To practice medicine, I think this includes diagnostic radiology, but not sure, you need to be licensed by the Medical Council of Hong Kong.
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the licensing exam is held once a year.
after passing the exam, (the passing rate is below 10%) you will need to complete 1 year of internship at HKHA before getting your license.
However, I have heard that private hospitals can sponsor foreign licensed doctors on temporary basis. (not sure if this is true.)