I think it depends on what they are scanning for and exactly what your consultant has requested (thinner slices of image means more detail and longer in the machine).
I’ve had six brain mri’s and have gone all the way in for all of them and several scans of other body areas where I was in up to my chest. The operators tend to be really lovely and understanding and for me they take me all the way through first, then back in. (I was highly sceptical when they suggested it, but it honestly does help.)
You will have a sort of plastic cradle/cage like thing called a coil placed over your head. This is nowhere as bad as it sounds (there are lots of images of them if you google) and it’s not to hold you still, it’s to help the machine direct the signal, as essentially it’s just radio-frequencies and magnets, which isn’t scary at all when you think about it.
At one hospital I was able to bring a cd and listened to an audiobook, which was really good for distracting me, but that was a long time ago and for more recent scans at our local hospital they just play music through the headphones. For my ds they let him pick his own music from a list.
You can see out and see the operator via the periscope/mirror. They are lovely if you ever do have to press the button to stop the scan. (I had to once when in a great deal of pain during the scan of an injury.)
They will speak to you through the headphones too for reassurance and to let you know what’s coming next and how long you have left.
I am claustrophobic and requested an open scan for my last brain MRI. To be honest it didn’t feel all that much different and ended up having to be done again, as the weighting was wrong for what my consultant needed to see.
Longest I have been in the machine for a brain scan was half an hour, but that was actually brain and neck/cervical spine.
I usually wear a pull on/over the head type sports bra with no metal in, yoga pans and a cosy top and slip on pumps, as that way I don’t need to change before I go in. As others have said, no metal/jewellery.
Be prepared for a wait/delay, as the clinic can start to run quite late if previous patients are anxious and stop the scan a lot.