Two dimensional arrays for real time 3D intravascular ultrasound
We have previously described 2D arrays operating at up to 10.0 MHz consisting of several thousand elements for transthoracic cardiac imaging and over a hundred elements for intracardiac imaging using 7 Fr to 12 Fr catheters. Other laboratories have proposed doing real time 3D intravascular ultrasound (IVUS) with synthetic aperture techniques. We have begun to explore forward looking real time 3D phased array intravascular ultrasound, which may require imaging depths of a few centimeters to look down the axis of a coronary vessel to view vulnerable atherosclerotic plaque. We obtained a new non-coaxial based cable technology that allowed 100 signal wires to be placed inside a 4.8 French IVUS lumen with an inner diameter of 1.3 mm. In order to obtain the desired penetration depth, we constructed an 8.5 MHz transducer array which includes 11 × 11 = 121 elements for real time 3D intravascular imaging. The transducer was constructed in the forward viewing configuration to allow simultaneous real time B-scans, C-scans and volumetric rendering of vessels and vascular stents. In order to conform to the round aperture of the IVUS lumen, the corners were cut off resulting in a total of 100 signal channels. Field simulations show a -6dB spatial resolution of 1.6 mm at a depth of 10 mm. The 50 Ohm insertion loss is -83 dB and the -6 dB bandwidth is 17%. Average cross talk on nearest neighbor elements is -27.6 dB when loaded by the Volumetrics Medical Imaging (Durham, NC) scanner, and -31.6 dB when loaded by 50 Ohms. Real time 3D images in tissue vascular phantoms have been made within a 4.5 mm diameter lumen. These in vitro images include the real time 3D rendering of a vascular stent.
