Hassfeld S

Intraoperative presentation of surgical planning and simulation results using a stereoscopic see-through head-mounted display

While many tools for preoperative planning and simulation of surgical interventions are available, the surgical procedure itself still lacks the computer based assistance. In this paper we present an approach for closing this gap using Augmented Reality techniques. The idea is to use a see- through head-mounted display for the superimposition of a patient with virtual dat. This technique enables surgeons to visualize and to re-use preoperatively calculated data directly in the operation field. At the Institute for Process Control and Robotics (IPR) at Universitaet Karlsruhe (TH) an experimental hardware setup for the Intraoperative Presentation of image data causes hard accuracy challenges. Main steps in the technical area are calibration, tracking and registration. We present our solutions for these machine vision related tasks. Afterwards we describe the way data is supplied and prepared for superimposition, and we also describe the presentation process. At the end of the paper clinical evaluation and future work will be discussed.

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.

Computer-based approaches for maxillofacial interventions

Computers used as supporting tools for diagnostics, operation planning and therapy are of increasing relevance in surgery. Rapid progress in imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRT) and ultrasound already allows to represent anatomical and physiological conditions with maximal authenticity. In order to simulate complex surgeries we must develop ergonomic and intuitively useable software tools, thus enabling a precise and fast virtual execution of the planned surgical intervention preoperatively. Intraoperative support will consist of passive navigation tools, available already today, supporting the intraoperative orientation and, in the future, robots performing specific steps autonomously. Methods of augmented reality for the interaction of virtual objects and the real surgical scene are also suitable for the visualization of planning data and other medically relevant information in the operation situs. In maxillofacial and craniofacial surgery the techniques mentioned have been applied in all fields from dental implantology up to the correction of craniofacial malformations and the resection of skull base tumors. Many applications are still being developed or are still in the form of a prototype. However, it is already clear that developments in this area will have a considerable effect on a surgeons routine work.

INPRES (intraoperative presentation of surgical planning and simulation results): augmented reality for craniofacial surgery

In this paper we present recent developments and pre-clinical validation results of our approach for augmented reality (AR, for short) in craniofacial surgery. A commercial Sony Glasstron display is used for optical see-through overlay of surgical planning and simulation results with a patient inside the operation room (OR). For the tracking of the glasses, of the patient and of various medical instruments an NDI Polaris system is used as standard solution. A complementary inside-out navigation approach has been realized with a panoramic camera. This device is mounted on the head of the surgeon for tracking of fiducials placed on the walls of the OR. Further tasks described include the calibration of the head-mounted display (HMD), the registration of virtual objects with the real world and the detection of occlusions in the object overlay with help of two miniature CCD cameras. The evaluation of our work took place in the laboratory environment and showed promising results. Future work will concentrate on the optimization of the technical features of the prototype and on the development of a system for everyday clinical use.

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.

Single-step robot guided bone resection and individual reconstruction of the skull

The TICC (Tomography Image processing CAD-CAM) processing chain allows the supply of existing craniofacial defects with individually prefabricated implants based on helical CT data [1, 2]. In combination with individual templates single-step bone resection and reconstruction is available [3, 4, 5, 6]. New developments in navigation and robotics allowed a robot guided bone resection according to the preoperative planning with the CAD system [7, 8, 9, 10]. This study shows results of resection experiments on ovine cadaver heads.

A system for facial reconstruction using distraction and symmetry considerations

Abstract The goal of the system presented in this paper is to support several facial surgeries that are aiming to transform an unsymmetrical face to a symmetric one. There are two main techniques to achieve this goal: distraction of the lower jaw and adding or removing tissue or bone at certain facial regions. Both planning tasks are done based on segmented CT or MRI data. The distraction of the lower jaw is simulated by cutting the jaw, moving it in 3D along a distraction axis and choosing a distractor for this procedure after determining, which is the best result. Furthermore, we are working on consideration of soft tissue movement so the patient can see what he or she will look like after the surgery. For supporting implants in craniofacial surgery, we are proposing a tool based on symmetry considerations. Nowadays, if implants have to be fitted to the patients bone, they are handmade while the surgery is running. This is quite time consuming and it would be helpful to shorten this procedure by producing the implants preoperatively. Our system allows to determine regions where implants should be set and proposes an initial contour for the implants.

Next generation's navigation systems

Abstract The data set correlation between the surgical site and the corresponding image data set in the operating room (OR) is the most time-consuming process for the surgeon. The next generations navigation systems ought to perform an automatic and highly accurate patient registration in the OR. Two systems that meet these criteria, the Surgical Segment Navigator SSN and the SSN++, are described. The SSN was developed in 1997 and is used for computer-assisted bone segment navigation. The SSN++, which has further been developed since 1999, utilizes laser scans of the surgical site. Both systems perform patient registration by just one click on a command button.

Clinical evaluation of patient misalignment during CT scans for computer assisted implantology — a new approach for compensation

Computer assisted implantology relies on good CT data. Therefore a strict protocol for acquiring the CT scan has to be adhered to. Most errors are introduced by misalignment and movement of the patient during scanning. We introduce a new method in terms of software algorithms and of clinical protocol changes, which allows for an optimal patient positioning to reduce movement artefacts and for compensating patient positioning misalignments.

REFERENZIERUNG DER PATIENTENLAGE MITTELS 3D-WEICHTEILLASERSCAN

Erlaubt ein 3D-Lasersurfacescan des Weichteilmantels des Gesichts eine Referenzierung der Patientenlage, oder machen Weichteilverlagerungen eine präzise Referenzierung über einen SD-Laserscan unmöglich? Zehn Patienten, die för einen computergestützten Eingriff mithilfe konventioneller röntgensichtbarer Marker geplant wurden, erhielten vor dem Eingriff zusätzlich einen SD-Laserscan mit einem Minolta 3D-Scanner VI 900, der an eine SSN++ Navigationsworkstation angeschlossen ist. Die Datenreferenzierung mittels Markern und SD-Laserscan wurden verglichen. Es zeigte sich nach Matchen ein Restvolumen von 4 bis 9 cm zwischen SD-Laserscan und CTDatensatz. Röntgenmarker wurden nach dem Datenmatchen mit einer Genauigkeit von l mm getroffen. Keywords—Navigation, Referenzierung, Datensatzkorrelation, SD-LaserScan, Gesichtsprofil, SSN++