Biomedical signal denoising techniques

• US 20040193065A1
• Filed: 03/31/2003
• Published: 09/30/2004
• Est. Priority Date: 03/31/2003
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Houben, Richard P.M.
• Granted Patent: US 7,099,714 B2
• Time in Patent Office: Days
• US Class Current: 600/509
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: G06F 2218/06 by applying a scale-space analysis, e.g. using wavelet analysis

Abstract

The invention is directed to denoising techniques for electrograms, or other biomedical signals, in which wavelet transformations are used in the denoising process. For example, an electrogram can be represented by a finite set of wavelets which comprise a decomposition of the electrogram in the scale-time domain. In accordance with the invention, an electrogram can be transformed into a set of wavelets, and thresholding can be performed on the wavelets to eliminate noise while preserving the information of the electrogram. Different thresholds can be used for the wavelets in different scales for improved denoising results. If a respective threshold exceeds a wavelet coefficient, the wavelet coefficient is reduced. Following the thresholding process, the wavelets can be converted into a denoised electrogram, which can be analyzed or processed. In this manner, wavelet transformations can be exploited for effective electrogram denoising.

Claims

1. An implantable medical device comprising:

a wavelet transform unit to transform an electrogram into a set of wavelets, the set of wavelets including different subsets of wavelets for different scales; and

a wavelet denoising unit to compare first wavelet coefficients of the wavelets in a first subset to a first threshold, compare second wavelet coefficients of the wavelets in a second subset to a second threshold, the second threshold being different than the first threshold, reduce one or more of the first wavelet coefficients that are less than the first threshold, and reduce one or more of the second wavelet coefficients that are less than the second threshold.

2. The implantable medical device of claim 1, further comprising an inverse wavelet transform unit to transform the set of wavelets into a denoised electrogram following reduction of one or more wavelet coefficients.

3. The implantable medical device of claim 1, wherein the wavelet denoising unit reduces one or more of the first and second wavelet coefficients by setting one or more of the first and second wavelet coefficients to zero.

4. The implantable medical device of claim 1, wherein the wavelet denoising unit compares wavelet coefficients of the wavelets in each respective subset to different thresholds, and reduces any given wavelet coefficient that is less than a respective threshold for the respective subset associated with that given wavelet coefficient.

5. The implantable medical device of claim 1, further comprising a telemetry unit to receive the first and second thresholds from a programmer prior to transforming the electrogram into the set of wavelets.

6. The implantable medical device of claim 1, wherein the medical device comprises a device selected from the following group:

an implantable medical device, an external medical device, a programmer and a diagnostic loop recorder.

7. An implantable medical device comprising:

a wavelet transform unit to transform a biomedical signal into a set of wavelets, the set of wavelets including different subsets of wavelets for different scales;

a wavelet denoising unit to compare first wavelet coefficients of the wavelets in a first subset to a first threshold, compare second wavelet coefficients of the wavelets in a second subset to a second threshold, the second threshold being different then the first threshold, reduce one or more of the first wavelet coefficients that are less than the first threshold, and reduce one or more of the second wavelet coefficients that are less than the second threshold.

8. A method comprising:

transforming an electrogram into a set of wavelets, the set of wavelets including different subsets of wavelets for different scales;

comparing first wavelet coefficients of the wavelets in a first subset to a first threshold;

comparing second wavelet coefficients of the wavelets in a second subset to a second threshold, the second threshold being different then the first threshold;

reducing one or more of the first wavelet coefficients that are less than the first threshold; and

reducing one or more of the second wavelet coefficients that are less than the second threshold.

9. The method of claim 8, further comprising transforming the set of wavelets into a denoised electrogram following reduction of one or more wavelet coefficients.

10. The method of claim 8, wherein reducing one or more of the first and second wavelet coefficients comprises setting one or more of the first and second wavelet coefficients to zero.

11. The method of claim 8, further comprising:

comparing wavelet coefficients of the wavelets in each respective subset to different thresholds; and

reducing any given wavelet coefficient that is less than a respective threshold for the respective subset associated with that given wavelet coefficient.

12. The method of claim 8, further comprising selecting the first and second thresholds prior to transforming the electrogram into the set of wavelets.

13. The method of claim 12, wherein selecting the first and second thresholds includes adjusting values of the first and second thresholds in response to analysis of one or more denoised electrograms.

14. The method of claim 12, wherein selecting the first and second thresholds includes:

instructing a patient to assume a position;

generating a denoised electrogram based on wavelet denoising of an electrogram sensed while the patient is in the position; and

adjusting values of the first and second thresholds in response to analysis of denoised electrograms.

15. A system comprising:

a first medical device to record electrograms and perform denoising of the electrograms by transforming an electrogram into a set of wavelets, the set of wavelets including different subsets of wavelets for different scales, comparing first wavelet coefficients of the wavelets in a first subset to a first threshold, comparing second wavelet coefficients of the wavelets in a second subset to a second threshold, the second threshold being different then the first threshold, reducing one or more of the first wavelet coefficients that are less than the first threshold, and reducing one or more of the second wavelet coefficients that are less than the second threshold; and

a second medial device to perform threshold estimation to establish the first and second thresholds and send the first and second thresholds to the first medical device.

16. The system of claim 15, wherein the first medical device comprises an implantable medical device and the second medical device comprises a programmer.

17. The system of claim 16, wherein the first medical device comprises an implantable diagnostic loop recorder.

18. A computer readable medium comprising computer readable instructions that when executed:

transform an electrogram into a set of wavelets, the set of wavelets including different subsets of wavelets for different scales;

compare first wavelet coefficients of the wavelets in a first subset to a first threshold;

compare second wavelet coefficients of the wavelets in a second subset to a second threshold, the second threshold being different then the first threshold;

reduce one or more of the first wavelet coefficients that are less than the first threshold; and

reduce one or more of the second wavelet coefficients that are less than the second threshold.

19. The computer readable medium of claim 18, wherein the instructions when executed transform the set of wavelets into a denoised electrogram following reduction of one or more wavelet coefficients.

20. The computer readable medium of claim 18, wherein the instructions when executed reduces one or more of the first and second wavelet coefficients by setting one or more of the first and second wavelet coefficients to zero.

21. The computer readable medium of claim 18, wherein the instructions when executed:

compare wavelet coefficients of the wavelets in each respective subset to different thresholds; and

reduce any given wavelet coefficient that is less than a respective threshold for the respective subset associated with that given wavelet coefficient.

22. An apparatus comprising:

means for transforming an electrogram into a set of wavelets, the set of wavelets including different subsets of wavelets for different scales;

means for comparing first wavelet coefficients of the wavelets in a first subset to a first threshold;

means for comparing second wavelet coefficients of the wavelets in a second subset to a second threshold, the second threshold being different then the first threshold;

means for reducing one or more of the first wavelet coefficients that are less than the first threshold; and

means for reducing one or more of the second wavelet coefficients that are less than the second threshold.

23. The apparatus of claim 22, further comprising means for transforming the set of wavelets into a denoised electrogram following reduction of one or more wavelet coefficients.

24. The apparatus of claim 22, wherein the means for reducing a respective wavelet coefficient comprises means for setting the respective wavelet coefficient to zero.

25. The apparatus of claim 22, further comprising:

means for comparing wavelet coefficients of the wavelets in each respective subset to different thresholds; and

means for reducing any given wavelet coefficient that is less than a respective threshold for the respective subset associated with that given wavelet coefficient.

26. The apparatus of claim 22, further comprising means for receiving selected first and second thresholds prior to transforming the electrogram into the set of wavelets.

27. A system comprising:

means for transforming an electrogram into a set of wavelets, the set of wavelets including different subsets of wavelets for different scales;

means for comparing first wavelet coefficients of the wavelets in a first subset to a first threshold;

means for comparing second wavelet coefficients of the wavelets in a second subset to a second threshold, the second threshold being different then the first threshold;

means for reducing one or more of the first wavelet coefficients that are less than the first threshold; and

means for reducing one or more of the second wavelet coefficients that are less than the second threshold; and

means for selecting the first and second thresholds prior to transforming the electrogram into the set of wavelets.

28. The apparatus of claim 27, wherein the means for selecting includes means for adjusting values of the first and second thresholds response to analysis of denoised electrograms.

29. A method comprising:

comparing first wavelet coefficients for first-scale wavelets representative of an electrogram to a first threshold;

comparing second wavelet coefficients for second-scale wavelets representative of the electrogram to a second threshold;

reducing the first wavelet coefficients that are less than the first threshold; and

reducing the second wavelet coefficients that are less than the second threshold, the second threshold being different than the first threshold.

30. The method of claim 29, wherein reducing the first and second wavelet coefficients comprises setting the first and second wavelet coefficients to zero.

31. A method comprising:

transforming a biomedical signal into a set of wavelets, the set of wavelets including different subsets of wavelets for different scales;

comparing first wavelet coefficients of the wavelets in a first subset to a first threshold;

comparing second wavelet coefficients of the wavelets in a second subset to a second threshold, the second threshold being different then the first threshold;

reducing one or more of the first wavelet coefficients that are less than the first threshold; and

reducing one or more of the second wavelet coefficients that are less than the second threshold.

32. The method of claim 31, further comprising transforming the set of wavelets into a denoised biomedical following reduction of one or more wavelet coefficients.

33. The method of claim 31, wherein the biomedical signal comprises a signal selected from the group consisting of:

an electrogram measured via external sensors, an electrogram measured via implanted sensors, and a signal measured by a biomedical sensor.