The Mri technician wasnt aware of your condition. involuntary movement can be RLS? restless leg syndrome, i had it pretty bad the first few days my neuropathies suddenly appear. I think its also the bodies way to move naturally when still as well though.
I was in an MRI for an hour(i think thats how long it took to see my head), and i felt like i wanted to move constantly, and i also dint have support for my legs, so i had to kept it bent in that position for almost half an hour, until they put a pillow under them to relieve the pressure, this was 2 years before my neuropathy started, and for an unrelated reason(which my current pcp/other doctors used against me). maybe you can have a pillow under your legs, so it can be comfortable