A full-range optical coherence tomography system and method

Abstract

The present invention discloses a full-range optical coherence tomography (OCT) system and method. Using a frequency-domain optical coherence tomography (OCT) system based on a Michelson interferometer, a transparent film with a continuous thickness difference is placed between the imaging objective lens and the sample to be measured in the sample arm. A Galvo scanning galvanometer scans along a one-dimensional direction to obtain a B-scan image. The optical path difference introduced by the film thickness difference can lead to a stable phase difference along the scanning direction, thereby generating a carrier frequency along that direction. Further processing can eliminate the mirror image generated by Fourier transform. This method aims to increase the imaging depth of OCT and obtain a higher signal-to-noise ratio by embedding films of equal thickness. It has the characteristics of simplicity, reliability, strong applicability, and low cost.

Description

Technical Field

[0001] The present invention relates to a full-range optical coherence tomography system and method, and in particular to a full-range optical coherence tomography system and method with strong applicability and effective elimination of mirror images and overlapping images, belonging to the field of bio-optical imaging. Background Art

[0002] Optical coherence tomography (OCT), based on the Michelson interferometer system, utilizes the principle of low-coherence light interference. It is a contactless, non-invasive, fast, and high-resolution real-time 2D and 3D imaging technology. It typically uses a broad near-infrared spectrum as a light source and can be broadly categorized into time-domain OCT and frequency-domain OCT. Frequency-domain OCT, due to its advantages such as faster speed and higher signal-to-noise ratio, is widely used for imaging the human eye, such as the cornea and retina. With its rapid development, it has also been applied to other tissues such as the skin and eardrum. From theoretical experiments to commercial medical devices, OCT has rapidly developed over the past three decades, making significant contributions to the early diagnosis of diseases such as macular degeneration, diabetes, glaucoma, and cataracts. In OCT systems, imaging depth and signal-to-noise ratio are two key parameters crucial to image quality. The signal-to-noise ratio is highest near the zero optical path difference of the interferometer. Therefore, if the zero optical path difference can be moved into the sample, even better quality OCT images can be obtained. However, due to the imaging symmetry caused by the Fourier transform, mirror twin images are generated, causing the positive and negative images to overlap, making it impossible to obtain a true and valid image. Usually, the sample to be tested is placed in a direction with zero optical path difference to avoid the error caused by the overlap of mirror images, but this also reduces the imaging signal-to-noise ratio.

[0003] In order to solve the above problems and improve the signal-to-noise ratio and imaging depth of OCT imaging, researchers have proposed a full-scale OCT technology based on carrier frequency extraction. For example, Japanese scientist Yoshiaki Yasuno proposed a method of synchronously controlling Galvo scanning and reference mirror movement. When the sample arm scans different points, the reference mirror moves longitudinally at the same time, so that the phase difference and carrier frequency along the scanning direction can be generated. Although this method can effectively achieve full-scale OCT imaging, it requires the use of high-precision piezoelectric ceramic devices and precise synchronous control, which greatly increases the cost and complexity of the system. Bernhard Baumann and Wang Ruikang offset the incident light beam of the sample arm from the center of the scanning galvanometer to form an optical path difference offset. As the galvanometer scans in one dimension, an interference phase difference will be generated, thereby achieving full-scale OCT reconstruction. However, their method requires moving the position of the incident light beam and changing the internal structure of the system, which reduces its practicality. In short, the existing full-scale OCT imaging methods still have defects such as poor applicability and increased system complexity.

[0004] With the rapid development of OCT in the medical device field both domestically and internationally, it has become increasingly important in ophthalmic imaging. To improve the signal-to-noise ratio and imaging depth, the search for a more convenient, reliable, and adaptable full-range OCT imaging technology remains a pressing challenge both domestically and internationally. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a full-range optical coherence tomography system and method, which has the characteristics of strong applicability, effective elimination of mirror images and overlapping images, acquisition of full-range OCT images, and effective improvement of OCT imaging signal-to-noise ratio and imaging depth.

[0006] To solve the above technical problems, the present invention provides a full-range optical coherence tomography system. The innovation of the system is that collimating lenses are sequentially arranged along the direction of light beam propagation, facing the near-infrared laser light source. The collimating lenses transmit the light beam to the beam splitting prisms in the reference arm and the sample arm respectively.

[0007] The reference arm is a reference plane mirror arranged opposite to the light beam transmitted by the beam splitter prism;

[0008] The sample arm includes a Galvo scanning galvanometer and a diffraction grating, which are respectively arranged opposite to each other and transmit the light beam through the beam splitter prism. The light beam after passing through the Galvo scanning galvanometer passes through the imaging objective lens and a transparent film with continuous thickness difference in sequence and then directly hits the sample to be tested;

[0009] The reference beam on the reference arm and the sample beam on the sample arm return to their original paths and generate interference through the beam splitter prism. Then, the beams after passing through the diffraction grating pass through the focusing lens and reach the linear camera.

[0010] Preferably, at least one transparent film with the continuous thickness difference is provided between the Galvo scanning oscillator and the sample to be measured, and the transparent film with the continuous thickness difference introduces an interference phase difference along the scanning direction and generates a carrier frequency along the direction.

[0011] Preferably, the maximum beam diameter of the Galvo scanning oscillator is 10 mm; the transparent film with continuous thickness difference is a material that transmits near-infrared light with high efficiency and has continuous thickness variation.

[0012] Preferably, the imaging objective lens has an effective focal length of 36 mm, a working distance of 25.1 mm, and a lateral resolution of 13 μm.

[0013] Preferably, the near-infrared laser light source is a near-infrared broadband laser light source, the near-infrared broadband laser light source has a central wavelength of 1310 nm, a bandwidth of 85 nm, and an adjustable maximum light intensity of 12.5 mW.

[0014] Preferably, the diffraction grating, focusing mirror and linear camera constitute a spectrometer, the spectrometer has 2048 pixels, covers a wavelength of 1100 nm-1500 nm, has a bandwidth of 400 nm and a resolution of 0.20 nm;

[0015] The spectrometer collects interference information in real time and saves it as two-dimensional matrix data, wherein each column of data is the interference spectrum of a single point of the sample to be measured.

[0016] A full-range optical coherence tomography method, using the full-range optical coherence tomography system, comprises the following steps:

[0017] Step S1: Based on the principle of Michelson interferometer, a near-infrared laser light source transmits the light beam to the reference arm and sample arm respectively through a beam splitter prism. In the sample arm, a Galvo scanning mirror is used to scan the sample to be measured point by point. A transparent film with a continuous thickness difference is placed between the imaging lens and the sample to be measured, thereby introducing an interference phase difference along the scanning direction and generating a carrier frequency along this direction.

[0018] Step S2: The reference beam on the reference arm and the sample beam on the sample arm return to their original paths and interfere with each other through a beam splitter prism. The beams after passing through the diffraction grating are then focused by a focusing lens and directed to a linear camera. The interference information is collected in real time and saved as two-dimensional matrix data, where each column of data is the interference spectrum of a single point of the sample.

[0019] Step S3: Process the two-dimensional matrix data obtained in step S2. First, perform a horizontal one-dimensional Fourier transform on the two-dimensional matrix data, extract half of its spectral information through a window function, and then perform an inverse Fourier transform to obtain its complex spectral information. Finally, perform a vertical one-dimensional Fourier transform on the complex spectral information and extract the absolute value to eliminate the mirror twin image and reconstruct the full-scale OCT image.

[0020] Preferably, the window function in step S3 is a Tukey function.

[0021] The advantages of the present invention lie in the following: Utilizing a frequency-domain optical coherence tomography (OCT) system based on a Michelson interferometer, the present invention places a transparent film with a continuous thickness difference between the imaging objective lens and the sample to be measured in a sample arm. A Galvo scanning mirror scans the film in one dimension to acquire a B-scan image. The optical path difference introduced by the film thickness difference results in a stable phase difference along the scanning direction, thereby generating a carrier frequency along that direction. Further processing can eliminate the mirror images generated by Fourier transforms.

[0022] This invention utilizes a frequency-domain OCT system, inserting a thin film of uniformly varying thickness between the imaging objective lens and the sample to be measured, enabling full-range OCT imaging. This method is simple, reliable, and highly adaptable. This method does not require changes to the original OCT system structure or the addition of expensive optical or mechanical scanning components, reducing costs and improving practicality compared to other methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

[0024] Figure 1 It is a structural schematic diagram of an imaging system in a full-range optical coherence tomography imaging system and method of the present invention.

[0025] Figure 2 This is traditional OCT imaging.

[0026] Figure 3 It is a full-range OCT image in a full-range optical coherence tomography system and method of the present invention.

[0027] In the figure: 1-near-infrared laser light source, 2-collimating lens, 3-beam splitter prism, 4-reference plane mirror, 5-Galvo scanning galvanometer, 6-transparent film with continuous thickness difference, 7-sample to be measured, 8-diffraction grating, 9-linear camera, 10-imaging objective lens, 11-focusing lens. DETAILED DESCRIPTION

[0028] The full-range optical coherence tomography system of the present invention is sequentially provided with a collimating lens 2 arranged opposite to a near-infrared laser light source 1 along the direction of light beam advancement, and the light beam is transmitted to a beam splitter prism 3 on a reference arm and a sample arm respectively through the collimating lens 2; the reference arm is a reference plane mirror 4 arranged opposite to the light beam transmitted through the beam splitter prism 3; the sample arm includes a Galvo scanning galvanometer 5 and a diffraction grating 8 arranged opposite to the light beam transmitted through the beam splitter prism 3 respectively, and the light beam after passing through the Galvo scanning galvanometer 5 is sequentially passed through an imaging objective lens 10 and a transparent film 6 with a continuous thickness difference and then directly irradiated on a sample to be measured 7; the reference light beam on the reference arm and the sample light beam on the sample arm return to their original paths and generate interference through the beam splitter prism 3, and then the light beam after passing through the diffraction grating 8 is passed through a focusing lens 11 and then reaches a linear camera 9.

[0029] The present invention utilizes a frequency-domain optical coherence tomography (OCT) system based on a Michelson interferometer, places a transparent film with a continuous thickness difference between the imaging objective lens and the sample to be measured in the sample arm, and obtains a B-scan image by scanning along a one-dimensional direction through a Galvo scanning galvanometer. The optical path difference introduced by the film thickness difference can lead to a stable phase difference along the scanning direction, thereby generating a carrier frequency along this direction, and further processing can eliminate the mirror image generated by the Fourier transform. The present invention uses a frequency-domain OCT system to embed a film with uniformly varying thickness between the imaging objective lens 10 and the sample to be measured 7, thereby achieving full-range OCT imaging, which is simple, reliable, and highly applicable. The present invention does not require changing the original OCT system structure, nor does it require adding expensive optical and mechanical moving scanning devices. Compared with other methods, it reduces costs and has greater practicality.

[0030] At least one transparent film 6 with a continuous thickness variation is positioned between the Galvo scanning mirror 5 and the sample to be measured 7. This film 6 introduces an interference phase difference along the scanning direction and generates a carrier frequency along that direction. The Galvo scanning mirror 5 has a maximum beam diameter of 10 mm. The transparent film 6 is made of a material that efficiently transmits near-infrared light and has a continuously varying thickness.

[0031] The imaging objective lens 10 of the present invention has an effective focal length of 36 mm, a working distance of 25.1 mm, and a lateral resolution of 13 μm. The near-infrared laser light source 1 is a near-infrared broadband laser light source with a central wavelength of 1310 nm, a bandwidth of 85 nm, and an adjustable maximum light intensity of 12.5 mW.

[0032] The diffraction grating 8, focusing lens 11 and linear camera 9 of the present invention constitute a spectrometer, which has 2048 pixels, covers a wavelength of 1100 nm-1500 nm, has a bandwidth of 400 nm and a resolution of 0.20 nm;

[0033] The spectrometer collects interference information in real time and saves it as two-dimensional matrix data, where each column of data is the interference spectrum of 7 single points of the sample to be tested.

[0034] A full-range optical coherence tomography method comprises the following steps:

[0035] Step S1: Based on the principle of Michelson interferometer, a near-infrared laser light source 1 transmits the light beam to the reference arm and the sample arm respectively through a beam splitter prism 3. In the sample arm, a Galvo scanning mirror 5 scans the sample 7 point by point. A transparent film 6 with a continuous thickness difference is placed between the imaging lens and the sample 7 to introduce an interference phase difference along the scanning direction and generate a carrier frequency along this direction.

[0036] Step S2: The reference beam on the reference arm and the sample beam on the sample arm return to their original paths and interfere with each other through the beam splitter prism 3. The beams after passing through the diffraction grating 8 are then passed through the focusing lens 11 and then to the linear camera 9. The interference information is collected in real time and saved as two-dimensional matrix data, where each column of data is the interference spectrum of a single point of the sample.

[0037] Step S3: Process the two-dimensional matrix data obtained in step S2. First, perform a horizontal one-dimensional Fourier transform on the two-dimensional matrix data, extract half of its spectral information through a window function, and then perform an inverse Fourier transform to obtain its complex spectral information. Finally, perform a vertical one-dimensional Fourier transform on the complex spectral information and extract the absolute value to eliminate the mirror twin image and reconstruct the full-scale OCT image.

[0038] The specific implementation plan is:

[0039] This full-range optical coherence tomography method based on film thickness difference does not require additional expensive optical devices and mechanical scanning parts, nor does it require modifications to the frequency domain OCT system itself. It only requires placing a transparent film with continuously varying thickness between the imaging objective lens 10 and the sample to be measured 7 to produce a carrier frequency, thereby eliminating mirror twin images and realizing a full-range method that can improve the imaging depth of OCT. It has the characteristics of simplicity, reliability, strong applicability, and low cost.

[0040] The present invention uses a near-infrared SLD laser light source with a central wavelength of 1310 nm. It is incident on a beamsplitter prism 3 through a collimator. One beam propagates to a reference arm, and the other propagates to a Galvo scanning mirror 5. It is then reflected by an imaging objective lens 10 and transmitted through a thin film before reaching a sample to be measured 7. The reference and sample beams return along their original paths and interfere with each other. The interference spectrum information is collected and stored in real time by a spectrometer.

[0041] In the sample arm, a Galvo scanning mirror 5 scans the sample 7 point by point. A transparent film 6 with a continuous thickness difference is placed between the imaging lens and the sample 7, introducing an interference phase difference along the scanning direction and generating a carrier frequency along that direction. Finally, a spectrometer consisting of a diffraction grating 8, a focusing lens 11, and a linear camera 9 collects the interference information in real time and stores it as a two-dimensional matrix data set, where each column of data represents the interference spectrum of a single sample point.

[0042] First, a horizontal one-dimensional Fourier transform is performed on the two-dimensional matrix data. Half of the spectrum information is extracted using a window function (Tukey function). Then, a one-dimensional inverse Fourier transform is performed to obtain the complex spectrum information. Finally, a vertical one-dimensional Fourier transform is performed on the complex spectrum information and the absolute value is extracted to eliminate the mirror twin images and reconstruct the full-scale OCT image.

[0043] The main devices in the present invention include: a near-infrared light source with a central wavelength of 1310 nm, several collimating lenses 2, a dichroic prism 3, a reference mirror, a scanning galvanometer, a transparent film, a spectrometer and a computer. The SLD near-infrared light source used is the S5FC1021S series from Thorlabs, which has a bandwidth of 85 nm and a maximum adjustable light intensity of 12.5 mW. The optimal light intensity can be adjusted according to different samples 7 to be tested. The Galvo scanning galvanometer 5 is the GVS112 / M series, with a beam diameter of up to 10 mm, which can cover all wavelength ranges in this experiment. The imaging objective lens 10 is the LSM03 series from Thorlabs, with an effective focal length of 36 mm, a working distance of 25.1 mm, and a lateral resolution of up to 13 μm. The film is a material that can transmit near-infrared light with high efficiency and needs to have a continuous thickness change. The spectrometer is a Cobra 1300 series from Wasatch, with a total of 2048 pixels, covering a wavelength of 1100 nm to 1500 nm, a total bandwidth of 400 nm, and a spectrometer resolution of 0.20 nm.

[0044] The present invention is based on the principle of Michelson interferometer. It uses a wide-spectrum near-infrared laser light source 1, which transmits the light beam to the reference arm and the sample arm respectively through a beam splitter prism 3. In the sample arm, a Galvo scanning galvanometer 5 is used to scan the sample 7 to be measured point by point. A transparent film with continuously varying thickness is placed between the imaging objective lens 10 and the sample 7 to introduce an interference phase difference along the scanning direction and generate a carrier frequency along this direction. Finally, the interference spectrum information is collected by a spectrometer and saved as two-dimensional matrix data information. The system structure diagram is shown in FIG. Figure 1 shown.

[0045] Figure 2 Traditional OCT imaging has mirror images and overlapping images, which seriously affect the quality of OCT reconstruction. Figure 3 The full-range OCT image of the present invention is shown. The acquired two-dimensional matrix data undergoes a transverse one-dimensional Fourier transform, and half of the spectral information is extracted using a window function. This is then inversely Fourier transformed to obtain the complex spectral information. Finally, the full-range OCT image is reconstructed by performing a longitudinal one-dimensional Fourier transform on the complex spectral information. The imaging method of the present invention eliminates mirror twin images, acquires full-range OCT images, and effectively improves the OCT imaging signal-to-noise ratio and imaging depth. It is simple, reliable, highly applicable, and low-cost.

[0046] Of course, in this example, to effectively eliminate mirror twinning, the film thickness must be appropriately selected, along with factors such as scanning speed, scanning range, and scanning pixel count, to achieve the full-range OCT imaging described in this invention. Furthermore, since the film is used to alter the optical path difference (OPD), changes in refractive index can also be used to introduce OPD, suggesting that GRIN lenses may also be potentially applicable to this approach in the future.

[0047] It should be understood that the above description is for illustration and not for limitation. Many embodiments and many applications beyond the examples provided will be apparent to those skilled in the art upon reading the above description. Therefore, the scope of this application should not be determined with reference to the above description, but rather with reference to the appended claims and the full scope of equivalents to which such claims are entitled. For the purpose of comprehensiveness, all articles and references, including disclosures of patent applications and publications, are incorporated herein by reference. The omission of any aspect of the subject matter disclosed herein in the foregoing claims is not a disclaimer of such subject matter, nor should it be assumed that the inventors did not consider such subject matter to be part of the disclosed utility model subject matter.

Claims

1. A full-range optical coherence tomography system, characterized by: The full-range optical coherence tomography system is provided with collimating lenses arranged opposite to the near-infrared laser light source in sequence along the direction of light beam advancement, and the light beam is transmitted to the beam splitting prisms of the reference arm and the sample arm respectively through the collimating lenses; The reference arm is a reference plane mirror arranged opposite to the light beam transmitted by the beam splitter prism; The sample arm includes a Galvo scanning galvanometer and a diffraction grating, each of which is arranged opposite to a light beam transmitted through a beam splitter prism. The light beam after passing through the Galvo scanning galvanometer passes through an imaging objective lens and a transparent film with a continuous thickness difference in sequence before being directly projected onto a sample to be measured. At least one transparent film with a continuous thickness difference is disposed between the Galvo scanning galvanometer and the sample to be measured. The transparent film with a continuous thickness difference introduces an interference phase difference along a scanning direction and generates a carrier frequency along that direction. The Galvo scanning galvanometer has a maximum beam diameter of 10 mm. The transparent film with a continuous thickness difference is a material that efficiently transmits near-infrared light and has a continuous thickness variation. The reference beam on the reference arm and the sample beam on the sample arm return to their original paths and generate interference through the beam splitter prism. Then, the beams after passing through the diffraction grating pass through the focusing lens and reach the linear camera.

2. The full-range optical coherence tomography system according to claim 1, wherein: The imaging objective lens has an effective focal length of 36 mm, a working distance of 25.1 mm, and a lateral resolution of 13 μm.

3. The full-range optical coherence tomography system according to claim 1, wherein: The near-infrared laser light source is a near-infrared broadband laser light source with a central wavelength of 1310 nm, a bandwidth of 85 nm, and an adjustable maximum light intensity of 12.5 mW.

4. The full-range optical coherence tomography system according to claim 1, wherein: The diffraction grating, focusing mirror and linear camera constitute a spectrometer, which has 2048 pixels, covers a wavelength of 1100 nm-1500 nm, has a bandwidth of 400 nm and a resolution of 0.20 nm; The spectrometer collects interference information in real time and saves it as two-dimensional matrix data, wherein each column of data is the interference spectrum of a single point of the sample to be measured.

5. A full-range optical coherence tomography method, using a full-range optical coherence tomography system according to any one of claims 1 to 4, characterized in that The following steps are involved: Step S1: Based on the principle of Michelson interferometer, a near-infrared laser light source transmits the light beam to the reference arm and sample arm respectively through a beam splitter prism. In the sample arm, a Galvo scanning mirror is used to scan the sample to be measured point by point. A transparent film with a continuous thickness difference is placed between the imaging lens and the sample to be measured, thereby introducing an interference phase difference along the scanning direction and generating a carrier frequency along this direction. Step S2: The reference beam on the reference arm and the sample beam on the sample arm return to their original paths and interfere with each other through a beam splitter prism. The beams after passing through the diffraction grating are then focused by a focusing lens and directed to a linear camera. The interference information is collected in real time and saved as two-dimensional matrix data, where each column of data is the interference spectrum of a single point of the sample. Step S3: Process the two-dimensional matrix data obtained in step S2. First, perform a horizontal one-dimensional Fourier transform on the two-dimensional matrix data, extract half of its spectral information through a window function, and then perform an inverse Fourier transform to obtain its complex spectral information. Finally, perform a vertical one-dimensional Fourier transform on the complex spectral information and extract the absolute value to eliminate the mirror twin image and reconstruct the full-scale OCT image.

6. The full-range optical coherence tomography method according to claim 5, characterized in that: The window function in step S3 is the Tukey function.

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