JP5679629B2 - Optical brain function measuring device - Google Patents

Description

  The present invention relates to an optical brain function that performs optical measurement using a light transmitting probe and a light receiving probe disposed on a scalp of a subject, measures brain activity from a detection signal (measures brain function information), and displays the same. It relates to a measuring device.

  Near-infrared light penetrates skin tissue and bone tissue and is absorbed by oxyhemoglobin and deoxyhemoglobin in blood. Optical brain function measurement device using near infrared spectroscopy (NIRS), which measures brain activity in Japan, is used.

  In the optical brain function measuring apparatus, near infrared light of a few different wavelengths is emitted from a plurality of light transmitting parts (light transmitting probes) arranged at a predetermined interval (for example, 30 mm interval) on the subject's scalp. Irradiated light diffusely reflected by the brain (brain cortex) is received by a plurality of light receiving units (light receiving probes) on the scalp to perform optical measurement. From the detection signal obtained by optical measurement, the oxyhemoglobin concentration and deoxyhemoglobin concentration at the measurement site located between the light transmitting unit and the light receiving unit are obtained. Then, image data of brain activity is created from these hemoglobin concentrations, and further image processing such as averaging processing is performed on the image data to display on the screen.

  The light detection signal measured by the optical brain function measuring device includes a signal from the blood of the brain (brain cortex) and other signals, for example, a signal from the skin blood flow, and also includes heartbeat and respiration. Signals accompanying changes in the autonomic nervous system such as blood pressure are superimposed.

Therefore, these are regarded as physiological noises, and signals that are unlikely to be physiological changes in the brain are excluded as unnecessary components (artifacts) by visual evaluation based on the behavior of oxyhemoglobin and deoxyhemoglobin. It has been broken.
However, in the method of determining whether it is an unnecessary component by visual evaluation, individual differences among the evaluators are likely to occur.
As one method to make it easy to distinguish whether it is an unnecessary component, a periodic task is given to the subject during the optical measurement (brain activation paradigm), and a signal synchronized with the cycle of the task is detected. It is handled as a signal (referred to as brain function signal), and other signals are excluded as noise.

  Specifically, the task, rest, task, and rest state are repeatedly given to the subject, all detection signals are collected and stored during this time, a Fourier transform signal is calculated for all detection signals, and the Fourier transform signal To extract the signal synchronized with the task and rest period. Since the brain function signal caused by the task can be extracted as a signal motivated by the task and rest cycle, it is possible to perform measurement by removing noise other than the brain function signal caused by the task using the Fourier transform signal. it can.

In addition, as one of the analysis methods, under the assumption that "the observation signal is a signal in which independent signals from each signal source are linearly mixed", the independence criteria are set for a plurality of detection signals. Independent component analysis in which an independent signal of a signal source is estimated from a detection signal by performing an operation using an algorithm for satisfying the standard is known (Non-Patent Document 1, Non-Patent Document 2). Then, by applying this independent component analysis to the light detection signal of the optical brain function measuring device, a method for excluding noise signals of other independent sources (such as heartbeats) other than the brain function signal has been proposed. (See Patent Document 1).
JP 2006-280421 A L, Molgedey and H. G. Shuster, Separation of a mixture of independent signals using time delayed correlations, Phys. Rev. Lett., Vol.72, No.23, PP3634-3637, 1994 J. CARDOSO and A. SOULOUMIAC, JACOBI ANGLES FOR SIMULTAEOUS DIAGONALIZATION, SIAM, J. MATRIX ANAL. APPL., Vol.17, No.1, PP.161-164, 1996

When physiological signals other than brain function signals resulting from brain activity (signals originating from heartbeat, respiration, pulse, etc.) are superimposed on the detection signal, until now, such accompanying signals have been Since it is unnecessary noise for signal measurement, it has been focused on how to remove the noise.
The above-mentioned accompanying signal is desirably removed when considered as physiological noise, but from another viewpoint, it can also be considered as an accompanying signal including physiological information.

  Therefore, the present invention does not view physiological accompanying signals other than brain function signals as noise, but also analyzes these accompanying signals, so that an optical brain can be obtained from brain function signals. It aims at providing a function measuring device.

The brain function measuring device of the present invention made to solve the above problems, a plurality of probe pairs consisting of a light transmitting probe and a light receiving probe are arranged on the subject's scalp, and irradiated with measuring light from the light transmitting probe, An optical brain function measuring apparatus that detects light diffusely reflected by the brain with a light receiving probe and measures brain activity from the detection signal, and has the following configuration. That is, in this apparatus, a signal detection unit that acquires time-series detection signals from a plurality of measurement sites determined corresponding to each probe pair, and the acquired detection signal or hemoglobin concentration calculated based on the detection signal and observed signal storage control unit for storing a time series like signal as an observed signal related to dividing the observed signal for each predetermined unit time width, a Fourier transform for each of the segmented observed signals, independently Ingredient analysis, the main A section analysis signal acquisition unit that acquires a section analysis signal for each unit time width by performing any analysis operation of component analysis and a section analysis signal display control section that displays the section analysis signal are provided.

Here, “time-series signal related to hemoglobin concentration” means, for example, “oxyhemoglobin concentration signal”, “deoxyhemoglobin concentration signal”, “total hemoglobin concentration signal” calculated from the light absorption signal when optical measurement is performed. It is.
Further, the “predetermined unit time width” is a time width that can be set in advance or can be set later, and one division analysis signal is acquired for each unit time width.

In the present invention, the time-series observation signals stored by the observation signal storage control unit include a brain function signal and other physiological accompanying signals (signals that originate from heartbeat, respiration, pulse, etc.). Assuming it is included. Classification analysis signal acquisition unit, time series like the observed signal, and classified by the unit set time width, a Fourier transform for each of the segmented observed signals, independently Ingredient analysis, one of the principal component analysis By performing the analysis operation, a segmented analysis signal for each unit time width is acquired. The acquired segment analysis signal includes an accompanying signal in each unit time width. Therefore, when the segment analysis signal display control unit displays the segment analysis signal, the accompanying signal for each corresponding time segment can be observed as a frequency component signal, an independent component signal, and a principal component signal.

  According to the present invention, it is possible to obtain a frequency component signal, an independent component signal, and a principal component signal for each time segment. As a result, the relationship between the brain function signal and the accompanying signal at each time point can be measured, and the temporal change in the relationship between the brain activity and the accompanying signal can be grasped.

In the above invention, it further comprises a task period information input unit for receiving information on a task period when measuring by giving a task to the subject, the classification analysis signal acquisition unit has a unit time width shorter than the task period, and a task The observation signal may be divided in synchronization with the start time of the period.
Thereby, when measuring the influence of the task on the brain activity, the change during the task can be measured by time division.

In the above invention, the analysis operation performed by the segmented analysis signal acquisition unit is Fourier transform, and the segmented analysis signal display control unit performs two-dimensional display of the segmented analysis signal by the frequency axis and the power axis in time series for each unit time width. Alternatively, a three-dimensional display arranged side by side may be performed.
In the above invention, the analysis operation performed by the segmented analysis signal acquisition unit is Fourier transform, and the segmented analysis signal display control unit displays the segmented analysis signal on a two-dimensional display of the frequency axis and the time axis. The power may be displayed in color or luminance.
According to these, the dynamic change of the accompanying signal decomposed | disassembled for every frequency can be confirmed visually.

  In this case, the measurement sites may be displayed side by side on the screen. Thereby, the change in brain activity can be confirmed two-dimensionally for each measurement site.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the optical brain function measuring apparatus of the present invention.

(Embodiment 1)
The optical brain function measuring apparatus 10 includes a measurement optical system 11, a signal detection unit 12, an observation signal storage control unit 13, a segment analysis signal display control unit 14, a segment analysis signal display control unit 15, and a display unit 16. The input device 17 and the memory 18 are provided. Among these, the measurement signal detection unit 12, the observation signal storage control unit 13, the segment analysis signal display control unit 14, and the segment analysis signal display control unit 15 are a computer 20 and software including a CPU, a ROM, a RAM, and the like. It is comprised by.

The measurement optical system 11 includes a plurality of light transmitting probes and a plurality of light receiving probes. The light transmitting probe irradiates light from the laser light source (three kinds of wavelength light (wavelengths 776, 804, 828 nm) for calculating the hemoglobin concentration) toward the brain, and the light receiving probe probes the light diffusely reflected by the brain. Lead to end detector. Each probe is alternately arranged with light transmitting probes and light receiving probes on the scalp by a lattice-like holder, so that the intermediate positions of the probe pairs of the adjacent light transmitting probes and light receiving probes are the measurement sites.
The detection operation by the probe pair is performed by controlling the light irradiation by the light transmitting probe and the light detection by the light receiving probe by a timing control circuit (not shown). Although there is no restriction | limiting in particular about the number of a measurement site | part, In this embodiment, it demonstrates as a measurement site | part being set as shown in FIG.

The signal detection unit 12 controls the measurement optical system 11 to detect detection signals X ₁ (t), X ₂ (t),..., X _n (t), (n = 24) from each measurement site. Control. Each detection signal is a time-series signal from the detection start to the detection end. Each detection signal is sampled at a minimum interval of 0.25 seconds, and the time series length from the start to the end is about 10 seconds to 10 minutes.

  The observation signal storage control unit 13 performs control to store the detected time-series detection signals from the respective measurement sites in the memory 18 as observation signals. Alternatively, control may be performed in which at least one time series signal of oxyhemoglobin concentration, deoxyhemoglobin concentration, and total hemoglobin concentration calculated from the detection signal is calculated and stored in the memory 18 as an observation signal.

  The segmented analysis signal acquisition unit 14 classifies the stored observation signal (detection signal or hemoglobin concentration signal) for each predetermined unit time width, and performs an analysis operation by Fourier transform on each of the segmented observation signals. As a result, an operation for obtaining a segmented analysis signal for each unit time width is performed.

  The division analysis signal display control unit 15 performs control to display the obtained division analysis signal on the screen.

Next, the operation of the optical brain function measuring apparatus 10 will be described.
FIG. 2 is a flowchart showing an example of the operation flow of the measurement operation by the optical brain function measuring apparatus 10. First, a case where brain activity is measured without giving a task will be described.

The measurement optical system 11 is set on the scalp, optical measurement is performed with a light transmitting probe and a light receiving probe, and detection signals X _n (t) and (n = 1 to 24) are collected at intervals of 0.25 seconds ( S101).
All the detection signals X _n (t) collected from the start of measurement to the end of measurement are sequentially stored in the memory 18 as observation signals (S102).
Subsequently, the detection signal X _n (t) is divided into time intervals with a unit time width that is initially set in advance or with a unit time width that is appropriately set by the input device 17 after the observation signal is stored (for example, at intervals of 10 seconds). Then, Fourier transform data (F (X _n (t))) for each unit time width is calculated by performing an analysis operation by Fourier transform on each of the divided observation signals, and the calculation result is used as the divided analysis signal. (S103).

Subsequently, the calculated division analysis signal is displayed on the display device 16 (S104). At this time, as shown in FIG. 3, for each measurement site (CH1 to CH24), a three-dimensional display in which two-dimensional display of the division analysis signal by the frequency axis and the power axis is arranged in time series for each unit time width. I do.
By displaying in this way, the frequency-resolved power spectrum at the time corresponding to the section can be obtained from the section analysis signal of one section, so that the influence of the accompanying signal at the time can be observed. For example, information related to breathing (10 to 20 times / minute) and heartbeat (60 to 75 times / minute) is superimposed with an accompanying signal having a frequency corresponding to the information. If it appears in the two-dimensional display, it can be understood that the influence of respiration and heartbeat is included in the signal. Furthermore, by displaying the two-dimensional display with the frequency axis and the power axis in a time-series manner for each unit time width and displaying it three-dimensionally, the time change of the accompanying signal can be dynamically displayed, and the state of the subject can be displayed. Visualize changes over time.

  In addition, as shown in FIG. 4, the spectral power can be displayed in color or luminance on a two-dimensional display of the frequency axis and the time axis based on the division analysis signal of each measurement site for each measurement site. . Displaying in this way facilitates visual grasp when there is a change in the accompanying signal.

(Embodiment 2)
Next, a case where a task is given and brain activity is measured will be described. FIG. 5 shows an optical brain function measuring apparatus 30 according to the second embodiment. About the same part as the optical brain function measuring apparatus 10 demonstrated in FIG. 1, description is abbreviate | omitted by attaching | subjecting a same sign. In the optical brain function measuring device 30, a task period information input unit 31 is added to the configuration of the optical brain function measuring device 10.
The task period information input unit 31 receives information on a task period when measurement is performed while giving a task to a subject by using an external device. For example, when a treadmill for walking (not shown) is used as an external device, an external output signal of the treadmill is input to the task period information input unit 31 and stored in the memory 17. With this external output signal, the task period and rest period of the treadmill can be grasped on the optical brain function measuring device 30 side.

And the division | segmentation analysis signal acquisition part 14 performs control which classifies an observation signal in synchronism with the start time of a task period with a unit time width shorter than a task period, when dividing the acquired observation signal. The unit time width has an initial value of 10 seconds, for example, and is set in advance. If it is desirable to change the setting, such as when the task period is short, an error display is performed to prompt the user to reset the appropriate unit time width.
Then, for example, as shown in FIG. 6, when the task, rest, task, and rest are repeated every 50 seconds, the task period is divided into unit time widths of 10 seconds and matched with the task start time.
By dividing in this way, the time division is divided in synchronization with the start time when the task is given, and the time change after giving the task can be accurately divided and observed for each unit time width. .

(Embodiment 3)
In the above embodiment, the segmented analysis signal acquisition unit 14 performs Fourier transform as an analysis operation, and performs frequency analysis for each unit time width. In this embodiment, independent component analysis is performed instead of frequency analysis by Fourier transform. That is, the segmented analysis signal acquisition unit 14 performs an analysis operation using an independent component analysis technique.

  Independent component analysis is performed using an observation signal vector (each detection signal Xn (t) in Embodiment 1 is a component of the observation signal vector), a mixing matrix, and an independent component signal vector that are related by the following equation (1). This is a calculation method for estimating a mixing matrix and an independent component signal from an observation signal vector.

  If the mixing matrix A is known, each component of the independent component signal vector S can be easily obtained by obtaining the inverse matrix of the mixing matrix A in the equation (1), but generally the mixing matrix A is also unknown. Therefore, various algorithms have been proposed to obtain them. For example, as described above, it is proposed in Non-Patent Documents 1 and 2.

  Therefore, by performing a known independent component analysis method according to the above-mentioned document from the equation (1) and performing an operation using an independence criterion and an algorithm for satisfying the criterion, the original signal can be obtained from the observed signal vector. Independent signal vectors and mixing matrices can be estimated. By the way, independent component analysis has been performed on the entire observation signal so far.

In the present embodiment, an independent component analysis is performed on the observation signal Xn (t) divided in time for each unit time width, and an operation for estimating the independent component signal S _n (t) for each unit time width is performed. Thereby, the independent component signal Sn (t) and the mixing matrix A for each time segment are obtained.
Therefore, for each independent component signal number obtained by the calculation, the independent component signal of each time section is two-dimensionally displayed with the horizontal axis representing the time axis instead of the frequency axis and the vertical axis representing the power axis. Then, in order to visualize the change for each time section, a three-dimensional display in which the two-dimensional display is arranged in time series for each time section is performed as in FIG.
The display in this case is obtained by changing the channel number in FIG. 3 to the independent component number and changing the frequency time axis to the time axis.

Thereby, each independent component signal can be displayed by time division, and the time change of the independent component can be grasped. Note that the mixing matrix A of the time segment can be displayed in correspondence with each independent component signal. Since the mixing matrix A is a weighting coefficient of the independent component signal forming the observation signal, the magnitude of the contribution of the independent component signal can be grasped.
The mixing matrix A can be displayed in color. In this case, it is utilized that each column component of the mixing matrix A is a weight component for each observation signal of each independent component signal. That is, a spatial map in which each column component of the mixing matrix A is made to correspond to the spatial arrangement of the observation signal is created, and this is color-displayed so as to correspond to FIG. 3 (the horizontal axis is the time axis and the vertical axis is the power axis) Display side by side. And the time transition of the space map is displayed. As a result, it is possible to display a spatial map of how each observation signal contributes to each independent component with time variation.

(Embodiment 4)
In the third embodiment, the classification analysis signal acquisition unit 14 performs the independent component analysis as the analysis calculation. However, in this embodiment, the principal component analysis is performed instead of the independent component analysis. That is, the segmented analysis signal acquisition unit 14 performs an analysis operation using a principal component analysis technique.

  The calculation method in the principal component analysis is similar to the independent component analysis. The observation signal vector Xn (t), the matrix A, and the principal component signal vector Sn (t) related by the same expression as the above expression (1) are used. From the observation signal vector Xn (t), the matrix A and When the principal component signal vector Sn (t) is estimated, it is not solved by using an independence criterion and an algorithm for satisfying the criterion, but only in that the eigenvalue problem is solved under a condition that maximizes the variance. The rest is the same. The solution of principal component analysis itself is well known.

  Therefore, by performing a calculation that maximizes the variance by performing a known principal component analysis method from the equation (1), the original principal component signal vector Sn (t) and the matrix A are calculated from the observed signal vector Xn (t). Can be estimated.

In this embodiment, the principal component analysis is performed on the observation signal Xn (t) time-divided for each unit time width, and the calculation for calculating the main component signal S _n (t) for each unit time width is performed.
Thereby, the principal component signal Sn (t) and the mixing matrix A for each time segment are obtained.
Therefore, for each principal component signal number obtained by the calculation, the principal component signal of each time segment is displayed two-dimensionally with the horizontal axis as the time axis and the vertical axis as the power axis. Then, in order to visualize the change for each time section, a three-dimensional display in which the two-dimensional display is arranged in time series for each time section is performed as in FIG.

  The present invention can be used for an optical brain function measuring device for measuring brain activity.

The block diagram which shows the structure of the optical brain function measuring device which is one Embodiment of this invention. The flowchart which shows the measurement operation | movement of the optical brain function measuring device which is one Embodiment of this invention. The figure which shows the example of a display of the measurement result by the optical brain function measuring apparatus of this invention. The figure which shows the example of a display of the measurement result by the optical brain function measuring apparatus of this invention. The block diagram which shows the structure of the optical brain function measuring apparatus which is other one Embodiment of this invention. The figure which shows an example of the time division performed when a task is given.

Explanation of symbols

10: Optical brain function measuring device 11: Measurement optical system 12: Signal detection unit 13: Observation signal storage control unit 14: Classification analysis signal acquisition unit 15: Classification analysis signal display control unit

Claims (3)

A plurality of probe pairs consisting of a light transmitting probe and a light receiving probe are arranged on the subject's scalp,
An optical brain function measuring device that measures brain activity from a detection signal by irradiating measurement light with a light transmitting probe and detecting light diffusely reflected by the brain with a light receiving probe,
A signal detection unit for acquiring time-series detection signals from a plurality of measurement sites determined corresponding to each probe pair;
An observation signal storage control unit that stores the detection signal or a time-series signal related to the hemoglobin concentration calculated based on the detection signal, as an observation signal;
A division analysis signal acquisition unit that divides the observation signal into predetermined unit time widths and acquires a division analysis signal for each unit time width by performing an analysis operation by independent component analysis for each of the divided observation signals. When,
A section analysis signal display control unit for displaying the section analysis signal;
A task period information input unit for receiving information on a task period when measuring by giving a task to a subject;
The optical brain function measuring apparatus characterized in that the division analysis signal acquisition unit classifies the observation signal in a unit time width shorter than the task period and in synchronization with the start time of the task period. The said division | segmentation analysis signal display control part performs the three-dimensional display which arranged the two-dimensional display of the division | segmentation analysis signal by a time axis and a power axis in time series for every unit time width. Optical brain function measuring device. The optical brain function measuring apparatus according to claim 2, wherein the display for each measurement site is arranged on the screen.