Ultrasonic Computed Tomography Research Articles

Experimental full waveform inversion for elastic material characterization with accurate transducer modeling

For quality assurance and in-service safety, sufficient characterization of the materials is essential during the development, manufacture, and processing of a material in any industrial setting. Evaluation of elastic coefficients, material microstructures, morphological features, and related mechanical properties are all part of the process of characterizing a material. Ultrasonic signals are sensitive to material properties such as wave speeds, attenuation, diffusion backscattering, microstructural variation, and elastic characteristics (e.g., elastic modulus, hardness, etc.). Ultrasonic computed tomography (USCT) is an emerging imaging method that can be implemented to obtain a quantitative estimation of material properties. In this study, a source estimation technique was initially proposed to obtain the source time function for accurate forward modeling by constructing a linear inverse problem for the unknown transducer modeling. Finally, a material characterization approach was proposed with accurate source estimation to extract wave speed distribution from an elastic material by employing a wave-based method, known as full waveform inversion (FWI). Systematic performance analysis of the proposed FWI model with accurate source estimation was assessed using experimental and synthetic data obtained from a 6061 aluminum sample. Overall, the proposed FWI technique has successfully reconstructed the wave speed distribution, exhibiting the potential of the proposed method of material characterization in various engineering applications.

Experimental Approach for Clarifying Initiation and Growth Behaviors of Internal Fatigue Cracks Using Synchrotron Radiation Multiscale X-ray Computed Tomography

Abstract The very high cycle fatigue (VHCF) phenomenon has been recognized and extensively studied in the past quarter century. One of the most peculiar and noticeable characteristics of VHCF is the transition of the origin site from the surface to the interior of the material in long-life regimes over 107 cycles. In particular, in high-strength metals, a tiny site can become an origin of internal fatigue cracks, such as nonmetallic inclusions of several micrometers to several tens of micrometers in high-strength steels and crystal grains of several tens of micrometers in titanium alloys. However, such small cracks are difficult to detect using conventional nondestructive approaches, such as industrial X-ray computed tomography (CT) or ultrasonic CT. Given this background, we have attempted to use a synchrotron radiation multiscale X-ray CT provided by SPring-8 in Japan. This system comprises a projection CT (micro-CT) with a spatial resolution of approximately 1 μm and a phase-contrast imaging CT (nano-CT) with a spatial resolution of approximately 200 nm or higher. The present study introduces our experimental approach to clarify internal fatigue crack behaviors using the multiscale X-ray CT with in situ fatigue testing. First, the principle of material selection focusing on the VHCF study is explained with the details of the materials used: (α+β) type Ti-6Al-4V, β type Ti-22V-4Al, and 17-4 precipitation-hardened martensite stainless steel. Afterward, the outline and primary performance of the multiscale X-ray CT are described. Subsequently, important points in conducting accurate in situ fatigue tests are discussed from the viewpoints of the development policies of the testing system and preparation of the special thin specimen for CT imaging. Finally, the multiscale X-ray CT is conducted for the above materials, and the initiation and growth behaviors of the internal fatigue cracks are compared and discussed for an in-depth understanding of the VHCF phenomenon.

Experimental investigation on interfacial defect detection for SCCS with conventional and novel contact NDT techniques

In order to ensure the mechanical performance and structural safety of steel–concrete composite structures (SCCS), advanced nondestructive testing (NDT) technique for bonding status at steel–concrete interfaces needs to be developed. In this study, the feasibility of multichannel analysis of surface waves (MASW)-based interfacial debonding detection is validated using the contact sensors array. Herein, the multichannel sensor arrays are composed of piezoceramic lead zirconate titanate patches and high-frequency acceleration meters, respectively. For comparison, the impact-response (IR) method and impact-transmission (IT) method are performed utilizing a force hammer and high-frequency acceleration meters, and corresponding damage imaging algorithms are developed. The applicability of ultrasonic computed tomography (CT) scanning test, scanning impact echo (IE) method, ultrasonic tomography (UT) technique on interfacial debonding detection is further discussed in depth. Research findings indicate that the developed contact MASW measurement can fully capture the variation of dispersion characteristics of surface waves induced by debonding defects in SCCS. The developed IR and IT methods are suitable for detecting interfacial debondings in different dimensions. Besides, the damage nephogram resolution of IR is higher than that of the IT method. In addition, the practicability of traditional ultrasonic CT scanning tests, scanning IE method, and UT techniques using commercial equipment is investigated. Experimental observations show that classical NDT testing techniques are incapable of effectively identifying the existence of interfacial damage and are unsuitable for NDT tests on SCCS. The research findings in this study clearly exhibit the precision and limitation of various contact NDT techniques and lay a solid foundation for interfacial debonding detection in practical SCCS.

A dual-scale morphological filtering method for composite damage identification using FBP

Delamination is the main type of defect that reduces the performance of carbon fiber-reinforced polymer (CFRP) composite materials and can be detected by traditional linear ultrasonic methods. However, the traditional ultrasonic inspection method only analyzes its position through the waveform change, and it is difficult to intuitively and accurately study the specific shape and position of the defect in the form of images. This study obtains delamination defect images of CFRP composite plates through fan-beam ultrasonic computed tomography (UCT) and finite element simulation. The Filtered back-projection method based on UCT is used as the basic algorithm for reconstructing layered defect images of CFRP plates. To obtain accurate defect size and location, a novel dual-scale morphological filtering (DSMF) method combined with Canny operator is proposed for edge detection of delamination defects. The DSMF method alternately filters by combining two structuring elements of different sizes while suppressing noise as much as possible and preserving the edge details of the image. As the results verify, the use of the DSMF method combined with Canny edge-detection for edge detection significantly reduces the average recognition error from 16.83% to 4.37% compared to existing methods. The results show that the DSMF method can effectively reduce the influence of artifact interference and non-edge pixels on defect-recognition; thus, the size and contour information of the obtained defects are more accurate than existing methods. Experimental studies using realistic composite plates further validated the proposed method. The method of ultrasonic tomography combined with Canny edge detection based on a DSMF method can be well applied to edge detection and contour recognition of layered defects in CFRP materials.

Deep learning based neural network application for automatic ultrasonic computed tomographic bone image segmentation.

Deep-learning techniques have led to technological progress in the area of medical imaging segmentation especially in the ultrasound domain. In this paper, the main goal of this study is to optimize a deep-learning-based neural network architecture for automatic segmentation in Ultrasonic Computed Tomography (USCT) bone images in a short time process. The proposed method is based on an end to end neural network architecture. First, the novelty is shown by the improvement of Variable Structure Model of Neuron (VSMN), which is trained for both USCT noise removal and dataset augmentation. Second, a VGG-SegNet neural network architecture is trained and tested on new USCT images not seen before for automatic bone segmentation. Therefore, we offer a free USCT dataset. In addition, the proposed model is implemented on both the CPU and the GPU, hence overcoming previous works by a value of 97.38% and 96% for training and validation and achieving high segmentation accuracy for testing with a small error of 0.006, in a short time process. The suggested method demonstrates its ability to augment USCT data and then to automatically segment USCT bone structures achieving excellent accuracy outperforming the state of the art.

An improved ultrasonic computerized tomography (UCT) technique for damage localization based on compressive sampling (CS) theory

An improved ultrasonic computerized tomography (UCT) technique for damage localization based on compressive sampling (CS) theory

Reconstruction Algorithm-Based Ultrasonic and Spiral CT Images in Evaluating the Effects of Dexmedetomidine Anesthesia for Acute Abdomen.

Objective The study focused on the application value of iteration reconstruction algorithm-based ultrasound and spiral computed tomography (CT) examinations, and the safety of dexmedetomidine anesthesia in acute abdominal surgery. Methods 80 cases having the acute abdomen surgery were selected as the research subjects. They were divided into group A (40 cases) and group B (40 cases) according to the anesthetic drugs used in the later period. The experimental group was injected with propofol, remifentanil, and atracurium combined with dexmedetomidine; the control group was injected with propofol, remifentanil, and atracurium only. After the operation, the patient was for observed for the pain, agitation, adverse reactions, heart rate (HR), and blood pressure. All patients received ultrasound and spiral CT examinations, and based on the characteristics of the back-projection algorithm, an accelerated algorithm was established and used to process the image, and according to which, the patient's condition and curative effects were evaluated. Results After image reconstruction, the ultrasound and spiral CT images were clearer with less noise and more prominent lesions than before reconstruction. Before image reconstruction, the accuracy rates of ultrasound and spiral CT in diagnosing acute abdomen were 92.3% and 91.1%, respectively. After reconstruction, the corresponding numbers were 96.3% and 98.1%, respectively. After reconstruction, the accuracy of the two methods in diagnosing acute abdomen was significantly improved compared with that before reconstruction, and the difference was statistically significant (P < 0.05). The Ramsay score of the experimental group was significantly higher than that of the control group at each time period, P < 0.05; the agitation score and visual analogue scale (VAS) score of the experimental group were significantly lower than the control group at each time period after waking up, P < 0.05. Conclusion Reconstruction algorithm-based ultrasound and spiral CT images have high application value in the diagnosis of patients with acute abdomen, and dexmedetomidine has good safety in anesthesia surgery.

Computer modeling of different shaped patches in classical carotid endarterectomy

Objective: to construct geometric models of carotid bifurcation and build a computer modeling for carotid endarterectomy (CEA) operations with patches of various configurations.Materials and methods. The method uses reconstructed models of a healthy blood vessel obtained from a preoperative computed tomography (CT) study of the affected blood vessel of a particular patient. Flow in the vessel is simulated by computational fluid dynamics using data from the patient's ultrasonic Doppler velocimetry and CT angiography. Risk factors are assessed by hemodynamic indices at the vessel wall associated with Wall Shear Stress (WSS).Results. We used the proposed method to study the hemodynamic results of 10 virtual CEA operations with patches of various shapes on a reconstructed healthy artery of a particular patient. The reason for patch implantation was to ensure that the vessel lumen is not narrowed as a result of the surgery, since closing the incision without a patch can reduce the vessel lumen circumference by 4–5 mm, which adversely affects blood flow. On the other hand, too wide a patch creates aneurysmorphic deformation of the internal carotid artery (ICA) mouth, which is not optimal due to formation of a large recirculation zone. In this case, it was found that the implanted patch width of about 3 mm provides an optimal hemodynamic outcome. Deviations from this median value, both upward and downward, impair hemodynamics. The absence of a patch gives the worst of the results considered.Conclusion: The proposed computer modeling technique is able to provide a personalized patch selection for classical CEA with low risk of restenosis in the long-term follow-up.

The application of compressive sampling in rapid ultrasonic computerized tomography (UCT) technique of steel tube slab (STS).

This paper explores a new method for rapid structural damage inspection of steel tube slab (STS) structures along randomly measured paths based on a combination of compressive sampling (CS) and ultrasonic computerized tomography (UCT). In the measurement stage, using fewer randomly selected paths rather than the whole measurement net is proposed to detect the underlying damage of a concrete-filled steel tube. In the imaging stage, the ℓ1-minimization algorithm is employed to recover the information of the microstructures based on the measurement data related to the internal situation of the STS structure. A numerical concrete tube model, with the various level of damage, was studied to demonstrate the performance of the rapid UCT technique. Real-world concrete-filled steel tubes in the Shenyang Metro stations were detected using the proposed UCT technique in a CS framework. Both the numerical and experimental results show the rapid UCT technique has the capability of damage detection in an STS structure with a high level of accuracy and with fewer required measurements, which is more convenient and efficient than the traditional UCT technique.

Comparison of clinical effects of ultrasonic examination, CT examination, and MR examination in diagnosis of pancreatic and ampullary cancer

Objective: This study compares the clinical effects of ultrasonic examination, Computed Tomography (CT) examination, and Magnetic Resonance (MR) examination in diagnosing pancreatic and ampullary cancer. Methods: A total of 60 patients with pancreatic and ampullary cancers admitted in our hospital from May 1st, 2015 to June 1st, 2017 were chosen as research objects. All patients received ultrasonic examination, CT examination, and MR examination. Results were compared with operation outcomes. Results: The accuracy of ultrasonic examination, CT examination, and MR examination were 48.33%, 63.33%, and 88.33%, respectively. The accuracy of MR examination was higher than those of the two examinations (p 0.05). Conclusions: Among the three examinations, MR examination was the most accurate in diagnosing pancreatic and ampullary cancers.

Improved Ultrasonic Computerized Tomography Method for STS (Steel Tube Slab) Structure Based on Compressive Sampling Algorithm

This paper developed a new ultrasonic computerized tomography (CT) method for damage inspections of a steel tube slab (STS) structure based on compressive sampling (CS). CS is a mathematic theory providing an approximate recovery for a sparse signal with minimal reconstruction error from under-sampled measurements. Considering the natural sparsity of the damage, CS algorithm is employed to image the defect in the concrete-filled steel tube of Shenyang Metro line 9 for reducing the work time. Thus, in the measurement stage, far fewer ultrasonic measurement paths were selected from the dense net of conventional ultrasonic CT techniques to capture the underlying damage information. Then, in the imaging stage, ℓ1-norm minimization algorithm of CS theory is selected to recover the internal damage via fusing measurement data and solving optimization problem. The functionality of the proposed method is validated by three numerical concrete tube models with various conditions. Additionally, both the conventional ultrasonic CT technique and the proposed one are employed for ultrasonic inspection of the STS structure in Shenyang Metro line 9. Both the numerical and experimental results indicate that the proposed ultrasonic CT improved by CS has a great potential for damage detection, which provides an alternative accurate and effective way for non-destructive testing/evaluation (NDT/E).

Non-Iterative Algorithm for Ultrasonic Computer Tomography

Non-Iterative Algorithm for Ultrasonic Computer Tomography

Compensation of transducer element positions in a ring array ultrasonic computer tomography system

An ultrasonic ring array system was newly developed and ultrasonic computer tomography (USCT) image reconstruction was performed. The USCT transducer of 104 mm diameter had a center frequency of 1.75 MHz and a −6 dB transmit and receive two-way fractional bandwidth of 66%. It had a full 360° circumference divided into four blocks, each of which had 256 elements. All 1024 elements were connected to a high-voltage multiplexer IC. The potential problem of image degradation, which might have been caused by insufficient alignment accuracy between the blocks, was solved by fitting and compensating the delay due to the misalignment. This resulted in a measured transmit and receive beam width of 0.20 mm, which is close to the theoretical value.

Noise reduction in ultrasonic computerized tomography by preprocessing for projection data

In this study, an ultrasonic computerized tomography (CT) using time-of-flights (TOFs) has been used for the nondestructive inspection of steel billets with high acoustic attenuation. One of the remaining problems of this method is noise in CT images, which makes it difficult to distinguish defects from noise. Conventionally, noise is suppressed by a low-pass filter (LPF) in the process of filtered back projection (FBP). However, it has been found that there is residual noise even after filtering. To cope with this problem, in this study, the noise observed in ultrasonic testing was examined. As a result, it was found that the TOF data used for CT processing contains impulse noise, which remains in the CT image even after filtering, owing to the existence of transducer directivity. To remove impulse noise selectively, we propose a noise reduction technique for ultrasonic CT for steel billet inspection, that is, preprocessing (outlier detection and removal) of TOF data. The performance of the proposed technique was evaluated experimentally. The obtained results suggest that the proposed technique can remove impulse noise selectively and markedly improve the quality of the CT image. Hence, the proposed technique can improve the performance of ultrasonic CT for steel billet inspection.

Travel-Time Ultrasonic Computed Tomography Applied to Quantitative 2-D Imaging of Standing Trees: A Comparative Numerical Modeling Study

The quality of the Ultrasonic Computed Tomography (UCT) imaging device, in term of spatial resolution, sensitivity or dynamic, is a function of the wavelength, the number of transducers, the ultrasonic field generated and the inversion algorithm. This latter factor was studied using four inversion techniques for the tomography of trees. Two new methods, Partial Least Squares method - PLS, and Layer Stripping - LS, are compared to two classical methods, Filtered Backprojection - FBP, and Simultaneous Iterative Reconstruction Technique - SIRT. An original numerical phantom of tree was used and the effects of the variation of the number of transducers and the noise level were analyzed. The PLS was found to converge slowly but reached a high performance for the reconstruction of the projection values (slowness). PLS method was also characterized by a fast computation time. However, the PLS method gave a poor image quality (high sensitivity to noise level and presence of outlier values). The main advantage of the LS method was its high robustness to the noise level. The computing time was however the weakest point of LS method. A combination of the two classic FBP-SIRT methods seemed the most suitable except for the computation time. However, an improvement of the convergence conditions of PLS method (very fast computing time; including also curved rays), with the use of SIRT method, would constitute a promising solution.

Application of ultrasonic computerized tomography using time-of-flight measured by transmission method to nondestructive inspection for high-attenuation billets

For the nondestructive inspection of steel billets, the pulse echo method is generally employed in their manufacturing process. However, for high-attenuation billets, the pulse echo method is useless owing to the low echo level, while the transmission method is expected to detect defects inside high-attenuation billets. In this study, we consider the effectiveness of ultrasonic computerized tomography (CT) using time-of-flight (TOF) measured by the transmission method compared with the pulse echo method. From the simulation and experimental results, even though it was difficult for the pulse echo method to detect defects inside high-attenuation billets, the defects could be visualized by ultrasonic CT using TOF measured by the transmission method. Therefore, ultrasonic CT using TOF measured by the transmission method is more effective for detecting defects inside high-attenuation billets than the pulse echo method.

Enhancement of photoacoustic tomography by ultrasonic computed tomography based on optical excitation of elements of a full-ring transducer array

Photoacoustic computed tomography (PACT) is a hybrid technique that combines optical excitation and ultrasonic detection to provide high-resolution images in deep tissues. In the image reconstruction, a constant speed of sound (SOS) is normally assumed. This assumption, however, is often not strictly satisfied in deep tissue imaging, due to acoustic heterogeneities within the object and between the object and the coupling medium. If these heterogeneities are not accounted for, they will cause distortions and artifacts in the reconstructed images. In this Letter, we incorporated ultrasonic computed tomography (USCT), which measures the SOS distribution within the object, into our full-ring array PACT system. Without the need for ultrasonic transmitting electronics, USCT was performed using the same laser beam as for PACT measurement. By scanning the laser beam on the array surface, we can sequentially fire different elements. As a first demonstration of the system, we studied the effect of acoustic heterogeneities on photoacoustic vascular imaging. We verified that constant SOS is a reasonable approximation when the SOS variation is small. When the variation is large, distortion will be observed in the periphery of the object, especially in the tangential direction.

Improvement Wood Computerized Tomography Images with Ultrasonic Wave Parallel Translation

The ultrasonic computerized tomography (UCT) method presented in this paper is an improvement of the maximum likelihood expectation maximization (ML-EM) algorithm for wooden pillars. For the purpose of removing distortions in ultrasonic computerized tomography (CT) images of wood, this paper proposes ultrasonic wave parallel translation based on predicted ultrasonic paths technique for taking into account the skewing effect in reconstruction images. Time of flight (TOF) data and transmission paths of ultrasonic wave were predicted by considering the change in wave velocity based on the annual ring angle of wood. The predicted paths were used to reconstruct images of wood section, the accuracy of defect detection in wood can be significantly improved.

Through-transmission medical imaging using phase-insensitive pyroelectric ultrasonic detectors

Ultrasonic Computed Tomography (UCT) has been unable to rival its x-ray counterpart in terms of reliably distinguishing different tissue pathologies. Conventional piezoelectric detectors deployed in UCT are phase-sensitive and it is well established that their use can give rise to phase-cancellation artefacts that mask true tissue structure. In contrast, phase-insensitive detectors are more immune to this effect, although sufficiently sensitive devices for clinical use are not yet available. This paper establishes proof-of-concept for a novel phase-insensitive transducer for UCT. The detector employs an acoustic absorber to convert received acoustic intensity into heat that is subsequently detected using the pyroelectric response of a thin piezoelectric membrane bonded intimately to the absorber. The paper explores UCT application of the phase-insensitive detectors, comparing with traditional detection methods. Results are presented for a range of detector apertures; tomographic reconstruction images being compared using stable two-phase phantoms containing inserts as small as 3 mm. The project has demonstrated that the new detectors are significantly less susceptible to refraction and phase-cancellation artefacts, generating realistic images in situations where conventional techniques were unable to do so. The novel detector holds promise as the basis of a new type of clinical UCT system.

Feasibility Study of Ultrasonic Computed Tomography–Guided High-Intensity Focused Ultrasound

The aim of this study was to establish a proof of concept for an ultrasonic image-guided high-intensity focused ultrasound (HIFU) breast treatment system. An ultrasonic computed tomography (UCT) scanner served as a platform for image acquisition and thermal mapping. With this system, images depicting the speed of sound (SOS) can be obtained. After HIFU activation, the resulting changes in SOS can be mapped. For the temperature range T ≤ 45°C, the temperature elevation is obtained directly from the change in SOS. For thermal ablation, monitoring is obtained by studying the temporal derivative of the SOS while continuous HIFU heating is applied. The method was implemented to in vitro tissue specimens and the ability for thermal monitoring was demonstrated. The results indicate that the suggested concept is indeed feasible.