U.S. patent number 3,848,586 [Application Number 05/316,019] was granted by the patent office on 1974-11-19 for signal detection system.
This patent grant is currently assigned to Hitachi Ltd.. Invention is credited to Toshio Ogawa, Takaji Suzuki.
United States Patent |
3,848,586 |
Suzuki , et al. |
November 19, 1974 |
SIGNAL DETECTION SYSTEM
Abstract
A signal detection system comprising detecting means for
detecting the differential between a first and a second sampled
value of an electrical signal subjected to sampling, comparing
means for comparing the output of the detecting means with a
predetermined first threshold value, discriminating means for
discriminating the polarity of the output of the detecting means,
adding means controlled by the output of the discriminating means
for adding a predetermined second threshold value to the first
sampled value, and means controlled by the output of the comparing
means for deriving the result of addition from the adding means.
The signal detection system serves for reducing or removing noises
involved in or superposed on an electrical signal and more
particularly a bioelectrical signal such as one recorded on an
electroencephalogram or electrocardiogram.
Inventors: |
Suzuki; Takaji (Kokubunji,
JA), Ogawa; Toshio (Hachioji, JA) |
Assignee: |
Hitachi Ltd. (Tokyo,
JA)
|
Family
ID: |
14312668 |
Appl.
No.: |
05/316,019 |
Filed: |
December 18, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Dec 17, 1971 [JA] |
|
|
46-101896 |
|
Current U.S.
Class: |
600/508;
340/146.2; 327/30; 327/94; 702/193; 128/901; 600/544 |
Current CPC
Class: |
A61B
5/369 (20210101); A61B 5/7203 (20130101); Y10S
128/901 (20130101) |
Current International
Class: |
A61B
5/0476 (20060101); A61b 005/04 () |
Field of
Search: |
;128/2R,2.5R,2.6RA,2.1B,2.6RB,2.1R ;307/235R,106
;328/151,165,167,168 ;325/65 ;235/183 ;340/146.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kamm; William E.
Attorney, Agent or Firm: Craig & Antonelli
Claims
We claim:
1. A signal detection system comprising holding means for holding
an electrical signal subjected to sampling, detecting means for
detecting the differential between sampled values x.sub.i and
x.sub.i.sub.+1 (where i is an integer) held in said holding means,
comparing means for comparing the output of said detecting means
with a predetermined first threshold value, discriminating means
for discriminating the polarity of the output of said detecting
means, adding means controlled by the output of said discriminating
means for adding a predetermined second threshold value to the
sampled value x.sub.i in response to the appearance of the sampled
value x.sub.i.sub.+1, means for applying the result of addition by
said adding means to said detecting means for the purpose of
detecting the differential between the result of addition and
another sampled value x.sub.i.sub.+2, and means controlled by the
output of said comparing means to be connected to said adding means
in lieu of said holding means for deriving the result of addition
from said adding means, said result of addition and said sampled
value being selectively derived depending on the appearance or
disappearance of the output from said comparing means.
2. A signal detection system as claimed in claim 1, further
comprising integrating means for integrating the differential
between said result of addition and said sampled value for a
predetermined period of time, another comparing means for comparing
the output of said integrating means with a predetermined third
threshold value, and means for displaying the output of said
comparing means.
3. A signal detection system comprising holding means for holding
an electrical signal subjected to sampling, a pair of first
detecting means for detecting the differentials between sampled
values x.sub.1 and x.sub.i.sub.+1 and between sampled values
x.sub.i.sub.+1 and x.sub.i.sub.+2 respectively (where i is an
integer) held in said holding means, second detecting means for
detecting the differential between the outputs of said first
detecting means, comparing means for comparing the output of said
second detecting means with a predetermined first threshold value,
discriminating means for discriminating the polarity of the output
of said second detecting means, adding means controlled by the
output of said discriminating means for adding a predetermined
second threshold value to the sampled value x.sub.i in response to
the appearance of the sampled value x.sub.i.sub.+2, means for
applying the result of addition by said adding means to said first
detecting means for the purpose of detecting the differential
between the result of addition and the sampled value
x.sub.i.sub.+2, and means controlled by the output of said
comparing means to be connected to said adding means in lieu of
said holding means for deriving the result of addition from said
adding means, said result of addition and said sampled value being
selectively derived depending on the appearance or disappearance of
the output from said comparing means.
4. A signal detection system as claimed in claim 3, further
comprising integrating means for integrating the differential
between said result of addition and said sampled value for a
predetermined period of time, another comparing means for comparing
the output of said integrating means with a predetermined third
threshold value, and means for displaying the output of said
comparing means.
5. A signal detection system comprising holding means for holding
an electrical signal subjected to sampling, detecting means for
detecting the differential between sampled values x.sub.i and
x.sub.i.sub.+1 (where i is an integer) held in said holding means,
means for dividing the output of said detecting means into 1/2,
comparing means for comparing the output of said detecting means
with a predetermined first threshold value, adding means for adding
the output of said dividing means to the sampled value x.sub.i,
determining means for determining the pattern of said electrical
signal depending on the appearance or disappearance of the output
from said comparing means, and means controlled by the output of
said determining means to be connected to said adding means in lieu
of said holding means for deriving the result of addition from said
adding means, said result of addition and said sampled value being
selectively derived depending on the appearance or disappearance of
the output from said determining means.
6. A signal detection system comprising holding means for holding
an electrical signal subjected to sampling, detecting means for
detecting the differential between sampled values x.sub.i and
x.sub.i.sub.+1 (where i is an integer) held in said holding means,
comparing means for comparing the output of said detecting means
with a predetermined threshold value, measuring means controlled by
the output of said comparing means for measuring the period of time
between successive outputs of said comparing means, determining
means for determining the pattern of said electrical signal
depending on the appearance or disappearance of the output from
said comparing means, a function generator for generating a linear
function on the basis of the sampled value x.sub.i and the output
of said measuring means, and means controlled by the output of said
determining means for deriving the sampled value x.sub.i.sub.+1 in
lieu of the linear function, said linear function and said sampled
value being selectively derived depending on the appearance or
disappearance of the output of said determining means.
7. A signal detection system comprising holding means for holding
an electrical signal subjected to sampling, detecting means for
detecting the differential between sampled values x.sub.i and
x.sub.i.sub.+1 (where i is an integer) held in said holding means,
comparing means for comparing the output of said detecting means
with a predetermined first threshold value, discriminating means
for discriminating the polarity of the output of said detecting
means, adding means controlled by the output of said discriminating
means for adding a predetermined second threshold value to the
sampled value x.sub.i in response to the appearance of the sampled
value x.sub.i.sub.+ 1, means controlled by the output of said
discriminating means for supplying the predetermined second
threshold value to said adding means for addition to thereby said
result of addition, and means controlled by the output of said
comparing means to be connected to said adding means in lieu of
said holding means for deriving said result of addition from said
adding means, said result of addition and said sampled value being
selectively derived depending on the appearance or disappearance of
the output from said comparing means.
Description
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
This invention relates to signal detection systems in which means
are provided for reducing or removing noises involved in or
superposed on an electrical signal so as to detect the electrical
signal with a high signal-to-noise ratio (S/N ratio), and more
particularly to a signal detection system preferably used for
detecting a bioelectrical signal such as one recorded on an
electroencephalogram or electrocardiogram with a high S/N ratio by
reducing or removing noises involved in or superposed on such
bioelectric signal.
2. DESCRIPTION OF THE PRIOR ART
The present invention will be described with reference to the
detection of a bioelectrical signal, for example, a brain wave
signal. The brain wave signal is generally derived and detected
from electrodes mounted on the scalp and this signal is detected in
many cases in a state in which noises or more specifically an
electromyogram is superposed on the electroencephalogram.
The electroencephalogram is used for the diagnosis and discovery of
brain diseases or persons having brain troubles by visual
observation of the picture by brain specialists. It is demanded to
remove the noise of the kind above described as much as possible
since the presence of such noise leads to an erroneous diagnosis.
An analog low-pass filter has been mainly employed in a prior art
system for the purpose of removing the electromyogram superposed on
the electroencephalogram. However, the prior art system employing
the analog low-pass filter has had the following defects:
1. When a high-frequency component, for example, a spike wave is
involved in an electroencephalogram signal, this high-frequency
component is greatly attenuated.
2. An artificially produced wave (artifact) tends to be involved in
the signal component obtained by removing noise from the
electroencephalogram.
In view of the above defects, it is common practice to compare an
electroencephalogram obtained by removing the electromyogram by the
use of the analog low-pass filter with an electroencephalogram
obtained without using this filter for the diagnosis of brain
diseases.
SUMMARY OF THE INVENTION
With a view to obviate prior art defects as above described, it is
an object of the present invention to provide a novel and improved
signal detection system in which means are provided for reducing a
muscle action potential signal relative to an
electroencephalographic signal involving such a muscle action
potential signal so as to detect the electroencephalographic signal
with a high signal-to-noise ratio.
Another object of the present invention is to provide a signal
detection system which can reproduce an electroencephalogram signal
with good reproducibility even after the reduction of the
noise.
A further object of the present invention is to provide a signal
detection system which enables to make an accurate diagnosis of
brain diseases on the basis of an electroencephalogram.
In an effort to attain the above objects, the inventors carried out
the following experiment. In view of the fact that the character of
a muscle action potential signal involved in an
electroencephalographic signal cannot be distinctly determined in
the case of measurement of the brain wave with prior art pen
recording, the inventors have employed a method comprising
subjecting such an electroencephalogram signal to analog-to-digital
conversion, stretching the time axis to about ten times that of the
original value, subjecting the A-D converted signal to
digital-to-analog conversion again, and recording the D-A converted
signal with a pen recorder for measuring the character of the
muscle action potential signal. The inventors have found very
interesting results as follows:
1. The gradient of the muscle action potential signal is steeper
than that of an abnormal electroencephalographic or spike wave
portion having a steepest gradient in the brain wave signal. It is
known that the gradient of the spike wave is biologically given by
3.41 .+-. 1.14 .mu. V/ms (mean value .+-. standard deviation).
Thus, when, for example, the signal is sampled at a sampling period
of 2.5 ms (400 Hz), the differential between the sampled values or
data of the spike wave sampled with the sampling period of 2.5 ms,
in other words, the gradient of the spike wave, is given by (3.41
.+-. 1.14) .times. 2.5 .apprxeq. 8.5 .+-. 2.9 .mu. V/2.5 ms. Due to
the fact that the differential in the case of the muscle action
potential signal is greater than the above value, the waveform
portion in which the differential between the sampled values
exceeds a predetermined value, that is, the waveform portion having
a gradient steeper than a predetermined value may be removed so as
to remove the electromyogram from the electroencephalogram.
2. The duration of the muscle action potential signal is less than
20 ms. Especially, the muscle action potential signal having a
duration of less than 10 ms is objectionable. Therefore,
observation of several sampled data can clearly identify the muscle
action potential signal when the electroencephalographic signal is
sampled at the sampling period of 2.5 ms.
On the basis of the above facts, the present invention contemplates
the provision of a process which comprises subjecting an
electroencephalographic signal including a muscle action potential
signal to sampling for obtaining first sampled data x.sub.i (i = 1,
2, 3, . . . ), seeking the differential y.sub.i (x.sub.i.sub.+1 -
x.sub.i) between the first sampled data x.sub.i, and correcting
x.sub.i.sub.+1 by the sum of x.sub.i and a predetermined
infinitesimal increment C.sub.2 for reducing the magnitude of
x.sub.i when the differential y.sub.i exceeds a predetermined
threshold value C.sub.1, or leaving x.sub.i.sub.+1 in the existing
value without correcting x.sub.i.sub.+ 1 when the differential
y.sub.i does not exceed the threshold value C.sub.1 so as to obtain
second sampled data. In this manner, any waveform portion in which
the differential exceeds the predetermined threshold value C.sub.1,
that is, any waveform portion having a steeper gradient than a
predetermined value can be removed for reducing the muscle action
potential signal component.
In other words, the present invention contemplates the provision of
a system in which a sampled data x.sub.i.sub.+1, which is replaced
by x.sub.i .+-. C.sub.2 when .vertline.y.sub.i .vertline. >
C.sub.1 (where x.sub.i + C.sub.2 is used if y.sub.i > C.sub.1
and x.sub.i - C.sub.2 is used if y.sub.1 < -C.sub.1) and which
remains in the existing values when .vertline.Y.sub.i .vertline.
< C.sub.1, is derived from data obtained by sampling an
electroencephalographic signal including a muscle action potential
signal so as to remove any waveform portion in which the
differential exceeds a predetermined value, that is, any waveform
portion having a gradient steeper than a predetermined value,
thereby reducing the objectionable muscle action potential signal
component to a minimum.
In the present invention, the threshold value C.sub.1 is selected
to be 15 .mu. V/2.5 ms in view of the gradient of the spike wave in
the electroencephalogram signal, and the infinitesimal increment
C.sub.2 is selected to be 5 .mu. V/2.5 ms taken into consideration
the reproducibility of the brain wave signal.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1a shows a waveform of an electroencephalogram signal (spike
wave) including a muscle action potential signal.
FIG. 1b shows a waveform of an output from an analog low-pass
filter when the signal waveform shown in FIG. 1a is passed through
a filter.
FIG. 2a shows a waveform of an electroencephalogram (slow wave)
including a muscle action potential signal.
FIG. 2b shows a waveform of an output from an analog low-pass
filter when the signal waveform shown in FIG. 2a is passed through
the filter.
FIG. 3a shows schematically a waveform obtained by sampling an
electroencephalogram including a muscle action potential signal
having a single peak.
FIGS. 3b and 3c show schematically waveforms obtained by sampling a
first differential and a second differential respectively of the
waveform shown in FIG. 3a.
FIG. 3d shows schematically a waveform obtained after correction of
the waveform shown in FIG. 3a according to the present
invention.
FIG. 4a shows schematically a waveform obtained by sampling an
electroencephalographic signal including a muscle action potential
signal having consecutive peaks.
FIGS. 4b and 4c show schematically waveforms obtained after
correction of the waveform shown in FIG. 4a according to the
present invention.
FIG. 5a shows schematically a waveform obtained by sampling an
electroencephalogram including a muscle action potential signal
having a sustained peak.
FIG. 5b shows schematically a waveform obtained after correction of
the waveform shown in FIG. 5a according to the present
invention.
FIGS. 6a to 6e are block diagrams showing the structure of
preferred embodiments of the present invention and of control
devices used therewith.
FIG. 7a shows schematically a waveform obtained by sampling an
abnormal electroencephalographic wave or spike wave contained in an
electroencephalogram.
FIGS. 7b and 7c show schematically waveforms obtained by sampling a
first differential and a second differential respectively of the
waveform shown in FIG. 7a.
FIG. 8 shows schematically a waveform obtained by sampling a noise
involved in an electroencephalogram.
FIG. 9 is a chart showing classified patterns of muscle action
potentials.
FIG. 10 is a block diagram showing the structure of another
embodiment of the present invention adapted for middle point
correction.
FIG. 11 is a block diagram showing the structure of a further
embodiment of the present invention adapted for linear
correction.
FIGS. 12a to 12c are block diagrams showing the structure of other
embodiments of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1a shows a waveform of an electroencephalogram including a
high-frequency component such as a spike wave. When such a waveform
is passed through a conventional analog low-pass filter, a muscle
action potential signal involved in and superposed on the
electroencephalogram is removed to a certain extent, but the
high-frequency component is also attenuated greatly as seen in FIG.
1b.
FIG. 2a shows a waveform of an electroencephalogram having a muscle
action potential signal involved and superposed thereon. When such
a waveform is passed through a conventional analog low-pass filter,
an artificially produced waveform portion or artifact as shown in
FIG. 2b tends to be involved in the output waveform in which the
muscle action potential signal is substantially removed by the
filter.
Electroencephalographic signals including a muscle action potential
signal as shown in FIGS. 1a and 2a are sampled at a frequency of
400 Hz and the electroencephalographic signal component in the
sampled signals is omitted. FIGS. 3a-5b show schematically such
waveforms and differentials between the sampled values. FIG. 3a
represents the case in which the muscle action potential signal
includes a single peak, and this case will hereinafter be called a
pattern A. FIG. 4a represents the case in which a plurality of
patterns A having different levels appear consecutively, and this
case will hereinafter be called a pattern B. FIG. 5a represents the
case in which the muscle action potential signal includes a
sustained peak having a duration which is two or three times the
duration (2.5 ms) of the pattern A, and this case will hereinafter
be called a pattern C. FIGS. 3b and 3c show schematically waveforms
obtained by sampling a first differential and a second differential
described later respectively. FIGS. 3d, 4b, 4c and 5b show
schematically waveforms obtained after reducing the muscle action
potential signal component in a manner as described later.
FIG. 6b is a block diagram showing the structure of an embodiment
of the present invention. The system shown in FIG. 6b is
constructed so that, in response to the application of a first
sampled signal including a muscle action potential signal component
of the kind corresponding to anyone of the patterns A, B and C, a
second sampled signal substantially free from the muscle action
potential signal component can be obtained at the output. FIG. 6a
is a block diagram showing the structure of a control device which
generates a plurality of control signals S.sub.1, S.sub.2 and
S.sub.3 for controlling the system shown in FIG. 6b. Referring to
FIG. 6a, a three-stage shift register SL is controlled by a train
of shift pulses S having a frequency which is three times the
sampling frequency of 400 Hz. Output signals S.sub.1 and S.sub.2 of
the first and second stages respectively of the shift register SL
are applied to an OR gate OR. An inhibit gate IN is connected to
the OR gate OR for inhibiting the output of the OR gate OR. The
control signals S.sub.1, S.sub.2 and S.sub.3 appear successively
from the first, second and third stages respectively of the shift
register SL in response to the shift action by the shift pulse S.
The control signals S.sub.1 and S.sub.2 are applied to the OR gate
OR and an input is applied from the OR gate OR to the inhibit gate
IN. In this case, no input is applied to the first stage of the
shift register SL. However, when the control signal S.sub.3 appears
from the shift register SL, an input is applied from the inhibit
gate IN to the first stage of the shift register SL to provide the
control signal S.sub.1. In this manner, the control signals appear
in the order of S.sub.3 .fwdarw.S.sub.1 .fwdarw.S.sub.2 within a
period of time of 2.5 ms in response to the application of the
shift pulses S.
Referring to FIG. 6b, the first sampled signal is applied to an
input terminal 1--1 of the system. A data selector 20 is controlled
by a control signal *3. A pair of holding circuits 2 and 3 are
controlled by the control signals S.sub.2 and S.sub.3 respectively
and are connected at their output terminals to a differential
amplifier 4. An absolute value detecting circuit 5 detects the
absolute value of the output of the differential amplifier 4. A
comparator 6 compares the output of the absolute value detecting
circuit 5 with a predetermined threshold voltage representing a
constant C.sub.1 = 15 .mu. V/2.5 ms applied through a terminal
TH.sub.6. The output of the comparator 6 and the control signal
S.sub.1 are applied to an AND gate 7, and a monostable
multivibrator 8 is triggered by the output of the AND gate 7. The
monostable multivibrator 8 delivers an output or control signal *3
for controlling a data selector 18 and the data selector 20
described above. More precisely, when the multivibrator 8 delivers
the output *3, the data selectors 18 and 20 are connected to an
adder 17 and a holding circuit 19 respectively, while when no
output appears from the multivibrator 8, the data selectors 18 and
20 are connected to the holding circuit 3. Another comparator 9 is
connected at one of the input terminals to the output terminal of
the differential amplifier 4 and is grounded at the other input
terminal. The output of the comparator 9 and the control signal
S.sub.1 are applied to an AND gate 10, and another monostable
multivibrator 11 is triggered by the output of the AND gate 10 to
deliver an output or control signal *4. An inhibit gate 12 is
connected to the output terminal of the comparator 9. The output of
the inhibit gate 12 and the control signal S.sub.1 are applied to
an AND gate 13, and another monostable multivibrator 14 is
triggered by the output of the AND gate 13 to deliver an output or
control signal *5. A pair of gates 15 and 16 are turned on in
response to the application of the control signals *4 and *5
respectively and remain in the off state in the absence of such
control signals. Predetermined threshold voltages representing a
constant C.sub.2 = 5 .mu. V/2.5 ms and a constant -C.sub.2 = -5
.mu. V/2.5 ms are applied to the gates 15 and 16 through terminals
TH.sub.15 and TH.sub.16 respectively. The output of the holding
circuit 2 and one of the predetermined threshold voltages C.sub.2
and -C.sub.2 are applied to the adder 17. In the presence of the
control signal *3, the value held in the holding circuit 19 is
supplied through the data selector 20 to be held in the holding
circuit 2 in response to the application of the control signal
S.sub.2 to the holding circuit 2.
In operation, when, for example, a first sampled signal having a
pattern A waveform as shown in FIG. 3a is applied to the input
terminal 1--1 of the system, a sampled value x.sub.1 is held in the
holding circuit 3 in response to the application of the control
signal S.sub.3 to the holding circuit 3. Since no sampled value is
held in the holding circuit 2 at this time, no output appears from
the differential amplifier 4. Therefore, even when the control
signal S.sub.1 is applied to the AND gate 7, no output appears from
the AND gate 7 due to the fact that no output is delivered from the
comparator 6. The data selector 20 is connected to the holding
circuit 3 due to the absence of the control signal *3, and the
holding circuit 2 operates in response to the application of the
control signal S.sub.2 to hold the sampled value x.sub.1 held in
the holding circuit 3. This completes one cycle of the control
signals in the order of S.sub.3 .fwdarw.S.sub.1 .fwdarw.
S.sub.2.
Subsequently, another or next sampled value x.sub.2 is applied to
the holding circuit 3 to be held therein in response to the
application of the control signal S.sub.3. The value x.sub.2 held
in the holding circuit 3 and the value x.sub.1 held in the holding
circuit 2 are applied to the differential amplifier 4 and an output
(x.sub.2 - x.sub.1) is delivered from the differential amplifier 4.
The absolute value detecting circuit 5 detects the absolute value
.vertline.x.sub.2 - x.sub.1 .vertline. of the output of the
differential amplifier 4. An output appears from the comparator 6
due to the fact that the absolute value .vertline.x.sub.2 - x.sub.1
.vertline. is greater than the threshold value C.sub.1 in the case
of the pattern A. An output appears from the AND gate 7 in response
to the application of the control signal S.sub.1. The monostable
multivibrator 8 is triggered thereby and delivers the control
signal *3 so that the data selectors 18 and 20 are connected to the
adder 17 and holding circuit 19 respectively. At the same time, the
comparator 9 compared the output (x.sub.2 - x.sub.1) of the
differential amplifier 4 with the zero potential so as to determine
whether (x.sub.2 - x.sub.1) is positive or negative.
Since x.sub.2 - x.sub.1 > 0 in the case of the pattern A, an
output appears from the comparator 9 to be applied to the AND gate
10, and an output appears from the AND gate 10 in response to the
application of the control signal S.sub.1 thereto. The monostable
multivibrator 11 is triggered by the output of the AND gate 10 and
delivers the control signal *4. Since no output appears from the
inhibit gate 12 in this case, no output appears from the AND gate
13 and the multivibrator 14 does not deliver the control signal *5.
The gate 15 is turned on in response to the application of the
control signal *4 and the predetermined threshold value C.sub.2 is
applied to the adder 17 through the terminal TH.sub.15 and gate 15.
The value x.sub.1 held in the holding circuit 2 is also applied to
the adder 17. Thus, a corrected output x.sub.2 ' = x.sub.1 +
C.sub.2 appears from the adder 17 to be applied through the data
selector 18 to the holding circuit 19 to be held therein. The
corrected output of the data selector 18 is held in the holding
circuit 19 for the sampling period of time of 2.5 ms and is then
delivered from an output terminal 1-2 of the system as an output
signal due to the fact that the holding circuit 19 is controlled by
the control signal S.sub.1. Subsequently, the corrected value is
transferred from the holding circuit 19 to the holding circuit 2
through the data selector 20 in response to the appearance of the
control signal S.sub.2. Another sampled value x.sub.3 is applied to
and held in the holding circuit 3 in response to the application of
the control signal S.sub.3 and an output (x.sub.3 - x.sub.2 ')
appears from the differential amplifier 4 to be applied to the
absolute value detecting circuit 5, thence to the comparator 6.
Since the value (x.sub.3 - x.sub.2 ') is smaller than the threshold
value C.sub.1 in the case of the pattern A, no output appears from
the comparator 6, and no output appears from the AND gate 7 even
with the application of the control signal S.sub.1 to the AND gate
7. The monostable multivibrator 8 is not triggered and the control
signal *3 does not appear from the multivibrator 8. Thus, the value
x.sub.3 held in the holding circuit 3 is supplied through the data
selector 18 to the holding circuit 19 to be held therein, and this
value is subsequently delivered from the output terminal 1-2 of the
system. In this manner, a second sampled signal as shown in FIG. 3d
is obtained at the output terminal 1-2 of the system in the case of
the pattern A. It will be seen from FIG. 3d that the level of the
muscle action potential signal component in this second sampled
signal is remarkably reduced.
On the other hand, when a first sampled signal having a pattern B
waveform as shown in FIG. 4 a is applied to the input terminal 1--1
of the system, an output appears from the AND gate 7 to trigger the
monostable multivibrator 8 in response to the application of the
control signal S.sub.1 to the AND gate 7 due to the fact that the
absolute value .vertline.x.sub.3 - x.sub.2 '.vertline. of the
differential (x.sub.3 - x.sub.2 ') is greater than the
predetermined threshold value C.sub.1. However, no output appears
from the AND gate 10 and the monostable multivibrator 11 is not
triggered since x.sub.3 - x.sub.2 ' < 0 in this case.
Consequently, the inhibit gate 12 delivers an output and the
control signal *5 is delivered from the monostable multivibrator 14
to turn on the gate 16. Due to the turn-on of the gate 16, the
predetermined threshold value -C.sub.2 is supplied to the adder 17
through the terminal TH.sub.16 and gate 16 to be added to the value
x.sub.2 ' = x.sub.1 + C.sub.2 held in the holding circuit 2 to give
the result x.sub.3 ' = x.sub.2 ' - C.sub.2 = x.sub.1 + C.sub.1 -
C.sub.2 = x.sub.1. This corrected value x.sub.3 ' is supplied from
the holding circuit 19 to the holding circuit 2 through the data
selector 20 in response to the appearance of the control signal
S.sub.2. Subsequently, a new sampled value x.sub.4 is applied to
and held in the holding circuit 3 in response to the appearance of
the control signal S.sub.3. The operation similar to that above
described is repeated thereafter. Consequently, a corrected
waveform or a second sampled signal waveform as shown in FIG. 4b
can be obtained.
When a first sampled signal having a pattern C waveform as shown in
FIG. 5a is applied to the input terminal 1--1 of the system, the
system operates in a manner entirely similar to that above
described so that a second sampled signal waveform as shown in FIG.
5b can be obtained.
The above description has referred to the case in which the
differential between a sampled value corrected by the threshold
value C.sub.2 and the next sampled value is compared with the
predetermined threshold value C.sub.1. However, the present
invention is in no way limited to the comparison between such
values, and the differentials between the sampled values, that is,
the differential between the sampled values x.sub.1 and x.sub.2 and
the differential between the sampled values x.sub.2 and x.sub.3 may
be compared with the threshold value C.sub.1 and correction may
then be applied to the result of comparison. In this case, the
system shown in FIG. 6b may be suitably modified as shown in FIG.
6e. Referring to FIG. 6e, the data selector 20 in FIG. 6b is
eliminated to directly connect the holding circuit 2 with the
holding circuit 3 and another holding circuit 20' is connected
between the holding circuit 19 and the adder 17. In the system
shown in FIG. 6e, the control signal S.sub.2 is applied to the
holding circuit 20' to supply a shift pulse, the output of the
holding circuit 19 is applied to the holding circuit 20' as an
input thereto, and the output of the holding circuit 20' is applied
to the adder 17 as one of the inputs thereto.
In the system shown in FIG. 6e, the holding circuit 20' responds to
the control signal S.sub.2 to hold the value held in the holding
circuit 19 and the value held in the holding circuit 20' is applied
to the adder 17. Thus, when the absolute value .vertline.x.sub.1 -
x.sub.2 .vertline. is greater than the threshold value C.sub.1, the
adder 17 delivers a corrected output x.sub.1 + C.sub.1. Therefore,
the patterns A and B can be corrected in a manner similar to that
described with reference to FIG. 6b. In the case of the pattern C,
any substantial correction is applied due to the fact that the
values except the value (x.sub.1 - x.sub.2) are zero as will be
apparent from FIG. 5a.
In the above description, the threshold value representing the
constant C.sub.1 has been set at 15 .mu.V/2.5 ms. However,
depending on persons whose electroencephalogram is to be measured,
there are some cases in which an electroencephalogram includes a
waveform portion which exceeds this threshold value and can still
be considered as a spike wave. If the threshold voltage is set at
the specified value and correction is applied in such a case, a
great reduction may occur in the amplitude of the peak point
(waveform portion having a greatest amplitude value) having an
especially steep gradient in the spike wave and poor
reproducibility of the electroencephalogram may result. In order to
deal with the case in which a spike wave having a steep gradient
exists in an electroencephalogram, the present invention employs an
arrangement in which means are provided for correcting the result
of measurement on the basis of a second differential for the
purpose of reducing the muscle action potential signal component
without attenuating the spike wave. In other words, a second
differential is derived from first differentials between sampled
values and correction is applied to the result of comparison
between this second differential and a predetermined threshold
value representing a constant C.sub.1 ' = 30 .mu.V/(2.5 ms).sup.2
instead of the threshold value C.sub.1 above described. Examples of
second differentials of the muscle action potential signal and
brain wave signal are shown in FIGS. 3c and 7c respectively.
FIG. 6d is a block diagram showing the structure of parts of
another embodiment of the present invention adapted for deriving
such a second differential, and FIG. 6c is a block diagram showing
the structure of a control device which generates a plurality of
control signals S.sub.1, S.sub.2, S.sub.3 and S.sub.4 for
controlling the system shown in FIG. 6d. Referring to FIG. 6c, a
four-stage shift register SL is controlled by a train of shift
pulses S having a frequency which is four times the sampling
frequency of 400 Hz. Output signals S.sub.1, S.sub.2 and S.sub.3 of
the first, second and third stages respectively of the shift
register SL are applied to an OR gate OR. An inhibit gate IN is
connected to the OR gate OR for inhibiting the output of the OR
gate OR. This control device operates in a manner similar to that
described with reference to FIG. 6a, and the control signals appear
in the order of S.sub.4 .fwdarw.S.sub.1 .fwdarw.S.sub.2
.fwdarw.S.sub.3 within a period of time of 2.5 ms.
The system shown in FIG. 6d is actually a modification of the
system shown in FIG. 6b and differs from the latter in that three
holding circuits 2-1, 2-2 and 2-3 and three differential amplifiers
4-1, 4-2 and 4-3 are provided in place of the holding circuits 2
and 3 and differential amplifier 4 and the data selector 20 is
eliminated.
When a first sampled signal having a pattern A waveform as shown in
FIG. 3a is applied to the input terminal 1--1 of the system, a
value x.sub.1 is held in the holding circuit 2-3 in response to the
application of the control signal S.sub.4. The control signal
S.sub.1 is subsequently applied to one of the input terminals of
the AND gate 7. At this time, the contents of the holding circuits
2-1 and 2-2 are zero and no outputs appear from the differential
amplifiers 4-1, 4-2 and 4-3. Thus, no input is applied to the other
input terminal of the AND gate 7 and the monostable multivibrator 8
is not triggered. Subsequently, the control signal S.sub.2 is
applied to the holding circuit 2-1, but the content of the holding
circuit 2-1 is zero due to the fact that the content of the holding
circuit 2-2 is zero at this time.
In response to the application of the control signal S.sub.3 to the
holding circuit 2-2, the value x.sub.1 held in the holding circuit
2-3 is transferred to the holding circuit 2-2. Another or next
value x.sub.2 is then supplied to and held in the holding circuit
2-3 in response to the application of the control signal S.sub.4.
However, the content of the holding circuit 2-1 is still zero at
this time and no outputs appear from the differential amplifiers
4-1 and 4-3. No output appears from the AND gate 7 and the
monostable multivibrator 8 is not triggered even when the control
signal S.sub.1 is applied to the AND gate 7. The value x.sub.1 held
in the holding circuit 2-2 is transferred to the holding circuit
2-1 in response to the application of the control signal S.sub.2,
the value x.sub.2 held in the holding circuit 2-3 is transferred to
the holding circuit 2-2 in response to the application of the
control signal S.sub.3, and a new value x.sub.3 is supplied to and
held in the holding circuit 2-3 in response to the application of
the control signal S.sub.4. Thus, the differential amplifiers 4-1,
4-2 and 4-3 deliver a first differential (x.sub.2 - x.sub.1), a
first differential (x.sub.3 - x.sub.2) and a second differential
[(x.sub.3 - x.sub.2) - (x.sub.2 - x.sub.1)] respectively. The
absolute value detecting circuit 5 detects the absolute value of
the second differential .vertline.(x.sub.3 - x.sub.2) - (x.sub.2 -
x.sub.1).vertline. and this absolute value is supplied to the
comparator 6 to be compared with a predetermined threshold value
representing the constant C.sub.1 ' = 30 .mu.V/(2.5 ms).sup.2
suppled through the terminal TH.sub.6. Due to the fact that this
second differential is greater than the threshold value C.sub.1 '
as seen in FIG. 3c in the case of the pattern A, an output appears
from the comparator 6 and an output appears from the AND gate 7 in
response to the application of the control signal S.sub.1. The
system operates thereafter in the same manner as that described
with reference to FIG. 6b, except that the predetermined threshold
value representing the constant C.sub.2 used for correction is 10
.mu.V/(2.5 ms).sup.2. In this manner, necessary correction is
applied to the result of sampling to obtain a second sampled
signal. A first sampled signal including a pattern B waveform as
shown in FIG. 4a can be similarly processed.
It can be seen from the above description that little attenuation
occurs in an portion (spike wave) of the electroencephalogram
having a steep gradient as shown in FIG. 7a. This is because the
peak point having a steep gradient is solely corrected relative to
the second differential due to the fact that the gradient of the
spike wave is not so steep at points except the peak point as seen
in FIG. 7b.
The above description has referred to the case in which an
electroencephalogram including a muscle action potential signal is
sampled to detect the muscle action potential signal component
having a gradient steeper than a predetermined value and the values
obtained by sampling are corrected by a predetermined threshold
value for reducing the muscle action potential signal component.
However, in the case of the pattern C, distortion may occur in the
electroencephalographic signal waveform after correction or an
artifact may be artificially produced in the corrected
electroencephalogram. FIG. 8 shows schematically a waveform
obtained after sampling a brain wave signal including such an
artifact and this waveform will hereinafter be called a pattern D.
In order to improve the reproducibility of such a waveform and also
to improve the reproducibility of the pattern B waveform, linear
correction or middle point correction is preferably employed. In
the linear correction, a first signal obtained by sampling an
electroencephalogram is corrected by a linearly approximated value
obtained by linear approximation of two sampled values and a period
of time therebetween. In the middle point correction, such a signal
is corrected by the middle point values.
In order to carry out such linear correction or middle point
correction, the differential between first sample values x.sub.i
and x.sub.i.sub.+1 of a signal obtained by sampling is compared
with the threshold value representing the constant C.sub.1 = 15
.mu.V/2.5 ms, and 1 is used to represent the case in which the
absolute value of the differential is greater than C.sub.1, while 0
is used to represent the case in which such value is not greater
than C.sub.1. Referring to FIG. 9, the patterns A to D of the
muscle action potential signal are represented by 5-bit coded
patterns of 1 and 0, and the linear correction or middle point
correction is applied or is not applied to the patterns A to D
depending on the coded patterns. The potterns A to D in the chart
shown in FIG. 9 are coded in the following manner:
1. In the case of the pattern A, the differential between sampled
values is either 1 or 0, an the pattern A is represented by, for
example, (00000) or (00110). In the pattern A waveform shown in
FIG. 3a, the absolute values of the differentials between x.sub.1
and x.sub.2 and between x.sub.2 and x.sub.3 are greater than
C.sub.1, and they are represented by 1, while the differentials
between any other values of x.sub.i and x.sub.i.sub.+1 are
represented by 0. Thus, the pattern A waveform shown in FIG. 3a is
represented by (01100).
2. The pattern B corresponds to the case in which the pattern A
appears consecutively. Thus, the pattern B includes more 1's than
the pattern A as seen in FIG. 9 and the patter B waveform shown in
FIG. 4a is represented by (01111).
3. The pattern C corresponds to the case in which the duration (2.5
ms) of the pattern A is increased to two or three times. The
pattern C is represented by, for example, (01010) or (01001) as
seen in FIG. 9 depending on the appearance of 1 and 0. The pattern
C waveform shown in FIG. 5 is represented by (01001) due to the
fact that the absolute values of the differentials between x.sub.1
and x.sub.2 and between x.sub.4 and x.sub.5 are greater than
C.sub.1.
4. the pattern D is a stepwise varying pattern. This pattern D is
represented by, for example, (00100) as seen in FIG. 9 due to the
fact that the absolute value of the differential between values
x.sub.i and x.sub.i.sub.+1 at the stepped portion is greater than
C.sub.1 and this case is represented by 1, while any other
differentials are represented by 0. The pattern D waveform shown in
FIG. 8 is represented by (01000) since the absolute value of the
differential between x.sub.2 and x.sub.3 is greater than C.sub.1.
In the case of this pattern D, no correction is applied to its
coded pattern in view of the fact that unsatisfactory waveform
reproducibility may result when corrected by a predetermined
threshold value as pointed out hereinbefore.
FIG. 10 is a block diagram showing the structure of another
embodiment of the present invention adapted for middle point
correction, and like reference numerals are used therein to denote
like parts appearing in FIG. 6b. Referring to FIG. 10, a first
signal obtained by sampling is applied through an input terminal
1--1 to a pair of delay means 20 and 21. The delay means 20 acts to
delay the input signal by five bits, while the delay means 21 acts
to delay the input signal by four bits. Another delay means 22 is
provided to delay the output of a differential amplifier 4 by five
bits. A voltage divider 23 divides the output of the delay means 22
into 1/2. A 5-stage shift register 24 is connected to a monostable
multivibrator 8 to receive the output of the latter. An inhibit
gate 25 inverts the output from the first stage of the shift
register 24. The output of the inhibit gate 25 and outputs from the
remaining stages of the shift register 24 are applied to an AND
gate 26.
In operation, suppose, for example, that a first sampled signal
including a muscle action potential signal component having a
pattern B vaveform as shown in FIG. 4a is applied to the input
terminal 1--1 of the system. In response to the application of such
an input signal, the differentials (x.sub.2 - x.sub.1), (x.sub.3 -
x.sub.2), (x.sub.4 - x.sub.3), . . . are successively delivered
from the differential amplifier 4. This output is applied through
an absolute value detecting circuit 5 to a comparator 6 to be
compared with a predetermined threshold value C.sub.1 supplied
through a terminal TH.sub.6. An output appears from the comparator
6 due to the fact that each differential is greater than the
threshold value C.sub.1 in the case of the pattern B. An AND gate 7
is turned on in response to the application of a control signal
S.sub.1, and the monostable multivibrator 8 is triggered to apply
its output to the shift register 24. As a result, the shift
register 24 registers (11110) and the output from the first stage
of the shift register 24 is inverted into 1 by the inhibit gate 25.
An output appears from the AND gate 26 due to the application of
all the inputs from the shift register 24.
On the other hand, the differentials are also applied from the
differential amplifier 4 to the delay means 22 to be delayed by
five bits thereby, and the output of the delay means 22 is divided
into 1/2 by the voltage divider 23, this divided voltage being then
applied to one of the input terminals of an adder 17. The values
x.sub.1, x.sub.2, x.sub.3, x.sub.4 and x.sub.5 of the first sampled
signal are successively applied to the other input terminal of the
adder 17 after being delayed by five bits by the delay means 21.
The adder 17 executes the addition of the half value of the
differential and the sampled value, for example, the addition of
1/2(x.sub.2 - x.sub.1) and x.sub.1. In the meantime, a data
selector 18 is controlled by the control signal applied from the
AND gate 26 and is placed in the position in which it supplies the
result of addition carried out by the adder 17 to a holding circuit
19. Thus, the result of addition of the sampled value to the half
value of the differential appears at an output terminal 1-2 of the
system as a second sample signal having a waveform as shown in FIG.
4c.
When the coded pattern corresponding to the pattern B does not
exist within the five bits of the first sampled signal, no control
signal appears from the AND gate 26 and the data selector 18 is
placed in the position in which it supplies the output of the delay
means 20 directly to the holding circuit 19 so that the values of
the first sampled signal appear successively at the output terminal
1-2 of the system. A plurality of combinations each consisting of a
shift register and an inhibit gate as above described may be
arranged in parallel so as to detect a group of coded patterns
corresponding to various kinds of the pattern B. In this manner,
the pattern B to be subjected to the middle point correction can be
detected and a second sampled signal substantially free from the
muscle action potential signal component of the pattern B can be
obtained.
FIG. 11 is a block diagram showing the structure of still another
embodiment of the present invention adapted for linear correction,
and like reference numerals are used therein to denote like parts
appearing in FIG. 6b. Referring to FIG. 11, a first signal obtained
by sampling is applied through an input terminal 1--1 to a delay
means 20 to be suitably delayed thereby. A function generator 21
generates a linear function for the purpose of linear correction. A
timer 27 is connected to a monostable multivibrator 8 to be
controlled by the output of the latter. A plurality of inhibit
gates 25-1, 25-2 and 25-3 are provided for inverting the outputs
from the first, third and fourth stages respectively of a
five-stage shift register 24.
In operation, suppose, for example, that a first sampled signal
including a muscle action potential signal component having a
pattern C waveform as shown in FIG. 5a is applied to the input
terminal 1--1 of the system to be subjected to linear correction.
In response to the application of such an input signal to the input
terminal 1-1, the differentials (x.sub.2 - x.sub.1), (x.sub.3 -
x.sub.2), (x.sub.4 - x.sub.3) and (x.sub.5 - x.sub.4) are
successively delivered from a differential amplifier 4 in a manner
similar to that described with reference to FIG. 11. Due to the
fact that the absolute values of the differentials (x.sub.2 -
x.sub.1) and (x.sub.5 - x.sub.4) are greater than a predetermined
threshold value C.sub.1, an output appears from the monostable
multivibrator 8 each time such differential appears from the
differential amplifier 4. As a result, the shift register 24
registers (01001) and the outputs from the first, third and fourth
stages of the shift register 24 are inverted into 1 by the
respective inhibit gates 25-1, 25-2 and 25-3. An output appears
from the AND gate 26 to be applied to a data selector 18 for
controlling same. The output of the monstable multivibrator 8 is
also applied to the timer 27, which is set in response to the first
pulse applied from the multivibrator 8 and is reset in response to
the application of the next input pulse so that the period of time
between these pulses is measured. The output of the timer 27 is
applied to the function generator 21. Since the data selector 18 is
now placed in the position in which it supplied the output of the
delay means 20 to the function generator 21 by being controlled by
the control signal applied from the AND gate 26, a linear function
obtained by linear correction of the sampled values x.sub.1 and
x.sub.5 and the period of time therebetween is generated from the
function generator 21 for the above period of time following the
sampled value x.sub.1. Thus, a linearly corrected second sampled
signal is applied through a holding circuit 19 to appear at an
output terminal 1-2 of the system.
When the coded pattern corresponding to the pattern C does not
exist within the five bits of the first sampled signal, no control
signal appears from the AND gate 26 and the data selector 18 is
placed in the position in which it supplies the output of the delay
means 20 directly to the holding circuit 19 so that the first
sampled signal appears at the output terminal 1-2 without being
subjected to the linear correction. A plurality of combinations
each consisting of a shift register and AND gates as above
described may be arranged in parallel so as to detect a group of
coded patterns corresponding to various kinds of the patterns A and
C. In this manner, the patterns A and C to be subjected to the
linear correction can be satisfactorily detected and the desired
reduction of the muscle action potential signal component can be
attained.
No correction is applied to the muscle action potential signal
component of the pattern D as described previously. Thus, even if
there is a correcting system including the shift registers and AND
gates, which exclusively detects the coded patterns except that
corresponding to the pattern D, the first sampled signal is not
detected, and thus, the desired objects can be attained.
It will be understood that a high S/N ratio can be obtained by
virtue of the fact that a muscle action potential signal superposed
on a brain wave signal can be substantially removed. Further, an
electroencephalogram having better reproducibility than heretofore
can be obtained and the diagnosis with better accuracy can be
expected. This contributes more to the advance of medical
science.
The foregoing description has referred to a system for reducing a
muscle action potential signal component superposed on or involved
in a brain wave signal and detecting the brain wave signal with
good reproducibility. However, the present invention is in no way
limited to such a system. Diagnostically very important is a system
which comprises means for measuring noise involved in an
electroencephalogram, means for automatically generating an alarm
to tell the clinical examiner the fact that the allowable quantity
of the noise exceeds a predetermined threshold value so that the
diagnosis can be automatically interrupted temporarily, and means
for restarting the detection of the brain wave signal after the
source of the noise has been removed.
In an effort to obtain such a system, the inventors have made
experiments to determine the allowable quantity of noise involved
in an electroencephalogram and found that the diagnosis should be
ceased when the integrated value of the noise measured for a
predetermined period of time of, for example, one second exceeds a
predetermined threshold value representing a constant voltage
gradient value of, for example, 15 mV/sec.
According to another aspect of the present invention, the present
invention contemplates the provision of a system which measures
noise continuously and integrates the quantity of the noise
involved in a brain wave signal so that the clinic examiner can
make an accurate diagnosis of brain diseases on an
electroencephalogram.
An embodiment of the present invention suitable for this purpose
will be described with reference to FIG. 12a and 12b. FIG. 12b is a
block diagram showing the structure of parts of such an embodiment
adapted for obtaining an integrated value of a noise, and FIG. 12a
is a block diagram showing the structure of a control device.
Referring to FIG. 12a, a four-stage shift register SL is controlled
by a train of shift pulses S having a frequency which is five times
the sampling frequency of 400 Hz. Outputs S.sub.1 ', S.sub.2 ' and
S.sub.3 ' from the first, second and third stages respectively of
the shift register SL are applied to an OR gate OR to which an
inhibit gate IN is connected. The operation of the control device
shown in FIG. 12a is similar to that of the control device shown in
FIG. 6c and the control signals appear in the order of S.sub.4 '
.fwdarw. S.sub.1 ' .fwdarw. S.sub.2 ' .fwdarw. S.sub.3 ' within a
period of time of 2.5 ms. The function of the control signals
S.sub.1 ', S.sub.2 ' and S.sub.4 ' is the same as that of the
respective control signals S.sub.1, S.sub.2 and S.sub.3 in FIG. 6a.
The control signal S.sub.3 ' is used for integration of a
noise.
In FIG. 12b in which like reference numerals are used to denote
like parts appearing in FIG. 6b, a plurality of blocks designated
by the reference numerals 201 to 207 are provided for attaining the
integration of the noise. A control signal S.sub.O is generated by
a pulse generator (not shown) at intervals of a predetermined
period of time of, for example, 1 second.
Referring to FIG. 12b, a monostable multivibrator 8 delivers a
control signal *3 for controlling a gate 201, and the output of the
gate 201 is applied to one of the input terminals of an adder 202
to the other input terminal of which another input is applied from
a holding circuit 204. A data selector 203 is connected between the
adder 202 and the holding circuit 204 and is changed over to be
connected to ground in response to the application of the control
signal S.sub.O. The output of the data selector 203 is applied to
the holding circuit 204 to be held therein in response to the
application of the control signal S.sub.3 '. A gate 205 is turned
on in response to the application of the control signal S.sub.0,
and the output of the gate 205 is applied to a comparator 206 to be
compared with a predetermined threshold value C' supplied through a
terminal TH.sub.206. A monostable multivibrator 207 is triggered by
the output of the comparator 206, and the output of the
multivibrator 207 appears at an output terminal 1-3. The output of
the gate 205 appears also at another output terminal 1-4.
In operation, suppose, for example, that a first sampled signal
including a pattern A waveform as shown in FIG. 3a is applied
through an input terminal 1-1 of the system to a holding circuit 3
to be held therein. The differential between the value held in the
holding circuit 3 and the preceding sampled value held in another
holding circuit 2 appears at the output terminal of a differential
amplifier 4 and this output is applied to a comparator 6 through an
absolute value detecting circuit 5 and to another comparator 9
directly. Outputs appear from the comparators 6 and 9 when this
input is greater than a predetermined threshold value supplied
through a terminal TH.sub.6 and is greater than the zero potential
respectively. The outputs of the comparators 6 and 9 are applied to
one of the input terminals of AND gates 7 and 10 respectively. In
response to the application of the control signal S.sub.1 ' to the
other input terminal of the AND gates 7 and 10, outputs appear from
the AND gates 7 and 10 to trigger the monostable multivibrators 8
and 11 and control signals *3 and *4 are generated from these
multivibrators 8 and 11 respectively. The control signal *3 is
applied to the gate 201 to turn on same. This control signal *3 is
also applied to a data selector 18 to connect same to an adder 17
for receiving a corrected output from the adder 17. A gate 15 is
turned on in response to the application of the control signal *4
so that a predetermined threshold value supplied through a terminal
TH.sub.15 is applied to the adder 17 for correction and the
corrected value is delivered from the adder 17. This corrected
value is supplied through the data selector 18 to a holding circuit
19 to be held therein, and in response to the application of the
control signal S.sub.2 ' to the holding circuit 2, the corrected
value is supplied through a data selector 20 to the holding circuit
2 to be held therein. Thus, the output of the differential
amplifier 4 is given by the differential between the corrected
value, for example, x.sub.2 ' held in the holding circuit 3.
At this time, the gate 201 is already in the on position due to the
application of the control signal *3 thereto. Therefore, the output
of the gate 201 represents the differential between the sampled
value x.sub.2 and the corrected value x.sub.2 ' of x.sub.2, that
is, the quantity of the removed noise which is the muscle action
potential signal component. The output of the gate 201 and the
output of the holding circuit 204 are added to each other in the
adder 202, and the result of addition is kept held in the holding
circuit 204 until the one-second signal S.sub.O is applied to the
data selector 203. In other words, integration is carried out for
this period of time. The gate 205 is turned on in response to the
application of the control signal S.sub.O, and the output of the
gate 205 representing the quantity of the noise appears at the
output terminal 1-4 and is applied to, for example, a digital
display means to be displayed thereon. At the same time, the
holding circuit 204 is reset due to the fact that the data selector
203 is connected to ground in response to the application of the
control signal S.sub.O. The output of the gate 205 is also applied
to one of the input terminals of the comparator 206 to be compared
with the predetermined threshold value C' supplied to the other
input terminal of the comparator 206 through the terminal
TH.sub.206. This threshold value representing the constant C' is,
for example, 15 mV/sec. Therefore, when the output of the holding
circuit 204 is greater than the threshold value C', an output
appears from the comparator 206 to trigger the monostable
multivibrator 207, and a control signal appears at the output
terminal 1-3 to inform the clinical examiner of the fact that the
muscle action potential signal component is included in a large
quantity in the electroencephalogram. An alarm means or the like
may be connected to the output terminal 1-3 to give an alarm for
the above situation so that the diagnosis can be interrupted
temporarily and restarted automatically after eliminating the
source of inclusion of the muscle action potential signal and
confirming the disappearance of the output at the output terminal
1-3.
While the system shown in FIG. 12b has been described with
reference to the integration of a noise for a predetermined period
of time in the case of the system shown in FIG. 6b, it will be
apparent to those skilled in the art that, in the case of the
system shown in FIG. 6d too, a system as shown in FIG. 12c may be
employed for the integration of a noise in a manner similar to that
described with reference to FIG. 12b.
It will be understood from the above description that the present
invention provides a system in which means are provided for
integrating the separated muscle action potential signal for a
predetermined period of time, continuously displaying the
integrated value and automatically issuing an alarm when the
integrated value exceeds a predetermined threshold value, so that
the diagnosis can be ceased temporarily and restarted automatically
when the integrated value is reduced to less than the threshold
value. Thus, an accurate diagnosis of brain diseases on the basis
of the electroencephalogram can be ensured.
Further, while the foregoing description has referred solely to the
removal of muscle action potentials involved in a brain wave
signal, it will be apparent to those skilled in the art that the
present invention is also effectively applicable to the detection
of noises involved in a heart action potential signal and any other
bioelectrical signals as well as in common electrical signals.
* * * * *