gms | German Medical Science

Objective: Intraoperative Optical Imaging (IOI) is a marker free and non-invasive imaging technique that can be utilized for visualization of metabolic changes within the cerebral cortex. During neurosurgical interventions, we use the method in clinical routine to visualize specific functional brain areas in their spatial extent. Here, we are presenting a novel analysis and visualization approach, that allows a more detailed look on the cortical metabolism within the activated areas, and therefore a refined assessment of the activations following different stimulation types.

Methods: Measurements of 22 patients (11 female, 11 male, median age 57.5 years) that underwent surgical resection of lesions were retrospectively evaluated with the new analysis approach. Different stimulation types were applied in the patients - sensory (electrical, median nerve, 15 patients), visual (flash light goggles, 3 patients), tactile (surgical rubber, 3 patients), and speech stimulation (awake surgery, 3 patients), resulting in 24 datasets. Two-dimensional maps of cortical activity, that are representing the location, spatial extent, as well as now the type and direction of metabolic change, were computed for each patient. We compared the maps, that are either based on changes in regional cerebral blood volume or changes in oxygenation, between the different groups.

Results: The results reveal that the new methodology can provide valuable additional information during the surgical procedure. We found significant differences in the nature of activations for the different stimulation types. On the primary sensory cortex, tactile stimulation evoked cerebral blood volume increases whereas electrical median nerve stimulation led in all patients to blood volume decreases, which might be an indication for neuronal deactivation following processing of noxious stimuli. The evaluation of speech activations revealed areas with increased metabolism, closely located to areas with decreased metabolism, whereas mainly the areas with decreased metabolism correlate with essential language areas identified latter during surgery by Electrical Stimulation Mapping (ESM).

Conclusion: The new evaluation and visualization approach reveals promising new insights into the nature of the underlying physiological processes of activated functional areas. This increases the reliability of IOI and may enable the use of the method in additional surgical fields of application in which the use was up to now limited, e.g. during language mapping.