New fabrication techniques for ring-array transducers for real-time 3D intravascular ultrasound

Abstract

We have previously described miniature 2D array transducers integrated into a Cook Medical, Inc. vena cava filter deployment device. While functional, the fabrication technique was very labor intensive and did not lend itself well to efficient fabrication of large numbers of devices. We developed two new fabrication methods that we believe can be used to efficiently manufacture these types of devices in greater than prototype numbers. One transducer consisted of 55 elements operating near 5 MHz. The interelement spacing is 0.20 mm. It was constructed on a flat piece of copper-clad polyimide and then wrapped around an 11 French catheter of a Cook Medical, Inc. inferior vena cava (IVC) filter deployment device. We used a braided wiring technology from Tyco Electronics Corp. to connect the elements to our real-time 3D ultrasound scanner. Typical measured transducer element bandwidth was 20% centered at 4.7 MHz and the 50 Omega round trip insertion loss was --82 dB. The mean of the nearest neighbor cross talk was -37.0 dB. The second method consisted of a 46-cm long single layer flex circuit from MicroConnex that terminates in an interconnect that plugs directly into our system cable. This transducer had 70 elements at 0.157 mm interelement spacing operating at 4.8 MHz. Typical measured transducer element bandwidth was 29% and the 50 Omega round trip insertion loss was -83 dB. The mean of the nearest neighbor cross talk was -33.0 dB.

FIG. 1

Schematic of the integrated transducer and vena cava filter deployment device. Real-time 3D ultrasound pyramidal scan is directed out from the end of the catheter and is coaxial with the deployment of the vena cava filter.

FIG. 2

Schematic of the steps in building the ring array transducers. We start with a metallized polyimide substrate (A) with an area without the metal to attach the PZT. We next attach the PZT beam (B) with nonconductive epoxy. After the epoxy cures, silver paint is used to connect the back electrode of the PZT with the metal trace (2C). The PZT is then diced and wrapped around a lumen. An 0.012 mm thick layer of liquid crystal polymer (LCP) is wrapped around the outer circumference of the PZT and polyimide substrate (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 (2E).

FIG. 3

Photograph of 46 cm long flex circuit.

FIG, 4

Close-up of ring array after dicing and bonding to the LCP.

FIG. 5

Close -up of wiring for 55-element transducer featuring Tyco-cable assembly. 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 (Advanced Polymers, Inc. Salem, NH).

FIG. 6

Typical pulse and spectrum from the transducer featuring Tyco Electronics Corp. wiring assembly. Center frequency is 4.7 MHz and –6 dB bandwidth is 20%.

FIG. 7

Photograph of Cook Medical, Inc. vena cava filter.

FIG. 8

Real-time, 3D-rendered view of Cook Medical, Inc. vena-cava filter made with 55-element ring-array transducer and Tyco Electronics Corp. wiring assembly. Depth of scan is 8 cm and the full dynamic range has been logarithmically compressed to make the target brighter.

FIG. 9

Close-up photograph of face of 70-element transducer built on a 46-cm long flexible circuit.

FIG. 10

Typical pulse and spectrum from transducer featuring 46-cm flexible circuit assembly. Center frequency is 4.8 MHz and –6 dB band width is 29%.

FIG. 11

7-cm deep B-scan (A) with simultaneous C-scan (B) and rendered image (C) of an aortic aneurysm graft with a needle inserted out the lumen of the catheter and into the graft. The C-scan is made at the depth indicated by the arrow in the right of A. The rendered image (C) has been logarithmically compressed to increase the brightness of the targets. A and B are displayed on a linear scale.