OK, on the whole, the folks in radiology (sometimes including the readiologist) are employed by the hospital; if the radiologist is not a formal employee of the hospital, he/she will probably be employed by a group of radiologists, or will be an independent contractor to the hospital. Either way, "X-Ray" (now more often known as "Diagnostic Imaging" since things other than X-rays are used to image things) tends to be a more or less autonomous department in the hospital, kind of self-contained.
Rather than try to detail that further, you might start by asking who the X-Ray tech is responsible to; that would be one or more supervisors. Then, who the supers are answerable to, on and on until you get to the "top" of the heap. Then, take a look at how an X-ray gets ordered, done and read and the report generated, and look at who is responsible to whom.
That should give you a good starting point, and frankly, if your buddy has been in an X-Ray department, he/she can ask a few of the folks he/she rubs elbows with, and you're off to a good start.
Crusty ol' MD