Ultrasound Transmission Measurements Research Articles

Concrete anisotropy estimated from ultrasonic signal amplitudes

Abstract The anisotropy of concrete is an essential issue in the construction industry. In this study, for the first time, ultrasonic compression and shear wave signals have been investigated for the orthogonal directions of unreinforced concrete by means of fast Fourier transformation (FFT). For this purpose, cubic concrete samples were prepared in 12 designs of different strengths for ultrasound transmission measurements. The characteristic amplitudes at dominant frequencies were determined by the FFT of these signals. The FFT amplitude differences in the compression and the shear wave signals on the orthogonally oriented surfaces provide essential information about the presence and degree of anisotropy. According to linear regression analysis, the FFT amplitude anisotropies and the amplitude ratios of the compression and shear waves decreased significantly according to increasing concrete strength. In addition, it was found that the anisotropy and the ratio of the FFT amplitudes increased proportionally to the water/cement ratio, the porosity and the water content of the various concrete designs.

A Lagrange-Newton Method for EIT/UT Dual-Modality Image Reconstruction.

An image reconstruction method is proposed based on Lagrange-Newton method for electrical impedance tomography (EIT) and ultrasound tomography (UT) dual-modality imaging. Since the change in conductivity distribution is usually accompanied with the change in acoustic impedance distribution, the reconstruction targets of EIT and UT are unified to the conductivity difference using the same mesh model. Some background medium distribution information obtained from ultrasound transmission and reflection measurements can be used to construct a hard constraint about the conductivity difference distribution. Then, the EIT/UT dual-modality inverse problem is constructed by an equality constraint equation, and the Lagrange multiplier method combining Newton-Raphson iteration is used to solve the EIT/UT dual-modality inverse problem. The numerical and experimental results show that the proposed dual-modality image reconstruction method has a better performance than the single-modality EIT method and is more robust to the measurement noise.

Acoustic transmission from a single crystal layer of nonlinear resonators in a soft elastic matrix

Ultrasound transmission measurements of a single crystal layer of identical nonlinear resonators are reported for frequencies under 1 MHz. The resonators are spherical gas-filled cavities embedded in a soft elastic matrix. The cavities are formed by injection of gas through a capillary tube in a polymer solution right before it cures. Sample characteristics such as the size or the spacing between the cavities are adjusted by varying the injection parameters. Typical size for the cavities ranges from 100 μm to 1 mm. The sample is immersed in water where transmission measurements are conducted. As allowed by acoustic transducer, amplitude and phase of the wave is measured in transmission as a function of the frequency and the amplitude of the initial incident pulse.

Multiscale assessment of cortical bone properties with quantitative ultrasound

Clinical bone quality assessment still relies strongly on bone mineral density (BMD). It is now well accepted that BMD predicts only around 60% of the individual fracture risk because it depends on geometrical dimensions of the bone and mechanical properties of its cortical shell. The tibia mid-shaft is a clinically relevant site for ultrasound axial transmission (AT) measurements, which allow simultaneous assessment of cortical thickness (Ct.Th) and tissue elasticity. This ex-vivo study investigated 19 representative human tibiae (native samples, mid-shaft, age range: 69–94 yrs) using AT with the aim to develop novel ultrasound biomarkers of cortical bone loss. Ct.ThAT was in good agreement with corresponding data from micro-computed tomography (R2 = 0.90). Resonant ultrasound spectroscopy was used to measure the transverse isotropic elasticity tensor of extracted bone cubes. Strong linear correlation between axial stiffness (c33) and mass density (R2 = 0.86) was found. Mechanical testing based strength was moderately correlated to c33 (R2 = 0.72) and mass density (R2 = 0.65). These findings indicate the potential of cortical elasticity to be an adequate biomarker of bone quality which combined with information about bone geometry (e.g., Ct.Th) could improve clinical fracture risk assessment.

Quantitative evaluation of polymer gel dosimeters by broadband ultrasound attenuation

Ultrasound has been examined previously as an alternative readout method for irradiated polymer gel dosimeters, with authors reporting varying dose response to ultrasound transmission measurements. In this current work we extend previous work to measure the broadband ultrasound attenuation (BUA) response of irradiated PAGAT gel dosimeters, using a novel ultrasound computed tomography system.

Experimental and simulation results on the effect of cortical bone mineralization in ultrasound axial transmission measurements: A model for fracture healing ultrasound monitoring

Ultrasound axial transmission (UAT), a technique using propagation of ultrasound waves along the cortex of cortical bones, has been proposed as a diagnostic technique for the evaluation of fracture healing. Quantitative ultrasound parameters have been reported to be sensitive to callus changes during the regeneration process. The aim of this work was to identify the specific effect of cortical bone mineralization on UAT measurements by means of numerical simulations and experiments using a reverse fracture healing approach. A cortical bovine femur sample was used, in which a 3 mm fracture gap was drilled. A 3 mm thick cortical bone slice, extracted from another location in the bone sample, was submitted to a progressive demineralization process with EDTA during 12 days. UAT measurements and simulations using a 1 MHz probe were performed with the demineralized slice placed into the fracture gap to mimic different stages of mineralization during the healing process. The calcium loss of the slice due to the EDTA treatment was recorded everyday, and its temporal evolution could be modeled by an exponential law. A 50 MHz scanning acoustic microscopy was also used to assess the mineralization degree of the bone slice at the end of the intervention. These data were used in the numerical simulations to derive a model of the time evolution of bone slice mechanical properties. From both the experiments and the simulations, a significant and progressive increase in the time of flight (TOF; p < 0.001) of the propagating waves measured by UAT was observed during the beginning of the demineralization process (first 4 days). Although the simulated TOF values were slightly larger than the experimental ones, they both exhibited a similar time-dependence, validating the simulation approach. Our results suggest that TOF measured in axial transmission is affected by local changes of speed of sound induced by changes in local mineralization. TOF may be an appropriate indicator to monitor callus maturation.

Ultrasound transmission measurements for tensile strength evaluation of tablets

Ultrasound transmission measurements were performed to evaluate the tensile strength of tablets. Tablets consisting of one ingredient were compressed from dibasic calcium phosphate dehydrate, two grades of microcrystalline cellulose and two grades of lactose monohydrate powders. From each powder, tablets with five different tensile strengths were directly compressed. Ultrasound transmission measurements were conducted on every tablet at frequencies of 2.25 MHz, 5 MHz and 10 MHz and the speed of sound was calculated from the acquired waveforms. The tensile strength of the tablets was determined using a diametrical mechanical testing machine and compared to the calculated speed of sound values. It was found that the speed of sound increased with the tensile strength for the tested excipients. There was a good correlation between the speed of sound and tensile strength. Moreover, based on the statistical tests, the groups with different tensile strengths can be differentiated from each other by measuring the speed of sound. Thus, the ultrasound transmission measurement technique is a potentially useful method for non-destructive and fast evaluation of the tensile strength of tablets.

Passive element enriched photoacoustic computed tomography (PER PACT) for simultaneous imaging of acoustic propagation properties and light absorption

We present a 'hybrid' imaging approach which can image both light absorption properties and acoustic transmission properties of an object in a two-dimensional slice using a computed tomography (CT) photoacoustic imager. The ultrasound transmission measurement method uses a strong optical absorber of small cross-section placed in the path of the light illuminating the sample. This absorber, which we call a passive element acts as a source of ultrasound. The interaction of ultrasound with the sample can be measured in transmission, using the same ultrasound detector used for photoacoustics. Such measurements are made at various angles around the sample in a CT approach. Images of the ultrasound propagation parameters, attenuation and speed of sound, can be reconstructed by inversion of a measurement model. We validate the method on specially designed phantoms and biological specimens. The obtained images are quantitative in terms of the shape, size, location, and acoustic properties of the examined heterogeneities.

Computational Evaluation of the Compositional Factors in Fracture Healing Affecting Ultrasound Axial Transmission Measurements

This work aimed at computationally evaluating the compositional factors in fracture healing affecting ultrasound axial transmission (UAT), using four numerical daily-changing healing models, representing more realistic clinical conditions. Using two-dimensional (2-D) simulations, a 1-MHz source and a receiver were positioned parallel to the bone surface to detect the first arriving signal (FAS). The time-of-flight of the FAS ( TOF FAS ) was found to be sensitive only to superficial modifications in the propagation path. It was also shown that callus mature bone better explained alone the variation in TOF FAS ( R 2 ≥ 0.70, p < 0.001). Better TOF FAS predictions are obtained when using the callus composition inside cortical fracture gap ( R 2 = 0.98, p < 0.01). Callus composition could not well explain the changes in energy attenuation. These results suggest that UAT may be an important clinical tool for fracture healing assessment, identifying callus degree of mineralization and possible consolidation delays and nonunions. (E-mail: cbmfisio@gmail.com)

Use of bacteria to repair cracks in concrete

As synthetic polymers, currently used for concrete repair, may be harmful to the environment, the use of a biological repair technique is investigated in this study. Ureolytic bacteria such as Bacillus sphaericus are able to precipitate CaCO 3 in their micro-environment by conversion of urea into ammonium and carbonate. The bacterial degradation of urea locally increases the pH and promotes the microbial deposition of carbonate as calcium carbonate in a calcium rich environment. These precipitated crystals can thus fill the cracks. The crack healing potential of bacteria and traditional repair techniques are compared in this research by means of water permeability tests, ultrasound transmission measurements and visual examination. Thermogravimetric analysis showed that bacteria were able to precipitate CaCO 3 crystals inside the cracks. It was seen that pure bacteria cultures were not able to bridge the cracks. However, when bacteria were protected in silica gel, cracks were filled completely.

Prediction of density and mechanical properties of human trabecular bone in vitro by using ultrasound transmission and backscattering measurements at 0.2–6.7 MHz frequency range

The ultrasound (US) backscattering method has been introduced as an alternative for the through-transmission measurement of sound attenuation and speed in diagnosis of osteoporosis. Both attenuation and backscattering depend strongly on the US frequency. In this study, 20 human trabecular bone samples were measured in transmission and pulse-echo geometry in vitro. The aim of the study was to find the most sensitive frequency range for the quantitative ultrasound (QUS) analyses. Normalized broadband US attenuation (nBUA), speed of sound (SOS), broadband US backscatter (BUB) and integrated reflection coefficient (IRC) were determined for each sample. The samples were spatially scanned with five pairs of US transducers covering a frequency range of 0.2–6.7 MHz. Furthermore, mechanical properties and density of the same samples were determined. At all frequencies, SOS, BUB and IRC showed statistically significant linear correlations with the mechanical properties or density of human trabecular bone (0.51 < r < 0.82, 0.54 < r < 0.81 and 0.70 < r < 0.85, respectively). In contrast to SOS, IRC and BUB, nBUA showed statistically significant correlations with mechanical parameters or density at the centre frequency of 1 MHz only. Our results suggest that frequencies up to 5 MHz can be useful in QUS analyses for the prediction of bone mechanical properties and density. Since the use of higher frequencies provides better axial and spatial resolution, improved structural analyses may be possible. While extensive attenuation of high frequencies in trabecular bone limits the clinically feasible frequency range, selection of optimal frequency range for in vivo QUS application should be carefully considered.

Bone marrow influences quantitative ultrasound measurements in human cancellous bone

Quantitative ultrasound (QUS) transmission and backscatter measurements were made in 46 human cancellous bone specimens from the calcaneus. All QUS measurements were made at 35°C, initially with marrow filling the pores and then repeated after substituting water for marrow. Bone mineral density (BMD) was determined using x-ray absorptiometry. Marrow significantly decreased ultrasound (US) velocity, but increased attenuation, attenuation slope and backscatter ( p < 0.001 for all) compared to the water-saturated state. The impact of marrow on QUS measurements was greater at lower BMD values ( p < 0.05), and was greater in women than in men ( p < 0.05). QUS measurements in marrow-saturated specimens correlated less strongly with BMD than did corresponding measurements in water-saturated specimens ( p < 0.05), consistent with interspecimen marrow heterogeneity. These data indicate that the potential impact of marrow should be considered when interpreting clinical QUS measurements. Understanding and exploiting these effects could lead to novel approaches for ultrasonic characterisation of both bone and marrow. (E-mail: patrick_nicholson@hotmail.com)

Ultrasonic Monitoring of Beef Temperature During Roasting

Ultrasound has appealing properties as a means to monitor quality of industrially manufactured food items. Changes in ultrasonic signal properties are associated with changes in raw material or process parameters. This paper introduces a concept based on an ultrasound transmission measurement which has shown ability to monitor the temperature of minced beef meat during simulated automated roasting. Commercially available beef samples were roasted, and the change in internal temperature of the beef was correlated to changes in the ultrasonic transmission signal. r2values of 0.94 were obtained.

Characterizing bubbles in bioreactors using light or ultrasound probes: Data analysis by classical means and by neural networks

AbstractThe applicability of neural networks to a typical biochemical engineering problem was investigated. The data treatment required for a novel technique for measuring the mean bubble size and the specific interfacial area in aerobic bioreactors was chosen as an appropriate example in case. The new measuring technique is based on either light or ultrasound transmission measurements through the dispersion. The function relating the results of such measurements to bubble size cannot be explicitly modelled. It was therefore approximated by a purely mathematical function fitted to numerically simulated examples. By training neural networks, the same unknown relationship could be mapped with similar or better precision without any prior knowledge of its structure or form and without any physical understanding of the problem.

Ultrasound transmission measurements through the os calcis

A method of measuring ultrasonic propagation in the os calcis was devised for assessing bone properties in humans. Speed-of-sound (SOS) and broadband ultrasound attenuation (BUA) were measured using broadband acoustic pulses transmitted and received by a pair of focused transducers. The transducers are mounted coaxially in a water tank with the subject's heel in between. Reproducibility of results in an adult male was 10% for the BUA and 1.2% for the SOS. Both SOS and BUA changed when the transmission path through the os calcis was varied. For a population of normal male subjects, SOS and BUA were correlated with densitometry results on the os calcis, but less well correlated to area density at remote sites.