I had one a few years ago when I was having pretty bad problems with persistent migraines. Doctor acted like it was a no-brainer (no pun intended) and they went right ahead with it.
Then told me that they apparently needed prior insurance authorization, which they never obtained, and tried to bill me for it. I wanna say it was like 5k. But I might be thinking of the colonoscopy I later had where they pretty much did the same thing. In both cases I pretty much told them to fuck off. I said that you, the hospital, are a bunch of incompetent douchebag crooks. So is the insurance company. Have fun duking it out with them. You will not receive a dime from me other than what was already disclosed and agreed upon.
Somebody paid somebody at some point. I could care less. Good god our medical industry is such a sham. And no, I'm not a hypochondriac. The migraine thing was pretty frightening and I went on all kinds of medications to try and address them. Usually (off-label, I assume) anti-convulsants, anti-psychotics, and other scary shit that made things far worse. The neurologist that was treating me deserves to be shot.
The other thing? Hemorrhoids. I endured much agony and worrying over 'prostate problems' (yes, including many exams) before finally being referred to a GI doctor who deemed the butt-scope necessary. After inspecting the entirety of my colon, they deduced that I had internal hemorrhoids. Right at my 'exit' (though they obviously gleefully mistook it for an entrance). The uncomfortable link to be made...I had some old dude shoving his wrinkly hand up my ass, pushing on butt-sores and saying 'oh, that hurts? Guess your prostate is inflamed.' Fuck. You. You. Motherfucker.
Pardon me if that's a bit too in-depth. I share this information freely so that others may be abhorred by the misery that doctors tend to needlessly inflict because of carelessness and 'specialization' that makes them (supposedly) good at treating small areas of the human body, but completely inept at treating actual human beings as a whole.
Testing bodily fluids is simple and can be done by simply walking into an independent lab and requesting the test, provided you can pay for it (the prices are much more reasonable). An MRI is not something I would advise before seeing some GOOD, thoroughly vetted doctors. If they'll do it at all. Others are saying 'sure, they'll do it if you're not trying to request a test at the expense of your insurance.' I find that dubious...yeah, they're in it to make money, but they need to have some assurance that you will actually pay that money. I cannot speak to how that side works (if prepayment may be accepted or some such).