CN104161508B - Fetus electrocardiogram signal extracting method - Google Patents

Abstract

The invention belongs to the technical field of biomedical signal processing, and particularly relates to a fetus electrocardiogram signal extracting method for extracting fetus electrocardiogram signals from mutually mixed electrocardiogram signals of a maternal body and a fetus. The fetus electrocardiogram signal extracting method comprises the steps that firstly, an electrode of test equipment is put on the abdominal wall of the maternal body, potential difference data caused by electrocardiogram conduction are recorded, multiple sets of data are recorded, and multiple paths of mixed electrocardiogram signals of the maternal body and the fetus are obtained; reference signals of the electrocardiogram signals of the maternal body are built, and then the electrocardiogram signals of the maternal body are extracted from the mixed electrocardiogram signals of the maternal body and the fetus through the reference signals; the components related to the extracted electrocardiogram signals of the maternal body are eliminated from the mixed electrocardiogram signals of the maternal body and the fetus, and therefore the purpose of extracting the fetus electrocardiogram signals is realized. The fetus electrocardiogram signal extracting method can effectively extract the fetus electrocardiogram signals from the mixed electrocardiogram signals of the maternal body and the fetus, is small in calculation amount, is low in complexity, is less dependent on parameters, is clear in extracted signals, and realizes the expectant purpose.

Description

A kind of Fetal ECG method for extracting signal

Technical field

The invention belongs to processing of biomedical signals technical field, and in particular to a kind of maternal fetus from mutual aliasing are mixed Close the Fetal ECG method for extracting signal of extraction Fetal ECG signal in electrocardiosignal.

Background technology

Fetal ECG signal is research heart of fetus one important objective indicator of physiological activity, reflects fetus in parent In growth situation and health status, therefore separate or extract clearly Fetal ECG signal become one significantly Work.

Current certain methods are all to concentrate on the extraction that Fetal ECG signal is carried out with the method for blind source separating.It is existing Method mainly using the prior information of Fetal ECG signal, corresponding reference signal is constructed, then using based on gradient or negative The blind source separation algorithm of entropy is separated and extracted to Fetal ECG signal.This kind of method can when reference signal chooses appropriate Good separating effect is obtained, but the electrocardiosignal of fetus is faint compared to the electrocardiosignal of parent, therefore obtain fetus The appropriate reference signal of electrocardiosignal is difficult.Meanwhile, repeatedly iteration is needed when with blind source separation algorithm, and need Suitable parameter is chosen, otherwise the effect extracted can be influenceed.The present invention is difficult to for the reference signal of Fetal ECG signal The difficulty of determination, obtains the reference signal of parent electrocardio signal first, then constructs corresponding optimized-type using this reference signal, Corresponding weight vector is obtained so as to extract parent electrocardio signal from maternal fetus mixing electrocardiosignal, finally from parent tire The related composition of the noisy parent electrocardio signal of band of removal and extraction in youngster's mixing electrocardiosignal, remaining is exactly our institutes The Fetal ECG signal to be extracted, iterations is more and parameter selection difficulty during the method overcomes blind source separating Problem, with certain practical value.

The content of the invention

A kind of method the purpose of the present invention is to propose to extract Fetal ECG signal in mixing electrocardiosignal from maternal fetus.

The object of the present invention is achieved like this：

(1.1) electrode of test equipment is put in maternal abdominal first, record electrocardio conducts caused potential difference data, Record multi-group data, obtains multichannel maternal fetus mixing electrocardiosignal；

(1.2) then construction parent electrocardio signal reference signal, then using the reference signal from maternal fetus mix Parent electrocardio signal is extracted in electrocardiosignal；

(1.3) and then by composition related to the parent electrocardio signal for extracting in maternal fetus mixing electrocardiosignal go Fall, the purpose of Fetal ECG signal is extracted so as to reach.

The beneficial effects of the present invention are：Using Fetal ECG method for extracting signal of the invention, can effectively from mother Fetal ECG signal is extracted in body fetus mixing electrocardiosignal.The method amount of calculation is small, and complexity is low, to the dependence of parameter Small, the signal of extraction is clear, has reached expected purpose.

Brief description of the drawings

Fig. 1 Fetal ECG signal extraction flow charts

Fig. 2 maternal fetus mixing electrocardiosignals；

The reference signal of the parent electrocardio signal of Fig. 3 constructions；

The parent electrocardio signal that Fig. 4 is extracted；

The Fetal ECG signal that Fig. 5 is extracted.

Specific embodiment

Below in conjunction with the accompanying drawings with specific embodiment to being further described in detail herein：

The method can avoid the problem that iterations is more and parameter selection is difficult during blind source separating.Using the parent heart The characteristics of electric signal is better than Fetal ECG signal, obtains the reference signal of parent electrocardio signal, using this reference signal from parent Parent electrocardio signal is extracted in fetus mixing electrocardiosignal, will finally be believed with parent electrocardio in maternal fetus mixing electrocardiosignal The composition of number correlation removes so as to extract Fetal ECG signal, from the effect of the Fetal ECG signal for extracting it can be found that this The validity and reasonability of method.

Core technology content of the invention is to propose a kind of Fetal ECG method for extracting signal, and multichannel parent is obtained first Fetus mixes electrocardiosignal, then constructs the reference signal of parent electrocardio signal, and mixed from maternal fetus using this reference signal Close and extract parent electrocardio signal in electrocardiosignal, finally by maternal fetus mixing electrocardiosignal with the parent electrocardio that extracts The related composition of signal removes, so that success has extracted Fetal ECG signal from maternal fetus mixing electrocardiosignal；

By the invention to extract parent electrocardio signal section, its main contents is：Maternal fetus electrocardiosignal is first The reference signal of parent electrocardio signal is obtained using the peak value of parent electrocardio signal and the periodicity of parent electrocardio signal, this The reference signal of signified parent electrocardio signal is exactly the signal for having similar structure with real parent electrocardio signal in invention, Here similar generally refers to periodically similar.Obtain after the reference signal of parent electrocardio signal, mixed using maternal fetus Close electrocardiosignal and this reference signal constructs corresponding optimized-type, corresponding weight vector, Jin Erti are obtained by derivation abbreviation Take out parent electrocardio signal.

By the invention to extract Fetal ECG signal section, its main contents is：By decorrelation formula by parent tire The composition related to the parent electrocardio signal for extracting removes in youngster's mixing electrocardiosignal, so as to finally give Fetal ECG letter Number.

1. maternal fetus mixing electrocardiosignal is obtained

The electrode of test equipment is put in maternal abdominal, the caused potential difference data of record electrocardio conduction records multigroup Data, why to have multi-group data is exactly for convenience in blind source extraction process.Here the data for obtaining are exactly maternal fetus Mixing electrocardiosignal.In this mixed signal, Fetal ECG signal is quite faint, and mother's electrocardiosignal is submerged in substantially In, and due to Hz noise, baseline drift, the noise caused by human body electrical phenomena, electrode contact noise, electromagnetic equipment interference Etc. the influence of factor, it appears Fetal ECG signal is more faint, therefore to expect pure Fetal ECG signal, Wo Menxu This mixed signal is processed using corresponding method, specific Fetal ECG signal extraction flow is as shown in Figure 1.

2. construct the reference signal of parent electrocardio signal and extract corresponding parent electrocardio signal

The reference signal for constructing parent electrocardio signal has two methods.We are needed according to maternal fetus mixing electrocardiosignal To construct corresponding reference signal, maternal fetus mixing electrocardiosignal is as shown in Figure 2.

Method one：One suitable threshold value is exactly set, all positive peak positions and negative peak position for meeting and requiring are found out Put, the amplitude of positive peak position is set to+1 afterwards, the amplitude of negative peak position is set to -1, the amplitude of other positions is set to 0.

Method two：One suitable threshold value is exactly set, the position of preceding several positive peaks is found out, two two-phases are then calculated Equispaced between adjacent peak value, the positive peak after being constructed according to this equispaced.The processing method of negative peak and just The processing method of peak value is identical.The amplitude of positive peak position is set to+1 afterwards, the amplitude of negative peak position is set to -1, other The amplitude of position is set to 0.

The reference signal of parent electrocardio signal can be constructed by above two method.Constructed using second method Parent electrocardio signal as shown in Figure 3.

For the greedy optimized algorithm of any projection tracking, a locally optimal solution necessarily has its domain of attraction, also It is to say the initial point in this region, can be converged on locally optimal solution under this optimized algorithm.

We can make vicinity of the initial weight vector in locally optimal solution using reference signal.If such a Projecting direction, it can cause that projection output in this direction reaches maximum with the function of the second order coefficient correlation of reference signal, So it is considered that this projection vector should dissociate it is closer.Following optimization problem can be proposed around this principle

Minimize：f(E(w₀x·r)) (1)

Constraints：||w₀| |=1 (2)

F () is a continuously differentiable monotonic decreasing function in above formula.R represent the reference signal of parent electrocardio signal to Amount, x is N-dimensional observation signal vector, w₀It is the mixed vector of solution.

The equality constraint of formula (2) shows that we are only concerned the direction of projection, so constraints can be expressed as w₀w₀ ^T=1.We are indifferent to signal variance in ICA problems, then we assume that N-dimensional observation signal vector x is white by PCA Change is processed, and obtains the vector z=Vx=VAs=Bs of the observation signal after albefaction (BB^T=I).(V is whitening matrix, and A is mixed moment Battle array, B is global matrix, and s is N-dimensional source signal vector)

We are designated as the Lagrange multiplier formula of this optimization problem

L(w₀, λ) and=f (E { w₀z·r})-λ(w₀w₀ ^T-1) (3)

Wherein λ is constant, and then our weight vectors to above formula seek partial derivative, then make it be equal to 0, then：

Can solve：

Because we are only concerned the direction of weight vector, so we are indifferent to the first product term (mark on the right side of above formula Amount) f'(E { w₀Zr })/2 λ, then weight vector can in the hope of for

By this method, we can not just directly obtain a weight vector by iterative learning, be weighed by this Value is vectorial, and we can just extract parent electrocardio signal

Y=w₀x (7)

The parent electrocardio signal y for obtaining is as shown in Figure 4.

3. we will be relevant with parent electrocardio signal in maternal fetus mixing electrocardiosignal using a kind of method of decorrelation Component remove, just obtained Fetal ECG signal

By above formula, we can just reach the purpose of the relevant portion that disappears, becauseSo we have just obtained Fetal ECG signal, the Fetal ECG signal for obtainingSuch as Shown in accompanying drawing 4.

We are it can be found that the method can be extracted from maternal fetus mixing electrocardiosignal well from accompanying drawing 5 Fetal ECG signal, and extraction effect is good.

Finally it should be noted that above example is only used to describe technical scheme rather than to this technology method Limited, the present invention application can above extend to other modifications, change, using and embodiment, and it is taken as that institute Have such modification, change, using, embodiment all in the range of spirit or teaching of the invention.

Claims (1)

1. a kind of Fetal ECG method for extracting signal, it is characterized in that：

(1) electrode of test equipment is put in maternal abdominal first, the caused potential difference data of record electrocardio conduction is recorded many Group data, obtain multichannel maternal fetus mixing electrocardiosignal；

(2) then construction parent electrocardio signal reference signal, and using the reference signal from maternal fetus mixing electrocardiosignal In extract parent electrocardio signal：

Threshold value is set, the position of several positive peaks before maternal fetus mixing electrocardiosignal is found out, preceding several positive peaks two are calculated Equispaced between two adjacent peaks, the positive peak after being constructed according to equispaced, the processing method of negative peak and just The processing method of peak value is identical, and the amplitude of positive peak position is set into+1 afterwards, and the amplitude of negative peak position is set into -1, other The amplitude of position is set to 0；The reference signal of parent electrocardio signal is constructed, initial weight vector is made in office using reference signal Near portion's optimal solution：

Minimize：f(E(w₀x·r))；

Constraints：||w₀| |=1；

F () is a continuously differentiable monotonic decreasing function, and r represents the reference signal vector of parent electrocardio signal, and x is N-dimensional Observation signal vector, w₀It is weight vector；

Constraints is expressed as w₀w₀ ^T=1, if N-dimensional observation signal vector x is, by PCA whitening processings, to obtain the sight after albefaction Survey signal vector z=Vx=VAs=Bs, BB^T=I, V are whitening matrix, and A is hybrid matrix, and B is global matrix, and s is N-dimensional source Signal vector；

Lagrange multiplier formula is designated as：L(w₀, λ) and=f (E { w₀z·r})-λ(w₀w₀ ^T-1)

Wherein λ is constant, and the weight vector to above formula seeks partial derivative, then makes it be equal to 0：

$\begin{array}{c}\frac{\∂L(w_0,\mathrm{\λ})}{\∂w_0}=\frac{\∂\{f\left(E\right\{w_{0}z\·r\left\}\right)-\mathrm{\λ}(w_0{w_0}^T-1)\}}{\∂w_0}\\ =f^{\′}\left(E\left\{w_{0}z\·r\right\}\right)E\left\{z^{T}r\right\}-2{\mathrm{\λw}}_0\\ =0\end{array}$

Solving weight vector is：

$w_0=\frac{f^{\′}\left(E\right\{w_{0}z\·r\left\}\right)}{2\mathrm{\λ}}E\{z^T\·r\}$

Ignore first product term, try to achieve for：

$w_0=\frac{1}{\left|\right|E\{z^T\·r\}\left|\right|}E\{z^T\·r\}$

Parent electrocardio signal is extracted by this weight vector：

Y=w₀x；

(3) finally composition E (ry) y related to the parent electrocardio signal for extracting in maternal fetus mixing electrocardiosignal is gone Fall, extract Fetal ECG signal

$\hat{r}=r-E\left(ry\right)y.$