Light-based measurement system and a method of collagen denaturation measurement and a skin treatment system

Abstract

The measurement system 110 comprises a light source 120 configured and arranged for emitting a light beam via a polarization modulator 130 to a target position inside the skin 160, wherein the polarization modulator 130 is configured and arranged to simultaneously provide, in use, a first and a second region in a cross-section of the light beam in the target position, the first and the second region being distinct and having a corresponding first and second direction of polarization, the first and the second polarization direction being different from each other, and the measurement system also comprises a detection unit 150 to simultaneously detect a first and a second intensity of reflected light 145, the first intensity corresponding to light reflected from the first region of the light beam in the target position 160, and the second intensity corresponding to light reflected from the second region of the light beam in the target position 160, and the measurement system further comprises a processor being coupled to the detection unit 150 for determining a difference between the first and the second intensity.

Claims

1. A measurement system for light-based measurement of collagen denaturation inside skin, the measurement system comprising: a light source configured and arranged for emitting a light beam, a polarization modulator configured and arranged to receive, in use, the light beam emitted by the light source and to spatially modulate a polarization direction of the light beam emitted by the light source, thereby generating a spatially modulated light beam, the measurement system being further configured and arranged to direct the spatially modulated light beam to a target position inside the skin, wherein the spatially modulated light beam has a spatially modulated polarization direction in a cross-section of the light beam extending perpendicularly to a propagation direction of the light beam, the polarization modulator being configured and arranged to simultaneously provide, in use, at least a first and a second direction of polarization in said cross-section of the spatially modulated light beam in, respectively, at least a first and a second region of the target position, the first and second regions being distinct and the first and second directions of polarization being different from each other, wherein the polarization directions of the light in the first and second regions in the target position are distinct and predetermined, the measurement system further comprising: a detection unit configured and arranged to simultaneously detect a first and a second intensity of reflected light, the first intensity corresponding to an intensity of light reflected from the first region of the target position, and the second intensity corresponding to an intensity of light reflected from the second region of the target position; and a processor which is coupled to the detection unit and which is configured and arranged to determine a difference between the first and the second intensity, obtained from the first and second regions, respectively.

2. The measurement system according to claim 1, wherein the processor is further configured to determine a degree of collagen denaturation using the difference between the first and the second intensity.

3. The measurement system according to claim 1, wherein the light beam emitted by the light source is linearly polarized.

4. The measurement system according to claim 1, wherein the first and the second direction of polarization each comprise a linear polarization, and an angular difference between the first and the second direction of polarization is approximately equal to 45 degrees.

5. The measurement system according to claim 1, wherein the measurement system further comprises an optical element for focusing the spatially modulated light beam into the target position inside the skin.

6. The measurement system according to claim 1, wherein the first and the second intensity detected by the detection unit correspond to an intensity of a second harmonic generated light (SHG) component reflected from, respectively, the first and the second region of the target position.

7. The measurement system according to claim 6, wherein the detection unit comprises a harmonic separator for separating the reflected second harmonic generated light (SHG) component from the light beam emitted by the light source.

8. The measurement system according to claim 1, wherein a wavelength of the light beam emitted by the light source is in a range from visible light to infrared light.

9. A skin treatment system for denaturation of collagen, wherein the skin treatment system comprises the measurement system according to claim 1.

10. The skin treatment system according to claim 9, wherein the measurement system is configured for measuring the difference between the first and the second intensity before and after a denaturation treatment by the skin treatment system, or for measuring the difference between the first and the second intensity during the denaturation treatment by the skin treatment system to thereby monitor efficacy or progress of the denaturation treatment.

11. A method of collagen denaturation measurement inside skin, the method comprising: providing a light source; configuring and arranging the light source to emit a light beam; providing a polarization modulator; configuring and arranging the polarization modulator to receive the light beam emitted by the light source and to spatially modulate a polarization direction of the light beam emitted by the light source, thereby generating a spatially modulated light beam; further configuring and arranging the measurement system to direct the spatially modulated light beam to a target position inside the skin; providing a detection unit; and providing a processor, coupled to the detection unit; wherein the spatially modulated light beam has a spatially modulated polarization direction in a cross-section of the light beam extending perpendicularly to a propagation direction of the light beam; wherein the polarization directions of the light in the first and second regions in the target position are distinct and predetermined, and in that the method further comprises: configuring and arranging the polarization modulator to simultaneously provide, in use, at least a first and a second direction of polarization in said cross-section of the spatially modulated light beam in, respectively, at least a first and a second region of the target position, the first and second regions being distinct and the first and second directions of polarization being different from each other; configuring and arranging the detection unit to simultaneously detect a first and a second intensity of reflected light, the first intensity corresponding to an intensity of light reflected from the first region of the target position, and the second intensity corresponding to an intensity of light reflected from the second region of the target position; and configuring and arranging the processor to determine a difference between the first and the second intensity obtained from the first and second regions, respectively.

12. The method of claim 11, wherein the method further comprises: further configuring the processor to determine a degree of collagen denaturation using the difference between the first and the second intensity.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 schematically shows a measurement system according to the invention,

(3) FIG. 2 shows a graph indicating the variation in difference between the intensities of light reflected by different regions of the target position during thermal denaturation of collagen tissue present in the target position, and

(4) FIGS. 3A to 3C schematically depict examples of polarization modulators generating spatially modulated linear polarization.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 schematically shows a skin measurement system 110 according to the invention. The measurement system 110 is configured and arranged for performing light-based measurement of collagen denaturation inside the skin 160. The measurement system 110 comprises a light source 120 for emitting light via a polarization modulator 130 to a target position inside the skin 160. The light source 120 is preferably a monochromatic source, such as laser or laser diode. A light source 120 with a narrow wavelength range may also be used.

(6) The polarization modulator 130 is configured and arranged to receive, in use, the light beam emitted by the light source 120, and to spatially modulate a polarization direction of the light beam emitted by the light source, thereby generating a spatially modulated light beam having a spatially modulated polarization direction in a cross-section of the light beam extending perpendicularly to a propagation direction of the light beam. Thus, the polarization modulator 130 provides, within the incident light beam 140, two or more areas of different polarization directions in said cross-section of the light beam, which are incident on an outer layer of skin during use.

(7) The light source 120 is configured and arranged such that the light emitted may penetrate through the outer layer of skin to reach the target position inside the skin.

(8) The polarization modulator 130 is configured and arranged to simultaneously provide, in use, at least a first and a second direction of polarization in said cross-section of the spatially modulated light beam in, respectively, at least a first and a second region of the target position. Thus, the polarization modulator 130 is configured and arranged to simultaneously provide, in use, two or more distinct regions in the cross-section of the light beam in the target position, in which distinct regions the polarization of the light has significantly different directions or orientations. The regions are distinctin other words, they may be adjacent, separate or they may even partially coincide, on the proviso that the measurement system can measure an intensity of the light reflected by each distinct region such that a difference in the intensity may be distinguished.

(9) During use, light is reflected from the target position. The measurement system 110 further comprises a detection unit 150 for detecting a first and second intensity of reflected light 145, the first intensity corresponding to light reflected from the first region of the target position 160, and the second intensity corresponding to light reflected from the second region of the target position 160. The first and second intensity represent the reflection of the incident light beam 140 by, respectively, the first and second regions of the target position.

(10) In the measurement system 110, a processor is coupled to the detection unit 150, and configured and arranged to simultaneously determine a difference in intensity between the first and second intensities.

(11) Additional optical elements known in the art may also be provided to further guide, and modify, the incident light beam 140 to the target position inside the skin 160, and to further guide and modify the reflected light beam 145 from the target position.

(12) During use, the measurement system 110 is brought into proximity of an outer layer of skin 160. The system 110 illuminates the target position with two or more regions of polarized lightthese regions are distinct and have a respective first and second direction of polarization, the polarization directions of the first and second regions being substantially different from each other. The polarization directions and the disposition of the regions are determined mainly by the configuration and arrangement of the polarization modulator 130.

(13) The invention is based on the insight that known techniques of collagen detection, such as disclosed in WO2013128330, may be simplified. It is well known that collagen is a birefringent tissue constituent, and the birefringence (n) is estimated to be 2.810-3-3.010-3. When linearly polarized light interacts with birefringent collagen structures, the intensity of backscattered light detected depends on the relative orientation of the incident polarization with respect to the collagen fibers.

(14) Known techniques of collagen detection require polarization rotators to better control the polarization of the light incident on or reflected from the collagen fibers to improve collagen detection. In addition, measurements must be repeated with the different polarization settings.

(15) In the invention, the target position is illuminated with at least two distinct regions of polarized light having polarization directions which are substantially different from each other. The intensity of the reflected light from these two regions is measured simultaneously, and a difference between the intensities of the light reflected from the two regions indicates the presence of collagen in the target position.

(16) The skilled person may use any spatially-varying polarization modulator 130 known in the art to simultaneously provide, in use, at least a first and a second direction of polarization in a cross-section of the spatially modulated light beam in suitable regions at the target position. In this context, the expression modulator may be understood as one or more optical components which work together to selectively transmit the required polarizations, or to modify the light characteristics to obtain the required polarizations, or some combination of filtering and modifying.

(17) A spatially-varying or spatially-modulated polarized light beam may be understood as a light beam having a cross-section in which different positions in the cross-section have different polarization directions.

(18) FIG. 3A schematically depicts an example of a polarization modulator 130. It has two segments 300, 350the first segment provides linear polarization direction 310 in the left-to-right direction (as schematically depicted) and the second segment provides linear polarization direction 360 in the up-to-down direction (as schematically depicted). To use the modulator of FIG. 3A, the measurement system 110 is configured and arranged such that the polarization modulator 130 provides areas in a beam cross-section with a predetermined or controlled polarization direction.

(19) For example, the modulator 130 of FIG. 3A may be transmissive and placed such that it intersects the light beam between the light source 130 and the target position inside the skin 160. Each segment 300, 350 provides distinct areas in a beam cross-section with a substantially different polarization direction. In this example, the areas are adjacent. For the invention, it is the difference in polarization direction or orientation that mainly determines the sensitivity and accuracy of the collagen denaturation measurement. In this case, the areas in a beam cross-section have polarization directions which differ by 90 degrees. The measurement system 110 will correspondingly provide distinct regions of the target position with polarization directions which differ by 90 degrees. In this example, the regions are also adjacent. The polarization direction of the incident light in a first region will correspond to the direction provided by the first segment 300, and the polarization direction of the incident light in a second region will correspond to the direction provided by the second segment 350.

(20) Such a polarization modulator 130 may be manufactured by cutting known transmissive polarization filters into segments of suitable size and bringing these segments in proximity of the required relative polarization orientation. Suitable selection of waveplates and SVR's (Spatially Varying Retarders)either individually or in combinationmay also be used.

(21) As the skilled person will be aware, the same distinct regions of different polarization in the target area may be achieved by using a reflective polarization modulator 130, such as an LCOS (Liquid Crystal On Silicon) element. In some embodiments, a combination of transmissive and reflective optical elements may also be advantageous.

(22) Similarly, FIG. 3B depicts schematically a further polarization modulator which may be provided using transmissive and/or reflective optical components. It comprises two distinct and adjacent segments 400, 450. The first segment 400 provides an area in a beam cross-section with a linear polarization direction 410 in the top left-to-bottom right direction (as schematically depicted) and the second segment provides linear polarization direction 340 in the top right-to-bottom left direction (as schematically depicted). As in FIG. 3A, the areas in a beam cross-section have polarization directions which differ by 90 degrees, and the corresponding regions in the target area in the skin will also comprise light with polarization directions which differ by 90 degrees.

(23) The measurement system 110 detects a first intensity associated with light reflected 145 from the first region and simultaneously detects a second intensity associated with light from the second region. The presence of collagen will result in a difference in intensity between the first and second intensity measurements. The skilled person may use trial and error to determine the most appropriate position in each region to measure the intensity.

(24) The skilled person may also use trial and error to determine the most appropriate configuration for the polarization modulator. For example, a further modulator 130 is depicted in FIG. 3C. It comprises four distinct and adjacent segments 500, 525, 550, 575 arranged symmetrically as four equal segments of the same square. The segments are numbered counter-clockwise. The first segment 500 provides an area in a beam cross-section with a linear polarization direction in the top left-to-bottom right direction (as schematically depicted), the second segment 525 provides an area in a beam cross-section with a linear polarization direction in the top-to-bottom direction (as schematically depicted), the third segment 550 provides a linear polarization direction in the top right-to-bottom left direction (as schematically depicted), and the fourth segment 575 provides an area in a beam cross-section with a linear polarization direction in the left-to-right direction (as schematically depicted).

(25) When using the modulator of FIG. 3C, the areas in a beam cross-section diagonally opposite to each other have polarization directions which differ by 90 degreesthe corresponding regions in the target area in the skin will also comprise light with polarization directions which differ by 90 degrees. Similarly, the areas in a beam cross-section facing each other have polarization directions which differ by 45 degreesthe corresponding regions in the target area in the skin will also comprise light with polarization directions which differ by 45 degrees.

(26) The most appropriate position in each region to measure the intensity may be routinely determined by the skilled person depending, inter alia, on the position on the body, the dimensions of the incident light beam on the skin and the expected distribution of the collagen. Measurements close to the intersection of the four regions may be more advantageous because it is more likely that the first and second intensity measurements will coincide with the same collagen deposit.

(27) The regions used for the first and second intensity may be predetermined and/or controlled to provide the most accurate measurement depending on, inter alia, the subject of the treatment, the position on the body, the moment in a treatment regime, the pigmentation of the skin, the type of treatment radiation.

(28) It may also be advantageous to simultaneously measure 4 intensities, each corresponding to a measurement in a different region of the target region. The presence of collagen may then be detected by determining the difference between each intensity measurement and an average of the four measurementsin the case of a lack of collagen (or advanced denaturation) the intensity measurements will be substantially the same. If collagen is present, one or more of the intensity measurements will differ substantially from an average of the four measurements.

(29) Based on initial measurements, at least 8 segments may be advantageous. Similarly, 2 to 8 simultaneous intensity measurements may be carried out, each one corresponding to an intensity measurement in a different region of the target area.

(30) The skilled person will also realize that multiple measurements may be performed in each of the regions where measurements are to be carried out. For example, 4 simultaneous measurements may be carried out in each of the regions corresponding to the segments when using the modulators of FIGS. 3A and 3B. Again, this will yield 8 intensity measurements, but the processor may be programmed, for example, to give a higher weighting to any difference between the two intensity measurement groups and a lower weighting to differences between measurements performed in the same region. Multiple intensity measurements may be performed using a detector array, such as a CCD array.

(31) The detection unit 150 may, for example, comprise at least two photodiodes or any other detector able to detect an intensity variation in the reflected light. A single path is depicted in FIG. 1 for the reflected light beam 145, but two separate paths may be provided when two separate detectors are utilized.

(32) The detection unit 150 may also be a detection array, such as a CCD array. The detection unit 150 is connected to a processor and the processor uses the signals from the detection unit 150 to determine the intensity differences between the different regions in the target region. The interaction of polarization incident light beam 140 with birefringent collagen fibers depends on the relative orientation of the polarization direction of the incident polarization light beam 140 with respect to the collagen fiber axis.

(33) FIG. 2 depicts a graph of the predicted intensity difference along the vertical axis 210 against time along the horizontal axis 220. The intensity difference 210 results from the use of two intensity measurements in regions with polarization directions differing by approximately 45 degrees. Conditions and settings are assumed to be close to optimal, allowing the maximum intensity difference to be obtained between the two regions of measurement.

(34) Before treatment 225, the difference in intensity is substantial (for example, 70-100% of the highest intensity measurement), and substantially constant due to the presence of sufficient collagen. During thermal denaturation of collagen, the birefringence property of collagen is lost, depending on the increase in temperature and this is depicted in FIG. 2 by a steadily decreasing difference in intensity during the treatment 227. Typically, the collagen is heated from approximately 40 degrees C. to at least 65 degrees C., resulting in a loss of birefringence by a factor of 10. At the end of the treatment, the difference is, for example 0-10%.

(35) Collagen denaturation and collagen fiber shrinkage under thermal treatment is described, for example, in Skin responses to fractional photothermolysis, Laubach, Tannous et al, Lasers Surg. Med., 38: 142-149 (2006). The polarization dependence of the signal on collagen shrinkage is disclosed in, for example, Collagen denaturation can be quantified in burned human skin using polarization-sensitive optical coherence tomography, Pierce, Sheridan et al, Burns, 30(6), (2004).

(36) The measurement system 110 may further comprise a harmonic separator such as a dichroic beam splitter together with a cut-off filter. This allows measurement of the Second Harmonic Generated SHG light component of the reflected light 145. This may improve the signal to noise ratio in the intensity measurements.

(37) The measurement system 110 may also be comprised in a skin treatment system comprising a treatment source. Such a treatment source may, for example, be an RF radiation source or, for example, a laser source for providing treatment light, typically a pulsed laser beam. The treatment source may, for example, be a Nd:YAG laser with emission at 1064 nm.

(38) The treatment beam path may be completely separate or partially integrated into the beam path of the measurement system. For example, if the treatment source is a laser, the same laser may be used as the light source 120. If the treatment beam is an R.F beam, then the measurement system 110 will be relatively separate from the treatment functions. In such an embodiment, the measurement system 110 may be used as feedback system for measuring an efficacy of the denaturation treatment of collagen fibers by the treatment source. In such a case, the processor may also be connected to the treatment source to control the treatment source, for example, to control the treatment duration or the treatment intensity.

(39) The measurement system 110 may perform real-time measurements continuously during the denaturation treatment, or may perform several measurements during the denaturation treatment which together provide feedback about the denaturation process and the current state of the denaturation treatment.

(40) Additionally or alternatively, the measurement system may be configured and arranged such that the paths of the incident light beam 140 and the reflected light beam 145 partially coincide. This may reduce the dimensions of the measurement system, and allows both the incident light beam 140 and the reflected light beam 145 to the approximately perpendicular to an outer layer of skin.

(41) The invention further relates to a method of collagen denaturation measurement inside skin, the method comprising: providing a light source 120; configuring and arranging the light source 120 to emit a light beam, providing a polarization modulator 130; configuring and arranging the polarization modulator 130 to receive the light beam emitted by the light source 120 and to spatially modulate a polarization direction of the light beam emitted by the light source, thereby generating a spatially modulated light beam; further configuring and arranging the measurement system to direct the spatially modulated light beam to a target position inside the skin; configuring and arranging the polarization modulator to simultaneously provide, in use, at least a first and a second direction of polarization in a cross-section of the spatially modulated light beam in, respectively, at least a first and a second region of the target position, the first and second regions being distinct and the first and second directions of polarization being different from each other, providing a detection unit 150; configuring and arranging the detection unit 150 to simultaneously detect a first and a second intensity of reflected light 145, the first intensity corresponding to an intensity of light reflected from the first region of the target position 160, and the second intensity corresponding to an intensity of light reflected from the second region of the target position 160; and providing a processor, coupled to the detection unit 150; and configuring and arranging the processor to determine a difference between the first and the second intensity.

(42) The measurement system 110 described above is configured and arranged to perform the method according to the invention. The detected difference between the intensities of the light reflected from the distinct regions in the target position may be presented to a user as a reliable indication of the status of the collagen denaturation process.

(43) It may also be advantageous for the user if the method further comprises further configuring the processor to determine a degree of collagen denaturation using the difference between the first and the second intensity. This may be used to provide a clear and accurate indication of the denaturation of the collagen, and the end of the treatment.

(44) Although the invention is particularly suited for collagen measurement, the skilled person will be able to configure the invention for use in detecting other skin birefringent structures, such as tendons, elastins, hair, and monitoring the changes in measurement due to the corresponding treatment, such as photoepilation.

(45) It will be appreciated that the inventionespecially many of the method steps indicated abovealso extends to computer programs, particularly computer programs on or in a carrier, adapted to put the invention into practice. The program may be in the form of a source code, an object code, a code intermediate source and object code such as a partially compiled form, or in any other form suitable for use in the implementation of the method according to the invention.

(46) It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb comprise and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article a or an preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the system claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.