As Robert says, just about the only way you'll get "proper" training on equipment of that kind will be by working as a service engineer with one of the manufacturers. But even after working with one manufacturer, you may not have "in depth" skills on another manufacturer's kit. And, as Neil has mentioned, once you
are working on the kit you probably won't get far without access to documentation, special tools - and parts!
However, there are also a number of "third party" service companies about; where you can gain good skills "across the board" - the various manufacturers - but, naturally enough, those companies (being small) are really looking for techs who can "hit the ground running", as it were (ready-trained, more or less).
But if you're lucky, you might find one or the other willing to give you a bit of training, then let you loose to "learn by doing" on the job; especially for ultrasound and (or) x-ray. In my opinion, that's as good a way as any for anyone who
really wants to learn (and understand):- total immersion, we might call it!
What stage are you at now (skill-wise, that is - experience, electronics
etc.)?
Lastly, I'm wondering what your aims are here; are you looking to get trained, then set up by yourself, or head off overseas, or some such thing? Or maybe you just don't fancy working for one of the Big Name companies (manufacturers)? Personally, I can relate to all of the above!
