Lots of great advice on the pacemaker issue. As advised, I think
we'll be contacting the pacemaker manufacturer to get their input and
find out the tolerance of the pacemaker toward magnetic fields. From
what Alan Ronemus said the pacemaker technology had improved greatly
and modern pacemakes shouldn't have a problem, although 5 gauss is
still the normal limit for anyone with a pacemaker. Elwood and
Robert suggested that I just provide the occupational safety office
and the users doctor with the magentic field info and let them take
care of it, I'll definitely give them the final call on safety.
The 5 gauss line for the narrow-bore unshielded 300MHz oxford
magnet is ~6'/2m axially, and ~5'/1.5m vertically (from the center of
the magnet). The Varian R2D2 is 1.7m both vertically and axially.
Thanks to all who replied, your input was greatly appreciated and
helpful. Cheers,
Chris
---------
Hi Chris:
Pacemakers were shown nearly 20 years ago to be affected by magnet fringe
fields when they reached 10G. Thus, the magic "safety" number we hear for
magnets is the 5G line, half that magnetic field strength. Today's
pacemakers are probably not nearly as sensitive to magnetic field as the old
ones, but the NMR field still uses 5G lines as the safety margins. You
probably have an idea of where the 5G lines are (that's where some form of
marking would have been put at the time of installation). If you don't have
them, you can use the following as a guide for the 300s.
Unshielded 300 - 5G line - 6' 0" horizontally (at the center of the magnet
about 34" off the floor, smaller as you go higher or lower, since the 5G
"volume" is ellipsoidal).
Unshielded 300 - 5G line - 4' 9" vertically (from the center, so add the
~34" off the floor to the vertical going up and subtract it going down)
While 300 unshielded magnets vary (Oxford shiny magnets, R2D2s, Magnex, or
Bruker), these numbers will not vary by more than a foot, so you should be
able to make up a safe distance to keep your guest safely out of a dangerous
fringe field.
Hope this helps!
Regards:
Paul Cope
Technical Sales Representative
Bruker BioSpin Corporation
-------
Usually, they say 5 gauss. However, someone in our lab received a
pacemaker a couple of years ago, and I called the device maker. They
told me 10 gauss. I think that was for constantly being in the field. I
think walking quickly through, they said it could go a little higher, but
who wants to take the chance.
My guess is that the technology has improved, but there still might be
people out there with older models. I would call the manufacturer and ask them
what field strength they need to stay out of.
We borrowed a gaussmeter from a local university and measured the stray
field ourselves. BU is Boston University, right? I am sure someone at
one of the facilities in Boston has a gauss meter. They cost a few hundred
dollars if you want to buy one.
My Oxford 300 (narrow bore, unshielded, ca. 1980) manual says the axial 5
gauss line is about 2.2 meters and the radial 5 gauss line is
about 1.7 meters from the center. The axial 10 gauss line 1.8 meters and
the radial 10 gauss line is 1.3 meters from the center.
Ben
Benjamin G.M. Chew, Ph.D.
Senior Staff Scientist
Coordinator, Spectroscopy and Microscopy Group
Analytical Services and Technology
Ashland Incorporated
-------
Hi Chris,
I would have the user contact the manufacture of the pace to find out this information.
Then have the user present this information to you and your safety people. That way you
and your facility are protected if something happens.
Elwood
-------
Chris
The magnetic field that is generally considered "safe" for persons with
medical implants is < 5 Gauss. Where that 5 Gauss line depends on several
factors. The field, the shielding, and the bore of the magnet (wide bore
vs narrow bore). We are currently using an unshielded Oxford 300MHz wide
bore magnet. The 5 Gauss line for this magnet is approximately 7.5 ft
radially, and 9 ft axially from the magnet center. If you have a narrow
bore magnet, these distances will be slightly less. If you do not have the
original documentation and specifications that came with the magnet, I
would suggest hiring an external company to come in and map the 5 gauss
lines (I think there are several that will provide this service).
Don't hesitate to drop me a note if you have any further questions, and if
you would like, I can send you a report and some references regarding
magnetic field safety.
Best of luck,
Chris Hudalla
-------
I have information for the Oxford Magnet.
5Gauss is the generally accepted field strength that begins to become a
hazard for people w/ medical implants.
These distances are from the CL or center line of the magnet, NOT FROM THE
FLOOR!! So, to find the overall axial field height add distance from the
floor to the center of your magnet.
For a 300/54mm bore: Radial 5G limit 1.70 meters (~5'8"), Axial 5G 2.2
meters (~7'3")
Just in case you have the 300/89mm bore: Radial 5G limit 2.2 meters
(~7'3"), Axial 5G 2.75 meters (~9')
Jim Simpson
Invista SRL
Orange, TX.
-------
Chris;
Modern pacemakers don't use a magnetic resets as early ones did, and all such units
are now out of service. The remaining concern might be induced EMFs on the leads, but
pacemaker leads are usually shielded. It is generally good practice to keep non-users
outside the 5 G line, more for the good of the NMR experiment than any risk to the user.
The small magnets you're dealing with won't be a problem on floors above and below,
although someone working in the ceiling below might disrupt an experiment. A request to
Varian would probably get you a copy of their pre-installation planning manual, which
includes stray field data for a variety of magnets.
Regards,
Alan
-------
The standard for "public" areas are 5 Gauss. This is a very old standard based upon the
poorest quality pacemaker made in the 1980's being sent into default mode at the 20 Gauss
level.
The fringe field numbers are available from the manufacturer. Anything greater than that
distance is safe, but the field will effect bulging monitors and test equipment at much
lower fields.
Rob
-------
We had one of our open shop users get a pacemaker and the manufacturer (or
hospital) came to our site and mapped out the "safe areas" throughout the
building. We had no problems with hallways or rooms surrounding our labs.
Unfortunately, he is no longer allowed to enter our labs, but the rest of
the building was safe.
-Carrie Furnish
-------
Chris,
I have manuals for both - I can fax the pages to you if you'd like.
On the R2D2, it looks like the 5 G line is about 1.7 m from the center both axial and
radial. In my Oxford manual it says a 300/54 would have the 5 G line 2.2 m axial and
1.77 radial.
--Sara
-------
Hi Chris,
The fringe fields of a 300 are not strong enough to affect a pacemaker on
the floors above or below. Vertically, the 5G line is 2.2 meters from the
magnet center.
Cheers, Jerry
Jerry Hirschinger, NMR Instrumentation Specialist
Purdue Interdepartmental NMR Facility
-------
Chris;
These spec's are device specific and should be a dual consultation between
the users doctor and the pacemaker manufacturer. You should not be involved
other than providing the field lines which are available in the varian
installation and planning book on their webspace.
Robert Harker
Engineer
-------
here's a quite recent official study about modern pacemakers and
magnetic fields (in MRI scanners). they seem to be surprisingly
immune against reasonable magnetic fields. I showed this to
our workplace safety people when we installed our latest 900 MHz
magnet, and they were amazed ("seems our generally used 5 Gauss limit
is completely irrelevant!").
hope you can use it,
ciao,
gg
Received on Thu Sep 01 2005 - 13:07:27 MST