Here is why they do not allow people to have metal objects on them while entering an MRI machine. The experiment was performed using a 4 tesla MRI magnet that was about to be decommissioned.

Note how magnetic objects let loose tend to oscillate along the magnet bore. That’s because the peak magnetic field gradients are at either end (near the magnet face), causing peak acceleration as the object enters, followed by progressively damped changes of direction.

And for those of you who are wondering how safe an MRI is for the human brain, I’ll let Youtuber Physics Girl take over to cover just that for me.

[practiCalfMRI Via LS]