The effect of angulation on intravascular ultrasound imaging observed in vascular phantoms

Purpose: To quantify the error introduced by noncoaxial intravascular ultrasound (IVUS) imaging and to evaluate the use of a balloon-tipped catheter in compensating for intraluminal angulation and subsequent dimensional inaccuracy. Methods: The effect of noncoaxial IVUS imaging was investigated in both a polyvinyl chloride phantom and an in vitro canine aorta using a calibrated setup to measure angulation off axis. Imaging was performed at increasing angulation (creating an elliptical image) in both phantoms, with the transducer centered and off center. Diameters were compared to the original coaxial diameter, as well as calculated diameters based on specific angles off axis. The percentage change (error) was also calculated at these angles. The measurements were repeated using a balloon-tipped catheter to center the transducer. Results: The measured diameters and percentage changes compared closely with their calculated counterpart. Up to 25 degrees off axis, the apparent increase in diameter measurement was nearly 10%. Angulation from 30 degrees to 70 degrees resulted in an increase of 15% to 192%. Use of the centering balloon reduced the amount of error by 70% to 85% but was limited to angles less than or equal to 25 degrees due to the design of the test apparatus. Conclusions: The error introduced by noncoaxial IVUS imaging can be significant and may be partially corrected by the use of a centering balloon. Further studies in the clinical application of a centering device are warranted.