JP4813128B2 - Functional near-infrared spectrometer signal analyzer, functional near-infrared spectrometer, and program - Google Patents

Description

  The present invention relates to a signal analysis method and signal analysis apparatus for a functional near-infrared spectrometer, a functional near-infrared spectrometer, and a signal analysis program, and in particular, analyzes a signal detected by the functional near-infrared spectrometer. The present invention relates to a signal analysis method and a signal analysis apparatus for a functional near-infrared spectrometer, a functional near-infrared spectrometer, and a signal analysis program.

  There is a functional magnetic resonance imaging (fMRI) inspection method as a non-invasive image inspection method for brain function. The fMRI examination makes it possible to observe the localization of oxygenated hemoglobin concentration changes in the brain as an image using magnetism, and greatly contributes to elucidation of higher-order brain functions such as language and cognition. However, the apparatus used for the fMRI inspection is one of the most expensive and large-sized apparatuses among the inspection apparatuses, and the use environment requires a large magnetic shield room that covers the apparatus main body. For this reason, the movement of the fMRI apparatus main body is impossible, and there are many restrictions in the experiment.

  On the other hand, in recent years, an inspection method called functional near-infrared spectroscopy (fNIRS) has become widespread (see Patent Documents 1 to 3). This is a non-invasive examination method that can examine increase / decrease of oxygenated hemoglobin or deoxygenated hemoglobin in tissue from near the body surface by near infrared light. The apparatus used for the fNIRS inspection method has a relatively simple configuration, is easy to move, and can be used in a normal environment.

By using this fNIRS inspection apparatus, many experiments that could not be performed by a large-scale apparatus such as an fMRI apparatus can be performed, which attracts attention.
JP 2001-87250 A Special table 2002-509453 gazette Japanese translation of PCT publication No. 2002-502653

  However, the time-series signal obtained by the fNIRS apparatus is basically a non-stationary signal and includes many various fluctuation components from the high frequency region to the low frequency region. Therefore, in these signals, the component to be inspected and other components are mixed, and signal processing that can accurately extract the component to be inspected from the signal is desired.

  The present invention has been made in view of the above points. A signal analysis method, a signal analysis apparatus, and a functional near infrared of a functional near infrared spectrometer capable of accurately extracting a component to be inspected from a detection signal by fNIRS. An object is to provide a spectroscopic device and a signal analysis program.

  The present invention relates to a signal analysis method for a functional near-infrared spectrometer that analyzes a signal detected by a functional near-infrared spectrometer, and obtains a detection signal detected by the functional near-infrared spectrometer. And a signal acquisition procedure, and an analysis procedure for performing multi-resolution analysis on the signal acquired by the signal acquisition procedure using wavelet transform.

  The present invention also relates to a signal analysis device for a functional near-infrared spectroscopic device that analyzes a function of a desired inspection target based on a signal detected by the functional near-infrared spectroscopic device. An analysis unit that performs multi-resolution analysis on a detection signal detected by the outer spectroscopic device using wavelet transform is provided.

  Furthermore, the present invention is a functional near-infrared spectrometer for detecting a signal by functional near-infrared spectroscopy and analyzing a desired function of an inspection object, which is detected by functional near-infrared spectroscopy. An analysis unit that performs multi-resolution analysis on a detection signal using wavelet transform is provided.

  In addition, the program of the present invention allows a computer to acquire a detection signal detected by a functional near-infrared spectrometer and to perform multi-resolution analysis using wavelet transform on the signal acquired by the signal acquisition procedure. And performing an analysis procedure.

  According to the present invention, a signal acquisition procedure for acquiring a detection signal detected by a functional near-infrared spectrometer, and by performing multi-resolution analysis using wavelet transform on the signal acquired by the signal acquisition procedure, Analysis can be performed using the component that most reflects the function to be inspected, and thus the state of the function to be inspected can be analyzed reliably. Further, the processing can be realized by a small computer by using discrete wavelet transform which is easy to process. In addition, analysis can be performed in real time.

〔System configuration〕
FIG. 1 shows a system configuration diagram of an embodiment of the present invention.

  The fNIRS inspection system 100 according to the present embodiment includes, for example, an fNIRS inspection apparatus 111 and an analysis apparatus 112. The fNIRS inspection apparatus 111 irradiates the inspection object with near infrared light, detects the reflected light, and supplies a detection signal to the analysis apparatus 112. The analysis device 112 analyzes the detection signal supplied from the fNIRS inspection device 111 and displays the waveform and the like.

[FNIRS inspection device 111]
FIG. 2 is a block diagram of the fNIRS inspection apparatus 111.

  The fNIRS inspection device 111 mainly includes holders 121 and 122, a light transmission fiber 123, a detection fiber 124, a near infrared light generation device 125, a light reception device 126, a processing device 127, an operation panel 128, a storage device 129, and a display device 130. The interface 131 is configured. The holders 121 and 122 are mounted with tips of a plurality of light transmission fibers 123 and a plurality of detection fibers 124. The holders 121 and 122 are attached to the inspection object 141 so that the tips of the plurality of light transmission fibers 123 and the plurality of detection fibers 124 are in close contact with the inspection object 141.

  The light transmission fiber 123 and the detection fiber 124 are arranged in a lattice shape with respect to the inspection object 141. At this time, the light transmission fibers 123 and the detection fibers 124 are alternately arranged.

  Near-infrared light is supplied from the near-infrared light generator 125 to the other end of the light transmission fiber 123. The light transmission fiber 123 sends near infrared light supplied from the near infrared light generator 125 to the other end from the tip, and irradiates the inspection object 141 such as a human body. Here, for example, blood flow of the brain, and blood, particularly oxygenated hemoglobin and deoxygenated hemoglobin are targeted.

  Near-infrared light transmitted from the light transmission fiber 123 enters the inspection object 141. Near-infrared light that has entered the inside of the inspection object 141 is reflected by hemoglobin or the like and enters the tip of the detection fiber 124. At this time, it is possible to detect oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) by analyzing light components.

  The other end of the detection fiber 124 is connected to the light receiving device 126. Near-infrared light incident on the tip of the detection fiber 124 enters the light receiving device 126 through the detection fiber 124.

  The light receiving device 126 converts near infrared light supplied from the other end of the detection fiber 124 into an electrical signal. The electrical signal converted by the light receiving device 126 is supplied to the processing device 127, converted into digital data, and separated into signals of oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb). Stored in the storage device 129.

  Signals of oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) stored in the storage device 129 are displayed on the display device 130 as needed by operating the operation panel 128. Further, the data is transmitted to the analysis device 112 through the interface 131.

[Analyzer 112]
For example, the analysis device 112 includes a personal computer system, and includes an interface 141, a processing device 142, a storage device 143, an input device 144, and a display device 145.

  The interface 141 is an interface with the fNIRS inspection apparatus 111 and enables data transmission / reception.

  The processing device 142 performs data processing based on the analysis program installed in the storage device 143, and stores data corresponding to the detection signal supplied from the interface 141 in the storage device 143. The storage device 143 includes a hard disk drive, a memory, a disk drive, and the like. The storage device 143 has an analysis program installed therein and stores signal data supplied from the fNRIS inspection device 111. The storage device 143 is also used as a working storage area for the processing device 142.

  The input device 144 includes a keyboard, a mouse, and the like, and is a device that inputs data and various commands to the processing device 142. The display device 145 includes a CRT, an LCD, etc., and displays the analysis result of the analysis program executed by the processing device 142.

〔processing〕
FIG. 3 shows a processing flowchart of an analysis program according to an embodiment of the present invention.

  When the processing device 142 obtains the detection signal in step S1-1, the processing device 142 executes analysis processing in step S1-2. The analysis process is performed by multi-resolution analysis using discrete wavelet transform. The processing device 142 displays the waveform of the analysis result on the display device 145 in step S1-3.

  When a waveform reflecting a necessary component is selected from the waveform of the analysis result of the display device 145 in step S1-4, the processing device 142 extracts the components of the frequency bands before and after that in step S1-5. It adds to the waveform of the component selected at step S1-6, and displays the waveform on the display device 145.

[Analysis processing]
Here, the analysis process in step S1-2 will be described. In the analysis processing of this embodiment, multi-resolution analysis is performed on the signal data acquired from the fNIRS inspection apparatus 111 using discrete wavelet transform.

(Waveform analysis)
First, waveform analysis will be described.

  As the waveform analysis, Fourier analysis is common. Fourier analysis is an analysis method in which information in the time domain is Fourier transformed and replaced with information in the frequency domain. However, time information is missing in normal Fourier analysis.

  For this reason, short-time Fourier transform, so-called window Fourier transform, has been proposed. However, in the short-time Fourier transform, the time-frequency analysis of the signal can be performed, but a certain amount of knowledge and prediction for the analysis target is required. For this reason, considerable effort was required to detect and analyze unknown signals.

  Therefore, in this embodiment, wavelet transform is used for waveform analysis.

  The wavelet transform used in the present embodiment represents a local state of a waveform f (t) to be analyzed by translating and expanding and contracting a small wave Ψ (t) called a mother wavelet, and the waveform is analyzed based on this. It will be.

  The wavelet transform formula is generally

Given in.

  In Expression (1), Ψ ((t−b) / a) is an operation for (1 / a) the frequency shifted in time (phase) by b. The transformation by these operations is called continuous wavelet transformation. As is clear from the equation (1), the continuous wavelet transform requires a considerable amount of calculation and overlaps information.

  In order to simplify this, a wavelet transform called a discrete wavelet transform has been proposed.

  The discrete wavelet transform is a discretization of a and b in Equation (1).

It is expressed by the formula. This discrete wavelet transform generally has a feature that the amount of information is smaller than that of the continuous wavelet transform, but it is efficient and can be analyzed with high accuracy. Therefore, in this embodiment, waveform analysis is performed by this discrete wavelet transform. In this embodiment, the multiresolution analysis is performed using the discrete wavelet transform at this time. As a result of the multiresolution analysis, the brain for the task is analyzed using the analysis result that most reflects the effect on the executed task. The state of blood flow is analyzed.

[Multi-resolution analysis]
Next, multiresolution analysis using discrete wavelet analysis will be described.

  FIG. 4 is a diagram for explaining the multi-resolution analysis.

  When the waveform to be analyzed is S, for example, as shown in FIG. 4, the waveform is composed of low frequency components (approximation) a1, a2, a3 and high frequency components (detail) d1, d2, d3 having different frequency bands. Decompose into six hierarchical structures.

At this time, the analysis target waveform S in the hierarchical structure shown in FIG.
S = a3 + d3 + d2 + d1 (3)
It is represented by

〔Analysis result〕
Next, an analysis result by multi-resolution analysis using the discrete wavelet transform will be described.

  Here, an analysis method for performing multi-resolution analysis on cerebral blood flow signals by discrete wavelet transform will be described. The cerebral blood flow signal is subjected to multi-resolution analysis by discrete wavelet transform, the cerebral blood flow is decomposed into all frequency components, and only frequency components including significant signals are reconstructed. As a result, unnecessary fluctuations and noise can be removed.

  Also, each frequency component has a different meaning, so by decomposing by frequency, various signals contained in the cerebral blood flow, such as brain activity status for tasks, psychological changes for experiments, fluctuations due to heartbeat, etc. Can be evaluated separately.

  In addition, by using discrete wavelet transform instead of continuous wavelet transform, analysis processing can be performed in real time, and the calculation is relatively simple, so the calculation load can be reduced. If analysis results are sequentially displayed on a monitor while performing multi-resolution analysis during measurement, various signals included in cerebral blood flow can be individually viewed while being measured. If the necessary frequency is known in advance, it is possible to measure while monitoring only significant information by setting how to reconstruct components obtained by multi-resolution analysis.

[First analysis example]
FIG. 5 is a diagram for explaining the contents of the experiment.
The subject was presented with a stimulus sentence on the screen, and a task of making a correct / incorrect determination was imposed. The reaction at that time was measured by the fNIRS inspection device 111. At this time, as shown in FIG. 5, a block design of a 14-second rest, a 34-second task, and a 14-second rest was adopted. Three types of different tasks, i.e., Stimulus 1 (Task A), Stimulus 2 (Task B), and Stimulus 3 (Task C), were set as 3 blocks at a time, and this was repeated 4 times for a total of 12 blocks for 744 seconds .
FIG. 6 is a diagram showing an example of a detection signal when the vicinity of the broker area of the brain is detected by the fNIRS inspection apparatus. In the figure, the gray colored area indicates the task portion.
As shown in FIG. 6, it can be seen that oxygenated hemoglobin tends to rise during the task, but it contains high frequency noise. In addition, an increase in oxygenated hemoglobin oxy-Hb and a decrease in deoxygenated hemoglobin deoxy-Hb are observed throughout the experiment. However, when viewing the activation state for a task, it is desirable to remove these unnecessary information.
[Additional average result]
FIG. 7 is a diagram showing a result of performing averaging for each task on the oxygenated hemoglobin detection signal of the fNIRS apparatus. FIG. 7A shows task A, FIG. 7B shows task B, and FIG.
By taking the addition average, noise is removed as shown in FIG. 7, the change for each task can be seen, and the activation state for the task can be evaluated. For example, as shown in FIG. 7C, it can be seen that task C is the stimulus that is most activated. However, in FIG. 6, even in the same task C, there is almost no change from 310 seconds to 372 seconds, whereas there is a very large change from 682 seconds to 744 seconds, and there is a large variation in the activation state. As can be seen, this information is made invisible by taking the averaging as shown in FIG. For this reason, in the averaging, it is easy to miss the activation state for the task.

[Multi-resolution analysis results]
FIG. 8 is a diagram showing the result of performing multi-resolution analysis on the detection signal of oxygenated hemoglobin.

  Since the period of one block is 62 seconds, the periodic blood flow change related to the task appears in the vicinity of the component d8 corresponding to 0.00888 to 0.0178 Hz. As shown in FIG. 8E, the component d8 has a tendency to increase at the time of task and to decrease at the time of rest. Therefore, the signals d7 and d9 shown in FIGS. 8F and 8D adjacent to d8 shown in FIG. 8E are added to reconstruct the signal.

  FIG. 9 is a diagram showing a signal reconstructed by adding the components d7, d8, d9 of the multiresolution analysis result shown in FIG.

  In the signal reconstructed by adding the components d7, d8, and d9 shown in FIG. 9, the long trend component is removed simultaneously with the removal of the high frequency noise, and only the change related to the task is extracted and can be clearly understood. .

  FIG. 10 is a view showing another example of the detection signal when the vicinity of the broker area of the brain is detected by the fNIRS inspection apparatus, and FIG. 11 is a view showing the result of performing multi-resolution analysis on the detection signal shown in FIG. FIG. 12 is a diagram showing a signal reconstructed by adding the components d7, d8, and d9 of the multiresolution analysis result shown in FIG.

  As shown in FIGS. 10 to 12, multi-resolution analysis is similarly performed on other detection signals using discrete wavelet transform, and necessary components are extracted and added, thereby performing high-frequency noise. It can be seen that the long trend component is removed at the same time as the removal, and only the change related to the task is extracted and can be clearly captured.

〔effect〕
According to the present embodiment, the analysis can be performed using the component that most reflects the function to be inspected, and thus the function to be inspected can be reliably analyzed.

  Further, since the analysis can be performed by a relatively simple process such as discrete wavelet transform, the analysis can be performed using a personal computer or the like.

  Furthermore, information may be lost if the signal and noise separation is ambiguous when using baseline correction, etc., but if wavelet transform is used, analysis should be performed without missing information. Can do.

[Others]
In the present embodiment, the analysis apparatus 112 analyzes the signal, but the fNIRS apparatus 111 may perform wavelet transform using wavelet transform.

  In this embodiment, an appropriate analysis result is selected from the multi-resolution analysis result. However, an optimal analysis result may be selected according to the examination content.

  Furthermore, in the present embodiment, the case where the brain function is examined is described, but it goes without saying that the examination can be generally applied to the examination performed using the fNIRS examination apparatus.

It is a system configuration figure of one example of the present invention. 2 is a block configuration diagram of an fNIRS inspection apparatus 111. FIG. It is a processing flowchart of the analysis program of one Example of this invention. It is a figure for demonstrating multi-resolution analysis. It is a figure for demonstrating the content of experiment. It is a figure which shows an example of the detection signal when detecting the broker field vicinity of a brain with a fNIRS test | inspection apparatus. It is a figure which shows the result of having performed the addition average according to the task with respect to the detection signal of the oxygenated hemoglobin of fNIRS apparatus. It is a figure which shows the result of having performed multi-resolution analysis with respect to the detection signal of oxygenated hemoglobin shown in FIG. It is a figure which shows the signal reconfigure | reconstructed by adding the components d7, d8, d9 of the multi-resolution analysis result shown in FIG. It is a figure which shows another example of the detection signal when the broker field near the brain is detected by the fNIRS inspection apparatus. It is a figure which shows the result of having performed multi-resolution analysis with respect to the detection signal of oxygenated hemoglobin shown in FIG. It is a figure which shows the signal reconfigure | reconstructed by adding the components d7, d8, d9 of the multi-resolution analysis result shown in FIG.

Explanation of symbols

100 system 111 fNIRS inspection device, 112 analysis device 121, 122 holder, 123 light transmission fiber, 124 detection fiber 125 near infrared light generation device, 126 light receiving device, 127 processing device, 128 operation panel 129 storage device, 130 display device, 131 interface 141 interface 142 processing device 143 storage device 144 input device 145 display device

Claims (6)

A signal analysis device for a functional near-infrared spectrometer that analyzes a function of a desired object to be inspected based on a signal detected by the functional near-infrared spectrometer,
A multi-resolution analysis is performed on the detection signal detected by the functional near-infrared spectrometer using a discrete wavelet transform, and as a result of the multi-resolution analysis, a component in which the state of the function to be inspected is reflected. A signal analysis device for a functional near-infrared spectroscopic device, comprising an analysis unit that outputs a component obtained by adding the components of the frequency bands before and after that as an analysis result. The signal analysis device for a functional near-infrared spectrometer according to claim 1, wherein the component reflecting the state of the function to be inspected is a component in a frequency band that includes an inverse of the inspection period. A functional near-infrared spectrometer that detects a signal by functional near-infrared spectroscopy and analyzes a desired function of an inspection object,
A multi-resolution analysis is performed using a discrete wavelet transform on the detection signal detected by the functional near-infrared spectroscopy, and as a result of the multi-resolution analysis, a component in which the state of the function to be inspected is reflected. A functional near-infrared spectrometer having an analysis unit that outputs a component obtained by adding the components in the frequency bands before and after the analysis result. The functional near-infrared spectrometer according to claim 3, wherein the component in which the state of the function to be inspected is reflected is a component in a frequency band including the reciprocal of the inspection period. On the computer,
A signal acquisition procedure for acquiring a detection signal detected by the functional near-infrared spectrometer;
A multi-resolution analysis is performed on the signal acquired by the signal acquisition procedure using a discrete wavelet transform, and the result of the multi-resolution analysis reflects the state of the frequency band before and after the component reflecting the state of the function to be inspected. An analysis procedure for outputting a component obtained by adding the components as an analysis result ,
A computer-readable program characterized by causing the program to be executed. The program according to claim 5, wherein the component in which the state of the function to be inspected is reflected is a frequency band component including a reciprocal of the inspection period.