Wave Speed Measurements Research Articles

Continuous Shear Wave Elastography: A New Method to Measure Viscoelastic Properties of Tendons in Vivo

Viscoelastic mechanical properties are frequently altered after tendon injuries and during recovery. Therefore, non-invasive measurements of shear viscoelastic properties may help evaluate tendon recovery and compare the effectiveness of different therapies. The objectives of this study were to describe an elastography method for measuring localized viscoelastic properties of tendons and to discuss the initial results in healthy and injured human Achilles and semitendinosus tendons. The technique used an external actuator to generate the shear waves in the tendon at different frequencies and plane wave imaging to measure shear wave displacements. For each of the excitation frequencies, maps of direction-specific wave speeds were calculated using local frequency estimation. Maps of viscoelastic properties were obtained using a pixel-wise curve fit of wave speed and frequency. The method was validated by comparing measurements of wave speed in agarose gels with those obtained using magnetic resonance elastography. Measurements in human healthy Achilles tendons revealed a pronounced increase in wave speed as a function of frequency, which highlights the importance of tendon viscoelasticity. Additionally, the viscoelastic properties of the Achilles tendon were larger than those reported for other tissues. Measurements in a tendinopathic Achilles tendon indicated that it is feasible to quantify local viscoelastic properties. Similarly, measurement in the semitendinosus tendon revealed substantial differences in viscoelastic properties between the healthy and contralateral tendons. Consequently, this technique has the potential to evaluate localized changes in tendon viscoelastic properties caused by injury and during recovery in a clinical setting.

Laboratory study on the mechanical behaviors of an anisotropic shale rock

Shale gas is becoming an important energy source worldwide. The geomechanical properties of shale rocks can have a major impact on the efficiency of shale gas exploration. This paper studied the mineralogical and mechanical characteristics of a typical gas shale in Ohio, USA. Scanning electron microscope (SEM) with energy dispersive X-ray (EDX) analyses was employed to measure the microstructure and material composition of the shale rock. The anisotropic behaviors of shale rock, including compressive and tensile strengths, were experimentally measured. The characteristics of shale rock were also studied by nondestructive wave speed measurements. The shale demonstrated strong anisotropic behaviors with the tensile strengths perpendicular to the bedding plane around 300–360 times of that parallel to bedding plane. Results of ultrasonic tests indicated that both compression and shear wave velocities show strong anisotropic patterns. The compression wave speed was the smallest in the direction perpendicular to the bedding plane; while the shear wave speed was the smallest in the direction parallel to the bedding plane. The ratio of wave speed anisotropy is around 1.3–1.4 for compression wave; the ratio of shear wave speed anisotropy is larger and more diverse compared with the compression wave anisotropy. This might be related to the larger variability in the frictional adhesive strength along bedding plane than the compressive adhesive strength.

Compressive evaluation of homogeneous and graded epoxy-glass particulate composites.

The propagation of stress waves in epoxy-glass particulate composites and graded materials was studied experimentally. Materials tested in this study consisted of an epoxy matrix with various concentrations of spherical glass particles having a mean diameter of 42μm. Plate impact experiments were performed using a gas gun. Embedded within the specimens were manganin stress gauges used to record propagating compressive longitudinal stress waves through the material. High strain rate experiments using a Split Hopkinson Pressure Bar (SHPB) apparatus were also performed to evaluate the dynamic strength of the specimens, while quasi-static compression tests were undertaken to characterize their quasi-static behavior. Ultrasonic wave speed measurements were carried-out in order to obtain additional material properties and characterize the gradation in functionally graded materials (FGM). It was found that low volume fractions of particles are detrimental to the performance of the material under impact loading, while concentrations in the range of about 30 to 45% by volume exhibit characteristics of higher degrees of scattering. This suggests that materials in this latter range would be more effective in the thwarting of destructive shock waves than the homogeneous matrix material. Impact testing of FGM specimens suggests that impact loading on the stiff (high volume fraction) face results in much higher levels of scattering. Therefore, such materials would be effective for use in light weight armor or as shielding materials due to their effective attenuation of mechanical impulses.

Wave Profile for Anti-force Waves with Maximum Possible Currents

In the theoretical investigation of the electrical breakdown of a gas, we apply a one-dimensional, steady state, constant velocity, three component fluid model and consider the electrons to be the main element in propagation of the wave. The electron gas temperature, and therefore the electron gas partial pressure, is considered to be large enough to provide the driving force. The wave is considered to have a shock front, followed by a thin dynamical transition region. Our set of electron fluid-dynamical equations consists of the equations of conservation of mass, momentum, and energy, plus the Poisson's equation. The set of equations is referred to as the electron fluid dynamical equations; and a successful solution therefor must meet a set of acceptable physical conditions at the trailing edge of the wave. For breakdown waves with a significant current behind the shock front, modifications must be made to the set of electron fluid dynamical equations, as well as the shock condition on electron temperature. Considering existence of current behind the shock front, we have derived the shock condition on electron temperature, and for a set of experimentally measured wave speeds, we have been able to find maximum current values for which solutions to our set of electron velocity, electron temperature, and electron number density within the dynamical transition region of the wave.

Wave intensity analysis in air-filled flexible vessels

Wave intensity analysis (WIA) is an analytical technique generally used to investigate the propagation of waves in the cardiovascular system. Despite its increasing usage in the cardiovascular system, to our knowledge WIA has never been applied to the respiratory system. Given the analogies between arteries and airways (i.e. fluid flow in flexible vessels), the aim of this work is to test the applicability of WIA with gas flow instead of liquid flow. The models employed in this study are similar to earlier studies used for arterial investigations. Simultaneous pressure (P) and velocity (U) measurements were initially made in a single tube and then in several flexible tubes connected in series. Wave speed was calculated using the foot-to-foot method (cf), which was used to separate analytically the measured P and U waveforms into their forward and backward components. Further, the data were used to calculate wave intensity, which was also separated into its forward and backward components. Although the measured wave speed was relatively high, the results showed that the onsets and the nature of reflections (compression/expansion) derived with WIA, corresponded well to those anticipated using the theory of waves in liquid-filled elastic tubes. On average the difference between the experimental and theoretical arrival time of reflection was 6.1% and 3.6% for the single vessel and multivessel experiment, respectively. The results suggest that WIA can provide relatively accurate information on reflections in air-filled flexible tubes, warranting further studies to explore the full potential of this technique in the respiratory system.

Laboratory P- and S-wave measurements of a reconstituted muddy sediment with comparison to card-house theory.

Laboratory measurements of acoustic wave propagation in a reconstituted kaolinite-based mud were performed. Pairs of ultrasonic transducers and bender elements were immersed in the sediment to transmit and receive compressional and shear waves, respectively. Estimates of wave speeds and attenuations were acquired by analyzing waveforms recorded at several transmitter/receiver separation distances. Measured wave speeds were in good agreement with predicted values from the Mallock-Wood equation for compressional wave speed and card-house theory for shear wave speed. To the knowledge of the authors, no comparison exists between shear wave speeds measured in a controlled laboratory setting and the card-house theory. Power law fits were obtained from the attenuation data to determine the frequency dependence, with f(0.73) for compressional waves in the 60 to 110 kHz range and f(1.46) for shear waves in the 100 to 400 Hz range.

Ultrasound shear wave elastography helps discriminate low-grade from high-grade bowel wall fibrosis in ex vivo human intestinal specimens.

To determine whether bowel wall fibrosis can be detected in freshly resected human intestinal specimens based on ultrasound-derived shear wave speed. Seventeen intact (>3-cm) bowel segments (15 small and 2 large intestine) from 12 patients with known or suspected inflammatory bowel disease were procured immediately after surgical resection. Ultrasound shear wave elastography of the bowel wall was performed by two methods (Virtual Touch Quantification [VTQ] and Virtual Touch-IQ [VT-IQ]; Siemens Medical Solutions USA, Inc, Mountain View, CA). Eighteen short-axis shear wave speed measurements were acquired from each specimen: 3 from the 9-, 12-, and 3-o'clock locations for each method. Imaging was performed in two areas for specimens greater than 10 cm in length (separated by ≥5 cm). A gastrointestinal pathologist scored correlative histologic slides for inflammation and fibrosis. Differences in mean shear wave speed between bowel segments with low and high inflammation/fibrosis scores were assessed by a Student t test. Receiver operating characteristic curve analysis was performed. High-fibrosis score (n = 11) bowel segments had a significantly greater mean shear wave speed than low-fibrosis score (n = 6) bowel segments (mean ± SD: VTQ, 1.59 ± 0.37 versus 1.18 ± 0.08 m/s; P= .004; VT-IQ, 1.87 ± 0.44 versus 1.50 ± 0.26 m/s; P= .049). There was no significant difference in mean shear wave speed between high-and low-inflammation score bowel segments (P > .05 for both VTQ and VT-IQ). Receiver operating characteristic curves showed areas under the curve of 0.91 (95% confidence interval, 0.67-0.99) for VTQ and 0.77 (95% confidence interval, 0.51-0.94) for VT-IQ in distinguishing low-from high-fibrosis score bowel segments. Ex vivo bowel wall shear wave speed measurements increase when transmural intestinal fibrosis is present.

Kidney shear wave speed values in subjects with and without renal pathology and inter-operator reproducibility of acoustic radiation force impulse elastography (ARFI)--preliminary results.

Aimto assess the inter-operator reproducibility of kidney shear wave speed, evaluated by means of Acoustic Radiation Force Impulse (ARFI) elastography, and the factors which influence it.MethodsOur prospective pilot study included 107 subjects with or without kidney pathology in which kidney shear wave speed was evaluated by means of ARFI elastography. Intraclass correlation coefficient (ICC) was used to assess ARFI elastography reproducibility.ResultsA strong agreement was obtained between kidney shear wave speed measurements obtained by the two operators: ICC = 0.71 (right kidney) and 0.69 (left kidney). Smaller ICCs were obtained in “healthy subjects”, as compared to patients with kidney diseases (0.68 vs. 0.75), in women as compared with men (0.59 vs. 0.78), in subjects younger than 50 years as compared with those aged at least 50 years (0.63 vs. 0.71), in obese as compared with normal weight and overweight subjects (0.36 vs. 0.66 and 0.78) and in case of measurements depth <4 cm or >6 cm as compared with those performed at a depth of 4–6 cm from the skin (0.32 and 0.60 vs. 0.81).ConclusionARFI elastography is a reproducible method for kidney shear wave speed assessment.

Characterization of the nonlinear elastic properties of soft tissues using the supersonic shear imaging (SSI) technique: inverse method, ex vivo and in vivo experiments.

Dynamic elastography has become a new clinical tool in recent years to characterize the elastic properties of soft tissues in vivo, which are important for the disease diagnosis, e.g., the detection of breast and thyroid cancer and liver fibrosis. This paper investigates the supersonic shear imaging (SSI) method commercialized in recent years with the purpose to determine the nonlinear elastic properties based on this promising technique. Particularly, we explore the propagation of the shear wave induced by the acoustic radiation force in a stressed hyperelastic soft tissue described via the Demiray-Fung model. Based on the elastodynamics theory, an analytical solution correlating the wave speed with the hyperelastic parameters of soft tissues is first derived. Then an inverse approach is established to determine the hyperelastic parameters of biological soft tissues based on the measured wave speeds at different stretch ratios. The property of the inverse method, e.g., the existence, uniqueness and stability of the solution, has been investigated. Numerical experiments based on finite element simulations and the experiments conducted on the phantom and pig livers have been employed to validate the new method. Experiments performed on the human breast tissue and human heel fat pads have demonstrated the capability of the proposed method for measuring the in vivo nonlinear elastic properties of soft tissues. Generalization of the inverse analysis to other material models and the implication of the results reported here for clinical diagnosis have been discussed.

Superficial ultrasound shear wave speed measurements in soft and hard elasticity phantoms: repeatability and reproducibility using two ultrasound systems.

There is a paucity of data available regarding the repeatability and reproducibility of superficial shear wave speed (SWS) measurements at imaging depths relevant to the pediatric population. To assess the repeatability and reproducibility of superficial shear wave speed measurements acquired from elasticity phantoms at varying imaging depths using three imaging methods, two US systems and multiple operators. Soft and hard elasticity phantoms manufactured by Computerized Imaging Reference Systems Inc. (Norfolk, VA) were utilized for our investigation. Institution No. 1 used an Acuson S3000 US system (Siemens Medical Solutions USA, Malvern, PA) and three shear wave imaging method/transducer combinations, while institution No. 2 used an Aixplorer US system (SuperSonic Imagine, Bothell, WA) and two different transducers. Ten stiffness measurements were acquired from each phantom at three depths (1.0cm, 2.5cm and 4.0cm) by four operators at each institution. Student's t-test was used to compare SWS measurements between imaging techniques, while SWS measurement agreement was assessed with two-way random effects single-measure intra-class correlation coefficients (ICCs) and coefficients of variation. Mixed model regression analysis determined the effect of predictor variables on SWS measurements. For the soft phantom, the average of mean SWS measurements across the various imaging methods and depths was 0.84 ± 0.04m/s (mean ± standard deviation) for the Acuson S3000 system and 0.90 ± 0.02m/s for the Aixplorer system (P = 0.003). For the hard phantom, the average of mean SWS measurements across the various imaging methods and depths was 2.14 ± 0.08m/s for the Acuson S3000 system and 2.07 ± 0.03m/s Aixplorer system (P > 0.05). The coefficients of variation were low (0.5-6.8%), and interoperator agreement was near-perfect (ICCs ≥ 0.99). Shear wave imaging method and imaging depth significantly affected measured SWS (P < 0.0001). Superficial shear wave speed measurements in elasticity phantoms demonstrate minimal variability across imaging method/transducer combinations, imaging depths and operators. The exact clinical significance of this variation is uncertain and may change according to organ and specific disease state.

Shear wave elastography helps differentiate biliary atresia from other neonatal/infantile liver diseases.

Biliary atresia is a rapidly progressive liver disease necessitating prompt diagnosis and surgical intervention, so it must be promptly distinguished from other neonatal/infantile liver diseases. To determine whether US shear wave elastography (SWE) can differentiate biliary atresia from other neonatal/infantile liver diseases based on liver hardness. Eleven children younger than 1 year who had suspected liver disease underwent anatomically and temporally-related hepatic shear wave elastography and clinically indicated percutaneous core needle biopsy. Shear wave elastography was performed immediately prior to liver biopsy at the targeted biopsy site using an Acuson S3000 US system/9L4 transducer (Siemens Medical Solutions USA, Malvern, PA). Shear wave elastography was performed using Virtual Touch Quantification (VTQ) and Virtual Touch IQ (VTIQ) modes, and six shear wave speed measurements were acquired from each subject for each mode. Children were placed in two groups based on histology, biliary atresia (n = 6) vs. non-biliary atresia (other neonatal/infantile liver diseases) (n = 5), and mean shear wave speed measurements were compared using the unpaired student's t-test (two-tailed). A P-value <0.05 was considered significant. Using the VTQ mode, mean liver shear wave speed was 2.08 ± 0.17 m/s for the biliary atresia group and 1.28 ± 0.13 m/s for the non-biliary atresia group (P < 0.0001). Using the VTIQ mode, mean liver shear wave speed was 3.14 ± 0.73 m/s for the biliary atresia group and 1.61 ± 0.23 m/s for the non-biliary atresia group (P = 0.003). Ishak liver fibrosis scores ranged from 3 to 6 for the biliary atresia group and from 0 to 1 for the non-biliary atresia group. Liver shear wave speed is abnormally increased in neonates and infants with biliary atresia.

Intervertebral disc characterization by shear wave elastography: An in vitro preliminary study.

Patient-specific numerical simulation of the spine is a useful tool both in clinic and research. While geometrical personalization of the spine is no more an issue, thanks to recent technological advances, non-invasive personalization of soft tissue's mechanical properties remains a challenge. Ultrasound elastography is a relatively recent measurement technique allowing the evaluation of soft tissue's elastic modulus through the measurement of shear wave speed. The aim of this study was to determine the feasibility of elastographic measurements in intervertebral disc. An in vitro approach was chosen to test the hypothesis that shear wave speed can be used to evaluate intervertebral disc mechanical properties and to assess measurement repeatability. In total, 11 oxtail intervertebral discs were tested in compression to determine their stiffness and apparent elastic modulus at rest and at 400 N. Elastographic measurements were performed in these two conditions and compared to these mechanical parameters. The protocol was repeated six times to determine elastographic measurement repeatability. Average shear wave speed over all samples was 5.3 ± 1.0 m/s, with a repeatability of 7% at rest and 4.6% at 400 N; stiffness and apparent elastic modulus were 266.3 ± 70.5 N/mm and 5.4 ± 1.1 MPa at rest, respectively, while at 400 N they were 781.0 ± 153.8 N/mm and 13.2 ± 2.4 MPa, respectively. Correlations were found between elastographic measurements and intervertebral disc mechanical properties; these preliminary results are promising for further in vivo application.

Broadband laboratory measurements of dispersion in thermally cracked and fluid-saturated quartzite and a synthetic analogue

In the field, the seismic waves used for active-source imaging typically contain frequencies from 10 to about 100 Hz, with corresponding wavelengths of tens of meters. This contrasts greatly with the ultrasonic (∼ 1-MHz) wave-speed measurements carried out in the laboratory, with millimeter wavelengths. The purpose of the laboratory measurements is, of course, to provide insight into seismic wave speeds in situ. However, with the presence of a pore fluid, velocity measurements are sensitive to the frequency at which velocity data are collected. A study focuses on such fluid-flow-related dispersion by performing a broadband measurement in the laboratory from millihertz (mHz) to megahertz (MHz) frequencies on a natural quartzite and on a synthetic sintered glass-bead sample. Thermal cracks that have small aspect ratios of about 10−4 to 10−3 were introduced in both samples, which are of low porosities (1% to 2%) even after thermal cracking. A seismic-frequency forced-oscillation method is combined with a high-frequency ultrasonic technique, providing access to a wide frequency range. Under water-saturated conditions, the observed seismic wave speeds display substantial variations between seismic and ultrasonic frequencies in the cracked quartzite. A systematic increase in shear modulus, attributed to the suppression of fluid flow, has been monitored on the cracked glass-bead specimen with both argon and water saturation at ultrasonic frequency.

Laboratory measurements of compressional and shear wave speed and attenuation in muddy sediments

As demonstrated by William M. Carey's field measurements in Dodge Pond, muddy sediments are characterized by a slow compressional wave speed and a low compressional wave attenuation [Carey and Pierce, POMA (5), 7001, 2009]. To gain insight into the measured data, a theoretical treatment of muddy sediments, named the Card House theory [Pierce and Carey, POMA (5), 7002, 2009], was developed. According the theory, isomorphous substitution causes each mud platelet to carry a net negative charge, and the resulting electrical interaction between platelets is responsible for creating a card-house structure. In this work, we examine laboratory measurements of compressional and shear wave properties in mud. Compared to the Dodge Pond measurements, which were affected by the size and distribution of gas bubbles present in the mud, the volume of gas in the laboratory samples was reduced by applying a vacuum. The estimated compressional wave speed is consistent with predicted values for a relatively gas-free mud. The estimated shear wave speed compares favorably with predicted values from the Card House theory. The electrochemical basis of the Card House model and its acoustical implications are also investigated. [Work supported by ARL:UT IR&amp;D.]

High-frequency ultrasonic measurement of vascularization in phantoms and Avastin-treated mice with breast tumors

Tissue vascularization is an important aspect of tissue engineering and oncology. The objective of this study was to determine if direct ultrasonic measurements in the 10–100 MHz range could be used as an in vivo vascularization assay. To simulate vascularization of tissue, phantoms were fabricated from agarose gel inclusions embedded in a gelatin-soluble fiber mixture. Ultrasonic tests were performed using two broadband ultrasonic transducers centered at 50 MHz. Results showed the samples with multiple agarose vasculature structures decreased the ultrasound wavespeed. As the level of vasculature decreased, the wavespeed of the ultrasound increased. Further investigation of vascularization included the in vivo evaluation of grafted breast cancer tumors in mice. The experimental group was composed of mice treated with Avastin, an angiogenesis inhibitor. The heterogeneity of the vasculature in the control tissue resulted in the scattering of the ultrasound, decreasing the wavespeed. Because the treated group contained less vascularized, more homogeneous tissue, the wavespeed was significantly higher. Results from both the phantom and mouse tumor studies revealed that the ultrasound wavespeed was inversely proportional to the level of vasculature. The results indicate that direct ultrasound wavespeed measurements in the 10–100 MHz range can be used to identify vascularization in tissue.

Shear Wave Speed and Dispersion Measurements Using Crawling Wave Chirps

This article demonstrates the measurement of shear wave speed and shear speed dispersion of biomaterials using a chirp signal that launches waves over a range of frequencies. A biomaterial is vibrated by two vibration sources that generate shear waves inside the medium, which is scanned by an ultrasound imaging system. Doppler processing of the acquired signal produces an image of the square of vibration amplitude that shows repetitive constructive and destructive interference patterns called "crawling waves." With a chirp vibration signal, successive Doppler frames are generated from different source frequencies. Collected frames generate a distinctive pattern which is used to calculate the shear speed and shear speed dispersion. A special reciprocal chirp is designed such that the equi-phase lines of a motion slice image are straight lines. Detailed analysis is provided to generate a closed-form solution for calculating the shear wave speed and the dispersion. Also several phantoms and an ex vivo human liver sample are scanned and the estimation results are presented.

Shore-Based Video Observations of Nonlinear Internal Waves across the Inner Shelf *,+

Abstract Shore-based video remote sensing is used to observe and continually monitor nonlinear internal waves propagating across the inner shelf. Month-long measurements of velocity from bottom-mounted acoustic Doppler current profilers and temperature from thermistor chains at the 10- and 20-m isobaths are combined with sea surface imagery from a suite of cameras (Argus) to provide a kinematic description of 11 borelike internal waves as they propagate across the central Oregon inner shelf. The surface expression of these waves, commonly seen by eye as alternating rough and smooth bands, are identified by increased pixel intensity in Argus imagery (average width 39 ± 6 m), caused by the convergence of internal wave-driven surface currents. These features are tracked through time and space using 2-min time exposure images and then compared to wave propagation speed and direction from in situ measurements. Internal waves are refracted by bathymetry, and the measured wave speed (~0.15 m s−1) is higher than predicted by linear theory (&amp;lt;0.1 m s−1). Propagating internal waves are also visible in subsampled Argus pixel time series (hourly collections of 17 min worth of 2-Hz pixel intensity from a subset of locations), thus extending the observational record to times without an in situ presence. Results from this 5-month record show that the preferred sea state for successful video observations occurs for wind speeds of 2–5 m s−1. Continued video measurements and analysis of extensive existing Argus data will allow a statistical estimate of internal wave occurrence at a variety of inner-shelf locations.

Wave speed in human coronary arteries is not influenced by microvascular vasodilation: implications for wave intensity analysis

Wave intensity analysis and wave separation are powerful tools for interrogating coronary, myocardial and microvascular physiology. Wave speed is integral to these calculations and is usually estimated by the single-point technique (SPc), a feasible but as yet unvalidated approach in coronary vessels. We aimed to directly measure wave speed in human coronary arteries and assess the impact of adenosine and nitrate administration. In 14 patients, the transit time Δt between two pressure signals was measured in angiographically normal coronary arteries using a microcatheter equipped with two high-fidelity pressure sensors located Δs=5cm apart. Simultaneously, intracoronary pressure and flow velocity were measured with a dual-sensor wire to derive SPc. Actual wave speed was calculated as DNc=Δs/Δt. Hemodynamic signals were recorded at baseline and during adenosine-induced hyperemia, before and after nitroglycerin administration. The energy of separated wave intensity components was assessed using SPc and DNc. At baseline, DNc equaled SPc (15.9±1.8 vs. 16.6±1.5m/s). Adenosine-induced hyperemia lowered SPc by 40% (p<0.005), while DNc remained unchanged, leading to marked differences in respective separated wave energies. Nitroglycerin did not affect DNc, whereas SPc transiently fell to 12.0±1.2m/s (p<0.02). Human coronary wave speed is reliably estimated by SPc under resting conditions but not during adenosine-induced vasodilation. Since coronary wave speed is unaffected by microvascular dilation, the SPc estimate at rest can serve as surrogate for separating wave intensity signals obtained during hyperemia, thus greatly extending the scope of WIA to study coronary physiology in humans.

Added value of Virtual Touch IQ shear wave elastography in the ultrasound assessment of breast lesions

PurposeTo determine the diagnostic performance of Acoustic Radiation Force Impulse (ARFI) Virtual Touch IQ shear wave elastography in the discrimination of benign and malignant breast lesions. Materials and methodsConventional B-mode and elasticity imaging were used to evaluate 110 breast lesions. Elastographic assessment of breast tissue abnormalities was done using a shear wave based technique, Virtual Touch IQ (VTIQ), implemented on a Siemens Acuson S3000 ultrasound machine. Tissue mechanical properties were interpreted as two-dimensional qualitative and quantitative colour maps displaying relative shear wave velocity. Wave speed measurements in m/s were possible at operator defined regions of interest. The pathologic diagnosis was established on samples obtained by ultrasound guided core biopsy or fine needle aspiration. ResultsBIRADS based B-mode evaluation of the 48 benign and 62 malignant lesions achieved 92% sensitivity and 62.5% specificity. Subsequently performed VTIQ elastography relying on visual interpretation of the colour overlay displaying relative shear wave velocities managed similar standalone diagnostic performance with 92% sensitivity and 64.6% specificity. Lesion and surrounding tissue shear wave speed values were calculated and a significant difference was found between the benign and malignant populations (Mann–Whitney U test, p<0.0001). By selecting a lesion cut-off value of 3.31m/s we achieved 80.4% sensitivity and 73% specificity. Applying this threshold only to BIRADS 4a masses, we reached overall levels of 92% sensitivity and 72.9% specificity. ConclusionVTIQ qualitative and quantitative elastography has the potential to further characterise B-mode detected breast lesions, increasing specificity and reducing the number of unnecessary biopsies.

Hydraulic and acoustic properties of the active Alpine Fault, New Zealand: Laboratory measurements on DFDP-1 drill core

We report on laboratory measurements of permeability and elastic wavespeed for a suite of samples obtained by drilling across the active Alpine Fault on the South Island of New Zealand, as part of the first phase of the Deep Fault Drilling Project (DFDP-1). We find that clay-rich cataclasite and principal slip zone (PSZ) samples exhibit low permeabilities (⩽10−18 m2), and that the permeability of hanging-wall cataclasites increases (from c. 10−18 m2 to 10−15 m2) with distance from the fault. Additionally, the PSZ exhibits a markedly lower P-wave velocity and Young's modulus relative to the wall rocks. Our laboratory data are in good agreement with in situ wireline logging measurements and are consistent with the identification of an alteration zone surrounding the PSZ defined by observations of core samples. The properties of this zone and the low permeability of the PSZ likely govern transient hydrologic processes during earthquake slip, including thermal pressurization and dilatancy strengthening.