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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 9 out of 330
| Title |
A hemisphere array for non-invasive ultrasound brain therapy and surgery. |
| Author |
Clement GT, Sun J, Giesecke T, Hynynen K. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
2000 |
| Abstract |
Abstract. Ultrasound phased arrays may offer a method for non-invasive deep brain surgery through the skull. In this study a hemispherical phased array system is developed to test the feasibility of trans-skull surgery. The hemispherical shape is incorporated to maximize the penetration area on the skull surface, thus minimizing unwanted heating. Simulations of a 15 cm
radius hemisphere divided into 11, 64, 228 and 512 elements are presented. It is determined that 64 elements are sufficient for correcting scattering and reflection caused by trans-skull propagation. An optimal operating frequency near 0.7 MHz is chosen for the array from numerical and experimental
thermal gain measurements comparing the power between the transducer focus and the skull surface. A 0.665 MHz air-backed PZT array is constructed and evaluated. The array is used to focus ultrasound through an ex vivo human skull and the resulting fields are measured before and after phase correction of the transducer elements. Finally, to demonstrate the feasibility of trans-skull therapy, thermally induced lesions are produced through a human skull in fresh tissue placed at the ultrasound focus inside the skull. |
| Title |
A high frequency intravascular ultrasound imaging system for investigation of vessel wall properties. |
| Author |
Ryan LK, Lockwood GR, Starkoski BG, Holdsworth DW, Rickey DW, Drangova M, Fenster A, Foster FS. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1992 |
| Abstract |
Intravascular ultrasound imaging systems have been shown to be effective in identifying and characterizing occlusive arterial disease. In order to investigate changes in vessel wall elasticity due to atherosclerosis, a real-time, high frequency intracvascular ultrasound imaging system has been developed for the study of excised artery sections in vitro. The system consists of a miniature ultrasound probe constructed from a 42 MHz lead zirconate titanate (PZT) transducer, a high frequency scan converter and a computer-controlled flow system. By correlating vessel wall displacement, determined from the ultrasound data, with intraluminal pressure variations recorded with a catheter-tip pressure transducer, the elastic properties of the vessel wall can be assessed. Dynamic vessel wall motion along one radial view, assessed using one-dimensional cross-correlation, corresponds well with the simultaneously measured intraluminal pressure waveform. Preliminary studies using a two-dimensional speckle tracking algorithm show potential for determination of regional variation in vessel elasticity. |
| Title |
A hybrid computational model for ultrasound phased-array heating in presence of strongly scattering obstacles. |
| Author |
Botros YY, Volakis JL, VanBaren P, Ebbini ES. |
| Journal |
IEEE Trans Biomed Eng |
| Volume |
|
| Year |
1997 |
| Abstract |
A computationally efficient hybrid ray-physical optics (HRPO) model is presented for the analysis and synthesis of multiple-focus ultrasound heating patterns through the human rib cage. In particular, a ray method is used to propagate the ultrasound fields from the source to the frontal plane of the rib cage. The physical-optics integration method is then employed to obtain the intensity pattern inside the rib cage. The solution of the matrix system is carried out by using the pseudo inverse technique to synthesize the desired heating pattern. The proposed technique guides the fields through the intercostal spacings between the solid ribs and, thus, minimal intensity levels are observed over the solid ribs. This simulation model allows for the design and optimization of large-aperture phased-array applicator systems for noninvasive ablative thermal surgery in the heart and liver through the rib cage.
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| Title |
A limitation on ultrasonic transmission tomography. |
| Author |
McKinnon GC, Bates RHT. |
| Journal |
Ultrason Imaging |
| Volume |
|
| Year |
1980 |
| Abstract |
Ultrasonic propagation can often be usefully described in terms of rays. As these rays are in general curved, transmission tomography is more complicated for ultrasound than for x-rays. It is shown here that in most media there are “forbidden” regions which are not intersected by any “minimum propagation time” rays. It is concluded that it is seldom feasible to obtain better images than those reconstructed on the assumption that the ultrasonic rays travel along straight lines. |
| Title |
A low frequency (220 kHz) ultrasound system for enhancement of gallstone dissolution. |
| Author |
Sanghvi NT, Fry FJ, Burney BT, Girffith SL, Wessling SM, Franklin TD, Morris RF. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1990 |
| Abstract |
A clinical system using 220 kHz broad-beam ultrasound for the dissolution of gallstones is presented. Ultrasound is applied in the transcutaneous mode and a gallstone solvent is introduced directly into the gallbladder using a uniquely designed catheter which is inserted through the skin surface to the gallbladder. Initial in vitro studies were conducted in a latex gallbladder simulation envelope containing human gallstones in appropriate solvents, with the entire system immersed in 37°C degassed water and illuminated with a broad-beam ultrasound configuration. Great acceleration was demonstrated in gallstone dissolution over that unaided by ultrasound irradiation. The system has recently been applied in the clinical arena. Animal studies have shown, in addition, the ability to produce gallbladder ablation by a change in the acoustic intensity parameter |
| Title |
A mass transfer probe for measurements of cavitation activity in ultrasonic fields. |
| Author |
Perusich SA, Alkire RC. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1989 |
| Abstract |
A new type of probe was developed to evaluate the distribution of kinetic, thermal, and acoustic energy in an ultrasonically induced cavitation field. The probe is based on an electrochemical mass transfer technique for direct measurement of the flux of reactants to a surface. Cavitation was generated in a focused ultrasonic field at 1.58 MHz over a large range of focal intensities. Electrochemical measurements of the reduction of ferricyanide to ferrocyanide in a NaOH solution show that the focal area dimensions (as characterized by the cavitation activity) increased almost an order of magnitude in the presence of intense cavitation. The cavitation activity is attributed to fluid motion generated by cavitation-induced jets and microstreaming. A mathematical model is proposed to predict the mass transfer rate at the surface under cavitation conditions and to relate the mass transfer coefficient to the acoustic focal intensity. The concept of the mass transfer probe resulted from the author?s previous work in the study of the electrochemistry of metals in the presence of ultrasound [S. Perusich, Ph.D. thesis, University of Illinois at Urbana, IL (1985)]. |
| Title |
A mechanism for the generation of cavitation maxima by pulsed ultrasound. |
| Author |
Flynn HG, Church CC. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1984 |
| Abstract |
A train of 1-MHz pulses can generate maxima of cavitation activity [V. Ciaravino, H.G. Flynn, and M. W. Miller, Ultrasound Med Biol 7, 159-166 (1981)] at pulse lengths of 6 and 60 ms and at pressure amplitudes, P(sub)A, between 5.4 and 9.4 bars (or intensities between 10 and 30 W/cm2). Generation of maxima at P(sub)A between these limits on pressure amplitude implies that the increase in cavitation activity originates from gas nuclei with radii lying in a critical size range centered at about 0.08 micrometers. The mechanism proposed for this phenomenon suggests that nuclei in this critical range are unstabilized nuclei generated in one pulse and surviving to the next with an appreciable fraction of the survivors lying in the critical range. Transient cavities that grow from such smal nuclei are shown to behave as isolated mechanical systems that on reaching maximum size collapse as imploding spheres. The maximum pressures reached in such imploding cavities would then approximate those calculated for the spherical collapse of cavities. The occurrence of the observed maxima is ascribed to the spherical collapse of transient cavities. |
| Title |
A method for spectra-color b-scan ultrasonography. |
| Author |
Holasek E, Gans LA, Purnell EW, Sokollu A. |
| Journal |
J Clin Ultrasound |
| Volume |
|
| Year |
1975 |
| Abstract |
A new technique which records color coded frequency information in B-scan ultrasonography is described. The frequency spectrum of a wide band transducer (6MHz-12MHz) is divided into three component bands each recorded as one of the three primary colors of light. The results of tissue model studies are presented |
| Title |
A method for stereological determination of the structure function from histological sections of isotropic scattering media |
| Author |
Han A |
| Journal |
IEEE TUFFC |
| Volume |
|
| Year |
2018 |
| Abstract |
The frequency-dependent ultrasonic backscatter coefficient (BSC) from tissues, a fundamental parameter estimated by quantitative ultrasound (QUS) techniques, contains microstructure information useful for tissue characterization. To extract the microstructure information from the BSC, the tissue under investigation is often modeled as a collection of discrete scatterers embedded in a homogeneous background. From a discrete scatterer point of view, the BSC is dependent on not only the properties of individual scatterers relative to the background but also the scatterer spatial arrangement [described by the structure function (SF)]. Recently, the 2-D SF was computed from histological tissue sections, and was shown to be related to the volumetric SF extracted from QUS measurements. In this paper, a stereological method is proposed to extract the volumetric (3-D) SF from 2-D histological tissue sections. Simulations and experimental cell pellet biophantom studies were conducted to evaluate the proposed method. Simulation results
verified the proposed method. Experimental results showed that the volumetric SF extracted using the proposed method had a significantly better agreement with the QUS-extracted SF than did the 2-D SF extracted in the previous study. The proposed
stereological approach provides a useful tool for predicting the SF from histology. |
| Title |
A method for three-dimensional prostate imaging using transrectal ultrasound. |
| Author |
Richard WD, Grimmell CK, Bedigian K, Frank KJ. |
| Journal |
Comput Med Imaging Graph |
| Volume |
|
| Year |
1993 |
| Abstract |
This paper describes a method for forming three-dimensional images of the prostate using transrectal ultrasound. This method extracts three-dimensional images of the prostate from sets of two-dimensional ultrasound images obtained via a special-purpose transrectal ultrasound probe. Each two-dimensional image is segmented and the results used to form a three-dimensional image of the prostate. A method for segmenting two-dimensional images of the prostate based on the Laplacian-of-Gaussian edge operator is described. The three-dimensional imaging method described provides a new, noninvasive method for monitoring gland pathology during radiation therapy. |
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