EP2385785A1

EP2385785A1 - Device for optically examining the interior of a turbid medium

Info

Publication number: EP2385785A1
Application number: EP09787339A
Authority: EP
Inventors: Wouter H. J. Rensen; Michael C. Van Beek; Rik Harbers
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Demcon Hemics BV
Priority date: 2008-10-03
Filing date: 2009-10-01
Publication date: 2011-11-16
Also published as: WO2010038207A1; CN102238899A

Abstract

A device for optically examining the interior of a turbid medium is provided. The device comprises a light source (3) adapted to emit light for irradiating the turbid medium; a detector unit (4) adapted for detecting light emanating from the turbid medium; and a light guide adapted for guiding light emitted by the light source to the turbid medium. The light guide comprises a support (10; 100) comprising a support surface (20; 120) for supporting the turbid medium to be examined and for coupling the light emitted by the light source (3) through the support surface (20; 120) into the turbid medium. The device is structured such that light from the light source (3) exits through the support surface (20; 120) only at positions at which the support surface is contacted.

Description

Device for optically examining the interior of a turbid medium

FIELD OF INVENTION

The present invention relates to a device for optically examining the interior of a turbid medium.

BACKGROUND OF THE INVENTION

In the context of the present application, the term light is to be understood to mean non-ionizing electromagnetic radiation, in particular with wavelengths in the range between 400 nm and 1400 nm. The term optically examining means examining by means of light. The term body part means a part of a human or animal body. In recent years, several different types of devices for optically examining the interior of turbid media have been developed in which the turbid medium under examination, such as a body part, is illuminated with light from a light source and light emanating from the turbid medium is detected by a detector unit in transmission or reflection geometry. In such devices, the detected light is used to gather information about the interior of the turbid medium. Depending on the type of device for optically examining the interior of a turbid medium, e.g. two-dimensional or three-dimensional images of the interior of the turbid medium can be reconstructed or information about concentrations of different substances inside the turbid medium can be extracted from the detected light.

US 5 415 655 shows a medical device for examining tissue by means of light. The medical device has a flexible light guide having a light energy input end adapted for connecting to a light energy source and a light energy output end. The light energy output end outputs a beam of light energy.

Recently, it has been suggested to use devices for optically examining the interior of turbid media to optically detect disease activity of joint diseases such as rheumatoid arthritis (RA) by illuminating both the joints and intermediate tissue of a body part under examination with light and detecting light emanating from the body part.

The treatment of such joint diseases is staged. Usually, a patient first receives pain killers. These are frequently followed by non- steroid anti- inflammatory drugs (NSAIDs) and disease modifying anti-rheumatic drugs (DMARDs). In many cases, the last stage in treatment with drugs is the use of biological therapies. In particular the last category is expensive and treatment can cost tens of thousands of dollars per year per patient. Additionally, the drugs used in later stages of treatment often cause more severe side effects. With respect to such joint diseases, medical professionals base their decisions on changes in therapy on disease activity which is given by the number and the severity of inflamed joints.

Since rheumatoid arthritis is a progressive disease and early diagnosis and start of treatment can help postponing adverse effects and high costs of treatment, there is a demand for methods and devices for providing satisfactory information about the condition of joints and which assist a medical professional to come to a conclusion with respect to the actual joint condition. Conventionally, rheumatologists use the so-called Disease Activity Score (DAS-28) for diagnosis and treatment monitoring. Since this method is time- consuming, operator-dependent, and has limited sensitivity, there is a demand for suitable devices for detecting disease activity. Use of devices for examining the respective body parts by means of light shows promising results as disease activity monitors. According to a device for optically examining the interior of turbid media known to the applicant which device is specifically adapted for detecting disease activity of joint diseases, a turbid medium formed by a body part containing at least one joint, such as a human hand, is placed on a plate made of a transparent material. For examination, the turbid medium is illuminated with an extended light source positioned below the plate and, in transmission geometry, light is detected by a detector unit situated on the opposite side of the turbid medium with respect to the light source. For example, the detector unit may be formed by a CCD camera. However, in such an arrangement, e.g. in a case in which the turbid medium is a hand which is a typical situation for joint disease activity monitoring, light used for illuminating the turbid medium will also be transmitted from the light source to the detector unit without passing through the turbid medium. For example, the light will be transmitted between the fingers in the case of the turbid medium being formed by a hand. Since such light will not have been attenuated in the turbid medium, the intensity on the detector unit of this part of the light will be high as compared to the other part of the light which has passed through the turbid medium. Thus, the light not having passed through the turbid medium can saturate the detector unit such that, as a result, the relevant light which has passed through the turbid medium can only be detected with less accuracy. SUMMARY OF THE INVENTION

It is an object of the present invention to provide a device for examining the interior of turbid media in which light attenuated by the turbid medium can be detected with higher accuracy and unattenuated light is prevented from saturating the detector unit. This object is achieved by a device for examining the interior of a turbid medium according to claim 1. The device comprises a light source adapted to emit light for irradiating the turbid medium; a detector unit adapted for detecting light emanating from the turbid medium; and a light guide adapted for guiding light emitted by the light source to the turbid medium. The light guide comprises a support comprising a support surface for supporting the turbid medium to be examined and adapted for coupling the light emitted by the light source through the support surface into the turbid medium. The device is structured such that light from the light source exits through the support surface only at positions at which the support surface is contacted. Thus, it is ensured that light only exits through the support surface at positions where the turbid medium is present and the light exiting the support is coupled into the turbid medium. As a consequence, no light from the light source which has not passed the turbid medium will reach and saturate the detector unit. As a consequence, light which has passed the turbid medium can be detected with improved accuracy.

Preferably, the support and the light path of the light from the light source in the support are adapted such that light is internally reflected at positions of the support surface at which the support surface is not contacted. In this case, exiting of light through the support surface at positions at which the support surface is not contacted can be conveniently prevented and coupling of light into the turbid medium can be conveniently ensured by exploiting differences in the refractive index with respect to light from the light source. If the support surface comprises a curved shape, in particular in the case of body parts of humans being the turbid medium to be examined, the comfort of the person under examination is increased. Preferably, the curved shape of the support surface is particularly adapted to the shape of the turbid medium to be examined. For example, the curved shape can be particularly adapted to the shape of a human hand. In this case, the device is particularly suited for optical detection of joint diseases such as rheumatoid arthritis.

According to a preferred aspect, the support surface is provided with a soft top layer for contacting a turbid medium to be examined. In this case, the contact area of the turbid medium to the support surface becomes enlarged by pressing the turbid medium into the soft top layer for optical examination. Thus, enhanced coupling of light into the turbid medium is achieved.

Preferably, the support comprises a force sensor for measuring the pressure with which the support surface is contacted. In this case, the contact pressure can be monitored and adjusted in case of too large or too small applied pressure. Thus, the quality of the results of the optical examination can be further improved.

According to one aspect, the support is a plate and both main surfaces of the plate are adapted such that total internal reflection of light from the light source occurs in the interior of the support. In this case, a particularly suitable space-saving and cost-efficient realization is achieved. Efficient guiding of light from the light source to the turbid medium is realized.

If the support is adapted to support a human hand as a turbid medium to be examined, optical detection of joint diseases such as rheumatoid arthritis is possible in a convenient way. Preferably, the device further comprises a camera arranged at the opposite side of the support with respect to the support surface. In this case, the contact of the turbid medium to the support surface can be monitored in a particular convenient manner. Further, the position of the turbid medium with respect to the support can be monitored and adjusted. Preferably, the device is a medical optical examination apparatus. According to a specific aspect, the device is adapted for optical detection of rheumatoid arthritis.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will arise from the detailed description of embodiments with reference to the enclosed drawings. Fig. 1 schematically shows a general set-up in a known device for optically examining the interior of turbid media.

Fig. 2 schematically shows the position of joints in a human hand as an example for a turbid medium to be examined.

Fig. 3 schematically shows an embodiment of a device for optically examining the interior of turbid media.

Fig. 4 schematically shows a modification of the embodiment.

Fig. 5 schematically shows a further modification of the embodiment. DETAILED DESCRIPTION OF EMBODIMENTS

First, the general set-up of a conventional device for optically examining the interior of turbid media which is specifically adapted for examining the condition of joints will be described with respect to Fig. 1. Fig. 1 schematically shows the set-up of such a device realizing transmission geometry. As can be seen in Fig. 1, a turbid medium 5 is placed on a support 1 comprising a support surface 2 against which the turbid medium 5 rests. In the example, the turbid medium 5 is formed by a human hand and the support 1 is formed by a transparent plate. Below the support 1, i.e. on the opposite side of the support with respect to the turbid medium 5, a light source 3 emitting light (schematically indicated by arrows 7) for illuminating the turbid medium 5 is located. On the opposite side of the turbid medium 5 as seen from the light source 3, a detector unit 4 is arranged for detecting light emanating from the turbid medium 5 (again schematically indicated by arrows). The detector unit 5 can e.g. be formed by a CCD camera. In the shown device, the whole turbid medium 5 is illuminated by the light source 3 and the light arriving at the other side of the turbid medium 5 is detected by the detector unit 5 in a two-dimensionally resolved manner. However, as has already been described above, in such an arrangement a portion of the light used for illuminating the turbid medium 5 will arrive at the detector unit 4 without having passed through the turbid medium 5. For example, in the shown example in which the turbid medium 5 is formed by a hand, a portion of the light used for illuminating may pass between the fingers. This portion of the light will be much less attenuated as compared to light having passed through the turbid medium 5. Thus, the less attenuated light can cause saturation of the detector unit 4 which in turn deteriorates the sensitivity with respect to light having passed through the turbid medium 5.

Fig. 2 exemplary shows the regions of interest for joint disease activity monitoring, namely the joints 6 present in the turbid medium 5. In the example shown in Fig. 2, the turbid medium 5 is formed by a human hand.

Now, an embodiment will be described with which the above described problems can be overcome. The general construction of the device for optically examining the interior of a turbid medium is similar to that described with reference to Fig. 1. However, the arrangement of the light source 3 and the structure of the support 20 are different as compared to Fig. 1. These differences will now be described in more detail with reference to Fig. 3.

Instead of the arrangement of the support 2 and the light source 3 shown in Fig. 1 in which the turbid medium 5 is illuminated as a whole through the support 2, a different arrangement is realized according to the embodiment. It should be noted that the detector unit 4 is not shown in the drawing. However, the detector unit 4 is provided in a transmission geometry position (e.g. similar to the situation depicted in Fig. 1). The light source 3 in the embodiment can for instance be a broadband light source, such as an incandescent lamp, or a single color light source, such as an LED or a laser. The detector unit can e.g. be formed by a CCD camera.

In the embodiment shown in Fig. 3, the support 10 is formed by a plate of transparent material. For example, the support can be made of transparent glass, PMMA, or other suitable transparent materials. First, a situation without turbid medium 5 contacting the support surface 20 will be described. The light 7 from the light source 3 is laterally introduced into the support 10. The refractive index of the support 10 with respect to the light from the light source 3 and the angle at which light from the light source 3 is introduced into the support 10 are chosen such that the light from the light source 3 is internally reflected in the support 10 and does not exit through the support surface 20 where the support surface 20 is not contacted on the outer side. As a consequence, the support 10 acts as a light guide in which the light from the light source 3 travels through total internal reflection. From another point of view, the arrangement is chosen such that total reflection occurs at the inner side of the support surface 20 and at the inner side of the opposite main surface 22. This means that the angle CC at which light from the light source 3 reaches the support surface 20 from the interior of the support 10 fulfills the requirement: α > CC_G with CC_G being the critical angle for total reflection. This critical angle CC_G fulfills the equation

with n₂ being the refraction index with respect to the light from the light source 3 at the exterior of the support surface 20 and ni being the corresponding refraction index of the material of the support 10. For reasons of simplicity, the medium at the exterior of the support surface can e.g. be formed by ambient air such that the refractive index n₂ corresponds approximately to the refractive index no in vacuum. Thus, the angle CC at which light from the light source 3 reaches the support surface 20 from the interior of the support 10 is selected to fulfill:

CC > CC_G = sin^"1 OVn₁) (2) Now, a situation with a turbid medium 5 contacting the support surface 20 will be described. In the relevant case for devices for optically examining the interior of turbid media, the turbid medium 5 to be examined will typically be a body part such as a human hand. This is particularly the case if the device for optically examining the interior of turbid media is adapted for joint disease monitoring. Such a turbid medium 5 will have a refraction index n_t which differs from the refraction index of ambient air. As a consequence, at positions at which the turbid medium 5 contacts the support surface 20, a different critical angle for total reflection CCGt will be valid with:

In the device for optically examining the interior of a turbid medium according to the embodiment, the angle α is selected to fulfill:

α_Gt > α > CCG (4).

As a consequence, at positions at which the support surface 20 is not contacted (i.e. for example ambient air or another suitable medium is present) total reflection of the light 7 from the light source 3 will occur inside the support 10 and the light will not exit through the support surface 20. On the other hand, at positions at which the support surface 20 is contacted by the turbid medium 5, the requirement for total reflection is no longer fulfilled and light from the light source 3 will enter the turbid medium 5 through the support surface 20. Because of the scattering properties of the turbid medium 5, the light will be distributed through the turbid medium 5. The light which has entered the turbid medium 5 will be detected after transmission through the turbid medium 5.

It should be noted that the surface 22 at the side of the support 10 opposite to the support surface 20 is provided in a corresponding way such that multiple total internal reflections of the light from the light source 3 are achieved inside the support 10 acting as a wave guide.

Thus, it is ensured that the turbid medium 5 is reliably illuminated with light from the light source 3 and, at the same time, no light will reach the detector unit 4 without having passed through the turbid medium 5. In other words, in areas where the turbid medium 5 is not in contact with the support surface 20, light will remain in the support 10 and cannot interfere with the signal on the detector unit 4. As a consequence, high sensitivity for light having passed through the turbid medium 5 is achieved.

To summarize, according to the embodiment light is inserted into the support 10 forming a wave guide at an appropriate angle which is larger than the critical angle for total reflection. The inserted light travels through the support 10. When a turbid medium 5 is placed in contact to the support surface 20 of the support 10, the index of refraction above the support surface 20 is changed and total internal reflection is frustrated. At this position, light is emitted from the support 10 into the turbid medium 5 via the support surface 20. Introduction of light form the light source 3 into the support 10 can be performed through an entrance window at one lateral side of the support 10. The opposite lateral side (facing away from the light source 3) can be provided with a beam dump for the non-absorbed light or can be provided with a reflector for recycling the non-emitted light. In the case of a reflector, proper care needs to be taken that the reflected light remains at the proper angle for total internal reflection. In case of a laser as a coherent light source 3, an angle of an entrance window and an angle of an exit window can e.g. be chosen differently to prevent reflected light from being coupled back into the laser.

Although in the embodiment shown in Fig. 3 a support 10 having a completely flat support surface 20 is shown, according to a modification of the embodiment the support surface 20 may also have a (slightly) curved shape. In particular, the curved shape of the support surface 20 can be specifically adapted to the shape of turbid media to be examined. For example, for the specific case of joint disease monitoring, the support surface 20 can be specifically adapted to the shape of a human hand. Such a curved shape results in enhanced comfort of the person the body part of which is under examination.

A preferred modification of the support 100 of the device for examining the interior of turbid media will now be described with respect to Fig. 4. The modification differs from the embodiment described above in the structure of the support surface. With respect to the total internal reflection of light from the light source 3 and to exiting of light only at positions of the support surface at which the support surface is contacted, the modification corresponds to the embodiment described above. In the following, only the differences to the embodiment will be described and a detailed description of corresponding features will not be repeated.

As schematically shown in Fig. 4, according to the preferred modification the support 100 is provided with a soft top layer 110 at the side of the support surface 120. The soft top layer 110 can e.g. be formed by a soft polymer, a gel, a fluid, or by a combination of these. The optical properties of the soft top layer 110 are selected such that the support 100 comprising the soft top layer 110 still acts as a wave guide and light from the light source 3 is only coupled out through the support surface 120 (via the soft top layer 110) at positions at which the support surface 120 is contacted by the turbid medium 5. According to the modification, this result is achieved as in the embodiment described above by exploiting total internal reflection and the change in the refractive index at the exterior of the support surface 120 when the turbid medium 5 contacts the support surface 120.

Due to the soft top layer 110 the turbid medium 5 to be examined can be pressed against the support surface 120 such that the soft top layer 110 is slightly compressed and the contact area between the turbid medium 5 and the support surface 120 becomes increased. As a result, more effective coupling of light into the turbid medium 5 is achieved. In a further preferred embodiment (not shown in the figures), a force sensor is attached to the support 10, 100 according to the embodiment (10) or according to the modification (100). With the force sensor, the pressure can be measured with which the turbid medium 5 is pressed against the support surface 20, 120. According to the modification, further a control unit is provided which monitors the force sensor and provides a feedback to adjust the pressure with which the turbid medium is pressed against the support surface 20, 120. The feedback can e.g. be provided as a visual or acoustic signal, e.g. to a person to which a body part forming a turbid medium under examination belongs or to an operator. According to the implementation comprising the force sensor, too high pressure can be avoided which, for instance in case of the turbid medium being formed by human hand, would cause blood to be pressed out of the tissue of the turbid medium. Further, a too low pressure resulting in too less contact between the turbid medium 5 and the support surface 20, 120 can be reliably prevented. Thus, a situation in which insufficient light is coupled into the turbid medium 5 can be prevented.

A still further modification of the device for optically examining the interior of a turbid medium is shown in Fig. 5. Although the modification is depicted based on the modification comprising the soft top layer 110, a combination with the base embodiment (without soft top layer) or with any one of the modifications is possible. According to the modification shown in Fig. 5, a camera 200 is placed on the side of the support 100 opposite to the support surface 120. At the position at which the turbid medium 5 is in contact with the support surface 120, light from the light source 3 will not only be coupled into the turbid medium 5, but will also be reflected off the tissue. This reflected light can travel through the material of the support 100 and exit the support 100 through the surface 22 at the side of the support 100 facing away from the turbid medium 5. According to the modification comprising the camera, this light is captured by the camera 200 such that the areas can be identified at which the turbid medium 5 is in contact with the support surface 120. Thus, with this implementation, the correct placement of the turbid medium 5 for examination can be assessed. Further, the amount of reflected light can also be used as a measure for the amount of light which is coupled into the turbid medium 5 via the support surface 120.

Further, the implementation comprising the camera 200 can be adapted such that the reflected light is monitored in a wavelength specific way. In particular, a combination of determining the location of e.g. joints and monitoring wavelength specific reflected light can assist in analyzing joint inflammation.

Specifically for optical detection of disease activity of rheumatoid arthritis or other joint diseases, both the joints and intermediate tissue of a body part, in particular of a human hand, are illuminated and the transmitted or reflected light is detected. The embodiments and modifications described above allow illuminating turbid media of interest, such as in particular body parts comprising joints, in a correct way such that unwanted light is prevented from reaching the detector unit. As a consequence, the desired information about the interior of the turbid medium under examination is provided with improved accuracy. This in turn allows earlier detection of e.g. joint diseases such as rheumatoid arthritis. Early and quantitative detection of the inflammation of joints allows early treatment and treatment monitoring which results in reduced costs for treatment of joint diseases.

According to the embodiments and modifications described above, improved illumination of turbid media to be examined is achieved by exploiting total reflection inside the support acting as a waveguide. However, in principle, instead of exploiting total reflection, for instance optical absorption at positions at which the support surface is not contacted could be exploited for preventing light from exiting through the support surface as an alternative.

Claims

CLAIMS:

1. Device for optically examining the interior of a turbid medium, comprising: a light source (3) adapted to emit light for irradiating the turbid medium; a detector unit (4) adapted for detecting light emanating from the turbid medium; and a light guide adapted for guiding light emitted by the light source to the turbid medium; wherein the light guide comprises a support (10; 100) comprising a support surface (20; 120) for supporting the turbid medium to be examined and adapted for coupling the light emitted by the light source (3) through the support surface (20; 120) into the turbid medium, wherein the device is structured such that light from the light source (3) exits through the support surface (20; 120) only at positions at which the support surface is contacted.

2. Device according to claim 1, wherein the support (10; 100) and the light path of the light from the light source (3) in the support are adapted such that light is internally reflected at positions of the support surface (20; 120) at which the support surface is not contacted.

3. Device according to any one of claims 1 or 2, wherein the support surface (20;

120) comprises a curved shape.

4. Device according to claim 3, wherein the curved shape of the support surface (20; 120) is particularly adapted to the shape of the turbid medium to be examined.

5. Device according to any one of claims 1 to 4, wherein the support surface (20; 120) is provided with a soft top layer (110) for contacting a turbid medium to be examined.

6. Device according to any one of claims 1 to 5, wherein the support (10; 100) comprises a force sensor for measuring the pressure with which the support surface is contacted.

7. Device according to any one of claims 1 to 6, wherein the support (10; 100) is a plate and both main surfaces of the plate are adapted such that total internal reflection of light from the light source (3) occurs in the interior of the support.

8. Device according to any one of claims 1 to 7, wherein the support (10; 100) is adapted to support a human hand as a turbid medium to be examined.

9. Device according to any one of claims 1 to 8, wherein the device further comprises a camera (200) arranged at the opposite side of the support (10; 100) with respect to the support surface (20; 120).

10. Device according to any one of claims 1 to 9, wherein the device is a medical optical examination apparatus.

11. Device according to any one of claims 1 to 10, wherein the device is adapted for optical detection of rheumatoid arthritis.