Device for evaluating the creasing of the skin in vivo

A device for evaluating the creasing of the skin in vivo. A zone of the skin to be examined is creased. The zone of the creased skin is scanned with an incident luminous beam which is emitted by a light source. The light reflected by the creased skin is detected. The detected light is converted into an electrical signal. At least one parameter representing the profile of the creased skin is extracted from the electrical signal. This device makes it possible to evaluate the mechanical properties of the dermis, such as its elasticity and firmness and the aging of the skin, as well as to evaluate the effectiveness of products intended to counteract such aging.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a device and a method for evaluating the 
deformation of the surface of the skin, in particular of the skin in vivo. 
More particularly, the invention relates to a device for the profilometry 
of the human skin, aiming at evaluating the mechanical properties of the 
dermis, such as its elasticity and its firmness, or the state of the 
ageing of the skin, by measuring in a simple and fast manner the depth of 
the creases induced by deformation. This device is, moreover, suitable for 
evaluating in series the effectiveness of new basic materials and 
formulations for counteracting the ageing of the skin which are developed 
in cosmetic or dermo-pharmaceutical laboratories. Thanks to this new 
device tests of the ageing of the skin can also be performed at the 
dermatologist or institutes for cosmetic care, without any need for 
relying on long and complicated procedures. 
2. Discussion of the Background 
From the Article of M. Assoul et al. "Three dimensional measurement of skin 
surface topography by triangulation with new laser profilometer" which 
appeared in the J. of Med. Eng. and Tech., 1994, 18, 11-21, a device is 
known for evaluating the state of the surface of the skin in vitro, using 
resin replicas reproduced on the basis of a skin specimen. These replicas 
are examined by means of an optoelectronic device operating according to 
the triangulation method. The prior art device for thus evaluating the 
state of the skin surface on the basis of resin replicas allows accurate 
results to be obtained but it is not suitable, on the one hand, for an 
evaluation in series, in particular in vivo, requiring the preparation and 
evaluation of the replicas by a specialist and, on the other hand, for 
permitting an evaluation in a short time. 
FR-A-2 607 929 describes a system for a one-way mechanical deformation of 
the human skin, but does not mention the optical processing of the results 
of this deformation in any way. Moreover, this document is not explicit as 
regards the type of deformation applied to the skin. Furthermore, this 
system does not make it possible to adapt an optoelectronic device of the 
above mentioned kind in a simple manner. 
SUMMARY OF THE INVENTION 
The object of the present invention is to improve this known device and to 
adapt it to the evaluation, in series, of deformations of the skin 
produced in a number of individuals; the cost of such a device is to be 
advantageous. The aim of the invention is, in particular, the fast 
evaluation of the relief of the surface of the skin after a deformation 
induced in vivo; it can be used by unqualified staff in cosmetic 
institutes, medical analytical laboratories or hospitals. In particular, 
the aim of the invention is to obtain the result of this evaluation in a 
virtually instantaneous manner. 
Thus, the first aspect of the present invention is a device for evaluating 
in vivo the creasing of the skin, in particular of the human skin, 
comprising: 
a) movable means for creasing a zone of the skin to be examined, parallel 
to its surface; 
b) movable means for scanning the zone of the creased skin with an incident 
light beam emitted by a light source; 
c) means for detecting the light diffusely reflected by the creased skin; 
d) means for converting the detected light into an electrical signal; and 
e) means for extracting from the electrical signal at least one parameter 
representing the profile of the creased skin. 
The means for detecting the reflected light comprise one or advantageously 
several position detectors. 
Advantageously, the detection of the light reflected by the illuminated 
creased skin is effected either (i) according to the triangulation method 
(see the article by the above mentioned M. Assoul together with Lee C S, 
Kim S W, Yim D Y, "An in process measurement technique using the laser for 
non-contact monitoring of roughness surface and form accuracy of ground 
surfaces". Annals CIRP 1987: 36: 332-339), or (ii) according to the 
focusing method. 
The triangulation method lies in passing a light beam onto a surface to be 
examined at a given angle of incidence, for instance 45.degree.. The 
position of the transmitted light beam is registered by a position 
detector. It is also possible to pass an incident light beam at an angle 
of substantially 0.degree., and to register the reflected light by two 
position detectors disposed at 45.degree. from the axis of the incident 
light in a plane which contains the axis of the incident beam. By way of 
simplification, it is preferable to use a single detector. 
According to an alternative, a so-called focusing method is used. With this 
focusing method a lens for focusing the incident light beam is displaced 
relative to the surface to be examined, so as to be always focused onto 
the surface to be investigated, and one registers the light beam reflected 
by a detector disposed symmetrically to the incident beam relative to the 
normal of the surface to be investigated. 
Advantageously, the parameter of the profile of the skin is chosen from the 
following parameters: R.sub.t, R.sub.a, S.sub.m, R and AR, etc . . . , 
R.sub.t being the maximum height of a crease, R.sub.a being the arithmetic 
mean of all the points of the profile, evaluated relative to the median 
line of the creases, S.sub.m being the mean value of the horizontal 
interspacing between the creases evaluated at the level of the median line 
of the profile, R being the mean depth of the whole set of creases and AR 
being the mean interspacing between the creases. 
Advantageously, the means for creasing the skin comprise two plates 
situated at a given interspacing d.sub.o from each other, and means for 
moving these plates towards each other by reducing the interspacing 
d.sub.o, so that the zone of the skin is subject to creasing over a 
reduced zone d.sub.1, the movable means for scanning the zone of the 
creased skin being displaced parallel to the surface of the skin, in the 
direction of the crease. 
To ensure a good adhesion of the plates on the zone of skin to be examined, 
the side of these plates in contact with the skin may be covered by an 
adhesive, to fix them momentarily on either side of said zone of the 
creased skin. Tests effected by the Applicant have shown that good results 
can be obtained by sticking these plates to the forearm of the person to 
be examined, for example, by means of a double-sided adhesive tape. 
Advantageously, the creasing of the zone of the skin to be examined is 
effected in such a way that d.sub.o -d.sub.1 represents approximately 2% 
to 50% of d.sub.o. The best results were obtained by the Applicant with a 
value of d.sub.0 -d.sub.1 of approximately 5 to 20% of d.sub.o, and more 
particularly of 10%. 
Advantageously, the bringing together of the plates can be controlled by a 
first electric motor connected to a shaft provided, for example, with a 
first portion comprising a right-hand thread, and a second portion 
comprising a left-hand thread. These portions of the motor shaft each 
cooperate with a plate carrier element comprising an internal thread 
complementary to the thread of the motor shaft. Thus by rotating the motor 
shaft, it is possible to cause the distance between the two plates to vary 
automatically, and to obtain the desired creasing of the skin by bringing 
the plates towards each other. 
The plate carriers, as well as the motor, may be mounted on a frame. 
Advantageously, this frame carries an optoelectronic system, movable in 
translation along the direction of the creasing of the skin. This 
translation may be automatically ensured by a second electric motor 
equipped with an adequate drive mechanism. The optoelectronic system 
comprises means for detecting the light reflected by the illuminated 
creased skin, the detection means being formed, for example, by at least 
one position detector. Moreover, the optoelectronic system comprises the 
light source constituting the means for illuminating the zone of the 
creased skin, this light source emitting the incident light beam. 
More precisely the light source, as well as the means for detecting the 
reflected light, are mounted in a fixed position with respect to each 
other and are movable relative to the zone of the skin to be examined. By 
this arrangement, the means for detecting the reflected light can 
simultaneously execute the same translational movement as the light 
source. 
With a view to simplifying the measurements of the parameters and to obtain 
them with precision, the light source is mounted on the support in such a 
way that the angle of incidence of the light beam on the skin is 
approximately 0.degree., the detector for registering the reflected light 
being disposed on an axis forming an angle of reflection of approximately 
45.degree. relative to the incident light beam. 
Preferably, the light source is a source of a laser beam, but any other 
light source capable of emitting a light beam, monochromatic or 
non-monochromatic, could be used. More particularly, the source of the 
laser beam is a laser diode whose incident light beam has a wave length 
comprised, for example, in the range extending from 400 nm to 1100 nm, and 
preferably comprised between 630 and 788 nm. 
Moreover, to obtain an optimum resolution of the parameters to be measured, 
this light beam may be focused on the skin by a first (lens-type) focusing 
system disposed between the light source and the zone of the skin to be 
examined. 
The means for registering the reflected light are constituted by one or 
several position detectors (position sensing detectors--PSD) 
advantageously two in number, converting the collected light into an 
electrical signal. With a view to obtaining a higher measurement accuracy, 
it is advantageous to use several detectors. This kind of detector is 
capable of registering the intensity, as well as the position of a 
reflected light beam incident on its surface. 
Advantageously, a second focusing system is disposed between the skin zone 
and the position detector, which focusing system recovers, then focuses 
the light reflected by the skin before the detection. The electrical 
signal provided by the detector and corresponding to the light diffused on 
the surface of the detector, is substantially transmitted to a data 
processing system where it is digitized. This processing system is, 
moreover, programmed to extract at least one of the above mentioned 
parameters R.sub.t, R.sub.A, S.sub.m, R and AR . . . of the electrical 
signal. Means such as a screen or a printer may be provided for displaying 
the extracted parameters. 
A second aspect of the invention is constituted by a method for evaluating 
the induced relief of the deformation of the surface of the skin in vivo, 
comprising the steps of: 
a) obtaining, in a zone of the skin to be examined, a creasing parallel to 
its surface by movable means; 
b) scanning the zone of the creased skin with an incident light beam 
transmitted by a light source; 
c) detecting the light reflected by the creased skin; 
d) converting the detected light into electric signals; and 
e) extracting from the electrical signals at least one of the parameters 
representing the profile of the creased skin. 
By way of example, the parameter is chosen from the following parameters: 
R.sub.t, R.sub.a, S.sub.m, R and AR . . . , R.sub.t being the maximum 
height of a crease, R.sub.a being the arithmetic mean of all the points of 
the profile, evaluated relative to the median line of the creases, S.sub.m 
being the mean value of the horizontal interspacing between the creases, 
evaluated at the level of the median line of the profile, R being the mean 
depth of the whole set of creases, and AR being the mean interspacing 
between the creases. 
This method is executed by means of the device which has been described 
above. 
Thanks to the device and method of the invention, it is possible to 
undertake in series the evaluation in vivo of the creasing of the surface 
of the skin of an individual, or the action of a product on it. This 
device and method have the advantage of not requiring the employment of a 
specialist, and can provide results virtually instantaneously at moderate 
cost. Moreover, the same skin zone can be scanned several times for 
comparative studies, for example, before and after the application of a 
treatment product.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In this FIGURE, Z designates a zone of the skin, for example the forearm, 
the creasing of which skin is intended to be examined. On the skin is 
positioned a frame S comprising a shaft 5 disposed parallel to the surface 
of the skin and movable in rotation. For this purpose, an electric motor 
M.sub.2 is provided to cause the shaft 5 to rotate. The shaft 5 consists 
of first and second portions 5a and 5b, the first portion 5a being 
provided with a left-hand thread and the second portion 5b being provided 
with a right-hand thread. The portions 5a and 5b engage with internal 
thread portions 2a and 3a respectively, cut in a plate-carrier element 2b, 
3b. The plate-carrier elements respectively support a plate 2, 3 of 
rectangular shape and having a substantially flat face, intended to come 
into contact with the skin and forming the means (E) for producing the 
creasing. 
Advantageously, the flat side of the plates has an adhesive layer 4, for 
example, a double-sided adhesive film. Thanks to this arrangement, the 
zone Z of the skin to be examined can be immobilized relative to the frame 
S. The initial interspacing d.sub.o between the plates 2, 3 is, for 
example, 48 mm. By causing the shaft 5 to rotate by means of the motor 
M.sub.2, these plates are brought towards each other until a distance 
d.sub.1 &lt;d.sub.o, for example 41 mm, is obtained. This bringing together 
then produces a pinching of the skin of approximately 15%, so that a 
creasing thereof is produced, forming creases P orientated perpendicularly 
to the shaft 5. Means (D) for scanning the skin, and means (PSD) for 
detecting the reflected light are mounted on the frame (S). The frame also 
carries means (E) for producing the creasing, as well as the light source 
(D). 
The frame S has, moreover, an optoelectronic system 0 mounted for 
translational movement along a shaft A relative to the frame, the shaft A 
being parallel to the shaft 5. An electric motor M.sub.1 is provided for 
controlling the translational movement. The optoelectronic system 
comprises, moreover, a light source, here a laser diode D, capable of 
emitting a laser beam L of a wave length of 630 to 788 nm. This laser beam 
L incident on the zone of the skin to be examined forms with its surface 
an angle .alpha. of approximately 0.degree.. To obtain a better 
resolution, a focusing system F.sub.1 is provided between the diode D and 
the skin zone Z to focus the beam L on the zone Z. The incident beam L is 
absorbed and reflected by the skin. To allow the quantity of light 
diffused in the form of a beam L.sub.1 to be collected, a PSD sensor 
(position sensing detector) is disposed in an axis passing through this 
beam and forming an angle .beta. of approximately 45.degree. with the axis 
of the incident light L. Between the skin zone Z and the detector PSD the 
beam L.sub.1 passes through a second focusing system F.sub.2, focusing 
this beam on the surface of the detector. The detector PSD is fixedly 
mounted relative to the laser diode D. 
Alternatively a fixed source of radiation is used, the scanning of the zone 
to be examined being obtained by directing the light beam onto a rotating 
mirror of a polygonal type with several reflecting facets. 
To be able to measure the surface profile of the creased skin zone Z to be 
examined, the optoelectronic system O is displaced along the axis A by the 
distance d.sub.1. During this translational movement, the beam L scans the 
skin zone Z between the two plates. At the same time, the sensor PSD 
registers on the one hand the intensity of the beam L.sub.1 and on the 
other hand the position whereat it arrives on the detector. In point of 
fact, according to the depth of a crease or a wrinkle P, the beam L.sub.1 
coming from a zone Z situated at the top of a plate is incident on a 
portion of the detector PSD different from that reached by the rays coming 
from the bottom of a crease. 
The beams incident on the detector PSD are converted into electrical 
signals which are transmitted to a data processing system T. This 
processing system T is programmed according to a mathematical calculation, 
for example, of the type taught by the above mentioned document of M. 
Assoul et al., to extract one, or several of the characteristic parameters 
of the profile of the creased skin, such as the parameters R.sub.t, 
R.sub.a, S.sub.m, R and AR, R.sub.t being the maximum height of a crease, 
R.sub.a being the arithmetic mean of all the points of the profile 
evaluated relative to the median line of the creases, S.sub.m being the 
mean value of the horizontal interspacing between the creases evaluated at 
the level of the median line of the profile, R being the mean depth of the 
whole set of creases, and AR being the mean interspacing between the 
creases. A screen V is provided to display these parameters. 
The device of the invention (apart from the processing system T and apart 
from the screen V) forms a small portable unit, connected to the processor 
system by a connecting cable. Because of this, its manipulation is easy 
during the measurements, both for the individual to be examined and for 
the operator who undertakes the measurements.