant for the promotion of industry—university collaboration at Nihon University) and by Hamamatsu Photonics KK (Hamamatsu, Japan).
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