The NHS is the largest employer of PACS Managers in the UK.
You'll most likely need NHS experience for any senior level post as a lot of the role involves navigating through corporate habits and budget restrictions! PACS jobs now generally request several years proven experience or a Masters level qualification, with PRINCE2 (http://www.apmg-international.com/en/qualifications/prince2/prince2.aspx) or other demonstrable project management experience.
It is rarer to find clinicians (MDs) working as a PACS Manager in the UK. Around half of all PACS Management jobs in the UK require you to have current Health & Care Professions Council registration as a practising Radiographer though. You will need very good knowledge of the systems involved, as well as HL7, DICOM, XDS etc.