Optical systems, endoscopes and medical image processing systems

Abstract

The present disclosure relates to an optical system, an endoscope, and a medical image processing system that can adjust the effect of extending the depth of field. The medical image processing system is provided with: a light source that illuminates an observation target with light; an image control unit that controls the imaging of the observation target illuminated with light; and a mirror that is made in a cylindrical shape using a rigid or flexible material; a camera that has a built-in imaging element for capturing images; and an endoscope that has an optical element insertion portion that is arranged between the lens barrel and the camera. The optical element insertion unit includes two or more optical elements that have an effect of extending the depth of field, and at least one of the optical elements is movable. The present technology can be applied to a medical image processing system including an EDOF optical system, for example.

Description

Technical Field

[0001] The present disclosure relates to an optical system, an endoscope, and a medical image processing system, and more particularly to an optical system, an endoscope, and a medical image processing system capable of adjusting the effect of extending the depth of field. Background Art

[0002] Generally, medical observation devices such as endoscopes and microscopes usually acquire images with a shallow depth of field. However, in many cases the surgical area is deep, and a medical observation device with a deep depth of field is required.

[0003] In view of this, in order to increase the depth of field, an endoscope, a microscope, or the like including an extended depth of field (EDOF) optical system for extending the depth of field has been proposed.

[0004] For example, the image processing device disclosed in patent document 1 includes an EDOF optical system, which includes a birefringent mask and a control unit, which uses a function for adjusting the blur amount according to conditions and enables the object image to be observed in a more appropriate manner according to the state, situation, etc. of observation of the object image.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2017-158764 Summary of the invention

[0008] Problems to be solved by the present invention

[0009] However, in conventional EDOF optical systems, noise may be generated in an image or the modulation transfer function may be reduced in a trade-off with the extension of the depth of field. Therefore, depending on the medical scenario, it is necessary to, for example, increase, reduce, cause or eliminate the effect of extending the depth of field. However, an EDOF optical system that meets this need has not yet been provided.

[0010] The present invention takes this situation into consideration, and an object thereof is to provide an EDOF optical system capable of adjusting the effect of extending the depth of field.

[0011] Problem Solution

[0012] An optical system according to one aspect of the present disclosure includes two or more optical elements having an effect of extending a depth of field, and at least one of the optical elements is movable.

[0013] An endoscope according to one aspect of the present disclosure includes: a scope having a tubular shape and made of a rigid or flexible material; and a camera including an imaging element for capturing an image, wherein: the imaging element receives light that has passed through an optical system including two or more optical elements having an effect of extending the depth of field; and at least one of the optical elements is movable.

[0014] A medical image processing system according to one aspect of the present disclosure includes: a light source that illuminates an observation target with light; an image capture control unit that controls the capture of an image of the observation target illuminated with light; and an endoscope including a mirror having a tubular shape and made of a rigid or flexible material and a camera including an imaging element that captures an image, wherein: the imaging element receives light that has passed through an optical system including two or more optical elements having an effect of extending depth of field; and at least one of the optical elements is movable.

[0015] In one aspect of the present disclosure, two or more optical elements having an extended depth of field effect are provided, and at least one of the optical elements is movable. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a block diagram showing a configuration example of an embodiment of a medical image processing system to which the present technology is applied.

[0017] Figure 2 It is a diagram for explaining the characteristics of a birefringent mask.

[0018] Figure 3 An example of the change in the modulation transfer function of a series optical system caused by inserting a birefringent mask is shown.

[0019] Figure 4 Shows a cross-sectional configuration example of a camera head and an optical element insertion unit.

[0020] Figure 5 A first configuration example of the EDOF optical system is shown.

[0021] Figure 6 A state in which the movable birefringence mask is rotated by 45 degrees is shown.

[0022] Figure 7 A second configuration example of the EDOF optical system is shown.

[0023] Figure 8 A third configuration example of the EDOF optical system is shown.

[0024] Fig. 9 A fourth configuration example of the EDOF optical system is shown. DETAILED DESCRIPTION

[0025] Hereinafter, specific embodiments to which the present technology is applied will be described in detail with reference to the accompanying drawings.

[0026] <Configuration Example of Medical Image Processing System>

[0027] Figure 1 is a block diagram showing a configuration example of an embodiment of a medical image processing system to which the present technology is applied.

[0028] like Figure 1 As shown, the medical image processing system 11 is formed by installing various endoscopic surgery devices on a cart 13 on which a display device 12 is placed, and for example, the medical image processing system 11 can perform image processing on an image acquired by an endoscope 14 for endoscopic surgery.

[0029] The display device 12 displays an image acquired by the endoscope 14 , an image obtained by performing image processing on the image, and the like.

[0030] exist Figure 1 In the example shown in FIG. 1 , a light source device 21 , a camera control unit (CCU) 22 , and a signal processing device 23 are installed on a cart 13 .

[0031] The light source device 21 includes, for example, an LED, a xenon lamp, a halogen lamp, a laser light source, or a light source corresponding to a combination thereof, and supplies irradiation light emitted toward an observation target to the endoscope 14 through a light guide.

[0032] The CCU 22 controls image capturing by the imaging element included in the camera head 32 , thereby providing an image of the observation target captured by the imaging element.

[0033] The signal processing device 23 performs signal processing based on the image acquired by the endoscope 14, thereby performing image processing on the image. For example, as described below, the signal processing device 23 performs signal processing to which the EDOF technique using a birefringence mask is applied, thereby performing image processing for further extending the depth of field of the image captured by the imaging element of the camera 32.

[0034] The endoscope 14 includes a lens barrel 31 and a camera head 32, and may include an optical element insertion unit 33 between the lens barrel 31 and the camera head 32. Note that, for example, not only a structure in which the optical element insertion unit 33 is detachable from the lens barrel 31 and the camera head 32 but also a structure in which the optical element insertion unit 33 is a part of the lens barrel 31, a structure in which the optical element insertion unit 33 is a part of the camera head 32, or other structures may be adopted.

[0035] The lens barrel 31 is a mirror with a tubular shape and made of rigid or flexible materials, and the part of the mirror from its far-end predetermined length is inserted into the body cavity of the patient. For example, the far-end of the lens barrel 31 has an opening, and the object lens is assembled into this opening. In addition, the side of the lens barrel 31 has an introduction part for introducing the light produced in the light source device 21 into the lens barrel 31. The introduction part is connected with the light source device 21 by light guide. Then, the light introduced into the lens barrel 31 is guided to the far-end of the lens barrel 31 by the light guide extending in the lens barrel 31, and is emitted to the observation target in the patient's body cavity by the object lens.

[0036] As later see Figure 4 As described above, the camera 32 includes an imaging element 53 that captures an image, an image forming optical system 51 that forms an image of an observation target, a diaphragm 52 that adjusts the amount of light, etc., and captures an image under the control of the CCU 22, thereby providing the image to the CCU 22.

[0037] The optical element insertion unit 33 provided between the lens barrel 31 and the camera 32 is a unit into which an optical element such as a birefringent mask (BM) 41 can be inserted. Note that examples of optical elements that can be inserted into the optical element insertion unit 33 include a cubic phase mask. Figure 4 The detailed configuration of the optical element insertion unit 33 is described.

[0038] For example, in the medical image processing system 11, various optical elements are inserted between the lens barrel 31 and the camera head 32 by using the optical element insertion unit 33. This makes it possible to change the optical characteristics of the series of optical systems that form an image of a subject on the imaging element in the camera head 32, thereby adjusting the blur amount of the image to be captured (for example, controlling the depth of field).

[0039] Here, the configuration of the optical element to be inserted into the optical element insertion unit 33 provided between the lens barrel 31 and the camera head 32 of the endoscope 14 will be described.

[0040] In recent years, the resolution of imaging elements (so-called image sensors) used in imaging devices such as cameras has increased. "HD (1280×720)" imaging elements, as well as "4K UHD (3840×2160)" and "8K UHD (7680×4320)" imaging elements have been proposed. Therefore, it is also desirable that medical observation devices (imaging devices) such as the endoscope 14 according to the present embodiment capture higher resolution images. At the same time, as the resolution increases, the pixel size of the imaging element tends to be smaller, and thus the amount of light gathered by each pixel tends to decrease relatively. In this case, for example, the insufficient amount of light can be compensated by further opening the aperture (i.e., further reducing the f-number). However, when the aperture is opened, the depth of field may be further reduced.

[0041] In view of the above, for example, a technique called EDOF for extending the depth of field can be applied. In this EDOF technique, the EDOF technique using a birefringent mask is applied to the endoscope 14 according to the present embodiment. This makes it possible to further extend the depth of field of the image to be captured. Specifically, as described above, the endoscope 14 according to the present embodiment is set so that the optical element can be inserted into the optical element insertion unit 33 provided between the lens barrel 31 and the camera 32, and the depth of field of the image to be captured is controlled by inserting the birefringent mask as the optical element.

[0042] For example, Figure 1 3. As an example of the birefringent mask 41 inserted into the optical element insertion unit 33, the configuration of the birefringent mask 41 as viewed from the optical axis direction of the camera 32 is shown. Figure 1 The birefringent mask 41 is Figure 1 The horizontal direction in the portion surrounded by the dotted line in is the x direction, the vertical direction therein is the y direction, and the depth direction therein (i.e., the optical axis direction of the camera 32) is the z direction. In addition, in the following description, unless otherwise defined, the optical axis direction (i.e., the depth direction) of the imaging element included in the camera 32 is the z direction, and the horizontal direction and the vertical direction (i.e., the direction perpendicular to the optical axis) of the image to be captured by the imaging element are the x direction and the y direction.

[0043] In the birefringent mask 41, a plurality of elementary polarization members 42 are arranged concentrically from the vicinity of the center to the outside, and Figure 1 In the example of the present invention, three polarization elements 42a to 42c are arranged. That is, in the birefringent mask 41, the three polarization elements 42a to 42c are arranged concentrically on the xy plane perpendicular to the optical axis. Figure 1 , arrows drawn in the birefringence mask 41 schematically indicate polarization directions of the polarization elements 42 in which the respective arrows are drawn. That is, the polarization elements 42a to 42c are arranged so that adjacent polarization elements have different (substantially orthogonal) polarization directions.

[0044] For example, in Figure 1 In the example of FIG. 4 , the polarization direction of the polarization element 42a is the x direction. Meanwhile, the polarization direction of the polarization element 42b adjacent to the polarization element 42a is the y direction, which is a direction rotated 90 degrees from the polarization direction (x direction) of the polarization element 42a. Similarly, the polarization direction of the polarization element 42c adjacent to the polarization element 42b is the x direction, which is a direction rotated 90 degrees from the polarization direction (y direction) of the polarization element 42b.

[0045] With such a configuration, light collected by the lens barrel 31 is incident on any one of the polarization elements 42a to 42c of the birefringent mask 41, depending on the position perpendicular to the optical axis (z direction) on the xy plane, and light polarized by one of the polarization elements 42a to 42c is incident on the camera 32.

[0046] Here, we will refer to Figure 2 describe Figure 1 Characteristics of the birefringent mask 41 in FIG.

[0047] Figure 2 : is an explanatory diagram for describing the characteristics of the birefringence mask 41 according to the present embodiment. Specifically, Figure 2 A is an example in which the birefringence mask 41 is not sandwiched between the lens barrel 31 and the camera 32, and schematically shows an optical path in which light collected by the lens barrel 31 is guided to the camera 32. In addition, Figure 2 B is an example in which the birefringence mask 41 is sandwiched between the lens barrel 31 and the camera 32 , and schematically shows the optical path of light to be collected by the lens barrel 31 and guided to the camera 32 via the birefringence mask 41 .

[0048] like Figure 2 As shown in FIG. 1A , the light collected by the lens barrel 31 is guided to the optical path of the camera 32 and is controlled by the image forming optical system of the camera 32 so that an image is formed on the image plane of the imaging element. Figure 2 In A, image v11 is a schematic object image formed at position p11. In addition, image v13 is a schematic object image formed at position p13.

[0049] At the same time, if Figure 2 As shown in FIG. 1B , the light collected by the lens barrel 31 is guided to the camera 32 through the birefringence mask 41 , and its optical path is controlled by the image forming optical system of the camera 32 . Figure 2 In B, image v21 is a schematic object image formed at position p11. In addition, image v23 is a schematic object image formed at position p13.

[0050] By comparing these images, it can be seen that the characteristics of the series optical system (hereinafter, also referred to as "series optical system") for forming the object image on the imaging element of the camera 32 are changed by inserting the birefringence mask 41. Specifically, when the birefringence mask 41 is inserted, the shape of the formed image of the object image (i.e., point spread function (PSF)) changes less between the position p11 and the position p13 than before the birefringence mask 41 is inserted.

[0051] For example, Figure 31 is an explanatory diagram for describing an example of the characteristics of the birefringence mask 41 applied to the endoscope 14 of the present embodiment, and shows an example of a change in the modulation transfer function (MTF) of the series optical system caused by inserting the birefringence mask 41.

[0052] exist Figure 3 In , the horizontal axis represents the deviation (i.e., the defocus amount) from the image forming plane (i.e., the in-focus position) of the series optical system in the optical axis direction, and the vertical axis represents the modulation transfer function (MTF). Figure 3 In FIG. 1 , the graph g11 shows an example of the modulation transfer function (MTF) of the series optical system, which is Figure 2 The birefringence mask 41 shown in A of FIG. 1 is obtained without inserting the birefringence mask 41 between the lens barrel 31 and the camera 32. In addition, the graph g13 shows an example of the modulation transfer function (MTF) of the series optical system, which is obtained when the birefringence mask 41 is not inserted between the lens barrel 31 and the camera 32. Figure 2 FIG. 1B is obtained when the birefringence mask 41 is inserted between the lens barrel 31 and the camera 32 .

[0053] like Figure 3 As shown, when the birefringence mask 41 is applied, the characteristics of the series optical system are changed so that the modulation transfer function (MTF) is distributed in a wider range in the optical axis direction compared to before the birefringence mask 41 is applied. That is, the depth of field can be further extended by applying the birefringence mask 41.

[0054] At the same time, as Figure 3 It can be seen that in the case where the birefringence mask 41 is applied, the value of the modulation transfer function (MTF) at the in-focus position decreases from the value before the birefringence mask 41 is applied. In view of this, Figure 2 As shown in FIG. 1B , the medical image processing system 1 according to the present embodiment performs restoration processing (image processing) on ​​the image captured by the camera 32, thereby restoring the image with respect to image degradation (so-called blur) of the object image caused by the reduction of the modulation transfer function (MTF). For example, in Figure 2 In B, image v25 is an example of a restored object image obtained by performing restoration processing on object image v23. Note that examples of restoration processing (e.g., processing for adjusting the amount of blur) include processing called deconvolution. Of course, the restoration processing applied to the image of the object image is not necessarily limited to deconvolution as long as it is possible to restore the degradation of the image.

[0055] Through the above-described control, it is possible to obtain, for example, an image in which the depth of field is extended and the observation target is more clearly presented (ie, a clearer image).

[0056] <Study of EDOF technology using birefringence mask>

[0057] A description will be given of technical problems caused by applying the EDOF technique using a birefringence mask as in the medical image processing system according to the present embodiment.

[0058] In the case of extending the depth of field by a combination of a birefringence mask and image processing (restoration processing), the details of the processing performed as the image processing are designed on the assumption that the optical characteristics of the birefringence mask and other optical systems are known.

[0059] Here, in the EDOF technology using a birefringent mask as described above, for example, a process called deconvolution for removing blur from an image captured by an optical system including a birefringent mask is applied as image processing. In the deconvolution, blur caused by inserting a birefringent mask is removed by adaptively switching the filter coefficient of the applied filter according to the optical characteristics of the optical system including the birefringent mask.

[0060] Note that examples of deconvolution filters include an inverse filter and a Wiener filter. The inverse filter corresponds to a filter designed, for example, based on the optical characteristics (e.g., modulation transfer function (MTF) etc.) of an optical system including a birefringent mask (e.g., the barrel of an endoscope etc.). That is, the inverse filter can be designed to have, for example, an inverse characteristic of the modulation transfer function of the optical system.

[0061] Furthermore, the spatial frequency characteristic WF of the Wiener filter is expressed by the following expression (1).

[0062] [Expression 1]

[0063]

[0064] In expression (1), in the case where the directions horizontal to the image plane and orthogonal to each other are the x and y directions, u and v represent the spatial frequencies in the x and y directions, respectively. In addition, H(u, v) represents the optical transfer function (OTF). Note that H * (u, v) represents the complex conjugate of H(u, v). In addition, S f (u, v) and S n (u, v) represent the power spectra of the original image and the noise respectively.

[0065] Meanwhile, medical devices such as a camera head and a lens barrel (e.g., a rigid mirror or a flexible mirror) of an endoscope used in a medical field such as surgery are sterilized by high pressure (high pressure steam) each time they are used. Therefore, in the case where, for example, the endoscope is repeatedly sterilized by high pressure, the optical characteristics of the optical system (i.e., the rigid mirror or the flexible mirror) of the endoscope, in particular, the optical characteristics of the birefringent mask may gradually change. In this case, the optical characteristics of the birefringent mask (i.e., the changed optical characteristics) may be different from the optical characteristics assumed in the image signal processing, thereby affecting the image quality of the image to be output.

[0066] Specifically, an example of the optical characteristics of the birefringent mask includes a parameter indicating a phase difference of light called retardation. The retardation is represented by the product Δnd of the refractive index difference Δn (=ne-no) and the thickness d of the birefringent substance. In the case where a so-called autoclave treatment (high-pressure steam treatment) such as an autoclave sterilization treatment is performed on the birefringent mask, a change in the characteristic of the refractive index difference Δn of the birefringent mask (i.e., a decrease in the refractive index difference Δn) can be estimated. For example, a decrease in the value of the refractive index difference Δn weakens the effect on the extended depth of field.

[0067] Thus, in the case where the delay of the birefringent mask changes as described above, in the case where image processing (restoration processing) similar to that before the delay change is performed on an image captured using the birefringent mask, it is highly likely that the output image has so-called over-emphasized image quality. Therefore, in some cases, it is desirable to adaptively switch the details of the image processing according to the change in the delay of the birefringent mask to output an image with more appropriate image quality.

[0068] Note that in the case where only a birefringent mask is provided, the optical properties (retardation) of the birefringent mask are measurable. However, in some cases, the birefringent mask is incorporated as part of the optical system of an endoscope (e.g., a rigid mirror), the optical system of a camera, etc., and in this case, it is difficult to measure the optical properties of the birefringent mask alone.

[0069] In addition, restoration processing is performed based on the PSF information. The PSF information is acquired based on the measurement result of the point spread function of the input image of the image captured by the camera 32. Therefore, the degradation (i.e., blur) of the image of the object image can be restored. An example of restoration processing includes so-called deconvolution. As a more specific example, image processing (e.g., filtering processing) based on the inverse characteristics of the acquired PSF information is performed on the input image, thereby restoring the image degradation (blur) caused by the optical characteristics indicated by the PSF information. Of course, the restoration processing performed on the input image is not necessarily limited to deconvolution, as long as the image degradation of the object image can be improved based on the PSF information. For example, a restoration processing using machine learning or the like can be adopted.

[0070] Here, the restoration process using machine learning can restore the degradation of the image by, for example, performing the following learning process. First, learning data including a pair of unstored and restored images is prepared. Next, the learning data is input to a predetermined learning model to perform learning, thereby generating parameters for estimating the restored image from the unstored image. Then, the unstored image is input to a restored image generation model adjusted using the parameters, thereby generating a restored image. Note that the learning model and the restored image generation model are preferably computational models using a multi-layer neural network, and more preferably a computational model using a reinforcement learning method using a multi-layer neural network.

[0071] Next, see Figure 4 The arrangement of the camera head 32 and the optical element insertion portion 33 will be described.

[0072] like Figure 4 As shown, an image forming optical system 51 , a diaphragm 52 , and an imaging element 53 are arranged in the camera 32 along an optical axis.

[0073] In the optical element insertion unit 33, a fixed birefringence mask 61, a movable birefringence mask 62, a driving unit 63, and an angle detection unit 64 are provided. The optical element insertion unit 33 is provided with a switch 65.

[0074] In the fixed birefringence mask 61 and the movable birefringence mask 62, for example, with reference Figure 1 The polarization elements 42a to 42c similar to the polarization element of the described birefringent mask 41 are arranged to form an EDOF optical system. For example, the fixed birefringent mask 61 is fixedly attached to the optical element insertion unit 33, and the movable birefringent mask 62 is rotatably attached to the optical element insertion unit 33 around the optical axis.

[0075] The driving unit 63 includes a motor for rotationally driving the movable birefringent mask 62 , a rotation transmission mechanism, and the like.

[0076] The angle detection unit 64 includes an encoder that detects the angle of the movable birefringence mask 62 rotated according to the rotational drive of the drive unit 63. For example, as described below, the angle detected by the angle detection unit 64 is used to stop the rotational drive of the movable birefringence mask 62 at a predetermined angle, such as 90 degrees or 45 degrees.

[0077] The switch 65 is an operation unit that is operated when instructing to rotationally drive the movable birefringence mask 62. For example, in response to the operation of the switch 65, the drive unit 63 can rotationally drive the movable birefringence mask 62 based on the angle detected by the angle detection unit 64.

[0078] The camera 32 and the optical element insertion unit 33 are configured as described above, and light from the observation target is incident on the camera 32 through the EDOF optical system including the fixed birefringence mask 61 and the movable birefringence mask 62. Therefore, the image captured by the imaging element 53 can have the EDOF effect of the EDOF optical system.

[0079] <Configuration example of EDOF optical system>

[0080] will be referred to Figures 5 to 9 to describe a configuration example of the EDOF optical system including the fixed birefringence mask 61 and the movable birefringence mask 62.

[0081] Figure 5 The first configuration example of the EDOF optical system is shown.

[0082] Figure 5 The example in the upper part of shows such a state in which the movable birefringence mask 62 is fixed so that the polarization directions of the polarization elements 42a to 42c of the fixed birefringence mask 61 are the same as the polarization directions of the polarization elements 42a to 42c of the movable birefringence mask 62. In this state, that is, when the polarization elements 42a to 42c of the same design are arranged to overlap each other so that the birefringence mask has a rotation angle of 0 degrees, the ordinary EDOF effect, that is, 100% of the EDOF effect, can be obtained.

[0083] Then, when the movable birefringence mask 62 is rotated by 90 degrees, as in the example in the lower part of Figure 5 the polarization directions of the polarization elements 42a to 42c of the fixed birefringence mask 61 are orthogonal to the polarization directions of the polarization elements 42a to 42c of the movable birefringence mask 62 at 90 degrees to each other. In such a state, that is, when the polarization elements 42a to 42c of the same design are arranged to overlap each other so that the birefringence mask has a rotation angle of 90 degrees, the phase difference of light is eliminated. As a result, 0% of the EDOF effect (elimination of the EDOF effect) can be obtained.

[0084] As described above, the EDOF optical system including the fixed birefringence mask 61 and the movable birefringence mask 62 can cause or eliminate the EDOF effect.

[0085] Furthermore, the EDOF effect can be obtained at a desired rate of change by adjusting the relative angle between the polarization directions of the polarization elements 42a to 42c of the fixed birefringence mask 61 and the polarization directions of the polarization elements 42a to 42c of the movable birefringence mask 62 within the range of 0 degrees and 90 degrees. That is, the EDOF effect can be increased or decreased by rotationally driving the movable birefringence mask 62 so that the movable birefringence mask 62 has an arbitrary angle.

[0086] For example, in Figure 6 In the state where the movable birefringence mask 62 is rotated 45 degrees as shown, an EDOF effect of an appropriate percentage between a normal EDOF effect (i.e., an EDOF effect of 100%) and an EDOF effect of 0% can be obtained. At this time, even in the state where the movable birefringence mask 62 is rotated 45 degrees, a 50% EDOF effect cannot always be obtained, and the rate of change of the characteristics may be different depending on the design of the patterns of the polarization elements 42a to 42c.

[0087] Figure 7 A second configuration example of the EDOF optical system is shown.

[0088] like Figure 7 As shown, in the fixed birefringent mask 61A, a non-polarizing element 43b having no polarization characteristics is arranged between the polarizing element 42a and the polarizing element 42c. In other words, in the fixed birefringent mask 61A, only the even-numbered rings are polarizing elements, and the odd-numbered rings are non-polarizing elements. For example, in the fixed birefringent mask 61A, the non-polarizing element 43b is replaced with the even-numbered rings. Figure 5 The polarizing element 42b of the fixed birefringent mask 61 is shown in FIG.

[0089] In addition, in the movable birefringent mask 62A, the polarizing element 42b is arranged between the non-polarizing elements 43a and 43c that do not have polarization characteristics. In other words, in the movable birefringent mask 62A, only the odd-numbered rings are polarizing elements, and the even-numbered rings are non-polarizing elements. For example, in the movable birefringent mask 62A, Figure 5 The polarization element 42a and the polarization element 42c of the movable birefringent mask 62 are replaced with the non-polarization element 43a and the non-polarization element 43c.

[0090] Figure 7 The example in the upper part of FIG. 1 shows a state in which the polarization directions of the polarization elements 42a and 42c of the fixed birefringent mask 61A and the polarization direction of the polarization element 42b of the movable birefringent mask 62A are orthogonal to each other at 90 degrees. That is, in this case, the fixed birefringent mask 61A and the movable birefringent mask 62A viewed in the optical axis direction have the same Figure 1A similar configuration to the birefringent mask 41 in FIG. 4 is used, and a normal EDOF effect, that is, an EDOF effect of 100% can be obtained.

[0091] Then, in the case where the movable birefringence mask 62A is rotated 90 degrees, as in Figure 7 In the example of the lower part of the embodiment, the polarization directions of the polarization elements 42a and 42c of the fixed birefringent mask 61A and the polarization direction of the polarization element 42b of the movable birefringent mask 62A are consistent with each other. In this state, all polarization directions are aligned. As a result, 0% EDOF effect (EDOF effect elimination) can be obtained.

[0092] As described above, the EDOF optical system including the fixed birefringence mask 61A and the movable birefringence mask 62A can cause or eliminate the EDOF effect. In addition, as described above, by adjusting the angle of the movable birefringence mask 62A, the EDOF effect can be obtained at a desired rate of change.

[0093] Furthermore, in the case where the EDOF optical system includes a pair of masks such as the fixed birefringent mask 61A and the movable birefringent mask 62A to, for example, halve the delay indicating the phase difference, the two masks can be the same member compared to the EDOF optical system including only a single mask. This provides a great advantage in terms of manufacturing, for example.

[0094] Figure 8 A third configuration example of the EDOF optical system is shown.

[0095] like Figure 8 As shown, the fixed birefringent mask 61B is divided into four sectors in a cross shape at its center, so that the upper left sector and the lower right sector serve as polarization elements 44a to 44c (the polarization directions are similar to the polarization directions of the upper left and lower right parts of the polarization elements 42a to 42c), and the upper right sector and the lower left sector serve as non-polarization elements 46.

[0096] In addition, the movable birefringent mask 62B is divided into four sectors in a cross shape at its center, so that the upper right sector and the lower left sector serve as polarization elements 45a to 45c (the polarization directions are similar to the polarization directions of the upper right and lower left parts of the polarization elements 42a to 42c), and the upper left sector and the lower right sector are non-polarization elements 46.

[0097] Figure 8 The example in the upper part of FIG. 6 shows a state in which the polarization directions of the polarization elements 44a to 44c of the fixed birefringence mask 61B and the polarization directions of the polarization elements 45a to 45c of the movable birefringence mask 62B coincide with each other. That is, in this case, the fixed birefringence mask 61B and the movable birefringence mask 62B viewed in the optical axis direction have the same Figure 1 The birefringence mask 41 in FIG. 4 is configured similarly, and a normal EDOF effect, that is, a 100% EDOF effect can be obtained.

[0098] Then, in the case where the movable birefringence mask 62B is rotated 90 degrees, as in Figure 8 In the example of the lower part of the embodiment, the polarization directions of the polarization elements 44a to 44c of the fixed birefringent mask 61B and the polarization directions of the polarization elements 45a to 45c of the movable birefringent mask 62B are orthogonal to each other at 90 degrees. In this state, the phase difference of light is eliminated. As a result, a 0% EDOF effect (EDOF effect elimination) can be obtained.

[0099] As described above, the EDOF optical system including the fixed birefringence mask 61B and the movable birefringence mask 62B can cause or eliminate the EDOF effect. In addition, as described above, by adjusting the angle of the movable birefringence mask 62B, the EDOF effect can be obtained at a desired rate of change.

[0100] Fig. 9 A fourth configuration example of the EDOF optical system is shown.

[0101] For example, Fig. 9 An example of a configuration in which a fixed birefringence mask 61C and a movable birefringence mask 62C correspond to two diameters (eg, 10 mm and 4 mm) of a rigid mirror is shown.

[0102] For example, in order to obtain the EDOF effect in two types of rigid mirrors having diameters of 10 mm and 4 mm, in the case where the diameter of the rigid mirror is 10 mm, light passes through all the circular polarization elements provided in the birefringent mask, whereas in the case where the diameter of the rigid mirror is 4 mm, light passes through only a limited number of circular polarization elements near the center. By such a configuration, the first fixed birefringent mask 61C has the same characteristics as the general birefringent mask 41 ( Figure 1 ) and the second movable birefringence mask 62C has a configuration in which a circular polarization element is provided only in the vicinity of its center.

[0103] That is, the polarization elements 42a to 42c and Figure 1 4 is arranged in the fixed birefringent mask 61C as in the birefringent mask 41 in FIG. Meanwhile, in the movable birefringent mask 62C, the same polarizing element 42a is provided, but the polarizing element 47b has an outer shape smaller than the polarizing element 42b. Furthermore, in the movable birefringent mask 62C, a non-polarizing element 48c wider than the polarizing element 42c is arranged outside the polarizing element 42b. Note that in Fig. 9, the two-dot chain line in the fixed birefringence mask 61C represents the outer shape of the polarization element 47b, and the two-dot chain line in the movable birefringence mask 62C represents the outer shape of the polarization element 42b.

[0104] also, Fig. 9 The example in the upper part shows a state in which the polarization directions of the polarization elements 42a and 42b of the fixed birefringent mask 61C and the polarization directions of the polarization elements 42a and 47b of the movable birefringent mask 62C are orthogonal to each other at 90 degrees. Therefore, in this case, the phase difference of light is eliminated. Therefore, a 0% EDOF effect (EDOF effect elimination) can be obtained in a rigid mirror with a diameter of 4 mm, and an EDOF effect can be obtained to a certain extent in a rigid mirror with a diameter of 10 mm.

[0105] Then, in the case where the movable birefringence mask 62B is rotated 90 degrees, as in Fig. 9 In the example of the lower part of FIG. 6 , the polarization directions of the polarization elements 42a and 42b of the fixed birefringent mask 61C and the polarization directions of the polarization elements 42a and 47b of the movable birefringent mask 62C coincide with each other. Therefore, in this case, the fixed birefringent mask 61C and the movable birefringent mask 62C viewed in the optical axis direction have the same polarization direction as FIG. Figure 1 The birefringence mask 41 in FIG. 4 is configured similarly, and a normal EDOF effect, that is, a 100% EDOF effect can be obtained.

[0106] Note that the fixed birefringence mask 61 and the movable birefringence mask 62 included in the EDOF optical system preferably have exactly the same size in consideration of ease of installation. Of course, the fixed birefringence mask 61 and the movable birefringence mask 62 may have different sizes.

[0107] In addition, the fixed birefringence mask 61 and the movable birefringence mask 62 are usually installed at the pupil position, so the two masks are installed as close as possible. In addition, the fixed birefringence mask 61 and the movable birefringence mask 62 are installed to overlap inside the optical element insertion unit 33. In addition, instead of providing the optical element insertion unit 33, the EDOF optical system may include one of the birefringence masks in the camera head 32 and the other of the birefringence masks in the lens barrel 31.

[0108] In addition, the EDOF effect can be caused, eliminated, increased or reduced, for example, by adopting a mechanism other than the rotational drive mechanism, such as a movable birefringence mask 62. For example, instead of the movable birefringence mask 62, a birefringence mask having a parallel movement (shift) mechanism or a birefringence mask having an upward flip (flip) mechanism can be adopted.

[0109] In addition, the signal processing device 23 can adjust the parameters of the image signal processing for causing the EDOF effect in association with the rotation angle of the movable birefringence mask 62 .

[0110] Note that the rotation angle of the movable birefringence mask 62 can be changed stepwise or continuously. In addition, the rotation range of the movable birefringence mask 62 can be limited to from 0 to 90 degrees, or can be rotated without restriction. For example, in the case of limiting the rotation range of the movable birefringence mask 62, it is preferred to provide a locking mechanism that prevents rotation beyond the limit.

[0111] Furthermore, the movable birefringence mask 62 may be rotationally driven by using a motor such as the driving unit 63, or may be manually rotated by a user.

[0112] Furthermore, even in the case where the rotation angle of the movable birefringence mask 62 is displayed and presented to the user, it is difficult for the user to intuitively recognize the EDOF effect caused by the rotation angle. Therefore, the degree of the EDOF effect may be presented to the user in association with the rotation angle of the movable birefringence mask 62. For example, a rotation angle of the movable birefringence mask 62 of 0 degrees presents a strong EDOF effect, a rotation angle of 45 degrees presents a moderate EDOF effect, a rotation angle of 60 degrees presents a weak EDOF effect, and a rotation angle of 90 degrees presents no EDOF effect.

[0113] In the above-described manner, the medical image processing system 11 can be used in the following usage scenarios by causing or eliminating the EDOF effect.

[0114] That is, by controlling the rotation angle of the movable birefringence mask 62 at high speed, the EDOF effect can be sequentially induced or eliminated. Therefore, the medical image processing system 11 can alternately capture images with the EDOF effect and images without the EDOF effect. Then, the two images are displayed separately to allow the user to simultaneously observe the presence / absence of the EDOF effect in the form of a moving image. Note that in this case, the frame rate is reduced to about half of the original.

[0115] Furthermore, in a case where the user is annoyed by noise in a moving image, the medical image processing system 11 may weaken the EDOF effect by controlling the rotation angle of the movable birefringence mask 62 to suppress the noise.

[0116] Furthermore, the type of the endoscope 14 used in the medical image processing system 11 can be identified, and the rotation angle of the movable birefringence mask 62 can be controlled according to the type. Therefore, in the medical image processing system 11, an appropriate EDOF effect can be selected according to the type of the endoscope 14. This enables more appropriate observation.

[0117] For example, in the case of switching general visible light observation to special light observation such as fluorescence observation, the medical image processing system 11 controls the rotation angle of the movable birefringence mask 62 to control the EDOF effect, thereby providing more appropriate observation.

[0118] In addition, the EDOF optical system only needs to include at least two or more birefringent masks, and for example may include a combination of N or more (N≥2) fixed birefringent masks 61 and at least M (N≥M≥1) movable birefringent masks 62 to adjust the EDOF effect.

[0119] Note that by using a wavefront encoding filter or a chromatic aberration filter as an optical element having an EDOF effect, instead of a birefringent mask, it is possible to have an effect similar to that of a birefringent mask.

[0120] <Configuration combination example>

[0121] Note that the present technology can have the following configurations. (1)

[0123] An optical system comprising:

[0124] Two or more optical elements having the effect of extending the depth of field, wherein

[0125] At least one optical element is movable. (2)

[0127] The optical system according to (1), wherein

[0128] The optical elements are birefringent masks in each of which polarization elements having predetermined polarization directions are arranged in combination. (3)

[0130] The optical system according to (2), wherein:

[0131] The optical element is a combination of N or more (N≥2) first birefringent masks and at least M (N≥M≥1) second birefringent masks, and the second birefringent masks are movable. (4)

[0133] The optical system according to (2) or (3), wherein

[0134] The optical element is a fixed first birefringent mask and a second birefringent mask rotatable around an optical axis, and the effect of extending the depth of field is adjusted by relatively changing the polarization directions of the polarization elements of the first birefringent mask and the second birefringent mask. (5)

[0136] The optical system according to (4), wherein:

[0137] In the first birefringence mask and the second birefringence mask, a plurality of polarization elements are concentrically arranged outward from near the center, and a polarization direction of each polarization element is rotated 90 degrees from a polarization direction of an adjacent one of the polarization elements; and

[0138] The effect of extending the depth of field is adjusted by rotationally driving the second birefringent mask rotatable about the optical axis relative to the fixed first birefringent mask. (6)

[0140] The optical system according to (5), wherein

[0141] The first birefringent mask includes even-numbered rings as polarizing elements and odd-numbered rings as non-polarizing elements, and the second birefringent mask includes odd-numbered rings as polarizing elements and even-numbered rings as non-polarizing elements. (7)

[0143] The optical system according to (5), wherein:

[0144] The first birefringent mask is divided into four sectors in a cross shape at its center, so that the upper left and lower right sectors are polarizing elements, and the upper right and lower left sectors are non-polarizing elements, and the second birefringent mask is divided into four sectors in a cross shape at its center, so that the upper left and lower left sectors are polarizing elements, and the upper left and lower right sectors are non-polarizing elements. (8)

[0146] The optical system according to (5), wherein

[0147] The predetermined polarization element provided in the second birefringence mask has an outer shape set according to the diameter of the rigid mirror. (9)

[0149] The optical system according to any one of (1) to (8), wherein

[0150] The optical element is a wavefront coding filter or a chromatic aberration filter. (10)

[0152] An endoscope comprising:

[0153] a mirror having a tubular shape and made of a rigid or flexible material; and

[0154] A camera comprising an imaging element for capturing an image, wherein:

[0155] The imaging element receives light that has passed through an optical system including two or more optical elements having an effect of extending the depth of field; and

[0156] At least one optical element is movable. (11)

[0158] The endoscope according to (10), wherein:

[0159] The optical element insertion unit is disposed between the mirror and the camera; and

[0160] The movable optical element is arranged in the optical element insertion unit. (12)

[0162] A medical image processing system, comprising:

[0163] a light source, which illuminates the observation target with light;

[0164] an image capturing control unit that controls capturing of an image of an observation target illuminated with light; and

[0165] An endoscope comprising a scope having a tubular shape and made of a rigid or flexible material, and a camera including an imaging element for capturing an image, wherein:

[0166] The imaging element receives light that has passed through an optical system including two or more optical elements having an effect of extending the depth of field; and

[0167] At least one optical element is movable. (13)

[0169] The medical image processing system according to (12), wherein:

[0170] The optical element insertion unit is disposed between the mirror and the camera; and

[0171] The movable optical element is arranged in the optical element insertion unit.

[0172] Note that the present embodiment is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present disclosure. In addition, the effects described in this specification are merely examples and not limitations, and additional effects can be obtained.

[0173] Reference numerals list

[0174] 11 Medical Image Processing System

[0175] 12 Display device

[0176] 13 Cart

[0177] 14 Endoscope

[0178] 21 Light source device

[0179] 22 CCU

[0180] 23 Signal processing device

[0181] 31. Lens tube

[0182] 32 Cameras

[0183] 33 Optical element insertion unit

[0184] 41 Birefringent Mask

[0185] 42a to 42c

[0186] Polarization Components

[0187] 51 Image forming optical system

[0188] 52 Aperture

[0189] 53 Imaging element

[0190] 61 Fixed birefringence mask

[0191] 62 Movable birefringent mask

[0192] 63 Drive Unit

[0193] 64 Angle detection unit

[0194] 65 switch.

Claims

1. An optical system, comprising: Two or more optical elements having an effect of extending the depth of field, wherein: At least one of the two or more optical elements is movable, The optical element is a birefringent mask in each of which a plurality of polarization elements having a predetermined polarization direction are arranged in combination, wherein the optical element is a fixed first birefringent mask and a second birefringent mask rotatable about an optical axis, and the effect of extending the depth of field can be adjusted by relatively changing the polarization direction of the polarization element of the first birefringent mask and the polarization direction of the polarization element of the second birefringent mask, wherein, in the first birefringence mask and the second birefringence mask, a plurality of the polarization elements are arranged concentrically from the center outward, and the polarization direction of each of the polarization elements is rotated 90 degrees from the polarization direction of an adjacent one of the polarization elements; and the effect of extending the depth of field is adjusted by rotationally driving the second birefringence mask capable of rotating around the optical axis relative to the fixed first birefringence mask; And wherein, the first birefringent mask is divided into four sectors in a cross shape at the center of the first birefringent mask, so that the upper left sector and the lower right sector are the polarization elements, and the upper right sector and the lower left sector are non-polarization elements, and the second birefringent mask is divided into four sectors in a cross shape at the center of the second birefringent mask, so that the upper right sector and the lower left sector are the polarization elements, and the upper left sector and the lower right sector are the non-polarization elements.

2. The optical system according to claim 1, wherein: The optical element is a combination of N or more first birefringent masks and at least M second birefringent masks, wherein N≥2, N≥M≥1, and the second birefringent masks are movable.

3. The optical system according to claim 1, wherein: The first birefringent mask includes only even-numbered rings as the polarizing elements and odd-numbered rings as non-polarizing elements, and the second birefringent mask includes only odd-numbered rings as the polarizing elements and even-numbered rings as the non-polarizing elements.

4. The optical system according to claim 1, wherein: The outer shape of the predetermined polarization element provided in the second birefringence mask is set according to the diameter of the rigid mirror.

5. The optical system according to claim 1, wherein: The optical element is a wavefront coding filter or a chromatic aberration filter.

6. An endoscope comprising: a mirror, having a tubular shape and made of a rigid or flexible material; as well as A camera, comprising an imaging element for capturing an image, wherein: The imaging element receives light that has passed through an optical system including two or more optical elements having an effect of extending the depth of field; and At least one of the two or more optical elements is movable, The optical element is a birefringent mask in each of which a plurality of polarization elements having a predetermined polarization direction are arranged in combination, wherein the optical element is a fixed first birefringent mask and a second birefringent mask rotatable about an optical axis, and the effect of extending the depth of field can be adjusted by relatively changing the polarization direction of the polarization element of the first birefringent mask and the polarization direction of the polarization element of the second birefringent mask, wherein, in the first birefringence mask and the second birefringence mask, a plurality of the polarization elements are arranged concentrically from the center outward, and the polarization direction of each of the polarization elements is rotated 90 degrees from the polarization direction of an adjacent one of the polarization elements; and the effect of extending the depth of field is adjusted by rotationally driving the second birefringence mask capable of rotating around the optical axis relative to the fixed first birefringence mask; And wherein, the first birefringent mask is divided into four sectors in a cross shape at the center of the first birefringent mask, so that the upper left sector and the lower right sector are the polarization elements, and the upper right sector and the lower left sector are non-polarization elements, and the second birefringent mask is divided into four sectors in a cross shape at the center of the second birefringent mask, so that the upper right sector and the lower left sector are the polarization elements, and the upper left sector and the lower right sector are the non-polarization elements.

7. The endoscope according to claim 6, wherein: An optical element insertion unit is disposed between the mirror and the camera; and The optical element that is movable is arranged in the optical element insertion unit.

8. A medical image processing system, comprising: Light source, using light to illuminate the target for observation; an image capturing control unit configured to control capturing an image obtained by irradiating the observation target with the light; as well as An endoscope comprising: a scope having a tubular shape and made of a rigid material or a flexible material; and a camera including an imaging element for capturing said image, wherein: The imaging element receives light that has passed through an optical system including two or more optical elements having an effect of extending the depth of field; and At least one of the two or more optical elements is movable, The optical element is a birefringent mask in each of which a plurality of polarization elements having a predetermined polarization direction are arranged in combination, wherein the optical element is a fixed first birefringent mask and a second birefringent mask rotatable about an optical axis, and the effect of extending the depth of field can be adjusted by relatively changing the polarization direction of the polarization element of the first birefringent mask and the polarization direction of the polarization element of the second birefringent mask, wherein, in the first birefringence mask and the second birefringence mask, a plurality of the polarization elements are arranged concentrically from the center outward, and the polarization direction of each of the polarization elements is rotated 90 degrees from the polarization direction of an adjacent one of the polarization elements; and the effect of extending the depth of field is adjusted by rotationally driving the second birefringence mask capable of rotating around the optical axis relative to the fixed first birefringence mask; And wherein, the first birefringent mask is divided into four sectors in a cross shape at the center of the first birefringent mask, so that the upper left sector and the lower right sector are the polarization elements, and the upper right sector and the lower left sector are non-polarization elements, and the second birefringent mask is divided into four sectors in a cross shape at the center of the second birefringent mask, so that the upper right sector and the lower left sector are the polarization elements, and the upper left sector and the lower right sector are the non-polarization elements.

9. The medical image processing system according to claim 8, wherein: An optical element insertion unit is disposed between the mirror and the camera; and The optical element that is movable is arranged in the optical element insertion unit.

Images