Medical imaging device and method suitable for observing a plurality of spectral bands

Abstract

The invention relates to a fluorescence imaging method and device (1) for surgical applications. Filtering means (10) are used that are configured to be able to generate, from the output signal, at least two images each corresponding to a different filtering operating mode over at least one wavelength range. The respective contribution to the intensity of the output signal obtained at a first wavelength and at a second wavelength, which are distinct from one another, is different with each of these two filtering operating modes. The filtering operating modes are chosen so as to highlight, in an image, the fluorescence emission of one substance relative to the fluorescence emission of another substance that might be present in a region of interest.

Description

[0001] DESCRIPTION

[0002] TITLE: Medical imaging device and method suitable for the observation of several spectral bands

[0003] Technical field

[0004] The invention relates to the field of medical imaging and in particular fluorescence imaging.

[0005] State of the art

[0006] In medicine, fluorescence imaging consists of injecting a fluorescent marker which, excited at certain wavelengths by a light source, generates fluorescence radiation which can be captured by a camera and visualized in real time (this is called exogenous fluorescence).

[0007] Some human tissues intrinsically emit (without added fluorescent label) fluorescent radiation when excited at certain wavelengths, this is called tissue autofluorescence (also called endogenous fluorescence)

[0008] The major advantage of autofluorescence imaging is that it is completely non-invasive for the patient (no intravenous or subcutaneous injection of tracer).

[0009] However, autofluorescence imaging and fluorescence imaging can provide additional information useful for clinical interpretation.

[0010] For example, during a thyroidectomy, the thyroid gland must be removed while preserving the parathyroid glands, which are generally very close to it. Locating the parathyroid glands is often difficult with the naked eye and requires considerable experience on the part of the surgeon. The autofluorescence of these glands makes them easier to locate.

[0011] Thus, some surgeons have been able to demonstrate that the number of postoperative complications decreases when the surgeon secures his procedure using autofluorescence imaging.

[0012] However, autofluorescence imaging only provides contextual information, namely "where are the parathyroid glands." But, during thyroid dissection, the surgeon also needs functional information: 1) identify the vessels that supply each of these parathyroid glands to avoid damaging them and preserve their functionality, 2) verify that the parathyroid glands are well vascularized. Autofluorescence imaging alone does not allow observation of the irrigating vessels or tissue perfusion. On the other hand, it is conventional to use the fluorescence of a marker such as indocyanine green (ICG) to visualize the vascular network that supplies the parathyroid glands.

[0013] Now, a thyroidectomy is performed in two stages. Both lobes of the thyroid are resected successively.

[0014] With the devices and methods of the prior art, during the dissection of the first lobe, only autofluorescence can be used to visualize the parathyroid glands. Indeed, the injection of indocyanine green can only be used after having visualized the parathyroid glands on the second side by autofluorescence. In fact, with current systems allowing the measurement of autofluorescence as well, it is no longer possible to visualize the autofluorescence of the parathyroid glands after an injection of indocyanine green. With the excitation wavelength and the detection wavelength band commonly used by systems allowing the measurement of autofluorescence and fluorescence of indocyanine green, after injection, the fluorescence of indocyanine green masks the autofluorescence of the parathyroid glands.Under these conditions, to be able to visualize the autofluorescence of the parathyroid glands after injection of indocyanine green, it would be necessary to wait for a period incompatible with the duration of the surgery itself (between half an hour and one hour), so that the concentration of indocyanine green is sufficiently low. But, even after such a waiting time, as the injection of indocyanine green is performed on tissues during dissection, many areas remain marked by indocyanine green which is not evacuated and therefore risk degrading the quality of the interpretation of the autofluorescence images by adding a large number of false positives. The injection of indocyanine green is therefore reserved for a stage of the thyroidectomy which no longer requires observation of the autofluorescence of the parathyroid glands. Perfusion imaging can therefore only be used for the second side operated on, at the end of the procedure.

[0015] However, the main disadvantage of not using perfusion imaging on the first side leads to (i) an increased risk of damaging the vascularization of the parathyroid glands of the first lobe, (ii) not knowing whether the parathyroid glands left in place are functional, which is of crucial importance in how to operate on the second lobe, especially if in this second lobe the parathyroid glands are difficult to protect.

[0016] It is therefore of prime importance to be able to visualize, in situ, the autofluorescence of the parathyroid glands even after the injection of indocyanine green.

[0017] Ideally, for each lobe, autofluorescence imaging of the parathyroid glands, fluorescence visualization of the vessels (fluorescence angiography) during dissection and validation of the perfusion of the parathyroid glands at the end of the lobectomy should be performed.

[0018] There is therefore a need to visualize autofluorescence alone (or almost) even after the injection of indocyanine green. But more generally, there is a need to separately visualize fluorescent substances whose fluorescence emission has sufficiently distinct emission spectra.

[0019] In this document, a fluorescent substance may consist of one molecule or several molecules.

[0020] Statement of the invention

[0021] The invention aims to provide at least a partial response to the aforementioned need. To this end, a fluorescence imaging method for surgical applications is provided comprising an operation of exciting at least a first and a second fluorescent substance potentially located in an area of ​​interest, with at least one excitation radiation having a maximum intensity defined by an excitation wavelength, this excitation wavelength being between 600 nm and 800 nm, or more particularly between 650-750 nm.The first substance has a fluorescence emission spectrum with a first intensity maximum at a first wavelength (e.g., it is the fluorescence of indocyanine green with an intensity maximum near 820 nm) and the second substance has a fluorescence emission spectrum with a second intensity maximum at a second wavelength (e.g., it is the autofluorescence of parathyroid glands with an intensity maximum near 711 nm). The fluorescence spectra of the first and second substances are distinct. The first and second wavelengths are distinct, and dependent on the excitation wavelength. For example, the maximum of the fluorescence spectrum of the first substance has a wavelength greater than the maximum of the fluorescence spectrum of the second substance, with the excitation wavelength used to excite fluorescence in the area of ​​interest.

[0022] The method according to the invention further comprises

[0023] - an operation of filtering at least part of the fluorescence radiation emitted by each fluorescent substance emitting, in the area of ​​interest, fluorescence radiation in response to the excitation radiation, and

[0024] - an operation of detection and acquisition, using a sensor, of at least part of the filtered fluorescence radiation, this detection operation being carried out in a detection range itself included in a wavelength range between 400 nm and 1000 nm (i.e. the conventional sensitivity zone of CMOS imaging sensors), possibly for example this detection length range extends between the excitation wavelength and 900 nm or 1000 nm, or even between the excitation wavelength and 870 nm, in other words, the detection operation can be carried out over a wavelength range which extends between a first wavelength greater than or equal to 400 nm and a second wavelength less than or equal to 1000 nm,

[0025] - an operation consisting of generating, from the radiation detected by the sensor, at least one output signal whose intensity is representative of the intensity of the fluorescence radiation detected by the sensor,

[0026] - an operation of displaying images formed from the output signal.

[0027] Furthermore, in this method the filtering operation is carried out according to at least two different operating modes, so as to generate from the output signal at least two images each respectively using one of these different operating modes, implemented one after the other. The respective contribution to the intensity of the output signal obtained at the first and second wavelengths is different with each of these two operating modes. For example, with one of the two operating modes, the contribution to the intensity of the output signal obtained at the second wavelength is greater than or equal to that obtained at the first wavelength. With the other operating mode, it is the opposite, the contribution to the intensity of the output signal obtained at the first wavelength is greater than or equal to that obtained at the second wavelength.

[0028] For example, consider the case where two fluorescent substances are present in the area of ​​interest illuminated by the excitation radiation and the radiation emitted by a first substance, in response to the excitation radiation, exhibits a first spectrum with a maximum at a first wavelength, while the radiation emitted by a second substance, in response to the excitation radiation, exhibits a second spectrum with a maximum at a second wavelength, the maxima of the first and second spectra being well separated (for example, they are separated by at least 30nm, or even by at least 50nm).In this case, by playing on the filtering of the radiation emitted by these substances, it is possible to favor on a part of the spectrum, the emission of one of the substances by reducing, on one of the images, the intensity of the signal corresponding to the fluorescence radiation detected on this part of the spectrum (of course, it is also possible to do the opposite, namely to favor on a part of the spectrum, the emission of one of the substances by increasing, on one of the images, the intensity of the signal corresponding to the fluorescence radiation detected on this part of the spectrum).

[0029] For example, in one embodiment of this method, the filtering operation is carried out using an operating mode in which a low-pass filter chosen to reduce the contribution of the signal emitted by the first substance is placed between the area of ​​interest and the detector (regardless of the position of this filter in the optical path, it can be before or after the other filters or lenses) and an operating mode in which this low-pass filter is removed.

[0030] Advantageously, the filter used for said filtering operation (in this example, a low-pass filter) is a removable filter. In this document, the adjective “removable” means that the filter can be easily placed on the optical path between the area of ​​interest and the detector, or removed from this optical path, i.e. without having to use a tool for example. The same is true for the adjective “retractable”, the “retracted” position of the filter corresponding to a position which is not on the optical path between the area of ​​interest and the detector. Similarly, an “adjustable” filter is considered in this document as a “removable” filter since its filtering function can easily be activated or removed. Thus, for example, the filtering operation makes it possible to reduce the contribution of the signal which, without filtering, would mask the less intense signal.For this filtering operation to be of interest, the substances whose fluorescence is to be observed must have spectrally shifted maxima in order to be able to more specifically filter the signal corresponding to one of these maxima in order to release another. The observed substances must therefore have respective responses (in particular in re-emission and without the filtering operation mentioned above) to the excitation radiation which differ by intensity maxima spectrally shifted relative to each other over the detected wavelength range.

[0031] Thus, thanks to the method according to the invention, it is possible to visualize at least two distinct images of the fluorescence radiation emitted, in response to the same excitation radiation, by fluorescent substances present in the area of ​​interest illuminated by this excitation radiation.

[0032] For example, if the first substance corresponds to indocyanine green and the second substance is the one responsible for the autofluorescence of the parathyroid glands, with an excitation wavelength of 680 nm, we observe for indocyanine green a first maximum of the fluorescence emission spectrum at a first wavelength close to 820 nm, whereas with this same excitation wavelength, we observe for autofluorescence a second maximum of the fluorescence emission spectrum at a second wavelength close to 711 nm (see figure 4). To obtain an image on which the parathyroid glands are more visible than the tissues labeled with indocyanine green, we can place in front of the sensor a low-pass filter with a cut-off wavelength between 750 and 800 nm (see figure 8).By removing this low-pass filter, the tissues marked with indocyanine green become more visible again, or even mask the autofluorescence because they are much more fluorescent. We can therefore obtain a first image in which, for fluorescence radiation emitted with a wavelength greater than the cut-off wavelength, the ratio between the intensity of the emitted radiation and the intensity of the output signal is different from that in the second image. In the first image, this ratio is lower than in the second image.

[0033] The method according to the invention also optionally comprises one and / or other of the following characteristics, each considered independently of the other or in combination with one or more others:

[0034] - at least one displayed image corresponds essentially to the contribution, in the output signal, of the emission of the fluorescence radiation of the first substance or to the contribution, in the output signal, of the emission of the fluorescence radiation of the second substance, and is calculated from a combination of output signals obtained respectively using the first filtering procedure and the second filtering procedure,

[0035] - it comprises the alternating production of at least one image of at least one parathyroid gland and at least one image of a vascular network supplying blood to this parathyroid gland,

[0036] - the image of the parathyroid gland is taken with a low-pass filter in place between the area of ​​interest and the sensor, and the image of the vascular network is taken without the low-pass filter between the area of ​​interest and the sensor,

[0037] - the image of the parathyroid gland is produced with a low-pass filter in place between the area of ​​interest and the sensor, and the image of the vascular network is produced with a high-pass filter in addition to or instead of the low-pass filter between the area of ​​interest and the sensor,

[0038] - more generally, for example, in the first filtering mode of operation, a band-pass filter is placed between the area of ​​interest and the detector and in the second filtering mode of operation, this band-pass filter is removed,

[0039] - for the excitation wavelength used to illuminate the area of ​​interest, the fluorescence yield of the first substance is greater than the fluorescence yield of the second substance;

[0040] - the excitation operation is carried out with a single excitation wavelength; for example, the excitation wavelength is chosen so as to favor the fluorescence re-emission function by the second substance compared to that of the first substance;

[0041] - the operation of generating at least two images from the output signal comprises at least one different optical or digital processing for each of these two images;

[0042] - the optical processing of one of said at least two images comprises the installation of a removable filter between the area of ​​interest and the sensor, while the optical processing of the other of said at least two images comprises the removal of the removable filter from the optical path between the area of ​​interest and the sensor; this removal may optionally be accompanied by the installation of a high-pass filter;

[0043] - the digital processing comprises an operation consisting of using the signals respectively obtained on different color channels to generate each of said at least two images;

[0044] - said at least two fluorescent substances are respectively indocyanine green and the substance responsible for the autofluorescence of the parathyroid glands;

[0045] - the excitation radiation has a maximum intensity between 600 and 720 nm, for example, between 650 and 700 nm;

[0046] - the excitation radiation has a maximum intensity at 680 nm;

[0047] - the detection and acquisition operation includes

[0048] * an acquisition operation according to the first operating mode, with the source producing the excitation radiation switched off,

[0049] * an acquisition operation according to the first operating mode, with the source producing the excitation radiation switched on,

[0050] * an acquisition operation according to the second operating mode, with the source producing the excitation radiation switched off,

[0051] * an acquisition operation according to the second operating mode, with the source producing the excitation radiation switched on, and operations consisting of calculating and displaying images of the contribution, in the output signal, of the emission of the fluorescence radiation of the first substance or of the contribution, in the output signal, of the emission of the fluorescence radiation of the second substance; - the operation of displaying images formed from the output signal comprises the display of an image representative of the coefficient a, on at least a portion of the area of ​​interest, where

[0052] With

[0053] Low= an image of the fluorescence radiation of the area of ​​interest with the bandpass filter and the source producing the excitation radiation switched on, bckLow= a background image with the bandpass filter and the source producing the excitation radiation switched off,

[0054] High= an image of the fluorescence radiation of the area of ​​interest without the bandpass filter and the source producing the excitation radiation switched on, bckHigh= a background image without the bandpass filter and the source producing the excitation radiation switched off.

[0055] — a corresponds to the proportion of the total autofluorescence signal of at least one parathyroid gland, in the output signal after filtering by the band-pass filter.

[0056] The invention also relates to a fluorescence imaging device, suitable for example for implementing the method mentioned above. It comprises at least one sensor, a filter, and an excitation light source.

[0057] For example, this device comprises an excitation light source configured to emit, on an area of ​​interest, an excitation radiation of autofluorescence or fluorescence. This excitation radiation is for example emitted in the form of a laser beam. This excitation radiation corresponds to an excitation wavelength defined by its maximum intensity on a spectrum. This excitation wavelength is for example included in a range of emission wavelengths between 600 nm and 850 nm.

[0058] This device also comprises a detector configured to detect fluorescence radiation. For example, the detector is a CMOS or CCD camera comprising a sensor configured to detect fluorescence radiation emitted by at least a portion of the area of ​​interest, in a detection range that can extend over (or included in) a detection wavelength band extending at least between 400 nm and 1000 nm. The sensor is also configured to generate at least one output signal whose intensity as a function of the wavelength of the fluorescence radiation is representative of the intensity of the fluorescence radiation detected by the sensor. This device further comprises filtering means.The filtering means are in particular configured to be able to implement at least two different operating modes, and to generate from the output signal at least two images, each respectively using one of these different filtering operating modes, the respective contribution to the intensity of the output signal obtained respectively at a first wavelength and a second wavelength distinct from the detection page, being different with each of these two filtering operating modes.For example, with one of the two operating modes, the contribution to the intensity of the output signal obtained at the second wavelength is greater than or equal to that obtained at the first wavelength, with the other operating mode, conversely, the contribution to the intensity of the output signal obtained at the first wavelength is greater than or equal to that obtained at the second wavelength.For example, the first and second operating modes are implemented one after the other, the first filtering operating mode favoring, when a first and a second substance are present in the area of ​​interest, the contribution of the emission of the fluorescence radiation of the second substance in the output signal, compared to the contribution of the emission of the fluorescence radiation of the first substance, and the second filtering operating mode favoring the contribution of the emission of the fluorescence radiation of the first substance in the output signal, compared to the contribution of the emission of the fluorescence radiation of the first substance in the output signal obtained with the first filtering operating mode.Furthermore, the device comprises calculation means configured to carry out operations consisting of calculating images obtained either, on the one hand, from the output signal obtained using the first filtering operating mode, and on the other hand, from the output signal obtained using the second filtering operating mode, or from a combination of output signals obtained respectively using the first filtering operating mode and the second filtering operating mode.

[0059] This device also includes display means for displaying images formed from the output signal.

[0060] This device also possibly includes one and / or other of the following characteristics, each considered independently of the other or in combination with one or more others:

[0061] - the excitation wavelength is included in a range of emission wavelengths between 650 nm and 700 nm, - the filtering means are configured so that with one of the two operating modes, the contribution to the intensity of the output signal obtained at the second wavelength is greater than that obtained at the first wavelength, and with the other operating mode, conversely, the contribution to the intensity of the output signal obtained at the first wavelength is greater than that obtained at the second wavelength,

[0062] - the filtering means comprise a removable filter; this removable filter is for example a low-pass filter having a cut-off wavelength between 720nm and 800nm, or between 720nm and 800nm;

[0063] - the removable filter is placed between the area of ​​interest and the sensor in the first operating mode and is removed in the second operating mode,

[0064] - it is configured to alternately produce at least one image of at least one parathyroid gland with the first operating mode and at least one image of the vascular network supplying blood to this parathyroid gland which is irrigated with indocyanine green, with the second operating mode, the device also being configured to receive a low-pass filter in the optical path located between the area of ​​interest and the sensor, in the first operating mode and to remove, in the second operating mode, this low-pass filter from the optical path, the low-pass filter has a cut-off wavelength adapted to limit the fluorescence of the indocyanine green emitted in the area of ​​interest

[0065] - it includes a protective cover for a camera including the sensor and in which the filter is placed on the cover or integrated into the cover,

[0066] - the output signal comprises the signal of at least two different color channels, this device comprising means for processing the output signal configured to produce linear combinations of the intensities obtained on the different color channels.

[0067] According to another aspect, the invention relates to a computer program comprising program code instructions for executing the above-mentioned method, when said program is executed on a computer.

[0068] In this document, the operations described as being performed on a signal or on an image correspond to operations on quantities representative of this signal (for example the signal generated at the level of a photosensitive element of a sensor) or values ​​associated with at least certain pixels of the image. Undescribed processing of the signal is possibly applied. For example, operations of summation, registration, normalization, colorization, etc. well known to those skilled in the art are possibly performed in addition to those described below.

[0069] Brief description of the drawings

[0070] Other features and advantages will become apparent in the detailed description of various embodiments of the invention, the description being accompanied by examples and references to the attached drawings.

[0071] Figure 1 is a schematic view of an exemplary embodiment of an imaging device according to the invention;

[0072] Figure 2 represents the transmission characteristics of a high-pass filter as a function of the wavelength, used in an exemplary implementation of the method according to the invention; Figure 3 is a schematic representation of a filter system used in an exemplary implementation of the method according to the invention;

[0073] Figure 4 is a normalized representation of the emission spectra of parathyroid gland autofluorescence and indocyanine green as seen by the camera for excitation at 680 nm (without the removable low-pass filter, but with other filters such as a Bayer filter and a long-pass filter);

[0074] Figure 5 represents the spectral characteristics of an example of a CMOS sensor used in an example of implementation of the method according to the invention;

[0075] Figure 6 represents an image of an area of ​​interest obtained by positioning a low-pass filter between this area of ​​interest and the sensor of the device according to the invention; we essentially observe the autofluorescence of a parathyroid gland;

[0076] Figure 7 represents an image equivalent to that of Figure 6, but obtained without the removable low-pass filter; we essentially observe the fluorescence of indocyanine green; Figure 8 is a normalized representation of the emission spectra of the autofluorescence of the parathyroid glands and of indocyanine green seen by the “filtered” camera for excitation at 680 nm (with the removable low-pass filter, and other filters such as a Bayer filter and a high-pass filter).

[0077] Detailed description of the implementation methods

[0078] An exemplary embodiment of a device 1 according to the invention is shown in Figure 1. It comprises an excitation light source 2, a detector 3 provided with an objective 4 comprising at least one optical lens. It also comprises filtering means 10 (it may be noted that the presence of a Bayer filter in the filtering means is optional). The device 1 also comprises calculation means (one or more computers or servers) configured to perform various operations from the output signal or signals of the detector 3.

[0079] The excitation light source 2 is, for example, a laser source. This laser source emits excitation radiation with a maximum intensity corresponding to an excitation wavelength of, for example, between 600 nm and 800 nm or, for example, between 650 and 720 nm. More particularly, the excitation wavelength is 680 nm.

[0080] Detector 3 is, for example, a camera equipped with a 5 CMOS or CCD sensor. This camera is, for example, a CMV 2000 type model marketed by XIMEA.

[0081] According to a first embodiment of the filtering means 10, these comprise, for example, a lighting filter 11, an excitation light source filter 12, a high-pass or band-pass filter 13 and a low-pass filter and / or a high-pass filter 14, advantageously removable. It will be noted that if a high-pass filter 13 may be sufficient in certain situations, in other situations and in particular if powerful ambient lighting is used, it will be preferable to use a band-pass filter with a cut-off frequency above 900nm (see document EP2840953A1). The filtering means 10 optionally further comprise a matrix of color filters 15 (for example a Bayer filter mosaic) placed in front of the detector 3 (As indicated above, the presence of this type of filter in the filtering means is optional).

[0082] The lighting filter 11 is placed between the area of ​​interest I which includes the fluorescent or autofluorescent tissues and the sensor 5. The lighting filter 11 is used to filter a white light produced by light-emitting diodes equipping the detector 3 and / or the operating lighting (for example that produced by a surgical light).

[0083] The excitation light source filter 12 is placed downstream of the excitation light source 2, between the latter and the area of ​​interest I. For example, the excitation light source filter 12 is a band-pass filter that passes the excitation radiation emitted by the excitation light source 2. The excitation light source filter 12 essentially passes the excitation radiation for example over plus or minus 10 nm around the excitation wavelength and blocks the radiation outside this range. The long-pass or band-pass filter 13 is placed between an area that includes the fluorescent or autofluorescent tissues of the area of ​​interest I and the detector 3. For example, the long-pass filter 13 is placed in front of the objective 4. The long-pass or band-pass filter 13 has a cut-off wavelength located above the excitation wavelength.For example, this long-pass filter 13 has a spectral response such as that shown in Figure 2, with a cutoff wavelength between 700 and 750 nm. In this example, the long-pass filter transmits more than 80% of the light between the cutoff wavelength and at least up to 900 nm. For example, the low-pass filter 14 has a cutoff wavelength that lies between the wavelengths of the intensity maxima of the fluorescence emission spectrum of two substances to be differentially imaged at a particular excitation wavelength. In particular, the cutoff wavelength is chosen to detect the substance having the intensity maxima at the lower wavelength when the low-pass filter is in place and to detect the substance having the intensity maxima at the higher wavelength when the low-pass filter is removed.The low-pass filter 14 is removable and can be placed between the area that includes the fluorescent or autofluorescent tissues and the detector 3. For example, the low-pass filter 14 is placed in front of the objective 4. The low-pass filter 14 has a cut-off wavelength located above the excitation wavelength (and above the cut-off wavelength of the long-pass filter 13). For example, this low-pass filter 14 has a cut-off wavelength between 750 and 800 nm. For example, this low-pass filter 14 has a cut-off wavelength around 775 nm.

[0084] The low-pass filter 14, and / or possibly a high-pass filter, can be placed in different configurations which depend on the solution adopted. For example, according to a “retractable” or “shutter” type solution, the low-pass filter 14 is placed on a filter wheel or a shutter (advantageously this shutter is integrated into the camera) so as to be able to be retracted or removed, or on the contrary placed on the optical path. Another solution can be provided by an “adjustable” filter, for example an activatable liquid crystal filter or with an adjustable or tunable cut-off wavelength as is the case for example with the VersaChrome Edge™ filters, marketed by the company Semrock, which make it possible to move the cut-off wavelength between 770 nm and 900 nm for example.

[0085] According to another solution, the low-pass filter 14 is placed on or in a sterile cover intended to protect the camera and its lens 4. For example, it is possible to use very simple filters with a cut-off power of 1.OD to 2.OD. Such filters can easily be added to an already existing fluorescence detection device. They are just used to significantly reduce a part of the signal. They can be made from very low-cost filters or plastic films sold in large widths to protect from the sun. For example, the sterile cover intended to protect the camera and its lens 4 is supplied with one or more sterile filters of this type which can be placed on the front face of the cover. The fixing of a filter on the cover can be done using a notch, a self-adhesive strip, a Velcro® type strip, a magnetic fastener integrated into the cover, etc.Thus, during surgery and depending on its progress, the surgeon can put on or remove a filter before using the camera.

[0086] Figure 3 schematically illustrates an example of filtering as a function of the wavelength, by the different filters of the filtering means 10 described previously. The filtering means 10 are adapted to be able to occupy at least two different configurations. According to a first configuration, the low-pass filter 14 is placed between the area of ​​interest I and the detector 3. According to a second configuration, the low-pass filter 14 is retracted or replaced by a high-pass or band-pass filter.

[0087] Figure 4 shows the emission spectra corresponding respectively to the autofluorescence of the parathyroid glands and to the fluorescence of indocyanine green when the excitation light source has an excitation wavelength at 680 nm. Using the device according to the invention described above, it is possible to implement the method according to the invention in several ways.

[0088] According to a first embodiment of the method according to the invention, a filtering operation is carried out according to a first and a second filtering operating mode different from each other and implemented one after the other. The first filtering operating mode is implemented using a low-pass filter placed in its first configuration (i.e. placed between the area of ​​interest I and the detector 3). This low-pass filter has a cut-off wavelength of less than 800 nm (for example 775 nm). The detector 3 can then detect 60% of the autofluorescence signal and 10% of the indocyanine green signal. Therefore, with a low-pass filter 14 of this type, the detected radiation essentially corresponds to the autofluorescence signal of the parathyroid glands. As illustrated in Figure 6, the image then generated to be displayed on the display means 16 essentially shows the autofluorescence of one or more parathyroid glands.

[0089] To further reduce the contribution of indocyanine green, a lower cutoff wavelength would have to be used for the low-pass filter 14, but this would be to the detriment of the quality of the measured autofluorescence signal. Indeed, detector 3 would detect less signal from the indocyanine green fluorescence, but also less autofluorescence signal because the detection will be done over a narrower bandwidth in which the measured intensity of the autofluorescence signal is low, or even very low.

[0090] On the other hand, if the low-pass filter 14 is in its second configuration (retracted), which corresponds to the second filtering operating mode, and the indocyanine green has not yet been injected, the parathyroid glands are very visible. Indeed, the parathyroid glands are then detected over a very large part of their emission spectrum, from 700 nm to 900 nm. In addition, with an excitation wavelength around 650-700 nm, the intensity of the autofluorescence is greater than with an excitation wavelength located between 700 and 800 nm, the parathyroid glands are therefore even more visible than with a device of the prior art using an excitation wavelength between 750 nm and 800 nm for example.

[0091] The autofluorescence signal from the parathyroid glands can still be observed while the indocyanine green has diffused little. However, when the indocyanine green perfusion is complete, detector 3 detects both the autofluorescence signal and the indocyanine green fluorescence signal, but because the latter is more intense, the signal from the parathyroid glands is masked (see Figure 7).

[0092] Furthermore, by positioning, between the area of ​​interest I and the detector 3 (first configuration), a low-pass filter 14 which has a cut-off wavelength between 700 and 900 nm or a high-pass filter which has a cut-off wavelength between 750 and 800 nm, it is possible to adjust the ratio of the respective signals of autofluorescence and indocyanine green fluorescence to produce a hybrid image (possibly with a similar or identical fluorescence level for each of the signals).

[0093] Potentially at least four types of images can be obtained with the device 1 described above.

[0094] 1) an image over a low wavelength range (below the cutoff of the low-pass filter 14) with the low-pass filter placed between the area of ​​interest I and the detector 3 (first configuration / first operating mode),

[0095] 2) an image over a detection range between 700 and 1000 nm, without the low-pass filter 14 (second configuration / second operating mode),

[0096] 3) an image over a high wavelength range, by replacing the low-pass filter 14 with a high-pass filter (third operating mode),

[0097] 4) a combined image if the low-pass filter 14 has a cut-off wavelength between 780 and 800 nm (fourth operating mode).

[0098] According to a second embodiment of the filtering means 10, these comprise for example a lighting filter 11, an excitation light source filter 12 and a high-pass or band-pass filter 13 such as those described above in relation to the first embodiment of the filtering means 10. According to this second example, the filtering means 10 comprise a matrix of color filters 15 (for example a Bayer filter mosaic) placed in front of the detector 3 (As indicated above, the presence of this type of filter in the filtering means is optional).

[0099] Thus, the filtering means 10 are configured to collect signals in different wavelength ranges depending on the color channel(s) used for processing the fluorescence images.

[0100] Indeed, as shown in Figure 5, the spectral response of the detector 3 provided with the color filter matrix 15 may differ depending on the colors, in particular in a spectral band between 700 and 900nm. Therefore, by using an appropriate color filter matrix 15, such as that giving the spectral response illustrated in Figure 5, it is possible to carry out digital filtering by considering certain channels and / or combining them. For example, by processing with appropriate signal processing means, the signals obtained from the red and blue channels (second filtering procedure), it is possible to detect, measure and visualize both the autofluorescence signal and the fluorescence signal. By processing the signals obtained from the blue channel, it is possible to detect, measure and visualize essentially the fluorescence signal.By subtracting the intensity of the signal obtained on the blue channel from that of the signal obtained on the red channel, it is possible to detect, measure and visualize essentially the autofluorescence signal (first filtering procedure). Other combinations are possible. By adding to the intensity of the signal obtained on the red channel, twice the intensity of the signal obtained on the green channel and subtracting three times the intensity of the signal obtained on the blue channel, it is possible to detect, measure and visualize essentially the autofluorescence signal. Other color filter matrices 15 than a Bayer filter mosaic can possibly be used. For example, to favor detection on one or more other wavelength ranges, it is possible to use a CYGM filter (cyan, yellow, green, magenta), an RGBE filter (red, green, blue, emerald), a CMYK filter (cyan, magenta, yellow and white), an RGBW filter (red, green, blue, white), etc.Similarly, rather than a mosaic of filters, three separate sensors (e.g., three separate CCD sensors) or even overlapping filters as in a Foveon X3 sensor, etc. can be used. This list of examples of filters and sensors is not exhaustive. In all cases, they can be used to select one or more channels and / or obtain various combinations of the signals obtained on different channels. It is also possible to combine the use of a removable filter (low-pass and / or high-pass) with filter matrices.

[0101] According to a third embodiment of the method according to the invention, this makes it possible to completely separate the respective contributions of indocyanine green and autofluorescence in the emission of fluorescence radiation by the area of ​​interest I. Furthermore, this third embodiment of the method according to the invention also makes it possible to measure the increase in the contribution of indocyanine green between two successive times, for example to measure the vascularization of a parathyroid gland. In order to determine the respective contributions of indocyanine green and autofluorescence in the fluorescence radiation collected by the sensor 5, it is assumed that this radiation only includes contributions from indocyanine green, autofluorescence and little contribution related to ambient light, which always contains a little infrared in the detection band of the device 1.Other potential contributions to the signal are neglected.

[0102] It is also assumed that the proportion of the signal emitted in autofluorescence or fluorescence by indocyanine green and detected according to the different measurement configurations, is constant regardless of the concentration of fluorescent material. It is known that, for example for indocyanine green, the emission spectrum depends partly on the concentration and, at very high concentrations, a "quenching" phenomenon (extinction of the signal) can be observed. However, this phenomenon is totally negligible with regard to the authorized injectable doses of indocyanine green.

[0103] Then, according to the third mode of implementation of the method according to the invention, the following acquisitions are carried out:

[0104] 1) With the low-pass filter 14 (IR-cut) placed between the area of ​​interest and the sensor 5: An acquisition (IA) with the excitation light source 2 (laser) switched off,

[0105] An acquisition (IB) with excitation light source 2 on.

[0106] 2) With the low-pass filter 14 (IR-cut) retracted (removed from the optical path): An acquisition (2A) with the excitation light source 2 switched off,

[0107] An acquisition (2B) with the excitation light source 2 on.

[0108] This series of acquisitions provides an image that contains only the contribution of the indocyanine green contained in the tissues to the fluorescence emission collected by sensor 5, and an image that contains only the contribution of the autofluorescence of the observed tissues (parathyroid glands) to the fluorescence emission collected by sensor 5. Acquisition (1 A) gives a background image with filter 14. This image is called bckLow.

[0109] Acquisition (IB) gives an image of the fluorescence radiation of the area of ​​interest with filter 14. This image is called Low.

[0110] Acquisition (2A) gives a background image without filter 14.

[0111] This image is named bckHigh.

[0112] Acquisition (2B) gives an image of the fluorescence radiation of the area of ​​interest without filter 14. This image is named High.

[0113] High = bckHigh + (AF + IGG) * ô / d 2 Or

[0114] AF corresponds to the total autofluorescence signal detected with device 1 without filter 14.

[0115] IGG corresponds to the total indocyanine green fluorescence signal detected with device 1 without filter 14. d corresponds to the distance between the excitation source 2 and the area of ​​interest I a corresponds to the proportion of the total autofluorescence signal detected with device 1, filtered by the low-pass filter 14.

[0116] P corresponding to the proportion of the total indocyanine green fluorescence signal detected with device 1, filtered by the low-pass filter 14. ô is the gain of detector 3. It has been verified that this gain is similar for indocyanine green fluorescence and for the autofluorescence of a parathyroid gland.

[0117] Calculation of an indocyanine green image and an autofluorescence image.

[0118] From the previous equations we obtain:

[0119] The combination provides the image of the contribution of indocyanine green fluorescence to a multiplicative factor varying with distance.

[0120] The combination provides the image of the contribution of the autofluorescence of the parathyroid glands to a multiplicative factor varying with the distance.

[0121] It is therefore possible to visualize the contribution of autofluorescence alone and indocyanine green fluorescence alone to within a multiplicative factor.

[0122] If the measurements are taken at a constant distance, using a shim for example, the values ​​can be compared between different surgeries. Alternatively, a device that measures the distance using a pointer of the type described in patent application FR1750361 A filed by Fluoptics® or of the type of the FLUOBEAM®LS device can be used. Measuring the distance means that there is no need to worry about the position of the probe at the time of measurement. This also makes it possible to obtain an absolute value of the signal level emitted at the area of ​​interest I.

[0123] Analysis of perfusion after injection of indocyanine green.

[0124] The same type of measurement can be used to quantify the signal increase during perfusion analysis following an injection of indocyanine green.

[0125] By taking up the previous notations, by indexing by 1 the acquisition series at a first time t and by 2 the acquisition series at a second time t' subsequent to t, and by using the fact that the parathyroid is the same and has an identical autofluorescence radiation at times t and t' (just before the injection and after) we have And

[0126] Which allows to obtain

[0127] Either

[0128] (AF + ICG^ * (LoWi — bckLow- ) = (a * AF + (3 * ICG * (Hig^ — bckHigh-^

[0129] And AF * (LoWi — bckLow^ — a * High^ — bckHigh^ )') = ICG- * (J3* (High- — bckHigh-P) — (Low — bckLow^p)

[0130] From where

[0131] By doing the same reasoning for the acquisition at the second time t', we obtain

[0132] It is therefore possible to provide distance-independent confidence values ​​that allow comparisons either between indocyanine green concentration levels between two measurement times (two data acquisitions using device 1). or between different surgeries, by a comparison of the increase in the indocyanine green signal compared to the autofluorescence of the parathyroid glands.

[0133] So, this process only requires knowing in advance the two parameters a and P. However, these values ​​can be measured by calibration.

[0134] Calibration

[0135] The purpose of the calibration is to estimate the proportion a of the autofluorescence signal and the proportion p of indocyanine green fluorescence, detected by the device 1, in the different measurement configurations and the different filtering operating modes. To this end, it is possible to determine these measurements, prior to the acquisition of fluorescence images in the different measurement configurations and the different filtering operating modes. It is possible to determine these values ​​once for all subsequent uses of the device 1, or even for all the devices 1 used meeting the same technical specifications (same type of sensor 5, same filters, etc.). Indeed, it has been possible to verify that these coefficients a and P are relatively independent of the conditions of acquisition of the fluorescence signal by the sensor 5.

[0136] Thus, an acquisition is carried out in total darkness, with only autofluorescence emission by the parathyroid and an acquisition is carried out in total darkness, with only fluorescence emission by indocyanine green.

[0137] We therefore obtain two series of measurements:

[0138] For autofluorescence alone

[0139] Therefore, the value of a can be determined from the filtered and unfiltered images acquired with only the autofluorescence emission from the parathyroid

[0140] (Low — bckLow) oc — -

[0141] (High — bckHigh)

[0142] It should be noted that the value of a depends on the type of fluorescence emission. Thus, the value of a is not the same for parathyroid autofluorescence as for fluorescence or autofluorescence of other tissues or substances. By producing one (or more) images from the values ​​of a (on an area or the entire region of interest I), it is possible to detect false positives, or even pathologies of the parathyroid).

[0143] For indocyanine green fluorescence alone

[0144] Therefore, the value of P can be determined from the filtered and unfiltered images acquired with only the indocyanine green emission alone.

[0145] (Low — bckLow) fi (High — bckHigh)

[0146] In any case, this calibration would have to be done for all the pixels of sensor 5. However, we can consider that the pixel responses vary from the black and gain value of each pixel. We can also consider that the spectral response of the pixels of sensor 5 is identical for all pixels. It follows from these hypotheses that it is sufficient to determine a and P on an area of ​​sensor 5, and that the values ​​thus determined will be the same for all the pixels. To follow the evolution of the perfusion of indocyanine green, it was chosen to base ourselves on

[0147] , the report

[0148] But, it is possible to base it on other quantities. For example, the ratio may be preferred if there is only one injection and this only occurs at the end of surgery.

[0149] For a quantitative measurement of indocyanine green and the autofluorescence value of the parathyroids, it is necessary to work at a constant distance (which is possible by using a shim, as already indicated above). If the different acquisitions (with light source 2 on or off, and by changing the filtering procedure) are carried out sufficiently quickly, it can also be considered that the distance has not varied significantly between these different acquisitions.

[0150] This disclosure includes the electronics, electronic instructions, processors, memory, displays and other means necessary to guide, control, display and record the systems and processes described herein.

[0151] This disclosure includes imaging systems and equipment for various medical uses, including, but not limited to, imaging thyroid and parathyroid tissues. The disclosure also includes methods of operating imaging systems and equipment, methods of differentially imaging human tissues for medical purposes, and methods of imaging parathyroid and thyroid tissues.

Claims

DEMANDS 1. Fluorescence imaging method for surgical applications comprising: - an excitation operation of at least one first and a second fluorescent substance potentially located in a region of interest (I), with at least one excitation radiation having a maximum intensity defined by an excitation wavelength, this excitation wavelength being between 600 nm and 800 nm, the first substance having a fluorescence emission spectrum with a first maximum intensity at a first wavelength and the second substance having a fluorescence emission spectrum with a second maximum intensity at a second wavelength, the first and second wavelengths being distinct, and dependent on the excitation wavelength, - a filtering operation of at least a portion of the fluorescence radiation emitted in the area of ​​interest (I) in response to the excitation radiation, - a detection and acquisition operation, using a sensor (5), of at least a portion of the fluorescence radiation filtered by the filtering operation, this detection operation being carried out in a detection range itself within a wavelength range between 410 nm and 1000 nm, - an operation consisting of generating, from the radiation detected by the sensor (5), at least one output signal whose intensity is representative of the intensity of the fluorescence radiation detected by the sensor (5), - an image display operation formed from the output signal, characterized in that the filtering operation is carried out according to at least one first and one second filtering operating mode, different from each other and implemented one after the other, the first filtering operating mode favoring, when the first and second substances are present in the region of interest (I), the contribution of the fluorescence emission of the second substance relative to the contribution of the fluorescence emission of the first substance, in the output signal, and the second filtering operating mode favoring the contribution of the fluorescence emission of the first substance in the output signal, relative to the contribution of the fluorescence emission of the first substance in the output signal obtained with the first filtering operating mode, and by the fact that it includes operations consisting of calculating and displaying images obtained either, on the one hand, from the output signal obtained using the first filtering operating mode, and on the other hand, from the output signal obtained using the second filtering operating mode, or from a combination of output signals obtained respectively using the first filtering operating mode and the second filtering operating mode.

2. A method according to claim 1, wherein at least one displayed image corresponds essentially to the contribution, in the output signal, of the emission of fluorescence radiation from the first substance or to the contribution, in the output signal, of the emission of fluorescence radiation from the second substance, and is calculated from a combination of output signals obtained respectively using the first filtering method and the second filtering method.

3. A method according to any one of the preceding claims, wherein said at least two fluorescent substances are respectively indocyanine green and the substance responsible for the autofluorescence of the parathyroid glands.

4. A method according to claim 3, comprising alternately producing at least one image of at least one parathyroid gland and at least one image of a vascular network supplying blood to that parathyroid gland.

5. Method according to claim 4, wherein the image of the parathyroid gland is made with a low-pass filter (14) in place between the area of ​​interest (I) and the sensor (5), and the image of the vascular network is made without the low-pass filter (14) between the area of ​​interest (I) and the sensor (5).

6. Method according to claim 4, wherein the image of the parathyroid gland is made with a low-pass filter (14) in place between the area of ​​interest (I) and the sensor (5), and the image of the vascular network is made with a high-pass filter in addition to or instead of the low-pass filter (14) between the area of ​​interest (I) and the sensor (5).

7. A method according to any one of claims 3 to 6, wherein the excitation radiation has a maximum intensity between 600 and 720 nm.

8. Method according to claim 7, wherein the excitation radiation has a maximum intensity between 650 and 700 nm.

9. Method according to claim 7 or 8, wherein the excitation radiation has a maximum intensity at 680 nm.

10. A method according to any one of the preceding claims, wherein, in the first filtering operating mode, a bandpass filter (14) is placed between the area of ​​interest (I) and the detector (5) and in the second filtering operating mode, this filter (14) is removed.

11. A method according to claim 10, wherein the detection and acquisition operation comprises - an acquisition operation (1 A) according to the first operating mode, with the source (2) producing the excitation radiation turned off, - an acquisition operation (IB) according to the first operating mode, with the source (2) producing the excitation radiation switched on, - an acquisition operation (2 A) according to the second operating mode, with the source (2) producing the excitation radiation turned off, - an acquisition operation (2B) according to the second operating mode, with the source (2) producing the excitation radiation switched on, and operations consisting of calculating and displaying images of the contribution, in the output signal, of the emission of fluorescence radiation from the first substance or of the contribution, in the output signal, of the emission of fluorescence radiation from the second substance.

12. A method according to claim 10 or 11, wherein the operation of displaying images formed from the output signal comprises displaying an image representative of the coefficient a, on at least a portion of the area of ​​interest (I), where (Low — bckLow oc — - High — bckHigl ) With Low = an image of the fluorescence radiation of the region of interest with the bandpass filter (14) and the source (2) producing the excitation radiation turned on, bckLow = a background image with the bandpass filter (14) and the source (2) producing the excitation radiation turned off, High = an image of the fluorescence radiation of the area of ​​interest without the bandpass filter (14) and the source (2) producing the excitation radiation turned on, bckHigh = a background image without the bandpass filter (14) and the source (2) producing the excitation radiation turned off.

13. Method according to claim 12, wherein a corresponds to the proportion of the total autofluorescence signal from at least one parathyroid gland, in the output signal after filtering by the bandpass filter (14).

14. A method according to any one of the preceding claims wherein, with one of the two operating modes, the contribution to the intensity of the output signal obtained at the second wavelength is greater than or equal to that obtained at the first wavelength, and with the other operating mode, the contribution to the intensity of the output signal obtained at the first wavelength is greater than or equal to that obtained at the second wavelength.

15. A method according to any one of the preceding claims, wherein, for the excitation wavelength used to illuminate the area of ​​interest, the fluorescence yield of the first substance is greater than the fluorescence yield of the second substance.

16. A method according to any one of the preceding claims, wherein the maximum of the fluorescence spectrum of the first substance has a wavelength greater than that of the maximum of the fluorescence spectrum of the second substance, with the excitation wavelength used to illuminate the area of ​​interest.

17. A method according to any one of the preceding claims, wherein the excitation wavelength is chosen so as to favor the fluorescence re-emission function of the second substance compared to that of the first substance.

18. A method according to any one of the preceding claims, wherein the operation of generating at least two images from the output signal comprises at least one different optical or digital processing for each of these two images.

19. A method according to claim 18, wherein the digital processing comprises an operation consisting of using the signals respectively obtained on different color channels to generate each of said at least two images.

20. Fluorescence imaging device (1) for surgical applications comprising a sensor (5), at least one filter (14) and an excitation light source (2), this device being configured to implement the method according to one of the preceding claims.

21. Fluorescence imaging device (1) for surgical applications comprising: - a light excitation source (2) configured to emit at least one excitation radiation, on an area of ​​interest (I), with a maximum intensity defined by an excitation wavelength, this excitation wavelength being within a range of emission wavelengths between 600 nm and 800 nm, - a sensor (5) configured to detect fluorescence radiation emitted by at least a portion of the area of ​​interest (I), within a detection range extending over a wavelength band between the excitation wavelength and 1000 nm, and to generate at least one output signal whose intensity is a function of the radiation wavelength The fluorescence intensity (Tl) is representative of the intensity of the fluorescence radiation detected by the sensor (5), - filtering means (10) configured to filter fluorescence radiation upstream of the sensor (5), - computing resources configured to perform output signal processing, - display means (16) for displaying images calculated from the output signal, characterized in that the filtering means (10) are further configured to be able to implement, one after the other, at least two different operating modes, the first filtering operating mode favoring, when a first and a second substance are present in the area of ​​interest (I), the contribution of the emission of fluorescence radiation from the second substance relative to the contribution of the emission of fluorescence radiation from the first substance, in the output signal, the second filtering operating mode favoring the contribution of the emission of fluorescence radiation from the first substance in the output signal, relative to the contribution of the emission of fluorescence radiation from the first substance in the output signal obtained with the first filtering operating mode.and by the fact that the computing means are configured to generate from the output signal at least two images, obtained either, on the one hand, from the output signal obtained using the first filtering operating mode, and on the other hand, from the output signal obtained using the second filtering operating mode, or from a combination of output signals obtained respectively using the first filtering operating mode and the second filtering operating mode.

22. Device (1) according to claim 21, wherein the excitation wavelength is within a range of emission wavelengths between 650 nm and 700 nm.

23. Device (1) according to any one of claims 21 or 22, wherein the filtering means are configured so that with one of the two operating modes, the contribution to the intensity of the output signal obtained at the second wavelength is greater than that obtained at the first wavelength, and with the other operating mode, conversely, the contribution to the intensity of the output signal obtained at the first wavelength is greater than that obtained at the second wavelength.

24. Device (1) according to claim 23, wherein the filtering means (10) comprise a removable filter (14).

25. Device according to claim 24, wherein the removable filter (14) is placed between the area of ​​interest (I) and the sensor (5) in the first operating mode and is removed in the second operating mode.

26. Device (1) according to claim 24 or 25, wherein the removable filter (14) is a low-pass filter having a cutoff wavelength between 720 and 800 nm.

27. Device (1) according to any one of claims 24 to 26, comprising a protective cover for a camera including the sensor (5) and in which the filter (14) is disposed on the cover or integrated into the cover.

28. Device (1) according to any one of claims 21 to 23, wherein the output signal comprises the signal from at least two different color channels, this device comprising means for processing the output signal configured to perform linear combinations of the intensities obtained on the different color channels.

29. Device (1) according to any one of claims 21 to 27, configured to alternately produce at least one image of at least one parathyroid gland with the first operating mode and at least one image of the vascular network supplying blood to this parathyroid gland which is irrigated with indocyanine green, with the second operating mode, the device (1) also being configured to receive a low-pass filter (14) in the optical path located between the area of ​​interest (I) and the sensor (5), in the first operating mode and to remove, in the second operating mode, this low-pass filter (14) from the optical path.

30. Device (1) according to claim 29, wherein the low-pass filter (14) has a cutoff wavelength adapted to limit the fluorescence of indocyanine green emitted in the area of ​​interest.

Images