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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 12 out of 330
| Title |
A new ultrasound mammography technique that provides improved correlation with x-ray mammography. |
| Author |
Kelly-Fry E, Jackson VP. |
| Journal |
Proc Twenty-Fourth Nat Conf Breast Cancer |
| Volume |
|
| Year |
1990 |
| Abstract |
The primary purpose of this study is to develop an ultrasound instrumentation technique that can provide images that correlate more closely with X-Ray mammography than those currently produced by standard ultrasound mammography. Secondary goals include decreasing the time required for ultrasound breast examination and improving the detection of small breast masses by the application of high ultrasound frequencies without experiencing undue attenuation of the beam. |
| Title |
A new ultrasound tissue-equivalent material. |
| Author |
Burlew MM Madsen EL Zagzebski JA Banjavic RA Sum SW. |
| Journal |
Radiology |
| Volume |
|
| Year |
1980 |
| Abstract |
Two limitations on the animal-hide gelatin and graphite powder tissue equivalent (TE) materials are that they cannot be produced consistently with speeds of sound less than 1,570 m/s at room temperature (22 degrees C) and that irreparable damage can result if the materials are raised to temperatures above 32.5 degrees C. An acceptable substitute polysaccharide gel (agar) has a high melting point (78 degrees C) and can be made to exhibit speeds of sound over the range 1,498 m/s to over 1,600 m/s at 22 degrees C. Thus TE material made with agar is environmentally stable and can be manufactured to exhibit the important speed of sound, 1,540 m/s.
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| Title |
A new velocity estimator for color flow mapping. |
| Author |
Bonnefous O, Pesque P, Bernard X. |
| Journal |
Proc Ultrason Symp IEEE |
| Volume |
|
| Year |
1986 |
| Abstract |
Recently, real-time blood flow imaging became possible thanks to the development of a velocity estimator based on the phase-shift measurement of the successive echoes obtained from moving blood [1]. However, this method suffers from the well-known limitations of pulse-Doppler instruments. These drawbacks are mainly the conflict between velocity precision and axial resolution requirements, and the velocity limitation due to the aliasing phenomenon. In this paper, a new principle for velocity estimation, based on time domain correlation [2], is shown to overcome these problems. A simplified version of the technique using only 1 bit signals has been derived. This processing scheme has been optimized through extensive computer simulations. Experiments carried out on recorded in-vivo data, have confirmed the feasibility of measuring velocity profiles accurately, without the high velocity limitation (aliasing). Moreover, the possibility of obtaining instantaneous and accurate velocity profiles by processing a limited number of echo responses (about 10 A-lines) should provide new potential modalities for clinical application of ultrasound. |
| Title |
A Newtonian rheological model for the interface of microbubble contrast agents. |
| Author |
Chatterjee D, Sarkar K. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2003 |
| Abstract |
A quantitative model of the dynamics of an encapsulated microbubble contrast agent will be a valuable tool in contrast ultrasound (US). Such a model must have predictive ability for widely varying frequencies and pressure amplitudes. We have developed a new model for contrast agents, and successfully investigated its applicability for a wide range of operating parameters. The encapsulation is modeled as a complex interface of an infinitesimal thickness. A Newtonian rheology with surface viscosities and interfacial tension is assumed for the interface, and a modified Rayleigh–Plesset equation is derived. The rheological parameters (surface tension and surface dilatational viscosity) for a number of contrast agents (Albunex®, Optison® and Quantison®) are determined by matching the linearized model dynamics with experimentally obtained attenuation data. The model behavior for Optison® (surface tension 0.9 N/m and surface dilatational viscosity 0.08 msP) was investigated in detail. Specifically, we have carried out a detailed interrogation of the model, fitted in the linear regime, for its nonlinear prediction. In contrast to existing models, the new model is found to capture the characteristic subharmonic emission of Optison® observed by [Shi et al., 1999]. A detailed parametric study of the bubble behavior was executed using the ratio of scattering to attenuation (STAR). It shows that the encapsulation drastically reduces the influence of resonance frequency on scattering cross-section, suggesting possible means of improvement in imaging at off-resonant frequencies. The predictive capability of the present model indicates that it can be used for characterizing different agents and designing new ones. |
| Title |
A non-invasive method for focusing ultrasound through the human skull. |
| Author |
Clement GT, Hynyen K. |
| Journal |
Phys Med Biol |
| Volume |
|
| Year |
2002 |
| Abstract |
A technique for focusing ultrasound through the human skull is described and verified. The approach is based on a layered wavevector-frequency domain model, which propagates ultrasound from a hemisphere-shaped transducer through the skull using input from CT scans of the head. The algorithm calculates the driving phase of each transducer element in order to maximize the signal at the intended focus. This approach is tested on ten ex vivo human skulls using a 0.74 MHz, 320-element array. A stereotaxic reference frame is affixed to the skulls in order to provide accurate registration between the CT images and the transducer. The focal quality is assessed with a hydrophone placed inside the skull. In each trial the phase correction algorithm successfully restored the focus inside the skull at a location within 1 mm from the intended focal point. The results demonstrate the feasibility of using the method for completely non-invasive ultrasound brain surgery and therapy. |
| Title |
A novel approach to quantitative ultrasonic naked gene delivery and its non-invasive assessment. |
| Author |
Wej W, Zhengzhong B, Yongjie W, Lafeng Y, Yalin M. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
2004 |
| Abstract |
The purpose of this study was to investigate practical, safe, easy-to-use, previous termnonnext term-cytotoxic, and reliable parameters to apply to an ultrasound (US) previous termnaked genenext term therapy system. The ultrasound pressure at the point of cell exposure was measured using previous termanext term calibrated hydrophone and the intensity calculated. An acoustic power meter calibrated using previous termanext term hydrophone was used to measure the power of the transducer. Four cell types were exposed to US with different exposure times and intensities. Fluorescent microscopy, spectrophotometry, scanning electron microscope, laser scanning confocal microscopy, flow cytometry and histogram analysis were used to evaluate the results of the study. The plasmid of green fluorescent protein (GFP) served as the reporter previous termgene.next term The energy accumulation E in US previous termgene deliverynext term for 90% cell survival was defined as the optimal parameters (E = 3.56 ± 0.06), and at 80% cell survival was defined as the damage threshold (E = 59.67 ± 3.54). US safely delivered GFP into S180 cells (35.1 kHz) at these optimal parameters without obvious damage or cytotoxity in vitro. Exposed cell function was proved normal in vivo. The transfection rate was 35.83 ± 2.53% (n = 6) in viable cells, corresponding to 90.17 ± 1.47% (n = 6) cell viability. The intensity of GFP expression showed previous termanext term higher fluorescent peak in the group of adeno-associated virus GFP vector (AVV-GFP) than in the control group (P < 0.001). The effect of US previous termgene deliverynext term and cell viability correlated as previous termanext term fifth order polynomial with US intensity and exposure time. With optimal parameters, US can safely deliver previous termnaked a gene into anext term cell without damage to cell function. Both optimal uptake and expression of previous termgenenext term depend on the energy E at 90% cell survival. E can be applied as previous termanext term control factor for bioeffects when combined with other parameters. Stable caviation results in optimal parameters for previous termgene deliverynext term and the transient caviation may cause cell damage, which will bring about previous termanext term sharp rise of permeabilization. The results may be applied to the development of previous terma novelnext term clinical previous termgenenext term therapeutic system. |
| Title |
A novel coded excitation scheme to improve spatial and contrast resolution of quantitative ultrasound imaging. |
| Author |
Sanchez JR,Pocci D,Oelze ML. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2009 |
| Abstract |
Quantitative ultrasound (QUS) imaging techniques based on ultrasonic backscatter have been used successfully to diagnose and monitor disease. A method for improving the contrast and axial resolution of QUS parametric images by using the resolution enhancement compression (REC) technique is proposed. Resolution enhancement compression is a coded excitation and pulse compression technique that enhances the −6-dB bandwidth of an ultrasonic imaging system. The objective of this study was to combine REC with QUS (REC-QUS) and evaluate and compare improvements in scatterer diameter estimates obtained using the REC technique to conventional pulsing methods. Simulations and experimental measurements were conducted with a single-element transducer (f/4) having a center frequency of 10 MHz and a −6-dB bandwidth of 80%. Using REC, the −6-dB bandwidth was enhanced to 155%. Images for both simulation and experimental measurements contained a signal-to-noise ratio of 28 dB. In simulations, to monitor the improvements in contrast a software phantom with a cylindrical lesion was evaluated. In experimental measurements, tissue-mimicking phantoms that contained glass spheres with different scatterer diameters were evaluated. Estimates of average scatterer diameter in the simulations and experiments were obtained by comparing the normalized backscattered power spectra to theory over the −6-dB bandwidth for both conventional pulsing and REC. Improvements in REC-QUS over conventional QUS were quantified through estimate bias and standard deviation, contrast-to-noise ratio, and histogram analysis of QUS parametric images. Overall, a 51% increase in contrast and a 60% decrease in the standard deviation of average scatterer diameter estimates were obtained during simulations, while a reduction of 34% to 71% was obtained in the standard deviation of average scatterer diameter for the experimental results. |
| Title |
A novel method for the intracellular delivery of siRNA using microbubble-enhanced focused ultrasound. |
| Author |
Kinoshita M, Hynynen K. |
| Journal |
Biochem Biophys Res Commun |
| Volume |
|
| Year |
2005 |
| Abstract |
Short interfering RNA (siRNA) has attracted much attention for clinical use in various diseases. However, its delivery, especially through the cell membrane, continues to present a challenge. Advances in ultrasound- and ultrasound contrast-agent technologies have made it possible to change transiently the permeability of the cell membrane and, using a focused ultrasound transducer, to narrow and focus the ultrasound energy on a small target, thereby avoiding damage to surrounding tissue. In this in vitro study, we demonstrate that it is possible to deliver siRNA intracellularly via microbubble-enhanced focused ultrasound. Although further optimization is necessary, our novel method for siRNA transduction represents a powerful tool for using siRNA in vivo and possibly in the clinical setting. |
| Title |
A novel method to control P+/P- ratio of the.shock wave pulses used in the extracorporeal.piezoelectric lithotripsy (EPL). |
| Author |
Lewin PA, Chapelon JY, Mestas JL, Birer A, Cathignol D. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1990 |
| Abstract |
There is growing evidence that acoustic cavitation plays an important role in stone.fragmentation during extracorporeal shock wave lithotripsy (ESL) treatment. In.addition, side effects of the treatment, such as the hemorrhage and destruction of the.tissue in the vicinity of the stone are also ascribed to cavitation phenomenon. Since.cavitation is associated with the maximum negative pressure in the shock pulse, it.would thus appear that possibility of controlling this pressure would be desirable in.ESL applications. This paper describes a novel technique developed to control the.ratio of compressional peak (P+) to rarefactional peak pressure (P-) of the shock.wave for use in lithotripsy treatment. The procedure is based on the finite amplitude.wave generation by focused piezoelectric transducers and subsequent interaction of.the shocked waves in the common focal region. The highly asymmetrical shock wave.is produced in the focal region by providing an appropriate time delay to each of the.high voltage electrical excitation signals which drive the transducers. The degree of.relative reduction of negative halfcycles and the corresponding positive halfcycles.amplification increases with the number of the acoustic sources used. The practical.implementation of the shock wave generator was obtained by using 5 cm diameter,.focused 1 MHz transmitter, and additional transducers of identical construction.having frequencies corresponding to the harmonics and subharmonics of the 1 MHz.frequency. The importance of the results for the future development of lithotripters,.and stone treatment efficiency is pointed out. |
| Title |
A novel phase assignment protocol and driving system for a high-density focused ultrasound array. |
| Author |
Caulfield RE, Yin X, Juste J, Hynynen K. |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
2007 |
| Abstract |
Currently, most phased-array systems intended for therapy are one-dimensional (1-D) and use between 5 and 200 elements, with a few two-dimensional (2-D) systems using several hundred elements. The move toward lambda/2 interelement spacing, which provides complete 3-D beam steering, would require a large number of closely spaced elements (0.15 mm to 3 mm). A solution to the resulting problem of cost and cable assembly size, which this study examines, is to quantize the phases available at the array input. By connecting elements with similar phases to a single wire, a significant reduction in the number of incoming lines can be achieved while maintaining focusing and beam steering capability. This study has explored the feasibility of such an approach using computer simulations and experiments with a test circuit driving a 100-element linear array. Simulation results demonstrated that adequate focusing can be obtained with only four phase signals without large increases in the grating lobes or the dimensions of the focus. Experiments showed that the method can be implemented in practice, and adequate focusing can be achieved with four phase signals with a reduction of 20% in the peak pressure amplitude squared when compared with the infinite-phase resolution case. Results indicate that the use of this technique would make it possible to drive more than 10,000 elements with 33 input lines. The implementation of this method could have a large impact on ultrasound therapy and diagnostic devices. |
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