I sometimes volunteer at a local detention facility, and they have a metal
detector. Last night I was up there and hadn't had time to change out of my work
clothes, and I triggered the metal detector even with no metal on my person
whatsover. The guy running the wand asked me if I happened to work in a machine
shop and I said yes, and he said work jeans from a machine shop or steel fab
shop can trigger a scanner no problem.

I would have never guessed. Turned out this particular officer used to be a
machinist, and he had specific knowledge on the subject.

I'll be danged.

GWE

Grant Erwin wrote:
I sometimes volunteer at a local detention facility, and they have a
metal detector. Last night I was up there and hadn't had time to change
out of my work clothes, and I triggered the metal detector even with no
metal on my person whatsover. The guy running the wand asked me if I
happened to work in a machine shop and I said yes, and he said work
jeans from a machine shop or steel fab shop can trigger a scanner no
problem.

I would have never guessed. Turned out this particular officer used to
be a machinist, and he had specific knowledge on the subject.

You sure it wasn't from all that lead
you absorbed from pouring the keel of
your boat (:

I think it's just the metal you're made of Grant!


"Grant Erwin" wrote in message
...
I sometimes volunteer at a local detention facility, and they have a metal
detector. Last night I was up there and hadn't had time to change out of my
work clothes, and I triggered the metal detector even with no metal on my
person whatsover. The guy running the wand asked me if I happened to work
in a machine shop and I said yes, and he said work jeans from a machine
shop or steel fab shop can trigger a scanner no problem.

I would have never guessed. Turned out this particular officer used to be
a machinist, and he had specific knowledge on the subject.

I'll be danged.

GWE

And if you go to get an MRI - our bodies might have metal flecks within.
Be sure to mention it - as the metal gets hot and burns.

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



Grant Erwin wrote:
I sometimes volunteer at a local detention facility, and they have a
metal detector. Last night I was up there and hadn't had time to change
out of my work clothes, and I triggered the metal detector even with no
metal on my person whatsover. The guy running the wand asked me if I
happened to work in a machine shop and I said yes, and he said work
jeans from a machine shop or steel fab shop can trigger a scanner no
problem.

I would have never guessed. Turned out this particular officer used to
be a machinist, and he had specific knowledge on the subject.

I'll be danged.

GWE

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On Thu, 26 Jan 2006 22:39:58 -0600, "Martin H. Eastburn"
wrote:

And if you go to get an MRI - our bodies might have metal flecks within.
Be sure to mention it - as the metal gets hot and burns.

Martin
I had to get a cat scan of my eyes before the MRI. They said the
magnet could drag any metal chips through my eyeball. Ouch. It was
interesting that my non-ferrous wedding ring moved with sound of the
thing.
ERS
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



Grant Erwin wrote:
I sometimes volunteer at a local detention facility, and they have a
metal detector. Last night I was up there and hadn't had time to change
out of my work clothes, and I triggered the metal detector even with no
metal on my person whatsover. The guy running the wand asked me if I
happened to work in a machine shop and I said yes, and he said work
jeans from a machine shop or steel fab shop can trigger a scanner no
problem.

I would have never guessed. Turned out this particular officer used to
be a machinist, and he had specific knowledge on the subject.

I'll be danged.

GWE

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On Thu, 26 Jan 2006 22:39:58 -0600, Martin H. Eastburn wrote:
And if you go to get an MRI - our bodies might have metal flecks within.
Be sure to mention it - as the metal gets hot and burns.

No, it doesn't get hot or burn. (I worked in engineering on MRI scanners
for ~12 years). It can cause image distortion localized around the
metal (very local effect for slivers, nearly invisible). If you've got
metal in your eyes, they may choose not to use MRI on you, though.

I'd be happy to discuss this in as much detail as you'd like.

Dave Hinz

On Fri, 27 Jan 2006 16:30:07 GMT, Ignoramus13653 wrote:
On 27 Jan 2006 16:18:23 GMT, Dave Hinz wrote:

I'd be happy to discuss this in as much detail as you'd like.

Dave, I am interested in MRIs in general, so if you have any stories
to share, or interesting facts, that would be great.

You and I really need to sit down somewhere and have a beer or three,
Iggy. email me your address again, I'll lend you my (only) copy of GE's
Magnet Safety videotape.

Dave

YEP! They covered that on Mythbusters just the other night. The "Exploding
Tattoo". :-)

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

"Dave Hinz" wrote in message
...
On Thu, 26 Jan 2006 22:39:58 -0600, Martin H. Eastburn
wrote:
And if you go to get an MRI - our bodies might have metal flecks within.
Be sure to mention it - as the metal gets hot and burns.

No, it doesn't get hot or burn. (I worked in engineering on MRI scanners
for ~12 years). It can cause image distortion localized around the
metal (very local effect for slivers, nearly invisible). If you've got
metal in your eyes, they may choose not to use MRI on you, though.

I'd be happy to discuss this in as much detail as you'd like.

Dave Hinz

Um, can you guys take this off line? - GWE

Ignoramus13653 wrote:

On 27 Jan 2006 16:51:40 GMT, Dave Hinz wrote:

On Fri, 27 Jan 2006 16:30:07 GMT, Ignoramus13653 wrote:

On 27 Jan 2006 16:18:23 GMT, Dave Hinz wrote:

I'd be happy to discuss this in as much detail as you'd like.

Dave, I am interested in MRIs in general, so if you have any stories
to share, or interesting facts, that would be great.

You and I really need to sit down somewhere and have a beer or three,
Iggy. email me your address again, I'll lend you my (only) copy of GE's
Magnet Safety videotape.


Thanks Dave... We need to get together for a beer indeed... If you
wanna sell my bearings, I give you a 50% commission on them. That is,
I want to be paid 45% of the closing price (that 45% figures in your
listing and paypal costs). You charge buyers a fair amount for
shipping. That's my offer. It expires in 1 week from now. Picking up
those bearings would be a good excuse to meet and have a beer and
watch that GE safety video.

i

There's the six year old killed by the flying oxygen tank
when the MRI was turned on.

http://www.mercola.com/2001/aug/15/mri.htm

Ignoramus13653 wrote:

Dave, I am interested in MRIs in general, so if you have any stories
to share, or interesting facts, that would be great.

i

"Martin H. Eastburn" wrote in message
...
And if you go to get an MRI - our bodies might have metal flecks within.
Be sure to mention it - as the metal gets hot and burns.

Martin

I have had several MRIs done over the years. Last one was last week, and
was the 3 Tesla variety, the latest and strongest MRI.

As with all, I checked the boxes where they asked if I welded or worked with
metal.

They were very concerned over my heart stent, but went ahead with the MRI
when they saw that the stent did not appear on a chest x ray, meaning it had
been removed during my heart surgery, or it was not metal.

But, I figured they would do x rays of my head because of the
welding/metalworking history. They didn't.

One of the tekkies said that the magnets caused metal to spin or be pulled
out of the body. He demonstrated how powerful it was by giving me a metal
object. I held it up at arms length about ten feet from the MRI, and it
felt like I was trying to twist a very stuck door knob.

Anyway, that's my MRI story. I go on the 8th for results. It was a brain
scan, and I hope they find some functioning tissue.

Steve

"Steve B" wrote in message
news:kctCf.14046$JT.13348@fed1read06...

"Martin H. Eastburn" wrote in message
...
And if you go to get an MRI - our bodies might have metal flecks within.
Be sure to mention it - as the metal gets hot and burns.

Martin

I have had several MRIs done over the years. Last one was last week, and
was the 3 Tesla variety, the latest and strongest MRI.

As with all, I checked the boxes where they asked if I welded or worked
with metal.

They were very concerned over my heart stent, but went ahead with the MRI
when they saw that the stent did not appear on a chest x ray, meaning it
had been removed during my heart surgery, or it was not metal.

But, I figured they would do x rays of my head because of the
welding/metalworking history. They didn't.

One of the tekkies said that the magnets caused metal to spin or be pulled
out of the body. He demonstrated how powerful it was by giving me a metal
object. I held it up at arms length about ten feet from the MRI, and it
felt like I was trying to twist a very stuck door knob.

Anyway, that's my MRI story. I go on the 8th for results. It was a brain
scan, and I hope they find some functioning tissue.

Steve

my silver alloy wedding ring jumped around when i was in the mri tube last,
but the Ti plate in my neck didn't seem to move around, although they were
worried about it some when i told them i had one.

On Fri, 27 Jan 2006 11:07:58 -0700, Charles Spitzer wrote:

"Steve B" wrote in message
news:kctCf.14046$JT.13348@fed1read06...

One of the tekkies said that the magnets caused metal to spin or be pulled
out of the body.

The tekkie in question should stick to pushing buttons, because he's not
qualified to describe the physics involved.

He demonstrated how powerful it was by giving me a metal
object.

The force on an object, at a given distance, is proportional to it's
mass. First, he shouldn't be bringing ferrous objects into the scan
room, ever, for any reason. Second, he shouldn't be telling people that
metal could "spin or be pulled out of the body" because it's complete
and utter horse****.

I held it up at arms length about ten feet from the MRI, and it
felt like I was trying to twist a very stuck door knob.

Well, sure. It aligns with the flux lines of the field. Just like a
tiny little metal sliver...only thousands of times more forcefully.

my silver alloy wedding ring jumped around when i was in the mri tube last,
but the Ti plate in my neck didn't seem to move around, although they were
worried about it some when i told them i had one.

That is another example of a scan tech who doesn't understand their
technology. Titaniaum hand tools are what we use when _working on/in_
the magnets. I'm curious about your ring - does a magnet stick to it?
Could the moving around have been, instead, a _reluctance_ to move
in the field? A subtle difference.

One fun trick with an MRI magnet - get an empty soda can. Hold it up
right on two fingertips, and let it tip. If you're tipping the length
of the bore, it'll take maybe 5 seconds to tip over. If you go across
the bore, it'll fall over normally. The magnetic field is inducing eddy
currents in the can if it falls in a way that changes which flux lines
it's cutting (the long way) which gives you that resistance to movement.
Same effect with a coin on edge, tipped over. LOTS of force
(resistance to movement) on a 2'x2' aluminum door on the test systems -
those don't get a full screen room, you just enclose the bore on both
ends. The trapdoor, when the magnet is down, takes a good 5-10 seconds
to open, and it doesn't matter much how hard you pull on the sucker, it
moves at it's own speed. Really fun when you open the door on a magnet
that's not at field, you nearly fall on your ass because there's not the
resistance you expect...

On Fri, 27 Jan 2006 18:18:47 GMT, Ignoramus13653 wrote:
On Fri, 27 Jan 2006 11:58:40 -0600, Mike Berger wrote:
There's the six year old killed by the flying oxygen tank
when the MRI was turned on.

http://www.mercola.com/2001/aug/15/mri.htm

Thanks. A very scary and fascinating story. A little below was a
mention of a police officer's handgun pulled out of his hands and
accidentally firing -- of interest to you due to your sentiments
related to guns.

Heh. Poor Mike won't know which machine to blame in that case. Me, I
blame the cop, but I'm a personal responsibility kind of person.

"Dave Hinz" wrote in message
...
On Fri, 27 Jan 2006 11:07:58 -0700, Charles Spitzer
wrote:

"Steve B" wrote in message
news:kctCf.14046$JT.13348@fed1read06...

One of the tekkies said that the magnets caused metal to spin or be
pulled
out of the body.

The tekkie in question should stick to pushing buttons, because he's not
qualified to describe the physics involved.

He demonstrated how powerful it was by giving me a metal
object.

The force on an object, at a given distance, is proportional to it's
mass. First, he shouldn't be bringing ferrous objects into the scan
room, ever, for any reason. Second, he shouldn't be telling people that
metal could "spin or be pulled out of the body" because it's complete
and utter horse****.

I held it up at arms length about ten feet from the MRI, and it
felt like I was trying to twist a very stuck door knob.

Well, sure. It aligns with the flux lines of the field. Just like a
tiny little metal sliver...only thousands of times more forcefully.

my silver alloy wedding ring jumped around when i was in the mri tube
last,
but the Ti plate in my neck didn't seem to move around, although they
were
worried about it some when i told them i had one.

That is another example of a scan tech who doesn't understand their
technology. Titaniaum hand tools are what we use when _working on/in_
the magnets. I'm curious about your ring - does a magnet stick to it?
Could the moving around have been, instead, a _reluctance_ to move
in the field? A subtle difference.

well, i'm not sure it's pure Ti, nor the screws used to hold it to the bone.
on an xray, the screws look like 1" fine thread drywall screws.

no, a magnet, even a super magnet doesn't stick to the ring. i thought it
was reluctance too, as it seemed to try to lineup a certain way in the tube.
it almost had enough force to move my finger if i relaxed my hand. do the
force lines move in an mri? i wondered if they'd generate eddy currents in
the ring at the time.

a neat trick: suspend a large horseshoe magnet on a string centered over an
Al plate that is on a low friction turntable. rotating the magnet will cause
the Al plate to rotate.

Better to be danged than dangled

On Fri, 27 Jan 2006 12:07:42 -0700, Charles Spitzer wrote:

"Dave Hinz" wrote in message
...

Titaniaum hand tools are what we use when _working on/in_
the magnets. I'm curious about your ring - does a magnet stick to it?
Could the moving around have been, instead, a _reluctance_ to move
in the field? A subtle difference.

well, i'm not sure it's pure Ti, nor the screws used to hold it to the bone.

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.

on an xray, the screws look like 1" fine thread drywall screws.

Yup.

no, a magnet, even a super magnet doesn't stick to the ring. i thought it
was reluctance too, as it seemed to try to lineup a certain way in the tube.
it almost had enough force to move my finger if i relaxed my hand. do the
force lines move in an mri?

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 wondered if they'd generate eddy currents in
the ring at the time.

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.

a neat trick: suspend a large horseshoe magnet on a string centered over an
Al plate that is on a low friction turntable. rotating the magnet will cause
the Al plate to rotate.

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...

On 27 Jan 2006 19:40:04 GMT, Dave Hinz wrote:

On Fri, 27 Jan 2006 12:07:42 -0700, Charles Spitzer wrote:

"Dave Hinz" wrote in message
...

Titaniaum hand tools are what we use when _working on/in_
the magnets. I'm curious about your ring - does a magnet stick to it?
Could the moving around have been, instead, a _reluctance_ to move
in the field? A subtle difference.

well, i'm not sure it's pure Ti, nor the screws used to hold it to the bone.

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.

on an xray, the screws look like 1" fine thread drywall screws.

Yup.

no, a magnet, even a super magnet doesn't stick to the ring. i thought it
was reluctance too, as it seemed to try to lineup a certain way in the tube.
it almost had enough force to move my finger if i relaxed my hand. do the
force lines move in an mri?

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 wondered if they'd generate eddy currents in
the ring at the time.

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.

a neat trick: suspend a large horseshoe magnet on a string centered over an
Al plate that is on a low friction turntable. rotating the magnet will cause
the Al plate to rotate.

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...
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

Ignoramus13653 wrote:

On 27 Jan 2006 16:18:23 GMT, Dave Hinz wrote:
On Thu, 26 Jan 2006 22:39:58 -0600, Martin H. Eastburn wrote:
And if you go to get an MRI - our bodies might have metal flecks within.
Be sure to mention it - as the metal gets hot and burns.

No, it doesn't get hot or burn. (I worked in engineering on MRI scanners
for ~12 years). It can cause image distortion localized around the
metal (very local effect for slivers, nearly invisible). If you've got
metal in your eyes, they may choose not to use MRI on you, though.

I'd be happy to discuss this in as much detail as you'd like.

Dave, I am interested in MRIs in general, so if you have any stories
to share, or interesting facts, that would be great.

i

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

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:
On Thu, 26 Jan 2006 22:39:58 -0600, "Martin H. Eastburn"
wrote:


And if you go to get an MRI - our bodies might have metal flecks within.
Be sure to mention it - as the metal gets hot and burns.

Martin

I had to get a cat scan of my eyes before the MRI. They said the
magnet could drag any metal chips through my eyeball. Ouch. It was
interesting that my non-ferrous wedding ring moved with sound of the
thing.
ERS

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



Grant Erwin wrote:

I sometimes volunteer at a local detention facility, and they have a
metal detector. Last night I was up there and hadn't had time to change
out of my work clothes, and I triggered the metal detector even with no
metal on my person whatsover. The guy running the wand asked me if I
happened to work in a machine shop and I said yes, and he said work
jeans from a machine shop or steel fab shop can trigger a scanner no
problem.

I would have never guessed. Turned out this particular officer used to
be a machinist, and he had specific knowledge on the subject.

I'll be danged.

GWE

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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 Hinz wrote:
On Thu, 26 Jan 2006 22:39:58 -0600, Martin H. Eastburn wrote:

And if you go to get an MRI - our bodies might have metal flecks within.
Be sure to mention it - as the metal gets hot and burns.


No, it doesn't get hot or burn. (I worked in engineering on MRI scanners
for ~12 years). It can cause image distortion localized around the
metal (very local effect for slivers, nearly invisible). If you've got
metal in your eyes, they may choose not to use MRI on you, though.

I'd be happy to discuss this in as much detail as you'd like.

Dave Hinz


----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
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----= East and West-Coast Server Farms - Total Privacy via Encryption =----

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:
"Dave Hinz" wrote in message
...

On Fri, 27 Jan 2006 11:07:58 -0700, Charles Spitzer
wrote:

"Steve B" wrote in message
news:kctCf.14046$JT.13348@fed1read06...

One of the tekkies said that the magnets caused metal to spin or be
pulled
out of the body.

The tekkie in question should stick to pushing buttons, because he's not
qualified to describe the physics involved.


He demonstrated how powerful it was by giving me a metal
object.

The force on an object, at a given distance, is proportional to it's
mass. First, he shouldn't be bringing ferrous objects into the scan
room, ever, for any reason. Second, he shouldn't be telling people that
metal could "spin or be pulled out of the body" because it's complete
and utter horse****.


I held it up at arms length about ten feet from the MRI, and it
felt like I was trying to twist a very stuck door knob.

Well, sure. It aligns with the flux lines of the field. Just like a
tiny little metal sliver...only thousands of times more forcefully.


my silver alloy wedding ring jumped around when i was in the mri tube
last,
but the Ti plate in my neck didn't seem to move around, although they
were
worried about it some when i told them i had one.

That is another example of a scan tech who doesn't understand their
technology. Titaniaum hand tools are what we use when _working on/in_
the magnets. I'm curious about your ring - does a magnet stick to it?
Could the moving around have been, instead, a _reluctance_ to move
in the field? A subtle difference.


well, i'm not sure it's pure Ti, nor the screws used to hold it to the bone.
on an xray, the screws look like 1" fine thread drywall screws.

no, a magnet, even a super magnet doesn't stick to the ring. i thought it
was reluctance too, as it seemed to try to lineup a certain way in the tube.
it almost had enough force to move my finger if i relaxed my hand. do the
force lines move in an mri? i wondered if they'd generate eddy currents in
the ring at the time.

a neat trick: suspend a large horseshoe magnet on a string centered over an
Al plate that is on a low friction turntable. rotating the magnet will cause
the Al plate to rotate.



----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

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 Hinz wrote:
On Fri, 27 Jan 2006 12:07:42 -0700, Charles Spitzer wrote:

"Dave Hinz" wrote in message
...


Titaniaum hand tools are what we use when _working on/in_
the magnets. I'm curious about your ring - does a magnet stick to it?
Could the moving around have been, instead, a _reluctance_ to move
in the field? A subtle difference.

well, i'm not sure it's pure Ti, nor the screws used to hold it to the bone.


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.


on an xray, the screws look like 1" fine thread drywall screws.


Yup.


no, a magnet, even a super magnet doesn't stick to the ring. i thought it
was reluctance too, as it seemed to try to lineup a certain way in the tube.
it almost had enough force to move my finger if i relaxed my hand. do the
force lines move in an mri?


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 wondered if they'd generate eddy currents in
the ring at the time.


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.


a neat trick: suspend a large horseshoe magnet on a string centered over an
Al plate that is on a low friction turntable. rotating the magnet will cause
the Al plate to rotate.


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...


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Charles Spitzer wrote:
....
a neat trick: suspend a large horseshoe magnet on a string centered over an
Al plate that is on a low friction turntable. rotating the magnet will cause
the Al plate to rotate.

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

On Fri, 27 Jan 2006 21:32:18 -0600, Martin H. Eastburn wrote:
Why did my friend get his body wanded and picked through - finding all before ?

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.

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

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

On Fri, 27 Jan 2006 21:45:44 -0600, Martin H. Eastburn wrote:
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.

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.

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:
Ignoramus13653 wrote:

On 27 Jan 2006 16:18:23 GMT, Dave Hinz wrote:

On Thu, 26 Jan 2006 22:39:58 -0600, Martin H. Eastburn wrote:

And if you go to get an MRI - our bodies might have metal flecks within.
Be sure to mention it - as the metal gets hot and burns.

No, it doesn't get hot or burn. (I worked in engineering on MRI scanners
for ~12 years). It can cause image distortion localized around the
metal (very local effect for slivers, nearly invisible). If you've got
metal in your eyes, they may choose not to use MRI on you, though.

I'd be happy to discuss this in as much detail as you'd like.

Dave, I am interested in MRIs in general, so if you have any stories
to share, or interesting facts, that would be great.

i


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

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Martin H. Eastburn wrote:

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.


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

On Sun, 29 Jan 2006 04:34:10 GMT, Richard Lamb wrote:

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 ?

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.

Or are we doing something else here?

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

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:
Martin H. Eastburn wrote:

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.


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

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Martin H. Eastburn wrote:

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



Thank you, Sir.


richard