Appropriate Objective Functions for Quantifying Iris Mechanical Properties Using Inverse Finite Element Modeling

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Anup D. Pant ◽  
Syril K. Dorairaj ◽  
Rouzbeh Amini
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Objective Function ◽  
Inverse Modeling ◽  
Measurement Errors ◽  
Ex Vivo ◽  
Treatment Strategies ◽  
Objective Functions ◽  
Estimation Of Parameters

Quantifying the mechanical properties of the iris is important, as it provides insight into the pathophysiology of glaucoma. Recent ex vivo studies have shown that the mechanical properties of the iris are different in glaucomatous eyes as compared to normal ones. Notwithstanding the importance of the ex vivo studies, such measurements are severely limited for diagnosis and preclude development of treatment strategies. With the advent of detailed imaging modalities, it is possible to determine the in vivo mechanical properties using inverse finite element (FE) modeling. An inverse modeling approach requires an appropriate objective function for reliable estimation of parameters. In the case of the iris, numerous measurements such as iris chord length (CL) and iris concavity (CV) are made routinely in clinical practice. In this study, we have evaluated five different objective functions chosen based on the iris biometrics (in the presence and absence of clinical measurement errors) to determine the appropriate criterion for inverse modeling. Our results showed that in the absence of experimental measurement error, a combination of iris CL and CV can be used as the objective function. However, with the addition of measurement errors, the objective functions that employ a large number of local displacement values provide more reliable outcomes.

scholarly journals Ocular Toxoplasmosis: Mechanisms of Retinal Infection and Experimental Models

Parasitologia ◽  
2021 ◽  
Vol 1 (2) ◽  
pp. 50-60
Author(s):  
Veronica Rodriguez Fernandez ◽  
Giovanni Casini ◽  
Fabrizio Bruschi
Keyword(s):  
Ex Vivo ◽  
Cell Damage ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Treatment Strategies ◽  
Experimental Models ◽  
Ocular Toxoplasmosis ◽  
Cell Infection

Ocular toxoplasmosis (OT) is caused by the parasite Toxoplasma gondii and affects many individuals throughout the world. Infection may occur through congenital or acquired routes. The parasites enter the blood circulation and reach both the retina and the retinal pigment epithelium, where they may cause cell damage and cell death. Different routes of access are used by T. gondii to reach the retina through the retinal endothelium: by transmission inside leukocytes, as free parasites through a paracellular route, or after endothelial cell infection. A main feature of OT is the induction of an important inflammatory state, and the course of infection has been shown to be influenced by the host immunogenetics. On the other hand, there is evidence that the T. gondii phenotype also has an impact on the distribution of the pathology in different areas. Although considerable knowledge has been acquired on OT, a deeper knowledge of its mechanisms is necessary to provide new, more targeted treatment strategies. In particular, in addition to in vitro and in vivo experimental models, organotypic, ex vivo retinal explants may be useful in this direction.

scholarly journals An imaged-based inverse finite element method to determine in-vivo mechanical properties of the human trabecular meshwork

2017 ◽  
Vol 1 (3) ◽  
pp. 100-111
Author(s):  
Anup D. Pant ◽  
Larry Kagemann ◽  
Joel S. Schuman ◽  
Ian A. Sigal ◽  
Rouzbeh Amini
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Shear Modulus ◽  
Trabecular Meshwork ◽  
Computational Simulation ◽  
Optimization Technique ◽  
Schlemm’S Canal ◽  
Aqueous Humor Outflow ◽  
Schlemm's Canal

Aim/Purpose: Previous studies have shown that the trabecular meshwork (TM) is mechanically stiffer in glaucomatous eyes as compared to normal eyes. It is believed that elevated TM stiffness increases resistance to the aqueous humor outflow, producing increased intraocular pressure (IOP).It would be advantageous to measure TM mechanical properties in vivo, as these properties are believed to play an important role in the pathophysiology of glaucoma and could be useful for identifying potential risk factors.  The purpose of this study was to develop a method to estimate in-vivo TM mechanical properties using clinically available exams and computer simulations.Design: Inverse finite element simulationMethods: A finite element model of the TM was constructed from optical coherence tomography (OCT) images of a healthy volunteer before and during IOP elevation. An axisymmetric model of the TM was then constructed. Images of the TM at a baseline IOP level of 11, and elevated level of 23 mmHg were treated as the undeformed and deformed configurations, respectively. An inverse modeling technique was subsequently used to estimate the TM shear modulus (G). An optimization technique was used to find the shear modulus that minimized the difference between Schlemm’s canal area in the in-vivo images and simulations.Results: Upon completion of inverse finite element modeling, the simulated area of the Schlemm’s canal changed from 8,889 μm2 to 2,088 μm2, similar to the experimentally measured areal change of the canal (from 8,889 μm2 to 2,100 μm2). The calculated value of shear modulus was found to be 1.93 kPa,  (implying an approximate Young’s modulus of 5.75 kPa), which is consistent with previous ex-vivo measurements.Conclusion: The combined imaging and computational simulation technique provides a unique approach to calculate the mechanical properties of the TM in vivo without any surgical intervention. Quantification of such mechanical properties will help us examine the mechanistic role of TM biomechanics in the regulation of IOP in healthy and glaucomatous eyes. 

scholarly journals Harmonic motion imaging of human breast masses: an in vivo clinical feasibility

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Niloufar Saharkhiz ◽  
Richard Ha ◽  
Bret Taback ◽  
Xiaoyue Judy Li ◽  
Rachel Weber ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Malignant Tumors ◽  
Ex Vivo ◽  
Benign Tumors ◽  
Cancerous Tissue ◽  
Breast Masses ◽  
Harmonic Motion ◽  
Harmonic Motion Imaging ◽  
Motion Imaging

Abstract Non-invasive diagnosis of breast cancer is still challenging due to the low specificity of the imaging modalities that calls for unnecessary biopsies. The diagnostic accuracy can be improved by assessing the breast tissue mechanical properties associated with pathological changes. Harmonic motion imaging (HMI) is an elasticity imaging technique that uses acoustic radiation force to evaluate the localized mechanical properties of the underlying tissue. Herein, we studied the in vivo feasibility of a clinical HMI system to differentiate breast tumors based on their relative HMI displacements, in human subjects. We performed HMI scans in 10 female subjects with breast masses: five benign and five malignant masses. Results revealed that both benign and malignant masses were stiffer than the surrounding tissues. However, malignant tumors underwent lower mean HMI displacement (1.1 ± 0.5 µm) compared to benign tumors (3.6 ± 1.5 µm) and the adjacent non-cancerous tissue (6.4 ± 2.5 µm), which allowed to differentiate between tumor types. Additionally, the excised breast specimens of the same patients (n = 5) were imaged post-surgically, where there was an excellent agreement between the in vivo and ex vivo findings, confirmed with histology. Higher displacement contrast between cancerous and non-cancerous tissue was found ex vivo, potentially due to the lower nonlinearity in the elastic properties of ex vivo tissue. This preliminary study lays the foundation for the potential complementary application of HMI in clinical practice in conjunction with the B-mode to classify suspicious breast masses.

Towards Uniformly Distributed Compliance in Compliant Mechanisms: A Multi-Objective Approach

2006 ◽  
Author(s):  
Stephen L. Canfield ◽  
Daniel L. Chlarson ◽  
Alexander Shibakov ◽  
Patrick V. Hull
Keyword(s):  
Finite Element ◽  
Objective Function ◽  
Compliant Mechanisms ◽  
Optimality Criteria ◽  
Optimal Designs ◽  
Limiting Factors ◽  
Objective Functions ◽  
Multi Objective ◽  
Simple Addition ◽  
Current Formulation

Researchers in the field of optimal synthesis of compliant mechanisms have been working to develop tools that yield distributed compliant devices to perform specific tasks. However, it has been demonstrated in the literature that much of this work has resulted in mechanisms that localize compliance rather than distribute it as desired. In fact, Yin and Ananthasuresh (2003) [1] demonstrate that based on the current formulation of optimality criteria and analysis via the finite element (FE) technique, a lumped compliant device will always exist as the minimizing solution to the objective function. The addition of constraints on allowable strain simply moves the solution back from this objective. Therefore, modification to the standard optimality criteria needs to take place. Yin and Ananthasuresh [1] proposed and compared several approaches that include distributivity-based measures within the optimality criteria, and demonstrated the effectiveness of this approach. In this paper, the authors propose to build on this problem. In a similar manner, a general approach to the topology synthesis problem will be suggested to yield mechanisms in which the compliance is distributed throughout the device. This work will be based on the idea of including compliance distribution directly within the objective functions, while addressing some of the potential limiting factors in past approaches. The technique will be generalized to allow simple addition of criteria in the future, and to deliver optimal designs through to manufacture. This work will first revisit and propose several quantitative definitions for distributed compliant devices. Then, a multi-objective formulation based on a non-dominating sort and Pareto set method will be incorporated that will provide information on the nature of the problem and compatibility of employed objective functions.

Regional vascular mechanical properties by 3-D intravascular ultrasound with finite-element analysis

1997 ◽  
Vol 272 (1) ◽  
pp. H425-H437 ◽  
Author(s):  
M. J. Vonesh ◽  
C. H. Cho ◽  
J. V. Pinto ◽  
B. J. Kane ◽  
D. S. Lee ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Elastic Modulus ◽  
Intravascular Ultrasound ◽  
Regional Distribution ◽  
Optimization Procedure ◽  
Element Analysis ◽  
Dimensionless Variable

A method employing intravascular ultrasound (IVUS) and simultaneous hemodynamic measurements, with resultant finite element analysis (FEA) of accurate three-dimensional IVUS reconstructions (3-DR), was developed to estimate the regional distribution of arterial elasticity. Human peripheral arterial specimens (iliac and femoral, n = 7) were collected postmortem and perfused at three static transmural pressures: 80, 120, and 160 mmHg. At each pressure, IVUS data were collected at 2.0-mm increments through a 20.0-mm segment and used to create an accurate 3-DR. Mechanical properties were determined over normotensive and hypertensive ranges. An FEA and optimization procedure was implemented in which the elemental elastic modulus was scaled to minimize the displacement error between the computer-predicted and actual deformations. The “optimized” elastic modulus (Eopt) represents an estimate of the component element material stiffness. A dimensionless variable (beta), quantifying structural stiffness, was computed. Eopt of nodiseased tissue regions (n = 80) was greater than atherosclerotic regions (n = 88) for both normotensive (Norm) and hypertensive (Hyp) pressurization: Norm, 9.3 +/- 0.98 vs. 3.5 +/- 0.30; Hyp, 11.3 +/- 0.72 vs. 8.5 +/- 0.47, respectively (mean +/- SE x 10(6) dyn/cm2; P < 0.01 vs. nondiseased). No differences in beta between nondiseased and atherosclerotic tissue were noted at Norm pressurization. With Hyp pressurization, beta of atherosclerotic regions were greater than nondiseased regions: 21.5 +/- 2.21 vs. 14.0 +/- 2.11, respectively (P < 0.03). This method provides a means to identify regional in vivo variations in mechanical properties of arterial tissue.

Rhodiola and salidroside in the treatment of metabolic disorders

2019 ◽  
Vol 19 (19) ◽  
pp. 1611-1626 ◽  
Author(s):  
Xiang-Li Bai ◽  
Xiu-Ling Deng ◽  
Guang-Jie Wu ◽  
Wen-Jing Li ◽  
Si Jin
Keyword(s):  
Metabolic Disorders ◽  
Energy Homeostasis ◽  
Molecular Mechanisms ◽  
Metabolic Diseases ◽  
Ex Vivo ◽  
Treatment Strategies ◽  
Ampk Signaling ◽  
Beneficial Effects

Over the past three decades, the knowledge gained about the mechanisms that underpin the potential use of Rhodiola in stress- and ageing-associated disorders has increased, and provided a universal framework for studies that focused on the use of Rhodiola in preventing or curing metabolic diseases. Of particular interest is the emerging role of Rhodiola in the maintenance of energy homeostasis. Moreover, over the last two decades, great efforts have been undertaken to unravel the underlying mechanisms of action of Rhodiola in the treatment of metabolic disorders. Extracts of Rhodiola and salidroside, the most abundant active compound in Rhodiola, are suggested to provide a beneficial effect in mental, behavioral, and metabolic disorders. Both in vivo and ex vivo studies, Rhodiola extracts and salidroside ameliorate metabolic disorders when administered acutely or prior to experimental injury. The mechanism involved includes multi-target effects by modulating various synergistic pathways that control oxidative stress, inflammation, mitochondria, autophagy, and cell death, as well as AMPK signaling that is associated with possible beneficial effects on metabolic disorders. However, evidence-based data supporting the effectiveness of Rhodiola or salidroside in treating metabolic disorders is limited. Therefore, a comprehensive review of available trials showing putative treatment strategies of metabolic disorders that include both clinical effective perspectives and fundamental molecular mechanisms is warranted. This review highlights studies that focus on the potential role of Rhodiola extracts and salidroside in type 2 diabetes and atherosclerosis, the two most common metabolic diseases.

Abstract 474: Early Events in Dissecting Aneurysms Induced by Angiotensin-II Infusion: The Geometry-Driven Aspect of a Multifaceted Problem

2017 ◽  
Vol 37 (suppl_1) ◽  
Author(s):  
Lydia Aslanidou ◽  
Bram Trachet ◽  
Mauro Ferraro ◽  
Alessandra Piersigilli ◽  
Rodrigo Fraga-Silva ◽  
...  
Keyword(s):  
Finite Element ◽  
Angiotensin Ii ◽  
Ex Vivo ◽  
Apoptotic Cell ◽  
Morphological Changes ◽  
Aortic Tissue ◽  
Isotropic Resolution ◽  
Circumferential Distribution ◽  
Dissecting Aneurysms

While research on dissecting aneurysms in Angiotensin-II infused mice spans more than a decade, the temporal sequence of initial events still remains unclear. Recent findings in our group suggested that focal medial tears at the vicinity of suprarenal side branches are the primary event in disease formation. In this study we used a combined experimental-computational approach to investigate the hypothesis that initial events of dissecting AAAs originate at branching sites along the aorta. Male apolipoprotein-deficient mice were infused with Angiotensin-II (n=11) and saline 0.9% (n=6) for 3 days and scanned with contrast-enhanced microCT prior to sacrifice. One animal presented an in-vivo rupture during the microCT scan, and was rescanned after 2.5 hours to observe real-time morphological changes. In all other animals, the excised aortic tissue was imaged with Phase Contrast X-Ray Tomographic Microscopy (PCXTM) at 6.5um isotropic resolution. An automatic morphing code was developed to map the ex-vivo geometry onto the in vivo geometry, and a finite element simulation yielded a stress distribution that represents an estimation of the wall tension, not only due to the pressurization, but also due to the local stretch field. We found that the nanoparticulate microCT contrast agent had infiltrated the aortic wall in 11/11 Ang-II infused animals, while no infiltration was observed in 6/6 control mice. The infiltration affected at least one pair of intercostal arteries in 11/11 mice, and in 9/11 mice the coeliac region was also affected. Image-guided histology allowed us to determine the circumferential distribution of microlesions at branching sites, including disruption of elastin fibers, apoptotic cell appearance, subintimal leukocyte infiltration and intramural hematomas. In the animal whose aorta had ruptured during the in vivo scan, the initial hematoma had originated around 3 pairs of intercostal arteries and quickly propagated afterwards. Mouse-specific finite element simulations revealed a co-location of computed peak stresses at the vessel wall and histologically identified vascular damage. We conclude that the aortic geometry, and side branches in particular, play a pivotal role in the onset of dissecting AAA.

Inverse Estimation of the In Vivo Mechanical Properties of the Human Cornea

2000 ◽  
Author(s):  
Shou-sung Chang ◽  
Peter M. Pinsky
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Finite Element Model ◽  
Element Model ◽  
Human Cornea ◽  
Corneal Tissue ◽  
Shear Moduli ◽  
Inverse Estimation ◽  
Nonlinear Finite Element Model

Abstract Various forms of refractive surgery for vision correction have come into clinical practice in which the corneal tissue is either incised, removed, added to, or redistributed. The outcomes of these procedures must be to a large extent determined by the intrinsic mechanical properties of the major structural layer of the cornea, the stroma1. If these mechanical properties, principally the Young’s modulus and shear modulus, are established for the human cornea, it will be possible to include them in a finite element model of the stroma that can help predict the outcome of keratorefractive procedures. In this study an opto-mechanical testing device was developed to measure the contour of a cornea deformed in situ by a mechanical probe. A nonlinear finite element model of the cornea was then constructed to simulate the experiment for use in inverse estimation of the in vivo Young’s and shear moduli of an individual eye.

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