Design, fabrication, and performance of high-frequency phased-array ultrasonic endoscopes
With a rapidly aging population, there is an imminent need to reduce healthcare costs and improve patient outcomes. Minimally invasive surgical procedures have the potential to help facilitate this objective due to shorter recovery times and improved outcomes. However, challenges with the visualization of tissues limit the adoption of these procedures. This work aims to help advance clinical practice by developing new techniques to produce high-resolution ultrasonic endoscopes for minimally invasive surgical procedures. Micro-fabrication techniques are incorporated into a novel endoscopic ultrasonic transducer design, allowing for a 64-element array with an element pitch of 38 μm and an encapsulated transducer size of 2.5 mm by 3.1 mm. Impulse response simulation scripts are developed and tested to aid in the design and construction of the transducers. Tests on wire-phantoms and cadaveric porcine tissue showed a dynamic range of up to 60 dB, an axial resolution of 40 μm, and a lateral resolution of 152 μm. An experimental design using Vernier element spacings was developed, modeled, constructed, and tested to passively reduce the effects of grating lobe image artifacts at high steering angles. The design utilizes a 128-element transducer with every third element providing pulse transmission and every fourth element providing pulse reception. The Vernier array design reduced the intensity of grating lobe image artifacts by 15 dB relative to the previously constructed array. However, the transducer’s overall signal strength was attenuated by 18.2 dB, limiting the potential applications. Kerfless array designs, without mechanical separation of the piezoelectric wafer be-tween elements, were investigated due to their improved manufacturability. Though existing literature and simulations predicted poor performance of the kerfless arrays, measurements of their acoustic radiation patterns showed higher signal levels at steer-ing angles beyond ± 20° than was expected. The simulation models were updated to include the effects of lateral acoustic emissions within the piezoelectric wafer. They provided a strong fit with experimental measurement, demonstrating the viability of kerfless array designs as a low-cost alternative to traditional arrays.