Other reasons for network connectivity include retrieving and sending image sequences and data files (basically the actual scans) which is done all day everyday.
The more alarming part is the retrieving of raw data which is the unreconstructed scan. This involves attaching a memory stick that is supposedly clean and uploading to that. Generally this stick is stuck into any old researcher PC and files are off loaded. Vendors don't particularly like this but getting 10-20 gig files off the scanner via command line is pretty clunky at the best of times.
That the NHS has not done this is their actual failing and negligence. It doesn't take that much money to move such devices to a quarantined network.