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Simulink model for Fetal ECG extraction (HDL Compatible algorithm)

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Simulink model for Fetal ECG extraction (HDL Compatible algorithm)


Igal (view profile)


This is an HDL Coder compatible Fetal ECG extraction algorithm.

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% Mother & Fetus hearbeat detection example - Med2011
% By Igal
%% Init
% clear all; close all;
Fs = 4e3;
Time = 40;
NumSamp = Time * Fs;
load Hd;

%% Mom's Heartbeat
% In this example, we shall simulate the shapes of the electrocardiogram 
% for both the mother and fetus. The following commands create an 
% electrocardiogram signal that a mother's heart might produce assuming 
% a 4000 Hz sampling rate. The heart rate for this signal is approximately 
% 89 beats per minute, and the peak voltage of the signal is 3.5 millivolts.
x1 = 3.5*ecg(2700).'; % gen synth ECG signal
y1 = sgolayfilt(kron(ones(1,ceil(NumSamp/2700)+1),x1),0,21); % repeat for NumSamp length and smooth
n = 1:Time*Fs';
del = round(2700*rand(1)); % pick a random offset
mhb = y1(n + del)'; %construct the ecg signal from some offset
t = 1/Fs:1/Fs:Time';
subplot(3,3,1); plot(t,mhb);
axis([0 2 -4 4]);
xlabel('Time [sec]');
ylabel('Voltage [mV]');
title('Maternal Heartbeat Signal');

%% Fetus Heartbeat
% The heart of a fetus beats noticeably faster than that of its mother, 
% with rates ranging from 120 to 160 beats per minute. The amplitude of the 
% fetal electrocardiogram is also much weaker than that of the maternal 
% electrocardiogram. The following series of commands creates an electrocardiogram 
% signal corresponding to a heart rate of 139 beats per minute and a peak voltage 
% of 0.25 millivolts.
x2 = 0.25*ecg(1725);
y2 = sgolayfilt(kron(ones(1,ceil(NumSamp/1725)+1),x2),0,17);
del = round(1725*rand(1));
fhb = y2(n + del)';
subplot(3,3,2); plot(t,fhb,'m');
axis([0 2 -0.5 0.5]);
xlabel('Time [sec]');
ylabel('Voltage [mV]');
title('Fetal Heartbeat Signal');

%% The measured signal
% The measured fetal electrocardiogram signal from the abdomen of the mother is 
% usually dominated by the maternal heartbeat signal that propagates from the 
% chest cavity to the abdomen. We shall describe this propagation path as a linear 
% FIR filter with 10 randomized coefficients. In addition, we shall add a small 
% amount of uncorrelated Gaussian noise to simulate any broadband noise sources 
% within the measurement. Can you determine the fetal heartbeat rate by looking 
% at this measured signal?
Wopt = [0 1.0 -0.5 -0.8 1.0  -0.1 0.2 -0.3 0.6 0.1];
%Wopt = rand(1,10);
d = filter(Wopt,1,mhb) + fhb + 0.02*randn(size(mhb));
subplot(3,3,3); plot(t,d,'r');
axis([0 2 -4 4]);
%axis tight;
xlabel('Time [sec]');
ylabel('Voltage [mV]');
title('Measured Signal');

%% Measured Mom's heartbeat
% The maternal electrocardiogram signal is obtained from the chest of the mother. 
% The goal of the adaptive noise canceller in this task is to adaptively remove the 
% maternal heartbeat signal from the fetal electrocardiogram signal. The canceller 
% needs a reference signal generated from a maternal electrocardiogram to perform this 
% task. Just like the fetal electrocardiogram signal, the maternal electrocardiogram 
% signal will contain some additive broadband noise.
x = mhb + 0.02*randn(size(mhb));
subplot(3,3,4); plot(t,x);
axis([0 2 -4 4]);
xlabel('Time [sec]');
ylabel('Voltage [mV]');
title('Reference Signal');

%% Applying the adaptive filter
% The adaptive noise canceller can use almost any adaptive procedure to perform its task. 
% For simplicity, we shall use the least-mean-square (LMS) adaptive filter with 15 
% coefficients and a step size of 0.00007. With these settings, the adaptive noise canceller 
% converges reasonably well after a few seconds of adaptation--certainly a reasonable 
% period to wait given this particular diagnostic application.

h = adaptfilt.lms(15, 0.001);
[y,e] = filter(h,x,d);

% [y,e] = FECG_detector(x,d);

subplot(3,3,5); plot(t,d,'c',t,e,'r');
%axis([0 7.0 -4 4]);
xlabel('Time [sec]');
ylabel('Voltage [mV]');
title('Convergence of Adaptive Noise Canceller');
legend('Measured Signal','Error Signal');

%% Recovering the fetus' hearbeat
% The output signal y(n) of the adaptive filter contains the estimated maternal 
% heartbeat signal, which is not the ultimate signal of interest. What remains in the 
% error signal e(n) after the system has converged is an estimate of the fetal heartbeat 
% signal along with residual measurement noise.
subplot(3,3,6); plot(t,e,'r'); hold on; plot(t,fhb,'b');
axis([Time-4 Time -0.5 0.5]);
grid on;
xlabel('Time [sec]');
ylabel('Voltage [mV]');
title('Steady-State Error Signal');
legend('Calc Fetus','Ref Fetus ECG');

%% Counting the peaks to detect the heart rate
% The idea is to clean up the signal, and then set some dynamic threshold, so that any signal
% crossing the threshold is considered a peak. The peaks can be counted per time window.
%[num,den] = fir1(100,100/2000);
filt_e = filter(Hd,e);
subplot(3,3,7); plot(t,fhb,'r'); hold on; plot(t,filt_e,'b');
axis([Time-4 Time -0.5 0.5]);
grid on;
xlabel('Time [sec]');
ylabel('Voltage [mV]');
title('Filtered signal');
legend('Ref Fetus','Filtered Fetus');
thresh = 4*mean(abs(filt_e))*ones(size(filt_e));
peak_e = (filt_e >= thresh);
edge_e = (diff([0; peak_e]) >0);
subplot(3,3,8); plot(t,filt_e,'c'); hold on; plot(t,thresh,'r'); plot(t,peak_e,'b');
xlabel('Time [sec]');
ylabel('Voltage [mV]');
title('Peak detection');
legend('Filtered fetus','Dyna thresh','Peak marker', 'Location','SouthEast');
axis([Time-4 Time -0.5 0.5]);
subplot(3,3,9); plot(t,filt_e,'r'); hold on; plot(t,edge_e,'b'); plot(0,0,'w');
fetus_calc = round((60/length(edge_e(16001:end))*Fs)* sum(edge_e(16001:end)));
fetus_bpm = ['Fetus Heart Rate =' mat2str(fetus_calc)];
xlabel('Time [sec]');
ylabel('Voltage [mV]');
title('Reconstructed fetus signal');
legend('Fetus Sig','Edge marker',fetus_bpm, 'Location','SouthEast');
axis([Time-4 Time -0.5 0.5]);

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