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Ultrasonics Symposium, 2000 IEEE

Date 22-25 Oct. 2000

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  • 2000 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.00CH37121)

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    Freely Available from IEEE
  • Author index

    Page(s): 1951 - 1958
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    Freely Available from IEEE
  • Diagnostic ultrasound for the imaging of teeth: a comparison between experimental results and simulation models

    Page(s): 1387 - 1390 vol.2
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    Diagnostic ultrasound is being applied to teeth in order to detect cavities, decay, fractures and even early indication of abscesses. Ultrasonic waves are particularly sensitive to tight cracks and interface conditions between layers-dental features often difficult to interpret from X-ray images. Most importantly, due to its nonionizing nature, ultrasound acquires a potential advantage over conventional X-ray imaging. When ultrasonic waves are used at low intensity levels, they do not cause any health risks. This paper presents the results of laboratory experiments conducted on extracted human second and third molars using a low-intensity, high-frequency setup. Three cases have been examined: an intact tooth, a tooth containing an amalgam restoration, and a tooth containing a machine-side-drilled hole in order to mimic a cavity at the enamel-dentin interface. However, due to this paper length limitation only the first two cases are presented. A- and C-scans have been acquired in this study. Initial analysis of these results reveals similarities to those produced earlier by finite element and transmission-line methods insofar the identification of the different layers in the host teeth, and that such results could be used to realize the design of appropriate transducers and equipment for dentistry applications View full abstract»

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  • Adaptive ultrasonic imaging using SONOLINE ElegraTM

    Page(s): 1655 - 1658 vol.2
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    Data acquisition, time delay estimation and correction for adaptive imaging are implemented on the SONOLINE ElegraTM system using the system CPU, the Crescendo(TM) processor, and the existing front-end electronics, with no hardware modifications. With the current implementation, phase aberration correction takes about 2 seconds from activation to completion. The effects of compensating the transmit beam are studied using the waveform similarity factor and single transmit imaging. On a scattering phantom plus a 1-D aberration layer with an rms time fluctuation of 40 ns and correlation length of 5 mm, the waveform similarity factor of randomly scattered waveforms improved from 0.362 to 0.477 by iteration. Correspondingly, the -20 dB lateral resolution improved from 1.62 mm to 0.77 mm, and the image contrast improved by 8.5 dB (the speckle region is 6 dB brighter while the echo-free region is 2.5 dB darker). Experiments with a 2-D aberration layer and with a special phase aberration phantom showed less image improvements. Preliminary body scan trials with adaptive imaging showed improved image contrast and details in some cases but the results are mixed and influenced by such factors as isoplanatic patch size and complex scattering structures View full abstract»

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  • Electromechanical coupling factor of electrostrictive P(VDF-TrFE) copolymer

    Page(s): 997 - 1000 vol.2
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    Electromechanical coupling factors of the high energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymer are characterized at the quasi-static (1 Hz) and high frequency resonance states. It is found that the transverse electromechanical coupling factor k31 of this material can reach more than 0.45. Furthermore, the result obtained from the resonance method is comparable to that from the quasi-static method View full abstract»

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  • Adaptive imaging using an 8×128 array

    Page(s): 1659 - 1663 vol.2
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    We present initial results from a new 1.75D array. The advantages of this array include: 1) Improved elevation focusing, 2) More effective phase aberration measurement and use of adaptive imaging techniques due to the increased sampling in the elevation dimension, 3) The ability to obtain individual channel data, and 4) Harmonic imaging capability View full abstract»

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  • Modeling and measurement of cryogel elasticity properties for calibrating of IVUS elasticity images

    Page(s): 1821 - 1824 vol.2
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    Ultrasound elastography allows the estimation of tissue elasticity and can be used to characterise atherosclerotic plaques. In order to quantify the difference in elasticity of the various plaque materials, our aim is to calibrate the intravascular elastography images. For that, we make comparison between the modeling and experiments on vessel mimicking phantoms. Use of phantoms permits one to control many parameters. The range of Young's modulus in arteries goes from 1 kPa for lipids to 1000 kPa for the axial Young's modulus of the adventicia. Experiments were done to characterise a vessel mimicking materials, polyvinyl alcohol cryogel, and were compared with arterial values. The process consists of creating a pattern on a lateral side of the homogenous sample, to apply a uniform controlled pressure loading, then a CCD camera takes a photograph of the patterned side before and after compression. Image correlation software estimates axial and lateral strain and permits one to calculate the elastic modulus. These values are then included in finite element modeling. Then we combine a finite element analysis with a simulation of ultrasound response of the phantom to generate echograms for different compression levels of the vessel. The compression is radial and uniform inside the vessel. An estimated elastogram is obtained from two images using an adaptive stretching algorithm. This study shows that cryogel is a good material to make vessel mimicking phantoms due to the similarity of its elastic modulus to that which we can find in an artery, and therefore its relative breaking resistance View full abstract»

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  • Mapping of airborne ultrasonic fields using optical heterodyne probing and tomography reconstruction

    Page(s): 1117 - 1120 vol.2
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    The application of an acousto-optic method to the measurement of airborne ultrasound is described. The method consists of an optical heterodyne interferometric probing of the pressure field emitted by a transducer combined with tomographic algorithm. The method is very sensitive in air (2 10-4 Pa / √Hz). The measurements of the ultrasonic fields are improved by screening the sound path from the surrounding to prevent from air disturbation. The temperature is measured to compensate velocity variations. Moreover, direct measurements in the cross-section are in good agreement with forward projections, using an inhomogeneous plane waves View full abstract»

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  • Improved in vivo abdominal image quality using real-time estimation and correction of wavefront arrival time errors

    Page(s): 1645 - 1653 vol.2
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    The speed of sound varies with tissue type, yet commercial ultrasound imagers assume it is constant. Sound speed variation in abdominal fat and muscle layers is widely believed to be largely responsible for poor image contrast and resolution in some patients. The simplest model of the abdominal wall assumes that it adds a spatially varying time delay to the ultrasound wavefront. We describe an adaptive imaging system consisting of a GE LOGIQ 700 imager connected to a multi-processor computer. Arrival time errors for each beamforming channel, estimated by correlating each channel signal with the beamsum signal, are used to correct the imager's transmit and receive beamforming time delays at the image frame rate. A multi-row transducer provides two dimensional sampling of wavefront arrival time errors. After beamforming time delay correction, we observe significant improvement in abdominal images of healthy male volunteers, including increased contrast of blood vessels, increased brightness of liver tissue, and improved definition of the renal capsule and splenic boundary View full abstract»

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  • Measured bioeffects of tone-burst ultrasound in combination with poly(propyl acrylic) acid (PPAA)

    Page(s): 1359 - 1362 vol.2
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    In this study, high intensity focused ultrasound (HIFU) is combined with the pH-sensitive cell membrane disrupting polymer PPAA (poly-propyl acrylic acid) at sublethal doses to achieve hemolysis of human erythrocytes and sonoporation of suspended cells. For our studies, a 1 mL sample of cells suspended in phosphate buffered saline (PBS) was simultaneously exposed to 1.1 MHz acoustic tone bursts and PPAA at a temperature of 37°C. We vary the pH of the suspension fluid and amount of PPAA added to assess the influence of its structural conformation, functionality, and concentration upon measured bioeffects. For hemolysis study, we suspended erythrocytes at a final concentration of 108 cells/mL. Damage to the cell suspension was determined by measuring the amount of hemoglobin released using a spectrophotometer. A passive cavitation detection system was utilized to monitor the acoustic emissions from the cell suspension during exposure to ultrasound. In the presence of PPAA, there is a significant increase in cavitation and bioeffects during ultrasound exposure at more acidic pH levels. This polymer/ultrasound synergy is pH independent, unlike the synergy of ultrasound with poly(ethyl acrylic acid). The levels of cavitation and hemolysis measured from HIFU/PPAA synergy was compared with levels measured from HIFU/Optison(R) synergy to assess the effectiveness of the polymer in an acoustic field View full abstract»

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  • Data processing for a fast rotating phased array real-time 3D acquisition unit

    Page(s): 1597 - 1600 vol.2
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    A fast rotating phased array transducer was designed in order to scan a conical section of the heart at high scan rates. Typical rotation rate is 240-480 rpm. Data is acquired in a period of 10 seconds using a GE Vingmed System V mainframe and stored in a PC as a sequence of frames in their raw (polar) format, i.e. range versus scan angle. The frames are linearly related to rotation angle. The data set is thus fully described in a spherical coordinate system. The contours of the left ventricle may be traced in the raw data frames without any scan conversion. The LV volume, contained in the sequence of contours along the azimuth direction in the spherical domain, can be obtained directly using a spherical volume integral. Another application of processing in the spherical domain is the fusion of multiple heartbeats into a synthesized single heartbeat. This can be achieved by realignment of the spherical data in the azimuth range using the ECG as synchronization. Asynchronous probe rotation produces a random interleaved volume sampling. We propose that the construction and analysis of three-dimensional data sets obtained from a fast rotating sector scanner is performed in the spherical coordinate system, produced by the probe itself. The procedure is efficient, accurate and time saving View full abstract»

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  • A new compounding approach for speckle reduction [diagnostic ultrasound]

    Page(s): 1699 - 1702 vol.2
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    A new compounding technique for reducing speckle brightness variations is proposed. This method is based on speckle decorrelation of signals under different strain states. The different strain states can be created using externally applied forces. Such forces produce 3D tissue motion. By correcting the in-plane motion, the images under different strain states have identical characteristics except for speckle appearance due to un-corrected out-of-plane motion. Therefore, speckle noise is reduced without affecting in-plane spatial resolution. Experimental results indicated that speckle brightness variations were reduced by more than 50% with an applied strain at 4.8% View full abstract»

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  • Nonlinear interactions of sound fields generated by a focused annular array: application to vibro-acoustography

    Page(s): 1573 - 1576 vol.2
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    In ultrasound-stimulated vibro-acoustography (USVA) imaging method, one tries to form an image of the deformability of a tissue submitted to a low frequency (LF) stress field. The “coherent acoustic emission” resulting from the object vibration is detected by a sensitive hydrophone and used to form an image. In the present literature the origin of this stress field has been identified to the LF radiation pressure of the two primary beams driven at two close frequencies. This work analyses another possible contribution to the LF field which is distributed in the volume of the object and created by the nonlinear interaction of two high frequency primary beams. To do this, a calculation method of the nonlinear field has been developed and applied to the case of multiple rings annular arrays View full abstract»

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  • Influence of the quarter wave matching layers on the response of bar transducers

    Page(s): 1135 - 1138 vol.2
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    Matching layers are widely used today for large area transducers and medical arrays. Geometrical and mechanical characteristics of these layers are usually chosen with the help of the 1D design formalism. However, it doesn't take into account of lateral waves propagation in the layer which could damage radiation pattern of the transducer. The Finite Element Model, with the help of the ATILA code, permits to take this kind of phenomenon into account. In this paper, the influence of mechanical and geometrical characteristics of the matching layer on appearance of lateral modes is examined. This study is concluded by the definition of a choice criterium guaranteeing no lateral mode in the bandwidth of the transducer View full abstract»

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  • Ultrasound surgery monitoring using vibroacoustography-a simulation study

    Page(s): 1577 - 1580 vol.2
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    Similar to other therapeutic methods, ultrasound surgery requires an imaging modality to monitor the extent of tissue damage during treatment. Currently, MRI is considered the gold standard method for monitoring tissue ablation, but it is considered to be costly and restrictive in its applications. In this paper, we considered the method of ultrasound-stimulated acoustic emission that uses two ultrasonic beams at high frequency (MHz) (same as that used for ablation) to locally perturb the tissue by generating a low difference frequency (kHz) radiation force. Recording of the tissue response at several locations yields an image. The amplitude of the tissue response depends on the mechanical and acoustic tissue properties, namely its stiffness and absorption. Those two properties were initially hypothesized to have opposite effects in the response amplitude, i.e., the amplitude should increase with absorption and decrease with stiffness. To check this hypothesis as well as the degree to which those properties influence the response, finite-element simulations of a uniform lesion formed in a homogeneous medium were used. The results show that the hypothesis holds at lower frequencies. At resonance and higher frequencies, those two properties have a synergistic effect on the tissue response to the applied radiation force View full abstract»

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  • Novel method for producing high frequency 2-2 composites from PZT ceramic

    Page(s): 969 - 972 vol.2
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    The fabrication of 2-2 PZT/epoxy composites by laminating ceramic tape printed with carbon black was investigated as a way to make very high frequency ultrasound transducers. When the laminates were fired, the tape layers densified to form the PZT beams and the carbon volatilized leaving behind kerf space. The kerf was then filled with epoxy, and resulting composites had properties equivalent to those routinely made by conventional dice and fill technology. Since tape casting and screen printing methods can provide feature sizes less than 5 μm, the techniques investigated in this work could potentially be used to fabricate linear and perhaps even phased arrays in the 30 to >50 MHz range View full abstract»

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  • Ultrasound-based noninvasive shear elasticity probe for soft tissues

    Page(s): 1799 - 1801 vol.2
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    An ultrasonic technique for measuring the viscoelastic properties of soft tissues is presented. This technique uses a transducer set up on a vibrator as a source of high frequency waves (ultrasound) and low frequency waves (shear wave) at the same time. Ultrasound (5 MHz) allows one to detect the displacements induced by the shear waves (200 Hz) inside soft biological tissues. These shear waves reveal pieces of information about the shear elasticity and the shear viscosity. Two kinds of media are investigated: agar-gelatin phantoms and in-vivo human biceps View full abstract»

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  • An efficient electrical addressing method using through-wafer vias for two-dimensional ultrasonic arrays

    Page(s): 1179 - 1182 vol.2
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    This paper presents a technology for high density and low parasitic capacitance electrical interconnects to arrays of Capacitive Micromachined Ultrasonic Transducers (CMUTs) on a silicon chip. Vertical wafer feedthroughs (vias) connect an array of sensors or actuators from the front side (transducer side) to the backside (packaging side) of the chip. A 20 to 1 high aspect ratio 20 μm diameter via is achieved by using Deep Reactive Ion Etching (DRIE). Reduction of the parasitic capacitance of the polysilicon pads to the substrate can be achieved by using Metal Insulator Semiconductor (MIS) operating in the depletion region. This three-dimensional architecture allows for elegant packaging through simple flip-chip bonding of the chip's back side to a printed circuit board (PCB) or a signal processing chip View full abstract»

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  • Clinical use and evaluation of coded excitation in B-mode images

    Page(s): 1689 - 1693 vol.2
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    Use of long encoded waveforms can be advantageous in ultrasound imaging, as long as the pulse compression mechanism ensures low range sidelobes and preserves both axial resolution and contrast. A coded excitation/compression scheme was previously presented by our group, which is based on a predistorted FM excitation and a mismatched compression filter designed for medical ultrasonic applications. The attenuation effect, analyzed in this paper using the ambiguity function and simulations, dictated the choice of the coded waveform. In this study clinical images, images of wire phantoms, and digital video demonstrate the applicability, clinical relevance, and improvement attained with the proposed scheme. A commercial scanner (B-K Medical 3535) was modified and interfaced to a software configurable transmitter board and to a sampling system with a 2 GB memory storage. The experimental system was programmed to allow alternating excitation on every second frame. That offers the possibility of direct comparison of the same set of image pairs; one with pulsed and one with encoded excitation. Abdominal clinical images from healthy volunteers were acquired and statistically analyzed by means of the auto-covariance matrix of the image data. The resolution laterally is retained, axially is improved, while there is a clear increase in penetration. Phantom images using the proposed FM-based scheme as well as complementary Golay codes were also acquired, in order to quantitatively evaluate the characteristics of the compressed output and its stability to attenuation. Images of a wire phantom in water show that the range sidelobes resulting from pulse compression are below the acoustic noise, which was at 50 dB for the pulsed images. For images acquired from an attenuation phantom, the proposed compression scheme was robust to frequency shifts resulting from attenuation. The range resolution is improved 12% by the coded scheme compared to a 2-cycle pulse excitation. For the maximum acquisition depth of 15 cm, where the coded excitations are primarily intended, the improvement in SNR was more than 10 dB, while the resolution was retained View full abstract»

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  • Quantitative 3D ultrasound imaging using an automated image tracking technique

    Page(s): 1593 - 1596 vol.2
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    A new method for acquiring dimensionally accurate 3D ultrasound data from multiple 2D image planes is proposed and tested. This is based on the use of a modified linear phased array comprising a central `Imaging' array that acquires multiple 2D slices as the transducer is passed through the tissue of interest. Small, perpendicularly oriented, `Tracking arrays' are integrally mounted on each end of the Imaging transducer. As the transducer is translated in an elevational direction, the images obtained by the Tracking arrays remain largely coplanar. The motion between successive Tracking images is determined using image matching based on the Minimum Sum of Absolute Differences (MSAD) criterion. Initial testing of a prototype 8 MHz array indicates that linear dimensional accuracy of approximately 5% is attainable. The applicability of the approach towards a low cost, rapid screening method for detecting stenosis in the carotid artery has been tested. Accurate estimates of stenosis, referenced to data acquired by Magnetic Resonance Angiography (MRA) or X-Ray angiography, were obtained in an average of 12 minutes as compared to approximately 45-50 minutes for conventional full duplex 2D/Color ultrasound scans View full abstract»

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  • Coronary atherosclerotic plaque characterization using IVUS elastography and Raman spectroscopy

    Page(s): 1775 - 1778 vol.2
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    The composition of atherosclerotic lesions is considered to be an important determinant for the development of acute coronary ischemic syndromes. We investigated the potentials of a combination of intravascular ultrasound (IVUS) elastography and intravascular near infrared Raman spectroscopy, to assess the geometry and physical and chemical composition of normal vessel wall and plaque. Intact human coronary arteries were mounted in an in vitro pressurized perfusion setup. At selected cross-sections, two echo-frames were acquired at different intraluminal pressures to obtain elastograms. Subsequently, Raman spectra were acquired in 30 seconds at four different angles using a sideways viewing Raman catheter. Spectra were modeled to extract quantitative chemical information. Calcified areas were identifiable on the echograms, elastograms and Raman spectra. A combination of geometric information provided by the echogram, chemical information as obtained with Raman spectroscopy, and high stress regions determined by the elastogram, may prove to be valuable for identification of vulnerable plaques in vivo View full abstract»

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  • Quantitative assessment of arthritic cartilage using high-frequency ultrasound

    Page(s): 1375 - 1378 vol.2
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    The current study aims at evaluating the ability of 55 MHz ultrasound (US) in assessing subtle cartilage changes during the time course of a model of arthritis induced in rat knees (intra-articular injection of Zymosan). Arthritic (n=24) and control (n=24) patellae were explored in vitro at 5, 14 and 21 days post-injections, using a 3-D US microscope. Cartilage thickness was measured on B-scan images. Changes in cartilage surface and matrix, and in cartilage/bone interface were characterized by the integrated reflection coefficient (IRC) and apparent integrated backscatter (AIB), respectively. US findings were compared to histologic results. Thickness of arthritic cartilage decreased at D5 (p<0.05), then increased at D14 (p<0.O5), but was similar to that of controls at D21. IRC mean values of Zymosan groups decreased significantly (p<0.O5) at D5 and D14, but did not vary at D21. IRC decrease was related to cartilage surface fibrillation. AIB from cartilage/bone interface increased significantly at D5 and D21 (p<0.05) due probably to changes in the interface morphology and/or structure. No significant change was observed in AIB from cartilage matrix. Current results show that 55 MHz US allows detection of lesions involving both cartilage and subchondral bone, as well as of partial restoration of cartilage View full abstract»

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  • A method for evaluation of regional elasticity of arterial wall with non-uniform wall thickness by measurement of its change in thickness during an entire heartbeat

    Page(s): 1829 - 1832 vol.2
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    The average elastic modulus of the artery has been evaluated previously by measurement of the pulse wave velocity and the change in arterial diameter during one heartbeat. On the other hand, we aim to measure the regional elastic modulus of the arterial wall by measurement of its small change in thickness during an entire heartbeat. In this paper, a method is proposed for measurement of the regional elastic modulus even if the artery has non-uniform wall thickness such as an atherosclerotic plaque. In a basic experiment, the proposed method is validated using a silicone rubber tube as a model of the artery. In in vivo experiments, the spatial distribution of the elastic modulus is measured around the human carotid atherosclerotic plaque. From this result, the difference in the regional elasticity around the atherosclerotic plaque can be observed and the soft region is found in the plaque. Such information seems to be useful for diagnosis whether the plaque easily ruptures or not View full abstract»

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  • Development of a new diagnostic system for human liver diseases based on conventional ultrasonic diagnostic equipment

    Page(s): 1395 - 1398 vol.2
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    The authors show the experimental results of a quantitative ultrasonic diagnosis technique for human liver diseases using the fractal dimensions (FD) of the shape of the power spectra (PS) of RF signals. We have developed an experimental system based on a conventional ultrasonic diagnostic system, and applied the signal processing technique to RF signals from the conventional system. As a result, we show that normal livers, fatty livers and liver cirrhosis can be identified by the FD values. We also show that the degree of fatty livers can be estimated by FD values View full abstract»

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  • Miniaturized circular array [for intravascular ultrasound]

    Page(s): 1253 - 1254 vol.2
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    Intravascular ultrasound demands miniature transducers that can be guided through tiny blood vessels. Other applications in medicine and industry can also benefit from a highly miniaturized catheter based transducer design. The smaller the geometry the more useful and versatile the resulting device will be. Design consideration of geometry versus performance tradeoffs, other acoustic properties in array design and the methods of synthetic aperture beamforming are well known. Therefore, we have focused our paper on the details and intricacies of manufacturing extremely small ultrasound arrays View full abstract»

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