Evaluation of blood flow parameters

A system for evaluating blood flow parameters, the system comprising one or more processors configured to:

• receive angiographic image data representing a motion of a front of an injected contrast agent along a vessel in each of a first haemodynamic state and a second haemodynamic state;
• analyse the angiographic image data to determine a transit time or a transit velocity, for the vessel in each state, the transit time in each state being calculated based on a time taken for the front to pass between a proximal position in the vessel and a distal position in the vessel, and the transit velocity in each state being calculated based on one or more distances traversed by the front between the proximal position in the vessel and the distal position in the vessel, and one or more corresponding time intervals;
• output a value of one or more blood flow parameters for the vessel, the value of the one or more blood flow parameters being calculated based on the values of the transit times or the values of the transit velocities;
• and
• output sequences of a first angiogram and a second angiogram, the first angiogram and the second angiogram being generated from the angiographic image data and depicting the motion of the fronts along the vessel in the first haemodynamic state and the second haemodynamic state, respectively;
• and
• wherein the sequences of the first angiogram and the second angiogram are synchronised such that the fronts in both angiograms leave the proximal position in the vessel simultaneously.