Til Aach

Universität zu Lübeck, Lübeck Hansestadt, Schleswig-Holstein, Germany

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Publications (325)201.45 Total impact

  • D. Toth · T. Aach · V. Metzler
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    ABSTRACT: The detection of moving objects in image sequences acquired by a static camera is a demanding task in the presence of noise. With fast illumination variations detection becomes even more difficult since simple motion detection will always be subject to illumination artifacts. To solve these problems, we propose a Bayesian spatio-temporal motion detection algorithm combined with homomorphic filtering. The image sequence is modelled as being generated by an illumination and a reflectance component that are approximately separated by the filter. Detection of changes in the reflectance component is directly related to scene changes, i.e. object motion. Experimental results show that the presented method is considerably less sensitive to noise and time-varying scene illumination.
    No preview · Article · Mar 2015
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    ABSTRACT: The organization of the keratin intermediate filament cytoskeleton is closely linked to epithelial function. To study keratin network plasticity and its regulation at different levels, tools are needed to localize and measure local network dynamics. In this paper, we present image analysis methods designed to determine the speed and direction of keratin filament motion and to identify locations of keratin filament polymerization and depolymerization at subcellular resolution. Using these methods, we have analyzed time-lapse fluorescence recordings of fluorescent keratin 13 in human vulva carcinoma-derived A431 cells. The fluorescent keratins integrated into the endogenous keratin cytoskeleton, and thereby served as reliable markers of keratin dynamics. We found that increased times after seeding correlated with down-regulation of inward-directed keratin filament movement. Bulk flow analyses further revealed that keratin filament polymerization in the cell periphery and keratin depolymerization in the more central cytoplasm were both reduced. Treating these cells and other human keratinocyte-derived cells with EGF reversed all these processes within a few minutes, coinciding with increased keratin phosphorylation. These results highlight the value of the newly developed tools for identifying modulators of keratin filament network dynamics and characterizing their mode of action, which, in turn, contributes to understanding the close link between keratin filament network plasticity and epithelial physiology.
    Full-text · Article · Jun 2013 · Proceedings of the National Academy of Sciences

  • No preview · Article · Jan 2013
  • Til Aach · Hartmut Fuhr
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    ABSTRACT: The linear periodically shift variant (LPSV) properties within critically sampled multirate FIR filter banks are generally analysed using deterministic signals. Periodic shift variance is, however, closely related to cyclostationarities introduced by the LPSV system into originally wide sense stationary (WSS) random signals passing through the system. We provide first a unified framework to measure both shift variance of the LPSV system and the amount of cyclostationarity it generates. In this respect, the key concept is the covariance operator associated to a random variable. Cyclostationarity of the variable translates to LPSV properties of the operators, and vice versa. We study several related concepts for the quantification of shift variance in operators and their interpretation in the stochastic setting. We then introduce a new concept called expected shift variance. Fourier-analytic expressions for the various measures are given, and subsequently used to derive explicit formulae for the case of critically sampled two-channel filter banks, as well as sharp upper bounds for unitary two-channel filter banks. Numerical evaluations of the measures show that they provide largely consistent rankings between various critically sampled two-channel filter banks.
    No preview · Article · Oct 2012 · IEEE Transactions on Signal Processing
  • P. Faltin · K. Chaisaowong · T. Aach
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    ABSTRACT: Registration of an image non-rigidly to another one causes deformations, which generally do not preserve the initial volume. Volume preservation is however indispensable for observing tumors in medical images. This paper presents the correction of B-spline based registration to preserve the volume in observed regions. In contrast to other approaches, our solution is not obtained through energy minimization, but by calculating the correction parameters for the deformation directly. Especially for high resolution image data this strategy is very efficient in terms of computational expenses. We derive a closed form solution to optimize the registration with respect to the compression at a single point and then extend the problem to multiple points. Finally we prove also that the correction terms do not have any significant influence on the registration quality.
    No preview · Conference Paper · Sep 2012
  • Qi Sun · Alexandra Groth · Til Aach
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    ABSTRACT: Recently, image-based computational fluid dynamic (CFD) simulations have been proposed to investigate the local hemodynamics inside human cerebral aneurysms. It was suggested that the knowledge of the computed three-dimensional flow fields can be used to assist clinical risk assessment and treatment decision making. Therefore, it was desired to know the reliability of CFD for cerebral blood flow simulation, and be able to provide clinical feedback. However, the validations were not yet comprehensive as they lack either patient-specific boundary conditions (BCs) required for CFD simulations or quantitative comparison methods. In this study, based on a recently proposed in-vitro quantitative CFD evaluation approach via virtual angiography, the CFD evaluation was extended from phantom to patient studies. In contrast to previous work, patient-specific blood flow rates obtained by transcranial color coded Doppler ultrasound measurements were used to impose CFD BCs. Virtual angiograms (VAs) were constructed which resemble clinically acquired angiograms (AAs). Quantitative measures were defined to thoroughly evaluate the correspondence of the detailed flow features between the AAs and the VAs, and thus, the reliability of CFD simulations. The proposed simulation pipeline provided a comprehensive validation method of CFD simulation for reproducing cerebral blood flow, with a focus on the aneurysm region. Six patient cases were tested and close similarities were found in terms of spatial and temporal variations of contrast agent (CA) distribution between AAs and VAs. For patient #1 to #5, discrepancies of less than 11% were found for the relative root mean square errors in time intensity curve comparisons from characteristic vasculature positions. For patient #6, where the CA concentration curve at vessel inlet cannot be directly extracted from the AAs and given as a BC, deviations about 20% were found. As a conclusion, the reliability of the CFD simulations was well confirmed. Besides, it was shown that the accuracy of CFD simulations was closely related to the input BCs.
    No preview · Article · Feb 2012 · Medical Physics
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    ABSTRACT: Early detection of cervical cancer can be achieved through visual analysis of cell anomalies. The established PAP smear achieves a sensitivity of 50-90%, most false negative results are caused by mistakes in the preparation of the specimen or reader variability in the subjective, visual investigation. Since cervical cancer is caused by human papillomavirus (HPV), the detection of HPV-infected cells opens new perspectives for screening of precancerous abnormalities. Immunocytochemical preparation marks HPV-positive cells in brush smears of the cervix with high sensitivity and specificity. The goal of this work is the automated detection of all marker-positive cells in microscopic images of a sample slide stained with an immunocytochemical marker. A color separation technique is used to estimate the concentrations of the immunocytochemical marker stain as well as of the counterstain used to color the nuclei. Segmentation methods based on Otsu's threshold selection method and Mean Shift are adapted to the task of segmenting marker-positive cells and their nuclei. The best detection performance of single marker-positive cells was achieved with the adapted thresholding method with a sensitivity of 95.9%. The contours differed by a modified Hausdorff Distance (MHD) of 2.8 μm. Nuclei of single marker positive cells were detected with a sensitivity of 95.9% and MHD = 1.02 μm.
    No preview · Article · Feb 2012 · Proceedings of SPIE - The International Society for Optical Engineering
  • Dorian Schneider · Til Aach
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    ABSTRACT: We develop a methodology for automatic in-line flaw detection in industrial woven fabrics. Where state of the art detection algorithms apply texture analysis methods to operate on low-resolved (~200 ppi) image data, we describe here a process flow to segment single yarns in high-resolved (~1000 ppi) textile images. Four yarn shape features are extracted, allowing a precise detection and measurement of defects. The degree of precision reached allows a classification of detected defects according to their nature, providing an innovation in the field of automatic fabric flaw detection. The design has been carried out to meet real time requirements and face adverse conditions caused by loom vibrations and dirt. The entire process flow is discussed followed by an evaluation using a database with real-life industrial fabric images. This work pertains to the construction of an on-loom defect detection system to be used in manufacturing practice.
    No preview · Article · Feb 2012 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Given two CT thorax images from the same patient taken at two different points in time, a detailed follow-up assessment of pleural thickenings and their growth requires a registration of the regarded image regions. While the spatio-temporal matching of thickenings could be achieved by a rigid registration, the direct visual comparison or the combination of thickening segmentations from different points in time require a more precise registration. We present a new method which provides a non-rigid registration of the 3D image data in the region close to the lung surface, where pleural thickenings are located. A B-spline based approach is used to compensate the non-rigid deformations of the lungs. The control-grid for the B-splines is determined using a non-iterative method, which requires matched feature points from the registered image pair. However, current non-rigid registration methods compensate all changes of the lung surface. This is in our case explicitly undesired for changes caused by pleural thickenings. Therefore, our approach takes the thickenings into account by choosing feature points not directly located on the lung surface. The number of feature points is reduced and only strong features are kept for a 3D block matching.
    No preview · Article · Feb 2012 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: Colon cancer is the third most commonly diagnosed type of cancer in the US. In recent years, however, early diagnosis and treatment have caused a significant rise in the five year survival rate. Preventive screening is often performed by colonoscopy (endoscopic inspection of the colon mucosa). Narrow Band Imaging (NBI) is a novel diagnostic approach highlighting blood vessel structures on polyps which are an indicator for future cancer risk. In this paper, we review our automated inter-and intra-observer independent system for the automated classification of polyps into hyperplasias and adenomas based on vessel structures to further improve the classification performance. To surpass the performance limitations we derive a novel vessel segmentation approach, extract 22 features to describe complex vessel topologies, and apply three feature selection strategies. Tests are conducted on 286 NBI images with diagnostically important and challenging polyps (10mm or smaller) taken from our representative polyp database. Evaluations are based on ground truth data determined by histopathological analysis. Feature selection by Simulated Annealing yields the best result with a prediction accuracy of 96.2% (sensitivity: 97.6%, specificity: 94.2%) using eight features. Future development aims at implementing a demonstrator platform to begin clinical trials at University Hospital Aachen.
    No preview · Conference Paper · Feb 2012
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    ABSTRACT: DNA Image Cytometry is a method for non-invasive cancer diagnosis which measures the DNA content of Feulgen-stained nuclei. DNA content is measured using a microscope system equipped with a digital camera as a densitometer and estimating the DNA content from the absorption of light when passing through the nuclei. However, a DNA Image Cytometry measurement is only valid if each nucleus is only measured once. To assist the user in preventing multiple measurements of the same nucleus, we have developed a unique digital identifier for the characterization of Feulgen-stained nuclei, the so called Nucleus Fingerprint. Only nuclei with a new fingerprint can be added to the measurement. This fingerprint is based on basic nucleus features, the contour of the nucleus and the spatial relationship to nuclei in the vicinity. Based on this characterization, a classifier for testing two nuclei for identity is presented. In a pairwise comparison of ~40000 pairs of mutually different nuclei, 99.5% were classified as different. In another 450 tests, the fingerprints of the same nucleus recorded a second time were in all cases judged identical. We therefore conclude that our Nucleus Fingerprint approach robustly prevents the repeated measurement of nuclei in DNA Image Cytometry.
    No preview · Article · Feb 2012 · Proceedings of SPIE - The International Society for Optical Engineering
  • Julie Klein · Til Aach
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    ABSTRACT: Aberrations occur in multispectral cameras featuring filter wheels because of color filters with different optical properties being present in the ray path. In order to ensure an exact compensation of these aberrations, a mathematical model of the distortions has to be developed and its parameters have to be calculated using the measured data. Such a model already exists for optical filters placed between the sensor and the lens, but not for bandpass filters placed in front of the lens. For this configuration, the rays are first distorted by the filters and then by the lens. In this paper, we derive a model for aberrations caused by filters placed in front of the lens in multispectral cameras. We compare this model with distortions obtained with simulations as well as with distortions measured during real multispectral acquisitions. In both cases, the difference between modeled and measured aberrations remains low, which corroborates the physical model. Multispectral acquisitions with filters placed between the sensor and the lens or in front of the lens are compared: the latter exhibit smaller distortions and the aberrations in both images can be compensated using the same algorithm.
    No preview · Article · Jan 2012 · Proceedings of SPIE - The International Society for Optical Engineering
  • Julie Klein · Til Aach
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    ABSTRACT: Stereo multispectral systems enable at the same time the acquisition of accurate spectral and depth information. The left and right cameras of the system can either present the same spectral sensitivities (e.g., a monochrome sensor with 7 different bandpass color filters sequentially placed in front of it for both cameras) or complementary sensitivities. The latter alternative can be accomplished by the utilization of two different filters or sets of filters for each camera of the stereo system. Even if each camera alone does not provide complete spectral information about the acquired scene, the estimation of the spectra becomes possible when both cameras are considered together. But since the reflectance spectrum of objects is a function of the wavelength, of the illumination angle and of the observation angle, the information from the left and the right cameras is generally different. This problem is already known from the RGB stereo imaging, and becomes even more relevant when it comes to multispectral stereo imaging, whose purpose is in addition an accurate color recording.In this paper, we analyze this problem experimentally by acquiring different series of stereo data and comparing them for determined regions of interest. We acquire two scenes under different lighting conditions with a standard color chart and objects whose reflectance spectra have a limited observation angle dependence. We utilize real multispectral data as well as spectra measured with a spectrophotometer to verify camera acquisition and compare them for different observation angles. We then estimate the acquired spectra using several of the possible spectral compositions, given by all the color channels available for the left and for the right camera. These estimated spectra are compared to the ground truth data and we show that the stereo system with 7 channels cameras using only 3 color channels from one camera and the 4 complementary color channels from the other camera has a good colorimetric accuracy.
    No preview · Article · Jan 2012

  • No preview · Article · Jan 2012

  • No preview · Conference Paper · Jan 2012
  • S. Gross · M. Klein · A. Behrens · T. Aach

    No preview · Article · Jan 2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: A prototype system for automatic in-line flaw detection in industrial woven fabrics is presented. Where state of the art systems operate on low-resolved (≈ 200 ppi) image data, we describe here the process flow to segment single yarns in high-resolved (≈ 1000 ppi) textile images. This work is partitioned into two parts: First, mechanics, machine integration, vibration cancelling and illumination scenarios are discussed based on the integration into a real loom. Subsequently, the software framework for high precision fabric defect detection is presented. The system is evaluated on a database of 54 industrial fabric images, achieving a detection rate of 100% with minimal false alarm rate and very high defect segmentation quality.
    No preview · Conference Paper · Jan 2012
  • Wei Li · M. Breier · T. Aach
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    ABSTRACT: Machines for automated PCB depaneling have greatly improved the industrial production efficiency of electronic products. But the preparation for automated depaneling could be very complex and time-consuming. In this paper, we propose a novel systematic solution for this problem. Using a vision-based assistant system, called ”Auto-Teaching”, all connection tabs that should be milled off panels are detected automatically. Highly accurate milling curves are generated with respect to the geometry of the corresponding tabs. Then they could be easily converted into CNC code which drive milling cutters later. Moreover, placement suggestions of supporting pins used to fix panels are obtained. All image analysis functions are implemented in C++ and optimized to meet the minimal hardware and time requirements. Thus the whole process of the preparation is simplified for users and the PCB manufactures can benefit from reduced idle running of machines and labor costs.
    No preview · Conference Paper · Jan 2012
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    ABSTRACT: Fluorescence confocal laser scanning microscopy (CLSM) has revolutionized imaging of subcellular structures in biomedical research by enabling the acquisition of 3D time-series of fluorescently-tagged proteins in living cells, hence forming the basis for an automated quantification of their morphological and dynamic characteristics. Due to the inherently weak fluorescence, CLSM images exhibit a low SNR. We present a novel model for the transfer of signal and noise in CLSM that is both theoretically sound as well as corroborated by a rigorous analysis of the pixel intensity statistics via measurement of the 3D noise power spectra, signal-dependence and distribution. Our model provides a better fit to the data than previously proposed models. Further, it forms the basis for (i) the simulation of the CLSM imaging process indispensable for the quantitative evaluation of CLSM image analysis algorithms, (ii) the application of Poisson denoising algorithms and (iii) the reconstruction of the fluorescence signal.
    No preview · Article · Jan 2012
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    ABSTRACT: Follow-up assessment of pleural thickenings requires the comparison of information from different points in time. The investigated image regions must be precisely registered to acquire this information. Since the thickenings' growth is the target value, this growth should not be compensated by the registration process. We therefore present a nonrigid registration method, which preserves the shape of the thickenings. The deformation of the volume image is carried out using B-splines. With focus on the image regions located around the lung surface, an efficient way of calculating corresponding points combined with the reuse of information from different scale levels leads to the non-rigid registration, which can be performed within a short computation time.
    No preview · Article · Jan 2012

Publication Stats

3k Citations
201.45 Total Impact Points

Institutions

  • 1999-2015
    • Universität zu Lübeck
      • • Institut für Signalverarbeitung
      • • Institut für Neuro-/Bioinformatik
      Lübeck Hansestadt, Schleswig-Holstein, Germany
    • Otto-von-Guericke-Universität Magdeburg
      Magdeburg, Saxony-Anhalt, Germany
  • 1-2013
    • RWTH Aachen University
      • Gastroenterology and Metabolic Disorders (Internal Medicine III)
      Aachen, North Rhine-Westphalia, Germany
  • 2007
    • Fachhochschule Aachen
      Aachen, North Rhine-Westphalia, Germany
  • 2004
    • Signal Processing Inc.
      Maryland, United States