To provide an image generation apparatus and a program capable of generating an image of a region of interest broken at any selected sectional plane. Reconstructed image voxel data in a three-dimensional space is received. Designation of two-dimensional regions of interest is received on a plurality of sectional planes of the image voxel data. At least one three-dimensional region of interest corresponding to the two-dimensional regions of interest is generated in the three-dimensional space, on the basis of the designated two-dimensional regions of interest. A contour is generated using region-of-interest voxel data which corresponds to the received image voxel data and has a voxel value which is made different depending on whether or not the region-of-interest voxel data is included in at least one three-dimensional region of interest. The contour is drawn together with the image voxel data included in the defined plane.
