Ultrasound Velocity Measurements Research Articles

Titanium powder sintering for preparation of a porous functionally graded material destined for orthopaedic implants.

This work focuses on basic research into a P/M processed, porous-surfaced and functionally graded material (FGM) destined for a permanent skeletal replacement implant with improved structural compatibility. Based on a perpendicular gradient in porosity the Young's modulus of the material is adapted to the elastic properties of bone in order to prevent stress shielding effects and to provide better long-term performance of the implant-bone system. Using coarse Ti particle fractions the sintering process was accelerated by silicon-assisted liquid-phase sintering (LPS) resulting in a substantial improvement of the neck geometry. A novel evaluation for the strength of the sinter contacts was proposed. The Young's modulus of uniform non-graded stacks ranged from 5 to 80 GPa as determined by ultrasound velocity measurements. Thus, the typical range for cortical bone (10-29 GPa) was covered. The magnitude of the Poisson's ratio proved to be distinctly dependent on the porosity. Specimens with porosity gradients were successfully fabricated and characterized using quantitative description of the microstructural geometry and acoustic microscopy.

Thermodynamic Properties of Some Antidepressant Drugs in Aqueous Solution

The apparent molal volumes and adiabatic compressibilities of aqueous solutions of the amphiphilic antidepressants amitriptyline, nortriptyline, and desipramine have been determined from density and ultrasound velocity measurements. Critical concentrations were obtained from both techniques. Positive deviations of the apparent molal volume of nortriptyline from the Debye−Hückel limiting law in dilute solution indicate premicellar association. The changes of molal volume accompanying aggregate formation suggest a tightly packed aggregate. Isentropic apparent molal adiabatic compressibilities were calculated by combining the ultrasound velocity and density data. Changes of this quantity were similar to those of typical surfactants, indicating a decrease of hydrophobic hydration in the association of the monomers of these drugs.

Adiabatic compressibility of red blood cell membrane: influence of skeleton

Measurements of ultrasound velocity and density were used for determination of the adiabatic compressibility of red blood cells (RBC) during detachment of the membrane skeleton. Skeleton detachment was induced by addition of nystatin into a low ionic strength RBC suspension resulting in an increase (10%) of the ultrasound velocity concentration increment, [ u], while the specific volume of cells, ϕ V, did not change significantly. Changes of the concentration increment had rather long kinetics and were not completed even after 60 min. Both [ u] and ϕ V values were used for calculation of the specific apparent adiabatic compressibility of RBC, ϕ K/ β 0. The value of the specific apparent compressibility decreases following addition of nystatin. This corresponds to an increase in the volume elastic modulus of RBC membranes during detachment of the membrane skeleton. Control experiments with large unilamellar liposomes at conditions similar to that performed with the RBC did not reveal significant changes of [ u] after the addition of nystatin. Our results show that the role of the membrane skeleton probably consists in maintaining higher compressibility of the RBC membranes. This may partly provide conditions for conformational changes of RBC membrane proteins.

Effect of contralateral carotid artery stenosis on carotid ultrasound velocity measurements.

Carotid ultrasonography is being increasingly performed as the sole investigation to assess internal carotid artery (ICA) stenosis. A potential source of error in using ultrasound peak systolic velocity (PSV) measurements is that the redistribution of blood flow due to severe stenosis in a contralateral carotid artery may lead to artificially elevated values. Ultrasonography was performed before and after carotid endarterectomy in symptomatic patients who participated in the North American Symptomatic Carotid Endarterectomy Trial (NASCET). The mean change in PSV in the unoperated artery was assessed across all degrees of angiographically defined stenosis. A simple theoretical resistance model of the cerebral circulation was also derived. Complete bilateral ultrasound examinations were performed within 90 days of the initial scan in 386 patients. In the presence of a contralateral severe (70% to 99%) ICA stenosis, the PSV in the unoperated artery was artificially elevated by a mean of 84 cm/s (P:=0.03; 95% CI, 10 to 159 cm/s). The mean elevation was less pronounced for lesser degrees of stenosis (11 to 21 cm/s). Small elevations (3 to 12 cm/s) were observed when the contralateral artery had <70% stenosis. The patterns of observed results were congruent with those from the theoretical model. The present study showed that a severely stenosed contralateral ICA can artificially elevate ultrasound PSV. Since the effect was greatest when bilaterally severe stenoses were present, caution must be exercised when assessing the degree of ICA stenosis on the basis of ultrasonography PSV measurements alone.

Acoustic anomalies inUPt3at high magnetic fields and low temperatures

Ultrasound velocity and attenuation measurements were performed on single crystals of the heavy fermion compound ${\mathrm{UPt}}_{3}$ in magnetic fields up to 33 T and at temperatures ranging from 2.4 K to below 0.1 K. With longitudinal sound propagated in the crystallographic basal plane, parallel to the applied field, the familiar elastic softening is observed at the metamagnetic transition field $H\ensuremath{\sim}20.2\mathrm{T}.$ More complicated structure emerges at low temperatures, including quantum acoustic oscillations and a second velocity minimum at \ensuremath{\sim}21.6 T. A weak frequency dependence (dispersion) is observed in the velocity. The ultrasonic data are analyzed using the Landau-Khalatnikov formalism, from which temperature- and field-dependent relaxation times are deduced.

Quantitative Ultrasound and Bone Densitometry to Evaluate the Risk of Nonspine Fractures: A Prospective Study

The ability of quantitative ultrasound (QUS) to estimate the risk of osteoporotic fractures was evaluated in a prospective study over a mean time of 5.47 years in 254 postmenopausal women (mean age 58.06+/-7.67 years). Baseline measurements of ultrasound transmission velocity (UTV) and bone mineral density (BMD) were taken at the distal radius (DR). UTV was also measured at the patella (P). Fifty nonspine fractures due to minor trauma were detected during annual check-ups with an incidence of 3.59/year. Fractures occurred in older women with a lower BMD and QUS. Using Cox regression analysis the relative risk (RR) per 1 standard deviation (SD) decrease in the unadjusted QUS and BMD measurements was: BMD-DR = 3.56, 95% confidence interval (CI) 1.57-8.09; 95% CI 2.08-9.68. The relationship between BMD and QUS variables and fracture risk persisted after adjusting for potential confounders apart from previous fractures, giving the following RR: BMD-DR = 2.99, 95% CI 1.06-8.41; UTV-DR = 3.69, 95% CI 1.18-11.49; UTV-P = 3.89, 95% CI 1.53-9.90. Correcting also for previous fractures, only UTV-P remained an effective predictor of fracture risk even after QUS measurement correction for BMD. Wrist fractures were best related to BMD-DR (RR 7.33, 95% CI 1.43-37.50) and UTV-DR (RR 10.94, 95% CI 1.10-108.45), while hip and ankle fractures were significantly associated only with UTV-P (hip: RR 32.14, 95% CI 1.83-562.80; ankle: RR 17.60, 95% CI 1.78-173.79). The combined use of BMD and QUS is a better predictor of fracture risk than either technique used separately. Comparison of the areas under the receiver operating characteristic (ROC) curves did not show differences in the ability of BMD and QUS to correctly distinguish fractures. In conclusion, QUS predicts fracture risk in osteoporotic women at least as well as BMD. UTV-DR and BMD-DR are good predictors of wrist fractures, while UTV-P is strongly related to hip and ankle fractures. QUS and BMD combined improve the diagnostic ability of each technique individually.

Nucleation kinetics of emulsified triglyceride mixtures

AbstractThe purpose of this study is to determine character istic nucleation parameters such as the surface free energy for nucleus formation in mixtures of fully hydrogenated palm oil (HP) in sunflower oil (SF). These parameters will be used to model the bulk crystallization kinetics of the same mixtures. This was achieved by determining the crystallization kinetics in emulsified triglyceride mixtures using differential scanning calorimetry, proton nuclear magnetic resonance, and ultrasound velocity measurements. The latter technique appeared to be very sensitive for monitoring the crystallization kinetics of fat dispersions containing triglycerides with a simple phase behavior. Isothermal crystallization of emulsified HP stabilized by sodium caseinate started at 7 K below the α clear point, and the kinetics were best fitted assuming heterogeneous nucleation. Isothermal crystallization of emulsified 10% HP in SF stabilized by caseinate started at 14 K below the α melting point, and the kinetics were best fitted assuming homogeneous nucleation. If the same dispersion was stabilized by Tween 20, crystallization started at 11 K below the α melting point, and the kinetics were fitted best using heterogeneous nucleation. Analysis of the temperature dependency of the fit parameters yielded a surface free energy of a nucleus of about 4 mJ.m−2 in the case of homogeneous nucleation. Pre‐exponential nucleation frequencies indicated that a large proportion of the triglyceride molecule should be in the right conformation to be incorporated in a nucleus.

On-Line Conversion Monitoring Through Ultrasound Velocity Measurements in Bulk Styrene Polymerization in a Recycle Reactor. Part II: Mathematical Model

This paper is the second part of a description of the online monitoring through ultrasound propagation velocity measurements of styrene polymn. in a continuous recycle reactor. A set of calibrations and a simple math. model are proposed to interpret the exptl. ultrasound propagation velocity measurements during the course of bulk and soln. polymns. The validity of this new method is shown by comparison of values obtained by Ultrasound Propagation Velocity (UPV) and traditional techniques. The model allows a good description of the exptl. results. [on SciFinder (R)]

Process monitoring of moulding compounds by ultrasonic measurements in a compression mould

Current research addresses ultrasonic quality sensor utilisation for inline cure monitoring, to control and analyse compression moulding. In this investigation, an ultrasonic impulse transmission method was applied to directly monitor changes in the mechanical properties of moulding compounds throughout the whole cure cycle. These measurements were performed during the processing using transducers which were designed to operate at elevated temperature and pressure in a compression mould. Measurements of ultrasound velocity and variation of attenuation coefficient of longitudinal waves were performed following the cure cycle. Ultrasonic measurements were used to investigate the influence of different types of moulding compounds, artificial weathering at elevated temperatures, filler volume, moisture content as well as amount of hardener on the curing process.

Implementation of spectral width Doppler in pulsatile flow measurements

In this paper, we present an automatic beam-vector (Doppler) angle and flow velocity measurement method and implement it in pulsatile flow measurements using a clinical Doppler ultrasound system. In current clinical Doppler ultrasound flow velocity measurements, the axis of the blood vessel needs to be set manually on the B-scan image to enable the estimation of the beam-vector angle and the beam-vector angle corrected flow velocity (the actual flow velocity). In this study, an annular array transducer was used to generate a conical-shaped and symmetrically focused ultrasound beam to measure the flow velocity vectors parallel and perpendicular to the ultrasound beam axis. The beam-vector angle and flow velocity is calculated from the mode frequency ( f d ) and the maximum Doppler frequency ( f max) of the Doppler spectrum. We develop a spectrum normalization algorithm to enable the Doppler spectrum averaging using the spectra obtained within a single cardiac cycle. The Doppler spectrum averaging process reduces the noise level in the Doppler spectrum and also enables the calculation of the beam-vector angle and flow velocity for pulsatile flows to be measured. We have verified the measurement method in vivo over a wide range of angles, from 52° to 80°, and the standard deviations of the measured beam-vector angles and flow velocities in the carotid artery are lower than 2.2° and 12 cm/s (about 13.3%), respectively.

Acoustical Method for Investigation of Pressure Influence on Absorption in Liquids

In this paper, the set-up for measurements of ultrasound velocity and absorption, as a function of pressure, is described. There are also presented some results of such research in liquid tetrahydrothiophene.

Thermodynamic Study of the Aggregation Behavior of Sodium n-Hexyl Sulfate in Aqueous Solution

The self-association of sodium n-hexyl sulfate (SHS) in aqueous solution has been examined at 25.0 and 35.0 °C. The critical micellar concentration (cmc) and the degree of counterion binding, β, were determined by conductivity measurements at 25.0 °C. Both quantities were used to calculate the standard Gibbs energy change on micellization. The standard enthalpy change on aggregation was measured by microcalorimetry at the same temperature. Good agreement has been found when comparing with the properties of other sodium alkyl sulfates. Densities were measured at the same temperatures. The apparent molal volumes and partial molal volumes have been evaluated at concentrations above and below the cmc. The change in partial molal volumes in the formation of micelles has been evaluated from these measurements. Ultrasound velocity measurements were used to obtain the cmc in water. Apparent adiabatic compressibilities were calculated from a combination of density and ultrasound velocity measurements. Surface tension was measured at a temperature of 25.0 °C. Surface properties were calculated from these data.

Titanium Powder Sintering for Preparation of a Porous FGM Destined as a Skeletal Replacement Implant

This contribution refers to basic research into a functionally graded material (FGM) as a permanent skeletal replacement implant with improved properties. The latter concerns elastic adaptation and structural compatibility in order to achieve faster bone tissue ingrowth and better long-term stability. Target is a sintered porous coating on a compact substrate with a perpendicular gradient of the porosity and, hence, of the Young's modulus. To achieve optimal porosity and pore size, coarse Ti powder fractions with diameters of up to 1000 μm were chosen. Additionally, an acceleration of the sintering progress was attempted using fine-grained secondary powder components, such as silicon or titanium hydride. Preliminarily, beam-like model specimens without gradient were produced to elucidate how powder characteristics and processing influence the general sinter behaviour, porosity, strength, and elastic properties. Silicon-assisted liquid phase sintenng (LPS) resulted in a substantial increase of the neck diameter (≤ 500 μm) and the strength of the sinter contacts. Milling the powder mixture was found to he superior to liquid-dispersed approaches in regard of uniform distribution of Si. The Young's modulus determined by ultrasound velocity measurements ranged from 5 to 80 GPa, covering typical values of cortical bone (12÷23 GPa). In dependence on porosity, a correlation was perceivable as predicted by application of the effective medium approach (EMA). Specimens with porosity gradients were successfully fabricated and characterized using acoustic microscopy and quantitative description of the microstructural geometry.

Acoustic and ultrasonic tissue characterization--assessment of osteoporosis.

Osteoporosis, often termed the 'silent epidemic', has been defined as 'a decrease in bone mass and architectural deterioration of bone tissue, leading to enhanced bone fragility and consequent increase in fracture risk'. In the United Kingdom alone, the annual health costs are in excess of 750 million Pounds, with 60,000 patients suffering a hip fracture each year. A quarter of these will die within 12 months of their fracture, half of the remainder will never regain independent living. The established procedure for assessing the risk of osteoporotic fracture is via bone mineral density (BMD) assessment using dual-energy X-ray absorptiometry (DXA). However, DXA is an expensive technique and is not widely available. Within the past 15 years, ultrasound assessment of bone has rapidly advanced in scientific understanding, technical development and clinical utility. Measurements of cancellous bone (particularly at the calcaneus) are generally performed in preference to those of cortical bone (tibial cortex). There are currently 15 commercial systems available and over 3500 systems are in use world-wide. The low cost and portability offered by ultrasound systems should enable an integrated community-based screening programme to be established in the near future. Ultrasound measurements of bone are generally obtained using transmission rather than pulse-echo techniques owing to its highly attenuating nature. Ultrasound velocity and attenuation measurements are utilized. For velocity, there are well-defined fundamental relationships describing the dependence upon the elasticity and density of bone.

Inline process monitoring of thermosets by ultrasonic measurements in a compression mould

Moulding compounds are heterogeneous materials and consist of granules or pellets, usually mixed with a special resin-hardener combination, reinforcing agents, accelerators, lubricants, pigments, and other additives ready for manufacturing. Thermosetting moulding compounds are defined as raw materials manufacturing plastic parts under the influence of pressure and heat, mainly by compression, transfer, and injection moulding. Current research addresses ultrasonic quality sensor utilization for inline cure monitoring, to control and analyze compression moulding. A ‘‘smart’’ process control would require the measurement of elastic moduli and viscosity during cure. In this research, an ultrasonic impulse-transmission method is used to directly monitor changes in the mechanical properties of moulding compounds throughout the cure cycle. Measurements were performed during the processing using transducers which were designed to operate at elevated temperatures and pressures in a compression mould. Measurements of ultrasound velocity and change of attenuation coefficient of longitudinal and shear waves were made throughout the process cycle. Use was made of the ultrasonic measurements to monitor the influence of various parameters on the manufacturing process, such as filler concentration, humidity content, artificial weathering at elevated temperatures, and hardener concentration. [Work supported by Deutsche Forschungsgemeinschaft (DFG).]

Elastic Anomalies and Acoustic de Haas-van Alphen Effects in Sr2RuO4

Ultrasound velocity measurements based on a phase comparison method for four different modes have been done on a copper-free layered perovskite superconductor Sr 2 RuO 4 with T c = 1.2 K. Anomalous softening is observed in the longitudinal C 11 and C 33 modes below 108 K, which is attributed to the coupling of the electronic states to the strain with Γ 1 representation in the tetragonal point group D 4h . The discontinuous change of the slope in C 11 and C 33 at T c is basically explained by the second-order strain dependence of T c , ∂ 2 T c /∂e 2 uk . From the initial slope of the upper critical field H c2 , the anisotropy ratio in the coherence length is found to be 28, in agreement with previous ac susceptibility measurements. Acoustic de Haas-van Alphen oscillations for the cylindrical α-Fermi surface with 3.2 m 0 are observed in C 33 as a function of the magnetic field applied perpendicular to the Q2D conducting plane. The area coefficient is evaluated to be ∣Λ zz ∣ = 20±5 from the Kataoka-Goto mode...

A Study of the Aggregation Behavior of Hexyltrimethylammonium Bromide in Aqueous Solution

The self-association of n-hexyltrimethylammonium bromide (C6TAB) in aqueous solution has been examined as a function of temperature and electrolyte concentration. The critical micelle concentration (CMC) and the degree of counterion binding (β) were determined by conductivity measurement at temperatures over the range 288.15–318.15 K. Ultrasound velocity measurements were used to obtain the CMC in water and in a range of concentrations of electrolyte (0.1 to 0.6 mol kg−1NaBr) and static light scattering to obtain the aggregation number and the degree of counterion binding in water at 298.15 K. The enthalpy change on micellization in water was measured by microcalorimetry. Apparent adiabatic compressibilities were calculated from a combination of density and ultrasound velocity measurements. Changes in the thermodynamic properties on micellization were determined by applying the mass action model; good agreement was found between experimental and theoretical enthalpy changes. From comparison with the properties of other n-alkyltrimethylammonium bromides it has been shown that the CMC of C6TAB in water is lower than that predicted from the linear relationships between CMC and the number of carbon atoms in the alkyl chain. Similarly, the standard Gibbs energy of micellization is less negative than predicted, and the degree of counterion binding is much lower than for other CnTABs. It is suggested that the anomalous behavior of C6TAB is a consequence of the more highly organized core of the aggregates of very low aggregation number (3–4) and the high degree of exposure of the micellar components to the aqueous environment.

Reproducibility and diagnostic sensitivity of ultrasonometry of the phalanges to assess osteoporosis

Objective: The present study was designed to assess the reproducibility and the diagnostic sensitivity of the amplitude-dependent speed of sound (SoS) at the distal metaphysis of the proximal phalanges. Method: Fourteen presumably healthy volunteers were repeatedly measured every 6 weeks for approximately 6 months in order to assess the reproducibility of the SoS of the phalanges. We recruited 91 post-menopausal women, aged 55–75 years, who were divided in three groups according to their lumbar bone mineral density (BMD) and the existence of prevalent vertebral fractures. The objective was to evaluate the diagnostic sensitivity of SoS measurements. We used DBM Sonic 1200 equipment, and assessed the velocity at which US cross the phalanx in a lateral-medial direction. In post-menopausal women, BMD was measured by dual energy X-ray absorptiometry (DXA) at the level of the lumbar spine, the total zone of the non-dominant hip and the femoral neck zone of the non-dominant hip. Results: The precision of the SoS measurements was 0.71±0.05% (mean±S.E.M) whereas the reproducibility was 0.95±0.06%. Subjects with low BMD or prevalent fractures had significantly lower values of SoS ( P<0.001) than the controls. ROC curve analysis applied to the study population confirmed that SoS was able to discriminate between the controls and osteoporotic subjects (area under the ROC curves were 0.82 (low bone mineral density) and 0.85 (prevalent fractures), respectively). Hip BMD was found to be the most significant variable when comparing the controls and the low density patients by stepwise discrimination and SoS significantly improved the discrimination between the groups when added to the hip BMD. The hip BMD was again the most discriminant variable when applying the same techniques to controls and patients with prevalent fractures, followed by SoS and lumbar BMD. A cut-off value of 1881 m/s is defined for SoS by logistic discrimination and likelihood ratio function. With this value, the sensitivity and the specificity for SoS used in the diagnosis of established osteoporosis were, 81.5% and 79.3%, respectively. Sensitivity and specificity were significantly improved when combining ultrasonometry and densitometry. Conclusion: Measurement of ultrasound velocity at the phalanges appears to be a precise and reproducible technique. SoS discriminates between normal post-menopausal women and patients with either low lumbar BMD or prevalent fractures to the same extent as BMD measurements.

Sound-tissue interaction: the physical basis of bone ultrasonometry and limitations of existing methods.

Ultrasound measurements of bone are generally obtained using transmission rather than pulse-echo techniques because of its highly attenuating nature. Ultrasound velocity and attenuation measurements are utilized. For velocity, there are well-defined fundamental relationships describing the dependence on the elasticity and density of bone. However, the practical implementation and signal processing of velocity measurements has led to a significant variability in results from different commercial systems. We may measure either phase of group velocity, for the latter, adopting a range of pulse arrival definitions. We are offered bone velocity, heel velocity, time of flight, and amplitude-dependent velocity. For attenuation measurements, however, the reverse is true. We generally record the increase in attenuation with frequency (0.2-0.6 MHz), termed broadband ultrasound attenuation (BUA). Although first described in 1984, because of the complex interplay of attenuation mechanisms, there still lacks a fundamental understanding of the dependence of BUA on the material and structural properties of cancellous bone. With the increasing number of commercial systems available, there is an urgent need to understand the intrinsic (artefact free) and system estimation of ultrasound velocity and attenuation parameters that may be implemented to characterise bone and provide clinical information.

Hydration of Polyethylene Glycol-Grafted Liposomes

This study aimed to characterize the effect of polyethylene glycol of 2000 molecular weight (PEG 2000) attached to a dialkylphosphatidic acid (dihexadecylphosphatidyl (DHP)-PEG 2000) on the hydration and thermodynamic stability of lipid assemblies. Differential scanning calorimetry, densitometry, and ultrasound velocity and absorption measurements were used for thermodynamic and hydrational characterization. Using a differential scanning calorimetry technique we showed that each molecule of PEG 2000 binds 136 ± 4 molecules of water. For PEG 2000 covalently attached to the lipid molecules organized in micelles, the water binding increases to 210 ± 6 water molecules. This demonstrates that the two different structural configurations of the PEG 2000, a random coil in the case of the free PEG and a brush in the case of DHP-PEG 2000 micelles, differ in their hydration level. Ultrasound absorption changes in liposomes reflect mainly the heterophase fluctuations and packing defects in the lipid bilayer. The PEG-induced excess ultrasound absorption of the lipid bilayer at 7.7 MHz for PEG-lipid concentrations over 5 mol % indicates the increase in the relaxation time of the headgroup rotation due to PEG-PEG interactions. The adiabatic compressibility (calculated from ultrasound velocity and density) of the lipid bilayer of the liposome increases monotonically with PEG-lipid concentration up to ∼7 mol %, reflecting release of water from the lipid headgroup region. Elimination of this water, induced by grafted PEG, leads to a decrease in bilayer defects and enhanced lateral packing of the phospholipid acyl chains. We assume that the dehydration of the lipid headgroup region in conjunction with the increase of the hydration of the outer layer by grafting PEG in brush configuration are responsible for increasing thermodynamic stability of the liposomes at 5–7 mol % of PEG-lipid. At higher PEG-lipid concentrations, compressibility and partial volume of the lipid phase of the samples decrease. This reflects the increase in hydration of the lipid headgroup region (up to five additional water molecules per lipid molecule for 12 mol % PEG-lipid) and the weakening of the bilayer packing due to the lateral repulsion of PEG chains.