JP2008155011A - Density measuring apparatus and its method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized and inexpensive density measuring apparatus capable of optically measuring the density inside a living body as bioinformation. <P>SOLUTION: This density measuring apparatus is characterized in having a light illumination section 20 for illuminating the inside of a measuring object by changing the intensity of the light, a light receiving section 30 for receiving the reflected light of the illuminated light from the inside of the measuring object, a variation tendency calculation section 201 calculating a variation tendency of the intensity of the received reflected light relative to the intensity of the illuminated light, and a density specification section 202 specifying the density of the measuring object based on the variation tendency. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a density measuring apparatus and method for measuring a density inside a living body non-invasively using light.

  There are various methods for measuring the inside of a living body. Conventionally, measurement methods using X-rays such as X-ray diagnostic apparatuses and X-ray CT apparatuses and measurement methods using ultrasonic waves such as ultrasonic echoes are currently established and useful as medical diagnostic apparatuses. The device is expensive and large. Furthermore, the measuring method using X-rays is harmful to the human body that is the object to be measured, and there is a problem that it causes an explosion. On the other hand, the measurement method using light has an advantage that a compound to be measured can be selected by selecting a wavelength without the problem of exposure.

  As a measuring device that measures biological information using light, it measures blood component concentrations such as blood glucose and biological component concentrations such as a biological oxygen monitor, and measures changes over time in hemoglobin and myoglobin in the brain and muscles. A measuring device, a measuring device for measuring a tissue or density inside a living body such as bone tissue and bone density, and the like have been proposed.

  A conventional measuring device that measures biological information using light irradiates light inside a living body by pressing an optical probe against the surface of the living body, and the transmitted or reflected light passes through the skin again and passes through the skin. The light emitted is received, and various biological information is calculated based on the received light. Further, from the received light, for example, biological information such as a measurement position, depth, concentration, and density is analyzed. As this analysis method, there is a method (time-resolving method) that uses a light source whose intensity changes with time and obtains information such as depth from the difference in the arrival time of light. Since the time resolution method divides the time response of an optical signal to correspond to information such as depth, a light source with a narrow time width and a photodetector with a fast time response are required (for example, see Patent Document 1).

In the measurement apparatus described in Patent Document 1 below, a pulse laser system using a laser beam is used as an optical probe, a pulsed laser beam is irradiated to a bone tissue, and a light scattering coefficient and light absorption in the bone tissue are measured by a time-resolved method. Find the coefficient. As a result, it is possible to analyze the bone structure change with higher accuracy.
JP 09-70404 A

  However, the conventional measuring apparatus has a problem that it is expensive and large.

  As described in Patent Document 1, a light source having a narrow time width and a device such as a pulse laser system that realizes a pulse laser beam as a photodetector having a quick time response are required. And since the apparatus which comprises such a system requires many system components, an apparatus becomes large inevitably and will become expensive.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a small and inexpensive density measuring device capable of measuring the density inside a living body with light as biological information.

In order to achieve the above object, the density measuring apparatus of the present invention is a density measuring apparatus for measuring a biological density, and is irradiated with light irradiating means for irradiating light inside the measurement object by changing the intensity of light. Light receiving means for receiving reflected light from the inside of the measurement object, change tendency calculating means for calculating a change tendency of the intensity of the reflected light received with respect to the intensity of the irradiated light, and based on the change tendency And density specifying means for specifying the density of the measurement object.

  With this configuration, the light irradiating means only needs to change the intensity of the irradiated light, and as a device constituting the light irradiating means, there are many system components such as a device having a short-time pulse or a multi-wavelength light source. No special equipment configuration is required. Conventionally, it has been necessary to calibrate the light source in order to remove the influence of the background, such as the change in thickness depending on the measurement location of the skin tissue and the influence of specifying the light source to be used. In the present invention, since the influence of the background can be removed by evaluating the change tendency, an apparatus configuration for calibrating a light source or the like is not required. Thereby, a small and inexpensive density measuring device can be realized.

  Further, the change tendency calculating means may calculate a change tendency from a change rate of the intensity of the reflected light received with respect to the intensity of the irradiated light. At this time, the density measuring device further includes an inflection point calculating means for calculating an inflection point of a curve of a change tendency obtained from a change rate of the intensity of the reflected light received with respect to the intensity of the irradiated light. The density specifying unit may specify the density of the measurement object based on the inflection point calculated by the inflection point calculating unit and the change tendency calculated by the change tendency calculating unit.

  With this configuration, the slope of the curve obtained from the relationship between the intensity of the irradiated light and the intensity change rate of the reflected light detected at that time, for example, the log ratio of the irradiated light intensity and the received reflected light intensity, It becomes possible to evaluate the density of the measurement object. Thereby, even when there is an intervening region that is not a measurement target before the measurement target, the density inside the living body can be evaluated without the influence. This eliminates the need for a special device configuration that requires many system components, such as a device having a short-time pulse or a multi-wavelength light source, so that a compact and inexpensive density measuring device can be realized.

  Further, the light irradiation means may change the intensity of light applied to the surface of the measurement object by changing a distance from the measurement object.

  With this configuration, the intensity of the irradiated light is changed by changing the distance between the light irradiation means and the measurement target. By the way, for example, when the light intensity itself of the light irradiating means is changed, the nonlinearity of the semiconductor may appear, which may be a factor that hinders accurate measurement. Here, the factor can be avoided and the same effect can be obtained.

  At this time, the density measuring apparatus may further include a reference scattering medium inserted between the light irradiation unit and the measurement target.

  With this configuration, by changing the thickness of the reference scattering medium inserted between the light irradiation means and the measurement target, the intensity of the irradiation light irradiated on the surface of the measurement target from the light irradiation means can be changed. Can do. Thereby, not only is it unnecessary to move the position of the light irradiation means and the measurement object itself, but when the reference scattering medium has a known light scattering characteristic, by utilizing the known light scattering characteristic, for example, It becomes possible to measure the density of the bone to be measured without being affected by the skin tissue interposed between the light irradiation means and the bone to be measured.

  Further, the change tendency calculation means may calculate the change tendency from a change rate of the intensity of reflected light received with respect to a distance between the light irradiation means and the measurement object.

  With this configuration, the density of the measurement target is evaluated based on the slope of the curve obtained from the relationship between the distance between the light irradiation means and the measurement target, the intensity of the light irradiated on the surface of the measurement target, and the rate of change in the intensity of the reflected light. It becomes possible to do. Thereby, even when there is an intervening region that is not a measurement target before the measurement target, the density inside the living body can be evaluated without the influence.

  The density specifying unit may further specify the density of the measurement target based on an integration of the change tendency with respect to a distance between the light irradiation unit and the measurement target.

  With this configuration, by integrating the curve obtained from the relationship between the distance of the light irradiation means and the measurement target, the intensity of the light irradiated on the surface of the measurement target, and the rate of change in the intensity of the reflected light, When there is an intervening region that is not the object to be measured, the influence of the intervening region can be removed. Thereby, it becomes possible to evaluate the density of a measuring object.

  Moreover, the near-infrared light may be sufficient as the light irradiated from the said light irradiation means.

  Thereby, it becomes possible to noninvasively evaluate the density of the living body to be measured by using near-infrared light with good living body permeability as the irradiated light. That is, the density inside the living body can be measured by light as biological information.

  The light irradiating means may be composed of a light emitting diode, and the light receiving means may be composed of a photodiode.

  Thereby, since the light emitting diode and the photodiode are small, inexpensive, and obtainable components, it is possible to realize a small and inexpensive density measuring device.

  The measurement object may be a bone and measure bone density.

  Thereby, bone density can be evaluated.

  Moreover, the optical axis of the light irradiated by the light irradiation means and the optical axis of the light received by the light receiving means may be arranged on the same axis.

  As a result, the shortest path length of the light until the irradiated light reaches the light receiving means is shortened. Therefore, even if the intensity of the irradiated light is weak, it becomes easy to reach the light receiving means, and the detection sensitivity for weakly irradiated light. Rise. As a result, the information on the shallower portion becomes accurate and the obtained biological density measurement value becomes accurate, so that a highly accurate density measuring device can be realized.

  Note that the present invention is not only realized as a device, but also realized as a method using processing means constituting the device as steps, a program that causes a computer to execute the steps, or a computer that records the program It can also be realized as a readable recording medium such as a CD-ROM, or as information, data or a signal indicating the program. These programs, information, data, and signals may be distributed via a communication network such as the Internet.

  ADVANTAGE OF THE INVENTION According to this invention, the small and cheap density measuring apparatus which can measure the density inside a biological body with light as biological information is realizable.

  Hereinafter, a density measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
An apparatus and a method for evaluating a biological density from the tendency of a change in the intensity of reflected light observed by changing the intensity of irradiated light (this will be referred to as an intensity decomposition method) will be described.

  FIG. 1 is a block diagram schematically showing an example of a density measuring apparatus according to the first embodiment of the present invention.

  The density measurement apparatus 1000 includes a light irradiation unit 20 that changes the intensity of light and irradiates the measurement target 10 with light, a light receiving unit 30 that receives reflected or scattered light, and the intensity of light emitted by the light irradiation unit 20. Control unit 200 that performs control to change the light intensity, and a change tendency calculation unit that calculates a change tendency based on the intensity of light emitted from the light irradiation unit 20 from the control unit 200 and the intensity of light received from the light receiving unit 30 201, a density specifying unit 202 that specifies a biological density based on the change tendency calculated by the change tendency calculating unit 201 and reference data 203 prepared in advance, and a biological density measured by the density specifying unit 202 are displayed. The display unit 204 is configured.

  FIG. 2 is a diagram schematically showing the measurement target 10, the light irradiation unit 20, and the light receiving unit 30 when measuring the measurement target 10 in the first embodiment of the present invention. FIG. 2 shows a region of light irradiated on the measuring object 10 when the intensity of light irradiated from the light irradiation unit 20 is increased in the order of FIGS. 2A, 2B, and 2C. 40 shows that the light reaches the inside of the measuring object 10 while spreading, and accordingly, the light reflected or scattered inside the measuring object 10 and received by the light receiving unit 30 increases.

  Here, as an example, the measuring object 10 is a bone, the irradiation unit 20 is a light emitting diode, and the light receiving unit 30 is a photodiode. The light emitting diode of the irradiating unit 20 uses, for example, near-infrared light having a wavelength range of 750 to 2500 nm that has good biological transparency. Hereinafter, the case where the bone density is evaluated as the biological density will be described.

  In FIG. 2, the light emitting diode that is the irradiation unit 20 is irradiated on the bone that is the measurement object 10 by changing the intensity of the near infrared light. The photodiode that is the light receiving unit 30 detects light that has reached the photodiode that is the light receiving unit 30 as a part of the irradiation light reflected and scattered inside the bone that is the measurement target 10. The intensity of the light detected by the photodiode of the light receiving unit 30 changes as the irradiation light intensity changes. Further, since the light intensity detected by the photodiode of the light receiving unit 30 reflects the light absorption / diffusion characteristics depending on the bone density, the bone density is evaluated from the data detected by the light receiving unit 30.

  FIG. 3 is a flowchart showing a procedure for measuring the biological density of the density measuring apparatus according to the first embodiment of the present invention.

  First, the light irradiation unit 20 is pressed against the measurement object 10 and controlled by the control unit 200 to change the light intensity and cause the light irradiation unit 20 to emit light (S101).

  Next, the light receiving unit 30 receives the light that is irradiated from the light irradiation unit 20 onto the measurement target 10, reflected or scattered inside the measurement target 10, and reaches the photodiode that is the light receiving unit 30 (S102).

  Next, the change tendency calculation unit 201 calculates a change tendency based on the light intensity of the light irradiation unit 20 from the control unit 200 and the intensity received from the light receiving unit 30 (S103).

  Next, the density specifying unit 202 measures the biological density based on the change tendency calculated by the change tendency calculation unit 201 (S104).

  Next, the display unit 204 displays the biological density measured by the density specifying unit 202.

  Next, the principle of the biological density measuring method of the density measuring apparatus 1000 according to the first embodiment of the present invention will be described below.

  In FIG. 2, the intensity of light emitted from the light emitting diode that is the irradiation unit 20 and the intensity of reflected / scattered light detected by the photodiode that is the light receiving unit 30 follow the Lambert-Beer law, It becomes. Here, Lambert-Beer's law is a law representing the relationship between concentration and light attenuation. Accordingly, the concentration can be expressed by an expression of a relationship proportional to the logarithm of the transmittance, that is, the absorbance.

Here, I ₀ is the irradiation light intensity, I is the reflected / scattered light intensity, μ _t is the attenuation coefficient in reflection, and L is the representative optical path length.

FIG. 4 is a diagram showing the relationship between the irradiation light intensity I ₀ and the reflected / scattered light intensity I. 4 (a) is a view conceptually showing a (number 1), 4 (b) is irradiation light intensity in the case of changing the damping coefficient mu _t (Equation 1) - reflected and scattered light It is a figure which shows typically the change of the inclination of an intensity curve (henceforth _I0- I curve).

As shown in FIG. 4A, in the equation (1), when the irradiation light intensity I ₀ is increased, the reflected / scattered light intensity I is also increased. The increase is caused by the attenuation coefficient μ _t and the representative optical path length. Defined by L. The representative optical path length L is regarded as a function of the irradiation light intensity I _0, increases as the irradiation light intensity I ₀ increases. That is, when the irradiation light intensity I ₀ increases, the irradiation light reaches the deeper part.

An I ₀ -I curve shown in FIG. 4B is obtained from the irradiation light intensity I ₀ obtained by changing the intensity of the irradiation light in the light irradiation unit 20 and the reflected / scattered light intensity I measured by the light receiving unit 30. Here, the horizontal axis indicates the irradiation light intensity I ₀ with the intensity changed, and the vertical axis indicates the measured reflected / scattered light intensity I. The slope of the I ₀ -I curve reflects the density state of the living body, for example, the bone density state. That is, the case where the attenuation coefficient μ _t is large indicates a state where the density inside the living body is low, here, a state where the bone density is low. In this case, the slope of the I ₀ -I curve becomes small. On the contrary, the case where the attenuation coefficient μ _t is small indicates that the bone density is high here when the density inside the living body is high. In this case, the slope of the I ₀ -I curve becomes large.

As described above, the density state inside the living body, for example, the bone density can be evaluated by examining the slope of the I ₀ -I curve, that is, the irradiation light intensity-reflected / scattered light intensity curve.

(Example)
Actually, the results of measuring the simulated bone tissue obtained by mixing cancellous bone chips collected from bovine femur with gelatin as the measurement object 10 are shown below. Gelatin and cancellous bone chips were mixed so that the spatial density of the prepared simulated bone tissue of the measurement object 10 was 20 and 90, 240, 340 mg / cm ³ . The upper part of the simulated bone sample of the measured object 10 was covered with gelatin having a thickness of 6 mm to form a simulated skin layer. The near-infrared light-emitting diode used as the irradiation unit 20 has a peak wavelength of 850 nm, and the photodiode used as the light-receiving unit 30 is a germanium photodiode.

FIG. 5A is a diagram showing the relationship between the slope of the I ₀ -I curve and the I ₀ -I curve and the bone density with respect to the gelatin simulated bone sample. Here, the horizontal axis indicates the irradiation light intensity I ₀ with the intensity changed, and the vertical axis indicates the measured reflected / scattered light intensity I.

FIG. 5A is an I ₀ -I curve for a tissue sample of each simulated bone that is the measurement object 10. In this experiment, the irradiation light intensity I ₀ is simply applied to the near-infrared light emitting diode as the irradiation unit 20, and the reflected / scattered light intensity I is applied to the photodiode as the light receiving unit 30. The detection voltage is used. The reflected / scattered light intensity I tended to increase as the irradiation light intensity I ₀ increased. The reflected / scattered light intensity I tended to increase as the cancellous bone tip density increased.

FIG. 5B is a strong emission intensity region (light emitting diode applied voltage 4 to 5 V of near-infrared light that is the light irradiation unit 20) more reflecting the difference in cancellous bone chip density in FIG. the slope of the I ₀ -I curve (calculated from the approximate straight line) and is a diagram showing the relationship between the cancellous bone chips density. Here, the horizontal axis indicates the bone density, and the vertical axis indicates the slope of the I ₀ -I curve. FIG. 5B shows that the relationship between both, that is, the slope of the I ₀ -I curve and the cancellous bone tip density shows a strong positive correlation (r2 = 0.948). From this result, it can be seen that the bone density can be evaluated using the slope of the I ₀ -I curve.

  In the above description, the near-infrared light emitting diode is described as an example of the light irradiation unit 20, but the wavelength and the optical device are not limited thereto. Similarly, a photodiode is described as an example of the light receiving unit 30, but is not limited thereto. Moreover, although the bone is described as an example of the measurement object 10, it is not limited thereto.

  In addition, it is preferable to arrange | position the light irradiation part 20 and the light-receiving part 30 closer, and it is still more preferable that the light irradiation part 20 and the light-receiving part 30 are arrange | positioned coaxially. Moreover, the light irradiation part 20 and the light-receiving part 30 may each consist of one each, and may be comprised as a pair of apparatus.

  It should be noted that the intensity decomposition method described above, that is, a method capable of evaluating the density of living tissue from a change in reflected light intensity observed by continuously changing the intensity of irradiation light, is within the scope of the present invention. Yes, it is not limited to the embodiment described above.

As described above, the density state inside the living body is determined by examining the slope of the I ₀ -I curve, that is, the irradiation light intensity-reflected / scattered light intensity curve, from the change in the reflected light intensity observed by changing the intensity of the irradiated light. For example, bone density can be evaluated.

  As described above, according to the first embodiment of the present invention, when the biological density is measured, the light irradiating unit 20 only needs to change the intensity of the irradiated light. As a special device that requires many system components such as short-time pulses is not required, as shown in the above example, it is small and can be composed of light emitting diodes and photodiodes of near-infrared light. An inexpensive density measuring device can be realized. Furthermore, since the living body density is measured using light, the living body density can be measured non-invasively without risk of being exposed to a human body.

(Second Embodiment)
Actually, when measuring the biological density, for example, the measurement is performed through an intervening tissue such as skin, but in the biodensity measurement of the first embodiment, the influence of the intervening tissue such as skin is negligible. It was considered. In the second embodiment, a method (hereinafter referred to as a spatial intensity decomposition method) and an apparatus for removing the influence of an intervening tissue such as skin and evaluating the density inside the living body will be described below.

  For example, when bone density is measured, if a tissue layer such as skin is present, it will be explained that the influence affects the data.

FIG. 6 is a diagram showing the influence of the skin layer on the slope of the I ₀ -I curve. FIG. 6 shows reflected / scattered light in the simulated bone tissue sample used in FIG. 5 when the thickness of the simulated skin layer (gelatin layer) is changed at the same cancellous bone chip density (240 mg / cm ³ ). It is the result of investigating the difference in the slope of the intensity distribution. Note that the inclination of the reflected / scattered light intensity distribution is the inclination of the result obtained by examining the emission intensity of the near-infrared light emitting diode, which is the irradiation unit 20, in the range of 4 to 5 V, as described above. From FIG. 6, it was confirmed that the inclination decreased as the thickness of the simulated skin layer (gelatin layer) increased. For example, when the thickness of the simulated skin layer was increased from 4 mm to 8 mm, it was shown that the inclination decreased by about 18%. The individual differences in the thickness of the skin layer at the distal ulna and heel, which are assumed to be measured in actual humans, are considered to be small, but in order to measure with higher accuracy, the upper layer tissue covering the bone It is necessary to remove the effect of the layer.

  FIG. 7 is a block diagram schematically showing an example of the density measuring apparatus according to the second embodiment of the present invention.

  The density measuring apparatus 1000 changes the light intensity of the light irradiation unit 20 that irradiates the measurement object 10 with light, the light receiving unit 30 that receives the reflected or scattered irradiation light, and the light intensity of the light irradiation unit 20. A control unit 200 that performs control to change, a change tendency calculation unit 201 that calculates a change tendency based on the intensity of light from the light irradiation unit 20 from the control unit 200 and the intensity received from the light receiving unit 30, and a change tendency An inflection point calculation unit 205 that calculates an inflection point from the change tendency calculated by the calculation unit 201, an inflection point calculated by the inflection point calculation unit 205, a change trend calculated by the change trend calculation unit 201, and a prepared in advance The density specifying unit 202 that specifies the living body density based on the reference data 203 that has been set, and the display unit 204 that displays the living body density measured by the density specifying unit 202 are configured.

  FIG. 8 is a diagram schematically showing the measurement target 10, the light irradiation unit 20, and the light receiving unit 30 when measuring the measurement target 10 according to the second embodiment of the present invention. In FIG. 8, the intensity of irradiation light of the irradiation unit 20 increases in the order of FIGS. 8A, 8 </ b> B, and 8 </ b> C, and accordingly, the region 40 of light irradiated to the intervening tissue unit 11. Extends from the intervening tissue part 11 to the intervening tissue part 11 and the measuring object 10 and reaches the deep part of the measuring object 10, and accordingly, the measuring object 10 that is the living tissue from the light reflected and scattered by the measuring object 10 that is the living tissue. The light reflected and scattered by the intervening tissue part 11 indicates that the light received by the light receiving part 30 increases.

  Here, as an example, the measurement object 10 is a bone, and the intervening tissue part 11 is skin. The irradiation unit 20 is a light emitting diode, and the light receiving unit 30 is a photodiode. The light emitting diode of the irradiating unit 20 uses, for example, near-infrared light having a wavelength range of 750 to 2500 nm that has good biological transparency. Hereinafter, the case where the bone density is evaluated as the density inside the living body will be described.

  From FIG. 8, the light emitting diode which is the irradiation unit 20 is irradiated on the bone which is the measurement object 10 by changing the intensity of the near infrared light. The photodiode that is the light receiving unit 30 reaches the bone layer that is the measurement target 10 through the skin layer that is the intervening tissue unit 11, and is part of the irradiation light that is reflected and scattered there, up to the photodiode that is the light receiving unit 30. The light that arrives is detected. The intensity of the light detected by the photodiode of the light receiving unit 30 changes as the irradiation light intensity changes. The intensity of light detected by the photodiode of the light receiving unit 30 reflects light absorption / diffusion characteristics depending on the bone density. However, the intensity of light detected by the photodiode of the light receiving unit 30 is affected by the thickness of the skin layer and the light scattering characteristics, and thus needs to be removed.

  FIG. 9 is a flowchart showing a procedure for measuring the biological density of the density measuring apparatus 1000 according to the second embodiment of the present invention.

  First, the light irradiation unit 20 is pressed against the intervening tissue unit 11 interposed in the measurement object 10, and the light irradiation unit 20 is caused to emit light by changing the light intensity by being controlled by the control unit 200 (S101).

  Next, the light receiving unit 30 receives the light that is irradiated from the light irradiation unit 20 to the measurement target 10, reflected or scattered inside the measurement target 10 and the intervening tissue unit 11, and reaches the photodiode that is the light receiving unit 30. (S102).

  Next, the change tendency calculation unit 201 calculates a change tendency based on the light intensity of the light irradiation unit 20 from the control unit 200 and the intensity received from the light receiving unit 30 (S103).

  Next, the inflection point calculation unit 205 calculates an inflection point from the change tendency calculated by the change tendency calculation unit 201 (S1031).

  Next, the density specifying unit 202 removes the influence of the skin layer thickness and light scattering characteristics based on the inflection point calculated by the inflection point calculation unit 205 and the change tendency calculated by the change tendency calculation unit 201. The density is measured (S104).

  Next, the display unit 204 displays the biological density measured by the density specifying unit 202.

  Subsequently, the principle of the biological density measuring method of the density measuring apparatus 1000 according to the second embodiment of the present invention will be described below.

FIG. 10 is a schematic diagram showing the principle of the spatial intensity decomposition method in the case of a two-layer model of a skin layer and a bone layer. The principle of the spatial intensity decomposition method, that is, the method of evaluating the density inside the living body by removing the influence of an intervening tissue such as skin will be described. As shown in FIG. 10, first, a two-layer model of a skin layer and a bone layer is considered, and formulation of light behavior is attempted based on Lambert-Beer law. Here, the skin layer represented as the thickness L ^skin is a model of the intervening tissue portion 11 in FIG. The bone layer represented by the light arrival depth L ^bone (I ₀ ) is obtained by modeling the measurement object 10 in FIG.

First, near-infrared light is irradiated with irradiation light intensity I ₀ from the surface of the skin layer of the intervening tissue part 11 by the light emitting diode which is the irradiation part 20. When the irradiation light intensity I ₀ is increased, the light reach distance in the skin layer of the intervening tissue part 11 increases, and the light reaches the thickness L ^skin of the skin layer as the intervening tissue part 11 with a certain irradiation light intensity I _0. To reach. At this time, the reflected / scattered light intensity I ^skin (hereinafter referred to as I ^skin ) detected from the photodiode, which is the light receiving unit 30 placed on the skin layer of the intervening tissue part 11, is based on Lambert-Beer's law. It becomes a relational expression shown by (Formula 2).

Here, μ _t ^skin is a light attenuation coefficient in the skin layer which is the intervening tissue part 11. The formula (2) is a light receiving unit 30 in which light that reciprocates through the skin layer of the intervening tissue part 11 with a certain irradiation light intensity I ₀ is installed on the skin layer of the intervening tissue part 11 as reflected / scattered light intensity I ^skin. Indicates that it is detected by a photodiode. The reason ^{why the} representative optical path length is 2L ^skin is that the distance of reciprocating the skin layer as the intervening tissue part 11 is 2L ^skin .

Similarly, the intensity I ₀ ^bone (hereinafter referred to as I ₀ ^bone ) of light irradiated from the skin layer as the intervening tissue part 11 to the bone layer as the measurement target 10 is expressed by the following equation (3). It becomes a relational expression shown by.

Here, the equation (3) represents that the light that has passed through the skin layer of the intervening tissue part 11 with a certain irradiation light intensity I0 and reached the bone layer becomes the intensity I ₀ ^{bone of} light incident on the bone layer. . The ^{reason why the} representative optical path length is L ^skin is that the distance that has passed through the skin layer that is the intervening tissue part 11 is L ^skin .

Observation is also made when the skin layer-bone layer interface, that is, the bone layer, which is the measurement object 10 at the interface between the skin layer, which is the intervening tissue portion 11, and the bone, which is the measurement object 10, is regarded as the light incident point. The reflected / scattered light intensity I ^bone (hereinafter referred to as I ^bone ) can be expressed by the following equation (4).

Here, μ _t ^bone is a light attenuation coefficient of the bone layer of the measurement target 10 and reflects the bone density of the measurement target 10. (Expression 4) indicates that light that reciprocates through the bone layer that is the measurement target 10 with a certain incident light intensity I ₀ ^bone becomes the reflected / scattered light intensity I ^bone that is incident on the skin layer that is the intervening tissue part 11. Represents. The reason ^{why the} representative optical path length is 2L ^bone (I ₀ ) is that the distance of reciprocating the bone layer of the measuring object 10 is 2L ^bone (I ₀ ). Further, the representative optical path length L ^bone in the bone layer of the measuring object 10 depends on the irradiation light intensity I ₀ . The reflected / scattered light having the intensity of I ^bone that is incident on the skin layer that is the intervening tissue part 11 from the bone layer that is the measurement object 10 passes through the skin layer that is the intervening tissue part 11, and finally the intensity. I ^{skin + bone} is detected by the photodiode that is the light receiving unit 30 on the skin layer that is the intervening tissue unit 11. Here, I ^{skin + bone} is a relational expression expressed by the following equation (5).

Here, the equation (5) indicates that light having passed through the skin layer of the intervening tissue part 11 with a certain incident light intensity I ^bone is reflected / scattered light intensity I ^{skin + bone} (hereinafter referred to as I ^{skin + bone} ). This means that the light is detected by a photodiode that is a light receiving unit 30 placed on the skin layer of the intervening tissue unit 11. The ^{reason why the} representative optical path length is L ^skin is that the distance that has passed through the skin layer that is the intervening tissue part 11 is L ^skin .

  Furthermore, (Equation 5) can be expressed as the following (Equation 6) from the above (Equation 3) and (Equation 4).

Here, attention is focused on the ratio between the incident light intensity I ₀ and the reflected / scattered light intensity I. When it is limited to the region of the bone layer of the measurement object 10, the following relationship is established from the equations (3) and (4).

(Formula 7) From the equation, the logarithm of the ratio of the incident light intensity I ₀ ^bone and the reflected / scattered light intensity I ^bone in the region of the bone layer of the measurement object 10 (hereinafter referred to as ln (I ^bone / I ₀ ^bone )) ^Indicates a value correlated with the light attenuation coefficient μ _t ^{bone of the} bone layer reflecting the bone density. That is, it can be seen that bone density can be evaluated by ln (I ^bone / I ₀ ^bone ).

However, since the representative optical path length L ^bone in the bone layer is a function of the incident light intensity I ₀ ,
In (I ^bone / I ₀ ^bone ) varies depending on the incident light intensity I ₀ . Therefore, the evaluation of the bone density varies depending on which incident light intensity I ₀ is used.

In the second embodiment of the present invention, the change of _{^{ln (I bone / I 0 bone}} ) is obtained for the irradiation light intensity I ₀ by causing the irradiation light intensity I ₀ continuously changed. The slope of the ln (I / I ₀ ) -I ₀ curve thus obtained can be a bone density evaluation parameter that is not affected by the magnitude of the irradiation light intensity I ₀ .

From the above, it can be seen that the bone density can be evaluated by obtaining the change of ln (I ^bone / I ₀ ^bone ) with respect to I ₀ ^bone . However, I ^bone and I ₀ ^bone cannot be directly known because they are values in a region inside the living body under the skin.

  By the way, the relationship expressed by the following (Equation 8) is established from the (Equation 2) and (Equation 6).

The right side of equation (8) is equal to the right side of equation (7). That is, it can be seen that ln (I ^{skin + bone} / I ^skin ) has the same value as ln (I ^bone / I ₀ ^bone ). Therefore, it can be seen that ln (I ^bone / I ₀ ^bone ) can be obtained by using the measured values I ^skin and I ^{skin + bone} .

Here, I ^{skin + bone} is measured by a photodiode serving as the light receiving unit 30, but I ^skin is not directly obtained from the measurement.

FIG. 11 is a diagram conceptually showing ln (I / I ₀ ) −I ₀ of the skin layer only model, the skin layer and bone layer two layer model, and the bone layer only model in FIG. Here, ln (I / I ₀ ) −I ₀ indicates the relationship between the logarithm of the ratio of the irradiated light intensity I ₀ to the irradiated light intensity I ₀ and the reflected / scattered light intensity I (hereinafter referred to as the irradiated light intensity I _0). The relationship between the irradiation light intensity I ₀ and the logarithm of the ratio of the reflected / scattered light intensity I is described as ln (I / I ₀ ) −I _{0. When} there is a subscript, the same notation is used for incident light. .) In FIG. 11, the vertical axis represents the logarithm ln (I / I ₀ ) of the ratio of the irradiation light intensity I ₀ and the reflected / scattered light intensity I, and the horizontal axis represents the irradiation light intensity I ₀ . However, since the representative optical path lengths L ^bone and L ^skin are functions of the irradiation light intensity I0, they are curved when accurately plotted. However, in order to conceptually describe ln (I / I ₀ ) −I ₀ , The optical path lengths L ^bone and L ^skin are plotted as a straight line as a linear function of I ₀ .

From FIG. _{11, ln (I / I 0} ) between the model and the Honeso only model of only skin layer in FIG. 10 -I0 becomes approximate line of the two-layer model of the skin layer and the bone layer ln (I / I ₀ ) An inflection point appears at −I ₀ . In the case of the two-layer model of the skin layer and the bone layer, the irradiation light intensity I _{0 up} to the inflection point is larger than the inflection point according to ln (I / I ₀ ) -I ₀ of the skin layer only model. It can be seen that the intensity I ₀ follows the same slope as ln (I / I ₀ ) −I _{0 of} the bone layer only model. As can be seen from the above, ln (I ^{skin + bone} / I ^skin ) has the same value as ln (I ^bone / I ₀ ^bone ).

Therefore, I ^skin can be known from the inflection point of the ln (I / I ₀ ) -I ₀ curve as shown in FIG. That is, at the inflection point indicated by the two-layer model of the skin layer and the bone layer, the reflected / scattered light intensity detected by the photodiode as the light receiving unit 30 is I ^skin .

From the above, it can be seen that by using the change tendency of the ln (I / I ₀ ) -I0 curve, the bone density can be evaluated without the influence of the skin, which is the upper layer tissue of the bone. This method is called a spatial intensity decomposition method.

(Example)
Next, a verification experiment was performed using a sample model to determine whether the density of the living body can be evaluated by removing the influence of interstitial tissues such as skin by the above-described spatial strength decomposition method.

  FIG. 12 is a diagram illustrating a configuration of a verification experiment system for the spatial intensity decomposition method. FIG. 12A shows the entire verification experiment system. The verification experiment system includes a computer 60, an interface board 70, a BNC connector box 80, a current driver 90 for the light emitting diode 21, a power source and amplifier 100 for the photodiode 31, a measuring unit 300, and a power source for the light emitting diode. 110. The measurement unit 300 includes a pair of light emitting diodes (LED) 21 (1550 nm / Epitex / Inc. / InGaAsP NIR LED, L1550-35) and a photodiode (PD) 31 (Judson, J16-5SP-R03M-SC). Has been. Each is connected to a computer 60 to control light emission and light reception. The light emitting diode 21 and the photodiode 31 are connected to each other through a signal conditioner, that is, a current driver 90 for the light emitting diode 21, a power source for the photodiode 31, and an amplifier 100 and a 16-bit interface board 70 (National Instruments, DAQCard-6036E). It is connected to a laptop computer 60 (1, Dell Inspiron 2200). Here, the light emitting diode (LED) 21 corresponds to the irradiation unit 20 in FIG. 7, and the photodiode (PD) 31 corresponds to the light receiving unit 30 in FIG. The current driver 90 for the light emitting diode 21 and the power source 110 for the light emitting diode correspond to the control unit 200 in FIG. The computer 60 corresponds to the computer including the change tendency calculating unit 201, the inflection point calculating unit 205, the density specifying unit 202, the reference data 203, and the display unit 204 in FIG.

  FIG. 12B shows a current drive circuit diagram for the light emitting diode. The light emitting diode current driving circuit is included in the light emitting diode 21 current driver 90, and the light emitting diode current driving circuit allows the light emitting diode 21 to emit light in a wide range from weak light to strong light.

  Note that the light emission control of the light emitting diode 21 and the acquisition and processing of the detection signal of the photodiode 31 were performed by a program created by Visual Basic.

  FIG. 13 is a diagram showing the relationship between the light emitting diode 21 and the photodiode 31 in this verification experiment. FIG. 13A is a diagram showing the positional relationship between the light emitting diode (LED) 21 and the photodiode (PD) 31 in this verification experiment, and FIG. 13B shows the current applied to the light emitting diode 21 ( It is a figure which shows the relationship between the light emission intensity | strength (PD output) of the light emitting diode detected by the photodiode 31 and Input Current to LED). As schematically shown in FIG. 13A, in this experiment, the light-emitting diode 21 and the photodiode 31 were arranged to face each other with an interval of about 30 mm. The current to the light emitting diode 21 was increased linearly, and the light emission intensity (V) of the light emitting diode 21 detected by the photodiode 31 at that time was set to I0. As a result, as shown in FIG. 13B, the relationship between the input current to the light emitting diode 21 and the light emission intensity was a non-linear relationship.

  FIG. 14 is a diagram showing a sample model used for verifying the spatial intensity decomposition method in this verification experiment. The sample is an experimental model consisting of two layers composed of glucomannan gel as the first layer and polyurethane sponge as the second layer. The water-containing glucomannan gel simulates the skin layer, and the polyurethane sponge simulates the bone layer. In the experiment, the glucomannan gel of the first layer was compared with the case of 6 mm and 14 mm, and the polyurethane sponge of the second layer was white, gray and black to change the light reflection and scattering characteristics. Three colors are used.

  Here, the three types of white, gray, and black colors used to change the light reflection / scattering characteristics correspond to cases where the bone density is different. FIG. 14A shows a case where the first layer of glucomannan gel is 6 mm and the second layer of polyurethane sponge is white (hereinafter referred to as White (6 mm)), and FIG. Shows the case where the first layer of glucomannan gel is 14 mm and the color of the second layer of polyurethane sponge is white (hereinafter referred to as White (14 mm)). FIG. 14C shows the case where the first layer of glucomannan gel is 6 mm and the color of the second layer of polyurethane sponge is gray (hereinafter referred to as Gray (6 mm)), and FIG. d) shows the case where the first layer of glucomannan gel is 14 mm and the second layer of polyurethane sponge is gray (hereinafter referred to as Gray (14 mm)). Further, FIG. 14E shows a case where the first layer of glucomannan gel is 6 mm and the color of the second layer of polyurethane sponge is black (hereinafter referred to as Black (6 mm)), and FIG. f) shows the case where the glucomannan gel of the first layer is 14 mm and the color of the polyurethane sponge of the second layer is black (hereinafter referred to as Black (14 mm)).

  The measurement was performed by manually pressing the measurement unit 300 composed of the light emitting diode 21 and the photodiode 31 against the surface of the first layer. Five measurements were performed under one condition, and the average was adopted.

FIG. 15 is a diagram illustrating a measurement result in the measurement unit 300 including the light emitting diode 21 and the photodiode 31. The horizontal axis represents the irradiation light intensity I, and the vertical axis represents the reflection / scattering light intensity I or the logarithm ratio ln (I / I ₀ ) of the irradiation light intensity I ₀ and the reflection / scattering light intensity I. Fig.15 (a) is a figure which shows the _I0- I curve of each sample in a measurement result. In all the samples shown in FIG. 14, the reflected / scattered light intensity I increased as the irradiation light intensity I0 increased. This tendency is particularly noticeable in the White (6 mm) sample, ie, the sample in which the first layer of glucomannan gel is 6 mm and the second layer of polyurethane sponge is white, Black (14 mm). That is, in the sample where the first layer of glucomannan gel was 14 mm and the color of the second layer of polyurethane sponge was black, the increase tendency was the weakest. In any sample, when the glucomannan gel of the first layer was thin, the increasing tendency of the reflected / scattered light intensity I appeared more strongly. FIG. 15B is a diagram showing an ln (I / I ₀ ) -I ₀ curve of each sample in the measurement result. As in the case of the I ₀ -I curve, although there is a difference when comparing each sample, the tendency of the curve in each sample was consistent until I ₀ was around 1 to 20. Therefore, as described above with reference to FIG. 12, in this I ₀ region, it can be determined that the reflected / scattered light is from the first layer of glucomannan gel.

FIG. 16 is a diagram showing extraction of inflection points in the ln (I / I ₀ ) -I ₀ curve in each sample of FIG. First, a linear part (approximate with a logarithmic curve) in the low irradiation light intensity region was determined, and a point at which it started to deviate from the straight line was defined as an inflection point. The reflected / scattered light intensity I at the determined inflection point was ^defined as I ^skin . FIG. 17 shows an ln (I ^{skin + bone} / I ^skin ) -I ^skin curve using I ^skin determined in this way.

FIG. 17 is a diagram in which an ln (I ^{skin + bone} / I ^skin ) −I ^skin curve is drawn as a log-log curve starting from I ^skin obtained in FIG. 16 for each sample. Where sponge layer
Is an area showing the second polyurethane sponge layer, and bottom surface is an area showing an experimental table under the sample used for evaluating the sample.

As shown in FIG. 17, the method of changing the curve differs depending on the difference in the polyurethane sponge of the second layer, but when the samples having the same polyurethane sponge of the second layer are compared, It can be seen that the same tendency is observed even when the gel thickness is different. FIG. 18 shows a comparison of the changing tendency of the low I ^skin region that is considered to reflect the polyurethane sponge of the second layer. Here, the low I ^skin region is approximated by a logarithmic function, and the coefficient is adopted as a parameter of the change tendency.

FIG. 18 shows that the density of the polyurethane sponge of the second layer is not affected by the difference in the thickness of the glucomannan gel of the first layer by using the ln (I ^{skin + bone} / I ^skin ) -I ^skin curve. It can be seen that the characteristics can be evaluated. That is, it can be seen that the bone density can be evaluated by removing the influence of the intervening tissue such as skin when measuring the bone density.

  In addition, although the near-infrared light emitting diode was demonstrated as an example as the irradiation part 20, for example, an optical fiber may be sufficient and it is not limited to an Example as a density measuring device. Similarly, a photodiode is described as an example of the light receiving unit 30, but is not limited thereto. Moreover, although the bone is used as the measurement object 10 and the skin is used as the intervening tissue part 11 as an example, it is not limited thereto.

  In addition, it is preferable to arrange | position the irradiation part 20 and the light-receiving part 30 closer, and it is still more preferable that the irradiation part 20 and the light-receiving part 30 arrange | position on the same axis | shaft. Moreover, the irradiation part 20 and the light-receiving part 30 may each consist of one each, and may be comprised as a pair of apparatus.

In addition, the above-described spatial intensity decomposition method, that is, the change tendency of the ln (I / I ₀ ) -I ₀ curve obtained by calculating from the reflected light intensity observed by changing the intensity of irradiation light is used. Any method that can evaluate the density inside the living body without the influence of the intervening tissue is within the scope of the present invention and is not limited to the above-described embodiment. For example, applications such as breast cancer screening and brain density screening are conceivable, but the measurement target 10 is not limited thereto.

  As described above, even when a tissue layer such as skin is present, the bone density can be evaluated without being affected by it. Therefore, the bone density and thus the density inside the living body can be evaluated non-invasively using light. Therefore, compared with the conventional method of measuring the inside of a living body, the irradiation unit 20 and the light receiving unit 30 are dense in a small and inexpensive device in which, for example, one light emitting diode and one photodiode are installed at the same location. A measuring device can be configured. Therefore, the apparatus can be reduced in size and price. Moreover, since the tendency (inclination) of the change of irradiation light intensity is taken, even if the irradiation part 20 is a light emission source which consists of 1 wavelength, it is not influenced by a background change.

  Thereby, a small and inexpensive device composed of a light emitting diode and a photodiode of near infrared light can be used for the configuration of the density measuring device. Therefore, there is no risk of being exposed to a human body by using light, and not only the density inside the living body can be measured non-invasively as biological information, but also a small and inexpensive density measuring device can be realized.

  Furthermore, in general, when the measurement object has light scattering characteristics, the intensity of the irradiation light and the average optical path length are not a simple proportional relationship, so it is unpredictable how much they will affect. Since the difference in intensity affects the measured value, the conventional method using a fixed irradiation light intensity always requires calibration of the irradiation light intensity. However, in principle, the present invention does not require calibration of the irradiation light intensity.

  Furthermore, when using the spatial intensity decomposition method, conventionally, a method using a photodiode array or a time decomposition method using pulsed laser light, both of which require more system components or relatively expensive components. On the other hand, the spatial intensity decomposition method using the intensity decomposition method can be realized with a small number of elements and at a low cost. That is, it is possible to realize a small and inexpensive density measuring device that can measure the density inside the living body as light by using light.

(Third embodiment)
In the biological density measurement according to the present invention, light is applied to the bone, and the non-invasive evaluation of the bone density is performed using the intensity of the reflected and scattered light intensity measured at that time. However, in order to obtain practical measurement accuracy, it is necessary to establish a method for compensating for the light attenuation due to the skin layer covering the bone. In the second embodiment, the change tendency of the ln (I / I ₀ ) -I ₀ curve obtained by calculating from the spatial intensity decomposition method, that is, the reflected light intensity observed by changing the intensity of irradiation light. The method of evaluating the density inside the living body by using the skin and excluding the influence of the skin as the intervening tissue has been described. In the third embodiment, the bone density can be evaluated without being influenced by a change in reflected light intensity observed by continuously changing the light source position even when a tissue layer such as skin is present. (Hereinafter referred to as the light source movement method) will be described.

  FIG. 19 is a block diagram schematically showing an example of a density measuring apparatus according to the third embodiment of the present invention.

  The density measuring device 4000 is reflected or scattered by the light irradiation unit 20 that changes the distance to the measurement target 10 and changes the intensity of light applied to the surface of the measurement target 10 to irradiate the measurement target 10 with light. The light receiving unit 30 that receives the received light, the control unit 400 that performs control to change the distance between the light irradiation unit 20 and the measurement object 10, the intensity of the light irradiated by the light irradiation unit 20, and the light received from the light receiving unit 30. A change trend calculating unit 401 that calculates a change trend based on the intensity of light, and a density specifying unit that specifies a biological density based on the change trend calculated by the change trend calculating unit 401 and reference data 403 prepared in advance. 402 and a display unit 204 that displays the biological density measured by the density specifying unit 402.

FIG. 20 schematically shows the light intensity I ₀ applied to the reference scattering medium 12 from the light irradiation unit 20 and the reflected light or scattered light I received by the light receiving unit 30 when measuring the measurement object 10. It is a figure. FIG. 20 shows the measurement object 10 and the intervention by increasing the intensity of the irradiation light irradiated from the irradiation unit 20 to the intervening tissue unit 11 in the order of FIGS. 20 (a), 20 (b) and 20 (c). It shows that the light penetration depth to the tissue part 11 is increased.

  Here, a reference scattering medium 12 having a predetermined light scattering characteristic is inserted between the measuring object 10 and the intervening tissue part 11 and the light irradiating part 20 which are the objects to be measured. By changing the thickness of the reference scattering medium 12 inserted between the intervening tissue part 11 and the light irradiation part 20, the intensity of the irradiation light irradiated from the irradiation part 20 onto the surface of the interstitial tissue part 11 is changed. can do. For example, by reducing the thickness of the reference scattering medium 12, it is possible to increase the intensity of irradiation light irradiated from the irradiation unit 20 to the surface of the intervening tissue unit 11.

  Next, a procedure for measuring the biological density of the density measuring apparatus 4000 according to the third embodiment will be described.

  The procedure for measuring the biological density of the density measuring apparatus 4000 can be described with reference to the flowchart shown in FIG.

  First, the light irradiation unit 20 is caused to emit light (S101). And the irradiation light irradiated to the surface of the intervening tissue part 11 from the irradiation part 20 by changing the thickness of the reference scattering medium 12 inserted between the light irradiation part 20 and the measurement object 10 and the intervening tissue part 11. The intensity of the. In other words, the control unit 400 changes the distance between the light irradiation unit 20 and the measurement target 10 to change the intensity of irradiation light irradiated from the irradiation unit 20 to the intervening tissue unit 11.

  Next, the light irradiated from the light irradiation unit 20 onto the surface of the intervening tissue unit 11 through the reference scattering medium 12 is reflected or scattered inside the measurement object 10 and the intervening tissue unit 11. The light receiving unit 30 receives light reaching the light receiving unit 30 with reflected or scattered light (S102).

Next, the change tendency calculation unit 401 includes the light intensity I ₀ applied to the reference scattering medium 12 from the light irradiation unit 20, the intensity I of light received by the light receiving unit 30, and the thickness of the reference scattering medium 12, that is, light. A change tendency is calculated based on the distance between the irradiation unit 20 and the intervening tissue unit 11 (S103).

  Next, the density specifying unit 202 measures the biological density based on the change tendency calculated by the change tendency calculation unit 401 (S104).

  Next, the display unit 204 displays the biological density measured by the density specifying unit 402.

  As described above, the biological density of the density measuring device 4000 can be measured.

  Next, the principle of the biological density measuring method of the density measuring apparatus 4000 will be described.

FIG. 21 is a schematic diagram illustrating the principle of the light source moving method in the case of a three-layer model in which a reference scattering medium is added to a two-layer model of a skin layer and a bone layer. Here, the principle of the light source moving method, that is, the incident light intensity (I ₀ ) is changed by moving the light source through the reference scattering medium 12, and the reflected / scattered light intensity (I) and Io obtained at that time are changed. By using this relationship, the principle of a method for evaluating the density inside a living body that is not influenced by intervening tissues such as skin will be described.

In FIG. 21, L ^skin is modeled on the thickness of the skin layer, that is, the thickness of the intervening tissue portion 11, and corresponds to the optical path length in the skin layer. L ^bone is modeled on the thickness of the bone layer, that is, the thickness of the measurement object 10, and corresponds to the optical path length in the bone layer. L ^ref is a model of the thickness of the reference scattering medium 12, that is, the thickness of the reference scattering medium 12, and corresponds to the optical path length in the reference scattering medium 12. In addition, the thickness of the intervening tissue part 11 which is a skin layer is constant.

μ _r ^skin is a light attenuation coefficient in the skin layer which is the intervening tissue part 11. μ _r ^bone is a light attenuation coefficient in the bone layer that is the measurement object 10. Further, μ _r ^ref is a light attenuation coefficient in the reference scattering medium that is the reference scattering medium 12.

In FIG. 21, as shown in FIG. 20, the irradiation unit 20 and the intervening tissue part are changed by changing the thickness of the reference scattering medium 12 between the intervening tissue part 11 that is the skin layer and the light irradiation unit 20. 11 is changed, and the intensity of irradiation light irradiated from the irradiation unit 20 to the surface of the intervening tissue unit 11 is changed. Therefore, the optical path length L ^ref is variable, and the optical path length L ^bone indicating the light penetration depth into the bone layer is the thickness of the reference scattering medium 12, that is, the distance between the light irradiation unit 20 and the surface of the intervening tissue unit 11. Along with this, the intensity of irradiation light irradiated from the irradiation unit 20 to the surface of the intervening tissue unit 11 changes. Moreover, since the thickness of the intervening tissue part 11 which is a skin layer is constant, the optical path length L ^skin is constant.

  In the three-layer model of the skin layer, the bone layer, and the reference scattering medium shown in FIG. 21, an attempt is made to formulate the behavior of light based on Lambert-Beer law.

  The obtained reflected / scattered light intensity (I) can be expressed by the following relational expression (Expression 9) based on Lambert-Beer's law, as in Expression (6) in FIG.

From the equation (9), the ratio of the incident light intensity I ₀ and the reflected / scattered light intensity I is expressed by the following relational expression (equation 10).

The logarithm of the ratio of the incident light intensity I ₀ and the reflected / scattered light intensity I corresponding to the light intensity I ₀ irradiated from the light irradiation unit 20 to the reference scattering medium 12 from the equation (Equation 10) is described above with reference to FIG. So as to reflect the bone density.

Here, the optical path length L ^skin of the skin layer is constant as described above. The term relating to the skin layer in the equation (10) can be expressed as the following equation (11).

In addition, from FIG. 20, the irradiation light irradiated from the irradiation unit 20 to the intervening tissue unit 11 by shortening the distance between the irradiation unit 20 and the intervening tissue unit 11, that is, by reducing the thickness of the reference scattering medium 12. And the depth of light penetration into the measurement object 10 can be increased. In Figure 21, in other words the content of the above, by shortening the optical path length L ^ref of the reference scattering medium 12, it is possible to lengthen the optical path length L ^bone at the bone layer.

  Therefore, from the above correlation, if the optical path length change (movement amount) in the reference scattering medium 12 is equal to the optical path length change in the bone layer, the relation is expressed by the following equation (12).

  As described above, the following equation (13) can be derived from the equation (9), the equation (10), the equation (11), and the equation (12).

Here, μ _r ^{ref in} equation (13) is a known constant. Therefore, μ _r ^bone can be evaluated from the slope of the ln (I / I ₀ ) -L ^ref curve indicating the relationship between the logarithm of the ratio of the irradiated light intensity I 0 and the reflected / scattered light intensity I to the optical path length L ^ref . it can.

FIG. 22 is a diagram conceptually illustrating ln (I / I ₀ ) −L ^ref of the three-layer model in which the reference scattering medium 12 is added to the skin layer and the bone layer in FIG.

  In the light source movement method, the light irradiation unit 20 irradiates light to the measurement target 10 (bone layer) and the intervening tissue part 11 (skin layer), which are measurement objects, via the reference scattering medium 12 having light scattering characteristics. The reflected / scattered light intensity is detected by the light receiving unit 30. By changing the thickness of the reference scattering medium 12, that is, the distance from the light irradiation unit 20 to the intervening tissue part 11 (skin layer) that is the measurement target, the measurement object 10 (bone layer) that is the measurement target is changed. The light penetration depth can be changed.

  First, when the distance between the light irradiation unit 20 and the intervening tissue part 11 (skin layer) that is the measurement target is sufficiently large, the light does not reach the intervening tissue part 11 (skin layer) that is the measurement target. The obtained reflected / scattered light intensity is a value reflecting only the optical characteristics of the reference scattering medium 12 (region (a) in FIG. 22).

  Next, when the distance between the light irradiation unit 20 and the intervening tissue part 11 (skin layer) that is the measurement object approaches, the light reaches the intervening tissue part 11 (skin layer) that is the measurement object. When light passes through the intervening tissue part 11 (skin layer), which is the measurement object, the light is attenuated by the intervening tissue part 11 (skin layer), which is the measurement object, and thus the reflected / scattered light intensity obtained is weakened. (Region (b) in FIG. 22).

  Next, when the distance between the light irradiation unit 20 and the intervening tissue part 11 (skin layer), which is a measurement object, further approaches, the light reaches the measurement object 10 (bone layer), which is a measurement object. When the light reaches the measurement object 10 (bone layer) that is the measurement object, the intensity of reflected / scattered light (detection light) obtained for reflection / scattering by the bone layer increases (region (c) in FIG. 22). .

Finally, when the distance between the light irradiation unit 20 and the intervening tissue part 11 (skin layer), which is the measurement object, further approaches, and the light source contacts the intervening tissue part 11 (skin layer), which is the measurement object, The intensity of the reflected / scattered light is a value determined only by the optical characteristics of the intervening tissue part 11 (skin layer) and the measurement object 10 (bone layer), which are measurement objects. Thereby, the reflected / scattered light intensity change (in (I / Io) -L ^ref curve slope) in the region (c) of FIG. 22 is constant without depending on the state of the intervening tissue part 11 (skin layer). It becomes.

  Therefore, the bone density evaluation which is not influenced by the intervening tissue part 11 (skin layer) can be performed by using this value (slope).

(Example)
Next, the principle of the light source movement method described in FIGS. 21 and 22 was confirmed by Monte Carlo simulation. Here, the Monte Carlo simulation is a numerical simulation using random numbers.

FIG. 23 is a diagram illustrating a simulation result when the light source movement method is applied to the case where there is no intervening tissue portion 11 (skin layer) (only bone). This is an example in which the light source movement method is applied to a single-layer tissue model of only bone, and here, the bone condition (scattering coefficient) is changed. As shown in FIG. 23, the slope of the In (I / Io) -L ^ref curve changes with changes in the bone scattering coefficient. Therefore, the bone scattering coefficient (a parameter related to bone density) can be predicted from the slope of the In (I / Io) -L ^ref curve.

FIG. 24 is a diagram showing a simulation result when the light source moving method is applied when there is an intervening tissue part 11 (skin layer). This is an example in which the light source movement method is applied to a two-layer tissue model of skin and bone. Here, the bone condition (scattering coefficient) is constant. As shown in FIG. 24, the slope of the In (I / Io) -L ^ref curve does not change even when the skin condition (thickness) changes.

FIG. 25 shows the In (I / Io) -L ^ref curve when there are no intervening tissue part 11 (skin layer) and when there is interstitial tissue part 11 (skin layer) under various bone conditions (scattering coefficients). It is the figure which compared the inclination. As shown in FIG. 25, the two agree well in any bone condition (scattering coefficient).

FIG. 26 is a diagram showing the relationship between the slope of the In (I / Io) -L ^ref curve and the bone scattering coefficient under various skin conditions (thicknesses). As shown in FIG. 25, both can be satisfactorily approximated by an exponential function. From this, it can be said that the slope of the In (I / Io) -L ^ref curve can be a bone density evaluation parameter that is not affected by the skin. Therefore, it can be confirmed that the bone scattering coefficient (bone density) can be predicted from the slope of the In (I / Io) -L ^ref curve.

  Next, an attempt was made to construct a relational expression for predicting bone density by Monte Carlo simulation.

  FIG. 27 is a diagram used to construct a relational expression for predicting bone density. The relational expression for predicting the bone density constructed by the Monte Carlo simulation can be expressed as the following (Expression 14) from FIG.

Therefore, by using the equation (14), the bone scattering coefficient (bone density) can be predicted from the slope of the In (I / Io) -L ^ref curve.

  As a method for predicting the bone scattering coefficient (bone density), there is a method for predicting by taking into account the attenuation due to the skin. Hereinafter, it will be described as a modification.

  FIG. 28 is a diagram conceptually showing a change in diffuse reflected light intensity with a change in light source distance in the three-layer model in which the reference scattering medium 12 is added to the skin layer and the bone layer in FIG. 28 (a), 28 (b), and 28 (c) show the same contents as FIG. 22 (a), FIG. 22 (b), and FIG. 22 (c) with the vertical axis as the diffuse reflectance. I will omit the explanation.

  In addition, the curve shown with the dotted line is a case without a skin layer, and the vertical axis | shaft is shown as a diffuse reflectance about the content similar to the area | region of Fig.22 (a). That is, the diffuse reflectance without the skin layer changes exponentially and depends on the light characteristics of the reference scattering medium 12.

  FIG. 29 is a diagram illustrating a simulation result of the relationship between the diffuse reflectance and the thickness of the reference scattering medium 12 under various conditions (thicknesses) in the light source moving method. The vertical axis represents the diffuse reflectance, and the horizontal axis represents the thickness of the reference scattering medium 12. Compared with FIG. 28, it can be seen that the diffuse reflectance at the time of contact with the light source in FIG. 29 reflects the bone density, but includes an attenuation due to the skin. That is, the size of the area indicated by ΣΔ (I / Io) in FIG. 29 indicates the magnitude of the skin effect.

  FIG. 30 is a diagram showing a simulation result for removing skin influence and predicting bone density. FIG. 30A is a diagram showing a simulation result showing a relationship between ΣΔ (I / Io) and the attenuation amount by the skin of the diffuse reflectance at the time of light source contact. FIG. 30B is a diagram showing a simulation result showing the relationship between the predicted diffuse reflectance at the time of light source contact and the diffuse reflectance at the time of light source contact.

  From FIG. 30, it is possible to know the amount of attenuation by the skin of the diffuse reflectance when the light source is in contact from ΣΔ (I / Io). Therefore, by adding the attenuation due to the skin, it is possible to know the diffuse reflectance at the time of contact with the light source of only the bone, and to predict the bone density.

  Next, a verification experiment system for verifying the relational expression for predicting the bone density constructed by the Monte Carlo simulation will be described below.

  FIG. 31 is a diagram showing a configuration of a verification experiment system for the light source movement method.

  FIG. 31 shows the entire verification experiment system. The verification experiment system includes a computer 60, an AD / DA interface board 71, a laser diode power source 420, a laser diode 421, a beam splitter 422, a light source moving mechanism 423, a convex lens 424, and a laser diode 421. Power supply and an amplifier 432.

  Here, correspondence with FIG. 20 will be described. The control unit 400 corresponds to the light source moving mechanism unit 423, and the light irradiation unit 20 corresponds to the laser diode 421. The change tendency calculating unit 401, the reference data 403, the density specifying unit 402, and the display unit 204 are included in the computer 60.

  FIG. 32 is an actual photograph of the configuration of the verification experiment system for the light source movement method.

  The verification experiment of the light source movement method described above can be performed by the verification experiment system of the light source movement method shown in FIGS.

As described above, according to the density measuring apparatus and the method thereof according to the embodiment of the present invention, the irradiation light intensity I ₀ is continuously changed, and the reflected / scattered light intensity detected at that time is analyzed. The in vivo density can be evaluated non-invasively. Specifically, (1) strength decomposition method, that is, a method of evaluating the bone density and hence the density inside the living body from the slope of the I ₀ -I curve, and (2) spatial strength decomposition method, that is, ln (I / I ₀ ). A method of evaluating the bone density and thus the density inside the living body without the influence of the upper layer tissue by using the change tendency of the −I ₀ curve, or (3) The light source moving method, that is, the light source position is continuously changed. By using light, the bone density and thus the density inside the living body can be non-invasively determined by a method that can evaluate the bone density without being affected by changes in the reflected light intensity observed by the Can be evaluated. Therefore, a small and inexpensive device can be used for the configuration of the density measuring device.

  Thereby, there is no danger of being exposed to a human body by using light, and not only the density inside the living body can be measured non-invasively as biological information, but also a small and inexpensive density measuring device can be realized.

  As described above, the density measuring device of the present invention has been described based on the embodiment, but the present invention is not limited to this embodiment. Unless it deviates from the meaning of this invention, the form which carried out the various deformation | transformation which those skilled in the art can think to this embodiment, and the structure constructed | assembled combining the component in different embodiment is also contained in the scope of the present invention. .

  INDUSTRIAL APPLICABILITY The present invention can be used in a density measuring device and a measuring method for measuring the density inside a living body, and in particular, can be used in a density measuring device and a measuring method for detecting bone density or detecting breast cancer lump.

It is a figure which shows roughly an example of the density measuring device in the 1st Embodiment of this invention. It is the figure which showed typically about the measuring object, the light irradiation part, and the light-receiving part in the 1st Embodiment of this invention. It is the flowchart which showed the procedure at the time of measuring the biological density of the density measuring device in the 1st Embodiment of this invention. Is a diagram showing the relationship between the irradiation light intensity I ₀ and the reflected and scattered light intensity I of the density measuring device according to the first embodiment of the present invention. It is a diagram showing a relationship between slope and bone density I ₀ -I curve and I ₀ -I curve for gelatin simulated bone sample in the first embodiment of the present invention. It is a figure which shows the influence of the skin layer on the inclination of the _I0- I curve of the gelatin simulated bone sample in the 2nd Embodiment of this invention. It is a figure which shows roughly an example of the density measuring apparatus in the 2nd Embodiment of this invention. It is the figure which showed typically about the measuring object 10, the light irradiation part 20, and the light-receiving part 30 at the time of measuring the measuring object 10 in the 2nd Embodiment of this invention. It is the flowchart which showed the procedure at the time of measuring the biological density of the density measuring device in the 2nd Embodiment of this invention. It is a schematic diagram for demonstrating the principle of the spatial intensity | strength decomposition method in the case of the two-layer model which consists of skin and the bone in the 2nd Embodiment of this invention. Is a diagram conceptually illustrating the _{ln (I / I 0) -I} 0 when consisting of only two layers and Honeso the skin layer only and skin layers and the bone layer. It is a figure which shows the structure of the verification experiment system of the spatial decomposition method in the 2nd Embodiment of this invention. It is the figure which showed the relationship between the light emitting diode of the verification experiment in the 2nd Embodiment of this invention, and a photodiode. It is the figure which showed the sample model used for the verification experiment in the 2nd Embodiment of this invention. It is a figure which shows the measurement result in the measurement part comprised by the light emitting diode and photodiode of the verification experiment system in the 2nd Embodiment of this invention. Is a diagram illustrating the extraction of inflection points of a 2 ln (I / I ₀₎ of each sample used in the verification experiment in the embodiment of -I ₀ curve of the present invention. FIG. 6 is a diagram in which an ln (I ^{skin + bone} / I ^skin ) -I ^skin curve is drawn as a log-log curve starting from the reflected / scattered light intensity at the inflection point obtained for each sample in the second embodiment of the present invention. It is. It is the figure which compared the change tendency of the low I ^skin area ^| region reflecting the polyurethane sponge layer of each sample used for the experiment in the 2nd Embodiment of this invention. It is a block diagram which shows roughly an example of the density measuring device in the 3rd Embodiment of this invention. FIG. 6 is a diagram schematically showing light intensity I ₀ applied to the reference scattering medium 12 from the light irradiation unit 20 and reflected light or scattered light I received by the light receiving unit 30 when measuring the measurement target 10. . It is a schematic diagram which shows the principle of the light source movement method in the case of the three-layer model which added the reference scattering medium to the two-layer model of the skin layer and the bone layer. Is a diagram conceptually illustrating the _{ln (I / I 0) -L} ref three layer model plus a reference scattering medium 12 and the skin layer and the bone layer. It is a figure which shows the simulation result at the time of applying the light source movement method when there is no intervening tissue part 11 (skin layer) (only a bone). It is a figure which shows the simulation result at the time of applying the light source movement method when there exists the intervening tissue part 11 (skin layer). In various bone conditions (scattering coefficients), the slopes of In (I / Io) -L ^ref curves were compared when there was no intervening tissue part 11 (skin layer) and when there was intervening tissue part 11 (skin layer). FIG. It is a diagram showing a relationship between an In (I / Io) the slope and bone scattering coefficient -L ^ref curve in various skin conditions (thickness). It is the figure used in order to build the relational expression which estimates bone density. It is a figure which shows notionally the change of diffuse reflected light intensity with the change of light source distance in the three-layer model which added the reference scattering medium 12 to the skin layer and the bone layer. It is a figure which shows the simulation result of the relationship between the diffuse reflectance in various conditions (thickness) and the thickness of the reference scattering medium 12 in the light source movement method. It is a figure which shows the simulation result for removing skin influence and predicting bone density. It is a figure which shows the structure of the verification experiment system of the light source movement method. It is a photograph of the actual thing about the structure of the verification experiment system of the light source movement method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Measurement object 11 Interstitial tissue part 12 Reference scattering medium 20 Irradiation part 21 Light emitting diode 30 Light receiving part 31 Photodiode 60 Computer 70 Interface board 71 AD / DA interface board 80 BNC connector box 90 Current driver for light emitting diode 100 Photodiode Power source and amplifier 110 Light emitting diode power source 200, 400 Control unit 201, 401 Change tendency calculation unit 202, 402 Density specifying unit 203, 403 Reference data 204 Display unit 205 Inflection point calculation unit 300 Measurement unit 420 Laser diode power source 421 Laser diode 422 Beam splitter 423 Light source moving mechanism 424 Convex lens 431 Photo diode 432 Laser diode power supply and amplifier 1000, 4000 Degree measuring device

Claims (15)

A density measuring device for measuring a biological density,
A light irradiating means for changing the intensity of light to irradiate light inside the object to be measured;
A light receiving means for receiving reflected light from the inside of the measurement object of the irradiated light;
A change tendency calculating means for calculating a change tendency of the intensity of the reflected light received with respect to the intensity of the irradiated light;
A density measurement device comprising: density specifying means for specifying the density of the measurement object based on the change tendency. The density measuring apparatus according to claim 1, wherein the change tendency calculating unit calculates a change tendency obtained from a rate of change of the intensity of the reflected light received with respect to the intensity of the irradiated light. The density measuring device further includes:
An inflection point calculating means for calculating the inflection point of the curve of the change tendency from the rate of change of the intensity of the reflected light received with respect to the intensity of the irradiated light,
3. The density according to claim 2, wherein the density specifying unit specifies the density of the measurement object based on the inflection point calculated by the inflection point calculation unit and the change tendency calculated by the change tendency calculation unit. Density measuring device. The density measuring apparatus according to claim 1, wherein the light irradiation unit changes the intensity of light applied to the surface of the measurement target by changing a distance from the measurement target. The density measurement apparatus according to claim 4, further comprising a reference scattering medium inserted between the light irradiation unit and the measurement target. 6. The density measuring apparatus according to claim 5, wherein the change tendency calculating means calculates the change tendency from a rate of change of the intensity of reflected light received with respect to a distance between the light irradiation means and the measurement object. . The density measuring apparatus according to claim 6, wherein the density specifying unit further specifies the density of the measurement target based on an integration of the change tendency with respect to a distance between the light irradiation unit and the measurement target. . The density measuring apparatus according to claim 1, wherein the light irradiated from the light irradiation unit is near infrared light. The light irradiation means comprises a light emitting diode,
The density measuring apparatus according to claim 1, wherein the light receiving unit is configured by a photodiode. The density measuring apparatus according to claim 9, wherein the measurement object is a bone and measures a bone density. An optical axis of light irradiated by the light irradiation means;
What is the optical axis of light received by the light receiving means?
The density measuring device according to claim 1, wherein the density measuring device is arranged on the same axis. A method for measuring biological density,
A light irradiation step for irradiating light inside the measurement object by changing the intensity of the light;
A light receiving step for receiving reflected light from the inside of the measurement target of the irradiated light;
A change tendency calculating step for calculating a change tendency of the intensity of the reflected light received with respect to the intensity of the irradiated light;
And a density specifying step for specifying the density of the measurement object based on the change tendency. A method for measuring biological density,
A light irradiation step of irradiating light inside the measurement object by changing the intensity of the light;
A light receiving step for receiving reflected light from the inside of the measurement target of the irradiated light;
A change trend calculating step for calculating a change trend obtained from the rate of change of the intensity of the reflected light received with respect to the intensity of the irradiated light;
An inflection point calculating step of calculating an inflection point of the curve of the change tendency;
A density specifying step for specifying the density of the measurement object based on the change tendency;
The living body density measuring method comprising: the density specifying step for specifying the density of the measurement object based on the calculated inflection point and the calculated change tendency. A program for realizing measurement of biological density,
A light irradiation step for irradiating light inside the measurement object by changing the intensity of the light;
A light receiving step for receiving reflected light from the inside of the measurement target of the irradiated light;
A change tendency calculating step for calculating a change tendency of the intensity of the reflected light received with respect to the intensity of the irradiated light;
A biological density measurement program for realizing, by a computer, a density specifying step for specifying the density of the measurement object based on the change tendency. A program for realizing measurement of biological density,
A light irradiation step for irradiating light inside the measurement object by changing the intensity of the light;
A light receiving step for receiving reflected light from the inside of the measurement target of the irradiated light;
A change trend calculating step for calculating a change trend obtained from the rate of change of the intensity of the reflected light received with respect to the intensity of the irradiated light;
An inflection point calculating step of calculating an inflection point of the curve of the change tendency;
A density specifying step for specifying the density of the measurement object based on the change tendency;
A biological density measurement program for realizing, by a computer, the calculated inflection point and the density specifying step for specifying the density of the measurement object based on the calculated change tendency.