Dear AMMRLer's
I reposting this since I understand there was some problem with the format
on the original summary.
Regards,
Joe Dumais
Thanks to everyone who responded to my question about the use of hearing
aids in NMR labs. There were quite a few replies and I have include them
below. Some of the responses discussed Cochlear implants and they are
mixed in with the responses about hearing aids.
The emails fell into two basic categories
1) People who have used them and have left them in their ears near magnets
of 11.74 T or higher with no permanent damage to the aid or their ears.
2) The better safe than sorry group that suggests removing the hearing
aids when near high field magnets.
There was one report of a hearing aid not working after exposure to the
stray field from an unshielded 11.74 T magnet and two emails placing the
acceptable stray fields near 40-50 Gauss.
It is hard to argue with the better safe than sorry idea given the cost of
the devices but removing them at the console (a multiuser station for
chemists) may lead to the device getting mislaid, dirty, chemically
contaminated or even crushed under logbooks, notebooks or manuals.
A few years back one of my biker type (motorcycle, not bicycle) users had
brought in a large dog's dish to temporarily store his many metallic
items, maybe I need to revive that bowl for a safe hearing aid location!
Thanks.
Regards,
Joe
________________________________________________
In short, let me summarize my reply to him in general terms.
Here is my story. I am the victim of sudden hearing loss. My left
side went out in the early 70's, below the threshold of a hearing aid.
1981 the right side followed, stabilized at about a 50 db loss. I have
worn hearing aids on the right since.
At first, fairly clunky analog models, followed by smaller analog
models. Presently I rely on a digital Widex Senso that I have had
for several years, with an older analog unit for backup.
My experience around magnets: Generally, there is no problem
with fills. With probe changes, i.e. getting your head close to the
underside of a magnet, the aid might go silent, due to the transducer
having magnetic parts. However, I never had an irreversible effect.
Moving away from the magnet every aid I had immediately went
back to normal.
Let me know if I can help you further
Cheers
_______________________________________________
I've used a Phonak (Savia) behind-the-ear aide for several years around
an unshielded 500 and a shielded 600 without any problems either to the
hearing aide or pull of the magnet on the aide itself.
____________________________________________
A graduate student here removed both hearing aids, put the sample in,
and put the hearing aids back on. Then she ran the spectra. This was
not a problem for her or me. To do anything else with an expensive
magnet, 2 expensive hearing aids, and the ears of a human being is
unthinkable.
___________________________________________
The largest problem would be any ferrite-core inductors, as they'd
pick up a field and the circuit tuning would change. Without knowing
the design details there's no way to know. I wouldn't expect a hazard
to the user as a hearing aid would be unlikely to contain enough
magnetic material to be dislodged from his ear; most metal parts in
hearing aids are copper, brass or stainless steel to resist corrision.
This phenomenon definitely affects pagers, as MDs in MRI
facilities learn (eventually). Normal operation can be restored by
degaussing. We keep a degaussing coil around for just this purpose, but
they're getting harder to find with the passing of the CRT. If your
user is willing to experiment, it's worth trying if you have a coil on
hand.
I can attest from personal experience that a watch with mechanical
parts (even if quartz-driven) will slow down or stop. I eventually gave
up and only use watches with electronic displays. An LCD display will
blank in a strong magnetic field, but works normally when removed from
the field.
_________________________________________
Try getting an account with
http://www.mrisafety.com/default.asp
____________________________________________________________
The problem with hearing aids is not only the device, but the battery.
There?s both the risk of displacement attractive forces and the
electromechanical effects on the sensitive workings of the hearing aid.
I?m not aware of any hearing aids that have been designated MR safe. I
think you?re probably looking at having the user remove the hearing aid
prior to approaching your magnet.
You might be interested in the video on this page which describes an
accident in which someone approaching an MRI had their hearing aids
destroyed...
http://mrimetaldetector.com/blog/?p=5
----------------------------------------------------
Any user having hearing aids have removed them prior to enter the 50 gauss
area. Given their costs (my wife has two) I think it's better to be safe
than sorry.
_____________________________
I recently had to address this issue in my lab. I am attaching three
correspondences that you might find informative. As a result of the
information that I found, I have a sign denying access to my lab with
anyone with a cochlear ear implant and recommending that anyone with
hearing aids remove them (just to be on the safe side). The highest field
instrument that I have in my lab is a shielded 500.
__________________
I would go directly to the manufacturers on this, as I really could not
tell you. I would guess that it is far more critical for cochlear
implants than for hearing aids. With hearing aids, any potential risk
would not be to the patient, but to the device; in the case of implants,
it is both.
Try a couple of manufacturers and see if you can speak with engineering:
GN Resound (Hearing Aids) - Tollfree: 800-248-4327
http://www.gnresound.com/
Cochlear Americas - (Implants) Tollfree: 1 800 523 5798
http://www.cochlearamericas.com/
___________________________________
I posed the question to someone on our research team who forwarded the
question on to the product development team in Denmark. The person who
provided the answer actually had studied this issue and could say that you
would be safe with 40 Gauss (a safety factor was built into that value).
________________________________________
I have heard back from one of the engineers. I am copying his response to
me below. I hope this is useful information for you. Please let me know
if you need me to attempt to find any other information for you.
"While there is no formal FDA approved guidance that I am aware of for the
US, the N24 devices have been shown to be safe for MRI up to 0.2 Tesla
with the magnet in place and up to 1.5 T with the magnet in place, but
with a compression bandage over the implant. These are the current
recommendations for the EU (Europe) and AP (Asia Pacific). 0.2 T is 2000
Gauss and therefore the N24 has been shown to be safe well above the 5 G
line for the implant. I know of no study that evaluated the externals for
MRI. Our guidance has always been to remove the externals prior to
entering the MRI scanner room. Generally the 5 G line is somewhere
outside the scanner room, so the 5 G line would seem to be acceptable for
externals.
________________________________________
I would imagine that to be safe all hearing aids should be removed prior
to
approaching a magnet, as they all presumably have small speakers in them
with magnetic components. Perhaps some of the speakers are
piezoelectrically driven, and maybe those would be ok (hearing loss is
usually confined to the upper frequency ranges, and piezo tweeters are
very
common in audio speaker technology).
I would be interested to see the results of your query.
_____________________________________
Any user having hearing aids have removed them prior to enter the 50 gauss
area. Given their costs (my wife has two) I think it's better to be safe
than sorry.
___________________________________________
My wife wears hearing aids, and she does removed them before approaching
our magnets.
She did inadvertently forget to remove them once when approaching our
unshielded 500MHz magnet. The effect she experienced was that her
hearing aid shut off. In fact, it may have fried the battery.
She has been much more careful ever since to make sure her hearing aids
are removed prior to approaching any of our magnets, even the actively
shielded ones.
I'm not exactly sure what is happening to the hearing aids in the
presence of a strong magnetic field (I can speculate about numerous
possibilities). But since these are rather expensive pieces of
technology, we do not take any chances.
I don't know the specific "brand" of hearing aids she uses, but I know
that the type of hearing loss that she has is with the high frequency
range. She basically has suffered 50-60 dB loss at about 1000Hz, and
the loss gets progressively worse to higher frequency. So the hearing
aids amplify higher frequencies and filter lower frequencies to the
point where she can "hear normally."
________________________________________
http://www.mrisafety.com/
Has this to say:
Hearing Aids and Other Hearing Systems
External hearing aids are included in the category of
electronically-activated devices that may be found in patients referred
for MR procedures. Exposure to the magnetic fields used for MR
examinations can easily damage these devices. Therefore, a patient or
other individual with an external hearing aid must not enter the MR
environment. Fortunately, to prevent damage, an external hearing aid can
be readily identified and removed from the patient or individual prior
to permitting entrance to the MR system room.
Other hearing devices may have external components as well as pieces
that are surgically implanted. Hearing devices with external and
internal components may be especially problematic for patients and
individuals in the MR environment. Accordingly, patients and individuals
with these particular hearing devices may not be allowed into the MR
environment because of the risk of damaging the components. The
manufacturers of these devices should be contacted for current MRI
information.
(For information on other hearing systems, refer to the section Cochlear
Implants.)
[MR healthcare professionals are advised to contact the respective
manufacturer in order to obtain the latest safety information to ensure
patient safety relative to the use of an MR procedure.]
REFERENCES
Shellock FG. Magnetic Resonance Procedures: Health Effects and Safety.
CRC Press, LLC, Boca Raton, FL, 2001.
Shellock FG, Kanal E. Magnetic Resonance: Bioeffects, Safety, and
Patient Management. Second Edition, Lippincott-Raven Press, New York,
1996.
[For these devices, MR healthcare professionals are advised to contact
the respective manufacturer to ensure that the latest safety information
is obtained and carefully followed in order to ensure patient safety
relative to the use of an MR procedure.]
REFERENCES
Shellock FG. Pocket Guide to MR Procedures and Metallic Objects: Update
2001, Seventh Edition, Lippincott Williams & Wilkins Healthcare,
Philadelphia, 2001.
Shellock FG. Reference Manual For Magnetic Resonance Safety, Implants,
and Devices: 2006 Edition. Biomedical Research Publishing Group, Los
Angeles, CA, 2006.
Shellock FG. Magnetic Resonance Procedures: Health Effects and Safety.
CRC Press, LLC, Boca Raton, FL, 2001.
Shellock FG, Kanal E. Magnetic Resonance: Bioeffects, Safety, and
Patient Management. Second Edition, Lippincott-Raven Press, New York,
1996.
http://www.mrisafety.com/safety_article.asp?subject=150
______________________________________
Joe Dumais, Ph. D.
Associate Research Professor
Director of Research Instrumentation Facility
Department of Chemistry / University of Nebraska Lincoln
834 Hamilton Hall / PO Box 880304
Lincoln, NE 68588-0304
Phone (402) 472 6255 / Fax (402) 472 9402
http://www.chem.unl.edu
Received on Mon Sep 22 2008 - 11:00:30 MST