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Omidvar, Amirhossein

University of British Columbia

Ultrasound imaging is an effective and affordable tool for visualizing anatomical structures. Conventional ultrasound probes have limitations in size, shape, and conformability due to their rigid construction. Flexible ultrasound arrays could better conform to patient anatomy, potentially improving acoustic coupling, and provide larger field of view with a single acquisition event. However, their performance under bending and varying shape during use pose new challenges. This thesis focuses on strategies to design, fabricate, and implement a new type of flexible transducer arrays to enable conformal sonography. A new fabrication process for flexible capacitive micromachined ultrasound transducer (CMUT) arrays is developed. Polymers are used as the structural materials, with the CMUT membranes and support structures built from SU-8 photoresist on a polyimide substrate. Electromechanical characterization shows good fabrication yield and uniformity across arrays. Acoustic tests demonstrate wide bandwidth and mechanical durability under repeated bending. The proposed technology enables low-cost batch production of flexible CMUT arrays in different shapes and configurations up to 15 MHz frequency, including small and large form factors and 1D and 2D arrays. Two computational methods, based on image sharpness and spatial coherence, are introduced to estimate the unknown shape of flexible arrays. Both methods are evaluated using simulation. Additionally, the coherence-based method is tested with tissue-mimicking phantoms and in vivo experiments. Compared to state-of-the-art methods, the spatial coherence approach demonstrates improved generalizability for imaging complex anatomical targets, while maintaining comparable estimation accuracy. Finally, the longest reported monolithic flexible CMUT array with 128 elements over 9 cm aperture is fabricated and used to capture ultrasound scans. This section represents the first preliminary implementation of flexible CMUT arrays for in vivo scanning. In conclusion, this thesis presents advances in the field of flexible ultrasound array technology in three areas: a polymer-based fabrication process for flexible CMUT arrays; computational methods for predicting the shape of (flexible) ultrasound arrays without external hardware; and preliminary imaging with a flexible CMUT array under bending conditions. While limitations remain before clinical viability is achieved, this work provides key contributions that could pave the way for future integration of flexible ultrasound arrays into practical clinical systems.

Text

2024-04-17

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/87865

Biomedical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/