Electroencephalogram (EEG) is often used in the confirmatory test for brain death diagnosis in clinical practice. Because EEG recording and monitoring is relatively safe for the patients in deep coma, it is believed to be valuable for either reducing the risk of brain death diagnosis (while comparing other tests such as the apnea) or preventing mistaken diagnosis. The objective of this paper is to study several statistical methods for quantitative EEG analysis in order to help bedside or ambulatory monitoring or diagnosis. We apply signal processing and quantitative statistical analysis for the EEG recordings of 32 adult patients. For EEG signal processing, independent component analysis (ICA) was applied to separate the independent source components, followed by Fourier and time-frequency analysis. For quantitative EEG analysis, we apply several statistical complexity measures to the EEG signals and evaluate the differences between two groups of patients: the subjects in deep coma, and the subjects who were categorized as brain death. We report statistically significant differences of quantitative statistics with real-life EEG recordings in such a clinical study, and we also present interpretation and discussions on the preliminary experimental results.
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Nevertheless, it was pointed out in Wijdicks (1995) that most patients meeting the clinical criterion for brain death might still have isoelectric EEGs (≤2 μV at a sensitivity of 2 μV/mm).
The CBF test involves the injection of a mild radioactive isotope into the blood stream. By placing a radioactivity counter over the head, one can measure the amount of blood flow into the brain. The cerebral blood flow study takes 20–30 min to perform. If there is no blood flow to the brain as demonstrated by this study, the brain is dead. A negative cerebral flow study is indisputable evidence of a dead brain.
The layout of the electrodes on the frontal regions of the brain is simply for the technical convenience without interfering with other medical treatment or moving the patient’s body. However, the EEG confirmatory test conducted at later stage (see the flowchart of Fig. 1) will require the electrodes cover the whole scalp.
Indeed, the presence of the slow activity (< 4 Hz) was always found in all measurements, which created a difficulty for discrimination.
All of quantitative analysis softwares were written in MATLAB© (MathWorks, Natick, MA) and are available from the authors upon request.
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This work was supported in part by the Japan Society for the Promotion Science (JSPS) and the National Natural Science Foundation of China (NSFC) in the Japan-China Research Cooperative Program. We thank two anonymous reviewers for many valuable comments.
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Chen, Z., Cao, J., Cao, Y. et al. An empirical EEG analysis in brain death diagnosis for adults. Cogn Neurodyn 2, 257 (2008). https://doi.org/10.1007/s11571-008-9047-z
- Brain death
- Quantitative EEG
- Independent component analysis
- Approximate entropy
- Detrended fluctuation analysis
- Pattern classification