Systems and methods for processing physiological signals in wavelet space
Methods and systems are disclosed for analyzing multiple scale bands in the scalogram of a physiological signal in order to obtain information about a physiological process. An analysis may be performed to identify multiple scale bands that are likely to contain the information sought. Each scale band may be assessed to determine a band quality, and multiple bands may be combined based on the band quality. Information about a physiological process may determined based on the combined band. In an embodiment, analyzing multiple scale bands in a scalogram arising from a wavelet transformation of a photoplethysmograph signal may yield clinically relevant information about, among other things, the blood oxygen saturation of a patient.
1. A method for processing a physiological signal, comprising:
receiving, from a sensor, an electronic signal representative of a physiological process;
using processor equipment for:
transforming the electronic signal into a transformed signal based at least in part on a continuous wavelet transformation,
generating a scalogram based at least in part on the transformed signal,
identifying, within the scalogram, a first scale band associated with the physiological process,
identifying, directly within the scalogram, a plurality of scale bands related to the first scale band,
determining a band quality associated with each identified scale band,
combining the identified scale bands based at least in part on the associated band qualities, and
determining information regarding the physiological process based at least in part on the combining; and
outputting the information to an output device.
2. The method of claim 1 , wherein the first scale band comprises a region of the scalogram localized around a scale associated with a pulse rate.
3. The method of claim 2 , wherein each of the plurality of scale bands comprises a region of the scalogram localized around a scale associated with a multiple of the pulse rate.
4. The method of claim 1 , wherein determining a band quality associated with a scale band comprises comparing a total energy in the scale band with a total energy in a region of the scalogram.
5. The method of claim 1 , wherein determining a band quality associated with a scale band comprises comparing a total energy in the scale band with a total energy in another scale band.
6. The method of claim 1 , wherein determining a band quality associated with a scale band comprises evaluating the consistency of an amplitude of the scalogram within the scale band.
7. The method of claim 1 , wherein combining the identified scale bands based at least in part on the associated band qualities comprises calculating a weighted combination of each of the scale bands, wherein the weight associated with a scale band is based at least in part on the associated band quality.
8. The method of claim 1 , wherein combining the identified scale bands based at least in part on the associated band qualities comprises concatenating a portion of each of the scale bands, wherein the portion of a scale band is based at least in part on the associated band quality.
9. The method of claim 1 , further comprising removing a portion of a scale band over a time interval based at least in part on a band quality over the time interval.
10. The method of claim 1 , wherein transforming the electronic signal into a transformed signal comprises:
calculating a first transformed signal from an electronic signal component associated with a first wavelength; and
calculating a second transformed signal from an electronic signal component associated with a second wavelength.
11. The method of claim 10 , wherein determining a band quality associated with a scale band comprises correlating a scale band within the first transformed signal with a corresponding scale band within the second transformed signal.
12. The method of claim 10 , further comprising removing a portion of a scale band over a time interval based at least in part on a band quality over the time interval.
13. A system for processing a physiological signal, comprising:
an output device, capable of receiving an electronic signal representative of information regarding a physiological process; and
a processor, communicably coupled to the output device and capable of receiving an electronic signal representative of a physiological process, the processor being capable of:
transforming the electronic signal representative of a physiological process into a transformed signal based at least in part on a continuous wavelet transformation,
generating a scalogram based at least in part on the transformed signal,
identifying, within the scalogram, a first scale band associated with the physiological process,
identifying, directly within the scalogram, a plurality of scale bands related to the first scale band,
determining a band quality associated with each identified scale band,
combining the identified scale bands based at least in part on the associated band qualities,
determining information regarding the physiological process based at least in part on the combining, and
outputting an electronic signal representative of the information to the output device.
14. The system of claim 13 , wherein the first scale band comprises a region of the scalogram localized around a scale associated with a pulse rate.
15. The system of claim 13 , wherein combining the scale bands based at least in part on the associated band qualities comprises calculating a weighted combination of each of the scale bands, wherein the weight associated with a scale band is based at least in part on the associated band quality.
16. The system of claim 13 , wherein transforming the electronic signal into a transformed signal comprises:
calculating a first transformed signal from an electronic signal component associated with a first wavelength; and
calculating a second transformed signal from an electronic signal component associated with a second wavelength.
17. The system of claim 16 , wherein determining a band quality associated with a scale band comprises correlating a scale band within the first transformed signal with a corresponding scale band within the second transformed signal.
18. Non-transitory computer-readable medium for use in processing a physiological signal, the non-transitory computer-readable medium having computer program instructions recorded thereon for:
transforming a signal representative of a physiological process into a transformed signal based at least in part on a continuous wavelet transformation,
generating a scalogram based at least in part on the transformed signal,
identifying, within the scalogram, a first scale band associated with the physiological process,
identifying, directly within the scalogram, a plurality of scale bands related to the first scale band,
determining a band quality associated with each identified scale band,
combining the identified scale bands based at least in part on the associated band qualities, and
determining information regarding the physiological process based at least in part on the combining.
19. The non-transitory computer-readable medium of claim 18 , wherein the first scale band comprises a region of the scalogram localized around a scale associated with a pulse rate.
20. The non-transitory computer-readable medium of claim 18 , wherein combining the scale bands based at least in part on the associated band qualities comprises calculating a weighted combination of each of the scale bands, wherein the weight associated with a scale band is based at least in part on the associated band quality.