Physical and Engineering Sciences in Medicine/Physical and engineering sciences in medicine, Feb 6, 2024
This paper presents a novel method for reconstructing skin parameters using Probabilistic Inverse... more This paper presents a novel method for reconstructing skin parameters using Probabilistic Inverse Problem (PIP) techniques and Torsional Wave Elastography (TWE) rheological modeling. A comprehensive examination was conducted to compare and analyze the theoretical, time-of-flight (TOF), and full-signal waveform (FSW) approaches. The objective was the identification of the most effective method for the estimation of mechanical parameters. Initially, the most appropriate rheological model for the simulation of skin tissue behavior was determined through the application and comparison of two models, spring pot (SP) and Kevin Voigt fractional derivative (KVFD). A numerical model was developed using the chosen rheological models. The collection of experimental data from 15 volunteers utilizing a TWE sensor was crucial for obtaining significant information for the reconstruction process. The study sample consisted of five male and ten female subjects ranging in age from 25 to 60 years. The procedure was performed on the ventral forearm region of the participants. The process of reconstructing skin tissue parameters was carried out using PIP techniques. The experimental findings were compared with the numerical results. The three methods considered (theoretical, TOF, FSW) have been used. The efficacy of TOF and FSW was then compared with theoretical method. The findings of the study demonstrate that the FSW and TOF techniques successfully reconstructed the parameters of the skin tissue in all of the models. The SP model's the skin tissue values ranged from 8 to 12 Pa ⋅ s , as indicated by the TOF reconstruction parameters. values found by the KVFD model ranged from 4.1 to 9.3 Pa ⋅ s. The values generated by the KVFD model range between 0.61 and 96.86 kPa. However, FSW parameters reveal that skin tissue values for the SP model ranged from 7.8 to 12 Pa ⋅ s. The KVFD model determined values between 6.3 and 9.5 Pa ⋅ s. The KVFD model presents values ranging between 26.02 and 122.19 kPa. It is shown that the rheological model that best describes the nature of the skin is the SP model and its simplicity as it requires only two parameters, in contrast to the three parameters required by the KVFD model. Therefore, this work provides a valuable addition to the area of dermatology, with possible implications for clinical practice.
Physical and Engineering Sciences in Medicine, Aug 28, 2023
Measuring the mechanical nonlinear properties of the cornea remains challenging due to the lack o... more Measuring the mechanical nonlinear properties of the cornea remains challenging due to the lack of consensus in the methodology and in the models that effectively predict its behaviour. This study proposed developing a procedure to reconstruct nonlinear fourth-order elastic properties of the cornea based on a mathematical model derived from the theory of Hamilton et al. and using the torsional wave elastography (TWE) technique. In order to validate its diagnostic capability of simulated pathological conditions, two different groups were studied, non-treated cornea samples (n=7), and ammonium hydroxide (NH 4 OH) treated samples (n=7). All the samples were measured in-plane by a torsional wave device by increasing IOP from 5 to 25 mmHg with 5 mmHg steps. The results show a nonlinear variation of the shear wave speed with the IOP, with higher values for higher IOPs. Moreover, the shear wave speed values of the control group were higher than those of the treated group. The study also revealed significant differences between the control and treated groups for the Lamé parameter (25.9-6.52 kPa), third-order elastic constant A (215.09-44.85 kPa), and fourth-order elastic constant D (523.5-129.63 kPa), with p-values of 0.010, 0.024, and 0.032, respectively. These findings demonstrate that the proposed procedure can distinguish between healthy and damaged corneas, making it a promising technique for detecting diseases associated with IOP alteration, such as corneal burns, glaucoma, or ocular hypertension.
The clinical ultrasound community demands mechanisms to obtain the viscoelastic biomarkers of sof... more The clinical ultrasound community demands mechanisms to obtain the viscoelastic biomarkers of soft tissue in order to quantify the tissue condition and to be able to track its consistency. Torsional Wave Elastography (TWE) is an emerging technique proposed for interrogating soft tissue mechanical viscoelastic constants. Torsional waves are a particular configuration of shear waves, which propagate asymmetrically in-depth and are radially transmitted by a disc and received by a ring. This configuration is shown to be particularly efficient in minimizing spurious p-waves components and is sensitive to mechanical constants, especially in cylinder-shaped organs. The objective of this work was to validate (TWE) technique against Shear Wave Elasticity Imaging (SWEI) technique through the determination of shear wave velocity, shear moduli, and viscosity of ex vivo chicken liver samples and tissue mimicking hydrogel phantoms. The results of shear moduli for ex vivo liver tissue vary 1.69-4.0 kPa using TWE technique and 1.32-4.48 kPa using SWEI technique for a range of frequencies from 200 to 800 Hz. Kelvin-Voigt viscoelastic parameters reported values of µ = 1.51 kPa and η = 0.54 Pa•s using TWE and µ = 1.02 kPa and η = 0.63 Pa•s using SWEI. Preliminary results show that the proposed technique successfully allows reconstructing shear wave velocity, shear moduli, and viscosity mechanical biomarkers from the propagated torsional wave, establishing a proof of principle and warranting further studies.
Corneal mechanical changes are believed to occur before any visible structural alterations observ... more Corneal mechanical changes are believed to occur before any visible structural alterations observed during routine clinical evaluation. This study proposed developing an elastography technique based on torsional waves (TWE) adapted to the specificities of the cornea. By measuring the displacements in the propagation plane perpendicular to the axis of the emitter, the effect of guided waves in platelike media was proven negligible. Ex vivo experiments were carried out on porcine corneal samples considering a group of control and one group of alkali burn treatment (NH 4 OH) that modified the mechanical properties. Phase speed was recovered as a function of intraocular pressure (IOP), and a Kelvin-Voigt rheological model was fitted to the dispersion curves to estimate viscoelastic parameters. A comparison with uniaxial tensile testing with thin-walled assumptions was also performed. Both shear elasticity and viscosity correlated positively with IOP, being the elasticity lower and the viscosity higher for the treated group. The viscoelastic parameters ranged from 21.33 to 63.17 kPa, and from 2.82 to 5.30 Pa s, for shear elasticity and viscosity, respectively. As far as the authors know, no other investigations have studied this mechanical plane under low strain ratios, typical of dynamic elastography in corneal tissue. TWE reflected mechanical properties changes after treatment, showing a high potential for clinical diagnosis due to its rapid performance time and paving the way for future in vivo studies. The mechanical state of the cornea is assumed to be defined almost exclusively by the stroma 1. The rest of the layers that comprise this tissue are believed to have indirect contributions, as in the case of the endothelium, which deturgesces the cornea to maintain adequate functionality 2. The main component to which mechanical stability is attributed is collagen, whose fibers are packed and arranged, forming stacked oriented lamellae 3 (Fig. 1a). Significant changes in the organization of this layer may lead to corneal disorders, including progressive and generalized weakening of the cornea, corneal opacity, and subsequent vision loss 4. Among those, chemical eye burns, keratoconus and other ectatic disorders 5,6 emerge as a priority because of their incidence, severity, and impact on the patient's quality of life. More than 70% of chemical burns in the eye are accidents that occur at work and 84% of them are due to alkali chemicals 7. These high pH chemical reactants show a high penetration that can cause severe injury to external organs and tissues like the cornea 8. They can even penetrate the anterior chamber damaging the lens, the ciliary body, and the trabecular meshwork, causing cataract and secondary glaucoma in severe cases. The damage caused depends on the exposure time to the chemical, showing different grades of severity 9. From a physiological perspective, the primary function of the cornea, together with the lens, is to redirect light to the retina. Whereas the lens can change its geometry to improve focus on objects near it, the cornea has a fixed focus 10. This means that pathologies or alterations in the cornea that manifest themselves as changes at the microstructure level directly affect its refractive capacity, primarily by modifying optical power and transparency 11. It is believed that early diagnosis of these states could be achieved by evaluating constitutive mechanical properties, since changes in these properties occur before any of the macroscopically visible structural changes observed during routine clinical evaluation 12,13. In addition, as a viscoelastic tissue, the relevance of
Journal of the Acoustical Society of America, Sep 1, 2018
The WHO estimates that 15 million babies yearly (1 in 10) will be born preterm. Worldwide, compli... more The WHO estimates that 15 million babies yearly (1 in 10) will be born preterm. Worldwide, complications of preterm births have supplanted pneumonia as the primary cause of child mortality [1]. The biology of cervical ripening that leads to birth is poorly understood, and there is no clinical tool to quantitatively evaluate the cervical biomechanical state, which in words of Feltovich [2]“… likely contributes to the reason the singleton spontaneous preterm birth rate has not changed appreciably in more than 100 years.” Towards this problem, we work on enabling new sensor technologies sentient to soft tissue biomechanics, to endow a new class of biomarkers that quantify the mechanical functionality of the cervix, and indeed any soft tissue, ranging pathologies from tumors, atherosclerosis, liver fibrosis to osteoarticular syndromes. Ultrasonic characterization of soft tissue has been developed as a clinical diagnostic tool [3] and evolved through different technologies including our torsional wave principle [4]. Our recent advances covering (a) torsional waves (shear elastic waves that propagate in quasifluids radially and in depth in a curled geometry), (b) sensors (based on a novel arrangement of concentric sandwiches of elements), (c) propagation models and (d) patient testing, are allowing to quantify the mechanical functionality beyond linear parameters: dispersive and nonlinear. [1] WHO, 2012; [2] Feltovich. AJOG207(2012):345–354 [3] Barr. Ultras Quart28(2012):13–20; [4] Melchor. Ultrasonics, 54(2014):1950–1962.
Mathematical Problems in Engineering, Feb 27, 2019
Pregnancy involves a gradual change in tissue consistency, where, as gestational age increases a ... more Pregnancy involves a gradual change in tissue consistency, where, as gestational age increases a drop in stiffness is noticeable. The extracellular matrix (ECM) of the cervix whose behavior is controlled by the collagen structure is reconfigured, due to hormonal and protein related factors that degraded it. There is an increase in cellular and water content. The collagen maintains a stable percentage, although the synthesis-solubility interaction causes a transformation in the network increasing its diameter and waviness, which destabilizes the mechanical integrity. Further understanding of the remodeling of the cervix becomes a key element in the progress against preterm birth. However, since the woman is in a very delicate state, the available information is scattered. The aim is to provide a framework where the variation of the histological properties is linked with the individual biomechanical evolution of the constituents; therefore a multiscale approach to the problem can be made. The results of different authors were reviewed to obtain values of each component depending on the gestational age, and then they were combined with the mechanical development of each variable obtained from the outputs of numerical simulations of another author. An additive function is proposed, in which the mechanical contribution of each constituent is added to a reference value established for a nonpregnant state. Results show how biochemistry models the mechanical behavior of the tissue through the histology and morphology of the ECM.
The reconstruction of viscous properties of soft tissues, and more specifically, of cervical tiss... more The reconstruction of viscous properties of soft tissues, and more specifically, of cervical tissue is a challenging problem. In this paper, a new method is proposed to reconstruct the viscoelastic parameters of cervical tissue-mimicking phantoms by a Torsional Wave Elastography (TWE) technique. The reconstruction method, based on a Probabilistic Inverse Problem (PIP) approach, is presented and experimentally validated against Shear Wave Elastography (SWE). The anatomy of the cervical tissue has been mimicked by means of a two-layer gelatine phantom that simulates the epithelial and connective layers. Five ad hoc oil-in-gelatine phantoms were fabricated at different proportion to test the new reconstruction technique. The PIP approach was used for reconstructing the Kelvin-Voigt (KV) viscoelastic parameters by comparing the measurements obtained from the TWE technique with the synthetic signals from a Finite Difference Time Domain (FDTD) KV wave propagation model. Additionally, SWE tests were realized in order to characterize the viscoelastic properties of each batch of gelatine. Finally, validation was carried out by comparing the KV parameters inferred from the PIP with those reconstructed from the shear wave dispersion curve obtained from the SWE measurements. In order to test the degree of agreement between both techniques, a Student's T-test and a Pearson's correlation study were performed. The results indicate that the proposed method is able to reconstruct the KV viscoelastic properties of the cervical tissue, for both the epithelial and connective layers, as well as the thickness of the first layer with acceptable accuracy.
Journal of The Mechanical Behavior of Biomedical Materials, Mar 1, 2021
The understanding of changes in the viscoelastic properties of cervical tissue during the gestati... more The understanding of changes in the viscoelastic properties of cervical tissue during the gestation process is a challenging problem. In this work, we explore the importance of considering the multilayer nature (epithelial and connective layers) of human cervical tissue for characterizing the viscoelastic parameters from torsional waves. For this purpose, torsional wave propagations are simulated in three multilayer cervical tissue models (pure elastic, Kelvin-Voigt (KV) and Maxwell) using the finite difference time domain method. High-speed camera measurements have been carried out in tissue-mimicking phantoms in order to obtain the boundary conditions of the numerical simulations. Finally, a parametric modeling study through a probabilistic inverse procedure was performed to rank the most plausible rheological model and to reconstruct the viscoelastic parameters. The procedure consist in comparing the experimental signals obtained in human cervical tissues using the Torsional Wave Elastography (TWE) technique with the synthetic signals from the numerical models. It is shown that the rheological model that best describes the nature of cervical tissue is the Kelvin-Voigt model. Once the most plausible model has been selected, the stiffness and viscosity parameters have been reconstructed of the epithelial and connective layers for the measurements of the 18 pregnant women, along with the thickness of the epithelial layer.
This paper presents the results of the comparison between a proposed Fourth Order Elastic Constan... more This paper presents the results of the comparison between a proposed Fourth Order Elastic Constants (FOECs) nonlinear model defined in the sense of Landau's theory, and the two most contrasted hyperelastic models in the literature, Mooney-Rivlin, and Ogden models. A mechanical testing protocol is developed to investigate the large-strain response of ex vivo cervical tissue samples in uniaxial tension in its two principal anatomical locations, the epithelial and connective layers. The final aim of this work is to compare the reconstructed shear modulus of the epithelial and connective layers of cervical tissue. According to the obtained results, the nonlinear parameter A from the proposed FOEC model could be an important biomarker in cervical tissue diagnosis. In addition, the calculated shear modulus depended on the anatomical location of the cervical tissue (µ epithelial = 1.29 ± 0.15 MPa, and µ connective = 3.60 ± 0.63 MPa) .
The adoption of multiscale approaches by the biomechanical community has caused a major improveme... more The adoption of multiscale approaches by the biomechanical community has caused a major improvement in quality in the mechanical characterization of soft tissues. The recent developments in elastography techniques are enabling in vivo and non-invasive quantification of tissues' mechanical properties. Elastic changes in a tissue are associated with a broad spectrum of pathologies, which stems from the tissue microstructure, histology and biochemistry. This knowledge is combined with research evidence to provide a powerful diagnostic range of highly prevalent pathologies, from birth and labor disorders (prematurity, induction failures, etc.), to solid tumors (e.g., prostate, cervix, breast, melanoma) and liver fibrosis, just to name a few. This review aims to elucidate the potential of viscous and nonlinear elastic parameters as conceivable diagnostic mechanical biomarkers. First, by providing an insight into the classic role of soft tissue microstructure in linear elasticity; secondly, by understanding how viscosity and nonlinearity could enhance the current diagnosis in elastography; and finally, by compounding preliminary investigations of those elastography parameters within different technologies. In conclusion, evidence of the diagnostic capability of elastic parameters beyond linear stiffness is gaining momentum as a result of the technological and imaging developments in the field of biomechanics.
The objective of this study was to evaluate which hyperelastic model could best describe the nonl... more The objective of this study was to evaluate which hyperelastic model could best describe the nonlinear mechanical behavior of the cornea, in order to characterize the capability of the non-linear model parameters to discriminate structural changes in a damaged cornea. Porcine corneas were used, establishing two different groups: control (non-treated) and NaOH-treated (damaged) corneas (n = 8). NaOH causes a chemical burn to the corneal tissue, simulating a disease associated to structural damage of the stromal layer. Quasi-static uniaxial tensile tests were performed in nasaltemporal direction immediately after preparing corneal strips from the two groups. Three non-linear hyperelastic models (i.e. Hamilton-Zabolotskaya model, Ogden model and Mooney-Rivlin model) were fitted to the stress-strain curves obtained in the tensile tests and statistically compared. The corneas from the two groups showed a non-linear mechanical behavior that was best described by the Hamilton-Zabolotskaya model, obtaining the highest coefficient of determination (R 2 > 0.95). Moreover, Hamilton-Zabolotskaya model showed the highest discriminative capability of the nonlinear model parameter (Parameter A) for the tissue structural changes between the two sample groups (p = 0.0005). The present work determines the best hyperelastic model with the highest discriminative capability in description of the non-linear mechanical behavior of the cornea. The cornea is the outermost layer of the eye, acting as a barrier against the external environment and as the main diopter of the visual system 1. Diseases that affect the cornea are one of the main causes of blindness in the world, ranking among the three most prevalent worldwide 2. Among those, corneal ectasia or corneal ectatic disorders stand as a main priority because of their incidence and impact in young population. These are corneal disorders, such as keratoconus or pellucid marginal corneal degeneration, that cause alterations in the corneal structure, leading to corneal topographical changes with decreased corneal thickness and abnormal corneal curvature 3. This abnormal structure of the cornea, as a result of non-linear mechanical changes, finally causes visual impairment to the patient. Currently, the diagnose of corneal degenerations and other corneal diseases are mainly based on structural measurements of the cornea (i.e. curvature, thickness, etc.), while some studies covered in-vivo non-structural measurements using Oculus Corvis ST and Ocular Response Analyzer systems 4-6. These new, non-invasive systems can analyze corneal biomechanical properties, such as corneal hysteresis, including an estimation of intraocular pressure. However, we propose that non-linear mechanical parameters can be obtained from non-invasive elastography or probing technologies such as non-linear torsional waves, non-linearity in probing, non-linearity by micro-indentation to be used in diagnostics in-vivo without removing the cornea 7-9. Hence, quantifying the non-linear mechanical parameters of soft tissues like the cornea might become more specific diagnostic criteria than structural measurements. This is supported by the fact that non-linear mechanical characterization and non-linear model parameters are very sensitive realistic approaches to measure the tissue structural damages 7,8. The feasibility of early diagnosis of corneal diseases such as keratoconus is however an open issue to be investigated in the future. This will depend on the precision of the nonlinearity parameter achievable by the selected probing technology, and thereof define the sensitivity and sensibility.
Corneal mechanical changes are believed to occur before any visible structural alterations observ... more Corneal mechanical changes are believed to occur before any visible structural alterations observed during routine clinical evaluation. This study proposed developing an elastography technique based on torsional waves (TWE) adapted to the specificities of the cornea. By measuring the displacements in the propagation plane perpendicular to the axis of the emitter, the effect of guided waves in plate-like media was proven negligible. Ex vivo experiments were carried out on porcine corneal samples considering a group of control and one group of alkali burn treatment ($$\hbox {NH}_\text {4}$$ NH 4 OH) that modified the mechanical properties. Phase speed was recovered as a function of intraocular pressure (IOP), and a Kelvin-Voigt rheological model was fitted to the dispersion curves to estimate viscoelastic parameters. A comparison with uniaxial tensile testing with thin-walled assumptions was also performed. Both shear elasticity and viscosity correlated positively with IOP, being the ...
Journal of the Mechanical Behavior of Biomedical Materials, 2021
The understanding of changes in the viscoelastic properties of cervical tissue during the gestati... more The understanding of changes in the viscoelastic properties of cervical tissue during the gestation process is a challenging problem. In this work, we explore the importance of considering the multilayer nature (epithelial and connective layers) of human cervical tissue for characterizing the viscoelastic parameters from torsional waves. For this purpose, torsional wave propagations are simulated in three multilayer cervical tissue models (pure elastic, Kelvin-Voigt (KV) and Maxwell) using the finite difference time domain method. High-speed camera measurements have been carried out in tissue-mimicking phantoms in order to obtain the boundary conditions of the numerical simulations. Finally, a parametric modeling study through a probabilistic inverse procedure was performed to rank the most plausible rheological model and to reconstruct the viscoelastic parameters. The procedure consist in comparing the experimental signals obtained in human cervical tissues using the Torsional Wave Elastography (TWE) technique with the synthetic signals from the numerical models. It is shown that the rheological model that best describes the nature of cervical tissue is the Kelvin-Voigt model. Once the most plausible model has been selected, the stiffness and viscosity parameters have been reconstructed of the epithelial and connective layers for the measurements of the 18 pregnant women, along with the thickness of the epithelial layer.
The adoption of multiscale approaches by the biomechanical community has caused a major improveme... more The adoption of multiscale approaches by the biomechanical community has caused a major improvement in quality in the mechanical characterization of soft tissues. The recent developments in elastography techniques are enabling in vivo and non-invasive quantification of tissues’ mechanical properties. Elastic changes in a tissue are associated with a broad spectrum of pathologies, which stems from the tissue microstructure, histology and biochemistry. This knowledge is combined with research evidence to provide a powerful diagnostic range of highly prevalent pathologies, from birth and labor disorders (prematurity, induction failures, etc.), to solid tumors (e.g., prostate, cervix, breast, melanoma) and liver fibrosis, just to name a few. This review aims to elucidate the potential of viscous and nonlinear elastic parameters as conceivable diagnostic mechanical biomarkers. First, by providing an insight into the classic role of soft tissue microstructure in linear elasticity; secondl...
This paper presents the results of the comparison between a proposed Fourth Order Elastic Constan... more This paper presents the results of the comparison between a proposed Fourth Order Elastic Constants (FOECs) nonlinear model defined in the sense of Landau’s theory, and the two most contrasted hyperelastic models in the literature, Mooney–Rivlin, and Ogden models. A mechanical testing protocol is developed to investigate the large-strain response of ex vivo cervical tissue samples in uniaxial tension in its two principal anatomical locations, the epithelial and connective layers. The final aim of this work is to compare the reconstructed shear modulus of the epithelial and connective layers of cervical tissue. According to the obtained results, the nonlinear parameter A from the proposed FOEC model could be an important biomarker in cervical tissue diagnosis. In addition, the calculated shear modulus depended on the anatomical location of the cervical tissue (μepithelial = 1.29 ± 0.15 MPa, and μconnective = 3.60 ± 0.63 MPa).
The clinical ultrasound community demands mechanisms to obtain the viscoelastic biomarkers of sof... more The clinical ultrasound community demands mechanisms to obtain the viscoelastic biomarkers of soft tissue in order to quantify the tissue condition and to be able to track its consistency. Torsional Wave Elastography (TWE) is an emerging technique proposed for interrogating soft tissue mechanical viscoelastic constants. Torsional waves are a particular configuration of shear waves, which propagate asymmetrically in-depth and are radially transmitted by a disc and received by a ring. This configuration is shown to be particularly efficient in minimizing spurious p-waves components and is sensitive to mechanical constants, especially in cylinder-shaped organs. The objective of this work was to validate (TWE) technique against Shear Wave Elasticity Imaging (SWEI) technique through the determination of shear wave velocity, shear moduli, and viscosity of ex vivo chicken liver samples and tissue mimicking hydrogel phantoms. The results of shear moduli for ex vivo liver tissue vary 1.69–4....
The Journal of the Acoustical Society of America, 2018
The WHO estimates that 15 million babies yearly (1 in 10) will be born preterm. Worldwide, compli... more The WHO estimates that 15 million babies yearly (1 in 10) will be born preterm. Worldwide, complications of preterm births have supplanted pneumonia as the primary cause of child mortality [1]. The biology of cervical ripening that leads to birth is poorly understood, and there is no clinical tool to quantitatively evaluate the cervical biomechanical state, which in words of Feltovich [2]“… likely contributes to the reason the singleton spontaneous preterm birth rate has not changed appreciably in more than 100 years.” Towards this problem, we work on enabling new sensor technologies sentient to soft tissue biomechanics, to endow a new class of biomarkers that quantify the mechanical functionality of the cervix, and indeed any soft tissue, ranging pathologies from tumors, atherosclerosis, liver fibrosis to osteoarticular syndromes. Ultrasonic characterization of soft tissue has been developed as a clinical diagnostic tool [3] and evolved through different technologies including our ...
The reconstruction of viscous properties of soft tissues, and more specifically, of cervical tiss... more The reconstruction of viscous properties of soft tissues, and more specifically, of cervical tissue is a challenging problem. In this paper, a new method is proposed to reconstruct the viscoelastic parameters of cervical tissue-mimicking phantoms by a Torsional Wave Elastography (TWE) technique. The reconstruction method, based on a Probabilistic Inverse Problem (PIP) approach, is presented and experimentally validated against Shear Wave Elastography (SWE). The anatomy of the cervical tissue has been mimicked by means of a two-layer gelatine phantom that simulates the epithelial and connective layers. Five ad hoc oil-in-gelatine phantoms were fabricated at different proportion to test the new reconstruction technique. The PIP approach was used for reconstructing the Kelvin-Voigt (KV) viscoelastic parameters by comparing the measurements obtained from the TWE technique with the synthetic signals from a Finite Difference Time Domain (FDTD) KV wave propagation model. Additionally, SWE ...
Pregnancy involves a gradual change in tissue consistency, where, as gestational age increases a ... more Pregnancy involves a gradual change in tissue consistency, where, as gestational age increases a drop in stiffness is noticeable. The extracellular matrix (ECM) of the cervix whose behavior is controlled by the collagen structure is reconfigured, due to hormonal and protein related factors that degraded it. There is an increase in cellular and water content. The collagen maintains a stable percentage, although the synthesis-solubility interaction causes a transformation in the network increasing its diameter and waviness, which destabilizes the mechanical integrity. Further understanding of the remodeling of the cervix becomes a key element in the progress against preterm birth. However, since the woman is in a very delicate state, the available information is scattered. The aim is to provide a framework where the variation of the histological properties is linked with the individual biomechanical evolution of the constituents; therefore a multiscale approach to the problem can be m...
The objective of this study was to evaluate which hyperelastic model could best describe the non-... more The objective of this study was to evaluate which hyperelastic model could best describe the non-linear mechanical behavior of the cornea, in order to characterize the capability of the non-linear model parameters to discriminate structural changes in a damaged cornea. Porcine corneas were used, establishing two different groups: control (non-treated) and NaOH-treated (damaged) corneas (n = 8). NaOH causes a chemical burn to the corneal tissue, simulating a disease associated to structural damage of the stromal layer. Quasi-static uniaxial tensile tests were performed in nasal-temporal direction immediately after preparing corneal strips from the two groups. Three non-linear hyperelastic models (i.e. Hamilton-Zabolotskaya model, Ogden model and Mooney-Rivlin model) were fitted to the stress–strain curves obtained in the tensile tests and statistically compared. The corneas from the two groups showed a non-linear mechanical behavior that was best described by the Hamilton-Zabolotskay...
Physical and Engineering Sciences in Medicine/Physical and engineering sciences in medicine, Feb 6, 2024
This paper presents a novel method for reconstructing skin parameters using Probabilistic Inverse... more This paper presents a novel method for reconstructing skin parameters using Probabilistic Inverse Problem (PIP) techniques and Torsional Wave Elastography (TWE) rheological modeling. A comprehensive examination was conducted to compare and analyze the theoretical, time-of-flight (TOF), and full-signal waveform (FSW) approaches. The objective was the identification of the most effective method for the estimation of mechanical parameters. Initially, the most appropriate rheological model for the simulation of skin tissue behavior was determined through the application and comparison of two models, spring pot (SP) and Kevin Voigt fractional derivative (KVFD). A numerical model was developed using the chosen rheological models. The collection of experimental data from 15 volunteers utilizing a TWE sensor was crucial for obtaining significant information for the reconstruction process. The study sample consisted of five male and ten female subjects ranging in age from 25 to 60 years. The procedure was performed on the ventral forearm region of the participants. The process of reconstructing skin tissue parameters was carried out using PIP techniques. The experimental findings were compared with the numerical results. The three methods considered (theoretical, TOF, FSW) have been used. The efficacy of TOF and FSW was then compared with theoretical method. The findings of the study demonstrate that the FSW and TOF techniques successfully reconstructed the parameters of the skin tissue in all of the models. The SP model's the skin tissue values ranged from 8 to 12 Pa ⋅ s , as indicated by the TOF reconstruction parameters. values found by the KVFD model ranged from 4.1 to 9.3 Pa ⋅ s. The values generated by the KVFD model range between 0.61 and 96.86 kPa. However, FSW parameters reveal that skin tissue values for the SP model ranged from 7.8 to 12 Pa ⋅ s. The KVFD model determined values between 6.3 and 9.5 Pa ⋅ s. The KVFD model presents values ranging between 26.02 and 122.19 kPa. It is shown that the rheological model that best describes the nature of the skin is the SP model and its simplicity as it requires only two parameters, in contrast to the three parameters required by the KVFD model. Therefore, this work provides a valuable addition to the area of dermatology, with possible implications for clinical practice.
Physical and Engineering Sciences in Medicine, Aug 28, 2023
Measuring the mechanical nonlinear properties of the cornea remains challenging due to the lack o... more Measuring the mechanical nonlinear properties of the cornea remains challenging due to the lack of consensus in the methodology and in the models that effectively predict its behaviour. This study proposed developing a procedure to reconstruct nonlinear fourth-order elastic properties of the cornea based on a mathematical model derived from the theory of Hamilton et al. and using the torsional wave elastography (TWE) technique. In order to validate its diagnostic capability of simulated pathological conditions, two different groups were studied, non-treated cornea samples (n=7), and ammonium hydroxide (NH 4 OH) treated samples (n=7). All the samples were measured in-plane by a torsional wave device by increasing IOP from 5 to 25 mmHg with 5 mmHg steps. The results show a nonlinear variation of the shear wave speed with the IOP, with higher values for higher IOPs. Moreover, the shear wave speed values of the control group were higher than those of the treated group. The study also revealed significant differences between the control and treated groups for the Lamé parameter (25.9-6.52 kPa), third-order elastic constant A (215.09-44.85 kPa), and fourth-order elastic constant D (523.5-129.63 kPa), with p-values of 0.010, 0.024, and 0.032, respectively. These findings demonstrate that the proposed procedure can distinguish between healthy and damaged corneas, making it a promising technique for detecting diseases associated with IOP alteration, such as corneal burns, glaucoma, or ocular hypertension.
The clinical ultrasound community demands mechanisms to obtain the viscoelastic biomarkers of sof... more The clinical ultrasound community demands mechanisms to obtain the viscoelastic biomarkers of soft tissue in order to quantify the tissue condition and to be able to track its consistency. Torsional Wave Elastography (TWE) is an emerging technique proposed for interrogating soft tissue mechanical viscoelastic constants. Torsional waves are a particular configuration of shear waves, which propagate asymmetrically in-depth and are radially transmitted by a disc and received by a ring. This configuration is shown to be particularly efficient in minimizing spurious p-waves components and is sensitive to mechanical constants, especially in cylinder-shaped organs. The objective of this work was to validate (TWE) technique against Shear Wave Elasticity Imaging (SWEI) technique through the determination of shear wave velocity, shear moduli, and viscosity of ex vivo chicken liver samples and tissue mimicking hydrogel phantoms. The results of shear moduli for ex vivo liver tissue vary 1.69-4.0 kPa using TWE technique and 1.32-4.48 kPa using SWEI technique for a range of frequencies from 200 to 800 Hz. Kelvin-Voigt viscoelastic parameters reported values of µ = 1.51 kPa and η = 0.54 Pa•s using TWE and µ = 1.02 kPa and η = 0.63 Pa•s using SWEI. Preliminary results show that the proposed technique successfully allows reconstructing shear wave velocity, shear moduli, and viscosity mechanical biomarkers from the propagated torsional wave, establishing a proof of principle and warranting further studies.
Corneal mechanical changes are believed to occur before any visible structural alterations observ... more Corneal mechanical changes are believed to occur before any visible structural alterations observed during routine clinical evaluation. This study proposed developing an elastography technique based on torsional waves (TWE) adapted to the specificities of the cornea. By measuring the displacements in the propagation plane perpendicular to the axis of the emitter, the effect of guided waves in platelike media was proven negligible. Ex vivo experiments were carried out on porcine corneal samples considering a group of control and one group of alkali burn treatment (NH 4 OH) that modified the mechanical properties. Phase speed was recovered as a function of intraocular pressure (IOP), and a Kelvin-Voigt rheological model was fitted to the dispersion curves to estimate viscoelastic parameters. A comparison with uniaxial tensile testing with thin-walled assumptions was also performed. Both shear elasticity and viscosity correlated positively with IOP, being the elasticity lower and the viscosity higher for the treated group. The viscoelastic parameters ranged from 21.33 to 63.17 kPa, and from 2.82 to 5.30 Pa s, for shear elasticity and viscosity, respectively. As far as the authors know, no other investigations have studied this mechanical plane under low strain ratios, typical of dynamic elastography in corneal tissue. TWE reflected mechanical properties changes after treatment, showing a high potential for clinical diagnosis due to its rapid performance time and paving the way for future in vivo studies. The mechanical state of the cornea is assumed to be defined almost exclusively by the stroma 1. The rest of the layers that comprise this tissue are believed to have indirect contributions, as in the case of the endothelium, which deturgesces the cornea to maintain adequate functionality 2. The main component to which mechanical stability is attributed is collagen, whose fibers are packed and arranged, forming stacked oriented lamellae 3 (Fig. 1a). Significant changes in the organization of this layer may lead to corneal disorders, including progressive and generalized weakening of the cornea, corneal opacity, and subsequent vision loss 4. Among those, chemical eye burns, keratoconus and other ectatic disorders 5,6 emerge as a priority because of their incidence, severity, and impact on the patient's quality of life. More than 70% of chemical burns in the eye are accidents that occur at work and 84% of them are due to alkali chemicals 7. These high pH chemical reactants show a high penetration that can cause severe injury to external organs and tissues like the cornea 8. They can even penetrate the anterior chamber damaging the lens, the ciliary body, and the trabecular meshwork, causing cataract and secondary glaucoma in severe cases. The damage caused depends on the exposure time to the chemical, showing different grades of severity 9. From a physiological perspective, the primary function of the cornea, together with the lens, is to redirect light to the retina. Whereas the lens can change its geometry to improve focus on objects near it, the cornea has a fixed focus 10. This means that pathologies or alterations in the cornea that manifest themselves as changes at the microstructure level directly affect its refractive capacity, primarily by modifying optical power and transparency 11. It is believed that early diagnosis of these states could be achieved by evaluating constitutive mechanical properties, since changes in these properties occur before any of the macroscopically visible structural changes observed during routine clinical evaluation 12,13. In addition, as a viscoelastic tissue, the relevance of
Journal of the Acoustical Society of America, Sep 1, 2018
The WHO estimates that 15 million babies yearly (1 in 10) will be born preterm. Worldwide, compli... more The WHO estimates that 15 million babies yearly (1 in 10) will be born preterm. Worldwide, complications of preterm births have supplanted pneumonia as the primary cause of child mortality [1]. The biology of cervical ripening that leads to birth is poorly understood, and there is no clinical tool to quantitatively evaluate the cervical biomechanical state, which in words of Feltovich [2]“… likely contributes to the reason the singleton spontaneous preterm birth rate has not changed appreciably in more than 100 years.” Towards this problem, we work on enabling new sensor technologies sentient to soft tissue biomechanics, to endow a new class of biomarkers that quantify the mechanical functionality of the cervix, and indeed any soft tissue, ranging pathologies from tumors, atherosclerosis, liver fibrosis to osteoarticular syndromes. Ultrasonic characterization of soft tissue has been developed as a clinical diagnostic tool [3] and evolved through different technologies including our torsional wave principle [4]. Our recent advances covering (a) torsional waves (shear elastic waves that propagate in quasifluids radially and in depth in a curled geometry), (b) sensors (based on a novel arrangement of concentric sandwiches of elements), (c) propagation models and (d) patient testing, are allowing to quantify the mechanical functionality beyond linear parameters: dispersive and nonlinear. [1] WHO, 2012; [2] Feltovich. AJOG207(2012):345–354 [3] Barr. Ultras Quart28(2012):13–20; [4] Melchor. Ultrasonics, 54(2014):1950–1962.
Mathematical Problems in Engineering, Feb 27, 2019
Pregnancy involves a gradual change in tissue consistency, where, as gestational age increases a ... more Pregnancy involves a gradual change in tissue consistency, where, as gestational age increases a drop in stiffness is noticeable. The extracellular matrix (ECM) of the cervix whose behavior is controlled by the collagen structure is reconfigured, due to hormonal and protein related factors that degraded it. There is an increase in cellular and water content. The collagen maintains a stable percentage, although the synthesis-solubility interaction causes a transformation in the network increasing its diameter and waviness, which destabilizes the mechanical integrity. Further understanding of the remodeling of the cervix becomes a key element in the progress against preterm birth. However, since the woman is in a very delicate state, the available information is scattered. The aim is to provide a framework where the variation of the histological properties is linked with the individual biomechanical evolution of the constituents; therefore a multiscale approach to the problem can be made. The results of different authors were reviewed to obtain values of each component depending on the gestational age, and then they were combined with the mechanical development of each variable obtained from the outputs of numerical simulations of another author. An additive function is proposed, in which the mechanical contribution of each constituent is added to a reference value established for a nonpregnant state. Results show how biochemistry models the mechanical behavior of the tissue through the histology and morphology of the ECM.
The reconstruction of viscous properties of soft tissues, and more specifically, of cervical tiss... more The reconstruction of viscous properties of soft tissues, and more specifically, of cervical tissue is a challenging problem. In this paper, a new method is proposed to reconstruct the viscoelastic parameters of cervical tissue-mimicking phantoms by a Torsional Wave Elastography (TWE) technique. The reconstruction method, based on a Probabilistic Inverse Problem (PIP) approach, is presented and experimentally validated against Shear Wave Elastography (SWE). The anatomy of the cervical tissue has been mimicked by means of a two-layer gelatine phantom that simulates the epithelial and connective layers. Five ad hoc oil-in-gelatine phantoms were fabricated at different proportion to test the new reconstruction technique. The PIP approach was used for reconstructing the Kelvin-Voigt (KV) viscoelastic parameters by comparing the measurements obtained from the TWE technique with the synthetic signals from a Finite Difference Time Domain (FDTD) KV wave propagation model. Additionally, SWE tests were realized in order to characterize the viscoelastic properties of each batch of gelatine. Finally, validation was carried out by comparing the KV parameters inferred from the PIP with those reconstructed from the shear wave dispersion curve obtained from the SWE measurements. In order to test the degree of agreement between both techniques, a Student's T-test and a Pearson's correlation study were performed. The results indicate that the proposed method is able to reconstruct the KV viscoelastic properties of the cervical tissue, for both the epithelial and connective layers, as well as the thickness of the first layer with acceptable accuracy.
Journal of The Mechanical Behavior of Biomedical Materials, Mar 1, 2021
The understanding of changes in the viscoelastic properties of cervical tissue during the gestati... more The understanding of changes in the viscoelastic properties of cervical tissue during the gestation process is a challenging problem. In this work, we explore the importance of considering the multilayer nature (epithelial and connective layers) of human cervical tissue for characterizing the viscoelastic parameters from torsional waves. For this purpose, torsional wave propagations are simulated in three multilayer cervical tissue models (pure elastic, Kelvin-Voigt (KV) and Maxwell) using the finite difference time domain method. High-speed camera measurements have been carried out in tissue-mimicking phantoms in order to obtain the boundary conditions of the numerical simulations. Finally, a parametric modeling study through a probabilistic inverse procedure was performed to rank the most plausible rheological model and to reconstruct the viscoelastic parameters. The procedure consist in comparing the experimental signals obtained in human cervical tissues using the Torsional Wave Elastography (TWE) technique with the synthetic signals from the numerical models. It is shown that the rheological model that best describes the nature of cervical tissue is the Kelvin-Voigt model. Once the most plausible model has been selected, the stiffness and viscosity parameters have been reconstructed of the epithelial and connective layers for the measurements of the 18 pregnant women, along with the thickness of the epithelial layer.
This paper presents the results of the comparison between a proposed Fourth Order Elastic Constan... more This paper presents the results of the comparison between a proposed Fourth Order Elastic Constants (FOECs) nonlinear model defined in the sense of Landau's theory, and the two most contrasted hyperelastic models in the literature, Mooney-Rivlin, and Ogden models. A mechanical testing protocol is developed to investigate the large-strain response of ex vivo cervical tissue samples in uniaxial tension in its two principal anatomical locations, the epithelial and connective layers. The final aim of this work is to compare the reconstructed shear modulus of the epithelial and connective layers of cervical tissue. According to the obtained results, the nonlinear parameter A from the proposed FOEC model could be an important biomarker in cervical tissue diagnosis. In addition, the calculated shear modulus depended on the anatomical location of the cervical tissue (µ epithelial = 1.29 ± 0.15 MPa, and µ connective = 3.60 ± 0.63 MPa) .
The adoption of multiscale approaches by the biomechanical community has caused a major improveme... more The adoption of multiscale approaches by the biomechanical community has caused a major improvement in quality in the mechanical characterization of soft tissues. The recent developments in elastography techniques are enabling in vivo and non-invasive quantification of tissues' mechanical properties. Elastic changes in a tissue are associated with a broad spectrum of pathologies, which stems from the tissue microstructure, histology and biochemistry. This knowledge is combined with research evidence to provide a powerful diagnostic range of highly prevalent pathologies, from birth and labor disorders (prematurity, induction failures, etc.), to solid tumors (e.g., prostate, cervix, breast, melanoma) and liver fibrosis, just to name a few. This review aims to elucidate the potential of viscous and nonlinear elastic parameters as conceivable diagnostic mechanical biomarkers. First, by providing an insight into the classic role of soft tissue microstructure in linear elasticity; secondly, by understanding how viscosity and nonlinearity could enhance the current diagnosis in elastography; and finally, by compounding preliminary investigations of those elastography parameters within different technologies. In conclusion, evidence of the diagnostic capability of elastic parameters beyond linear stiffness is gaining momentum as a result of the technological and imaging developments in the field of biomechanics.
The objective of this study was to evaluate which hyperelastic model could best describe the nonl... more The objective of this study was to evaluate which hyperelastic model could best describe the nonlinear mechanical behavior of the cornea, in order to characterize the capability of the non-linear model parameters to discriminate structural changes in a damaged cornea. Porcine corneas were used, establishing two different groups: control (non-treated) and NaOH-treated (damaged) corneas (n = 8). NaOH causes a chemical burn to the corneal tissue, simulating a disease associated to structural damage of the stromal layer. Quasi-static uniaxial tensile tests were performed in nasaltemporal direction immediately after preparing corneal strips from the two groups. Three non-linear hyperelastic models (i.e. Hamilton-Zabolotskaya model, Ogden model and Mooney-Rivlin model) were fitted to the stress-strain curves obtained in the tensile tests and statistically compared. The corneas from the two groups showed a non-linear mechanical behavior that was best described by the Hamilton-Zabolotskaya model, obtaining the highest coefficient of determination (R 2 > 0.95). Moreover, Hamilton-Zabolotskaya model showed the highest discriminative capability of the nonlinear model parameter (Parameter A) for the tissue structural changes between the two sample groups (p = 0.0005). The present work determines the best hyperelastic model with the highest discriminative capability in description of the non-linear mechanical behavior of the cornea. The cornea is the outermost layer of the eye, acting as a barrier against the external environment and as the main diopter of the visual system 1. Diseases that affect the cornea are one of the main causes of blindness in the world, ranking among the three most prevalent worldwide 2. Among those, corneal ectasia or corneal ectatic disorders stand as a main priority because of their incidence and impact in young population. These are corneal disorders, such as keratoconus or pellucid marginal corneal degeneration, that cause alterations in the corneal structure, leading to corneal topographical changes with decreased corneal thickness and abnormal corneal curvature 3. This abnormal structure of the cornea, as a result of non-linear mechanical changes, finally causes visual impairment to the patient. Currently, the diagnose of corneal degenerations and other corneal diseases are mainly based on structural measurements of the cornea (i.e. curvature, thickness, etc.), while some studies covered in-vivo non-structural measurements using Oculus Corvis ST and Ocular Response Analyzer systems 4-6. These new, non-invasive systems can analyze corneal biomechanical properties, such as corneal hysteresis, including an estimation of intraocular pressure. However, we propose that non-linear mechanical parameters can be obtained from non-invasive elastography or probing technologies such as non-linear torsional waves, non-linearity in probing, non-linearity by micro-indentation to be used in diagnostics in-vivo without removing the cornea 7-9. Hence, quantifying the non-linear mechanical parameters of soft tissues like the cornea might become more specific diagnostic criteria than structural measurements. This is supported by the fact that non-linear mechanical characterization and non-linear model parameters are very sensitive realistic approaches to measure the tissue structural damages 7,8. The feasibility of early diagnosis of corneal diseases such as keratoconus is however an open issue to be investigated in the future. This will depend on the precision of the nonlinearity parameter achievable by the selected probing technology, and thereof define the sensitivity and sensibility.
Corneal mechanical changes are believed to occur before any visible structural alterations observ... more Corneal mechanical changes are believed to occur before any visible structural alterations observed during routine clinical evaluation. This study proposed developing an elastography technique based on torsional waves (TWE) adapted to the specificities of the cornea. By measuring the displacements in the propagation plane perpendicular to the axis of the emitter, the effect of guided waves in plate-like media was proven negligible. Ex vivo experiments were carried out on porcine corneal samples considering a group of control and one group of alkali burn treatment ($$\hbox {NH}_\text {4}$$ NH 4 OH) that modified the mechanical properties. Phase speed was recovered as a function of intraocular pressure (IOP), and a Kelvin-Voigt rheological model was fitted to the dispersion curves to estimate viscoelastic parameters. A comparison with uniaxial tensile testing with thin-walled assumptions was also performed. Both shear elasticity and viscosity correlated positively with IOP, being the ...
Journal of the Mechanical Behavior of Biomedical Materials, 2021
The understanding of changes in the viscoelastic properties of cervical tissue during the gestati... more The understanding of changes in the viscoelastic properties of cervical tissue during the gestation process is a challenging problem. In this work, we explore the importance of considering the multilayer nature (epithelial and connective layers) of human cervical tissue for characterizing the viscoelastic parameters from torsional waves. For this purpose, torsional wave propagations are simulated in three multilayer cervical tissue models (pure elastic, Kelvin-Voigt (KV) and Maxwell) using the finite difference time domain method. High-speed camera measurements have been carried out in tissue-mimicking phantoms in order to obtain the boundary conditions of the numerical simulations. Finally, a parametric modeling study through a probabilistic inverse procedure was performed to rank the most plausible rheological model and to reconstruct the viscoelastic parameters. The procedure consist in comparing the experimental signals obtained in human cervical tissues using the Torsional Wave Elastography (TWE) technique with the synthetic signals from the numerical models. It is shown that the rheological model that best describes the nature of cervical tissue is the Kelvin-Voigt model. Once the most plausible model has been selected, the stiffness and viscosity parameters have been reconstructed of the epithelial and connective layers for the measurements of the 18 pregnant women, along with the thickness of the epithelial layer.
The adoption of multiscale approaches by the biomechanical community has caused a major improveme... more The adoption of multiscale approaches by the biomechanical community has caused a major improvement in quality in the mechanical characterization of soft tissues. The recent developments in elastography techniques are enabling in vivo and non-invasive quantification of tissues’ mechanical properties. Elastic changes in a tissue are associated with a broad spectrum of pathologies, which stems from the tissue microstructure, histology and biochemistry. This knowledge is combined with research evidence to provide a powerful diagnostic range of highly prevalent pathologies, from birth and labor disorders (prematurity, induction failures, etc.), to solid tumors (e.g., prostate, cervix, breast, melanoma) and liver fibrosis, just to name a few. This review aims to elucidate the potential of viscous and nonlinear elastic parameters as conceivable diagnostic mechanical biomarkers. First, by providing an insight into the classic role of soft tissue microstructure in linear elasticity; secondl...
This paper presents the results of the comparison between a proposed Fourth Order Elastic Constan... more This paper presents the results of the comparison between a proposed Fourth Order Elastic Constants (FOECs) nonlinear model defined in the sense of Landau’s theory, and the two most contrasted hyperelastic models in the literature, Mooney–Rivlin, and Ogden models. A mechanical testing protocol is developed to investigate the large-strain response of ex vivo cervical tissue samples in uniaxial tension in its two principal anatomical locations, the epithelial and connective layers. The final aim of this work is to compare the reconstructed shear modulus of the epithelial and connective layers of cervical tissue. According to the obtained results, the nonlinear parameter A from the proposed FOEC model could be an important biomarker in cervical tissue diagnosis. In addition, the calculated shear modulus depended on the anatomical location of the cervical tissue (μepithelial = 1.29 ± 0.15 MPa, and μconnective = 3.60 ± 0.63 MPa).
The clinical ultrasound community demands mechanisms to obtain the viscoelastic biomarkers of sof... more The clinical ultrasound community demands mechanisms to obtain the viscoelastic biomarkers of soft tissue in order to quantify the tissue condition and to be able to track its consistency. Torsional Wave Elastography (TWE) is an emerging technique proposed for interrogating soft tissue mechanical viscoelastic constants. Torsional waves are a particular configuration of shear waves, which propagate asymmetrically in-depth and are radially transmitted by a disc and received by a ring. This configuration is shown to be particularly efficient in minimizing spurious p-waves components and is sensitive to mechanical constants, especially in cylinder-shaped organs. The objective of this work was to validate (TWE) technique against Shear Wave Elasticity Imaging (SWEI) technique through the determination of shear wave velocity, shear moduli, and viscosity of ex vivo chicken liver samples and tissue mimicking hydrogel phantoms. The results of shear moduli for ex vivo liver tissue vary 1.69–4....
The Journal of the Acoustical Society of America, 2018
The WHO estimates that 15 million babies yearly (1 in 10) will be born preterm. Worldwide, compli... more The WHO estimates that 15 million babies yearly (1 in 10) will be born preterm. Worldwide, complications of preterm births have supplanted pneumonia as the primary cause of child mortality [1]. The biology of cervical ripening that leads to birth is poorly understood, and there is no clinical tool to quantitatively evaluate the cervical biomechanical state, which in words of Feltovich [2]“… likely contributes to the reason the singleton spontaneous preterm birth rate has not changed appreciably in more than 100 years.” Towards this problem, we work on enabling new sensor technologies sentient to soft tissue biomechanics, to endow a new class of biomarkers that quantify the mechanical functionality of the cervix, and indeed any soft tissue, ranging pathologies from tumors, atherosclerosis, liver fibrosis to osteoarticular syndromes. Ultrasonic characterization of soft tissue has been developed as a clinical diagnostic tool [3] and evolved through different technologies including our ...
The reconstruction of viscous properties of soft tissues, and more specifically, of cervical tiss... more The reconstruction of viscous properties of soft tissues, and more specifically, of cervical tissue is a challenging problem. In this paper, a new method is proposed to reconstruct the viscoelastic parameters of cervical tissue-mimicking phantoms by a Torsional Wave Elastography (TWE) technique. The reconstruction method, based on a Probabilistic Inverse Problem (PIP) approach, is presented and experimentally validated against Shear Wave Elastography (SWE). The anatomy of the cervical tissue has been mimicked by means of a two-layer gelatine phantom that simulates the epithelial and connective layers. Five ad hoc oil-in-gelatine phantoms were fabricated at different proportion to test the new reconstruction technique. The PIP approach was used for reconstructing the Kelvin-Voigt (KV) viscoelastic parameters by comparing the measurements obtained from the TWE technique with the synthetic signals from a Finite Difference Time Domain (FDTD) KV wave propagation model. Additionally, SWE ...
Pregnancy involves a gradual change in tissue consistency, where, as gestational age increases a ... more Pregnancy involves a gradual change in tissue consistency, where, as gestational age increases a drop in stiffness is noticeable. The extracellular matrix (ECM) of the cervix whose behavior is controlled by the collagen structure is reconfigured, due to hormonal and protein related factors that degraded it. There is an increase in cellular and water content. The collagen maintains a stable percentage, although the synthesis-solubility interaction causes a transformation in the network increasing its diameter and waviness, which destabilizes the mechanical integrity. Further understanding of the remodeling of the cervix becomes a key element in the progress against preterm birth. However, since the woman is in a very delicate state, the available information is scattered. The aim is to provide a framework where the variation of the histological properties is linked with the individual biomechanical evolution of the constituents; therefore a multiscale approach to the problem can be m...
The objective of this study was to evaluate which hyperelastic model could best describe the non-... more The objective of this study was to evaluate which hyperelastic model could best describe the non-linear mechanical behavior of the cornea, in order to characterize the capability of the non-linear model parameters to discriminate structural changes in a damaged cornea. Porcine corneas were used, establishing two different groups: control (non-treated) and NaOH-treated (damaged) corneas (n = 8). NaOH causes a chemical burn to the corneal tissue, simulating a disease associated to structural damage of the stromal layer. Quasi-static uniaxial tensile tests were performed in nasal-temporal direction immediately after preparing corneal strips from the two groups. Three non-linear hyperelastic models (i.e. Hamilton-Zabolotskaya model, Ogden model and Mooney-Rivlin model) were fitted to the stress–strain curves obtained in the tensile tests and statistically compared. The corneas from the two groups showed a non-linear mechanical behavior that was best described by the Hamilton-Zabolotskay...
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Papers by Inas H Faris