1. A computer implemented method of registering a 3-dimensional (3D) model of a coronary artery tree with two or more 2-dimensional (2D) images, the method executed by a computer comprising the steps of: solving for matrices R, P i , i=1,. .. , N, that minimize a cost function Σ i=1 N ∥Ψ i RX−I i P i ∥ 2,1 subject to constraints that R∈conv(SO(3)), P i ∈[0,1] n i ×m , and P i 1≦1, 1 T P i =1, for i∈{1, N}, wherein N is a number of 2D images, R is a rotation matrix, conv(SO(3)) denotes a convex hull of the special orthogonal group in 3 dimensions, X denotes a 3D centerline model of a coronary artery tree with m points, I i denotes the ith 2D image with n i points, Ψ i denotes a transformation between the 3D centerline model X and the ith 2D image I i , 1 is an all-ones vector, P i is a permutation matrix whose values represent a probability of a point in the ith 2D image I i corresponding to a point in the 3D centerline model X, and the subscript 2,1 refers to a mixed l 2 /l 1 norm; and rounding a solution R to a nearest orthogonal matrix R* in SO(3); wherein R* aligns the 3D centerline model X of the coronary artery tree with 2D fluoroscopic images acquired during a percutaneous coronary intervention procedure.