1. A method of tracking coronary artery motion in a sequence of 2D images, comprising the steps of: constructing a centerline model of a segmented vascular structure in a base phase image in a sequence of 2D images of coronary arteries acquired over one or more cardiac phases; computing, for each pixel in a region-of-interest (ROI) in each subsequent image in the sequence of 2D images, a velocity vector that represent a change in position between the subsequent image and base phase image in the sequence of 2D images; calculating positions of control points i in each phase p using the velocity vectors v i T =(v i,x , v i,y ) T ; and applying PCA to a P×2N data matrix X T constructed from position vectors (x, y) of N centerline control points {V 0 (p) , V 1 (p) ,. .. , V N−1 (p) } for P phases to identify d eigenvectors corresponding to the largest eigenvalues of XX T to obtain d-dimensional linear motion model α ^ p ← m _ p + ∑ i = 1 d ⁢ ⁢ α p , i ⁢ v i , where m p is a mean value of 2N control points positions (x, y) at phase p of the cardiac cycle, v i is an eigenvector of U=cov(XX T ), and the α p,i 's are determined for each phase p, wherein a centerline model for a new image at phase p+1 is estimated by adding {circumflex over (α)} p to each centerline control point of a previous frame at phase p.