University of Twente Student Theses
Dynamics of ultrasound-driven coated microbubbles confined in viscoelastic capillaries
Vialle, F. (2024) Dynamics of ultrasound-driven coated microbubbles confined in viscoelastic capillaries.
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| Abstract: | Phospholipid coated microbubbles are widely used as ultrasound contrast agents for both diagnostic and therapeutic applications. The dynamics of ultrasound-driven coated microbubbles have been primarily investigated in unbounded fluids. However, when microbubbles are in the bloodstream, they are often confined in viscoelastic capillaries. Numerical and few experimental studies have shown that the viscoelastic confinement affects the resonance response of microbubbles. To increase the sensitivity of diagnostic and therapeutic ultrasound in small vessels, we need to model the relation between bubble response and vessel properties, such as stiffness and diameter. In this work, we have taken the initial steps towards this model by performing experimental research, studying methods for signal filtering and developing a 2D numerical simulation. We have built an experimental setup combining ultrasound imaging and optical high speed imaging. The acoustic response from nonlinear microbubbles and linear hollow glass beads inside a capillary phantom has been measured using chirp and narrowband pulses. Using Pulse Inversion (PI) the fundamental and harmonic responses have been successfully isolated. We have demonstrated that SVD filtering allows for a quantitative analysis of the frequency response. However, the relation between the obtained amplitudes after SVD filtering and the acoustic response from microbubbles and beads is yet to be investigated. Both the beads and bubbles showed higher harmonics implying that the measurements currently lack the sensitivity to distinguish the nonlinear microbubble response from nonlinear propagation effects. The numerical simulation of a microbubble between elastic walls showed microbubble oscillations and wall displacement driven by the ultrasound. The oscillation amplitude of the microbubble showed a resonance behaviour, where a decrease in resonance frequency was observed with increasing ultrasound pressure consistent with literature. No dependence of resonance frequency on wall stiffness was observed because the microbubble was not sufficiently confined by the walls. In future research, the effects of nonlinear propagation should be quantified and reduced, the use of SVD filtering and other filtering methods needs to be further studied and the numerical simulation should be transitioned to 3D. |
| Item Type: | Essay (Master) |
| Faculty: | TNW: Science and Technology |
| Subject: | 33 physics |
| Programme: | Biomedical Engineering MSc (66226) |
| Link to this item: | https://purl.utwente.nl/essays/98376 |
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