quantification of skin ageing by 3d measurement

8/12/2019 Quantification of skin ageing by 3D measurement

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Quantification of skin aging by three-dimensional measurem entof skin surface contour

Tateki Uchida, Takashi Komeda, Masao Miyagi, Hiroyuki Koyama, Hiroyasu FunakuboCenter of Education ResearchShibaura Institute of Technology

307 Fukasaku, Omiya-city, Saitama 330, JapanABSTRACT

In order to quantify the skin aging, the skin surface contoursfor 72 male subjects from in his 20s to in his 60swere measured three-dimensionally and analyzed by twodimensional Fourier Transform method. The measuring partof the body was the back of the hand. The results of thethree-dimensional measurements showed that the patterncomposed of longitudinal, oblique, and transverse ridges onthe skin surface changedwt age.The results of two dimensional Fourier analysis of skinsurface contours showed,that the skin surface contours ofyoung male subjects included much o f high spa tial frequencycomponents while the skin surface contours of aged malesubjects included low spatial frequency components mainly.The aging parameter for 72 male subjects, which expressedthe skin aging quantitatively, was calculated by summing upthe Fourier coefficients within a specified area on the X-Yspatial frequency plane. The ag ing parameter decreased withage. However the aging parameter showed wide scattering.This wide scattering might be caused by the low frequencycomponents such as the waviness or the inclination ofthe skin surface itself. The wide scattering of the agingparameter will be removed by applying the high pass digitalfilter to the skin surface contours.

1. INTRODUCTIONIn recent years the population of aged people in Japan hasincreased greatly and Japan is becoming an aged societyrapidly. Now much attention is being paid to aging.Especially quantitative evaluation of the degree of aging isrequired while many scientists are trying to elucidate themechanism of aging itself. In our study we focus on the skinaging because skin plays an important role as barrier to thesurroundings outside our body. Skin is also important fromthe view point of beauty culture and the quantification of theskin aging is significant.Physiological and morphological characteristics of the facialskin such as skin surface conductance, skin color, skinsurface microtopography by means of im age and so forth, had

been investigated in relation to aging [l],quantification of skin aging had not succeeded adequately.Our study is aiming to find a quantitative relation betweenskin aging and skin surface contours. However, it is difficultto measure the human skin surface directly due to themovement of human body. In our study a measuring object isa negative replica of the skin surface. Using an opticalmeasuring system, we measured the skin surface contours ofmale subjects and also analyzed the skin surface contours bytwo-dimensional Fourier Transform in order to obtam thequantitative parame ter of skIn this paper we describe Its of three-dimensionalmeasurements of skin surface contours for the back of thehand of male subjects from in his 20s to 60s. We alsodescribe the results of the frequency analysis of the skinsurface contours by two-dimensional Fourier T ransform andthe aging paiameter obtained from the results of Fourieranalysis, which expresses the skin aging quantitatively

2. MEASURING SYSTEM FOR SKIN SURFACEOur measuring system needs twenty or thirty minutesto measure a skin surface contour and the accuracy ofmeasurement is required to be 1 pm. Therefore it is difficultto measure a hu man skin surface directly and accurately dueto the movements of a human body during the measurement.In our study a measuring object is a negative replica of skinsurface which is m ade of silicone rubber.Fig.1 shows the constnicti of our tluee-dimension almeasuring system for skin suiface csystem consists of a laser measurisliding table, and a personal computer.The laser measuring instrument is a kind of range find er andit consists of a measuring probe and a control unit. Accordingto the command from the control unit, laser beam is emittedfrom the measuring probe and reflects on the surface of ameasuring object. Reflected laser beam is focused on thePSD (Position Sensitive Device) photodetector inside themeasuring probe and the PSD photodetector detects the

CONTOUR

0-7803-3280-6/96/ 5.00 @ 1996IEEE - 450


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laser measuringinstrument

for X-Y sliding tableConstruction of three-dimensional optical measuring system for skin su rface contour

Resolution b m lLaser beam diameter [pm]Working distance [Output power rmw l

Fig. 1

0.140120.2

position of the laser beam on the PSD photodetector. Usingthis position data of the laser beam, the control unitcalculates the distance between the PSD photodetector andthe surface of the measuring object based on the triangulationmethod. Therefore, the laser measuring instrument allows usto measure the distance between the measuring instrumentand a certain point on the surface of the replica where thelaser beam reflects. Tab le.1 shows the specifications of thelaser measuring instru men t. The resolution of the m easuringinstrument is 0.1 pm and the diameter of the laser beam isabout 40 pm.When we carry out a three-dimensional measurement of askin surface contour, the negative replica of a skin surface isfixed to the X-Y sliding table. The three-dimensional surfacecontour of the negative replica is measured With the lasermeasuring instrument by scanning the surface of the replicatwo-dim ensionally with the X-Y sliding table. Positioningaccuracy of the X-Y sliding table is 1 pm Measured data ofthe skin surface contour are transferred to the personalcomputer and the skin surface contour is displayed onthe CRT. The X-Y sliding table and the laser measuringinstrument are controlled by th e personal computer throughYO port or RS-232C interface respectively.

Table.1 Specifications of laser measuringinstrumentMeasuring range [ I 0.4

3. THREE-DIMENSIONAL MEASUREMENTS OFSKIN SURFACE CONTOUR

3.1 MethodThe measuring pait of the body is the back of the handbecause our preliminary experiments showed that the s k 5surface contour of the back of the hand expressed most closerelation to aging. Subjects are male from in his 20 s to 60 s.The total number of subjects is 72. In this study we selectedthe subjects who we re mainly engaged in desk work indoors.The skin surfaces of the subjects, who have been workingmainly outdoors, have been damaged by ultraviolet. Photo-aging will be much disturbance for us to observe the pureaging of skin. Therefore we selected such subjects as staffofsome universities or research laboratories of some companiesto remove a s much effect of photo-aging as poss ible from theskin surface.The skin surface contour vanes depending on the tensionapplied to the skin. The skin surface contour of the back ofthe hand varies depending on the bending angles of a wristand fingers and the experimental condition has to be keptconstant. Therefore, when a negative replica of the back ofthe hand is taken from the subjects, the subjects are requiredto keep their wrist as straight as possible and close their fistlightly with a te nnis ball inside.The measuring range of a skin surface is 5 mm square aroundthe center of the replica and the measuring interval is 20 pinin both X and Y direction. The total number of measuredpoints for one replica is 251 ~2 51= 630 01 .3.2 Result and DiscussionFig.2 shows the skin surface contour of a typical subject ofeach age group from in his 20 s to 60 s. This figure showsthe surfaces of negative replicas. Therefore the ridges andfurrows are inverted. These ridges in this figure correspond

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to the fkows of human skin surface. In each figure, rightside is the finger direction and left side is the wrist direction.As showii in fig.2(a), the skin surface of the male subjectin his 20s showed high and clear longitudinal ridges andalso showed oblique and transverse ridges. The height ofthese ridges was about 100 pm and the interval between twolongitudinal ridges was about mm. We could easilyrecognize that the skin surface of the young subject showed aclear pattern composed of ridges.hi fig.2(b), the skin surface of the male subject in his 30sstill showed longitudinal, oblique, and transverse ridges.However the ridges were lower and more round than those

a) a male subject in his 20s

(b) a male subject in his 30s

of the sub ject in his 20s.In fig.Z(c), the skin surface of the male subject in his 40smainly consisted of longitudinal ridges, but the number ofthe longitudinal ridges decreased compared with the youngsubjects. Transverse and oblique ridges were very low aiidthe skin surface between ridges became smooths shown in fig.2(d), the ridges of the male subject in his

5 s were lower and more round than those of the subjectin his 40s and the skin surface between ridges becamesmoother.s shown in fig.2(e), the skin surface of the m ale subject inhis 60s showed a few of longitudinal ridges. How ever theywere very low and the pattem composed of ridges almostdisappeared, and the total skin surface became very smooth

The skin surface contours of 72 subjects were measuredand the skin surface contours of each age group showedthe similar pattem. However some variations betweenindividuals existed. The skin surfaces of some young subjectsshowed low ridges. H owever their skin surface patteniscomposed of longitudinal, oblique, and transverse ridgesappeared and they were very similar to the pattems of thetypical young subjects above-mentioned. The skin surfacesof some aged subjects showed high a nd wide longitudinal

Fig.2 Skin surface contours of male subjects452


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ridges which seemed to be a kind of wrinkles. Howeversuch high longitudinal ridges were only a few and transverseand oblique ridges almost disappeared. Furthermore theirskin surfaces between longitudinal ridges were very smooth.Therefore the skin surface pattern composed of longitudinal,oblique and transverse ridges almost disappeared, 2nd theirskin surface patterns were very similar to the patterns ofthe typical aged subjects.From these results, we confirmed that the skin surfacepattern composed of ridges changed with age.

4. FOURIER ANALYSIS OF SKIN SURFACECONTOURSIn order to obtain the quantitative parameter of skin aging,we analyzed the skin surface contours by two-dimensionalFourier Transfomi method.4 1 MethodAccording to the formula (1) we calculated the Fouriercoefficients F(m,n by integrating the measured data withinthe measuring range. The Fourier coefficients F( m ,n ) ofthe spatial frequencies from 0 Hz to 25 Hz were obtainedat the spatial frequency interval of 0.1 Hz for the X and Yaxes. The spatial frequency of 1 Hz means a sine wave with aspatial period of 5 mm

4.2 Result and DiscussionFig.3 shows the results of Fourier analysis for 5 typicalsubjects from in his 20s to ~ O S ,which correspond to theskin surface conto urs of the typical sub jects in fig.2.In this figure, high peaks appeared in the low frequency areaaround 0 Hz These high peaks correspond to the lowfrequency components such as the w aviness or the curve ofthe skin surface itself and the inclination of the replica on theX-Y sliding table. The sidelobes of these high peaks alsoappeared especially along the X and Y axes on the spatialfrequency plane. Th erefore the difference between age groupsis not clear.s shown fig.3(a), however, the result of frequency analysisfor the young subject in his 20s showed many low peaksin the high frequency area around from 5 Hz o 20 Hz of bothX and Y axes. These low peaks were considered to show thefrequency components which corresponded to the ridges onthe skin surface.s shown fig.3(e), the result of frequency analysis for theaged subject in his 60s showed that p eaks concentrated inthe low frequency area around 0 Hz and that the height ofpeaks became lower than that of the young subject. The lowpeaks for the young subjects appeared in larger area than theaged subjects, especially in high frequency area of the X andY axes. On the other hand, the high frequency area wt no

=cos2jcY sin2sY- 2 n j Xnr [ H z ]

d x [pm].x [pm] :

21 [pm] :l

S X>Y) IpmI :

spatial frequency of the X axismeasuring interval in the X directionX coordina te of measuring pointmeasuring range in the X directiontotal number of measured p in tsin the X directionmeasu red value of skin surface contour at the position of the coordinates . x , y )

i t [Hz] spatial frequency of the Y axisdy [ p i ] : measuring interval in the Y direction

[pin] : Y coordinate of measuring pointN [ p i ] : measuring range in the Y directionL

( x = k d x ) y=ld v )

: total number of measured pointsin the Y direction

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(a) a male subject in his 20s

(d) a male subject in his 50s

(b) a male sub ject in his 30s

(e) a male subject in his 60s

(c) a male subject in his 40sFig.3 Fourier analysis of skin surface contours

peaks for the aged subjects was larger compared with theyoung subjects. Therefore we confirmed that the result ofFourier analysis changed with age.

5 AGING PARAMETERWe tried to obtain the aging parameter from the results ofFourier analysis which could express the skin agingquantitatively.5 1 MethodThe aging parameter w as obtained from the result of the twodimensional Fourier Transfonn by summing up the Fourier

coeficients within a specified area on the spatial frequencyplane.As shown in fig.4, the tlueshold frequency xo or yo wasdetermined on the spatial frequency plane and the area wasspecified so as to be the area of the frequencies more than hesame threshold frequency X O ~ O )f the X and Y axesIn other words, the aging parameter was calculated bysumming up the all Fourier coefficients in the area of thefrequencies more than the threshold frequency on the spatialfrequency plane.

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Spatial fiequency of X ax i s

25 [Fig.4 Specified area for aging parameter

xo : threshold frequency of X axisyo : threshold frequency of Y axis

The threshold frequency was changed from 0 Hz o 24 Hz atthe frequency interval of 1 Hz and 25 aging param eters werecalculated for 72 male subjects.However, the aging parameter for one threshold frequencycould not be compared directly with othe r aging parametersfor other threshold frequencies because the value of the agingparameter for a large sp ecified area was much larger than theaging parameter for a small specified area. Therefore, theaging paranieter, which was divided by the average value ofthe aging parameter for 72 male subjects, was employedfinally.5.2 Result and DiscussionAmong the 25 aging parameters which were calculated bychanging the threshold frequency at the frequency interval of1 Hz he aging parameter for the threshold fiequency of 12.5Hz showe d the best co rrelation with age.Fig5 shows the value of the aging parameter for 72 malesubjects, which was obtained by summing up the Fouriercoefficients within the specified area of the frequencies morethan the threshold frequency of 12 .5HzAs shown in fig.5, the aging parameter decreased with age.However the aging parameter showed wide scatteringespecially among the young subjects. This scattering may becaused mainly by the low frequency components such asthe waviness or the inclination of the skin surface itself. Asshown in fig.3, the results of Fourier analysis showed highpeaks around 0 Hz which corresponded to the waviness orinclination of skin surface. These low frequency componentsmight cause the sidelobes in the high frequency area andaffect the frequency components which corresponded to thepattern composed of ridges, because we employed Discrete

1 8

Bl[ .2

Mm 0 9

9 0 6d-3

0.320 3 40 50 60 70age

Fig .5 Aging parameterFourier Transform (DFT) method within the fmite interval.In order to obtain the ap propriate aging parameter with lessscattering, therefore, the low frequency components have tobe removed from the skin surface contours by ineans of highpass digital filter.

6. CONCLUSIONThe skin surface contours of the back of the hand for 72male subjects from in his 20s to in his 60s were measured.The results of the measurements showed that the pattenicomposed of ridges on the skin surface changed with ageand that the skin surface contours of aged sub jects becamesmooth.Analyzing the skin surface contours by two-dimensionalFourier Transform, we found that the skin surface contours oiyoung subjects showed much of high spatial frequencycomponents compared with aged subjects.The aging parameter, which was obtained from the result oftwo-dimensional Fourier analysis, showed wide scattering.This wide scattering may be caused by the low frequencycomponents such as the waviness of skin surface itself. Thisscattering will be removed by applying the high pass digitalfilter to the slun surface contours.

7. REFERENCES[l]H. Kumagai, et. al. Physiological and MorphologicalChanges in Facial Skin with Aging (I) J. Soc. CosmetChem. Japan, Vo1.23, No.1, 1989, pp.9-21, (in Japanese)[2] M. Takahashi, et. al. Physiological and MorphologicalChanges in Facial Skin with Aging II) J. Soc. CosmetChem. Japan, Vo1.23, No.1, 1989, pp.22-30, (in Japanese)

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quantification of skin ageing by 3d measurement

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