Artifact removal from physiological signals

• US 5,603,321 A
• Filed: 08/07/1995
• Issued: 02/18/1997
• Est. Priority Date: 08/07/1995
• Status: Expired due to Fees

• Current Assignee: Biomagnetic Technologies, Inc.
• Original Assignee: Biomagnetic Technologies, Inc.
• Inventors: Wilson, Steven, Kynor, David B., Haupt, Christopher
• Primary Examiner(s): Smith, Ruth S.
• Application Number:
  US08/511,992
• Time in Patent Office: 561 Days
• Field of Search: 128/630, 128/653.1, 128/696, 128/704, 128/708, 128/901, 324/244, 324/248, 324/260
• US Class Current: 600/409
• CPC Class Codes: A61B 5/243 specially adapted for magnetocardiographic [MCG] signals
• CPC Class Codes: A61B 5/349 Detecting specific parameters of the electrocardiograph cycle
• CPC Class Codes: Y10S 128/901 Suppression of noise in electric signal

Abstract

A measured magnetocardiography signal has a relatively small heart signal mixed with a large noise signal. To produce a heart signal having a reduced noise content, the times of occurrence of a time-series of isoelectric intervals of the measured signal is first determined and a time-series isoelectric artifact curve is formed from the measurements made at those times of occurrence. A time-series non-isoelectric artifact curve for other times is determined from this information. The time-series isoelectric and nonisoelectric artifact curve is subtracted from the measured magnetocardiography time-series signal to yield a time-series heart amplitude signal having reduced noise and undistorted form.

Claims

1. Apparatus for measuring a time-series signal generated by the heart and producing a time-series heart signal having a reduced noise content, the apparatus comprising:

sensor means for measuring a time-series of measured heart output amplitude signals having a noise component mixed therewith; and

processing means for receiving the time-series of measured heart output amplitude signals and for producing a time-series heart amplitude signal having a reduced noise content, the processing means including

identification means for identifying the times of occurrence of a time-series of corresponding;

isoelectric intervals in the time-series of measured heart output amplitude signals,

artifact modelling means for forming a corresponding isoelectric time-series of artifact amplitudes at the times of occurrence of the corresponding isoelectric intervals and for forming a non-isoelectric series of artifact amplitudes from the isoelectric time-series of artifact amplitudes, the isoelectric and the non-isoelectric series together comprising the time-series of artifact amplitudes; and

subtraction means for subtracting the time-series of artifact amplitudes from the time-series of measured heart output amplitude signals to yield a time-series heart signal having reduced noise content.

2. The apparatus of claim 1, wherein the sensor means comprises

a biomagnetometer including

a magnetic field sensor having a sensor output, and

a room temperature electronics unit which receives the sensor output, the room temperature electronics unit including a filter and an amplifier.

3. The apparatus of claim 1, wherein the processing means comprises a programmable computer.

4. The apparatus of claim 1, wherein the identification means comprises a programmable computer configured to identify an R-peak of the measured heart output signal and to determine the isoelectric interval relative to the R-peak.

5. The apparatus of claim 1, wherein the identification means comprises

means for high-pass filtering the measured heart output amplitude signal to form a filtered heart output signal;

means for detecting portions of the filtered heart output signal having an amplitude greater than a preselected amplitude value as a time series of R-peaks; and

means for selecting an isoelectric interval at a preselected time fraction of the interval between succeeding R-peaks of the time series of R-peaks.

6. The apparatus of claim 1, wherein the artifact modelling means comprises a programmable computer configured to fit a polynomial function to a time-series.

7. The apparatus of claim 1, wherein the subtraction means comprises a programmable computer configured to subtract the corresponding time-series of artifact amplitudes from the time-series of measured heart output amplitude signals.

8. The apparatus of claim 1, wherein the sensor means comprises

a plurality of magnetic field sensor channels, each sensor channel having a sensor channel output, and wherein the processing means comprises

multichannel processing means for receiving each sensor channel output and producing a corrected heart signal having a reduced noise content for each sensor channel output, on a channel-by-channel basis.

9. Apparatus for measuring a time-series signal generated by a living subject and producing a time-series physiological signal having a reduced noise content, the apparatus comprising:

a biomagnetometer including

a magnetic field sensor having a sensor output, and

an electronics unit which receives the sensor output and produces a measured physiological output signal, the electronics unit including a filter and an amplifier; and

a computer configured to first

identify the times of occurrence of a time-series of corresponding isoelectric intervals in the time-series of measured physiological output amplitude signals, second

form a time-series of corresponding isoelectric artifact amplitudes at the times of occurrence of the isoelectric intervals, third

form a lime-series of non-isoelectric artifact amplitudes from the isoelectric time-series of artifact amplitudes, and fourth

subtract the time-series of isoelectric and non-isoelectric artifact amplitudes from the time-series of measured physiological output amplitude signals to yield a time-series physiological signal having reduced noise content.

10. A method for obtaining a time-series heart signal, comprising the steps of

measuring a time-series of measured heart output amplitude signals having a noise component mixed therewith;

and

receiving the time-series of measured heart output amplitude signals and producing a time-series heart amplitude signal having a reduced noise content, the step of receiving including the steps of

identify the times of occurrence of a time-series of corresponding isoelectric intervals in the time-series of measured heart output amplitude signals,

forming a corresponding time-series of isoelectric artifact amplitudes at the times of occurrence of the corresponding isoelectric intervals and a time-series of non-isoelectric artifact amplitudes at other times, and

subtracting the corresponding time-series of isoelectric and non-isoelectric artifact amplitudes from the time-series of measured heart output amplitude signals to yield a time-series heart signal having reduced noise content.

11. The method of claim 10, wherein the step of measuring includes the step of

providing a biomagnetometer including

a magnetic field sensor having a sensor output, and

an electronics unit which receives the sensor output, the electronics unit including a filter and an amplifier.

12. The method of claim 10, wherein the step of receiving includes the step of

providing a programmable computer.