Optical coherence tomography sidelobe artifact suppression method

Abstract

An optical coherence tomography sidelobe artifact suppression method comprises the steps that in an optical coherence tomography system, Fourier transform of an interference spectrum is collected to serve as longitudinal intensity distribution to be processed, and phase lag and advanced longitudinal intensity distribution is obtained through Hilbert transform; and obtaining longitudinal intensity distribution of sidelobe artifact suppression by using weighted multiplication and root extraction. And finally, performing the operation on each column of interference spectrum to obtain an optical coherence tomography image with side lobe artifact suppression. According to the method, side lobe artifacts in OCT imaging are effectively inhibited, meanwhile, the width of a main lobe is reduced, the signal-to-noise ratio is increased, and images with higher quality are provided for biomedical research and clinical application. In addition, the method avoids the limitation of a traditional method, such as the problems of main lobe broadening and overhigh side lobe intensity caused by window function selection, possible amplification of high-frequency noise in a deconvolution reconstruction method and the like, and has a wide application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of image processing, and in particular relates to a method for suppressing sidelobe artifacts in optical coherence tomography. Background Art

[0002] Optical coherence tomography (OCT) is a non-invasive, high-resolution imaging technique that can obtain deep structural images of biological tissues and has been widely used in medicine, industry, and biomedical research. However, spectral leakage in optical coherence tomography can cause sidelobe artifacts in the axial point spread function (PSF), which usually appear as alternating light and dark lines extending along the axial direction of the reflective surface. Sidelobe artifacts reduce the contrast of OCT images and confuse the reconstructed signals of adjacent samples with lower intensity.

[0003] Typically, the sidelobe artifact problem is solved by spectrum shaping in the spectral domain. Windowing the spectrum is the most widely used technique, which includes using Gaussian, Hamming, and Hanning window functions to correct the shape of the acquired spectrum in post-processing. Although these methods can effectively suppress sidelobes, spectrum shaping techniques reduce the resolution of the spectrum. At the same time, some researchers have proposed multi-window reconstruction techniques that can suppress sidelobe artifacts while ensuring axial resolution. However, the degree of sidelobe artifact suppression achieved by this technology is limited, and it is difficult to accurately remove sidelobe artifacts from OCT images containing complex structures.

[0004] In the image domain, since these sidelobe artifacts can be modeled as the convolution of the longitudinal reflectivity distribution of the sample and the axial PSF of the OCT system, if the axial PSF of the OCT system is known, deconvolution techniques can be used to suppress the generation of artifacts. Compared with spectral domain processing methods, these image-based reconstruction methods generally perform better sidelobe artifact suppression effects. However, these deconvolution methods rely on prior knowledge of the PSF, which requires numerical simulation or experimental measurement to obtain. In addition, when the image is severely corrupted by noise, the task of image sidelobe suppression becomes more challenging, and the deconvolution algorithm will amplify noise with similar shapes, which will have a negative impact on image recognition.

[0005] Therefore, how to effectively suppress sidelobe artifacts while maintaining image quality remains a key issue that needs to be urgently addressed in the current development of OCT technology. Summary of the invention

[0006] In order to overcome the defects of the above-mentioned prior art, the present invention provides an optical coherence tomography sidelobe artifact suppression method, which can effectively solve the balance between the axial resolution of frequency domain OCT and the sidelobe suppression effect, and does not require any measurement and a priori estimation of the system PSF.

[0007] The technical solution of the present invention is

[0008] An optical coherence tomography sidelobe artifact suppression method comprises the following steps:

[0009] (1) In an optical coherence tomography system, the Fourier transform result of the interference spectrum is collected as the intensity distribution Ir(z) to be processed;

[0010] (2) Using Hilport transform to process the intensity distribution Ir(z) to obtain the intensity distribution Iib(z) with a phase lag of π / 2 and the intensity distribution Iif(z) with a phase advance of π / 2;

[0011] (3) Using weighted multiplication, multiply the weighted sum of Ir(z) and Iif(z) by the weighted sum of Ir(z) and Iib(z) to obtain the product vector I to be processed 2 (z);

[0012] (4) For the product vector I 2 (z) Use the square root operation to obtain the real part real[I(z)] of the result I(z), which is the longitudinal intensity distribution of sidelobe artifact suppression;

[0013] The step (2) specifically comprises:

[0014] Directly apply Hilport transform to Ir(z) to obtain the intensity distribution Iib(z) with a phase lag of π / 2;

[0015] Arrange Ir(z) in reverse order to obtain Ir_rev(z), perform Hilbert transform on Ir_rev(z) to obtain the signal Ir_rev_h(z), and then arrange Ir_rev_h(z) in reverse order to obtain the intensity distribution Iif(z) with a phase advance of π / 2.

[0016] The step (3) specifically comprises:

[0017] Set the harmonic coefficient k to a constant between 0 and 1;

[0018] The weighted sum of the original intensity distribution Ir(z) and Iif(z) is solved as Ir(z)+k*Iif(z);

[0019] The weighted sum of the original intensity distribution Ir(z) and Iib(z) is solved as Ir(z)+k*Iib(z);

[0020] Solve for the product of two weighted sums I 2 (z) is [Ir(z)+k*Iif(z)]*[Ir(z)+k*Iib(z)].

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The axial intensity distribution after the frequency domain OCT Fourier transform is processed by using the strategy of phase modulation and conjugate multiplication, and the side lobe part in the point spread function is calculated as a negative value and an imaginary part; and the main lobe insensitive to phase modulation and conjugate multiplication is reconciled in the point spread function by weighted multiplication, so that the main lobe in the final calculated point spread function is narrower and the side lobe almost disappears. Compared with the method of adding windows to the interference spectrum, the method of the present invention avoids the trade-off between the widening of the main lobe and the excessive intensity of the side lobe when selecting the window function; compared with the deconvolution reconstruction method in the image domain, the present invention will not amplify the noise by identifying the high-frequency noise as the light source point spread function, and does not require any measurement and prior estimation of the frequency domain OCT system. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Flow chart of the optical coherence tomography sidelobe artifact suppression method of the present invention

[0024] Figure 2 This is the interference spectrum diagram collected by the embodiment

[0025] Figure 3 The longitudinal intensity distribution of the interference spectrum is obtained by Fourier transform without windowing.

[0026] Figure 4 is the result of Hilbert transform of the longitudinal intensity distribution in the embodiment

[0027] Figure 5 is the weighted multiplication product obtained in the embodiment

[0028] Figure 6 is the longitudinal intensity distribution of the sidelobe artifact suppression obtained in the embodiment DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with examples, but these examples should not be used to limit the scope of protection of the present invention.

[0030] See also Figure 1 , Figure 1 1 is a flow chart of the optical coherence tomography sidelobe artifact suppression method of the present invention. As shown in the figure, the optical coherence tomography sidelobe artifact suppression method comprises the following steps:

[0031] S1. Collecting the axial intensity distribution of OCT: In the optical coherence tomography system, the Fourier transform result of the interference spectrum is collected as the intensity distribution Ir(z) of the sample in the depth method (z axis).

[0032] In this embodiment, the light source scanning range is 1260-1360nm, the spectrum shape is flat-top type, and the collected interference spectrum length is 2048. Its shape and intensity are as follows Figure 2 As shown; the corresponding longitudinal intensity distribution is obtained by using Fourier transform without windowing as shown Figure 3 As shown, obvious side lobes can be seen.

[0033] S2. Apply Hilport transform to the collected intensity distribution Ir(z) to obtain the intensity distribution Iib(z) with a phase lag of π / 2 and the intensity distribution Iif(z) with a phase advance of π / 2, as shown in Figure 4 As shown, the solid line is Iif(z) and the dashed line is Iib(z). It can be seen that the side lobe part has shown the opposite rule. Specifically, the intensity distribution Ir(z) is reversed to obtain Ir_rev(z), and then the Hilbert transform is applied to Ir_rev(z) to obtain the signal Ir_rev_h(z), and then Ir_rev_h(z) is reversed to obtain the intensity distribution Iif(z) with a phase advance of π / 2.

[0034] S3. Perform weighted addition of the original intensity distribution Ir(z) and the intensity distribution Iif(z) with a phase advance of π / 2, and multiply it with the weighted addition of the original intensity distribution Ir(z) and the intensity distribution Iib(z) with a phase lag of π / 2 to obtain the product vector I 2 (z). Specifically, the harmonic coefficient k is set to a constant between 0 and 1, and the weighted sum of the original intensity distribution Ir(z) and the intensity distribution Iif(z) with a phase advance of π / 2 is Ir(z)+k*Iif(z), and the weighted sum of the original intensity distribution Ir(z) and the intensity distribution Iib(z) with a phase lag of π / 2 is Ir(z)+k*Iib(z). The product of the two weighted sums is I 2 (z) is [Ir(z)+k*Iif(z)]*[Ir(z)+k*Iib(z)].

[0035] In this embodiment, the coefficient k=1 is used, that is, the original intensity distribution and the phase-delayed or phase-advanced intensity distribution each account for half in the summation, and the product vector to be processed I 2 (z) Figure 5 As shown, it can be seen that the intensity of the main lobe is positive and the intensity of the side lobe is negative.

[0036] S4. The product vector I obtained in step S3 2 The square root operation is performed on I(z), and the real part real[I(z)] of the result I(z) is taken to obtain the longitudinal intensity distribution after sidelobe artifact suppression.

[0037] The intensity distribution of sidelobe artifact suppression obtained in this embodiment is as follows: Figure 6As shown, it can be seen that the side lobes are suppressed to almost disappear, while the main lobe intensity is consistent with the main lobe intensity of the original longitudinal intensity distribution, but the main lobe width is reduced. This phenomenon is characterized by improved axial resolution and improved signal-to-noise ratio in OCT images.

[0038] Finally, the above operation is performed on each column of the interference spectrum to obtain an optical coherence tomography image with sidelobe artifacts suppressed.

[0039] Compared with existing technologies, this method does not require any prior knowledge, has significant improvements in sidelobe suppression and reducing the main lobe width, and consumes very little computing resources, making it very suitable for deployment on computers and signal processing chips.

[0040] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principle and purpose of the present invention. The protection scope of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. Each implementation scheme within its scope shall be subject to the constraints of the present invention.

Claims

1. A method for suppressing sidelobe artifacts in optical coherence tomography, characterized in that: The following steps are involved: S1. In an optical coherence tomography system, collecting a Fourier transform result of an interference spectrum as an intensity distribution Ir(z) to be processed; S2. Processing the intensity distribution Ir(z) using Hilport transform to obtain an intensity distribution Iib(z) with a phase lag of π / 2 and an intensity distribution Iif(z) with a phase advance of π / 2; S3. Using weighted multiplication, multiply the weighted sum of the intensity distribution Ir(z) and the intensity distribution Iif(z) with a phase advance of π / 2 by the weighted sum of the intensity distribution Ir(z) and the intensity distribution Iib(z) with a phase lag of π / 2 to obtain a product vector I to be processed. 2 (z); S4. For the product vector I 2 (z) uses the square root operation and takes the real part real[I(z)] of the result I(z) to obtain the longitudinal intensity distribution with sidelobe artifact suppression.

2. The optical coherence tomography sidelobe artifact suppression method according to claim 1, characterized in that: Also includes: S5. Performing a logarithmic operation on the longitudinal intensity distribution real[I(z)] with sidelobe artifact suppression, obtains an OCT image with sidelobe artifact suppression.

3. The optical coherence tomography sidelobe artifact suppression method according to claim 1, characterized in that: The step S2 specifically includes: S2.1 Applying Hilport transformation to the intensity distribution Ir(z) to obtain an intensity distribution Iib(z) with a phase lag of π / 2; S2.2 After the intensity distribution Ir(z) is arranged in reverse order, a Hilbert transform signal is performed, and the obtained signal is arranged in reverse order again to obtain an intensity distribution Iif(z) with a phase advance of π / 2.

4. The optical coherence tomography sidelobe artifact suppression method according to claim 1, characterized in that: The step S3 specifically includes: S3.1 sets the harmonic coefficient k to a constant between 0 and 1; S3.2 solve the weighted sum of the intensity distribution Ir(z) and the intensity distribution Iif(z) with a phase advance of π / 2 as Ir(z)+k*Iif(z); S3.3 solve the weighted sum of the intensity distribution Ir(z) and the intensity distribution Iib(z) with a phase lag of π / 2 as Ir(z)+k*Iib(z); S3.4 Solving the Product of Two Weighted Sums I 2 (z) is [Ir(z)+k*Iif(z)]*[Ir(z)+k*Iib(z)].

5. The optical coherence tomography sidelobe artifact suppression method according to claim 4, characterized in that: The harmonic coefficient k used in the weighted multiplication is 1, that is, the original intensity distribution and the phase-delayed or phase-advanced intensity distribution each account for half in the addition.

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