1. A computer-implemented method of coronary vessel segmentation and visualization, the method performed by the computer comprising the steps of: providing a digitized coronary image, said image comprising a plurality of intensities associated with a 3-dimensional grid of voxels; placing a plurality of seed points along an estimated centerline of a coronary vessel; selecting a seed point and constructing a cyclic graph around said seed point in a plane perpendicular to the centerline at the seed point; performing a multi-scale-mean shift filtering in said perpendicular plane to estimate image gradient values; detecting a boundary of said vessel using a minimum-mean-cycle optimization that minimizes a ratio of a cost of a cycle in said graph to a length of said cycle; constructing a sub-voxel accurate vessel boundary about a point on said centerline; and refining the location of said centerline point from said sub-voxel accurate boundary, wherein said steps of constructing a sub-voxel accurate vessel boundary and refining the centerline point location are repeated until convergence; constructing a 3-dimensional triangulated surface model from said sub-voxel accurate vessel boundaries to form a tubular mesh representing said coronary vessel; and rendering the tubular mesh from a viewer-specified direction by specifying a less-than Z-buffer for said tubular mesh wherein every visible point in the resulting Z-buffer specifies the distance, along a viewing direction, from a viewer to a nearest visible part of the tubular mesh: generating a set of two-dimensional points by extracting all Z-buffer points that are on a boundary between visible and non-visible parts of the tubular mesh; generating a triangular mesh from said set of two-dimensional points; projecting the triangular mesh into a 3-dimensional space adding to each point of said mesh a Z coordinate calculated from a corresponding less-than Z-buffer function value and a known model-view transformation of the specific viewing direction; creating a complete Z-buffer representation of the projected 3-dimensional triangular mesh representing said vessels by adding near-plane Z-buffer values of the projected 3-dimensional triangular mesh to corresponding non-visible points of the less-than Z-buffer function; and volume rendering said 3-dimensional triangular mesh by calculating ray starting points and direction from the complete Z-buffer values and the specified viewing direction.