We use a mobile service for PET, MRI, and/or CT. Who has to be accredited, the mobile company or us?

For starters, the accreditation programs involve not just the equipment and image quality, but also personnel qualifications, policies and procedures, quality assurance, etc. Taken together these requirements involve not only the equipment, but the radiologists and the facility as well. So unless the mobile company provides complete turnkey service, including image reading, billing, quality assurance, etc., the responsibility for accreditation falls on the facility. In addition, the accreditation requirements of the MIPPA fall on the entity who bills Medicare, which in most cases would be the facility, not the mobile company.