I think I tend to mix up one type of scan with another, but I've been in the tube with all the noise having a brain scan. They tell me they found nothing, which sort of figures.
I think different folk tend to get nervous at different levels about different things. I just told myself it won't take long, closed my eyes much of the time. (Would you be allowed an MP£ playeer or would that interfere ?) I can only guess but suspect any sudden movements, whilst not ideal, are likely to only cause small blurs or whatever, but do ask at the hospital.