Measurement device for thoracic bioimpedance spectroscopy

Abstract

A bioimpedance measuring device for measuring breast tissue is provided, comprising a control unit and at least one measurement applicator having at least four contact electrodes connected or connectable to the control unit via electrical wiring, wherein the control unit is configured to generate and output an alternating current signal to two of the at least four contact electrodes, causing the two contact electrodes to function as current electrodes, and further configured to receive an alternating voltage signal between two of the at least four contact electrodes, causing them to function as voltage electrodes, wherein the at least two contact electrodes that function as voltage electrodes do not simultaneously function as current electrodes.

Description

[Technical Field]

[0001] The present invention relates to a measurement device and a measurement method for measuring the bioimpedance profile of human breast tissue. [Background technology]

[0002] In Germany and other countries, breast cancer is considered one of the leading causes of disability among women and one of the most common causes of death: in Germany, approximately 72,000 women develop breast cancer each year and approximately 17,000 women die from the disease each year.

[0003] The prospects for treating breast cancer depend largely on the stage at which the disease is detected, therefore early detection is one of the most effective ways to limit the progression of the disease.

[0004] Common methods used for the early detection of breast cancer include physical examination, ultrasound, and mammography. While physical examination and ultrasound can be difficult to reliably detect small tumors, mammography is a very uncomfortable test for patients, and the associated radiation exposure and tissue compression pose risk factors for malignant transformation in pathologically altered breast tissue.

[0005] In recent years, a method for measuring the composition of human tissue using electrical impulses has become known. In this method, a small alternating current is passed through the tissue to measure its impedance. Because the current used is extremely small, it does not stimulate the tissue. This method is called "bioimpedance measurement" and is primarily used to measure body fat percentage in nutritional guidance. Summary of the Invention [Problem to be solved by the invention]

[0006] It is therefore an object of the present invention to provide an alternative approach for the early detection of tissue changes in human breast tissue, allowing further differential diagnostic tests to be performed in a timely manner and, if necessary, early treatment to be initiated.

[0007] A further object of the invention is to provide a measuring device suitable for corresponding alternative methods. [Means for solving the problem]

[0008] According to one embodiment of the present invention, the problem is solved by a bioimpedance measuring device for measuring breast tissue, the device comprising a control unit and at least one measurement applicator, the measurement applicator having at least four contact electrodes, the contact electrodes being connected or connectable to the control unit via electrical wiring, the control unit being configured to generate an alternating current signal to two of the at least four contact electrodes, causing the two contact electrodes to function as current electrodes, and further to receive an alternating voltage signal between two of the at least four contact electrodes, causing them to function as voltage electrodes, wherein the at least two contact electrodes that function as voltage electrodes do not simultaneously function as current electrodes.

[0009] The present invention is based on the discovery that localized measurements of breast tissue are possible by making bioimpedance measurements of the breast tissue via appropriately placed contact electrodes.

[0010] In an advantageous configuration of the bioimpedance measuring device, the contact electrodes of at least one measuring applicator are arranged at the vertices of a regular polygon. Such an arrangement facilitates highly reproducible bioimpedance measurements and allows easy comparison of measurement results performed at regular intervals. Preferably, the measuring applicator comprises four contact electrodes arranged at the vertices of a quadrangle.

[0011] In one embodiment, the measurement applicator comprises a carrier region with arm-like extensions, at the ends of which the contact electrodes are arranged, this design allowing the measurement applicator to be applied to the breast tissue to be examined with a particularly small contact area.

[0012] The carrier region may include an opening located at the center point of the regular polygon. The measurement applicator may be placed on the breast tissue so that the nipple is visible through the opening. In this manner, reproducible positioning of the measurement applicator may be easily achieved, allowing for repeatable measurements.

[0013] The carrier region of the measurement applicator may be made of a preferably flexible material to allow flexible placement of the measurement applicator against breast tissue, suitable biocompatible materials include, for example, silicone.

[0014] In a preferred embodiment, the contact electrodes are detachably connected to the measuring applicator, which means, for example, that disposable contact electrodes can be used in combination with a reusable measuring applicator.

[0015] In one configuration, the control unit of the bioimpedance measuring device is configured to generate an alternating current signal at a variable frequency. Measuring the bioimpedance at different frequencies allows for a more accurate characterization of the breast tissue being measured.

[0016] The control unit is preferably configured to alternately control different contact electrodes as voltage electrodes, by which a spatially resolved bioimpedance profile of the examined tissue can be measured.

[0017] In an advantageous embodiment of the invention, the bioimpedance measuring device may comprise a calculation unit configured to calculate the spatial impedance distribution of the examined breast tissue from alternating voltage signals recorded at different frequencies and / or different electrode configurations.

[0018] The control unit preferably includes a memory device and is configured to store the calculated impedance profiles and / or alternating voltage signals recorded at different frequencies and / or different electrode configurations.

[0019] In one embodiment, the control unit of the bioimpedance measuring device is located in a movable housing, which allows it to be easily positioned relative to the examination table on which the subject lies, for example, a medical equipment trolley can be used as the movable housing.

[0020] The mobile housing may include an extension arm along which electrical wiring is arranged or can be arranged, thereby preventing the electrical wiring from contacting the skin surface of the test subject.

[0021] In a particularly advantageous embodiment, the bioimpedance measuring device can include two measuring applicators that allow simultaneous measurement of both breasts of the subject.

[0022] The object of the present invention is further achieved by a method for recording a bioimpedance profile of human breast tissue, the method comprising applying a measuring applicator with at least four contact electrodes to the breast tissue to be examined, supplying an alternating current signal via two of the at least four contact electrodes functioning as current electrodes, and recording an alternating voltage signal between two of the at least four contact electrodes functioning as voltage electrodes, wherein the frequency of the alternating current signal varies within a predetermined frequency range and the function of each of the at least four contact electrodes alternates between being a current electrode and a voltage electrode. The method according to the present invention allows for the generation of a bioimpedance profile of breast tissue with spatial resolution.

[0023] In a preferred embodiment of the method according to the invention, the measurement applicator comprises four contact electrodes arranged at the corners of a rectangle, wherein in a first measurement interval the first and second contact electrodes function as current electrodes and the third and fourth contact electrodes function as voltage electrodes, in a second measurement interval the first and third contact electrodes function as current electrodes and the second and fourth contact electrodes function as voltage electrodes, in a third measurement interval the first and fourth contact electrodes function as current electrodes and the second and third contact electrodes function as voltage electrodes, in a fourth measurement interval the second and third contact electrodes function as current electrodes and the first and fourth contact electrodes function as voltage electrodes, in a fifth measurement interval the second and fourth contact electrodes function as current electrodes and the first and third contact electrodes function as voltage electrodes, and in a sixth measurement interval the third and fourth contact electrodes function as current electrodes and the first and second contact electrodes function as voltage electrodes.

[0024] In a further preferred embodiment of the method according to the invention, the frequency of the alternating current signal is varied in a number of frequency steps for each measurement interval within the frequency range of 1 kHz to 1 MHz.

[0025] At each measurement interval and frequency step, the amplitude and phase of the voltage signal can be measured, allowing a spatially and frequency-resolved bioimpedance profile of the tissue being examined to be generated. For this purpose, the recorded measurements are saved.

[0026] A bioimpedance profile stored in this way can be compared with a previously recorded bioimpedance profile of the same tissue, which may have been recorded during a previous routine medical examination.

[0027] If the comparison of the bioimpedance profile with a previously recorded bioimpedance profile reveals a change above a predetermined level, a change signal can be generated that can indicate the need to initiate further differential diagnostic procedures to rule out or confirm the presence of pathological tissue changes. [Brief explanation of the drawings]

[0028] The following figure is shown. [Figure 1] FIG. 1 is a schematic diagram of bioimpedance measurements of breast tissue. [Figure 2A] This is a connection configuration of the contact electrodes. [Figure 2B] This is a connection configuration of the contact electrodes. [Figure 2C] This is a connection configuration of the contact electrodes. [Figure 2D] This is a connection configuration of the contact electrodes. [Figure 2E] This is a connection configuration of the contact electrodes. [Figure 2F] This is a connection configuration of the contact electrodes. [Figure 3A] 2A to 2F show the inspection area in the connection configuration of FIG. 2A to FIG. 2F. [Figure 3B] 2A to 2F show the inspection area in the connection configuration of FIG. 2A to FIG. 2F. [Figure 3C] 2A to 2F show the inspection area in the connection configuration of FIG. 2A to FIG. 2F. [Figure 3D] 2A to 2F show the inspection area in the connection configuration of FIG. 2A to FIG. 2F. [Figure 3E] 2A to 2F show the inspection area in the connection configuration of FIG. 2A to FIG. 2F. [Figure 3F] 2A to 2F show the inspection area in the connection configuration of FIG. 2A to FIG. 2F. [Figure 4] A measuring applicator. [Figure 5] A bioimpedance measurement system. [Figure 6] It is an inspection system. DETAILED DESCRIPTION OF THE INVENTION

[0029] The invention will now be explained in more detail with the aid of some exemplary drawings, which are intended for a better understanding of the invention and are not intended to be limiting.

[0030] Figure 1 shows a female torso with breast tissue being the subject of bioimpedance measurements. For this purpose, four contact electrodes 1, 2, 3, and 4 are attached to the left breast. Contact electrodes 1 and 2 are connected to an AC power source 6 via electrical wiring 5 and thus function as current electrodes. The AC power source 6 introduces a current signal in the form of a weak, high-frequency alternating current into the breast tissue being examined. This generates an electromagnetic field within the breast tissue, represented by field lines 7. This electromagnetic field generates a potential difference between contact electrodes 3 and 4, which is measured by a voltmeter 8. The voltmeter 8 is connected to contact electrodes 3 and 4 via wire 9 and thus functions as a voltage electrode.

[0031] The path of the magnetic field lines 7, which is shown very simply in Figure 1, depends on the frequency of the applied alternating current and the composition of the breast tissue in the region between the current electrodes 1, 2 and the voltage electrodes 3, 4. By varying the frequency of the applied alternating current, the composition of the breast tissue in the measurement region can be determined.

[0032] The bioimpedance measurements described herein do not require the actual determination of physiological tissue composition. Rather, it is sufficient to record the variations in the amplitude and phase of the voltage signal as a function of the frequency of the current signal. This is because early detection of tissue changes is achieved simply by recognizing changes in physiological tissue composition as reflected in variations in the amplitude and phase shifts of the voltage signal.

[0033] 2A to 2F show how contact electrodes 1, 2, 3, and 4 are sequentially connected to an AC power supply 6 and a voltage measuring device 8 when recording an impedance profile.

[0034] FIG. 2A shows the configuration already shown in FIG. 1, with contact electrodes 1 and 2 connected as current electrodes to an AC power supply 6 and contact electrodes 3 and 4 connected as voltage electrodes to a voltmeter 8.

[0035] FIG. 2B shows a configuration in which contact electrodes 1 and 3 are connected to an AC power source 6 as current electrodes, and contact electrodes 2 and 4 are connected to a voltmeter 8 as voltage electrodes.

[0036] FIG. 2C shows a configuration in which contact electrodes 1 and 4 are connected to an AC power source 6 as current electrodes, and contact electrodes 2 and 3 are connected to a voltmeter 8 as voltage electrodes.

[0037] FIG. 2D shows a configuration in which contact electrodes 2 and 3 are connected to an AC power supply 6 as current electrodes, and contact electrodes 1 and 4 are connected to a voltage measuring device 8 as voltage electrodes.

[0038] FIG. 2E shows a configuration in which contact electrodes 2 and 4 are connected to an AC power source 6 as current electrodes, and contact electrodes 1 and 3 are connected to a voltmeter 8 as voltage electrodes.

[0039] FIG. 2F shows a configuration in which contact electrodes 3 and 4 are connected as current electrodes to an alternating current source 6, and contact electrodes 1 and 2 are connected as voltage electrodes to a voltmeter 8.

[0040] Figures 3A-3F show the regions of breast tissue through which the alternating current signal flows in the contact electrode configuration shown in Figures 2A-2F. The four regions of the breast are labeled I-IV.

[0041] FIG. 4 shows a measuring applicator 10 of a bioimpedance measuring device according to the present invention. The measuring applicator comprises a carrier region 11 with four arm-like extensions 12, at the ends of which are arranged holders 13 for contact electrodes. Contact electrodes (not shown in FIG. 4 ) can be inserted into the holder 13 through slits 14 in the holder 13. When the measuring applicator 10 is attached to the breast tissue of the test subject, the contact electrodes come into contact with the breast tissue. The carrier region 11 with the extensions 12 is made of a flexible, biocompatible material such as silicone. Therefore, when the measuring applicator 10 is attached to the breast tissue of the test subject, the extensions 12 gently contact the breast tissue, eliminating the need to apply pressure to the measuring applicator 10.

[0042] The measurement applicator 10 has a central opening 15 that allows the nipple to be visualized when the measurement applicator 10 is applied to breast tissue, making it easier to place the measurement applicator 10 in the same location on the breast tissue being examined for successive measurements.

[0043] Figure 5 shows a bioimpedance measurement system 20. The bioimpedance measurement system 20 includes a control unit 21 equipped with an AC power supply and a voltmeter, but for simplicity of explanation, these devices are not shown separately. Two measurement applicators 22 and 23 configured similarly to the measurement applicator 10 shown in Figure 4 are connected to the control unit 21. Using the two measurement applicators 22 and 23, both breasts of the subject can be measured simultaneously.

[0044] The bioimpedance measurement system 20 is further connected to a computer 25, which records and evaluates the phase and amplitude of the voltage signals recorded at different frequencies of the alternating current signal and at different electrode configurations to form a spatial impedance distribution of the examined breast tissue. Spatial impedance distribution does not necessarily mean an impedance distribution with precise spatial resolution in the sense of a slice of a tomographic image, in which an independent impedance measurement value is obtained for each spatial element of the examined breast tissue. In the context of the present invention, spatial impedance distribution is understood to mean a multidimensional characteristic field in which the amplitude and phase of the voltage signals at different electrode configurations and different measurement frequencies are plotted.

[0045] The control unit 21 can vary the frequency of the AC signal in several steps, for example, between 1 kHz and 1 MHz, for each electrode configuration. The frequency can be increased, for example, by 1 kHz, until a frequency of 1 MHz is reached after 1000 steps. A short measurement time, for example, 0.1 seconds for each frequency step, is sufficient to determine the phase and amplitude measurements of the AC voltage. Therefore, 1000 frequency steps require less than two minutes, and a complete measurement of breast tissue using all six electrode configurations can be completed in approximately 10 minutes.

[0046] The measurement results can be analyzed immediately by computer after the measurement. Reference values ​​that indicate normal changes in measurements in healthy tissue can be used to analyze the measurement results. However, such reference values ​​are only a guide, so it is appropriate to compare the measurement results of one test with those of previous tests of the same breast tissue. For example, by performing bioimpedance measurements according to the present invention periodically, yearly, suspected changes in tissue composition can be detected relatively early, before palpable or ultrasound-visible changes appear.

[0047] An example of a test system for performing bioimpedance measurements according to the present invention is shown in Figure 6. The test system 50 includes an equipment cart 51 incorporating the bioimpedance measurement system 20 shown in Figure 5. The equipment cart 51 is provided with casters 52 for positioning an examination table 53 on which the subject can be positioned horizontally. The equipment cart 51 also includes an extension arm 55 along which electrical wiring from the control unit 21 (not shown in Figure 6) is routed. The patient-side end of the extension arm 55 is provided with a connection area 56 through which the electrical wiring is freely accessible. Eight electrical wirings are provided for connecting two measurement applicators (each with four contact electrodes). For clarity, only two wirings are shown in Figure 6.

[0048] The extension arm 55 can be positioned above the subject and a measuring applicator (not shown in Figure 6) can be placed on either side of the breast tissue without placing electrical cables in the way of the subject's skin. The free ends of the electrical wires can be connected to disposable contact electrodes, which are then inserted into the respective holders of the measuring applicator.

[0049] A control panel 58 on the equipment cart 61 is used by the user to operate the bioimpedance measurement system. The control panel 58 may be connected to the computer 25 or may be configured as part of the computer.

[0050] The following sections describe various embodiments of the present invention.

[0051] 1. A bioimpedance measuring device for measuring breast tissue comprises a control unit and at least one measuring applicator having at least four contact electrodes connected or connectable to the control unit via electrical wiring, the control unit being configured to generate and output an alternating current signal to two of the at least four contact electrodes so that they function as current electrodes, and to receive an alternating voltage signal between two of the at least four contact electrodes so that they function as voltage electrodes, and the at least two contact electrodes that function as voltage electrodes do not simultaneously function as current electrodes.

[0052] 2. A bioimpedance measuring device as described in section 1, wherein the contact electrodes of at least one measuring applicator are arranged at the corners of a regular polygon.

[0053] 3. A bioimpedance measuring device according to section 1 or 2, wherein the measuring applicator has four contact electrodes.

[0054] 4. A bioimpedance measuring device according to section 2 or 3, wherein the measuring applicator comprises a carrier region with arm-like extensions at the ends of which contact electrodes are arranged.

[0055] 5. A bioimpedance measuring device as described in any one of sections 2 to 4, wherein the carrier region is positioned at the centre point of a regular polygon and has an opening that allows the measuring applicator to be placed in a reproducible position on the nipple of the breast to be measured.

[0056] 6. A bioimpedance measuring device according to section 4 or 5, wherein the carrier region is made from a flexible material.

[0057] 7. A bioimpedance measuring device according to any of the preceding sections, wherein the contact electrodes are detachably connected to the measuring applicator.

[0058] 8. A bioimpedance measurement device according to any of the preceding sections, wherein the control device is configured to generate an alternating current signal of variable frequency.

[0059] 9. A bioimpedance measuring device according to any of the preceding sections, wherein the control device is configured to alternately control different contact electrodes as current electrodes.

[0060] 10. A bioimpedance measuring device according to any of the preceding sections, wherein the control device is configured to alternately control different contact electrodes as voltage electrodes.

[0061] 11. A bioimpedance measuring device according to any of the preceding sections, wherein the control device comprises a calculation unit configured to calculate the spatial impedance distribution of the breast tissue under test from alternating voltage signals recorded at different frequencies and / or different electrode configurations.

[0062] 12. A bioimpedance measuring device according to any of the preceding sections, wherein the control device comprises a memory device and is configured to store the calculated impedance distribution and / or the AC voltage signals recorded at different frequencies and / or different electrode configurations.

[0063] 13. A bioimpedance measuring device according to any of the preceding sections, wherein the control device is disposed in a movable housing.

[0064] 14. A bioimpedance measuring device as described in section 13, wherein the movable housing comprises an extension arm along which the electrical wiring is guided or can be guided.

[0065] 15. A bioimpedance measuring device according to any of the preceding sections, the bioimpedance measuring device comprising two measuring applicators.

[0066] 16. A measurement applicator for a bioimpedance measuring device according to any one of sections 1 to 7.

[0067] 17. A method for recording a bioimpedance profile of human breast tissue, comprising applying a measuring applicator having at least four contact electrodes to the breast tissue to be tested, supplying an alternating current signal via two of the at least four contact electrodes functioning as current electrodes, and recording an alternating voltage signal via two of the at least four contact electrodes functioning as voltage electrodes, wherein the frequency of the alternating current signal varies within a predetermined frequency range, and the function of each of the at least four contact electrodes varies between being a current electrode and a voltage electrode.

[0068] 18. The method of section 17, wherein the measurement applicator comprises four contact electrodes arranged at the corners of a rectangle, wherein in a first measurement interval, the first and second contact electrodes function as current electrodes and the third and fourth contact electrodes function as voltage electrodes; in a second measurement interval, the first and third contact electrodes function as current electrodes and the second and fourth contact electrodes function as voltage electrodes; in a third measurement interval, the first and fourth contact electrodes function as current electrodes and the second and third contact electrodes function as voltage electrodes; in a fourth measurement interval, the second and third contact electrodes function as current electrodes and the first and fourth contact electrodes function as voltage electrodes; in a fifth measurement interval, the second and fourth contact electrodes function as current electrodes and the first and third contact electrodes function as voltage electrodes; and in a sixth measurement interval, the third and fourth contact electrodes function as current electrodes and the first and second contact electrodes function as voltage electrodes.

[0069] 19. The method of section 18, wherein the frequency of the alternating current signal is varied in multiple frequency steps for each measurement interval within a frequency range of 1 kHz to 1 MHz.

[0070] 20. The method of section 19, wherein the amplitude and phase of the voltage signal are measured at each measurement interval and each frequency step.

[0071] 21. The method of any of sections 17 to 20, wherein the recorded measurements are stored as a bioimpedance profile.

[0072] 22. The method of section 21, wherein the stored bioimpedance profile is compared with a previously recorded bioimpedance profile of the same tissue.

[0073] 23. The method of section 22, wherein a change signal is generated when a change in the bioimpedance profile exceeds a predetermined level.

Claims

1. a control unit; at least one measurement applicator disposed at a corner of the rectangle and including first, second, third and fourth connection electrodes connected or connectable to said control unit via electrical wiring; the control unit is configured to generate and output an alternating current signal to two of the four contact electrodes, causing them to function as current electrodes, and to receive an alternating voltage signal between two of the four contact electrodes, causing them to function as voltage electrodes; At least two contact electrodes functioning as voltage electrodes do not simultaneously function as current electrodes; The control unit further comprises: simultaneously to the first and second contact electrodes, simultaneously to the first and third contact electrodes, simultaneously to the first and fourth contact electrodes, simultaneously to the second and third contact electrodes, simultaneously to the second and fourth contact electrodes, and simultaneously to the third and fourth contact electrodes, configured to sequentially apply a varying alternating current signal; 1. A bioimpedance measuring device for measuring breast tissue, wherein the control unit includes a calculation unit configured to calculate a spatial impedance distribution of the breast tissue under test from the AC voltage signals recorded with different electrode configurations.

2. 2. A bioimpedance measuring device according to claim 1, wherein the measuring applicator comprises a carrier region with arm-like extensions on the ends of which the contact electrodes are arranged.

3. 3. A bioimpedance measuring device according to claim 1, wherein the carrier region is arranged at the centre point of a regular polygon and includes an opening which allows the measuring applicator to be placed in a reproducible position on the nipple of the breast to be measured.

4. 4. The bioimpedance measuring device according to claim 2, wherein the carrier region is made of a flexible material.

5. 10. A bioimpedance measuring device according to claim 1, wherein the contact electrodes are detachably connected to the measuring applicator.

6. 10. Bioimpedance measuring device according to one of the previous claims, wherein the control unit is adapted to generate an alternating current signal of variable frequency.

7. 10. Bioimpedance measuring device according to one of the previous claims, wherein the control unit is adapted to alternately control different contact electrodes as current electrodes.

8. 10. Bioimpedance measuring device according to one of the previous claims, wherein the control unit is adapted to alternately control different contact electrodes as voltage electrodes.

9. 10. Bioimpedance measuring device according to one of the previous claims, wherein the calculation unit is configured to calculate the spatial impedance distribution of the examined breast tissue from the alternating voltage signals recorded at different frequencies.

10. 10. A bioimpedance measuring device according to claim 1, wherein the control unit comprises a memory device configured to store the calculated impedance distribution and / or the AC voltage signals recorded at different frequencies and / or different electrode configurations.

11. 10. A bioimpedance measuring device according to claim 1, wherein the control unit is arranged in a movable housing.

12. 12. The bioimpedance measuring device of claim 11, wherein the movable housing comprises an extension arm along which the electrical wiring is guided or can be guided.

13. 10. Bioimpedance measuring device according to one of the previous claims, comprising two measuring applicators.

14. 6. A measuring applicator for a bioimpedance measuring device according to claim 1.

15. applying a measuring applicator including four contact electrodes to the breast tissue to be examined; supplying an alternating current signal via two of the four contact electrodes that function as current electrodes; and recording an AC voltage signal via two of the four contact electrodes that function as voltage electrodes; the frequency of the alternating current signal varies within a predetermined frequency range; The function of each of the four contact electrodes changes between a current electrode and a voltage electrode; the measuring applicator includes four contact electrodes arranged at the corners of a rectangle; during a first measurement interval, the first and second contacting electrodes function as current electrodes and the third and fourth contacting electrodes function as voltage electrodes; during a second measurement interval, the first and third contacting electrodes function as current electrodes and the second and fourth contacting electrodes function as voltage electrodes; during a third measurement interval, the first and fourth contacting electrodes function as current electrodes and the second and third contacting electrodes function as voltage electrodes; during a fourth measurement interval, the second and third contacting electrodes function as current electrodes and the first and fourth contacting electrodes function as voltage electrodes; during a fifth measurement interval, the second and fourth contacting electrodes function as current electrodes and the first and third contacting electrodes function as voltage electrodes; during a sixth measurement interval, the third and fourth contacting electrodes function as current electrodes and the first and second contacting electrodes function as voltage electrodes; A method for recording a bioimpedance profile of human thoracic tissue, wherein a spatial impedance distribution of the examined thoracic tissue is calculated by a calculation unit from the AC voltage signals recorded with different electrode configurations.

16. 16. The method of claim 15, wherein the frequency of the alternating current signal is varied in multiple frequency steps for each measurement interval within a frequency range of 1 kHz to 1 MHz.

17. 17. The method of claim 16, wherein the amplitude and phase of the voltage signal are measured at each measurement interval and each frequency step.

18. 18. The method according to claim 15, wherein the recorded measurements are stored as a bioimpedance profile.

19. 20. The method of claim 18, wherein the stored bioimpedance profile is compared to a previously recorded bioimpedance profile of the same tissue.

20. 20. The method of claim 19, wherein a change signal is generated when the change in the bioimpedance profile exceeds a predetermined level.

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