Scattering of High-frequency Ultrasound by Individual Bound Microbubbles

Targeted imaging with microbubbles may resolve the molecular expression within the abnormal blood vessels of tumours. Optimal imaging requires understanding the interaction between targeted microbubbles and high-frequency ultrasound. Therefore, the subharmonic signal, and backscattering cross-section of individual bound microbubbles were examined with coaligned 30 MHz pulses and optical images. The peak subharmonic signal was generated for 1.6 µm diameter microbubbles for 20% and 11% bandwidth pulses and 1.8 µm for 45% bandwidth pulses at 200 kPa, consistent with estimations of the resonant size of microbubble's at 15 MHz. In order to measure the scattering cross-section, a new method was proposed to measure the receive transfer function of a transducer. Measurements of the backscattering cross-section scaled with the square of the radius, with signi cant size-independent variability. The results of this thesis will help optimise the parameters for targeted imaging, as well as further our understanding of the behaviour of microbubbles.MAS