An Axial Array for Three-Dimensional Intravascular Ultrasound

With intravascular ultrasound, high resolution cross-sectional images of arterial walls can be obtained. By pulling a catheter through the artery in the axial direction and stacking consecutive cross-sectional images, a three-dimensional image is obtained. However, cardiac and respiratory motion, combined with a high pull-back rate and a narrow axial radiation pattern, result in poor axial resolution and significant image distortion. To avoid these limitations, in this work the design of an axial linear transducer array is presented with which volumetric rather than cross-sectional images are obtained in every pullback position. The prototype consists of eight elements of dimensions 100 mu m by 350 mu m, with a kerf of 100 mu m, operating at a center frequency of 21 MHz with a bandwidth of more than 80 %. For both an ex vivo bovine artery and a stent-emulating phantom, the image quality in the circumferential and radial directions is similar to that of a conventional catheter. However, in the axial direction a significant increase in image quality is achieved. With the array, it is possible to image both the struts of a stent phantom and the underlying structures, whereas with the conventional catheter the struts are not properly localised and the underlying tissue is not distinguishable from the stent.