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Biomedical subjects

H Wörn

Publications and source records attributed to H Wörn.

16 recordsLinked to original sources
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↗
PubMed2000

3D norm data: the first step towards semiautomatic virtual craniofacial surgery.

When planning craniofacial surgical interventions, the ideal appearance of the patient is very important. The final appearance should be as close as possible to that which the patient would have if he/she were without defects. Our first step towards achieving this is to build a database containing sets of three-dimensional CT images that allows for comparison of the shape of a patient with defects to the typical shape of an age- and sex-matched "average" person without defects. We started to collect CT data from patients without pathologies and, in co-operation with two radiology institutes (in Mannheim and Heidelberg), over 100 CT data sets have now been collected and classified according to age and sex. It is necessary to choose an appropriate statistical method to calculate the norm data from the different data sets. Based on the statistical method, an age- and sex-matched "average" model of the anatomy will be created.

Adolescent↗
PubMed2000

[Computer-assisted oral, maxillary and facial surgery].

BACKGROUND: Methods from the area of virtual reality are used in oral and maxillofacial surgery for the planning and three-dimensional individual simulation of surgeries. SIMULATION: In order to simulate complex surgeries with the aid of a computer, the diagnostic image data and especially various imaging modalities (CT, MRT, US) must be arranged in relation to each other, thus enabling rapid switching between the various modalities as well as the viewing of mixed images. Segmenting techniques for the reconstruction of three-dimensional representations of soft-tissue and osseous areas are required. We must develop ergonomic and intuitively useable interaction methods for the surgeon, thus allowing for precise and fast entry of the planned surgical intervention in the planning and simulation phase. SURGERY: During the surgical phase, instrument navigation tools offer the surgeon interactive support through operation guidance and control of potential dangers. This feature is already available today. Future intraoperative assistance will take the form of such passive tools for the support of intraoperative orientation as well as so-called tracking systems (semi-active systems) which accompany and support the surgeons' work. The final form are robots which execute specific steps completely autonomously. DISCUSSION: The techniques of virtual reality keep gaining in importance for medical applications. 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 the surgeon's routine work.

Computer Simulation↗
PubMed2000

Intuitive operation planning based on force feedback.

In the craniofacial surgery image-slices obtained from tomographies are used for planning and simulation of surgical interventions. Using these image-slices three-dimensional geometric models can be reconstructed, representing bones and soft tissue. However, for planning complex surgical interventions simulation methods are needed additionally to the pure visualisation. Exemplary, planning a Frontal Orbital Advancement (FOA) operation the cutting trajectories, their depth and orientation in each point, the drill hole, the position, orientation and deformation of bones, etc. are the point of interest. Especially for intraoperative execution supported by navigation systems or robots. In order to be able to plan such complex interventions with the help of computers, geometrical and haptical models must be generated from the image-slices. On the one hand these models represent the anatomical structures exactly, on the other hand they are needed for the simulation of the different activities, which have to be performed during the surgical intervention like drilling, milling, deforming, positioning, etc. Beside the geometrical and haptical models methods for interactions must be supplied to the physician for an accurate and intuitive planning of the surgical intervention. We developed such an operation planning system which is already used in clinical practise in Heidelberg.

Artificial Intelligence↗
PubMed2000

A pattern catalogue of surgical interventions for computer-supported operation planning.

In this paper we present a new operation planning system which was evaluated in the clinic for Cranio-Maxillo-Facial-Surgery at the University of Heidelberg. In opposite to commercial systems our goal was, that the system considers the complete surgical intervention and not only a single procedure of it. A second goal was, that the system enables managing of complex operations, independent of which way the intervention will be intraoperatively performed (without technical support, with passive navigation support or active support by robots). Our system supports the surgeon during the preoperative planning as well as during the intraoperative execution phase. Therefore we developed a course model by which the managing of surgical interventions is possible. The focus of this paper is on this course model. At first we introduce instruction graphs and describe the structure of each activity observing its attributes and their context. Additionally, various surgical scopes will be presented which enable the surgeon to select one view among different ones of the individual operation procedures in accordance to medical and technical knowledge as well as in accordance to different degrees of abstraction. At last we demonstrate operation patterns, used as expert knowledge.

Computer Simulation↗
PubMed2000

Clinical evaluation of a highly accurate algorithm for CT bone contour segmentation.

Planning, visualisation and intraoperative navigation in a robot assisted environment for craniofacial surgery require highly accurate methods for the segmentation of bone structures in CT data. Clinical systems are still based on time consuming interactive methods like the seed-point segmentation. Faster methods with no need for interactivity lacks in precision. In the following we will present an automatic and highly accurate algorithm for the segmentation of bone contours in CT data. It is based on an algorithm for the automatic calculation of a grey-value tissue relation model for CT and MRI data.

Algorithms↗
PubMed2000

A real-time CORBA based system architecture for robot assisted craniofacial surgery.

We present the concept of a system architecture for the computer aided craniofacial surgery. The architecture is based on CORBA, an industrial standard specification for the development of distributed applications. Our concept includes a fundamental behaviour oriented communication model and some fundamental software safety considerations. We've developed a standard library for the integration of new services and devices into our system architecture. It decreases development time noticeably. We tested the performance and usability of our concept on an evaluation set up consisting of a surgery robot system, an infrared navigation system, a force-torque sensor and a visualisation software, obtaining excellent results. Future work will consist in the integration of further devices and the extension of our safety concept. An accurate clinical evaluation will take place continuously.

Computer Graphics↗
PubMed2000

Texture mapping based visualisation methods for the manipulation of CT data: interaction and ergonomics.

The manipulation of large CT datasets needs fast visualisation methods for a comfortable user interaction. Modern visualisation techniques make use texture hardware in graphics workstations extensively. In the following we will present an interactive tool for the positioning of anatomical landmarks in CT datasets of non-pathological children. The tool includes a fast visualisation of CT cross sections based on a texture mapping technique and an interactive three-dimensional view of the segmented CT dataset.

Cephalometry↗
PubMed1989

The diagnosis, therapy and prognosis of diffuse malignant mesothelioma.

Between 1969 and 1985, 245 patients with diffuse malignant mesothelioma were treated (157 male, 88 female). The average age was 55.8 years and the sex ratio was 1.8:1 in favour of males. The right side was more frequently affected than the left (56.7% vs. 43.3%). A pleural effusion and dyspnoea were the presenting signs and symptoms in 83.7% of the patients and unilateral chest pain in 64.2%. Noninvasive diagnostic procedures included a chest X-ray and computed tomography of the thorax. Pleural effusion and pleural thickening were detected most frequently. Malignant cells were identified by pleural fluid cytology in 45.3% and by needle biopsy of the pleura in 42.7% of the patients. Forty-five patients were treated conservatively and 200 patients underwent operation: diagnostic thoracotomy (78); partial pleurectomy (72); total pleurectomy (46); extended pleuropneumonectomy (2); partial removal of the diaphragm (1) and total pleurectomy and upper lobectomy (1). The perioperative mortality was 6%. The conservative and postoperative treatment depended on the patients' symptoms and included radiotherapy and chemotherapy alone or in combination. The mean survival time of the 222 non-survivors was 9.2 months. After 1 year, 36% of the patients were still alive, after 2 years, 10.8% and the 5-year survival was 4.1%. The median survival time in patients treated non-operatively was 6 months--a little over half that of the patients treated surgically (10.1 months).

Adult↗
PubMed1988

[Surgery of lung metastases].

Between 1975 and 1985 76 patients underwent surgery of pulmonary metastases in our hospital. Most often the primary tumor was located in carcinomas of the colon and rectum (19 patients), followed by carcinomas of the kidney (14 patients), the breast (13 patients) and the skin (malignant melanoma: 9 patients). Conditions for pulmonary metastasectomy are radical removal of the primary tumor, metastases located only in the lung, resectability of the metastases and low operative risk. Three years after pulmonary metastasectomy 35% of the patients were still alive, the 5 year survival rate was 18%. The median survival time was 22 months. The prognosis in patients with pulmonary metastases is largely dependant upon tumor type. Pulmonary metastases of breast carcinomas and carcinomas of colon and rectum can be treated best by surgical intervention. (5 year survival rate: 35% and 33%). Hypernephroma and malignant melanoma have a 5 year survival rate of 0% and 23%. Other prognostic factors are the number of pulmonary metastases and the disease-free interval between surgery of the primary tumor and pulmonary metastasectomy. Furthermore resection techniques are of prognostic importance. Lobectomy and segmental resection showed a better 5 year survival rate than pneumonectomy (21%, 24%, 0%). Median sternotomy is recommended as standard access for pulmonary metastasectomy. Surgery of pulmonary metastases is encouraging.

Female↗