Multicamera Optical Tracker Assessment for Computer Aided Surgery Applications

Image-guided interventions enable the surgeon to display the position of instruments and devices with respect to the patient's imaging studies during surgery by means of a tracker device. Optical trackers are commonly chosen for many surgical applications when high accuracy and robustness are required. OptiTrack is a multicamera optical tracker whose number of sensors and their spatial configuration can be adapted to the application requirements, making it suitable for surgical settings. Nonetheless, no extensive studies of its accuracy are available. The purpose of this paper was to evaluate an eight-camera optical tracker in terms of accuracy, miscalibration sensitivity, camera occlusions, and tool detection in a feasible clinical setup. We studied the tracking accuracy of the system using a robotic arm (~μm precision) as the gold standard, a single reflective marker, and various tracked objects while the system was installed in an operating room. Miscalibration sensitivity was 0.16°. Mean target error was 0.24 mm for a single marker, decreasing to 0.05 mm for tracked tools. Single-marker error increased up to 1.65 mm when five cameras where occluded although 75% of the working volume showed an error lower than 0.23 mm. The accuracy was sufficient for navigating the collimator in intraoperative electron radiation therapy, improving redundancy and allowing large-working volumes. The tracker assessment we present and the validated miscalibration protocol are important contributions to image-guided surgery, where the choice of the tracker is critical and the knowledge of the accuracy in situations of camera occlusion is mandatory during surgical navigation

MITK-IGT für die computerassistierte Weichgewebepunktion

Im Bereich der Krebsdiagnose und -therapie gewinnen neue minimalinvasive Verfahren zunehmend an Bedeutung. Beispiele hierfür sind Nadelpunktionen, bei denen zur Diagnose eine Gewebsprobe entnommen (Biopsie) oder durch Zerstörung des Gewebes im Bereich der Nadelspitze eine Krebserkrankung therapiert wird (Ablation). Eine zentrale Herausforderung hierbei ist die genaue Platzierung der Nadel. Am deutschen Krebsforschungszentrum (DKFZ) wurde ein computergestütztes Navigationssystem für Nadelinsertionen entwickelt, das sich im in-vivo Versuch als höchst akkurat zeigte. Trotz der vielversprechenden Ergebnisse kam das System bisher jedoch nicht am Patienten zum Einsatz. Dies ist unter anderem auf die schwierige Integration des Systems in den klinischen Workflow und die erhöhte Invasivität zurückzuführen. Vor diesem Hintergrund war das Ziel dieser Arbeit zum einen die Entwicklung einer flexiblen, erweiterbare Software für die navigierte Weichgewebepunktion, zum anderen die Weiterentwicklung des Navigationssystems durch die Einbindung eines neuen Feldgenerators für das elektromagnetische Trackingsystem NDI Aurora. Die Implementierung der Software erfolgte aufbauend auf der Bibliothek MITK und dem enthaltenen Modul MITK-IGT. Dabei wurde ein komponentenweiser Aufbau umgesetzt, welcher einen einfachen Austausch oder Erweiterungen der einzelnen Komponenten ermöglicht. Des Weiteren wurde der neue Feldgenerator bezüglich Genauigkeit und Präzision in der Einsatzumgebung evaluiert und es erfolgte ein Test des Navigationssystems unter klinischen Bedingungen. Abschließend kann festgestellt werden, dass durch die gezeigte Flexibilität und Erweiterbarkeit der entwickelten Software zahlreiche Möglichkeiten zur Weiterentwicklung offen stehen. Bezüglich des Feldgenerators zeigte sich das vielversprechende Potential dieses Geräts für die Weiterentwicklung medizinischer Navigationssysteme

Image-Guided Robot-Assisted Needle Intervention Devices and Methods to Improve Targeting Accuracy

This dissertation addresses the development of medical devices, image-guided robots, and their application in needle-based interventions, as well as methods to improve accuracy and safety in clinical procedures. Needle access is an essential component of minimally invasive diagnostic and therapeutic procedures. Image-guiding devices are often required to help physicians handle the needle based on the images. Integrating robotic accuracy and precision with digital medical imaging has the potential to improve the clinical outcomes. The dissertation presents two robotic devices for interventions under Magnetic Resonance Imaging (MRI) respectively Computed Tomography (CT) – Ultrasound(US) cross modality guidance. The MRI robot is a MR Safe Remote Center of Motion (RCM) robot for direct image-guided needle interventions such as brain surgery. The dissertation also presents the integration of the robot with an intraoperative MRI scanner, and preclinical tests for deep brain needle access. The CT-Ultrasound guidance uses a robotic manipulator to handle an US probe within a CT scanner. The dissertation presents methods related to the co-registration of multi-image spaces with an intermediary frame, experiments for needle targeting. The dissertation also presents method on using optical tracking measurements specifically for medical robots. The method was derived to test the robots presented above. With advanced image-guidance, such as the robotic approaches, needle targeting accuracy may still be deteriorated by errors related to needle defections. Methods and associated devices for needle steering on the straight path are presented. These are a robotic approach that uses real-time ultrasound guidance to steer the needle; Modeling and testing of a method to markedly reduce targeting errors with bevel-point needles; Dynamic design, manufacturing, and testing of a novel core biopsy needle with straighter path, power assistance, reduced noise, and safer operation. Overall, the dissertation presents several developments that contribute to the field of medical devices, image-guided robots, and needle interventions. These include robot testing methods that can be used by other researchers, needle steering methods that can be used directly by physicians or for robotic devices, as well as several methods to improve the accuracy in image-guided interventions. Collectively, these contribute to the field and may have a significant clinical impact