Ring array transducers for real-time 3-D imaging of an atrial septal occluder

Abstract

We developed new miniature ring array transducers integrated into interventional device catheters such as used to deploy atrial septal occluders. Each ring array consisted of 55 elements operating near 5 MHz with interelement spacing of 0.20 mm. It was constructed on a flat piece of copper-clad polyimide and then wrapped around an 11 French O.D. catheter. We used a braided cabling technology from Tyco Electronics Corporation to connect the elements to the Volumetric Medical Imaging (VMI) real-time 3-D ultrasound scanner. Transducer performance yielded a -6 dB fractional bandwidth of 20% centered at 4.7 MHz without a matching layer vs. average bandwidth of 60% centered at 4.4 MHz with a matching layer. Real-time 3-D rendered images of an en face view of a Gore Helex septal occluder in a water tank showed a finer texture of the device surface from the ring array with the matching layer.

Figure 1

Schematic of the integrated transducer and septal occluder deployment device. The real-time 3D ultrasound pyramidal scan is directed outward from the distal end of the device and is co-axial with the deployment of the septal occluder.

Figure 2

A schematic of the steps to build the ring arrays. We start with a metallized polyimide substrate (Figure 2A) having a metal-free shelf area to attach the PZT. We next attach the PZT beam / matching layer (Figure 2B1 / 2B2) with non-conductive epoxy. After the epoxy cures, silver paint is used to connect the back electrode of the PZT with the metal trace (Figure 2C). The PZT is then diced, and wrapped around a catheter lumen. A 0.012 mm thick layer of liquid crystal polymer (LCP) is wrapped around the outer circumference of the PZT and polyimide substrate (Figure 2D). This LCP layer is metallized with gold (shown in black) on one side only, the outer side, so that it does not risk shorting the traces together. A layer of gold is sputtered on the face of the elements and connected to the gold on the outside of the LCP (Figure 2E1 / 2E2).

Figure 3

Close up of ring arrays without matching layer (A) and with matching layer (B) after dicing and bonding to the LCP.

Figure 4

Close up of the cabling for a 55 element ring array transducer. The signal wires are hidden by the green ground wires. The overall shield braid increases the lumen O.D. to 13 French. After wiring, the extra shield braid is cut back, and the exposed wires are sealed with 0.013 mm thick heat shrink.

Figure 5

Typical pulse echo response and spectrum of control array. The center frequency is 4.7 MHz and the −6 dB bandwidth is 20%.

Figure 6

Pulse echo response(A) and spectrum (B) from the transducer constructed with a single matching layer. The center frequency is 4.2 MHz and the –6 dB bandwidth is 68%.

Figure 7

Gore Septal Occluder photograph (A), B-mode plane with 1 cm scale marks (B), En face 3D rendered view from control array (C) versus matching layer array (D).