Article
Functional cortical mapping using optical far infrared thermographic imaging
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Published: | September 16, 2010 |
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Objective: Regional mapping of functional areas during neurosurgical interventions is currently limited to electrophysiological point-measurements. The aim of the current study was to evaluate an optical imaging method in combination with advanced image processing algorithms that can be used during regular OR conditions to identify regions of cortical activity by intrinsic infrared “thermographic” imaging.
Methods: 12 patients who underwent a craniotomy for extratemporal epilepsy surgery or other indications around the somatosensory cortex were imaged during regular surgical conditions using conventional white light illumination. A conventional thermography camera was used. Consecutive activation using somatosensory evoked potentials was performed in a standard fashion using surface electrodes. Epilepsy foci were mapped using cortical grids. Active areas as depicted by these methods were registered with the neuronavigational system.
Results: Thermographic images were continuously registered over a period of 2–4 minutes. The data cube was subsequently processed by custom made in-house programs in the MatLab software package. Motion correction and principal component analyses were performed which identified activated areas in the respective cortical regions as confirmed by intraoperative EEG-mapping or electrophysiological SSEP mapping. The thermographic images were coregistered to the microscopic surface images and confirmed the expected anatomical distribution of the electrophysiological data. The extent of cortical activation was usually beyond the point measurement possible for SSEP, but more localized compared to EEG electrode grid assessment.
Conclusions: This is the first report of advanced processing of intrinsic tissue heat dissipation by thermography that is able to identify cortical areas of activity. Whether the underlying principle is purely due to increased blood flow or heat-generation by increased metabolic demand of active cortical areas remains to be evaluated. The method is completely label-free without any additional excitation light. This imaging method may be used as a continuous online imaging tool.