JP2010046181A - Electromagnetic wave transmitter/receiver and system with the electromagnetic wave transmitter/receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow more electromagnetic waves to enter the living body by an electromagnetic wave transmitter/receiver in a system for obtaining the difference and/or change in the dielectric constant of the living tissue by utilizing electromagnetic waves. <P>SOLUTION: The electromagnetic wave transmitter/receiver includes a transmitting means 2 for transmitting electromagnetic waves into the living body of a subject; a receiving means 2 for detecting the reflection waves of the electromagnetic waves transmitted into the living body from inside the living body; and n-layered dielectric layers 4 and 5 disposed without gaps between the transmitting and receiving means 2 and the skin 8 of the subject 7. The relation among the dielectric constant of the n-th dielectric layer ε<SB>n</SB>, the dielectric constant of air ε<SB>a</SB>and the dielectric constant of the skin of the subject ε<SB>b</SB>is; ε<SB>a</SB><ε<SB>1</SB><ε<SB>2</SB><...ε<SB>n</SB><ε<SB>b</SB>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a system for acquiring in-vivo information by causing electromagnetic waves to enter a living body and detecting a difference and / or change in dielectric constant of a living tissue from the reflected wave, and an electromagnetic wave transmitting / receiving device used in the system. Is.

  Currently, biometric information acquisition methods that detect differences or changes in the dielectric constant of biological tissues based on reflected waves of electromagnetic waves (microwaves) have been studied (Patent Document 1).

The principle of acquiring biological information using electromagnetic waves will be briefly described.
Substances are not limited to living tissues but have characteristic impedances that depend on the constituent medium. When radio waves propagate from one medium to another, reflection occurs at the interface and part of it is transmitted.

The characteristic impedance in vacuum is expressed by the following formula:

The impedance in a lossless medium with dielectric constant ε _r is

It is represented by

6, the dielectric constant epsilon _1, the dielectric D ₁ and the dielectric constant epsilon ₂ of the relative permeability mu _1, an electromagnetic wave reflection and transmission of the interface of the dielectric D ₂ relative permeability mu ₂ schematically illustrates It is a figure. The magnitude of the reflected / transmitted wave at the dielectric interface can be considered in the same way as the transmission line concept.

When an electromagnetic wave is incident from a dielectric having a characteristic impedance Z ₁ (relative permittivity ε ₁ ) to a dielectric having Z ₂ (relative permittivity ε ₂ ), the reflection coefficient Γ is expressed by the following equation (1).

Therefore, assuming that the incident signal E _i , the transmitted signal is E _t = (1 + Γ) · E _i
The reflected signal is E _r = Γ · E _i
It is expressed.

In general, the wavelength of electromagnetic waves in a medium is

Double. Since a living body is considered to be a non-magnetic material (relative magnetic permeability μ _r = 1),

Doubled.

  By applying this principle, early detection systems such as breast cancer have been studied. Breast cancer is close to the body surface and is in a tissue composed of relatively uniform fat (low noise). The difference in dielectric constant between cancer tissue and normal tissue is large, making it easy to take contrast. It is considered suitable. The relative permittivity of normal tissue and cancer tissue is 10 and 50 (for 2 GHz electromagnetic waves), and the reflectance at the interface between them is about 0.4.

  In Non-Patent Document 1, a simulation using a numerical phantom is performed, and it has been reported that a cancer having a size of 2 mm can be detected by the simulation using the numerical phantom.

In Non-Patent Document 2, as a method for measuring the internal temperature distribution of a living body or the like using electromagnetic waves (microwaves) by detecting a change in dielectric constant of the living tissue, the living body or the like is irradiated with microwaves. Measurement methods for measuring transmission characteristics have been proposed.
JP 2005-514996 A Bond, EJ; Xu Li; Hagness, SC; Van Veen, BD Microwave imaging via space-time beamforming for early detection of breast cancer, Antennas and Propagation, IEEE Transactions on Volume 51, Issue 8, Aug. 2003 1690-1705 Biological Information Visualization Technology Chapter 5 “Visualization of Electromagnetic Waves and Biological Information” Biological Information Visualization Technology Editorial Committee 1997 Corona

  As described above, a device that detects the difference in the dielectric constant of biological tissue and detects breast cancer early, or detects the change in dielectric constant due to the temperature of biological tissue and measures the temperature is researched. Although it has been developed, at present, the algorithm is mainly developed, and the practical application has not been sufficiently studied.

  When electromagnetic waves are actually incident into a living body, the difference in permittivity between air and skin is so large that most of the incident waves are reflected by the skin and cannot be sufficiently penetrated into the living body. Non-Patent Document 1 also shows that the intensity of the incident wave reflected by the skin is nearly three orders of magnitude (1000 times) greater than the reflected wave from the living body.

  At the present stage, which is an experimental stage, measurement is performed with a measurement object and an antenna placed in saline or oil with a constant dielectric constant, and cannot be applied to actual living body measurement as it is. In addition, the simulation in the above non-patent document shows that the reflected amount on the skin is subtracted from the acquired data in order to correct the reflection on the skin. When the dynamic range such as the number is matched with the reflected wave from the skin, there arises a problem that the sensitivity of detecting the reflected wave from the inside of the living body is remarkably lowered.

  This invention is made | formed in view of the said situation, Comprising: It aims at providing the electromagnetic wave transmitter / receiver which can propagate more incident waves in the living body. It is another object of the present invention to provide a system that can acquire a signal from a living body with good S / N.

The electromagnetic wave transmission / reception apparatus of the present invention is an electromagnetic wave transmission / reception apparatus that is used by being placed outside a test living body in a system that obtains a difference and / or change in dielectric constant of a biological tissue using electromagnetic waves,
A transmitting means for injecting electromagnetic waves into the living body of the test living body;
Receiving means for detecting a reflected wave from the inside of the living body of the electromagnetic wave incident on the inside of the living body;
When obtaining the difference and / or change in the dielectric constant, the transmission means and the reception means, and n dielectric layers disposed without gaps between the skin of the subject living body (here, , N is a natural number of 2 or more, and is 1, 2,... From the transmitting means or receiving means side.
When the dielectric constant of the nth dielectric layer is ε _n , the dielectric constant of air is ε _a , and the dielectric constant of the living body skin is ε _b ,
ε _a <ε ₁ <ε ₂ <... ε _n <ε _b
It is characterized by being in the relationship.

  Here, it is desirable that the total thickness of all the dielectric layers of the n dielectric layers is not less than the wavelength λ of the electromagnetic wave.

The dielectric constant of the n dielectric layers preferably satisfies the following formula.

  Moreover, it is desirable that the transmission means also serves as the reception means.

  A temperature measurement system according to the present invention includes the electromagnetic wave transmission / reception apparatus according to the present invention.

  The tumor detection system of the present invention comprises the electromagnetic wave transmitting / receiving apparatus of the present invention.

  According to the electromagnetic wave transmitting / receiving apparatus of the present invention, n dielectric layers (n ≧ 2) are provided between the transmitting means and the receiving means and the skin of the test organism, and the dielectric constant of the dielectric layer approaches the skin. Since the n or more dielectric layers are arranged so as to be close to the dielectric constant of the skin, the reflection of electromagnetic waves incident on the living body is suppressed on the skin, and the transmittance into the living body is increased. can do. Since reflection on the skin can be suppressed and the rate of incidence of incident waves into the living body can be increased, S / N can be improved.

  In addition, since the transmitting means and the receiving means are not brought into direct contact with the skin, it is possible to prevent rust and corrosion of the transmitting means and the receiving means and performance changes associated therewith.

  Furthermore, if the thickness of at least one dielectric layer is equal to or greater than the wavelength of the electromagnetic wave, the influence of the reflected wave from the skin can be excluded in terms of distance, and various in vivo information can be obtained from the reflected wave. This eliminates the need for a process for eliminating the reflected wave from the skin by calculation.

  Embodiments of the present invention will be described below.

<Electromagnetic wave transceiver>
First, an embodiment of the electromagnetic wave transmitting / receiving apparatus of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram of an electromagnetic wave transmitting / receiving apparatus according to the first embodiment.

An electromagnetic wave transmission / reception device 1 according to the first embodiment shown in FIG. 1 includes an antenna 2 serving as a transmission unit and a reception unit, and a printed resin substrate 4 (a first dielectric layer disposed so as to sandwich the antenna 2). FR4: Flame Retardant Type 4, dielectric constant ε ₁ ≈4) and polyurethane 5 (dielectric constant ε ₂ ≈6) which is the second dielectric layer disposed outside the printed resin substrate. The thickness d of the second dielectric layer is preferably equal to or greater than the wavelength λ of the electromagnetic wave transmitted and received. At the time of electromagnetic wave transmission / reception measurement using the electromagnetic wave transmission / reception device 1, the surface of the polyurethane 5 is disposed and used so as to contact the skin surface 8 of the test organism 7.

  For example, the antenna 2 is formed of a metal body. As the first dielectric layer, Teflon (registered trademark), FPC (polyimide), or the like may be used. As the second dielectric layer on the side in contact with the skin 8, it is desirable to select alcohols, urethane, and the like that are easily available and have a dielectric constant close to that of living skin.

The relative permittivity of air ε _a = 1, the permittivity of living body skin ε _b ≈38, and the relative permittivity of the first and second dielectric layers is ε _a <ε ₁ <ε ₂ <ε _b There is a relationship.

  The first and second dielectric layers 4 and 5 may be fixed so as not to be detached from the antenna 2, may be detachable, and at least transmit and reflect electromagnetic waves to the living body. It suffices if it can be inserted between the living body skin surface 8 and the antenna 2 with no gap when performing wave reception measurement.

Here, the effect of the electromagnetic wave transmitting / receiving apparatus of the present invention will be verified.
When no dielectric layer is inserted between the antenna 2 and the skin surface 8 of the living body, the relative dielectric constant ε _a = 1 of air and the dielectric constant ε _b = 38 of living body skin are radiated from the antenna. The transmission coefficient T (= 1 + Γ) when the electromagnetic wave incident on the skin of the living body is obtained from the above equation (1).

It is. On the other hand, for example, when urethane is inserted between the antenna and the skin of the living body, the relative permittivity of urethane is ε ₂ = 6, and the permittivity of the living body skin is ε _b = 38. The transmission coefficient T (= 1 + Γ) when incident on the skin of a living body is

It is.

  Thus, when there is no dielectric layer between the antenna and the skin of the living body, 28% is transmitted, whereas when a dielectric layer with a relative dielectric constant of 6 is present, 57% is transmitted. Will be.

  Thus, by inserting a dielectric layer having a dielectric constant between the dielectric constant of air and skin between the antenna and the skin of the living body, reflection of electromagnetic waves on the skin can be suppressed, and more It can be seen that the electromagnetic wave can be propagated into the living body.

  Even when the dielectric layer is provided, the incident wave is reflected with a reflectance of about 40%. At this time, in order to suppress interference between the incident wave and the reflected wave, it is desirable that the dielectric layer has a thickness of about one wavelength of the incident wave.

  In the above description, the case where only one dielectric layer is present has been described in order to simply explain the effects of the present invention. However, in the present invention, two layers are provided between the antenna serving as the transmitting / receiving means and the skin of the living body. The above dielectric layers are disposed. When two or more dielectric layers are arranged, the arrangement is made so that the dielectric constant of the dielectric layer on the living body side sequentially increases from the dielectric constant of the dielectric layer on the antenna side. In particular, it is possible to suppress reflection of electromagnetic waves at the dielectric layers and at each interface with the skin of the living body.

When the dielectric layer is multi-layered, it is preferable to select the dielectric material so that the product obtained by multiplying the dielectric layers and the reflection coefficient at each interface with the skin of the living body becomes small.
As shown in FIG. 1, when two dielectric layers are inserted between the antenna and the living skin, the dielectric constant of the first dielectric layer in contact with the antenna is ε ₁ , and the first dielectric When the dielectric constant of the second dielectric layer inserted between the body and the skin is ε ₂ and the skin is ε _b , after satisfying ε _a <ε ₁ <ε ₂ <ε _b ,

It is most preferred to select a dielectric material such that

Furthermore, when the dielectric layer is an n layer, the dielectric constant ε _n of the material of each dielectric layer satisfies ε _a <ε ₁ <ε ₂ <... Ε _n <ε _b ,

It is preferable to select materials so that By selecting the material in this way, the reflectance at the interface of each dielectric layer and the interface with the skin can be further suppressed, and the incident wave can be propagated into the living body more efficiently.

[Design change example]
In the embodiment shown in FIG. 1 described above, an example in which the antenna 2 is sandwiched between the printed resin substrates 4 is given. However, like the electromagnetic wave transmission / reception device 11 shown in FIG. 2, the antenna 2 is connected to the first dielectric layer. 14, and the second dielectric layer 15 may be arranged on the living body side.

<Embodiment of temperature measurement system>
An embodiment of a temperature measurement system provided with the electromagnetic wave transmitting / receiving apparatus of the present invention will be described with reference to FIG. The temperature measurement system is a system that detects a temperature change of a dielectric constant by detecting a temperature change of a dielectric constant. Here, a one-dimensional measurement system will be described.

  For example, when an electromagnetic wave of 1.5 GHz is used, the change in relative dielectric constant due to temperature change is 0.7% / deg. By utilizing the temperature dependence of the relative permittivity, changes in the temperature distribution in the body can be measured non-invasively.

The temperature measurement system 20 of this embodiment includes an electromagnetic wave transmission / reception apparatus 1 shown in FIG. 1, a control unit 21 that controls transmission / reception of electromagnetic waves by the antenna 2, and an oscillation unit 22 that oscillates transmission electromagnetic waves E _i transmitted from the antenna 2. And a temperature detector 23 for detecting the temperature based on the reflected wave _Er received by the antenna 2.

  At the time of temperature measurement, as shown in FIG. 3, the temperature in the target tissue 9 is measured with the surface of the second dielectric layer 5 of the electromagnetic wave transmitting / receiving apparatus 1 in contact with the skin surface 8 of the test organism 7.

  First, an ultrashort pulse is transmitted from the antenna. The pulse is a differential Gaussian pulse having a width of 200 ps, for example, and has a center frequency of about 4 GHz. Note that when a 4 GHz electromagnetic wave is used, the change in relative dielectric constant due to temperature change is 0.5% / deg. The reflected wave of this pulse is received by the antenna and recorded in the temperature detector.

  In the temperature detection unit, the change in dielectric constant of the portion corresponding to the time delay corresponding to the measurement distance previously measured by MRI or the like of the reflected wave, such as the thickness of fat, is converted into a temperature change. Since the S / N in reflected wave detection can be improved by providing the electromagnetic wave transmission / reception device of the present invention like the temperature measurement system 20, the accuracy of temperature measurement can also be improved.

<Embodiment of tumor detection system>
Next, a breast cancer detection system will be described as an embodiment of a tumor detection system provided with the electromagnetic wave transmission / reception device of the present invention.

  As shown in FIG. 4, the breast cancer detection system 30 of the present embodiment includes a plurality of (herein, twelve) electromagnetic wave transmission / reception devices 1A to 1L and a control unit 31 that controls transmission / reception of electromagnetic waves by the electromagnetic wave transmission / reception devices 1A to 1L, An oscillation unit 32 that oscillates a transmission electromagnetic wave transmitted from an antenna, and a detection unit 33 that detects breast cancer based on a reflected wave received by the antenna are provided.

  At the time of measurement, as shown in FIG. 4, a plurality (here, 12) of electromagnetic wave transmitting / receiving devices are arranged in contact with the mammo 35.

  FIG. 5 is a diagram for explaining a two-dimensional cross section of a mammo 35 having a tumor portion 36, an arrangement of the electromagnetic wave transmitting / receiving devices 1A to 1L with respect to the mammo 35, and a radar algorithm in an XY cross section. As shown in FIG. 5, the electromagnetic wave transmission / reception devices 1 </ b> A to 1 </ b> L are respectively arranged at X coordinates of X <b> 1 to X <b> 12 in the XY cross section. By dividing the cross section of the mammo 35 into a plurality of regions and calculating the intensity of the reflected wave from the region for each of the divided regions (coordinate points), the dielectric constant difference in each region can be imaged. .

Hereinafter, a radar algorithm for the tumor portion 36 in the mammo 35 will be described.
As shown in FIG. 4 and FIG. 5, measurement is performed in a state where a plurality (m = 12) of electromagnetic wave transmitting / receiving devices are arranged in contact with the surface of the mammo 35 along the surface of the mammo 35.

1) Ultrashort pulses are transmitted from the antennas of the electromagnetic wave transmitting / receiving apparatuses 1A to 1L. The ultrashort pulse is a differential Gaussian pulse with a width of 200 ps and has a center frequency of about 4 GHz.

2) The reflected wave of this pulse is received by the antenna and recorded by the detector 33. It is recorded as a reflected wave sequence for m antennas.

3) In this reflected wave series, the reflection of the incident wave on the skin is dominant, but the scattered signal due to the non-uniformity of the normal waveform of the reflected waveform from the tumor is averaged and the scattered signal is negligible. It has become. However, the reflection on the skin is small compared to the case where there is no dielectric layer between the skin and the antenna. When there is no dielectric layer between the skin and the antenna, in each reflected wave train, the reflection from the skin appears large at the earliest time and is an unnecessary signal. It is necessary to remove it. In that case, m waveform sequences are added and a reference waveform sequence is generated by taking an average, and by subtracting this reference waveform sequence from each of the m wave sequences, an incident wave and a reflected wave from the skin are obtained. The corrected m wave series removed are obtained.
In this embodiment, since the dielectric layer is inserted between the antenna and the skin, reflection on the skin is suppressed, and the thickness of the dielectric layer is one or more wavelengths of the transmitted / received electromagnetic wave. There is no need to eliminate the signal due to the reflected wave.

4) Taking a moving average of the total reflected wave trains and subtracting from each reflected wave train eliminates the low frequency signal and generates m target wave sequences.

5) The amplitude intensity of the coordinate point is derived by adding the waveform sequence obtained by shifting the distance from the coordinate point of the mammo 35 specifying these m waveform sequences to each antenna to the time.

6) Repeat the operation of 5) for the divided coordinate points. For example, the division is performed at 1 mm intervals and coordinated.

7) An amplitude intensity at each coordinate point is obtained, and by imaging this, a relative difference in dielectric constant for each coordinate in the XY cross section can be expressed.

  Since the S / N in reflected wave detection can be improved by providing the electromagnetic wave transmission / reception apparatus of the present invention like the present breast cancer detection system 30, the accuracy of tumor detection can also be improved.

The schematic diagram which shows embodiment of the electromagnetic wave transmitter-receiver of this invention The schematic diagram which shows the example of a change of the electromagnetic wave transmitter-receiver of this invention Overall view showing an embodiment of the temperature detection system of the present invention Overall view showing an embodiment of the breast cancer detection system of the present invention Schematic diagram showing cross section of mammo and arrangement of electromagnetic wave transmitting / receiving device Diagram for explaining reflection and transmission of electromagnetic waves

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 11, 1A-1L Electromagnetic wave transmission / reception apparatus 2 Antenna 4, 14 1st dielectric layer 5, 15 2nd dielectric layer 20 Temperature detection system 21 Control part 22 Oscillation part 23 Temperature detection part 30 Breast cancer detection system 31 Control Unit 32 Oscillating unit 33 Detection unit 35 Mammo (breast)
36 Tumor

Claims (6)

In a system for obtaining a difference and / or change in dielectric constant of a living tissue using electromagnetic waves, an electromagnetic wave transmitting / receiving device used by being placed outside a test organism,
A transmitting means for injecting electromagnetic waves into the living body of the test living body;
Receiving means for detecting a reflected wave from the inside of the living body of the electromagnetic wave incident on the inside of the living body;
When obtaining the difference and / or change in the dielectric constant, the transmission means and the reception means, and n dielectric layers disposed without gaps between the skin of the subject living body (here, , N is a natural number of 2 or more, and is 1, 2,... From the transmitting means or receiving means side.
When the dielectric constant of the nth dielectric layer is ε _n , the dielectric constant of air is ε _a , and the dielectric constant of the living body skin is ε _b ,
ε _a <ε ₁ <ε ₂ <... ε _n <ε _b
An electromagnetic wave transmitting and receiving apparatus characterized by   2. The electromagnetic wave transmitting / receiving apparatus according to claim 1, wherein a total thickness of all the dielectric layers of the n dielectric layers is not less than a wavelength [lambda] of the electromagnetic wave. 3. The electromagnetic wave transmitting / receiving apparatus according to claim 1, wherein a dielectric constant of the n dielectric layers satisfies the following formula.

  The electromagnetic wave transmission / reception apparatus according to claim 1, wherein the transmission unit also serves as the reception unit.   A temperature measurement system comprising the electromagnetic wave transmission / reception device according to claim 1.   A tumor detection system comprising the electromagnetic wave transmission / reception device according to any one of claims 1 to 4.

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