Abstract:
A scanning endoscope apparatus includes: a light source; first and second polarization sections; third and fourth polarization sections; a first wavelength separation section; a second wavelength separation section; a first detection section; and a second detection section. The scanning endoscope apparatus further includes: a first judgment section comparing light intensities of at least two of the light having a first wavelength band transmitted through the first wavelength separation section, the light having a second wavelength band transmitted through the first wavelength separation section, the light having the first wavelength band transmitted through the second wavelength separation section and the light having the second wavelength band transmitted through the second wavelength separation section to observe the return light on a surface area; and a second judgment section comparing light intensities of two which are not used by the first judgment section to observe the return light in a deep-part area of the subject.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation application of PCT/JP2012/057967 filed on Mar. 27, 2012 and claims benefit of Japanese Application No. 2011-080251 filed in Japan on Mar. 31, 2011, the entire contents of which are incorporated herein by this reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a scanning endoscope apparatus. 
         [0004]    2. Description of the Related Art 
         [0005]    Conventionally, a scanning endoscope apparatus has been proposed which causes a distal end of an optical fiber guiding unpolarized light from a light source to perform scanning and receives return light from a subject with an optical fiber bundle arranged around the optical fiber to generate an image using a light intensity signal sequentially detected over time (see, for example, Japanese Patent Application Laid-Open Publication No. 2003-535659). 
         [0006]    Furthermore, an endoscope apparatus is proposed which is for, at the time of performing observation and the like using an endoscope, observing a polarized image using polarization, for example, for diagnosis of early-stage cancer and the like, in addition to observation using unpolarized light (see, for example, Japanese Patent Application Laid-Open Publication No. 2009-213649, and Japanese Patent Application Laid-Open Publication No. 2010-104422). 
         [0007]    In the endoscope apparatus of Japanese Patent Application Laid-Open Publication No. 2009-213649, by providing a polarization separation device and an image pickup device such as a CCD, at a distal end portion of an endoscope distal end, a polarization component of return light of light illuminating a living body can be separated. 
         [0008]    The endoscope apparatus of Japanese Patent Application Laid-Open Publication No. 2010-104422 sequentially radiates multiple illumination lights in different polarization states to an observation site for each different wavelength spectrum by sequentially switching among respective multiple color filters and multiple illumination light polarization filters. Then, after polarizing return light from the observation site with a polarization filter section provided at a distal end portion of an endoscope in a predetermined direction, the endoscope apparatus performs image pickup with an image pickup device such as a CCD. 
       SUMMARY OF THE INVENTION 
       [0009]    A scanning endoscope apparatus of an aspect of the present invention is a scanning endoscope apparatus for scanning illumination light to generate an endoscopic image of a subject, the scanning endoscope apparatus including: a light source emitting first illumination light of a first wavelength band and second illumination light of a second wavelength band different from the first wavelength band; a first polarization section transmitting light in a first polarization direction of the first illumination light, which is to be radiated to the subject; a second polarization section transmitting light in a second polarization direction of the second illumination light, which is to be radiated to the subject, the second polarization direction being different from the first polarization direction; a third polarization section receiving return light from the subject and transmitting the light in the first polarization direction; a fourth polarization section receiving the return light from the subject and transmitting the light in the second polarization direction; a first wavelength separation section separating the light transmitted through the third polarization section into light of the first wavelength band and light of the second wavelength band; a second wavelength separation section separating the light transmitted through the fourth polarization section into the light of the first wavelength band and the light of the second wavelength band; a first detection section detecting light intensities of the light having the first wavelength band transmitted through the first wavelength separation section and the light having the second wavelength band transmitted through the first wavelength separation section; a second detection section detecting light intensities of the light having the first wavelength band transmitted through the second wavelength separation section and the light having the second wavelength band transmitted through the second wavelength separation section; a first judgment section comparing the light intensities of at least two of the light having the first wavelength band transmitted through the first wavelength separation section, the light having the second wavelength band transmitted through the first wavelength separation section, the light having the first wavelength band transmitted through the second wavelength separation section and the light having the second wavelength band transmitted through the second wavelength separation section in order to observe the return light on a surface area of the subject; and a second judgment section comparing the light intensities of two of the light having the first wavelength band transmitted through the first wavelength separation section, the light having the second wavelength band transmitted through the first wavelength separation section, the light having the first wavelength band transmitted through the second wavelength separation section and the light having the second wavelength band transmitted through the second wavelength separation section in order to observe the return light in a deep-part area of the subject, the two lights not being used by the first judgment section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a diagram showing a configuration of an endoscope apparatus according to a first embodiment; 
           [0011]      FIG. 2  is a perspective view showing a configuration of a distal end portion of the endoscope apparatus; 
           [0012]      FIG. 3  is a diagram for illustrating arrangement of polarization filters on the distal end portion; 
           [0013]      FIG. 4A  is a diagram for illustrating another example of arrangement of polarization filters on the distal end portion; 
           [0014]      FIG. 4B  is a diagram for illustrating another example of arrangement of polarization filters on the distal end portion; 
           [0015]      FIG. 4C  is a diagram for illustrating another example of arrangement of polarization filters on the distal end portion; 
           [0016]      FIG. 5  is a diagram for illustrating operation of an endoscope apparatus  1 ; 
           [0017]      FIG. 6  is a flowchart for illustrating an example of a process flow of polarized image diagnosis using the endoscope apparatus  1 ; 
           [0018]      FIG. 7  is a flowchart for illustrating an example of a flow of treatment using the endoscope apparatus  1 ; 
           [0019]      FIG. 8  is a diagram showing a configuration of an endoscope apparatus according to a first modification of the first embodiment; 
           [0020]      FIG. 9  is a diagram showing a configuration of an endoscope apparatus according to a second modification of the first embodiment; 
           [0021]      FIG. 10  is a perspective view showing a distal end configuration of an endoscope apparatus of a second embodiment; 
           [0022]      FIG. 11  is a side view showing the distal end configuration of the second embodiment and a diagram showing a configuration of an inner surface of a cap; and 
           [0023]      FIG. 12  is a diagram showing another distal end configuration of the endoscope apparatus. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    Embodiments of the present invention will be described below with reference to drawings. 
       First Embodiment 
       [0025]    A first embodiment will be described below. 
         [0026]    First, a configuration of an endoscope apparatus of the first embodiment will be described with the use of  FIGS. 1 to 3 . 
         [0027]      FIG. 1  is a diagram showing the configuration of the endoscope apparatus according to the first embodiment;  FIG. 2  is a perspective view showing a configuration of a distal end portion of the endoscope apparatus; and  FIG. 3  is a diagram for illustrating arrangement of polarization filters on the distal end portion. 
         [0028]    As shown in  FIG. 1 , an endoscope apparatus  1  is configured to have a scanning endoscope  2  which radiates illumination light to a subject while scanning the illumination light, and obtains return light from the subject, a body apparatus  3  connected to the endoscope  2 , and a monitor  4  which displays a subject image obtained by the body apparatus  3 . 
         [0029]    The endoscope  2  has an elongated insertion portion  11  configured mainly with a tube body having predetermined flexibility. On the distal end side of the insertion portion  11 , a distal end portion  12  is provided. On the proximal end side of the insertion portion  11 , a connector and the like not shown are provided. The endoscope  2  is configured being detachably connectable to the body apparatus  3  via the connector and the like. 
         [0030]    On the distal end face of the distal end portion  12 , a distal end optical system  13  configured with illumination lenses  13   a  and  13   b  is provided. Inside the insertion portion  11 , an illumination fiber  14  as an optical device, which is inserted from the proximal end side to the distal end side to guide light from a light source unit  24  to be described later, and an actuator  15  provided on the distal end side of the illumination fiber  14  to cause the distal end of the illumination fiber  14  to perform scanning in a desired direction on the basis of a driving signal from a driver unit  25  to be described later are provided. By such a configuration, illumination light from the light source unit  24  guided by the illumination fiber  14  is radiated to the subject. 
         [0031]    Inside the insertion portion  11 , a detection fiber  16   a  inserted from the proximal end side to the distal end side along the internal circumference of the insertion portion  11  to guide a first polarization component as a light reception section which receives return light from the subject and a detection fiber  16   b  which guides a second polarization component are provided. Each of the detection fibers  16   a  and  16   b  may be a fiber bundle constituted by at least two or more fibers. When the endoscope  2  is connected to the body apparatus  3 , the detection fibers  16   a  and  16   b  are connected to splitters  37   a  and  37   b  to be described later. 
         [0032]    As shown in  FIG. 3 , on the distal end face of the distal end portion  12 , a polarization filter  17   a  which transmits return light in a first polarization direction from the subject and a polarization filter  17   b  which transmits return light in a second polarization direction from the subject are symmetrically provided around the distal end optical system  13 . As shown in  FIG. 1 , the polarization filters  17   a  and  17   b  are provided such that the polarization filters  17   a  and  17   b  cover the distal ends of the detection fibers  16   a  and  16   b.  The polarization filter  17   a  as a first polarization filter and the polarization filter  17   b  as a second polarization filter are provided between the subject and the detection fibers  16   a  and  16   b,  respectively, to polarize return light from the subject in a desired direction. Note that, in  FIG. 1 , the polarization filters  17   a  and  17   b  are arranged on the upper side and the lower side, respectively, for convenience. Arrangement of the polarization filters  17   a  and  17   b  on the distal end portion  12  is not limited to  FIG. 3 . 
         [0033]      FIGS. 4A to 4C  are diagrams for illustrating other examples of arrangement of the polarization filters on the distal end portion. 
         [0034]    On the distal end face in  FIG. 4A , polarization filters  17   a   1  and  17   a   2  for the first polarization direction and polarization filters  17   b   1  and  17   b   2  for the second polarization direction are arranged in circular symmetry. Due to such arrangement, it is possible to suppress lack of balance of detected quantity of light of each polarization component dependent on arrangement of the detection fibers  16   a  and  16   b  on the distal end. 
         [0035]    On the distal end face in  FIG. 4B , polarization filters  17   a   3  and  17   a   4  for the first polarization direction are arranged vertically relative to the surface of the sheet and polarization filters  17   b   3  and  17   b   4  for the second polarization direction are arranged horizontally relative to the surface of the sheet. By arranging the polarization filters  17   a   3 ,  17   a   4 ,  17   b   3  and  17   b   4  at equal intervals in circular symmetry as described above, return light from the subject may be received by the detection fibers  16   a  and  16   b  without polarizing the return light, at positions around the distal end optical system  13  where the polarization filters  17   a   3 ,  17   a   4 ,  17   b   3  and  17   b   4  are not arranged. 
         [0036]    On the distal end face in  FIG. 4C , two areas are defined by a line segment passing through the center of the distal end face of the endoscope  2 . Each of the two areas is divided into multiple areas, four areas here, from the center toward the circumference, and polarization filters  17   a   5  and  17   b   5  with different polarization characteristics are alternately provided for the multiple areas, with a line segment passing through the center of the distal end face of the endoscope  2  as a border. Due to such arrangement, it is possible to suppress lack of balance of detected quantity of light in the horizontal direction and in the direction from the center toward the circumference, similarly to  FIG. 4A . 
         [0037]    Returning to  FIG. 1 , a memory  18  storing various information about the endoscope  2  is provided inside the insertion portion  11 . When the endoscope  2  is connected to the body apparatus  3 , the memory  18  is connected to a controller  23  to be described later via a signal line not shown, and the various information about the endoscope  2  is read by the controller  23 . 
         [0038]    The body apparatus  3  is configured to have a power source  21 , a memory  22 , the controller  23 , the light source unit  24 , the driver unit  25  and a detection unit  26 . 
         [0039]    The light source unit  24  is configured to have two light sources  31   a  and  31   b,  two polarizers  32   a  and  32   b,  and a multiplexer  33 . 
         [0040]    The driver unit  25  is configured to have a signal generator  34 , digital-analog (hereinafter referred to as D/A) converters  35   a  and  35   b,  and an amplifier  36 . 
         [0041]    The detection unit  26  is configured to have the splitters  37   a  and  37   b,  detectors  38   a  to  38   d,  and analog-digital (hereinafter referred to as A/D) converters  39   a  to  39   d.    
         [0042]    The power source  21  controls supply of a power source to the controller  23  according to an operation of a power source switch or the like not shown. The memory  22  stores a control program and the like for controlling the whole body apparatus  3 . 
         [0043]    When a power source is supplied from the power source  21 , the controller  23  reads the control program from the memory  22  to control the light source unit  24  and the driver unit  25 , and analyzes the light intensity of return light from the subject detected by the detection unit  26  to perform control to display an obtained subject image on the monitor  4 . 
         [0044]    The light sources  31   a  and  31   b  of the light source unit  24  adjust polarization directions of lights of different wavelength bands with the use of the polarizers  32   a  and  32   b,  respectively, on the basis of control by the controller  23 . More specifically, the light source  31   a  emits light λ 1  of a first wavelength band of 390 nm to 445 nm or 530 nm to 550 nm to the polarizer  32   a,  and the light source  31   b  emits light λ 2  of a second wavelength band of 600 nm to 1100 nm to the polarizer  32   b.  Especially, it is desirable that the light λ 1  of the first wavelength band is 415 nm and the light λ 2  of the second wavelength band is 600 nm. 
         [0045]    The polarizers  32   a  and  32   b  have different polarization characteristics, respectively, and polarize the lights λ 1  and λ 2  emitted from the light sources  31   a  and  31   b.  More specifically, the polarizer  32   a  polarizes the light λ 1  of the first wavelength band from the light source  31   a  in a first polarization direction (P polarization). The polarizer  32   b  polarizes the light λ 2  of the second wavelength band from the light source  31   b  in a second polarization direction (S polarization) which is different from the first polarization direction. Here, the lights λ 1  and λ 2  polarized by the polarizers  32   a  and  32   b  are referred to as lights λ 1P  and λ 2S , respectively. The first wavelength band having the first polarization direction has a light absorption characteristic of the subject, and the second wavelength band having the second polarization direction has a light absorption characteristic lower than the light absorption characteristic of the first wavelength band. 
         [0046]    The multiplexer  33  multiplexes the light λ 1P  of the first wavelength band polarized into the first polarization direction and the light λ 2S  of the second wavelength band polarized into the second polarization direction. Thereby, the lights λ 1P  and λ 2S  having the different polarization characteristics are emitted from the light source unit  24  to the illumination fiber  14  through the two wavelength bands. 
         [0047]    Thus, the light source unit  24  constitutes a light source section which emits lights having different polarization characteristics through at least two wavelength bands. 
         [0048]    The signal generator  34  of the driver unit  25  outputs a driving signal for causing the distal end of the illumination fiber  14  to perform scanning in a desired direction, for example, in a spiral shape, on the basis of control by the controller  23 . More specifically, the signal generator  34  outputs a driving signal for driving the distal end of the illumination fiber  14  in a horizontal direction (X-axis direction) relative to an insertion axis of the insertion portion  11 , to the D/A converter  35   a,  and outputs a driving signal for driving the distal end of the illumination fiber  14  in a vertical direction (Y-axis direction) relative to the insertion axis of the insertion portion  11 , to the D/A converter  35   b.    
         [0049]    The D/A converters  35   a  and  35   b  convert the respective inputted driving signals from digital signals to analog signals, and output the analog signals to the amplifier  36 . The amplifier  36  amplifies the inputted driving signals and outputs the signals to the actuator  15 . The actuator  15  causes the distal end of the illumination fiber  14  to perform scanning in a spiral shape, on the basis of the driving signals from the amplifier  36 . Thereby, the lights λ 1P  and λ 2S  emitted from the light source unit  24  to the illumination fiber  14  are sequentially radiated to the subject in a spiral shape. 
         [0050]    Thus, the driver unit  25  constitutes a driving section which causes an end of the illumination fiber  14  to perform scanning. 
         [0051]    From the light λ 1P  radiated to the subject, return light λ 1P  reflected from a surface-part area of the subject, the polarization characteristic of which has not changed, and return light λ 1S  reflected from a deep-part area of the subject, the polarization characteristic of which has changed, are obtained. Similarly, from the light λ 2S  radiated to the subject, return light λ 2S  reflected from the surface-part area of the subject, the polarization characteristic of which has not changed, and return light λ 2P  reflected from the deep-part area of the subject, the polarization characteristic of which has changed, are obtained. The polarization filter  17   a  transmits the return lights λ 1P  and λ 2P , and the polarization filter  17   b  transmits the return lights λ 1S  and λ 2S . The return lights λ 1P  and λ 2P  and the return lights λ 1S  and λ 2S  are received by the detection fibers  16   a  and  16   b,  respectively. The return lights λ 1P  and λ 2P  received by the detection fiber  16   a  are guided to the splitter  37   a,  and the return lights λ 1S  and λ 2S  received by the detection fiber  16   b  are guided to the splitter  37   b.    
         [0052]    The splitters  37   a  and  37   b  are, for example, dichroic mirrors or the like, and the splitters  37   a  and  37   b  split return light in a predetermined wavelength band. More specifically, the splitter  37   a  splits the return lights λ 1P  and λ 2P  guided by the detection fiber  16   a  into return light λ 1P  of the first wavelength band and return light λ 2P  of the second wavelength band and outputs the return lights λ 1P  and λ 2P  to the detectors  38   a  and  38   b,  respectively. Similarly, the splitter  37   b  splits the return lights λ 1S  and λ 2S  guided by the detection fiber  16   b  into return light λ 1S  of the first wavelength band and return light λ 2S  of the second wavelength band and outputs the return lights λ 1S  and λ 2S  to the detectors  38   c  and  38   d,  respectively. 
         [0053]    The detector  38   a  detects the light intensity of the return light λ 1P  of the first wavelength band in the first polarization direction, and the detector  38   b  detects the light intensity of the return light λ 2P  of the second wavelength band in the first polarization direction. Similarly, the detector  38   c  detects the light intensity of the return light λ 1S  of the first wavelength band in the second polarization direction, and the detector  38   d  detects the light intensity of the return light λ 2S  of the second wavelength band in the second polarization direction. Signals of the light intensities detected by the detectors  38   a  to  38   d  are outputted to the A/D converters  39   a  to  39   d,  respectively. Thus, the detectors  38   a  to  38   d  constitute a detection section which detects the light intensities of return lights from a subject. 
         [0054]    The A/D converters  39   a  to  39   d  convert the signals of the light intensities outputted from the detectors  38   a  to  38   d,  respectively, from analog signals to digital signals and output the digital signals to the controller  23 . 
         [0055]    The controller  23  performs comparison between the light intensity in the first polarization direction and the light intensity in the second polarization direction on the surface-part area of the subject and comparison between the light intensity in the first polarization direction and the light intensity in the second polarization direction in the deep-part area of the subject. The comparisons between the light intensities is performed, for example, by performing division or subtraction between the light intensity in the first polarization direction and the light intensity in the second polarization direction on the surface-part area of the subject. Thus, the controller  23  constitutes a calculation section which performs division or subtraction between the light intensity in the first polarization direction and the light intensity in the second polarization direction. 
         [0056]    More specifically, the controller  23  performs comparison between the light intensity of the return light λ 1P  detected by the detector  38   a  and the light intensity of the return light λ 2S  detected by the detector  38   d,  and comparison between the light intensity of the return light λ 2P  detected by the detector  38   b  and the light intensity of the return light λ 1S  detected by the detector  38   c.  By performing comparison of the light intensities for the respective wavelengths on the surface-part area and comparison of the light intensities for the respective wavelengths in the deep-part area, the controller  23  generates pseudo-color images for different depths of the subject and displays the images on the monitor  4 . Furthermore, the controller  23  judges whether or not there is a lesion, such as a tumor, on the surface-part area and in the deep-part area by detecting whether or not the compared light intensities are lower than a predetermined threshold. 
         [0057]    Next, operation of the endoscope apparatus  1  configured as described above will be described with the use of  FIG. 5 . 
         [0058]      FIG. 5  is a diagram for illustrating operation of the endoscope apparatus  1 . 
         [0059]    First, when the power source switch is turned on by an operator, and a power source from the power source  21  is supplied to the controller  23 , light λ 1  of the first wavelength band and light λ 2  of the second wavelength band are outputted from the light sources  31   a  and  31   b,  respectively. The light λ 1  of the first wavelength band outputted from the light source  31   a  is polarized into the first polarization direction by the polarizer  32   a,  and the light λ 2  of the second wavelength band outputted from the light source  31   b  is polarized into the second polarization direction by the polarizer  32   b.  Light λ 1P  of the first wavelength band which has been polarized into the first polarization direction and light λ 2S  of the second wavelength band which has been polarized into the second polarization direction are emitted from the illumination fiber  14  and radiated to the subject. Return lights λ 1P  and λ 2S  reflected on a surface part and return lights λ 1S  and λ 2P  reflected in a deep part are obtained from the subject. 
         [0060]    The return lights λ 1P , λ 2S , λ 1S  and λ 2P  are separated into the return lights λ 1P  and λ 2P  in the first polarization direction by the polarization filters  17   a,  and the return lights λ 1S  and λ 2S  in the second polarization direction by the polarization filter  17   b.  The return lights λ 1P  and λ 2P  separated by the polarization filter  17   a  are split at a predetermined wavelength band by the splitter  37   a,  and return lights λ 1S  and λ 2S  separated by the polarization filter  17   b  are split at a predetermined wavelength band by the splitter  37   b.    
         [0061]    The light intensities of the return lights λ 1P  and λ 2P  split by the splitter  37   a  are detected by the detectors  38   a  and  38   b,  respectively, and the light intensities of the return lights λ 1S  and λ 2S  split by the splitter  37   b  are detected by the detectors  38   c  and  38   d,  respectively. Comparison of the detected light intensities for the respective wavelengths on the surface-part area and comparison of the detected light intensities for the respective wavelengths in the deep part are performed by the controller  23  to judge existence or nonexistence of a tumor or the like on the surface-part area and in the deep part. 
         [0062]    Next, a method for analyzing polarized image diagnosis using the endoscope apparatus  1  will be described. 
         [0063]      FIG. 6  is a flowchart for illustrating an example of a process flow of the polarized image diagnosis using the endoscope apparatus  1 . 
         [0064]    First, the distal end portion of the illumination fiber  14  is caused to perform scanning, and light λ 1P  of the first wavelength band having a predetermined polarization component and light λ 2S  of the second wavelength band having a polarization component orthogonal to the predetermined polarization component are radiated to living tissue (step S 1 ). Next, return light is polarized into the predetermined polarization component and the polarization component orthogonal to the predetermined polarization component (step S 2 ). Here, the center wavelength of the first wavelength band is assumed to be 415 nm, and the center wavelength of the second wavelength band is assumed to be 600 nm. Next, the return lights are divided into lights of the first wavelength band and the second wavelength band (step S 3 ). The light intensities for the polarization components and the wavelength bands are detected, and analysis of detected signals is performed (step S 4 ). 
         [0065]    Next, it is judged whether or not a result of division between light intensity I 415-P  of the return light of the first wavelength band from the surface part of the subject and light intensity I 600-S  of the return light of the second wavelength band from the surface part of the subject is smaller than a threshold (step S 5 ). If it is judged that the result of the light intensity I 415-P /the light intensity I 600-S  of the return light from the surface part is smaller than the threshold, the judgment result is YES, and it is judged that there is a high possibility that a lot of hemoglobin having a 415-nm absorption characteristic exist on the surface part (step S 6 ). On the other hand, if it is judged that the result of the light intensity I 415-P /the light intensity I 600-S  of the return light from the surface part is equal to or above the threshold, the judgment result is NO, and it is judged that the surface part is normal (step S 7 ). 
         [0066]    Furthermore, it is judged whether or not a result of division between light intensity I 415-S  of the return light of the first wavelength band from the deep part of the subject and light intensity I 600-P  of the return light of the second wavelength band from the deep part of the subject is smaller than a threshold (step S 8 ). The process of step S 8  is executed in parallel with the process of step S 5 . If it is judged that the result of the light intensity I 415-S /the light intensity I 600-P  of the return light from the deep part is smaller than the threshold, the judgment result is YES, and it is judged that there is a high possibility that a lot of hemoglobin exist in the deep part (step S 9 ). On the other hand, if it is judged that the result of the light intensity I 415-S /the light intensity I 600-P  of the return light from the deep part is equal to or above the threshold, the judgment result is NO, and it is judged that the deep part is normal (step S 10 ). Then, when existence or nonexistence of a tumor on the surface part of the subject and in the deep part thereof is judged, the process ends. 
         [0067]    Next, treatment using the endoscope apparatus  1  performed when a tumor or the like is detected by the method for analyzing polarized image diagnosis will be described. 
         [0068]      FIG. 7  is a flowchart for illustrating an example of a flow of the treatment using the endoscope apparatus  1 . 
         [0069]    First, a polarized image with a wide range of field of view is displayed on the monitor  4  (step S 11 ). Next, an area of threshold indicating an abnormal value is identified (step S 12 ). Lastly, therapeutic light is radiated to the identified area of concern (step S 13 ), and the process ends. 
         [0070]    As described above, the endoscope apparatus  1  scans the light λ 1P  of the first wavelength band having the first polarization direction (polarization characteristic) and the light λ 2S  of the second wavelength band having the second polarization direction (polarization characteristic) to a subject, and polarizes return lights from the subject with the polarization filters  17   a  and  17   b  on the distal end portion  12 . Then, the endoscope apparatus  1  separates the return lights polarized by the polarization filters  17   a  and  17   b  at a predetermined wavelength band, detects light intensities and obtains a polarized image. As a result, it becomes unnecessary to provide an image pickup device, such as a CCD, for the distal end portion  12 , and it is possible to obtain a polarized image with a high image quality while the small diameter of the insertion portion  11  is maintained. 
         [0071]    Thus, according to the endoscope apparatus of the present embodiment, it is possible to obtain an image with a high image quality while the small diameter of the insertion portion is maintained. 
       (Modifications) 
       [0072]    In the case of a common fiber, there may be a case where, even if polarized light enters, the polarization state cannot be retained in light emitted from the fiber due to influence of change in the structure of the fiber caused by bending or the like of an insertion portion. Therefore, in the present modifications, description will be made on endoscope apparatuses capable of, even if a fiber structure changes due to bending or the like of an insertion portion, retaining a polarization state. 
         [0073]      FIG. 8  is a diagram showing a configuration of an endoscope apparatus according to a first modification of the first embodiment. 
         [0074]    As shown in  FIG. 8 , in an endoscope apparatus la of the present modification, phase compensation sections  41   a  and  41   b  are provided at output stages of the polarizers  32   a  and  32   b  of the endoscope apparatus  1  in  FIG. 1 , and a polarization control section  42  is provided at an output stage of the multiplexer  33 . The endoscope apparatus  1   a  of the present modification is configured with a single-mode fiber  43  instead of the illumination fiber  14  in  FIG. 1 . 
         [0075]    The phase compensation section  41   a  performs phase compensation of the light λ 1P  of the first wavelength band in the first polarization direction emitted from the polarizer  32   a  and emits the light λ 1P  to the multiplexer  33 . The phase compensation section  41   b  performs phase compensation of the light λ 2S  of the second wavelength band in the second polarization direction emitted from the polarizer  32   b  and emits the light λ 2S  to the multiplexer  33 . 
         [0076]    The polarization control section  42  adjusts the polarization direction of illumination light from the multiplexer  33  and emits the illumination light to the single-mode fiber  43 . The single-mode fiber  43  emits the illumination light from the polarization control section  42  from the distal end face and radiates the illumination light to a subject via the distal end optical system  13 . Since other components are similar to those of the endoscope apparatus  1  of the first embodiment, description thereof are omitted. 
         [0077]    Due to such a configuration, the endoscope apparatus  1   a  can retain the polarization state of illumination light even if the fiber structure changes due to bending or the like of the insertion portion  11 . 
         [0078]      FIG. 9  is a diagram showing a configuration of an endoscope apparatus according to a second modification of the first embodiment. 
         [0079]    As shown in  FIG. 9 , an endoscope apparatus  1   b  is configured such that the polarization control section  42  of the endoscope apparatus  1   a  of the first modification is eliminated and a polarization retention fiber  44  is used instead of the single-mode fiber  43 . 
         [0080]    The polarization retention fiber  44  is such a fiber that polarizations of input and output correspond to each other. The polarization retention fiber  44  retains polarization of illumination light inputted from the multiplexer  33  and radiates the illumination light to a subject from the distal end face. Since other components are similar to those of the endoscope apparatus  1   a  of the first modification, description thereof are omitted. Furthermore, polarization retention fibers may be used for the detection fibers  16   a  and  16   b.    
         [0081]    Due to such a configuration, the endoscope apparatus  1   b  can retain the polarization state of illumination light even if the fiber structure changes due to bending or the like of the insertion portion  11 , similarly to the endoscope apparatus  1   a  of the first modification. 
       Second Embodiment 
       [0082]    Next, a second embodiment will be described. 
         [0083]      FIG. 10  is a perspective view showing a distal end configuration of an endoscope apparatus of the second embodiment;  FIG. 11  is a side view showing the distal end configuration of the second embodiment and a diagram showing a configuration of an inner surface of a cap; and  FIG. 12  is a diagram showing another distal end configuration of the endoscope apparatus. Note that the same components as those of the endoscope apparatus  1  of the first embodiment will be given the same reference numerals, and description thereof are omitted. 
         [0084]    An endoscope apparatus  1   c  of the present embodiment is configured to have an endoscope  2   a  and a cap  50  in a cylindrical shape which is attachable to and detachable from the distal end portion  12  of the endoscope  2   a,  in addition to the body apparatus  3  and the monitor  4  of the first embodiment. 
         [0085]    An illumination lens  13   a  is provided on the distal end face of the distal end portion  12 , and the detection fiber  16   a  guiding a first polarization component and the detection fiber  16   b  guiding a second polarization component are arranged around the illumination lens  13   a.    
         [0086]    The cap  50  as an endoscope cap may be provided with an illumination lens cover  13   c,  such as a flat lens, for covering the illumination lens  13   a.  The illumination lens cover  13   c  constitutes an optical member which transmits light radiated from the illumination fiber  14  to a subject. 
         [0087]    The cap  50  is provided with polarization filters  51   a  and  51   b  for P-polarization and polarization filters  51   c  and  51   d  for S-polarization covering the detection fibers  16   a  and  16   b.  The polarization filters  51   a  and  51   b  and the polarization filters  51   c  and  51   d  for S-polarization are arranged in circular symmetry. The polarization filters  51   a  to  51   d  constitute a polarization filter section which separates return light from the subject according to polarization characteristics. In the present embodiment, arrangement of the polarization filters  51   a  to  51   d  is similar to the arrangement in  FIG. 4A  described above. Note that the arrangement of the polarization filters  51   a  to  51   d  may be the arrangement in  FIG. 3 ,  FIG. 4B  or  FIG. 4C  described above. 
         [0088]    Four protruding portions  52   a  to  52   d  are provided on the outer circumferential face of the distal end portion  12 . Note that, in  FIG. 11 , since the protruding portion  52   d  is arranged on the back side of the protruding portion  52   b,  the reference numeral of the protruding portion  52   d  is omitted. Four groove portions  53   a  to  53   d  into which the four protruding portions  52   a  to  52   d  can be fitted, respectively, are provided on the inner surface of the cap  50 . The groove portions  53   a  to  53   d  constitute a fitting section for attachment to and detachment from the endoscope  2 . The groove portions  53   a  to  53   d  constitute a concavo-convex portion for preventing the cap  50  from rotating relative to the endoscope  2 . The cap  50  is fitted to the distal end portion  12  in a state that the protruding portions  52   a  to  52   d  are fitted with the groove portions  53   a  to  53   d.    
         [0089]    Note that, though description has been made on the assumption of the configuration in which the distal end portion  12  is provided with the protruding portions  52   a  to  52   d,  and the cap  50  is provided with the groove portions  53   a  to  53   d,  for example, such a configuration is also possible that the distal end portion is provided with the groove portions, and the cap  50  is provided with the protruding portions. Each of the number of the protruding portions  52   a  to  52   d  and the number of the groove portions  53   a  to  53   d  is not limited to four and may be three or fewer or five or more. Furthermore, the cap  50  and the distal end portion  12  may be fixed with screws or the like. 
         [0090]    Furthermore, as shown in  FIG. 12 , a protruding portion  54  constituting a cam may be provided on the inner surface of the cap  50 , and the distal end portion  12  may be provided with a cam groove  55 . An operator fixes the cap  50  and the distal end portion  12  by rotating the cap  50  after fitting the protruding portion  54  into the cam groove  55 . The protruding portion  54  constitutes a rotation prevention section which prevents rotation of the cap  50  relative to the endoscope  2 . 
         [0091]    In order to further prevent the cap from coming off while preventing rotation of the cap, flexible elastic material having elasticity, for example, silicon, urethane or the like may be used for the material of a part of the cap  50  covering the endoscope  2 . 
         [0092]    According to such a configuration, when desiring to obtain a polarized image having a polarization characteristic different from that of the cap  50 , the operator can easily obtain the polarized image having a different polarization characteristic only by fitting a cap provided with a polarization filter having the polarization characteristic different from that of the cap  50  to the distal end portion  12 . 
         [0093]    Thus, according to the endoscope apparatus  1   c  of the present embodiment, it is possible to easily obtain a polarized image having a different polarization characteristic. 
         [0094]    Note that, as for the respective steps in each flowchart in the present specification, it is also possible to change the execution order, execute multiple steps at the same time, or execute the steps in different order for each execution as long as such change is not inconsistent with the nature of the steps. 
         [0095]    The present invention is not limited to the embodiments and modifications described above, and various modifications, alterations and the like are possible within a range not departing from the spirit of the present invention.