Patent Publication Number: US-2021169306-A1

Title: Medical image processing apparatus, endoscope system, and method for operating medical image processing apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of PCT International Application No. PCT/JP2019/032168 filed on 16 Aug. 2019, which claims priority under 35 U.S.C § 119(a) to Japanese Patent Application No. 2018-156407 filed on 23 Aug. 2018. The above application is hereby expressly incorporated by reference, in its entirety, into the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a medical image processing apparatus, an endoscope system, and a method for operating the medical image processing apparatus that are for recognizing a region of interest such as a lesion portion. 
     2. Description of the Related Art 
     In the medical field, image diagnosis is performed for diagnosing a disease of a patient, performing follow-up, or the like by using a medical image such as an endoscopic image, an X-ray image, a computed tomography (CT) image, or a magnetic resonance (MR) image. A medical doctor or the like determines a course of treatment on the basis of such image diagnosis. 
     In recent years, image diagnosis using medical images has been employing a way of recognizing, by using a medical image processing apparatus, a region of interest to be carefully observed in a medical image, such as a lesion or a tumor in an organ. In particular, a method of machine learning such as deep learning contributes to improvement of recognition processing for a region of interest. 
     JP2016-158828A describes a medical image processing apparatus that performs recognition processing on individual medical images and that displays, in a case where a region of interest is recognized, a result of the recognition on a monitor or the like. In the medical image processing apparatus described in JP2016-158828A, either a graph in which a feature quantity of a medical image (a feature quantity of a region of interest) is plotted, or a label displaying text indicating the item name and value of a feature quantity of a medical image, is displayed near the region of interest of the medical image, and switching between graph display and label display is performed in response to input by a user. 
     SUMMARY OF THE INVENTION 
     When a medical doctor performs image diagnosis using a medical image, he/she is requested to observe not only a result of recognition processing performed on the medical image but also the medical image acquired by an imaging unit. However, in the medical image processing apparatus described in JP2016-158828A, when there are many recognition results displayed near a region of interest of a medical image, the recognition results may be overlapped with the medical image, which may disturb observation of the medical image. 
     An object of the present invention is to provide a medical image processing apparatus, an endoscope system, and a method for operating the medical image processing apparatus that prevent display of a recognition result obtained through recognition processing from hindering observation of a medical image. 
     A medical image processing apparatus of the present invention includes a medical image acquiring unit, a recognition processing unit, and a display control unit. The medical image acquiring unit acquires a medical image through imaging of an observation target. The recognition processing unit performs recognition processing on the medical image acquired by the medical image acquiring unit. The display control unit switches between a first display method in which the medical image acquired by the medical image acquiring unit is displayed in a display unit, and a second display method in which a plurality of recognition results are displayed in the display unit, the plurality of recognition results being obtained by performing the recognition processing on the medical image acquired by the medical image acquiring unit. 
     Preferably, the medical image processing apparatus may include an input unit that inputs an instruction to switch a display method to the display control unit. 
     Preferably, the display control unit may perform switching from the second display method to the first display method after a certain time period elapses from switching to the second display method. 
     Preferably, the display control unit may perform switching from the first display method to the second display method after a certain time period elapses from when the recognition processing unit ends the recognition processing. 
     Preferably, in a case of performing display on the display unit by using the second display method, the display control unit may display the medical image together with the plurality of recognition results. 
     Preferably, each of the plurality of recognition results may be a type of lesion. Preferably, each of the plurality of recognition results may be presence or absence of a lesion portion. Preferably, each of the plurality of recognition results may be a position of a lesion portion. 
     An endoscope system of the present invention includes a light source device, an endoscope, a medical image acquiring unit, a recognition processing unit, a display control unit, and a display unit. The light source device generates illumination light for illuminating an observation target. The endoscope has an imaging unit that performs imaging of the observation target illuminated with the illumination light. The medical image acquiring unit acquires a medical image through imaging of the observation target. The recognition processing unit performs recognition processing on the medical image acquired by the medical image acquiring unit. The display control unit switches between a first display method in which the medical image acquired by the medical image acquiring unit is displayed, and a second display method in which a plurality of recognition results are displayed, the plurality of recognition results being obtained by performing the recognition processing on the medical image acquired by the medical image acquiring unit. The display unit displays the medical image by using the first display method and the plurality of recognition results by using the second display method. 
     Preferably, the endoscope may include an input unit that inputs an instruction to switch a display method to the display control unit. 
     A method for operating a medical image processing apparatus of the present invention includes a step of, with a medical image acquiring unit, acquiring a medical image through imaging of an observation target; a step of, with a recognition processing unit, performing recognition processing on the medical image acquired by the medical image acquiring unit; and a step of, with a display control unit, switching between a first display method in which the medical image acquired by the medical image acquiring unit is displayed on a display unit, and a second display method in which a plurality of recognition results are displayed on the display unit, the plurality of recognition results being obtained by performing the recognition processing on the medical image acquired by the medical image acquiring unit. 
     According to the present invention, it is possible to prevent display of a recognition result obtained through recognition processing from hindering observation of a medical image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external appearance diagram of an endoscope system; 
         FIG. 2  is a block diagram illustrating the functions of the endoscope system according to a first embodiment including a plurality of LED light sources; 
         FIG. 3  is a graph illustrating a spectrum of violet light V, blue light B, blue light Bx, green light G, and red light R; 
         FIG. 4  is a graph illustrating a spectrum of normal light according to the first embodiment; 
         FIG. 5  is a graph illustrating a spectrum of special light according to the first embodiment; 
         FIG. 6  is a block diagram illustrating the functions of a region-of-interest-mode image processing unit including a recognition processing unit; 
         FIG. 7  is an explanatory diagram illustrating an example of display screens in a first display method (part (A)) and a second display method (part (B)) in a case where a display control unit performs switching control; 
         FIG. 8  is a flowchart illustrating a flow of a region-of-interest mode; 
         FIG. 9  is an explanatory diagram illustrating an example of display screens in the first display method (part (A)) and the second display method (part (B)) in a case where the display control unit performs switching control according to a second embodiment; and 
         FIG. 10  is an explanatory diagram illustrating an example of display screens in the first display method (part (A)) and the second display method (part (B)) in a case where the display control unit performs switching control according to a third embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     As illustrated in  FIG. 1 , an endoscope system  10  has an endoscope  12 , a light source device  14 , a processor device  16 , a monitor  18  (display unit), and a console  19 . The endoscope  12  is optically connected to the light source device  14  and is electrically connected to the processor device  16 . The endoscope  12  has an insertion section  12   a  to be inserted into a subject, an operation section  12   b  provided at a base end portion of the insertion section  12   a , and a bending portion  12   c  and a distal end portion  12   d  that are provided on a distal end side of the insertion section  12   a . Operating of an angle knob  13   a  of the operation section  12   b  causes the bending portion  12   c  to perform a bending operation. The bending operation causes the distal end portion  12   d  to be directed in a desired direction. 
     The operation section  12   b  is provided with, in addition to the angle knob  13   a , a still image acquiring unit  13   b  to be used for an operation of acquiring a still image, a mode switching unit  13   c  to be used for an operation of switching an observation mode, a zoom operation unit  13   d  to be used for an operation of changing zoom magnification, and a display switching operation unit  13   e  serving as a dedicated input unit to be used to provide an instruction to switch a display method in a region-of-interest mode. The still image acquiring unit  13   b  is capable of performing a freeze operation of displaying a still image of an observation target on the monitor  18  and a release operation of storing a still image in storage. 
     The endoscope system  10  has a normal mode, a special mode, and a region-of-interest mode as observation modes. When the observation mode is the normal mode, normal light generated by combining light beams of a plurality of colors at a light amount ratio Lc for the normal mode is emitted. When the observation mode is the special mode, special light generated by combining light beams of a plurality of colors at a light amount ratio Ls for the special mode is emitted. 
     When the observation mode is the region-of-interest mode, illumination light for the region-of-interest mode is emitted. In this embodiment, normal light is emitted as the illumination light for the region-of-interest mode. Alternatively, special light may be emitted. 
     The processor device  16  is electrically connected to the monitor  18  and the console  19 . The monitor  18  outputs and displays an image of an observation target, information accompanying the image, and so forth. The console  19  functions as a user interface that receives an input operation for designating a region of interest (ROI), setting a function, or the like. 
     As illustrated in  FIG. 2 , the light source device  14  includes a light source unit  20  that emits illumination light to be used to illuminate an observation target, and a light source control unit  22  that controls the light source unit  20 . The light source unit  20  is a semiconductor light source, such as light emitting diodes (LEDs) of a plurality of colors. The light source control unit  22  turns ON/OFF the LEDs or the like and adjusts driving currents and driving voltages for the LEDs or the like, thereby controlling the amount of illumination light to be emitted. In addition, the light source control unit  22  controls the wavelength range of the illumination light by, for example, changing an optical filter. 
     In the first embodiment, the light source unit  20  has LEDs of four colors: a violet light emitting diode (V-LED)  20   a ; a blue light emitting diode (B-LED)  20   b ; a green light emitting diode (G-LED)  20   c ; and a red light emitting diode (R-LED)  20   d , and a wavelength cut filter  23 . As illustrated in  FIG. 3 , the V-LED  20   a  emits violet light V in a wavelength range of 380 nm to 420 nm. 
     The B-LED  20   b  emits blue light B in a wavelength range of 420 nm to 500 nm. Of the blue light B emitted by the B-LED  20   b , at least the longer wavelength side with respect to a peak wavelength of 460 nm is cut off by the wavelength cut filter  23 . Accordingly, blue light Bx that has passed through the wavelength cut filter  23  is in a wavelength range of 420 nm to 460 nm. The light in the wavelength range on the longer wavelength side with respect to 460 nm is cut off because the light in the wavelength range on the longer wavelength side with respect to 460 nm is a factor in decreasing the contrast of blood vessels as an observation target. The wavelength cut filter  23  may decrease the amount of light in the wavelength range on the longer wavelength side with respect to 460 nm instead of cutting off the light in the wavelength range on the longer wavelength side with respect to 460 nm. 
     The G-LED  20   c  emits green light G in a wavelength range of 480 nm to 600 nm. The R-LED  20   d  emits red light R in a wavelength range of 600 nm to 650 nm. The light emitted by each of the LEDs  20   a  to  20   d  may have a center wavelength and a peak wavelength that are identical to or different from each other. 
     The light source control unit  22  controls ON/OFF of each of the LEDs  20   a  to  20   d  and the amount of light emission in an ON state independently from each other, thereby adjusting the emission timing, emission period, amount of light, and spectrum of illumination light. The ON/OFF control by the light source control unit  22  varies according to an observation mode. A reference brightness can be set by a brightness setting unit of the light source device  14 , the console  19 , or the like. 
     In the normal mode or the region-of-interest mode, the light source control unit  22  turns on all of the V-LED  20   a , the B-LED  20   b , the G-LED  20   c , and the R-LED  20   d . At this time, as illustrated in  FIG. 4 , the light amount ratio Lc among the violet light V, the blue light Bx, the green light G, and the red light R is set such that the peak intensity of the blue light Bx is higher than each of the peak intensities of the violet light V, the green light G, and the red light R. Accordingly, in the normal mode or the region-of-interest mode, the light source device  14  emits, as normal light, multicolor light for the normal mode or the region-of-interest mode including the violet light V, the blue light Bx, the green light G, and the red light R. The normal light has a certain intensity or more in the blue range to the red range and is thus substantially white. 
     In the special mode, the light source control unit  22  turns on all of the V-LED  20   a , the B-LED  20   b , the G-LED  20   c , and the R-LED  20   d . At this time, as illustrated in  FIG. 5 , the light amount ratio Ls among the violet light V, the blue light Bx, the green light G, and the red light R is set such that the peak intensity of the violet light V is higher than each of the peak intensities of the blue light Bx, the green light G, and the red light R and such that each of the peak intensities of the green light G and the red light R is lower than each of the peak intensities of the violet light V and the blue light Bx. Accordingly, in the special mode, the light source device  14  emits, as special light, multicolor light for the special mode including the violet light V, the blue light Bx, the green light G, and the red light R. The special light has a large proportion of the violet light V and is thus bluish. The special light does not necessarily need to include light of all the four colors, and may include light from at least one of the LEDs  20   a  to  20   d  of four colors. Preferably, the special light may have a main wavelength range, for example, a peak wavelength or a center wavelength, in a range that is 450 nm or less. 
     As illustrated in  FIG. 2 , the illumination light emitted by the light source unit  20  passes through a light path coupling unit (not illustrated) formed of a mirror, a lens, and the like and then enters a light guide  24  that extends through the insertion section  12   a . The light guide  24  is built in the endoscope  12  and a universal cord, and causes the illumination light to propagate to the distal end portion  12   d  of the endoscope  12 . The universal cord is a cord that connects the endoscope  12  to the light source device  14  and the processor device  16 . A multimode fiber may be used as the light guide  24 . As an example, a small-diameter fiber cable with a core diameter of 105 μm, a clad diameter of 125 μm, and a diameter including a protective layer serving as an outer cover of ϕ0.3 mm to ϕ0.5 mm may be used as the light guide  24 . 
     The distal end portion  12   d  of the endoscope  12  is provided with an illumination optical system  30   a  and an imaging optical system  30   b . The illumination optical system  30   a  has an illumination lens  32 . An observation target is illuminated, via the illumination lens  32 , with illumination light that has propagated through the light guide  24 . The imaging optical system  30   b  has an objective lens  34 , a magnifying optical system  36 , and an image sensor  38  (corresponding to the “imaging unit” of the present invention). Various types of light, such as reflected light, scattered light, and fluorescence from the observation target, enters the image sensor  38  through the objective lens  34  and the magnifying optical system  36 . Accordingly, an image of the observation target is formed on the image sensor  38 . 
     The magnifying optical system  36  includes a zoom lens  36   a  that magnifies an observation target, and a lens driving unit  36   b  that moves the zoom lens  36   a  in optical-axis directions CL. The zoom lens  36   a  is freely moved between a telephoto end and a wide end in accordance with zoom control by the lens driving unit  36   b , thereby magnifying or demagnifying the image of the observation target formed on the image sensor  38 . 
     The image sensor  38  is a color image sensor that performs imaging of an observation target irradiated with illumination light. Each of the pixels of the image sensor  38  is provided with a red (R) color filter, a green (G) color filter, or a blue (B) color filter. The image sensor  38  receives violet to blue light by using B pixels provided with the B color filter, receives green light by using G pixels provided with the G color filter, and receives red light by using R pixels provided with the R color filter. The image sensor  38  outputs image signals of individual colors of RGB from the pixels of the individual colors. The image sensor  38  transmits the output image signals to a correlated double sampling (CDS) circuit  40 . 
     In the normal mode or the region-of-interest mode, the image sensor  38  performs imaging of an observation target illuminated with normal light, thereby outputting Bc image signals from the B pixels, outputting Gc image signals from the G pixels, and outputting Rc image signals from the R pixels. In the special mode, the image sensor  38  performs imaging of an observation target illuminated with special light, thereby outputting Bs image signals from the B pixels, outputting Gs image signals from the G pixels, and outputting Rs image signals from the R pixels. 
     A charge coupled device (CCD) image sensor, a complementary metal-oxide semiconductor (CMOS) image sensor, or the like can be used as the image sensor  38 . Instead of the image sensor  38  provided with color filters of the primary colors RGB, a complementary-color image sensor including complementary-color filters of cyan (C), magenta (M), yellow (Y), and green (G) may be used. In the case of using the complementary-color image sensor, image signals of four colors CMYG are output. Thus, as a result of converting image signals of four colors CMYG into image signals of three colors RGB by using complementary color to primary color conversion, image signals of individual colors RGB similar to those in the image sensor  38  can be acquired. Alternatively, a monochrome sensor not provided with color filters may be used instead of the image sensor  38 . 
     The CDS circuit  40  performs correlated double sampling (CDS) on analog image signals received from the image sensor  38 . The image signals output from the CDS circuit  40  are input to an automatic gain control (AGC) circuit  42 . The AGC circuit  42  performs automatic gain control (AGC) on the image signals input thereto. An analog to digital (A/D) conversion circuit  44  converts the analog image signals output from the AGC circuit  42  into digital image signals. The A/D conversion circuit  44  inputs the digital image signals generated through the A/D conversion to the processor device  16 . 
     As illustrated in  FIG. 2 , the processor device  16  includes an image signal acquiring unit  50  (corresponding to the “medical image acquiring unit” of the present invention), a digital signal processor (DSP)  52 , a noise reducing unit  54 , an image processing unit  56 , and a display control unit  58 . 
     The image signal acquiring unit  50  acquires digital image signals corresponding to an observation mode from the endoscope  12 . In the normal mode or the region-of-interest mode, the image signal acquiring unit  50  acquires Bc image signals, Gc image signals, and Rc image signals. In the special mode, the image signal acquiring unit  50  acquires Bs image signals, Gs image signals, and Rs image signals. In the region-of-interest mode, the image signal acquiring unit  50  acquires Bc image signals, Gc image signals, and Rc image signals of one frame during illumination with normal light, and acquires Bs image signals, Gs image signals, and Rs image signals of one frame during illumination with special light. 
     The DSP  52  performs various signal processing operations, such as defect correction processing, offset processing, DSP gain correction processing, linear matrix processing, gamma conversion processing, and demosaicing processing, on the image signals acquired by the image signal acquiring unit  50 . The defect correction processing corrects a signal of a defective pixel of the image sensor  38 . The offset processing removes a dark current component from the image signal that has been subjected to the defect correction processing and sets an accurate zero level. The DSP gain correction processing multiplies the image signal that has been subjected to the offset processing by a specific DSP gain, thereby adjusting the signal level. 
     The linear matrix processing increases the color reproducibility of the image signal that has been subjected to the DSP gain correction processing. The gamma conversion processing adjusts the brightness and chroma of the image signal that has been subjected to the linear matrix processing. The image signal that has been subjected to the gamma conversion processing is subjected to demosaicing processing (also referred to as isotropic processing or synchronization processing), thereby generating, through interpolation, a signal of a color insufficient in each pixel. The demosaicing processing enables all pixels to have signals of individual colors RGB. The noise reducing unit  54  performs noise reduction processing using, for example, a moving-average method, a median filter method, or the like, on the image signal that has been subjected to the demosaicing processing and so forth in the DSP  52 , thereby reducing noise. The image signal that has been subjected to the noise reduction is input to the image processing unit  56 . 
     The image processing unit  56  includes a normal-mode image processing unit  60 , a special-mode image processing unit  62 , and a region-of-interest-mode image processing unit  64 . The normal-mode image processing unit  60  operates when the normal mode is set, and performs color conversion processing, color enhancement processing, and structure enhancement processing on the Bc image signals, Gc image signals, and Rc image signals that have been received. In the color conversion processing, color conversion processing is performed on the RGB image signals by using 3×3 matrix processing, gradation transformation processing, three-dimensional look up table (LUT) processing, and the like. 
     The color enhancement processing is performed on the RGB image signals that have been subjected to color conversion processing. The structure enhancement processing is processing of enhancing the structure of an observation target and is performed on the RGB image signals that have been subjected to the color enhancement processing. The above-described various image processing operations enable a normal image to be acquired. The normal image is an image acquired on the basis of normal light including the violet light V, the blue light Bx, the green light G, and the red light R with a well-balanced ratio, and is thus an image with natural colors. The normal image is input to the display control unit  58 . 
     The special-mode image processing unit  62  operates when the special mode is set. The special-mode image processing unit  62  performs color conversion processing, color enhancement processing, and structure enhancement processing on the Bs image signals, Gs image signals, and Rs image signals that have been received. The processing performed in the color conversion processing, the color enhancement processing, and the structure enhancement processing is similar to that performed by the normal-mode image processing unit  60 . The above-described various image processing operations enable a special image to be acquired. The special image is an image acquired on the basis of special light in which the amount of the violet light V having a high hemoglobin absorption coefficient of blood vessels is larger than the amount of the blue light Bx, the green light G, and the red light R, and thus the resolution of a blood vessel structure and a gland duct structure is higher than that of other structures. The special image is input to the display control unit  58 . 
     The region-of-interest-mode image processing unit  64  operates when the region-of-interest mode is set. The region-of-interest-mode image processing unit  64  performs image processing similar to that performed by the normal-mode image processing unit  60 , such as color conversion processing, on the Bc image signals, Gc image signals, and Rc image signals that have been received. 
     As illustrated in  FIG. 6 , the region-of-interest-mode image processing unit  64  includes a normal image processing unit  70 , an image-for-recognition processing unit  71 , a recognition processing unit  72 , and a recognition result storage unit  73 . The normal image processing unit  70  performs image processing similar to that performed by the normal-mode image processing unit  60 , thereby sequentially acquiring endoscopic images. On the other hand, the image-for-recognition processing unit  71  acquires a still image of an observation target obtained when the still image acquiring unit  13   b  is operated, as an image for recognition to be used for recognizing a region of interest. The image for recognition is stored in the recognition result storage unit  73 . 
     The recognition processing unit  72  analyzes an image for recognition and performs recognition processing. The recognition processing performed by the recognition processing unit  72  includes detection processing of detecting a region of interest from an image for recognition and discrimination processing of discriminating the type or the like of a lesion included in the image for recognition. Specifically, in the discrimination processing, a discrimination result of a region of interest may be output, or a discrimination result of the entire image for recognition may be output. In this embodiment, the recognition processing unit  72  performs detection processing of detecting a lesion portion which is a region of interest from an image for recognition. In this case, the recognition processing unit  72  first divides the image for recognition into a plurality of small regions, for example, square regions each formed of a certain number of pixels. Subsequently, the recognition processing unit  72  calculates image feature quantities from the divided image for recognition. Subsequently, the recognition processing unit  72  determines, on the basis of the calculated feature quantities, whether or not each of the small regions is a lesion portion. Preferably, such a determination method may be a machine learning algorithm such as a convolutional neural network or deep learning. 
     Preferably, a feature quantity calculated from an image for recognition by the recognition processing unit  72  may be the shape or color of a predetermined portion in an observation target, or an index value acquired from the shape or color. Preferably, for example, the feature quantity may be at least any one of the density of a blood vessel, the shape of a blood vessel, the number of branches of a blood vessel, the thickness of a blood vessel, the length of a blood vessel, the degree of meandering of a blood vessel, the depth of a blood vessel, the shape of a gland duct, the shape of an opening portion of a gland duct, the length of a gland duct, the degree of meandering of a gland duct, or color information, or the value of a combination of two or more of them. 
     Finally, the recognition processing unit  72  extracts a group of small regions specified as the same type as one lesion portion. The recognition processing unit  72  stores information indicating the presence or absence of the lesion portion in the recognition result storage unit  73  in association with the image for recognition. The region-of-interest-mode image processing unit  64  outputs, in accordance with control by the display control unit  58 , either the endoscopic image or the image for recognition associated with the information indicating the presence or absence of the lesion portion to the display control unit  58 . 
     The display control unit  58  performs display control for displaying an image or data from the image processing unit  56  on the monitor  18 . When the normal mode is set, the display control unit  58  performs control to display a normal image on the monitor  18 . When the special mode is set, the display control unit  58  performs control to display a special image on the monitor  18 . 
     When the region-of-interest mode is set, the display control unit  58  switches between a first display method and a second display method. An instruction to switch the display method to the display control unit  58  is input by operating the display switching operation unit  13   e . As illustrated in part (A) of  FIG. 7 , the first display method is a display method of sequentially acquiring endoscopic images  75  (images similar to normal images) captured by the image sensor  38  and processed by the region-of-interest-mode image processing unit  64  and displaying the endoscopic images  75  in real time on a display screen  76  of the monitor  18 . 
     On the other hand, the second display method is a display method of displaying a plurality of recognition results on the display screen  76  of the monitor  18 , the recognition results being obtained through recognition processing performed on images for recognition by the recognition processing unit  72 . Specifically, as illustrated in part (B) of  FIG. 7 , in the second display method, a recognition result list  77  is displayed on the display screen  76  of the monitor  18 , the recognition result list  77  including thumbnail images  78  of a plurality of images for recognition and lesion portion presence/absence labels  79  as recognition results corresponding to the respective images for recognition. In this case, the display control unit  58  displays the thumbnail images  78  and the lesion portion presence/absence labels  79  on the basis of the images for recognition output from the region-of-interest-mode image processing unit  64  and information indicating the presence or absence of a lesion portion associated with the images for recognition. Each lesion portion presence/absence label  79  is displayed near the thumbnail image  78  of the corresponding image for recognition. In the example illustrated in part (B) of  FIG. 7 , six thumbnail images  78  and six lesion portion presence/absence labels  79  as recognition results are displayed as the recognition result list  77 . Alternatively, the number and disposition of images and recognition results to be displayed may be appropriately changed in accordance with the size, aspect ratio, or the like of the display screen and images. Also in the following embodiments, the number and disposition of images and recognition results are not limited. 
     In the thumbnail images  78  displayed as a recognition result list, the region of the lesion portion extracted by the recognition processing unit  72  may be displayed, for example, with the color, gradation, or the like thereof being changed. In a case where any one of the thumbnail images  78  is selected through input in the console  19 , the original image for recognition may be displayed. 
     Next, a flow of the region-of-interest mode will be described with reference to the flowchart illustrated in  FIG. 8 . A medical doctor who is a user operates the mode switching unit  13   c  to switch the mode to the region-of-interest mode (S 11 ). Accordingly, an observation target is irradiated with illumination light for the region-of-interest mode. The image sensor  38  performs imaging of the observation target irradiated with the illumination light for the region-of-interest mode, and thereby an endoscopic image is acquired. In this embodiment, the first display method is set in an initial state of the display control unit  58 . Thus, upon switching to the region-of-interest mode, the endoscopic image  75  is displayed on the display screen  76  of the monitor  18  in real time (S 12 ). In this case, only the endoscopic image  75  is displayed and a recognition result is not displayed on the display screen  76 . Thus, observation of the endoscopic image  75  by the medical doctor is not hindered. 
     During the real-time display in the first display method, the medical doctor who is observing the endoscopic image operates the still image acquiring unit  13   b  to acquire an image for recognition (S 13 ). In a case where the image for recognition has been acquired, recognition processing for detecting a lesion portion is performed on the image for recognition (S 14 ). A recognition result obtained through the recognition processing is stored in the recognition result storage unit  73  in association with the image for recognition (S 15 ). 
     Subsequently, when the medical doctor inputs an instruction to switch the display method by using the display switching operation unit  13   e , the display control unit  58  switches the display method from the first display method to the second display method (S 16 ). Upon switching to the second display method, the recognition result list  77  is displayed on the display screen  76  of the monitor  18  (S 17 ). The lesion portion presence/absence labels  79  as recognition results are displayed in a list view together with the thumbnail images  78  of the images for recognition, and thus the medical doctor is able to easily check the recognition results of regions of interest. 
     When the endoscopic image  75  is to be observed again after checking the recognition results of regions of interest, the medical doctor inputs an instruction to switch the display method by using the display switching operation unit  13   e . Accordingly, the display control unit  58  switches the display method from the second display method to the first display method and displays the endoscopic image  75  on the display screen  76  of the monitor  18  in real time. The display switching operation unit  13   e  for inputting an instruction to switch the display method is provided on the endoscope  12 , and thus the medical doctor is able to easily switch between the first and second display methods. 
     Second Embodiment 
     In the above-described first embodiment, lesion portion presence/absence labels are displayed as recognition results in the recognition result list in the second display method. Alternatively, lesion portion position labels may be displayed as recognition results. Specifically, as illustrated in part (B) of  FIG. 9 , in a recognition result list  80 , thumbnail images  81  of a plurality of images for recognition and lesion portion position labels  82  as recognition results corresponding to the respective images for recognition are displayed on the display screen  76  of the monitor  18 . In the first display method, as illustrated in part (A) of  FIG. 9 , the endoscopic images  75  are sequentially acquired and displayed on the monitor  18  in real time as in the first embodiment. The switching of the display method is similar to that in the region-of-interest mode in the above-described first embodiment except that lesion portion position labels are displayed in the second display method. 
     In this case, the recognition processing unit  72  divides the image for recognition into a plurality of small regions, as in the first embodiment. Subsequently, the recognition processing unit  72  calculates image feature quantities from the divided image for recognition, and determines whether or not each of the small regions is a lesion portion on the basis of the calculated feature quantities. Subsequently, the recognition processing unit  72  extracts position information of each small region determined to be a lesion portion, for example, coordinate information in the image for recognition. The recognition processing unit  72  stores the extracted coordinate information of the lesion portion in the recognition result storage unit  73  in association with the image for recognition. The region-of-interest-mode image processing unit  64  outputs, in accordance with control by the display control unit  58 , either the endoscopic image or the image for recognition associated with the recognition result to the display control unit  58  as in the first embodiment. 
     In the case of performing the second display method, the display control unit  58  displays the thumbnail images  78  of the images for recognition and the lesion portion position labels  82  as recognition results on the display screen  76  of the monitor  18  on the basis of the images for recognition and coordinate information associated with the images for recognition. In part (B) of  FIG. 9 , each lesion portion position label  82  is shown by displaying the individual small regions recognized as a lesion portion by using a matrix of squares. Alternatively, any display manner may be used as long as the lesion portion position label  82  is recognized, for example, the color or gradation may be changed. Alternatively, text information representing coordinate information using characters may be used. 
     In the above-described first and second embodiments, images for recognition (including thumbnail images) and recognition results displayed in the recognition result list in the second display method are based on previous endoscopic images, that is, obtained by performing recognition processing on endoscopic images acquired as the image for recognition when the still image acquiring unit  13   b  is operated. Alternatively, a recognition result based on the latest endoscopic image acquired through imaging performed by the image sensor  38  may be included in the recognition result list. In this case, while the image sensor  38  is sequentially acquiring endoscopic images in the region-of-interest mode, recognition processing is constantly performed on the endoscopic images. 
     Recognition processing is constantly performed on the latest endoscopic images that are sequentially acquired to acquire recognition results. Preferably, the images for recognition and recognition results displayed in the recognition result list in the second display method may include those based on the latest endoscopic image acquired by the image sensor  38 . Furthermore, in this case, it is preferable that the recognition result list in the second display method be displayed such that the image for recognition and the recognition result based on the latest endoscopic image are placed at the top (the image for recognition and the recognition result denoted by a number “1” in part (B) of  FIG. 7  or part (B) of  FIG. 9 ) and thereafter the images for recognition and the recognition results acquired through previous recognition processing are arranged in reverse chronological order, from a new one to an old one (the images for recognition and the recognition results denoted by numbers “2”, “3”, “4”, and the like in part (B) of  FIG. 7  or part (B) of  FIG. 9 ). 
     Recognition processing is not necessarily performed on all the endoscopic images sequentially acquired by the image sensor  38 . Thinned-out processing may be performed, that is, images for recognition may be acquired at predetermined time intervals or every predetermined frames from among all the endoscopic images, and recognition processing may be performed on the thinned out images for recognition to acquire recognition results. 
     Third Embodiment 
     In the above-described first and second embodiments, in the case of performing display by using the second display method, only a recognition result list is displayed. Alternatively, an endoscopic image may be displayed in real time together with the recognition result list. In the first display method, the endoscopic images  75  are sequentially acquired and displayed on the monitor  18  in real time as in the first embodiment, as illustrated in part (A) of  FIG. 10 . 
     As illustrated in part (B) of  FIG. 10 , in the second display method, an endoscopic image  86  is displayed in real time together with a recognition result list  85  similar to that in the first embodiment. In this case, the recognition processing unit  72  performs recognition processing in a manner similar to that in the first embodiment. The recognition processing unit  72  stores information indicating the presence or absence of a detected lesion portion in the recognition result storage unit  73  in association with an image for recognition. The region-of-interest-mode image processing unit  64  outputs, in accordance with control by the display control unit  58 , only the endoscopic image or both the endoscopic image and the image for recognition associated with the recognition result to the display control unit  58 . 
     In the case of performing the second display method, the display control unit  58  displays the real-time endoscopic image  86  on the display screen  76  of the monitor  18 , together with the recognition result list  85  including the thumbnail images  78  of the images for recognition and the lesion portion presence/absence labels  79  as recognition results, on the basis of the endoscopic image, the images for recognition, and information associated with the images for recognition. In the real-time display in the second display method, the endoscopic images  86  that are captured by the image sensor  38  and processed by the region-of-interest-mode image processing unit  64  are sequentially acquired and displayed in real time, as in the first display method. In part (B) of  FIG. 10 , lesion portion presence/absence labels are displayed as recognition results as in the first embodiment. Alternatively, lesion portion position labels may be displayed as recognition results as in the second embodiment. 
     In each of the above-described embodiments, a result of detection processing performed on a lesion portion by the recognition processing unit  72  is displayed as a recognition result in the second display method. Alternatively, a result of discrimination processing performed by the recognition processing unit  72  may be displayed as a recognition result. That is, the recognition processing unit  72  may detect a lesion portion from an image for recognition as in each of the above-described embodiments, and may perform discrimination processing of discriminating the type of lesion or the like on the detected lesion portion or perform discrimination processing on the entire image for recognition, thereby displaying a discrimination result. Preferably, the discrimination processing by the recognition processing unit  72  may be performed by using artificial intelligence (AI), deep learning, convolutional neural network, template matching, texture analysis, frequency analysis, or the like. 
     Specifically, the display control unit  58  may cause the type of lesion discriminated by the recognition processing unit  72  to be displayed as a recognition result in the second display method. In this case, for example, it is preferable that the types of lesions discriminated by the recognition processing unit  72  be predetermined according to the portion to be diagnosed. For example, in diagnosis of the large intestine, the portion to be discriminated is classified to any one of normal, hyperplastic polyp (HP), sessile serrated adenoma/polyp (SSA/P), traditional serrated adenoma (TSA), laterally spreading tumor (LST), and cancer. The types of lesions to be discriminated may be set by input in the console  19 , for example. 
     In each of the above-described embodiments, the display switching operation unit  13   e  for inputting an instruction to switch the display method to the display control unit  58  is provided on the endoscope  12 . Alternatively, any input unit for inputting an instruction to switch the display method to the display control unit  58  may be used. For example, an input unit having a similar function of inputting a switching instruction may be provided in the medical image processing apparatus. 
     In each of the above-described embodiments, an example is illustrated in which the display method is switched from the first display method to the second display method and then a switching instruction is input again by using the input unit to return the display method to the first display method. Alternatively, the display control unit  58  may switch the display method from the second display method to the first display method after a certain time period elapses from switching to the second display method. In this case, the certain time period from the switching to the second display method to the switching to the first display method may be a time period sufficient for a medical doctor as a user to check a recognition result and may be set in advance. Alternatively, the time period from the switching to the second display method to the switching to the first display method may be set by using, for example, input in the console  19 . 
     In each of the above-described embodiments, an example is illustrated in which the display method is switched from the first display method to the second display method in response to an instruction of the input unit. Alternatively, the display control unit  58  may switch the display method from the first display method to the second display method after a certain time period elapses from when the recognition processing unit  72  ends the recognition processing. In this case, it is preferable to perform recognition processing and switch the display method from the first display method to the second display method every time a still image of an observation target is acquired as an image for recognition when the still image acquiring unit  13   b  is operated. The certain time period from the end of the recognition processing to the switching from the first display method to the second display method may be a time period sufficient for the display control unit  58  to create an image of a recognition result list and display a display screen after the recognition processing performed by the recognition processing unit  72  and may be set in advance. Alternatively, the time period to the switching from the first display method to the second display method may be set by using, for example, input in the console  19 . 
     Although an observation target is illuminated by using the four-color LEDs  20   a  to  20   d  in each of the above-described embodiments, the observation target may be illuminated by using a laser light source and a fluorescent body. Although an observation target is illuminated by using the four-color LEDs  20   a  to  20   d  in each of the above-described embodiments, the observation target may be illuminated by using a white light source such as a xenon lamp and a rotary filter. Imaging of an observation target may be performed by using a monochrome image sensor instead of the color image sensor  38 . 
     In the above-described embodiments, the medical image processing apparatus of the present invention is applied to an endoscope system that acquires an endoscopic image as a medical image. Obviously, the medical image processing apparatus of the present invention can be applied to various types of endoscope systems, such as a capsule endoscope. Also, the medical image processing apparatus of the present invention can be applied to various types of medical image apparatuses that acquire other types of medical images, such as an X-ray image, a CT image, an MR image, an ultrasound image, a pathological image, and a positron emission tomography (PET) image. 
     In the above-described embodiments, the hardware structure of a processing unit that executes various processing operations, such as the image processing unit  56 , may be various types of processors described below. The various types of processors include a central processing unit (CPU), which is a general-purpose processor executing software (program) and functioning as various processing units; a graphical processing unit (GPU); a programmable logic device (PLD), which is a processor whose circuit configuration is changeable after manufacturing, such as a field programmable gate array (FPGA); a dedicated electric circuit, which is a processor having a circuit configuration designed exclusively for executing various processing operations, and the like. 
     A single processing unit may be constituted by one of these various types of processors or may be constituted by a combination of two or more processors of the same type or different types (for example, a combination of a plurality of FPGAs, a combination of a CPU and an FPGA, or a combination of a CPU and a GPU). A plurality of processing units may be constituted by a single processor. Examples of constituting a plurality of processing units by a single processor are as follows. First, as represented by a computer of a client or server, a single processor is constituted by a combination of one or more CPUs and software, and the processor functions as a plurality of processing units. Secondly, as represented by a system on chip (SoC), a processor in which a single integrated circuit (IC) chip implements the function of an entire system including a plurality of processing units is used. In this way, various types of processing units are constituted by using one or more of the above-described various types of processors as a hardware structure. 
     Furthermore, the hardware structure of these various types of processors is, more specifically, electric circuitry including a combination of circuit elements, such as semiconductor elements. 
     REFERENCE SIGNS LIST 
     
         
         
           
               10  endoscope system 
               12  endoscope 
               12   a  insertion section 
               12   b  operation section 
               12   c  bending portion 
               12   d  distal end portion 
               13   a  angle knob 
               13   b  still image acquiring unit 
               13   c  mode switching unit 
               13   d  zoom operation unit 
               14  light source device 
               16  processor device 
               18  monitor 
               9  console 
               20  light source unit 
               20   a  V-LED 
               20   b  B-LED 
               20   c  G-LED 
               20   d  R-LED 
               22  light source control unit 
               23  wavelength cut filter 
               24  light guide 
               30   a  illumination optical system 
               30   b  imaging optical system 
               32  illumination lens 
               34  objective lens 
               36  magnifying optical system 
               36   a  zoom lens 
               36   b  lens driving unit 
               38  image sensor 
               40  CDS circuit 
               42  AGC circuit 
               44  A/D conversion circuit 
               50  image signal acquiring unit 
               52  DSP 
               54  noise reducing unit 
               56  image processing unit 
               58  display control unit 
               60  normal-mode image processing unit 
               62  special-mode image processing unit 
               64  region-of-interest-mode image processing unit 
               70  normal image processing unit 
               71  image-for-recognition processing unit 
               72  recognition processing unit 
               73  recognition result storage unit 
               75  endoscopic image 
               76  display screen 
               77  recognition result list 
               78  thumbnail image 
               79  lesion portion presence/absence label 
               80  recognition result list 
               81  thumbnail image 
               82  lesion portion position label 
               85  recognition result list 
               86  endoscopic image