SWENet: A Physics-Informed Deep Neural Network (PINN) for Shear Wave Elastography.

Shear wave elastography (SWE) enables the measurement of elastic properties of soft materials in a non-invasive manner and finds broad applications in various disciplines. The state-of-the-art SWE methods rely on the measurement of local shear wave speeds to infer material parameters and suffer from wave diffraction when applied to soft materials with strong heterogeneity. In the present study, we overcome this challenge by proposing a physics-informed neural network (PINN)-based SWE (SWENet) method. The spatial variation of elastic properties of inhomogeneous materials has been introduced in the governing equations, which are encoded in SWENet as loss functions. Snapshots of wave motions have been used to train neural networks, and during this course, the elastic properties within a region of interest illuminated by shear waves are inferred simultaneously. We performed finite element simulations, tissue-mimicking phantom experiments, and ex vivo experiments to validate the method. Our results show that the shear moduli of soft composites consisting of matrix and inclusions of several millimeters in cross-section dimensions with either regular or irregular geometries can be identified with excellent accuracy. The advantages of the SWENet over conventional SWE methods consist of using more features of the wave motions and enabling seamless integration of multi-source data in the inverse analysis. Given the advantages of SWENet, it may find broad applications where full wave fields get involved to infer heterogeneous mechanical properties, such as identifying small solid tumors with ultrasound SWE, and differentiating gray and white matters of the brain with magnetic resonance elastography.

Simultaneous tensile and shear measurement of the human cornea in vivo using S0- and A0-wave optical coherence elastography.

Understanding corneal stiffness is valuable for improving refractive surgery, detecting corneal abnormalities, and assessing intraocular pressure. However, accurately measuring the elastic properties, specifically the tensile and shear moduli that govern mechanical deformation, has been challenging. To tackle this issue, we have developed guided-wave optical coherence elastography that can simultaneously excite and analyze symmetric (S0) and anti-symmetric (A0) elastic waves in the cornea at around 10 kHz frequencies, enabling us to extract tensile and shear properties from measured wave dispersion curves. We verified the technique using elastomer phantoms and ex vivo porcine corneas and investigated the dependence on intraocular pressure using acoustoelastic theory that incorporates corneal tension and a nonlinear constitutive tissue model. In a pilot study involving six healthy human subjects aged 31 to 62, we measured shear moduli (Gzx) of 94±20 kPa (mean±standard deviation) and tensile moduli (Exx) of 4.0±1.1 MPa at central corneas. Our preliminary analysis of age-dependence revealed contrasting trends: -8.3±4.5 kPa/decade for shear and 0.30±0.21 MPa/decade for tensile modulus. This OCE technique has the potential to become a highly useful clinical tool for the quantitative biomechanical assessment of the cornea. STATEMENT OF SIGNIFICANCE: This article reports an innovative elastography technique using two guided elastic waves, demonstrating the measurement of both tensile and shear moduli in human cornea in vivo with unprecedented precision. This technique paves the way for comprehensive investigations into corneal mechanics and holds clinical significance in various aspects of corneal health and disease management.

In vivo Optical Coherence Elastography Unveils Spatial Variation of Human Corneal Stiffness.

OBJECTIVE: The mechanical properties of corneal tissues play a crucial role in determining corneal shape and have significant implications in vision care. This study aimed to address the challenge of obtaining accurate in vivo data for the human cornea. METHODS: We have developed a high-frequency optical coherence elastography (OCE) technique using shear-like antisymmetric (A0)-mode Lamb waves at frequencies above 10 kHz. RESULTS: By incorporating an anisotropic, nonlinear constitutive model and utilizing the acoustoelastic theory, we gained quantitative insights into the influence of corneal tension on wave speeds and elastic moduli. Our study revealed significant spatial variations in the shear modulus of the corneal stroma on healthy subjects for the first time. Over an age span from 21 to 34 (N = 6), the central corneas exhibited a mean shear modulus of 87 kPa, while the corneal periphery showed a significant decrease to 44 kPa. The central cornea's shear modulus decreases with age with a slope of -19 +/- 8 kPa per decade, whereas the periphery showed non-significant age dependence. The limbus demonstrated an increased shear modulus exceeding 100 kPa. We obtained wave displacement profiles that are consistent with highly anisotropic corneal tissues. CONCLUSION: Our approach enabled precise measurement of corneal tissue elastic moduli in situ with high precision (< 7%) and high spatial resolution (< 1 mm). Our results revealed significant stiffness variation from the central to peripheral corneas. SIGNIFICANCE: The high-frequency OCE technique holds promise for biomechanical evaluation in clinical settings, providing valuable information for refractive surgeries, degenerative disorder diagnoses, and intraocular pressure assessments.

Simultaneous tensile and shear measurement of the human cornea in vivo using S0- and A0-wave optical coherence elastography.

Understanding corneal stiffness is valuable for improving refractive surgery, detecting corneal abnormalities, and assessing intraocular pressure. However, accurately measuring the elastic properties, particularly the tensile and shear moduli that govern mechanical deformation, has been challenging. To tackle this issue, we have developed guided-wave optical coherence elastography that can simultaneously excite and analyze symmetric (S0) and anti-symmetric (A0) elastic waves in the cornea at frequencies around 10 kHz and allows us to extract tensile and shear properties from measured wave dispersion curves. By applying acoustoelastic theory that incorporates corneal tension and a nonlinear constitutive tissue model, we verified the technique using elastomer phantoms and ex vivo porcine corneas and investigated the dependence on intraocular pressure. For two healthy human subjects, we measured a mean tensile modulus of 3.6 MPa and a mean shear modulus of 76 kPa in vivo with estimated errors of < 4%. This technique shows promise for the quantitative biomechanical assessment of the cornea in a clinical setting.

Ultra-wideband optical coherence elastography from acoustic to ultrasonic frequencies.

Visualizing viscoelastic waves in materials and tissues through noninvasive imaging is valuable for analyzing their mechanical properties and detecting internal anomalies. However, traditional elastography techniques have been limited by a maximum wave frequency below 1-10 kHz, which hampers temporal and spatial resolution. Here, we introduce an optical coherence elastography technique that overcomes the limitation by extending the frequency range to MHz. Our system can measure the stiffness of hard materials including bones and extract viscoelastic shear moduli for polymers and hydrogels in conventionally inaccessible ranges between 100 Hz and 1 MHz. The dispersion of Rayleigh surface waves across the ultrawide band allowed us to profile depth-dependent shear modulus in cartilages ex vivo and human skin in vivo with sub-mm anatomical resolution. This technique holds immense potential as a noninvasive measurement tool for material sciences, tissue engineering, and medical diagnostics.

Noninvasive measurement of local stress inside soft materials with programmed shear waves.

Mechanical stresses across different length scales play a fundamental role in understanding biological systems' functions and engineering soft machines and devices. However, it is challenging to noninvasively probe local mechanical stresses in situ, particularly when the mechanical properties are unknown. We propose an acoustoelastic imaging-based method to infer the local stresses in soft materials by measuring the speeds of shear waves induced by custom-programmed acoustic radiation force. Using an ultrasound transducer to excite and track the shear waves remotely, we demonstrate the application of the method by imaging uniaxial and bending stresses in an isotropic hydrogel and the passive uniaxial stress in a skeletal muscle. These measurements were all done without the knowledge of the constitutive parameters of the materials. The experiments indicate that our method will find broad applications, ranging from health monitoring of soft structures and machines to diagnosing diseases that alter stresses in soft tissues.

In situ measurement of the stiffness increase in the posterior sclera after UV-riboflavin crosslinking by optical coherence elastography.

Scleral crosslinking may provide a way to prevent or treat myopia by stiffening scleral tissues. The ability to measure the stiffness of scleral tissues in situ pre and post scleral crosslinking would be useful but has not been established. Here, we tested the feasibility of optical coherence elastography (OCE) to measure shear modulus of scleral tissues and evaluate the impact of crosslinking on different posterior scleral regions using ex vivo porcine eyes as a model. From measured elastic wave speeds at 6 - 16 kHz, we obtained out-of-plane shear modulus value of 0.71 ± 0.12 MPa (n = 20) for normal porcine scleral tissues. After riboflavin-assisted UV crosslinking, the shear modulus increased to 1.50 ± 0.39 MPa (n = 20). This 2-fold change was consistent with the increase of static Young's modulus from 5.5 ± 1.1 MPa to 9.3 ± 1.9 MPa after crosslinking, which we measured using conventional uniaxial extensometry on tissue stripes. OCE revealed regional stiffness differences across the temporal, nasal, and deeper posterior sclera. Our results show the potential of OCE as a noninvasive tool to evaluate the effect of scleral crosslinking.

In vivo stiffness measurement of epidermis, dermis, and hypodermis using broadband Rayleigh-wave optical coherence elastography.

Traveling-wave optical coherence elastography (OCE) is a promising technique to measure the stiffness of biological tissues. While OCE has been applied to relatively homogeneous samples, tissues with significantly varying elasticity through depth pose a challenge, requiring depth-resolved measurement with sufficient resolution and accuracy. Here, we develop a broadband Rayleigh-wave OCE technique capable of measuring the elastic moduli of the 3 major skin layers (epidermis, dermis, and hypodermis) reliably by analyzing the dispersion of leaky Rayleigh surface waves over a wide frequency range of 0.1-10 kHz. We show that a previously unexplored, high frequency range of 4-10 kHz is critical to resolve the thin epidermis, while a low frequency range of 0.2-1 kHz is adequate to probe the dermis and deeper hypodermis. We develop a dual bilayer-based inverse model to determine the elastic moduli in all 3 layers and verify its high accuracy with finite element analysis and skin-mimicking phantoms. Finally, the technique is applied to measure the forearm skin of healthy volunteers. The Young's modulus of the epidermis (including the stratum corneum) is measured to be ∼ 4 MPa at 4-10 kHz, whereas Young's moduli of the dermis and hypodermis are about 40 and 15 kPa, respectively, at 0.2-1 kHz. Besides dermatologic applications, this method may be useful for the mechanical analysis of various other layered tissues with sub-mm depth resolution. STATEMENT OF SIGNIFICANCE: To our knowledge, this is the first study that resolves the stiffness of the thin epidermis from the dermis and hypodermis, made possible by using high-frequency (4 - 10 kHz) elastic waves and optical coherence elastography. Beyond the skin, this technique may be useful for mechanical characterizations of various layered biomaterials and tissues.

Probing the Mechanical Properties of Large Arteries by Measuring Their Deformation In Vivo with Ultrasound.

Aging and cardiovascular diseases (CVDs) may alter the microstructures of arteries and hence their mechanical properties. Therefore, the measurement of intrinsic artery mechanical properties in vivo can provide valuable information in understanding aging and CVDs and is of clinical significance. The accuracy of advanced ultrasound imaging techniques in measuring the deformation of large arteries under blood pressure is good. However, the assessment of arterial stiffness in vivo remains a challenge. An inverse method to infer the constitutive parameters of arteries in vivo from the blood pressure-arterial radius relationship (P-r curve) is proposed here. The stability analysis reveals that a key constitutive parameter, bθ, which measures the circumferential hardening of an artery, can be reliably identified. An in vivo experiment was performed on the common carotid arteries of 41 healthy volunteers (age: 37 ± 17 y). The value of bθ varies significantly (from 0.55 ± 0.15 for the young group to 0.93 ± 0.29 for the older group, p < 0.01) and is positively correlated with age (r = 0.673, p < 0.01). Furthermore, our theoretical analysis and experimental study have revealed a strong correlation between the clinic-used stiffness index ß and bθ. This study shows that the arterial material parameter bθ can be measured in vivo, which makes it promising as a new biomarker in the diagnosis of CVDs.

Arterial Stiffness Probed by Dynamic Ultrasound Elastography Characterizes Waveform of Blood Pressure.

The clinical and economic burdens of cardiovascular diseases pose a global challenge. Growing evidence suggests an early assessment of arterial stiffness can provide insights into the pathogenesis of cardiovascular diseases. However, it remains difficult to quantitatively characterize local arterial stiffness in vivo. Here we utilize guided axial waves continuously excited and detected by ultrasound to probe local blood pressures and mechanical properties of common carotid arteries simultaneously. In a pilot study of 17 healthy volunteers, we observe a  âˆ¼ 20 % variation in the group velocities of the guided axial waves (5.16 ± 0.55 m/s in systole and 4.31 ± 0.49 m/s in diastole) induced by the variation of the blood pressures. A linear relationship between the square of group velocity and blood pressure is revealed by the experiments and finite element analysis, which enables us to measure the waveform of the blood pressures by the group velocities. Furthermore, we propose a wavelet analysis-based method to extract the dispersion relations of the guided axial waves. We then determined the shear modulus by fitting the dispersion relations in diastole with the leaky Lamb wave model. The average shear modulus of all the volunteers is 166.3 ± 32.8 kPa. No gender differences are found. This study shows the group velocity and dispersion relation of the guided axial waves can be utilized to probe blood pressure and arterial stiffness locally in a noninvasive manner and thus promising for early diagnosis of cardiovascular diseases.

Non-destructive mapping of stress and strain in soft thin films through sound waves.

Measuring the in-plane mechanical stress in a taut membrane is challenging, especially if its material parameters are unknown or altered by the stress. Yet being able to measure the stress is of fundamental interest to basic research and practical applications that use soft membranes, from engineering to tissues. Here we present a robust non-destructive technique to measure directly in-situ stress and strain in soft thin films without the need to calibrate material parameters. Our method relies on measuring the speed of elastic waves propagating in the film. Using optical coherence tomography, we verify our method experimentally for a stretched rubber membrane, a piece of cling film (about 10 µm thick), and the leather skin of a traditional Irish frame drum. We find that our stress predictions are highly accurate and anticipate that our technique could be useful in applications ranging from soft matter devices to biomaterial engineering and medical diagnosis.

Supershear surface waves reveal prestress and anisotropy of soft materials.

Surface waves play important roles in many fundamental and applied areas from seismic detection to material characterizations. Supershear surface waves with propagation speeds greater than bulk shear waves have recently been reported, but their properties are not well understood. Here we describe theoretical and experimental results on supershear surface waves in rubbery materials. We find that supershear surface waves can be supported in viscoelastic materials with no restriction on the shear quality factor. Interestingly, the effect of prestress on the speed of the supershear surface wave is opposite to that of the Rayleigh surface wave. Furthermore, anisotropy of material affects the supershear wave much more strongly than the Rayleigh surface wave. We offer heuristic interpretation as well as theoretical verification of our experimental observations. Our work points to the potential applications of supershear waves for characterizing the bulk mechanical properties of soft solid from the free surface.

AFM-based indentation method for measuring the relaxation property of living cells.

Probing the mechanical properties of cells is critical for understanding their deformation behaviors and biological functions. Although some methods have been proposed to characterize the elastic properties of cells, it is still difficult to measure their time-dependent properties. This paper investigates the use of atomic force microscope (AFM) to determine the reduced relaxation modulus of cells. In principle, AFM is hard to perform an indentation relaxation test that requires a constant indenter displacement during load relaxation, whereas the real AFM indenter displacement usually varies with time during relaxation due to the relatively small bending stiffness of its cantilever. We investigate this issue through a combined theoretical, computational, and experimental effort. A protocol relying on the choice of appropriate cantilever bending stiffness is proposed to perform an AFM-based indentation relaxation test of cells, which enables the measurement of reduced relaxation modulus with high accuracy. This protocol is first validated by performing nanoindentation relaxation tests on a soft material and by comparing the results with those from independent measurements. Then indentation tests of cartilage cells are conducted to demonstrate this method in determining time-dependent properties of living cells. Finally, the change in the viscoelasticity of MCF-7 cells under hyperthermia is investigated.

Textual research on classical prescriptions in Mongolian medicine / 中国中药杂志

Mongolians have a long history of using prescriptions, which can be classified into four stages as follows: the germination and experience accumulation stage before the 13 th century, the theoretical formation stage from the 13 th to 16 th century, the rapid development stage from the 17 th to 20 th century, and the leaping development stage from the mid-20 th century to the present. The prescriptions from the ancient classical or representative medical books have always been used by Mongolian physicians for generations, and they are still in use due to the definite curative effects. In 2008, the Notice on Issuing the Supplementary Provisions to the Registration and Management of Traditional Chinese Medicine(TCM) described that China has attached more importance to the excavation and development of classical prescriptions. As stipulated in the Law of the People's Republic of China on Traditional Chinese Medicine, the classical prescriptions should be those available in ancient TCM classics and still in wide use, with exact curative effects, distinct features, and obvious advantages. This paper expounded the historical formation and development of classical prescriptions in Mongo-lian medicine, introduced the five most influential ancient medical books revealing the formation and development of these classic prescriptions, and traced the origin of such classical prescriptions as Wenguanmu Siwei Decoction, Shouzhangshen Bawei Decoction, Jianghuang Siwei Decoction and summarized the origin, development history and characteristics of classical prescriptions in Mongolian medicine, aiming to provide a reference for their further research and development.

An ultrasonic method to measure stress without calibration: The angled shear wave method.

Measuring stress levels in loaded structures is crucial to assess and monitor structure health and to predict the length of remaining structural life. Many ultrasonic methods are able to accurately predict in-plane stresses inside a controlled laboratory environment but struggle to be robust outside, in a real-world setting. That is because these methods rely either on knowing beforehand the material constants (which are difficult to acquire) or require significant calibration for each specimen. This paper presents an ultrasonic method to evaluate the in-plane stress in situ directly, without knowing any material constants. The method is simple in principle, as it only requires measuring the speed of two angled shear waves. It is based on a formula that is exact for incompressible solids, such as soft gels or tissues, and is approximately true for compressible "hard" solids, such as steel and other metals. The formula is validated by finite element simulations, showing that it displays excellent accuracy, with a small error on the order of 1%.

Comparative Mitochondrial Analysis of Cnaphalocrocis exigua (Lepidoptera: Crambidae) and Its Close Relative C. medinalis.

Rice leaffolders are important pests on rice in Asia, Oceania, and Africa, causing serious loss to rice production. There are two main rice leaffolders in China, namely Cnaphalocrocis medinalis (Guenée) and C. exigua (Butler) with the former having the ability of long-distance migration. To reveal the differences in the mitochondrial genomes (mitogenome) between them, we compared the completed mitogenome of C. exigua with three C. medinalis individuals. Although phylogenetic analysis based on the mitogenomic data strongly supported the close relationship between these two species, many differences were still being revealed. The results showed that the mitogenome of C. exigua was shorter in length (15,262 bp) and slight lower in AT content than that of C. medinalis. Except for the different start codons of nad3 and nad6 gene, we also found the cox1 gene had a typical start codon 'ATG' which suggested that the starting position of this gene must be reconsidered in the entire superfamily Pyraloidea. All tRNAs have a typical clover-leaf structure, except for the dihydrouridine (DHU) stem losing of trnS1, which has the atypical anticondon 'TCT' instead of 'GCT' in C. medinalis and most Pyraloidea species. Two intergenic regions (between trnY and cox1, nad3 and trnA) featured by AT repeats were only found in C. medinalis and even rarely appeared in reported Pyraloidea species. Furthermore, regardless of interspecific comparison or intraspecific comparison of these two species, protein coding genes, especially the atp8 genes, had quite different evolutionary rates.

[Effects of different land use patterns on soil potassium distribution in Chengdu Plain, China]. / æˆéƒ½å¹³åŽŸä¸åŒåœŸåœ°åˆ©ç”¨æ–¹å¼å¯¹åœŸå£¤å‰–é¢é’¾ç´ åˆ†å¸ƒçš„å½±å“.

To explore the effects of land use change on the potassium in soil profile under the background of rapid urbanization, we collected data of 187 soil profiles from four typical land use patterns (rice-wheat, rice-vegetable, rice-oil and garden) in Chengdu Plain. The contents of available potassium (AP), slow-acting potassium (SP), mineral potassium (MP), and total potassium (TP) in soil profile under different land use patterns and their relationships were analyzed. Our results showed that compared with the traditional rotation (rice-wheat, rice-oil), soil AP and SP contents significantly varied among different land use patterns. Rice-vegetable rotation increased the contents of AP and SP in the surface soil, while garden land increased the consumption of AP and SP in the soil. For the more stable forms, soil MP and TP, there was no significant difference in their contents under different land use patterns. In the deep soil, the content of AP in the rice-vegetable rotation pattern was significantly decreased with deepening soil layer, and the AP in traditional rotation was significantly higher than that in garden land. The trend of SP was opposite to that of AP. The difference of MP and TP in different land use patterns was small. Among the four land use patterns, the ratio of AP to TP and SP to TP in the lower layer of rice-vegetable rotation was higher than that in other patterns, while the ratio of AP to TP decreased significantly under different land use patterns at 20-40 cm. The change of SP to TP with the downward ratio of soil layer was opposite to that of AP to TP. Additionally, the ratio of MP to TP was relatively stable under different land use patterns. Therefore, different land use patterns exerted significant effects on the distribution of AP and SP in the soil profile of Chengdu Plain.

Mechanical characterization of functionally graded soft materials with ultrasound elastography.

Functionally graded soft materials (FGSMs) with microstructures and mechanical properties exhibiting gradients across a spatial volume to satisfy specific functions have received interests in recent years. How to characterize the mechanical properties of these FGSMs in vivo/in situ and/or in a non-destructive manner is a great challenge. This paper investigates the use of ultrasound elastography in the mechanical characterization of FGSMs. An efficient finite-element model was built to calculate the dispersion relation for surface waves in FGSMs. For FGSMs with large elastic gradients, the measured dispersion relation can be used to identify mechanical parameters. In the case where the elastic gradient is smaller than a certain critical value calculated here, our analysis on transient wave motion in FGSMs shows that the group velocities measured at different depths can infer the local mechanical properties. Experiments have been performed on polyvinyl alcohol (PVA) cryogel to demonstrate the usefulness of the method. Our analysis and the results may not only find broad applications in mechanical characterization of FGSMs but also facilitate the use of shear wave elastography in clinics because many diseases change the local elastic properties of soft tissues and lead to different material gradients. This article is part of the theme issue 'Rivlin's legacy in continuum mechanics and applied mathematics'.

Guided wave elastography of layered soft tissues.

In vivo mechanical characterization of soft biological tissues has broad applications ranging from disease diagnosis to tissue engineering. Shear wave elastography based on the bulk wave theory has been widely used to measure the mechanical properties of soft tissues. Given that most soft tissues basically have layered structures, the dispersive feature of elastic waves should be considered when the thickness of the interested layer is comparable to or smaller than the wavelength. Bearing this fundamental issue in mind, we propose an ultrasound-based guided wave elastography (GWE) method to characterize the mechanical properties of layered soft tissues. The dispersion relations of guided waves in layered structures were derived first, and its explicit expression was achieved. An inverse approach based on the dispersion relation to characterize the mechanical properties of layered soft tissues was then established. Both finite element analysis (FEA) and phantom experiments were carried out to validate the new method. In vivo experiments on forearm skin demonstrate the usefulness of the present method in characterizing layered soft tissues. STATEMENT OF SIGNIFICANCE: Layered soft tissues and artificial soft materials are ubiquitous in both nature and engineering. Imaging their in vivo/in situ mechanical properties finds important applications and remains a great challenge to date. Here, we propose an ultrasound-based guided wave elastography method to in vivo/in situ characterize the elastic properties of layered soft materials. We validate the method via finite element analysis and phantom experiments and further demonstrate its usefulness in practice by performing in vivo measurements on forearm skins. Given that the dispersive feature of elastic waves in layered soft media is considered in our method, it provides the opportunity to assess the intrinsic elastic properties of an individual layer in a non-destructive manner as shown in our experiments.

Effects of active and passive smoking on salivary cytokines levels in rats: A pilot study.

Cigarette smoking is an established risk factor for some oral diseases. As an essential fluid in the oral cavity, saliva is crucial to maintain oral health. Relative to active smoking, there are very few studies assessing the effect of passive smoking on salivary cytokines levels. In the present study, we established the rat models by the means of the intraoral cigarette smoking or whole body cigarette smoke exposure to simulate human active or passive smoking, respectively. The effects of active or passive smoking on salivary cytokines levels were assessed by using ProcartaPlex multiplex immunoassays. The results of the current study indicated that both active and passive smoking diminished the body weights of rats and increased the levels of some blood counts. Intriguingly, active smoking enhanced the salivary levels of IL-6 and IL-12 p70 and passive smoking elevated the salivary IL-6 level. Moreover, active smoking appeared to have a more prominent activation effect on the salivary IL-6 level. It was noted that active or passive smoking had no significant effect on the salivary IFN-γ level. Active or passive smoking could have potential effects on the salivary levels of some pro-inflammatory cytokines.