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Biomedical subjects

H Wörn

Publications and source records attributed to H Wörn.

At least 19 recordsLinked to original sources
PubMed2006

Computer- and robot-aided head surgery.

In this paper new methods and devices for computer and robot based head surgery are presented. A computer based planning system for CMF-surgery allows the surgeon to plan complex trajectories on the head of the patient for operations where bone segments were cut out and shifted. Different registration methods have been developed and tested. A surgical robot system for bone cutting on the head has been developed and evaluated at the patient in the operating theatre. In future, laser cutting of bones with a robot will be seen as a new powerful method for robot based surgery. A 3D augmented reality system will assist the surgeon in the future by augmenting virtual anatomical structure into the situs.

Humans↗
PubMed2005

Robot-assisted craniotomy.

In the Special Research Centre 414 of the German Research Funding (DFG, Bonn) a system for robot-assisted cranial surgery was developed. It is designed for the accurate and safe execution of craniotomies and repositioning of bone pieces. The system is intended for use in the surgical therapy of craniosynostosis. Preoperatively, CT imaging is performed. In a computerized planning system the position and shape of the intended craniotomy is intuitively planned on a virtual model of the patient's skull. Intraoperatively, after conventional removal of the covering soft tissue, the robot performs the craniotomy autonomously. Extensive testing in phantom studies and animal tests confirmed the reliability and accuracy of the system. A thorough risk analysis of the system was performed. In this paper, the first clinical use of the system on a patient is described and the clinical importance is discussed.

Bone Cysts↗
PubMed2002

[Ultrasonography of tumors of the locomotor system].

Sonography is an integral part of primary tumor diagnosis and follow-up for the great majority of organ systems. However, its value in the field of space-occupying processes of the locomotor system, especially of malignant bone tumors, has mostly been underestimated. The sonographic examination has to investigate the whole tumor region and the corresponding lymph nodes statically and dynamically. The examination procedure should be standardized and the documentation reliable. Evaluation criteria are the localization, dimensions, and volume of the tumors, echogenicity and homogeneity, peri- and intratumoral vascularization (vessel density and architecture), borders of the tumor, and neighboring structures. Pathologic changes not only of the soft tissues but also of the bones can be evaluated sonographically. Even subtle analysis does not permit definitive assessment of tumor status. Taking its physical limitations into consideration, high-resolution sonography, enhanced by color/PowerDoppler and three-dimensional techniques, is a valuable adjunct to improve diagnosis, therapy planning, monitoring, and posttherapeutic care of tumors of the locomotor system.

Bone Neoplasms↗
PubMed2002

[3D-ultrasound: a valuable adjunct for therapy planning and follow-up of head and neck tumours].

AIM: The three-dimensional visualization of orofacial tumours and adjacent organs at risk of infiltration is an important requirement for staging, therapy planning and follow-up. Artifacts from the mandible or metal implants often reduce the diagnostic power of computed tomography (CT). The value of 3D-ultrasound (3D-US) in respect to the standard methods CT and magnetic resonance imaging (MRI) was therefore analyzed. METHOD: Between 9/97 and 10/99 the visualization of orofacial tumours in 243 patients by 3D-US was examined, classified on a five-point scale and compared to the corresponding CT and MRI scans. RESULTS: Complete visualization of the tumours was possible in 85.6 % by 3D-US, whereas the rates of MRI and CT were lower with 77.4 % and 61.3 % respectively, mainly because of artifacts. The best combinations of methods, 3D-US + CT (96.7 %) and 3D-US + MRI (95.1 %) gave almost equivalent results, whereas CT + MRI (83.5 %) was inferior. In 2.5 % of the cases none of the methods produced adequate results. CONCLUSION: By free selection of sectional planes and direct correlation to the clinical findings 3D-ultrasound can improve staging, therapy planning and follow-up of orofacial tumours, especially in the case of small tumour size, dental crowns/inlays, metal implants or contraindications to MRI.

Head and Neck Neoplasms↗
PubMed2002

Analysing the variations of shapes based on surface-models.

In this paper we present a freely available application with which surface models, e.g. triangle meshes can be registered rigidly as well as by using similarity or affine transformations. Registered surfaces can be analysed, i.e. their difference can be calculated and visualised in various ways. The software is addressing the problem of evaluating shape differences of generated surface models due to mesh relaxation, decimation, object (in our case: patient) variation, different co-ordinate systems, etc. We invite all interested research personnel to download and use the software.

Artifacts↗
PubMed2002

["Computer- and Sensor-Assisted Surgery" Special Research Area 414--goals and concepts].

This paper presents an overview of our research in computer assisted surgery within the "Sonderforschungsbereich 414--Information Technology in Medicine: Computer and Sensor Supported Surgery". The overall goal is to achieve improved operation methods including higher quality, more safety and also more economy due to shorter operation time and less postoperative treatment. The SFB 414 is divided into three different sections focusing on projects concerning the heart, projects supporting cranio-facial interventions and interconnecting projects that serve both categories.

Germany↗
PubMed2002

[Processing medical image data for head surgery].

Three-dimensional models of the patient's anatomy are the basis for modern applications in computer-assisted surgery or radiology. To create these models the data is processed in a series of steps that transforms the initial raw data (generally CT/MRT volume images) into the three-dimensional models (e.g. triangle meshes). In doing so, a multitude of parameters adjustments, interactions and decisions are necessary to be made by the physician in order to create the models adapted to the specific needs of the patient and to the surgery. The quality of the models therefore strongly depends on that process chain. As a result of the high requirements on the quality and security of a clinical application the quality of the models itself and the capability to use them flexibly are essential. This work present a method to adjust and optimise the creation of the models and to asses their quality afterwards.

Artifacts↗
PubMed2002

[Expanded reality in head surgery].

The preoperative planning of complex craniofacial surgical interventions is increasingly realized with the aid of appropriate planning systems in order to achieve high precision, minimal invasion and protection of risk areas. But the most important step from the planning to the actual intervention consists of providing the planning data intraoperatively in a reasonable and easy to handle way. In this regard, augmented reality is one of the most challenging and promising techniques to solve this problem. In this paper we present two different systems based on see-through glasses resp. a common video projector to directly visualize the planning data in the surgeon's field of view. The work is funded by the 'Deutsche Forschungsgemeinschaft (DFG)' and Stryker Leibinger Freiburg/Germany.

Computer Simulation↗
PubMed2001

Statistical analysis of the morphology of three-dimensional objects and pathologic structures using spherical harmonics.

To support diagnosis and therapy, it is a fundamental aim of medical image processing to describe morphological characteristics of pathological structures or image objects in general. Different authors propose quantitative methods of description like bounding boxes[1], fourier descriptors[2] or contour moments[3]. Unfortunately, these methods either don't supply a complete, respectively precise description of the object or only operate on two-dimensional images. Among the range of application are systems to classify lung nodules [4] or to help the diagnosis of brain tumors [5]. In this paper we present a method to analyze the morphology or shape of any three-dimensional object in order to describe it mathematically well-defined. We show how the description can be used to perform statistical operations on morphologies. The method presented in this paper was developed to assist the planning of craniofacial surgery. We analyze the shape of a given set of skull CT-data and use the mathematical description to statistically calculate the average shape of the skulls.

Cephalometry↗
PubMed2001

Virtual simulation system for collision avoidance for medical robot.

For the collision avoidance with a medical robot with 6 DOF a virtual simulation system is presented. Manipulator and obstacles are modelled by geometric primitives. Collisions are detected in the Cartesian workspace by hierarchical distance computation based on the given CAD model. The application initially being addressed is maxillofacial surgery, where the safety of the patient is the main requirement,because of the closeness to vital parts. The simulation system allows the surgeon to check up the trajectory of the robot before the current operation begins.

Computer Graphics↗
PubMed2001

Intraoperative visualization of surgical planning data using video projectors.

The Institute for Process Control and Robotics has developed a new system using projector based augmented reality for the intraoperative visualization of preoperatively defined surgical planning data. Projector based augmented reality in medical applications represents a new field of research and gives an alternative solution to the commonly used Head Mounted Display technology. Moreover, the projector is not only used for visualization, but also for registration of the patient without the usage of invasive fiducial techniques as e.g. screw markers or frames. Recent results showed an achieved accuracy of +/- 1.5 mm which roughly meets clinical demands.

Data Display↗
PubMed2001

An endoscopic navigation system.

Endoscopy is an important procedure for the diagnostic and therapy of various pathologies. We develop extensive and automated systems for this field. Due to application of these new systems, a patient is subject to considerably less strains, as opposed to prevailing commercial systems. The capability of such instruments, unlike the presently used systems, to independently follow anatomical peculiarities of the body means also a reduced risk of complications for a patient. A further advantage is that difficult to access regions deep inside the body, like the small intestine or peripheral parts of the bronchial tubes, can thus be reached. We use a complex navigation system for our new endoscopic system.

Computer Simulation↗
PubMed2001

A new concept for intraoperative matching of 3D ultrasound and CT.

Matching of ultrasound images with CT or MRI scans is an awkward and unsatisfactory task when using conventional methods. Wide ranging differences in modality of ultrasound and CT/MRI require new techniques to be explored for successful alignment. Ultrasound images characteristically show comparable high noise ratio due to scattering inside the region of interest and the surrounding area. Additionally, shadowing and tissue dependent echo response time produce geometric artifacts. These image distortions are sophisticated to recover. Though image quality and geometric relationship are poor, ultrasound images show the potential for fast, low-cost, non-invasive and flexible image acquisition, predestinated for intraoperative application. The fusion of intraoperative ultrasound and preoperatively acquired CT/MRI images provides both, geometric invariance and flexible fast image acquisition, merging in a powerful tool for augmented three dimensional reality. In this paper we describe a completely new concept for alignment with abstaining from direct rigid or elastic matching of ultrasound to CT/MRI. Instead of placing those images in direct relationship, our approach involves a simulation of ultrasound wave behavior in order to predict B-mode images.

Computer Simulation↗