Filter set, system and method for fluorescence observation of protoporphyrin ix

Abstract

The present invention relates to a fluorescence observation system, to a method for carrying out a fluorescence observation and to a filter set that can be used for this purpose for simultaneously observing fluorescent light of protoporphyrin IX in an object and non-fluorescent regions of the object in an almost true-colour representation. The filter set comprises an illumination filter and an observation filter. A transmittance of the illumination filter has an average value of at least 90% from 405 nm to 452 nm, is at most 0.01% in at least 95% of a wavelength range extending from 466 nm to 524 nm, has an average value of at least 0.028% and at most 0.044% from 535 nm to 595 nm, and is at most 0.003% in at least 95% of a wavelength range extending from 610 nm to 750 nm. A transmittance of the observation filter has an average value of at least 0.143% and at most 0.187% from 404 nm to 438 nm, is at most 0.01% in at least 95% of a wavelength range extending from 444 nm to 534 nm, and has an average value of at least 90% from 544 nm to 722 nm.

Description

[0001] Filter set, system and method for fluorescence observation of protoporphyrin IX

[0002] The present invention relates to a fluorescence observation system, a method for performing a fluorescence observation and a filter set usable for this purpose.

[0003] An object of the present invention is to propose a filter set, a fluorescence observation system, and a method for performing fluorescence observation, which enable the simultaneous observation of the fluorescence of protoporphyrin IX in an object and of non-fluorescent areas of the object with near-perfect color fidelity. This means that the non-fluorescent areas of the object should be observable in almost the same colors as they appear under conventional white light illumination without the use of optical filters. Furthermore, the filter set should be easy to manufacture and robust against manufacturing-related performance variations.

[0004] Subject of the invention

[0005] The problem is solved by the subject matter of the independent claims. Advantageous further developments are defined in the dependent claims.

[0006] A filter set according to one embodiment serves for the simultaneous observation of fluorescence light from protoporphyrin IX in an object and of non-fluorescent areas of the object with near-color fidelity. The filter set comprises an illumination filter and an observation filter. The operating principles of the illumination filter and the observation filter are described by a wavelength-dependent transmittance of the respective filter. The transmittance of an optical filter denotes a value of the quotient of the light intensity transmitted through the optical filter to the light intensity incident on the optical filter. Hereinafter, the transmittance of the illumination filter is referred to as Ti and the transmittance of the observation filter as To.

[0007] General explanations

[0008] The values ​​given herein for the transmittance refer to an angle of incidence of 0°.

[0009] A long-pass slope refers to a wavelength range of a transmittance in which the transmittance increases significantly from short to long wavelengths. For example, a long-pass slope refers to a continuous (i.e., uninterrupted) wavelength range of a transmittance in which the transmittance increases by an average of at least 0.001% / nm, in particular at least 0.002% / nm, and further, in particular at least 0.01% / nm.

[0010] A short-pass slope refers to a wavelength range of a transmittance in which the transmittance decreases significantly from short to long wavelengths. For example, a short-pass slope refers to a continuous (i.e., uninterrupted) wavelength range of a transmittance in which the transmittance decreases by an average of at least 0.001% / nm, in particular at least 0.002% / nm, and further, in particular at least 0.01% / nm.

[0011] The expression "Ti has a value of Y% in at least X% of a wavelength range extending from a first wavelength to a second wavelength" means that the condition "Ti has a value of Y%" is not met in at most 100%–X% of the wavelength range extending from the first wavelength to the second wavelength. For example, the expression "Ti has a value of at most 0.1% in at least 95% of a wavelength range extending from 300 nm to 385 nm" means that the condition "Ti has a value of at most 0.1%" is not met in at most 5% of the wavelength range extending from 300 nm to 385 nm. The value of 95% is given here as an example for each wavelength range. However, the value can be chosen differently from wavelength range to wavelength range. As an alternative to the value of 95%, the value can be chosen to be, for example, 98% or 99%.

[0012] The expression "the transmittance exhibits a long-pass edge between a first wavelength and a second wavelength" means that the long-pass edge is present at at least one wavelength within a region extending from the first wavelength to the second wavelength. Similarly, the expression "the transmittance exhibits a short-pass edge between a first wavelength and a second wavelength" means that the short-pass edge is present at at least one wavelength within a region extending from the first wavelength to the second wavelength.

[0013] The expression "mean of a transmittance from a first wavelength to a second wavelength" refers, for example, to an arithmetic mean of the transmittance in a wavelength range extending from the first wavelength to the second wavelength.

[0014] The expression "average of at least X% and at most Y%" means that the average is at least X% and at most Y%. Lighting filters

[0015] According to one embodiment, Ti is at most 0.1% in at least 95% of a wavelength range extending from 300 nm to 385 nm.

[0016] According to one embodiment, Ti has a long-pass slope between 395 nm and 400 nm. This long-pass slope can have a gradient of at least 20% / nm from Ti=20% to Ti=80%.

[0017] According to one embodiment, Ti has an average value of at least 90% from 405 nm to 452 nm.

[0018] According to one embodiment, Ti has a short-pass slope between 454 nm and 460 nm.

[0019] According to one embodiment, Ti is at most 0.01% in at least 95% of a wavelength range extending from 466 nm to 524 nm.

[0020] According to one embodiment, Ti has a long-pass slope between 524 nm and 535 nm.

[0021] According to one embodiment, Ti has an average value of at least 0.028% and at most 0.044% from 535 nm to 595 nm. According to one embodiment, Ti satisfies the following condition: In this context, AbsO refers to a function that returns an absolute value of the function's argument.

[0022] According to one embodiment, Ti has a short-pass slope between 595 nm and 610 nm.

[0023] According to one embodiment, Ti is at most 0.003% in at least 95% of a wavelength range extending from 610 nm to 750 nm. According to another embodiment, Ti has an average value of at most 0.001% from 610 nm to 750 nm.

[0024] According to one embodiment, Ti has a long-pass slope between 750 nm and 770 nm.

[0025] According to one embodiment, Ti is at most 0.1% in at least 95% of a wavelength range extending from 770 nm to 1150 nm. According to another embodiment, Ti is at least 0.01% in at least 95% of a wavelength range extending from 770 nm to 1150 nm.

[0026] Observation filter

[0027] According to one embodiment, To is at most 1% in at least 95% of a wavelength range extending from 300 nm to 395 nm.

[0028] According to one embodiment, To has a short-pass slope between 390 nm and 395 nm. According to another embodiment, To is at most 0.1% in at least 95% of a wavelength range extending from 395 nm to 400 nm.

[0029] According to one embodiment, To has a long-pass slope between 400 nm and 404 nm.

[0030] According to one embodiment, To has an average value of at least 0.143% and at most 0.187% from 404 nm to 438 nm. According to one embodiment, To satisfies the following condition:

[0031] In this context, AbsO refers to a function that returns an absolute value of the function's argument.

[0032] According to one embodiment, To has a short-pass slope between 438 nm and 444 nm.

[0033] According to one embodiment, To is at most 0.01% in at least 95% of a wavelength range extending from 444 nm to 534 nm. According to another embodiment, To has an average value of at most 0.001% from 444 nm to 534 nm.

[0034] According to one embodiment, To has a long-pass slope between 537 nm and 543 nm. This long-pass slope can have a gradient of at least 20% / nm from Ti=20% to Ti=80%. According to another embodiment, To has an average gradient of at least 90% from 544 nm to 722 nm.

[0035] According to one embodiment, To has a short-pass slope between 723 nm and 733 nm. This short-pass slope can have a gradient of at least 10% / nm from Ti=80% to Ti=20%.

[0036] According to one embodiment, To is at most 0.1% in at least 95% of a wavelength range extending from 738 nm to a first cutoff wavelength. The first cutoff wavelength is, for example, in the range of 800 nm to 1100 nm, and particularly in the range of 950 nm to 1050 nm.

[0037] According to one embodiment, To has a long-pass slope in the range of 800 nm to 1100 nm, particularly in the range of 950 nm to 1050 nm.

[0038] According to one embodiment, To is at most 1% in at least 95% of a wavelength range extending from a second cutoff wavelength to 1150 nm. According to another embodiment, To is at least 0.1% in at least 95% of a wavelength range extending from the second cutoff wavelength to 1150 nm. The second cutoff wavelength is larger than the first cutoff wavelength and is, for example, in the range of 800 nm to 1100 nm, and particularly in the range of 950 nm to

[0039] 1050 nm. Functioning of the filter set

[0040] The filter set is designed to be used with a white light source to illuminate an object containing the fluorescent dye protoporphyrin IX. Suitable white light sources include, for example, a xenon lamp, a halogen lamp, or an LED lighting device.

[0041] The filter set enables the excitation of protoporphyrin IX fluorescence by the high-transmission band (at least 90%) of the illumination filter in the range of 405 nm to 452 nm and the observation of protoporphyrin IX fluorescence by the high-transmission band (at least 90%) of the observation filter in the range of 544 nm to 722 nm, with the fluorescence itself only becoming significant from approximately 610 nm. While the human eye is no longer very sensitive in the wavelength range above approximately 700 nm, suitable cameras can be sensitive to the fluorescence of protoporphyrin IX in this wavelength range. This wavelength range can therefore be used for image acquisition with a camera.

[0042] In addition to exciting protoporphyrin IX and observing its fluorescence, the filter set also enables the simultaneous observation of non-fluorescent regions of the object (i.e., those sections of the object that do not contain protoporphyrin IX) in near-color fidelity. Therefore, sections of the object containing protoporphyrin IX and sections that do not can be observed simultaneously. This color fidelity is primarily achieved through two bands of high total transmission across the illumination filter and the observation filter. Total transmission is defined as the product (multiplication) of the wavelength-dependent transmittance of the illumination filter and the wavelength-dependent transmittance of the observation filter. The first band of high total transmission lies in the range of approximately 404 nm to 438 nm.In the first high transmission band, the total transmission is approximately 0.15%. A second high transmission band lies in the range of approximately 544 nm to 595 nm. In this second high transmission band, the total transmission is approximately 0.033%. The first and second high transmission bands are very precisely matched with respect to both their wavelength ranges and their total transmissions. This matching allows for color-accurate observation of the non-fluorescent areas of the object. This means that when using the filter set with a white light source, the non-fluorescent areas of the object can be observed in almost the same colors as when observing the object without any optical filters.

[0043] The observation filter's band, ranging from 404 nm to 438 nm and contributing to the first high-transmission band, is relatively broad. In particular, the short-wavelength limit of the band is at approximately 404 nm, placing it well within the short-wavelength range. Due to this relatively wide band, the observation filter can be manufactured more easily and reliably than filters with narrower bands. This, in particular, allows for high robustness in the color-accurate rendering of non-fluorescent areas of the object.

[0044] A first band of low total transmission lies in the range of approximately 466 nm to 534 nm. In this first band of low total transmission, the total transmission is approximately 0.000001% (i.e., 10 8This low overall transmission results in strong suppression in a wavelength range where the human eye exhibits particularly high sensitivity. This low overall transmission therefore contributes significantly to the function of the filter set, enabling non-fluorescent areas of the object to be observed with accurate color reproduction by a human observer.

[0045] The illumination filter has a low transmittance of at most 0.1% in the range of approximately 300 nm to approximately 385 nm. This suppresses the UV components of the illumination light, preventing them from being transmitted to the object being observed. Such UV components can cause damage to some objects, which must be avoided. UV components reflected from the object being observed and reaching the observer's eye can also damage the observer's eyes, which must be prevented.

[0046] The transmittance of the illumination filter and the transmittance of the observation filter are specified up to a wavelength of approximately 1150 nm. While the human eye is no longer sensitive in the wavelength range of approximately 800 nm to 1150 nm, suitable cameras can be sensitive in this range. Therefore, this wavelength range can be used for image generation with a camera.

[0047] robustness

[0048] According to one embodiment, Ti has a long-pass edge between 395 nm and 400 nm. In the wavelength range of this long-pass edge, To has neither a long-pass nor a short-pass edge.

[0049] According to one embodiment, Ti has a short-pass filter edge between 454 nm and 460 nm. In the wavelength range of this short-pass filter edge, To has neither a long-pass nor a short-pass filter edge. According to another embodiment, Ti has a long-pass filter edge between 524 nm and 535 nm. In the wavelength range of this long-pass filter edge, To has neither a long-pass nor a short-pass filter edge.

[0050] According to one embodiment, Ti exhibits a short-pass filter edge between 595 nm and 610 nm. Within the wavelength range of this short-pass filter edge, To exhibits neither a long-pass nor a short-pass filter edge.

[0051] According to one embodiment, Ti has a long-pass filter edge between 750 nm and 770 nm. In the wavelength range of this long-pass filter edge, To has neither a long-pass nor a short-pass filter edge.

[0052] According to one embodiment, To exhibits a short-pass filter edge between 390 nm and 395 nm. Within the wavelength range of this short-pass filter edge, Ti exhibits neither a long-pass nor a short-pass filter edge.

[0053] According to one embodiment, To exhibits a long-pass slope between 400 nm and 404 nm. In the wavelength range of this long-pass slope, Ti exhibits neither a long-pass nor a short-pass slope.

[0054] According to one embodiment, To exhibits a short-pass slope between 438 nm and 444 nm. Within the wavelength range of this short-pass slope, Ti exhibits neither a long-pass nor a short-pass slope.

[0055] According to one embodiment, To has a long-pass filter slope between 537 nm and 543 nm. Within the wavelength range of this long-pass filter slope, Ti has neither a long-pass nor a short-pass filter slope. According to another embodiment, To has a short-pass filter slope between 723 nm and 733 nm. Within the wavelength range of this short-pass filter slope, Ti has neither a long-pass nor a short-pass filter slope.

[0056] According to the embodiments described above, the transmittance Ti of the illumination filter and the transmittance To of the observation filter can be matched so that the transmittance slopes of the two filters (e.g., low-pass slope, high-pass slope) do not overlap. During the manufacturing of optical filters, variations can occur with respect to the wavelength positions of the slopes and the resulting transmittances. Such variations are particularly problematic when the transmittance slopes of several optical filters in a filter set overlap spectrally, since even a small variation in the wavelength positions of the slopes and the resulting transmittances can have a significant impact on the performance of the filter set.In order to achieve high robustness against manufacturing-related variations, the edges in the transmittance of the illumination filter and the edges in the transmittance of the observation filter of the present filter set were matched so that they do not spectrally overlap.

[0057] Fluorescence observation system

[0058] A fluorescence observation system according to one embodiment for the simultaneous observation of protoporphyrin IX in an object and of non-fluorescent areas of the object in nearly color-accurate representation comprises a light source for illuminating the object, an observation optics for observing the object, wherein the observation optics comprise a camera and / or an eyepiece, and a filter set according to one embodiment, wherein the illumination filter of the filter set can be arranged / is arranged in an illumination beam path between the light source and the object, and the observation filter of the filter set can be arranged / is arranged in a beam path of the observation optics.

[0059] Proceedings

[0060] A method according to one embodiment for the simultaneous observation of protoporphyrin IX in an object and of non-fluorescent areas of the object in nearly color-accurate representation using a filter set according to one embodiment comprises: filtering illumination light directed at the object containing protoporphyrin IX with the illumination filter of the filter set, and filtering light emanating from the object with the observation filter of the filter set.

[0061] Brief description of the drawings

[0062] Figure 1 shows a schematic representation of a fluorescence observation system according to one embodiment.

[0063] Figure 2 shows a schematic representation of a wavelength-dependent transmittance of an illumination filter of a filter set according to one embodiment.

[0064] Figure 3 shows a schematic representation of a wavelength-dependent transmittance of an observation filter of a filter set according to one embodiment.

[0065] Figure 4 shows a schematic representation of the overall transmission of a filter set according to one embodiment. A fluorescence observation system 1 according to one embodiment is explained below using a surgical microscope. However, embodiments of the fluorescence observation system are not limited to such surgical microscopes, but rather include any fluorescence observation system in which illumination light directed at an object is filtered by an illumination filter and light emanating from the object is filtered by an observation filter.

[0066] Referring to Figure 1, the fluorescence observation system 1, or microscope 1, comprises a microscope optic (observation optic) 3 with an objective 5 having an optical axis 7. An object 9 to be examined is positioned in an object plane of the objective 5. Light emanating from the object 9 is directed by the objective 5 into an image-side beam 11, in which two zoom systems 12 and 13, arranged at a distance from the optical axis 7, are located. These systems extract partial beams 14 and 15 from the beam 11 and direct them, via deflecting prisms (not shown in Figure 1), to eyepieces 16 and 17, respectively. An observer looks into these eyepieces with their left eye 18 and right eye 19, respectively, to perceive a magnified image of the object 9. Unlike the example above, the fluorescence observation system 1 does not need to be designed as a stereo microscope. A single observation channel is sufficient.

[0067] A partially reflective mirror 21 can be arranged in the partial beam 15 to couple out a portion of the partial beam 15 as a partial beam 23, which is fed to a camera system 24. The camera system 24 comprises a camera 32, to which light from the partial beam 23 is supplied via a camera adapter optic 31, and which captures an image of the supplied light. The image captured by the camera 32 is transmitted via a data connection 33 to a controller 35 and can be stored in a memory 95 therein.

[0068] A partially reflective mirror 37 can be arranged in the partial beam 14 to extract a portion of the partial beam 14 as a partial beam 39, which is then fed to a camera system. The camera system comprises a camera 43, to which light from the partial beam 39 is supplied via a camera adapter optic 41, and which captures an image of the supplied light. The image captured by the camera 43 is transmitted to the controller 35 via a data connection 45 and can be stored in the memory 95 therein.

[0069] The images detected by the cameras 32, 43 can be output by the control unit 35 via a data connection 47 to a display device 49, for example a head-mounted display. The head-mounted display includes two displays 51, 52 for the right and left eyes of the viewer, respectively.

[0070] Contrary to the example above, the fluorescence observation system 1 does not need to include both the eyepieces 16 and 17 and the camera systems. It is sufficient if only the eyepieces 16 and 17 are provided. It is also sufficient if only the camera systems are provided.

[0071] The microscope 1 further comprises an illumination system 63 for generating illumination 81 directed onto the object 9. For this purpose, the illumination system 63 includes a broadband (white-light-like) light source 71, such as a halogen lamp, a xenon lamp, or an LED light source, a reflector 72, and a collimator 73 to generate a collimated beam of light 74, which can be directed by means of one or more lenses 75 onto an entry end 76 of an optical fiber bundle 77 in order to couple light emitted by the lamp 71 into the optical fiber bundle 77. The light is transported through the optical fiber bundle 77 to the vicinity of the object 9, exits at an exit end 78 of the optical fiber bundle 77, and is then focused by optics 79 to form the illumination 81 directed onto the object 9.

[0072] The illumination system 63 further comprises an illumination filter 84 of a filter set for the simultaneous observation of protoporphyrin IX in the object 9 and of non-fluorescent areas of the object 9 in nearly color-accurate representation. A drive 87, controlled by the control unit 35 via a switch 97, is provided to selectively position the illumination filter 84 either inside or outside the light beam 74, as indicated by an arrow 88.

[0073] In an observation beam path of the observation optics 3, for example in the beam bundle 11 or the partial beam bundles 14 and 15, a

[0074] Observation filter 91 of a filter set for the simultaneous observation of protoporphyrin IX in the object 9 and of non-fluorescent areas of the object 9 in nearly color-accurate representation. A drive 93, controlled by the control unit 35 via the switch 97, is provided to selectively position the observation filter 91 either inside or outside the observation beam path of the observation optics 3, as indicated by the arrow 94.

[0075] When using the filter set, the illumination filter 84 and the observation filter 91 are simultaneously arranged within their respective beam paths. In the illustrated example, the illumination filter 84 and the observation filter 91 are inserted into and removed from the beam paths by actuators controlled by a controller. However, it is also possible for the filters to be provided in filter holders, which are operated directly by hand by the observer to insert or remove them from the beam paths.

[0076] Figure 2 shows a schematic representation of the wavelength-dependent transmittance Ti of an illumination filter 84 of a filter set according to one embodiment. Figure 3 shows a schematic representation of the wavelength-dependent transmittance To of an observation filter 91 of a filter set according to one embodiment. Figure 4 shows a schematic representation of the overall transmittance of a filter set according to one embodiment.

[0077] The embodiments described herein can be combined with each other in any way desired.

Claims

Patent claims 1. Filter set for the simultaneous observation of fluorescence light from Protoporphyrin IX in an object (9) and of non-fluorescent areas of the object (9) in nearly color-accurate representation, wherein the filter set comprises an illumination filter (84) and an observation filter (91), wherein a transmittance (Ti) of the illumination filter (84) from 405 nm to 452 nm has an average value of at least 90%, in at least 95% of a wavelength range extending from 466 nm to extending from 524 nm, has a maximum transmittance of 0.01%, from 535 nm to 595 nm has a mean of at least 0.028% and at most 0.044%, and in at least 95% of a wavelength range extending from 610 nm to 750 nm has a maximum transmittance of 0.003%; wherein the transmittance (To) of the observation filter (91) from 404 nm to 438 nm has a mean of at least 0.143% and at most 0.187%, in at least 95% of a wavelength range extending from 444 nm to 534 nm has a maximum transmittance of 0.01%, and from 544 nm to 722 nm has a mean transmittance of at least 90%.

2. Filter set according to claim 1, wherein the transmittance (Ti) of the illumination filter (84) is at least 95% in a wavelength range extending from 300 nm to extends to 385 nm, is at most 0.1%, and / or has an average of at most 0.001% from 610 nm to 750 nm, and / or in at least 95% of a wavelength range extending from 770 nm to extends over 1150 nm, amounting to a maximum of 0.1%; and / or wherein the transmittance (To) of the observation filter (91) is at most 1% in at least 95% of a wavelength range extending from 300 nm to 395 nm, and / or is at most 0.1% in at least 95% of a wavelength range extending from 395 nm to 400 nm, and / or has an average value of at most 0.001% from 444 nm to 534 nm, and / or is at most 0.1% in at least 95% of a wavelength range extending from 738 nm to a first cutoff wavelength, and is at most 1% in at least 95% of a wavelength range extending from a second cutoff wavelength to 1150 nm, wherein the second cutoff wavelength is greater than the first cutoff wavelength and the first cutoff wavelength and the second cutoff wavelength are in the range from 800 nm to 1100 nm nm lie.

3. Filter set according to claim 1 or 2, wherein the transmittance (Ti) of the illumination filter (84) has a long-pass slope between 395 nm and 400 nm and / or has a short-pass slope between 454 nm and 460 nm and / or has a long-pass slope between 524 nm and 535 nm and / or has a short-pass slope between 595 nm and 610 nm and / or has a long-pass slope between 750 nm and 770 nm and / or wherein the transmittance (To) of the observation filter (91) has a short-pass slope between 390 nm and 395 nm and / or has a long-pass slope between 400 nm and 404 nm and / or has a short-pass slope between 438 nm and 444 nm and / or exhibits a long-pass slope between 537 nm and 543 nm and / or a short-pass slope between 723 nm and 733 nm.

4. Filter set according to any one of claims 1 to 3, wherein the transmittance (Ti) of the illumination filter (84) has a first long-pass slope between 395 nm and 400 nm and the transmittance (To) of the observation filter (91) has neither a long-pass slope nor a short-pass slope in a wavelength range of the first long-pass slope of the illumination filter (84); and / or wherein the transmittance (Ti) of the illumination filter (84) has a first short-pass slope between 454 nm and 460 nm and the transmittance (To) of the observation filter (91) has neither a long-pass slope nor a short-pass slope in a wavelength range of the first short-pass slope of the illumination filter (84);and / or wherein the transmittance (Ti) of the illumination filter (84) has a second long-pass slope between 524 nm and 535 nm and the transmittance (To) of the observation filter (91) has neither a long-pass slope nor a short-pass slope in a wavelength range of the second long-pass slope of the illumination filter (84); and / or wherein the transmittance (Ti) of the illumination filter (84) has a second short-pass slope between 595 nm and 610 nm and the transmittance (To) of the observation filter (91) has neither a long-pass slope nor a short-pass slope in a wavelength range of the second short-pass slope of the illumination filter (84);and / or wherein the transmittance (Ti) of the illumination filter (84) has a third long-pass slope between 750 nm and 770 nm and the transmittance (To) of the observation filter (91) has neither a long-pass slope nor a short-pass slope in a wavelength range of the third long-pass slope of the illumination filter (84); and / or; wherein the transmittance (To) of the observation filter (91) is between 390 nm and 395 nm has a first short-pass edge and the transmittance (Ti) of the illumination filter (84) in a wavelength range of the first short-pass edge of the observation filter (91) has neither a long-pass edge nor a short-pass edge; and / or wherein the transmittance (To) of the observation filter (91) has a first long-pass edge between 400 nm and 404 nm and the transmittance (Ti) of the illumination filter (84) in a wavelength range of the first long-pass edge of the observation filter (91) has neither a long-pass edge nor a short-pass edge; and / or wherein the transmittance (To) of the observation filter (91) has a second short-pass slope between 438 nm and 444 nm and the transmittance (Ti) of the illumination filter (84) has neither a long-pass slope nor a short-pass slope in a wavelength range of the second short-pass slope of the observation filter (91);and / or wherein the transmittance (To) of the observation filter (91) has a second long-pass slope between 537 nm and 543 nm and the transmittance (Ti) of the illumination filter (84) has neither a long-pass nor a short-pass slope in a wavelength range of the second long-pass slope of the observation filter (91); and / or wherein the transmittance (To) of the observation filter (91) has a third short-pass slope between 723 nm and 733 nm and the transmittance (Ti) of the illumination filter (84) has neither a long-pass nor a short-pass slope in a wavelength range of the third short-pass slope of the observation filter (91).

5. Filter set according to one of claims 1 to 4, wherein the transmittance (Ti) of the illumination filter (84) fulfilled and / or wherein the transmittance (To) of the observation filter (91) fulfilled.

6. Fluorescence observation system for the simultaneous observation of protoporphyrin IX in an object (9) and of non-fluorescent areas of the object (9) in nearly color-accurate representation, comprising: a light source (71) for illuminating the object (9), an observation optics (3) for observing the object (9), wherein the observation optics (3) comprises a camera (32, 43) and / or an eyepiece (16, 17), and a filter set according to any one of claims 1 to 5, wherein the illumination filter (84) of the filter set is arranged in a beam path (74, 81) between the light source (71) and the object (9), and the observation filter (91) of the filter set is arranged in a beam path (14, 15) of the observation optics (3).

7. Method for the simultaneous observation of protoporphyrin IX in an object (9) and of non-fluorescent areas of the object (9) in nearly color-accurate representation using the filter set according to any one of claims 1 to 5, wherein the method comprises: filtering illumination light (74, 81) directed onto the object (9) containing protoporphyrin IX with the illumination filter (84) of the filter set, and Filtering light emanating from the object (9) with the observation filter (91) of the filter set.

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