High-Frequency Endoscopic Linear Arrays for Intraluminal Imaging

We present ongoing work to fabricate an endoscopic micro-ultrasound array for gastrointestinal (GI) tract imaging. Micro-ultrasound can improve detection and evaluation of small tumors, which would benefit treatment guidance and outcomes. The goal of this work is to miniaturize the transducer and cabling into an endoscopic form factor to facilitate clinical translation. We present results of prototype arrays fabricated with laser micromachining. A custom made flexible printed circuit fanout was patterned using laser lithography and chemical etching. Miniaturization for packaging in an endoscope was achieved by aligning and fixing the fanout along its thickness direction to the array elements. The electrical connection was made using metal evaporation and separation of neighboring elements achieved by laser micromachining. A mass spring matching layer and a quarter wavelength matching layer were vacuum deposited to improve sensitivity. Prototype 20-element transducer arrays operating at 66 MHz center frequency were fabricated and characterized. Electrical impedance measurements show that all elements of the array were connected and agree with simulations. Pulse-echo measurements after deposition of matching layers show a two-way fractional bandwidth of 62%, a significant improvement over the 40% bandwidth with no matching layers. Matching layer vacuum deposition has shown to be appropriate for high frequency transducers in which fabrication of thin films (<10 µm), by conventional lapping and polishing, is challenging. Extension of the number of array elements and addition of a focusing lens are discussed.