The “quasi-stable” lipid shelled microbubble in response to consecutive ultrasound pulses
Click to view
(a) Sequence of 8 frames with inter-frame time of 152 ns taken from the Brandaris camera, showing the compression phase of oscillation, in response to an incident pulse of 300 kPa. The bubble can be seen to fragment in frame 4, and shedding of a small lipid bubble is observed. Initial resting radius was R0 = 4.8 μm, and the final resting radius R0 = 3.5 μm. The R0 = 3.5 μm microbubble was observed to remain spherical and stable after the insonation. At lower pressures, this loss of shell material is not visible. (b)–(d) Radial oscillations of three microbubbles in response to non-consecutive 1.7 MHz 100 kPa pulses (1st, 5th, and 20th pulse are shown, with 80 ms between pulses). Initial radii are (b) above resonance R0 = 3.0 μm, (c) approximately at resonance R0 = 2.7 μm, and (d) above resonance R0 = 2.2 μm. At the end of each of these three oscillations, a reduction in radii of (a) 0.1 μm, (b) 0.3 μm and (c) 0.8 μm had occurred. No reduction in radius was observed between oscillations. (e) The respective change in microbubble radius of six microbubbles (R0), and how the fundamental amplitude of oscillation is affected in each case. Also plotted is the fitted resonance curved from 43 microbubble’s 1st pulse responses (dashed line), with 95% confidence interval shown (faded dashed line). Microbubble decay follows a “controlled path” on the resonance curve, suggesting microbubbles which have reduced in radius behave as if insonated for the first time.
Click to view
Calculated loss of area from 32 microbubble radial oscillations, which show radius reductions from 1% to 15%. Change in area ΔA has been plotted against relative compression ratio (C = D0 − Dmin)/D0, with signals classified by their expansion to compression ratio (E/C), where E = (Dmax − D0)/D0.
Article metrics loading...
Full text loading...