JP6180877B2 - Optical image measuring device - Google Patents

Description

  The present invention relates to an optical image measurement device that acquires an image of an object to be measured using optical coherence tomography (hereinafter referred to as OCT).

  In recent years, OCT that forms an image representing the surface form or internal form of an object to be measured using a light beam from a laser light source or the like has attracted attention. Since OCT has no invasiveness to the human body like X-ray CT (Computed Tomography), it is expected to be applied particularly in the medical field and the biological field. For example, in the field of ophthalmology, an apparatus for forming an image of the fundus oculi or cornea has been put into practical use.

  Patent Document 1 discloses an apparatus using a so-called Fourier domain OCT (Fourier Domain OCT) technique. That is, this apparatus irradiates the object to be measured with a beam of low coherence light, superimposes the reflected light and the reference light to generate interference light, acquires the spectral intensity distribution of the interference light, and performs Fourier transform. By performing the conversion, the form of the object to be measured in the depth direction (z direction) is imaged. Further, this apparatus includes a galvanometer mirror that scans a light beam (signal light) in one direction (x direction) orthogonal to the z direction, thereby forming an image of a desired measurement target region of the object to be measured. It has become. An image formed by this apparatus is a two-dimensional tomographic image in the depth direction (z direction) along the scanning direction (x direction) of the light beam. Note that this technique is also called a spectral domain.

  In Patent Document 2, a plurality of horizontal two-dimensional tomographic images are formed by scanning (scanning) signal light in the horizontal direction (x direction) and the vertical direction (y direction), and based on the plurality of tomographic images. A technique for acquiring and imaging three-dimensional tomographic information of a measurement range is disclosed. As this three-dimensional imaging technology, for example, a method of displaying a plurality of tomographic images side by side (called stack data), volume data (voxel data) is generated based on the stack data, and rendering processing is performed on the volume data. And a method for forming a three-dimensional image.

  Patent Documents 3 and 4 disclose other types of OCT apparatuses. In Patent Document 3, the wavelength of light irradiated to a measured object is scanned (wavelength sweep), and interference intensity obtained by superimposing reflected light of each wavelength and reference light is detected to detect spectral intensity distribution. Is obtained, and an apparatus for imaging the form of the object to be measured by performing Fourier transform on the obtained image is described. Such a device is called a swept source type. The swept source type is a kind of Fourier domain type.

  In Patent Document 4, the traveling direction of light is obtained by irradiating the object to be measured with light having a predetermined beam diameter, and analyzing the component of interference light obtained by superimposing the reflected light and the reference light. An OCT apparatus for forming an image of an object to be measured in a cross-section orthogonal to is described. Such an OCT apparatus is called a full-field type or an en-face type.

  Patent Document 5 discloses a configuration in which OCT is applied to the ophthalmic field. Prior to the application of OCT, fundus cameras, slit lamps, SLOs, and the like were used as devices for observing the eye to be examined (see, for example, Patent Document 6, Patent Document 7, and Patent Document 8). A fundus camera is a device that shoots the fundus by illuminating the subject's eye with illumination light and receiving the fundus reflection light. A slit lamp is a device that acquires an image of a cross-section of the cornea by cutting off a light section of the cornea using slit light. The SLO is an apparatus that images the fundus surface by scanning the fundus with laser light and detecting the reflected light with a highly sensitive element such as a photomultiplier tube.

  An apparatus using OCT has an advantage over a fundus camera or the like in that a high-definition image can be acquired, and further, a tomographic image or a three-dimensional image can be acquired.

  As described above, an apparatus using OCT can be applied to observation of various parts of an eye to be examined, and can acquire high-definition images, and thus has been applied to diagnosis of various ophthalmic diseases.

  Among apparatuses using OCT, it is known that fixed pattern noise (hereinafter referred to as FPN) appears in an acquired image in an apparatus using a Fourier domain OCT technique.

  FIG. 16 shows an explanatory diagram of FPN. FIG. 16 shows an example of a fundus tomographic image (B-scan image), where the vertical direction represents the depth direction (z direction) and the horizontal direction represents the scanning direction (predetermined direction on the xy plane). The scanning means provided in the apparatus using OCT scans the irradiation position of the signal light on the eye to be examined (fundus) in the scanning direction. The tomographic image IMG2 is a B scan image, and is acquired by arranging A scan images at the respective irradiation positions in the scanning direction. In FIG. 16, the tomographic image IMG2 is configured using, for example, an A-scan image for 1024 lines. The A scan image is acquired based on the spectrum of the interference light of the A line at the designated irradiation position. In the tomographic image IMG2, for example, noises N1 to N5 appear as FPN at positions in a predetermined depth direction regardless of the irradiation position (position of the A line).

  In an apparatus using a spectral domain method (hereinafter referred to as SD-OCT), an average spectrum is calculated in the A-line direction at each irradiation position, and the average spectrum is subtracted from the measured spectrum, for example, the FPN shown in FIG. Can be removed.

  However, the swept source type apparatus (hereinafter referred to as SS-OCT) cannot remove the FPN as shown in FIG. 16 even if a technique similar to that of SD-OCT is used. As this factor, a multiple reflection in the optical member constituting the optical system, a shift between the light source control timing and the light emission timing from the light source, and the like are considered. Therefore, in SS-OCT, as a pre-process, FPN is generally removed by forming an image after matching the phases of all interference light spectra. Various techniques for removing FPN in such SS-OCT have been proposed (Non-Patent Documents 1 to 3, Patent Documents 9 and 10).

  Non-Patent Document 1 separately prepares a Mach-Zehnder interferometer, measures the spectrum of light obtained by further branching the reference light, and corrects the phase shift of the interference signal based on the phase of the measured spectrum. Technology is disclosed.

  Non-Patent Document 2 discloses a technology that incorporates a fiber Bragg grating (FBG), generates an A-line trigger signal, and corrects a phase shift of an interference signal based on the trigger signal. .

  In Non-Patent Document 3 and Patent Document 9, the spectrum of the reference light is used for one of the two adjacent A lines, the phase shift is obtained according to a predetermined formula, and the phase of the interference signal is calculated based on the obtained phase shift. Techniques for correcting are disclosed.

  Patent Document 10 acquires phase information of a signal corresponding to a noise component included in a spectrum signal output from a detector that has received interference light, and corrects a phase shift of the spectrum signal based on the acquired phase information. Techniques to do this are disclosed.

JP 11-325849 A JP 2002-139421 A JP 2007-24677 A JP 2006-153838 A JP 2008-73099 A JP-A-9-276232 JP 2008-259544 A JP 2009-11811 A International Publication No. 2013/103080 JP 2013-156229 A

J. et al. F. de Boer et al. "Phase-stabilized optical frequency domain imaging at 1-μm for measurement of blood in the human choroid", OPTIC EXPRESS. 2011 October 24, Vol. 19, no. 22, pp. 20886-20903 M.M. T Tsai et al. , “Microvascular Imaging Usage Swept-Source Optical Coherence Tomography with Single-Channel Acquisition”, Applied Physics Express, 4 (20). 09701-1 to 097001-3 Y. Yasuno et al. "High-penetration swept source Doppler optical coherence by full numeric phase stabilization", OPTIC EXPRESS. 2012 January 30, Vol. 20, no. 3, pp. 2740-2760

  Techniques for removing FPN in SS-OCT are disclosed in Patent Documents 9 and 10 and Non-Patent Documents 1 to 3 among Patent Documents 1 to 10 and Non-Patent Documents 1 to 3. However, the techniques disclosed in Patent Document 9 and Non-Patent Document 3 sometimes cannot remove the FPN depending on the intensity or phase of the spectrum of the interference light, and remove the FPN regardless of the mode of the image or noise. I can't. In addition, the techniques disclosed in Non-Patent Documents 1 and 2 require a significant addition of hardware, leading to high costs and large equipment. Further, in the technique disclosed in Patent Document 10, it is difficult to identify the FPN with high accuracy because the position where the FPN is generated on the tomographic image is detected. Depending on the image, the FPN can be removed. There are cases where it is not possible.

  The present invention has been made in order to solve the above-mentioned problems, and one of its purposes is that of an image from which FPN is removed regardless of the mode of the image or noise without adding a large amount of hardware. It is to provide a technology that can be acquired.

In order to achieve the above object, the invention described in claim 1 divides light from a wavelength scanning light source into signal light and reference light, and provides the signal light and the reference light that have passed through the object to be measured. An interference optical system for detecting interference light, and image forming means for forming an image of the object to be measured based on the interference light detected by the interference optical system, wherein the interference optical system An optical member disposed in the optical path or the optical path of the reference light, and the image forming unit obtains a phase shift by the optical member and corrects the phase of the spectrum of the interference light based on the obtained phase shift. The optical image measurement device forms the image based on the corrected spectrum of the interference light.
The invention according to claim 2 is the optical image measurement device according to claim 1, wherein the image forming unit corrects the phase of the spectrum of the interference light at a pixel level based on the phase shift. .
The invention according to claim 3 is the optical image measurement device according to claim 2, wherein the image forming unit converts the phase shift into a phase shift corresponding to a pixel level, and the converted Based on the phase shift corresponding to the pixel level, the phase of the spectrum of the interference light is corrected.
According to a fourth aspect of the present invention, there is provided the optical image measurement device according to any one of the first to third aspects, wherein the scanning unit scans the irradiation position of the signal light on the object to be measured. The image forming means obtains a phase shift in the optical member for the A line at each irradiation position, and corrects the phase of the spectrum of the interference light based on the obtained phase shift; and A spectrum calculation unit that subtracts a reference spectrum calculated in advance from the spectrum of the interference light corrected by the phase correction unit for each A line, and forms the image based on the spectrum obtained by the spectrum calculation unit To do.
The invention according to claim 5 is the optical image measurement device according to claim 4, wherein the image forming unit has a plurality of spectra of the interference light at a plurality of irradiation positions scanned by the scanning unit. Reference spectrum calculating means for calculating the reference spectrum based on
The invention according to claim 6 is the optical image measurement device according to claim 5, wherein the reference spectrum calculation means calculates a representative value of the spectrum of the plurality of interference lights, and calculates the representative value. Obtained as the reference spectrum.
The invention according to claim 7 is the optical image measurement device according to claim 6, wherein the representative value is a median value of a spectrum of the plurality of interference lights.
The invention according to claim 8 is the optical image measurement device according to claim 7, wherein the reference spectrum calculation means is obtained by performing Fourier transform on the spectrum of the plurality of interference lights. Each of the plurality of real parts and the plurality of imaginary parts is sorted in ascending or descending order, and the real part obtained by performing inverse Fourier transform on the real part and imaginary part that are the median value is obtained as the reference spectrum.
The invention according to claim 9 is the optical image measurement device according to any one of claims 1 to 8, wherein the image forming unit includes a reference spectrum having a reference phase and the reference spectrum. The phase shift in the optical member is obtained based on the correlation value with the spectrum of the interference light.
The invention according to claim 10 is the optical image measurement device according to claim 9, wherein the reference spectrum is obtained by scanning the irradiation position of the signal light with respect to the object to be measured. It is the spectrum of the interference light in any one of a plurality of A lines.
The invention according to claim 11 is the optical image measurement device according to claim 9 or 10, wherein the reference spectrum is an interference of the first A line scanned with respect to the object to be measured. It is the spectrum of light.
Moreover, invention of Claim 12 is an optical image measuring device as described in any one of Claims 1-11, Comprising: The said optical member is a polarizer.
The invention according to claim 13 is the optical image measurement device according to any one of claims 1 to 12, wherein the optical member changes an optical distance of light passing through the member. Is configured to be possible.
The invention according to claim 14 is the optical image measurement device according to claim 13, wherein the optical member includes a plurality of optical elements having different optical distances, and the plurality of optical elements includes: It is selectively disposed in the optical path of the signal light or the optical path of the reference light.
The invention according to claim 15 is the optical image measurement device according to any one of claims 1 to 14, wherein the interference optical system is configured to transmit an optical path of the signal light or the reference light. The image forming unit includes a plurality of optical members arranged in an optical path, and obtains a phase shift in any one of the plurality of optical members.
The invention according to claim 16 is the optical image measurement device according to any one of claims 1 to 15, comprising intensity detecting means for detecting the intensity of a noise component by the optical member. The image forming unit forms the image using the corrected spectrum of the interference light when the intensity detected by the intensity detecting unit is equal to or greater than a threshold value.
The invention according to claim 17 is the optical image measurement device according to any one of claims 1 to 16, wherein the object to be measured is a living eye.

  According to the present invention, when the light from the light source is divided into the signal light and the reference light, and the image of the measured object is formed based on the interference light between the signal light and the reference light that has passed through the measured object, A phase shift by an optical member disposed in the optical path of the light or the optical path of the reference light is obtained, and an image of the object to be measured is formed using the spectrum of the interference light whose phase is corrected based on the obtained phase shift. Therefore, it is possible to obtain an image from which the FPN has been removed, regardless of the mode of the image or noise, without significantly adding hardware.

It is a schematic diagram showing an example of composition of a fundus photographing device concerning an embodiment. It is a schematic diagram showing an example of composition of a fundus photographing device concerning an embodiment. It is a schematic block diagram showing an example of composition of a fundus photographing device concerning an embodiment. It is a schematic block diagram showing an example of composition of a fundus photographing device concerning an embodiment. It is a flowchart showing the operation example of the fundus imaging apparatus according to the embodiment. It is the schematic for demonstrating the operation example of the fundus imaging apparatus which concerns on embodiment. It is a flowchart showing the operation example of the fundus imaging apparatus according to the embodiment. It is a flowchart showing the operation example of the fundus imaging apparatus according to the embodiment. It is a flowchart showing the operation example of the fundus imaging apparatus according to the embodiment. It is a flowchart showing the operation example of the fundus imaging apparatus according to the embodiment. It is the schematic for demonstrating the operation example of the fundus imaging apparatus which concerns on embodiment. It is the schematic for demonstrating the operation example of the fundus imaging apparatus which concerns on embodiment. It is the schematic for demonstrating the operation example of the fundus imaging apparatus which concerns on embodiment. It is a schematic diagram showing an example of composition of a fundus photographing device concerning an embodiment. It is a schematic block diagram showing an example of composition of a fundus photographing device concerning an embodiment. It is explanatory drawing of FPN which concerns on embodiment.

  An example of an embodiment of an optical image measurement device according to the present invention will be described in detail with reference to the drawings. The optical image measurement device according to the present invention forms a tomographic image or a three-dimensional image of an object to be measured using OCT. In this specification, images acquired by OCT may be collectively referred to as OCT images. In addition, a measurement operation for forming an OCT image may be referred to as OCT measurement. In addition, it is possible to use suitably the description content of the literature described in this specification as the content of the following embodiment.

  In the following embodiments, a fundus imaging apparatus to which an optical image measurement device that performs OCT measurement of the fundus by a Fourier domain type OCT method using a living body eye (examined eye, fundus) as an object to be measured will be described. In particular, the fundus imaging apparatus according to the embodiment can acquire both an OCT image and a fundus image of the fundus using a swept source type OCT technique. Note that the configuration according to the present invention can be applied to an optical image measurement apparatus using a type other than the swept source type, for example, a spectral domain OCT technique. In this embodiment, an apparatus combining an OCT apparatus and a fundus camera will be described. However, this embodiment may be applied to a fundus imaging apparatus other than a fundus camera, such as an SLO (Scanning Laser Ophthalmoscope), a slit lamp, an ophthalmic surgical microscope, and the like. It is also possible to combine an OCT apparatus having the configuration according to the above. In addition, the configuration according to this embodiment can be incorporated into a single OCT apparatus.

[Constitution]
As shown in FIGS. 1 and 2, the fundus imaging apparatus 1 includes a fundus camera unit 2, an OCT unit 100, and an arithmetic control unit 200. The retinal camera unit 2 has almost the same optical system as a conventional retinal camera. The OCT unit 100 is provided with an optical system for acquiring an OCT image of the fundus. The arithmetic control unit 200 includes a computer that executes various arithmetic processes and control processes.

[Fundus camera unit]
The fundus camera unit 2 shown in FIG. 1 is provided with an optical system for acquiring a front image (fundus image) of the eye E of the eye E viewed from the cornea side. The fundus image includes an observation image and a captured image. The observation image is, for example, a monochrome moving image formed at a predetermined frame rate using near infrared light. The captured image may be, for example, a color image obtained by flashing visible light, or a monochrome still image using near infrared light or visible light as illumination light. The fundus camera unit 2 may be configured to be able to acquire images other than these, such as a fluorescein fluorescent image, an indocyanine green fluorescent image, a spontaneous fluorescent image, and the like.

  The retinal camera unit 2 is provided with a chin rest and a forehead support for supporting the subject's face. Further, the fundus camera unit 2 is provided with an illumination optical system 10 and a photographing optical system 30. The illumination optical system 10 irradiates the fundus oculi Ef with illumination light. The photographing optical system 30 guides the fundus reflection light of the illumination light to an imaging device (CCD image sensor (sometimes simply referred to as a CCD) 35, 38). The imaging optical system 30 guides the signal light from the OCT unit 100 to the fundus oculi Ef and guides the signal light passing through the fundus oculi Ef to the OCT unit 100.

  The observation light source 11 of the illumination optical system 10 is constituted by a halogen lamp, for example. The light (observation illumination light) output from the observation light source 11 is reflected by the reflection mirror 12 having a curved reflection surface, passes through the condensing lens 13, passes through the visible cut filter 14, and is converted into near infrared light. Become. Further, the observation illumination light is once converged in the vicinity of the photographing light source 15, reflected by the mirror 16, and passes through the relay lenses 17 and 18, the diaphragm 19 and the relay lens 20. Then, the observation illumination light is reflected at the peripheral portion (region around the hole portion) of the aperture mirror 21, passes through the dichroic mirror 46, and is refracted by the objective lens 22 to illuminate the fundus oculi Ef. An LED (Light Emitting Diode) can also be used as the observation light source.

  The fundus reflection light of the observation illumination light is refracted by the objective lens 22, passes through the dichroic mirror 46, passes through the hole formed in the central region of the perforated mirror 21, passes through the dichroic mirror 55, and is a focusing lens. It is reflected by the mirror 32 via 31. Further, the fundus reflection light passes through the half mirror 33A, is reflected by the dichroic mirror 33, and forms an image on the light receiving surface of the CCD image sensor 35 by the condenser lens. The CCD image sensor 35 detects fundus reflected light at a predetermined frame rate, for example. On the display device 3, an image (observation image) based on fundus reflection light detected by the CCD image sensor 35 is displayed. When the photographing optical system 30 is focused on the anterior segment, an observation image of the anterior segment of the eye E is displayed.

  The imaging light source 15 is constituted by, for example, a xenon lamp. The light (imaging illumination light) output from the imaging light source 15 is applied to the fundus oculi Ef through the same path as the observation illumination light. The fundus reflection light of the imaging illumination light is guided to the dichroic mirror 33 through the same path as that of the observation illumination light, passes through the dichroic mirror 33, is reflected by the mirror 36, and is reflected by the condenser lens 37 of the CCD image sensor 38. An image is formed on the light receiving surface. On the display device 3, an image (captured image) based on fundus reflection light detected by the CCD image sensor 38 is displayed. Note that the display device 3 that displays the observation image and the display device 3 that displays the captured image may be the same or different. In addition, when similar imaging is performed by illuminating the eye E with infrared light, an infrared captured image is displayed. It is also possible to use an LED as a photographing light source.

  An LCD (Liquid Crystal Display) 39 displays a fixation target and an eyesight measurement index. The fixation target is an index for fixing the eye E to be examined, and is used at the time of fundus photographing or OCT measurement.

  A part of the light output from the LCD 39 is reflected by the half mirror 33A, reflected by the mirror 32, passes through the focusing lens 31 and the dichroic mirror 55, passes through the hole of the perforated mirror 21, and reaches the dichroic. The light passes through the mirror 46, is refracted by the objective lens 22, and is projected onto the fundus oculi Ef.

  By changing the display position of the fixation target on the screen of the LCD 39, the fixation position of the eye E can be changed. As the fixation position of the eye E, for example, a position for acquiring an image centered on the macular portion of the fundus oculi Ef, or a position for acquiring an image centered on the optic disc as in the case of a conventional fundus camera And a position for acquiring an image centered on the fundus center between the macula and the optic disc. It is also possible to arbitrarily change the display position of the fixation target.

  Further, the fundus camera unit 2 is provided with an alignment optical system 50 and a focus optical system 60 as in a conventional fundus camera. The alignment optical system 50 generates an index (alignment index) for performing alignment (alignment) of the apparatus optical system with respect to the eye E. The focus optical system 60 generates an index (split index) for focusing on the fundus oculi Ef.

  The light (alignment light) output from the LED 51 of the alignment optical system 50 is reflected by the dichroic mirror 55 via the apertures 52 and 53 and the relay lens 54, passes through the hole of the aperture mirror 21, and reaches the dichroic mirror 46. And is projected onto the cornea of the eye E by the objective lens 22.

  The cornea-reflected light of the alignment light passes through the objective lens 22, the dichroic mirror 46, and the hole, part of which passes through the dichroic mirror 55, passes through the focusing lens 31, and is reflected by the mirror 32. The light passes through 33A, is reflected by the dichroic mirror 33, and is projected onto the light receiving surface of the CCD image sensor 35 by the condenser lens. The light reception image (alignment index) by the CCD image sensor 35 is displayed on the display device 3 together with the observation image. The user performs alignment by performing the same operation as that of a conventional fundus camera. Further, the arithmetic control unit 200 may perform alignment by analyzing the position of the alignment index and moving the optical system (auto-alignment function).

  When performing the focus adjustment, the reflecting surface of the reflecting rod 67 is obliquely provided on the optical path of the illumination optical system 10. The light (focus light) output from the LED 61 of the focus optical system 60 passes through the relay lens 62, is separated into two light beams by the split indicator plate 63, passes through the two-hole aperture 64, and is reflected by the mirror 65, The light is focused on the reflecting surface of the reflecting bar 67 by the condenser lens 66 and reflected. Further, the focus light passes through the relay lens 20, is reflected by the perforated mirror 21, passes through the dichroic mirror 46, is refracted by the objective lens 22, and is projected onto the fundus oculi Ef.

  The fundus reflection light of the focus light is detected by the CCD image sensor 35 through the same path as the cornea reflection light of the alignment light. A light reception image (split index) by the CCD image sensor 35 is displayed on the display device 3 together with the observation image. The arithmetic control unit 200 analyzes the position of the split index and moves the focusing lens 31 and the focus optical system 60 to perform focusing as in the conventional case (autofocus function). Alternatively, focusing may be performed manually while visually checking the split indicator.

  The dichroic mirror 46 branches the optical path for OCT measurement from the optical path for fundus photography. The dichroic mirror 46 reflects light in a wavelength band used for OCT measurement and transmits light for fundus photographing. In this optical path for OCT measurement, a collimator lens unit 40, an optical path length changing unit 41, a galvano scanner 42, a focusing lens 43, a mirror 44, and a relay lens 45 are provided in this order from the OCT unit 100 side. It has been.

  The optical path length changing unit 41 is movable in the direction of the arrow shown in FIG. 1 and changes the optical path length of the optical path for OCT measurement. This change in the optical path length is used for correcting the optical path length according to the axial length of the eye E or adjusting the interference state. The optical path length changing unit 41 includes, for example, a corner cube and a mechanism for moving the corner cube.

  The galvano scanner 42 changes the traveling direction of light (signal light LS) passing through the optical path for OCT measurement. Thereby, the fundus oculi Ef can be scanned with the signal light LS. The galvano scanner 42 includes, for example, a galvano mirror that scans the signal light LS in the x direction, a galvano mirror that scans in the y direction, and a mechanism that drives these independently. Thereby, the signal light LS can be scanned in an arbitrary direction on the xy plane. In this embodiment, the galvano scanner 42 is an example of a “scanning unit” that scans the irradiation position of the signal light LS on the eye to be examined.

[OCT unit]
An example of the configuration of the OCT unit 100 will be described with reference to FIG. The OCT unit 100 is provided with an optical system for acquiring an OCT image of the fundus oculi Ef. This optical system has the same configuration as a conventional swept source type OCT apparatus. That is, this optical system splits light from a wavelength scanning (wavelength sweep) light source into signal light and reference light, and causes signal light passing through the fundus oculi Ef and reference light passing through the reference optical path to interfere with each other. This is an interference optical system that generates interference light and detects the interference light. The detection result (detection signal) of the interference light in the interference optical system is a signal indicating the spectrum of the interference light, and is sent to the arithmetic control unit 200.

  The light source unit 101 includes a wavelength scanning type (wavelength sweeping type) light source capable of scanning (sweeping) the wavelength of the emitted light, as in a general swept source type OCT apparatus. The light source unit 101 temporally changes the output wavelength in the near-infrared wavelength band that cannot be visually recognized by the human eye. The light output from the light source unit 101 is indicated by a symbol L0.

  The light L0 output from the light source unit 101 is guided to the polarization controller 103 by the optical fiber 102 and its polarization state is adjusted. The polarization controller 103 adjusts the polarization state of the light L0 guided through the optical fiber 102, for example, by applying stress from the outside to the looped optical fiber 102.

  The light L0 whose polarization state is adjusted by the polarization controller 103 is guided to the fiber coupler 105 by the optical fiber 104, and is divided into the signal light LS and the reference light LR.

  The reference light LR is guided to the collimator 111 by the optical fiber 110 and becomes a parallel light beam. The reference light LR that has become a parallel light beam is guided to the corner cube 114 via the optical path length correction member 112 and the dispersion compensation member 113. The optical path length correction member 112 functions as a delay unit for matching the optical path lengths (optical distances) of the reference light LR and the signal light LS. The dispersion compensation member 113 functions as a dispersion compensation means for matching the dispersion characteristics of the reference light LR and the signal light LS.

  The corner cube 114 folds the traveling direction of the reference light LR that has become a parallel light beam by the collimator 111 in the reverse direction. The optical path of the reference light LR incident on the corner cube 114 and the optical path of the reference light LR emitted from the corner cube 114 are parallel. The corner cube 114 is movable in a direction along the incident optical path and the outgoing optical path of the reference light LR. By this movement, the length of the optical path (reference optical path) of the reference light LR is changed.

  The reference light LR that has passed through the corner cube 114 passes through a wave plate 115 (for example, a λ / 4 plate or a λ / 2 plate) 115, a dispersion compensation member 113, and an optical path length correction member 112, and is collimated from a parallel light beam by a collimator 116. And is incident on the optical fiber 117 and guided to the polarization controller 118 to adjust the polarization state of the reference light LR. The wave plate 115 is an optical member that adjusts the polarization direction. The wave plate 115 is used for obtaining a phase shift of the reference light LR. In FIG. 2, the wave plate 115 is disposed in the optical path of the reference light LR. The wave plate 115 is an example of the “optical member” in this embodiment.

  For example, the polarization controller 118 has the same configuration as the polarization controller 103. The reference light LR whose polarization state is adjusted by the polarization controller 118 is guided to the attenuator 120 by the optical fiber 119, and the light quantity is adjusted under the control of the arithmetic control unit 200. The reference light LR whose light amount has been adjusted by the attenuator 120 is guided to the fiber coupler 122 by the optical fiber 121.

  The signal light LS generated by the fiber coupler 105 is guided by the optical fiber 127 and converted into a parallel light beam by the collimator lens unit 40. The signal light LS converted into a parallel light beam reaches the dichroic mirror 46 via the optical path length changing unit 41, the galvano scanner 42, the focusing lens 43, the mirror 44, and the relay lens 45. The signal light LS is reflected by the dichroic mirror 46, is refracted by the objective lens 22, and is applied to the fundus oculi Ef. The signal light LS is scattered (including reflection) at various depth positions of the fundus oculi Ef. The backscattered light of the signal light LS from the fundus oculi Ef travels in the same direction as the forward path in the reverse direction, is guided to the fiber coupler 105, and reaches the fiber coupler 122 via the optical fiber 128.

  The fiber coupler 122 combines (interferes) the signal light LS incident through the optical fiber 128 and the reference light LR incident through the optical fiber 121 to generate interference light. The fiber coupler 122 branches the interference light between the signal light LS and the reference light LR at a predetermined branching ratio (for example, 1: 1), thereby generating a pair of interference lights LC. The pair of interference lights LC emitted from the fiber coupler 122 are guided to the detector 125 by optical fibers 123 and 124, respectively.

  The detector 125 is, for example, a balanced photodiode (hereinafter referred to as BPD) that includes a pair of photodetectors that respectively detect a pair of interference lights LC and outputs a difference between detection results obtained by the pair of photodetectors. The detector 125 sends the detection result (detection signal) to the arithmetic control unit 200. The arithmetic control unit 200 forms a tomographic image by performing Fourier transform or the like on the spectrum distribution based on the detection result obtained by the detector 125 for each series of wavelength scans (for each A line), for example. The arithmetic control unit 200 causes the display device 3 to display the formed image.

  In this embodiment, a Michelson type interferometer is employed, but any type of interferometer such as a Mach-Zehnder type can be appropriately employed. In this embodiment, the interference optical system includes fiber couplers 105 and 122, a detector 125, and optical fibers and various optical elements that guide the reference light LR and the signal light LS therebetween. The interference optical system may further include a light source unit 101. This interference optical system is an example of the “interference optical system” in this embodiment.

[Calculation control unit]
The configuration of the arithmetic control unit 200 will be described. The arithmetic control unit 200 analyzes the detection signal input from the detector 125 and forms an OCT image of the fundus oculi Ef. The arithmetic processing for this is the same as that of a conventional swept source type OCT apparatus.

  The arithmetic control unit 200 controls each part of the fundus camera unit 2, the display device 3, and the OCT unit 100. For example, the arithmetic control unit 200 displays an OCT image of the fundus oculi Ef on the display device 3.

  As the control of the fundus camera unit 2, the arithmetic control unit 200 controls the operation of the observation light source 11, the imaging light source 15 and the LEDs 51 and 61, the operation control of the LCD 39, the movement control of the focusing lenses 31 and 43, and the reflector 67. Movement control, movement control of the focus optical system 60, movement control of the optical path length changing unit 41, operation control of the galvano scanner 42, and the like are performed.

  As the control of the OCT unit 100, the arithmetic control unit 200 controls the operation of the light source unit 101, the movement control of the corner cube 114, the operation control of the detector 125, the operation control of the attenuator 120, and the operations of the polarization controllers 103 and 118. Control and so on.

  The arithmetic control unit 200 includes, for example, a microprocessor, a RAM, a ROM, a hard disk drive, a communication interface, etc., as in a conventional computer. A computer program for controlling the fundus imaging apparatus 1 is stored in a storage device such as a hard disk drive. The arithmetic control unit 200 may include various circuit boards, for example, a circuit board for forming an OCT image. The arithmetic control unit 200 may include an operation device (input device) such as a keyboard and a mouse, and a display device such as an LCD.

  The fundus camera unit 2, the display device 3, the OCT unit 100, and the calculation control unit 200 may be configured integrally (that is, in a single housing) or separated into two or more housings. It may be.

[Control system]
The configuration of the control system of the fundus imaging apparatus 1 will be described with reference to FIGS. 3 and 4.

(Control part)
The control system of the fundus imaging apparatus 1 is configured around the control unit 210. The control unit 210 includes, for example, the aforementioned microprocessor, RAM, ROM, hard disk drive, communication interface, and the like. The control unit 210 is provided with a main control unit 211 and a storage unit 212.

(Main control unit)
The main control unit 211 performs the various controls described above. In particular, the main control unit 211 includes a focus driving unit 31A of the fundus camera unit 2, an optical path length changing unit 41 and a galvano scanner 42, a light source unit 101 of the OCT unit 100, a reference driving unit 114A, a polarization controller 103, 118, The attenuator 120 and the detector 125 are controlled.

  The focusing drive unit 31A moves the focusing lens 31 in the optical axis direction. Thereby, the focus position of the photographic optical system 30 is changed. The main control unit 211 can control an optical system drive unit (not shown) to move the optical system provided in the fundus camera unit 2 three-dimensionally. This control is used in alignment and tracking. Tracking refers to moving the apparatus optical system in accordance with the movement of the eye E. When tracking is performed, alignment and focusing are performed in advance. Tracking maintains a suitable positional relationship in which the alignment and focus are achieved by moving the apparatus optical system in real time according to the position and orientation of the eye E based on an image obtained by taking a moving image of the eye E. It is a function.

  114 A of reference drive parts move the corner cube 114 provided in the optical path of reference light along this optical path. Thereby, the optical path length of the reference light is changed.

  Further, the main control unit 211 performs processing for writing data into the storage unit 212 and processing for reading data from the storage unit 212.

(Memory part)
The storage unit 212 stores various data. Examples of the data stored in the storage unit 212 include OCT image image data, fundus image data, and examined eye information. The eye information includes information about the subject such as patient ID and name, and information about the eye such as left / right eye identification information. The storage unit 212 stores various programs and data for operating the fundus photographing apparatus 1.

(Image forming part)
The image forming unit 220 forms image data of a tomographic image of the fundus oculi Ef based on the detection signal from the detector 125. In this process, as in the conventional swept source type optical coherence tomography, in addition to processes such as noise removal (noise reduction), filter processing, and FFT (Fast Fourier Transform), a process for removing FPN, which will be described later, is performed. include. The image forming unit 220 is an example of an “image forming unit” in this embodiment.

  The image forming unit 220 includes, for example, the circuit board described above. In this specification, “image data” and “image” based thereon may be identified.

  The image forming unit 220 forms an image of the eye E based on the interference light LC detected by the interference optical system. At this time, the image forming unit 220 obtains a phase shift by the wave plate 115 (optical member), corrects the phase of the spectrum of the interference light based on the obtained phase shift, and based on the corrected spectrum of the interference light. An image of the eye E is formed. The spectrum of the interference light is output from the detector 125.

  Further, the image forming unit 220 can correct the phase of the spectrum of the interference light at the pixel level based on the obtained phase shift. As one of the factors of FPN, an operation clock of a means for capturing a detection signal of interference light (for example, DAQ (Data Acquisition Board)), a wavelength scanning timing (so-called k clock) in a wavelength scanning light source (light source unit 101), and There is a phase shift of. This phase shift shifts the detection signal capture timing at the pixel level. Therefore, by correcting the phase of the interference light spectrum at the pixel level, it is possible to remove the FPN based on the above cause. In addition, it is possible to avoid a situation in which the FPN cannot be removed by correcting the phase of the spectrum of the interference light at the subpixel level and the image quality is deteriorated.

  Further, the image forming unit 220 can convert the obtained phase shift into a phase shift corresponding to the pixel level, and correct the phase of the spectrum of the interference light based on the phase shift corresponding to the converted pixel level. It is. As a result, after correcting the phase of the interference light spectrum based on the phase shift at the sub-pixel level, the phase correction is simplified compared to the case of converting the phase correction to the pixel level. Can do.

  Such an image forming unit 220 includes a phase correction unit 221, a spectrum calculation unit 222, and a reference spectrum calculation unit 223.

  The phase correction unit 221 obtains a phase shift by the wave plate 115 for the A line at each irradiation position of the signal light LS, and corrects the phase of the spectrum of the interference light based on the obtained phase shift. The irradiation position is scanned with respect to the eye E by the galvano scanner 42. The spectrum calculation unit 222 subtracts a reference spectrum calculated in advance from the spectrum of the interference light whose phase is corrected by the phase correction unit 221 for each A line.

  The reference spectrum is calculated based on the spectrum of the interference light. The reference spectrum calculation unit 223 calculates a reference spectrum based on a plurality of interference light spectra at a plurality of irradiation positions scanned by the galvano scanner 42. This eliminates the need to capture a background spectrum separately. The background spectrum is acquired by switching the optical system to a predetermined path, but may be affected by the influence of the optical system path after switching or the measurement environment. For example, depending on the path of the optical system after switching, the degree of influence on the background spectrum may be different due to the reflected light. Further, for example, the background spectrum itself may change due to a difference in measurement environment. If the interference light spectrum is corrected using such a background spectrum as a reference spectrum, the image quality may deteriorate. According to this embodiment, it is possible to remove the FPN without being affected by the various effects described above.

  The phase correction unit 221 is an example of the “phase correction unit” in this embodiment. The spectrum calculation unit 222 is an example of the “spectrum calculation means” in this embodiment. The reference spectrum calculation unit 223 is an example of the “reference spectrum calculation unit” in this embodiment.

  The image forming unit 220 forms an image of the eye E based on the spectrum obtained by the spectrum calculation unit 222. That is, the image forming unit 220 forms an image of the eye E by subjecting the spectrum obtained by the spectrum calculating unit 222 to Fourier transform or the like.

(Image processing unit)
The image processing unit 230 performs various types of image processing and analysis processing on the image formed by the image forming unit 220. For example, the image processing unit 230 executes various correction processes such as image brightness correction and dispersion correction. The image processing unit 230 performs various types of image processing and analysis processing on the image (fundus image, anterior eye image, etc.) obtained by the fundus camera unit 2. For example, the image processing unit 230 performs processing for obtaining the position and orientation of the eye E by analyzing an image obtained by capturing a moving image of the anterior eye part of the eye E during tracking.

  The image processing unit 230 executes known image processing such as interpolation processing for interpolating pixels between tomographic images to form image data of a three-dimensional image of the fundus oculi Ef. Note that the image data of a three-dimensional image means image data in which pixel positions are defined by a three-dimensional coordinate system. As image data of a three-dimensional image, there is image data composed of voxels arranged three-dimensionally. This image data is called volume data or voxel data. When displaying an image based on volume data, the image processing unit 230 performs rendering processing (volume rendering, MIP (Maximum Intensity Projection), etc.) on the volume data, and views the image from a specific gaze direction. Image data of a pseudo three-dimensional image is formed. This pseudo three-dimensional image is displayed on a display device such as the display unit 240A.

  It is also possible to form stack data of a plurality of tomographic images as image data of a three-dimensional image. The stack data is image data obtained by three-dimensionally arranging a plurality of tomographic images obtained along a plurality of scanning lines based on the positional relationship of the scanning lines. That is, the stack data is image data obtained by expressing a plurality of tomographic images originally defined by individual two-dimensional coordinate systems using one three-dimensional coordinate system (that is, embedding in one three-dimensional space). is there.

  The image processing unit 230 that functions as described above includes, for example, the aforementioned microprocessor, RAM, ROM, hard disk drive, circuit board, and the like. In a storage device such as a hard disk drive, a computer program for causing the microprocessor to execute the above functions is stored in advance.

(User interface)
The user interface 240 includes a display unit 240A and an operation unit 240B. The display unit 240A includes the display device of the arithmetic control unit 200 and the display device 3 described above. The operation unit 240B includes the operation device of the arithmetic control unit 200 described above. The operation unit 240B may include various buttons and keys provided on the housing of the fundus photographing apparatus 1 or outside. For example, when the fundus camera unit 2 has a housing similar to that of a conventional fundus camera, the operation unit 240B may include a joystick, an operation panel, or the like provided on the housing. The display unit 240 </ b> A may include various display devices such as a touch panel provided on the housing of the fundus camera unit 2.

  The display unit 240A and the operation unit 240B do not need to be configured as individual devices. For example, a device in which a display function and an operation function are integrated, such as a touch panel, can be used. In that case, the operation unit 240B includes the touch panel and a computer program. The operation content for the operation unit 240B is input to the control unit 210 as an electrical signal. Further, operations and information input may be performed using a graphical user interface (GUI) displayed on the display unit 240A and the operation unit 240B.

[Operation]
The operation of the fundus imaging apparatus 1 will be described.

  FIG. 5 shows an example of the operation of the fundus imaging apparatus 1. This operation example includes a process for aligning the eye E to be examined and the apparatus optical system based on an image, and a process for setting a scanning region based on the image. The alignment processing includes alignment for OCT measurement (auto alignment), focusing (auto focus), and tracking (auto tracking).

(S1: Start acquiring real-time near-infrared video)
First, acquisition of a near-infrared moving image of the fundus oculi Ef is started by continuously illuminating the fundus oculi Ef with illumination light from the observation light source 11 (which becomes near-infrared light by the visible cut filter 14). This near-infrared moving image is obtained in real time until the continuous illumination ends. The image of each frame constituting this moving image is temporarily stored in the frame memory (storage unit 212) and sequentially sent to the image processing unit 230.

  Note that an alignment index by the alignment optical system 50 and a split index by the focus optical system 60 are projected onto the eye E to be examined. Therefore, the alignment index and the split index are drawn on the near-infrared moving image. These indices can be used for alignment and focusing. A fixation target by the LCD 39 is also projected onto the eye E. The subject is instructed to stare at the fixation target.

(S2: Alignment)
The image processing unit 230 sequentially analyzes frames obtained by taking a moving image of the eye E with the optical system, obtains the position of the alignment target, and calculates the movement amount of the optical system. The control unit 210 performs auto alignment by controlling an optical system driving unit (not shown) based on the movement amount of the optical system calculated by the image processing unit 230.

(S3: Focusing)
The image processing unit 230 sequentially analyzes frames obtained by taking a moving image of the eye E with the optical system, obtains the position of the split target, and calculates the movement amount of the focusing lens 31. The control unit 210 performs autofocus by controlling the focusing drive unit 31A based on the movement amount of the focusing lens 31 calculated by the image processing unit 230.

(S4: Start tracking)
Subsequently, the control unit 210 starts auto-tracking. Specifically, the image processing unit 230 analyzes in real time frames obtained sequentially by taking a moving image of the eye E with the optical system, and monitors the movement (position change) of the eye E. The control unit 210 controls an optical system driving unit (not shown) so as to move the optical system in accordance with the position of the eye E to be sequentially acquired. As a result, the optical system can follow the movement of the eye E in real time, and it is possible to maintain a suitable positional relationship in which the alignment is in focus.

(S5: Set scanning area)
The control unit 210 displays the near-infrared moving image on the display unit 240A in real time. The user sets a scanning region on the near-infrared moving image by using the operation unit 240B. The scanning area to be set may be a one-dimensional area or a two-dimensional area.

  When the scanning mode of the signal light LS and the site of interest (optic nerve head, macula, lesion, etc.) are set in advance, the control unit 210 sets the scanning area based on these settings. It is also possible to configure. Specifically, a region of interest is identified by image analysis by the image processing unit 230, and the control unit 210 defines a region of a predetermined pattern so as to include the region of interest (for example, the region of interest is located at the center). Set.

  Further, when setting the same scanning region as the OCT measurement performed in the past (so-called follow-up), the control unit 210 can reproduce and set the past scanning region on the real-time near-infrared moving image. . As a specific example, the control unit 210 includes information (scanning mode or the like) indicating a scanning area set in a past examination, and a near-infrared fundus image (a still image, for example, a frame) in which the scanning area is set. Are associated with each other and stored in the storage unit 212 (practically associated with patient ID and left and right eye information). The control unit 210 aligns the past near-infrared fundus image and the frame of the current near-infrared moving image, and in the current near-infrared moving image corresponding to the scanning region in the past near-infrared fundus image. Specify the image area. Thereby, the scanning area applied in the past examination is set for the current near-infrared moving image.

(S6: OCT measurement)
The control unit 210 controls the light source unit 101 and the optical path length changing unit 41, and controls the galvano scanner 42 based on the scanning region set in step S5, thereby performing OCT measurement of the fundus oculi Ef.

  The image forming unit 220 forms a tomographic image of the fundus oculi Ef based on the spectrum of the interference light obtained by the OCT measurement. When the scanning mode is a three-dimensional scan, the image processing unit 230 forms a three-dimensional image of the fundus oculi Ef based on a plurality of tomographic images formed by the image forming unit 220. This is the end of this operation example (end).

  Note that the order of steps S4 and S5 may be changed. In steps S4 and S5, a near-infrared moving image is displayed and a scanning area is set on the near-infrared moving image. However, the setting mode of the scanning area is not limited to this. For example, an image of one frame (referred to as a reference image) in the near-infrared moving image is displayed, and auto tracking is executed in the background. When the scanning area is set on the reference image, the control unit 210 performs alignment between the reference image and the image currently used for auto-tracking, thereby setting the scanning area set on the reference image. An image region in the real-time near-infrared moving image corresponding to is specified. This process can also set the scanning area in the real-time near-infrared moving image as in steps S4 and S5. Further, according to this method, since the scanning area can be set on the still image, the work can be facilitated and ensured as compared with the case of setting on the moving image that is actually auto-tracked.

  In this embodiment, the following profile is obtained by performing Fourier transform on the spectrum of the interference light obtained by the detector 125.

  FIG. 6 shows an example of a profile in this embodiment. In FIG. 6, the horizontal axis represents the index, and the vertical axis represents the average power (average intensity). The index is a variable representing a frequency in Fourier transform. Since the wave number is proportional to the frequency, the index is also a variable representing the wave number. The index is also a variable corresponding to the coordinate position of the fundus oculi Ef in the depth (z) direction.

  In the profile shown in FIG. 6, FPN appears in a portion where the average power changes in a substantially pulse shape. By specifying the index at which the FPN appears, the frequency corresponding to the specified index can also be specified, and the factor of the FPN may be specified. In FIG. 6, noises FN2 and FN3 are FPN caused by the light source and the electrical system, and a pattern FN4 is a signal of the retinal layer. The noise FN6 is noise caused by multiple reflections on the front and rear surfaces of the wave plate 115, and is stable at a high average power.

  Therefore, in this embodiment, by obtaining the phase shift based on the FPN in the wave plate 115 as described below, it is possible to obtain an image from which the FPN has been removed regardless of the mode of the image or noise.

[FPN removal process]
FIG. 7 shows an example of a specific FPN removal process in the fundus imaging apparatus 1 according to this embodiment. This operation example is processing executed by the image forming unit 220 after the interference light spectrum is obtained by the OCT measurement in step S6 and before the tomographic image is formed. In the process shown in FIG. 7, the phase shift of the wave plate 115 is obtained for each A line, the process of correcting the phase of the spectrum of the interference light based on the obtained phase shift, and one reference spectrum in one tomographic image. The calculation process and the process of removing the FPN for each A line are included.

(S11: Acquire spectrum of tomographic image)
In the OCT measurement in step S6 of FIG. 5, the spectrum of the interference light obtained by detecting the interference light at each irradiation position on the fundus oculi Ef is stored in the storage unit 212, for example. Here, it is assumed that one tomographic image (B scan image) is composed of 1024 lines of A scan images. When a spectrum of 1024 lines corresponding to one tomographic image is obtained, the image forming unit 220 acquires the spectrum of the interference light of the one tomographic image by loading them into an internal storage unit (not shown). The image forming unit 220 performs processing on the spectrum loaded in the storage unit.

(S12: Correct the phase of the interference light spectrum)
The image forming unit 220 obtains the phase shift of the wave plate 115 for each A line in the phase correction unit 221 and corrects the phase of the interference light spectrum of the A line in a direction in which the obtained phase shift becomes zero. . At this time, for each A line, the phase correction unit 221 obtains the phase shift of the wave plate 115 based on the correlation value between the reference spectrum having a reference phase and the spectrum of the interference light of the A line. The reference spectrum can be a spectrum of interference light in any one of a plurality of A lines obtained by scanning the irradiation position of the signal light LS on the eye to be examined. Specific processing contents of step S12 will be described later.

(S13: Calculate reference spectrum)
The image forming unit 220 calculates a reference spectrum in the reference spectrum calculation unit 223. As described above, the reference spectrum calculation unit 223 calculates a reference spectrum based on a plurality of A-line interference light spectra at a plurality of irradiation positions of the signal light LC with respect to the eye E. In this embodiment, the reference spectrum calculation unit 223 obtains a representative value of a plurality of interference light spectra as a reference spectrum. Here, the reference spectrum calculation unit 223 obtains a median value of a plurality of interference light spectra as a representative value. As a specific example, the reference spectrum calculation unit 223 includes a plurality of real parts obtained by performing FFT processing (Fourier transform processing in a broad sense; the same applies hereinafter) on a plurality of interference light spectra of A lines. Each of the plurality of imaginary parts is sorted in ascending or descending order, and the real part is obtained by performing inverse Fourier transform on the real part and imaginary part that are the median value. This real part is used as a reference spectrum. Details of the processing in step S13 will be described later. Subsequent steps S14 to S19 are executed for each A line.

(S14: FPN removed)
The image forming unit 220 removes the FPN by subtracting the reference spectrum calculated in step S13 from the interference light spectrum of the A line phase-corrected in step S12 for each A line in the spectrum calculation unit 222. .

(S15: Apodization process)
The image forming unit 220 performs an apodization process on the spectrum obtained in step S14 in an apodization processing unit (not shown). The apodization process is a process of increasing the dynamic range by reducing the amplitude of the side lobe while suppressing the decrease in the amplitude of the main lobe to some extent by multiplying the spectrum obtained in step S14 by the apodization function. As the apodization function, there are known window functions such as a Hanning window, a Gauss window, and a rectangular window.

(S16: Dispersion compensation)
The image forming unit 220 numerically compensates for variations in dispersion characteristics and the like in a dispersion compensation unit (not shown). As a specific example, the dispersion compensation unit obtains the spectrum S ₁ (ζ) after dispersion compensation for the spectrum S ₀ (ζ) of the interference light of the A line after the apodization processing according to the following equation (1). .

In equation (1), the coefficient a ₂ is a coefficient of a predetermined quadratic function f ₂ (ζ), and the coefficient a ₃ is a coefficient of a predetermined cubic function f ₃ (ζ). The coefficients a ₂ and a ₃ can be changed afterwards. Note that ζ is the index described with reference to FIG. Expression (1) is an expression for compensating for dispersion by multiplying the phase term of the spectrum S ₀ (ζ) by (a ₂ · f ₂ (ζ) + a ₃ · f ₃ (ζ)).

(S17: FFT processing, S18: Calculation of amplitude component)
The image forming unit 220 performs a known FFT on the spectrum S ₁ (ζ) after dispersion compensation. Thereafter, the image forming unit 220 uses the real part Re and the imaginary part Im obtained by the FFT processing to obtain the amplitude component Ap according to the following equation (2) for the value of each index ζ. In equation (2), ζ is an index. Thereby, an amplitude component is obtained for each pixel of the A line.

(S19: Next A line?)
When the processing for the number of A lines (1024 lines) constituting the B-scan image loaded in step S11 is completed (step S19: NO), the image forming unit 220 ends a series of processing (end). On the other hand, when the processing for the number of A lines constituting the B-scan image loaded in step S11 has not been completed (step S19: YES), the image forming unit 220 returns to step S14 and performs the next A line. Repeat the same process.

When the amplitude components of all the pixels constituting one tomographic image are obtained, the image forming unit 220 performs logarithmic conversion on the amplitude component Am, for example, by 20 × log ₁₀ (Am + 1). Thereafter, the image processing unit 220 determines a reference noise level in one tomographic image, and with respect to each pixel within a predetermined luminance value range according to the amplitude component logarithmically converted as described above with reference to the reference noise level. Assign one of the values. The image forming unit 220 forms an image using the assigned luminance value of each pixel.

[Phase correction of interference light spectrum]
FIG. 8 shows a flowchart of a specific processing example of step S12 of FIG. The process of step S12 includes a process of performing FFT on the reference spectrum, a process of performing FFT on the interference light spectrum of each A line, and a correlation value between the reference spectrum and the interference light spectrum of each A line. A process for calculating, a process for calculating a phase shift corresponding to the pixel level, and a process for correcting the phase of the spectrum of the interference light based on the calculated phase shift.

(S21: FFT processing for reference spectrum)
The phase correction unit 221 performs FFT on the reference spectrum. This FFT processing is performed with a data size (for example, “1376”) corresponding to the range of index ζ (for example, 0 to 1375). The reference spectrum is one of a plurality of A-line interference light spectra at a plurality of irradiation positions scanned by the galvano scanner 42, for example, the A-line interference at the first irradiation position scanned by the galvano scanner 42. It can be the spectrum of light.

(S22: Save real part and imaginary part)
The phase correction unit 221 uses the real part Re (R) [0] to Re (R) [1375] and the imaginary part Im (R) [0] to Im (R) [1375] obtained by the FFT process in step S22. ] Is stored in a storage unit (not shown). In step S23 and subsequent steps, processing is executed for each A line.

(S23: FFT processing for target spectrum)
The phase correction unit 221 performs FFT on the spectrum (target spectrum) of the interference light of the A line. This FFT processing is performed with a data size (for example, “1376”) corresponding to the range of the index ζ.

(S24: Calculate correlation value)
The phase correction unit 221 calculates a correlation value between the reference spectrum and the interference light spectrum (target spectrum) of the A line for each of the real part and the imaginary part. As a specific example, the phase correction unit 221 obtains the correlation value ReX of the real part and the correlation value ImX of the imaginary part according to the following equation (3). In Equation (3), Re (R) [ζ] represents the real part of the reference spectrum, Im (R) [ζ] represents the imaginary part of the target spectrum, and Re (T) [ζ] is Represents the real part of the target spectrum, and Im (T) [ζ] represents the imaginary part of the target spectrum.

(S25: Calculate the phase shift by the wave plate)
The phase correction unit 221 calculates the phase shift caused by the wave plate 115 based on the correlation value calculated in step S24. Here, an index ζ = 566 corresponding to the front surface of the wave plate 115 is set, and an index ζ = 577 corresponding to the rear surface of the wave plate 115 is set. By analyzing a profile as shown in FIG. 6, it is possible to obtain in advance indexes corresponding to the front and rear surfaces of the wave plate 115. The phase shift φ [rad] due to the front surface (index ζ = 566) of the wave plate 115 is obtained according to the following equation (4).

(S26: Pixel level phase shift is calculated)
The phase correction unit 221 calculates a phase shift corresponding to the pixel level from the subpixel level phase shift calculated in step S25. Specific processing contents of step S26 will be described later.

(S27: Inverse FFT processing by multiplying conjugate phase)
The phase correction unit 221 corrects the phase of the interference light spectrum of the A line so that the phase shift corresponding to the pixel level calculated in step S26 becomes zero. As a specific example, the phase correction unit 221 multiplies the phase shift corresponding to the pixel level calculated in step S26 by a conjugate phase corresponding thereto and performs inverse FFT on the spectrum of the interference light of the A line. .

  For example, as will be described later, the phase correction unit 221 divides the phase shift at the pixel level by the index ζ = 566 corresponding to the wave plate 115 to obtain the phase shift φ1 corresponding to one wave number. The phase correction unit 221 uses the phase correction amount φ2 (ζ) = φ1 × ζ and multiplies the conjugate phase according to the following equation.

  Subsequently, the phase correction unit 221 performs inverse FFT on the real part Re1 (ζ) and the imaginary part Im1 (ζ) obtained by Expression (5).

(S28: Output the real part)
The phase correction unit 221 outputs the real part Re1 (ζ) of the real part Re1 (ζ) and the imaginary part Im1 (ζ) obtained by the inverse FFT process in step S27 as a phase-corrected spectrum.

(S29: Next A line?)
When the processing for the number of A lines (1024 lines) constituting one tomographic image is completed (step S29: NO), the phase correction unit 221 ends a series of processing (end). On the other hand, when the processing for the number of A lines constituting one tomographic image has not been completed (step S29: YES), the phase correction unit 221 returns to step S23 and repeats the same processing for the next A line. .

[Calculation of phase shift equivalent to pixel level]
In step S26 in FIG. 8, when the number of pixels to be shifted within a pixel shift range set in advance is p, the phase shift φ is expressed as in Expression (6).

  The phase correction unit 221 calculates a phase shift corresponding to the pixel level within the pixel shift range by dividing the case into a range in consideration of the error d (for example, 0.5). Here, it is assumed that the number of pixels p in the pixel shift range is -1, 0, 1, or 2.

On the front surface of the wave plate 115 (index ζ = 566), from equation (6), when p = −1, 0, 1, 2, the pixel level phase shifts φ _{−1 to} φ ₂ [rad] are as follows: become.
p = −1: φ ₋₁ = 2π × (−1) /1376×566=−2.5845808 [rad]
p = 0: φ ₀ = 2π × 0/1376 × 566 = 0 [rad]
p = 1: φ ₁ = 2π × 1/1376 × 566 = 2.584508 [rad]
p = 2: φ ₂ = 2π × 2/1376 × 566-2π = −1.114169 [rad]

  The phase correction unit 221 calculates a phase shift corresponding to the pixel level as follows for the phase shift φ obtained in step S25.

  FIG. 9 illustrates an example of a phase shift calculation process corresponding to the pixel level by the phase correction unit 221.

(S31: φ> φ ₀ −d and φ <φ ₀ + d?)
When φ> (φ ₀ −d) and φ <(φ ₀ + d) with respect to the phase shift φ at the sub-pixel level obtained in step S25 (step S31: YES), the phase correction unit 221 performs step S32. Migrate to When φ> (φ ₀ −d) and φ <(φ ₀ + d) are not satisfied (step S31: NO), the phase correction unit 221 proceeds to step S33.

_{(S32: φ1 = φ 0/} 566)
The phase correction unit 221 calculates a pixel level phase shift φ1 corresponding to the number of pixels p = 0. Here, the phase correcting unit 221 obtains a _{(φ 0 / ζ) = (} φ 0/566) the phase shift φ1 pixel-level per wave number by determining the.

(S33: φ> φ ₁ −d and φ <φ ₁ + d?)
When φ> (φ ₁ −d) and φ <(φ ₁ + d) are satisfied with respect to the sub-pixel level phase shift φ obtained in step S25 (step S33: YES), the phase correction unit 221 performs step S34. Migrate to When φ> (φ ₁ −d) and φ <(φ ₁ + d) are not satisfied (step S33: NO), the phase correction unit 221 proceeds to step S35.

_{(S34: φ1 = φ 1/} 566)
The phase correction unit 221 calculates a pixel level phase shift φ1 corresponding to the number of pixels p = 1. Here, the phase correcting unit 221 obtains a _{(φ 1 / ζ) = (} φ 1/566) the phase shift φ1 pixel-level per wave number by determining the.

(S35: φ> φ ₂ −d and φ <φ ₂ + d?)
When φ> (φ ₂ −d) and φ <(φ ₂ + d) are satisfied for the sub-pixel level phase shift φ obtained in step S25 (step S35: YES), the phase correction unit 221 performs step S36. Migrate to When φ> (φ ₂ −d) and φ <(φ ₂ + d) are not satisfied (step S35: NO), the phase correction unit 221 proceeds to step S37.

_{(S36: φ1 = φ 2/} 566)
The phase correction unit 221 obtains a pixel level phase shift φ1 corresponding to the number of pixels p = 2. Here, the phase correcting unit 221 obtains the _{(φ 2 / ζ) = (} φ 2/566) the phase shift φ1 pixel-level per wave number by determining the.

(S37: φ> φ ₋₁ -d and φ <φ ₋₁ + d?)
When φ> (φ ₋₁ −d) and φ <(φ ₋₁ + d) for the phase shift φ at the sub-pixel level obtained in step S25 (step S37: YES), the phase correction unit 221 Control goes to step S38. When φ> (φ ₋₁ −d) and φ <(φ ₋₁ + d) are not satisfied (step S37: NO), the phase correction unit 221 proceeds to step S39.

(S38: φ1 = φ ₋₁ / 566)
The phase correction unit 221 calculates a pixel level phase shift φ1 corresponding to the number of pixels p = −1. Here, the phase correction unit 221 obtains a pixel level phase shift φ1 per wave number by obtaining (φ ₋₁ / ζ) = (φ ₋₁ / 566).

(S39: φ1 = 0)
The phase correction unit 221 sets 0 as the phase shift φ1 of the pixel level per wave number. Step S39 is a process executed when a phase shift within a pixel shift range set in advance cannot be calculated, and a value other than 0 may be set as the phase shift φ1.

  Subsequent to steps S32, S34, S36, S38, and S39, the phase correction unit 221 ends a series of operations (end).

[Reference spectrum calculation process]
FIG. 10 shows a flowchart of a specific processing example of step S13 in FIG. The process in step S13 includes an FFT process for the interference light spectrum of each A line, a process for calculating the median of the FFT process result, and a process for obtaining a reference spectrum.

(S41: i = 0)
The reference spectrum calculation unit 223 initializes a variable i for specifying one of the plurality of A lines. Here, 0 is set as the initial value of the variable i.

(S42: FFT processing for spectrum of interference light of i-th A line)
The reference spectrum calculation unit 223 performs an FFT process (data size = 1376) on the interference light spectrum of the i-th A-line.

(S43: next A line ?, S44: i is incremented)
When the processing for the number of A lines (1024 lines) constituting one tomographic image is completed (step S43: YES), the reference spectrum calculation unit 223 increments the variable i (step S44), and proceeds to step S42. . On the other hand, when the processing for the number of A lines constituting one tomographic image has not been completed (step S43: NO), the reference spectrum calculation unit 223 proceeds to step S45.

(S45: Calculate the median of the real part)
The reference spectrum calculation unit 223 calculates the median value of the plurality of real parts obtained by the FFT process in step S42. As a specific example, the reference spectrum calculation unit 223 sorts a plurality of real parts in ascending or descending order, and calculates the median value. When the number of A lines constituting one tomographic image is 2n (n is a natural number; the same applies hereinafter), the reference spectrum calculation unit 223 performs the nth real part and (n + 1) th real number obtained by sorting. The average value with the part can be calculated as the median value. When the number of A lines is (2n + 1), the reference spectrum calculation unit 223 can calculate the (n + 1) th real part obtained by sorting as the median value.

(S46: Calculate the median of the imaginary part)
The reference spectrum calculation unit 223 calculates the median value of the plurality of imaginary parts obtained by the FFT process in step S42. As a specific example, the reference spectrum calculation unit 223 sorts a plurality of imaginary parts in ascending order or descending order, and calculates the median value. When the number of A lines constituting one tomographic image is 2n, the reference spectrum calculation unit 223 calculates an average value of the nth imaginary part and the (n + 1) th imaginary part obtained by sorting as a median value. can do. When the number of A lines is (2n + 1), the reference spectrum calculation unit 223 can calculate the (n + 1) th imaginary part obtained by sorting as the median.

(S47: Inverse FFT processing for the calculated real part and imaginary part)
The reference spectrum calculation unit 223 performs inverse FFT on the median value of the real part calculated in step S45 and the median value of the imaginary part calculated in step S46.

(S48: Output the real part)
The reference spectrum calculation unit 223 outputs the real part as a reference spectrum among the real part and the imaginary part obtained by the inverse FFT process in step S47. This is the end of this operation example (end).

[Example of processing results]
11 and 12 show an example of the calculation result of the phase shift near the index corresponding to the FPN factor. FIG. 11 shows an example of the calculation result of the phase shift near the index (= 566) corresponding to the wave plate 115. FIG. 12 shows an example of the calculation result of the phase shift near the index (= 110) corresponding to the light source or the electrical system. In FIGS. 11 and 12, the horizontal axis represents the index, and the vertical axis represents the phase shift φ [rad] corresponding to the sub-pixel level, and represents the phase shift for each A line.

  As shown in FIG. 11, in the vicinity of the index corresponding to the front surface of the wave plate 115, the phase shift is stable, and the number of pixels to be shifted can be assigned to -1, 0, 1 or 2. is there. On the other hand, as shown in FIG. 12, in the vicinity of the index corresponding to the light source or the electrical system, the phase shift is unstable, and it is possible to assign the number of pixels to be shifted to -1, 0, 1, or 2. Impossible. Therefore, by correcting the phase of the spectrum of the interference light based on the stable phase shift on the front surface of the wave plate 115, it becomes possible to remove the FPN, which has been difficult to remove completely, with high accuracy. .

  FIG. 13 shows an example of a tomographic image acquired by the fundus imaging apparatus 1 according to this embodiment. FIG. 13 is a tomographic image (B-scan image) of the fundus, where the vertical direction represents the depth direction (z direction) and the horizontal direction represents the scanning direction (predetermined direction on the xy plane).

  The tomographic image IMG1 shown in FIG. 13 is acquired by arranging the A scan images at the respective irradiation positions in the scanning direction. The A-scan image is obtained using the spectrum of interference light that has been phase-corrected based on the phase shift caused by the front surface of the wave plate 115 as described above. According to this embodiment, it is possible to stably acquire a tomographic image of the fundus oculi Ef from which the FPN that has appeared in FIG. 16 has been removed.

  In this embodiment, the case where the wave plate 115 as the optical member is arranged in the optical path of the reference light LR has been described, but the wave plate 115 may be arranged in the optical path of the signal light LS. For example, the wave plate 115 is disposed in the optical path of the signal light LS between the fiber couplers 105 and 122 in FIG.

[effect]
The fundus imaging apparatus 1 is an example of a fundus imaging apparatus to which the optical image measurement device according to the embodiment is applied. Hereinafter, effects of the optical image measurement device according to the embodiment will be described.

  The optical image measurement device according to the embodiment includes an interference optical system (for example, fiber couplers 105 and 122, a detector 125, and an optical fiber and various optical elements that guide the reference light LR and the signal light LS therebetween), and image formation. Means (for example, image forming unit 220). The interference optical system has an optical member (for example, a wave plate 115).

  The interference optical system divides light from a wavelength scanning light source (for example, a wavelength scanning light source included in the light source unit 101) into signal light (for example, signal light LS) and reference light (for example, reference light LR) to be measured. Interference light (for example, interference light LC) between the signal light and the reference light that passes through the object (for example, eye E) is detected. The optical member is disposed in the optical path of the signal light or the optical path of the reference light. The image forming unit forms an image of the object to be measured based on the interference light detected by the interference optical system. The image forming means obtains a phase shift by the optical member, corrects the phase of the interference light spectrum based on the obtained phase shift, and forms an image based on the corrected interference light spectrum.

  In SS-OCT, it is known that FPN appears in acquired images due to wavelength scanning light sources, electrical jitter, multiple reflections of various optical elements, and the like. In this embodiment, paying attention to the fact that the phase is stable in the optical member arranged in the optical path of the signal light and the reference light, the image forming unit obtains the phase shift by the optical member, and the calculated phase shift is obtained. An image of the object to be measured is formed based on the spectrum of the interference light corrected based on it. This makes it possible to stably correct the phase shift of the spectrum of the interference light that has caused the FPN regardless of the light source, the electrical system, the image, and the noise, and the image acquired in SS-OCT can be corrected. It becomes possible to remove the appearing FPN. Further, since it is not necessary to remove the FPN by image processing, it is possible to contribute to the reduction of processing load and the acquisition of an image from which the FPN has been removed in real time.

  In the optical image measurement device according to the embodiment, the image forming unit may correct the phase of the spectrum of the interference light at the pixel level based on the phase shift.

  One of the causes of FPN is a phase shift between the operation clock of the means for capturing the detection signal of the interference light and the wavelength scanning timing in the wavelength scanning light source. This phase shift shifts the capture timing of the interference light detection signal at the pixel level. Therefore, it is possible to remove the FPN based on the above factors by correcting the phase of the interference light spectrum at the pixel level. In addition, it is possible to avoid a situation in which the FPN cannot be removed by correcting the phase of the spectrum of the interference light at the subpixel level and the image quality is deteriorated.

  In the optical image measurement device according to the embodiment, the image forming unit converts the phase shift into a phase shift corresponding to the pixel level, and corrects the phase of the spectrum of the interference light based on the phase shift corresponding to the converted pixel level. You may make it do.

  According to such an optical image measurement device, after correcting the phase of the spectrum of the interference light based on the phase shift at the sub-pixel level, compared with the case where this phase correction is converted to the pixel level, a highly accurate phase is obtained. The correction process can be simplified.

  The optical image measurement device according to the embodiment may include a scanning unit, and the image forming unit may include a phase correction unit and a spectrum calculation unit.

  The scanning means scans the irradiation position of the signal light on the object to be measured. The phase correction unit obtains a phase shift by the optical member for the A line at each irradiation position, and corrects the phase of the spectrum of the interference light based on the obtained phase shift. The spectrum calculation means subtracts a reference spectrum calculated in advance from the interference light spectrum corrected by the phase correction means for each A line. The image forming means forms an image of the object to be measured based on the spectrum obtained by the spectrum calculating means.

  According to such an optical image measurement device, the FPN is removed by subtracting the reference spectrum from the spectrum of the interference light whose phase is corrected based on the phase shift by the optical member for each A line. It is possible to provide an optical image measurement device capable of removing FPN by a simple spectrum calculation process without significantly adding wear.

  In the optical image measurement device according to the embodiment, the image forming unit may include a reference spectrum calculating unit. The reference spectrum calculation means calculates a reference spectrum based on the spectra of the plurality of interference lights at the plurality of irradiation positions scanned by the scanning means.

  According to such an optical image measurement device, since the reference spectrum is calculated from the spectrum of the interference light, it is not necessary to separately acquire a background spectrum. The background spectrum can be acquired by switching the optical system to a predetermined path, but it may be affected by the path and measurement environment, and the image quality may be degraded when the background spectrum is used as a reference. . According to this embodiment, it is possible to remove the FPN without being affected by the above.

  In the optical image measurement device according to the embodiment, the reference spectrum calculation unit may calculate a representative value of a plurality of interference light spectra and obtain the representative value as a reference spectrum. The reference spectrum calculation means may calculate a median value of a plurality of interference light spectra as a representative value.

  According to such an optical image measurement device, it is possible to calculate a reference spectrum by a simple process without separately acquiring a background spectrum.

  In the optical image measurement device according to the embodiment, the reference spectrum calculation unit performs each of a plurality of real parts and a plurality of imaginary parts obtained in an ascending or descending order by performing Fourier transform processing on the spectra of the plurality of interference lights. You may make it obtain | require as a reference spectrum the real part obtained by sorting and performing an inverse Fourier transform with respect to the real part and imaginary part which become a median value.

  According to such an optical image measurement device, the reference spectrum can be calculated without being affected by the intensity or phase bias of the plurality of interference light spectra. For example, when obtaining the average of the interference spectrum as the reference spectrum Compared to the above, FPN can be removed with higher accuracy.

  In the optical image measurement device according to the embodiment, the image forming unit may obtain the phase shift by the optical member based on the correlation value between the reference spectrum and the interference light spectrum.

  According to such an optical image measurement device, it is possible to provide an optical image measurement device capable of calculating a stable phase shift in an optical member by arithmetic processing and stably removing FPN.

  In the optical image measurement device according to the embodiment, the reference spectrum may be the interference light spectrum of any one of a plurality of A lines obtained by scanning the irradiation position of the signal light with respect to the object to be measured. Good.

  According to such an optical image measurement device, it is possible to provide an optical image measurement device capable of removing FPN by a simple calculation process without taking in a background spectrum.

  In the optical image measurement device according to the embodiment, the reference spectrum may be a spectrum of the first A-line interference light scanned with respect to the object to be measured.

  According to such an optical image measurement device, it is possible to simplify the arithmetic processing for obtaining the reference spectrum.

  In the optical image measurement device according to the embodiment, the optical member may be a polarizer.

  According to such an optical image measurement device, it is possible to detect a stable phase shift and perform highly accurate FPN removal without affecting the acquired image.

  In the optical image measurement device according to the embodiment, the measured object may be a living eye.

  According to such an optical image measurement device, a tomographic image of the fundus from which the FPN has been removed can be acquired.

[Modification]
A modification of the above embodiment will be described. The following modifications can be combined with any configuration described in the above embodiment.

(First modification)
In the above embodiment, the case where one wavelength plate 115 is arranged in the optical path of the reference light has been described. However, a plurality of wavelength plates may be arranged in the optical path of the signal light or the optical path of the reference light. That is, a plurality of optical members may be arranged in the optical path of the signal light or the optical path of the reference light in the interference optical system. Hereinafter, the fundus imaging apparatus to which the optical image measurement apparatus according to the first modification is applied will be described focusing on differences from the above-described embodiment.

  FIG. 14 illustrates an example of the configuration of the OCT unit according to the first modification. 14, parts similar to those in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  The configuration of the OCT unit 100a according to the first modification is different from the configuration of the OCT unit 100 shown in FIG. 2 in that wavelength plates 115a and 115b are added instead of the wavelength plate 115. The wave plate 115 a is disposed at the same position as the wave plate 115. The wave plate 115 b is disposed between the collimator 111 and the optical path length correction member 112. The image forming unit 220 calculates a phase shift due to any one of the wave plates 115a and 115b, and corrects the phase of the spectrum of the interference light based on the calculated phase shift to form an image of the eye E. For example, of the wave plates 115a and 115b, the wave plate having the smaller number of multiple reflections can be a wave plate suitable for removing FPN. In this case, the phase shift by the wave plate having the smaller number of multiple reflections is obtained, and based on this, the phase of the spectrum of the interference light is corrected. For example, the wavelength plate with the smaller number of multiple reflections (the wave plate with the least number of multiple reflections) of the wave plates 115a and 115b is identified, for example, the wave plate with the higher noise intensity (the highest noise intensity) It is considered possible by specifying the wave plate. Since other configurations and operations are the same as those in the above embodiment, the description thereof is omitted.

[effect]
The optical image measurement device according to this modification has the following effects in addition to the effects of the above embodiment.

  In the optical image measurement device according to this modification, the interference optical system may be configured to include a plurality of optical members arranged in the optical path of the signal light or the optical path of the reference light. The image forming unit obtains a phase shift caused by any one of the plurality of optical members.

  According to such an optical image measurement device, the phase shift suitable for the removal of FPN is obtained by obtaining the phase shift of any one of a plurality of optical members arranged in the optical path of the signal light or the optical path of the reference light. By correcting the phase of the spectrum of the interference light, an image from which the FPN has been removed can be formed. Note that the phase of the spectrum of the interference light may be corrected based on the phase shift caused by each of the plurality of optical members arranged in the optical path of the signal light or the optical path of the reference light.

(Second modification)
In the above embodiment, the optical distance of the light passing through the optical member (wavelength plate 115) may be changed. Such an optical member includes, for example, a plurality of optical elements having different optical distances of light passing through the member, and is arbitrarily selected and disposed in the optical path of the signal light or the optical path of the reference light. To do. By changing the optical distance of the light passing through the inside of the optical member, for example, the index in the profile shown in FIG. 6 can be changed. An example of a method for changing the optical distance of light passing through the optical member is a method of changing the distance between the incident surface and the exit surface of the optical member.

[effect]
The optical image measurement device according to this modification has the following effects in addition to the effects of the above embodiment.

  In the optical image measurement device according to this modified example, at least one of the optical member (for example, the wave plate 115) or the plurality of optical members (for example, the wave plates 115a and 115b) changes the optical distance of the light passing through the member. It may be configured to be possible.

  According to such an optical image measurement device, even when aging of various members constituting the optical system or a change in measurement environment occurs, the phase shift of the optical member can be obtained with high accuracy, and the obtained phase It becomes possible to remove the FPN based on the deviation.

  In the optical image measurement device according to this modification, the optical member includes a plurality of optical elements having different optical distances of light passing through the member, and the plurality of optical elements are in the optical path of the signal light or the optical path of the reference light. It may be selectively arranged.

  According to such an optical image measurement device, the thickness of the optical member can be changed without significantly changing the hardware.

(Third Modification)
In the above embodiment, the FPN may be removed only when a stable phase shift can be obtained in the wave plate 115. Hereinafter, the fundus imaging apparatus to which the optical image measurement device according to the third modification is applied will be described focusing on differences from the above-described embodiment.

  FIG. 15 is a block diagram illustrating a configuration example of an image forming unit according to a third modification. FIG. 15 also shows a control unit according to a third modification, and the same parts as those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  The image forming unit 220b includes a phase correction unit 221, a spectrum calculation unit 222, a reference spectrum calculation unit 223, and an intensity detection unit 224b. The image forming unit 220b is different from the image forming unit 220 shown in FIG. 4 in that an intensity detecting unit 224b is added. The intensity detector 224b detects the intensity of the noise component (spectrum) in the wave plate 115 as an optical member. The detection result obtained by the intensity detector 224b is sent to the controller 210b. Based on the detection result obtained by the intensity detection unit 224b, the control unit 210b uses the interference light spectrum phase-corrected as in the above-described embodiment when the detected intensity is equal to or greater than the threshold value. Form an image.

  The threshold value can be changed afterwards. The higher the threshold value, the more stable the phase shift caused by the wave plate 115 can be obtained, and therefore the FPN removal based on the obtained phase shift can be performed stably. However, when the intensity of the noise component in the wave plate 115 is less than the threshold value, a case where the FPN cannot be removed occurs. On the other hand, as the threshold value is lower, it is possible to obtain a phase shift by the wave plate 115 even for a noise component having a low intensity. However, the obtained phase shift becomes unstable, and the FPN can be stably removed. There is a case that cannot be done. It is desirable that the threshold value be changed afterwards to a value suitable for FPN removal in consideration of the measurement environment and the like.

  The image forming unit 220b is provided in place of the image forming unit 220 in FIG. The control unit 210b is provided in place of the control unit 210 in FIG. Since other configurations and operations are the same as those in the above embodiment, the description thereof is omitted. The intensity detector 224b is an example of the “intensity detector” in this modification.

[effect]
The optical image measurement device according to this modification has the following effects in addition to the effects of the above embodiment.

  The optical image measurement device according to this modification is configured to include intensity detection means (for example, intensity detection unit 224b). The intensity detecting means detects the intensity of the noise component in the optical member (for example, the wave plate 115). The image forming unit (for example, the image forming unit 220b) forms an image of the object to be measured by using the phase-corrected spectrum of the interference light when the intensity detected by the intensity detecting unit is equal to or greater than the threshold value.

  It is desirable that the phase shift due to the optical member is stable, and the greater the intensity of the noise component, the easier it is to detect. By using such a phase shift of the optical member, it is possible to stably remove the FPN. According to such an optical image measurement device, it is determined that the phase shift due to the optical member is unstable when the intensity is less than the threshold, and the situation in which the image quality of the acquired image is deteriorated by performing the phase correction is avoided. can do.

(Other variations)
The configuration described above is merely an example for favorably implementing the present invention. Therefore, arbitrary modifications (omitted, replacement, addition, etc.) within the scope of the present invention can be made as appropriate.

  In the above embodiment or its modification, the case where the wave plate 115 (wave plate 115a, 115b) as an optical member is arranged in the optical path of the signal light or the optical path of the reference light has been described. The optical member may also be used as the existing optical member shown in FIG. 2 (excluding the wave plate 115, for example, the optical path length correcting member 112, the dispersion compensating member 113, and other optical members). That is, any one of the optical members shown in FIG. 2 excluding the wave plate 115 may act as an optical member for obtaining a phase shift in the above-described embodiment or its modification.

  In the above embodiment, the optical path length difference between the optical path of the signal light LS and the optical path of the reference light LR is changed by changing the position of the optical path length changing unit 41, but this optical path length difference is changed. The method is not limited to this. For example, it is possible to change the optical path length difference by disposing a reflection mirror (reference mirror) in the optical path of the reference light and moving the reference mirror in the traveling direction of the reference light to change the optical path length of the reference light. Is possible. Further, the optical path length difference may be changed by moving the fundus camera unit 2 or the OCT units 100 and 100a with respect to the eye E to change the optical path length of the signal light LS. In particular, when the measured object is not a living body part, the optical path length difference can be changed by moving the measured object in the depth direction (z direction).

  A computer program for realizing the above-described embodiment or its modification can be stored in any recording medium readable by a computer. Examples of the recording medium include a semiconductor memory, an optical disk, a magneto-optical disk (CD-ROM / DVD-RAM / DVD-ROM / MO, etc.), a magnetic storage medium (hard disk / floppy (registered trademark) disk / ZIP, etc.), and the like. Can be used.

  It is also possible to transmit / receive this program through a network such as the Internet or a LAN.

DESCRIPTION OF SYMBOLS 1 Fundus imaging apparatus 2 Fundus camera unit 10 Illumination optical system 30 Imaging optical system 31 Focusing lens 31A Focusing drive unit 41 Optical path length changing unit 42 Galvano scanner 50 Alignment optical system 60 Focus optical system 100, 100a OCT unit 101 Light source unit 105 122 Fiber coupler 114 Corner cube 114A Reference drive unit 115, 115a, 115b Wave plate 125 Detector 200 Operation control unit 210, 210b Control unit 211 Main control unit 212 Storage unit 220, 220b Image forming unit 221 Phase correction unit 222 Spectral calculation Unit 223 reference spectrum calculation unit 224b intensity detection unit 230 image processing unit 240A display unit 240B operation unit E eye Ef fundus LS signal light LR reference light LC interference light

Claims (17)

An interference optical system that divides light from a wavelength scanning light source into signal light and reference light, and detects interference light between the signal light and the reference light that has passed through the object to be measured;
Image forming means for forming an image of the object to be measured based on the interference light detected by the interference optical system,
The interference optical system is
An optical member disposed in the optical path of the signal light or the optical path of the reference light,
The image forming unit includes:
Obtaining a phase shift by the optical member, correcting a phase of the spectrum of the interference light based on the determined phase shift, and forming the image based on the corrected spectrum of the interference light;
An optical image measuring device characterized by that. The image forming unit includes:
The optical image measurement apparatus according to claim 1, wherein the phase of the spectrum of the interference light is corrected at a pixel level based on the phase shift. The image forming unit includes:
The phase shift of the interference light is corrected based on the phase shift corresponding to the converted pixel level and the phase shift corresponding to the pixel level. Optical image measurement device. Scanning means for scanning the irradiation position of the signal light on the object to be measured;
The image forming unit includes:
Phase correction means for obtaining a phase shift in the optical member for the A line at each irradiation position, and correcting the phase of the spectrum of the interference light based on the obtained phase shift;
Spectrum calculation means for subtracting a reference spectrum calculated in advance from the spectrum of the interference light corrected by the phase correction means for each A line,
Forming the image based on the spectrum obtained by the spectrum calculating means;
The optical image measurement device according to any one of claims 1 to 3, wherein The image forming unit includes:
5. The optical image measurement device according to claim 4, further comprising reference spectrum calculation means for calculating the reference spectrum based on a plurality of spectra of the interference light at a plurality of irradiation positions scanned by the scanning means.   The optical image measurement apparatus according to claim 5, wherein the reference spectrum calculation unit calculates a representative value of the spectrum of the plurality of interference lights, and obtains the representative value as the reference spectrum.   The optical image measurement device according to claim 6, wherein the representative value is a median value of a spectrum of the plurality of interference lights.   The reference spectrum calculation means sorts each of a plurality of real parts and a plurality of imaginary parts obtained by performing Fourier transform on the spectra of the plurality of interference lights, in ascending or descending order, and becomes a median value real part The optical image measurement apparatus according to claim 7, wherein a real part obtained by performing inverse Fourier transform on the imaginary part is obtained as the reference spectrum. The image forming unit includes:
9. The light according to claim 1, wherein a phase shift in the optical member is obtained based on a correlation value between a reference spectrum having a reference phase and the spectrum of the interference light. Image measuring device.   The reference spectrum is a spectrum of interference light in any one of a plurality of A lines obtained by scanning an irradiation position of the signal light with respect to the object to be measured. The optical image measuring device described in 1.   The optical image measurement device according to claim 9, wherein the reference spectrum is a spectrum of the first A-line interference light scanned with respect to the object to be measured.   The optical image measurement device according to claim 1, wherein the optical member is a polarizer.   The optical image measuring device according to any one of claims 1 to 12, wherein the optical member is configured to be capable of changing an optical distance of light passing through the member. The optical member includes a plurality of optical elements having different optical distances,
The optical image measurement device according to claim 13, wherein the plurality of optical elements are selectively arranged in an optical path of the signal light or an optical path of the reference light. The interference optical system includes a plurality of optical members arranged in the optical path of the signal light or the optical path of the reference light,
The image forming unit obtains a phase shift in any one of the plurality of optical members;
The optical image measurement device according to claim 1, wherein the optical image measurement device is an optical image measurement device. Including intensity detecting means for detecting the intensity of a noise component by the optical member;
The image forming unit forms the image using the corrected spectrum of the interference light when the intensity detected by the intensity detection unit is equal to or greater than a threshold;
The optical image measurement device according to any one of claims 1 to 15, wherein the optical image measurement device is an optical image measurement device.   The optical image measuring device according to claim 1, wherein the object to be measured is a living eye.

Images