A medical image diagnosis apparatus according to an embodiment includes an input circuitry, a scan control circuitry, and a reconstruction control circuitry. The input circuitry receives a specifying operation for specifying, from a region of a first medical image acquired such that the first medical image contains less noise, a region for which a second medical image that is a higher-definition image than the first medical image is acquired. The scan control circuitry adjusts an irradiation region of X-rays in a slice direction and a channel direction such that a part corresponding to the region on which the specifying operation is received by the input circuitry is irradiated with the X-rays. The reconstruction control circuitry performs reconstruction, on the first medical image as an initial image, by the successive approximation method by using projection data collected after the irradiation region of the X-rays is adjusted by the scan control circuitry.
