JP2018169246A - Outgoing beam controller of optical deflector - Google Patents

Abstract

To provide a needle-shaped outgoing beam controller capable of precisely guiding an optical beam to an organic detection object.SOLUTION: A needle-shaped outgoing beam controller includes: a GRIN lens for allowing light emitted from an optical deflector to enter; and an objective lens which is optically connected posterior to the GRIN lens, and which condenses light emitted from the GRIN lens relative to a detection object.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an outgoing light control device for an optical deflector used as an OCT (Optical Coherence Tomography) probe.

  In recent years, imaging that measures and images sample information is also used in the medical field. For example, a microscope detects the surface of a living tissue, and an endoscope (gastrocamera) acquires an image for examination or diagnosis of a digestive organ. The imaging may be performed using a rigid endoscope called a laparoscope.

  In such an imaging apparatus, an image guide using a spatial lens system (including a relay lens system) or an optical fiber is used, and the surface of a living tissue is acquired as a two-dimensional image as white light or laser illumination. Technology to establish. As a technique for obtaining optical biological tissue information, an optical coherence tomography (OCT) using tomographic imaging utilizing optical interference has been developed, and OCT has been rapidly used in ophthalmology or cardiovascular medicine. Yes.

  OCT, which obtains an image by using interference of low-coherence light, is attracting attention as a technique that can observe a tissue of 1 to 2 mm under the surface of a living body noninvasively and in real time with a spatial resolution of around 10 μm. (Non-Patent Document 1). In addition to fundus examination, various clinical applications such as observation of sweat glands and capillaries, imaging of blood vessels using endoscopic OCT, and observation of the stomach wall have been performed.

FIG. 1 is a diagram for explaining the principle of the conventional OCT proposed first.
In FIG. 1, a Michelson interferometer 100 includes a light source 101, a beam splitter 102, a reference light mirror 103, a photodetector 105 such as a PD (Photo Diode), and a computer 106. The reference mirror 103 is movable within the range of “M” shown in FIG.

  The low-coherent light d10 from the light source 101 is separated into reference light d20 and measurement light d30 by the beam splitter 102, and the reference light d20 is reflected by the reference mirror 103 and returns to the beam splitter 102 as return light d21. On the other hand, the measurement light d30 is reflected by the sample (sample) 104 and returns to the beam splitter 102 as the sample light d31.

  In the photodetector 105, when the optical path length difference between the lights d21 and d31 returning to the beam splitter 102 is smaller than the coherent length, the lights d21 and d31 interfere with each other to obtain an interference signal d40. Then, the computer 106 obtains two-dimensional information of the sample 104 based on the interference signal d40.

  In FIG. 1, by moving the reference beam mirror 103, the computer 106 can also obtain information in the depth direction inside the sample 104 according to the position of the reference beam mirror 103. Furthermore, when the sample light d31 is scanned on a two-dimensional plane by a mirror (not shown), a B-mode image such as an ultrasonic wave is also obtained.

  An apparatus for moving the reference light mirror 103 to obtain the information in the depth direction described above is called time domain OCT (TD-OCT). Conventionally, TD-OCT has been used for various clinical applications, and a new possibility of OCT has been expected. However, since it is necessary to move the reference light mirror 103 mechanically, the imaging speed is relatively slow. Further, even if the reference light mirror 103 can be moved at a high speed, there is a problem in that the bandwidth is increased accordingly, and as a result, the detection sensitivity is lowered.

  The Fourier domain OCT (FD-OCT) has been proposed to cope with such problems and to increase the speed. As a kind of OCT of the FD-OCT, there is a swept source OCT (SS-OCT).

FIG. 2 is a diagram for explaining the principle of conventional SS-OCT. In the following description of FIG. 2, the reference numerals and the like used in the description of FIG.
2, the SS-OCT system 200 includes a light source 101, a beam splitter 102, a reference light mirror 103, a photodetector 105, and a computer 106, as in the case shown in FIG. On the other hand, unlike the one shown in FIG. 1, the light source 101 is a swept light source, and the reference light mirror 103 is fixed.

  In the SS-OCT system 200, since the wavelength of the light beam d10 from the light source 101 is periodically swept, the arm of the reference light d20 (the distance between the reference light mirror 103 and the beam splitter 102 in FIG. 2) is moved. The frequency of the interference signal d60 is determined according to the difference between the optical path length Lr shown and the optical path length Ls showing the arm of the sample light d31 (the distance between the sample 104 and the beam splitter 102 in FIG. 2).

  In FIG. 2, since the frequency of the interference signal d60 is given in correspondence with the position d of the sample 104, the interference signal d60 is Fourier-transformed by the computer 106, so that information on the depth direction of the sample 104 is obtained. Is obtained. In this case, unlike the one shown in FIG. 1, it is not necessary to move the reference light mirror 104, so that the reference light mirror 104 is stably fixed by mechanical means. Furthermore, the SS-OCT system 200 can perform high-speed processing at the repetition frequency of the light source 101 (usually several tens of kHz to 100 kHz), and can obtain a highly sensitive OCT image.

  In recent years, the development of the OCT system as described above has been progressing rapidly, and the laser light source, the light receiving optical system, the interferometer, and the data processing system have been commercialized except for some functions. Used in the field. Under such circumstances, the functionality of the OCT system can be improved by adding birefringence measurement using polarized light or blood flow measurement using the Doppler effect to add value to the OCT system. Is being considered.

  The development of an OCT probe is important in terms of expanding the application range of the OCT system. The OCT probe is for irradiating the affected area with laser light and detecting return light from the affected area.

  For example, in ophthalmic applications, a patient's head is fixed and laser light is emitted to the eyes as in a conventional fundus examination. In this case, the laser light is emitted from a galvano scanner installed in an OCT probe. Thus, two-dimensional scanning (planar scanning) is performed. In the OCT system for coronary arteries, an optical fiber is inserted into a catheter, and laser light is irradiated in a direction perpendicular to the optical fiber by an OCT probe (optical element) at the distal end of the catheter guided into the coronary artery. Then, the optical fiber is extracted while being rotated, and a tomographic image of the coronary artery is acquired in the longitudinal direction. Thus, in order to expand the application range of the OCT system, an OCT probe suitable for the application is required.

  A conventional orthopedic OCT probe is described in a research report (Non-Patent Document 2), but there is no example in which this is put into practical use. In orthopedic surgery, arthritis, chondrosis, etc. will be handled, but since many of these are in the joints, the OCT system is insufficiently penetrated and cannot be diagnosed from the skin surface. Therefore, diagnosis of such an affected part requires an OCT probe that guides a rigid endoscope (endoscope) to the vicinity of the affected part, irradiates laser light, and detects the return light. In a conventional rigid endoscope used in orthopedics, only the surface of the affected area is imaged by a CCD camera or the like, and information on the depth direction of the tissue of the affected area cannot be obtained.

  Here, an optical scanner using a potassium tantalate niobate (KTN) crystal, which is an electro-optic crystal, has been developed to realize high-speed and flexible optical scanning. This optical scanner is an electro-optic deflector (EO deflector) that electrically deflects a beam, and is a transmissive optical deflector. For this reason, the EO deflector can be smaller and lighter than a deflector that mechanically moves the mirror.

  In addition to the EO deflector, the use of MEMS (Micro Electro Mechanical Systems) or the like is being studied. However, although it is small in size, it is difficult to obtain a pen-shaped OCT probe. It was.

  The KTN optical deflector is a scanner using an electro-optic effect. With a KTN optical deflector, optical scanning is possible if there is a cross-sectional area through which laser light is transmitted. That is, there is no movable part by voltage control, and stable light scanning is possible. Further, since the KTN optical deflector is a transmission optical system, it can be miniaturized and mounted for use as a rigid endoscope.

  Since one KTN optical deflector can scan one axis (x), a two-dimensional image can be obtained by scanning two axes (x, y) with two KTN deflectors. Further, by combining this with imaging in the depth direction, a three-dimensional image of a living body can be imaged at high speed and in real time.

D.Huang and 8 others, “Optical coherence tomography”, Science. 254, pp. 1178-1181 Christopher Rashidifard and 4 others, “The Application of Optical Coherence Tomography in Musculoskeletal Disease”, Arthritis, Volume 2013 (2013)

  The optical deflector as described above enables imaging of a living body. However, in in vivo imaging, it may be difficult to irradiate a detection target with laser light depending on a part in the living body.

  In view of the above-described viewpoints, an object of the present invention is to provide an OCT probe tip device that can reliably guide a light beam to a detection target of a living body and detect return light from the detection target. is there.

  In order to solve the above-described problem, the present invention is optically coupled to a GRIN (Gradient Index Rod) lens that receives an optical signal emitted from an optical deflector of an OCT probe, and a subsequent stage of the GRIN lens, An objective lens that collects an optical signal emitted from the green lens with respect to a detection target of a living body, and the objective lens and the green lens reflect the optical signal reflected by the detection target to the optical deflector It is configured to return again.

  The distance between the light exit surface of the green lens and the principal point of the objective lens may be set to be equal to the condensing distance of the objective lens.

  The OCT probe includes two relay lenses after the optical deflector, and the focusing distance of the objective lens can be changed by changing the distance between the two relay lenses. Good.

  The green lens and the objective lens may be arranged so as to be a telecentric optical system on the detection target side.

  According to the present invention, it is possible to reliably guide a light beam to a detection target of a living body and to detect return light from the detection target.

It is a figure for demonstrating the principle of the conventional OCT. It is a figure for demonstrating the principle of the conventional wavelength sweep type | mold OCT. It is the schematic which shows an example of the whole structure of the OCT system in embodiment. FIG. 4 is a schematic diagram illustrating in detail a configuration example of the two-dimensional optical deflector and the emitted light control device of FIG. 3. It is a figure for demonstrating the telecentric optical system implement | achieved by the front-end | tip apparatus of FIG. It is a figure which shows a mode that a light beam propagates. It is a figure which shows an example of the OCT image obtained by the OCT system.

  Hereinafter, an OCT system including an OCT probe tip device according to the present embodiment will be described with reference to the drawings. The OCT system of this embodiment is an optical frequency sweep type OCT (SS-OCT) using a coupler.

FIG. 3 is a schematic diagram illustrating an example of the overall configuration of the OCT system 300 in the present embodiment.
As shown in FIG. 3, the OCT system 300 includes a wavelength swept light source 1, a polarization controller 2, a Mach-Zehnder unit 3, a reference light mirror 4, a balance detector 5, a signal processing device 6, and a function generator 7. , A driver 8, a two-dimensional light deflector (scanning unit) 9, and a tip device (emitted light control device) 10.

  The wavelength sweep light source 1 sweeps the oscillation light frequency. In this embodiment, for example, since it is assumed to be used in orthopedics, the center wavelength of the swept optical frequency is set to 1310 nm (1250 nm to 1360 nm). The wavelength sweep light source 1 sweeps the wavelength of the light beam at a high frequency of 100 kHz, for example. The average output is 20 mW.

  The polarization controller 2 linearly polarizes the light beam from the wavelength swept light source 1.

  The Mach-Zehnder unit 3 includes couplers 31 and 34 and circulators 32 and 33, and the constituent elements 31 to 34 are connected by an optical fiber 35. The coupler 31 is configured with one input and two outputs, and the reference beam d12 and the measurement beam d13 are obtained by splitting the light beam d11 from the polarization controller 2 with a branching ratio of 10 (reference light mirror 4 side): 90 (OCT probe 9 side). Branch to and output.

  The circulator 32 takes out the return light d14 of the reference light d12 reflected by the reference light mirror 4 and outputs it to the coupler 34. The circulator 33 takes out the return light d15 of the measurement light d13 reflected by the sample 104 and outputs it to the coupler 34. The coupler 34 has two inputs and two outputs, branches the return light d14 from the circulator 32 and the return light d15 from the circulator 33 at a 50:50 branching ratio, and detects the balanced optical signals d16 and d17. Output to the device 5.

  The balance detector 5 reduces the noise by taking the difference between the two optical signals d16 and d17, converts the signal based on the difference into an interference signal d18 as an electrical signal, and outputs it. The balance detector 5 includes a PD (Photo Diode) and the like.

  For example, the signal processing device 6 detects the intensity and time shift of the return light d15 from the sample 104 based on the above-described interference signal d18 to obtain an OCT image to be described later. The OCT image includes two-dimensional information or three-dimensional information.

  In this embodiment, the signal processing device 6 is equipped with a 12-bit DAQ (data acquisition) board, and the DAQ board collects the interference signal d18 from the balance detector 5 by performing A / D conversion at high speed. To do. Further, the signal processing device 6 performs discrete Fourier transform on the collected interference signal d18 to obtain an OCT image.

  The signal processing device 6 outputs a frame trigger signal d19 for generating the OCT image.

  The function generator 7 outputs triangular wave signals (100 Hz) d20 and d21 based on the frame trigger signal d19 in synchronization with the A-line trigger signal (100 kHz) d100 from the wavelength swept light source 1.

  The driver 8 outputs drive signals d22 and d23 to be applied to one-dimensional optical deflectors 91a and 91b, which will be described later, according to the triangular wave signals d20 and d21 from the function generator 7. The drive signals d22 and d23 are voltage signals such as triangular waves, for example.

  A tip device 10 that guides measurement light (light beam) d13 to the sample 104 is attached to the two-dimensional optical deflector 9. The measurement light d13 incident on the two-dimensional optical deflector 9 is irradiated from the tip device 10 onto a sample (detection target) 104 such as a living tissue. Then, the return light d15 reflected by the measurement light d13 by the sample 104 is returned again to the one-dimensional optical deflector 91b side in the two-dimensional optical deflector 9 via the tip device 10.

FIG. 4 is a diagram illustrating a schematic configuration example of the inside of the optical deflector 9 and the tip device 10.
As shown in FIG. 4, the two-dimensional optical deflector 9 includes two one-dimensional optical deflectors 91a and 91b arranged in series. The one-dimensional optical deflectors 91a and 91b are arranged so that the directions in which the drive signals d22 and d23 are applied are orthogonal. In this embodiment, the one-dimensional light deflector 91a scans the light beam in the X direction (planar scanning), and the one-dimensional light deflector 91b scans the light beam in the Y direction.

  The one-dimensional optical deflectors 91a and 91b are optical deflectors using, for example, potassium tantalate niobate (KTN) crystals. When drive signals d22 and d23 are given to the KTN crystal, the refractive index in the KTN crystal changes, and the light beam in the KTN crystal is deflected. With such a configuration, the one-dimensional optical deflectors 91a and 91b can scan the light beam in the X direction or the Y direction.

  The half-wave plate 95 is provided between the two one-dimensional optical deflectors 91a and 91b, and rotates the polarization direction of the light beam by 90 degrees. The half-wave plate 95 is, for example, a polarizer.

  The four lenses 92, 93, 94, and 96 are provided to compensate the light deflection by the one-dimensional optical deflectors 91a and 91b. As the lens 92, for example, a cylindrical lens is used, and as the lenses 93, 94, 96, for example, spherical concave lenses are used. However, the present invention is not limited thereto, and as the lenses 92 to 94, 96, for example, a spherical biconcave lens, a cylindrical lens, a green lens, or the like can be used.

  The relay lenses 97 and 98 are configured such that the scan origins in the X direction and the Y direction coincide with each other on the emission surface side of the optical deflector 91b. In the example of FIG. 4, the distance between the relay lenses 97 and 98 is, for example, 21.11 mm (optical design standard).

The tip device 10 includes a green lens 11 and an objective lens 12. As will be described later, the tip device 10 is formed in a needle shape so as to guide the measurement light d13 to the sample 104 and to detect the return light d15 reflected by the measurement light d13 by the sample 104.
In general, the glass constituting the lens system has a uniform refractive index. However, the green lens has a refractive index distribution that is not uniform. In this embodiment, for example, SELFOC (registered trademark) whose medium itself has a refractive index distribution is used as the grind lens. For example, a lens having a refractive index distribution in the vertical direction from the optical axis is used. You may make it use.

  The green lens 11 is configured to guide the measurement light d13 to the living tissue as the sample 104 and return the return light d15 of the measurement light d13 reflected by the sample 104 to the OCT probe 9 side again. The dimensions of the green lens 11 are set in consideration of, for example, the depth from the epidermis to the living tissue (sample) (part in the living body). In this embodiment, the cylindrical grind lens has a diameter of 2.0 mm and a length of 21.0 mm, for example, based on optical design standards, but may be changed.

  The objective lens 12 is, for example, a convex lens. The objective lens 12 is disposed between the green lens 11 and the sample 104. In the example of FIG. 4, both the distance between the objective lens 12 and the green lens 11 and the distance between the objective lens 12 and the sample 104 are “F”. This realizes a telecentric optical system in which the optical axis and the principal ray can be regarded as parallel on the sample 104 side, and the image observed on the display device of the information processing device 6 is image height (image point and light). A high-quality image that does not vary depending on the height of the axis. In this embodiment, the telecentric angle indicating the angle deviation of the principal ray with respect to the optical axis is, for example, 0.11 ° at the maximum.

FIG. 5 illustrates the simulation result of the optical path in the tip device 10.
In the example shown in FIG. 5, for example, a window glass (thickness: 0.5 mm) 301 containing SiO ₂ as a main component is used. In FIG. 5, the condensing position L from the objective lens 12 indicates a position in the medium (refractive index: 1.4) located at a distance of 1.0 mm from the window glass 301. This condensing position L corresponds to the position of the sample 104 shown in FIG.

FIG. 6 is a diagram illustrating a state in which a light beam propagates in the two-dimensional optical deflector 9 and the tip device 10, and FIG. 6A shows the internal arrangement of the two-dimensional light deflector 9 and the tip device 10, and b) shows the height between the image point in the X direction and the optical axis, and (c) shows the height between the image point in the Y direction and the optical axis.
In the example shown in FIG. 6, the light beam is collected on the surface of the sample 104, and this light collection position is changed by changing the distance D between the two relay lenses 97 and 98, thereby collimating the light beam. Since the beam diameter changes, it can be changed. This is equivalent to the tip device 10 becoming a needle having a relay lens function (one that collects light on the sample 104 with a predetermined spot size), whereby the OCT diagnosis of the sample 104 can be performed reliably.

FIG. 7 illustrates an OCT image obtained by the OCT system.
The OCT image illustrated in FIG. 7 is a human fingertip (sample 104), and the epidermis and sweat glands of the fingertip can be observed.

  This OCT image was obtained by applying a triangular wave voltage (480 V, 100 Hz) as the drive signal d22 to only one one-dimensional optical deflector 91a. The beam power of the return light d14 from the reference light mirror 4 was 107 μW, and the beam power of the return light d15 from the sample 104 (fingertip) was 164 μW.

  From the above result and the average value of the optical path length difference between the reference light d12 (including the return light d14) and the measurement light d13 (including the return light d15), the refractive index of the fingertip (living body) is set to 1. Assuming 41, the imaging range in the Z (optical axis) direction was 1.49 mm. As shown in FIG. 7, it was shown that the tip device 10 attached to the two-dimensional optical deflector 9 can obtain a two-dimensional OCT image of the sample 104 as a human fingertip.

  The tip device 10 of the present embodiment described above is emitted from the green lens 11 with respect to the green lens 11 that receives the measurement light d13 from the two-dimensional optical deflector 9 (one-dimensional optical deflector 91b) and the sample 104. The objective lens 12 and the green lens 11 return the measurement light d13 reflected by the sample 104 to the two-dimensional optical deflector 9 (one-dimensional optical deflector 91b) again. . Here, since the sample 104 is a living tissue or the like, the measurement light d13 can be reliably guided to the living tissue or the like, and the return light d15 from the living tissue or the like can be detected.

  In this case, it is possible to realize a medical optical deflector tip device 10 capable of acquiring in real time two-dimensional and three-dimensional images of the inside of a living body by laser scanning, which could not be realized by a conventional OCT system. Unlike conventional rigid endoscopes, it is possible to configure a rigid endoscope that allows treatment while performing tissue diagnosis in real time, not just imaging by illumination. In particular, the needle-like outgoing light control device including the green lens 11 according to the present embodiment is expected to be effective in that the OCT that has simply remained in imaging of the epidermis can be applied to treatment such as laparoscopic surgery. it can.

  The OCT system 300 is not limited to that exemplified in the above embodiment. For example, the one-dimensional optical deflectors 91a and 91b may use a KLTN crystal doped with lithium in addition to the KTN crystal.

DESCRIPTION OF SYMBOLS 1 Wavelength sweep light source 2 Polarization controller 3 Mach-Zehnder part 4 Reference light mirror 5 Balance detector 6 Signal processing device 7 Function generator 8 Driver 9 Two-dimensional optical deflector 10 Advanced device 300 OCT system d12 Reference light d13 Measurement light

Claims (4)

A green lens for entering an optical signal emitted from the optical deflector;
An objective lens that is optically coupled to a subsequent stage of the green lens and collects an optical signal emitted from the green lens with respect to a living body detection target;
The needle-like emission light control device, wherein the objective lens and the green lens are configured to return the optical signal reflected by the detection target to the optical deflector again.   2. The needle-shaped needle according to claim 1, wherein a distance between a light exit surface of the green lens and a principal point of the objective lens is set to be equal to a condensing distance of the objective lens. Emission light control device.   The two stages of the optical deflector include two relay lenses, and the focusing distance of the objective lens is variable by changing the distance between the two relay lenses. A needle-like outgoing light control device according to claim 1.   The needle-shaped outgoing light control device according to claim 3, wherein the green lens and the objective lens are arranged so as to be a telecentric optical system on the detection target side.