Body-driven pseudorandom signal injection for biomedical acquisition channel calibration

• US 9,968,301 B2
• Filed: 07/09/2014
• Issued: 05/15/2018
• Est. Priority Date: 07/09/2014
• Status: Active Grant

• Current Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Original Assignee: Board of Regents of the University of Texas System (University of Texas System)
• Inventors: Chiu, Yun, Song, Jingyi
• Primary Examiner(s): ABOUELELA, MAY A
• Application Number:
  US14/327,283
• Publication Number:
  US 20160007928A1
• Time in Patent Office: 1,406 Days
• Field of Search: 600547, 600383, 600508
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/0002 Remote monitoring of patients using telemetry, e.g. transmission of vital signals via a communication network A61B5/07 takes precedence; transmission systems for measured values G08C; transmission H04B; transmission of digital information H04L; wireless communication networks H04W
• CPC Class Codes: A61B 5/259 using conductive adhesive means, e.g. gels
• CPC Class Codes: A61B 5/282 Holders for multiple electrodes for introduction into the body A61B5/287
• CPC Class Codes: A61B 5/291 for electroencephalography [EEG]
• CPC Class Codes: A61B 5/316 Modalities, i.e. specific diagnostic methods
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/369 Electroencephalography [EEG] devices for psychotechnics A61B5/16
• CPC Class Codes: A61B 5/6833 Adhesive patches
• 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
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7246 using correlation, e.g. template matching or determination of similarity
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence

Abstract

Disclosed are systems and methods for monitoring biopotential signals in biomedical devices. The disclosure provides a mixed signal background calibration that stabilizes the time-varying coupling gain between the body and an electrode due to motion artifacts. The calibration technique involves a low-level test signal in the form of a one-bit pseudorandom bit-sequence that is injected through a reference electrode to the body, detected by the sensing electrode and recorded along with the bio signals. A digital algorithm is employed in the backend to identify the acquisition channel characteristics while maintaining its normal operation of recording. Programmable gain stages in analog or digital domain(s) can be used to stabilize the overall gain of the channel. The disclosed technique is in the background and not interfering with the normal recording operation(s), and provides continuous monitoring of the ETI and continuous correction of the ensuing channel characteristic degradation due to the ETI variation.

Claims

1. A method comprising:

measuring biopotential signals produced by a patient'"'"'s body, wherein the measuring is at a sensing electrode configured to be coupled to the patient'"'"'s body, wherein the measuring comprises;

driving, via a monitoring circuitry, a pseudorandom noise (PN) signal, said PN signal being driven to the patient'"'"'s body at a reference electrode configured to be coupled to the patient'"'"'s body;

receiving at the sensing electrode a biopotential signal and a distorted PN signal;

synchronizing, via the monitoring circuitry, the PN signal driven to the patient'"'"'s body and the distorted PN signal received at the sensing electrode;

determining, via the monitoring circuit, a signal-path gain A(t) based on the PN signal driven to the reference electrode and the distorted signal received by the sensing electrode;

detecting, via the monitoring circuitry, a multiplicative motion artifact (MMA) using the signal-path gain A(t); and

adjusting and employing, via the monitoring circuitry, a digital or analog programmable gain compensator to stabilize the signal-path gain A(t).

2. The method of claim 1, wherein said PN signal is an injected test signal g(t).

3. The method of claim 2, wherein the monitoring circuitry applies a voltage transfer function, said voltage transfer function comprising:

V_out(t)=A(t)·

[V_in(t)+g(t)+V_hc(t)]+noise,

wherein;

Vin(t) is the biopotential signal for a biomedical recording device associated with the patient'"'"'s body,

Vout(t) is an output of a recording front end of an analog front end (AFE), wherein said output is a distorted version of a summation of Vin(t) and g(t),

Vhc(t) is a time-varying half-cell potential introduced at an interface between skin of the patient'"'"'s body and the sensing electrode, and

noise is electrical signals received by the patient'"'"'s body and sensed by the sensing electrode.

4. The method of claim 3, wherein the signal-path gain A(t) is experienced between Vin(t) and g(t), wherein A(t) comprises:

5. The method of claim 4, wherein said digital or analog programmable gain compensator comprises a gain set to A(t)⁻

1.

6. The method of claim 3, further comprising:

Producing, via the monitoring circuitry, a post-calibration output V′

out(t) which is a linear function of Vin(t).

7. The method of claim 6, wherein said PN signal comprises a white spectrum.

8. The method of claim 7, further comprising:

removing, via the monitoring circuitry, the distorted PN signal of the post-calibration output V′

out(t) via an adaptive noise cancellation loop.

9. The method of claim 1, further comprising:

determining, via the monitoring circuitry, an additive motion artifact (AMA) based on a time-varying half-cell potential; and

identifying, via the monitoring circuitry, a baseline wander based on said AMA.

10. The method of claim 9, further comprising:

applying, via the monitoring circuitry, a moving average filter to said baseline wander; and

applying, via the monitoring circuitry, the moving average filter to said AMA.

11. The method of claim 10, wherein said moving average filter comprises sample-by-sample average functions as a high-pass filter (HPF) with a low cut-off frequency.

12. The method of claim 11, wherein said application of the moving average filter occurs after said employment of said digital or analog programmable gain compensator.

13. The method of claim 1, wherein said stabilization of A(t) occurs in the background without interference with recording said biopotential signals.