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ECG Signal Quality Measurement. Client: Alan Clapp - Senior Electrical Engineer, GE Medical Systems Advisor: John G. Webster, Ph. D Group Members: Paul Anheier, Michael Piché, John Puccinelli, Scott Wiese. Problem Statement:.

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Ecg signal quality measurement

ECG Signal Quality Measurement

Client: Alan Clapp - Senior Electrical Engineer, GE Medical Systems

Advisor: John G. Webster, Ph. D

Group Members: Paul Anheier, Michael Piché,

John Puccinelli, Scott Wiese


Problem statement
Problem Statement:

  • Although modern ECGs sufficiently eliminate many types of interference, more optimization is possible and necessary. The focus of the project, therefore, is to further improve signal quality and develop a reliable alert system to detect signal degradation whether through procedural guidelines and/or hardware modifications.


Background
Background

  • Poor ECG signals can have many causes:

    • Electrical interference from other instruments/power lines/lights

    • Improper electrode placement

    • Poor electrode adhesion

    • Electrode aging/degradation

  • Most common causes occur at the skin/electrode interface

  • Poor contact or old electrodes result in high impedance at the skin/electrode interface

  • This results in a degradation of signal amplitude and an increased susceptibility to motion artifact


Background1
Background

  • What is deemed “good” signal quality is highly subjective

  • It is impractical to determine a universally acceptable signal quality due to subjectivity

  • Solution?...


Proposed solution
Proposed Solution

  • Include as a feature on future electrocardiographs a graphical display of measured skin impedance over time

  • Graph would have fixed scale to make interpretation easier

  • Clinicians could make their own decisions on signal quality based on trends in the graph



Requirements for implementation
Requirements for Implementation

  • We must determine a suitable scale to use for graph of skin resistance

  • Determination of the best carrier signal to measure impedance (DC, ~.2 Hz, 250 Hz)

  • Determine impedance level above which problems frequently occur

  • Determination a typical response of skin impedance over a long time interval (24 hours)


Carrier signal testing
Carrier Signal Testing

  • Goal: Identify most reliable/accurate carrier signal for measuring impedance.

  • Skin is not perfect resistor, must determine behavior at different frequencies

  • Candidates (at request of GE engineers)

    • DC

    • 250 Hz

    • .2 Hz



Carrier signal testing2
Carrier Signal Testing

  • Human Subjects Committee has conditionally approved public participants.

    • With this approval, we can maximize test subject diversity

      • ↑ subjects = ↑ skin types = more realistic results

  • Considerations for Analysis

    • Input impedance of oscilloscope

    • Skin resistance changes over time


Skin impedance testing
Skin Impedance Testing

  • Goal: Collect data over 24 hours of impedance change at skin-resistor interface. Use to establish a scale.

  • Study is to include multiple types of electrodes.

  • Necessary for implementation of a graphical display of skin impedance change versus time.


Future directions
Future Directions

  • Complete carrier signal testing and analysis.

  • Establish resistance scale.

  • Develop layout of graphical display.

  • Characterize quality/response of various electrodes.

  • Submit to GE for review and possible implementation.

  • Publish the findings.


Conclusions
Conclusions

  • Graphical representation of skin impedance will provide useful data and help make decisions on signal/electrode quality

  • Determining a signal carrier is a key component of representing resistance changes.


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