Advances in two dimensional arrays for real time 3D intravascular ultrasound
Real time 3D IVUS may require imaging depths of a few centimeters to look down the axis of a coronary vessel to view vulnerable atherosclerotic plaque. We have previously described 2D array transducers for forward looking real time 3D intravascular ultrasound (IVUS). 1 We developed two transducers for different applications. Both transducers were constructed in the forward viewing configuration to allow simultaneous real time B-scans, C-scans and volumetric rendering of vessels, vascular stents and other devices implanted in the peripheral vessels. The first is a 14 French catheter transducer intended to guide the placement and retrieval of devices in the peripheral vessels. It operates at 5 MHz and features 112 active channels in a 10 × 14 array. This transducer was originally designed for intracardiac echo applications, and has been previously reported. 2 The second is a 5 French catheter transducer for use in smaller vessels. It operates at 10.0 MHz, and the array is 11 × 11 = 121 elements. We used non-coaxial cabling to obtain the needed number of conductors in the small lumen. In order to conform to the round aperture of the IVUS lumen, the corners were cut off resulting in a total of 97 signal channels. The 50 Ohm insertion loss is -83 dB and the -6 dB bandwidth is 25%. Average cross talk on nearest neighbor elements is -31.6 dB when loaded by 50 Ohms. However, our earlier processes led to poor yield and image quality. A new process, based on a custom fixture, improved the flatness of the wireguide. This improved our bonding and dicing techniques and increased our yield by 50%. Real time 3D images include tissue vascular phantoms with a 4.0 mm diameter lumen, a vascular stent before and after deployment in a tissue mimic phantom, and images of the aorta of an excised sheep heart. We have also pursued the fabrication of another 2D array transducer for IVUS that was constructed with non-rectilinear element placement. Using the same cabling. 61 elements were diced out with a laser. Preliminary pulse and spectrum show a -6 dB bandwidth of 55% centered at 13 MHz. © 2004 IEEE.
