A medical diagnostic imaging apparatus includes identification-information-changing circuitry and comparison-result-calculating circuitry. The identification-information-changing circuitry changes identification information given to a plurality of points corresponding to contours of tissue in first medical-image-data in a first medical-image-data group each including a plurality of pieces of medical-image-data of different time phases. The comparison-result-calculating circuitry associates the identification information on the points in the first medical-image-data after a change and identification information given to a plurality of points corresponding to the contours of tissue in second medical-image-data corresponding to the time phase of the first medical-image-data out of a second medical-image-data group each including a plurality of pieces of medical-image-data of different time phases, compares pieces of motion information representing motion of the tissue in the respective pieces of medical-image-data in the first and the second medical-image-data groups between corresponding time phases based on the association, and calculates a comparison result.
