Method and apparatus for imaging using polarimetry and matrix based image reconstruction

• US 20040012853A1
• Filed: 05/13/2003
• Published: 01/22/2004
• Est. Priority Date: 05/13/2002
• Status: Active Grant

• Current Assignee: Juan Manuel Bueno Garcia, Melanie C.W. Campbell
• Original Assignee: Juan Manuel Bueno Garcia, Melanie C.W. Campbell
• Inventors: Garcia, Juan Manuel Bueno, Campbell, Melanie C.W.
• Granted Patent: US 6,927,888 B2
• Time in Patent Office: Days
• US Class Current: 359/485
• CPC Class Codes: A61B 3/1025 for confocal scanning
• CPC Class Codes: G02B 21/0028 specially adapted for specific applications, e.g. for endoscopes, ophthalmoscopes, attachments to conventional microscopes
• CPC Class Codes: G02B 21/0068 arrangements using polarisation
• CPC Class Codes: G02B 21/008 Details of detection or image processing, including general computer control
• CPC Class Codes: G02B 27/286 for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another G02B5/3083 takes precedence; light guide coupling means utilising polarising elements G02B6/34
• CPC Class Codes: G02B 5/3025 Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state G02B5/3008, G02B5/3016 take precedence
• CPC Class Codes: Y10S 359/90 Methods

Abstract

The present invention provides a method and apparatus for improving the signal to noise ratio, the contrast and the resolution in images recorded using an optical imaging system which produces a spatially resolved image. The method is based on the incorporation of a polarimeter into the setup and polarization calculations to produce better images. After calculating the spatially resolved Mueller matrix of a sample, images for incident light with different states of polarization were reconstructed. In a shorter method, only a polarization generator is used and the first row of the Mueller matrix is calculated. In each method, both the best and the worst images were computed. In both reflection and transmission microscope and Macroscope and ophthalmoscope modes, the best images are better than any of the original images recorded. In contrast, the worst images are poorer. This technique is useful in different fields such as confocal microscopy, Macroscopy and retinal imaging.

Claims

1. A method for producing images of an object or region of interest of the object, comprising the steps of:

a) producing an incident beam of light in a pre-selected polarization state and scanning said incident beam of light point by point across an object or region of interest of the object;

b) detecting light intensity signals corresponding to beams of light in a pre-selected number of polarization states reflected point by point from the object or region of interest of the object and storing electronic signals corresponding to the detected light intensity signals;

c) repeating steps a) and b) for an effective number of pre-selected polarization states of the incident beam of light;

d) constructing a spatially resolved matrix of the object point by point from the detected light intensity signals and from said spatially resolved matrix constructing spatially resolved images of the object or region of interest of the object for a set of theoretical polarization states of the incident beam of light in addition to those input states generated in the incident beam of light, said matrix being selected to describe the effect of the object on the polarization properties of light;

e) characterizing image quality of each image in accordance with an effective image quality parameter and based upon said characterization selecting a best image of said object or region of said object; and

f) visually displaying said best image.

2. The method according to claim 1 wherein the matrix is a 4×

4 Mueller matrix, and wherein said effective number of pre-selected polarization states of the incident beam of light is four, and wherein said pre-selected number of polarization states in the pathway which records the reflected point by point signal from the object is four.

3. The method according to claim 1 wherein the effective image quality parameter is the signal-to-noise ratio.

4. The method according to claim 1 wherein the step of detecting an array of light signals reflected from the object or region of interest of the object includes detecting light reflected from multiple locations on the object or region of interest of the object point by point using a movable detector.

5. A method for producing images of an object or region of interest of the object, comprising the steps of:

a) producing an incident beam of light in a pre-selected polarization state and scanning said incident beam of light point by point across an object or region of interest of the object;

b) detecting light intensity signals corresponding to beams of light reflected point by point from the object or region of interest of the object and storing electronic signals corresponding to the detected light intensity signals;

c) repeating steps a) and b) for an effective number of pre-selected polarization states of the incident beam of light;

d) constructing a spatially resolved vector of the object point by point from the detected light intensity signals and from said spatially resolved vector constructing spatially resolved images of the object or region of interest of the object for a set of theoretical polarization states of the incident beam of light in addition to those input states generated in the incident beam of light, said vector comprised of independent elements of a matrix being selected to describe the effect of the object on the polarization properties of light;

e) characterizing image quality of each image in accordance with an effective image quality parameter and based upon said characterization selecting a best image of said object; and

f) visually displaying said best image.

6. The method according to claim 5 wherein the vector is the first row of the matrix and the matrix is a 4×

4 Mueller matrix, and wherein said effective number of pre-selected polarization states of the incident beam of light is four.

7. The method according to claim 5 wherein the effective image quality parameter is the signal-to-noise ratio.

8. The method according to claim 5 wherein the step of detecting light signals reflected from the object or region of interest of the object includes detecting light reflected from multiple locations on the object or region of interest of the object point by point using a movable detector.

9. A method for producing images of an object or region of interest of the object, comprising the steps of:

a) producing an incident beam of light in a pre-selected polarization state and illuminating an object or region of interest of the object with the selectively polarized beam of light;

b) detecting an array of light intensity signals reflected from spatially distinct points of the object or region of interest of the object and storing electronic signals corresponding to said detected array of light signals;

c) repeating steps a) and b) for an effective number of pre-selected polarization states of the incident beam of light;

d) constructing a vector comprised of independent elements of a spatially resolved matrix of the object point by point from the detected light intensity signals and from said spatially resolved vector constructing spatially resolved images of the object or region of interest of the object for a set of theoretical polarization states of the incident beam of light in addition to those input states generated in the incident beam of light, said matrix being selected to describe the effect of the object on the polarization properties of light;

e) characterizing image quality of each image in accordance with an effective image quality parameter and based upon said characterization selecting a best image of said object; and

f) visually displaying said best image.

10. The method according to claim 9 wherein the step of detecting an array of light signals reflected from the object or region of interest of the object includes simultaneously detecting light reflected from multiple locations on the object or region of interest of the object using an array detector.

11. The method according to claim 10 wherein the array detector is a charge coupled detector.

12. The method according to claim 9 wherein the step of detecting an array of light signals reflected from the object or region of interest of the object includes detecting light reflected from multiple locations on the object or region of interest of the object point by point using a movable detector.

13. The method according to claim 9 wherein the effective image quality parameter is signal-to-noise ratio.

14. A method for producing images of an object or region of interest of the object, comprising the steps of:

a) producing an incident beam of light in a pre-selected polarization state and illuminating an object or region of interest of the object with the selectively polarized beam of light;

b) detecting an array of light intensity signals reflected from spatially distinct points of the object or region of interest of the object and storing electronic signals corresponding to said detected array of light signals;

c) repeating steps a) and b) for an effective number of pre-selected polarization states of the incident beam of light;

d) constructing a spatially resolved matrix of the object from the detected light intensity signals and from said spatially resolved matrix constructing spatially resolved images of the object or region of interest of the object for a set of theoretical polarization states of the incident beam of light in addition to those input states generated in the incident beam of light, said matrix being selected to describe the effect of the object on the polarization properties of light;

e) characterizing image quality of each image in accordance with an effective image quality parameter and based upon said characterization selecting a best image of said object; and

f) visually displaying said bet image.

15. The method according to claim 14 wherein the step of detecting an array of light signals reflected from the object or region of interest of the object includes simultaneously detecting light reflected from multiple locations on the object or region of interest of the object using an array detector.

16. The method according to claim 15 wherein the array detector is a charge coupled detector.

17. The method according to claim 14 wherein the step of detecting an array of light signals reflected from the object or region of interest of the object includes detecting light reflected from multiple locations on the object or region of interest of the object point by point using a movable detector.

18. The method according to claim 14 wherein the effective image quality parameter is signal-to-noise ratio.

19. A method for producing images of an object using confocal scanning laser microscopy, comprising the steps of:

a) calibrating a confocal scanning laser microscope modified to include a polarization generator and a polarization analyzer to obtain a Mueller matrix

$M_{\mathrm{SCN}}^{\left(1\right)},$

of the instrument in the incoming direction, wherein a matrix of 16 intensity values results from intensity measurements with a rotating ¼

wave plate located in said generator positioned in each of four positions including 45 degrees, 0 degrees, 30 degrees and 60 degrees, while a ¼

wave plate located in said analyzer is placed in each of the same four positions;

b) calibrating said modified confocal scanning instrument to obtain a Mueller matrix

$M_{\mathrm{SCN}}^{\left(2\right)},$

of the instrument in the outgoing direction, wherein a matrix of 16 intensity values results from intensity measurements with a rotating ¼

wave plate located in said generator positioned in each of four positions including 45 degrees, 0 degrees, 30 degrees and 60 degrees, while a ¼

wave plate located in said analyzer is placed in each of the same four positions;

c) placing said object in said modified confocal scanning apparatus and focusing light onto said object and recording sixteen gray scale images with the object in place for each of four generator states with a ¼

wave plate at 45, 0, 30 and 60 degrees combined with each of the four analyzer states ¼

wave plate at 45, 0, 30 and 60 degrees;

d) placing said sixteen grey scale values for each pixel into a spatially resolved matrix, I^(mn), which is a first element of a Stokes vector,

$S_D^{\left(\mathrm{mn}\right)}$

reaching the photodetector;

e) from I^(mn) calculate M_out from equation 2;

f) from equation 3, calculate M, the spatially resolved Mueller matrix of the object;

g) choosing values of an incident Stokes vector, S_IN, around a Poincaré

sphere in predetermined increments of χ and

φ

which represent, respectively, the azimuth and ellipticity of the incident Stokes vector on the Poincaré

sphere;

h) applying equation 4 to reconstruct images, I^(out), pixel by pixel for each incident Stokes vector;

i) for each image, calculate the image quality measure of choice, for example SNR as defined in equation 5; and

j) display the image with best value of the image quality measure.

20. The method according to claim 19 wherein said object is an inanimate object, and wherein said step of focusing light onto said object includes directing light through a focussing lens onto said object and capturing and processing images propagating back through said focussing lens reflected from said object.

21. The method according to claim 20 wherein said object is an animate object, and wherein said step of focusing light onto said object includes directing light through a focussing lens onto said object and capturing and processing images propagating back through said focussing lens reflected from said object.

22. The method according to claim 19 wherein said object is a patients eye, and wherein said confocal scanning laser microscope is a confocal scanning laser ophthalmoscope (in this case the objective of the scanning laser microscope is replaced by the optics of the eye), and wherein the step of focusing light onto said eye includes directing light into the eyeball and capturing and processing images propagating back through said eyeball.

23. An optical scanning apparatus for producing images of an object, comprising:

a) a light source for producing a light beam;

b) polarization generator for producing selected polarization states in the light beam upon passage of the light beam through said polarization generator to produce a selectively polarized light beam;

c) scanning mechanism for receiving the selectively polarized light beam and spatially scanning the selectively polarized light beam in two dimensions across an object point by point;

d) polarization analyzer for transmitting light beams of selected polarization, including directing and focusing optics for directing the reflected light beams reflected point by point from the object to said polarization analyzer;

e) detector and light shaping and focusing optics for directing and focusing the reflected or transmitted light beams of selected polarization onto said detector;

f) computer processor connected to said detector, said computer processor including image analysis means for processing signals from said detector due to the reflected light beams of selected polarization detected by said detector and producing therefrom images of the object; and

g) display means for displaying an image of the object produced by said processing means.

24. The apparatus according to claim 23 wherein said light source is a laser for producing coherent or partially coherent light beams.

25. The apparatus according to claim 23 wherein said light shaping and focusing means includes a beam splitter positioned to transmit the selectively polarized light beam from said polarization generation means to said scanning means and to direct the light beams reflected point by point from the object to the polarization analyzer means, and wherein said light shaping and focusing means includes a confocal pinhole and focusing lens positioned between said detection means and said polarization analyzer means for focusing light beams reflected point by point from the object and having the selected polarization onto said detection means.

26. The apparatus according to claim 23 wherein said polarization generator means includes a linear polarizer and a rotatable quarter wave plate, and wherein said polarization analyzer means includes a linear polarizer and a rotatable quarter wave plate.

27. The apparatus according to claim 23 wherein said polarization generator includes an electro-optical device for polarizing the incident light beam, and wherein said polarization analyzer includes an electro-optical device.

28. The apparatus according to claim 27 wherein said electro-optical devices are one of a liquid crystal modulator and a photoelastic modulator.

29. The apparatus according to claim 23 wherein the object is a person'"'"'s eye and said apparatus is a scanning laser ophthalmoscope or confocal scanning laser ophthalmoscope, and including positioning means for holding a person'"'"'s head in position with the person'"'"'s eye positioned so the light beam having selected polarization is scanned across the eye.

30. The apparatus according to claim 23 including focusing optics for receiving the selectively polarized light beams from said scanning means and focussing the selectively polarized light beams onto the object, and wherein said apparatus is a confocal scanning laser microscope or a scanning laser microscope.

31. An optical scanning apparatus for producing images of an object, comprising:

a) a light source for producing a light beam;

b) polarization generator means for producing selected polarization states in the light beam upon passage of the light beam through said polarization generator means to produce a selectively polarized light beam;

c) a beam splitter for transmitting the selectively polarized light beam;

d) scanning means for receiving the selectively polarized light beam from said beam splitter and spatially scanning the selectively polarized light beam in two dimensions across an object point by point and receiving light beams reflected back from different positions on the object and directing the reflected light beams to said beam splitter;

e) polarization analyzer means positioned to receive reflected light beams reflected from said beam splitter for transmitting reflected light beams of selected polarization;

f) detection means and light shaping and focusing means for directing and focusing the reflected light beams of selected polarization onto said detection means;

g) computer processing means connected to said detection means, said computer processing means including image analysis means for processing signals from the detector due to the reflected light beams of selected polarization detected by said detection means and producing therefrom images of the object; and

h) display means for displaying an image of the object produced by said processing means.

32. The apparatus according to claim 31 wherein said light source is a laser for producing coherent or partially coherent light beams.

33. The apparatus according to claim 31 wherein said polarization generator means includes a linear polarizer and a rotatable quarter wave plate, and wherein said polarization analyzer means includes a linear polarizer and a rotatable quarter wave plate.

34. The apparatus according to claim 31 wherein said light shaping and focusing means for directing and focusing the reflected light beams of selected polarization onto said detection means includes a confocal pinhole and focusing lens positioned between said detection means and said polarization analyzer means for focusing light beams reflected point by point from the object and having the selected polarization onto said detection means.

35. The apparatus according to claim 32 wherein the object is a person'"'"'s eye and said apparatus is a confocal scanning laser ophthalmoscope, and including positioning means for holding a person'"'"'s head in position with the person'"'"'s eye positioned so said laser beam is scanned across the eye.

36. The apparatus according to claim 34 including light beam directing and focusing optics for receiving said selectively polarized light beam from said scanning means and directing and focussing said selectively polarized coherent light beam onto the object, and wherein said apparatus is a confocal scanning laser microscope.

37. A method for producing images of an object or region of interest of the object, comprising the steps of:

a) producing an incident beam of light in a pre-selected polarization state and scanning said incident beam of light point by point across and/or along an object or region of interest of the object;

b) detecting light intensity signals corresponding to beams of light in a pre-selected number of polarization states reflected or transmitted point by point from the object or region of interest of the object and storing electronic signals corresponding to the detected light intensity signals;

c) repeating steps a) and b) for an effective number of pre-selected polarization states of the incident beam of light;

d) constructing a spatially resolved matrix of the object point by point from the detected light intensity signals and from said spatially resolved matrix constructing spatially resolved images of the object or region of interest of the object for a set of theoretical polarization states of the incident beam of light in addition to those input states generated in the incident beam of light, said matrix being selected to describe the effect of the object on the polarization properties of light;

e) characterizing image quality of each image in accordance with an effective image quality parameter and based upon said characterization selecting a best image of said object or region of said object; and

f) visually displaying said best image.

38. A method for producing images of an object or region of interest of the object, comprising the steps of:

a) producing an incident beam of light in a pre-selected polarization state and scanning said incident beam of light point by point across an object or region or along an object or a region of interest of the object by moving the object with respect to the incident beam or by moving the object in 1 dimension with respect to the incident beam and scanning the beam in a perpendicular direction with respect to the object;

b) detecting light intensity signals corresponding to beams of light reflected or transmitted point by point from the object or region of interest of the object and storing electronic signals corresponding to the detected light intensity signals;

c) repeating steps a) and b) for an effective number of pre-selected polarization states of the incident beam of light;

d) constructing a spatially resolved vector of the object point by point from the detected light intensity signals and from said spatially resolved vector constructing spatially resolved images of the object or region of interest of the object for a set of theoretical polarization states of the incident beam of light in addition to those input states generated in the incident beam of light, said vector comprised of independent elements of a matrix being selected to describe the effect of the object on the polarization properties of light;

e) characterizing image quality of each image in accordance with an effective image quality parameter and based upon said characterization selecting a best image of said object; and

f) visually displaying said best image.

39. A method for producing images of an object using scanning laser microscopy or macroscopy, in transmission mode, comprising the steps of:

a) calibrating a scanning laser microscope or macroscope modified to include a polarization generator and a polarization analyzer to obtain a Mueller matrix M_SCN⁽¹⁾, of the instrument in the incoming direction, wherein a matrix of 16 intensity values results from intensity measurements with a rotating ¼

wave plate located in said generator positioned in each of four positions including 45 degrees, 0 degrees, 30 degrees and 60 degrees, while a ¼

wave plate located in said analyzer is placed in each of the same four positions;

b) placing said object in said modified confocal scanning apparatus and focusing light onto said object and recording sixteen gray scale images with the object in place for each of four generator states with a ¼

wave plate at 45, 0, 30 and 60 degrees combined with each of the four analyzer states ¼

wave plate at 45, 0, 30 and 60 degrees;

c) placing said sixteen grey scale values for each pixel into a spatially resolved matrix, I^(mn), which is a first element of a Stokes vector,

$S_D^{\left(\mathrm{mn}\right)}$

reaching the photodetector;

d) from I^(mn) calculate M_out from equation (equation

     2);

e) from equation 5, calculate M, the spatially resolved Mueller matrix of the object;

f) choosing values of an incident Stokes vector, S_IN, around a Poincaré

sphere in predetermined increments of χ and

φ

which represent, respectively, the azimuth and ellipticity of the incident Stokes vector on the Poincaré

sphere;

g) applying equation 6 to reconstruct images, I^(out), pixel by pixel for each incident Stokes vector;

h) for each image, calculating the image quality measure of choice, for example SNR as defined in equation 7; and

i) displaying the image with best value of the image quality measure.

40. An optical scanning apparatus for producing images of an object, comprising;

a) a light source for producing a light beam;

b) polarization generator means for producing selected polarization states in the light beam upon passage of the light beam through said polarization generator means to produce a selectively polarized light beam;

c) scanning means for receiving the selectively polarized light beam and spatially scanning the selectively polarized light beam in two dimensions across an object point by point scanning the sample with respect to the laser beam or scanning the beam in 1 or 2 dimensions and the sample in the perpendicular direction;

d) polarization analyzer means for transmitting light beams of selected polarization, including directing and focusing optics for directing the reflected light beams reflected point by point from the object to said polarization analyzer means;

e) detection means and light shaping and focusing means for directing and focusing the reflected light beams of selected polarization onto said detection means;

f) computer processing means connected to said detection means, said computer processing means including image analysis means for processing signals from said detector due to the reflected light beams of selected polarization detected by said detection means and producing therefrom images of the object; and

g) display means for displaying an image of the object produced by said processing means.