Intraoperative Optical Imaging (IOI) is a neuro-imaging technique that allows the visualization of changes in optical properties of the brain cortex. Recent developments enhanced the method regarding the robustness under intraoperative conditions. However, the necessity of additional hardware still limits the use in the operating room (OR). Since modern surgical microscopes are potentially equipped with all required hardware for imaging, we investigated the possible use of such standard RGB camera for IOI. Measurements were performed on eight patients. Changes in optical properties of the cortical surface were acquired with a monochrome CCD camera (AxioCam MRm) and simultaneously with a standard RGB camera (Trio 610). Maps of cortical activity were calculated from the image data and the quality of these maps was assessed with a spatial signal-to-noise ratio. Activity maps calculated from AxioCam MRm data showed highest SNR in six out of eight patients. In two patients the activity map calculated from Trio 610 red channel performed best overall. The Trio 610 maps calculated from red channel data performed best in three out of eight cases like the activity maps calculated from green channel data, whereas the activity map calculated from blue channel data performed best in only two cases. If the color channel with the highest SNR is chosen in each patient for comparison to AxioCam MRm, the median of the SNR (SNRAxioCam/SNRBestColorChannel) is 84 % (Quartile 1 (Q1): 78 %, Quartile 3 (Q3): 99%). Results reveal that the integration of the Intraoperative Optical Imaging method into the OR and surgical workflow can be further improved by using RGB camera equipment. A robust identification of somato-sensory areas seems possible. Due to the gain of information from different wavelength bands the need for intelligent evaluation algorithms is increased and should therefore be topic of future research.

Oelschlägel M., Institut für Biomedizinische Technik, Technische Universität Dresden, Dresden, Deutschland Meyer T., Institut für Biomedizinische Technik, Technische Universität Dresden, Dresden, Deutschland Sobottka S.B., Klinik für Neurochirurgie, Universitätsklinikum Dresden, Dresden, Deutschland Kirsch M., Klinik für Neurochirurgie, Universitätsklinikum Dresden, Dresden, Deutschland Schackert G., Klinik für Neurochirurgie, Universitätsklinikum Dresden, Dresden, Deutschland Morgenstern U., Institut für Biomedizinische Technik, Technische Universität Dresden, Dresden, Deutschland

Using a 3D-demonstrator system for application in neurosurgery, an integrated tool for epilepsy surgery evaluation has been developed to visualize subdural electrodes derived from postoperative CT datasets on the cortical surface by 3D-rendering preoperative MRI datasets. Difficulties result from postoperative deformations caused by hematoma. To investigate deformation and resultant electrode localization errors, patient data, online database and also phantoms as a kind of well-known reference are used. A head phantom was designed to evaluate occurring errors, respectively. The developed tool works fully automated and takes about 2 minutes to visualize electrodes' position. The measured electrodes' position error does not fulfill clinical requirements yet; phantom data must be used for further investigations.

Introduction: The long-term follow-up of treated cerebral aneurysms is mostly performed analyzing 2D images. The objective of the present study was to evaluate 3D-visualisation techniques for quantification and classification of regrowth patterns of treated aneurysms.

A system for optical imaging of intrinsic signals and visualization of functional maps overlaid with the 3D reconstruction of the cortex is presented. Optical imaging of intrinsic signals is an advantageous method for monitoring functional representation of eloquent areas of the cortex. The non-invasive method works free of contact and generates a map of cortical activation with a spatial resolution of less than 1 mm based on the changes in optical parameters of brain tissue during cortical activation. A system containing an illumination device, a surgical microscope, and a camera is described. Computation of the cortical activation map is done by comparison of recordings during rest and stimulation. 3D reconstruction of the cortex and overlay with the optical recording is achieved using the 3D visualization software AMIRA. Optical imaging of intrinsic signals can increase the identification of eloquent regions of the brain. The 3D visualization is beneficial for identifying the region and for inter-individual comparison of the cortical representation of eloquent areas.

Objective: Fluorescence video angiography has recently been introduced to neurosurgery. For intraoperative control, blood flow in the brain vessels can be visualized by means of near-infrared fluorescence dye Indocyanine Green. Until now the sufficiency of the blood flow has to be assessed qualitatively by the surgeon. Therefore, an objective quantification of the blood flow by means of video analysis is desirable.Methods: Two different methods for the determination of the blood flow velocity have been developed, one based on the transit time and the other on the velocity-proportional increase of fluorescence intensity during the inflow process of the dye. Both methods were implemented in software to analyze video data obtained from a digital PAL-standard IR-sensitive imaging system. Verification was realized by means of a flow phantom which emulates the blood flow and fluorescence of the dye in cerebral vessels.Results: Good fluorescence image quality comparable to clinical recordings could be obtained from simulation using the phantom. Determined velocities using transit time exceed the scheduled values by a factor k approximate to 1.5 depending on the vessel diameter and the flow characteristics. The flow profile and the limited penetration depth of the exposing light are supposed to be the cause of this k-factor. After correction, an accuracy of +/- 20 % in velocity determination could be achieved, which is not unusual when comparing with clinical sonographic Doppler measurement. The rise time of fluorescence intensity shows an inverse proportional behavior to flow velocity. The proportionality factor changes according to the vessel diameter.Conclusions: Evaluation of velocity distribution in vessels with variant diameter (e.g. stenosis) solely by means of the rise time is not possible. Transit time measurement is a suitable method for flow velocity determination. The detectable range and accuracy are limited by some further influences on the imaging process. At the moment velocities up to 10 cm/s for a typical visible vessel length of 20 mm can be detected with sufficient accuracy. For clinical studies the algorithms have to be enhanced since an eightfold flow velocity is expected in the large brain arteries. Further investigations are necessary for a robust k-factor correction in-vivo.