How long does it take to earn a Ph.D in radiology?

In general, it could take two to three years once you complete the

Masters level. However, it is not always easy to determine an exact length of time. There are always a variety of variables to consider, including whether the individual is attending on a full-time or part-time basis, type of field, dissertation length and ability to defend it successfully etc.

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There is more explanation and details (country, continent, range) on this Web page: http://www.academicjoy.net/phd-timetodegree.html