Method for detecting artifacts in data

• US 7,254,425 B2
• Filed: 01/23/2004
• Issued: 08/07/2007
• Est. Priority Date: 01/23/2004
• Status: Active Grant

• Current Assignee: Abbott Diabetes Care Incorporated (Abbott Laboratories Incorporated)
• Original Assignee: Abbott Laboratories Incorporated
• Inventors: Khalil, Omar S., Lowery, Michael G., Shain, Eric B.
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US10/763,548
• Publication Number:
  US 20050165316A1
• Time in Patent Office: 1,292 Days
• Field of Search: 600/336, 600/310, 600/322, 600/330, 600/316
• US Class Current: 600/310
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/14535 for measuring haematocrit
• CPC Class Codes: A61B 5/1455 using optical sensors, e.g. spectral photometrical oximeters
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: G01N 21/49 within a body or fluid

Abstract

A method for identifying artifacts occurring during a measurement of the concentration of an analyte in a biological sample by means of an apparatus that employs temperature-controlled optical probes, introduces electromagnetic radiation into tissue, and collects and detects radiation emitted at a distance from the point at which the electromagnetic radiation is introduced. The values of intensity of radiation emitted at different wavelengths, at different distances between the light introduction site(s) and the light collection site(s), and at different temperatures are collected and used in the method to generate a relationship between these values and the concentration of an analyte in the tissue or the disease state of a patient. The method involves the use of an algorithm that identifies artifacts in the data resulting from motion of the patient and allows the rejection of data sets that contain these artifacts. The algorithm identifies sudden changes in the magnitude and direction in a sequence of collected signals.

Claims

1. A method for identifying artifacts in optical measurements conducted for the purpose of determination of concentration of an analyte in a tissue, or value of a physiological parameter, or a combination of the forgoing, the method comprising the steps of:

(a) providing an apparatus for measuring at least one optical property of the tissue;

(b) introducing electromagnetic radiation at at least one wavelength into the tissue by means of the apparatus;

(c) collecting optical data from the tissue over a selected period of time;

(d) introducing the collected data into an algorithm to identify an artifact in the optical data, the artifact resulting from movement of the probe or the tissue during a brief period of time; and

(e) determining whether an artifact has appeared in the optical data,

wherein the algorithm utilizes equations for calculating a set of values from the optical data, which optical data comprise a plurality of data points, the equations comprising;

S(i)=[1−

P]·

S(i−

1)+P·

[X(i)−

X(i−

1)] 

 

(1)

A(i)=[1−

P]·

[A(i−

1)+S(i)]+P·

X(i) 

 

(2)

D(i)=|X(i)−

A(i)| 

 

(3)

Where;

N=effective quantity of data points in the moving average for the algorithm (N=value greater than 1, as specified by user)

Dc=artifact threshold value for D(i) (Dc=value greater than 0, as specified by user)

P=algorithm constant (P=2/[N+1])

i=current data point number (i is greater than

     1)

X(i)=value of the current data point

X(i−

1)=value of the previous data point

X(1)=value of the first data point

S(i)=value of slope parameter at the current data point

S(i−

1)=value of slope parameter at the previous data point

S(1)=value of slope parameter at the first data point (S(1)=0)

A(i) =value of moving average at the current data point

A(i−

1)=value of moving average at the previous data point A(1)=value of moving average at the first data point (A(1)=X(1))

D(i)=absolute difference between X(i) and A(i) at the current data point.

2. The method of claim 1, further including the step of (f) providing a signal to an operator to indicate the occurrence of an artifact or to identify optical data that are suspect.

3. The method of claim 1, wherein the optical data comprises reflectance measurements derived from introduction of light at at least one light introduction site by means of at least one light introducing element and collection of light at at least one light collection site by means of at least one light collecting element, the at least one light introducing element and the at least one light collecting element being in contact with the tissue.

4. The method of claim 1, wherein the optical data are collected in a sequential manner to determine a change in blood pressure.

5. The method of claim 1, wherein the optical data are collected in a sequential manner to determine a change in at least one value selected from the group consisting of blood oxygen saturation, the concentration of hemoglobin, value of hematocrit, and the concentration of glucose.

6. The method of claim 1, wherein the electromagnetic radiation has a wavelength in the range of from about 400 nm to about 2200 nm.

7. The method of claim 1, wherein the electromagnetic radiation has a wavelength in the range of from about 400 nm to about 1100 nm.

8. The method of claim 1, wherein the optical data is collected sequentially.

9. The method of claim 1, wherein the algorithm employs a user-selected threshold and the slope parameter to detect motion artifacts in optical signals that do not depend on the periodicity of heartbeats.

10. The method of claim 1, wherein the algorithm is applied to the optical data in real-time.

11. The method of claim 1, further comprising the step of alerting the operator of an occurrence of an artifact.

12. The method of claim 1, further comprising the step of alerting the operator to exclude data that contains an artifact from subsequent calculation.