1. A medical image processing apparatus comprising: processing circuitry configured to: extract an image region having an image element value larger than a predetermined image element value from a first image of a plurality of time phases collected in first non-contrast CT imaging and second images of a plurality of time phases collected in second contrast CT imaging; calculate a feature quantity that fluctuates in accordance with motion of the image region for the first image of the plurality of time phases and the second images of the time phases, calculate a plurality of feature quantity scores corresponding to respective types of the feature quantity for the first image of at least the one time phase and the second images of the time phases, and calculate general scores based on the feature quantity scores for all combinations of the first image of at least the one time phase and the second images of the time phases; select the first image and the second image related to the combination with the highest general score from among all the combinations of the first image and the second images; and generate a subtraction image based on the selected first image and the selected second image.