An image processing apparatus according to an embodiment comprises processing circuitry configured to acquire morphology image data including a site of a subject and function image data including the site, extract a blood vessel region that corresponds to a blood vessel included in the morphology image data, calculate a fluid index in the blood vessel region, and based on the fluid index, calculate a first function index as an index indicating a function of a tissue to which a nutrient is supplied from the blood vessel, acquire a second function index as an index indicating a function of the tissue based on the function image data, detect a mismatch between the first function index and the second function index, and determine a spatial region that corresponds to the mismatch in the site.