RF Echo Research Articles

The mean scatterer spacing estimation with the Gabor atoms selected based on the Nakagami distribution

Abstract Mean scatterer spacing (MSS) is a quantitative signature for disease diagnosis and tissue characterization. However, it is difficult to objectively extract the coherent components from the ultrasound RF echo signals to improve the accuracy performance of the MSS estimation. In the present study, a novel MSS estimation method with the matched Gabor atoms selected based on Nakagami parameters is proposed. Firstly, the ultrasound signals are decomposed into a series of Gabor atoms, and the envelopes of the residual signals are fitted with the Nakagami distribution. Then, the second order difference (SOD) of the shape parameters in Nakagami distribution is calculated to select the optimal atoms to match the coherent components. Finally, the locations of the selected Gabor atoms are used to estimate the MSS. In order to evaluate the performance of the proposed method, the simulated RF echo signals are modelled based on four regular degrees of the scatterer distributions, and then the optimally matched atoms are selected to estimate MSSs. The results based on simulated signals demonstrate that the propose method can provide accurate MSS estimation, which are advantageous for improving quantitative diagnosis of diseases and tissue characterization

Evaluating the effect of tissue stimulation at different frequencies on breast lesion classification based on nonlinear features using a novel radio frequency time series approach

ObjectiveRadio Frequency Time Series (RF TS) is a cutting-edge ultrasound approach in tissue typing. The RF TS does not provide dynamic insights into the propagation medium; when the tissue and probe are fixed. We previously proposed the innovative RFTSDP method in which the RF data are recorded while stimulating the tissue. Applying stimulation can unveil the mechanical characteristics of the tissue in RF echo. Materials and methodsIn this study, an apparatus was developed to induce vibrations at different frequencies to the medium. Data were collected from four PVA phantoms simulating the nonlinear behaviors of healthy, fibroadenoma, cyst, and cancerous breast tissues. Raw focused, raw, and beamformed ultrafast data were collected under conditions of no stimulation, constant force, and various vibrational stimulations using the Supersonic Imagine Aixplorer clinical/research ultrasound imaging system. Time domain (TD), spectral, and nonlinear features were extracted from each RF TS. Support Vector Machine (SVM), Random Forest, and Decision Tree algorithms were employed for classification. ResultsThe optimal outcome was achieved using the SVM classifier considering 19 features extracted from beamformed ultrafast data recorded while applying vibration at the frequency of 65 Hz. The classification accuracy, specificity, and precision were 98.44 ± 0.20 %, 99.49± 0.01 %, and 98.53± 0.04 %, respectively. Applying RFTSDP, a notable 24.45 % improvement in accuracy was observed compared to the case of fixed probe assessing the recorded raw focused data. ConclusionsExternal vibration at an appropriate frequency, as applied in RFTSDP, incorporates beneficial information about the medium and its dynamic characteristics into the RF TS, which can improve tissue characterization.

An Ultrasonic RF Acquisition System for Plant Stems Based on Labview Double Layer Multiple Triggering.

Ultrasound is widely used in medical and engineering inspections due to its non-destructive and easy-to-use characteristics. However, the complex internal structure of plant stems presents challenges for ultrasound testing. The density and thickness differences in various types of stems can cause different attenuation of ultrasonic signal propagation and the formation of different echo locations. To detect structural changes in plant stems, it is crucial to acquire complete ultrasonic echo RF signals. However, there is currently no dedicated ultrasonic RF detection equipment for plant stems, and some ultrasonic acquisition equipment has limited memory capacity that cannot store a complete echo signal. To address this problem, this paper proposes a double-layer multiple-timing trigger method, which can store multiple trigger sampling memories to meet the sampling needs of different plant stems with different ultrasonic echo locations. The method was tested in experiments and found to be effective in acquiring complete ultrasonic RF echo signals for plant stems. This approach has practical significance for the ultrasonic detection of plant stems.

Decorrelated compounding of synthetic aperture ultrasound imaging to detect low contrast thermal lesions induced by focused ultrasound

PurposeDecorrelated Compounding (DC) for synthetic aperture ultrasound can reduce speckle variation in images, suggesting enhanced detectability of low-contrast targets in tissue including thermal lesions produced by focused ultrasound (FUS). The DC imaging method has primarily been investigated in simulation and in phantom studies. This work investigates the feasibility of the DC method in monitoring thermal therapy via image guidance and non-invasive thermometry based on the change in backscattered energy (CBE). MethodsEx vivo porcine tissue was exposed to FUS exposures at acoustic powers of 5 W and 1 W, with peak pressure amplitudes of 0.64 MPa and 0.27 MPa respectively. During FUS exposure, RF echo data frames was acquired using a 7.8 MHz linear array probe and a Verasonics VantageTM ultrasound scanner (Verasonics Inc., Redmond, WA). RF echo data was taken to produce B-mode images, as reference images. Synthetic aperture RF echo data was also acquired and processed using delay-and-sum (DAS), a combination of spatial and frequency compounding referred to as Traditional Compounding (TC), and the proposed DC imaging methods. Image quality was assessed using the contrast-to-noise ratio (CNR) at the FUS beam focus, and the speckle SNR (sSNR) of the background region as preliminary metrics. A calibrated thermocouple was placed near the FUS beam focus for temperature measurements and calibrations using the CBE method. ResultsThe DC imaging method significantly improved image quality to detect low contrast thermal lesions in treated ex vivo porcine tissue in comparison to other imaging methods. In comparison to B-mode imaging, the lesion CNR measured using the DC imaging was shown to improve up to a factor of approximately 5.5. The corresponding sSNR improved by a factor of approximately 4.2 in comparison to B-mode imaging. CBE calculation using the DC imaging method yielded more precise measurements of the backscattered energy compared to other imaging methods studied. ConclusionsThe despeckling performance of the DC imaging method significantly improves the lesion CNR in comparison to B-mode imaging. This suggests that the proposed method can detect low-contrast thermal lesions induced by FUS therapy that are not detectable using standard B-mode imaging. Furthermore, the signal change at the focal point were more precisely measured by DC imaging, and the signal change in response to FUS exposure follows the temperature profile more closely than changes measured using B-mode, as well as synthetic aperture DAS and TC images. These suggest that DC imaging can potentially be used with the CBE method to improve non-invasive thermometry.

2Pa5-1 Improvement of Precision in Strain Rate Measurement Using Spatial Distribution of Envelope of RF Echoes

2Pa5-1 Improvement of Precision in Strain Rate Measurement Using Spatial Distribution of Envelope of RF Echoes

High-frequency quantitative ultrasound to assess chemical crosslinking induced changes in the posterior sclera

Myopia alters the collagen microstructure of the sclera which changes the tissue biomechanical properties. Although most forms of myopia are mild, progression of the disease to high or pathologic myopia can lead to significant weakening of the sclera and greatly increase the risk for the formation of a posterior staphyloma, a sight-threatening condition. Potential treatments to counteract effects of myopia on the sclera include chemical crosslinking (CXL). Formaldehyde releasing agents like sodium hydroxymethylglycinate (SHMG) are an attractive option for the posterior sclera because they increase tissue stiffness and require no light activation. Previous research has demonstrated that high-frequency quantitative ultrasound (QUS) is sensitive to the microstructural changes in the sclera caused by myopia. In this study, we investigate the ability of QUS to monitor microstructural changes caused by CXL. Ex vivo pig eyes were immersed in a 26.5 mM SHMG solution and scanned by an 80MHz ultrasound transducer at regular time intervals. RF echo data were analyzed to compute QUS parameters from the backscatter coefficient, normalized power spectrum, and echo envelope statistics. Correlations between QUS parameters and immersion time were investigated to evaluate the efficacy of QUS for monitoring CXL treatment. Results of this study demonstrate the capability to high-frequency QUS to assess changes in tissue microstructure caused by CXL with SHMG.

Analysis and Investigation of Disturbance in Radar Systems Using New Techniques of Electronic Attack

With the end of World War II and the rapid advent of war technology, wars have shifted to electronic warfare, and today a nation can win wars that are more powerful in the field of telecommunications and electronic warfare. The purpose of this article is to promote new content in the field of electronic warfare and we try to introduce and introduce new techniques of electronic attacks on victim radar systems. With the exception of false targets created by point or sweep jams, most false targets are created with automatic responders or repeaters. An automatic response generator for producing false targets includes a receiver, a variable delay circuit, a signal generator, a power amplifier, and an antenna. Upon receiving a pulse from the threatening radar, the transponder waits for the time corresponding to the target man's distance to the false target, and then sends a similar echo signal to the radar. . As soon as the pulse is received from the threatening radar, the transponder delays it sufficiently to cause the difference in distance to create a false target. Then, a pulse similar to the RF echo pulse of the radar is returned to it.

Basic study on estimation method of wall shear stress in common carotid artery using blood flow imaging

In this paper, we propose a method for adaptive selection of the kernel size used in estimation of the wall shear stress (WSS) based on flow velocity profiles obtained by the blood flow imaging method based on enhancement of RF echo signals from blood cells using a singular value decomposition based clutter filter. Two simulation phantom experiments with the Field II program were performed to validate the proposed method. In the simulation experiments, the average bias error (BE) between the WSSs estimated by the conventional method and theoretical one was 16.5%. The proposed method could reduce the average BE to 12.3%. Also, the proposed method was applied to RF echo signals from a common carotid artery (CCA) of a healthy male subject. The WSSs in the CCA were estimated during one cardiac cycle and in a range similar to that in previous reports.

Locations of optimally matched Gabor atoms from ultrasound RF echoes for inter-scatterer spacing estimation

Background and objectiveThe resolvable scatterer spacing related to biological tissue microstructures is a quantitative signature used for the disease diagnosis and tissue classification. In the present study, a method by locating optimally matched Gabor atoms (LOMGA) from ultrasound RF echo signals is proposed to improve the inter-scatterer spacing (ISS) estimation. MethodA series of Gabor atoms are obtained from the signals with a matching pursuit algorithm. Then, the optimum atoms highly correlated with the coherent components are automatically selected according to the second-order difference of the reconstructed signal-to-residue ratio. The distances between the locations of adjacent atoms are applied to estimate the ISSs. In the simulation experiments, four regular degrees of the scatterer distributions are modeled with the Gamma distribution. One hundred sets of ultrasound RF echo signals are simulated based on the regular and diffuse scatterer distributions, and then combined to generate signals with preset coherent-to-diffuse ratios (CDRs). The accuracy performance of the LOMGA method is compared with that based on wavelet transform (WT) algorithm. In the microwave ablation experiments, the ultrasound RF echo signals of the region of interest (ROI) are collected from the normal and coagulated porcine liver tissues. The means and standard deviations of the LOMGA-based ISSs are compared with the WT-based results. ResultsThe results based on simulated signals with CDRs from 10 dB to −10 dB demonstrate that the proposed method improves the estimation accuracies of the mean ISSs by 5.10%, 9.00%, 19.80%, and 23.82%, and reduces the mean standard deviations by 27.20%, 22.50%, 11.50%, and 4.49% more than the WT method for the four regularities, respectively. The performance of the LOMGA method is also verified with the ultrasound RF echo signals from ex vivo porcine liver tissues in microwave ablation experiments. ConclusionsIt is concluded that the LOMGA method can provide more accurate and stable ISS estimation, which improves the performance of the tissue characterization with ISS-based quantitative ultrasound.

A new technique for the measurement and assessment of carotid artery wall vibrations using ultrasound RF echoes

Atherosclerosis is known as the leading cause of heart attacks and brain strokes. One of the symptoms of this disease is the reduction of artery wall motion caused by age. This study presents a novel method to extract high frequency components of wall motion, wall vibrations, based on discrete wavelet transform. The fractal dimension, largest Lyapunov exponent, and spectral entropy are then analyzed to indicate the chaotic behavior in wall vibrations. Phase information from demodulated radiofrequency signals is extracted and the entropy of phase-difference is computed as a statistical measure for better characterization of the artery wall tissue. The results show that these features correlate with age (P $

Blood flow imaging using singular value decomposition filter during high-intensity focused ultrasound exposure

High-intensity focused ultrasound (HIFU) is a minimally invasive treatment modality to induce thermal coagulation. In clinical cases, noninvasive blood flow occlusion was successfully achieved by HIFU exposure. However, it is difficult to monitor the blood flow during HIFU exposure due to the interference of HIFU noise with RF echo signals. In this study, we proposed a novel filtering method for monitoring blood flow during HIFU exposure by combining an singular value decomposition (SVD) filter with the HIFU noise reduction method. The HIFU noise was reducted by subtracting the RF signals of passive imaging from the RF signals of active imaging while keeping the tissue and blood flow signals intact. After that, the blood flow signals were identified by employing the SVD filter, on the basis of the spatiotemporal characteristics and amplitudes of these signals. The results imply that the proposed filtering method is useful for monitoring of blood flow during HIFU exposure.

Repeatability and Reproducibility of the Ultrasonic Attenuation Coefficient and Backscatter Coefficient Measured in the Right Lobe of the Liver in Adults With Known or Suspected Nonalcoholic Fatty Liver Disease.

To assess the repeatability and reproducibility of the ultrasonic attenuation coefficient (AC) and backscatter coefficient (BSC) measured in the livers of adults with known or suspected nonalcoholic fatty liver disease (NAFLD). The Institutional Review Board approved this Health Insurance Portability and Accountability Act-compliant prospective study; informed consent was obtained. Forty-one research participants with known or suspected NAFLD were recruited and underwent same-day ultrasound examinations of the right liver lobe with a clinical scanner by a clinical sonographer. Each participant underwent 2 scanning trials, with participant repositioning between trials. Two transducers were used in each trial. For each transducer, machine settings were optimized by the sonographer but then kept constant while 3 data acquisitions were obtained from the liver without participant repositioning and then from an external calibrated phantom. Raw RF echo data were recorded. The AC and BSC were measured within 2.6 to 3.0 MHz from a user-defined hepatic field of interest from each acquisition. The repeatability and reproducibility were analyzed by random-effects models. The mean AC and log-transformed BSC (logBSC) were 0.94 dB/cm-MHz and -27.0 dB, respectively. Intraclass correlation coefficients were 0.88 to 0.94 for the AC and 0.87 to 0.95 for the logBSC acquired without participant repositioning. For between-trial repeated scans with participant repositioning, the intraclass correlation coefficients were 0.80 to 0.84 for the AC and 0.69 to 0.82 for the logBSC after averaging results from 3 within-trial images. The variability introduced by the transducer was less than the repeatability error. Hepatic AC and BSC measures using a reference phantom technique on a clinical scanner are repeatable and reproducible between transducers in adults with known or suspected NAFLD.

Design and Control of a Quadruple-Input Double-Output Coherent Radar Test Platform Composed of Test & Measurement Equipment and Custom Hardware

A radar test platform composed of commercial off-the-shelf test and measurement equipment and custom hardware has been built. This platform, which enables production of dual-channel coherent radar transmitting signals with a bandwidth up to 500MHz, and reception of four parallel channels of RF injection signals or echoes, can simulate various types of radar emitters or to simulate the multiple modes of operation for a single type radar. A software is also programmed with C++ language to control the waveforms, frequencies, phases, time delays and all other aspects of the test platform’s operation at all stages. At last, an application example is given when the platform is used for ISAR imaging verification.

Expanding Acquisition and Clutter Filter Dimensions for Improved Perfusion Sensitivity.

A method is explored for increasing the sensitivity of power-Doppler imaging without contrast enhancement. We acquire 1-10 s of echo signals and arrange it into a 3-D spatiotemporal data array. An eigenfilter developed to preserve all three dimensions of the array yields power estimates for blood flow and perfusion that are well separated from tissue clutter. This method is applied at high frequency (24-MHz pulses) to a murine model of an ischemic hindlimb. We demonstrate enhancements to tissue perfusion maps in normal and ischemic tissues. The method can be applied to data from any ultrasonic instrument that provides beamformed RF echo data.

Comparison analysis of four processing methods employed in dynamic elastography to estimate viscoelastic parameters of a medium: tests using computational simulation and experiment

Dynamic ultrasound elastography is a method commonly used to quantify the mechanical parameters, such as shear elasticity modulus, and shear viscosity modulus, of biological tissues. Basically, the method employs four processing techniques, in order to estimate the mentioned parameters, denominated: phase velocity dispersion, PVD, attenuation-velocity, AV, complex shear elasticity modulus, CSM, and shear wave velocity, SV. The accuracy and precision of estimated values for and depend on the processing technique and the purpose of this paper is to compare the results obtained with PVD, AV, CSM and SV processing techniques by means of two cases: computer simulation and experiments. In the first case, the processing techniques were evaluated, via simulation, at different conditions for the signal-to-noise-ratio of the ultrasound RF echo signal used to probe the medium with vibrations due to the propagation of shear wave, the vibration amplitude and the viscoelastic properties of the medium itself. The corresponding results are expressed as the magnitudes of the mean and standard deviation of the relative error. In the second case, experiments were conducted based on a dynamic elastographic system with a cylindrical shear wave induced by a repetitive acoustic radiation force, with pulse repetition frequency of 50 Hz. A 4.98 MHz pulse-echo ultrasound system was used to probe the medium, a 3% gelatin phantom, traversed by the shear wave and the received RF echo signals were processed using the four techniques to yield the phantom values of and The results from computer simulation indicate that, in general, the CSM and AV techniques presented highest accuracy and precision. The experimental results obtained in this study are consistent with the values reported in the literature and the values of the shear elasticity modulus estimated by the four processing techniques did not differ significantly.

High Resolution Microultrasound (μUS) Investigation of the Gastrointestinal (GI) Tract.

High resolution, microultrasound (μUS) scanning of the gastrointestinal (GI) tract has potential as an important transmural imaging modality to aid in diagnosis. Operating at higher frequencies than conventional clinical ultrasound instruments, μUS is capable of providing scanned images of the GI tract with higher resolution. To investigate the use of μUS for this application, a phantom which is cost effective, within ethical guidelines and, most importantly, similar in histology to the human GI tract is necessary. Therefore, a phantom utilizing porcine small bowel tissue has been developed for custom assembled μUS scanning systems. Two such systems, a stepping scanner and a continuous sweep scanner were utilized to repeatedly scan regions of prepared samples of porcine small bowel tissue. The porcine small bowel tissue phantom was perfused with degassed phosphate buffer saline (dPBS) solution through a cannula inserted in its mesenteric vessel to simulate in vivo conditions and achieve better μUS mucosal characterization. The μUS system scans a transducer across the tissue phantom to acquire RF echo data, which is then processed using MATLAB. A B-scan reconstruction produces 2D images with relative echo strength mapped to a color map of the user's choice. The phantom developed also allows for modifications such as the insertion of fiducial markers to detect tissue change over time and simultaneous perfusion and scanning, providing a platform for more detailed research and investigation into μUS scanning of the GI tract.

Feasibility of real-time treatment feedback using novel filter for eliminating therapeutic ultrasound noise with high-speed ultrasonic imaging in ultrasound-guided high-intensity focused ultrasound treatment

In the conventional ultrasonic monitoring of high-intensity focused ultrasound (HIFU) treatment, a significant interval between HIFU shots is required when monitoring target tissue to avoid interference between HIFU noise and RF echo signals. In our previous study, a new filtering method to eliminate only HIFU noise while maintaining tissue signals intact was proposed, and it was shown that the thermal coagulation could be detected during simultaneous HIFU irradiation through off-line processing. In this study, the filtering method and a real-time coagulation detection algorithm were implemented in an ultrasound imaging system, whose use for sequential exposure with multiple foci was demonstrated similarly to a commercial HIFU ablation system. The coagulation was automatically detected by the proposed method during real-time simultaneous HIFU irradiation, and the HIFU exposure time was controlled according to the changes in the tissue. The results imply that ultrasonic monitoring with the filtering and detection methods is useful for true real-time detection of changes in the tissue due to thermal coagulation during HIFU exposure.

Shear wave arrival time estimates correlate with local speckle pattern.

We present simulation and phantom studies demonstrating a strong correlation between errors in shear wave arrival time estimates and the lateral position of the local speckle pattern in targets with fully developed speckle. We hypothesize that the observed arrival time variations are largely due to the underlying speckle pattern, and call the effect speckle bias. Arrival time estimation is a key step in quantitative shear wave elastography, performed by tracking tissue motion via cross-correlation of RF ultrasound echoes or similar methods. Variations in scatterer strength and interference of echoes from scatterers within the tracking beam result in an echo that does not necessarily describe the average motion within the beam, but one favoring areas of constructive interference and strong scattering. A swept-receive image, formed by fixing the transmit beam and sweeping the receive aperture over the region of interest, is used to estimate the local speckle pattern. Metrics for the lateral position of the speckle are found to correlate strongly (r > 0.7) with the estimated shear wave arrival times both in simulations and in phantoms. Lateral weighting of the swept-receive pattern improved the correlation between arrival time estimates and speckle position. The simulations indicate that high RF echo correlation does not equate to an accurate shear wave arrival time estimate-a high correlation coefficient indicates that motion is being tracked with high precision, but the location tracked is uncertain within the tracking beam width. The presence of a strong on-axis speckle is seen to imply high RF correlation and low bias. The converse does not appear to be true-highly correlated RF echoes can still produce biased arrival time estimates. The shear wave arrival time bias is relatively stable with variations in shear wave amplitude and sign (-20 μm to 20 μm simulated) compared with the variation with different speckle realizations obtained along a given tracking vector. We show that the arrival time bias is weakly dependent on shear wave amplitude compared with the variation with axial position/ local speckle pattern. Apertures of f/3 to f/8 on transmit and f/2 and f/4 on receive were simulated. Arrival time error and correlation with speckle pattern are most strongly determined by the receive aperture.

Visualizing the Tumor Microvasculature With a Nonlinear Plane-Wave Doppler Imaging Scheme Based on Amplitude Modulation

Imaging with ultrasonic plane waves enables the combination of Doppler and microbubble contrast-enhanced imaging without compromising the Doppler ensemble length, as is the case for conventional line-by-line imaging, thus maintaining flow sensitivity. This permits the separation of conduit flow in large vessels from the perfusion background and the presentation of velocity estimates in real-time. However, the ability to differentiate perfusion from the tissue signal is limited by the contrast-to-tissue (CTR) ratio achieved with the contrast-enhanced pulsing sequence, independently of the acquisition length. One way to improve the CTR is to use a Doppler sequence based on amplitude modulation instead of one based on pulse inversion. In this work, we discuss how amplitude modulation can be adapted to Doppler processing. We show that amplitude modulation Doppler, like pulse inversion Doppler, can separate the signal of moving tissue from that of moving microbubbles, while achieving a better contrast-to-tissue ratio than pulse inversion Doppler, both in vitro and in vivo. Both amplitude modulation Doppler and pulse inversion Doppler yield similar velocity estimates when the bandwidth of the RF echo is properly compensated. Finally, we demonstrate how amplitude modulation Doppler can be used to reveal both the conduit flow and the capillary perfusion at high frame rates in an in vivo tumor.

A flexible multichannel FPGA and PC-Based ultrasound system for medical imaging research: initial phantom experiments

IntroductionIn this paper, we present the initial results of a fully programmable 128-channel FPGA and PC-based system that has been developed for medical ultrasound (US) imaging research in our University laboratory (Federal University of Technology - Parana, Brazil).MethodsIn order to demonstrate the feasibility of the US research system, two applications involving unfocused plane wave transmission and conventional B-mode beamforming were evaluated using a commercial tissue-mimicking phantom and a 3.2 MHz 128-element convex array transducer.ResultsTesting results show that the hardware platform is able to synthesize arbitrary pulses up to 100 Vpp with second order harmonic distortion below 80 dB. For the first application, a 41-tap digital FIR bandpass filter was applied to the acquired RF echoes, sampled at 40 MHz with 12-bit resolution, to improve the noise suppression. In the second application, after offline apodization weighting, filtering, delay-and-sum processing, envelope detection, log compression and scan conversion, the reconstructed B-mode image is displayed over a 50 dB range.DiscussionThe presented results indicate that the open US imaging system can be used to support different ultrasonic transmission and reception strategies, which typically cannot be implemented in conventional data flow architectures that are mainly based on hardware.