title: Baseline correction of intraoperative electromyography using discrete wavelet transform.
abstract: OBJECTIVE
  In intraoperative analysis of electromygraphic signals (EMG) for monitoring purposes, baseline artefacts frequently pose considerable problems. Since artefact sources in the operating room can only be reduced to a limited degree, signal-processing methods are needed to correct the registered data online without major changes to the relevant data itself. We describe a method for baseline correction based on "discrete wavelet transform" (DWT) and evaluate its performance compared to commonly used digital filters.
  
  
  METHODS
  EMG data from 10 patients who underwent removal of acoustic neuromas were processed. Effectiveness, preservation of relevant EMG patterns and processing speed of a DWT based correction method was assessed and compared to a range of commonly used Butterworth, Resistor-Capacitor and Gaussian filters.
  
  
  RESULTS
  Butterworth and DWT filters showed better performance regarding artefact correction and pattern preservation compared to Resistor-Capacitor and Gaussian filters. Assuming equal weighting of both characteristics, DWT outperformed the other methods: While Butterworth, Resistor-Capacitor and Gaussian provided good pattern preservation, the effectiveness was low and vice versa, while DWT baseline correction at level 6 performed well in both characteristics.
  
  
  CONCLUSIONS
  The DWT method allows reliable and efficient intraoperative baseline correction in real-time. It is superior to commonly used methods and may be crucial for intraoperative analysis of EMG data, for example for intraoperative assessment of facial nerve function.
authors.affiliation: Department of Neurosurgery, University of Halle-Wittenberg, Ernst-Grube-Str. 40, Halle (Saale), Germany. srampp@tiscali.de
authors.forename: Stefan
authors.initials: S
authors.lastname: Rampp
authors.forename: Julian
authors.initials: J
authors.lastname: Prell
authors.forename: Henning
authors.initials: H
authors.lastname: Thielemann
authors.forename: Stefan
authors.initials: S
authors.lastname: Posch
authors.forename: Christian
authors.initials: C
authors.lastname: Strauss
authors.forename: Johann
authors.initials: J
authors.lastname: Romstöck
mesh_terms: D004576:Electromyography / Q000379:methods* / Q000706:statistics & numerical data; D005154:Facial Nerve / Q000503:physiopathology; D006801:Humans; D016343:Monitoring, Intraoperative / Q000379:methods* / Q000706:statistics & numerical data; D009464:Neuroma, Acoustic / Q000503:physiopathology / Q000601:surgery; D012815:Signal Processing, Computer-Assisted