scholarly journals A new method for the in vivo identification of degenerated material property ranges of the human eye: feasibility analysis based on synthetic data

2021 ◽  
Author(s):  
Stefan Muench ◽  
Mike Roellig ◽  
Daniel Balzani
Keyword(s):  
Real Time ◽  
Test Data ◽  
Synthetic Data ◽  
New Method ◽  
Data Sets ◽  
New Approach ◽  
Full Field ◽  
Material Parameters ◽  
Virtual Test

AbstractThis paper proposes a new method for in vivo and almost real-time identification of biomechanical properties of the human cornea based on non-contact tonometer data. Further goal is to demonstrate the method’s functionality based on synthetic data serving as reference. For this purpose, a finite element model of the human eye is constructed to synthetically generate full-field displacements from different data sets with keratoconus-like degradations. Then, a new approach based on the equilibrium gap method combined with a mechanical morphing approach is proposed and used to identify the material parameters from virtual test data sets. In a further step, random absolute noise is added to the virtual test data to investigate the sensitivity of the new approach to noise. As a result, the proposed method shows a relevant accuracy in identifying material parameters based on full-field displacements. At the same time, the method turns out to work almost in real time (order of a few minutes on a regular workstation) and is thus much faster than inverse problems solved by typical forward approaches. On the other hand, the method shows a noticeable sensitivity to rather small noise amplitudes rendering the method not accurate enough for the precise identification of individual parameter values. However, analysis show that the accuracy is sufficient for the identification of property ranges which might be related to diseased tissues. Thereby, the proposed approach turns out promising with view to diagnostic purposes.

Quasi-2D inversion of DCR and TDEM data for shallow investigations

Geophysics ◽  
2011 ◽  
Vol 76 (4) ◽  
pp. F239-F250 ◽  
Author(s):  
Fernando A. Monteiro Santos ◽  
Hesham M. El-Kaliouby
Keyword(s):  
Joint Inversion ◽  
Synthetic Data ◽  
Data Sets ◽  
Complex Environments ◽  
Inversion Algorithm ◽  
2D Inversion ◽  
New Approach ◽  
Earth Models ◽  
Time Domain Electromagnetic ◽  
Inversion Techniques

Joint or sequential inversion of direct current resistivity (DCR) and time-domain electromagnetic (TDEM) data commonly are performed for individual soundings assuming layered earth models. DCR and TDEM have different and complementary sensitivity to resistive and conductive structures, making them suitable methods for the application of joint inversion techniques. This potential joint inversion of DCR and TDEM methods has been used by several authors to reduce the ambiguities of the models calculated from each method separately. A new approach for joint inversion of these data sets, based on a laterally constrained algorithm, was found. The method was developed for the interpretation of soundings collected along a line over a 1D or 2D geology. The inversion algorithm was tested on two synthetic data sets, as well as on field data from Saudi Arabia. The results show that the algorithm is efficient and stable in producing quasi-2D models from DCR and TDEM data acquired in relatively complex environments.

scholarly journals Full-Field Viscoelastic Inflation Response of Bovine Cornea

2008 ◽  
Author(s):  
B. L. Boyce ◽  
T. D. Nguyen ◽  
R. E. Jones
Keyword(s):  
Real Time ◽  
Experimental Studies ◽  
Time Dependent ◽  
Full Field ◽  
3 Dimensional ◽  
Displacement Mapping ◽  
Mapping Tool ◽  
Unique Approach ◽  
In Vivo Characterization

Most previous experimental studies and mechanical cornea models have ignored time-dependence of the cornea’s modulus, with only a few notable exceptions [1–3]. The purpose of the present work was to evaluate the time-dependent properties of cornea tissue independent of scleral contributions in a condition that is as physiologically-relevant as possible without resorting to costly and difficult in vivo characterization. A non-contact 3-dimensional displacement mapping tool was employed to image the entire deformation field across the entire cornea in real-time during pressurization. Unlike prior inflation-based studies, the present study’s unique approach permits dynamic real-time full-field mapping of deformation during inflation for the examination of viscoelasticity, isotropy, and homogeneity.

scholarly journals Using control charts for on-line video summarisation

2019 ◽  
Vol 277 ◽  
pp. 01012 ◽  
Author(s):  
Clare E. Matthews ◽  
Paria Yousefi ◽  
Ludmila I. Kuncheva
Keyword(s):  
Feature Extraction ◽  
Control Chart ◽  
Control Charts ◽  
State Of The Art ◽  
Synthetic Data ◽  
New Method ◽  
Data Sets ◽  
On Line ◽  
Memory Constraints ◽  
Video Summarisation

Many existing methods for video summarisation are not suitable for on-line applications, where computational and memory constraints mean that feature extraction and frame selection must be simple and efficient. Our proposed method uses RGB moments to represent frames, and a control-chart procedure to identify shots from which keyframes are then selected. The new method produces summaries of higher quality than two state-of-the-art on-line video summarisation methods identified as the best among nine such methods in our previous study. The summary quality is measured against an objective ideal for synthetic data sets, and compared to user-generated summaries of real videos.

scholarly journals Leukocyte recruitment in the airways: an intravital microscopic study of rat tracheal microcirculation

2002 ◽  
Vol 282 (5) ◽  
pp. L959-L967 ◽  
Author(s):  
Lina H. K. Lim ◽  
Bruce S. Bochner ◽  
Elizabeth M. Wagner
Keyword(s):  
Real Time ◽  
Leukocyte Recruitment ◽  
New Method ◽  
Histological Evaluation ◽  
Leukocyte Rolling ◽  
Adherent Cells ◽  
Rolling Velocity ◽  
Leukocyte Extravasation ◽  
Local Superfusion

Because of its relative inaccessibility, inflammatory cell extravasation within the airway circulation in vivo has been difficult to investigate in real time. A new method has been established using intravital microscopy in the anesthetized rat to visualize leukocytes in superficial postcapillary venules of the trachea. This technique has been validated using local superfusion of lipopolysaccharide (LPS) and N-formyl-methionyl-leucyl-phenylalanine (FMLP). Basal leukocyte rolling velocity (55.4 ± 9.3 μm/s) and adhesion (1.4 ± 0.3 cells/100 μm) were monitored in postcapillary venules (33.9 ± 1.3 μm diameter). At all time points up to 90 min, these parameters were unaltered in control rats ( n= 7). In contrast, vessels exposed to 1 μg/ml of LPS ( n = 6) exhibited a 57% reduction in leukocyte rolling velocity and an increase in the number of adherent cells (4.7 ± 1 cells/100 μm, P < 0.05). Superfusion with 0.1 μM of FMLP ( n = 6) also resulted in a 45% reduction in rolling velocity and an increase in adherent cells (4 ± 0.7 cells/100 μm, P < 0.05). Histological evaluation confirmed local stimulus-induced leukocyte extravasation. These results demonstrate leukocyte recruitment in the airway microvasculature and provide an important new method to study airway inflammation in real time.

From migration to inversion velocity analysis

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. S207-S223 ◽  
Author(s):  
Hervé Chauris ◽  
Emmanuel Cocher
Keyword(s):  
Objective Function ◽  
Synthetic Data ◽  
Velocity Model ◽  
Specific Power ◽  
Model Parameters ◽  
Data Sets ◽  
Velocity Analysis ◽  
Low Velocity ◽  
Image Domain ◽  
New Approach

Migration velocity analysis (MVA) is a technique defined in the image domain to determine the background velocity model controlling the kinematics of wave propagation. In the presence of discontinuous interfaces, the velocity gradient used to iteratively update the velocity model exhibits spurious oscillations. For more stable results, we replace the migration part by an inversion scheme. By definition, migration is the adjoint of the Born modeling operator, whereas inversion is its asymptotic inverse. We have developed new expressions in 1D and 2D cases based on two-way wave-equation operators. The objective function measures the quality of the images obtained by inversion in the extended domain depending on the subsurface offset. In terms of implementation, the new approach is very similar to classic MVA. A 1D analysis found that oscillatory terms around the interface positions can be removed by multiplying the inversion result with the velocity at a specific power before evaluating the objective function. Several 2D synthetic data sets are discussed through the computation of the gradient needed to update the model parameters. Even for discontinuous reflectivity models, the new approach provides results without artificial oscillations. The model update corresponds to a gradient of an existing objective function, which was not the case for the horizontal contraction approach proposed as an alternative to deal with gradient artifacts. It also correctly handles low-velocity anomalies, contrary to the horizontal contraction approach. Inversion velocity analysis offers new perspectives for the applicability of image-domain velocity analysis.

scholarly journals Inversion of controlled-source electromagnetic reflection responses

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. F49-F57 ◽  
Author(s):  
Jürg Hunziker ◽  
Jan Thorbecke ◽  
Joeri Brackenhoff ◽  
Evert Slob
Keyword(s):  
Electromagnetic Fields ◽  
Synthetic Data ◽  
Water Layer ◽  
Gradient Algorithm ◽  
Data Driven ◽  
Data Sets ◽  
Controlled Source ◽  
Material Parameters ◽  
Nonlinear Conjugate Gradient ◽  
Position And Orientation

Marine controlled-source electromagnetic reflection responses can be retrieved by interferometry. These reflection responses are free of effects related to the water layer and the air above it and do not suffer from uncertainties related to the source position and orientation. Interferometry is a data-driven process requiring proper sampling of the electromagnetic field as well as knowledge of the material parameters at the receiver level, i.e., the sediment just below the receivers. We have inverted synthetic data sets using the reflection responses or the original electromagnetic fields with the goal of extracting the conductivity model of the subsurface. For the inversion, a genetic algorithm and a nonlinear conjugate-gradient algorithm were used. Our results show that an inversion of the reflection responses produces worse estimates of the vertical conductivity but superior estimates of the horizontal conductivity (especially for the reservoir) with respect to the original electromagnetic fields.

scholarly journals An inverse method for mechanical characterization of heterogeneous diseased arteries using intravascular imaging

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bharath Narayanan ◽  
Max L. Olender ◽  
David Marlevi ◽  
Elazer R. Edelman ◽  
Farhad R. Nezami
Keyword(s):  
In Silico ◽  
Mechanical Characterization ◽  
Imaging Data ◽  
New Approach ◽  
Parameter Recovery ◽  
Material Parameters ◽  
Linear Elastic ◽  
Novel Method

AbstractThe increasing prevalence of finite element (FE) simulations in the study of atherosclerosis has spawned numerous inverse FE methods for the mechanical characterization of diseased tissue in vivo. Current approaches are however limited to either homogenized or simplified material representations. This paper presents a novel method to account for tissue heterogeneity and material nonlinearity in the recovery of constitutive behavior using imaging data acquired at differing intravascular pressures by incorporating interfaces between various intra-plaque tissue types into the objective function definition. Method verification was performed in silico by recovering assigned material parameters from a pair of vessel geometries: one derived from coronary optical coherence tomography (OCT); one generated from in silico-based simulation. In repeated tests, the method consistently recovered 4 linear elastic (0.1 ± 0.1% error) and 8 nonlinear hyperelastic (3.3 ± 3.0% error) material parameters. Method robustness was also highlighted in noise sensitivity analysis, where linear elastic parameters were recovered with average errors of 1.3 ± 1.6% and 8.3 ± 10.5%, at 5% and 20% noise, respectively. Reproducibility was substantiated through the recovery of 9 material parameters in two more models, with mean errors of 3.0 ± 4.7%. The results highlight the potential of this new approach, enabling high-fidelity material parameter recovery for use in complex cardiovascular computational studies.

A New Approach for Determining In-Situ Rock Strength While Drilling

1996 ◽  
Vol 118 (4) ◽  
pp. 249-255 ◽  
Author(s):  
L. L. Hoberock ◽  
G. J. Bratcher
Keyword(s):  
Field Experiment ◽  
Test Data ◽  
Rock Strength ◽  
New Method ◽  
Drill Bit ◽  
New Approach ◽  
Drilling Data

A new method is developed for determining rock strength while drilling with a tri-cone roller bit. The technique employs the well-known “drill-off” test, using commonly measured drilling data, and does not require knowledge of drill bit parameters. The method was evaluated with drill-off test data collected from the Gas Research Institute’s SFE (staged field experiment) well no. 4 and compared with calculated in-situ compressive rock strengths provided by Hareland (1992). The results indicate that the proposed approach produces reasonable results and is easily implemented.

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