Synthetic Aperture Focusing Method Research Articles

Actuated Reflector-Based 3-D Ultrasound Imaging With Synthetic Aperture Focusing.

Three-dimensional (3D) ultrasound (US) imaging addresses the limitation in field-of-view (FOV) in conventional two-dimensional (2D) US imaging by providing 3D viewing of the anatomy. 3D US imaging has been extensively adapted for diagnosis and image-guided surgical intervention. However, conventional approaches to implement 3D US imaging require either expensive and sophisticated 2D array transducers or external actuation mechanisms to move a one-dimensional array mechanically. Here, we propose a 3D US imaging mechanism using actuated acoustic reflector instead of the sensor elements for volume acquisition with significantly extended 3D FOV, which can be implemented with simple hardware and compact size. To improve image quality on the elevation plane, we implemented the synthetic aperture focusing (SAF) method according to the diagonal geometry of the virtual element array in the proposed imaging mechanism for elevation beamforming. We first evaluated the proposed imaging mechanism and SAF with simulated point targets and cyst targets. Results of point targets suggested improved image quality on the elevation plane, and results of cysts targets demonstrated a potential to improve 3D visualization of human anatomy. We built a prototype imaging system with a 3D FOV of 38 mm (lateral) by 38 mm (elevation) by 50 mm (axial) and collected data in imaging experiments with phantoms. Experimental data showed consistency with simulation results. The SAF method enhanced quantifying the cyst volume size in the breast mimicking phantom compared to without elevation beamforming. These results suggested that the proposed 3D US imaging mechanism could potentially be applied in clinical scenarios.

Acoustic Signal Imaging Method Based on Synthetic Aperture Focusing and Full Matrix Capture

In order to observe and understand the effect of acoustic signal detection more intuitively, imaging analysis is needed to obtain clearer detection results, and the detection situation is analyzed manually. The commonly used imaging method is B-scan imaging, which is also widely used in medical imaging. In this paper, an acoustic signal imaging method based on synthetic aperture focusing and full matrix capture is proposed. The application of synthetic aperture focusing method in acoustic signal imaging was improved. Hilbert transformation was used to construct complex signal sequence, and the imaging processing process of full matrix method is proposed. From the aspects of data acquisition, analysis and processing, the echo signals are analyzed, and the differences between synthetic aperture focusing and full matrix method in acoustic signal imaging are compared.

Three-dimensional reconstruction of ceramic membrane with internal defects based on ultrasound imaging technique applying triangular matrix-synthetic aperture focusing

To realize a three-dimensional (3D) visual display and evaluate the internal defects of a ceramic hollow plate membrane, a method for creating a 3D reconstruction of the internal defects based on an ultrasound imaging technique applying triangular matrix–synthetic aperture focusing is proposed. First, a phased array detector is used to scan the surface of the ceramic membrane, and ultrasound imaging is achieved based on the triangular matrix–synthetic aperture focusing technology. The acquired B-scan images are pre-processed and a 3D reconstruction is achieved based on the contours of the internal defects. Finally, a 3D visualization of the internal defects of a hollow plate ceramic membrane is realized. The use of a triangular matrix focusing method can improve the detection efficiency because the amount of data acquired and the number of calculations are reduced by nearly half. In addition, the synthetic aperture focusing method can ensure a high imaging resolution, which leads to an improved recognition accuracy of the defect size. As a result, the error of the diameter measurements of the inner hole defects ranges between 2% and 3%, and the error of the diameter and length measurements of the crack line defects ranges between 2% and 4%. Experimental results with real datasets are presented to demonstrate the efficiency and accuracy of our method as compared with traditional methods.

The development and current state of methods for the nondestructive testing and acoustic tomography of concrete

The development of acoustic methods for the nondestructive testing of concrete during the recent decades is described. The main characteristic problems and tasks of acoustic tomography of concrete are outlined and the evolution of the methods of their solution is analyzed. The advantages and disadvantages of the synthetic-aperture focusing method as a tool for the visualization of the internal structure of concrete are discussed. Possible directions of further progress in theory, as well as practical acoustic tomography methods, including those using phase information, are indicated.

Imaging and Testing of Ultrasonic Sh Guided Waves in Plate with Lap Welding Structure

The imaging and testing of ultrasonic SH (Shear Horizontal) guided waves may be used into testing and SHM (Structure Health Monitoring) of industrial plate with welding structure in service, which have much more important applied potential. During imaging and testing for steel plate with lap welding structure, photoelastic experiment on propagation of guided waves in Plexiglas plate was studied to clearly see the excellent advantages of SH guided waves. The mode of SH guided waves was analyzed to select the zero order mode SH0 and the SH guided waves transducer with SH0 mode was developed. Based on the synthetic aperture focusing method，a multichannel ultrasonic imaging and testing experimental system of ultrasonic SH guided waves was constructed，the imaging of plate with lap welding structure was mainly studied. The research results shows the ultrasonic SH guided waves and the transducers are fit for long distance testing for the plate with lap welding structure. The ultrasound scattering nearby the weld may cause a blind testing zone, about 150 mm wide, in which the less size corrosion defects at the blind zone could not be revealed in image, so as to lead to defects “no testing”. The imaging and testing of ultrasonic SH guided waves would be used for non-destructive testing of plate with lap welding structure, which image both can characterize the corrosion defects and lap welding structure, and realize the precise location of the weld. The proposed research provides important foundation for improving ultrasonic guided waves imaging and testing quality and SHM of industrial in-site plate with lap welding and larger size.

Synthetic aperture focusing for a single-element transducer undergoing helical motion

This paper describes the application of 3-D synthetic aperture focusing (SAF) to a single-element trans-rectal ultrasound transducer. The transducer samples a 3-D volume by simultaneous rotation and translation, giving a helical motion. Two different 3-D SAF methods are investigated, a direct and a two-step approach. Both methods perform almost identically for simulated scatterers and give a significant improvement in azimuth resolution and a constant resolution in elevation. Side lobes below -60 dB are achievable for both methods. Validation of the method is achieved by scanning a simple wire phantom and a complex phantom containing wires in azimuth and elevation. The simple wire phantom shows the same results as that found through simulation. The complex phantom shows simultaneous focusing in azimuth and elevation for the wire scatterers. Consideration of the processing requirements for both 3-D SAF methods shows that the two-step approach can give equivalent performance using an order of magnitude fewer calculations. This reduction requires a temporary storage of 9.1 GB of data for the investigated setup.

A new synthetic aperture focusing method to suppress the diffraction of ultrasound

Spatial resolution of an ultrasound image is limited by diffraction of ultrasound as it propagates along the axial direction. This paper proposes a method for reducing the diffraction spreading effect of ultrasound by using a synthetic aperture focusing (SAF) method that uses plane waves instead of spherical waves. The new method performs data acquisition and beamforming in the same manner as conventional SAF methods. The main difference is that all array elements are used on each firing to generate a plane wave, the traveling angle of which varies with the position of a receive subaperture. On reception, each scan line is formed by synthesizing RF samples acquired by relevant receive subapertures with delays to force the plane waves to meet at each imaging point. Theoretical analysis and computer simulation with infinite transmit aperture show that the proposed method is capable of suppressing the diffraction of ultrasound and especially causing the lateral beam width to remain unchanged beyond a certain depth determined by the size of a receive subaperture and the maximum traveling angle of plane waves. It is demonstrated that the proposed method is realizable using a linear array transducer. It is also shown that the lateral radiation pattern produced by the proposed method has smaller beam width than that using conventional SAF methods in the region of interest because it suppresses the diffraction of ultrasound.

Wave equation-based imaging of mode converted waves in ultrasonic NDI, with suppressed leakage from nonmode converted waves

The value of imaging techniques in ultrasonic nondestructive inspection (NDI) to find and characterize defects in steel components has already been demonstrated. The imaging techniques based on the integral representation of the wave equation, the Rayleigh integrals for wave field extrapolation, are becoming feasible and attractive due to advances in array technology and due to faster computers. Known implementations are the total focusing method (TFM), the synthetic aperture focusing method (SAFT), and the inverse wave field extrapolation method (IWEX). In principle, these techniques compensate propagation effects from sources to a scatterer such as a defect and propagation effects from the scatterer to receivers. Currently, this approach is applied to wave fronts of single modes (pure longitudinal or pure transversal). In practice, multiple wave fronts from the scatterer will be received as a result of mode conversion. These arrivals will not have the same arrival time because of the difference in sound velocity between longitudinal and transversal waves. Images of mode converted waves are obtained by choosing the appropriate sound velocity that corresponds with the mode-converted scattered wave in the imaging process. Therefore, the nonmode converted waves will image as leakage artifacts in the mode-converted images, and vice versa. This may lead to false interpretations. In this paper, such artifacts will be identified and explained with the help of an analytical example. Measurements from steel test pieces with a 4 MHz linear array transducer with 64 elements will be used to demonstrate the artifacts. Furthermore, a procedure to predict the artifacts and the subsequent suppression from the input measurements will be presented and demonstrated.

Calculation of high frequency ultrasonic signals for shear wave insonification in solid material

The goal of the theoretical part is to simulate an automatic ultrasonic inspection with contact technique shear wave probes, where the high frequency signals are captured and used to perform a reconstruction based on the synthetic aperture focusing method “SAFT”. Therefore the ultrasonic probe, the scanning path and the defects are parameters in a CAD model. The scattering behavior of the defect is calculated by the Kirchhoff approximation in its elastodynamic version. The result of the simulation––the high frequency data––and the result of the SAFT-reconstructions are compared with experimental results on a steel test block with side drilled and flat bottom holes. The model is validated by the experiment. One of the applications of the model is to identify multiple reflections.

An Experimental Study of Synthetic Aperture Ultrasonic Imaging by Fourier Domain Reconstruction Method (FDR)

This paper describes experimental study of the Fourier domain reconstruction method (FDR), which was proposed by the author previously to improve lateral resolution of the ultrasonic B-scope. Imaging properties of the method for planar objects, that is, extended objects generally, are remarkably superior to those of the conventional synthetic aperture focusing methods, commonly known as the delay and sum methods (D&S). Faithful images of several objects have been reconstructed experimentally by FDR. A brief review of a new algorithm for the pruning FFT which is adopted to FDR is also presented.