Cardiac Shear Wave Elastography Using a Clinical Ultrasound System

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, the velocity of the wave induced by aortic valve closure in the interventricular septum increased in patients with expected increased wall stiffness.     

Cardiac Shear Wave Velocity Detection in the Porcine Heart

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.     

Acoustic Radiation Force Impulse Imaging with Virtual Touch Tissue Quantification: Measurements of Normal Breast Tissue and Dependence on the Degree of Pre-compression

Acoustic radiation force impulse imaging (ARFI) with Virtual Touch tissue quantification (VTTQ) enables the determination of shear wave velocity in meters per second (m/s). We investigated shear wave velocity in normal breast tissue and analyzed the influence of the degree of pre-compression on the measurements. In repeated measurements and with normal pre-compression, the mean shear wave velocity in breast parenchyma was significantly higher than that in breast adipose tissue (3.33 ± 1.18 m/s vs. 2.90 ± 1.10 m/s; p < 0.001; 712 measurements in 89 patients). Furthermore, we found a significant positive correlation between degree of pre-compression and velocity measurements. Shear wave velocities with low, moderate and high pre-compression were 1.89, 3.18 and 4.39 m/s in parenchyma, compared with 1.46, 2.55 and 3.64 m/s in adipose tissue, respectively (p < 0.001; 360 measurements in 60 patients). VTTQ of breast tissue is a feasible method with high accuracy; however, the degree of pre-compression applied may significantly influence the measurements.     

Reduced Patellar Tendon Elasticity with Aging: In Vivo Assessment by Shear Wave Elastography

How aging affects the elasticity of tendons has long been debated, partly because of the limited methods for in vivo evaluation, which differ vastly from those for in vitro animal studies. In this study, we tested the reliability of shear wave elastography (SWE) in the evaluation of patellar tendons and their change in elasticity with age. We recruited 62 healthy participants in three age groups: 20–30 years (group 1), 40–50 years (group 2) and 60–70 years (group 3). Shear wave velocity and elastic modulus were measured at the proximal, middle and distal areas of the patellar tendon. Reliability was excellent at the middle area and fair to good at both ends. Compared with the other groups, group 3 had significantly decreased elastic modulus and shear wave velocity values (p ≤ 0.001 vs. group 1 or 2), with significant increased side-to-side differences. SWE may be valuable in detecting aging tendons before visible abnormalities are observed on B-mode ultrasonography.     

Prostate Cancer Detection Using 3-D Shear Wave Elasticity Imaging

Transrectal ultrasound (TRUS) B-mode imaging provides insufficient sensitivity and specificity for prostate cancer (PCa) targeting when used for biopsy guidance. Shear wave elasticity imaging (SWEI) is an elasticity imaging technique that has been commercially implemented and is sensitive and specific for PCa. We have developed a SWEI system capable of 3-D data acquisition using a dense acoustic radiation force (ARF) push approach that leads to enhanced shear wave signal-to-noise ratio compared with that of the commercially available SWEI systems and facilitates screening of the entire gland before biopsy. Additionally, we imaged and assessed 36 patients undergoing radical prostatectomy using 3-D SWEI and determined a shear wave speed threshold separating PCa from healthy prostate tissue with sensitivities and specificities akin to those for multiparametric magnetic resonance imaging fusion biopsy. The approach measured the mean shear wave speed in each prostate region to be 4.8 m/s (Young's modulus E = 69.1 kPa) in the peripheral zone, 5.3 m/s (E = 84.3 kPa) in the central gland and 6.0 m/s (E = 108.0 kPa) for PCa with statistically significant (p < 0.0001) differences among all regions. Three-dimensional SWEI receiver operating characteristic analyses identified a threshold of 5.6 m/s (E = 94.1 kPa) to separate PCa from healthy tissue with a sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and area under the curve (AUC) of 81%, 82%, 69%, 89% and 0.84, respectively. Additionally, a shear wave speed ratio was assessed to normalize for tissue compression and patient variability, which yielded a threshold of 1.11 to separate PCa from healthy prostate tissue and was accompanied by a substantial increase in specificity, PPV and AUC, where the sensitivity, specificity, PPV, NPV and AUC were 75%, 90%, 79%, 88% and 0.90, respectively. This work illustrates the feasibility of using 3-D SWEI data to detect and localize PCa and demonstrates the benefits of normalizing for applied compression during data acquisition for use in biopsy targeting studies.     

声脉冲辐射力成像技术定量诊断慢性肝病

目的 探讨声脉冲辐射力成像(ARFI)技术定量检测慢性肝病肝纤维化的价值。方法 研究对象包括61例乙型肝炎病毒阳性患者(慢性肝病组)、29例肝硬化患者(肝硬化组)及109名健康对照者(对照组)。采用ARFI技术定量测量肝实质剪切波速度。结果 慢性肝病组、肝硬化组、对照组肝脏平均剪切波速分别为(1.59±0.38)m/s、(2.35±0.53)m/s、(1.11±0.18)m/s,两两比较差异均有统计学意义(P<0.05)。结论 ARFI可无创测量肝实质剪切波速度,客观反映肝组织的弹性模量,有望成为定量评估肝纤维化的客观准确的新方法。     

Detection of Changes in Cervical Softness Using Shear Wave Speed in Early versus Late Pregnancy: An in Vivo Cross-Sectional Study

The aim of this study was to assess the ability of shear wave elasticity imaging (SWEI) to detect changes in cervical softness between early and late pregnancy. Using a cross-sectional study design, shear wave speed (SWS) measurements were obtained from women in the first trimester (5–14?wk of gestation) and compared with estimates from a previous study of women at term (37–41?wk). Two sets of five SWS measurements were made using commercial SWEI applications on an ultrasound system equipped with a prototype catheter transducer (128 elements, 3-mm diameter, 14-mm aperture). Average SWS estimates were 4.42?±?0.32?m/s (n?=?12) for the first trimester and 2.13?±?0.66?m/s (n?=?18) for the third trimester (p?<0.0001). The area under the curve was 0.95 (95% confidence interval: 0.82–0.99) with a sensitivity and specificity of 83%. SWS estimates indicated that the third-trimester cervix is significantly softer than the first-trimester cervix. SWEI methods may be promising for assessing changes in cervical softness.     

Shear wave velocity measurement of upper trapezius muscle by color Doppler shear wave imaging

Purpose

Skeletal muscle stiffness is thought to be the result of increased tissue hardness, but measurement accuracy has been dependent on operator technique. We have proposed a novel shear wave real-time imaging method (color Doppler shear wave imaging: CD SWI) with continuous shear waves excited from the tissue surface by a mechanical vibrator.

Methods

Using the method, shear wave velocity was measured for the upper trapezius muscle. Adaptive shear wave velocity measurement by means of quality estimation of shear wave wavefront was adopted. We recruited 23 male volunteers with no history of orthopedic disease and recorded shear wave propagation to assess the intra- and inter-observer reliability. For intra-observer reliability, one observer took two measurements separated by a time delay, and the intra-class correlation coefficient (ICC) was calculated (1,1). For inter-observer reliability, ICC (2,1) was calculated from both observers’ measurements.

Results

Mean propagation speed was 3.75 ± 0.47 (first) and 3.71 ± 0.49 m/s (second) for Observer A (ICC (1,1) = 0.91 [95% CI 0.76–0.96]) and 3.80 ± 0.53 m/s for Observer B (ICC (2,1) = 0.83 [95% CI 0.56–0.94]).

Conclusions

This result suggests that our technique is satisfactorily reliable and has potential for future application in various fields, such as evaluation of muscle condition or the effects of rehabilitation.

     

Pre-operative Conventional Ultrasound and Sonoelastography Evaluation for Predicting Axillary Lymph Node Metastasis in Patients with Malignant Breast Lesions

The objective of our study was to evaluate the association between the sonoelastography features of breast tumor and axillary lymph node metastasis (ALNM) in patients with breast cancer. In a cohort of 106 women with breast cancer, the conventional ultrasound features and elasticity parameters by elasticity imaging and Virtual Touch Tissue Imaging & Quantification (VTIQ) were retrospectively analyzed. Ultrasound and elastography findings were compared with pathologic axillary lymph node status. Receiver operating characteristic curve analysis was used to evaluate diagnostic performance. Pathologically, the overall incidence of ALNM was 39.6% (42/106) in the final analysis. ALNM was significantly more frequent in tumors with elasticity imaging scores >4.5, maximal shear wave velocity values (S_max) >6.42 m/s and mean shear wave velocity values (S_mean) >5.66 m/s, respectively. The sensitivity, specificity and accuracy were 78.6%, 54.7% and 64.2% for elasticity imaging score; 85.7%, 54.7% and 67.0% for S_max; and 59.5%, 79.7% and 71.7% for S_mean, respectively Elastography features, including elasticity imaging score and VTIQ, can be used to supplement conventional ultrasound to predict ALNM in patients with breast cancers.     

Time-Harmonic Ultrasound elastography of the Descending Abdominal Aorta: Initial Results

Stiffening of central large vessels is considered a key pathophysiologic factor within the cardiovascular system. Current diagnostic parameters such as pulse wave velocity (PWV) indirectly measure aortic stiffness, a hallmark of coronary diseases. The aim of the present study was to perform elastography of the proximal abdominal aorta based on externally induced time-harmonic shear waves. Experiments were performed in 30 healthy volunteers (25 young, 5 old, >50 y) and 5 patients with longstanding hypertension (PWV >10 m/s). B-Mode-guided sonographic time-harmonic elastography was used for measurement of externally induced shear waves at 30-Hz vibration frequency. Thirty-hertz shear wave amplitudes (SWAs) within the abdominal aorta were measured and displayed in real time and processed offline for differences in SWA between systole and diastole (ΔSWA). Data were analyzed using the Kruskal–Wallis test and receiver operating characteristic curve analysis. The change in SWA over the cardiac cycle was reduced significantly in all patients as assessed with ΔSWA (volunteers: mean = 10 ± 5 μm, patients: mean = 4 ± 1 μm; p < 0.001). The best separation of healthy volunteers from patients was obtained with a ΔSWA threshold of 4.7 μm, resulting in a sensitivity of 0.9 and a specificity of 1.0, with an overall area under the curve of 0.96. Time harmonic elastography of the abdominal aorta is feasible and shows promise for the exploitation of time-varying shear wave amplitudes as a diagnostic marker for aortic wall stiffening. Patients with elevated PWVs suggesting increased aortic wall stiffness were best identified by ΔSWA—a parameter that could be related to the ability of the vessel walls to distend on passages of the pulse wave.     

Effect of toe dorsiflexion on the regional distribution of plantar fascia shear wave velocity

BackgroundThe plantar fascia is exposed to repetitive tensile stress induced by cyclic loads associated with daily activities, such as walking and running. Due to overuse or abnormal foot alignment, insertional and distal (i.e., mid-substance) regions within the plantar fascia may exhibit microtears, which leads to plantar fasciopathy. Ultrasound shear wave elastography is an imaging technique to measure shear wave velocity propagating through biological tissues, considered herein as an index of tensile stress. This study aimed to quantify the effect of toe dorsiflexion on the regional distribution of plantar fascia shear wave velocity.MethodsShear wave velocity of the plantar fascia was measured in the insertional and distal regions using ultrasound shear wave elastography in sixteen healthy participants (7 males and 9 females). The measurements were performed while the toes were maintained in neutral or dorsiflexed positions.FindingsWhen considering the insertional region, there was no significant difference in shear wave velocity between neutral toe position [mean (SEM): 5.4 (0.6) m/s] and dorsiflexed toe position [5.5 (0.5) m/s] (P = 0.88; effect size = 0.05). When considering the distal region, there was a significant difference in shear wave velocity between the neutral position [7.8 (0.4) m/s] and dorsiflexed position [9.9 (0.3) m/s] (P = 0.002; effect size = 0.88). The difference in shear wave velocity between the insertional and distal regions showed a large effect size for either neutral (P = 0.010; effect size = 0.75) or dorsiflexed toe position (P = 0.003; effect size = 0.86).InterpretationIn contrast to clinical beliefs, these findings suggest that toe dorsiflexion induces non-homogeneous changes in tensile stress within the plantar fascia.     

超声弹性成像观察肝脏凝固灶:体外实验

目的 运用实验手段探讨超声弹性成像(EI)在肝脏凝固灶中的应用.方法 选取新鲜离体猪肝,通过无水乙醇注射和微波消融两种方法产生不同形态的凝固灶,观察实验前、后的EI图,利用虚拟声触诊定量(VTQ)技术测定作用区的剪切波传播速度.实验结束后切开标本记录实际凝固灶形态、范围.结果 无水乙醇注射和微波消融均可使局部肝组织发生凝固性坏死,EI图上表现为红色硬变区,且不随时间延长而衰减,较常规二维超声更接近凝固灶形态,但与实际仍有一定差异.作用区的剪切波速度较实验前明显增高(P＜0.01),也表明凝固性坏死的肝组织硬度增加.结论 EI可从力学角度提供凝固灶信息,应用简捷、无创,是常规超声的有益补充.     

Shear wave elasticity imaging based on acoustic radiation force and optical detection

Tissue elasticity is closely related to the velocity of shear waves within biologic tissue. Shear waves can be generated by an acoustic radiation force and tracked by, e.g., ultrasound or magnetic resonance imaging (MRI) measurements. This has been shown to be able to noninvasively map tissue elasticity in depth and has great potential in a wide range of clinical applications including cancer and cardiovascular diseases. In this study, a highly sensitive optical measurement technique is proposed as an alternative way to track shear waves generated by the acoustic radiation force. A charge coupled device (CCD) camera was used to capture diffuse photons from tissue mimicking phantoms illuminated by a laser source at 532 nm. CCD images were recorded at different delays after the transmission of an ultrasound burst and were processed to obtain the time of flight for the shear wave. A differential measurement scheme involving generation of shear waves at two different positions was used to improve the accuracy and spatial resolution of the system. The results from measurements on both homogeneous and heterogeneous phantoms were compared with measurements from other instruments and demonstrate the feasibility and accuracy of the technique for imaging and quantifying elasticity. The relative error in estimation of shear wave velocity can be as low as 3.3% with a spatial resolution of 2 mm, and increases to 8.8% with a spatial resolution of 1 mm for the medium stiffness phantom. The system is shown to be highly sensitive and is able to track shear waves propagating over several centimetres given the ultrasound excitation amplitude and the phantom material used in this study. It was also found that the reflection of shear waves from boundaries between regions with different elastic properties can cause significant bias in the estimation of elasticity, which also applies to other shear wave tracking techniques. This bias can be reduced at the expense of reduced spatial resolution.     

SWAVE Imaging of Placental Elasticity and Viscosity: Proof of Concept

The placenta is the interface between the fetus and the mother and is vital for fetal development. Ultrasound elastography provides a non-invasive way to examine in vivo the stiffness of the placenta; increased stiffness has previously been linked to fetal growth restriction. This study used a previously developed dynamic elastography method, called shear wave absolute vibro-elastography, to study 61 post-delivery clinically normal placentas. The shear wave speeds in the placenta were recorded under five different low-frequency mechanical excitations. The elasticity and viscosity were estimated through rheological modeling. The shear wave speeds at excitation frequencies of 60, 80, 90, 100 and 120 Hz were measured to be 1.23 ± 0.44, 1.67 ± 0.76, 1.74 ± 0.72, 1.80 ± 0.78 and 2.25 ± 0.80 m/s. The shear wave speed values we obtained are consistent with previous studies. In addition, our multi-frequency acquisition approach enables us to provide viscosity estimates that have not been previously reported.     

正常人腕部正中神经剪切波弹性成像的研究

摘要目的本研究探讨正常人腕部正中神经不同位置的剪切波测值差异。方法剪切波弹性成像检查56例健康志愿者的112条腕管处的正中神经,比较近、远端腕骨处正中神经剪切波速度的差异,并分析与年龄、性别和BMI等相关性。结果受试者正中神经近端腕骨水平剪切波速度是（3.80±0.45）m/s,95%置信区间是（3.67,3.93）m/s;远端腕骨水平剪切波速度是（4.63±0.47）m/s,95%置信区间为（4.49,4.76）m/s。正中神经剪切波速度与年龄呈正相关,不同性别、同一水平的正中神经剪切波速度测值差异有统计学意义。结论正中神经在腕部不同区域的剪切波速度是不同的,性别、年龄均是影响剪切波速度测值的重要因素,这些可为进一步的临床研究提供参考。     

Differential diagnosis of idiopathic granulomatous mastitis and breast cancer using acoustic radiation force impulse imaging

Purpose

Differentiation of idiopathic granulomatous mastitis (IGM) from carcinoma with routine imaging methods, such as ultrasonography (US) and mammography, is difficult. Therefore, we evaluated the value of a newly developed noninvasive technique called acoustic radiation force impulse imaging in differentiating IGM versus malignant lesions in the breast.

Methods

Four hundred and eighty-six patients, who were referred to us with a presumptive diagnosis of a mass, underwent Virtual Touch tissue imaging (VTI; Siemens) and Virtual Touch tissue quantification (VTQ; Siemens) after conventional gray-scale US. US-guided percutaneous needle biopsy was then performed on 276 lesions with clinically and radiologically suspicious features. Malignant lesions (n = 122) and IGM (n = 48) were included in the final study group.

Results

There was a statistically significant difference in shear wave velocity marginal and internal values between the IGM and malignant lesions. The median marginal velocity for IGM and malignant lesions was 3.19 m/s (minimum–maximum 2.49–5.82) and 5.05 m/s (minimum–maximum 2.09–8.46), respectively (p < 0.001). The median internal velocity for IGM and malignant lesions was 2.76 m/s (minimum–maximum 1.14–4.12) and 4.79 m/s (minimum–maximum 2.12–8.02), respectively (p < 0.001).

Conclusion

The combination of VTI and VTQ as a complement to conventional US provides viscoelastic properties of tissues, and thus has the potential to increase the specificity of US.

     

Viscoelastic and Anisotropic Mechanical Properties of in vivo Muscle Tissue Assessed by Supersonic Shear Imaging

The in vivo assessment of the biomechanical properties of the skeletal muscle is a complex issue because the muscle is an anisotropic, viscoelastic and dynamic medium. In this article, these mechanical properties are characterized for the brachialis muscle in vivo using a noninvasive ultrasound-based technique. This supersonic shear imaging technique combines an ultra-fast ultrasonic system and the remote generation of transient mechanical forces into tissue via the radiation force of focused ultrasonic beams. Such an ultrasonic radiation force is induced deep within the muscle by a conventional ultrasonic probe and the resulting shear waves are then imaged with the same probe (5 MHz) at an ultra-fast framerate (up to 5000 frames/s). Local tissue velocity maps are obtained with a conventional speckle tracking technique and provide a full movie of the shear wave propagation through the entire muscle. Shear wave group velocities are then estimated using a time of flight algorithm. This approach provides a complete set of quantitative and in vivo parameters describing the muscle’s mechanical properties as a function of active voluntary contraction as well as passive extension of healthy volunteers. Anisotropic properties are also estimated by tilting the probe head with respects to the main muscular fibers direction. Finally, the dispersion of the shear waves is studied for these different configurations and shear modulus and shear viscosity are quantitatively assessed assuming the viscoelastic Voigt’s model. (E-mail: jl.gennisson@espci.fr)     

Imaging Two-Dimensional Mechanical Waves of Skeletal Muscle Contraction

Skeletal muscle contraction is related to rapid mechanical shortening and thickening. Recently, specialized ultrasound systems have been applied to demonstrate and quantify transient tissue velocities and one-dimensional (1-D) propagation of mechanical waves during muscle contraction. Such waves could potentially provide novel information on musculoskeletal characteristics, function and disorders. In this work, we demonstrate two-dimensional (2-D) mechanical wave imaging following the skeletal muscle contraction. B-mode image acquisition during multiple consecutive electrostimulations, speckle-tracking and a time-stamp sorting protocol were used to obtain 1.4 kHz frame rate 2-D tissue velocity imaging of the biceps brachii muscle contraction. The results present novel information on tissue velocity profiles and mechanical wave propagation. In particular, counter-propagating compressional and shear waves in the longitudinal direction were observed in the contracting tissue (speed 2.8–4.4 m/s) and a compressional wave in the transverse direction of the non-contracting muscle tissue (1.2–1.9 m/s). In conclusion, analysing transient 2-D tissue velocity allows simultaneous assessment of both active and passive muscle tissue properties.     

Tissue elasticity of in vivo skeletal muscles measured in the transverse and longitudinal planes using shear wave elastography

The aim of the present study was to measure in vivo skeletal muscle elasticity in the transverse and longitudinal planes using shear wave elastography and then to compare the image stability, measurement values and measurement repeatability between these imaging planes. Thirty‐one healthy males participated in this study. Tissue elasticity (shear wave velocity) of the medial gastrocnemius, rectus femoris, biceps brachii and rectus abdominis was measured in both the transverse and longitudinal planes using shear wave elastography. Image stability was evaluated by the standard deviation of the colour distribution in the shear wave elastography image. Measurement repeatability was assessed by the coefficient of variance obtained from three measurement values. Image stability of all tested muscles was significantly higher in the longitudinal plane (P<0·001), but measurement repeatability did not differ significantly between the imaging planes (P>0·05), except in the biceps brachii (P = 0·001). Measurement values of the medial gastrocnemius, rectus femoris and biceps brachii were significantly different between the imaging planes (P<0·001). Image stability and measurement values of shear wave elastography images varied with imaging plane, which indicates that imaging plane should be considered when measuring skeletal muscle tissue elasticity by shear wave elastography.     

Acoustic radiation force-driven assessment of myocardial elasticity using the displacement ratio rate (DRR) method

A noninvasive method of characterizing myocardial stiffness could have significant implications in diagnosing cardiac disease. Acoustic radiation force (ARF)-driven techniques have demonstrated their ability to discern elastic properties of soft tissue. For the purpose of myocardial elasticity imaging, a novel ARF-based imaging technique, the displacement ratio rate (DRR) method, was developed to rank the relative stiffnesses of dynamically varying tissue. The basis and performance of this technique was demonstrated through numerical and phantom imaging results. This new method requires a relatively small temporal (<1 ms) and spatial (tenths of mm²) sampling window and appears to be independent of applied ARF magnitude. The DRR method was implemented in two in vivo canine studies, during which data were acquired through the full cardiac cycle by imaging directly on the exposed epicardium. These data were then compared with results obtained by acoustic radiation force impulse (ARFI) imaging and shear wave velocimetry, with the latter being used as the gold standard. Through the cardiac cycle, velocimetry results portray a range of shear wave velocities from 0.76-1.97 m/s, with the highest velocities observed during systole and the lowest observed during diastole. If a basic shear wave elasticity model is assumed, such a velocity result would suggest a period of increased stiffness during systole (when compared with diastole). Despite drawbacks of the DRR method (i.e., sensitivity to noise and limited stiffness range), its results predicted a similar cyclic stiffness variation to that offered by velocimetry while being insensitive to variations in applied radiation force.