Shear Wave Propagation Speed Research Articles

Shear wave speed, dispersion slope and anisotropy evaluation using cardiac shear wave elastography in patients with Fabry disease

Abstract Background Cardiac shear wave imaging has been proposed to investigate left ventricular myocardial alterations non-invasively. Dispersion slope and anisotropy are fundamental properties that have not been studied in Fabry disease (FD) patients yet. Purpose The aim of this study was to determine and compare shear wave propagation speed, dispersion slope and fractional anisotropy in FD patients and healthy controls. Methods We prospectively included 20 FD patients and 20 healthy controls (HC). Shear wave speed, dispersion slope and fractional anisotropy were measured non-invasively in anteroseptal basal segment using an ultrasound for cardiac shear wave imaging. Echocardiography, electrocardiogram and laboratory evaluations were performed. Results Shear wave propagation speed was higher in FD patients than in HC group (1.46 ± 0.12 m/s and 1.36 ± 0.17 m/s, p = 0.03). No difference was found in dispersion slope (11.4 m/s/kHz in FD group and 11.3 m/s/kHz in HC group, p = 0.6). Fractional anisotropy was 0.05 ± 0.04 in FD group and 0.05 ± 0.04 in HC group, p = 0.4. Conclusion Shear wave speed was higher in FD patients compared to control group. Dispersion slope and fractional anisotropy in FD group did not reveal significant difference to the control group.

Effectiveness of two-dimensional shear-wave sonoelastography in the diagnosis and follow-up of infantile hypertrophic pyloric stenosis

IntroductionWe sought to determine the effectiveness and utility of two-dimensional shear-wave sonoelastography (2D-SW-SE) in the diagnosis and postoperative follow-up of infantile hypertrophic pyloric stenosis (IHPS).Materials and MethodsTwenty-three infants were included in the study, 13 in the IHPS group and 10 in the control group (CG). Preoperative B-mode ultrasonography measurements (longitudinal length and single-wall thickness of the pylorus) and 2D-SW-SE measurements (pylorus tissue stiffness and shear-wave propagation speed) were compared between the groups. The infants with IHPS then underwent Ramstedt pyloromyotomy and were invited for follow-ups on the tenth day and the first, third, and sixth months postoperatively. Measurements taken at the follow-ups were compared with the preoperative values.ResultsNo differences were found between the groups regarding age, gender, body weight, or week of birth. The pyloric lengths in the IHPS group were longer than in the CG (p < 0.001), and the single-wall thicknesses were thicker (p < 0.001). The pylorus in the IHPS group was four times stiffer than in the CG (27.4 kPa versus 7.66 kPa), and the shear-wave propagation speed in the tissue was higher (1.34 m/s versus 2.69 m/s; p < 0.001). Both values decreased over time in the IHPS group and were normal by the third postoperative month.Conclusions2D-SW-SE can be used as an assistive imaging tool alongside B-mode ultrasound for diagnosing IHPS. It can also be used to identify inadequate surgery by detecting whether the pyloric tissue has softened at follow-up.

Shear wave elastography in chronic kidney disease - the physics and clinical application.

Chronic kidney disease is a leading public health problem worldwide. The global prevalence of chronic kidney disease is nearly five hundred million people, with almost one million deaths worldwide. Estimated glomerular filtration rate, imaging such as conventional ultrasound, and histopathological findings are necessary as each technique provides specific information which, when taken together, may help to detect and arrest the development of chronic kidney disease, besides managing its adverse outcomes. However, estimated glomerular filtration rate measurements are hampered by substantial error margins while conventional ultrasound involves subjective assessment. Although histopathological assessment is the best tool for evaluating the severity of the renal pathology, it may lead to renal insufficiency and haemorrhage if complications occurred. Ultrasound shear wave elastography, an emerging imaging that quantifies tissue stiffness non-invasively has gained interest recently. This method applies acoustic force pulses to generate shear wave within the tissue that propagate perpendicular to the main ultrasound beam. By measuring the speed of shear wave propagation, the tissue stiffness is estimated. This paper reviews the literature and presents our combined experience and knowledge in renal shear wave elastography research. It discusses and highlights the confounding factors on shear wave elastography, current and future possibilities in ultrasound renal imaging and is not limited to new sophisticated techniques.

Natural shear wave measurements detect changes in operational stiffness induced by mechanical ventilation in sheep

Abstract Shear wave elastography (SWE) has the potential to non-invasively measure myocardial stiffness, based on the propagation speed of shear waves traveling through the myocardium after valve closure. However, shear wave propagation speed (SWS) is related to the operational stiffness of the heart, which is defined by the slope of the end-diastolic stress-strain relationship at the operating volume/pressure. Therefore, operational stiffness can be altered by both changes in intrinsic myocardial stiffness and myocardial loading conditions. We aimed to investigate whether SWE can detect differences in operational stiffness induced by loading changes during mechanical ventilation, and whether SWE combined with respiratory hold manoeuvres could detect an evolution in stiffness during the course of ischemic cardiomyopathy (ICM). We assessed SWS in 8 sedated and mechanically ventilated sheep: 1 healthy control, 3 within 8 weeks, and 4 after at least 16 weeks following left coronary artery ligation (early vs. late ICM). Left ventricular parasternal long-axis views were acquired with a state-of-the-art ultrasound scanner with high frame rate technology (&amp;gt; 1100 Hz). Shear waves after mitral valve closure were considered during an inspiratory hold at 30 cmH2O and 15 cmH2O and expiratory hold at 0 cmH2O (atmospheric pressure). We used linear regression to assess the trend of the SWS during ventilation manoeuvres per animal and a two-tailed Student’s T-test to assess changes between ICM stages and their respective response to ventilation manoeuvres. In all but one sheep, SWS declined with higher inspiratory pressures (see fig. 1), possibly due to a reduction in preload at higher inspiratory pressures resulting in a shift towards a reduced slope on the myocardial stress-strain relation. The sheep with a positive slope was excluded from further analyses. SWS during expiratory hold at atmospheric pressure was 3.4 m/s in the healthy control and was significantly lower in early vs. late ICM (mean±SD 4.0±0.6 vs. 9.0±1.7 m/s; p=0.007). Furthermore, the change in SWS was larger in late vs. early ICM (slope of regression line -0.16 vs. -0.05 m/s/cmH2O; p=0.03). These observations suggest loading on a steeper part of the end-diastolic stress strain relationship in late ICM. In conclusion, our results suggest that SWE is able to detect differences in operational stiffness induced by mechanical ventilation. Secondly, SWE appears to distinguish between different time points in the course of ICM based on the magnitude of the SWS during expiratory hold at atmospheric pressure, but also on the magnitude of the SWS change during loading alterations induced by mechanical ventilation. Further work should assess whether SWE combined with respiratory hold manoeuvres could contribute to differentiate intrinsic from hemodynamic stiffening, and to exploit its full potential as a non-invasive bedside method for the assessment of operational stiffness.

The change in propagation speed of natural shear waves by altering preload might differentiate patients with increased myocardial stiffness

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation Flanders - FWO. Background Shear wave (SW) elastography (SWE) is a novel ultrasound-based technique for the assessment of myocardial stiffness. SWE tracks the propagation of SWs travelling through the myocardium, induced by e.g. mitral valve closure (MVC). The speed of SWs is related to myocardial stiffness. As myocardial stiffness is defined by a non-linear stress-strain relation, it is dependent on the operating stress levels and thus left ventricular (LV) loading. As a result, elevated SW speed values could be caused by both increased LV preload or structural remodelling of the myocardium. In this way, performing SWE measurements at different loading states could potentially provide additional information aiding with the interpretation of these measurements. Purpose to investigate if performing SWE before and after a loading change could provide more information on tissue properties of the myocardium. Methods Twelve patients [age: 76(41–82)] receiving intermittent hemodialysis (HD) and 12 age-matched healthy volunteers [age: 67(47–71); p = 0.19] were included. Patients were scanned before and 1 hour after the start of HD. Parasternal long-axis views were acquired using an experimental ultrasound scanner with an average frame rate of 1086±185 Hz. Patients were divided into 2 equal groups based on the grade of diastolic dysfunction (DD), determined using conventional echo parameters (group 1: DD grade 0–1 and group 2: DD grade 2−3). SWs after MVC were visualized on M-mode maps along the septum which were colour coded for tissue acceleration (Figure A). The speed was semi-automatically calculated by measuring the slope of the SW. Results The average ultra-filtrated volume after 1h of HD was 0.64±.27 L, which did not significantly differ between patient groups (p = 0.44). Patients in group 2 had significantly higher indexed LV wall mass compared to group 1 (128±39 g/m² vs. 72±24 g/m²; p = 0.02), indicative of LV structural remodelling. SW speed after MVC was significantly different between healthy volunteers and the patient groups at baseline (p&amp;lt;0.01) (Figure B). After 1h of HD, SW speed decreased in both groups, with the largest decrease in group 2 (Figure B). Furthermore, SW speed values of patient group 1 decreased to values similar to healthy volunteers, while patient group 2 still had significantly increased SW propagation speed. Conclusions Overall, myocardial stiffness, assessed using SW propagation speed, of patients with end-stage kidney disease was increased compared to healthy volunteers. This could result from increased LV preload or structural remodelling. Our data indicate that in addition to single measurements, assessing the change in SW speed by altering the loading state might aid in differentiating these causal mechanisms underlying increased myocardial stiffness. Therefore, adding a loading challenge, e.g. leg lifting, when doing SWE could provide additional information. Further research needs to confirm these initial findings.

Quantitative Ultrasound Techniques Used for Peripheral Nerve Assessment.

This review article describes quantitative ultrasound (QUS) techniques and summarizes their strengths and limitations when applied to peripheral nerves. A systematic review was conducted on publications after 1990 in Google Scholar, Scopus, and PubMed databases. The search terms "peripheral nerve", "quantitative ultrasound", and "elastography ultrasound" were used to identify studies related to this investigation. Based on this literature review, QUS investigations performed on peripheral nerves can be categorized into three main groups: (1) B-mode echogenicity measurements, which are affected by a variety of post-processing algorithms applied during image formation and in subsequent B-mode images; (2) ultrasound (US) elastography, which examines tissue stiffness or elasticity through modalities such as strain ultrasonography or shear wave elastography (SWE). With strain ultrasonography, induced tissue strain, caused by internal or external compression stimuli that distort the tissue, is measured by tracking detectable speckles in the B-mode images. In SWE, the propagation speed of shear waves, generated by externally applied mechanical vibrations or internal US "push pulse" stimuli, is measured to estimate tissue elasticity; (3) the characterization of raw backscattered ultrasound radiofrequency (RF) signals, which provide fundamental ultrasonic tissue parameters, such as the acoustic attenuation and backscattered coefficients, that reflect tissue composition and microstructural properties. QUS techniques allow the objective evaluation of peripheral nerves and reduce operator- or system-associated biases that can influence qualitative B-mode imaging. The application of QUS techniques to peripheral nerves, including their strengths and limitations, were described and discussed in this review to enhance clinical translation.

Biomechanical evaluation of the spring ligament and the posterior tibial tendon by shear-waves elastography: validation of a reliable and reproducible measurement protocol

PurposeThe anatomy of the spring ligament complex, as well as its pathology, is not well known in daily clinical practice. The purpose of this study was to evaluate the shear-wave elastography properties of the spring ligament and the posterior tibial tendon in healthy adults, and to assess the reliability and reproducibility of these measurements.MethodsShear-wave elastography was used to evaluate both ankles in 20 healthy patients (10 females/10 males) resting on a hinge support with their ankles in neutral, valgus 20° and varus 30° positions. The stiffness of the spring ligament and posterior tibial tendon was assessed by measuring the speed of shear wave propagation through each structure.ResultsPosterior tibial tendon and spring ligament reach a maximum estimated stiffness in valgus 20° position (7.43 m/s vs 5.73 m/s, respectively). Flat feet were associated with greater spring ligament stiffness in the 20° valgus position (p = 0.01), but not for the posterior tibial tendon (p = 0.71). The physiologic weightbearing hindfoot attitude had no impact on the stiffness of the posterior tibial tendon or the spring ligament, regardless of the analysis position. Intra- and inter-observer agreements were all excellent for spring ligament stiffness, regardless of ankle position, and were good or excellent for posterior tibial tendon.ConclusionsThis study describes a protocol to assess the stiffness of tibialis posterior and the spring ligament by shear-wave elastography, which is reliable, reproducible, and defines a corridor of normality. Further studies should be conducted to define the role of elastography for diagnosis/ evaluation of pathology, follow-up, or surgical strategies.

Fatigue state characterisation of steel pipes using ultrasonic shear waves.

The phenomenon of the reduction in the propagation speed of an ultrasonic wave when it travels through a fatigue zone has been well studied in the literature. Additionally, it has been established that shear waves are more severely affected by the presence of such a zone, compared with longitudinal waves. Our study utilises these phenomena to develop a method able to characterise the fatigue state of steel pipes. Initially, the existing theory regarding the increased sensitivity of shear waves to the presence of fatigue is validated through measuring and comparing the change in propagation speed of both longitudinal and bulk shear waves on flat geometries, at different fatigue states. The comparison is achieved with the aid of ultrasonic speed C-scans of both longitudinal and shear waves, with the latter now being obtainable through our implementation of advances in Electromagnetic Acoustic Transducers (EMAT) technology. EMATs have not been traditionally used for producing C-scans, and their ability do to so with adequate repeatability is demonstrated here; we show that shear wave scanning with EMATs now provides a possibility for inspection of fatigue damage on the inner surface of pressure-containing components in the nuclear power industry. We find that the change in ultrasonic wave speed is amplified when shear waves are used, with the magnitude of this amplification agreeing well with the theory. Following the verification of the theory, the use of EMATs allowed us to tailor the shear wave scanning method to pipe geometries, where C-scans with conventional piezoelectric transducers would not have been possible, with the results successfully revealing the presence of fatigue zones.

Predictors of shear wave propagation speed assessed by shear wave elastography

Abstract Background Cardiac shear wave elastography (SWE) is a novel ultrasound-based method that assesses the propagation speed of shear waves travelling in the myocardium induced by e.g. mitral valve closure (MVC). The propagation speed of these waves is related to the stiffness of the myocardium. The capability of SWE to evaluate myocardial stiffness has already been demonstrated in several publications. However, which factors beside the intrinsic mechanical properties of the myocardium influence shear wave speed in vivo has not been extensively investigated. Purpose The aim of this study was to investigate the influence of clinical parameters as well as echocardiographic indicators of myocardial tissue properties and left ventricular (LV) filling pressures on shear wave propagation speed after MVC. Methods 219 subjects (59±17 years; 140 males) were included in the study. Of those, 49 were healthy volunteers, 25 were patients with cardiac amyloidosis, 42 with hypertrophic cardiomyopathy, 35 with hypertensive heart disease and 68 with coronary artery disease. Subjects were scanned with an experimental ultrasound scanner using diverging wave imaging to acquire images at a high temporal resolution (average frame rate: 1167±414 Hz). Shear waves after MVC were visualized on M-mode maps along the interventricular septum which were colour coded for tissue acceleration (Figure 1). The propagation speed was calculated by semi-automatically measuring the spatiotemporal slope of the shear wave. Univariate and multivariate linear regression analysis was performed to identify variables associated with shear wave propagation speed. Results Univariate regression analysis revealed an association of the following variables with shear wave speed: age, BMI, systolic blood pressure, E wave, average e', E/e', left atrial volume index (LAVI), grade of diastolic dysfunction, isovolumic relaxation time, septal wall thickness, LV wall mass and presence of cardiomyopathy. These variables were added to a multivariate model. Predictors of shear wave speed after MVC were BMI, E wave, average e', LAVI, LV wall mass and presence of cardiomyopathy (R2=0.53) (Table 1). Conclusions The results of this study indicate that both myocardial structural properties (reflected by predictors LV wall mass and presence of cardiomyopathy) and LV filling pressures (reflected by predictors E wave, average e' and LAVI) affect shear wave speed. These findings suggest that SWE has the potential to assess structural as well as functional changes to the LV, which should be further explored. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research foundation Flanders - FWO

Shear wave tensiometry tracks reductions in collateral ligament tension due to incremental releases.

Surgeons routinely perform incremental releases on overly tight ligaments during total knee arthroplasty (TKA) to reduce ligament tension and achieve their desired implant alignment. However, current methods to assess whether the surgeon achieved their desired reduction in the tension of a released ligament are subjective and/or do not provide a quantitative metric of tension in an individual ligament. Accordingly, the purpose of this study was to determine whether shear wave tensiometry, a novel method to assess tension in individual ligaments based on the speed of shear wave propagation, can detect changes in ligament tension following incremental releases. In seven medial and eight lateral collateral porcine ligaments (MCL and LCL, respectively), we measured shear wave speeds and ligament tensions before and after incremental releases consisting of punctures with an 18-gauge needle. We found that shear wave speed squared decreased linearly with decreasing tension in both the MCL (average coefficient of determination(R2 avg ) = 0.76) and LCL (R2 avg = 0.94). We determined that errors in predicting tension following incremental releases were 26.2 and 14.2 N in the MCL and LCL, respectively, using ligament-specific calibrations. These results suggest shear wave tensiometry is a promising method to objectively measure the tension reduction in released structures.Clinical Significance: Direct, objective measurements of the tension changes in individual ligaments following release could enhance surgical precision during soft tissue balancing in total knee arthroplasty. Thus, shear wave tensiometry could help surgeons reduce the risk of poor outcomes associated with overly tight ligaments, including residual knee pain and stiffness.

Contribution of UltraFast™ Ultrasound and Shear Wave Elastography in the Imaging of Carotid Artery Disease.

Carotid artery disease is one of the main global causes of disability and premature mortality in the spectrum of cardiovascular diseases. One of its main consequences, stroke, is the second biggest global contributor to disability and burden via Disability Adjusted Life Years after ischemic heart disease. In the last decades, B-mode and Doppler-based ultrasound imaging techniques have become an indispensable part of modern medical imaging of carotid artery disease. However, they have limited abilities in carotid artery plaque and wall characterization and are unable to provide simultaneous quantitative and qualitative flow information while the images are burdened by low framerates. UltraFast™ ultrasound is able to overcome these obstacles by providing simultaneous quantitative and qualitative flow analysis information in high frame rates via UltraFast™ Doppler. Another newly developed ultrasound technique, shear wave elastography, is based on the visualization of induced shear waves and the measurement of the shear wave propagation speed in the examined tissues which enables real-time carotid plaque and wall analysis. These newly developed ultrasound modalities have potential to significantly improve workflow efficiency and are able to provide a plethora of additional imaging information of carotid artery disease in comparison to conventional ultrasound techniques.

Characterizing Musculoskeletal Tissue Mechanics Based on Shear Wave Propagation: A Systematic Review of Current Methods and Reported Measurements.

Developing methods for the non-invasive characterization of the mechanics of musculoskeletal tissues is an ongoing research focus in biomechanics. Often, these methods use the speed of shear wave propagation to characterize tissue mechanics (e.g., shear wave elastography and shear wave tensiometry). The primary purpose of this systematic review was to identify, compare, and contrast current methods for exciting and measuring shear wave propagation in musculoskeletal tissues. We conducted searches in the Web of Science, PubMed, and Scopus databases for studies published from January 1, 1900, to May 1, 2020. These searches targeted both shear wave excitation using acoustic pushes and mechanical taps, and shear wave speed measurement using ultrasound, magnetic resonance imaging, accelerometers, and laser Doppler vibrometers. Two reviewers independently screened and reviewed the articles, identifying 524 articles that met our search criteria. Regarding shear wave excitation, we found that acoustic pushes are useful for exciting shear waves through the thickness of the tissue of interest, and mechanical taps are useful for exciting shear waves in wearable applications. Regarding shear wave speed measurement, we found that ultrasound is used most broadly to measure shear waves due to its ability to study regional differences and target specific tissues of interest. The strengths of magnetic resonance imaging, accelerometers, and laser Doppler vibrometers make them advantageous to measure shear wave speeds for high-resolution shear wave imaging, wearable measurements, and non-contact ex vivo measurements, respectively. The advantages that each method offers for exciting and measuring shear waves indicate that a variety of systems can be assembled using currently available technologies to determine musculoskeletal tissue material behavior across a range of innovative applications.

On the interplay of loading, myocardial stiffness and contractility in transthoracic acoustic radiation force-induced shear wave measurements in pigs

Abstract Funding Acknowledgements Type of funding sources: Public Institution(s). Main funding source(s): Research Foundation Flanders (FWO grant number 1211620N) &amp; TTW-Dutch Heart Foundation partnership program "Early recognition of cardiovascular diseases" (project number 14740) Background Acoustic radiation force-based shear wave elastography (SWE) is a promising technique to non-invasively assess mechanical properties of the heart based on the propagation speed of acoustically induced shear waves. However, the interpretation of cardiac SWE measurements remains complex, and it is unclear how other factors such as loading affect shear wave propagation speed (SWS) measurements in diastole and systole. Purpose We applied transthoracic SWE in a pig model to investigate the dependencies of diastolic and systolic SWS on pressure-volume (PV) loop derived indices of loading, myocardial stiffness and contractility. Methods In 7 pigs, loading conditions were altered (increasing or decreasing preload; increasing afterload) and myocardial stiffness was changed (LAD occlusion for 60-100 minutes followed by 40 minutes of reperfusion). For each intervention, transthoracic SWE measurements were performed in a parasternal long-axis view with a high frame rate ultrasound system (&amp;gt; 6.2 kHz). Recordings of 28 ms were repeated at 34 Hz during 1.5 s to track shear waves throughout the cardiac cycle. To determine systolic and diastolic SWS in a robust manner, a piecewise linear model was fitted to the SWS data of each intervention representing multiple acquisitions, heartbeats and M-lines (fig. 1a). PV loops were recorded simultaneously with SWE measurements to estimate end-diastolic pressure (EDP), end-systolic pressure (ESP), end-diastolic pressure volume relation (EDPVR with exponential coefficient β in fig. 1b) and preload-recruitable stroke work (PRSW). Passive chamber stiffness was evaluated as the local slope of the EDPVR, i.e. β·EDP. Linear regressions and Pearson’s correlation coefficients were calculated. Results Diastolic SWS was significantly correlated to EDP when altering loading (blue in fig. 2a: R = 0.55; p &amp;lt; 0.01) and stiffness (orange in fig. 2a: R = 0.66; p &amp;lt; 0.01). A similar correlation is found between SWS and passive chamber stiffness β·EDP (fig. 2b). Diastolic SWS is more sensitive to changes in stiffness than in loading, as reflected by the larger slope of the regression line (0.79 vs. 0.28 in fig. 2b). Furthermore, systolic SWS significantly correlated with measures of contractility during loading alterations: ESP in fig. 2c (R = 0.69; p &amp;lt; 0.001) and PRSW in fig. 2d (R = 0.63; p = 0.02). However, no significant correlation was found between systolic SWS and contractility during infarct/reperfusion. Conclusion This study shows that diastolic SWS reflects the instantaneous stiffness of the myocardium, but is not a load-independent measure of the intrinsic passive mechanical properties of the heart. Instantaneous stiffness, and thus diastolic SWS, might be altered by loading (due to material non-linearity) or intrinsic mechanical changes. Furthermore, loading experiments suggest that systolic SWS is related to contractility. The relation between SWS and contractility in the presence of myocardial infarct deserves further study. Abstract Figure. Fig. 1: SWS and PV analysis. Abstract Figure. Fig. 2: SWS vs. PV-derived indices.

Systolic shear wave propagation speed as a novel non-invasive marker of myocardial contractility

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundation Flanders - FWO Background Shear wave elastography is a novel echocardiographic method that tracks shear wave propagation in the cardiac wall using high frame rate ultrasound. Shear waves can be induced by e.g. aortic valve closure (AVC). The propagation speed of these waves is related to the stiffness of the myocardium. Previous work has suggested that systolic shear wave speed is related to myocardial contractility. The current gold standard reference method for the evaluation of left ventricular (LV) contractility is pressure-volume loop analysis. However, the invasive nature of this method limits its clinical applicability. Purpose To compare non-invasively assessed shear wave propagation speed after AVC to invasive pressure-volume loop-derived measurements of contractility. Methods In 12 pigs (31.9 ± 4.3 kg), dobutamine was administered intravenously. Conventional and high frame rate echocardiographic images were acquired simultaneously with invasively measured pressure-volume loops before and after the administration of dobutamine. High frame rate echocardiographic datasets were acquired with an experimental ultrasound scanner at an average frame rate of 1304 ± 115 frames per second. Shear waves after AVC were visualized on M-mode displays along the interventricular septum which were colour coded for tissue acceleration (Figure 1A). The propagation speed was calculated by semi-automatically measuring the spatiotemporal slope of the shear wave. A set of pressure-volume loops were acquired during preload reduction by balloon occlusion of the vena cava inferior. The end-systolic elastance (Ees) of the ESPVR and preload recruitable stroke work (PRSW) were used as measures of contractility. Results Heart rate (72 ± 20 bpm vs. 105 ± 25 bpm; p &amp;lt; 0.05) and LV ejection fraction (61 ± 4% vs. 74 ± 7%; p &amp;lt; 0.001) significantly increased after the administration of dobutamine, while the LV end-systolic pressure remained similar (92 ± 21 mmHg vs. 106 ± 23 mmHg; p = 0.08). Pressure-volume loop-derived measures of contractility increased during dobutamine infusion (Ees: 1.3 ± 0.5 mmHg/ml vs. 2.1 ± 1.0 mmHg/ml; p &amp;lt; 0.01 and PRSW: 41 ± 25 mmHg vs. 86 ± 23 mmHg; p &amp;lt; 0.01). Likewise, shear wave propagation speed after AVC increased after dobutamine administration compared to baseline (3.1 ± 0.6 m/s vs. 5.3 ± 1.1 m/s; p &amp;lt; 0.001). Shear wave speed after AVC had a strong positive correlation with Ees (r = 0.68; p &amp;lt; 0.001) (Figure 1B) and PRSW (r = 0.65; p = 0.001) (Figure 1C). Conclusions Systolic shear wave propagation speed is related to invasively determined measurements of LV contractility. The results of this study indicate the potential of shear wave speed after AVC as a novel non-invasive parameter for the assessment of LV contractile function. Abstract Figure.

Myocardial stiffness assessed by shear wave elastography relates to pressure-volume loop derived measurements of chamber stiffness

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Research Foundations Flanders Background Increased myocardial stiffness is an important cause of diastolic dysfunction. Currently, invasive pressure-volume loop analysis is the gold standard method for the assessment of the left ventricular (LV) chamber stiffness. Its non-invasive assessment in the clinic is cumbersome, requires the combination of several parameters and has limited reliability. Shear wave elastography (SWE) is a novel method that evaluates the propagation of shear waves travelling along the myocardium using high frame rate echocardiography. The propagation speed is directly related to myocardial stiffness. Shear waves can be induced naturally by mitral valve closure (MVC). So far, the in vivo validation of SWE against an invasive gold standard reference method is still lacking. Purpose To compare myocardial stiffness assessed by shear wave propagation speed after MVC to invasive pressure-volume loop derived measurements of chamber stiffness. Methods Fifteen pigs (31.2 ± 4.1 kg) were included in the study. The instantaneous stiffness of the myocardium was altered by performing the following interventions: 1) preload reduction, 2) afterload increase, 3) preload increase and 4) induction of ischemia/reperfusion (I/R) injury by balloon occlusion of the proximal LAD for 90 min. with subsequent reperfusion of 40 min. To obtain the end-diastolic pressure-volume loop relation (EDPVR), a set of pressure-volume loops was acquired under preload reduction. From the EDPVR, the chamber stiffness constant β and operating chamber stiffness dP/dV were derived. SWE datasets in a parasternal long-axis view were acquired with an experimental ultrasound scanner at an average frame rate of 1304 ± 115 Hz. Shear waves after MVC were visualized on tissue acceleration maps by drawing an M-mode line along the interventricular septum (Figure 1A). The propagation speed was calculated by semi-automatically measuring the spatiotemporal slope. Results The chamber stiffness constant β significantly increased after the induction of the I/R injury (0.05 ± 0.01 1/ml vs. 0.09 ± 0.03 1/ml; p &amp;lt; 0.001). The operating chamber stiffness dP/dV decreased by reducing preload and increased by increasing afterload, increasing preload or by inducing an I/R injury (0.50 ± 0.18 mmHg/ml vs. 0.09 ± 0.05 mmHg/ml, 0.67 ± 0.19 mmHg/ml, 0.78 ± 0.35 mmHg/ml and 1.09 ± 0.38 mmHg/ml, respectively; p &amp;lt; 0.01). Likewise, shear wave propagation speed after MVC increased by increasing pre- and afterload (p = 0.001) and by inducing I/R injury (p &amp;lt; 0.001) (Figure 1B). Preload reduction had no significant influence (p = 0.118). Shear wave speed had a strong positive correlation with β (r = 0.63; p &amp;lt; 0.001) (Figure 1C) and dP/dV (r = 0.81; p &amp;lt; 0.001) (Figure 1D). Conclusions Shear wave speed after MVC is strongly related to invasive pressure-volume loop derived measures of chamber stiffness. The results of this study indicate the potential of SWE as a novel non-invasive method for the assessment of the instantaneous stiffness of the myocardium. Abstract Figure.

Can cardiac shear wave elastography detect the presence of septal scar in patients with left bundle branch block?

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): FWO: Fonds Wetenschappelijk Onderzoek (fund for scientific research Flanders) Background Cardiac resynchronization therapy (CRT) is an established treatment for heart failure patients with left bundle branch block (LBBB). Regardless, CRT has proven to be less effective in patients with ischemic cardiomyopathy, in particular when the septum is affected. The detection of septal scar prior to CRT implantation could therefore help to improve response rate. However, magnetic resonance imaging (MRI), the gold standard to assess myocardial scar, cannot be used in every patient due to already implanted devices or impaired renal function. Cardiac shear wave elastography (SWE) allows for the non-invasive assessment of myocardial stiffness via the detection of shear waves, for example induced by mitral valve closure (MVC), that travel through the myocardium. Shear wave speed is directly related to tissue stiffness. Recently, SWE has shown to be capable to detect myocardial scar, however this has never been demonstrated in the presence of LBBB. Purpose To evaluate whether SWE is able to detect the presence of septal scar in patients with LBBB. Methods We included 34 heart failure patients with LBBB (age: 69 ± 13 y; 56% males) and with ischemic (n = 9) or non-ischemic (n = 25) cardiomyopathy and 9 age-matched healthy volunteers (age: 68 ± 4 y; 66% males) as controls. In order to obtain native ventricular conduction biventricular (BiV) pacing was turned off. All ischemic patients had septal scar only, proven by MRI or scintigraphy. For SWE, left ventricular parasternal long-axis views were acquired with an experimental high frame rate ultrasound scanner (frame rate: 932 ± 32 fps). Shear waves were visualized in M-modes of the septum, colour coded for tissue acceleration. The slope of the shear waves in the M-mode represents their propagation speed (Figure A). Results Patient characteristics including echocardiographic parameters are shown in Table 1. Shear wave speed after MVC was significantly higher in patients with LBBB with or without septal scar compared to healthy controls (7.9 ± 1.2 m/s vs 4.5 ± 1.1 m/s; p = 0.044; 5.6 ± 1.2 m/s vs 4.5 ± 1.1 m/s: p &amp;lt; 0.001; figure B). This implies that the presence of LBBB alone increases myocardial stiffness. Most importantly, however, shear wave speed was significantly higher in LBBB patients with a septal scar compared to LBBB patients without a septal scar (7.9 ± 1.2 m/s vs 5.6 ± 1.2 m/s; p &amp;lt; 0.001; figure B), indicating that the presence of scar increases myocardial stiffness even more than LBBB alone. Conclusions LBBB causes a mild but significant increase in shear wave propagation speed in non-ischemic patients compared to controls. The presence of septal scarring leads to an additional and more significant increase. This indicates that SWE is capable of detecting stiffer scarred myocardium even in the presence of LBBB. Therefore, SWE could potentially be used as a novel method to detect septal scarring in LBBB patients before CRT implantation. Abstract Figure. Abstract Figure.

Externally-induced shear waves in the right ventricular free wall throughout the cardiac cycle

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): 1. NWO STW/Dutch Heart foundation 2. NWO Vidi TTW Background The right ventricular (RV) size and function have prognostic value, not only in right heart conditions (pulmonary hypertension, congenital heart disease), but also in left ventricular (LV) disease states. There is currently no noninvasive method for measuring the elastic properties of the RV walls. Increased RV diastolic stiffness however, as determined invasively, is linked to adverse prognosis in pulmonary arterial hypertension. In the LV, new high frame rate (HFR) echocardiography applications have been used in order to determine the propagation speed of naturally-occurring or externally-induced shear waves (SW) in the septum, which is related to myocardial stiffness. Purpose We show for the first time that SWs in the RV free wall (RVFW) can be externally induced and imaged transthoracically with ultrasound. Methods SW imaging was performed using a linear array with a programmable research ultrasound system, aimed at the parasternal long-axis view of a 5-weeks-old Yorkshire-Landrace pig (Fig. 1a). SWs were induced by a high intensity focused beam (f0 = 4.5 MHz) on the RVFW (Fig. 1a). This push beam generates a downwards force at the focus, which induces SWs that propagate left and right from the focus along the RVFW, visible on tissue Doppler images (TDI) shown in Figure 1b-c. SW propagation was imaged (f0 = 5.2 MHz) using HFR ultrasound (Fig. 1b, frame rate = 3 kHz). Three acquisitions of 1 second were performed, where 14 SWs were sequentially induced during each acquisition. ECG signal was captured simultaneously and synchronized offline. SW speeds were estimated using a custom, semi-automatic pipeline that includes TDI calculation, and SW speed estimation along a manually traced spline on the RVFW. This was repeated two times to include variability due to the manual processes. Up to four SW speed estimates were made after each push beam. SW speed estimation was repeated for all push pulses throughout the cardiac cycle, and the mean and standard deviation of the estimates were plotted (Fig. 2). Results At least 85% of the waves were tracked successfully for all acquisitions. Diastole and systole were identified using the ECG signal (Fig. 2a). The average SW speed was 0.6 ± 0.1 m/s at end-diastole (Fig. 2b). The measured speeds ranged from 0.5 ± 0.1 m/s during diastole to 1.9 ± 0.3 m/s during systole. The changes in SW speeds correspond to the expected variation in muscle stiffness during the heart cycle as the RV relaxes and contracts. Conclusions We demonstrate for the first time the induction and tracking of shear waves in the RVFW of a closed-chest pig. The possibility to noninvasively quantify RV wall stiffness opens a large field of translational research, with direct applications in pulmonary hypertension, congenital heart disease and heart failure in general. Pathological increase in stiffness should be further investigated in longitudinal case/control studies. Abstract Figure. Fig1: Induction and tracking of RV SW Abstract Figure. Fig2: SW speeds during cardiac cycle

Dyssynchrony significantly increases myocardial stiffness at mitral valve closure

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): FWO: Fonds Wetenschappelijk Onderzoek (fund for Scientific Research Flanders) Background Recently, shear wave elastography (SWE) has emerged as a promising, non-invasive technique to determine myocardial tissue stiffness. SWE is based on the detection of shear waves, for example induced by mitral valve closure (MVC), that propagate through the myocardium. The propagation speed of these shear waves is directly dependent on myocardial stiffness. However, the effect of a dyssynchronous contraction pattern – as it occurs in left bundle branch block (LBBB) – on shear wave speed is currently unknown. Purpose To investigate the effect of the dyssynchronous contraction pattern caused by LBBB on shear wave speed. Methods We included 25 non-ischemic heart failure patients with LBBB (age: 68 ± 15y; 52% males), all implanted with a CRT device. Dyssynchrony was reintroduced by turning biventricular (BiV) pacing off to allow native ventricular conduction. Echocardiographic images were taken during BiV pacing on and BiV pacing off, both with a conventional ultrasound machine and an experimental high frame rate ultrasound scanner (frame rate: 932 ± 32 fps). For SWE, left ventricular parasternal long-axis views were acquired. Shear waves were visualized in M-modes of the septum, colour coded for tissue acceleration. The slope of the shear waves in the M-mode represents their propagation speed. Speckle tracking of the four-chamber apical view was used to asses longitudinal strain of the mid-septal segment. To further investigate how dyssynchrony affects shear wave speed, the following time points were measured: onset of QRS, MVC and onset of septal contraction. Results Acutely switching BiV pacing on and off did not significantly affect left ventricular ejection fraction, nor end-diastolic or end-systolic volumes (all p &amp;gt; 0.05). Shear wave speed was significantly higher during BiV pacing off compared to BiV pacing on (5.6 ± 1.2 m/s vs 4.9 ± 1.3 m/s; p = 0.003; figure A). Furthermore, the onset of septal contraction was significantly earlier during BiV off (11 ± 15 ms vs 105 ± 57 ms; p &amp;lt; 0.0001). As a result, during BiV pacing off, the septal wall was further into the contraction phase at the time of MVC, leading to an increased myocardial stiffness, and thus increased shear wave speed (figure B). Our interpretation that increased shear wave speed could be attributed to an earlier onset of contraction of the septum was further strengthened by a strong correlation between the change in shear wave speed and the change in septal longitudinal strain at MVC when BiV pacing is turned off (r = 0.83; p &amp;lt; 0.001; figure C). Conclusion A dyssynchronous contraction caused by LBBB significantly increases shear wave propagation speed at MVC. This could be attributed to the early-systolic contraction of the septum during dyssynchrony. These results indicate that changes in contraction pattern caused by LBBB significantly influence myocardial stiffness at MVC. Abstract Figure.

ROLE OF SHEAR WAVE ELASTOGRAPHY IN CHARACTERIZATION OF BREAST MASSES USING HISTOPATHOLOGY AS GOLD STANDARD

Background: More recent ultrasound technique like SWE have led to better degrees of breast mass characterization by estimating tissue stiffness based on the acoustically generated shear wave propagation speed through the tissue. To nd out the sensitivity and Aims and Objectives: specicity of shear wave elastography in characterizing palpable breast masses using histopathology as gold standard. Materials and methods: This prospective, cross-sectional study was from may 2020 to June 2021. All patients underwent B-mode ultrasound, SWE and USG guided core biopsy of breast mass, BI-RADS on USG with modications by SWE assigned, cut-off values for qualitative and quantitative variables of SWE for differentiation between benign and malignant masses were estimated. SWE ndings were corelated with histopathology. Results: On histopathology amongst 55 patients 27 (49%) were benign and 28 (51%) were malignant. On USG, 19 were BI-RADS3 and 36 were BI-RADS 4 (4a, n = 18; 4b, n = 14; 4c, n = 4) leading to 78.57% sensitivity and 48.15% specicity. On modied BI-RADS' using E-color and Emean/E-max, specicity improved to 66.67% and 77.78% respectively. Addition of SWE to ul Conclusion: trasound improves characterization of BI-RADS 3 and 4a masses. E-max, E-mean and E-color are the most useful SWE parameters to differentiate between malignant and benign breast masses

Performance of Shear Wave Speed Measurements by Using Reverberant Optical Coherence Elastography

Elasticity of biological tissue is important to understand its properties, which could play important role in medical diagnosis and treatment, especially in its early stage of pathology. Optical Coherence Elastography (OCE) has been intensively developed for mapping the elasticity contrast of various biological tissues. OCE techniques based on tracking of shear vibrational wave propagation is one of the most popular techniques. The high speed of shear wave propagation in biological media leads to challenges in both data acquisition and data processing. Recently, the concept of reverberant shear wave fi eld has been applied to OCE, called Rev3D-OCE. In this work, we experimentally investigate the performance of Rev3D-OCE to differentiate gelatin phantoms with a slight difference of elasticity. We verifi ed that Rev3D-OCE can differentiate different shear wave speeds associated with different concentrations of gelatin phantoms, where higher shear wave speed was observed in a higher concentration of the phantom as expected. The average shear wave speed of gelatin with 3 wt% and 4 wt% concentrations were measured as 1.3 ± 0.2 m/s and 1.5 ± 0.1 m/s with about 11% and 14% of errors as compared with that obtained by standard mechanical testing, respectively. In addition, the spatial resolution of Rev3D-OCE as determined from the edge response measurement at the boundary between two gelatins of 3 wt% and 4 wt% concentrations was measured to be 0.3 millimeters.