Wave Speed Measurements Research Articles

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.

Determination of Mechanical Properties of Battery Films from Acoustic Measurements

Measuring the mechanical properties of lithium-ion battery films, such as thickness and elasticity, is important for predicting and improving homogeneity of the film and performance of the battery. Problems with film heterogeneity could be identified and addressed early on through accurate, non-destructive inspection of the electrode as it is being manufactured. There are several techniques currently used to measure the mechanical characteristics of films, including nanoindentation and laser-induced surface acoustic waves (SAW). However, their use for analyzing battery electrodes is fairly limited. This research investigates the use of acoustic measurements as an alternative means of non-destructive quality control that could be adapted for on-line use. Mechanical properties of thin films, including elastic modulus and thickness, have been determined using SAW [1,2]. Additionally, acoustic time-of-flight measurements have been taken on complete battery cells to find the state of charge [3]. Here we report on our efforts to measure mechanical properties with SAW. A film under tension is excited to produce a wave. This wave is measured at multiple points along the film to determine the speed of the wave. Because wave dispersion is based on properties such as elasticity and density, we can calculate mechanical properties of the film from the wave speed measurements. Preliminary results indicate that acoustic tests can demonstrate observable differences between films with different properties, and that changes in the stiffness of the film (such as what happens during the drying process for battery films) can also be detected as a difference in wave speed.

Experimentation of Premixed Rotating Detonation Engine Using Variable Slot Feed Plenum

A premixed supply of fuel and oxidizer was fed through five concentric feed slots and detonated in a rotating detonation engine, representing the first known successful airbreathing premixed rotating detonation engine. The premixed feed system successfully arrested flashback. An operating map was constructed and compared to a nonpremixed rotating detonation engine. Mixing effects were shown to be important by comparing measured wave speeds to theoretical Chapman–Jouguet detonation velocities, published computational fluid dynamics results, and similar nonpremixed rotating detonation engines. High-speed imagery indicated that the wave speed measurements should account for the circumferential velocity of the gases relative to the detonation and that the Chapman–Jouguet calculation should account for partial mixing with combustion products.

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.

Shock wave interactions with liquid sheets

Shock wave interactions with a liquid sheet are investigated by impacting planar liquid sheets of varying thicknesses with a planar shock wave. A square frame was designed to hold a rectangular liquid sheet, with a thickness of 5 or 10 mm, using plastic membranes and cotton wires to maintain the planar shape and minimize bulge. The flat liquid sheet, consisting of either water or a cornstarch and water mixture, was suspended in the test section of a shock tube. Incident shock waves with Mach numbers of \(M_\mathrm{s} = 1.34\) and 1.46 were considered. A schlieren technique with a high-speed camera was used to visualize the shock wave interaction with the liquid sheets. High-frequency pressure sensors were used to measure wave speed, overpressure, and impulse both upstream and downstream of the liquid sheet. Results showed that no transmitted shock wave could be observed through the liquid sheets, but compression waves induced by the shock-accelerated liquid coalesced into a shock wave farther downstream. A thicker liquid sheet resulted in a lower peak overpressure and impulse, and a cornstarch suspension sheet showed a higher attenuation factor compared to a water sheet.

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.

Effect of spatial discretization of energy on detonation wave propagation

Detonation propagation in the limit of highly spatially discretized energy sources is investigated. The model of this problem begins with a medium consisting of a calorically perfect gas with a prescribed energy release per unit mass. The energy release is collected into sheet-like sources that are embedded in an inert gas that fills the spaces between them. The release of energy in the first sheet results in a planar blast wave that propagates to the next source, which is triggered after a prescribed delay, generating a new blast, and so forth. The resulting wave dynamics as the front passes through hundreds of such sources is computationally simulated by numerically solving the governing one-dimensional Euler equations in the laboratory-fixed reference frame. Two different solvers are used: one with a fixed uniform grid and the other using an unstructured, adaptively refined grid enabling the limit of highly concentrated, spatially discrete sources to be examined. The two different solvers generate consistent results, agreeing within the accuracy of the measured wave speeds. The average wave speed for each simulation is measured once the wave propagation has reached a quasi-periodic solution. The effect of source delay time, source energy density, specific heat ratio and the spatial discreteness of the sources on the wave speed is studied. Sources fixed in the laboratory reference frame versus sources that convect with the flow are compared. Simulations using an Arrhenius-rate-dependent energy release are performed as well. The average wave speed is compared to the ideal Chapman–Jouguet (CJ) speed of the equivalent homogenized media. Velocities in excess of the CJ speed are found as the sources are made increasingly discrete, with the deviation above CJ being as great as 15 %. The deviation above the CJ value increases with decreasing values of specific heat ratio $\unicode[STIX]{x1D6FE}$. The total energy release, delay time and whether the sources remain laboratory-fixed or are convected with the flow do not have a significant influence on the deviation of the average wave speed away from CJ. A simple, ad hoc analytic model is proposed to treat the case of zero delay time (i.e. source energy released at the shock front) that exhibits qualitative agreement with the computational solutions and may explain why the deviation from CJ increases with decreasing $\unicode[STIX]{x1D6FE}$. When the sources are sufficiently spread out so as to make the energy release of the media nearly continuous, the classic CJ solution is obtained for the average wave speed. Such continuous waves can also be shown to have a time-averaged structure consistent with the classical Zel’dovich–von Neumann–Döring (ZND) structure of a detonation. In the limit of highly discrete sources, temporal averaging of the wave structure shows that the effective sonic surface does not correspond to an equilibrium state. The average state of the flow leaving the wave in this case does eventually reach the equilibrium Hugoniot, but only after the effective sonic surface has been crossed. Thus, the super-CJ waves observed in the limit of highly discretized sources can be understood as weak detonations due to the non-equilibrium state at the effective sonic surface. These results have implications for the validity of the CJ criterion as applied to highly unstable detonations in gases and heterogeneous detonations in condensed phase and multiphase media.

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.

Decompression wave speed and crack velocity measurements during S4 test in water pressurized plastic pipes: Part 2. Criteria for onset of rapid crack propagation

The rapid crack propagation behavior in pressurized plastic pipes was investigated to establish the criteria for onset of rapid crack propagation in terms of the relationship between decompression wave speed and crack velocity. The study was performed by using an instrumented S4 test apparatus, the methodology for which is described in Part 1 of this paper. To establish the criteria for the onset of rapid crack propagation in water-filled plastic pipes, PVC pipes of 440 mm outside diameter having dimensional ratios of 14, 18 and 25 were tested following the procedure described in ISO 13477. From the measurements made on decompression wave speed and crack velocity, it was determined that, for rapid crack propagation to occur in the S4 test, two conditions were required. The decompression wave speed, Cw,S4, needs to be lower than the rapid crack velocity, a˙. Also, the crack velocity must be equal to or above the critical crack velocity, a˙crit. That is,Cw,S4≤a˙a˙≥a˙critIt was shown that this critical crack velocity is always greater than the theoretical decompression wave speed in water filled pipes. Until now, the criterion for rapid crack propagation in S4 was understood to only involve the former condition in water pipes. With this and the latter condition proposed, more complete criteria for rapid crack propagation in water filled plastic pipes using the S4 method is now established.

Risk stratification of thyroid nodules with Bethesda category III results on fine-needle aspiration cytology: The additional value of acoustic radiation force impulse elastography.

To assess the value of conventional ultrasound, conventional strain elastography (CSE) and acoustic radiation force impulse (ARFI) elastography in differentiating likelihood of malignancy for Bethesda category III thyroid nodules. 103 thyroid nodules with Bethesda category III results on fine-needle aspiration cytology (FNAC) in 103 patients were included and all were pathologically confirmed after surgery. Conventional ultrasound, CSE and ARFI elastography including ARFI imaging and point shear wave speed (SWS) measurement were performed. Univariate and multivariate analyses were performed to identify the independent factors associated with malignancy. Area under the receiver operating characteristic curve (Az) was calculated to assess the diagnostic performance. Pathologically, 65 nodules were benign and 38 were malignant. Significant differences were found between benign and malignant nodules in ARFI. The cut-off points were ARFI imaging grade ≥ 4, SWS > 2.94 m/s and SWS ratio > 1.09, respectively. ARFI imaging (Az: 0.861) had the highest diagnostic performance to differentiate malignant from benign nodules, following by conventional ultrasound (Az: 0.606 - 0.744), CSE (Az: 0.660) and point SWS measurement (Az: 0.725 - 0.735). Multivariate logistic regression analysis showed that ARFI imaging grade ≥ 4 was the most significant independent predictor. The combination of ARFI imaging with point SWS measurement significantly improved the specificity (100% vs. 80.0%) and positive predictive value (100 % vs. 72.9%) in comparison with ARFI imaging alone. ARFI elastography is a useful tool in differentiating malignant from benign thyroid nodules with Bethesda category III results on FNAC.

Effects of arterial wall models and measurement uncertainties on cardiovascular model predictions

We developed a methodology to assess and compare the prediction quality of cardiovascular models for patient-specific simulations calibrated with uncertainty-hampered measurements. The methodology was applied in a one-dimensional blood flow model to estimate the impact of measurement uncertainty in wall model parameters on the predictions of pressure and flow in an arterial network. We assessed the prediction quality of three wall models that have been widely used in one-dimensional blood flow simulations. A 37-artery network, previously used in one experimental and several simulation studies, was adapted to patient-specific conditions with a set of three clinically measurable inputs: carotid–femoral wave speed, mean arterial pressure and area in the brachial artery. We quantified the uncertainty of the predicted pressure and flow waves in eight locations in the network and assessed the sensitivity of the model prediction with respect to the measurements of wave speed, pressure and cross-sectional area. Furthermore, we developed novel time-averaged sensitivity indices to assess the contribution of model parameters to the uncertainty of time-varying quantities (e.g., pressure and flow). The results from our patient-specific network model demonstrated that our novel indices allowed for a more accurate sensitivity analysis of time-varying quantities compared to conventional Sobol sensitivity indices.

Chemiluminescence imaging of an optically accessible non-premixed rotating detonation engine

The detonations propagating through the annular channel of an optically accessible rotating detonation engine (RDE) operating on hydrogen–air are visualized using OH* chemiluminescence imaging. The images are useful for observing the instantaneous size and shape of the detonation structure, oblique shock wave, and possible presence of deflagration between the fuel-fill zone and expansion region containing detonation products. The detonation increases in height as the air flow rate is increased for low flow rates, experiences subtle changes for intermediate flow rates, and transitions from one to two waves for higher flow rates. The two detonation waves typically propagate in the same azimuthal direction. Counter-rotating waves resulting in detonation–detonation interactions are observed for some configurations with a reduced number of fuel injection jets. Time-dependent static pressure measurements show that acoustic interactions between the detonation channel and air plenum are important for low air flow rates and large air injection areas. The OH* chemiluminescence images, pressure, and wave speed measurements provide benchmark data that are useful for evaluating RDE models and simulations, improving fundamental understanding of the detonation structure in RDEs, and identifying critical design parameters that influence RDE operation and performance.

In situ measurements of sediment acoustic properties in Currituck Sound and comparison to models.

In situ measurements of compressional and shear wave speed and attenuation were collected 30 cm below the water-sediment interface in Currituck Sound, North Carolina at two field locations having distinctly different sediment types: medium-to-fine-grained sand and fine-grained sand with approximately 10% mud content. Shear wave measurements were performed with bimorph transducers to generate and receive horizontally polarized shear waves in the 300 Hz to 1 kHz band, and compressional wave measurements were performed using hydrophones operated in the 5 kHz to 100 kHz band. Sediment samples were collected at both measurement sites and later analyzed in the laboratory to characterize the sediment grain size distribution for each field location. Compressional and shear wave speed and attenuation were estimated from the acoustic measurements, and preliminary comparisons to the extended Biot model by Chotiros and Isakson [J. Acoust. Soc. 135, 3264-3279 (2014)] and the viscous grain-shearing theory by Buckingham [J. Acoust. Soc. 136, 2478-2488 (2014)] were performed.

A study on behavior of steel structures subjected to fire using non-destructive testing

Due to its earthquake resistant properties, most building structures are constructed with reinforced concrete on a steel structure. As the temperature of steel increases especially during a fire, it will reduce the strength of a structure. Since the properties of steel, such as the Young’s modulus and yielding strength, drop rapidly with increasing temperature, during a fire the load capacity of such structures will decline dramatically. However, it is important to evaluate the structural performance of steel frames after a fire for reuse and reconstruction due to the high cost of reconstructive building. This study is concerned with the development of nondestructive testing techniques to investigate the structural behavior of steel subjected to fire. The results of ultrasonic wave speed measurement show that heating up to 1000°C and cooling by water produces a large change in wave speed. Under metallurgical microscope observation, the texture could be seen to have changed into bainite and martensite. In the study, the properties of the structure became hard and brittle due to phase change.

A comparison between direct measurements and inference results from an acoustic propagation experiment in Currituck Sound

An acoustic propagation experiment was conducted in Currituck Sound to characterize low frequency propagation in a very shallow-water environment with water depths of only a few meters. Signals from a Combustive Sound Source (CSS) were recorded on bottom mounted geophones and a vertical array of hydrophones. The CSS produces a broadband signal with significant low frequency energy, and the analysis presented in this paper focuses on frequencies below 2.5 kHz. A statistical inference method was applied to obtain an estimate of the sediment sound-speed profile as a function of depth in the seabed. During the experiment, in situ measurements of compressional and shear wave speed and attenuation were also collected 30 cm below the sediment-water interface. Bimorph bender elements were employed to generate and receive horizontally polarized shear waves in the frequency range from 200 Hz to 1 kHz. Compressional waves were measured using cylindrically shaped piezoelectric elements operated in the 5 kHz to 100 kH...

Measurements of Decompression Wave Speed in Binary Mixtures of Carbon Dioxide and Impurities

Shock tube tests were conducted on a number of binary CO2 mixtures with N2, O2, CH4, H2, CO, and Ar impurities, from a range of initial pressures and temperatures. This paper provides examples of results from these tests. The resulting decompression wave speeds are compared with predictions made utilizing different equations of state (EOS). It was found that, for the most part (except for binaries with H2), the GERG-2008 EOS shows much better performance than the Peng–Robinson (PR) EOS. All binaries showed a very long plateau in the decompression wave speed curves. It was also shown that tangency of the fracture propagation speed curve would normally occur on the pressure plateau, and hence, the accuracy of the calculated arrest toughness for pipelines transporting these binary mixtures is highly dependent on the accuracy of the predicted plateau pressure. Again, for the most part, GERG-2008 predictions of the plateau are in good agreement with the measurements in binary mixtures with N2, O2, and CH4. An example of the determination of pipeline material toughness required to arrest ductile fracture is presented, which shows that prediction by GERG-2008 is generally more conservative and is therefore recommended. However, both GERG-2008 and PR EOS show much worse performance for the other three binaries: CO2 + H2, CO2 + CO, and CO2 + Ar, with CO2 + H2 being the worst. This is likely due to the lack of experimental data for these three binary mixtures that were used in the development of these EOS.

Measurements of Decompression Wave Speed in Simulated Anthropogenic Carbon Dioxide Mixtures Containing Hydrogen

In order to determine the material fracture resistance necessary to provide adequate control of ductile fracture propagation in a pipeline, a knowledge of the decompression wave speed following the quasi-instantaneous formation of an unstable, full-bore rupture is necessary. The thermodynamic and fluid dynamics background of such calculations is understood, but predictions based on specific equations of state (EOS) need to be validated against experimental measurements. A program of tests has been conducted using a specially constructed shock tube to determine the impact of impurities on the decompression wave speed in carbon dioxide (CO2), so that the results can be compared to two existing theoretical models. In this paper, data and analysis results are presented for three shock tube tests involving anthropogenic CO2 mixtures containing hydrogen as the primary impurity. The first mixture was intended to represent a typical scenario of precombustion carbon capture and storage (CCS) technology, where typically the concentration of CO2 is around 95–97% (mole). The second mixture represents a worst case scenario of this technology with high level of impurities (with CO2 concentration around 85%). The third test represents a typical chemical-looping combustion process. It was found that the extent of the plateau on the decompression wave speed curves in these tests depends on the location of the phase boundary crossing along the bubble-point curve. The closer the phase boundary crossing to the critical point, the shorter the plateau. This is primarily due to the change in magnitude of the drop in the speed of sound at phase boundary crossing. For the most part, the predictions of the plateau pressure by both of the EOS that were evaluated, GERG-2008 and Peng–Robinson (PR), are in good agreement with measurements by the shock tube. This by no means reflects overall good performance of either EOS, but was rather due to the fact that the isentropes intersected the phase envelope near the critical point, or that the concentration of H2 was relatively low, either in absolute terms or relative to other impurity constituents. Hence, its influence in causing inaccurate prediction of the plateau pressure is lessened. An example of pipeline material toughness required to arrest ductile fracture is presented which shows that predictions by GERG-2008 are more conservative and are therefore recommended.

Shear wave elastography with a new reliability indicator.

Non-invasive methods for liver stiffness assessment have been introduced over recent years. Of these, two main methods for estimating liver fibrosis using ultrasound elastography have become established in clinical practice: shear wave elastography and quasi-static or strain elastography. Shear waves are waves with a motion perpendicular (lateral) to the direction of the generating force. Shear waves travel relatively slowly (between 1 and 10 m/s). The stiffness of the liver tissue can be assessed based on shear wave velocity (the stiffness increases with the speed). The European Federation of Societies for Ultrasound in Medicine and Biology has published Guidelines and Recommendations that describe these technologies and provide recommendations for their clinical use. Most of the data available to date has been published using the Fibroscan (Echosens, France), point shear wave speed measurement using an acoustic radiation force impulse (Siemens, Germany) and 2D shear wave elastography using the Aixplorer (SuperSonic Imagine, France). More recently, also other manufacturers have introduced shear wave elastography technology into the market. A comparison of data obtained using different techniques for shear wave propagation and velocity measurement is of key interest for future studies, recommendations and guidelines. Here, we present a recently introduced shear wave elastography technology from Hitachi and discuss its reproducibility and comparability to the already established technologies.

Examining the effects of microstructure on geoacoustic parameters in fine-grained sediments

This paper presents a set of controlled laboratory experiments designed to develop a basis for understanding the relationship between microscopic and macroscopic properties of fine-grained sediments. Two samples of kaolinite platelets were selected for this study, and effects of sediment microstructure on geoacoustic properties are deduced from a comparison of the measured properties. To provide additional interpretation of the acoustic measurements, compressional and shear wave properties are compared to predicted values from sediment-acoustic models. First, the shear wave speed was compared to predictions from card-house theory, a model with an electrochemical basis that incorporates the aggregation of clay platelets. The wave speed predicted by card-house theory showed good agreement with the measured wave speeds for the mud sample made up of card-house flocs. Next, viscous grain shearing theory, which treats unconsolidated sediments as a two-phase medium with internal losses arising from grain-to-grain contacts, was applied to predict the frequency dispersion of all four geoacoustic parameters. Overall, good agreement between the measurements and values calculated by viscous grain shearing theory was observed for both samples of mud.

Two-Dimensional Time-Harmonic Elastography of the Human Liver and Spleen

Measurement of shear wave speed of the liver and spleen by elastography is an established diagnostic procedure for the detection of hepatic fibrosis, portal hypertension and esophageal varices. However, current elastography systems are limited by the size and penetration depth of elastographic windows. In this study, 2D time-harmonic elastography is proposed for generating full field-of-view shear wave speed maps in great depth. Two-dimensional time-harmonic elastography uses external harmonic stimulation at multiple frequencies to create compound shear wave speed maps. The method is tested in a phantom with soft and stiff inclusions and used for elastography of the liver and spleen in 13 asymptomatic volunteers. Each volunteer was scanned twice to determine the sensitivity of the method to physiologic variations: first, after 2 h of fasting, and a second time, 15 min after drinking 1 L of water. The wave speed maps of the phantom clearly identified the soft and stiff inclusions, yielding values that were consistent with those from magnetic resonance elastography. In vivo wave speed values were 1.49 ± 0.11 m/s for the liver and 2.03 ± 0.15 m/s for the spleen in a lower-frequency band centered at 40 Hz and 3.15 ± 0.30 m/s for the spleen in a higher-frequency band centered at 120 Hz. After water intake, wave speed values increased by 6% in the liver (p = 0.002) and decreased in the spleen by 4% (p = 0.021, low-frequency band) and 6% (p = 0.0002, high-frequency band), suggesting the high sensitivity of the method to altered blood flow and perfusion pressure. Two-dimensional time-harmonic elastography of the liver and spleen is a promising method for measuring tissue stiffness at different states of blood flow and perfusion in a large tissue window and at great penetration depth.