There is provided a method for calculation of a functional index parameter in at least one blood vessel of a patient, comprises: receiving a dataset of registered functional image data and anatomical image data, wherein the functional image data and the anatomical image data include data indicative of anatomical and functional data for at least one blood vessel of a certain patient； calculating at least one value for at least one functional index parameter for at least one of: (i) at least one blood vessel, and (ii) for the anatomical region of the at least one blood vessel, wherein the at least one value of the at least one functional index parameter is computed based on the functional image data of the dataset； and outputting the calculated at least one value for the at least one functional index parameter for the at least one blood vessel of the certain patient.
