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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 10 out of 330
| Title |
A model based upon pseudo regular spacing of cells combined with the randomisation of the nuclei can explain the significant changes in high-frequency ultrasound signals during apoptosis. |
| Author |
Hunt JW, Worthington AE, Xuan A, Kolios MC, Czarnota GJ, Sherar MD. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2002 |
| Abstract |
Recent ultrasound (US) experiments on packed myeloid leukaemia cells have shown that, at frequencies from 32 to 40 MHz, significant increases of signal amplitude were observed during apoptosis. This paper is an attempt to explain these signal increases based upon a simulation of the backscattered signals from the cells nuclei. The simulation is an expansion of work in which a condensed sample of cells, with fairly regular sizes, could be considered as an imperfect crystal. Thus, destructive interference could occur and this would be observed as a large reduced value of backscattered signals compared with the values obtained from a similar, but random, scattering source. This current paper explores the possibility that simple changes in the nuclei, such as their observed condensation or the small loss of nuclei scatterers from cells, could cause a significant increase in the observed backscattered signals. This model indicates that the greater backscattered signals can be explained by further randomisation of the average positions of the scattering sources in each cell. When these "microechoes" are added together, so that the destructive interference is reduced, a large increase in the signal is predicted. The simplified model strongly suggests that much of observed large increases of the backscattered signals could be simply explained by the randomisation of the position of the condensed nuclei during apoptosis, and the destruction of the nuclei could produce further signal amplitude changes due to disruption of the cloud of backscattered waves. |
| Title |
A model for estimating ultrasound attenuation along the propagation path to the fetus from backscattered waveforms. |
| Author |
Bigelow TA, O'Brien WD Jr. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2005 |
| Abstract |
Accurate estimates of the ultrasound pressure and/or intensity incident on the developing fetus on a patient-specific basis could improve the diagnostic potential of medical ultrasound by allowing the clinician to increase the transmit power while still avoiding the potential for harmful bioeffects. Neglecting nonlinear effects, the pressure/intensity can be estimated if an accurate estimate of the attenuation along the propagation path (i.e. total attenuation) can be obtained. Herein, a method for determining the total attenuation from the backscattered power spectrum from the developing fetus is proposed.. The boundaries between amnion and either the fetus? skull or soft tissue are each modeled as planar impedance boundaries at an unknown orientation with respect to the sound beam. A mathematical analysis demonstrates that the normalized returned voltage spectrum from this model is independent of the planes orientation. Hence, the total attenuation can be estimated by comparing the location of the spectral peak in the reflection from the fetus to the location of the spectral peak in a reflection obtained from a rigid plane in a water bath. The independence of the attenuation estimate and plane orientation is then demonstrated experimentally using a Plexiglas plate, a rat?s skull, and a tissue-mimicking phantom. |
| Title |
A model for the propagation and scattering of ultrasound in tissue. |
| Author |
Jensen JA. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1991 |
| Abstract |
An inhomogeneous wave equation is derived describing propagation and scattering of ultrasound in an inhomogeneous medium. The scattering term is a function of density and propagation velocity perturbations. The integral solution to the wave equation is combined with a general description of the field from typical transducers used in clinical ultrasound to yield a model for the received pulse-echo pressure field. Analytic expressions are found in the literature for a number of transducers, and any transducer excitation can be incorporated into the model. An example is given for a concave, nonapodized transducer in which the predicted pressure field is compared to a measured field. |
| Title |
A model for ultrasonic scattering from tissues based on the K distribution. |
| Author |
Shankar PM. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
1995 |
| Abstract |
A model for the backscattered ultrasound echo from tissues is presented. The model takes into.account the fact that the range cell being insonified may contain only a few scatterers and the.number may not be large enough to justify the use of a Gaussian model which results in.Rayleight statistics for the echo. Furthermore, the model also considers the case where the.echogenicity of the scatterers in the range cell may not be uniform, the lack of uniformity.resulting from variations in scattering cross-sections produced by the chemical as well as.biochemical changes brought on by the presence of disease, growth of benign or malignant.tumours, etc. The model is developed from the fundamental principles of scattering using the.results available in radar. This new model results in a two-parameter distribution, namely the K.distribution for the echo, thereby making it possible to gain information on the number as well as.scattering cross-sections of the scatterers in the range cell. The model is extended to include the.effects due to the presence of scatterers having some regular or periodic orientation in the range.cell, resulting in the so-called generalized K distribution which approximates to Rayleight,.Rician, or Gaussian under various limiting cases. Results of computer simulations and.experiments on tissue-mimicking phantoms are also provided, which strongly suggest that this.new model offers potential for tissue characterization. |
| Title |
A multimode real time scanner. |
| Author |
Carpenter DA, Dadd MJ, Kossoff G. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1980 |
| Abstract |
A real time scanner which images in compound scan as well as simple scan mode offers advantages over a conventional unit which only produces simple scans in one format. A linear array scanner in which the line of sight can be steered gives a variety of formats for both simple scan and compound scan imaging. The design considerations and capabilities of a scanner with these multiple modes of operation is discussed. The initial clinical results and potential applications are presented. |
| Title |
A myocardial backscatter parameter with maximal sensitivity to cyclic variation. |
| Author |
Rhyne TL, Sagar KB, Wann SL, Haasler G. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1986 |
| Abstract |
This paper presents an integrated backscatter parameter called the Integrated Backscatter Rayleigh 5 MHz corrected (IBR5), which is an absolute measure of the backscatter per cm that is independent of the instrumentation and diffraction. An optimal measurement method for IBR5 is developed. It consists of filtering the backscatter to achieve equal spectral weighting followed by squaring and averaging. Equal spectral weighting is achieved by inverse filtering the frequency response of: 1) the trasmitted signal, 2) the transducer and instrumentation, 3) the diffraction, and 4) the myocardium (using a power law spectrum). We suggest that the power law spectrum be set to p=2 so that the IBR5 represents the Rayleigh spectrum at 5 MHz. Human and canine data are used to compare IBR5 and three other "conventional" integrated backscatter measures. Using the ultrasound equation the mechanization of this measurement is discussed for a wide range of clinical measurements. |
| Title |
A new anechoic material for medical ultrasonic applications. |
| Author |
Zeqiri B, Bickley CJ. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2000 |
| Abstract |
This paper describes a newly developed material with acoustic properties that make it ideal for applications as radiation force balance-absorbing targets. The material is now commercially available from National Physical Laboratory (NPL) and is based on a polyurethane rubber. It exhibits an echo reduction of 45 dB, and single-pass transmission loss of 30 dB, both determined at an acoustic frequency of 1 MHz. The composition and structure of the new NPL absorber are presented, along with values for the frequency and temperature variation of the echo reduction and transmission loss. Over the frequency range 1 to 10 MHz, its acoustic properties comply with the requirements for force balance-absorbing targets specified in IEC 61161. |
| Title |
A new approach for detecting attenuation changes during high -intensity focused ultrasound. |
| Author |
Kemmerer J, Chang S, Oelze M. |
| Journal |
IEEE Int Ultrasonics Symp Proc |
| Volume |
|
| Year |
2010 |
| Abstract |
NO Abstract Available. |
| Title |
A new approach to testing the effect of.ultrasound on tissue growth and differentiation. |
| Author |
Pizzarello DJ, Wolsky A, Becker MH, Keegan AF. |
| Journal |
Oncology |
| Volume |
|
| Year |
1975 |
| Abstract |
Pulsed ultrasound from a Picker Ultrasonoscopy Model 102, with a frequency of 500.Hz and an energy of 2.2 MHz was applied to the amputated left forelimbs of 24 adult.newts. Exposure time was 5 min in half of the animals and 10 min in the remainder..The right forelimbs of these newts were also amputated at the same time, at the same.anatomical level, and by the same operator of the left forelimbs, but were not exposed.to sonication. Regeneration of both forelimbs was compared and found to be.generally slower in the ultrasonicated limb. In 75% there was a definite retardation of.growth. The results suggest that the the growth of rapidly proliferating embryonic.tissue (newt regenerates are formed from embryonic cells in the stump) is inhibited by.ultrasonication. |
| Title |
A new calculation procedure for spatial impulse responses in ultrasound. |
| Author |
Jensen JA. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1999 |
| Abstract |
A new procedure for the calculation of spatial impulse responses for linear sound fields is introduced. This calculation procedure uses the well known technique of calculating the spatial impulse response from the intersection of a circle emanating from the projected spherical wave with the boundary of the emitting aperture. This general result holds for all aperture boundaries for a flat transducer surface, and is used in the procedure to yield the response for all types of flat transducers. An arbitrary apodization function over the aperture can be incorporated through a simple one-dimensional integration. The case of a soft baffle mounting of the aperture is also included. Specific solutions for transducer boundaries made from lines are given, so that any polygon transducer can be handled. Specific solutions for circles are also given. Finally, a solution for a general boundary is stated, and all these boundary elements can be combined to, e.g., handle annular arrays or semi-circle transducers. Results from an implementation of the approach are given and compared to previously developed solutions for a simple aperture, a complex aperture, and a Gaussian apodized circular transducer. ©1999 Acoustical Society of America. |
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