A method for distortion correction of an OCT imaging system

Abstract

The application discloses an OCT imaging system distortion correction method, comprising the following steps: the first step, first, the components in the transformation matrix are obtained through a plane mirror, and the components in the transformation matrix are obtained through a distortion correction plate; the second step, then, the transformation matrix of original data in the direction and the transformation matrix of original data in the direction are obtained respectively; the third step, then, the total transformation matrix in the direction is obtained; the fourth step, finally, the distortion is corrected by resampling the original data according to the total transformation matrix in the direction. The method removes the distortion caused by the galvanometer scanning and system optical design, obtains the image information in the real scanning range, and unifies the phenomenon that the resolution of each pixel point in each direction is uneven due to the distortion.

Description

Technical Field

[0001] This invention relates to the technical field of distortion correction methods, and in particular to a distortion correction method for an OCT imaging system. Background Technology

[0002] Optical Coherence Tomography (OCT) is a non-contact, high-precision three-dimensional scanning imaging technique with numerous applications in medical and industrial inspection. This technology images a sample by measuring the back-reflected light at different depths. Specifically, each scanning point can image A points at that location. These A points are located at different depths of the sample, and this data of length A is called an Aline. Figure 1 As shown; then, by rotating galvanometers 1 and 2 to change the scanning position, the entire B×C region is scanned. Since A points can be obtained in each scan, a cube of size A×B×C can be obtained in the end. Through image algorithms, the corresponding three-dimensional scan image of the sample can be obtained.

[0003] Generally, due to the optical design and scanning method of the scanning galvanometer in the system, distortion will occur in all directions, meaning that the position of a certain point will change from... It will become Based on the direction of distortion, distortion can be classified according to the direction of light incidence. Distortion in the x and y directions, with the distortion in the direction of light incidence being... Distortion in the xy direction refers to distortion in the plane perpendicular to the direction of light incidence.

[0004] For optical design within a system, distortion is unavoidable. Figure 2 This is a simulated distribution of light spots on the image plane under equal scanning intervals. Based on the data... Figure 2 The light spots in the image are not uniformly distributed, that is, in There is optical distortion on the surface. Although this distortion is small, it is still best to eliminate it through correction for precise measurements.

[0005] For galvanometers, the distortion caused mainly comes from two aspects: one is due to the scanning path. Orientation distortion is caused by the scanning method on the other hand. Distortion of direction. Specifically, it manifests as: 1. The deflection angle of the galvanometer is controlled by voltage. The voltage and the deflection angle of the galvanometer are roughly linearly related. If the voltage of the galvanometer continuously cycles between [-v, v], the galvanometer will continuously scan back and forth between the deflection angle [-A, A]. Due to the limitation of the galvanometer's maximum operating frequency, when the galvanometer changes its scanning direction (i.e., turns around), it needs to gradually decelerate to 0 and then accelerate back to the scanning speed in the opposite direction. Therefore, when the galvanometer turns around, it will operate in the non-linear region. In this region, the number of scanned points remains the same, but the scanned area becomes smaller. Therefore, the image resolution in this region is different from that in the linear region. At this time, the image appears to produce a non-linear image. Distortion in direction.

[0006] II. This OCT imaging system uses two galvanometers to respectively... and The direction is scanned, and for each galvanometer, the light reflected from the galvanometer is not parallel but divergent in a fan shape, such as... Figure 3 As shown, this phenomenon results in the distribution of equipathic surfaces in actual space as curved surfaces (i.e., Figure 3 (dashed lines), which results in the final image being... Severe distortion occurred. Summary of the Invention

[0007] The present invention aims to solve at least one of the technical problems existing in the prior art.

[0008] Therefore, this invention proposes a distortion correction method for OCT imaging systems to remove distortions caused by galvanometer scanning and system optical design, thereby obtaining true image information within the scanning range and unifying the image. The phenomenon of uneven resolution of pixels caused by distortion in different directions.

[0009] According to an embodiment of the present invention, a distortion correction method for an OCT imaging system obtains the transformation matrix before and after distortion correction by measurement. Using the transformation matrix The original data is resampled to complete distortion correction, including the following steps: Step 1: First, obtain the transformation matrix using a plane mirror. The z-component in the image is transformed using a distortion correction plate to obtain the transformation matrix. xy components in; Step 2: Then, obtain the original data respectively. Direction transformation matrix and in Direction transformation matrix ; Step 3, next, obtain Total transformation matrix of directions ; Step 4, finally, by processing the raw data according to... Total transformation matrix of directions Resampling can correct distortion.

[0010] The beneficial effects of this invention are that the method is simple, requiring no complex optical-mechanical modeling to derive the image plane or ray distribution, and no calibration or measurement of relevant system parameters, making it highly operable; the method obtains the correction matrix... The entire data space can be quickly corrected, meeting the real-time requirements of the measurement site; digital correction eliminates the need for additional hardware, saving costs; the correction matrix of this method includes low-order and high-order aberrations caused by various factors, resulting in high accuracy.

[0011] According to an embodiment of the present invention, in the first step, obtaining The steps for componentization are: Step 1-1-1: Place a plane mirror sample near the focal plane and use an OCT device to image the plane mirror sample to obtain its curved image in three-dimensional space. Step 1-1-2: Determine the spatial distribution of the plane mirror surface by analyzing the light intensity distribution; Step 1-1-3, regarding this By performing polynomial fitting, the plane mirror's position can be obtained. Curved surface Mz in direction ; Step 1-1-4, and then obtain matrix Mz. ,in, This indicates that the plane mirror is in The depth of the direction, the matrix Mz That is, depth place Transformation matrix; Step 1-1-5: Change the position of the plane mirror using the displacement device. Direction position ,in, It is a positive integer greater than or equal to 1; use the same method as in step 1-1-4 to obtain the corresponding depth. Transformation matrix ; Step 1-1-6: Since light travels in a straight line, a series of... Transformation matrix Perform linear interpolation to obtain the values ​​for the entire region. Transformation matrix Mz .

[0012] According to one embodiment of the present invention, in step 1-1-2, as shown in formula (1): (1) In formula (1), each symbol represents the following meaning: This indicates that the image of a plane mirror sample formed in an OCT imaging system travels along the three-dimensional space. Distribution of directions; Indicates median filtering; Indicates obtaining The location of the maximum grayscale value in a direction can also represent the location of the maximum grayscale value on each Aline.

[0013] According to an embodiment of the present invention, in the first step, obtaining The steps for componentization are: Step 1-2-1: Place a distortion correction plate at the focal plane and image the distortion correction plate. Step 1-2-2: After removing uneven background light intensity from the image of the distortion correction plate obtained in step 1-2-1, the cross intersection points are extracted to obtain the coordinate matrix of each cross intersection point on the tangent plane of the 3D image of the distortion correction plate at the focal plane. The coordinate matrix It is the distortion correction matrix of that plane; Steps 1-2-3: Adjust the coordinate matrix Interpolation is performed to obtain a transformation matrix that corresponds to the actual number of pixels. That is, to obtain the depth of Direction transformation matrix ; Steps 1-2-4: Adjusting the distortion correction plate using a displacement device. Direction position ,in, It is a positive integer greater than or equal to 1; use the same method to obtain the corresponding depth. Transformation matrix ; Steps 1-2-5: Since light travels in a straight line, we can obtain a series of xy-axis transformation matrices. Perform linear interpolation to obtain the values ​​for the entire region. Transformation matrix .

[0014] According to one embodiment of the present invention, in step 1-2-1, the distortion correction plate is composed of equidistant, intersecting lines.

[0015] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention are realized and obtained through the structures particularly pointed out in the description and the drawings.

[0016] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of OCT three-dimensional scanning imaging; Figure 2 This is a schematic diagram of the distribution of light spots on the image plane in a Zemax simulation. Figure 3 This is a schematic diagram of galvanometer scanning; Figure 4 It is an OCT image of the plane mirror sample in the XY direction; Figure 5 It is an OCT image of the plane mirror sample in the XZ direction; Figure 6 It is an OCT image of the plane mirror sample in the YZ direction; Figure 7 It is a cross-sectional fitting image of the plane mirror sample in the XY direction; Figure 8 This is a schematic diagram of a distortion correction plate; Figure 9 It is the image of the distortion correction plate in the XY direction at the focal plane; Figure 10 These are the coordinates of the distortion correction points extracted from the distortion correction plate; Figure 11 This is the overall flowchart of the distortion correction of this invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] In the description of this invention, it should be understood that the terms "one side", "the other side", "both sides", "between", "middle", "upper end", "lower end", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0021] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "set" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0022] The following describes in detail, with reference to the accompanying drawings, an embodiment of the present invention for distortion correction of an OCT imaging system.

[0023] See Figures 3 to 11 The present invention provides a distortion correction method for an OCT imaging system, which obtains the transformation matrix before and after distortion correction by measurement. Using the transformation matrix The original data is resampled to complete distortion correction, including the following steps: Step 1: First, obtain the transformation matrix using a plane mirror. In The components are transformed using a distortion correction plate to obtain the transformation matrix. In The components are the transformation matrices obtained through a plane mirror and a distortion correction plate, respectively, using different methods. In Components and Quantity; Among them, obtaining The steps for componentization are: Step 1-1-1: Place a plane mirror sample near the focal plane and use an OCT device to image the plane mirror sample, obtaining its curved image in three-dimensional space. Its three views (sections) are as follows. Figure 4 , Figure 5 , Figure 6 As shown; Figure 4 The top view shows that the brightness distribution is uneven due to distortion, and the overall distribution presents a saddle shape. Figure 5 , Figure 6 The image is a side view of the sample, showing that the image in the plane mirror is distorted due to the scanning aberration of the galvanometer.

[0024] Step 1-1-2: Determine the spatial distribution of the plane mirror surface through the light intensity distribution, as shown in formula (1): (1) In formula (1), each symbol represents the following meaning: This indicates that the image of a plane mirror sample formed in an OCT imaging system travels along the three-dimensional space. Distribution of directions; Indicates median filtering; Indicates obtaining The location of the maximum grayscale value in a direction can also represent the location of the maximum grayscale value on each Aline.

[0025] Step 1-1-3, regarding this By performing polynomial fitting, the plane mirror's position can be obtained. Curved surface Mz in direction ,like Figure 7 As shown. In Figure 7 In the middle, the horizontal axis represents The direction is represented by pixels, ranging from 0 to 1000; the vertical coordinate represents... The direction is represented by pixels, ranging from 0 to 1000; the numerical representation... Depth in the direction, in pixels.

[0026] Step 1-1-4, and then obtain matrix Mz. ,in, This indicates that the plane mirror is in The depth of the direction, the matrix Mz That is, depth place Transformation matrix; Step 1-1-5: Change the position of the plane mirror using the displacement device. Direction position ,in, It is a positive integer greater than or equal to 1; use the same method as in step 1-1-4 to obtain the corresponding depth. Transformation matrix ; Step 1-1-6: Since light travels in a straight line, a series of... Transformation matrix Perform linear interpolation to obtain the values ​​for the entire region. Transformation matrix Mz .

[0027] in, The components will be obtained using a distortion correction plate. The steps for componentization are: Step 1-2-1: Place a distortion correction plate at the focal plane and image the distortion correction plate, such as... Figure 9 As shown; See Figure 8 A distortion correction plate with a period of 500µm is used. The plate consists of equidistant, interlaced lines. By measuring the offset of these equidistant lines after passing through the optical imaging system, the distortion correction of the OCT imaging system in that area can be obtained. Distortion within the plane; Step 1-2-2: After removing uneven background light intensity from the image of the distortion correction plate obtained in step 1-2-1 (i.e., the cross-section of the 3D image of the distortion correction plate at the focal plane), extract the cross intersection points to obtain the coordinate matrix of each cross intersection point on the cross-section of the 3D image of the distortion correction plate at the focal plane. ,like Figure 10 As shown in the figure, the position of the colored point is the coordinate of the cross intersection.

[0028] Since the coordinates of these points are equidistantly distributed in the actual coordinate space, the distortion causes the extracted coordinates to no longer be equidistantly distributed. Therefore, this coordinate matrix... It is the distortion correction matrix of that plane.

[0029] Steps 1-2-3: In order to correct every point in the plane, the coordinate matrix needs to be adjusted. Interpolation is performed to obtain a transformation matrix that corresponds to the actual number of pixels. That is, to obtain the depth of Direction transformation matrix ; Steps 1-2-4: Adjusting the distortion correction plate using a displacement device. Direction position ,in, It is a positive integer greater than or equal to 1; use the same method to obtain the corresponding depth. Transformation matrix ; Steps 1-2-5: Since light travels in a straight line, a series of... Transformation matrix Perform linear interpolation to obtain the values ​​for the entire region. Transformation matrix .

[0030] Step 2: Then, obtain the original data respectively. Direction transformation matrix and in Direction transformation matrix In other words, through step 1, we obtained... Transformation matrix and Transformation matrix .

[0031] Step 3, next, obtain Total transformation matrix of directions Through merger Transformation matrix and Transformation matrix ,available Overall transformation matrix in three directions .

[0032] Step 4, finally, by processing the raw data according to... Total transformation matrix of directions Resampling can correct distortion.

[0033] The distortion correction method for the OCT imaging system of this invention has a simple process, requiring no complex optical-mechanical modeling to derive the image plane or ray distribution, nor any calibration measurement of relevant system parameters, making it highly operable; this method obtains the correction matrix... The entire data space can be quickly corrected, meeting the real-time requirements of the measurement site; digital correction eliminates the need for additional hardware, saving costs; the correction matrix of this method includes low-order and high-order aberrations caused by various factors, resulting in high accuracy.

[0034] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A distortion correction method for an OCT imaging system, characterized in that, The transformation matrix before and after distortion correction was obtained by measurement. Using the transformation matrix The original data is resampled to complete distortion correction, including the following steps: Step 1: First, obtain the transformation matrix using a plane mirror. In The components are transformed using a distortion correction plate to obtain the transformation matrix. In Quantity; Get The steps for componentization are: Step 1-1-1: Place a plane mirror sample near the focal plane and use an OCT device to image the plane mirror sample to obtain its curved image in three-dimensional space. Step 1-1-2: Determine the spatial distribution of the plane mirror surface through the light intensity distribution, as shown in formula (1): (1) In formula (1), each symbol represents the following meaning: This indicates that the image of a plane mirror sample formed in an OCT imaging system travels along the three-dimensional space. Distribution of directions; Indicates median filtering; Indicates obtaining The location of the maximum grayscale value in a direction can also represent the location of the maximum grayscale value on each Aline; Step 1-1-3, regarding this By performing polynomial fitting, the plane mirror's position can be obtained. Curved surface Mz in direction ; Step 1-1-4, and then obtain matrix Mz. ,in, This indicates that the plane mirror is in The depth of the direction, the matrix Mz That is, depth place Transformation matrix; Step 1-1-5: Change the position of the plane mirror using the displacement device. Direction position ,in, It is a positive integer greater than or equal to 1; use the same method as in step 1-1-4 to obtain the corresponding depth. Transformation matrix ; Step 1-1-6: Since light travels in a straight line, a series of... Transformation matrix Perform linear interpolation to obtain the values ​​for the entire region. Transformation matrix Mz ; Get The steps for componentization are: Step 1-2-1: Place a distortion correction plate at the focal plane and image the distortion correction plate. Step 1-2-2: After removing uneven background light intensity from the image of the distortion correction plate obtained in step 1-2-1, the cross intersection points are extracted to obtain the coordinate matrix of each cross intersection point on the tangent plane of the 3D image of the distortion correction plate at the focal plane. The coordinate matrix It is the distortion correction matrix of that plane; Steps 1-2-3: Adjust the coordinate matrix Interpolation is performed to obtain a transformation matrix that corresponds to the actual number of pixels. That is, to obtain the depth of Direction transformation matrix ; Steps 1-2-4: Adjusting the distortion correction plate using a displacement device. Direction position ,in, It is a positive integer greater than or equal to 1; use the same method to obtain the corresponding depth. Transformation matrix ; Steps 1-2-5: Since light travels in a straight line, we can obtain a series of xy-axis transformation matrices. Perform linear interpolation to obtain the values ​​for the entire region. Transformation matrix ; Step 2: Then, obtain the original data respectively. Direction transformation matrix and in Direction transformation matrix ; Step 3, next, obtain Total transformation matrix of directions ; Step 4, finally, by processing the raw data according to... Total transformation matrix of directions Resampling can correct distortion.

2. The distortion correction method for an OCT imaging system according to claim 1, characterized in that: In step 1-2-1, the distortion correction plate is composed of equidistant, intersecting lines.

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