A method for determining a state of a blood vessel is presented. The method includes accessing a first medical image of the blood vessel in a first condition, measuring a first radius of the blood vessel in the first image at a first position in the blood vessel, accessing a second medical image of the blood vessel in a second condition, measuring a second radius of the blood vessel in the second image at a second position in the blood vessel corresponding to the first position, and determining the state of the blood vessel by calculating a ratio of the first radius and the second radius.
