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Is platinum magnetic?

HopkinsMedStudent said:
I wear my platinum wedding ring into the MRI scanner room every day and I havent noticed any force being pulled on it. I dont know how pure the ring is, but if theres any impurities in it, they are not of sufficient magnitude to produce a noticeable force in a standard 1.5T field.

Welders and other people who work with metal cutting can accumulate very small particles of iron or other ferromagnetic metals into their eyes. If put into an MRI machine, they may be able to feel heat or pain in their eyes, so of course you are supposed to exclude anybody who fits this profile from getting a scan.

Some older tattoos used iron in the mettalic inks which could cause skin burns. However, most of the tattoos of the last 20 years or so use iron-free inks, so if its a recent tattoo the chances are greater of having no complications. We use a voice monitor to make sure that there is no local RF heating for people with tattoos, and if there is, we immediately cancel the scan. We've never had any serious burns with tattooed patients, just some minor pain that subsided immediately after leaving the scanner room.

Kumar,

MRI has NOTHING to do with imaging iron. Conventional MR scanning is based on hydrogen, not iron. MR spectroscopy uses other species such as sodium for example, but iron is not one of them.
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i know this sounds so dumb, but would CA++ set off an MRI's magnet?

Or is that just regular ol' calcium?
 
INRM said:
i know this sounds so dumb, but would CA++ set off an MRI's magnet?

Or is that just regular ol' calcium?
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Both regular calcium and Ca2+ have fully paired electron orbitals, so for all practical purposes calcium is immune to the effects of the magnetic field.

For an element to react to a magnetic field in an MR scanner, it must have unpaired electrons, this is because paired electrons (spin up and spin down) cancel each other's magnetic moment out to result in zero net magnetic moment per atom.

Diamagnetic objects have interactions with the MR magnetic field that are too weak to produce substantial force. Every material has some diamagnetic properties. Diamagnetic objects in a magnetic field generates a very small repulsive force.

Paramagnetic objects have unpaired electrons in which each atom produces a net magnetic moment. However, across the whole object, the magnetic moments are oriented in a random fashion, and therefore, there are no large magnetic domains.

All ferromagnetic objects are also paramagnetic. HOWEVER, in addition to being paramagnetic, instead of having their magnetic moments spread randomly throughout the sample, they have large magnetic domains that comprise trillions of atoms with the same magnetic moment. These large magnetic domains interact with an external magnetic field to generate a noticeable force on the object. All paramagnetic materials generate forces in a magnetic field, but the paramagnetic forces are observable only in a microenvironment, whereas ferromagnetic forces produce a net force vector for the whole object. So if you took an iron wrench into the MR scanner room you would feel the magnet trying to pull it out of your grasp.

On a macroscopic level, the only dangerous items in the context of MR scanners are ferromagnetic objects. Paramagnetic materials dont transition into the large magnetic domains that draw a substantial force from the magnetic field.
 
What a coincidence; as I read this post, I happen to have both a few grams of platinum on my finger and a small Nd magnet in a drawer. I've never noticed any reaction between the two.

For a more accurate test, I was able to balance my wedding ring on edge on a flat table. I was unable to disturb it in the slightest by waving the magnet nearby.
 
Matabiri said:
At the risk of being highly pedantic, as I understand it electricity and magnetism work in the same way, gravity works differently...
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Well yes. The main differences being my levels of understanding.

I was thinking about fields when I said that;
Magnetic fields
Electric fields,
Gravitational fields.

You are correct about gravity being different, but the physics one uses to play with it is very similar.

I was wrong to say they work the same way, just that we can model them very similarly.

I remember finding it all fascinating when I was taught about 14 years ago ... I regret forgetting most of it, maybe I should read a book!
 
Just on a point(less?) of clarification; the magnetism (ferromagnetism) we commonly refer to arises from spinning electrons. The magnetic field measured by a MRI or NMR machine derives from nuclear spins (some orders of magnitude less intense than that propagated by electrons). I believe the MRI machine in medical use responds to the nuclei in hydrogen (one of the most MRI receptive nuclei and of course a major component of biological entities) to give a powerful diagnostic tool. The nucleus in a proton can be either spin aligned (alpha – lower energy state) or spin unaligned (beta) with respect to the permanent magnetic field supplied by the electromagnetic in the MRI machine. Flipping the protons from one state to the other is a process requiring very little energy yet the instruments are sensitive enough to measure the transitions.

As an aside, MRI (or Nuclear Magnetic Resonance - they changed the name to Magnetic Resonance Imaging to keep those pesky nuclei out of hospitals) was 1st used to characterize the shifts of small(ish) organic molecules (which of course contain protons) in solution. Even a relatively simple molecule can give rise to a complicated (and characteristic) NMR spectrum. It is beyond me how the spectra of a human body supplied by an MRI machine can give interpretable results but they demonstrably can.
 
Re: Re: Is platinum magnetic?

Rob Lister said:
All matter is magnetic.

http://www.geo.umn.edu/orgs/irm/hg2m/hg2m_b/hg2m_b.html
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In the same way, we could say that all substances are water soluble. What varies is the level of solubility.
When we say that glass is insoluble in water, what we really mean is that the silicate ions, that are in solution, are so few that we can ignore them.
I wonder what is the point in a homeopathic preparation where there are more particles of glass then of the 'active' principle in the water.
By the way, the distilled water used in the preparation has other impurities besides glass. What is the therapeutic effect of all these impurities?
 
Re: Re: Re: Re: Is platinum magnetic?

I know this sounds SO neurotic...

but, can you answer this question anyway?

1.) I sucked in some dust yesterday, and a chunk that had a metallic taste to it. Is that a danger?

2.) I've been playing with a lot of magnets, and then I scratched the back of my neck... nothing will happen will it, even if a piece of the magnet ( a small sliver) was on, or slightly in my skin... if I walk into the MRI room, will it get sucked forward, through my brain-stem and kill me instantly? Or will it have no effect, or will it burn a little?

I'm so scared.

-INRM
 
We can't help you. Tell the radiologists before your scan, and they'll come up with an appropriate course of action.
 
anor277 said:
I believe the MRI machine in medical use responds to the nuclei in hydrogen (one of the most MRI receptive nuclei and of course a major component of biological entities) to give a powerful diagnostic tool.
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Yes. The key to MRI is that there are billions of atoms of hydrogen in a small packed volume in our bodies. Thats absolutely key, because as you suggested, the magnetic flux generated by hydrogen protons is very small, so you need trillions of them concentrated in a small space to get good signal.

The nucleus in a proton can be either spin aligned (alpha – lower energy state) or spin unaligned (beta) with respect to the permanent magnetic field supplied by the electromagnetic in the MRI machine.
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Yes, interestingly a typical field strength of 1.5T is only sufficient to tip a tiny minority of the total spins in the direction of the aligned field. Its on the order of one excess spin per million. This is somewhat unfortunate, because you could get much better signal if ALL the spins lined up parallel to the field. Higher field strengths give better images because a higher field causes more of the spins to line up parallel to the field. However, there are engineering design problems to building high field strength magnets that are also suitable for human imaging purposes.

A lot of people are claustrophobic, so they cant be scanned in a regular closed bore system. We have open MRIs that use 2 panels instead of a bore system, but the field strength for those is much less than conventional MRI (0.5T - 1.0T max). As a result, the images from the open MRI systems are not as good as the closed bore systems.

Flipping the protons from one state to the other is a process requiring very little energy yet the instruments are sensitive enough to measure the transitions.
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Yeah as I said the key is that although the magnetic flux measurable from one proton is very small, there are trillions and trillions of hydrogen protons in a small volume size, so when you add up a small signal from such a large number of protons, the resulting flux is measurable by the coils in the MR scanner.


It is beyond me how the spectra of a human body supplied by an MRI machine can give interpretable results but they demonstrably can.
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MRI is basically an NMR system with 3 magnetic gradient fields. With magnetic gradient fields, you can spatially encode the magnetic spin flux generated by the sample. NMR systems use RF pulses to generate signal from the sample, but it doesnt have any gradient fields to parse out WHERE in the sample those spin flux contributions are coming from, so the overall result for NMR is a spin reading of the whole sample.

With 3 gradient fields as is typical for an MRI system, you can control which part of the sample gets excited (slice select) and then use the 2 other gradients to get an x,y encoded matrix of magnetic flux. Its very cool stuff. The guys who won last year's Nobel Prize for Medicine were the engineers/physicists who discovered the use of gradients to turn NMR systems into a true imaging system.
 
HopkinsMedStudent said:
Yes. The key to MRI is that there are billions of atoms of hydrogen in a small packed volume in our bodies. Thats absolutely key, because as you suggested, the magnetic flux generated by hydrogen protons is very small, so you need trillions of them concentrated in a small space to get good signal.
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Small correction: MRI does not measure magnetic flux of H nuclei. It only uses a magnetic field to split the energies of the nuclear spin states, and then uses normal EM radiation to carry out the spectroscopy.

MRI itself is a little more complicated than that, using relaxation times to identify the environment of the protons, but it is still the decay of EM absorption.
 
pgwenthold said:
Small correction: MRI does not measure magnetic flux of H nuclei.
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Fair enough, I should have used the term "field" or "moment" instead of "flux." I was just trying to emphasize that the individual signal contribution from a single proton is very small, so you need lots of them to generate sufficient signal that can be captured by the receive coil in the scanner.

PET scans are much better than MRI in terms of sensitivity, because it can use a much smaller number of nuclei to get good signal. However, MRI is much better in terms of spatial resolution. Usually when we want to do a PET scan we cross register is with MR images so that we can take advantage of the great spatial resolution of MRI and the great sensitivity that PET offers.
 
My interest was tweaked when I read this thread as my doctoral thesis was on doping palladium and platinum with small amounts of ferromagnetic ions (things like iron, nickel and cobalt) in order to drive them through an enhanced paramagnetic state to ferromagnetism. Strongly ferromagnetic ions like cobalt and iron cause small domains of ferromagnetism to occur while nickel atoms only do this when the doped atoms are close enough to form doublets and triplets. Less than 2.5% of doped nickel will cause the entire palladium crystal to flip into a ferromagnetic state with a much smaller amount of iron causing this. Platinum I seem to remember needed even less. Platinum and especially palladium had rather odd magnetic behaviour due to very high electron-electron interactions.

I am also aware of an accident at a lab whereby a wrench was accidently let loose and pulled into the bore of a superconducting magnet. The major problem is that the forces on the windings can exceed design specs resulting in them moving within their potting material. The movement can not only crack the wire but cause enough frictional heating to cause the magnet to quench. If that wasn't enough to damage the magnet, the chances are that the windings are no longer positioned precisely and the homogenity of the magnetic field is messed up rendering the experiment impossible.
 
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