10-04-2017, 08:39 PM
ECG Analysis using Wavelet Transforms
[attachment=341]
Electrocardiograph
Electrical activity of the heart, condition of the heart muscle.
Waves are inscribed on ECG during myocardial depolarization and repolarization.
Usually time-domain ECG signals are used.
New computerized ECG recorders utilize frequency information to detect pathological condition.
ECG consists of P-wave, QRS-complex, the T-wave and U-wave.
P-wave-depolarization of atria.
QRS-complex-depolarization of ventricles.
T-wave-repolarization of ventricles.
Repolarization of the atria not visible.
QRS complex detection-most important task in automatic ECG analysis.
Why wavelet transform?
ECG signal-sequence of cardiac cycles or beats .
ECG is not strictly a periodic signal-differences in period and amplitude level of beats.
Each region has different frequency components-QRS has high frequency oscillations,T region has lower frequencies,P and U regions have very low frequencies.
Signal contains noise components due to various sources that are suppressed during processing of ECG signal.
Fourier Transform - provides only frequency information, time information is lost.
Short Term Fourier Transform (STFT) - provides both time and frequency information, but resolves all frequencies equally.
Wavelet transform - provides good time resolution and poor frequency resolution at high frequencies and good frequency resolution and poor time resolution at low frequencies.
Useful approach when signal at hand has high frequency components for short duration and low frequency components for long duration as in ECG.
Discrete Wavelet Transform (DWT)
Time-scale representation of signal obtained using digital filtering techniques.
Resolution of the signal is changed by filtering operations.
Scale is changed by upsampling and downsampling (subsampling) operations.
Subsampling-reducing sampling rate, or removing some of the samples of the signal.
Upsampling-increasing sampling rate by adding new samples to the signal.
[attachment=341]
Electrocardiograph
Electrical activity of the heart, condition of the heart muscle.
Waves are inscribed on ECG during myocardial depolarization and repolarization.
Usually time-domain ECG signals are used.
New computerized ECG recorders utilize frequency information to detect pathological condition.
ECG consists of P-wave, QRS-complex, the T-wave and U-wave.
P-wave-depolarization of atria.
QRS-complex-depolarization of ventricles.
T-wave-repolarization of ventricles.
Repolarization of the atria not visible.
QRS complex detection-most important task in automatic ECG analysis.
Why wavelet transform?
ECG signal-sequence of cardiac cycles or beats .
ECG is not strictly a periodic signal-differences in period and amplitude level of beats.
Each region has different frequency components-QRS has high frequency oscillations,T region has lower frequencies,P and U regions have very low frequencies.
Signal contains noise components due to various sources that are suppressed during processing of ECG signal.
Fourier Transform - provides only frequency information, time information is lost.
Short Term Fourier Transform (STFT) - provides both time and frequency information, but resolves all frequencies equally.
Wavelet transform - provides good time resolution and poor frequency resolution at high frequencies and good frequency resolution and poor time resolution at low frequencies.
Useful approach when signal at hand has high frequency components for short duration and low frequency components for long duration as in ECG.
Discrete Wavelet Transform (DWT)
Time-scale representation of signal obtained using digital filtering techniques.
Resolution of the signal is changed by filtering operations.
Scale is changed by upsampling and downsampling (subsampling) operations.
Subsampling-reducing sampling rate, or removing some of the samples of the signal.
Upsampling-increasing sampling rate by adding new samples to the signal.