Optimizing EMG/ESTIM BoNT injection Guidance

We would like to review Myoguide electrode Strategies for Optimizing EMG/ESTIM BoNT Injection Guidance Results. We have been received quite a few inquiries about what the optimal surface electrode placement approaches should be for procedures involving injection guidance using hypodermic needle electrodes and Myoguide EMG/ESTIM BoNT injection guidance system.

Firstly, I would like to refer you to our Myoguide training page. Please review the video instructions and have a look at the accordion file at the bottom of the page. I created the content in response to questions, issues, and the quest to acquire the best signal quality for EMG guidance, and most reliable stimulation experience for ESTIM guidance procedures.

Please keep in mind that Myoguide is a differential amplifier.  In other words, it functions by measuring the signal of interest (at the hypodermic electrode) and the signals from the surrounding area (surface electrode/ reference), and then subtracts those two signals from the signal acquired from the hypodermic electrode, leaving the salient signal of interest while subtracting the noise, referred to the ground (surface electrode).  

We refer to common mode rejection as the ability to discard the common noise signal that exists between the hypodermic needle electrode and the surface electrode.  Both these signals are referenced to the ground.  

Three leads are used:

  1. One “business end“: electrode (hypodermic needle electrode)
  2. One reference electrode (surface electrode nearby)
  3. One ground electrode (conveniently located surface electrode, if bilateral injections are in order, otherwise unilaterally placed to advantage).  

It’s all about planning what injections you wish to carry out, and then designing your electrode placement for convenience.  If you can’t locate your reference electrode optimized for bilateral injections, please simply place it close to the injection site on both sides.  It’s not worth risking the quality of your signal if you can’t find a reasonable midpoint.  

Hand with surface electrodes for testing

Please play with your Myoguide with surface electrodes following the “Test Drive Your Myoguide” tab in the accordion file ( Myoguide training page).  Use extreme examples to illustrate this to yourself.  This is an important exercise if you have not used Myoguide before! The last thing you want is to learn how to use Myoguide on your patient, when you need to inject.

Please review the “Best Practices” tab in the accordion file ( Myoguide training page), to gain a better understanding.   If you will be carrying out bilateral injections, sometimes you may be able to place the reference electrode equidistant from those sites to avoid having to move either the ground or reference electrode.  Otherwise keep your electrodes grouped reasonably close.

Another issue we see is using electrodes that have electrode leads that are way too long .  Please see the “Best Practices” tab again.  The leads on the electrodes are part of the high impedance side of the equation as they are present before the signal connects to Myoguide.  

In other words, they are good noise antennas.  They will want to pick up noise as they present the optimal conditions to do so. It is not until these signals get into Myoguide’s EMG amplifier that stray noise is minimized (the low impedance side).

These concepts are true for all electrophysiological amplifiers.

Myoguide’s white input cable is actively shielded to protect the integrity of the input signal and actively able to reduce noise.  So, the approach should be to minimize the length of the unshielded electrode wires.  This is especially so, when operating in electrically noisy environments, e.g. fluorescent lights, motorized chairs/beds, etc..  We want to avoid skipping rope length electrode wires!  

If you are stuck with long electrode wires, you may try to twist them together to form a pseudo shield from the wrapped ground wire.  It does not have to be a tight twist, just as long as the ground wire wraps around the reference and input wire.  Once it gets to Myoguide’s actively shielded white input cable, it’s a far better situation.

Actually, the best approach is to use tab electrodes and the alligator adapters to minimize the unshielded cable lengths for your reference and ground.  Hypodermic needle electrodes are better with shorter leads.  Of course, it also depends how long you need to be able to carry out the injections comfortably.  

Suffice it to say that Myoguide can be located fairly close to the patient.  If you need a longer shielded input cable, we have a 1.5 times longer input cable exclusively available on the Myoguide Store.  (part # 8008-CT15) We designed this cable specifically to address this issue.

We have a lot of resources on our website to help you get the most out of your clinical sessions using Myoguide EMG/ESTIM BoNT injection guidance system.  We also have an eLearning course on “The Benefits of Injection Guidance”.  There’s some background about injection guidance using toxins, as well as Myoguide training.

You can visit the Myoguide page for more product details, features, benefits, and specifications if you wish to learn more.

You may purchase your Myoguide EMG/ESTIM BoNT injection guidance system, accessories, and electrodes, directly from the Myoguide Store!  Credit card payments and quotations can be accommodated directly from our website, for your convenience.