U.S. patent application number 14/396381 was filed with the patent office on 2015-03-26 for fluorescence imaging system for an operating room.
This patent application is currently assigned to FLUOPTICS. The applicant listed for this patent is FLUOPTICS. Invention is credited to Norman Mangeret, Philippe Rizo.
Application Number | 20150083932 14/396381 |
Document ID | / |
Family ID | 48142809 |
Filed Date | 2015-03-26 |
United States Patent
Application |
20150083932 |
Kind Code |
A1 |
Rizo; Philippe ; et
al. |
March 26, 2015 |
FLUORESCENCE IMAGING SYSTEM FOR AN OPERATING ROOM
Abstract
Fluorescence imaging system for an operating theatre, comprising
a device illuminating the operating theatre and emitting a white
light, and a fluorescence imaging device. Said fluorescence imaging
device comprises a light source emitting radiation for excitation
of a fluorescent marker in a range of emission wavelengths of
between 600 and 900 nm. The light emitted by the illuminating
device is filtered by a low-pass filter, of which the cut-off
wavelength is below the emission range of the fluorescent marker,
but is nonetheless able to show an increase or fluctuations in the
attenuation for wavelengths above the emission range of the
fluorescent marker, the product of the attenuation of the filter of
the detector and of the attenuation of the low-pass filter of the
illuminating device leading to an attenuation by a factor of at
least 10.sup.6.
Inventors: |
Rizo; Philippe; (La Tronche,
FR) ; Mangeret; Norman; (Jarrie, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FLUOPTICS |
Grenoble |
|
FR |
|
|
Assignee: |
FLUOPTICS
Grenoble
FR
|
Family ID: |
48142809 |
Appl. No.: |
14/396381 |
Filed: |
April 23, 2013 |
PCT Filed: |
April 23, 2013 |
PCT NO: |
PCT/EP2013/058352 |
371 Date: |
October 22, 2014 |
Current U.S.
Class: |
250/458.1 ;
250/226 |
Current CPC
Class: |
G01N 2201/062 20130101;
A61B 2090/309 20160201; A61B 5/0071 20130101; A61B 90/361 20160201;
G01N 21/6486 20130101; G01N 21/6456 20130101; A61B 2090/3941
20160201; A61B 2090/395 20160201; F21W 2131/205 20130101 |
Class at
Publication: |
250/458.1 ;
250/226 |
International
Class: |
A61B 19/00 20060101
A61B019/00; G01N 21/64 20060101 G01N021/64 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2012 |
FR |
1253786 |
Claims
1. A fluorescence imaging system for an operating room comprising
an operating room illuminating device capable of emitting white
light, and a fluorescence imaging device, the fluorescence imaging
device comprising: a light source capable of emitting excitation
radiation to excite a fluorescent marker in a range of emission
wavelengths of between 600 and 900 nm; a detector adapted to detect
the fluorescent radiation emitted by the marker under the effect of
excitation by the light source; a filter for the detector adapted
to attenuate the excitation radiation and to transmit to the
detector those photons having a wavelength included in the range of
wavelengths of fluorescent radiation emitted by the marker, the
light emitted by the illuminating device being filtered by a
low-pass filter having a cut-off wavelength below the emission
range of the fluorescent marker, the low-pass filter nonetheless
being able to exhibit attenuation peaking or fluctuations at
wavelengths above the emission range of the fluorescent marker,
wherein in a range of wavelengths extending from an upper cut-off
wavelength below the wavelength on and after which attenuation
peaking or fluctuations of the low-pass filter of the illuminating
device are observed, the product of attenuation by the filter of
the detector and of attenuation by the low-pass filter of the
illuminating device leads to an attenuation by a factor of at least
10.sup.6.
2. The system of claim 1, wherein the wavelength of excitation
radiation is between 630 and 810 nm.
3. The system of claim 1, wherein the bandwidth in which the filter
of the detector transmits fluorescent radiation is between 50 and
70 nm.
4. The system of claim 1, wherein the range of wavelengths, in
which the product of attenuation by the detector filter and of
attenuation by the low-pass filter of the illuminating device leads
to attenuation by a factor of at least 10.sup.6, extends at least
as far as the limit detection wavelength of the detector.
5. The system of claim 1, wherein the range of wavelengths, in
which the product of attenuation by the filter of the detector and
of attenuation by the low-pass filter of the illuminating device
leads to attenuation by a factor of at least 10.sup.6, extends at
least as far as 1000 nm, preferably as far as 1150 nm.
6. The system of claim 1, wherein in the range of wavelengths
transmitted by the detector filter, the low-pass filter of the
illuminating device exhibits attenuation by a factor of at least
10.sup.6.
7. The system of claim 1, wherein the illuminating device comprises
a dome-shaped light-head which can be positioned via a hinged
arm.
8. The system of claim 1, wherein the illuminating device comprises
a headlamp.
9. The system of claim 1, wherein the illuminating device is
adapted to provide continuous lighting.
10. The system of claim 1, wherein the illuminating device is
adapted to provide pulsed lighting.
11. The system of claim 1, wherein the illuminating device
comprises light-emitting diodes.
12. The system of claim 1, wherein the power of the illuminating
device is 40 kLux or higher.
13. The system of claim 1, wherein the detector is a CCD or CMOS
camera.
14. The system of claim 1, wherein the excitation wavelength is 780
nm and the filter of the detector transmits radiation in a band
between 820 and 850 nm.
15. The system of claim 1, wherein the excitation wavelength is 750
nm and the filter of the detector transmits radiation in a band
between 780 and 870 nm.
Description
FIELD OF THE INVENTION
[0001] The present invention concerns a fluorescence imaging system
for an operating room comprising a device illuminating the
operating room and a fluorescence medical imaging device.
BACKGROUND OF THE INVENTION
[0002] Fluorescence medical imaging is a promising technique in
particular for surgical procedures for the purpose of guiding a
surgeon's action.
[0003] This technique is based on administering a substance to a
patient that contains a fluorescent marker e.g. for observation of
a target organ or tissue which is to undergo surgical procedure, or
for observation of a flow monitored by the marker.
[0004] By means of the presence of the fluorescent marker in or
close to the target organ or tissue, the illumination of the region
of the patient comprising the organ has the effect of exciting the
marker which in turn emits radiation at a wavelength slightly
longer than the excitation wavelength.
[0005] The chief applications are in the Near InfraRed (NIR) i.e.
the excitation radiation and the fluorescence radiation lie in a
wavelength range of between 700 and 900 nm. Once detected, the
fluorescent radiation can be superimposed over an image of the
organ concerned to view the target organ or tissue in relation to
the outer visible portion of the organ.
[0006] The Applicant provides a fluorescence medical imaging device
marketed under the trade name Fluobeam.TM..
[0007] The principle of fluorescence imaging is schematically
illustrated in FIG. 1.
[0008] The imaging device I comprises a light source S intended to
excite the fluorescent marker located in a region O of which it is
desired to obtain images (the marker possibly being concentrated in
this region or passing therethrough in a flow) the radiation
L.sub.S provided by the light source having the effect of making
the marker fluorescent.
[0009] In medical applications, the region O is generally located
underneath the patient's skin P.
[0010] It is made fluorescent by administering to the patient a
substance containing a fluorescent marker so that the marker
concentrates in or passes through the region O, and by exciting the
marker via radiation emitted by the light source S.
[0011] The device I also comprises a detector D adapted to detect
and record the fluorescent radiation L.sub.F emitted by the marker
located in the region O and excited by the source S.
[0012] For example the detector comprises a CCD camera.
[0013] For this purpose the light source S is filtered (filter
F.sub.S) so as to excite the fluorescent marker with radiation
L.sub.E not containing wavelengths corresponding to the
fluorescence to be measured.
[0014] For example when the fluorescence to be measured is in the
near infrared (i.e. in a wavelength range of between 700 and 900
nm) it is necessary fully to eliminate the wavelengths in the
fluorescence range, not only in the excitation radiation but also
in ambient light.
[0015] If not, these wavelengths would be detected by the detector
D and would generate noise on the fluorescence image, harming the
quality thereof.
[0016] Upstream of the detector D, the device comprises a filter
F.sub.D adapted so as only to allow those photons L.sub.F to pass
towards the detector whose wavelength is the fluorescence
wavelength.
[0017] For fluorescence in the near infrared, the filter F.sub.D is
generally a high-pass filter which transmits all the wavelengths
above a given threshold.
[0018] FIG. 2 illustrates the filtering principle of such a
fluorescence imaging device and gives the transmission curves T as
a function of the wavelength .lamda. for ambient light (curve
f.sub.A), the excitation light source (curve f.sub.E), and the
detector (curve f.sub.D).
[0019] In the example illustrated in this Figure, the excitation
wavelength is 780 nm, ambient light is filtered so as essentially
to contain wavelengths between 400 and 750 nm, whilst the detector
is filtered so as to receive all wavelengths longer than about 820
nm.
[0020] During surgical procedure, the patient is installed on a
table in the operating room and the region to be operated is
illuminated with specific lighting device present in the room.
[0021] Said device for example may be a lighting device commonly
called a <<surgical luminaire>>, in the form of a
dome-shaped light-head carried by an arm and oriented in the
direction of the patient so as to avoid any shadow area.
[0022] The fluorescence imaging device described above is also
installed in the operating room and positioned for adequate viewing
of the region in the patient of which it is desired to images and
to detect the fluorescence emitted by this region.
[0023] The excitation light source can be fixed to the surgical
luminaire itself, for example using a suitable attachment
system.
[0024] On account of its very strong power (typically between 40
and 150 kLux), the lighting in the operating room may perturb
detection of fluorescence radiation by producing photons which are
detected by the detector.
[0025] So as not to deteriorate the quality of the fluorescence
image, the light provided by the surgical luminaire must be
filtered so that it does not contain wavelengths corresponding to
the fluorescence to be measured.
[0026] Yet at 150 kLux, even a very slight leakage of light from
the operating room lighting in the range of wavelengths measured by
the detector through its filter is able to limit the quality of
fluorescence images.
[0027] In addition, requirements in terms of quality of surgical
lighting are drastic.
[0028] In this respect, standard NF EN 60601-2-41 can be cited
concerning the particular safety rules for surgical luminaires and
diagnostic lighting.
[0029] For example, the emitted light is white light which must
have a colour temperature generally of between 3000 K and 6700
K.
[0030] It is additionally stipulated in the standard that the
colour rendering index (CRI) must be between 85 and 100%,
preferably in the order of 95%.
[0031] As a result, the filtering of the light emitted by the
surgical luminaire must not lead to degradation of the
aforementioned characteristics.
[0032] Also, on account of the large surface area to be filtered
for a surgical luminaire (in the order 0.5 m.sup.2), it is
necessary to design a low-cost filter.
[0033] Fluorescence imaging devices have already been described to
guide surgical procedures.
[0034] Some systems, in particular the PDE.TM. system proposed by
Hamamatsu and the SPY.TM. system proposed by Novadaq overcome the
influence of white light by switching off the surgical luminaire
when conducting fluorescence imaging.
[0035] However the switching-off of lighting ill lends itself to
surgical procedure.
[0036] Other fluorescence imaging devices have been designed to
provide continuous lighting.
[0037] The Flare.TM. device in particular and its variant the
Mini-Flare.TM. have been the subject of several publications.
[0038] For use in an operating room, the white light emitted by the
surgical luminaire or the imaging device is filtered on and after
the excitation wavelength so as not to contain photons of longer
wavelength than the excitation wavelength which, for the Flare.TM.
and Mini-Flare.TM. devices may be 670 or 760 nm [1].
[0039] The filtering principle of the lighting system adapted to
the Flare.TM. device is described in [2].
[0040] The fluorescence detector at 700 nm is filtered with a
band-pass filter of 689 to 725 nm, whilst the detector of
fluorescence at 800 nm is filtered with a band-pass filter of 800
to 848 nm.
[0041] These band-pass filters are intended only to allow detection
of wavelengths corresponding to the fluorescence signal,
eliminating longer wavelengths.
[0042] The filtering principle of the lighting system adapted to
the Mini-Flare.TM. device is described in [3].
[0043] In this device a single detector is intended to detect the
fluorescence wavelengths around 700 nm and 800 nm.
[0044] The detector is filtered by a dual band-pass filter with a
first bandwidth of between 689 and 725 nm, and a second bandwidth
of between 803 and 853 nm.
[0045] The band-pass filters used for the Flare.TM. and
Mini-Flare.TM. devices are marketed by Chroma under reference HQ
817/25.
[0046] A competing device proposed by SurgOptics is described in
[4].
[0047] The excitation light source is a laser diode at a wavelength
of 750 nm, whilst the lighting of the operating room is provided by
a halogen lamp emitting white light.
[0048] A Chroma HQ 795/50 band-pass filter is positioned upstream
of the detector to prevent transmission thereto of wavelengths
longer than the fluorescence wavelength.
[0049] However, with all the above-described devices a fluorescent
background can be seen in the images obtained which reduces the
contrast with the fluorescence emitted by the organ or tissue of
interest.
[0050] The authors generally attribute this phenomenon to tissue
autofluorescence.
[0051] However, for the wavelengths of the near infrared under
consideration, autofluorescence is negligible and cannot alone
account for the observed fluorescent background.
[0052] Another hypothesis to explain this unsatisfactory quality of
images could be insufficient filtering of the excitation light
source.
[0053] At all events, there subsists a need to improve the quality
of fluorescence images in the setting of an operating room.
[0054] It is therefore one objective of the invention to propose a
lighting and filtering system for operating room adapted for
application of fluorescence, imaging, and which in particular
allows optimised quality of a fluorescence image even in the
presence of intense continuous illumination of the surgical
field.
[0055] A further objective of the invention is to propose a
filtering system which can easily be adapted to existing lighting
equipment in an operating room and at moderate cost.
BRIEF DESCRIPTION OF THE INVENTION
[0056] For this purpose, a fluorescence imaging is proposed for
operating room comprising an operating room illuminating device
capable of emitting white light and a fluorescence imaging
device;
[0057] said fluorescence imaging device comprising: [0058] a light
source capable of emitting radiation to excite a fluorescent marker
in a wavelength emission range of between 600 and 900 nm; [0059] a
detector adapted to detect the fluorescent radiation emitted by the
marker under the effect of excitation by the light source; [0060] a
filter for the detector adapted to attenuate the excitation
radiation and to transmit those photons to the detector which have
a wavelength included in the range of fluorescent radiation
wavelengths emitted by the marker;
[0061] the light emitted by the illuminating device being filtered
by a low-pass filter of which the cut-off wavelength is below the
emission range of the fluorescent marker, said low-pass filter
nonetheless being able to exhibit attenuation peaking or
fluctuations at wavelengths above the emission range of the
fluorescent marker.
[0062] According to the invention, in a range of wavelengths
extending from an upper cut-off wavelength of the detector filter
that is below the wavelength on and after which attenuation peaking
or fluctuations of the low-pass filter of the illuminating device
are observed, the product of the attenuation of the detector filter
and of the attenuation of the low-pass filter of the illuminating
device leads to an attenuation by a factor of at least
10.sup.6.
[0063] Herein the term <<filter>> may encompass an
elementary filter or a combination of filters.
[0064] As explained in detail below, the effect of this filtering
of the detector is to eliminate bias and background noise due to
peaking of the low-pass filter of the illuminating device which,
due to the intensity of operating room lighting, allows parasitic
light to pass that is sufficiently intense to mask some of the
fluorescence photons derived from deep regions and which are
therefore few in number.
[0065] By means of this filtering, the detector becomes more
sensitive to the fluorescence signal emitted from the deep layers
and produces more contrasted images.
[0066] Also, since this filtering is applied to the detector which
has a small surface area, it has no resultant effect on the cost of
the system
[0067] According to one embodiment of the invention, the wavelength
of excitation radiation is between 630 and 810 nm.
[0068] Preferably, the bandwidth in which the detector filter
transmits fluorescent radiation is between 50 and 70 nm.
[0069] According to one particularly advantageous embodiment of the
invention, the range of wavelengths in which the product of the
attenuation of the detector filter and the attenuation of the
low-pass filter of the illuminating device leads to an attenuation
by a factor of at least 10.sup.6, extends at least up to the limit
detection wavelength of the detector
[0070] Therefore the range of wavelengths in which the product of
detector filter attenuation and low-pass filter attenuation by the
illuminating device leads to an attenuation by a factor of at least
10.sup.6 preferably extends at least up to 1000 nm, and even
further preferably up to 1150 nm.
[0071] In addition, in the range of wavelengths transmitted by the
detector filter, the low-pass filter of the illuminating device
exhibits attenuation by a factor of at least 10.sup.6.
[0072] The illuminating device may comprise a light-head placed in
position via a hinged arm.
[0073] Alternatively, the illuminating device may comprise a
headlamp intended to be placed over the surgeon's head.
[0074] According to one embodiment, the illuminating device is
adapted to provide continuous lighting.
[0075] According to another embodiment, the illuminating device is
adapted to provide pulsed lighting.
[0076] Preferably, the illuminating device comprises light-emitting
diodes.
[0077] Also, the power of the illuminating device is advantageously
40 kLux or stronger.
[0078] The detector may be a CCD or CMOS camera.
[0079] According to one particular embodiment, the excitation
wavelength is 780 nm and the detector filter transmits radiation in
a band between 820 and 850 nm.
[0080] According to another embodiment, the excitation wavelength
is 750 nm and the detector filter transmits radiation in a band
between 780 and 870 nm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0081] Other characteristics and advantages of the invention will
become apparent from the following detailed description which
refers to the appended drawings in which:
[0082] FIG. 1 is a block diagram of the principle of fluorescence
imaging;
[0083] FIG. 2 is a graph showing the principle of filtering ambient
light, excitation light and of detector filtering in fluorescence
imaging;
[0084] FIG. 3 is a block diagram of an imaging system according to
the invention;
[0085] FIGS. 4A and 4B respectively illustrate operating room
lighting spectra of halogen lamps and light-emitting diodes;
[0086] FIG. 5 illustrates the transmission curve of a low-pass
filter used in existing operating room lighting and having
attenuation bouncing between 800 and 900 nm;
[0087] FIG. 6 illustrates the transmission curve of a low-pass
filter able to be used to filter operating room lighting;
[0088] FIGS. 7A and 7B give transmission curves of band-pass
filters used to filter the detector in some fluorescence imaging
devices on the market;
[0089] FIG. 8A gives the sensitivity curve of a CCD sensor of the
detector as a function of wavelength;
[0090] FIG. 8B gives the quantum efficiency curve of a CMOS sensor
of the detector as a function of wavelength;
[0091] FIGS. 9a to 9c respectively illustrate the transmission
curves of the low-pass filter in operating room lighting, of the
low-pass filter of the detector in one embodiment of the invention,
and of the band-pass filter of the detector;
[0092] FIGS. 10A and 10B are fluorescence images respectively
obtained with filtering system of the detector in the prior art and
with a system conforming to the invention;
[0093] FIG. 11 gives histograms respectively obtained with a
filtering system of the detector in the prior art and with a system
conforming to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0094] FIG. 3 is an overall schematic of the system according to
one embodiment of the invention.
[0095] This system comprises an operating room illuminating device
B and a fluorescence imaging device I directed towards a region O
symbolising the part of a patient (human being or animal) of which
it is desired to obtain fluorescence images and into which a
fluorescent marker is injected for this purpose.
[0096] The fluorescence imaging device I is advantageously a device
marketed by the Applicant under the trade name Fluobeam.TM..
[0097] This device I comprises a light source S able to emit
excitation radiation L.sub.E to excite the fluorescent marker
located in or passing through the region O to be observed, in a
range of emission wavelengths L.sub.F between 600 and 900 nm, and a
detector D adapted to detect the fluorescent radiation L.sub.F
emitted by the marker under the effect of excitation by the light
source S.
[0098] To perform fluorescence measurement, the detector is
filtered with a filter F.sub.D which eliminates visible radiation
wavelengths which correspond to operating room lighting, whilst
allowing the passing of near infra-red wavelengths corresponding to
fluorescence.
[0099] According to one preferred embodiment, the filter of the
detector comprises a band-pass filter F.sub.D1 whose bandwidth lies
in the wavelengths of the near infra-red corresponding to
fluorescence. An example of a transmission curve of such a
band-pass filter is shown in FIGS. 7A and 7B, which are commented
on below.
[0100] Alliteratively, the detector filter may also transmit
wavelengths shorter than visible radiation without departing from
the scope of the invention. However, for reasons of conciseness the
term <<band-pass>> will be used for these two
variants.
[0101] The filter F.sub.D may therefore be formed of a combination
of filters allowing the desired ranges of attenuation and
transmission to be obtained.
[0102] According to one embodiment of the invention illustrated in
FIG. 3, the operating room illuminating device is a surgical
light-head i.e. a light source of large size intended to illuminate
the surgical field with white light preventing any shadowing formed
for example by the surgeon's head and hands, the instruments used,
etc.
[0103] It is a very powerful light source (40 kLux or more, often
up to 150 kLux).
[0104] The NF EN 60601-2-41 standard cited above lays down the
requirement of a certain colour temperature range and a certain
colour rendering index (CRI).
[0105] At the current time, the colour temperature must generally
be between 3000 K and 6700 K and the colour rendering index must be
between 85 and 100%, preferably in the order of 95%.
[0106] A surgical light is typically in the form of a dome having a
plurality of lamps.
[0107] This dome is generally joined to a hinged arm attached to
the ceiling or to any suitable support in the operating room, so
that it can be directed towards the operating area to provide the
surgeon with lighting having the best possible contrast.
[0108] According to another embodiment of the invention (not
illustrated) the operating room lighting device is a headlamp
intended to be placed over the surgeon's head.
[0109] Aside from the fact that the light beam is better focused
with such a headlamp than with an overhead surgical light, the
constraints related to the quality of lighting (in particular in
terms of power, colour temperature and colour rendering index) are
the same for these two types of devices.
[0110] Therefore the filtering solution of the invention which is
described in detail below applies to any operating room
illuminating device whether an overhead surgical light or a
headlamp.
[0111] Current operating room lighting comprises either halogen
lamps or light-emitting diodes (LEDs), the latter tending to
replace the former.
[0112] FIG. 4A shows the spectrum of halogen-type lighting which
has a colour rendering index of 91.5, a luminous flux per unit
surface area of 66 kLux and colour temperature of 4000 K.
[0113] FIG. 4B gives the spectrum of light with light-emitting
diodes (LEDs), which has a colour rendering index of 90.5, a
luminous flux per unit surface area of 60 kLux and colour
temperature of 3719 K.
[0114] The comparison between these two spectra shows that the LED
lighting provides a much lower light level at wavelengths longer
than 700 nm than halogen lighting.
[0115] It would therefore be advantageous, in order to conduct
fluorescence imaging in the near infra-red in the operating room,
to choose LED lighting which allows easier elimination of the
infra-red component.
[0116] To prevent transmission of infra-red wavelengths of the
illuminating device, a low-pass filter Fe is placed in front of it
having a cut-off frequency in the order of 700 to 750 nm.
[0117] FIG. 5 shows the spectrum of a low-pass interference filter
commonly used to cut off the near infra-red from lighting in an
operating room.
[0118] On account of the large surface area of the illuminating
device (typically in the order of 0.5 m.sup.2), the technical
solution that is economically most reasonable for filtering the
lighting of the operating room is the use of a low-cost
interference filter.
[0119] However attenuation bouncing is observed on this type of
filter (designated by arrows) at between 800 and 900 nm, which
generate parasitic light in the fluorescence wavelengths.
[0120] Such a filter cannot therefore be used for the intended
application.
[0121] A better performing interference filter in the range of
fluorescence wavelengths must therefore be chosen which allows
sharp-cut filtering of illumination from an overhead surgical light
or headlamp over a wavelength range above 700 or 750 nm, so as not
to deteriorate the colour rendering index or at least to obtain
possible restoring thereof by adding a red component.
[0122] It is within the reach of persons skilled in the art to
choose a filter among those on the market which has the required
performance level or to have an adequate filter manufactured by a
specialised company on the basis of specifications provided.
[0123] FIG. 6 shows the spectrum of an interference filter which
can be used to filter an overhead surgical light or headlamp to
implement the invention.
[0124] This filter shows good attenuation between 800 and 900 nm
but significant peaking of attenuation (designated by arrows) above
900 nm.
[0125] When an overhead surgical light or headlamp is filtered with
this type of filter there is therefore parasitic light in the
illumination spectrum in the long wavelengths of the near infra-red
i.e. around 900 nm.
[0126] This parasitic light is designated by the reference Lp in
FIG. 3.
[0127] As will be seen below, this peaking can be offset by
low-pass filtering of the detector to cut off the corresponding
long wavelengths.
[0128] In addition as is known per se the filtering of the detector
D generally comprises a band-pass filter F.sub.D1 designed so that
only those photons corresponding to the fluorescence L.sub.F
emitted by the marker are detected.
[0129] In general, a band-pass width in the order of 50 to 70 nm is
appropriate, the value of the lower and upper cut-off wavelengths
(respectively denoted .lamda..sub.lower and .lamda..sub.upper)
being selected as a function of the fluorescence emission spectrum
of the marker under consideration.
[0130] Yet the inventors have found that the band-pass filters used
in the devices on the market in fact exhibit attenuation peaking or
bouncing at wavelengths between 800 and 1000 nm.
[0131] FIG. 7A for example shows the spectrum of a Chroma HQ817-25
filter which is used in the Flare.TM. and Mini-Flare.TM. systems
for example described above.
[0132] Very good attenuation is observed between 850 and 1040 nm,
but major bouncing (designated by the arrows) occurs on and after
1050 nm.
[0133] FIG. 7B shows the spectrum of a Chroma HQ795/50 filter which
is used for example in the SurgOptix system mentioned above.
[0134] Very good attenuation is observed between 830 and 940 nm,
but significant bouncing (designated by the arrows) at between 950
and 1050 nm.
[0135] It is not usual to examine the filter behaviour at
wavelengths longer than 900 nm.
[0136] It is effectively generally considered that at these
wavelengths the sensitivity of the detectors (CCD or CMOS sensors)
is low and that the LEDS of the operating room lighting no longer
emit.
[0137] In addition, in conventional florescence applications,
ambient lighting is relatively low-powered which means that the
parasitic light at such wavelengths has little influence on the
signal measured by the detector.
[0138] However, the inventors have ascertained that a detector
still has some sensitivity up 15 to 1000 nm, and even higher.
[0139] FIG. 8A therefore illustrates the sensitivity as a function
of wavelength of a CCD sensor typically used in a fluorescence
imaging device such as the Fluobeam.TM. device.
[0140] FIG. 8B illustrates the quantum efficiency (QE) as a
function of wavelength of a CMOS sensor which could also be used in
the fluorescence imaging device.
[0141] These types of sensors exhibit high sensitivity at visible
wavelengths and lower but still significant sensitivity at
wavelengths corresponding to the near infra-red.
[0142] Although this sensitivity is low, insofar as the lighting
provided by the operating room device is very powerful (possibly
reaching 150 kLux), the parasitic light--resulting from poor
attenuation by the low-pass filter of the overhead surgical light
or headlamp and the band-pass filter of the detector--is
sufficiently strong to produce significant background noise in the
fluorescence signal measured by the sensor.
[0143] On the basis of these considerations, an intuitive approach
would be to improve the filtering of the operating room
illuminating device.
[0144] It can effectively be considered that if it were given
proper use, the filtering would allow all parasitic photons to be
eliminated at the source. The detector would therefore only detect
the fluorescence photons, in particular those corresponding to the
longest wavelengths.
[0145] However, as indicated above, having regard to the surface
area of the operating room illuminating device (in the order of 0.5
m.sup.2 for an overhead surgical light) the cost of an adequate
filter would be prohibitive.
[0146] Also, even if this solution would allow greater photon
detection, these photons are few in number and the sensitivity of
the detector at the corresponding wavelengths is low.
[0147] Finally the adding of an additional filter would risk
modifying the colour rendering index and the colour temperature of
the operating room lighting.
[0148] On the contrary, the inventors have chosen to apply an
additional filter to the detector, despite the loss of photons
detectable by the detector, thereby going against preconceived
opinion according to which an additional filter would lead to
reduced quality of the signal measured by the detector.
[0149] It could effectively be feared that by further filtering the
detector an insufficient number of photons would be detected to
provide images having sufficient contrast.
[0150] The additional filtering of the detector is formed of a
low-pass filter which, above the cut-off wavelength, exhibits very
strong attenuation.
[0151] In other words, the filter F.sub.D of the detector D
comprises a band-pass or high-pass filter F.sub.D1 (cf. FIG. 9c)
combined with a low-pass filter F.sub.D2 (cf. FIG. 9b) which
transmits the wavelengths of the near infra-red to be detected by
the detector and in which, above its upper cut-off wavelength
.lamda..sub.max, the product of the attenuations of the filter of
the operating room illuminating device and of the detector filter
leads to an attenuation by a factor of at least 10.sup.6.
[0152] This condition must preferably be heeded at least up to the
detection limit of the detector D.
[0153] The range of wavelengths concerned by this drastic
attenuation is schematised by the zone Z.sub.D in FIG. 9b, which
simultaneously shows the transmission curves of the filter of the
operating room lighting (FIG. 9a corresponding to FIG. 6 described
above), of an example of an additional low-pass filter F.sub.D2
suitable for the detector (FIG. 9b), and of an example of a
band-pass filter F.sub.D1 of the detector (FIG. 9c, corresponding
to FIG. 7A commented on above).
[0154] Evidently the transmission curves shown here are solely
illustrative, and persons skilled in the art may vary the
characteristics of transmission and cut-off wavelengths in relation
to the specificities of the operating room lighting and of the
imaging device under consideration.
[0155] Regarding the choice of filter for the operating room
illuminating device, care must also be taken to ensure that the
low-pass filter Fe of the overhead surgical light or headlamp does
not transmit any wavelength to be measured by the detector (in
other words the cut-off wavelength .lamda..sub.Bmax of the low-pass
filter F.sub.B is shorter than the lower cut-off wavelength
.lamda..sub.lower of the band-pass filter F.sub.D1 whose band-pass
width BP lies within zone Z.sub.B in FIG. 9a, corresponding to
attenuation of the operating room lighting by a factor of at least
10.sup.6, preferably at least 10.sup.7) and to ensure that the
attenuation peaking or fluctuations of the low-pass filter F of the
overhead surgical light or headlamp only occur at wavelengths above
the band-pass width BP of the detector filter.
[0156] As illustrated in FIGS. 9a and 9b, the peaking of the
low-pass filter Fe of the overhead surgical light or headlamp
starts at a wavelength above the bandwidth BP of the detector but
since it lies above the cut-off frequency .lamda..sub.max, this
peaking is attenuated by the filter F.sub.D2 (zone ZD in FIG.
9b).
[0157] In FIG. 9b it can be seen that the additional filter
F.sub.D2 of the detector shows strong peaking at around 1200 nm;
however this wavelength is longer than the limit detection
wavelength of the detector which means that this peaking has no
incidence on the quality of images.
[0158] It is within the reach of persons skilled in the art to
choose a filter among the filters on the market which have the
required performance level or to have manufactured an adequate
filter by a specialised company on the basis of specifications for
detector filtering.
[0159] The inventors have surprisingly verified that the quality of
the images and the separation between the different structures is
distinctly improved with this additional filtering of the
detector.
[0160] In particular, they observed that this additional filtering
allowed elimination of bias and background noise which masked the
fluorescence photons derived from deep regions, and which are
therefore few in number.
[0161] The detector filtered in this manner is more sensitive to
the fluorescence signal originating from the deep layers and
produces more contrasted images.
[0162] In addition, since the surface area of the detector is much
smaller than that of an overhead surgical light, the use of a high
performance filter to obtain attenuation by a factor of more than
10.sup.6 at longer wavelengths does not penalise the system
financially.
[0163] As a non-limiting illustration, in a first embodiment the
Fluobeam.TM. device marketed by the Applicant has an excitation
wavelength of 780 nm and a bandwidth of the band-pass filter
F.sub.D of between 820 and 850 nm; in a second embodiment, the
excitation wavelength is 750 nm and the bandwidth of the band-pass
filter F.sub.D is between 780 and 870 nm.
[0164] Evidently the numerical values given above are solely
illustrative and those skilled in the art, as a function of the
filters available and the fluorescence wavelengths to be detected,
are able to develop adequate filters for the operating room
lighting and for the detector.
[0165] Experimental Results
[0166] Surgical procedure was performed on the heart of an animal
using the system described above and under the same experimental
conditions, with the exception in the second case that the
additional filtering of the detector described above was added (the
transmission curve of which is given in FIG. 9b).
[0167] FIGS. 10A and 10B are fluorescence images of the heart
recorded after injection of indocyanine green (ICG), with and
without the additional low-pass filter of the detector
respectively.
[0168] It is observed that with the system conforming to the
invention many more deep-lying blood vessels can be seen.
[0169] This result can also be observed in FIG. 11 which gives a
histogram obtained in a region outside the coronaries, without
(curve (a)) and with (curve (b)) the additional low-pass filter of
the detector.
[0170] In this histogram one of the modes corresponds to the
surface of the heart and the other to the deep vessels.
[0171] A comparison between these two curves clearly shows that the
bimodal appearance of the histogram is much stronger in the image
acquired with the additional low-pass filter of the detector than
the image acquired without this filter.
[0172] It therefore follows that the additional filter
substantially increases the contrast of the deep vessels.
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