Systems and methods for resolving the continuous wavelet transform of a signal

• US 8,594,759 B2
• Filed: 07/30/2009
• Issued: 11/26/2013
• Est. Priority Date: 07/30/2009
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Van Slyke, Braddon M., Addison, Paul Stanley, Watson, James Nicholas
• Primary Examiner(s): NEGIN, RUSSELL SCOTT
• Application Number:
  US12/512,113
• Publication Number:
  US 20110028810A1
• Time in Patent Office: 1,580 Days
• Field of Search: None
• US Class Current: 600/323
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/726 using Wavelet transforms
• CPC Class Codes: G06F 17/148 Wavelet transforms
• CPC Class Codes: G06F 2218/06 by applying a scale-space analysis, e.g. using wavelet analysis

Abstract

According to an embodiment, techniques for estimating scalogram energy values in a wedge region of a scalogram are disclosed. A pulse oximetry system including a sensor or probe may be used to receive a photoplethysmograph (PPG) signal from a patient or subject. A scalogram, corresponding to the obtained PPG signal, may be determined. In an approach, energy values in the wedge region of the scalogram may be estimated by performing convolution-based or convolution-like operations on the obtained PPG signal, or a transformed version thereof, and the scalogram may be updated according to the estimated values. In an approach, a deskewing technique may be used to align data prior to adding the data to the scalogram. In an approach, one or more signal parameters may be determined based on the resolved and estimated values of the scalogram.

Claims

1. A method for processing a scalogram, the method comprising:

receiving a signal from a signal generator;

using processing equipment for;

sampling the signal to generate a set of samples,

generating the scalogram based at least in part on a continuous wavelet transform of the set of samples,

updating the set of samples with at least one new sample of the signal to generate an updated set of samples,

convolving the updated set of samples with wavelet coefficients to produce skewed scalogram samples, wherein the skewed scalogram samples are skewed in time relative to the scalogram,

deskewing the skewed scalogram samples to produce scalogram update samples, wherein deskewing comprises aligning the skewed scalogram samples in time relative to the scalogram,

updating the scalogram by adding the scalogram update samples to the scalogram, and

determining information from the signal based at least in part on the updated scalogram; and

outputting the information to an output device.

2. The method of claim 1, wherein the signal comprises a photoplethysmograph (PPG) signal.

3. The method of claim 2, wherein the information comprises a patient respiration rate.

4. The method of claim 2, wherein the information comprises a patient oxygen saturation level.

5. The method of claim 2, wherein the information comprises a patient respiration effort level.

6. The method of claim 2, wherein the sampling is performed at a substantially constant time-rate.

7. The method of claim 1, wherein the updating is performed at a refresh rate that depends at least in part on an expected time-rate of change of at least one patient parameter.

8. The method of claim 1, wherein the output device comprises a display.

9. The method of claim 1, wherein the convolving is performed at least in part by at least one processor, and wherein the at least one processor performs one or more matrix multiplications.

10. The method of claim 1, wherein the wavelet coefficients correspond to a truncated Morlet wavelet.

11. The method of claim 1, wherein the wavelet coefficients are stored in a wavelet table and wherein the wavelet coefficients for at least two scales are misaligned in time.

12. The method of claim 1, wherein the skewed scalogram samples comprise samples for at least two scales and wherein the deskewing comprises mapping the skewed scalogram samples for each scale to a different time position to produce the scalogram update samples.

13. A system for processing a scalogram, the system comprising:

a sensor for receiving a signal from a signal generator;

one or more processors coupled to the sensor, wherein the one or more processors are configured to;

sample the signal to generate a set of samples,

generate the scalogram based at least in part on a continuous wavelet transform of the set of samples,

update the set of samples with at least one new sample of the signal to generate an updated set of samples,

convolve the updated set of samples with wavelet coefficients to produce skewed scalogram samples, wherein the skewed scalogram samples are skewed in time relative to the scalogram,

deskew the skewed scalogram samples to produce scalogram update samples, wherein the skewed scalogram samples are deskewed by aligning the skewed scalogram samples in time relative to the scalogram,

update the scalogram by adding the scalogram update samples to the scalogram, and

determine information from the signal based at least in part on the updated scalogram; and

an output device configured to output the information.

14. The system of claim 13, wherein the signal comprises a photoplethysmograph (PPG) signal.

15. The system of claim 14, wherein the information comprises a patient respiration rate.

16. The system of claim 14, wherein the information comprises a patient oxygen saturation level.

17. The system of claim 14, wherein the information comprises a patient respiration effort level.

18. The system of claim 14, wherein the sampling is performed at a substantially constant time-rate.

19. The system of claim 13, wherein the updating is performed at a refresh rate that depends at least in part on an expected time-rate of change of at least one patient parameter.

20. The system of claim 13, wherein the output device comprises a display.

21. The system of claim 13, wherein the convolving is performed at least in part by at least one processor, and wherein the at least one processor performs one or more matrix multiplications.

22. The system of claim 13, wherein the wavelet coefficients correspond to a truncated Morlet wavelet.

23. The system of claim 13, wherein the wavelet coefficients are stored in a wavelet table and wherein the wavelet coefficients for at least two scales are misaligned in time.

24. The system of claim 13, wherein the skewed scalogram samples comprise samples for at least two scales and wherein the deskewing comprises mapping the skewed scalogram samples for each scale to a different time position to produce the scalogram update samples.