bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of local activation times on the tension development of human cardiomyocytes in a computational model
Authors: Müller Armin , Kovacheva Ekaterina , Schuler Steffen , Dössel Olaf , Baron Lukas 
Published: September 2018

Abstract
The human heart is an organ of high complexity and hence, very challenging to simulate. To calculate the force developed by the human heart and therefore the tension of the muscle fibers, accurate models are necessary. The force generated by the cardiac muscle has physiologically imposed limits and depends on various characteristics such as the length, strain and the contraction velocity of the cardiomyocytes. Another characteristic is the activation time of each cardiomyocyte, which is a wave and not a static value for all cardiomyocytes. To simulate a physiologically correct excitation, the functionality of the cardiac simulation framework CardioMechanics was extended to incorporate inhomogeneous activation times. The functionality was then used to evaluate the effects of local activation times with two different tension models. The active stress generated by the cardiomyocytes was calculated by (i) an explicit function and (ii) an ode-based model. The results of the simulations showed that the maximum pressure in the left ventricle dropped by 2.3% for the DoubleHill model and by 5.3% for the Lumens model. In the right ventricle the simulations showed similar results. The maximum pressure in both the left and the right atrium increased using both models. Given that the simulation of the inhomogeneously activated cardiomyocytes increases the simulation time when used with the more precise Lumens model, the small drop in maximum pressure seems to be negligible in favor of a simpler simulation model
Fluid-structure interaction of heart valve dynamics in comparison to finite-element analysis
Authors: Borowski Finja , Sämann Michael , Pfensig Sylvia , Wüstenhagen Carolin , Ott Robert , Kaule Sebastian , Siewert Stefan , Grabow Niels , Schmitz Klaus-Peter , Stiehm Michael 
Published: September 2018

Abstract
An established therapy for aortic valve stenosis and insufficiency is the transcatheter aortic valve replacement. By means of numerical simulation the valve dynamics can be investigated to improve the valve prostheses performance. This study examines the influence of the hemodynamic properties on the valve dynamics utilizing fluidstructure interaction (FSI) compared with results of finiteelement analysis (FEA). FEA and FSI were conducted using a previously published aortic valve model combined with a new developed model of the aortic root. Boundary conditions for a physiological pressurization were based on measurements of ventricular and aortic pressure from in vitro hydrodynamic studies of a commercially available heart valve prosthesis using a pulse duplicator system. A linear elastic behavior was assumed for leaflet material properties and blood was specified as a homogeneous, Newtonian incompressible fluid. The type of fluid domain discretization can be described with an arbitrary Lagrangian-Eulerian formulation. Comparison of significant points of time and the leaflet opening area were used to investigate the valve opening behavior of both analyses. Numerical results show that total valve opening modelled by FEA is faster compared to FSI by a factor of 5. In conclusion the inertia of the fluid, which surrounds the valve leaflets, has an important influence on leaflet deformation. Therefore, fluid dynamics should not be neglected in numerical analysis of heart valve prostheses.
In vivo myocardial tissue characterization of all four chambers using high-resolution quantitative MRI
Authors: Becker Kirsten M. , Schulz-Menger Jeanette , Schaeffter Tobias , Kolbitsch Christoph 
Published: September 2018

Abstract
Quantitative native T1 Mapping of the myocardium without the application of contrast agents can be used to detect fibrosis in the left ventricle. Spatial resolution of standard native T1 mapping is limited by cardiac motion and hence is not sufficient to resolve small myocardial structures, such as the right ventricle and the atria. Here, we present a novel MR approach which provides cardiac motion information and native T1 maps from the same data. Motion information is utilized to optimize data selection for T1 mapping and a model-based iterative reconstruction scheme ensures high-resolution T1 maps for the entire heart. Feasibility of the approach was demonstrated in three healthy volunteers. In the T1 maps, the myocardium of all four chambers can be visualized and T1 values of the left atrium and right chambers were comparable to left ventricular T1 values.
Monte-Carlo Simulation of Light Tissue Interaction in Medical Hyperspectral Imaging Applications
Authors: Herrmann Bert. H. , Hornberger Christoph 
Published: September 2018

Abstract
In Hyperspectral imaging (HSI) applications in medicine a uniform illumination is used and the illuminated surface is recorded with a camera with spectral resolution. Unlike in tissue reflectance spectroscopy with fixed light source - detector distances, in HSI the contribution of the influence of different tissue layers to the absorption signal is poorly understood. In this work a Monte-Carlo simulation is implemented which simulates the specific HSI illumination and detector geometry. A four-layer tissue model with variable blood volume fraction and oxygen saturation is used. With 5 % blood volume fraction and 75 % oxygen saturation, SaO2, of surrounding tissue, saturation changes in 1 mm and 2 mm deep layers lead to a change in remission of up to 3 % and up to 1 % respectively. Changes in deeper layers are hardly detectable. Further simulations will be focused on different tissue models as the depth resolution is expected to vary with tissue parameters like blood volume fraction.
A demonstrator for a flexible active microelectrode array with high electrode number
Authors: Heid Andreas , Bleck Lena , Metzen Rene von , Bucher Volker 
Published: September 2018

Abstract
The integration of dies is a possibility to reduce the number of conducting tracks within electrical active implants. For passive microelectrode arrays the number of conducting tracks limits the number of electrodes. By embedding an array of small dies (250 μm edge length) employed to amplify and multiplex the signals of 25 electrodes each into a flexible foil we create a flexible active microelectrode array with more than 1000 electrodes. A fabrication process was developed containing a transfer process for the dies as well as an embedding procedure. Here a non-functional Dummy-System is presented as a demonstrator proving the feasibility of the proposed microelectrode array.
Development of a Stair Climbing Mechanism for a Novel Mechatronic Transport Aid: Preliminary Results
Authors: Schleer Philipp , Kinzius Max , Verjans Mark , Kähler Ferdinand , Radermacher Klaus 
Published: September 2018

Abstract
Emergency medical service (EMS) is an essential part of health care with the main task to transport and monitor patients. However, this duty often becomes a challenge due to obstacles - especially stairs - on the way. Associated lifting and carrying of patients regularly imposes high loads in unergonomic working postures on paramedics, leading to the highest work induced injury rates among all industries also due to a deficient usability of existing transport aids. Therefore our goal is the development of a stair climbing mechanism for a novel mechatronic transport aid characterized by high mobility and a small footprint, whereby particular attention has to be paid to application specific requirements. This paper presents the general approach accompanied by results of a functional model from an initial concept study. Acceleration and jerk measurements showed promising results, while most predefined velocities on the model test parkour rise could be reached.
A New Method of Measuring Stimulation Threshold
Authors: Irnich Werner 
Published: September 2018

Abstract
Louis Lapicque introduced the hyperbolic stimulation law with the key parameters “rheobase” and “chronaxie” that were obtained with rectangular current pulses. With rectangular pulses rheobase cannot be measured. It was found recently that hyperbolic stimulation rules are also valid for non-rectangular pulses and that their rheobase or chronaxie values are identical with that of their rectangular counterparts. Threshold measuring with exponential pulses allow for determining rheobase directly and chronaxie by calculation with only two measurements. The measuring procedure is described in detail.
Residual U-Net Convolutional Neural Network Architecture for Low-Dose CT Denoising
Authors: Heinrich Mattias P. , Stille Maik , Buzug Thorsten M. 
Published: September 2018

Abstract
Low-dose CT has received increasing attention in the recent years and is considered a promising method to reduce the risk of cancer in patients. However, the reduction of the dosage leads to quantum noise in the raw data, which is carried on in the reconstructed images. Two different multilayer convolutional neural network (CNN) architectures for the denoising of CT images are investigated. ResFCN is based on a fully-convolutional network that consists of three blocks of 5×5 convolutions filters and a ResUNet that is trained with 10 convolutional blocks that are arranged in a multi-scale fashion. Both architectures feature a residual connection of the input image to ease learning. Training images are based on realistic simulations by using the XCAT phantom. The ResUNet approach shows the most promising results with a peak signal to noise ratio of 44.00 compared to ResFCN with 41.79.
Method Comparison of In Vitro Wound Area Measurements
Authors: Gdoura Ahmed , Parente Jacquelyn D. , Hensler Sabine , Krüger-Ziolek Sabine , Kuehlbach Claudia , Mueller Margareta M. , Möller Knut 
Published: September 2018

Abstract
Wound area is a primary outcome measure in wound healing studies. This method comparison study evaluates differences of wound area measurements of a newly developed image analysis method based on wound edge contour to an existing method based on contrast tolerance. Digital images of 64 wounds were taken immediately after wounding matured in vitro 3D organotypic tissues with a biopsy punch. Wound area measurements were calculated using each image analysis method and then normalized. The method comparison study evaluates the difference of each paired measurements for all 64 wound areas. Measurement differences are demonstrated and evaluated in normalized data boxplots, scatter plots with a line of equality, data histogram and Normal probability plots, and a Bland-Altman plot of paired measure difference against mean. The measured wound areas using the tolerance method have large variability in comparison to the contour method measures. The tolerance method measures often underestimate and overestimate what is assumed to be an approximately repeatable initial wound size. Skewness in comparison plots are due to the ‘fat tails’ introduced by the variability of measurements of the tolerance method. In contrast, the contour method results in larger wound area measurements on average at a statistically significant level of difference. The relatively less variable range of contour method measurements suggest this method has more potential to agree with the ‘true’ wound area. Future work to improve the method are proposed for application of image analysis methods to distinguish true wound area and measurement error in time for wound healing treatment-control experiments.
Reflection on boon and bane of Water Absorbing Components in Active Implants during Package Testing and Operation
Authors: Koker Liane , Gengenbach Ulrich , Bretthauer Georg 
Published: September 2018

Abstract
For package testing of active implants internal humidity measurements are performed. Thereby, the water absorbency of the measurement components can affect the measurement result, leading to an erroneously prolonged predicted lifetime. Here, the influence of internal components is discussed using an exemplary setup. It is described how to model and consider the components’ absorbencies for lifetime estimation and how beneficial they are during implant operation.
Volumetric 3D stitching of optical coherence tomography volumes
Authors: Laves Max-Heinrich , Kahrs Lüder A. , Ortmaier Tobias 
Published: September 2018

Abstract
Optical coherence tomography (OCT) is a noninvasive medical imaging modality, which provides highresolution transectional images of biological tissue. However, its potential is limited due to a relatively small field of view. To overcome this drawback, we describe a scheme for fully automated stitching of multiple 3D OCT volumes for panoramic imaging. The voxel displacements between two adjacent images are calculated by extending the Lucas-Kanade optical flow a lgorithm to dense volumetric images. A RANSAC robust estimator is used to obtain rigid transformations out of the resulting flow v ectors. T he i mages a re t ransformed into the same coordinate frame and overlapping areas are blended. The accuracy of the proposed stitching scheme is evaluated on two datasets of 7 and 4 OCT volumes, respectively. By placing the specimens on a high-accuracy motorized translational stage, ground truth transformations are available. This results in a mean translational error between two adjacent volumes of 16.6 ± 0.8 μm (2.8 ± 0.13 voxels). To the author’s knowledge, this is the first reported stitching of multiple 3D OCT volumes by using dense voxel information in the registration process. The achieved results are sufficient for providing high accuracy OCT panoramic images. Combined with a recently available high-speed 4D OCT, our method enables interactive stitching of hand-guided acquisitions.
Development of a compact stand-alone esophageal pressure measurement device
Authors: Richter Andre J. , Schnabel Christian , Spieth Peter , Koch Emdund 
Published: September 2018

Abstract
Mechanical ventilation requires optimal parameter setting for every single patient. For instance sufficient positive end-expiratory pressure (PEEP) may ensure oxygenation and prevent overdistension of lungs or alveolar collapse. To find optimal PEEP, transpulmonary pressure (airway pressure minus pleural pressure) guides as an indicator for both, chest wall mechanics and lung characteristic. Since measurement of pleural pressure is impractical in clinical routine, esophageal pressure can be used to estimate pleural pressure and may help to assure protective mechanical ventilation. We developed a PESO (derived from PESO = esophageal pressure) measurement system, which provides a compact stand-alone device to measure the esophageal pressure during mechanical ventilation of patients. In addition to the esophageal pressure, air way pressure is also measured to provide the synchronized data independent of the ventilator manufacturer. The device works with two commercial pressure transducers, whose signals are conditioned and digitized with an Arduino Nano microcontroller, which samples data with 62 kHz and transmits averaged data with 100 Hz to a mobile tablet PC, which acts as process, display and record unit. The compact system provides a working time of 5 hours. Therefore, the system supports the progress for mechanical ventilation research. This paper describes technical details as well as functionality.
An HMM-based averaging approach for creating mean motion data from a full-body Motion Capture system to support the development of a biomechanical model
Authors: Kitzig Andreas , Demmer Julia , Bolten Tobias , Naroska Edwin , Stockmanns Gudrun , Viga Reinhard , Grabmaier Anton 
Published: September 2018

Abstract
Motion capture systems or MoCap systems are used for game development and in the field of sports for the assessment and digitalization of human movement. Furthermore, MoCap systems are also used in the medical and therapeutic field for the analysis of human movement patterns. As examples gait analysis or examination of the musculoskeletal system and its function should be mentioned. Most application relate to a specific person and their movement or to the comparison of movements of different people. Within the scope of this paper an averaged motion sequence is supposed to be generated from MoCap data in order to be able to use it in the field of biomechanical modeling and simulation. For the averaging of individual movement sequences of different persons a Hidden Markov Model (HMM) based approach is presented.
Experimental and numerical investigations of fluid flow in bioreactors for optimized in vitro stem cell loading in xenografts
Authors: Ott Robert , Wüstenhagen Carolin , Stiehm Michael , Schmitz Klaus-Peter , Siewert Stefan , Schmidt Wolfram , Martin Heiner , Grabow Niels , Kasten Annika , Liese Jan , Fechner Carsten , Frerich Bernhard , Einnolf Nadia 
Published: September 2018

Abstract
In tissue engineering and regenerative medicine mesenchymal stem cells (MSC) are widely used to replace and restore the function of dysfunctional or missing tissue. Recent studies have shown significant enhancements of the in vivo healing process following dentofacial bone augmentation procedures employing stem cell-loaded xenografts. We conducted experimental and numerical investigations in perfusion flow bioreactor-xenograft-systems to identify flow conditions as well as bioreactor design features that allow for homogeneous MSC-distribution in Geistlich Bio- Oss Block xenografts. Pressure gradient - velocity characteristics and flow distributions were investigated experimentally and numerically for two bioreactor designs at steady-state flow conditions with Reynolds numbers (Re) ranging from 0.01 ≤ Re ≤ 0.32. Distilled water at 20°C with a dynamic viscosity of 1.002 mPa∙s and a density of 998 kg/m3 was used. The geometry of the xenograft utilized in three-dimensional computational fluid dynamics (CFD) simulation was obtained by means of micro-computed tomography (μCT) at an isotropic spatial resolution of 9.5 μm. The permeability values calculated from the experimental data are in good accordance with the numerical results. The investigations showed that the increase of the inflow- and outflow-area diameter, as well as the decrease of the volumetric flow rate, result in a decreasing heterogeneity of the flow distribution within the xenograft. The calculated wall shear stress rates in the three-dimensional (3D) scaffold range from 1∙10-12Pa ≤ τ ≤ 0.2 Pa. Experimentally validated CFD simulations introduced in this study provide an applicable tool to assess optimal flow conditions for homogeneous MSC distribution in bioreactor-xenograft-systems.
Synchronized Sensor Insoles for Clinical Gait Analysis in Home-Monitoring Applications
Authors: Roth Nils , Martindale Christine F. , Eskofier Bjoern M. , Gaßner Heiko , Kohl Zacharias , Klucken Jochen 
Published: September 2018

Abstract
Wearable sensor systems are of increasing interest in clinical gait analysis. However, little information about gait dynamics of patients under free living conditions is available, due to the challenges of integrating such systems unobtrusively into a patient’s everyday live. To address this limitation, new, fully integrated low power sensor insoles are proposed, to target applications particularly in home-monitoring scenarios. The insoles combine inertial as well as pressure sensors and feature wireless synchronization to acquire biomechanical data of both feet with a mean timing offset of 15.0 μs. The proposed system was evaluated on 15 patients with mild to severe gait disorders against the GAITRite® system as reference. Gait events based on the insoles’ pressure sensors were manually extracted to calculate temporal gait features such as double support time and double support. Compared to the reference system a mean error of 0.06 s ±0.06 s and 3.89 % ±2.61 % was achieved, respectively. The proposed insoles proved their ability to acquire synchronized gait parameters and address the requirements for home-monitoring scenarios, pushing the boundaries of clinical gait analysis.
Detecting Lamellipodia in Epithelial Cell Clusters Using a Fully Convolutional Neural Network for Phase Contrast Microscopy Images
Authors: Grützmacher Simon , Kemkemer Ralf , Thies Christian , Curio Cristóbal 
Published: September 2018

Abstract
We present an approach for segmenting individual cells and lamellipodia in epithelial cell clusters using fully convolutional neural networks. The method will set the basis for measuring cell cluster dynamics and expansion to improve the investigation of collective cell migration phenomena. The fully learning-based front-end avoids classical feature engineering, yet the network architecture needs to be designed carefully. Our network predicts how likely each pixel belongs to one of the classes and, thus, is able to segment the image. Besides characterizing segmentation performance, we discuss how the network will be further employed.
Improving electrocorticograms of awake and anaesthetized mice using wavelet denoising
Authors: Schweigmann Michael , Koch Klaus Peter , Auler Fabian , Kirchhoff Frank 
Published: September 2018

Abstract
The quality of bioelectrical signals is essential for functional evaluation of cellular circuits. The electrical activity recorded from the cortical brain surface represents the average of many individual synaptic processes. By downsizing micro-electrode arrays, the spatial resolution of electrocortico-grams (ECoGs) can be increased. But, upon increasing electrode impedance, recorded noise from the electrode-tissue interface and the surroundings will become more prominent. Frequently, signal interpretation is improved by post-processing using filtering or pattern recognition. For a variety of applications, wavelet denoising has become an accepted tool. Here, we present how wavelet denoising affects the signal-to-noise ratio of ECoGs. The recording qualities from awake and anesthetized mice was artificially reduced by adding two noise models prior to filtering. Raw and filtered signals were compared by calculating the linear correlation coefficient.
Cryoballoon model and simulation of catheter ablation for pulmonary vein isolation in atrial fibrillation
Authors: Müssig Robin , Müssig Robin , Hörth Johannes 
Published: September 2018

Abstract
Pulmonary vein isolation (PVI) is a common therapy in atrial fibrillation (AF). The cryoballoon was invented to isolate the pulmonary vein in one step and in a shorter time than a point-by-point radiofrequency (RF) ablation. The aim of the study was to model two cryoballoon catheters, one RF catheter and to integrate them into a heart rhythm model for the static and dynamic simulation of PVI by cryoablation and RF ablation in AF. The modeling and simulation were carried out using the electromagnetic and thermal simulation software CST (CST, Darmstadt). Two cryoballons and one RF ablation catheter were modeled based on the technical manuals of the manufacturers Medtronic and Osypka. The PVI especially the isolation of the left inferior pulmonary vein using a cryoballoon catheter was performed with a -50 °C heatsource and an exponential signal. The temperature at the balloon surface was -50 °C after 20 s ablation time, -24 °C from the balloon 0,5 mm in the myocardium, at a distance of 1 mm -3 °C, at 2 mm 18 °C and at a distance of 3mm 29 °C. PVI with RF energy was simulated with an applied power of 5 W at 420 kHz at the distal 8 mm ablation electrode. The temperature at the tip electrode was 110 °C after 15 s ablation time, 75 °C from the balloon at 0,5 mm in the myocardium, at a distance of 1 mm 58 °C, at 2 mm 45 °C and at a distance of 3 mm 38 °C. Virtual heart rhythm and catheter models as well as the simulation of the temperature allow the simulation of PVI in AF by cryo ablation and RF ablation. The 3D simulation of the temperature profile may be used to optimize RF and cryo ablation.