In Vivo Measurement of Cervical Elasticity on Pregnant Women by Torsional Wave Technique: A Preliminary Study

Nonlinear fourth-order elastic characterization of the cornea using torsional wave elastography

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 ([Formula: see text]) 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 [Formula: see text] (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.

Quantitative strain elastography of the uterine cervix assessed by the GE Voluson E10 system in combination with a force-measuring device

OBJECTIVE

During pregnancy, the stiffness of the cervical tissue decreases long before the cervical length decreases. Therefore, several approaches have been proposed in order to ensure a more objective assessment of cervical stiffness than that achieved by digital evaluation. Strain elastography has shown promising results. This technique is based on an ultrasound assessment of the tissue deformation that occurs when the examiner applies pressure on the tissue with the ultrasound probe. However, the results are only semi-quantitative as they depend on the unmeasured force used by the examiner. We, therefore, hypothesized that a force-measuring device applied to the handle of the ultrasound probe may render the technique quantitative. With this approach, the stiffness is the force (measured by the device) divided by the compression (measured by the elastography platform). One perspective is the early identification of women at risk of preterm birth in whom cervical stiffness may decrease long before cervical shortening. Another perspective is cervical evaluation when planning labor induction. In this feasibility study, we aimed to evaluate how quantitative strain elastography performs when a commercially available strain elastography platform (by which the algorithm is unavailable) is combined with a custom-made, force-measuring device. We studied how the assessments were associated with the gestational age in women with uncomplicated pregnancies and how they were associated with cervical dilatation time from 4 to 10 cm in women undergoing labor induction.

METHODS

In the analysis, we included quantitative strain elastography assessments from 47 women with uncomplicated singleton pregnancies, with gestational age between 12⁺⁰ and 40⁺⁰, and from 27 singleton term-pregnant women undergoing labor induction. The force-measuring device was mounted on the handle of a transvaginal probe. The strain values (i.e. the compression of the cervical tissue) were obtained by the elastography software of the ultrasound scanner (GE Voluson E10). The region of interest was placed within the central part of the anterior cervical lip. Based on the force data and strain values, we calculated the outcomes cervical elastography index_GE (CEI_GE) and the cervical strength index_GE (CEI_GE x cervical length: CSI_GE).

RESULTS

The average CEI_GE was 0.24 N at week 12 and 0.15 N at week 30-34. For CSI_GE these figures were 8.2 and 4.7 N mm, respectively (p = 0.002). Among women undergoing labor induction, the CEI_GE was associated with a cervical dilatation time (4-10 cm) beyond 7 h. For nulliparous women, this area under the ROC curve was 0.94.

CONCLUSION

Quantitative strain elastography may constitute a tool for the evaluation of a uterine cervix with normal length in women at risk of preterm birth and in women undergoing labor induction. The performance of this tool deserves evaluation in larger clinical trials.

Reproducibility and usability assessment of the novel Fine Birth device for threatened preterm labor diagnosis

BACKGROUND

Preterm delivery is considered the leading cause of mortality worldwide in children under 5 years old. Approximately 45 million pregnant women are hospitalized yearly for threatened preterm labor. However, only 50% of pregnancies complicated by threatened preterm labor end in delivery before the estimated date, classifying the rest as false threatened preterm labor. The ability of current diagnostic methods to predict threatened preterm labor is low (low positive predictive value), ranging between 8% and 30%. This highlights the need for a solution that accurately detects and differentiates between false and real threatened preterm labors in women who attend obstetrical clinics and hospital emergency departments with delivery symptoms.

OBJECTIVE

Primarily, this aimed to assess the reproducibility and usability of a novel medical device, the Fine Birth, aimed at accurately diagnosing threatened preterm labor through the objective quantification of pregnant women's cervical consistency. Secondarily, this study aimed to evaluate the effect of training and the incorporation of a lateral microcamera on the device's reliability and usability outcomes.

STUDY DESIGN

A total of 77 singleton pregnant women were recruited during their follow-up visits to the obstetrical and gynecologic departments at 5 Spanish hospitals. The eligibility criteria included pregnant women aged ≥18 years; women with a normal fetus and uncomplicated pregnancy; women without prolapse of membranes, uterine anomalies, previous cervical surgery, or latex allergy; and women signing the informed written consent. Cervical tissue stiffness was assessed using the Fine Birth device, whose technology is based on the propagation of torsional waves through the studied tissue. Cervical consistency measurements were taken for each woman until obtaining 2 valid measurements by 2 different operators. The intraobserver and interobserver reproducibilities of the Fine Birth measurements were assessed using the intraclass correlation coefficients with a 95% confidence interval and the Fisher test P value. The usability was evaluated on the basis of the clinicians' and participants' feedback.

RESULTS

There was good intraobserver reproducibility (intraclass correlation coefficient, 0.88; 95% confidence interval, 0.84-0.95; Fisher test P value<.05). As the results obtained for the interobserver reproducibility did not reach the desired acceptable values (intraclass correlation coefficient of <0.75), a lateral microcamera was added to the Fine Birth intravaginal probe, and the operators involved in the clinical investigation received the corresponding training with the modified device. The analysis of 16 additional subjects demonstrated excellent interobserver reproducibility (intraclass correlation coefficient, 0.93; 95% confidence interval, 0.78-0.97) and an improvement after the intervention (P<.0001).

CONCLUSION

The robust reproducibility and usability results obtained after the insertion of a lateral microcamera and the corresponding training make the Fine Birth a promising novel device to objectively quantify the patient's cervical consistency, diagnose threatened preterm labor, and, thus, predict the risk of spontaneous preterm birth. Further research is needed to demonstrate the clinical utility of the device.

Quantitative sonoelastography of the uterine cervix in predicting successful outcome of induction of labour

Objectives

The aim of the study was to evaluate the stiffness of cervix and determine its significance in predicting successful outcome of induction of labour. The primary objective was to determine the differences in elastography indices of different areas of cervix between the outcome groups of successful and failed induction of labour. A secondary objective was to find out the correlation of these elastography indices with Bishop's score and cervical length.

Methods

This was a prospective, observational study conducted over a period of 6 months on pregnant women admitted in the labour room for induction of labour. Establishment of adequate regular uterine contractions - at least three contractions lasting 40-45 s in a 10-min period - was taken as end point for successful outcome of induction of labour. Even after 24 h of initiation of induction of labour, regular, adequate and painful uterine contractions were not established, then induction of labour was described as having failed. Prior to induction, cervical length measurement, Bishop's scoring and elastographic evaluation of the cervix were done by stress-strain elastography. A colour map was produced from purple to red and a five-step scale - the elastography index - was used to describe the various parts of the cervix. The differences between elastography indices of different parts of cervix were estimated using Mann-Whitney U test. Correlation of the indices with cervical length and Bishop's score was determined by Spearman's correlation coefficient.

Results

A total of 64 women were included in the study. A significant difference (p < 0.001) was found in the elastography index of internal os between the two outcome groups of success (1.76 ± 0.64) and failure (0.54 ± 0.18). However, the elastography index of central cervical canal, external os, anterior lip and posterior lips did not differ significantly across the outcome groups. A significant positive correlation was found between elastography index of internal os and cervical length (Spearman's correlation coefficient, r = 0.441, p < 0.001) and between elastography index of external os and cervical length (r = 0.347, p = 0.005), whereas a negative correlation was seen between elastography index of external os and Bishop's score (r = -0.270, p = 0.031).

Conclusion

Elastography index of internal os can be used to predict outcome of induction of labour. Cervical elastography is a promising new technique for cervical consistency assessment. Further larger studies are required to determine some cut-off point for elastography index of internal os in prediction of outcome of induction of labour and to strongly establish the usefulness of cervical elastography for pregnancy management, preventing preterm delivery and establishment of cut-off points to determine successful induction.

Torsional wave elastography to assess the mechanical properties of the cornea

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 (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {NH}_\text {4}$$\end{document}NH4OH) 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.

Experimental Evidence of Generation and Reception by a Transluminal Axisymmetric Shear Wave Elastography Prototype

Experimental evidence on testing a non-ultrasonic-based probe for a new approach in transluminal elastography was presented. The proposed modality generated shear waves by inducing oscillatory rotation on the lumen wall. Detection of the propagated waves was achieved at a set of receivers in mechanical contact with the lumen wall. The excitation element of the probe was an electromagnetic rotational actuator whilst the sensing element was comprised by a uniform anglewise arrangement of four piezoelectric receivers. The prototype was tested in two soft-tissue-mimicking phantoms that contained lumenlike conduits and stiffer inclusions. The shear wave speed of the different components of the phantoms was characterized using shear wave elastography. These values were used to estimate the time-of-flight of the expected reflections. Ultrafast ultrasound imaging, based on Loupas’ algorithm, was used to estimate the displacement field in transversal planes to the lumenlike conduit and to compare against the readouts from the transluminal transmission–reception tests. Experimental observations between ultrafast imaging and the transluminal probe were in good agreement, and reflections due to the stiffer inclusions were detected by the transluminal probe. The obtained experimental evidence provided proof-of-concept for the transluminal elastography probe and encouraged further exploration of clinical applications.

Smart Sensors for Healthcare and Medical Applications

This special issue on "Smart Sensors for Healthcare and Medical Applications" focuses on new sensing technologies, measurement techniques, and their applications in medicine and healthcare [...].

Viscoelastic model characterization of human cervical tissue by torsional waves

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.

Hyperelastic Ex Vivo Cervical Tissue Mechanical Characterization

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).

Why Are Viscosity and Nonlinearity Bound to Make an Impact in Clinical Elastographic Diagnosis?

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.

Viscoelastic Biomarkers of Ex Vivo Liver Samples via Torsional Wave Elastography

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 1.69–4.0kPa using TWE technique and 1.32–4.48kPa using SWEI technique for a range of frequencies from 200 to 800Hz. Kelvin–Voigt viscoelastic parameters reported values of μ = 1.51kPa and η = 0.54Pa·s using TWE and μ = 1.02kPa and η = 0.63Pa·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.

Electro-Mechanical Ionic Channel Modeling for Uterine Contractions and Oxytocin Effect during Pregnancy

Uterine contractions during normal pregnancy and preterm birth are an important physiological activity. Although the cause of preterm labor is usually unknown, preterm birth creates very serious health concerns in many cases. Therefore, understanding normal birth and predicting preterm birth can help both newborn babies and their families. In our previous work, we developed a multiscale dynamic electrophysiology model of uterine contractions. In this paper, we mainly focus on the cellular level and use electromyography (EMG) and cell force generation methods to construct a new ionic channel model and a corresponding mechanical force model. Specifically, the ionic channel model takes into consideration the knowledge of individual ionic channels, which include the electrochemical and bioelectrical characteristics of individual myocytes. We develop a new sodium channel and a new potassium channel based on the experimental data from the human myometrium and the average correlations are 0.9946 and 0.9945, respectively. The model is able to generate the single spike, plateau type and bursting type of action potentials. Moreover, we incorporate the effect of oxytocin on changing the properties of the L-type and T-type calcium channels and further influencing the output action potentials. In addition, we develop a mechanical force model based on the new ionic channel model that describes the detailed ionic dynamics. Our model produces cellular mechanical force that propagates to the tissue level. We illustrate the relationship between the cellular mechanical force and the intracellular ionic dynamics and discuss the relationship between the application of oxytocin and the output mechanical force. We also propose a simplified version of the model to enable large scale simulations using sensitivity analysis method. Our results show that the model is able to reproduce the bioelectrical and electromechanical characteristics of uterine contractions during pregnancy.