ELECTRICAL IMPEDANCE TOMOGRAPHY DEVICE AND PROCESS

• US 20130002264A1
• Filed: 06/12/2012
• Published: 01/03/2013
• Est. Priority Date: 07/02/2011
• Status: Active Grant

• Current Assignee: Dragerwerk AG & Company KGaA (FPS Vermögensverwaltung GmbH)
• Original Assignee: Drager Medical GmbH (FPS Vermögensverwaltung GmbH)
• Inventors: GÄRBER, Yvo
• Granted Patent: US 9,730,607 B2
• Time in Patent Office: Days
• US Class Current: 324/600
• 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 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 controlling a supply of alternating current or with an alternating voltage to an electrode pair as a feeding electrode pair and receiving the voltage signal or current signal of each electrode pair from all other electrode pairs as measured signals of a measuring channel, and to successively change said feeding electrode pair through said plurality of electrodes in order to thus receive and to process measured signals (U₁, . . . , K_M) and reconstructing therefrom an impedance distribution of the body with a reconstruction algorithm, said control unit further continuously determining at least one property (e₁, . . . , e_M) each from said measured signals (U₁, . . . , U_M) of all measuring channels and at least one of correcting measured signals of said measuring channels on the basis of said properties and adapting the reconstruction algorithm on the basis of the properties.

2. An electrical impedance tomography device in accordance with claim 1, wherein said control unit furthermore determines N properties e_m^α

(U_M) (α

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

determined in advance, and corrects the measured signals of the measuring channels on the basis of the results of the comparison based on the properties or adapts the reconstruction algorithm on the basis of the properties.

3. An electrical impedance tomography device in accordance with claim 2, wherein said control unit furthermore determines a plurality of properties from the following group of properties as properties e_m^α

(U_M) of the measured signal in each measuring channel;

Signal/noise ratio (SNR);

mean value;

phase or real and imaginary part of the measured signal;

mean deviation of the measured signal from the mean value;

a mean square deviation from the mean value, crosstalk estimations of the measured signal, determined common mode estimations of the measured signals, signal drift, correlations between reciprocal signal time series over a certain time period, correlations between measured signals and ventilation data, a value and phase of the electrode-skin contact impedances, characteristic properties of value and phase distributions of the frequency spectra of the measured signals over a certain time period including at least one of maximum value and phase distributions of the frequency spectra, standard deviation of the value and phase distributions of the frequency spectra and shape parameters of the spectral distributions of the frequency spectra.

4. An electrical impedance tomography device in accordance with claim 2, wherein said control unit determines channel-specific 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 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 are weighted less strongly than measuring channels with quality parameters that are indicative of signals with a higher quality.

5. An electrical impedance tomography device in accordance with claim 4, wherein said control unit combines the quality parameters q_m^α

(e_m^α

, e_sollm^α

) into a channel-specific quality parameter 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 [0,1], 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.

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

and/or the property quality parameters derived therefrom and/or the combined channel-specific quality parameters, wherein the determination is performed over a time window that is carried along.

7. An electrical impedance tomography 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, from properties thereof and/or from technical operating variables of the electrical impedance tomography device, wherein the global properties include maxima, minima or mean values or combinations of the channel-specific properties e_m^α

and/or of the channel-specific quality parameters q_m^α

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

with expected desired values and/or desired value ranges E_soll^β

and determines global quality parameters Q^β

(E^β

) on the basis of the results of the comparison.

8. An electrical impedance tomography device in accordance with claim 7, 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 the interval [0,1] and uses the global quality index for the quality classification of the EIT measurements.

9. An electrical impedance tomography device in accordance with claim 8, wherein said control unit displays the global quality index graphically or alphanumerically on a display.

10. An electrical impedance tomography device in accordance with claim 8, 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 the adjacent intervals, by interpolation or averaging, or with preset values, wherein the replaced time intervals are marked separately.

11. A process for analyzing measured signals of an electrical impedance tomography 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 voltage signal or current signal as a measured signal of each electrode pair from all other electrode pairs as a measured signal;

changing the feeding electrode pair successively to pass through the plurality of electrodes in order to thus 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), in order to reconstruct therefrom an impedance distribution of the body in the electrode plane with a reconstruction algorithm with the control unit;

continuously determining, with the control unit, at least one property (e₁, . . . , e_M) from the measured signals of all measured signals of all measuring channels; and

correcting measured signals on the basis of the properties or adapting the reconstruction algorithm on the basis of the properties.

12. A process for analyzing measured signals of an electrical impedance tomography in accordance with claim 11, wherein the control unit determines 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 and/or desired ranges e_sollm^α

determined in advance, and corrects the measured signals of the measuring channels on the basis of the results of the comparison based on the properties or to adapt the reconstruction algorithm on the basis of the properties.

13. A process for analyzing measured signals of an electrical impedance tomography in accordance with claim 12, wherein said control unit determines a plurality of properties from the following group of properties as properties e_m^α

(U_M) of the measured signal in each measuring channel;

Signal/noise ratio (SNR);

mean value;

phase or real and imaginary part of the measured signal;

mean deviation of the measured signal from the mean value;

a mean square deviation from the mean value, crosstalk estimations of the measured signal, determined common mode estimations of the measured signals, signal drift, correlations between reciprocal signal time series over a certain time period, correlations between measured signals and ventilation data, value and phase of the electrode-skin contact impedances, characteristic properties of value and phase distributions of the frequency spectra of the measured signals over a certain time period including at least one of maximum value and phase distributions of the frequency spectra, standard deviation of the value and phase distributions of the frequency spectra and shape parameters of the spectral distributions.

14. A process for analyzing measured signals of an electrical impedance tomography in accordance with claim 12, wherein said control unit determines channel-specific 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 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 are weighted less strongly than measuring channels with quality parameters that are indicative of signals with a higher quality.

15. A process for analyzing measured signals of an electrical impedance tomography in accordance with claim 14, wherein said control unit combines the quality parameters q_m^α

(e_m^α

, e_sollm^α

) into a channel-specific quality parameter 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 [0,1], 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.

16. A process for analyzing measured signals of an electrical impedance tomography in accordance with claim 11, wherein said control unit continuously updates the determination of the properties e_m^α

and/or the property quality parameters derived therefrom and/or the combined channel-specific quality parameters, wherein the determination is performed over a time window that is carried along.

17. A process for analyzing measured signals of an electrical impedance tomography in accordance with claim 11, wherein said control unit continuously determines a plurality of global properties E^β

, β

=1 . . . G from the measured signals of the measuring channels, from properties thereof and/or from technical operating variables of the electrical impedance tomography device, wherein the global properties include maxima, minima or mean values or combinations of the channel-specific properties e_m^α

and/or of the channel-specific quality parameters q_m^α

and/or operating current intensities, gain factors, dynamic range of the voltages, 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 and/or desired value ranges E_soll^β

and determines global quality parameters Q^β

(E^β

) on the basis of the results of the comparison.

18. A process for analyzing measured signals of an electrical impedance tomography in accordance with claim 17, 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 the interval [0,1] and uses the global quality index for the quality classification of the EIT measurements.

19. A process for analyzing measured signals of an electrical impedance tomography in accordance with claim 18, wherein said control unit displays the global quality index graphically or alphanumerically on a display.

20. A process for analyzing measured signals of an electrical impedance tomography in accordance with claim 18, 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 the adjacent intervals, by interpolation or averaging, or with preset values, wherein the replaced time intervals are marked separately.