Multi-channel fNIRS Signal Acquisition System Based on Time-domain Interference Modulation

Abstract

The present invention provides a multi-channel fNIRS signal acquisition system based on time-domain interference modulation, which relates to the technical field of data acquisition. The system includes: a processor and a plurality of signal acquisition modules; the signal acquisition module includes a detector, a first light source, and a second light source; the detector, the first light source, and the second light source are sequentially arranged on the same straight line; the first modulated optical carrier signal emitted by the first light source and the second modulated optical carrier signal emitted by the second light source are subjected to interference modulation at the position to be measured to obtain a time-domain interference signal; the time-domain interference signal irradiates the substance to be detected in the position to be measured, diffuses, and is received by the detector to obtain an fNIRS signal; the processor demodulates the fNIRS signal to obtain a blood oxygen signal. The present invention realizes time-domain interference modulation through a dual light source, can distinguish the artifact signal from the fNIRS signal, realizes the suppression of artifacts during the acquisition process, and can eliminate the 1 / f noise in the signal.

Description

Technical Field

[0001] The present invention relates to the technical field of data acquisition, and particularly to a multi-channel fNIRS signal acquisition system based on time-domain interference modulation. Background Art

[0002] The acquisition of fNIRS needs to be based on two different wavelengths and at least one set of light sources and photodetectors, and reflects neural activities by measuring the changes in the properties of photons after diffusion in tissues. In a typical detection structure, near-infrared photons will first pass through the artifact area of non-neural activities, and then the modulation of signals related to neural activities can be achieved. Since the light intensity will decay with the increase of the diffusion path, the blood oxygen signal generated by the artifact accounts for the largest proportion after demodulation, and there are strong non-neural activity artifacts in the finally acquired blood oxygen signal, which affects the measurement effect.

[0003] To solve the above problems, it is a common solution at present to estimate the artifact components and suppress the estimated artifact components from the acquired signals to achieve noise filtering. However, there are some problems with the current solution. First, since the generation of artifacts is related to physiological activities and is accidental, it is difficult to accurately estimate the artifact components, and it is impossible to ensure the complete filtering of the artifact signals. Second, the separation process of the traditional solution needs to rely on statistical analysis methods, and it is necessary to estimate the artifact characteristics from the trend of the time series, and it cannot be processed in real time.

[0004] On the other hand, since the positions where artifacts are generated during detection are different from the target signals, by distinguishing and extracting signals at scales with spatial differences, it is also possible to avoid the introduction of artifacts during the acquisition process to achieve acquisition. However, photon diffusion is continuous in space, and it is impossible to simply avoid the introduction of artifacts under the premise of non-invasiveness.

[0005] At the same time, due to the inherent characteristics of the detector transistors, there is always flicker noise, also known as 1 / f noise, in the low-frequency passband. Therefore, there is often flicker noise in the acquired functional near-infrared spectroscopy (fNRIS) signals. As Figure 3 shown, the density distribution of flicker noise is inversely proportional to the frequency, and it accounts for the main component in the low-frequency narrowband noise below 100 Hz. Moreover, the probability distribution of flicker noise is the result of the superposition of multiple noise distributions. To remove flicker noise, the common method in the prior art is to improve the flicker noise density of the device itself, but this makes the detector expensive. Summary of the Invention

[0006] The object of the present invention is to provide a multi-channel fNIRS signal acquisition system based on time-domain interference modulation. By using a dual-light source to achieve time-domain interference modulation, artifact signals can be distinguished from fNIRS signals, suppressing artifacts during the acquisition process, and capable of eliminating 1 / f noise in the signals.

[0007] A multi-channel fNIRS signal acquisition system based on time-domain interference modulation, comprising: a processor and a plurality of signal acquisition modules; the number of the signal acquisition modules is the same as the number of channels;

[0008] The signal acquisition module includes a detector, a first light source, and a second light source;

[0009] The detector, the first light source, and the second light source are sequentially arranged on the same straight line; a perpendicular line is drawn from the position to be measured to the straight line, and the intersection point of the perpendicular line and the straight line is the center point between the detector and the first light source; the first modulated optical carrier signal emitted by the first light source and the second modulated optical carrier signal emitted by the second light source undergo interference modulation at the position to be measured to obtain a time-domain interference signal;

[0010] The first modulated optical carrier signal includes a first-wavelength modulated optical carrier signal and a second-wavelength modulated optical carrier signal, the second modulated optical carrier signal includes a third-wavelength modulated optical carrier signal and a fourth-wavelength modulated optical carrier signal, and the time-domain interference signal includes a first-wavelength time-domain interference signal and a second-wavelength time-domain interference signal;

[0011] The first-wavelength modulated optical carrier signal and the third-wavelength modulated optical carrier signal have the same wavelength, and the first-wavelength modulated optical carrier signal and the third-wavelength modulated optical carrier signal undergo interference modulation at the position to be measured to obtain the first-wavelength time-domain interference signal;

[0012] The second-wavelength modulated optical carrier signal and the fourth-wavelength modulated optical carrier signal have the same wavelength, and the second-wavelength modulated optical carrier signal and the fourth-wavelength modulated optical carrier signal undergo interference modulation at the position to be measured to obtain the second-wavelength time-domain interference signal;

[0013] Let i = 1, i ∈ K, where K is the number of signal acquisition modules;

[0014] The controller controls the i-th signal acquisition module to generate the first-wavelength time-domain interference signal and the second-wavelength time-domain interference signal;

[0015] The i-th first-wavelength time-domain interference signal irradiates the substance to be detected at the position to be measured, undergoes diffusion, and is received by the detector to obtain a first-wavelength fNIRS signal; the i-th second-wavelength time-domain interference signal irradiates the substance to be detected at the position to be measured, undergoes diffusion, and is received by the detector to obtain a second-wavelength fNIRS signal;

[0016] The processor performs envelope center demodulation on the first-wavelength fNIRS signal to obtain an initial oxyhemoglobin signal, and the processor performs envelope center demodulation on the second-wavelength fNIRS signal to obtain an initial deoxyhemoglobin signal;

[0017] The processor performs envelope center demodulation on the initial oxyhemoglobin signal to obtain an oxyhemoglobin signal, and the processor performs envelope center demodulation on the initial deoxyhemoglobin signal to obtain a deoxyhemoglobin signal;

[0018] The processor judges i. If i < K, then let i = i + 1 and return to "the controller controls the i-th signal acquisition module to generate the first-wavelength time-domain interference signal and the second-wavelength time-domain interference signal". If i ≥ K, then K pieces of the oxyhemoglobin signal and K pieces of the deoxyhemoglobin signal are obtained.

[0019] Optionally, the expressions of the first modulation optical carrier signal and the second modulation optical carrier signal are:

[0020]

[0021] In the formula: E1(t) is the first modulation optical carrier signal, E2(t) is the second modulation optical carrier signal, a is the amplitude of the first modulation optical carrier signal, b is the amplitude of the second modulation optical carrier signal, N1 is the DC component of the first modulation optical carrier signal, N2 is the DC component of the second modulation optical carrier signal, f1 is the frequency of the first modulation optical carrier signal, f2 is the frequency of the second modulation optical carrier signal, and t is time.

[0022] Optionally, the expression of the time-domain interference signal is:

[0023]

[0024] In the formula: E tot is the time-domain interference signal.

[0025] Optionally, the detection depth of the first-wavelength modulation optical carrier signal is greater than the vertical distance between the position to be measured and the straight line, and the detection depth of the second-wavelength modulation optical carrier signal is greater than the vertical distance between the position to be measured and the straight line.

[0026] Optionally, the expression of the detection depth of the first-wavelength modulation optical carrier signal is:

[0027]

[0028] In the formula: Z max is the detection depth of the first-wavelength modulation optical carrier signal, and d is the distance between the first light source and the detector.

[0029] Optionally, the expression of the first wavelength fNIRS signal is:

[0030]

[0031] Where: S(t) is the first wavelength fNIRS signal, and ρ1(t) is the initial oxygenated hemoglobin signal;

[0032] Optionally, the expression of the initial oxygenated hemoglobin signal is:

[0033]

[0034] Where: ρ2(t) is the oxygenated hemoglobin signal;

[0035] Optionally, the oxygenated hemoglobin signal is:

[0036]

[0037] Where: c is the amplitude of the oxygenated hemoglobin signal, A(t) is the AC component of the oxygenated hemoglobin signal, and N3 is the DC component of the oxygenated hemoglobin signal.

[0038] Optionally, the processor obtains the oxygenated blood oxygen value according to the oxygenated hemoglobin signal, and the processor obtains the deoxygenated blood oxygen value according to the deoxygenated hemoglobin signal;

[0039] Optionally, the expression of the oxygenated blood oxygen value is:

[0040]

[0041] Where: ρ2(t) is the oxygenated hemoglobin signal, and X(t) is the oxygenated blood oxygen value.

[0042] The effects of the present invention are as follows:

[0043] The multi-channel fNIRS signal acquisition system based on time-domain interference modulation of the present invention extracts the blood oxygen components at the spatial position of the target signal by using the time-domain interference carrier generated at the overlapping position of the photon diffusion paths based on the position difference between the artifact generation and the target signal, and realizes the filtering of the artifact signal.

[0044] The multi-channel fNIRS signal acquisition system based on time-domain interference modulation of the present invention can realize the filtering of the artifact signal without estimating the artifact characteristics and statistical classification.

[0045] An invention relates to a multi-channel fNIRS signal acquisition system based on time-domain interference modulation. By modulating an optical carrier signal, the original blood oxygen signal is modulated, causing the passband of the original blood oxygen signal to shift, achieving the migration of the low-frequency original blood oxygen signal to a high bandwidth and removing the 1 / f noise in the original blood oxygen signal.

[0046] The multi-channel fNIRS signal acquisition system of the present invention based on time-domain interference modulation avoids the influence brought by carrier oscillation during light source switching through time-division modulation and central sampling. Brief Description of the Drawings

[0047] Figure 1 is the schematic diagram of the time-domain interference modulation of the present invention;

[0048] Figure 2 is the schematic diagram of the frequency band migration of the original blood oxygen signal of the present invention;

[0049] Figure 3 is the schematic diagram of the flicker noise in functional near-infrared spectroscopy. Detailed Embodiments

[0050] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0051] Figure 1 is the schematic diagram of the time-domain interference modulation of the present invention. As Figure 1 shown, the present invention provides a multi-channel fNIRS signal acquisition system based on time-domain interference modulation, which includes: a processor and a plurality of signal acquisition modules; the number of signal acquisition modules is the same as the number of channels.

[0052] The signal acquisition module includes a detector, a first light source, and a second light source.

[0053] The detector, the first light source, and the second light source are sequentially arranged on the same straight line; a perpendicular line is drawn from the position to be measured to the straight line, and the intersection point of the perpendicular line and the straight line is the center point between the detector and the first light source; the first modulated optical carrier signal emitted by the first light source and the second modulated optical carrier signal emitted by the second light source are interferometrically modulated at the position to be measured to obtain a time-domain interference signal.

[0054] The time-domain interference signal will modulate the original blood oxygen signal, causing the frequency band of the original blood oxygen signal to shift, achieving the migration of the low-frequency original blood oxygen signal to a high bandwidth and eliminating the 1 / f noise in the original blood oxygen signal, as Figure 2 shown.

[0055] Specifically, the expressions of the first modulated optical carrier signal and the second modulated optical carrier signal are:

[0056]

[0057] Where: E1(t) is the first modulated optical carrier signal, E2(t) is the second modulated optical carrier signal, a is the amplitude of the first modulated optical carrier signal, b is the amplitude of the second modulated optical carrier signal, N1 is the DC component of the first modulated optical carrier signal, N2 is the DC component of the second modulated optical carrier signal, f1 is the frequency of the first modulated optical carrier signal, f2 is the frequency of the second modulated optical carrier signal, and t is time.

[0058] The expression of the time-domain interference signal is:

[0059]

[0060] Where: E tot is the time-domain interference signal.

[0061] The first modulated optical carrier signal includes a first wavelength-modulated optical carrier signal and a second wavelength-modulated optical carrier signal, the second modulated optical carrier signal includes a third wavelength-modulated optical carrier signal and a fourth wavelength-modulated optical carrier signal, and the time-domain interference signal includes a first wavelength time-domain interference signal and a second wavelength time-domain interference signal. The first wavelength time-domain interference signal and the second wavelength time-domain interference signal can refer to the time-domain interference signal. The detection depth of the first wavelength-modulated optical carrier signal is greater than the vertical distance between the position to be measured and the straight line, and the detection depth of the second wavelength-modulated optical carrier signal is greater than the vertical distance between the position to be measured and the straight line.

[0062] The expression of the detection depth of the first wavelength-modulated optical carrier signal is:

[0063]

[0064] Where: Z max is the detection depth of the first wavelength-modulated optical carrier signal, and d is the distance between the first light source and the detector.

[0065] The detection depth of the second wavelength-modulated optical carrier signal refers to the detection depth of the first wavelength-modulated optical carrier signal.

[0066] The first wavelength-modulated optical carrier signal and the third wavelength-modulated optical carrier signal have the same wavelength, and the first wavelength-modulated optical carrier signal and the third wavelength-modulated optical carrier signal perform interference modulation at the position to be measured to obtain the first wavelength time-domain interference signal.

[0067] The second wavelength-modulated optical carrier signal and the fourth wavelength-modulated optical carrier signal have the same wavelength, and the second wavelength-modulated optical carrier signal and the fourth wavelength-modulated optical carrier signal perform interference modulation at the position to be measured to obtain the second wavelength time-domain interference signal.

[0068] Let i = 1, i ∈ K, where K is the number of signal acquisition modules.

[0069] The controller controls the $i$-th signal acquisition module to generate a first-wavelength time-domain interference signal and a second-wavelength time-domain interference signal.

[0070] The $i$-th first-wavelength time-domain interference signal irradiates the substance to be detected at the position to be measured. After diffusion, it is received by the detector to obtain a first-wavelength fNIRS signal; the $i$-th second-wavelength time-domain interference signal irradiates the substance to be detected at the position to be measured. After diffusion, it is received by the detector to obtain a second-wavelength fNIRS signal.

[0071] Preferably, the expression of the first-wavelength fNIRS signal is:

[0072]

[0073] In the formula: $S(t)$ is the first-wavelength fNIRS signal, and $\rho_1(t)$ is the initial oxygenated hemoglobin signal.

[0074] The second-wavelength fNIRS signal can refer to the first-wavelength fNIRS signal.

[0075] The processor performs envelope center demodulation on the first-wavelength fNIRS signal to obtain the initial oxygenated hemoglobin signal, and the processor performs envelope center demodulation on the second-wavelength fNIRS signal to obtain the initial deoxygenated hemoglobin signal.

[0076] Furthermore, the expression of the initial oxygenated hemoglobin signal is:

[0077]

[0078] In the formula: $\rho_2(t)$ is the oxygenated hemoglobin signal.

[0079] The initial deoxygenated hemoglobin signal can refer to the initial oxygenated hemoglobin signal.

[0080] The processor performs envelope center demodulation on the initial oxygenated hemoglobin signal to obtain the oxygenated hemoglobin signal, and the processor performs envelope center demodulation on the initial deoxygenated hemoglobin signal to obtain the deoxygenated hemoglobin signal.

[0081] Specifically, the oxygenated hemoglobin signal is:

[0082]

[0083] In the formula: $c$ is the amplitude of the oxygenated hemoglobin signal, $A(t)$ is the AC component of the oxygenated hemoglobin signal, and $N_3$ is the DC component of the oxygenated hemoglobin signal.

[0084] The deoxygenated hemoglobin signal can refer to the oxygenated hemoglobin signal.

[0085] The processor determines i. If i < K, then let i = i + 1 and return to "the controller controls the ith signal acquisition module to generate a first-wavelength time-domain interference signal and a second-wavelength time-domain interference signal". If i ≥ K, then K oxyhemoglobin signals and K deoxyhemoglobin signals are obtained.

[0086] Preferably, the processor obtains an oxyhemoglobin oxygen value according to the oxyhemoglobin signal, and the processor obtains a deoxyhemoglobin oxygen value according to the deoxyhemoglobin signal.

[0087] The expression of the oxyhemoglobin oxygen value is:

[0088]

[0089] In the formula: ρ2(t) is the oxyhemoglobin signal, and X(t) is the oxyhemoglobin oxygen value.

[0090] Figure 1 In the following, taking the number of signal acquisition modules as 8 as an example, λ1 is the first wavelength, λ2 is the second wavelength, S1 - S8 represent 8 groups of light sources, each group of light sources includes a first light source and a second light source, each channel sequentially modulates a time-domain interference signal with a time length of T, and the period for completing the blood oxygen calculation of all channels once is 16T. Y is the first-wavelength fNIRS signal.

[0091] The above embodiments only describe the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A multi-channel fNIRS signal acquisition system based on time-domain interference modulation, characterized in that, It includes: a processor and a plurality of signal acquisition modules; the number of the signal acquisition modules is the same as the number of channels; each signal acquisition module includes a detector, a first light source, and a second light source; the detector, the first light source, and the second light source are sequentially arranged on the same straight line; a perpendicular line is drawn from the position to be measured to the straight line, and the intersection point of the perpendicular line and the straight line is the center point between the detector and the first light source; a first modulated optical carrier signal emitted by the first light source and a second modulated optical carrier signal emitted by the second light source are interferometrically modulated at the position to be measured to obtain a time-domain interference signal; the first modulated optical carrier signal includes a first wavelength modulated optical carrier signal and a second wavelength modulated optical carrier signal, the second modulated optical carrier signal includes a third wavelength modulated optical carrier signal and a fourth wavelength modulated optical carrier signal, and the time-domain interference signal includes a first wavelength time-domain interference signal and a second wavelength time-domain interference signal; the first wavelength modulated optical carrier signal and the third wavelength modulated optical carrier signal have the same wavelength, and the first wavelength modulated optical carrier signal and the third wavelength modulated optical carrier signal are interferometrically modulated at the position to be measured to obtain the first wavelength time-domain interference signal; the second wavelength modulated optical carrier signal and the fourth wavelength modulated optical carrier signal have the same wavelength, and the second wavelength modulated optical carrier signal and the fourth wavelength modulated optical carrier signal are interferometrically modulated at the position to be measured to obtain the second wavelength time-domain interference signal; let i = 1, i ∈ K, where K is the number of signal acquisition modules; the controller controls the i-th signal acquisition module to generate the first wavelength time-domain interference signal and the second wavelength time-domain interference signal; the i-th first wavelength time-domain interference signal irradiates the substance to be detected in the position to be measured, and after diffusion, it is received by the detector to obtain a first wavelength fNIRS signal; the i-th second wavelength time-domain interference signal irradiates the substance to be detected in the position to be measured, and after diffusion, it is received by the detector to obtain a second wavelength fNIRS signal; the processor performs envelope center demodulation on the first wavelength fNIRS signal to obtain an initial oxygenated hemoglobin signal, and the processor performs envelope center demodulation on the second wavelength fNIRS signal to obtain an initial deoxygenated hemoglobin signal; the processor performs envelope center demodulation on the initial oxygenated hemoglobin signal to obtain an oxygenated hemoglobin signal, and the processor performs envelope center demodulation on the initial deoxygenated hemoglobin signal to obtain a deoxygenated hemoglobin signal; the processor judges i, if i < K, then let i = i + 1 and return to "the controller controls the i-th signal acquisition module to generate the first wavelength time-domain interference signal and the second wavelength time-domain interference signal", if i ≥ K, then K oxygenated hemoglobin signals and K deoxygenated hemoglobin signals are obtained; The expressions of the first modulated optical carrier signal and the second modulated optical carrier signal are: Where: E1(t) is the first modulated optical carrier signal, E2(t) is the second modulated optical carrier signal, a is the amplitude of the first modulated optical carrier signal, b is the amplitude of the second modulated optical carrier signal, N1 is the DC component of the first modulated optical carrier signal, N2 is the DC component of the second modulated optical carrier signal, f1 is the frequency of the first modulated optical carrier signal, f2 is the frequency of the second modulated optical carrier signal, and t is time; The expression of the time-domain interference signal is: Where: E tot is the time-domain interference signal.

2. The multi-channel fNIRS signal acquisition system based on time-domain interference modulation according to claim 1, wherein The detection depth of the first wavelength-modulated optical carrier signal is greater than the vertical distance between the position to be measured and the straight line, and the detection depth of the second wavelength-modulated optical carrier signal is greater than the vertical distance between the position to be measured and the straight line.

3. The multi-channel fNIRS signal acquisition system based on time-domain interference modulation according to claim 2, wherein The expression for the detection depth of the first wavelength-modulated optical carrier signal is: Where: Z max is the detection depth of the first wavelength-modulated optical carrier signal, and d is the distance between the first light source and the detector.

4. The multi-channel fNIRS signal acquisition system based on time-domain interference modulation according to claim 1, wherein The expression for the first wavelength fNIRS signal is: Where: S(t) is the first wavelength fNIRS signal, and ρ1(t) is the initial oxygenated hemoglobin signal.

5. The multi-channel fNIRS signal acquisition system based on time-domain interference modulation according to claim 4, wherein, The expression for the initial oxygenated hemoglobin signal is: Where: ρ2(t) is the oxygenated hemoglobin signal.

6. The multi-channel fNIRS signal acquisition system based on time-domain interference modulation according to claim 5, wherein The oxygenated hemoglobin signal is: Where: c is the amplitude of the oxygenated hemoglobin signal, A(t) is the AC component of the oxygenated hemoglobin signal, and N3 is the DC component of the oxygenated hemoglobin signal.

7. The multi-channel fNIRS signal acquisition system based on time-domain interference modulation according to claim 1, wherein The processor obtains the oxygenated blood oxygen value according to the oxygenated hemoglobin signal, and the processor obtains the deoxygenated blood oxygen value according to the deoxygenated hemoglobin signal.

8. The multi-channel fNIRS signal acquisition system based on time-domain interference modulation according to claim 7, characterized in that, The expression for the oxygenated blood oxygen value is: Where: ρ2(t) is the oxygenated hemoglobin signal, and X(t) is the oxygenated blood oxygen value.

Images