A method and a system for determining a blood velocity between a first point and a second point in a blood vessel are presented. In the method, a time series of registered images of the blood vessel are received and subsequently scanned to select a base image and a test image. The base image corresponds to a begin time that represents a time instance when a contrast agent reached the first point. The test image corresponds to an end time that represents a time instance when the contrast agent reached the second point. A time elapsed between the begin time and the end time is determined. A length of the blood vessel is determined. The blood velocity is calculated by comparing the length of the blood vessel and the elapsed time.
