Development of Renal Denervation Catheter Based on Piezoelectric Ultrasonic Transducer

In this manuscript, a miniaturized ultrasonic Renal Denervation (RDN) catheter for removing sympathetic nerves around the renal artery is proposed. The RDN catheter consists of an ultrasonic transducer, a balloon catheter and a control system. Owing to the use of a piezoelectric ceramic tube as the ultrasonic transducer, the RDN catheter is designed to provide 360° circumferential acoustic exposure around the renal artery. The piezoelectric ceramic tube has an active length of 6 mm, an inner diameter of 1.1 mm, and an outer diameter of 1.6 mm and the material of piezoelectric ceramic tube is PZT8. The balloon catheter of the proposed RDN catheter is designed and optimized so that the diameter of the portion inserted into the vessel is ≤1.8 mm, with the aim of enabling access to the renal artery via Transradial Access (TRA). In addition, a liquid circulation system is integrated into the balloon catheter to cool the ultrasonic transducer, with the aim of limiting heating near the renal artery wall. The measured resonant and anti-resonant frequencies of the ultrasonic transducer are 8.72 MHz and 9.69 MHz, respectively. Under 70 W input electrical excitation at 9.69 MHz, the average acoustic pressure measured at 6-7 mm from the catheter surface is 2.11 MPa. In addition, the control system prototype is also developed. Finally, the thermal feasibility of the proposed catheter is evaluated through phantoms and ex vivo tissues. In the phantom, visible whitening appears by 0.5 s, and an annular whitened region is evident by 8 s; at 15 s, its image-estimated thickness is approximately 3.6 mm, with an adjacent transparent interval of approximately 1.2 mm. Ex vivo porcine liver also shows macroscopic discoloration consistent with thermal denaturation. These observations support the preliminary acoustic and thermal feasibility of the proposed RDN catheter.