Apparatus and Method for Performing Othogonal Polarized Spectral Imaging (Opsi)

Abstract

Provided is a method and an apparatus for detection of objects below the surface of diffuse scattering media, in particular blood capillaries in organs such as the skin of human beings, using Orthogonal Polarized Spectral Imaging (OPSI), according to the invention comprising the steps of: imaging the object in question at at least two different angles so as to obtain a shift of position in the imaging plane; and subsequently comparing relative shifts of objects in the two images so as to obtain coordinates of the imaged objects with respect to the organ surface.

Description

Further features and advantages of the present invention will become more apparent for those skilled in the art upon reading of the following description of preferred embodiments in connection with the annexed Figures, in which:

FIG. 1 is a schematic representation of a setup for OPSI;

FIG. 2 a is a schematic representation of the exit pupil of the imaging objective with OPSI light paths using parallel beams in plan view;

FIG. 2 b is a side view of FIG. 2a;

FIG. 3 shows an embodiment of the OPSI setup using parallel imaging beams;

FIG. 4 shows an embodiment using the same objective and tilted imaging beams; and

FIG. 5 shows the schematic position of blood vessels in an image as a function of the viewing angle and position relative to the focal plane.

FIG. 1 schematic ally shows a typical setup for OPSI, comprising a light source 1, such as a lamp, a laser, an LED, etc., a condenser 2, diaphragm 3, a color filter 4, a polarizer 5, a polarizing beam splitter 6, and an objective 7. Furthermore, FIG. 1 shows a skin 8 consisting of (a) epidermis, and (b) dermis, together with blood capillaries 9. Finally, an analyzer 10 is shown, wherein polarization is effected perpendicularly to polarizer 4, a lens 11, and a CCD camera 12.

FIG. 2 a is a plan view of an exit pupil 13 of the imaging objective with OPSI light paths using parallel beams 14, 15. A non-invasive blood analyzer uses an objective with a NA of 0.9. A lateral resolution of 1 or 2 μm is required for OPSI imaging, which can be achieved by using an objective with a NA of 0.35. Since the NA required for OPSI (0.35) is much smaller than the NA available (0.9), it is possible to use only a fraction of the pupil 13 area for imaging. The different stereoscopic angles can be achieved by illuminating different areas of the pupil 13. Using parallel beams 14, 15, the blood vessels 9 in the focal plane are imaged in the same position if observed at the two stereoscopic angles. Vessels 9 that lie in front of or behind the focal plane have different positions in the two images. A possible embodiment is shown in FIG. 3.

The position of the imaging beam in the objective pupil 13 can be shifted by means of a scanning (rotating) mirror 16 and a relaying lens 17. If the distance between this lens 17 and the scanning mirror 16 equals the focal distance of the relaying lens 17, a tilt of the mirror 16 results in a parallel displacement of the imaging beam in the objective pupil 13. The distance between the objective pupil 13 and the blood vessel 9 is equal to the focal distance of the objective pupil 13 (corrected for the refractive index of human skin).

An alternative embodiment is shown in FIG. 4, where the same elements as in the previous Figures have been provided with corresponding reference signs. A polarizing beam splitter 6 separates the light paths of the illumination system and the imaging system. The imaging system contains a scanning mirror 16 and a relaying lens 17 such that the pivot point on the scanning mirror 16 is imaged on the center of the objective lens 13. An imaging lens is used to image the focal plane of the objective lens 13 onto a CCD camera.

As the scanning mirror 16 performs a wobbling motion, the OPSI image moves. Objects that are in front of or above the focal plane will move less than objects behind or below the focal plane. Objects that are in the focal plane will move over a distance Mf tan β, where M is the magnification factor of the OPSI system, f is the focal length of the objective, and β is the viewing angle through the microscope objective. β is related to the scanning angle σ of scanning mirror 16 as follows: tan β=(A/B ) tan 2 σ, where A is the distance from the scanning mirror 16 to the relaying lens 17 and B is the distance from the relaying lens 17 to the objective lens 13.

Objects that are at a distance delta above the focal plane will move over a distance that is slightly smaller, M (f−δ) tan β, whereas objects at a distance δ below the focal plane will move over a distance that is slightly greater, M (f+δ) tan β, cf. FIG. 5.

FIG. 5 shows the schematic positions of blood vessels 18, The three blood vessels 18a, 18b, 18c shown in FIG. 5 all overlap in the case of β=0, but their projections on the focal plane all have different displacements for β≠0.

Besides the embodiments described above, other embodiments are possible such as, for example, a single imaging device which includes a replacement for the scanning mirror by a rotating wedge or by two shifting wedges. It is also possible to use two imaging devices looking through the objective at different angles. This has the advantage that there are no moving parts and that the images from both sides can be detected simultaneously. The amount of de-focus can be determined from the obtained images by means of a correlation function or by subtracting the two images.

Provided is a method and an apparatus for detection of objects below the surface of diffuse scattering media, in particular blood capillaries in organs such as the skin of human beings, using Orthogonal Polarized Spectral Imaging (OPSI), according to the invention comprising the steps of: imaging the object in question at least two different angles so as to obtain a shift of position in the imaging plane; and subsequently comparing relative shifts of objects in the two images so as to obtain coordinates of the imaged objects with respect to the organ surface.

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. The word “comprising” does not exclude the presence of other elements or steps than those listed in a claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements.

Claims

1. An apparatus for performing Orthogonal Polarized Spectral Imaging for imaging objects below the surface of diffuse scattering media, comprising a light source for providing polarized light, an imaging device, a beam splitter, a focusing device, and means for imaging the object at two different imaging angles.

2. The apparatus according to claim 1, wherein the means for imaging the object is formed by two objectives having different imaging angles.

3. The apparatus according to claim 1, wherein the means for imaging the object is formed by a main objective, a scanning mirror, and at least one of a rotating wedge and two shifting wedges for shifting an imaging beam path from the polarizing beam splitter to the imaging device .

4. The apparatus according to claim 1, wherein a separate imaging device is provided for each image.

5. The apparatus according to claim 4, wherein a shutter is provided for transmitting each of the two images in alternation.

6. The apparatus according to claim 5, wherein the shutter is located between the polarizing beam splitter (6) and the imaging device.

7. The apparatus according to claim 5, wherein the shutter is one of a rotating-aperture shutter and a liquid crystal cell shutter.

8. (canceled)

9. The apparatus according to claim 1, wherein the two imaging angles differ by at least approximately 10 degrees.

10. Apparatus according to claim 1, wherein the imaging devices are one of CCD-cameras, CMOS-sensors, and a combination of CCD-cameras and CMOS-sensors.

11. (canceled)

12. The apparatus according to claim 1, characterized in further comprising a data processor for determining a position of the object, the position including at least information about the z-axis which is parallel to the optical axis.

13. The apparatus according to claim 12, further comprising a spectroscopic analysis system, with a spectroscopic light source and a spectroscopic light beam positioning device for directing the spectroscopic light beam to the object in dependence of the position of the object determined by the data processor.

14. A method for detection of objects below the surface of diffuse scattering media using Orthogonal Polarized Spectral Imaging, comprising the steps of: imaging the object in question at at least two different angles so as to obtain a shift of position in an imaging plane; and determining a shift in the object imaged at the two different angles so as to obtain coordinates of the imaged objects.

15. The method according to claim 14, wherein a direction of the shift determines whether the imaged object is above or below focal plane.

16. The method according to claim 14, wherein a distance between the object and a focal plane is calculated from the size of the shift.

17. The method according to claim 14, wherein the two imaging angles differ by at least approximately 10 degrees.

18. (canceled)

19. The method according to claim 18, wherein part of the objective (7) is illuminated with a parallel beam so as to obtain the at least two images.

20. The method according to claim 18, wherein the entire objective is illuminated at a defined angle so as to obtain the at least two images.

21. A blood analysis system comprising: a light source for providing polarized light directed toward an object,means for imaging the object at two different imaging angles to obtain a shift of position in an imaging plane; andmeans for determining a shift of the object imaged at the two different angles so as to obtain coordinates of the imaged object.

22. The blood analysis system of claim 21, wherein a direction of the shift determines whether the imaged object is above or below a focal plane.

23. The blood analysis system of claim 21, wherein a distance between the object and a focal plane is calculated from the size of the shift.