1. A computed tomography (CT) apparatus, comprising: an X-ray source to emit X-rays; and processing circuitry configured to receive a desired detectability index set by a user, the desired detectability index determining a desired image quality of a CT scan of an object; determine an X-ray tube current that will result in the desired detectability index set by the user; and cause the X-ray source to perform a scan of the object using the determined tube current.