From the information I have, it depends on the type of shunt valve you have. Some valves have a fixed pressure and MRI scans have no effect on these valves. My previous shunt was a fixed pressure device and I had numerous MRI's without any issues.
My shunt was revised and a variable pressure valve was inserted. Since this I have been given mixed messages about MRI's. I have been told that I can no longer have MRI's or that if I have an MRI there must be a neurosurgeon available to reset the valve pressure. Since the variable valve has been inserted I have not had an MRI and only had CT scans. The radiologist informed me that if there was an issue it would show on a CT, then for a more refined image an MRI could be ordered within a hospital setting, where there would need to be a neurosurgeon available to make the required adjustments to the valve settings.
Hope it helps
Merl1n