COMPENSATION OF MOTION ARTIFACTS IN CAPACITIVE MEASUREMENT OF ELECTROPHYSIOLOGICAL SIGNALS

• US 20110137200A1
• Filed: 08/24/2009
• Published: 06/09/2011
• Est. Priority Date: 08/29/2008
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Meftah, Mohammed, Ikkink, Teunis Jan, Yin, Bin
• Granted Patent: US 8,515,532 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/282 Holders for multiple electrodes for introduction into the body A61B5/287
• CPC Class Codes: A61B 5/302 for capacitive or ionised electrodes, e.g. metal-oxide-semiconductor field-effect transistors [MOSFET]
• CPC Class Codes: A61B 5/7214 using signal cancellation, e.g. based on input of two identical physiological sensors spaced apart, or based on two signals derived from the same sensor, for different optical wavelengths

Abstract

The invention relates to a system and a method in which an electrophysiological signal is sensed capacitively with at least two closely spaced electrodes such that the electrodes experience strongly correlated skin-electrode distance variations. To be able to derive a motion artifact signal, the capacitive coupling between the electrodes and skin is made intentionally different. With a signal processing means the motion artifact signal can be removed from the measured signal to leave only the desired electrophysiological signal. Since the measured quantity is dependant on the electrode-skin distance itself, the system and method do not need to rely on the constancy of a transfer function. Hereby, they give reliable motion artifact free output signals.

Claims

1. A system (10) for providing motion compensated capacitive measurement of electrophysiological signals, the system comprising:

a sensor probe (30;

30a;

30b;

30c) comprising a first (P1;

P1′

;

P1″

) and a second capacitive plate (P2;

P2′

;

P2″

) arranged to be placed in the proximity of the skin of a human or animal body, wherein the first capacitance (C_e1) between the first capacitive plate and the skin of the human or animal body is different from the second capacitance (C_e2) between the second capacitive plate and the skin of the human or animal body, and wherein the first and second capacitive plates are arranged for providing a first and second measurement signal (V₀₁, V₀₂) as a measure of an electrophysiological signal of the human or animal body,

processor means (50) arranged for;

receiving said first and second measurement signals (V₀₁, V₀₂) from the first and second capacitive plates (P1;

P1′

;

P1″

;

P2;

P2′

;

P2″

);

determining a motion modulated signal (V_m) from the first and/or second measurement signals (V₀₁, V₀₂);

providing a motion compensated output signal ({tilde over (V)}_o1⁽ⁿ⁾) from the motion modulated signal (V_m) and the first and/or second measurement signals (V₀₁, V₀₂).

2. A system according to claim 1, wherein the first and second capacitive plates (P1;

P1′

;

P1″

;

P2;

P2′

;

P2″

) of the sensor probe (30;

30a;

30b;

30c) have different distances to a measurement surface of the sensor probe and/or the first and second capacitive plates (P1;

P1′

;

P1″

;

P2;

P2′

;

P2″

) have mutually different areas.

3. A system according to claim 1, wherein the sensor probe (30;

30a;

30b;

30c) moreover comprises an active shield (3a, 3b, 3c;

3a′

, 3b′

, 3c′

;

3a″

, 3b″

, 3c″

).

4. A system according to claim 1, wherein the determination of the motion modulated signal (V_m) comprises calculating the difference of the first measurement signal and a factor applied to the second measurement signal.

5. A system according to claim 1, wherein the determination of the motion modulated signal (V_m) comprises averaging or low pass filtering of the first and second measurement signals (V₀₁, V₀₂) over a predetermined time interval.

6. A system according to claim 1, wherein the provision of the motion compensated output signal ({tilde over (V)}_o1⁽ⁿ⁾) comprises using a least-mean-square algorithm to adaptively remove the effect of the motion modulated signal from the first and/or second measurement signals (V₀₁, V₀₂).

10. A computer program product being adapted to enable a computer system comprising at least one computer having data storage means associated therewith to control a signal processing unit according to claim 6.

7. A signal processing unit (50) for compensating for motion, said signal processing unit comprising means (In1, In2) for receiving first and second measurement signals (V₀₁, V₀₂) from a sensor probe comprising a first and a second capacitive plate arranged to be placed in the proximity of the skin of a human or animal body, wherein the first capacitance (C_e1) between the first capacitive plate and the skin of the human or animal body is different from the second capacitance (C_e2) between the second capacitive plate and the skin of the human or animal body, wherein the first and second measurement signals (V₀₁, V₀₂) are measures of an electrophysiological signal of the human or animal body, said signal processing unit being arranged for:

determining a motion modulated signal (V_m) from the first and/or second measurement signals (V₀₁, V₀₂); and

providing a motion compensated output signal ({tilde over (V)}_o1⁽ⁿ⁾) from the motion modulated signal (V_m) and the first and/or second measurement signals (V₀₁, V₀₂).

8. A method for providing motion compensated capacitive measurement of electrophysiological signals, the method comprising:

placing a sensor probe in the proximity of the skin of a human or animal body, wherein said sensor probe comprises a first and a second capacitive plate, wherein the first capacitance (C_e1) between the first capacitive plate and the skin of the human or animal body is different from the second capacitance (C_e2) between the second capacitive plate and the skin of the human or animal body;

providing a first and second measurement signals (V₀₁, V₀₂) as a measure of an electrophysiological signal from the first and second capacitive plates;

determining a motion modulated signal (Vm) from the first and/or second measurement signals (V₀₁, V₀₂); and

providing a motion compensated output signal ({tilde over (V)}_o1⁽ⁿ⁾) from the motion modulated signal (V_m) and the first and/or second measurement signals (V₀₁, V₀₂).

9. A sensor probe (30;

30a;

30b;

30c) for providing motion compensated capacitive measurement of electrophysiological signals, the probe comprising a first (P1;

P1′

;

P1″

) and a second capacitive plate (P2;

P2′

;

P2″

) arranged to be placed in the proximity of the skin of a human or animal body, wherein the first capacitance (C_e1) between the first capacitive plate and the skin of the human or animal body is different from the second capacitance (C_e2) between the second capacitive plate and the skin of the human or animal body, and wherein the first and second capacitive plates are arranged for providing a first and second measurement signal (V₀₁, V₀₂) as a measure of an electrophysiological signal of the human or animal body.