Automated calculation of the axial orientation of intravascular ultrasound images by fusion with biplane angiography

This paper presents an approach for fusion of the two major cardiovascular imaging modalities, angiography and intravascular ultrasound (IVUS). While the path of the IVUS catheter, which follows the vessel curvature during pullback, is reconstructed from biplane angiograms, cross-sectional information about the vessel is derived from IVUS. However, after mapping of the IVUS frames into their correct 3-D locations along the catheter path, their orientations remain ambiguous. We determine the relative catheter twisting analytically, followed by a statistical method for finding the absolute orientation from the out-of-center position of the IVUS catheter. Our results as obtained from studies with cadaveric pig hearts and from three patients undergoing routine coronary intervention showed a good match of the absolute orientation by the algorithm. In all tested cases, the method determined the visually correct orientations of the IVUS frames. Local distortions were reliably identified and discarded.