Microbubble Oscillation due to Harmonic, Pulsed and Frequency Modulated Excitation with Ultrasound

Improved visualization of blood vessels by ultrasound contrast agents requires insonation that is adapted to the dynamics of the contrast agent bubbles. To evaluate the interrelation between parameters of the exciting pressure field and the contrast agent, the dynamics of air filled microbubbles immersed in water are examined by numerical evaluation of the Rayleigh-Plesset equation. Unsymmetrical oscillation is obtained for resonant harmonic excitation, frequency doubling occurs for subresonant excitation and nearly sinusoidal oscillation is exhibited for superresonant excitation. Continuous harmonic and pulsed pressure waves are shown to be unsuitable to excite a mixture of differently sized bubbles due to their non-uniform resonance behaviour. As an alternative, excitation with a linear frequency modulated wave is examined and shown to be a feasible option for adapted contrast agent insonation.