Use this URL to cite or link to this record in EThOS:
Title: Microbubble interaction with ultrasound : stochastic and chaotic dynamics
Author: Retkute, Renata
ISNI:       0000 0001 3514 3149
Awarding Body: Glasgow Caledonian University
Current Institution: Glasgow Caledonian University
Date of Award: 2007
Availability of Full Text:
Access from EThOS:
In recent years interest in therapeutic ultrasound has grown rapidly with several emerging imaging techniques becoming very powerful diagnostic tools in medical applications. There is however, an ongoing need to improve the contrast and resolution of scanned images to enable medical practitioners to make reliable and timely diagnosis. This thesis focuses on modelling ultrasound contrast agent (DCA) microbubbles, specially coated gas bodies of controlled size that can pass through the vascular system after intravenous injection. These highly echogenic bubbles greatly enhance the backscattered signal and provide ncw opport.unit.kA<; for thc imaging of vascular volumc and flow rate directly and in real time. More recently a new area of research has proposed that the bubbles can be employed for localised drug and gene delivery. The full potential of contrast agent microbubbles in clinical applications will only be realised when we have a clear understanding of the interaction of ultrasound and bubbles. The aim of this thesis is to contribute to that understanding. The dynamics of cavities will be addressed by analysing these problems in terms of a hierarchy of mathematical models, from gas bubbles to contrast agents, from isolated cavities to a population thereof, from deterministic to stochastic interactions, with appropriate variations in the frequency, amplitude, phase and pulse of the insonating field. In this thesis two main areas of interest are identified: nonlinearity and randomness. Extensive simulations are used to gain an understanding of the expected nonlinear response which, in some cases, leads to chaotic behaviour. The bubbles are nonlinear resonators that, under certain conditions, can change size, cavitate, fragment, or be moved. A transition to chaos has been identified as one of the general characteristics of the motion of a sinusoidally driven single gas bubble or contrast agent microbubble. A new equation is derived to describe the radial oscillations of an encapsulated gas bubble. The model accounts for the finite speed of sound in both the liquid and shell media. In the multibubble case, an important issue is the effect of interaction between bubbles and the influence of the separation distance between them. Several factors including the amplitude and frequency of the driving acoustic field, the number of bubbles present and their initial radii determine whether the bubbles settle down to periodic oscillations or undergo a transition to chaos. To Illodel the Illotion of DCA bubbl~ Illoving through a fluid a uew equation is constructed that incorporates the dynamics of both radial and translational motion. The interplay between chaos and noise in the system is modelled using the stochastic approach whereby a Brownian motion term is incorporated in the bubble model to represent the iufluence of other bubbles or the environment. The principal effect of additive noise on a periodically driven acoustic bubble is to alter the structure of the deterministic attractor and to activate additional orbits and enlarge the attractor. It is anticipated that, when validated by experiment, the results obtained in this thesis have the potential to serve as a guide for the applications of microbubbles in medical ultrasound. The methodologies presented here also provide the basis for interesting challenges and for future research.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available