Jakob Brief

Precision of landmark positioning on digitized models from patients with cleft lip and palate.

Objective To quantify the precision of landmark positioning on digitized casts of patients with unilateral cleft lip and palate. Patients Forty plaster models of newborns up to 8 months of age were selected from the archive of the Department of Orthodontics of the University of Heidelberg. Material and Method The plaster-cast models were digitized with a Micromeasure 70 three-dimensional laser scanner (Micromeasure, Bischoffen, Germany). The laser scanner used in this study operates with a precision of 0.15 mm on the x- and y-axes and 0.06 mm on the z-axis. In the intraobserver study, a single observer placed anatomical landmarks in four rounds, with at least 4 weeks between each round. In the interobserver study, four different observers each placed the same landmarks once. For the two different studies, an ideal location for each landmark was calculated by averaging the landmark positions of the four rounds or observers. The distance between each of the four landmark positions and the ideal landmark was measured. Results A 95% confidence interval for the landmark positioning error was calculated. For the intraobserver investigation, this error was 0.34 to 1.30 mm, and for the interobserver investigation it was 0.7 to 2.00 mm. Conclusion Because both investigations displayed comparable error intervals, it was concluded that different observers could perform landmark positioning for the same studies.

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.

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.

Robot Assistant for Dental Implantology

We introduce a method to apply a preoperative 3D plan for inserting dental implants with an assisting medical robot. The treatment plan is based on the 3D visualization of the CT data of the patients maxilla and mandible, and supplies the location of the implants in the patients coordinates. The plan is then transferred to the surgical robots coordinate system. The robot guides the tool, a drill guide. Position, orientation, and depth of the initial drilling is defined with the tool held by the robot while the surgeon drills. The robot assists the dentist, and the optimal treatment plan will be applied directly to the patient.

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.

Evaluation of a computer aided planning and surgical robot system for craniofacial surgery

Craniofacial surgery requires skillful and experienced surgeons. Due to the vicinity to vital parts and the great impact of bone repositionings at the complex anatomic structures of the skull, the interventions have to be conducted with high precision. Therefore, we have developed two systems: KasOp, an operation planning system on the basis of 3D-patient-models and RobaCKa, a surgical robot system. After several tests using dummies and animal experiments, which prove the overall system to be safe and accurate, a first test has been conducted on a human test subject.

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.

Simulation of frontal orbital advancement

In this paper, we present a system for performing a complex surgical intervention using virtual reality (VR) technology. With the aid of the system, the intervention can be planned and simulated exactly before performing it in reality and important additional information can be achieved during the simulation. Before working in VR, finite element models of the patients head are generated form CT-images. Based on these models, additional work is done in VR, where the patients skull is cut into several pieces, which are then re-positioned. Based on moving and shifting the obtained pieces, the goal is to increase the volume inside the skull, which is called intracranial volume. Until now, it was not possible to measure the achieved increase of the intracranial volume. However, by using our system is it now possible to calculate this volume online during each step of our virtual intervention. The obtained results are used for the surgical intervention in reality.

CT-basierte 3D-Planung für die dentale Implantologie

Beschrieben wird ein 3D-Planungssytem fur die dentale Implantologie. Wir haben einen Algorithmus fur die automatisierte Detektion Alveolarnervs entwickelt, der nur eine minimale Benutzerinitialisierung erfordert. Um eine interaktive Implantatpositionierung auf vergleichsweise preiswerter PC-Hardware zu ermoglichen, wurden Methoden zur Hybridvisualisierung entwickelt, die auch ohne grose Texturspeicher und spezielle Graphikprozessoren auskommen.