DISTORTION OF INTRAVASCULAR ULTRASOUND IMAGES BECAUSE OF NONUNIFORM ANGULAR VELOCITY OF MECHANICAL-TYPE TRANSDUCERS

The purpose of this study was to quantify nonuniform rotation in a cur rent mechanical intravascular ultrasound (IVUS) instrument and its eff ect on are, area, and diameter measurements. The accurate reconstructi on of IVUS two-dimensional images is dependent on uniform rotation of the catheter tip. Prior investigations suggested that bends in the cat heter driveshaft may be responsible for poor torque transmission, nonu niform rotation, and consequent errors in IVUS measurements. Eight 30 MHz mechanically driven IVUS catheters were evaluated in a model simul ating the catheter course through the aorta and coronary ostium in a c linical study. Angular velocity and posiion profiles of the transducer , image angle, and diameter and area measurement errors were obtained from each catheter by imaging a vascular phantom with eight equispaced echogenic markers from concentric and eccentric positions. Six cathet ers also were tested for comparison in a simple curvature model. Rotat ional error was found in all catheters tested and worsened in the aort ic model. Maximal angular error, defined as the largest angle between actual and presumed transducer direction, increased when measured in t he aortic model as compared with the simple curvature model (17 +/- 12 degrees to 45 +/- 25 degrees; p<0.05). Angles of 45 degrees were misr epresented with a mean range of values of 26 to 63 degrees. With eccen tric catheter placement, area and diameters had average maximal absolu te errors of 26% +/- 7.8% and 23% +/- 10%, respectively. In conclusion , nonuniform rotation of mechanical IVUS transducers constitutes a sig nificant potential source of error in IVUS measurement of arcs of calc ification, and lumen shape, area, and diameter.