Werner Korb

Development and First Patient Trial of a Surgical Robot for Complex Trajectory Milling

Objective: Todays surgical robots normally perform “simple” trajectories, e.g., assisting as tool-holding devices in neurosurgery, or milling linear paths for cavities in total hip replacement. From a clinical point of view, it is still a complex undertaking to implement robots in the operating room. Until now, robot systems have not been used in patient trials to mill “complex” trajectories, which involve many positional and orientation changes and are often necessary in cranio-maxillofacial (CMF) surgery. This paper presents the RobaCKa surgical robot system, which allows more precise execution of surgical interventions and milling of “complex” trajectories. Materials and Methods: The main components of the RobaCKa system are a (former) CASPAR robot system, a POLARIS system, and a force-torque sensor. Results: In the first patient trial (April 2003) the planned trajectory was executed with an error of 0.66 ± 0.2 mm. Conclusions: The use of former industrial robots for surgical applications is possible but complex. The advantages are improved precision and quality and the possibility of documentation. The use of such systems is normally limited to research institutions or large clinics, because it is hardly possible to implement the necessary technical and logistic efforts in routine surgical work.

Location decision for a robot milling complex trajectories in craniofacial surgery

Abstract The aim of the surgical robot system RobaCKa is to support the surgeon manipulating (drill, mill, saw) the skull bone. In particular, we intend to assist the surgeon in craniofacial surgery who carries out bone repositionings close to vital parts and which changes the later patient appearance in a high degree. Since the complexity of the trajectories, the workspace within the resultant robot path that can be performed is very restricted. This paper presents an algorithm, which provides the possibility to preoperatively determine the best alignment of robot and patient.

Risk analysis for a reliable and safe surgical robot system

Abstract This paper shows the basic methods of quality assurance and risk analysis. It is particularly intended for researchers in the clinical field who have to implement safe systems with minimal resources and staff. The methods were applied to the robot system RobaCKa for craniotomies. Since surgical robots are complex mechatronic systems, it is important to apply systematic approaches for fault-free design, error detection and quality assurance. In universities and research centers, it is not often possible to apply the same measures for software design and error analysis as what is usually required for suppliers of medical products. Nevertheless, it is necessary to maintain basic regulations particularly for in vivo studies and clinical investigations. It makes sense to apply quality management right in the very beginning of a project, which would facilitate the its possible transformation into a commercial product later.

Image data acquisition and segmentation for accurate modeling of the calvarium

ABSTRACT Accuracy of the patient-model is a critical point in robot assisted surgery. When performing craniotomies, the dura mater must not be perforated. Hence bone width is of particular interest. The influence of imaging and segmentation on accuracy of the width of the bone-model was investigated. A human cadaver head was scanned with a CT-scanner under a variety of image acquisition parameters. Bone was segmented from these image data sets using threshold based segmentation with different settings for the lower threshold. From these volume data sets surface models of the bone were generated. The real width of the bone of the skull was measured at several positions. Using fiducial marker registration, these measured values were compared to the corresponding positions in the bone-models. CT-scan imaging with a slice thickness and slice distance of 1.5 to 2mm and a segmentation of bone with a lower threshold of 300 or 400 Hounsfield Units resulted in models with an average accuracy of 0.4mm for bone-width. However, at some points these models were too thin by up to 0.9mm. More accurate models are needed. It has to be evaluated, whether CT imaging with higher resolution or more sophisticated segmentation algorithms can reduce the scatter. Keywords: Segmentation, Modeling, Accuracy, Image Guided Surgery

Data reduction for manipulator path planning

Today, in robot applications continuous paths often result from CAD or other planning tools. We present here an approach to the question that has been discussed for a long time, i.e. how to approximate a given path by a second one in such a way that the latter lies in a tube of given radius e around the first. The approximation should be a (normally cubic) spline with a small number of breakpoints. The strategy is based on algorithms used in “computer aided geometric design” and is applied to examples from industrial and surgical robotics.

Chirurgieroboter für Kraniotomien – Risikoanalyse und erster Patientenversuch (Surgical Robot for Craniotomies – Risk Analysis and First Patient Trial)

Abstract Innerhalb des Sonderforschungsbereiches SFB 414 — Informationstechnolgie in der Medizin: Rechner- und Sensorgestützte Chirurgie — wurde RobaCKa = Roboter-assistiertes Chirurgiesystem Karlsruhe) entwickelt. Es dient beispielsweise zum Fräsen von Trajektorien im knöchernen Schädel in der cranio-maxillofacialen Chirurgie. Da es sich bei Robotern um komplexe mechatronische Systeme handelt, ist eine systematische Analyse für fehlerfreies Design, Fehlerdetektion und Qualitätssicherung unumgänglich. In Universitäten und Forschungszentren kann hierfür nicht derselbe Aufwand wie in der Industrie bei der Fertigung von Medizinprodukten betrieben werden, da oft nur ein bis zwei Wissenschaftler an solchen Projekten arbeiten. Trotzdem ist es notwendig, ein Qualitätmanagement zu etablieren, nicht zuletzt da ein solches auch für klinische Studien vorgeschrieben ist. Außerdem vereinfacht es später den möglichen Technologietransfer. Außer den Risikomanagementmethoden werden in dieser Arbeit die Tests an Phantomen, Probanden und eine erste Operation am Patienten beschrieben und die Ergebnisse diskutiert.

Genauigkeit der CT-basierten Modellerstellung des menschlichen Schädels

Die Erstellung korrekter Modelle basierend auf CT-Datensatzen fur die roboterassistierte Chirurgie ist von hoher Bedeutung. Der Einfluss einzelner Parameter auf die Prozesskette zur Erstellung von Kalottenmodellen aus CT-Daten wurde untersucht. Hierbei wurde die Qualitat der erstellten Modelle durch direkte Messung des zuvor untersuchten Kopfes verifiziert. Es konnte ein optimaler Bereich fur die Schwellwertsegmentierung von Schadelknochen identifiziert werden.