gms | German Medical Science

Objective: Intraoperative Optical Imaging (IOI) is a technique that can be utilized to visualize metabolic changes after Direct Cortical Stimulation (DCS) of the exposed cortical surface. It allows the evaluation of spatiotemporal characteristics of stimulation induced effects. In the past, we demonstrated that this technique might be a promising tool for tissue differentiation. To enhance the ease of use of this technique and to simplify the data acquisition, we investigated whether measurements can be performed with the surgical microscope integrated RGB camera instead of the highly sensitive CCD camera that was used in the past.

Methods: We performed measurements on four patients that underwent resection of cortical lesions. A total amount of 22 cortical stimulations was recorded. The spatiotemporal stimulation answers were simultaneously recorded using a standard integrated RGB camera (8 Bit digitalization) and a CCD camera (monochrome, 12 Bit digitalization, 568nm wavelength filter) attached via beam splitter to the surgical microscope. From each color channel of both cameras the spatial extent of the activated area was calculated, and compared. Furthermore, we compared the light reflectance change time courses measured around the electrode positions between the color channels and in respect to CCD reference camera.

Results: The results reveal, that IOI of DCS induced cortical activation using RGB camera equipment is possible and useful. The time courses extracted from the green channel (~ 480nm – 600nm) are showing highest correlation coefficient towards reference camera data (CC=0.73±0.26). This is in line with the expectation: the reference filtering wavelength of 568nm lies within the spectral sensitivity range of the green channel. The red channel (~ 570nm – 700nm) shows lowest correlation (CC=0.25±0.41), indicating that the dominating metabolic component is not the blood volume change but oxygenation variability of the tissue. The maximum mean amplitude of the green channel RGB signal is half of the amplitude measured with the reference camera (ΔR/RCCD=-5.2%; ΔR/RRGB=-2.6%).

Conclusion: The intraoperative use of an RGB camera of a commonly used operation microscope is possible and useful to analyze DCS induced cortical activation. Although the signal amplitude is reduced, measurements with the RGB camera can even be advantageous since through the three wideband filters of the color channels different metabolic sources can be simultaneously observed.