A study of the quantitative and qualitative impact of catheter shaft angulation in a mechanical intravascular ultrasound system

Abstract

Nonuniform rotation of mechanical intravascular ultrasound transducers may give rise to a geometric distortion of the ultrasound image known as the rotation angle artefact. This investigation studied the influence of different degrees and combinations of catheter shaft angulation on image morphology and the quantitative impact of the artefact using a circular perspex phantom and 3.5 F, 30 MHz Boston Scientific “Sonicath” catheters connected to a Hewlett Packard Sonos intravascular scanner. Major and minor diameters, cross-sectional area and circumference of the phantom lumen were measured and a “distortion index” calculated. Visually apparent geometric distortion was graded from 1 (absent) to 4 (severe). As expected, eccentric transducer location was associated much more frequently with identifiable distortion (70%) than was a concentric location (6%). Greater distortion occurred with increasing degrees of catheter shaft angulation, and was more pronounced in images from older catheters. The lumen area measurements in images in which no artefact was identified were accurate to within ±10% in 97% of cases, compared to only 81% of cases when an artefact was noted. The quantitative accuracy of an image in which geometric distortion is identified is thus not reliable. The direction of the quantitative error cannot be confidently predicted in any given case, although the mean lumen area tends to increase as the grade of distortion increases.