Method and apparatus for analyzing an electro-encephalogram

Apparatus for analyzing an electro-encephalogram (EEG) in which at least one electrical signal derived from the EEG is applied to a threshold detector and the output is examined for a particular kind of brain activity, comprising:

• analog to digital conversion means, wherein the electrical signal derived from an EEG channel is converted to digital form by the analog to digital conversion means at a sampling frequency sufficiently high to detect pulses in the electrical signal and the resulting digital signal is applied to a comparator means for comparison with a digital threshold signal;
• timing means for measuring time intervals between successive output signals produced by the threshold detector and for providing output values representing the time intervals;
• selecting means for selecting only those output values that represent time intervals longer than a predetermined minimum time;
• adding means for accumulating the selected output values representing time intervals occurring within a section of the EEG obtained during a time period of predetermined duration to produce a total value;
• display means for producing a visible output including a plurality of total values derived respectively from sections of the EEG obtained during consecutive time periods of the predetermined duration;
• wherein in the comparator means the electrical signal derived from an EEG channel is converted to digital form in an analog to digital converter, one of the converter reference voltages being at the threshold level, and comparison is effected by detecting non-zero digits in the digital signal at least as significant as that corresponding to the threshold level.

Apparatus for analyzing electro-encephalograms (EEGs) in which electrical signals derived from several channels of EEG are applied to a threshold detector and detector output signals are examined for a particular kind of brain activity, comprising:

• means for multiplexing electrical signals derived from several channels of EEG from several patients to the input terminals;
• timing means for measuring time intervals between successive output signals produced by the threshold detector and for providing output values representing the time intervals;
• selecting means for selecting only those output values that represent time intervals longer than a predetermined minimum time;
• adding means for accumulating the selected output values representing time intervals occurring within a section of the EEG obtained during a time period of predetermined duration to produce a total value;
• and
• display means for producing a visible output including a plurality of total values derived respectively from sections of the EEG obtained during consecutive time periods of the predetermined duration.

Apparatus for analyzing an electro-encephalogram (EEG) using the amplitude of the EEG as a criterion in assessing the brain activity comprising:

• sampling means for sampling electrical signals derived from plural EEG channels at regular time intervals from both sides of the head of a patient and holding the samples;
• analog to digital conversion means connected to receive the samples held successively by the sampling means and producing therefrom digital outputs representing the magnitudes of the samples;
• a digital computer programmed to receive the digital outputs associated with each of said plural EEG channels in succession from the analog to digital conversion means and having means for processing substantially simultaneously the digital outputs from each of the plural EEG channels including:
• means for comparing digital outputs from each with a threshold value;
• means for determining a time interval between a current digital outputs and immediately preceding digital outputs which exceed the threshold value, and
• means for accumulating a total of time intervals exceeding a minimum duration during a particular time period and generating signals representative of total time intervals accumulated during consecutive time periods;
• and
• display means for displaying side by side the representative signals for each channel.

A method of analyzing an electro-encephalogram (EEG) in which the amplitude of the EEG is used as a criterion in assessing the brain activity, wherein the EEG is represented by a plurality of digital values respectively corresponding to the amplitude of the EEG signal at a succession of instants spaced apart by predetermined equal time periods, comprising:

• comparing sequentially the digital values with a threshold value;
• indicating whether or not the digital values exceed the threshold value,
• measuring each time interval during which successive digital values are smaller than the threshold value;
• summing the measurements of the time intervals having at least a certain minimum duration during an extended time period to provide a total of the measurements for each of a plurality of consecutive extended time periods;
• and
• producing an output display dependent on the totals of the measurements.