JP7253457B2 - Correction method, correction device and imaging device - Google Patents

Description

The present invention relates to a technique for correcting intensity distribution in the depth direction of electromagnetic waves reflected from an object.

Optical coherence tomography (OCT) is known as a technique for acquiring a tomographic image of an object nondestructively and noninvasively. OCT, in particular, is widely used for image diagnosis of eyeballs and skin, and is also used, for example, for observing cultured cells (or cell spheroids) and microorganisms in containers (see, for example, patent documents 1 and Patent Document 2).

In OCT, low-coherence light emitted from a light source is made incident on an object as illumination light, and the intensity of interference light between reflected light from the object and reference light with a known optical path length is detected. Then, based on the intensity (signal intensity) of the detected interference light, the intensity distribution in the depth direction of the reflected light from the object is obtained. In addition, by scanning the incident position of the illumination light in the plane direction, the intensity distribution of the reflected light is obtained one-dimensionally or two-dimensionally, and a tomographic image of the object is generated based on the reflected light intensity distribution. be.

JP 2018-105683 A JP 2018-089055 A

In OCT, scattered light of incident light is mainly detected. Therefore, the pixel value (reflected light intensity) of each pixel indicated by the tomographic image, which is the reflected light intensity distribution obtained by measurement, greatly depends on the structure of each position in the depth direction of the object. Here, when it is assumed that the intensity of the incident light is constant regardless of the position in the depth direction, the reflected light intensity distribution appropriately reflects the internal structure of the object. However, in practice, incident light may attenuate according to the Beer-Lambert law as it travels deeper into the object. Similarly, reflected light from each reflection position can also be attenuated from the reflection position to the detector. Then, the signal intensity detected by the detector is generally large on the incident side (shallow side) of the object and small on the deep side of the object. Therefore, in a tomographic image that expresses the intensity distribution of reflected light, pixels with brightness representing high intensity on the incident side and pixels with low brightness representing low intensity of reflected light on the deep side are dominant. distributed. As a result, it has sometimes been difficult to accurately grasp the position, shape, or the like of a structure within an object in a tomographic image. Therefore, a technique for effectively reducing such luminance difference (intensity difference) has been desired.

（式（１）において、「Ｃ」は、任意パラメータである。） Patent Document 2 describes generating a tomographic image using a value obtained by logarithmically transforming the absolute value (amplitude component) of the complex signal data of the detected light as the intensity information of the tomographic image. As this logarithmic transformation, for example, using the following formula (1), the pixel value S(z) (luminance) of the pixel corresponding to the position z in the depth direction is logarithmically transformed into the corrected pixel value S'(z). can be considered.

(In formula (1), "C" is an optional parameter.)

In the logarithmic transformation shown in Equation (1), the corrected pixel value S'(z) is obtained depending on the pixel value S(z) at the position z and C, which is an arbitrary parameter. That is, the equation (1) does not take into account any depth information and does not compensate for the effects of attenuation caused by the light traveling through the object. Therefore, even if the logarithmic transformation of Equation (1) is applied, it is difficult to correct the decrease in pixel value due to attenuation. Therefore, even if formula (1) is applied, a luminance difference still occurs between pixels on the incident side and pixels on the exit side.

An object of the present invention is to provide a technique for appropriately correcting the reflected electromagnetic wave intensity distribution in the depth direction based on the signal intensity of the electromagnetic wave reflected by the object according to the attenuation received by the electromagnetic wave as it travels through the object. to do.

In order to solve the above problems, the first aspect is a correction method for correcting the reflected electromagnetic wave intensity distribution in the depth direction based on the signal intensity of the electromagnetic wave reflected by the object and focused by the object optical system, (a) setting a correction target position in the reflected electromagnetic wave intensity distribution; and (b) a position in the reflected electromagnetic wave intensity distribution on the object optical system side of the correction target position in the depth direction. and a position closer to the object optical system than the correction target position, wherein (c) determining a correction coefficient based on an integrated value obtained by accumulating values relating to reflected electromagnetic wave intensity at a plurality of positions different from the correction target position in a plane direction parallel to a plane orthogonal to the depth direction; multiplying the reflected electromagnetic wave intensity at the correction target position by a coefficient to calculate a correction value for the reflected electromagnetic wave intensity at the correction target position.

A second aspect is a correction method for correcting a reflected electromagnetic wave intensity distribution in a depth direction based on a signal intensity of an electromagnetic wave reflected by an object and focused by an object optical system, comprising: (a) the reflected electromagnetic wave intensity ; (b) an integration obtained by accumulating values relating to the reflected electromagnetic wave intensity at a plurality of positions on the object optical system side of the correction target position in the reflected electromagnetic wave intensity distribution; (c) calculating a correction value for the reflected electromagnetic wave intensity at the correction target position by multiplying the reflected electromagnetic wave intensity at the correction target position by the correction coefficient; , the step (b) includes reflecting electromagnetic waves at a position closer to the object optical system than the correction target position and at a position different from the correction target position with respect to a plane direction parallel to a plane perpendicular to the depth direction. The step (b) includes integrating values related to intensity, and the step (b) includes: (b-1) obtaining the integrated value for each of a plurality of paths connecting from the correction target position to the object optical system; Including .

A third aspect is the correction method of the first aspect or the second aspect, wherein the step (b) calculates a value related to the reflected electromagnetic wave intensity at each position within an integration target area set with the correction target position as a starting point. Including accumulating.

A fourth aspect is the correction method according to the third aspect, wherein the integration target area has a fan shape extending in the planar direction from the correction target position toward the object optical system.

A fifth aspect is the correction method of the second aspect, wherein the step (b) comprises: (b-2) the integrated value of each of the plurality of paths obtained by the step ( b -1); (b-3) accumulating the product of each of the plurality of routes obtained in the step ( b -2); .

A sixth aspect is the correction method according to the fifth aspect, wherein in the step (b-2), the weight coefficient of each of the plurality of paths increases as the inclination with respect to the depth direction decreases.

A seventh aspect is the correction method according to any one of the first to sixth aspects, wherein the step c) includes (c-1) the product of the reflected electromagnetic wave intensity at the correction target position multiplied by the correction coefficient and (c-2) normalizing the product value obtained in step (c-1) according to a predetermined condition.

An eighth aspect is a correction device for correcting a reflected electromagnetic wave intensity distribution in a depth direction based on the signal intensity of an electromagnetic wave reflected by an object and focused by an object optical system, wherein the reflected electromagnetic wave intensity distribution includes: a setting unit for setting a position to be corrected; and a setting unit for setting a position to be corrected in the reflected electromagnetic wave intensity distribution at a position closer to the object optical system than the position to be corrected and in a plane direction parallel to a plane perpendicular to the depth direction. an integrated value obtained by accumulating values relating to the intensity of reflected electromagnetic waves at a plurality of positions that are the same as the target position ; and a correction coefficient determination unit that determines a correction coefficient based on an integrated value obtained by accumulating values relating to the reflected electromagnetic wave intensity at a plurality of positions different from the correction target position; and a correction unit that calculates a correction value of the reflected electromagnetic wave intensity at the correction target position.

A ninth aspect is an imaging device for imaging an object, comprising: a dividing unit that divides an electromagnetic wave emitted from an electromagnetic wave source into an electromagnetic wave for irradiation and an electromagnetic wave for reference; an object optical system for converging the electromagnetic wave reflected by the object, and an electromagnetic wave from the object focused by the object optical system and the electromagnetic wave interfering with the reference electromagnetic wave. a detector that outputs an interference signal corresponding to the signal intensity of the interference electromagnetic wave, and a reflected electromagnetic wave intensity that expresses the intensity distribution in the depth direction of the electromagnetic wave reflected by the object by processing the interference signal. A signal processing unit that generates a distribution, and the correction device of the eighth aspect.

According to the correction method of the first aspect, the reflected electromagnetic wave intensity at each position closer to the object optical system than the correction target position can be correlated with the attenuation of the electromagnetic wave reflected at the correction target position. Therefore, by accumulating values relating to the reflected electromagnetic wave intensity at each of these positions, it is possible to obtain a correction coefficient that reflects the attenuation received by the electromagnetic wave from the correction target position. By multiplying the reflected electromagnetic wave intensity at the correction target position by the correction coefficient, the electromagnetic wave intensity can be effectively corrected in accordance with the attenuation of the electromagnetic wave occurring inside the object.

Further, according to the correction method of the first aspect, the reflected electromagnetic wave intensity at a position different in the plane direction from the correction target position is integrated. In this case, the attenuation received by the electromagnetic wave from the correction target position at different positions in the plane direction can be reflected in the correction coefficient.

According to the correction method of the third aspect, the attenuation received by the electromagnetic wave from the correction target position at each position within the integration target region set with the correction target position as the starting point can be reflected in the correction coefficient.

According to the correction method of the fourth aspect, the reflected electromagnetic wave intensity is integrated in the fan-shaped integration target region that spreads in the planar direction from the correction target position toward the object optical system. Therefore, it is possible to integrate values related to the intensity of the reflected electromagnetic wave at positions on each path of the reflected electromagnetic wave that diffuses from the correction target position to the object optical system. Therefore, the attenuation received by the reflected electromagnetic wave from the correction target position diffusing toward the object optical system can be reflected in the correction coefficient.

According to the correction method of the second aspect, the intensity of reflected electromagnetic waves is integrated for each of a plurality of paths connecting the position to be corrected and the object optical system. In this case, the attenuation that the electromagnetic wave from the correction target position receives in each path can be reflected in the correction coefficient.

According to the correction method of the fifth aspect, a weighting factor is set for each of a plurality of routes, a product of an integrated value and a weighting factor is calculated for each route, and the products are integrated to obtain a correction coefficient. . In this case, the attenuation of the electromagnetic wave from the correction target position through multiple paths can be reflected in the correction coefficient according to the position of each path.

According to the correction method of the sixth aspect, when the center of the incident electromagnetic wave incident on the object and the center of the electromagnetic wave from the object are focused on the optical axis of the object optical system, the reflected electromagnetic wave at the position to be corrected increases as the object becomes parallel to the optical axis of the optical system. In this case, the closer the path of the electromagnetic wave is parallel to the optical axis, the more likely the electromagnetic wave is to be attenuated. Therefore, by increasing the weighting factor as the path becomes parallel to the depth direction, the attenuation of the electromagnetic wave from the correction target position on each path can be effectively reflected in the correction factor.

According to the correction method of the seventh aspect, a normalized reflected electromagnetic wave intensity distribution can be generated by normalizing the product value obtained by multiplying the reflected electromagnetic wave intensity by the correction coefficient for each of the plurality of correction target positions. As a result, the reflected electromagnetic wave intensity distribution can be easily applied to generation of a tomographic image or the like.

According to the correction device of the eighth aspect, the reflected electromagnetic wave intensity at each position closer to the object optical system than the correction target position can be correlated with the attenuation of the electromagnetic wave reflected at the correction target position. Therefore, by accumulating values relating to the reflected electromagnetic wave intensity at each of these positions, it is possible to obtain a correction coefficient that reflects the attenuation received by the electromagnetic wave from the correction target position. By multiplying the reflected electromagnetic wave intensity at the correction target position by the correction coefficient, the electromagnetic wave intensity can be effectively corrected in accordance with the attenuation of the electromagnetic wave occurring inside the object.

According to the imaging apparatus of the ninth aspect, the reflected electromagnetic wave intensity at each position closer to the object optical system than the correction target position can be correlated with the attenuation of the electromagnetic wave reflected at the correction target position. Therefore, by accumulating values relating to the reflected electromagnetic wave intensity at each of these positions, it is possible to obtain a correction coefficient that reflects the attenuation received by the electromagnetic wave from the correction target position. By multiplying the reflected electromagnetic wave intensity at the correction target position by the correction coefficient, the electromagnetic wave intensity can be effectively corrected in accordance with the attenuation of the electromagnetic wave occurring inside the object.

It is a figure which shows the structural example of the imaging device which concerns on embodiment. It is a schematic diagram for demonstrating the imaging principle in an imaging device. FIG. 4 is a schematic diagram showing a state of tomographic imaging of spheroids. It is a figure showing the example of composition of the imaging device concerning the 1st modification of an embodiment. It is a figure showing the example of composition of the imaging device concerning the 2nd modification of an embodiment. FIG. 4 is a diagram schematically showing the positional relationship between the focal depth of the object optical system and the reference plane; FIG. 4 is a diagram showing the flow of one tomography performed in the imaging apparatus; FIG. 4 is a diagram showing a tomographic image before correction processing; FIG. 10 is a diagram showing a corrected tomographic image obtained by correcting the tomographic image by the correction processing unit; FIG. 10 is a diagram showing the flow of correction processing executed on a tomographic image by a correction processing unit; 9 is a diagram conceptually showing a plurality of pixels arranged on a straight line in the tomographic image shown in FIG. 8; FIG. FIG. 10 is a conceptual diagram for explaining another method of obtaining a correction coefficient; FIG. 10 is a conceptual diagram for explaining another method of obtaining a correction coefficient; FIG. 2 is a diagram conceptually showing a plurality of objects arranged in the depth direction inside an object;

Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be noted that the constituent elements described in this embodiment are merely examples, and are not intended to limit the scope of the present invention only to them. In the drawings, for ease of understanding, the dimensions and numbers of each part may be exaggerated or simplified as necessary.

Expressions indicating relative or absolute positional relationships (e.g., "in one direction", "along one direction", "parallel", "perpendicular", "center", "concentric", "coaxial", etc.) are used unless otherwise specified. Not only the positional relationship is strictly expressed, but also the relatively displaced state in terms of angle or distance within the range of tolerance or equivalent function. Expressions indicating equality (e.g., "identical", "equal", "homogeneous", etc.), unless otherwise specified, not only express quantitatively strictly equality, but also have tolerances or equivalent functions It shall also represent the state in which there is a difference. Expressions indicating shapes (e.g., "square shape" or "cylindrical shape"), unless otherwise specified, not only represent the shape strictly geometrically, but also to the extent that the same degree of effect can be obtained, such as Shapes having unevenness, chamfering, etc. are also represented. Unless otherwise specified, "on" includes two elements in contact as well as two elements apart from each other.

<1. embodiment>
FIG. 1 is a diagram showing a configuration example of an imaging device 1 according to an embodiment. The imaging device 1 performs tomographic imaging of a spheroid Sp (cell clump) cultured in a medium as an object, and generates a tomographic image or a stereoscopic image of the spheroid Sp from the obtained data. Here, a case in which the spheroid Sp placed in the medium M is used as the object will be described, but the object is not limited to this. XYZ orthogonal coordinate axes are defined as shown in FIG. 1 in order to uniformly indicate the directions in the following figures. Here, the XY plane is the horizontal plane and the Z axis is the vertical axis. In the XYZ orthogonal coordinate axes shown in FIG. 1, the direction in which the tip of the arrow points is the + (plus) direction, and the opposite direction is the - (minus) direction. Here, the -Z direction is vertically downward.

The imaging device 1 includes a holding section 10 that holds a container 11 . The container 11 is called a shallow dish having a transparent flat bottom surface 110 made of glass or resin. The holding part 10 holds the container 11 so that the opening surface of the container 11 faces upward and the flat bottom surface 110 of the container 11 is parallel to the horizontal plane. A predetermined amount of medium M is injected into the container 11 in advance. Also, in the medium M, spheroids Sp are cultured on the container bottom 111 of the container 11 . In FIG. 1, a single spheroid Sp is illustrated on the flat bottom surface 110 within the single container 11, but a plurality of spheroids Sp may be cultured.

The imaging device 1 includes an imaging unit 20 . The imaging unit 20 is arranged below the container 11 held by the holding section 10 . The imaging unit 20 is configured as an optical coherence tomography (OCT) apparatus capable of non-contact and non-destructive (non-invasive) imaging of a tomographic image of an object to be imaged. Specifically, the imaging unit 20 includes a light source 21 (electromagnetic wave source), a beam splitter 22 (splitting section), an object optical system 23 , a reference mirror 24 , a spectroscope 25 and a photodetector 26 .

The light source 21 has a light emitting element such as a light emitting diode or a superluminescent diode (SLD). The light source 21 is a low coherence light source with a coherence length of 1 [μm] to 15 [μm], for example.

The imaging device 1 includes a control unit 30 that controls the operation of the device, and a drive control section 40 that controls the movable mechanism of the imaging unit 20 . The control unit 30 includes a CPU (Central Processing Unit) 31 , an A/D converter 32 , a signal processing section 33 , a 3D reconstruction section 34 , an interface (IF) section 35 , an image memory 36 and a memory 37 . Each element provided in the control unit 30 is electrically connected to each other via a bus or the like.

The CPU 31 controls the overall operation of the imaging apparatus 1 by executing a predetermined control program. Control programs executed by the CPU 31 or data generated during processing are stored in the memory 37 as appropriate. The A/D converter 32 converts the signal output from the photodetector 26 of the imaging unit 20 according to the amount of received light into digital data. The signal processing unit 33 performs signal processing, which will be described later, based on the digital data output from the A/D converter 32, and creates a tomographic image of the object to be imaged. The 3D reconstruction unit 34 has a function of creating a stereoscopic image (3D image) of the imaged cell cluster based on image data of a plurality of imaged tomographic images. The image data of the tomographic image created by the signal processing unit 33 and the image data of the stereoscopic image created by the 3D reconstruction unit 34 are appropriately stored in the image memory 36 .

The control unit 30 also includes a correction processing section 38 electrically connected to the CPU 31 via a bus or the like. The correction processing unit 38 executes correction processing for correcting the tomographic image It (reflected light intensity distribution) obtained by the signal processing unit 33 . More specifically, the correction processing unit 38 includes a correction coefficient determination unit 381 that determines correction coefficients, and a correction calculation unit 383 that calculates correction values. A correction coefficient is a value by which a pixel value to be corrected (reflected light intensity) is multiplied in order to correct the pixel value. Details of the correction processing executed by the correction processing unit 38 will be described later.

Each of the signal processing unit 33, the 3D reconstruction unit 34, and the correction processing unit 38 may be a function realized by the CPU 31 operating according to a program, or may be configured by a dedicated circuit. Also, the signal processing unit 33, the 3D reconstruction unit 34, and the correction processing unit 38 may be functions realized by a computer other than the computer including the CPU 31. FIG.

The interface unit 35 has a function of mediating communication between the imaging device 1 and an external device. The interface unit 35 has a communication function for communicating with an external device, and a user interface function for receiving operation input from the user and notifying the user of various types of information. An input device 351 and a display section 352 are connected to the interface section 35 . The input device 351 includes, for example, a keyboard, mouse, touch panel, and the like. The input device 351 receives operation inputs related to function selection, operating condition setting, and the like of the imaging apparatus 1 . The input device 351 includes, for example, a touch panel liquid crystal display. The display unit 352 displays various processing results such as a tomographic image generated by the signal processing unit 33 or a stereoscopic image generated by the 3D reconstruction unit 34 .

The CPU 31 gives a control command to the drive control section 40 . The drive control section 40 causes the movable mechanism of the imaging unit 20 to perform a predetermined operation according to a control command from the CPU 31 . Specifically, a tomographic image of the spheroid Sp, which is the object to be imaged, is acquired by combining the scanning movement of the imaging unit 20 executed by the drive control unit 40 and the detection of the amount of light received by the photodetector 26. .

FIG. 2 is a schematic diagram for explaining the principle of imaging in the imaging device 1. As shown in FIG. FIG. 3 is a schematic diagram showing a state of tomographic imaging of spheroids Sp. When performing tomography, the light source 21 of the imaging unit 20 emits a light beam L1 containing broadband wavelength components. This light beam L1 is low coherence light. The light beam L1 is incident on the beam splitter 22 (splitting section) and split into two. Specifically, part of the light beam L1 travels toward the container 11 as incident light L2, as indicated by the dashed arrow in FIG. Another part of the light beam L1 travels toward the reference mirror 24 as the reference light L3 (reference electromagnetic wave), as indicated by the dashed-dotted line arrow in FIG.

Incident light L2 directed toward the container 11 passes through the object optical system 23 and enters the container 11 . More specifically, the incident light L2 emitted from the beam splitter 22 is incident on the container bottom 111 via the object optical system 23 . The object optical system 23 has optical elements such as an objective lens. The object optical system 23 has a function of converging the incident light L2 directed from the beam splitter 22 toward the container 11 onto the object (spheroid Sp) in the container 11, and converging the reflected light emitted from the object to form a beam It has the function of directing it to the splitter 22 . Although FIG. 2 shows a single objective lens as an element of the object optical system 23, it may have a plurality of optical elements.

The object optical system 23 is movably supported in the Z-axis direction by a focus adjustment mechanism 41 provided in the drive control section 40 . Therefore, the focal position of the object optical system 23 with respect to the object can be changed in the Z-axis direction. Hereinafter, the focal position of the object optical system 23 in the depth direction (Z-axis direction) may be referred to as "focal depth". The optical axis AX1 of the object optical system 23 is parallel to the vertical direction (Z-axis direction) and perpendicular to the planar container bottom 111 . Also, the incident direction of the incident light L2 to the object optical system 23 is parallel to the optical axis AX1. Also, the object optical system 23 is arranged so that the center of the incident light L2 coincides with the optical axis AX1.

If the spheroid Sp has some degree of transparency to the incident light L2, the incident light L2 enters the interior of the spheroid Sp and then reflects according to the internal structures of the spheroid Sp. When the incident light L2 is, for example, near-infrared rays, the incident light L2 can reach the inside of the spheroid Sp. The light reflected inside the spheroid Sp is radiated in various directions as scattered light. Of the scattered light, the reflected light L4 (reflected electromagnetic wave) radiated within the condensing range of the object optical system 23 is converged by the object optical system 23 and sent to the beam splitter 22 .

A mirror drive mechanism 42 provided in the drive control unit 40 supports the reference mirror 24 so that the reflecting surface of the reference mirror 24 is perpendicular to the incident direction of the reference light L3. Further, the mirror driving mechanism 42 moves the reference mirror 24 in the direction along the incident direction of the reference light L3 (Y-axis direction in FIG. 2). The reference light L3 incident on the reference mirror 24 is reflected by the reflecting surface of the reference mirror 24, travels in the opposite direction (-Y direction in FIG. 2) along the incident optical path of the reference light L3, and travels toward the beam splitter 22. As the mirror drive mechanism 42 changes the position of the reference mirror 24, the optical path length of the reference light L3 changes.

The reference light L3 reflected by the reference mirror 24 and the reflected light L4 reflected by the surface or internal reflecting surface of the spheroid Sp enter the photodetector 26 via the beam splitter 22 . At this time, interference between the reference light L3 and the reflected light L4 causes an interference light L5 (interference electromagnetic wave) corresponding to the phase difference between them.

The spectroscope 25 is arranged on the optical path of the interference light L5 from the beam splitter 22 to the photodetector 26 . Spectroscope 25 has, for example, a prism or a diffraction grating. The interference light L5 is split into different wavelength components by the spectroscope 25 and enters the photodetector 26 .

The spectral spectrum of the interference light L5 incident on the photodetector 26 differs according to the depth of the reflecting surface of the spheroid Sp. That is, the spectral spectrum of the interference light L5 has information in the depth direction of the object. Therefore, the intensity distribution of the reflected light in the depth direction of the object can be obtained by spectrally dispersing the interference light L5 for each wavelength, detecting the light amount, and Fourier transforming the detected interference signal. OCT based on such a principle is called Spectral Domain OCT (SD-OCT) of Fourier Domain OCT (FD-OCT).

By Fourier transforming the interference signal output from the photodetector 26, the reflected light intensity distribution of the spheroid Sp in the depth direction at the incident position of the incident light L2, that is, in the Z-axis direction is obtained. In addition, by scanning the incident light L2 incident on the container 11 in the X-axis direction, the reflected light intensity distribution on a plane parallel to the XZ plane is obtained, and from the result, a tomographic image of the spheroid Sp having a cross section of the plane is obtained. is generated. In the following description, a series of operations for acquiring one tomographic image It in a cross section parallel to the XZ plane by beam scanning in the X-axis direction is referred to as one tomographic imaging.

Moreover, if necessary, the incident position of the incident light L2 is changed in multiple stages at a predetermined pitch in the Y-axis direction, and one tomographic imaging is performed each time. As shown in FIG. 3, a plurality of tomographic images It representing cross-sectional images parallel to the XZ plane of the spheroid Sp are obtained by performing the tomographic imaging multiple times. By reducing the pitch in the Y-axis direction, it is possible to acquire image data with sufficient resolution to grasp the three-dimensional structure of the spheroids Sp.

The drive control unit 40 may include an optical component (eg, a galvanomirror) (not shown) that changes the optical path of the incident light L2. In this case, the drive control unit 40 may move the incident position of the incident light L2 on the spheroid Sp in the X-axis direction and the Y-axis direction by operating the optical component. Alternatively, the drive control section 40 may include a moving mechanism that moves either one of the holding section 10 and the imaging unit 20, or both of them, in the X-axis direction and the Y-axis direction. In this case, the drive control unit 40 operates the moving mechanism to change the relative positional relationship between the container 11 and the imaging unit 20, thereby changing the incident position of the incident light L2 with respect to the spheroids Sp in the X-axis direction and It may be moved in the Y-axis direction.

In the explanation of the principle of FIG. 2, the splitting function of splitting the light from the light source 21 into the illumination light and the reference light in the imaging unit 20 and the function of synthesizing the signal light and the reference light to generate interference light are: It is implemented by a beam splitter 22 . In recent years, as shown in FIG. 4, an optical fiber coupler may be used in an OCT apparatus to perform such demultiplexing/multiplexing functions.

FIG. 4 is a diagram showing a configuration example of an imaging device 1A according to a first modified example of the embodiment. In the following description, elements that are the same as or have the same function as elements provided in the imaging apparatus 1 shown in FIG. Since the imaging principle of the imaging device 1A is the same as the imaging principle of the imaging device 1, detailed description thereof will be omitted.

The imaging device 1A includes an imaging unit 20A. The imaging unit 20A includes an optical fiber coupler 220 as a demultiplexer/multiplexer in place of the beam splitter 22 . Four optical fibers 221 , 222 , 224 and 226 are connected to the optical fiber coupler 220 . The optical fiber 221 is connected to the light source 21 and inputs the light beam L1, which is low coherence light emitted from the light source 21 , to the optical fiber coupler 220 . The optical fiber coupler 220 splits the light beam L1 from the light source 21 into optical fibers 222 and 224 . Optical fiber 222 is the object system optical path. More specifically, the light (incident light L2) emitted from the end of the optical fiber 222 enters the object optical system 23 via the collimator lens 223, is focused by the object optical system 23, and enters the ferroid Sp. do. Also, the reflected light L4 (signal light) from the spheroid Sp enters the optical fiber 222 via the object optical system 23 and the collimator lens 223 .

Optical fiber 224 is the reference optical path. More specifically, the light (reference light L3) emitted from the end of the optical fiber 224 enters the reference mirror 24 via the collimator lens 225 . Reflected light (reference light L3) from the reference mirror 24 enters the optical fiber 224 via the collimator lens 225 . The reflected light L4 (signal light) propagating through the optical fiber 222 and the reference light L3 propagating through the optical fiber 224 interfere at the optical fiber coupler 220 to generate interference light L5. The interference light L5 enters the photodetector 26 via the optical fiber 226 and the spectroscope 25 . From the spectral spectrum of the interference light L5 detected by the photodetector 26, the reflected light intensity distribution in the depth direction for the spheroid Sp is obtained.

FIG. 5 is a diagram illustrating a configuration example of an imaging device 1B according to a second modification of the embodiment. The imaging device 1B is different from the imaging device 1A in that it does not have an optical fiber 224 although it has an optical fiber coupler 220 . The imaging device 1B also includes a collimator lens 223 and a beam splitter 227 (splitting section) on the optical path of light emitted from the optical fiber 222 . In the imaging device 1B, the beam splitter 227 splits the light beam L1 from the light source 21 into the incident light L2 and the reference light L3. An object optical system 23 is arranged on the optical path of the incident light L2, and a reference mirror 24 is arranged on the optical path of the reference light L3. In this case, the beam splitter 227 synthesizes the reflected light L4 (signal light) and the reference light L3. Interference light L5 generated by beam splitter 227 is guided to spectroscope 25 and photodetector 26 through optical fibers 222 and 226 .

In imaging device 1, each light passes through space, whereas in imaging devices 1A and 1B, part of the optical path is replaced with an optical fiber. However, the principle of operation of the imaging devices 1A and 1B is substantially the same as that of the imaging device 1. FIG. In the imaging devices 1A and 1B as well, the focal depth of the object optical system 23 with respect to the spheroid Sp is adjusted by moving the object optical system 23 toward or away from the container 11 by the focus adjustment mechanism 41 . Further, the optical path length of the reference light L3 is changed by moving the reference mirror 24 along the optical axis of the reference light L3. Since the image capturing principles of the image capturing apparatuses 1, 1A, and 1B are the same, the image capturing operation of the image capturing apparatus 1 will be described below.

FIG. 6 is a diagram schematically showing the positional relationship between the focal depth DT of the object optical system 23 and the reference plane Sr. In the imaging apparatus 1, the position where the optical path length of the reflected light L4 is the same as the optical path length of the reference light L3 is the reference position in the depth direction (Z-axis direction) on the basis of the principle of low-coherence light interference. Hereinafter, as shown in FIG. 6, in the object system optical path through which the reflected light L4 propagates, a surface corresponding to the reflecting surface of the reference mirror 24 in the reference system optical path ) is called a reference plane Sr. A plane including the focal point FP of the object optical system 23 and perpendicular to the optical axis AX1 of the object optical system 23 is called a focal plane Sf. Also, the distance in the Z-axis direction from the predetermined reference position to the focal plane Sf is referred to as the focal depth DT. Here, the reference position of the depth of focus DT is the flat bottom surface 110 (see FIG. 1) of the container 11 in which the spheroids Sp are placed.

In the object system optical path, if there is a virtual reflecting surface on the reference surface Sr, the optical path length of the light reflected by the reflecting surface (the optical path length of the incident light L2 and the reflected light L4 from the light source 21 to the photodetector 26 ) is equal to the optical path length of the light reflected by the reflecting surface of the reference mirror 24 (the optical path length of the reference light L3 from the light source 21 to the photodetector 26).

When the spheroid Sp has a reflecting surface on the focal plane Sf, in the reflected light intensity distribution after Fourier transform, a signal having a magnitude corresponding to the reflected light intensity from the reflecting surface is transmitted from the reference surface Sr to the reflecting surface ( That is, it appears at a depth position corresponding to the distance to the focal plane Sf). In an actual object to be imaged, signals corresponding to reflected light from reflecting surfaces at various depths appear at each position.

FIG. 7 is a diagram showing the flow of one tomography performed in the imaging apparatus 1. As shown in FIG. First, the container 11 in which the spheroid Sp, which is an object to be imaged, is placed is held at a fixed position by the holding section 10 of the imaging device 1 (step S10). The setting of the container 11 on the holding portion 10 may be performed by an operator, or may be performed by a transport device (transport robot or the like) (not shown).

Subsequently, the control unit 30 drives the focus adjustment mechanism 41 to match the focal depth DT of the object optical system 23 to a predetermined initial value (step S11). Following step S11, the control unit 30 drives the mirror drive mechanism 42 to place the reference mirror 24 at a position corresponding to the focal depth DT (step S12).

After step S12, the control unit 30 scans the spheroids Sp in the X-axis direction with the incident light L2 (step S13). Specifically, the interference light L5 between the reference light L3 from the reference mirror 24 and the reflected light L4 from the spheroid Sp is separated by the spectroscope 25, and the signal intensity for each wavelength is detected by the photodetector 26. The photodetector 26 outputs the signal intensity (spectral spectrum information) for each wavelength to the CPU 31 . Further, in step S13, the drive control unit 40 changes the incident position of the incident light L2 on the spheroid Sp at a predetermined pitch in the X-axis direction, and each time, the spectral information is obtained.

The signal processing unit 33 obtains the reflection intensity distribution from the reflecting surface present at the focal depth DT by Fourier transforming the spectral information obtained in step S13 (step S14). Note that derivation of the reflected light intensity distribution may be performed after all imaging is completed.

After step S14, the CPU 31 determines whether the depth of focus DT has reached a predetermined final value (step S15). If the depth of focus DT is less than the final value in step S15 (No), the depth of focus DT is changed by one predetermined pitch (step S16). Then, steps S12 to S15 are executed again. In this way, the main scanning in the X-axis direction is repeated until the focal depth DT reaches the final value, thereby acquiring the spectroscopic information. In step S16, the pitch at which the focal depth DT is changed may be determined in advance, or may be appropriately set according to an input from the operator.

In step S15, if the depth of focus DT is the final value (Yes), a tomographic image is generated. Specifically, the signal processing unit 33 creates a tomographic image It of the spheroid Sp in one cross section parallel to the XZ plane by superimposing the partial images acquired for each focal depth DT in the depth direction. (Step S17).

Sub-scanning in the Y-axis direction may be performed as necessary. That is, by changing the incident position of the incident light L2 with respect to the spheroids Sp at a predetermined pitch in the Y-axis direction and performing steps S11 to S16 each time, the reflection intensity distribution of the entire spheroids Sp can be obtained. Thereby, tomographic images It at different positions in the Y-axis direction can be obtained. The 3D reconstruction unit 34 generates a stereoscopic image of the spheroid Sp from the plurality of acquired tomographic images It.

FIG. 8 is a diagram showing a tomographic image It1 before correction processing. In the tomographic image It1 shown in FIG. 8, the vertical direction corresponds to the Z-axis direction, the downward vertical direction corresponds to the −Z side (that is, the object optical system 23 side), and the upward vertical direction corresponds to the +Z side. Also, in the tomographic image It1, the horizontal direction corresponds to the X-axis direction. A graph 991 shown in FIG. 8 shows the reflected light intensity distribution on a straight line LN1 along the vertical direction shown on the tomographic image It1. In the tomographic image It1, the high-brightness image extending linearly in the horizontal direction is the image of the flat bottom surface 110 of the container 11 .

Spheroids Sp have structures (cells, organelles, etc.) that differ in shape, size, and refractive index. Such a structure attenuates the incident light L2 incident on the spheroid Sp as a scatterer. For this reason, as shown by the tomographic image It1 and the graph 991 in FIG. become smaller.

FIG. 9 is a diagram showing a corrected tomographic image It2 obtained by correcting the tomographic image It1 by the correction processing unit 38. As shown in FIG. A graph 992 shown in FIG. 9 shows the reflected light intensity distribution on the straight line LN1 shown in the tomographic image It2. A graph 992 is data obtained by correcting the graph 991 (reflected high intensity distribution) by the correction processing unit 38 . As shown in FIG. 9, in the corrected tomographic image It2, the difference in pixel values (reflected light intensity) between the -Z side and the +Z side is smaller than in the tomographic image It1. Therefore, the tomographic image It2 is a high-contrast image suitable for observation of the spheroids Sp compared to the tomographic image It1 before correction. In this manner, the correction processing unit 38 corrects the pixel values in consideration of the attenuation of light that occurs within the spheroid Sp, which is the object. The correction processing executed by the correction processing unit 38 will be described below. Here, as an example, a case of correcting the tomographic image It1 shown in FIG. 8 will be described.

FIG. 10 is a diagram showing the flow of correction processing executed by the correction processing unit 38 on the tomographic image It. FIG. 11 is a diagram conceptually showing a plurality of pixels arranged on the straight line LN1 of the tomographic image It1 shown in FIG. Pixel P _{(x, 1)} , pixel P _{(x, 2) ,} . Also, let the pixel values of these pixels be S _{(x, 1)} , S _{(x, 2)} , . . . , S _{(x, z)} . These pixel values indicate the reflected light intensity (reflected electromagnetic wave intensity) from the position of each pixel.

As shown in FIG. 10, when starting the correction processing, the correction processing unit 38 first reads the tomographic image It1 (step S21). Subsequently, the correction processing unit 38 sets correction target pixels to be corrected in the tomographic image It1 (step S22). In this embodiment, the correction processing section 38 has the function of a setting section that sets the correction target position. In step S22, the correction processing unit 38 acquires the pixel value of the correction target pixel and stores it in the memory 37 or the like. For example, assume that the correction processing unit 38 sets the n-th pixel P _{(x, n)} among the plurality of pixels shown in FIG. 11 as the correction target pixel. In this case, the pixel value S _{(x, n)} of the pixel P _{(x, n)} is obtained and stored in the memory 37 or the like.

Subsequently, the correction coefficient determination unit 381 of the correction processing unit 38 determines the correction coefficient of the correction target pixel (step S23). The correction coefficient is a value for obtaining a correction value S' _(x,n) by multiplying the pixel value S _(x,n) of the correction target pixel P _(x,n) . That is, when the correction coefficient of the correction target pixel P _(x,n) is "c _(x,n) ", the correction value S' _(x,n) is represented by Equation (2).

In step S23, the correction coefficient determination unit 381 calculates the value obtained by integrating the pixel values of the incident-side pixels on the object optical system 23 side (−Z side) of the correction target pixel in the tomographic image It1 as the correction coefficient. and For example, in the example shown in FIG. 11, pixels P _{(x, 1) ,} P _{(x, 2)} , . . . , P _{(x , n−1)} exist. The correction coefficient determination unit 381 multiplies these pixel values S _{(x, 1) ,} S _{(x, 2) , . )} . That is, the correction coefficient c _{(x, n)} is represented by Equation (3).

When the correction coefficient c _{(x, n)} is determined in step S23, the correction calculation unit 383 of the correction processing unit 38 calculates the correction coefficient c _{(x, n)} as the correction target pixel P By multiplying the pixel value S ( _{x, n) of ( x, n)} , the correction value S' _{(x, n) of the correction target pixel P ( x, n} ) is calculated (step S24).

In step S24, the correction processing unit 38 stores the obtained correction value S' _{(x,n) of the correction target pixel P( x,n)} in the memory 37 or the like. Then, the correction processing unit 38 determines whether correction processing for obtaining correction values has been performed for all pixels of the tomographic image It1 read in step S21 (step S25). If there is an uncorrected pixel (NO in step S25), the correction processing unit 38 returns to step S22 and calculates the correction value of the uncorrected pixel. Note that it is not essential that all the pixels of the tomographic image It are subjected to the correction process, and only some of the pixels may be subjected to the correction process. In this case, the correction processing unit 38 may receive designation of the pixel group to be corrected by the operator, and the correction processing unit 38 may calculate the correction value for the designated pixel group.

When the correction processing is completed for all pixels (YES in step S25), the correction processing unit 38 executes normalization processing (step S26). Normalization processing means converting the calculated correction value into a pixel value that can be expressed on a computer according to a predetermined rule. In the normalization process, for example, the correction value of each pixel is converted so that the average value and standard deviation of the corrected correction value after conversion are set to respective default values.

When the normalization process is completed, the correction processing unit 38 outputs the corrected tomographic image It2 based on the normalized correction value to the display unit 352 (step S27). As a result, the corrected tomographic image It2 is displayed on the display unit 352 .

In the imaging device 1, the reflected light L4 from the reflecting surface of the spheroid Sp is attenuated by the structure located closer to the object optical system 23 than its position. That is, the incident light L2 incident on the position of the correction target pixel P _(x,n) or the reflected light L4 from the correction target pixel P _(x,n) is more object-oriented than the correction target pixel P _(x,n). The reflected light L4 is attenuated by being reflected, scattered or absorbed by the structures present at the respective positions of the pixels P _{(x, 1)} to P _{(x, n-1)} on the optical system 23 side. Therefore, the magnitude of attenuation that the reflected light L4 receives at each position of the pixels P _{(x, 1) to} P ( _{x, n-1)} is It is considered to be correlated with the pixel values S _{(x, 1)} to S _{(x, n-1)} . For this reason, the value obtained by integrating the pixel values S _{(x, 1)} to S _{(x, n-1)} reflects the attenuation received by the reflected light L4 from the correction target pixel P _{(x, n).} It can be a correction factor C _(x,n) . Therefore, by multiplying the pixel value S _{(x, n)} of the correction target pixel _{(x, n)} by the correction coefficient c _{(x, n)} , the pixel value S _(x,n) can be effectively corrected.

Note that _the correction _coefficient determination unit 381 determines the pixel values _{S (} It is not essential to multiply _x,1) to S _(x,n-1) . The correction coefficient determination unit 381 discretely integrates the pixel values of only some of all the pixels P _{(x, 1)} to P _{(x, n-1)} to determine the correction coefficient c _{(x, n)} may be determined.

In the above description, the correction coefficient c _{(x, n)} is obtained from the pixel values (reflected light intensity) of pixels arranged on a one-dimensional straight line (for example, straight line LN1). That is, the pixel values S _{(x, 1) to S (x , n−1)} , the correction coefficient c _{(x, n)} is obtained. However, the correction coefficient c _{(x, n)} may be obtained by integrating the pixel values (reflected light intensity) of pixels at positions different in the XY plane direction from the correction target position P _{(x, n).} .

FIG. 12 is a conceptual diagram for explaining another method of obtaining the correction coefficient c _{(x, n)} . In the example shown in FIG. 12, the correction coefficient determination unit 381 sets the integration target area RA1 in order to obtain the correction coefficient c _{(x,n) of the correction target pixel P(x ,n} ). Here, the area to be integrated RA1 extends from the pixel to be corrected P _{(x, n)} toward the −Z side corresponding to the object optical system 23 in the +X direction and the −X direction orthogonal to the depth direction. It is a fan-shaped two-dimensional area that extends in both directions. In this example, the integration target area RA1 is an isosceles triangle with the correction target pixel P _{(x, n)} as the vertex. The correction coefficient determination unit 381 obtains the correction coefficient c _(x,n) by integrating the pixel values of each pixel corresponding to each position included in the integration target area RA1.

In the example shown in FIG. 12, in addition to the pixel values of the pixel group at the same position as the correction target pixel P _{(x, n)} in the X-axis direction, the correction target pixel P _{(x, n)} is Pixel values of pixel groups at different positions are also integrated. Therefore, not only the attenuation of the incident light L2 or the reflected light L4 parallel to the Z-axis direction, but also the attenuation of the incident light L2 or the reflected light L4 inclined with respect to the Z-axis direction is included in the correction coefficient c _{(x, n).} can be reflected.

By integrating the pixel values of each pixel in the integration target area RA1, the correction coefficient c _{(x, n)} reflecting the attenuation caused by the incident light L2 or the reflected light L4 passing through the integration target area RA1 is obtained. can ask. By applying this correction coefficient c _{(x, n)} to the correction process, the attenuation of light received by the reflected light L4 from the correction target pixel P _{(x, n)} at each position of the integration target area RA1 is corrected. It can be reflected in the coefficient c _{(x, n)} . Therefore, it is possible to effectively correct the intensity of the reflected light according to the attenuation of the reflected light L4 within the object.

In particular, when the shape of the integration target area RA1 is made to match the path of the incident light L2 converged by the object optical system 23, the incident light L2 passes from the object optical system 23 to the position of the correction target pixel P _{(x, n).} Attenuation experienced before arrival can be reflected in the correction coefficient c _(x,n) .

Further, by matching the shape of the integration target area RA1 to the path of the reflected light L4 incident on the object optical system 23, the reflected light L4 from the correction target pixel P _{(x, n)} reaches the object optical system 23. can be reflected in the correction factor c _(x,n) . In the imaging device 1, the path of the incident light L2 converged by the object optical system 23 and the path of the reflected light L4 incident on the object optical system 23 match. Therefore, matching the integration target area RA1 with the path of the incident light L2 is equivalent to matching the path of the reflected light L4 incident on the object optical system .

Note that the shape of the integration target area RA1 may be narrower than the path of the incident light L2 converged by the object optical system 23 or the path of the reflected light L4 incident on the object optical system 23. FIG. In either case, the attenuation of the reflected light L4 from the position of the correction target pixel P _{(x, n)} at each position of the integration target region RA1 can be reflected in the correction coefficient c _{(x, n).} .

An integrated value of pixel values may be obtained for each of a plurality of paths from the position of the correction target pixel P _{(x, n)} toward the object optical system 23 side. Further, a product value may be obtained by multiplying the integrated value of each of the plurality of routes by a weighting factor corresponding to the position of each of the plurality of routes. Then, the correction coefficient c _{(x, n)} may be obtained by accumulating the obtained product values.

For example, as shown in FIG. 12, two straight lines LN1 and LN2 passing through the correction target pixel P _{(x, n)} are assumed. Each of the straight lines LN1 and LN2 corresponds to the path of the reflected light L4. The correction coefficient determination unit 381 obtains integrated values of pixels on the straight lines LN1 and LN2. Assume that the integrated value on the straight line LN1 is "ΣS1", and the integrated value on the straight line LN1 is "ΣS2". Thereby, the reflected light intensity for each path (straight lines LN1, LN2) of the reflected light L4 diffused from the position of the correction target pixel P _{(x, n)} to the object optical system 23 can be integrated. Therefore, the attenuation received by the reflected light L4 from the position of the correction target pixel P _{(x, n)} diffusing toward the object optical system 23 can be reflected in the correction coefficient C _{(x, n).} .

Further, the correction coefficient determination unit 381 multiplies the integrated values ΣS1 and ΣS2 by weighting coefficients w1 and w2 corresponding to the positions of the straight lines LN1 and LN2. Then, the correction coefficient determination unit 381 may obtain the correction coefficient c _{(x, n)} by integrating these products (w1×ΣS1, w2×ΣS2).

In the imaging device 1, the intensity distribution of the incident light L2 or the reflected light L4 converged by the object optical system 23 is highest on the optical axis AX1 and decreases as the distance from the optical axis AX1 increases in the horizontal direction. That is, the intensity of the incident light L2 from the object optical system 23 toward the depth of the spheroid Sp and the reflected light L4 from the reflecting surface of the spheroid Sp toward the object optical system 23 decreases as the tilt with respect to the optical axis AX1 increases. Also, the greater the intensity of the incident light L2 or the reflected light L4, the more susceptible it is to attenuation. Therefore, focusing on the correction target pixel P _{(x, n)} , the integrated value ΣS1 of the straight line LN1 parallel to the optical axis AX1 is multiplied by the largest weighting factor w1, and the integrated value of the straight line LN2 having a greater inclination θ than the straight line LN1 is obtained. By multiplying ΣS2 by w2, which is smaller than the weighting factor w1, the attenuation received by the incident light L2 or the reflected light L4 along each path is effectively reflected in the correction coefficient c _(x,n) according to the position of the path. can do.

FIG. 13 is a conceptual diagram for explaining another method of obtaining the correction coefficient c _{(x, n)} . In the calculation example of the correction coefficient c _(x,n) shown in FIG. 13, the correction coefficient determination unit 381 sets a three-dimensional accumulation target area RA2 with the correction target pixel P _(x,n) as a starting point. The integration target area RA2 spreads in the X-axis direction and the Y-axis direction from the correction target pixel P _{(x, n)} toward the object optical system 23 side, and more specifically, the correction target pixel P _(x, It is conical with _n) as the vertex. The correction coefficient determination unit 381 obtains the correction coefficient c _(x,n) by integrating the pixel values of the pixels included in the integration target area RA2 set in this way.

In the example shown in FIG. 13, the correction target pixel P _{(x, n)} is not only the pixel value of the pixel group at the same position as the correction target pixel P _{(x, n} ) in the X-axis direction and the Y-axis direction. Pixel values of pixel groups at different positions are also integrated. Therefore, not only the attenuation of the incident light L2 or the reflected light L4 parallel to the Z-axis direction, but also the attenuation of the incident light L2 or the reflected light L4 inclined with respect to the Z-axis direction is included in the correction coefficient c _{(x, n).} can be reflected. Note that pixel values of pixels at different positions in the Y-axis direction are appropriately acquired from a tomographic image showing a plane in the Y-axis direction different from the position of the tomographic image It1.

The shape of the integration target area RA2 may be a shape that matches the path of the incident light L2 focused by the object optical system 23, or a shape that is narrower than that. Also, the shape of the area to be integrated RA2 may be a shape that matches the path of the reflected light L4 incident on the object optical system 23, or a shape that is narrower than that.

<Study on correction factor>
Now consider the correction factor. FIG. 14 is a diagram conceptually showing a plurality of objects P ₁ to P _n arranged in the depth direction inside the object. Here, as shown in FIG. 14, the signal intensity of the reflected light L4 reflected by the n-th object _Pn is examined.

When the incident light L2 passes through the objects P ₁ to P _n−1 , its intensity decreases and it scatters at the objects P _n . Of the scattered light, the scattered light directed toward the object optical system 23 is detected by the photodetector 26 as reflected light L4 after passing through the objects P _n−1 to P ₁ . In FIG. 14, dashed arrows indicate scattered light that is not detected by the photodetector 26 among the light that has passed through each of the objects P1 to Pn. Let I ₁ to I _n denote the intensity of the incident light L2 when it is incident on each of the objects P ₁ to P _n . Further, the intensity of the reflected light L4 immediately after passing through each of the objects P ₁ to P _n is assumed to be I' ₁ to I' _n .

物体Ｐ_{（ｉ＋１）}に入射する入射光Ｌ２の強度Ｉ_ｉ＋１は、式（５）で表される。

Here, in the tomographic image It, the pixel value _Sn of the pixel corresponding to the position of the object _Pn is calculated only from the reflected light L4 from the object _Pn . The objects P ₁ to P _n are sufficiently larger than the wavelength of the incident light L2, and the reflectance, absorption, and transmittance of the objects P ₁ to P _n are independent values. Let R _i be the reflectance, T _i be the transmittance, and α _i be the absorptance of the object P _i (where i is a natural number between 1 and n), and equation (4) holds.

The intensity I _i+1 of the incident light L2 incident on the object P _(i+1) is represented by Equation (5).

Here, if the amount of light intensity loss L _i before and after the incident light L2 is incident on the object P _(i) is defined as in Equation (6), the above Equation (5) becomes Equation (7).

そして、物体Ｐ_ｎでの反射光Ｌ４の強度Ｉ’_ｎは、式（９）で表される。

Let _Rsi be the ratio of light (reflected light L4) that contributes to the generation of the tomographic image It, and _{Rexi be} the ratio of light that does not contribute to the generation of the tomographic image It (scattered light). The intensity In of the incident light _L2 incident on the object _Pn is represented by Equation (8) from Equation (7).

Then, the intensity _I'n of the reflected light L4 at the object _Pn is represented by Equation (9).

Assuming that the intensity of the reflected light L4 from the object _Pn decreases in the same way as in Equation (5) before it passes through the object _P1 again, the intensity _I'1 when it passes through the object _P1 again is given by the equation (10).

仮に、各物体Ｐ_１～Ｐ_ｎを透過する際の損失量をゼロとした場合、画素値Ｓ_ｎの真値Ｓ_{ｎ＿ｔｒｕｅ}は、次の式（１２）に示すように、Ｒｓ_ｎとＩ_１の積に比例する。

しかしながら、入射光Ｌ２の強度は、光路に依存して減衰する。このため、実際の画素値Ｓ_ｎは、真値よりも小さくなる。ここで、式（１３）に示すように、画素値Ｓ_ｎとの積をとることによって、画素値Ｓ_ｎの真値Ｓ_{ｎ＿ｔｒｕｅ}を求めることが可能な補正係数Ｃ_ｎを定義する。

Also, the pixel value _Sn of the tomographic image It finally output is proportional to the intensity _I'1 as shown in equation (11).

Assuming that the amount of loss when passing through each of the objects P ₁ to P _n is zero, the true value S _{n_true} of the pixel value S _n is the value of Rs _n and I ₁ as shown in the following equation (12). Proportional to the product.

However, the intensity of the incident light L2 is attenuated depending on the optical path. Therefore, the actual pixel value _Sn is smaller than the true value. Here, as shown in Equation (13 ₎ , a correction coefficient _Cn is defined that can obtain the true value _{Sn_true} of the pixel value _Sn by multiplying it with the pixel value Sn.

In order to strictly determine the correction coefficient c _n , it is necessary to determine the optical properties of each of the objects P ₁ to P _n on the path of the incident light L2 and to calculate the intensity I _i to each of the objects P ₁ to P _n. There is However, such calculations are not realistic when the object is heterogeneous and heterogeneous, such as a cell. Furthermore, only pixel values are available in the tomographic image It. Therefore, here, the relationship between the correction coefficient _cn and the pixel value _Sn will be examined.

The correction coefficient _cn is represented by the following equation (14) where 1≤k≤n-1. However, n is an integer of 2 or more, and c ₁ =1.

As shown in equation (15), the portion enclosed in curly braces in the fourth line of equation (14) is set to “A”, and Taylor expansion of equation (14) around A=0 yields a correction coefficient C _n is represented by the formula (16).

Considering the right hand side in equation (16) up to the first order terms for "A", ie only the highest order, equation (16) is transformed into equation (17) below.

よって、補正係数ｃ_ｎおよび画素値Ｓ_ｎの関係は、Ｓ_ｋ∝Ｒｓ_ｋ、かつ、Ｓ_ｋがＲｓ_ｎに対して独立であることを用いて、式（１９）で表される。

The loss amounts _Lk and L' _K are given by Equation (18) from the definitions of Equations (6) and (10).

Therefore, the relationship between the correction coefficient c _n and the pixel value S _n is represented by Equation (19) using S _k ∝ Rs _k and that S _k is independent of Rs _n .

Equation (19) states that the correction coefficient c _n for the pixel value derived from the n-th object P _n is proportional to the sum of the pixel values S ₁ to S _n−1 corresponding to the objects P ₁ to P _n−1. indicates Therefore, the sum (integrated value) of the pixel values S ₁ to S _n−1 is defined as a correction coefficient c _n , and the pixel value S _n is multiplied by the correction coefficient C _n to obtain the true value S _{n_true} (corrected value) of the pixel value S _n value) can be obtained.

With respect to equation (16), here we consider a first-order term for "A", but second-order and higher-order terms may also be considered. For example, if up to n-order terms are considered, the value obtained by multiplying the n-th power of each of the pixel values S ₁ to S _n−1 may be used as the correction coefficient C _n for the pixel value S _n . good.

<2. Variation>
Although the embodiments have been described above, the present invention is not limited to the above, and various modifications are possible.

For example, in the above embodiment, the correction processing by the correction processing unit 38 is applied to the reflected light intensity distribution (tomographic image It) acquired by the imaging device 1 based on SD-OCT. However, this correction process can also be applied to correction of reflected light intensity distributions obtained by other OCT-based devices. As other OCT, for example, Swept Source OCT (SS-OCT) and Time Domain OCT (TD-OCT) are known.

In SD-OCT, as described above, the spectroscope 25 disperses the interference light to detect the signal intensity for each wavelength. On the other hand, in SS-OCT, the signal intensity for each wavelength is detected by sweeping the wavelength of light emitted from the light source at high speed. Also, in TD-OCT, by moving the reference mirror, the reflection position is specified from the position of the reference mirror when the intensity increases.

Further, the correction processing by the correction processing unit 38 can also be applied to the reflected electromagnetic wave intensity distribution acquired by imaging devices other than OCT. For example, this correction process can be applied to the reflected light intensity distribution in the depth direction acquired by a confocal microscope.

Also, in the imaging devices 1, 1A, and 1B, the incident light L2 and the reflected light L4 are coaxial, but they are not necessarily coaxial. For example, the reflected light intensity distribution may be acquired by obliquely irradiating the object with the incident light L2 and detecting the reflected light L4 reflected in a direction different from the direction of the incident light L2.

Although the present invention has been described in detail, the above description is, in all aspects, illustrative and not intended to limit the present invention. It is understood that numerous variations not illustrated can be envisioned without departing from the scope of the invention. Each configuration described in each of the above embodiments and modifications can be appropriately combined or omitted as long as they do not contradict each other.

Reference Signs List 1, 1A, 1B imaging device 20, 20A, 20B imaging unit 21 light source (electromagnetic wave source)
22, 227 beam splitter (dividing part)
23 object optical system 26 photodetector 30 control unit 33 signal processing section 38 correction processing section (setting section)
381 correction coefficient determination unit 383 correction calculation unit AX1 optical axis It1, It2 tomographic image (reflected electromagnetic wave intensity distribution)
L2 incident light (incident electromagnetic wave)
L3 reference light (reference electromagnetic wave)
L4 reflected light (reflected electromagnetic wave)
L5 interference light (interference electromagnetic waves)
LN1, LN2 straight line (route)
Sp spheroid (object)

Claims (9)

A correction method for correcting the reflected electromagnetic wave intensity distribution in the depth direction based on the signal intensity of the electromagnetic wave reflected by the object and focused by the object optical system,
(a) setting a correction target position in the reflected electromagnetic wave intensity distribution;
(b) in the reflected electromagnetic wave intensity distribution, a plurality of positions that are closer to the object optical system than the correction target position and that are the same as the correction target position with respect to a plane direction parallel to a plane perpendicular to the depth direction; and a position closer to the object optical system than the correction target position and different from the correction target position with respect to a plane direction parallel to a plane orthogonal to the depth direction a step of determining a correction coefficient based on an integrated value obtained by integrating values relating to reflected electromagnetic wave intensities at a plurality of positions ;
(c) calculating a correction value of the reflected electromagnetic wave intensity at the correction target position by multiplying the reflected electromagnetic wave intensity at the correction target position by the correction coefficient;
Correction methods, including A correction method for correcting the reflected electromagnetic wave intensity distribution in the depth direction based on the signal intensity of the electromagnetic wave reflected by the object and focused by the object optical system,
(a) setting a correction target position in the reflected electromagnetic wave intensity distribution;
(b) determining a correction coefficient based on an integrated value obtained by integrating values relating to the reflected electromagnetic wave intensity at a plurality of positions closer to the object optical system than the correction target position in the reflected electromagnetic wave intensity distribution;
(c) calculating a correction value of the reflected electromagnetic wave intensity at the correction target position by multiplying the reflected electromagnetic wave intensity at the correction target position by the correction coefficient;
including
The step (b) is
accumulating values related to the reflected electromagnetic wave intensity at a position closer to the object optical system than the correction target position and different from the correction target position with respect to a plane direction parallel to a plane perpendicular to the depth direction; including
The step (b) is
(b-1) obtaining the integrated value for each of a plurality of paths connecting the correction target position to the object optical system;
Correction methods, including A correction method according to claim 1 or claim 2,
The step (b) is
A correction method, comprising: accumulating values relating to reflected electromagnetic wave intensity at each position within an integration target area set with the correction target position as a starting point. A correction method according to claim 3,
The correction method, wherein the integration target area has a fan shape extending in the planar direction from the correction target position toward the object optical system. A correction method according to claim 2,
The step (b) is
(b-2) calculating the product of the integrated value of each of the plurality of routes obtained in step ( b -1) and a weighting factor corresponding to the position of each of the plurality of routes;
(b-3) a step of accumulating the product of each of the plurality of paths obtained in step ( b -2);
Further comprising a correction method.
A correction method according to claim 5 ,
In the step (b-2), the weighting factor of each of the plurality of paths increases as the inclination with respect to the depth direction decreases. The correction method according to any one of claims 1 to 6 ,
Said step c) is
(c-1) calculating a product value obtained by multiplying the reflected electromagnetic wave intensity at the correction target position by the correction coefficient;
(c-2) normalizing the product value obtained in step (c-1) according to a predetermined condition;
A correction method, further comprising: A correction device for correcting the reflected electromagnetic wave intensity distribution in the depth direction based on the signal intensity of the electromagnetic wave reflected by the object and focused by the object optical system,
a setting unit that sets a correction target position in the reflected electromagnetic wave intensity distribution;
Reflected electromagnetic waves at a plurality of positions on the object optical system side of the correction target position in the reflected electromagnetic wave intensity distribution, which are the same as the correction target position with respect to a plane direction parallel to a plane orthogonal to the depth direction. an integrated value obtained by accumulating values relating to intensity, and a plurality of positions that are closer to the object optical system than the correction target position and that differ from the correction target position with respect to a plane direction parallel to a plane orthogonal to the depth direction. A correction coefficient determination unit that determines a correction coefficient based on an integrated value obtained by integrating values relating to the reflected electromagnetic wave intensity of
a correction unit that multiplies the reflected electromagnetic wave intensity at the correction target position by the correction coefficient to calculate a correction value for the reflected electromagnetic wave intensity at the correction target position;
a compensator. An imaging device for imaging an object,
a dividing unit that divides an electromagnetic wave emitted from an electromagnetic wave source into an electromagnetic wave for irradiation and an electromagnetic wave for reference;
an object optical system that converges the electromagnetic wave for irradiation and makes it incident on an object, and converges the electromagnetic wave reflected by the object;
a detector that outputs an interference signal according to the signal strength of the interference electromagnetic wave by detecting the interference electromagnetic wave between the electromagnetic wave from the object focused by the object optical system and the reference electromagnetic wave;
a signal processing unit that processes the interference signal to generate a reflected electromagnetic wave intensity distribution representing an intensity distribution of the electromagnetic wave reflected by the object in a depth direction;
a correction device according to claim 8 ;
An imaging device comprising:

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