JP7524958B2 - TEMPERATURE ESTIMATION METHOD, TEMPERATURE ESTIMATION PROGRAM, AND TEMPERATURE ESTIMATION DEVICE - Google Patents

Description

The present invention relates to a temperature estimation method, a temperature estimation program, and a temperature estimation device for estimating the internal temperature of a subject such as a living body.

A method for estimating the deep body temperature of a living body is known, as disclosed in Patent Document 1. The method disclosed in Patent Document 1 estimates the deep body temperature T _CBT of the living body 100 using a thermal equivalent circuit model of the living body 100 and the sensor 101 as shown in FIG. 10. The sensor 101 measures the temperature T _skin of the skin surface of the living body 100 and the heat flux H _S of the skin surface. T _top is the temperature of the top surface of the sensor 101 opposite to the surface in contact with the skin of the living body 100, T _Air is the outside air temperature, R _B is the thermal resistance of the living body 100, R _S is the thermal resistance of the sensor 101, and R _A is the thermal resistance of the outside air. The equation for estimating the deep body temperature T _CBT is as follows.
T _CBT = T _skin + AH _S ... (1)

The proportionality coefficient A in formula (1) is determined by the thermal property value of the living body 100. In general, the proportionality coefficient A can be calculated by using the deep body temperature T _CBT , which is the rectal temperature or tympanic membrane temperature measured using a different sensor during initial calibration, and this deep body temperature T _CBT , the temperature T _skin measured by the sensor 101, and the heat flux H _S .

In the conventional method, the thermal property values of the living body 100 are constant, and the proportionality coefficient A is also constant. However, the thermal property values vary from person to person, and also fluctuate if the blood flow of the living body 100 increases or decreases during measurement of the deep body temperature T _CBT . Due to this fluctuation in the thermal property values, the conventional method has a problem in that errors occur in the estimation of the deep body temperature T _CBT .

JP 2020-3291 A

The present invention has been made to solve the above-mentioned problems, and aims to provide a temperature estimation method, a temperature estimation program, and a temperature estimation device that can reduce the estimation error of the internal temperature of a subject such as a living body.

The temperature estimation method of the present invention includes a first step of measuring a temperature of a surface of an object to be measured by a third temperature sensor before an insulating material having a first temperature sensor and a second temperature sensor provided on both sides thereof comes into contact with an object to be measured; a second step of measuring a temperature of the insulating material before contact between the insulating material and the object to be measured by the second temperature sensor provided on a surface of the insulating material opposite to the surface of the insulating material facing the object to be measured; a third step of measuring a temperature of the surface of the object to be measured after contact between the insulating material and the object to be measured by the first temperature sensor provided on the surface of the insulating material facing the object to be measured; a fourth step of measuring a temperature of the insulating material before contact between the insulating material and the object to be measured, the temperature of the insulating material before contact between the insulating material and the object to be measured, the temperature of the surface of the object to be measured before contact between the insulating material and the object to be measured, and the temperature of the surface of the object to be measured after contact between the insulating material and the object to be measured. a fifth step of calculating the thermal diffusivity of the specimen based on the temperature of the specimen; a sixth step of deriving a proportionality coefficient that depends on the thermal property value of the specimen based on the thermal diffusivity; a seventh step of measuring the temperature of the surface of the specimen using the first temperature sensor; an eighth step of measuring the temperature at a position away from the specimen using the second temperature sensor; and a ninth step of calculating the internal temperature of the specimen based on the measurement results of the seventh and eighth steps and the proportionality coefficient , wherein the fifth step includes a step of calculating a temperature by correcting the measurement result of the third step based on the temperatures measured in the third and fourth steps after contact between the insulating material and the specimen and the temperatures measured again in the third and fourth steps after a predetermined time has elapsed, and setting this corrected temperature as the surface temperature of the specimen after contact between the insulating material and the specimen .
A temperature estimation program according to the present invention is characterized in that it causes a computer to execute the fifth, sixth and ninth steps.

The temperature estimation device of the present invention is characterized in that it comprises an insulating material, a first temperature sensor provided on a surface of the insulating material facing the specimen, a second temperature sensor provided on a surface of the insulating material opposite to the surface facing the specimen, a third temperature sensor configured to measure the temperature of the surface of the specimen before contact between the insulating material and the specimen, a thermal diffusivity calculation unit configured to calculate the thermal diffusivity of the specimen based on the temperature of the insulating material measured by the second temperature sensor before contact between the insulating material and the specimen, the temperature of the surface of the specimen measured by the third temperature sensor before contact between the insulating material and the specimen, and the temperature of the surface of the specimen measured by the first temperature sensor after contact between the insulating material and the specimen, a proportionality coefficient derivation unit configured to derive a proportionality coefficient that depends on a thermal property value of the specimen based on the thermal diffusivity, and a temperature calculation unit configured to calculate the internal temperature of the specimen based on the measurement results of the first and second temperature sensors after contact between the insulating material and the specimen and the proportionality coefficient.

According to the present invention, the thermal diffusivity of the specimen is calculated based on the temperature of the insulating material before contact between the insulating material and the specimen, the temperature of the surface of the specimen before contact between the insulating material and the specimen, and the temperature of the surface of the specimen after contact between the insulating material and the specimen; a proportionality coefficient that depends on the thermal property values of the specimen is derived based on the thermal diffusivity; and the internal temperature of the specimen is calculated based on the surface temperature of the specimen, the temperature at a position away from the specimen, and the proportionality coefficient. This makes it possible to correct the proportionality coefficient that varies depending on individual differences and blood flow in the specimen, thereby reducing the estimation error of the internal temperature of the specimen.

FIG. 1 is a diagram showing an example of changes in temperature of a sensor and a living body over time. FIG. 2 is a diagram showing an example of the relationship between the skin surface temperature of a living body after contact with an object and the thermal diffusivity of the living body. FIG. 3 is a block diagram showing a configuration of a temperature estimation device according to an embodiment of the present invention. FIG. 4 is a diagram showing a thermal equivalent circuit model of a heat insulating material, a temperature sensor, and a living body according to an embodiment of the present invention. FIG. 5 is a flowchart illustrating the operation of the temperature estimation device according to the embodiment of the present invention. FIG. 6 is a diagram illustrating the operation of the temperature correction unit according to the embodiment of the present invention. FIG. 7 is a diagram showing an example of the relationship between the proportionality coefficient and the thermal diffusivity of a living body. FIG. 8 is a diagram showing the deep body temperature estimated by the temperature estimation device according to the embodiment of the present invention and the tympanic membrane temperature measured by a tympanic membrane thermometer. FIG. 9 is a block diagram showing an example of the configuration of a computer that realizes a temperature estimation device according to an embodiment of the present invention. FIG. 10 is a diagram showing a thermal equivalent circuit model of a living body and a sensor.

[Principle of the Invention]
The way heat is transferred is generally described by the heat conduction equation (2).

In formula (2), α is the thermal diffusivity, which is an inherent value of an object, T is the temperature, z is the coordinate in the depth direction, and t is time. Consider one-dimensional heat transfer as shown in Fig. 10. Here, consider the case where the object is sufficiently thick or the temperature observation time is short. When expressed as a Fourier number F = αt/ ^L2 (L is the thickness of the object), it is desirable for F < 0.1 to be true.

As shown in Figure 1, when the sensor 101 and the living body 100 come into contact, heat is exchanged between the sensor 101 and the living body 100 via the contact interface, causing a change in temperature. The temperature inside the living body 100 changes from moment to moment. In the example of Figure 1, as time t passes, the temperature changes from the temperature indicated by Ta to the temperature indicated by Tb, and then to the temperature indicated by Tc. Meanwhile, the temperature of the contact interface between the sensor 101 and the living body 100 (Td in Figure 1) remains constant from the time of contact.

From equation (2), the temperature distribution T(z, t) within the living body 100 and the heat flux q at the contact interface can be calculated using the internal temperature T _i of the living body 100 before contact with the sensor 101 as shown in equations (3) and (4).

In formula (3), erf() is an error function. Since the heat flux q at the contact interface is continuous between the sensor side and the living body side, according to formula (4), the skin surface temperature T _skin of the living body 100 after contact with the sensor 101 is determined by the temperature T _sensor of the sensor 101 before contact and the skin surface temperature T _body of the living body 100 before contact, as shown in formula (5).

In formula (5), α _sensor is the thermal diffusivity of the sensor 101, and α _body is the thermal diffusivity of the living body 100. An example of the relationship between the skin surface temperature T _skin of the living body 100 and the thermal diffusivity α body of the living body 100 after the living body 100 at 35° C. is brought into contact with an object at 20° C. that has a thermal diffusivity similar to that of the living _body 100 is shown in FIG.

By modifying equation (5), the thermal diffusivity α _body of the living body 100, which is an unknown parameter, can be solved as in equation (6).

If the temperature T _sensor of the sensor 101 before contact, the skin surface temperature T _body of the living body 100 before contact, and the skin surface temperature T _skin of the living body 100 after contact can be measured, the thermal diffusivity coefficient α _body , which is a thermal characteristic of the living body 100, can be calculated by equation (6). Then, it becomes possible to derive the proportionality coefficient A from the thermal diffusivity coefficient α _body .

[Example]
An embodiment of the present invention will now be described with reference to the accompanying drawings, in which: Fig. 3 is a block diagram showing the configuration of a temperature estimation device according to an embodiment of the present invention; The temperature estimation device comprises an insulating material 1, a temperature sensor 2 provided on the surface of the insulating material 1 facing the living body 100 (subject), a temperature sensor 3 provided on the surface of the insulating material 1 opposite the surface facing the living body, a temperature sensor 4 for measuring the skin surface temperature T _body of the living body 100 before contact between the insulating material 1 and the living body 100, a memory unit 5 for pre-storing a calibration table in which a proportionality coefficient A corresponding to the thermal diffusivity coefficient α _body of the living body 100 is registered, a temperature correction unit 6 for correcting the temperature measured by the temperature sensor 2 after contact between the insulating material 1 and the living body 100, a thermal diffusivity calculation unit 7 for calculating the thermal diffusivity coefficient α _body of the living body 100, a proportionality coefficient derivation unit 8 for deriving the proportionality coefficient A based on the thermal diffusivity coefficient α _body of the living body 100, a temperature calculation unit 9 for calculating a deep body temperature T _CBT (internal temperature) of the living body 100 based on the measurement results of the temperature sensors 2 and 3 and the proportionality coefficient A, and a communication unit 10 for transmitting the calculation result of the deep body temperature T _CBT to an external terminal 11.

The temperature estimation device is positioned so that the insulating material 1 is in contact with the skin of the living body 100. The temperature sensor 2 is provided on the surface of the insulating material 1 facing the living body. The temperature sensor 3 is provided on the surface of the insulating material 1 opposite the surface facing the living body so as to be in contact with the air. The insulating material 1 holds the temperature sensors 2 and 3, and acts as a resistor against the heat flowing into the temperature sensor 2. As the temperature sensors 2 and 3, for example, a known thermistor or a thermopile using a thermocouple can be used.

On the other hand, the temperature sensor 4 measures the skin surface temperature T _body of the living body 100 before contact between the insulating material 1 and the living body 100. As the temperature sensor 4, a sensor capable of measuring with minimal effect on the temperature of the living body 100 is preferable. Such a temperature sensor 4 may be a non-contact radiation thermometer or a small sensor probe with a small heat capacity.

Figure 4 shows a thermal equivalent circuit model of the insulating material 1, temperature sensors 2 and 3, and the living body 100. In this embodiment, the thermal equivalent circuit model is the same as in the conventional embodiment, so it will be explained using the same symbols as in Figure 10.

5 is a flow chart for explaining the operation of the temperature estimation device of this embodiment. First, the temperature sensor 4 measures the skin surface temperature T _body of the living body 100 before the heat insulating material 1 comes into contact with the living body 100 (step S100 in FIG. 5). The measurement data of the temperature sensor 4 is stored in the memory unit 5.

The temperature sensor 3 measures the temperature T _sensor of the heat insulating material 1 before the heat insulating material 1 comes into contact with the living body 100 (step S101 in FIG. 5). The measurement data of the temperature sensor 3 is stored in the storage unit 5.
It is preferable that before contact with the living body 100, the temperature measured by the temperature sensor 2 and the temperature measured by the temperature sensor 3 are substantially equal.

Next, the user of the temperature estimation device brings the insulating material 1 into contact with the living body 100. The temperature sensor 2 measures the skin surface temperature _T1 of the living body 100 (step S102 in FIG. 5). The temperature sensor 3 measures the temperature _T2 at a position away from the living body 100 (step S103 in FIG. 5). The measurement data of the temperature sensors 2 and 3 are stored in the memory unit 5.

The temperatures _T1 and _T2 are continuously measured. When the time Δt has elapsed (YES in step S104 in FIG. 5), the temperature correction unit 6 calculates the skin surface temperature T skin by correcting the temperature _T1 based on the temperatures _T1 and _T2 measured by the temperature sensors 2 and ₃ and the temperatures T1 and _T2 measured again by the temperature sensors 2 and ₃ after the time Δt has elapsed (step S105 in FIG. 5).

6 is a diagram for explaining the operation of the temperature correction unit 6. Depending on the size of the temperature sensor 2 itself, the temperature sensor 2 may be measuring a temperature slightly distant from the skin surface of the living body 100. Therefore, it is desirable to obtain the skin surface temperature T _skin by extrapolation using the temperature T2 measured by the temperature sensor 3 as well.

Specifically, the temperature correction unit 6 estimates the temperature data (straight line L0 in Figure 6) for each position by extrapolation based on the temperatures _T1to , _T2t0 measured by the temperature sensors 2, ₃ at time _t0 after contact between the insulating material 1 and the living body 100.
Similarly, the temperature correction unit 6 estimates the temperature data (straight _{line L1 in Figure 6) for each position by extrapolation based on the temperatures T1t1 , T2t1} measured by the temperature sensors 2, 3 at time _t1 ( _t1 > _t0 ), which is Δt after time _t0 .

Then, the temperature correction unit 6 _determines the intersection of a straight line _L0 of the temperature data sequence estimated from the temperatures _T1to and _T2t0 at time _t0 and a straight line _L1 of the temperature data sequence estimated from the temperatures _T1t1 and _T2t1 at time t1 as the skin surface temperature _Tskin . Since the distance between the temperature sensors 2 and 3 is known, it is possible to estimate temperature data for each position closer to the living body 100 than the temperature sensor 2.

In this embodiment, it is necessary for the temperature estimation device to be able to recognize contact between the insulating material 1 and the living body 100. For example, a user of the temperature estimation device inputs a measurement start command signal to the temperature estimation device after bringing the insulating material 1 into contact with the living body 100. By inputting this measurement start command signal, the temperature correction unit 6 of the temperature estimation device can recognize that the insulating material 1 and the living body 100 have come into contact.

Next, the thermal diffusivity calculation unit 7 calculates the thermal diffusivity α body of the living body 100 by equation (6) based on the temperature T _sensor of the insulating material 1 measured by the temperature sensor 3 before the contact between the insulating material 1 and the living body 100 (before the measurement start command signal is input), the skin surface temperature T _body of the living body 100 measured by the temperature _sensor 4 before the contact, and the skin surface temperature T _skin of the living body 100 after the contact (step S106 in FIG. 5). The thermal diffusivity α _sensor of the insulating material 1 is a known value.

In this embodiment, the skin surface temperature T _skin obtained by the temperature correction unit 6 is used, but the temperature correction unit 6 is not an essential component of the present invention. The temperature T ₁ measured by the temperature sensor 2 after the heat insulating material 1 comes into contact with the living body 100 may be used as the skin surface temperature T _skin as it is.

Next, the storage unit 5 stores in advance a calibration table in which the proportionality coefficient A is registered for each thermal diffusivity α _body .
The proportionality coefficient derivation unit 8 obtains the value of the proportionality coefficient A corresponding to the thermal diffusivity α _body calculated by the thermal diffusivity calculation unit 7 from the calibration table in the storage unit 5, thereby deriving the proportionality coefficient A (step S107 in FIG. 5).

7 is a diagram showing an example of the relationship between the proportionality coefficient A and the thermal diffusivity α _body . In this embodiment, the equation for estimating the core body temperature T _CBT of the living body 100 is as follows.
T _CBT = T _skin + A (T _skin - T _top ) ... (7)

To obtain the experimental value of the proportionality coefficient A plotted in Fig. 7, the temperature T _skin of the surface of a pseudo-biological sample such as a polymer whose thermal diffusivity α is known in advance is measured by the temperature sensor 2, and the temperature T _top of a position away from the pseudo-biological sample is measured by the temperature sensor 3. Furthermore, if the internal temperature T _CBT of the pseudo-biological sample in the area around the thermal insulation material 1 is measured by, for example, the heat flow compensation method, the proportionality coefficient A corresponding to the thermal diffusivity α can be calculated by the formula (7). By obtaining such experimental values of the proportionality coefficient A for various pseudo-biological samples with different thermal diffusivities α, a calibration table can be created in advance. Alternatively, the relationship between the proportionality coefficient A and the thermal diffusivity α _body may be obtained by numerical calculation.

Next, the temperature sensor 2 measures the skin surface temperature T _skin of the living body 100 (step S108 in FIG. 5). The temperature sensor 3 measures the temperature T _top at a position away from the living body 100 (step S109 in FIG. 5). The measurement data of the temperature sensors 2 and 3 are stored in the memory unit 5.

The temperature calculation unit 9 calculates the core body temperature T _CBT of the living body 100 using equation (7) based on the temperatures T _skin and T _top measured by the temperature sensors 2 and 3 and the proportionality coefficient A derived by the proportionality coefficient derivation unit 8 (step S110 in FIG. 5). Note that calculating T _skin -T _top as in equation (7) is equivalent to calculating the heat flux H _S in equation (1). Also, as in step S105, the value obtained by correcting the temperature measured by the temperature sensor 2 using the temperature correction unit 6 may be set as T _skin .

The communication unit 10 transmits the calculation result of the temperature calculation unit 9 to the external terminal 11 (step S111 in FIG. 5). The external terminal 11, which may be a PC (Personal Computer) or a smartphone, displays the value of the core body temperature T _CBT received from the temperature estimation device.

The temperature estimation device performs the above steps S108 to S111 at regular intervals, for example, until the user instructs the device to end measurement (YES in step S112 in Figure 5).

Fig. 8 shows the deep body temperature T _CBT estimated in this embodiment and the deep body temperature (tympanic membrane temperature) measured by a tympanic membrane thermometer for comparison. 80, 81, 82, and 83 in Fig. 8 show the results for different living bodies 100. Fig. 8 shows that the estimation result close to the tympanic membrane temperature is obtained by this embodiment.

The memory unit 5, temperature correction unit 6, thermal diffusivity calculation unit 7, proportionality coefficient derivation unit 8, temperature calculation unit 9, and communication unit 10 described in this embodiment can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in Figure 9.

The computer comprises a CPU 200, a storage device 201, and an interface device (I/F) 202. The I/F 202 is connected to the hardware of the sensors 2 to 4 and the communication unit 10. In such a computer, a temperature estimation program for realizing the temperature estimation method of the present invention is stored in the storage device 201. The CPU 200 executes the processing described in this embodiment in accordance with the program stored in the storage device 201.

The present invention can be applied to technology for estimating the internal temperature of a subject such as a living body.

1...insulating material, 2 to 4...temperature sensors, 5...memory unit, 6...temperature correction unit, 7...thermal diffusivity calculation unit, 8...proportionality coefficient derivation unit, 9...temperature calculation unit, 10...communication unit, 11...external terminal.

Claims (6)

a first step of measuring a temperature of a surface of an object to be inspected by a third temperature sensor before an insulating material having a first temperature sensor and a second temperature sensor provided on both sides of the insulating material contacts the object;
a second step of measuring a temperature of the heat insulating material before the heat insulating material comes into contact with the test object by the second temperature sensor provided on a surface of the heat insulating material opposite to the surface of the heat insulating material facing the test object;
a third step of measuring a temperature of a surface of the test object after the heat insulating material comes into contact with the test object by the first temperature sensor provided on the surface of the test object of the heat insulating material;
a fourth step of measuring a temperature at a position away from the test object by the second temperature sensor after the heat insulating material comes into contact with the test object ;
a fifth step of calculating a thermal diffusivity of the specimen based on a temperature of the insulating material before contact between the insulating material and the specimen, a temperature of a surface of the specimen before contact between the insulating material and the specimen, and a temperature of the surface of the specimen after contact between the insulating material and the specimen;
a sixth step of deriving a proportionality coefficient that depends on a thermal property value of the object based on the thermal diffusivity;
a seventh step of measuring a temperature of the surface of the object by the first temperature sensor;
an eighth step of measuring a temperature at a position away from the subject by the second temperature sensor;
a ninth step of calculating an internal temperature of the object based on the measurement results of the seventh and eighth steps and the proportionality coefficient ;
The temperature estimation method characterized in that the fifth step includes a step of calculating a temperature by correcting the measurement result of the third step based on the temperature measured in the third and fourth steps after contact between the insulating material and the specimen and the temperature measured again in the third and fourth steps after a predetermined time has elapsed, and setting this corrected temperature as the temperature of the surface of the specimen after contact between the insulating material and the specimen . 2. The temperature estimation method according to claim 1,
The temperature estimation method, wherein the sixth step includes a step of deriving a proportionality coefficient by obtaining a value of the proportionality coefficient corresponding to the thermal diffusivity calculated in the fifth step from a calibration table stored in advance. 3. A temperature estimation program for causing a computer to execute the fifth step, the sixth step, and the ninth step according to claim 1 or 2 . Insulation material;
a first temperature sensor provided on a surface of the thermal insulation material facing the subject;
a second temperature sensor provided on a surface of the heat insulating material opposite to the surface on the subject side;
a third temperature sensor configured to measure a temperature of a surface of the specimen before contact between the insulating material and the specimen;
a thermal diffusivity calculation unit configured to calculate a thermal diffusivity of the specimen based on a temperature of the insulating material measured by the second temperature sensor before contact between the insulating material and the specimen, a surface temperature of the specimen measured by the third temperature sensor before contact between the insulating material and the specimen, and a surface temperature of the specimen measured by the first temperature sensor after contact between the insulating material and the specimen;
a proportionality coefficient derivation unit configured to derive a proportionality coefficient that depends on a thermal property value of the subject based on the thermal diffusivity;
A temperature estimation device comprising: a temperature calculation unit configured to calculate the internal temperature of the subject based on the measurement results of the first and second temperature sensors after contact between the insulating material and the subject and the proportionality coefficient. 5. The temperature estimation device according to claim 4 ,
a storage unit configured to store in advance a calibration table in which the proportionality coefficient corresponding to the thermal diffusivity is registered for each thermal diffusivity,
The temperature estimation device, characterized in that the proportionality coefficient derivation unit derives the proportionality coefficient by obtaining a proportionality coefficient value corresponding to the thermal diffusivity calculated by the thermal diffusivity calculation unit from the calibration table. 6. The temperature estimation device according to claim 4 ,
a temperature correction unit configured to calculate a temperature obtained by correcting the measurement result of the first temperature sensor based on temperatures measured by the first and second temperature sensors after the heat insulating material comes into contact with the test object and temperatures measured again by the first and second temperature sensors after a predetermined time has elapsed,
The temperature estimation device, wherein the thermal diffusivity calculation unit uses the temperature corrected by the temperature correction unit as a temperature of the surface of the test object after contact between the insulating material and the test object.

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