Retrospective in silico evaluation of optimized preoperative planning for temporal bone surgery.

PURPOSE: Robot-assisted surgery at the temporal bone utilizing a flexible drilling unit would allow safer access to clinical targets such as the cochlea or the internal auditory canal by navigating along nonlinear trajectories. One key sub-step for clinical realization of such a procedure is automated preoperative surgical planning that incorporates both segmentation of risk structures and optimized trajectory planning. METHODS: We automatically segment risk structures using 3D U-Nets with probabilistic active shape models. For nonlinear trajectory planning, we adapt bidirectional rapidly exploring random trees on Bézier Splines followed by sequential convex optimization. Functional evaluation, assessing segmentation quality based on the subsequent trajectory planning step, shows the suitability of our novel segmentation approach for this two-step preoperative pipeline. RESULTS: Based on 24 data sets of the temporal bone, we perform a functional evaluation of preoperative surgical planning. Our experiments show that the automated segmentation provides safe and coherent surface models that can be used in collision detection during motion planning. The source code of the algorithms will be made publicly available. CONCLUSION: Optimized trajectory planning based on shape regularized segmentation leads to safe access canals for temporal bone surgery. Functional evaluation shows the promising results for both 3D U-Net and Bézier Spline trajectories.

i3PosNet: instrument pose estimation from X-ray in temporal bone surgery.

PURPOSE: Accurate estimation of the position and orientation (pose) of surgical instruments is crucial for delicate minimally invasive temporal bone surgery. Current techniques lack in accuracy and/or line-of-sight constraints (conventional tracking systems) or expose the patient to prohibitive ionizing radiation (intra-operative CT). A possible solution is to capture the instrument with a c-arm at irregular intervals and recover the pose from the image. METHODS: i3PosNet infers the position and orientation of instruments from images using a pose estimation network. Said framework considers localized patches and outputs pseudo-landmarks. The pose is reconstructed from pseudo-landmarks by geometric considerations. RESULTS: We show i3PosNet reaches errors [Formula: see text] mm. It outperforms conventional image registration-based approaches reducing average and maximum errors by at least two thirds. i3PosNet trained on synthetic images generalizes to real X-rays without any further adaptation. CONCLUSION: The translation of deep learning-based methods to surgical applications is difficult, because large representative datasets for training and testing are not available. This work empirically shows sub-millimeter pose estimation trained solely based on synthetic training data.

High-precision evaluation of electromagnetic tracking.

PURPOSE: Navigation in high-precision minimally invasive surgery (HP-MIS) demands high tracking accuracy in the absence of line of sight (LOS). Currently, no tracking technology can satisfy this requirement. Electromagnetic tracking (EMT) is the best tracking paradigm in the absence of LOS despite limited accuracy and robustness. Novel evaluation protocols are needed to ensure high-precision and robust EMT for navigation in HP-MIS. METHODS: We introduce a novel protocol for EMT measurement evaluation featuring a high-accuracy phantom based on LEGO[Formula: see text], which is calibrated by a coordinate measuring machine to ensure accuracy. Our protocol includes relative sequential positions and an uncertainty estimation of positioning. We show effects on distortion compensation using a learned interpolation model. RESULTS: Our high-precision protocol clarifies properties of errors and uncertainties of EMT for high-precision use cases. For EMT errors reaching clinically relevant 0.2 mm, our design is 5-10 times more accurate than previous protocols with 95% confidence margins of 0.02 mm. This high-precision protocol ensures the performance improvement in compensated EMT by 0.05 mm. CONCLUSION: Our protocol improves the reliability of EMT evaluations because of significantly lower protocol-inherent uncertainties. To reduce patient risk in HP-MIS and to evaluate magnetic field distortion compensation, more high-accuracy protocols such as the one proposed here are required.

Toward an automatic preoperative pipeline for image-guided temporal bone surgery.

PURPOSE: Minimally invasive surgery is often built upon a time-consuming preoperative step consisting of segmentation and trajectory planning. At the temporal bone, a complete automation of these two tasks might lead to faster interventions and more reproducible results, benefiting clinical workflow and patient health. METHODS: We propose an automatic segmentation and trajectory planning pipeline for image-guided interventions at the temporal bone. For segmentation, we use a shape regularized deep learning approach that is capable of automatically detecting even the cluttered tiny structures specific for this anatomy. We then perform trajectory planning for both linear and nonlinear interventions on these automatically segmented risk structures. RESULTS: We evaluate the usability of segmentation algorithms for planning access canals to the cochlea and the internal auditory canal on 24 CT data sets of real patients. Our new approach achieves similar results to the existing semiautomatic method in terms of Dice but provides more accurate organ shapes for the subsequent trajectory planning step. The source code of the algorithms is publicly available. CONCLUSION: Automatic segmentation and trajectory planning for various clinical procedures at the temporal bone are feasible. The proposed automatic pipeline leads to an efficient and unbiased workflow for preoperative planning.

Robotic cochlear implantation: feasibility of a multiport approach in an ex vivo model.

PURPOSE: A recent clinical trial has shown the feasibility of robotic cochlear implantation. The electrode was inserted through the robotically drilled tunnel and an additional access through the external auditory canal was created to provide for means of visualization and manipulation. To obviate the need for this additional access, the utilization of multiple robotically drilled tunnels targeting the round window has been proposed. The objective of this study was to assess the feasibility of electrode insertion through a robotic multiport approach. METHODS: In four ex vivo human head specimens (left side), four trajectories through the facial recess (2x) and the retrofacial and suprameatal region were planned and robotically drilled. Optimal three-port configurations were determined for each specimen by analyzing combinations of three of the four trajectories, where the three trajectories were used for the electrode, endoscopic visualization and manipulative assistance. Finally, electrode insertions were conducted through the optimal configurations. RESULTS: The electrodes could successfully be inserted, and the procedure sufficiently visualized through the facial recess drill tunnels in all specimens. Effective manipulative assistance for sealing the round window could be provided through the retrofacial tunnel. CONCLUSIONS: Electrode insertion through a robotic three-port approach is feasible. Drill tunnels through the facial recess for the electrode and endoscope allow for optimized insertion angles and sufficient visualization. Through a retrofacial tunnel effective manipulation for sealing is possible.

Quality of Life After Translabyrinthine Vestibular Schwannoma Resection-Reliability of the German PANQOL Questionnaire.

OBJECTIVE: To quantify the postoperative quality of life (QOL) of patients after translabyrinthine surgery for vestibular schwannoma (VS) using the German version of the Penn acoustic neuroma quality-of-life questionnaire (PANQOL) in a university hospital. METHODS: The PANQOL questionnaire was administered to 72 patients who were treated in our department with translabyrinthine surgery for VS between January 2007 and January 2017. Descriptive evaluations of results were performed in addition to analyses of the reliability and convergent validity of the results and a subgroup analysis. RESULTS: For the first time, QOL was measured in German-speaking VS patients after translabyrinthine surgery. Cronbach's alpha for internal consistency and Guttman's split half, used as measures of reliability, showed values between 0.39 and 0.92 (raw alpha) and 0.58 and 0.98 (Lambda 4), respectively. DESCRIPTIVE STATISTICS: The mean total PANQOL score of patients after translabyrinthine VS resection was 61.96. The domain "hearing" had the lowest score (50.87), while "facial dysfunction" had the highest score (74.88). Subgroup analysis showed that neither preoperative tumor size nor elapsed time postoperatively significantly influenced QOL outcomes. CONCLUSIONS: Depending on the different domains the German PANQOL questionnaire showed poor to good internal consistency, reliability, and convergent validity. Moreover, some VS patients suffer from reduced QOL for a long time after the translabyrinthine procedure, thus psycho-oncological care should be recommended in these cases.

Multistep translation and cultural adaptation of the Penn acoustic neuroma quality-of-life scale for German-speaking patients.

BACKGROUND: Monitoring the health-related quality of life (HRQOL) for patients with vestibular schwannoma (VS) has garnered increasing interest. In German-speaking countries, there is no disease-specific questionnaire available similar to the "Penn Acoustic Neuroma Quality-of-life Scale" (PANQOL). METHOD: We translated the PANQOL for German-speaking patients based on a multistep protocol that included not only a forward-backward translation but also linguistic and sociocultural adaptations. The process consists of translation, synthesis, back translation, review by an expert committee, administration of the prefinal version to our patients, submission and appraisal of all written documents by our research team. The required multidisciplinary team for translation comprised head and neck surgeons, language professionals (German and English), a professional translator, and bilingual participants. A total of 123 patients with VS underwent microsurgical procedures via different approaches at our clinic between January 2007 and January 2017. Among these, 72 patients who underwent the translabyrinthine approach participated in the testing of the German-translated PANQOL. RESULT: The first German version of the PANQOL questionnaire was created by a multistep translation process. The responses indicate that the questionnaire is simple to administer and applicable to our patients. CONCLUSION: The use of a multistep process to translate quality-of-life questionnaires is complex and time-consuming. However, this process was performed properly and resulted in a version of the PANQOL for assessing the quality of life of German-speaking patients with VS.

Minimally invasive, multi-port approach to the lateral skull base: a first in vitro evaluation.

PURPOSE: The aim of the study was to validate a minimally invasive, multi-port approach to the internal auditory canal at the lateral skull base on a cadaver specimen. METHODS: Fiducials and a custom baseplate were fixed on a cadaver skull, and a computed tomography image was acquired. Three trajectories from the mastoid surface to the internal auditory canal were computed with a custom planning tool. A self-developed positioning system with a drill guide was attached to the baseplate. After referencing on a high precision coordinate measuring machine, the drill guide was aligned according to the planned trajectories. Drilling of three trajectories was performed with a medical stainless steel drill bit. RESULTS: The process of planning and drilling three trajectories to the internal auditory canal with the presented workflow and tools was successful. The mean drilling error of the system (Euclidian distance between the planned trajectory and centerline of the actual drilled canal) was [Formula: see text] mm at the entry point and [Formula: see text] mm at the target. The inaccuracy of the drill process itself and its physical limitations were identified as the main contributing factors. CONCLUSION: The presented system allows the planning and drilling of multiple minimally invasive canals at the lateral skull base. Further studies are required to reduce the drilling error and evaluate the clinical application of the system.

Minimally invasive multiport surgery of the lateral skull base.

OBJECTIVE: Minimally invasive procedures minimize iatrogenic tissue damage and lead to a lower complication rate and high patient satisfaction. To date only experimental minimally invasive single-port approaches to the lateral skull base have been attempted. The aim of this study was to verify the feasibility of a minimally invasive multiport approach for advanced manipulation capability and visual control and develop a software tool for preoperative planning. METHODS: Anatomical 3D models were extracted from twenty regular temporal bone CT scans. Collision-free trajectories, targeting the internal auditory canal, round window, and petrous apex, were simulated with a specially designed planning software tool. A set of three collision-free trajectories was selected by skull base surgeons concerning the maximization of the distance to critical structures and the angles between the trajectories. RESULTS: A set of three collision-free trajectories could be successfully simulated to the three targets in each temporal bone model without violating critical anatomical structures. CONCLUSION: A minimally invasive multiport approach to the lateral skull base is feasible. The developed software is the first step for preoperative planning. Further studies will focus on cadaveric and clinical translation.