CN104873222A - Fetal heart rate detection method based on smart mobile terminal - Google Patents

Abstract

The invention discloses a fetal heart rate detection method based on a smart mobile terminal. The smart mobile terminal is used for processing a fetal heart signal input through an audio interface. The method comprises A/D sampling, downing sampling, rectification, sliding average filtering, biased estimation autocorrelation calculation, unbiased estimation autocorrelation calculation, and fetal heart rate determination and selection, and the fetal heart rate can be obtained after the above operation. In the fetal heart rate detection method based on the smart mobile terminal, the fetal heart rate detection and calculation method can be modified through strong data processing capability of the smart mobile terminal, the measuring precision can be raised, the responds time can be reduced, and the stability of the detection result can be improved. The hardware structure of an ultrasonic Doppler detection terminal can be simplified, and the power consumption and cost can be reduced. At the same time, a traditional autocorrelation algorithm is modified, a main peak can be more accurately judged combining with an unbiased estimation autocorrelation algorithm, frequency multiplication will not easily occur, and the accuracy and stability of the algorithm can be raised.

Description

A kind of Fetal Heart Rate detection method based on intelligent mobile terminal

Technical field

The invention belongs to technical field of medical equipment, be specifically related to a kind of Fetal Heart Rate detection method based on intelligent mobile terminal.

Background technology

It is a kind of conventional fetus monitoring method being evaluated fetal safety in uterus by the change of monitoring Fetal Heart Rate that fetal rhythm detects, and contributes to improving delivery of fetus quality, reduces fetal anomaly rate and mortality rate.A kind of non-invasive monitoring method the most frequently used in the world and ultrasound Doppler's method, it have detectivity high, easy to use, on the fetus impact advantage such as low.

Correlation method is method the most frequently used in ultrasonic doppler measurements fetal heart frequency, its feature utilizing the cycle of auto-correlation function consistent with the signal period, finds out the cycle of auto-correlation function, can obtain fetal heart rate values.The auto-correlation function of signal is the similarity measurement between the time delayed signal of signal and this signal itself, and auto-correlation function has following feature:

1) auto-correlation function of periodic signal is also the cycle, and both cycles are equal;

2) lie in the auto-correlation function of noise in useful signal, along with the increase of delay value, there will be and decay faster than useful signal auto-correlation function.

When amount of delay T equals 0 or equal signal period of integral multiple, the auto-correlation function of signal obtains peak value at T point place.Like this, by finding the position of maximum point in signal auto-correlation function, and calculating the sequence length of two adjacent maximum points, just can obtain the periodicity contained in the signal by sound pollution.

Because the heart beating of fetus itself is more weak, add the interference of maternal environment, ultrasound echo signal comparison of ingredients is complicated, and interference is large.Therefore, the signal of collection disturbs more sometimes, and now, the simple auto-correlation function adopting auto-correlation algorithm to obtain, when cycle detection, easily causes doubling or reducing by half of cycle.

In addition, existing fetus-voice meter is subject to the restriction of the factors such as external form size, cost, power consumption, and its processing module is often made up of simple MCU, cannot accomplish large date processing, and thus data processing speed is limited, and precision does not reach very high requirement.

Summary of the invention

For the above-mentioned technical problem existing for prior art, the invention provides a kind of Fetal Heart Rate detection method based on intelligent mobile terminal, rely on the data-handling capacity that intelligent mobile terminal is powerful, fetal heart rate signal is carried out to process obtains accurately, reliable fetal heart frequency, particularly when signal difference.

Based on a Fetal Heart Rate detection method for intelligent mobile terminal, comprise the steps:

(1) fetal heart rate signal that intelligent mobile terminal is provided by audio interface reception fetus-voice meter is utilized;

(2) pretreatment is carried out to described fetal heart rate signal and obtain fetal rhythm Doppler envelope signal sequence;

(3) autocorrelation analysis is carried out to described fetal rhythm Doppler envelope signal sequence, obtained partial autocorrelation sequence and without partial autocorrelation sequence;

(4) process is judged, in the hope of obtaining Fetal Heart Rate to described having partial autocorrelation sequence and carry out contrast without partial autocorrelation sequence.

Described step (2) to (4) realizes process by intelligent mobile terminal internal processor; Described intelligent mobile terminal can be smart mobile phone or panel computer.

It is as follows that described step (2) carries out pretreated concrete steps to fetal heart rate signal:

Fetal heart rate signal described in 2.1 pairs carries out A/D sampling, obtains the sampled value sequence of fetal heart rate signal;

Sampled value sequence described in 2.2 pairs carries out down-sampled process, obtains down-sampled value sequence;

Down-sampled value sequence described in 2.3 pairs carries out absolute value process, obtains rectified value sequence;

Rectified value sequence described in 2.4 pairs carries out moving average filter process, obtains fetal rhythm Doppler envelope signal sequence.

By following formula, moving average filter process is carried out to rectified value sequence in described step 2.4:

$D\left(n\right)=\frac{1}{m}\underset{i=0}{\overset{m-1}{\mathrm{\Σ}}}C(n+i)$

Wherein: C (n+i) is the numerical value of the n-th+i in rectified value sequence, and D (n) is the n-th signal value in fetal rhythm Doppler envelope signal sequence, n be greater than 0 natural number, m is the preset length of slip signals window.

The concrete steps that described step (3) carries out autocorrelation analysis to fetal rhythm Doppler envelope signal sequence are as follows:

Fetal rhythm Doppler envelope signal sequence described in 3.1 pairs carries out fast Fourier transformation operation, obtains sequence of complex numbers;

Sequence of complex numbers described in 3.2 pairs carries out computing module-square process, obtains corresponding mould square sequence;

Mould square sequence described in 3.3 pairs carries out Fast Fourier Transform Inverse computing, has obtained partial autocorrelation sequence;

3.4 to have partial autocorrelation sequence to calculate corresponding to partial autocorrelation sequence according to described.

By following formula, computing module-square process is carried out to sequence of complex numbers in described step 3.2:

R(k)＝D*(k)D(k)＝|D(k)| ²

Wherein: R (k) is the numerical value of the kth in mould square sequence, D (k) is the plural number of the kth in sequence of complex numbers, D ^*k conjugate complex number that () is D (k), | D (k) | be the mould of D (k), k is natural number and 1≤k≤N, N are the signal value number of fetal rhythm Doppler envelope signal sequence.

In described step 3.4 by following formulae discovery without partial autocorrelation sequence:

$R_{\mathrm{XX}2}\left(j\right)=\frac{N-j}{N}*R_{\mathrm{XX}1}\left(j\right)$

Wherein: R _xx1(j) and R _xx2j () is respectively partial autocorrelation sequence and without the numerical value of the jth in partial autocorrelation sequence, N is the signal value number of fetal rhythm Doppler envelope signal sequence, and j is natural number and 1≤j≤N.

To having partial autocorrelation sequence and carrying out contrasting without partial autocorrelation sequence, described step (4) judges that the detailed process of process is as follows:

4.1 from there being partial autocorrelation sequence the train interval length n determined between two adjacent peak ₁;

4.2 from without the train interval length n determined partial autocorrelation sequence between two adjacent peak ₂;

4.3 according to described train interval length n ₁and n ₂, calculate corresponding interval T ₁and T ₂;

4.4 according to described interval T ₁and T ₂, judge to ask for obtain described Fetal Heart Rate.

Described train interval length n is made in described step 4.3 ₁and n ₂respectively divided by down-sampled frequency, obtain corresponding interval T ₁and T ₂.

Judge to ask for Fetal Heart Rate according to following relation in described step 4.4:

If T ₁=T ₂, then Fetal Heart Rate F=60/T ₁;

If T ₁=2T ₂, then Fetal Heart Rate F=60/T ₂;

If T ₁=T ₂/ 2, then Fetal Heart Rate F=60/T ₁;

In other situations, Fetal Heart Rate F=60/T ₁.

Weak for traditional Doppler's Fetal Heart Rate detector data-handling capacity, certainty of measurement is low, and reaction is slow, the poor stability problems such as power consumption is large simultaneously; The present invention utilizes intelligent mobile terminal audio interface, the fetal heart rate signal obtained by ultrasonic doppler sense terminals is passed to intelligent mobile terminal, and the data-handling capacity utilizing intelligent mobile terminal powerful, the Fetal Heart Rate detection algorithm of operational development, improve certainty of measurement, reduce the response time, increase testing result stability; Simplify the hardware configuration of ultrasonic doppler sense terminals simultaneously, reduce power consumption and cost.

In addition, for the complicated component of fetal heart rate signal, inside include more interference and become signal, adopt traditional auto-correlation algorithm to calculate Fetal Heart Rate time error large, and easily occur the problem of frequency multiplication phenomenon; The present invention improves traditional auto-correlation algorithm, and the auto-correlation algorithm in conjunction with unbiased esti-mator strengthens the correct judgement of main peak, overcomes the shortcoming easily occurring frequency multiplication, improves accuracy and the stability of algorithm.

Accompanying drawing explanation

The steps flow chart schematic diagram of Fig. 1 Fetal Heart Rate detection method of the present invention.

Fig. 2 fetal heart rate signal A/D sample sequence schematic diagram.

The down-sampled sequence diagram of Fig. 3 fetal heart rate signal

Fig. 4 fetal heart rate signal rectification moving average filter sequence diagram

The biased estimation autocorrelation sequence schematic diagram of Fig. 5 fetal heart rate signal.

Fig. 6 fetal heart rate signal unbiased esti-mator autocorrelation sequence schematic diagram.

Fig. 7 is the contrast schematic diagram of the present invention and prior art Fetal Heart Rate simulation test sum of sguares of deviation from mean.

Detailed description of the invention

In order to more specifically describe the present invention, below in conjunction with the drawings and the specific embodiments, technical scheme of the present invention is described in detail.

As shown in Figure 1, the present invention is based on the Fetal Heart Rate detection method of intelligent mobile terminal, comprise the following steps:

Step 1. pair fetal heart rate signal carries out pretreatment and obtains fetal rhythm Doppler envelope signal.

1.1 pairs of fetal heart rate signals inputted by audio interface, carry out sample rate f _s1for the A/D of 44.1KHz samples, obtain sampled value sequence A (n), this signal sequence as shown in Figure 2;

Sampled value sequence A (n) obtained is carried out sample rate f by 1.2 again _s2for the down-sampled process of 4.41KHz, obtain down-sampled value sequence B (n), this signal sequence as shown in Figure 3;

1.3 pairs of down-sampled value sequences B (n) judge, if sequential value is just, then do not process, if sequential value is negative, then do absolute value process to this sequential value.After above rectification process, obtain rectified value sequence C (n).

1.4 pairs of rectified values sequence C (n) carry out moving average filter process, obtain fetal rhythm Doppler envelope signal.That is:

$D\left(n\right)=\frac{1}{m}{\mathrm{\Σ}}_{i=0}^{m-1}C(n+i),$ Wherein m=10;

Specific practice is: from C (n) sequence first value, chooses front 10 sequential values of C (n) sequence successively, as first of sequence D (n) sequential digit values after being averaged; Afterwards from C (n) sequence second value, choose 10 sequential values of C (n) sequence more successively, as second of sequence D (n) sequential digit values after being averaged, the like, until take all numerical value of sequence C (n), obtain fetal rhythm Doppler's envelope signal sequence D (n), this signal sequence as shown in Figure 4.

Step 2. pair fetal rhythm Doppler envelope signal carries out autocorrelation analysis, obtains processing signals.

Biased estimation auto-correlation processing is carried out to fetal rhythm Doppler envelope signal, obtains biased estimation autocorrelation sequence, then ask for unbiased esti-mator autocorrelation sequence.Autocorrelation sequence to ask for step as follows:

2.1 couples of D (n) carry out FFT computing, obtain D (k);

2.2 calculating R (k)=D* (k) D (k)=| D (k) | ²;

2.3 finally do IFFT computing to R (k), and what obtain D (n) has partial autocorrelation sequence, as shown in Figure 5;

Specific implementation principle is: set the expression formula of the auto-correlation function of sequence x (n) as:

$r_x\left(i\right)={\mathrm{\Σ}}_{n=0}^{N-1}x\left(n\right)x(n+i)$

Wherein: the sequence of x (n) to be length be N.If X (k) represents the discrete Fourier transform of x (n).That is:

x(n)＝IDFT{X(k)}

$r_x\left(i\right)={\mathrm{\Σ}}_{n=0}^{N-1}x\left(n\right)x(n+i)={\mathrm{\Σ}}_{n=0}^{N-1}\left[\frac{1}{N}{\mathrm{\Σ}}_{k=0}^{N-1}X\left(k\right)e^{j\frac{2\mathrm{\π}}{N}\mathrm{kn}}\right]\left[\frac{1}{N}{\mathrm{\Σ}}_{l=0}^{N-1}X\left(l\right)e^{j\frac{2\mathrm{\π}}{N}l(n+i)}\right]---\left(1\right)$

Because sequence x (n) is real sequence in practice, i.e. x (n)=x ^*(n).

Due to:

$r_x\left(i\right)={\mathrm{\Σ}}_{n=0}^{N-1}\left[\frac{1}{N}{\mathrm{\Σ}}_{k=0}^{N-1}{X}^{*}\left(k\right)e^{-j\frac{2\mathrm{\π}}{N}\mathrm{kn}}\right]\left[\frac{1}{N}{\mathrm{\Σ}}_{l=0}^{N-1}X\left(l\right)e^{j\frac{2\mathrm{\π}}{N}l(n+i)}\right]---\left(2\right)$

$=\frac{1}{N}{\mathrm{\Σ}}_{k=0}^{N-1}{\mathrm{\Σ}}_{l=0}^{N-1}{X}^{*}\left(k\right)X\left(l\right)e^{j\frac{2\mathrm{\π}}{N}\mathrm{li}}\left[\frac{1}{N}{\mathrm{\Σ}}_{k=0}^{N-1}{e}^{j\frac{2\mathrm{\π}}{N}n(l-k)}\right]---\left(3\right)$

$\frac{1}{N}{\mathrm{\Σ}}_{k=0}^{N-1}{e}^{j\frac{2\mathrm{\π}}{N}n(l-k)}=\frac{1}{N}\frac{1-e^{j\frac{2\mathrm{\π}}{N}N(l-k)}}{1-e^{j\frac{2\mathrm{\π}}{N}(l-k)}}=\left\{\begin{array}{cc}1& l=k\\ 0& l\≠k\end{array}\right.---\left(4\right)$

Can obtain:

$r_x\left(i\right)={\mathrm{\Σ}}_{n=0}^{N-1}x\left(n\right)x(n+i)=\frac{1}{N}{\mathrm{\Σ}}_{n=0}^{N-1}{X}^{*}\left(k\right)X\left(k\right)e^{j\frac{2\mathrm{\π}}{N}\mathrm{ki}}=\frac{1}{N}{\mathrm{\Σ}}_{n=0}^{N-1}{\left|X\left(k\right)\right|}^2{e}^{j\frac{2\mathrm{\π}}{N}\mathrm{ki}}---\left(5\right)$

From formula (5), the calculating of auto-correlation function can obtain by calculating FFT and IFFT.

FFT computing, i.e. fast Fourier transformation operation are the fast algorithm of discrete fourier transform, and it is the characteristic such as odd, even, empty, real according to discrete fourier transform, are to carry out improving to the algorithm of discrete Fourier transform obtaining.IFFT computing, i.e. Fast Fourier Transform Inverse computing.

$R_{\mathrm{XX}1}\left(m\right)=\frac{1}{N-m}*{\mathrm{\Σ}}_{n=0}^{N-m-1}{X}_n*X_{n+m}---\left(6\right)$

$R_{\mathrm{XX}2}\left(m\right)=\frac{1}{N}*{\mathrm{\Σ}}_{n=0}^{N-m-1}{X}_n*X_{n+m}---\left(7\right)$

$R_{\mathrm{XX}2}\left(m\right)=\frac{N-m}{N}*\frac{1}{N-m}*{\mathrm{\Σ}}_{n=0}^{N-m-1}{X}_n*X_{n+m}=\frac{N-m}{N}*R_{\mathrm{XX}1}\left(m\right)---\left(8\right)$

Wherein, m=1,2 ..., N; Formula (6) is called biased estimation auto-correlation, and formula (7) is called unbiased esti-mator auto-correlation, is undertaken that unbiased esti-mator is autocorrelative to be asked for by formula (8), without partial autocorrelation sequence as shown in Figure 6.

Step 3. pair processing signals is carried out contrast and is judged process, asks for fetal heart frequency.

The 3.1 pairs of processing signals obtained (have partial autocorrelation sequence and without partial autocorrelation sequence) compare, and find out maximum, by the position of maximizing point, and calculate the train interval length n of two adjacent maxima points from sequence ₁and n ₂;

3.2, by the train interval length between said determination peak value, obtain the interval T between adjacent peak in two auto-correlation result sequences respectively ₁and T ₂;

T ₁=n ₁/ f _s2, T ₂=n ₂/ f _s2, f in formula _s2for the down-sampled frequency of fetal heart rate signal.

If above-mentioned T ₁=T ₂, then fetal heart frequency F=60/T ₁;

If above-mentioned T ₁=2T ₂, then fetal heart frequency F=60/T ₂;

If above-mentioned T ₁=T ₂/ 2, then fetal heart frequency F=60/T ₁.

In order to verify the Stability and veracity that Fetal Heart Rate of the present invention is measured, measure and indication range test with reference to Fetal Heart Rate in People's Republic of China's pharmaceuticals industry standard ultrasound Doppler foetal monitor (YY0449-2009), contrived experiment scheme.Simulation fetal heart rate signal is produced by ultrasonic doppler fetus measuring instrument checkout gear (model FS-3) of China National Measuring Science Research Inst..

Test by driving steel ball repeatedly to move up and down in the container being full of liquid, simulate beating of fetal rhythm, its beats can be arranged.For evaluating Fetal Heart Rate measuring accuracy of the present invention and stability further, elitely getting a domestic ultrasound doppler baby ' s heart instrument of mainstream vendor Jing Bai company on market and test as a comparison.In experiment, the frequency of simulation Fetal Heart Rate signal is set from 240 times/min to 60 times/min, the 15 times/min in interval, range of error ± 0.1 of frequency time/min, measures respectively carrying out 30 times.Finally calculate the standard deviation of each frequency measurement, its result is as shown in table 1:

Table 1

As shown in Table 1, the standard deviation order of magnitude less of the standard deviation of matched group that the present invention measures, and there is serious frequency multiplication phenomenon in matched group in experimentation when analogue signal is 120 times/min, measurement result is 223 ± 2 times/min; And the present invention is in measuring process, there is not frequency multiplication phenomenon.

In order to evaluate stability of the present invention, calculate the sum of sguares of deviation from mean DEVSQ of above-mentioned each frequency of measurement, formula is as follows:

$\mathrm{DEVSQ}=\mathrm{\Σ}{(x-\stackrel{\‾}{x})}^2$

Result of calculation is depicted as block diagram, as shown in Figure 7; From Fig. 7, can find out the present invention measure each simulation fetal rhythm frequency time, its sum of sguares of deviation from mean DEVSQ when this two frequencies of 90 times/min and 75/min and matched group very close, other are all much little than matched group.This illustrates that the dispersion degree of measurement Fetal Heart Rate result of the present invention is less than matched group, and stability is higher.

Above-mentioned is can understand and apply the invention for ease of those skilled in the art to the description of embodiment.Person skilled in the art obviously easily can make various amendment to above-described embodiment, and General Principle described herein is applied in other embodiments and need not through performing creative labour.Therefore, the invention is not restricted to above-described embodiment, those skilled in the art are according to announcement of the present invention, and the improvement made for the present invention and amendment all should within protection scope of the present invention.

Claims (10)

1., based on a Fetal Heart Rate detection method for intelligent mobile terminal, comprise the steps:

(1) fetal heart rate signal that intelligent mobile terminal is provided by audio interface reception fetus-voice meter is utilized;

(2) pretreatment is carried out to described fetal heart rate signal and obtain fetal rhythm Doppler envelope signal sequence;

(3) autocorrelation analysis is carried out to described fetal rhythm Doppler envelope signal sequence, obtained partial autocorrelation sequence and without partial autocorrelation sequence;

(4) process is judged, in the hope of obtaining Fetal Heart Rate to described having partial autocorrelation sequence and carry out contrast without partial autocorrelation sequence.

2. Fetal Heart Rate detection method according to claim 1, is characterized in that: described step (2) to (4) realizes process by intelligent mobile terminal internal processor; Described intelligent mobile terminal is smart mobile phone or panel computer.

3. Fetal Heart Rate detection method according to claim 1, is characterized in that: it is as follows that described step (2) carries out pretreated concrete steps to fetal heart rate signal:

Fetal heart rate signal described in 2.1 pairs carries out A/D sampling, obtains the sampled value sequence of fetal heart rate signal;

Sampled value sequence described in 2.2 pairs carries out down-sampled process, obtains down-sampled value sequence;

Down-sampled value sequence described in 2.3 pairs carries out absolute value process, obtains rectified value sequence;

Rectified value sequence described in 2.4 pairs carries out moving average filter process, obtains fetal rhythm Doppler envelope signal sequence.

4. Fetal Heart Rate detection method according to claim 3, is characterized in that: carry out moving average filter process by following formula to rectified value sequence in described step 2.4:

$D\left(n\right)=\frac{1}{m}\underset{i=0}{\overset{m-1}{\mathrm{\Σ}}}c(n+i)$

Wherein: C (n+i) is the numerical value of the n-th+i in rectified value sequence, and D (n) is the n-th signal value in fetal rhythm Doppler envelope signal sequence, n be greater than 0 natural number, m is the preset length of slip signals window.

5. Fetal Heart Rate detection method according to claim 1, is characterized in that: the concrete steps that described step (3) carries out autocorrelation analysis to fetal rhythm Doppler envelope signal sequence are as follows:

Fetal rhythm Doppler envelope signal sequence described in 3.1 pairs carries out fast Fourier transformation operation, obtains sequence of complex numbers;

Sequence of complex numbers described in 3.2 pairs carries out computing module-square process, obtains corresponding mould square sequence;

Mould square sequence described in 3.3 pairs carries out Fast Fourier Transform Inverse computing, has obtained partial autocorrelation sequence;

3.4 to have partial autocorrelation sequence to calculate corresponding to partial autocorrelation sequence according to described.

6. Fetal Heart Rate detection method according to claim 5, is characterized in that: carry out computing module-square process by following formula to sequence of complex numbers in described step 3.2:

R(k)=D ^*(k)D(k)＝｜D(k)｜ ^２

Wherein: R (k) is the numerical value of the kth in mould square sequence, D (k) is the plural number of the kth in sequence of complex numbers, D ^*k conjugate complex number that () is D (k), | D (k) | be the mould of D (k), k is natural number and 1≤k≤N, N are the signal value number of fetal rhythm Doppler envelope signal sequence.

7. Fetal Heart Rate detection method according to claim 5, is characterized in that: in described step 3.4 by following formulae discovery without partial autocorrelation sequence:

$R_{\mathrm{XX}2}\left(j\right)=\frac{N-j}{N}*R_{\mathrm{XX}1}\left(j\right)$

Wherein: R _xx1(j) and R _xx2j () is respectively partial autocorrelation sequence and without the numerical value of the jth in partial autocorrelation sequence, N is the signal value number of fetal rhythm Doppler envelope signal sequence, and j is natural number and 1≤j≤N.

8. Fetal Heart Rate detection method according to claim 3, is characterized in that: to having partial autocorrelation sequence and carrying out contrasting without partial autocorrelation sequence, described step (4) judges that the detailed process of process is as follows:

4.1 from there being partial autocorrelation sequence the train interval length n determined between two adjacent peak ₁;

4.2 from without the train interval length n determined partial autocorrelation sequence between two adjacent peak ₂;

4.3 according to described train interval length n ₁and n ₂, calculate corresponding interval T ₁and T ₂;

4.4 according to described interval T ₁and T ₂, judge to ask for obtain described Fetal Heart Rate.

9. Fetal Heart Rate detection method according to claim 8, is characterized in that: make described train interval length n in described step 4.3 ₁and n ₂respectively divided by down-sampled frequency, obtain corresponding interval T ₁and T ₂.

10. Fetal Heart Rate detection method according to claim 8, is characterized in that: judge to ask for Fetal Heart Rate according to following relation in described step 4.4:

If T ₁=T ₂, then Fetal Heart Rate F=60/T ₁;

If T ₁=2T ₂, then Fetal Heart Rate F=60/T ₂;

If T ₁=T ₂/ 2, then Fetal Heart Rate F=60/T ₁;

In other situations, Fetal Heart Rate F=60/T ₁.