Electrical impedance tomography device and process

• US 9,730,607 B2
• Filed: 06/12/2012
• Issued: 08/15/2017
• Est. Priority Date: 07/02/2011
• Status: Active Grant

• Current Assignee: Dragerwerk AG & Company KGaA (FPS Vermögensverwaltung GmbH)
• Original Assignee: Dragerwerk AG & Company KGaA (FPS Vermögensverwaltung GmbH)
• Inventors: Grber, Yvo
• Primary Examiner(s): LAURITZEN, AMANDA L
• Application Number:
  US13/494,585
• Publication Number:
  US 20130002264A1
• Time in Patent Office: 1,890 Days
• CPC Class Codes: A61B 5/0536 Impedance imaging, e.g. by tomography
• CPC Class Codes: A61B 5/08 Detecting, measuring or recording devices for evaluating the respiratory organs A61B5/0205 takes precedence
• CPC Class Codes: G06T 7/0012 Biomedical image inspection
• CPC Class Codes: G06T 7/0016 involving temporal comparison
• CPC Class Codes: G06T 7/30 Determination of transform parameters for the alignment of images, i.e. image registration

Abstract

An EIT device has a plurality of electrodes (4) that can be arranged on a body in order to reconstruct the impedance distribution of the body with a reconstruction algorithm. The control unit (10) of the EIT device is set up by suitable programming to continuously determine at least one property (e1, . . . , eM) each from the measured signals (U1, . . . , UM) of all measuring channels and to correct measured signals of the measuring channels on the basis of the properties or to adapt the reconstruction algorithm on the basis of the properties.

Claims

1. An electrical impedance tomography (EIT) device comprising:

a plurality of electrodes, which can be placed on a body;

control and measuring circuits to feed alternating current or alternating voltage to said electrodes and to receive voltage or current signals received from said electrodes as measured signals;

a control unit connected to said control and measuring circuits and configured to control a supply of alternating current or with an alternating voltage to an electrode pair as a feeding electrode pair and configured to receive measured voltage signal or measured current signal of each electrode pair from all other electrode pairs as measured signals, and to successively change said feeding electrode pair through said plurality of electrodes and to receive and to process the measured signals (U₁, . . . , U_M) of a plurality of (M) individual measuring channels (K₁, . . . , K_M) and to reconstruct therefrom an impedance distribution of the body with a reconstruction algorithm, said control unit further configured to continuously determine at least one property (e^α

₁, . . . , e^α

_M) of a set (α

) of properties to determine channel-specific quality parameters (q₁, . . . , q_M) by a comparison of said at least one property of each channel with predetermined desired values, the properties comprising signal-to-noise ratio of the measured signals, freak value of the measured signals, mean value of the measured signals, phase or real and imaginary part of the measured signals, crosstalk of the measured signals, common mode of the measured signals reciprocity of the measured signals, measured signal drifts, current feed fluctuations, and value and phase of the electrode-skin contact impedances, each from said measured signals (U₁, . . . , U_M) of all measuring channels and configured to correct measured signals of said measuring channels based on said at least one property by adapting the reconstruction algorithm based on the at least one property by including the channel-specific quality parameters (q₁, . . . , q_M) among channel-specific properties in the reconstruction algorithm in a matrix that comprises a weighting matrix W(q₁, . . . , q_M) that comprises the channel-specific quality parameters (q₁, . . . , q_M), wherein

said control unit furthermore determines at least another property so as to determine N properties e_m^α

(U_M)(α

=1, . . . , N) of the set (α

) of properties in all measuring channels for each measured signal (U₁, . . . U_M) and compares the N properties with desired values or with desired ranges e_sollm^α

determined in advance or with both the desired values and with the desired ranges determined in advance, to provide results of a comparison, and corrects the measured signals of the measuring channels based on the results of the comparison based on the properties or adapts the reconstruction algorithm based on the properties;

said control unit determines channel-specific quality parameters and property-specific quality parameters q_m^α

(e_m^α

, e_sollm^α

) from the comparison of the determined properties e_m^α

of each channel m=1, . . . , M with desired values or desired value ranges e_sollm^α

determined in advance, wherein the channel-specific quality parameters are included in the reconstruction algorithm in such a manner that measuring channels with channel-specific quality parameters that are indicative of signals of a lower quality relative to other signals are weighted less strongly than measuring channels with quality parameters that are indicative of signals with a higher quality relative to other signals; and

said control unit forms each of the channel-specific quality parameters from the property-specific quality parameters q_m^α

(e_m^α

, e_sollm^α

), to provide the channel-specific quality parameters q_m(q₁¹, . . . , q_m^α

, . . . , q_M^N), by arithmetic or geometric averaging of the property-specific quality parameters q_m^α

(e_m^α

, e_sollm^α

) for each measuring channel, wherein the channel-specific quality parameters are standardized for an interval, wherein the lowest quality is assigned to the value 0 and the highest quality is assigned to the value 1, and wherein the measuring channels are weighted according to this standardized quality parameter in the reconstruction algorithm.

2. An electrical impedance tomography (EIT) device in accordance with claim 1, wherein said control unit continuously updates determination of the properties e_m^α

or the property-specific quality parameters derived therefrom or the combined channel-specific quality parameters or any combination of the properties, the property-specific quality parameters derived therefrom and the channel-specific quality parameters, wherein the determination is performed over a time window.

3. An electrical impedance tomography device according to claim 1, wherein adapting the reconstruction algorithm comprises forming an adaptation of the reconstruction matrix A with the integrated weighting matrix W(q1, . . . , qM) that comprises the channel-specific quality parameters (q1, . . . , qM), wherein:

a sensitivity matrix-based Newton-Raphson method is used to reconstruct a vector Δ

pⁿ of the relative impedance change from the relative voltage change Δ

uⁿ, with Δ

pⁿ (t)=AΔ

uⁿ (t);

the adaptation of the reconstruction matrix A is in the form;

A=R(S^TWS+λ

L^TL)<sup>−

1</sup>S^TW, and the sensitivity matrix S is determined from a finite element model (FEM) using the linearized Geselowits relation, the matrix L designates a regularization matrix, the scalar variable λ

designates a regularization parameter, and matrix R represents a filtered registration matrix from the FEM system to the pixel system of the EIT image.

4. An electrical impedance tomography (EIT) device in accordance with claim 1, wherein said control unit continuously determines a plurality of global properties E^β

, β

=1 . . . G from the measured signals of the measuring channels, or from properties thereof or from technical operating variables of the electrical impedance tomography device or from any combination of the measured signals of the measuring channels, from properties thereof and from technical operating variables of the electrical impedance tomography device, wherein the global properties are at least one of the properties selected from the group of properties that include maxima, minima or mean values or combinations of the properties e_m^α

and of the channel-specific quality parameters q_m^α

and operating current intensities, gain factors, dynamic range of the measured signals, operating frequencies, and the standard of differential EIT images with and without adaptation of the reconstruction algorithm, wherein the control unit furthermore compares the global properties E^β

with expected desired values or desired value ranges E_soll^β

, or with both expected desired values and desired value ranges, to provide results of a comparison and determines global quality parameters Q^β

(E^β

) based on of the results of the comparison.

5. An electrical impedance tomography (EIT) device in accordance with claim 4, wherein said control unit combines the global quality parameters Q^β

(E^β

) into a global quality index Q(Q¹, . . . , Q^G), by arithmetic or geometric averaging of the global quality parameters, wherein the control unit standardizes the global quality index to an interval and uses the global quality index for the quality classification of the EIT measurements.

6. An electrical impedance tomography (EIT) device in accordance with claim 5, wherein said control unit displays the global quality index graphically or alphanumerically on a display.

7. An electrical impedance tomography (EIT) device in accordance with claim 5, wherein said control unit marks time intervals separately in which the quality index is below a preset minimum criterion for derived variables, which variables are derived from the measured impedance distribution, and which have a development course over time shown on a display, and replaces values for the time analysis of the values with values derived from adjacent intervals, by interpolation or averaging, or with preset values to provide replaced time intervals, wherein the replaced time intervals are marked separately.

8. A process for analyzing measured signals of an electrical impedance tomography (EIT) device, the process comprising:

providing a plurality of electrodes, which can be applied to a body, control and measuring circuits to feed alternating current or alternating voltage to the electrodes and to receive voltage or current signals received from the electrodes;

connecting a control unit to the control and measuring circuits;

supplying one electrode pair, as a feeding electrode pair, with an alternating current or with an alternating voltage with the control unit;

receiving the measured voltage signal or measured current signal as a measured signal of each electrode pair from all other electrode pairs as measured signals;

changing the feeding electrode pair successively to pass through the plurality of electrodes and receive measured signals (U₁, . . . , U_M) in a number of M measuring channels (K₁, . . . , K_M);

processing the received measured signals (U₁, . . . , U_M) in the number of M measuring channels (K₁, . . . , K_M) including reconstructing therefrom an impedance distribution of the body in an electrode plane, of the plurality of electrodes, with a reconstruction algorithm with the control unit;

continuously determining, with the control unit, at least one property (e₁, . . . , e_M) of a set (α

) of properties comprising signal-to-noise ratio of the measured signals, freak value of of the measured signals mean value of the measured signals, phase or real and imaginary part of the measured signals, crosstalk of the measured signals common mode of the measured signals reciprocity of the measured signals, measured signal drifts, current feed fluctuations, and value and phase of the electrode-skin contact impedances, of all measured signals of all measuring channels;

determining, with the control unit, channel-specific quality parameters (q₁, . . . , q_M) by a comparison of said at least one property of each channel with predetermined desired values;

and

correcting measured signals of said measuring channels based on said at least one property by adapting the reconstruction algorithm based on the at least one property by including the channel-specific quality parameters (q₁, . . . , q_M) among channel-specific properties in the reconstruction algorithm in a matrix that comprises a weighting matrix W(q₁, . . . , q_M) that comprises the channel-specific quality parameters (q₁, . . . , q_M), wherein

the control unit determines at least another property so as to determine N properties e_m^α

(U_M) (α

=1, . . . , N) in all measuring channels for each measured signal (U₁, . . . U_M), and compares the determined N properties with desired values or desired ranges e_sollm^α

determined in advance or both desired values and desired ranges determined in advance to provide results of a comparison, and corrects the measured signals of the measuring channels based on the results of the comparison based on the properties or to adapt the reconstruction algorithm based on the properties;

said control unit determines channel-specific quality parameters and property-specific quality parameters q_m^α

(e_m^α

, e_sollm^α

) from the comparison of the determined properties e_m^α

of each channel m=1, . . . , M with desired values or desired value ranges e_sollm^α

determined in advance, wherein the channel-specific quality parameters are included in the reconstruction algorithm in such a manner that measuring channels with quality parameters that are indicative of signals of a lower quality relative to other signals are weighted less strongly than measuring channels with quality parameters that are indicative of signals with a higher quality relative to other signals; and

said control unit forms each of the channel-specific quality parameters from the property-specific quality parameters q_m^α

(e_m^α

, e_sollm^α

), to provide the channel-specific quality parameters q_m(q₁¹, . . . , q_m^α

, . . . , q_M^N), by arithmetic or geometric averaging of the property-specific quality parameters q_m^α

(e_m^α

, e_sollm^α

) for each measuring channel, wherein the channel-specific quality parameters are standardized for an interval, wherein the lowest quality is assigned to the value 0 and the highest quality is assigned to the value 1, and wherein the measuring channels are weighted according to this standardized quality parameter in the reconstruction algorithm.

9. A process for analyzing measured signals of an electrical impedance tomography (EIT) device in accordance with claim 8, wherein said control unit continuously updates a determination of the properties e_m^α

or the property quality parameters derived therefrom or the combined channel-specific quality parameters or any combination of the determination of the properties and the property quality parameters derived therefrom and the combined channel-specific quality parameters, wherein the determination is performed over a time window.

10. A process for analyzing measured signals of an electrical impedance tomography (EIT) device in accordance with claim 8, wherein said control unit continuously determines a plurality of global properties E^β

, β

=1 . . . G from at least one of the properties of the group of properties comprising the measured signals of the measuring channels, from properties thereof and from technical operating variables of the electrical impedance tomography device or from any combination of the measured signals of the measuring channels, from properties thereof and from technical operating variables of the electrical impedance tomography device, wherein the global properties are at least one of the properties selected from the group of properties that include maxima, minima or mean values or combinations of the channel-specific properties e_m^α

and the channel-specific quality parameters q_m^α

and operating current intensities, gain factors, dynamic range of the measured signals, operating frequencies, and the standard of differential EIT images with and without adaptation of the reconstruction algorithm, wherein the control unit compares the global properties E^β

with expected desired values or desired value ranges E_soll^β

or with both expected desired values and desired value ranges to provide results of a comparison and determines global quality parameters Q^β

(E^β

) on the basis of the results of the comparison.

11. A process for analyzing measured signals of an electrical impedance tomography (EIT) device in accordance with claim 10, wherein said control unit combines the global quality parameters Q^β

(E^β

) into a global quality index Q(Q¹, . . . , Q^G), by arithmetic or geometric averaging of the global quality parameters, wherein the control unit standardizes the global quality index to an interval and uses the global quality index for the quality classification of the EIT measurements.

12. A process for analyzing measured signals of an electrical impedance tomography (EIT) device in accordance with claim 11, wherein said control unit displays the global quality index graphically or alphanumerically on a display.

13. A process for analyzing measured signals of an electrical impedance tomography (EIT) device in accordance with claim 11, wherein said control unit marks time intervals separately in which the quality index is below a preset minimum criterion for derived variables, which variables are derived from the measured impedance distribution, and which have a development course over time shown on a display, and replaces values for the time analysis of the values with values derived from adjacent intervals, by interpolation or averaging, or with preset values to provide replaced time intervals, wherein the replaced time intervals are marked separately.