A system for characterizing the polarization of targets.

Abstract

A system (1) for polarimetric characterization of a target (S), comprising: a liquid light guide (LLG) (15) for transmitting light from a light source (30) to the target (S); a polarization state analyzer (PSA) (41) operable to analyze the polarization of the light propagating within the LLG (15) and reflected by the target; and a polarization state generator (PSG) (40) for modulating the polarization of light injected into the LLG (15); and at least one of a photodetector (20) for detecting light backscattered by the target (S) illuminated by the LLG (15); The system (1) comprises:

Description

Technical Field

[0001] The present invention relates to systems and related methods for polarimetric characterization of targets. More particularly, but not limited to, the present invention relates to in vivo endoscopic Mueller polarimetric characterization of biological tissues.

Background Art

[0002] Endoscopes are imaging instruments widely used in many diagnostic and surgical biomedical applications. Narrow and difficult-to-reach areas within the cavities of the human body (such as the large intestine, stomach, lungs, etc.) can be visualized with high resolution and minimal invasiveness by using such systems. Endoscopes are generally used by surgeons to identify suspicious areas where biopsies are performed to confirm the presence of cancer or pre-cancerous lesions, and during surgery to excise them. An accurate determination of the area to be biopsied is very important for obtaining a correct diagnosis and identifying the most appropriate treatment, and for enabling the rapid management of the patient. Similarly, a clear identification of the surgical margins of diseased parts is very important for removing them completely and leaving as much healthy tissue as possible.

[0003] Flexible endoscopes typically rely on fiber optic or chip-on-a-tip designs and are used to reach internal parts of the human body through tubular structures, such as the stomach or esophagus, small intestine, large intestine, etc., characterized by strong flexion.

[0004] In contrast, rigid endoscopes, such as laparoscopes, are non-flexible straight tubes, which are always, if possible, preferred over flexible endoscopes due to their excellent image quality and sterility. They are more convenient for examining non-tubular structures, such as the abdominal cavity, thoracic cavity, etc.

[0005] Most endoscopes currently used in medical practice rely on white visible light, which is not very specific for detecting cancer or precancerous areas. For this reason, pathological areas that should be biopsied or removed during surgery can easily be missed by the operator, which can have very serious consequences for the patient. Inability to properly determine surgical margins can, for example, increase the likelihood of cancer recurrence and may require supplemental surgery and procedures.

[0006] Therefore, contrast enhancement technology is necessary to improve endoscopic systems.

[0007] Mueller polarization measurement imaging enhances contrast for cancer detection in various tissues.

[0008] The conventional Müller matrix of a sample acts on a 4x1 Stokes vector representing the incident polarization state entering the sample to create a transformed 4x1 Stokes vector representing the backscattered polarization state coming from the sample. This Müller matrix is ​​typically a 4x4 matrix with real coefficients representing the signature of the sample's complete polarization measurement response. In some cases, the Müller matrix under consideration may be an incomplete 3x3 matrix containing less information.

[0009] Therefore, Mueller polarization characterization of samples has been shown to enhance contrast for various biological tissues, providing polarization information that has proven useful in identifying pathological areas, such as precancerous and cancerous lesions.

[0010] Mueller polarization measurement relies on the use of a Polarization State Generator (PSG) and a Polarization State Analyzer (PSA).

[0011] The in vivo use of Müller polarization measurement reduces motion artifacts and is preferable for biomedical diagnostic applications, with a maximum range of several centimeters. 2To obtain a wide-field image, the system is required to be able to sequentially acquire at least 16 intensity images necessary to extract the complete Müller matrix of the target within approximately 2 seconds.

[0012] In conventional endoscopes, light is transmitted to the distal end of the endoscope by a bundle of optical fibers wrapped around an imaging channel, and both the imaging channel and the optical fibers are sealed within a stainless steel tubular body that can withstand pressurized sterilization. Illumination of the target through a PSG located in the proximal fiber port of the endoscope is not possible due to the depolarization effect of the fiber bundle. In most known systems, both the PSG and PSA are mounted at the distal end of the endoscope, which raises serious compactness and sterilization problems.

[0013] Several proposals have been made by Y. Fu et al. in the paper "Flexible 3x3 Mueller matrix endoscope prototype for cancer detection", IEEE Trans. Instrum. Meas. 67, (2018), or by J. Qi et al. in "Narrow band 3x3 Mueller polarimetric endoscopy", Biomed. Opt. Express 4, 2433-49 (2013), the latter of which relies on determining a 3x3 Mueller matrix.

[0014] Another proposed solution, disclosed by J. Qi et al. in "A high definition Mueller polarimetric endoscope for tissue characterization" Sci.Rep.6,25953 (2016), involves integrating the PSG components within a sheath surrounding the endoscope, with the sheath being rotated by a motor. This solution is impractical for clinical settings because the image acquisition becomes too slow due to the need to rotate the sheath. Furthermore, the mechanical movement destabilizes the system, making it difficult to use in medical practice.

[0015] International Publication No. 2018 / 126497 discloses an endoscopic system in which the distal end of the endoscope is equipped with a PSG and PSA having rotating components.

[0016] Japanese Patent Publication No. 2012-24252 discloses various endoscopic systems for Müller polarization measurement. In some systems, the imaging channel and illumination channel are separated and angled relative to each other, thus requiring two different introduction routes into the body. In some other systems disclosed in the application, polarized light is introduced from the proximal end of a single optical fiber, thereby limiting the intensity of the light illuminating the target. Some other systems use a single optical fiber for signal acquisition. Such systems enable temporally accurate polarization measurement. In practice, the use of a single optical fiber does not allow image creation until a scan is performed, which significantly increases the acquisition time for generating macroscopic images. To generate an image in less than 2 seconds (a time consistent with in vivo applications), the resulting image size becomes very small (~100 μm), making the image completely unusable for in vivo applications.

[0017] A single-mode silica optical fiber carries a very small amount of light. A multimode silica optical fiber allows for the transport of more light, but it has strong depolarization properties. A bundle of multimode silica optical fibers can allow for the transport of more light to the target. However, the space between individual fibers remains unused. These dead spots do not transmit the light, thereby significantly reducing the transmission efficiency of the bundle. Furthermore, the bundle can be damaged quite easily. Finally, it completely depolarizes the light being transported.

[0018] A paper by Arvid Linderg et al., published at the European Conference on Biomedical Optics on August 27, 2019, in Munich, Germany, entitled "Mueller polarimetric imaging through a rigid endoscope," discloses an experimental mechanism for Mueller polarization measurement characterization of the imaging channel of a conventional rigid endoscope. The PSG is positioned downstream of the optical guide and illuminates a sandblasted metal plate imaged by the endoscope.

[0019] U.S. Patent No. 5,608,834 discloses a liquid light guide for use in endoscopes. However, this patent makes no mention of the polarization measurement characteristics of the liquid light guide. [Overview of the Initiative] [Problems that the invention aims to solve]

[0020] The present invention aims to improve polarization measurement systems and to address at least some of the shortcomings of the prior art revealed above. [Means for solving the problem]

[0021] An exemplary embodiment of the present invention is a system for polarization measurement characterization of a target, Light is directed from the light source to the target (S). propagation A liquid light guide (LLG) is used to achieve this, Within the LLG propagation and a polarization state analyzer (PSA) that analyzes the polarization of the light reflected by the target, A polarization state generator (PSG) for modulating the polarization of the light injected into the LLG, At least one of the following, A photodetector for detecting light backscattered by the target illuminated by the LLG, The above-mentioned system is equipped with the above-mentioned features.

[0022] Such detection can be carried out for at least two different probe states of the PSA and / or PSG.

[0023] The present invention enables Mueller polarimetry and other polarimetry techniques, such as Stokes polarimetry and orthogonal state contrast (OSC), to be carried out depending on the application and the polarimetry parameters to be generated. The present invention enables the measurement of a 4×4 or 3×3 Mueller matrix. The present invention can use all or some (at least one) of the coefficients of the measured Mueller matrix as parameters of interest. The present invention may also use combinations of these parameters. From the measured Mueller matrix, other polarimetry parameters, such as depolarization index, purity index, entropy, etc., can be obtained.

[0024] The Mueller matrix can be decomposed to extract some polarimetry parameter, such as depolarization, phase retardation, or dichroism. Various decompositions of the Mueller matrix, such as, inter alia, Lu-Chipman decomposition, symmetric decomposition or inverse decomposition, can be used.

[0025] The number of different polarization probe states of the PSA and / or PSG is selected according to the type of polarization measurement detection selected and the polarization measurement parameters of interest.

[0026] By Mueller polarimetry characterization, it is meant the determination of at least the 3×3 coefficients of the Mueller matrix, more preferably the 4×4 coefficients of the complete Mueller matrix.

[0027] By Stokes polarimetry, it is meant the determination of Stokes parameters.

[0028] Compared to conventional silica optical fiber bundles, this LLG enables the transmission of light with higher intensity and spatial uniformity, which has proven advantageous for in vivo polarization measurements. Furthermore, the amount of light can be increased, thereby enabling the analysis of larger surfaces of the target.

[0029] Unlike a bundle of optical fibers, the LLG does not depolarize the light in a significant way. The use of the LLG enables: i) modulation of the polarization of the light near the proximal end of the LLG; and ii) efficient delivery of the polarized light to the surface of the object being examined near the distal end of the LLG, which is close to the surface of the object being examined, without the need to insert an internal optical system into the light path. When applied to endoscopic examinations, this makes it possible to obtain a compact endoscope.

[0030] The present invention also enables, if desired, access to all polarization measurement information of a biological sample by completely determining the 4x4 Müller matrix of the target under observation, and enables rapid multispectral Müller polarization measurement imaging of biological tissues with relatively low error, e.g., less than 1%.

[0031] Furthermore, the present invention eliminates the need for additional incisions for illumination, minimizes modifications to endoscopic surgery, and allows the use of standard endoscopic white light sources. The operating wavelength can be easily changed, for example, by modifying a band-pass filter located upstream of the photodetector. Using a 3CCD or 3CMOS camera coupled with a 3-band filter, polarization measurement images can be acquired at three different wavelengths, e.g., within the blue, green, and red portions of the visible spectral range. Using a specific 3CCD or 3CMOS camera, it is also possible to extend the spectral range of interest to near-infrared light up to approximately 1000 nm.

[0032] In some embodiments, the system includes a detection channel through which light propagates before reaching the photodetector, particularly a detection channel comprising an optical relay, such as a continuum of rod lenses, as in the case of a conventional rigid endoscope, or a detection channel made of a different LLG that serves to illuminate the target. The LLG may extend within a rigid tubular body, for example, made of stainless steel.

[0033] The detection channel may be an imaging channel, enabling the photodetector to capture an image of the target, in which case the photodetector is a camera.

[0034] In some embodiments, the LLG extends along the detection channel. The LLG may extend parallel to the detection channel for at least a portion of its length.

[0035] The detection channel may extend within a rigid housing, which preferably comprises a tubular body, preferably made of stainless steel, and preferably both the detection channel and the liquid light guide extend within it.

[0036] In particular, in the case of Müller polarization measurement, the system comprises a PSG through which light is injected into the LLG, and a PSA through which light reaches the photodetector.

[0037] In some embodiments, the light backscattered by the target is directly focused by the photodetector without propagating through a detection channel, such as an imaging channel in an endoscope, which includes an LLG or an optical relay, such as a continuum of rod lenses.

[0038] The system may include a band-pass filter to narrow the bandwidth of the light reaching the photodetector. The bandwidth is preferably 30 nm FWHM or less, more preferably 20 nm FWHM or less. The system may be configured to acquire light at two or more different wavelengths and to calculate Müller parameters or other polarization measurement parameters at those wavelengths.

[0039] The PSG and / or PSA preferably comprises ferroelectric liquid crystals. They allow for reduced acquisition time and a wide field of view. Other modulators, such as nematic liquid crystals and photoelastic modulators, may also be used, as will be described in detail below.

[0040] The polarization measurement system may include a control system for controlling the PSG and / or PSA, recording signals, particularly images, from the photodetector, and calculating the Stokes parameters, Mueller matrix, or OSC image of the target, and displaying the corresponding information.

[0041] The photodetector may be a monochromatic CCD or CMOS camera or a multichromatic camera, such as a 3CCD or 3CMOS camera or a hyperspectral camera. The photodetector may also be a single photodiode or spectrometer.

[0042] A polarization measurement image may be displayed in which the brightness or color of each pixel represents the measured Müller matrix or the values ​​of the corresponding polarization measurement parameters, such as depolarization, phase lag, or dichroism, or all other possible polarization measurement parameters, or combinations thereof. The image may be displayed as rows and / or columns. A histogram of the intensity, depolarization, phase lag, or dichroism, or combinations thereof, calculated for the whole or a part of the target may also be displayed. Various parameters, such as depolarization index, purity index, entropy, etc., can be extracted from the measured Müller matrix. By using different types of decomposition, other parameters, such as depolarization, phase lag, and dichroism, can be extracted from the measured Müller matrix.

[0043] The term "control system" should be understood in a broad sense, encompassing any data processing equipment configured to perform required operations and actions, such as a personal computer, microcomputer, field programmable gate array (FPGA), microcontroller, or dedicated electronic circuitry, and including any required control circuits or human-machine interfaces, such as a display, keyboard, or control buttons. This equipment may be local or remote, and some control or data processing may be performed via a communication channel, such as the internet or a mobile network.

[0044] The control system may operate a program to calculate the Müller matrix of the target or any other polarization measurement information based on the detected intensities for different polarization states of the PSG and / or PSA, and information obtained during the prior calibration of the polarization measurement system.

[0045] The control system can run a program to calculate various polarization parameters based on the Müller matrix of the target by using various data processing techniques (such as Müller matrix decomposition, machine learning algorithms, and adaptive polarization measurement). The polarization measurement information can be calculated for each pixel of a digital image, and an array of images can be displayed simultaneously, with each image having corresponding polarization measurement information.

[0046] An exemplary embodiment of the present invention is a method for polarimetric characterization of a target, particularly in vivo characterization of tissue, using a system according to the present invention as defined above, Illuminating the target via LLG, The light reflected by the illuminated target is collected by a photodetector. Selecting at least one probe state of PSA and PSG and controlling the PSA to analyze at least two different states of polarization of the light reflected by the target and guided to the photodetector, and / or controlling the PSG to illuminate the target in at least two different states of polarization and analyze the light reflected by the target, and To calculate at least one polarization measurement parameter of the target from the corresponding light intensity measured by the detector. Regarding the above methods, including

[0047] The detection can be performed at one or more wavelengths, preferably at three wavelengths using a 3CCD or 3CMOS camera.

[0048] The detection may be performed by a detection channel created by an LLG separate from the LLG that illuminates the target, or by an imaging channel comprising an optical relay, such as a continuum of rod lenses in a rigid endoscope.

[0049] The method may include illuminating the target with polarized light via a PSG through which light is injected into the LLG, and modulating the polarization state of the injected light.

[0050] The method is, To illuminate the target by sequentially passing different polarization probe states generated by the PSG, where the polarized light propagates within the LLG. The illuminated target is then analyzed through the PSA, and the corresponding intensity signal, particularly the intensity image, is recorded for each generator probe state and analyzer probe state. Based on the recorded intensity signal and the knowledge of the polarization measurement characteristics of the system obtained during the prior calibration of the system, the Müller matrix of the target being observed is determined.

[0051]

number

[0052] During calibration of the system, the surface under observation may be a uniformly diffusive, unpolished surface, such as a metal sandblasted plate, as is (i.e., without the arrangement of additional optical components). The calibration may include arranging one or more polarizing optical elements in the path of light. For example, in the case of 4x4 Müller polarization measurement in particular, the calibration may include the sequential arrangement of at least three different polarizing optical elements, e.g., P0°, P90°, and L30°, at one or more positions, e.g., three different positions. These positions may include upstream of the LLG, the output of the LLG, or the input to the detection channel, and downstream of the detection channel. [Brief explanation of the drawing]

[0053] [Figure 1] Figure 1 shows a partial and schematic diagram of an example of a Müller polarimetric endoscope system manufactured according to the present invention. [Figure 2] Figure 2 shows a schematic cross-section of the system. [Figure 3] Figure 3 shows a partial, schematic axial cross-section of the detection channel. [Figure 4] Figure 4 is a schematic diagram of a first modified embodiment of the present invention. [Figure 5] Figure 5 is a schematic diagram of a second modified embodiment of the present invention. [Figure 6] Figure 6 is a schematic diagram of a third modified embodiment of the present invention. [Modes for carrying out the invention]

[0054] The system 1 shown in Figure 1 comprises a rigid housing 10 configured for introduction into the body of a human or animal to image a target S of tissue T.

[0055] The housing 10 may be 15 to 35 cm in length and may include a tubular body configured for introduction into the body of a human or animal.

[0056] The system 1 includes a detection channel extending inside the housing 10. This detection channel can be formed by a conventional endoscope 11.

[0057] The detection channel can be manufactured in a conventional manner using an optical relay, preferably made from a continuum of rod lenses 17, as shown in Figure 3. The design of the detection channel may be based on the design of Hopkins rod lenses, which consist of a continuum of lenses characterized by the diameter and length of each lens being greater than the isolation distance.

[0058] The detection channel may be equipped with an eyepiece near its proximal end and an objective lens near its distal end. The objective lens forms an image of the target, which is transmitted to the proximal end by an optical relay system. The focal plane of the eyepiece may coincide with the image plane of the optical relay, so that light rays exit the eyepiece parallel to each other, creating the image of the target at infinity.

[0059] The structure of the endoscope 11 is identical or similar to that of a laparoscope commercialized by Karl Storz under designation 26003 AA, for example.

[0060] The endoscope 11 may have a circular or nearly circular cross-section, as shown in Figure 2, and its diameter may be in the range of, for example, 2.5 to 10 mm.

[0061] In the modified example, the detection channel is directly integrated into the rigid housing 10 and is not part of the completed endoscope before being introduced into the housing 10.

[0062] The system 1 also includes an illumination channel that extends parallel to the detection channel inside the tubular body.

[0063] According to the present invention, the illumination channel is made from a liquid light guide (LLG) 15. The LLG may be identical or similar to a commercial liquid light guide, for example, one commercialized by Thorlabs under the designation LLG-04H, but the present invention is not limited to any particular type of LLG.

[0064] The LLG15 may have a circular or nearly circular cross-section and a diameter in the range of, for example, 2 to 8 mm.

[0065] The outer diameter D of the tubular body of the housing 10 is, for example, in the range of 10 to 20 mm, and preferably 12 mm or less.

[0066] The LLG15 is closed at its end in any suitable known manner.

[0067] The system 1 includes a digital camera 20 as a photodetector that receives light reflected by the surface S illuminated by the LLG 15.

[0068] The system 1 includes a light source 30 that provides light to be injected into the LLG 15.

[0069] A PSG40 is interposed between the light source 30 and the LLG15 in the light path, and a PSA41 is interposed between the endoscope 11 and the camera 20 in the light path.

[0070] The PSG40 and PSA41 are controlled directly or indirectly by a computer or any other suitable controller 50. This controller 50 may also be connected to the camera 20 to record and process images from the camera 20. The controller 50 enables synchronization between the switching of the PSG and PSA and the acquisition of intensity images by the camera.

[0071] The light source 30 may be a white light source, such as a xenon lamp, LED lamp, or halogen lamp, and light may be supplied from this light source to the PSG by a fiber bundle 31 or any other suitable optical system.

[0072] A monochromatic bandpass filter 22 may be interposed between the PSA 41 and the camera 20 in the path of the light, in which case the camera is monochromatic. Those skilled in the art may also use a 3CDD or 3CMOS camera and a 3-band filter.

[0073] The measurement can be performed at a given wavelength of 340 to 1000 nm, for example, 450 nm to 700 nm, by selecting the band-pass filter 22.

[0074] In an example using a monochromatic camera 20, the band-pass filter 22 is a filter with a center wavelength of 550 nm and a bandwidth of less than 30 nm FWHM. In another example, the filter 22 has a center wavelength of 532 nm with a spectral bandwidth of 10 nm FWMH. In yet another example, a 3-band filter is used with a 3CCD or 3CMOS camera.

[0075] The light from the output of the PSG40 is injected into the LLG15.

[0076] Various optics 43, such as a system of lenses, may be placed before and / or after the PSG in order to optimize the injection of light into the LLG and thereby improve the efficiency of light transmission.

[0077] The PSG40 and PSA41 are known in themselves and are electrically controlled. The PSG allows for the generation of four different states of polarization required by 4x4 Müller polarization measurements, and the PSA allows for the generation of four different configurations of analysis.

[0078] The PSG40 comprises, for example, a linear polarizer, a first electrically controllable liquid crystal cell, preferably a ferroelectric liquid crystal, a quarter-wave plate, and a second electrically controllable liquid crystal cell, preferably a ferroelectric liquid crystal, but other PSG configurations may be used. The four Stokes vectors corresponding to the four polarization states thus produced are independent,

[0079]

number

[0080] The PSA may comprise optical elements identical to those of the PSG, but arranged in reverse order with respect to the direction of light propagation. The Stokes vectors corresponding to the four polarization configurations by the PSA are:

[0081]

number

[0082] In Müller polarization measurements, the PSG temporally modulates the polarization of the light illuminating the target under observation by successively generating four independent probing polarization states. Each of the four polarization states generated by the PSG after interaction with the sample under observation is analyzed through the four consecutive polarization configurations of the PSA. In this way, at least 16 measurements are performed sequentially over a finite time interval and stacked into a matrix of actual values. This operation can be repeated multiple times to obtain a 16-component intensity matrix N times. This allows for improvement of the signal-to-noise ratio through an averaging method.

[0083] For each of the four polarization states generated by the PSG and analyzed through the polarization configuration of the PSA, intensity measurements are performed for each pixel of the camera in the imaging configuration.

[0084] The system is calibrated to take into account the polarization measurement characteristics of the optical components of the system, and more particularly, the polarization measurement characteristics of the LLG and the detection channel.

[0085] Calibration can be performed in a conventional manner by placing appropriate optical components after the PSG and before the PSA.

[0086] If you wish to describe in detail the polarization measurement characteristics of the LLG and the detection channel, they can be determined by measuring the Müller matrix of those characteristics in a Triple Step Eigenvalue Calibration Method (TS ECM) calibration process. Otherwise, the system can be directly calibrated in a Single Step Eigenvalue Calibration Method (SS ECM) calibration process. Both processes are described in detail below in this specification.

[0087] In such a process, a reflective surface S made from a sandblasted metal plate is positioned in front of the distal end of the imaging channel and oriented perpendicular to the longitudinal axis of the imaging channel.

[0088] If you want to obtain detailed information regarding the polarization measurement characteristics of the optical component, particularly the LLG15 or the imaging channel of the endoscope 11, you can use the three-step eigenvalue calibration method (TS ECM).

[0089] In this case, the first step consists of performing the measurement without inserting any optical components into the system 1.

[0090] In this case, the intensity matrix of the 16 components.

[0091]

number

[0092]

number

[0093]

number

[0094]

number

[0095] Several optical components, in particular a polarizer whose transmission axis is oriented at 0° with respect to the system's reference frame (P0°), a polarizer whose transmission axis is oriented at 90° with respect to the P0° transmission axis (P90°), and a waveplate whose neutral axis is oriented at 30° with respect to the P0° transmission axis, are arranged in a continuous manner on C1.

[0096] In this case, the following formula

[0097]

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[0098]

number

[0099] Next, the optical components are arranged in a continuous manner on C2, and the following equation

[0100]

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[0101]

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[0102] Next, they are arranged in a continuous manner in C3, and the following equation

[0103]

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[0104]

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[0105] By multiplying equations (2) and (3) by the reciprocal of equation (1) on the left side, and equations (3) and (4) by the reciprocal of equation (1) on the right side, the following equations are obtained.

[0106]

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[0107]

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[0108]

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[0109]

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[0110] matrix

[0111]

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[0112]

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[0113]

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[0114]

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[0115]

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[0116]

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[0117] the matrix

[0118]

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[0119]

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[0120] matrix

[0121]

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[0122]

number

[0123] lastly,

[0124]

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[0125]

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[0126] In this way, the polarization measurement characteristics of the optical component of the system are characterized.

[0127] Target Müller matrix

[0128]

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[0129] next,

[0130]

number

[0131]

number

[0132] (13)

[0133]

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[0134]

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[0135]

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[0136]

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[0137] If detailed polarization measurement characterization of the LLG or the detection channel is not required, a single-step eigenvalue calibration method (SS EMS) can be used.

[0138] In this case, the first step consists of performing the measurement without inserting any optical components into the system 1.

[0139] In this case, the intensity matrix of 16 components in equation (1)

[0140]

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[0141]

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[0142] By multiplying equation (3) by the reciprocal of equation (1) on the left side, we can obtain equation (6).

[0143]

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[0144]

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[0145] Next, the matrix

[0146]

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[0147]

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[0148] Next, determined during calibration

[0149]

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[0150]

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[0151]

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[0152] Polarization measurement parameters, such as depolarization, phase lag, and dichroism, are measured using the Müller matrix, for example, by using the Lu-Chipman decomposition.

[0153]

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[0154] The present invention is not limited to the embodiments described above.

[0155] In a modified example where it is desired to measure a 3x3 Müller matrix, it is sufficient that the PSG generates three different probe polarization states and the PSA generates three different polarization probe configurations.

[0156] Each probe polarization generated by the PSG is analyzed through the three probe polarization configurations of the PSA over a total of nine intensity measurements.

[0157] In this case, system 1 can be calibrated using a slightly modified eigenvalue calibration method, as described in the paper by Ji Qi et al, Eigenvalue calibration method for 3x3 Mueller polarimeters, 2362 Vol 44, No.9 / 1 May 2019 Optics Letters.

[0158] In Stokes polarization measurement, the PSA is retained, while the PSG is replaced by a polarizer (straight line, circle, or ellipse). In the modified example, the PSG is retained, and the PSA is replaced by a polarizer (straight line, circle, or ellipse).

[0159] In the case of orthogonal state contrast (OSC) polarization measurement, the intensity measurement is parallel to the polarization state generated by the PSG.

[0160]

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[0161]

number

[0162]

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[0163]

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[0164] The strength of the OSC is obtained by the following formula.

[0165]

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[0166] The system 1 may include a second LLG 112 for focusing reflected light in place of the endoscope 11, as shown in Figure 4. The second LLG used to focus reflected light from the sample is different from the LLG used to illuminate the sample.

[0167] In this example, the camera is replaced with a photodiode detector 20 for rapid single-point detection. In this modification, there is no imaging of the target. Such a system is primarily useful for characterizing large areas of a target with spatially uniform polarization measurement characteristics.

[0168] The system shown in Figure 4 can be used for 4x4 or 3x3 Müller polarization measurements.

[0169] For calibration using S-ECM, a calibration optical component can be placed in front of the LLG112 of C.

[0170] In the example in Figure 5, the difference from Figure 4 is that there is no PSG, only a PSA41. Completely depolarized light can be injected into the LLG for Stokes polarization measurement.

[0171] Alternatively, in the case of OSC or Stokes polarization measurements, a polarizer (not shown), such as a linear, circular, or elliptical polarizer, can replace the PSG in order to inject polarized light into the LLG.

[0172] In Stokes polarization measurement, the PSA will take four probe states in succession. In OSC polarization measurement, the PSA will take two probe states in succession.

[0173] In a modified example (not shown), the configuration is the same as in Figure 5, except that the PSA is removed or replaced with a polarizer. The PSG is then reintroduced.

[0174] In the embodiment shown in Figure 6, reflected light propagates from the target to the PSA 41 without being guided by an LLG, or an endoscopic imaging channel with a rod lens, or another optical system, as described above. The target is illuminated by an LLG 15, which can be fixed to a mount 160 that holds its distal end. The mount may be movable and transported, for example, by an electric arm, allowing for changes in its azimuth angle about the optical axis z of the PSA 41, and / or changes in its distance from the target, and / or changes in its angle of incidence. Adapted optics (not shown) can be placed at the output of the LLG to obtain different sizes of rays illuminating the sample. Such embodiments can be used for in vivo and ex vivo polarization measurements, or for non-medical applications where there is room to move the LLG about the imaging axis. Obtaining the polarization measurement response as a function of the angle of incidence can serve to generate data for reconstructing the 3D structure of the target, for example. The embodiment shown in Figure 6 can be used for 4x4 Müller polarization measurement, 3x3 Müller polarization measurement, Stokes polarization measurement, or OSC polarization measurement.

[0175] In all embodiments described above, the PSG and PSA may be based on components other than ferroelectric liquid crystals, such as photoelastic modulators (PEMs) or nematic liquid crystals. The PSG and PSA may also be simplified to generate fewer than four polarization states, if possible, for example, a 3x3 Müller matrix, Stokes polarization measurement, or OSC. The PSG and PSA should preferably be fast enough to acquire an image in up to 2 seconds and should allow for a large field of view, making them ideal for in vivo applications.

[0176] The photodetector may also be a focal plane splitting polarization camera consisting of a micropolarizer array, such as the one commercialized by 4D Technology under the name PolarCam. In this case, the PSA can be simplified, as it no longer requires any polarizers and only requires a two-retarder configuration instead of the usual four to measure the 4x4 Müller matrix.

[0177] This invention can be used for polarization measurement characterization of targets other than human or animal tissue. It may be of interest in any application requiring an endoscope. This can encompass industrial applications where bulky optical components cannot be used or where remote inspection is required. The present invention may be configured as follows. [Section 1] A system (1) for polarization measurement characterization of a target (S), Light is directed from the light source (30) to the target (S). propagation A liquid light guide (LLG) (15) for this purpose, Within the LLG(15) propagation and a polarization state analyzer (PSA) (41) that analyzes the polarization of the light reflected by the target, A polarization state generator (PSG) (40) for modulating the polarization of the light injected into the LLG (15), At least one of the following, A photodetector (20) for detecting light backscattered by the target (S) illuminated by the LLG (15) and The system (1) is equipped with the following: [Section 2] Before the light reaches the photodetector propagation The system according to item 1, further comprising a detection channel, in particular an imaging channel having a continuum of rod lenses (17), or a detection channel made by a different LLG (112) that serves to illuminate the target. [Section 3] The system according to claim 2, wherein the LLG(15) and the detection channel are separate, the LLG extends along the detection channel, and preferably the LLG(15) extends parallel to the detection channel over at least a portion of its length. [Section 4] The system according to item 2 or 3, wherein the detection channel extends within a rigid endoscope (11). [Section 5] The system according to any one of claims 2 to 4, wherein the LLG and the detection channel extend within a rigid housing (10), the housing (10) preferably comprises a tubular body, preferably made of stainless steel. [Section 6] The system according to any one of claims 1 to 5, comprising both a PSG(40) through which light is injected into the LLG, and a PSA(41) through which light reaches the photodetector, wherein the PSG(40) and / or PSA(41) preferably comprise a ferroelectric liquid crystal. [Section 7] The light reflected by the target is transmitted through a detection channel comprising an LLG or an optical relay, such as a continuum of rod lenses. propagation The system according to item 1, wherein the light from the target is detected by the photodetector without causing any action. [Section 8] The system according to any one of claims 1 to 7, comprising a control system (50) for controlling the PSA (41) and / or PSG (40), recording signals from the photodetector (20), calculating the polarization measurement parameters and / or the Müller matrix of the target, and displaying the corresponding information. [Section 9] The system according to any one of claims 1 to 8, comprising a band-pass filter (22) or a three-band filter for narrowing the bandwidth of the light reaching the photodetector, wherein the bandwidth is preferably 30 nm or less, and preferably 20 nm or less. [Section 10] A method for characterizing the polarization of a target (S) using a system described in any one of items 1 to 9, particularly for generating a Müller matrix of the target, preferably a 4*4 Müller matrix, or for generating polarization measurement parameters of the target, Illuminating the target via the LLG(15), The light reflected by the illuminated target (S) is collected by the photodetector (20). Selecting at least one probe state of PSA(41) and PSG(40), controlling the PSA to analyze at least two different states of polarization of the light reflected by the target and guided to the photodetector, and / or controlling the PSG to illuminate the target in at least two different states of polarization and analyze the light reflected by the target, and To calculate at least one polarization measurement parameter of the target from the corresponding light intensity measured by the detector. The method, including the method described above. [Section 11] The method according to item 10, wherein the focusing of light is performed at one or more wavelengths, preferably at three wavelengths using a 3CCD or 3CMOS camera (20). [Section 12] The method according to claim 10 or 11, wherein the focusing of light is performed through a detection channel separate from the LLG(15), preferably an imaging channel comprising a continuum of rod lenses (17) in a rigid endoscope (11), or through an LLG(112) separate from the LLG(15) that serves to illuminate the target. [Section 13] The method according to any one of claims 10 to 12, comprising illuminating the target with polarized light via a PSG (40) through which light is injected into the LLG (15), and modulating the polarization state of the injected light. [Section 14] To illuminate the target by sequentially passing different polarization probe states generated by the PSG(40) over time, where the polarized light passes through the LLG(15) propagation do, The illuminated target is then analyzed through the PSA(41), and the corresponding intensity signal, particularly the intensity image, is recorded for each generator probe state and analyzer probe state. Based on the recorded intensity signal and the knowledge of the polarization measurement characteristics of the system obtained during the prior calibration of the system, the Müller matrix of the target being observed, M s、 To decide The method described in paragraph 13, including the method described in paragraph 13.

Claims

1. A system (1) for polarization measurement characterization of a target (S), A liquid light guide (LLG) (15) for propagating polarized light from a light source (30) to the target (S), A polarization state analyzer (PSA) (41) that propagates within the LLG (15) and analyzes the polarization of the polarized light reflected by the target, and A polarization state generator (PSG) (40) for modulating the polarization of light injected into the LLG (15), wherein light is injected into the LLG through the polarization state generator (PSG) (40), At least one of the following, A photodetector (20) for detecting light backscattered by the target (S) illuminated by the LLG (15) and The system (1) is equipped with the above.

2. The system according to claim 1, further comprising a detection channel that propagates before light reaches the photodetector, or a detection channel created by a different LLG (112) that serves to illuminate the target.

3. The system according to claim 2, wherein the LLG (15) and the detection channel are separate, and the LLG extends along the detection channel.

4. The system according to claim 2 or 3, wherein the detection channel extends within the rigid endoscope (11).

5. The system according to any one of claims 2 to 4, wherein the LLG (15) and the detection channel extend within a rigid housing (10).

6. The system according to any one of claims 1 to 5, comprising both a PSG (40) through which light is injected into the LLG, and a PSA (41) through which light reaches the photodetector, the PSA (41) propagating within the LLG (15) and performing the function of analyzing the polarization of light reflected by the target.

7. The system according to claim 1, wherein the light reflected by the target is detected by the photodetector without propagating the light through a detection channel equipped with an LLG or optical relay.

8. The system according to any one of claims 1 to 7, further comprising a control system (50) for controlling the PSA (41) and / or PSG (40), recording signals from the photodetector (20), calculating the polarization measurement parameters and / or Müller matrix of the target, and displaying the corresponding information.

9. The system according to any one of claims 1 to 8, further comprising a band-pass filter (22) or a three-band filter for narrowing the bandwidth of the light reaching the photodetector.

10. A method for controlling the system according to claim 8 for characterizing the polarization of a target (S), The photodetector (20) collects light reflected by the target (S) which is illuminated by polarized light via the LLG (15). The control system (50) controls the PSA to analyze at least two different states of polarization of the light reflected by the target and guided to the photodetector, and / or the control system (50) controls the PSG to illuminate the target in at least two different states of polarization, and the PSA analyzes the light reflected by the target, and The control system (50) calculates at least one polarization measurement parameter of the target from the corresponding light intensity measured by the detector. The method, including the method described above.

11. The method according to claim 10, wherein the focusing of light is performed at one or more wavelengths.

12. The method according to claim 10 or 11, wherein the focusing of light is performed through a detection channel separate from the LLG (15), or through an LLG (112) separate from the LLG (15) that serves to illuminate the target.

13. The method according to any one of claims 10 to 12, wherein the control system (50) controls the PSG (40) to modulate the polarization state of the light injected into the LLG (15) and illuminating the target.

14. The PSG (40) generates different polarization probe states that are continuous in time, where the polarized light illuminating the target propagates within the LLG (15). The control system (50) analyzes the illuminated target through the PSA (41), and the control system (50) records the corresponding intensity signal for each generator probe state and analyzer probe state. The control system (50), based on the recorded intensity signal and the knowledge of the polarization measurement characteristics of the system obtained during the prior calibration of the system, determines the Müller matrix of the target being observed, M s、 To decide The method according to claim 13, including the method described in claim 13.

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