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Shear wave elasticity imaging (SWEI) was employed to track acoustic radiation force impulse (ARFI)-induced shear waves in the mid-myocardium of the left ventricular free wall (LVFW) of a beating canine heart. Shear waves were generated and tracked with a linear ultrasound transducer that was placed directly on the exposed epicardium. Acquisition wa...
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The understanding of internal processes that affect the changes of consistency of soft tissue is a challenging problem. An ultrasound-monitoring Petri dish has been designed to monitor the evolution of relevant mechanical parameters during engineered tissue formation processes in real time. A better understanding of the measured ultrasonic signals...
![Fig. 3 CIRS 049A elastography phantom [30]](publication/331725892/figure/fig2/AS:736176545734660@1552529574543/CIRS-049A-elastography-phantom-30_Q320.jpg)
Background
The resources of ultrafast technology can be used to add another analysis to ultrasound imaging: assessment of tissue viscoelasticity. Ultrafast image formation can be utilized to find transitory shear waves propagating in soft tissue, which permits quantification of the mechanical properties of the tissue via elastography. This techniqu...
Citations
... Briefly, an acoustic radiation force impulse excitation "push" of 900 cycles at a 6.25-MHz center frequency was focused at a 20-mm depth within the phantom, 5-mm laterally from each target (Fig 2E), to generate a shear wave that was then tracked with pulse-echo US to determine local SWS of the material. Shear wave velocity through the phantom background and the inclusions was measured [39,41] to obtain Young's modulus estimates assuming a linear, isotropic, elastic medium. Each phantom was imaged 10 times for statistical analysis. ...
... Shear wave imaging data for the compliant elasticity phantom (Phantom 12) showed mean shear wave velocities between 1.6±0.1 and 2.3±0.1 m/s within regions of 5 and 12.5 seconds of cure time, respectively (S2 Table). These shear wave velocities correspond to Young's moduli of 7.6 and 15.6 kPa, respectively, assuming a linear, isotropic, elastic medium; these values are within the range reported for in vivo imaging of soft tissue [41]. The stiff elasticity phantom (Phantom 13) presented a similar trend of increasing shear wave velocity with cure time; however, Young's modulus estimates within the inclusions were significantly higher than typical soft tissue values, ranging from 72.9 to 123.6 kPa (S2 Table). ...
Modern ultrasound (US) imaging is increasing its clinical impact, particularly with the introduction of US-based quantitative imaging biomarkers. Continued development and validation of such novel imaging approaches requires imaging phantoms that recapitulate the underlying anatomy and pathology of interest. However, current US phantom designs are generally too simplistic to emulate the structure and variability of the human body. Therefore, there is a need to create a platform that is capable of generating well-characterized phantoms that can mimic the basic anatomical, functional, and mechanical properties of native tissues and pathologies. Using a 3D-printing technique based on stereolithography, we fabricated US phantoms using soft materials in a single fabrication session, without the need for material casting or back-filling. With this technique, we induced variable levels of stable US backscatter in our printed materials in anatomically relevant 3D patterns. Additionally, we controlled phantom stiffness from 7 to >120 kPa at the voxel level to generate isotropic and anisotropic phantoms for elasticity imaging. Lastly, we demonstrated the fabrication of channels with diameters as small as 60 micrometers and with complex geometry (e.g., tortuosity) capable of supporting blood-mimicking fluid flow. Collectively, these results show that projection-based stereolithography allows for customizable fabrication of complex US phantoms.
... The shear wave elasticity imaging (SWEI) [40] technique was used to track mechanical waves due to radiation force in the left-ventricular myocardium of an open chest dog at several positions and depths in the LV free wall and reported speeds ranging from 0.82 to 2.65 m s −1 [41,42]. A similar method, supersonic shear imaging (SSI) [43], uses focused acoustic radiation force to generate mechanical waves in tissue by moving the source of vibration at a supersonic speed along the line of excitation, creating a wave front. ...
Diastolic dysfunction causes close to half of congestive heart failures and is associated with increased stiffness in left-ventricular myocardium. A clinical tool capable of measuring viscoelasticity of the myocardium could be beneficial in clinical settings. We used Lamb wave Dispersion Ultrasound Vibrometry (LDUV) for assessing the feasibility of making in vivo non-invasive measurements of myocardial elasticity and viscosity in pigs. In vivo open-chest measurements of myocardial elasticity and viscosity obtained using a Fourier space based analysis of Lamb wave dispersion are reported. The approach was used to perform ECG-gated transthoracic in vivo measurements of group velocity, elasticity and viscosity throughout a single heart cycle. Group velocity, elasticity and viscosity in the frequency range 50-500 Hz increased from diastole to systole, consistent with contraction and relaxation of the myocardium. Systolic group velocity, elasticity and viscosity were 5.0 m s⁻¹, 19.1 kPa, 6.8 Pa • s, respectively. In diastole, the measured group velocity, elasticity and viscosity were 1.5 m s⁻¹, 5.1 kPa and 3.2 Pa • s, respectively.
... It is targeted mainly at radiology applications such as liver cirrhosis and breast cancer diagnosis (Parker et al. 2011 ). The suspected correlation between diastolic dysfunction and myocardial stiffness led to several ultrasound studies on the use of shear waves to measure the myocardial stiffness (Bouchard et al. 2009; Hollender et al. 2012; Kanai 2005; Song et al. 2013; Urban et al. 2013; Vos et al. Ultrasound in Med. ...
... They reported the propagation of a wave front along the anterior left ventricular wall with a propagation velocity that correlates well to the derived diastolic elasticity of the wall. Alternatively, the waves can be induced by external sources (Bouchard et al. 2009; Hollender et al. 2012; Song et al. 2013; Urban et al. 2013). Shear waves in soft biological tissue have a propagation velocity of 1–10 m/s, and this velocity is influenced by the stiffness of cardiac tissue (Couade et al. 2011; Kanai 2005; Urban et al. 2013). ...
Cardiac muscle stiffness can potentially be estimated non-invasively with shear wave elastography. Shear waves are present on the septal wall after mitral and aortic valve closure, thus providing an opportunity to assess stiffness in early systole and early diastole. We report on the shear wave recordings of 22 minipigs with high-frame-rate echocardiography. The waves were captured with 4000 frames/s using a programmable commercial ultrasound machine. The wave pattern was extracted from the data through a local tissue velocity estimator based on one-lag autocorrelation. The wave propagation velocity was determined with a normalized Radon transform, resulting in median wave propagation velocities of 2.2 m/s after mitral valve closure and 4.2 m/s after aortic valve closure. Overall the velocities ranged between 0.8 and 6.3 m/s in a 95% confidence interval. By dispersion analysis we found that the propagation velocity only mildly increased with shear wave frequency.
... M. Pernot is with the Langevin Institute, promising tool for direct assessment of ventricular diastolic function. Several animal studies have demonstrated the technical feasibility to generate and track shear waves (SWs) in the myocardium of a perfused animal heart ex vivo [1] and during open-heart surgery [2]–[5]. Furthermore, these studies also showed that SWE-derived mechanical parameters (elasticity and viscoelasticity) varied throughout the cardiac cycle and that local ischemia [3], [5] affected shear wave speed. ...
Shear wave elastography (SWE) is a potentially valuable tool to non-invasively assess ventricular function in children with cardiac disorders, which could help in the early detection of abnormalities in muscle characteristics. Initial experiments demonstrated the potential of this technique in measuring ventricular stiffness, however, its performance remains to be validated as complicated shear wave (SW) propagation characteristics are expected to arise due to the complex non-homogeneous structure of the myocardium. In this work, we investigated (i) the accuracy of different shear modulus estimation techniques (time-of-flight method and phase velocity analysis) across myocardial thickness and (ii) the effect of the ventricular geometry, surroundings, acoustic loading and material viscoelasticity on SW physics. A generic pediatric (10-15 year old) left ventricular model was studied numerically and experimentally. For the SWE-experiments, a polyvinylalcohol (PVA) replicate of the cardiac geometry was fabricated and SW-acquisitions were performed on different ventricular areas using varying probe orientations. Additionally, the phantom’s stiffness was obtained via mechanical tests. The results of the SWE-experiments revealed the following trends for stiffness estimation across the phantom’s thickness: a slight stiffness overestimation for phase speed analysis and a clear stiffness underestimation for the time-of-flight method for all acquisitions. The computational model provided valuable 3D insights in the physical factors influencing SW patterns, especially the surroundings (water), interface force and viscoelasticity. In conclusion, this work presents a validation study of two commonly used shear modulus estimators for different ventricular locations and the essential role of SW-modeling in understanding SW physics in the pediatric myocardium.
... Hence, very complex signal processing methods are required to accurately estimate the motion353637. This method has been used for investigation of phantoms, liver, prostate, and cardiac tissue [38, 39]. ...
Conventional imaging of diagnostic ultrasound is widely used. Although it makes the differences in the soft tissues echogenicities’ apparent and clear, it fails in describing and estimating the soft tissue mechanical properties. It cannot portray their mechanical properties, such as the elasticity and stiffness. Estimating the mechanical properties increases chances of the identification of lesions or any pathological changes. Physicians are now characterizing the tissue’s mechanical properties as diagnostic metrics. Estimating the tissue’s mechanical properties is achieved by applying a force on the tissue and calculating the resulted shear wave speed. Due to the difficulty of calculating the shear wave speed precisely inside the tissue, it is estimated by analyzing ultrasound images of the tissue at a very high frame rate. In this paper, the shear wave speed is estimated using finite element analysis. A model is constructed to simulate the tissue’s mechanical properties. For a generalized soft tissue model, Agar-gelatine model is used because it has properties similar to that of the soft tissue. A point force is applied at the center of the proposed model. As a result of this force, a deformation is caused. Peak displacements are tracked along the lateral dimension of the model for estimating the shear wave speed of the propagating wave using the Time-To-Peak displacement (TTP) method. Experimental results have shown that the estimated speed of the shear wave is 5.2 m/sec. The speed value is calculated according to shear wave speed equation equals about 5.7 m/sec; this means that our speed estimation system’s accuracy is about 91 %, which is reasonable shear wave speed estimation accuracy with a less computational power compared to other tracking methods.
... In addition, variation of the wave speed through the thickness of the myocardium at different angles in an explanted heart sample was also reported. A study in open chest dogs using waves generated using ARF was reported by Bouchard et al (2009). Variation of shear modulus in Langendorff perfused isolated rat and rabbit hearts was also explored using ARF methods , Vejdani-Jahromi et al 2015. ...
The myocardium is known to be an anisotropic medium where the muscle fiber orientation changes through the thickness of the wall. Shear wave elastography methods use propagating waves which are measured by ultrasound or magnetic resonance imaging (MRI) techniques to characterize the mechanical properties of various tissues. Ultrasound- or MR-based methods have been used and the excitation frequency ranges for these various methods cover a large range from 24–500 Hz. Some of the ultrasound-based methods have been shown to be able to estimate the fiber direction. We constructed a model with layers of elastic, transversely isotropic materials that were oriented at different angles to simulate the heart wall in systole and diastole. We investigated the effect of frequency on the wave propagation and the estimation of fiber direction and wave speeds in the different layers of the assembled models. We found that waves propagating at low frequencies such as 30 or 50 Hz showed low sensitivity to the fiber direction but also had substantial bias in estimating the wave speeds in the layers. Using waves with higher frequency content (>200 Hz) allowed for more accurate fiber direction and wave speed estimation. These results have particular relevance for MR- and ultrasound-based elastography applications in the heart.
... In addition, variation of the wave speed through the thickness of the myocardium at different angles in an explanted heart sample was also reported. A study in open chest dogs using waves generated using ARF was reported by Bouchard et al (2009). Variation of shear modulus in Langendorff perfused isolated rat and rabbit hearts was also explored using ARF methods , Vejdani-Jahromi et al 2015. ...
Shear wave elastography with acoustic radiation force (ARF) or harmonic vibration (HV) has been applied in animals and humans to evaluate myocardial material properties. The anisotropic myocardial structure presents a unique challenge to wave propagation methods because the fiber direction changes through the wall thickness. To investigate the effects of the frequency of excitation in the myocardium we constructed systolic and diastolic finite element models (FEMs) and performed an experiment on an ex vivo porcine heart. Both models were constructed with multiple elastic, transverse isotropic layers with a shear wave velocity (SWV) along and across the fibers where each layer has 1 mm thickness with the top and bottom in contact with water. The orientation of the muscle fibers was changed for each layer ranging from −50° to 80° from top to bottom. Harmonic excitations at 30, 50, 100, and 200 Hz and an impulsive force were used. An ex vivo porcine heart was tested using ARF excitations with a transesophogeal probe driven with a Verasonics ultrasound system applied directly to the left ventricular wall. We evaluated the measured orientation of the fibers in each layer by evaluating the angle with the highest SWV. The 30 and 50 Hz results showed little or no variation in the measured orientation angle in the layers. The 100 and 200 Hz results showed some variation of the orientation with respect to the layer. The impulse simulation results showed good agreement with the true orientations except near the top and bottom boundaries. The values of SWV were found to have different levels of bias depending on the excitation. The experimental results in the ex vivo heart showed similar trends as the FEM model results where the waves at lower frequencies had lower sensitivity to fiber direction. This multi-layered anisotropic model demonstrates how to resolve different anisotropic layers in the myocardium using ARF or HV while also revealing that using lower frequencies results in measurements that are less sensitive to anisotropy variation through the thickness of the myocardial wall.
... ARFI elastography has two modes: the tissue displacement at longitudinal direction provides a qualitative response for virtual tissue imaging (VTI), which measures qualitatively by the area ratio (AR); and a quantitative response for virtual touch tissue quantification (VTQ), which measures transverse SWV values in m/sec. Compared with previous conventional strain elastography, ARFI could evaluate the breast tissue stiffness without external compression and provide qualitative and quantitative information to help differentiation between malignant and benign breast lesions19202122. ...
This meta-analysis was aimed to assess the diagnostic performance of acoustic radiation force impulse (ARFI) elastography for the differentiation of malignant and benign breast lesions. The databases of PubMed, Web of Science(TM), WanFang, Vip, SinoMed and China National Knowledge Infrastructure were searched for all studies that evaluated the diagnostic performance of ARFI including virtual touch tissue quantification (VTQ) and virtual touch tissue imaging (VTI). All the studies were published prior to Mar. 21, 2014. The studies published in English or Chinese were collected. A total of 11 studies, including 1,408 breast lesions from 1,245 women, were analyzed. The values of summary sensitivity and summary specificity were 0.843 (95% confidence interval [CI]: 0.811-0.872) and 0.932 (95% CI: 0.913-0.948) for VTQ of ARFI, and 0.864 (95% CI: 0.799-0.914) and 0.882 (95% CI: 0.832-0.922) for VTI of ARFI, respectively. Subgroup analysis excluding mucinous carcinoma and carcinoma in situ showed higher summary sensitivity (0.877 95% CI: 0.835-0.911), higher summary specificity (0.943 95% CI: 0.921-0.960) and lower heterogeneity (I(2)=23.5%). The cut-off values for shear wave velocity of VTQ ranged widely from 2.89 to 6.71 m/s, while the VTI ranged narrowly from 1.37 to 1.66. In general, ARFI elastography seems to be a good method for differentiation between benign and malignant breast lesions. However, its usefulness for identifying breast mucinous carcinoma and breast carcinoma in situ is limited. VTI seems to be more reliable and repeatable than VTQ.
... In addition, variation of the wave speed through the thickness of the myocardium at different angles in an explanted heart sample was also reported. A study in open chest dogs using waves generated using ARF was reported by Bouchard et al (2009). Variation of shear modulus in Langendorff perfused isolated rat and rabbit hearts was also explored using ARF methods , Vejdani-Jahromi et al 2015. ...
The myocardium is known to be an anisotropic medium where the muscle fiber orientation changes through the thickness of the wall. Shear wave elastography methods use propagating waves which are measured by ultrasound or magnetic resonance imaging (MRI) techniques to characterize the mechanical properties of various tissues. Ultrasound- or MR-based methods have been used and the excitation frequency ranges for these various methods cover a large range from 24-500 Hz. Some of the ultrasound-based methods have been shown to be able to estimate the fiber direction. We constructed a model with layers of elastic, transversely isotropic materials that were oriented at different angles to simulate the heart wall in systole and diastole. We investigated the effect of frequency on the wave propagation and the estimation of fiber direction and wave speeds in the different layers of the assembled models. We found that waves propagating at low frequencies such as 30 or 50 Hz showed low sensitivity to the fiber direction but also had substantial bias in estimating the wave speeds in the layers. Using waves with higher frequency content (>200 Hz) allowed for more accurate fiber direction and wave speed estimation. These results have particular relevance for MR- and ultrasound-based elastography applications in the heart.
... Similar in principle methods proposed by using magnetic resonance imaging (MRI) [18, 19] or by using ECG-2 gated technique [20]. More direct tissue characterization methods have been developed as well, typically referred to as elastography, and applied for the assessment of soft, bulky tissues like the liver [21, 22], breast [23], prostate [24], skeletal muscles [25], kidneys [26], and heart [27, 28] . These elasticity imaging techniques rely on the application of a force to an area of interest in the tissue and measure tissue's mechanical response. ...
Supersonic shear wave imaging (SSI) is a noninvasive, ultrasound-based technique to quantify the mechanical properties of bulk tissues by measuring the propagation speed of shear waves (SW) induced in the tissue with an ultrasound transducer. The technique has been successfully validated in liver and breast (tumor) diagnostics and is potentially useful for the assessment of the stiffness of arteries. However, SW propagation in arteries is subjected to different wave phenomena potentially affecting the measurement accuracy. Therefore, we assessed SSI in a less complex ex vivo setup, that is, a thick-walled and rectangular slab of an excised equine aorta. Dynamic uniaxial mechanical testing was performed during the SSI measurements, to dispose of a reference material assessment. An ultrasound probe was fixed in an angle position controller with respect to the tissue to investigate the effect of arterial anisotropy on SSI results. Results indicated that SSI was able to pick up stretch-induced stiffening of the aorta. SW velocities were significantly higher along the specimen's circumferential direction than in the axial direction, consistent with the circumferential orientation of collagen fibers. Hence, we established a first step in studying SW propagation in anisotropic tissues to gain more insight into the feasibility of SSI-based measurements in arteries.
