Abstract:
A fluorescent-light image obtaining apparatus for obtaining an autofluorescent-light image emitted from a target tissue irradiated by an excitation light, wherein the safety of the patient is ensured against injury from exposure to excessive excitation light when the distance between the output end of the excitation light projector and the target tissue is short. A contact detector detects that the end of the excitation light projector of the endoscope is in contact with the target tissue. Then, an excitation light output controller receives a signal indicating that the end of the excitation light projector is in contact with the target tissue. In response to this signal, the excitation light output controller stops the emission of the excitation light, or reduces the intensity of the emitted excitation light to a safe intensity for the patient even while the end of the excitation light projector and the target tissue are in contact.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fluorescent-light image obtaining apparatus for obtaining a fluorescent-light image of the fluorescent-light emitted from a target tissue upon irradiation thereof by an excitation light. 
     2. Description of the Related Art 
     There have been proposed technologies for irradiating a target tissue with an excitation light of a wavelength within the wavelength range of the intrinsic tissue fluorophores of the target tissue, and receiving the fluorescent-light emitted from the intrinsic tissue fluorophores of the target tissue thereupon, wherein, utilizing the difference between the fluorescent-light emitted from a normal tissue and the fluorescent-light emitted by a diseased tissue upon irradiation thereof by an excitation light of a predetermined wavelength, a fluorescent-light image of the location of the diseased tissue and its range of lesion is displayed. 
     Normally, when irradiated by excitation light, as shown by the solid line in  FIG. 1 , because a strong fluorescent-light is emitted by a normal tissue and a fluorescent-light weaker than that emitted from the normal tissue is emitted from a diseased tissue, as shown by the broken line in the same figure, by measuring the intensity of the fluorescent-light, it can be determined whether the target tissue is in a normal state or a diseased state. However, the fluorescent-light emitted from a target tissue is extremely weak, and because the detection thereof is difficult, as large intensity of fluorescent-light as possible is desirable. However, because there is a fear that injury to the patient result from too strong an excitation light, it must be controlled to be of a uniform intensity below a certain level. Levels of intensity of excitation light that do not cause injury to a patient are defined as MPE values according to the JIS standard, etc. Further, because the excitation light is spread at an angle of 100° at the excitation light emitting end of the endoscope insertion portion, as shown in  FIG. 2 , the relationship of the distance between the distal end of excitation light emitting means and the target area to the intensity of the excitation light received at the target area is such that the intensity of the excitation light becomes greater as the distance becomes shorter. Accordingly, the distance between the distal end of excitation light emitting means and the target area facilitating operation below the MPE value of 2000 W/m2 shown in  FIG. 2  is 3 mm or more. 
     However, in using a fluorescence endoscope apparatus, etc., because the target tissue is a tube-shaped organ, the excitation light emitting end of the endoscope insertion portion cannot be fixed in place and the distance between the target area an the excitation light emitting end of the endoscope insertion portion is not uniform. Therefore, when the intensity of the excitation light has been set close to the MPE value in order to obtain adequate fluorescent-light, if the distance between the excitation light emitting end of the endoscope insertion portion and the target area becomes less than 3 mm, it is possible for the target tissue of the target area be injured. On the other hand, under all measurement-taking conditions, including cases in which the distance between the excitation light emitting end of the endoscope insertion portion and the target area becomes less than 3 mm, for cases in which the intensity of the excitation light has been set so as to ensure for the safety of the target tissue of the target area, at the far end of the normal operational distance range (50-100 mm), the intensity of the excitation light becomes weak and an adequate intensity of fluorescent-light is not obtained, whereby the accuracy of the detection is reduced. Further, for cases in which the sensitivity of the detection system has been increased in order to detect such weak levels of fluorescent-light, the increase in the cost of the system is extremely high. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed in consideration of the circumstances described above, and it is a primary object of the present invention to provide a fluorescent-light image obtaining apparatus in which the safety of the patient is ensured and no deterioration to the detection, or exorbitant increase in the cost of the apparatus is incurred. 
     A fluorescent-light image obtaining apparatus according to the present invention comprises an excitation light emitting means for projecting excitation light onto a target tissue, an illuminating light emitting means for projecting illuminating light onto the target tissue, a fluorescent-light image obtaining means for obtaining a fluorescent-light image formed of the fluorescent-light emitted from the target tissue upon irradiation thereof by the excitation light, a normal-image obtaining means for obtaining a normal-image formed of the illuminating light reflected from the target tissue upon irradiation thereof by the illuminating light, further comprising a contact detecting means for detecting that the distal end of excitation light emitting means has come into contact with the target tissue, and an excitation light emission controlling means for controlling, in response to the detection signal of the contact detecting means, the output of the excitation light emitted from the excitation light emitting means. 
     According to the fluorescent-light image obtaining apparatus of the present invention, the contact detecting means detects whether or not the excitation light emitting end of the endoscope insertion portion is in contact with the target tissue. Then, a detection signal indicating that the distal end of excitation light emitting means is in contact with the target tissue is output to an excitation light emission controlling means, which controls, according to the detection signal, the output of the excitation light emitted from the excitation light emitting means. 
     The excitation light emission controlling means can stop the emission of excitation light from the excitation light emitting means. 
     In addition, the excitation light emission controlling means can control the intensity of the excitation light output from the excitation light emitting means to be below a predetermined intensity. Here, “predetermined intensity” refers to an excitation light intensity safe to the patient, that is, an intensity of excitation light at which injury is not caused to the target tissue of the target area, even under conditions in which the distal end of excitation light emitting means is in contact with the target tissue. 
     Another fluorescent-light image obtaining apparatus according to the present invention comprises an excitation light emitting means for projecting excitation light onto a target tissue, an illuminating light emitting means for projecting illuminating light onto the target tissue, a fluorescent-light image obtaining means for obtaining a fluorescent-light image formed of the fluorescent-light emitted from the target tissue upon irradiation thereof by the excitation light, a normal-image obtaining means for obtaining a normal-image formed of the illuminating light reflected from the target tissue upon irradiation thereof by the illuminating light, further comprising a distance parameter detecting means for detecting a parameter correlating the distance between the distal end of excitation light emitting means and the target tissue, and an excitation light emission controlling means for controlling, based on the distance parameter of the contact detecting means, the output of the excitation light emitted from the excitation light emitting means. 
     According to the fluorescent-light image obtaining apparatus of the present invention, the distance parameter detecting means detects whether or not the excitation light emitting end of the endoscope insertion portion is in contact with the target tissue. Then, the detected distance parameter is output to an excitation light emission controlling means, which controls, according to the detected distance parameter, the output of the excitation light emitted from the excitation light emitting means. 
     Aforementioned parameter can be based on the light intensity of a fluorescent-light image photographed by the fluorescent-light image obtaining means. Here, for example, the excitation light emission controlling means computes, based on the detected light intensity of the fluorescent-light image detected by the distance parameter detecting means, the percentage of the entire image or a portion of a specified image occupied by pixels of a size larger than a predetermined threshold value. Then, when this percentage is above a predetermined threshold value, the excitation light emission controlling means can control the output of the excitation light. 
     Further, the peak measured light value (the largest value of the pixel values) can be obtained for the entire fluorescent-light image or a specified portion thereof, and when this value is larger than a predetermined threshold value, the output of the excitation light from the excitation light emitting means can be controlled. 
     Instead, aforementioned parameter can be based on the light intensity of a normal image photographed by the normal-image obtaining means. Here, for example, the excitation light emission controlling means computes, based on the detected light intensity of the normal image detected by the distance parameter detecting means, the percentage of the entire image or a portion of a specified image occupied by pixels of a size larger than a predetermined threshold value. Then, when this percentage is above a predetermined threshold value, the excitation light emission controlling means can control the output of the excitation light. 
     Further, the peak measured light value (the largest value of the pixel values) can be obtained for the entire normal-image or a specified portion thereof, and when this value is larger than a predetermined threshold value, the output of the excitation light from the excitation light emitting means can be controlled. 
     In addition, yet another fluorescent-light image obtaining apparatus according to the present invention comprises a reference light emitting means for projecting reference light onto a target tissue, and a reflected-image obtaining means for obtaining a reflected-image formed of the reference light reflected from the target tissue upon irradiation thereof by the reference light, wherein the parameter detected by the distance parameter detecting means can be based on the light intensity of the reflected-image. Here, the excitation light emission controlling means computes, based on the detected light intensity of the reflected-image detected by the distance parameter detecting means, the percentage of the entire image or a portion of a specified image occupied by pixels of a size larger than a predetermined threshold value. Then, when this percentage is above a predetermined threshold value, the excitation light emission controlling means can control the output of the excitation light. 
     Further, the peak measured light value (the largest value of the pixel values) can be obtained for the entire reflected-light image or a specified portion thereof, and when this value is larger than a predetermined threshold value, the output of the excitation light from the excitation light emitting means can be controlled. 
     Still further, the excitation light emission controlling means can be a current controlling means for controlling the current of the excitation light source of the excitation light emitting means. 
     The excitation light emission controlling means can stop the emission of excitation light from the excitation light emitting means. 
     Further, the excitation light emission controlling means can control the intensity of the excitation light output from the excitation light emitting means to be below a predetermined intensity. Here, “predetermined intensity” refers to a light intensity safe to the patient; that is, an excitation light intensity not causing injury to the target tissue when the distance between the excitation light emitting end of the endoscope insertion portion and the target tissue is set at a certain distance satisfying the aforementioned threshold value conditions. 
     According to fluorescent-light image obtaining apparatus of the configuration described above according to the present invention, that the target tissue and the excitation light emitting end of the endoscope insertion portion have come in contact is detected, and the emission of the excitation light from the excitation light emitting means can be stopped in response to this signal, or controlled so as to be of an intensity that, even while the end of the excitation light projector and the target tissue are in contact, does not cause injury to the target tissue, whereby the safety of the patient can be ensured. 
     In addition, according to fluorescent-light image obtaining apparatus of the configuration described above according to the present invention, a parameter correlating the distance between the excitation light emitting end of the endoscope insertion portion and the target tissue is detected, and the emission of the excitation light from the excitation light emitting means is stopped in response to this signal, or controlled so as to be of an intensity that, even while the end of the excitation light projector and the target tissue are in contact, does not cause injury to the target tissue, whereby the safety of the patient can be ensured. 
     Further, aforementioned parameter can be based on the light intensity of a fluorescent-light image, a normal-image, or a reflected-light image, whereby the configuration of the apparatus can be kept simple and the cost kept down. 
     Still further, according to the fluorescent-light image obtaining apparatus of the present invention, the light intensity of a fluorescent-light image, a normal image or a reflected-image, that is, the percentage of an entire image or of a portion of an image occupied by pixels having a pixel value larger than a predetermined threshold value is computed. When this percentage is above a predetermined threshold value, the excitation light emitted from the excitation light emitting means can be stopped or controlled so as to be of a light intensity safe to the patient, that is, an excitation light intensity not causing injury to the target tissue when the distance between the excitation light emitting end of the endoscope insertion portion and the target tissue is set at a certain distance satisfying the aforementioned threshold value conditions. Further, by selecting an appropriate threshold value, the safety of the patient can be ensured with a higher degree of reliability. 
     In addition, by performing control of the output of the excitation light, such as that described above, deterioration of the degree of accuracy of detection or increase in cost is not incurred, and the safety of the patient can be ensured. 
     Further, for cases in which the peak measured light value (the largest value of the pixel values) is obtained for the entire reflected-light image or a specified portion thereof, and the output of the excitation light from the excitation light emitting means is controlled when this value is larger than a predetermined threshold value, because only a peak value holding circuit needs to be provided, control of the emission of the excitation light of the can be carried out by an even further simplified configuration. 
     Still further, for cases in which the target tissue is a tube-shaped organ, if the peak measured light value, etc. is obtained of the specified circumference portion of fluorescent-light image, a reflected-light image, or a normal-image, control of the emission of excitation light can be performed such that the distance is more accurately reflected. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a drawing provided for explanation of the distribution of the intensity of the fluorescence spectra in an autofluorescent-light image, 
         FIG. 2  shows the energy density of the excitation light received at the target area relative to the distance between the excitation light emitting end of the endoscope insertion portion and the target area, 
         FIG. 3  is a schematic drawing of a fluorescence endoscope apparatus according to the first embodiment of the present invention, 
         FIG. 4  is a schematic drawing of the optical transmitting filter used in the fist, second, third, and fourth embodiments of a fluorescence endoscope apparatus according to the present invention, 
         FIG. 5  is a schematic drawing of a fluorescence endoscope apparatus according to the second and third embodiments of the present invention, 
         FIG. 6  is a schematic drawing of a fluorescence endoscope apparatus according to the fourth embodiment of the present invention, and 
         FIG. 7  is a schematic drawing of the endoscope insertion portion, for cases in which the image fiber is a composite glass fiber, used in the first, second, third, and fourth embodiments of a fluorescence endoscope apparatus according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, with reference to the drawings, the preferred embodiments of the present invention will be explained.  FIG. 3  is a schematic drawing of a fluorescence endoscope apparatus implementing the fluorescent-light image display apparatus according to the present invention. 
     The fluorescence endoscope apparatus according to the first embodiment of the present invention comprises: an image signal processing portion  1  provided with an endoscope insertion portion  100  to be inserted into the body of the patient to the position at which the primary nidus of a disease and areas of suspected secondary infection are located, an illuminating unit  110  provided with 2 light sources, one for emitting normal-image use white-light Lw and one for emitting autofluorescent-light image use excitation light Lr, an image detecting unit  300  for obtaining an autofluorescent-light image Zj of the autofluorescent-light emitted from a target tissue  10  upon irradiation thereof by the excitation light Lr, and digitizing and outputting said autofluorescent-light image Zj as two-dimensional digital data, an image computing unit  400  for computing a distance correction value, etc. from the two-dimensional data output from the image detecting unit  300  and computing a computed-image, and comparing the data of each pixel to prerecorded standards values and outputting a signal based on the results of said comparison, a display signal processing means  500  for digitizing a normal-image and obtaining a two-dimensional data thereof, and converting said two-dimensional data and the signal output from the image computing unit  400  to a video signal and outputting said video signal, an excitation light emission controlling means  120  for controlling, in response to a detection signal that the excitation light emitting end of the endoscope insertion portion  100  and the target tissue  10  are in contact, the output of the excitation light, a control computer  200 , which is connected to each of the units, for controlling the operation timing thereof; a monitor  600  for displaying as a visible image the signal processed by the display-signal processing unit  500 , and a foot-switch  140  for initiating emission of the excitation light. 
     The endoscope insertion portion  100  comprises a light guide  101  extending to the forward end in the internal portion, a CCD cable  102 , an image fiber  103 , and a detection signal line  131 . The forward end portion of the light guide  101  and the CCD cable  102 , that is, the forward end portion of the endoscope insertion portion  100 , is provided with an illuminating lens  104  and an objective lens  105 . Further, the image fiber  103  is a silicon glass fiber, and a focusing lens  106  is provided at the forward end thereof. A normal-image use detecting element  107  is connected to the forward end of the CCD cable  102 , and a reflection-use prism  108  is attached to said normal-image use detecting element  107 . The light guide  101  is an integrated cable in which a white-light  101   a  formed of composite glass fiber and an excitation light guide  101   b  formed of silicon glass fiber are bundled, and the white-light guide  101   a  and the excitation light guide  101   b  are connected to the illuminating unit  110 . One end of the CCD cable  102  is connected to the display signal processing unit  140 . One end of the image fiber  103  is connected to the image detecting unit  300 , and one end of the detection signal line is connected to the excitation light emission controlling means  120 . 
     The illuminating unit  110  comprises: a white-light source  111  for emitting normal-image use white-light Lw and a white-light use power source  112  electrically connected to said white-light source  111 , and a white-light use focusing lens  113  for focusing the white light emitted from the white-light source; a GaN semiconductor laser  114  for emitting fluorescent-light image obtaining-use excitation light L 2  and a semiconductor-laser use power source  115  electrically connected to said GaN semiconductor laser  114 , and an excitation light use focusing lens  116  for focusing the excitation light emitted from the GaN semiconductor laser  114 . 
     The image detecting unit  300  is connected to an image fiber  103 , and comprises a fluorescent-light use collimator lens  301  for guiding to a focusing system an autofluorescent-light image Zj conveyed through the image fiber  103 , an excitation light cutoff filter  302  for cutting off from the autofluorescent-light image light having a wavelength near that of the excitation light, an optical transmitting filter  303  for extracting a desired wavelength band from the autofluorescent-light image transmitted by the cutoff filter  302 , a filter rotating apparatus  304  for rotating the optical transmitting filter  303 , a fluorescent-light use focusing lens  305  for focusing the autofluorescent-light image Zj transmitted by the optical transmitting filter  303 , a high-sensitivity fluorescent-light image use detecting element  306  for obtaining the autofluorescent-light image Zj focused by the focusing lens  305 , and an A/D converter  307  for digitizing the autofluorescent-light image Zj obtained by the high-sensitivity fluorescent-light image use detecting element  306  and outputting said digitized autofluorescent-light image Zj as a two-dimensional image data. 
     The optical transmitting filter  303 , as shown in  FIG. 4 , is formed of two types of optical filters: an optical filter  303   a,  which is a band-pass filter for transmitting light in the 430-730 nm wavelength range, and an optical filter  303   b,  which is a band-pass filter for transmitting light in the 430-470 nm wavelength range. 
     The image computing unit  400  comprises an image data memory  401  for storing digitized autofluorescent-light images, a standard-values use memory  402  in which a set of standard-value RE have been prerecording for use in determining whether a tissue of which an image has been obtained is a diseased tissue or a normal tissue, an interimage computing portion  403  for computing, based on the ratio between the pixels of each of the two images formed of a different wavelength band stored in the image data memory  401 , a computed value for each of said pixels, and for performing a comparison of said computed values for each of said pixels to the prerecorded standard-value RE stored in the standard-values use memory  402  and forming and outputting a computed image according to the results of said comparison. 
     The standard-values RE are set according to the pixel values of standard autofluorescent-light images of a diseased tissue and a normal tissue obtained in advance. 
     The display signal processing unit  500  comprises an A/D converter for digitizing a visual-image signal obtained by the normal-image use detecting element  107 , a normal-image data memory  502  for storing digitized normal-image signals, and a video signal converting circuit  503  for converting an image signal output from the normal-image memory  502  and the computed image formed by the interimage computing portion  403  to video signals. 
     The monitor unit  600  comprises a normal-image use monitor  601  and a computed image use monitor  602 . 
     Hereinafter, the operation of a fluorescence endoscope apparatus of the configuration described above implementing the fluorescent-light image obtaining apparatus according to the current embodiment of the present invention will be explained. 
     First, by use of a displayed normal-image, which has been produced by illuminating-light, for guidance, the endoscope insertion portion  100  is inserted into the body of the patient to the position at which the target tissue  10  of the target area is located. Next, by pressing the foot switch  140 , excitation light is caused to be emitted so that a computed image can now be displayed. First, the operation occurring when a normal-image is to be displayed and the operation occurring when a computed image is to be displayed will be explained. 
     When a computed image is to be displayed, the excitation light use power source  115  is activated based on a signal from the control computer  200  and excitation light Lr having a wavelength of 410 nm is emitted from the GaN semiconductor laser. The excitation light Lr is transmitted by an excitation light use lens  116  and enters the excitation light light guide  101   b, and after being guided to the excitation light emitting end of the endoscope insertion portion, is projected onto the target tissue  10  by an illuminating lens  104 . 
     The autofluorescent-light transmitted by the excitation light cutoff filter  302  enters the optical transmitting filter  303 . Note that the excitation light cutoff filter  302  is a long-pass cutoff filter transmitting all fluorescent-light of a wavelength of 420 nm or larger. Because the excitation light Lr has a wavelength of 410 nm, the excitation light reflected from the target tissue  10  is cutoff by the excitation light cutoff filter  302  and does not enter the optical transmitting filter  303 . 
     The filter rotating apparatus  304  is activated by the control computer  200 , and after being transmitted by the optical transmitting filter  303   a  or  303   b,  the fluorescent-light is focused by the fluorescent-light use lens  305  and a fluorescent-light image thereof is obtained by the high-sensitivity fluorescent-light image use detecting element  306 ; a visible-image signal thereof is input from the to the high-sensitivity fluorescent-light image use detecting element  306  to the A/D converting circuit  307 , where it is converted to digital data, and then stored in the image data memory  401 . 
     Computations corresponding to the ratio of each pixel value of each of the images stored in the imaged data memory  401  are performed by the interimage computing portion  403 , and a comparison of the computed values obtained thereby and the standard-value RE prerecorded in the standard-values memory  402  is performed and a determination is made as to whether each pixel represents a normal tissue or a diseased tissue, based upon which a computed image is computed and formed. The standard-values RE are set according to the pixel values of standard autofluorescent-light images of a diseased tissue and a normal tissue obtained in advance, and the determination as to whether a tissue is a normal tissue or a diseased tissue is performed so as to determine whether the computed value of each pixel value of each image is large or small relative to the standard-value RE. 
     The computed image is displayed on the computed-image use monitor  602 . By allotting different display colors to a measured zone in which the computed value is smaller than the standard-value RE and a measured zone in which the computed value is larger than the standard-value RE, it is possible for an operator to recognize the comparison results in an instant. 
     Next, the operation occurring when a normal-image is to be displayed will be explained. When a normal-image is to be displayed, the white-light source power source  112  is activated based on a signal from the control computer  200  and white-light Lw is emitted from the white-light source  111 . The white-light Lw enters the white-light light guide  101   a  via the white-light use focusing lens  113 , and after being guided to the excitation light emitting end of the endoscope insertion portion, the white-light Lw is projected onto the target tissue  10  by the illuminating lens  104 . The white light Lw reflected from the target tissue  10  is focused by an objective lens  105  and is reflected by a reflection-use prism  108 , and is focused on a normal-image use detecting element  107 . The visible-image signal from the normal-image use detecting element  107  is input to the A/D converter  501  where it is digitized, after which it is stored in the normal-image data memory  502 . The normal-image signal stored by the normal-image data memory  502  is D/A converted by the video signal processing circuit  503 , after which it is input to the normal-image use monitor  601  and displayed as a visual image thereon. The continuous operation described above is controlled by the control computer  200 . 
     Then, while a computed image is being displayed, that is, while excitation light is being emitted, when the excitation light emitting end of the endoscope insertion portion  100  comes into contact with the target tissue  10 , said contact is detected, and a detection signal indicative thereof is output to the excitation light emission controlling means  120  by way of the detection signal line  131 . The excitation light emission controlling means causes the emission of the excitation light to cease upon reception of said detection signal, or sends a signal to the control computer  200  so that the control computer  200  can control the emission of the excitation light so that the excitation light is emitted at an intensity that does not cause injury to the target tissue and ensures for the safety of the patient even when the excitation light emitting end of the endoscope insertion portion and the target tissue are in contact. Afterwards, it is possible to again cause the excitation light to be emitted at image-obtaining intensity by pressing the foot switch  140 . 
     According to a fluorescence endoscope apparatus of the configuration described above and implementing the fluorescent-light image obtaining apparatus according to the present invention, that the excitation light emitting end of the endoscope insertion portion  100  and the target tissue have  10  come into contact is detected, and based on a detection signal indicative thereof, the emission of the excitation light from the excitation light emitting end of the endoscope insertion portion is ceased or controlled so as to be emitted at a safe intensity not causing injury to the target tissue  10 , whereby the safety of the patient from the exposure to excessive excitation light can be ensured. 
     Next, the second embodiment of the present invention will be explained.  FIG. 5  is a schematic drawing of a fluorescence endoscope apparatus implementing the fluorescent-light image obtaining apparatus according to the present invention. Note that in so far as further explanation of elements that are the same as those of the first embodiment shown in  FIG. 3  is not required, it has been omitted. 
     The fluorescence endoscope apparatus according to the current embodiment excludes the contact detecting means  130  and the detecting line  131  occurring in the first embodiment, and is provided with an excitation light emission controlling unit  700  comprising a distance parameter detecting means  701  for detecting the pixel data of an obtained fluorescent-light image as a parameter correlated to the distance between the endoscope insertion portion  100  and the target tissue  10 , and an excitation light emission controlling means  702  for causing, based on said parameter, the emission of the excitation light to cease, or causing the excitation light to be emitted at a safe intensity not causing injury to the target tissue. 
     Next, the operation of a fluorescence endoscope apparatus of the configuration described above according to the current embodiment of the present invention will be explained. 
     First, by use of a displayed normal-image, which has been produced by illuminating-light, for guidance, the endoscope insertion portion  100  is inserted into the body of the patient to the position at which the target tissue  10  of the target area is located. Next, by pressing the foot switch  140 , excitation light is caused to be emitted so that a computed image can now be displayed. Note that the intensity of the excitation light output when the emission of the excitation light is initiated is of a safe intensity to the patient not causing injury to the target tissue of the target area, regardless of the distance between the excitation light emitting end of the endoscope insertion portion and the target tissue. 
     Then, while a computed image is being displayed, the pixel data of an obtained fluorescent-light image is detected by the distance parameter detecting means  701 . The detection data thereof is output to the excitation light emission controlling means  702 , and with regard to this detection data, that is, the data of the size of each pixel value of the fluorescent-light image, the percentage of the entire image or a specified portion of the image occupied by pixels having a value over a predetermined threshold value is computed. Then, when this percentage is above a predetermined threshold value, the emission of the excitation light is ceased, or a signal is output to the control computer  200  so that the control computer  200  can control the emission of the excitation light so that it is emitted at a safe intensity not causing injury to the target tissue  10  when the distance between the excitation light emitting end of the endoscope insertion portion  100  and the target tissue  10  satisfies the aforementioned threshold value conditions. Afterwards, it is possible to again cause the excitation light to be emitted at image-obtaining intensity by pressing the foot switch  140 . Other operations are the same as those occurring in the first embodiment. 
     According to a fluorescence endoscope apparatus of the configuration described above and implementing the fluorescent-light image obtaining apparatus according to the present invention, a parameter correlating the distance between the excitation light emitting end of the endoscope insertion portion  100  and the target tissue have  10  (in the current embodiment, the light strength of a fluorescent-light image) is detected, and based on said detected parameter, the emission of the excitation light from the excitation light emitting end of the endoscope insertion portion is ceased or controlled so as to be emitted at a safe intensity not causing injury to the target tissue  10 , whereby the safety of the patient from the exposure to excessive excitation light can be ensured when the distance between the excitation light emitting end of the endoscope insertion portion and the target tissue  10  is extremely close. 
     Next, the third embodiment of the present invention will be explained. Because the configuration thereof is substantially the same as that of the second embodiment shown in  FIGS. 4 and 5 , reference numbers have been assigned in  FIGS. 4 and 5  only to elements that differ with those of the second embodiment, and the explanation is provided thereof. Note that in so far as further explanation of those elements in common with the second embodiment is not required, it has been omitted. 
     The fluorescence endoscope apparatus according to the current embodiment utilizes the white-light source  111  of the second embodiment as a reference-light source, and is provided with an image detecting unit  800  which is provided with a optical transmitting filter  801  instead of an optical transmitting filter  303 . Because the white-light Lw emitted from the white-light source  111  contains wavelength bands that can be used as reference-light, the white-light source  111  can be used as a reference-light source. 
     In addition, the optical transmitting filter  801  comprises an optical transmitting filter  801   a  for transmitting a fluorescent-light image, and an optical transmitting filter  801   b  for transmitting an reference-light image: the optical filter  801   a  is a band-pass filter transmitting light having a wavelength in the 430-730 nm range, and the optical transmitting filter  801   b  is a band-pass filter transmitting light having a wavelength in the 750-900 nm range. 
     Further, the distance parameter detecting means  701  occurring in the second embodiment has been made so as to detect the pixel data of a reflected-light image, which is obtained upon the irradiation of the target tissue by the reference-light, as a parameter correlated to the distance between the excitation light emitting end of the endoscope insertion portion  100  and the target tissue  10 . 
     Next, the operation of a fluorescence endoscope apparatus of the configuration described above according to the current embodiment of the present invention will be explained. 
     First, by use of a displayed normal-image, which has been produced by illuminating-light, for guidance, the endoscope insertion portion  100  is inserted into the body of the patient to the position at which the target tissue  10  of the target area is located. Next, by pressing the foot switch  140 , excitation light is caused to be emitted so that a computed image can now be displayed. 
     Here, the operation occurring when a computed image, which is based on an autofluorescent-light image and a reference-light image, is to be displayed will be explained. When a computed image is to be displayed, the white-light source power source  112  is activated based on a signal from the control computer  200  and white light Lw is emitted. This white-light Lw contains the reference-light Ls, which has a wavelength within the 750-900 nm wavelength band. The white-light Lw containing the reference light Ls is transmitted by a lens  113  and enters the white-light light guide  101   a,  and after being guided to the excitation light emitting end of the endoscope insertion portion, the white-light Lw containing the reference-light Ls is projected onto the target tissue  10  by the illuminating lens  104 . 
     The reflected-light reflected from the target tissue upon irradiation thereof by the white-light Lw containing the reference-light Ls is focused by the focusing lens  106  and enters the forward end of the image fiber  103 , and passes through the image fiber  103  and enters the excitation light cutoff filter  302 . The fluorescent-light transmitted by the excitation light cutoff filter  302  enters the optical transmitting filter  801 . 
     The filter rotating apparatus  304  is activated by the control computer  200 , and after a reference-light image Zs is transmitted by the optical filter  801   b,  said reference-light image is focused by a fluorescent-light use focusing lens  305  and obtained by the high-sensitivity fluorescent-light image use detecting element  306 , and a visible image signal is input from the high-sensitivity fluorescent-light image use detecting element  306  to the A/D converting circuit  307  where it is digitized, after which it is stored in the image data memory  401 . Here, only the reference-light image Zs formed of the reflected-light reflected from the target tissue  10  upon irradiation thereof by the white-light Lw containing the reference-light Ls is transmitted by the optical filter  801   b.  Further, the reference-light image data is stored in a memory zone different from that in which the autofluorescent-light image data is stored within the image data memory  401 . The operation with respect to an autofluorescent-light image is the same up to the storage thereof in the image data memory  401  as occurred in the first embodiment. 
     Computations according to the ratio of each of the pixel values of an autofluorescent-light image and a reference-light image stored in the image data memory  401  are performed by the interimage computing portion  403 , and the computed values obtained thereby and the standard-value RE prerecorded in the standard-value memory  402  are compared and a determination is made as to whether each pixel represents a normal tissue or a diseased tissue, based upon which a computed image is computed and formed. The standard-values RE are set according to the pixel values of standard autofluorescent-light images of a diseased tissue and a normal tissue obtained in advance. 
     Then, while a computed image is being displayed, the pixel data of an obtained reflected-light image is detected by the distance parameter detecting means  701 . The detection data thereof is output to the excitation light emission controlling means  702 , and with regard to this detection data, that is, the data of the size of each pixel value of the reflected-light image, the percentage of the entire image or a specified portion of the image occupied by pixels having a value over a predetermined threshold value is computed. Then, when this percentage is above a predetermined threshold value, the emission of the excitation light is ceased, or a signal is output to the control computer  200  so that the control computer  200  can control the emission of the excitation light so that it is emitted at a safe intensity not causing injury to the target tissue  10  when the distance between the excitation light emitting end of the endoscope insertion portion  100  and the target tissue  10  satisfies the aforementioned threshold value conditions. Afterwards, it is possible to again cause the excitation light to be emitted at image-obtaining intensity by pressing the foot switch  140 . Other operations are the same as those occurring in the second embodiment. 
     Note that according to the embodiment described above, because the white-light source is used as the reference-light source, when the excitation light is controlled so as to be of a predetermined strength, it is desirable that the strength of the reference-light, that is, the strength of the white-light be controlled at the same time. In this case, when a halogen lamp, an Xe lamp, etc. is used as the white-light source  111 , the strength of the white-light can be controlled by, for example, controlling a filter or a diaphragm that has been provided between the white-light source  111  and the white-light use lens  113 . 
     According to a fluorescence endoscope apparatus of the configuration described above implementing the fluorescent-light image obtaining apparatus according to the present invention, by utilizing a distance parameter based on a clear reference-light image in order to estimate the distance between the excitation light emitting end of the endoscope insertion portion and the target tissue, in addition to the results obtained in the second embodiment, the emission of the excitation light can be more precisely controlled. 
     Next, the fourth embodiment of the present invention will be explained.  FIG. 6  is a schematic drawing of a fluorescence endoscope apparatus implementing the fluorescent-light image obtaining apparatus according to the present invention. Note that in so far as further explanation of elements that are the same as those of the third embodiment is not required, it has been omitted. 
     According to the fluorescence endoscope apparatus of to the current embodiment, the distance parameter detecting means  701  occurring in the third embodiment has been made so as to detect the pixel data of a normal-image, which is obtained upon the irradiation of the target tissue by the white-light Lw, as a parameter correlated to the distance between the excitation light emitting end of the endoscope insertion portion  100  and the target tissue  10 , and is designated as distance parameter detecting device  901 . Next, the operation of a fluorescence endoscope apparatus of the configuration described above according to the current embodiment of the present invention will be explained. 
     First, by use of a displayed normal-image, which has been produced by illuminating-light, for guidance, the endoscope insertion portion  100  is inserted into the body of the patient to the position at which the target tissue  10  of the target area is located. Next, by pressing the foot switch  140 , excitation light is caused to be emitted so that a computed image can now displayed. 
     Then, while a computed image is being displayed, the pixel data of an obtained normal-image is detected by the distance parameter detecting means  901 . The detection data thereof is output to the excitation light emission controlling means  902 , and with regard to this detection data, that is, the data of the size of each pixel value of the reflected-light image, the percentage of the entire image or a specified portion of the image occupied by pixels having a value over a predetermined threshold value is computed. Then, when this percentage is above a predetermined threshold value, the emission of the excitation light is ceased, or a signal is output to the control computer  200  so that the control computer  200  can control the emission of the excitation light so that it is emitted at a safe intensity not causing injury to the target tissue  10  when the distance between the excitation light emitting end of the endoscope insertion portion  100  and the target tissue  10  satisfies the aforementioned threshold value conditions. Afterwards, it is possible to again cause the excitation light to be emitted at image-obtaining intensity by pressing the foot switch  140 . Other operations are the same as those occurring in the third embodiment. 
     According to a fluorescence endoscope apparatus of the configuration described above implementing the fluorescent-light image obtaining apparatus according to the present invention, the same results obtained in the third embodiment can be obtained. 
     In addition, according to each of the embodiments of the present invention described above, control of the emission of the excitation light can be performed by controlling the direct current in the semiconductor-laser use power source. By employing this current-control method to control the emission of the excitation light, the configuration of the apparatus can be simplified. Further, by employing a direct current modulating method of high-responsivity, safety can be ensured when the subject has come too close, and also, the operability and performance can be improved as the excitation light is capable of being rapidly restored to original strength when the subject is located again at an appropriate distance. 
     Further, a mercury lamp, etc., and not a semiconductor laser can be used as the excitation light source; in this case, control of the emission of the excitation light can be performed by, for example, controlling a filter or a diaphragm that has been provided between the excitation light source and the excitation light use lens. 
     Additionally, in each of the above described embodiments of the present invention, the image fiber  163  can be a composite glass fiber instead of a silicon fiber. In this case, because fluorescent-light is emitted from a composite glass fiber upon the introduction thereto of the excitation light, the excitation light cutoff filter shown in  FIG. 7  (the contact detecting means and the detection signal line occurring in the first embodiment are not shown) must be disposed between the focusing lens  106  and the autofluorescent-light image input face of the image fiber  163 , and not within the image signal processing portion. By using a composite glass fiber instead of a silicon fiber, the cost can be reduced. 
     Further, the fluorescent-light image obtaining apparatus according to the present invention can be applied for detecting the fluorescent-light emitted from a target tissue, which has absorbed a fluorescence diagnosing drug beforehand, upon the irradiation thereof by an excitation light. 
     Still further, the fluorescent-light image obtaining apparatus according to the present invention can be implemented in a colposcope or a laparoscope utilizing the fluorescent-light emitted due to the irradiation of an excitation light.