Yeah, we have enough problems with MRI machines generating scary magnetic fields inside a building, imagine the same thing but affecting everything within a 50km x 100+km swath of terrain.
The biggest power consumer in an MRI system is the gradient system, which is only necessary for generating images. These need powerful amplifiers to generate the RF pulses.
I looked it up BTW, and the maximum extent of the fringe field for a 1.5T MRI scanner drops to 1Gauss at about 4 meters from isocentre. Fun fact, the field strength of an MRI scanner refers to the strength at isocentre, whereas the maximum field strength generated by a 3T scanner is beyond 11 Tesla.