Having metals near the MRI machine is dangerous and should be avoided. The best rule of thumb is to
always leave all metal in the waiting room outside the MRI room. If you have any questions about this make sure
you ask the MRI technician before you go into the MRI room. If you have metalic implants of some sort
you will need to be sure that the doctors/technicians know exactly what is in you before you get anywhere
near the MRI. There are many implants that are MRI-safe, but the doctors will need to personally make sure
yours is on the safe list.
The MRI machine has a very powerful magnet in it (usually between 1.5 and 7 Tesla) and thus the most dangerous types of metals are the ferromagnetic
metals, as they will be powerfully attracted. However, even metal alloys with only a small amount of
a ferromagnetic metal in them can still be very dangerous because the MRI magnet is so strong. These ferromagnetic
metals will be pulled to the exact center of the magnet, with the pulling force increasing the closer you get
to the magnet.
However, even metals that are not attracted to the MRI magnet can still be dangerous because the MRI machine
also uses changing magnetic fields. The changing magnetic fields can cause eddy currents in any metal because
metal is conductive. Any kind of metal in the MRI can still heat up or twist or move because of the changing
magnetic fields. Metal will also mess up the MRI picture the doctors get in the area of your body close to the metal.
Although it poses no physical risk, you should also leave your credit cards outside the MRI room because the
strong MRI magnet will erase the information stored on the little black bar on your card and you will have to get
a new card.
The bottom line when it comes to metal and the MRI machine is that they should not mix. The MRI magnet is always
on, even if there is no power to the room or even the building. The magnet is always completely on because it doesn't need electricity to be on and
to turn it off and then on again it would cost tens of thousands of dollars. Just always assume it is on no matter
what. Keep all metal out of the MRI room, and be extra sure to talk with the MRI technician beforehand if you have
The following is a collection of public YouTube videos that illustrate the power of the MRI magnet.
To see the source of each video simply click the "YouTube" button inside the player.
Measuring the force with which the MRI pulls on a number of objects.