WO2009027898A1

WO2009027898A1 - Method and apparatuses for measuring skin properties

Info

Publication number: WO2009027898A1
Application number: PCT/IB2008/053322
Authority: WO
Inventors: Runze Wu; Natallia Uzunbajakava; Yan Shi; Markus Laubscher; Golo Von Basum; Thomas Vollmer
Original assignee: Koninklijke Philips Electronics N.V.; Philips Intellectual Property & Standards Gmbh
Priority date: 2007-08-24
Filing date: 2008-08-20
Publication date: 2009-03-05

Abstract

To improve the accuracy of detection of the dehydration level, this invention provides an apparatus comprising: a positioning unit, configured to position the apparatus over the piece of skin; a laser sensor, configured to measure the distance between the laser sensor and the piece of skin by utilizing the self-mixing technology; wherein the positioning unit is further configured to generate a negative pressure on the piece of skin so as to raise the surface of the piece of skin, and position the laser sensor at a pre-determined location. By using the provided apparatus, the dehydration level can be measured accurately and earlier, which provides the opportunity for early medical treatment.

Description

METHOD AND APPARATUSES FOR MEASURING SKIN PROPERTIES

Field of the Invention

The present invention relates to the use of optical skin measurements, and more particularly to laser measurements.

Background of the Invention

Human beings and many animals need water to stay alive. Water is essential to many biological and biochemical reactions that take place. However, the water balance of the body may be disturbed due to a variety of reasons such as, for example, insufficient water intake. More generally, dehydration refers to water loss with or without accompanied electrolyte loss, particularly sodium. Water loss of only a few percent of the body weight causes discomfort and impaired body function. As dehydration levels increase, people become fatigued and irritable, with symptoms of dry mouth, less frequent urination and tachycardia.

It is appreciated that early identification of dehydration followed by prompt and adequate water intake can substantially reduce the risk of severe dehydration, and the potentially severe complications thereof.

Commonly, the clinical assessment of the level of hydration is mainly based on physical examination. Symptoms of dehydration include dry mouth and mucous membrane, sunken eyes, orthostatic hypotension, delayed capillary refill, and poor skin turgor. These symptoms are often recognized by physical examination. However, the clinical assessments can be subjective and have a low sensitivity and specificity in general.

Prior art document US patent application US20060239547, discloses a method of using optical skin measurements to determine skin properties, such as surface topography, hydration, elasticity, dermal thickness, and age of the skin. Fig. 1 illustrates an apparatus, disclosed in US20060239547, used for measuring the dehydration level of the kin. The apparatus 100 comprises a collimated light source 110, a lens 120, a vacuum chamber with transparent walls 130, a vacuum pump 140, a liner detector array 150, and a processor 160 for signal conversion and algorithm processing. The collimated light source 110 can be directed parallel to the relaxed skin surface and toward the linear detector array 150 of photodetectors. The tissue 180 bulged up by the vacuum pump 140 then casts a shadow on the detector array 150, allowing the height of the bulge to be determined. This information can be used to examine the deflection of the tissue for a known pressure change and to measure the time required for the tissue to return to its normal un-deflected state after the vacuum is removed.

Summary of the Invention

An object of the present invention is to provide methods and apparatuses to measure skin properties, including dehydration level, especially by using a laser sensor. The apparatus can be small- sized because a laser sensor is used to transmit and receive laser light signals.

In accordance with an example embodiment, there is provided an apparatus for measuring a skin property of a piece of skin. The apparatus comprises: a positioning unit, configured to position the apparatus over the piece of skin; a laser sensor, configured to measure a distance between the laser sensor and the piece of skin by utilizing the self-mixing technology; wherein the positioning unit is further configured to generate a negative pressure on the piece of skin so as to raise the surface of the piece of skin, and position the laser sensor at a predetermined location.

Because the laser sensor accomplishes the function of transmitting a laser light signal, and receiving a reflected laser light signal, there is no need to have two separate devices: light source and detector. Thus, the size of the apparatus is reduced.

In another embodiment, the laser sensor comprises a photodiode for measuring the power fluctuation of a mixed laser light signal, wherein the mixed laser light signal is formed by mixing a first laser light signal and a second laser light signal, the first laser light signal being transmitted by the laser sensor toward the piece of skin, and the second laser light signal being formed when the first laser light signal is reflected by the piece of skin and received by the laser sensor.

In accordance with one embodiment, the laser sensor further comprises a processor to calculate the recoil velocity of the piece of skin, based on the change of the power fluctuation of the mixed laser light signal over time. Further, the recoil velocity can be used to determine a skin property, for example, the dehydration level of the piece of skin.

Optionally, a polarizer can be located between the laser sensor and the piece of skin. It is advantageous that the polarization directions of the first laser light signal and the second laser light signal are the same, and interference of diffused laser light reflected by the piece of skin and light from other sources is suppressed. Thus, the measurement accuracy is improved.

Optionally, the apparatus further comprises a force sensor to suppress the influence of a change in negative pressure on the position of the laser sensor. This enables the laser sensor to be positioned at a pre-determined location. Thus, the distance between the laser sensor and the piece of skin can be measured more accurately.

The wavelength of the laser can be in the visible and near-infrared range, i.e., from approximately 400 nm to 2000nm. The wavelength range of 400 - 1100 nm is preferred, since it can be used with a low-cost silicon light detector. The wavelength range of 400-700 nm is preferred due to the availability of laser sensors and a relatively low penetration of light into the skin. Due to the latter, most of the light, detected by the sensor, will originate from the skin surface.

The present invention also discloses a method of measuring skin properties of a piece of skin. The method can be used by the proposed apparatus. Other objects and effects of the present invention will become more apparent from the following description and the appended claims when taken in conjunction with the accompanying drawings, and a more comprehensive understanding of the present invention will be gained.

Brief Description of the Drawings

Fig. 1 illustrates an apparatus, disclosed by US20060239547, for measuring the dehydration level.

Fig. 2 illustrates an exemplary apparatus suited for measuring the dehydration level in accordance with one embodiment of the present invention.

Fig. 3 illustrates a laser sensor comprising a photo-diode.

Fig. 4 illustrates the working principle of a laser sensor.

Fig. 5 illustrates a method of measuring skin properties in accordance with one embodiment of the present invention.

Throughout the above drawings, like reference numerals will be understood to refer to like, similar or corresponding features or functions.

Detailed Description of the Embodiments

Fig. 1 shows that the collimated light source 110 and the linear detector array 150 are disposed oppositely at two sides of the target tissue 180. Thus, the size of the whole apparatus is quite substantial. Another disadvantage , which can be attributed to the existence of transparent walls, is that diffusion and refraction of the collimated light cannot be avoided, which further affects the measurement accuracy of the linear detector array 160.

Fig. 2 illustrates an exemplary apparatus for measuring the dehydration level in accordance with one embodiment of the present invention. The apparatus 200 comprises a positioning unit 210 and a laser sensor 220. The positioning unit 210 can dispose the apparatus 200 over a piece of skin. Due to the known arrangement of the laser sensor 220 in the apparatus 200, the relative location of the laser sensor 220 over the piece of skin is determined. The positioning unit 210 further comprises a vacuum device 212 for generating a negative pressure on the piece of skin. The negative pressure can be generated by sucking air out of the apparatus 200, or by any other known available methods. The purpose of generating a negative pressure is to raise the surface of the piece of skin 280. After that, the negative pressure can be released, and the surface of the piece of skin recoils. The laser sensor 220 is capable of transmitting a first laser light signal towards the piece of skin, and receiving a second laser light signal, which is reflected by the piece of skin. Based on the two laser light signals, the laser sensor 220 can utilize the self-mixing technology to measure the distance between the laser sensor and the piece of skin. By continuously measuring the distance when the piece of skin recoils, which may be the result of releasing the negative pressure, a recoil velocity over time can be obtained. With a known relationship between recoil velocity and dehydration level, the dehydration level can be determined. In a more detailed exemplary embodiment, the laser sensor comprises a photodiode for measuring the power fluctuation of a mixed laser light signal. The mixed laser light signal is formed by mixing the first laser light signal and the reflected second laser light signal. The measurement of the recoil velocity and the determination of the dehydration level can be accomplished by a processor, which is not shown in Fig. 2. The processor can be part of the laser sensor, and also can be an independent device located outside of the laser sensor.

In another embodiment, a polarizer 230 can be added between the laser sensor 220 and the piece of skin. The purpose of the polarizer 230 is to suppress any interference, which may be caused by reflected diffused laser light and other light from other sources. The first laser light signal traverses the polarizer 230 and is polarized in a predefined polarization direction. It is known in the art that when light is reflected or refracted, its polarization direction may be changed. In other words, the reflected laser light may be decomposed into two mutually perpendicular polarized laser lights. With the help of the polarizer 230, the decomposed polarized laser light having the same polarization direction as the polarizer 230 can traverse the polarizer 230 and reach the laser sensor 220, i.e., this decomposed polarized laser light is the second laser light. Another decomposed polarized laser light having a perpendicular polarization direction with respect to the polarizer 230 is blocked by the polarizer 230 and cannot reach the laser sensor 220. Thus, interference from the perpendicular laser light can be suppressed. Due to the same reason, other lights having different polarization directions also can be blocked. The laser sensor 220 can measure the distance more accurately, based on the first laser light signal and the second laser light signal, which have the same polarization direction.

In another embodiment, the apparatus 200 further comprises a force sensor, which is not shown in Fig. 2, to suppress the influence of a change of the negative pressure on the position of the laser sensor. This enables the laser sensor to be positioned at a pre-determined location and a known distance from the skin surface.

The wavelength of the laser can be in the visible and near-infrared range, i.e., from approximately 400 nm to 2000nm. The wavelength range of 400 - 1100 nm is preferable, since it can be used with a low-cost silicon light detector. The wavelength range of 400-700 nm is preferable due to the availability of laser sensors and a relatively low penetration of light into the skin. Due to the latter, most of the light, detected by the sensor, will originate from the skin surface.

An exemplary block diagram of a laser sensor is depicted in Fig. 3. The laser sensor 300 comprises a laser cavity 310 and a photodiode 320. The laser cavity 310 can be used to generate the first laser light signal 330 and receive an incoming laser light signal 340. In the laser cavity 310, the first laser light signal 330 and the incoming laser light signal 340 can be mixed, in a constructive way or deconstructive way. The photodiode 320 can be used to measure the power fluctuation, especially by detection of the power pattern, of the mixed laser light signal. When the incoming laser light signal 340 is formed by part of the first laser light signal 330 when it is reflected by an object 380, the laser sensor can be used to measure the distance between the laser sensor and the object 380. When the object 380 moves, the power pattern of the mixed laser light signal varies, thus the distance change can be measured.

The working principle of the laser sensor 220 can be conceptually illustrated in Fig. 4. Each first laser light signal 410/460 has a phase. When the first laser light signal is transmitted through the distance between the laser sensor 220 and the piece of skin, is reflected by the piece of skin and then reaches the laser sensor 220 as a second laser light signal 420/470, it has changed phase. When the first laser light signal 410/460 and the second laser light signal 420/470 mix together, the amplitude of the mixed laser light signal 430/480 can be varied due to the difference between the two phases of the first and the second laser light signal. The mixed laser light signals 430 and 480 illustrate constructive mixing and deconstructive mixing, respectively. When the piece of skin recoils, the distance varies over time. The phase of the second laser light signal 420/470 varies. Thus, the amplitude of the mixed light signal 430/480 varies over time. Based on prior-art knowledge, by detecting the change of the amplitude of the mixed light, the change of the distance between the laser sensor 220 and the piece of skin can be determined. In other words, the recoil velocity of the piece of skin can be measured. The laser sensor can be a Philips twin-eye laser sensor, which utilizes self-mixing technology. A Philips twin-eye laser sensor can be embedded in an advanced System in Package (SiP), which substantially reduces its size. Therefore the size of the apparatus 200 can be substantially reduced.

Fig. 5 illustrates a method of measuring skin properties by using a laser sensor, which can transmit and receive laser light, and measure the distance, based on the two laser lights. In step S410, an apparatus, e.g., apparatus 200 in Fig. 2, is disposed over a piece of skin. Thus, the location of a laser sensor is determined. In step S420, a negative pressure is exerted on the piece of skin to raise its surface. Optionally, in step S430, the negative pressure is released so as to enable the surface of the piece of skin to recoil back. In step S440, a first laser light signal is transmitted toward the piece of skin, and the second laser light signal is received in step S450. In step S460, a recoil velocity of the piece of skin can be measured based on the first laser light signal and the second laser light signal, more particularly, based on the change of their phases over time. After the recoil velocity is measured, in step S470, skin properties, including dehydration level, can be determined based on the measured recoil velocity.

Optionally, after S440, the first laser light signal and the second laser light signal can be polarized in step S442 and S444 respectively for suppressing interferences.

Laser light has a lot of technical advantages, such as ease of generating light with a specific wavelength, anti-interference, low energy, etc. By using laser light, more accurate measurements can be achieved than with normal lights. Using a single laser sensor capable of transmitting and receiving laser light signals, the size of the apparatus can be substantially reduced.

It should be known by the skilled person in the art that other kinds of laser sensors can be used, for example, a Doppler velocimeter.

The above described embodiments are only illustrative, and not intended to limit the scope of the present invention. Those skilled in the art will understand that the embodiments of the present invention can be modified or replaced without departing from the spirit and scope of the embodiments of the present invention, which will also fall within the protective scope of the claims of the present invention.

Claims

Claims:

1. An apparatus for measuring a skin property of a piece of skin, comprising: a positioning unit (210), configured to position the apparatus over the piece of skin; a laser sensor (220), configured to measure the distance between the laser sensor and the piece of skin by utilizing the self -mixing technology; wherein the positioning unit is further configured to position the laser sensor at a predetermined location and generate a negative pressure on the piece of skin so as to raise the surface of the piece of skin.

2. An apparatus as claimed in Claim 1, wherein the laser sensor comprises a photodiode (320) for measuring the power fluctuation of a mixed laser light signal, wherein the mixed laser light signal is formed by mixing a first laser light signal and a second laser light signal, the first laser signal being transmitted by the laser sensor toward the piece of skin, and the second laser light signal being formed when the first laser light signal is reflected by the piece of skin and received by the laser sensor.

3. An apparatus as claimed in Claim 2, wherein the laser sensor comprises a processor for calculating the recoil velocity of the piece of skin, based on the change of the power fluctuation of the mixed laser light signal over time.

4. An apparatus as claimed in Claim 3, wherein the processor is further configured to measure the skin property by processing data of the measured recoil velocity.

5. An apparatus as claimed in Claim 1, further comprising: a polarizer (230) located between the laser sensor and the piece of skin to suppress the interference of diffused laser light reflected by the piece of skin.

6. An apparatus as claimed in Claim 1, wherein the skin property is the dehydration level of the piece of skin.

7. An apparatus as claimed in Claim 1, wherein the positioning unit is further configured to release the negative pressure after the generation thereof.

8. An apparatus as claimed in Claim 1, further comprising: a force sensor, for positioning, by detecting change of the negative pressure, the laser sensor at the pre-determined position so as to suppress the influence of change of the negative pressure on the position of the laser sensor.

9. An apparatus as claimed in Claim 1, wherein the first laser light has a wavelength in any one of the visible or near- infrared ranges of the spectrum.

10. An apparatus as claimed in Claim 10, wherein the first laser light has a wavelength in the range of 400~700nm.

11. A method of measuring a skin property of a piece of skin, comprising the steps of: a) Disposing a laser sensor over the piece of skin; b) Generating a negative pressure on the piece of skin to raise the surface of the piece of skin; c) Transmitting a first laser light signal to the piece of skin; d) Receiving a second laser light signal reflected by the piece of skin; and e) Measuring the recoil velocity of the piece of skin over time based on the first laser light signal and the second laser light signal by utilizing the self -mixing technology; wherein the second laser light signal is formed when the first laser light signal is reflected by the piece of skin and received by the laser sensor.

12. A method as claimed in Claim 11, wherein, after step b), the method further comprises a step of: f) Releasing the negative pressure so as to enable the piece of skin to recoil.

13. A method as claimed in Claim 11, further comprising the steps of: g) Polarizing the first laser light after step c); and h) Polarizing the second laser light before step d); wherein the polarization direction of the steps g) and h) is the same.

14. A method as claimed in Claim 11, further comprising a step of: i) Detecting the dehydration level of the piece of skin, based on the measured recoil velocity.