Surgery – Diagnostic testing – Detecting brain electric signal
Patent
1997-12-01
1999-03-23
Manuel, George
Surgery
Diagnostic testing
Detecting brain electric signal
A61B 5048
Patent
active
058852239
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for evaluating electrical brain current signals picked off from the top of the skull over a given time interval, and to a device which is suitable for this purpose.
German Laid-Open Specification 15 41 173 discloses a method for information compression of electroencephalograms, time intervals being determined for which the upper and lower curve inversion point of a brain current signal is the governing factor. German Laid Open Specification 22 47 572 discloses a method and an apparatus for automatic analysis of brain current signals, in which method a signal is produced from an analog EEG the EEG signal. These methods for brain current representation have the disadvantage that they do not provide the doctor with any cohesive, simple, easily viewed information about the detected brain activity.
EP-A-0 150 125 discloses a method for evaluating electrically detected brain activity, in which a signal which is picked off from the top of the skull over a predetermined time interval is converted at a predetermined sampling frequency into a sequence of data words from which the amplitudes as well as the frequency associated with each amplitude are extracted in accordance with a predetermined scheme, for example a Fourier transformation, in an arithmetic unit, in such a manner that intermediate data words are formed, each of which represents an amplitude and is stored at a memory address. Furthermore, mean values are formed from the intermediate data words in the known apparatus, and all the mean values are passed, with the associated frequency, to an indicator device for display on a frequency/amplitude graph.
The invention is thus based on the object of making it easier for the doctor to assess brain activity.
To this end, the invention provides that the signal is converted at a given sampling frequency into a sequence of data words from which the amplitudes and the frequency associated with each amplitude are extracted in accordance with a predetermined scheme (Fourier transformation or the like) in an arithmetic unit, in such a manner that intermediate data words are formed, each of which represents an amplitude and is saved at a memory address which is governed by the frequency associated with the intermediate data word, furthermore, of all the intermediate data words, those maximum intermediate data words being determined which are a relative maximum, and in such a manner that a mean value is formed from the maximum intermediate data words for each frequency and all the mean values are passed with the associated frequency to an indicating device for display using a frequency/amplitude graph.
There is thus a so-called sum spectrum for each recorded track on the electroencephalogram, from which the doctor can use the position of the maxima for the individual frequencies to draw conclusions about brain activity directly. The basic activity and any pathological activity of the brain activity can thus be taken from a single curve profile, and can easily be assessed medically.
In a preferred refinement of the invention, in order to form the mean value, the sum of the maximum intermediate data words present per frequency is multiplied by the number of said words and is divided by a given reference variable.
Furthermore, it is recommended that, with the time interval being subdivided into a number of time units, the extraction be carried out for each time unit (sampling second), the intermediate data words formed for each time unit being saved at memory addresses which are defined unambiguously for the time unit by the frequency associated with the intermediate data word, and the number of time units in the time interval being chosen as the reference variable. The mean value data words fed to the indicating device (30) are preferably passed via a low-pass filter.
For deeper evaluation by the doctor and as a continuation of the invention, it is possible to determine from the mean value data words those which are a relative minimum, the frequency associated with each minimum mean value
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