A weight-bearing CT is a CT scan taken while you stand on your foot — the position in which most foot and ankle problems actually show up. It uses a low dose of radiation, takes only a few minutes, and shows things a standing X-ray simply cannot, from subtle deformities to small amounts of joint looseness. For some patients it changes the diagnosis and the plan for surgery entirely. It is not needed for every foot or ankle problem, but when it is relevant, it is one of the most useful scans available.