Vicki,

I've had several back MRI's in the years since my treatment (although I don't recall being in a situation where excess saliva/mucus was an issue). However, each time, there has been an emergency button I could press if I needed to interrupt the process for any reason, so I would assume if he needed to get rid of the excess from time to time they could pause to let him slide out and do that. Also, since the machine isn't continuously taking pictures for the entire time, there are breaks where he won't have to be perfectly still.

I'd suggest that he discuss this ahead of time with his doctor or the technicians who will be doing the test to figure out how best to deal with it.

Cathy