JPH0772701B2 - Biomedical thermography device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention measures infrared emissivity for each pixel, displays an emissivity distribution and a surface temperature distribution with the emissivity corrected, and displays the thermal effusivity near the target surface. The present invention relates to a thermographic device capable of calculating and displaying its distribution as an image.

[0002]

2. Description of the Related Art Conventionally, thermography of the type in which thermal radiation in the infrared wavelength range is detected to measure the temperature distribution on the target surface has been widely used in industry and medicine. In particular, in the medical field, in order to measure the temperature distribution on the body surface, a wavelength around 10 μm where the radiant energy is maximum near the body temperature, for example, a wavelength range of 8-14 μm has been used. In the past, in this wavelength range, it was considered that the skin was a black body, that is, the emissivity was 1.0, but in reality, the emissivity is 0.97.
Recent studies have revealed that the degree of reflection is about 3%. Therefore, an error occurs due to the influence of the radiation temperature of the environment. Therefore, in order to accurately measure the surface temperature, it is necessary to measure the emissivity in advance and perform correction based on the environmental emissivity temperature and the emissivity. But,
When the emissivity of the target surface is not uniform, the conventional thermographic device does not have a means for measuring the emissivity of each pixel, so that the emissivity cannot be accurately corrected.

[0003]

In a thermographic device, in order to accurately perform emissivity correction on an object with uneven emissivity, the emissivity is measured for each pixel and the emissivity is measured for each pixel. It is necessary to correct the rate. As a method for measuring the emissivity, a method of calculating from the change in the radiant energy from the target surface when the environmental radiant temperature is changed stepwise has been developed by the present inventor and used for measuring the skin emissivity ( Togawa, T., Clin. Phys. Physio
l. Meas., Vol. 10, No. 1, pp. 39-48, 1989.
Issued year). However, it has not been attempted to apply this method to thermography to measure the emissivity of each pixel and perform emissivity correction for each pixel, and an accurate surface temperature image could not be obtained. Therefore, the influence of the radiation temperature of the environment causes an error.

Therefore, if the emissivity can be measured for each pixel, an image of the emissivity distribution can be constructed,
If the emissivity of a living body reflects the properties of the skin, it can be expected to use the emissivity image as biological information. Furthermore, if the effect of heat conduction from the skin surface to the deep part of the body can be evaluated in the process of emissivity measurement, that information can be imaged as the thermal properties of the skin, and it can be expected to open the way to diagnostic use as biological information. See. The present invention is
It is assumed that the emissivity is measured for each pixel and that the emissivity is corrected for each pixel, and that the above-mentioned drawbacks are eliminated and a thermographic device that obtains a substantially accurate surface temperature image is provided. It is something to achieve.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a radiation source disposed opposite an object surface and a movable room temperature shade and high temperature in front of a thermographic camera between the radiation source and the object surface. Shades are arranged, and these are moved alternately by an exchange means to change the environmental radiation temperature of the target surface in a stepwise manner, and after that, the target surface temperature is changed by heat flow change, and the radiation temperature before and after the change is measured. Then, the thermal effusivity of the medium is calculated from the gradient of the straight line connecting the measured temperatures, and the emissivity of each pixel by the thermogram photography before and after the exchange of the plurality of shades, the emissivity-corrected surface temperature, and each of the above A biothermographic device for displaying a thermal effusivity distribution image, an emissivity distribution image, and a thermogram of a medium on a target surface corresponding to a pixel.

Further, it is preferably provided by having the following features. That is, for a living body that displays and images the distribution of the emissivity, the true temperature and the thermal effusivity of the target surface for each pixel from the thermograms of one sheet before the stepwise change of the ambient radiation temperature and two sheets after the change This is the case with a thermographic device. Furthermore, when the radiation source has an umbrella shape that covers the entire field of view, the high temperature shade is further reduced to 40 mm.
It is provided by a thermographic device for living body when kept at about ° C.

[0007]

In a thermographic device, an object having uneven emissivity is subject to emissivity correction. First, the environmental radiation temperature of the target surface is changed stepwise, and the emissivity and emissivity-corrected surface temperature of each pixel are calculated from the thermograms taken before and after that. From this result, an emissivity distribution image and a thermogram are displayed.
Furthermore, the thermal effusivity distribution of the medium on the target surface corresponding to each pixel can be calculated. Specifically, a movable room temperature shade and a high temperature shade are sequentially arranged between the target surface and the camera for thermography, and these are alternately moved by an exchange means to change the environmental radiation temperature of the target surface in a stepwise manner. Then, the thermogram photography is performed by the thermogram photography before and after the exchange of the plurality of shades. The emissivity and emissivity-corrected surface temperature of each pixel are calculated from this thermogram, and the emissivity distribution image and thermogram are displayed.

[0008]

EXAMPLES Examples will be described with reference to the drawings.
FIG. 1 is an explanatory view of the emissivity measuring principle used in the present invention. The state where the radiometer 11 is directed toward the object 12 having the temperature T _S is shown. The energy radiated from the object 12 is as shown in Formula 1 according to Planck's radiation formula.

[Equation 1] Here, P (T) is the energy radiated from the unit area to the unit time in the wavelength range from the wavelength λ ₁ to λ ₂ from the black body at the absolute temperature T. C ₁ and C ₂ are constants. If the object is not a black body and the emissivity is ε (<1), the energy radiated from the object at the absolute temperature T is εP (T). At this time, the reflectance of the object surface is γ = 1-ε. Therefore, assuming that the ambient radiation temperature is T _a , energy corresponding to γP (T _a ) is reflected on the object surface. As a result, the energy P (T _r ) radiated from the object having the absolute temperature T _s of the surface per unit area per unit time is given by Equation 2.

[Equation 2]

Here, T _r is the apparent radiation temperature, that is, the temperature output of the radiometer calibrated with a black body. Therefore, if the ambient radiation temperature is increased stepwise from T _aL to T _aH ,
Before and after that, energies P (T _rL ) and P (T _rH ) radiated from a unit surface area in a unit time are given by _Formulas 3 and 4.

[Equation 3]

[Equation 4] When the emissivity ε is solved from the equations 3 and 4, the equation 5 is obtained.

[Equation 5] Here, if the environmental radiation temperatures T _aL and T _aH are known,
Since T _rL and T _rH are obtained from the output of the radiometer, the emissivity can be calculated.

When the emissivity is calculated, the equation 6 is obtained by solving the equation 3.

[Equation 6] From this, the true surface temperature T _s can be calculated by Planck's radiation formula, Equation 1. Here, P (T _s ) is energy radiated from a black body having a true surface temperature T _s per unit area per unit time.

In practice, it is difficult to instantaneously change the ambient radiation temperature, and therefore there is a slight time delay from the start of the ambient radiation temperature change until the radiation temperature stabilizes and a thermogram is captured. In the meantime, the state of heat radiation changes on the target surface, and the surface temperature changes. It is known that at a uniform medium boundary, the surface temperature changes in proportion to the square root of the time from the time of the step change with respect to the stepwise heat flow change (Buettner K.,
J. Appl. Physiol. Vol. 3, No. 12, 691-702
Page, published in June 1951). That is, when the surface temperature T _{s0 is} in the equilibrium state, the surface temperature change T _s (t) can be approximated by Equation 7 by adding a heat flow of Q per unit area in a stepwise manner.

[Equation 7]

Here, t is the time when the time of the step change is 0, κ is the thermal conductivity, ρ is the density, and c is the specific heat. Therefore, when the time change of the temperature output of the radiometer is plotted against √t (square root of t), it becomes almost a straight line as shown in FIG. Therefore, from the time of the step change, t ₁ and t
_Assuming that the radiation temperatures after passing ₂ are T _r1 and T _r2 ,
Two points A and B in the figure are obtained, and the straight line connecting AB is extended to t
If the point C of = 0 is obtained, it can be expected that this is a good approximation of the radiation temperature T _rH immediately after the ideal stepwise heat flow change is given. That is, as long as the approximation of Equation 7 can be applied, after changing the ambient radiation temperature of the heat flow, an appropriate 2
From the radiation temperature at the time of the point, information equivalent to that obtained by changing the environmental radiation temperature in steps and measuring the radiation temperature immediately after that is obtained.

Since the slope of the straight line connecting AB in FIG. 2 is 2Q / √ (πκρc) from the equation 7, the heat flow Q
If is known, the thermal permeability, that is, √ (πκρc) is obtained. Based on the above principle, the ambient temperature is changed in a stepwise manner, and the emissivity of the surface, the true surface temperature, and the thermal permeability of the medium near the surface are measured by measuring the radiation temperature once before and twice after the change. it can. If this method is applied to thermography, the emissivity of the surface, the true temperature and the heat can be obtained by applying the above-mentioned principle for each pixel from the thermogram of one sheet before the stepwise change of the environmental radiation temperature and two sheets after the change. It is possible to obtain the distribution of the permeability as an image.

Next, the present invention will be specifically described by using the above principle. In order to obtain images of the emissivity, true surface temperature and thermal effusivity of the surface of the object, a means for changing the environmental temperature in steps and a thermographic device with a screen scanning speed as fast as possible are required. To set the ambient radiant temperature, the entire circumference of the object surface is surrounded by a black body wall that is kept constant. Further, the stepwise change of the ambient radiation temperature may be the stepwise change of the temperature of the wall of the black body, but it is difficult and difficult to realize the rapid temperature change due to the heat capacity of the wall material. Therefore, for example, the entire wall surface surrounding the target surface may be mechanically movable. It is effective to mechanically move the entire wall surface so that it can be replaced with a wall surface set to a different temperature.

FIG. 3 shows an embodiment of the thermographic device. A thermographic camera 2 is aimed at the target object 1, and a room temperature shade 3 surrounds the target surface. The room temperature shade 3 can be moved by a drive shaft 7 together with a high temperature shade 6 which is kept at a temperature higher than room temperature by a thermostat 4 and a heater 5. These two shades move when the motor 8 rotates the drive shaft 7, and the motor controller 9 controls the stop when the high temperature shade 6 comes to the position where the room temperature shade 3 was. The computer 10 manages thermogram imaging control, data management, image display of results, data storage, and the like. Further, temperature measurement (not shown) and recording of these two shades are executed by the temperature measuring means.

The procedure of measurement operation is as follows. First, the room temperature shade 3 is installed in front of the camera 2, and the target object 1 is placed in the field of view in front of it.
Place and take the first thermogram. Although the shade is moved immediately after photographing, the high temperature shade 6 is moved to the position where the room temperature shade 3 was originally located. The second thermogram photography is performed immediately after the high temperature shade 6 stops at the predetermined position. Further, after a lapse of a fixed time, for example, about 10 seconds, the third thermogram photography is performed, and the measurement operation is finished. 3 thermograms taken and room and high temperature shades 6
Temperature, the emissivity, true surface temperature and thermal effusivity of each pixel are calculated by the computer 1 according to the principle described above.
It is also possible to perform arithmetic processing by 0 and display it on the screen as an image, and to save data, output hard copy, and use arithmetic, diagnosis, etc. by other devices through the interface as well.

Embodiment 1 It is desirable that the thermographic device has a high frame rate in image processing. In the present invention, Agema Corp. Thermovision 870 type was used. As a shade, the front opening had a size of 32 × 32 cm and a length of 70 cm, and a black body paint was applied to the inner surface. In the high temperature shade 6, surface heaters were attached to the four surfaces, the temperature was controlled by a thermostat, and the temperature was maintained at about 40 ° C. Shade movement is performed in about 0.5 seconds using the linear motion mechanism, and the second movement is performed 1 second after the movement starts.
I took a thermogram of. Furthermore, about 5 to 10
A third thermogram was taken after a second. From this result, it was possible to obtain the emissivity-corrected surface temperature T _s by calculating the emissivity for each pixel using Equation 5 and solving Equation 6. In addition, the thermal effusivity could be calculated by solving Equation 7. Here, Q of the equation 7 is calculated by the equation 8. In Expression 8, σ is a Stefan Boltzmann constant.

[Equation 8]

Example 2 Emissivity measurement in thermography and automatic correction of surface temperature were performed using the emissivity measurement apparatus of FIG. The radiation source 15 has a size of 17 cm × 17 cm and faces the target surface 13. The target surface 13 was covered with an aluminum wall 17 to eliminate the influence of disturbance. The radiation temperature was changed stepwise by opening the shutter 16 covering the radiation source 15 facing the target surface 13. Each was carried out first with a room temperature shade 3 and then with a high temperature shade 6. Each of them was photographed by the thermography device 14, and the correction value T _s of the emissivity ε and the surface temperature of each pixel was calculated by Equations 9 and 10.

[Equation 9]

[Equation 10] Here, C is a constant determined by the device, and P (T) is the energy emitted from a unit area to a unit time in the wavelength range from the wavelength λ ₁ to λ ₂ from the black body at the absolute temperature T. T ₁ and T
₂ is the radiation temperature before and after opening the shutter. T _r is the temperature of the radiation source (40 ° C.), and T _a is the average radiation temperature of the entire field of view before opening the shutter. First, C was determined using an object of known emissivity, and the back of the subject's hands and the like were measured. As an object with a known emissivity, (Togawa, T., Cli
n. Phys. Physiol. Meas.) The emissivity was determined by the method of about 20 kinds of objects having emissivity in the range of 0.50 to 0.99.

Results: The value of C was obtained for an object with a known emissivity, and the result was 2.50, which was in good agreement with the case of the method of the above literature, and the correlation coefficient was 0.988. 20
Emissivity measurement and surface temperature correction were then performed on the thermogram of the back of the hand, excluding two types of objects of which the surface was close to a smooth surface. The results were reasonable. In particular, in the skin where foundation cream was applied to the backs of the subjects, the emissivity of clean skin was 0.97 ± 0.01, while it decreased to 0.94 to 0.95, and the maximum 0.5 ° C.
It has been confirmed that a reasonable correction value is given, although there may be some surface temperature error. Also, the above 2
Since the surface of the seed object is close to a smooth surface, diffuse reflection does not occur, and only the reflection from the hole in the center of the radiation source is incident on the camera, so the effect of radiation from the radiation source when the shutter is opened is recognized. Not considered.

As the radiation source, for example, an umbrella-shaped radiation source that covers the entire field of view can be used to enable more accurate measurement. Further, the moving means for the room temperature shade 3 and the high temperature shade 6 can be manual or automated.

[0021]

As described above, according to the present invention, in addition to the conventional thermogram, an emissivity distribution image, an emissivity-corrected thermogram for each pixel, and the thermal effusivity of the medium near the target surface are obtained. The distribution can be measured. Therefore, the thermal information, which cannot be obtained by the conventional thermogram, can be accurately obtained, and the quality of the image can be improved. Further, the temperature accuracy of the current thermographic device has been increased to about 0.1 ° C., but accurate temperature determination cannot be performed unless the emissivity is added to this. Therefore, according to the present invention, it was confirmed that the emissivity of the skin can be accurately measured and the temperature can be accurately determined by changing the environmental radiation temperature stepwise.

[0022]

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a state of a radiant energy component incident on a radiometer for explaining a principle of measuring an emissivity in a thermographic device of the present invention.

FIG. 2 is a graph showing a relationship between a square root of time from a time point of a stepwise change of environmental temperature and a temperature output of a radiometer for explaining a method of calculating an emissivity and a thermal effusivity.

FIG. 3 is a block diagram showing an embodiment of the thermographic device of the present invention.

FIG. 4 is a device for measuring emissivity used in another embodiment.

[Explanation of symbols]

 1 Target Object 2 Camera 3 Room Temperature Shade 6 High Temperature Shade 11 Radiometer 13 Target Surface 14 Thermography Device 15 Radiation Source 16 Shutter

Claims (4)

[Claims] 1. A radiation source arranged to face a target surface ;
A movable room temperature shade and a high temperature shade are arranged in front of the camera of the thermography between the radiation source and the target surface, and these are alternately moved by the exchange means to step the environmental radiation temperature of the target surface. is varied, its
After that, the target surface temperature is changed by the heat flow change,
Of the radiation temperature before and after the change of
Calculates the thermal effusivity of the medium from the gradient of emissivity of each pixel by thermogram captured before and after the replacement of the plurality of shade, emissivity corrected surface temperature, each image
A thermographic device for a living body, which displays a thermal effusivity distribution image, an emissivity distribution image, and a thermogram of a medium on a target surface corresponding to an element . 2. One sheet before the stepwise change of the ambient radiation temperature
And the target table for each pixel from the two thermograms after the change
Image showing surface emissivity, true temperature and thermal effusivity distribution
The thermographic device for living body according to claim 1, 3. The radiation source is in the shape of an umbrella covering the entire field of view.
Item 1. The thermographic device for living body according to Item 1 or 2 . 4. The high temperature shade is maintained at about 40.degree.
The thermographic device for living body according to any one of claims 1 and 3.