Integration of a dual-mode catheter for ultrasound image guidance and HIFU ablation using a 2-D CMUT array

Image-guided high-intensity focused ultrasound (HIFU) is widely used not only for non-invasive therapy but also for a precise approach for tissue ablation. Most HIFU systems use piezoelectric transducers, which are typically bulky due to active cooling, and separate imaging and HIFU transducers, and are therefore impractical for catheter-based applications. Taking advantage of a single 2-D capacitive micromachined ultrasonic transducer (CMUT) array, we developed a dual-mode catheter that can switch between ultrasound imaging mode and HIFU ablation mode. The catheter is equipped with an application-specific integrated circuit (ASIC) and a 32 × 32-element 2-D CMUT array. Both ASIC and CMUT are flip-chip bonded to a custom-designed flexible printed circuit board (flex PCB) via 100-μm and 80-μm solder balls. Then, the flex legs are folded and terminated with pads for a micro zero insertion force (μZIF) connector, allowing easy assembly replacement without the extra cost of coaxial cable assembly. Next, the micro-coaxial cables are assembled at the end of the μZIF connectors. After integration with a 3-D printed tip and encapsulating with polydimethylsiloxane (PDMS), the catheter is finalized in a 22-mm diameter shaft. We successfully validated the functionality of both modes of the dual-mode catheter in oil. We are currently preparing the test for an animal study.