Signal processing method and device for signal-to-noise improvement

• US 7,027,850 B2
• Filed: 07/23/2003
• Issued: 04/11/2006
• Est. Priority Date: 09/13/2001
• Status: Expired due to Term

• Current Assignee: Conmed Corporation (Jefferies Financial Group, Inc.)
• Original Assignee: Conmed Corporation (Jefferies Financial Group, Inc.)
• Inventors: Wasserman, Yoram
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US10/625,250
• Publication Number:
  US 20040087846A1
• Time in Patent Office: 993 Days
• Field of Search: 600/300, 600/301, 600/322, 600/323, 600/330, 600/481
• US Class Current: 600/330
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

A method and apparatus extract a signal component of a measured signal using one of two methods. If the signal component in the measured signal is a periodic signal with a certain well-defined peak-to-peak intensity value, upper and lower envelopes of the measured signal are determined and analyzed to extract said signal component of the measured signal. This signal component can further be used to calculate a desired parameter of the sample. The DC component of the signal is determined as the median value of the upper envelope, and the AC component is determined as the median value of the difference between the upper and lower envelopes. If the signal component of the measured signal is a periodic signal characterized by a specific asymmetric shape, a specific adaptive filtering is applied to the measured signal, resulting in the enhancement of the signal component relative to a noise component. This adaptive filtering is based on a derivative of the Gaussian Kernel having specific parameters matching the characteristics of the signal component.

Claims

1. A signal processing method for use in determination of a desired parameter of a sample, the method comprising the steps of:

providing a measured signal representative of a response of the sample to an external field, the measured signal comprising a signal component indicative of the desired parameter, and a noise component, the signal component being a substantially periodic signal characterized by a substantially well-defined peak-to-peak intensity value;

determining upper and lower envelope of the measured signal;

determining lower and lower envelope of the measured signal; and

analyzing the upper and lower envelope values to extract the signal component from the measured signal, to enable further processing of the extracted signal component to determine the desired parameter, wherein the analyzing step includes the step of determining a median of the difference between the upper and lower envelope values as an AC component.

2. The method, as set forth in claim 1, wherein the step of providing the measured signal includes the step of sampling and frequency filtering of the response.

3. A method for processing a measured signal including a first signal component in the form of a substantially periodic signal with substantially well-defined peak-to-peak intensity value, and a second signal component characterized by a specific asymmetric shape, to extract the signal components from noise components, the method comprising the steps of:

processing the measured signal by determining upper and lower envelopes thereof, and analyzing the upper and lower envelope values to extract the first signal component, wherein the analyzing step includes the step of determining a median of the difference between the upper and lower envelope values as an AC component; and

defining a kernel function being a derivative of a Gaussian with parameters matching characteristics of the second signal component, and processing the measured signal by filtering it with the kernel function parameters, thereby enhancing the second signal component relative to the noise component in the filtered measured signal.

4. A control unit for use with a measurement device to receive and process a measured signal generated by the measurement device so as to extract a signal component from a noise component in the measured signal, the signal component being a substantially periodic signal with substantially well-define peak-to-peak intensity value, the control unit comprising a data processing and analyzing utility preprogrammed to determine upper and lower envelopes of the measured signal, and analyzing the upper and lower envelope values to extract the signal component by determining a median of the difference between the upper and lower envelope values as an AC component.

5. A computer program storage device readable by a machine, tangibly embodying a program of instructions executable by a machine to perform method steps of processing a measured signal to extract a signal component and suppress a noise component of the measured signal, wherein the signal component is a substantially periodic signal characterized by a substantially well-defined peak-to-peak intensity value, which method comprises the steps of:

(i) determining an upper envelope of the measured signal;

(ii) determining a lower envelope of the measured signal, and

(iii) analyzing the upper and lower envelope values to extract the signal component from the measured signal, wherein the analyzing step includes the step of determining a median of the difference between the upper and lower envelope values as an AC component.

6. A method for determining first and second parameters of a signal, the signal having first and second signal components, comprising:

(i) determining upper envelope of the signal;

(ii) determining a lower envelope of the signal,

(iii) analyzing the upper and lower envelopes to extract the first signal component of the signal, wherein the analyzing step includes the step of determining a median of the difference between the upper and lower envelopes as an AC component;

(iv) determining the first parameter of the signal as a function of the first signal component;

(v) defining a kernel function as a derivative of a Gaussian with parameters matching characteristics of the second signal component;

(vi) applying a spectral filter to the signal, the spectral filter using the kernel function and responsively enhancing the second signal component; and

,

(vii) determining a second parameter of the signal as a function of the enhanced second signal component.

7. An apparatus, comprising:

a detector for receiving a measured signal; and

, a controller coupled to the detector and adapted to receive the measured signal, determine upper and lower envelopes of the measured signal, analyze the upper and lower envelopes to extract a signal component of the signal by determining a median of the difference between the upper and lower envelopes as an AC component and to determine a parameter of the signal as a function of the signal component.

8. An apparatus, as set for in claim 7, wherein the signal component is substantially periodic.

9. An apparatus, as set forth in claim 7, wherein the signal component has a substantially defined peak-to-peak intensity value.

10. An apparatus, as set forth in claim 7, including an emitter to apply an external field to a sample, wherein the signal is a response of the sample to the external field.

11. An apparatus, as set forth in claim 10, wherein the parameter of the signal corresponds to a physiological parameter of the sample.

12. An apparatus, as set forth in claim 11, wherein the physiological parameter is pulsatile blood-related.

13. An apparatus, as set forth in claim 11, wherein the physiological parameter is oxyhemoglobin saturation.

14. An apparatus, as set forth in claim 7, wherein the controller is adapted to extract the signal component of the signal by determining a median of the difference between upper and lower envelope values.

15. An apparatus, as set forth in claim 14, wherein the median is an alternating value in the signal component.

16. An apparatus, as set forth in claim 14, wherein the median is a constant value in the signal component.