JPH06101384B2 - Method for measuring the temperature of the object to be heated in electromagnetic wave heating - Google Patents

Description

TECHNICAL FIELD The present invention relates to a temperature measuring method, and more particularly to a method of measuring a temperature of an object to be heated in electromagnetic wave heating.

(Prior Art) In recent years, hyperthermia has been attracting attention for the treatment of cancer. At that time, an accurate local temperature measurement technique including cancer cells and surrounding normal cells is essential.

Conventionally, in measuring the temperature in a living body, a sensor in which a piezoelectric vibrator having a resonance frequency having a temperature dependency such as a crystal resonator is connected to an antenna coil is surgically embedded in a desired portion in the living body. Is supplied to the piezoelectric vibrator through the antenna coil while irradiating it with electromagnetic wave energy of a required frequency from outside the body and observing the energy absorption phenomenon when it resonates, or the electromagnetic wave energy. There is a method of measuring the temperature by detecting the resonance frequency of the piezoelectric vibrator by, for example, receiving the reverberation of the piezoelectric vibrator immediately after the irradiation of No. 1 is stopped through the antenna coil.

As described above, the method of using the electromagnetic wave and using the piezoelectric vibrator such as the crystal vibrator for the temperature sensor is extremely effective in eliminating the cable between the in-vivo sensor and the extracorporeal device and performing accurate temperature measurement. In addition, as described above, it is extremely effective to configure the temperature sensor with a passive circuit so that there is no power supply when it is embedded in a living body for a long period of time.

However, as described above, in the method of utilizing the electromagnetic wave absorption phenomenon or the reverberation phenomenon using the temperature sensor with the passive circuit, the electromagnetic wave level obtained from this is extremely weak, and the measurement is very difficult.
There is a drawback in that the separation distance between the coil and the pick-up coil of the in vitro device cannot be made large.

Experiments show that the antenna coil of the in-vivo sensor and the pick of the extracorporeal device which are acceptable in the above-mentioned conventional method
The separation distance of the up coil is at most about 5 cm. For example, when measuring the temperature of the central part of the human body, the distance between the both coils is about 15 cm or more and it is impossible to measure as it is, so the sensor's piezoelectric vibrator and antenna It has been attempted to position the antenna coil near the surface of the human body by making the coil a long and narrow shape with a required separation or by extending both of them with a cable, but the sensor becomes large and it is extremely inconvenient. Met.

(Object of the Invention) The present invention has been made in view of the problems of the above-described temperature or pressure measuring method, and the measurement can be performed by increasing the electromagnetic wave energy level including the temperature information derived from the sensor. It is an object of the present invention to provide a method for measuring the temperature of an object to be heated in electromagnetic wave heating, which can be accurately and easily performed and can increase the separation distance between the sensor and the in vitro pick-up coil.

(Outline of the Invention) In order to achieve the above object, the present invention takes the following means.

That is, as one method of the thermotherapy for cancer described above, the affected area is irradiated with a high frequency of, for example, 13.56MHz or 2.45GHz, but the irradiation power at this time is generally extremely large, and if an example is given, it is 1.5KW. There is a degree.

Therefore, it would be convenient if the temperature of the object to be heated could be measured by effectively utilizing such high frequency heating electromagnetic waves.

Therefore, in the present invention, in addition to the high-power electromagnetic wave for heating, a small-power electromagnetic wave of a frequency different from this is similarly irradiated, and a nonlinear element for mixing the both high frequencies to the sensor and the frequency f _{mn of} this mixed component = Mf ₁ + nf ₂ (where m and n are positive or negative integers), the piezoelectric vibrator is selected so that electromagnetic waves generated as a result of the piezoelectric vibrator resonating are transmitted to the outside via the transmitting antenna coil. The temperature of the object to be heated is measured by radiating the electromagnetic waves to the outside and observing this electromagnetic wave outside.

(Example) Hereinafter, the present invention will be described in detail based on illustrated examples.

FIG. 1 is a circuit diagram showing an embodiment of a temperature sensor used in the present invention.

In the figure, L ₁ is a receiving antenna coil, a tuning capacitor C ₁ and a varactor as a non-linear element.
The diode D ₁ and the three elements are connected in parallel, and a series circuit of the crystal oscillator X and the transmission coil L ₂ is further added to form a sensor.

One example of a value of each element of the thus constructed sensor, a high-output electromagnetic wave f ₁ for irradiating from outside the heating now 13.5
The low output electromagnetic wave f ₂ emitted at the same time as 6MHz is 8MHz.
Then, the parallel resonance frequency of the antenna coil L ₁ and the capacitor C ₁ is set to, for example, a low output electromagnetic wave f ₂ = 8 MHz, and the resonance frequency ₀ of the crystal unit X is set to the sum of the two electromagnetic waves, that is, f _It is selected so that ₁ + f ₂ = 21.56 MHz, and the transmitting antenna coil L ₂ is a coil having a small inductance such that the resonance frequency ₀ of the crystal resonator X is not greatly changed.

Now, for example, when the sensor configured as described above is inserted into a required part of a human body and the high power electromagnetic wave for heating f ₁ = 13.56 MHz and the low power electromagnetic wave f ₂ = 8 MHz are simultaneously radiated to the antenna,
Both high frequency currents flow through the varactor diode D ₁ via the coil L ₁ and the capacitor C ₁ .

As is well known, in the varactor diode, the reactance component changes depending on the voltage applied across the varactor diode, and when another frequency component is applied to this, a combined frequency component of both is generated. This can be shown by a formula as follows.

f _mn = mf ₁ + nf ₂ (1) (where m; n is a positive or negative integer) The most important of these is the case of m = n = 1, which is expressed by the following formula f ₁₁ = f ₁ + f ₂ = 21.56MHz ……… It is the frequency component of the sum of both expressed by (2).

However, if the other _two frequency signals are applied to an element whose impedance changes with the applied voltage of frequency ₁ like the above-mentioned varactor diode and a high frequency signal is extracted from the combined frequency signals of both, the frequency The energy increases with the conversion, that is, an amplification effect is exhibited. The amplification degree G at this time is The gain G increases when converted to a frequency as high as possible. This is a so-called parametric amplification, which is a phenomenon generally used in an oscillation circuit.

Therefore, if the resonance frequency of the crystal resonator of the probe is set to be the sum of the electromagnetic waves f ₁ and f ₂ as described above, a larger resonance energy can be derived by utilizing the above-mentioned parametric amplification action.

That is, the varactor diode D ₁ causes a reactance change at a frequency of f ₁ = 13.56 MHz by the high power electromagnetic wave for heating and simultaneously emits a low power electromagnetic wave f ₂ = 8 MHz which is mixed with this and has a sum frequency of 21.56. It produces a signal component of MHz. The amplification degree at that time is G = 21.56 / 8≅2.7, which can be derived as larger energy by simply mixing the two to obtain the sum frequency component.

The signal current having a frequency of 21.56 MHz obtained in this way becomes maximum when resonating with the crystal oscillator, and is re-radiated to the outside through the transmitting antenna coil L ₂ .

Therefore, while observing the re-radiated electromagnetic wave, the frequency _{2 of the} low-output electromagnetic wave among the electromagnetic waves emitted from the outside is slightly changed, and the re-radiated electromagnetic wave frequency when the re-radiated electromagnetic wave energy is maximized is measured. Since it is the resonance frequency of the crystal oscillator X, the temperature of the object to be heated can be measured if the relation between the oscillator and the temperature is clear in advance.

In the above example, the frequency of the low-power electromagnetic wave f ₂ of the _two electromagnetic waves emitted from the outside is changed because it is generally easier for the low-power oscillator to change the frequency.
It is clear that the present invention is not limited to this, and the high-power electromagnetic wave f ₁ may be changed, and further various kinds of modulation may be applied to these.

Furthermore, the external measuring device may be any device as long as it fulfills the functions described above, but if it is constructed as shown in FIG. 2, for example, the measurement becomes easier.

That is, FIG. 2 is a block diagram showing an embodiment of an extracorporeal device used in the present invention, and the heating high-power electromagnetic wave generator is a separate device, and is not shown.

In the figure, reference numeral 1 is a variable frequency oscillator to which a transmitting antenna coil L ₃ is added, for example, a voltage controlled variable frequency oscillator (VO
C) and has a frequency control terminal 2 and an attenuator A
A DC voltage V is applied via TT.

Further, in order to observe the electromagnetic waves re-radiated by the probe, as shown in the figure, a high frequency amplifier 3 is connected to the receiving antenna coil L ₄ , and its output is observed by a level meter 4 and the frequency is measured by a frequency counter 5. To do.

In order to perform the above-mentioned temperature measurement using the external measuring device configured as described above, a high-power electromagnetic wave oscillator for heating (not shown) may be installed in parallel and two electromagnetic waves may be simultaneously irradiated.

In addition, if a circuit for detecting the peak of the re-radiated electromagnetic wave level is added to the external measuring device and the variable frequency oscillator 1 is controlled by its output so that the re-radiated electromagnetic wave level is always maximized, the temperature Automatic measurement is possible.

(Effect of the invention) As described above, the present invention utilizes high-power electromagnetic waves generally used as heating means, and applies low-power electromagnetic waves to a non-linear element such as a varactor diode whose impedance is changed by the electromagnetic waves. The temperature of the object to be heated is measured by observing the frequency at which the mixed frequency signal resonates with the temperature-dependent piezoelectric vibrator. Parametric amplification is performed because conversion to a high frequency is performed. Since it is possible to obtain a larger electromagnetic energy as compared with the conventional dip method or reverberation method, it is effective in facilitating the measurement and allowing a large distance between the sensor and the external measuring device.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a sensor used in the present invention, and FIG. 2 is a block diagram showing an embodiment of an extracorporeal measuring device used in the present invention. 1 ...... variable frequency oscillator, 2 ...... said variable frequency oscillator of a frequency control terminal, 3 ...... high frequency amplifier, 4 ...... level meter, 5 ...... frequency counter, L _1, L _2, L ₃ and L ₄ ...... Antenna coil C ₁ ... capacitor, D ₁ ... varactor diode.

Claims (2)

[Claims] 1. When measuring the temperature of an object to be heated by irradiating an electromagnetic wave (f ₁ ), a second electromagnetic wave (f ₂ ) different from the frequency (f ₁ ) of the electromagnetic wave is simultaneously irradiated. , A non-linear element for mixing the receiving antenna coil and the two electromagnetic waves, and a frequency f _mn = mf ₁ + nf ₂ (where, (m, n are positive or negative integers), and a sensor composed of a piezoelectric vibrator and a transmitting antenna coil whose resonance frequency has temperature dependence is attached to the outside of the heated object. In the electromagnetic wave heating method, the temperature of the object to be heated is measured by observing the frequency of the electromagnetic energy re-radiated by the sensor. 2. The receiving antenna coil and the transmitting antenna coil share the same coil, or one of them shares a part of the other coil. (1) A method for measuring a temperature of a heated object in heating an electromagnetic wave.