JPH067825B2 - Real evoked potential extractor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to an actual evoked potential extraction device.

(B) Conventional technology In order to extract an evoked potential generated in response to a stimulus from an electroencephalogram waveform mixed with miscellaneous waves, the derived electroencephalogram waveform is divided at the same timing as the stimulus, and the divided same waveform is extracted. It is performed that the evoked potential waveform is obtained by averaging.

(C) Problems to be Solved by the Invention However, since the level of the miscellaneous wave component caused by the electrocardiogram is extremely high, it takes an average of several hundreds of times or more to eliminate this component. Cannot be faithfully expressed, and in particular, the low-level short latency that is emitted until the stimulus propagates from the brain stem to each part of the brain and the part of the brain corresponding to the stimulus site activates to generate an evoked potential. The evoked potential required the reference electrode to be placed on a part other than the head such as the hand or foot, and it was extremely difficult to read because it was masked by miscellaneous waves due to the electrocardiogram.

In addition, it was attempted to block low-frequency components by using a high-pass filter to remove the miscellaneous wave components caused by the electrocardiogram. There was a defect that distortion occurred in the material, and it was impossible to put it into practical use.

(D) Means for Solving Problems In the present invention, a pair of electrodes including an active electrode and a reference electrode for creating an electroencephalogram from a potential difference between two electrodes, and a pair of electrodes connected to the electrodes For increasing the potential difference of the digital signal, an A / D converter for connecting the potential difference to a digital signal, and an A / D converter for converting the potential difference into a digital signal, and the digital signal A temporary storage device for accommodating an electrocardiogram waveform, a pair of electrodes for deriving an electrocardiogram waveform, a trigger signal generation unit that is connected to the electrodes, generates a trigger signal from the electrocardiogram waveform and sends the trigger signal to the temporary storage device, and a temporary storage device. Connected to the operation unit that can connect and extract the actual EEG waveform, connect to the operation unit, divide the actual EEG waveform in synchronization with the stimulus, and perform sequential averaging to extract the evoked potential waveform from the EEG waveform mixed with miscellaneous waves. It is composed of a second calculation unit for extracting, and The calculation unit divides the electroencephalogram waveform into individual segments, starting from the point of time when the trigger signal from the trigger signal generation unit has been traced back for a predetermined time, and obtains the estimated waveform of the mixed electrocardiogram by sequentially averaging each segment and estimating this. It is intended to provide an actual evoked potential extraction device characterized by being configured so as to extract an actual EEG waveform by subtracting it from the original EEG waveform in which miscellaneous waves are mixed while synchronizing the waveform origins.

(E) Action and effect In the present invention, a pair of electrodes, an active electrode and a reference electrode for deriving an electroencephalogram waveform, is provided, and a pair of electrodes for deriving an electrocardiogram waveform is provided, and an electrocardiogram waveform is provided in the trigger signal generator. A trigger signal is generated from the calculation unit, the estimated waveform of the miscellaneous wave is subtracted from the EEG waveform in the calculation unit so that the actual EEG waveform can be extracted, and the second calculation unit divides the actual EEG waveform in synchronization with the stimulus, and sequentially adds and averages Then, the evoked potential waveform is extracted from the electroencephalogram waveform containing mixed waves.

Therefore, evoked potentials including short-latency evoked potentials, ECG-induced miscellaneous waves, and background EEG potentially emitted from the brain have an extremely high degree of independence. Waveforms mixed with miscellaneous waves are divided in synchronization with the electrocardiogram, the divided electroencephalogram waveforms are sequentially added and averaged, and the estimated electroencephalogram-induced miscellaneous waves are erased from the electroencephalogram electroencephalogram waveform to obtain the actual electroencephalogram waveform, and then , This real EEG waveform is divided and averaged in synchronism with the stimulus to eliminate the background EEG and extract the evoked potential waveform. By processing the derived electroencephalograms in two steps, low-level short-latency evoked potentials can be clearly expressed, which greatly contributes to functional analysis and diagnosis of the brain.

(F) Example To explain the example of the present invention in detail with reference to the drawings, FIGS. 1 to 5 are schematic diagrams for explanation, and FIG. 1 shows an electroencephalogram and a trigger signal ( 1) shows an electrocardiogram for generating the electroencephalogram, in which the active electrode (2) is placed near the target site on the scalp and the reference electrode (3) is placed on the hand or foot, It is derived from the potential difference of the above, and the target evoked potential waveform, the background electroencephalogram, and the waveform derived from the electrocardiogram are mixed in this waveform.

It is not necessary to consider the magnitude of the electrocardiogram-derived miscellaneous wave level in the electrode installation, and the point is to select a position where the desired evoked potential can be derived most significantly.

In addition, it can be seen from this waveform that the waveform period derived from the electrocardiogram is not always constant, and that the target evoked potential and the frequency band of the miscellaneous wave to be eliminated overlap, and this has traditionally led to the extraction of the actual evoked potential. It was difficult.

The trigger signal (1) is to increase the electrocardiogram waveform (4) to an appropriate level and generate the R wave (5) showing the maximum peak in the waveform (4) as a marker.

Incidentally, there is a P wave (6) preceding the R wave (5) of the electrocardiogram waveform (4), and the preceding time is usually within 200 msec.

FIG. 2 shows a waveform obtained by synchronously dividing the electroencephalogram waveform of FIG. 1 into the trigger signal (1).

The synchronous division referred to here means the temporal matching of the electroencephalogram waveform (7) and the liger signal (1), that is, the electrocardiogram waveform (4),
Specifically, the EEG waveform (7) is 200m from the trigger signal (1).
sec It is to divide the time up to the same phase of the next wave into one segment (9) with the starting point (8) as the starting point (8), and by using 200 msec before the trigger signal (1) as the starting point (8) of the division, the electrocardiogram waveform The P wave (6) component of (4) is located at the front of the segment (9).

FIG. 3 shows a waveform obtained by sequentially adding and averaging the segment (9) that was divided synchronously in FIG. 2 in synchronization with the starting point, and the electrocardiogram in the electroencephalogram waveform (7) shown in FIG. 1 by this successive addition and averaging. Only the waveform that is synchronized with is manifested by superimposing it, the waveform that is not synchronized is smoothed, and only the synchronized waveform is extracted.The manifested synchronized waveform is the estimated waveform of the miscellaneous wave caused by the electrocardiogram (10 ). In addition, this sequential addition average is calculated by multiplying the past addition average value by a weighting index, multiplying the newly arrived segment numerical value by a value obtained by subtracting the same index from 1, and adding both. , Estimated waveform (1
0) is sequentially updated to dynamically follow the waveform of the general wave of the subject. The weighting index can be set arbitrarily between 0 and 1.

The above processing is performed in this embodiment in the active and reference electrodes.
Increase the potential difference between (2) and (3) to a maximum of ± 5V, and
This is D conversion and digital processing, and the specifications of A / D conversion are a sampling interval of 0.5 msec and a resolution of 12 bits. The evoked potential is an electrical vibration within about 1000 Hz, and the derived potential difference is signaled in binary 12 bits, that is, divided into 4096 steps, so sufficient accuracy is guaranteed for this purpose. There is.

Then, the digital signals of the brain potential that sequentially arrive are stored in a time series, and the trigger signals (1) to (2) obtained from the electrocardiogram are stored.
A series of digital signals obtained from the starting point (8) at a time point of 00 msec as a starting point (8) is defined as the segment (9), and the sequentially arriving segment (9) is synchronized with the starting point (8) to successively add and average by the above calculation method to obtain the latest Estimated waveform (10). Estimated waveform (1
(0) is not updated after all the series of digital signals that make up the segment (9) are input, but the segment is not updated for each digital signal input that arrives in time series.
It is sequentially updated from the part corresponding to the signal of (9), which increases the processing speed.

In addition, the waveform caused by the electrocardiogram is the R wave showing the maximum peak.
(5) and P wave (6) preceding R wave is the main component, and R wave (5)
Since it decays rapidly after the occurrence and the fluctuation of the cycle becomes large, in order to extract the repetitive waveform synchronized with the electrocardiogram waveform (4), it is synchronized with 200 msec before the R wave including the P wave (6) as the starting point. By performing division and successive addition and averaging, sufficient accuracy can be obtained for this purpose. Furthermore, the starting point
The retrograde time in (8) can be adjusted to accommodate individual differences among subjects.

Fig. 4 shows the target EEG waveform (11), which is obtained by subtracting the EEG waveform (10) in Fig. 3 from the EEG waveform (7) with miscellaneous waves in synchronization with the starting point (8). Is.

In addition, in FIG. 4, the waveform amplitude is enlarged by about 20 times.

FIG. 5 shows the target evoked potential waveform (26), which is obtained by dividing the real electroencephalogram waveform (11) with the stimulus signal (27) in FIG. 4 and performing sequential averaging in the same manner as above. The background electroencephalogram waveform is smoothed, and the evoked potential waveform (26) in which the phases are aligned is revealed, and the evoked potential is analyzed by this waveform (26).
It is used for diagnosis.

In order to execute the above processing, a device configuration as shown in FIG. 6 was implemented.

That is, (2) and (3) respectively indicate an active electrode and a reference electrode, which are attached to the scalp and the skin of the hand of a subject with a conductive paste containing a large amount of an electrolyte. (12), (12 ′)
Are electrodes for deriving the electrocardiogram waveform (4), which are attached to the skin other than the head of the subject.

The potential difference between the active and reference electrodes (2) and (3) is increased to a maximum of ± 5V by a widening device (13) with a constant widening ratio, and is a binary 12-bit by the A / D converter (14). Is converted into a digital signal and stored in the temporary storage device (15). This A / D conversion is performed at a sampling interval of 0.5 msec and is sequentially stored in the addresses of the storage device (15) corresponding to the time series.

On the other hand, the electrode (12) derived from the electrocardiogram waveform (4) is connected to the trigger signal generator (19) containing the Schmitt element (17) and the differentiating element (18) via the amplifier (16), Waveform
(4) A trigger signal (1) is generated by capturing the rising edge when the R wave (5) crosses the reference voltage from below, and the trigger signal (1) is synchronized with the temporary storage device (15). 200 ms from the current time of stored brain wave waveform (7) memory
ec The device from the address corresponding to the time when it was traced back (15)
Is accessed and output to the arithmetic unit (20).

In addition, in order to generate the trigger signal (1) by digital processing, the electrocardiogram waveform (4) is amplified and A / D converted, and the values of the sequentially input digital signals are compared before and after. Alternatively, the trigger signal (1) may be generated when the value of the previous signal is equal to or smaller than the value of the previous signal.

The computing unit (20) has a register (21) built in, and the register (21) stores the estimated waveform (10) of the miscellaneous waves that have been successively averaged until then, and the newly input temporary storage apparatus
The electroencephalogram waveform (7) from (15) is averaged and the latest arithmetic mean value, that is, the estimated waveform (10) of miscellaneous waves is always stored. Then, the estimated waveform (1
0) is subtracted from the EEG waveform (7) from the temporary storage device (15) to obtain the actual EEG waveform (11) online with a delay of 200 msec.

The arithmetic unit (20) has a built-in clock (20 ′), and all timings such as sampling strobes are obtained by dividing (20 ″) the pulse from the clock (20 ′). The entire device operates synchronously and in synchronism, and the time backward trace of 200 msec from the trigger signal (1) is the relative address of the address of the temporary storage device (15) at the time of the signal (1) being -4.
It is obtained by starting access from 00, and this retroactive time is calculated by the keyboard (24) connected to the arithmetic unit.
It can be changed and set by the operation of.

The real electroencephalogram waveform (11) thus obtained is obtained by the second calculation unit (28).
It is divided in synchronism with the stimulus signal (27) and is sequentially added and averaged as described above.
Since the phase is more uniform in (26), the same waveform (26) becomes apparent.

The evoked potential waveform (26) thus obtained clearly shows the short-latency evoked potential (29) immediately after the stimulation signal (27), and can be written online with the pen via the D / A converter (22). It is displayed on the recorder (23).

It is also possible to output from the computing unit (20) to a computer (25) for diagnosis or the like, and perform processing such as diagnosis using a program and a database built in the computer (25).

The operation unit (20) can be carried out by loading the program of the above procedure into a general-purpose computer, and if it is a high-speed computer, the brain waves from the active electrodes of several channels are scanned and processed simultaneously. However, to cover more channels, the amplifier (1
This is realized by integrating 3) to the D / A converter (22) in an integrated circuit and arranging a large number of these in parallel, which is preferable from the viewpoint of equipment operation and handling.

Even if the above process is performed, the actual EEG waveform (1
In 1), if the influence of the R wave part of the miscellaneous wave due to the electrocardiogram remains, the data corresponding to several 10 msec before and after the time when the trigger pulse appears in the data of the actual EEG waveform (11) is set as block 0. , The evoked potential waveform (26) with higher accuracy in which the influence of the R wave is completely eliminated by performing successive addition in synchronization with the stimulation signal 27 after the second operation unit (28) using the windowed data. ) Can be obtained. The data blocked by the actual EEG waveform is smaller in amount than the whole data, and therefore the evoked potential waveform is not lost.

[Brief description of drawings]

 FIG. 1 is an electroencephalogram and an electrocardiogram. FIG. 2 shows a waveform obtained by synchronous division. FIG. 3 shows a waveform obtained by successive addition and averaging (estimated waveform of miscellaneous waves). FIG. 4 shows a real brain wave waveform. FIG. 5 shows an evoked potential waveform. FIG. 6 is a block diagram of a device configuration. (1): Trigger signal (4): Electrocardiogram waveform (7): EEG waveform (8): Origin (9): Segment (10): Estimated waveform of miscellaneous waves (11): Real EEG waveform (26): Evoked potential Waveform (27): Stimulation signal

Claims (1)

[Claims] 1. A pair of electrodes composed of an active electrode (2) and a reference electrode (3) for creating an electroencephalogram from a potential difference between two electrodes, and a pair of electrodes (2) connected to the electrodes, An amplifier (13) for increasing the potential difference of (3), an A / D converter (14) connected to the amplifier (13) for converting the potential difference into a digital signal, A temporary storage device (15) connected to the A / D converter (14) and storing the digital signal, and a pair of electrodes (12), (12 ') for deriving an electrocardiogram waveform (4).
And a trigger signal generator (19) connected to the electrodes (12) and (12 ') to generate a trigger signal (1) from the electrocardiogram waveform (4) and send it to a temporary storage device (15), and a temporary storage An EEG waveform (11) that is connected to the device (15) and is capable of extracting the EEG waveform (11) and an operation unit (20) that is connected to the stimulus and synchronized with the stimulus.
And a second arithmetic unit (28) for dividing and averaging to extract the evoked potential waveform (26) from the electroencephalogram waveform containing mixed waves, and the arithmetic unit (20) is a trigger signal generating unit. The EEG waveform (7) is divided into individual segments (9) starting from the point (8), which is a retrospective time from the trigger signal (1) from (19), and each segment (9) is sequentially added and averaged and mixed. Estimated waveform of electrocardiogram
After obtaining (10), the estimated waveform (10) was configured to be able to extract the actual EEG waveform (11) by subtracting it from the original EEG waveform (7) with mixed miscellaneous waves while synchronizing the starting point (8). An actual evoked potential extraction device characterized in that