A CT scan is never done to determine healing of rib fractures. It's too expensive, uses too much radiation and is unneccesary. Alan is right. Standard rib X-Rays would be done. Usually, all that is necessary is the initial diagnosis of rib fracture. It will have been found on the initial rib S-Rays done that made the diagnosis. Most of the time, X-Rays aren't necessary to follow up on these.
I broke three ribs in a motorcycle accident 20 years ago. The rib X-Rays confirmed it, and nothing was needed to follow up on it outside of my ability to move without much pain. The only time it might be concerning, is if the ribs punctured a lung, and then, only a chest X-Ray would be necessary.
If the rib fractures were initially found on a CT scan, it is considered an incidental finding. A CT would still not be done as a followup procedure.