DE102020118673A1 - Method and system for measuring fluorescence in open surgery - Google Patents

Abstract

The invention relates to a method and a system for measuring fluorescence in open surgery, in which a fluorescence agent is used whose absorption and fluorescence spectra are known. The treated tissue (2) of the patient is illuminated during the intervention with a broadband ambient light (4) and additionally illuminated at least temporarily with an excitation light (12) for the fluorescence agent, the maximum of which has a shorter wavelength than a maximum of the fluorescence spectrum of the fluorescence agent. A part of the de-excitation light (16) of the fluorescent agent and the tissue (2) reflected ambient light (6) enters a measuring device (20). The light is in the measuring device (20) by means of one or two beam splitters (22, 24) in divided into two or three beam paths (30, 32, 34). To determine a background offset through reflected ambient light (6), part of the light is passed through a first filter (30A), designed as a bandpass filter for the de-excitation light (16) of the fluorescence agent, onto a first image sensor (30B). A second part of the light is passed through a second filter (32A), designed as a bandpass filter for a reference frequency band (32A'), which is adjacent to the bandpass of the first filter (30A) and is separated from a maximum of the spectral distribution (12') of the excitation light (12 ) is spaced, directed to a second image sensor (32B).

Description

The invention relates to a method and a system for measuring fluorescence in open surgery.

Fluorescent dyes are used in open surgery and in many other applications. During the operation, the exposed tissue is illuminated with a light that is suitable for exciting the fluorescent dye, often in the near-infrared range. In order to excite the fluorescent dye, the excitation light used is adapted to the absorption spectrum inherent to the fluorescent dye. As a result of the absorption of the excitation light, the fluorescence dye is shifted into an energetically higher state and spontaneously falls back into the ground state, emitting a fluorescence depletion light with a fluorescence spectrum typical of the fluorescence dye. In the case of applications in the blood of a patient, complex molecules are generally used as fluorescence agents, the deactivation light of which is generally lower in energy, ie has a longer wavelength, than the excitation light. This is due to the fact that during electronic excitation, higher vibrational states of the excited state are first occupied, which then release their energy through vibrational relaxation before spontaneous fluorescence depletion occurs. Therefore, more energy is used for excitation than is given off for emission.

With suitable image acquisition and image evaluation, the acquired fluorescence images and tissue images can be superimposed, it being possible for the tissue supplied with fluorescent dye to be identified, for example, by means of a false color representation in the superimposed image.

Since this excitation illumination takes place in the surgical environment, in which the exposed tissue is also illuminated with ambient light in the visible range, the spectral distribution of which can extend beyond the visible spectrum to the range of the wavelength of the fluorescent light, the problem arises that the Fluorescence dye emitted fluorescence light or deactivation light compared to the reflected ambient light has a low intensity. For imaging, the fluorescence image must be highly intensified. The disturbing spectral components of the reflected ambient light are also amplified, which falsifies the fluorescence images.

A measure known from the prior art to counteract this disadvantage is to increase the intensity of the fluorescent light emitted by the fluorescent dye by using a strong excitation light source.

To further eliminate the disadvantages described, according to DE 10 2005 045 961 A1 proposed to illuminate the tissue containing the fluorescent dye with a first light suitable for exciting the fluorescent dye at a clock frequency given by a periodic sequence of illumination and dark phases, first fluorescence images generated during the illumination phases, and second fluorescence images generated during the dark phases are generated by illuminating the tissue with a second light or ambient light, to be recorded separately, to correct the first fluorescence images by subtracting corresponding second fluorescence images and to generate overall images by overlaying the corrected first fluorescence images with corresponding native tissue images depicting a tissue surface. The interfering fluorescence components contained in the second light are subtracted, as a result of which the correspondingly corrected first fluorescence images are particularly exact.

A fluorescent dye used in various diagnostic applications is indocyanine green (ICG), whose absorption and emission characteristics are well known. Indocyanine green dissolved in blood is excited with light of wavelength between 600 nm and 900 nm, with a narrow maximum at about 810 nm, and emits at about 830 nm, with flat tails to 750 nm and 950 nm. Applications of ICG as Fluorescent media in surgery is, for example, perfusion diagnostics of tissues and organs. However, ICG cannot currently be used in open surgery because the ambient light in the operating room from overhead lighting, operating room lights, etc. also potentially emits light in the emission wavelength of the fluorescent agent, which in turn is reflected by the tissue in the wound area. A camera cannot distinguish whether the detected light of the corresponding wavelength at around 830 nm was actually emitted by the fluorescent agent or is reflected light from the ambient lighting.

Other fluorescers that can be used in the context of the present invention are, for example and not exclusively, SGM-101 with an absorption maximum at about 682 nm, OTL38 at about 753 nm, IRDye 800BK at about 752 nm, Bevacizumab-IRDye800CW at about 752 nm or LUM015 at approx. 650 nm.

The object of the present invention is to provide a method and a system with which it is possible to use fluorescence in open surgery.

This object is achieved by a method for measuring ICG fluorescence in open surgery, in which a fluorescent agent, in particular indocyanine green (ICG), dissolved in the blood of a patient, is used, the absorption and fluorescence spectra of which are known, the treated tissue of the patient is illuminated during the intervention with a broadband, in particular white, ambient light and is additionally illuminated at least temporarily with an excitation light for the fluorescence agent with a known spectral distribution, in particular in the infrared range, the maximum of which has a shorter wavelength than a maximum of the fluorescence spectrum of the fluorescence agent , in which, to determine a background offset to the de-excitation light emitted by the fluorescent agent due to ambient light reflected from the tissue, part of the light reflected and emitted by the tissue enters a measuring device and in the measuring device by means of a beam lsplitter is split into two beam paths or by means of two beam splitters into three beam paths, with a first part of the light in a first beam path being directed through a first filter, which is designed as a bandpass filter for the deactivation light of the fluorescent agent, onto a first image sensor and a second part of the light in a second beam path through a second filter, which is directed onto a second image sensor as a bandpass filter for a reference frequency band which is adjacent to the bandpass of the first filter and is spaced from a maximum of the spectral distribution of the excitation light.

In the context of the invention, the fluorescence spectrum of the fluorescence agent is synonymous with the spectrum of the fluorescence deactivation light or deactivation light. According to the invention, the first image sensor, like the second image sensor, receives light that is not primarily excitation light but is spectrally centered on the one hand on the fluorescence depletion and on the other hand on a reference area away from, but adjacent to, the maximum of the fluorescence depletion. This spectral analysis allows the evaluation according to the invention of the background, which is assumed to be essentially spectrally constant or flat, from reflected broadband illumination light.

In embodiments, the bandpass of the second filter is at shorter or longer wavelengths than the bandpass of the first filter. The reference frequency band can thus be arranged spectrally either between the excitation light and the maximum of the fluorescence deactivation (shorter wavelength) or on the side of the maximum of the fluorescence deactivation (longer wavelength) opposite the excitation light. In the long-wave case, the influence of the reflected excitation light is smaller than in the shorter-wave case due to the greater distance to the excitation spectrum, but the shorter-wave alternative of arranging the reference frequency band can be advantageous due to an asymmetry of the fluorescence spectrum.

There is preferably a spectral spacing of 0 to 10 nm, in particular 1 to 4 nm, between the bandpass filters of the first filter and the second filter. This ensures that the assumption that the spectral distribution of the ambient light is essentially constant remains valid.

In embodiments with two beam splitters and three beam paths, a third part of the light is guided in a third beam path onto a third image sensor for imaging in visible light, with the third beam path in particular having a third filter, in particular a UV filter and/or an IR filter , includes. This enables the full image to be displayed and overlaid in visible light (VIS) with a fluorescence image corrected for the background offset components, which results from further processing of the images from the first and second image sensors.

Unlike the one from DE 10 2005 045 961 A1 known method, the method according to the invention with the first and the second image sensor does not use a time-division multiplex method with excitation lighting switched on and off in order to differentiate between the components of fluorescent light and reflected light, but instead a division and analysis takes place in the spectral range.

Specifically, the first optical path having the first filter and the first image sensor serves to mainly capture the fluorescence depletion light. For this purpose, the first filter is designed as a bandpass filter for the fluorescence depletion light, in particular in the case of ICG narrow to the intensity maximum around approx. 830 nm of ICG. This image signal contains a proportion of reflected ambient light that has a very broad and flat spectral distribution. A narrow limitation to the intensity maximum of the fluorescence depletion thus serves to maximize the signal-to-background ratio. The wider the bandpass, i.e. the frequency band in which the filter is transparent, is made, the more light is collected, which reduces noise and thus increases image quality, but at the cost of reducing the ratio of light from fluorescence depletion to reflected light ambient light decreases. The width of the bandpass of the first filter is determined by the manufacturer, who undertakes appropriate tests to achieve good quality and contrast results.

The second beam path with the second filter and the second image sensor serves as a reference for determining the strength of the reflected ambient light. On the one hand, this reference should contain as little fluorescence-excitation light as possible, but on the other hand it should be close to the wavelength range of the first filter, in particular at a distance of a few nanometers. As a result, due to the flat profile of the spectral distribution of the ambient light in the near IR range, it can be assumed to a very good approximation that the intensity level of the reflected ambient light in the frequency band (or wavelength band) of the second filter is the same as in the frequency band of the first filter.

If the bandpass widths of the first filter and the second filter are the same, it can be assumed that the first image sensor receives the same amount of reflected ambient light as the second image sensor. Since the bandpass of the second filter is close to the bandpass of the first filter, part of the light passing through the bandpass of the second filter is also fluorescence depletion light, but is strongly suppressed compared to the part in the bandpass of the first filter. Furthermore, the bandpass of the second filter also includes as few portions as possible of the excitation light itself, which has its maximum at somewhat shorter wavelengths, and in return completely excludes the maximum of the spectral distribution of the excitation light. The image signal from the second image sensor thus contains a measure of the quantity and the spatial distribution of the reflected ambient light and thus serves as a basis for comparison for the background-affected fluorescence images from the first image sensor.

Unavoidable overlaps in the bandpass filters of the first and second filters with the spectral distributions of the excitation light and the fluorescence depletion light can be taken into account in the comparison, since both the different emission and absorption spectra and the profiles of the filter functions are known or can be measured and processed by calculation can be, while the spectral distribution of the reflected ambient light can be assumed to be approximately constant in the very narrow wavelength range. A further simplification of the calculation of the various components is achieved in embodiments if the excitation light is passed through an edge or bandpass filter before exiting an excitation light source unit, which filters out components of the excitation light whose wavelengths are in the range of the bandpass filters of the first filter and the second filter lie. As a result, no reflected excitation light can reach the first and second image sensors either.

In embodiments of the method, to remove the background offset, the illuminance measured by the second image sensor is subtracted from the illuminance measured by the first image sensor using a previously determined calibration factor. The known curves of the spectra of the various bandpass filters and of the fluorescence excitation light and the excitation light source unit are included in the calibration factor, as described above. Furthermore, a possibly different amplification of the two image sensor signals is included in the calculation of the calibration factor. The result of the subtraction is a fluorescence image corrected for the background from reflected ambient light.

In embodiments in which ICG is used as a fluorescer, the spectral distribution of the excitation light has a maximum at 810 nm ± 5 nm, in particular at 810 nm ± 3 nm, the spectral distribution of the excitation light in particular having a full width at half maximum (FWHM) of up to 10 nm , especially up to 5 nm.

Additionally or alternatively, in this case the reference frequency band is centered on a wavelength in the range from 820 nm to 826 nm or in the range from 835 nm to 841 nm, the reference frequency band in particular having a full width at half maximum (FWHM) of up to 4 nm, in particular up to 2 nm. Within the scope of the present invention, the reference frequency band is understood to mean the bandpass of the second filter, ie the transparent window of the second filter.

Furthermore, in embodiments, the bandpass of the first filter is additionally or alternatively centered on a maximum of the emission of the fluorescer, in particular a wavelength between 828 nm and 833 nm, and in particular has a full width at half maximum (FWHM) of up to 4 nm, in particular up to 2 nm Bandpass of the first filter is the frequency range or wavelength range in which the first filter is transparent.

The above values for the spectral distribution of the excitation light, the reference frequency band and the transparent frequency band of the first filter can be used individually, in pairs or together within the scope of the invention and adjusted accordingly when using fluorescence agents other than ICG.

$$G_{ICG}^R={\displaystyle \underset{\lambda }{\int }{F}_{ICG}\left(\lambda \right)F_R\left(\lambda \right)},G_{Ref}^R={\displaystyle \underset{\lambda }{\int }{F}_{Ref}\left(\lambda \right)F_R\left(\lambda \right)},$$

$$G_{ICG}^E={\displaystyle \underset{\lambda }{\int }{F}_{ICG}\left(\lambda \right)F_E\left(\lambda \right)},G_{Ref}^E={\displaystyle \underset{\lambda }{\int }{F}_{Ref}\left(\lambda \right)F_E\left(\lambda \right)}.$$

Dabei stehen F_{ICG, Ref} und FF,R,E für die Spektralfunktionen der Bandpässe ICG und Ref sowie der Lichtanteile F, R und E. In dem Fall, in dem das Anregungslicht zu den größeren Wellenlängen hin gefiltert wird und keinen Überlapp mit den transparenten Fenstern der beiden Bandpässe hat, sind die Gewichtungsfaktoren $G_{ICG}^E,G_{Ref}^E$

gleich Null.In embodiments of the method, overlaps of the spectral distributions of the excitation light and of the de-excitation light with the frequency curves of the first filter and of the second filter are included in the calibration factor. This is done using the example of ICG as a fluorescent agent _{wise in that the weightings G F,R,E are} calculated for the reference frequency band, i.e. the bandpass of the second filter, and for the bandpass of the first filter, with which the proportions of fluorescent or de-excitation light (F), reflected ambient light (R) and excitation light (E) flow into the reference frequency band (Ref) of the second filter and the bandpass (e.g. ICG) of the first filter. This can be done by calculating the integral of the products of the spectral functions of the bandpass filters (Ref, ICG) on the one hand and the spectral functions of F, R and E on the other hand over the wavelengths λ in the range of the respective bandpass filters of the two filters. The following applies, for example, to the six combinations of bandpasses ICG, REF and light components F, R and E: $$G_{ICG}^f={\displaystyle \underset{\lambda }{\int }{f}_{ICG}\left(\lambda \right)f_f\left(\lambda \right)},G_{Ref}^f={\displaystyle \underset{\lambda }{\int }{f}_{Ref}\left(\lambda \right)f_f\left(\lambda \right)},$$

$$G_{ICG}^R={\displaystyle \underset{\lambda }{\int }{f}_{ICG}\left(\lambda \right)f_R\left(\lambda \right)},G_{Ref}^R={\displaystyle \underset{\lambda }{\int }{f}_{Ref}\left(\lambda \right)f_R\left(\lambda \right)},$$

$$G_{ICG}^E={\displaystyle \underset{\lambda }{\int }{f}_{ICG}\left(\lambda \right)f_E\left(\lambda \right)},G_{Ref}^E={\displaystyle \underset{\lambda }{\int }{f}_{Ref}\left(\lambda \right)f_E\left(\lambda \right)}.$$

F _{ICG, Ref} and FF,R,E stand for the spectral functions of the bandpasses ICG and Ref as well as the light components F, R and E. In the case in which the excitation light is filtered towards the larger wavelengths and no overlap with the transparent ones windows of the two bandpass filters are the weighting factors $G_{ICG}^E,G_{Ref}^E$

equals zero.

während die vom zweiten Bildsensor gemessene Lichtintensität I_S2 sich für jedes Pixel aus $$I_{S2}=I_F{G}_{Ref}^F+I_R{G}_{Ref}^R+I_E{G}_{Ref}^E$$

zusammensetzt. Falls die Bandpässe ICG und Ref unterschiedlich breit sind, können diese Intensitäten I_S1 und I_S2 noch mit einem Normierungsfaktor T für die Transparenz der beiden Filter normiert werden: $$T_{ICG}={\displaystyle \underset{\lambda }{\int }{F}_{ICG}\left(\lambda \right)},T_{Ref}={\displaystyle \underset{\lambda }{\int }{F}_{Ref}\left(\lambda \right)}$$

und $${\overline{I}}_{S1}=\frac{I_{S1}}{T_{ICG}},{\overline{I}}_{S2}=\frac{I_{S2}}{T_{Ref}}.$$

_{The light intensity I S1} measured by the first image sensor is then made up for each pixel $$I_{S1}=I_f{G}_{ICG}^f+I_R{G}_{ICG}^R+I_E{G}_{ICG}^E,$$

_{while the light intensity I S2} measured by the second image sensor varies for each pixel $$I_{S2}=I_f{G}_{Ref}^f+I_R{G}_{Ref}^R+I_E{G}_{Ref}^E$$

composed. If the bandpasses ICG and Ref have different widths, these intensities I _S1 and I _{S2 can} still be normalized with a normalization factor T for the transparency of the two filters: $$T_{ICG}={\displaystyle \underset{\lambda }{\int }{f}_{ICG}\left(\lambda \right)},T_{Ref}={\displaystyle \underset{\lambda }{\int }{f}_{Ref}\left(\lambda \right)}$$

and $${\overline{I}}_{S1}=\frac{I_{S1}}{T_{ICG}},{\overline{I}}_{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="DE102020118673A1\_0011.png"\; state="\{\{state\}\}">S</figure-callout>}2}=\frac{I_{S2}}{T_{Ref}}.$$

Further calibration factors can result from the amplification factors and offsets of the image sensors, as well as from the fact that the light incident on the measuring device has possibly been split differently often on the way to the different image sensors if two beam splitters are used. The light branched off from the main beam path by the first beam splitter then represents, for example, half of the incident light, while the two beam paths split by the second beam splitter each have only a quarter of the incident light. For the ICG fluorescence of interest, it is therefore advantageous to use that beam path in which only one beam splitter is arranged. This example is not final. The designation ICG is replaced by the respective designation if other fluorescers are selected.

The offsets relevant for the other calibration factors result from dark measurements, the amplification factors can be determined when the excitation light is switched off. The intensities of the light components can be determined by linear transformations of these equations, which is simplified if the factors that go back to the excitation light are set to zero by suitable filtering of the excitation light.

This direct calculation is an exemplary possibility of removing the reflected ambient light components from the fluorescence image. Other possibilities arise through the use of lookup tables that have been previously filled, or by suitable models for various combinations of output I _S1 and I _S2, the light components, for example, by interpolation between predetermined values.

ebenso wie $G_{ICG}^F,G_{Ref}^F$

gleich Null sind.In order to achieve additional differentiation, the excitation light is clocked on and off in embodiments, with the offsets in the measurement signals of the first image sensor and the second image sensor being compensated for and/or recalibration taking place in the phases without excitation light. Clocking can also only take place in phases in order to verify that the calibration factors are still correct and to update them if necessary, since in the phases without excitation light the components $G_{ICG}^E,G_{Ref}^E$

as well as $G_{ICG}^f,G_{Ref}^f$

are equal to zero.

The object on which the invention is based is also comprehensively achieved by a system for measuring fluorescence in open surgery, in which a fluorescent agent dissolved in the blood of a patient, in particular indocyanine green (ICG), whose absorption and fluorescence spectra are known, is used one or more light sources for illuminating a patient's tissue to be treated with broadband, in particular white, ambient light and a light source ing light source unit that is designed and arranged to illuminate the tissue at least temporarily with an excitation light for the fluorescent agent with a known spectral distribution, in particular in the infrared range, the maximum of which is shorter-wavelength than a maximum of the fluorescence spectrum of the fluorescent agent, which is further developed in that a measuring device is included, which is arranged in such a way that part of the light reflected and emitted by the tissue enters the measuring device, which includes a beam splitter or two beam splitters, by means of which the entering light is directed into a first beam path, a second beam path and, if two beam splitters are present, a third beam path is divided, the first beam path comprising a first filter, which is designed as a bandpass filter for the deactivation light of the fluorescence agent, and a first image sensor, and the second beam path second filter, which as a bandpass filter for a reference frequency band which is adjacent to the bandpass of the first filter and is spaced apart from a maximum of the spectral distribution of the excitation light, and a second image sensor, wherein an evaluation device is included, which is designed and set up from the measurement signals of the second image sensor, and in particular additionally of the first image sensor, to determine a background offset to the de-excitation light emitted by the fluorescence agent on the basis of ambient light reflected on the tissue.

The system thus realizes the same features, properties and advantages as the method according to the invention.

In embodiments, the bandpass of the second filter is at shorter or longer wavelengths than the bandpass of the first filter. There is preferably a spectral spacing of 0 to 10 nm, in particular 1 to 4 nm, between the bandpass filters of the first filter and the second filter.

The first filter, the second filter and/or a filter in the third beam path is/are designed as an independent optical component or as a coating of the beam splitter or one of the beam splitters. In the second alternative, the beam splitter or beam splitters are spectrally selective.

In embodiments, the evaluation device is designed and set up to subtract the illuminance measured by the second image sensor from the illuminance measured by the first image sensor using a previously determined calibration factor.

In embodiments in which ICG is used as a fluorescer, the spectral distribution of the excitation light has a maximum at 810 nm ± 5 nm, in particular at 810 nm ± 3 nm, the spectral distribution of the excitation light in particular having a full width at half maximum (FWHM) of up to 10 nm , in particular up to 5 nm, and/or the reference frequency band is centered on a wavelength in the range from 820 nm to 826 nm or in the range from 835 nm to 841 nm, the reference frequency band in particular having a full width at half maximum (FWHM) of up to 4 nm , in particular up to 2 nm, and/or the bandpass of the first filter is centered on a maximum of the emission of the fluorescer, in particular a wavelength between 828 nm and 833 nm, in particular has a full width at half maximum (FWHM) of up to 4 nm, in particular up to 2 nm. The widths of the bandpass filters of the first filter and of the second filter can be the same in embodiments.

In developments of the system, a control unit of the system and the evaluation device are designed and set up to switch the excitation light on and off in a clocked manner and to compensate for the offsets in the measurement signals of the first image sensor and the second image sensor in the phases without excitation light. The evaluation unit can also be integrated into the control unit, in particular as an additional functional unit.

In embodiments, the excitation light source unit comprises a filter designed as a bandpass filter with a narrow-band bandpass, which allows light in the infrared range to pass, with the band that passes centered in particular on a wavelength of 810 nm ± 8 nm and a full-width at half maximum (FWHM) of up to 15 nm , In particular of up to 8 nm. This filtering ensures that no reflected excitation light reaches the first and second image sensors. This makes it easier to determine the pure fluorescent light component.

Further features of the invention will be apparent from the description of embodiments of the invention taken together with the claims and the accompanying drawings. Embodiments according to the invention can fulfill individual features or a combination of several features.

Within the scope of the invention, features that are marked “particularly” or “preferably” are to be understood as optional features.

• 1 eine schematische Darstellung der Beleuchtungssituation in offener Chirurgie mit Fluoreszenz-Anregungsbeleuchtung und Umgebungsbeleuchtung,
• 2 eine schematische Darstellung einer Messvorrichtung eines erfindungsgemäßen Systems,
• 3 eine schematische Darstellung der Bandpässe sowie der Spektralverteilungen der Lichtquellen und des Abregungslichts in dem erfindungsgemäßen Verfahren und
• 4 eine schematische Darstellung eines zeitlichen Verlaufs von Beleuchtung und Signalantworten.

The invention is described below with reference to exemplary embodiments without restricting the general inventive idea Described with reference to the drawings, with respect to all details of the invention not explained in more detail in the text, reference is expressly made to the drawings. Show it:

• 1 a schematic representation of the lighting situation in open surgery with fluorescence excitation lighting and ambient lighting,
• 2 a schematic representation of a measuring device of a system according to the invention,
• 3 a schematic representation of the bandpass filters and the spectral distributions of the light sources and the deactivation light in the method according to the invention and
• 4 a schematic representation of a time course of illumination and signal responses.

In the drawings, elements and/or parts that are the same or of the same type are provided with the same reference numbers, so that they are not presented again in each case.

In 1 the lighting situation in an environment of open surgery is shown schematically. A tissue 2 to be treated is illuminated with ambient light 4 . This is a white or whitish light from a ceiling light and possibly one or more surgical lamps that illuminate the surgical field with the aim of optimal visibility of tissue structures. For the purpose of measuring ICG fluorescence, the tissue 2 is additionally illuminated with an excitation light 12 from an excitation light source unit 10, which is aimed directly at the site of the tissue 2 to be treated. The excitation light source unit 10 emits infrared light suitable for excitation of fluorescence in the fluorescent agent ICG. This applies in particular to the wavelength range from approximately 800 nm to 810 nm. The excitation light source unit 10 can also have a filter, in particular a bandpass filter, which only allows a narrow wavelength range around 800 nm to 810 nm to pass.

ICG is taken here as an example of a fluorescence agent, but the explanations in this regard also apply analogously to other fluorescence agents, with the information on the frequency or wavelength ranges having to be adapted accordingly.

The light emitted and reflected by the tissue 2 contains portions of reflected ambient light 6, reflected excitation light 12 and the fluorescent light or de-excitation light 16 emitted by the fluorescence agent that is of only interest for measuring the ICG fluorescence. The light with these portions reaches a measuring device 20, which is set up to measure ICG fluorescence according to the method of the present invention.

A corresponding measuring device 20 is in 2 shown schematically. The measuring device 20 has an imaging optics 26, which can consist of one or more lenses, and which is designed as an objective to image the tissue 2 located in an object plane of the imaging optics 26 onto one or more image sensors 30B, 32B, 34B, each can be embodied as matrix sensors with a large number of pixels. This can be, for example, CCD sensors or CMOS sensors. Depending on the task, these should be sensitive in the visible light range and/or in the near infrared range.

Two beam splitters 22, 24 are arranged in the beam path of the measuring device 20, each splitting the incident light. If it is assumed that each of the two beam splitters 22, 24 divides the incident light into two equal parts, then half of the incident light is deflected into the first beam path 30, and a quarter of the incident light in each case passes further into the second beam path 32 and the third beam path 34. The exact ratios depend on the type and arrangement of the beam splitters 22, 24. Since approximately half of the incident light is deflected into the first beam path 30, it is favorable to use this first beam path 30 for measuring the ICG de-excitation. Correspondingly, a bandpass filter 30A is connected in front of the first image sensor 30B at the end of the first beam path 30, which only lets through light components in the region of the maximum of the de-excitation light of indocyanine green.

A combination of a bandpass filter 32A and an image sensor 32B, which enable a reference measurement, is arranged in the second beam path 32 generated by the second beam splitter 24 . For this purpose, the bandpass filter 32A has a narrow reference frequency band as a passable band, which is adjacent to the fluorescence frequency band of the first filter 30A, but excludes the maximum of the spectral distribution of the ICG excitation light. The light that is let through by the second filter 32A is thus dominated by the reflected ambient light 6 .

An evaluation unit, not shown, receives the image signals from the first image sensor 30B and 32B and processes them by weighting the signals from the second image sensor 32B with suitable weighting and taking into account suitable Offsets are subtracted from the signals of the first image sensor 30B or another type of correction of the image signals of the first image sensor 30B is carried out using the image signals of the second image sensor 32B. It is assumed here that the intensity of the reflected ambient light 6 does not differ between the two closely adjacent bandpass filters of the first filter 30A and the second filter 32A, or that the difference is negligible.

A third beam path 34 directs the remaining light, optionally filtered using a UV and/or IR filter 34A, to a third image sensor 34B, which receives the visible light in the optically visible range and is therefore used for digital imaging with normal colors. The result of the evaluation of the ICG fluorescence with false colors can be superimposed on this normal image.

All three image sensors 30B, 32B, 34B are arranged in the image plane of the respective beam path 30, 32, 34. The images therefore correspond to each other. The beam splitters 22, 24 are designed in such a way that they deflect the spectral components of the incident light that are relevant for the respective image sensor 30B, 32B, 34B to the image sensors 30B, 32B, 34B. This can be achieved, for example, by suitably selected coatings. For example, it is sufficient if the beam splitters only reflect the infrared component and allow the white light component to be transmitted. This would be advantageous since it would not reduce the intensity of the white light reaching the image sensor 34B. The beam splitter 22 preferably allows the wavelengths relevant for the imager unit 32B to pass in whole or in part. Furthermore, the bandpass filter functions of the bandpass filters 30A, 32A can also be integrated directly into the beam splitter coatings, as a result of which separate bandpass filters 30A, 32A can be omitted.

3 shows an example and a sketch of the spectral conditions with the wavelength λ in nanometers on the horizontal axis and the respective intensity or transparency in arbitrary units (“au”) on the vertical axis. The near infrared range between about 780 nm and about 850 nm is shown. In this area, the spectral distribution 4' is essentially constant. The excitation light 12 has a highly focused spectral distribution 12' centered around approximately 810 nm. This can be achieved, for example, by using a narrow-band light source, for example LEDs, and/or by filtering the emitted light through a narrow-band bandpass filter.

The fluorescent light of the fluorescence agent ICG dissolved in the blood, also called de-excitation light 16 in the context of the present patent application, mainly has a narrow spectral distribution around approx. 830 nm. Weak sidebands and extensions of the spectral distribution have been omitted for reasons of clarity. The intensity of the de-excitation light 16 is significantly lower than that of the excitation light 12. The fluorescence frequency band 30B' of the first filter 30A is centered on the maximum of the spectral distribution 16' of the de-excitation light 16, so that the main part of the de-excitation light 16 is within the bandpass, i.e. the fluorescence frequency band 30B' of the first filter 30A.

Furthermore, the reference frequency band 32B' of the second filter 32B is arranged in the gap between the fluorescence frequency band 30B' and the spectral distribution 12' of the excitation light 12, at a small distance from the fluorescence frequency band 30B'. In the idealized representation of 3 only light from the spectrum 4' of the ambient light is present in the reference frequency band 32B'. Also, since in the idealized example the 3 the width or area of the two band-pass filters is approximately the same, the amount of reflected ambient light 6 is also the same in both cases, so that the measurement from reference frequency band 32B' essentially corresponds to the proportion of reflected ambient light in fluorescence frequency band 30B' and is treated accordingly can be.

In reality there can be weak tails of the spectra 12', 16' of the excitation light 12 and of the de-excitation light 16. If these are not negligible, they are taken into account appropriately when weighting the image signals. Since the individual frequency curves of the various light components and the band-pass filters are known, it is possible in the image signal processing from the distribution of the measured intensities in the image sensors 30B, 32B to infer the intensities of the light components that are due to the de-excitation light 16 on the one hand and the reflected ambient light 6 return on the other hand.

In 4 a further development of the method according to the invention is shown schematically. The horizontal axis is a time axis with arbitrary units, while the vertical axis represents intensity in arbitrary units. On the one hand, the intensities of the ambient light 4, which does not change, and of the excitation light 12, which is switched on and off periodically, are displayed over time. Also shown is the ICG fluorescence signal of the deactivation light 16, which, following the time profile of the excitation light 12, also has a rectangular shape. The excitation light signal has an offset of 16 ^offs and a signal deviation (amplitude) of 16 ^sign , with the offset 16 ^offs essentially being due to the constant component of the reflected ambient light 6 goes back The signal swing 16 ^Sign , on the other hand, is based on the light from the ICG fluorescence depletion.

This in 4 The switching on and off shown represents a time-division multiplex measurement and can take place at times in order to check that the measurement results and assumptions used in the spectral comparison according to the invention are still correct. Possible reasons for shifts are fluctuations in the ambient brightness, drifts in the amplification factors of the image sensors, etc. As soon as the adjustment and, if necessary, readjustments of the calibrations have taken place, the stroboscopic-like illumination from the excitation light source unit can change back to continuous illumination.

All of the features mentioned, including those that can be taken from the drawings alone and also individual features that are disclosed in combination with other features, are considered essential to the invention alone and in combination. Embodiments according to the invention can be fulfilled by individual features or a combination of several features.

Reference List

2

tissue

4

ambient light

4'

Spectral distribution of the ambient light

6

reflected ambient light

10

excitation light source unit

12

excitation light

12'

Spectral distribution of the excitation light

16

de-excitation light

16'

Spectral distribution of de-excitation light (ICG in blood)

16 sign

fluorescence signal

16Offs

Fluorescence signal offset

20

measuring device

22

beam splitter

24

beam splitter

26

imaging optics

30

first beam path

30A

first filter

30B'

fluorescence frequency band

30B

first image sensor

32

second beam path

32A

second filter

32B'

reference frequency band

32B

second image sensor

34

third beam

34A

third filter

34B

third image sensor

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102005045961 A1 [0006, 0015]

Claims (15)

Method for measuring fluorescence in open surgery, in which a fluorescent agent dissolved in the blood of a patient, in particular indocyanine green (ICG), is used, the absorption and fluorescence spectra of which are known, the treated tissue (2) of the patient during procedure is illuminated with a broadband, in particular white, ambient light (4) and is additionally illuminated at least temporarily with an excitation light (12) for the fluorescent agent with a known spectral distribution (12'), in particular in the infrared range, the maximum of which has a shorter wavelength than a maximum of the fluorescence spectrum of the fluorescence agent, characterized in that to determine a background offset to the de-excitation light (16) emitted by the fluorescence agent due to ambient light (6) reflected by the tissue, part of the light (6, 16) reflected and emitted by the tissue is converted into a Measuring device (20) occurs and in the measuring device ng (20) by means of a beam splitter (22, 24) into two beam paths (30, 32) or by means of two beam splitters (22, 24) into three beam paths (30, 32, 34), with a first part of the light in one first beam path (30) through a first filter (30A), which is designed as a bandpass filter for the de-excitation light (16) of the fluorescence agent, onto a first image sensor (30B) and a second part of the light in a second beam path (32). a second filter (32A), which acts as a bandpass filter for a reference frequency band (32A'), which is adjacent to the bandpass of the first filter (30A) and is spaced from a maximum of the spectral distribution (12') of the excitation light (12), to a second Image sensor (32B) is passed. procedure after claim 1 , characterized in that the bandpass of the second filter (32A) is at shorter or longer wavelengths than the bandpass of the first filter (30A). procedure after claim 1 or 2 , characterized in that between the band-pass filters of the first filter (30A) and the second filter (32A) there is a spectral distance of 0 to 10 nm, in particular of 1 to 4 nm. Procedure according to one of Claims 1 until 3 , characterized in that a third part of the light is guided in a third beam path (34) to a third image sensor (34B) for imaging in visible light, the third beam path (34) in particular a third filter (34A), in particular a UV filter and/or an IR filter. Procedure according to one of Claims 1 until 4 , characterized in that to remove the background offset, the illuminance measured by the second image sensor (32B) is subtracted from the illuminance measured by the first image sensor (30B) using a previously determined calibration factor. Procedure according to one of Claims 1 until 5 , characterized in that - the spectral distribution (12') of the excitation light (12) has a maximum at 810 nm ± 5 nm, in particular at 810 nm ± 3 nm, the spectral distribution (12') of the excitation light (12) in particular having a half-width (FWHM) of up to 10 nm, in particular up to 5 nm, and/or - that the reference frequency band (32A') is centered on a wavelength in the range from 820 nm to 826 nm or in the range from 835 nm to 841 nm , wherein the reference frequency band (32A') has in particular a full width at half maximum (FWHM) of up to 4 nm, in particular up to 2 nm, and/or - that the bandpass of the first filter (30A) is set to a maximum of the emission of the fluorescent agent, in particular a wavelength between 828 nm and 833 nm, and in particular has a full width at half maximum (FWHM) of up to 4 nm, in particular up to 2 nm. Procedure according to one of Claims 1 until 6 , characterized in that overlaps of the spectral distributions (12', 16') of the excitation light (12) and the de-excitation light (16') with the frequency curves of the first filter (30A) and the second filter (32A) flow into the calibration factor. Procedure according to one of Claims 1 until 7 , characterized in that the excitation light (12) is switched on and off in a clocked manner, with the offsets in the measurement signals of the first image sensor (30B) and the second image sensor (32B) and/or a recalibration done. System for measuring fluorescence in open surgery, in which a fluorescent agent dissolved in the blood of a patient, in particular indocyanine green (ICG), is used, the absorption and fluorescence spectra of which are known, comprising one or more light sources for illuminating a tissue to be treated ( 2) of the patient with broadband, in particular white, ambient light and an excitation light source unit (10), which is designed and arranged, the tissue (2) at least at times with an excitation light (12) for the fluorescent agent with a known spectral distribution (12'), in particular in the infrared range, whose maximum is of shorter wavelength than a maximum of the fluorescence spectrum of the fluorescent agent, characterized in that a measuring device (20) which is arranged in such a way that part of the light (6, 16) reflected and emitted by the tissue (2) enters the measuring device (20), which has a beam splitter (22, 24) or two beam splitters (22, 24 ) comprises, by means of which or by means of which the entering light is divided into a first beam path (30), a second beam path (32) and, if two beam splitters (22, 24) are present, a third beam path (34), the first Beam path (30) includes a first filter (30A), which is designed as a bandpass filter for the de-excitation light (16) of the fluorescent agent, and a first image sensor (30B), and the second beam path (32) includes a second filter (32A), which is designed as a bandpass filter for a reference frequency band (32A'), which is adjacent to the bandpass of the first filter (30A) and is spaced apart from a maximum of the spectral distribution of the excitation light (12), and a second image sensor (32B), wherein an evaluation device u is designed and set up, from the measurement signals of the second image sensor (32B), and in particular additionally of the first image sensor (32A), a background offset to the de-excitation light (16) emitted by the fluorescence agent due to the tissue (2) reflected To determine ambient light (6). system after claim 9 , characterized in that the bandpass of the second filter (32A) is at shorter or longer wavelengths than the bandpass of the first filter (30A). procedure after claim 9 or 10 , characterized in that between the band-pass filters of the first filter (30A) and the second filter (32A) there is a spectral distance of 0 to 10 nm, in particular of 1 to 4 nm. system according to one of the claims 9 until 11 , characterized in that the evaluation device is designed and set up to subtract the illuminance measured by the second image sensor (32B) from the illuminance measured by the first image sensor (30B) using a previously determined calibration factor. system according to one of the claims 9 until 12 , characterized in that - the spectral distribution (12') of the excitation light (12) has a maximum at 810 nm ± 5 nm, in particular at 810 nm ± 3 nm, the spectral distribution (12') of the excitation light (12) in particular having a half-width (FWHM) of up to 10 nm, in particular up to 5 nm, and/or - that the reference frequency band (32A') is centered on a wavelength in the range from 820 nm to 826 nm or in the range from 835 nm to 841 nm , wherein the reference frequency band (32A') has in particular a full width at half maximum (FWHM) of up to 4 nm, in particular up to 2 nm, and/or - that the bandpass of the first filter (30A) is set to a maximum of the emission of the fluorescent agent, in particular a wavelength between 828 nm and 833 nm, and in particular has a full width at half maximum (FWHM) of up to 4 nm, in particular up to 2 nm. system according to one of the claims 9 until 13 , characterized in that a control unit of the system and the evaluation device are designed and set up to switch the excitation light (12) on and off in a clocked manner and to compensate for the offsets in the measurement signals of the first image sensor (30B) and the second image sensor in the phases without excitation light (32B) to undertake. system according to one of the claims 9 until 14 , characterized in that the excitation light source unit (10) comprises a filter designed as a band-pass filter with a narrow-band band-pass, which allows light in the infrared range to pass, the passed band being centered in particular on a wavelength of 810 nm ± 8 nm and having a half-value width ( FWHM) of up to 15 nm, in particular of up to 8 nm.

Images