By Topic

Ultrasonics Symposium, 1998. Proceedings., 1998 IEEE

Date 5-8 Oct. 1998

Go

Filter Results

Displaying Results 1 - 25 of 209
  • 1998 IEEE Ultrasonics Symposium

    Page(s): 0_2 - 0_25
    Save to Project icon | Request Permissions | PDF file iconPDF (2903 KB)  
    Freely Available from IEEE
  • Author index

    Page(s): 1893 - 1900
    Save to Project icon | Request Permissions | PDF file iconPDF (343 KB)  
    Freely Available from IEEE
  • New sensing elements based on the delay line principle

    Page(s): 1095 - 1098 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB)  

    A new delay line arrangement based on the characteristics' modification of the acoustic waves generated and detected by means of magnetostrictive elements (made of Fe-rich amorphous ribbons or thin films) and which propagate along a non magnetostrictive acoustic waveguide is presented. The elastic properties of the acoustic waveguide can be modified by stress and torsion thus resulting in a change of the propagating acoustic signal. The experimental results concerning the tensile stress and torsion influence on the delay line indicate a nonlinear but monotonic response and absence of hysteresis View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A new tissue harmonic imaging scheme with better fundamental frequency cancellation and higher signal-to-noise ratio

    Page(s): 1589 - 1594 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    Tissue Harmonic Imaging (THI) is a new ultrasound imaging technique, which uses the harmonic components generated by nonlinear acoustic propagation through human tissues to form an image. Several factors affect THI image quality. First, strong suppression of the fundamental signals is necessary to allow the full dynamic range of the harmonic signals to be seen. This will allow the full benefits of harmonic imaging to be seen. Second, since the harmonic components are much weaker (15-20 dB lower) than the fundamental, they must be enhanced as much as possible relative to noise. This will allow the maximum possible image penetration. This paper will compare the phase inversion technique with another data acquisition and processing scheme from the literature in terms of suppression of fundamental frequencies, and signal-to-noise ratio (SNR) improvement. The comparison will be both theoretical, using a very simple model, and experimental, using data acquired in vitro. The phase inversion technique appears to be a better choice to realize THI in an ultrasound imaging system. This technique gives better cancellation of the fundamental frequencies while simultaneously improving SNR View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Magnetic microparticles as labeling or contrast medium for medical imaging, an in-vitro feasibility study

    Page(s): 1807 - 1810 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (928 KB)  

    Magnetic microparticles such as ferrite or magnetite are suggested for another contrast media than the micro gas bubble family. It can be magnetically agitated when sent to a moving or non-moving body fluid in a body cavity or the capillary system. In vitro phantom tests using 4-5 micron soft ferrite powder proves its feasibility as contrast or labeling media, although safe and controlled admission for animals or humans is yet largely unknown View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dielectric and mechanical absorption mechanisms for time and frequency domain transducer modeling

    Page(s): 1019 - 1024 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    In all practical transduction systems-such as biomedical imaging arrays, underwater sonar systems or piezoelectric actuators and transformers, electromechanical losses impact overall system performance. Adverse effects of these losses include heat generation, sub-optimal electrical matching, and reduced operational efficiency. Consequently, it is imperative to fully understand the implications of loss mechanisms and incorporate them properly in numerical and analytical models. In this paper, time-domain electromechanical absorption mechanisms are studied in terms of their physical mechanisms and frequency-domain counterparts. We examine the mechanical and dielectric losses of some common piezoelectric materials and discuss some of the issues that arise in attempting to measure and model them View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Real-time implementation of lateral flow estimation using spatial quadrature

    Page(s): 1483 - 1487 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    The first real-time implementation of lateral flow estimation using spatial quadrature is described and results of its application in flow-phantom experiments presented. Spatial quadrature (SQ) is a recently-introduced technique for two- or three-dimensional flow velocity estimation. In its most basic form, this technique interrogates the region of interest with a pair of point spread functions which have weightings in the lateral dimension with a quadrature relationship. These weightings produce a modulation in the echoes from scatterers moving laterally through a resolution volume. This modulation can be decoded to quantify the lateral velocity component. In this SQ implementation, summed radio-frequency echo data was captured in an M-mode scan geometry using 2:1 parallel processing in spatial quadrature with a 7.5 MHz linear array and a conventional ultrasound scanner. The target for these experiments was a phantom vessel composed of an 8 mm latex tube in a water tank. Using a computer-controlled calibrated flow pump, blood-mimicking fluid was circulated through this vessel at constant volume flow rates of 5-25 ml/s, corresponding to peak flow velocities in the range of 10-45 cm/s. Laminar flow was established in the vessel through the use of a long, straight in-flow tube leading into the vessel. Lateral velocity estimates were subsequently processed off-line to produce velocity profiles over range. These velocity profiles show the parabolic shape characteristic of laminar flow. Volume flow rates were estimated from these profiles using a parabolic curve fit. At optimum pulse repetition frequencies, these SQ-based estimates agreed with the known volume flow to ⩽5.1% for all flow rates tested View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Agents promoting and suppressing acoustic cavitation

    Page(s): 1443 - 1446 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    In therapeutic application of ultrasound, promotion and suppression of cavitational effects are both important. The authors have reported that rose bengal (RB) can reduce the intensity threshold for cavitation in murine liver tissue. This effect was pharmacokinetically studied here. It decreased gradually as the time elapsed after the RB administration, but not as rapidly as the decrease in RB concentration in the liver. As for chemicals suppressing aqueous cavitation, the authors found that sodium ascorbate is quite effective View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Advantages of split-focus approach in coagulation therapy

    Page(s): 1431 - 1434 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    A most critical problem in the coagulation therapy with a single-spot focus is that the hot spots formed in tissue tends to migrate from the focal zone towards the transducer when the ultrasonic power deposition is higher than the optimum. The authors found that the split-focus approach is effective for improving the throughput of ultrasonic coagulation therapy not only due to its large heating pattern but also through preventing this hot-spot problem. The tissue temperature distribution during split-focus exposure was analyzed using some approximation. The temperature at the central acoustic zero in the split focus reaches the spatial peak within the order of a second after the start of the exposure, when the focused transducer has an F-number of around one and an ultrasonic frequency higher than the order of a megahertz. The problem above can be prevented in this approach because the hot spots may be created only near the acoustic zero View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Perfusion imaging with pulse inversion Doppler and microbubble contrast agents: in vivo studies of the myocardium

    Page(s): 1783 - 1786 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (332 KB)  

    Pulse Inversion Doppler (PID) is a recently developed, multi-pulse imaging technique for detecting microbubble contrast agents in tissue. By transmitting as few as 2 pulses per line of sight, then applying modified colour Doppler wall filters together with power or colour Doppler processing, PID can suppress linear tissue echoes while imaging nonlinear microbubble echoes in real-time, even when microbubble and tissue are moving at the same velocity. Filtering efficiency improves as more transmit pulses are used. By transmitting 4 or more high intensity pulses per line of sight and applying appropriate wall filters, both linear and nonlinear clutter can be suppressed while moving or disrupting microbubbles are imaged. The flexibility of pulse inversion Doppler allows imaging parameters to be optimized according to clinical application, transmit pulse intensity, and agent properties. Prototype PID imaging was implemented on a clinical scanner, and myocardial contrast imaging was performed in anaesthetized dogs with perfluorocarbon and air based agents. Fundamental and harmonic grey-scale, conventional Doppler and PID techniques were compared at different transmit intensities. At low transmit intensity, PID produced up to 15 dB more agent to tissue contrast than harmonic imaging, allowing realtime imaging of myocardial perfusion. At high transmit intensities, both PID and conventional Doppler provided strong myocardial enhancement. Effects were agent dependent. Doppler filter design and implementation are discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Two light beams diffraction by a surface acoustic wave in an anisotropic solid

    Page(s): 1151 - 1154 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB)  

    The results of a theoretical investigation of simultaneous two light beams diffraction by a surface acoustic wave (SAW) in crystals are considered. They form the theoretical basis of descriptive work of a new acoustooptic method of SAW velocity measurement based on a two optical beams interferometer. The influence of elastic anisotropy of a solid on the diffraction and interference of light beams and accuracy of measurement of phase and group SAW velocities in anisotropic mediums are considered. It is shown how to realize direct measurement of a SAW steering beam angle. The obtained results considerably increase possibilities of the given method for measurement of the basic characteristics of acoustic waves in crystals View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analytic modeling of loss and cross-coupling in capacitive micromachined ultrasonic transducers

    Page(s): 1025 - 1028 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    The structural loss mechanism of capacitive micromachined ultrasonic transducer (cMUT) is investigated using finite element analysis and the normal mode theory. A single micromachined transducer membrane on an infinite silicon substrate is simulated by incorporating absorbing boundary conditions in the finite element method. This enables direct evaluation of the mechanical impedance of the membrane. Furthermore, the field distribution along the thickness of the silicon substrate due to outward radiating wave modes is obtained. The normal mode theory is applied to extract the contributions of different wave modes to the complicated field distributions. It is found that, the lowest order Lamb wave modes are responsible for the loss. Evaluation of absolute and relative power losses due to individual modes indicate that the lowest order anti-symmetric (A0) mode is the dominant radial mode in agreement with experimental measurements. The results of the analysis are used to derive a detailed equivalent circuit model of a cMUT with structural loss View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Estimation of physical constants of silicon-based polymer thin films using surface acoustic waves and their application to liquid sensor

    Page(s): 1231 - 1234 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    Physical constants of poly(di-methyl silane) are estimated from the characteristics of the surface acoustic wave (SAW) propagating along poly(di-methyl silane)/(128°rot.Y-X) LiNbO3 structure. The values of c11 and c44 are estimated to be (5.9±0.9)×1010 and (1.2±0.3)×1010 N/m2, respectively. Using the obtained stiffness constants and density of poly(di-methyl silane), the leaky SAW propagation character is estimated from the numerical calculation based on the first-principle-equations. As a result, it is found that liquid/polysilane/(128°rot.Y-X) LiNbO3 structure is useful for estimating physical constants of the liquid loaded on the device surface, i.e., the surface of the polysilane thin film View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Accurate measurements of longitudinal-wave velocity in IIW-type calibration blocks

    Page(s): 1159 - 1162 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (308 KB)  

    A proposed ISO standard specifies tolerances on longitudinal-wave velocity measurements made on IIW-type calibration blocks. These specifications conflict with current ASTM standards for velocity measurements. We evaluate the tolerances of the proposed ISO standard by measuring the longitudinal-wave velocities on a series of blocks, discuss the uncertainties in the measurements, and evaluate the practicality of the proposed standard View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Piezoelectric photoacoustic spectra of bulk CuInS2 single crystals grown by the traveling heater method

    Page(s): 1239 - 1242 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB)  

    The piezoelectric photoacoustic (PPA) spectra of bulk CuInS2 single crystals grown by a traveling heater method were observed at 80 K. Two PPA signals which are due to bandgap energy and an intrinsic defect are clearly observed. The activation energy of the intrinsic defect is estimated to be about 70 meV are obtained as nonradiative recombination centers for the first time View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A 3.5 MHz phased array probe using 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 single crystal

    Page(s): 1847 - 1850 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    A novel 128-channel phased array probe for echocardiography with a center frequency of 3.5 MHz, using 0.91Pb(Zn1/3Nb2/3 )O3-0.09PbTiO3 (PZN-9%PT) single crystal has been fabricated to realize greater sensitivity and broader bandwidth properties. The echo amplitude of the PZN-9%PT single-crystal probe is about 5 dB higher than that of the conventional lead zirconate titanate (PZT) ceramic probe, and the fractional bandwidth is about 25 percentage points broader. The quality of a B mode image obtained by the PZN-9%PT probe satisfies the performance of the conventional PZT ceramic probe which has a center frequency of 3.75 MHz. At the reference frequency of 3 MHz, the Doppler sensitivity of the PZN-9%PT probe is about 5 dB higher than that of the PZT probe; the blood flow of a pulmonary vein in a hard-to-image patient is much more clearly imaged than in the case of using the PZT probe. These superior images are attributable to the use of sufficiently large PZN-9%PT single crystals obtained by the self-flux method View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Measurement of local elasticity of human carotid arterial walls and its relationship with risk index of atherosclerosis

    Page(s): 1451 - 1454 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB)  

    We have proposed a new method for evaluating the local elasticity of the arterial wall in order to diagnose the early stage atherosclerosis. In the case of the early stage atherosclerosis, the macular lesion is several millimeters in diameter. Therefore, it, is necessary to find the local change in the elasticity of the arterial wall. In the proposed method, the small change in thickness of the arterial wall during cardiac cycle is accurately measured using ultrasound, and the elasticity of the arterial wall can be evaluated in every small region of about 1 millimeter, which corresponds to the width of the ultrasonic beam. In the report, the proposed method is applied to human carotid arteries of 54 male patients and 30 healthy male subjects, where the patients have high risk factor of coronary heart diseases. From this results, the difference in the elasticity of the arterial walls between healthy subjects and patients is investigated View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A novel approach for a bias-free reduction of image variance in ultrasonic diffraction tomography

    Page(s): 1627 - 1630 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    In this work, we considered the optimal noise control in image reconstruction in ultrasonic diffraction tomography (UDT). We revealed the existence of statistically complementary information inherent in the scattered data and proposed a linear strategy that makes use of this information to achieve a bias-free reduction of the image variance in UDT. This strategy leads to the development of an infinite class of hybrid algorithms that reconstruct UDT images from the measured scattered data. We also developed infinite classes of generalized filtered backpropagation (GFBPP) algorithms that include the widely used filtered backpropagation (FBPP) algorithm as a special member. Furthermore, we established the corresponding relationship between the hybrid and GFBPP algorithms. In the absence of noise, these hybrid and GFBPP algorithms are identical. However, they respond to noise and the effect of finite sampling differently. Our simulation studies validate these theoretical results View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Noninvasive evaluation of bone stiffness by combining microdefocusing method and reflectance method

    Page(s): 1459 - 1462 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    Acoustic and elastic properties of bone obtained by ultrasonic-based methods are highly useful in the direct evaluation of bone characteristics. Thus, many methods and systems, which are based on the measurement of velocity and/or attenuation of bone, have been developed. On the other hand, bone stiffness has been considered as an effective index for diagnosis of bone disease such as osteoporosis. In the paper, therefore, we propose a new method and system based on the stiffness measurement of bone. In the proposed method, stiffness is determined from the velocity of the leaky surface skimming compressional waves (LSSCWs) obtained by the microdefocusing method and the acoustic impedance obtained by the reflectance method. Each stiffness of a Bakelite and a PMMA samples is accurately determined in a preliminary experiments, and the principle of the method and system performance are confirmed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Novel silicon nitride micromachined wide bandwidth ultrasonic transducers

    Page(s): 1081 - 1084 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    Silicon micromachined ultrasonic devices have been fabricated using a CMOS-compatible process. Devices of up to 1 mm in size have been tested, with silicon nitride membranes of 1 μm and 2 μm thickness. The work has investigated the response of these ultrasonic receivers, as a function of membrane thickness and lateral dimensions. It is shown that the resultant surface micromachined transducers can operate over a wide bandwidth in air, without the resonant behaviour associated with previous devices View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Anomalous absorption of bulk longitudinal acoustic waves in a layered structure with viscous fluid

    Page(s): 1203 - 1206 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    It is demonstrated theoretically that the absorptivity of bulk longitudinal waves by an ultra-thin layer of viscous fluid between two different elastic media has a strong maximum (dozens of percent) at an optimal layer thickness. This thickness is usually much smaller than penetration depths and lengths of transverse and longitudinal waves in the fluid. The angular dependence of the absorptivity is demonstrated to have significant structure near critical angles of incidence, where the overall dissipation can be noticeably increased. The effect of non-Newtonian properties of the fluid on the anomalous absorption is also investigated. In particular, it is shown that increase of frequency and/or relaxation times in the fluid results in a noticeable decrease of the absorptivity maximum and optimal layer thickness View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An automatic Doppler angle and flow velocity measurement method

    Page(s): 1579 - 1582 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB)  

    Current Doppler flow velocity measurements require the operator to manually set the direction of the flow velocity vector along the blood vessel axis on the 2D ultrasound scan image to determine the Doppler angle, and then to estimate the real flow velocity. In this article, we present an automatic flow velocity and Doppler angle measurement method, which exploits the symmetric focusing property of annular array transducers to enable the measurement of the flow in any three-dimensional direction. The method uses the information of fd (energy peak frequency) and fmax (maximum frequency) to obtain an automatic and direct estimation of flow velocity and Doppler angle. Successful measurements in phantom and on human subjects are presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Ferroelectric polymer transducers for transverse ultrasonic waves

    Page(s): 1047 - 1050 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    Polymer ultrasonic transducers for 1.5-10 MHz transverse waves were first developed using thickness shear resonators composed of multi-layered lamellar crystalline films or single crystalline films of P(VDF/TrFE), and their performance was evaluated. These transducers can transmit and receive pure shear waves with high efficiency. The S/N ratio of these transducers is higher than that of conventional PZT shear mode transducers. The developed transducers are usable for practical applications such as NDE and physical acoustics after some trivial improvements View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Degradation diagnosis of polymeric materials using ultrasonic waves

    Page(s): 1167 - 1170 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    To develop a non-destructive technique for evaluating heat degradation in cable sheaths and insulation, relations between physical properties and ultrasonic wave velocity in heat degraded polymeric materials such as polyvinyl chloride, polyethylene and ethylene propylene rubber were investigated. Ultrasonic wave velocity increased while breaking elongation decreased with the heat degradation in all of the tested material. There was obvious correlation between the ultrasonic wave velocity and the breaking elongation. Using ultrasonic wave velocity, this correlation has made possible a non-destructive diagnosis for determining the degree of degradation in cable sheaths and insulation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Image reconstruction of diffraction tomography using linograms

    Page(s): 1655 - 1658 vol.2
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    The linogram data acquisition method and image reconstruction method considering the diffraction effect of sound waves were previously suggested. This imaging method gives accurate images because no interpolation operation is performed in the image reconstruction and no theoretical errors are caused. An image was obtained by computer simulation to check the validity of the method. For the reconstructed image, it was proved that an accurate image is obtained in the real part. Also, the relationship between the value of the real part of the reconstructed image and the compression rate (speed) distribution was examined. It was proved that the speed distribution of an object can be estimated from the image intensity when it is not largely different from that of the surrounding medium View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.