FILTER SET, FLUORESCENCE OBSERVATION SYSTEM AND METHOD FOR SIMULTANEOUSLY OBSERVING FLUORESCENT AND NON-FLUORESCENT REGIONS OF AN OBJECT

Abstract

The present invention relates to a filter set, to a fluorescence observation system and to a method for simultaneously observing fluorescent and non-fluorescent regions of an object. The filter set comprises an illumination filter and an observation filter. The illumination filter is configured such that it efficiently transmits visible light having short wavelengths and efficiently blocks light having a long wavelength. The observation filter is configured such that it efficiently blocks visible light having short wavelengths and efficiently transmits light having a long wavelength. The illumination filter and the observation filter are configured such that the product of the transmittance of the illumination filter T.sup.I(λ) and the transmittance of the observation filter T.sup.O(λ) are very constant over a high proportion of the visible wavelength range.

Claims

1. Filter set for simultaneously observing fluorescent and non-fluorescent regions of an object, comprising: an illumination filter and an observation filter; wherein the average value of T.sup.I(λ) over a first wavelength range from a wavelength λ.sub.VIS,MIN up to a wavelength λ.sub.1 is greater than a first value W1; wherein the average value of T.sup.I(λ) over a second wavelength range from a wavelength λ.sub.2 up to a wavelength λ.sub.VIS,MAX is smaller than a second value W2; wherein the average value of T.sup.O(λ) over the first wavelength range is smaller than the second value W2; wherein the average value of T.sup.O(λ) over the second wavelength range is greater than the first value W1; wherein the average value of $.Math.{\log }_{10}\left(\frac{T^1\left(\lambda \right).Math.T^O\left(\lambda \right)}{{\mathrm{.Math.}}_{\mathrm{WLB}3}}\right).Math.$ over a third wavelength range, which is the combination of the first and the second wavelength ranges, is smaller than a third value W3, wherein μ.sub.WLB3 is the average value of T.sup.I(λ).Math.T.sup.O(λ) over the third wavelength range, with the result that the object can be observed with colour fidelity; wherein T.sup.I(λ) is the wavelength-dependent transmittance of the illumination filter, wherein T.sup.O(λ) is the wavelength-dependent transmittance of the observation filter; wherein λ.sub.VIS,MIN<λ.sub.1<λ.sub.2<λ.sub.VIS,MAX, λ.sub.VIS,MIN=380 nm and λ.sub.VIS,MAX=780 nm; wherein W1>100.Math.W2; and wherein W3<1.5.

2. Filter set according to claim 1, wherein W3<1.0, W3<1.0, in particular W3<0.7, more particularly W3<0.4 or W3<0.1 or W3<0.05 or W3<0.01 or W3<0.001.

3. Filter set according to claim 1, wherein $.Math.{\log }_{10}\left(\frac{T^1\left(\lambda \right).Math.T^O\left(\lambda \right)}{{\mathrm{.Math.}}_{\mathrm{WLB}3}}\right).Math.\le W4$ for each wavelength λ within the third wavelength range with W4=1.5, in particular W4=1.0, more particularly W4=0.7 or W4=0.1 or W4=0.05 or W4=0.01.

4. Filter set according to claim 1, wherein μ.sub.WLB3>0.00001, in particular μ.sub.WLB3>0.0001, more particularly μ.sub.WLB3>0.0005; and/or wherein μ.sub.WLB3<0.01, in particular μ.sub.WLB3<0.001.

5. Filter set according to claim 1, wherein |λ.sub.1−λ.sub.2|≤100 nm, in particular |λ.sub.1−λ.sub.2|≤50 nm, more particularly |λ.sub.1−λ.sub.2≤30 nm; and/or wherein |λ.sub.1−λ.sub.2|≥10 nm, in particular |λ.sub.1−λ.sub.2|≥20 nm, more particularly |λ.sub.1−λ.sub.2|≥30 nm.

6. Filter set according to claim 1, wherein
μ.sub.WLB3>K1.Math.μ.sub.WLB4 with K1=10 in particular K1=100 more particularly K1=1000 or K1=10 000 or K1=100 000, wherein μ.sub.WLB4 is the average value of T.sup.I(λ).Math.T.sup.O(λ) over a fourth wavelength range from the wavelength λ.sub.1 up to the wavelength λ.sub.2.

7. Filter set according to claim 1, wherein
K2.Math.μ.sub.WLB3>T.sup.I(λ).Math.T.sup.O(λ) for each wavelength λ within the fourth wavelength range with K2=1.5, in particular K2=1.1, more particularly K2=1.0.

8. Filter set according to claim 1, wherein W1>200.Math.W2, in particular W1>500.Math.W2, more particularly W1>1000.Math.W2 or W1>10 000.Math.W2 or W1>100 000.Math.W2.

9. Filter set according to claim 1, wherein W1≥0.1, in particular W1≥0.5, more particularly W1≥0.9; and/or wherein W2≤0.05, in particular W2<0.01, more particularly W2≤0.005.

10. Filter set according to claim 1, wherein for use of the filter set for protoporphyrin IX: 400 nm≤λ.sub.1≤650 nm and λ.sub.2≤650 nm, in particular 420 nm≤λ.sub.1≤600 nm and λ.sub.2≤600 nm.

11. Filter set according to claim 1, wherein for use of the filter set for fluorescein: 450 nm≤λ.sub.1≤510 nm and λ.sub.2≤530 nm, in particular 470 nm≤λ.sub.1≤510 nm and λ.sub.2≤600 nm.

12. Fluorescence observation system for simultaneously observing fluorescent and non-fluorescent regions of an object, comprising: an illumination system having a light source for illuminating an object, an observation system for imaging the object and a filter set according to claim 1, wherein the illumination filter of the filter set is arranged in an illumination beam path between the light source and the object and the observation filter of the filter set is arranged in a beam path of the observation system.

13. Method for simultaneously observing fluorescent and non-fluorescent regions of an object using the filter set according to claim 1, wherein the method comprises: filtering an illumination light beam, which is directed onto an object, using the illumination filter of the filter set; and filtering light emanating from the object using the observation filter of the filter set.

Description

[0023] Embodiments of the invention are explained in greater detail below with reference to figures, in which:

[0024] FIG. 1 shows a fluorescence observation system according to an embodiment of the invention,

[0025] FIG. 2A shows the absorption spectrum and the emission spectrum of an exemplary fluorescent dye,

[0026] FIG. 2B shows the wavelength-dependent transmittance of an illumination filter of a filter set according to one embodiment of the invention,

[0027] FIG. 2C shows the wavelength-dependent transmittance of an observation filter of the filter set,

[0028] FIG. 2D shows the product of the transmittance of the illumination filter, shown in FIG. 2B, and the transmittance of the observation filter, shown in FIG. 2C.

[0029] FIG. 1 shows an embodiment of a fluorescence observation system 1. The fluorescence observation system 1 comprises an illumination system 3, which comprises at least one light source 5 and one illumination optical unit 7. The at least one light source 5 may comprise a plurality of different light sources so as to be able to produce illumination light. The illumination system 3 provides, by way of the illumination optical unit 7, an illumination beam path 11, with which illumination light can be directed onto an object region 13. The light produced by the light source 5 is, for example, white light.

[0030] Arranged in the beam path 11 is an illumination filter 9 of a filter set, through which the illumination light produced by the illumination system 3 is filtered. As shown in FIG. 1, the illumination filter 9 may be arranged within the illumination system 3. However, the illumination filter 9 can also be arranged outside the illumination system 3. Furthermore, the illumination filter 9 can optionally be inserted into the beam path 11 and be guided out of the beam path 11, for example using an actuator (not illustrated in FIG. 1).

[0031] An object 15, which may contain a fluorescent dye, in particular protoporphyrin IX (PpIX), fluorescein or the like, can be arranged in the object region 13. The absorption spectrum and the emission spectrum of the fluorescent dye can lie in the wavelength range that is visible to human beings.

[0032] The fluorescent dye in the object 15 can be excited by the illumination light that is filtered using the illumination filter 9, as a result of which the fluorescent dye emits fluorescent light. Furthermore, the illumination light that is filtered using the illumination filter 9 and is incident on the object 15 is at least partially reflected by the latter. Light emanating from the object 15 therefore comprises both fluorescent light and reflected illumination light.

[0033] The light emanating from the object 15 is detected by an observation system 17. By way of example, the observation system 17 may comprise a lens 19, a zoom system consisting of the lens elements 21 and 22, and a spatially resolving camera 23. An observation filter 27 of the filter set is arranged in a beam path 25 between the object region 13 and the camera 23.

[0034] The fluorescence observation system 1 may further comprise a controller 29 which is connected, firstly, to the illumination system 3 via a connection 31 and, secondly, to the camera 23 via a connection 33. The controller 29 can control the illumination system 3 via the connection 31. By way of example, the controller 29 may control the emission intensity of the at least one light source 5 or control the individual light sources 5 and/or switch these on and off. If a plurality of illumination filters 9 are provided in a filter changer, in particular a filter wheel, the controller 29 can select the illumination filter to be inserted into the beam path 11 and can cause said illumination filter to be introduced into the beam path 11.

[0035] The controller 29 receives the images detected by the camera 23 via the connection 33. The controller 29 can process the received images and prompt the presentation thereof on a display device. By way of example, a screen or other image-presenting devices may be considered as a display device.

[0036] As an alternative or in addition to the camera 23, an eyepiece may be provided, with which an observer can directly observe the image of the object 15 produced by the observation system 17. For this purpose, a further beam path can be branched off from the beam path 25, which further beam path is guided to the eyepiece or the camera 23.

[0037] FIGS. 2A to 2D are used to explain an embodiment of a filter set that is suitable for observing the fluorescent dye PpIX. The concept of the filter set described herein, however, can be applied to further fluorescent dyes, in particular to fluorescent dyes having an absorption spectrum and emission spectrum that each lies at least partially in the visible wavelength range from λ.sub.VIS,MIN=380 nm to λ.sub.VIS,MAX=780 nm.

[0038] FIG. 2A shows the absorption spectrum (A) and the emission spectrum (E) of the fluorescent dye PpIX. The absorption spectrum (A) of the fluorescent dye PpIX has a maximum at approximately 405 nm. The emission spectrum (E) has a main maximum at approximately 635 nm and a secondary maximum at approximately 705 nm. The absorption spectrum (A) and the emission spectrum (E) are normalized to its respective maximum absorption and emission.

[0039] FIG. 2B shows the wavelength-dependent transmittance of the illumination filter 9, abbreviated to T.sup.I(λ), as a graph 37. The abscissa represents the wavelength λ in nanometres (nm). The ordinate represents the transmittance with a logarithmic scale. The transmittance T.sup.I(λ) of the illumination filter 9 is approximately 1 from λ.sub.VIS,MIN=380 nm to λ.sub.1≈510 nm, decreases continuously from λ.sub.1≈510 nm to λ.sub.2≈580 nm to approximately 10.sup.−4 and from λ.sub.2≈580 nm to λ.sub.VIS,MAX=780 nm is approximately 10.sup.−4.

[0040] FIG. 2C shows the wavelength-dependent transmittance of the observation filter 27, abbreviated to T.sup.O(λ), as a graph 39. The abscissa represents the wavelength λ in nanometres (nm). The ordinate represents the transmittance with a logarithmic scale. The transmittance T.sup.O(λ) of the observation filter 27 from λ.sub.VIS,MIN=380 nm to λ.sub.1≈510 nm is approximately 10.sup.−4, increases continuously from λ.sub.1≈510 nm to λ.sub.2≈580 nm to approximately 1 and from λ.sub.2≈580 nm to λ.sub.VIS,MAX=780 nm is approximately 1.

[0041] FIG. 2D shows the product of the wavelength-dependent transmittance of the illumination filter 9 and the wavelength-dependent transmittance of the observation filter 27, abbreviated to T.sup.I(λ).Math.T.sup.O(λ), as a graph 41. The abscissa represents the wavelength λ in nanometres (nm). The ordinate represents the product with a logarithmic scale. The product T.sup.I(λ).Math.T.sup.O(λ) from λ.sub.VIS,MIN=380 nm to λ.sub.1≈510 nm is approximately 10.sup.−4, decreases from λ.sub.1≈510 nm to approximately 10.sup.−8, then increases up to λ.sub.2≈580 nm to approximately 10.sup.−4 and from λ.sub.2≈580 nm to λ.sub.VIS,MAX=780 nm is approximately 10.sup.−4.

[0042] The wavelength range from λ.sub.VIS,MIN=380 nm to λ.sub.1≈510 nm is denoted as the first wavelength range. The average value of T.sup.I(λ) over the first wavelength range is greater than a first value W1, which is a lower limit for the average value of T.sup.I(λ) over the first wavelength range. The average value of T.sup.O(λ) over the first wavelength range is smaller than the second value W2, which is an upper limit for the average value of T.sup.O(λ) over the first wavelength range. To sufficiently suppress reflected illumination light of the first wavelength range: W1>100.Math.W2, in particular W1>200.Math.W2 or W1>500.Math.W2 or W1>1000.Math.W2 or W1>10 000.Math.W2 or W1>100 000.Math.W2. With preference: W1≥0.1, in particular W1≥0.5, more particularly W1≥0.9. With preference: W2≤0.05, in particular W2≤0.01, more particularly W2≤0.005.

[0043] The wavelength range from λ.sub.2≈580 nm to λ.sub.VIS,MAX=780 nm us debited as the second wavelength range. The average value of T.sup.I(λ) over the second wavelength range is smaller than the second value W2, which is an upper limit for the average value of T.sup.I(λ) over the second wavelength range. The average value from T.sup.I(λ) over the second wavelength range is greater than the first value W1, which is a lower limit for the average value of T.sup.O(λ) over the second wavelength range.

[0044] The combination of the first and second wavelength ranges is denoted as the third wavelength range. The wavelength range from λ.sub.1≈510 nm to λ.sub.2≈580 nm is denoted as the fourth wavelength range. The product T.sup.I(λ).Math.T.sup.O(λ) in the fourth wavelength range has significantly smaller values than in the third wavelength range. The fourth wavelength range serves for separating the region of high transmission of the illumination filter in the first wavelength range from the region of high transmission of the observation filter in the second wavelength range. This avoids overexposure of the fluorescent light.

[0045] To ensure that the object 15 can be observed with the greatest colour fidelity, T.sup.I(λ) and T.sup.O(λ) in the third wavelength range are matched to one another such that the product T.sup.I(λ).Math.T.sup.O(λ) in the third wavelength range is as constant as possible. This is achieved for example by the average value of

[00003]$.Math.{\log }_{10}\left(\frac{T^1\left(\lambda \right).Math.T^O\left(\lambda \right)}{{\mathrm{.Math.}}_{\mathrm{WLB}3}}\right).Math.$

over the third wavelength range being smaller than a third value W3, wherein μ.sub.WLB3 is the average value of T.sup.I(λ).Math.T.sup.O(λ) over the third wavelength range and W3<1.5. The expression restricts a factor that is the ratio of the product T.sup.I(λ).Math.T.sup.O(λ) to μ.sub.WLB3 on average to an upper limit of a maximum of 10.sup.1.5. The smaller the value of the expression is, the more constant is the product T.sup.I(λ).Math.T.sup.O(λ) in the third wavelength range round the value μ.sub.WLB3. With preference: W3<1.0, in particular W3<0.7, more particularly W3<0.4. With further preference: W3<0.1 or W3<0.05 or W3<0.01 or W3<0.001.

[0046] Alternatively or additionally, the constancy of the product T.sup.I(λ).Math.T.sup.O(λ) in the third wavelength range can be expressed in that

[00004]$.Math.{\log }_{10}\left(\frac{T^1\left(\lambda \right).Math.T^O\left(\lambda \right)}{{\mathrm{.Math.}}_{\mathrm{WLB}3}}\right).Math.\le W4$

for each wavelength λ within the third wavelength range with W4=1.5. The expression means that there must not be any wavelength within the third wavelength range at which T.sup.I(λ).Math.T.sup.O(λ)>10.sup.W4.Math.μ.sub.WLB3 or T.sup.I(λ).Math.T.sup.O(λ)<10.sup.−4.Math.μ.sub.WLB3 is met. Preferably: W4=1.0 or W4=0.7 or W4=0.1 or W4=0.05 or W4=0.01.

[0047] According to one exemplary embodiment, T.sup.I(λ) and T.sup.O(λ) are matched to one another such that: μ.sub.WLB3>0.00001, in particular μ.sub.WLB3>0.0001, more particularly μ.sub.WLB3>0.0005, wherein μ.sub.WLB3 is the average value of T.sup.I(λ).Math.T.sup.O(λ) over the third wavelength range. This ensures that light that is transmitted through the illumination filter 9, reflected at the object 15 and then transmitted through the observation filter 27 has an intensity that is large enough to be able to be observed. The intensity lies in the region of the intensity of fluorescent light, which means that fluorescent regions of the object 15 and non-fluorescent regions of the object 15 can be perceived with similar intensity.

[0048] According to one exemplary embodiment, T.sup.I(λ) and T.sup.O(λ) are matched to one another such that: μ.sub.WLB3<0.01, in particular μ.sub.WLB3<0.001. This ensures that light that is transmitted through the illumination filter 9, reflected at the object 15 and then transmitted through the observation filter 27 has an intensity that is small enough to not overexpose fluorescent light.

[0049] According to one exemplary embodiment, T.sup.I(λ) and T.sup.O(λ) are matched to one another such that: |λ.sub.1−λ.sub.2|≤100 nm, in particular |.sub.2−λ.sub.2|≤50 nm, more particularly |λ.sub.1−λ.sub.2|≤30 nm and/or |λ.sub.1−λ.sub.2|≥10 nm, in particular |λ.sub.1−λ.sub.2|≥20 nm, more particularly |λ.sub.1−λ.sub.2|≥30 nm. The smaller the distance between λ.sub.1 and λ.sub.2 is, the better the colour fidelity with which the object 15 can be observed, because the third wavelength range comprises a larger bandwidth. If the distance between λ.sub.1 and λ.sub.2 is very small, the production may be more difficult. With the ranges stated, the filters are easy to produce and still offer good colour fidelity. In addition, with a larger distance it is easier to ensure that the wavelength range in which the illumination filter has a high transmission and the wavelength range in which the observation filter has a high transmission do not overlap.

[0050] According to one exemplary embodiment, T.sup.I(λ) and T.sup.O(λ) are matched to one another such that: μ.sub.WLB3>K1.Math.μ.sub.WLB4 with K1=10, wherein μ.sub.WLB3 is the average value of T.sup.I(λ).Math.T.sup.O(λ) over the third wavelength range and μ.sub.WLB4 is the average value of T.sup.I(λ).Math.T.sup.O(λ) over the fourth wavelength range from the wavelength λ.sub.1 up to the wavelength λ.sub.2. This ensures that the product T.sup.I(λ).Math.T.sup.O(λ) within the fourth wavelength range is sufficiently smaller than the product T.sup.I(λ).Math.T.sup.O(λ) within the third wavelength range. With preference: K1=100 or K1=1000 or K1=10 000 or K1=100 000.

[0051] According to an exemplary embodiment, T.sup.I(λ) and T.sup.O(λ) are matched to one another such that for each wavelength λ within the fourth wavelength range: K2.Math.μ.sub.WLB3>T.sup.I(λ).Math.T.sup.O(λ) with K2=1.5, in particular K2=1.1, more particularly K2=1.0. This ensures that the product T.sup.I(λ).Math.T.sup.O(λ) within the fourth wavelength range is sufficiently smaller than the product T.sup.I(λ).Math.T.sup.O(λ) within the third wavelength range.

[0052] The concept of the filter set was explained above using the example of PpIX. For application with PpIX, the wavelengths λ.sub.1 and λ.sub.2 can be selected for example from the following ranges: 400 nm≤λ.sub.1≤650 nm, in particular 420 nm≤λ.sub.1≤600 nm; λ.sub.2≤650 nm, in particular λ.sub.2≤600 nm.

[0053] For application with fluorescein, the wavelengths λ.sub.1 and λ.sub.2 can be selected for example from the following ranges: 450 nm≤λ.sub.1≤510 nm, in particular 450 nm≤λ.sub.1≤510 nm; λ.sub.2≤530 nm, in particular λ.sub.2≤600 nm.