Ultrasonic attenuation and backscatter from flowing whole blood are dependent on shear rate and hematocrit between 10 and 50 MHz

Ultrasonic backscatter has recently been used extensively to investigate erythrocyte aggregation, which is an inherent hematological phenomenon in the blood circulation system. The size of rouleaux can be estimated by measuring certain parameters of signals backscattered from flowing blood. However, most measurements of backscatter from blood use a constant value for the attenuation coefficient to compensate for the loss of ultrasound energy. This correction may be inaccurate because the attenuation varies with the blood properties, which prompted us to explore the effects of hemodynamic properties on ultrasonic attenuation and backscatter to better understand the blood rheological behaviors. Experiments were performed on porcine whole blood in a Couette flow apparatus. Ultrasonic attenuation and the backscattering coefficient of blood were measured at various frequencies (from 10 to 50 MHz), hematocrits (from 0 to 60%), and shear rates (from 0.1 to 200 s?1). The results indicated that the attenuation and backscattering coefficients of blood are highly variable, depending in a complex manner on shear rate, hematocrit, and the measurement ultrasound frequency. The attenuation of blood decreased rapidly with increasing shear rates, eventually reaching a steady state asymptotically, and increased linearly with the hematocrit from 10 to 50 MHz at various shear rates, and also with the ultrasound frequency. The effect of erythrocyte aggregation means that the change in ultrasonic attenuation in blood with shear rate may be attributed to the absorption mechanism, which is enhanced by the increased blood viscosity at lower shear rates. Compensating the measured backscattering coefficients of blood for the shear-rate-dependent attenuation coefficient increased the accuracy of erythrocyte aggregation assessments. Together, the experimental results suggest that the shear-rate-dependent attenuation coefficient should be considered in future developments of ultrasonic technologies for characterizing blood rheology when the ultrasound frequency is higher than 20 MHz.     

Ultrasonic attenuation studies in molybdenum

The electronic attenuation of longitudinal and shear waves has been measured in both the normal and superconducting states of molybdenum. In all cases the limiting attenuation is an order of magnitude larger than the free-electron prediction. A model based on the tight-binding approximation is proposed to explain these results and the absence of a rapid-fall region in the superconducting shear wave attenuation.Work supported by National Science Foundation.     

Optimization of attenuation estimation in reflection for in vivo human dermis characterization at 20 MHz

In vivo skin attenuation estimators must be applicable to backscattered radio frequency signals obtained in a pulse-echo configuration. This work compares three such estimators: short-time Fourier multinarrowband (MNB), short-time Fourier centroid shift (FC), and autoregressive centroid shift (ARC). All provide estimations of the attenuation slope (/spl beta/, dB.cm/sup -1/.MHz/sup -1/); MNB also provides an independent estimation of the mean attenuation level (IA, dB.cm/sup -1/). Practical approaches are proposed for data windowing, spectral variance characterization, and bandwidth selection. Then, based on simulated data, FC and ARC were selected as the best (compromise between bias and variance) attenuation slope estimators. The FC, ARC, and MNB were applied to in vivo human skin data acquired at 20 MHz to estimate /spl beta//sub FC/, /spl beta//sub ARC/, and IA/sub MNB/, respectively (without diffraction correction, between 11 and 27 MHz). Lateral heterogeneity had less effect and day-today reproducibility was smaller for IA than for /spl beta/. The IA and /spl beta//sub ARC/ were dependent on pressure applied to skin during acquisition and IA on room and skin-surface temperatures. Negative values of IA imply that IA and /spl beta/ may be influenced not only by skin's attenuation but also by structural heterogeneity across dermal depth. Even so, IA was correlated to subject age and IA, /spl beta//sub FC/, and /spl beta//sub ARC/ were dependent on subject gender. Thus, in vivo attenuation measurements reveal interesting variations with subject age and gender and thus appeared promising to detect skin structure modifications.     

Ultrasonic attenuation in quenched railway wheels

Ultrasonic attenuation in the fine pearlitic steel used for railway wheels has been measured. Several structural factors that significantly affect ultrasonic wave attenuation in the frequency range 2–10 MHz have been found. These factors are: the grain and its distribution, the grain boundaries, the history of the grain and the content of the ferritic component.     

Ultrasonic attenuation in commercial lead-silicate glasses

The ultrasonic attenuation of a range of commercial lead—silicate glasses has been studied over the temperature range 4.2 to 360 K. Measurements of shear-wave ultrasonic attenuation,A, over the frequency range 5 to 50 MHz have revealed peaks in the attenuation below room temperature and these are interpreted in terms of the resonant movement of oxygen ions in the silica networks. In some cases the effects of the peaks are seen to extend to room temperature in some of these glasses. Frequency dependence of the attenuation,A, can be fitted to a relation of the formA F ^N , whereF is the frequency andN is a constant. Shear-wave velocities are also measured to aid characterization of the glasses.     

Ultrasonic velocity and attenuation in glass

Ultrasonic velocity and attenuation in glasses exhibit anomalous properties and the current theory most successful in explaining these anomalous properties in the high temperature range has been presented. The model considers that the disorder inherent in amorphous network results in a double well potential corresponding to two equilibrium configurations and a particle is ascribed to move in the double-well potential. Acoustic behaviours in glasses have been interpreted in terms of a thermally activated relaxation process. Improvement of this basic model has also been discussed. Mention has also been made of some behaviours at high temperature that need further research for convincing explanation.     

Ultrasonic attenuation in hcp 4He

The ultrasonic attenuation was measured for longitudinal sound waves in solid hcp ⁴He at frequencies of 5, 15, and 25 MHz from 0.25 to 3.5 K. Near melting, the attenuation is very small and in agreement with theoretical predictions. In most samples the attenuation rises gradually with falling temperature until a point is reached which approximately corresponds to the onset of a previously observed velocity anomaly. Then the attenuation rises more quickly and remains very large to the lowest temperatures measured. Two samples exhibit neither a steep rise in attenuation nor a velocity anomaly. A number of explanations for the large attenuation are considered.Research supported by grants from the National Research Council of Canada.     

Ultrasonic attenuation in voided fibre-reinforced plastics

Details are given of a model for attenuation of ultrasonic pulses propagating through a fibre-reinforced plastic in which the matrix material contains small voids. The model is developed to a form which gives good qualitative agreement with published experimental results and suggestions are made for further improvements.     

The effect of phase cancellation on estimates of broadband ultrasound attenuation and backscatter coefficient in human calcaneus in vitro

Broadband ultrasound attenuation (BUA) is a clinically proven indicator of osteoporotic fracture risk. BUA measurements are typically performed in through- transmission with single-element phase sensitive (PS) receivers and therefore can be compromised by phase cancellation artifact. Phase-insensitive (PI) receivers suppress phase cancellation artifact. To study the effect of phase cancellation on BUA measurements, through-transmission measurements were performed on 16 human calcaneus samples in vitro using a two-dimensional receiver array that enabled PS and PI BUA estimation. The means plus or minus standard deviations for BUA measurements were 22.1 plusmn 15.8 dB/MHz (PS) and 17.6 plusmn 7.2 dB/MHz (PI), suggesting that, on the average, approximately 20% of PS BUA values in vitro can be attributed to phase cancellation artifact. Therefore, although cortical plates are often regarded as the primary source of phase cancellation artifact, the heterogeneity of cancellous bone in the calcaneal interior may also be a significant source. Backscatter coefficient estimates in human calcaneus that are based on PS attenuation compensation overestimate 1) average magnitude of backscatter coefficient at 500 kHz by a factor of about 1.6 plusmn 0.3 and 2) average exponent (n) of frequency dependence by about 0.34 plusmn 0.12 (where backscatter coefficient is fit to a power law form proportional to frequency to the nth power).     

Ultrasonic attenuation in normal and superconducting indium

Measurements have been made of the ultrasonic attenuation in the normal and superconducting states of pure In single crystals. The measurements spanned the frequency range of 6–66 MHz. The data, taken in the amplitude-independent regime, displayed the expected deviations from the BCS-type attenuation which are generally attributed to dislocation attenuation as described by Granato and Lücke. Earlier attempts to use this theory to study the amplitude-independent dislocation attenuation of ultrasound in superconductors (e.g., Mason) were generally limited to very narrow frequency ranges. These earlier results were in general agreement with the Granato and Lücke theory. However, the present multiple-frequency measurements are shown to be inconsistent with the Granato and Lücke theory.Supported by the Applied Research Laboratory of The Pennsylvania State University, under contract with the U.S. Naval Sea Systems Command.     

Ultrasonic attenuation in the intermediate state of tin

Attenuation of ultrasound has been measured in the intermediate state of single crystals of tin at 3.3 MHz in the temperature range 1.5–3.7 K. A small measurable change of the frequency v_O of the collective modes of excitations has been observed very near the critical magnetic field.     

Ultrasound characterization of normal ocular tissue in thefrequency range from 50 MHz to 100 MHz

The ultrasonic properties of ocular tissues including sclera, cornea, ciliary body and iris have been quantitatively evaluated over the frequency range from 50 MHz to 100 MHz at 37°C. Measurements were made with a wideband 60 MHz PVDF copolymer transducer in conjunction with a C-scan microscopy system developed in the authors' laboratory. Using this system, high resolution overview images were produced to identify homogeneous tissue regions for detailed quantitative analysis. The speed of sound for the four eye tissues ranged from 1542 m/s for iris to 1622 m/s for sclera. At 50 MHz the attenuation coefficient ranged from 1.3 dB/mm for cornea to 4.3 dB/mm for sclera. Scleral tissue also had the highest backscatter coefficient (0.0157 Sr^-1 mm^-1), while iris had the lowest (0.00184 Sr^-1 mm^-1). The measured ultrasonic properties are qualitatively related to their histological structure and imaging characteristics     

Ultrasonic attenuation in the mixed state of a dirty superconductor

Transport coefficients in the mixed state have simple expressions when the response is local. For dirty materials the ultrasonic attenuation is given by the local expression over the whole mixed-state regime because of the Coulomb interaction between the electrons, and responses of the order parameter and magnetic field to the sound wave do not contribute to the attenuation. Computations based on the theory are compared with experiment.On leave of absence from Research Institute of Electrical Communication, Tohoku University, Sendai, Japan.     

Ultrasonic attenuation of longitudinal and shear waves in superconducting lead

Longitudinal and shear wave ultrasonic attenuations have been measured in high-purity Pb on two single crystals obtained from the same ingot. The measurements were done at low temperatures, at different frequencies, and in transverse magnetic fields, up to a field of 7.3 kG. The propagation directions in the two crystals were along [100] and [110]. For some propagation and polarization directions the _s / _n ratio is found to be frequency-independent, while for others, large divergences in the _s / _n ratios at different frequencies are observed. A sharp decrease of _s / _n nearT _c is observed for a particular longitudinal wave propagation, but not in any shear wave propagation. In some cases _s / _n is found to be abnormally high and this feature is associated with a peak in attenuation _n and a relatively high _n at 7.2 K. None of the _s / _n curves fits closely to any BCS energy gap. For longitudinal waves the high magnetic field (H) dependence of the normal state attenuation was found to agree qualitatively with the free electron theory for propagation along [100], but not for propagation along [110]. For shear waves the high-field attenuations do not extrapolate to zero asH tends to infinity. For all propagation and polarization directions the high-field attenuations show 1/H ² field dependence.     

Ultrasonic attenuation and thermal conductivity in clean,type II superconductors

Based on the reformulation of the Gor'kov equations by Eilenberger, Larkin, and Ovchinnikov, we propose a calculational method for transport coefficients in clean, type II superconductors. For the ultrasonic attenuation rate (qB) and the thermal conductivity (T B) we give analytical expressions near the upper critical field H _c2 at low temperatures. Comparison with experiment leads to satisfactory agreement with the theoretical results.See Maki¹ for a comprehensive review     

Hydrophone spatial averaging corrections from 1 to 40 MHz

The purpose of this study was to develop and experimentally verify a practical spatial averaging model for frequencies up to 40 MHz. The model is applicable to focused sources of circular geometry, accounts for the effects of hydrophone probe finite aperture, and allows calibration by substitution to be performed when the active elements of reference and tested hydrophone probes differ significantly. Several broadband sources with focal numbers between 3 and 20 were used to produce ultrasound fields with frequencies up to 40 MHz. The effective diameters of the ultrasonic hydrophone probes calibrated in the focal plane of the sources ranged from 150 to 500 μm. Prior to application of the spatial averaging corrections, the hydrophones with diameters smaller than that of the reference hydrophone exhibited experimentally determined absolute sensitivities higher than the true ones. This discrepancy increased with decreasing focal numbers and increasing frequency. It was determined that the error was governed by the cross-section of the beam in the focal plane and the ratio of the effective diameters of the reference and tested hydrophone probes. In addition, the error was found to be reliant on the frequency-dependent effective hydrophone radius. After applying the spatial averaging correction, the overall uncertainty in the hydrophone calibration was on the order of ±1 dB. The model developed is being extended to be applicable to frequencies beyond 40 MHz, which are becoming increasingly important in diagnostic ultrasound imaging applications     

Ultrasonic velocity and attenuation measurements at the metamagnetic transition in UPt3

The longitudinal ultrasonic attenuation and velocity were measured on a single crystal of UPt₃ in a high magnetic field of up to 23T. Earlier ultrasonic measurements had seen a softening of the lattice as evidenced by a huge drop in the velocity at a field of 20T. Both the attenuation and velocity have been measured in field sweeps. Accompanying the large dip in the velocity is a large attenuation peak at this metamagnetic transition. Measurements were also done at several frequencies.     

Ultrasonic attenuation in the mixed state of V-42 at % Ti

The ultrasonic attenuation in the mixed state of V-42 at % Ti was measured at T = 4.14K, using shear and longitudinal waves with frequencies 10–130 MHz, in magnetic fields up to 100 kG. The results are compared to a phenomenological model in which the mixed-state resistivity is used as an effective resistivity in the Alpher-Rubin theory. For our V-42 at % Ti, pinning forces are weak, so that the mixed-state attenuation is particularly sensitive to the dc flux-flow resistivity. For magnetic fields 40–60 kG, the attenuation is in quantitative agreement with a model employing the dc flux-flow resistivity of Kim et al., % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4baFfea0dXde9vqpa0lb9% cq0dXdb9IqFHe9FjuP0-iq0dXdbba9pe0lb9hs0dXda91qaq-xfr-x% fj-hmeGabaqaciGacaGaaeqabaWaaeaaeaaakeaacqaHbpGCdaWgaa% WcbaacbaGaa8NzaaqabaGccqGH9aqpcqaHbpGCdaWgaaWcbaGaa8NB% aaqabaGccaWFibGaai4laiaa-HeadaqhaaWcbaGaam4yaiaaikdaae% aacaGGQaaaaOGaaiikaiaaicdacaGGPaaaaa!400D!\[\rho _f = \rho _n H/H_{c2}^* (0)\]. For high frequencies, where pinning may be neglected, the magnetic field dependence of the attenuation for HH_c2 is in better agreement with the use of the flux-flow resistivity calculated from the time-dependent Ginzburg-Landau equation.Research supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq).Supported by Comissão de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).     

Ultrasonic attenuation of the excitonic state in pure bismuth in high magnetic fields

The ultrasonic attenuation of the excitonic state in pure Bi in high magnetic fields is studied theoretically. Use is made of the mean-field approximation to describe the excitonic state in pure Bi in the extreme quantum limit, where the motion of the electron and the hole is limited only in the direction parallel to the magnetic field. The attenuation constant of the longitudinal sound has a broad peak below the excitonic transition temperatureT _c and then decreases rapidly as the temperature decreases, which agrees qualitatively with a recent observation by Sakaiet al.     

Thermal conductivity of Grafoil from 0.2 to 3 K

The thermal conductivity of compressed exfoliated graphite was measured in the directions parallel (K ) and normal (K ) to the rolling plane, in the temperature range of 0.2–3 K. The temperature dependence was determined in both cases. ForK=aT ^b in the temperature range of 0.2–0.7 K we get values forb of 0.95 forK and 1.6 forK ; in the range 0.7–2 K we get 1.6 forK and 2.1 forK ; and in the range 2–3 K we get 1.9 forK . TheK temperature dependence forT<0.7 K is smaller than what would be expected. ForK , evaluations of lattice and electronic contributions show that below 0.7 K the thermal conductivity is basically electronic. Above 2 K, where results are found in the literature, our data are in good agreement with them.