An imaging system configured to segment a vessel lumen, comprising: a vessel centerline generator configured to generate a centerline through a lumen of a vessel selected to be segmented and to receive a reconstructed image and to determine from the received image, either automatically or manually, the centerline of the vessel lumen from an image volume; a sub-resolution luminal narrowing detector configured to detect sub-resolution narrowing of the vessel lumen in the image volume by a centerline profile analysis and to compute a sub-resolution determined diameter by modifying an approximated visible lumen diameter with the detected sub-resolution narrowing, wherein detecting sub-resolution narrowing means that narrowing of the vessel lumen is detected at a precision greater than a visible resolution of the imaging system, wherein the approximated visible lumen diameter is determined from diameters computed using a full-width at half maximum rule for the intensity profiles for each cross-section along the centerline of the to be segmented vessel lumen, wherein the centerline profile analysis detects the sub-resolution narrowing based on intensity values along the centerline of the to be segmented vessel lumen that are either lower than a predetermined threshold or greater than a predetermined threshold; a graph min-cut variation segmenter configured to construct a graph with each voxel in a segmented region represented by a node, each node connected to a lumen node and a background node, and edges connecting each node to the lumen node weighted with a product of a likelihood, L i, that the voxel is part of a segmented vessel lumen according to an intensity of a closest centerline voxel and a trained model, and a likelihood, L d, that the voxel is part of the segmented vessel lumen based on a spatial distance of the voxel from a closest centerline point and the sub-resolution determined diameter, and edges connecting each node to the background node weighted by 1 -L i *L d, and edges between neighboring voxels weighted by a smoothness penalty, and cut the graph, which separates the graph into a first portion connected to the lumen node and a second portion connected to the background node based on a minimal cost and the nodes in the first portion segment the vessel lumen. a vessel centerline generator configured to generate a centerline through a lumen of a vessel selected to be segmented and to receive a reconstructed image and to determine from the received image, either automatically or manually, the centerline of the vessel lumen from an image volume; a sub-resolution luminal narrowing detector configured to detect sub-resolution narrowing of the vessel lumen in the image volume by a centerline profile analysis and to compute a sub-resolution determined diameter by modifying an approximated visible lumen diameter with the detected sub-resolution narrowing, wherein detecting sub-resolution narrowing means that narrowing of the vessel lumen is detected at a precision greater than a visible resolution of the imaging system, wherein the approximated visible lumen diameter is determined from diameters computed using a full-width at half maximum rule for the intensity profiles for each cross-section along the centerline of the to be segmented vessel lumen, wherein the centerline profile analysis detects the sub-resolution narrowing based on intensity values along the centerline of the to be segmented vessel lumen that are either lower than a predetermined threshold or greater than a predetermined threshold; a graph min-cut variation segmenter configured to construct a graph with each voxel in a segmented region represented by a node, each node connected to a lumen node and a background node, and edges connecting each node to the lumen node weighted with a product of a likelihood, L i, that the voxel is part of a segmented vessel lumen according to an intensity of a closest centerline voxel and a trained model, and a likelihood, L d, that the voxel is part of the segmented vessel lumen based on a spatial distance of the voxel from a closest centerline point and the sub-resolution determined diameter, and edges connecting each node to the background node weighted by 1 -L i *L d, and edges between neighboring voxels weighted by a smoothness penalty, and cut the graph, which separates the graph into a first portion connected to the lumen node and a second portion connected to the background node based on a minimal cost and the nodes in the first portion segment the vessel lumen.