Ultrasonic Imaging Method Research Articles

FEA-Based Ultrasonic Focusing Method in Anisotropic Media for Phased Array Systems

Traditional ultrasonic imaging methods have a low accuracy in the localization of defects in austenitic welds because the anisotropy and inhomogeneity of the welds cause distortion of the ultrasonic wave propagation paths in anisotropic media. The distribution of the grain orientation in the welds influences the ultrasonic wave velocity and ultrasonic wave propagation paths. To overcome this issue, a finite element analysis (FEA)-based ultrasonic imaging methodology for austenitic welds is proposed in this study. The proposed ultrasonic imaging method uses a wave propagation database to synthetically focus the inter-element signal recorded with a phased array system using a delay-and-sum strategy. The wave propagation database was constructed using FEA considering the grain orientation distribution and the anisotropic elastic constants in the welds. The grain orientation was extracted from a macrograph obtained from a dissimilar metal weld specimen, after which the elastic constants were optimized using FEA with grain orientation information. FEA was performed to calculate a full matrix of time-domain signals for all combinations of the transmitting and receiving elements in the phased array system. The proposed approach was assessed for an FEA-based simulated model embedded in a defect. The simulation results proved that the newly proposed ultrasonic imaging method can be used for defect localization in austenitic welds.

Using Lamb wave TDTE method to realize ultrasonic array super-resolution imaging of multiple asymmetric defects

Lamb waves are characterized by frequency dispersion and mode conversion. The imaging results obtained with traditional ultrasonic array imaging methods suffer from artifacts, reducing the imaging accuracy. In addition, traditional methods are subjected to the Rayleigh criterion and cannot image multiple defects with spacing smaller than the resolution threshold of ultrasound array imaging. In this paper, an ultrasonic Lamb wave inverse scattering topological imaging method based on time-domain topological energy (TDTE) was proposed. In this method, the topological progressive process of the inverse scattering topological imaging method was transformed into solving the direct and the adjoint sound fields. Then, by inverting the time of the adjoint sound field, the direct and the adjoint sound field can focus adaptively at the defect, which overcomes the influence of Lamb wave mode conversion and dispersion on the imaging results, and improves the imaging accuracy and resolution. Finally, the direct and the adjoint sound field are fused, and the TDTE value was taken as the pixel value of imaging. Accordingly, the limitation of the Rayleigh criterion was broken; the resolution of imaging was improved; the multi asymmetric defect imaging with the interval was realized less than the resolution threshold of the ultrasonic array imaging. The experimental results show that the TDTE method for multiple asymmetric defects can achieve super-resolution than the total focus method (TFM) and time-reversal (TR) method and can accurately distinguish the asymmetric defects when the defect spacing is smaller than the resolution threshold of the ultrasonic array imaging.

Ray tracing method for ultrasonic array imaging of CFRP corner part using homogenization method

A reliable nondestructive evaluation technique that can effectively detect and quantify the internal defects of corner parts in complex-shaped carbon fiber reinforced plastic (CFRP) structures is highly demanded for assuring safety and reliability of safety-critical structures. The conventional methods generally utilize normal incidence ultrasound and suffer from poor image quality due to the unfocused beam. To produce a fully focused image of the CFRP corner part, the delay-and-sum total focusing method (TFM) is preferred. The prerequisite for TFM imaging is to calculate ultrasonic ray paths, which is challenged by the curved shape, elastic anisotropy and multilayered microstructure. In this paper, the complex ultrasonic ray paths transmitting through the corner parts of CFRP structures from the concave side are calculated for ultrasonic array imaging. A ray theory-based homogenization method is firstly proposed to describe the wave velocity distribution of corner parts, which is critically important to the subsequent ray tracing calculation. A ray tracing method based on Dijkstra's algorithm is further developed for rapid calculation of multiple ray paths between two specified points when the ultrasound is incident from the corner's concave surface. To demonstrate the validity of ray tracing method, the TFM images of an CFRP corner part with side drilled holes (SDH) at different depths obtained using three different types of ray paths, are compared and analyzed. Results show that TFM images using ray paths with the minimum or maximum ultrasonic travel time present unsatisfactory image quality due to the obvious structural noises from ply reflections. In contrast, the signal to noise ratio of the image is significantly improved when TFM uses the ray paths with the weakest refraction, and all SDHs are detected and accurately positioned. This paper proves that the proposed ray tracing method is an effective method for imaging the corner parts of CFRP structures.

Reference Phantom Method for Ultrasonic Imaging of Thin Dynamic Constructs

Quantitative ultrasound has a great potential for the non-destructive evaluation of tissue engineered constructs, where the local attenuation and the integrated backscatter coefficient (IBC) can be used for monitoring the development of biological processes. The local determination of both parameters can be achieved using the reference phantom method (RPM). However, its accuracy can be affected when evaluating constructs of evolving sound speed, attenuation and thickness, for example, when evaluating biodegradable hydrogels developing neocartilage. To assess the feasibility of using the RPM under such dynamic conditions while employing a 50-MHz transducer, we conducted a series of experiments on 3-mm-thick acellular hydrogels laden with microspheres. The ultrasonic evaluation procedure used was validated by detecting and compensating for large attenuation variations occurring in the construct, up to 20-fold with respect to the reference phantom, with estimations errors below 1%. We found that sound speed mismatch does not affect the local attenuation estimation, but causes a strong diffraction effect by reducing the backscatter intensity. Such intensity reduction was compensated by determining the IBC percentage change (IBCΔ) as function of sound speed mismatch with respect to the reference phantom (ΔSS), with the equation IBCΔ = (0.63 ± 0.07) ΔSS + (8.54 ± 0.76) 10–3 ΔSS2. The investigated ΔSS interval was up to 120 m/s and using two different concentrations of microspheres, with estimation errors below 7% relative to the construct's actual IBC. Finally, we found that the spectral difference method is sufficient to measure within a few millimetres in depth mismatch, and when combining with sound speed mismatch, we found negligible additional effects. These results pave the way for the use of a generic reference phantom for the evaluation of thin dynamic constructs, thus simplifying the need for using different phantoms depending on the construct's properties.

Biotin-streptavidin-guided two-step pretargeting approach using PLGA for molecular ultrasound imaging and chemotherapy for ovarian cancer.

BackgroundOvarian cancer seriously threatens the lives and health of women, and early diagnosis and treatment are still challenging. Pre-targeting is a promising strategy to improve the treatment efficacy of ovarian cancer and the results of ultrasound imaging.PurposeTo explore the effects of a pre-targeting strategy using streptavidin (SA) and paclitaxel (PTX)-loaded phase-shifting poly lactic-co-glycolic acid (PLGA) nanoparticles with perfluoro-n-pentane (PTX-PLGA-SA/PFPs) on the treatment and ultrasound imaging of ovarian cancer.MethodsPTX-PLGA/PFPs were prepared with a single emulsion (O/W) solvent evaporation method and SA was attached using carbodiimide. The encapsulation efficiency of PTX and the release characteristics were assessed with high performance liquid chromatography. The phase-change characteristics of the PTX-PLGA-SA/PFPs were investigated. The anti-carcinoembryonic antigen (CEA) antibody (Ab) was covalently attached to PTX-PLGA/PFPs via carbodiimide to create PTX-PLGA-Ab/PFPs. The targeting efficiency of the nanoparticles and the viability of ovarian cancer SKOV3 cells were evaluated in each group using a microscope, flow cytometry, and cell counting kit 8 assays.ResultsTHE PTX-PLGA-SA/PFPs were spheres with a size of 383.0 ± 75.59 nm. The encapsulation efficiency and loading capability of the nanoparticles for PTX were 71.56 ± 6.51% and 6.57 ± 0.61%, respectively. PTX was burst-released up to 70% in 2–3 d. When irradiated at 7.5 W for 3 min, the PTX-PLGA-SA/PFPs visibly enhanced the ultrasonography images (P < 0.05). At temperatures of 45°C and 60°C the nanoparticles phase-shifted into micro-bubbles and the sizes increased. The binding efficiencies of SA and Ab to the PTX-PLGA/PFPs were 97.16 ± 1.20% and 92.74 ± 5.75%, respectively. Pre-targeting resulted in a high binding efficacy and killing effect on SKOV3 cells (P < 0.05).ConclusionsThe two-step pre-targeting process can significantly enhance the targeting ability of PTX-loaded PLGA nanoparticles for ovarian cancer cells and substantially improve the therapeutic efficacy. This technique provides a new method for ultrasonic imaging and precise chemotherapy for ovarian cancer.

An optimized laser ultrasonic synthetic aperture imaging method using differential technique

Laser ultrasonic synthetic aperture focusing technique (SAFT) is susceptible to multiple modes of ultrasonic generated by laser pulse. In this work, we propose an optimized synthetic aperture imaging method based on the differential technique, resulting in the effective detection of internal defects. The laser ultrasonic SAFT finite element model is established, and the models are calculated in the case of existing internal defect or not. Thereby, the original ultrasonic data containing the defect reflected waves and the differential data are obtained, and the internal defects are reconstructed by the delay superposition algorithm. The results show that the defect imaging is submerged in the high-amplitude background noise superimposed by the surface acoustic wave; when only the original data are used. However, the optimized SAFT imaging based on the differential technique can not only reduce the interference of other mode waves on the imaging area significantly, but also retain the defect reflected waves effectively. Moreover, the imaging and precise locating of multiple defects are realized, which pave the way for enhancing the internal defects detection ability of laser ultrasonic.

An ultrasonic multi-wave focusing and imaging method for linear phased arrays* *Project supported by the National Natural Science Foundation of China (Grant No. 11774377).

To overcome the inherent limits of traditional single wave imaging for nondestructive testing, the multi-wave focusing and imaging method is thoroughly studied. This method makes the compressional waves and shear waves focused in both emission and reception processes, which strengthens the focusing energy and improves the signal-to-noise ratio of received signals. A numerical model is developed to study the characteristics of a multi-wave focusing field. It is shown that the element width approaching 0.8 wavelengths of shear waves can keep a balance between the radiation energy of two waves, which can achieve a desirable multi-wave focusing performance. And an experiment using different imaging methods for a linear phased array is performed. It can be concluded that due to the combination of the propagation and reflection characteristics of two waves, the multi-wave focusing and imaging method can significantly improve the imaging distinguishability of defects and expand the available sweeping range to a sector of –65° to 65°.

Shedding Damage Detection of Metal Underwater Pipeline External Anticorrosive Coating by Ultrasonic Imaging Based on HOG + SVM

Underwater pipelines are the channels for oil transportation in the sea. In the course of pipeline operation, leakage accidents occur from time to time for natural and man-made reasons which result in economic losses and environmental pollution. To avoid economic losses and environmental pollution, damage detection of underwater pipelines must be carried out. In this paper, based on the histogram of oriented gradient (HOG) and support vector machine (SVM), a non-contact ultrasonic imaging method is proposed to detect the shedding damage of the metal underwater pipeline external anti-corrosion layer. Firstly, the principle of acoustic scattering characteristics for detecting the metal underwater pipelines is introduced. Following this, a HOG+SVM image-extracting algorithm is used to extract the pipeline area from the underwater ultrasonic image. According to the difference of mean gray value in the horizontal direction of the pipeline project area, the shedding damage parts are identified. Subsequently, taking the metal underwater pipelines with three layers of polyethylene outer anti-corrosive coatings as the detection object, an Autonomous Surface Vehicle (ASV) for underwater pipelines defect detection is developed to verify the detection effect of the method. Finally, the underwater ultrasonic image which used to detect the metal underwater pipeline shedding damage is obtained by acoustic sensor. The results show that the shedding damage can be detected by the proposed method. With the increase of shedding damage width, the effect of pipeline defect location detection is better.

Research on frequency domain synthetic aperture focusing pipeline guided wave imaging based on phase migration

In order to overcome the limitations of traditional ultrasonic imaging methods, which cannot directly give the imaging results of defects in a pipeline and have low imaging quality, a frequency domain synthetic aperture focusing pipeline imaging method based on phase migration is proposed. The measured data were reconstructed by frequency domain synthetic aperture focusing, and the results were compared with those of time-domain synthetic aperture focusing imaging. The results show that the frequency domain synthetic aperture imaging method is more accurate for the location and quantification of defects in a pipeline, the influence of noise waves on the imaging transverse resolution is reduced, and the imaging resolution is increased by nearly 30%. It was found that the quantitative errors of axial double defects are 5.2% and 17.9%, and that of circumferential defects is 7.5%. These results show that the frequency domain synthetic aperture focusing pipeline imaging algorithm based on phase migration can achieve the accurate determination of multiple defects in pipelines.

Fracture processes imaging in concrete using nonlinear ultrasound

This paper shows the complementarity of two nonlinear ultrasonic imaging methods to characterize closed macro cracks in concrete. A time reversal mirror is used to locally probe and image the nonlinearity of a cracked region. Two nonlinear parameters are extracted to map the cracked region. The image obtained using the first parameter relates the harmonic generation due to the contact and frictional behaviors at the crack lips, correlated with vibro-thermography imaging of the same crack. The image obtained using the second parameter is based on the conditioning of the material induced by distributed micro cracks arising from the fracture process zone. These results show a great potential for characterization of fracture processes in concrete, with the possibility to uncouple the effects of the crack itself from surrounding distributed micro damage.

An Industrial B‐Mode Phased Array Ultrasonic Imaging Reconstruction Algorithm Based on FRI Sampling

Firstly, a novel FRI sampling model has been proposed according to the characteristics of ultrasonic signals. The model has the advantages such as good stability, strong antinoise ability, simple circuit implementation, and fewer preconditions, compared to the traditional methods. Then, in order to verify the validity of the sampling model, the method is applied to B‐type ultrasonic imaging, and a B‐type phased array ultrasonic imaging algorithm based on FRI sampling model is proposed. Finally, the algorithm simulation experiment is designed, and the results show that the sampling point required by the proposed FRI sampling model is only 0.1% of the traditional B‐type phased array ultrasonic imaging method, and the sampling frequency of the proposed ultrasonic imaging algorithm is only 0.0077% of the traditional B‐type ultrasonic imaging method. Additionally, the experiment result indicates that this algorithm is more applicable to phased array ultrasonic imaging than the SOS filter is.

1Pa5-8 Investigation on application conditions of the ultrasonic velocity change imaging method to living body

1Pa5-8 Investigation on application conditions of the ultrasonic velocity change imaging method to living body

Full-Matrix Phase Shift Migration Method for Transcranial Ultrasonic Imaging.

A spectrum-domain method, called full-matrix phase shift migration (FM-PSM), is presented for transcranial ultrasound phase correction and imaging with ideal synthetic aperture focusing technology. The simulated data obtained using the pseudospectral time-domain method are used to evaluate the feasibility of the method. The experimental data measured from a 3-D printed skull phantom are used to evaluate the algorithm performance in terms of resolution, contrast-to-noise ratio (CNR), and eccentricity comparing with the classical ray-tracing delay and sum (DAS) method. In wire imaging experiment, FM-PSM has a lateral resolution of 0.22 mm and ray-tracing DAS has a lateral resolution of 0.24 mm measured at -6-dB drop using a transducer with a center frequency of 6.25 MHz. In cylinder imaging experiment, FM-PSM has a CNR of 2.14 and ray-tracing DAS has a CNR of 1.82, which illustrates about 17% improvement. For a J -element array and an output image with pixels M ×N (lateral × axial), the computational cost of the DAS is of O(J ×M2×N2) ; on the contrary, it reduces to O(J ×M ×N2) with the proposed FM-PSM. The results suggest that FM-PSM is an efficiency method for transcranial ultrasonic imaging.

Reverberation-based high-speed guided-wave ultrasonic propagation imager for structural inspection of thick composites

Increasing use of thick composite structures in many fields, including the aerospace and shipbuilding industries, necessitates appropriate inspection techniques to ensure structural integrity. Of many nondestructive testing techniques, laser ultrasonic testing is a non-contact method that yields accurate inspection results with high spatial resolution; this method was adopted in this study for the inspection of thick composite structures. We propose a novel guided-wave ultrasonic propagation imaging (UPI) method, called the reverberation wave UPI (R-wave UPI), which is capable of faster target scanning and clearer highlighting of confining waves. To prove the merits of the R-wave UPI, a relatively thin carbon/epoxy composite (thickness, 12 mm) was first tested using the proposed method and the conventional through-transmission UPI. The R-wave UPI modifies the guided-wave UPI with a faster pulse repetition frequency (PRF) laser and ultrasonic energy mapping with straightforward parameter determination. The through-transmission UPI consisting of a raster mechanical scanner, a Q-switched laser, and a laser Doppler vibrometer, was used as a reference, whereas the R-wave UPI consisting of an angular laser mirror scanner, a Q-switched laser, and a PZT sensor was operated at a high PRF in the kilohertz regime to induce reverberation. The reverberation phenomenon was used in the post-image processing, called ultrasonic energy mapping (UEM). UEM with a high PRF was then compared to the through-transmission inspection reference to verify its accuracy and reliability for mapping of structural anomalies. Finally, a thick and curved composite blade with a rough and curved surface that could not be inspected using the conventional through-transmission UPI was tested using 7 kHz PRF and its delamination was successfully visualized using the UEM.

Photothermal testing of composite materials: Virtual wave concept with prior information for parameter estimation and image reconstruction

In this paper, we propose a new parameter estimation and image reconstruction approach for the photothermal testing of composite materials. Therefore, the full multidimensional evaluation method, virtual wave concept, is extended to estimate the orthotropic thermal diffusivity tensor and to reconstruct the initial temperature distribution after a laser spot heating in an orthotropic material. We establish a formal relationship between the virtual speed of sound tensor and the thermal diffusivity tensor. Furthermore, we show how prior information in the form of positivity and sparsity can be incorporated in the regularization process to improve the solution of the inverse imaging problem. In a second step, the initial temperature distribution is reconstructed by applying ultrasonic imaging methods on the calculated 3D bimodal virtual wave field. This new approach is validated on simulation and experimental data of a unidirectional carbon fiber reinforced polymer. The information loss that results from entropy production during heat diffusion can be partly compensated by including prior information. This allows an accurate parameter estimation and a high-resolution image reconstruction.

Non-Destructive Detection of GIS Aluminum Alloy Shell Weld Based on Oblique Incidence Full Focus Method

In this paper, a new ultrasonic phased array full focus imaging method based on oblique incidence is proposed to solve the problem of the non-destructive testing of the internal defects in the GIS (gas insulated switchgear) shell welds. By using wedge coupling, the measured weld is far away from the near-field range of the transducer, and the detection angle range can be increased by changing the propagation direction of the acoustic beam. Based on Snell's law, the propagation characteristics of the ultrasonic wave in the interface are studied. On the basis of the conventional ultrasonic array matrix and the full focus imaging algorithm, by introducing the energy attenuation calibration coefficient of the acoustic wave propagation through the wedge, the correction amplitude of the specific focus point p(x, z) is obtained, The non-destructive testing of weld defects of GIS shell in the spot is carried out, and the test results show that the qualitative and quantitative detection of the weld defects can be well realized by using this method.

Ultrasonic inspection of grouted splice sleeves in precast concrete structures using elastic reverse time migration method

Precast concrete (PC) structure has been widely employed for building construction in recent years, and grouted splice sleeve is commonly used for component connection. The compactness of the grouted splice sleeve connections plays a decisive role in structural safety, especially for its capacity to resist an earthquake. In this study, an ultrasonic imaging method is proposed for inspecting the grouted splice sleeves in PC structures using reverse time migration (RTM) algorithm based on an elastic wave equation. Numerical and laboratory experiments are carried out to assess the feasibility of our proposed method. In the numerical experiment, three numerical models, i.e. three-quarter grouted, fully-grouted, and non-grouted, are established. The results show that the proposed RTM method can reconstruct images of the buried sleeves with a higher resolution and a greatly-improved accuracy, compared with the traditional ultrasonic imaging method. Moreover, the grouting condition in the three models can be readily distinguished and even the interface between the grouting material and the air defect in the three-quarter grouted model can be clearly identified. In the laboratory experiment, two sleeves, one is fully-grouted and the other one is insufficiently-grouted with certain air defects, are embedded in a concrete model. The top of the two sleeves can be clearly imaged, and the insufficiently-grouted sleeve has a reflection, which is about 9 dB stronger than the other one. We conclude that the proposed ultrasonic imaging method can be used for inspecting the grouting quality of splice sleeves in PC constructions in field.

An Improved Ultrasonic Imaging Method for Austenitic Welds Based on Grain Orientation Distribution Inversion Algorithm

Traditional ultrasonic imaging inspection does not perform well for austenitic welds, in which the defect locating accuracy is insufficient due to the distortion of propagation paths caused by the weld’s anisotropy and inhomogeneity. The distribution of grain orientation (DGO) contributes to the velocity distribution in austenitic welds and influences the ultrasonic propagation paths. An improved ultrasonic imaging method for austenitic welds based on a DGO inversion algorithm is proposed in this paper. A DGO model is established using an iterative disturbance method of local parameters. The model is optimized by an evolution strategy based on the model error evaluated by propagation times of known reflectors. Inspection experiments were carried out, in which a reference specimen was used to acquire the DGO inversion result and the inspection images of a target specimen were generated based on the optimized DGO model. Experimental results have proved that the improved ultrasonic imaging method can obviously increase the defect locating accuracy and effectively improve the imaging performance for austenitic welds.

Ultrasonic Phased Array Sparse TFM Imaging Based on Virtual Source and Phase Coherent Weighting

Total focus method (TFM) is an ultrasonic phased array imaging method and has a larger dynamic focusing range and higher spatial resolution than traditional imaging methods. But TFM needs to process a large amount of data, resulting in a long imaging time, which greatly limits its application and development in the industrial field. The sparse method can improve the computing efficiency by reducing the amount of data, but the resolution and intensity of sparse image are very low. This paper proposes a virtual source sparse TFM (VSSTFM) method based on phase coherent weighting (PCW) to improve the spatial resolution and intensity of the sparse TFM imaging. The layout of virtual sources in the virtual source array is designed and optimized by genetic algorithm. According to the phase distribution characteristics of the ultrasonic testing signal, a phase coherence factor is constructed to weight the VSSTFM image to further improve the image quality. Experimental results show that compared with conventional TFM, the proposed method can improve the imaging efficiency by 66.56 % while providing significantly higher image quality than TFM imaging.

Study on Ultrasonic Multi-mode Composite Total Focusing Imaging Method for Welds Defect Inspection in Small-diameter Tube of Austenitic Stainless Steel

Study on Ultrasonic Multi-mode Composite Total Focusing Imaging Method for Welds Defect Inspection in Small-diameter Tube of Austenitic Stainless Steel