Effective January 1, 1968, diagnostic X-ray services furnished by a portable X-ray
      supplier are covered when furnished in a place of residence used as the patient's
      home and in nonparticipating institutions. These services must be performed under
      the  general (but not direct, personal) supervision of a physician and certain conditions relating
      to health and safety (as prescribed by the Secretary) must be met. The scope of covered
      portable X-ray services is limited to specific films to avoid hazard to the patient.