176 research outputs found
Marker-Free Tracking for Motion Artifact Compensation and Deformation Measurements in Optical Mapping Videos of Contracting Hearts
Optical mapping is a high-resolution fluorescence imaging technique, which provides highly detailed visualizations of the electrophysiological wave phenomena, which trigger the beating of the heart. Recent advancements in optical mapping have demonstrated that the technique can now be performed with moving and contracting hearts and that motion and motion artifacts, once a major limitation, can now be overcome by numerically tracking and stabilizing the heart's motion. As a result, the optical measurement of electrical activity can be obtained from the moving heart surface in a co-moving frame of reference and motion artifacts can be reduced substantially. The aim of this study is to assess and validate the performance of a 2D marker-free motion tracking algorithm, which tracks motion and non-rigid deformations in video images. Because the tracking algorithm does not require markers to be attached to the tissue, it is necessary to verify that it accurately tracks the displacements of the cardiac tissue surface, which not only contracts and deforms, but also fluoresces and exhibits spatio-temporal physiology-related intensity changes. We used computer simulations to generate synthetic optical mapping videos, which show the contracting and fluorescing ventricular heart surface. The synthetic data reproduces experimental data as closely as possible and shows electrical waves propagating across the deforming tissue surface, as seen during voltage-sensitive imaging. We then tested the motion tracking and motion-stabilization algorithm on the synthetic as well as on experimental data. The motion tracking and motion-stabilization algorithm decreases motion artifacts approximately by 80% and achieves sub-pixel precision when tracking motion of 1–10 pixels (in a video image with 100 by 100 pixels), effectively inhibiting motion such that little residual motion remains after tracking and motion-stabilization. To demonstrate the performance of the algorithm, we present optical maps with a substantial reduction in motion artifacts showing action potential waves propagating across the moving and strongly deforming ventricular heart surface. The tracking algorithm reliably tracks motion if the tissue surface is illuminated homogeneously and shows sufficient contrast or texture which can be tracked or if the contrast is artificially or numerically enhanced. In this study, we also show how a reduction in dissociation-related motion artifacts can be quantified and linked to tracking precision. Our results can be used to advance optical mapping techniques, enabling them to image contracting hearts, with the ultimate goal of studying the mutual coupling of electrical and mechanical phenomena in healthy and diseased hearts
CaosDB - Research Data Management for Complex, Changing, and Automated Research Workflows
Here we present CaosDB, a Research Data Management System (RDMS) designed to
ensure seamless integration of inhomogeneous data sources and repositories of
legacy data. Its primary purpose is the management of data from biomedical
sciences, both from simulations and experiments during the complete research
data lifecycle. An RDMS for this domain faces particular challenges: Research
data arise in huge amounts, from a wide variety of sources, and traverse a
highly branched path of further processing. To be accepted by its users, an
RDMS must be built around workflows of the scientists and practices and thus
support changes in workflow and data structure. Nevertheless it should
encourage and support the development and observation of standards and
furthermore facilitate the automation of data acquisition and processing with
specialized software. The storage data model of an RDMS must reflect these
complexities with appropriate semantics and ontologies while offering simple
methods for finding, retrieving, and understanding relevant data. We show how
CaosDB responds to these challenges and give an overview of the CaosDB Server,
its data model and its easy-to-learn CaosDB Query Language. We briefly discuss
the status of the implementation, how we currently use CaosDB, and how we plan
to use and extend it
Basin structure of optimization based state and parameter estimation
Most data based state and parameter estimation methods require suitable
initial values or guesses to achieve convergence to the desired solution, which
typically is a global minimum of some cost function. Unfortunately, however,
other stable solutions (e.g., local minima) may exist and provide suboptimal or
even wrong estimates. Here we demonstrate for a 9-dimensional Lorenz-96 model
how to characterize the basin size of the global minimum when applying some
particular optimization based estimation algorithm. We compare three different
strategies for generating suitable initial guesses and we investigate the
dependence of the solution on the given trajectory segment (underlying the
measured time series). To address the question of how many state variables have
to be measured for optimal performance, different types of multivariate time
series are considered consisting of 1, 2, or 3 variables. Based on these time
series the local observability of state variables and parameters of the
Lorenz-96 model is investigated and confirmed using delay coordinates. This
result is in good agreement with the observation that correct state and
parameter estimation results are obtained if the optimization algorithm is
initialized with initial guesses close to the true solution. In contrast,
initialization with other exact solutions of the model equations (different
from the true solution used to generate the time series) typically fails, i.e.
the optimization procedure ends up in local minima different from the true
solution. Initialization using random values in a box around the attractor
exhibits success rates depending on the number of observables and the available
time series (trajectory segment).Comment: 15 pages, 2 figure
Intravascular tissue factor initiates coagulation via circulating microvesicles and platelets
Although tissue factor (TF), the principial initiator of physiological coagulation and pathological thrombosis, has recently been proposed to be present in human blood, the functional significance and location of the intravascular TF is unknown. In the plasma portion of blood, we found TF to be mainly associated with circulating microvesicles. By cell sorting with the specific marker CD42b, platelet-derived microvesicles were identified as a major location of the plasma TF. This was confirmed by the presence of full-length TF in microvesicles acutely shedded from the activated platelets. TF was observed to be stored in the α-granules and the open canalicular system of resting platelets and to be exposed on the cell surface after platelet activation. Functional competence of the blood-based TF was enabled when the microvesicles and platelets adhered to neutrophils, as mediated by P-selectin and neutrophil counterreceptor (PSGL-1, CD18 integrins) interactions. Moreover, neutrophil-secreted oxygen radical species supported the intravascular TF activity. The pools of platelet and microvesicle TF contributed additively and to a comparable extent to the overall blood TF activity, indicating a substantial participation of the microvesicle TF. Our results introduce a new concept of TF-mediated coagulation crucially dependent on TF associated with microvesicles and activated platelets, which principally enables the entire coagulation system to proceed on a restricted cell surface
Flow equation approach to the sine-Gordon model
A continuous sequence of infinitesimal unitary transformations is used to
diagonalize the quantum sine-Gordon model for \beta^2\in(2\pi,\infty). This
approach can be understood as an extension of perturbative scaling theory since
it links weak- to strong-coupling behavior in a systematic expansion: a small
expansion parameter is identified and this parameter remains small throughout
the entire flow unlike the diverging running coupling constant of perturbative
scaling. Our approximation consists in neglecting higher orders in this small
parameter. We find very accurate results for the single-particle/hole spectrum
in the strong-coupling phase and can describe the full crossover from weak to
strong-coupling. The integrable structure of the sine-Gordon model is not used
in our approach. Our new method should be of interest for the investigation of
nonintegrable perturbations and for other strong-coupling problems.Comment: 38 pages, 7 figure
Flow equation solution for the weak to strong-coupling crossover in the sine-Gordon model
A continuous sequence of infinitesimal unitary transformations, combined with
an operator product expansion for vertex operators, is used to diagonalize the
quantum sine-Gordon model for 2 pi < beta^2 < infinity. The leading order of
this approximation already gives very accurate results for the single-particle
gap in the strong-coupling phase. This approach can be understood as an
extension of perturbative scaling theory since it links weak to strong-coupling
behavior in a systematic expansion. The approach should also be useful for
other strong-coupling problems that can be formulated in terms of vertex
operators.Comment: 4 pages, 1 figure, minor changes (typo in Eq. (3) corrected,
references added), published versio
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