Ambient pressure sensitivity of microbubbles investigated through a parameter study

Abstract

Measurements on microbubbles clearly indicate a relation between the ambient pressure and the acoustic behavior of the bubble. The purpose of this study was to optimize the sensitivity of ambient pressure measurements, using the subharmonic component, through microbubble response simulations. The behavior of two microbubbles corresponding to two different contrast agents was investigated as a function of driving pulse and ambient overpressure pov. Simulations of Levovist using a rectangular driving pulse show an almost linear reduction in the subharmonic component as pov is increased. For a 20 cycle driving pulse, a reduction of 4.6 dB is observed when changing pov from 0 to 25 kPa. Increasing the pulse duration makes the reduction even clearer. For a pulse with 64 cycles, the reduction is 9.9 dB. This simulation is in good correspondence with measurement results presented in the literature. Further simulations of Levovist show that also the shape and the acoustic pressure of the driving pulse are very important factors. The best pressure sensitivity of Levovist was found to be 0.88 dB/kPa. For Sonazoid, a sensitivity of 1.14 dB/kPa has been found, although the reduction is not completely linear as a function of the ambient pressure.

Quantitative contrast-enhanced ultrasound imaging: a review of sources of variability

“…The effect can be exacerbated if the bubbles are kept in a heated environment, since raising the temperature above room temperature is known to influence the bubble stability and size distribution [117] as above. Bubble buoyancy means that suspensions must be re-suspended to ensure homogeneity immediately prior to use, and their susceptibility to local changes in pressure [119] means that vials should be vented using a sterile open needle or a pressure-controlling device (e.g. a MiniSpike in the case of Sonovue) during withdrawal to prevent destruction.…”

Excitation threshold for subharmonic generation from contrast microbubbles

“…In comparison with the model by de Jong, this model limits the increase in the effective surface tension during bubble expansion. For the given model-specific properties of Sonazoid microbubbles (Andersen and Jensen, 2009), the effective surface tension increases to a maximum of 2.57 times the air-water surface tension value. On the other hand, during compression, this model predicts a steep increase in compressive interfacial stress (c=c w ¼ À70 at R=R 0 ¼ 0:5).…”

“…For the FFT, we only use the part of the simulation where transients have subsided. We use the peak values corresponding to the different frequencies (i.e., fundamental or different harmonic) in contrast to an integrated value around the peak used in other references (Andersen and Jensen, 2009;Frinking et al, 2010). The resonance frequency used to normalize excitation frequency for a particular model is model specific and has been determined by appropriate formula.…”

Modeling subharmonic response from contrast microbubbles as a function of ambient static pressure

“…To simulate the dynamics of an encapsulated microbubble and compare with the numerical investigations of Andersen and Jensen, 18 we use the BUBBLESIM code. It is a variation of the Rayleigh-Plesset equation.…”

“…14-17 Andersen and Jensen 18 recently simulated subharmonic response decrease with ambient pressure from the contrast agents Levovist (Schering AG, Berlin, Germany) and Sonazoid (GE Healthcare, Oslo, Norway) using the bubble dynamics code BUBBLESIM. 19 Here, we report a detailed numerical investigation of the subharmonic response of microbubbles to show that as per single bubble dynamics, subharmonic response may either decrease or increase with ambient pressure depending on other parameters, and explain the underlying physics.…”