Electrodiagnostic Study Instrument Design Requirements

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Introduction  

Electrodiagnostic (EDX) physicians rely on high-quality nerve conduction studies (NCSs) and needle electromyography (EMG) instruments to diagnose neuromuscular disorders. Instrumentation has changed due to improved electronic technology and new research findings in EDX medicine. This statement defines the minimum requirements and technical specifications necessary for an EDX instrument to perform comprehensive EDX testing and support accurate clinical diagnosis and patient care. Devices that cannot meet these requirements should not be considered substitutes for a complete EDX system.


Electrical Safety 

Safety standards are required for any electrical medical device. The EDX instruments must follow FDA standards for safety, including acceptable current leakage requirements.1 The EDX equipment must be routinely maintained per the manufacturer’s guidelines.

Data Integrity 

An EDX instrument must provide password-controlled access to maintain patient record confidentiality. The instrument must support inclusion of unique patient identifiers, including a medical record number or equivalent identifier to ensure accurate patient identification and record matching.

EDX Instrument Design 

The purpose of an EDX instrument is to objectively record, amplify, display, and store low-amplitude neurophysiological signals despite the expected presence of ambient noise, interference, and stimulus artifacts. EDX instruments have three separate functional components: stimulus output and signal input, processing, and output.2–7    
 

I. Stimulus Output and Signal Input:

A. Electrodes

Signal Input:  Electrodes

Stimulating Electrode (Stimulator)

  • cathode and anode clearly identified
  • support for monopolar needle stimulation
  • adjustable stimulus tip spacing for pediatric studies
  • continuously adjustable intensity
  • constant current or constant voltage stimulus modes
  • adjustable stimulus duration from 0.05 to 1 millisecond (ms)
  • adjustable stimulation frequency from 0.1 to 50 Hertz (Hz) 2-4
Recording Electrodes
  • connections for three individual electrodes active (E1), reference (E2), and ground (E0) using DIN type plug
  • touch-proof preamplifier connections for patient safety 
  • ability to use surface and needle recording electrodes for NCSs
  • ability to use monopolar and concentric needle electrodes for needle EMG

 

Temperature indicator and temperature probe

  • built in or an external temperature probe
B. AmplifiersSignal Processing
Differential amplifier

Magnifies the potential difference between the active and reference inputs to improve signal-to-noise ratio. 

  • high input impedance of the amplifier (>1,000M-Ohms) 
  • high common-mode rejection ratio (CMRR), e.g. >100 dB 
  • noise level with input shorted being less than 0.6 µVRMS
  • channel selection mechanism if multiple channels are needed
Gain (Sensitivity)
  • ability to acquire signals from 1 microvolt (µV) to 50 millivolts (mV) 2-4 
Filters

Amplifiers use a band-pass filter to attenuate noise. The band-pass filter is characterized by adjustable low and high cut-off frequency settings.

  • adjustable lower frequency (high pass filter) setting from .2 to 2,000 Hz 
  • adjustable high frequency (low pass filter) setting from 30 to 10,000 Hz2–6
  • notch filter for 50 Hz or 60 Hz for noise elimination (This is to attenuate the power line frequency but should not be active by default because of potential amplitude reduction and ringing.)
Analog-to-digital converter
  • converts biological (analog) signals to digital waveforms
  • ability to display and store waveforms in a digital format
  • adequate sampling frequency to provide adequate resolution in measurements and to prevent waveform distortion from aliasing
II. Signal ProcessingSignal Output

Processing includes amplification and filtering of incoming signals to improve signal-to-noise ratio and prepare the waveform for accurate measurement and analysis. It also includes conversion of biological analog signals into digital waveforms with adequate sampling to preserve waveform fidelity and avoid aliasing.

III. Output

Signal display
  • sensitivity/gain control to determine the amplitude of potentials, with a range of 1 µV to 10 mV per division
  • sweep speed adjustment, with a range of 0.1 ms to 5 sec per division
  • trace area appearance of a rectangular grid, with the gain and sweep speed clearly labeled
  • adequate vertical and horizontal resolution on monitor to enable visual analysis of waveforms   
  • automatic cursor/marker placement at onset, peak and end of recognizable potentials, to measure latencies (onset and peak) and amplitudes (baseline-to-peak and peak-to-peak)
  • manual adjustment of cursors for measurements during both NCSs and EMG testing
  • automatic calculation of conduction velocity when distance values are entered
  • free running and triggered modes

The free running mode updates signal display continuously, showing live electrophysiological signals as they are recorded. The triggered mode is necessary to record signals when a certain event (the trigger) occurs to assess signal variability and reproducibility. For triggered modes, the occurrence of the event (stimulus) should be synchronized to the acquisition of data point for accurate time zero calculation. For motor unit potential analysis, an adjustable level trigger should be available. A function of window triggering is optional. A function of delay line with adjustable delay time should be available to allow observation and analysis of signals preceding the trigger.  


  • capability of trace raster/superimpose
Auditory Speaker
  • high quality audio amplifier and loudspeakers for the production of characteristic sounds, for both potential recognition and criterion analysis 
  • volume adjustment
Data storage and report generation 
  • Exports numerical data directly into the final report 
Data are objective and based on real time measurement of biological signals without subjective input from the patient and are independent of psychophysical responses from patients. 
  • Includes the ability for report editing
  • Lists normal reference values
  • Includes the ability for permanent storage, retrieval, export, and printing of acquired waveforms for clinical documentation, quality review, and accreditation purposes.
 
Conclusion

The EDX instrument must provide the original numerical NCS/EMG data delineated in the AANEM position statement “Reporting the Results of Needle EMG and Nerve Conduction Studies: An Educational Report.”8 The updated version includes an option to specify the EDX instrument manufacturer and model on the report.9

Finally, efficient usage of EDX instruments requires performance by or oversight of an appropriately trained EDX physician. The AANEM position statement “Who is Qualified to Practice Electrodiagnostic Medicine” defines recommended qualifications for an EDX physician.10

An instrument that does not provide the capabilities described in this statement should not be considered a comprehensive EDX system.

References

  1. ISO. Medical Electrical Equipment. Published online June 2014:IEC 60601-1-12.
  2. Dumitru D, Barkhaus PE, Nandedkar SD. Instrumentation: Fundamental Concepts and Pitfalls. Muscle Nerve. 2026;73(2):149-208. doi:10.1002/mus.70060
  3. Oh SJ. Chapter 3: Basic Components of Electromyography Instruments. In: Clinical Electromyography: Nerve Conduction Studies. 3rd ed. Lippincott Williams & Wilkins; 2003:25-36.
  4. Dumitru D, Zwarts M, Amato A. Instrumentation. In: Electrodiagnostic Medicine. 2nd ed. Hanley & Belfus; 2002:69-97.
  5. Nandedkar SD. Instrumentation. In: Johnson’s Practical Electromyography. Lippincott Williams & Wilkins; 2007:87-103.
  6. Preston DC, Shapiro BE. Basic Nerve Conduction Studies. In: Electromyography and Neuromuscular Disorders: Clinical-Electrophysiologic Correlations. 4th ed. Elsevier Sanders; 2021:23-30.
  7. American Association of Electrodiagnostic Medicine. Reporting the Results of Nerve Conduction Studies and Needle EMG. 
  8. American Association of Electrodiagnostic Medicine. Model Report.
  9. American Association of Electrodiagnostic Medicine. Who Is Qualified to Practice Electrodiagnostic Medicine?

 (Links to AANEM position statements above are to the most recent version of the document.)

Document History

Approved by the American Association of Neuromuscular & Electrodiagnostic Medicine: July 2015. Reviewed and reapproved December 2020, July 2026. 
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