A MINIATURE HIGH RESOLUTION ENDOSCOPE FOR 3D ULTRASOUND IMAGING

Abstract

Miniaturized ultrasound imaging arrays have many potential clinical applications, specifically, in guiding surgical procedures. 3D capable probes are also particularly suited to endoscopic applications because of the large amount of information that can be gathered without being sensitive to the position of the tool within the patient. A 3D dataset can provide imaging access to hard to view planes, accuracy in volume measurements and flexibility in image display. Unfortunately, for a fully sampled 2D array capable of 3D imaging, the fabrication challenges inherent to requiring thousands of small piezoelectric array elements are prohibitive when considering endoscopic packaging constraints. This dissertation presents an approach to developing a low channel count, endoscopic, real-time capable 3D imaging system using a crossed electrode array architecture and bias-sensitive piezoelectrics. A 30 MHz, 128 element crossed electrode array based on a 1-3 relaxor composite substrate was fabricated for this work. The reduction in the total element count of the crossed electrode array eases the challenges of electrically connecting a fully sampled 2D array. However, there is still a challenge in connecting to back-side and front-side elements. A process has also been developed that uses a thinly diced strip of flexible circuit board to bring the back-side connections to a front-facing bond surface, which allows the final size of the forward-looking endoscope to measure only 6 mm x 5 mm. The imaging techniques developed for this array build on the concept of an electrically steerable elevation lens for 3D imaging. New beamforming techniques have been developed to improve the image quality in the elevation plane by creating an electrically reconfigurable lens with a bias-sensitive array substrate. In the first technique, a Fresnel mimicking lens is created along the elevation dimension of the crossed electrode array. Compounding a set of Fresnel patterns creates a high-quality, two-way elevation lens focus and can be steered to a moderate range of angles (±15°). Alternatively, the second approach uses a Fresnel lens on transmit for elevation slice selection combined with Hadamard receive coding. Using either of these steerable elevation lenses, imaging in azimuth is completed simultaneously. Therefore, when ultrafast imaging is employed in azimuth, each elevation slice can be collected at high frame rates and full volume images can be generated in real-time (19.5 volumes/s).