An image data processing apparatus comprising a image data processing unit for obtaining segmented image data segmented using a segmentation process and including a representation of a vessel, wherein a region of the vessel is missing from the representation, a boundary identification unit for identifying at least one point at or near a boundary of the missing region, wherein the image data processing unit is configured to perform a further segmentation process to identify the missing region of the vessel, using the location of the at least one identified point at or near the boundary of the missing region, and the image data processing unit is further configured to generate a revised representation of the vessel including the missing region of the vessel.
