Shear Wave Elastography Imaging Research Articles

Evaluation of median nerve by shear wave elastography and diffusion tensor imaging in carpal tunnel syndrome

PurposeThe aim of the current study is to investigate the diagnostic role of shear-wave elastography and diffusion tensor imaging in patients with carpal tunnel syndrome. Material and methodsThe study included a total of 77 wrists; 18 normal, 35 wrists with mild, 9 wrists with moderate and 15 wrists with severe carpal tunnel syndrome. Elastography of the median nerve was performed by defining the boundaries of a segment of the nerve at sagittal plane at the level of proximal carpal row. Additionally, the cross-sectional area of the median nerve was evaluated. Fractional anisotropy and apparent diffusion coefficient measurements were carried out by placing region-of-interest at three levels: at pisiform bone (carpal tunnel inlet), mid carpal tunnel, and hook of hamate (carpal tunnel outlet). ResultsPatients with carpal tunnel syndrome had higher elasticity values of median nerve (53.0 kPa; IQR 40.8–77.0 kPa) compared to control subjects. (36.8 kPa; IQR 31.0–39.9 kPa) Patients with moderate-severe carpal tunnel syndrome had higher elasticity values (82 kPa; IQR 64.0–95.5 kPa) compared to patients with mild carpal tunnel syndrome. (44 kPa; IQR 32.5–59.5 kPa)Patients with carpal tunnel syndrome had lower fractional anisotropy at mid-carpal level (0.382; IQR 0.330–0.495) compared to the control group. (0.494; IQR 0.434–0.537) Patients with moderate-severe carpal tunnel syndrome had lower fractional anisotropy values (0.366; IQR 0.331–0.407) and higher apparent diffusion coefficient values (1.509 mm2/s; IQR 1.374–1.733 mm2/s) compared to patients with mild carpal tunnel syndrome. (0,423; IQR 0.324–0.526 and 1.293 mm2/s; IQR 0.967–1.514 mm2/s) ConclusionShear-wave elastography and diffusion tensor imaging are helpful imaging modalities in diagnosing carpal tunnel syndrome and assessing its severity.

Shear wave elastography for characterization of breast lesions: Shearlet transform and local binary pattern histogram techniques

Shear wave elastography (SWE) examination using ultrasound elastography (USE) is a popular imaging procedure for obtaining elasticity information of breast lesions. Elasticity parameters obtained through SWE can be used as biomarkers that can distinguish malignant breast lesions from benign ones. Furthermore, the elasticity parameters extracted from SWE can speed up the diagnosis and possibly reduce human errors. In this paper, Shearlet transform and local binary pattern histograms (LBPH) are proposed as an original algorithm to differentiate malignant and benign breast lesions. First, Shearlet transform is applied on the SWE images to acquire low frequency, horizontal and vertical cone coefficients. Next, LBPH features are extracted from the Shearlet transform coefficients and subjected to dimensionality reduction using locality sensitivity discriminating analysis (LSDA). The reduced LSDA components are ranked and then fed to several classifiers for the automated classification of breast lesions. A probabilistic neural network classifier trained only with seven top ranked features performed best, and achieved 98.08% accuracy, 98.63% sensitivity, and 97.59% specificity in distinguishing malignant from benign breast lesions. The high sensitivity and specificity of our system indicates that it can be employed as a primary screening tool for faster diagnosis of breast malignancies, thereby possibly reducing the mortality rate due to breast cancer.

Non-invasive Myocardial Shear Wave Elastography Device for Clinical Applications in Cardiology

BackgroundUltrasound Shear Wave Elastography has been widely used in clinical practice to access tissues' stiffness non-invasively. However, the application of this technique to access myocardial stiffness clinically and non-invasively was yet not demonstrated. In this study, we introduce a new prototype for clinical application purposes, the Myocardial Shear Wave Elastography imaging (MSWEi) device. MethodsThe MSWEi device lays on a linear phased-array probe (2.75-MHz, Vermon S.A., Tours, France) connected to an ultrafast ultrasound scanner (Aixplorer, Supersonic Imagine, Aix-en-Provence, France), a dedicated sequence of Shear Wave Elastography and unfocused emissions at very high frame rate for myocardial stiffness evaluation, and a dedicated graphical user interface for physicians use in clinical settings. ResultsThis prototype was evaluated and validated in-vitro using calibrated mimicking tissue phantoms, providing accurate and robust measurements for tissues' stiffness up to 25 kPa. The device was also validated for stiffness estimation on different thin layers for thickness superior to 5-mm, showing a bias estimation inferior to 15%. Finally, the in-vivo and non-invasive application of the prototype was also evaluated on a patient. ConclusionThis study presented a new device to evaluate non-invasively myocardial stiffness using an ultrafast ultrasound scanner in a clinical setting. The in-vivo, non-invasive and clinical feasibility was demonstrated showing the potential of the device to evaluate myocardial stiffness accurately up to 25 KPa and for myocardial wall thickness superior to 5-mm.

Modeling of the acoustic radiation force in elastography

Elastography is a non-invasive imaging technique that can assess in vivo tissue stiffness. Shear wave elastography imaging uses the acoustic radiation force (ARF) to produce shear waves. Numerical models rely on different formulations of the ARF. We present three existing formulations for the ARF: its full expression in the second-order approximation and two simplified formulations using a quasi-plane wave and an attenuated plane wave approximation. Analytical expressions for the ARF are derived for the special cases of a spherical concave source and for a quasi-Gaussian beam. They show discrepancies between the different formulations. For strongly divergent or highly focused beams the result from the second-order approximation differs from both simplified formulations. However the second-order and quasi-plane wave approximations create identical shear displacements. The k-Wave simulation package is used to compute the ARF and the ensuing transient displacement produced by an ultrasound probe. The second-order approximation and the quasi-plane wave approximation give different forces but identical displacements. The results using the plane wave approximation significantly differ. It is concluded that for highly focused transducers only the second-order approximation accurately estimates the ARF. For estimating shear displacements the second-order or quasi-plane wave approximation are equivalent and preferable to the plane wave approximation.

Modeling of the acoustic radiation force in elastography.

Elastography is a non-invasive imaging technique that can assess in vivo tissue stiffness. In shear wave elastography imaging, the acoustic radiation force (ARF) produced by focused ultrasound generates a local force that produces shear waves. The authors compare three existing formulations for the ARF: its full expression in the second-order approximation and two simplified formulations using a quasi-plane wave and an attenuated plane wave approximation. Analytical expressions for the ARF are derived for the special cases of a concave spherical source and a quasi-Gaussian beam. They provide expressions for the resulting ARF and show discrepancies between the different formulations. For strongly divergent or highly focused beams the ARF expressed by the second-order approximation significantly differs from both simplified formulations. However, despite those differences the second-order and quasi-plane wave approximations create identical shear displacements in tissue. To compute the ARF and the displacements produced by a conventional ultrasound probe, the three formulations were incorporated into the k-Wave simulation package. The second-order and quasi-plane wave approximations give different forces but nearly identical displacements while the plane wave approximation significantly differs. It is concluded that to properly take into account the ultrasound field structure, the second-order or quasi-plane wave approximations should be preferably used.

Effects of age and pathology on shear wave speed of the human rotator cuff.

Rotator cuff tears are common and often repaired surgically, but post-operative repair tissue healing, and shoulder function can be unpredictable. Tear chronicity is believed to influence clinical outcomes, but conventional clinical approaches for assessing tear chronicity are subjective. Shear wave elastography (SWE) is a promising technique for assessing soft tissue via estimates of shear wave speed (SWS), but this technique has not been used extensively on the rotator cuff. Specifically, the effects of age and pathology on rotator cuff SWS are not well known. The objectives of this study were to assess the association between SWS and age in healthy, asymptomatic subjects, and to compare measures of SWS between patients with a rotator cuff tear and healthy, asymptomatic subjects. SWE images of the supraspinatus muscle and intramuscular tendon were acquired from 19 asymptomatic subjects and 11 patients with a rotator cuff tear. Images were acquired with the supraspinatus under passive and active (i.e., minimal activation) conditions. Mean SWS was positively associated with age in the supraspinatus muscle and tendon under passive and active conditions (p ≤ 0.049). Compared to asymptomatic subjects, patients had a lower mean SWS in their muscle and tendon under active conditions (p ≤ 0.024), but no differences were detected under passive conditions (p ≥ 0.783). These findings identify the influences of age and pathology on SWS in the rotator cuff. These preliminary findings are an important step toward evaluating the clinical utility of SWE for assessing rotator cuff pathology. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:282-288, 2018.

A Machine-Learning Algorithm Toward Color Analysis for Chronic Liver Disease Classification, Employing Ultrasound Shear Wave Elastography

The purpose of the present study was to employ a computer-aided diagnosis system that classifies chronic liver disease (CLD) using ultrasound shear wave elastography (SWE) imaging, with a stiffness value-clustering and machine-learning algorithm. A clinical data set of 126 patients (56 healthy controls, 70 with CLD) was analyzed. First, an RGB-to-stiffness inverse mapping technique was employed. A five-cluster segmentation was then performed associating corresponding different-color regions with certain stiffness value ranges acquired from the SWE manufacturer-provided color bar. Subsequently, 35 features (7 for each cluster), indicative of physical characteristics existing within the SWE image, were extracted. A stepwise regression analysis toward feature reduction was used to derive a reduced feature subset that was fed into the support vector machine classification algorithm to classify CLD from healthy cases. The highest accuracy in classification of healthy to CLD subject discrimination from the support vector machine model was 87.3% with sensitivity and specificity values of 93.5% and 81.2%, respectively. Receiver operating characteristic curve analysis gave an area under the curve value of 0.87 (confidence interval: 0.77–0.92). A machine-learning algorithm that quantifies color information in terms of stiffness values from SWE images and discriminates CLD from healthy cases is introduced. New objective parameters and criteria for CLD diagnosis employing SWE images provided by the present study can be considered an important step toward color-based interpretation, and could assist radiologists' diagnostic performance on a daily basis after being installed in a PC and employed retrospectively, immediately after the examination.

Evaluation of hepatic fibrosis: a review from the society of abdominal radiology disease focus panel.

Hepatic fibrosis is potentially reversible; however early diagnosis is necessary for treatment in order to halt progression to cirrhosis and development of complications including portal hypertension and hepatocellular carcinoma. Morphologic signs of cirrhosis on ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) alone are unreliable and are seen with more advanced disease. Newer imaging techniques to diagnose liver fibrosis are reliable and accurate, and include magnetic resonance elastography and US elastography (one-dimensional transient elastography and point shear wave elastography or acoustic radiation force impulse imaging). Research is ongoing with multiple other techniques for the noninvasive diagnosis of hepatic fibrosis, including MRI with diffusion-weighted imaging, hepatobiliary contrast enhancement, and perfusion; CT using perfusion, fractional extracellular space techniques, and dual-energy, contrast-enhanced US, texture analysis in multiple modalities, quantitative mapping, and direct molecular imaging probes. Efforts to advance the noninvasive imaging assessment of hepatic fibrosis will facilitate earlier diagnosis and improve patient monitoring with the goal of preventing the progression to cirrhosis and its complications.

Comparison of 3D and 2D shear-wave elastography for differentiating benign and malignant breast masses: focus on the diagnostic performance

To evaluate the diagnostic performance of three-dimensional (3D) image shear-wave elastography (SWE) for differentiating benign from malignant breast masses compared to two-dimensional (2D) SWE and B-mode ultrasound (US). This study consisted of 205 breast lesions from 199 patients who underwent B-mode US and SWE before biopsy from January 2014 to March 2016. Quantitative elasticity values (maximum and mean elasticity, Emax and Emean) obtained from 2D and 3D SWE (axial, sagittal, and coronal images) were reviewed retrospectively, in addition to the histopathological findings including immunohistochemistry profiles (luminal A, luminal B, human epidermal growth factor receptor 2 (HER2)-enriched, and triple-negative breast cancer) in cases of malignancy. Histopathological findings were regarded as the reference standard. The diagnostic performance of each data set was evaluated using the area under the receiver operating characteristic (ROC) curve (AUC) analysis to compare sensitivity and specificity. Among 205 lesions, 105 (51.22%) were malignant and 100 (48.78%) were benign. Compared to benign masses, malignant masses had higher values of Emax and Emean on both 2D and 3D SWE, the differences of which were statistically significant (p<0.001). The AUCs of 2D, 3D axial, and sagittal SWE were significantly higher than that of 3D coronal SWE (p<0.05). In addition, the sensitivities of axial, sagittal, and coronal 3D SWE were all higher than that of 2D SWE for Emean (81.9%, 87.6%, and 89.5% versus 70.5%, respectively, p<0.05). Conversely, the specificity of 2D and 3D axial SWE was higher than that of 3D sagittal and coronal SWE (Emax, 84%, 83% versus 76%, 73%; Emean, 85%, 81% versus 68%, 50%, respectively, p<0.05). We also assessed changes in Breast Imaging-Reporting and Data System (BI-RADS) category 3 and category 4a lesions by adding each of the parameters for 2D and 3D SWE in B-mode US. The specificity, PPV, and accuracy of combined 2D or combined 3D SWE with B-mode US was statistically higher than that of B-mode US alone for differentiating benign and malignant lesions (p<0.05). Among SWE images, 2D SWE, and 3D SWE axial and sagittal images exhibited superior diagnostic performance compared to 3D coronal images. Addition of 3D SWE images to B-mode US improved the diagnostic performance for distinguishing benign from malignant masses.

Reproducibility of 2‐Dimensional Shear Wave Elastography Assessment of the Liver: A Direct Comparison With Point Shear Wave Elastography in Healthy Volunteers

Two-dimensional shear wave elastography (2D-SWE) imaging for the noninvasive assessment of tissue stiffness was assessed for reproducibility in healthy volunteers in quantifying liver elasticity, compared with an established point shear wave elastography (p-SWE) technique also known as virtual touch quantification (VTQ) (SIEMENS). Eleven healthy volunteers were examined by four experienced operators on two occasions, separated by two weeks (sessions A and B). Ten 2D-SWE using LOGIQ E9 and p-SWE measurements using VTQ (in meters per second) were consecutively taken from deep portions of liver segments 5 or 6 away from vascular structures, using standard techniques. Inter- and intra-observer agreement was assessed by intraclass coefficient (ICC). A total of 880 2D-SWE and p-SWE velocities were recorded. Mean values from the four operators ranged between 1.188 and 1.196 m/s for 2D-SWE and 1.170 to 1.207 m/s for p-SWE. Interobserver reproducibility was good for both sessions with ICCs of 0.88 and 0.93 (2D-SWE) and 0.87 and 0.93 (p-SWE). The overall intra-operator reproducibility between sessions A and B was good for both p-SWE and 2D-SWE with ICC of 0.87 and 0.83, respectively. For inter- and intra-observer variability, the ICC was more than or equal to 0.71, indicating that the results were reliable. There was a strong and significant correlation between the 2D-SWE and p-SWE measurements (r = 0.87, P = .0006), but their velocities did not agree equally across different velocities. Two-dimensional SWE using LOGIQ E9 is a reliable and reproducible method for measuring elasticity in healthy volunteers and has a similar degree of reliability as p-SWE using VTQ, but absolute measurements from the two techniques should not be used interchangeably.

Ultrasound Shear Wave Elastography: A Novel Method to Evaluate Bladder Pressure

Children with bladder dysfunction resulting in increased storage pressure are at risk for renal deterioration. The current gold standard for evaluation of bladder pressure is urodynamics, an invasive test requiring catheterization. We evaluated ultrasound shear wave elastography as a novel means of assessing bladder biomechanical properties associated with increased bladder pressure. Concurrent shear wave elastography and urodynamics were performed. Ultrasound shear wave elastography images were obtained of the anterior and posterior wall when empty and at 25%, 50%, 75% and 100% expected bladder capacity, and end fill volume. Regions of interest were confirmed by a pediatric radiologist. Bladder cohorts were defined as compliant (capacity detrusor pressure less than 25 cm H2O) and noncompliant (25 cm H2O or greater). Pearson correlation coefficients and a mixed effects model evaluated the relationship between shear wave speed and detrusor pressure, compliance and normalized compliance. An unpaired t-test was used for between cohort analyses. In all 23 subjects mean shear wave speed of the anterior and posterior bladder walls significantly correlated with detrusor pressure throughout filling. When comparing compliant and noncompliant bladders, mean shear wave speed and detrusor shear wave speed of the anterior wall significantly increased with filling of noncompliant bladders. Shear wave speed remained at baseline levels in compliant bladders. Mean shear wave speed of the anterior wall was significantly correlated with compliance and normalized compliance. Ultrasound shear wave elastography bladder measurements correlate well with bladder storage pressure, and shear wave speed measurements differ between compliant and noncompliant bladders. This is the first known study to demonstrate that shear wave elastography is promising as a bedside modality for the assessment of bladder dysfunction in children.

Ultrafast Synthetic Transmit Aperture Imaging Using Hadamard-Encoded Virtual Sources With Overlapping Sub-Apertures.

The development of ultrafast ultrasound imaging offers great opportunities to improve imaging technologies, such as shear wave elastography and ultrafast Doppler imaging. In ultrafast imaging, there are tradeoffs among image signal-to-noise ratio (SNR), resolution, and post-compounded frame rate. Various approaches have been proposed to solve this tradeoff, such as multiplane wave imaging or the attempts of implementing synthetic transmit aperture imaging. In this paper, we propose an ultrafast synthetic transmit aperture (USTA) imaging technique using Hadamard-encoded virtual sources with overlapping sub-apertures to enhance both image SNR and resolution without sacrificing frame rate. This method includes three steps: 1) create virtual sources using sub-apertures; 2) encode virtual sources using Hadamard matrix; and 3) add short time intervals (a few microseconds) between transmissions of different virtual sources to allow overlapping sub-apertures. The USTA was tested experimentally with a point target, a B-mode phantom, and in vivo human kidney micro-vessel imaging. Compared with standard coherent diverging wave compounding with the same frame rate, improvements on image SNR, lateral resolution (+33%, with B-mode phantom imaging), and contrast ratio (+3.8 dB, with in vivo human kidney micro-vessel imaging) have been achieved. The f-number of virtual sources, the number of virtual sources used, and the number of elements used in each sub-aperture can be flexibly adjusted to enhance resolution and SNR. This allows very flexible optimization of USTA for different applications.

Computer-aided tumor diagnosis using shear wave breast elastography

The shear wave elastography (SWE) uses the acoustic radiation force to measure the stiffness of tissues and is less operator dependent in data acquisition compared to strain elastography. However, the reproducibility of the result is still interpreter dependent. The purpose of this study is to develop a computer-aided diagnosis (CAD) method to differentiate benign from malignant breast tumors using SWE images. After applying the level set method to automatically segment the tumor contour and hue-saturation-value color transformation, SWE features including average tissue elasticity, sectional stiffness ratio, and normalized minimum distance for grouped stiffer pixels are calculated. Finally, the performance of CAD based on SWE features are compared with those based on B-mode ultrasound (morphologic and textural) features, and a combination of both feature sets to differentiate benign from malignant tumors. In this study, we use 109 biopsy-proved breast tumors composed of 57 benign and 52 malignant cases. The experimental results show that the sensitivity, specificity, accuracy and the area under the receiver operating characteristic ROC curve (Az value) of CAD are 86.5%, 93.0%, 89.9%, and 0.905 for SWE features whereas they are 86.5%, 80.7%, 83.5% and 0.893 for B-mode features and 90.4%, 94.7%, 92.3% and 0.961 for the combined features. The Az value of combined feature set is significantly higher compared to the B-mode and SWE feature sets (p=0.0296 and p=0.0204, respectively). Our results suggest that the CAD based on SWE features has the potential to improve the performance of classifying breast tumors with US.

The applied research of shear wave elastography and superb microvascular imaging in pathological grading of breast invasive ductal carcinoma

Objective To discuss the application value of shear wave elastography (SWE) and superb microvascular imaging (SMI) in pathological grading of breast invasive ductal carcinoma (IDC). Methods Sixty patients with breast tumor were selected, which were totally 64 lesions. Before operation, SWE and SMI pattern were started to detect the lesions. And images in SWE and SMI pattern were saved. All lesions were proved to be IDC and pathological gradings were got according to the pathological result. The mean of Young′s modulus(AveT1) and maximum of Young′s modulus(AveT2) were recorded in SWE pattern, and degree of blood was recorded in SMI pattern followed Adler′s grading standard. Then differences of AveT1, AveT2 and degree of blood in different pathological grading of invasive ductal carcinoma were evaluated. Results ①In pathological grading 1 group, the average of AveT1 was (62.1±10.4)kPa, and the average of AveT2 was (93.0±20.1)kPa. In pathological grading 2 group, the average of AveT1 was (79.8±8.6)kPa, and the average of AveT2 was (120.6±18.7)kPa. In pathological grading 3 group, the average of AveT1 was (92.6±12.1)kPa, and the average of AveT2 was (137.3±21.5)kPa. The AveT1 and AveT2 were gradually growing with higher pathological grading of breast invasive ductal carcinoma, which were statistically significant (P<0.05). ②In pathological grading 1 group, there were 7 cases in the degree of blood 0-Ⅰ and 14 in the degree of blood Ⅱ-Ⅲ. In pathological grading 2 group, there were 3 cases in the degree of blood 0-Ⅰ and 18 cases in the degree of blood Ⅱ-Ⅲ. In pathological grading 3 group, there were only 1 case in the degree of blood 0-Ⅰ and 21 cases in the degree of blood Ⅱ-Ⅲ. There were more lesions of rich blood with higher pathological grading of breast invasive ductal carcinoma, which was statistically significant (P<0.05). Conclusions There are differences of elastography and degree of blood in different pathological grading of breast invasive ductal carcinoma, SWE and SMI can prompt pathological grading and provide important clinical reference value. Key words: Ultrasonography; Breast neoplasms; Invasive ductal carcinoma; Shear wave elastography; Superb microvascular imaging

Shear Wave Elastography Imaging for the Features of Symptomatic Carotid Plaques: A Feasibility Study.

Shear wave elastography (SWE) was performed to evaluate the Young's modulus of carotid plaques in patients presenting with cerebrovascular incidents, to estimate the clinical value and feasibility of this approach. Sixty-one patients (mean age, 65 years; 45 men) underwent common duplex ultrasonic examination and SWE evaluation. The patients were divided into the symptomatic and asymptomatic groups based on the presence of unilateral focal neurological symptoms. Elasticity and echogenicity of the carotid plaque was assessed by Young's modulus and Gray-Weale classification, respectively. A total of 271 carotid plaques were assessed through duplex ultrasonic examination and SWE imaging. The Bland-Altman test revealed a perfect reproducibility of Young's modulus measurement using SWE. The interframe coefficient of variation was 16% within the 271 plaques. In the 61 representative plaques, significant correlations were found between Gray-Weale classification and mean Young's modulus (r = 0.728, P < .01) when the confounding factors were controlled. The mean Young's modulus of representative plaques in symptomatic group was lower than those in asymptomatic groups (mean Young's modulus: 81 kPa versus 115 kPa; P < .01). Logistic regression combined with receiver operating characteristic analysis suggested increased sensitivity and specificity for the identification of symptomatic carotid plaques when the mean Young's modulus was combined with stenosis rate. Shear wave elastography can evaluate the Young's modulus of carotid plaque stably, and could serve as an additional method for the detection of symptomatic carotid plaques, which, in combination with common ultrasound, can promote the efficiency of differentiating symptomatic carotid plaques.

Building an open-source simulation platform of acoustic radiation force-based breast elastography

Ultrasound-based elastography including strain elastography, acoustic radiation force impulse (ARFI) imaging, point shear wave elastography and supersonic shear imaging (SSI) have been used to differentiate breast tumors among other clinical applications. The objective of this study is to extend a previously published virtual simulation platform built for ultrasound quasi-static breast elastography toward acoustic radiation force-based breast elastography. Consequently, the extended virtual breast elastography simulation platform can be used to validate image pixels with known underlying soft tissue properties (i.e. ‘ground truth’) in complex, heterogeneous media, enhancing confidence in elastographic image interpretations.The proposed virtual breast elastography system inherited four key components from the previously published virtual simulation platform: an ultrasound simulator (Field II), a mesh generator (Tetgen), a finite element solver (FEBio) and a visualization and data processing package (VTK). Using a simple message passing mechanism, functionalities have now been extended to acoustic radiation force-based elastography simulations.Examples involving three different numerical breast models with increasing complexity—one uniform model, one simple inclusion model and one virtual complex breast model derived from magnetic resonance imaging data, were used to demonstrate capabilities of this extended virtual platform. Overall, simulation results were compared with the published results. In the uniform model, the estimated shear wave speed (SWS) values were within 4% compared to the predetermined SWS values. In the simple inclusion and the complex breast models, SWS values of all hard inclusions in soft backgrounds were slightly underestimated, similar to what has been reported. The elastic contrast values and visual observation show that ARFI images have higher spatial resolution, while SSI images can provide higher inclusion-to-background contrast.In summary, our initial results were consistent with our expectations and what have been reported in the literature. The proposed (open-source) simulation platform can serve as a single gateway to perform many elastographic simulations in a transparent manner, thereby promoting collaborative developments.

Shear wave elastography imaging for detecting malignant lesions of the liver: a systematic review and pooled meta-analysis

To investigate the clinical utility of shear wave elastography (SWE) imaging in the identification of malignant andbenign lesions of the liver lesions by conducting a meta-analysis. The Cochrane library, Embase andPubmed were searched for relevant studies with publication data through February 2016. Studies evaluating the diagnosticaccuracy of SWE in the identification of malignant and benign lesions of the liver using SWE technology were selected. Thecytology, histology or clinical imaging was used as the reference standard. The pooled sensitivity, specificity, diagnostic oddsratio, likelihood ratio, and the area under hierarchical summary receiver operating characteristic curve (HSROC) were used toexamine the diagnostic accuracy. A total of 9 cohort studies involving 1046 liver lesions (malignant 679) from 968patients were identified. All of the 9 studies were prospective studies. The pooled sensitivity, specificity, positive likelihoodratio, negative likelihood ratio, and diagnostic odds ratio of SWE in differentiating malignant and benign liver lesions were82.2% (95% CI: 73.4-88.5), 80.2% (95% CI: 73.3-85.7), 4.159 (95% CI: 2.899-5.966), 0.222 (95% CI: 0.140-0.352), and18.749 (95% CI: 8.746-40.195), respectively. The area under the HSROC curve was 87% (95% CI: 84-90). This meta-analysis indicates that SWE is useful in evaluating the stiffness of liver lesions and in differentiating between malignantand benign lesions. Due to the high sensitivity, specificity, and diagnostic odds ratio, SWE can be considered as a usefulcomplement to conventional ultrasonography.

Shear wave elastography of the supraspinatus muscle and tendon: Repeatability and preliminary findings

Shear wave elastography (SWE) is a promising tool for estimating musculoskeletal tissue properties, but few studies have rigorously assessed its repeatability and sources of error. The objectives of this study were to assess: (1) the extent to which probe positioning error and human user error influence measurement accuracy, (2) intra-user, inter-user, and day-to-day repeatability, and (3) the extent to which active and passive conditions affect shear wave speed (SWS) repeatability. Probe positioning and human usage errors were assessed by acquiring SWE images from custom ultrasound phantoms. Intra- and inter-user repeatability were assessed by two users acquiring five trials of supraspinatus muscle and tendon SWE images from ten human subjects. To assess day-to-day repeatability, five of the subjects were tested a second time, approximately 24h later. Imaging of the phantoms indicated high inter-user repeatability, with intraclass correlation coefficient (ICC) values of 0.68–0.85, and RMS errors of no more than 4.1%. SWE imaging of the supraspinatus muscle and tendon had high repeatability, with intra- and inter-user ICC values of greater than 0.87 and 0.73, respectively. Day-to-day repeatability demonstrated ICC values greater than 0.33 for passive muscle, 0.48 for passive tendon, 0.65 for active muscle, and 0.94 for active tendon. This study indicates the technique has good to very good intra- and inter-user repeatability, and day-to-day repeatability is appreciably higher when SWE images are acquired under a low level of muscle activation. The findings from this study establish the feasibility and repeatability of SWE for acquiring data longitudinally in human subjects.

How Shear Wave is Generated by Acoustic Radiation Force and Propagates in Kidney

We have experienced frequent failure of shear wave elastography (SWE) on kidney. In our past investigation, the shear wave (SW) arrival was unclear, or could not be distinguished from the background fluctuation in the displacement profile. In this study, we investigated the physical mechanism of this phenomenon in detail. Here we made three hypotheses: (1) Generated SW is obscured because of blood flow, (2) Push-pulse cannot generate SW in kidney, (3) Complicated structure with dense and fine renal vessels interferes with the propagation of SW. We analyzed received IQ data of SWE for three excised swine kidneys, a natural sponge (to mimic porous structure of the kidney), and two healthy volunteers (liver and kidney). The swine kidneys and the sponge were scanned in water. The ultrasound scanner used was LOGIQ E9 (GE Healthcare) with a 3.5 MHz convex probe (C1-6-D). For the volunteer scan, acoustic intensity of the push-pulse was varied between three levels: same level as clinical recommendation, a half of it, and zero (no push). When scanning livers, we included a large portal vein intentionally for comparison. Acquired IQ data (echo signals of a series of tracking pulses) were transferred into a PC and analyzed into the velocity distribution and its change over time after push-pulse insonification. Those changes of velocity distribution were visually inspected, while average velocity and standard deviation were calculated over time inside the area of push-pulse insonification. For the swine kidney, SWE images were sufficiently homogeneous. IQ data analysis revealed an evident propagation of SW. For the volunteer, typical velocity peak was observed in liver and kidney. Amplitudes of SW were sufficient compared to the background fluctuation by blood flow, and this fluctuation was larger in kidney than in liver. At the same time, however, kidney contained many pixels which indicate irregular velocity profiles. In those pixels, background velocity fluctuation was large, and therefore a typical pattern of shear wave arrival was not recognized. Such signals were also observed in a large portal vein. In addition, the shape of generated SW was different between the two organs, especially in one of the two volunteers. The region of excitation (area of deformation induced by push-pulse) was wide and not smooth in kidney. The sponge also presented such a rough velocity distribution, while the average velocity induced by the push-pulse was comparable with that for livers and kidneys. The background fluctuation in velocity profile decreased with higher push-pulse intensity level in both liver and kidney. This implies that the shear wave has an effect of pushing blood flow out from its traveling area. From all the above results, we concluded that all the three hypotheses were reasonable. As for the second hypothesis, based on the sponge experiment results, it is suggested that it is rather inhomogeneous and porous structure than vascularity that affects the appearance of generated shear wave. Considering the result of swine kidney, however, the vascularity is thought to contribute to the characteristic structure of kidney. The question remains why the clear SW generation was observed in one volunteer’s kidney (and why not in the other’s). The difference in speed and pressure of the blood flow might be one of the possible factors.

Evaluation of Liver Ablation Using Two-Dimensional Shear-Wave Elastography in the Rabbit Liver Model

To explore the Shear Wave Elastography (SWE) cut-off value of the radiofrequency (RF) ablations and the optimal scale of SWE to delineate the ablation zone. The Institutional Animal Care and Use Committee approved this study. The livers of 30 healthy rabbits were radio-frequency ablated. Conventional ultrasound, contrast enhanced ultrasound (CEUS) and two-dimensional SWE were performed to depict the ablation zone 1h, 2h, 3h, 1d, 7d and 28d after ablation (six groups, five rabbits for each group). Then the livers were harvested for NADH staining. SWE parameters, elasticity distribution, SWE min of the ablation zone and SWE max of the liver tissue beside the ablation boundary were measured. The Receiver Operating Characteristic Curve was obtained to calculate the SWE cut-off value of the ablation zone. Reset the scale of SWE image according to the cut-off value. The overlap percent between elasticity maturation region of SWE image and non-enhanced region of CEUS image was assessed. Highest SWE value was found in the center and that decreased gradually to the peripheral. Non-enhanced regions in CEUS images overlapped well with the ablative tissue in NADH images in 96% specimens. The SWE cut-off value of ablative tissue was 49 kPa – 50 kPa. The elasticity maturation region in SWE image with scale of 50 kPa well delineated the non-enhanced region of the CEUS image in 88% specimens. There was regular elasticity distribution in the ablation area. The SWE cut-off value of ablative tissue is 49 kPa – 50 kPa. The optimal scale for SWE to delineate the ablation zone is 50 kPa.