1. A method of visualizing changes in blood flow in a digital subtraction angiography (DSA) image sequence, comprising: a. generating a time-contrast curve for all pixels in each image of the DSA image sequence; b. specifying a reference parameter for each time-contrast curve to be used as a first time point; c. determining the value of the reference parameter for each time-contrast curve; d. specifying an arbitrary parameter for each time-contrast curve to be used as a second time point; and e. producing an output image by applying a color-coding of the difference between the first time point and the second time point to all pixels.