JP2001128927A - Method and device for producing fluorescent image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high quality fluorescent image by detecting an image with a high S/N ratio with self fluorescence generated from a tissue by the irradiation of excitation light. SOLUTION: In this fluorescent image producing device, the self-fluorescence Kj generated from a tissue 1 by the irradiation of excitation light Le on the tissue 1 is detected by a sensitive imaging device 24 through plural excitation light cutting filters 22 and 23 to produce a fluorescence image. A filter which doesn't generate fluorescence by the irradiation of excitation light is used as the first step filter 22 of the plural excitation light cutting filters.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for acquiring a fluorescence image, and more particularly to a method and an apparatus for acquiring a fluorescent image as an image by irradiating excitation light with autofluorescence generated from a living tissue. .

[0002]

2. Description of the Related Art Conventionally, there has been provided a diagnostic apparatus which detects auto-fluorescence emitted from an endogenous dye in a living tissue by irradiation with excitation light, and analyzes the auto-fluorescence to identify a change in tissue properties associated with various diseases. Has been studied.

For example, a fluorescence endoscope apparatus to which this technique is applied captures an image by auto-fluorescence generated from a living tissue by irradiation of excitation light on an imaging device by an imaging optical system. In addition, an excitation light cut filter is inserted into an optical system so that excitation light reflected by the living tissue together with autofluorescence generated from the living tissue does not enter the imaging device, and the intensity of the excitation light is attenuated. In addition, two or more excitation light cut filters may be used in order to suppress the intensity of the excitation light mixed into the weak autofluorescence to a low level. There are used an absorption filter formed of colored glass colored with, a wavelength-selective filter in which a wavelength-selective film formed of a multilayer film is coated on a substrate, and the like.

[0004]

However, merely by inserting the excitation light cut filter to attenuate the amount of excitation light, fluorescence is generated from the excitation light cut filter by irradiation of the excitation light and generated from living tissue. There is a problem that it is difficult to obtain a high-quality fluorescence image by detecting an image due to the auto-fluorescence at a high S / N ratio because the auto-fluorescence may be mixed and detected.

The present invention has been made in view of the above circumstances, and an object of the present invention is to obtain an image of autofluorescence generated from a living tissue by irradiation of excitation light at a high S / N ratio to obtain a high-quality fluorescent image. It is an object of the present invention to provide a fluorescence image acquiring method and apparatus capable of performing the above.

[0006]

According to the fluorescence image acquiring method of the present invention, a fluorescent image is obtained by irradiating a living tissue with excitation light to detect auto-fluorescence generated from the living tissue through a plurality of excitation light cut filters. In the fluorescence image acquisition method described above, the detection is performed using a filter that does not generate fluorescence due to the irradiation of the excitation light at the first stage of the plurality of excitation light cut filters.

[0007] A fluorescence image acquiring apparatus according to the present invention comprises: an irradiating means for irradiating a living tissue with excitation light; and a detecting means for detecting auto-fluorescence generated from the living tissue by irradiation of the excitation light through a plurality of excitation light cut filters. And a fluorescence image acquisition device comprising: an image acquisition unit that acquires a fluorescence image based on autofluorescence detected by the detection unit, wherein a first-stage excitation light cut filter of the plurality of excitation light cut filters The filter is characterized in that it does not generate fluorescence by irradiation.

The first-stage excitation light cut filter can be a wavelength-selective film. Further, an excitation light absorption filter can be provided after the first-stage excitation light cut filter.

[0009] The fluorescence image acquiring apparatus may include an absorber for absorbing the excitation light separated by the excitation light cut filter in the first stage.

[0010] The first-stage excitation light cut filter may attenuate the excitation light to 1/100 or less.

The "first-stage excitation light cut filter" means a filter of a plurality of excitation light cut filters arranged in an optical system for acquiring a fluorescence image, on which light emitted from a subject enters first. I do.

[0012] The phrase "provided with an excitation light absorption filter after the first-stage excitation light cut filter" means that light emitted from a subject enters the excitation light absorption filter after passing through the first-stage excitation light cut filter. This means that an excitation light absorption filter is arranged, and this excitation light absorption filter may be arranged at any position of a plurality of excitation light cut filters as long as it is a position other than the first stage excitation light cut filter.

The excitation light cut filter includes a filter having transmission and reflection characteristics for transmitting the excitation light and reflecting the light to be measured, in addition to a filter for blocking or reflecting the excitation light.

[0014]

According to the fluorescence image acquiring method and apparatus of the present invention, a filter that does not generate fluorescence by irradiating excitation light is arranged at the first stage of a plurality of excitation light cut filters to detect autofluorescence. The excitation light can be attenuated by the first-stage excitation light cut filter without generating fluorescence, and the excitation light is already attenuated even if there is an excitation light cut filter that emits fluorescence by irradiation of the excitation light at the subsequent stage. Therefore, the intensity of the fluorescence generated from the excitation light cut filter at the subsequent stage can be suppressed low. Therefore, compared to the case where an excitation light cut filter that generates fluorescence by irradiation of excitation light is arranged at the first stage where excitation light of high intensity before being attenuated is irradiated, fluorescence is generated by irradiation of excitation light at the first stage. In the case where a filter that does not perform the detection is arranged, the generation of fluorescence that is a noise outside the detection target is small, the autofluorescence can be detected at a high S / N ratio, and a high-quality fluorescence image can be obtained.

That is, the filter that generates fluorescence by irradiating the excitation light generates fluorescence with an intensity corresponding to the intensity of the excitation light, so that the intensity of the excitation light is higher in the first stage. When a filter that generates fluorescent light by irradiation is used, the intensity of the fluorescent light generated from this filter also increases, and the intensity of the fluorescent light is detected without being attenuated by the first and subsequent filters. However, if a filter that does not generate fluorescence by irradiating the excitation light is disposed in the first-stage filter, the intensity of the excitation light is temporarily attenuated.
Even if a filter that generates fluorescence by irradiation with excitation light is provided after the first stage, the intensity of fluorescence generated by irradiation with excitation light whose intensity has been attenuated is kept low, and fluorescence mixed when detecting autofluorescence is detected. To a lower level.

If the first-stage excitation light cut filter is a wavelength-selective film, the wavelength-selective film does not generate fluorescence upon irradiation with the excitation light, so that the generation of fluorescence upon irradiation with the excitation light is more reliably prevented. can do.

In some excitation light cut filters, the attenuation rate depends on the incident angle. However, since the attenuation rate of the excitation light absorption filter does not depend on the incident angle, the excitation light cut filter is disposed downstream of the first excitation light cut filter. If an excitation light absorption filter is provided, the excitation light can be cut at a constant attenuation rate regardless of the angle at which the excitation light enters the excitation light absorption filter. Regarding the property of the excitation light absorbing filter, which is a drawback of generating fluorescence when irradiated with the excitation light, the intensity of the excitation light is attenuated by the excitation light cut filter at the preceding stage. Even if fluorescence is generated from the excitation light absorption filter, the intensity of the fluorescence is extremely weak, so that the intensity of the fluorescence generated from the excitation light cut filter is kept low and even if the excitation light is incident at any incident angle. Excitation light can be attenuated, and the auto-fluorescence
/ N ratio.

If an absorber is provided for absorbing the excitation light separated by the first-stage excitation light cut filter, the separated excitation light is reflected and scattered to become stray light, and enters the optical path for capturing an autofluorescence image. Since it can be prevented from being detected together with the auto-fluorescence, the auto-
It can be detected by N ratio.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a fluorescent endoscope in which a fluorescent image acquiring method is applied to an endoscope apparatus as a first embodiment of the present invention.

As shown in FIG. 1, a fluorescent endoscope 800 irradiates a living tissue 1 with a light source unit 100 having a light source of excitation light for irradiating the living tissue 1, and excitation light guided from the light source unit 100. An image due to the autofluorescence Kj generated in the living tissue 1 by the irradiation of the excitation light Le (hereinafter, an autofluorescence image Jz)
), An endoscope head unit 200 for imaging and converting it into an electric analog image signal
An image processing unit 300 that converts an analog image signal captured and converted into a digital signal, further calculates the digital signal, converts the result into a video signal, and outputs the video signal, and a video signal output from the image processing unit 300. It is composed of a main part consisting of a display device 400 for performing display based on the display.

The light source unit 100 includes an excitation light source 11 for emitting excitation light Le in a wavelength region near 405 nm, an excitation light condensing lens 12 for condensing excitation light emitted from the excitation light source 11, and excitation light. Le to the light source unit 100
Fiber 1 propagating from the endoscope to the endoscope tip unit 200
The excitation light Le emitted from the excitation light source 11 is condensed by the excitation light condensing lens 12, enters the end surface 13 a of the optical fiber 13, and is viewed by the optical fiber 13. The light is transmitted to the mirror tip unit 200.

The endoscope distal end unit 200 receives the excitation light Le propagated by the optical fiber 13 and irradiates the living tissue 1 with the excitation lens Le. An image pickup unit 201 for picking up a fluorescent image Jz is provided, and an analog image signal picked up by the image pickup unit 201 and converted into an electric signal is output via the image pickup cable 29 and input to the image operation unit 300. You.

The image processing unit 300 includes an imaging unit 20
A / A which receives and converts an analog image signal captured and converted by 1 into a digital value and outputs it as image data
A pixel section calculator 3 that converts and outputs pixel sections of image data output from the D / D converter 30 and the A / D converter 30
1. An image memory 32 for storing image data in which pixel sections are converted, a standardized image arithmetic unit 33 for performing an arithmetic operation using the value of the image data stored in the image memory 32, and a standardized image arithmetic unit 33 A discriminator 34 for discriminating, for each pixel of the image data, whether the tissue is a normal tissue or a diseased tissue by comparing the result with a threshold.
A video signal processing circuit 35 for converting the image data representing the result identified by the image signal into a video signal as an analog signal and outputting the video signal is provided. The analog image signal input via the imaging cable 29 is a digital signal. After being converted into image data composed of the following, arithmetic and identification are performed and further converted into a video signal by the video signal processing circuit 35 and output.

The video signal output by the video signal processing circuit 35 is input to the display 400 and displayed.

The "image data" means a set of digital signal values representing an image.
01 is converted into an analog image signal
Between the time when the signal is converted into a digital signal by the / D converter 30 and the time when the signal is converted again by the video signal processing circuit 35 into a video signal which is an analog signal, the pixel partitioning operation unit 31
And a set of digital signal values representing an image to be subjected to processing such as calculation and identification by the classifier 34 and the like.

Here, the case where the autofluorescent image Jz is captured by the image capturing section 201 will be described in detail. FIG. 2 is an enlarged view showing details of the imaging unit 201.

The autofluorescence image Jz generated on the living tissue 1 by the irradiation of the excitation light Le is formed on the image-side optical axis of the imaging lens 21 which forms an image on the high-sensitivity imager 24 described later. The dichroic mirror 22 is disposed at an angle of 45 degrees. The light propagating along the optical axis of the imaging lens 21 passes through the dichroic mirror 22. Are arranged. on the other hand,
On the optical path formed by the light propagating along the optical axis of the imaging lens 21 being reflected by the dichroic mirror 22 at a substantially right angle, an absorption filter 23 that cuts off the excitation light and a light source that captures the auto-fluorescence image Jz. The sensitivity imagers 24 are arranged in this order.

The dichroic mirror 22 is formed by forming a wavelength-selective film 22b on a quartz glass substrate 22a. As shown in FIG. 3, the dichroic mirror 22 has a reflection characteristic of reflecting light in a wavelength region exceeding about 405 nm. Wavelength 405nm
It has reflection and transmission characteristics of reflecting 1% of the amount of light in the vicinity and transmitting 99% of the light, and does not generate fluorescence by irradiation with excitation light. The absorption filter 23 is formed of colored glass, and has a transmission characteristic of transmitting light in a wavelength region exceeding about 405 nm as shown in FIG.
It has the property of blocking 99% of the light amount of light near 5 nm and transmitting 1%, and has the property of generating fluorescence when irradiated with excitation light. In addition, the absorber 25 is formed by adding 4
It is a mixture of a dye that absorbs light in the wavelength region around 05 nm and has a characteristic of absorbing excitation light.

It should be noted that the high-sensitivity image pickup device 24 is formed by closely integrating an on-chip mosaic filter 24a on a high-sensitivity image pickup device 24b, and the on-chip mosaic filter 24a covers an entire wavelength region as shown in FIG. Filter W having a transmission characteristic of transmitting light having a wavelength
As shown in FIG. 6, the filter G is formed by alternately arranging a filter G having a transmission characteristic of transmitting light in a green wavelength region of 530 nm in correspondence with each pixel of the high-sensitivity image sensor 24b. .

The autofluorescence image Jz generated in the living tissue 1 by the irradiation of the excitation light Le is reflected by the dichroic mirror 22 through the imaging lens 21 at a substantially right angle, passes through the absorption filter 23, and then passes through the high-sensitivity imaging device. 24.

On the other hand, the imaging lens 2 reflected by the living tissue 1
The excitation light Le that enters the dichroic mirror 22 via the light source 1 has 99% of its light intensity 99%.
And then enter the absorber 25 and be absorbed, so that it does not return to the optical path where the autofluorescent image Jz is captured again as stray light due to reflection or scattering. Also, 1% of the light amount of the excitation light incident on the dichroic mirror 22 is reflected by the dichroic mirror 22 at a substantially right angle (the light amount is attenuated to 1/100) and the absorption filter 2
3, and 99% of the amount of the exciting light that has entered further is absorbed by the absorption filter 23, and the remaining 1% of the light passes through the absorption filter 23 (the amount of light is further attenuated to 1/100) (high sensitivity imaging). Incident on the vessel 24. When the excitation light is incident on the absorption filter 23, the amount of fluorescent light corresponding to 1% of the amount of the incident excitation light is reduced by the absorption filter 23.
And enters the high-sensitivity imager 24.

Here, assuming that the amount of auto-fluorescence generated from a diseased tissue is about β% (the fluorescence yield is about β%) of the amount of excitation light applied to the tissue (the fluorescence yield is It means the ratio between the intensity of the excitation light irradiated to the site of the living tissue and the intensity of the auto-fluorescence generated from the site due to the irradiation of the excitation light). The ratio of the amount of fluorescent light to the amount of excitation light mixed as noise and the amount of fluorescent light generated from the absorption filter 23 is as follows.

That is, as shown in FIG. 7, the excitation light Le irradiates the diseased body portion By of the living tissue 1 with a light amount of 10.
If 0, the light quantity of the auto-fluorescence Kj generated from the site By is β, and the auto-fluorescence Kj generated from the site By is
Is assumed that 0.5% of the generated amount of light is transmitted to the high-sensitivity image pickup device 24 and is received with little loss of light amount after being incident on the optical system of the image pickup unit 201 (the light collection efficiency Ee of the image pickup unit 201).
= 0.5%), the light amount of the auto-fluorescence Kj1 received by the high-sensitivity imager 24 is β × 0.005.

On the other hand, if the reflectance of the excitation light by the living tissue 1 is the same between the diseased tissue and the normal tissue and its value is 2% (that is, if the tissue reflectance Rt = 2%), the light amount is 10%.
The excitation light Le of 0 is reflected by the part By and the amount of the reflected light becomes 2. When 0.5% of the amount of the reflected excitation light Le1 is condensed by the imaging lens 21, the imaging lens 21 The amount of excitation light Le2 passing through
(Attenuated to 1/10000). When the excitation light Le2 is reflected by the dichroic mirror 22, the light amount is attenuated to 1/100 and 1 × 10 ^−4.
(Excitation light Le3), and when the excitation light Le3 passes through the absorption filter 23, the light amount is 1/100.
To 1 × 10 ⁻⁶ (excitation light Le4). Further, when the excitation light Le3 enters the absorption filter 23, fluorescence is generated, and the fluorescence Kk of 1/100 of the amount of the incident excitation light, that is, the fluorescence Kk of 1 × 10 ⁻⁶ is generated. Incident on.

Therefore, the ratio of the amount of the autofluorescence Kj1 generated from the site By of the diseased tissue and received by the high-sensitivity imager 24 to the amount of the excitation light Le4 and the amount of fluorescence Kk received as noise is β × 0.005: (1 × 1
0 ⁻⁶ + 1 × 10 ⁻⁶ ) = β: 4 × 10 ⁻⁴

Therefore, even if the fluorescence yield β of the diseased tissue becomes an extremely small value of less than 1%, a high-quality autofluorescence image Jz that can be used for diagnosis can be captured.
In addition, the fluorescence yield of the normal tissue is about 1% of the fluorescence yield of the diseased tissue.
Since the ratio of the amount of excitation light mixed in detecting the autofluorescence and the ratio of the amount of fluorescence generated from the absorption filter 23 is further reduced, it is possible to capture a higher quality autofluorescence image Jz. it can.

The fluorescence yield, the reflection characteristics and the transmission characteristics of the dichroic mirror 22 and the absorption filter 23,
The absorption characteristics and the excitation light irradiation make the absorption filter 23
The amount of emitted fluorescent light and the like vary depending on the site of the living tissue irradiated with the excitation light, the wavelength-selective film configuration, the material of the absorption filter, and the like, and do not always coincide with the above numerical values.

Next, the operation performed by the image operation unit 300 will be described in detail. The autofluorescence image Jz captured by the high-sensitivity image capturing device 24 as described above is converted into an electric analog image signal, and is output from the image capturing unit 201 to the image calculation unit 300 via the image capturing cable 29. The analog image signal input to the image operation unit 300 is converted into a digital value by the A / D converter 30 and output to the pixel section converter 31 as image data, and the pixel section converter 31 converts the pixel section.

That is, as shown in FIGS. 8A, 8B, and 8C, four pixels in the mosaic filter 24a are set as new pixels in one section, and the newly set pixels are set. Pxy (1,1) and Pxy obtained from the pixel where the filter W is located at the position (x, y)
The sum with (2, 2) is defined as the value of the image data W (x, y),
The value Pxy obtained from the pixel where the filter G is arranged
The sum of (1,2) and Pxy (2,1) is calculated as image data G
(X, y). Therefore, if this conversion is performed for all the pixels, the number of pixels after conversion by the pixel division converter 31 is １ ／ of the number of pixels before conversion by the pixel division converter 31.

The value of the image data W and the value of the image data G converted by the pixel section converter 31 are output to and stored in the image memory 32W and the image memory 32G, respectively.

Next, the image data W stored in the image memory 32W and the image data G stored in the image memory 32G are stored.
Means that the following operation is performed between pixels input to the standardized image calculator 33 and obtained from the same pixel position (x, y).

GW (x, y) = G (x, y) / W (x, y) That is, the normalized intensity Gw obtained by dividing the intensity of the auto-fluorescence in the green wavelength region by the intensity of the auto-fluorescence in the entire wavelength region. (X,
y) is required. The above operation is performed for all the pixels to obtain the normalized intensity GW, and the value of the normalized intensity GW obtained by these operations is input to the discriminator 34, and is previously obtained from the normal tissue by the same method as described above. The value is compared with a threshold value Q obtained as an intermediate value between the value of the normalized intensity and the value of the normalized intensity obtained from the diseased tissue in the same manner as described above.

Here, the ratio of the intensity of the auto-fluorescence in the green wavelength region to the intensity of the auto-fluorescence over the entire wavelength region generated from the diseased tissue is the ratio of the intensity of the green fluorescence to the intensity of the auto-fluorescence over the entire wavelength region generated from the normal tissue. , The normalized intensity GW (x, y) having a value exceeding the threshold Q corresponds to the corresponding pixel position (x, y).
y) is identified as a normal tissue, and an identification value S1 is assigned. A pixel position (x, y) corresponding to the normalized intensity GW (x, y) having a value equal to or less than the threshold value Q is identified as a diseased tissue and the identification value S2. Is assigned. Then, these discrimination values are obtained for all pixels, output from the discriminator 34, converted into video signals by the video signal processing circuit 35, and displayed on the display 400.

It is to be noted that a dichroic cube beam splitter 60 as shown in FIG. 9 can be used in place of the dichroic mirror 22 and the absorber 25. That is, a wavelength-selective film is formed on the boundary face fa, and has transmission characteristics and reflection characteristics equivalent to those of the dichroic mirror 22. Further, the absorber 61 is adhered to the surface fb to provide excitation light absorption characteristics equivalent to the absorber 25. A dichroic cube beam splitter provided can also be used.

In place of the dichroic mirror 22, a dichroic prism 70 as shown in FIG.
Can also be used. That is, a dichroic prism having a wavelength-selective film formed on the boundary surface fc and having transmission characteristics and reflection characteristics equivalent to those of the dichroic mirror 22 can be used.

Further, instead of the dichroic mirror 22 and the absorption filter 23, a combination of an excitation light cut filter 80 and a prism 81 as shown in FIG. 11 can be used. That is, a wavelength-selective film fd is formed on the incident side of the color glass substrate 80a that blocks the excitation light, and the excitation light cut filter integrates the functions of the two types of filters and the reflection film fe that reflects light in all wavelength regions. However, a prism formed on the slope can also be used.

According to the second embodiment of the present invention, the
The imaging unit 500 configured to image the auto-fluorescence is configured to have the configuration shown in FIG.
Lens 51 that forms an autofluorescence image Jz generated from the image on an end face 53a of an image fiber 53, which will be described later, and an autofluorescence image J formed on the end face 53a by the imaging lens 51.
an image fiber 53 that propagates z to the end face 53b, a wavelength selection filter 52 in which a wavelength-selective film is formed on a glass substrate disposed between the imaging lens 51 and the end face 53a of the image fiber 53, an image fiber A relay lens 5 for relaying the auto-fluorescent image Jz propagated to the end face 53b of the 53 on a high-sensitivity imager 56 in which an on-chip mosaic filter 56a and a high-sensitivity image sensor 56b are integrated.
5, and an absorption filter 54 made of colored glass that is disposed between the relay lens 55 and the high-sensitivity imaging device 56 and cuts off the excitation light.

The wavelength selection filter 52 has a wavelength of 405 nm.
It has a transmission wavelength characteristic for transmitting light in a wavelength region exceeding the vicinity, and a transmission characteristic for blocking 99% of the light amount of light having a wavelength near 405 nm and transmitting the remaining 1% light amount, and emits fluorescence by irradiation with excitation light. It does not occur. Absorption filter 5
Reference numeral 4 denotes a wavelength characteristic for transmitting light in a wavelength region exceeding 405 nm and a light amount of light having a wavelength of 405 nm of 99%.
It has a wavelength characteristic of blocking and transmitting the remaining 1% of the light amount, and generates fluorescent light of a light amount corresponding to 1% of the light amount of the irradiated excitation light. The imaging lens 51 is an optical system that is telecentric on the image side, and the principal ray is substantially parallel to the optical axis.
The light imaged on 6 enters the wavelength selection filter 52 almost perpendicularly. Also, the on-chip mosaic filter 56a
Is a high-sensitivity image sensor 56b that includes a filter that transmits light in the green wavelength region and a filter that transmits light in the entire wavelength region.
Are formed alternately in correspondence with the respective pixels, and are integrated in close contact with the high-sensitivity image sensor 56b to form the high-sensitivity imager 56.

The operation of picking up the autofluorescence image Jz by the image pick-up section 500 having such a configuration will be described. 4
The auto-fluorescent image Jz generated in the living tissue 1 by the irradiation of the excitation light having the wavelength of 05 nm is transmitted through the wavelength selection filter 52 and the end face 53 of the image fiber 53 by the imaging lens 51.
a is formed on the end face 53 by the image fiber 53.
b, is formed on the high-sensitivity imager 56 by the relay lens 55 via the absorption filter 54, and is imaged. During this time, the auto-fluorescence is propagated with almost no attenuation.

On the other hand, the excitation light reflected by the living tissue 1 passes through the imaging lens 51 and enters the wavelength selection filter 52. The imaging lens 51 has a telecentric optical system on the image side. Since the light is incident on the wavelength selection filter 52 almost perpendicularly, the light passes through the wavelength selection filter 52 without being affected by the change in the transmission characteristic and the reflection characteristic depending on the incident angle of the wavelength selective film, and is reflected by the living tissue 1. The amount of the excited excitation light can be attenuated to 1/100 uniformly. The excitation light transmitted through the wavelength selection filter 52 and attenuated enters the end face 53a of the image fiber, propagates through the image fiber 53, exits from the end face 53b, and enters the absorption filter 54 via the relay lens 55.
Here, the principal ray of the excitation light that is emitted from the end face 53b and enters the absorption filter 54 via the relay lens 55 does not perpendicularly enter the absorption filter 54 but enters the absorption filter 54 at a different angle depending on the location. Since the transmission characteristics and reflection characteristics do not change depending on the incident angle, the amount of incident excitation light can be uniformly attenuated to 1/100 or less. Further, at this time, the absorption filter 54 generates the fluorescence of the light amount corresponding to 1% of the light amount of the irradiated excitation light. Then, the excitation light attenuated by the absorption filter 54 and the fluorescence generated from the absorption filter 54 enter the high-sensitivity imager 56.

Here, the relationship between the amount of autofluorescence received by the high-sensitivity imager 56 and the amount of excitation light and fluorescence received as noise will be described. The fluorescence yield at the site of the diseased tissue in the living tissue 1 is 0.01%, the tissue reflectance Rt for the excitation light of the living tissue 1 is 2% for both the normal tissue and the diseased tissue, and the excitation light reflected by the living tissue is generated. Light collection efficiency E of autofluorescence by the imaging unit 500
e is assumed to be 50%. When the site of the diseased tissue is irradiated with the excitation light having a light amount of 100, the amount of autofluorescence generated from the site of the diseased tissue and received by the high-sensitivity imager 56 becomes 0.0
5 (100 × 0.01% × 50% = 0.005), and the light amount is hardly attenuated by the optical system of the imaging unit 500.

On the other hand, the amount of excitation light received by the high-sensitivity imager 56 is 0.0001 (100 × 2% × 50).
% X 1/100 x 1/100 = 0.0001),
The fluorescence generated from the absorption filter 54 and received by the high-sensitivity imager 56 is 0.0001 (100 × 2% × 50%).
× 1/100 × 1% = 0.0001).

Therefore, the ratio of the amount of autofluorescence to be measured and received by the high-sensitivity imager 56 to the amount of excitation light and fluorescence as noise is 0.005: (0.0
001 + 0.0001) = 50: 2 = 25: 1.
On the other hand, the fluorescence yield of the normal tissue is 10% of the fluorescence yield of the diseased tissue.
Therefore, the ratio of the amount of autofluorescence to be measured, which is generated from normal tissue and received by the high-sensitivity imager 56, to the amount of excitation light and fluorescence that becomes noise is 250: 1.
Becomes These ratios are constant regardless of the position where the excitation light is received by the high-sensitivity imager 56 because the excitation light enters the wavelength selection filter almost perpendicularly and is uniformly attenuated.

Therefore, the amount of the excitation light and the amount of fluorescence received as noise by the high-sensitivity imager 56 is sufficiently low as compared with the amount of the auto-fluorescence to be measured, so that the auto-fluorescence image has a high S / F. Images can be taken at the N ratio. Other configurations and operations are the same as those of the first embodiment.

As described above, according to the present invention, it is possible to detect an image due to autofluorescence generated from a living tissue by irradiation of excitation light at a high S / N ratio and obtain a high-quality fluorescence image.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a fluorescence endoscope according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of an imaging unit.

FIG. 3 is a diagram showing reflection characteristics of a dichroic mirror;

FIG. 4 is a diagram showing transmission characteristics of an absorption filter.

FIG. 5 is a diagram showing transmission characteristics of an on-chip mosaic filter.

FIG. 6 is a diagram showing the structure of an on-chip mosaic filter.

FIG. 7 is a diagram showing a process in which excitation light is attenuated.

FIG. 8 is a diagram showing a process of converting a pixel section.

FIG. 9 is a diagram showing a configuration of a dichroic cube beam splitter.

FIG. 10 is a diagram showing a configuration of a dichroic prism.

FIG. 11 is a diagram showing a configuration using a filter in which a color glass and a wavelength-selective film are combined.

FIG. 12 is a schematic configuration diagram of an imaging unit of the fluorescence endoscope according to the first embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Living tissue 11 Excitation light source 12 Excitation light condensing lens 13 Optical fiber 21 Irradiation lens 29 Imaging cable 201 Imaging part 30 A / D converter 32 Image memory 33 Normalized image arithmetic unit 34 Identifier 35 Video signal processing circuit 100 Light source Unit 200 Endoscope tip unit 300 Image processing unit 400 Display 800 Fluorescent endoscope

Claims (6)

[Claims] 1. A fluorescence image acquiring method for irradiating living tissue with excitation light to detect auto-fluorescence generated from the living tissue through a plurality of excitation light cut filters to acquire a fluorescence image, A fluorescence image acquiring method, wherein a filter that does not generate fluorescence by irradiation of the excitation light is used as a first stage of the excitation light cut filter. 2. Irradiation means for irradiating a living tissue with excitation light, detection means for detecting auto-fluorescence generated from the living tissue by irradiation of the excitation light through a plurality of excitation light cut filters, and detection by the detection means A fluorescence image acquisition device comprising: an image acquisition unit that acquires a fluorescence image based on autofluorescence that has been obtained. A filter in which a first-stage excitation light cut filter among the plurality of excitation light cut filters does not generate fluorescence due to irradiation with the excitation light. A fluorescence image acquisition device, characterized in that: 3. The fluorescence image acquiring apparatus according to claim 2, wherein the first-stage excitation light cut filter is a wavelength-selective film. 4. The fluorescence image acquiring apparatus according to claim 2, wherein an excitation light absorption filter is provided after the first-stage excitation light cut filter. 5. The fluorescence image acquiring apparatus according to claim 2, further comprising an absorber that absorbs the excitation light separated by the first-stage excitation light cut filter. 6. The fluorescence image acquiring apparatus according to claim 2, wherein the first-stage excitation light cut filter attenuates the excitation light to 1/100 or less.