| The goal of this research is to improve the understanding of individual contrast agent oscillations and the resulting received echoes. This in turn, can lead to more sophisticated microbubble detection techniques by designing pulsing schemes to elicit a specific microbubble response.; In this study, experimental and theoretical tools are uniquely combined to aid in the understanding of a microbubble's response during insonation. A theoretical model has been developed to predict a single microbubble's radial oscillations and the resulting received echoes.; This dissertation investigates two physical mechanisms for differentiating the echoes from microbubbles and tissue and the resulting signal processing schemes. In the first case, the microbubble and shell are intact and consistent echoes are received. In the second case, repeated pulsing results in changes in the microbubble composition or causes microbubble destruction. Based on these studies, two specific detection strategies are suggested. The non-destructive strategy takes advantage of differences in the frequency content of the echoes received following the transmission of wideband pulses with opposite phases. The second technique utilizes repeated pulsing to elicit changes in the echoes from a thin-shelled microbubble.; In the non-destructive imaging case, the effects of imaging parameters are evaluated using the experimental and theoretical tools and it is shown that a significant opportunity to detect microbubbles occurs with changes in the phase of transmission. A preliminary evaluation of a new phase inversion microbubble detection technique based on these differences in mean frequency is presented.; For the transmission of a train of pulses, a polymer-shelled agent is shown to exhibit an increase in echo amplitude with each successive pulse. This change in amplitude is due to changes in the shell that occur as the microbubble oscillates; therefore the increase in amplitude is dependent on both the transmitted pressure and pulse length, as well as the number of pulses. An imaging scheme is proposed that detects this increase in echo amplitude in order to better differentiate the bubble echoes from tissue echoes. (Abstract shortened by UMI.)... |
