This might not be at all helpful, but my hope is that you won’t find it offensive…
So, I’ve had a number of phobias throughout my life, but by far the biggie is a dental phobia. And not just dentists either, teeth in general. For years I couldn’t look at even my own teeth; someone showing me their teeth was simply an unbearable thought. As a child I was actually banned from our local dentist because after putting on an absolutely ungodly display (I was a child, but well above the age where you should stop having complete screaming and crying fits) a dentist told me he was just going to look at my teeth, then proceeded to touch. I responded by biting him. Then I was banned LOL.
This continued throughout my childhood and teenage years, and it wasn’t helped by the fact that I had night-time bruxism which was so severe I actually started pushing my teeth loose. It was always accompanied by nightmares about my teeth falling out, which I understand is a common variety of dream, but which made everything worse. I was in constant pain from all the pressure I was putting on my jaws and teeth, and years of fear of my teeth and no dental care meant they were in appalling condition (I also didn’t brush much and floss wasn’t a thing I learned about until I was an adult).
Basically nothing could get me into a dentist chair. Nothing except…
Pretending to be someone else. I would listen to screaming heavy metal and wear black makeup and I would spend 15-20 minutes before the appointment getting into the mindset of a tough, scary rocker. It didn’t matter that I was actually a total dweeb, because in that moment, I wasn’t. I was Ozzy Osborne, I was Marilyn Manson, I was a person who wasn’t afraid of anything. And it worked.
Years later I heard about a similar therapeutic approach for kids who have phobias. They dress up like superheroes - people who wouldn’t be afraid of the thing that they’re afraid of - they pretend to be them, and they’re able to do the things that scare them. I heard about one little girl who was terrified of… I think it was a vaccination… so she dressed up like her hero, Amelia Earhart. Amelia flew planes, she was a badas*! She wouldn’t be afraid of a needle! And so the kiddo wasn’t either. Given my previous experience, it made perfect sense to me.
I’ve since had a similar experience as an adult with Pap smears. I experienced sexual violence when I was younger and was never able to get a smear. I just couldn’t face any kind of internal exam. For years I was honest with my nurses and told them that I was just too scared, and they were understanding. What wound up working for me was actually not saying anything; a new nurse started at my practice and I decided to go in there without telling her my history and just be someone who was fine taking their knickers off for whatever. And it worked.
I’m not saying this will work for you; clearly you’ve been through a terrible experience and you have every right to be afraid. Definitely take the sedative, and also give yourself a week or however long you need to just let the idea of trying again sit in your mind. Don’t rush yourself; this is at your own pace. Maybe it would help to talk to a professional too, if you’re not already; it sounds like you experienced an incredible trauma, and it’s absolutely understandable - logical, even - that it would have had such an effect on you. It might be possible to have not just a sedative to relax you, but enough to actually put you to sleep, so talk to your doctor. Sometimes I know they can also play radio or whatnot so that you can have some distraction while you’re in there. If you have a podcast or anything that you find particularly relaxing, it’s worth calling radiology and asking whether it’s possible to have something of your choosing played through the speakers. It’s possible that with the right support this could actually even be therapeutic for you, allowing you to regain a sense of control over something that has been taken from you. If you do have a therapist or councillor, speak to them and your technician and see if they could come with you on the day, and maybe coach you through it. You may also find that it might help to spend some time around the machine itself and the space, though this of course relies on the hospital and technicians being willing to allow you to spend a little extra time in the room (you could maybe watch some MRIs taking place on YouTube as an alternative). You may also find it helpful to research the machine you would be in; again, you’d need to call and ask the type ahead of time. Just anything to help you feel more comfortable and in control. One thing I will say is that I had my eyes closed from the moment I lay down, and I’m not sure I would have enjoyed it much if I had taken the time to look at the space I was in! I was instead playing little games in my head and was for all practical purposes many miles away lol.
Good luck. And if ultimately you decide that you can’t do it, then that’s okay too. This is your decision.