JP6011970B2 - Optical coherence tomography device - Google Patents

Description

  The present invention relates to an optical coherence tomography apparatus, and more particularly to an optical coherence tomography apparatus that generates an optical tomographic image of a subject using reflected light obtained by irradiating the subject with low interference light.

  In the field of molecular imaging, a method for detecting a target molecule with high sensitivity using optical information is the main force. Among them, an OCT apparatus (Optical Coherent Tomography) capable of acquiring information in the depth direction with high resolution by using low interference light is drawing attention.

  In the ophthalmologic field, there is a need for more accurate diagnosis by acquiring not only the retina surface information (surface image) but also the depth direction information, and the OCT apparatus is practically used as a fundus imaging apparatus. It has become.

  In order to collect three-dimensional information with an OCT apparatus, it is necessary to scan a light beam output from a light source called SLD (Super Luminescent Diode) in the horizontal and vertical directions. For example, an optical coherence tomography apparatus described in Patent Document 1 is shown in FIG. In this optical coherence tomography apparatus, the light beam output from the SLD light source 1 via the collimator 2 is separated into the reference light and the measurement light by the beam splitter 3, and the biaxial galvanometer mirrors 17 and 18 are separated from the separated measurement light. Is used to mechanically scan the light beam horizontally and vertically. The scanned measurement light is reflected by each layer of the measurement object T input through the objective lens 9 and returns to the beam splitter 3 again as the drive signal S. In the beam splitter 3, the measurement light returned as the drive signal S is merged again with the reference light reflected by the movable mirror 10 and enters the PD 11. The signal processing device 12 detects the intensity and time shift of the measurement light based on the interference phenomenon caused by the measurement light and the reference light at the time of merging, and derives a spatial positional relationship (three-dimensional information).

  OCT apparatuses that acquire tomographic images using low coherence interference include TD-OCT (Time domain optical coherence tomography) and SD-OCT (Spectral domain optical coherence tomography).

US Pat. No. 5,975,697

J. Miyazu, Y. Sasaki, K. Naganuma, T. Imai, S. Toyoda, T. Yanagawa, M. Sasaura, S. Yagi and K. Fujiura, “400 kHz Beam Scanning Using KTa1-xNbxO3 Crystals” Proc. Of 2010 Conf. On Lasers and Electro-Optics, CTuG5, 2010

  Since the response performance of the galvanometer mirrors 17 and 18 is generally about 100 Hz, and the maximum is 1 kHz, the light beam cannot be scanned at high speed in the horizontal and vertical directions. Therefore, the conventional OCT apparatus has a problem that it cannot collect two-dimensional and three-dimensional data at high speed. For example, taking an SD-OCT apparatus, which is an OCT apparatus that can acquire image information at a relatively high speed, as an example, the two-dimensional image information acquisition speed is about 0.01 seconds even if it is a general one. It takes about 2 seconds to reach the information acquisition time. These are due to the fact that the galvanometer mirror does not move at high speed.

  From the viewpoint of realizing high-speed beam scanning, an acousto-optic deflector (a light beam is applied to a diffraction grating formed by applying a high frequency voltage of several tens of MHz to several GHz on a piezoelectric crystal, and the light beam is deflected using diffraction. Element) may be used, but the deflection angle is not large. For this reason, if it is introduced into the OCT apparatus, high-speed scanning is possible, but there is a problem that the scanning range cannot be increased.

  The present invention can achieve both high-speed scanning and a large scanning range, and can scan light beams at high speeds in the horizontal and vertical directions to collect two-dimensional data and further three-dimensional data at high speed. An object is to provide an optical coherence tomography apparatus.

In order to solve the above-described problems, the present invention provides an optical coherence tomography apparatus that generates an optical tomographic image of a subject using reflected light obtained by irradiating the subject with low interference light. A light source that outputs light, a beam splitter that divides the low-interference light into two directions and outputs it as reference light and measurement light, and irradiates the subject with the measurement light in a plane scan. Planar scanning means for inputting the reflected light reflected from the specimen to the beam splitter again, a reference light mirror for reflecting the reference light output from the beam splitter and inputting it again to the beam splitter, the reference light and the reflected light And a light detection means for detecting the light combined by the beam splitter, and a signal processing device for analyzing the interference of the light detected by the light detection means and generating an optical tomographic image of the subject, Planar scanning means A light beam deflecting unit using an electro-optic crystal, and data of a surface perpendicular to the incident direction of light is obtained for each layer, and the light beam deflecting unit is applied with a voltage applied to the electro-optic crystal. In addition, the incident light beam is deflected by an electric field formed by the voltage, and a refractive index distribution is induced in the electro-optic crystal. The refractive index distribution has a refractive index convex with respect to the deflection direction. has the function of the inclined convex lenses, the focal point of said convex lens, Ru movable der and horizontally scanning axis to allow the scanning direction of the scan.

  According to the present invention, a light beam can be scanned at high speed in the horizontal and vertical directions, and two-dimensional data or three-dimensional data can be collected at high speed.

It is a figure which shows the structural example of the optical coherence tomography apparatus concerning 1st Embodiment. It is a figure which shows the structural example of the beam scanning part of 1st Embodiment. It is a flowchart which shows the processing flow of the scanning operation | movement concerning 1st Embodiment. It is a figure explaining the scanning operation | movement concerning 1st Embodiment. It is a figure which shows the applied voltage waveform of the scanning operation | movement concerning 1st Embodiment. It is a figure which shows the structural example of the optical coherence tomography apparatus concerning 2nd Embodiment. It is a figure which shows the structural example of the beam scanning part of 2nd Embodiment. It is a figure which shows the structural example of the optical coherence tomography apparatus concerning 3rd Embodiment. It is a figure which shows the structural example of the beam scanning part of 3rd Embodiment. It is a flowchart which shows the processing flow of the scanning operation | movement concerning 3rd Embodiment. It is a figure explaining the scanning operation | movement concerning 3rd Embodiment. It is a figure which shows the applied voltage waveform of the scanning operation | movement concerning 3rd Embodiment. It is a figure which shows the structural example of the optical coherence tomography apparatus concerning a prior art example. It is a figure for demonstrating the convex lens effect of KTN.

  Exemplary embodiments of an optical coherence tomographic apparatus (OCT apparatus) according to the present invention will be described below in detail with reference to the accompanying drawings.

(First embodiment)
The optical coherence tomography apparatus according to the first embodiment includes a KTN, a single concave lens, and a galvanomirror system as means for scanning a light beam of TD-OCT low interference light (beam scanning unit). It is the composition which is.

<About TD-OCT and 3D images>
First, the configuration of the optical coherence tomography apparatus according to the present embodiment will be described. FIG. 1 shows a configuration of an optical coherence tomography apparatus according to the present embodiment, and FIG. 2 shows a configuration example of a beam scanning unit that is a portion surrounded by a broken line in FIG. As shown in FIG. 1, this optical coherence tomography apparatus includes a light source 1, a collimator 2, a beam splitter 3, a KTN element (X) 4, an X deflection electrode pair 5, and an X deflection KTN power supply 6. And a concave lens 7, a movable sample mirror 8, an objective lens 9, a movable mirror 10 for reference light, a photodetector 11 such as a PD, and a signal processing unit device 12. The beam scanning unit is arranged on the optical path of the measurement beam between the beam splitter 3 and the objective lens 9 and performs a plane scan (plane scan) on the measurement beam. That is, in the present embodiment, as shown in FIG. 2, the beam scanning unit includes a KTN element 4 and an electrode pair 5 and a single concave lens as means for planar scanning with a light beam of TD-OCT low interference light. 7 and a galvanometer mirror system 8.

  A general operation mechanism of the sample movable mirror 8 is a galvanometer mirror system, and its operation speed is 1 kHz at the maximum. A general operation mechanism of the reference light movable mirror 10 is a stepping motor, and its operation speed is about several tens of Hz.

  As the light source 1, a light source called SLD (Super Luminescent Diode) can be used. The SLD is linearly polarized light, and is installed so that the polarization direction is the same as the electric field applied to the KTN. The light source 1 generates a light beam having low coherence, and the generated light beam is converted into parallel light having a beam diameter of 0.5 mm by a collimator. Thereafter, the beam is split by the beam splitter 2 into a measurement light beam and a reference light beam.

  The light beam for measurement passes through the KTN element 4 and the concave lens 7, is directed to the sample by the sample movable mirror 8, is condensed by the objective lens 9, and reaches the sample T. The reached light is reflected as reflected light S by each reflecting surface inside the sample T. The reflected light S is reflected by the objective lens 9, the movable sample mirror 8, the concave lens 7, the KTN element 4, and the beam splitter 3. After that, it enters the photodetector (PD) 11 as a light beam of measurement light.

  On the other hand, the reference light beam is reflected by the reference light movable mirror 10, passes through the beam splitter 3, and enters the photodetector 11 as a reference light beam. The photodetector 11 detects the light intensity of the interference light and outputs the detected light intensity to the signal processing device 12. It is possible to compensate for the dispersion of light with the measurement light beam by inserting a lens similar to the objective lens 9 through which the measurement beam passes before the reference movable mirror 10.

  Here, by moving the reference light movable mirror 10 slightly to slightly change the optical path length of the reference light, the information of the sample T at the depth where the optical path lengths of the reference light and the measurement light coincide with each other can be obtained. It can be obtained as light intensity. That is, information in the depth direction (Z direction) in the sample T can be obtained by finely moving the reference light movable mirror 10. In addition to scanning the reference light movable mirror 10 in the depth direction by minute movement, the sample movable mirror 8 scans a beam incident on the sample T in a direction perpendicular to the incident (X direction, Y direction) (planar scan). ) Can be obtained in the X direction, Y direction, and Z direction of the sample T, and a three-dimensional tomographic image of the sample T can be constructed.

<About KTN characteristics>
Next, KTN will be described. Potassium tantalate niobate (KTa _1-x Nb _x O ₃ (0 <x <1): KTN) crystal and lithium-doped (K _1-y Li _y Ta _1-x Nb _x O ₃ (0 < x <1, 0 <y <0.1): KLTN) The crystal functions as an electro-optic deflector and can also have a convex lens function (effect) (see Non-Patent Document 1). For example, when the upper and lower surfaces of the KTN chip are made to be uniform titanium electrodes, electrons are injected into the crystal by applying a DC voltage. Since an electron trap exists in the KTN crystal, an electron trapped in the trap in the crystal exists even after the DC voltage is applied. Here, it is assumed that electrons trapped in the trap are spatially uniform, and the charge density is ρ. When a modulation voltage is applied to the KTN chip in this state, the electric field distribution E (x) when the distance from the electrode is x is expressed by the following formula (1) according to Gauss's law. In Equation (1), ρ is the charge density, ε is the relative dielectric constant, d is the thickness of the KTN crystal, and V is the voltage applied to the electrode.

  Further, the refractive index distribution Δn (x) of the electro-optic deflector can be expressed by Expression (2). In equation (2), gij is the electro-optic coefficient, and n0 is the refractive index of the electro-optic deflector before the DC voltage is applied.

  FIG. 14 is a diagram for explaining the refractive index distribution in the KTN crystal. As can be seen from the equations (1) and (2), by applying a voltage to the electrodes 5 provided on both sides of the KTN crystal 4, the electric field distribution E (x) generated in the KTN crystal 4 is x Although the function is linear, the refractive index change Δn is a quadratic function of x. Therefore, the refractive index distribution has a quadratic function profile that is not a broken line in FIG. 14 but a solid line.

  If the refractive index profile is a linear profile with a broken line, the beam will not diverge or converge. However, when the refractive index distribution profile is tilted in a mountain state on the plus side as indicated by a solid line, the refractive index tilt in a convex state as referred to as a lens is obtained. As a result, the beam in the KTN crystal is converged by the lens effect of this refractive index. Thus, the refractive index distribution is spatially convex in the chip cross section, and the KTN crystal itself has the function of a convex lens.

  The light deflection effect by KTN is caused by applying a voltage to the electrode pair 5 installed on both end faces of the KTN crystal 4. When a voltage is applied to the X-deflection electrode 5 provided at an orthogonal position so as to sandwich the KTN crystal 4, the refractive index state in the KTN crystal 4 changes, thereby changing the voltage applied to the KTN crystal 4. Since the focal point of the convex lens developed in the KTN crystal 4 moves horizontally with respect to the x-axis, the light is deflected. Therefore, the light can be scanned in the X direction by changing the voltage applied to the X deflection electrode.

  It has been reported that the response speed can be up to 500 MHz, and scanning can be performed faster than a general mechanical movable device.

  The angle at which light by KTN can be deflected, that is, the scan angle is very large among electro-optic crystals. Near infrared light with a wavelength of 1300 nm was incident on a 4 × 4 × 1.5 mm KTN device in a 1.5 mm gap, and DC ± 500 V was applied as an initial voltage to electrodes formed on both sides of a 4 mm square. Later, when an AC voltage of ± 400 V was applied, the light beam was deflected by about ± 5 degrees.

<Inserting concave lenses>
Here, by applying an initial voltage of DC ± 500V, the convex lens effect as described above was exhibited in KTN. The convex lens effect at this time was about f = 15 mm as the focal length of the lens. About the lens effect of KTN, although there exists dependence with respect to the individual difference for every crystal | crystallization, or an applied voltage difference, about f4-20 is expressed. Further, the convex lens effect with respect to the initial voltage condition is reproduced without being different each time if the same crystal is used.

  Although the distance from the light emitting surface of the KTN element to the sample, that is, the working distance depends on the device design, it is considered that at least about 50 mm is necessary in consideration of the size of the sample fixing part and the like. Since the distance is more than twice as long as the focal length due to the developed convex lens effect, the beam diameter when the light emitted from the KTN reaches the sample is wider than when the light is emitted. In this way, when the beam diameter when irradiated onto the sample is not sufficiently collected, the reflected light intensity from the sample cannot be obtained sufficiently, and the reflection point covers a wide range, causing an image blur.

  Therefore, a concave lens that can compensate for the lens effect described above is inserted before, after, or before and after the KTN element, and an objective lens for condensing light on the sample surface is inserted in the vicinity of the sample. In the present embodiment, a configuration is shown in which the concave lens 7 is inserted behind the KTN element 4 (on the sample movable mirror side). With this configuration, even if the convex lens effect appears in the KTN element, the inserted concave lens makes the parallel light, and the light is sufficiently condensed on the sample by adjusting the objective lens near the sample. For this reason, the working distance from the KTN element to the sample can be sufficiently secured.

  When a concave lens is inserted behind the KTN element (on the sample movable mirror side), not only is it made parallel light, but there is also an effect of widening the deflection angle. Near infrared light with a wavelength of 1300 nm was incident on a 4 × 4 × 1.5 mm KTN device in a 1.5 mm gap, and DC ± 500 V was applied as an initial voltage to electrodes formed on both sides of a 4 mm square. Later, when an AC voltage of ± 400 V was applied, the deflection angle when an f = −20 mm lens was inserted expanded to about ± 10 degrees. For this reason, the deflection angle of light can be increased by inserting the concave lens behind the KTN element.

  The concave lens to be inserted is arranged so that collimated light is output from the concave lens when parallel light is input to the KTN element. If the concave lens to be inserted at this time is a plano-concave lens, adjustment is easy. That is, one side of the plano-concave lens is a flat part, and when it is inserted, each plane can be easily determined because the plane part of the plano-concave lens and the end face of the KTN element face each other.

<About optical deflection characteristics by KTN>
The light deflection effect by KTN affects only the polarization component in the direction of the internal electric field, that is, the TE mode, of the light beam incident on KTN. For this reason, in order to efficiently deflect the traveling direction of the measurement light from KTN, the light beam incident on KTN is linearly polarized light, and the polarization direction is preferably the same as the direction of the electric field applied to KTN. For this reason, it is desirable that the polarization component of the light source is only the TE mode, or that the polarizer is transmitted immediately after emission from the light source. In the present embodiment, the light source emits linearly polarized light having the same electric field direction applied to the KTN.

<Measurement of KTN-TD-OCT>
In the present embodiment, a voltage that periodically fluctuates with an amplitude of ± 400 V and 200 kHz is applied to KTN4, the sample movable mirror 8 is driven by 1 kHz, the light is deflected, and the sample T is scanned. Thereby, a two-dimensional scan in the plane direction can be performed. Further, as described above, the information in the depth direction can be obtained by driving the reference light mirror 10 at about 10 Hz, and the signal processing device 12 uses the light intensity detected by the photodetector 11 and the X deflection electrode. The information on the sample T is organized based on the voltage 5, the driving voltage of the sample movable mirror 8, and the position of the reference light movable mirror 10, and the image is reconstructed and displayed. Thereby, a three-dimensional image can be taken.

<Applied voltage waveform of KTN>
As described above, in this embodiment, the operating speed of the component that controls the light is 200 kHz for the KTN element, 1 kHz for the movable mirror for sample, and 10 Hz for the movable mirror for reference light. Therefore, when acquiring a three-dimensional image, after scanning along the sample surface, move the reference light movable mirror and scan the surface again to obtain information on the next layer. Is desirable. This is because when the movable mirror for reference light is gradually moved and the depth direction at a certain point of the sample is acquired and then moved in the plane direction, the operation speed of the movable mirror for reference light determines the data acquisition speed. It is.

  FIG. 3 is a flowchart showing the processing flow of the scan operation of this embodiment, and FIG. 4 is a diagram for explaining the scan operation. In the present embodiment, a sample T (see FIG. 1) in which the fingerprint 40 is formed on the surface of the epidermis 41 having the sweat glands 42 is scanned. In the scan, a plane scan is performed parallel to the surface of the fingerprint 40 (X direction and Y direction), and then moved in the depth direction (Z direction) of the epidermis 41 to perform a plane scan for the next layer. As shown in FIG. 3, a planar scan is started for the first layer by the KTN element 4 and the sample movable mirror 8 (S1), and after completion (S2), the reference light movable mirror 10 is moved by one step (S3). ) To move to the next layer. The same operation as S1 to S3 can be repeated to perform a three-dimensional scan. Since the operation speed of the reference light movable mirror is significantly slower than other operation speeds, the same measurement as described above is possible even if the reference light movable mirror is moved simultaneously.

  In the case of this embodiment, when the number of measurement points in the scanning direction by KTN is 200 points, three-dimensional image data of 200 points (X) × 400 points (Y) × 100 points (Z) is acquired in 0.1 seconds. be able to. Thus, by driving the KTN element and the sample movable mirror to deflect the light and scanning the sample, three-dimensional data can be collected at high speed.

  KTN indicates a response corresponding to the shape of the applied voltage waveform. Thus, for example, when an AC voltage is applied, the light is deflected at a sinusoidal speed.

  When scanning a light beam to obtain a two-dimensional image or a three-dimensional image with a general OCT apparatus, the AD conversion interval used for measurement sampling is constant, so the scan speed of the sample is also constant. It is desirable to do. For this reason, the applied voltage waveform to KTN is preferably a sawtooth wave, a triangular wave, or the like (see FIG. 5A).

  Similarly to the above, the applied voltage waveform of the galvanometer mirror can be used as a desirable waveform such as a sawtooth wave or a triangular wave that can be scanned at a constant speed. However, when the applied voltage waveform changes abruptly at the mirror return point as in the sawtooth wave, the response is slower than when the applied voltage waveform changes slowly at the mirror return point as in the triangular wave. Becomes unstable. This is because a high frequency component is superimposed on the applied voltage. For this reason, the triangular wave is more desirable than the sawtooth wave (FIG. 5B). Alternatively, it is desirable to use a sawtooth wave shape in which the change in the applied voltage waveform at the turning point of the mirror is gradual (FIG. 5C). This is because the superposition of the high-frequency component of the applied voltage can be suppressed by gradually changing the applied voltage waveform at the mirror turning point.

  However, if it is not constant, there is a difference in the number of measurement points for each measurement part of the sample. In this case, it is necessary to change the sampling interval according to the scanning speed of KTN.

  In addition, by using the optical coherence tomography apparatus according to the present embodiment for the fundus imaging apparatus, it is possible to reduce the blur of the image due to motion artifacts such as blinking of the patient and the burden on the patient for maintaining the posture.

(Second Embodiment)
The optical coherence tomography apparatus according to the second embodiment has a KTN, one concave lens, and a galvanomirror system as means for scanning a light beam of TD-OCT low interference light (beam scanning unit), In this configuration, a deflection filter is provided at the subsequent stage of the light source.

  First, the configuration of the optical coherence tomography apparatus according to the present embodiment will be described. FIG. 6 shows a configuration of the optical coherence tomography apparatus according to the present embodiment, and FIG. 7 shows a configuration example of a beam scanning unit that is a portion surrounded by a broken line in FIG. As shown in FIG. 6, the optical coherence tomography apparatus includes a light source 1 including a collimator 2 in a light emitting portion, a polarizing filter 13, a beam splitter 3, a KTN element (X) 4, and an X deflection electrode pair. 5, a power source 6 for X deflection, a concave lens 7, a movable mirror 8 for a sample, an objective lens 9, a movable mirror 10 for reference light, a photodetector 11 such as a PD, and a signal processor 12. And is configured. Further, in the present embodiment, as shown in FIG. 7, the beam scanning unit includes a KTN element 4 and an electrode pair 5 and a single concave lens as means for planar scanning with a light beam of TD-OCT low interference light. 7 and a galvanometer mirror system 8.

  The light source 1 includes the TM mode as well as the TE mode in the same electric field direction applied to the KTN element.

  The polarizing filter 13 emits linearly polarized light having the same electric field direction applied to the KTN element.

  A general operation mechanism of the reference light movable mirror 10 is a stepping motor, and its operation speed is about several tens of Hz.

  Since the operation method, KTN characteristics, and the like are the same as those in the first embodiment, they are omitted.

  If the polarization filter 13 also includes a TM mode that is irrelevant to the KTN deflection direction, the interference component due to the TM mode is measured as noise with respect to a desired signal, and as a result, the SN ratio is degraded. Will end up. The polarization filter 13 filters the components that are not deflected by the KTN, thereby improving the S / N ratio of the measurement.

  In addition, by using the optical coherence tomography apparatus according to the present embodiment for the fundus imaging apparatus, it is possible to reduce the blur of the image due to the blink of the patient and the burden on the patient for maintaining the posture. In addition, by using the light beam deflection portion of the optical coherence tomography apparatus according to the present embodiment for a blood vessel endoscope, a mechanism for mechanically rotating a micromirror for observing a blood vessel wall becomes unnecessary, and spatial resolution is reduced. It is possible to take a three-dimensional image inside the blood vessel without doing so.

  Since the operation speed of the component that controls light is the same as that of the first embodiment, it is omitted.

(Third embodiment)
The optical coherence tomography apparatus according to the third embodiment has two KTN, a λ / 2 plate, and two flat planes as means (plane scanning unit) for scanning a light beam of TD-OCT low interference light. And a concave lens system.

  First, the configuration of the optical coherence tomography apparatus according to the present embodiment will be described. FIG. 8 shows a configuration of the optical coherence tomography apparatus according to the present embodiment, and FIG. 9 shows a configuration example of a beam scanning unit that is a portion surrounded by a broken line in FIG. As shown in FIG. 8, the optical coherence tomography apparatus includes a light source 1 including a collimator 2 in a light emitting portion, a beam splitter 3, a KTN element (X) 4a, an X-direction deflection electrode 5a, and an X-deflection. KTN power supply 6a, concave lens 7a, polarizer 14, KTN element (Y) 4b, Y-direction deflection electrode 5b, X-deflection KTN power supply 6b, concave lens 7b, objective lens 9, It has a reference light movable mirror 10, a photodetector 11 such as a PD, and a signal processing device 12. Further, in this embodiment, as shown in FIG. 9, the beam scanning unit includes two sets of KTN elements 4a and 4b and an electrode pair 5a as means for planar scanning with a light beam of low interference light of TD-OCT. 5b, a λ / 2 plate 14, and two concave lenses 7a and 7b.

  The light source 1 emits linearly polarized light in the same direction as the direction of the electric field applied to the KTN element (X) 4a.

  A general operation mechanism of the reference light movable mirror 10 is a stepping motor, and its operation speed is about several tens of Hz.

  The operation method, KTN characteristics, and the like are the same as in the first embodiment.

  The convex lens effect that appears in the KTN elements 4a and 4b described above is a concave lens that can compensate for the X-axis and Y-axis convex lens effects, just after each KTN element 4a and 4b, just before, or on both sides. Compensate by inserting. In the present embodiment, it is inserted immediately after each KTN element 4a, 4b.

  The concave lenses 7a and 7b to be inserted are selected based on the convex lens power of the KTN to be compensated and the distance from the KTN element to the concave lens. As the type of lens to be inserted, a spherical plano-concave lens, a spherical biconcave lens, a cylindrical lens, a GRIN lens, or the like is desirable. In the present embodiment, the convex lens powers of the two KTNs are compensated by the two cylindrical lenses.

  In this embodiment, scanning is performed with respect to two axes (X axis and Y axis) using two KTNs. Each KTN electrode pair is installed on a side surface orthogonal to the other KTN electrode pair. When scanning with respect to two axes (X-axis and Y-axis), voltages applied to the two pairs of electrodes Is controlled to guide the beam to a desired part.

  As described above, light deflection by KTN is in the same direction as the voltage direction of KTN, that is, only in the TM mode. For this reason, when a beam is scanned using two KTNs 4a and 4b, a polarizer 14 such as a λ / 2 plate is inserted between the two KTNs 4a and 4b, and a deflection component is deflected in the direction of deflecting the light. Need to rotate. If a polarizer 14 such as a λ / 2 plate is not inserted between the two KTNs 4a and 4b, light deflection by one KTN 4a and 4b cannot be obtained, so that biaxial scanning cannot be performed.

<Applied voltage waveform of KTN>
As described above, in this embodiment, the operating speed of the component that controls the light is 200 kHz for the KTN element (X), 1 kHz for the KTN element (Y), and 10 Hz for the movable mirror for reference light. Therefore, when acquiring a three-dimensional image, after scanning along the sample surface, move the reference light movable mirror and scan the surface again to obtain information on the next layer. Is desirable. This is because when the movable mirror for reference light is gradually moved and the depth direction at a certain point of the sample is acquired and then moved in the plane direction, the operation speed of the movable mirror for reference light determines the data acquisition speed. It is.

  FIG. 10 is a flowchart showing the processing flow of the scanning operation of this embodiment, and FIG. 11 is a diagram for explaining the scanning operation. In the present embodiment, a sample T (see FIG. 8) in which the fingerprint 40 is formed on the surface of the epidermis 41 having the sweat glands 42 is scanned. In the scan, a plane scan is performed parallel to the surface of the fingerprint 40 (X direction and Y direction), and then moved in the depth direction (Z direction) of the epidermis 41 to perform a plane scan for the next layer. As shown in FIG. 11, a planar scan is started for the first layer by the KTN element 4 and the sample movable mirror 8 (S1), and after completion (S2), the reference light movable mirror 10 is moved by one step (S3). ) To move to the next layer. The same operation as S1 to S3 can be repeated to perform a three-dimensional scan. Since the operation speed of the reference light movable mirror is significantly slower than other operation speeds, the same measurement as described above is possible even if the reference light movable mirror is moved simultaneously.

  In the case of this embodiment, when the number of measurement points in the scanning direction by KTN is 200 points. 200 points (X) × 400 points (Y) × 100 points (Z) of three-dimensional image data can be acquired in 0.1 seconds. Thus, by driving the KTN element and the sample movable mirror to deflect the light and scanning the sample, three-dimensional data can be collected at high speed.

  KTN indicates a response corresponding to the shape of the applied voltage waveform. Thus, for example, when an AC voltage is applied, the light is deflected at a sinusoidal speed.

  When scanning a light beam to obtain a two-dimensional image or a three-dimensional image with a general OCT apparatus, the AD conversion interval used for measurement sampling is constant, so the scan speed of the sample is also constant. It is desirable to do. For this reason, the applied voltage waveform to KTN is preferably a sawtooth wave, a triangular wave, or the like (see FIG. 12).

  However, if it is not constant, there is a difference in the number of measurement points for each measurement part of the sample. In this case, it is necessary to change the sampling interval according to the scanning speed of KTN.

  In addition, by using the optical coherence tomography apparatus according to the present embodiment for the fundus imaging apparatus, it is possible to reduce the blur of the image due to the blink of the patient and the burden on the patient for maintaining the posture. In addition, by using the light beam deflection portion of the optical coherence tomography apparatus according to the present embodiment for a blood vessel endoscope, a mechanism for mechanically rotating a micromirror for observing a blood vessel wall becomes unnecessary, and spatial resolution is reduced. It is possible to take a three-dimensional image inside the blood vessel without doing so.

The present invention is useful for a three-dimensional tomographic imaging apparatus near the surface of a living body.

DESCRIPTION OF SYMBOLS 1 Light source 2 Collimator 3 Beam splitter 4 KTN element 5 Electrode pair 6 KTN power supply 7 Concave lens 8 Specimen movable mirror 9 Objective lens 10 Reference light movable mirror 11 Photo detector 12 Signal processing unit 40 Fingerprint 41 Epidermis 42 Sweat gland T Sample S reflected light

Claims (10)

An optical coherence tomography apparatus that generates an optical tomographic image of a subject using reflected light obtained by irradiating the subject with low interference light,
A light source that outputs low interference light,
A beam splitter that divides the low interference light into two directions and outputs it as reference light and measurement light;
Plane scanning means for irradiating the subject with the measurement light by plane scanning, and inputting the reflected light reflected from the subject again to the beam splitter;
A reference light mirror that reflects the reference light output from the beam splitter and inputs it again to the beam splitter;
A light detecting means for detecting light in which the reference light and the reflected light are combined by the beam splitter;
A signal processing device that analyzes the interference of light detected by the light detection means and generates an optical tomographic image of the subject,
The plane scanning unit has a light beam deflecting unit using an electro-optic crystal, acquires data of a plane perpendicular to the incident direction of light for each layer,
The light beam deflecting means deflects an incident light beam by an electric field formed by the voltage when a voltage is applied to the electro-optic crystal and induces a refractive index distribution in the electro-optic crystal. ,
The refractive index distribution has a function of a convex lens whose refractive index is convexly inclined with respect to the deflection direction, and the focal point of the convex lens can be moved horizontally with respect to the scanning axis so that scanning in the scanning axis direction can be performed. An optical coherence tomography apparatus.   2. The optical coherence tomography apparatus according to claim 1, wherein the planar scanning unit includes a concave lens in a front stage or a rear stage of the electro-optic crystal of the light beam deflecting unit, or in both the front stage and the rear stage. .   The optical coherence tomography apparatus according to claim 1, wherein a DC voltage is applied to the electro-optic crystal before the voltage is applied.   The electro-optic crystal is formed in a rectangular parallelepiped shape, and further includes an electrode for applying a voltage to the electro-optic crystal on the opposing electro-optic crystal surface of the rectangular parallelepiped shape. The optical coherence tomography apparatus according to any one of claims 1 to 3. The electro-optic crystal is a potassium tantalate niobate (KTa _1-x Nb _x O ₃ (0 <x <1): KTN) crystal or lithium-doped (K _1-y Li _y Ta _1-x Nb _x 5. The optical coherence tomography apparatus according to claim 1, wherein the optical coherence tomography apparatus is an O ₃ (0 <x <1, 0 <y <0.1): KLTN) crystal.   The optical coherence tomography apparatus according to claim 1, wherein the plane scanning unit scans the measurement light at a constant speed.   7. The optical coherence tomography apparatus according to claim 1, wherein the planar scanning unit performs planar scanning of the measurement light by a light beam deflecting unit using two or more electro-optic crystals. .   7. The planar scanning unit further includes a galvano mirror, and the measurement light is planar scanned by the galvano mirror and a light beam deflecting unit using the electro-optic crystal. The optical coherence tomography device according to item 1.   The optical coherence tomography apparatus according to claim 8, wherein the galvanometer mirror is driven by a triangular wave.   9. The optical coherence tomography apparatus according to claim 8, wherein the galvanometer mirror has a sawtooth wave shape and is driven by a drive waveform in which a change in applied voltage waveform at a mirror turning point is gentle.

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