| This thesis is motivated by movement towards minimally invasive and noninvasive procedures, which reduce patient morbidity and mortality, reduce costs, and increase accessibility of procedures for many patients. Minimally invasive and noninvasive surgeries benefit a variety of applications from treatment of heart arrhythmias, blood coagulation, and cancers of the prostate, liver, kidney, brain, and uterine fibroids, to name a few.;Current therapeutic technologies like radiofrequency (RF), microwave, and laser ablation are too invasive for these procedures. Ultrasound is advantageous because pressure waves can be focused to a point of interest without harming intervening tissues.;Traditionally piezoelectric transducers have been used for ultrasound, but recent developments have made capacitive micromachined ultrasonic transducers (CMUTs) highly competitive. CMUTs are advantageous because of their ease of fabrication and improved performance, including wide bandwidth, minimal self-heating, and MR compatibility.;This thesis shows the first results of CMUTs simulated, designed, and fabricated for therapeutic ultrasound. Finite element models used to design CMUT devices are presented. One of these models accounts for the fabrication-related temperature effects during processing. These models are used to design CMUTs with different topography, cell shape, and cavity types. These cells were fabricated and characterized for their output pressure and reliability.;After successful development of a conventional CMUT design for therapeutic ultrasound, system levels testing and principles are demonstrated. Noninvasive and minimally invasive procedures rely on imaging technology to guide and provide real-time feedback on the status of the treatment. This is especially important in thermal therapy procedures because the site of interest cannot be seen optically and the blood flow to the region of the body is often unpredictable. An unfocused CMUT was demonstrated to successfully heated a HIFU phantom while monitored using MR-temperature maps.;After demonstrating unfocused heating, continuous wave (CW) focusing of a transducer designed for ablation of upper abdominal cancers was also shown. The measured and simulated beam profiles matched well, though there were difficulties with the yield of the device. CMUTs are shown to be competitive to conventional piezoelectric transducers and advantageous for therapeutic ultrasound. |
