Device and method for non-invasive optical imaging and positioning through scattering media

Abstract

A device for non-invasive optical imaging and positioning through a scattering medium, comprising a scattering medium layer, an aperture and a CCD camera, wherein the aperture is located between the scattering medium layer and the CCD camera and is in close contact with the scattering medium layer, and the CCD camera can be used to identify the complete envelope of the intensity distribution of the scattered speckle pattern and the size of each speckle particle, and the object to be measured, the scattering medium layer, the aperture and the CCD camera are coaxial; and a method for non-invasive optical imaging and positioning. The present invention does not require any auxiliary means or information behind the scattering medium, is completely non-invasive, and can extract all information with a single exposure, and can perform real-time non-destructive optical imaging. It has a wide range of potential applications in optical imaging of biological tissues, fluorescence imaging, anti-terrorism monitoring, underwater scanning, etc.

Description

Technical Field

[0001] The invention belongs to the technical field of speckle autocorrelation imaging, and in particular relates to a device and method for performing optical imaging and positioning through a scattering medium. Background Art

[0002] When the light emitted by an object passes through a medium such as a shower curtain, frosted glass, or biological tissue, due to its internal non-uniformity, the light is scattered multiple times and the wavefront is completely randomized. What is obtained after passing through the medium is random speckle, and the point-to-point relationship in traditional imaging is destroyed. The direct consequence is that the object cannot be imaged, let alone located. In order to solve the problem of imaging through scattering media, researchers have proposed techniques such as optical phase conjugation, iterative wavefront shaping, scattering matrix measurement, speckle autocorrelation, and speckle deconvolution imaging to make full use of scattered light for imaging. Among them, optical phase conjugation, iterative wavefront shaping, scattering matrix measurement, and speckle deconvolution imaging all require the introduction of reference points or reference objects for pre-measurement, and real-time lossless imaging cannot be achieved. In the absence of auxiliary information, all of these methods can only identify the shape of an object, but cannot determine its position and actual size.

[0003] Speckle autocorrelation imaging technology has been a hot topic in recent years. Compared with other imaging technologies through scattering media, its advantages are simple structure, non-invasiveness, and single exposure for imaging. The basic device and principle of this technology are as follows: Figure 1 As shown in the figure, after the light emitted by the object passes through the scattering medium 2, speckles are formed on the CCD detection surface. In order to meet the requirements of ensemble average, the device arrangement often requires that the speckle field distribution is larger than the photosensitive surface of the CCD, so as to detect a uniform speckle envelope distribution. The autocorrelation of the speckle pattern is equal to the autocorrelation of the object. The image of the object is extracted from the speckle pattern using image extraction algorithms such as the GS algorithm and the HIO algorithm. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention proposes a device and method for optical imaging and positioning through a scattering medium. The scattering medium can be regarded as a combination of countless randomly arranged pinhole cameras, and the corresponding speckle is the superposition of a large number of center-shifted pinhole images. In pinhole imaging, the object and the image satisfy a geometric projection relationship. The random pinhole camera theory proves that there is also a projection relationship between the object, the scattering medium and the speckle, which provides a basis for the positioning of the object behind the scattering medium. Once the position of the object is determined, the scaling relationship between the object and the image can be calculated. The speckle autocorrelation imaging can be used to quickly identify the pattern of the object, and the absolute size of the object can be determined in combination with the scaling relationship.

[0005] The technical solution of the present invention is as follows:

[0006] A non-invasive optical imaging and positioning device through a scattering medium comprises a scattering medium layer, an aperture and a CCD camera, wherein the aperture is located between the scattering medium layer and the CCD camera and is in close contact with the scattering medium layer, the CCD camera can be used to identify the complete envelope of the intensity distribution of a scattered speckle pattern and the size of each speckle particle, and the object to be measured, the scattering medium layer, the aperture and the CCD camera are on the same optical axis.

[0007] The light emitted by the object is detected by the CCD camera after passing through the scattering medium. The pixel size of the camera must meet the sampling rate requirements, and the camera's photosensitive surface must be large enough to observe the envelope of the energy distribution.

[0008] A spectral filter and / or a polarization filter is also placed between the scattering medium layer and the CCD camera.

[0009] The aperture can be a real aperture or a virtual aperture. For example, when the spot size irradiated on the scattering medium is limited, the spot size determines the aperture diameter.

[0010] A method for non-invasive optical imaging and positioning through a scattering medium is characterized in that it comprises the following steps:

[0011] Step 1. Obtain the speckle pattern through a CCD camera. The camera area must be large enough to obtain the complete envelope of the speckle intensity distribution, and the pixels must be small enough to identify the speckle particles.

[0012] Step 2. Use the centroid positioning algorithm to calculate the position of the centroid of the entire speckle pattern. The centroid of the object is on the reverse extension line of the line connecting the speckle centroid and the center of the aperture.

[0013] Step 3. Take the tangential average of the intensity of the whole speckle to extract the intensity envelope, and then use the fitting function, such as the step function in the middle and the Gaussian function at the edge, to fit the intensity envelope, extract the sum of the width of the step function and the half-height width of the Gaussian function as the projection diameter, measure the diameter of the aperture and the image distance v, and calculate the object distance u using the geometric similarity relationship, so as to determine the position of the object in the three-dimensional space behind the scattering medium layer; then the magnification M = v / u and the 3D position of the object's center of mass can be known.

[0014] Step 4. Cut off the projection part in the middle of the speckle pattern, use the speckle autocorrelation imaging method to extract the image of the object, such as the GS or HIO algorithm, and combine the pixel size and magnification M to determine the actual size of the object, thus realizing the imaging, three-dimensional positioning and size of the object behind the scattering medium.

[0015] Compared with the prior art, the technical effect of the present invention is: no auxiliary means or information behind the scattering medium is required, it is completely non-invasive, and all information can be extracted with a single exposure, and real-time non-destructive optical imaging can be performed. In order to improve the accuracy of imaging positioning, the image distance and / or aperture size can be changed, and multiple measurements can be made to perform fitting positioning. The above method is not limited to scattering media and transmission modes, and the reflection mode of rough surfaces can also be applied. The method has a wide range of potential applications in optical imaging of biological tissues, fluorescence imaging, anti-terrorism monitoring, underwater scanning, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the structure of traditional speckle autocorrelation imaging.

[0017] Figure 2 This is a schematic diagram of the structure of the non-invasive optical imaging and positioning through the scattering medium of the present invention.

[0018] In the figure: 1-target object, 2-scattering medium layer, 3-CCD camera, 4-aperture, u-distance from target object to scattering medium layer, v1-distance from the back surface of scattering medium layer to camera, v2-distance from aperture to camera. DETAILED DESCRIPTION

[0019] The following is a detailed description of the embodiments of the present invention: This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

[0020] See also Figure 2 , Figure 2 It is a structural schematic diagram of non-invasive optical imaging and positioning through a scattering medium of the present invention. As shown in the figure, a device for non-invasive optical imaging and positioning through a scattering medium comprises a scattering medium layer 2, an aperture 4 and a CCD camera 3. The aperture 4 is located between the scattering medium layer 2 and the CCD camera 3 and is in close contact with the scattering medium layer 2. The CCD camera 3 can be used to identify the complete envelope of the intensity distribution of the scattered speckle pattern and the size of each speckle particle. The object to be measured, the scattering medium layer 2, the aperture 4 and the CCD camera 3 are on the same optical axis.

[0021] When the object distance is fixed, it is necessary to adjust the appropriate image distance and aperture diameter.

[0022] A method for non-invasive optical imaging and positioning through a scattering medium comprises the following steps:

[0023] Step 1. Obtain the speckle pattern through a CCD camera. The camera area must be large enough to obtain the complete envelope of the speckle intensity distribution, and the pixels must be small enough to identify the speckle particles.

[0024] Step 2. Use the centroid positioning algorithm to calculate the position of the centroid of the entire speckle pattern. The centroid of the object is on the reverse extension line of the line connecting the speckle centroid and the center of the aperture.

[0025] Step 3. Take tangential average of the intensity of the whole speckle to extract the intensity envelope, and then use the matching function, such as the step function in the middle and the Gaussian function at the edge, to fit the intensity envelope, extract the sum of the width of the step function and the half-height width of the Gaussian function as the projection diameter, measure the diameter of the aperture and the image distance v, and calculate the object distance u using the geometric similarity relationship, so as to determine the position of the object in the three-dimensional space behind the scattering medium layer;

[0026] Step 4. Cut off the projection part in the middle of the speckle pattern, use the GS or HIO algorithm to extract the image of the object, and determine the actual size of the object by combining the pixel size and magnification.

Claims

1. A method for realizing optical imaging and positioning using a non-invasive optical imaging and positioning device that transmits a scattering medium, the device comprising a scattering medium layer (2), an aperture (4) and a CCD camera (3), the aperture (4) being located between the scattering medium layer (2) and the CCD camera (3) and being in close contact with the scattering medium layer (2), the CCD camera (3) being capable of identifying the complete envelope of the intensity distribution of a scattered speckle pattern and the size of each speckle particle, the object to be measured, the scattering medium layer (2), the aperture (4) and the CCD camera (3) being coaxial; characterized in that: The steps include: Step 1. Obtain the speckle pattern through a CCD camera. The camera area must be large enough to obtain the complete envelope of the speckle intensity distribution, and the pixels must be small enough to identify the speckle particles. Step 2. Use the centroid positioning algorithm to calculate the position of the centroid of the entire speckle pattern. The centroid of the object is on the reverse extension line of the line connecting the speckle centroid and the center of the aperture. Step 3. Take tangential average of the intensity of the whole speckle to extract the intensity envelope, and then use the matching function, such as the step function in the middle and the Gaussian function at the edge, to fit the intensity envelope, extract the sum of the width of the step function and the half-height width of the Gaussian function as the projection diameter, measure the diameter of the aperture and the image distance v, and calculate the object distance u using the geometric similarity relationship, so as to determine the position of the object in the three-dimensional space behind the scattering medium layer; Step 4. Cut off the projection part in the middle of the speckle pattern, use the GS or HIO algorithm to extract the image of the object, and determine the actual size of the object by combining the pixel size and magnification.

2. The optical imaging and positioning method according to claim 1, characterized in that: When the object distance is fixed, it is necessary to adjust the appropriate image distance and aperture diameter.

3. The optical imaging and positioning method according to claim 1 or 2, characterized in that: A spectral filter and / or a polarization filter is also placed between the scattering medium layer (2) and the CCD camera (3).

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