Due to the recent resurgence of interest in cochlear implants, I am
sending my summary which apparently I never managed to get out when I
brought up this issue on Jan. 18, 2006. Here is my original post:
I thought I'd seen all of the safety issues in NMR, but here is a new
one for me. A student with cochlear implants wants to be trained on
our Gemini-200, and we are wondering if she should be within the 5
Gauss line (or even in the room). She says that her doctor won't let
her into an MRI magnet. The implants are some kind of sound
transducer mechanically linked to the eardrum and a wire which makes
electrical contact with a nerve. I don't know if it has active
electronics (batteries, etc.) or not. It's possible that the problem
with MRI is the rapid gradients inducing currents in the wires,
rather than the magnetic field. Of course, the field is also much
stronger in the MRI than the stray field experienced inserting a
sample. Does anyone have any authoritative information on this
subject, or anecdotal for that matter? I would appreciate any
help. We could have someone insert the sample for her but she really
wants to be independent.
I got a very large number of responses, ranging from "She shouldn't
go near the NMR room" to "she will be fine using the instrument". In
the end the student decided to opt out of the NMR experiment
entirely, although she did enter the room and sat a few meters from
the magnet and watched the other students and participated and asked
questions. She said that even at that distance she could "hear" a
lot of weird stuff from the magnet and possibly from the RF
pulses. Here is a summary of the responses:
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Neil,
I'd ask the student to ask her doctor who makes the device, and I'd
go right to the source for the best information. The manufacturer
should be able to supply you with a list of what materials are
present in the device and maybe give you a non-proprietary spiel on
how it works.
Based on the no-MRI rule, I'd say that the no-NMR is probably the way
to go. Eddy currents from moving around in a fringe field might
generate relatively large (and uncomfortable) currents in the wire on
the nerve...ow.
Remember, you're talking about maybe messing up somebody's brain, here.
Dear Neil,
For more detailed information regarding the safety of certain implants check
out
http://www.mrisafety.com/ by Dr frank Shelock. It is a great source of
information regarding MR safety of all types of medical implants. It
appears one type of implant is Magnet safe, but you would have to check
which type your student has.
Part of the issue with implants of this nature is the fact that strong
magnetic fields may disable the implant and render it in-operable, in
addition to the possibility of injury. So while it may be safe from a
personal injury stand point, the stray field near the magnet may lead to the
implant no longer working, requiring surgery to rectify, or replace the
device. My advice, in the absence of very strong evidence to the contrary
is that it would not be safe, or in the students best interests to be within
the 5 Gauss line, we certainly would not let her into the MRI scan rooms
here at our imaging facility (unless she had a cochlear implant that is
considered safe).
I hope this is helpful.
Neil,
It would be bad to let her near the magnet.
My mom just got a cochlear implant about a month ago. I haven't seen
it yet, as we live in different states, but she tells me she's had
fun sticking paper clips to the potent magnet implanted under her
skin. At least that's the idea I've gotten of her arrangement.
Also, my mom's doctors are very concerned about static shocks
damaging the electronics of the implant.
I'm afraid your user may have to settle.
Neil,
According to Magnetic Resonance; Bioeffects, Safety and Patient
Management, 2nd Ed., Shellock, Frank G, 1996, some cochlear implants
contain strong cobalt samarium magnets to align and retain an RF
coil. Others are electronically activated. Consequently MR procedures
are strictly contraindicated in people with these types of implants
because of risk of injuring the person (the book includes an image,
where a portion of an implant pierced the soft tissue inside a
patients ear!) and/or damaging or altering the function of the implant.
Granted, the fringe field of the 200 is going to be 3 orders of
magnitude less than the main field of an imaging mangnet, but I still
wouldn't let the user inside the 5G line without her doctor's written
permission (especially if she has the magnetic implant).
Just my two cents.
Neil,
I have a cochlear implant, and before I had it "put in" my doctor and I
worried about the magnetism issue, since there is actually a small magnet
implanted under the skin of the head. I also worried thought of the issue of
whether the magnetic field near the machine would cause induced electrical
currents within the internal or external electronics that would do some kind
of damage. Shortly before the surgery to implant the internal components, my
doctor informed me that his contacts with the device's manufacturer assured
him that there would be no issue with the magnet at the field strengths
observed outside the NMR machine. When I first arrived here, for the first
few months, I would shut off the external electronics before using the NMR
but after several incidents when I accidently forgot to and nothing went
wrong, I have since not given it another thought. I have never observed any
indication of electrical interference (i.e., buzzing sounds or other changes
in sound) when I approach the NMR machine so I don't think its an issue. For
the last three years or so, I always behave normally around the NMR machine
and I don't shut off the implant or do anything else different.
Neil,
Here is an excellent web resource for Magnetic Resonance Safety. The
specific article I forwarded talks about several different types of
auditory devices relative to magnetic safety. You may need to make a
login ID to see the article.
http://www.mrisafety.com/safety_article.asp?subject=22
While all the issues you mention may be why her doctor doesn't want
her in an MRI, but I suspect another problem is that the large RF
Fields generated by the RF pulse will induce currents along any wires
which will cause them to heat up like a light bulb filament. There
are documented cases of patients in MRI's with cardiac monitoring
leads burning the patient.
Does she know who the manufacturer of the implant is? They would know
better than the doctor.
Regards,
Neil,
Here is the e-mail response from one of our best CI people:
"Hi Bill,
The cochlear implant has a magnet implanted under the skin. She
should not go near the MRI. It could potentially dislodge the device.
She may want to be independent, but she should be careful. There is
the potential that the MRI machine could result in the device
extruding from the cochlea."
In a phone call the difference between NMR user and MRI subject was
discussed. Dislocation could still be a problem, but dislodgement
was considered to be less likely. It was also mentioned that there
were real possibilities of "serious discomfort" from currents
generated when the device moves in the field.
The last and the most strongly emphasized piece of advice from the
phone call was that you should get the name of the maker from the
student and talk to one of their engineers directly. They have a
strong interest in giving you accurate information.
This website:
http://www.wasa-shhh.org/cochlear_implants.htm
has these links to the manufacturers:
Cochlear Corp. (Cochlear Americas), maker of Nucleus system devices -
www.cochlearamericas.com.
Advanced Bionics, maker of High Resolution devices - www.advancedbionics.com.
Med-El Corp., makers of Pulsar and Combi 40+ devices - www.medel.com.
Hope this helps
Hi Neil,
A remarkable Australian invention I believe.
Cochlear implants have two components: an external part, consisting
of a microphone, digitiser and transmitter; and the internal implant,
which consists of a receiver and electrode array connected to the
cochlear. Of major significance is the fact that the implant contains
a magnet placed in the temporal bone, which holds the external
equipment against the head. There are now a number of cochlear
manufacturers, and a variety of models available, and of course there
have been a few studies done regarding the use of MRI with the
implants. The latest one that I know of is by Wackym et al., The
Laryngoscope, 2004, 114(8), pp1355-1361, which looks at a number of
manufacturer specific implants.
A number of cochlear models now have removable magnets - this may be
an option for MRI, but I doubt it is practical for putting your
sample in the NMR magnet, given that it requires two surgical procedures!
I don't think the main concern for NMR relates to the torque, induced
heating etc that is often associated with NMR and MRI, but rather the
demagnetisation of the implant magnet, and magnetisation of the
external microphone and associated electronic components. Some
studies have shown that the implant magnet can be partially
demagnetised up to 80% in 1-1.5 Tesla fields. This may render the
implant inoperable if it can no longer support the external
equipment. Recent studies, however, have shown no significant
demagnetisation but required specific head orientation, so I don't
think there is a clear answer.
One important thing to remember is that cochlear implants are for
life; any damage will involve significant medical procedures to
correct, and is not as simple as having to get a new VISA card
because we walked too close to the magnet.
Just my two cents worth, but my suggestion would be (as in every
situation) to put operator safety before any other option, and have
your student remain outside the 5 Gauss line.
I hope this helps with your decision.
Regards,
Neil,
Try the following links as starting points:
<
http://www.zak.co.il/deaf-info/old/ci-faq.html>
http://www.zak.co.il/deaf-info/old/ci-faq.html
http://www.nidcd.nih.gov/health/hearing/coch.asp
Let me know if you find something else related to that.
Hi Neil,
The 5G line of a 200 is so close to the magnet, she should be able use the
instrument and never cross it with her ears. However, I would not recommend
it due to the probability that the transducer could become magnetized or
dislodged from an accidental exposure. To know for sure, you would have to
check with the implant manufacturer. Also, you might check with your
insurance provider to see if the U. would be liable for any problem.
Good luck,
Neil,
If the doctor is so concerned then the lady should be wearing a medic alert
bracelet shouldn't she since he alrready told her no MRI?
To be absolutely sure with a good CYA, measure the maximum field exposure
possible inserting, probe tuning etc. Have your student get her doctor to
fire off a letter to the implant maker with the data because this has had to
have come up before. It might already be published in the device spec's.
If they should be willing to certify in writing no problems up to 25, 30, 45
.. guass etc. then you should feel Ok with it too.
Even with that I would ask your local safety officer for guidance as well
and if it were me I'd have her sign a special waiver of liability for any
known and unknown risks.
Neil,
I just read your post about your student with the cochlear implant.
You're right to be concerned about anyone with any biostimulation
implant. That includes pacemakers, insulin pumps, shunts, cardiac
monitors, implanted defibrillators, and cochlear implants (among a
host of others).
Depending upon the device, the concerns can be about magnetic
attraction (translational / torque forces), induced current, device
interference. Depending upon the device, the threat to the person's
health may not be from the immediate exposure to the magnetic field,
but rather from damage to the device or changes to the settings for the device.
There is a fairly extensive list of medical devices (implants and
onplants) available from the website www.MRIsafety.com
I would suggest investigating the specific model of the cochlear
implant on MRIsafety.com and find out what the limitations are for
magnetic exposure, and what concerns there may be for device
interference. It might turn out that the student can be in the fringe
field of the magnet, but it is advisable to prohibit anyone with an
implanted device to enter the magnet room without clearance from
their physician.
If you have any other questions or if I can be of any further
assistance, please don't hesitate to contact me.
Neil,
This email was forwarded to my by my co-worker Dr Margaret Eastman
since my daughter recently received a cochlear implant. Of course,
me working with big magnetic fields, I had the same concerns
regarding her implant and its safety around magnets so here are the
answers that I got from her audiologist and her implant team in Oklahoma City.
Briefly described, the implant itself has 2 parts, one implanted
inside and an outside part. The implanted part consists of
electrodes inside the cochlea (well within the ear), and a processor
(without batteries) with a magnet under the skin on top of the
skull. The outside part (totally removable) also has a magnet (that
attaches thru the skin to the implanted magnet to connect the 2 parts
together allowing the signals to get thru) and a processor, which
holds the programming along with a battery pack.
So, before an MRI I was told that the inside magnet must be removed
(thru a small incision) and obviously the outside part must be
removed and kept afar from the MRI instrument. I had no direct
answers regarding NMR but they told me that the major fear is that
the magnets will be affected by the magnetic fields. There is no
data of continuous exposure of the implanted part to magnetic fields,
since an MRI is most likely a one-time deal, so they don't know if a
constant exposure to magnetic fields will affect or not the inside
device. So, from these answers I would not allow my daughter to
enter the gauss line even without her outside device (without it, the
implanted person cannot hear) for fear that her inside magnet would
be affected and or damaged. If the student in question has no fear
that the magnet would be affected then I guess the student could be
allowed to enter the gauss line to insert the samples, but I would
strongly recommend not to expose the outside device to a strong magnetic field.
I hope this helps. Should you need more answers, please do not
hesitate to contact me, as I could put you in contact with my
daughter's audiologist.
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Thanks to all of you who responded, it was very helpful to us and to
the student and her family to have a wide variety of points of view.
Neil E. Jacobsen, Ph.D.
NMR Facility Manager
Department of Chemistry
119 Old Chemistry
1306 E. University
University of Arizona
Tucson, AZ 85721
520-621-8146
FAX 520-621-8407
Received on Thu Sep 27 2007 - 15:28:49 MST