Ultrasound Reflection Research Articles

Integrated organosilica nanomedicine enables sonoimaging, sonochemistry and antitumor sonodynamic therapy.

Sonography with its non-invasive and deep tissue-penetrating characteristics, not only contributes to promising developments in clinical disease diagnosis but also obtains acknowledgments as a prospective therapeutic approach in the field of tumor treatment. However, it remains a challenge for sonography simultaneously to achieve efficient imaging and therapeutic functionality. Here, we present an innovative integrated diagnosis and treatment paradigm by developing the nanomedicine of percarbamide-bromide-mesoporous organosilica spheres (MOS) with RGD peptide modification (PBMR) by loading percarbamide and bromide in MOS which were prepared by a one-step O/W microemulsion method. The PBMR nanomedicine effectively modifies the tumor acoustic environment to improve sonoimaging efficacy and induces sonochemical reactions to enhance the production of reactive oxygen species (ROS) for tumor treatment efficiency under sonography. The combination of PBMR nanomedicine and SDT achieved multiple ROS generation through the controlled sonochemical reactions and significantly boosted the potency of sonodynamic therapy and induced significant tumor regression with non-invasive tissue penetrability and minimizing damage to healthy tissues. Simultaneously, the generation of oxygen gas in the sonochemical process augments ultrasound reflection, resulting in a 4.9-fold increase in imaging grayscale. Our research establishes an effective platform for the synergistic integration of sonoimaging and sonodynamic antitumor therapy, offering a novel approach for precise antitumor treatment in the potential clinical applications.

Experimental investigation of acoustic moiré effect controlled by twisted bilayer gratings

Recently, the moiré pattern has attracted lots of attention by superimposing two planar structures of regular geometries, such as two sets of metasurfaces or gratings. Here, we show the experimental investigation of acoustic moiré effect by using twisted bilayer gratings (i.e., one grating twisted with respect to the other). We observed the guided resonance that occurred when the incident ultrasound beam was coupled with the guiding modes in a meta-grating, significantly influencing the reflection and transmission. Tunable guided resonances from the moiré effect with complete ultrasound reflection at different frequencies were further demonstrated in experiments. Combining the measurements of transmission spectra and the Fast Fourier Transform analyses, we reveal the guided resonance frequencies of moiré ultrasonic metasurface can be effectively controlled by adjusting the twisting angle of the bilayer gratings. Our results can be explained in a simplified model based on the band folding theory, providing a reliable prediction on the precise control of ultrasound reflection via the twisting angle adjustment. Our work extends the moiré metasurface from optics into acoustics, which shows more possibilities for the ultrasound beam engineering from the moiré effect and enables the exploration of functional acoustic devices for ultrasound imaging, treatment and diagnosis.

An overview of cutaneous squamous cell carcinoma imaging diagnosis methods.

Cutaneous squamous cell carcinoma, a type of non-melanoma skin cancer, is a form of keratinocyte carcinoma that stands as one of the most prevalent cancers, exhibiting a rising frequency. This review provides an overview of the latest literature on imaging methods for diagnosing squamous cell carcinoma (SCC) and actinic keratosis (AK). It discusses the diagnostic criteria, advantages, and disadvantages of various techniques such as dermatoscopy, skin ultrasound (US), in vivo and ex-vivo reflectance confocal microscopy (RCM), and line-field confocal optical coherence tomography (LC-OCT). These methods offer benefits including non-invasiveness, rapidity, comprehensive lesion imaging, and enhanced sensitivity, but face challenges like high costs and the need for specialized expertise. Despite obstacles, the use of these innovative techniques is expected to increase with ongoing technological advancements, improving diagnosis and treatment planning for keratinocyte carcinomas. Standardizing LC-OCT imaging algorithms for AK, Bowen's disease, and SCC remains an area for further research.

Generalized Abel equations and applications to translation invariant Radon transforms

Abstract Generalized Abel equations have been employed in the recent literature to invert Radon transforms which arise in a number of important imaging applications, including Compton Scatter Tomography (CST), Ultrasound Reflection Tomography (URT), and X-ray CT. In this paper, we present novel injectivity results and inversion methods for generalized Abel operators. We apply our theory to a new Radon transform, R j \mathcal{R}_{j} , of interest in URT, which integrates a square integrable function of compact support, 𝑓, over ellipsoid and hyperboloid surfaces with centers on a plane. Using our newly established theory on generalized Abel equations, we show that R j \mathcal{R}_{j} is injective and provide an inversion method based on Neumann series. In addition, using algebraic methods, we present image phantom reconstructions from R j ⁢ f \mathcal{R}_{j}f data with added pseudo-random noise.

Is myocardial fibrosis appropriately assessed by 2D strain derived integrated backscatter?

Abstract Introduction Calibrated integrated backscatter (cIB) may be obtained from bidimensional (2D) strain echocardiography as a quantification measurement of myocardial ultrasound reflectivity. Increased collagen content of the myocardium modifies tissue reflectivity and cIB is suggested as a marker of left ventricular (LV) fibrosis. However, its diagnostic accuracy is not fully established. Aim To assess the correlation between cIB by 2D strain and LV myocardial fibrosis (MF), as evaluated by non-invasive imaging and histopathology. Methods Correlation study from a cohort of 157 patients with severe symptomatic aortic stenosis (AS) referred for surgical aortic valve replacement (AVR). Patients with complete preoperative transthoracic echocardiography, cardiac magnetic resonance (CMR) and endomyocardial biopsy (EMB) obtained from the anterior basal septum at the time of AVR were selected. Two groups of 30 patients were evaluated, with and without late gadolinium enhancement (LGE) at CMR. Integrated Backscatter was obtained at QRS peak in decibels (dB) from both parasternal long axis (PLAX) and apical-three-chamber (A3C) cine clips at Qanalysis. cIB was calculated by subtracting the pericardial intensity from the average of the anteroseptal and basal inferolateral wall values. Correlation analysis was performed for the whole group of patients with global and segmental (anterior basal septum) values of native T1 and extracellular volume (ECV), and EMB collagen volume fraction (CVF) from Masson´s Trichrome staining. IBS values were compared in both group of patients. Results 60 patients (74 [36-74] years, 45% male) with high gradient (mean gradient: 63±20mmHg), normal flow (45±10mL/m2), preserved ejection fraction (60±9%) AS were included. Basal septal cIB was –9.17±9.45dB and –17.45 (–31.2–10.95) dB from A3C and PLAX views, respectively. These indexes did not correlate with basal septum thickness or global LV mass. Absolute and cIB did not correlate neither with global and regional T1 and ECV values, nor with CVF at EMB. These were not significantly different in both groups of patients and there was no correlation between cIB values and mass of replacement MF in patients with LGE. Conclusion In these cohort of patients with classical severe AS, there was no correlation of cIB with imaging markers of both replacement and diffuse MF. cIB also didn´t correlate with CVF at histopathology. These findings suggest that reflectivity indexes are not suitable for myocardial tissue characterization in this setting.

SonarGuard: Ultrasonic Face Liveness Detection on Mobile Devices

Liveness detection has been widely applied in face authentication systems to combat malicious attacks. However, existing methods purely depending on visual frames become vulnerable once visual perception is not reliable. The emerging face spoof and forge techniques urge the systems to exploit the defensive potential of non-visual modalities. To tackle this challenge, we introduce SonarGuard, a system combining ultrasonic and visual information to achieve robust liveness detection on mobile devices. More specifically, SonarGuard simultaneously extracts micro-doppler signatures from ultrasound reflections and motion trajectories from video frames both corresponding to the user’s lip movement. To further confirm the collected ultrasonic and visual information is not derived from malicious audio/video attacks, we consolidate the system via introducing a cross-modal matching mechanism, which demands the inherent consistency between these two modalities. Extensive experiments on a new dataset collected with existing mobile devices demonstrate that the proposed system could achieve average classification error rate of 0.91% under presentation attacks. This result indicates that SonarGuard can boost the security of face authenfication systems in real world usage without additional hardware modification.

Application of deep neural networks for inferring pressure in polymeric acoustic transponders/sensors

Passive sensor-transponders have raised interest for the last few decades, due to their capability of low-cost remote monitoring without the need for energy storage. Their operating principle includes receiving a signal from a source and then reflecting the signal. While well-established transponders operate through electromagnetic antennas, those with a fully acoustic design have advantages such as lower cost and simplicity. Therefore, detection of pressures using the ultrasound signal that is backscattered from an acoustic resonator has been of interest recently. In order to infer the pressure from the backscattered signal, the established approach has been based upon the principle of detection of the shift to the frequency of resonance. Nevertheless, regression of the pressure from the signal with a small error is challenging and has been subject to research. Here in this paper, we explore an approach that employs deep learning for inferring pressure from the ultrasound reflections of polymeric resonators. We assess if neural network regressors can efficiently infer pressure reflected from a fully acoustic transponder. For this purpose, we compare the performance of several regressors such as a convolutional neural network, a network inspired by the ResNet, and a fully connected neural network. We observe that deep neural networks are advantageous in inferring pressure information with a minimal need for analyzing the signal. Our work suggests that a deep learning approach has the potential to be integrated with or replace other traditional approaches for inferring pressure from an ultrasound signal reflected from fully acoustic transponders or passive sensors.

Measuring integrated backscatter in patients undergoing transcatheter aortic valve implantation

Abstract Funding Acknowledgements Type of funding sources: None. Background Calibrated integrated backscatter (cIB) derived by 2D echocardiography quantifies myocardial ultrasound reflectivity, and it has been used in previous studies as a surrogate for myocardial fibrosis. Before the advent of other cardiac imaging techniques, it was a major focus of tissue characterization research. Purpose We examined whether cIB may help identify patients undergoing transcatheter aortic valve implantation (TAVI) at risk of procedure-related complications. Methods Consecutive patients submitted to transfemoral TAVI between January and December 2021 were routinely imaged by echocardiography in the five days peri-procedure. Calibrated integrated backscatter was obtained from the parasternal long-axis view (PLAX) by subtracting pericardial cIB intensity from myocardial septal and posterior wall average cIB. Patients with poor PLAX views were excluded from the study. Measurements of cIB, expressed in decibels, were performed at end-diastole. The primary endpoint was the occurrence of major TAVI-related complications. Results Of 149 patients that underwent TAVI during the study period, 131 had a reasonable acoustic window for cIB measurement and were included in the study. Patient mean age was 82.1±6.9 years, and 62% were female. At baseline, 84% of patients had preserved left ventricle function, the mean aortic mean gradient was 47.3±14.8 mmHg, and the mean Euroscore II was 5.34±3.24. The global mean cIB measured was 19.74±7.56 dB. No significant differences were found in the myocardial wall ultrasound reflectivity in patients with TAVI-related major complications (20.63±10.8 vs 19.6±6.9 dB, p = 0.587), which were defined according to the Valve Academic Research Consortium-2 consensus. However, cIB was significantly higher in patients who had post-TAVI conduction disturbances (21.09±7.72 vs 18.11±7.06 dB, p = 0.026), including left bundle branch block and atrioventricular block. There was also a negative correlation of cIB with aortic annulus area as measured by computed tomography (r(129)= −0.19, p = 0.032), and cIB was also significantly higher in patients who had a pre-TAVI estimated glomerular filtration rate of less than 30 mL/min/1.73m2 (22.42±7.17 vs 19.56±6.88 dB, p = 0.043). Conclusion Our data disfavors the use of cIB as a predictor of major TAVI-related complications, but it suggests that cIB assessment could add value in identifying patients at risk of conduction disturbances in post-TAVI procedures.

Is myocardial fibrosis appropriately assessed by 2D strain derived integrated backscatter?

Abstract Funding Acknowledgements Type of funding sources: None. Introduction Calibrated integrated backscatter (cIBS) may be obtained from bidimensional (2D) strain echocardiography as a quantification measurement of myocardial ultrasound reflectivity. Increased collagen content of the myocardium modifies tissue reflectivity and cIBS is suggested as a marker of left ventricular (LV) fibrosis. However, its diagnostic accuracy is not established. Aim To assess the correlation between cIBS by 2D strain and LV myocardial fibrosis (MF), as evaluated by non-invasive imaging and histopathology. Methods Correlation study from a cohort of 157 patients with severe symptomatic aortic stenosis (AS) referred for surgical aortic valve replacement (AVR). Patients with complete preoperative transthoracic echocardiography, cardiac magnetic resonance (CMR) and endomyocardial biopsy (EMB) obtained from the anterior basal septum at the time of AVR were selected. Two groups of 30 patients were evaluated, with and without late gadolinium enhancement (LGE) at CMR. IBS was obtained at QRS peak in decibels (dB) from both parasternal long axis (PLAX) and apical three chamber (A3C) cine clips at Qanalysis (Figure 1A). cIBS was calculated by subtracting the pericardial intensity from the average of the anteroseptal and basal inferolateral wall values. Correlation analysis was performed for the whole group of patients with global and segmental (anterior basal septum) values of native T1 and extracellular volume (ECV), and EMB collagen volume fraction (CVF) from Masson´s Trichrome staining. IBS values were compared in both group of patients. Results 60 patients (73 [68–74] years, 45% male) with high gradient (mean gradient: 64±20mmHg), normal flow (45±10mL/m2), preserved ejection fraction (60±9%) AS. Basal septal cIBS was −9.2±9.5dB and −16.3±7.9dB from A3C and PLAX views, respectively. These indexes did not correlate with basal septum thickness or global LV mass. Absolute and cIBS did not correlate neither with global and regional T1 and ECV values, nor with CVF at EMB (Figure 1B). These were not significantly different in both groups of patients and there was no correlation between cIBS values and mass of replacement MF in patients with LGE. Conclusion In these cohort of patients with classical severe AS, there was no correlation of cIBS with imaging markers of both replacement and diffuse MF. cIBS also didn´t correlate with CVF at histopathology. These findings suggest that reflectivity indexes are not suitable for myocardial tissue characterization in this setting.

Ellipsoidal and hyperbolic Radon transforms; microlocal properties and injectivity

We present novel microlocal and injectivity analyses of ellipsoid and hyperboloid Radon transforms. We introduce a new Radon transform, R, which defines the integrals of a compactly supported L2 function, f, over ellipsoids and hyperboloids with centers on a smooth connected surface, S. Our transform is shown to be a Fourier Integral Operator (FIO) and in our main theorem we prove that R satisfies the Bolker condition if the support of f is contained in a connected open set that is not intersected by any plane tangent to S. Under certain conditions, this is an equivalence. We give examples where our theory can be applied. Focusing specifically on a cylindrical geometry of interest in Ultrasound Reflection Tomography (URT), we prove injectivity results and investigate the visible singularities. In addition, we present example reconstructions of image phantoms in two-dimensions and validate our microlocal theory.

Prognostic significance of calibrated integrated backscatter in patients submitted to transcatheter aortic valve implantation

Abstract Funding Acknowledgements Type of funding sources: None. Background There is a reported association between calibrated integrated backscatter (cIB) and myocardial fibrosis, mostly noted in cardiomyopathies and aortic stenosis cases. But whether this measure of myocardial ultrasound reflectivity could help predict outcomes in patients submitted to transcatheter aortic valve implantation has not been previously tested. Purpose To demonstrate whether cIB may help differentiate patients undergoing transcatheter aortic valve implantation (TAVI) at risk of major cardiovascular events. Methods Consecutive patients submitted to transfemoral TAVI between October 2020 and December 2021 were routinely imaged by echocardiography in the five days peri-procedure. Calibrated integrated backscatter was obtained from the parasternal long-axis view (PLAX) by subtracting pericardial cIB intensity from myocardial septal and posterior wall average cIB. Patients with poor PLAX views were excluded from the study. All measurements of cIB were performed at end-diastole. The primary endpoint was the occurrence of major cardiovascular events at one year of follow-up. Results A total of 184 patients underwent a TAVI procedure during the study period. Of these, 159 had a reasonable acoustic window for cIB measurement and were included in the study. Patient mean age was 81.1±6.1 years, and 58% were female. At baseline, 81% of patients had preserved left ventricle function, the mean aortic mean gradient was 44.8±15.1 mmHg, and the mean Euroscore II was 5.55±3.75. No significant association was found between cIB and TAVI-related major acute complications (21.02±10.4 vs 19.8±7.1 dB, p = 0.544). There was also no significant correlation of cIB with major cardiovascular events (19.71±7.25 vs 20.39±10.47 dB, p = 0.478) or with valve safety (19.59±7.07 vs 18.84±10.32 dB, p = 0.709), defined accordingly to the Valve Academic Research Consortium-2 consensus, at one-year follow-up. There was, however, a positive association between cIB and all-cause mortality (19.24±7.06 vs 22.92±9.36, p = 0.021) at one-year follow-up, with deaths occurring due to multiple causes, mainly cardiovascular, infectious, and neoplastic. Measured cIB was also significantly higher in patients with a pre-TAVI estimated glomerular filtration rate of less than 30 mL/min/1.73m2 (22.42±7.17 vs 19.56±6.88 dB, p = 0.043). Conclusion Higher cIB was not associated with a higher risk of major cardiovascular events or with valve safety in patients submitted to TAVI, but it can potentially have prognostic value in differentiating patients at increased risk of all-cause mortality.

Early monitoring of pore wetting in membrane distillation using ultrasonic time-domain reflectometry (UTDR)

Pore wetting induced by surfactants and salt scaling is a major obstacle to the industrial application of membrane distillation (MD). Identifying the transition of wetting stages and achieving early monitoring of pore wetting are crucial for wetting control. Herein, we made a pioneering attempt to use ultrasonic time-domain reflectometry (UTDR) technique to non-invasively detect the pore wetting in a direct contact MD, and explain the UTDR waveform with the help of optical coherence tomography (OCT) imaging. The results showed that the water–vapor interface had a strong reflection to ultrasound (reflection coefficient = 0.9995), while the water-membrane and water-scaling layer interfaces showed relatively weak reflection. Therefore, UTDR could effectively detect the movement of water–vapor interface with the low interference from the signals generated by the membrane and scaling layer. For the surfactant-induced wetting, the occurrence of wetting could be successfully detected by the right-shift in phase and the reduction in amplitude of the UTDR waveform. Moreover, the wetting depth could be accurately calculated by the time of flight (ToF) and ultrasonic velocity. For scaling-induced wetting, the waveform slightly shifted to the left at the beginning due to the growth of scaling layer, then to the right because the left-shift was surpassed by the right-shift of the waveform caused by pore wetting. Both for the surfactant- and scaling-induced wetting, the variation of the UTDR waveform was sensitive to wetting dynamics, and the right-shift of phase and the reduction in amplitude of the waveform could act as early monitoring signals to the occurrence of wetting.

Phase Distribution Measurement of Liquid–Solid Media Using Multimode Ultrasound

Ultrasound tomography (UT) is an emerging technique for phase distribution measurement in industrial multiphase flow monitoring. A multimode UT combining the ultrasound transmission and reflection modes is proposed to measure stratified phase distribution and sound speed of liquid–solid mixtures in the horizontal pipe. First, the acoustic attenuation is used to reconstruct the phase distribution with a modified matrix regularization algorithm, and the time-of-flight (TOF) of ultrasound is used to extract the boundary of multiphase layers with the weight Akaike information criterion algorithm. Second, a wavelet fusion method based on the principal component averaging is proposed to fuse the reconstruction images of UT transmission and reflection. Third, numerical investigations are carried out to validate the feasibility of the proposed method. According to the quantitative indexes, the proposed method can effectively reconstruct the phase distribution of multiphase media. Finally, an experimental test pipeline Section is established, and sand–water and oil–water–sand liquid–solid media are investigated. The minimum relative error (RE) and the maximum correlation coefficient (CC) of experimental fusion results can reach 0.33 and 0.94, respectively, and the average measurement error (ME) of the layer height is 3.80%.

An efficient analysis of oblique reflection of airborne ultrasound beams from thin membranes for gas sensing.

The use of the angular spectrum method (ASM) to simulate the reflection of airborne ultrasound beams from a thin membrane separating air from a mixture of air and another gas is examined. The main advantage of this method is its high computing speed and efficiency for practical design calculations, suitable for sensing applications. The implemented ASM code is validated against custom Rayleigh integral code in a pure propagation simulation. In addition, ultrasound beam reflection calculations using ASM with finite element numerical results and experimental measurements are compared, finding good agreement in both cases. Then, ASM is used to estimate the sensitivity of specular reflection signals to variations in the composition of the incidence medium as a function of the angle of incidence. Conditions for which a reflection signal using inexpensive commercial ultrasound emitter/receiver at 40 kHz, in a simple configuration, offer a high enough sensitivity suitable for monitoring air quality indoors are found.

Alleviation of cartilage degeneration by laser acupuncture: An ultrasound biomicroscopic study of early postmenopausal osteoarthritis in rats

This study aims to evaluate the therapeutic effects of laser acupuncture (LA) on articular cartilage degradation at the early stage of postmenopausal osteoarthritis (PMOA) by an ultrasound biomicroscopic technology. Twenty-one healthy female Sprague-Dawley rats were randomly and evenly divided into three groups - sham, ovariectomized (OVX) and OVX ​+ ​LA groups. Only the peri-ovarian fatty tissue of the sham rats was exteriorized. The animals in the OVX and OVX ​+ ​LA groups underwent bilateral ovariectomy to create a menopause model. On day 8 after the ovariectomy, the 2-week LA therapy at acupoints Guanyuan (CV-4), Sanyinjiao (SP-6), and Zusanli (ST-36) was performed in the OVX ​+ ​LA group, while the sham and OVX groups had a sham treatment. All the animals were sacrificed on day 22. The cartilage tissues in the left knee joint were examined by ultrasound and histology. Compared with the sham group, the significantly degenerate alterations (p ​< ​0.01) in ultrasound roughness index (URI), reflection coefficient (RC1) and cartilage thickness were found in the OVX group, while the values of these parameters were significantly recovered (p ​< ​0.01) in the OVX ​+ ​LA group. The LA treatment enhanced proteoglycans (PGs) content with a significant reduce of the modified Mankin score (p ​< ​0.01). The acoustic assessment strongly correlated with the histologic evaluation. The results showed that LA treatment could alleviate the postmenopause-induced cartilage degradation and promote tissue repair. LA has potential to be a simple and safe non-pharmacological countermeasure against PMOA for geriatric patient population. The ultrasound biomicroscopic technology could be a quantitative evaluation tool of the structural and morphological responses of articular cartilage to LA intervention.

Modeling of airborne ultrasound reflection from water surface waves

Airborne ultrasound reflection from water surface waves is modelled to advance uses of acoustic signals to measure water surface waves and apply the measurements to explore interactions of water waves with rigid structures in a laboratory setting. When the ultrasound is incident on a moving periodic water surface wave, the reflected signal can be treated as diffraction from a moving corrugated reflection grating. Under the condition that the amplitude of the water surface waves is much less than the incident acoustic wavelength, diffraction theory leads to analytical formulas for the spectra of the acoustic signal relating to the water wave amplitudes and frequencies. Complementary modeling based on ray theory and wave superposition illustrates the diffraction and validates formulas of water wave reflection from a surface-piercing barrier structure, where two counter-propagating water waves are involved.

A VGG attention vision transformer network for benign and malignant classification of breast ultrasound images.

Breast cancer is the most commonly occurring cancer worldwide. The ultrasound reflectivity imaging technique can be used to obtain breast ultrasound (BUS) images, which can be used to classify benign and malignant tumors. However, the classification is subjective and dependent on the experience and skill of operators and doctors. The automatic classification method can assist doctors and improve the objectivity, but current convolution neural network (CNN) is not good at learning global features and vision transformer (ViT) is not good at extraction local features. In this study, we proposed a visual geometry group attention ViT (VGGA-ViT) network to overcome their disadvantages. In the proposed method, we used a CNN module to extract the local features and employed a ViT module to learn the global relationship among different regions and enhance the relevant local features. The CNN module was named the VGGA module. It was composed of a VGG backbone, a feature extraction fully connected layer, and a squeeze-and-excitation block. Both the VGG backbone and the ViT module were pretrained on the ImageNet dataset and retrained using BUS samples in this study. Two BUS datasets were employed for validation. Cross-validation was conducted on two BUS datasets. For the Dataset A, the proposed VGGA-ViT network achieved high accuracy (88.71 1.55%), recall (90.73 1.57%), specificity (85.58 3.35%), precision (90.77 1.98%), F1 score (90.73 1.24%), and Matthews correlation coefficient (MCC) (76.34 3.29%), which were better than those of all compared previous networks in this study. The Dataset B was used as a separate test set, the test results showed that the VGGA-ViT had highest accuracy (81.72 2.99%), recall (64.45 2.96%), specificity (90.28 3.51%), precision (77.08 7.21%), F1 score (70.11 4.25%), and MCC (57.64 6.88%). In this study, we proposed the VGGA-ViT for the BUS classification, which was good at learning both local and global features. The proposed network achieved higher accuracy than the compared previous methods.

Ultrasound transmission and reflection tomography for nondestructive testing using experimental data

The possibility of reconstructing the velocity structure of inspected objects with a high spatial resolution and high sensitivity in ultrasonic tomographic nondestructive testing within the framework of a wave model has been demonstrated in a real experiment. In this study, a scheme of a tomographic experiment with rotation is proposed, which provides sounding of an inspected object from multiple sides. A tomographic scheme of the experiment with linear antenna transducer arrays operating at a frequency of ∼5 MHz was used. The experiment was conducted on dedicated samples including inserts with different sound propagation velocities. It was shown that the velocity structure and the boundaries of inserts can be reconstructed in the transmission and the reflection schemes. The reconstruction of the velocity structure was formulated as a nonlinear coefficient inverse problem for a scalar wave equation. Efficient iterative methods for its solution on a supercomputer were developed using direct formulas to compute the gradient of the residual functional between the computed and experimentally measured wave field at the detectors. Nonlinearity of the inverse problem of ultrasound tomography leads to multiple local minima of the residual functional. A two-stage iterative method was used for velocity reconstruction. The transmission scheme enables a spatial resolution of approximately 1 mm with a velocity contrast of 2%.

Spatio-Spectral Ultrasound Characterization of Reflection and Transmission Through Bone With Temperature Dependence.

Transcranial focused ultrasound (tFUS) is a promising approach for the treatment of neurological disorders. It has proven useful in several clinical applications, with promising outcomes reported in the recent literature. Furthermore, it is currently being investigated in a range of neuromodulation (NM) and ablative applications, including epilepsy. In this application, tFUS access through the temporal window is the key to optimizing the treatment safety and efficacy. Traditional approaches have utilized transducers with low operating frequencies for tFUS applications. Modern array transducers and driving systems allow for more intelligent use of the temporal window by exploiting the spatio-spectral transmission bandwidth to a specified target or targets within the brain. To demonstrate the feasibility of this approach, we have investigated the ultrasound reflection and transmission characteristics for different access points within the temporal window of human skull samples ex vivo. Different transmit-receive (Rx) configurations are used for characterization of the spatio-spectral variability in reflection and transmission through the temporal window. In this article, we show results from a dual-piston transducer set up in the frequency range of 2-7 MHz. Broadband pulses as well as synthesized orthogonal frequency division multiplexed (OFDM) waveforms were used. The latter was used to improve the magnitude and phase measurements in 100-kHz subbands within the 2-7 MHz spectral window. A temperature-controlled water bath was used to characterize the change in reflection and transmission characteristics with temperature in the 25°C-43°C range. The measured values of the complex reflection and transmission coefficients exhibited significant variations with space, frequency, and temperature. On the other hand, the measured transmission phase varied more with location and frequency, with smaller sensitivity to temperature. A measurement-based hybrid angular spectrum (HAS) simulation through the human temporal bone was used to demonstrate the dependence of focusing gain on the skull profile and spatial distribution of change of speed of sound (SOS) at different skull temperatures.

Assessing Bone Quality of the Spine in Children with Scoliosis Using the Ultrasound Reflection Frequency Amplitude Index Method: A Preliminary Study.

Osteopenia is considered a common phenomenon in patients who have scoliosis. Quantitative ultrasound has been used to assess skeletal status for decades, and recently ultrasound imaging using reflection signals from vertebrae were as well applied to measure spinal curvatures in children with scoliosis. The objectives of this study were to develop a new method that can robustly extract a parameter from ultrasound spinal data for estimating bone quality of scoliotic patients and to investigate the potential of the parameter in predicting curve progression. The frequency amplitude index (FAI) was calculated based on the spectrum of the original radiofrequency signals reflected from the tissue-vertebra interface. The correlation between FAI and reflection coefficient was validated using decalcified bovine bone samples in vitro, and the FAIs of scoliotic subjects were investigated in vivo with reference to body mass index, Cobb angles and curve progression status. The results revealed that the intra-rater measures were highly reliable between different trials (intra-class correlation coefficient=0.997). The FAI value was strongly correlated with the reflection coefficient of bone tissue (R2=0.824), and the lower FAI indicated the higher risk of curve progression for the non-mild scoliosis cases. This preliminary study found that the FAI method can provide a feasible and robust approach to assessment of the bone quality of spine and may be a promising factor in monitoring curve progression of patients who have adolescent idiopathic scoliosis.