Shear Wave Speed Measurements Research Articles

Complex cystic and solid breast lesions: Diagnostic performance of conventional ultrasound, strain imaging and point shear wave speed measurement.

To assess the performance of conventional high frequency ultrasound (US) and US elastography in diagnosis of complex cystic and solid breast lesions. Ninety three lesions in 93 patients underwent conventional US and US elastography, including strain elastography, acoustic radiation force impulse (ARFI) imaging, and point shear wave speed (SWS) measurement. Pathological examination revealed 31 (33.3%) of the 93 lesions were malignant and the remaining 62 (66.7%) were benign. Multivariate analysis showed that elder patient (OR: 25.301), internal vascularity (OR: 4.518), and not circumscribed margin (OR: 3.813) were independent predictors for malignancy, while predominately cystic lesions (OR: 0.178) was a predictor for benign lesions (all p < 0.05). Invalid SWS measurement was occurred in 19 of 31 (61.3%) malignant lesions and 16 of 62 (25.8%) benign lesions, respectively (p < 0.05). The mean SWS value for malignant lesions was significantly lower than that for benign ones, being 1.60±0.63 m/s (range, 0.68-2.70 m/s) versus 2.33±0.77 m/s (range, 0.67-3.97 m/s) (p < 0.05). Areas under the ROC curve (Azs) for Breast Imaging Reporting and Data System (BI-RADS) assessment, strain elasticity score, ARFI imaging and valid point SWS measurement were 0.844, 0.734, 0.763 and 0.778,respectively. US BI-RADS category, strain elastography score, ARFI imaging patterns and point SWS measurement are useful for malignancy prediction of complex cystic and solid breast lesions. The result that SWS for malignant lesions is lower than benign one should be carefully interpreted since invalid SWS measurement is excluded for analysis. The true stiffness of malignant cystic and solid lesions should be further evaluated with a new generation of two-dimensional SWS imaging.

Inter-sonographer reproducibility of quantitative ultrasound outcomes and shear wave speed measured in the right lobe of the liver in adults with known or suspected non-alcoholic fatty liver disease.

To assess inter-sonographer reproducibility of ultrasound attenuation coefficient (AC), backscatter coefficient (BSC) and shear wave speed (SWS) in adults with known/suspected non-alcoholic fatty liver disease (NAFLD). The institutional review board approved this HIPAA-compliant prospective study; informed consent was obtained. Participants with known/suspected NAFLD were recruited and underwent same-day liver examinations with a clinical scanner. Each participant was scanned by two of the six trained sonographers. Each sonographer performed multiple data acquisitions in the right liver lobe using a lateral intercostal approach. A data acquisition was a single operator button press that recorded a B-mode image, radio-frequency data, and the SWS value. AC and BSC were calculated from the radio-frequency data using the reference phantom method. SWS was calculated automatically using product software. Intraclass correlation coefficient (ICC) and within-subject coefficient of variation (wCV) were calculated for applicable metrics. Sixty-one participants were recruited. Inter-sonographer ICC was 0.86 (95% confidence interval: 0.77-0.92) for AC and 0.87 (0.78-0.92) for log-transformed BSC (logBSC = 10log10BSC) using one acquisition per sonographer. ICC was 0.88 (0.80-0.93) for both AC and logBSC averaging 5 acquisitions. ICC for SWS was 0.57 (0.29-0.74) using one acquisition per sonographer, and 0.84 (0.66-0.93) using 10 acquisitions. The wCV was ~7% for AC, and 19-43% for SWS, depending on number of acquisitions. Hepatic AC, BSC and SWS measures on a clinical scanner have good inter-sonographer reproducibility in adults with known or suspected NAFLD. Multiple acquisitions are required for SWS but not AC or BSC to achieve good inter-sonographer reproducibility. • AC, BSC and SWS measurements are reproducible in adults with NAFLD. • Inter-sonographer reproducibility of SWS measurement improves with more acquisitions being averaged. • Multiple acquisitions are required for SWS but not AC or BSC.

Criteria to Determine Reliability of Noninvasive Assessment of Liver Fibrosis With Virtual Touch Quantification

Virtual Touch Quantification (VTQ) evaluates liver fibrosis in patients with chronic liver diseases by measuring shear wave speed in the liver. We aimed to determine the reliability criteria of VTQ examination. We performed a prospective study of 1094 patients with chronic liver disease from November 2009 through October 2016 at Angers University Hospital, and between April 2010 and May 2015 at Bordeaux University Hospital, in France. All patients underwent liver biopsy analysis (reference standard), and VTQ examination was made by experienced operators on the same day, or no more than 3 months before or afterward. Advanced liver fibrosis was defined as fibrosis stage F ≥ 3 according to the scoring system of the Nonalcoholic Steatohepatitis Clinical Research Network, or fibrosis stage F ≥ 2 according to the Metavir scoring system. The diagnostic accuracy of VTQ in detection of advanced fibrosis or cirrhosis was assessed using the area under the receiver operating characteristic (AUROC) and the rate of correctly classified patients. Reliability criteria were defined from the intrinsic characteristics of VTQ examination, which were shown to influence the diagnostic accuracy. VTQ identified patients with advanced fibrosis with an AUROC of 0.773 ± 0.014 and correctly classified 72.0% of patients using a diagnostic cut-off value of 1.37 m/s. VTQ identified patients with cirrhosis with an AUROC value of 0.839 ± 0.014 and correctly classified 78.4% of patients using a cut-off value of 1.87 m/s. The reliability of VTQ decreased with an increasing ratio of interquartile range/median (IQR/M) in patients with intermediate-high VTQ results. We defined 3 reliability categories for VTQ: unreliable (IQR/M ≥0.35 with VTQ result ≥1.37 m/s), reliable (IQR/M ≥0.35 with VTQ result <1.37 m/s or IQR/M 0.15-0.34), and very reliable (IQR/M <0.15). For advanced fibrosis, VTQ correctly classified 57.8% of patients in the unreliable group, 73.7% of patients in the reliable group, and 80.9% of patients in the very reliable group (P < .001); for cirrhosis, these values were 50.0%, 83.4%, and 92.6%, respectively (P < .001). Of the VTQ examinations made, 21.4% were unreliable, 55.0% were reliable, and 23.6% were very reliable. The skin-liver capsule distance was independently associated with an unreliable VTQ examination, which occurred in 52.7% of patients with a distance of 30 mm or more. In a study to determine the reliability of VTQ findings, compared with results from biopsy analysis, we assigned VTQ examinations to 3 categories (unreliable, reliable, and very reliable). VTQ examinations with IQR/M ≥0.35 and ≥1.37 m/s had very low diagnostic accuracy. Our reliability criteria for liver fibrosis assessment with VTQ will help physicians to accurately evaluate the severity of chronic liver diseases and monitor their progression.

Fourier-Domain Shift Matching: A Robust Time-of-Flight Approach for Shear Wave Speed Estimation.

Our primary objective of this work was to design and test a new time-of-flight (TOF) method that allows measurements of shear wave speed (SWS) following impulsive excitation in soft tissues. Particularly, under the assumption of the local plane shear wave, this work named the Fourier-domain shift matching (FDSM) method, estimates SWS by aligning a series of shear waveforms either temporally or spatially using a solution space deduced by characteristic curves of the well-known 1-D wave equation. The proposed SWS estimation method was tested using computer-simulated data, and tissue-mimicking phantom and ex vivo tissue experiments. Its performance was then compared with three other known TOF methods: lateral time-to-peak (TTP) method with robust random sampling consensus (RANSAC) fitting method, Radon sum transformation method, and a modified cross correlation method. Hereafter, these three TOF methods are referred to as the TTP-RANSAC, Radon sum, and X-corr methods, respectively. In addition to an adapted form of the 2-D Fourier transform (2-D FT)-based method in which the (group) SWS was approximated by averaging phase SWS values was considered for comparison. Based on data evaluated, we found that the overall performance of the above-mentioned temporal implementation of the proposed FDSM method was most similar to the established Radon sum method (correlation = 0.99, scale factor = 1.03, and mean difference = 0.07 m/s), and the 2-D FT (correlation = 0.98, scale factor = 1.00, and mean difference = 0.10 m/s) at high signal quality. However, results obtained from the 2-D FT method diverged (correlation = 0.201) from these of the proposed temporal implementation in the presence of diminished signal quality, whereas the agreement between the Radon sum approach and the proposed temporal implementation largely remained the same (correlation = 0.98).

Quantitative assessment of cervical softening during pregnancy in the Rhesus macaque with shear wave elasticity imaging

Abnormal parturition, e.g. pre- or post-term birth, is associated with maternal and neonatal morbidity and increased economic burden. This could potentially be prevented by accurate detection of abnormal softening of the uterine cervix. Shear wave elasticity imaging (SWEI) techniques that quantify tissue softness, such as shear wave speed (SWS) measurement, are promising for evaluation of the cervix. Still, interpretation of results can be complicated by biological variability (i.e. spatial variations of cervix stiffness, parity), as well as by experimental factors (i.e. type of transducer, posture during scanning). Here we investigated the ability of SWEI to detect cervical softening, as well as sources of SWS variability that can affect this task, in the pregnant and nonpregnant Rhesus macaque. Specifically, we evaluated SWS differences when imaging the cervix transabdominally with a typical linear array abdominal transducer, and transrectally with a prototype intracavitary linear array transducer. Linear mixed effects (LME) models were used to model SWS as a function of menstrual cycle day (in nonpregnant animals) and gestational age (in pregnant animals). Other variables included parity, shear wave direction, and cervix side (anterior versus posterior). In the nonpregnant cervix, the LME model indicated that SWS increased by 2% (95% confidence interval 0–3%) per day, starting eight days before menstruation. During pregnancy, SWS significantly decreased at a rate of 6% (95% CI 5–7%) per week (intracavitary approach) and 3% (95% CI 2–4%) per week (transabdominal approach), and interactions between the scanning approach and other fixed effects were also significant. These results suggest that, while absolute SWS values are influenced by factors such as scanning approach and SWEI implementation, these sources of variability do not compromise the sensitivity of SWEI to cervical softening. Our results also highlight the importance of standardizing SWEI approaches to improve their accuracy for cervical assessment.

Acoustic Structure Quantification Versus Point Shear Wave Speed Measurement for the Assessment of Liver Fibrosis in Viral Hepatitis B

This study was conducted to evaluate the value of acoustic structure quantification (ASQ) technology versus that of point shear wave speed measurement (PSWSM) imaging technology for the assessment of liver fibrosis stage. A total of 104 patients with chronic hepatitis B (CHB) and 30 healthy control patients underwent ASQ and PSWSM examinations. Seven quantitative parameters were obtained from ASQ, and a principal component analysis was used to establish the integrative indicators. A quantitative parameter, known as the shear wave speed (SWS, m/s), was obtained from the PSWSM. The METAVIR scores for the assessment of pathologic liver fibrosis were used as a benchmark. Liver fibrosis stages exhibited a good correlation with the integrative indicators and SWS (r = 0.682, p < 0.001; r = 0.651, p < 0.001). The areas under the receiver operating characteristic curves for ASQ and PSWSM were 0.705 and 0.854 for mild liver fibrosis (F ≥ 1, p = 0.045), 0.813 and 0.743 for significant liver fibrosis (F ≥ 2, p = 0.115), 0.839 and 0.857 for severe liver fibrosis (F ≥ 3, p = 0.417) and 0.874 and 0.971 for liver cirrhosis (F = 4, p = 0.016), respectively. In conclusion, both ASQ and PSWSM were promising ultrasonic methods for assessing liver fibrosis in patients with CHB; however, PSWSM was more valuable for identifying mild liver fibrosis (F ≥ 1) and cirrhosis (F = 4) than ASQ, and the combination of PSWSM and ASQ improved the accuracy of diagnosing severe liver fibrosis (F ≥ 3).

Shear Wave Speed of the Lesion in Preoperative Breast Ultrasonography: Association with Disease-free Survival of Patients with Primary Operable Invasive Breast Cancer

We aimed to investigate the relationship between shear wave speed (SWS) of the lesion on preoperative breast ultrasonography (US) and disease-free survival of patients with primary operable invasive breast cancer. This retrospective study was approved by our Institutional Review Board. The requirement for informed consent was waived. A total of 195 consecutive newly diagnosed invasive breast cancer patients (age 33-83 years; mean 54.0 years) with preoperative breast US with SWS measurement of the lesion were identified. They underwent surgery between May 2012 and May 2013. SWS was measured at the center and three marginal zones in the main tumors, and the maximum value was used for analyses. For 35 patients who underwent primary systemic therapy (PST), the maximum SWS before PST was used. Cox proportional hazards modeling was used to identify the relationship between clinical-pathologic factors and disease-free survival. Fourteen recurrences occurred at 6-47 months (mean 22.3 months) after surgery. On multivariate analysis, a positive history of PST (hazard ratio [HR] = 4.93; 95% confidence interval [CI]: 1.66, 14.70; P = .004), adjuvant chemotherapy (HR = 3.67; 95% CI: 1.11, 12.1; P = .033), and higher maximum SWS (HR = 1.55; 95% CI: 1.07, 2.23; P = .020) were associated with poorer disease-free survival. Higher maximum SWS on preoperative US, in addition to a positive history of PST and adjuvant chemotherapy, was significantly associated with poorer disease-free survival of patients with invasive breast cancer.

Finite element analysis of lung ultrasound surface wave elastography

Interstitial lung disease manifested as fibrotic and stiffened lung tissue, resulting in symptoms such as dyspnea and may lead to respiratory failure. We recently developed a lung ultrasound surface wave elastography for evaluating the elastic properties of superficial lung tissue. In this abstract, we present a finite element analysis to investigate the effects of pleural effusion on the shear wave propagation of superficial lung tissue. The muscle, pleural effusion, and lung tissue were simulated by a 2D planar model of an infinite elastic medium with densities for different materials. A nearly incompressible, linear elastic model was used to model muscle, pleural effusion and lung. The model was excited using a line source on the muscle surface. Harmonic excitations were performed at 100, 150 and 200 Hz with duration of 0.1 s. The boundaries of lung and muscle were attached to an infinite. The mesh of muscle, pleural effusion, and lung were constructed using linear quadrilateral elements. The infinite region was meshed by infinite elements (type CINPE4). The dynamic responses of the tissue model to the excitations were solved by the ABAQUS explicit dynamic solver with automatic step size control. Insignificant difference in shear wave speeds of lung tissue at different excitation frequencies was found in both simulations with and without taking into account the pleural effusion, indicating that pleural effusion does not affect the measurements of shear wave speeds in ultrasound elastography.Interstitial lung disease manifested as fibrotic and stiffened lung tissue, resulting in symptoms such as dyspnea and may lead to respiratory failure. We recently developed a lung ultrasound surface wave elastography for evaluating the elastic properties of superficial lung tissue. In this abstract, we present a finite element analysis to investigate the effects of pleural effusion on the shear wave propagation of superficial lung tissue. The muscle, pleural effusion, and lung tissue were simulated by a 2D planar model of an infinite elastic medium with densities for different materials. A nearly incompressible, linear elastic model was used to model muscle, pleural effusion and lung. The model was excited using a line source on the muscle surface. Harmonic excitations were performed at 100, 150 and 200 Hz with duration of 0.1 s. The boundaries of lung and muscle were attached to an infinite. The mesh of muscle, pleural effusion, and lung were constructed using linear quadrilateral elements. The infinite ...

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.

Evaluating the Benefit of Elevated Acoustic Output in Harmonic Motion Estimation in Ultrasonic Shear Wave Elasticity Imaging

Harmonic imaging techniques have been applied in ultrasonic elasticity imaging to obtain higher-quality tissue motion tracking data. However, harmonic tracking can be signal-to-noise ratio and penetration depth limited during clinical imaging, resulting in decreased yield of successful shear wave speed measurements. A logical approach is to increase the source pressure, but the in situ pressures used in diagnostic ultrasound have been subject to a de facto upper limit based on the Food and Drug Administration guideline for the mechanical index (MI <1.9). A recent American Institute of Ultrasound in Medicine report concluded that an in situ MI up to 4.0 could be warranted without concern for increased risk of cavitation in non-fetal tissues without gas bodies if there were a concurrent clinical benefit. This work evaluates the impact of using an elevated MI in harmonic motion tracking for hepatic shear wave elasticity imaging. The studies indicate that high-MI harmonic tracking increased shear wave speed estimation yield by 27% at a focal depth of 5 cm, with larger yield increase in more difficult-to-image patients. High-MI tracking improved harmonic tracking data quality by increasing the signal-to-noise ratio and decreasing jitter in the tissue motion data. We conclude that there is clinical benefit to use of elevated acoustic output in shear wave tracking, particularly in difficult-to-image patients.

Thee-Dimensional Single-Track-Location Shear Wave Elasticity Imaging.

Conventional multiple-track-location shear wave elasticity imaging (MTL-SWEI) is a powerful tool for noninvasively estimating tissue elasticity. The resolution and noise levels of MTL-SWEI systems, however, are limited by ultrasound speckle. Single-track-location SWEI (STL-SWEI) is a novel variant which fixes the position of the tracking beam and modulates the push location to effectively cancel out the effects of speckle-induced bias. We present here a 3-D STL-SWEI system, which provides full suppression of lateral and elevation speckle bias for high-resolution volumetric elasticity imaging, and requires no spatial smoothing to make accurate measurements of shear wave speed. We demonstrate and analyze the system's performance in homogeneous and layered elasticity phantoms.

Influence of Tissue Microstructure on Shear Wave Speed Measurements in Plane Shear Wave Elastography: A Computational Study in Lossless Fibrotic Liver Media.

Shear wave elastography (SWE) has been used to measure viscoelastic properties for characterization of fibrotic livers. In this technique, external mechanical vibrations or acoustic radiation forces are first transmitted to the tissue being imaged to induce shear waves. Ultrasonically measured displacement/velocity is then utilized to obtain elastographic measurements related to shear wave propagation. Using an open-source wave simulator, k-Wave, we conducted a case study of the relationship between plane shear wave measurements and the microstructure of fibrotic liver tissues. Particularly, three different virtual tissue models (i.e., a histology-based model, a statistics-based model, and a simple inclusion model) were used to represent underlying microstructures of fibrotic liver tissues. We found underlying microstructures affected the estimated mean group shear wave speed (SWS) under the plane shear wave assumption by as much as 56%. Also, the elastic shear wave scattering resulted in frequency-dependent attenuation coefficients and introduced changes in the estimated group SWS. Similarly, the slope of group SWS changes with respect to the excitation frequency differed as much as 78% among three models investigated. This new finding may motivate further studies examining how elastic scattering may contribute to frequency-dependent shear wave dispersion and attenuation in biological tissues.

Ultrasound-Based Shear Wave Elastography in the Assessment of Patients with Diabetic Kidney Disease

In previous studies of acoustic radiation force impulse (ARFI) elastography, using Virtual Touch tissue quantification (VTQ) (Siemens Acuson S2000), it was reported that the measurement of renal shear wave speed in patients with chronic kidney disease (CKD) is not influenced exclusively by renal fibrosis. The purpose of the present study was to analyze the role of VTQ in patients with diabetic kidney disease, considered the main cause of CKD. The study group included 164 patients: 80 patients with diabetic kidney disease (DKD) and 84 without renal disease or diabetes mellitus. In each subject in lateral decubitus, five valid VTQ measurements were performed in each kidney and a median value was calculated, the result being expressed in meters/second. The following means of the median values were obtained In DKD patients, the means of the median values were for VTQ right kidney, 2.21 ± 0.71 m/s, and for VTQ left kidney, 2.13 ± 0.72 m/s, whereas in the normal controls statistically significant higher values were obtained: 2.58 ± 0.78 m/s for VTQ right kidney (p = 0.0017) and 2.46 ± 0.81 m/s for VTQ left kidney (p = 0.006). Patients with an estimated glomerular filtration rate (eGFR) >60 mL/min (DKD stages 1 and 2 together with normal controls) had a significantly higher kidney shear wave speed compared with patients with an eGFR <60 mL/min (2.53 m/s vs. 2.09 m/s, p < 0.05). In the DKD group, there was a significant correlation between eGFR and VTQ levels for the right kidney (r = 0.28, p = 0.04). There was no correlation of VTQ values with proteinuria level, stage of diabetic retinopathy or glycated hemoglobin. Our study indicates that shear wave speed values in patients with diabetic kidney disease and eGFRs <60 mL/min are significantly lower compared with those of patients with eGFRs >60 mL/min (either normal controls or diabetic patients with DKD stages 1 and 2), and values decrease with the decrease in eGFR. However, proteinuria, diabetic retinopathy and glycated hemoglobin have no influence on VTQ.

Quality Measurement of Two-dimensional Shear Wave Speed Imaging for Breast Lesions: the Associated Factors and the Impact to Diagnostic Performance

This study aimed to identify the associated factors for quality measurement (QM) of shear wave speed (SWS) imaging and to validate the additional value of QM in the diagnosis of breast lesions. From September 2014 to February 2015, conventional ultrasound and SWS imaging were performed in 338 women with 361 breast lesions. Binary logistic regression was used to identify associated factors for QM. Sensitivity, specificity and the area under receiver operating characteristic (ROC) curve (AUC) among maximum SWS (SWSmax), QM and SWSmax plus QM (SWSmax+QM) were compared to validate additional value of QM. Pathology confirmed 263 (72.9%) benign lesions and 98 (27.1%) malignancies. Maximum depth (Odds ratio [OR]: 1.398) and posterior features (OR: 1.206) were identified as independent associated factors for QM. Compared with SWSmax and QM, the sensitivity of SWSmax+QM increased from 67.3%, 64.3% to 83.7% whereas the specificity decreased from 90.5%, 72.6% to 65.4% (all P < 0.05). SWSmax had the highest AUC in comparison with QM and SWSmax+QM (0.849 vs. 0.685 vs. 0.745; P < 0.05). QM for breast lesions is associated with maximum depth and posterior features. Adding QM to SWSmax is useful for breast cancer screening and SWSmax alone is useful for breast cancer differentiation.

Shear waves in pressurized poroelastic media

Shear wave elastography measures shear wave speed in soft tissues for diagnostic purposes. In Rotemberg et al. [J. Biomech. 46(11), (2013), pp. 1875-1881] and Rotemberg et al. [Phys. Med. Biol. 57(2), (2012), pp. 329-341], shear wave speed measurements were shown to depend on prestrain, but not necessarily prestress, in a perfused canine liver. We model this phenomenon by examining incremental waves in a pressurized poroelastic medium with incompressible phases. For a poroelastic material with strain energy function W, which due to pressurization undergoes a volume expansion of Δ, we find the following general expression for the shear wave speed: c2/c02=(W1(Δ) + W2(Δ) Δ2/3)/Δ2/3 (W1(1) + W2(1)). Here, c0 is the shear wave speed in the unpressurized material, Wj = ∂ W/∂ Ij, and Ij is an invariant of the Cauchy-Green strain tensor. We also find important restrictions on the form of the strain energy function, which are typically not satisfied by strain energy functions commonly assumed for soft tissues.

Magnetoelastic waves in a soft electrically conducting solid in a strong magnetic field

Shear wave motion of a soft, electrically conducting solid in the presence of a strong magnetic field excites eddy currents in the solid. These, in turn, give rise to Lorentz forces that resist the wave motion. We derive a mathematical model for linear elastic wave propagation in a soft electrically conducting solid in the presence of a strong magnetic field. The model reduces to an effective anisotropic dissipation term resembling an anisotropic viscous foundation. We consider the application to magnetic resonance elastography, which uses strong magnetic fields to measure shear wave speed in soft tissues for diagnostic purposes. We find that for typical values of magnetic field, mass density, and electrical conductivity of soft tissues, eddy current dissipation is negligible. For materials with higher conductivity (e.g., metals), the effect can be stronger.

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.

A pilot study of ultrasound elastography as a non-invasive method to monitor liver disease in children with short bowel syndrome

BackgroundOur objective was to evaluate the accuracy of acoustic radiation force impulse (ARFI) elastography in determining extent of liver fibrosis in pediatric patients with short bowel syndrome (SBS). MethodsThis prospective cohort study included pediatric patients with SBS who underwent ultrasound with ARFI measurements of shear wave speed (SWS) and liver biopsy within 30days of each other between 12/2014–9/2015. The mean and median SWS were compared to the stage of fibrosis. Receiver operating characteristic curves (ROC) were also generated to assess the classification accuracy of SWS measurements for mild (F0-F1) versus moderate/severe fibrosis (F2-F4). ResultsTwelve patients were included with median age 1.4years and median weight 11.3kg. The median direct bilirubin level was 0.3mg/dL at the time of biopsy. On liver biopsy, 6 patients had mild fibrosis (F1), 3 had septal fibrosis (F3), and 3 had cirrhosis (F4). The area under the ROC curve for elastography to differentiate moderate/severe liver fibrosis from mild disease was 0.83 (95CI 0.58–1.00) and 0.86 (95CI 0.63–1.00) for the median SWS and mean SWS, respectively. ConclusionsThese early results suggest that ARFI ultrasound elastography may be a reliable non-invasive method to monitor liver fibrosis in pediatric patients with SBS. Type of studyProspective observational cohort. Level of evidence3.

Improved shear wave motion detection using coded excitation for transient elastography

Transient elastography (TE) is well adapted for use in studying liver elasticity. However, because the shear wave motion signal is extracted from the ultrasound signal, the weak ultrasound signal can significantly deteriorate the shear wave motion tracking process and make it challenging to detect the shear wave motion in a severe noise environment, such as within deep tissues and within obese patients. This paper, therefore, investigated the feasibility of implementing coded excitation in TE for shear wave detection, with the hypothesis that coded ultrasound signals can provide robustness to weak ultrasound signals compared with traditional short pulse. The Barker 7, Barker 13, and short pulse were used for detecting the shear wave in the TE application. Two phantom experiments and one in vitro liver experiment were done to explore the performances of the coded excitation in TE measurement. The results show that both coded pulses outperform the short pulse by providing superior shear wave signal-to-noise ratios (SNR), robust shear wave speed measurement, and higher penetration intensity. In conclusion, this study proved the feasibility of applying coded excitation in shear wave detection for TE application. The proposed method has the potential to facilitate robust shear elasticity measurements of tissue.

LIPOPROTEINS, STATIN THERAPY, CAROTID ATHEROSCLEROTIC PLAQUE VULNERABILITY AND STIFFNESS: A STUDY OF NOVEL ULTRASOUND METHODS UTILIZING MICROBUBBLE CONTRAST ENHANCEMENT AND SHEAR WAVE ELASTOGRAPHY

Background: Microbubble contrast-enhanced ultrasound (CEUS) detects intraplaque neovascularization (IPN) associated with plaque vulnerability. Shear wave elastography (SWE) assesses mechanical stiffness of tissues by measuring shear wave speed (SWS): SWS is faster in stiffer tissues. We explored the