Author(s)

A. A. Doinikov & P. A. Dayton

Abstract

Encapsulated gas microbubbles, known as contrast agents, are widely used in ultrasound medical applications. The present study is devoted to modelling of the spatio-temporal dynamics of lipid-shelled contrast agents. A theoretical model is proposed that describes the radial and translational motion of a lipid-shelled microbubble in an ultrasound field. The model approximates the behaviour of the lipid shell by the linear 3-constant Oldroyd constitutive equation, incorporates the translational motion of the bubble, and accounts for acoustic radiation losses due to the compressibility of the surrounding liquid. The values of the shell parameters appearing in the model are evaluated by fitting simulated radius-time curves to experimental ones. The results are then used for the simulation of the translational motion of contrast agent bubbles of various radii and the evaluation of the relationship between equilibrium radii of lipid-shelled agents and their resonance frequencies in the regime of nonlinear oscillation. Keywords: contrast agents, encapsulated bubbles, lipid shell, ultrasound, radial oscillation, translational motion, resonance frequencies. 1 Introduction Ultrasound contrast agents are micron-sized encapsulated gas bubbles which are produced by pharmaceutical companies for medical ultrasound applications [1]. They are normally injected into the bloodstream of the patient in order to increase blood-tissue contrast during an ultrasonic examination and thereby to improve the quality of ultrasonic images. Contrast agents are also used in targeted imaging and ultrasound-assisted localized drug delivery [2, 3]. Targeted agents are taken up by specific tissues or adhere to specific sites in the body.

Keywords

contrast agents, encapsulated bubbles, lipid shell, ultrasound, radial oscillation, translational motion, resonance frequencies.