Axial strain calculation using a low-pass digital differentiator in ultrasound elastography

In ultrasound elastography, tissue axial strains are calculated from the gradient of the estimated axial displacements. However, the common differentiation operation amplifies the noises in the displacement estimation, especially at high frequencies. In this paper, a low-pass digital differentiator (LPDD) is proposed to calculate the axial strain from the estimated tissue displacement. Several LPDDs that have been well developed in the field of digital signal processing are presented. The corresponding performances are compared qualitatively and quantitatively in computer simulations and in preliminary phantom and in vitro experiments. The results are consistent with the theoretical analysis of the LPDDs.     

Testing the limitations of 2-D companding for strain imaging using phantoms

Companding may be used as a technique for generating low-noise strain images. It involves warping radio-frequency echo fields in two dimensions and at several spatial scales to minimize decorrelation errors in correlation-based displacement estimates. For the appropriate experimental conditions, companding increases the sensitivity and dynamic range of strain images without degrading contrast or spatial resolution significantly. In this paper, we examine the conditions that limit the effectiveness of 2-D local companding through a series of experiments using phantoms with tissue-like acoustic and elasticity properties. We found that strain noise remained relatively unchanged as the applied compression increased to 5% of the phantom height, while target contrast increased in proportion to the compression. Controlling the image noise at high compressions improves target visibility over the broad range induced in elastically heterogeneous media, such as biological tissues. Compressions greater than 5% introduce large strains and complex motions that reduce the effectiveness of companding. Control of boundary conditions and ultrasonic data sampling rates is critical for a successful implementation of our algorithms.     

Three-dimensional spatial and temporal temperature imaging in gel phantoms using backscattered ultrasound

Thermal therapies such as radio frequency, heated saline, and high-intensity focused ultrasound ablations are often performed suboptimally due to the inability to monitor the spatial and temporal distribution of delivered heat and the extent of tissue necrosis. Ultrasound-based temperature imaging recently was proposed as a means to measure noninvasively the deposition of heat by tracking the echo arrival time shifts in the ultrasound backscatter caused by changes in speed of sound and tissue thermal expansion. However, the clinical applicability of these techniques has been hampered by the two-dimensional (2-D) nature of traditional ultrasound imaging, and the complexity of the temperature dependence of sound speed for biological tissues. In this paper, we present methodology, results, and validation of a 3-D spatial and temporal ultrasound temperature estimation technique in an alginate-based gel phantom to track the evolution of heat deposition over a treatment volume. The technique was experimentally validated for temperature rises up to approximately 10 degrees C by comparison with measurements from thermocouples that were embedded in the gel. Good agreement (rms difference = 0.12 degrees C, maximum difference = 0.24 degrees C) was observed between the noninvasive ultrasound temperature estimates and thermocouple measurements. Based on the results obtained for the temperature range studied in this paper, the technique demonstrates potential for applicability in image guidance of thermal therapy for determining the location of the therapeutic focal spot and assessing the extent of the heated region at subablative intensities.     

A time-efficient and accurate strain estimation concept for ultrasonic elastography using iterative phase zero estimation

In ultrasonic elastography, the exact estimation of temporal displacements between two signals is the key to estimating strain. An algorithm was previously proposed that estimates these displacements using phase differences of the corresponding base-band signals. A major advantage of these algorithms compared with correlation techniques is the computational efficiency. In this paper, an extension of the algorithm is presented that iteratively takes into account the time shifts of the signals to overcome the problems of aliasing and accuracy in the estimation of the phase shift. Thus, it can be proven that the algorithm is equivalent to the search of the maximum of the correlation function. Furthermore, a robust logarithmic compression is proposed that only compresses the envelope of the signal. This compression does not introduce systematic errors and significantly reduces decorrelation noise. The resulting algorithm is a computationally simple and very fast alternative to conventional correlation techniques, and the accuracy of strain images is improved.     

Inducing and imaging thermal strain using a single ultrasound linear array

For the first time, the feasibility of inducing and imaging thermal strain using an ultrasound imaging array is demonstrated. A commercial ultrasound scanner was used to heat and image a gelatin phantom with a cylindrical rubber inclusion. The inclusion was successfully characterized as an oil-bearing material using thermal strain imaging.     

Estimations of fiber Bragg grating parameters and strain gauge factor using optical spectrum and strain distribution information

An inverse approach based on an optimization technique is proposed to characterize a fiber Bragg grating (FBG) and the strain gauge factor (GF) when the FBG is bonded on a structure. By bonding an FBG on a substrate and simply straining this FBG into a chirped fiber Bragg grating with a predesignated strain, the proposed method, based on an optimization technique, can be used to reconstruct seven parameters of the FBG from the corresponding reflective spectrum. The parameters identified are the length of an FBG, the grating period, the average refractive index, the index modulation, the apodization coefficient, the starting point bonded on the plate, and the strain GF. The information from the predesignated strain, as well as the measured reflective spectrum, is used as the objective function during the optimal search. As a result, the design sensitivity for the optimal search is much improved compared with the design sensitivity when only the reflective spectrum is used. In particular, the strain GF, which depends on the adhesive, the bonding layer characteristics, etc., can be determined in order to provide a reference for an FBG used as a strain sensor. Results from numerical simulations and experiments show that seven parameters of an FBG can be obtained accurately and efficiently.     

Determination of strain field and heterogeneity in radial forging of tube using finite element method and microhardness test

Utilizing the Finite Element Method (FEM), the strain field in the radial forging process of tube is calculated at different process conditions and compared with the experimental results achieved using the microhardness test. The effect of various process parameters such as friction, axial feed, back push and front pull forces and die angles on the strain field are investigated. Using the results of the analysis, it is shown that the deformation inhomogeneity, introduced by an Inhomogeneity Factor (IF), is maximum in the inner zone of tube, while the minimum and the maximum effective strains are appeared at the inner zone of tube and about the core of the tube thickness, respectively. Also, it was found that inhomogeneity decreases by increasing the die angle, decreasing the back push force and decreasing the friction factor.     

Quantitative assessment on the orientation and distribution of carbon fibers in a conductive polymer composite using high-frequency ultrasound

Conductive polymer composites, typically fabricated from a mix of conductive fillers and a polymer substrate, are commonly applied as bipolar plates in a fuel cell stack. Electrical conductivity is a crucial property that greatly depends on the distribution and orientation of the fillers. In this study, a 50-MHz ultrasound imaging system and analysis techniques capable of nondestructively assessing the properties of carbon fibers (CFs) in conductive polymer composites were developed. Composite materials containing a mix of polycarbonate substrates and 0 to 0.3 wt% of CFs were prepared using an injection molding technique. Ultrasonic A-line signals and C-scan images were acquired from each composite sample in regions at a depth of 0.15 mm beneath the sample surface (region A) and those at a depth of 0.3 mm (region B). The integrated backscatter (IB) and the Nakagami statistical parameter were calculated to quantitatively assess the samples. The area ratio, defined as the percentage of areas composed of CF images normalized by that of the whole C-scan image, was applied to further quantify the orientation of CFs perpendicular to the sample surface. Corresponding to the increase in CF concentrations from 0.1 to 0.3 wt%, the average IB and Nakagami parameter (m) of the composite samples increased from -78.10 ± 2.20 (mean ± standard deviation) to -72.66 ± 1.40 dB and from 0.024 ± 0.012 to 0.048 ± 0.011, respectively. The corresponding area ratios were respectively estimated to be 0.78 ± 0.35%, 2.33 ± 0.66%, and 2.20 ± 0.60% in region A of the samples; those of CFs with a perpendicular orientation were 0.04 ± 0.03%, 0.08 ± 0.02%, and 0.12 ± 0.05%. The area ratios in region B of the samples were calculated to be 1.19 ± 0.54%, 2.81 ± 0.42%, and 2.64 ± 0.76%, and those of CFs with a perpendicular orientation were 0.07 ± 0.04%, 0.12 ± 0.04%, and 0.14 ± 0.03%. According to the results of the orientations and ultrasonic images, CFs tended to distribute more uniformly in the deeper regions of the samples. This study validates that the distribution and orientation of CFs in conductive polymer composites could be sensitively and quantitatively assessed by high-frequency ultrasound in conjunction with current analysis methods.     

Ultrasound-based radial and longitudinal strain estimation of the carotid artery: a feasibility study

Ultrasound-based estimation of arterial wall elasticity is commonly used to assess arterial stiffness. However, previous elastography studies have mostly addressed radial strain measurements, and the longitudinal strain has been more or less ignored. This study shows the feasibility of a speckle-tracking-based algorithm for simultaneous estimation of radial and longitudinal strain in the carotid artery in silico. Additionally, these results were preliminarily confirmed in vivo.     

Study of the structure of As0.3Se0.2S0.4Ge0.1 chalcogenide glass using the radial distribution function

In the present work, the structure of As_0.3Se_o.3S_0.4Ge_0.1 chalcogenide glass has been studied using the radial distribution function (RDF). Moreover, the effect of annealing temperature on the short range order of this glass has been investigated. The results revealed that the short range order structure of the as-prepared and annealed As_0.3Se_0.2S_0.4Ge_0.1 chalcogenide glass is close to a regular tetrahedron. The medium range order of As_0.3Se_0.4S_0.4Ge_0.1 chalcogenide glass is topology order. The topological structure of the medium range order can be described by the Phillips model. The structure of As_0.3Se_0.2S_0.4Ge_0.1 chalcogenide glass is stable in the annealing temperature range 324–523 K.     

Local ordering structure of meta-kaolinite and meta-dickite by the X-ray radial distribution function analysis

X-ray diffraction measurements on the structure of meta-kaolinite and meta-dickite have been carried out to obtain the radial distribution function (RDF). The distances and corresponding coordination numbers for Si-O and Al-O pairs were estimated by applying the pair function method. The SiO₄ tetrahedron remains unchanged in the dehydrated samples presently investigated, and the oxygen coordination number around aluminium was also found to be four. This implies the overall preference of AlO₄ tetrahedron at the expense of the parent AlO₂ (OH)₄ octahedron.     

Evaluation of interfacial shear stress between multi-walled carbon nanotubes and epoxy based on strain distribution measurement using Raman spectroscopy

This study investigated the stress recovery of aligned multi-walled carbon nanotubes (MWCNTs) embedded in epoxy using Raman spectroscopy, and evaluated interfacial shear stress between MWCNTs and epoxy using shear-lag analysis. To this end, ultralong aligned MWCNTs (3.8 mm long) were embedded in epoxy to obtain Raman spectra at multiple points along the MWCNTs. Downshift of the G′-band due to tensile strain was measured from the nanotube end to the center, and the strain distribution of embedded MWCNTs was evaluated successfully. Interfacial shear stress was then estimated by minimizing the error between the shear-lag analysis and measured strain distribution. The maximum interfacial shear stress between the embedded MWCNTs and epoxy was 10.3–24.1 MPa at the failure strain of aligned MWCNT-reinforced epoxy composites (0.46% strain). Furthermore, the interfacial shear stress between an individual MWCNT and epoxy was investigated.     

Energy balance and stability of crack propagation within the limits of the strain criterion of failure

According to the materials presented at 1st All-Union Conference on Fracture Mechanics of Materials, Lvov, October 20–22, 1987.     

Superresolution of ultrasound images using the first and second harmonic signal

This paper presents a new method of blind two-dimensional (2-D) homomorphic deconvolution and speckle reduction applied to medical ultrasound images. The deconvolution technique is based on an improved 2-D phase unwrapping scheme for pulse estimation. The input images are decomposed into minimum-phase and allpass components. The 2-D phase unwrapping is applied only to the allpass component. The 2-D phase of the minimum-phase component is derived by a Hilbert transform. The accuracy of 2-D phase unwrapping is also improved by processing small (16 x 16 pixels) overlapping subimages separately. This takes the spatial variance of the ultrasound pulse into account. The deconvolution algorithm is applied separately to the first and second harmonic images, producing much sharper images of approximately the same resolution and different speckle patterns. Speckle reduction is made by adding the envelope images of the deconvolved first and second harmonic images. Neither the spatial resolution nor the frame rate decreases, as the common compounding speckle reduction techniques do. The method is tested on sequences of clinical ultrasound images, resulting in high-resolution ultrasound images with reduced speckle noise.     

Effect of ultrasound radiation on the size and size distribution of synthesized copper particles

The effect of ultrasound radiation on the size and size distribution of synthesized copper particles was investigated under various concentrations of ethylene glycol (E.G.) as a capping agent. Monodispersed copper particles were produced by the reduction of an aqueous copper (II) sulfate solution at the presence of hydrazine monohydrate. X-ray diffraction and scanning electron microscopy analysis revealed that the morphology, size, and size distribution of produced particles were influenced by the reducing agent injection rate, capping agent concentration, and sonication. Increasing the injection rate of reducing agent to an amount higher than a critical value decreases the size of copper particles and also converts the monodispersed particles to polydispersed particles. Results of using a sonifier at the reduction stage revealed that finer monodispersed copper particles can be achieved at higher injection rates related to the critical value. Increasing the concentration of E.G. as a capping agent decreases the size of copper particles, while applying ultrasound radiation along with increasing the concentration of E.G. increases the size of copper particles. Morphology of particles varies by the concentration and type of the capping agent. Higher reducing agent injection rates and the application of a sonifier at the instance of reduction result in smaller spherical particles at various capping agent concentrations.     

Monte Carlo simulation of radial distribution of DNA strand breaks along the C and Ne ion paths

Radial energy deposition distribution, the distribution of DNA strand breaks and their yields were simulated by Monte Carlo track structure simulation for C and Ne ions with the same linear energy transfer (LET) around 450 keV/μm. The radial DNA damage distribution shows different pattern for C and Ne ions. Double strand break (DSB) are mostly formed in the central area, while the single strand break (SSB) tends to spread to the surrounding area. It is also shown that the production efficiency of the SSB and DSB depends on the radial distance. This result shows reasonable agreement with the recently obtained experimental observation, which indicates that different types of DNA damage shows different distribution patterns around C and Ne ion paths in cell nuclei.     

Contact-free measurement and numerical and analytical evaluation of the strain distribution in a wood-FRP lap-joint

Wood specimens to each of which a laminate of carbon fibre reinforcement polymers (FRP) was glued (creating a lap joint in each case) were loaded to failure. A total of 15 specimens of three types differing in the glued length (anchorage length) of the FRP laminate (50, 150 and 250 mm respectively) were tested, their strength, stiffness and strain distribution being evaluated. Synchronized digital cameras (charge-coupled devices) used in testing enabled strain fields on surfaces they were directed at during the loading procedure to be measured. These results were also evaluated both analytically on the basis of generalized Volkersen theory and numerically by use of the finite element method. The lap joints showed a high level of stiffness as compared with mechanical joints. A high degree of accuracy in the evaluation of stiffness was achieved through the use of the contact-free evaluation system. The load-bearing capacity of joints of this type was found to be dependent upon the anchorage length in a non-linear fashion. The experimental, analytical and numerical results were shown to be in close agreement with respect to the strength and the strain distribution obtained.