JP2023000902A - Skin condition evaluation method - Google Patents

Abstract

To provide a skin condition evaluation method based on simple and speedy measurement of an intra-skin tissue.SOLUTION: The method constructs three-dimensional image data in the depth direction and the in-plane direction of a skin from a reflection wave of an ultrasonic wave applied to the skin, identifies the position of a basal membrane from the three-dimensional image data, determines a range from the basal membrane to a predetermined depth as an evaluation space, and quantifies the density or fibrous state of collagen in the evaluation space.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a skin condition evaluation method, and more particularly to evaluation of the collagen condition inside the skin using ultrasound.

Collagen is a kind of protein and is involved in the flexibility and elasticity of living tissue. In particular, collagen contained in the skin greatly affects the firmness and strength of the skin. In the skin, 70 to 80% of the dermal layer, which is directly under the epidermal layer, is composed of collagen fibers. Collagen fibers are bundles of regular arrangements of collagen molecules. When collagen fibers are thin and fragile, they appear as changes in appearance such as wrinkles and sagging. When the amount of collagen distribution is large, the skin has firmness and strength. Maintaining the correct level of collagen in your skin can help keep your skin young and healthy.

A method of detecting the second harmonic (SHG light) generated by irradiating the inside of the skin with ultrashort pulse light and quantifying the density of collagen in the skin based on the SHG light image has been proposed (for example, See Patent Document 1). On the other hand, a method of estimating the layer interface or thickness by irradiating a thin layer structure such as skin with ultrasonic waves and calculating the acoustic impedance from the reflected wave from the tissue boundary with different physical properties has been proposed (for example, See Patent Documents 2 and 3).

Japanese Patent No. 5707226 Japanese Patent No. 6361001 JP 2020-174856 A

Measurement using an SHG microscope can visualize collagen fibers inside the skin with high resolution, but the system configuration is large and it takes time for measurement and analysis. A method using an acoustic microscope cannot perform imaging with a super-high resolution comparable to that of an SHG microscope, but it is capable of simple and short-time measurement and analysis. The above-described Patent Document 2 aims at constructing an image of the skin in the depth direction, and cannot analyze and evaluate the living tissue contained in a specific layer. Patent Document 3 estimates the position or thickness of the stratum corneum from the point of inflection obtained by differentiating the acoustic impedance of the reflected wave twice. Analysis and evaluation have not been realized.

An object of the present invention is to provide a skin condition evaluation method based on simple and rapid measurement of internal skin tissue.

In one aspect of the present invention, the skin condition evaluation method comprises:
Ultrasound is applied to the skin and the reflected wave is measured,
constructing three-dimensional image data in the depth direction and in-plane direction of the skin from the intensity of the reflected wave;
identifying the position of the basement membrane from the three-dimensional image data and determining a range from the basement membrane to a predetermined depth as an evaluation space;
The density or fiber state of collagen in the evaluation space is evaluated.

A skin condition evaluation method based on simple and rapid measurement of the internal tissue of the skin is realized.

It is a figure explaining the form of the skin of a measuring object. 4 is a flowchart showing basic operations of a skin condition evaluation method; It is a figure explaining irradiation of an ultrasonic wave and acquisition of a reflected wave. It is an example of xz-plane image data generated from the intensity distribution of reflected waves. It is a figure explaining specification of a basement membrane. It is a figure explaining quantification of a collagen state based on three-dimensional data. It is a figure explaining quantification of collagen distribution amount. 1 is a flow chart of quantification of collagen distribution amount. It is the figure which plotted the relationship between collagen distribution amount and age. 1 is a flow chart for quantification of collagen fiber strength (or thickness). It is a figure explaining acquisition of the one-dimensional spatial frequency distribution of a power spectrum. It is a figure explaining the fitting to the exponential function of a power spectrum. FIG. 4 is a diagram plotting the relationship between an index representing the strength of collagen fibers and age. FIG. 10 is a diagram showing measurement results of an embodiment using an acoustic microscope in comparison with measurement results using an SHG microscope; It is a figure which shows an example of skin condition evaluation based on the quantified index.

A specific method for skin condition evaluation will be described below with reference to the drawings. In the embodiment, three-dimensional image data is constructed from reflected waves obtained by irradiating the skin with ultrasonic waves, and information on collagen is extracted. Irradiation of ultrasonic waves and measurement of reflected waves are performed using a general acoustic impedance microscope. In the embodiment, the distribution amount of collagen and the strength (thickness) of collagen fibers are quantified as an example of information about collagen.

FIG. 1 is a diagram for explaining the morphology of the skin to be measured. The skin has a three-layer structure of epidermis, dermis, and subcutaneous tissue from the outside. The stratum corneum having a thickness of about 20 μm is the outermost layer of the epidermis, and the epidermis layer is located below the stratum corneum. The dermis is located between the epidermis and the subcutaneous tissue, and contains glycosaminoglycans such as hyaluronic acid in addition to collagen fibers, which are the major constituents. The dermis layer maintains the mechanical and morphological properties of the skin by performing functions such as firmness, elasticity and water retention. In an embodiment, ultrasonic measurement is performed from the surface of the skin to a depth of about 300 μm. The measurement results are analyzed to quantify the density (distribution amount) of collagen, which is a major component in the dermis layer deeper than the epidermis, or the strength of collagen fibers. Multifaceted quantification of the collagen state inside the skin enables objective evaluation of the skin state with high accuracy.

Ultrasonic waves are used because the measurement time and analysis time are shorter than those of the SHG microscope, and the measurement can be performed with a general-purpose acoustic microscope. As will be described later, a predetermined area of the subject's skin is scanned with ultrasonic waves, and the state of collagen is specified based on the reflected waves from the inside of the skin to obtain measurement results that match those of the SHG microscope.

FIG. 2 is a flow chart showing the basic operation of the skin condition evaluation method of the embodiment. First, ultrasonic waves are applied to the skin of a person to be measured, and reflected waves are measured (S1). As an example of the skin of the person to be measured, cheek skin is measured. The measurement may be performed by pressing the acoustic window at the tip of the probe of the acoustic microscope against the subject's cheek, or by pressing the subject's cheek against a fixed measurement plate. It is desirable to apply couplant such as water or gel to the cheeks to fill in the gaps between the fine unevenness of the skin surface and the probe's acoustic window or measurement plate.

FIG. 3 is a diagram for explaining irradiation of ultrasonic waves and acquisition of reflected waves. When ultrasonic pulses of about 20 to 320 MHz are sent into the body, reflected waves from tissue interfaces with different physical properties can be obtained. Let the surface of the skin be the xy plane and the depth direction be the z direction. Ultrasonic waves transmitted from the skin surface into the living body are reflected at the interface between the couplant and the skin, the interface between the stratum corneum and the epidermis, the interface between the epidermis and the dermis, and the like to obtain reflected waves.

The acoustic microscope is connected to a personal computer (PC). Reflected waves obtained by two-dimensionally scanning the cheek with ultrasonic waves are received by a receiver provided inside the probe or directly under the measurement plate, converted to electrical signals, and input to the PC. A PC Fourier-transforms the reflected wave, and calculates the acoustic impedance from the Fourier-transformed reflected signal. To increase the accuracy of extracting the acoustic impedance from the tissue interface inside the skin, the maximum value of the cross-correlation between the reference waveform from a reference material such as a measuring plate, couplant, etc. and the reflected wave from the tissue interface may be taken. By maximizing the cross-correlation, it is possible to reduce the interference of the reflected wave from inside the skin and the influence of unevenness on the skin surface, and obtain the acoustic impedance with high accuracy.

Returning to FIG. 2, three-dimensional image data is constructed from the signal intensity or acoustic impedance of the reflected wave (S2). The three dimensions are, as shown in FIG. 3, the xy plane parallel to the skin surface and the depth direction (z direction) of the skin. Reflected waves in the xy plane are obtained by two-dimensionally scanning the skin with ultrasonic waves. Data in the depth direction are obtained from the waveform of the reflected wave and the z-direction intensity profile of the acoustic impedance. Three-dimensional image data can be obtained by three-dimensionally mapping the signal intensity or the intensity of the acoustic impedance.

As an example, we construct three-dimensional data from 45000 reflected waves over an area of 2.4×2.4 mm ² and ranging from the skin surface to a depth of 300 μm. In pixel units, (x, y, z) = (300, 150, 200) pixels. The resolution is (Δx, Δy, Δz)=(8, 16, 15) μm.

FIG. 4 shows an example of an xz-plane image in constructed three-dimensional image data. The signal intensity of the reflected wave of the ultrasonic wave scanned in the x direction is mapped to pixels in the xz plane as grayscale data. In this image data, the image area A forming a fine wave pattern indicates the presence of collagen. Part of the ultrasonic wave is reflected by the collagen fibers, and a fine wave pattern appears on the image data in which the intensity of the reflected wave is mapped in gradation. A flat area B without a pattern is an area in which almost no reflected signal is obtained, that is, an area in which there are few collagen fibers.

Returning to FIG. 2, the position of the basement membrane is specified from the three-dimensional image data, and the range from the basement membrane to a predetermined depth is determined as the evaluation space (S3). The basement membrane is located between the epidermis and dermis and is a thin membranous structure made up of extracellular matrix molecules. In the evaluation of the skin condition of the embodiment, the fibrous collagen present directly under the basement membrane, that is, in the upper dermis is evaluated. In normal evaluation of collagen inside the skin, measurement is performed at a predetermined depth from the outermost surface of the skin to a predetermined depth. On the other hand, in the embodiment, the evaluation space is defined as a predetermined depth from the basement membrane. The position of the basement membrane, that is, the thickness of the epidermis, varies depending on the measurement subject and age, and type I collagen, which forms collagen fibers, exists directly under the basement membrane.

FIG. 5 is a diagram for explaining identification of the basement membrane. The position of the basement membrane may be identified by a second derivative technique, as described in US Pat. However, since the reflected wave from the basement membrane is smaller than the reflected wave obtained from the interface between the stratum corneum and the epidermis, it may be difficult to identify the basement membrane by the method of second differentiation. As one method, the basilar membrane is specified from the waveform obtained by differentiating the reflected wave once.

Although the basement membrane also contains collagen, the collagen contained in the basement membrane is non-fibrous type IV collagen, unlike the fibrous type I collagen that forms the dermis. At the interface between the basement membrane and the dermis, which have different physical properties, the acoustic impedance changes in the direction of increasing. The second peak in the intensity profile obtained by differentiating the reflected wave once may be identified as the position of the basilar membrane. The first peak indicates the position of the interface between the couplant and the stratum corneum.

Alternatively, the position of the basement membrane may be specified based on the three-dimensional image data generated in step S2. The three-dimensional image data generated in S2 is subjected to filtering processing such as edge detection using a primary differential filter to extract a wavy striped pattern in the image. This edge detection removes areas where there is no signal or where the signal change is below a predetermined level.

FIG. 5 shows image data after filtering. In the xz plane, areas with small signal variations are hollowed out, leaving a wavy striped pattern. Large signal-free undulations running parallel to the plane of measurement in the filtered image represent epidermal layers. The striped pattern left unremoved indicates the presence of collagen fibers. In the data after edge detection, the luminance (signal intensity) is traced in the depth direction from the region representing the removed epidermal layer, and the depth position where the first luminance peak appears is defined as the position of the basement membrane. Edge detection and detection of luminance peaks in the depth direction can be performed with general-purpose image processing software and software packages based on programming languages such as Python. A range from the basement membrane to a predetermined depth, for example, a space of 40 to 120 μm just below the basement membrane is used as an evaluation space.

Returning to FIG. 2, the state of collagen in the evaluation space is measured and evaluated (S4). Measurement and evaluation of collagen status includes quantification of collagen status.

FIG. 6 is a diagram explaining the quantification of the collagen state based on three-dimensional data. A region in which collagen exists is specified from the three-dimensional image data generated in step S2. As in step S3, image processing is performed on the three-dimensional data to identify the position of the basement membrane, and a predetermined range immediately below the basement membrane is defined as an evaluation space. Characterize the state of the collagen in the evaluation space. As features of the collagen state, the amount of collagen distribution, the strength (thickness) of collagen fibers, and the like are quantified.

In general, the more collagen distribution, the firmer the skin. In addition, the thicker the collagen fibers, the more rigid the skin. Specific methods for quantifying the distribution amount of collagen and the strength of collagen fibers will be described below.

<Quantification of distribution amount of collagen>
FIG. 7 is a diagram illustrating quantification of collagen distribution amount. A volume filling factor (VFF) is used as an index representing the amount of collagen distribution. VFF is the ratio of the number of pixels occupied by collagen to the total number of pixels in the evaluation space. Which part of the evaluation space is occupied by collagen can be obtained from three-dimensional data image-processed as shown in FIG.

A range of 80±40 μm just below the basement membrane is set as the evaluation space just below the basement membrane, that is, the calculation volume of VFF. As an example, if the evaluation space is (x,y,z)=(300,150,50) in pixels, then the total number of pixels in the evaluation space is 2,250,000. Among them, the remaining pixels that have not been removed by the filtering process are counted as collagen pixels. Thereby, the proportion of collagen in a given volume is obtained.

FIG. 8 is a flowchart of quantification of collagen distribution. A specific pattern is extracted from the three-dimensional image data (S11). The particular pattern, in this example, is a wavy pattern indicative of collagen fibers.

A ratio of the number of pixels included in the specific pattern to the total number of pixels in the evaluation space is calculated as the distribution amount of collagen (S12). Reference data is prepared in order to evaluate the skin condition using the calculated distribution amount (S13). As reference data, the average distribution amount of collagen by age may be acquired. By comparing the measured collagen distribution amount with the average distribution amount of collagen by age, the skin condition is younger than the actual age, aged, average condition of the same generation, etc. can be evaluated. can be done.

FIG. 9 is a diagram plotting the relationship between collagen distribution amount and age. 84 men and women aged 20 to 69 were measured, and the VFF calculated from the measurement results of each person was plotted in association with age. All measurement sites were cheeks, reflected waves were measured using the same sonic microscope, the basement membrane was identified based on the data after the image processing described above, and VFF was calculated in the same size evaluation space.

From FIG. 9, it can be seen that there is a moderate inverse correlation between age and VFF, and that collagen distribution decreases with age. In this figure, the correlation coefficient r is −0.459±0.005, and the p-value of the correlation coefficient, ie, the correlation coefficient r is −0.459±0.005 by chance or mistake in the absence of correlation. is less than 0.001 (0.1%).

The skin condition can be objectively evaluated by quantifying the collagen condition as the collagen distribution amount. Note that step S13 in the flow of FIG. 8 may be performed before step S11.

<Strength of collagen fibers>
Another evaluation index is to quantify the strength (or thickness) of collagen fibers. If the collagen fibers are thick and in large bundles, the collagen fibers can be evaluated as strong. When the collagen fibers are thin and fragile, it can be evaluated that the collagen fibers are weak. One challenge is how to quantify the strength of collagen fibers.

FIG. 10 is a flowchart for quantification of collagen fiber strength (or thickness). First, the one-dimensional spatial frequency distribution of the power spectrum P(k) in the evaluation space is obtained (S21). The one-dimensional spatial frequency distribution of the power spectrum P(k) is obtained, for example, by Fourier transforming the in-plane intensity distribution at a predetermined depth in the enhancement space. More specifically, among the three-dimensional image data shown in FIG. 6, the intensity distribution in the xy plane in the evaluation space is subjected to Fourier transform to first transform into two-dimensional spatial frequency data.

FIG. 11 is a diagram illustrating acquisition of a one-dimensional spatial frequency distribution of a power spectrum from two-dimensional spatial frequency data. The horizontal axis is the spatial frequency k _x in the x direction, and the vertical axis is the spatial frequency k _y in the y direction. The indicator on the right is the logarithm of the power spectrum P in two-dimensional frequency space.

The Fourier-transformed frequency-domain power spectrum P(k) is

で表される。ここでＦＴはフーリエ変換を表し、

is represented by where FT stands for Fourier transform,

は輝度分布、ｋは空間周波数である。

is the luminance distribution and k is the spatial frequency.

In order to obtain a one-dimensional spatial frequency distribution from the two-dimensional spatial frequency distribution in FIG.

での輝度分布の平均をとる。すなわち、パワースペクトルＰ（ｋ）は、

Take the average of the luminance distribution at That is, the power spectrum P(k) is

と表される。

is represented.

Next, the power spectrum P(k) of the one-dimensional spatial frequency distribution is fitted to an exponential function (power function), and the slope p of the exponential function is determined as a value representing the strength (roughness) of collagen fibers (S22 ).

FIG. 12 is a diagram illustrating fitting of the power spectrum P(k) to an exponential function (power function). The black points are the one-dimensional power spectrum, and the gray point set in the background is the data before angle averaging. The image data representing the luminance distribution in the xy plane on the left side of the arrow is subjected to Fourier transform as described above to obtain a one-dimensional spatial frequency power spectrum P(k) averaged in all directions. By fitting this power spectrum P(k) to an exponential function, a fitting curve shown on the right side of the arrow is obtained. The horizontal axis is the one-dimensional spatial frequency k, and the vertical axis is the logarithmic intensity of the power spectrum P(k). P(k) is proportional to 1/kp.

The slope p of the fitting curve is used as an index representing the collagen fiber texture (CFT). The slope p represents the balance between the thickness and thinness of collagen fibers. The logarithmic intensity is large in the region where the spatial frequency is small, that is, the region where the collagen fibers are thick and rough. The logarithmic intensity is small in the region where the spatial frequency is high, that is, the collagen fibers are thin and the spatial density is high.

FIG. 13 is a diagram plotting the relationship between CFT, which is an index showing the strength of collagen fibers, and age. As described above, the CFT is the slope of the exponential function representing the relationship between the spatial frequency of the evaluation area and the logarithmic intensity of the reflected wave. When the CFT is large, the slope of the exponential function is steep. When the CFT is small, the slope of the exponential function is flat.

When the slope p of the exponential function is steep, it indicates that the thickness and thinness of the collagen fibers are well balanced and the collagen state is good. That is, the spatial frequency is low and the collagen fibers are densely present in a portion where thick bundles of collagen fibers are present. When the slope p is flat, it indicates that the thickness and thinness of the collagen fibers are out of balance and the state of the collagen is degraded. A power spectrum is not obtained from the region where the collagen fibers should be thick and coarse, indicating that the fibers are cut or missing inside the collagen fibers.

CFT tends to decrease with age. When the CFT was calculated from the ultrasound measurement results of 84 persons aged 20 to 69, the same as the VFF measurement evaluation, and plotted against age, a weak inverse correlation was observed. The correlation coefficient r is -0.356 ± 0.045, and the p-value of the correlation coefficient, i.e. the probability that the correlation coefficient r is -0.356 ± 0.045 by chance or mistake in the absence of correlation, is 0.001+0.059−0.001. It can be seen that the CFT value of collagen fibers can be used satisfactorily for skin condition evaluation.

In the above description, the logarithmic intensity of the power spectrum of the reflected wave is used for easy evaluation, but the normalized relative intensity or the intensity of the acoustic impedance itself may be used instead of the logarithmic intensity. The function representing the relationship between the spatial frequency of the evaluation space and the reflected wave intensity is optimally an exponential function, but is not limited to the exponential function, and any suitable function describing the fitting line may be used.

Returning to FIG. 10, the average value of CFT by age (average gradient of reflected wave intensity as a function of spatial frequency) is obtained in advance (S23). The skin condition is evaluated by comparing the measured and calculated CFT value with the age-specific average CFT value obtained in advance (S24). This makes it possible to objectively evaluate the state of collagen inside the skin.

FIG. 14 is a diagram showing the measurement results of the embodiment using the acoustic microscope in comparison with the measurement results of the SHG microscope. (A) of FIG. 14 is the measurement result of the embodiment obtained using an acoustic microscope, and (B) is the measurement result of an SHG microscope. In (A) of FIG. 14, in the image data (xz cross section) inside the skin of a subject in his twenties, there are few filtered areas, that is, areas with poor signal change, and many collagen fibers are present. You can see that visually.

In the image data (xz cross section) inside the skin of a subject in his 60s, it can be visually seen that the filtered area, that is, the area with poor signal change, has increased and the collagen fibers have decreased. . Based on each image data, the VFF value quantified as an objective numerical value is 0.7 for people in their 20s and 0.5 for people in their 60s. Similarly, the CFT value for people in their 20s is 3.1, and the CFT value for people in their 60s is 2.5.

According to the image obtained by irradiating the subject's cheek with ultrashort pulses with an SHG microscope in FIG. Collagen fibers become thinner and weaker with age.

A comparison of FIGS. 14A and 14B reveals that the locations, ratios, and densities occupied by the collagen fibers match in the state of the image data. Therefore, it is possible to visually evaluate the state of collagen fibers using only the image data generated from the measurement results of the acoustic microscope.

By using the VFF value or CFT value that quantifies the collagen state, the visually recognized collagen state can be indicated as an objective numerical value. The collagen status indicated by the VFF and CFT values is in good agreement with the results of observation by SHG microscopy. That is, collagen distribution volume (VFF) decreases with aging, and collagen fibers become finer and thinner (decrease in CFT value). It can be seen that the tendency of aging can be objectively evaluated with high accuracy using an acoustic microscope.

In the measurement of FIG. 14, the measurement result (A) using the acoustic microscope was obtained in a total of 4 minutes, 2 minutes for measurement and 2 minutes for analysis. It took 60 minutes for measurement and 20 minutes for analysis, totaling 80 minutes, to obtain the measurement result (B) using the SHG microscope. The method of the embodiment using acoustic microscopy is realized in 1/20 the time of SHG measurement. This measurement result indicates the possibility of practical and speedy analysis by the technique of the embodiment.

FIG. 15 shows an example of skin condition evaluation based on quantified indices. The horizontal axis represents the amount of collagen distribution (VFF value), the vertical axis represents the strength of collagen fibers (CFT value), and the VFF and CFT values calculated from the measurement results are plotted in four quadrants. The origin is, for example, the overall mean value of the VFF and CFF values. When both the VFF value and the CFF value are above average, it is plotted in the first quadrant and the skin condition is evaluated as good.

When the CFT value is above average but the VFF value is below average, it is plotted in the second quadrant and the need for enhancement of collagen content within the skin is assessed. VFF values above average but CFT values below average are plotted in quadrant 4 and assessed as needing collagen fiber reinforcement. When both the CFT value and the VFF value do not reach the average, it is plotted in the third quadrant, and it is evaluated that the amount of collagen is insufficient and the collagen fibers are fragile. In this case, both an increase in collagen content and strengthening of collagen fibers are desired.

Based on the objective evaluation shown in FIG. 15, it is possible to give appropriate advice on how to take supplements, skin care, and the like.

Although the invention has been described with reference to specific embodiments, the invention is not limited to the examples described above. Using an acoustic microscope is useful for short-time and simple skin evaluation, but the evaluation method based on VFF or SFT of the above-described embodiment, and the method of specifying the basement membrane and setting the evaluation space are not suitable for SHG microscope or It can also be applied to skin measurement using OCT (Optical Coherence Tomography). Filtering processing for the constructed three-dimensional image data and identification of the basement membrane may be automated using a programming language and software package such as "python" and "openCV-Phthon".

According to the present invention, it is possible to quantify the state of collagen in the skin from various angles and to evaluate the skin state objectively with high accuracy. The measurement and evaluation methods of the embodiments can be usefully used in the fields of beauty care and skin care.

Claims (10)

Constructing three-dimensional image data in the depth direction and in-plane direction of the skin from the reflected waves of ultrasonic waves irradiated to the skin,
Identifying the position of the basement membrane from the three-dimensional image data,
determining a range from the basement membrane to a predetermined depth as an evaluation space;
quantifying the density or fiber state of collagen in the evaluation space;
Evaluation method of skin condition. quantifying the ratio of collagen contained in a certain volume of the evaluation space as the density or distribution amount of collagen;
The method for evaluating a skin condition according to claim 1. Filtering the three-dimensional image data to extract a specific pattern,
calculating a ratio of pixels containing the specific pattern to all pixels in the evaluation space as a distribution amount of the collagen;
The skin condition evaluation method according to claim 2. Obtain the average distribution amount of collagen by age in advance,
The skin condition evaluation method according to claim 2 or 3, wherein the skin condition is evaluated based on the average distribution amount and the measured distribution amount of the collagen. obtaining a one-dimensional spatial frequency distribution of the power spectrum of the evaluation space;
fitting the one-dimensional spatial frequency distribution;
Determining the slope of the fitting line as a value indicating the strength of collagen fibers,
The method for evaluating a skin condition according to claim 1. The one-dimensional spatial frequency distribution represents an average of spatial frequency distributions in all directions in a two-dimensional spatial frequency domain obtained by Fourier transforming the in-plane intensity distribution in the evaluation space.
The skin condition evaluation method according to claim 5. Obtaining in advance the average slope of the fitting line by age,
7. The skin condition evaluation method according to claim 5, wherein the skin condition is evaluated based on the average slope and the measured slope of the fitting line. performing edge detection using a primary differential filter on the three-dimensional image data;
detecting the filtered-out area extending horizontally with the surface of the skin as an epidermal layer;
Determining the peak position of the intensity that first appears in the depth direction of the skin from the epidermis layer as the basement membrane,
The skin condition evaluation method according to any one of claims 1 to 7. Calculate the acoustic impedance in the depth direction of the skin based on the reflected wave, and determine the second peak position appearing in the rate of change obtained by differentiating the acoustic impedance once as the basement membrane.
The skin condition evaluation method according to any one of claims 1 to 7. The distribution amount of collagen determined by the method according to any one of claims 2 to 4 is represented by the first axis,
The slope of the fitting line determined by the method of any one of claims 5 to 7 is represented by a second axis orthogonal to the first axis,
Plotting the distribution amount of the collagen and the slope of the fitting line in one of the four quadrants,
evaluating the skin condition based on the plot;
Evaluation method of skin condition.

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