I always describe MRI as very noisy and very boring! In fact, it is so boring that a fair percentage of people fall asleep (no kidding!).
Your son won’t notice what scan is being done when as they’ll almost certainly just run them one after the other without getting him out. As meme already said, head and orbital is head and eyes. They will scan both of these using a couple of different types of scan from different directions. Diffusion weighted is a newer type of scan that is good for detecting “active” lesions, ie lesions associated with a current attack. So, they will do a diffusion weighted scan of his head and eyes as well as the other types of scan. Diffusion weighted scans are beginning to replace the contrast scans that meme mentioned.
MRI is completely safe as long as we satisfy the screening questions (things like do you have a pacemaker? any shrapnel in your body? etc). It’s important not to have any loose metal on us because the scanner is actually a giant magnet so it’s not a good idea to have metal flying about.
Although the hole in the middle (the “bore”) seems too close for some people’s comfort, the scanner cannot move or fall in on someone.
The noise is just radio waves, but they are very loud so you have to protect your ears with either headphones or/and ear plugs. (The radio waves are used to generate the data that make the images.) Because the noise is very loud, it can make the bed move a bit, just like something sat next to very loud music coming through a big speaker. So your son should expect it to be very noisy and for the bed to vibrate. Different types of scan make different noises so one way to pass the time is to guess how many scans have been done and even what direction they are taking the images from because the noise gives it away!
Most people will have a sort of birdcage thing put over their head for a head scan (the “headcoil”). This helps to get really good data and has the added benefit of keeping people’s heads still which is very important.
So, all in all, very noisy and, since the most interesting thing to do while you’re in there is try and work out which direction the noise is going(!), very boring! But very important too.
Btw, you can pay for a copy of your scans on CD. My local hospital charges £18.50, but it varies. It’s pretty cool to get pictures of your brain - if you’re a geek like me at least