CN115778318B - Visible light OCT system based on double-spectrometer detection and image reconstruction method - Google Patents

Abstract

The present invention provides a visible light OCT system and image reconstruction method based on dual-spectrometer detection, which obtain a first interference light signal of a first spectrometer and a second interference light signal of a second spectrometer; subtract the first interference light signal from the second interference light signal, remove a DC signal and an autocorrelation signal in the interference signal, and obtain a cross-correlation signal; perform k-domain linear interpolation, dispersion compensation and fast Fourier transform on the obtained cross-correlation signal in sequence to obtain an image reconstruction result; the present invention suppresses noise by subtracting signals collected by two spectrometers, which can greatly improve the scanning speed of the OCT system compared with a method of suppressing noise by extending the exposure time.

Description

Visible light OCT system and image reconstruction method based on dual spectrometer detection

Technical Field

The present invention relates to the technical field of optical coherence tomography, and in particular to a visible light OCT system based on dual-spectrometer detection and an image reconstruction method.

Background technique

The statements in this section merely provide background art related to the present invention and do not necessarily constitute prior art.

Optical Coherence Tomography (OCT) is a three-dimensional tomography method based on the principle of low-coherence light interference. It obtains cross-sections and three-dimensional images of sample tissues by measuring the reflected light or backscattered light of sample tissues. It has the advantages of high resolution, non-contact, non-invasive, high real-time performance, and high sensitivity. It has been widely used in the diagnosis of ophthalmology, cardiovascular, skin and other diseases. Since the invention of OCT technology, near-infrared light sources have been mostly used for imaging. Near-infrared light sources have the advantages of low price, stable light source power, and good beam quality.

Visible light OCT is an emerging OCT technology in recent years. It uses a light source in the visible light band for scanning and imaging. Because the wavelength of the visible light band beam is shorter, it can obtain higher resolution images compared to OCT systems that use near-infrared light sources.

The inventors have discovered that the light source used in the current visible light OCT technology is a supercontinuum light source. Compared with near-infrared light source technology, the relative intensity noise of this light source is larger, which reduces the signal-to-noise ratio of the acquired image. This problem limits the improvement of the imaging quality of the visible light OCT technology; increasing the exposure time of the spectrometer camera can reduce the influence of the relative intensity noise of the light source to a certain extent, but the increase in exposure time will reduce the scanning speed of the spectrometer camera, increase the scanning time, and make the motion artifact problem in the scanning process more serious; at the same time, compared with near-infrared OCT, the visible light OCT sample arm has a lower safe eye power, and faces the problem of weak sample arm signal reducing imaging quality.

Summary of the invention

In order to solve the problems existing in the current visible light OCT technology, such as large relative intensity noise of the light source, low imaging quality caused by low eye power, low scanning speed caused by long exposure time, and serious motion artifacts, the present invention provides a visible light OCT system and image reconstruction method based on dual-spectrometer detection. The signals collected by the two spectrometers are subtracted to suppress noise. Compared with the method of extending the exposure time to suppress noise, the scanning speed of the OCT system can be greatly improved.

In order to achieve the above object, the present invention adopts the following technical solution:

A first aspect of the present invention provides a visible light OCT system based on dual-spectrometer detection.

A visible light OCT system based on dual spectrometer detection includes: a visible light source, a first collimator, a filter, a first coupler, a second coupler, a third coupler, a first spectrometer, a second spectrometer, a processor, a sample arm, and a reference arm;

The visible light source, the first collimator, the filter and the first coupler are arranged in sequence along the optical path, the second coupler is used to split the light received from the first coupler into two beams, and the sample arm is used to receive the first split light sent by the second coupler;

The second coupler is also used to receive the retinal reflected light or backscattered light from the sample arm and send it to the third coupler. The light beams returned by the sample arm and the reference arm interfere in the third coupler. The third coupler is used to split the interfered light beam into two parts and send them to the first spectrometer and the second spectrometer respectively. The processor is used to receive the output signals of the first spectrometer and the second spectrometer.

As an optional implementation of the first aspect of the present invention, the splitting ratio of the second coupler is 90:10, 90% of the light beam of the second coupler is transmitted to the reference arm via the circulator, and 10% of the light beam is transmitted to the sample arm.

As an optional implementation of the first aspect of the present invention, the reference arm includes a second collimator, a dispersion compensation lens, an adjustable attenuator and a reflector arranged in sequence along the optical path, wherein the second collimator is used to receive the light beam transmitted by the second port of the circulator, and to transmit the reflected light to the second port of the circulator.

As an optional implementation of the first aspect of the present invention, the sample arm includes a third collimator, an XY scanning galvanometer, and a 4f system arranged in sequence along the optical path;

Among them, the third collimator is used to receive the light beam transmitted by the second coupler, and to transmit the retinal reflected light or backscattered light to the second coupler; the 4f system is used to output light to the human eye, and to receive the retinal reflected light or backscattered light.

As an optional implementation of the first aspect of the present invention, the invention further includes a circulator, wherein the first port of the circulator is used to receive the second split light beam sent by the second coupler, and the reference arm is used to receive the second split light beam sent by the second port of the circulator;

The second port of the circulator is further used for receiving the reflected light of the reference arm, and the third port of the circulator is used for sending the received reflected light of the reference arm to the third coupler.

As an optional implementation of the first aspect of the present invention, the splitting ratio of the third coupler is 50:50.

As an optional implementation manner of the first aspect of the present invention, the first spectrometer and the second spectrometer are of the same model and parameters.

A second aspect of the present invention provides an OCT system image reconstruction method.

An OCT system image reconstruction method, using the visible light OCT system based on dual spectrometer detection according to the first aspect of the present invention, comprises the following process:

Acquire a first interference light signal of the first spectrometer and a second interference light signal of the second spectrometer;

Subtracting the first interference light signal from the second interference light signal, removing the DC signal and the autocorrelation signal in the interference signal, and obtaining a cross-correlation signal;

The obtained cross-correlation signal is subjected to k-domain linear interpolation, dispersion compensation and fast Fourier transform in sequence to obtain an image reconstruction result.

As an optional implementation of the second aspect of the present invention, the first spectrometer and the second spectrometer use the same trigger signal to control the processor to collect the first interference light signal and the second interference light signal.

As an optional implementation of the second aspect of the present invention, the obtained cross-correlation signal is:

Wherein, s(k) is the spectral information of the visible light source, h is the response coefficient of the spectrometer CCD camera, R _Sn is the reflectivity at different depths of the sample arm tissue, z _Sn is the tissue position of the return signal at different depths in the sample arm, R _R is the reflectivity of the reference arm reflector, and z _R is the position of the reference arm reflector.

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

1. In the visible light OCT system and image reconstruction method based on dual-spectrometer detection described in the present invention, the interference signal in the third coupler is divided into two beams (50:50), which are collected separately using two spectrometers (i.e., the first spectrometer and the second spectrometer), both of which are controlled by the same trigger signal, and then the signals collected by the two are subtracted to suppress the light source noise contained in the signal, and at the same time, the DC signal and autocorrelation signal in the interference signal can be removed, thereby improving the signal-to-noise ratio and the image quality.

2. The visible light OCT system and image reconstruction method based on dual-spectrometer detection described in the present invention, and the method of suppressing noise by subtracting the signals collected by the two spectrometers, greatly improve the scanning speed of the OCT system compared to the method of suppressing noise by extending the exposure time.

3. In the visible light OCT system and image reconstruction method based on dual-spectrometer detection described in the present invention, the splitting ratio of the reference arm to the sample arm is 90:10. While ensuring a low power entering the eye, the power of the reference arm is increased. Compared with a splitting ratio of 50:50, the backscattered light signal of the sample arm can be further amplified, thereby improving the imaging quality.

Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

FIG1 is a schematic diagram of an optical path of a visible light OCT system based on dual spectrometer detection provided in Example 1 of the present invention;

FIG2 is a schematic flow chart of an OCT system image reconstruction method provided in Example 2 of the present invention;

FIG3 is a schematic diagram of a signal subtraction process of a spectrometer provided in Example 2 of the present invention;

Among them, 1-visible light source; 2-first collimator; 3-filter; 4-first coupler; 5-second coupler; 6-third coupler; 7-circulator; 8-reference arm; 9-sample arm; 10-first spectrometer; 11-second spectrometer; 12-processor; 13-camera acquisition trigger signal; 14-second collimator; 15-dispersion compensation lens; 16-adjustable attenuator; 17-reflector; 18-third collimator; 19-XY scanning galvanometer; 20-4f system; 21-human eye.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and/or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and/or combinations thereof.

In the present invention, terms such as "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "side", "bottom" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings. They are relational words determined only for the convenience of describing the structural relationships of the various parts or elements of the present invention, and do not specifically refer to any part or element in the present invention and should not be understood as limitations on the present invention.

In the present invention, terms such as "fixed connection", "connected", "connection", etc. should be understood in a broad sense, indicating that it can be fixedly connected, integrally connected or detachably connected; it can be directly connected or indirectly connected through an intermediate medium. Relevant scientific research or technical personnel in this field can determine the specific meanings of the above terms in the present invention according to specific circumstances, and they should not be understood as limiting the present invention.

In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

Embodiment 1:

As shown in FIG1 , Embodiment 1 of the present invention provides a visible light OCT system based on dual-spectrometer detection, comprising: a visible light source 1, a first collimator 2, a filter 3, a first coupler 4, a second coupler 5, a third coupler 6, a circulator 7, a first spectrometer 10, a second spectrometer 11, a processor 12, a sample arm 9, and a reference arm 8;

A visible light source 1, a first collimator 2, a filter 3 and a first coupler 4 are arranged in sequence along an optical path; a second coupler 5 is used to split the light received from the first coupler 4 into two beams; a sample arm 9 is used to receive the first split light beam sent by the second coupler 5; a first port of the circulator 7 is used to receive the second split light beam sent by the second coupler 5; and a reference arm 8 is used to receive the second split light beam sent by the second port of the circulator 7;

The second port of the circulator 7 is also used to receive the reflected light of the reference arm 8, the third port of the circulator 7 is used to send the received reflected light of the reference arm 8 to the third coupler 6, and the second coupler 5 is also used to receive the retinal reflected light or backscattered light of the sample arm 9 and send it to the third coupler 6;

The light beams returned by the sample arm 9 and the reference arm 8 interfere in the third coupler 6. The third coupler 6 is used to split the interfered light beams into two parts and send them to the first spectrometer 10 and the second spectrometer 11 respectively. The processor 12 is used to receive the output signals of the first spectrometer 10 and the second spectrometer 11.

Optionally, the splitting ratio of the second coupler 5 is 90:10, 90% of the light beam of the second coupler 5 is transmitted to the reference arm 8 via the circulator 7, and 10% of the light beam is transmitted to the sample arm 9; it can be understood that in some other embodiments, the splitting ratio of the second coupler 5 can also be other values, such as 80:20 or 70:30, etc., as long as the splitting ratio obtained by the reference arm 8 is greater than that of the sample arm 9. Those skilled in the art can make a choice according to the specific working conditions, which will not be repeated here.

Optionally, the reference arm 8 includes a second collimator 14, a dispersion compensation lens 15, an adjustable attenuator 16 and a reflector 17 arranged in sequence along the optical path, wherein the second collimator 14 is used to receive the light beam transmitted from the second port of the circulator 7, and to transmit the reflected light to the second port of the circulator 7.

Optionally, the sample arm 9 includes a third collimator 18, an XY scanning galvanometer 19 and a 4f system 20 arranged in sequence along the optical path;

Among them, the third collimator 18 is used to receive the light beam transmitted by the second coupler 5, and to transmit the retinal reflected light or backscattered light of the human eye 21 to the second coupler 5; the 4f system 20 is used to output light to the human eye 21, and to receive the retinal reflected light or backscattered light of the human eye 21.

In this embodiment, the 4f system is used to output parallel light to the human eye, the splitting ratio of the third coupler 6 is 50:50, and the first spectrometer 10 and the second spectrometer 11 are of the same model and parameters.

In this embodiment, the visible light source 1 is connected to the first collimator 2 via an optical fiber, and the second collimator 2, the filter 3 and the fourth coupler 4 are sequentially arranged to transmit light;

The first coupler 4 is connected to the second coupler 5 through an optical fiber, the second coupler 5 is connected to the third collimator 18 through an optical fiber, the second coupler 5 is connected to the first port (i.e., port a) of the circulator 7 through an optical fiber, the second port (i.e., port b) of the circulator 7 is connected to the second collimator 14 through an optical fiber, and the third port (i.e., port c) of the circulator 7 is connected to the third coupler 6 through an optical fiber;

The second coupler 5 and the third coupler 6 are connected via an optical fiber, the third coupler 6 is connected to the first spectrometer 10 and the second spectrometer 11 respectively via optical fibers, the first spectrometer 10 and the second spectrometer 12 are connected to the processor via signal lines respectively, and the processor 12 is also connected to the first spectrometer 10 and the second spectrometer 12 respectively via trigger signal lines;

The second collimator 14, the dispersion compensation lens 15, the adjustable attenuator 16 and the reflector 17 are sequentially arranged along the optical path for transmitting light;

The third collimator 18 , the XY scanning galvanometer 19 and the 4f system 20 are sequentially arranged along the optical path. The output light of the third collimator 18 is converted into horizontal light by the XY scanning galvanometer 19 and then transmitted to the 4f system 20 and then enters the human eye 21 horizontally.

More specifically, the light propagation path includes:

The light beam emitted by the visible light source 1 is transmitted to the first collimator 2 through the optical fiber, and then incident on the filter 3. After passing through the filter 3, a light beam within the visible light band is obtained, which is incident on the first coupler 4 and then transmitted to the second coupler 5. The splitting ratio of the second coupler 5 is 90:10. 90% of the light beam of the second coupler 5 is transmitted to the reference arm 8, and 10% of the light beam is transmitted to the sample arm 9.

The light beam transmitted to the reference arm 8 enters port a of the circulator 7, exits from port b and is then transmitted to the collimator, becoming parallel light and incident on the reflector 17. The light beam returned by the reflector 17 enters port b of the circulator 7, then exits from port c and is transmitted to the third coupler 6.

The light beam from the sample arm 9 is transmitted to the third collimator 18, and after being collimated into parallel light, it is incident on the XY scanning galvanometer 19, and then passes through the 4f system 20 (composed of two lenses, and the positional relationship of the components is related to the four focal lengths of the two lenses, so it is called the 4f system. After refraction by the 4f system, the scanning light beam of the XY scanning galvanometer 19 can be converted into parallel light that always passes through the pupil of the human eye, ensuring that the entry range of the scanning light beam is always within the range of the pupil) and is incident on the human eye 21 in the form of parallel light. The light beam passes through the human eye lens and is focused on the retina, and the reflected light or backscattered light of the retina returns along the original path and is transmitted to the third coupler 6.

The light beam returned by the reference arm 8 interferes with the light beam returned by the sample arm 9 in the third coupler 6, and then the interference signal is evenly divided into the first spectrometer 10 and the second spectrometer 11, and the two spectrometers detect simultaneously, and then transmit the data to the processor 12 for imaging processing. The two spectrometers are controlled by the same camera to collect trigger signals (divided into two paths connected to the first spectrometer 10 and the second spectrometer 11 respectively) to ensure the synchronization of signal acquisition.

Embodiment 2:

As shown in FIG. 2 , Embodiment 2 of the present invention provides an OCT system image reconstruction method, including the following process:

Acquire a first interference light signal of the first spectrometer 10 and a second interference light signal of the second spectrometer 11;

Subtracting the first interference light signal from the second interference light signal, removing the DC signal and the autocorrelation signal in the interference signal, and obtaining a cross-correlation signal;

The obtained cross-correlation signal is subjected to k-domain linear interpolation, dispersion compensation and fast Fourier transform in sequence to obtain an image reconstruction result.

More specifically, they include:

Assume the reference arm signal is:

Where _Ei is the complex electric field signal representing the light source beam, i is the imaginary unit, k is the wave number, R _R is the reflectivity of the reference arm reflector, and z _R is the position of the reference arm reflector.

The sample arm signal is:

Wherein, n represents the serial number of tissues at different depths, N is the total number of tissues at different depths for which the sample arm can return signals, R _Sn is the reflectivity of the sample arm tissue at different depths, and z _Sn is the position of the reference arm reflector.

The resulting interference signal is:

Wherein, w is the angular frequency of the interference signal, * represents the conjugate of the signal, h is the response coefficient of the CCD camera of the spectrometer, and the reference arm signal and the sample arm signal entering the third coupler 6 interfere with each other in the third coupler 6 to generate an interference signal, which is then output from the two output ports of the third coupler 6 and detected by the first spectrometer 10 and the second spectrometer 11 respectively.

The interference signals output by the first spectrometer 10 and the second spectrometer 11 are respectively signal 1 and signal 2, and the interference signal 1 is:

Among them, m has the same meaning as n, indicating the label of tissue at different depths, and s(k) is the spectral information of the light source.

It can be seen from the above formula that the interference signal consists of three parts: DC signal, cross-correlation signal and autocorrelation signal.

Interference signal 2 is:

Interference signal 1 and interference signal 2 have a phase difference of π. When the two are subtracted, the DC signal and the autocorrelation signal cancel each other out, leaving only the cross-correlation signal, and we can get:

Therefore, by subtracting the signals from the two spectrometers, the autocorrelation signal in the interference signal can be retained, and the DC signal and the autocorrelation signal in the interference signal can be subtracted to improve the imaging quality.

The signal fluctuation caused by the relative intensity noise of the light source has the same impact on the two spectrometers. In the process of subtracting the two signals, the relative intensity noise signal of the light source can also be subtracted to achieve the purpose of suppressing noise and improving the signal-to-noise ratio. The specific signal processing process is shown in Figure 3.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (5)

1. A visible light OCT system based on double-spectrometer detection is characterized in that,

Comprising the following steps: the device comprises a visible light source, a first collimator, a light filter, a first coupler, a second coupler, a third coupler, a first spectrometer, a second spectrometer, a processor, a sample arm and a reference arm;

The visible light source, the first collimator, the optical filter and the first coupler are sequentially arranged along the light path, the second coupler is used for dividing the received light sent by the first coupler into two beams, and the sample arm is used for receiving the first beam splitting light sent by the second coupler;

The second coupler is also used for receiving retina reflected light or back scattered light of the sample arm and sending the retina reflected light or back scattered light to the third coupler, the light beams returned by the sample arm and the reference arm are interfered in the third coupler, the third coupler is used for equally dividing the interfered light beams into two parts and respectively sending the two parts to the first spectrometer and the second spectrometer, the processor is used for receiving output signals of the first spectrometer and the second spectrometer, obtaining a first interference light signal of the first spectrometer and a second interference light signal of the second spectrometer, making a difference between the first interference light signal and the second interference light signal, and removing a direct current signal and an autocorrelation signal in the interference signals to obtain a cross-correlation signal;

The reference arm is used for receiving the second beam splitting light sent by the second port of the circulator;

the second port of the circulator is also used for receiving the reflected light of the reference arm, and the third port of the circulator is used for sending the received reflected light of the reference arm to the third coupler;

The reference arm comprises a second collimator, a dispersion compensation lens, an adjustable attenuator and a reflecting mirror which are sequentially arranged along the optical path, wherein the second collimator is used for receiving the light beam transmitted by the second port of the circulator and transmitting the reflected light to the second port of the circulator;

the split ratio of the second coupler is 90:10, 90% of the beam of the second coupler is transmitted to the reference arm via the circulator, 10% of the beam is transmitted to the sample arm;

the first spectrometer and the second spectrometer have the same model and parameters, and are controlled by the same trigger signal.

2. The visible light OCT system based on dual-spectrometer detection as recited in claim 1, wherein,

The sample arm comprises a third collimator, an XY scanning galvanometer and a 4f system which are sequentially arranged along the light path;

The third collimator is used for receiving the light beam transmitted by the second coupler and transmitting the retina reflected light or back scattered light to the second coupler; the 4f system is used to output light to the human eye and to receive retinal reflected light or backscattered light.

3. The visible light OCT system based on dual-spectrometer detection as recited in claim 1, wherein,

The third coupler has a split ratio of 50:50.

4. An OCT system image reconstruction method is characterized in that,

A visible light OCT system based on dual-spectrometer detection according to any one of claims 1-3, comprising the following process:

acquiring a first interference light signal of a first spectrometer and a second interference light signal of a second spectrometer;

the first interference light signal and the second interference light signal are subjected to difference, and a direct current signal and an autocorrelation signal in the interference signals are removed to obtain a cross-correlation signal;

And sequentially performing k-domain linear interpolation, dispersion compensation and fast Fourier transformation on the obtained cross-correlation signals to obtain an image reconstruction result.

5. The OCT system image reconstruction method of claim 4, wherein,

The obtained cross-correlation signal is:

Wherein, Is the spectrum information of the visible light source, h is the response coefficient of the CCD camera of the spectrometer,/>For the reflectivity of the sample arm tissue at different depths,/>For tissue locations of different depths of the return signal in the sample arm,/>For the reflectivity of the reference arm mirror,/>Is the reference arm mirror position.