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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 82 out of 330
| Title |
Design of ultrasound transducers using new piezoelectric ceramic materials. |
| Author |
Fukumoto A, Kawabuchi M, Sato J. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1981 |
| Abstract |
Three parameters α, DR and Dn(A), i.e. the efficiency, the dynamic range and the normalized axial resolution are used to evaluate the performance of ultrasound transducers for diagnostic imaging equipment. These parameters determine optimum conditions for use in the design of high frequency array transducers. A newly-developed piezoelectric ceramic material composed of (Pb,Sr)(Ti,Zr)O3 or Pb[(Mg 1/3,Nb 2/3)Ti,Zr]O3 which satisfies the above-mentioned conditions was used to fabricate a co-phase array ultrasound transducer. The transducer showed good electrical and acoustic performance in accordance with theoretical considerations.
Keywords: Ultrasound; Acoustic; Transducers; Piezoelectric materials; Piezoelectric ceramics; Transducer characteristics; Transducer efficiency; Transducer dynamic range; Transducer axial resolution. |
| Title |
Destruction of contrast microbubbles and the association with inertial cavitation. |
| Author |
Shi WT, Forsberg F, Tornes A, Ostensen J, Goldberg BB. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2000 |
| Abstract |
The destruction of insonified Sonazoid microbubbles and its association with inertial cavitation in vitro utilizing an active acoustic detector was investigated. The experimental observation indicated that contrast microbubbles could be damaged at moderate acoustic pressures of 0.6-1.6 MPa (0.4-1.0 in mechanical index, MI). A damaged bubble could be dissolved into the medium on the order of 1 ms, implying that the destruction at moderate pressures is a relatively slow (relative to inertial bubble collapse), nonviolent dissolution process following the disruption of encapsulating surface materials. Inertial cavitation events in the presence of contrast microbubbles were observed using multiple highly intense ultrasound (US) pulses (>1.6 MPa). This observation suggested that intense US might disintegrate contrast microbubbles, and fragments of disintegrated microbubbles could be activated by an upcoming highly intense imaging pulse. The above results imply that inertial cavitation is unlikely to take place in the presence of Sonazoid contrast microbubbles when exposed to diagnostic US with an MI <1. |
| Title |
Destruction of contrast microbubbles by ultrasound efects on myocardial function,coronary perfusion pressure, and microvascular integrity. |
| Author |
Ay T,Havaux X,Camp GV, Campanelli B,Gisellu G,Pasquet A,Denef J,Melin JA,Vanoverschelde JJ. |
| Journal |
Circulation |
| Volume |
|
| Year |
2001 |
| Abstract |
Background— Recent experimental data indicate that ultrasound-induced destruction of ultrasound contrast microbubbles can cause immediate rupture of the microvessels in which these microbubbles are located.
Methods and Results— To examine the functional and morphological significance of these findings in the heart, isolated rabbit hearts were perfused retrogradely with buffer containing ultrasound contrast agents and were insonated at increasing levels of acoustic energy with a broadband transducer emitting at 1.8 MHz and receiving at 3.6 MHz and operated in the triggered mode (1 Hz). At the end of each experiment, the hearts were fixed in glutaraldehyde and examined with light microscopy. Neither exposure to ultrasound alone or to contrast alone affected left ventricular developed pressure. By contrast, simultaneous exposure to contrast and ultrasound resulted in a reversible, transient mechanical index (MI)-dependent decrease in left ventricular developed pressure (to 83±5% of baseline at an MI of 1.6) and a transient MI-dependent increase in coronary perfusion pressure (to 120±6% of baseline at an MI of 1.6). Myocardial lactate release also showed significant increases with increasing MIs. Macroscopically, areas of intramural hemorrhage were identified over the beam elevation in hearts exposed to both contrast and high-MI ultrasound. Light microscopy revealed the presence of capillary ruptures, erythrocyte extravasation, and endothelial cell damage. The mean percentage of capillaries ruptured at an MI of 1.6 was 3.6±1.4%.
Conclusions— Simultaneous exposure of isolated rabbit hearts to ultrasound and contrast agents results in an MI-dependent, transient depression of left ventricular contractile function, a rise in coronary perfusion pressure, an increase in lactate production, and limited capillary ruptures.
Key Words: contrast media • echocardiography.
|
| Title |
Detectability of small blood vessels with high-frequency power doppler and selection of wall filter cut-off velocity for microvascular imaging. |
| Author |
Pinter SZ, Lacefield JC. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2009 |
| Abstract |
Power Doppler imaging of physiologic and pathologic angiogenesis is widely used in preclinical studies to track normal development, disease progression and treatment efficacy but can be challenging given the presence of small blood vessels and slow flow velocities. Power Doppler images can be plagued with false-positive color pixels or undetected vessels, thereby complicating the interpretation of vascularity metrics such as color pixel density (CPD). As an initial step toward improved microvascular quantification, flow-phantom experiments were performed to establish relationships between vessel detection and various combinations of vessel size (160, 200, 250, 300 and 360 μm), flow velocity (4, 3, 2, 1 and 0.5 mm/s) and transducer frequency (30 and 40 MHz) while varying the wall filter cut-off velocity. Receiver operating characteristic (ROC) curves and areas under ROC curves indicate that good vessel detection performance can be achieved with a 40-MHz transducer for flow velocities ≥2 mm/s and with a 30-MHz transducer for flow velocities ≥1 mm/s. In the second part of the analysis, CPD was plotted as a function of wall filter cut-off velocity for each flow-phantom data set. Three distinct regions were observed: overestimation of CPD at low cut-offs, underestimation of CPD at high cut-offs and a plateau at intermediate cut-offs. The CPD at the plateau closely matched the phantom's vascular volume fraction and the length of the plateau corresponded with the flow-detection performance of the Doppler system assessed using ROC analysis. Color pixel density vs. wall filter cut-off curves from analogous in vivo experiments exhibited the same shape, including a distinct CPD plateau. The similar shape of the flow-phantom and in vivo curves suggests that the presence of a plateau in vivo can be used to identify the best-estimate CPD value that can be treated as a quantitative vascularity metric. The ability to identify the best CPD estimate is expected to improve quantification of angiogenesis and anti-vascular treatment responses with power Doppler. |
| Title |
Detection of acoustic cavitation in the heart with microbubble contrast agents in vivo: A mechanism for ultrasound-induced arrhythmias. |
| Author |
Rota C, Raeman CH, Child SZ, Dalecki D. |
| Journal |
J Acoust Soc Am |
| Volume |
|
| Year |
2006 |
| Abstract |
Ultrasound fields can produce premature cardiac contractions under appropriate exposure conditions. The pressure threshold for ultrasound-induced premature contractions is significantly lowered when microbubble contrast agents are present in the vasculature. The objective of this study was to measure directly ultrasound-induced cavitation in the murine heart in vivo and correlate the occurrence of cavitation with the production of premature cardiac contractions. A passive cavitation detection technique was used to quantify cavitation activity in the heart. Experiments were performed with anesthetized, adult mice given intravenous injections of either a contrast agent (Optison) or saline. Murine hearts were exposed to ultrasound pulses (200 kHz, 1 ms, 0.1-0.25 MPa). Premature beats were produced in mice injected with Optison and the likelihood of producing a premature beat increased with increasing pressure amplitude. Similarly, cavitation was detected in mice injected with Optison and the amplitude of the passive cavitation detector signal increased with increasing exposure amplitude. Furthermore, there was a direct correlation between the extent of cavitation and the likelihood of ultrasound producing a premature beat. Neither premature beats nor cavitation activity were observed in animals injected with saline and exposed to ultrasound. These results are consistent with acoustic cavitation as a mechanism for this bioeffect. |
| Title |
Detection of cardiomyopathic changes induced by doxorubicin based on quantitative analysis of ultrasonic backscatter. |
| Author |
Mimbs JW, O'Donnell M, Miller JG, Sobel BE. |
| Journal |
Am J Cardiol |
| Volume |
|
| Year |
1981 |
| Abstract |
Ultrasonic measurements are valuable in characterizing cardiac dimensions and structure. Recently, analysis of ultrasonic properties of tissue has proved useful in detecting morphologic changes such as those accompanying myocardial infarction. This study was undertaken to determine whether acoustic properties of tissue can be utilized to detect cardiomyopathic changes as well. Cardiomyopathy was induced by prolonged administration of doxorubicin (Adriamycin) (1.2 mg/kg twice.weekly) in 25 rabbits and results were compared with those in normal control rabbits, housed identically. The 15 surviving treated animals were killed at selected intervals to 10 to 18 weeks after initiation of drug administration and the hearts were.analyzed for collagen content based on hydroxyproline. Regional ultrasonic backscatter was assessed with a frequency-averaging procedure to minimize effects of phase cancellation and with an independent method employing spectral display over the frequency range of 1 to 11 megahertz from which an index of backscatter at a single frequency (2.25 megahertz) could be calculated. In hearts from treated animals, collagen content was significantly increased (p less than.0.05). Integrated ultrasonic backscatter was markedly increased (by more than 500 percent, that is, equivalent to 7 decibels) in fibrotic regions and significantly, although less markedly, in myopathic regions without marked collagen deposition. Thus, increased backscatter correlated with collagen deposition. Backscatter at 2.25 megahertz was significantly increased (by more than 500 percent, that is, equivalent to 7 decibels) in fibrotic regions. These results indicate that alterations in.acoustic properties occur in cardiomyopathic tissue and that such alterations can be detected with the use of reflected ultrasound. Accordingly, assessment of integrated backscatter offers a promising approach for early clinical detection and characterization of evolution of cardiomyopathy induced by doxorubicin or of other causes. |
| Title |
Detection of carotid artery bifurcation stenosis by Doppler ultrasound. Preliminary report. |
| Author |
Brinker RA, Landiss DJ, Croley TF. |
| Journal |
J Neurosurg |
| Volume |
|
| Year |
1968 |
| Abstract |
No abstract available |
| Title |
Detection of contrast microbubble shell rupture. |
| Author |
Ammi A, Cleveland R, Mamou J, Wang G, Bridal L, O'Brien WD Jr. |
| Journal |
Book Chapter |
| Volume |
|
| Year |
2006 |
| Abstract |
The goal of this work is to detect experimentally and quantitatively the destruction of Optison™ ultrasound contrast agent (UCA) microbubbles. Two experimental systems were used. The first system consisted of a passive cavitation detector (PCD) with transmitted pulses at one of three frequencies (0.9, 2.8 and 4.6 MHz), one of three pulse durations (3, 5 or 7 cycles) and peak rarefactional pressures from 0.07 to 5.4 MPa. UCAs in solution were diluted so that the transmitted pulse interacted, on average, with a single UCA. The UCA response and acoustic emissions were detected with a 13-MHz center-frequency receiver. The second system consisted of a PCD setup (transmit 7 cycles at .99 MHz at peak rarefactional pressures of 0.3 or 0.8 MPa, receive at a center frequency of 9.8 MHz) coupled to an optical microscope. UCAs were isolated in a 200-μm-diameter cellulose fiber aligned at the focal positions of the transducers and the microscope. Optical data were acquired with a digital camera synchronized to the transmit acoustic pulse. Post-excitation acoustic emissions with broadband spectral content from the PCD time traces were used to characterize UCA destruction thresholds. Microscopic data provided independent confirmation that only a single microbubble was interrogated and whether that was destroyed by the incident acoustic pulse. Results characterize Optison™ destruction thresholds. The PCD technique presented in this work provides a straight-forward evaluation of UCA destruction. |
| Title |
Detection of intracardiac blood flow by pulsed echo-ranging ultrasound. |
| Author |
Gramiak R, Shah PM. |
| Journal |
Radiology |
| Volume |
|
| Year |
1971 |
| Abstract |
Intracardiac echoes can be derived from the blood in the cardiac chambers, using pulsed echoranging techniques. The physiological origin of these echoes has been established by showing patterns of changing echo intensity that are related to the cardiac cycle. It appears that circulating microbubbles are the most likely source and that they are produced by stable cavitation. |
| Title |
Detection of ischemic myocardium in vivo through the chest wall by quantitative ultrasonic tissue characterization. |
| Author |
Cohen RD, Mottley JG, Miller JG, Kurnik PB, Sobel BE. |
| Journal |
Am J Cardiol |
| Volume |
|
| Year |
1982 |
| Abstract |
Quantitative analysis of ultrasound offers a potentially valuable method for noninvasive differentiation of specific types of cardiac disease and for assessment of their severity. Clinical application necessitates quantitative measurement through the chest wall. This study was designed to determine whether such measurements could be made noninvasively with the aid of conventional M mode echocardiographic guidance and to characterize the quantitative effects of intervening tissue (chest wall) on the ultrasonic signals backscattered by ischemic and normal myocardium. Frequency-dependent ultrasonic backscatter (2 to 7 MHz) from normal myocardium was measured in dogs in vivo through the closed chest with the use of M mode guidance and with the chest open, directly from the myocardium. Closed-chest and open-chest measurements were repeated after ligation of the left anterior descending coronary artery in the same animals. Closed-chest data were compensated by correcting for the average value for the slope of the attenuation-frequency function of chest wall, which was determined from measurements obtained by analysis on excised tissue. Compensated closed-chest measurements correlated with measurements obtained from the epicardial surface of the heart. The differentiation of normal from ischemic myocardium with both the closed- and open-chest measurements was consistent (p<0.005). The successful differentiation of normal from ischemic myocardium by determination of quantitative backscatter through the intervening chest wall supports the concept that tissue characterization by quantitative analysis of backscattered ultrasound is a potentially useful, clinically applicable approach to noninvasive detection and differentiation of intrinsic properties of normal and diseased myocardium. |
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