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Biomedical subjects

Klaus Radermacher

Publications and source records attributed to Klaus Radermacher.

6 recordsLinked to original sources
PubMed2006

A software framework for the development of Web-based medical education using learning object classes.

A software framework for the development of Web-based medical education is proposed. The objective is to optimize the development process by introducing Learning Objects (LO) and Learning Object Classes (LO Classes) so that the content preparation can be separated from the educational issues, ergonomic design, and technical realization. Based on the concept of case-based, problem-oriented education, different learning scenarios were analysed and then modelled as different LOs. These LOs can be further abstracted in several reusable LO Classes that represent certain patterns of content structure, pedagogical concept, and user interface. With the help of LO input templates, the educational material can be prepared by the authors in the authoring process easily and appropriately. An LO content management system was developed to store and maintain different LOs and to generate the Web-presentation of LOs adaptively and dynamically in the tutoring process. This software framework has been applied to the exemplary development of an interactive course in orthopaedics. The LOs and LO Classes also help to maintain consistency of the course representation to users. As a result, more efficiency in the development phase and good usability and quality of the end products can be achieved.

Education, Medical↗
PubMed2005

Fluoroscopy-based 3-D reconstruction of femoral bone cement: a new approach for revision total hip replacement.

In revision total hip replacement the removal of the distal femoral bone cement can be a time consuming and risky operation due to the difficulty in determining the three-dimensional (3-D) boundary of the cement. We present a new approach to reconstruct the bone cement volume by using just a small number of calibrated multiplanar X-ray images. The modular system design allows the surgeon to react intraoperatively to problems arising during the individual situation. When encountering problems during conventional cement removal, the system can be used on demand to acquire a few calibrated X-ray images. After a semi-automatic segmentation and 3-D reconstruction of the cement with a deformable model, the system guides the surgeon through a free-hand navigated or robot-assisted cement removal. The experimental evaluation using plastic test implants cemented into anatomic specimen of human femoral bone has shown the potential of this method with a maximal error of 1.2 mm (0.5 mm RMS) for the distal cement based on just 4-5 multiplanar X-ray images. A first test of the complete system, comparing the 3-D-reconstruction with a computed tompgraphy data set, confirmed these results with a mean error about 1 mm.

Arthroplasty, Replacement, Hip↗
PubMed2003

Concept and development of an orthotropic FE model of the proximal femur.

PURPOSE: In contrast to many isotropic finite-element (FE) models of the femur in literature, it was the object of our study to develop an orthotropic FE "model femur" to realistically simulate three-dimensional bone remodelling. METHODS: The three-dimensional geometry of the proximal femur was reconstructed by CT scans of a pair of cadaveric femurs at equal distances of 2mm. These three-dimensional CT models were implemented into an FE simulation tool. Well-known "density-determined" bony material properties (Young's modulus; Poisson's ratio; ultimate strength in pressure, tension and torsion; shear modulus) were assigned to each FE of the same "CT-density-characterized" volumetric group. In order to fix the principal directions of stiffness in FE areas with the same "density characterization", the cadaveric femurs were cut in 2mm slices in frontal (left femur) and sagittal plane (right femur). Each femoral slice was scanned into a computer-based image processing system. On these images, the principal directions of stiffness of cancellous and cortical bone were determined manually using the orientation of the trabecular structures and the Haversian system. Finally, these geometric data were matched with the "CT-density characterized" three-dimensional femur model. In addition, the time and density-dependent adaptive behaviour of bone remodelling was taken into account by implementation of Carter's criterion. RESULTS: In the constructed "model femur", each FE is characterized by the principal directions of the stiffness and the "CT-density-determined" material properties of cortical and cancellous bone. Thus, on the basis of anatomic data a three-dimensional FE simulation reference model of the proximal femur was realized considering orthotropic conditions of bone behaviour. CONCLUSIONS: With the orthotropic "model femur", the fundamental basis has been formed to realize realistic simulations of the dynamical processes of bone remodelling under different loading conditions or operative procedures (osteotomies, total hip replacements, etc).

Absorptiometry, Photon↗
PubMed2002

[Examining the accuracy of mechanical stiffness of the C-arm in navigation procedures].

During x-ray based navigation a number of errors causes distortions in the output image. These errors lead to a fail position of the surgical instrument relative to the patients anatomy. To minimize these influences and to develop dewarping techniques an exact error source identification is necessary. This paper examines the mechanical shift of the x-ray source relative to the image intensifier. Therefore three measurement methods will be used: an optical tracking system, a x-ray opaque probe and the integrated laser cross of the C-arm. The results of this examination show a notable shift of the C-arm geometry. However, no hysteresis effects could be found.

Algorithms↗
PubMedDate not supplied

Computer-assisted optimization of correction osteotomies on lower extremities.

Automated methods are presented for the planning of correction osteotomies and osteosynthesis on lower extremities. Intraoperative calibrated X-ray images and kinematic measurements using optical tracking systems are the basis for the identification of the individual anatomy of the patient. The correction input of the surgeon, together with optimization algorithms, allows the calculation of the position and orientation of the osteotomies and the repositioning of the bone fragments. A navigation module supports the surgeon during the execution of osteotomies and repositioning, as well as osteosynthesis. So far, the approach has been evaluated in laboratory trials and ex vivo tests.

Cadaver↗