U.S. patent application number 11/122267 was filed with the patent office on 2006-10-26 for filter for use with imaging endoscopes.
This patent application is currently assigned to Xillix Technologies Corp.. Invention is credited to John J.P. Fengler, Francis Regamey.
Application Number | 20060241496 11/122267 |
Document ID | / |
Family ID | 37307550 |
Filed Date | 2006-10-26 |
United States Patent
Application |
20060241496 |
Kind Code |
A1 |
Fengler; John J.P. ; et
al. |
October 26, 2006 |
Filter for use with imaging endoscopes
Abstract
A fluorescence endoscopy video system includes a multi-mode
light source that produces light for white light and fluorescence
imaging modes. A filter is positioned at the distal end of an
imaging endoscope so that the endoscope can produce fluorescence
and white light images of a tissue sample.
Inventors: |
Fengler; John J.P.; (North
Vancouver, CA) ; Regamey; Francis; (Vancouver,
CA) |
Correspondence
Address: |
CHRISTENSEN, O'CONNOR, JOHNSON, KINDNESS, PLLC
1420 FIFTH AVENUE
SUITE 2800
SEATTLE
WA
98101-2347
US
|
Assignee: |
Xillix Technologies Corp.
Richmond
CA
|
Family ID: |
37307550 |
Appl. No.: |
11/122267 |
Filed: |
May 4, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11009965 |
Dec 10, 2004 |
|
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11122267 |
May 4, 2005 |
|
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|
10050601 |
Jan 15, 2002 |
6899675 |
|
|
11009965 |
Dec 10, 2004 |
|
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Current U.S.
Class: |
600/476 |
Current CPC
Class: |
A61B 1/00045 20130101;
A61B 1/00009 20130101; G02B 23/2423 20130101; A61B 1/043 20130101;
A61B 1/0646 20130101; A61B 1/05 20130101; A61B 1/0661 20130101;
H04N 2005/2255 20130101; A61B 1/00006 20130101; A61B 1/0638
20130101; A61B 1/00186 20130101; A61B 1/00101 20130101; H04N 5/2254
20130101; H04N 5/2256 20130101 |
Class at
Publication: |
600/476 |
International
Class: |
A61B 6/00 20060101
A61B006/00 |
Claims
1. A filter assembly for use with an imaging endoscope, comprising:
a filter adapted to be positioned in front of an imaging lens of
the endoscope, the filter blocking excitation light from reaching
an image sensor of the endoscope so that the image sensor can
produce fluorescence images, the filter also passing an amount of
blue light so that the image sensor can produce white light images
of the tissue.
2. The filter assembly of claim 1, wherein the filter blocks
excitation light having wavelengths in a range of 370 to 450
nm.
3. The filter assembly of claim 2, wherein the filter passes light
having wavelengths in a range of 450-480 nm.
4. The filter assembly of claim 1, further comprising means for
securing the filter to a distal end of the endoscope.
5. The filter assembly of claim 4, wherein the means for securing
the filter includes one or more tabs that are secured to the
endoscope.
6. The filter assembly of claim 4, wherein the means for securing
the filter includes an adhesive.
7. The cap of claim 4, wherein the means for securing the filter
includes a magnet.
8. The cap of claim 1, wherein the means for securing the filter
includes a sleeve that fits over a distal end of the endoscope.
9. A system for producing fluorescence and white light images with
an imaging endoscope that includes an image sensor, comprising: a
removable filter that is placed in front of an imaging lens of the
endoscope that filters excitation light from reaching the image
sensor and passes an amount of blue light; an image processor that
produces images from image signals received from the image sensor;
a light source for producing excitation light for use in a
fluorescence imaging mode and illumination light for use in a white
light imaging mode, wherein the illumination light produced by the
light source compensates for the effects of the filter so that the
images produced from the image sensor can be white balanced.
10. The system of claim 9, wherein the illumination light produced
by the light source has an increased amount of blue light in a
wavelength band that passes through the filter compared with an
amount of red and green light in the illumination light.
11. The system of claim 9, wherein the illumination light produced
by the light source has a decreased amount of green and red light
so that that the red, green and blue light received at the image
sensor have substantially equal magnitudes.
12. The system of claim 9, wherein the light source produces an
amount of reflectance light when operating in a fluorescence
imaging mode.
13. The system of claim 12, wherein the reflectance light is red
light.
14. The system of claim 12, wherein the reflectance light is green
light.
15. The system of claim 12, wherein the reflectance light is blue
light having wavelengths that pass through the filter.
16. The system of claim 9, wherein the image sensor is a color
image sensor and the illumination light includes red, green and
blue spectral components.
17. The system of claim 9, wherein the image sensor is a monochrome
sensor and the illumination light includes sequentially produced
red, green and blue spectral components.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 11/009,965, filed Dec. 10, 2004, which is a
continuation of U.S. patent application Ser. No. 10/050,601, filed
Jan. 15, 2002, the benefit of the filing dates of which are being
claimed under 35 U.S.C. .sctn. 120.
FIELD OF THE INVENTION
[0002] The present invention relates to medical imaging systems in
general, and in particular to fluorescence endoscopy video
systems.
BACKGROUND OF THE INVENTION
[0003] Fluorescence endoscopy utilizes differences in the
fluorescence response of normal tissue and tissue suspicious for
early cancer as a tool in the detection and localization of such
cancer. The fluorescing compounds or fluorophores that are excited
during fluorescence endoscopy may be exogenously applied
photo-active drugs that accumulate preferentially in suspicious
tissues, or they may be the endogenous fluorophores that are
present in all tissue. In the latter case, the fluorescence from
the tissue is typically referred to as autofluorescence or native
fluorescence. Tissue autofluorescence is typically due to
fluorophores with absorption bands in the UV and blue portion of
the visible spectrum and emission bands in the green to red
portions of the visible spectrum. In tissue suspicious for early
cancer, the green portion of the autofluorescence spectrum is
significantly suppressed. Fluorescence endoscopy that is based on
tissue autofluorescence utilizes this spectral difference to
distinguish normal from suspicious tissue.
[0004] Since the concentration and/or quantum efficiency of the
endogenous fluorophores in tissue is relatively low, the
fluorescence emitted by these fluorophores is not typically visible
to the naked eye. Fluorescence endoscopy is consequently performed
by employing low light image sensors to acquire images of the
fluorescing tissue through the endoscope. The images acquired by
these sensors are most often encoded as video signals and displayed
on a color video monitor. Representative fluorescence endoscopy
video systems that image tissue autofluorescence are disclosed in
U.S. Pat. No. 5,507,287, issued to Palcic et al.; U.S. Pat. No.
5,590,660, issued to MacAulay et al.; U.S. Pat. No. 5,827,190,
issued to Palcic et al., U.S. patent application Ser. No.
09/615,965, and U.S. patent application Ser. No. 09/905,642, all of
which are herein incorporated by reference. Each of these is
assigned to Xillix Technologies Corp. of Richmond, British
Columbia, Canada, the assignee of the present application.
[0005] While the systems disclosed in the above-referenced patents
are significant advances in the field of early cancer detection,
improvements can be made. In particular, it is desirable to reduce
the size, cost, weight, and complexity of the camera.
SUMMARY OF THE INVENTION
[0006] A fluorescence endoscopy video system in accordance with the
present invention includes an endoscopic light source that is
capable of operating in multiple modes to produce either white
light, reflectance light, fluorescence excitation light, or
fluorescence excitation light with reference reflectance light. An
endoscope incorporates a light guide for transmitting light to the
tissue under observation and includes either an imaging guide or a
compact camera disposed in the insertion portion of the endoscope
for receiving light from the tissue under observation. A compact
camera includes at least one low light imaging sensor that receives
light from the tissue and is capable of operating in multiple
imaging modes to acquire color or multi-channel fluorescence and
reflectance images. The system further includes an image processor
and system controller that digitizes, processes and encodes the
image signals produced by the image sensor(s) as a color video
signal and a color video monitor that displays the processed video
images.
[0007] In one embodiment of the invention, a filter is placed at
the distal end of the endoscope in order to produce both
autofluorescence and white light images from an image sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The foregoing aspects and many of the attendant advantages
of this invention will become more readily appreciated as the same
become better understood by reference to the following detailed
description, when taken in conjunction with the accompanying
drawings, wherein:
[0009] FIGS. 1A-1B are block diagrams of a fluorescence endoscopy
video system according to one embodiment of the present
invention;
[0010] FIGS. 2A-2B are block diagrams of a multi-mode light source
in accordance with different embodiments of the present
invention;
[0011] FIG. 3 shows a filter wheel and optical filters for the
multi-mode light source;
[0012] FIGS. 4A-4C illustrate a number of alternative embodiments
of a camera that can acquire color and/or fluorescence/reflectance
images according to one embodiment of the present invention with
optional placement for collimation and imaging optics;
[0013] FIGS. 5A-5C illustrate a number of camera beamsplitter
configurations;
[0014] FIGS. 6A-6E are graphs illustrating presently preferred
transmission characteristics of filters utilized for color imaging
and fluorescence/reflectance imaging with the camera embodiments
shown in FIGS. 4A-4C;
[0015] FIGS. 7A-7B illustrate additional embodiments of a camera
according to the present invention that can acquire color,
fluorescence/reflectance, and/or fluorescence/fluorescence images
according to an embodiment of the present invention with optional
placement for collimation and imaging optics;
[0016] FIGS. 8A-8F are graphs illustrating presently preferred
transmission characteristics of filters for color imaging,
fluorescence/fluorescence imaging, and fluorescence/reflectance
imaging with the camera embodiment shown in FIGS. 7A-7B;
[0017] FIG. 9 illustrates a distal end filter in accordance with
another embodiment of the present invention that allows a
conventional endoscope to perform both fluorescence and white light
imaging;
[0018] FIGS. 10A and 10B illustrate how the distal end filter
allows the endoscope to perform fluorescence and white light
imaging in accordance with one embodiment of the present invention;
and
[0019] FIG. 11 illustrates one embodiment of a distal end filter
that can be secured to a conventional endoscope in accordance with
the present invention.
DETAILED DESCRIPTION
[0020] FIG. 1A is a block diagram of a fluorescence endoscopy video
system 50 in accordance with one embodiment of the present
invention. The system includes a multi-mode light source 52 that
generates light for obtaining color and fluorescence images. The
use of the light source for obtaining different kinds of images
will be described in further detail below. Light from the light
source 52 is supplied to an illumination guide 54 of an endoscope
60, which then illuminates a tissue sample 58 that is to be
imaged.
[0021] As shown in FIG. 1A, the system also includes a multi-mode
camera 100, which is located at the insertion end of the endoscope
60. The light from the tissue is directly captured by the
multi-mode camera 100. With the multi-mode camera 100 located at
the insertion end of the endoscope, the resulting endoscope 60 can
be characterized as a fluorescence video endoscope, similar to
video endoscopes currently on the market (such as the Olympus
CF-240L) in utility, but with the ability to be utilized for
fluorescence/reflectance and/or fluorescence/fluorescence imaging,
in additional to conventional color imaging.
Fluorescence/reflectance and fluorescence/fluorescence imaging will
be described in detail below. By locating the camera at the
insertion end of the endoscope, the inherent advantages of a video
endoscope can be obtained: namely, the light available to form an
image and the image resolution are improved compared to the case
when the image is transmitted outside the body through an endoscope
imaging guide or relay lens system.
[0022] A processor/controller 64 controls the multi-mode camera 100
and the light source 52, and produces video signals that are
displayed on a video monitor 66. The processor/controller 64
communicates with the multi-mode camera 100 with wires or other
signal carrying devices that are routed within the endoscope.
Alternatively, communication between the processor/controller 64
and the camera 100 can be conducted over a wireless link.
[0023] FIG. 1B is a block diagram of an alternative fluorescence
endoscopy video system 50, which differs from that shown in FIG. 1A
in that endoscope 60 also incorporates an image guide 56 and the
multi-mode camera 100 is attached to an external portion of the
endoscope that is outside the body. The light that is collected
from the tissue by endoscope 60 is transmitted through the image
guide 56 and projected into the multi-mode camera 100. Other than
the addition of the image guide 56 to endoscope 100 and the
location of the multi-mode camera 100 at the external end of the
endoscope, the system of FIG. 1B is identical to that shown in FIG.
1A.
[0024] FIG. 2A shows the components of the light source 52 in
greater detail. The light source 52 includes an arc lamp 70 that is
surrounded by a reflector 72. In the preferred embodiment of the
invention, the arc lamp 70 is a high pressure mercury arc lamp
(such as the Osram VIP R 150/P24). Alternatively, other arc lamps,
solid state devices (such as light emitting diodes or diode
lasers), or broadband light sources may be used, but a high
pressure mercury lamp is currently preferred for its combination of
high blue light output, reasonably flat white light-spectrum, and
small arc size.
[0025] The light from the arc lamp 70 is coupled to a light guide
54 of the endoscope 60 through appropriate optics 74, 76, and 78
for light collection, spectral filtering and focusing respectively.
The light from the arc lamp is spectrally filtered by one of a
number of optical filters 76A, 76B, 76C . . . that operate to pass
or reject desired wavelengths of light in accordance with the
operating mode of the system. As used herein, "wavelength" is to be
interpreted broadly to include not only a single wavelength, but a
range of wavelengths as well.
[0026] An intensity control 80 that adjusts the amount of light
transmitted along the light path is positioned at an appropriate
location between the arc lamp 70 and the endoscope light guide 54.
The intensity control 80 adjusts the amount of light that is
coupled to the light guide 54. In addition, a shutter mechanism 82
may be positioned in the same optical path in order to block any of
the light from the lamp from reaching the light guide. A controller
86 operates an actuator 77 that moves the filters 76A, 76B or 76C
into and out of the light path. The controller 86 also controls the
position of the intensity control 80 and the operation of the
shutter mechanism 82.
[0027] The transmission characteristics of filters 76A, 76B, 76C, .
. . , the characteristics of the actuator 77 mechanism, and the
time available for motion of the filters 76A, 76B, 76C, . . . ,
into and out of the light path, depend on the mode of operation
required for use with the various camera embodiments. The
requirements fall into two classes. If the light source shown in
FIG. 2A is of the class wherein only one filter is utilized per
imaging mode, the appropriate filter is moved in or out of the
light path only when the imaging mode is changed. In that case, the
actuator 77 only need change the filter in a time of approximately
1.0 second. The optical filter characteristics of filters 76A, 76B
. . . are tailored for each imaging mode. For example, optical
filter 76A, used for color imaging, reduces any spectral peaks and
modifies the color temperature of the arc lamp 70 so that the
output spectrum simulates sunlight. Optical filter 76B transmits
only fluorescence excitation light for use with the
fluorescence/fluorescence imaging mode and optical filter 76C
transmits both fluorescence excitation light and reference
reflectance light for use with the fluorescence/reflectance imaging
mode.
[0028] A light source 52A of a second class is illustrated in FIG.
2B; only the differences from the light source shown in FIG. 2A
will be elucidated. The light source 52A uses multiple filters
during each imaging mode. For example, light source filters, which
provide red, green, and blue illumination sequentially for periods
corresponding to a video frame or field, can be used for the
acquisition of a color or a multi-spectral image with a monochrome
image sensor, with the different wavelength components of the image
each acquired at slightly different times. Such rapid filter
changing requires a considerably different actuator than
necessitated for the light source 52 of FIG. 2A. As shown in FIG.
2B, the filters are mounted on a filter wheel 79 that is rotated by
a motor, which is synchronized to the video field or frame rate.
The layout of the blue, red and green filters, 79A, 79B, and 79C
respectively, in filter wheel 79 are shown in FIG. 3.
[0029] The transmission characteristics of light source filters,
the characteristics of the filter actuator mechanism, and the time
available for motion of the filters into and out of the light path,
for the two different classes of light sources are described in
more detail below in the context of the various camera
embodiments.
[0030] Because fluorescence endoscopy is generally used in
conjunction with white light endoscopy, each of the various
embodiments of the multi-mode camera 100 described below may be
used both for color and fluorescence/reflectance and/or
fluorescence/fluorescence imaging. These camera embodiments
particularly lend themselves to incorporation within a fluorescence
video endoscope due to their compactness and their ability to be
implemented with no moving parts.
[0031] In a first embodiment, shown in FIG. 4A, a camera 100A
receives light from the tissue 58, either directly from the tissue
in the case of a camera located at the insertion end of an
endoscope, as shown in FIG. 1A, or by virtue of an endoscope image
guide 56, which transmits the light from the tissue to the camera,
as shown in FIG. 1B. The light is directed towards a monochrome
image sensor 102 and a low light image sensor 104 by a fixed
optical beamsplitter 106 that splits the incoming light into two
beams. The light beam is split such that a smaller proportion of
the light received from the tissue 58 is directed towards the
monochrome image sensor 102 and a larger proportion of the incoming
light is directed towards the low light image sensor 104. In this
embodiment, the beamsplitter may be a standard commercially
available single plate 88, single cube 89, or single pellicle
design 90, as shown in FIGS. 5A-5C. It should be noted that, if the
optical path between the tissue 58 and the image sensors contains
an uneven number of reflections (e.g., such as from a single
component beamsplitter), the image projected onto the sensor will
be left-to-right inverted. The orientation of such images will need
to be corrected by image processing.
[0032] In FIG. 4A, light collimating optics 110 are positioned in
front of the beamsplitter 106, and imaging optics 112 and 114 are
positioned immediately preceding the monochrome image sensor 102
and the low light image sensor 104, respectively. A spectral filter
118 is located in the optical path between the beamsplitter 106 and
the low light image sensor 104. Alternatively, the spectral filter
118 may be incorporated as an element of the beamsplitter 106.
[0033] FIG. 4B illustrates another embodiment of the camera 100. A
camera 100B is the same as the camera 100A described above except
that the light collimating optics 110 and imaging optics 112 and
114 have been eliminated and replaced with a single set of imaging
optics 113 located between the tissue and beamsplitter 106. The
advantage of this configuration is that all imaging is performed
and controlled by the same imaging optics 113. Such a configuration
requires all beam paths to have the same optical path length,
however, and this restriction must be considered in the design of
the beamsplitter 106 and spectral filter 118 that is located in the
path to the low light image sensor 104. In addition, the fact that
these optical elements are located in a converging beam path must
be considered in specifying these elements and in the design of the
imaging optics 113.
[0034] The low light image sensor 104 preferably comprises a charge
coupled device with charge carrier multiplication (of the same type
as the Texas Instruments TC253 or the Marconi Technologies CCD65),
electron beam charge coupled device (EBCCD), intensified charge
coupled device (ICCD), charge injection device (CID), charge
modulation device (CMD), complementary metal oxide semiconductor
image sensor (CMOS) or charge coupled device (CCD) type sensor. The
monochrome image sensor 102 is preferably a CCD or a CMOS image
sensor.
[0035] An alternative configuration of the camera 100B is shown in
FIG. 4C. All aspects of this embodiment of this camera 100C are
similar to the camera 100B shown in FIG. 4B except for differences
which arise from reducing the width of the camera by mounting both
image sensors 102 and 104 perpendicular to the camera front
surface. In this alternative configuration, the low light image
sensor 104 and the monochrome image sensor 102 are mounted with
their image planes perpendicular to the input image plane of the
camera. Light received from the tissue 58 is projected by imaging
optics 113 through beamsplitter 106 onto the image sensors 102 and
104. The beamsplitter 106 directs a portion of the incoming light
in one beam towards one of the sensors 102, 104. Another portion of
the incoming light in a second light beam passes straight through
the beamsplitter 106 and is directed by a mirror 108 towards the
other of the sensors 102, 104. In addition, a second set of imaging
optics 115 is utilized to account for the longer optical path to
this second sensor. The images projected onto both sensors will be
left-to-right inverted and should be inverted by image
processing.
[0036] The processor/controller 64 as shown in FIGS. 1A and 1B
receives the transduced image signals from the camera 100 and
digitizes and processes these signals. The processed signals are
then encoded in a video format and displayed on a color video
monitor 66.
[0037] Based on operator input, the processor/controller 64 also
provides control functions for the fluorescence endoscopy video
system. These control functions include providing control signals
that control the camera gain in all imaging modes, coordinating the
imaging modes of the camera and light source, and providing a light
level control signal for the light source.
[0038] The reason that two separate images in different wavelength
bands are acquired in fluorescence imaging modes of the
fluorescence endoscopy video systems described herein, and the
nature of the fluorescence/reflectance and
fluorescence/fluorescence imaging, will now be explained. It is
known that the intensity of the autofluorescence at certain
wavelengths changes as tissues become increasingly abnormal (i.e.
as they progress from normal to frank cancer). When visualizing
images formed from such a band of wavelengths of autofluorescence,
however, it is not easy to distinguish between those changes in the
signal strength that are due to pathology and those that are due to
imaging geometry and shadows. A second fluorescence image acquired
in a band of wavelengths in which the image signal is not
significantly affected by tissue pathology, utilized for
fluorescence/fluorescence imaging, or a reflected light image
acquired in a band of wavelengths in which the image signal is not
significantly affected by tissue pathology consisting of light that
has undergone scattering within the tissue (known as diffuse
reflectance), utilized for fluorescence/reflectance imaging, may be
used as a reference signal with which the signal strength of the
first fluorescence image can be "normalized." Such normalization is
described in two patents previously incorporated herein by
reference: U.S. Pat. No. 5,507,287, issued to Palcic et al.
describes fluorescence/fluorescence imaging and U.S. Pat. No.
5,590,660, issued to MacAulay et al. describes
fluorescence/reflectance imaging.
[0039] One technique for performing the normalization is to assign
each of the two image signals a different display color, e.g., by
supplying the image signals to different color inputs of a color
video monitor. When displayed on a color video monitor, the two
images are effectively combined to form a single image, the
combined color of which represents the relative strengths of the
signals from the two images. Since light originating from
fluorescence within tissue and diffuse reflectance light which has
undergone scattering within the tissue are both emitted from the
tissue with a similar spatial distribution of intensities, the
color of a combined image is independent of the absolute strength
of the separate image signals, and will not change as a result of
changes in the distance or angle of the endoscope 60 to the tissue
sample 58, or changes in other imaging geometry factors. If,
however, there is a change in the shape of the autofluorescence
spectrum of the observed tissue that gives rise to a change in the
relative strength of the two image signals, such a change will be
represented as a change in the color of the displayed image.
Another technique for performing the normalization is to calculate
the ratio of the pixel intensities at each location in the two
images. A new image can then be created wherein each pixel has an
intensity and color related to the ratio computed. The new image
can then be displayed by supplying it to a color video monitor.
[0040] The mixture of colors with which normal tissue and tissue
suspicious for early cancer are displayed depends on the gain
applied to each of the two separate image signals. There is an
optimal gain ratio for which tissue suspicious for early cancer in
a fluorescence image will appear as a distinctly different color
than normal tissue. This gain ratio is said to provide the operator
with the best combination of sensitivity (ability to detect suspect
tissue) and specificity (ability to discriminate correctly). If the
gain applied to the reference image signal is too high compared to
the gain applied to the fluorescence image signal, the number of
tissue areas that appear suspicious, but whose pathology turns out
to be normal, increases. Conversely, if the relative gain applied
to the reference image signal is too low, sensitivity decreases and
suspect tissue will appear like normal tissue. For optimal system
performance, therefore, the ratio of the gains applied to the image
signals must be maintained at all times. The control of the gain
ratio is described in two patent applications previously
incorporated herein by reference: U.S. patent application Ser. No.
09/615,965, and U.S. patent application Ser. No. 09/905,642.
[0041] In vivo spectroscopy has been used to determine which
differences in tissue autofluorescence and reflectance spectra have
a pathological basis. The properties of these spectra determine the
particular wavelength bands of autofluorescence and reflected light
required for the fluorescence/reflectance imaging mode, or the
particular two wavelength bands of autofluorescence required for
fluorescence/fluorescence imaging mode. Since the properties of the
spectra depend on the tissue type, the wavelengths of the important
autofluorescence band(s) may depend on the type of tissue being
imaged. The specifications of the optical filters described below
are a consequence of these spectral characteristics, and are chosen
to be optimal for the tissues to be imaged.
[0042] As indicated above, the filters in the light source and
camera should be optimized for the imaging mode of the camera, the
type of tissue to be examined and/or the type of pre-cancerous
tissue to be detected. Although all of the filters described below
can be made to order using standard, commercially available
components, the appropriate wavelength range of transmission and
degree of blocking outside of the desired transmission range for
the described fluorescence endoscopy images are important to the
proper operation of the system. The importance of other issues in
the specification of such filters, such as the fluorescence
properties of the filter materials and the proper use of
anti-reflection coatings, are taken to be understood.
[0043] FIGS. 6A-6E illustrate the preferred filter characteristics
for use in a fluorescence endoscopy system having a camera of the
type shown in FIGS. 4A-4C and light source as shown in FIG. 2B,
that operates in a fluorescence/reflectance imaging mode, or a
color imaging mode. There are several possible configurations of
fluorescence endoscopy video systems, operating in the
fluorescence/reflectance imaging mode including green fluorescence
with either red or blue reflectance, and red fluorescence with
either green or blue reflectance. The particular configuration
utilized depends on the target clinical organ and application. The
filter characteristics will now be described for each of these four
configurations.
[0044] FIG. 6A illustrates the composition of the light transmitted
by a blue filter, such as filter 79A, which is used to produce
excitation light in the system light source. This filter transmits
light in the wavelength range from 370-460 nm or any subset of
wavelengths in this range. Of the light transmitted by this filter,
less than 0.001% is in the fluorescence imaging band from 480-750
nm (or whatever desired subsets of this range is within the
specified transmission range of the primary and reference
fluorescence image filters described below).
[0045] FIG. 6B illustrates the composition of the light transmitted
by a red filter, such as filter 79B, which is used to produce red
reflectance light in the system light source. This filter transmits
light in the wavelength range from 590-750 nm or any subset of
wavelengths in this range. Light transmitted outside this range
should not exceed 1%.
[0046] FIG. 6C illustrates the composition of the light transmitted
by a green filter, such as filter 79C, which is used to produce
green reflectance light in the system light source. This filter
transmits light in the wavelength range from 480-570 nm or any
subset of wavelengths in this range. Light transmitted outside this
range should not exceed 1%.
[0047] FIG. 6D shows the composition of the light transmitted by a
camera spectral filter, such as filter 118, for defining the
primary fluorescence image in the green spectral band. In this
configuration, the filter blocks excitation light and red
fluorescence light while transmitting green fluorescence light in
the wavelength range of 480-570 nm or any subset of wavelengths in
this range. When used in a fluorescence endoscopy video system with
the light source filter 79A described above, the filter
characteristics are such that any light outside of the wavelength
range of 480-570 nm, or any desired subset of wavelengths in this
range, contributes no more than 0.1% to the light transmitted by
the filter.
[0048] FIG. 6E shows the composition of the light transmitted by a
camera filter, such as filter 118, for defining the primary
fluorescence image in the red spectral band. In this configuration,
the filter blocks excitation light and green fluorescence light
while transmitting red fluorescence light in the wavelength range
of 590-750 nm or any subset of wavelengths in this range. When used
in a fluorescence endoscopy video system with the light source
filter 79A described above, the filter characteristics are such
that any light outside of the wavelength range of 590-750 nm, or
any desired subset of wavelengths in this range, contributes no
more than 0.1% to the light transmitted by the filter.
[0049] The operation of the preferred embodiment of the
fluorescence endoscopy video system will now be described. The
cameras 100A as shown in FIGS. 4A and 100B as shown in FIG. 4B or
100C as shown in FIG. 4C are capable of operating in color and
fluorescence/reflectance imaging modes. A light source of the type
shown in FIG. 2B, that provides a different output every video
frame or field is required. In the color imaging mode, the
processor/controller 64 provides a control signal to the multi-mode
light source 52 that indicates the light source should be operating
in the white light mode and provides a synchronizing signal. The
light source 52 sequentially outputs filtered red, green, and blue
light, synchronously with the video field or frame of the image
sensors 102 and 104. The filtered light from the light source 52 is
projected into the endoscope light guide 54 and is transmitted to
the tip of the endoscope 60 to illuminate the tissue 58.
[0050] The processor/controller 64 also protects the sensitive low
light image sensor 104 during color imaging by decreasing the gain
of the amplification stage of the sensor. The light reflected by
the tissue 58 is collected and transmitted by the endoscope image
guide 56 to the camera where it is projected through beamsplitter
106 onto the monochrome image sensor 102, or the light is directly
projected through the camera beamsplitter 106 onto the monochrome
image sensor 102 if the sensor is located within the insertion
portion of the endoscope. The image projected during each of red,
green, blue illuminations is transduced by the monochrome image
sensor 102 and the resulting image signals are transmitted to the
processor/controller 64.
[0051] Based on the brightness of the images captured, the
processor/controller 64 provides a control signal to the multi-mode
light source 52 to adjust the intensity control 80 and thereby
adjust the level of light output by the endoscope light guide 54.
The processor/controller 64 may also send a control signal to the
camera 100A, 100B or 100C to adjust the gain of the monochrome
image sensor 102.
[0052] The processor/controller 64 interpolates the images acquired
during sequential periods of red, green, and blue illumination to
create a complete color image during all time periods, and encodes
that color image as video signals. The video signals are connected
to color video monitor 66 for display of the color image. All of
the imaging operations occur at analog video display rates (30
frames per second for NTSC format and 25 frames per second for PAL
format).
[0053] When switching to the fluorescence/reflectance imaging mode,
the processor/controller 64 provides a control signal to the
multi-mode light source 52 to indicate that it should be operating
in fluorescence/reflectance mode. In response to this signal, the
light source filter wheel 79 stops rotating and the light source 52
selects and positions the appropriate blue optical filter 79A
continuously into the optical path between the arc lamp 70 and the
endoscope light guide 54. This change from sequentially changing
filters to a static filter occurs in a period of approximately one
second. Filter 79A transmits only those wavelengths of light that
will induce the tissue 58 under examination to fluoresce. All other
wavelengths of light are substantially blocked as described above.
The filtered light is then projected into the endoscope light guide
54 and transmitted to the tip of the endoscope 60 to illuminate the
tissue 58.
[0054] As part of setting the system in the
fluorescence/reflectance mode, the processor/controller 64 also
increases the gain of the amplification stage of the low light
image sensor 104. The fluorescence emitted and excitation light
reflected by the tissue 58 are either collected by the endoscope
image guide 56 and projected through the camera beamsplitter 106
onto the low light image sensor 104 and the image sensor 102, or
are collected and directly projected through the camera
beamsplitter 106 onto the low light image sensor 104 and the image
sensor 102 at the insertion tip of the endoscope 60. Spectral
filter 118 limits the light transmitted to the low light image
sensor 104 to either green or red autofluorescence light only and
substantially blocks the light in the excitation wavelength band.
The autofluorescence image is transduced by the low light image
sensor 104. The reference reflected excitation light image is
transduced by the monochrome image sensor 102 and the resulting
image signals are transmitted to the processor/controller 64.
[0055] Based on the brightness of the transduced images, the
processor/controller 64 may provide a control signal to the
multi-mode light source 52 to adjust the intensity control 80 and
thereby adjust the level of light delivered to the endoscope 60.
The processor/controller 64 may also send control signals to the
cameras 100A, 100B or 100C to adjust the gains of the low light
image sensor 104 and the monochrome image sensor 102, in order to
maintain constant image brightness while keeping the relative gain
constant.
[0056] After being processed, the images from the two sensors are
encoded as video signals by processor/controller 64. The
fluorescence/reflectance image is displayed by applying the video
signals to different color inputs on the color video monitor
66.
[0057] In order for the combined image to have optimal clinical
meaning, for a given proportion of fluorescence to reference light
signals emitted by the tissue and received by the system, a
consistent proportion must also exist between the processed image
signals that are displayed on the video monitor. This implies that
the (light) signal response of the fluorescence endoscopy video
system is calibrated. One suitable calibration technique is
described in two patent applications previously incorporated herein
by reference: U.S. patent application Ser. No. 09/615,965, and U.S.
patent application Ser. No. 09/905,642.
[0058] The cameras 100A, 100B, 100C can be operated in a variation
of the fluorescence/reflectance mode to simultaneously obtain
fluorescence images and reflectance images with red, green, and
blue illumination. The operation of the system is similar to that
described previously for color imaging, so only the points of
difference from the color imaging mode will be described.
[0059] In this variation of the fluorescence/reflectance mode,
instead of changing from sequential red, green, and blue
illumination to static blue illumination when switching from color
imaging to fluorescence/reflectance imaging, the multi-mode light
source 52 provides the same sequential illumination utilized in the
color imaging mode, for all imaging modes. Capture and display of
the light reflected by the tissue is similar to that described
previously for the color imaging mode. However, in addition to the
reflectance images captured in that mode, the gain of the
amplification stage of the low light image sensor 104 is adjusted
to a value that makes it possible to capture autofluorescence
images during blue illumination. During red and green illumination,
the gain of amplification stage of the low light sensor is
decreased to protect the sensor while the image sensor 102 captures
reflectance images.
[0060] In this modified fluorescence/reflectance mode, the camera
captures both reflectance and fluorescence images during the blue
illumination period, in addition to reflected light images during
the red and green illumination periods. As for the color imaging
mode, the reflectance images are interpolated and displayed on the
corresponding red, green and blue channels of a color video monitor
to produce a color image. Like the previously described
fluorescence/reflectance mode, a fluorescence/reflectance image is
produced by overlaying the fluorescence image and one or more of
the reflectance images displayed in different colors on a color
video monitor.
[0061] Since individual reflectance and fluorescence images are
concurrently captured, both a color image and a
fluorescence/reflectance image can be displayed simultaneously on
the color video monitor. In this case, there is no need to utilize
a separate color imaging mode. Alternatively, as described for the
previous version of fluorescence/reflectance operation, only the
fluorescence/reflectance image may be displayed during
fluorescence/reflectance imaging and a color image displayed solely
in the color imaging mode.
[0062] Yet another embodiment of this invention will now be
described. All points of similarity with the first embodiment will
be assumed understood and only points that differ will be
described.
[0063] In this second embodiment, all aspects of the fluorescence
endoscopy video system are similar to those of the first embodiment
except for the camera and the light source. A camera 100D for this
embodiment of a system is as shown in FIG. 7A. It differs from the
cameras 100A, 100B or 100C as described above in that all imaging
modes utilize a single, low light color image sensor 103
(preferably a color CCD with charge carrier multiplication such as
the Texas Instruments TC252) and that no beamsplitter is required.
Alternatively, the color image sensor 103 may be a three-CCD with
charge carrier multiplication color image sensor assembly, a color
CCD, a three-CCD color image sensor assembly, a color CMOS image
sensor, or a three-CMOS color image sensor assembly.
[0064] Each of the pixel elements on the low light color sensor 103
is covered by an integrated filter, typically red, green or blue.
These filters define the wavelength bands of fluorescence and
reflectance light that reach the individual pixel elements. Such
mosaic filters typically have considerable overlap between the red,
green, and blue passbands, which can lead to considerable crosstalk
when imaging dim autofluorescence light in the presence of intense
reflected excitation light. Therefore, a separate filter 118 is
provided to reduce the intensity of reflected excitation light to
the same level as that of the autofluorescence light and, at the
same time, pass autofluorescence light.
[0065] In this embodiment, the primary fluorescence and reference
images are projected onto the same image sensor 103, but, because
of the individual filters placed over each pixel, these different
images are detected by separate sensor pixels. As a result,
individual primary fluorescence and reference image signals can be
produced by processor/controller 64 from the single CCD image
signal.
[0066] In FIG. 7A, light collimating optics 110 is positioned
between the tissue 58 and filter 118 and imaging optics 112 is
positioned immediately preceding the color image sensor 103. In an
alternative optical configuration, camera 100E, as shown in FIG.
7B, eliminates the collimating optics 110 and imaging optics 112
and replaces them with a single imaging optics 113 located between
the tissue 58 and filter 118. The advantage of this configuration
is that all imaging is performed and controlled by the same imaging
optics 113. The fact that filter 118 is located in a converging
beam path must be considered in specifying that element and in the
design of the imaging optics.
[0067] The operation of a system based on camera 100D of FIG. 7A or
100E of FIG. 7B will now be described. The cameras 100D and 100E
are capable of operation in the color, fluorescence/fluorescence,
and fluorescence/reflectance imaging modes. For a system based on
camera 100D or 100E, a light source of the type shown in FIG. 2A,
provides steady state output in each imaging mode. As described
below, the light transmission specifications of the light source
filters 76A, 76B, and 76C, the filter 118, and the mosaic color
filters integrated with the image sensor 103 are selected such that
the intensity of the reflected light and fluorescence light at the
color image sensor's active elements results in transduced image
signals with good signal-to-noise characteristics and without
significant saturation. At the same time these filters have
appropriate light transmission specifications for excitation and
imaging of the primary fluorescence and for color imaging. The
filter transmission characteristics are chosen to provide the
desired ratio of relative primary fluorescence to reference light
intensity at the image sensor.
[0068] In the color imaging mode, the processor/controller 64
provides a control signal to the multimode light source 52 that it
should be in white light mode. The light source selects and
positions the appropriate optical filter 76A into the optical path
between the arc lamp 70 and endoscope light guide 54. Given the
presence of filter 118 in cameras 100D, 100E which have reduced
transmission for excitation light at blue wavelengths, the light
source filter 76A should incorporate reduced transmission at red
and green wavelengths to obtain a balanced color image at image
sensor 103 with the proper proportions of red, green, and blue
components.
[0069] Image signals from the color low light sensor 103 are
processed by processor/controller 64. Standard techniques are
utilized to produce a color image from a single color sensor: the
image signals from pixels having the same filter characteristics
are interpolated by processor/controller 64 to produce an image
signal, related to the pass band of each element of the mosaic
filter (e.g., red, green, and blue), at every pixel location. The
resulting multiple images, which when combined produce a color
image, are encoded by processor/controller 64 as video signals. The
color image is displayed by connecting the video signals to the
appropriate inputs of color video monitor 66.
[0070] Processor/controller 64 also maintains the overall image
brightness at a set level by monitoring the brightness of the image
signal at each pixel and adjusting the intensity of the light
source output and camera amplifier gains according to a programmed
algorithm.
[0071] When switching to the fluorescence/fluorescence imaging
mode, processor/controller 64 provides a control signal to the
multi-mode light source 52 to indicate that it should be in
fluorescence/fluorescence mode. The light source 52 moves light
source filter 76B into position in the light beam. Filter 76B
transmits excitation light and blocks the transmission of light at
the green and red fluorescence detection wavelengths, as described
below. The characteristics of light source fluorescence excitation
filter 76B and excitation filter 118, along with the mosaic filter
elements on the color sensor 103, are such that the intensity of
blue light at the color sensor is less than the intensities of red
and green autofluorescence at the sensor, and are such that the
ratio of the intensity of red autofluorescence to the intensity of
green autofluorescence at the color sensor 103 has the appropriate
value for optimal differentiation between normal and abnormal
tissue. The fluorescence images are processed, as previously
described for color imaging, by processor/controller 64 to produce
separate images corresponding to each of the pass bands of the
mosaic filter (e.g., red, green, and blue). These separate images
are encoded as video signals by processor/controller 64. A
composite fluorescence/fluorescence image is displayed on the color
video monitor 66 by applying the video signals from red and green
pass bands of the mosaic filter to different color inputs of the
monitor.
[0072] When switching to the fluorescence/reflectance imaging mode,
processor/controller 64 provides a control signal to the multi-mode
light source 52 to indicate that it should be in
fluorescence/reflectance mode. The light source 52 moves light
source filter 76C into position in the light beam. Filter 76C
transmits both excitation light and reference light and blocks the
transmission of light at fluorescence detection wavelengths, as
described below. The characteristics of the light source filter 76C
for fluorescence excitation and the reflectance illumination and
the camera filter 118, along with the mosaic filter on the color
sensor 103, as detailed below, are such that the intensity of
reflected excitation light at the color sensor is comparable to the
intensity of autofluorescence at the sensor, and should be such
that the ratio of the intensity of autofluorescence to the
intensity of reflected reference light at the color sensor 103 has
the appropriate value. The fluorescence and reflectance images are
processed, as previously described for color imaging, by
processor/controller 64 to produce separate images corresponding to
each of the pass bands of the mosaic filter (e.g., red, green, and
blue). These separate images are encoded as video signals by
processor/controller 64. A composite fluorescence/reflectance image
is displayed on color video monitor 66 by applying the video
signals from the appropriate mosaic filter pass bands (as discussed
below) to different color inputs of the monitor.
[0073] As indicated above, the filters in the light source and
camera should be optimized for the imaging mode of the camera, the
type of tissue to be examined and/or the type of pre-cancerous
tissue to be detected. Although all of the filters described below
can be made to order using standard, commercially available
components, the appropriate wavelength range of transmission and
degree of blocking outside of the desired transmission range for
the described fluorescence endoscopy images modes are important to
the proper operation of the system. The importance of other issues
in the specification of such filters such as the fluorescence
properties of the filter materials and the proper use of
anti-reflection coatings are taken to be understood.
[0074] As discussed above, the filters in the light source and
camera should be optimized for the imaging mode of the camera, the
type of tissue to be examined and/or the type of pre-cancerous
tissue to be detected, based on in vivo spectroscopy measurements.
The preferred filter characteristics for use in the fluorescence
endoscopy video systems with a camera of the type shown in FIGS. 7A
and 7B, operating in a fluorescence/reflectance imaging mode, or a
fluorescence/fluorescence imaging mode, are shown in FIGS. 8A-8F.
There are several possible configurations of fluorescence endoscopy
video systems, operating in the fluorescence/reflectance imaging
mode including green fluorescence with red reflectance, and red
fluorescence with green reflectance and red or green fluorescence
with blue reflectance. The particular configuration utilized
depends on the target clinical organ and application. The filter
characteristics will now be described for each of these four
configurations.
[0075] FIGS. 8A-8B illustrate a preferred composition of the light
transmitted by filters for a color imaging mode. FIG. 8A
illustrates the composition of the light transmitted by the light
source filter, such as filter 76A, which is used to produce light
for color imaging. The spectral filter 118 remains in place during
color imaging since there are no moving parts in the present camera
embodiment. Accordingly, to achieve correct color rendition during
color imaging it is necessary for the transmission of light source
filter 76A to be modified, compared to the usual white light
transmission for color imaging, such that the light received by the
high sensitivity color sensor 103 is white when a white reflectance
standard is viewed with the camera. Therefore, to balance the
effect of spectral filter 118, the transmission of filter 76A in
the red and green spectral bands must be less than the transmission
in the blue, and the transmission of filter 76A in the blue must
extend to a long enough wavelength that there is an overlap with
the short wavelength region of appreciable transmission of filter
1118. Filter 76A transmits light in the blue wavelength range from
370-480 nm or any subset of wavelengths in this range at the
maximum possible transmission. The transmission of Filter 76A in
the green and red wavelength range from 500 nm-750 nm, or any
subsets of wavelengths in this range, is preferably reduced by at
least a factor of ten compared to the transmission in the blue, in
order to achieve a balanced color image at the high sensitivity
color sensor 103, after taking into account the effect of filter
118.
[0076] FIG. 8B shows the composition of the light transmitted by
the spectral filter 118, which is used for all imaging modes. In
this configuration, the filter blocks the blue excitation light in
the range 370-450 nm while transmitting red and green light in the
wavelength range of 470-750 nm or any subsets of wavelengths in
this range. When used in a fluorescence endoscopy video system in
combination with the light source filter 76A described above, the
filter characteristics are such that the intensity of light
captured by high sensitivity color sensor 103 in the wavelength
bands transmitted by the different regions of the sensor's mosaic
filter are comparable, when a white reflectance standard is imaged.
When used in a fluorescence endoscopy video system for
fluorescence/fluorescence imaging in combination with the light
source filter 76B described below, the filter characteristics are
such that any light outside of the wavelength range of 470-750 nm
(or any desired subset of wavelengths in this range) contributes no
more than 0.1% to the light transmitted by the filter.
[0077] FIG. 8C illustrates the composition of the light transmitted
by a filter, such as filter 76B, which is used to produce
excitation light in the system light source. This filter transmits
light in the wavelength range from 370-450 nm or any subset of
wavelengths in this range. Of the light transmitted by this filter,
preferably less than 0.001% is in the fluorescence imaging band
from 470-750 nm (or whatever desired subsets of this range is
within the transmission range of the primary and reference
fluorescence wavelength bands defined by the transmission of the
mosaic filter incorporated in the high sensitivity color sensor
103).
[0078] FIG. 8D illustrates the composition of the light transmitted
by the light source filter, such as filter 76C, which is used to
produce blue excitation light and red reference light for a green
fluorescence and red reflectance imaging mode. This filter
transmits light in the blue wavelength range from 370-450 nm, or
any subset of wavelengths in this range. It also transmits light in
the red wavelength range of 590-750 nm, or any subset of
wavelengths in this range. The light transmitted in the red
wavelength range (or subset of that range) is adjusted, as part of
the system design, to be an appropriate fraction of the light
transmitted in the blue wavelength range. This fraction is selected
to meet the need to match the intensity of the reflected reference
light projected on the color image sensor to the requirements of
the sensor, at the same time as maintaining sufficient fluorescence
excitation. Of the light transmitted by this filter, less than
0.001% is in the green wavelength range of 470-570 nm (or whatever
desired subset of this range is specified as the transmission range
of the primary fluorescence wavelength band).
[0079] FIG. 8E illustrates the composition of the light transmitted
by a light source filter which is used to produce excitation light
such as filter 76C described above for a red fluorescence and green
reflectance imaging mode. This filter transmits light in the blue
wavelength range from 370-450 nm or any subset of wavelengths in
this range. It also transmits light in the green wavelength range
of 470-570 nm or any subset of wavelengths in this range. The light
transmitted in the green wavelength range (or subset of that range)
is adjusted, as part of the system design, to be an appropriate
fraction of the light transmitted in the blue wavelength range.
This fraction is selected to meet the need to match the intensity
of the reflected reference light projected on the color image
sensor to the requirements of the sensor, at the same time as
maintaining sufficient fluorescence excitation. Of the light
transmitted by this filter, less than 0.001% is in the red
fluorescence imaging wavelength range of 590-750 nm (or whatever
desired subset of this range is specified as the transmission range
of the primary fluorescence wavelength band).
[0080] FIG. 8F illustrates the composition of the light transmitted
by a light source filter which is used to produce excitation light
such as filter 76C described above for a red or green fluorescence
and blue reflectance imaging mode. This filter transmits light in
the blue wavelength range from 370-470 nm or any subset of
wavelengths in this range. The light transmitted in the 450-470 nm
wavelength range (or subset of that range) is adjusted, as part of
the system design, to meet the need to match the intensity of the
reflected reference light projected on the color image sensor to
the requirements of the sensor and to provide the appropriate ratio
of reference reflected light to fluorescence light, at the same
time as maintaining sufficient fluorescence excitation. Of the
light transmitted by this filter, less than 0.001% is in the
fluorescence imaging wavelength range of 490-750 nm (or whatever
desired subset of this range is specified as the transmission range
of the primary fluorescence wavelength band).
[0081] In an alternative embodiment of the present invention,
fluorescence and white light images can be obtained by placing a
filter on the distal tip of a video endoscope. A limitation of
current fluorescence videoendoscopy systems is that they typically
employ the use of dedicated endoscopes. Fluorescence imaging with
such endoscopes is enabled by the use of an excitation barrier
filter to block the strong excitation light used to excite the
tissue fluorescence these systems are intended to image. These
barrier filters are built in to the endoscope distal end (typically
between the objective lens and the low light image sensor) and this
built-in filter distinguishes these endoscopes from those used for
conventional videoendoscopy. The alternative embodiment of the
present invention describes the use of an externally mounted filter
in conjunction with a videoendoscope that contains a sufficiently
sensitive image sensor to image tissue fluorescence. This
combination of a conventional video endoscope and an externally
mounted barrier filter can be used in conjunction with an
appropriate endoscopic light source to image both in both color and
fluorescence modes.
[0082] FIG. 9 illustrates one embodiment of a distal filter 202
that can be placed over the distal end of a conventional white
light imaging endoscope to allow the endoscope to perform
fluorescence and white light examinations of a patient. As will be
described below, the filter 202 blocks excess excitation light from
reaching the image sensor 103 but allows some blue light to pass in
order to obtain white light images.
[0083] FIGS. 10A and 10B illustrate the operation of the distal
filter 202 in further detail. An endoscope 250 includes
illumination ports 252, 254 that supply illumination light to an
area of interest. A port 256 is the distal entrance to a working
channel through which endoscopic tools can be passed in order to
perform a desired task such as obtaining a biopsy sample, marking
tissue with dye or perform some other diagnostic or therapeutic
procedures. Light that is reflected from the tissue 350 is captured
by a lens 258 that images the light onto a low light color sensor.
In this embodiment, the low light sensor comprises a mosaic filter
260 that is positioned in front of a CCD, CMOS or equivalent image
sensor 262. Image signals produced by the image sensor are
transmitted to an image processor (not shown) that converts the
signals into video signals that are displayed on a monitor. In
addition the video signals may be recorded on a video tape, DVD or
other storage media for later review or comparison.
[0084] In order to allow the endoscope to obtain both fluorescence
and white light images of the tissue 350, the endoscope 250 may be
fitted with the distal end filter 202. In the embodiment shown, the
filter 202 is included in a filter assembly 300 that does not
obscure the illumination ports 252, 254 in order to allow the
illumination light to reach the tissue under examination. In
addition the filter assembly 300 does not interfere with other
distal tip features including but not limited to features such as
water/air nozzles, electrodes, confocal imaging ports, or the
working channel 256 so that tools can still be routed through the
endoscope. The filter assembly is made of appropriately inert and
non-conductive materials such as plastic or glass or stainless
steel, so as also not to interfere with the particular material or
electrical characteristics of the endoscope tip that may be
required for use in conjunction with endotherapy techniques, such
as argon ion plasma coagulation (APC), electrocautery, cryotherapy,
or photodynamic therapy (PDT)
[0085] The filter 202 is positioned in front of the imaging lens
258 and prevents excitation light from reaching the image sensor.
In one embodiment, the filter removes the excitation light having
wavelengths in the range of 370-450 nm. or some subset of this
range but passes some blue light, for example 451-480 nm. for use
in white light imaging as will be described below. Because most
endoscope have objective lenses with a wide field of view, the
filter should block excitation light over a corresponding wide
field of view and over the range of angles of incidence of light
collected by the endoscope objective. The filter should also be
thin enough not to introduce optical aberrations or interfere with
the mechanical properties and maneuverability of the endoscope tip.
Dye-based absorption filters that block the desired range of
excitation light and operate over a wide field of view may
therefore be preferred for this application. Specific examples of
such filters include Kodak Wratten gel filters. For durability, the
filter is preferably constructed in a manner similar to optically
protective eyewear such as laser goggles. As shown in FIG. 10A, the
distal filter 202 allows fluorescence images to be obtained in at
least two modes. In a first mode, excitation light, typically in
the blue wavelength spectral band, is provided from a light source
(not shown) and through the illumination ports 252, 254 whereupon
it strikes the tissue sample 350. A portion of the excitation light
is absorbed by the tissue and causes a tissue sample to produce
fluorescence light while a portion of the excitation light is
reflected off the surface of the tissue 350. Excitation light
reflecting from the surface of the tissue 350 is blocked by the
filter 202 in the filter assembly 300, while the fluorescence light
and light in other spectral bands passes through the filter
202.
[0086] In one fluorescence imaging mode, only fluorescence light is
used to produce video images of the tissue. In another mode, the
tissue is illuminated with the excitation light and some amount of
reflectance light. As shown in FIG. 10A, the reflectance light is
in the red spectral band. The reflectance light passes through the
filter 202 and the filter 260 in front of the image sensor 262.
Images of the tissue are obtained by combining for example, the
green pixels from the image sensor 262 to obtain a fluorescence
image in the green spectral band and the red pixels from the image
sensor 262 to obtain a reflectance image in the red spectral band.
Alternatively, the reflectance light may be provided in the green
spectral band and a red fluorescence image obtained. In yet another
embodiment, blue reflectance light having wavelengths that are not
filtered by the filter 202 can be used to produce the reflectance
image. The fluorescence and reflectance images may be combined for
display for a viewer. In order to prevent the reflectance image
from overpowering the fluorescence image, the amount of reflectance
light supplied from the light source is selected to be comparable
to the amount of fluorescence light received by the image sensor
262.
[0087] As shown in FIG. 10B, the endoscope 250 can also be used to
obtain white light images of the tissue 350 by illuminating the
tissue with light including red, green and blue spectral
components. The illumination light is reflected by the tissue
sample 350, passes through the filter 202 and is focused onto the
filter 260 by the endoscope's imaging lens 258. Because the filter
202 removes most of the blue reflectance light, the light received
by the image sensor 262 includes excess red and green light. To
compensate for the reduced blue light at the image sensor, the
illumination light should either contain excess blue light in the
band that passes through the filter 202 or contain reduced green
and red light so that the resulting image produced by the image
sensor may be white balanced. Additional fine tuning of the white
balance of the images produced by the image sensor 262 can be
accomplished by image processing software in the image processing
board (not shown).
[0088] One embodiment of a filter assembly 200 that is placed on
the distal tip of an endoscope is shown in FIG. 11. A filter 202
may be mounted in a frame that is snap-fitted over the distal end
face of an endoscope. The filter and/or frame are secured to the
endoscope with a mechanical, adhesive, magnetic force or other
means. In one embodiment, the frame includes a set of proximally
extending tabs 204, 206 that are secured to the outer circumference
of the endoscope tip.
[0089] The filter 202 is positioned in front of the imaging lens of
the endoscope. As indicated above, the filter 202 operates to
remove a substantial portion of reflected blue excitation light
used during the fluorescence imaging mode. In the embodiment shown
in FIG. 11, the frame also includes a hole 210 that is positioned
over the working channel of the endoscope in order to allow tools,
such as biopsy forceps, snares, cytology brushes, etc., to be
passed through the working channel. Positioned on either side of
the frame are holes 212, 214 that allow light from the illumination
guides to pass through the frame.
[0090] Another embodiment of the present invention also utilizes a
filter on the distal tip of a video endoscope. Some videoendoscope
systems do not employ the use of color image sensors and instead
use sequential illumination in various spectral (e.g blue, green,
red) bands and then combine monochrome images to produce full color
images. An external barrier filter 202 can be used in an endoscope
of the type shown in FIG. 9 with the high sensitivity color sensor
103 replaced by a monochrome image sensor and sequential
illumination of the type discussed in connection with FIG. 2B.
[0091] Briefly, in accordance with one embodiment of the invention,
autofluorescence images are obtained by illuminating with an
excitation light. Color images are obtained by sequential
illumination with red, green and blue light; wherein the blue light
either includes wavelengths or is limited to wavelengths not
blocked by the filter 202.
[0092] The fluorescence endoscopy video systems described in the
above embodiments have been optimized for imaging endogenous tissue
fluorescence. They are not limited to this application, however,
and may also be used for photo-dynamic diagnosis (PDD)
applications. As mentioned above, PDD applications utilize
photo-active drugs that preferentially accumulate in tissues
suspicious for early cancer. Since effective versions of such drugs
are currently in development stages, this invention does not
specify the filter characteristics that are optimized for such
drugs. With the appropriate light source camera filter
combinations, however, a fluorescence endoscopy video system
operating in either fluorescence/fluorescence or
fluorescence/reflectance imaging mode as described herein may be
used to image the fluorescence from such drugs.
[0093] As will be appreciated, each of the embodiments of a camera
for a fluorescence endoscopy video system described above, due to
their simplicity, naturally lend themselves to miniaturization and
implementation in a fluorescence video endoscope, with the camera
being incorporated into the insertion portion of the endoscope. The
cameras can be utilized for both color imaging and fluorescence
imaging, and in their most compact form contain no moving
parts.
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