CN112704470B - Spectrum-splitting frequency domain coherence tomography system - Google Patents
Spectrum-splitting frequency domain coherence tomography system Download PDFInfo
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Abstract
The invention discloses a spectral frequency domain coherence tomography system, which utilizes an adjustable filter to filter light waves output by a broad spectrum light source into a plurality of spectral spectrums with narrower bandwidths, respectively and sequentially inputs an interferometer based on a frequency domain optical coherence tomography system, and sequentially detects corresponding spectral interference signals; and through data post-processing, integrating the spectral interference signals into a synthesized interference signal in a phase alignment manner, and performing Fourier transform to obtain a sample tomographic image with higher resolution and higher signal-to-noise ratio for analyzing different depths of the object. Because the spectral output irradiates the sample with lower light intensity, the imaging system can avoid the sample damage or discomfort caused to the sample, and simultaneously can synthesize a plurality of lower light intensity original signals into an image with high signal-to-noise ratio through subsequent data processing, thereby improving the performance of spectral domain optical coherence tomography, and being easy for clinical transformation and application.
Description
Technical Field
The invention relates to the field of optical imaging, in particular to a spectral frequency domain coherence tomography system.
Background
Optical Coherence Tomography (OCT) is a tomographic imaging technique based on the principle of light interference, and uses the interference of a reference arm light and a sample arm light to detect reflected or scattered signals of light at different depths of a sample, thereby obtaining the tomographic structure information of the sample. OCT has been widely used in the field of ophthalmology and cardiovascular diagnosis in clinical practice, and has become the gold standard for diagnosis of ophthalmic diseases in particular. The currently mainstream OCT system is based on the Fourier Domain OCT (FDOCT) imaging principle. FDOCT is mainly classified into two types, one is spectral-Domain OCT (SDOCT), i.e., spectral-Domain OCT, in which the intensity of interference signals of different wavelengths or wave numbers is detected by a spectrometer at a detection end, and a sample tomographic image is further obtained by fourier transform. The other technique is Swept-Source OCT (SS OCT), which uses a fast Swept-Source to transform the input wavelength, thereby detecting the intensity of interference signals of different wavelengths or wave numbers, and further obtains a sample tomographic image through fourier transform. The SDOCT and the SSOCT are two different implementation forms of the FDOCT, the principle based on which is similar in nature is used for equivalently acquiring information of different depths of a sample by detecting interference signals with different wavelengths or wave numbers, and the mechanical position movement of a reference arm of a time domain OCT system is avoided, so that the imaging speed and the signal-to-noise ratio of an image are remarkably improved. The invention belongs to a new technology of SDOCT branching.
OCT is used for biomedical tissue imaging. Generally, in order to avoid damage to the imaged biomedical tissue, the OCT incident light intensity is controlled within a certain safety threshold. The light intensity safety threshold for maximum light incidence in OCT varies from application to application and from type to type of biological tissue being illuminated. In general, it is desirable to increase the incident light intensity as much as possible within a safe threshold because the signal-to-noise ratio of the image is directly and positively correlated with the incident light intensity. However, for certain clinical-specific applications, such as ophthalmic imaging, too strong incident light is likely to cause discomfort to the patient's eye. Although ophthalmic OCT generally employs near-infrared bands, such as those around 830nm or 1064nm, the patient's eye is not sensitive to near-infrared light intensity; however, OCT of visible light rapidly developed in recent years [ Xiao Shu et al, 'design visual-light optical coherence tomography logics', Quant Imaging Med Surg 2019; 769 (5) 769-781) the imaging technique uses the visible light band between 450-700nm, which causes discomfort to the eyes of the patient during imaging. Because OCT imaging needs eyes to keep still, and focus positioning is carried out by watching a certain target; the use of more sensitive visible light imaging makes it difficult for the patient to keep the eye still and in focus during imaging, which may be accompanied by eye movement, significantly affecting the imaging quality. It is therefore desirable that the incident light intensity is not too high in terms of patient comfort and avoidance of imaging artifacts, but this is in contrast to the clinical need to improve the image signal-to-noise ratio and image quality to obtain high-resolution images for disease diagnosis. The visible light OCT has a shorter wavelength, has a higher resolution than the current mainstream near-infrared light OCT, and can acquire blood flow and blood oxygen information required for diagnosing a number of major diseases while performing structural imaging because blood in a living body is more sensitive to absorption of visible light, so that the visible light OCT is a new imaging technology which is emerging at present and is generally seen in the field. However, the clinical transformation and application of visible light OCT is limited due to the inherent contradiction between the discomfort of imaging the diseased eye and the improvement of the image signal-to-noise ratio. Therefore, there is a need for a new technique that can make the OCT system obtain a high snr image with a low incident light intensity, not only can make the visible light OCT technique practical and further implement clinical transformation, but also can be used in any existing SDOCT system to enhance the snr and image quality of the image.
Disclosure of Invention
The invention aims to provide a spectral frequency domain coherence tomography system which can irradiate a sample with lower light intensity, avoid sample damage or discomfort to the sample, and simultaneously can synthesize a plurality of lower light intensity original signals into an image with high signal to noise ratio through subsequent data processing, thereby improving the performance and the practicability of spectral domain OCT (optical coherence tomography), particularly visible light OCT, and facilitating clinical transformation and application of related technologies.
In order to achieve the purpose, the invention discloses a spectral frequency domain coherence tomography system, which is characterized in that a wide spectrum light source used by OCT is externally connected with a wavelength tunable filter, light waves output by the wide spectrum light source are filtered into a plurality of spectral spectrums with narrower bandwidths, the spectral spectrums are respectively and sequentially input into an interferometer of the OCT system, and corresponding spectral spectrum interference signals are detected; and aligning the phases of the spectral interference signals through data post-processing, splicing the spectral interference signals into a synthesized interference signal, and finally obtaining the OCT image with higher resolution and higher signal-to-noise ratio for analyzing different depths of the object through Fourier transform.
The invention provides a spectral frequency domain coherence tomography system which mainly comprises a broad spectrum light source, an adjustable filter, a beam splitter, a plurality of polarization regulators for optical fiber polarization regulation, a plurality of lenses for focusing and collimation, a reference arm plane mirror, a sample arm scanning lens, a grating of a spectrometer part, a line scanning camera and other core elements. The imaging principle of the spectral frequency domain coherence tomography system is that light waves generated by a broad spectrum light source are output from an adjustable filter, and after the light waves are split by a light splitter, one path of light is led to a reference arm and is reflected by a plane mirror of the reference arm; the other light is directed to the sample arm, and the sample is illuminated by a scanning device, such as a scanning galvanometer or a motor, and the light reflected or scattered back from the sample interferes with the light wave reflected from the reference arm. The interference light wave is divided into components with different wavelengths through the grating, and after being focused by the lens, the components of the interference signals with different wavelengths are detected by the line scanning camera. When the tunable filter changes the output wavelength range, interference signals of different wavelength components passing through the grating are focused on pixels at different positions of the line scanning camera. Therefore, by sequentially changing the output of the tunable filter, interference signals in different wavelength ranges corresponding to different spectral spectrums, i.e., spectral spectrum interference signals, can be sequentially detected. And further carrying out data post-processing to match the phases of the interference signals in different wavelength ranges, and further splicing the interference signals into a synthesized interference signal to finally obtain a synthesized image. Compared with an image obtained by single spectral imaging, the synthetic image has higher resolution and higher signal-to-noise ratio.
An important component of the spectral frequency domain coherence tomography system is to splice spectral interference signals detected by a line scanning camera, i.e. interference signals of different wavelength ranges corresponding to different spectral spectrums, through frequency axes, after phase alignment, the synthesized interference signals are obtained by splicing. And further carrying out Fourier transform on the synthesized interference signal to obtain a synthesized high-resolution and high-signal-to-noise-ratio image. Preferably, an implementation method for phase-aligning and splicing the spectral interference signals into the synthetic interference signal can be implemented by the following steps: first, a single reflective element, such as a transparent glass plate, is placed outside the imaging range of the sample (e.g., sample depth position of 0-1mm, >1mm outside the sample imaging range), as allowed by the OCT system. Because the interference signals obtained by the OCT system contain the interference signals of samples with different depths (including the added single reflection element based on the frequency domain OCT imaging principle), the interference signals corresponding to the single reflection element can be separated by a time domain filtering or Fourier domain filtering method. And further carrying out Fourier transform on interference signals corresponding to the separated single reflection elements to obtain phases of different spectral interference signals, comparing and registering the phases, matching the phase of one spectral interference signal with the phase of the other spectral interference signal, and splicing the spectral interference signals into a synthesized interference signal. For other spectral interference signals, the synthesis can be performed step by step in the above manner.
According to the invention, by means of a spectrum spectral frequency domain coherence tomography technology, a spectrum interference signal obtained by irradiating a sample with a spectrum with lower light intensity is spliced through a frequency axis in a data post-processing process, and after phases are aligned, a synthesized interference signal is obtained by splicing; and further, a high-resolution and high-signal-to-noise-ratio synthetic image is obtained through Fourier transform, a practical method which is more friendly to sample imaging and can simultaneously obtain a high-signal-to-noise-ratio image is provided for the clinical application sensitive to light intensity, and the large-scale clinical application of spectral domain OCT (optical coherence tomography), particularly visible light OCT technology, is facilitated. The technology provided by the invention can also be used for splicing interference signals obtained by sequentially irradiating a sample by a plurality of independent spectral light sources, and a synthetic interference signal is obtained by splicing through frequency axis splicing and phase matching in the data post-processing process; further obtaining a synthetic image through Fourier transform; the resolution and signal-to-noise ratio of the composite image are significantly enhanced over images obtained from a single light source.
Drawings
FIG. 1 is a schematic diagram of a spectral spectrum frequency domain coherence tomography system provided by the present invention
FIG. 2 is a diagram of a conventional frequency-domain OCT system
FIG. 3 is a schematic diagram of the output of the spectrum of a broad spectrum light source through a tunable filter as a series of sub-spectral outputs
FIG. 4 is a method for splicing spectral interference signals into synthesized interference signals and obtaining a synthesized image
FIG. 5 is a method for splicing synthetic interference signals based on phase matching of interference signals corresponding to a single reflective element
FIG. 6 is a method for extracting and separating interference signals corresponding to single reflection elements from interference signals based on time-domain filtering
FIG. 7 is a Fourier domain filtering-based method for extracting and separating interference signals corresponding to single reflection elements from the interference signals
FIG. 8 is a schematic diagram of splicing a spectroscopic interference signal into a composite interference signal
FIG. 9 shows that the light intensity of the sample irradiated by the spectral output light wave is much less than the light intensity of the sample irradiated by the original broad spectrum light source
FIG. 10 is a spectral band coherence tomography system integrating multiple light sources of different wavelengths
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.
As shown in fig. 1, a spectral-domain coherence tomography system 50 provided by the present invention mainly includes a broad spectrum light source 1, an adjustable filter 21, a beam splitter 3, a polarization adjuster 4, a lens 5, a reference arm plane mirror 6, a sample arm scanning galvanometer 9, a grating 7 of a spectrometer part, a line scanning camera 8, and other core elements. The imaging principle of the spectral frequency domain coherence tomography system is that after light waves generated by a broad spectrum light source 1 are output from an adjustable filter 21 and split by a light splitter, one path of light is led to a reference arm and is reflected by a reference arm plane mirror 6 after being collimated by a lens 5; the other path of light is led to a sample arm and irradiates a sample through a scanning galvanometer 9, such as different positions of human eyes; light reflected or scattered back from the sample interferes with the light waves reflected from the reference arm. The polarization adjuster 4 in fig. 1 is used to adjust the polarization state of the light waves of the reference arm and the sample arm. The interference light waves are divided into different wavelength components by the grating, focused by the lens and detected by the line scanning camera 8. That is, the interference signal detected by the line scanning camera 8 is a component of the interference signal of different wavelengths. When the tunable filter 21 changes the output wavelength range, interference signals of different wavelength components passing through the grating are focused on pixels at different positions of the line scan camera. Therefore, by sequentially changing the output of the tunable filter 21, interference signals of different wavelength ranges corresponding to different spectral spectrums, i.e., the spectral interference signal 31, can be sequentially detected. Further, through data post-processing, the interference signals in different wavelength ranges are sequentially subjected to frequency axis splicing 32 and phase alignment 33, and further spliced into a composite interference signal 34, and the composite interference signal 34 is sequentially subjected to spectrum shaping 35 and Fourier transform 42, so that a synthesized image 36 is finally obtained. The synthesized image 36 has a higher resolution and a higher signal-to-noise ratio than images obtained by single spectral imaging.
As shown in fig. 1, a key component of the spectral frequency domain coherence tomography system 50 is the tunable filter 21. Preferably, the output wavelength (or frequency) of the tunable filter 21 can be dynamically adjusted in real time by using a control software running on a computer, and using USB or internet or bluetooth or other communication control methods. In the spectral-domain coherence tomography system, the tunable filter 21 filters the light waves output from the broad-spectrum light source 1 into a plurality of spectral spectrums 22 with narrower bandwidths.
Preferably, to facilitate phase alignment of the spectral interference signals and further splicing into a composite interference signal, a single semi-transparent reflective element 15, such as a transparent glass plate, is placed outside the imaging distance of the sample 10 (e.g., sample depth position is 0-1mm, and outside the sample imaging distance is >1mm), within the allowed imaging range of the OCT system. In subsequent signal processing, extracting an interference signal corresponding to the single reflection element assists in phase alignment and splicing of spectral interference signals, and further details can be found in fig. 5 and related description.
Fig. 2 is a schematic diagram of a conventional frequency domain oct (sdoct) system. It can be seen that, compared with the spectral spectrum domain coherence fault system provided by the present invention, the conventional SDOCT does not have the tunable filter 21 to regulate the output wavelength of the light source, and emits light of all wavelengths at the same time; the spectral spectrum domain coherence tomography system only outputs light with a part of wavelengths through the tunable filter 21 at a time, and outputs light waves with different wave bands through rapidly adjusting the output wavelengths of the tunable filter 21. In addition, the conventional SDOCT uses a spectrometer to simultaneously detect interference signals of all wavelengths by the line scanning camera 8, and the spectral spectrum coherence fault layer system sequentially detects interference signals of wavelengths corresponding to different spectral spectrums, i.e., the spectral interference signals 23 (or 31), and interference signals obtained by each spectral spectrum correspond to different pixel positions of the line scanning camera.
As shown in fig. 3, the tunable filter 21 adjusts the wavelength band of the broad spectrum light source through the frequency band of the filter, and outputs a series of spectral outputs in different wavelength band ranges. Assuming a wide-spectrum light source output wavelength range of lambdas1And λs2Or corresponding to wave number ks1And ks2Wherein k is 2 pi/λ. Preferably, for OCT imaging, the light source bandwidth is at least 30nm, i.e. λ is satisfieds2-λs1Is more than or equal to 30 nm. The output of the adjustable filter is n sub-spectrums with narrower bandwidth, wherein n is an integer within 1-10000; let the ith spectral wavelength range be λi1And λi2Wherein i is more than or equal to 1 and less than or equal to n, the output wavelength of the spectrum needs to satisfy the following conditions: lambda [ alpha ]s1≤λi1≤λi2≤λs2(ii) a And for all 1 ≦ i<j is less than or equal to n, has lambdai1<λj1，λi2<λj2. Preferably, λs1The value range can be 380nm-1350nm，λs2The value range can be 410nm-1380 nm. According to the above definition, there may be a coincidence of the wavelength ranges between two successive sub-spectra, i.e. satisfying λi1≤λ(i+1)1≤λi2≤λ(i+1)2I is less than or equal to n-1 for all 1, and the bandwidths of the sub-spectra are not necessarily equal.
For an OCT system, its axial resolution can be described by the following equation:
where Δ λ is the light source bandwidth. That is, the wider the bandwidth of the light source, the smaller the scale that the OCT system can resolve, i.e., the higher the axial resolution. The bandwidth of the light wave 22 output by the tunable filter 21 is narrower than that of the output 2 of the original broad-spectrum light source, but after the light wave is spliced into a synthesized interference signal through a subsequent frequency axis, the bandwidth of the original broad-spectrum light source can be restored, so that higher axial resolution is obtained.
Fig. 4 is a method of stitching the spectral interference signals 31 into a composite interference signal 34 and ultimately resulting in a composite image 36. As mentioned above, since there may be overlap of wavelength ranges between the spectra, wavelength and frequency bands not containing repeated bands can be spliced together by the frequency axis splicing 32. Because interference signals of different spectral spectrums are subjected to grating light splitting and lens focusing and then are detected by pixels at different positions of a line scanning camera, the corresponding wavelength of each spectral spectrum interference signal can be identified according to the coordinate position of the detected signal, signals with repeated wavelengths are removed, and non-repeated but continuous wavelength axes are spliced together. On this basis, the wavelength-segmented interference signals are phase-aligned 33 and spliced into a composite interference signal 34. Finally, the synthesized interference signal is subjected to spectral waveform shaping 35, and a fourier transform 42 is performed to obtain a synthesized image 36. Preferably, one method of spectral shaping is to shape the interference signal of an arbitrary envelope into an interference signal having a gaussian-like envelope by multiplying by a window function. Common window functions include Hamming window function, Hanning window function, gaussian window function, etc.
Fig. 5 is a method for extracting an interference signal corresponding to a single reflection element in two spectral interference signals 31, that is, extracting a single-plane interference signal 41 to obtain spectral single-plane interference signals, then obtaining phases of the two spectral single-plane interference signals through fourier transform 42, performing phase comparison 43, performing linear wave number interpolation 44, fourier transform 42, phase delay 45, and inverse fourier transform 46 on one of the original spectral interference signals 31 by using phase comparison information, and further splicing the original spectral interference signals with the other original spectral interference signal 31 to form a composite interference signal 34. As mentioned above, the extraction of the interference signal corresponding to the single reflective element can be achieved by adding a transparent glass plate or similar sample outside the imaging range of the sample, or within the imaging range of OCT. If the sample has a single plane reflecting surface, the single plane reflecting surface can be directly used for extracting phase information.
Fig. 6 is a method for extracting a spectroscopic single-plane interference signal from the spectroscopic interference signal 31 by using a time-domain filtering 47 method. Since the single plane reflects a signal corresponding to one depth, that is, a frequency component in the fourier domain OCT, the signal of the reflecting surface can be effectively extracted by setting a band-pass filter of an appropriate frequency. Because the signal collected by the line scanning camera is an interference signal with uniformly distributed wavelengths obtained by grating dispersion 7, the signal is re-sampled by linear wave number interpolation 44 from linear wavelengths to linear wave number frequency axes in the post-processing process, so as to obtain a spectrum single-plane interference signal corresponding to the frequency axes uniformly distributed in wave numbers.
Fig. 7 is a method of extracting a spectroscopic monoplane interference signal from the spectroscopic interference signal 31 using fourier filtering 49. At this time, it is necessary to perform linear wavenumber interpolation 44 from linear wavelength to linear wavenumber frequency axis on the spectral interference signal 31, then transform the signal to fourier domain by fourier domain filtering, reserve the frequency of the interference signal corresponding to the single reflection element, filter out other frequency bands, and obtain the filtered spectral single-plane interference signal by fourier inverse transformation.
Fig. 8 shows a schematic diagram of the spectroscopic interference signal 31 and the resulting composite interference signal 34. It can be seen that the frequency of the interference signal is lower due to the narrower bandwidth of the sub-spectral band. By phase alignment, the interference signal obtained after splicing is similar to that obtained by directly imaging with an original broad-spectrum light source. The difference is that the optical fiber is spliced by a series of spectral interference signals with lower incident energy, and the sample sensitive to light intensity is more friendly when being imaged.
Fig. 9 compares the light intensity comparison graphs of the spectral incident sample and the original wide-spectrum light source full-spectrum incident sample (the spectral light intensity 56 compares the full-spectrum light intensity 57. obviously, the incident light intensity can be obviously reduced by using the spectral light waves and inputting the samples in sequence, and for the application represented by visible light OCT, the discomfort of the patient in the imaging process is reduced, the rapid eye movement in the imaging process is avoided, the imaging quality is improved.
As shown in fig. 10, another implementation method of the spectral coherence tomography system proposed by the present invention is to input n light sources 61 with narrow bandwidth into the SDOCT system interferometer through the optical switch 63, wherein n is an integer within 1-10000. Interference signals of different wavelength ranges corresponding to different light sources, namely the spectral interference signal 31, are sequentially detected by the spectrometer. Further, through data post-processing, interference signals of different wavelength ranges are phase-matched and further spliced into a composite interference signal 34, and finally a composite image 36 is obtained. The combined image 36 has a higher resolution and a higher signal-to-noise ratio than images obtained by imaging with a single light source.
In the system shown in FIG. 10, which includes n narrow-bandwidth light sources as inputs, assume that the ith light source output wavelength 62 ranges from λi1And λi2Wherein i is more than or equal to 1 and less than or equal to n and lambdai1≤λi2. Preferably, λi1The value range can be 380nm-1380nm, lambdai2The value range can be 380nm-1380 nm. According to the above definition, there may be coincidence of wavelength ranges between different light sources, and the bandwidth of each light source outputNot necessarily equal. The interference signals obtained by the incidence of each light source are respectively used for finding out the corresponding wavelength or frequency range through the pixel position detected on the line scanning camera, after the size sorting, the repeated wavelength or frequency components are removed, and after the phase positions are aligned, the synthetic interference signals are obtained by splicing.
The embodiments described above are only a part of the embodiments of the present invention, and not all of them. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Claims (7)
1. A spectral frequency domain coherence tomography system is characterized in that the spectral frequency domain coherence tomography system (50) utilizes an adjustable filter (21) to filter light waves output by a broad spectrum light source (1) into a plurality of spectral spectrums (22) with wide light intensity and narrow light band width output by the broad spectrum light source (1), the spectral spectrums (22) are respectively and sequentially input into an interferometer based on a frequency domain optical coherence tomography (SDOCT) system, and corresponding spectral interference signals (23 or 31) are sequentially detected; after data processing, aligning and splicing the phase of the spectral interference signal (23 or 31) into a synthetic interference signal (34), and finally obtaining a high-resolution high-signal-to-noise-ratio SDOCT image of the object analyzed at different depths through Fourier transform;
the adjustable filter (21) controls the output central wavelength and the bandwidth range through a program, and can quickly adjust the output range of the adjustable filter in the imaging process; the interferometer part of the SDOCT system comprises a light splitter (3), a polarization regulator (4), a lens (5), a reference arm plane mirror (6), a sample arm scanning galvanometer (9), a grating (7) of the spectrometer part and a line scanning camera (8), wherein the polarization regulator (4) is used for regulating the polarization state of light waves of the reference arm and the sample arm; the imaging principle of the spectral frequency domain coherence tomography system is that light waves output from a broad spectrum light source are output through an adjustable filter and split through a light splitter, and one path of light is led to a reference arm and reflected by a plane mirror (6); the other path of light passes through the sample arm, the sample (10) is irradiated by the sample arm scanning galvanometer (9), and the light reflected or scattered from the sample (10) interferes with the light wave reflected from the reference arm; the interference light wave is divided into different wavelength components through the grating, and is detected by the line scanning camera (8) after being focused by the lens, namely, the interference signal detected by the line scanning camera (8) is the component of the interference signal with different wavelengths; when the adjustable filter (21) changes the output wavelength range, interference signals of different wavelength components passing through the grating can be focused on pixels at different positions of the line scanning camera (8) by the lens, so that the line scanning camera (8) sequentially detects interference signals of different wavelength ranges corresponding to different spectral spectrums, namely spectral spectrum interference signals (31), by sequentially changing the output of the adjustable filter (21); further performing data post-processing, sequentially performing frequency axis splicing (32) and phase alignment (33) on interference signals in different wavelength ranges, further splicing the interference signals into a synthesized interference signal (34), and sequentially performing spectrum shaping (35) and Fourier transform (42) on the synthesized interference signal (34) to finally obtain a synthesized image (36), wherein the synthesized image (36) has higher resolution and higher signal-to-noise ratio than an image obtained by single spectral imaging;
the spectral spectrum frequency domain coherence tomography imaging system (50) utilizes the adjustable filter (21) to filter the light waves output by the broad spectrum light source (1) into a plurality of narrower spectral spectrums (22), and the light intensity corresponding to each spectral spectrum is smaller than that corresponding to the original broad spectrum light source, so that a sample sensitive to the light intensity is prevented from being damaged;
the output wavelength of the adjustable filter (21) is dynamically adjusted in real time by USB or network cable or Bluetooth through control software running on a computer;
a method of stitching interference signals of different wavelength ranges corresponding to different sub-spectra into a composite interference signal (34) and finally obtaining a composite image (36) is achieved by the steps of: because wavelength ranges among all the spectral spectrums are overlapped, wavelength frequency sections which do not contain repeated sections are spliced together by a frequency axis splicing method (32), and because different spectral interference signals are subjected to grating light splitting and lens focusing and then are detected by pixels at different positions of a line scanning camera, the corresponding wavelength of each spectral interference signal is identified according to the coordinate position of the detected signal, the signals with repeated wavelengths are removed, and the frequency axes with non-repeated but continuous wavelengths are spliced together; on the basis, phase alignment (33) is carried out on each wavelength segmentation interference signal, and the wavelength segmentation interference signals are spliced into a composite interference signal (34); finally, the spectral shaping (35) of the composite interference signal (34) is carried out, and a synthesized image (36) is obtained through Fourier transform (42), wherein the spectral shaping method is that the interference signal with any envelope is shaped through multiplying a window function, and the window function comprises a Hamming window function, a Hanning window function and a Gaussian window function;
the method for splicing the interference signals in different wavelength ranges corresponding to the two different sub-spectra into a composite interference signal (34) specifically comprises the following steps: in order to facilitate phase alignment of interference signals in different wavelength ranges corresponding to different sub-spectra and further splicing the interference signals into a synthesized interference signal (34), a semi-transparent single reflection element (15) is placed outside the imaging distance of a sample (10) and within the allowed imaging range of an SDOCT system, interference signals corresponding to the single reflection element in the two sub-spectrum interference signals (31) are respectively extracted, namely single-plane interference signals (41) are extracted to obtain two sub-spectrum single-plane interference signals, the phases of the two sub-spectrum single-plane interference signals are respectively obtained through Fourier transformation (42), phase comparison (43) is carried out, linear wave number interpolation (44), Fourier transformation (42), phase delay (45) and inverse Fourier transformation (46) are carried out on one sub-spectrum interference signal (31) by utilizing phase comparison information, and further spliced with another spectral interference signal (31) to form a composite interference signal (34).
2. The spectroscopic frequency domain coherence tomography system of claim 1, wherein the spectroscopic frequency domain coherence tomography system (50) utilizes a tunable filter (21) to collimate the broad lightThe light wave filtering output by the spectrum light source (1) is a plurality of light wave spectrums (22) with wide light intensity and narrow band width, wherein the light wave intensities output by the spectrum light source (1) with wide light intensity are different, and the light band widths output by the spectrum light source (1) with wide band width are different; the output wavelength range of the broad spectrum light source (1) is𝜆 s1 And𝜆 s2 the bandwidth of the light source is at least 30nm, namely the bandwidth satisfies𝜆 s2 -𝜆 s1 More than or equal to 30 nm; the output of the tunable filter (21) isnA narrow bandwidth spectral distribution, whereinnIs an integer within 1-10000; suppose thatiA spectral wavelength range of𝜆 i1 And𝜆 i2 wherein 1 is less than or equal toi≤nThen the spectral output wavelength satisfies the following condition:𝜆 s1 ≤𝜆 i1 ≤𝜆 i2 ≤𝜆 s2 (ii) a And for all 1. ltoreqi<j≤n，Is provided with𝜆 i1 <𝜆 j1 ，𝜆 i2 <𝜆 j2 (ii) a Between two successive sub-spectra𝜆 i1 ≤𝜆 (i+1)1 ≤𝜆 i2 ≤𝜆 (i+1)2 For all 1. ltoreqi≤n-1。
3. Spectroscopic frequency domain coherence tomography system according to claim 2, the broad spectrum light source (1) outputting a wavelength range𝜆 s1 And𝜆 s2 and the tunable filter (21) outputs a spectral wavelength range𝜆 i1 And𝜆 i2 wherein 1 is less than or equal toi≤nAnd is an integer which is the number of the whole,𝜆 s1 the value range is 380nm-1350nm,𝜆 s2 the value range is 410nm-1380 nm.
4. The spectroscopic frequency domain coherence tomography system of claim 3, wherein one method of extracting a single plane interference signal (41) from the spectroscopic interference signal (31) to obtain a spectroscopic single plane interference signal specifically comprises: firstly, time domain filtering (47) is carried out on a spectral interference signal (31), signals collected by a line scanning camera are interference signals with uniformly distributed wavelengths obtained through grating dispersion 7, and the signals after time domain filtering are resampled through linear wave number interpolation (44) from linear wavelengths to linear wave number frequency axes in a post-processing process to obtain spectral single-plane interference signals corresponding to the frequency axes uniformly distributed in wave numbers.
5. The spectroscopic frequency domain coherence tomography system of claim 3, wherein the further method of extracting a single-plane interference signal (41) from the spectroscopic interference signal (31) to obtain a spectroscopic single-plane interference signal comprises: the spectral interference signal (31) is divided, linear wave number interpolation (44) from linear wavelength to linear wave number frequency axis is firstly carried out, then the signal after resampling interpolation from the linear wavelength to the linear wave number frequency axis is converted to Fourier domain through Fourier domain filtering, the frequency of the interference signal corresponding to the single reflection element is reserved, other frequency bands are filtered, and then the filtered spectral single-plane interference signal is obtained through Fourier inverse transformation.
6. A spectroscopic frequency domain coherence tomography system according to claim 3, wherein said semi-transparent single reflecting element (15) is a transparent glass sheet.
7. A spectral frequency domain coherence tomography system is characterized in that the imaging system is provided with a light sourcenThe light sources with wider bandwidth and narrow spectrum light sources are respectively and sequentially input into an interferometer based on a frequency domain optical coherence tomography (SDOCT) system, and corresponding spectrum interference signals are sequentially detected (23); through data post-processing, the spectral interference signals (23) are spliced into a composite interference signal (34) in a phase alignment manner, and finally, the SDOCT composite image of different depth analysis of the object is obtained through Fourier transform, and the resolution and the signal-to-noise ratio of the composite image are superior to those of a single light source serving as an SDOCT light sourceThe resulting image;
the imaging system is powered bynA light source with different wavelength ranges, whereinnIs an integer within 1-10000; suppose thatiA spectral wavelength range of𝜆 i1 And𝜆 i2 wherein 1 is less than or equal toi≤nThen there is𝜆 i1 ≤𝜆 i2 And is and𝜆 i1 the value range is 380nm-1380nm,𝜆 i2 the value range is 380nm-1380 nm;
the method for splicing the spectral interference signals (23) into a synthesized interference signal (34) and finally obtaining the SDOCT synthesized image is realized by the following steps: because wavelength ranges among all the spectral spectrums are overlapped, wavelength frequency sections which do not contain repeated sections are spliced together by a frequency axis splicing method (32), and because different spectral interference signals are subjected to grating light splitting and lens focusing and then are detected by pixels at different positions of a line scanning camera, the corresponding wavelength of each spectral interference signal is identified according to the coordinate position of the detected signal, the signals with repeated wavelengths are removed, and the frequency axes with non-repeated but continuous wavelengths are spliced together; on the basis, phase alignment (33) is carried out on each wavelength segmentation interference signal, and the wavelength segmentation interference signals are spliced into a composite interference signal (34); finally, performing spectral shaping (35) on the synthesized interference signal (34), and obtaining an SDOCT synthesized image through Fourier transform (42), wherein the spectral shaping method is to shape the interference signal with any envelope by multiplying a window function, and the window function comprises a Hamming window function, a Hanning window function and a Gaussian window function;
the method for splicing the two spectral interference signals into a composite interference signal (34) specifically comprises the following steps: in order to facilitate phase alignment of interference signals in different wavelength ranges corresponding to different sub-spectra and further splicing the interference signals into a synthesized interference signal (34), a semi-transparent single reflection element (15) is placed outside the imaging distance of a sample (10) and within the allowed imaging range of an SDOCT system, interference signals corresponding to the single reflection element in the two sub-spectrum interference signals (23) are respectively extracted, namely single-plane interference signals (41) are extracted to obtain two sub-spectrum single-plane interference signals, the phases of the two sub-spectrum single-plane interference signals are respectively obtained through Fourier transformation (42), phase comparison (43) is carried out, and linear wave number interpolation (44), Fourier transformation (42), phase delay (45) and inverse Fourier transformation (46) are carried out on one sub-spectrum interference signal (23) by utilizing phase comparison information, and further spliced with another spectral interference signal (23) to form a composite interference signal (34).
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