81 is generally for laboratories which would probably not be correct for a radiology group. 22 would only be correct if your facility is owned by a hospital and the hospital is billing your technical components on a UB form. Otherwise, 11 is most likely correct - CMS defines POS 11 as a "location, other than a hospital, skilled nursing facility (SNF), military treatment facility, community health center, State or local public health clinic, or intermediate care facility (ICF), where the health professional routinely provides health examinations, diagnosis, and treatment of illness or injury on an ambulatory basis." That encompasses what you've described, but the other alternative would be 49 - "A location, not part of a hospital and not described by any other Place of Service code, that is organized and operated to provide preventive, diagnostic, therapeutic, rehabilitative, or palliative services to outpatients only."
I'd recommend reaching out to your payers for guidance on this because the way payments and contracted rates are set up in their claim systems may vary and may affect the way you need to bill your place of service.