Mean Sound Speed Research Articles

Seabed Geoacoustic Analysis Using Scientific Single Beam Echosounder

Graphical Abstract Highlight Research Geoacoustic quantification. Sediment identification. Sediment classification. Geoacoustic characteristic. Sediment type spatial distribution in Lancang Island. AbstractHydroacoustic technology was able to quantify the seabed substrate and can be estimated accurately and near real time on the acoustic characters of each substrate. The purpose of the research was to identify the geoacoustic characteristics and spatial mapping of the seabed substrate in Lancang Island. Acoustic data was acquired using a Simrad EK-15 Single Beam Echosounder instrument operating at 200 kHz. Sediment samples were taken using an Ekman grab, which will be used to validate the acoustic data. The results of this study indicated that the acoustic backscatter values of the seabed substrate based on the surface backscattering strength value and sediment particle size at fourteen sampling stations are -28.03 decibels to -20.02 decibels divided into 9 sediment type groups, namely medium and very coarse sand mixture; medium sand; medium, fine and coarse sand mixture; medium and fine sand mixture; fine and medium sand mixture; medium and very fine sand mixture; very fine and medium sand mixture; fine and very fine sand mixture; and fine sand. The accuracy level of k-Nearest Neighbour and Random Forest computational used has very good accuracy of 98.21 % and 96.43 % and Naevi Bayes has a lower accuracy of 58.93 %. The identified geoacoustic characteristics included the mean grain size, sound speed, density, acoustic impedance, and reflection coefficient. Faster, more effective, and efficient computational processes with high accuracy make k-Nearest Neighbour and Random Forest models the best alternative to be used as geoacoustic computational models of seafloor substrates.

Sound speed and attenuation of human pancreas and pancreatic tumors and their influence on focused ultrasound thermal and mechanical therapies.

There is increasing interest in using ultrasound for thermal ablation, histotripsy, and thermal or cavitational enhancement of drug delivery for the treatment of pancreatic cancer. Ultrasonic and thermal modelling conducted as part of the treatment planning process requires acoustic property values for all constituent tissues, but the literature contains no data for the human pancreas. This study presents the first acoustic property measurements of human pancreatic samples and provides examples of how these properties impact a broad range of ultrasound therapies. Data were collected on human pancreatic tissue samples at physiological temperature from 23 consented patients in cooperation with a hospital pathology laboratory. Propagation of ultrasound over the 2.1-4.5MHz frequency range through samples of various thicknesses and pathologies was measured using a set of custom-built ultrasonic calipers, with the data processed to estimate sound speed and attenuation. The results were used in acoustic and thermal simulations to illustrate the impacts on extracorporeal ultrasound therapies for mild hyperthermia, thermal ablation, and histotripsy implemented with a CE-marked clinical system operating at 0.96MHz. The mean sound speed and attenuation coefficient values for human samples were well below the range of values in the literature for non-human pancreata, while the human attenuation power law exponents were substantially higher. The simulated impacts on ultrasound mediated therapies for the pancreas indicated that when using the human data instead of the literature average, there was a 30% reduction in median temperature elevation in the treatment volume for mild hyperthermia and 43% smaller volume within a 60°C contour for thermal ablation, all driven by attenuation. By comparison, impacts on boiling and intrinsic threshold histotripsy were minor, with peak pressures changing by less than 15% (positive) and 1% (negative) as a consequence of the counteracting effects of attenuation and sound speed. This study provides the most complete set of speed of sound and attenuation data available for the human pancreas, and it reiterates the importance of acoustic material properties in the planning and conduct of ultrasound-mediated procedures, particularly thermal therapies.

Generalized acoustic Helmholtz equation and its boundary conditions in a quasi 1-D duct with arbitrary mean properties and mean flow

We derive the generalized Helmholtz equation governing the acoustic pressure field in a quasi one-dimensional duct with axially varying cross-section and arbitrary (axially inhomogeneous) mean properties such as the velocity, temperature, density and pressure. To express the Helmholtz equation exclusively in terms of the fluctuating pressure field pˆ, we developed an expression relating density and pressure fluctuations, which is a differential equation for the generalized case of a duct with arbitrary mean properties. The “classical” algebraic expression for the density fluctuation field, ρˆ=pˆ/c̄2, is strictly valid for a constant cross-section duct with uniform mean properties and uniform or zero mean flow (c̄ is the mean sound speed). We show that using the classical ρˆ–pˆ relation in deriving the Helmholtz equation may lead to significant errors in both the phase and amplitude of the acoustic field pˆ. These errors arise because the Helmholtz equation thus obtained fails to account for the boundary condition on density fluctuations at the duct inlet. Furthermore, a linearly-exact derivative boundary condition to the Helmholtz equation of the form dpˆdx=f(pˆ,uˆ,ρˆ;ω) is developed, where uˆ is the velocity fluctuation field and ω is the angular frequency. The pˆ field obtained by solving the generalized Helmholtz equation in conjunction with the derivative boundary condition shows excellent agreement with that obtained through the solution of the linearized Euler equations.

The Fat-glandular Interface and Breast Tumor Locations: Appearances on Ultrasound Tomography Are Supported by Quantitative Peritumoral Analyses.

To analyze the preferred tissue locations of common breast masses in relation to anatomic quadrants and the fat-glandular interface (FGI) using ultrasound tomography (UST). Ultrasound tomography scanning was performed in 206 consecutive women with 298 mammographically and/or sonographically visible, benign and malignant breast masses following written informed consent to participate in an 8-site multicenter, Institutional Review Board-approved cohort study. Mass locations were categorized by their anatomic breast quadrant and the FGI, which was defined by UST as the high-contrast circumferential junction of fat and fibroglandular tissue on coronal sound speed imaging. Quantitative UST mass comparisons were done for each tumor and peritumoral region using mean sound speed and percentage of fibroglandular tissue. Chi-squared and analysis of variance tests were used to assess differences. Cancers were noted at the FGI in 95% (74/78) compared to 51% (98/194) of fibroadenomas and cysts combined (P < 0.001). No intra-quadrant differences between cancer and benign masses were noted for tumor location by anatomic quadrants (P = 0.66). Quantitative peritumoral sound speed properties showed that cancers were surrounded by lower mean sound speeds (1477 m/s) and percent fibroglandular tissue (47%), compared to fibroadenomas (1496 m/s; 65.3%) and cysts (1518 m/s; 84%) (P < 0.001; P < 0.001, respectively). Breast cancers form adjacent to fat and UST localized the vast majority to the FGI, while cysts were most often completely surrounded by dense tissue. These observations were supported by quantitative peritumoral analyses of sound speed values for fat and fibroglandular tissue.

Dimer rattling mode induced low thermal conductivity in an excellent acoustic conductor

A solid with larger sound speeds usually exhibits higher lattice thermal conductivity. Here, we report an exception that CuP2 has a quite large mean sound speed of 4155 m s−1, comparable to GaAs, but single crystals show very low lattice thermal conductivity of about 4 W m−1 K−1 at room temperature, one order of magnitude smaller than GaAs. To understand such a puzzling thermal transport behavior, we have thoroughly investigated the atomic structures and lattice dynamics by combining neutron scattering techniques with first-principles simulations. This compound crystallizes in a layered structure where Cu atoms forming dimers are sandwiched in between P atomic networks. In this work, we reveal that Cu atomic dimers vibrate as a rattling mode with frequency around 11 meV, which is manifested to be remarkably anharmonic and strongly scatters acoustic phonons to achieve the low lattice thermal conductivity.

Numerical and Asymptotic Solutions of the Pridmore-Brown Equation

A study is made of acoustic duct modes in two-dimensional and axisymmetric three-dimensional lined ducts with an isentropic inviscid transversely nonuniform mean flow and sound speed. These modes are described by a one-dimensional eigenvalue problem consisting of a Pridmore-Brown equation complemented by hard-wall or impedance-wall boundary conditions. A numerical solution, based on a Galerkin projection and an efficient method for the resulting nonlinear eigenvalue problem, is compared with analytical approximations for low and high frequencies. A collection of results is presented and discussed. Modal wave numbers are traced in the complex plane for varying impedance, showing the usual regular modes and surface waves. A study of a vanishing boundary layer (the Ingard limit) showed that, in contrast to the smoothly converging acoustic modes and downstream running acoustic surface wave, the convergence of the other surface waves is numerically more difficult. Effects of (transverse) turning points and exponential decay are discussed. Especially the occurrence of modes insensitive to the wall impedance is pointed out. Cut-on wave numbers of hard-wall modes are presented as a function of frequency. A strongly nonuniform mean flow gives rise to considerable differences between the modal behavior for low and for high frequencies.

A Computationally Efficient Mean Sound Speed Estimation Method Based on an Evaluation of Focusing Quality for Medical Ultrasound Imaging

Generally, ultrasound receive beamformers calculate the focusing time delays of fixed sound speeds in human tissue (e.g., 1540 m/s). However, phase distortions occur due to variations of sound speeds in soft tissues, resulting in degradation of image quality. Thus, an optimal estimation of sound speed is required in order to improve image quality. Implementation of real-time sound speed estimation is challenging due to high computational and hardware complexities. In this paper, an optimal sound speed estimation method with a low-cost hardware resource is presented. In the proposed method, the optimal mean sound speed is determined by measuring the amplitude variance of pre-beamformed radio-frequency (RF) data. The proposed method was evaluated with phantom and in vivo experiments, and implemented on Virtex-4 with Xilinx ISE 12.4 using VHDL. Experiment results indicate that the proposed method could estimate the mean optimal sound speed and enhance spatial resolution with a negligible increase in the hardware resource usage.

Study on sound-speed dispersion in a sandy sediment at frequency ranges of 0.5–3 kHz and 90–170 kHz

In order to study the properties of sound-speed dispersion in a sandy sediment, the sound speed was measured both at high frequency (90–170 kHz) and low frequency (0.5–3 kHz) in laboratory environments. At high frequency, a sampling measurement was conducted with boiled and uncooked sand samples collected from the bottom of a large water tank. The sound speed was directly obtained through transmission measurement using single source and single hydrophone. At low frequency, an in situ measurement was conducted in the water tank, where the sandy sediment had been homogeneously paved at the bottom for a long time. The sound speed was indirectly inverted according to the traveling time of signals received by three buried hydrophones in the sandy sediment and the geometry in experiment. The results show that the mean sound speed is approximate 1710–1713 m/s with a weak positive gradient in the sand sample after being boiled (as a method to eliminate bubbles as much as possible) at high frequency, which agrees well with the predictions of Biot theory, the effective density fluid model (EDFM) and Buckingham’s theory. However, the sound speed in the uncooked sandy sediment obviously decreases (about 80%) both at high frequency and low frequency due to plenty of bubbles in existence. And the sound-speed dispersion performs a weak negative gradient at high frequency. Finally, a water-unsaturated Biot model is presented for trying to explain the decrease of sound speed in the sandy sediment with plenty of bubbles.

A passive range method of underwater source based on single hydrophone

Aiming at the passive impulse wideband source range problem in shallow water waveguides, a passive source range method with single hydrophone which is applied to the shallow water waveguide with a bottom of liquid semi-infinite space is presented in this paper by combining the group delay theory and warping transformation. The receive signal is composed of several normal modes, and each mode represents many characteristics of the waveguide environment. Warping transformation is a good tool which can achieve the separation and extraction of normal modes from the received signal, and it is also an unitary and reversible transformation, so the warped signal of each normal mode can be recovered completely. The dispersion curves of normal modes can be extracted by warping transformation, and the relation between arrival time and frequency of each order normal mode can also be calculated, and then the time delay of arriving hydrophone between arbitrary two different normal modes is obtained. According to the group delay theory, different order normal mode has different arrival time at the same frequency, and the arrival time of normal mode is determined at its group speed when the distance between the source and hydrophone is certain. So the propagation range can be estimated when the time delay and the slow group speed difference between two different normal modes are known. When the waveguide environmental parameters are known, the slow group speed difference of arbitrary two normal modes can be calculated by KRAKEN. However, when the bottom parameters are unknown, the bottom reflection phase shift parameter is an important parameter describing the acoustic parameters of the bottom, and it contains nearly all the bottom information, what is more, the bottom reflection phase shift parameter is also a parameter that can be extracted by some experimental data easily. When the depth and the average sound speed of the water column are known, the slow group speed difference between two order normal modes can be represented by the seafloor phase shift parameter. Therefore, the source range can be represented by the bottom reflection phase shift parameter, the sea depth and the mean sound speed in the waveguide, and under this condition, the source location can be estimated by one single hydrophone. The effectiveness and accuracy of the method are proved by the numerical simulation results and sea experimental data processing, in which the signals are both received by a single hydrophone. The sea experimental data contain linear frequency modulation impulse source signal and explosion sound source signal, and the mean relative error of range estimation is less than 10%.

Using Speed of Sound Imaging to Characterize Breast Density

A population of 165 women with negative mammographic screens also received an ultrasound tomography (UST) examination at the Karmanos Cancer Institute in Detroit, MI. Standard statistical techniques were employed to measure the associations between the various mammographic- and UST-related density measures and various participant characteristics such as age, weight and height. The mammographic percent density (MPD) was found to have similar strength associations with UST mean sound speed (Spearman coefficient, rs = 0.722, p < 0.001) and UST median sound speed (rs = 0.737, p < 0.001). Both were stronger than the associations between MPD with two separate measures of UST percent density, a k-means (rs = 0.568, p < 0.001) or a threshold (rs = 0.715, p < 0.001) measure. Segmentation of the UST sound speed images into dense and non-dense volumes showed weak to moderate associations with the mammographically equivalent measures. Relationships were found to be inversely and weakly associated between age and the UST mean sound speed (rs = −0.239, p = 0.002), UST median sound speed (rs = −0.226, p = 0.004) and MPD (rs = −0.204, p = 0.008). Relationships were found to be inversely and moderately associated between body mass index (BMI) and the UST mean sound speed (rs = −0.429, p < 0.001), UST median sound speed (rs = −0.447, p < 0.001) and MPD (rs = −0.489, p < 0.001). The results confirm and strengthen findings presented in previous work indicating that UST sound speed imaging yields viable markers of breast density in a manner consistent with mammography, the current clinical standard. These results lay the groundwork for further studies to assess the role of sound speed imaging in risk prediction.

CO-dark gas and molecular filaments in Milky Way-type galaxies – II. The temperature distribution of the gas

We investigate the temperature distribution of CO-dark molecular hydrogen (H2) in a series of disk galaxies simulated using the AREPO moving-mesh code. In conditions similar to those in the Milky Way, we find that H2 has a flat temperature distribution ranging from 10 - 100 K. At $T < 30$ K the gas is almost fully molecular and has a high CO content, whereas at $T > 30$ K, the H2 fraction spans a broader range and the CO content is small, allowing us to classify gas in these two regimes as CO-bright and CO-dark, respectively. The mean sound speed in the CO-dark H2 is 0.64 km/s, significantly lower than the value in the cold atomic gas (1.15 km/s), implying that the CO-dark molecular phase is more susceptible to turbulent compression and gravitational collapse than its atomic counterpart. We further show that the temperature of the CO-dark H2 is highly sensitive to the strength of the interstellar radiation field, but that conditions in the CO-bright H2 remain largely unchanged. Finally, we examine the usefulness of the [CII] and [OI] fine structure lines as tracers of the CO-dark gas. We show that in Milky Way-like conditions, diffuse [CII] emission from this gas should be detectable. However, it is a problematic tracer of this gas, as there is only a weak correlation between the brightness of the emission and the H2 surface density. The situation is even worse for the [OI] line, which shows no correlation with the H2 surface density.

Probabilistic infrasound propagation using realistic atmospheric perturbations

AbstractThis study demonstrates probabilistic infrasound propagation modeling using realistic perturbations. The ensembles of perturbed analyses, provided by the European Centre for Medium‐Range Weather Forecasts (ECMWF), include error variances of both model and assimilated observations. Ensemble spread profiles indicate a yearly mean effective sound speed variation of up to 8 ms−1 in the stratosphere, exceeding occasionally 25 ms−1 for a single ensemble set. It is shown that errors in point estimates of effective sound speed are dominated by variations in wind strength and direction. One year of large mining explosions in the Aitik mine, northern Sweden, observed at infrasound array IS37 in northern Norway are simulated using 3‐D ray tracing. Probabilistic propagation modeling using the ensembles demonstrates that small‐scale fluctuations are not always necessary to improve the match between predictions and observations.

Photoacoustic image quality enhancement by estimating mean sound speed based on optimum focusing

A constant sound speed (i.e., 1540 m/s) is generally used in various ultrasound (US) and photoacoustic (PA) image reconstruction algorithms based on the assumption of a homogeneous sound speed in human tissue. However, the variation of the sound speed in human tissue can be as great as 10%, which can lead to low contrast, distortion, and blurring in reconstruction images. We proposed an automatic method of selecting the mean sound speed based on optimum focusing of received PA signals to enhance the quality of reconstructed PA images. Optimum focusing is quantified by calculating the minimum sum of the deviation of beamformed PA signals from their mean value for various sound speeds. The proposed method was demonstrated by homogeneous and heterogeneous sound speed simulation models, and also evaluated by experiments with agar and porcine tissue-mimicking phantoms. The central vertical and lateral profiles of reconstructed absorbers verified the improvement of contrast, signal-to-noise ratio (SNR), and spatial resolution by using the estimated mean sound speed.

Sound speed profile inversion using a horizontal line array in shallow water

It is better to use a simple configuration to enhance the applicability of ocean environment inversion in shallow water. A matched-field inversion method based on a horizontal line array (HLA) is used to retrieve the variation of sound speed profile. The performance of the inversion method is verified in the South China Sea in June, 2010. An HLA laid at bottom was used to receive signals from a bottom-mounted transducer. Inverted mean sound speed profiles from 9-hour long acoustic signals are in good agreement with measurements from two temperature chains at the sites of the source and receiver. The results show that an HLA can be used to monitor the variability of shallow-water sound speed profile.

Elastic, electronic and optical properties of cotunnite TiO2 from first principles calculations

The ultrasoft pseudopotential technique is used to explore the elastic, electronic and optical properties of cotunnite TiO2 using LDA and GGA proposed by Perdew Wang (PW91), Perdew–Burke–Ernzerhof (PBE) functional as defined by Wu and Cohen (PBEWC) and PBE functional for solids (PBESOL). The calculated elastic constants bulk modulus, shear modulus and Young’s modulus are in agreement with the previous theoretical reports. From our investigated shear anisotropy factors (A1 ,A 2, and A3), we infer that cotunnite TiO2 is strong anisotropy in case of A1 and A2 and less anisotropy in case of A3. The value of mean sound speed and Debye temperature are calculated using the obtained values of elastic moduli. The calculated structural parameters are in accord with the reported experiment and theoretical results. Our obtained values of direct bandgaps show an improvement over the other previous theoretical reports. The values of the dielectric constant (e1(o)) of cotunnite TiO2 calculated within LDA and GGA approximations are 7.655 (LDA (CA-PZ)), 7.578 (GGA (PW91)), 7.685 (GGA (WC)) and 7.655 (GGA (PBESOL)), which are slightly higher than the experimental values of rutile (6.69) and anatase (6.55) polymorphs. The obtained values of the refractive index are consistent with rutile TiO2 and higher than anatase phase. The investigated imaginary part of dielectric constant and absorption spectrum reflect that the cotunnite TiO2 is a weak photocatalytic material as compared to anatase and similar to rutile phases.

In vitro estimation of mean sound speed based on minimum average phase variance in medical ultrasound imaging

Effective receive beamforming in medical ultrasound imaging is important for enhancing spatial and contrast resolution. In current ultrasound receive beamforming, a constant sound speed (e.g., 1540 m/s) is assumed. However, the variations of sound speed in soft tissues could introduce phase distortions, leading to degradation in spatial and contrast resolution. This degradation becomes even more severe in imaging fatty tissues (e.g., breast) and with obese patients. In this paper, a mean sound speed estimation method where phase variance of radio-frequency channel data in the region of interest is evaluated is presented for improving spatial and contrast resolution. The proposed estimation method was validated by the Field II simulation and the tissue mimicking phantom experiments. In the simulation, the sound speed of the medium was set to 1450 m/s and the proposed method was capable of capturing this value correctly. From the phantom experiments, the −18-dB lateral resolution of the point target at 50 mm obtained with the estimated mean sound speed was improved by a factor of 1.3, i.e., from 3.9 mm to 2.9 mm. The proposed estimation method also provides an improvement of 0.4 in the contrast-to-noise ratio, i.e., from 2.4 to 2.8. These results indicate that the proposed mean sound speed estimation method could enhance the spatial and contrast resolution in the medical ultrasound imaging systems.

Seismic imaging of variable water layer sound speed in Rockall Trough, NE Atlantic and implications for seismic surveying in deep water

Abstract Natural variation in sound speed within ocean water can degrade sub-seabed images from 2D, 3D and 4D seismic reflection datasets. Degrading effects include vertical offset of reflections between adjacent or intersecting sail lines and difficulties in suppressing multiples from water layer reverberations. Here we investigate water layer variability in Rockall Trough, offshore Ireland, in water depths ranging from 200 m to 3.5 km. A compilation of vertical sound speed profiles, calculated from temperature and salinity profiles obtained by probes lowered from ships, shows that the mean sound speed in the water layer mostly varies between 1490 and 1500 m s −1 . Vertical offsets of up to about 15 ms two-way travel time are predicted at seismic line intersections. A significant amount of the total observed sound speed variability can occur along a single seismic sail line. These effects result mainly from spatial and temporal fluctuations in the thicknesses of, and vertical sound speed gradients within, an upper layer of North Atlantic Central Water and a mid-depth layer of Mediterranean Outflow Water. Seismic sections across Rockall Trough commonly show lateral variability in reflectivity within these same two water layers. Some reflective packages contain lens-shaped structures consisting of reflective rims and transparent cores and with diameters between 10 and 50 km. Other reflective packages have abrupt, almost vertical boundaries and no distinct transparent core. We infer that the lateral boundaries of the reflective packages are likely to be associated with significant variations in average water layer sound speed. When processing 2D, 3D and 4D seismic surveys of regions of high oceanic variability, such as Rockall Trough, it is necessary to employ techniques that can solve for and then remove the effect of significant fluctuations in water layer sound speed over time periods as short as a few hours and distances as short as a kilometre.

On the Propagation of Sound in a High-Speed Non-Isothermal Shear Flow

The propagation of sound in shear flows is relevant to the acoustics of wall and duct boundary layers, and to jet shear layers. The acoustic wave equation in a shear flow has been solved exactly only for a plane unidirectional homentropic mean shear flow, in the case of three velocity profiles: linear, exponential and hyperbolic tangent. The assumption of homentropic mean flow restricts application to isothermal shear flows. In the present paper the wave equation in an plane unidirectional shear flow with a linear velocity profile is solved in an isentropic non-homentropic case, which allows for the presence of transverse temperature gradients associated with the ***non-uniform sound speed. The sound speed profile is specified by the condition of constant enthalpy, i.e. homenergetic shear flow. In this case the acoustic wave equation has three singularities at finite distance (besides the point at infinity), viz. the critical layer where the Doppler shifted frequency vanishes, and the critical flow points where the sound speed vanishes. By matching pairs of solutions around the singular and regular points, the amplitude and phase of the acoustic pressure in calculated and plotted for several combinations of wavelength and wave frequency, mean flow vorticity and sound speed, demonstrating, among others, some cases of sound suppression at the critical layer.

Inversion for range-dependent water column sound speed profiles in shallow water.

Spatial and temporal variability of the sound speed field in the water column can have a significant impact on acoustic propagation. It is difficult or sometimes impractical to measure fine scale variations in water column properties over an acoustic propagation path. When measurements are not available, water column properties must be approximated. In past work, inverse methods based on acoustic tomography and matched-field processing have been used to estimate mean water column sound speed profiles. The drawback of these methods is their inability to capture fluctuations in the water column sound speed profile. In this work, a perturbative scheme using modal wave numbers is used to obtain range-dependent features of the water column. Based on the work of Rajan et al. (1987), a technique has been developed to estimate water column sound speed profiles using historical data to constrain the inversion. This constraint allows for a robust inversion; the result is accurate both when the inputs are noisy and when the bottom is poorly known. The new technique is demonstrated using data from the Shallow Water 2006 (SW06) experiment. Inversion results are compared to in situ measurements from the towed CTD chain. [Work supported by NDSEG and ONR.]

MO-D-342-01: Breakthroughs in Ultrasound Imaging

Similar to the paradigm change of the 1980's, when ultrasound labs shifted from large, manual scanners to cart‐based, real‐time scanners, we now see a move in the industry towards small, portable ultrasound units (PUU) having sophisticated imaging capabilities. Unlike their predecessors, however, the cart‐based scan consoles are likely to continue to play an important role in medical imaging, with PUU's significantly expanding the tasks carried out by this modality. This presentation highlights these anticipated changes. Ultrasound machines continue to use sequential, line‐by‐line echo acquisition and traditional array beam forming. This limits frame rates because of the sound propagation speed in tissue, a significant problem as 2D arrays producing 3D data sets are developed. One manufacturer has developed a “zone” transmission method with synthetic aperture processing of element data. This improves frame rate and offers new capabilities, such as adaptive mean sound speed corrections. Operator controls, even on very basic machines, are numerous and encompass many echo acquisition and signal processing functions. Although application specific presets simplify the task of precise adjustment of these controls, there is a growing trend to develop machines that do away with traditional operator adjustments and automatically set important functions, such as overall gain, TGC, and transmit focus. Echo amplitude information continues to serve as the primary data presented to users in non‐Doppler operating modes. This now is being supplemented by elasticityimaging, where tissue stiffness images are formed and displayed, and may soon be extended further by displays of tissueproperties that are not evident in conventional B‐mode, such as scatter sizes and attenuation. Much development activity is taking place in PUU's, with varying capabilities and intended uses. Full featured portable machines allow sonographers to access patients not easily scanned with larger cart based machines. Inexpensive, special purpose PUU's are being directed to new users, such as emergency room physicians, and anesthesiologists. Educational Objectives: 1. Understand how current ultrasound machines operate and appreciate limitations of these devices. 2. Understand tradeoffs when choosing high end vs. portable ultrasound machines. 3. Understand sources of new information from ultrasoundscanners.