JP4790231B2 - Skin analysis method - Google Patents

Description

  The present invention relates to a method for analyzing an epidermis by a low interference light interferometry method.

Skin epidermis (approximately 100-200 [mu] m) from the surface in order, consists of the dermis (about 2 m m) and subcutaneous tissues. Of these, the epidermis includes a stratum corneum having a thickness of about 20 μm, and the form and appearance differ depending on the influence of the outside world and the pathological condition. Therefore, the form of the epidermis is used as an index of skin evaluation, and it is necessary to measure it accurately.

  On the other hand, as one of the techniques for non-invasive analysis of the internal structure of a living body or an object, interference measurement of reflected light or scattered light from the sample is performed using low coherence light in the visible or near infrared region. There is an optical coherence tomography (hereinafter abbreviated as OCT) based on the principle of low coherence reflectometry for analyzing internal structures. Has been attracting attention as a novel analysis technique and has been improved so that it can be used for skin measurement (Patent Document 1).

FIG. 14 is an explanatory diagram of the OCT measurement principle. The OCT measurement apparatus 1 guides light emitted from a low-coherence light source 2 that emits low-coherence light having a wavelength of 1300 nm to 1550 nm through an optical fiber 3, branches the light amount into 1: 1 by a coupler 4, and The probes 5 and 6 at the tip are brought into contact with the sample S and the reference mirror 7 respectively, and light is incident thereon. Here, the reference mirror 7 moves in the depth direction z of the sample S. The reflected light from the sample S and the reflected light from the reference mirror 7 are received by the probes 5 and 6, respectively, sent to the analyzer 8, and the combined reflection intensity is measured. Here, when the optical path difference between the reflected light from the sample S and the reflected light from the reference mirror 7 is zero, a peak (interference signal) is observed in the reflection intensity in the analyzer 8 due to interference of both reflected lights. . Accordingly, when the refractive index of air and n ^*, the the sample S, reflective interface to the position of the optical depth n ^* z corresponding to the moving distance z of the reference mirror 7 when the interfering signal is observed It can be seen that the sample S has two layers having different optical properties with the position of the optical depth n ^* z as an interface. According to this OCT measurement, it is possible to measure a wide region from the sample surface to a depth of about 20 μm to a depth of several hundred μm.

Further, when an interference signal is observed in the OCT measurement, the intensity of the interference signal rapidly attenuates as the depth direction z increases according to the light scattering intensity of the layer on which the interference signal is based. Therefore, according to the OCT measurement, the light scattering intensity of the layer inside the sample S can be known from the peak shape of the interference signal. That is, the profile of the optical thickness n ^* z of the interference signal measured by the analyzer 8 and its intensity (reflectance [dB]) is theoretically expressed by the following equation (1).

(Wherein, Iz: intensity of backscattering I _i: intensity of incident light sigma _b: medium-specific backscattering coefficient sigma _t: medium-specific attenuation coefficient n ^* Z _s: Optical Thickness k: proportionality constant determined by the measurement conditions)

Therefore, as shown in FIG. 15, when the sample S in which the layer S-1 having a low light scattering intensity and the layer S-2 having a high light scattering intensity are stacked is subjected to OCT measurement, the optical thickness n ^{* of the} interference signal to be measured is measured ^. The profile of z and intensity (reflectance [dB]) has two peaks p1 and p2, as schematically shown in FIG. Peak p1 is the peak observed in the optical thickness n * z ₁ by interfacial reflection between the lower layer S-1 of the probe 5 and the light scattering intensity, the light scattering intensity is gradually attenuated with progress of the light. The peak p2 further in the optical thickness n * z ₂ where the light has progressed deeply, be a peak observed by interfacial reflection between the light lower layer of scattering intensity S-1 and high light scattering intensities layer S-2 The light scattering intensity decreases rapidly with the progress of light.

FIG. 16 is a profile of the optical thickness n ^* z and intensity (reflectance [dB]) of an interference signal obtained by actually performing OCT measurement on human skin (45 years old, female, inner right upper arm). FIG. 17 shows that a predetermined range of skin can be measured simultaneously by arranging a plurality of interferometers on the subject's skin (cheek), and measurement data is imaged by converting the obtained interference signal into lightness. In the OCT image, the site where the interference signal is strong (high reflectance) is bright and the site where the interference signal is weak (low reflectance) is dark. FIG. 18 is an OCT image of the palm.

  As described with reference to FIG. 14, when the refractive index or light scattering intensity of the two layers in contact with each other is different, a peak appears in the OCT measurement data. Of the two peaks observed in FIG. 16, the optical thickness is about 0 μm. The peak that suddenly rises and gradually attenuates includes the peak due to the interface between the sensor tip and the skin surface, and the peak due to the boundary between the stratum corneum and the granular layer having an optical thickness of about 20 μm. The presence of a boundary between the layer and the granule layer is confirmed as a light layer by H / E staining in terms of histoanatomy. Further, it is considered that the peak rising at an optical thickness of about 100 μm and gradually attenuated is due to the boundary between the epidermis and the dermis.

  Since the peak in FIG. 16 corresponds to the bright region of the images in FIGS. 17 and 18, the stratum corneum is monotonically decreased from the skin surface A1 to the intermediate brightness region A2 and the dark region A3 as shown in FIG. As shown in FIG. 17, the epidermis is deeper than the stratum corneum in the depth direction in the depth direction, as shown in FIG. 17, the intermediate brightness area A5, dark area A6, bright area A7, dark When the area A8 is observed sequentially, it is considered to be before the bright area A7. Accordingly, the dark region A6 in FIG. 17 is considered to be epidermal tissue. In the figure, line L1 is a glass constituting the probe, and between line L1 and skin surface A1 is a gel applied to the skin surface during measurement.

Japanese Patent No. 3414173

  However, the present inventor verifies the observation result of the skin obtained by the OCT measurement with a confocal laser microscope or the like, so that there is a dermal papilla present in the dermal tissue in the dark region A6 observed in FIG. Therefore, it has been found that this dark region A6 is not the epidermal tissue but the dermal tissue, and therefore the conventional OCT measurement analysis method cannot accurately analyze the layer structure of the skin epidermis and dermis.

  Conventionally, the analysis result of the layer structure of the skin by OCT measurement and the microscopic observation of the skin tissue collected from a human have been made to correspond to each other, but most of the observed human skin tissue has a lesion on the skin. It is a tissue of a patient who has a part or a tissue collected from a dead infant or elderly person, and since it was immersed and stored in formalin after collection, the epidermis is thickened, the stratum corneum is bent, It is swollen or contracted. Therefore, it is considered that accurate data of living tissues could not be obtained from these observations.

  On the other hand, an object of the present invention is to make it possible to accurately analyze the layer structure of the skin, particularly the skin thickness, from the data of OCT measurement.

  In analyzing the layer structure of the skin from an image obtained by converting the interference signal of the OCT measurement data into lightness, the inventor has a skin layer with an optical thickness of about 20 μm as in the conventional analysis method. When the brightness first increases after the monotonous decrease from the skin surface to the intermediate brightness area and dark area in the vicinity, it will be before the light area, but the epidermis should take a specific analysis method different from the conventional one. More specifically, when the intermediate brightness area, dark area, and bright area are observed in the depth direction in the deeper area than the stratum corneum, from the skin surface to the front of the dark area. As for the epidermis, it was found that the results obtained when a healthy skin was measured non-invasively using a confocal laser microscope were consistent with the results.

That is, the present invention measures a predetermined range of skin by optical coherence tomography (OCT), converts the interference signal intensity of the optical thickness and intensity profile of the interference signal into brightness, and images the measurement data, A method for analyzing the layer structure of the skin from the obtained image,
In the image, when the intermediate brightness area where the interference signal profile monotonously attenuates in the depth direction in the deeper area than the stratum corneum, the dark area where the interference signal profile is flat, and the bright area are observed sequentially, the skin surface A method for analyzing the layer structure of the skin having the epidermis from the dark region to the front of the dark region is provided.

In addition, the present invention constructs a database that associates the skin thickness and age determined by the above-described analysis method for a plurality of healthy persons, determines the skin thickness by the above-described analysis method for any subject, and the database A method for determining the skin age corresponding to the skin thickness of the subject based on the above is provided.

In particular , the present invention provides an optical coherence tomography method for the above-described analysis method, wherein a predetermined range of the skin before and after application of a predetermined treatment (UV irradiation, cosmetics, agent, desiccant, wetting agent, etc.) to a subject is detected. Provides a method of measuring with .

  According to the analysis method of the present invention, the thickness, shape, distribution and the like of the epidermis in the layer structure of the skin of a living body can be obtained non-invasively and accurately.

  Therefore, (1) the difference in the skin thickness depending on the measurement site, (2) the relationship between the surface properties of the skin, such as the area and height of the cuticle, the distribution and depth of the skin groove, the color of the skin, and the epidermis inside (3) Age-related changes in skin thickness, (4) Effects of ultraviolet rays and cosmetics on the skin can be accurately examined. Therefore, by accumulating data related to these, it becomes possible to evaluate the skin age of the subject from the epidermis thickness of the subject, and it is possible to evaluate cosmetics and drugs applied to the skin. It is possible to provide desirable skin care advice for the skin.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In each figure, the same numerals indicate the same or equivalent components.

  The analysis method of the present invention is a method in which a predetermined range of skin is subjected to OCT measurement, the interference signal is converted into lightness, the measurement data is imaged, and the layer structure of the skin is analyzed from the obtained image.

  Here, OCT measurement itself can be performed using a commercially available apparatus as described in Patent Document 1, for example. In addition, OCT measurement is performed so as to scan a predetermined range of the skin, the obtained interference signal is converted into lightness, and the measurement data is imaged using a commercially available apparatus in which a plurality of interferometers are arranged, Measurement data can be processed by image processing software.

  However, the wavelength of low coherence light used for OCT measurement is preferably 500 to 1700 nm. If the wavelength is too short, the light does not reach the dermis, whereas if the wavelength is too long, the resolution is lowered and it becomes difficult to measure a stratum corneum having a thickness of about 20 μm.

  By performing OCT measurement on a predetermined area of the skin, converting the interference signal into lightness, and imaging it, the images as shown in FIGS. 17 and 18 can be obtained. In determining the thickness, shape, distribution, etc. of the skin, as shown in FIG. 1, when the intermediate brightness area A5, dark area A6 and bright area A7 are observed in the depth direction in the deeper area than the stratum corneum. The skin surface A1 to the front of the dark area A6 is defined as the epidermis. Therefore, the dermis becomes a region below the dark region A6. On the other hand, as shown in FIG. 18, the stratum corneum is observed from the skin surface to the bright area A4 when the intermediate brightness area A2, dark area A3, and bright area A4 are sequentially observed in the depth direction near the skin surface. Until the front.

When the division of the epidermis region or the stratum corneum region is made to correspond to the profile of the optical thickness n ^* z of the interference signal obtained by OCT measurement and its intensity (reflectance [dB]), as shown in FIG. The peak that rises sharply at an optical thickness of about 0 μm and gradually attenuates includes a peak due to the interface between the sensor and the skin surface, and an optical thickness of about 20 μm includes a peak due to the boundary between the stratum corneum and the granular layer. The flat portion with a thickness of about 60 to 90 μm is a dark region A6 with a dermal papilla, and the peak rising at an optical thickness of about 100 is due to the boundary with the underlying connective tissue.

  FIG. 3 shows a profile obtained by performing OCT measurement by placing a skin piece collected only from a human and peeled off on a glass plate in order to obtain an interference signal of the epidermis. From the figure, it can be seen that the peak of the skin surface monotonously attenuates to an optical thickness of about 70 μm and then becomes flat. Accordingly, the epidermis is monotonically attenuated from the first peak, and the subsequent flat portion corresponds to the dermal papilla. The peak at an optical thickness of about 180 μm is due to the interface between the skin piece and the glass plate.

  In the image of FIG. 1, the dark region A6 is not the epidermis but the dermis. As shown in the examples below, the horizontal cross-sectional image of this region is obtained using a confocal laser microscope. Can be confirmed by observing the cross-section of the dermal papilla in an island shape in the epidermal tissue.

  In the image of FIG. 1, the reason why the bright region is not observed at the boundary between the epidermis and the dermis and the dark region A6 is observed is not clear. May be absorbed, or the tissue forming the dermal papilla has the property of absorbing light. In addition, the bright region A7 is observed under the dark region A6 with the dermal papilla because the connective tissue in this region has a different refractive index or orientation with respect to the region with the dermal papilla above, or It can be considered to have scattering properties.

  In the analysis method of the present invention, as a specific method for obtaining the skin thickness from the image obtained by converting the interference signal of the OCT measurement into the lightness, for example, in FIG. 1, the boundary between the intermediate lightness region A5 and the dark region A6 (that is, The observer traces the boundary between the epidermis and the dermis, measures the distance between the trace line and the skin surface at a plurality of locations, and calculates the average. In that case, if the distance between the skin surface and the trace line is the distance (curve width) in the direction perpendicular to the skin surface at each measurement point, rather than the distance in the skin depth direction, the variation in the measured value is reduced. can do.

  From the relationship between the shape of the trace line and the skin groove, the state of the skin surface (texture and wrinkle) can be examined from the internal structure. As a specific method for obtaining this relationship, for example, as shown in FIG. The patterns of the skin groove observed from the window having a width of 100 μm and the shape of the trace line described above may be classified into three types A, B, and C, and the appearance rate of each pattern may be obtained for each observation site.

  According to the analysis method of the present invention, since the skin thickness and shape of the skin of a living body can be accurately measured in a non-invasive manner, the color of the skin, the texture, the size of the skin, the distribution and depth of the cleft, the pores It is possible to accurately examine the relationship between the surface properties of the skin such as the degree of conspicuousness, the skin thickness, the skin shape, the progress of skin thickening, and the like.

  Therefore, the skin thickness, stratum corneum thickness, skin shape, etc. of the skin at a predetermined site are obtained from a large number of healthy persons by the analysis method of the present invention, and information such as age, sex, etc. is obtained. If a database is established, the skin age of any subject can be evaluated by measuring the skin thickness and the like by the analysis method of the present invention.

  Moreover, if the skin thickness is measured by the analysis method of the present invention before and after the subject's skin is subjected to treatment such as UV irradiation, drying, humidification, application of cosmetics or drugs, the effect of the treatment on the skin thickness is evaluated. be able to.

  Furthermore, when the subject continuously measures the skin thickness and the like at a predetermined site using the analysis method of the present invention, the skin health of the subject can be managed.

  Also, prescribed treatments for the skin, changes in the skin thickness when the treatment is performed on the skin, skin color, texture, size of the skin, distribution and depth of the skin groove, conspicuousness of pores, etc. By constructing a database that correlates with changes in the surface texture of the skin, it is possible to propose a desired treatment as skin care to the subject by measuring the skin thickness etc. for any subject using the analysis method of the present invention. it can.

Example 1
Using a OCT measuring device (SkinDex300, ISIS) with eight Michelson interferometers, the forearm inner part of the subject was subjected to OCT measurement (measurement condition: irradiation wavelength 1300 nm). In this case, a total of 28 consecutive slice images were obtained by moving the 135 μ width of the surface by 5 μ steps and acquiring images, and arbitrarily extracted three of them to represent the measurement points. Next, imaging processing for converting reflectance into luminance was performed using image measurement software (Image-Pro, Media Cybernetics). An image thus obtained is shown in FIG.

  By visually observing the image obtained from FIG. 5, it was confirmed that there was a dark region at a depth of 50 to 70 μm from the skin surface.

  On the other hand, using a confocal laser microscope (Vivscope 1000, Lucid) (laser wavelength 830 nm (gallium-arsenic laser), output 16 mW, objective lens 30 times, observation field 450 μm × 400 μm, vertical resolution 5 μm), the same measurement site, The measurement depth was set to 207 μm at an interval of 6.7 μm from the skin surface, and horizontal cross-sectional images at each measurement depth were acquired. By comparing these images, the cross section of the dermal papilla was observed in an island shape in the epidermal tissue at a measurement depth of 50 to 70 μm. FIG. 6 shows a cross-sectional image of the dermal papilla at a measurement depth of 60 μm.

  Therefore, it was confirmed that the dark region in the image obtained by the above-described imaging is the dermis where the dermal papilla exists.

Example 2
Using the OCT measuring device (SkinDex300, ISIS), under the same measurement conditions as in Example 1, OCT measurement was performed 5 times for the same part inside the forearm of 5 adult men and 5 adult women, respectively. -Pro, Media Cybernetics, Inc.) was used to perform the imaging process to convert the reflectance into luminance.

  By visually observing the obtained image, the boundary between the skin surface and the dermis is traced, and as the skin thickness, as shown in FIG. 7, there are two types of vertical width HT and curve width CT between the trace line L3 and the skin surface. Were automatically measured at 200 locations at random for each subject, and the coefficient of variation CV (= standard deviation / average value) for each subject and the coefficient of variation CV for all subjects were determined. The results are shown in Table 1.

  From Table 1, the skin thickness on the inner side of the forearm is vertical width HT61.7-77.8μm or curve width CT56.7-70.4μm, which is measured lower than the skin thickness that was conventionally about 100-200μm. You can see that

  It can also be seen that the curve width CT has a smaller variation coefficient than the vertical width HT. Therefore, in the following examples, the curve width was measured as the skin thickness.

Example 3: Age-related change in epidermis thickness for each part 116 females in their teens to 60s living in the Tokyo metropolitan area (approximately 20 each age) were subjects, and OCT measurement was performed in the same manner as in Example 2 to perform imaging processing. The horny layer thickness and the skin thickness of each subject were determined from the curve width CT of the horny layer or the epidermis in the obtained image. In this case, as shown in FIG. 8, the measurement site was the forehead, cheek, inner upper arm, inner forearm, outer forearm, back of hand, abdomen, back, inner thigh, inner lower leg, and shin. In FIG. 8, the arrow indicates the direction of the tomographic image obtained by the imaging process. Each measurement site was measured three times, and the average was taken as the stratum corneum thickness or skin thickness. The results are shown in Table 2, Table 3, FIG. 9 and FIG.

  For the cheeks and the inner side of the upper arm, the age of the subject and the measured epidermis thickness were plotted. The results are shown in FIGS.

  From these results, it can be seen that according to this example, the skin thickness, which was conventionally about 100 to 200 μm, was measured to be about 60 to 100 μm, which is lower than the conventional value.

  In addition to the back of the hand, abdomen, and back, it can be seen that there is a correlation between the skin thickness and age.

Example 4: Effect of UV irradiation on skin thickness Using 12 adult men as subjects, the relationship between the number of days after irradiation and skin thickness when UV (B-B) was irradiated on the skin was examined.

  In this case, the irradiation site was the outer forearm, the inner upper arm, the abdomen, the back, and the inner thigh, and the irradiation area was 10 mm × 0.5 mm per location. The irradiation energy was adjusted so that 2 MED was obtained in the range of 20 to 200 mJ.

  On the 0th day, 1st day, 2nd day, 3rd day, 7th day, 10th day, 20th day, 30th day, 40th day and 50th day after the irradiation, OCT measurement was carried out in the same manner as in Example 2, and the skin thickness and stratum corneum thickness were measured. Asked.

  As a result, even after the skin redness disappeared 3 to 4 days after the ultraviolet irradiation, as shown in FIG. 13, the skin thickness increased until 5 to 7 days after the ultraviolet irradiation. It can be seen that the change in the epidermis can be traced by looking for it.

  In addition, although the stratum corneum was thickened by ultraviolet irradiation, depending on the part, it peeled off 3 to 4 days after irradiation, and finally the stratum corneum thickness was about the same as before irradiation.

  The evaluation method of the present invention is useful in fields such as analysis of the layer structure of the skin, evaluation of the effects of UV irradiation, drying, humidification, application of cosmetics and drugs, etc. on the skin.

It is explanatory drawing of the method of calculating | requiring a skin area | region from the image obtained by converting the interference signal of OCT measurement into the brightness. It is a profile of an interference signal. It is a profile of an interference signal. It is explanatory drawing of the shape of the line which traced the boundary of an epidermis and a dermis, and the pattern of a skin groove. (Example 1) which is the image obtained by imaging the OCT measurement value. (Example 1) which is the image of the horizontal cross section of the skin taken using the confocal laser microscope. (Example 2) which is explanatory drawing of the measuring method of skin epidermis thickness (vertical width, curve width). (Example 3) which is explanatory drawing of a measurement site | part. It is the figure which showed the stratum corneum thickness of each measurement part (Example 3). It is the figure which showed the skin thickness of each measurement part (Example 3). (Example 3) which is a relationship figure of age and the epidermis thickness of a cheek. FIG. 6 is a diagram showing the relationship between age and epidermis thickness inside the upper arm (Example 3). It is a figure showing the daily change of the skin thickness after ultraviolet irradiation (Example 4). It is explanatory drawing of the measurement principle of OCT. It is explanatory drawing of the profile of an interference signal. It is a profile of the optical thickness of human skin and the intensity (reflectance) of an interference signal by OCT measurement. It is an OCT image of skin (cheek). It is an OCT image of skin (palm).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measuring apparatus 2 Low coherence light source 3 Optical fiber 4 Coupler 5 Probe 6 Probe 7 Reference mirror 8 Analyzer A1 Skin surface A2 Medium brightness area A3 Dark area A4 Bright area A5 Intermediate brightness area A6 Dark area A7 Bright area A8 Dark area S Sample S-1 Layer with low light scattering intensity S-2 Layer with high light scattering intensity z Depth direction of sample

Claims (4)

Measurement of the predetermined range of the skin by optical coherence tomography, converting the interference signal intensity of the optical thickness and intensity profile of the interference signal into lightness, and imaging the measurement data from the obtained image, the layer structure of the skin Is a method of analyzing
In the image, when the intermediate brightness area where the interference signal profile monotonously attenuates in the depth direction in the deeper area than the stratum corneum, the dark area where the interference signal profile is flat, and the bright area are observed sequentially, the skin surface To analyze the layer structure of the skin with the epidermis from the dark area to the front of the dark area. When the intermediate brightness area, dark area, and bright area are observed in the depth direction near the skin surface, the stratum from the skin surface to the front of the bright area is the stratum corneum, and the depth direction is deeper than the stratum corneum. The analysis method according to claim 1, wherein the interference signal intensity is monotonously attenuated in an area that is an epidermis from the skin surface to the front of the dark area when an intermediate brightness area, a dark area, and a bright area are sequentially observed.   The analysis method according to claim 1, wherein a predetermined range of the skin before and after application of the predetermined treatment is measured by optical coherence tomography.   A database in which the skin thickness and age determined by the analysis method according to claim 1 are related for a plurality of healthy persons is constructed, and the skin thickness is determined by the analysis method according to claim 1 for any subject, and the database The skin age corresponding to the skin thickness of the subject is determined based on the above.

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