POWER LINE INTERFERENCE REMOVAL DEVICE FOR ECG
DEVICES
A) TECHNICAL FIELD
[1] The present invention generally relates to a noise removal device for medical devices and more specifically to a noise removal device for removing the power line interference signals from acquired diagnostic signals from ECG device, ECG module for star/planet 55 using a subtraction process.
B) BACKGROUND OF THE INVENTION
[2] Modern bio-medical amplifiers have a very high common mode rejection ratio. Moreover the recorded signals are distorted with residual power line interference signal due to difference in the electrode impedances and the stray currents passed through the patient and the cables. Any residual power line interference may interfere with the correct delineation of ECG wave boundaries and disrupt the proper functioning of an automatic ECG analysis unit. The hardware solutions are developed increase the common mode rejection ratio by equalizing the cable shield and right leg potential to reduce the influence of the stray currents through the body. But this method does not significantly reduce the power line interference. Normally the analog and digital filters are used to suppress the ECG components near the power line frequency. Various types of digital notch filters are widely used to filter the ECG signals mixed with power line interference signals but they are ineffective with a larger power line frequency deviation. Moreover the resulting transient time is often long. Thus the adaptive filtering technique introduces unacceptable transient response time especially after steep and large QRS complexes. Other techniques such as Fourier transform do not work in real time.
[0003] The adaptive filtering process has several drawbacks. The drawbacks are listed as follows. There is a ringing effect in the ST Segment of ECG. In order to achieve a complete removal of the frequency of power line noise in the input signal, the designed FIR Filter needs to have sharp cut-off frequencies near the frequency of interest i.e. a sharp roll-off in the frequency domain with high dB of attenuation in the stop band. As a result, the filter response has ringing effects in the frequency domain near the desired frequency level. Further the optimization of the filter performed to meet the requirements along with
reduction in the ringing effect in the frequency domain results in the ringing effect in the time domain i.e. in the ST segment of ECG.
[4] The FIR Filter is not adaptive to the changes in the wave shape of the noise. The actual wave shape of the noise gets distorted because of the numerous interferences. The filter assumes that the wave shape of the noise in the noisy input signal is equal to that of a sinusoidal wave. Hence, the chances of distorting the actual wave shape of the input signal by the filter it self could not be ruled out during the removal of the noise from an input signal.
[5] The Filter is not adaptive to the changes in the noise frequency levels. The filter is designed for a fixed frequency level of the power line noise. In a real-time situation, the frequency of the power line noise does not remain stable and fluctuates. When the frequency of the noise is out of the range of the filter, the filter could not remove the noise from the signal. In order to take care of this situation, the filter bandwidth is widened a little more to take care of the band of frequencies near the desired frequency.
[6] Hence a subtraction process is then developed to remove the power line interference signal from the acquired ECG diagnostic signals. But no system is developed so far to apply the subtraction process to remove the power line interference signal from the acquired ECG diagnostic signal. So, there is a need to provide an algorithm to remove the power line interference from the acquired ECG diagnostic signals using a subtraction process.
[7] The US Patent 6807442 issued to Myklebust et al discloses a system for reducing the signal disturbances from the composite signals containing the ECG signals. The digital filters calculate an estimate of a signal disturbance as a correlation function between a disturbance signal and a reference signal.
[8] The US. Patent No.6785573 issued to Kovtun et al discloses a low distortion ECG filter to remove the noise superimposed on the ECG Signal. Several low pass FIR filters are connected in tandem between the signal input point and signal output point. Each filter has a distinct cut-off frequency characteristic. A scaled noise signal falling within a preset frequency band is subtracted from the stored data sample to remove the noise from the ECG signals.
[9] The US Patent No.6041250 issued to De pinto discloses an adaptive noise canceller and detector for ECG signals. The system has a baseline wander filter, high and low pass filters, an adaptive line canceller and noise detector to identify and remove unwanted signal from an ECG signal. The ECG signal is conditioned to remove various portions of ECG signal prior to processing in noise detectors.
[10] The US Patent No.5876350 issued to LO et al discloses an EKG based heart monitor with digital filter provided with recursive structure. The filter has a recursive coefficient to simplify and speed up calculations.
[11] The US Patent No.5772603 issued to Ohlsson et al discloses a device for filtering ECG signals provided with a filter unit coupled to A/d converter. The filter unit has several filters with a non-linear phase response so that the signals in the pass band frequency of filter are delayed more than that in a transition band frequency.
The US Patent No. 576208 issued to De Pinto discloses an ECG filter and slew rate limiter to restrict the slope of the ECG signals above and below a pre selected cut off level. A delay circuit delays the received input ECG signal by a time greater than that required for passing the ECG signals through a low pass filter which receives the ECG signals above a preset level. The out put of the delay circuit is subtracted from the output of a slew rate limiter.
[13] The US Patent No. 4420815 issued to Prancis discloses a devise and a method for removing a sinusoidal noise from a sampled signal. The filter device uses a programmable gain amplifier to control the amplitude and phase of a discreet sine wave generator. The output of the sine wave generator is phase shifted to cancel the sinusoidal noise from a sampled analog signal.
[14] The US Pre-grant publication No. 20050277826 Al issued to Dungeath et al discloses a device and a method for reducing the interference noise signal from a diagnostic signal. The device is provided with a Bessel type low pass filter to subtract the interference signal on a reference line from that in a signal line to reduce a noise generated by the electromagnetic fields.
[15] The US Patent No.4458691 issued to Netravali discloses a system and a method for predicting ventricular tachycardia. The system samples the input ECG signal periodically during each ECG cycle. The representative ECG samples are stored corresponding to each sample period. The high pass filter filters the signals for each ECG cycle to provide a filter output corresponding to the high frequency content of the ECG output. The system removes the ringing of a signal waveform.
[16] The US Pre grant publication No. 20030114768A1 discloses a signal processing method and a device. The device applies an adaptive filtering process to the measured signal to improve the signal to noise ratio. The adaptive filtering is performed based on the derivative of the Gaussian Kernel having specific parameters matching the signal component characteristics.
[17] Thus none of the prior art devices provide a complete device to execute a subtraction process to remove the power line interference from an acquired ECG signal. Hence there is a need for a device or algorithm to perform the subtraction process effectively and efficiendy to remove the power line noise from the ECG signals or acquired diagnostic signals.
C) OBJECT OF THE INVENTION
[18] The primary object of the invention is to provide a power line noise removal device to remove the power line interference signal from the acquired ECG signals using an application executing a subtraction process.
[19] Another objective of the invention is to provide a power line noise removal device from the ECG signals to prevent the distortion of the actual wave shape of the input ECG signal.
[20] Yet another objective of the invention is to provide a power line noise removal device from the ECG signals to remove the ringing effect present in the ST segment of the acquired ECG signal and to prevent the generation of ringing effect in frequency and time domain of the input signal.
[21] Yet another object of the invention is to provide a power line noise removal device to remove the power line interference signal from the acquired ECG signals using an application executing a subtraction process thereby eliminating the need for a filter with sharp cut -off characteristics.
Yet another object of the present invention is to provide a power line noise removal device to remove the power line interference signal from the acquired ECG signals using an application executing a subtraction process so that filter may be improved to be adaptive to the variations in the power line frequency.
[23] Yet another object of the present invention is to provide a power line noise removal device to remove the power line interference signal from the acquired ECG signals using an application executing a subtraction process so that filter may be improved to be adaptive to the variations in the frequency levels of a noise signal.
[24] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THIS INVENTION
[25] The abovementioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
[26] The various embodiments of the present invention provide a system and a method to develop a device to remove the power line noise from the acquired ECG signals.
[27] The present invention provides a noise removal device for removing the power line interference from the acquired ECG signals using a subtraction process. The ECG signals contain both linear components and non-linear components. A digital filtering operation is applied in the subtraction process to remove the interference components from the linear segments of the signal. The detected or removed noise components from the linear segments are removed from the non-linear segments of the signals to obtain noise free ECG diagnostic signals efficiently and effectively so that the wave form of the acquired diagnostic signals are not distorted.
[28] According to one embodiment of the present invention, the power line noise removal device has a noise removal circuit provided with a processor to execute a noise removal algorithm to remove the power line interference noise from the acquired ECG signals. The ECG signals contain both linear components and non-linear components. A digital filtering operation is applied in the subtraction process to remove the interference components from the linear segments of the signal. The detected or removed noise components from the linear segments are removed from the non-linear segments of the signals to
obtain noise free ECG diagnostic signals efficiently and effectively so that the wave form of the acquired diagnostic signals are not distorted.
[0029] According to another embodiment of the present invention, a method is provided for removing the power line noise from the acquired ECG signals from a patient using a subtraction process. The ECG signals acquired from a patient are amplified. The amplified signals are passed through a filter to remove the unwanted noise components. Then the output signal from the filter is passed through a noise removal device to remove the power line interference signal from the ECG. An application software is executed on a processor to remove the power line noise from the acquired ECG signals. The ECG signals contain both linear components and non-linear components. A digital filtering operation is applied in the subtraction process to remove the interference components from the linear segments of the signal. The detected or removed noise components from the linear segments are removed from the non-linear segments of the signals to obtain noise free ECG diagnostic signals efficiently and effectively so that the wave form of the acquired diagnostic signals are not distorted.
[30] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[31] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[32] FIGURE .1 illustrates a block diagram of power line interference removal device for ECG signals according to one embodiment of the present invention.
FIGURE. 2 illustrates a functional block diagram of a power line interference removal device for ECG signals according to one embodiment of the present invention.
[34] FIGURE. 3 illustrates a flow chart explaining the method for removing the power line interference removal signal from ECG signals using a power line interference removal device for ECG signals according to one embodiment of the present invention.
[35] Although specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE INVENTION
[36] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[37] The various embodiments of the present invention provide a system and a method to develop a device to remove the power line noise from the acquired ECG signals.
[38] According to one embodiment of the present invention, a noise removal device is provided for removing the power line interference from the acquired ECG signals using a subtraction process and a software algorithm. The ECG signals contain both linear components and non-linear components. A digital filtering operation is applied in the subtraction process to remove the interference components from the linear segments of the signal. The detected or removed noise components from the linear segments are removed from the non-linear segments of the signals to obtain noise free ECG diagnostic signals efficiently and effectively so that the wave form of the acquired diagnostic signals are not distorted.
[39] According to one embodiment of the present invention, the power line noise removal device has a noise removal circuit provided with a processor to execute a noise removal algorithm to remove the power line interference noise from the acquired ECG signals. The ECG signals contain both linear components and non-linear components. A digital filtering operation is applied in the subtraction process to remove the interference components from the linear segments of the signal. The detected or removed noise components from the linear segments are removed from the non-linear segments of the signals to obtain noise free ECG diagnostic signals efficiendy and effectively so that the wave form of the acquired diagnostic signals are not distorted.
[0040] According to another embodiment of the present invention, a method is provided for removing the power line noise from the acquired ECG signals from a patient using a subtraction process. The ECG signals acquired from a patient are amplified. The amplified signals are passed through a filter to remove the unwanted noise components. Then the output signal from the filter is passed through a noise removal device to remove the power line interference signal from the ECG. An application software is executed on a processor to remove the power line noise from the acquired ECG signals. The ECG signals contain both linear components and non-linear components. A digital filtering operation is applied in the subtraction process to remove the interference components from the linear segments of the signal. The detected or removed noise components from the linear segments are removed from the non-linear segments of the signals to obtain noise free ECG diagnostic signals efficiently and effectively so that the wave form of the acquired diagnostic signals are not distorted.
[41] According to one embodiment of the present invention, the noise removal device has an amplifier to amplify the ECG signals collected from a patient. The acquired ECG signals are passed through a hardware filter to remove the unwanted noise signals. The output signal from the filter is digitized using an analog to digital converter. The digital signal is passed through a software filter to remove the high and low frequency components present in the digital ECG measurement signal. Then the signal removed with the high and low frequency components are passed through a power line noise removal circuit to remove the power line noise present in the acquired ECG signal. The power line noise removed signal is passed to a recorder or to a display to output an actual noise free ECG value.
[42] The power line noise removal circuit removes the power line noise from the acquired ECG diagnostic signals. The acquired ECG signals mixed with power line noise are input into a linear and non-linear signal component detection block. The waveform of the input signals contains both a linear component and a non-linear component. The linear and the non-linear components present in an input signal are detected by the linear and non-linear components detection block based on a threshold value. Then the ECG signal mixed with noise is input into a linear phase comb filter with a given frequency response characteristics. The comb filter removes the noise component from the input ECG signal mixed with power line interference. The noise extraction block removes the noise present in the linear component of the input ECG signal and the output signal from the comb filter. A noise buffer is updated with the latest noise component, which removed from the ECG signal mixed with noise by a noise extraction block. The detected and extracted noise component present in the linear component of the input signal is fedback so that the detected and fed back noise component is removed from the non¬linear component of the input signal by a noise subtraction block. The noise subtraction block maintains the phase of the noise. A dynamic threshold calculator block computes a threshold based on the frequency and the amplitude of the input ECG signal and the comb filter output signal, as a fixed or constant threshold value cannot be used to classify the linear and the non linear components in an input signal with different amplitude levels. The threshold value is updated based on the amplitude of the input signal. Thus a power line noise removal device uses an algorithm to detect a noise component and to subtract the noise component from the acquired ECG signals mixed with noise.
[0043] The FIG. 1 illustrates a block diagram of power line interference removal device for ECG signals according to one embodiment of the present invention. The noise removal device has an amplifier to amplify the ECG signals collected from a patient. The acquired ECG signals are passed through a hardware filter to remove the unwanted noise signals. The output signal from the filter is digitized using an analog to digital converter. The digital signal is passed through a software filter to remove the high and low frequency components present in the digital ECG measurement signal. Then the signal removed with the high and low frequency components are passed through a power line noise removal circuit to remove the power line noise present in the acquired ECG signal. The power line noise removed signal is passed to a recorder or printer or to a display to output an actual noise free ECG value. The device has a key board to input the user required data to label the measured ECG signals with patient name, time and date of measurement, etc. the input data are passed to a driver to display the input data on a user interface. A control unit is provided to regulate the entire operation of the noise removal device.
[0044] The FIG. 2 illustrates a functional block diagram of a power line interference removal device for ECG signals according to one embodiment of the present invention. The power line noise removal circuit removes the power line noise from the acquired ECG diagnostic signals. The acquired ECG signals mixed with power line noise are input into a linear and non-linear signal component detection block. The waveform of the input signals contains both a linear component and a non-linear component. The linear and the non-linear components present in an input signal are detected by the linear and non-linear components detection block based on a threshold value. Then the ECG signal mixed with noise is input into a linear phase comb filter with a given frequency response characteristics. The comb filter removes the noise component from the input ECG signal mixed with power line interference. The noise extraction block removes the noise present in the linear component of the input ECG signal and the output signal from the comb filter. A noise buffer is updated with the latest noise component, which removed from the ECG signal mixed with noise by a noise extraction block. The detected and extracted noise component present in the linear component of the input signal is fedback so that the detected and fed back noise component is removed from the non¬linear component of the input signal by a noise subtraction block. The noise subtraction block maintains the phase of the noise. A dynamic threshold calculator block computes a threshold based on the frequency and the amplitude of the input ECG signal and the comb filter output signal, as a fixed or constant threshold value cannot be used to classify the linear and the non linear components in an input signal with different amplitude levels. The threshold value is updated based on the amplitude of the input signal. Thus a power line noise removal device uses an algorithm to detect a noise component and to subtract the noise component from the acquired ECG signals mixed with noise.
[0045] The FIG.3 illustrates a flow chart explaining the method for removing the power line interference removal signal from ECG signals using a power line interference removal device for ECG signals according to one embodiment of the present invention. The method is used for removing the power line noise from the acquired ECG signals from a patient using a subtraction process. The ECG signals acquired from a patient are amplified (302). The amplified signals are passed through a filter to remove the unwanted noise components (304). The out put signal from the filter after the removal of the unwanted noise is digitized using an analog to digital converter (ADC) (306). The digital output signal from the ADC is passed through a filter for removing the high and low frequency components in the input digital ECG signal (308). The out put from
the filter is passed to a power line noise removal circuit to remove the power line interference signal from the ECG (310).
[46] An application software is executed to remove the power line noise from the acquired ECG signals. The ECG signals contain both linear components and non-linear components. A digital filtering operation is applied in the subtraction process to remove the interference components from the linear segments of the signal. The detected or removed noise components from the linear segments are removed from the non-linear segments of the signals to obtain noise free ECG diagnostic signals efficiently and effectively so that the wave form of the acquired diagnostic signals are not distorted.
[47] Thus a power line noise removal device uses an algorithm to detect a noise component and to subtract the noise component from the acquired ECG signals mixed with noise. The algorithm can be improved to be adaptive to the variations in the power line frequency. Since the algorithm is executed to detect and estimate the noise from the input ECG signal mixed with noise and to subtract it from the input noise mixed ECG signals, a filter with sharp cut-off characteristics is not required. Thus the ringing effect is not generated either in frequency or time domain and the ringing effect present in the ST segment of
ECG signal waveform is removed. The algorithm also judges the wave shape of the noise from the input ECG signal mixed with noise input signal and subtracts the detected noise wave shape in proper phase. Hence the distortion of the actual wave shape of the input signal during the noise removal process is prevented. The algorithm can further be improved to be adaptive to the variations in the frequency levels of a noise signal.
G) ADVANTAGES OF THE PRESENT INVENTION
[48] The various embodiments of the present invention provide a system and a method to develop a device to remove the power line noise from the acquired ECG signals.
[49] Thus a power line noise removal device uses an algorithm to detect a noise component and to subtract the noise component from the acquired ECG signals mixed with noise. The algorithm can be improved to be adaptive to the variations in the power line frequency. Since the algorithm is executed to detect and estimate the noise from the input ECG signal mixed with noise and to subtract it from the input noise mixed ECG signals, a filter with sharp cut-off characteristics is not required. Thus the ringing effect is not generated either in frequency or time domain and the ringing effect present in the ST segment of ECG signal waveform is removed. The algorithm also judges the wave shape of the noise from the input ECG signal mixed with noise input signal and subtracts the detected noise wave shape in proper phase. Hence the distortion of the actual wave shape of the input signal during the noise removal process is prevented. The algorithm can further be improved to be adaptive to the variations in the frequency levels of a noise signal.
[50] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[51] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.

CLAIMS
WHAT IS CLAIMED IS:
1. A power line interference noise removal device for ECG signals collected from a monitor using an ECG device, the device comprising:
A detection block to identify a linear component and a non linear component in an input ECG signal.
A comb filter to remove the noise present in the detected linear component present in the input ECG signal;
A noise subtraction circuit to remove the noise present in the nonlinear component of the input ECG signal based on the removed noise signal present in the linear component of the input ECG signal.
2. The device according to claim 1, wherein the noise removal circuit uses an algorithm to remove the power line noise present the input ECG signal.
3. The device according to claim 1, further comprises a filter to remove the unwanted noise signal from the input ECG signal.
4. The device according to claim 1, further comprises an amplifier to amplify the input ECG signals.
5. The device according to claim 1, further comprises an analog to digital filter to digitize the input amplified ECG signals.
6. The device according to claim 1, further comprises another filter to remove the high and low frequency noise components present in the input digitized ECG signal.
7. The device according to claim 1, further comprises a dynamic threshold calculator to compute a threshold value based on the frequency and the amplitude of the input ECG signals to detect thee linear component and the non linear component present in the input ECG signal mixed with power line noise.
8. a power line noise removal method from the ECG signals using a subtraction process, the method comprising:
amplifying the input ECG signal;
filtering the amplified input ECG signal to remove the unwanted noise present in the input ECG signal;
converting the noise removed ECG signal into a digital signal using an analog to digital converter;
filtering the input digital signal to remove the low and the high frequency noise components in the input ECG digital signal.
Passing the ECG signal removed with the high and the low frequency noise components through a power line noise removal circuit to remove the power line noise superimposed with the input ECG signal.
9. The method according to claim 8, wherein the power line noise is removed from the input ECG signal using an algorithm to apply a subtraction process.
10. The method according to 8, wherein the linear and the non linear signal components of the input ECG signal are detected.
11. The method according to claim 8, wherein the noise present in the linear signal component of the input ECG signal is detected and removed using a comb filter
12. The method according to claim 8, wherein the noise present in the non linear signal component of the input ECG signal is removed based on the detected and removed noise present in the linear signal component, to obtain a power line noise removed ECG signal.