JP2012205604A - Bioimpedance measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily measure the anisotropy of the electric impedance of a tissue.SOLUTION: An eddy current generating device 10 includes two or more electromagnets M1-M3 arranged at almost equal intervals in an almost concentric fashion. End faces of the electromagnets M1-M3 are arranged to oppose to a surface of the living tissue 2, and each of the electromagnets M1-M3 generates an eddy current corresponding to a driving current flowing in each coil L1-L3. The eddy current generating device 10 changes the driving current flowing in the coils L1-L3 so that the direction of a combined current of the eddy current generated by the electromagnets M1-M3 changes over time. An electric potential difference measuring device 30 has two or more measuring electrodes e1-e4 arranged on the surface of the living tissue 2, and measures a potential difference generated in the living tissue by the eddy current, using the two pair of measuring electrodes.

Description

  The present invention relates to a technique for non-invasively measuring a living tissue.

  A living organ having a complicated structure and each tissue constituting the living organ have electrical anisotropy. Measurement of electrical impedance anisotropy is expected to provide quality information related to tissue composition and electrical properties, which is of great value in physiological research and clinical applications.

  A four-electrode method is known as a method for measuring the electrical impedance of a living body. While the four-electrode method has the advantage of being less affected by unstable contact resistance between the measurement object and the electrode, it is clear which part of the cross-section of the living body is being measured due to the complexity of the shape of the living tissue. Therefore, there is a problem that the correspondence between the measured result and the physiological phenomenon is not reliable.

Japanese Patent No. 19009038

  As a technique for measuring the electrical impedance of a living body, the present inventors have proposed the technique described in Patent Document 1. However, in the technique described in the document, it is necessary to sandwich a living tissue between two electromagnets, and there is a limit to its use.

  The present invention has been made in view of the above problems, and one of the exemplary purposes of an embodiment thereof is to provide an apparatus that can easily measure the electrical impedance anisotropy of a tissue.

  One embodiment of the present invention relates to a bioimpedance measuring apparatus that measures impedance of a living tissue. The bioimpedance measurement device includes an eddy current generator and a potential difference measurement device. The eddy current generator is m electromagnets (m is an integer of 2 or more) arranged at substantially equal intervals on a substantially concentric circle, and each end surface thereof is arranged to face the surface of a living tissue. Having one electromagnet. Each electromagnet generates an eddy current corresponding to the drive current flowing through the coil. The eddy current generator changes the drive current flowing through the coils of each of the m electromagnets so that the direction of the combined current of the eddy currents generated by the m electromagnets in the living tissue changes with time. The potential difference measuring device has a plurality of measurement electrodes arranged on the surface of a living tissue, and measures a potential difference generated in the living tissue by an eddy current using a pair of two measuring electrodes.

  According to this aspect, an eddy current is generated in the living tissue by supplying a driving current to the plurality of electromagnets. The direction in which the combined current of the eddy current flows can be changed according to the strength of the drive current applied to the coils of each electromagnet or the combination of the amplitudes. Therefore, an electric current can be passed through the living tissue in an arbitrary direction, and the anisotropy of the bioimpedance can be easily and / or accurately measured by measuring a potential difference caused by the electric current using a pair of electrodes for measurement. It becomes possible to measure. Moreover, according to this aspect, since it is not necessary to pinch | interpose a sample between several electromagnets, it can utilize for a wide use compared with a prior art.

  The coils of each of the m electromagnets may be supplied with a high-frequency driving current having the same frequency and having a phase shifted by approximately (360 / m) degrees. A synthetic current whose flowing direction rotates in synchronization with the drive current may be generated in the living tissue.

  m = 3, the three electromagnets may be arranged on substantially concentric circles that are 120 degrees apart spatially, and a three-phase symmetrical high-frequency driving current may be supplied to the coils of each electromagnet.

  The eddy current generator generates m drive currents by amplitude-modulating a high-frequency carrier current having a first frequency with m modulation signals having a second frequency lower than the first frequency, and generates m drive currents. A synthetic current whose flowing direction changes in synchronization with the modulation signal may be generated in the living tissue by causing each current to flow through each coil of the m electromagnets.

  m = 3, and the three electromagnets may be arranged on substantially concentric circles spatially separated by 120 degrees. The m modulation signals may be components of a three-phase symmetrical alternating current having a second frequency whose phases are shifted by 120 degrees from each other.

  The potentiometric device according to an aspect may further include a plurality of cancel electrodes arranged on the surface of the biological tissue. The canceling electrode is controlled by controlling the amplitude and phase of the high-frequency current that flows between the corresponding pair of cancel electrodes so that the potential difference generated between the two pairs of measurement electrodes is substantially zero. The impedance in the direction formed by the corresponding pair of electrodes for measurement may be measured from the current value flowing between the pair.

  The plurality of measurement electrodes may be installed in planes that are parallel to the surface formed by the end surfaces of the m electromagnets and have different depths.

  At least one of the plurality of measurement electrodes and the plurality of cancellation electrodes may be disposed in a plane that is parallel to a surface formed by end surfaces of the m electromagnets and has different depths.

The bioimpedance measuring device according to an aspect may further include a ferrite that is magnetically coupled in common to the second end faces of the m electromagnets. The distance between the ferrite and the second end face of the m electromagnets may be adjustable.
According to this aspect, the depth at which the magnetic field generated by the electromagnet penetrates into the living tissue can be adjusted according to the distance between the ferrite and the electromagnet, and the impedance distribution in the depth direction can be measured.

  Note that any combination of the above-described components, or a conversion of the expression of the present invention between methods, apparatuses, and the like is also effective as an aspect of the present invention.

  According to an aspect of the present invention, the anisotropy of the electrical impedance of a living tissue can be easily measured.

FIGS. 1A and 1B are diagrams showing the configuration of the bioimpedance measurement apparatus according to the first embodiment. FIGS. 2A and 2B are diagrams showing directions of three-phase symmetrical high-frequency driving current and combined current. It is a block diagram which shows the structural example of the drive part which performs a 2nd drive system. 4A and 4B are waveform diagrams showing the operation of the drive unit of FIG. It is a figure which shows the structure of the bioimpedance measuring apparatus which concerns on 2nd Embodiment. FIG. 6 is a circuit diagram illustrating a configuration example of a control circuit in FIG. 5. It is a figure which shows the structure of the bioimpedance measuring apparatus which concerns on 3rd Embodiment. It is a figure which shows the structure of the bioimpedance measuring apparatus which concerns on 4th Embodiment.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

(First embodiment)
FIGS. 1A and 1B are diagrams illustrating a configuration of a bioimpedance measurement apparatus 100 according to the first embodiment. The bioimpedance measuring apparatus 100 is used for measuring the impedance of a living tissue. 1A is a perspective view of the bioimpedance measuring apparatus 100, and FIG. 1B is an upper cross-sectional view. The bioimpedance measuring apparatus 100 mainly includes eddy current generators 10 and 30.

  The eddy current generator 10 includes a plurality of m (m is an integer of 2 or more) electromagnets M1 to Mm and a drive unit 12. In the present embodiment, a case where m = 3 will be described, but the present invention is not limited thereto.

The plurality of electromagnets M <b> 1 to M <b> 3 are arranged at substantially equal intervals on a substantially concentric circle. The lower end surface of each of the electromagnets M1 to M3 is disposed so as to face the surface of the sample (also referred to as a biological tissue) 2 to be measured. Preferably, the three electromagnets M1 to M3 are arranged on a substantially concentric circle spatially separated by 120 degrees. Drive currents I _{L1 to} I ₁₃ are supplied from the drive unit 12 to the coils _L1 to L3 of the electromagnets M1 to M3. As a result, the electromagnets M1 to M3 generate eddy currents in the sample 2 according to the drive currents I _{L1 to} I _L3 .

The driving unit 12 drives the driving currents flowing in the coils L1 to L3 of the plurality of electromagnets M1 to M3 so that the direction of the combined current of eddy currents generated by the plurality of electromagnets M1 to M3 in the living tissue changes with time. I _{L1 to} I _L3 are changed.

Reference is made to FIG. It is assumed that the xy plane is parallel to the surface of the sample 2. It is assumed that the first electromagnet M1 is disposed at θ = 180 degrees, the second electromagnet M2 is disposed at θ = 300 degrees, and the third electromagnet M3 is disposed at θ = 60 degrees. At this time, the eddy current J1 generated by the first electromagnet M1 at the observation point near the origin O is given by Expression (1) using the current _IL1 flowing through the coil L1.
_{J 1 = k 1 × I L1} × h 1 ... (1)
Here, h ₁ is a unit vector having a direction of θ = 90 degrees, and k ₁ is a coefficient determined by the shape of the electromagnet M1, the material, the number of turns of the coil, the positional relationship between the magnet and the observation point, and the like.

Similarly, an eddy current _{J 2} of the second electromagnet M1 is generated, an eddy current _{J 3} of the third electromagnet M3 is generated respectively, using the current _{I L2, I L3} flowing through the coil L2, L3, formula (2 ) And (3).
_{J 2 = k 2 × I L2} × h 2 ... (2)
J ₃ = k ₃ × IL ₃ × h ₃ (3)
h ₂ is a unit vector having a direction of θ = 210 degrees, h ₃ is a unit vector having a direction of θ = 330 degrees, and k ₂ and k ₃ are coefficients similar to k ₁ .

In the observation point, resultant current _{J total} eddy current J1~J3 make three electromagnets M1~M3 is given by Equation (4).
J _total = Σ _{i = 1: m} J _i = J ₁ + J ₂ + J _{3
= K 1 × I L1 × h} 1 + k 2 × I L2 × h 2 + k 3 × I L3 × h 3 ... (4)
Here, Σ _{i = 1: m} J _i represents the total sum of J ₁ to J _m .

Therefore, according to the eddy current generator 10 of FIG. 1, the direction and / or magnitude of the combined current J _total can be changed every moment by changing the drive currents I _{L1 to} I _L3 every moment. it can.

Subsequently, a method for generating some preferable drive currents I _{L1 to} I _L3 will be described.

(First driving method)
In a preferred embodiment, the drive unit 12 supplies high-frequency drive currents I _{L1 to} I _L3 having the same frequency, the phases of which are mutually shifted by approximately (360 / m) degrees, to the coils _{L1 to L3} of the electromagnets M1 to M3. That is, three-phase symmetrical high-frequency drive currents I _{L1 to} I _L3 having an angular frequency ω are supplied to the coils _{L1 to L3 of the} electromagnets M1 to M3. FIGS. 2A and 2B are diagrams showing the directions of the three-phase symmetrical high-frequency drive currents I _{L1 to} I _L3 and the combined current Jtotal.
I _L1 = I ₀ · cos (ωt) (5a)
I _L2 = I ₀ · cos (ωt−2π / 3) (5b)
I _L3 = I ₀ · cos (ωt−4π / 3) (5c)

Now, there from the observation point three electromagnets M1~M3 equidistant, the shape of the electromagnets, if properties are _equal, can be regarded as _{k 1 = k 2 = k 3} = k. At this time, the combined current _Jtotal of the equation (4) is given by the equation (6).
J _total = k × (I _L1 × h ₁ + I _L2 × h ₂ + I _L3 × h ₃ ) (6)

When the expressions (5a) to (5c) are substituted into the expression (6), the expression (7) is obtained.
J _total = k × I ₀ × {h ₁ · cos (ωt) + h ₂ · cos (ωt−2π / 3) + h ₃ · cos (ωt−4π / 3)} (7)

When the combined current J _total of the equation (7) is decomposed into the x component Jx and the y component Jy, equations (8a) and (8b) are obtained.
Jx = − (3/2) k · I ₀ · sin (ωt) (8a)
Jy = (3/2) k · I ₀ · cos (ωt) (8b)

Expressions (8a) and (8b) represent a current field that rotates every moment at the angular frequency ω, and the direction of the combined current J _total is given by θ = ωt [rad]. That is, according to the eddy current generator 10 of FIG. 1A, a combined current whose flowing direction rotates in synchronization with the drive currents I _{L1 to} I _L3 can be generated in the living tissue.

  Returning to FIG. The potential difference measuring device 30 includes a plurality of measurement electrodes e1 to e4 arranged on the surface of a living tissue (not shown). The number of the plurality of measurement electrodes e1 to e4 is not particularly limited, and may be six, eight, or more. The plurality of measurement electrodes e <b> 1 to e <b> 4 may be arranged and fixed on a disk (disk) 32.

Two measuring electrodes e1 and e2 facing each other make a pair, and e3 and e4 make a pair. When the combined current J _total is generated by the eddy current generator 10 as described above, the combined current J _total flows through the biological tissue having impedance, thereby generating a potential difference (voltage drop) between the two points of the biological tissue. To do. Specifically, a potential difference of ΔVx = Rx × Jx is generated between Ohm's law between the pair of measurement electrodes e1 and e2, and ΔVy = Ry × Jy between the measurement electrodes e3 and e4. A voltage drop occurs. Rx and Ry represent impedance components in the x direction and the y direction.

  Thus, according to the bioelectrical impedance measuring apparatus 100 according to the embodiment, the anisotropy of impedance can be measured by measuring the potential difference ΔV generated between a pair of opposing measuring electrodes.

(Second driving method)
Driver 12, a high-frequency carrier currents having a first frequency omega _1, the m drive current by amplitude modulated by m modulated signals S1~Sm having a second frequency omega ₂ lower than the first frequency omega ₁ I _{L1 to} I _Lm are generated. Then, by flowing m driving currents I _{L1 to} I _Lm through the coils _{L1 to Lm} of the electromagnets M1 to Mm, a combined current Jtotal whose flowing direction changes in synchronization with the modulation signals S1 to Sm is input into the living tissue. generate.

FIG. 3 is a block diagram illustrating a configuration example of the driving unit 12 that performs the second driving method. The high frequency oscillator 14 generates a carrier signal S4 (= cos ω ₁ t) having the first frequency ω ₁ . The modulation signal generation unit 15 generates three modulation signals S1 to S3. The multipliers 16a to 16c perform amplitude modulation by multiplying the carrier signal S4 by the modulation signals S1 to S3. The amplifiers 18a to 18c supply the outputs S5a to S5c of the multipliers 16a to 16c to the corresponding coils L1 to L3.

In a preferred embodiment, m = 3, and the three electromagnets M1 to M3 are arranged on substantially concentric circles that are spatially separated by 120 degrees. The m modulation signals S1 to S3 are the components of the three-phase symmetrical alternating current of the second frequency ω ₂ whose phases are shifted from each other by 120 degrees, and are given by the equations (9a) to (9c).
S1 = cos (ω ₂ t) (9a)
S2 = cos (ω ₂ t−2π / 3) (9b)
S3 = cos (ω ₂ t−4π / 3) (9c)

At this time, drive currents I _{L1 to} I _L3 are given by equations (10a) to (10c).
I _L1 = I ₀ · cos (ω ₁ t) · cos (ω ₂ t) (10a)
I _L2 = I ₀ · cos (ω ₁ t) · cos (ω ₂ t−2π / 3) (10b)
I _L3 = I ₀ · cos (ω ₁ t) · cos (ω ₂ t−4π / 3) (10c)

At this time, the x component and the y component of the combined current J _total are given by the equations (11a) and (11b), respectively.
Jx = − (3/2) k · I ₀ · cos (ω ₁ t) sin (ω ₂ t) (11a)
_{Jy = (3/2) k · I} 0 · cos (ω 1 t) · cos (ω 2 t) (11b)

In this driving method, the direction θ of the combined current J _total is given by ω ₂ t [rad], and a current field that rotates in synchronization with the second angular frequency ω ₂ can be generated.

4A and 4B are waveform diagrams showing the operation of the drive unit 12 of FIG. As shown in FIG. 4A, the modulation signals S1 to S3 may be signals obtained by quantizing (sampling) the signals given by the equations (9a) to (9c). FIG. 4A shows a case where a signal sampled by 12 times is used. In each of the time intervals A to F, the modulation signals S1 to S3 have the same level. As shown in FIG. 4 (b), the direction of the resultant current _{J total} for each time interval A~F may be discretely rotate with time.

Note that the modulation signals S1 to S3 do not necessarily need to be discretized, and three-phase AC components may be used as they are.
Alternatively, the waveforms of the modulation signals S1 to S3 are not limited to those in FIG. 4A, and for example, the phase angle θ may be scrambled. In other words, the order of the time intervals A to F may be arbitrarily changed.

(Second Embodiment)
FIG. 5 is a diagram illustrating a configuration of a bioimpedance measurement apparatus 100a according to the second embodiment. In the bioimpedance measuring apparatus 100a, the eddy current generating apparatus 10 is configured in the same manner as in FIG. 1A, and the configuration of the potential difference measuring apparatus 30a is different. Note that illustration and description of the configuration common to FIG.

  The potential difference measuring device 30a further includes a plurality of cancel electrodes (second electrodes) E1 to E6 and a control circuit 34 in addition to the plurality of measurement electrodes e1 to e6. The cancel electrodes E1 to E6 are arranged on the surface of the living tissue in the same manner as the measurement electrodes e1 to e6.

The control circuit 34 is connected to the plurality of measurement electrodes e1 to e6 and the plurality of cancellation electrodes E1 to E6. In FIG. 5, only the electrodes E1, e1, e4, E4 arranged on the same radiation are drawn to be connected to the control circuit 34, but the other electrodes are similarly connected. The control circuit 34 also has a function of the drive unit 12 that supplies drive currents I _{L1 to} I _L3 to the coils _{L1 to L3} .

In the bioimpedance measuring apparatus 100a of FIG. 5, the eddy current generator 10 changes the direction θ of the combined current _Jtotal . Then, in accordance with the direction θ of the resultant current _{J total,} among the plurality of measuring electrodes E1 to E6, the resultant current _J measurement electrodes disposed along a direction θ of the _total e1, e4 pair of e2 and e5 The impedance in the θ direction can be suitably measured by selecting one of the pair, e3 and e6, and measuring the potential difference generated in the selected pair of electrodes for measurement.

  In the measurement using only the measurement electrodes e1 to e6, the impedance near the surface of the living tissue can be measured. Below, the method of measuring the impedance of a deeper part from the surface of a biological body by combining the cancellation electrodes E1 to E6 with this will be described.

  The plurality of cancel electrodes E1 to E6 are arranged on the outer peripheral side of the plurality of measurement electrodes e1 to e6 at substantially equal intervals on a substantially concentric circle. The i-th cancel electrode Ei and the measurement electrode ei corresponding to each other are arranged in the same direction. Further, two opposing canceling electrodes E1 and E4, E2 and E5, and E3 and E6 form a pair. The impedance of the living body can be measured as follows by combining the canceling electrodes E1 to E6 and the measuring electrodes e1 to e6.

  Specifically, the control circuit 34 sets the pair of canceling electrodes E1 and E4 corresponding thereto so that the potential difference ΔV generated between the two opposing measuring electrodes e1 and e4 is substantially zero. The amplitude and phase of the high-frequency current energized during the period are controlled.

  As the control circuit 34, the technique described in Patent Document 1 (Japanese Patent No. 19009038) can be suitably used. FIG. 6 is a circuit diagram showing a configuration example of the control circuit 34 of FIG. The drive unit 12 includes a high-frequency oscillator 14, 120-degree phase shifters 17 and 19, and amplifiers 18a to 18c. The high frequency oscillator 14 generates a high frequency signal having a predetermined frequency. The phase shifters 17 and 19 shift the phase of the input high-frequency signal by 120 degrees. The amplifiers 18a to 18c output a three-phase AC signal whose phase is shifted by 120 degrees to the corresponding coils L1 to L3.

  Each of the multipliers 40a to 40c receives one corresponding potential difference among the pair of measurement electrodes (e25, e36, e41) and one corresponding among the three-phase AC signals, and multiplies them. Each of the rectifier / integrators 42a to 42c rectifies and integrates the output of the corresponding multiplier 40. Each of the multipliers 44a to 44c receives an output from the corresponding multiplier 40 and a corresponding one of the three-phase AC signals, and multiplies them. Each of the amplifiers 46a to 46c outputs a signal corresponding to the output of the corresponding multiplier 44 to any one of the corresponding cancel electrodes E25, E36, and E41. Refer to Patent Document 1 for details of the operation of the control circuit 34.

The operation of the bioimpedance measuring apparatus 100a in FIG. 5 will be described.
Assume that the combined current _Jtotal flows in the direction θ formed by the pair of measurement electrodes e1 and e4. At this time, by applying a voltage between the pair of cancel electrodes E1 and E4, a cancel current J _{cancel in the} opposite direction to the combined current J _total generated by the electromagnets M1 to M3 is generated. Since the cancel current J _cancel flows near the surface of the living tissue, the composite current J _total near the tissue surface can be canceled by the _cancel current J _cancel . At this time, the current value flowing between the pair of canceling electrodes E1 and E4 shows the impedance in the direction θ in a deep portion of the living tissue. Therefore, according to the bioimpedance measuring apparatus 100a of FIG. 5, it is possible to measure the impedance of a deep portion of the living tissue based on the value of the current flowing through the canceling electrode.

(Third embodiment)
FIG. 7 is a diagram illustrating a configuration of a bioimpedance measurement apparatus 100b according to the third embodiment. The bioimpedance measurement apparatus 100b according to the third embodiment can be used in combination with the bioimpedance measurement apparatus according to the first or second embodiment.

  The bioimpedance measurement apparatus 100b includes a plurality of measurement electrodes ee1, ff1, gg1 to ee6, ff6, and gg6 in addition to the plurality of measurement electrodes and / or cancellation electrodes arranged on the disk 32. The plurality of measurement electrodes ee1, ff1, gg1 to ee6, ff6, gg6 are arranged on the disk 36.

The operation of the bioimpedance measuring apparatus 100b will be described. The disk 32 and the disk 36 are arranged so as to sandwich the sample 2. That is, the plurality of measurement electrodes arranged on the disk 36 are installed in planes having different depths parallel to the surface formed by the lower end surfaces (end surfaces on the sample side) of the electromagnets M1 to M3. . In this state, a combined current J _total is generated by the disk 32 and the direction of the resultant is changed, and a pair of measurement electrodes adjacent in the radial direction (for example, ee1 and ff1, gg1 and ff1, ee4 and ff4, ff4 and gg4), respectively. By measuring the potential difference generated between the two, the impedance at the depth where the disk 36 is provided can be measured.

  In the third embodiment, only the cancel electrodes E1 to E6 may be provided on the disk 32 side, and the measurement electrodes e1 to e6 may be omitted.

(Fourth embodiment)
FIG. 8 is a diagram illustrating a configuration of a bioimpedance measurement apparatus 100c according to the fourth embodiment. The bioimpedance measurement apparatus 100c according to the fourth embodiment can be used in combination with the bioimpedance measurement apparatus according to the first or second embodiment.

  The bioimpedance measuring apparatus 100b includes a ferrite 50 and a spacer 52. The ferrite 50 is magnetically coupled in common to the second end surfaces of the plurality of electromagnets M1 to M3 (the surface opposite to the sample 2). A spacer 52 having a thickness d is inserted between the ferrite 50 and the second end faces of the electromagnets M1 to M3. The distance between the ferrite 50 and the electromagnets M1 to M3 can be adjusted by the spacer 52.

According to the bioimpedance measuring apparatus 100c of FIG. 7, the magnetic field distribution inside the sample 2 can be changed according to the thickness d of the spacer 52, and as a result, the depth at which the combined current _Jtotal is generated is changed. be able to. That is, when the distance d between the ferrite 50 and the electromagnets M1 to M3 is reduced, the magnetic field can be concentrated on the shallow layer portion of the sample 2, and the impedance of the shallow portion can be measured. On the contrary, when the distance d between the ferrite 50 and the electromagnets M1 to M3 is increased, the magnetic field can be concentrated on the deep layer portion of the sample 2 and the impedance of the deep portion can be measured.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 100 ... Bioimpedance measuring device, 10 ... Eddy current generator, 12 ... Drive part, 30 ... Potential difference measuring device, 32 ... Disk, 34 ... Control circuit, 36 ... Disk, 40 ... Multiplier, 42 ... Rectifier / integrator, 44 ... multiplier, 46 ... amplifier, 50 ... ferrite, 52 ... spacer, 2 ... sample.

Claims (9)

A bioimpedance measuring device for measuring impedance of a living tissue,
M electromagnets (m is an integer of 2 or more) arranged at substantially equal intervals on a substantially concentric circle, each end face being arranged to face the surface of the living tissue, and each electromagnet is connected to each coil. So as to change the direction of the combined current of eddy currents generated by the m electromagnets in the living tissue with time. An eddy current generator for changing the drive current flowing in the coils of each of the m electromagnets;
A potential difference measuring device having a plurality of measurement electrodes arranged on the surface of a biological tissue, and measuring a potential difference generated in the biological tissue by the eddy current using a pair of two measurement electrodes;
A bioimpedance measuring apparatus comprising:   The coils of each of the m electromagnets are supplied with a high-frequency drive current having the same frequency and shifted in phase by approximately (360 / M) degrees, and the flowing direction is synchronized with the drive current in the living tissue. The bioelectrical impedance measuring apparatus according to claim 1, wherein the combined current that rotates is generated.   M = 3, and the three electromagnets are arranged on substantially concentric circles separated by 120 degrees spatially, and a three-phase symmetrical high-frequency driving current is supplied to the coils of each electromagnet. The bioimpedance measurement apparatus according to claim 2.   The eddy current generator generates m drive currents by amplitude-modulating a high frequency carrier current having a first frequency with m modulation signals having a second frequency lower than the first frequency, and generates m drive currents. 2. The combined current in which the direction of flow changes in synchronization with the modulation signal is generated in the living tissue by flowing each of the drive currents of each of the currents through the coils of the m electromagnets. The bioimpedance measuring apparatus as described.   M = 3, the three electromagnets are arranged on substantially concentric circles spatially separated by 120 degrees, and the m modulation signals are three-phase symmetrical with the second frequency whose phases are shifted by 120 degrees from each other. The bioimpedance measuring apparatus according to claim 4, wherein each of the components is an alternating current component. The potential difference measuring device includes:
It further has a plurality of cancel electrodes arranged on the surface of the biological tissue,
This cancellation is performed by controlling the amplitude and phase of the high-frequency current that flows between the corresponding pair of cancel electrodes so that the potential difference generated between the two pairs of measurement electrodes facing each other becomes substantially zero. 6. The bioimpedance measuring apparatus according to claim 1, wherein an impedance in a direction formed by a corresponding pair of measurement electrodes is measured from a current value flowing between the pair of electrodes for measurement.   2. The bioimpedance measurement apparatus according to claim 1, wherein the plurality of measurement electrodes are installed in planes parallel to a plane formed by end faces of the m electromagnets and having different depths.   The at least one of the plurality of measurement electrodes and the plurality of cancellation electrodes is disposed in a plane parallel to a surface formed by end surfaces of the m electromagnets and having different depths. The bioimpedance measuring apparatus as described.   The second end face of the m electromagnets is further provided with a magnetically coupled ferrite, and the distance between the ferrite and the second end face of the m electromagnets is adjustable. The bioimpedance measuring apparatus according to any one of claims 1 to 8.

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