There is provided an image processing apparatus for using OCT to process a plurality of cross-sectional images obtained by moving an imaging core inside a catheter in an axial direction while rotating the imaging core. Data relating to the cross-sectional images is stored in association with position information in the axial direction when each of the cross-sectional images is acquired. A first cross-sectional image in which a disappearance section enabling determination that there is a disappeared portion of an external elastic membrane included in a vascular tomographic image starts, and a second cross-sectional image in which the disappearance section ends are extracted from the plurality of cross-sectional images. The position information in the axial direction which is stored for the first cross-sectional image and the second cross-sectional image is acquired, and an ablation range influenced by ablation at a position associated with the disappearance section is calculated based on a difference in the acquired position information in the axial direction.
