Spatial control of cavitation in therapeutic ultrasound

Inertial cavitation has been implicated as the primary mechanism for a host of emerging applications. In all these applications, the main concern is to induce cavitation in perfectly controlled locations in the field; this means specifically to be able to achieve cavitation threshold at the geometrical focus of the transducer without stimulating its near field. In this study, we make use of dual-frequency methods to preferentially lower the cavitation threshold at the focus relative to the rest of the field. One family of dual-frequency driving waveforms is evaluated in a bubble model incorporating rectified diffusion. Theoretical predictions based on Sokka's work (Sokka 2003a) are confirmed in vitro using Optison[TM], a commercially available contrast agent. The performance of the rest of acoustic field in suppressing cavitation when cavitation is induced at the focus is investigated theoretically and checked experimentally. This first part shows that dual-frequency phased arrays could be used to precisely control cavitation. Cavitation threshold is proved to be 1.2 times higher in the near field than at the focus. One of the main limitations of the aforementioned protocol is that it is tightly controlled. As an example, Optison[TM] has a mean bubble size of 2 - 4.5 [micro]m, which means that the initial bubble radii will fall in this range. Since cavitation threshold has been proved to depend on this parameter, using ultrasound contrast agents allows for more predictable results. Therefore, in the second half of this study, we propose a focused ultrasound protocol that induces and monitors gas bubbles at the focus and allows for ex vivo validation of the aforementioned theoretical results. The experiments involve fresh rabbit tissue and a statistical analysis is performed over data collected from back muscle.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Electrical Engineering and Computer Science.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2005

Author dc:creator

• Gauthier, Thomas P., 1980-

Advisor dc:contributor.advisor

• Kullervo Hynynen.

• Electrical Engineering and Computer Science.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/30171

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/30171