A medical diagnosis apparatus of embodiments includes a scanner and processing circuitry. The scanner configured to scan a three-dimensional region including a target region and acquire data of the three-dimensional region. The processing circuitry is configured to discretely arrange fixed points framing three-dimensional shape of the target region in a first medical image based on the data. The processing circuitry is configured to set a boundary of region of interest (ROI) on the three-dimensional shape of the target region according to a position of the fixed point. The processing circuitry is configured to receive an instruction to change a position of the boundary from an input device controlled by a user. The processing circuitry is configured to change the position of the boundary based on a position or positions of at least one of the fixed points according to the instruction while maintaining positions of the fixed points.
