feeling a magnetic field

No but the missus could hear the channel on the satellite box when it was turned off.....

The main thing about MRI is just how noisy it is. I hadn't really thought about just how violent the magnetic scanning must be. Even from outside it is loud but in the chamber you need ear plugs.

It does if they attach the pulsed magnets to your head transcranial magnetic stimulation. One of the BBC "trust me I'm a medic" series had their presenter have his speech centre temporarily disabled by one.

Only when I inadvertently had something ferromagnetic in my pocket.

I have trashed quite few bank cards working on fast high power magnetic kit back when they were all magnetic stripe. I was more wary of the HT side of things that would be fatal if you made a mistake.

Maybe not until the 10s of T, or higher dB/dt like they use in neural stimulation (~1T or less, but in 10s us? ms? I don't know the pulse widths offhand).

People have made claims of electrostatic "force fields" in the plastic film industry, but if you don't mind my saying, let's just say that might be something Bill Beaty could speak more about. ;)

Tim

-- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website:

In the famous "levitating frog" experiment, the frog was subjected to ridiculously powerful magnetic fields - far greater than in an MRI. And it didn't seem to be particularly bothered as it floated around.

I'm not sure the scientists involved conducted very detailed interviews with the subject afterwards.

However, I think it is reasonable to assume that the magnetic field itself will have no directly detectable effect.

Some animals (like pigeons) appear to have magnetic minerals used to help navigation - they might feel the MRI magnetic fields as the equivalent to a bright flash or a loud bang. No such minerals or magnetic sense organs have been found in humans.

With a stable AC field, however, you would induce currents in conducting pathways in the body - and you would be able to feel them if they were strong enough. I suspect the currents induced by an MRI are too weak, too short-lived, and too local to have any detectable effect.

That's actually not true, aiui. Erythrocytes have a net magnetic moment, so they'll align with a sufficiently strong field. Capillaries are too small for then to go through sideways, so you wind up with impaired blood flow. It's not good to have that for too long, especially in your central nervous system.

Cheers

Phil Hobbs

No but I hear that Ted Bundy felt an electric current

Some people (including me) feel a sense of disorientation or something like that when around MRI magnets. It is a fairly well-reported effect. Might be "ALL in their heads", of course, at least for me it is a REALLY vague sensation.

Jon

In pre-superconductor days, large magnets were rare but you could actually enter the field. A nuclear researcher of my acquaintance recalls vertigo-like symptoms if he moved briskly when inside the big magnet (something about an Oak Ridge location).

He also recalls that the oscilloscope didn't work well in that location. A superconducting magnet next door to my old lab had enough field that the CRT touch-screen controller buttons were in locations that the label overlay did NOT indicate. So, the physiological effect there was raised blood pressure, and a disorder characterized by verbal muttering...

No, but beer can:

Then there is (or was?) "Magnetic Brewing" on Magnatron Boulevard in San Diego.

Our Blood is diamagnetic, FYI

Cheers

They were running some trials, 9 or 10 years ago, concerning the efficacy (or otherwise) of rTMS in treating patients suffering from depression. I never heard anything more about it, though. Presumably it didn't work! :-/

Some bio-hackers say that they sense magnetic fields. One magnetic bio-hack involves the placement of a small neodymium disk magnet, coated with an inert material, under the skin of a finger tip:

Thank you,

Yeah, Grab a big screw driver or other hunk of iron, (with both hands) and walk up to the fringing field of a decent super conducting magnet. The induced force goes as r^6 (sixth power of the distance) so it increases quickly.. hence two hands. I always had new grad students do it.

We also sell this kit that uses a balance to weight para-magnetic materials... it's pretty cool, shameless plug, (not my idea or implementation).

George H.

Sorry I guess that's just like frig magnets. GH

Ten Tesla Wide Bore Magnet at my former employer could briefly make you feel "light headed" if you walked briskly near it. Some people reported "changes" in their current thoughts, jumping to some other stream of thought if they got too close.

I always stayed way away from that area.

Steve

Meaningless; minds are well known (as a studied fact) to change by random coincidence, and by environment; when's the last time you walked to the other room to get something and actually remembered what you were there for? :-)

Tim

You mean this happens to other people??

I thought the Mag field was constant with microwave pulses.

Greg

Currents will form moving through field.

Greg