Quantitative Assessment of Skin Stiffness Using Ultrasound Shear Wave Elastography in Systemic Sclerosis

This study was aimed at investigating the performance of ultrasound shear wave elastography (US-SWE) in the assessment of skin (the dermis) stiffness in patients with systemic sclerosis (SSc). The thickness and elastic modulus of the skin were measured using US-SWE at 6 sites in 60 SSc patients and 60 healthy volunteers: the bilateral middle fingers and forearms and the anterior chest and abdomen. To evaluate clinical scores, the measurements were also extended to 17 skin sites in 30 patients. The diagnostic performance of US-SWE in the differentiation of SSc from healthy skin was determined by receiver operating characteristic (ROC) curve analysis, and the reliability of the measurement was evaluated with intra- and inter-class correlation coefficients. The results of US-SWE were compared with modified Rodnan skin thickness scores. Our results indicated that (i) the elastic modulus values were significantly higher in SSc patients than in controls, with or without normalization by skin thickness; (ii) receiver operating characteristic analysis revealed normalized US-SWE cutoff values with a very high accuracy for right and left fingers (areas under the curve?=?0.974 and 0.949), followed by left forearm (0.841), anterior abdomen (0.797), right forearm (0.772) and anterior chest (0.726); (iii) the reliability of US-SWE measurements was good for all examined sites with intra-observer correlation coefficients of 0.845–0.996 and inter-observer correlation coefficients of 0.824–0.985; and (iv) total scores of skin involvement determined at 17 sites (modified Rodnan skin thickness scores) correlated with skin stiffness (r?=?0.832) and thickness (r?=?0.736). In conclusion, US-SWE is a quantitative method with high specificity, sensitivity and reliability in the detection of SSc involvement. This non-invasive, real-time and operator-independent imaging technique could be an ideal tool for the assessment of SSc disease.     

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.     

Evaluation of Post-Stroke Spastic Muscle Stiffness Using Shear Wave Ultrasound Elastography

Current clinical evaluations of post-stroke upper limb spasticity are subjective and qualitative. We proposed a quantitative measurement of post-stroke spastic muscle stiffness by using shear-wave ultrasound elastography and tested its reliability. Acoustic radiation force impulse with shear wave velocity (SWV) detection was used to evaluate stiffness of the biceps brachii muscles at 90° and 0° elbow flexion. In 21 control subjects, SWV did not significantly differ between dominant and non-dominant sides at either flexion angle (0°: p = 0.311, 90°: p = 0.436). In 31 patients who had recent stroke, SWV was significantly greater on the paretic side than on the non-paretic side at both 90° (2.23 ± 0.15 m/s vs. 1.88 ± 0.08 m/s, p = 0.036) and 0° (3.28 ± 0.11 m/s vs. 2.93 ± 0.06 m/s, p = 0.002). The physical appearance of arms and forearms of our patients and controls prevented blinding of the rater to paretic or non-paretic side. At 90°, SWV on the paretic side correlated positively with modified Ashworth scale and modified Tardieu scale (spasticity severity) and negatively with Stroke Rehabilitation Assessment of Movement score (motor function impairment). The intra-class correlation coefficients of intra-rater and inter-rater reliability for SWV measurements were classified as excellent. In conclusion, high SWV was associated with high spasticity and poor function of the post-stroke upper limb, suggesting possible use as a reliable quantitative measure for disease progression and treatment follow-up.     

Image Processing Pipeline for Liver Fibrosis Classification Using Ultrasound Shear Wave Elastography

The purpose of this study was to develop an automated method for classifying liver fibrosis stage ≥F2 based on ultrasound shear wave elastography (SWE) and to assess the system's performance in comparison with a reference manual approach. The reference approach consists of manually selecting a region of interest from each of eight or more SWE images, computing the mean tissue stiffness within each of the regions of interest and computing a resulting stiffness value as the median of the means. The 527-subject database consisted of 5526 SWE images and pathologist-scored biopsies, with data collected from a single system at a single site. The automated method integrates three modules that assess SWE image quality, select a region of interest from each SWE measurement and perform machine learning-based, multi-image SWE classification for fibrosis stage ≥F2. Several classification methods were developed and tested using fivefold cross-validation with training, validation and test sets partitioned by subject. Performance metrics were area under receiver operating characteristic curve (AUROC), specificity at 95% sensitivity and number of SWE images required. The final automated method yielded an AUROC of 0.93 (95% confidence interval: 0.90–0.94) versus 0.69 (95% confidence interval: 0.65–0.72) for the reference method, 71% specificity with 95% sensitivity versus 5% and four images per decision versus eight or more. In conclusion, the automated method reported in this study significantly improved the accuracy for ≥F2 classification of SWE measurements as well as reduced the number of measurements needed, which has the potential to reduce clinical workflow.     

Non-invasive Quantitative Assessment of Muscle Force Based on Ultrasonic Shear Wave Elastography

The objective of this study was to investigate the feasibility of using shear wave elastography (SWE) to indirectly measure passive muscle force and to examine the effects of muscle mass and scan angle. We measured the Young's moduli of 24 specimens from six muscles of four swine at different passive muscle loads under different scan angles (0°, 30°, 60° and 90°) using SWE. Highly linear relationships between Young's modulus E and passive muscle force F were found for all 24 muscle specimens at 0^o scan angle with coefficients of determination R² ranging from 0.984 to 0.999. The results indicate that the muscle mass has no significant effect on the muscle E–F relationship, whereas E–F linearity decreases disproportionately with increased scan angle. These findings suggest that SWE, when carefully applied, can provide a highly reliable tool to measure muscle Young's modulus, and could be used to assess the muscle force quantitatively.     

Quantitative Assessment of Healthy Skin Elasticity: Reliability and Feasibility of Shear Wave Elastography

The goal of this study was to investigate the reliability and feasibility of shear wave elastography by assessing the elasticity of the healthy skin of 40 volunteers. Young's moduli for bilateral fingers, forearms, anterior chest (sternum), and anterior abdomen were determined with both transverse and longitudinal sectional measurements. Reliability of measurements was evaluated using intra- and inter-class correlation coefficients with two observers. Our results revealed that the elastic modulus values of the skin between symmetric parts of fingers and forearms did not statistically different. No differences were found between the transverse and longitudinal sections of forearms, anterior chest, and abdomen (p > 0.05), except for middle fingers (p = 0.004). Inter-observer and intra-observer repeatability (inter- and intra-class correlation coefficients) varied from moderate to excellent depending on the skin site (0.62–0.91). In conclusion, shear wave elastography reached a good consistency in measuring healthy skin elasticity. Further studies are needed to provide more information on the factors that influence the reliability of shear wave elastography measurements in both healthy and diseased skin.     

Quantitative Assessment of Skin Stiffness in Localized Scleroderma Using Ultrasound Shear-Wave Elastography

The purpose of this study was to evaluate the usefulness of ultrasound shear-wave elastography (US-SWE) in characterization of localized scleroderma (LS), as well as in the disease staging. A total of 21 patients with 37 LS lesions were enrolled in this study. The pathologic stage (edema, sclerosis or atrophy) of the lesions was characterized by pathologic examination. The skin elastic modulus (E-values including E_mean, E_min, E_max and E_sd) and thickness (h) was evaluated both in LS lesions and site-matched unaffected skin (normal controls) using US-SWE. The relative difference of E-values (E_RD) was calculated between each pair of lesions and its normal control for comparison among different pathologic stages. Of the 37 LS lesions, 2 were in edema, 22 were in sclerosis and 13 were in atrophy. US-SWE results showed a significant increase of skin elastic modulus and thickness in all lesions (p < 0.001 in sclerosis and p < 0.05 in atrophy) compared with the normal controls. The measured skin elastic modulus and thickness were greater in sclerosis than in atrophy. However, once normalized by skin thickness, the atrophic lesions, which were on average thinner, appeared significantly stiffer than those of the sclerosis (normalized E_RD: an increase of 316.3% in atrophy vs. 50.6% in sclerosis compared with the controls, p = 0.007). These findings suggest that US-SWE allows for quantitative evaluation of the skin stiffness of LS lesions in different stages; however, the E-values directly provided by the US-SWE system alone do not distinguish between the stages, and the normalization by skin thickness is necessary. This non-invasive, real-time imaging technique is an ideal tool for assessing and monitoring LS disease severity and progression.     

Assessment of Diastolic Function Using Ultrasound Elastography

Shear wave elasticity imaging (SWEI) is a novel ultrasound elastography technique for assessing tissue stiffness. In this study, we investigate the potential of SWEI for providing diastolic functional assessment. In 11 isolated rabbit hearts, pressure-volume (PV) measurements were recorded simultaneously with SWEI recordings from the left ventricle free wall before and after induction of global ischemia. PV-based end diastolic stiffness increased by 100% after ischemia (p?<0.05), and SWEI stiffness showed an increase of 103% (p?<0.05). The relaxation time constant (τ) before and after ischemia derived from pressure and SWEI curves showed increases of 79% and 76%, respectively (p?<0.05). A linear regression between pressure-derived and SWEI-based (τ) showed a slope of 1.164 with R²?=?0.80, indicating the near equivalence of the two assessments. SWEI can be used to derive (τ) values and myocardial end diastolic stiffness. In global conditions, these measurements are consistent with PV measurements of diastolic function.     

Characterization of Testicular Masses in Adults: Performance of Combined Quantitative Shear Wave Elastography and Conventional Ultrasound

We prospectively evaluated the performance of combined shear wave elastography (SWE) and conventional ultrasound (US) for the characterization of 89 testicular focal masses. Testes were evaluated with B-mode, color Doppler and SWE measurements, locating a region of interest on the normal and pathologic parenchyma. Thirty-seven malignant tumors (MTs), 12 burned out tumors (BOTs), 28 Leydig cell tumors (LCTs), 2 dermoid cysts and other benign lesions were included. MTs?+?BOTs exhibited more microliths and macrocalcifications compared with benign lesions (p < 10^–4). LCTs manifested mostly a dominant peripheral vascularization pattern compared with other lesions. MTs?+?BOTs were stiffer compared with benign lesions (p < 2?×?10^–4) but with a moderate area under the receiver operating characteristic curve (AUROC) of 80%. By focusing on LCTs versus MTs?+?BOTs, diagnostic performance led to an AUROC of 89% for the best stiffness parameter. For combined conventional US and SWE, the diagnostic performance to differentiate all benign lesions versus MTs?+?BOTs and LCTs versus MTs?+?BOTs increased to AUROCs of 93% and 98%, respectively.     

常规超声联合实时剪切波弹性成像定量参数对大网膜结核的诊断价值

目的探讨常规超声与剪切波弹性成像(SWE)定量参数单独及联合应用时对大网膜结核的诊断价值。方法选取于我院在网膜穿刺活检前均行常规超声及SWE检查的80例患者,根据病理结果将其分为结核组(30例)和非结核组(50例),分析常规超声对网膜结核诊断的灵敏度、特异度及准确度;对结核组与非结核组SWE定量参数(Emean、Emin、Emax、SD)进行统计分析并建立ROC曲线评价其诊断效能;分析常规超声联合SWE后对网膜结核的诊断效能。结果常规超声检查诊断网膜结核的灵敏度、特异度及准确度分别为86.67%、82.00%、83.75%;结核组与非结核组杨氏模量值Emean、Emin、Emax、SD差异均有统计学意义(P<0.001),其中Emean诊断效能最大,以29.7kPa为诊断网膜结核的界值时,其灵敏度、特异度及准确度分别为100%、63.83%、82.50%;常规超声联合SWE诊断网膜结核的灵敏度、特异度、准确度分别为96.67%、94.00%、95.00%。结论实时剪切波弹性成像可作为网膜结核穿刺前有效、无创的辅助检查方法,联合常规超声检查后对网膜结核的诊断效能优于两者的独立应用。     

Quantitative Assessment of Arterial Wall Biomechanical Properties Using Shear Wave Imaging

A new ultrasound-based technique is proposed to assess the arterial stiffness: the radiation force of an ultrasonic beam focused on the arterial wall induces a transient shear wave (∼10 ms) whose propagation is tracked by ultrafast imaging. The large and high-frequency content (100 to 1500 Hz) of the induced wave enables studying the wave dispersion, which is shown experimentally in vitro and numerically to be linked to arterial wall stiffness and geometry. The proposed method is applied in vivo. By repeating the acquisition up to 10 times per second (theoretical maximal frame rate is ∼100 Hz), it is possible to assess in vivo the arterial wall elasticity dynamics: shear modulus of a healthy volunteer carotid wall is shown to vary strongly during the cardiac cycle and measured to be 130 ± 15 kPa in systole and 80 ± 10 kPa in diastole. (E-mail: mathieu.couade@gmail.com)     

In vivo Ultrafast Quantitative Ultrasound and Shear Wave Elastography Imaging on Farm-Raised Duck Livers during Force Feeding

Shear wave elastography (speed and dispersion), local attenuation coefficient slope and homodyned-K parametric imaging were used for liver steatosis grading. These ultrasound biomarkers rely on physical interactions between shear and compression waves with tissues at both macroscopic and microscopic scales. These techniques were applied in a context not yet studied with ultrasound imaging, that is, monitoring steatosis of force-fed duck livers from pre-force-fed to foie gras stages. Each estimated feature presented a statistically significant trend along the feeding process (p values <10^–3). However, whereas a monotonic increase in the shear wave speed was observed along the process, most quantitative ultrasound features exhibited an absolute maximum value halfway through the process. As the liver fat fraction in foie gras is much higher than that seen clinically, we hypothesized that a change in the ultrasound scattering regime is encountered for high-fat fractions, and consequently, care has to be taken when applying ultrasound biomarkers to grading of severe states of steatosis.     

超声剪切波弹性成像在脑卒中患者小腿康复评定中的应用

目的 探讨超声剪切波弹性成像对脑卒中下肢运动障碍患者小腿三头肌和跟腱进行康复评定的价值。方法 2018年至2019年,脑卒中后单侧下肢运动障碍住院患者32例,于康复治疗前后,对患者双侧小腿三头肌和跟腱行超声二维测量和剪切波弹性成像检查,记录剪切波速度(SWV)以及跟腱(比目鱼肌肌腱)长度和厚度。结果 治疗前,患侧跟腱和小腿三头肌SWV较健侧增高(t > 2.426, P < 0.05);患侧跟腱长度较健侧显著增加( t = 11.801, P < 0.001);治疗后,患侧小腿三头肌SWV减低( t > 2.447, P < 0.05);患侧跟腱长度显著缩短( t = 8.577, P < 0.001)。 结论 康复治疗可降低脑卒中下肢运动障碍患者小腿三头肌肌张力。超声剪切波弹性成像可用于评价跟腱和小腿三头肌弹性特征,指导脑卒中康复。     

Development of Oil-in-Gelatin Phantoms for Viscoelasticity Measurement in Ultrasound Shear Wave Elastography

Because tissues consist of solid and fluid materials, their mechanical properties should be characterized in terms of both elasticity and viscosity. Although the elastic properties of tissue-mimicking phantoms have been extensively studied and well characterized in commercially available phantoms, their viscous properties have not been fully investigated. In this article, a set of 14 tissue-mimicking phantoms with different concentrations of gelatin and castor oil were fabricated and characterized in terms of acoustic and viscoelastic properties. The results indicate that adding castor oil to gelatin phantoms decreases shear modulus, but increases shear wave dispersion. For 3% gelatin phantoms containing 0%, 10%, 20% and 40% oil, the measured shear moduli are 2.01 ± 0.26, 1.68 ± 0.25, 1.10 ± 0.22 and 0.88 ± 0.17 kPa, and the Voigt-model coupled shear viscosities are 0.60 ± 0.11, 0.89 ± 0.07, 1.05 ± 0.11 and 1.06 ± 0.13 Pa·s, respectively. The results also confirm that increasing the gelatin concentration increases shear modulus. For phantoms containing 3%, 4%, 5%, 6% and 7% gelatin, the measured shear moduli are 2.01 ± 0.26, 3.10 ± 0.34, 4.18 ± 0.84, 8.05 ± 1.00 and 10.24 ± 1.80 kPa at 0% oil and 1.10 ± 0.22, 1.97 ± 0.20, 3.13 ± 0.63, 4.60 ± 0.60 and 8.43 ± 1.39 kPa at 20% oil, respectively. The phantom recipe developed in this study can be used in validating ultrasound shear wave elastography techniques for soft tissues.