Rufus knows what he's talking about. A conventional 1.5T or 3T clinical scanner with active shielding makes the danger zone of the fringe field more compact, b

Rufus knows what he's talking about. A conventional 1.5T or 3T clinical scanner with active shielding makes the danger zone of the fringe field more compact, but also makes the transition zone between where a ferromagnetic object experiences little force and where it experiences intense force that makes it a dangerous projectile quite small in space (and therefore quite difficult for a human being to predict). If you've got a ferromagnetic object within the 5 gauss line on a modern clinical system, you are playing a dangerous game of chicken. On a system without active shielding, that transition zone is more gradual. The quoted field strength of a magnet can be very deceptive. That number indicates the strength of the field at the magnet's isocenter. It says absolutely nothing about the characteristics of the fringe field. There are small 9T animal magnets that you can work on with a steel crescent wrench and 1.5T magnets that you wouldn't dare to even consider walking in the room with ferromagnetic tools.