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

Abstract

The present invention relates to a fluorescence observation system, a method for performing fluorescence observation, and a filter set usable therefor for the simultaneous observation of fluorescent light from protoporphyrin IX in an object and of non-fluorescent areas of the object in a nearly color-accurate representation. The filter set comprises an illumination filter and an observation filter. The 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.The 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

The present invention relates to a fluorescence observation system, a method for performing fluorescence observation, and a filter set usable therefor.An object of the present invention is to provide a filter set, a fluorescence observation system, and a method for performing fluorescence observation that enable simultaneous observation of fluorescence of protoporphyrin IX in an object and non-fluorescent regions of the object in near-color fidelity. This means that the non-fluorescent areas of the object are to be observed in almost the same colors in which they appear with conventional white light illumination without the use of optical filters. Furthermore, the filter set should be simple to produce and robust with respect to production-related power fluctuations.The subject matter of the invention is provided by the inventionThe object is achieved by the subject matters of the independent claims. Advantageous further developments are defined in the dependent claims.A filter set according to an embodiment serves for simultaneously observing fluorescent light of protoporphyrin IX in an object and non-fluorescent regions of the object in a near color-fidelity representation. The filter set includes an illumination filter and an observation filter. The modes of operation of the illumination filter and of the observation filter are described by a wavelength-dependent transmittance of the respective filter. The transmittance of an optical filter denotes a value of a quotient of a light intensity transmitted through the optical filter to a light intensity irradiated onto the optical filter. Hereinafter, the transmittance of the illumination filter is referred to as Ti and the transmittance of the observation filter is referred to as To.General ExplanationsThe transmittance values reported herein relate to an angle of incidence of 0°.A long-pass edge denotes a wavelength range of a transmittance in which the transmittance significantly increases from short wavelength to long wavelength. For example, a long-pass flank denotes a contiguous (i.e. uninterrupted) wavelength range of a transmittance in which the transmittance increases on average from short-wave to long-wave by at least 0.001% / nm, in particular at least 0.002% / nm, more particularly at least 0.01% / nm.A short-pass edge denotes a wavelength range of a transmittance in which the transmittance significantly decreases from short wavelength to long wavelength. For example, a short-pass flank denotes a contiguous (i.e. uninterrupted) wavelength range of a transmittance in which the transmittance decreases on average from short-wave to long-wave by at least 0.001% / nm, in particular at least 0.002% / nm, more particularly at least 0.01% / nm.The expression "Ti is a value of Y % in at least X % of a wavelength range extending from a first wavelength to a second wavelength", that the condition "Ti is a value of Y %" is not satisfied at most 100%-X % of the wavelength range extending from the first wavelength to the second wavelength. For example, the expression "Ti is at most 0.1%" in at least 95% of a wavelength range extending from 300 nm to 385 nm means that the condition "Ti is at most 0.1%" is not satisfied in at most 5% of the wavelength range extending from 300 nm to 385 nm. The 95% value for each wavelength range is exemplified herein. However, the value may be chosen to be different from wavelength range to wavelength range. Alternatively to the value of 95%, the value may be chosen to be, for example, 98% or 99%.The expression "the transmittance has 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 of a region extending from the first wavelength to the second wavelength. Analogously, the expression "the transmittance has 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 of a region which extends from the first wavelength to the second wavelength.The term "average value of transmittance from a first wavelength to a second wavelength" denotes, for example, an arithmetic average value of transmittance in a wavelength range extending from the first wavelength to the second wavelength.The expression "average value of at least X % and at most Y %" means that the average value is at least X % and at most Y %.Illumination FilterAccording to an embodiment, Ti is at most 0.1% in at least 95% of a wavelength range extending from 300 nm to 385 nm.According to an embodiment, Ti has a long pass edge between 395 nm and 400 nm. This long-pass flank can have a slope of at least 20% / nm of Ti=20% to Ti=80%.According to one embodiment, Ti has an average of at least 90% from 405 nm to 452 nm.According to one embodiment, Ti has a short-pass edge between 454 nm and 460 nm.According to an embodiment, Ti is at most 0.01% in at least 95% of a wavelength range extending from 466 nm to 524 nm.According to one embodiment, Ti has a long pass edge between 524 nm and 535 nm.According to one embodiment, Ti has an average 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:Here, Abs() denotes a function which returns an absolute value of the argument of the function.According to an embodiment, Ti has a short-pass edge between 595 nm and 610 nm.According to an embodiment, Ti is at most 0.003% in at least 95% of a wavelength range extending from 610 nm to 750 nm. According to one embodiment, Ti has an average of at most 0.001% from 610 nm to 750 nm.According to an embodiment, Ti has a long pass edge between 750 nm and 770 nm.According to an embodiment, Ti is at most 0.1% in at least 95% of a wavelength range extending from 770 nm to 1150 nm. According to an embodiment, Ti is at least 0.01% in at least 95% of a wavelength range extending from 770 nm to 1150 nm.Observation FilterAccording to an embodiment, To is at most 1% in at least 95% of a wavelength range extending from 300 nm to 395 nm.According to an embodiment, To has a short-pass edge between 390 nm and 395 nm.According to an embodiment, To is at most 0.1% in at least 95% of a wavelength range extending from 395 nm to 400 nm.According to an embodiment, To has a long pass edge between 400 nm and 404 nm.According to one embodiment, To has an average 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:Here, Abs() denotes a function which returns an absolute value of the argument of the function.According to one embodiment, To has a short-pass edge between 438 nm and 444 nm.According to an embodiment, To is at most 0.01% in at least 95% of a wavelength range extending from 444 nm to 534 nm. According to one embodiment, To has an average of at most 0.001% from 444 nm to 534 nm.According to an embodiment, To has a long pass edge between 537 nm and 543 nm. This long-pass flank can have a slope of at least 20% / nm of Ti=20% to Ti=80%.According to one embodiment, To has an average of at least 90% from 544 nm to 722 nm.According to one embodiment, To has a short-pass edge between 723 nm and 733 nm. This short-pass flank can have a slope of at least 10% / nm of Ti=80% to Ti=20%.According to an embodiment, To is at most 0.1% in at least 95% of a wavelength range extending from 738 nm to a first cut-off wavelength. According to an embodiment, To is at least 0.1% in at least 95% of a wavelength range extending from 738 nm to the first cut-off wavelength. The first cut-off wavelength is, for example, in the range from 800 nm to 1100 nm, in particular in the range from 950 nm to 1050 nm.According to one embodiment, To has a long-pass flank in the range from 800 nm to 1100 nm, in particular in the range from 950 nm to 1050 nm.According to an embodiment, To is at most 1% in at least 95% of a wavelength range extending from a second cut-off wavelength to 1150 nm. According to an embodiment, To is at least 0.1% in at least 95% of a wavelength range extending from the second cut-off wavelength to 1150 nm. The second limit wavelength is greater than the first limit wavelength and is, for example, in the range from 800 nm to 1100 nm, in particular in the range from 950 nm to 1050 nm.Functioning of the Filter SetThe filter set is designed to be used with a white light source for illuminating an object to be observed, which contains the fluorescent dye protoporphyrin IX. A suitable white light source is, for example, a xenon lamp, a halogen lamp or an LED lighting device.The filter set enables excitation of the fluorescence of protoporphyrin IX by the high transmission band (at least 90%) of the illumination filter in the range from 405 nm to 452 nm and observation of the fluorescence of protoporphyrin IX by the high transmission band (at least 90%) of the observation filter in the range from 544 nm to 722 nm, wherein the fluorescence itself only occurs significantly starting from approximately 610 nm. Although the human eye is no longer very sensitive in the wavelength range from about 700 nm, suitable cameras in this wavelength range can be sensitive to the fluorescence of protoporphyrin IX. This wavelength range can therefore be used for image generation by means of a camera.In addition to exciting protoporphyrin IX and observing the fluorescence of protoporphyrin IX, the filter set also permits simultaneous observation of nonfluorescence areas of the object (i.e., those portions of the object that do not contain protoporphyrin IX) in near color fidelity. Therefore, portions of the object containing protoporphyrin IX and portions of the object not containing protoporphyrin IX can be simultaneously observed. Observation in color fidelity is accomplished primarily by two bands of high overall transmission through the illumination filter and observation filter. The total transmission denotes the product (multiplication) of the wavelength-dependent transmittance of the illumination filter and the wavelength-dependent transmittance of the observation filter.A first band of high total transmission is in the range of about 404 nm to 438 nm. In the first band of high total transmission, the total transmission is about 0.15%. A second band of high total transmission is in the range of about 544 nm to 595 nm. In the second band of high total transmission, the total transmission is about 0.033%. The first band of high total transmission and the second band of high total transmission are matched very accurately to one another both with regard to their wavelength ranges and with regard to their total transmissions. This tuning allows observation of the non-fluorescent regions of the object in color fidelity. That is, the non-fluorescent regions of the object can be observed in almost the same colors when the filter set is applied with a white light source as when the object is observed without optical filters.The band of the observation filter from 404 nm to 438 nm, which contributes to the first band of high total transmission, is relatively wide. In particular, the short-wave limit of the band at approximately 404 nm is far in the short wave. Due to the relatively large width of the band, the observation filter can be manufactured more easily and reliably than is the case with filters with bands of small width. In particular, this can achieve a high degree of robustness with respect to the color-fidelity display of non-fluorescent regions of the object.A first band of low total transmission is in the range of about 466 nm to 534 nm. In the first low total transmission band, the total transmission is about 0.000001% (i.e., 10 -8). This low total transmission brings about a strong suppression in a wavelength range in which the human eye has a particularly high sensitivity. This low total transmission therefore contributes substantially to the function of the filter set, according to which non-fluorescent regions of the object can be observed in colour-true representation by a human observer.The illumination filter has a low transmittance of at most 0.1% in the range from about 300 nm to about 385 nm. As a result, UV components of the illumination light are suppressed. This prevents these UV components from being transferred to the object to be observed. Such UV components can cause damage in some objects, which is to be avoided. Such UV components, which are reflected on the object to be observed and are supplied to an eye of an observer, can damage the eye of the observer, which is to be avoided.The transmittance of the illumination filter and the transmittance of the observation filter are set up to a wavelength of about 1150 nm. Although the human eye is no longer sensitive in the wavelength range from approximately 800 nm to 1150 nm, suitable cameras can be sensitive in this wavelength range. This wavelength range can therefore be used for image generation by means of a camera.Robustness Is Robustness RobustnessAccording to an 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 edge nor a short-pass edge.According to one embodiment, Ti has a short-pass edge between 454 nm and 460 nm. In the wavelength range of this short-pass edge, To has neither a long-pass edge nor a short-pass edge.According to one embodiment, Ti has a long pass edge between 524 nm and 535 nm. In the wavelength range of this long-pass edge, To has neither a long-pass edge nor a short-pass edge.According to an embodiment, Ti has a short-pass edge between 595 nm and 610 nm. In the wavelength range of this short-pass edge, To has neither a long-pass edge nor a short-pass edge.According to an embodiment, Ti has a long pass edge between 750 nm and 770 nm. In the wavelength range of this long-pass edge, To has neither a long-pass edge nor a short-pass edge.According to an embodiment, To has a short-pass edge between 390 nm and 395 nm. In the wavelength range of this short-pass edge, Ti has neither a long-pass edge nor a short-pass edge.According to an embodiment, To has a long pass edge between 400 nm and 404 nm. In the wavelength range of this long-pass edge, Ti has neither a long-pass edge nor a short-pass edge.According to one embodiment, To has a short-pass edge between 438 nm and 444 nm. In the wavelength range of this short-pass edge, Ti has neither a long-pass edge nor a short-pass edge.According to an embodiment, To has a long pass edge between 537 nm and 543 nm. In the wavelength range of this long-pass edge, Ti has neither a long-pass edge nor a short-pass edge.According to one embodiment, To has a short-pass edge between 723 nm and 733 nm. In the wavelength range of this short-pass edge, Ti has neither a long-pass edge nor a short-pass edge.According to the above embodiments, the transmittance Ti of the illumination filter and the transmittance To of the observation filter can be matched to one another such that edges of the transmittances of the two filters (for example, low-pass edge, high-pass edge) do not overlap. In the production of optical filters, production-related fluctuations can occur with regard to achieved wavelength-related positions of edges and achieved transmission rates. Such manufacturing-related fluctuations are particularly problematic if edges of the transmission levels of a plurality of optical filters of a filter set spectrally overlap, since even a small fluctuation with regard to achieved wavelength-related positions of edges and achieved transmission levels can have a great effect on the functioning of the filter set. In order to achieve high robustness with respect to manufacturing-related fluctuations, 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 to one another such that they do not spectrally overlap one another.Fluorescence Observation SystemA fluorescence observation system according to an embodiment for simultaneously observing protoporphyrin IX in an object and non-fluorescent regions of the object in a near color-true 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 an embodiment, wherein the illumination filter of the filter set is arrangeable / arranged in an illumination beam path between the light source and the object and the observation filter of the filter set is arrangeable / arranged in a beam path of the observation optics.MethodA method according to an embodiment for simultaneously observing protoporphyrin IX in an object and non-fluorescent regions of the object in near color fidelity representation using a filter set according to an embodiment comprises: filtering illumination light directed to 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.Brief Description of the DrawingsFIG. 1 is a schematic diagram of a fluorescence observation system according to an embodiment. FIG. 2 shows a schematic illustration of a wavelength-dependent transmittance of an illumination filter of a filter set according to one embodiment. FIG. 3 shows a schematic illustration of a wavelength-dependent transmittance of an observation filter of a filter set according to one embodiment. FIG. 4 shows a schematic illustration of an overall transmission of a filter set according to an embodiment.A fluorescence observation system 1 according to an embodiment is explained below with reference to a surgical microscope. However, embodiments of the fluorescence observation system are not limited to such surgical microscopes, but rather comprise any fluorescence observation systems in which illumination light directed onto an object is filtered with an illumination filter and light emanating from the object is filtered with an observation filter.With reference to FIG. 1, the fluorescence observation system 1 or microscope 1 comprises a microscope optical unit (observation optical unit) 3 having an objective 5 with an optical axis 7. Light emanating from the object 9 is transferred by the objective 5 into an image-side beam 11 in which two zoom systems 12, 13 are arranged at a distance from the optical axis 7 and a partial beam 14 or 15 each emerge from the beam 11 and feed eyepieces 16 and 17 via deflection prisms, not shown in FIG. 1, into which eyepieces a viewer takes his left eye 18 or his right eye 19 to perceive an enlarged representation of the object 9 as an image. Contrary to the above example, the fluorescence observation system 1 does not have to be designed as a stereo microscope. A single observation channel is sufficient.A partially transmissive mirror 21 can be arranged in the partial beam bundle 15 in order to couple out a part of the partial beam bundle 15 as partial beam bundle 23, which is fed to a camera system 24. The camera system 24 comprises a camera 32, to which light of the partial beam bundle 23 is supplied via a camera adapter optics 31 and records an image of the supplied light. The image recorded by the camera 32 is transmitted via a data connection 33 to a controller 35 and can be stored therein in a memory 95.A partially transmissive mirror 37 can be arranged in the partial beam 14 in order to couple out a part of the partial beam 14 as partial beam 39, which is fed to a camera system. The camera system comprises a camera 43, to which light of the partial beam 39 is supplied via a camera adapter optics 41 and captures an image of the supplied light. The image recorded by the camera 43 is transmitted to the controller 35 via a data connection 45 and can be stored therein in the memory 95.The images detected by the cameras 32, 43 can be output by the controller 35 via a data connection 47 to a display device 49, for example a head mounted display ("head mounted display"). For this purpose, the head-mounted viewing device comprises two displays 51, 52 for the right or left eye of the observer.Contrary to the above example, the fluorescence observation system 1 does not have to include both the eyepieces 16, 17 and the camera systems. It is sufficient if only the eyepieces 16, 17 are provided. It is also sufficient if only the camera systems are provided.The microscope 1 further comprises an illumination system 63 for generating an illumination light 81 directed onto the object 9, for which purpose the illumination system 63 comprises 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 for generating a collimated light beam bundle 74, which can be directed onto an inlet end 76 of a glass fiber bundle 77 by means of one or more lenses 75 in order to couple light emitted by the lamp 71 into the glass fiber bundle 77. The light is transported by the glass fiber bundle 77 into the vicinity of the object 9, exits there at an exit end 78 of the glass fiber bundle 77 and is then bundled by an optical system 79 to form the illumination light 81 directed onto the object 9.The illumination system 63 further comprises an illumination filter 84 of a filter set for simultaneously observing protoporphyrin IX in the object 9 and non-fluorescent regions of the object 9 in a near color fidelity representation. A drive 87 controlled by the controller 35 via a switch 97 is provided in order to arrange the illumination filter 84 selectively inside or outside the light beam bundle 74, as is indicated by an arrow 88.In an observation beam path of the observation optical unit 3, for example in the beam bundle 11 or the partial beams bundles 14 and 15, an observation filter 91 of a filter set for simultaneous observation of protoporphyrin IX in the object 9 and of non-fluorescent regions of the object 9 is arranged in a virtually color-true representation. A drive 93 controlled by the controller 35 via the switch 97 is provided in order to optionally arrange the observation filter 91 inside or outside the observation beam path of the observation optical unit 3, as is indicated by the arrow 94.When the filter set is used, the illumination filter 84 and the observation filter 91 are simultaneously arranged within the respective optical paths. In the example shown, the illumination filter 84 and the observation filter 91 are introduced into and removed from the beam paths by drives under the control of a controller. However, it is also possible for the filters to be provided in filter holders which are operated directly by the observer with his hand in order to insert them into the beam paths or remove them from them.FIG. 2 shows a schematic illustration of a wavelength-dependent transmittance Ti of an illumination filter 84 of a filter set according to one embodiment. FIG. 3 shows a schematic illustration of a wavelength-dependent transmittance To of an observation filter 91 of a filter set according to one embodiment. FIG. 4 shows a schematic illustration of an overall transmission of a filter set according to an embodiment.Embodiments described herein may be combined with each other as desired.

Claims

A filter set for simultaneously observing fluorescent light of protoporphyrin IX in an object (9) and non-fluorescent regions of the object (9) in near-color representation, the filter set comprising an illumination filter (84) and an observation filter (91), wherein a transmittance (Ti) of the illumination filter (84) of 405 nm to 452 nm has an average value of at least 90%, is at most 0.01% in at least 95% of a wavelength range extending from 466 nm to 524 nm, is at most 0.01%, is at most 535 nm to 595 nm has an average value of at least 0.028% and at most 0.044%, and is at most 0.003% in at least 95% of a wavelength range extending from 610 nm to 750 nm; wherein a transmittance (To) of the observation filter (91) of 404 nm to 438 nm has an average value of at least 0.143% and at most 0.187%, 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% of 544 nm to 722 nm.The filter set according to claim 1, wherein the transmittance (Ti) of the illumination filter (84) is at most 0.1% in at least 95% of a wavelength range extending from 300 nm to 385 nm, and / or from 610 nm to 750 nm has an average value of at most 0.001%, and / or is at most 0.1% in at least 95% of a wavelength range extending from 770 nm to 1150 nm; 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 limit wavelength, and is at most 1% in at least 95% of a wavelength range extending from a second limit wavelength to 1150 nm, wherein the second limit wavelength is greater than the first limit wavelength and the first limit wavelength and the second limit wavelength are in the range from 800 nm to 1100 nm.Filter set according to claim 1 or 2, wherein the transmittance (Ti) of the illumination filter (84) has a long-pass flank between 395 nm and 400 nm and / or has a short-pass flank between 454 nm and 460 nm and / or has a long-pass flank between 524 nm and 535 nm and / or has a short-pass flank between 595 nm and 610 nm and / or has a long-pass flank between 750 nm and 770 nm and / or wherein the transmittance (To) of the observation filter (91) has a short-pass flank between 390 nm and 395 nm and / or has a long-pass flank between 400 nm and 404 nm and / or has a short-pass flank between 438 nm and 444 nm and / or has a long-pass flank between 537 nm and 543 nm and / or has a short-pass flank between 723 nm and 733 nm.Filter set according to one of claims 1 to 3, wherein the transmittance (Ti) of the illumination filter (84) has a first long-pass edge between 395 nm and 400 nm and the transmittance (To) of the observation filter (91) has neither a long-pass edge nor a short-pass edge in a wavelength range of the first long-pass edge of the illumination filter (84); and / or wherein the transmittance (Ti) of the illumination filter (84) has a first short-pass edge between 454 nm and 460 nm and the transmittance (To) of the observation filter (91) has neither a long-pass edge nor a short-pass edge in a wavelength range of the first short-pass edge of the illumination filter (84); and / or wherein the transmittance (Ti) of the illumination filter (84) has a second long-pass edge between 524 nm and 535 nm and the transmittance (To) of the observation filter (91) has neither a long-pass edge nor a short-pass edge in a wavelength range of the second long-pass edge of the illumination filter (84); and / or wherein the transmittance (Ti) of the illumination filter (84) has a second short-pass edge between 595 nm and 610 nm and the transmittance (To) of the observation filter (91) has neither a long-pass edge nor a short-pass edge in a wavelength range of the second short-pass edge of the illumination filter (84); and / or wherein the transmittance (Ti) of the illumination filter (84) has a third long-pass edge between 750 nm and 770 nm and the transmittance (To) of the observation filter (91) has neither a long-pass edge nor a short-pass edge in a wavelength range of the third long-pass edge of the illumination filter (84); and / or wherein the transmittance (To) of the observation filter (91) has a first short-pass edge between 390 nm and 395 nm and the transmittance (Ti) of the illumination filter (84) has neither a long-pass edge nor a short-pass edge in a wavelength range of the first short-pass edge of the observation filter (91); 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) has neither a long-pass edge nor a short-pass edge in a wavelength range of the first long-pass edge of the observation filter (91); and / or wherein the transmittance (To) of the observation filter (91) has a second short-pass edge between 438 nm and 444 nm and the transmittance (Ti) of the illumination filter (84) has neither a long-pass edge nor a short-pass edge in a wavelength range of the second short-pass edge of the observation filter (91); and / or wherein the transmittance (To) of the observation filter (91) has a second long-pass edge between 537 nm and 543 nm and the transmittance (Ti) of the illumination filter (84) has neither a long-pass edge nor a short-pass edge in a wavelength range of the second long-pass edge of the observation filter (91); and / or wherein the transmittance (To) of the observation filter (91) has a third short-pass edge between 723 nm and 733 nm and the transmittance (Ti) of the illumination filter (84) has neither a long-pass edge nor a short-pass edge in a wavelength range of the third short-pass edge of the observation filter (91).The filter set according to any one of claims 1 to 4, wherein the transmittance (Ti) of the illumination filter (84) satisfies following following following following following following n m 595 n m A b s ( T i ( λ ) - 0.036 % ) ⋅ d λ ≤ 1.5 % ⋅ n m and / or wherein the transmittance (To) of the observation filter (91) satisfies following following n m 438 n m A b s ( T o ( λ ) - 0.165 % ) ⋅ d λ ≤ 1.5 % ⋅ n m .A fluorescence observation system for simultaneously observing protoporphyrin IX in an object (9) and non-fluorescent areas of the object (9) in a near color-true 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) comprise 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).A method for simultaneously observing protoporphyrin IX in an object (9) and non-fluorescent regions of the object (9) in near color fidelity representation using the filter set according to any one of claims 1 to 5, the method comprising: filtering illumination light (74, 81) directed to 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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