Patent Publication Number: US-2018049630-A1

Title: Endoscope system

Description:
TECHNICAL FIELD 
     The present invention relates to an endoscope system that irradiates a subject with light. 
     BACKGROUND ART 
     Endoscope systems that can capture special images are known. A specific configuration of this type of endoscope system is disclosed in WO 2012/108420 pamphlet (called “Patent Document 1” hereinafter), for example. 
     The endoscope system disclosed in Patent Document 1 includes a light source apparatus that is provided with a rotating filter. The rotating filter is an optical filter that allows only light in a specific wavelength region to pass, and rather than having a simple disk shape; has a special shape in which a portion of the outer circumferential region is cut away. A controller drives the rotating filter to rotate at a constant rotation period such that the optical filter portion and the cutaway portion successively enter the light path of irradiation light, and an image of biological tissue formed by irradiation light that passed through the optical filter portion and an image of biological tissue formed by irradiation light that passed through the cutaway portion (i.e., unfiltered irradiation light) are successively captured. The controller generates one observation image based on captured image data regarding the biological tissue irradiated by irradiation light that passed through the optical filter portion, generates another observation image based on captured image data regarding biological tissue illuminated with unfiltered irradiation light, and displays these two types of generated observation images side-by-side on the display screen of a monitor. 
     SUMMARY OF INVENTION 
     Silk lines for detecting the rotation position of the rotating filter are printed on the central portion of the rotating filter disclosed in Patent Document 1. However, the silk lines are extremely small, and therefore there is a problem in that the rotation position of the rotating filter cannot be precisely detected if there is even a slight error in the silk lines. 
     The present invention was achieved in light of the above-described circumstances, and an object of the present invention is to provide an endoscope system that is suited to irradiating a subject with two types of irradiation light that have different wavelength regions. 
     An endoscope system according to one embodiment of the present invention includes: a first light source portion that emits first light; a first light guiding member that guides the first light received from the first light source portion toward a subject; a second light source portion that emits second light having a different wavelength region from the first light; a second light guiding member that guides the second light received from the second light source portion toward the subject; and a blocking portion that alternatingly blocks the first light traveling from the first light source portion toward the first light guiding member and the second light traveling from the second light source portion toward the second light guiding member. 
     Also, in the endoscope system according to the embodiment of the present invention, a configuration is possible in which the blocking portion alternatingly blocks the first light and the second light in accordance with a timing synchronized with a predetermined imaging cycle. 
     Also, an endoscope system according to one embodiment of the present invention includes: a first light source portion that emits first light; a first light guiding member that guides the first light received from the first light source portion toward a subject; a second light source portion that emits second light having a different wavelength region from the first light; a second light guiding member that guides the second light received from the second light source portion toward the subject; and a control portion that, by alternatingly turning on a light source of the first light source portion and a light source of the second light source portion, alternatingly allows the first light and the second light to enter the first light guiding member and the second light guiding member. 
     Also, in the endoscope system according to the embodiment of the present invention, a configuration is possible in which the control portion alternatingly turns on and off the light source of the first light source portion and the light source of the second light source portion in accordance with a timing synchronized with a predetermined imaging cycle. 
     Also, in the endoscope system according to the embodiment of the present invention, a configuration is possible in which the first light source portion has a light source that emits the first light, and the second light source portion has a light source that emits third light, and an optical filter that filters the third light to obtain the second light. 
     According to the embodiment of the present invention, an endoscope system that is suited to irradiating a subject with two types of irradiation light that have different wavelength regions is provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of an electronic endoscope system according to an embodiment of the present invention. 
         FIG. 2  is a diagram showing a spectral intensity distribution of LEDs included in the electronic endoscope system of the embodiment of the present invention. 
         FIG. 3  is a diagram showing spectral characteristics of a narrow-band light filter included in the electronic endoscope system of the embodiment of the present invention. 
         FIG. 4  is a diagram showing a configuration of a shutter portion included in the electronic endoscope system of the embodiment of the present invention. 
         FIG. 5  is a diagram schematically showing a configuration of a connection portion of an electronic endoscope and a processor according to the embodiment of the present invention. 
         FIG. 6  is a block diagram showing a configuration of an electronic endoscope system according to a first variation of the embodiment of the present invention. 
         FIG. 7  is a block diagram showing a configuration of an electronic endoscope system according to a second variation of the embodiment of the present invention. 
         FIG. 8  is a block diagram showing a configuration of an electronic endoscope system according to a third variation of the embodiment of the present invention. 
         FIG. 9  is a block diagram showing a configuration of an electronic endoscope system according to a fourth variation of the embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that an electronic endoscope system is taken as an example of an embodiment of the present invention in the following description. 
       FIG. 1  is a block diagram showing the configuration of an electronic endoscope system  1  according to an embodiment of the present invention. As shown in  FIG. 1 , the electronic endoscope system  1  is a system specialized for medical use, and includes an electronic endoscope  100 , a processor  200 , and a monitor  300 . 
     The processor  200  includes a system controller  202  and a timing controller  204 . The system controller  202  executes various programs stored in a memory  222  and performs overall control of the electronic endoscope system  1 . Also, the system controller  202  is connected to an operation panel  224 . The system controller  202  changes operations of the electronic endoscope system  1  and parameters for various operations in accordance with instructions from an operator that are input using the operation panel  224 . One example of an instruction input by an operator is an instruction for switching the observation mode of the electronic endoscope system  1 . Examples of observation modes include a normal observation mode, a special observation mode, and a twin observation mode. The timing controller  204  outputs a clock pulse, which is for adjustment of the timing of the operations of portions, to circuits in the electronic endoscope system  1 . 
     The processor  200  includes white LEDs (Light Emitting Diodes)  206 A and  206 B.  FIG. 2( a )  shows an example of the spectral intensity distribution of the white LEDs  206 A and  206 B. As shown in  FIG. 2( a ) , the white LEDs  206 A and  206 B are so-called pseudo white light sources that have an uneven emission spectrum. 
     The processor  200  also includes a purple LED  210 B.  FIG. 2( b )  shows an example of the spectral intensity distribution of the purple LED  210 B. As shown in  FIG. 2( b ) , the purple LED  210 B is a light source that emits only light in the purple region. 
     The white LED  206 A is one example of a first light source portion. White light emitted by the white LED  206 A passes through a collimator lens  208 A and enters a shutter portion  240 . 
     The white LED  206 B, the purple LED  210 B, and a dichroic mirror  214 B are one example of a second light source portion. White light emitted by the white LED  206 B and purple light emitted by the purple LED  210 B respectively pass through collimator lenses  208 B and  212 B and are incident on the dichroic mirror  214 B. In other words, light that is a combination of white light and purple light (light having the spectral intensity distribution illustrated in  FIG. 2( c ) ) is incident on the dichroic mirror  214 B. Hereinafter, for the sake of convenience in the description, this light that is a combination of white light and purple light will be referred to as “superimposed light”. 
     The superimposed light that is incident on the dichroic mirror  214 B is filtered by a narrow-band light filter  216 B and then enters the shutter portion  240 . Here, the narrow-band light filter  216 B is attached to the case of the processor  200  and has a fixed position in the case. The narrow-band light filter  216 B is shaped as a simple disk, for example. 
       FIG. 3( a )  shows an example of the spectral characteristics of the narrow-band light filter  216 B. Also,  FIG. 3( b )  shows an example of different spectral characteristics from  FIG. 3( a )  for the narrow-band light filter  216 B. As shown in  FIGS. 3( a ) and 3( b ) , the narrow-band light filter  216 B has a spectral characteristic of allowing only light in a specific wavelength region to pass. For the sake of convenience in the description, light filtered by the narrow-band light filter  216 B will be referred to as “special light”. 
       FIG. 4  shows the configuration of the shutter portion  240 . The shutter portion  240  functions as a light blocking portion that alternatingly blocks light from the first light source portion and light from the second light source portion, and includes a rotating disk  241  as shown in  FIG. 4 . The rotating disk  241  is a member made of a metal such as stainless steel, and an opening  241   a  is formed therein as shown in  FIG. 4( a ) . The opening  241   a  is shaped as a fan that spreads out over approximately 180°. 
     When a shutter control circuit  220  performs control to drive a DC motor  242  under control of the system controller  202 , driving force from the DC motor  242  is transmitted to a rotation shaft  244  via a transmission mechanism (belt)  243 , and thus the rotation shaft  244  rotates. Accordingly, the rotating disk  241  rotates about the rotation shaft  244 . 
     The rotating disk  241  blocks the light path of either the white light or the special light according to its rotation position, and at the same time the opening  241   a  is inserted into the other light path, thereby allowing light on the other light path to pass. Hereinafter, for the sake of convenience in the description, the state where the opening  241   a  is located in the light path of white light (in other words, the state of blocking only the light path of special light) will be referred to as the “white light transmission state”, and the state where the opening  241   a  is located in the light path of special light (in other words, the state of blocking only the light path of white light) will be referred to as the “special light transmission state”. 
     The position of the opening  241   a  alternatingly switches between the light path of white light and the light path of special light due to the rotating disk  241  rotating about the rotation shaft  244 . Hereinafter, for the sake of convenience in the description, during rotation of the rotating disk  241 , the period in which the opening  241   a  is located in the light path of white light will be referred to as the “white light transmission period”, and the period in which the opening  241   a  is located in the light path of special light will be referred to as the “special light transmission period”. Note that the angular range of the opening  241   a  is slightly less than 180°, and therefore a very small blocking period in which the light paths of both white light and special light are blocked exists between the white light transmission period and the special light transmission period. 
     In the white light transmission period, white light that passed through the collimator lens  208 A passes through the opening  241   a  and enters a condensing lens  218 A. The white light that entered the condensing lens  218 A is condensed on the entrance surface of an LCB (Light Carrying Bundle)  1 . 02 A by the condensing lens  218 A, and enters the LCB  102 A. 
     The LCB  102 A functions as a first light guiding member that guides light from the first light source portion to the subject. The white light that entered the LCB  102 A propagates inside the LCB  102 A. The white light that propagated inside the LCB  102 A exits from the exit surface of the LCB  102 A arranged at the distal end of the electronic endoscope  100 , passes through a light distribution lens  104 A, and irradiates the subject. Returning light from the subject irradiated by the white light from the light distribution lens  104 A passes through an objective lens  106  and forms an optical image on the light receiving surface of a solid-state image sensor  108 . 
     In the special light transmission period, special light that passed through the narrow-band light filter  216 B passes through the opening  241   a  and enters a condensing lens  218 B. The special light that entered the condensing lens  218 B is condensed on the entrance surface of an LCB  102 B by the condensing lens  218 B, and enters the LCB  102 B. 
     The LCB  102 B functions as a second light guiding member that guides light from the second light source portion to the subject. The special light that entered the LCB  102 B propagates inside the LCB  102 B. The special light that propagated inside the LCB  102 B exits from the exit surface of the LCB  102 B arranged at the distal end of the electronic endoscope  100 , passes through a light distribution lens  104 B, and irradiates the subject. Returning light from the subject irradiated by the special light from the light distribution lens  104 B passes through the objective lens  106  and forms an optical image on the light receiving surface of the solid-state image sensor  108 . 
     The solid-state image sensor  108  is a single-plate color CCD (Charge Coupled Device) image sensor that has a Bayer pixel arrangement. The solid-state image sensor  108  accumulates charge according to the light quantity of an optical image formed on pixels on the light receiving surface, generates R (Red), G (Green), and B (Blue) image signals, and outputs the image signals. Note that the solid-state image sensor  108  is not limited to being a CCD image sensor, and may be replaced with a CMOS (Complementary Metal Oxide Semiconductor) image sensor or another type of imaging apparatus. The solid-state image sensor  108  may be an element that includes a complementary color filter. 
     A driver signal processing circuit  110  is provided in the connection portion of the electronic endoscope  100 . Image signals of the subject irradiated by light from the light distribution lens  104 A or the light distribution lens  104 B are input by the solid-state image sensor  108  to the driver signal processing circuit  110  at a frame cycle. Note that the terms “frame” and “field” may be switched in the following description. In the present embodiment, the frame cycle and the field cycle are respectively 1/30 seconds and 1/60 seconds. The image signals input from the solid-state image sensor  108  are subjected to predetermined processing by the driver signal processing circuit  110  and output to a pre-stage signal processing circuit  226  of the processor  200 . 
     The driver signal processing circuit  110  also accesses a memory  112  and reads out unique information regarding the electronic endoscope  100 . The unique information regarding the electronic endoscope  100  recorded in the memory  112  includes, for example, the pixel count, sensitivity, operable frame rate, and model number of the solid-state image sensor  108 . The unique information read out from the memory  112  is output by the driver signal processing circuit  110  to the system controller  202 . 
     The system controller  202  generates control signals by performing various computation based on the unique information regarding the electronic endoscope  100 . The system controller  202  uses the generated control signals to control the operations of and the timing of various circuits in the processor  200  so as to perform processing suited to the electronic endoscope that is connected to the processor  200 . 
     A timing controller  204  supplies a clock pulse to the driver signal processing circuit  110  in accordance with timing control performed by the system controller  202 . In accordance with the clock pulse supplied from the timing controller  204 , the driver signal processing circuit  110  controls the driving of the solid-state image sensor  108  according to a timing synchronized with the frame rate of the images processed by the processor  200 . 
     The pre-stage signal processing circuit.  226  performs predetermined signal processing such as demosaicing, processing, matrix computation, and Y/C separation on the image signal received in one frame cycle from the driver signal processing circuit  110 , and outputs the result to an image memory  228 . 
     The image memory  228  buffers image signals received from the pre-stage signal processing circuit  226 , and outputs the image signals to a post-stage signal processing circuit  230  in accordance with timing control performed by the timing controller  204 . 
     The post-stage signal processing circuit  230  performs processing on the image signals received from the image memory  228  to generate screen data for monitor display, and converts the generated monitor display screen data into a predetermined video format signal. The converted video format signal is output to the monitor  300 . Accordingly, subject images are displayed on the display screen of the monitor  300 . 
       FIG. 5  is a diagram schematically showing the configuration of a connection portion of the electronic endoscope  100  and the processor  200 . As shown in  FIG. 5 , a connector portion  150  of the electronic endoscope  100  is provided with a guide tube  152  and an electrical connector  154 . The guide tube  152  holds a base end portion  102 Aa of the LCB  102 A and a base end portion  102 Ba of the LCB  102 B. Also, a connector portion  250  of the processor  200  is provided with a guide tube receiving portion  252  and an electrical connector receiving portion  254 . 
     When the guide tube  152  and the guide tube receiving portion  252  are connected, the LCB  102 A and the condensing lens  218 A are coupled, and the LCB  102 B and the condensing lens  218 B are coupled. Accordingly, the electronic endoscope  100  and the processor  200  are optically connected. Also, when the electrical connector  154  and the electrical connector receiving portion  254  are connected, the electronic endoscope  100  and the processor  200  are electrically connected. 
     Next, operations of the electronic endoscope system  1  in various observation modes will be described. 
     Normal Observation Mode 
     The following describes operations of the electronic endoscope system  1  in the normal observation mode. 
     In the normal observation mode, the white LEDs  206 A and  206 B and the purple LED  210 B are on at all times. Also, the rotating disk  241  is stopped in the white light transmission state. For this reason, white light emitted by the white LED  206 A passes through the rotating disk  241  (opening  241   a ), and irradiates the subject via the condensing lens  218 A, the LCB  102 A, and the light distribution lens  104 A. On the other hand, white light and purple light emitted by the white LED  206 B and the purple LED  210 B are filtered by the narrowband light filter  216 B, but are blocked by the rotating disk  241  and therefore do not irradiate the subject. In other words, the subject is irradiated by white light that has the spectral intensity distribution shown in  FIG. 2( a ) . 
     Note that a configuration is possible in which in the normal observation mode, the white LED  206 A is on at all times, and the white LED  206 B and the purple LED  210 B are off at all times. 
     The solid-state image sensor  108  images the subject irradiated by white light, and outputs the image signal to the pre-stage signal processing circuit  226  via the driver signal processing circuit  110 . The image signal is processed by the pre-stage signal processing circuit  226 , the image memory  228 , and the post-stage signal processing circuit  230  and then output to the monitor  300 , and thus a normal color image of the subject is displayed on the display screen of the monitor  300 . 
     Special Observation Mode 
     The following describes operations of the electronic endoscope system  1  in the special observation mode. 
     In the special observation mode, the white LEDs  206 A and  206 B and the purple LED  210 B are on at all times. Also, the rotating disk  241  is stopped in the special light transmission state. For this reason, white light and purple light emitted by the white LED  206 B and the purple LED  210 B is filtered by the narrow-band light filter  216 B, passes through the rotating disk  241  (opening  241   a ), and irradiates the subject via the condensing lens  218 B, the LCB  102 B, and the light distribution lens  104 B. On the other hand, white light emitted by the white LED  206 A is blocked by the rotating disk  241 , and therefore does not irradiate the subject. In other words, the subject is irradiated by special light, which is the result of superimposed light having the spectral intensity distribution shown in  FIG. 2( c )  being filtered by the narrow-band light filter  216 B. 
     Note that a configuration is possible in which in the special observation mode, the white LED  206 A is off at all times, mid the white LED  206 B and the purple LED  210 B are on at all times. 
     The solid-state image sensor  108  images the subject irradiated by special light, and outputs the image signal to the pre-stage signal processing circuit  226  via the driver signal processing circuit  110 . Here, this special light is light that is highly absorbed by a specific biological structure. For this reason, the image signal is processed by the pre-stage signal processing circuit  226 , the image memory  228 , and the post-stage signal processing circuit  230  and then output to the monitor  300 , and thus a spectral image in which a specific biological structure is enhanced is displayed on the display screen of the monitor  300 . 
     Twin Observation Mode 
     The following describes operations of the electronic endoscope system  1  in the twin observation mode. 
     In the twin observation mode, the white LEDs  206 A and  206 B and the purple LED  210 B are on at all times. Also, the rotating disk  241  rotates about the rotation shaft  244  such that the position of the opening  241   a  alternatingly switches between the light path of white light and the light path of special light at a timing synchronized with the frame cycle (one frame at a time) (i.e., so as to alternatingly switch between the white light transmission period and the special light transmission period one frame at a time). For this reason, the subject is alternatingly irradiated by white light and special light at a timing synchronized with the frame cycle (one frame at a time). 
     In one frame, the solid-state image sensor  108  images the subject irradiated by white light and outputs the image signal to the pre-stage signal processing circuit  226  via the driver signal processing circuit  110 , and then in the next frame, images the subject irradiated by special light and outputs the image signal to the pre-stage signal processing circuit  226  via the driver signal processing circuit  110 . In other words, the solid-state image sensor  108  alternatingly outputs an image signal of the subject irradiated by white light and an image signal of the subject irradiated by special light to the pre-stage signal processing circuit  226  via the driver signal processing circuit  110 . The former and latter image signals are processed by the pre-stage signal processing circuit  226 , the image memory  228 , and the post-stage signal processing circuit  230  and then output to the monitor  300 . 
     Two regions for displaying observation images are arranged side-by-side in the display screen of the monitor  300 . A normal color image of the subject irradiated by white light is displayed in one of the regions, and a spectral image in which the subject irradiated by special light (specific biological structure) is enhanced is displayed in the other region. In other words, a normal color image and a spectral image of the subject are displayed side-by-side on the display screen of the monitor  300 . 
     In this way, according to the present embodiment, the narrow-band light filter  216 B is not a moved member, but rather is a member that is fixed inside the case of the processor  200 , and therefore there is no need for indicators for detecting the rotation position such as silk lines. Also, because the narrow-band light filter  216 B is not a moved member, there are few constraints in terms of its shape, and it may have a simple disk shape for example. In other words, according to the present embodiment, there is no need for indicators required to have strict tolerance management, and there are few constraints on the shape of the narrow-band light filter  216 B, thereby achieving advantages in terms of manufacturing (e.g., the yield is easily improved). 
     An illustrative embodiment of the present invention has been described above. The embodiments of the present invention are not limited to the embodiment described above, and various changes can be made without departing from the scope of the technical idea of the present invention. For example, appropriate combinations of embodiments and the like explicitly given as examples in this specification and obvious embodiments and the like are also encompassed in embodiments of the present invention. 
     The light source apparatus is provided inside the processor  200  in the above embodiment, but in another embodiment, a configuration is possible in which the processor  200  and the light source apparatus are separate. In this case, a wired or wireless communication means for exchanging timing signals is provided between the processor  200  and the light source apparatus. 
       FIG. 6  is a block diagram showing the configuration of an electronic endoscope system  1   z  according to a first variation of the present embodiment. As shown in  FIG. 6 , the electronic endoscope system  1   z  includes the electronic endoscope  100 , a processor  200   z , and the monitor  300 . The electronic endoscope system  1   z  of the first variation has the same configuration as the electronic endoscope system  1  of the above embodiment, with the exception that the processor  200   z  does not have the shutter control circuit  220  or the shutter portion  240 . 
     The following describes operations of the electronic endoscope system  1   z  in various observation modes according to the first variation. 
     Normal Observation Mode 
     The following describes operations of the electronic endoscope system  1   z  in the normal observation mode according to the first variation. 
     In the normal observation mode, the white LED  206 A is on at all times, and the white LED  206 B and the purple LED  210 B are off at all times. For this reason, the subject is irradiated by white light. 
     The solid-state image sensor  108  images the subject irradiated by white light, and outputs the image signal to the pre-stage signal processing circuit  226  via the driver signal processing circuit  110 . The image signal is processed by the pre-stage signal processing circuit  226 , the image memory  228 , and the post-stage signal processing circuit  230  and then output to the monitor  300 , and thus a normal color image of the subject is displayed on the display screen of the monitor  300 . 
     Note that the purple LED  210 B may be on at all times in the normal observation mode in order to improve color rendering. 
     Special Observation Mode 
     The following describes operations of the electronic endoscope system  1   z  in the special observation mode according to the first variation. 
     In the special observation mode, the white LED  206 A is off at all times, and the white LED  206 B and the purple LED  210 B are on at all times. For this reason, the subject is irradiated by special light filtered by the narrow-band light filter  216 B. 
     The solid-state image sensor  108  images the subject irradiated by special light, and outputs the image signal to the pre-stage signal processing circuit  226  via the driver signal processing circuit  110 . For this reason, the image signal is processed by the pre-stage signal processing circuit  226 , the image memory  228 , and the post-stage signal processing circuit  230  and then output to the monitor  300 , and thus a spectral image in which a specific biological structure is enhanced is displayed on the display screen of the monitor  300 . 
     Twin Observation Mode 
     The following describes operations of the electronic endoscope system  1   z  in the twin observation mode according to the first variation. 
     The system controller  202  alternatingly turns on the light sources of the first and second light source portions, thus operating as a control portion for alternatingly causing the two types of light to enter the first and second light guiding members. In the twin observation mode, the white LED  206 A is alternatingly turned on and off by the system controller  202  in accordance with a timing synchronized with the frame cycle (one frame at a time). The white LED  206 B and the purple LED  210 B are also alternatingly turned on and off by the system controller  202  in accordance with a timing synchronized with the frame cycle (one frame at a time). More specifically, in a frame in which the white LED  206 A is turned on, the white LED  206 B and the purple LED  210 B are turned off, and in a frame in which the white LED  206 A is turned off, the white LED  206 B and the purple LED  210 B are turned on. 
     For this reason, the subject is alternatingly irradiated by white light and special light at a timing synchronized with the frame cycle (one frame at a time). 
     In one frame, the solid-state image sensor  108  images the subject irradiated by white light and outputs the image signal to the pre-stage signal processing circuit  226  via the driver signal processing circuit  110 , and then in the next frame, images the subject irradiated by special light and outputs the image signal to the pre-stage signal processing circuit  226  via the driver signal processing circuit  110 . The former and latter image signals are processed by the pre-stage signal processing circuit  226 , the image memory  228 , and the post-stage signal processing circuit  230  and then output to the monitor  300 . Accordingly, a normal color image and a spectral image of the subject are displayed side-by-side on the display screen of the monitor  300 . 
     Note that the purple LED  210 B may be on at all times in the twin observation mode in order to improve color rendering in the normal color image. 
     In this way in the first variation, the shutter control circuit  220  and the shutter portion  240  are not necessary, thus achieving an advantage in terms of manufacturing cost. 
       FIG. 7  is a block diagram showing the configuration of an electronic endoscope system  1   y  according to a second variation of the present embodiment. As shown in  FIG. 7 , the electronic endoscope system  1   y  includes the electronic endoscope  100 , a processor  200   y , and the monitor  300 . The electronic endoscope system  1   y  of the second variation has the same configuration as the electronic endoscope system  1  shown in  FIG. 1 , with the exception that the processor  200   y  has a dichroic mirror  214 A. 
     The following describes operations of the electronic endoscope system  1   y  in various observation modes according to the second variation. 
     Normal Observation Mode 
     The following describes operations of the electronic endoscope system  1   y  in the normal observation mode according to the second variation. 
     In the normal observation mode, the white LEDs  206 A and  206 B and the purple LED  210 B are on at all times. Also, the rotating disk  241  is stopped in the white light transmission state. 
     The dichroic mirror  214 B simultaneously transmits 50% and reflects 50% of the purple light emitted by the purple LED  210 B. For this reason, the portion of the purple light that passed through the dichroic mirror  214 B is incident on the dichroic mirror  214 A. The purple light that is incident on the dichroic mirror  214 A and the white light emitted by the white LED  206 A are combined by the dichroic mirror  214 A (become superimposed light that has the spectral characteristics shown in  FIG. 2( c ) ), then pass through the rotating disk  241  (opening  241   a ) and irradiate the subject via the condensing lens  218 A, the LCB  102 A, and the light distribution lens  104 A. 
     In other words, the subject is irradiated by superimposed light. An image signal of the subject irradiated by superimposed light is processed such that a normal color image of the subject having improved color rendering is displayed on the display screen of the monitor  300 . Note that the purple light reflected by the dichroic mirror  214 B and the white light emitted by the white LED  206 B are filtered by the narrow-band light filter  216 B, but are blocked by the rotating disk  241  and do not irradiate the subject. 
     Special Observation Mode 
     The following describes operations of the electronic endoscope system  1   y  in the special observation mode according to the second variation. 
     In the special observation mode, the white LEDs  206 A and  206 B and the purple LED  210 B are on at all times. Also, the rotating disk  241  is stopped in the special light transmission state. For this reason, white light and purple light emitted by the white LED  206 B and the purple LED  210 B is filtered by the narrow-band light filter  216 B, passes through the rotating disk  241  (opening  241   a ), and irradiates the subject via the condensing lens  218 B, the LCB  102 B, and the light distribution lens  104 B. 
     In other words, the subject is irradiated by special light. Note that the purple light reflected by the dichroic mirror  214 A and the white light emitted by the white LED  206 A are blocked by the rotating disk  241  and do not irradiate the subject. An image signal of the subject irradiated by special light is processed such that a spectral image in which a specific biological structure is enhanced is displayed on the display screen of the monitor  300 . 
     Twin Observation Mode 
     The following describes operations of the electronic endoscope system  1   y  in the twin observation mode according to the second variation. 
     In the twin observation mode, the white LED  206 A is alternatingly turned on and off in accordance with a timing synchronized with the frame cycle (one frame at a time). The white LED  206 B is also alternatingly turned on and off in accordance with a timing synchronized with the frame cycle (one frame at a time). More specifically, in a frame in which the white LED  206 A is turned on, the white LED  206 B is turned off, and in a frame in which the white LED  206 A is turned off, the white LED  206 B is turned on. Also, the purple LED  210 B is on at all times. Also, the rotating disk  241  rotates about the rotation shaft  244  such that the position of the opening  241   a  alternatingly switches between the light path of superimposed light and the light path of special light at a timing synchronized with the frame cycle (one frame at a time). More specifically, the opening  241   a  is arranged in the light path of superimposed light in a frame in which the white LED  206 A is turned on, and is arranged in the light path of special light in a frame in which the white LED  206 B is turned on. For this reason, the subject is alternatingly irradiated by superimposed light and special light at a timing synchronized with the frame cycle (one frame at a time). Image signals of the subject irradiated by these types of light are processed such that an image including a normal color image and a spectral image side-by-side is displayed on the display screen of the monitor  300 . The subject is irradiated by superimposed light in the normal color image, and therefore color rendering in the normal color image is improved in the twin observation mode as well. 
       FIG. 8  is a block diagram showing the configuration of an electronic endoscope system  1   x  according to a third variation of the present embodiment. As shown in  FIG. 8 , the electronic endoscope system  1   x  includes the electronic endoscope  100 , a processor  200   x , and the monitor  300 . The electronic endoscope system  1   x  according to the third variation has the same configuration as the electronic endoscope system  1  shown in  FIG. 1 , with the exception that the processor  200   x  has a purple LED  210 A, a collimator lens  212 A, and a dichroic mirror  214 A. 
     The following describes operations of the electronic endoscope system  1   x  in various observation modes according to the third variation. 
     Normal Observation Mode 
     The following describes operations of the electronic endoscope system  1   x  in the normal observation mode according to the third variation. 
     In the normal observation mode, the white LEDs  206 A and  206 B and the purple LEDs  210 A and  210 B are on at all times. Also, the rotating disk  241  is stopped in the white light transmission state. The purple light emitted by the purple LED  210 A passes through the collimator lens  212 A, is reflected by the dichroic mirror  214 A, and is combined with white light emitted by the white LED  206 A (obtaining superimposed light that has the spectral characteristics shown in  FIG. 2( c ) ), then passes through the rotating disk  241  (opening  241   a ) and irradiates the subject via the condensing lens  218 A, the LCB  102 A, and the light distribution lens  104 A. 
     In other words, the subject is irradiated by superimposed light. An image signal of the subject irradiated by superimposed light is processed such that a normal color image of the subject having improved color rendering is displayed on the display screen of the monitor  300 . Note that white light and purple light emitted by the white LED  206 B and the purple LED  210 B are filtered by the narrow-band light filter  216 B, but are blocked by the rotating disk  241  and therefore do not irradiate the subject. 
     Special Observation Mode 
     The following describes operations of the electronic endoscope system  1   x  in the special observation mode according to the third variation. 
     In the special observation mode, the white LEDs  206 A and  206 B and the purple LEDs  210 A and  210 B are on at all times. Also, the rotating disk  241  is stopped in the special light transmission state. For this reason, white light and purple light emitted by the white LED  206 B and the purple LED  210 B is filtered by the narrowband light filter  216 B passes through the rotating disk  241  (opening  241   a ), and irradiates the subject via the condensing lens  218 B, the LCB  102 B, and the light distribution lens  104 B. 
     In other words, the subject is irradiated by special light. Note that white light and purple light emitted by the white LED  206 A and the purple LED  210 A are blocked by the rotating disk  241  and do not irradiate the subject. An image signal of the subject irradiated by special light is processed such that a spectral image in which a specific biological structure is enhanced is displayed on the display screen of the monitor  300 . 
     Twin Observation Mode 
     The following describes operations of the electronic endoscope system  1   x  in the twin observation mode according to the third variation. 
     In the twin observation mode, the white LED  206 A and the purple LED  210 A are alternatingly turned on and off in accordance with a timing synchronized with the frame cycle (one frame at a time). The white LED  206 B and the purple LED  210 B are also alternatingly turned on and off in accordance with a dining synchronized with the frame cycle (one frame at a time). More specifically, in a frame in which the white LED  206 A and the purple LED  210 A are turned on, the white LED  206 B and the purple LED  210 B are turned off, and in a frame in which the white LED  206 A and the purple LED  210 A are turned off, the white LED  206 B and the purple LED  210 B are turned on. Also, the rotating disk  241  rotates about the rotation shaft  244  such that the position of the opening  241   a  alternatingly switches between the light path of superimposed light and the light path of special light at a timing synchronized with the frame cycle (one frame at a time). More specifically, the opening  241   a  is arranged in the light path of superimposed light in a frame in which the white LED  206 A is turned on, and is arranged in the light path of special light in a frame in which the white LED  206 B is turned on. For this reason, the subject is alternatingly irradiated by superimposed light and special light at a timing synchronized with the frame cycle (one frame at a time). Image signals of the subject irradiated by these types of light are processed such that an image including a normal color image and a spectral image side-by-side is displayed on the display screen of the monitor  300 . The subject is irradiated by superimposed light in the normal color image, and therefore color rendering in the normal color image is improved in the twin observation mode as well. 
       FIG. 9  is a block diagram showing the configuration of an electronic endoscope system  1   w  according to a fourth variation of the present embodiment. As shown in  FIG. 9 , the electronic endoscope system  1   w  includes the electronic endoscope  100 , a processor  200   w , and the monitor  300 . The electronic endoscope system  1   w  according to the fourth variation has the same configuration as the electronic endoscope system  1  shown in  FIG. 1 , with the exception that the processor  200   w  has a green LED  206 B′ instead of the white LED  206 B, and does not have the narrow-band light filter  216 B. 
     The following describes operations of the electronic endoscope system  1   w  in various observation modes according to the fourth variation. 
     Normal Observation Mode 
     The following describes operations of the electronic endoscope system  1   w  in the normal observation mode according to the fourth variation. 
     In the normal observation mode, the white LED  206 A, the green LED  206 B′, and the purple LED  210 B are on at all times. Also, the rotating disk  241  is stopped in the white light transmission state. For this reason, white light emitted by the white LED  206 A passes through the rotating disk  241  (opening  241   a ), and irradiates the subject via the condensing lens  218 A, the LCB  102 A, and the light distribution lens  104 A. On the other hand, green light and purple light emitted by the green LED  206 B′ and the purple LED  210 B are blocked by the rotating disk  241  and do not irradiate the subject. An image signal of the subject irradiated by white light is processed such that a normal color image of the subject is displayed on the display screen of the monitor  300 . 
     Special Observation Mode 
     The following describes operations of the electronic endoscope system  1   w  in the special observation mode according to the fourth variation. 
     In the special observation mode, the white LED  206 A, the green LED  206 B′, and the purple LED  210 B are on at all times. Also, the rotating disk  241  is stopped in the special light transmission state. For this reason, green light and purple light emitted by the green LED  206 B′ and the purple LED  210 B pass through the rotating disk  241  (opening  241   a ) and irradiate the subject via the condensing lens  218 B, the LCB  102 B, and the light distribution lens  104 B. 
     In other words, the subject is irradiated by light that is a combination of green light and purple light and has characteristics approximating the spectral characteristics shown in  FIG. 3( b ) . Note that white light emitted by the white LED  206 A is blocked by the rotating disk  241 , and therefore does not irradiate the subject. An image signal of the subject irradiated by light having the above-described characteristics is processed such that a spectral image in which a specific biological structure is enhanced is displayed on the display screen of the monitor  300 . 
     Twin Observation Mode 
     The following describes operations of the electronic endoscope system  1   w  in the twin observation mode according to the fourth variation. 
     In the twin observation mode, the white LED  206 A is alternatingly turned on and off in accordance with a timing synchronized with the frame cycle (one frame at a time). The green LED  206 B′ and the purple LED  210 B are also alternatingly turned on and off in accordance with a timing synchronized with the frame cycle (one frame at a time). More specifically, in a frame in which the white LED  206 A is turned on, the green LED  206 B′ and the purple LED  210 B are turned off, and in a frame in which the white LED  206 A is turned off, the green LED  206 B′ and the purple LED  210 B are turned on. Also, the rotating disk  241  rotates about the rotation shaft  244  such that the position of the opening  241   a  alternatingly switches between the light path of white light and the light path of special light (green light+purple light) at a timing synchronized with the frame cycle (one frame at a time). More specifically, the opening  241   a  is arranged in the light path of white light in a frame in which the white LED  206 A is turned on, and is arranged in the light path of special light (green light+purple light) in a frame in which the green LED  206 B′ is turned on. For this reason, the subject is alternatingly irradiated by white light and light having characteristics approximating the spectral characteristics shown in  FIG. 3( b )  at a timing synchronized with the frame cycle (one frame at a time). Image signals of the subject irradiated by these types of light are processed such that an image including a normal color image and a spectral image side-by-side is displayed on the display screen of the monitor  300 . The electronic endoscope system  1   w  according to the fourth variation has no need for the narrow-band light filter  216 B, and thus has a configuration that is advantageous to cost reduction. 
     Note that a configuration further including a red LED is conceivable as a further variation of the fourth variation. In this case, the red LED, the green LED  206 B′, and the purple LED  210 B can be used to irradiate the subject with light that has characteristics approximating the spectral characteristics shown in  FIG. 3( a ) . Accordingly, a spectral image different from those of the above embodiment, variations, and the like is obtained. 
     Also, although the example of a configuration having the shutter control circuit  220  and the shutter portion  240  is given in the third and fourth variations, in another variation, this configuration may be replaced with a configuration not including the shutter control circuit  220  or the shutter portion  240  similarly to the first variation.