Klaus Erhard
Philips
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Publication
Featured researches published by Klaus Erhard.
Inverse Problems | 2008
Fabrice Delbary; Klaus Erhard; Rainer Kress; Roland Potthast; J. Schulz
The detection of metallic objects is an important application in state-of-the-art security technology. In particular, for humanitarian mine detection the task is to detect objects that are buried in soil. Usually hand-held mine detectors create an electromagnetic pulse via a current in some wire loop and evaluate the scattered electromagnetic field via induction in a receiver loop that is moved together with the sender loop. This receiver signal can then be employed in identifying the location and the shape of metallic objects. Here, we model the full electromagnetic scattering problem in a two-layered medium from a perfectly conducting obstacle using boundary integral equations. The scattered field is modeled via a boundary layer approach and for its kernel the Greens matrix for the two-layered medium is constructed. We establish uniqueness and existence for the solution of the corresponding boundary integral equation. In the second part of the paper, we employ a direct search method for parameter estimation to find the location and size of some simple metallic objects from measurements of the induced voltage for a number of sender–receiver-loop positions.
Proceedings of SPIE | 2009
Eberhard Sebastian Hansis; Hermann Schomberg; Klaus Erhard; Olaf Dössel; Michael Grass
The tomographic reconstruction of the beating heart requires dedicated methods. One possibility is gated reconstruction, where only data corresponding to a certain motion state are incorporated. Another one is motioncompensated reconstruction with a pre-computed motion vector field, which requires a preceding estimation of the motion. Here, results of a new approach are presented: simultaneous reconstruction of a three-dimensional object and its motion over time, yielding a fully four-dimensional representation. The object motion is modeled by a time-dependent elastic transformation. The reconstruction is carried out with an iterative gradient-descent algorithm which simultaneously optimizes the three-dimensional image and the motion parameters. The method was tested on a simulated rotational X-ray acquisition of a dynamic coronary artery phantom, acquired on a C-arm system with a slowly rotating C-arm. Accurate reconstruction of both absorption coefficient and motion could be achieved. First results from experiments on clinical rotational X-ray coronary angiography data are shown. The resulting reconstructions enable the analysis of both static properties, such as vessel geometry and cross-sectional areas, and dynamic properties, like magnitude, speed, and synchrony of motion during the cardiac cycle.
SIAM Journal on Scientific Computing | 2006
Klaus Erhard; Roland Potthast
The goal of this work is the numerical realization of the probe method suggested by Ikehata for the detection of an obstacle D in inverse scattering. The main idea of the method is to use probes in the form of point source
Investigative Radiology | 2016
Klaus Erhard; Fleur Kilburn-Toppin; Paula Willsher; Elin Moa; Erik Fredenberg; Nataly Wieberneit; Thomas Buelow; Matthew G. Wallis
\Phi(\cdot,z)
Proceedings of SPIE | 2011
Klaus Erhard; Michael Grass; Tim Nielsen
with source point z to define an indicator function
Medical Physics | 2017
Henrik Johansson; Miriam von Tiedemann; Klaus Erhard; Harald S. Heese; H Ding; Sabee Molloi; Erik Fredenberg
\hat{I}(z)
Proceedings of SPIE | 2012
Klaus Erhard; Michael Grass; Sebastian Hitziger; Armin Iske; Tim Nielsen
which can be reconstructed from Cauchy data or far field data. The indicator function
international conference on breast imaging | 2012
André Gooßen; Harald S. Heese; Klaus Erhard; Björn Norell
\hat{I}(z)
ieee nuclear science symposium | 2008
Klaus Erhard
can be shown to blow off when the source point z tends to the boundary
international conference on breast imaging | 2012
André Gooßen; Harald S. Heese; Klaus Erhard
\partial D