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May 1978

Volume 63, Issue S1, pp. S1-S87

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back to top Session N. Engineering Acoustics I: Medical Ultrasonic Arrays and Systems
Invited Papers
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Transducer arrays in medical ultrasonics (A)

P. P. Lele

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S38-S38 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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Ultrasonic instrumentation based on linear and phased array transducers is increasingly being used in clinical diagnosis and yields information not hitherto available. However, the use of ultrasonic arrays is not necessarily restricted to diagnosis. They may, in the future, play an important role in therapy as well. Fundamentals of arrays, current status of systems, and some of the ongoing research on beam shaping by apodization will be briefly reviewed. An attempt will be made to guess at the future based on the current work in various laboratories. [Work supported by NIH.]
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Phased array ultrasound imaging of the heart (A)

Fredrick L. Thurstone

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S38-S38 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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Pulse‐echo ultrasound has been widely used for investigating the status and function of the heart. Recently, a number of systems have been developed which produce real‐time tomographic images of heart structures. Many of these employ either a switched array of transducers or a phased array for beam steering. The development of such phased array systems, their capabilities, and limitations will be the subject of this presentation. As in all pulse‐echo ultrasound used for medical diagnosis, this imaging technique is basically a diffraction‐limited process. There are additional imaging constraints imposed by the inhomogeneity of the tissue structures under investigation. These include reverberation effects, aberration effects produced by varying propagation velocity, and amplitude variations due to varying absorption. Still other constraints are imposed by technical limitations on the ultrasound transducer elements themselves. These include the compromise between sensitivity and bandwidth, the directional character of such elements, and other factors. The development of a practical cardiac imaging system together with an on‐line image‐processing facility will be presented.
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Ultrasound imaging for characterization of biological tissue and function (A)

Balu Rajagopalan, James F. Greenleaf, and S. A. Johnson

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S38-S39 (1978); (2 pages)

Online Publication Date: 11 Aug 2005

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Quantitative images of acoustic speed distribution in excised human tissues, in excised dog myocardium, and in in vivo female breasts were obtained by ultrasound computerized tomography. The in vitro study was carried over a temperature from 20° to 40 °C. Results indicate (1) acoustic speed in human tissues (except fat) increase monotonically with temperature in this range, (2) fat shows an anomalous decrease in acoustic speed around 35 °C, (3) average acoustic speed is higher in breasts with cancer and with fibrocystic disease compared to normal breasts, and (4) acoustic speed is a function of age. The reconstruction problem in ultrasound computerized tomography is unlike its x‐ray analog because of the refraction and diffraction effects. Methods to correct for the consequent degradation are discussed. The backscattering properties of in vivo myocardial tissue of dogs were studied by a high‐resolution B‐scanner and the potential of (renovist and indocyanine green) as ultrasound contrast agents to quantitate perfusion in the myocardium will be discussed. [Work supported by NCI‐CB‐64041, HV 72928, HL‐07111, HL‐00060, HL‐00170.]
Contributed Papers
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Medical ultrasonic arrays (A)

J. L. Rose, P. A. Meyer, and M. S. Good

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S39-S39 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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The subject of multielement ultrasonic transducers is presented, with emphasis on describing the ultrasonic transducer design techniques and time‐delay pulsing schedules used to achieve real‐time imaging, beam steering, and beam focusing. Transducer design techniques make use of a first‐order scattering theory in fluids, which model quite nicely many basic problems in diagnostic ultrasound. The various sidelobe energy and resolution problems are explored as a function of such transducer array design parameters as gapping effects, numbers of elements, ultrasonic excitation waveform shapes and frequencies, element size, and element electronic time‐delay pulsing schedules. The electronic time‐delay pulsing schedules are responsible for waveform constructive and destructive interference phenomena at points of interest in the ultrasonic field; the time‐delay schedules can, therefore, be used to achieve focusing and steering, in both linear array and rectangular array transducer systems. Time‐delay analysis and mechanical rotation concepts are used to achieve focusing and steering in annular array transducers. A comparison of the resolution characteristics of annular and linear array transducers is discussed. Axial and lateral resolution as a function of depth and various dynamic focusing concepts are also presented. An introduction to the problems and advantages of rectangular array transducer design is outlined. Sample theoretical and experimental results are presented to highlight the principle concepts associated with the design and utilization of ultrasonic transducer arrays in the medical field.
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Design of a variable‐aperture phased array beamformer for use in echocardiography (A)

E. G. Crenshaw, K. Ishimaru, N. B. Miller, and J. M. Lawther

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S39-S39 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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A beamformer for evaluation of dynamic aperture control to maximize lateral resolution of an ultrasonic phased array is under development at The Applied Research Laboratory of The Pennsylvania State University. For echocardiographic applications, the beamformer offers the advantages of fast scanning with good lateral resolution at all ranges. Techniques for improving lateral resolution at unlimited depth of field over that obtainable by a fixed focus system include the farfield variable aperture and previously reported dynamic focusing approaches. The relative performance limits and the effects of these techniques on beam‐former complexity are compared. An electronic beamformer configuration for implementing the less complex variable aperture approach is described. The ultrasonic array and packaging concepts are presented along with acoustic performance data relating to the individual array elements. Measurements of damping and cross coupling and analyses of predicted performance have been made and are included. Results from computer models of the beamformer and array are also presented which compare the patterns obtained by (1) multiplicative pattern analysis, (2) taking into account the effect of different element patterns, and (3) varying the size of the element. [This work was supported in part by NIH grant R01HL20872‐02.]
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Optical determination of the transmit pulse characteristics of medical transducer arrays (A)

W. A. Riley and R. W. Barnes

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S39-S39 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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Two medical ultrasound array systems are currently being developed and evaluated within the Cerebrovascular Research Center at the Bowman Gray School of Medicine. One objective of these systems is to image intracranial and extracranial arteries and provide clinical information pertinent to atherosclerosis and other stroke‐related diseases. An optical system with a bandwidth exceeding 10 MHz has been constructed to study the spatial and temporal characteristics of the wide‐bandwidth pulses transmitted by 1‐ and 5‐MHz arrays used in these systems. The optical system is based upon the optical nearfield method of Cook [J. Acoust. Soc. Am. 60, 95–99 ( 1976)] for studying ultrasonic pulse waveforms. The use of this wide‐band system makes it possible to experimentally separate the transmit and receive characteristics of the arrays which could be used in a variety of transmit‐receive configurations. The general process of array field formation can be experimentally studied and the beam profiles and transmitted power determined. [This work was supported by NINCDS grant NS‐06655 and a grant from North Carolina United Way.]
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An experimental evaluation of the impulse response approach for predictions of transient acoustic pressures (A)

G. A. Fisher, W. Lamb, and P. R. Stepanishen

J. Acoust. Soc. Am. Volume 63, Issue S1, pp. S39-S39 (1978); (1 page)

Online Publication Date: 11 Aug 2005

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A measurement system has been constructed which combines a computer‐controlled positioning carriage and an A/D converter with an effective sampling rate of 100 MHz. This system has been used to investigate the acoustic transient pressure field of biomedical transducers which operate in the megahertz range. Since the pressure at any point in the field can be expressed as the convolution of an impulse response and the acceleration of the radiating surface of the transducer [P. R. Stepanishen, J. Acoust. Soc. Am. 49, 1029–1038, (1971)], a deconvolution is required to verify the impulse response method. A digital computer program for deconvolution which is based on iterative techniques has been developed. Extensive acoustic transient measurements have been obtained via the use of a microprobe hydrophone. A comparison of the theoretical and experimental impulse responses is presented along with a discussion of the results. [Work supported by NIH.]
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