Studying the complex thorax breathing motion is an important research topic for medical (e.g. fus... more Studying the complex thorax breathing motion is an important research topic for medical (e.g. fusion of function and anatomy, radiotherapy planning) and engineering (reduction of motion artifacts) questions. In this paper we present first results on investigating the 4D motion of segmented lung surfaces from CT scans at several different breathing states. For this registra-tion task we extend the shape context approach for shape matching by Belongie et al. [2] from 2D shapes to 3D surfaces and apply it to segmented lung data. Resulting point correspondences can be used e.g. for non-rigid thin-plate-spline registration. We describe our experiments on phantom and real thorax data and show our promising results.
In the last years the need for forensic age estimations in living adolescents increased with migr... more In the last years the need for forensic age estimations in living adolescents increased with migration, particularly from countries where birth dates are not reliably documented. To date, the gold standard of dental age estimation is to evaluate the mineralization and eruption stages of the third molars using an orthopantomogram (OPG). Based on published reference values, the stages are converted in an age estimate in years. However, the use of ionizing radiation without medical indication is ethically controversial and not permitted in many countries. Thus, the aim of this study was to investigate if dental MRI can be used for the assessment of dental age with equally good results as when using an OPG. Methods: 27 healthy volunteers (19♀, 8♂, age range 13.56-23.11y, median 18.92) with at least two present third molars underwent an MRI scan of the jaw within 14 days after a clinically indicated OPG. The examinations were performed on a 3T Magnetom scanner (TimTrio, Siemens AG, Erlan...
We present an optical flow deformable registration method which is based on robust measures for d... more We present an optical flow deformable registration method which is based on robust measures for data and regularization terms. We show two specific implementations of the method, where one penalizes gradients in the displacement field in an isotropic fashion and the other one regularizes by weighting the penalization according to the image gradients anisotropically. Our data term consists of the L 1 -norm of the standard optical flow constraint. We show a numerical algorithm that solves the two proposed models in a primal-dual optimization setup. Our algorithm works in a multi-resolution manner and it is applied to the 20 data sets of the EMPIRE10 registration challenge. Our results show room for improvement. Our rather simple model does not penalize non-diffeomorphic transformations, which leads to bad results on one of the evaluation measures, and it seems unsuited for large deformations cases. However, our algorithm is able to perform registrations of data set sizes around 400 3 ...
Pulmonary hypertension (PH) is a chronic disorder of the pulmonary circulation, marked by an elev... more Pulmonary hypertension (PH) is a chronic disorder of the pulmonary circulation, marked by an elevated vascular resistance and pressure. Our objective is to find an automatic, non-invasive method for estimating the pulmonary pressure based on lung vessels from contrast enhanced CT images. We present a pulmonary vessel extraction algorithm which is fast, fully automatic and robust. It uses a coarse airway tree segmentation and a left and right lung labeled volume to restrict the response of an offset medialness vessel enhancement filter. On a data set of 24 patients, we show that quantitative indices derived from the vascular tree are applicable to distinguish patients with and without PH.
2013 IEEE International Conference on Computer Vision Workshops, 2013
ABSTRACT Integral image data structures are very useful in computer vision applications that invo... more ABSTRACT Integral image data structures are very useful in computer vision applications that involve machine learning approaches based on ensembles of weak learners. The weak learners often are simply several regional sums of intensities subtracted from each other. In this work we present a memory efficient integral volume data structure, that allows reduction of required RAM storage size in such a supervised learning framework using 3D training data. We evaluate our proposed data structure in terms of the tradeoff between computational effort and storage, and show an application for 3D object detection of liver CT data.
2014 IEEE 11th International Symposium on Biomedical Imaging (ISBI), 2014
ABSTRACT The determination of an individual’s legal majority age is becoming increasingly importa... more ABSTRACT The determination of an individual’s legal majority age is becoming increasingly important in forensic practice. Established age estimation methods are based on 2D X-rays, but suffer from problems due to projective imaging and exposure to ionizing radiation, which, without proper medical or criminal indication, is ethically questionable and legally prohibited in many countries. We propose an automatic 3D method for the determination of legal maturity from MR images based on the ossification of the radius bone. Age estimation is performed by a linear regression model of the epiphyseal gap volume over the known ground truth age of training data. Results are comparable with the established Greulich/Pyle (GP) and Tanner/Whitehouse (TW) methods, but do not involve harmful radiation.
Nonlinear image registration is an initial step for a large number of medical image analysis appl... more Nonlinear image registration is an initial step for a large number of medical image analysis applications. Optical flow based intensity registration is often used for dealing with intra-modality applications involving motion differences. In this work we present an energy functional which uses a novel, second-order regularization prior of the displacement field. Compared to other methods our scheme is robust to non-Gaussian noise and does not penalize locally affine deformation fields in homogeneous areas. We propose an efficient and stable numerical scheme to find the minimizer of the presented energy. We implemented our algorithm using modern consumer graphics processing units and thereby increased the execution performance dramatically. We further show experimental evaluations on clinical CT thorax data sets at different breathing states and on dynamic 4D CT cardiac data sets.
Studying the complex thorax breathing motion is an important research topic for medical (e.g. fus... more Studying the complex thorax breathing motion is an important research topic for medical (e.g. fusion of function and anatomy, radiotherapy planning) and engineering (reduction of motion artifacts) questions. In this paper we present first results on investigating the 4D motion of segmented lung surfaces from CT scans at several different breathing states. For this registra-tion task we extend the shape context approach for shape matching by Belongie et al. [2] from 2D shapes to 3D surfaces and apply it to segmented lung data. Resulting point correspondences can be used e.g. for non-rigid thin-plate-spline registration. We describe our experiments on phantom and real thorax data and show our promising results.
In the last years the need for forensic age estimations in living adolescents increased with migr... more In the last years the need for forensic age estimations in living adolescents increased with migration, particularly from countries where birth dates are not reliably documented. To date, the gold standard of dental age estimation is to evaluate the mineralization and eruption stages of the third molars using an orthopantomogram (OPG). Based on published reference values, the stages are converted in an age estimate in years. However, the use of ionizing radiation without medical indication is ethically controversial and not permitted in many countries. Thus, the aim of this study was to investigate if dental MRI can be used for the assessment of dental age with equally good results as when using an OPG. Methods: 27 healthy volunteers (19♀, 8♂, age range 13.56-23.11y, median 18.92) with at least two present third molars underwent an MRI scan of the jaw within 14 days after a clinically indicated OPG. The examinations were performed on a 3T Magnetom scanner (TimTrio, Siemens AG, Erlan...
We present an optical flow deformable registration method which is based on robust measures for d... more We present an optical flow deformable registration method which is based on robust measures for data and regularization terms. We show two specific implementations of the method, where one penalizes gradients in the displacement field in an isotropic fashion and the other one regularizes by weighting the penalization according to the image gradients anisotropically. Our data term consists of the L 1 -norm of the standard optical flow constraint. We show a numerical algorithm that solves the two proposed models in a primal-dual optimization setup. Our algorithm works in a multi-resolution manner and it is applied to the 20 data sets of the EMPIRE10 registration challenge. Our results show room for improvement. Our rather simple model does not penalize non-diffeomorphic transformations, which leads to bad results on one of the evaluation measures, and it seems unsuited for large deformations cases. However, our algorithm is able to perform registrations of data set sizes around 400 3 ...
Pulmonary hypertension (PH) is a chronic disorder of the pulmonary circulation, marked by an elev... more Pulmonary hypertension (PH) is a chronic disorder of the pulmonary circulation, marked by an elevated vascular resistance and pressure. Our objective is to find an automatic, non-invasive method for estimating the pulmonary pressure based on lung vessels from contrast enhanced CT images. We present a pulmonary vessel extraction algorithm which is fast, fully automatic and robust. It uses a coarse airway tree segmentation and a left and right lung labeled volume to restrict the response of an offset medialness vessel enhancement filter. On a data set of 24 patients, we show that quantitative indices derived from the vascular tree are applicable to distinguish patients with and without PH.
2013 IEEE International Conference on Computer Vision Workshops, 2013
ABSTRACT Integral image data structures are very useful in computer vision applications that invo... more ABSTRACT Integral image data structures are very useful in computer vision applications that involve machine learning approaches based on ensembles of weak learners. The weak learners often are simply several regional sums of intensities subtracted from each other. In this work we present a memory efficient integral volume data structure, that allows reduction of required RAM storage size in such a supervised learning framework using 3D training data. We evaluate our proposed data structure in terms of the tradeoff between computational effort and storage, and show an application for 3D object detection of liver CT data.
2014 IEEE 11th International Symposium on Biomedical Imaging (ISBI), 2014
ABSTRACT The determination of an individual’s legal majority age is becoming increasingly importa... more ABSTRACT The determination of an individual’s legal majority age is becoming increasingly important in forensic practice. Established age estimation methods are based on 2D X-rays, but suffer from problems due to projective imaging and exposure to ionizing radiation, which, without proper medical or criminal indication, is ethically questionable and legally prohibited in many countries. We propose an automatic 3D method for the determination of legal maturity from MR images based on the ossification of the radius bone. Age estimation is performed by a linear regression model of the epiphyseal gap volume over the known ground truth age of training data. Results are comparable with the established Greulich/Pyle (GP) and Tanner/Whitehouse (TW) methods, but do not involve harmful radiation.
Nonlinear image registration is an initial step for a large number of medical image analysis appl... more Nonlinear image registration is an initial step for a large number of medical image analysis applications. Optical flow based intensity registration is often used for dealing with intra-modality applications involving motion differences. In this work we present an energy functional which uses a novel, second-order regularization prior of the displacement field. Compared to other methods our scheme is robust to non-Gaussian noise and does not penalize locally affine deformation fields in homogeneous areas. We propose an efficient and stable numerical scheme to find the minimizer of the presented energy. We implemented our algorithm using modern consumer graphics processing units and thereby increased the execution performance dramatically. We further show experimental evaluations on clinical CT thorax data sets at different breathing states and on dynamic 4D CT cardiac data sets.
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Papers by Martin Urschler