AAEM minimonograph #16: instrumentation and measurement in electrodiagnostic medicine--Part I

Technical and instrumentation factors play an important role in obtaining reliable information during electrodiagnostic studies. With contemporary electrodiagnostic equipment, neurophysiologic potentials are detected using a variety of electrodes and undergo differential amplification, filtering, conversion to digital form, and finally, analysis and display. Understanding the signal processing principles, limitations, and sources of errors that can occur during this multistep process can improve the technical quality of studies, minimize preventable errors, and improve clinical interpretation. Part I of this minimonograph reviews the basic principles of action potential generation and overviews electrodiagnostic instrumentation. The concept of waveform frequency content is related to the role of filters in suppressing noise while preserving waveform latency, amplitude, and morphology. The electrical characteristics of various surface and needle electrodes influence instrument design and the nature of the potentials recorded. This is especially important in understanding the differences in motor unit characteristics obtained from monopolar and concentric needle electrodes.