Modeling geometric artefacts in intravascular ultrasound imaging

A model has been developed for estimating the geometric distortions in intravascular ultrasound (IVUS) imaging caused by the position of the ultrasound catheter within the artery. Geometric distortion causes degradation on cross-sectional images of the vessel wall where, for characteristic positioning of the transducer within the vessel, a circular artery is seen on IVUS images as a noncircular vessel represented by more or less complex shapes. Artefacts, therefore, have a clinical impact on the accuracy of qualitative and quantitative intravascular analyses. The main distortions are due to the inclination and the off-centered position of the transducer within the vessel. These effects are increased by two factors: first, the point of origin of the ultrasound beam does not coincide with the rotation axis of the catheter; second, in the case of a mechanical rotating transducer, the ultrasound beam is not perpendicular to the long axis of the catheter, but has an inclination such that the transducer looks forward from the emitting point. All these parameters are taken into account in the three-dimensional (3-D) geometric model developed in this paper. The model was formulated to predict the geometric deformation for artery contour of various shapes and can model artefacts during stent implantation (Finet et al. 1998). Simulations were made for various geometric configurations and compared to in vitro and in vivo IVUS images. The model results are consistent with the experimental results. Finally, the model was used for estimating the values of the geometric parameters that cause distortions on ultrasonic images.