CN101972148B - Disturbance elimination method of near infrared brain function detection based on empirical mode decomposition - Google Patents

Abstract

The invention relates to a disturbance elimination method of near infrared brain function detection based on empirical mode decomposition, which belongs to the field of optics and solves the problems that the physiological disturbance during the brain function detection cannot be effectively eliminated in an all-round way by utilizing low pass filtering, and additional equipment is needed when a self-adaptive filtering technology is utilized, and the structure is complex. The method comprises the following steps of: firstly, placing a near infrared probe consisting of a double-wavelength light source and a detector on a surface of scalp of a brain tissue to be detected to obtain an optical density variation time series; secondly, obtaining an oxyhemoglobin concentration variation time series delta[HbO2] (t) and a reduced hemoglobin concentration variation time series delta[HHb] (t) by utilizing a corrected lambert-beer law; thirdly, respectively carrying out the empirical mode decomposition on the delta[HbO2] (t) and the delta[HHb] (t) to obtain all IMF (Intrinsic Mode Function) components; and fourthly, carrying out Hilbert transform on all IMF components and eliminating the IMF components with the instantaneous frequency in the range of respiratory frequency and heart beat frequency of an ordinary person so as to eliminate the physiological disturbance during the near infrared brain function detection.

Description

The disturbance removing method of the Near-infrared Brain Function detection of decomposing based on empirical modal

Technical field

The present invention relates to disturbance removing method, belong to optical field based on the Near-infrared Brain Function detection of empirical modal decomposition.

Background technology

Near-infrared spectrum technique (NIRS) can provide the information of the cerebral cortex blood oxygen metabolism in the cerebration process---HbO2 Oxyhemoglobin concentration change (Δ [HbO ₂]) and reduced hemoglobin concentration change (Δ [HHb]), can be used for the detection of cerebration.With other the brain function detection method as: functional magnetic resonance resonance, magnetoencephalography, positron emission tomography and EECG are compared, easy to use, easy enforcement that near-infrared spectrum technique has, temporal resolution height, safety, advantage such as cheap.Yet, utilize near-infrared spectrum technique to bring out the detection of when excitation cerebration, can be subjected to the influence that the physiological activity such as the heart of human body are beated, breathed, be referred to as the physiology disturbance.This physiology disturbance not only appears in the outer cerebral tissue such as scalp, skull and cerebrospinal fluid, also appears in the deep layer cerebral tissue such as ectocinerea and alba, has had a strong impact on the accurate measurement of cerebration.

At the influence of physiology disturbance to the Near-infrared Brain Function detection, the most direct processing method is to utilize low-pass filtering technique.Low-pass filtering technique can filter the disturbance that heartbeat causes effectively, because the forcing frequency that heartbeat causes is apparently higher than the cerebration signal.But low-pass filtering technique can't effectively filter the disturbance that breathing causes, this is because the forcing frequency that breathing causes is very low, and low excessively cut-off frequency has also caused the distortion of cerebration signal in this type of turbulent while of elimination.Auto-adaptive filtering technique is as one of turbulent removing method of physiology, showed de-noising characteristic preferably, can reduce the influence that the physiology disturbance detects at brain function near-infrared spectrum technique, but adaptive technique need be by means of pulse blood oxygen instrument or extra path channels, complex structure.

Summary of the invention

The present invention seeks in order to solve the multiple physiology disturbance when adopting low-pass filtering can't remove brain function comprehensively and effectively to detect; The turbulent method of physiology when adopting auto-adaptive filtering technique to eliminate brain function to detect exists need be by extra equipment, baroque problem, and a kind of disturbance removing method of Near-infrared Brain Function detection of decomposing based on empirical modal is provided.

The inventive method may further comprise the steps:

Step 1, place the near-infrared probe that constitutes by double-wavelength light source and detector in the scalp surface of cerebral tissue to be measured, diffuse-reflectance light intensity under the detector recording brain rest state and brain are in the diffuse-reflectance light intensity of bringing out when excitation, the time series of the optical density variable quantity when obtaining two different wave lengths: With

T is the time, t=1, and 2 ..., N;

The time series of step 2, the optical density variable quantity that obtains according to step 1, and adopt and revise the time series Δ [HbO that langbobier law obtains HbO2 Oxyhemoglobin concentration change amount ₂] (t) and the time series Δ [HHb] of reduced hemoglobin concentration change amount (t);

$\mathrm{\Δ}\left[{\mathrm{HbO}}_2\right]\left(t\right)=\frac{({\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_1\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_2}\left(t\right)/\mathrm{DPF})-({\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_2\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_1}\left(t\right)/\mathrm{DPF})}{r({\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_2\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_1\right)-{\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_1\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_2\right))},$

$\mathrm{\Δ}\left[\mathrm{HHb}\right]\left(t\right)=\frac{({\mathrm{\ϵ}}_{\mathrm{Hb}{O}_2}\left({\mathrm{\λ}}_2\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_1}\left(t\right)/\mathrm{DPF})-({\mathrm{\ϵ}}_{\mathrm{Hb}{O}_2}\left({\mathrm{\λ}}_1\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_2}\left(t\right)/\mathrm{DPF})}{r({\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_2\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_1\right)-{\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_1\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_2\right))},$

Wherein, ε _HHb(λ ₁) for the wavelength of probe light source be λ ₁The time HHb extinction coefficient,

ε _HHb(λ ₂) for the wavelength of probe light source be λ ₂The time HHb extinction coefficient,

For the wavelength of probe light source is λ ₁The time HbO ₂Extinction coefficient,

For the wavelength of probe light source is λ ₂The time HbO ₂Extinction coefficient,

R is the air line distance of light source to detector,

DPF is the differential path factor,

Time series Δ [the HbO of step 3, HbO2 Oxyhemoglobin concentration change amount that step 2 is obtained ₂] (t) and the time series Δ [HHb] of reduced hemoglobin concentration change amount (t) carry out empirical modal respectively and decompose, obtain all IMF (intrinsic mode function, in accumulate mode function) component;

Step 4, all IMF components that step 3 is obtained carry out Hilbert transform, ask for the instantaneous frequency of each IMF component, instantaneous frequency is in IMF component rejection in normal person's respiratory frequency and the heartbeat frequency range, the physiology disturbance when eliminating the Near-infrared Brain Function detection.

Advantage of the present invention: the inventive method only need utilize easy probe can realize effectively eliminating the physiology disturbance, the inventive method adopts empirical modal to decompose this time frequency analysis method, handle the non-stationary nonlinear properties, complicated original signal is resolved into limited simple component, be called the IMF component, it has good Hilbert transform characteristic, makes instantaneous frequency to calculate.This decomposition method makes instantaneous frequency have the actual physical meaning, thereby can determine effectively rejecting of physiology disturbance in conjunction with human body physiological parameter.Δ [HbO when empirical modal decomposition and Hilbert transform can be applicable to cerebration ₂] and the reconstruct of Δ [HHb], can eliminate more than 90% by the physiology disturbance of breathing and heartbeat causes.

Description of drawings

To be the present invention carry out the flow chart that decomposes based on empirical modal to the IMF component to Fig. 1.

The specific embodiment

The specific embodiment one: below in conjunction with Fig. 1 present embodiment is described, the present embodiment method may further comprise the steps:

Step 1, place the near-infrared probe that constitutes by double-wavelength light source and detector in the scalp surface of cerebral tissue to be measured, diffuse-reflectance light intensity under the detector recording brain rest state and brain are in the diffuse-reflectance light intensity of bringing out when excitation, the time series of the optical density variable quantity when obtaining two different wave lengths:

With

T is the time, t=1, and 2 ..., N;

The time series of step 2, the optical density variable quantity that obtains according to step 1, and adopt and revise the time series Δ [HbO that langbobier law obtains HbO2 Oxyhemoglobin concentration change amount ₂] (t) and the time series Δ [HHb] of reduced hemoglobin concentration change amount (t);

$\mathrm{\Δ}\left[{\mathrm{HbO}}_2\right]\left(t\right)=\frac{({\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_1\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_2}\left(t\right)/\mathrm{DPF})-({\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_2\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_1}\left(t\right)/\mathrm{DPF})}{r({\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_2\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_1\right)-{\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_1\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_2\right))},$

$\mathrm{\Δ}\left[\mathrm{HHb}\right]\left(t\right)=\frac{({\mathrm{\ϵ}}_{\mathrm{Hb}{O}_2}\left({\mathrm{\λ}}_2\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_1}\left(t\right)/\mathrm{DPF})-({\mathrm{\ϵ}}_{\mathrm{Hb}{O}_2}\left({\mathrm{\λ}}_1\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_2}\left(t\right)/\mathrm{DPF})}{r({\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_2\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_1\right)-{\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_1\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_2\right))},$

Wherein, ε _HHb(λ ₁) for the wavelength of probe light source be λ ₁The time HHb extinction coefficient, depend on wavelength and specific absorbing material, be constant,

ε _HHb(λ ₂) for the wavelength of probe light source be λ ₂The time HHb extinction coefficient,

For the wavelength of probe light source is λ ₁The time HbO ₂Extinction coefficient,

For the wavelength of probe light source is λ ₂The time HbO ₂Extinction coefficient,

R is the air line distance of light source to detector,

DPF is the differential path factor, DPF (differential pathlength factor,), can measure with frequency domain spectroscopy or time-resolved spectroscopy method, also can obtain by Monte Carlo simulation calculation, little with wavelength change, be constant, adult brain tissue value 5.6, child's value 4.3.

Time series Δ [the HbO of step 3, HbO2 Oxyhemoglobin concentration change amount that step 2 is obtained ₂] (t) and the time series Δ [HHb] of reduced hemoglobin concentration change amount (t) carry out empirical modal respectively and decompose, obtain all IMF components;

Step 4, all IMF components that step 3 is obtained carry out Hilbert transform, ask for the instantaneous frequency of each IMF component, instantaneous frequency is in IMF component rejection in normal person's respiratory frequency and the heartbeat frequency range, the physiology disturbance when eliminating the Near-infrared Brain Function detection.

The technical scheme of present embodiment is achieved in that the sonde configuration that utilizes single light source list detector, and light source adopts double-wavelength light source (λ ₁=750nm, λ ₂=830nm), light source is 45mm to the air line distance (light source detection device spacing) of detector.Light source detection device spacing is approximately the twice of near infrared light investigation depth, and investigation depth can reach 20-22mm when light source detection device spacing was 45mm, and setting can make near infrared light can effectively penetrate cerebral cortex like this.Change the optical density variation that obtains into HbO2 Oxyhemoglobin Δ [HbO by revising langbobier law ₂] and the concentration change amount Δ [HHb] of reduced hemoglobin, the Δ [HbO of this moment ₂] and Δ [HHb] doping physiology turbulent noise even flooded by turbulent noise.Utilize EMD (empirical modal decomposition) with Δ [HbO ₂] be decomposed into IMF component with Δ [HHb] with different local features, and the IMF component is carried out Hilbert transform ask for instantaneous frequency.Utilize the instantaneous frequency of all IMF components, the IMF component that can determine physiology disturbance correspondence in conjunction with normal person's breathing and heartbeat frequency.Reject the IMF component of physiology disturbance correspondence, reconstruct cerebration signal.

Wherein, two kinds of wavelength sending of the described double-wavelength light source of step 1 are respectively λ ₁=750nm, λ ₂=830nm.

The time series of optical density variable quantity in the step 1 Obtain by following formula:

${\mathrm{\ΔOD}}_{{\mathrm{\λ}}_1}\left(t\right)=\log I_{\mathrm{base}}\left({\mathrm{\λ}}_1\right)/I_{\mathrm{stim}}\left({\mathrm{\λ}}_1\right),$

Wherein: I _Base(λ ₁) for the wavelength of probe light source be λ ₁The time, brain is in the rest state output intensity in following time, and in the initial moment, brain is under the rest state, and the diffuse-reflectance light intensity that the record detector receives is as test benchmark.

I _Stim(λ ₁) for the wavelength of probe light source be λ ₁The time, brain is in the output intensity when bringing out excitation,

At near infrared band HbO ₂With HHb be main absorber, and there is significant difference in its absorption spectra.Therefore, based on the Near-infrared Brain Function detection of continuous spectrum technology, mainly be to measure HbO2 Oxyhemoglobin (HbO ₂) and the concentration change of reduced hemoglobin (HHb).

Detect for brain function, adopt dual wavelength continuous light near-infrared measuring system, the time series of optical density variable quantity

Obtain by following formula:

${\mathrm{\ΔOD}}_{{\mathrm{\λ}}_2}\left(t\right)=\log I_{\mathrm{base}}\left({\mathrm{\λ}}_2\right)/I_{\mathrm{stim}}\left({\mathrm{\λ}}_2\right),$

Wherein: I _Base(λ ₂) for the wavelength of probe light source be λ ₂The time, brain is in the rest state output intensity in following time,

I _Stim(λ ₂) for the wavelength of probe light source be λ ₂The time, brain is in the output intensity when bringing out excitation.

In the step 3 to the time series Δ [HbO of HbO2 Oxyhemoglobin concentration change amount ₂] (t) (t) to carry out the process that empirical modal decomposes identical with the time series Δ [HHb] of reduced hemoglobin concentration change amount, it is a kind of analytical method of non-linear, nonstationary time series that empirical modal decomposes, it can carry out linearisation to original series, tranquilization is handled, and keeps the feature of original series self in catabolic process.The time scale feature of its basis signal itself, with signal decomposition is to contain the different time yardstick and satisfy in a group of following two definite conditions and accumulate mode function (IMF): 1. in whole data sequence, the number of signal extreme point must differ one identical or at most with the number of signal zero crossing; 2. at any time on, the average of signal local maximum envelope and signal local minimum envelope is zero.

Described optical density signal is converted to Δ [HbO ₂] (t) and Δ [HHb] (t) carry out EMD then and decompose, the effectiveness of EMD method is to decompose Δ [HbO ₂] (t) and Δ [HHb] (t) rather than directly decompose and comprise the turbulent signal that diffuses of physiology because diffuse signal and Δ [HbO ₂] (t) and Δ [HHb] be index relation (t), the EMD algorithm decomposes the signal that diffuses can't realize separating fully the IMF component of physiology disturbance correspondence, thereby can't eliminate the physiology disturbance.

Below with Δ [HbO ₂] (t) and Δ [HHb] (t) be referred to as C _Ij(t), which IMF component i is, i=1, and 2 ..., n, j is the estimation number of times, initialization i=1, j=1 is to time series C _Ij(t) carry out empirical modal and decompose the acquisition process that obtains all IMF components:

Step 1, adopt the local extremum method to determine to lead to look for time series C _Ij(t) all maximum and minimum make up time series C with cubic spline interpolation respectively to all maximum value minimums that obtain _Ij(t) coenvelope line e _Max(t) and lower envelope line e _Min(t);

Step 2, obtain the average of upper and lower envelope

$\stackrel{\‾}{e\left(t\right)}=\frac{e_{\max }\left(t\right)+e_{\min }\left(t\right)}{2},$

Estimate h the j time of step 3, i IMF component of acquisition time sequence _Ij(t):

$h_{\mathrm{ij}}\left(t\right)=C_{\mathrm{ij}}\left(t\right)-\stackrel{\‾}{e\left(t\right)},$

Step 4, judge whether following formula is set up:

ε＞0 wherein, and fully near 0,

Judged result is for being, execution in step 5,

Judged result makes j=j+1, C for not _{I (j+1)}(t)=h _Ij(t), and return execution in step 1,

Step 5, obtain i IMF component: C _i(t)=h _IjAnd obtain i residual error (t):

r _i(t)＝C _ij(t)-h _ij(t)，

Step 6, i residual error r of judgement _i(t) whether be monotonic function,

Judged result makes i=i+1 for not, j=1, and return execution in step 1,

Judged result is for being to finish time series C _Ij(t) carry out the empirical modal decomposition and obtain all IMF components: C _i(t).

The acquisition methods of the instantaneous frequency of IMF component is in the step 4:

Step 41, acquisition IMF component C _i(t) Hilbert transform y (t):

$y\left(t\right)=H\left[C_i\left(t\right)\right]=\frac{1}{\mathrm{\π}}P{\∫}_{-\∞}^{\∞}\frac{C_i\left(t^{\′}\right)}{t-t^{\′}}{\mathrm{dt}}^{\′},$

Wherein, P represents Cauchy's principal value,

Step 42, IMF component C _i(t) analytic signal is z (t)=C (t)+iy (t)=a (t) exp[i θ (t)],

Wherein, a (t) is an instantaneous amplitude, and θ (t) is a phase function,

Step 43, obtain IMF component C _i(t) instantaneous frequency f (t) is:

Normal person's respiratory frequency scope is 0.15Hz～0.4Hz, and the heartbeat frequency range is 1.0Hz～1.7Hz.

The instantaneous frequency of IMF component has embodied the internal feature of IMF component, according to normal person's respiratory frequency and heartbeat frequency, determines the IMF component of physiology disturbance correspondence.With the IMF component rejection of physiology disturbance correspondence, utilize other IMF component reconstruct to obtain the turbulent cerebration signal of physiology.

Described optical density signal is converted to Δ [HbO ₂] (t) and Δ [HHb] (t) carry out EMD then and decompose, the effectiveness of EMD method is to decompose Δ [HbO ₂] (t) and Δ [HHb] (t) rather than directly decompose and comprise the turbulent signal that diffuses of physiology because diffuse signal and Δ [HbO ₂] (t) and Δ [HHb] be index relation (t), the EMD algorithm decomposes the signal that diffuses can't realize separating fully the IMF component of physiology disturbance correspondence, thereby can't eliminate the physiology disturbance.

Claims (6)

1. the disturbance removing method of the Near-infrared Brain Function detection of decomposing based on empirical modal is characterized in that it may further comprise the steps:

Step 1, place the near-infrared probe that constitutes by double-wavelength light source and detector in the scalp surface of cerebral tissue to be measured, diffuse-reflectance light intensity under the detector recording brain rest state and brain are in the diffuse-reflectance light intensity of bringing out when excitation, the time series of the optical density variable quantity when obtaining two different wave lengths:

With

T is the time, t=1, and 2 ..., N;

The time series of step 2, the optical density variable quantity that obtains according to step 1, and adopt and revise the time series Δ [HbO that langbobier law obtains HbO2 Oxyhemoglobin concentration change amount ₂] (t) and the time series Δ [HHb] of reduced hemoglobin concentration change amount (t);

$\mathrm{\Δ}\left[{\mathrm{HbO}}_2\right]\left(t\right)=\frac{({\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_1\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_2}\left(t\right)/\mathrm{DPF})-({\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_2\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_1}\left(t\right)/\mathrm{DPF})}{r({\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_2\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_1\right)-{\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_1\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_2\right))},$

$\mathrm{\Δ}\left[\mathrm{HHb}\right]\left(t\right)=\frac{({\mathrm{\ϵ}}_{\mathrm{Hb}{O}_2}\left({\mathrm{\λ}}_2\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_1}\left(t\right)/\mathrm{DPF})-({\mathrm{\ϵ}}_{\mathrm{Hb}{O}_2}\left({\mathrm{\λ}}_1\right){\mathrm{\ΔOD}}_{{\mathrm{\λ}}_2}\left(t\right)/\mathrm{DPF})}{r({\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_2\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_1\right)-{\mathrm{\ϵ}}_{{\mathrm{HbO}}_2}\left({\mathrm{\λ}}_1\right){\mathrm{\ϵ}}_{\mathrm{HHb}}\left({\mathrm{\λ}}_2\right))},$

Wherein, ε _HHb(λ ₁) for the wavelength of probe light source be λ ₁The time HHb extinction coefficient,

ε _HHb(λ ₂) for the wavelength of probe light source be λ ₂The time HHb extinction coefficient,

For the wavelength of probe light source is λ ₁The time HbO ₂Extinction coefficient,

For the wavelength of probe light source is λ ₂The time HbO ₂Extinction coefficient,

R is the air line distance of light source to detector,

DPF is the differential path factor,

Time series Δ [the HbO of step 3, HbO2 Oxyhemoglobin concentration change amount that step 2 is obtained ₂] (t) and the time series Δ [HHb] of reduced hemoglobin concentration change amount (t) carry out empirical modal respectively and decompose, obtain all IMF components;

Step 4, all IMF components that step 3 is obtained carry out Hilbert transform, ask for the instantaneous frequency of each IMF component, instantaneous frequency is in IMF component rejection in normal person's respiratory frequency and the heartbeat frequency range, the physiology disturbance when eliminating the Near-infrared Brain Function detection.

2. the disturbance removing method of Near-infrared Brain Function detection of decomposing based on empirical modal according to claim 1 is characterized in that two kinds of wavelength that the described double-wavelength light source of step 1 sends are respectively λ ₁=750nm, λ ₂=830nm.

3. the disturbance removing method of Near-infrared Brain Function detection of decomposing based on empirical modal according to claim 1 is characterized in that the time series of optical density variable quantity in the step 1 Obtain by following formula:

${\mathrm{\ΔOD}}_{{\mathrm{\λ}}_1}\left(t\right)=\log I_{\mathrm{base}}\left({\mathrm{\λ}}_1\right)/I_{\mathrm{stim}}\left({\mathrm{\λ}}_1\right),$

Wherein: I _Base(λ ₁) for the wavelength of probe light source be λ ₁The time, brain is in the rest state output intensity in following time,

I _Stim(λ ₁) for the wavelength of probe light source be λ ₁The time, brain is in the output intensity when bringing out excitation,

The time series of optical density variable quantity

Obtain by following formula:

${\mathrm{\ΔOD}}_{{\mathrm{\λ}}_2}\left(t\right)=\log I_{\mathrm{base}}\left({\mathrm{\λ}}_2\right)/I_{\mathrm{stim}}\left({\mathrm{\λ}}_2\right),$

Wherein: I _Base(λ ₂) for the wavelength of probe light source be λ ₂The time, brain is in the rest state output intensity in following time,

I _Stim(λ ₂) for the wavelength of probe light source be λ ₂The time, brain is in the output intensity when bringing out excitation.

4. the disturbance removing method of Near-infrared Brain Function detection of decomposing based on empirical modal according to claim 1 is characterized in that, in the step 3 to the time series Δ [HbO of HbO2 Oxyhemoglobin concentration change amount ₂] (t) (t) to carry out the process that empirical modal decomposes identical with the time series Δ [HHb] of reduced hemoglobin concentration change amount, below with Δ [HbO ₂] (t) and Δ [HHb] (t) be referred to as C _Ij(t), which IMF component i is, i=1, and 2 ..., n, j is the estimation number of times, initialization i=1, j=1 is to time series C _Ij(t) carry out empirical modal and decompose the acquisition process that obtains all IMF components:

Step 1, employing local extremum method are determined the hunting time sequence C _Ij(t) all maximum and minimum make up time series C with cubic spline interpolation respectively to all maximum value minimums that obtain _Ij(t) coenvelope line e _Max(t) and lower envelope line e _Min(t);

Step 2, obtain the average of upper and lower envelope

$\stackrel{\‾}{e\left(t\right)}=\frac{e_{\max }\left(t\right)+e_{\min }\left(t\right)}{2},$

Estimate h the j time of step 3, i IMF component of acquisition time sequence _Ij(t):

$h_{\mathrm{ij}}\left(t\right)=C_{\mathrm{ij}}\left(t\right)-\stackrel{\‾}{e\left(t\right)},$

Step 4, judge whether following formula is set up:

ε＞0 wherein, and fully near 0,

Judged result is for being, execution in step 5,

Judged result makes j=j+1, C for not _{I (j+1)}(t)=h _Ij(t), and return execution in step 1,

Step 5, obtain i IMF component: C _i(t)=h _IjAnd obtain i residual error (t):

r _i(t)＝C _ij(t)-h _ij(t)，

Step 6, i residual error r of judgement _i(t) whether be monotonic function,

Judged result makes i=i+1 for not, j=1, and return execution in step 1,

Judged result is for being to finish time series C _Ij(t) carry out the empirical modal decomposition and obtain all IMF components: C _i(t).

5. the disturbance removing method of Near-infrared Brain Function detection of decomposing based on empirical modal according to claim 1 is characterized in that the acquisition methods of the instantaneous frequency of IMF component is in the step 4:

Step 41, acquisition IMF component C _i(t) Hilbert transform y (t):

$y\left(t\right)=H\left[C_i\left(t\right)\right]=\frac{1}{\mathrm{\π}}P{\∫}_{-\∞}^{\∞}\frac{C_i\left(t^{\′}\right)}{t-t^{\′}}{\mathrm{dt}}^{\′},$

Wherein, P represents Cauchy's principal value,

Step 42, IMF component C _i(t) analytic signal is z (t)=C (t)+iy (t)=a (t) exp[i θ (t)],

Wherein, a (t) is an instantaneous amplitude, and θ (t) is a phase function,

Step 43, obtain IMF component C _i(t) instantaneous frequency f (t) is:

6. the disturbance removing method of Near-infrared Brain Function detection of decomposing based on empirical modal according to claim 1 is characterized in that normal person's respiratory frequency scope is 0.15Hz～0.4Hz, and the heartbeat frequency range is 1.0Hz～1.7Hz.

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