Resolution Ultrasonic Imaging Research Articles

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.

Ultrasonic imaging, particle detection, and V(z) measurements in molten zinc using focused clad buffer rods

Ultrasonic imaging, particle detection, and V(z) measurements have been performed using focused clad buffer rods in molten zinc at temperature more than 600 °C. The focused ultrasonic waves are generated by a spherical or cylindrical acoustic lens which is fabricated at the end of the clad buffer rod. In order to evaluate its focusing ability, several experiments are carried out at 10 MHz in a pulse-echo mode. The lateral resolution at the focus of the spherical acoustic lens in molten zinc is quantitatively examined and compared with that in water using a thin stainless wire with a diameter of 380 μm. High resolution ultrasonic imaging is carried out by the common C-scan technique. The signal-to-noise ratio of the reflected signals from the flat sample surface at the focus is better than 35 dB. Ultrasonic images are obtained from the amplitude and time delay variations of the reflected signals. An attempt has also been made to detect particles suspended in molten zinc. Backscattered signals from particles are clearly visible at the focal region of the lens. For quantitative materials evaluation, V(z) curve measurements are performed using both spherical and cylindrical surface lenses and the leaky surface acoustic wave velocity of a ceramic (SiC) plate immersed in molten zinc is successfully determined.

703 溶融金属中での高分解能超音波イメージング(O.S.7-1 高速/高温現象と可視化1)(オーガナイズドセッション7 : 高速/高温現象と可視化)

703 溶融金属中での高分解能超音波イメージング(O.S.7-1 高速/高温現象と可視化1)(オーガナイズドセッション7 : 高速/高温現象と可視化)

High-resolution ultrasonic imaging of wood

Ultrasonic nondestructive evaluation holds the promise of significantly improving predictions of the load bearing capacity of wood. The inhomogeneity, anisotropy and natural variability of wood pose a formidable challenge to the realization of that promise. As a first, qualitative step in correlating known wood mechanical properties and their natural patterns of variability with parameters of ultrasonic wave propagation, high resolution ultrasonic images of transmitted and reflected energy are presented. The experiments were carefully designed to observe only bulk waves. The results show that surface echoes and backscatter from subsurface features contain useful and as yet untapped information on local wood properties and structure. Transmitted signals were found to always contain more than one image of the outgoing pulse, indicating another source of information so far overlooked. The high spatial sampling density used here allows the generation of images in which the human eye can distinguish familiar features even in the presence of significant noise. Combining qualitative information on wood properties and their distribution with high resolution imaging can be used to remove noise and extract image features one knows to be present by appropriate application of image processing.

Spatial undersampling for synthetic aperture ultrasonic imaging via digital spotlighting technique

High resolution ultrasonic imaging may be achieved via the synthetic aperture focusing technique, provided that the synthetic antenna is correctly spatially sampled. We show that spatial undersampling is possible, using a digital spotlighting technique that permits to recover the correct reconstructed images from aliased data. The proposed method is applied to experimental ultrasonic data.

High-frequency backscatter measurements of bovine tissues with unfocused and focused transducers

In order to improve resolution of ultrasonic imaging, high-frequency scanners which are employed in the range 20–50 MHz are needed. As a result, it is critical to obtain data on ultrasonic scattering and attenuation in this frequency range. At these high frequencies, it is not feasible to make scattering measurements with unfocused transducers, therefore focused transducers are needed. Using the standard substitution method to calculate the backscatter coefficient, as is used with unfocused transducers, yields erroneous results for focused transducers. The assumption that the reflected echo from a perfect reflector in the far field can be calculated as though the transducer acts like a point source does not hold for focused transducers. Therefore a method is presented for focused transducers where the flat reflector is substituted by a particulate reference medium whose backscatter coefficient is well known and documented. Unfocused transducers in the range 10–20 MHz will be used in comparison with focused transducers to measure backscatter. For 15–35 MHz, focused transducers will be used. Results for the backscatter coefficient will be presented for various bovine tissues.

Parallel Processing in Real-Time Ultrasonic Imaging

An ultrasonic imaging system based on a parallel processing architecture is presented. The system exploits different forms of intrinsic parallelism frequently associated to the process of ultrasonic imaging. Beam focusing and scanning techniques are developed and applied for increasing image spatial resolution. Parallel interpolation algorithms are implemented for improving resolution of ultrasonic imaging. These algorithms are assesed, considering performance in achieving the required speed for real-time ultrasonic imaging applications. The flexibility and scalability of the system allows to incorporate new developments in technology and utilise more complex algorithms for improving image visual appearence and achieve realtime response.

Ultrasonic high resolution images for defect detection in ceramic materials

The final ceramic integrity was investigated by means of high resolution ultrasonic images. To ensure a better evaluation of the defect shape, both spectral and time-domain parameters were used to build the images. A new investigation technique, based on an indirect defect detection, is proposed which exploits the filtering effect that the flaw induces on the forward propagating ultrasonic wave.

Ultrasonic High Resolution Images for Defect Detection in Ceramic Materials

Abstract The final ceramic integrity was investigated by means of high resolution ultrasonic images. To ensure a better evaluation of the defect shape, both spectral and time-domain parameters were used to build the images. A new investigation technique, based on an indirect defect detection, is proposed which exploits the filtering effect that the flaw induces on the forward propagating ultrasonic wave.

High resolution ultrasonic imaging using 2-D echo filtering

High resolution ultrasonic imaging using 2-D echo filtering

Estimation of tissue parameters derived from reflected ultrasound.

We propose a method of estimating two tissue parameters, that is, the reflection coefficient and attenuation coefficient from the reflected ultrasound for the purpose of improving the resolution of ultrasonic images and obtaining information on tissue characterization. The reflection coefficient is estimated by deconvolution technique using Kalman filter taking into account the distortion of the propagating pulse due to the frequency-dependent attenuation. The attenuation is estimated by adaptive processings based upon the criterion function calculated using estimates of the reflection coefficient. Simulated signals are used to investigate the ability of this method. Additionally, actual reflected signals from soft tissues are processed by the method. The results show that the method can be applied in clinical cases.

Ultrasonic signal/image restoration for quantitative NDE

Our overall objective is to improve the spatial resolution of ultrasonic images used for quantitative non-destructive evaluation of materials. These images contain distortion due to the band-pass frequency responses of the associated transducers and propagation paths. Our specific objective is to estimate the impulse responses of flaws and interfaces in material samples. Thus, we are attacking the restoration problem, which is, in general, ill-posed and difficult to solve in practice. We have applied several techniques for regularizing the problem, including both time- and frequency-domain methods, and some constrained optimization algorithms. Our new results demonstrate that regularization techniques can allow successful, practical solutions to this ill-posed problem. Our work concentrates mainly upon the problem in which the impulse response is expected to be impulsive (consisting of a weighted sum of delayed impulses). Our results show that some problems of practical interest are tractable by using a two-step procedure involving first system identification and then spectrum extrapolation to obtain sharper spatial impulses. The paper presents the results of experiments using actual laboratory signals, in which we demonstrate improved spatial resolution for impulsive signals, allowing more meaningful interpretation of ultrasonic A- and B-scans.

Improvement of the spatial resolution of ultrasonic imaging using the holographic technique

AbstractIn the conventional synthetic aperture technique the antenna directivity is assumed to be wide enough that sufficient phase information can be obtained with antenna scanning. This assumption is made in the experimental studies as well. With a sharp antenna directivity, however, sufficient phase information cannot be obtained and the reconstructed image obtained by the conventional synthetic aperture technique has poor resolution. On the other hand, if the real aperture technique is employed, an image of improved quality can be obtained with a sharp antenna directivity and the resolution increases as the directivity becomes sharper. The present paper deals with the case of directivity which is too sharp for the synthetic aperture technique and too wide for the real aperture technique. Theoretical and experimental studies are made on ultrasonic imaging by using the modified synthetic aperture technique for this case. Specifically, the actually measured point spread function is used in the synthetic aperture technique and it is confirmed that a higher resolution can be obtained in this way than by the conventional synthetic or real aperture technique.

Prior inverse filtering for the improvement of axial resolution

A prior inverse filtering technique is applied to improve the axial resolution in ultrasonic imaging. The ultrasound transducer is excited by a synthesized signal corresponding to the impulse response of the inverse filter. The diffraction effects of the transducer and the observed scatterer, which limit the performance of the inverse filter, are examined experimentally as well as theoretically. Using a B-scan image of a tissue-equivalent phantom, we demonstrate the possibility of applying the prior inverse filtering method to improve medical ultrasound images.

Prior inverse filtering for the improvement of axial resolution.

A prior inverse filtering technique is applied to improve the axial resolution in ultrasonic imaging. The ultrasound transducer is excited by a synthesized signal corresponding to the impulse response of the inverse filter. The diffraction effects of the transducer and the observed scatterer, which limit the performance of the inverse filter, are examined experimentally as well as theoretically. Using a B-scan image of a tissue-equivalent phantom, we demonstrate the possibility of applying the prior inverse filtering method to improve medical ultrasound images.

Improved mirror systems for high resolution ultrasonic imaging

High resolution ultrasonic imaging in a water bath, for example breast imaging, demands a transducer of large aperture. Such an aperture is most easily achieved by the use of mirrors. Previous such mirror systems suffered problems from reverberations between and within their component parts. Changes in the design of the system, and the use of thin metal reflectors, reduce these reverberations to an acceptable level. There is no sacrifice in the focusing performance, and losses in the system are minimized.

Characteristics of the Piano-Convex Ultrasonic Transducer

The plano-convex transducer has the superior features of broad frequency bandwidth, transmission and reception of a very short ultrasonic pulse and radiation of focused ultrasonic waves. Those features can improve the resolution in ultrasonic imaging and non-destructive testing. In order to design and use these sorts of transducers, more detailed characteristics are necessary. The following characteristics are investigated in this paper: radiation patterns for continuous and pulse waves in water, vibration modes, ringing for an applied impulse voltage and its suppression, and radiation patterns of impulse waves in steel and focal distance.

Improvement of the Resolution in Ultrasonic Imaging with Real-Synthetic Hybrid Aperture

The spatial resolution of conventional real aperture imaging is generally poor in comparison with that of imaging by the synthetic aperture technique, since the resolution is determined by the beam profile of transducers. In a case where the beam profile is not sharp, there is a possibility of improving the resolution by the synthetic aperture technique. Using data of the point transfer function measured in the experiment system, we have improved the spatial resolution. The simulations, experimental results and theoretical analysis are presented.

High resolution ultrasonic imaging by controlled averaging of backscattered signals

A new synthetic aperture technique for obtaining ultrasonic images with a high resolution is described. The attained resolution is in the order of the ultrasonic wavelength and, when using a 5 MHz unfocussed beam, amounts to 0.3 ± 0.1 mm, i.e. it is much smaller than the diameter of the sound beam. Measurements have been performed on a model specimen consisting of a two-dimensional array of threads. The distance between the threads were chosen to approximate to the macroscopic fibre spacing of 1.5 mm ± 0.3 mm in human muscle.

A new technique for noninvasive evaluation of femoral arterial and venous anatomy before and after percutaneous cardiac catheterization in children and infants

A new ultrasonic method was applied to image the femoral artery and vein in children for evaluation of short- and long-term effects of cardiac Catheterization with femoral percutaneous cannulation. Sixty-six children and infants (aged 5 days to 20 years) were studied with a 9 megahertz electronically focused real time scanner. Adequate studies were obtained in 46 patients before Catheterization, in 26 of 30 short-term follow-up studies and in 14 long-term follow-up studies. Femoral arterial size could be quantitatively measured at the inguinal ligament and a correlation existed between imaged femoral arterial diameter and body weight (r = + 0.82) or body surface area ( r = + 0.80). Short-term follow-up ultrasonic imaging studies allowed diagnosis of spasm and other complications of percutaneous femoral arterial puncture. Long-term follow-up studies were performed 4 months to 3 years after Catheterization in 14 patients who had no complications recorded at the time of Catheterization. These revealed significant differences between vessels on the catheterized and uncatheterized (control) sides in only 3 of the 14. High resolution ultrasonic imaging can provide anatomic and functional information about femoral arteries and veins and appears to be of assistance in planning cardiac Catheterization and in studying the short- and long-term effects of percutaneous femoral cannulation.