Shear Wave Speed Measurements Research Articles

Repeatability and Agreement of Shear Wave Speed Measurements in Phantoms and Human Livers Across 6 Ultrasound 2-Dimensional Shear Wave Elastography Systems.

Ultrasound shear wave elastography (SWE) is an imaging technique that quantifies liver stiffness. However, comparison data across newest ultrasound systems are sparse. The purpose of this study was to assess repeatability and agreement of shear wave speeds (SWSs) across 6 ultrasound 2-dimensional (2D) SWE systems. This cross-sectional, Health Insurance Portability and Accountability Act-compliant study received institutional review board approval. Written informed consent was obtained. Serial 2D SWE examinations were performed with 6 ultrasound systems (Aplio i800, Canon Medical Systems; LOGIQ E10, GE Healthcare; Resona 7, Mindray North America; EPIQ Elite, Philips Healthcare; ACUSON Sequoia, Siemens Medical Solutions; and Aixplorer MACH 30, SuperSonic Imagine) on 4 elastic phantoms (SWS range, 0.82-3.51 m/s) and on livers of 24 adults (healthy volunteers and patients with known liver stiffening). Participants were imaged 2 times per ultrasound system, with 90 to 120 minutes between examinations. Median SWS was calculated from separately acquired SWS measurements per examination (40 phantom measurements and 10 liver measurements per examination). Overall intraclass correlation coefficient (ICC) for intersystem agreement of median SWS across systems was 0.99 (95% confidence interval, 0.96-1.0) in phantoms and 0.66 to 0.69 (95% confidence interval, 0.47-0.84) in humans across systems. Means of median SWS measurements in humans ranged from 1.24 to 1.56 m/s. Average individual subject-level variance (interquartile range/median SWS) across all examinations was 0.07, with an average coefficient of variation of 6.0%. Pairwise ICCs for intersystem agreement in subjects across systems ranged from 0.41 to 0.91; test-retest repeatability in subjects was excellent for all systems, with ICCs ranging from 0.87 to 0.97. There is good to excellent intersystem agreement of measured SWS in elastic phantoms and in vivo livers across 6 ultrasound 2D SWE systems. Test-retest repeatability was excellent for all systems.

Liver Shear Wave Speed and Other Quantitative Ultrasound Measures of Liver Parenchyma: Prospective Evaluation in Healthy Children and Adults.

OBJECTIVE. The purpose of this study was to use 2D ultrasound shear wave elastography (SWE) to define expected ranges for liver shear wave speed and shear wave dispersion in children and adults without a known history of liver disease. The study also sought to define liver attenuation in adults. SUBJECTS AND METHODS. This was an institutional review board-approved prospective study of 128 children (younger than 18 years old) and 32 adults without liver disease who underwent 2D SWE of the liver with a Canon Aplio i800 ultrasound system (i8CX1 transducer). Ten shear wave speed and shear wave dispersion measurements were obtained. In adults, five attenuation measurements were also obtained. Pearson correlation and t tests were used to define relationships between shear wave speed and dispersion values and predictor variables. Multivariable logistic regression with forward selection was used to generate models. RESULTS. Median age was 5.04 years old for the pediatric participants and 48.92 years old for the adult participants. Mean median shear wave speed and shear wave dispersion were 1.29 ± 0.13 m/s and 11.43 ± 1.75 (m/s)/kHz, respectively, for the pediatric participants and 1.32 ± 0.13 m/s and 10.24 ± 1.65 (m/s)/kHz, respectively, for the adults. Mean median attenuation in adults was 0.52 ± 0.11 dB/cm/MHz. On multivariable modeling, height was the only significant predictor of shear wave speed in children (0.0012 m/s per cm, p < 0.0001) and abdominal wall thickness was the only predictor of shear wave speed in adults (0.12 m/s per cm, p = 0.0008). CONCLUSION. Liver shear wave speed and shear wave dispersion data for children and adults without liver disease provides data against which results from patients with liver disease can be compared. Liver shear wave speed increases during childhood associated with increases in height and shear wave speed increases in adulthood with increasing abdominal wall thickness.

Development and characterization of a tissue mimicking psyllium husk gelatin phantom for ultrasound and magnetic resonance imaging

Purpose To develop and characterize a tissue-mimicking phantom that enables the direct comparison of magnetic resonance (MR) and ultrasound (US) imaging techniques useful for monitoring high-intensity focused ultrasound (HIFU) treatments. With no additions, gelatin phantoms produce little if any scattering required for US imaging. This study characterizes the MR and US image characteristics as a function of psyllium husk concentration, which was added to increase US scattering. Methods Gelatin phantoms were constructed with varying concentrations of psyllium husk. The effects of psyllium husk concentration on US B-mode and MR imaging were evaluated at nine different concentrations. T1, T2, and T2* MR maps were acquired. Acoustic properties (attenuation and speed of sound) were measured at frequencies of 0.6, 1.0, 1.8, and 3.0 MHz using a through-transmission technique. Phantom elastic properties were evaluated for both time and temperature dependence. Results Ultrasound image echogenicity increased with increasing psyllium husk concentration while quality of gradient-recalled echo MR images decreased with increasing concentration. For all phantoms, the measured speed of sound ranged between 1567–1569 m/s and the attenuation ranged between 0.42–0.44 dB/(cm·MHz). Measured T1 ranged from 974–1051 ms. The T2 and T2* values ranged from 97–108 ms and 48–88 ms, respectively, with both showing a decreasing trend with increased psyllium husk concentration. Phantom stiffness, measured using US shear-wave speed measurements, increased with age and decreased with increasing temperature. Conclusions The presented dual-use tissue-mimicking phantom is easy to manufacture and can be used to compare and evaluate US-guided and MR-guided HIFU imaging protocols.

Passive elastography: Extracting mechanical properties of soft tissues from natural elastic waves

Clinical devices that give elastography imaging from a shear wave speed measurement within tissues uses controlled sources for elastic wave generation. It can be a mechanical vibrator for transient elastography and magnetic resonance elastography (MRE) or ultrasound radiation pressure for ARFI and shear wave elastography technique. Generally speaking, the main drawback of all these methods is the drop of efficiency for deep regions and obese patient. Delivering robust elastic waves in depth is an issue. We have proposed in the past a solution that avoid the problem of shear wave penetration using active sources. It consists in using natural shear waves that exist everywhere in living tissues. These natural shear wave are created thanks to heart beating, to pulse wave within arteries or to muscle activities. Since a few years now, we have been tracking natural shear waves in different soft tissues of the human body and we have not yet been disappointed. Using uncontrolled shear wave needs a change in the group velocity measurement paradigm. This approach is the so-called noise correlation technique developed in the field of seismology.

Blood viscosity could explain shear wave dispersion in the liver

We recently showed that the observed shear wave dispersion in a soft, porous, water-saturated tissue can be explained by Biot’s theory of poroelasticity. The theory explains the shear wave velocity increase with frequency due to a relative movement between the solid and the viscous fluid. We propose that fluid-solid interaction explains the observed shear wave dispersion in the liver, a naturally saturated organ. The liver is drawn through by a network of blood vessels and exposes a total porosity of about 14% [1]. Blood viscosity changes from patient to patient and depends on different factors such as hydration and fitness. We included the blood viscosity for a 14% porosity liver into the elasticity estimation from shear wave speed measurements for a given shear wave elastography dataset [2]. For 11 out of 50 patients, the fibrosis classification would change if blood viscosity is included. [1] C. Debbaut et al., “Perfusion characteristics of the human hepatic microcirculation based on three-dimensional reconstructions and computational fluid dynamic analysis,” J. Biomech. Eng. 134(1), 011003 (2012). [2] Jang et al., “Hemorheological alteration in patients clinically diagnosed with chronic liver diseases,” J. Korean Med. Sci. 31(12), 1943–1948 (2016).

Prospective Assessment of Ultrasound Shear Wave Elastography for Discriminating Biliary Atresia from other Causes of Neonatal Cholestasis

To prospectively assess the diagnostic performance of ultrasound shear wave elastography (SWE) and hepatobiliary laboratory biomarkers for discriminating biliary atresia from other causes of neonatal cholestasis. Forty-one patients <3months of age with neonatal cholestasis (direct bilirubin >2mg/dL) and possible biliary atresia were prospectively enrolled. Both 2-dimensional (2D) and point ultrasound SWE were performed prior to knowing the final diagnosis. Median 2D (8) and point (10) shear wave speed measurements were calculated for each subject and used for analyses. The Mann-Whitney U test was used to compare shear wave speed and laboratory measurements between patients with and without biliary atresia. Receiver operating characteristic curve analyses and multivariable logistic regression were used to evaluate diagnostic performance. Thirteen subjects (31.7%) were diagnosed with biliary atresia, and 28 subjects (68.3%) were diagnosed with other causes of neonatal cholestasis. Median age at the time of ultrasound SWE was 37days. Median 2D (2.08 vs 1.49m/s, P=.0001) and point (1.95 vs 1.21m/s, P=.0014) ultrasound SWE measurements were significantly different between subjects with and without biliary atresia. Using a cut-off value of >1.84m/s, 2D ultrasound SWE had a sensitivity=92.3%, specificity=78.6%, and area under the receiver operating characteristic curve (AuROC) of 0.89 (P<.0001). Using a cut-off value of >320 (U/L), gamma-glutamyl transferase (GGT) had a sensitivity=100.0%, specificity=77.8%, and AuROC of 0.85 (P<.0001). Multivariable logistic regression demonstrated an AuROC of 0.93 (P<.0001), with 2 significant covariates (2D ultrasound SWE [OR=23.06, P=.01]; GGT [OR=1.003, P=.036]). Ultrasound SWE and GGT can help discriminate biliary atresia from other causes of neonatal cholestasis.

The influence of body temperature on tissue stiffness, blood perfusion, and water diffusion in the mouse brain

While hypothermia of the brain is used to reduce neuronal damage in patients with conditions such as traumatic brain injury or stroke, little is known about how temperature affects the biophysical properties of in vivo brain tissue. Therefore, we measured shear wave speed (SWS), apparent diffusion coefficient (ADC), and cerebral blood flow (CBF) in the mouse brain at different body temperatures to investigate the relationship between temperature and tissue stiffness, water diffusion, and blood perfusion in the living brain. Multifrequency magnetic resonance elastography (MRE), diffusion-weighted imaging (DWI), and arterial spin labeling (ASL) were performed in seven mice while increasing and recording body temperature from hypothermia (28–30 °C) to normothermia (36–38 °C). SWS, ADC, and CBF were analyzed in regions of whole brain, cortex, hippocampus, and diencephalon. Our results show that SWS decreases while ADC and CBF increase from hypothermia to normothermia (whole brain SWS: −6.2%, ADC: +34.0%, CBF: +80.2%; cortex SWS: −10.1%, ADC: +30.9%, CBF: +82.4%; all p > 0.05). We found a significant inverse correlation between SWS and both ADC and CBF in all analyzed regions except diencephalon (whole brain SWS-ADC: r = −0.8, p < 0.005; SWS-CBF: r = −0.84, p < 0.005; cortex SWS-ADC: r = −0.74, p < 0.05; SWS-CBF: r = −0.65, p < 0.05). These results show that in vivo brain stiffness is inversely correlated with temperature, extracellular water mobility, and microvascular blood flow. Regional differences indicate that cortical areas are more markedly affected by hypothermia than central regions such as diencephalon. Temperature should be considered as a confounder in elastographic measurements, especially in preclinical settings. Statement of SignificanceHibernating mammals lower their body temperature and metabolic activity. A hypothermic state can also be induced for medical purposes to reduce the risk of neural damage in patients with neurological disease or injury. However, little is known how physical soft-tissue properties of the in-vivo brain such as water diffusion, blood perfusion or mechanical parameters correlate with each other when temperature changes. Our study demonstrates for the first time that those quantitative imaging markers are tightly linked to changes in body temperature. While water diffusion and blood perfusion are reduced during hypothermia, brain stiffness significantly increases, suggesting that multiparametric quantitative MRI should be used for the noninvasive assessment of brain metabolic activity.

MM-MRE: a new technique to quantify individual muscle forces during isometric tasks of the wrist using MR elastography.

Non-invasive in-vivo measurement of individual muscle force is limited by the infeasibility of placing force sensing elements in series with the musculo-tendon structures. While different methods based either on shear wave elastography or electromyography have been recently proposed to non-invasively estimate individual muscle forces, they can only be used to quantity forces in a limited set of superficial muscles. As such, they are not suitable to study the neuromuscular control of movements that require coordinated action of multiple muscles. In this work, we present multi-muscle magnetic resonance elastography (MM-MRE), a new technique capable of quantifying force for each muscle in the forearm, thus enabling the study of the neuromuscular control of wrist movements. To quantity individual muscle force, MM-MRE integrates measurements of joint torque provided by an MRI-compatible instrumented handle with muscle-specific measurements of shear wave speed obtained via MRE into a forward dynamic muscle force estimator based on a realistic musculoskeletal model of the forearm. A single-subject pilot experiment demonstrates the possibility of obtaining measurements from individual muscles and establishes that MM-MRE has sufficient sensitivity to detect changes in the muscle specific measurement of shear-wave speed following the application of isometric flexion and extension torques with self-selected intensity.

Rational arrangement of measuring shear wave speed in the liver.

BACKGROUNDShear wave speed has been widely applied to quantify a degree of liver fibrosis. However, there is no standardized procedure, which makes it difficult to utilize the speed universally.AIMTo provide procedural standardization of shear wave speed measurement.METHODSPoint shear wave elastography (pSWE) was measured in 781 patients, and two-dimensional shear wave elastography (2dSWE) was measured on the same day in 18 cases. Regions-of-interest were placed at 12 sites, and the median and robust coefficient-of-variation (CVR) were calculated. A residual sum-of-square (Σdi2) was computed for bootstrap values of 1000 iterations in 18 cases with each assumption of 1 to 12 measurements. The proportion of the Σdi2 (%Σdi2) was calculated as the ratio of Σdi2 to pSWE after converting it based on the correlation between pSWE and 2dSWE.RESULTSThe CVR showed a significantly broader distribution in the left lobe (P < 0.0001), and the smallest CVR in the right anterior segment that covered 95% cases was 40.4%. pSWE was significantly higher in the left lobe than in the right lobe (1.63 ± 0.78 m/s vs 1.61 ± 0.78 m/s, P = 0.0004), and the difference between the lobes became further discrete when the subjects were limited to the cases with a CVR less than 40.4% in any segment (1.76 ± 0.80 m/s vs 1.70 ± 0.82 m/s, P < 0.0001). The highest values of the CVR in every 0.1 m/s interval were plotted in convex upward along pSWE and peaked at 1.93 m/s. pSWE and 2dSWE were significantly correlated (P < 0.0001, r = 0.95). In 216000 resamples from 18 cases, the %Σdi2 of 12 sites was 8.0% and gradually increased as the acquisition sites decreased to reach a significant difference with a %Σdi2 of 7 sites (P = 0.027).CONCLUSIONThese data suggest that shear wave speed should be measured at 8 or more sites of spreading in both lobes.

Developing and using fast shear wave elastography to quantify physiologically-relevant tendon forces

Direct quantification of physiologically-relevant tendon forces can be used in a wide range of clinical applications. However, tendon forces have usually been estimated either indirectly by computational models or invasively using force transducers, and direct non-invasive measurement of forces remains a big challenge. The aim of this study was to investigate the feasibility of using Shear Wave Elastography (SWE) for quantifying human tendon forces at physiological levels. An experimental protocol was developed to measure Shear Wave Speed (SWS) and tensile force in a human patellar tendon using SWE and conventional tensile testing to quantify the correlation between SWS and load. The SWE system was customised to allow imaging of fast shear waves expected in human tendons under physiological loading which is outside the normal range of the existing SWE systems. SWS increased from 10.8 m/s to 36.1 m/s with the increasing tensile load from 8 N to 935 N and a strong linear correlation between SWS and load (r = 0.99, p < 0.01) was observed. The findings in this study suggest that SWE can be used as a potential non-invasive method for direct quantification of physiologically-relevant tendon forces, as well as for validating the estimated forces from other methods such as computational models.

Frequency of technical success of two-dimensional ultrasound shear wave elastography in a large pediatric and young adult cohort: a clinical effectiveness study.

There is a paucity of available literature describing the frequency of technical success of liver two-dimensional (2-D) ultrasound (US) shear wave elastography (SWE) in children and young adults. To determine the frequency of technical success of liver 2-D ultrasound (US) SWE in children and young adults based on the interquartile range (IQR)/median of 10 shear wave speed (SWS) measurements. Clinical 2-D US SWE exams performed between February 2016 and March 2018 were retrospectively identified. Patient age and gender, median/mean liver stiffness (10 SWS measurements), IQR/median, abdominal wall thickness, body mass index (BMI) and serum alanine aminotransferase (ALT) were documented. The number of technically inadequate exams was calculated using three methods: 1) IQR/median >0.3, 2) IQR/median >95th percentile for our study population and 3) statistical outlier identification using the Tukey method. The effect of age, gender, median SWS, abdominal wall thickness, BMI, US transducer and ALT on measurement variability (IQR/median) was assessed using multivariable linear regression. During the study period, 573 exams were performed. Mean age was 12.6±7.1years; 274 (47.8%) exams were in male patients. Average median liver stiffness was 1.75±0.47m/s. Based on Methods 1, 2 and 3, 29/573 (5.1%), 28/573 (4.9%, IQR/median cutoff value=0.303) and 30/573 (5.2%) exams were technically inadequate. Predictors of IQR/median included age (P=0.03), abdominal wall thickness (P=0.003), median SWS (P<0.0001) and transducer (P<0.0001). Approximately 95% of liver 2-D US SWE exams are technically successful based on IQR/median in children and young adults.

Ultrasound Elastography to Quantify Liver Disease Severity in Autosomal Recessive Polycystic Kidney Disease

To evaluate the diagnostic accuracy of ultrasound elastography with acoustic radiation force impulse (ARFI) to detect congenital hepatic fibrosis and portal hypertension in children with autosomal recessive polycystic kidney disease (ARPKD). Cross-sectional study of 25 children with ARPKD and 24 healthy controls. Ultrasound ARFI elastography (Acuson S3000, Siemens Medical Solutions USA, Inc, Malvern, Pennsylvania) was performed to measure shear wave speed (SWS) in the right and left liver lobes and the spleen. Liver and spleen SWS were compared in controls vs ARPKD, and ARPKD without vs with portal hypertension. Linear correlations between liver and spleen SWS, spleen length, and platelet counts were analyzed. Receiver operating characteristic analysis was used to evaluate diagnostic accuracy of ultrasound ARFI elastography. Participants with ARPKD had significantly higher median liver and spleen SWS than controls. At a proposed SWS cut-off value of 1.56m/s, the left liver lobe had the highest sensitivity (92%) and specificity (96%) for distinguishing participants with ARPKD from controls (receiver operating characteristic area 0.92; 95% CI 0.82-1.00). Participants with ARPKD with portal hypertension (splenomegaly and low platelet counts) had significantly higher median liver and spleen stiffness than those without portal hypertension. The left liver lobe also had the highest sensitivity and specificity for distinguishing subjects with ARPKD with portal hypertension. Ultrasound ARFI elastography of the liver and spleen, particularly of the left liver lobe, is a usefulnoninvasive biomarker to detect and quantify liver fibrosis and portal hypertension in children with ARPKD.

Measured power law attenuation of shear waves in swine liver

To characterize the attenuation and dispersion behavior of shear waves in excised swine liver samples, the complex shear modulus was measured with a Rheospectris C500 + from 10 Hz to 2000 Hz. The shear wave attenuation and shear wave speed were calculated from the complex modulus measurements. A power law fit was evaluated for the shear wave attenuation, and a power law fit with and without a constant offset was evaluated for the shear wave speed. The power law closely matches the measured shear wave attenuation over most of the frequency range evaluated, although some differences are observed in several of the samples below 400 Hz. The power law without the constant offset closely matches the measured shear wave speed above 200 Hz in all measurements, where the addition of the constant offset achieves a much closer fit in all measurements that contain discrepancies below 200 Hz. The results demonstrate that shear wave attenuation in swine liver follows a power law and that a power law with a constant offset is an effective model for the shear wave speed in swine liver. [Work supported in part by NIH Grants DK092255, EB023051, and EB012079.]

Ultrasound Elastography as a Non-Invasive Method to Monitor Liver Disease in Children with Short Bowel Syndrome: Updated Results

PurposeThe purpose of the study was to determine the accuracy of acoustic radiation force impulse (ARFI) ultrasound elastography in assessing the degree of liver disease in children with short bowel syndrome (SBS). MethodsA prospective observational cohort study of patients with SBS who underwent a liver biopsy and ARFI elastography was performed. Mean shear wave speed (SWS) and stage of fibrosis was evaluated using t-tests. Receiver operating characteristic curves (ROC) were generated and the area under the curves (AUC) estimated in order to assess the accuracy of SWS measurements to discriminate between stages of fibrosis. ResultsThirty-seven paired elastography and biopsy samples from 31 patients were included. The median age was 0.6 years, and 61% were male. There was a significant positive correlation between stage of fibrosis and mean SWS (β=0.16 m/s increase per stage, p=<0.001). ROC analysis revealed that mean SWS had good accuracy for discriminating between mild liver fibrosis (F0-F1) and moderate to severe fibrosis (F2-F4) (AUC=0.80, 95% CI 0.65-0.95). In addition, ROC analysis demonstrated that mean SWS can also accurately discriminate between mild to moderate fibrosis (F0-F2) and more severe fibrosis (F3-F4) (AUC=0.84, 95% CI 0.71-0.96). ConclusionARFI elastography is an accurate, non-invasive method to monitor liver disease in children with SBS. Type of StudyRetrospective Cohort Study Level of EvidenceII

RSNA/QIBA efforts to standardize shear wave speed as a biomarker for liver fibrosis staging

Commercial shear elasticity systems have been available to clinicians for several years for characterizing liver stiffness. The Radiological Society of North America (RSNA) established a Quantitative Imaging Biomarker Alliance (QIBA) committee on Ultrasound Shear Wave Speed to help achieve better consistency between the shear wave speed and elastic modulus values reported by different manufacturer systems. An inter-laboratory study of shear wave speed estimation was conducted at academic, industry and clinical laboratories using commercial ultrasound and magnetic resonance elastography systems in elastic (Phase I) and viscoelastic (Phase II) homogeneous, isotropic tissue-mimicking phantoms. In the elastic phantoms, shear wave speeds from different systems were within ±5% of the grand mean of all system measurements. Different appraisers and replicate measurements at a given site were not sources of significant variability in shear wave speed measurements. In the viscoelastic phantoms, shear wave speeds from different systems were within ±15% of the grand mean of all systems, with the stiffest phantoms at the deepest focal depth (7 cm) having the greatest measurement variance. Magnetic resonance elastography measurements at 140 Hz in the viscoelastic phantoms were consistent to within ±5% of thosemade with the ultrasound shear elasticity systems, while measurements made at 60 Hz had a mean bias of -2.6% relative to ultrasound systems. A method for reporting group shear wave velocities using both displacement and velocity data, along with shear wave phase velocity analysis, has been developed as a common calibration approach for the phantoms. An open-source repository of research scanner shear wave sequences and processing code has been created to allow manufacturers to have a calibration standard to assess compliance with the QIBA US shear wave speed profile and to achieve more consistent results to facilitate more rapid clinical adoption of this technology to evaluate liver fibrosis.

Transvaginal Ultrasound Vibro-elastography for Measuring Uterine Viscoelasticity: A Phantom Study

The purpose of this research was to determine the feasibility of a transvaginal ultrasound vibro-elastography (TUVE) technique for generating and measuring shear wave propagation in the uterus. In TUVE, a 0.1-s harmonic vibration at a low frequency is generated on the abdomen of a subject via a handheld vibrator. A transvaginal ultrasound probe is used to measure the resulting shear wave propagation in the uterus. TUVE was evaluated on a female ultrasound phantom. The shear wave speeds in the region of interest of the uterus of the female ultrasound phantom were measured in the frequency range of 100–300 Hz. The viscoelasticity was analyzed based on the wave speed dispersion with frequency. The measurement of shear wave speed suggests that the uterus of this female ultrasound phantom is much stiffer than the human uterus. This research illustrates the feasibility of TUVE for generating and measuring shear wave propagation in the uterus of a female ultrasound phantom. We will further evaluate TUVE in patients, both normal controls and those with uterine diseases such as adenomyosis.

Thermomechanical model for monotonic and cyclic loading of PEEK

An internal state variable (ISV) model for polyether ether ketone (PEEK) is developed to capture experimental measurements conducted below its glass transition temperature. The model is based on the response of two relaxing components put in parallel, one having a back stress response that softens with plastic flow. This softening allows reproducing both monotonic and cyclic loading, and is possibly associated with detangling, melting of network junctions, and/or change in crystallinity. The resulting model, which is thermodynamic and multidimensional, was used to capture the response of PEEK 450G using thermal expansion (23 °C to 120 °C), heat capacity (−40 °C to 140 °C), monotonic extension and compression (−85 °C to 150 °C; 0.0001 s−1 to 3000 s−1; strains up to 40–80%), equilibrium stress measurements in compression (23 °C to 120 °C; strains up to 60%), and ultrasonic longitudinal and shear wave speed measurements along and transverse to the directions of compression (23 °C to 120 °C; up to 50% plastic compression). The model is compared to the response under monotonic and cyclic shear and internal dissipation is assessed using the equivalent adiabatic temperature rise.

Shear wave elastography of the maternal cervix: A transabdominal technique.

Reduced cervical length as seen on transvaginal ultrasound is a strong indicator of spontaneous preterm birth in the high-risk population. In low-risk women the appropriate method to assess this risk is still debatable. Ultrasound elastography has been used to assess cervical strength. This research aimed to assess the accuracy of shear wave speeds (SWS) obtained deep to echo free fluid-filled structures, and the use of two-dimensional shear wave on the maternal cervix using a transabdominal ultrasound approach. Agreement of SWS measurements obtained through fluid and directly onto an ultrasound phantom was assessed for accuracy. Speed measurements were obtained in the anterior and posterior portions of the internal and external cervical os on 50 gravid participants in the mid-trimester of pregnancy. No difference in SWS was obtained in the phantom with either direct contact or through the saline water-bath (P>0.05). In 50 participants, measurements were obtainable at the external os anterior and posterior in 49 and 38 participants, respectively, and in 47 and 42 participants for internal os anterior and posterior. The mean speed obtained at the external os anterior and posterior was 2.01±0.51 and 2.38±0.47m/s, respectively, and at the internal os anterior and posterior, 2.49±0.50 and 2.58±0.41m/s. Shear wave speed measurements can be obtained in the maternal cervix using a transabdominal approach with a moderately full maternal bladder in most patients, with a larger number of shear wave measurements obtained in the anterior cervix compared to posterior.

Intraoperative Shear Wave Elastography vs. Contrast-Enhanced Ultrasound for the Characterization and Differentiation of Focal LiverLesions to Optimize Liver Tumor Surgery.

Assessment of intraoperative quantitative shear wave elastography (SWE) and contrast-enhanced ultrasound (CEUS) for the characterization of focal liver lesions (FLLs) during liver surgery using postoperative histopathological results as the gold standard. US data of 79 consecutive patients with 98 FLLs who underwent liver surgery between 08/2015 - 06/2017 were prospectively acquired and retrospectively analyzed. Multifrequency linear/T-shaped probes (6 - 9 MHz) were used to store cine loops of at least 5 s and images of B-mode, SWE and CEUS. The first CEUS loop was continuously documented over 1 min. in each case. Quantitative SWE analysis of FLLs was performed by placing 5 regions of interest to measure shear wave speed (m/s) and stiffness (kPa). CEUS was evaluated during the arterial, portal venous and late phase after i. v. bolus injections of 2.4 - 10 ml sulfur hexafluoride microbubbles. Postoperative histopathology after tumor resection or intraoperative biopsy was obtained to confirm findings of SWE and CEUS. Of 98 FLLs in 79 patients (mean age: 58 years sd ± 12y) 88 were malignant and 10 were benign ranging from 0.69 to 15.2 cm in size (mean: 2.8 cm, sd ± 2.25 cm). SWE characterized 73/88 FLLs correctly as malignant and 7/10 as benign using a cut-off value of 2.5 m/s/21.3 kPa (p < 0.0005). The sensitivity was 83 %, specificity 70 %, accuracy 82 %. CEUS could correctly identify 86/88 malignant and 8/10 benign FLLs. The sensitivity was 98 %, specificity 80 %, accuracy 96 %. SWE could correctly identify 2 malignant FLLs which CEUS falsely characterized as benign. Intraoperative CEUS and SWE are excellent tools for the highly accurate visualization, characterization and malignancy assessment of hepatic tumors during liver surgery.

Effects of benthic biology on geoacoustic properties of marine sediments

Infauna dwell in the benthic zone and have the capacity to modify the physical and acoustic properties of the seabed through bioturbation. To investigate such effects, in situ measurements of compressional and shear wave speed and attenuation were conducted in Petit Bois Pass, near the mouth of Mobile Bay, Alabama, USA. The measurement system was deployed at multiple locations within the pass, and acoustic measurements were conducted at depths up to 20 cm into the sediment to scan the portion of the seabed where most infauna live. Additionally, diver cores were collected and analyzed for infauna abundance and geotechnical properties, such as porosity and grain size distribution, for comparison with the acoustic data. While sediment geoacoustic models do not explicitly account for effects of biology, they do allow for parameterization of various physical properties like porosity, grain size, or pore fluid viscosity, all of which can be modified by the presence of biological organisms and bioturbation. Results from the in situ acoustic measurements and core analysis will be compared with such models to determine if any additional insight into the acoustic effects of infauna can be gained. [Work supported by ONR and ARL:UT IR&amp;D.]