1. A medical imaging apparatus comprising: an X-ray imaging apparatus; and a nuclear medicine imaging apparatus, wherein the X-ray imaging apparatus includes an X-ray tube configured to emit X-rays for generating an X-ray CT image, the nuclear medicine imaging apparatus includes a detector configured to detect radiation for generating a nuclear medicine image, and at least one of the X-ray imaging apparatus and the nuclear medicine imaging apparatus includes a determining unit configured to determine whether the detector detects the X-rays emitted by the X-ray tube, thereby determining whether there is a failure in the detector.