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Detection limit in low-amplitude EEG measurement
Muneyuki Horikawa1, Hajime Harada, Masaru Yarita
1Department of Bio-Medical Engineering, Tokai University School of High-Technology for Human Welfare, Numazu, Japan.
Summary
Determining cerebral death requires careful consideration of electroencephalogram (EEG) noise. Excess scalp noise, beyond thermal noise, significantly impacts low-amplitude EEG measurements, necessitating advanced noise analysis.
Area of Science:
- Biomedical Engineering
- Neurophysiology
Background:
- Electrocerebral inactivity is crucial for diagnosing cerebral death.
- Surface biopotential electrodes introduce noise from skin-gel and gel-electrode interfaces.
Purpose of the Study:
- To analyze noise sources in electroencephalogram (EEG) recordings for cerebral death determination.
- To quantify excess noise beyond thermal noise in scalp recordings.
Main Methods:
- Autocorrelation and fast Fourier transformation used to obtain power spectral density (S(f)).
- Synchronous rectification employed for interelectrode resistance (R(f)) measurement.
- Equivalent noise resistance (Rn) calculated using the formula Rn = S(f)/4kT.
Main Results:
- A parameter Rn/R was derived to normalize measured noise.
- Rn/R values greater than 1 indicate the presence of excess noise (e.g., 1/f, tissue noise).
- The mean square root of scalp noise (Rn/R) was 10.8 at 10 Hz, signifying substantial excess noise.
Conclusions:
- Excess noise is a significant factor in low-amplitude EEG measurements.
- Accurate determination of cerebral death necessitates accounting for this excess noise.