Multispektrale Intraoperative Optische Bildgebung – Vergleich verschiedener Wellenlängenbänder zur Generierung von funktionellen Aktivitätskarten

Intraoperative Optical Imaging (IOI) is a non-invasive imaging technique that is able to visualize functional areas of the cerebral cortex based on the actual intraoperative scene. Dependent of the used light wavelength either changes in cerebral blood volume (CBV) or changes in blood oxygenation are mainly contributing to the observed intrinsic signal. Here we are investigating and assessing the reliability of three different light wavelength bands, captured simultaneously with a customized multispectral imaging camera setup, for the generation of maps of cortical activity.

Imaging was performed in eight patients (4 male, 4 female, median age 47.5) undergoing tumor resection. Stimulation to induce cortical activation was performed by electrical stimulation of the median nerve (5 patients), visual stimulation using flashlight goggles (2 patients) or by motor tasks during awake surgery (1 patient). Data from three different light wavelength bands that are sensitive either to changes in CBV, Oxy-, or Deoxyhemoglobgin (HbO / Hbr) was acquired simultaneously during stimulation and later analyzed using a Fourier-based data analysis approach. For each wavelength band a two-dimensional map of cortical activity was generated and the three resulting maps were compared in respect to their similarity using the structural similarity (SSIM) index. Furthermore, a signal-to-noise ratio of the maps was calculated for each light wavelength band.

The results are revealing, that activity maps generated from HbO channel are having highest similarity with CBV channel resulting in a mean SSIM of 0.85 ± 0.02, whereas HbO channel and Hbr channel respectively CBV channel and Hbr channel are showing a lower and comparable SSIM (0.69 ± 0.07 / 0.70 ± 0.07) towards each other over all patients. SNR was calculated for patients that were stimulated electrically on the median nerve. Here, the Hbr outperforms on average the CBV channel and the HbO channel (12.6 % / 14.2 % increased SNR).

Overall, the findings are suggesting that a light wavelength band sensitive towards Hbr changes may result in best results for the generation of activity maps. Nevertheless, further investigations are mandatory to assess the reliability especially in respect towards different tumor entities and their influence on cortical hemodynamics.