WO2021149173A1

WO2021149173A1 - Optical coherence tomography apparatus and method for controlling same

Info

Publication number: WO2021149173A1
Application number: PCT/JP2020/002056
Authority: WO
Inventors: 洋紀矢澤; 久美子西村; 勇輝照井; 秀太朗大西; 朝陽福田; 俊亀井; 中山　繁
Original assignee: 株式会社ニコン
Priority date: 2020-01-22
Filing date: 2020-01-22
Publication date: 2021-07-29
Also published as: JP7327521B2; JPWO2021149173A1

Abstract

Provided is an optical coherence tomography apparatus comprising: a wavelength-sweeping type light source for emitting laser light, the light source capable of wavelength-sweeping the wavelength of the emitted laser light over a sweeping range Δλ = λN - λ1 from a wavelength λ1 to a wavelength λN; a branching unit for branching the laser light emitted from the light source into measurement light and reference light; a scanning unit for directing the measurement light toward a predetermined region of an object to scan the same; an interference unit for generating interference light of reflection light from the predetermined region of the object and the reference light; a detection unit for detecting the interference light and outputting a detection signal; and a controlling unit for controlling the light source and the scanning unit such that the scanning unit scans the predetermined region M times and an irradiation initiation wavelength λm in the m-th scan satisfies λm = λ1 + (m - 1) × Δλ / M, where M and m are integers of M > m> 1, so as to obtain a tomographic image of the predetermined region of the object.

Description

Control method of optical coherence tomography and optical coherence tomography

The present invention relates to an optical coherence tomography and an optical coherence tomography.

International Publication No. 2010/123892 discloses an optical coherence tomography that acquires tomographic images using a wavelength sweep light source.

The optical interference tomometer of the technique of the present disclosure is a wavelength sweep type light source that emits laser light and can sweep the wavelength of the emitted laser light with a sweep width Δλ = λN−λ1 from wavelength λ1 to wavelength λN. , A branch portion that branches the laser light emitted from the light source into a measurement light and a reference light, a scanning unit that scans the measurement light toward a predetermined region of the object, and reflection from the predetermined region of the object. An interference unit that generates interference light between light and the reference light, a detection unit that detects the interference light and outputs a detection signal, and the predetermined area in order to acquire a tomographic image of a predetermined area of the object. M (M and m are integers, M> m> 1) scans, and the irradiation start wavelength λm in the mth scan is set to λm = λ1 + (m-1) × Δλ / M. It includes a light source and a control unit that controls the scanning unit.

It is a figure which shows the schematic structure of the ophthalmic apparatus 110. It is a figure which shows the relationship between the wavelength sweep and the scanning of the measurement light in the prior art. It is a figure which shows the relationship between the wavelength sweep and the scanning of the measurement light in the 1st Embodiment. It is a timing chart which shows the relationship between the wavelength sweep and the scanning of the measurement light in 1st Embodiment. It is a figure which shows the principle that SNR is improved by scanning of the measurement light in 1st Embodiment. It is a figure which shows the schematic structure of the ophthalmic apparatus 110 of the 2nd Embodiment. It is a timing chart which shows the relationship between the wavelength sweep and the scanning of the measurement light of the 2nd Embodiment. It is a timing chart which shows the relationship between the wavelength sweep and the drive timing of a polygon mirror 24. It is a figure which shows the construction method of A-Scan data. It is a timing chart which shows the relationship between the wavelength sweep and the scanning of the measurement light in the modification of the 2nd Embodiment. It is a timing chart which shows the relationship between the wavelength sweep of 3rd Embodiment, and the drive timing of a polygon mirror 24. It is a figure which shows the schematic structure of the photographing optical system 19T of the ophthalmic apparatus 110 of 4th Embodiment. It is a figure which shows the schematic structure of the photographing optical system 19U of the ophthalmic apparatus 110 of the 5th Embodiment. 6 is a timing chart showing the relationship between wavelength sweeping and scanning of measurement light when acquiring a B-Scan image according to the fifth embodiment. 6 is a timing chart showing the relationship between wavelength sweeping and scanning of measurement light when acquiring a B-Scan image of the sixth embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
Hereinafter, the ophthalmic apparatus according to the first embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of the ophthalmic apparatus 110.
The ophthalmic apparatus 110 is an example of the "optical coherence tomography" of the technique of the present disclosure.

For convenience of explanation, the optical coherence tomography is referred to as "OCT".

When the ophthalmic apparatus 110 is installed on a horizontal plane, the horizontal direction is the "X direction" and the direction perpendicular to the horizontal plane is the "Y direction", connecting the center of the pupil of the anterior segment of the eye 12 to the center of the eyeball. The direction is "Z direction". Therefore, the X, Y, and Z directions are perpendicular to each other.

The ophthalmic apparatus 110 includes a control device 16, an OCT unit 20, and an imaging optical system 19. The OCT unit 20 and the photographing optical system 19 are controlled by the control device 16. A tomographic image or frontal image (en-face image) of the retina created based on the OCT data acquired by the OCT unit 20 is referred to as an OCT image.

The control device 16 includes a computer having a CPU (Central Processing Unit) 16A, a RAM (Random Access Memory) 16B, a ROM (Read-Only memory) 16C, and an input / output (I / O) port 16D. ing.

The control device 16 includes an input / display device 16E connected to the CPU 16A via the I / O port 16D. The input / display device 16E has a graphic user interface for displaying an image of the eye 12 to be inspected and receiving various instructions from the user. The graphic user interface includes a touch panel display.

Further, the control device 16 includes an image processing device 17 connected to the I / O port 16D. The image processing device 17 generates an image of the eye to be inspected 12.
The image processing device 17 is an example of the “tomographic image generation unit” of the technique of the present disclosure.

As described above, in FIG. 1, the control device 16 of the ophthalmic device 110 includes the input / display device 16E, but the technique of the present disclosure is not limited to this. For example, the control device 16 of the ophthalmic apparatus 110 may not include the input / display device 16E, but may include an input / display device that is physically independent of the ophthalmic apparatus 110. In this case, the display device includes an image processing processor unit that operates under the control of the CPU 16A of the control device 16. The image processing processor unit may display a tomographic image or the like based on the image signal output instructed by the CPU 16A.

The OCT unit 20 includes a light source 20A, a sensor (detection element) 20B, a first optical coupler 20C, a reference optical system 20D, a collimating lens 20E, and a second optical coupler 20F.

The light source 20A of the OCT unit 20 emits wavelength sweep type light (laser light) under the control of the CPU 16A. More specifically, as the light source 20A, a tunable light source (wavelength scanning light source) that changes the emission wavelength at high speed in time is used. The light source 20A is composed of, for example, a laser medium, a resonator, and a wavelength selection filter. Examples of the wavelength selection filter include a combination of a diffraction grating and a polygon mirror, and a filter using Fabry-Perot Etalon. Further, as the light source 20A, a VCSEL type tunable light source may be used. In the first embodiment, the CPU 16A controls the diffraction grating and the polygon mirror so that light having a desired wavelength (measurement light described later) is emitted at a desired time. As a result, the light source 20A sweeps the wavelength with the sweep width Δλ = λN−λ1 from the wavelength λ1 to the wavelength λN and the sweep time Tswept.

The photographing optical system 19 includes a KTN scanner 23, a reflection mirror 25, and a relay optical system 30.

The KTN scanner 23 has a property that the refractive index can be freely changed by applying a voltage of a KTN crystal (an oxide crystal composed of potassium (K), tantalum (Ta), and niobium (Nb)) (space charge control electro-optical effect). It is a high-speed and compact optical scanner with no moving parts. The scanning time of the measurement light of the KTN scanner 23 is the same as the sweep time Tswept of the wavelength of the light source 20A. In the first embodiment, the CPU 16A synchronizes the wavelength sweep of the light source 20A and the scanning of the measurement light of the KTN scanner 23. The CPU 16A has the light source 20A and the KTN scanner 23 so that the start timing and end timing of the wavelength sweep of the light source 20A and the start timing and end timing of scanning the measurement light by the KTN scanner 23 are the same. To control.

The relay optical system 30 is composed of a plurality of lenses. Further, the relay optical system 30 is configured so that the position of the KTN scanner 23 and the position of the pupil are conjugated.

The light emitted from the light source 20A is branched by the first optical coupler 20C. One of the branched lights is made into parallel light by the collimating lens 20E as measurement light, and then is incident on the photographing optical system 19. The measurement light is scanned by the KTN scanner 23 in a predetermined direction (for example, the Y direction). The scanning light is applied to the fundus through the relay optical system 30 and the pupil. The measurement light reflected by the fundus is incident on the OCT unit 20 via the relay optical system 30 and the KTN scanner 23, and is incident on the second optical coupler 20F via the collimating lens 20E and the first optical coupler 20C. do.

The other light emitted from the light source 20A and branched by the first optical coupler 20C is incident on the reference optical system 20D as reference light, and is incident on the second optical coupler 20F via the reference optical system 20D. do.

These lights incident on the second optical coupler 20F, that is, the measurement light reflected by the fundus and the reference light are interfered with by the second optical coupler 20F to generate interference light. The interference light is received by the sensor 20B. The image processing device 17 operating under the control of the CPU 16A generates an OCT image such as a tomographic image of the fundus (retina) or an en-face image based on the OCT data detected by the sensor 20B. It is also possible to generate an OCT image such as a tomographic image or an en-face image of the anterior segment of the eye by reflecting the measurement light not only on the fundus but also on the anterior segment of the cornea or the crystalline lens.
The first optical coupler 20C, the KTN scanner 23, the second optical coupler 20F, and the sensor (detection element) 20B are the "branch portion", "scanning portion", "interference portion", and "interference portion" of the techniques of the present disclosure, respectively. This is an example of a "detector".

Next, the relationship between the wavelength sweep and the scanning of the measurement light will be described with reference to FIG. 2A and FIGS. 2B and 3.

FIG. 2A shows the relationship between wavelength sweeping and scanning of measurement light in the prior art. A case where a straight line region is designated as a region for acquiring a tomographic image of the fundus will be described. As shown in FIG. 2A, in the scanning of the measurement light in the conventional technique, the wavelength of the light source is swept at one point on the retina, the interference light is detected, and a one-dimensional tomographic image (A-Scan image) is acquired. The measurement light is scanned at the measurement point of. This is repeated to construct a two-dimensional tomographic image (B-Scan image) G1. In this way, the measurement light irradiates one point on the retina while sweeping the wavelengths from λ1 to λN. Therefore, the time during which the measurement light is irradiated to one point of the retina is longer than the corresponding time in the first embodiment described in detail later.

FIG. 2B shows the relationship between the wavelength sweep and the scanning of the measurement light in the first embodiment. As shown in FIG. 2B, in the first embodiment, the measurement light in the scanning direction F is scanned a plurality of times (S1, S2, ... SM) for the range RI for acquiring the tomographic image as follows. At the same time, the wavelength of the measurement light irradiated to each region (for example, a point) of the range RI is different in each scan (S1, S2, ... SM).

First, let Tscan be the time required to scan the range RI for acquiring a tomographic image once, and Tswept be the time required for wavelength sweeping.
Tscan = Tswept
Is.

Then, the scanning of the measurement light is repeated while shifting the wavelength sweep timing. Specifically, the measurement light is scanned M (M and m are integers, M> m> 1) times in the range RI for acquiring the tomographic image, and the irradiation start wavelength λm in the mth scan is set to λm. The CPU 16A controls the light source 20A and the KTN scanner 23 so that = λ1 + (m-1) × Δλ / M. Note that λ1 is the wavelength at which the scanning start region RS in the range RI for acquiring the tomographic image in the first scanning is irradiated.

In particular,
λ2-λ1 = Δλ / M, λ2 = λ1 + Δλ / M,
λ3-λ2 = Δλ / M, λ3 = λ1 + 2 × Δλ / M,
...
λN-λN-1 = Δλ / M, λN = λ1 + (M-1) × Δλ / M
Is.

More specifically, it is as follows.
(1) In the first scanning S1, as the measurement light is scanned from the start region RS to the end region RE of the scan in the range RI for acquiring the tomographic image, the wavelength of the measurement light applied to the range RI is λ1. , Λ2, ... λN.
(2) When the scan end region RE is scanned in the first scan S1, the wavelength can be swept from λ2 by the time the scan start region RS of the second scan S2 is scanned. , Light source 20A is controlled.
(3) In the second scanning S2, the wavelength of the measurement light applied to the range RI is from λ2 to λN as the measurement light is scanned from the start region RS to the end region RE of the scan in the range RI. It is swept and finally swept to λ1 in the end region RE. The irradiation start wavelength λ2 in the m (= 2) th scan is
λ2 = λ1 + (2-1) × Δλ / M.
(4) When the scanning end region of the second scanning S2 is scanned, the wavelength can be swept from λ3 by the time the scanning start region RS of the third scanning S3 is scanned. The light source 20A is controlled.
(5) The irradiation start wavelength λ3 in the third scan S3 is
λ3 = λ1 + (3-1) × Δλ / M.
Such control of the light source 20A and the KTN scanner 23 is repeated, the range RI for acquiring the tomographic image is performed a plurality of (M) times, and the detection signal for generating the final tomographic image G110 can be acquired. ..
The range RI for acquiring tomographic images is an example of a "predetermined area" of the technique of the present disclosure.

The scanning performed while shifting the wavelength sweep timing of the measurement light will be described in detail with reference to FIG. In the first embodiment, in order to acquire B-Scan data which is a tomographic image, a linear scan is performed on the range in which the tomographic image is acquired in the retina. That is, the measurement light is applied to the predetermined line segment section RI, which is the range for acquiring the tomographic image. The scanning performed for acquiring the B-Scan data for the line segment section RI has been performed once in the past, but in the first embodiment, it is performed a plurality of (M) times (2000 times in FIG. 3).

In the first scanning S1 of the measurement light, the light source 20A and the KTN scanner 23 are controlled so that the measurement light from the light source 20A is scanned for the line segment section RI while the wavelength is swept from the wavelength λ1 to the wavelength λ2000. .. Specifically, first, the first region R1 of the line segment section RI is irradiated with the measurement light having the wavelength λ1. As the KTN scanner 23 is driven, the measurement light moves in the line segment section RI in the B-Scan scanning direction. For example, the region R2 adjacent to the region R1 is irradiated with the measurement light having the wavelength λ2. In this way, in the line segment section RI, when the measurement light is scanned from left to right on the paper surface of FIG. 2, the wavelength of the measurement light changes from λ1 to λN (for example, λ2000). Therefore, each region (for example, a point) of the line segment section RI is irradiated with measurement light having a different wavelength.

In the second scanning S2 of the measurement light, the light source 20A and the KTN scanner 23 are controlled so that the measurement light having the wavelength λ2 is irradiated to the first region R1 of the line segment section RI. After the region R2, the wavelength of the measurement light is swept up to the region R1999 immediately before the last region R2000, as in the first scan. Specifically, at the timing when the wavelength λ3 is reached, the measurement light of the wavelength λ3 is irradiated to the region R2 adjacent to the region R1, and at the timing when the wavelength λ4 is reached, the measurement light of the wavelength λ4 is the region next to the region R2. R3 is irradiated, and the region R1999 is irradiated with measurement light having a wavelength of λ2000. Then, the final region R2000 is irradiated with the measurement light having the wavelength R1.

The above is repeated until the total M (2000 in FIG. 3) scan of the measurement light. As a result, for example, the first region R1 in the line segment section RI is irradiated with light of all wavelengths from λ1 to λ2000 by 2000 scans. This means that the measurement light to the region R1 is divided into 2000 times and irradiated, and the total energy amount of the light continuously irradiated to the region R1 is the case of the scanning method of FIG. 2A of the prior art. Becomes smaller. That is, in the scanning method of FIG. 2A of the conventional technique, the scanning start region is continuously irradiated with the measurement light in the range of λ1 to λN (λ2000) for the wavelength sweep time. Therefore, the amount of energy of the light continuously irradiated to the region R1 is larger than that of the first embodiment.
The time during which the measurement light is continuously irradiated to each region (for example, a point) in the line segment section RI, which is the range for acquiring the tomographic image, is shown in FIG. 2B by the scanning method of FIG. 2A of the conventional technique. The scanning method of the first embodiment is shorter.

The time required for 2000 scans of the measurement light in the first embodiment is as follows.
For example, if the wavelength sweep period is 200 kHz and the wavelength sweep argument is 2000 (λ1 to λ2000),
(1/200 kHz) x (2000) = 0.01 (seconds)

This can be twice as fast as the time required for scanning the measurement light in the above-mentioned conventional technique.

In the first embodiment, IEC6025-1 (2014 version), which is one of the world standards, is adopted as a laser safety standard for the eyes. According to the criteria, the acceptable laser power incident on the eye (Maximum Permissible Exposure: MPE) is derived by the following equation.
18 × t ^0.75 × C4 × C6 (Jm- ² ) ・・・ (1)

Here, C4 and C6 are constants, and t is the total irradiation time of the laser irradiated per retina. The MPE derived here is a value on the cornea of the eye.

As specified in equation (1), MPE is proportional to t to the 0.75th power. That is, when the sweep speed of the wavelength sweep light source is increased and the irradiation time per retina is shortened, the laser power cannot be increased proportionally. That is, a simple speedup results in a reduction in the SNR (SN ratio: signal-to-noise ratio) of the OCT image at the same time.

In the scanning of the measurement light of the first embodiment, the irradiation time t of the derivation formula (1) of the laser safety standard for the eye is an extremely short time during which one of the total sweep wavelengths is oscillating. For example, if the wavelength sweep period is 200 kHz and the wavelength sweep argument is 2000 (λ1 to λ2000),
t = (1/2000 kHz) x (1/2000) = 2.5 x ^10-9 (seconds)
Will be.

The measurement light scanned in the conventional art, t = (1 / 200kHz) = 5.0x10 -6 becomes seconds.

Since MPE is proportional to the 0.75th power of t, it is possible to increase the permissible incident laser power in the scanning of the measurement light of the first embodiment. Therefore, the SNR can be improved.

FIG. 4 shows the principle that the SNR is improved by scanning the measurement light in the first embodiment. In FIG. 4, the vertical axis represents the intensity of the laser beam and the horizontal axis represents the time of irradiation, and in order to maintain safety, the irradiation time of irradiating a certain area (for example, a point) with the laser light and the irradiation of the area. It is a figure which showed the relationship with the intensity of the laser light.
As shown in FIG. 4, in the conventional technique, for example, in scanning the measurement light having a wavelength sweep speed of 100 kHz, the irradiation time for continuously irradiating each region of the range in which the tomographic image is acquired with the laser light becomes long. For safety reasons, the laser intensity needs to be low (see rectangular area I in FIG. 4). Further, in the conventional technique, for example, when scanning the measurement light having a wavelength sweep speed of 200 kHz, the wavelength sweep speed increases, so that the irradiation time of continuously irradiating each region of the tomographic image acquisition range with the laser beam is 100 kHz. It will be shorter than. Therefore, the intensity of the laser beam for maintaining safety can be increased as compared with the case of 100 kHz (see the rectangular region II in FIG. 4).
On the other hand, in the scanning of the measurement light of the first embodiment (for example, when the wavelength sweep speed is 200 kHz), since a plurality of tomographic image acquisition ranges are scanned, the time for continuously irradiating the laser light is increased. It can be shortened and the intensity of the laser beam per unit time can be increased (see rectangular region III in FIG. 4). As described above, in the scanning of the measurement light of the first embodiment, since the laser light having high intensity can be used, the SNR becomes high.

Focusing on only one of the total sweep wavelengths (for example, λ1), the time it is irradiated per retina is the same as the scanning of the measurement light of the conventional technique.

Speaking of the following relative SNR derivation formula (2), it is possible to realize a situation in which the allowable incident laser power is improved but the irradiation time does not change.

Relative SNR = [(Allowable incident laser power / 100 kHz allowable incident laser power) x (Irradiation time per retina / 100 kHz irradiation time)] ^0.5 ... (2)

Calculating from the derivation formulas (1) and (2), it is possible to realize a relative SNR improvement of about 1.99 times.

As described above, by scanning the measurement light of the first embodiment, it is possible to simultaneously realize high-speed acquisition of the tomographic image and improvement of SNR in the tomographic image.

[Second Embodiment]

Next, the ophthalmic apparatus of the second embodiment will be described with reference to the drawings. Since the configuration of the ophthalmic apparatus of the second embodiment is substantially the same as the configuration of the ophthalmic apparatus of the first embodiment, the same parts are designated by the same reference numerals, the description thereof will be omitted, and mainly. Only the different parts will be described.

FIG. 5 shows a schematic configuration of the ophthalmic apparatus 110 of the second embodiment. As shown in FIG. 5, in the ophthalmic apparatus 110 of the second embodiment, the polygon mirror 24 is used instead of the KTN scanner 23 and the reflection mirror 25 of the photographing optical system 19 of the ophthalmic apparatus 110 of the first embodiment. I have. The ophthalmologic apparatus 110 scans the area R1, the area R2, ... the area R100 ... the area RN obtained by dividing the range RI for acquiring the tomographic image of the retina, and obtains the A-Scan data of the range RI.

FIG. 6 shows the relationship between the wavelength sweep of the second embodiment and the scanning of the measurement light. FIG. 7 shows the relationship between the wavelength sweep and the drive timing of the polygon mirror 24.

As shown in FIGS. 6 and 7, in the second embodiment, a tomographic image is acquired by using a polygon mirror 24 in which the wavelength sweep time Tswept and the time Tscan required for one scan are controlled so as to be different. A method of shifting the wavelength of irradiation at each point in the range to be used is used.

Specifically, as shown in FIG. 7A, the light source 20A starts wavelength sweeping (λ1 to λ2000) every time a drive signal from the CPU 16A is input in a cycle of 200 KHz. As shown in FIG. 7B, when the drive signal output from the CPU 16A to the polygon mirror 24 changes from −d to d, the polygon mirror 24 rotates by a predetermined angle corresponding to one scan.

In the first scan S1, the wavelength sweep from λ1 to λ2000 is repeated, for example, four times, and the angle of one reflecting surface of the polygon mirror 24 on which the measurement light is incident changes with respect to the eye to be inspected. The measurement light is scanned once for the range RI for which a tomographic image is acquired.

In the second scanning S2, when the scanning of the first measurement light is completed, the CPU 16A changes the drive signal output to the polygon mirror 24 from d to −d, and the measurement is performed by the next reflecting surface of the polygon mirror 24. Allows scanning of light.
On the other hand, in the second scanning S2, the CPU 16A requires a predetermined time T0 (for example, sweeping 20 wavelengths) from the time when the first scanning of the measurement light is completed at the timing of outputting the drive signal to the light source 20A. The time, that is, the time required for sweeping the wavelength widths of λ1 to λ20 and λ21 to λ40) is delayed, and the wavelength sweep is repeated four times. Therefore, the irradiation start timing at the time of the second scanning is when a predetermined time T0 has elapsed from the time when the first scanning is completed.

In the third scanning S3, when the second scanning of the measurement light is completed, the CPU 16A changes the drive signal output to the polygon mirror 24 from d to −d in the same manner as described above.
On the other hand, in the third scan S2, the CPU 16A delays the timing of outputting the drive signal to the light source 20A by a predetermined time T0 from the time when the fourth wavelength sweep for the second scan S2 is completed. This timing is when 2 × T0 has elapsed from the end of the second scanning of the measurement light (that is, when the drive signal from the CPU 16A to the polygon mirror 24 becomes d). 2 × T0 is the time required to sweep 40 wavelengths.

In this way, the measurement light is scanned M (M>m> 1, an integer) times for the range RI for acquiring the tomographic image, and the m-th irradiation start timing Tm is from the time when the m-1th scan is completed. ,
Tm = (m-1) x Tswept / M = (m-1) x T0
The CPU 16A controls at least one of the light source 20A and the polygon mirror 24 so that the time has passed. As a result, the final B-Scan image is generated.

Explaining the above in more detail, as shown in FIG. 6, the measurement light is scanned M times for the range RI for acquiring the tomographic image, and the area R1 for acquiring the tomographic image is divided into the divided regions R1 and R2 .. A-Scan data can be obtained for each region of the region R100 ... region RN (PN). In the second embodiment, in each region for acquiring an A-Scan image, a predetermined number of wavelength ranges (for example, a wavelength range from λ1 to λ20) are swept in one scan. The measurement light is irradiated.

Specifically, the first region R1 in the first scan S1 is irradiated with the swept measurement light from λ1 to λ20. The second region R2 is irradiated with the measurement light swept from λ21 to λ40. Similarly, the 100th region R100 is irradiated with the measurement light swept from λ1981 to λ2000, as shown in the frame f200 also shown on the left side of FIG. When the wavelength of the light source 20A is swept from λ1 to λ2000, it returns to λ1 and is swept again. Since the wavelength sweep (λ1 to λ2000) of the light source 20A is repeated, the measurement light swept from λ1 to λ20 is applied to the 101st region R101. The irradiation of the measurement term by such wavelength sweep is repeated until the last region RN in the range in which the tomographic image is acquired. In the example shown in FIG. 6, the wavelength sweep is performed four times in one scan of the range in which the tomographic image is acquired. That is, the wavelength sweep from λ1 to λ2000 is repeated four times. Therefore, the time Tscan required to scan the range RI for acquiring a tomographic image once and the time Tswept required for wavelength sweep have the following relationship.
Tscan = 4 × Tswept

The technique of the present disclosure is not limited to performing four sweeps in one scan. For example, two, three, five ... may be swept in one scan. Therefore,
Tscan ≧ α × Tswept (α is an integer of 2 or more)
Is.

In the second scan S2 of the measurement light, the start timing of the wavelength sweep is shifted by T2 = (2-1) × Tswept / 100 (m = 2, M = 100).
For convenience of explanation, assuming that the wavelength λ1 is counted as one and the wavelength λ2 is similarly counted as one, the number of wavelengths swept between λ1 and λ20 is 20.
In the second scan of the measurement light, the time for sweeping and the start timing of wavelength sweep are delayed by 20 wavelengths.

As described above, each region R1 to RN of the retina is irradiated with measurement light whose wavelength has been swept by 20 wavelengths. Therefore, in the second scan of the measurement light, the measurement light is not applied to the first region R1 in the range in which the tomographic image is acquired. The measurement light is emitted from the second region R2. Specifically, the second region R2 is irradiated with the measurement light swept from λ1 to λ20. The third region R3 is irradiated with the measurement light swept from λ21 to λ40. The 100th region R100 is irradiated with the measurement light swept from λ1961 to λ1980. It is repeated until the last region RN in the range where the tomographic image is acquired. The last region RN is irradiated with the measurement light swept from λ1961 to λ1980. The timing at which the measurement light swept from λ1981 to λ2000, which is the range A of the next sweep (the rectangular area shaded in FIG. 6), is irradiated is the tomographic image in the third scan of the measurement light. This is the timing at which the measurement light is applied to the first region R1 in the acquisition range.

In the third scan S3 of the measurement light, the first region R1 in the range in which the tomographic image is acquired is irradiated with the measurement light swept from λ1981 to λ2000 as described above. After that, as in the second scan, the start timing of the wavelength sweep is delayed by 20 wavelengths. Therefore, in the third scan of the measurement light, the measurement light is not irradiated to the second region R2 in the range in which the tomographic image is acquired. The third region R3 is irradiated with the measurement light swept from λ1 to λ20. The last region RN in the range for acquiring the tomographic image is irradiated with the measurement light swept from λ1941 to λ1960. The timing at which the measurement light swept from λ1961 to λ1980, which is the next sweep range B (rectangular range not shaded in FIG. 6), is irradiated is the fault in the fourth scan S4 of the measurement light. This is the timing at which the measurement light is applied to the first region R1 in the range in which the image is acquired. Further, the timing at which the measurement light swept from λ1981 to λ2000, which is the next sweep range A, is irradiated is measured in the second region R2 in the range for acquiring the tomographic image in the fourth scan S4 of the measurement light. It is the timing when the light is irradiated.

In the example shown in FIG. 6, the above is performed up to the 100th scan (M = 100).
Assuming that the wavelength sweep from λ1 to λ2000 is performed in 100 scans, the area R1 to R99 in the range for acquiring the tomographic image is 20 of any of λ1 to λ2000 in the wavelength range from λ1 to λ2000. The measurement light in the wavelength range is not irradiated. For example, the region R1 is irradiated with the measurement light in the range of λ1 to λ20 and the range of λ41 to λ2000, but is not irradiated with the measurement light in the range of λ21 to λ40. This is because, as described above, in the second scan, the start timing of the wavelength sweep is delayed by 20 wavelengths.

On the other hand, in the region R100 to the region RN, the measurement light having a wavelength of λ1 to λ2000 is irradiated by scanning 100 times. For example, in the 100th region R100, λ1981 to λ2000 were swept by the first scan, λ1961 to λ1980 by the second scan, λ1981 to λ2000 by the third scan, and λ1 to λ20 were swept in the 100th scan. The measurement light is irradiated. That is, since all wavelengths between λ1 and λ2000 are not irradiated from region R1 to region R99, A-SCAN data is not created, and all wavelengths between λ1 and λ2000 are irradiated from region R100 to region. A-scan data is generated by RN.

The A-Scan data of the region R100 is constructed from the detection signal of the interference light between the return light of the measurement light irradiated to the region R100 and the reference light.
Since the detection signal in the region R100 is the first scan, the second scan, ... the 100th scan, and the data obtained discretely rather than continuously in time (lower side of FIG. 6). (Refer to the wavelength range in the rectangle surrounded by R100), the detection signal of each scan is stored in the memory. Then, by extracting the detection signal of the timing at each scanning time in which the area R100 is scanned from the memory, the detection signal necessary for constructing the A-Scan data of the area R100 can be obtained.

The timing at which the area R100 is scanned in the mth scan in the M times (100 times in FIG. 6) is assumed to be zero (start time) when the start time of each scan (the time when the area R1 is scanned) is set to zero (start time).
(Mm) x Tswept / M
And it can be expressed.

In the first scan, during the elapse of (100-1) × Tswept / 100 to Tswept / 100,
In the second scan, during the elapse of (100-2) × Tswept / 100 to Tswept / 100,
...
In the 100th scan, (100-100) × Tswept / 100 = zero, that is, Tswept / 100 elapses from the start time.

Therefore, since the timing at each scanning time in which the region R100 is scanned is determined by calculation, the detection signal necessary for constructing the A-Scan data in the region R100 is specified. By performing such processing from the region R100 to the region RN, a plurality of A-scan data in the region R100 to the region RN are generated, and a tomographic image which is B-scan data is generated.
..

The timing at which the region R99 is scanned is as follows.
In the first scan, during the elapse of (100-2) × Tswept / 100 to Tswept / 100,
In the second scan, during the elapse of (100-3) × Tswept / 100 to Tswept / 100,
...
In the 99th scan, (100-100) × Tswept / 100 = zero, that is, Tswept / 100 elapses from the start time.

The method of constructing A-Scan data will be specifically described with reference to FIG. As shown in FIG. 8, in the sensor 20B, for example, focusing on the detection signal corresponding to the 100th region R100, λ1981 to λ2000, λ1961 to λ1980, ... The detection signals H1, H2, ... H100 corresponding to the measurement light swept from ..λ1 to λ20 are cut out. The cut-out detection signals are aligned (H100, ... H2, H1) along the wavelength axis. This aligned detection signal corresponds to an interference spectrum signal. The image processing apparatus 17 constructs A-Scan data by performing a fast Fourier transform on the interference spectrum signal. The image processing device 17 performs the above processing for each point to construct A-Scan data. Then, these are arranged in the order of the regions R1 to RN in the range in which the tomographic image is acquired to generate B-Scan data (tomographic image data of the retina or OCT data). The range for acquiring the tomographic image may be scanned not only linearly but also rectangularly or circularly. OCT volume data can be obtained by scanning a rectangle or a circle, and stereoscopic image data of the retina can be obtained.

The generalization of the parameters realized in the second embodiment is as follows.

Total number of scans = (number of sweep wavelengths) / (timing shift amount per scan)
Total measurement speed = (1 / scanner speed) x (total number of scans)
Number of data samples = (total number of scans) x (wavelength sweep speed / scanner speed)
For example, the polygon mirror 24 assumes a hexahedral rotating six-sided mirror at a rotation speed of 100 kRPM (scanning angle 120-deg, scanning speed equivalent to 10 kHz).

Assuming that the timing shift amount for each scan is 20 wavelengths, the number of scans for generating B-Scan data is (2000) / (20) = 100 times. As a result, the total measurement speed is estimated as follows.
(1/10 kHz) x (100) = 0.01 (seconds)

The number of data samples of the OCT tomographic image in this case is
(2000/20) x (200 kHz / 10 kHz) = 2000 points.

In the conventional technique using a light source with a wavelength sweep speed of 100 kHz, when the number of data samples is 2000, the measurement speed is
(100kHz / 2000) = 50Hz
Therefore, it is possible to realize twice the speed as compared with it.

Assuming that the timing shift amount is 40 wavelengths, the total number of scans is (2000/40) = 50 times. And the total measurement speed is
(1/10 kHz) x (50) = 0.005 (s),
That is, it becomes 200 Hz, which is four times faster.

Next, the SNR improvement effect of this configuration will be described.

The scanning angle is 120-deg, which corresponds to about 33.5 mm in the range of the retina. This range is irradiated with wavelengths of (total sweep wavelength 2000) x (wavelength sweep speed 200 kHz / scanner speed 10 kHz) = 40,000 points. Then, the irradiation range per wavelength becomes 33.5 mm / 40,000 = 0.84 um.

Assuming that the diameter of the incident beam to the pupil of the eye to be inspected is 2 mm, the diameter of the focused spot on the retina is 6.62 um. Therefore, 6.62um / 0.84um = 7.88 per retina.
Therefore, about 8 wavelengths will continue to be irradiated.
When converted to time
8 x (1/2000 kHz) x (1/2000) = 20 ns
Will be.

In this case, the relative SNR is about 1.54 times when calculated according to the derivation formulas (1) and (2).

In the conventional technique using a wavelength sweep light source of 200 kHz, the relative SNR is lowered to 0.77.

In the second embodiment described above, the measurement light is scanned while repeating the wavelength sweep (λ1 to λ2000) of the light source 20A, and the start timing of the wavelength sweep is shifted in the second and subsequent scans. The techniques of the present disclosure are not limited to this.

As shown in FIG. 9, the first region R1 of each scan after the second measurement light is irradiated with the measurement light of λ1981 to λ2000, which is the last 20 wavelengths in the previous scan. This is realized by the CPU 16A adjusting the wavelength sweep of the light source 20A.

Specifically, in the first scan of the measurement light, the first region R1 in the range in which the tomographic image is acquired is irradiated with the measurement light swept from λ1 to λ20. The second region R2 is irradiated with the measurement light swept from λ21 to λ40. The third region R3 is irradiated with the measurement light swept from λ41 to λ60. The 100th region R100 is irradiated with the measurement light swept from λ1981 to λ2000.

In the second scan of the range for acquiring the tomographic image, the first region R1 is irradiated with the measurement light swept from λ1981 to λ2000. The second region R2 is irradiated with the measurement light swept from λ1 to λ20. The third region R3 is irradiated with the measurement light swept from λ21 to λ40. The 100th region R100 is irradiated with the measurement light swept from λ1961 to λ1980.

In the third scan of the range for acquiring the tomographic image, the first region R1 is irradiated with the measurement light swept from λ1961 to λ1980. The second region R2 is irradiated with the measurement light swept from λ1981 to λ2000. The third region R3 is irradiated with the measurement light swept from λ1 to λ20. The 100th region R100 is irradiated with the measurement light swept from λ1941 to λ1960.

In the example shown in FIG. 9, the scanning is performed up to the 100th scan. Therefore, each region R1 to R100 is irradiated with all the sweep wavelengths (λ1 to λ2000) divided in time into 100 times. Then, A-Scan data is generated and tomographic image data can be generated by the same method as in FIG.

[Third Embodiment]

Next, the ophthalmic apparatus of the third embodiment will be described with reference to the drawings. Since the configuration of the ophthalmic apparatus of the third embodiment is the same as the configuration of the ophthalmic apparatus of the second embodiment (see FIG. 5), the description thereof will be omitted.

FIG. 10 shows the relationship between the wavelength sweep and the drive timing of the polygon mirror 24. The third embodiment is also a method of shifting the wavelength to be irradiated to each region in the range in which the tomographic image is acquired by using the polygon mirror 24 in which the wavelength sweep time and the time required for one scanning are different.

For example, the light source 20A is a light source having a wavelength sweep argument of 2000 and a wavelength sweep frequency of 200 kHz. The rotation frequency of the polygon mirror 24 is 198 kHz. The wavelength irradiated to each region in the range in which the tomographic image is acquired shifts by 20 wavelengths in each scanning cycle. This is repeated for each scan 100 times.

More specifically, as shown in FIG. 10, in the first scan, the start timing of the drive signal of the polygon mirror 24 and the start timing of the wavelength sweep of the light source 20A coincide with each other. However, the time for one scan is the time obtained by adding the time for four wavelength sweeps of the light source 20A and the time for wavelength sweeps for 20 wavelengths (for convenience of explanation, one wavelength λ1 is used. , The wavelength λ2 is similarly counted as one. For example, the wavelengths λ1 to λ20 are 20 wavelengths). Therefore, the first region R in the range for acquiring the tomographic image is irradiated with the measurement light swept from λ1 to λ20. The region immediately before the end is irradiated with the measurement light swept from λ1981 to λ2000. The last region is irradiated with the measurement light swept from λ1 to λ20.

Therefore, in the second scan, the measurement light swept from λ21 to λ40 is irradiated to the first region in the range in which the tomographic image is acquired. The last region is irradiated with the measurement light swept from λ21 to λ40.

The above process is repeated, and each region of the tomographic image acquisition range is irradiated with measurement light of all wavelengths in the wavelength sweep range, and a tomographic image is obtained.

It is also possible to lower the rotation frequency of the polygon mirror 24. For example, in the case of 9.995 kHz, 20 wavelength sweeps and 20 wavelength shifts are performed in one scan. The measurement time in this case is as follows.
(1 / 9.995 kHz) × (100) = 0.010005 (seconds)

The third embodiment is different from the second embodiment in the wavelength shifting method, and the irradiation time on the retina does not change. Therefore, the relative SNR of the third embodiment is also about 1.54 times.

[Fourth Embodiment]

Next, the ophthalmic apparatus of the fourth embodiment will be described with reference to the drawings. Since the configuration of the ophthalmic apparatus of the fourth embodiment is substantially the same as the configuration of the ophthalmic apparatus of the first embodiment, the same parts are designated by the same reference numerals, the description thereof will be omitted, and mainly. Only the different parts will be described.

FIG. 11 shows a schematic configuration of the photographing optical system 19T of the ophthalmic apparatus 110 of the fourth embodiment. As shown in FIG. 11, in the photographing optical system 19T of the fourth embodiment, instead of the relay optical system 30 of the photographing optical system 19 of the ophthalmic apparatus 110 of the first embodiment, the image is received from the KTN scanner 23 side. A first relay optical system 30A and a second relay optical system 30B are provided on the optometry side. The first relay optical system 30A and the second relay optical system 30B are each composed of a plurality of lenses.

The position of the KTN scanner 23 is conjugated by the first relay optical system 30A and the intermediate position between the first relay optical system 30A and the second relay optical system 30B, and the second relay optical system 30B causes the position of the KTN scanner 23 to be conjugated. , The intermediate position and the position of the eye to be inspected are conjugate.

By the way, the scanning angle of the KTN scanner 23 is a predetermined angle (for example, 10-deg (10 degrees)).

In the fourth embodiment, the scanning angle of the measurement light is expanded by the first relay optical system 30A. Specifically, the first relay optical system 30A has a magnification (horizontal magnification) of, for example, (1/7) times. As a result, the scanning angle can be increased 7 times (70-deg (70 degrees)).

[Fifth Embodiment]

Next, the ophthalmic apparatus of the fifth embodiment will be described with reference to the drawings. Since the configuration of the ophthalmic apparatus of the fifth embodiment is substantially the same as the configuration of the ophthalmic apparatus of the first embodiment, the same parts are designated by the same reference numerals, the description thereof will be omitted, and mainly. Only the different parts will be described.

FIG. 12 shows a schematic configuration of the photographing optical system 19U of the ophthalmic apparatus 110 according to the fifth embodiment. As shown in FIG. 12, in the photographing optical system 19U of the fifth embodiment, the scanning mirror is replaced with the reflection mirror 25 and the relay optical system 30 of the photographing optical system 19 of the ophthalmic apparatus 110 of the first embodiment. It includes 25C and a relay optical system 30C. The scanning mirror 25C moves the region scanned by the measurement light each time the measurement light is scanned by the KTN scanner 23. With the relay lens 30C, the position of the KTN scanner 23 and the position of the eye to be inspected are conjugated.

In the fifth embodiment, the scannable range in the first embodiment is expanded by a method different from that in the fourth embodiment. That is, in the fifth embodiment, the angle of view that can be scanned is widened by the combination of the KTN scanner 23 and the scanning mirror 25C. Therefore, the fundus region of the eye to be inspected in FIG. 12 can be photographed with a wider angle of view than in the first to fourth embodiments. This means that it is possible to acquire a tomographic image of a wider fundus region (a region including not only the central part of the fundus but also the peripheral part of the fundus). It is possible to acquire not only a ballistic image of a region including the optic nerve head and the macula existing in the central part of the fundus, but also a tomographic image of a region including lesions, new blood vessels, vortex veins, etc. around the fundus.

FIG. 13 shows the relationship between the wavelength sweep and the scanning of the measurement light when acquiring the tomographic image data (B-Scan data) by scanning the wide angle of view according to the fifth embodiment. There is.

First, a tomographic image of the first region Rc (see FIG. 12), which is the central part of the fundus, is acquired.
In the first scan S1 of the measurement light (see the top of FIG. 13), the measurement light in which λ1 to λ10 is swept in the first region R1 in the first region Rc within the range for acquiring the tomographic image. Is irradiated. The region R2 adjacent to the first region R1 is irradiated with the measurement light swept from λ11 to λ20. The last region R200 of the first region Rc is irradiated with the measurement light swept from λ1991 to λ2000.

In the second scan S2 of the measurement light (see the second from the top of FIG. 13), the first region R1 in the first region Rc within the range for acquiring the tomographic image was swept from λ11 to λ20. Light is emitted. The second region R2 is irradiated with the measurement light swept from λ21 to λ30. The last region RN point of the first region Rc is irradiated with the measurement light swept from λ1 to λ10.

In the final scan SM (200th scan, see bottom of FIG. 13), the first region R1 in the first region Rc within the range to acquire the tomographic image was swept from λ1991 to λ2000. Light is emitted. The second region R2 is irradiated with the measurement light swept from λ1 to λ10. The last region RN of the first region Rc is irradiated with the measurement light swept from λ1981 to λ1990.

By the above multiple scans, the central tomographic image data of the region Rc can be obtained.

Next, the scanning mirror 25C moves the scanning region to the first peripheral region Rp1 adjacent to the region Rc on the upper side. After the scanning region is moved by the scanning mirror 25C, the first peripheral tomographic image data of the adjacent region Rp1 is acquired in the same manner as the multiple scans of the region Rc shown in FIG.

Then, in the same manner, the second peripheral tomographic image data of the second peripheral region Rp2 adjacent to the lower side of the region Rc is acquired. Then, by synthesizing the central tomographic image data, the first peripheral tomographic image data, and the second peripheral tomographic image data of the second peripheral region Rp2 by the image processing apparatus 17, the first to fourth embodiments are performed. It is possible to generate tomographic image data of a wide range of RL.
In the above, the tomographic image is acquired by dividing into three regions of the central region Rc, the first peripheral region Rp1, and the second peripheral region Rp2. The tomographic image may be acquired by dividing it into an arbitrary number of regions.

[Sixth Embodiment]

Next, the ophthalmic apparatus of the sixth embodiment will be described with reference to the drawings. As the configuration of the ophthalmic apparatus according to the sixth embodiment, any configuration from the first embodiment to the fifth embodiment can be adopted.

FIG. 14 shows the relationship between the wavelength sweep and the scanning of the measurement light when acquiring the tomographic image data.

As shown in FIG. 14, in the sixth embodiment, the wavelength is fixed in each scan. When one scan is completed, the wavelength is swept, for example, one wavelength, and scanning is performed again at that wavelength. This is repeated to generate the final tomographic image data. It differs from the first embodiment to the fifth embodiment in that the wavelength of the measurement light is fixed during one scan and the wavelength is swept during the entire plurality of scans.

In the sixth embodiment, since the wavelength is fixed during one scan, the required wavelength sweep speed can be slowed down.

Each process explained above is just an example. Therefore, it goes without saying that unnecessary steps may be deleted, new steps may be added, or the processing order may be changed within a range that does not deviate from the purpose.

All documents, patent applications, and technical standards described herein are as if the individual documents, patent applications, and technical standards were specifically and individually stated to be incorporated by reference. Incorporated herein by reference.

Claims

A wavelength sweep type light source that emits laser light and can sweep the wavelength of the emitted laser light with a sweep width Δλ = λN−λ1 from wavelength λ1 to wavelength λN.
A branching portion that splits the laser light emitted from the light source into measurement light and reference light.
A scanning unit that scans the measurement light toward a predetermined area of an object, and
An interference portion that generates interference light between the reflected light from a predetermined region of the object and the reference light.
A detection unit that detects the interference light and outputs a detection signal,
To obtain a tomographic image of a predetermined area of the object
The predetermined area was scanned M (M and m are integers, M>m> 1) times.
The irradiation start wavelength λm in the mth scan,
λm = λ1 + (m-1) × Δλ / M
A control unit that controls the light source and the scanning unit so as to
Optical coherence tomography.
The time required to scan the predetermined area once is Tscan,
The time required for the wavelength sweep is Tswept,
When
Tscan = Tswept
The optical coherence tomography according to claim 1.
A tomographic image generation unit that generates a tomographic image of the predetermined region by using the detection signal obtained by scanning the predetermined region M times.
The optical coherence tomography according to claim 1 or 2, further comprising.
A wavelength sweep type light source that emits laser light and can sweep the wavelength of the emitted laser light with a sweep width Δλ = λN−λ1 from wavelength λ1 to wavelength λN and a sweep time Tswept.
A branching portion that splits the laser light emitted from the light source into measurement light and reference light.
A scanning unit that scans the measurement light toward a predetermined area of an object, and
An interference portion that generates interference light between the reflected light from a predetermined region of the object and the reference light.
A detection unit that detects the interference light and outputs a detection signal,
To obtain a tomographic image of a predetermined area of the object
The predetermined area was scanned M (M and m are integers, M>m> 1) times.
The m-th irradiation start timing is the time when the time of (m-1) × Tswept / M elapses from the end of the m-1st scan, and the control unit that controls the light source and the scanning unit. ,
Optical coherence tomography.
Let Tscan be the time required to scan the predetermined area once.
Tscan ≧ α × Tswept (α is an integer of 2 or more)
The optical coherence tomography according to claim 4.
The optical coherence tomography according to any one of claims 1 to 5, further comprising a tomographic image generation unit that generates a tomographic image of the predetermined region based on the detection signal.
The method for controlling an optical coherence tomography according to any one of claims 1 to 3.
The control unit
To obtain a tomographic image of a predetermined area of the object
The predetermined area was scanned M (M and m are integers, M>m> 1) times.
The irradiation start wavelength λm in the mth scan,
λm = λ1 + (m-1) × Δλ / M
The light source and the scanning unit are controlled so as to be.
How to control an optical coherence tomography.
The method for controlling an optical coherence tomography according to any one of claims 4 to 6.
The control unit
To obtain a tomographic image of a predetermined area of the object
The predetermined area was scanned M (M and m are integers, M>m> 1) times.
The light source and the scanning unit are controlled so that the m-th irradiation start timing is when the time of (m-1) × Tswept / M elapses from the end of the m-1th scanning.
How to control an optical coherence tomography.