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Abstract

Disclosed is a real time cerebral diagnostic apparatus and method for quantitatively evaluating, in a noninvasive manner, cerebral phenomena such as the depth and adequacy of anesthesia pain responses during surgical stress, acute cerebral ischemia, level of consciousness, degree of intoxication and ongoing normal and abnormal cognitive processes. A suitable electrode and amplifier system is used to obtain high resolution biopotentials from the regions of interest. Surface electroencephalographic (EEG) signals are filtered to allow the acquisition of frequencies between 2 and 500 Hz, then digitized and transmitted over a high speed serial line to a host computer where a 32 second long signal is divided into 128 consecutive 0.25 second intervals. Digital EEG data from unipolar leads is normalized and the dynamic phase and density relations within the signal are then characterized by estimating the third-order autocorrelation function or autobispectrum using either a frequency domain, or parametric approach. Paired EEG data from corresponding left and right hemisphere leads is used to characterize the dynamic phase and density relations between hemispheres by estimating the third order crosscorrelation function or crossbispectrum using either frequency domain or parametric techniques. Under certain specific filtering circumstances the power spectrum and crosspower spectrum are also computed. A reference clinical database is used to identify frequency pairs most sensitive to particular interventions or diagnostic states of interest. The values at these frequency pairs are then extracted from the patient's autobicoherence, autobispectral density, autobiphase, crossbicoherence, crossbispectral density, and crossbiphase arrays. The ensemble of values for the particular diagnostic determination is used to compute an index which serves as the diagnostic criterion by which the patient's state is judged. Any diagnostic index can be continuously displayed on a graphics terminal for real-time diagnostic monitoring or can be sent to a hard copy device to generate reports for the medical record.

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