Bimodal OCT-FBG optical fiber probe and temperature measurement and imaging system and method for measured tissue

Abstract

The invention provides a bimodal OCT-FBG optical fiber probe and a temperature measurement and imaging system and method.The bimodal OCT-FBG optical fiber probe comprises an integrated optical fiber probe and a protective shell, and the integrated optical fiber probe is arranged in the protective shell; the integrated optical fiber probe comprises a single-mode optical fiber, a graded-index optical fiber and a coreless optical fiber which are welded from the tail part to the end part in sequence; a Bragg grating is written into the core layer of the single-mode fiber. According to the dual-mode OCT-FBG optical fiber probe, the problem that the temperature of an existing probe is combined with OCT imaging is solved, the temperature measuring function and the OCT imaging function are combined in one optical fiber probe, and temperature data can be obtained while OCT imaging information is obtained. The device has the possibility of being applied to various occasions, for example, the ablation effect is monitored in the laser ablation process, and overheating is prevented; and deep tissue imaging, temperature measurement and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of medical devices, in particular to a dual-mode OCT-FBG optical fiber probe and a temperature measurement and imaging system and method for a measured tissue. BACKGROUND

[0002] Optical coherence tomography (OCT) is a non-invasive and non-destructive imaging technology based on the principle of low coherence light interference, which uses the coherence of scattered / reflected light from the sample arm and reference light. It has a micron-level resolution and a millimeter-level imaging depth. Currently, the combination of OCT imaging technology with other imaging or sensing technologies and the auxiliary endoscopy technology make it possible to apply OCT imaging technology to multiple fields. Miniaturized all-fiber integrated probes are the mainstream of OCT endoscopic imaging carriers at present, which are generally composed of a single-mode optical fiber, a glass spacer, and an optical focusing device (a graded-index fiber or a fiber ball lens). Such fiber probes composed of all-fiber devices have a very small volume and can be effectively placed in narrow body cavities such as blood vessels and gastrointestinal tracts to provide OCT imaging information.

[0003] In order to diversify the functions of the imaging probe to provide more detailed diagnostic information, the development of multifunctional OCT has been steadily ongoing. Among them, the design of multifunctional integrated fiber probes based on double-clad fibers has attracted much attention. It is to realize the combination of OCT imaging and other functions such as pH, pressure, displacement, and temperature by using the two concentric light guide regions of the double-clad fiber. In 2018, Jiawen et al. prepared a rare earth ion-containing convex lens at the distal end of a double-clad fiber, which was the first time to combine OCT imaging and rare earth ion temperature measurement in one fiber and to perform OCT imaging and temperature detection in the mouse brain. The swept laser source and the fluorescence were coupled into the fiber core of the double-clad fiber through a wavelength division multiplexing coupler and transmitted into the rare earth glass lens, among which the OCT light source entered the tissue through the lens, and the generated interference signal was received by the fiber core and transmitted into the imaging system; while the fluorescence excited the rare earth ions to generate a temperature-dependent fluorescence signal which was received by the cladding region of the double-clad fiber and transmitted into the spectrometer for analysis.

[0004] However, the use of double-clad fiber not only effectively couples the OCT imaging with the temperature, but also brings negative effects to the OCT imaging. In the double-clad fiber, the generated OCT interference signal is not only collected by the fiber core, but also a part of the signal is coupled into the cladding, and then coupled back into the fiber core at the fiber joint or interface, and the balanced photodetector detects the artifact of the OCT image. At present, the artifact problem caused by the double-clad fiber is still difficult to solve. Studies have shown that the delay between the artifact and the main image is proportional to the length of the double-clad fiber used, so extending the length of the catheter or increasing the length of the double-clad fiber between each fiber joint will push the artifact out of the imaging range, which can improve the imaging quality of the OCT. Some studies have also shown that using a W-shaped triple-clad fiber can also effectively reduce the artifact problem. However, there is still no practical solution to the image artifact caused by the double-clad fiber, and it is still being explored. SUMMARY

[0005] The purpose of the present application is to improve the problem of combining the temperature of the existing probe with the OCT imaging, and therefore a dual-mode OCT-FBG fiber probe and a temperature measurement and imaging system and method for the measured tissue are proposed.

[0006] To achieve the above purpose, the present application proposes a dual-mode OCT-FBG fiber probe, which comprises an integrated fiber probe and a protective shell, the integrated fiber probe is arranged in the protective shell, and the integrated fiber probe is sequentially provided with a single-mode fiber, a graded-index fiber and a coreless fiber which are fusion spliced from the tail to the end; and a Bragg grating is written in the core layer of the single-mode fiber.

[0007] Further, the material of the protective shell is paper, the end is a metal needle tip, and a through hole is formed on the side of the protective shell close to the metal needle tip; and the integrated fiber probe is fixed by photoresist after being placed in the protective shell.

[0008] Further, the Bragg wavelength of the Bragg grating is 1300 nm, and the length is 3-5 mm; and the coating on the surface of the single-mode fiber is stripped at the distribution of the Bragg grating.

[0009] Further, the length of the graded-index fiber is 0.25 pitch length.

[0010] Further, the receiving end of the coreless fiber is polished to form a 40° refracting surface, and a layer of metal film is coated on the refracting surface.

[0011] Further, the diameters of the fibers are all 125 μm, the core diameter of the single-mode fiber is 8.2 μm, and the core diameter of the graded-index fiber is 50 μm.

[0012] The application also provides a temperature measurement and imaging system for a measured tissue, which comprises a light source, an 80 / 20 coupler, a first circulator, a coupler, an FBG demodulation system, a second circulator, a reference arm, a 50 / 50 coupler, a balanced photodetector and a computer.

[0013] The light source is connected with the first circulator and the second circulator through the 80 / 20 coupler, the first circulator is connected with the FBG demodulation system and the bimodal OCT-FBG fiber probe through the coupler, the second circulator is connected with the reference arm and the 50 / 50 coupler, the 50 / 50 coupler is connected with the balanced photodetector, and the balanced photodetector is connected with the computer.

[0014] The application also provides a temperature measurement and imaging method for a measured tissue, which comprises the following steps: placing a bimodal OCT-FBG fiber probe on a surface of a measured tissue, aligning an imaging window of the probe with a measured part, and moving the probe to obtain imaging information and temperature data in a range.

[0015] After the light source passes through the 80 / 20 coupler, 80% of the light enters the bimodal OCT-FBG fiber probe through the first circulator, and 20% of the light enters the reference arm through the second circulator; the light signal carrying the depth information of the measured tissue passes through the coupler, interferes with the reflected light from the reference arm, is detected by the balanced photodetector through the 50 / 50 coupler, and generates an image on the computer; meanwhile, the light signal reflected back by the Bragg grating and having a relationship with the temperature passes through the coupler and is demodulated by the FBG demodulation system to obtain an FBG reflection spectrum; the center wavelength of the reflection spectrum has a linear relationship with the grating temperature, and the temperature data of the measured tissue can be obtained from the center wavelength of the reflection spectrum by pre-measuring the relationship curve.

[0016] Compared with the prior art, the application has the following advantages:

[0017] 1. The bimodal OCT-FBG fiber probe of the application is not suitable for double-clad optical fibers, so that the OCT imaging will not have a large number of artifacts, and the temperature measurement of the probe relies on the probe itself and does not introduce external fluorescent dyes which are difficult to handle in the human body. The temperature measurement accuracy of the probe can reach 0.1 DEG C, and the temperature measurement function and the OCT imaging function are combined in one optical fiber probe, unlike the thermistor, thermocouple and OCT imaging which need two functional partitions to realize.

[0018] 2. The bimodal OCT-FBG fiber probe of the application can obtain temperature data while obtaining OCT imaging information. It has the possibility of being applied to various occasions, such as monitoring the ablation effect and preventing overheating in the laser ablation process, deep tissue imaging and temperature measurement, etc. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Fig. 1 is a schematic diagram of the overall structure of the bimodal OCT-FBG fiber probe in Embodiment 1 of the application.

[0020] Figure 2 This is a schematic diagram of writing the Bragg grating in Embodiment 1 of the present invention;

[0021] Figure 3 This is a schematic diagram of the temperature measurement and imaging system for the tissue under test in Embodiment 2 of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be further described below.

[0023] Example 1:

[0024] To address the limitations of existing methods for combining temperature measurement with OCT imaging, this invention proposes a dual-mode OCT-FBG fiber probe. This probe can simultaneously perform OCT imaging and temperature measurement. A Bragg grating structure is incorporated into the single-mode fiber of the OCT imaging probe. Temperature-induced changes in the refractive index of the single-mode fiber core cause a shift in the center wavelength of the grating's reflection spectrum. Measuring the relationship between the reflected wavelength and temperature change allows for temperature measurement of the probe while simultaneously performing OCT imaging. The temperature-induced change in the grating's Bragg wavelength can be expressed as: Δλ B =λ B (ξ+α)ΔT,λ B Let λ be the Bragg wavelength, α be the coefficient of thermal expansion of the glass, and ξ be the thermo-optical coefficient, both of which are 5.5 × 10⁻⁶. -7 ℃ -1 7×10 -6 ℃ -1 Therefore, the theoretical temperature sensitivity of a Bragg grating with a wavelength of 1300 nm is 9.8 pm / ℃.

[0025] Specifically, such as Figure 1 As shown, the dual-mode OCT-FBG fiber optic probe consists of an integrated fiber optic probe and a protective shell. The integrated fiber optic probe is formed by sequentially fusion splicing a single-mode fiber 1, a graded-index fiber 2, and a coreless fiber 3. The single-mode fiber 1, graded-index fiber 2, and coreless fiber 3 used are all 125 μm in diameter to ensure consistency in the mode field diameter at the splice. Figure 2 As shown, a section of the coating on the single-mode fiber 1 is stripped, and two 248nm ultraviolet lasers 5 are used to write a Bragg grating 11 into the core region at a certain intersection angle. This angle can be selected according to the formula... The grating period Λ is determined by the formula λB = 2neffΛ. λB is the Bragg wavelength, which is selected as 1300 nm for this probe.

[0026] The protective shell is made of No. 5 stainless steel, the end is a No. 5 stainless steel needle tip 4, the inner diameter of the protective shell is consistent with the diameter of the optical fiber probe, only a very narrow gap (about 0.1 mm) is provided, so that the Bragg grating 11 cannot be bent, and the stainless steel shell can protect the probe from damage. The length of the rigid part of the optical fiber probe depends on the length of the protective shell, and different lengths of needle tips can be selected according to the use requirements. The selection of the graded-index fiber 2 mainly involves the resolution and imaging depth of the optical fiber probe. Considering the requirements of both, the length of the fiber is selected as 0.25P, which can obtain a larger imaging depth, and the lateral resolution is in the micrometer level. The selection of the hollow core fiber 3 depends on the imaging requirements. If only forward imaging is required, the hollow core fiber 3 is not needed, and if side imaging is required, the length needs to meet the requirements of the mirror surface 31. At the same time, in order to make the fiber fully reflect on the mirror surface 31, the mirror surface is 40° and a metal film 31 is coated on the mirror surface. The graded-index fiber (GIF50D, Thorlabs) with a length of 714 μm, the hollow core fiber (FG125LA, Thorlabs) with a length of 185 μm, and the single-mode fiber (SMF-28, Corning) are selected to manufacture the optical fiber probe according to the above requirements, and the imaging depth is about 2 mm, the lateral resolution is about 31 μm, and the axial resolution is about 7.4 μm.

[0027] The dual-mode OCT-FBG optical fiber probe imaging of the present application is not applicable to double-clad optical fibers, so that the OCT imaging will not have a large number of artifacts, and the temperature measurement of the probe relies on the probe itself without introducing external fluorescent dyes which are difficult to handle in the human body. The temperature measurement accuracy of the probe can reach 0.1℃, and the temperature measurement function and the OCT imaging function are combined in one optical fiber probe, unlike the thermal resistance, thermocouple and OCT imaging which need two functional partitions to realize.

[0028] Example 2

[0029] The present embodiment proposes a temperature measurement and imaging system for a measured tissue, which is composed of a swept laser source 6, an 80 / 20 coupler 7, a first circulator 8, a coupler 13, an FBG demodulation system 12, a second circulator 17, a reference arm 9, a 50 / 50 coupler 16, a balanced photodetector 15, a computer 10 and a dual-mode OCT-FBG optical fiber probe 14.

[0030] As shown in Figure 3 The swept laser source 6 is connected to the first circulator 8 and the second circulator 17 through the 80 / 20 coupler 7, the first circulator 8 is connected to the FBG demodulation system 12 and the dual-mode OCT-FBG optical fiber probe 14 through the coupler, the second circulator 17 is connected to the reference arm 9 and the 50 / 50 coupler 16, the 50 / 50 coupler 16 is connected to the balanced photodetector 15, and the balanced photodetector 15 is connected to the computer 10.

[0031] The application also provides a temperature measurement and imaging method for measured tissue. The bimodal OCT-FBG optical fiber probe 14 is placed on the surface of the measured tissue, the imaging window of the probe 14 is aligned with the measured part, and the probe 14 is moved to obtain the imaging information and temperature data in the range. The specific steps are as follows: after the light source passes through the 80 / 20 coupler 7, 80% of the light enters the bimodal OCT-FBG optical fiber probe 14 through the first circulator 8, and 20% of the light enters the reference arm 9 through the second circulator 17; the light signal carrying the depth information of the measured tissue passes through the coupler, interferes with the reflected light from the reference arm 9, and is detected by the balanced photodetector 15 through the 50 / 50 coupler 16 to generate an image on the computer 10; at the same time, the light signal reflected back by the Bragg grating and having the temperature is passed through the coupler and demodulated by the FBG demodulation system 12 to obtain the FBG reflection spectrum; the center wavelength of the reflection spectrum has a linear relationship with the grating temperature, and the relationship curve is measured in advance, so that the temperature data of the measured tissue can be obtained from the center wavelength of the reflection spectrum.

[0032] The above is only the preferred embodiment of the present application, and does not limit the present application. Any person skilled in the art can make any equivalent replacement, modification or change to the technical scheme and technical content disclosed by the present application without departing from the scope of the technical scheme of the present application, which still belongs to the protection scope of the present application.

Claims

1. A dual-mode OCT-FBG fiber optic probe, characterized in that, It includes an integrated fiber optic probe and a protective housing. The integrated fiber optic probe is located inside the protective housing. From tail to tip, the integrated fiber optic probe consists of a fused single-mode fiber, a graded-index fiber, and a coreless fiber. A Bragg grating is written into the core layer of the single-mode fiber.

2. The dual-mode OCT-FBG fiber probe according to claim 1, characterized in that, The protective shell is made of metal and has a metal needle tip at the end. A through hole is provided on the side of the protective shell near the metal needle tip. The integrated fiber optic probe is placed in the protective shell and fixed with photoresist.

3. The dual-mode OCT-FBG fiber probe according to claim 1, characterized in that, The Bragg grating has a Bragg wavelength of 1300nm and a length of 3-5mm; at the distribution points of the Bragg grating, the coating on the surface of the single-mode fiber is stripped off.

4. The dual-mode OCT-FBG fiber probe according to claim 1, characterized in that, The length of the graded refractive index fiber is 0.25 pitch.

5. The dual-mode OCT-FBG fiber probe according to claim 1, characterized in that, The receiving end of the coreless optical fiber is polished to form a 40° refractive surface, and a metal film is deposited on the refractive surface.

6. The dual-mode OCT-FBG fiber probe according to claim 1, characterized in that, The diameter of all optical fibers is 125 μm, the core diameter of the single-mode optical fiber is 8.2 μm, and the core diameter of the graded-index optical fiber is 50 μm.

7. A temperature measurement and imaging system for a tissue under test, using a dual-mode OCT-FBG fiber optic probe as described in any one of claims 1-6, characterized in that, It includes a light source, an 80 / 20 coupler, a first circulator, a coupler, an FBG modulation system, a second circulator, a reference arm, a 50 / 50 coupler, a balanced photodetector, and a computer.

8. The light source is connected to the first circulator and the second circulator via the 80 / 20 coupler. The first circulator is connected to the FBG demodulation system and the dual-mode OCT-FBG fiber probe via the coupler. The second circulator is connected to the reference arm and the 50 / 50 coupler. The 50 / 50 coupler is connected to the balanced photodetector. The balanced photodetector is connected to the computer.

9. A method for temperature measurement and imaging of a tissue under test, using the temperature measurement and imaging system as described in claim 7, characterized in that, Place the dual-mode OCT-FBG fiber optic probe on the surface of the tissue to be tested, align the probe imaging window with the part to be tested, and move the probe to obtain imaging information and temperature data within the range. After passing through an 80 / 20 coupler, 80% of the light from the light source enters the dual-mode OCT-FBG fiber probe via the first circulator, while 20% enters the reference arm via the second circulator. The light signal carrying the depth information of the tissue being measured passes through the coupler and interferes with the reflected light from the reference arm. It is then detected by a balanced photodetector via a 50 / 50 coupler, generating an image on the computer. Simultaneously, the temperature-related signal reflected back by the Bragg grating passes through the coupler and is demodulated by the FBG demodulation system to obtain the FBG reflection spectrum. The center wavelength of this reflection spectrum has a linear relationship with the grating temperature. By pre-measuring this relationship curve, the temperature data of the tissue being measured can be obtained from the center wavelength of the reflection spectrum.

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