What Materials Can Shield Electronics from a 3-Tesla MRI Magnetic Field?

[Sodagit]

So hypothetically you bring a container into an MRI room. Inside the container is a USB drive, a crypto hardware token, an electronic tablet, and a Walkman.

Then you run the room's MRI machine, which has a magnetic field strength of 3 Teslas. What kind of container could prevent any damage/data loss to the items listed above? What material(s) could shield the items from the magnetic field issuing from the machine?

Thanks in advance for any replies.

 

[Baluncore]

Welcome to PF.

Any small container that could shield the items, would be attracted to the magnet of the machine, so would not be allowed into the room because it would damage the MRI machine.

 

[sophiecentaur]

Welcome to PF.

Any small container that could shield the items, would be attracted to the magnet of the machine, so would not be allowed into the room because it would damage the MRI machine.

Agreed; the proposed scenario is either nonsense or insufficiently specified - there is no answer to the unstoppable force and immovable object question.

 

[Dale]

would not be allowed into the room because it would damage the MRI machine

Of greater concern would be injury to humans in the room.

a USB drive, a crypto hardware token, an electronic tablet, and a Walkman

The Walkman would be absolutely forbidden because the motors inside could easily turn it into a projectile.

The other items would need to be tested. Solid state electronics are ok, they will not experience major forces and will even function in the MR environment. However, often there are ferromagnetic parts used in the housing. So each model of device needs to be separately tested.

The testing takes anywhere from an hour to a day, depending on the use case. You don’t just bring such devices into the MR suite. You only bring them in with a specific purpose, and the required testing depends on that purpose

 

[Sodagit]

Thanks for the replies. I'll post the following quote (taken from a Wikipedia entry on "electromagnetic shielding") as an FYI:

"Equipment sometimes requires isolation from external magnetic fields. . .In these cases shields made of high magnetic permeability metal alloys can be used, such as sheets of permalloy and mu-metal or with nanocrystalline grain structure ferromagnetic metal coatings. These materials do not block the magnetic field, as with electric shielding, but rather draw the field into themselves, providing a path for the magnetic field lines around the shielded volume. The best shape for magnetic shields is thus a closed container surrounding the shielded volume. The effectiveness of this type of shielding depends on the material's permeability, which generally drops off at both very low magnetic field strengths and high field strengths where the material becomes saturated. Therefore, to achieve low residual fields, magnetic shields often consist of several enclosures, one inside the other, each of which successively reduces the field inside it. Entry holes within shielding surfaces may degrade their performance significantly.

"Because of the above limitations of passive shielding, an alternative used with static or low-frequency fields is active shielding, in which a field created by electromagnets cancels the ambient field within a volume. Solenoids and Helmholtz coils are types of coils that can be used for this purpose, as well as more complex wire patterns designed using methods adapted from those used in coil design for magnetic resonance imaging. Active shields may also be designed accounting for the electromagnetic coupling with passive shields, referred to as hybrid shielding, so that there is broadband shielding from the passive shield and additional cancellation of specific components using the active system.

"Additionally, superconducting materials can expel magnetic fields via the Meissner effect."

Would any of these types of magnetic shielding--active, passive, or hybrid--be feasible in protecting the items listed above (including the Walkman) in the face of a 3-Tesla magnetic field? For our purposes, let's assume that money is no object.

 

[Baluncore]

Would any of these types of magnetic shielding--active, passive, or hybrid--be feasible in protecting the items listed above (including the Walkman) in the face of a 3-Tesla magnetic field? For our purposes, let's assume that money is no object.

It could be done, but how will you hold down a container, made from magnetic material, in the presence of a 3 T field ?
How will you hold the 3 T magnet ?

 

[renormalize]

Would any of these types of magnetic shielding--active, passive, or hybrid--be feasible in protecting the items listed above (including the Walkman) in the face of a 3-Tesla magnetic field? For our purposes, let's assume that money is no object.

Any ferrous container intended to shield sensitive objects would have to be built-in to the MRI room (e.g., bolted to the floor) for safety. From https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4848040:
"The static magnetic field B0 of an MRI machine attracts ferromagnetic objects and accelerates them toward the center of the bore of the MRI scanner. Ferromagnetic objects such as coins, hairpins, steel oxygen tanks or scissors can be accelerated or torqued by B0 and become dangerous projectiles. The MRI safety program of the facility needs to warn about the misconception that larger objects will resist attraction to the field and need to emphasize the relationship between object size, material components, and projectile risk. Insufficient MRI safety training of ancillary medical personnel has led to fatal accidents when medical and other equipment was accelerated into the bore of the magnet."

 

[Vanadium 50]

but how will you hold down a container, made from magnetic material, in the presence of a 3 T field ?

With a bigger magnet of course!

 

[marcusl]

Sodagit, the magnet is always energized. The field doesn’t turn on when you run the MRI machine and then turn off, it’s always on.

 

[PeterDonis]

a Wikipedia entry

Please give a link.

 

[Baluncore]

I think the quote in post #5 comes from:
https://en.wikipedia.org/wiki/Electromagnetic_shielding#Magnetic_shielding

 

[Sodagit]

Yes, that is the correct link.

 

[Sodagit]

Sodagit, the magnet is always energized. The field doesn’t turn on when you run the MRI machine and then turn off, it’s always on.

This explains why I stock shelves at Target.

Well it looks like this will be a bit of a challenge to pull off. (In a hypothetical sense, of course.) Thanks for all the feedback.