Optical coherence tomography image dislocation correction method based on galvanometer waveform iteration and position waveform acquisition device

Abstract

The invention relates to the technical field of image dislocation correction, in particular to an optical coherence tomography image dislocation correction method based on galvanometer waveform iteration and a position waveform acquisition device.The position waveform acquisition device comprises a scanning galvanometer and a reflecting mirror which is obliquely arranged and located below the scanning galvanometer; the scanning lens is arranged between the scanning galvanometer and the reflecting mirror, a forward scanning waveform is obtained through the device, and a forward scanning resampling curve is calculated; the original voltage waveform is sampled again according to the original voltage waveform, a new voltage waveform curve is obtained to serve as input of galvanometer motion, a new round of data acquisition is conducted to obtain a new position waveform, and the new position waveform is used for calculating the theoretical error correction image dislocation with the previous round of position waveform. According to the scheme, the inclined reflecting mirror is arranged, so that the plane position observation of the galvanometer is changed into easy-to-measure depth position information. The waveform curve is continuously iteratively scanned through a resampling technology, the gap with one-way scanning is reduced, and the overall level of the image is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of image misregistration correction, and particularly relates to an optical coherence tomography image misregistration correction method based on a galvanometer waveform iteration and a position waveform acquisition device. BACKGROUND

[0002] Optical coherence tomography (OCT) obtains one-dimensional depth information (referred to as A-scan) of a sample to be measured by measuring an autocorrelation function modulated by an optical structure (mainly refractive index distribution) of the sample to be measured. According to the Wiener-Sinai theorem, there is a Fourier transform relationship between the autocorrelation function of a random process signal and its power spectral density. Therefore, according to this property, OCT can be divided into two categories: (1) time domain OCT (TD-OCT) and frequency domain OCT (FD-OCT). The TD-OCT uses a method of mechanically moving a reference arm to obtain autocorrelation signals at different depths in the sample, and the A-scan rate is only KHz, which is not suitable for high-speed imaging applications. The FD-OCT directly measures the power spectral density (spectrum) of the imaging system using a spectrometer or a wavelength-tunable light source and then performs inverse Fourier transform to obtain the structure information of the sample at a high speed, and the A-scan rate can reach hundreds of KHz.

[0003] For point scanning OCT, there are currently two main methods, unidirectional scanning and bidirectional scanning. The unidirectional scanning adopts a sawtooth wave, and the scanning efficiency is low due to the return empty load. If the return is shortened in order to improve the scanning efficiency, it is easy to cause overheating of the galvanometer and other problems. The bidirectional scanning adopts a triangular wave, and the scanning efficiency is high, but the image misregistration problem of forward scanning and reverse scanning needs to be solved. SUMMARY

[0004] The technical problem to be solved by the present application is that the image misregistration problem occurs during bidirectional scanning of OCT, resulting in poor image scanning effect.

[0005] To this end, the present application provides an optical coherence tomography image misregistration correction method based on a galvanometer waveform iteration and a position waveform acquisition device.

[0006] The technical scheme adopted by the present application to solve the technical problem is: A position waveform acquisition device, comprising: a scanning galvanometer, and a mirror, the mirror being located below the scanning galvanometer, and the mirror being obliquely arranged. A scanning lens is arranged between the scanning galvanometer and the mirror, the collimated light is reflected by the scanning galvanometer and then passes through the scanning lens, and finally is emitted by the mirror.

[0007] Further, the mirror inclination angle θ is in the range of [30, 45].

[0008] Further, the scanning galvanometer swings around the O point, and a line between the O point and the optical center of the scanning lens is perpendicular to the collimated light incident direction.

[0009] An optical coherence tomography image misregistration correction method based on galvanometer waveform iteration, comprising the following steps: Step one, using the position waveform obtained by the position waveform acquisition device, obtain the forward scanning waveform to adjust the voltage waveform of the reverse scanning; Step two, calculate the resampling curve of the forward scanning; Step three, according to the obtained resampling curve, resample the original voltage waveform to obtain a new voltage waveform curve; Step four, use the voltage waveform curve obtained by resampling as the input of the galvanometer movement to perform a new round of data acquisition to obtain a new position waveform, and use the new position waveform to calculate the image misregistration correction image error correction image misregistration of the previous position waveform.

[0010] Further, in the step one, the coordinates δz of the image depth direction and the transverse coordinates δy of the forward scanning waveform are in a proportional relationship: δz=δy×tan(θ).

[0011] Further, in the step two, the right side intersection point of the curve contour is calculated for each sampling point of the forward scanning, the corresponding waveform under the new time sequence is obtained, and the new resampling curve is obtained.

[0012] The beneficial effects of the present application are that the present application changes the galvanometer plane position observation into the easily measured depth position information by arranging an inclined glass plate as a mirror. Through the resampling technology, the scanning waveform curve is iterated continuously until the error of the forward scanning and the reverse scanning does not exceed 0.5 pixels. This method not only improves the pixel misregistration of the image center, but also greatly relieves the image distortion of the edge. Without losing the scanning efficiency, the difference with the unidirectional scanning is reduced, and the overall image level is improved. BRIEF DESCRIPTION OF DRAWINGS

[0013] The present application will be further described below in combination with the drawings and examples.

[0014] Figure 1 It is a structure schematic view of the position waveform acquisition device in the present application.

[0015] Figure 2is the implementation flow chart of the optical coherence tomography image misalignment correction method based on the galvanometer waveform iteration in the application.

[0016] Figure 3 is the schematic diagram of the result of the waveform acquisition in the application.

[0017] Figure 4 is the schematic diagram of the resampling process in the application.

[0018] Figure 5 is the schematic diagram of the resampling curve in the application.

[0019] Figure 6 is the comparison diagram between the voltage waveform after resampling and the original voltage waveform in the application.

[0020] Figure 7 is the schematic diagram of the voltage waveform curve correction iteration process in the application.

[0021] Figure 8 is the comparison diagram between the image corrected by the optical coherence tomography image misalignment correction method based on the galvanometer waveform iteration in the application and the original identification image.

[0022] In the figure: 1, scanning galvanometer; 2, scanning lens; 3, mirror. DETAILED DESCRIPTION

[0023] The application will now be described in further detail with reference to the drawings. These drawings are simplified schematic diagrams, and only schematically show the basic structure of the application, and thus only show the configurations related to the application.

[0024] In the description of the application, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and thus cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus cannot be understood as limiting the application. In addition, the features defined as "first" and "second" can explicitly or implicitly include one or more of the features. In the description of the application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0025] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "linking" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0026] A position waveform acquisition device, comprising a mirror 3, a scanning lens 2 and a scanning galvanometer 1, the mirror 3, the scanning lens 2 and the scanning galvanometer 1 constitute a two-dimensional scanning galvanometer 1 system, the scanning lens 2 is arranged between the scanning galvanometer 1 and the mirror 3, the mirror 3 is arranged obliquely, the inclination angle of the mirror 3 is θ, referring to Figure 1 , the optical axis of the scanning lens 2 is arranged along the Z-axis direction.

[0027] The collimated light is reflected by the scanning galvanometer 1, then passes through the scanning lens 2, and finally exits through the mirror 3. It should be noted that the scanning galvanometer 1 swings around the O point, and the line between the O point and the optical center of the scanning lens 2 is perpendicular to the direction of the collimated light incidence.

[0028] The design of telecentric scanning makes the chief ray of the focused light beam passing through the scanning lens 2 at different deflection angles along the z-axis direction. In telecentric scanning, when the scanning mirror (such as a galvanometer or a MEMS scanning mirror) changes the angle, the light ray incident on the sample always remains parallel to the optical axis; that is, the position of the scanning point moves on the sample plane, but the light beam incidence angle does not change with the scanning angle.

[0029] The sample to be measured is replaced by a plane mirror 3 with an inclination angle θ, 30°≤θ≤45°, and the center point passes through the focal plane of the scanning lens 2. In this way, in the B-scan image composed of a certain number of A-scans (1000 A-scans in this case) in OCT, since the sample is placed at a certain inclination angle, we can replace the lateral coordinate δy with the image depth coordinate δz (in proportion) to realize quantitative description of the galvanometer motion, complete the extraction of the galvanometer waveform, and the horizontal coordinate is still time t (the camera is equally spaced). The image depth coordinate δz and its lateral coordinate δy are in a proportional relationship, δz=δy×tan(θ).

[0030] On the other hand, in the case of strict synchronization of the camera row trigger signal, the lateral coordinate δy and the time t are in a linear relationship, and since the longitudinal coordinate δz equivalently describes the lateral spatial position of the focal point, through this transformation, the t-δy curve of the position of the light beam focus point changing with time during forward and reverse scanning can be equivalently and quantitatively described by the δy-δz image curve of the mirror surface in the B-scan image.

[0031] A method for correcting optical coherence tomography image misalignment based on galvanometer waveform iteration includes the following steps: Step 1: Position Waveform Extraction The purpose of this step is to extract the waveform of the galvanometer's motion during the scanning process, such as... Figure 3 As shown, especially in the edge region, the galvanometer undergoes a process of deceleration followed by reverse acceleration.

[0032] Symmetry between forward and reverse scanning: The goals of forward and reverse scanning are centrally symmetrical, but due to the physical characteristics of the galvanometer itself (delay issues, edge nonlinearity), scanning in both directions is not a completely reversible process. To correct this deviation, we need to adjust the voltage waveform of the reverse scanning based on the actual position and shape of the forward scanning as a reference, so that the reverse scanning trajectory can be aligned with the forward scanning as much as possible.

[0033] Calculate symmetry: By calculating the difference between the reverse scan and the forward scan, a misalignment measure can be obtained, thereby determining the direction of waveform adjustment.

[0034] Step 2: Calculate the resampling curve In the forward scan time series, we obtain the position (i.e., position waveform) corresponding to each moment. For reverse scanning, the deviation at each moment (i.e., the difference in symmetry with forward scanning) is known. Therefore, we can use resampling techniques to adjust the waveform of reverse scanning to match the data at the forward scanning position.

[0035] Resampling involves re-interpolating the original waveform to obtain the corresponding waveform in the new time series. For each moment of the reverse scan, we can find a new moment corresponding to it, satisfying the symmetry of the forward and reverse scans (if the resampling result at that point is itself, it means that it has converged to the optimal point). Specifically, for any forward scan position A, there is a corresponding time point B (the two are centrally symmetrical in time), and the height difference between A and B represents the degree of image misalignment. Simultaneously, for position A, there is also a corresponding time point B' (the two are located at the same spatial position). The goal of resampling is to make the position of time point B as close as possible to time point B', achieving symmetry with A. Therefore, we only need to find the rightmost intersection point of the curves at the same height for each sampling point in the forward scan to obtain the new resampling curve.

[0036] Reference Figure 4 , 5 The forward scan portion remains unchanged (self-sampling, strictly linear), while the right side (reverse scan) is slightly adjusted (re-sampling, not strictly linear).

[0037] Step 3: Resample to obtain a new mirror voltage waveform Based on the obtained resampling curve, the original voltage waveform is resampled to obtain a new voltage waveform curve, such as... Figure 6 As shown.

[0038] Step 4: Iteration Process and Convergence Reference Figure 7 The resampled voltage waveform is used as input for the galvanometer motion in a new round of data acquisition. Based on the new position waveform, the theoretical error of the previous optimization can be calculated to indicate the effectiveness of the image misalignment optimization. When the theoretical error is less than 0.5 pixels, it indicates that the misalignment has been well corrected. Otherwise, the above steps are repeated until the error is within an acceptable range.

[0039] When the forward and reverse scans are perfectly symmetrical, the resampling curve is a perfect linear equation (y=x), converging to the theoretical optimum. However, for real physical systems, there are inherent fluctuations, so further optimization is impossible after a certain convergence. Experiments show that after three iterations, the overall error can be controlled to within 0.5 pixels. Figure 8 (a) shows the original recognized image, and (b) shows the image recognized after applying the optical coherence tomography image misalignment correction method based on galvanometer waveform iteration in this application. It can be seen that the image recognized after correction using the method of this application has clearer edges.

[0040] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined by the scope of the claims.

Claims

1. A position waveform acquisition apparatus characterized by comprising: The application relates to a scanning mirror (1) which reflects incident collimated light, a mirror (3) which is located below the scanning mirror (1) and is arranged at an angle, and a scanning lens (2) which is arranged between the scanning mirror (1) and the mirror (3) and through which the collimated light passes after being reflected by the scanning mirror (1) and finally exits through the mirror (3). The angle of the mirror (3) is in the range of [30, 45]. The scanning mirror (1) swings around the O point, and the line between the O point and the optical center of the scanning lens (2) is perpendicular to the direction of the incident collimated light. The application further relates to a method for adjusting the voltage waveform of a scanning mirror (1) which comprises the following steps:

2. The position waveform acquisition apparatus according to claim 1, characterized by Step one: obtaining a forward scanning waveform by using the position waveform obtained by the position waveform acquisition device according to any one of claims 1-3, so as to adjust the voltage waveform of reverse scanning; 3. The position waveform acquisition apparatus according to claim 1, characterized by Step two: calculating the resampling curve of forward scanning; 4. An optical coherence tomography image misregistration correction method based on a galvanometer waveform iteration, characterized by, Step three: resampling the original voltage waveform according to the obtained resampling curve to obtain a new voltage waveform curve; Step four: using the voltage waveform curve obtained by resampling as the input of the movement of the scanning mirror to perform a new round of data acquisition to obtain a new position waveform, and using the new position waveform to calculate the image displacement correction diagram of the theoretical error of the previous round of position waveforms. In the step one, the coordinate dz of the image depth direction and the transverse coordinate dy in the forward scanning waveform are in a proportional relationship: dz = dy x tan (theta). In the step two, the right intersection point of the curve contour is calculated for each sampling point of the forward scanning, the corresponding waveform under the new time sequence is obtained, and the new resampling curve is obtained. ​ 5. The optical coherence tomography image misalignment correction method based on galvanometer waveform iteration according to claim 4, characterized in that, ​ 6. The optical coherence tomography image misalignment correction method based on galvanometer waveform iteration according to claim 4, characterized in that, ​

Images