I had an MRI done of my back spine, I was also in for like 40 min. I was wearing underwear with my **** went over the balls and the tip ended up in the spot right under the balls. I am uncut. I was also fine for a little bit and then It felt so good with the vibrations. I was worried cause they offered a blanket but I didn't take it cause I didn't think I needed it. it was so warm. When I started getting hard I felt like they could see it with me just being covered with that thin robe, which I thought was falling off of my crotch. I was supposed to hold still but I was like ok... I am about to cum so I was moving around hah. I ejaculated, it actually felt super good. Like it was an amazing orgasm :) MRI is best sex toy. they guy asked me to hold still over the speaker. I played there with my **** pulsating and cum dripping everywhere for like another 15 min. The whole time I was thinking they could see the whole thing cause my crotch was facing their window, my legs spread apart a little. :) I thought it was a good experience. Makes me want to get another MRI
Before I answer, just one question - have you been diagnosed with (or suspected of having) prostate cancer? From what I've heard, they often do an MRI of the prostate to locate possible tumors ahead of planned treatment. I had prostate cancer surgery myself Jul 31, 2018, mostly recovered, but will need further treatment.
As to your question, I did not have that type of MRI myself, I know that the machines often make some loud sounds & possibly vibrations, so you're almost certainly not the first guy that had that happen. I have no idea how common it is - maybe a reader who's had experience as an MRI Tech could answer it for us. But from everything I've read about various procedures, medical personnel have seen just about everything. If they did notice, they probably wouldn't think much about it because, again, they've probably seen it before. Massage therapists are not shocked if a guy becomes aroused during a massage, it's a somewhat normal physiological response, they've seen it often enough that it's usually not a big deal to them, and the same for nurses, techs & other medical professionals. I hope someone in the medical field with direct experience can provide a more specific answer.