Mr. Nico Becherer Profile

Nico Becherer

at Univ Mannheim

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Proceedings Article | 22 March 2007 Paper

Interactive physical simulation of catheter motion within mayor vessel structures and cavities for ASD/VSD treatment

Nico Becherer, Jürgen Hesser, Ulrike Kornmesser, Dietmar Schranz, Reinhard Männer

Proceedings Volume 6509, 65090U (2007) https://doi.org/10.1117/12.708354

KEYWORDS: Device simulation, Computer simulations, Instrument modeling, 3D modeling, Tissues, Motion models, Virtual reality, Systems modeling, Heart, Modeling

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Simulation systems are becoming increasingly essential in medical education. Hereby, capturing the physical behaviour of the real world requires a sophisticated modelling of instruments within the virtual environment. Most models currently used are not capable of user interactive simulations due to the computation of the complex underlying analytical equations. Alternatives are often based on simplifying mass-spring systems, being able to deliver high update rates that come at the cost of less realistic motion. In addition, most techniques are limited to narrow and tubular vessel structures or restrict shape alterations to two degrees of freedom, not allowing instrument deformations like torsion. In contrast, our approach combines high update rates with highly realistic motion and can in addition be used with respect to arbitrary structures like vessels or cavities (e.g. atrium, ventricle) without limiting the degrees of freedom. Based on energy minimization, bending energies and vessel structures are considered as linear elastic elements; energies are evaluated at regularly spaced points on the instrument, while the distance of the points is fixed, i.e. we simulate an articulated structure of joints with fixed connections between them. Arbitrary tissue structures are modeled through adaptive distance fields and are connected by nodes via an undirected graph system. The instrument points are linked to nodes by a system of rules. Energy minimization uses a Quasi Newton method without preconditioning and, hereby, gradients are estimated using a combination of analytical and numerical terms. Results show a high quality in motion simulation when compared to a phantom model. The approach is also robust and fast. Simulating an instrument with 100 joints runs at 100 Hz on a 3 GHz PC.

Proceedings Article | 2 February 2006 Paper

On soft clipping of Zernike moments for deblurring and enhancement of optical point spread functions

Nico Becherer, Hanna Jödicke, Gregor Schlosser, Jürgen Hesser, Frank Zeilfelder, Reinhard Männer

Proceedings Volume 6065, 60650C (2006) https://doi.org/10.1117/12.642272

KEYWORDS: Point spread functions, Zernike polynomials, Data modeling, Denoising, Visualization, Volume rendering, Image segmentation, Microscopes, Wavefronts, Wavelets

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Blur and noise originating from the physical imaging processes degrade the microscope data. Accurate deblurring techniques require, however, an accurate estimation of the underlying point-spread function (PSF). A good representation of PSFs can be achieved by Zernike Polynomials since they offer a compact representation where low-order coefficients represent typical aberrations of optical wavefronts while noise is represented in higher order coefficients. A quantitative description of the noise distribution (Gaussian) over the Zernike moments of various orders is given which is the basis for the new soft clipping approach for denoising of PSFs. Instead of discarding moments beyond a certain order, those Zernike moments that are more sensitive to noise are dampened according to the measured distribution and the present noise model. Further, a new scheme to combine experimental and theoretical PSFs in Zernike space is presented. According to our experimental reconstructions, using the new improved PSF the correlation between reconstructed and original volume is raised by 15% on average cases and up to 85% in the case of thin fibre structures, compared to reconstructions where a non improved PSF was used. Finally, we demonstrate the advantages of our approach on 3D images of confocal microscopes by generating visually improved volumes. Additionally, we are presenting a method to render the reconstructed results using a new volume rendering method that is almost artifact-free. The new approach is based on a Shear-Warp technique, wavelet data encoding techniques and a recent approach to approximate the gray value distribution by a Super spline model.

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