Signal processing device, signal processing method, and signal processing program

Abstract

The objective is to retain the target signal included in the measurement signal while removing noise signals caused by coherence revival. [Solution] The signal processing device comprises: a measurement signal acquisition unit that acquires a measurement signal indicating the measurement result of an object to be measured by an OCT optical system; and a signal processing unit that performs wavelength dispersion correction on the measurement signal using wavelength dispersion formulas corresponding to each of the different wavelength dispersion characteristics, associates the signals included in the correction signal with each of the wavelength dispersion characteristics based on the corrected correction signal obtained for each wavelength dispersion characteristic, extracts a signal corresponding to the wavelength dispersion characteristic of the signal to be detected from the correction signal, and removes the signal corresponding to the wavelength dispersion characteristic of coherence revival in the OCT optical system.

Description

[Technical Field]

[0001] The present invention relates to a signal processing device, a signal processing method, and a signal processing program. [Background technology]

[0002] Optical Coherence Tomography (OCT) is a well-known technique that uses the coherence of light to measure the position of an object. Within OCT, the Fourier Domain-OCT (FD-OCT) method is also known. The measurement signal in FD-OCT includes signals corresponding to the target area, such as the cornea or lens, and noise signals. One example of noise is coherence revival, as described in Non-Patent Document 1. [Prior art documents] [Patent Documents]

[0003] [Non-Patent Document 1] Complex conjugate resolved heterodyne swept source optical coherence tomography using coherence revival (1 March 2012 / Vol.3, No.3 / BIOMEDICAL OPTICS EXPRESS 633) [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Conventionally, it has been difficult to distinguish between the signal to be detected and noise signals caused by coherence revival from the measurement signals of FD-OCT. This invention has been made in view of these problems, and aims to retain the signal to be detected included in the measurement signal while removing noise signals caused by coherence revival. [Means for solving the problem]

[0005] To achieve the above objective, the signal processing device includes a measurement signal acquisition unit that acquires a measurement signal indicating the measurement result of an object to be measured by an OCT optical system, and a signal processing unit that performs wavelength dispersion correction on the measurement signal using wavelength dispersion formulas corresponding to each of the different wavelength dispersion characteristics, associates the signals included in the measurement signal with each of the wavelength dispersion characteristics based on the corrected signals obtained for each wavelength dispersion characteristic, extracts a signal corresponding to the wavelength dispersion characteristic of the signal to be detected from the measurement signal, and removes the signal corresponding to the wavelength dispersion characteristic of coherence revival in the OCT optical system.

[0006] In other words, when a signal processing device performs chromatic dispersion correction on a measurement signal for each chromatic dispersion characteristic, the effect of the chromatic dispersion correction differs for each chromatic dispersion characteristic of the signal. Therefore, the signals included in the corrected signal can be associated with each chromatic dispersion characteristic. Once the signals included in the corrected signal are associated with each chromatic dispersion characteristic, the signals included in the measurement signal can be extracted or removed for each chromatic dispersion characteristic. The chromatic dispersion characteristics of the signal to be detected and the chromatic dispersion characteristics of coherence revival can be determined in advance. Therefore, the signal to be detected can be extracted, and noise signals caused by coherence revival can be removed. [Brief explanation of the drawing]

[0007] [Figure 1] This is a diagram showing the configuration of an optical coherence tomography (OCT) system. [Figure 2] This is a diagram showing the configuration of the scanning-alignment optical system. [Figure 3] This is a diagram showing the configuration of a signal processing device. [Figure 4] Figures 4A and 4B show examples of signals obtained by FD-OCT. [Figure 5] Figures 5A and 5B show examples of signals obtained by interference light without the effects of wavelength dispersion using FD-OCT. [Figure 6] This flowchart shows the process for identifying wavelength dispersion characteristics. [Figure 7] This figure shows an example of a corrected signal (0) when wavelength dispersion correction is performed by setting parameters b2 and b3 to 0. [Figure 8] This figure shows the corrected signal after the Fourier transform for multiple parameters. [Figure 9] This is a flowchart for extracting the target signal and performing noise reduction processing. [Figure 10] This figure shows some examples of correction signals (0) to (mmax). [Figure 11] This figure shows the inverse and recorrection of signals for a specific label. [Figure 12] This figure shows the corrected signal after the signal of a specific label has been removed. [Figure 13] This is a diagram showing the restored signal. [Modes for carrying out the invention]

[0008] Here, an example of an embodiment of the present invention will be described in the following order. (1) Configuration of the optical coherence tomography system: (2) Wavelength dispersive specific processing: (3) Extraction of detection targets, noise reduction processing: (4) Other embodiments: (1) Configuration of the optical coherence tomography system: The optical coherence tomography (OCT) apparatus 1 using the signal processing device 500 according to this embodiment will be described below. In this embodiment, the OCT apparatus 1 is an ophthalmic device that obtains a tomographic image of the anterior segment of the eye under examination by optical coherence tomography. Figure 1 is an overall configuration diagram of the OCT apparatus 1. The OCT apparatus 1 mainly comprises a wavelength-swept light source 10, an SMFC (single-mode fiber coupler) 101, an OCT optical system 100, an interference optical system 400 for k-clock generation, and a signal processing device 500.

[0009] The OCT optical system 100 is an optical system for obtaining a tomographic image of the anterior segment of the eye under examination using optical coherence tomography (OCT). In this embodiment, an example in which SS-OCT (Swept Source-OCT) is used as the OCT method will be described. The wavelength-swept light source 10 is a light source that outputs light while scanning by changing the wavelength over time. As this wavelength-swept light source 10, for example, a light source capable of high-speed scanning of 50 kHz or higher with a central wavelength of 1 μm or more and a sweep width of 70 nm or more is used. The light emitted from the wavelength-swept light source 10 is guided by an optical fiber such as a single-mode fiber and is used for acquiring a tomographic image of the sample 20, as well as for generating the k-clock. In this embodiment, the sample 20 is the eyeball (eye under examination) of the subject.

[0010] Light emitted from the wavelength-swept light source 10 is branched by the SMFC 101 and incident on the OCT optical system 100 and the k-clock generation interference optical system 400.

[0011] The OCT optical system 100 includes SMFCs 102 and 103, a measurement-side circulator 104, a reference-side circulator 105, a balanced detector 110, a polarization controller 120, a scanning-alignment optical system 200, and a reference optical system 300. One of the incident light branches off in SMFC 101 is further branched in SMFC 102, with the other light entering the scanning-alignment optical system 200 and the other light entering the reference optical system 300.

[0012] The optical path from the wavelength-swept light source 10 to SMFC 101, 102, reference-side circulator 105, and reference optical system 300, and further from the reference optical system 300 to the reference-side circulator 105, polarization controller 120, SMFC 103, and balanced detector 110, is called the reference optical path, and the optical system forming this reference optical path is called the reference arm. The optical path from the wavelength-swept light source 10 to SMFC 101, 102, measurement-side circulator 104, and scanning-alignment optical system 200, and further from the scanning-alignment optical system 200 to the measurement-side circulator 104, SMFC 103, and balanced detector 110, is called the measurement optical path, and the optical system forming this measurement optical path is called the measurement arm.

[0013] One of the beams of light split by the SMFC102 enters the scanning-alignment optical system 200 via the measurement-side circulator 104. The measurement-side circulator 104 is an optical element positioned between the SMFC102, the scanning-alignment optical system 200, and the SMFC103. The scanning-alignment optical system 200 is an optical system that irradiates the sample 20 with incident light and guides the reflected light from the sample 20 to the SMFC103 via the measurement-side circulator 104. Details of the scanning-alignment optical system 200 will be described later with reference to Figure 2.

[0014] The other beam of light, branched by the SMFC102, enters the reference optical system 300 via the reference-side circulator 105. The reference-side circulator 105 is an optical element positioned between the SMFC102, the reference unit 301, and the SMFC103. The reference optical system 300 is provided with a reference unit 301 that converts incident light into reference light. In this embodiment, the reference unit 301 is a prism that emits incident light as reference light. The reference unit 301 is movable in order to match the optical path length of the scanning-alignment optical system 200 with the optical path length of the reference optical system 300 before measuring the sample 20. During the measurement of the sample 20, the position of the reference unit 301 is fixed.

[0015] Light incident on the reference optical system 300 becomes reference light through the reference unit 301 and is guided to the SMFC 103 via the reference-side circulator 105 and polarization controller 120. The polarization controller 120 is an element that controls the polarization of the reference light guided from the reference optical system 300 to the SMFC 103. Various types of polarization controllers, such as in-line type and paddle type, can be used for the polarization controller 120.

[0016] The SMFC103 generates measurement interference light by combining reflected light from the scanning-alignment optical system 200 and reference light from the reference optical system 300. The SMFC103 then splits the combined measurement interference light into two measurement interference lights with a 180° phase difference and leads them to the balanced detector 110.

[0017] The balanced detector 110 includes a photodetector and receives the measurement interference light, outputting an interference signal. The interference signal is input to the signal processing device 500. The signal processing device 500 generates a tomographic image of sample 20 from the interference signal by performing calculations.

[0018] Figure 2 shows the configuration of the scanning-alignment optical system 200. The scanning-alignment optical system 200 includes a scanning optical system, an anterior segment imaging system, a fixation target optical system, and an alignment optical system.

[0019] The scanning optical system is an optical system for obtaining tomographic images. In the scanning optical system, light from the measurement-side circulator 104 via an optical fiber passes through the collimator lens 201 and enters the galvanoscanner 202. The galvanoscanner 202 is a device for scanning the incident light and is driven by a galvanoscanner driver (not shown). The light that has passed through the galvanoscanner 202 is reflected at a 90° angle by the hot mirror 203 and enters the eye E, which is the sample 20, through the objective lens 204. The light that enters the eye E is reflected by various tissue parts of the anterior segment Ec (cornea, anterior chamber, iris, lens, etc.) to become measurement light. Then, the measurement light passes in the reverse order of above through the objective lens 204, hot mirror 203, galvanoscanner 202, and collimator lens 201 and is guided to the SMFC 103 via the measurement-side circulator 104. The galvanometer scanner 202 is a device that changes the optical path of the measurement light in the measurement arm within a predetermined range centered on a predetermined optical axis. The galvanometer scanner 202 is an example of an optical path changing unit.

[0020] In the SMFC103, reflected light from the anterior segment Ec (measurement light) and reference light are combined, and the resulting signal is input to the balanced detector 110. In the balanced detector 110, interference for each wavelength is measured, and the measured interference signal is input to the signal processing device 500. The signal processing device 500 acquires the measurement signal indicating the interference signal and obtains a tomographic image of the anterior segment Ec after performing various processing based on the measurement signal.

[0021] The anterior segment imaging system is an imaging system for obtaining a two-dimensional image of the anterior segment. The anterior segment imaging system includes illumination light sources 205a and 205b, an objective lens 204, a hot mirror 203, a beam splitter 206, an imaging lens 207, and an area sensor 208. Illumination light sources 205a and 205b irradiate the front of the eye E under examination with illumination light in the visible light range. The illumination light is reflected by the eye E under examination, and the reflected light is guided to the area sensor 208 through the objective lens 204, hot mirror 203, beam splitter 206, and imaging lens 207. This captures a frontal image of the anterior segment of the eye E under examination, and the captured frontal image is input to the signal processing device 500. Here, the frontal image is a two-dimensional image of the anterior segment viewed from the optical axis direction of the reflected light, with the left and right of the subject as the left-right direction of the image and the up-down direction of the subject as the vertical direction.

[0022] The fixation target optical system is designed to minimize eye movement (the eye being examined E) by having the subject gaze at the fixation target. The fixation target optical system includes a fixation target light source 210, a variable focus movable lens 211, a cold mirror 212, a hot mirror 213, a relay lens 214, a beam splitter 215, a beam splitter 206, a hot mirror 203, and an objective lens 204. Light emitted from the fixation target light source 210 passes through the variable focus movable lens 211, the cold mirror 212, the hot mirror 213, the relay lens 214, the beam splitter 215, the beam splitter 206, the hot mirror 203, and the objective lens 204 in that order before reaching the eye being examined E.

[0023] Here, the variable-focus movable lens 211 is configured to be movable so that the focus of the fixation target can be freely changed. For example, the variable-focus movable lens 211 can be moved so that the fixation target is in focus at the refractive power value of the eye E being examined, thereby allowing the subject to see naturally (a state in which no load is placed on the lens).

[0024] The alignment optical system is an optical system for aligning the eye E under examination. Although not shown in the diagram, the optical coherence tomography (OCT) apparatus 1 comprises an apparatus body and a support stand that supports the apparatus body. On the front side (patient side) of the apparatus body, there is a fixed chin rest for the patient to rest their chin on and a forehead rest for the patient to rest their forehead on. When the forehead is placed on the forehead rest, the patient's eye (eye under examination E) is positioned directly in front of the examination window located on the front of the apparatus body.

[0025] Furthermore, the device body is supported so as to be movable in the X, Y, and Z directions relative to the holding base. The device body can be moved in the X, Y, and Z directions relative to the holding base under the control of the signal processing device 500. Here, the X direction corresponds to the left-right direction of the device body and the left-right direction of the head of the subject fixed to the device. The Y direction corresponds to the up-down direction of the device body and the up-down direction of the subject fixed to the forehead rest, etc. The Z direction corresponds to the depth direction of the device body and the front-to-back direction of the subject fixed to the forehead rest, etc. In the examination of the subject's eye E, it is necessary to move the device body so that the subject's eye E is set in a predetermined position on the device body, and the alignment optical system is an optical system for determining the amount of movement of the device body.

[0026] The alignment optical system includes an XY direction position detection system and a Z direction position detection system. The XY direction position detection system is configured to detect the position of the eye E (corneal apex) in the XY direction (up, down, left, and right displacement relative to the device body). The Z direction position detection system is configured to detect the position of the eye E (corneal apex) in the anterior-posterior direction (Z direction displacement).

[0027] The XY directional position detection system includes an XY position detection light source 216, a hot mirror 213, a relay lens 214, a beam splitter 215, a beam splitter 206, a hot mirror 203, an objective lens 204, an imaging lens 217, and a two-dimensional position sensor 218. Alignment light for position detection emitted from the XY position detection light source 216 reaches the anterior segment Ec (cornea) of the eye E under examination via the hot mirror 213, relay lens 214, beam splitter 215, beam splitter 206, hot mirror 203, and objective lens 204.

[0028] Because the corneal surface of eye E is spherical, the alignment light is reflected off the corneal surface in such a way that it forms a bright spot image inside the corneal apex of eye E. The reflected light from the corneal surface is guided to the objective lens 204. The reflected light from the corneal apex is input to the two-dimensional position sensor 218 via the objective lens 204, hot mirror 203, beam splitter 206, beam splitter 215, and imaging lens 217. The two-dimensional position sensor 218 detects the position of the bright spot as the position of the corneal apex (position in the X and Y directions).

[0029] The detection signal from the 2D position sensor 218 is input to the signal processing device 500. In this embodiment, the signal processing device 500 has a preset normal position for the corneal apex, which is the position where the corneal apex should be positioned after alignment has been performed between the 2D position sensor 218 and the anterior segment imaging system. This normal position of the corneal apex is the position that should be tracked when acquiring tomographic images, and is, for example, the center position of the image captured by the image sensor. Based on the detection from the 2D position sensor 218, the signal processing device 500 determines the normal position and the amount of positional displacement in the X and Y directions of the detected corneal apex (bright spot).

[0030] The Z-direction position detection system includes a Z-position detection light source 219, an imaging lens 220, and a line sensor 221. The Z-position detection light source 219 illuminates the eye E under examination from an oblique direction with detection light (slit light or spot light). The illuminated light is reflected obliquely by the cornea, and the reflected light is guided to the line sensor 221 via the imaging lens 220. Since the incident position of the reflected light incident on the line sensor 221 differs depending on the anterior-posterior (Z-direction) position of the eye E under examination, the Z-direction position of the eye E under examination is detected.

[0031] The signal processing device 500 moves the device body relative to the holding base so that the positional displacement amounts in the X and Y directions of the corneal apex (bright spot) detected by the XY direction position detection system, and the positional displacement amount of the eye E detected by the Z direction position detection system, are all set to zero. This completes the alignment.

[0032] The k-clock generation interference optical system 400 shown in Figure 1 is a device that optically generates a sample clock (k-clock) from input light branched from the SMFC 101 in order to sample interference signals at equally spaced frequencies. The k-clock signal generated by the k-clock generation interference optical system 400 is input to the signal processing device 500. By referring to the k-clock signal, the signal processing device 500 suppresses distortion of the interference signal and prevents deterioration of resolution.

[0033] Figure 3 is a diagram of the signal processing device 500. The signal processing device 500 comprises a control unit 510, a storage medium 520, a display unit 530, and an operation unit 540. The control unit 510 includes a processor, ROM, and RAM (not shown). The control unit 510 performs various processes by executing a program stored in the storage medium 520. The control unit 510 controls, for example, the various control targets of the OCT optical system 100, the scanning-alignment optical system 200, the reference optical system 300, and the k-clock generation interference optical system 400, such as the motor for alignment and the area sensor 208. The control unit 510 also acquires a measurement signal based on information output from the scanning-alignment optical system 200, performs wavelength dispersion correction based on the measurement signal, and extracts the signal to be detected and removes noise signals based on the corrected signal. Then, the control unit 510 generates (acquires) a tomographic image based on the obtained signal.

[0034] The storage medium 520 stores various programs and information. The information stored in the storage medium 520 includes wavelength dispersion information 521. Wavelength dispersion information 521 is information that indicates the parameters used when performing wavelength dispersion correction, and this information is defined for each wavelength dispersion characteristic. Details of wavelength dispersion information 521 will be described later.

[0035] The display unit 530 is a display that shows various information. For example, the display unit 530 displays tomographic images and frontal images of the anterior segment of the eye. The operation unit 540 accepts input from the user. The operation unit 540 is, for example, a keyboard or mouse. In another example, the operation unit 540 may be a touch panel integrated with the display unit 530.

[0036] The control unit 510 functions as a measurement signal acquisition unit 511 and a signal processing unit 512 by executing a program stored in the storage medium 520. The measurement signal acquisition unit 511 controls the OCT optical system 100, the scanning-alignment optical system 200 (galvanometer scanner 202, etc.), and the k-clock generation interference optical system 400 to acquire a measurement signal indicating the measurement result of the eye under examination.

[0037] Specifically, in the OCT optical system 100, light passing through the measurement arm and light passing through the reference arm are interfered with, and the interfered light is detected by a photodetector (balanced detector 110). The measurement signal acquisition unit 511 detects a current signal corresponding to the intensity of the interference signal as a measurement signal.

[0038] The signal processing unit 512 extracts the signal to be detected based on the measurement signal and removes noise signals caused by coherence revival. The signal processing unit 512 also performs predetermined processing based on the signal to be detected to generate a tomographic image of the detected object and displays it on the display unit 530. In this embodiment, the objects to be detected are the cornea and the lens.

[0039] Here, we will explain the signal obtained by FD-OCT. When the measurement signal detected by the photodetector is subjected to a discrete Fourier transform, a symmetrical signal is obtained on both the positive and negative frequency sides. An example of a signal obtained by FD-OCT is shown in the dashed graph of Figure 4A. In Figure 4A, the dashed lines indicate an example where peaks corresponding to the sample exist symmetrically on both the positive and negative frequency sides. One of these peaks is the original signal, and the other is the complex conjugate component of the original signal. A signal that appears in a frequency band with the opposite positive and negative sign to the original signal is called a mirror signal.

[0040] By applying wavelength dispersion correction to these signals, it becomes possible to distinguish between the original signal and the mirrored signal. In other words, by applying a process to correct for the effects of wavelength dispersion to the current signal obtained through the photodetector, the peak corresponding to the sample becomes sharper (narrower width and stronger signal intensity) in the Z-space after the discrete Fourier transform, while the other peaks become broader.

[0041] The following explains wavelength dispersion correction. In an OCT interferometer, when interfering measurement light and reference light are received by a photodetector, the current signal I output from the photodetector is expressed by the following equation 1.

[0042] [Number] u with a bar written above Equation 1 sample (Hereinafter, it will be referred to as u - sample ), u reference (Hereinafter, it will be referred to as u - reference ) is the energy of each of the two interfering lights. η is the quantum efficiency of the light-receiving element (the ratio of incident photons that are converted into electrons as signals). h is Planck's constant. q is the elementary charge. λ is the wavelength of light. k is the wave number of light (the reciprocal of the wavelength λ). Δz is the optical path length difference between the two interfering lights (measurement light, reference light). The third term in Equation 1 represents the influence of light interference.

[0043] Here, assume that a part of the reference optical path is a medium with wavelength dispersion. Also, assume that the remaining optical path is a medium without wavelength dispersion (air). Then, the optical path length difference Δz is expressed by the following Equation 2.

[0044] [Number] In Equation 2, z sample is the optical path length of the measurement optical path. z reference is the optical path length of the reference optical path. z zero-dispersion is the optical path length of the optical path that can be regarded as having approximately no wavelength dispersion characteristics in the reference optical path (the optical path length of the part excluding the wavelength dispersion member part). L is the length of the wavelength dispersion member in the optical path provided in the measurement optical path. n(k) is the refractive index of light with wave number k in the wavelength dispersion member.

[0045] The phase φ of the current signal I is expressed by the following Equation 3 as a function of wave number k from the argument of cos in the third term of Equation 1.

[0046] [Number] Also, when n(k) in Equation 3 is Taylor-expanded with respect to wave number k based on a predetermined wave number k0, it becomes as follows in Equation 4.

[0047]

number

[0048]

number

[0049]

number

[0050]

number

[0051] Once φ in equation 5 is found, the found φ can be expressed as a polynomial Σ j=0 (a j (k-k0) j By approximating with ), we can obtain the approximate formula for Equation 5. Then, by subtracting the zeroth and first-degree terms from this polynomial, we can obtain the information for the third term of Equation 5. Here, a j This indicates the coefficient of the j-th degree term. Also, φ in equation 5 is a polynomial Σ j=0 (a j (k-k0) j Alternatively, we can approximate it as follows and consider the quadratic and subsequent components as information for the third term of Equation 5.

[0052] The third term of Equation 5 is a dimensionless value φ that indicates the magnitude of wavelength dispersion. dispersion Far away. φ dispersion This is expressed by the following equation 8.

[0053]

number

[0054]

number

[0055]

number

[0056] exp(iφ dispersionWhen I multiplied by ) is subjected to a Discrete Fourier Transform, in Z space, two signals are generated: one related to the third term of Equation 10, and another related to the fourth term in the frequency band with the opposite sign to the signal related to the third term. The signal related to the third term becomes sharper as the effect of chromatic dispersion is reduced. The signal related to the fourth term becomes broader as the effect of chromatic dispersion is increased. That is, the interference signal related to the measurement light from the sample becomes sharp, while the mirror signal becomes broad. Using these characteristics, it is possible to distinguish between the sample signal and the mirror signal, which appears symmetrically in Z space. Figure 4B shows the signal when chromatic dispersion correction is applied to the signal represented by the solid line graph in Figure 4A. Compared to Figure 4A, it can be seen that the peak on the positive frequency side is sharper, and the peak on the negative frequency side is broader. From this, it can be seen that the signal on the positive frequency side corresponds to the sample signal, and the signal on the negative frequency side is the mirror signal. In this way, it is possible to distinguish between the original signal and the mirror signal.

[0057] If the current signal I is not affected by the difference in wavelength dispersion characteristics in the optical path, then exp(iφ) dispersion When wavelength dispersion correction is applied, the signal after the discrete Fourier transform becomes broad on both the positive and negative frequency sides. Specifically, the current signal I of interference light from two optical paths with the same wavelength dispersion characteristics is expressed by the following equation 11.

[0058]

number

[0059]

number

[0060] In this embodiment, the control unit 510 uses these features to extract signals related to each interference light from the measurement signal. The functions and processing details of the optical coherence tomography apparatus 1 will be described below.

[0061] When interference light, resulting from the interference between the measurement light traveling along the measurement optical path of the OCT optical system 100 and the reference light traveling along the reference optical path, is received by the photodetector, a current signal is output from the photodetector. The control unit 510, using the function of the measurement signal acquisition unit 511, samples the current signal output from the photodetector as a digital signal. In this specification, the sampled signal is referred to as the measurement signal. The control unit 510, using the function of the signal processing unit 512, performs wavelength dispersion correction and discrete Fourier transform on the current signal I to remove noise.

[0062] In this embodiment, noise reduction based on wavelength dispersion correction is a process that leaves signals with specific wavelength dispersion characteristics and removes signals corresponding to the wavelength dispersion characteristics of coherence revival, and details will be described later. Furthermore, in order to perform wavelength dispersion correction, the wavelength dispersion characteristics of multiple signals included in the measurement signal obtained by measuring the eye under examination must be identified in advance. The process for identifying the wavelength dispersion characteristics of each signal will also be described in detail later, but the wavelength dispersion characteristics of the signal to be detected are identified in advance, and the wavelength dispersion characteristics of the noise signal to be removed are also identified in advance. Therefore, in this embodiment, by performing wavelength dispersion correction corresponding to each wavelength dispersion characteristic, the signals to be left and the signals to be removed become clear.

[0063] As a result of the above processing, noise signals are removed, leaving only the signal to be detected. The control unit 510 performs various processing using the functions of the signal processing unit 512 to generate a three-dimensional image of the detected object, i.e., the cornea and lens, and displays it on the display unit 530. In the optical coherence tomography apparatus 1, when a signal is generated from an object, a signal is acquired that reflects the wavelength dispersion characteristics of the material contained in all of the optical paths (measurement optical paths) where light is output from the light source, irradiated onto the object through a predetermined optical path, reflected from the object, and reaches the photodetector through a predetermined optical path, as well as all of the reference optical paths. Therefore, the signal reflects the wavelength dispersion characteristics of each optical path. In this specification, the wavelength dispersion characteristics of each optical path in the signal are referred to as the wavelength dispersion characteristics of the signal.

[0064] (2) Wavelength dispersion characteristic identification process: This section describes in detail the chromatic dispersion characteristic identification process for determining the chromatic dispersion characteristics of each signal. Figure 6 is a flowchart of the chromatic dispersion characteristic identification process. In this embodiment, determining the chromatic dispersion characteristics is equivalent to determining the parameters of the chromatic dispersion formula used for chromatic dispersion correction. Equation 13 shows the chromatic dispersion formula.

[0065]

number

[0066] The wavelength dispersion formula is the formula exp(iφ) used for wavelength dispersion correction. dispersion This is one example. When wavelength dispersion correction is repeated while changing parameters b2 and b3, if the peak width of a certain signal becomes the minimum and symmetrical, then the values ​​of parameters b2 and b3 can be said to be the values ​​that most appropriately correct that signal. For this reason, the values ​​of parameters b2 and b3 can be said to be the values ​​corresponding to the wavelength dispersion characteristics of the signal in question.

[0067] First, the control unit 510 acquires a measurement signal using the function of the measurement signal acquisition unit 511 (step S100). That is, the control unit 510 controls the OCT optical system 100, the scanning-alignment optical system 200, etc., and acquires a measurement signal indicating the measurement result of the eye being measured (step S100).

[0068] Next, the control unit 510 sets the initial values ​​of parameters b2 and b3 using the function of the signal processing unit 512 (step S102). In this implementation, the minimum value of parameters b2 and b3 is set to 0 as the initial value. In this case, no correction is performed in effect.

[0069] Next, the control unit 510 multiplies the measurement signal by a wavelength dispersion formula including parameters b2 and b3, using the functions of the signal processing unit 512 (step S104). That is, the control unit 510 performs wavelength dispersion correction with parameters b2 and b3 set to their initial values. Next, the control unit 510 performs a Fourier transform based on the result obtained in step S104 (step S106).

[0070] Next, the control unit 510, through the function of the signal processing unit 512, determines m with a peak in the positive frequency domain. max Identify individual signals (step S108). In Figure 7, the signal after wavelength dispersion correction with the initial value set in step S102 and the Fourier transform in step S106 is schematically shown as the corrected signal (0). Since the corrected signal (0) contains signals equivalent to both positive and negative values, in this embodiment, processing is limited to the positive frequency domain. As shown in Figure 7, the corrected signal (0) contains signals with multiple peaks. Here, the signals identified based on the peaks are shown as m1 to m6. In this example, m max The value is 6. Note that in Figure 7, each signal is shown separately (and so on), but in actual signal waveforms, each signal is added together, and it is difficult to distinguish between signals in parts other than the peaks.

[0071] The correction signal (0) includes the signal to be detected and the noise signal. In this embodiment, the targets for detection are the cornea and the lens, and the frequency band in which the signal corresponding to the targets appears is generally known. Therefore, once the correction signal (0) is obtained, it is possible to identify the peak that is estimated to be the peak of the signal to be detected.

[0072] Furthermore, in this embodiment, the noise signal is a noise signal caused by coherence revival. The noise signal caused by coherence revival appears periodically in the frequency domain. Therefore, the peak that appears periodically from the correction signal (0) can be identified as the peak of the noise signal caused by coherence revival.

[0073] The control unit 510 refers to the correction signal (0) obtained in step S106 and identifies peaks from known frequency bands in which the signal to be detected appears. It also identifies periodically appearing peaks. In this way m max The state in which individual peaks have been identified corresponds to the state in the corrected signal (0) in Figure 7 where peaks m1 to m6 have been identified.

[0074] Next, the control unit 510, using the functions of the signal processing unit 512, identifies the label m1 for the first detection target and the label m2 for the second detection target (step S110). Specifically, the control unit 510 identifies the largest peak within the known frequency band in which the signal corresponding to the cornea, the first detection target, appears, and assigns it to label m1. The control unit 510 also identifies the largest peak within the known frequency band in which the signal corresponding to the lens, the second detection target, appears, and assigns it to label m2. The labels m1 and m2 shown in the corrected signal (0) in Figure 7 are the labels of the peaks identified in this way.

[0075] Next, the control unit 510 performs wavelength dispersion correction by setting the possible values ​​for each of the parameters b2 and b3. To do this, the control unit 510 increases the value of parameter b2 by a predetermined change step Δb2 using the function of the signal processing unit 512 (step S112). In other words, in this embodiment, the increase amount Δb2 of parameter b2 is predetermined, and the control unit 510 increases parameter b2 by the increase amount Δb2 in each loop processing step S112 to S118.

[0076] Next, the control unit 510 multiplies the measurement signal by a wavelength dispersion formula including parameters b2 and b3, using the functions of the signal processing unit 512 (step S114). That is, the control unit 510 performs wavelength dispersion correction with parameters b2 and b3 set to their current values. Next, the control unit 510 performs a Fourier transform based on the result obtained in step S114 (step S116). The control unit 510 sets parameter b2 to a preset maximum value b 2max Determine whether or not it has reached the maximum value b (step S118), 2max The process from step S112 onward is repeated until it is determined that the condition has been met.

[0077] Next, the control unit 510 increases the value of parameter b3 by a predetermined change step Δb3 using the function of the signal processing unit 512 (step S120). That is, in this embodiment, parameter b3 The increment amount Δb3 is predetermined, and the control unit 510 increases the parameter b3 by the increment amount Δb3 in each loop processing step S120 to S126.

[0078] Next, the control unit 510 multiplies the measurement signal by a wavelength dispersion formula including parameters b2 and b3, using the functions of the signal processing unit 512 (step S122). That is, the control unit 510 performs wavelength dispersion correction with parameters b2 and b3 set to their current values. Next, the control unit 510 performs a Fourier transform based on the result obtained in step S122 (step S124). The control unit 510 sets parameter b3 to a preset maximum value b 3maxDetermine whether or not it has reached the maximum value b (step S126), 3max The process from step S120 onward is repeated until it is determined that the condition has been met.

[0079] Following the above process, wavelength dispersion correction is performed based on the possible values ​​of the wavelength dispersion parameters b2 and b3. Next, the control unit 510 assigns labels 1 to m based on the obtained results. max This identifies parameters b2 and b3 that represent the chromatic dispersion characteristics corresponding to each of the associated signals.

[0080] To this end, first, the control unit 510 initializes label m to 0 using the function of the signal processing unit 512 (step S128), and then increments label m (step S130). Next, the control unit 510 uses the function of the signal processing unit 512 to set b2 such that the width of peak m is minimized. 2m (Step S132). That is, the control unit 510 identifies the peak of label m from the Fourier transformed signal obtained in step S116, identifies the b2 that minimizes the peak width, and sets the parameter b2 of label m, i.e., b 2m It is identified as such. The peak width can be defined, for example, by the full width at half maximum (FWHM).

[0081] Next, the control unit 510, through the function of the signal processing unit 512, sets b3 such that the peak m is symmetrical. 3m (Step S134). That is, the control unit 510 identifies the peak of label m from the Fourier transformed signal obtained in step S124, identifies the b3 with the highest left-right symmetry of the peak, and sets the parameter b3 of label m, i.e., b 3m This is how it is identified. The left-right symmetry of the peak can be determined based on the area on the left and right sides of the peak, and the shift in signal intensity when the signal intensity on the left side of the peak is inverted to the right side.

[0082] In Figure 8, the state after the Fourier transform in step S116 is shown using three parameters b 21 ,b 22 ,b23 The value of is schematically shown. Here, for simplicity, we assume that the total number of parameters b2 is 3. Focusing on the label m1 in this example, parameter b 21 The peak width is smallest when corrected by this method. In this case, parameter b 21 parameter b 2m1 Therefore, based on the state after the Fourier transform in step S124, if we identify the b3 with the highest left-right symmetry for the peak of label m1, then the parameter b 3m1 This can be obtained.

[0083] The control unit 510, through the function of the signal processing unit 512, determines that label m is m max It is determined whether or not it matches (step S136), and in step S136, if label m is m max The process from step S130 onward is repeated until a match is determined.

[0084] In step S136, label m is m max If it is determined that this matches, the control unit 510, using the function of the signal processing unit 512, will b for all m 2m , b 3m Save (step S138). That is, by processing in steps S130 to S136, labels 1 to m are saved. max For all of them, parameter b 2m ,b 3m Since the parameters have been identified, the control unit 510 determines each parameter b of each label. 2m ,b 3m This is stored in the storage medium 520 as wavelength-dispersive information 521.

[0085] Through the above processing, the chromatic dispersion characteristics corresponding to all of the peak signals identified in step S108 can be determined. Specifically, the peaks identified in step S108 include the peaks of noise signals caused by coherence revival. Then, through the processing up to step S138, the parameter b corresponding to the label of the noise signal can be determined. 2m ,b 3mThe state in which this has been identified means that a wavelength dispersion formula that appropriately corrects the noise signal has been identified. As a result, it becomes possible to remove the noise signal through the processing described later.

[0086] Furthermore, the wavelength dispersion characteristics corresponding to the signals of labels m1 and m2, respectively, which are identified in step S110 as the first detection target (cornea) and the second detection target (lens), are determined. That is, the wavelength dispersion characteristics in the measurement optical path, which reaches the cornea of ​​the eye under examination from the wavelength-swept light source 10 included in the OCT optical system 100 and from the cornea to the photodetector included in the OCT optical system 100, correspond to the parameter b of the signal of label m1. 2m1 ,b 3m1 It is identified as such. Note that here it is assumed that the reference optical path has virtually no wavelength dispersion characteristics, but parameter b 2m ,b 3m This parameter may reflect the wavelength dispersion characteristics of the measurement optical path and the reference optical path.

[0087] Furthermore, the wavelength dispersion characteristics in the measurement optical path, which reaches the lens of the eye under examination from the wavelength-swept light source 10 included in the OCT optical system 100, and from the lens to the photodetector included in the OCT optical system 100, correspond to the parameter b of the label m2 signal. 2m2 ,b 3m2 This is how it is identified. In this state, where the parameters corresponding to the signals of each label m1 and m2 have been identified, it is the same as identifying a wavelength dispersion formula that appropriately corrects the signal to be detected. As a result, it becomes possible to extract the signal to be detected through the processing described later.

[0088] In this embodiment, since the signals of labels m1 and m2 correspond to the cornea and lens, which are the targets of detection, the signals of labels other than m1 and m2 are, in principle, considered to be noise signals and are to be removed. However, if there are signals that are difficult to distinguish from the signals of labels m1 and m2, removing these signals may result in the removal of the signals that are intended for detection.

[0089] Therefore, the control unit 510, through the function of the signal processing unit 512, determines the parameter b in label m1. 2m1 ,b 3m1 and the parameter b in other labels 2m ,b 3m The control unit 510 compares the two and identifies labels whose differences are below a threshold (step S140). That is, the control unit 510 refers to the wavelength-dispersive information 521 and parameter b 2m1 and parameter b 2m (However, m is 0 to m) max The control unit 510 compares the values ​​(excluding m1) with other values ​​within the set of parameters b and identifies the difference. The control unit 510 also refers to the wavelength dispersive information 521 and checks the parameter b 3m1 and parameter b 3m The control unit 510 compares the obtained values ​​(where m is a value other than m1) and identifies the differences. If there is a label for which both of the obtained differences are below a predetermined threshold, the control unit 510 identifies that label and stores it in the storage medium 520 as a label to be not removed.

[0090] In Figure 7, label m3 corresponds to the signal to be excluded. For example, when the frequency bands of the signals labeled m1 and m3 are close together, parameter b is used to properly correct the signal shape by wavelength dispersion correction. 2m ,b 3m The values ​​of can be close together. In such cases, removing the signal of label m3 may remove a portion of the signal of label m1, potentially removing part of the information to be detected. Therefore, in this embodiment, to prevent such removal, parameter b 2m ,b 3m If the difference between the parameters is below the threshold, signals with labels different from the target signal's label will not be removed.

[0091] The same applies to label m2, and the control unit 510, through the function of the signal processing unit 512, controls the parameter b in label m2. 2m2 ,b 3m2 and the parameter b in other labels 2m ,b 3mCompare them and identify the label whose difference is below the threshold (step S142). That is, the control unit 510 refers to the wavelength dispersion information 521 and the parameter b 2m2 and the parameter b 2m (where m is a value other than m2) are compared to identify the difference. Also, the control unit 510 refers to the wavelength dispersion information 521 and the parameter b 3m2 and the parameter b 3m (where m is a value other than m2) are compared to identify the difference. Then, when there is a label for which both of the obtained two differences are below a predetermined threshold, the control unit 510 identifies that label and stores it in the storage medium 520 as a non-removal target.

[0092] In addition, in steps S140 and S142, if no label whose difference is below the threshold is identified, the signals of labels other than the detection target labels m1 and m2 may all be regarded as removal targets. Also, if a plurality of labels whose differences are below the threshold are identified, the signals of each of the plurality of labels may be excluded from the removal targets.

[0093] (3) Detection target signal extraction, noise removal processing: Next, a process for extracting the detection target signal from the measurement signal and removing the noise signal will be described. FIG. 9 is a flowchart of this process. In this process, the control unit 510 acquires the measurement signal by the function of the measurement signal acquisition unit 511 (step S200). That is, the control unit 510 acquires the measurement signal for the same eye to be examined that was measured in step S100 of FIG. 6 in order to determine parameters and the like.

[0094] Next, the control unit 510 sets m to 0 by the function of the signal processing unit 512 (step S202) and performs a Fourier transform (step S204). Here, since the parameters b 2m , b 3m are 0 when m = 0, the signal after the Fourier transform obtained in step S204 is the parameter b 2m , b 3mIt can be regarded as a correction signal (0) for which wavelength dispersion correction has been performed with 0. The upper part of FIG. 10 shows an example of the correction signal (0).

[0095] Next, the control unit 510 increments m (step S206), and the parameter b 2m , b 3m is multiplied by the wavelength dispersion formula including it to the measurement signal (step S208). Specifically, the control unit 510 substitutes the parameter b 2m , b 3m into the parameters b2 and b3 of the wavelength dispersion formula (Equation 13), and performs wavelength dispersion correction based on the wavelength dispersion formula. Since step S208 is a process within the loop of steps S206 to S212 performed for different m, in step S208, the control unit 510 performs wavelength dispersion correction on the measurement signal using each of the wavelength dispersion formulas corresponding to each of the different wavelength dispersion characteristics.

[0096] Next, the control unit 510 executes a Fourier transform based on the result obtained in step S208 (step S210). Then, the control unit 510 determines whether or not the label m matches m max by the function of the signal processing unit 512 (step S212), and repeats the processing after step S206 until it is determined in step S212 that the label m matches m max .

[0097] According to the above processing, correction signals for which wavelength dispersion correction has been performed with the wavelength dispersion formulas corresponding to each of the signals of labels 1 to m max are obtained. Here, each correction signal is called correction signal (1) to correction signal (m max ). In FIG. 10, a part of the correction signals (1) to the correction signals (m max ), that is, the correction signals (m1) and the correction signals (m4) are extracted and shown in the middle and lower parts.

[0098] Next, the control unit 510, using the functions of the signal processing unit 512, identifies the signal with the largest peak in the positive frequency domain (step S214). That is, the control unit 510 limits the analysis target to signals in the positive frequency domain and corrects the signal (1) to the corrected signal (m max The control unit 510 identifies the signal with the highest signal strength from each of the ). Furthermore, the control unit 510 identifies the signal with the highest signal strength among the identified signal strengths. For example, in the example shown in Figure 10, the signal with the highest signal strength in the positive frequency domain of correction signal (0) is the signal labeled m1. The signal with the highest signal strength in the positive frequency domain of correction signal (m1) is the signal labeled m1, and the signal with the highest signal strength in the positive frequency domain of correction signal (m4) is the signal labeled m4.

[0099] The control unit 510 compares these signals and identifies the largest signal. That is, the control unit 510 compares all correction signals (0) to correction signals (m4), including correction signal (0), correction signal (m1), and correction signal (m4) shown in Figure 10. max The signals extracted from the source are compared, and the signal with the highest signal strength is identified. In the example shown in Figure 10, it is assumed that the signal with label m1 in the correction signal (m1) is the signal with the highest strength.

[0100] In the above processing, the signal with the largest peak identified is the peak that has been sharpened by the wavelength dispersion correction in step S208. This wavelength dispersion correction is performed using parameter b for each wavelength dispersion characteristic. 2m ,b 3m This is performed by different methods, and if the wavelength dispersion correction formula (i.e., wavelength dispersion characteristics) is different, the signal that reaches the maximum peak will be different. Therefore, the process in step S214 in which the signal with the maximum peak is identified is equivalent to identifying the wavelength dispersion correction formula (i.e., wavelength dispersion characteristics) that maximizes the peak of the signal. Therefore, the process in step S214 in which the signal with the maximum peak is identified corresponds to the process of associating the signals included in the correction signal with the wavelength dispersion characteristics. Note that correction signal (0) to correction signal (m maxAlthough the signal has signals on both the positive and negative sides, in this embodiment, the processing described above is limited to the positive side. With this configuration, it is possible to narrow down the processing target by half, thus enabling high-speed processing.

[0101] Next, the control unit 510 identifies the signal to be subtracted based on the maximum peak signal (step S216). In this embodiment, based on the maximum peak signal identified in step S214, the correction signal (0) to the correction signal (m max From each of these, the signal corresponding to the maximum peak signal is subtracted. Specifically, the control unit 510 identifies the signal from the correction signal that includes the maximum peak signal identified in step S214.

[0102] In the example shown in Figure 10, the control unit 510 identifies the signal for label m1 from the correction signal (m1). In the middle section of Figure 11, the signal for label m1 identified from the example of the correction signal (m1) shown in the middle section of Figure 10 is shown by a solid line. In the correction signal (m1), the signal for label m1 is the signal with the highest peak, so its signal intensity is large compared to other signals and it can be easily distinguished from other signals. Therefore, the control unit 510 identifies the signal for label m1 by extracting the signal with the highest peak from the correction signal (m1).

[0103] On the other hand, in other correction signals, for example, in the correction signal (m4) shown in Figure 10, the signal for label m1 is broadened by wavelength dispersion correction, and its signal intensity is not large. Therefore, it is difficult to distinguish the signal for label m1 from other signals based on the shape characteristics of the signal. Thus, the control unit 510 identifies the signal to be subtracted based on the signal for label m1 identified in the correction signal (m1). Specifically, the control unit 510 returns only the signal for label m1 identified in the correction signal (m1) to its state before wavelength dispersion correction, and then again applies the correction to labels 1 to m max The parameter b corresponding to each of these 2m ,b 3m Wavelength dispersion correction is performed. According to this process, the signal labeled m1 becomes corrected signal (0) ~ corrected signal (m maxIt is possible to identify the location and shape of the object within the parentheses.

[0104] Specifically, in the middle section of Figure 11, if the inverse correction of wavelength dispersion correction is applied only to the signal of label m1 extracted from the correction signal (m1), it is possible to generate only the signal of label m1 included in the correction signal (0), as shown by the solid line in the upper section of Figure 11, in the state before correction. Then, the signal of label m1 included in the correction signal (0) is again corrected for labels 1 to m max The parameter b corresponding to each of these 2m ,b 3m When wavelength dispersion correction is performed, the correction signal (1) ~ correction signal (m max Only the signal labeled m1, contained in each of the above, can be generated. In the lower part of Figure 11, the signal labeled m1 contained in the correction signal (m4) is shown by a solid line.

[0105] As described above, the process of reverting to the state before wavelength dispersion correction and then correcting again can be achieved by the following equation 14.

[0106]

number

[0107]

number

[0108] According to the above processing, correction signal (0) ~ correction signal (m max From this, the signal corresponding to the maximum peak signal identified in step S214 can be easily identified. Correction signal (0) ~ Correction signal (m max In reality, as shown in Figure 10, the signals for each label are not distinguished and are in an overlapping state (a state of summation of the signal strengths of each signal). Therefore, it is not easy to distinguish the signal of each label from the signal waveform. However, in this embodiment, since inverse and re-transformation of wavelength dispersion correction is used, it is possible to easily extract only the signal of a specific label included in each corrected signal.

[0109] In this embodiment, the control unit 510 also generates a mirror signal. The process of generating a mirror signal can be achieved by calculating the following equation 16 and then inverting the sign of the dependent variable to obtain its complex conjugate.

[0110]

number

[0111] The control unit 510 performs the processing shown in equation (16) on the signal with the maximum peak identified in step S214. Specifically, in equation 16, the first term in F, which represents the Fourier transform, represents the inverse correction of the wavelength dispersion correction. Therefore, due to the presence of this term, for example, the signal with label m1, shown by the solid line in the middle of Figure 11, is transformed into the signal with label m1 in the corrected signal (0), shown by the solid line in the upper part. Furthermore, the second term in F, which represents the Fourier transform, represents the complex conjugate of the wavelength dispersion correction again. That is, for the signal with label m1 in the corrected signal (0), labels 0 to m max Using each of these wavelength dispersion formulas, a mirror signal of the wavelength-dispersion-corrected signal can be obtained.

[0112] As a result, correction signal (0) ~ correction signal (m max Of the signals, only the complex conjugate of the signal labeled m1 is identified. In Figure 11, the complex conjugates of the signal labeled m1 in correction signal (0), correction signal (m1), and correction signal (m4) are shown by dashed lines. Through the above process, the signal with the largest peak in the positive frequency domain is identified within a specific correction signal, the signal with the same label is identified within other correction signals, and the complex conjugate of each signal is identified. Here, among the identified signals, the signal other than the signal with the largest peak is called the signal from which is subtracted.

[0113] The control unit 510, using the functions of the signal processing unit 512, removes the maximum peak signal and the signal to be subtracted from the measurement signal (step S218). For example, in the example shown in Figures 10 and 11, the signals shown in Figure 11 are removed from the measurement signal (0). Figure 12 shows the state after the signals have been removed for correction signal (0), correction signal (m1), and correction signal (m4). The information indicating each of the removed signals is stored in the storage medium 520.

[0114] Next, the control unit 510 determines whether the termination condition has been met based on the function of the signal processing unit 512 (step S220). The termination condition is a predetermined condition for terminating the loop processing in steps S214 to S220. The termination condition is not limited, but examples include satisfying either the signal intensity of the maximum peak signal being less than a predetermined value, or the number of repetitions of the loop processing in steps S214 to S220 being greater than the number of data points.

[0115] If it is determined in step S220 that the termination condition has not been met, the control unit 510 repeats the processing from step S214 onward. On the other hand, if it is determined in step S220 that the termination condition has been met, the control unit 510 restores the signals of labels m1 and m2 and the signals excluded from the removal target using the function of the signal processing unit 512 (step S224). In this embodiment, the control unit 510 refers to the storage medium 520 and extracts the signals removed in step S218 as the maximum peak signals for each of labels m1 and m2, and restores them in frequency space. Furthermore, the control unit 510 refers to the storage medium 520 and also extracts the signals removed in S218 for the labels identified in S140 and S142, and restores them in frequency space.

[0116] The above process corresponds to extracting a signal corresponding to the wavelength dispersion characteristics of the signal to be detected from the correction signal and removing the signal corresponding to the wavelength dispersion characteristics of coherence revival in the OCT optical system 100. Figure 13 shows the restored signals for labels m1 and m2, respectively. Also in Figure 13, it is assumed that the label identified in S140 and S142 is label m3, and this label m3 has also been restored.

[0117] Through the above processing, it is possible to generate a signal that restores the signal after wavelength dispersion correction has been applied to the signal of each label based on the wavelength dispersion characteristics corresponding to each signal. Therefore, when the control unit 510 generates a tomographic image of, for example, the cornea or lens based on this signal, it is possible to generate a tomographic image while suppressing the influence of noise signals. In the example shown in Figure 13, the signals of labels m4, m5, and m6, which are noise signals caused by coherence revival, have been removed.

[0118] Furthermore, in this embodiment, a signal is generated by reconstructing the signal after applying wavelength dispersion correction to the signal of each label based on the wavelength dispersion characteristics corresponding to each signal. Therefore, wavelength dispersion correction can be performed individually for each signal based on the wavelength dispersion characteristics corresponding to each signal. As a result, it is possible to measure the target area with high accuracy.

[0119] Furthermore, in this embodiment, since the signal is reconstructed including the label identified in S140 and S142, the signal of label m3, which is close to the signal corresponding to the cornea or lens that is the target of detection, is not mistakenly removed. Therefore, it is possible to prevent the loss of important information.

[0120] (4) Other embodiments: The embodiments described above are merely examples for carrying out the present invention, and various other embodiments can be adopted. For example, at least some of the components of the above-described embodiments may be omitted or replaced. Furthermore, at least some of the functions of the measurement signal acquisition unit 511 and the signal processing unit 512 may be incorporated into a device other than the signal processing device 500.

[0121] Furthermore, in the above-described embodiment, the optical coherence tomography (OCT) apparatus 1 performs measurements using the SS-OCT method. However, the OCT apparatus 1 may also be other FD-OCT methods, such as the SD-OCT method. Also, in the above-described embodiment, the detection target is the cornea and lens, but the detection target may be other parts of the eye being examined (iris, conjunctiva, etc.). Moreover, the interferometer equipped in the OCT apparatus 1 is not limited, and various interferometers such as Michelson interferometers, balanced Michelson interferometers, and Mach-Zehnder interferometers can be used.

[0122] The measurement signal acquisition unit only needs to be able to acquire a measurement signal that indicates the measurement result of the object being measured by the OCT optical system. In other words, the measurement signal acquisition unit only needs to be able to acquire a measurement signal that includes the signal of the object being detected and other noise signals. The OCT optical system comprises a measurement arm and a reference arm, and only needs to be able to generate a measurement signal by interfering the light passing through each arm. The configuration of the OCT optical system is not limited, and any optical system that realizes the FD-OCT method can be used as the OCT optical system.

[0123] The object to be measured is not limited and can be any object. For example, in the above example where the detection target is the cornea and lens, the object to be measured is the eye under examination. Of course, when the eye under examination is the object to be measured, other parts besides the cornea and lens, such as the retina, may also be detected. The measurement signal only needs to be a signal generated by the interference of light irradiated from the light source of the OCT optical system onto the object to be measured and light irradiated from the light source onto a reference object, and the form of the measurement signal can be various.

[0124] The signal processing unit performs wavelength dispersion correction on the measurement signal using wavelength dispersion formulas corresponding to each of the different wavelength dispersion characteristics. Based on the corrected correction signals obtained for each wavelength dispersion characteristic, it associates the signals included in the correction signal with each of the wavelength dispersion characteristics. It then extracts the signal corresponding to the wavelength dispersion characteristic of the signal to be detected from the correction signal, and removes the signal corresponding to the wavelength dispersion characteristic of coherence revival in the OCT optical system.

[0125] In other words, the signal processing unit only needs to be able to separate the correction signal into multiple signals based on their wavelength dispersion characteristics, extract the signal to be detected based on its wavelength dispersion characteristics, and remove the noise signal caused by coherence revival based on its wavelength dispersion characteristics. The wavelength dispersion formula is an equation used for wavelength dispersion correction and only needs to be defined for each wavelength dispersion characteristic. The wavelength dispersion formula only needs to be defined in a way that allows for wavelength dispersion correction that applies changes to the measurement signal according to its wavelength dispersion characteristics, and is not limited to the formulas described above.

[0126] Furthermore, the signal processing unit may extract signals corresponding to at least two types of wavelength dispersion characteristics from the correction signal as the signal to be detected. Therefore, the embodiment is not limited to the above-described embodiment, and for example, the two types of wavelength dispersion characteristics may be wavelength dispersion characteristics corresponding to the optical paths of the signals representing each of the two detection targets. Alternatively, the two types of wavelength dispersion characteristics may be similar to the wavelength dispersion characteristics corresponding to the optical path of the signal representing one detection target.

[0127] Furthermore, various processing steps may be taken to increase the speed of the measurement. For example, the measurement signal may be configured to perform wavelength dispersion correction on the measurement light generated by the reference light and the measurement light that passes through a portion of a predetermined range scannable by the optical path changing unit composed of the galvanoscanner 202. The portion of the predetermined range only needs to include the signal from the object to be detected. In other words, processing may be performed to remove noise signals only in the range that includes the signal from the object to be detected. This configuration makes it possible to speed up the processing.

[0128] Furthermore, the present invention is also applicable as a program or method. For example, it is possible to provide a method or program implemented with the above-described apparatus. Moreover, it can be modified as appropriate, such as having part be software and part be hardware. Furthermore, the invention also works as a recording medium for programs. Of course, the recording medium for the software may be a magnetic recording medium, a semiconductor memory, or any recording medium developed in the future. [Explanation of symbols]

[0129] 1…Optical coherence tomography system, 10…Wavelength sweep light source, 20…Sample, 100…OCT optics, 104…Measurement-side circulator, 105…Reference-side circulator, 110…Balanced detector, 120…Polarization controller, 200…Alignment optics, 201…Collimator lens, 202…Galvanometer scanner, 203…Hot mirror, 204…Objective lens, 205a…Illumination light source, 205b…Illumination light source, 206…Beam splitter, 207…Imaging lens, 208…Area sensor, 210…Fixation target light source, 211…Movable for variable focus 212…Cold mirror, 213…Hot mirror, 214…Relay lens, 215…Beam splitter, 216…XY position detection light source, 217…Imaging lens, 218…2D position sensor, 219…Z position detection light source, 220…Imaging lens, 221…Line sensor, 300…Reference optical system, 301…Reference unit, 400…Interference optical system for k-clock generation, 500…Signal processing unit, 510…Control unit, 511…Measurement signal acquisition unit, 512…Signal processing unit, 520…Storage medium, 521…Wavelength dispersive information, 530…Display unit, 540…Operation unit

Claims

1. A measurement signal acquisition unit that acquires a measurement signal indicating the measurement result of the object to be measured using an OCT optical system, A signal processing unit performs wavelength dispersion correction on the measurement signal using wavelength dispersion formulas corresponding to each of the different wavelength dispersion characteristics, associates the signals included in the correction signal with each of the wavelength dispersion characteristics based on the corrected correction signal obtained for each wavelength dispersion characteristic, extracts a signal corresponding to the wavelength dispersion characteristic of the signal to be detected from the correction signal, and removes the signal corresponding to the wavelength dispersion characteristic of coherence revival in the OCT optical system. A signal processing device equipped with the following features.

2. The signal processing unit, A signal corresponding to at least two types of wavelength dispersion characteristics is extracted from the correction signal as the signal to be detected. The signal processing apparatus according to claim 1.

3. The object to be measured is the eye being examined. The two types of wavelength dispersion characteristics are, The wavelength dispersion characteristics in the optical path from the light source included in the OCT optical system to the cornea of ​​the eye under examination, and from the cornea to the photodetector included in the OCT optical system, The wavelength dispersion characteristics in the optical path from the light source included in the OCT optical system to the lens of the eye under examination, and from the lens to the photodetector included in the OCT optical system, The signal processing apparatus according to claim 2.

4. One of the two types of wavelength dispersion characteristics is the wavelength dispersion characteristic of the signal to be detected, and the other is a wavelength dispersion characteristic whose difference from the wavelength dispersion characteristic of the signal to be detected is below a threshold. The signal processing apparatus according to claim 2.

5. The OCT optical system includes an optical path changing unit that changes the optical path of the measurement light in the measurement arm within a predetermined range centered on a predetermined optical axis. The signal processing unit, The wavelength dispersion correction is performed on the measurement signal generated by the measurement light passing through a portion of the predetermined range and the reference light. The signal processing apparatus according to claim 1.

6. The signal processing unit, The signals included in either the positive frequency domain or the negative frequency domain of the measurement signal are associated with the respective wavelength dispersion characteristics. The signal processing apparatus according to claim 1.

7. A measurement signal acquisition step involves acquiring a measurement signal that indicates the measurement result of the object to be measured using an OCT optical system, and A signal processing step which involves performing wavelength dispersion correction on the measurement signal using wavelength dispersion formulas corresponding to each of the different wavelength dispersion characteristics, associating the signals included in the correction signal with each of the wavelength dispersion characteristics based on the corrected signal obtained for each wavelength dispersion characteristic, extracting a signal corresponding to the wavelength dispersion characteristic of the signal to be detected from the measurement signal, and removing the signal corresponding to the wavelength dispersion characteristic of coherence revival in the OCT optical system, A signal processing method that includes this.

8. Computers, A measurement signal acquisition unit that acquires a measurement signal indicating the measurement result of an object to be measured using an OCT optical system. A signal processing unit performs wavelength dispersion correction on the measurement signal using wavelength dispersion formulas corresponding to each of the different wavelength dispersion characteristics, associates the signals included in the correction signal with each of the wavelength dispersion characteristics based on the corrected signal obtained for each wavelength dispersion characteristic, extracts a signal corresponding to the wavelength dispersion characteristic of the signal to be detected from the measurement signal, and removes the signal corresponding to the wavelength dispersion characteristic of coherence revival in the OCT optical system. A signal processing program that functions as such.

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