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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 235 out of 330
| Title |
Speckle in ultrasound B-mode scans. |
| Author |
Burckhardt CB. |
| Journal |
IEEE Trans Sonics Ultrason |
| Volume |
|
| Year |
1978 |
| Abstract |
Ultrasound images obtained with a simple linear or sector scan show a granular appearance, called "speckle". This speckle is analyzed. The reduction in speckle that can be obtained with a compound scan with maximum amplitude writing is computed. The reduction in speckle is almost as large as can be obtained with averaging. It depends on the number of independent amplitude values that are measured. The condition for the independence of two amplitude values is derived, and thus a limit is given for the possible reduction in speckle... |
| Title |
Speckle motion artifact under tissue rotation. |
| Author |
Kallel F, Bertrand M, Meunier J |
| Journal |
IEEE Trans UFFC |
| Volume |
|
| Year |
1994 |
| Abstract |
Speckle patterns in ultrasound images may move in a way which bears no simple relationship to the motion of the corresponding tissues. In some instances the speckle motion replicates the underlying tissue motion, in others it does not. We name "speckle motion artifact" the difference between the speckle and the underlying tissue motion. In this paper an echographic image formation model is used to study the motion artifact produced by a rotating phantom and observed by a linear scan imaging system with a Gaussian beam. We propose that when the tissue is modeled as a random array of small and numerous scatterers, such motion aberration be accounted for by the 2-D phase characteristics of the imaging system. An analytic prediction of this motion artifact in relation to the imaging system characteristics (beam width, transducer frequency, pulse duration) is presented. It is shown that the artifact results from the curvature of the system point spread function, which in turn determines the curvature of the 2-D phase characteristics. To our knowledge, it is the first time a comprehensive model of ultrasonic speckle motion artifact is presented. The model has been developed to study rotation-induced artifact; the method is however quite general and can be extended to study the effects of other tissue motion, in particular deformation and shear. |
| Title |
Spectral and temporal signal modifications occuring between stable and transient inertial cavitation. |
| Author |
Santin M, Bridal SL, Haak A, O'Brien WD Jr. |
| Journal |
IEEE Int Ultrasonics Symp Proc |
| Volume |
|
| Year |
2008 |
| Abstract |
The goal of this work is to investigate temporal and spectral modifications in passive cavitation detection (PCD) measurements from ultrasound contrast microbubbles (MBs) related to MB rupture. Contrast MB pressure-time responses are modelled with the Marmottant model. Results demonstrate that post-excitation signals occur on simulated pressure-time traces for MBs only when radial oscillations exceed the modelled breakup radius within a range of sizes near the resonant size. PCD signals are acquired from MBs of Optison, Definity and Sonovue (acoustic excitation at 2.8-MHz, 5-cycle transmit; confocal 13-MHz receiver). Although data are acquired at relatively high incident acoustic pressures (peak rarefactional pressure of 1.6, 2.0 and 2.4 ± 0.2 MPa), subsets of data with and without post-excitation signals are identified for each MB type and pressure range. Post-excitation signals are used to identify which PCD signals indicate MB break-up [1] then average values of peak-to-peak voltage, 2nd harmonic, 3rd and 4th harmonic and broadband noise are calculated for responses from groups of ruptured and nonruptured MBs for each pressure range and MB type. The signal to noise ratio (SNR) is high (10 to 49 dB) both for ruptured (with post-excitation signals) and nonruptured (no post-excitation signals) MBs for all pressures and MBs. The average parameter values from ruptured MBs are approximately 3 to 8 dB higher than for nonruptured MBs although differences vary with the type of MB. Results contribute to better understand the link between PCD spectral and temporal modifications and MB break-up. |
| Title |
Spectral power determinations of compressibility and density variations inmodel media and calf liver using ultrasound. |
| Author |
Waag RC, Dalecki D, Christopher PE. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
1989 |
| Abstract |
A model of scattering is used to relate average differential scattering cross section.and power spectra of scattering medium variations. The model expresses the.average differential scattering cross section as a sum of the power spectrum of.medium compressibility variations, the power spectrum of density variations.weighted by the square of the cosine of the scattering angle, and the cross-power.spectrum of compressibility and density variations weighted by twice the cosine.of the scattering angle. Known values of the average differential scattering cross.section at a minimum of three different scattering angles and temporal.frequencies corresponding to the same spatial frequency are used to calculate.each of the three power spectra. Since noise and statistical fluctuations are.present in actual measurements of average differential scattering cross section,.the calculations of power spectra are obtained from an overdetermined set of.equations to which a solution is found by using a singular value decomposition..Data derived from a model for scattering from a cloud of correlated particles are.employed to show the influence of additive noise. Calculations are also made.from measurements of scattering from three suspensions of particles that have a.different average radius in each suspension but are similarly modeled by.scattering from a cloud. Additionally, the calculations are applied to.measurements of average differential scattering cross section of calf liver. The.results show that determination of the power spectra of scattering medium.variations can be made under practical conditions, and also imply that density.variations contribute significantly to scattering by calf liver. . |
| Title |
Speed of ultrasound in amniotic fluid. |
| Author |
Povall JM, Aindow JD, Chivers RC, Driscoll AM. |
| Journal |
Acoust Lett |
| Volume |
|
| Year |
1984 |
| Abstract |
Measurements on eleven samples of human amniotic fluid at temperatures of approximately 20 and 37 C are reported using a miniature hydrophone and time-interval-averaging system, with a precision of ? 1m/s. The results confirm those previously published for amniotic fluid at 25 C, and indicate a value of 1534 m/s at body temperatures. The measurement procedure is of interest in permitting measurements to be made on samples of 0.5 ml or less. |
| Title |
Spontaneous homogeneous nucleation,inertial cavitation and the safety of diagnostic ultrasound. |
| Author |
Church CC. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2002 |
| Abstract |
Gas bubbles of sufficient size to serve as cavitation nuclei may form spontaneously in tissue in regions of very low interfacial tension. In the absence of an acoustic wave or other mechanical stress, such nuclei will quickly dissolve and disappear from the medium. Under the influence of an acoustic wave, however, these microbubbles may grow to many times their initial size and then collapse violently, a process known as inertial cavitation. In this work, the in vivo energetics and dynamics of the nucleation-cavitation process were modeled by treating tissue as a homogeneous fluid. The assumption of a viscosity of 10-3 Pa s (i.e., that of water) resulted in the lowest acoustic rarefactional pressure threshold for nucleation-cavitation events, approximately 4.0 MPa, which was essentially frequency-independent over the range 1 to 15 MHz. The rarefactional pressure threshold for a viscosity of 5 x 10-3 Pa s (that of blood) also was approximately 4.0 MPa at 1 MHz, but the threshold for this higher viscosity increased nearly linearly with frequency above approximately 5 MHz, never being more than approximately 0.2 MPa below the equivalent derated peak rarefactional pressure calculated assuming MI = 1.9, the current USFDA guideline. |
| Title |
Stability of alteplase in presence of cavitation. |
| Author |
Soltani A, Prokop AF, Vaezy S. |
| Journal |
Ultrasonics |
| Volume |
|
| Year |
2008 |
| Abstract |
Several experimental studies have demonstrated that ultrasound (US) can accelerate enzymatic fibrinolysis and this effect is further enhanced in the presence of ultrasound contrast agents (UCA). Although UCA have been shown to be safe when administered to ischemic stroke patients, safety information of these agents in the thrombolysis setting is limited. Therefore, in this study we investigated potential adverse effects of acoustic cavitation generated by UCA on alteplase (t-PA), the drug used for treatment of ischemic stroke patients. A volume of 0.9 mL of alteplase was dispensed into a custom-made polyester sample tube. For treatments in the presence or absence of cavitation either 0.1 mL Optison or phosphate buffer saline was combined with alteplase. Three independent samples of each treatment group were exposed to ultrasound of 2 MHz frequency at three different peak negative acoustic pressures of 0.5, 1.7, and 3.5 MPa for a duration of 60 min. All treatments were carried out in a cavitation detection system which was used to insonify the samples and record acoustic emissions generated within the sample. After ultrasound exposure, the treated samples and three untreated drug samples were tested for their enzymatic activity using a chromogenic substrate. The insonified samples containing Optison demonstrated cavitational activity proportional to acoustic pressure. No significant cavitation activity was observed in the absence of Optison. Enzymatic activity of alteplase in both insonified groups was comparable to that in the control group. These tests demonstrated that exposure of alteplase to 60 min of 2 MHz ultrasound at acoustic pressures ranging from 0.5 MPa to 3.5 MPa, in the presence or absence of Optison had no adverse effects on the stability of this therapeutic compound. |
| Title |
Stable cavitation at low ultrasonic intensities induces cell death and inhibits 3H-TdR incorporation by Con-A-stimulated murine lymphocytes in vitro. |
| Author |
Vivino AA, Boraker DK, Miller D, Nyborg W. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1985 |
| Abstract |
Murine spleen cell suspensions stimulated by Concanavalin A (Con-A) were exposed.to 1.6-MHz continuous-wave ultrasound at low intensities (spatial-peak values.ranging from 16 to 300 mW/cm2) in the presence of a Nuclepore membrane that contained stabilized gas bodies. The ultrasonically activated gas bodies induced cell lysis and reduced the fraction of intact cells that excluded trypan blue. At a spatial-peak intensity of 75 mW/cm2 (spatial-average intensity 15 mW/cm2), Con-A-induced Methyl[3H]thymidine (3H-TdR) incorporation was reduced in.cultures exposed at 24 or 48 hr after addition of Con-A but not at 7 or 13 hr. There was no observable effect on cell survival or 3H-TdR incorporation at spatial-peak intensities below 75 mW/cm2. |
| Title |
Stand-alone front-end system for high- frequency, high-frame-rate coded excitation ultrasonic imaging. |
| Author |
Park J, Hu C, Shung KK. |
| Journal |
IEEE Trans Ultrason Ferroelectr Freq Control |
| Volume |
|
| Year |
2011 |
| Abstract |
A stand-alone front-end system for high-frequency coded excitation imaging was implemented to achieve a wider dynamic range. The system included an arbitrary waveform amplifier, an arbitrary waveform generator, an analog receiver, a motor position interpreter, a motor controller and power supplies. The digitized arbitrary waveforms at a sampling rate of 150 MHz could be programmed and converted to an analog signal. The pulse was subsequently amplified to excite an ultrasound transducer, and the maximum output voltage level achieved was 120 Vpp. The bandwidth of the arbitrary waveform amplifier was from 1 to 70 MHz. The noise figure of the preamplifier was less than 7.7 dB and the bandwidth was 95 MHz. Phantoms and biological tissues were imaged at a frame rate as high as 68 frames per second (fps) to evaluate the performance of the system. During the measurement, 40-MHz lithium niobate (LiNbO3) single-element lightweight (<;0.28 g) transducers were utilized. The wire target measure- ment showed that the -6-dB axial resolution of a chirp-coded excitation was 50 μm and lateral resolution was 120 μm. The echo signal-to-noise ratios were found to be 54 and 65 dB for the short burst and coded excitation, respectively. The contrast resolution in a sphere phantom study was estimated to be 24 dB for the chirp-coded excitation and 15 dB for the short burst modes. In an in vivo study, zebrafish and mouse hearts were imaged. Boundaries of the zebrafish heart in the image could be differentiated because of the low-noise operation of the implemented system. In mouse heart images, valves and chambers could be readily visualized with the coded excitation. |
| Title |
Standard methods for testing single-element pulse-echo ultrasonic transducers: Interim standard and appendixes I-VI. |
| Author |
Erikson K, Banjavic R, Bernardi R, Carson PL, Eggleton R, Flynn M, Fowler KA, Harris J, Meyer PA, Stewart H, Zagzebski J. |
| Journal |
J Ultrasound Med |
| Volume |
|
| Year |
1982 |
| Abstract |
No abstract available. |
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