M. Kraus

Automatic no-reference quality assessment for retinal fundus images using vessel segmentation

Fundus imaging is the most commonly used modality to collect information about the human eye background. Objective and quantitative assessment of quality for the acquired images is essential for manual, computer-aided and fully automatic diagnosis. In this paper, we present a no-reference quality metric to quantify image noise and blur and its application to fundus image quality assessment. The proposed metric takes the vessel tree visible on the retina as guidance to determine an image quality score. In our experiments, the performance of this approach is demonstrated by correlation analysis with the established full-reference metrics peak-signal-to-noise ratio (PSNR) and structural similarity (SSIM). We found a Spearman rank correlation for PSNR and SSIM of 0.89 and 0.91. For real data, our metric correlates reasonable to a human observer, indicating high agreement to human visual perception.

Pattern classification of kinematic and kinetic running data to distinguish gender, shod/barefoot and injury groups with feature ranking

The identification of differences between groups is often important in biomechanics. This paper presents group classification tasks using kinetic and kinematic data from a prospective running injury study. Groups composed of gender, of shod/barefoot running and of runners who developed patellofemoral pain syndrome (PFPS) during the study, and asymptotic runners were classified. The features computed from the biomechanical data were deliberately chosen to be generic. Therefore, they were suited for different biomechanical measurements and classification tasks without adaptation to the input signals. Feature ranking was applied to reveal the relevance of each feature to the classification task. Data from 80 runners were analysed for gender and shod/barefoot classification, while 12 runners were investigated in the injury classification task. Gender groups could be differentiated with 84.7%, shod/barefoot running with 98.3%, and PFPS with 100% classification rate. For the latter group, one single variable could be identified that alone allowed discrimination.

Heavy ion irradiation effects inc-axis oriented thin films of YBa2(Cu0.9757Fe0.03)3O7 studied by CEMS

Fullyc-axis oriented thin films of YBa2 (Cu0.9757Fe0.03)3O7 on <100> SrTiO3 substrate were irradiated with different fluences ϕ of 500 MeV127I parallel to thec-axis. The samples were investigated by means of x-ray diffraction, resistiveTc measurements and conversion electron Mößbauer spectroscopy (CEMS). Irradiation results in the appearance of a fourth quadrupole doubletE in the CEMS-spectra (EQ=1.1 mm/s, IS=0.26 mm/s), whose intensity increases with increasing ϕ. The Debye Waller factor of the new Fe-speciesE is only about 60% of that of the speciesA, B, andC proving that irradiation with high energy heavy ions results in latent tracks of lower density. from the hyperfine parameters of speciesE we conclude that the latent tracks are mainly formed by the “green phase” Y2BaCuO5. We derived the radius of the latent tracks to be about 26 Å.

GPU-Accelerated Time-of-Flight Super-Resolution for Image-Guided Surgery

In the field of image-guided surgery, Time-of-Flight (ToF) sensors are of interest due to their fast acquisition of 3-D surfaces. However, the poor signal-to-noise ratio and low spatial resolution of today’s ToF sensors require preprocessing of the acquired range data. Superresolution is a technique for image restoration and resolution enhancement by utilizing information from successive raw frames of an image sequence. We propose a super-resolution framework using the graphics processing unit. Our framework enables interactive frame rates, computing an upsampled image from 10 noisy frames of 200 × 200 px with an upsampling factor of 2 in 109 ms. The root-mean-square error of the super-resolved surface with respect to ground truth data is improved by more than 20 % relative to a single raw frame.

Angel resolved measurements of the transport critical current density of YBCO thin films containing columnar defects of various orientations

Abstract We present measurements of the transport critical current density jc of an epitaxial YBa2Cu3O7−δ (YBCO) thin film containing columnar latent tracks in two different orientations. The data show, that the such a creation of tracts with varying orientation is a convenient method to achieve even stronger pinning effects, compared to an irradiation solely along the c-axis of the compound.

Effect of columnar defects on the Jc anisotropy of YBa2Cu3O7−δ thin films and YBa2Cu3O7−δ/PrBa2Cu3O7−δ multilayers

Epitaxial YBa2Cu3O7−δ thin films (YBCO) and YBa2Cu3O7−δ/PrBa2Cu3O7−δ multilayers (Y/Pr) were irradiated with high-energy heavy ions (770 Mev208Pb) under various directionsφ relative to thec-axis. The irradiation resulted in columnar defects tilted byφ from thec-axis. The angular dependence of their pinning activity was studied by measuring the anisotropy of the critical current density. TheJc(B, T,ϑ) behavior of the irradiated YBCO thin films showed an additional peak, which exceeds the intrinsic pinning peak, exactly at the irradiation direction. The Y/Pr multilayers, however, showed an isotropicTc-enhancement by a factor of 5, without any additional structure in theJc(B, T,ϑ) curve.

4D dynamic imaging of the eye using ultrahigh speed SS-OCT

Recent advances in swept-source / Fourier domain optical coherence tomography (SS-OCT) technology enable in vivo ultrahigh speed imaging, offering a promising technique for four-dimensional (4-D) imaging of the eye. Using an ultrahigh speed tunable vertical cavity surface emitting laser (VCSEL) light source based SS-OCT prototype system, we performed imaging of human eye dynamics in four different imaging modes: 1) Pupillary reaction to light at 200,000 axial scans per second and 9 μm resolution in tissue. 2) Anterior eye focusing dynamics at 100,000 axial scans per second and 9 μm resolution in tissue. 3) Tear film break up at 50,000 axial scans per second and 19 μm resolution in tissue. 4) Retinal blood flow at 800,000 axial scans per second and 12 μm resolution in tissue. The combination of tunable ultrahigh speeds and long coherence length of the VCSEL along with the outstanding roll-off performance of SS-OCT makes this technology an ideal tool for time-resolved volumetric imaging of the eye. Visualization and quantitative analysis of 4-D OCT data can potentially provide insight to functional and structural changes in the eye during disease progression. Ultrahigh speed imaging using SS-OCT promises to enable novel 4-D visualization of realtime dynamic processes of the human eye. Furthermore, this non-invasive imaging technology is a promising tool for research to characterize and understand a variety of visual functions.

OCT-OCTA segmentation: A novel framework and an application to segment Bruch’s Membrane in the presence of Drusen

In this work, a novel paradigm for segmenting optical coherence tomography (OCT) and optical coherence tomography angiography (OCTA) is presented [1]. Since it uses OCT and OCTA information jointly it is called “OCT-OCTA segmentation” and its usefulness is demonstrated by segmenting the Bruch’s Membrane (BM) in the presence of drusen. Therefore a fully automatic graph-cut algorithm was developed and evaluated by comparing the automatic segmentation results with manual segmentation in 7 eyes (6 patients; 73.8 ± 5.7 y/o) with nascent geographic atrophy and/or drusen associated geographic atrophy.