WO2018079326A1 - 光干渉断層画像撮像装置および計測方法 - Google Patents
光干渉断層画像撮像装置および計測方法 Download PDFInfo
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- WO2018079326A1 WO2018079326A1 PCT/JP2017/037415 JP2017037415W WO2018079326A1 WO 2018079326 A1 WO2018079326 A1 WO 2018079326A1 JP 2017037415 W JP2017037415 W JP 2017037415W WO 2018079326 A1 WO2018079326 A1 WO 2018079326A1
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
- A61B5/0062—Arrangements for scanning
- A61B5/0066—Optical coherence imaging
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/0059—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence
- A61B5/0073—Measuring for diagnostic purposes; Identification of persons using light, e.g. diagnosis by transillumination, diascopy, fluorescence by tomography, i.e. reconstruction of 3D images from 2D projections
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B5/00—Measuring for diagnostic purposes; Identification of persons
- A61B5/44—Detecting, measuring or recording for evaluating the integumentary system, e.g. skin, hair or nails
- A61B5/441—Skin evaluation, e.g. for skin disorder diagnosis
- A61B5/443—Evaluating skin constituents, e.g. elastin, melanin, water
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/0209—Low-coherence interferometers
- G01B9/02091—Tomographic interferometers, e.g. based on optical coherence
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/47—Scattering, i.e. diffuse reflection
- G01N21/4795—Scattering, i.e. diffuse reflection spatially resolved investigating of object in scattering medium
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B2290/00—Aspects of interferometers not specifically covered by any group under G01B9/02
- G01B2290/45—Multiple detectors for detecting interferometer signals
Definitions
- the present invention relates to an optical coherent tomographic imaging apparatus, and more particularly to an optical coherent tomographic imaging apparatus capable of acquiring a full-color optical coherent tomographic image.
- the present invention also relates to a measurement method using an optical coherence tomographic imaging apparatus.
- an optical coherence tomographic imaging apparatus (hereinafter sometimes referred to as an OCT (Optical Coherence Tomography) apparatus) is known.
- OCT Optical Coherence Tomography
- near-infrared light (1.3 ⁇ m or 1.5 ⁇ m) is used. ing.
- the practical near-infrared OCT apparatus has a depth resolution of about 20 ⁇ m and is not suitable for high-resolution observation of the skin.
- the skin layer structure was keratin (thickness 10 to 30 ⁇ m), epidermis (thickness 100 to 300 ⁇ m), and dermis (thickness 1 mm or more) from the surface side, and a resolution of 20 ⁇ m was not sufficient.
- JP2013-108766A No. 1, JP-A-2015-163862, JP-T-2007-523386, and the like.
- red (R), green (G), and blue (B) low-coherent light in the visible light range is generated by an SLD (Super Luminescent Diode) light source of each color to create a skin replica.
- SLD Super Luminescent Diode
- a method has been devised in which a foundation is applied to evaluate the surface irregularities and the thickness of the foundation layer.
- the RGB-OCT apparatus disclosed in Japanese Patent Application Laid-Open No. 2013-108766 includes a SLD light source for each color of R, G, and B as a light source in the visible light range, the wavelength of the light source provided It is limited to the measurement with, and measurement with any color is not possible.
- the OCT apparatus disclosed in Japanese Patent Application Laid-Open No. 2015-163862 has a white light source and a spectrum shaping unit that cuts out an arbitrary wavelength region in the light source unit, an optical coherence tomography using an arbitrary wavelength in the visible light region Images can be acquired.
- OCT images are measured in a state where the skin of the back of an albino mouse with a very thin pigment is thinly stretched and fixed between chambers, and information up to a relatively deep depth exceeding 130 ⁇ m can be acquired.
- Japanese Patent Application Publication No. 2007-523386 proposes an apparatus capable of acquiring a full color OCT image.
- the measurement light irradiated on the surface of the measurement object enters the measurement object, is scattered inside, returns to the surface side, and is detected by a detector via an optical component such as a lens.
- an optical component such as a lens.
- light attenuation due to light absorption or scattering by the pigment present in the measurement object actually occurs. Therefore, even if a signal (interference light) based on the scattered light from the inside of the measurement target can be detected, the color of the scattered light is a pseudo color including the influence of light absorption and the like. I can not say.
- the present invention has been made in view of the above circumstances, and provides an optical coherence tomographic imaging apparatus capable of acquiring a true color inside a measurement object and a measurement method using the optical coherent tomographic imaging apparatus. With the goal.
- the optical coherence tomographic imaging apparatus of the present invention includes a light source unit that simultaneously emits red wavelength low coherent light, green wavelength low coherent light, and blue wavelength low coherent light, A light splitting unit that splits low-coherent light emitted from the light source unit into measurement light and reference light; A measurement light irradiation optical system for irradiating measurement light to a measurement object; A multiplexing unit that superimposes the reflected light from the measurement object and the reference light when the measurement light is irradiated on the measurement object; An interference light detection unit that detects interference light between the reflected light and the reference light combined by the multiplexing unit; An image generation unit that generates an optical coherence tomographic image of the measurement object from the interference light detected by the interference light detection unit, The image generation unit calculates an attenuation-related value related to signal attenuation in the first depth region of the signal intensity of the interference light of the red wavelength, the green wavelength, and the blue wavelength, and the second deeper than the first depth region.
- a correction signal of interference light is obtained by correcting the signal intensity in the depth region according to the attenuation-related value, and a full-color optical coherence tomographic image is obtained using the correction signals obtained for the red wavelength, the green wavelength, and the blue wavelength, respectively. It is an optical coherence tomographic imaging apparatus to be generated.
- the image generation unit calculates the attenuation constant in the first depth region of the signal intensity of the interference light having the red wavelength, the green wavelength, and the blue wavelength as an attenuation-related value.
- a constant calculation unit and a signal correction calculation unit that obtains a correction signal by correcting the signal intensity in the second depth region using the attenuation constant obtained by the attenuation constant calculation unit may be provided.
- the optical coherence tomographic imaging apparatus of the present invention further includes a spectral reflectance measurement unit that measures the spectral reflectance on the surface of the measurement target, and the image generation unit is included in the first depth region from the spectral reflectance. Based on the dye concentration calculated by the dye concentration calculation unit for obtaining the dye concentration and the dye concentration obtained by the dye concentration calculation unit, the attenuation of light by the dye is obtained as an attenuation-related value, and the signal intensity in the second depth region is corrected. Then, a signal correction calculation unit for obtaining a correction signal may be provided.
- the pigment concentration calculation unit can determine the concentration of melanin as the pigment.
- the red wavelength is 612 nm
- the green wavelength is 537 nm
- the blue wavelength is 448 nm.
- the wavelength is a peak wavelength in each color of low-coherent light emitted from the light source unit.
- the low-coherent light of each color emitted from the light source unit has a spectrum with a Gaussian distribution shape centered on the peak wavelength.
- the interference light detection unit includes a photodetector that detects interference light with a red wavelength, a photodetector that detects interference light with a green wavelength, and interference light with a blue wavelength. It is preferable that each photodetector to be detected is provided separately.
- the optical coherence tomographic imaging apparatus of the present invention may be a spectral domain type or a time domain type, but the spectral domain type is preferable from the viewpoint of shortening the measurement time.
- the measurement light irradiation optical system includes a first cylindrical lens that irradiates measurement light in a line shape on the measurement target, and the first cylindrical lens and the cylinder of each other are provided between the multiplexing unit and the interference light detection unit.
- the second cylindrical lens with the axes orthogonally arranged is provided, the interference light detection unit spectrally detects the interference light, and the image generation unit outputs a signal based on the interference light spectrally detected by the interference light detection unit.
- the spectral domain type optical coherence tomographic imaging apparatus configured to convert into depth information by Fourier transform is preferable.
- the measurement method of the present invention uses the optical coherence tomographic imaging apparatus of the present invention, Irradiate the measurement object with measurement light, Detects the interference light between the reference light and the reflected light from the measurement object, Generate an optical coherence tomographic image of the measurement target, This is a measurement method in which an optical coherence tomographic image is displayed on an image display device, and the surface or internal optical features of the measurement target are obtained from the interference light and displayed on the image display device.
- Optical characteristics include the reflected light intensity at the surface of the measurement object or an arbitrary location inside, the depth profile of the reflected light intensity, or the attenuation constant.
- the reflected light intensity includes light caused by scattered light.
- Measured objects include paint films, human skin, plants, printed materials, paintings that cannot be destroyed, and precious antiquities.
- the measurement target is human skin
- generate optical coherence tomographic images of human skin before and after application of any cosmetics or pharmaceuticals to human skin determine optical characteristics, and It is preferable to display the optical coherence tomographic image and optical features after coating on the image display device. Further, since it is difficult to fix the human skin so that it does not move on the micron order within the measurement time, it is preferable to perform measurement with one shot.
- the image generation unit calculates attenuation-related values related to signal attenuation in the first depth region of the signal intensity of the interference light having the red wavelength, the green wavelength, and the blue wavelength. Then, the correction signal of the interference light is obtained by correcting the signal intensity of the second depth region deeper than the first depth region according to the attenuation-related value, and is obtained for each of the red wavelength, the green wavelength, and the blue wavelength. Since the full-color optical coherence tomographic image is generated using the corrected signal, the true color inside the measurement object can be acquired.
- FIG. 1 is a schematic diagram illustrating an overall configuration of an optical coherence tomographic imaging apparatus according to an embodiment of the present invention. It is a figure which shows the transmittance
- FIG. 3 is a schematic cross-sectional view of a skin composed of first to nth depth regions. It is a cross-sectional schematic diagram of the coating film of 3 layer structure.
- Diagram for explaining colorization procedure (part 1) Diagram for explaining colorization procedure (Part 2) Diagram for explaining the colorization procedure (Part 3) It is the schematic of model skin. It is a figure which shows the external appearance (A) and OCT image (B) of a white skin model. It is a figure which shows the external appearance (A) and OCT image (B) of a skin model with strong yellowishness.
- the optical coherence tomographic imaging apparatus of this embodiment is the OCT image acquired in each wavelength range of red, green, and blue acquired by human skin measurement. It is a figure for demonstrating the 1st correction method, and is the OCT image acquired in the green wavelength range. It is a figure for demonstrating the 1st correction method, and is a figure which shows the one-dimensional profile in the depth direction of the signal strength acquired from the image data of FIG. 13A. It is a figure which shows the full-color OCT image before correction
- FIG. 1 is a diagram schematically showing the overall configuration of an OCT apparatus 1 according to an embodiment of the present invention. As shown in FIG. 1
- OCT apparatus 1 of this embodiment is a light source unit 10 for emitting the low coherence light L 0, the light source unit measurement light L 1 to the low coherence light L 0 emitted from the 10 and the reference light L 2 a light splitting unit 3 for dividing the bets, the measurement light L 1 measured S a (in this case, human skin) and the measurement light irradiation optical system 20 that irradiates the linearly, the measurement light L 1 is irradiated onto the measurement target S interference light L and the reflected light L 3 from the measurement target S and the reference beam L 2 and the multiplexing section 4 of overlapping, and the reflected light L 3, which are multiplexed by the multiplexing section 4 and the reference light L 2 when the 4 R light, G light, and dichroic filters 42 and 44 for separating the B light, the B interference light detector 30B for the B light (B interference light) L 4B spectroscopic detection of the interference light L 4, G light and G interference light detector 30G for spectrally detecting (G
- the light source unit 10 emits a red wavelength low-coherent light, a green wavelength low-coherent light, and a blue wavelength low-coherent light simultaneously.
- the light source unit 10 emits light including a wavelength range of at least 400 nm to 800 nm.
- One light source 11 and a spectrum shaping unit 12 that performs spectrum shaping by cutting out a red wavelength region, a green wavelength region, and a blue wavelength region from light emitted from the light source 11 are provided.
- the light source unit 10 emits low-coherent light L 0 including low-coherent light having a spectrally shaped red wavelength, low-coherent light having a spectrally shaped green wavelength, and low-coherent light having a spectrally shaped blue wavelength.
- the light source 11 is a white light source including a visible light region of at least 400 nm to 800 nm, and in particular, a white light source that emits supercontinuum light is suitable.
- the spectrum shaping unit 12 is a Gaussian filter that cuts out an arbitrary wavelength region from light in a band including the entire visible light emitted from the light source 11 and shapes the spectrum into a Gaussian distribution.
- a Gaussian filter having a plurality of peaks in which at least three primary colors of red, green, and blue are individually spectrally shaped and transmitted simultaneously, for example, having a transmission spectrum as shown in FIG. As shown in FIG. 2, in a filter having a transmission spectrum of a plurality of peaks, each peak has a Gaussian distribution.
- the wavelength ranges of R, G, and B may be any combination that can reproduce full color, but in particular, 448 nm as the blue peak wavelength, 537 nm as the green peak wavelength, and 612 nm as the red peak wavelength. It is preferable to use it.
- WA Thornton (1973) uses a computer program to generate a large number of conditional color pairs, calculate the frequency distribution of the same white crossing wavelength, and the crossing wavelengths are concentrated around 448 nm, 537 nm and 612 nm. Is heading. By using these wavelengths, the white reproduction performance is very good.
- the light source unit may include a light source that emits R light, a light source that emits G light, and a light source that emits B light, instead of the above-described configuration including the white light source and the spectrum shaping unit. .
- a light source SLD of each color of R, G, and B is suitable.
- the light splitting unit 3 that separates the low-coherent light L 0 emitted from the light source unit 10 into the measurement light L 1 and the reference light L 2 is composed of a quartz plate (hereinafter referred to as the quartz plate 3 and This also functions as a combining unit 4 that combines the reflected light L 3 of the measuring light L 1 irradiated to the measuring object S and the reference light L 2 .
- a predetermined incident angle low coherence light L 0 is not 0 ° to the incident surface (e.g., 45 °) enters, the low coherence light incident on the incident surface of the quartz plate 3 (4) Of the L 0 , the light reflected by the incident surface is irradiated to the measuring object S as the measurement light L 1 , and the light transmitted through the quartz plate 3 (4) among the low coherent light L 0 incident on the incident surface is the reference light L 2. As shown in FIG.
- a general beam splitter, half mirror, or the like can be used as the light splitting unit 3 and the multiplexing unit 4, but the quartz plate is inexpensive and the reflected light is very low at about 4%. By using this reflected light as measurement light, irritation to human skin can be suppressed, which is very preferable.
- a quartz plate 5 is disposed on the optical path of the measurement light L 1.
- the quartz plate 5 for dispersion compensation has the same shape as the quartz plate 3 that is a light splitting portion, and is disposed substantially parallel to the quartz plate 3.
- a measuring light irradiation optical system 20 is provided between the quartz plate 3 (4) and the measuring object S.
- the measurement light irradiation optical system 20 includes a first cylindrical lens 21, and the first cylindrical lens 21 extends in the uniaxial (depth direction in FIG. 1) direction y on the surface of the measurement target S. It is configured to irradiate the measurement light L 1 to Jo.
- As the first cylindrical lens 21, for example, a lens having a focal length f 75 mm is provided.
- the measurement light irradiation optical system 20 may include other optical systems such as a polarizer and a zoom lens which are not shown.
- Reflective member 6 is made of a mirror for example, it arranged to reflect the reference light L 2 which are separated by the light splitting unit 3 to the multiplexing unit 4 side.
- the combining unit 4 combines the reference light L 2 reflected by the reflecting member 6 and the reflected light L 3 from the measurement target S and emits the combined light to the interference light detecting unit side.
- the multiplexing unit 4 is configured by a quartz plate that also serves as the light dividing unit 3.
- a cylindrical lens 25 is provided.
- the measurement of the measurement light L 1 irradiated to the subject S, so measuring the reflected light L 3, which returns to the multiplexing unit 4 is reflected from the object S is very small, the reference light L 2 and the reflected light L 3 to ensure symmetry, and a neutral density filter (ND filter) 27 for being reduced intensity of the reference light L 2 in the optical path of the reference light L 2.
- ND filter neutral density filter
- an optical path adjustment mechanism 28 is provided on the optical path of the measurement light L 1 in order to compensate for the optical path difference caused by the neutral density filter 27.
- the optical path adjustment mechanism 28 is not particularly limited as long as it can compensate for the optical path difference generated by the neutral density filter 27. Specifically, a quartz plate with an adjusted thickness can be used.
- the optical system is configured so that the optical path length of the reference light L 2 is equal to the optical path length of the measurement light L 1 irradiated on the reference point of the measurement target S (here, the surface of the measurement target S). It is preferable.
- Three interference light detecting unit 30B, 30G, 30R is, B component of the interference light L 4 of the reflected light L 3, which is combined by each multiplexing unit 4 and the reference light L 2, a G component and the R component Further, the light is split and detected for each wavelength component, and includes a spectroscope 31 that splits the interference light L 4 and a two-dimensional photodetector 32.
- the first dichroic filter 42 reflects B light and transmits other colors.
- the second dichroic filter 44 reflects the G light and transmits other colors.
- the reflectance profile of the dichroic filter 42 is as shown in FIG. 3A and reflects the B light.
- the reflectance profile of the dichroic filter 44 is as shown in FIG. 3B, and reflects the G light, and the transmittance profile of the dichroic filter 44 transmits the R light as shown in FIG. 3C.
- the B interference light detection unit 30B is arranged at a position for receiving the B interference light L 4B reflected by the first dichroic filter 42, and the G interference light detection unit 30G is a G interference light reflected by the second dichroic filter 44.
- the R interference light detection unit 30R is disposed at a position for receiving L 4G , and the R interference light detection unit 30R is disposed at a position for receiving R interference light L 4R that passes through the second dichroic filter 44.
- the spectroscope 31 various known techniques can be used.
- the spectroscope 31 can be constituted by a diffraction grating or the like.
- the photodetector 32 can be constituted by a two-dimensional photosensor in which light receiving elements such as CCDs or photodiodes are arranged two-dimensionally.
- each color is detected by each photodetector 32 of the individual interference light detectors 30B, 30G, and 30R, the wavelength resolution can be increased, and as a result, an OCT image in a range extending from the surface to a depth exceeding 130200 ⁇ m is acquired. be able to. Even if the configuration is such that one interference light detection unit detects three colors of interference light, the two-dimensional photosensor has the same depth as long as the number of pixels of the two-dimensional photosensor is three. The OCT image can be acquired.
- the longitudinal axis (cylindrical axis) of the cylinder is orthogonal to the first cylindrical lens 21 disposed in the measurement light irradiation optical system 20 for performing linear irradiation.
- Light-receiving element of an XY-axis two-dimensional optical sensor constituting the light detector 32 are arranged in a two-dimensional XY direction indicated schematically in the middle photodetector 32 1, the spectroscope 31 disperses the interference light L 4 And it arrange
- interference light caused by reflected light at each position in the line direction (y direction) of the linear measurement light on the measurement surface is incident on the light receiving elements arranged in the Y-axis direction.
- Information in the depth direction (z direction) can be obtained by Fourier transforming the light in the x direction compressed by the first cylindrical lens 21.
- the present OCT apparatus 1 light having information on the surface direction (y direction) and the depth direction (z direction) of the measurement object is simultaneously incident on the two-dimensional optical sensor, so that the two-dimensional in the y direction and the z direction
- An optical coherence tomographic image can be acquired by one exposure (one shot).
- the image generation unit 50 can be configured by, for example, a personal computer and a program incorporated in the computer for causing the computer to execute image generation processing.
- 4 and 5 are block diagrams of a first configuration example and a second configuration example of the image generation unit 50.
- the image generation unit 50 generates the optical coherence tomographic image data (OCT image data) of each color from the interference light of each color detected by the interference light detection units 30B, 30G, and 30R. From the signal processing unit 51 and the OCT image data of each color, an attenuation-related value related to the signal attenuation in the first depth region of the signal intensity of the interference light of the red wavelength, the green wavelength, and the blue wavelength is calculated.
- OCT image data optical coherence tomographic image data
- the correction processing unit 52 that corrects the signal intensity of the second depth region deeper than the depth region according to the attenuation-related value to obtain a correction signal of the interference light, and the red wavelength, the green wavelength, and the blue wavelength are obtained respectively.
- a color image generation unit 58 that generates a full-color optical coherence tomographic image using the correction signal.
- the interference light detector 30B, 30G, by frequency interference light L 4 detected analyzed in 30R specifically, the light receiving elements arranged in the X-axis direction of the two-dimensional photosensor
- the wavelength is converted into wave number, and Fourier transform (FT) is performed to obtain reflection information at the depth position z of the measuring object S, and generate OCT image data of each color.
- FT Fourier transform
- the correction processing unit 52 obtains an attenuation-related value related to the signal attenuation in the first depth region in the depth direction of the measurement target from the OCT image data of each color.
- the attenuation-related value relates to the attenuation of the measurement light and the reflected light (scattered light) inside the measurement target, and can be a factor applicable to the correction of the signal intensity of the correction of the detection signal from the second depth region.
- the measurement object is composed of a first depth region and a second depth region deeper than the first depth region in the depth direction from the surface, and from the first depth region.
- the signal of the second depth region is corrected using the acquired attenuation-related value
- the depth direction of the measurement target is subdivided to have an n-layer configuration from the surface side to the nth region. Therefore, the i-th region signal may be corrected using the attenuation-related value obtained from the (i ⁇ 1) -th region.
- the signal in the i-th region is affected by light attenuation in the region (i ⁇ 1) from the surface, in the case of signal correction calculation, the signal from the surface to the (i ⁇ 1) -th region What is necessary is just to calculate including a correction
- FIG. 6A The first and second depth regions in a specific measurement target will be described with reference to FIGS. 6A, 6B, and 7.
- FIG. 6A The first and second depth regions in a specific measurement target will be described with reference to FIGS. 6A, 6B, and 7.
- FIG. 6A The first and second depth regions in a specific measurement target will be described with reference to FIGS. 6A, 6B, and 7.
- FIG. 6B The first and second depth regions in a specific measurement target will be described with reference to FIGS. 6A, 6B, and 7.
- the skin has a configuration of a horny layer 82, an epidermis 84, and a dermis 86 from the skin surface 80 to which the measurement light L 1 is irradiated.
- d 1 the dermis 86 is regarded as the second depth region d 2 .
- the stratum corneum 82 is thinner and transparent than the other layers, and is treated as an integral part of the epidermis because the attenuation of light is small. Then, to correct the second depth region d 2 signal using the attenuation associated value in the first depth region d 1.
- the range of the first depth region d 1 and the second depth region d 2 and / or the boundary between both may be appropriately determined from an OCT image or a one-dimensional profile in the depth direction of measurement light. Further, the region may be determined based on the thickness from the average skin surface to the dermis 86 or the like.
- the skin surface 80 may be subdivided into a plurality of three or more regions in the depth direction.
- each depth in the depth direction is independent of the boundary between the epidermis and the dermis.
- An area may be defined.
- Each depth region may be determined at a constant interval in the depth direction, or may be determined such that the interval increases as the depth increases.
- FIG. 7 shows a configuration in which a coating film 98 including a base layer 92, a colored layer 94, and a clear coating layer 96 is provided on the surface of a base body (for example, a car body of a car) 90 from the base body 90 side.
- the thickness is, for example, about 100 ⁇ m for each layer. If the clear coating layer 96 is hardly damped in a transparent light, as shown in FIG.
- the layer 94 may be the first depth region d 1
- the base layer 92 may be the second depth region d 2 .
- the layer boundary can be recognized from the acquired OCT image, each region may be designated by the observer, and the boundary in the image It may be determined automatically by processing.
- the measurement object is not a boundary that can be clearly determined, such as the skin composed of the epidermis and dermis shown in FIGS. 6A and 6B, and the coating film composed of a plurality of layers shown in FIG. Even if the boundary cannot be observed, the influence of light attenuation, etc. in the depth region (first depth region) in which the depth region (second depth region) of interest to the observer is shallower than that. If the measurement object is received, it can be regarded that the measurement object is composed of the first depth region and the second depth region.
- the measurement light When acquiring the optical coherence tomographic image, the measurement light is irradiated on the surface of the measurement object. As the measurement light enters the measurement object in the depth direction, that is, as the depth increases, the amount of light attenuates due to absorption by the dye existing inside and scattering in the internal structure. That is, the deeper the region, the less light reaches. Further, even for return light from a deep region, absorption by the dye and scattering in the internal structure occur again in the optical path to the surface of the measurement object, so that further attenuation occurs in the detected light intensity. For example, when only a specific color is absorbed due to the absorption of a specific dye, information about the specific color in the original data is lost.
- the image generation unit 50 of the OCT apparatus 1 includes a correction processing unit 52, the correction processing unit 52 calculates an attenuation-related value and a correction signal, and generates a full-color image using the correction signal. The true color inside the measurement object can be reproduced.
- the depth z is obtained by Fourier transforming the wave number, but the reflection information at an arbitrary depth position z includes the optical to be measured.
- the optical features include reflected light intensity on the surface of the measurement object, reflected light intensity including scattered light at an arbitrary depth, a one-dimensional profile in the depth direction, an attenuation constant described later, and the like. It is desirable that the image generation unit 50 is configured to obtain such an arbitrary optical feature in conjunction with the generation of the OCT image.
- the image display device 60 displays the full-color OCT image generated by the image generation unit 50 as described above and the optical features of the measurement target.
- the image display device 60 can be composed of a liquid crystal display or the like. By displaying the OCT image and the optical features of the measurement target on the image display device 60, the observer sees the measurement target that has been imaged or digitized, and the measurement target. Can be evaluated.
- the display of the OCT image and the display of the optical feature on the image display device 60 may be performed simultaneously or sequentially.
- FIG. 4 shows a first configuration example.
- the correction processing unit 52 of the image generation unit 50 of FIG. 4 includes an attenuation constant calculation unit 53 that calculates an attenuation constant in the first depth region of the signal intensity of the interference light of each RGB color as an attenuation related value, and an attenuation constant calculation. Using the attenuation constant obtained by the unit 53, a signal correction calculation unit 54 that corrects the signal intensity in the second depth region to obtain a correction signal is provided.
- FIG. 5 shows a second configuration example of the correction processing unit 52.
- the image generation unit 50 in FIG. 5 calculates a dye concentration calculation unit that obtains the concentration of the dye contained in the first depth region from the spectral reflectance measured on the surface of the measurement target S (the same part as the part where the OCT image is acquired). 55 and a signal for obtaining a correction signal by obtaining the attenuation amount of light due to the dye as an attenuation-related value based on the dye concentration obtained by the dye concentration calculation unit 55 and correcting the signal intensity in the second depth region.
- a correction calculation unit 56 is provided.
- the OCT apparatus further includes a spectral reflectance measurement unit 59 that acquires the spectral reflectance on the surface of the measurement target.
- the spectral reflectance measurement unit 59 may be provided separately, the spectroscope 31 of any one of the interference light detection units 30B, 30G, or 30R in the OCT apparatus 1 illustrated in FIG. 1 also serves as the spectral reflectance measurement unit 59. May be.
- the attenuation-related value is obtained from the OCT image data (original data) of each color obtained in the original signal processing unit 51, the original data of each color is corrected, and the corrected image data is converted into the corrected image data.
- a full-color OCT image can be generated by the color image generation unit 58 using the corrected image data of each color.
- the original data obtained in the original signal processing unit 51 is used to generate a full color OCT image in the color image generation unit 58, and then the signal correction obtained in the correction processing unit 52 is performed on the full color OCT image.
- Data correction processing may be performed. That is, the correction signal obtained by the signal correction calculation unit 54 or 56 may be corrected image data of each color as described above, or may be signal correction data applied to a full color OCT image. Good.
- the procedure for generating a full-color image from R, G, and B OCT image data is as follows.
- a case where colorization is performed using the optical coherence tomographic image data of each color as shown in FIG. 8A obtained in the original signal processing unit 51 will be described.
- a full color image using the corrected image data of each color is described.
- a similar procedure can be used for the generation.
- the scattered light spectrum I ( ⁇ ) is obtained from the corresponding position of the OCT data for each color.
- the scattered light spectrum I ( ⁇ ) at each corresponding position (a, b) in each image of FIG. 8A is obtained (FIG. 8B).
- the scattered light spectrum I ( ⁇ ) at each position is integrated by applying the color matching functions x ( ⁇ ), y ( ⁇ ), z ( ⁇ ) (FIG. 8C, Equation 1 below).
- stimulus values X, Y, and Z in the CIE (International Commission on Illumination) -XYZ color system are obtained.
- the stimulus values X, Y, and Z are converted into the RGB color system by the calculation represented by the following formula 2, and are converted to 256 gradations to calculate full-color tomographic image data.
- Equation 2 the content of the 3 ⁇ 3 matrix is a conversion equation in the case of the D65 light source, and this is optional because it depends on the optical system and the conditions for color reproduction.
- Rw, Gw, and Bw are 80000 here, these values can also be changed depending on the measurement system and the white standard sample.
- the inventors of the present invention acquired a full color OCT image of a commercially available color checker by the above method, and confirmed that white and yellow of the color checker can be accurately reproduced. Below, the imaging result of the full-color OCT image with respect to model skin is demonstrated.
- FIG. 9 is a diagram showing a schematic configuration of the model skin.
- a model skin was prepared by placing gelatin particles containing polystyrene particles (particle size 200 nm, concentration 0.8 wt%) and yellow pigment 0 wt% or 0.3 wt% in a glass container 101 having a bottom thickness t of about 170 ⁇ m. Since the skin has a multilayer structure of epidermis and dermis, the glass container 101 is regarded as the epidermis and the gelatin 102 in the container 101 is regarded as the dermis. 10 and 11 are an external view A and a full-color OCT image B taken from below A of the bottom surface of the glass container 101 in FIG. 9 (the correction process is not performed here).
- FIG. 10 is a model of white skin in which no yellow pigment is contained in gelatin (pigment 0 wt%)
- FIG. 11 is a model of skin with strong yellowness in which 0.3 wt% of yellow pigment is contained in gelatin.
- a signal backscattered light
- the surface of the glass simulating the epidermis was observed on the surface of the glass simulating the epidermis, and it was confirmed that the signal was dark in the transparent region below. From deeper areas, signals from gelatin simulating the dermis were observed.
- the color is not clear, but in the color image corresponding to FIGS. 10 and 11, in the white skin model, the gelatin region corresponding to the dermis is white, and the skin model is strongly yellowish. Then, it was confirmed that the gelatin region corresponding to the dermis was displayed in yellow, and that the color difference at the deep position corresponding to the dermis of the model skin could be shown by the color image.
- the inventors of the present invention performed one-shot imaging of human skin with the OCT apparatus 1 configured as shown in FIG. 1, and acquired RGB OCT images. It was confirmed that a red OCT image, a green OCT image, and a blue OCT image as shown in FIG. 12 can be obtained by frequency analysis in the original signal processing unit 51 of the image generation unit 50.
- the vicinity of the vertical axis of 100 ⁇ m is the surface of human skin, and the deeper region is the inside of the skin.
- the signal near the depth of 0 to 30 ⁇ m from the surface position is keratinous, the dark region having a depth of 30 to 100 ⁇ m is the epidermis, and the region having a depth of 100 ⁇ m or more is the dermis.
- the epidermis is relatively transparent and the scattered light is small, and the dermis contains collagen, so the scattered light is stronger than the epidermis. It is clear that the signals from the dermis can be observed for each of the RGB colors, and that the same location can be measured. In addition, observation up to a very deep range of 400 ⁇ m in depth is possible.
- a full color image can be obtained by obtaining stimulus values X, Y, and Z in the CIE-XYZ color system using these three colors of OCT image data (original data) and performing RGB conversion.
- original data original data
- RGB conversion RGB conversion
- a true color cannot be displayed using original data including the influence of light attenuation due to hue or the like.
- the image generation unit 50 performs correction processing on the OCT image data of each color to generate correction data.
- 13A is a green OCT image of human skin
- FIG. 13B shows the OCT signal intensity with respect to the depth extracted from the OCT image data of FIG. 13A.
- the white shining region near the vertical axis of 100 ⁇ m is the keratin
- the vertical axis around 120 to 190 ⁇ m is the epidermis.
- the true OCT signal intensity when not affected by the epidermis can be obtained.
- the attenuation amount in the OCT signal is attenuated by the round-trip optical path 2 ⁇ D, but there is no problem if this constant 2 is treated as being incorporated in ⁇ in this correction calculation.
- the electric field E is used in place of the light intensity I and calculation is performed on a straight line of ⁇ (exp ( ⁇ D)) + C.
- the attenuation constant calculation unit 53 calculates the attenuation constant of the first depth region in the image data of each color. Then, the signal correction calculation unit 54 calculates corrected data obtained by correcting the data of the second depth region using the obtained attenuation constant. The color image generation unit 58 generates full color image data based on the corrected data.
- FIG. 14 shows a full-color OCT image (before correction) generated from the original data of each RGB color not subjected to correction processing and a full-color OCT image (after correction) generated from the corrected data corrected by the above processing. Yes. From the comparison of the OCT images before and after correction shown in FIG. 14, after correction, the amount of white scattered light in the dermis region is increased because the attenuation of the light intensity inside is corrected and the light intensity is increased. Can be confirmed.
- FIG. 13A is an example shown for explaining the correction method
- FIG. 14 is an example of a full-color OCT image corrected using the same correction method, and the measurement objects of both do not match.
- the spectral reflectance measurement unit 59 measures the spectral reflectance on the surface at the same location as the measurement target OCT image measurement position. Then, the melanin concentration in the epidermis (first depth region) is estimated from the spectral reflectance.
- the human skin is assumed to be composed of a total three-layer structure consisting of the epidermis (here the skin is included in the epidermis) and the dermis, and the dermis is a two-layer structure.
- the melanin and hemoglobin concentrations are calculated based on the skin scattering coefficient and the absorption spectra of melanin and hemoglobin described in known literature. It is assumed that the epidermis contains melanin, the upper layer of the two-layered dermis does not contain pigment, and the lower layer, which is a deeper region, contains hemoglobin. Here, the upper layer of the two layers constituting the dermis is defined as the second depth region. Note that the lower layer of the dermis is a deep region that cannot be acquired with an OCT image.
- the thickness of the epidermis is 100 ⁇ m
- the upper layer in the dermis particularly the 200 ⁇ m thick region corresponding to the vicinity of the papillary layer
- the thickness of the lower layer in the dermis is 2.8 mm.
- the scattering coefficients of the epidermis and dermis were the same.
- the concentration ratio of oxidized hemoglobin to reduced hemoglobin was 1: 1.
- the spectral reflectance in the visible region was calculated by the Monte Carlo method using the melanin concentration and the hemoglobin concentration, and the melanin concentration and the hemoglobin concentration that were closest to the actual measurement were obtained.
- FIG. 15 shows the spectral reflectance of human skin measured using a reflectance measuring machine V-7200 manufactured by JASCO, and the closest spectral reflectance (melanin concentration of 1.9) obtained by the above method with respect to the measured value. %) And a factor other than the melanin concentration in the epidermis (first depth region) are common, and the spectral reflectance is shown when the melanin concentration is 0%.
- the spectral reflectance obtained by simulation with a melanin concentration of 1.9% agrees with the measured spectral reflectance behavior with high accuracy, and the melanin concentration in the epidermis is 1.9%. Desired.
- the attenuation of light due to melanin in the epidermis that can be obtained from the melanin concentration in the epidermis is corrected with respect to the signal intensity from the dermis (second depth region). Thereby, a color tomographic image of the dermis that is not affected by the color of the epidermis is obtained.
- the dye concentration calculation unit 55 performs the Monte Carlo calculation from the spectral reflectance obtained from the surface of the measurement object as described above, the known structure and the contained dye for the measurement object, and the dye concentration in the first depth region. Is calculated. Then, the signal correction calculation unit 56 calculates corrected data obtained by correcting the data in the second depth region using the attenuation obtained from the dye density. The color image generation unit 58 generates full color image data based on the corrected data.
- FIG. 16 shows a full color OCT image (before correction) generated from the original data of each RGB color that has not been corrected, and a full color OCT image (after correction) generated from the corrected data corrected by the above processing. Yes. From the comparison of the OCT images before and after the correction shown in FIG. 16, after the correction, the attenuation amount of the light intensity inside is corrected and the light intensity is increased, so that the ratio of white scattered light in the dermis region is increased. It can be confirmed that the dermis is bright.
- the true color of the measurement object at least not corrected
- OCT having a color closer to the true color can reproduce an image.
- the measurement target is human skin.
- the measurement target is a coating film (a coating film formed on a substrate)
- the true color in the depth direction is similarly applied. Obviously, it can be used as a non-invasive means of measuring.
- an SD (spectral domain) type OCT apparatus that uses a broadband white light source and obtains a depth distribution from the spectrum of interference light has been described, but the present invention mechanically changes the optical path length.
- a TD (time domain) type OCT apparatus having the above mechanism may be used. If the measurement object is a static object, there is no particular problem whether it is TD or SD type, and if the measurement object is an object that is prone to blur such as human skin or animal skin. It is preferable to use the SD type configured as described above, which can be photographed in one shot.
- the measurement method of the present invention using the optical coherence tomographic imaging apparatus of the present embodiment will be described.
- the measurement target is human skin
- the subject's skin human skin
- the interference light between the measurement light and reference light is spectrally detected
- the interference light is frequency analyzed
- two-dimensional image data is generated.
- Correction processing is performed to correct the amount of light attenuation, and a full-color OCT image is generated from the RGB three-color corrected image data, and the optical characteristics of the surface of or inside the human skin are obtained from the spectrally detected interference light.
- the full-color OCT image and optical features are displayed on the image display device. Images and optical features may be displayed simultaneously on the image display device or may be displayed sequentially.
- Optical features include reflected light intensity on the surface of human skin or an arbitrary location inside human skin acquired from image data of a specific color (for example, red), a one-dimensional profile of the reflected light intensity in the depth direction, and an attenuation constant. Each numerical value or graph is displayed.
- a measurer or a diagnostician can easily evaluate the skin condition from the displayed content.
- Samples from a large number of subjects are obtained for brightness, depth profile, etc. in the OCT image, and a numerical range that can be regarded as healthy and abnormal is prepared in the analysis unit in advance as data, and the healthy by comparing these numerical values and measured values
- evaluations such as abnormalities may be displayed together.
- OCT images are acquired before and after application to human skin, optical characteristics are obtained, and the OCT images and optical characteristics before and after application are simultaneously or sequentially applied to the image display device.
- OCT images and optical characteristics before and after application are simultaneously or sequentially applied to the image display device.
- a difference between OCT images before and after application and a difference in optical characteristics may be obtained, and these differences may be displayed on the image display device as changes before and after application.
- each skin such as white skin or black skin (here, assumed to be pale or dark skin in a yellow race), transparent skin, and full skin. It is possible to clarify the true color inside and to present new values regarding the distribution of pigments in the skin and the mechanism of color expression.
- the measurement method using the optical coherence tomography apparatus of the present invention it is possible to easily evaluate the effect of active ingredients such as cosmetics, quasi drugs, and pharmaceuticals on the skin. Specifically, evaluate the effects of rough skin improvers, moisturizers, whitening agents, anti-wrinkle agents, acne improvers, keratin thickening improvers, turnover improvers, pore astringents, hair restorers, antioxidants, etc. It is also useful, but is not particularly limited.
- the optical coherence tomography apparatus of the present invention is an apparatus capable of obtaining a full-color OCT image in real time with high temporal resolution. Regardless of cosmetics, diagnosis and analysis of skin including injuries and diseases, and film production It can be used for monitoring or color image analysis in a tomographic direction such as a coating film provided on the surface of various substrates, and the measurement object is not limited.
- the two-dimensional OCT image has been described.
- Optical coherence tomographic imaging system OCT system
- OCT system Light splitting part
- Quartz plate 4
- Quartz plate 6
- Reflective member (mirror) DESCRIPTION OF SYMBOLS 10
- Light source part 11
- Light source 12 Spectrum shaping part 20
- Neutral filter 28
- Optical path adjustment mechanism 30B, 30G, 30R Interference light detection part
- Spectroscope 32 Two-dimensional photodetector 35, 36, 37 Imaging lens 50
- Image generation unit 51
- Original signal processing unit 52
- Correction processing unit 53
- Attenuation constant calculation unit 54
- Signal correction calculation unit 55
- Dye concentration calculation unit 58
- Color image generation unit 59
- Spectral reflectance measurement unit 60
- Image display Apparatus 80 skin surface 82 keratin 84 epidermis 86 dermis 90 base 92 base layer 94 colored layer 96 clear coating layer 98 coating 101 glass container 102
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Abstract
Description
一方、特開2015-163862号公報に開示されているOCT装置は、光源部に白色光源と任意の波長域を切り出すスペクトル成形部を有するため、可視光域の任意の波長を用いた光干渉断層画像を取得することができる。
光源部から射出された低コヒーレント光を測定光と参照光とに分割する光分割部と、
測定光を測定対象に照射する測定光照射光学系と、
測定光が測定対象に照射されたときの測定対象からの反射光と参照光とを重ね合わせる合波部と、
合波部により合波された反射光と参照光との干渉光を検出する干渉光検出部と、
干渉光検出部により検出された干渉光から測定対象の光干渉断層画像を生成する画像生成部とを有し、
画像生成部が、赤色波長、緑色波長および青色波長の干渉光の信号強度の、第1の深さ領域での信号減衰に関する減衰関連値を算出し、第1の深さ領域よりも深い第2の深さ領域の信号強度を減衰関連値に応じて補正して干渉光の補正信号を求め、赤色波長、緑色波長および青色波長についてそれぞれ求められた補正信号を用いてフルカラーの光干渉断層画像を生成する光干渉断層画像撮像装置である。
ここで、色素濃度算出部においては、色素としてメラニンの濃度を求めるものとすることができる。
なお、光源部から射出される各色の低コヒーレント光はピーク波長を中心とする、概ねガウシアン分布形状のスペクトルを有する。
特には、測定光照射光学系として測定対象に測定光をライン状に照射する第1のシリンドリカルレンズを備え、合波部と干渉光検出部との間に、第1のシリンドリカルレンズと互いの円筒軸が直交配置された第2のシリンドリカルレンズを備え、干渉光検出部が、干渉光を分光検出するものであり、画像生成部が、干渉光検出部により分光検出された干渉光に基づく信号を、フーリエ変換により深さ情報に変換する構成のスペクトラルドメイン型の光干渉断層画像撮像装置であることが好ましい。
測定対象に対して、測定光を照射し、
参照光と測定対象からの反射光との干渉光を検出し、
測定対象の光干渉断層画像を生成し、
光干渉断層画像を画像表示装置に表示し、干渉光から測定対象の表面もしくは内部の光学的特長を求めて画像表示装置に表示する計測方法である。
図1は、本発明の一実施形態に係るOCT装置1の全体構成を模式的に示した図である。
図1に示すように、本実施形態のOCT装置1は低コヒーレント光L0を射出する光源部10と、光源部10から射出された低コヒーレント光L0を測定光L1と参照光L2とに分割する光分割部3と、測定光L1を測定対象S(ここでは、ヒト肌)にライン状に照射する測定光照射光学系20と、測定光L1が測定対象Sに照射されたときの測定対象Sからの反射光L3と参照光L2とを重ね合わせる合波部4と、合波部4により合波された反射光L3と参照光L2との干渉光L4をR光、G光、B光に分離するダイクロイックフィルタ42、44と、干渉光L4のうちのB光(B干渉光)L4Bを分光検出するB干渉光検出部30Bと、G光(G干渉光)L4Gを分光検出するG干渉光検出部30Gと、R光(R干渉光)L4Rを分光検出するR干渉光検出部30Rと、各干渉光検出部30R,30G,30Bにより検出された干渉光から測定対象の光干渉断層画像(以下においてOCT画像という。)を生成する画像生成部50と、OCT画像を表示する画像表示装置60を有する。
なお、測定光照射光学系20には、図示していない偏光子、ズームレンズ等の他の光学系を備えていてもよい。
合波部4は、反射部材6により反射された参照光L2と測定対象Sからの反射光L3とを合波し干渉光検出部側に射出するものであり、既述の通り、本実施形態において、合波部4は光分割部3を兼ねる石英板により構成されている。
なお、1つの干渉光検出部で3色の干渉光を検出する構成であっても、二次元光センサの画素数が3つの光検出器を備えた場合と同等であれば、同程度の深さのOCT画像を取得することができる。
第2のシリンドリカルレンズ26は、測定光照射光学系20中に配置されたライン状照射を行うための第1のシリンドリカルレンズ21に対して円筒の長さ方向の軸(円筒軸)が互いに直交するように配置される。
図4および図5に示すように、画像生成部50は、干渉光検出部30B、30G、30Rで検出された各色の干渉光から各色の光干渉断層画像データ(OCT画像データ)を生成するオリジナル信号処理部51と、各色のOCT画像データから、赤色波長、緑色波長および青色波長の干渉光の信号強度の、第1の深さ領域での信号減衰に関する減衰関連値を算出し、第1の深さ領域よりも深い第2の深さ領域の信号強度を減衰関連値に応じて補正して干渉光の補正信号を求める補正処理部52および、赤色波長、緑色波長および青色波長についてそれぞれ求められた補正信号を用いてフルカラーの光干渉断層画像を生成するカラー画像生成部58を備えている。
図6Aに示すように、肌は測定光L1が照射される肌表面80から角質82、表皮84および真皮86の構成を有するが、例えば、肌表面80から表皮84を第1の深さ領域d1、真皮86を第2の深さ領域d2と見做す。ここでは、角質82は他の層に比べて薄く、透明であり、光の減衰が小さいため表皮と一体として扱っている。そして、第1の深さ領域d1における減衰関連値を用いて第2の深さ領域d2の信号を補正する。第1の深さ領域d1、第2の深さ領域d2の範囲および/または両者の境界は、OCT画像あるいは、測定光の深さ方向の一次元プロファイルから適宜定めればよい。また、平均的な肌表面から真皮86までの厚み等から領域を定めても構わない。
図7は、基体(例えば自動車の車体)90の表面に、下地層92、着色層94およびクリアコーティング層96からなる塗膜98が基体90側から設けられた構成を示している。厚みは、例えば、各層100μm程度である。クリアコーティング層96が透明であり光の減衰はほとんどない場合には、図7に示すように、塗膜98の測定光L1が照射される表面側からクリアコーティング層96は無視して、着色層94を第1の深さ領域d1、下地層92を第2の深さ領域d2としてもよい。図7に示すような複数層からなる塗膜の場合には、取得されるOCT画像からその層境界は認識可能であり、各領域は観察者が指定してもよいし、画像における境界を画像処理により求めて自動的に定めるようにしてもよい。
ここでは、オリジナル信号処理部51において得られた、図8Aに示すような各色の光干渉断層画像データを用いてカラー化する場合について説明するが、各色の補正済み画像データを用いたフルカラー画像を生成する場合も同様の手順で実施可能である。
各位置の散乱光スペクトルI(λ)に等色関数x(λ),y(λ),z(λ)をかけて積分する(図8C、下記数式1)。これにより、CIE(国際照明委員会)-XYZ表色系における刺激値X,Y,Zが得られる。
下記数式2で示す演算により、上記刺激値X,Y,Zを、RGB表色系に変換し、256階調化してフルカラー断層画像データを算出する。
以下に、モデル皮膚に対するフルカラーOCT画像の撮像結果について説明する。
図13Aは、ヒト肌の緑色OCT画像であり、図13Bは、図13AのOCT画像データから抜き出した深さに対するOCT信号強度を示している。図13Aに示すように、縦軸100μm近傍の白く光る領域が角質であり、縦軸120~190μm辺りが表皮である。この画像に対応する図13BのOCT信号プロファイルの表皮領域(第1の深さ領域)に対して、exp(-αD)+Cの直線(図の破線)で最小二乗法にてフィッティングを行い、表皮領域の減衰定数αを求める。上記フィッティング直線においてDは深さ、Cは装置定数(装置に依存して定まる値)である。Lambert-beerの法則に則り、光の強度Iは、減衰していない表面での強度I0に対し、深さ方向Dに伴ってI=I0×exp(-αD)で減衰する。したがって、表皮よりも深い領域(第2の深さ領域)の信号強度をI0/I=exp(αD)倍すれば、表皮の影響を受けなかった際の真のOCTシグナル強度を求めることができる。なお、OCT信号における減衰量は厳密には往復光路2×Dによって減衰するが、本補正計算においてはこの定数2がαの中に組み込まれているとして扱えば問題ない。また、光の強度Iの代わりに電場Eを用いて、√(exp(-αD))+Cの直線にのるとして計算しても同じことである。
カラー画像生成部58においては、この補正済みデータに基づいてフルカラー画像データを生成する。
まず、分光反射率測定部59により、測定対象のOCT画像測定位置と同一箇所の表面における分光反射率を測定する。そして、その分光反射率から表皮(第1の深さ領域)におけるメラニン濃度の推定を行う。具体的には、ヒト肌を、表皮(ここでは角質を表皮に含む)と真皮からなり、その真皮を2層構造とする計3層構造からなるものと想定し、この3層構造に対してモンテカルロ計算を実施し、公知文献に記載されている肌の散乱係数、およびメラニン、ヘモグロビンの吸収スペクトルを元にして、メラニン、およびヘモグロビン濃度を算出する。なお、表皮にはメラニンが含まれ、2層構造の真皮のうち、上層には色素が含まれず、より深い領域である下層にはヘモグロビンが含まれているものと仮定する。ここでは、真皮を構成する2層のうちの上層を第2の深さ領域とする。なお、真皮の下層はOCT画像では取得できない深い領域である。本計算では、表皮の厚みを100μmとし、真皮中の上層、とくに乳頭層付近に相当する厚み200μmの領域を色素が存在しない領域と、さらに真皮中の下層の厚みを2.8mmと仮定して計算を行った。なお、表皮、真皮の散乱係数は同一とした。また、血液中のヘモグロビンについては、酸化ヘモグロビンと還元ヘモグロビンの濃度比が1:1であると仮定した。以上の条件下にて、メラニン濃度とヘモグロビンの濃度をふってモンテカルロ法で可視域の分光反射率の計算を行い、実測と最も近くなったときのメラニン濃度とヘモグロビン濃度を求めた。
カラー画像生成部58においては、この補正済みデータに基づいてフルカラー画像データを生成する。
ここでは、測定対象がヒト肌である場合について説明するが、測定対象が塗膜等である場合にも同様である。被験者の肌(ヒト肌)に対して、測定光を照射し、測定光と参照光との干渉光を分光検出し、干渉光を周波数解析して二次元画像データを生成し、さらに深さ方向における光減衰分を補正する補正処理を行い、RGB3色の補正画像データからフルカラーのOCT画像を生成し、また、分光検出した干渉光からヒト肌の表面もしくは内部の光学的特長を求める。そして、フルカラーOCT画像および光学的特長を画像表示装置に表示させる。画像と光学的特長とを画像表示装置に同時に表示させてもよいし、逐次表示させてもよい。
3 光分割部(石英板)
4 合波部
5 石英板
6 反射部材(ミラー)
10 光源部
11 光源
12 スペクトル成形部
20 測定光照射光学系
21、25、26 シリンドリカルレンズ
27 減光フィルタ
28 光路調整機構
30B,30G,30R 干渉光検出部
31 分光器
32 二次元光検出器
35,36,37 結像レンズ
50 画像生成部
51 オリジナル信号処理部
52 補正処理部
53 減衰定数算出部
54、56 信号補正演算部
55 色素濃度算出部
58 カラー画像生成部
59 分光反射率測定部
60 画像表示装置
80 肌表面
82 角質
84 表皮
86 真皮
90 基体
92 下地層
94 着色層
96 クリアコーティング層
98 塗膜
101 ガラス容器
102 ゼラチン
Claims (12)
- 赤色波長の低コヒーレント光、緑色波長の低コヒーレント光および青色波長の低コヒーレント光を同時に射出する光源部と、
該光源部から射出された低コヒーレント光を測定光と参照光とに分割する光分割部と、
前記測定光を測定対象に照射する測定光照射光学系と、
前記測定光が前記測定対象に照射されたときの該測定対象からの反射光と前記参照光とを重ね合わせる合波部と、
該合波部により合波された前記反射光と前記参照光との干渉光を検出する干渉光検出部と、
該干渉光検出部により検出された前記干渉光から前記測定対象の光干渉断層画像を生成する画像生成部とを有し、
該画像生成部が、前記赤色波長、前記緑色波長および前記青色波長の前記干渉光の信号強度の、第1の深さ領域での信号減衰に関する減衰関連値を算出し、前記第1の深さ領域よりも深い第2の深さ領域の前記信号強度を前記減衰関連値に応じて補正して前記干渉光の補正信号を求め、前記赤色波長、前記緑色波長および前記青色波長についてそれぞれ求められた補正信号を用いてフルカラーの光干渉断層画像を生成する光干渉断層画像撮像装置。 - 前記画像生成部が、前記赤色波長、前記緑色波長および前記青色波長の前記干渉光の前記信号強度の、前記第1の深さ領域における減衰定数を前記減衰関連値として算出する減衰定数算出部と、該減衰定数算出部で得られた前記減衰定数を用いて、前記第2の深さ領域における前記信号強度を補正して前記補正信号を求める信号補正演算部を備えている請求項1記載の光干渉断層画像撮像装置。
- 前記測定対象の表面における分光反射率を測定する分光反射率測定部をさらに備え、
前記画像生成部が、前記分光反射率から前記第1の深さ領域に含まれる色素の濃度を求める色素濃度算出部と、該色素濃度算出部において得られた前記色素の濃度に基づいて、該色素による光の減衰量を前記減衰関連値として求め、前記第2の深さ領域における前記信号強度を補正して前記補正信号を求める信号補正演算部を備えている請求項1記載の光干渉断層画像撮像装置。 - 前記色素濃度算出部が、前記色素としてメラニンの濃度を求める請求項3記載の光干渉断層画像撮像装置。
- 前記赤色波長が612nmであり、前記緑色波長が537nmであり、前記青色波長が448nmである請求項1から4のいずれか1項に記載の光干渉断層画像撮像装置。
- 前記干渉光検出部が、前記赤色波長の干渉光を検出する光検出器と、前記緑色波長の干渉光を検出する光検出器と前記青色波長の干渉光を検出する光検出器をそれぞれ別個に備えている請求項1から5のいずれか1項に記載の光干渉断層画像撮像装置。
- 前記測定光照射光学系として前記測定対象に前記測定光をライン状に照射する第1のシリンドリカルレンズを備え、
前記合波部と前記干渉光検出部との間に、前記第1のシリンドリカルレンズと互いの円筒軸が直交配置された第2のシリンドリカルレンズを備え、
前記干渉光検出部が、前記干渉光を分光検出するものであり、
前記画像生成部が、前記干渉光検出部により分光検出された前記干渉光に基づく信号を、フーリエ変換により深さ情報に変換する請求項1から6のいずれか1項に記載の光干渉断層画像撮像装置。 - 請求項1から7のいずれか1項に記載の光干渉断層画像撮像装置を用い、
測定対象に対して、前記測定光を照射し、
前記干渉光を検出し、
前記測定対象の光干渉断層画像を生成し、
該光干渉断層画像を画像表示装置に表示し、前記干渉光から前記測定対象の表面もしくは内部の光学的特長を求めて前記画像表示装置に表示する計測方法。 - 前記光学的特長として、前記測定対象の表面もしくは内部の任意箇所における反射光強度、反射光強度の深さ方向プロファイル、あるいは減衰定数を求める請求項8記載の計測方法。
- 前記測定対象が塗膜である請求項8または9記載の計測方法。
- 前記測定対象がヒト肌である請求項8または9記載の計測方法。
- 前記ヒト肌に対する任意の化粧品もしくは医薬品の塗布前、および塗布後のそれぞれの場合の前記ヒト肌についての前記光干渉断層画像を生成し、前記光学的特長を求め、
前記塗布前および前記塗布後の前記光干渉断層画像および前記光学的特長をそれぞれ前記画像表示装置に表示する請求項11に記載の計測方法。
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US11357403B2 (en) | 2022-06-14 |
EP3534147B1 (en) | 2022-03-16 |
JP6745349B2 (ja) | 2020-08-26 |
CN109906370B (zh) | 2021-07-27 |
KR20190054155A (ko) | 2019-05-21 |
KR102227336B1 (ko) | 2021-03-11 |
CN109906370A (zh) | 2019-06-18 |
JPWO2018079326A1 (ja) | 2019-09-26 |
EP3534147A1 (en) | 2019-09-04 |
US20190246906A1 (en) | 2019-08-15 |
EP3534147A4 (en) | 2019-09-04 |
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