Detect and remove the artifacts in PPG signal via MATLAB

Hi,

There is the sample PPG data file, and there are 100 different PPG signals' data.

The sample frequency is about 30 Hz.

When I choose the 85th signal, the wavefrom is looked like this.

Obviously, the motion artifacts is between 200 sec to 500 sec.

I want to design a MATLAB code for detect whether the artfacts are and remove them.

Could anyone tell me how to do that?

I want to separate the whole waveform into different waveforms. Basicially, one waveform is for one period of PPG.

Then, to find the maximum and minimum points and calculate the difference. The parts with a great difference shall be the artifacts.

Could anyone tell how to do that via MATLAB code?

Thanks

[Mathieu NOE]

hello

it's not yet a firm answer , but this code was first to look at the data and see which criteria could be used to remove outliers

more work needed

infile='Examples.mat';
% read the sample waveform
data = load(infile);

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% FFT parameters
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
NFFT = 256;    % 
NOVERLAP = round(0.75*NFFT);
w = hanning(NFFT);     % Hanning window / Use the HANN function to get a Hanning window which has the first and last zero-weighted samples.

% spectrogram dB scale
spectrogram_dB_scale = 80;  % dB range scale (means , the lowest displayed level is XX dB below the max level)

for ck = 1:10
x = data.ppg(ck).data;
samples = length(x);
Fs = 1;
time =(0:samples-1)/Fs;

% create a RMS enveloppe of the signal 
N = 100; % buffer size for averaging
envelop = sqrt(myslidingavg(abs(x.^2), N));

% plot
figure(3*ck);
plot(time,x,'b',time,envelop,'r');grid
title('input waveform');

% measure zero crossing periods 
threshold = mean(envelop);
[ind_crossing,x_crossing,y_crossing]= crossing_V6(x,time,threshold,'linear');
% keep only positive slope crossing points 
ind = (1:2:length(ind_crossing));
period_time_interval = [diff(x_crossing(ind))];
figure(3*ck+1);
subplot(2,1,1),plot(time,x,'b',x_crossing(ind),y_crossing(ind),'+r');grid
subplot(2,1,2),plot(period_time_interval,'+r');grid

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% time / frequency analysis : spectrogram demo
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

[sg,fsg,tsg] = specgram(x,NFFT,Fs,w,NOVERLAP);  

% FFT normalisation and conversion amplitude from linear to dB (peak)
sg_dBpeak = 20*log10(abs(sg))+20*log10(2/length(fsg));     % NB : X=fft(x.*hanning(N))*4/N; % hanning only

% saturation of the dB range : 
% saturation_dB = 60;  % dB range scale (means , the lowest displayed level is XX dB below the max level)
min_disp_dB = round(max(max(sg_dBpeak))) - spectrogram_dB_scale;
sg_dBpeak(sg_dBpeak<min_disp_dB) = min_disp_dB;

% plots spectrogram
figure(3*ck+2);
imagesc(tsg,fsg,sg_dBpeak);colormap('jet');
axis('xy');colorbar('vert');grid
title(['Spectrogram / Fs = ' num2str(Fs) ' Hz / Delta f = ' num2str(fsg(2)-fsg(1)) ' Hz ']);
xlabel('Time (s)');ylabel('Frequency (Hz)');


end

[Leo David]

My idea is the local maximal and local minimal for each period or pulse shall be lower or similar.

I know "findpeaks" function, but not know how to find which one is the maximal or mininal.

Could you tell me how to do that?

I am also not sure what the good PPG signal's performance is? like the difference between maximal and minimal.

[Roya Sabbaghi]

What is the source of the example PPG signals?