PDA

View Full Version : Summary of responses for doing EMG inside an MRI



Daniel Magnusson
11-26-1998, 04:38 AM
Hello all,

As promised here is a summary of the responses I got to the question I
posted on doing EMG in an MRI. Thanks to all that replied. I got a number of
good leads. I will repeat the question I posed and then summarize the
answers. One group, lead by Dr. Seong-Gi Kim out of the University of
Minnesota seems to have solved the problem. Thanks to Anita Vasavada for
that information.
----------------------------------------------------------------------------
---------------------------------------------------
The Questions
----------------------------------------------------------------------------
---------------------------------------------------

I am interested in the possibility of doing some EMG measurements using
surface and/or indwelling (a.k.a. needle, fine-wire) electrodes while human
subjects are in a Magnetic Resonance Imaging (MRI) scanner. I am aware that
wires (even non-ferric ones) placed in a magnetic field may cause a current
to be generated. The resultant heat and current in the wire(s) may be
harmful/painful to the subjects, and is experimentally (and ethically)
undesirable. I will have access to a 0.2 T MRI machine, and (potentially),
some machines with a higher field strength.

After a comprehensive literature search, I have not been able to find any
articles which have attempted to do this type of experiment (in any muscle
group).

My first question to the Biomech-L community: Does anyone know of any
individual or group, anywhere, that has made any attempts to do this type of
research? What type of success did they have with it? what kind of setup did
they use? How can I contact them?

My second question to the Biomech-L community: Assuming that no one has been
able to do this successfully, does anyone have any suggestions as to how
this could potentially be setup?

I have thought of utilizing magnetically shielded components (like wires and
pre-amplifiers) but I am not sure if such devices actually exist. All
searches (via web search engines) have failed to turn up any responses to
"magnetically shielded wires/cables/components". I have also contacted some
manufacturers directly to see if there is anyone who may be able to supply
such equipment. If anyone has used these type of components before, or knows
of any manufacturers/distributors who can supply these devices, I would
appreciate getting all relevant contact information.

__________________________________________________ ____________________
The Answers
__________________________________________________ ____________________

EKG (surface EMG!) is often monitored in the magnets. I suggest
you start there... I'd be interested in what you find.

-Francisco

************************************************** *************
Francisco Valero-Cuevas, PhD
__________________________________________________ _____________________

You should contact:

Tony Hill
Magnetic Resonance Unit
4150 Clement St, 114M
San Francisco, CA 94121
(415) 750-2158

Lee Barnes
B & L Engineering
TEL: (714) 505-9492
FAX: (714) 505-9493
Email: lee@bleng.com
Web Site: www.bleng.com
__________________________________________________ ____________________


When you collect EMG you are receiving a very small signal from the
surface of the skin, amplifying it and sending it on for processing. You
know that electrical noise is a problem especially since the human body
acts like an antenna collecting and amplifying signals nearby.
Most EMG amps filter out 60hz noise produced by lights etc. How do you
intend to overcome noise problems produced by the RMI electrical system.
Ditto for the energy absorbed into the body and transmitted to your
electrodes.
Noise issues aside, your electrode wires will act like an antenna
sending (hopefully small) electrical signals into the muscle possibly
giving you an abnormal muscle picture.
Accoustic systems have been mentioned on this newsgroup and may be
better for you.

Dave Grimshire
Dalhousie University
Halifax
__________________________________________________ _____________________

I have done some measurements in hand muscles with fine wire electrodes
while
magnetically stimulating the cerebral cortex of the subjects. The
artifact was always huge. I do not know how the more uniform magnetic field
will
influence your measurements, I expect it will. However, there are these
goggles
that you can put on while you are in the MRI and watch video clips. I
suppose
the manufacturers of these mini screens had the same problem.
They obviously solved it. I once watched Tom and Jerry in one experimental
session while being in the magnet. It was so funny that I shook with
laugther
which marred all the measurements.

In addition, in the trauma industry Titanium implants are said to disrupt
images

less than Stainless Steel implants, maybe that might be a hint. I do not
know
how silver wires or electrodes behave.

Greetings
Erhard
Erhard J. Huesler
Biomechanics Lab
Osteo AG

__________________________________________________ _____________________

Contact Dick Stegeman from Nijmegen
e-mail: d.stegeman@czzo.knf.azn.nl

Best wishes,
At Hof
Department of Medical Physiology
University of Groningen
__________________________________________________ ___________________

I am not aware of any work on recording EMG in an MR
environment. The nearest application I know of is the
recording of EEG and evoked potentials from surface
electrodes. Several groups have had some success with this
in MR scanners. I suggest you look at Muri et al, Magn.
Reson. Med. 39;18-22 (1998) to start with. Your literature
searches should pick this up, and there will be other
related articles I'm sure.

Hope this is helpful.

Your sincerely

Ian Marshall


Ian Marshall, PhD
Senior Lecturer
Department of Medical Physics
Western General Hospital
EDINBURGH
__________________________________________________ _____________________

A colleague of mine has informed me that Seong-Gi Kim at University of
Minnesota has been able to measure EMG activity in MRI. You may want to
contact him. Electrodes may be available from Kappa Medical or Conmed.
I'm sorry, I don't have much more information than that.

Anita Vasavada
Northwestern University
__________________________________________________ _____________________

Yes, we did have solution to do it. There is not much information, but you
can check
NeuroReport, Vol 8, 1257-1261 (Ricter et al.).

Seong-Gi Kim
__________________________________________________ _____________________

There are both magnetic and radio frequency fields in an MRI to be
considered. In the .2T magnet, the RF will be at about 8 MHz, and may be
more of a problem than the constant magnetic field form the magnet. An
older, but excellent reference on shielding for this sort of
interference is Ralph Morrison's book _Shields and Grounds in
Instrumentation_ (approximate title, but it starts with Shields and
Grounds. This was written sometime in the '60s and reflects his
experience in design and production of amplifiers and power supplies for
rocket test stands, where 10 mv signals must be measured in the presence
of hundreds of volts of common mode interference. Bob

Bob Woolery
__________________________________________________ __________________

I think that the book that you're thinking of is "Grounding and Shielding
Techniques in Instrumentation" which seems to have been out of print since
that late 80's.
Ralph Morrison has another book called just "Grounding and Shielding
Techniques" which came out in February 1998.

Regards,
Edmund Cramp,
Motion Lab Systems, Inc.
__________________________________________________ _____________________

I supposed to respond you about EMG. We did get EMG signals, but it is not
clear whether EMG activity is dominat in signals.
Anyway, I will fax you a manuscript about EMG setup. You can find detail
setups in this manuscript. Please acknowledge the following paper for your
future publications;
W. Richter, P.M. Andersen, A.P. Georgopoulos, S.-G. Kim, Sequential activity
in human motor area during a delayed cued finger movement task studied by
time-resolved fMRI, NeuroReport, 8, 1257-1261, 1997.

Good luck.

Seong-Gi Kim
__________________________________________________ _____________________

Our setup is based on surface electrodes (carbon-based). We used the same
setup for detecting eye movements during fMRI. Theoretically, as long as
you
use carbon-based electrodes and wires, it will be okay. However, in your
case,
surface elctrode may not be good enough to detect EMG. If you can find
carbon-based elctrodes, I think it will be fine.

Grounding information came from one of my colleagues, who is doing lots of
EMG
recording in patients. We found that setup was very effective to reduce
noises.

I hope this is helpful for you.

Seong-Gi Kim
__________________________________________________ _____________________

Again thanks to all who responded. If anyone is interested in contacting
some of the people that I have listed above, I do have the e-mail addresses
of most of them.

Regards,

Daniel Magnusson B.Sc.
Master's student in Biomechanics
Human Performance Laboratory
Faculty of Kinesiology
University of Calgary
Calgary, Alberta, CANADA
T2N 1N4
Tel: 1 403 220-3432
Fax: 1 403 284-3553
email: dan@kin.ucalgary.ca

---------------------------------------------------------------
To unsubscribe send SIGNOFF BIOMCH-L to LISTSERV@nic.surfnet.nl
For information and archives: http://isb.ri.ccf.org/biomch-l
---------------------------------------------------------------