JP2019126659A - Skin evaluation method - Google Patents

Abstract

To provide a technology to perform accurate skin evaluation using viscoelastic characteristics of the skin.SOLUTION: A skin evaluation method includes: a process for acquiring a measurement value of viscoelasticity measurement for the skin of a subject; a process for calculating an approximate expression a recovery curve indicating time characteristics of creep recovery described using one or more creep recovery characteristic components whose time constants are different from each other based on the acquired measurement value; and a process for generating viscoelasticity information on the skin of the subject using the calculated approximate expression.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a skin evaluation technique, and more particularly to a technique for evaluation using skin viscoelastic characteristics.

As a device for measuring the viscoelasticity of the skin (skin), there are a suction type measuring device, a rotation type measuring device, and the like. In the suction method, a negative pressure is applied to the skin with a probe, the skin surface is sucked for a certain period of time, and then the displacement of the skin surface during the release process is measured. In the rotation method, a rotation torque is applied to the skin surface by a probe for a predetermined time, and the rotation is measured.
By using the value measured by such a measuring device, the firmness (elasticity) of the skin and the like are evaluated. Patent Document 1 proposes a method of measuring skin elasticity of skin surface layer and evaluating skin care by comparing the measured viscoelasticity with a viscoelastic reference value.

JP 2012-161371 A

Nils Krueger, etc., "Age-related changes in skin mechanical properties: a quantitative evaluation of 120 female subjects", Skin Research & Technology, Volume 17, Issue 2, May 2011, Pages 141-148 Kuwasui, et al., "Effect of aging on wrinkle formation of facial skin", 55th Theoretical and Applied Mechanics Lecture Proceedings Session ID: 3F13, March 25, 2006

  The present inventors have clarified that there is a problem in accuracy in the viscoelasticity evaluation of the skin performed using the value itself measured by the measuring apparatus as described above. As one of the main causes, the present inventors paid attention to variations in measurement conditions, particularly variations in measurement conditions during creep recovery. For example, it is necessary to keep the distance between the probe of the measuring device and the skin surface constant for a predetermined measurement time after the creep recovery, that is, after the suction force or rotational torque is released. That is very difficult.

FIG. 9 is a graph showing temporal changes in the amount of deformation of the skin obtained by measuring the viscoelasticity of the skin.
Typical skin viscoelasticity evaluations are shown in FIG. 9, each measured value such as Ue, Uv, Uf, Ur, Ua or the ratio between the measured values (Ua / Uf, Ur / Uf, Ur / Ue, etc. It is done using).
The present inventors have found that the measurement value itself obtained by measuring the viscoelasticity of the skin, particularly the measurement value at the time of creep recovery, has a problem in accuracy that cannot be solved by normalization alone. Furthermore, the present inventors have confirmed the relationship between such viscoelastic parameters and age (see Non-Patent Document 1 above), and it is known that skin firmness originally decreases with age. Nevertheless, focusing on the fact that the correlation between the measured value itself and the age is relatively low, it was considered difficult to accurately evaluate the viscoelasticity of the skin with the measured value itself and its ratio.

This invention is made | formed in view of such a subject, and is related with the technique which enables highly accurate skin evaluation using the viscoelastic property of skin.
In the present specification, "skin" is used without distinction from "skin".

The aspect of the present invention adopts the following configuration in order to solve the problems described above.
An aspect of the present invention relates to a skin evaluation method. The skin evaluation method is described using a measurement value acquisition step for acquiring a measurement value of a viscoelasticity measurement for a subject's skin, and one or more creep recovery characteristic components having different time constants based on the acquired measurement value. A calculation step of calculating an approximate expression of a recovery curve indicating a time characteristic of creep recovery, and a generation step of generating viscoelasticity information of the subject's skin using the calculated approximate expression.

  Another aspect of the present invention relates to, for example, a skin evaluation apparatus (information processing apparatus, computer) that executes the skin evaluation method according to the above aspect, and relates to a program that causes a computer to execute the skin evaluation method according to the above aspect. The present invention relates to a computer-readable storage medium storing such a program. This recording medium includes a non-transitory tangible medium.

  According to the said aspect, the technique which enables the highly accurate skin evaluation using the viscoelastic property of skin can be provided.

It is a flowchart which shows the skin evaluation method which concerns on 1st embodiment. It is a graph which shows the example of the time change of the deformation amount of the skin obtained by the viscoelasticity measurement of skin. It is a flowchart which shows the skin evaluation method in 2nd embodiment. It is a figure which shows notionally the hardware structural example of a skin evaluation apparatus. It is a graph which shows each curve based on the creep deformation curve and creep recovery curve based on an approximate expression, and a measured value. It is a graph which shows each curve based on the creep deformation curve and creep recovery curve based on an approximate expression, and a measured value. It is a graph which shows the result of a 1st test. It is a graph which shows the result of a 2nd test. It is a graph which shows the time change of the deformation amount of the skin obtained by the viscoelasticity measurement of skin.

  Hereinafter, an example of a preferred embodiment of the present invention (hereinafter referred to as this embodiment) will be described. In addition, each embodiment listed below is each illustration, and this invention is not limited to the structure of the following each embodiment.

First Embodiment
The skin evaluation method according to the first embodiment will be described.
FIG. 1 is a flowchart showing a skin evaluation method according to the first embodiment.
The skin evaluation method according to the first embodiment includes the step (S11), the step (S13), and the step (S15), and based on the viscoelastic information of the skin generated in the step (S15), the skin of the subject evaluate.

In the step (S11), a measurement value of viscoelasticity measurement for the skin of the subject is acquired.
Here, “viscoelasticity measurement on the skin” refers to a process in which the skin deforms with time by applying a certain load to the skin (skin) for a predetermined period of time and releasing the load from the skin (stop applying to the skin ) Means to measure the process of skin getting back with time. In the present embodiment, the specific measurement method of the viscoelasticity measurement is not limited, and may be the suction method or the rotation method described above, or may be another method.
In this specification, the phenomenon of the first half process measured by this viscoelasticity measurement is referred to as "creep deformation", and the decrease of the second half process is referred to as "creep recovery". That is, "creep deformation" means a phenomenon in which the skin deforms with time by applying a load to the skin (skin), and "creep recovery" means releasing the load to allow the skin to recover from time. It means the phenomenon that it tries to return to.

The measurement value acquired in the step (S11) may be a part or all of the measurement value obtained by the viscoelasticity measurement on the skin. For example, only creep deformation measurements or only creep recovery measurements may be obtained.
Moreover, the said measured value should just be a value based on the physical quantity obtained by viscoelasticity measurement. For example, the measurement value may be a deformation amount (suction length) measured by a suction method, or may be a deformation amount (angle) measured by a rotation method.
Furthermore, the measured value may not be the measured value itself. For example, the measured value may be a strain value which is a ratio of an amount of deformation to a deformation amount, or may be an elastic modulus, creep compliance (reciprocal of elastic modulus), or the like. Further, the measurement value may be a measurement value (relative value) normalized (standardized) by some standard. For example, in the step (S11), a measurement value (relative value) normalized by the measurement value at the start of creep recovery (at the time of maximum displacement) can be acquired. Moreover, the measured value which normalized (averaged) each measured value obtained by the several times of measurement implemented with respect to a test subject's skin may be acquired. By obtaining the normalized measurement value in this manner, it is possible to reduce the variation in the measurement condition.

  Further, the measurement value acquired in the step (S11) is acquired in a state where it can be associated with the time (hereinafter, sometimes referred to as measurement time) when the value was measured in the viscoelasticity measurement. When the measurement time is determined in advance, only the measurement value of the measurement time needs to be acquired. For example, each measurement time and each measurement value determined in advance according to the measurement value acquisition order can be associated with each other. A pair of a measurement value and a measurement time may be acquired.

  Moreover, the acquisition method in the step (S11) is not limited. For example, when the step (S11) is executed by a measuring device, the step (S11) may include measuring viscoelasticity and measuring the measured value. In addition, when the step (S11) is executed by a computer other than the measuring device, the step (S11) acquires the measurement value from the measuring device via wireless or wired communication or a portable recording medium. Or acquisition by inputting the measurement value by a user of the computer.

  In step (S13), an approximation of the recovery curve indicating the time characteristics of creep recovery described using one or more creep recovery characteristic components having different time constants based on the measurement values obtained in step (S11). An expression is calculated. Step (S13) is executed by a device, a computer, or the like. However, the execution opportunity of the step (S13) may be given by a human, or may be automatically determined by the computer itself after the step (S11).

Here, "a recovery curve showing a time characteristic of creep recovery" is a curve indicated by a time axis and an index value axis of creep recovery, and means a curve representing a time change of creep recovery. Hereinafter, this "recovery curve showing time characteristics of creep recovery" may be referred to as a creep recovery curve. The creep recovery curve in FIG. 2 described later is an example. However, the creep recovery curve is not limited to the example of FIG. For example, a similarity curve obtained by symmetrically shifting the creep recovery curve shown in FIG. 2 may be used as the creep recovery curve. The creep recovery curve in this case has a shape close to a deformation curve indicating the time characteristic of creep deformation.
On the other hand, the notation “creep deformation curve” is sometimes used. The “creep deformation curve” is a deformation curve indicating the time characteristic of creep deformation, and is a curve represented by a time axis and an index value axis of creep deformation, and means a curve representing a time change of creep deformation. . The creep deformation curve in FIG. 2 described later is an example.

FIG. 2 is a graph showing an example of the time change of the amount of deformation of the skin obtained by measuring the viscoelasticity of the skin.
In the example of FIG. 2, creep deformation is started by applying a load to the skin at 0 seconds at the time of measurement, and the load is released at 2 seconds at the time of measurement to start creep recovery. Therefore, the time change of deformation from 0 seconds to 2 seconds at the time of measurement is expressed as a creep deformation curve, and the time change of deformation after 2 seconds at the time of measurement is expressed as a creep recovery curve.

The present inventors have succeeded in modeling the creep deformation curve of the skin by a model in which a plurality of simple forked models are vertically connected. The simple forked model is a mechanical model in which an elastic spring and a viscous dashpot are connected in parallel. That is, the present inventors succeeded in approximating the creep deformation curve by an equation described by the sum of a plurality of creep deformation characteristic components having different time constants. Here, “creep deformation characteristic component” means one component of the time characteristic of creep deformation which forms a creep deformation curve, and can be represented by an exponential equation having an inherent time constant.
Here, the “time constant” is {(1-e ⁻¹ ) × 100} percent (e is the Napier number (base of natural logarithm)) of the limit value of each creep deformation characteristic component, and is about 63%. It is time to reach).
“The limit value of the creep deformation characteristic component” is a value before the index value of the creep deformation characteristic component converges with the passage of time, and is a value indicating the amount of deformation, strain, elastic modulus, creep compliance, etc. is there.

Furthermore, the present inventors consider that it may be possible to model the creep recovery curve of the skin by using the simple Voigt model used in the approximation of the creep deformation curve, and one or more creeps having different time constants from each other It was found that the creep recovery curve can be approximated by the formula described using the recovery characteristic component. The term "creep recovery characteristic component" as used herein means one component of the creep recovery time characteristic that forms a creep recovery curve, and can be represented by an exponential equation having an inherent time constant.
Here, the “time constant” is {(1-e ⁻¹ ) × 100} percent (e is the Napier number (base of natural logarithm)) of the limit value of each creep recovery characteristic component from the start point of creep recovery. , Which is about 63%).
“The limit value of the creep recovery characteristic component” is the value before the index value of the creep recovery characteristic component converges with the passage of time, and is a value indicating the amount of deformation, strain, elastic modulus, creep compliance, etc. is there.

上記式は、クリープ回復の開始値を正規化された「１」とし、その開始値からクリープ回復の変位量（回復量）の時間変化を表す曲線を近似する式である。但し、本実施形態におけるクリープ回復曲線の近似式は、一以上のクリープ回復特性成分を用いていればよく、このような式に限定されない。例えば、クリープ回復の開始値は、０．９、１．１など１以外の値でもよい。また、上記式で近似される曲線を対称移動させた曲線（クリープ変形曲線に似た形状の曲線）をクリープ回復曲線とする場合には、当該近似式は、クリープ回復の開始値を用いることなく、上記式の第２項のみを用いて算出されてもよい。 The approximate expression of the creep recovery curve calculated in the step (S13) may be calculated as the following equation which subtracts the sum of one or more creep recovery characteristic components from the creep recovery start value. In the following equation, i represents an individual creep recovery characteristic component, N represents the number of creep recovery characteristic components, g _i represents the limit value of the i-th creep recovery characteristic component, and τ _i is The time constant of the ith creep recovery characteristic component is shown.

The above equation is an equation that sets the start value of creep recovery as “1” normalized, and approximates a curve representing the time change of the displacement amount (recovery amount) of creep recovery from the start value. However, the approximate expression of the creep recovery curve in the present embodiment only needs to use one or more creep recovery characteristic components, and is not limited to such an equation. For example, the creep recovery start value may be a value other than 1 such as 0.9 or 1.1. Further, in the case where a curve obtained by symmetrically moving the curve approximated by the above equation (curve having a shape similar to a creep deformation curve) is used as a creep recovery curve, the approximate equation does not use the creep recovery start value. And may be calculated using only the second term of the above equation.

The number of creep recovery characteristic components used in the approximation of the creep recovery curve, as well as the individual time constants, is predetermined.
The number of creep recovery characteristic components is set to one or more.
At this time, a predetermined time including at least a time shorter than the measurement time of the instantaneous recovery value (Ur) used in the measurement of the viscoelasticity of the skin is used as the time constant. The instantaneous recovery value (Ur) indicates a recovery amount measured in a predetermined time (0.1 second in the example of FIG. 9) from the start of creep recovery, and is also called a negative pressure release value.
Since the time constant of the creep recovery characteristic component corresponds to the elapsed time from the start of creep recovery, the creep recovery characteristic component having a smaller time constant becomes dominant in the creep recovery curve. For this reason, when the number of creep recovery characteristic components is 1, it is desirable to set a time shorter than the measurement time of the instantaneous recovery value (Ur) as a time constant, and the number of creep recovery characteristic components is 2 or more. In this case, it is desirable to set the time constant shorter and longer than the measurement time of the instantaneous recovery value (Ur) as a boundary. Thereby, the approximation accuracy of the creep recovery curve can be improved.

There are various methods for calculating the approximate expression of the creep recovery curve in the step (S13). In the present embodiment, the specific calculation method is not limited as long as it is a calculation method based on the measurement value acquired in step (S11).
The calculation methods can be roughly classified into a first method using information of an approximate expression of a creep deformation curve and a second method not using information of an approximate expression of a creep deformation curve. Since the first method will be described later as the second embodiment, in the first embodiment, the second method will be described. However, also in the first embodiment, the approximate expression may be calculated using the first method.

In the step (S13) using the second method, the recovery limit value of the creep recovery curve is estimated based on the measurement value acquired in the step (S11). This “recovery limit value” is the limit value at which the creep recovery curve converges with the passage of time after the load is released.
When one creep recovery characteristic component is used (N = 1 in the above equation), the recovery limit value may be calculated as the limit value of the creep recovery characteristic component (g ₁ in the above equation).
When two or more creep recovery characteristic components are used (N> = 2 in the above formula), the limit value of each creep recovery characteristic component is determined using the recovery limit value and the measured value obtained in step (S11). Each is calculated. For example, the limit value of each creep recovery characteristic component is calculated using the least square method such that the sum of the limit values of each creep recovery characteristic component becomes the recovery limit value of the estimated creep recovery curve. The calculation formula in this case can be expressed, for example, as follows. In the following equation, measurement data (measurement time, index value) is indicated by (t _i , Y _i ), approximate data (measurement time, index value) is indicated by (t _i , y _i ), and m is creep recovery. The curve's recovery limit is shown.

The recovery limit value of the creep recovery curve calculated by the second method and the limit value (g _i ) of each creep recovery characteristic component are the same values as the measured values acquired in the step (S11). The values may be different or different. For example, when the measured value acquired in the step (S11) is a deformation amount, the limit value calculated in the step (S13) may be a deformation amount, or it can be calculated from the deformation amount, It may be strain value, elastic modulus or creep compliance. When the strain value is calculated, the original value may be determined in advance, or may be acquired together with the measured value in the step (S11). When the elastic modulus or the creep compliance is calculated, the deforming force (such as suction force or torque) applied to the skin may be determined in advance, or may be acquired together with the measurement value in the step (S11).

In step (S15), viscoelasticity information of the subject's skin is generated using the approximate expression calculated in step (S13).
The "skin viscoelasticity information" is information indicating the elasticity or viscosity of the skin or both of them.
In the step (S15), at least one limit value (including the recovery limit value) of the one or more creep recovery characteristic components calculated in the step (S13) may be used as the viscoelastic information as it is, or the ratio of the limit value May be considered as viscoelastic information.
For example, visco-elasticity information is generated in which pairs of values of time constants that can identify each creep recovery characteristic component and the limit values of the respective creep recovery characteristic components are included as many as creep recovery characteristic components. In addition, a stacked bar graph, a band graph, a circle graph, or the like in which limit values are color-coded for each creep recovery characteristic component can also be generated as viscoelastic information. If these graphs do not have numerical limits, they will show the percentage of the limit.
Also, visco-elastic information may be generated that numerically indicates the ratio of the limit value of each creep recovery characteristic component. For example, the ratio of the limit value of the creep recovery characteristic component having the smallest time constant to the sum of the limit values of the creep recovery characteristic components may be generated as the viscoelastic information indicating the elasticity of the skin. A ratio of the sum of the limit values of the creep recovery characteristic component having the smallest time constant and the second smallest time constant to the sum may be generated as the viscoelastic information indicating the elasticity of the skin.

Each creep recovery characteristic component determined as described above can be considered to indicate the following skin information. For example, the creep recovery characteristic component having a time constant set to a time shorter than the time from the start of creep recovery to the time of measurement of the instantaneous recovery value (Ur) forms the stratum corneum, the epidermis, the dermis, and the subcutaneous tissue. It is believed to exhibit the visco-elastic response of the A creep recovery characteristic component having a time constant longer than that time has a smaller instantaneous displacement than the above component, so that viscosity affected by intercellular lipids, blood vessels and lymph vessels, lymph fluid flowing through them, blood, etc. It can be considered to exhibit an elastic response.
Therefore, according to the approximate expression described by the sum of the respective creep recovery characteristic components, it is possible to specify the viscoelastic response characteristic corresponding to the tissue forming the skin, that is, the viscoelastic information of the skin.

In addition, according to the limit value or the ratio of each creep recovery characteristic component, it is possible to indicate the degree of skin firmness (elasticity), skin moistness and the like. For example, the average index value for each age is stored in advance for at least one creep recovery characteristic component, and the calculated limit value of the creep recovery characteristic component is compared with the average index value of the subject's skin. Skin age related to firmness or moistness may be generated as viscoelastic information. In addition, a sample limit value obtained from a sample skin with an average of firmness or moisture of the skin is held in advance, and the subject is compared by comparing the sample limit value with the limit value calculated for the subject's skin. Viscoelastic information may be generated to indicate whether the skin firmness or moistness of the skin is good.
In addition, as the viscoelastic information, information of any one or more elastic modulus of a plurality of layers including at least the stratum corneum, the epidermis, and the dermis of the subject's skin can be generated. In a suction-type viscoelasticity measuring device, measured values are acquired for each probe using a plurality of types of probes having different diameters of the opening measurement portion, and a difference in the limit value for each probe calculated from the measured values is used to determine whether or not a certain layer The modulus of elasticity can be calculated.

Although the skin evaluation method according to the first embodiment is not illustrated in FIG. 1, the skin of the subject is evaluated using the viscoelastic information generated in the step (S15). The evaluation method here is not limited at all. By presenting the viscoelastic information generated in the step (S15) to a subject, an evaluator, or the like, a person who has received the presentation can independently perform skin evaluation.
For example, the viscoelasticity information generated in the step (S15) is presented in the state where the average index value for each age, the sample limit value, etc. are presented. By doing this, it is possible to evaluate the skin elasticity or moisture of the subject (or himself / herself), skin age, and the like.
Of course, the viscoelastic information generated in the step (S15) may indicate the result of skin evaluation. For example, as described above, the viscoelasticity information may indicate whether or not the subject's skin firmness or moistness is good, and may indicate the subject's skin age related to the firmness or moistness. In this case, the skin evaluation using the viscoelastic information may not be performed separately.

  As described above, in the first embodiment, an approximate expression of a creep recovery curve is calculated based on a dynamic model of viscoelasticity, and parameters (extreme values) of one or more components in the recovery curve are skin viscoelasticity information. Used as Therefore, according to the first embodiment, the skin evaluation can be performed based on the new index indicating the viscoelasticity of the skin. By using this new index, it is possible to reduce the variation in the measurement conditions included in the measured value compared to the evaluation performed using the measured value of creep deformation as it is, so that highly accurate skin evaluation is realized. Can do.

Second Embodiment
Hereinafter, the skin evaluation method in the second embodiment will be described. The second embodiment differs from the first embodiment in that the first method described above is used as a method for calculating an approximate expression for a creep recovery curve. The following description will be made focusing on the contents different from the first embodiment, and the contents similar to the first embodiment will be omitted as appropriate.

FIG. 3 is a flowchart showing a skin evaluation method in the second embodiment.
The skin evaluation method according to the second embodiment includes a step (S21), a step (S23), a step (S25), a step (S27), and a step (S29), and the skin viscosity generated in the step (S29). Evaluate the subject's skin based on the elasticity information.

  Step (S21) is the same as step (S11) in the first embodiment. However, in the second embodiment, measured values at the time of creep deformation and at the time of creep recovery are acquired.

In the step (S23), the measured value obtained in the step (S21) is normalized by the amount of deformation at the start of creep recovery (or at the end of creep deformation). The amount of deformation at the start of creep recovery is the starting value of creep recovery. Also, this start value corresponds to the parameter Uf of FIG.
For this start value, the measurement value itself acquired in the step (S21) may be used, or the acquired measurement value group at the time of creep deformation or the value group normalized by the maximum deformation amount are used. The limit value of the creep deformation curve estimated in this way may be used.
Further, the normalization may be executed so as to take a value not less than 0 and not more than 1 with a creep recovery start value as a reference value (for example, 1), or based on a measurement value group in which the start value is normalized. In the case of an estimated value, the start value itself may be normalized as a reference value.

In the step (S25), the approximate expression of the creep deformation curve is calculated based on the measurement value group during creep deformation in the measurement value group normalized in the step (S23). The approximate expression of the creep deformation curve can be expressed by the sum of a plurality of creep deformation characteristic components having different time constants, that is, the following expression. In the following equation, i represents an individual creep deformation characteristic component, N represents the number of creep deformation characteristic components, k _i represents the limit value of the i-th creep deformation characteristic component, and τ _i is The time constant of the i-th creep deformation characteristic component is shown.

The number of creep deformation characteristic components used in the approximation of the creep deformation curve is predetermined with the individual time constants.
The number of creep deformation characteristic components is set to 2 or more. At this time, the time constant is determined in advance including at least a time shorter than this measurement time and a time longer than this measurement time based on the measurement time of the instantaneous elongation value (Ue) used in the viscoelasticity measurement of the skin. Times are used. Since the time constant of the creep deformation characteristic component corresponds to the elapsed time from the creep deformation start time, the creep deformation characteristic component having a smaller time constant becomes dominant in the creep deformation curve. For this reason, the approximation accuracy of the creep deformation curve can be improved by setting the time constant shorter and longer than the measurement time of the instantaneous elongation value (Ue) as the time constant.

  Furthermore, it is desirable that the number of creep deformation characteristic components is set to four. In this case, the time constant includes a time shorter than the measurement time of the instantaneous elongation value (Ue), a time longer than the measurement time, and a time shorter than the force application time for applying the deformation force to the skin in the viscoelasticity measurement of the skin, It is desirable to use four predetermined times, a force application time and a time longer than the force application time. In this way, it is possible to prevent an increase in calculation load while improving the approximation accuracy of the creep deformation curve. For example, when the measurement time of the instantaneous extension value (Ue) is set to 0.1 seconds and the force application time is set to 5 seconds, 0.05 seconds, 0.5 seconds, 5 seconds, and 50 seconds Four time constants are used.

In the step (S25), based on the measured value group normalized in the step (S23), the limit value at which the creep deformation curve converges is estimated, and each measured value and the limit value of the estimated creep deformation curve are calculated. And to calculate the limit value of each creep deformation characteristic component. For example, the limit value of each creep deformation characteristic component is calculated using the least square method so that the sum of the limit values of each creep deformation characteristic component becomes the limit value of the estimated creep deformation curve. The calculation formula in this case can be expressed as follows, for example. In the following equation, measurement data (measurement time, index value) is shown by (t _i , Y _i ), approximate data (measurement time, index value) is shown by (t _i , y _i ), and m is creep deformation Indicates the limit value of the curve.

In the step (S27), approximation of the creep recovery curve is performed using the information of the approximation formula of the creep deformation curve calculated in the step (S25) and the measurement value group at the time of creep recovery normalized in the step (S23). An equation is calculated. In the second embodiment, the approximate expression of the creep recovery curve is calculated using the first method that uses the information of the approximate expression of the creep deformation curve. Of course, the second method described in the first embodiment is used. The approximate expression may be calculated.
The approximate expression of the creep recovery curve calculated in the second embodiment can be expressed by the following expression. In the following equation, i represents an individual creep recovery characteristic component, N represents the number of creep recovery characteristic components, p represents a correction coefficient, and k ₁ represents the first (minimum time constant) creep deformation. indicates the ultimate value of the characteristic components, m _i denotes the contribution factor of the i-th creep recovery characteristic components, tau _i denotes the time constant of creep restoration characteristics component of i-th.

As shown in the above equation, the limit value (k ₁ ) of the creep deformation characteristic component having the minimum time constant is used as information on the approximate equation of the creep deformation curve.
Since the deformation of the skin observed in the visco-elastic measurement is visco-elastic deformation, the creep deformation curve and the creep recovery curve are symmetrical, and the creep recovery curve seems to converge to the state before creep deformation (zero). However, it does not converge to the state before deformation (see FIG. 2). We focus on such specificity in the skin, which is derived from components other than the cell solids that form the structure of the skin, especially the stratum corneum, epidermis, dermis, and subcutaneous tissue of the skin. I thought it was a thing. Therefore, the present inventors hypothesized that at least components of cellular solids forming the stratum corneum of the skin, the epidermis, the dermis, and the subcutaneous tissue exhibit the same visco-elastic response during creep recovery as during creep deformation. By conducting an experiment based on this hypothesis (see the example), the creep recovery curve can be accurately obtained by using the limit value (k ₁ ) of the creep deformation characteristic component having the minimum time constant corresponding to the component of the cell solid. I found that I could approximate.

In addition, the inventors have also found that the recovery limit value of the creep recovery curve can be approximated by the limit value (k ₁ ) of the creep deformation characteristic component having the minimum time constant. Thereby, in the second embodiment, an approximate expression of the creep recovery curve is calculated using the limit value (k ₁ ) of the creep deformation characteristic component having the minimum time constant as the recovery limit value of the creep recovery curve. For this reason, the step (S25) can also be called a recovery information acquisition step of acquiring the recovery limit value of the creep recovery curve.

In the step (S27), the approximate data (index value y _i ) calculated by the above equation using the limit value (k ₁ ) of the creep deformation characteristic component having the minimum time constant calculated in the step (S25) is converted into the step (S27). to approximate the normalized measurements group during creep recovery S23), the contribution factor m _i of each creep recovery characteristic component are calculated by the least square method. Furthermore, the correction coefficient p is calculated such that the approximate data (index value y _i ) calculated using the calculated contribution coefficient m _i and the limit value k ₁ further approaches the measurement value group. For example, the correction coefficient p is set to a value of 0.8 or more and 1.2 or less.

The number of creep recovery characteristic components used in the approximation of the creep recovery curve in the second embodiment is set to one or more.
At this time, the number of creep recovery characteristic components can be made smaller than the number of creep deformation characteristic components included in the approximate expression of the creep deformation curve. In creep recovery, the recovery component for a long time is smaller than that in creep deformation, so the approximation formula can be calculated with sufficient accuracy even if the number of creep recovery characteristic components is small. By reducing the number of creep recovery characteristic components, the calculation amount and the calculation time can be reduced.
As described above, since it is desirable that the number of creep deformation characteristic components be set to four, it is desirable that the number of creep recovery characteristic components be set to three in the approximation accuracy.

Further, the value of the time constant of the creep recovery characteristic component is preferably made common with the value of the time constant of the creep deformation characteristic component. Specifically, it is preferable that the value of the time constant of one or more creep recovery characteristic components be selected in order from the smaller value among the time constants of the plurality of creep deformation characteristic components. Thus, by sharing the value of the time constant of the creep recovery characteristic component with the time constant of the creep deformation characteristic component, a highly accurate approximate expression can be calculated.
For example, when four time constants of 0.05 seconds, 0.5 seconds, 5 seconds, and 50 seconds are used in the approximation of the creep deformation curve, 0.05 seconds in the approximation of the creep recovery curve. Three time constants of 5 seconds and 5 seconds are used.

Step (S29) in the step (S27) at least one or step (S25) the limit value of the creep deformation characteristics components of the calculated minimum time constant in the contribution factor of each creep recovery characteristic component calculated (m _i) with Viscoelastic information of the skin of the subject is generated using (k ₁ ) or both. Skin viscoelasticity information is as described in the first embodiment.

As will be described later in the Examples section, the contribution coefficient (m ₁ ) of the creep recovery characteristic component with the minimum time constant has a high correlation with the existing parameters R5 (Ur / Ue) and R7 (Ur / Uf) of the viscoelasticity measurement. It has been demonstrated that the limit value (k ₁ ) of the creep deformation characteristic component of the minimum time constant shows a high correlation with the existing parameters R2 (Ua / Uf) and R6 (Uv / Ue). Therefore, by using at least the contribution coefficient (m ₁ ) of the creep recovery characteristic component with the minimum time constant and the limit value (k ₁ ) of the creep deformation characteristic component with the minimum time constant, the existing parameters R2, R5, R6, and A skin viscoelasticity index equal to or higher than that of R7 can be obtained. Furthermore, since the contribution coefficient (m _i ) and the limit value (k ₁ ) can reduce variations in measurement conditions included in the measurement value, the viscoelasticity index of the skin with higher accuracy than the existing parameters can be obtained. You can get it.

In the second embodiment described above, the limit value (k ₁ ) of the creep deformation characteristic component with the minimum time constant is used as the recovery limit value of the creep recovery curve, but the existing parameter Ua obtained by viscoelasticity measurement is used. Alternatively, as described in the first embodiment, a recovery limit value calculated from a measured value group at the time of creep recovery may be used. In the case of such a modification, the above-described step (S25) is replaced with a step of obtaining the recovery limit value of the creep recovery curve. Specifically, in the step (S25), the existing parameter Ua obtained by the visco-elastic measurement is obtained, or the creep recovery curve of the creep recovery curve based on the group of measurement values at the time of creep recovery normalized in the step (S23). Recovery limit values are calculated. Further, in the case of this modification, in the step (S21), it is only necessary to acquire the measurement value at the time of creep recovery.

  In the plurality of flowcharts used in the above description, a plurality of steps (processes) are described in order, but the execution order of the steps executed in each embodiment is not limited to the description order. In each embodiment, the order of the illustrated steps can be changed within the scope of the content. Moreover, each above-mentioned embodiment and modification can be combined in the range with which the content does not conflict.

[Skin evaluation device]
The skin evaluation method according to each of the embodiments and the modifications described above can be executed by the skin evaluation device illustrated in FIG. 4.
FIG. 4: is a figure which shows notionally the hardware structural example of the skin evaluation apparatus 10. As shown in FIG.
The skin evaluation device 10 is a so-called computer (information processing device), and for example, a CPU (Central Processing Unit) 11, a memory 12, an input / output interface (I / F) 13, and a communication unit 14 mutually connected by a bus. Etc. The number of hardware elements forming the skin evaluation device 10 is not limited, and these hardware elements can be collectively referred to as an information processing circuit. The skin evaluation apparatus 10 may include hardware elements not shown in FIG. 4, and the hardware configuration is not limited.

The CPU 11 may be configured by an application specific integrated circuit (ASIC), a DSP (Digital Signal Processor), a GPU (Graphics Processing Unit) or the like, in addition to a general CPU.
The memory 12 is a random access memory (RAM), a read only memory (ROM), or an auxiliary storage device (such as a hard disk).
The input / output I / F 13 can be connected to user interface devices such as the output device 15 and the input device 16. The output device 15 is at least one of a device such as a liquid crystal display (LCD) or a cathode ray tube (CRT) display that displays a screen corresponding to drawing data processed by the CPU 11 or the like, a printing device, or the like. The input device 16 is a device such as a keyboard, a mouse or the like that receives an input of a user operation. The output device 15 and the input device 16 may be integrated and realized as a touch panel.
The communication unit 14 performs communication with other computers via a communication network, exchanges signals with other devices, and the like. A portable recording medium or the like may also be connected to the communication unit 14. In addition, the communication unit 14 may be connected to a device (viscoelasticity measuring device) that measures the viscoelasticity of the rotation type or suction type skin.
The skin evaluation apparatus 10 may be a viscoelasticity measurement apparatus itself.

  A skin evaluation program (computer program) 18 is stored in the memory 12, and the skin evaluation apparatus 10 is loaded and executed on the CPU 11, so that the skin evaluation apparatus 10 can perform the skin according to the above-described embodiments and modifications. An evaluation method can be implemented. That is, the skin evaluation apparatus 10 (CPU 11) may sequentially execute the step (S11), the step (S13), and the step (S15), or the step (S21), the step (S23), the step (S25), You may perform a process (S27) and a process (S29) sequentially. The processing content of each process is as described above, but the processing content of each process is supplemented as appropriate below.

  In step (S11) or step (S21), skin evaluation device 10 may directly acquire the measurement value from the viscoelasticity measurement device by communication, or acquire the measurement value from another computer or a portable recording medium. May be. Moreover, when the skin evaluation apparatus 10 is a viscoelasticity measuring apparatus itself, a measured value can be acquired by a signal from a probe.

The number of creep recovery characteristic components and individual time constants to be calculated in step (S13) or step (S27) may be implemented in advance in skin evaluation program 18, or may be set via input device 16 as setting parameters. It may be input.
The same applies to the number of creep deformation characteristic components to be calculated in the step (S25) and the individual time constants.
When the limit value of the creep recovery curve is acquired from outside the skin evaluation device 10 because of the approximate expression of the creep recovery curve calculated in the step (S13) or step (S27), the skin evaluation device 10 The limit value may be acquired from another computer or a portable recording medium, or may be acquired by input via the input device 16.

In the step (S15) or the step (S29), the skin evaluation apparatus 10 may generate and output the limit value or the contribution coefficient of each creep recovery characteristic component or the limit value of the creep recovery curve as the viscoelastic information of the skin as it is it can. The skin evaluation device 10 holds the average index value for each age in the memory 12 and compares the value generated as the viscoelastic information of the skin with the average index value to obtain the elasticity of the subject's skin ( ) Can be generated as viscoelasticity information. In addition, the skin evaluation device 10 holds, in the memory 12, sample values obtained from a sample skin having an average skin elasticity (harness), and uses the sample values and the viscoelastic information generated for the skin of the subject. Viscoelasticity information indicating whether the skin elasticity of the subject is good or not can be generated by comparing the value shown with the magnitude.
Moreover, the skin evaluation apparatus 10 is elastic for each of a plurality of layers including at least the stratum corneum, the epidermis, and the dermis using the approximate expression calculated in the step (S13), the step (S25), or the step (S27). The rate may be calculated.

  Examples will be given below to explain the above-mentioned contents in more detail. The description of the following examples does not limit the above-described embodiments and modifications.

  The approximation formula calculated using the first method adopted in the second embodiment described above demonstrates that the creep recovery curve based on the measurement value obtained by the actual skin viscoelasticity measurement can be approximated as follows. It was.

FIG. 5 is a graph showing a creep deformation curve based on an approximate expression, a creep recovery curve, and respective curves based on measured values. FIG. 5A shows a graph based on the viscoelasticity measurement on the skin of a female subject in the 20s, and FIG. 5B shows a graph based on the viscoelasticity measurement on the skin of a female subject in the 40s. (C) shows the graph based on the viscoelasticity measurement with respect to the skin of the test subject of a 50s male. In FIG. 5, "approximate-suction" indicates a creep deformation curve based on the approximate expression, and "approximate-release" indicates a creep recovery curve based on the approximate expression.
Viscoelasticity measurement was performed a plurality of times using a suction-type measuring instrument called Cutometer, and the average value was used as a measured value.

In FIG. 5, an equation described by the sum of four creep deformation characteristic components having time constants of 0.05 seconds, 0.5 seconds, 5 seconds, and 50 seconds is used as an approximation of the creep deformation curve. The following equation described using one creep recovery characteristic component having a time constant of 0.05 seconds was used as an approximation of the creep recovery curve. K ₁ in the following equation represents the limit value of the creep deformation characteristic component having the minimum time constant (0.05) in the approximate equation of the creep deformation curve, and p represents a correction coefficient.

_{K 1} in the above formula is calculated as "0.91" In FIG. 5 (a), calculated as "0.79" in Fig 5 (b) is calculated as "0.91", 5 in (c) It was done.
And the value of each k ₁ which is such calculated, FIG. 5 (a), when comparing the extreme values of the creep recovery curve based on the measured values in FIGS. 5 (b) and 5 FIG. 5 (c), the approximate to each other I understand that.
This demonstrates that the limit value of the creep recovery curve can be replaced by the limit value of the creep deformation characteristic component having the minimum time constant in the approximation of the creep deformation curve.
The correction coefficient p is set to "1.0" in FIG. 5A, is set to "1.0" in FIG. 5B, and is set to "1.0" in FIG. 5C. It was done.

According to FIG. 5 (a), it can be seen that the viscoelasticity index of the skin of the female test subject in the 20s can be approximated with high accuracy both during creep deformation and during creep recovery.
However, as shown in FIGS. 5 (b) and 5 (c), in subjects in their 40s and 50s, an error occurs at the time of creep recovery. Specifically, it can be seen that the actual skin recovery is delayed more than the value obtained by the approximation formula.
This is because the creep recovery curve approximation equation used in FIG. 5 approximates only the creep recovery characteristic component with the minimum time constant (0.05), that is, the instantaneous recovery component. It is thought that the elastic component of the corresponding cell solid has decreased over time.
Therefore, it has been demonstrated that, for skins of the age of 20 years where the elasticity of cellular solid of skin is large, approximation can be made with sufficient accuracy by one creep deformation characteristic component.

Here, the result of approximation by increasing the creep recovery characteristic component is shown in FIG. FIG. 6 is a graph showing a creep deformation curve and a creep recovery curve based on the approximate expression and respective curves based on the measured values, as in FIG.
In FIG. 6, the approximate expression of the creep deformation curve is the same as that of FIG. 5, and in the approximate expression of the creep recovery curve, three creep recovery characteristic components having time constants of 0.05 seconds, 0.5 seconds and 5 seconds. The following equation described using is used: In the following equation, k ₁ represents the limit value of the creep deformation characteristic component having the minimum time constant (0.05) in the approximate expression of the creep deformation curve, and m ₁ , m _2, and m ₃ represent the respective creep recovery characteristic components. And p indicates a correction factor.

According to FIGS. 6 (a), 6 (b) and 6 (c), the viscoelasticity index of the skin of all subjects in their 20s, 40s and 50s, both during creep deformation and during creep recovery. , It can be seen that the approximation can be made with high accuracy.
That is, FIG. 6 demonstrates that the creep recovery curve can be approximated with high accuracy by the approximation formula described by the sum of a plurality of creep recovery characteristic components having different time constants.

Furthermore, the contribution coefficient m ₁ of the creep recovery characteristic component of the minimum time constant (0.05) obtained by the above-mentioned approximate expression (Eq. 6) and the limit value k of the creep deformation characteristic component of the minimum time constant (0.05) _The following two tests were conducted to verify the correlation between ₁ and the existing viscoelastic parameters.
In the first test, viscoelasticity measurements were performed on the buccal skin of each subject, with 220 women aged 20 to 49 as the subject population. In this viscoelasticity measurement, the skin of each subject was aspirated for 2 seconds at an aspiration pressure of 300 mbar using a probe with an aspiration diameter of 2 mm, and was measured for 2 seconds after release.
In the second test, visco-elastic measurement was performed on the buccal skin of each subject, with 51 females aged 31 to 34 and 54 females aged 51 to 54 as subject populations. In this viscoelasticity measurement, the skin of each subject was aspirated for 3 seconds at an aspiration pressure of 300 mbar using a probe with an aspiration diameter of 2 mm, and was measured for 3 seconds after release.

FIG. 7 is a graph showing the results of the first test, and FIG. 8 is a graph showing the results of the second test.
The first test and the second test result, as shown in FIGS. 7 and 8, the creep deformation characteristics component extreme value _{k 1} and existing viscoelastic parameters R2 (Ua / Uf) and R6 is a (Uv / Ue) A high correlation was exhibited, and the contribution coefficient m ₁ of the creep recovery characteristic component having the minimum time constant (0.05) and the existing viscoelastic parameters R5 (Ur / Ue) and R7 (Ur / Uf) showed a high correlation.
This demonstrates that the contribution coefficient m ₁ of the creep recovery characteristic component of the minimum time constant and the limit value k ₁ of the creep deformation characteristic component of the minimum time constant can be used as a new index indicating the viscoelasticity of the skin. .
Here, since the limit value k ₁ of the creep deformation characteristic component of the minimum time constant has been proved to approximate to the limit value of the creep recovery curve, it can be substituted by the limit value calculated from the measurement value at the time of creep recovery. It is. Also, although the accuracy is lower than the contribution coefficient m1, the limit value of the creep recovery characteristic component of the minimum time constant formed by multiplying m ₁ and k ₁ and the correction coefficient p can be used instead of the contribution coefficient m ₁ is there.

10 skin evaluation device 11 CPU
12 Memory 13 I / O I / F
14 communication unit 15 output device 16 input device 18 skin evaluation program

Claims (8)

A measurement value acquisition step of acquiring measurement values of viscoelasticity measurement on the skin of the subject;
Calculating an approximate expression of a recovery curve indicating a time characteristic of creep recovery described based on the acquired measured values using one or more creep recovery characteristic components having different time constants;
A generation step of generating visco-elastic information of the skin of the subject using the calculated approximate expression;
Skin evaluation methods including Each of the time constants of the one or more creep recovery characteristic components is set to {(1−e ⁻¹ ) × 100} percent (e is the number of Napiers) of the limit value of each creep recovery characteristic component from the start of creep recovery. It is time to reach and is set to a predetermined time,
In the calculation step, an approximate expression of the recovery curve is calculated by subtracting the one or more creep recovery characteristic components from the creep recovery start value obtained from the measured value;
In the generating step, the viscoelastic information is generated using at least one of the limit values of the one or more creep recovery characteristic components.
The skin evaluation method according to claim 1. A recovery information acquisition step of acquiring a recovery limit value of the recovery curve,
Further include
The approximate expression is calculated using a plurality of the creep recovery characteristic components,
The limit value of each creep recovery characteristic component is indicated by the product of the recovery limit value of the recovery curve and the contribution coefficient of each creep recovery characteristic component,
In the generation step, the visco-elastic information is generated using at least one of the contribution coefficient of each creep recovery characteristic component, the recovery limit value of the recovery curve, or both of them.
The skin evaluation method according to claim 2. The acquired recovery limit value is a time characteristic of creep deformation described by a sum of a plurality of creep deformation characteristic components having different time constants, calculated based on a measured value of creep deformation in the viscoelasticity measurement. It is the limit value of the creep deformation characteristic component with the minimum time constant in the approximate expression of the deformation curve shown,
The time constant of each creep deformation characteristic component is a time required to reach {(1-e ⁻¹ ) × 100} percent (e is the number of Napiers) of the limit value of each creep deformation characteristic component. Each set to a given time,
The skin evaluation method according to claim 3. The number of creep recovery characteristic components included in the approximate expression of the recovery curve is smaller than the number of creep deformation characteristic components included in the approximate expression of the deformation curve,
The skin evaluation method according to claim 4. The value of the time constant of the creep recovery characteristic component is common to the value of the time constant of the creep deformation characteristic component,
The skin evaluation method according to claim 5. For the time constant of the one or more creep recovery characteristic components, a predetermined time including at least a time shorter than the measurement time of the instantaneous recovery value (Ur) used in the viscoelasticity measurement is used.
The skin evaluation method according to any one of claims 1 to 6.   The skin evaluation apparatus which performs the skin evaluation method as described in any one of Claim 1 to 7.

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