Progress in ring array transducers for real-time 3D ultrasound guidance of cardiac interventional devices.

As a treatment for aortic stenosis, several companies have recently introduced prosthetic heart valves designed to be deployed through a catheter using an intravenous or transapical approach. This procedure can either take the place of open heart surgery with some ofthe devices or delay it with others. Real-time 3D ultrasound could enable continuous monitoring of these structures before, during and after deployment. We have developed a 2D ring array integrated with a 30 French catheter that is used for transapical prosthetic heart valve implantation. The transducer array was built using three 46 cm long flex circuits from MicroConnex (Snoqualmie, WA) which terminate in an interconnect that plugs directly into our system cable; thus, no cable soldering is required. This transducer consists of 210 elements at 0.157 mm interelement spacing and operates at 5 MHz. Average measured element bandwidth was 26% and average round-trip 50 ohm insertion loss was -58.1 dB after correcting for diffractive losses. The transducer was wrapped around the 1 cm diameter lumen of a heart-valve deployment catheter. Prosthetic heart valve images were obtained in water-tank studies.