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EP-4339691-B1 - OPTICAL SYSTEM FOR RIGID SCOPE, IMAGING DEVICE, AND ENDOSCOPIC SYSTEM

EP4339691B1EP 4339691 B1EP4339691 B1EP 4339691B1EP-4339691-B1

Inventors

  • KIKUCHI, Naomichi
  • NAGAE, SATOSHI

Dates

Publication Date
20260513
Application Date
20190225

Claims (9)

  1. A rigid-scope optical system (1) for an endoscope, the rigid-scope optical system comprising: an image-formation optical system (10) configured to cause an image in each of wavelength bands to be formed in a predetermined imaging device, the wavelength bands including a fluorescence wavelength band belonging to a near-infrared light wavelength band and a visible light wavelength band; and a color-separation-prism optical system (20) having a dichroic film (203) configured to separate an optical path of light to be imaged by the image-formation optical system into an optical path of the visible light wavelength band and an optical path of the fluorescence wavelength band, wherein the image-formation optical system is configured to cause the respective images to be formed in a fluorescence imaging device (4) and a visible light imaging device (3), the fluorescence imaging device and the visible light imaging device being disposed to cause an amount of misalignment between a fluorescence image formation position and a visible light image formation position caused by the image-formation optical system to correspond to a difference between an optical path length of fluorescence and an optical path length of visible light, the fluorescence and the visible light forming the respective images via the color-separation-prism optical system, and, characterized in that a focal length of the image-formation optical system is represented by f [mm], and an air-equivalent optical path length from the image-formation optical system to an imaging device is represented by Fb [mm], the image-formation optical system has the focal length and the air-equivalent optical path length that satisfy a condition represented by the following expression (1), Fb / f > 0.72 and Fb / f < 1.00 wherein the image-formation optical system includes, in order from object side to image side, at least a diaphragm (101), a first lens group (103) having a positive refractive power, and a second lens group (105) having a positive refractive power, the first lens group including, in order from the object side to the image side, a lens having a negative refractive power with a concave surface facing the object side, and at least one lens having a positive refractive power, the second lens group being a focus group that is configured to perform focusing depending on an object distance.
  2. The rigid-scope optical system according to claim 1, wherein the image-formation optical system further includes, between the diaphragm and the first lens group, in order from the object side to the image side, at least one of a third lens group (107) having a positive refractive power or a fourth lens group (109) having a negative refractive power.
  3. The rigid-scope optical system according to claim 2, wherein the image-formation optical system includes the third lens group, and the second lens group further satisfies a relationship represented by the following expression (2), where a curvature radius at an object-side surface of a lens located on most object side in the third lens group is represented by R3 [mm], 0.85 < R 3 / f
  4. The rigid-scope optical system according to claim 1, wherein the image-formation optical system satisfies a condition represented by the following expression (3), where a focal length at a fluorescence wavelength of the image-formation optical system is represented by f(NIR) [mm], and a focal length at a visible light wavelength of the image-formation optical system is represented by f(V) [mm], 0.0025 < f NIR − f V / f V < 0.0060
  5. The rigid-scope optical system according to claim 4, wherein the visible light imaging device is fixed at a position on an image-formation surface of the image-formation optical system, and the fluorescence imaging device is fixed at a position in which an optical path difference satisfies the expression (3).
  6. The rigid-scope optical system according to claim 1, wherein the color-separation-prism optical system includes a color-separating prism (201) including the dichroic film, and a bandpass filter (215) provided between the color-separating prism and the fluorescence imaging device, the bandpass filter having an entrance surface perpendicular to an optical axis.
  7. The rigid-scope optical system according to claim 6, wherein the dichroic film has a transmittance of 90% or more in a wavelength band of 780 to 880 nm, and a transmittance of 10% or less in a wavelength band of 400 to 720 nm, and the bandpass filter has a transmittance of 90% or more in a wavelength band of 813 to 850 nm, and a transmittance of 10% or less in a wavelength band of 350 to 805 nm.
  8. An imaging apparatus comprising the rigid-scope optical system according to any one of claims 1 to 7.
  9. An endoscope unit comprising: a rigid-scope unit (501) that generates an image of a predetermined imaging target of a fluorescence wavelength band belonging to a near-infrared light wavelength band and an image of the predetermined imaging target of a visible light wavelength band; an imaging unit (503) that includes a rigid-scope optical system (1) according to any of claims 1 to 7 coupled to the rigid-scope unit, a visible light imaging device in which the image of the visible light wavelength band is formed, and a fluorescence imaging device in which the image of the fluorescence wavelength band is formed, and configured to generate a captured picture image of the imaging target of the fluorescence wavelength band and a captured picture image of the imaging target of the visible light wavelength band.

Description

Technical Field The present disclosure relates to a rigid-scope optical system, an imaging apparatus, and an endoscope system. Background Art In recent years, in the medical field, there has been an increasing demand for not only observation of an affected area using light belonging to the visible light wavelength band but also observation of an affected area using fluorescence belonging to the near-infrared wavelength band when performing a surgery using an endoscopy. This is because surgery using an ICG (indocyanine green) reagent, which emits fluorescence having a wavelength of 830 to 840 nm by being irradiated with near-infrared excitation light having a wavelength of around 800 nm, as a marker in the body for identifying a site, has begun to become widespread. The above-described ICG reagent is a safe reagent which is not toxic even when injected into the body, and is particularly used for the presence or absence of blood flow in brain surgery, identification of cancer in a sentinel lymph node in breast cancer, etc., and clinical research for endoscopic surgery is proceeding. However, most of the fluorescent reagents used in the medical field, such as ICG and the like, have very low fluorescence efficiency, so that a highly sensitive camera is used to image a subject of interest (i.e., a site emitting fluorescence). Because ICG-compatible endoscopic camera heads and photographing systems that are available on the market today use, as imaging devices, existing visible light RGB single-plate or three-plate sensors, a sensitivity in the near-infrared wavelength band is not sufficient, and image quality and resolution are not comparable to those of a visible light picture image. Further, the above-described sensor mainly utilizing R, G, and B is not able to image a visible light ray and a near-infrared ray at a time, and is only able to perform imaging in one of the wavelength bands. Therefore, it is not possible to compare the affected area identified by the near-infrared ray (i.e., fluorescence) with a video of the visible light ray, and there has been a possibility that accuracy of the surgery is decreased due to misalignment of the site caused by the switching. For ensuring the accuracy of the surgery, there has been proposed an imaging method called a time division method in which a picture image captured under the visible light ray and a picture image captured under the near-infrared ray are simultaneously displayed in a pseudo manner by simultaneously and timely switching modes of a light source and a imaging device every frame. For example, PTL 1 proposes, for achieving imaging in the time division method described above, installing a special band-pass filter in a preceding stage of a visible light RGB sensor, and performing strict switching control between an imaging mode and a light source illumination mode of the sensor. However, in a case of the technique borrowing an imaging device of the visible light band described in PTL 1, a lens group in which chromatic aberration is corrected specialized for the visible light band is often used, and in such a case, a picture image of the near-infrared wavelength band inevitably becomes blurred due to chromatic aberration. In addition, in the system using the above-described time division format, it is very difficult to focus on each frame by auto-focus every time the switching is performed, and a picture image of one of the wavelength bands is inevitably simultaneously imaged with a poor resolution at all times. For this reason, as a method of achieving simultaneous acquisition of a picture image of the visible light wavelength band and a picture image of the near-infrared wavelength band in a method other than the time division method, a method has been proposed in which an optical path to which light of an acquired image is guided is branched into an optical path for the visible light wavelength band and an optical path for the near-infrared wavelength band, and then an imaging device for the visible light and an imaging device for the near-infrared light are used (see, for example, PTL 2 and PTL 3). Citation List Patent Literature PTL 1: Japanese Patent No. 6088629PTL 2: Japanese Unexamined Patent Application Publication No. 2017-53890PTL 3: Japanese Patent No. 6147455 Summary of the Invention Problems to be Solved by the Invention Here, considering endoscopic observations in the medical field, it is necessary to further increase the resolution of a picture image to be acquired for further improving safety of a procedure performed by a physician or the like. In the case of the technique of the time division method as disclosed in PTL 1: it is demanded to increase the resolution only by design change on the optical system to be used for further increasing the resolution of the picture image, thereby inevitably increasing the number of lenses to be used; and it is necessary to use a glass material having a low anomalous dispersibility for causing the vi