Integration and accuracy evaluation of exoscope-based stereovision for image updating in neurosurgery

In image-guided neurosurgery, intraoperative navigation typically relies on pre-operative magnetic resonance (pMR) images. However, after dural opening, the accuracy of image guidance degrades due to factors such as gravity, loss of cerebrospinal fluid, intracranial pressure changes, and medication. Consequently, the brain can deform up to 1 cm, rendering pMR image guidance beyond the acceptable range. We developed an image-updating approach to account for intraoperative brain deformation by deforming pMR to match the surgical scene, achieving a target registration error (TRE) of 1.60 ± 0.43 mm. The image updating system uses a navigation system for tracking and an intraoperative stereovision system (iSV) mounted to a surgical microscope for obtaining the intraoperative surface profile of the exposed brain. Recently, exoscopes, such as Synaptive Modus X, which integrates navigation and 3D visualization, have become popular in neurosurgery as they allow multiple users to have depth perception simultaneously. We aim to integrate stereovision data from an exoscope system into the existing image updating pipeline. Although the exoscope provides depth perception, quantitative reconstruction and localization of the surgical scene are not currently available. In this study, we adapted our iSV acquisition and reconstruction for exoscope systems. Navigation information was acquired via OpenIGTLink, and image data via frame grabbers. Stereo parameters and the spatial relationship between cameras and tracker were calibrated using a tracked checkerboard. The accuracy of stereo calibration and reconstruction was compared to our previous microscope-based implementation. Results showed that the exoscope-based and microscope-based iSV systems were comparable. The calibration error for the exoscope was 0.6±0.2 mm, while the microscope exhibited an error of 0.6±0.1 mm. The iSV reconstruction errors were 1.4±0.5 mm and 1.4±1.4 mm for the exoscope and microscope, respectively, suggesting that the exoscope-based iSV system can provide intraoperative data for brain deformation compensation.