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Neurosurgical techniques often require accurate targeting of deep-brain structures even in the presence of deformation due intervention and egress of Cerebrospinal Fluid (CSF) during surgical access. Prior work reported Simultaneous Localization and Mapping (SLAM) methods for endoscopic guidance using 3D reconstruction. In this work, methods for correcting the geometric distortion of a neuroendoscope are reported in a form that have been translated intraoperative use in first clinical studies. Furthermore, SLAM methods are evaluated in first clinical studies for real-time 3D endoscopic navigation with near real-time registration in the presence of deep-brain tissue deformation. A custom calibration jig with swivel mounts was designed and manufactured for neuroendoscope calibration in the operating room. The process is potentially suitable to intraoperative use while maintaining sterility of the endoscope, although the current calibration system was used in the Operating Room (OR) immediately following the case for offline analysis. A six by seven checkerboard pattern was used to obtain corner locations for calibration, and the method was evaluated in terms of Reprojection Error (RPE). Neuroendoscopic video was acquired under an IRB-approved clinical study, demonstrating rich vascular features and other structures on the interior walls of the lateral ventricles for 3D point-cloud reconstruction. Geometric accuracy was evaluated in terms of Projected Error (PE) on a ground truth surface defined from MR or cone-beam CT (CBCT) images. Intraoperative neuroendoscope calibration was achieved with sub-pixel [0.61 ± 0.20 px] error. The calibration yielded a focal length of 816.42 px and 822.71 px in X and Y directions respectively, along with radial distortion coefficients of -0.432 (first order term [𝑘1]) and 0.158 (second order term [𝑘2]). The 3D reconstruction was performed successfully with a PE of 0.23 ± 0.15 mm compared to the ground truth surface. The system for neuroendoscopic guidance based on SLAM 3D point-cloud reconstruction provided a promising platform for the development of 3D neuroendoscopy. The studies reported in this work presented an important means of neuroendoscope calibration in the OR and provided preliminary evidence for accurate 3D video reconstruction in first clinical studies. Future work aims to further extend the clinical evaluation and improve reconstruction accuracy using ventricular shape priors.
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