Hi Emily
I think that LordKat's point is perfectly valid - you can always request a gown.
Also, thinking about it, in most places the radiographer only handles the x-ray situation and shouldn't deal with any other follow-up. At this point in time, you can always cite gynaecomastia, but I really fully and totally understand how you feel.
Regarding your worst nightmare, you remember how I looked when I got thrown off a bike 6 weeks ago and broke my arm? It was a nightmare. The local police radio'd the emergency services to say they had a girl down, and when they arrived my wig got pulled off when they put a neck brace on me. In the ambulance to the hospital I just calmly told the paramedics about my trans status, and in the hospital they just didn't care. I did care however, A LOT, because there I was, dressed like a girl, with a bit of makeup, but quite clearly "something different". Honestly, when you're feeling so battered and bruised you just get on with it. Of course, we are talking about Spain, and I am part of a formal transgender program, so I have social/legal protection. But yes, it was one of the more humiliating days of my life. On the other hand, in accident and emergency departments the staff just deal with cases, not people. Their job is to patch you up and get you out, and not to worry about anthing other than treating the fundamental trauma problem.