Noninvasive ultrasound image guided surface wave method for measuring the wave speed and estimating the elasticity of lungs: A feasibility study

Lung Elastance and Microvascularization as Quantitative Non-Invasive Biomarkers for the Aetiological Diagnosis of Lung Consolidations in Children (ELASMIC Study)

Background: Acute lower respiratory tract conditions are highly prevalent in paediatrics. Many of these conditions present as consolidations on imaging studies. One of the most common causes is bacterial pneumonia (BP), which requires an accurate diagnosis to implement the best treatment plan. Despite the fact that major guidelines constrain the use of invasive tests, chest X-ray (CXR) or blood tests are still routinely used for the diagnosis. In this regard, the introduction of lung ultrasound (LUS) signified an advancement in reducing the invasiveness of diagnosis. However, there are still situations where distinguishing between different aetiologies remains challenging, especially in the case of atelectasis. Methods: This is a prospective cohort study to assess the diagnostic accuracy of new non-invasive, quantifiable, and reproducible imaging biomarkers (lung elastance and microvascularization ratio) for differentiating BP from another major entity that causes the appearance of consolidation in imaging tests, atelectasis. It will be conducted at Sant Joan de Déu Hospital in Spain from June 2025 to June 2027. Firstly, imaging biomarkers will be measured in well-aerated lung tissue without consolidation to establish their values in healthy lung tissue, according to a predefined imaging acquisition protocol. Subsequently, the imaging biomarkers will be assessed in patients with confirmed lung consolidation by LUS (Group 1: BP; Group 2: atelectasis). Results: The study aims to determine whether there are statistically significant differences in the biomarker values in relation to the normal values and between the different etiological groups. Conclusions: The demonstration of the reliable diagnostic accuracy of these biomarkers could significantly reduce the need for invasive techniques and improve the therapeutic management of many patients with BP and other pulmonary conditions presenting with consolidation in imaging tests.

Analysis wave speed of optic nerve and optic nerve head for assessing normal tension glaucoma by using vibro-elastography technique

BACKGROUND

This research aims to evaluate wave speed and viscoelasticity of ocular tissues including the optic nerve and optic nerve head of human eyes between normal tension glaucoma patients and healthy controls by using vibro-elastography techniques.

METHODS

Participants included 12 patients and 12 controls. Wave speed was measured at the optic nerve and optic nerve head in each subject and viscoelasticity was estimated by using Voigt model. Wave speed and viscoelasticity of the optic nerve and optic nerve head were compared between patients and controls by linear mixed models via a restricted maximum likelihood method. The correlation between intraocular pressure and wave speed, elasticity, and viscosity of patients was performed using the Pearson correlation coefficient.

FINDINGS

Significant differences in wave speed (p < 0.0005), elasticity (p = 0.0001) and viscosity p < 0.0001) between patients and controls at the optic nerve head. There was a moderate negative correlation (r = -0.50, p < 0.05) between wave speed and elasticity and intraocular pressure at the optic nerve of patients but no correlation (p > 0.05) between wave speed, elasticity, and viscosity and intraocular pressure at the optic nerve head of patients. No significant difference and correlation among wave speed, elasticity, and viscosity vs. intraocular pressure of the control group at the optic nerve and optic nerve head.

INTERPRETATION

Ultrasound vibro-elastography is useful for noninvasive measurement of viscoelasticity of ocular structures. The glaucoma patient is associated with biomechanical property changes in the optic nerve and optic nerve head, suggesting another way to assess glaucoma focusing on the optic nerve and optic nerve head.

Screening value of lung ultrasound and pleural shear wave elastography in connective tissue disease-related interstitial lung disease: a preliminary study

OBJECTIVE

To explore the diagnostic value of lung ultrasound (LUS) and pleural shear wave elastography (SWE) for connective tissue disease-interstitial lung disease (CTD-ILD).

METHODS

We selected 104 patients diagnosed with connective tissue disease (CTD) at our hospital. All patients underwent LUS, SWE, and high-resolution computed tomography (HRCT). With HRCT as the imaging gold standard for diagnosis, patients were categorized into CTD-ILD and CTD-non-ILD groups. We employed paired chi-square tests to compare the diagnostic differences between HRCT and LUS for ILD. Receiver operating characteristic (ROC) curves were used to assess the diagnostic value of pleural SWE for ILD. Correlation analysis was performed between pleural elasticity values and lung ultrasound scores.

RESULTS

The sensitivity, specificity, positive likelihood ratio, and negative likelihood ratio of LUS for diagnosing CTD-ILD were 93.3%, 86.2%, 6.761, and 0.078, respectively. There was no statistically significant difference in the results between HRCT and LUS (P = 1.000), with a kappa value of 0.720 (P < 0.001). There was a statistically significant difference in the pleural elasticity in the bilateral lower back region between the case and control groups (P < 0.001). The area under the receiver operating characteristic (ROC) curve (AUC) for pleural SWE in diagnosing CTD-ILD was 0.685. In CTD-ILD patients, there was no significant correlation between pleural elasticity values and LUS scores (P > 0.05).

CONCLUSION

The LUS can serve as an important imaging method for screening for CTD-ILD and assessing the severity of the disease. However, pleural SWE has been shown to demonstrate lower diagnostic efficacy for CTD-ILD, and its ability to assess disease severity is limited.

Ultrasonic surface acoustic wave elastography: A review of basic theories, technical developments, and medical applications

Physiological and pathological changes in tissues often cause changes in tissue mechanical properties, making tissue elastography an effective modality in medical imaging. Among the existing elastography methods, ultrasound elastography is of great interest due to the inherent advantages of ultrasound imaging technology, such as low cost, portability, safety, and wide availability. However, most current ultrasound elastography methods are based on the bulk shear wave; they can image deep tissues but cannot image superficial tissues. To address this challenge, ultrasonic elastography methods based on surface acoustic waves have been proposed. In this paper, we present a comprehensive review of ultrasound-based surface acoustic wave elastography techniques, including their theoretical foundations, technical implementations, and existing medical applications. The goal is to provide a concise summary of the state-of-the-art of this field, hoping to offer a reliable reference for the further development of these techniques and foster the expansion of their medical applications.

Evaluation of connective tissue disease-related interstitial lung disease using ultrasound elastography: a preliminary study

BACKGROUND

Interstitial lung disease (ILD) is a common pulmonary complication of connective tissue disease (CTD), which can lead to shortened survival. This article explores the ability of shear wave elastography (SWE) to assess lung surface elastic properties and to distinguish healthy lungs from diseased lungs with connective tissue disease-related interstitial lung disease (CTD-ILD). We aimed to determine whether SWE can be used to assess the severity of CTD-ILD.

METHODS

A total of 65 CTD-ILD patients and 60 healthy volunteers were included for the case group and the control group, respectively. All participants underwent lung ultrasound (count of B-line and measurement of pleural line thickness) and SWE [measurement of Young's modulus (Emean) and shear wave velocity (SMV) (Cmean)] examinations at 50 lung sites. All participants also underwent an examination with high-resolution computed tomography (HRCT) and a pulmonary function test (PFT). For SWE assessment, the Q-box was set to its minimum size (1 mm) and manually placed on the pleural line, rather than inside the lung, to measure the stiffness of the lung surface. The intra- and inter-reliability of SWE measurements of healthy controls (HC), the receiver operating characteristic (ROC) curve for SWE for CTD-ILD, and correlations between different assessment methods were analyzed.

RESULTS

Excellent intra- and inter-reliability of SWE measurements on the mid-anterior lung site of HCs (correlation coefficient >0.97; P<0.01) were found. The results of the lung ultrasound of case group participants were significantly higher than those of HCs at each site (P<0.001). The SWE results revealed a significant increase in both Emean and Cmean in CTD-ILD patients (P<0.001) compared with HCs at certain sites (P<0.001). The areas under the curve (AUC) of Emean and Cmean for CTD-ILD were 0.646 and 0.647 (P<0.05), respectively, and the cutoff values for Emean and Cmean to distinguish CTD-ILD from healthy lungs were 15.81 kPa and 2.31 m/s, respectively. There was no significant correlation between the SWE measured values and the number of B-lines, or the HRCT and PFT results, respectively (P>0.05).

CONCLUSIONS

As a noninvasive ultrasound elastography (UE) technique, SWE may provide a novel method to differentiate CTD-ILD-affected lungs and healthy lungs. It is a reliable way to measure the stiffness of a healthy lung surface in the supine position. However, the ability of SWE to evaluate the severity of CTD-ILD may be limited.

Surface wave elastography using high speed full-field optical interferometry

The assessment of mechanical stiffness is an essential diagnostic tool for investigating the biomechanical properties of biological tissues. Surface wave elastography (SWE) is an emerging technique to quantify elastic properties of tissues in clinical diagnosis. High-speed optical imaging combined with SWE has enormous potential in quantifying the elastic properties of tissues at microscale resolutions. In this study, we implement surface wave elastography using high-speed optical interferometry to characterize the elastic properties of tissue-mimicking phantoms andex-vivonative caprine liver tissue by imaging the surface wave induced by an electromechanical actuator. The sinusoidal mechanical excitations ranging from 120 Hz to 1.2 kHz on the surface of tissues are captured using a high-speed camera with a frame rate of 4 kHz at micrometer resolutions. The surface wavefront reconstruction is performed using a phase-shifting algorithm and linear regression is used to calculate the surface wave velocity. The mechanical stiffness estimated from the optical system is compared with the results of mechanical compression testing measurements. The results from this multimodal platform combining optical interferometry and vibrational spectroscopy using SWE are highly promising towards a non-invasive or minimally invasive imaging forin-vivoandex-vivomechanical characterization of tissues with future clinical applications.

Lung mass density prediction using machine learning based on ultrasound surface wave elastography and pulmonary function testing

OBJECTIVE

The objective of this study is to predict in vivo lung mass density for patients with interstitial lung disease using different gradient boosting decision tree (GBDT) algorithms based on measurements from lung ultrasound surface wave elastography (LUSWE) and pulmonary function testing (PFT).

METHODS

Age and weight of study subjects (57 patients with interstitial lung disease and 20 healthy subjects), surface wave speeds at three vibration frequencies (100, 150, and 200 Hz) from LUSWE, and predicted forced expiratory volume (FEV1% pre) and ratio of forced expiratory volume to forced vital capacity (FEV1%/FVC%) from PFT were used as inputs while lung mass densities based on the Hounsfield Unit from high resolution computed tomography (HRCT) were used as labels to train the regressor in three GBDT algorithms, XGBoost, CatBoost, and LightGBM. 80% (20%) of the dataset was used for training (testing).

RESULTS

The results showed that predictions using XGBoost regressor obtained an accuracy of 0.98 in the test dataset.

CONCLUSION

The obtained results suggest that XGBoost regressor based on the measurements from LUSWE and PFT may be able to noninvasively assess lung mass density in vivo for patients with pulmonary disease.

A Review of Early Experience in Lung Ultrasound in the Diagnosis and Management of COVID-19

A novel coronavirus (2019-nCoV) was identified as the cause of a cluster of pneumonia in Wuhan, China, at the end of 2019. Since then more than eight million confirmed cases of coronavirus disease 2019 (COVID-19) have been reported around the globe. The current gold standard for etiologic diagnosis is reverse transcription-polymerase chain reaction analysis of respiratory-tract specimens, but the test has a high false-negative rate owing to both nasopharyngeal swab sampling error and viral burden. Hence diagnostic imaging has emerged as a fundamental component of current management of COVID-19. Currently, high-resolution computed tomography is the main imaging tool for primary diagnosis and evaluation of disease severity in patients. Lung ultrasound (LUS) imaging has become a safe bedside imaging alternative that does not expose the patient to radiation and minimizes the risk of contamination. Although the number of studies to date is limited, LUS findings have demonstrated high diagnostic sensitivity and accuracy, comparable with those of chest computed tomography scans. In this note we review the current state of the art of LUS in evaluating pulmonary changes induced by COVID-19. The goal is to identify characteristic sonographic findings most suited for the diagnosis of COVID-19 pneumonia infections.

Ultrasound Surface Wave Elastography for Assessing Scleroderma

Scleroderma, or systemic sclerosis (SSc), is a multi-organ connective tissue disease characterized by immune dysregulation and tissue fibrosis. Skin disease is both a disabling feature of SSc and a predictor of visceral involvement and increased mortality. The Modified Rodnan Skin Score (MRSS) is currently the most common clinical method for assessing skin. We developed ultrasound surface wave elastography (USWE) techniques to measure skin surface wave speeds and analyze skin viscoelasticity. The objective of this research was to determine the correlations of skin surface wave speed and skin viscoelasticity with MRSS. Twenty-six SSc patients were studied using USWE and the MRSS. The subject was tested in a sitting position while his or her left or right forearm and upper arm were placed horizontally on a pillow in a relaxed state. The skin of both left and right forearms and upper arms of patients was tested using USWE. Surface wave speeds are positively correlated with the MRSS. Skin elasticity is also positively correlated with the MRSS. However, there was no correlation between skin viscosity and the MRSS for these SSc patients. We will further study if skin viscosity is sensitive enough to detect early edema from inflammation changes of SSc.

An ex vivo technique for quantifying mouse lung injury using ultrasound surface wave elastography

Idiopathic pulmonary fibrosis is a progressively fatal disease with limited treatments. The bleomycin mouse model is often used to simulate the disease process in laboratory studies. The aim of this study was to develop an ex vivo technique for assessing mice lung injury using lung ultrasound surface wave elastography (LUSWE) in the bleomycin mouse model. The surface wave speeds were measured at three frequencies of 100, 200, and 300 Hz for mice lungs from control, mild, and severe groups. The results showed significant differences in the lung surface wave speeds, pulse oximetry, and compliance between control mice and mice with severe pulmonary fibrosis. LUSWE is an evolving technique for evaluating lung stiffness and may be useful for assessing pulmonary fibrosis in the bleomycin mouse model.

A Pilot Study of Wet Lung Using Lung Ultrasound Surface Wave Elastography in an Ex Vivo Swine Lung Model

Extravascular lung water (EVLW) is a basic symptom of congestive heart failure and other conditions. Computed tomography (CT) is standard to assess EVLW, but it requires ionizing radiation and radiology facilities. Lung ultrasound reverberation artifacts called B-lines have been used to assess EVLW. However, B-line artifact analysis relies on visual interpretation and subjects to inter-observer variability. We developed lung ultrasound surface wave elastography (LUSWE) to measure lung surface wave speed. This research aims to develop LUSWE to measure the change of lung surface wave speed due to lung water in an ex vivo swine lung model. The surface wave speeds of a fresh ex vivo swine lung were measured at four frequencies of 100 Hz, 200 Hz, 300 Hz, and 400 Hz. An amount of water was then filled into the lung through its trachea. Ultrasound imaging was used to guide the water filling until significant changes were visible on the imaging. The lung surface wave speeds were measured. An additional 120 ml of water was then filled into the lung. The lung surface wave speeds were then measured again. The results demonstrated that the lung surface wave speed decreased with respect to water content.

Effect of a Thin Fluid Layer on Surface Wave Speed Measurements: A Lung Phantom Study

Lung ultrasound (US) surface wave elastography (SWE) is a novel technique that measures superficial lung tissue elastic properties. A thin pleural fluid layer covers a lung, but its effect on lung measurements in SWE is unknown. We modeled a lung and pleural fluid with sponges and a thin layer of US transmission gel. Sponge surface wave speeds measured from SWE were compared for sponges without and with the thin US gel layer at 3 wave excitation frequencies. The comparison showed that the sponge surface wave speed measurements were not affected by the thin gel layer.

Lung US Surface Wave Elastography in Interstitial Lung Disease Staging

Background Lung US surface wave elastography (SWE) can noninvasively quantify lung surface stiffness or fibrosis by evaluating the rate of surface wave propagation. Purpose To assess the utility of lung US SWE for evaluation of interstitial lung disease. Materials and Methods In this prospective study, lung US SWE was used to assess 91 participants (women, 51; men, 40; mean age ± standard deviation [SD], 62.4 years ± 12.9) with interstitial lung disease and 30 healthy subjects (women, 16; men, 14; mean age, 45.4 years ± 14.6) from February 2016 through May 2017. Severity of interstitial lung disease was graded as none (healthy lung [F0]), mild (F1), moderate (F2), or severe (F3) based on pulmonary function tests, high-resolution CT, and clinical assessments. We propagated surface waves on the lung through gentle mechanical excitation of the external chest wall and measured the lung surface wave speed with a US probe. Lung US SWE performance was assessed, and the optimal cutoff wave speed values for fibrosis grades F0 through F3 were determined with receiver operating characteristic (ROC) curve analysis. Results Lung US SWE had a sensitivity of 92% (95% confidence intervals [CI]: 84%, 96%; P < .001) and a specificity of 89% (95% CI: 81%, 94%; P < .001) for differentiating between healthy subjects (F0) and participants with any grade of interstitial lung disease (F1-F3). It had a sensitivity of 50% and a specificity of 81% for differentiating interstitial lung disease grades F0-F2 from F3. The sensitivity was 88% and the specificity was 97% for differentiating between F0 and F1. The highest area under the ROC curve (AUC) values were obtained at 200 Hz and ranged from 0.83 to 0.94 to distinguish between healthy subjects and study participants with any interstitial lung disease. Conclusion Lung US surface wave elastography may be adjunct to high-resolution CT for noninvasive evaluation of interstitial lung disease. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Verschakelen in this issue.

A Lung Phantom Model to Study Pulmonary Edema Using Lung Ultrasound Surface Wave Elastography

Lung ultrasound surface wave elastography (LUSWE) is a novel technique used to measure superficial lung tissue stiffness. A phantom study was carried out in the study described here to evaluate the application of LUSWE to assess lung water for pulmonary edema. A lung phantom model with cellulose sponge was used; various volumes of water were injected into the sponge to model lung water. Shaker-generated surface wave propagation on the sponge surface was recorded by a 10-MHz ultrasound probe at three shaker frequencies: 100, 150 and 200Hz. Surface wave speeds were calculated but did not exhibit dependence on the volume of injected water. However, the shear viscosity of the sponge increased with water content, and shear elasticity also exhibited a subtle increase. This study suggests that sponge viscoelasticity might change with the water content, which can be detected by LUSWE.

Acoustic Methods for Pulmonary Diagnosis

Recent developments in sensor technology and computational analysis methods enable new strategies to measure and interpret lung acoustic signals that originate internally, such as breathing or vocal sounds, or are externally introduced, such as in chest percussion or airway insonification. A better understanding of these sounds has resulted in a new instrumentation that allows for highly accurate as well as portable options for measurement in the hospital, in the clinic, and even at home. This review outlines the instrumentation for acoustic stimulation and measurement of the lungs. We first review the fundamentals of acoustic lung signals and the pathophysiology of the diseases that these signals are used to detect. Then, we focus on different methods of measuring and creating signals that have been used in recent research for pulmonary disease diagnosis. These new methods, combined with signal processing and modeling techniques, lead to a reduction in noise and allow improved feature extraction and signal classification. We conclude by presenting the results of human subject studies taking advantage of both the instrumentation and signal processing tools to accurately diagnose common lung diseases. This paper emphasizes the active areas of research within modern lung acoustics and encourages the standardization of future work in this field.

A Novel Noninvasive Ultrasound Vibro-elastography Technique for Assessing Patients With Erectile Dysfunction and Peyronie Disease

OBJECTIVE

To translate a novel ultrasound vibro-elastography (UVE) technique for noninvasively measuring viscoelasticity of the penis.

METHODS

A pilot study of UVE was performed in men with erectile dysfunction or Peyronie disease. Assessments were performed in triplicate on the lateral aspect of the penis (bilaterally) at 100, 150, and 200 Hz before and after erectogenic injection administration. Viscoelasticity of the corpora was also calculated and compared before and after injection and against measures of erectile function, including the International Index of Erectile Function-Erectile Function Domain, and the total erectogenic medication volume required for achieving a firm erection.

RESULTS

Significant increases in viscoelasticity were found after erectogenic injection, validating the ability of UVE to measure dynamic changes with erections. Baseline measures also significantly correlated with the volume of erectogenic medication required to achieve an erection (100 Hz, parameter estimate [PE] 2.21, P <.001; 150 Hz, PE 0.53, P = .03; 200 Hz, PE 0.34, P = .07) but not with age and International Index of Erectile Function-Erectile Function Domain. As erectogenic medications likely represent the most accurate measure of erectile function, these findings suggest a potential role for UVE as a viable diagnostic modality for erectile dysfunction.

CONCLUSION

This first report of the use of elastography with erectile function in humans demonstrates significant associations with responsiveness to erectogenic injection medications. These data have significant potential implications for broader clinical practice and merit further study and validation.

A noninvasive surface wave technique for measuring finger's skin stiffness

The purpose of this work was to develop a compact surface wave elastography (CSWE) device for measuring finger's skin stiffness. The motivation was to develop a noninvasive technique for assessing limited cutaneous systemic sclerosis (lcSSc) in accordance with new ACR/EULAR clarification criteria. Currently, the Modified Rodnan Skin Score (MRSS) is widely used for assessing systemic sclerosis but is challenging for assessing patients with lcSSc. The novelty of CSWE is to develop a noninvasive technique to measure the elastic properties of skin of fingers. In the CSWE device, a local harmonic vibration was generated on the finger's skin. The surface wave speed on the finger's skin was measured without contact using a compact optical probe. The CSWE device was first validated with an ultrasound-based surface wave elastography (USWE) device on a phantom. The CSWE device was then validated with the USWE device on both the dorsal and ventral arms of a volunteer. The CSWE device was evaluated to measure the surface wave speed of four fingers for the volunteer. The CSWE device may be useful for measuring skin stiffness over multiple areas of fingers and hands for assessing lcSSc.

An Ultrasound Surface Wave Technique for Assessing Skin and Lung Diseases

Systemic sclerosis (SSc) is a multi-organ connective tissue disease characterized by immune dysregulation and organ fibrosis. Severe organ involvement, especially of the skin and lung, is the cause of morbidity and mortality in SSc. Interstitial lung disease (ILD) includes multiple lung disorders in which the lung tissue is fibrotic and stiffened. The purpose of this study was to translate ultrasound surface wave elastography (USWE) for assessing patients with SSc and/or ILD via measuring surface wave speeds of both skin and superficial lung tissue. Forty-one patients with both SSc and ILD and 30 healthy patients were enrolled in this study. An external harmonic vibration was used to generate the wave propagation on the skin or lung. Three excitation frequencies of 100, 150 and 200 Hz were used. An ultrasound probe was used to measure the wave propagation in the tissue non-invasively. Surface wave speeds were measured on the forearm and upper arm of both left and right arm, as well as the upper and lower lungs, through six intercostal spaces of patients and healthy patients. Viscoelasticity of the skin was calculated by the wave speed dispersion with frequency using the Voigt model. The magnitudes of surface wave speed and viscoelasticity of patients' skin were significantly higher than those of healthy patients (p <0.0001) for each location and each frequency. The surface wave speeds of patients' lung were significantly higher than those of healthy patients (p <0.0001) for each location and each frequency. USWE is a non-invasive and non-ionizing technique for measuring both skin and lung surface wave speed and may be useful for quantitative assessment of SSc and/or ILD.

In Vivo Noninvasive Measurement of Young's Modulus of Elasticity in Human Eyes: A Feasibility Study

PURPOSE

Abnormal ocular biomechanical properties may be important for understanding the risk of glaucoma. However, there are no clinical methods for measuring standard material properties in patients. In this feasibility study we demonstrated proof-of-principle for a novel method, ultrasound surface wave elastography (USWE), to determine the in vivo Young's modulus of elasticity of corneas in normal human eyes.

METHODS

In total, 20 eyes of 10 healthy subjects (mean age, 51.4±7.2; ±SD; range, 43 to 64 y) were studied. A spherical-tipped probe (3-mm diameter) was placed on closed eyelids and generated a gentle harmonic vibration at 100 Hz for 0.1 second. Wave speed propagation in the cornea was measured by USWE, and Young's modulus was calculated from the wave speed. Associations between Young's modulus and intraocular pressure (IOP), age, central corneal thickness, and axial length were explored by the Pearson correlation. Statistical significance was determined by using generalized estimating equation models to account for possible correlation between fellow eyes.

RESULTS

Mean IOP was 12.8±2.7 mm Hg. Mean wave speed in the cornea was 1.82±0.10 m/s. Young's modulus of elasticity was 696±113 kPa and was correlated with IOP (r=0.57; P=0.004), but none of the other variables (P>0.1).

CONCLUSIONS

USWE is a novel noninvasive technique for measuring ocular biomechanical properties. Corneal Young's modulus in normal eyes is associated with IOP, consistent with measurements in cadaver eyes. Further work is needed to determine elasticity in other ocular tissues, particularly the sclera, and if elasticity is altered in glaucoma patients.

Noninvasive measurement of wave speed of porcine cornea in ex vivo porcine eyes for various intraocular pressures

The objective of this study was to extend an ultrasound surface wave elastography (USWE) technique for noninvasive measurement of ocular tissue elastic properties. In particular, we aim to establish the relationship between the wave speed of cornea and the intraocular pressure (IOP). Normal ranges of IOP are between 12 and 22mmHg. Ex vivo porcine eye balls were used in this research. The porcine eye ball was supported by the gelatin phantom in a testing container. Some water was pour into the container for the ultrasound measurement. A local harmonic vibration was generated on the side of the eye ball. An ultrasound probe was used to measure the wave propagation in the cornea noninvasively. A 25 gauge butterfly needle was inserted into the vitreous humor of the eye ball under the ultrasound imaging guidance. The needle was connected to a syringe. The IOP was obtained by the water height difference between the water level in the syringe and the water level in the testing container. The IOP was adjusted between 5mmHg and 30mmHg with a 5mmHg interval. The wave speed was measured at each IOP for three frequencies of 100, 150 and 200Hz. Finite element method (FEM) was used to simulate the wave propagation in the corneal according to our experimental setup. A linear viscoelastic FEM model was used to compare the experimental data. Both the experiments and the FEM analyses showed that the wave speed of cornea increased with IOP.

Near field effect on elasticity measurement for cartilage-bone structure using Lamb wave method

Background

Cartilage elasticity changes with cartilage degeneration. Hence, cartilage elasticity detection might be an alternative to traditional imaging methods for the early diagnosis of osteoarthritis. Based on the wave propagation measurement, Shear wave elastography (SWE) become an emerging non-invasive elasticity detection method. The wave propagation model, which is affected by tissue shapes, is crucial for elasticity estimating in SWE. However, wave propagation model for cartilage was unclear.

Methods

This study aimed to establish a wave propagation model for the cartilage-bone structure. We fabricated a cartilage-bone structure, and studied the elasticity measurement and wave propagation by experimental and numerical Lamb wave method (LWM).

Results

Results indicated the wave propagation model satisfied the lamb wave theory for two-layered structure. Moreover, a near field region, which affects wave speed measurements and whose occurrence can be prevented if the wave frequency is larger than one critical frequency, was observed.

Conclusion

Our findings would provide a theoretical foundation for further application of LWM in elasticity measurement of cartilage in vivo. It can help the application of LWM to the diagnosis of osteoarthritis.

Association between kidney intracapsular pressure and ultrasound elastography

Background

Kidney congestion is a common pathophysiologic pathway of acute kidney injury (AKI) in sepsis and heart failure. There is no noninvasive tool to measure kidney intracapsular pressure (KIP) directly.

Methods

We evaluated the correlation of KIP with kidney elasticity measured by ultrasound surface wave elastography (USWE). We directly measured transcatheter KIP in three pigs at baseline and after bolus infusion of normal saline, norepinephrine, vasopressin, dopamine, and fenoldopam; infiltration of 2-L peritoneal dialysis solution in the intra-abdominal space; and venous, arterial, and ureteral clamping. KIP was compared with USWE wave speed.

Results

Only intra-abdominal installation of peritoneal dialysis fluid was associated with significant change in KIP (mean (95% CI) increase, 3.7 (3.2–4.2)] mmHg; P < .001). Although intraperitoneal pressure and KIP did not differ under any experimental condition, bladder pressure was consistently and significantly greater than KIP under all circumstances (mean (95% CI) bladder pressure vs. KIP, 3.8 (2.9–4.) mmHg; P < .001). USWE wave speed significantly correlated with KIP (adjusted coefficient of determination, 0.71; P < .001). Estimate (95% CI) USWE speed for KIP prediction stayed significant after adjustment for KIP hypertension (−0.8 (− 1.4 to − 0.2) m/s; P = .008) whereas systolic and diastolic blood pressures were not significant predictors of KIP.

Conclusions

In a pilot study of the swine model, we found ultrasound surface wave elastography speed is significantly correlated with transcatheter measurement of kidney intracapsular and intra-abdominal pressures, while bladder pressure overestimated kidney intracapsular pressure.

Lung Ultrasound Surface Wave Elastography: A Pilot Clinical Study

A lung ultrasound surface wave elastography (LUSWE) technique is developed to measure superficial lung tissue elastic properties. The purpose of this paper was to translate LUSWE into clinical studies for assessing patients with interstitial lung disease (ILD) and present the pilot data from lung measurements on 10 healthy subjects and 10 patients with ILD. ILD includes multiple lung disorders in which the lung tissue is distorted and stiffened by tissue fibrosis. Chest radiography and computed tomography are the most commonly used techniques for assessing lung disease, but they are associated with radiation and cannot directly measure lung elastic properties. LUSWE provides a noninvasive and nonionizing technique to measure the elastic properties of superficial lung tissue. LUSWE was used to measure regions of both lungs through six intercostal spaces for patients and healthy subjects. The data are presented as wave speed at 100, 150, and 200 Hz at the six intercostal spaces. As an example, the surface wave speeds are, respectively, 1.88 ± 0.11 m/s at 100 Hz, 2.74 ± 0.26 m/s at 150 Hz, and 3.62 ± 0.13 m/s at 200 Hz for a healthy subject in the upper right lung; this is in comparison to measurements from an ILD patient of 3.3 ± 0.37 m/s at 100 Hz, 4.38 ± 0.33 m/s at 150 Hz, and 5.24 ± 0.44 m/s at 200 Hz in the same lung space. Significant differences in wave speed between healthy subjects and ILD patients were found. LUSWE is a safe and noninvasive technique which may be useful for assessing ILD.

A surface wave elastography technique for measuring tissue viscoelastic properties

A surface wave elastography method is proposed to study the viscoelastic properties of skin by measuring the surface wave speed and attenuation on the skin. Experiments were carried out on porcine skin tissues. The surface wave speed is measured by the change of phase with distance. The wave attenuation is measured by the decay of wave amplitude with distance. The change of viscoelastic properties with temperature was studied at room and body temperatures. The wave speed was 1.83m/s at 22°C but reduced to 1.52m/s at 33°C. The viscoelastic ratio was almost constant from 22°C to 33°C. Fresh and decayed tissues were studied. The wave speed of the decayed tissue increased from 1.83m/s of fresh state to 2.73m/s. The viscoelastic ratio was 0.412/mm at the decayed state compared to 0.215/mm at the fresh state. More tissue samples are needed to study these viscoelastic parameters according to specific applications.

Quantitative assessment of lung stiffness in patients with interstitial lung disease using MR elastography

PURPOSE

To investigate the use of magnetic resonance elastography (MRE) in the quantitative assessment of pulmonary fibrosis by comparing quantitative shear stiffness measurements of lung parenchyma in patients diagnosed with fibrotic interstitial lung disease (ILD) and healthy controls.

MATERIALS AND METHODS

A 1.5T spin-echo, echo planar imaging MRE (SE-EPI MRE) pulse sequence was utilized to assess absolute lung shear stiffness in 15 patients with diagnosed ILD and in 11 healthy controls. Data were collected at residual volume (RV) and total lung capacity (TLC). Spirometry data were obtained immediately prior to scanning. To test for statistical significance between RV and TLC shear stiffness estimates a two-sample t-test was performed. To assess variability within individual subject shear stiffness estimates, the intraclass correlation coefficient (ICC) and Krippendorff's alpha were calculated.

RESULTS

Patients with ILD exhibited an average (±1 standard deviation) shear stiffness of 2.74 (±0.896) kPa at TLC and 1.32 (±0.300) kPa at RV. The corresponding values for healthy individuals were 1.33 (±0.195) kPa and 0.849 (±0.250) kPa, respectively. The difference in shear stiffness between RV and TLC was statistically significant (P < 0.001). At TLC, the ICC and alpha values were 0.909 and 0.887, respectively. At RV, the ICC and alpha values were 0.852 and 0.862, respectively.

CONCLUSION

In subjects with known fibrotic interstitial lung disease, parenchymal shear stiffness is increased when compared to normal controls at both RV and TLC, with TLC demonstrating the most significant difference. MRE-derived parenchymal shear stiffness is a promising new noninvasive imaging-based biomarker of interstitial lung disease.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;46:365-374.

Identification of the Rayleigh surface waves for estimation of viscoelasticity using the surface wave elastography technique

The purpose of this Letter to the Editor is to demonstrate an effective method for estimating viscoelasticity based on measurements of the Rayleigh surface wave speed. It is important to identify the surface wave mode for measuring surface wave speed. A concept of start frequency of surface waves is proposed. The surface wave speeds above the start frequency should be used to estimate the viscoelasticity of tissue. The motivation was to develop a noninvasive surface wave elastography (SWE) technique for assessing skin disease by measuring skin viscoelastic properties. Using an optical based SWE system, the author generated a local harmonic vibration on the surface of phantom using an electromechanical shaker and measured the resulting surface waves on the phantom using an optical vibrometer system. The surface wave speed was measured using a phase gradient method. It was shown that different standing wave modes were generated below the start frequency because of wave reflection. However, the pure symmetric surface waves were generated from the excitation above the start frequency. Using the wave speed dispersion above the start frequency, the viscoelasticity of the phantom can be correctly estimated.

A noninvasive ultrasound elastography technique for measuring surface waves on the lung

The purpose of this work was to demonstrate an ultrasound based surface wave elastography (SWE) technique for generating and detecting surface waves on the lung. The motivation was to develop a noninvasive technique for assessing superficial lung tissue disease including interstitial lung disease (ILD). ILD comprises a number of lung disorders in which the lung tissue is stiffened and damaged due to fibrosis of the lung tissue. Currently, chest radiographs and computed tomography (CT) are the most common clinical methods for evaluating lung disease, but they are associated with radiation and cannot measure lung mechanical properties. The novelty of SWE is to develop a noninvasive and nonionizing technique to measure the elastic properties of superficial lung tissue. We propose to generate waves on the lung surface through wave propagation from a local harmonic vibration excitation on the chest through an intercostal space. The resulting surface wave propagation on the lung is detected using an ultrasound probe through the intercostal space. To demonstrate that surface waves can be generated on the lung, an ex vivo muscle-lung model was developed to evaluate lung surface wave generation and detection. In this model, swine muscle was laid atop a swine lung. A vibration excitation of 0.1s 100Hz wave was generated on the muscle surface and the surface waves on the lung were detected using a linear array ultrasound probe at 5MHz. To test its feasibility for patient use, SWE was used to measure both lungs of an ILD patient through eight intercostal spaces. The mean wave speed was 1.71±0.20m/s (±SD) at the functional residual capacity, while the mean wave speed was 2.36±0.33m/s at the total lung capacity. These studies support the feasibility of SWE for noninvasive measurement of elastic properties of lung and demonstrate potential for assessment of ILD.

Optical tracking of local surface wave for skin viscoelasticity

Rapid and effective determination of biomechanical properties is important in examining and diagnosing skin thermal injury. Among the methods used, viscoelasticity quantification is one of the most effective methods in determining such properties. This study aims to rapidly determine skin viscoelasticity by optically tracking the local surface wave. New elastic and viscous coefficients were proposed to indicate skin viscoelasticity based on a single impulse response of the skin. Experiments were performed using fresh porcine skin samples. Surface wave was generated in a single impulse using a vibrator with a ball-tipped device and was detected using a laser Doppler vibrometer. The motions along the depth direction were monitored using an ultrasound system. The ultrasound monitoring results indicated the multi-layered viscoelasticity of the epidermis and dermis. The viscoelastic coefficients from four healthy samples show a potential viscoelasticity variation of porcine skin. In one sample, the two coefficients were evidently higher than those in a healthy area if the skin was slightly burned. These results indicate that the proposed method is sensitive, effective, and quick in determining skin viscoelasticity.

Estimation of the absolute shear stiffness of human lung parenchyma using (1) H spin echo, echo planar MR elastography

PURPOSE

To develop a rapid proton MR elastography (MRE) technique that can quantify the absolute shear stiffness of lung parenchyma, to investigate the ability to differentiate respiration-dependent stiffness variations of the lung, and to demonstrate clinical feasibility.

MATERIALS AND METHODS

A spin-echo echo planar imaging MRE sequence (SE-EPI MRE) with a very short echo time was developed and tested in a series of five healthy volunteers at three different lung volumes: (i) residual volume (RV), (ii) total lung capacity (TLC), (iii) and midway between RV and TLC (MID). At each volume, lung density was quantified using a MR-based density mapping sequence. For reference, data were acquired using the previously described spin-echo lung MRE sequence (SE-MRE). MRE data were also acquired in a patient with proven Idiopathic Pulmonary Fibrosis (IPF) to test clinical feasibility.

RESULTS

The SE-EPIMRE sequence reduced total acquisition time by a factor of 2 compared with the SE-MRE sequence. Lung parenchyma median shear stiffness for the 5 volunteers quantified with the SE-EPI MRE sequence was 0.9 kPa, 1.1 kPa, and 1.6 kPa at RV, MID, and TLC, respectively. The corresponding values obtained with the SE-MRE sequence were 0.9 kPa, 1.1 kPa, and 1.5 kPa. Absolute shear stiffness was also successfully measured in the IPF patient.

CONCLUSION

The results indicate that stiffness variations due to respiration could be measured with the SE-EPIMRE technique and were equivalent to values generated by the previously described SE-MRE approach. Preliminary data obtained from the patient demonstrate clinical feasibility.

Acoustic waves in medical imaging and diagnostics

Up until about two decades ago acoustic imaging and ultrasound imaging were synonymous. The term ultrasonography, or its abbreviated version sonography, meant an imaging modality based on the use of ultrasonic compressional bulk waves. Beginning in the 1990s, there started to emerge numerous acoustic imaging modalities based on the use of a different mode of acoustic wave: shear waves. Imaging with these waves was shown to provide very useful and very different information about the biological tissue being examined. We discuss the physical basis for the differences between these two basic modes of acoustic waves used in medical imaging and analyze the advantages associated with shear acoustic imaging. A comprehensive analysis of the range of acoustic wavelengths, velocities and frequencies that have been used in different imaging applications is presented. We discuss the potential for future shear wave imaging applications.

Measurement of viscoelastic properties of in vivo swine myocardium using lamb wave dispersion ultrasound vibrometry (LDUV)

Viscoelastic properties of the myocardium are important for normal cardiac function and may be altered by disease. Thus, quantification of these properties may aid with evaluation of the health of the heart. Lamb wave dispersion ultrasound vibrometry (LDUV) is a shear wave-based method that uses wave velocity dispersion to measure the underlying viscoelastic material properties of soft tissue with plate-like geometries. We tested this method in eight pigs in an open-chest preparation. A mechanical actuator was used to create harmonic, propagating mechanical waves in the myocardial wall. The motion was tracked using a high frame rate acquisition sequence, typically 2500 Hz. The velocities of wave propagation were measured over the 50-400 Hz frequency range in 50 Hz increments. Data were acquired over several cardiac cycles. Dispersion curves were fit with a viscoelastic, anti-symmetric Lamb wave model to obtain estimates of the shear elasticity, μ(1), and viscosity, μ(2) as defined by the Kelvin-Voigt rheological model. The sensitivity of the Lamb wave model was also studied using simulated data. We demonstrated that wave velocity measurements and Lamb wave theory allow one to estimate the variation of viscoelastic moduli of the myocardial walls in vivo throughout the course of the cardiac cycle.

A non-invasive technique for estimating carpal tunnel pressure by measuring shear wave speed in tendon: a feasibility study

Although a close relationship between carpal tunnel pressure and median nerve dysfunction has been found, the current methods for pressure measurements are invasive, using a catheter in the carpal canal to monitor the pressure. A noninvasive method for quantifying carpal tunnel pressure would be useful as an alternative to the catheter method. In this study, a simplified experimental model was developed to measure the shear wave speed in a canine Achilles tendon under different tunnel pressures. The results showed that the speed of waves through the inside-tunnel tendon had a linear relationship with the pressure in the tunnel (first measurement: r=0.966, P<0.001; second measurement: r=0.970, P<0.001). This indicates that the tendon could serve as a strain gauge to evaluate the tunnel pressure by detecting the changes of wave propagation speed. However, further validations in human cadavers and clinical subjects are necessary.

Application of 1-D transient elastography for the shear modulus assessment of thin-layered soft tissue: comparison with supersonic shear imaging technique

Elasticity estimation of thin-layered soft tissues has gained increasing interest propelled by medical applications like skin, corneal, or arterial wall shear modulus assessment. In this work, the authors propose one-dimensional transient elastography (1DTE) for the shear modulus assessment of thin-layered soft tissue. Experiments on three phantoms with different elasticities and plate thicknesses were performed. First, using 1DTE, the shear wave speed dispersion curve inside the plate was obtained and validated with finite difference simulation. No dispersive effects were observed and the shear wave speed was directly retrieved from time-of-flight measurements. Second, the supersonic shear imaging (SSI) technique (considered to be a gold standard) was performed. For the SSI technique, the propagating wave inside the plate is guided as a Lamb wave. Experimental SSI dispersion curves were compared with finite difference simulation and fitted using a generalized Lamb model to retrieve the plate bulk shear wave speed. Although they are based on totally different mechanical sources and induce completely different diffraction patterns for the shear wave propagation, the 1DTE and SSI techniques resulted in similar shear wave speed estimations. The main advantage of the 1DTE technique is that bulk shear wave speed can be directly retrieved without requiring a dispersion model.

Magnetic resonance elastography of the lung parenchyma in an in situ porcine model with a noninvasive mechanical driver: correlation of shear stiffness with trans-respiratory system pressures

Quantification of the mechanical properties of lung parenchyma is an active field of research due to the association of this metric with normal function, disease initiation and progression. A phase contrast MRI-based elasticity imaging technique known as magnetic resonance elastography is being investigated as a method for measuring the shear stiffness of lung parenchyma. Previous experiments performed with small animals using invasive drivers in direct contact with the lungs have indicated that the quantification of lung shear modulus with (1) H based magnetic resonance elastography is feasible. This technique has been extended to an in situ porcine model with a noninvasive mechanical driver placed on the chest wall. This approach was tested to measure the change in parenchymal stiffness as a function of airway opening pressure (P(ao) ) in 10 adult pigs. In all animals, shear stiffness was successfully quantified at four different P(ao) values. Mean (±STD error of mean) pulmonary parenchyma density corrected stiffness values were calculated to be 1.48 (±0.09), 1.68 (±0.10), 2.05 (±0.13), and 2.23 (±0.17) kPa for P(ao) values of 5, 10, 15, and 20 cm H2O, respectively. Shear stiffness increased with increasing P(ao) , in agreement with the literature. It is concluded that in an in situ porcine lung shear stiffness can be quantitated with (1) H magnetic resonance elastography using a noninvasive mechanical driver and that it is feasible to measure the change in shear stiffness due to change in P(ao) .