System for assessing stenosis severity in a blood vessel in a body, said body comprising - a first blood vessel comprising a stenosis; and - a second blood vessel that is substantially symmetric to the first blood vessel, said system comprising - non-invasive imaging means (11, 11', 12, 12') configured to simultaneously generate image data of the first blood vessel and the second blood vessel; and - hemodynamic property determining means are configured to: - determine hemodynamic properties relating to a section of the second blood vessel corresponding to the section of the first blood vessel comprising the stenosis from the image data of the second blood vessel; and - determine the hemodynamic properties relating to the section of the first blood vessel comprising the stenosis from image data of the first blood vessel by using a hemodynamic property model based on input parameters including 3D segmentation of the image data and structural data of the first blood vessel derived therefrom and boundary conditions at inlets and outlets the first blood vessel and wherein said input parameters are at least partly based on properties derived from the image data relating to the section of the second blood vessel corresponding to the section of the first blood vessel comprising the stenosis; wherein the hemodynamic property determining means are configured to generate input for assessing hemodynamic properties relating to the section of the first blood vessel comprising the stenosis based on the determined hemodynamic properties relating to the section of the second blood vessel corresponding to the section of the first blood vessel comprising the stenosis, wherein one or more hemodynamic properties are selected from a group comprising fractional flow reserve, blood pressure drop and stenotic resistance. - a first blood vessel comprising a stenosis; and - a second blood vessel that is substantially symmetric to the first blood vessel, - non-invasive imaging means (11, 11', 12, 12') configured to simultaneously generate image data of the first blood vessel and the second blood vessel; and - hemodynamic property determining means are configured to: - determine hemodynamic properties relating to a section of the second blood vessel corresponding to the section of the first blood vessel comprising the stenosis from the image data of the second blood vessel; and - determine the hemodynamic properties relating to the section of the first blood vessel comprising the stenosis from image data of the first blood vessel by using a hemodynamic property model based on input parameters including 3D segmentation of the image data and structural data of the first blood vessel derived therefrom and boundary conditions at inlets and outlets the first blood vessel and wherein said input parameters are at least partly based on properties derived from the image data relating to the section of the second blood vessel corresponding to the section of the first blood vessel comprising the stenosis; wherein the hemodynamic property determining means are configured to generate input for assessing hemodynamic properties relating to the section of the first blood vessel comprising the stenosis based on the determined hemodynamic properties relating to the section of the second blood vessel corresponding to the section of the first blood vessel comprising the stenosis, wherein one or more hemodynamic properties are selected from a group comprising fractional flow reserve, blood pressure drop and stenotic resistance. - determine hemodynamic properties relating to a section of the second blood vessel corresponding to the section of the first blood vessel comprising the stenosis from the image data of the second blood vessel; and - determine the hemodynamic properties relating to the section of the first blood vessel comprising the stenosis from image data of the first blood vessel by using a hemodynamic property model based on input parameters including 3D segmentation of the image data and structural data of the first blood vessel derived therefrom and boundary conditions at inlets and outlets the first blood vessel and wherein said input parameters are at least partly based on properties derived from the image data relating to the section of the second blood vessel corresponding to the section of the first blood vessel comprising the stenosis; wherein the hemodynamic property determining means are configured to generate input for assessing hemodynamic properties relating to the section of the first blood vessel comprising the stenosis based on the determined hemodynamic properties relating to the section of the second blood vessel corresponding to the section of the first blood vessel comprising the stenosis, wherein one or more hemodynamic properties are selected from a group comprising fractional flow reserve, blood pressure drop and stenotic resistance.