# US 2021/0330236 A1 · Efficient fetal-maternal ecg signal separation from two maternal abdominal leads via diffusion-based channel selection

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 2021/0330236 A1
- Document ID: US20210330236A1
- Status: Published application
- Kind: A1
- Application number: 16/490,320
- Filed: 2018-03-01
- Published: 2021-10-28
- Earliest claimed: 2017-03-01
- Assignees: University of Washington; The Governing Council of the University of Toronto
- Applicants: University of Washington; The Governing Council of the University of Toronto
- Inventors: Martin G. Frasch; Hau-tieng Wu
- Web page: https://patentgrep.com/patent/US20210330236A1

## CPC

- A61B 5/344: Foetal cardiography
- A61B 5/7278: {Artificial waveform generation or derivation, e.g. synthesizing signals from measured signals}
- A61B 5/271: Arrangements of electrodes with cords, cables or leads, e.g. single leads or patient cord assemblies
- A61B 5/327: Generation of artificial ECG signals based on measured signals, e.g. to compensate for missing leads
- A61B 5/339: Displays specially adapted therefor
- A61B 5/352: Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
- A61B 5/7257: {using Fourier transforms}
- A61B 2560/02: Operational features
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)

## Abstract

In some embodiments, techniques capable of obtaining high-quality fetal ECG (fECG) information using as few as two composite (maternal and fetal) maternal abdominal ECG (aECG) signals to derive the fetal ECG information are provided. In some embodiments, maternal ECG information and fetal ECG information are both obtained from the aECG signals, and are either presented or stored. The techniques may use novel proposed diffusion-based channel selection criteria. To validate the proposed techniques, analysis results of two publicly available databases are described, and compared with other available techniques in the literature.

## Claims

### Claim 1

A system for non-invasive measurement of heartbeat characteristics, the system comprising:
a set of maternal abdominal leads, including a first maternal abdominal lead and a second maternal abdominal lead; and
an abdominal electrocardiogram (aECG) device communicatively coupled to the maternal abdominal leads, comprising at least one processor and a non-transitory computer-readable medium, wherein the non-transitory computer-readable medium has instructions stored thereon that, in response to execution by the at least one processor, cause the aECG device to measure heartbeat characteristics by:
creating a set of linear combinations using signals from the set of maternal abdominal leads;
determining a set of rough fECGs based on the set of linear combinations;
selecting a channel based on the set of rough fECGs; and
measuring the heartbeat characteristics using the selected channel.

### Claim 2 (depends on 1)

The system of claim 1, wherein the heartbeat characteristics are fetal R peaks or a fetal heart rate.

### Claim 3 (depends on 1)

The system of claim 1, wherein the instructions further cause the aECG device to preprocess the signals from the set of maternal abdominal leads by performing at least one of applying a low pass filter, applying one or more notch filters to suppress power line interference, and subtracting an estimated trend.

### Claim 4 (depends on 1)

The system of claim 1, wherein creating the set of linear combinations includes:
determining a set of θ values; and
for each θ value of the set of θ values, create a linear combination zθ as:
zθ=θx+√{square root over (1−θ2)}y
wherein x is a time series representing a signal of the first maternal abdominal lead, and y is a time series representing a signal of the second maternal abdominal lead.

### Claim 5 (depends on 1)

The system of claim 1, wherein the set of maternal abdominal leads further includes at least a third abdominal lead, and wherein creating the set of linear combinations includes:
determining a pair of leads from the set of maternal abdominal leads;
determining a set of θ values; and
for each θ value of the set of θ values, create a linear combination zθ as:
zθ=θx+√{square root over (1−θ2)}y
wherein x is a time series representing a signal of a first lead of the pair of leads, and y is a time series representing a signal of a second lead of the pair of leads.

### Claim 6 (depends on 5)

The system of claim 5, wherein creating the set of linear combinations further includes:
determining a new pair of leads from the set of maternal abdominal leads;
determining a set of θ values;
creating a linear combination for the new pair of leads for each θ value of the set of θ values; and
repeating the actions of determining a new pair of leads, determining a set of θ values, and creating a linear combination for the new pair of leads for each θ value of the set of θ values for each pairwise combination of leads in the set of maternal abdominal leads.

### Claim 7 (depends on 1)

The system of claim 1, wherein determining a set of rough fECGs includes, for each linear combination of the set of linear combinations:
estimating a maternal ECG based on the linear combination; and
subtracting the estimated maternal ECG from the linear combination.

### Claim 8 (depends on 7)

The system of claim 7, wherein estimating a maternal ECG based on the linear combination includes at least one of storing the maternal ECG in an ECG data store and presenting the maternal ECG on a display device.

### Claim 9 (depends on 7)

The system of claim 7, wherein estimating a maternal ECG based on the linear combination includes:
applying a de-shape short time Fourier transform (dsSTFT) to the linear combination and extracting the dominant curve to obtain an estimated maternal instantaneous heart rate (IHR);
determining a polarity of the linear combination and multiplying the linear combination by −1 if the determined polarity is negative to create a polarity-corrected linear combination;
computing locations of maternal R-peaks using the estimated maternal IHR and the polarity-corrected linear combination;
adjusting the computed locations of the maternal R-peaks by searching for a maximum in the polarity-corrected linear combination around each computed location; and
applying the nonlocal median to estimate the maternal ECG in the linear combination based on the adjusted maternal R-peak locations.

### Claim 10 (depends on 1)

The system of any of claims 1 9 claim 1, wherein selecting a channel includes:
determining a signal quality index (SQI) for each rough fECG of the set of rough fECGs; and
selecting a channel associated with a rough fECG having a highest SQI.

### Claim 11 (depends on 10)

The system of claim 10, wherein the SQI is determined by:
applying an L-step lag map to the rough fECG to create an embedded point cloud χθ,f;
applying a 1-normalization diffusion map to χθ,f; and
determining the SQI Sθas:
S
θ
=
⁢

ϕ
^
θ
,
1
⁡
(
ξ
)

2
⁢
d
⁢
⁢
ξ
⁢

ϕ
^
θ
,
1
⁡
(
ξ
)

2
⁢
d
⁢
⁢
ξ
wherein ϕθ1 is a first nontrivial eigenvector of a corresponding graph Laplacian;
wherein |{circumflex over (ϕ)}θ,1|2 is a power spectrum of ϕθ,1;
wherein ξθ,1, ξθ,2, . . . , ξθ,ncs>0, wherein ncs ∈ is a number of peaks chosen by a user to be frequencies associated with highest ncs peaks in |{circumflex over (ϕ)}θ,1|2;
wherein Lcs>0; and
wherein θ:=Uj=1ncs [ξθ,1−Lcs, ξθ,i+Lcs].

### Claim at position 12

12-27. (canceled)

### Claim 28

A non-transitory computer-readable medium, wherein the non-transitory computer-readable medium has computer-executable instructions stored thereon that, in response to execution by at least one processor of an abdominal electrocardiogram (aECG) device, cause the aECG device to measure heartbeat characteristics by:
creating a set of linear combinations using signals from a first maternal abdominal lead and a second maternal abdominal lead;
determining a set of rough fECGs based on the set of linear combinations;
selecting a channel based on the set of rough fECGs; and
measuring the heartbeat characteristics using the selected channel.

### Claim 29 (depends on 28)

The computer-readable medium of claim 28, wherein the heartbeat characteristics are fetal R peaks or a fetal heart rate.

### Claim 30 (depends on 28)

The computer-readable medium of claim 28, wherein the instructions further cause the aECG device to preprocess the signals from the abdominal leads by performing at least one of applying a low pass filter, applying one or more notch filters to suppress power line interference, and subtracting an estimated trend.

### Claim 31 (depends on 28)

The computer-readable medium of claim 28, wherein creating the set of linear combinations includes:
determining a set of θ values; and
for each θ value of the set of θ values, create a linear combination zθ as:
zθ=θx+√{square root over (1−θ2)}y
wherein x is a time series representing a signal of the first abdominal lead, and y is a time series representing a signal of the second abdominal lead.

### Claim 32 (depends on 31)

The computer-readable medium of claim 31, wherein creating the set of linear combinations includes:
receiving a third signal from a third maternal abdominal lead; and
for each θ value of the set of θ values, create a linear combination zθ as:
zθ=θx+√{square root over (1−θ2)}y′
wherein x is a time series representing a signal of the first abdominal lead, and y′ is a time series representing a signal of the second abdominal lead.

### Claim 33 (depends on 28)

The computer-readable medium of claim 28, wherein determining a set of rough fECGs includes, for each linear combination of the set of linear combinations:
estimating a maternal ECG based on the linear combination; and
subtracting the estimated maternal ECG from the linear combination; and
wherein the actions further comprise at least one of storing the maternal ECG in an ECG data store and presenting the maternal ECG on a display device.

### Claim 34

(canceled)

### Claim 35 (depends on 33)

The computer-readable medium of claim 33, wherein estimating a maternal ECG based on the linear combination includes:
applying a de-shape short time Fourier transform (dsSTFT) to the linear combination and extracting the dominant curve to obtain an estimated maternal instantaneous heart rate (IHR);
determining a polarity of the linear combination and multiplying the linear combination by −1 if the determined polarity is negative to create a polarity-corrected linear combination;
computing locations of maternal R-peaks using the estimated maternal IHR and the polarity-corrected linear combination;
adjusting the computed locations of the maternal R-peaks by searching for a maximum in the polarity-corrected linear combination around each computed location; and
applying the nonlocal median to estimate the maternal ECG in the linear combination based on the adjusted maternal R-peak locations.

### Claim 36 (depends on 28)

The computer-readable medium of claim 28, wherein selecting a channel includes:
determining a signal quality index (SQI) for each rough fECG of the set of rough fECGs; and
selecting a channel associated with a rough fECG having a highest SQI.

### Claim 37 (depends on 36)

The computer-readable medium of claim 36, wherein the SQI is determined by:
applying an L-step lag map to the rough fECG to create an embedded point cloud χθ,f;
applying a 1-normalization diffusion map to χθ,f; and determining the SQI Sθ as:
S
θ
=
⁢

ϕ
^
θ
,
1
⁡
(
ξ
)

2
⁢
d
⁢
⁢
ξ
⁢

ϕ
^
θ
,
1
⁡
(
ξ
)

2
⁢
d
⁢
⁢
ξ
wherein υθ,1 is a first nontrivial eigenvector of a corresponding graph Laplacian;
wherein |{circumflex over (ϕ)}θ,1|2 is a power spectrum of ϕθ,1;
wherein ξθ,1, ξθ,2, . . . , ξθ,ncs>0, wherein ncs ∈ is a number of peaks chosen by a user to be frequencies associated with highest ncs peaks in |{circumflex over (ϕ)}θ,1|2;
wherein Lcs>0; and
wherein θ:=Uj−1ncs, [ξθ,i−Lcs, ξcs,ξθ,i+Lcs].

### Claim at position 23

38-40. (canceled)