DESIGN AND EVALUATION OF A 2-D PLANAR THERAPEUTIC ULTRASOUND PHASED ARRAY by Danish

Focused ultrasound continues to be investigated as an exciting technique for several medical therapy applications including tissue ablation. Phased array transducers serve as important devices for delivering the high intensity focused ultrasound to the targeted tissue. These arrays often produce undesired secondary foci called grating lobes that can result in heating of non-targeted healthy tissue. Grating lobes can be eliminated by setting the element-spacing between adjacent elements to V/2 or less. The aim of this research is to construct and evaluate a 2-D planar phased array with close to X/2 element-spacing. A 7x7 element array with element-spacing of 0.762mm was constructed using 1,3-piezocomposite material. Acoustic field measurements of the array focused at three different locations were taken to demonstrate its ability to scan the focus in a volume. In addition, a maximum average intensity of 5.54W/cm 2 was measured for the unfocused array using radiation force measurements. Thesis Advisor: Kullervo Hynynen, PhD Title: Professor of Radiology, Harvard Medical School, Brigham and Women's Hospital ACKNOWLEDGEMENTS I would like to thank my advisor, Professor Kullervo Hynynen, for the opportunity to work in such an exciting research field and for his guidance, mentorship and availability throughout my time at the Focused Ultrasound Laboratory. His achievements and immense contributions to the therapeutic ultrasound field are inspiring and I am deeply honored to have been one of his students. In addition, I also thank Professor Roger Mark for his role as my on-campus advisor. I am grateful for the friendship, advice and mentorship of everyone at the FUL. I would like to thank Jose Juste for his advice, mentorship and lessons on the ins-and-outs of the VUDS system, Phillip Jason White and (Professor) Greg Clement for their advice in matters of ultrasound and experiment setups. It was a great joy discussing circuits with Sai-Chun Tang, a passionate and friendly circuits engineer and enthusiast. I thank XiangTao Yin for his comprehensive Matlab software to simulate the acoustic fields from phased arrays and Russell Erich Caulfield for his advice and motivating discussions. I am grateful to Susan (Sue) Agabian for teaching me to use the mill and sharing her tremendous knowledge in machining and adhesives. I thank Keiko Fujiwara for her help with all the formalities of being a graduate student. I also thank Thomas Gauthier, Sonali Palchaudri, Anne Yu, Lisa (LT) Treat, Manabu Kinoshita, Anthony (Mr. T) Ross, Janne Heikkila, Hao-Li Liu, Nickolai Sheikov, Vince Colucci, Nathan McDannold, Yong-Zhi Zhang, Karen Tam and Natalia Vykhodtseva for making the lab enjoyable to work in. They have all been as good friends as they have been research colleagues. Finally, I would like to thank my family: my sister Sameera, my brother Fayaz, Nizam, Lindsey and my adorable nephews Naheel, Saajid and niece Nailah. Most importantly, I am deeply grateful to my parents, Munira and Suleiman Khatri, for their tremendous support and guidance without which I would never have made it to M.I.T. This thesis is dedicated to them.