# US 8,786,444 B2 · Systems and methods for determining signal quality of a physiological signal using a wavelet transform and an identified noise floor

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- Number: US 8,786,444 B2
- Document ID: US8786444B2
- Status: Granted
- Kind: B2
- Application number: 13/746,291
- Filed: 2013-01-21
- Published: 2013-05-30
- Granted: 2014-07-22
- Earliest claimed: 2008-07-15
- Applicants: Nellcor Puritan Bennett Ireland
- Inventors: James Nicholas Watson; Paul Stanley Addison; Edward M. McKenna; James P. Ochs
- Web page: https://patentgrep.com/patent/US8786444B2

## CPC

- A61B 5/14551: {for measuring blood gases}
- A61B 5/726: {using Wavelet transforms}
- G16Z 99/00: Subject matter not provided for in other main groups of this subclass
- A61B 5/7207: {of noise induced by motion artifacts}
- G06F 2218/06: by applying a scale-space analysis, e.g. using wavelet analysis
- G16H 40/67: for remote operation
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)
- G16Z: INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR SPECIFIC APPLICATION FIELDS, NOT OTHERWISE PROVIDED FOR
- G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N)
- G16H: HEALTHCARE INFORMATICS, i.e. INFORMATION AND COMMUNICATION TECHNOLOGY [ICT] SPECIALLY ADAPTED FOR THE HANDLING OR PROCESSING OF MEDICAL OR HEALTHCARE DATA

## Abstract

A method and system are provided for evaluating in patient monitoring whether a signal is sensed optimally by receiving a signal, transforming the signal using a wavelet transform, generating a scalogram based at least in part on the transformed signal, identifying a pulse band in the scalogram, identifying a characteristic of the pulse band, determining, based on the characteristic of the pulse band, whether the signal is sensed optimally; and triggering an event. The characteristics of the pulse band and scalogram may be used to provide an indication of monitoring conditions.

## Claims

### Claim 1

A method comprising:
using a processor for:
receiving a physiological signal;
transforming the physiological signal based at least in part on a wavelet transform;
generating scalogram data based at least in part on the transformed signal;
identifying a band in the scalogram data;
identifying a characteristic of the band;
identifying a noise floor of the scalogram data; and
determining signal quality of the physiological signal based at least in part on the characteristic of the band and the noise floor.

### Claim 2 (depends on 1)

The method of claim 1 wherein the characteristic of the band comprises one or more of a height of the band, a width of the band, an amplitude of the band, a strength of the band, and a shape of the band.

### Claim 3 (depends on 1)

The method of claim 1 wherein the characteristic of the band comprises a width of the band and wherein the signal quality of the physiological signal is inversely related to the width of the band.

### Claim 4 (depends on 1)

The method of claim 1 wherein the characteristic of the band is identified by comparing a shape of the band with one or more shape types.

### Claim 5 (depends on 1)

The method of claim 1 further comprising:
generating a template of a noiseless slice of the scalogram data based on the physiological signal during one or more periods when noise is not present; and
comparing current scalogram data with the template, wherein determining signal quality is further based at least in part on the comparison.

### Claim 6 (depends on 1)

The method of claim 1 further comprising identifying a marker region corresponding to a high amplitude region adjacent to the band, wherein determining signal quality is further based at least in part on the marker region.

### Claim 7 (depends on 1)

The method of claim 1 wherein the noise floor is identified outside of the band.

### Claim 8 (depends on 1)

The method of claim 1 wherein identifying the noise floor comprises determining a minimum value between two bands in the scalogram data.

### Claim 9 (depends on 1)

The method of claim 1 wherein the physiological signal comprises a photoplethysmograph signal.

### Claim 10 (depends on 9)

The method of claim 9 wherein the band comprises a pulse band.

### Claim 11

A system comprising:
a processor capable of:
receiving a physiological signal;
transforming the physiological signal based at least in part on a wavelet transform;
generating scalogram data based at least in part on the transformed signal;
identifying a band in the scalogram data;
identifying a characteristic of the band;
identifying a noise floor of the scalogram data; and
determining signal quality of the physiological signal based at least in part on the characteristic of the band and the noise floor; and
a display for displaying information based at least in part on the physiological signal.

### Claim 12 (depends on 11)

The system of claim 11 wherein the characteristic of the band comprises one or more of a height of the band, a width of the band, an amplitude of the band, a strength of the band, and a shape of the band.

### Claim 13 (depends on 11)

The system of claim 11 wherein the characteristic of the band comprises a width of the band and wherein the signal quality of the physiological signal is inversely related to the width of the band.

### Claim 14 (depends on 11)

The system of claim 11 wherein the characteristic of the band is identified by comparing a shape of the band with one or more shape types.

### Claim 15 (depends on 11)

The system of claim 11 wherein the processor is further capable of:
generating a template of a noiseless slice of the scalogram data based on the physiological signal during one or more periods when noise is not present; and
comparing current scalogram data with the template, wherein determining signal quality is further based at least in part on the comparison.

### Claim 16 (depends on 11)

The system of claim 11 wherein the processor is further capable of identifying a marker region corresponding to a high amplitude region adjacent to the band, wherein determining signal quality is further based at least in part on the marker region.

### Claim 17 (depends on 11)

The system of claim 11 wherein the noise floor is identified outside of the band.

### Claim 18 (depends on 11)

The system of claim 11 wherein identifying the noise floor comprises determining a minimum value between two bands in the scalogram data.

### Claim 19 (depends on 11)

The system of claim 11 wherein the physiological signal comprises a photoplethysmograph signal detected by a sensor.

### Claim 20 (depends on 19)

The system of claim 19 wherein the band comprises a pulse band.