Improved shear wave motion detection using pulse-inversion harmonic imaging with a phased array transducer (original) (raw)
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Cardiac Shear Wave Elastography Using a Clinical Ultrasound System
Ultrasound in medicine & biology, 2017
The propagation velocity of shear waves relates to tissue stiffness. We prove that a regular clinical cardiac ultrasound system can determine shear wave velocity with a conventional unmodified tissue Doppler imaging (TDI) application. The investigation was performed on five tissue phantoms with different stiffness using a research platform capable of inducing and tracking shear waves and a clinical cardiac system (Philips iE33, achieving frame rates of 400-700 Hz in TDI by tuning the normal system settings). We also tested the technique in vivo on a normal individual and on typical pathologies modifying the consistency of the left ventricular wall. The research platform scanner was used as reference. Shear wave velocities measured with TDI on the clinical cardiac system were very close to those measured by the research platform scanner. The mean difference between the clinical and research systems was 0.18 ± 0.22 m/s, and the limits of agreement, from -0.27 to +0.63 m/s. In vivo, th...
2015
Recent advancement in cardiac shear wave elastography (SWE) using pulse-inversion harmonic imaging showed substantial improvement of shear wave motion detection and demonstrated feasibility of transthoracic measurement of human myocardial stiffness. This study aimed at systematically investigating the feasible echocardiographic views for cardiac SWE and the impact of myocardial anisotropy when measuring myocardial stiffness from different scan views transthoracically. Ten healthy volunteers were recruited and scanned three times on three different days. A cardiac SWE sequence with pulse-inversion harmonic imaging and time-aligned sequential tracking was used to measure quantitative myocardial stiffness in late diastole. Seven combinations of echocardiography views and left ventricular (LV) segments were found to be feasible for transthoracic cardiac SWE: basal interventricular septum (IVS) under parasternal short-axis and long-axis views; mid IVS under parasternal short-axis and long-axis views; anterior LV free wall under parasternal short-axis and long-axis views; and posterior LV free wall under parasternal short-axis view. On the same LV segment, the mean diastolic shear wave speed (SWS) measurements from the short-axis view were statistically different from the long-axis view: 1.82 vs. 1.29 m/s for basal IVS; 1.81 vs. 1.45 m/s for mid IVS; and 1.96 vs. 1.77 m/s for anterior LV free wall, indicating that myocardial anisotropy plays a significant role in cardiac SWE measurements. These results establish the preliminary normal range of myocardial SWS under different scan views and provide important guidance for future clinical studies using cardiac SWE.
2015
Monitoring myocardial stiffness changes with shear wave elastography (SWE) has promising potential for assessing chemotherapy-induced cardiotoxicity for pediatric cancer patients. While ultrasound B-scan with adult cardiac probes on children is commonly acceptable, SWE can be challenging due to the narrow intercostal spaces of children, which hinders the effective transmission of the push beam and detection beam for shear wave generation and shear wave detection. This study aimed at addressing this challenge by implementing cardiac SWE on a pediatric cardiac probe (P7-4) with pulse-inversion harmonic imaging (PIHI) and time-aligned sequential tracking (TAST). The performance of the proposed pediatric cardiac SWE sequence (P7-4 PIHI-TAST) was systematically compared with an adult cardiac transducer equipped with the same PIHI and TAST cardiac SWE sequence (P4-2 PIHI-TAST), and a pediatric cardiac SWE sequence with fundamental imaging TAST shear wave detection (P7-4 Fundamental-TAST). In vivo transthoracic scans in healthy pediatric volunteers demonstrated substantial improvement of shear wave signal quality using the P7-4 PIHI-TAST sequence, as compared to the adult P4-2 PIHI-TAST sequence and the pediatric P7-4 Fundamental-TAST sequence. The results showed higher increase in SWE success rate among younger children when using the pediatric transducer. Also agreeing with previous studies, this study demonstrated that PIHI shear wave detection could substantially improve the shear wave signal quality as compared to fundamental imaging shear wave detection.
2014 IEEE International Ultrasonics Symposium, 2014
End-diastolic left ventricular (EDLV) stiffness is a strong biomarker of diastolic heart failure (DHF). Ultrasound shear wave elastography (SWE) can provide a quantitative and noninvasive measure of myocardial stiffness, which makes SWE a promising tool for clinical diagnosis of DHF. In practice, however, in vivo transthoracic heart study with SWE is very challenging due to the difficult imaging situation of the heart. Recently, we proposed a pulse-inversion harmonic imaging (PIHI) approach for shear wave detection and showed substantial improvement of shear wave signal quality from the heart. In this study, we further developed a multi-zone PIHI shear wave detection method to enhance harmonic excitation and further improve shear wave signal quality. We also developed a cardiac shear wave speed (SWS) calculation method that allows manual tracing of the shear wave propagation path. This path length is used to estimate the SWS using an algorithm based on the Radon transform of the motion data. A pilot study was conducted to test the repeatability of measuring EDLV stiffness of healthy subjects with the multi-zone PIHI approach and the cardiac SWS calculation method. Five subjects were recruited and studied on three different days. Statistical analyses showed good repeatability of SWS measurements across 3 days for subjects 1 and 4, and between days 2 and 3 for subjects 1, 2, 3 and 4. The overall success rates of detecting robust shear waves from subjects 1 to 5 are 94%, 83%, 96%, 98%, and 27%, respectively. The overall SWS measurements for all subjects are in good agreement with literature values from animal studies. These results indicate that the proposed SWE methods with multi-zone PIHI detection and cardiac SWS calculation is reliable in measuring EDLV stiffness and has great potential for diagnosing DHF in future studies.
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.
Shear wave elasticity imaging: a new ultrasonic technology of medical diagnostics
Ultrasound in Medicine & Biology, 1998
Shear wave elasticity imaging (SWEI) is a new approach to imaging and characterizing tissue structures based on the use of shear acoustic waves remotely induced by the radiation force of a focused ultrasonic beam. SWEI provides the physician with a virtual "finger" to probe the elasticity of the internal regions of the body. In SWEI, compared to other approaches in elasticity imaging, the induced strain in the tissue can be highly localized, because the remotely induced shear waves are attenuated fully within a very limited area of tissue in the vicinity of the focal point of a focused ultrasound beam. SWEI may add a new quality to conventional ultrasonic imaging or magnetic resonance imaging. Adding shear elasticity data ("palpation information") by superimposing color-coded elasticity data over ultrasonic or magnetic resonance images may enable better differentiation of tissues and further enhance diagnosis. This article presents a physical and mathematical basis of SWEI with some experimental results of pilot studies proving feasibility of this new ultrasonic technology. A theoretical model of shear oscillations in soft biological tissue remotely induced by the radiation force of focused ultrasound is described. Experimental studies based on optical and magnetic resonance imaging detection of these shear waves are presented. Recorded spatial and temporal profiles of propagating shear waves fully confirm the results of mathematical modeling. Finally, the safety of the SWEI method is discussed, and it is shown that typical ultrasonic exposure of SWEI is significantly below the threshold of damaging effects of focused ultrasound. © 1998 World Federation for Ultrasound in Medicine & Biology.
2015
Quantification of liver elasticity is a major application of shear wave elasticity imaging (SWEI) to noninvasively assess liver fibrosis stages. SWEI measurements can be highly affected by ultrasound image quality. Ultrasound harmonic imaging has shown a significant improvement in ultrasound image quality as well as for SWEI measurements. This has been previously demonstrated in cardiac SWEI. The purpose of this study was to evaluate liver shear wave motion detection and shear wave velocity (SWV) measurements with fundamental and harmonic ultrasound imaging. In a cohort of 14 subjects with no history of liver disease, a 2.5 fold increase in maximum shear wave motion and 0.08 m/s decreases in overall interquartile range and median of SWV, as well as a 14.3% increase in the success rate of SWV measurements was found when using harmonic imaging instead of fundamental imaging.
Journal of Ultrasound in Medicine, 2016
A Pilot Study ltrasound shear wave elastography (SWE) is an emerging imaging technique that can remotely "palpate" tissue and provide a direct and quantitative assessment of tissue stiffness. 1,2 It has been shown to possess considerable clinical diagnostic value in many applications, such as liver fibrosis staging and breast cancer detection, and is gradually becoming part of clinical practice. 3-6 Shear wave elastography uses acoustic radiation force to remotely generate transient shear waves inside the tissue, and then tissue stiffness is quantified in terms of the shear modulus (μ) based on μ = ρc s 2 , where ρ is the density of the tissue and is commonly assumed to be 1000 kg/m 3 , and c s is the shear wave speed (SWS),
Applied Sciences
Plane wave imaging in Shear Wave Elastography (SWE) captures shear wave propagation in real-time at ultrafast frame rates. To assess the capability of this technique in accurately visualizing the underlying shear wave mechanics, this work presents a multiphysics modeling approach providing access to the true biomechanical wave propagation behind the virtual image. This methodology was applied to a pediatric ventricular model, a setting shown to induce complex shear wave propagation due to geometry. Phantom experiments are conducted in support of the simulations. The model revealed that plane wave imaging altered the visualization of the shear wave pattern in the time (broadened front and negatively biased velocity estimates) and frequency domain (shifted and/or decreased signal frequency content). Furthermore, coherent plane wave compounding (effective frame rate of 2.3 kHz) altered the visual appearance of shear wave dispersion in both the experiment and model. This mainly affected stiffness characterization based on group speed, whereas phase velocity analysis provided a more accurate and robust stiffness estimate independent of the use of the compounding technique. This paper thus presents a versatile and flexible simulation environment to identify potential pitfalls in accurately capturing shear wave propagation in dispersive settings.
Physics in Medicine and Biology, 2020
Two-dimensional (2-D) ultrasound shear wave elastography (SWE) has been widely used for soft tissue properties assessment. Given that shear waves propagate in three dimensions (3-D), extending SWE from 2-D to 3-D is important for comprehensive and accurate stiffness measurement. However, implementation of 3-D SWE on a conventional ultrasound scanner is challenging due to the low volume rate (tens of Hertz) associated with limited parallel receive capability of the scanner's hardware beamformer. Therefore, we developed an external mechanical vibration-based 3-D SWE technique allowing robust 3-D shear wave tracking and speed reconstruction for conventional scanners. The aliased shear wave signal detected with a sub-Nyquist sampling frequency was corrected by leveraging the cyclic nature of the sinusoidal shear wave generated by the external vibrator. Shear wave signals from different sub-volumes were aligned in temporal direction to correct time delays from sequential pulse-echo events, followed by 3-D speed reconstruction using a 3-D local frequency estimation algorithm. The technique was validated on liver fibrosis phantoms with different stiffness, showing good correlation (r = 0.99, p < 0.001) with values measured from a state-of-the-art SWE system (GE LOGIQ E9). The phantoms with different stiffnesses can be well-differentiated regardless of the external vibrator position, indicating the feasibility of the 3-D SWE with regard to different shear wave propagation scenarios. Finally, shear wave speed calculated by the 3-D method correlated well with magnetic resonance elastography performed on human liver (r = 0.93, p = 0.02), demonstrating the in vivo feasibility. The proposed technique relies on low volume rate imaging and can be implemented on