Determination of postexcitation thresholds for single ultrasound contrast agent microbubbles using double passive cavitation detection (original) (raw)
Related papers
Using passive cavitation detection to observe postexcitation response of ultrasound contrast agents
2009 IEEE International Ultrasonics Symposium, 2009
Passive cavitation detection was used to improve the experimental characterization of single ultrasound contrast agent microbubble responses to short, large amplitude pulses. Two situations were examined: isolated microbubbles in an unconstrained environment, and isolated microbubbles flowing through a tube. The microbubbles were categorized according to a classification scheme based on the presence or absence of postexcitation signals, which are secondary broadband spikes that may follow the principle oscillation of the ultrasound contrast agent in response to an insonifying pulse. Experiments were conducted for different frequencies, peak rarefactional pressures, flow rates, and types of microbubble. Postexcitation activity was found to increase as frequency decreased, acoustic pressure increased, and flow rate increased. Additionally, lipidshelled microbubbles were found to exhibit greater postexcitation at lower acoustic pressure thresholds than albumin-shelled microbubbles.
Gauging the likelihood of stable cavitation from ultrasound contrast agents
The Journal of the Acoustical Society of America, 2012
The mechanical index (MI) was formulated to gauge the likelihood of adverse bioeffects from inertial cavitation. However, the MI formulation did not consider bubble activity from stable cavitation. This type of bubble activity can be readily nucleated from ultrasound contrast agents (UCAs) and has the potential to promote beneficial bioeffects. Here, the presence of stable cavitation is determined numerically by tracking the onset of subharmonic oscillations within a population of bubbles for frequencies up to 7 MHz and peak rarefactional pressures up to 3 MPa. In addition, the acoustic pressure rupture threshold of an UCA population was determined using the Marmottant model. The threshold for subharmonic emissions of optimally sized bubbles was found to be lower than the inertial cavitation threshold for all frequencies studied. The rupture thresholds of optimally sized UCAs were found to be lower than the threshold for subharmonic emissions for either single cycle or steady state acoustic excitations. Because the thresholds of both subharmonic emissions and UCA rupture are linearly dependent on frequency, an index of the form I CAV = P r /f (where P r is the peak rarefactional pressure in MPa and f is the frequency in MHz) was derived to gauge the likelihood of subharmonic emissions due to stable cavitation activity nucleated from UCAs.
Ultrasound contrast agent behavior near the fragmentation threshold
2000 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.00CH37121), 2000
Abstrucf -Understanding the fragmentation process of ultrasound contrast agents is important in therapeutic ultrasound applications (such as ultrasound-enhanced drug delivery), as well as in certain imaging applications (such as "flash echo" imaging[ I]). In the fragmentation of Optisonm microbubbles, our observations suggest that there are two pressure thresholds, a threshold which leads to shell rupture and the production of smaller daughter bubbles, and another one leading to the onset of sustained inertial cavitation (IC) activity. Between the shell-disruption threshold and sustained IC threshold is a region where intermittent inertial cavitation activity was detected. The acoustic signature of the intermittent region, the pressure level for the various thresholds, and the strength of the subsequent cavitation activity are all highly dependent on the acoustic pulse parameters.
Microbubble contrast agent destruction using 20-25 MHz ultrasound
IEEE Ultrasonics Symposium, 2005., 2005
The purpose of this preliminary study was to quantify the destruction of a microbubble contrast agent (Definity TM , 0.01 % volume fraction) by 20 or 25 MHz ultrasound under varying conditions of exposure, including peak negative pressure (0.3 to 2.1 MPa), frequency (20 or 25 MHz), number of cycles (NC= 1, 5, 10, 15 or 20 cycles), flow rate (6 or 12 mm/s) and frame rate (FR= 31, 47, 79 or 110 Hz). Experiments were performed in a 800 µm diameter flow phantom, using two Vevo770 scanners (VisualSonics Inc.) equipped with an RMV710 probe (20-25 MHz, diam.= 7.1 mm, F#2.1) for the upstream microbubble destruction and an RMV704 probe (40 MHz, diam.=3 mm, F#2) for downstream linear imaging of the microbubbles at 40 MHz. RF data were acquired downstream before and during exposure to the destruction beam. To estimate the extent of destruction, the integrated backscattered power (IP) was calculated in a 600 µm diameter region of interest (ROI) in the center of the vessel. The difference in IP between pre exposure and exposure to the destruction beam was normalized to the pre exposure IP and expressed as ∆IP in percentage. A decrease in IP was detected during exposure to the 20 and 25 MHz beams. ∆IP ranged from 0% (peak negative pressure=0.3 MPa at 20 MHz, NC=1, FR=31 fps) to close to 100% (peak negative pressure= 2.1 MPa at 20 MHz, NC=20, FR=110 Hz). ∆IP became more important as the pressure, the number of cycles, or the frame rate increased. At similar pressure level, ∆IP was higher at 20 MHz than at 25 MHz. At a given frequency and given pressure level, ∆IP was found to be higher for a flow rate of 6 mm/s than for a flow rate of 12 mm/s. This study shows that 20-25 MHz ultrasound at pressures in a range of pressure relevant to ultrasound biomicroscopy is effective in destroying Definity TM microbubbles. In addition expected increases of destruction were observed as the number of cycles in the transmit pulse and the frame rate were increased, and as the flow rate decreased. This information could be useful for the measurement of flow at high frequency in the microvasculature in mouse cancer model, and for destruction/reperfusion measurements using microbubble contrast agents
The Journal of the Acoustical Society of America, 2003
Contrast bubble destruction is important in several new diagnostic and therapeutic applications. The pressure threshold of destruction is determined by the shell material, while the propensity for of the bubbles to undergo inertial cavitation ͑IC͒ depends both on the gas and shell properties of the ultrasound contrast agent ͑UCA͒. The ultrasonic fragmentation thresholds of three specific UCAs ͑Optison, Sonazoid, and biSpheres͒, each with different shell and gas properties, were determined under various acoustic conditions. The acoustic emissions generated by the agents, or their derivatives, characteristic of IC after fragmentation, was also compared, using cumulated broadband-noise emissions ͑IC ''dose''͒. Albumin-shelled Optison and surfactant-shelled Sonazoid had low fragmentation thresholds (meanϭ0.13 and 0.15 MPa at 1.1 MHz, 0.48 and 0.58 MPa at 3.5 MHz, respectively͒, while polymer-shelled biSpheres had a significant higher threshold (mean ϭ0.19 and 0.23 MPa at 1.1 MHz, 0.73 and 0.96 MPa for thin-and thick-shell biSpheres at 3.5 MHz, respectively, pϽ0.01). At comparable initial concentrations, surfactant-shelled Sonazoid produced a much larger IC dose after shell destruction than did either biSpheres or Optison (pϽ0.01). Thick-shelled biSpheres had the highest fragmentation threshold and produced the lowest IC dose. More than two and five acoustic cycles, respectively, were necessary for the thin-and thick-shell biSpheres to reach a steady-state fragmentation threshold.
The disappearance of ultrasound contrast bubbles
Ultrasound in Medicine & Biology, 2002
The destruction process of biSphere™ and Optison™ ultrasound (US) contrast microbubbles were studied at 1.1 MHz. High-amplitude tone bursts caused shell disruption and/or fragmentation of the microbubbles, leading to dissolution of the freed gas. The bubble destruction and subsequent dissolution process was imaged with a high pulse-repetition frequency (PRF) 10-cycle, 5-MHz bistatic transducer configuration. Three types of dissolution profiles were measured: In one case, biSphere™ microbubbles showed evidence of dissolution through resonance, during which a temporary increase in the scattering amplitude was observed. In another case, both biSphere™ and Optison™ microbubbles showed evidence of fragmentation, during which the scattering amplitude decreased rapidly. Finally, in some cases, we observed the impulsive growth and subsequent rapid decay of signals that appear to be due to cavitation nucleation. Simulations of bubble dissolution curves show good agreement with experiments. (E-mail: matula@apl.washington.edu) © 2002 World Federation for Ultrasound in Medicine & Biology.
Nonspherical Oscillations of Ultrasound Contrast Agent Microbubbles
Ultrasound in Medicine & Biology, 2008
The occurrence of nonspherical oscillations (or surface modes) of coated microbubbles, used as ultrasound contrast agents in medical imaging, is investigated using ultra-high-speed optical imaging. Optical tweezers designed to micromanipulate single bubbles in 3-D are used to trap the bubbles far from any boundary, enabling a controlled study of the nonspherical oscillations of free-floating bubbles. Nonspherical oscillations appear as a parametric instability and display subharmonic behavior: they oscillate at half the forcing frequency, which was fixed at 1.7 MHz in this study. Surface modes are shown to preferentially develop for a bubble radius near the resonance of radial oscillations. In the studied range of acoustic pressures, the growth of surface modes saturates at a level far below bubble breakage. With the definition of a single, dimensionless deformation parameter, the amplitude of nonspherical deformation is quantified as a function of the bubble radius (between 1.5 and 5 m) and of the acoustic pressure (up to 200 kPa). (
Ultrasound in Medicine & Biology
The destruction process of biSphere and Optison ultrasound (US) contrast microbubbles were studied at 1.1 MHz. High-amplitude tone bursts caused shell disruption and/or fragmentation of the microbubbles, leading to dissolution of the freed gas. The bubble destruction and subsequent dissolution process was imaged with a high pulse-repetition frequency (PRF) 10-cycle, 5-MHz bistatic transducer configuration. Three types of dissolution profiles were measured: In one case, biSphere microbubbles showed evidence of dissolution through resonance, during which a temporary increase in the scattering amplitude was observed. In another case, both biSphere and Optison microbubbles showed evidence of fragmentation, during which the scattering amplitude decreased rapidly. Finally, in some cases, we observed the impulsive growth and subsequent rapid decay of signals that appear to be due to cavitation nucleation. Simulations of bubble dissolution curves show good agreement with experiments.
Destruction of Contrast Microbubbles by Ultrasound
Circulation, 2001
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 basel...