JP2017159032A - Bone density measurement device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measurement device of a bone density having higher measuring accuracy of the bone density of a bone under a skin, and possibly serving as a compact handy type one and to provide a measurement method of bone density using the same.SOLUTION: A measurement device of the bone density of a bone existing under a skin has a light irradiation part which irradiates a subject with light of a predetermined strength, filter means which removes scattered light reflected from a skin of the subject, light collection means of reflection light from which the scattered light is removed, and a light detection part which measures the strength of light collected by the light collection means.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an apparatus for measuring bone density and a measurement method using the same, and more particularly to optical bone density measurement using light.

Currently, an apparatus using X-rays is used for osteoporosis diagnosis. However, such an apparatus is large and difficult to operate as a simple measurement such as early detection of a decrease in bone density.
On the other hand, near-infrared light has been studied in various medical fields as a means for obtaining in vivo information in a destructive manner.
The present inventor has proposed Patent Documents 1 and 2 as optical bone density measuring devices.
The present invention further improves the measurement accuracy, and particularly suppresses the influence of living tissue such as the thickness and color of the skin layer existing outside the bone.

JP 2007-007267 A JP 2008-155011 A

  An object of the present invention is to provide a bone density measuring device that has high accuracy in measuring bone density of bones under the skin and is also a compact handy type, and a bone density measuring method using the same.

  A bone density measuring apparatus according to the present invention is a bone density measuring apparatus that exists below the skin, and is reflected from the skin of the subject, a light irradiating unit that injects light of a predetermined intensity onto the subject. A filter unit that removes scattered light, a condensing unit for reflected light from which the scattered light has been removed, and a light detection unit that measures the intensity of the light collected by the condensing unit. And

The present invention focuses on the existence of quasi-straight light in which light that has penetrated deeply into the bone part rebounds and scattered light that repels in the skin layer when light is irradiated from the light irradiation part toward the subject. However, the scattered light is removed by a filter means.
The quasi-straight light attenuates and rebounds in the bone, but its intensity distribution attenuates in the radial direction from the incident position of the light.
It is noted that this radial attenuation decreases rapidly as the bone density increases.

In the present invention, a movement control unit having an optical unit incorporating the light irradiation unit, the light detection unit, a filter unit, and a light collecting unit, and capable of moving and controlling the distance of the optical unit from the subject, and the light irradiation unit And an absorbance calculation means for calculating the absorbance from the light detection unit.
If it does in this way, it will become a compact structure and will become a handy type measuring device.

In the present invention, the light condensing means may be a pair of lenses, and the filter means may be a slit plate.
In this way, it is possible to remove scattered light rebounding from the skin layer at a portion other than the slit portion while allowing quasi-linear light rebounding from the slit portion of the slit plate to pass.
Further, various lenses can be combined as long as the lens collects light toward the light detection unit.

  In the present invention, scattered light reflected from the skin can be removed, but in order to obtain skin thickness information, the light irradiation unit has a plurality of irradiation sources having different wavelengths, and the light detection unit has the plurality of irradiations. It is preferable to have means for detecting the difference in intensity of the light between the sources.

A bone density measuring method according to the present invention is a bone density measuring method using the bone density measuring device according to any one of claims 1 to 3, wherein the light irradiation unit and a subject are changed in distance, and the light The bone density is measured based on a change in the detected intensity detected by the light detecting unit with respect to the incident intensity of the incident light irradiated from the irradiating unit.
The change in detection intensity detected by the light detection unit obtained in this way is known in advance because, for example, the slope of attenuation in the radial direction from the position irradiated with light changes depending on the level of bone density. The bone density of the subject can be obtained using calibration curves of measured values of various samples.

  The bone density measuring method using the bone density measuring device according to claim 4, wherein the incident intensity of the incident light irradiated from the light irradiation unit is changed by changing a distance between the light irradiation unit and the subject. The bone density can be measured based on the light intensity distribution obtained from the detected intensity detected by the light detecting unit and the skin thickness information obtained by the light intensity difference detecting means.

The present invention can measure the intensity distribution of the absorbance while moving the slit plate and the lens toward the subject while removing the influence of the skin tissue layer with the slit plate, so that the handy type compact measurement is possible. It becomes a device.
Further, by using a plurality of irradiation sources having different wavelengths, such as near infrared light and visible light, and detecting skin thickness information from the difference in light intensity, the bone density measurement accuracy is further improved.

The structural example of the optical unit which concerns on this invention is shown. The explanatory view of the measurement principle of bone density is shown. (A)-(c) shows typically removal of the scattered light from a skin layer, (d) shows explanatory drawing of an absorbance distribution, (e) shows the relationship between a bone density and the inclination of attenuation distribution. The structural example of the measuring device which concerns on this invention is shown, (a) is a block diagram, (b) is an external view, (c) shows a measurement state. It shows the measured values using the laser beam irradiation wavelength 650 nm, (a) shows the intensity distribution of the 9-point measurement using a phantom density 258 mg / cm ³ in the graph, (b) the density of 253mg ^/ cm 3, 175mg / ^cm 3, shows a graph of the mean value curves of the 9-point measurement of 115 mg / cm ^3. (A) shows the inclination graph of the range of Z = 10-17 mm, (b) shows the graph which plotted the relationship of the inclination with respect to the change of a density. It shows a graph obtained by measuring the absorbance distribution using the irradiation wavelength 850 nm, bone density (a) is 258mg / ^cm 3, (b) is 178mg / ^cm 3, (c) is a 151 mg / cm ^3, the skin The intensity distribution of absorbance assuming thicknesses of 0, 0.2, 0.5, 1.0, and 2.0 mm is shown. The relationship between the inclination of the absorbance in the measurement range Z = 18 to 25 mm and the bone density (mg / cm ³ ) is shown. An example in which a plurality of irradiation sources are provided is shown. The relationship between an irradiation wavelength and the penetration depth to skin is shown typically. (A) shows the influence which light receives from a biological body. (B) shows the reach | attainment depth of the light in skin. (C) shows the change in light intensity depending on the wavelength. The graph of the skin thickness in each wavelength and its light intensity change is shown. (A) represents the position of the peak of the light intensity distribution at wavelengths 515 nm and 850 nm as Z. (B) shows the relationship between the peak light intensity of two irradiation sources and the skin thickness difference. The correlation of the prediction bone density computed by Formula (3) and the measurement density by μCT is shown.

  A configuration example and a measurement method example of a bone density measuring apparatus according to the present invention will be described below, but the present invention is not limited to this.

FIG. 1 shows a configuration example of the optical unit, and FIG. 2 shows an explanatory diagram of the measurement principle.
A light irradiation unit 13 that irradiates light toward the subject 1, and a first slit plate 11a and a second slit plate 11b as filter means for removing noise caused by scattered light from the light returned from the subject. The light passing through the slit of the first slit plate 11a is refracted into substantially parallel light by the first lens 12a made of a plano-convex lens, and the light passed through the slit of the second slit plate 11b is made a second made of a convex lens. The light is condensed toward the light detection unit by the lens, and the light intensity is detected by the light detection unit.
Here, assuming that the intensity of light incident from the light irradiating unit is incident light intensity I ₀ and the intensity of light detected by the light detecting unit is detected light intensity I, the absorbance A is obtained by the following equation (1). .

The measurement principle of bone density will be described with reference to FIG.
The light incident on the subject passes through Skin (skin tissue), passes through the bone (bone), and returns to the quasi-straight-forward light and scattered light returning from the skin tissue layer.
By providing the slit plate, as shown in FIGS. 2A to 2C, the quasi-straight light is allowed to pass through the slit of the slit plate, and the scattered light from the skin tissue layer is removed at a portion other than the slit of the slit plate. be able to.
Therefore, as shown in FIG. 2D, when the distance Z from the subject of the slit and the lens is moved, the intensity distribution of the quasi-straight-ahead light that returns while being attenuated in the radial direction from the incident position of the light is detected. Can do.
Here, since the attenuation in the radial direction increases as the bone density increases, the bone density can be measured using the magnitude of the inclination as an index.

A configuration example of the bone density measuring device 20 used specifically for measuring the bone density is shown in FIG.
This is a measuring device 20 in which the optical unit 10 is incorporated in a handy-type housing that is a gun type.
In the optical unit 10, a laser diode is arranged in the light irradiation unit 13, a first lens 12a and a first slit plate 11a are provided on the tip side, and a second slit plate 11b and a second lens 12b are provided behind the laser diode. The intensity of the collected light is measured by the light detection unit 14 made of a photodiode.
The optical unit 10 is attached to an actuator 21 and is controlled to move forward and backward by a step motor 22.
A detection signal amplifier 23 for a signal detected by the light detection unit, a step motor control unit 24, a microcomputer 25, and the like are incorporated.
A battery 26 is built under the handy grip.
Optical unit movement distance data, detected light intensity data, and the like are taken into the personal computer 27 by serial communication.

A verification experiment using ashed bovine cancellous bone as a phantom will be described below.
As the incinerated bovine cancellous bone, a cancellous bone was cut from a bovine femur into a block shape of about 4 cm on one side, the bone marrow was boiled and removed, and an ashing treatment was performed at 600 ° C. for 24 hours.
The specimen, the ashing bovine cancellous bone was dissolved in hydrochloric acid, was used for density ^{253mg / cm 3, 178mg / cm} 3, 151mg / cm 3.
A laser diode (# 57-101) manufactured by Edmond Optics was used as the light source of the light irradiation section.
This has an output wavelength of 655 nm and a maximum output of 3 mW.
As the measurement of the absorbance A, the position from the subject, which is the focal point distance of the lens, was set as Z = 0, and the depth direction of the subject was measured as the positive direction.
FIG. 4A shows a measurement graph of the movement amount Z and the absorbance A at nine different positions using a density of 258 mg / cm ³ phantom.
The absorbance distribution at each position showed similar changes.
FIG 4 (b) shows the trend graph of the density of ^{258mg / cm 3, 178mg / cm} 3, 151mg / cm 3 each 9-point measurement average value.
Focusing on the slope of Z = 10 mm or more among them, the absorbance attenuation straight line with the movement amount Z = 11 to 18 mn is shown in FIG.
FIG. 5B shows the relationship between the density of the phantom and the slope of the attenuation line shown in FIG.
As a result, it can be seen that the bone density can be measured using the slope of attenuation of absorbance as an index.

Next, a laser diode (LDM115G / 850/1) manufactured by Imatronic was used as the light source of the light irradiation unit.
This has a wavelength of 850 nm and a maximum output of 1 mW.
FIG. 6 shows a measurement graph of the amount of movement Z and the absorbance measured in the same manner as in Example 1.
In Example 2, in order to investigate the influence of the thickness of the skin layer, specimens having thicknesses of 0, 0.2, 0.5, 1.0, and 2.0 mm were used.
As the skin layer, simulated skin in which 2% intralipid solution was sealed between two cover glasses and the thickness thereof was adjusted was used.
Note that 2% intralipid has been reported to have the same optical properties as human skin (Troy, S., et al., Journal of biomedical optics, vol. 6, pp. 167-176, 2001).
FIG. 7 shows the relationship between the inclination obtained by linearly approximating the inclination between Z = 18 and 25 mm and the bone density.
From this graph, it was inferred that there was an effect when skin tissue was present.

Next, as schematically shown in FIG. 8, in order to obtain skin thickness information in addition to the irradiation source (light irradiation unit) 13 for measuring bone density, two irradiation sources 13a and 13b having different wavelengths are provided. The mounting was evaluated.
Specifically, two circular slits (slit diameter: 10 mm, slit width: 2 mm, thickness 5 mm), two single convex lenses (Edmund Optics, 48795, and 48797), three laser diodes [for density measurement (center) : Egismos, H838501D (850nm, 1mW), For skin thickness measurement: S638501D (850nm, 1mW), H635151R (515nm, 1mW)], and PD (Hamamatsu, C12703-01) are combined into one optical unit and stepped The actuator (Misumi, LX2005P-MX-B1-T2028-150) driven by a motor (Orientalmoter, PKP225) can be moved in the Z direction.
The detection signal obtained from the PD was subjected to ADC conversion by an ADC element (Microchip, MCP3208, 12 bits) through a secondary anti-aliasing filter circuit.
Motors and lasers are controlled by a single board computer (Raspberry Pi, RS Components, Raspberry Pi 2 Model B), and the detection results are saved in a CSV text file. Based on this data, a graph of the relationship between travel distance and absorbance That is, the light intensity distribution is displayed on the display.
In addition, experiments were performed using ashed bovine cancellous bone, ashed bovine dense bone, and silicone (cemedine strain, silicone sealant) as simulated skin.
Ashed bovine cancellous bone is cut from canine femur into blocks of 4cm on a side, boiled to remove bone marrow, and then ashed at 600 ° C for 24 hours in an electric furnace. Nine samples were made.
The ashed bovine cancellous bone has a variation in density peculiar to living bodies depending on the location.
Therefore, scan with μCT (Shimadzu, inspeXio SMX-90CT Plus), select a cubic range of 1 cm on each side at three different positions for each sample, and bone morphology measurement software (Ratok System Engineering Co., Ltd., TRI / 3D-) BON-FCS64) was used to calculate the bone density in the same range.
The dense bone portion was obtained by ashing a slice of 0.3 mm thick parallel to the axial direction from the trabecular portion of the bovine femur.
The fine bone thickness was determined by reading the cortical bone thickness at the distal end of the radius from the section image of Visible Human FTP Resource, which is a database of the National Library of Medicine, and referring to this value.
In order to simulate the optical characteristics of the skin, a liquid sample of 2% intralipid is often used. In this experiment, a solid sample that is easier to handle was made of silicone.
Since it was confirmed that silicone mixed with white and clear at 1: 6 has the same absorbance characteristics as 2% Intralipid, simulated skin having different thicknesses of 1-2 mm using this is used. Was made.
These simulated skin, dense bone, and cancellous bone were arranged in order and used as an experimental sample.
Two wavelengths of 850 nm and 515 nm were arranged as shown in FIG. 8, and an experiment was conducted using the above-described simulated sample.
FIG. 12A shows the position of the peak of the light intensity distribution obtained from the 850 nm and 515 nm lasers using Z.
In addition, the value of each plot has shown the average of 15 measurements.
FIG. 12B shows a value obtained by subtracting a value from 850 nm to 515 nm, that is, a relation between the peak distance and δ, and a relationship between the value and the skin thickness.
δ shows a negative correlation with the skin thickness, and this relationship is considered to arise from the difference in the depth of arrival at the skin layer of each wavelength and the light scattering characteristics.
Generally, 850 nm light penetrates deeper into the skin than 515 nm light, so the peak shift is large with respect to skin thickness. Conversely, 515 nm light is not significantly affected by skin thickness. .
The influence of the skin thickness due to the wavelength is shown in FIGS.
For this reason, it is considered that δ, which is the difference in peak due to each wavelength, changed with respect to the skin thickness.
When an approximate plane indicating the relationship between δ, slope, and BMD is obtained, the following equation is obtained.
The approximate plane was determined by the Monte Carlo method using the PyStan module of Python (Python 3.5).
Using this approximate expression, the formula for predicting BMD from the measured Slope and δ is as follows.
Here, sdpBMD (slope and delta predicted bone mineral density) is a BMD predicted from Slope and δ.
FIG. 13 shows the relationship between the predicted bone density calculated from Equation (3) and the bone density measured by μCT.
The bone density predicted from Slope and δ was almost the same value as the bone density obtained by μCT and showed a good positive correlation (r ² = 0.72581).
From this, it is possible to measure the bone density with higher accuracy by obtaining the thickness information of the skin layer from the intensity difference moved in the Z direction using different wavelengths.

DESCRIPTION OF SYMBOLS 1 Subject 10 Optical unit 11a 1st slit board 11b 2nd slit board 12a 1st lens 12b 2nd lens 13 Light irradiation part 14 Light detection part 20 Apparatus 21 Actuator

Claims (6)

A device for measuring bone density under the skin,
A light irradiating unit for injecting light of a predetermined intensity to the subject;
Filter means for removing scattered light reflected from the skin of the subject, light collecting means for reflected light from which the scattered light has been removed, and light for measuring the intensity of the light collected by the light collecting means A bone density measuring apparatus comprising: a detection unit.   A movement control unit having an optical unit incorporating the light irradiation unit, a light detection unit, a filter unit, and a light collecting unit, and capable of moving and controlling the distance of the optical unit from the subject; and the light irradiation unit and the light detection unit The bone density measuring device according to claim 1, further comprising: an absorbance calculation unit that calculates absorbance from   3. The bone density measuring apparatus according to claim 1, wherein the light collecting means is a pair of lenses, and the filter means is a slit plate. The light irradiation unit has a plurality of irradiation sources having different wavelengths,
The bone density measuring apparatus according to any one of claims 1 to 3, wherein the light detection unit includes a means for detecting a difference in intensity of the light among the plurality of irradiation sources. A bone density measuring method using the bone density measuring device according to any one of claims 1 to 3,
Based on the light intensity distribution obtained from the detection intensity detected by the light detection unit with respect to the incident intensity of the incident light irradiated from the light irradiation unit by changing the distance between the light irradiation unit and the subject. A bone density measuring method characterized by measuring density. A bone density measuring method using the bone density measuring device according to claim 4,
The distance between the light irradiation unit and the subject is changed, and the light intensity distribution obtained from the detection intensity detected by the light detection unit with respect to the incident intensity of the incident light irradiated from the light irradiation unit and the light A bone density measuring method, wherein bone density is measured based on skin thickness information obtained by a strength difference detecting means.