Resolution Ultrasonic Imaging Research Articles

Frequency-domain synthetic aperture focusing for helical ultrasonic imaging

The synthetic aperture focusing technique (SAFT) is widely used to provide significant improvement in the lateral resolution of ultrasonic images. Frequency-domain SAFT has shown higher accuracy and greater efficiency than time-domain SAFT. However, frequency-domain SAFT should be helix-based for ultrasonic scanning of cylindrical structures such as pipes and axletrees. In this study, a frequency-domain SAFT is proposed for 3D helical ultrasonic imaging applications. This technique adjusts the phase spectra of the images to complete the synthetic aperture focusing process. The focused image is precise because the proposed algorithm is established on the basis of the wave equation in a helical coordinate system. In addition, the algorithm can efficiently separate out point scatterers and present volume scatterers. The experimental results show that the proposed algorithm yields lower side lobes and enhances the angular resolution of the ultrasonic image to approximately 1°– 1.5°, which is much better than the performance of time-domain SAFT. The maximum deviations are only 0.6 mm, 0.5°, and 0.4 mm along the r-axes, θ-axes, and z-axes, respectively, which are appropriate for normal ultrasonic nondestructive testing.

Increasing Axial Resolution of Ultrasonic Imaging With a Joint Sparse Representation Model.

The axial resolution of ultrasonic imaging is confined by the temporal width of acoustic pulse generated by the transducer, which has a limited bandwidth. Deconvolution can eliminate this effect and, therefore, improve the resolution. However, most ultrasonic imaging methods perform deconvolution scan line by scan line, and therefore the information embedded within the neighbor scan lines is unexplored, especially for those materials with layered structures such as blood vessels. In this paper, a joint sparse representation model is proposed to increase the axial resolution of ultrasonic imaging. The proposed model combines the sparse deconvolution along the axial direction with a sparsity-favoring constraint along the lateral direction. Since the constraint explores the information embedded within neighbor scan lines by connecting nearby pixels in the ultrasound image, the axial resolution of the image improves after deconvolution. The results on simulated data showed that the proposed method can increase resolution and discover layered structure. Moreover, the results on real data showed that the proposed method can measure carotid intima-media thickness automatically with good quality ( 0.56±0.03 versus 0.60±0.06 mm manually).

Nonlinear ultrasonic phased array for closed crack imaging

In nondestructive ultrasonic inspection, closed cracks can lead to the underestimation or overlook, resulting in the catastrophic accidents. To solve this problem, nonlinear ultrasonics has been expected as a most promising approach. In nonlinear ultrasonics, by irradiating large amplitude, the nonlinear interaction between closed cracks and ultrasonics generates nonlinear components. Among them, we found that subharmonics has a higher selectivity than the others including higher harmonics. We also found that the subharmonics has higher temporal resolution, providing the high spatial resolution in ultrasonic imaging. Based on these findings, we have developed a novel imaging method, subharmonic phased array for crack evaluation (SPACE), based on the subharmonic generation at closed cracks due to large-amplitude short burst waves input and phased array imaging with frequency filtering. As a result of applying SPACE to closed-crack specimens, SPACE visualized the closed part of cracks, which were not observed in the conventional methods. It was substantiated that SPACE is useful in accurately measuring closed-crack depths.

High temporal and spatial resolution ultrasonic imaging and application to cardiovascular imaging

Recently, high frame rate ultrasound has become used for various imaging scenarios. It creates multiple scan lines at the same time using unfocused transmit beam to reduce the number of transmissions per image frame. Consequently, high frame rate ultrasound can realize a frame rate of over 1 kHz, but the lateral spatial resolution is degraded by using unfocused transmit beams, such as plane and diverging waves. To overcome such a problem, we have developed novel beamforming methods based on adaptive procedures, such as phase coherence imaging and minimum variance beamforming. As a result, high temporal and spatial resolution could be realized simultaneously. The developed high frame rate imaging methods were applied to imaging of cardiovascular dynamics. Blood flow in the carotid artery and cardiac left ventricle were imaged at frame rates of 2500 Hz and 6250 Hz with plane wave and diverging wave transmissions, respectively, and vortices in the carotid bifurcation and left ventricle could be observed. The...

CMOS Ultrasonic Receiver With On-Chip Analog-to-Digital Front End for High-Resolution Ultrasound Imaging Systems

CMOS capacitive micromachined ultrasonic transducer (CMUT) with integrated front-end circuits for portable high resolution ultrasonic imaging systems is presented. The CMUT array operates with 30 V power supply. In addition, the interlayer metal CMUTs with non-uniform membrane are proposed to improve the sensitivity in this paper. A prototype chip containing 48 elements as 12 channels is implemented. The conversion efficiency of the proposed CMUTs is 5.84 times higher than that in the published literatures. The maximum ultrasonic signal bandwidth is 4.5 MHz. CMUT array and the transimpedance amplifiers are integrated on the same chip. In addition, a multibit continuous-time $\Delta \Sigma $ modulator was designed and fabricated in another chip using 0.18- $\mu \text{m}$ standard CMOS process. The chips size are 1.84 and 0.177 mm2, and the total power consumption in the receiving mode is approximately 3.01 mW with 1.8 V power supply.

Ultrahigh Frequency (100 MHz–300 MHz) Ultrasonic Transducers for Optical Resolution Medical Imagining

High resolution ultrasonic imaging requires high frequency wide band ultrasonic transducers, which produce short pulses and highly focused beam. However, currently the frequency of ultrasonic transducers is limited to below 100 MHz, mainly because of the challenge in precise control of fabrication parameters. This paper reports the design, fabrication, and characterization of sensitive broadband lithium niobate (LiNbO3) single element ultrasonic transducers in the range of 100–300 MHz, as well as their applications in high resolution imaging. All transducers were built for an f-number close to 1.0, which was achieved by press-focusing the piezoelectric layer into a spherical curvature. Characterization results demonstrated their high sensitivity and a −6 dB bandwidth greater than 40%. Resolutions better than 6.4 μm in the lateral direction and 6.2 μm in the axial direction were achieved by scanning a 4 μm tungsten wire target. Ultrasonic biomicroscopy images of zebrafish eyes were obtained with these transducers which demonstrate the feasibility of high resolution imaging with a performance comparable to optical resolution.

Holey-structured metamaterial lens for subwavelength resolution in ultrasonic characterization of metallic components

This paper presents the implementation of holey structured metamaterial lens for ultrasonic characterization of subwavelength subsurface defects in metallic components. Experimental results are presented, demonstrating ultrasound-based resolution of side drilled through-holes spaced (λ/5) in an aluminum block. Numerical simulation is then used to investigate the parameters that can help improve the resolution performance of the metamaterial lens, particularly, the addition of end-conditions. This work has important implications for higher resolution ultrasonic imaging in the context of practical non-destructive imaging and non-invasive material diagnostics.

Improved optoacoustic microscopy through three-dimensional spatial impulse response synthetic aperture focusing technique.

Synthetic aperture focusing technique (SAFT) is effective in restoring lateral resolution of ultrasonic images for scans with focusing-related distortions. Although successfully applied in pulse-echo ultrasonics, the physical nature of an optoacoustic modality requires a modified algorithm to return accurate results. The SIR-SAFT method reported here uses the spatial impulse response (SIR) of the transducer to weight the contributions to the SAFT and is tailored to provide significant resolution and signal gains for out-of-focus sources in scanning optoacoustic microscopy systems. Furthermore, the SIR-SAFT is implemented in full three dimensions, applicable to signals both far of and at the focus of the ultrasonic detector. The method has been further shown to outperform conventional SAFT algorithms for both simulated and experimental optoacoustic data.

Multiple Moving Membrane CMUT With Enlarged Membrane Displacement and Low Pull-Down Voltage

A multiple moving membrane capacitive micromachined ultrasonic transducer ( M3-CMUT) has been fabricated and is shown to exhibit a significantly enlarged total membrane displacement ( ~ 280 nm) compared with the displacement of a conventional CMUT ( ~ 85 nm) for the same bias voltage. The M3-CMUT exhibits a significant reduction of the device pull-down voltage, while showing a much higher capacitance change, 100 fF for the M3-CMUT compared with only 20 fF for CMUT, at a dc bias of 25 V. The device performance, sensitivity, and acoustic power generation capability are primarily associated with the magnitude of the displacement of the membrane, and therefore, are enhanced through employing multiple deflectable membranes in M3-CMUT device. This high performance M3-CMUT is a promising candidate for high resolution ultrasonic imaging application.

Enhancement of ultrasonic images for sizing of defects by time-of-flight diffraction

A signal processing technique is presented for significantly sharpening the resolution of ultrasonic images, similar to those acquired in the nondestructive evaluation of girth welds in oil/gas pipelines. This enhancement allows a much improved estimate of the exact size of any detected anomaly in the weld, such that fracture mechanics can be used to gauge the probability of weld failure. The algorithm is based on the synthetic aperture focusing technique (SAFT), combined with a variation of Wiener filtering and autoregressive spectral extrapolation. An analytical model of the transducer is used to construct an appropriate reference spectrum for the deconvolution operation, and accounts for the dependence of a beam's frequency spectrum on the position of a flaw relative to the transmitter. Experimental results are used to provide an estimate of the improvement in flaw sizing accuracy.

2P5-1 An orientation-controlled KNbO_3 thick film transducer for high resolution ultrasonic imaging(Poster Session)

2P5-1 An orientation-controlled KNbO_3 thick film transducer for high resolution ultrasonic imaging(Poster Session)

Discontinuity detection ahead of a tunnel face utilizing ultrasonic reflection: Laboratory scale application

Predicting ground conditions ahead of the tunnel face has been one of the most important requirements of tunnel construction. This study investigates the development and application of a high resolution ultrasonic wave imaging system, which captures the multiple reflections of ultrasonic waves at the interface, to detect discontinuities at laboratory scale rock mass model. Ultrasonic wave reflection imaging based on A- and B-modes is obtained through stacking, signal compensation, demodulation, and display. Experiments are carried out by using horizontal scanning and new rotational scanning devices. Experimental studies show that the rotational devices are able to identify horizontal and inclined discontinuities and the cavity on the plaster block at a fixed location. Furthermore, two discontinuities including horizontal and inclined discontinuity planes are detected. The rotating scanning technique produces images similar to those obtained by the typical horizontal scanning technique. This study suggests that the new rotational technique can be an economical and effective tool for the detection of discontinuity on a rock mass for the investigation of the ground condition in front of the tunnel face.

Introduction to the Special Issue on High Resolution Ultrasonic Imaging in Industrial, Material and Biomaterial Applications

This special issue introduces recent advances in high-resolution ultrasonic imaging techniques and their applications to industrial materials and biomaterials evaluation. Various papers with novel results and techniques, developed by leaders in this field and some research groups are presented.

APPLICATION OF DIGITAL ULTRASONIC IMAGE CONSTRUCTION SYSTEM FOR THE DETECTION OF CRACKS IN WATER DISTRIBUTION SYSTEM

A digital ultrasonic image construction system was developed for the nondestructive detection of cracks in water distribution pipes. The system consists of PC based ultrasonic testing system and a scanning device. The PC based ultrasonic system has an ultrasonic pulse/receive board for the generation and reception of ultrasonic signals, an analogue to digital conversion board for the digitization of the received ultrasonic signals, and transducers for the ultrasonic sensors. Using this system, the digitized ultrasonic signals were properly constructed in accordance with the position information obtained by scanning device that moves an ultrasonic transducer along the outer surface of pipes. In the construction of the ultrasonic signals, signal processing concepts, such as spatial average and array concept, were considered to enhance the resolution of ultrasonic images of pipe wall. Using the developed system, crack detection experiments were performed in both laboratory and field, which shows promise for crack detection in the water distribution system.

Call for Papers - Special Issue on High Resolution Ultrasonic Imaging in Industrial, Material and Biomaterial Applications 2006

Call for Papers - Special Issue on High Resolution Ultrasonic Imaging in Industrial, Material and Biomaterial Applications 2006

Call for Papers Special Issue on High Resolution Ultrasonic Imaging in Industrial, Material and Biomaterial Applications (Submission deadline: April 30, 2006)

Call for Papers Special Issue on High Resolution Ultrasonic Imaging in Industrial, Material and Biomaterial Applications (Submission deadline: April 30, 2006)

Call for papers - Special issue on high resolution ultrasonic imaging in industrial, material and biomaterial applications

Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers.

Call for Papers: Special Issue on High Resolution Ultrasonic Imaging in Industrial, Material and Biomaterial Applications

Call for Papers: Special Issue on High Resolution Ultrasonic Imaging in Industrial, Material and Biomaterial Applications

A WAVELET-BASED BLIND DECONVOLUTION ALGORITHM FOR ULTRASONIC IMAGE PROCESSING

The low resolution of ultrasonic images is mainly caused by the convolution between the reflect function of the measured tissues and the system impulse response. In this paper, the system impulse response is first estimated on the envelope ultrasonic image data using higher-order spectra. Subsequently, wavelet-based deconvolution is implemented. The algorithm proposed in this paper removes the coupling problem between the tissue signals and the impulse response, which has been a puzzle in homomorphic deconvolution. It also preserves spatial components of ultrasonic images much better compared to Fourier domain deconvolution. The resulting images behave clearer in velamen boundary and tissue layers, and the texture information also appears more detailed. The deconvolved images achieve good resolution gains in both axial and lateral directions.

Real-Time Deconvolution in Ultrasonic Imaging Systems

We address the problem of improving the lateral resolution of ultrasonic images by a regularization technique in the wavelet domain. With a very low additional computational cost, the proposed approach increases the efficiency of the standard regularization technique because it efficiently remove the additive noise. Under the assumption that the point spread function is known, we applied our restoration technique to both synthetic and real ultrasonic imaging data. Moreover, experimental results show that the proposed method reduces also speckle artifacts, which generally are enhanced by the deconvolution.