go figger

I can't speak for your surgeons, of course, but the whole point of going to titanium was to provide MRI-compatible implants. Even stainless normally thought of as non-magnetic is magnetic at 1.5 or 3T.

Yup.

Well, there's the static field, which is very very (to a few parts per billion) even within the imaging area. Then there's the dynamic (Gradient) fields, in the x,y, and z directions. Those are at mostly audio frequencies, which is why the scans are as noisy as they are.

So. Ring on a finger, dynamic magnetic field, inducing current into...

I can see how that could create _torque_, if the ring was at an angle to the flux lines. Hm. If I still worked there, I'd do a little experiment. Ah well.

Sounds like the same eddy current effect I was describing with the coin, can, and aluminum plate, yup. If that was more portable, it'd be a great bar-bet...

Reply to
Dave Hinz
Loading thread data ...

A really neat show is to slide a supermagnet down an aluminum, or any non-magnetic metal, and see how it creeps down. Dropping a magnet down an aluminum tube is neat too. If you slide a washer down the aluminum first it really shows the difference. ERS

Reply to
Eric R Snow

They had the theory of MRI's NMR's back in the sixties. The chem lab was doing research in that area. The big problem was processing the data with the days technology. They could receive the signals from the excited molecules but could not do the processing to locate the exact sorce and make a picture as they do today.

John

Reply to
John

Remember - a metal ring conducts current in a changing magnet field. Silver and gold are very good conductors.

When working with high field magnets in the labs - I had to remove rings, watches, wallets, - everything in the pockets - special pencils non-carbon - and a safe method. The magnets would pull a hand into the field and didn't mind pulling a ring through a finger!

The gradient spikes of energy is really bad - so we did soft enables.

I'm surprised you didn't get that in a tray.

Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder

Eric R Snow wrote:

Reply to
Martin H. Eastburn

Why did my friend get his body wanded and picked through - finding all before ?

Maybe the term isn't MRI - might be a different function.

Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder

Dave H> >

Reply to
Martin H. Eastburn

Come on you guys - set up a magnetic field. Hold a sheet of metal or better a ring. If the field changes - as in frequency or intensity or direction - flux lines will be cut and current will pass. A ring will have a short current. It will solenoid off the finger or just get hot.

It is the things that transformers are made from. It is door bell theory... Martin

Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder

Charles Spitzer wrote:

Reply to
Martin H. Eastburn

Actually - all elements are responding to the field. You are flipping electrons in the outer shell. Add enough energy and you might get 'light'! when an electron is ripped off. People don't work well in that level for very long.

Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder

Dave H> >

Reply to
Martin H. Eastburn

Charles Spitzer wrote: ...

Ah - that's the phenomenon used in mechanical speedometers. A magnet rotated by the cable, an aluminum disk fastened to the needle, & restrained by a spring.

Bob

Reply to
Bob Engelhardt

If it's big enough, yeah, it's a concern. But slivers? They're not going to spin, they're not going to "catch fire". They'll cause image artifacts, sure.

No, probably was MRI. Metal isn't desirable, but it won't catch fire or throw you across the room.

Reply to
Dave Hinz

Close. You're aligning any nucleii which have a magnetic moment (hydrogen is a great one because it's just one proton) with the field. An RF pulse then tweaks _that_, which then cause an electron to jump to the next energy level and back down, giving off that energy in a predictable way. You're not ionizing anything, you're just bumping the leectron up a shell and then back donw.

No electrons are being ripped off, though, it's not that kind of a pulse.

Reply to
Dave Hinz

I did some research in the 60's. As it turns out every element has a signature. Once that was determined - then compounds were tested and oh what fun - guessing game.

We used a sample with a coil around it. e.g. a 20 turn coil that went to the LNA. LNA - low noise amplifier - somewhat like on a Dish antenna...

The magnetic field was applied at right angles. This field was swept in RF frequencies. As the identifying frequency (as the electron of the sample flipped) the LNA would issue this flipping waveform (to our scope).

Frequency and character determined the signature. It is simply the case of finding the frequency for the element electron shell to absorb energy. The shell begins to expand and there is a breaking point where the energy must be flung off (in Neon it is light - you know that) and the electrons flip as the shells decrease to normal.

Kinda fun toy - the people connection - was finding the density difference between the cancer cells to normal tissue and bone. Then sweep around that.

Once a map is determined anything goes - and software was the only holdup.

Martin

Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder

John wrote:

Reply to
Martin H. Eastburn

Possibly a dumb question (tm), Martin, but while you are flipping these electrons around - where do the go?

Do they hop out to the next valence band/shell/level ?

Or are we doing something else here?

Richard

Reply to
Richard Lamb

I'm not Martin, but yes. You're exciting those electrons with a pulse of RF energy (in a typical MRI scanner of 1.5 Tesla magnet strength, the RF pulse is at 63.86 MHz). That RF pulse bumps the electron up to the next band. After a predictable time, it falls back down and gives off an echo of the RF pulse that put it up there in the first place. That echo is what we pick up, run through a fast-fourier transform (twice) and come up with the image. Oversimplified but essentially true.

It's not unlike sonar, but the ping and echo are with RF rather than audio. Again way oversimplified but not a wrong way to look at it.

Dave Hinz

Reply to
Dave Hinz

The electron will flip in the same shell - but remember there are mini-shells as well. By providing the harmonic frequency for the element - you force the electron to a higher state - and as it returns the dipole moment of the electron is in one of two directions.

Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder

Richard Lamb wrote:

Reply to
Martin H. Eastburn

Thank you, Sir.

richard

Reply to
Richard Lamb

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.