U.S. patent application number 09/727701 was filed with the patent office on 2001-04-19 for fundus photographing device.
Invention is credited to Nanjo, Tsuguo, Yoneya, Shin.
Application Number | 20010000317 09/727701 |
Document ID | / |
Family ID | 18406927 |
Filed Date | 2001-04-19 |
United States Patent
Application |
20010000317 |
Kind Code |
A1 |
Yoneya, Shin ; et
al. |
April 19, 2001 |
Fundus photographing device
Abstract
A fundus photographing device for conducting infrared
fluorescence photography on a fundus of an examines's eye after
intravenously injecting a fluorescent agent which emits
fluorescence of an infrared region into veins is disclosed. This
device includes an illumination optical system 1 for illuminating
the fundus with exciting light, thereby exciting the injected
fluorescent agent, the exciting light being of wavelengths in a
wavelength region of not maximum absorption but maximum fluorescent
intensity of the fluorescent agent.
Inventors: |
Yoneya, Shin; (Maebashi-shi,
JP) ; Nanjo, Tsuguo; (Toyohashi-shi, JP) |
Correspondence
Address: |
Oliff & Berridge PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Family ID: |
18406927 |
Appl. No.: |
09/727701 |
Filed: |
December 4, 2000 |
Current U.S.
Class: |
396/18 |
Current CPC
Class: |
A61B 3/145 20130101;
A61B 3/1241 20130101 |
Class at
Publication: |
396/18 |
International
Class: |
G03B 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 12, 1999 |
JP |
11-349908 |
Claims
What is claimed is:
1. A fundus photographing device for conducting infrared
fluorescence photography on a fundus of an examinee's eye after
intravenously injecting a fluorescent agent which emits
fluorescence of an infrared region into veins, the device
including: an illumination optical system for illuminating the
fundus with exciting light, thereby exciting the injected
fluorescent agent, the exciting light being of wavelengths in a
wavelength region of not maximum absorption but maximum fluorescent
intensity of the fluorescent agent.
2. The fundus photographing device according to claim 1, wherein
the illumination optical system includes a laser source for
emitting a laser beam used as the exciting light, the laser beam
being of the wavelengths in the wavelength region of not the
maximum absorption but the maximum fluorescent intensity.
3. The fundus photographing device according to claim 1, wherein
the illumination optical system includes an illumination light
source for emitting illumination light used as the exciting light
and an exciter filter having a property of transmitting the
wavelengths of the illumination light in the wavelength region of
not the maximum absorption but the maximum fluorescent
intensity.
4. A fundus photographing device for conducting infrared
fluorescence photography on a fundus of an examinee's eye after
intravenously injecting a fluorescent agent which emits
fluorescence of an infrared region into veins, the device
including: an illumination optical system for illuminating the
fundus with exciting light, thereby exciting the injected
fluorescent agent, the exciting light being of wavelengths with a
peak in a range of approximately 725 nm to 745 nm; and a
photographing optical system including filtering means for
filtering infrared fluorescence from the injected fluorescent agent
and a photographing element for photographing an image of the
fundus with the infrared fluorescence filtered through the
filtering means.
5. The fundus photographing device according to claim 4, wherein
the illumination optical system includes a laser source for
emitting a laser beam used as the exciting light, the laser beam
being of the wavelengths with the peak in the range of
approximately 725 nm to 745 nm.
6. The fundus photographing device according to claim 4, wherein
the illumination optical system includes an illumination light
source for emitting illumination light used as the exciting light
and an exciter filter having a property of transmitting the
wavelengths of the illumination light with the peak in the range of
approximately 725 nm to 745 nm.
7. The fundus photographing device according to claim 4, wherein
the filtering means includes a barrier filter disposed in the
photographing optical system, and the barrier filter has a property
of cutting wavelengths of at least approximately 760 nm or less and
transmitting wavelengths of approximately 800 nm or more.
8. The fundus photographing device according to claim 7, wherein
the barrier filter has a property of transmitting approximately 50%
or more of wavelengths of at least approximately 800 nm to 860
nm.
9. A fundus photographing device for conducting infrared
fluorescence photography on a fundus of an examinee's eye after
intravenously injecting a fluorescent agent which emits
fluorescence of an infrared region into veins, the device
including: a illumination optical system for illuminating the
fundus with exciting light of wavelengths in a predetermined
wavelength region, thereby exciting the injected fluorescent agent;
and a photographing optical system including a barrier filter for
filtering infrared fluorescence from the injected fluorescent agent
and a photographing element for photographing an image of the
fundus with the infrared fluorescence filtered through the barrier
filter, the barrier filter having a property of transmitting
wavelengths in a predetermined wavelength region different from the
wavelength region of the exciting light.
10. The fundus photographing device according to claim 9, wherein
the illumination optical system includes a laser source for
emitting a laser beam used as the exciting light, the laser beam
being of wavelengths of approximately 780 nm or less.
11. The fundus photographing device according to claim 10, wherein
the barrier filter has a property of cutting wavelengths of
approximately 780 nm or less and transmitting wavelengths of
approximately 800 nm or more.
12. The fundus photographing device according to claim 11, wherein
the barrier filter has a property of transmitting approximately 50%
or more of wavelengths of at least approximately 800 nm to 860
nm.
13. The fundus photographing device according to claim 9, wherein
the illumination optical system includes an illumination light
source for emitting illumination light used as the exciting light
and an exciter filter having a property of transmitting wavelengths
of the illumination light of approximately 780 nm or less.
14. The fundus photographing device according to claim 13, wherein
the barrier filter has a property of cutting wavelengths of
approximately 780 nm or less and transmitting wavelengths of
approximately 800 nm or more.
15. The fundus photographing device according to claim 14, wherein
the barrier filter has a property of transmitting approximately 50%
or more of wavelengths of at least approximately 800 nm to 860 nm.
Description
BACKGROUND OF THE INVENTION
1. 1. Field of the Invention
2. The present invention relates to a fundus photographing device
to be used in ophthalmology clinics, and particularly to a fundus
photographing device for fluorescence photography with infrared
light.
3. 2. Description of Related Art
4. There has been known a fundus photographing device for of
photographing an image of a fundus with infrared fluorescence
emitted from choroidal veins of an examinee's eye. For the
photography, indocyanine green (hereinafter referred to as ICG)
which is a fluorescent agent is intravenously injected at first
into the choroidal veins. The fundus of the examinee's eye is then
illuminated with infrared light to excite the ICG circulated in the
fundus (the choroidal veins). thus the image of the fundus is
photographed by the fundus photographing device with the infrared
fluorescence emitted from the choroidal veins.
5. ICG has a peak absorption wavelength in a range of about 780 nm
to 805 nm. In the infrared fluorescence photography using ICG,
generally, the fundus is illuminated with exciting light through an
exciter filter capable of sufficiently transmitting light of
wavelengths of about 780 nm, while cutting light of wavelengths of
about 900 nm or more. On the other hand, the ICG circulated in the
fundus (the choroidal veins) and excited by the exciting light will
emit fluorescence with a peak of about 830 nm. To prevent false
fluorescence resulting from the exciting light from being mixed in
a fluorescence photograph, the photography is carried out through a
barrier filter capable of filtering fluorescence to allow
transmission of the fluorescence having long wavelengths of about
820 nm or more.
6. Instead of the device using the exciter filter, there has
recently been proposed a photographing device using, as an exciting
light source, a laser diode which is a light source that emits
light of a single wavelength having a peak of about 790 nm.
7. However, the infrared fluorescence of ICG emitted from the
fundus (the choroidal veins) is very faint, which is about 1/25 to
1/50 in fluorescent intensity as compared with the fluorescence in
a visible fluorescence photography using fluorescein as a
fluorescent agent. Thus, the conventional device could only
photograph the eye fundus with fluorescence of very low luminance.
Therefore, there are tendencies that only the sites where blood
vessels lie on top of one another or plural blood vessels gather
can be observed. In particular, the fluorescence at the early stage
of ICG injection into the choroidal veins could hardly be captured.
As a result, there were many insufficiencies in observation and
photography of the choroidal circulation dynamics.
SUMMARY OF THE INVENTION
8. The present invention has been made in view of the above
circumstances and has an object to overcome the above problems and
to provide a fundus photographing device capable of efficiently
photographing the fundus of an examinee's eye with infrared
fluorescence of high luminance, thereby providing more detailed
information for diagnosis of choroidal circulation dynamics of the
examines's eye.
9. Additional objects and advantages of the invention will be set
forth in part in the description which follows and in part will be
obvious from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and attained by means of the instrumentalities and
combinations particularly pointed out in the appended claims.
10. To achieve the purpose of the invention, there is provided a
fundus photographing device for conducting infrared fluorescence
photography on a fundus of an examinee's eye after intravenously
injecting a fluorescent agent which exits fluorescence of an
infrared region into veins, the device including: an illumination
optical system for illuminating the fundus with exciting light,
thereby exciting the injected fluorescent agent, the exciting light
being of wavelength in a wavelength region of not maximum
absorption but maximum fluorescent intensity of the fluorescent
agent.
11. According to another aspect of the present invention, there is
provided a fundus photographing device for conducting infrared
fluorescence photography on a fundus of an examinee's eye after
intravenously injecting a fluorescent agent which emits
fluorescence of an infrared region into veins, the device
including; an illumination optical system for illuminating the
fundus with exciting light, thereby exciting the injected
fluorescent agent, the exciting light being of wavelengths with a
peak in a range of approximately 725 nm to 745 nm; and a
photographing optical system including filtering means for
filtering infrared fluorescence from the injected fluorescent agent
and a photographing element for photographing an image of the
fundus with the infrared fluorescence filtered through the
filtering means.
12. Moreover, according to another aspect of the present invention,
there is provided a fundus photographing device for conducting
infrared fluorescence photography on a fundus of an examinee's eye
after intravenously injecting a fluorescent agent which emits
fluorescence of an infrared region into veins, the device
including: an illumination optical system for illuminating the
fundus with exciting light of wavelengths in a predetermined
wavelength region, thereby exciting the injected fluorescent agent;
and a photographing optical system including a barrier filter for
filtering infrared fluorescence from the injected fluorescent agent
and a photographing element for photographing an image of the
fundus with the infrared fluorescence filtered through the barrier
filter, the barrier filter having a property of transmitting
wavelengths in a predetermined wavelength region different from the
wavelength region of the exciting light.
BRIEF DESCRIPTION OF THE DRAWINGS
13. The accompanying drawings, which are incorporated in and
constitute a part of this specification illustrate an embodiment of
the invention and, together with the description, serve to explain
the objects, advantages and principles of the inventions
14. In the drawings,
15. FIG. 1 is a graph showing an excitation spectrum obtained by
measurements of fluorescent intensity of wavelength of about 830 nm
of ICG injected into human serum;
16. FIG. 2 is a table showing measurement results on maximum
fluorescence wavelengths and respective fluorescent intensity on
condition that a wavelength of exciting light is set to 735 nm, 780
nm, and 790 nm respectively;
17. FIG. 3 is a graph showing a fluorescence spectrum obtained by
measurements of fluorescent intensity on condition that the
exciting light is of a wavelength of about 735 nm;
18. FIG. 4 is a graph schematically showing preferable spectral
transmittance properties of an exciter filter and a barrier filter
used in an infrared fluorescence photography using ICG;
19. FIG. 5 is a schematic structural view of a fundus photographing
device in an embodiment according to the present invention;
20. FIG. 6 is a schematic structural view of a fundus photographing
device in another example;
21. FIG. 7 is a graph showing an absorption spectrum of Pinacyanol
iodide which is a cyanine base dye;
22. FIG. 8 is a graph showing an excitation spectrum of Pinacyanol
iodide of a fluorescence wavelength of about 625 nm; and
23. FIG. 9 is a graph showing a fluorescence spectrum of Pinacyanol
iodide on condition that the exciting light is of a wavelength of
about 325 nm.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
24. A detailed description of a preferred embodiment of a fundus
photographing device embodying the present invention will now be
given referring to the accompanying drawings.
25. At first, explanation will be made on wavelengths of exciting
light and wavelengths of fluorescence for ICG fluorescence
photography.
26. As mentioned above, ICG has the maximum absorption wavelength
in a range of about 780 nm to 805 nm. When injected into blood and
excited by exciting light, the ICG will emit fluorescence with the
peak wavelength of about 830 nm. In the conventional ICG
fluorescence photography, the wavelengths of the exciting light and
the property of a barrier filter provided in the photographing side
have been determined based on the above properties. However,
applicants reviewed and examined as to whether the use of the
exciting light of wavelengths in the range of about 780 nm to 805
nm really could provide the best excitation efficiency.
27. When human serum samples containing ICG are excited by
whichever wavelengths of the exciting light, the fluorescence shows
the maximum fluorescent intensity when the fluorescence wavelength
is about 830 nm. It is therefore conceivable that, when the
fluorescent intensity of the fluorescence wavelengths of about 830
nm is measured while shifting the wavelength of the exciting light,
the excitation wavelength whereby the maximum fluorescent intensity
is obtained corresponds to the wavelength of the exciting light
capable of providing the beat excitation efficiency. Hence, the
fluorescent intensity with respect to the fluorescence wavelengths
of about 830 nm were measured with a monochromator, a photoelectric
multiplier or the like with respect to a human serum sample
containing ICG poured into a triangular cell on condition that the
wavelength of the exciting light was selectively shifted in a range
of about 660 nm to 810 nm. Measurement results thereon are shown as
an excitation spectrum in FIG. 1.
28. As seen in the excitation spectrum in FIG. 1, the fluorescent
intensity of wavelengths of about 830 nm became the maximum when
the ICG was excited by the exciting light of wavelengths of about
732-735 nm, and the second intensity was obtained with respect to
about 762-766 nm. The fluorescent intensity resulting from the
exciting light of wavelengths of about 780-805 nm was low. This
indicates that, in the infrared fluorescence photography using ICG,
the use of the exciting light having its center wavelength of about
735 nm is more effective than that with wavelengths of about
780-805 nm which correspond to the maximum absorption wavelength of
ICG.
29. In general, the maximum fluorescent intensity is obtained when
a fluorescent agent is excited by exciting light of wavelengths
close to the maximum absorption wavelength in an absorption
spectrum. One example of the fluorescent agent is fluorescein used
in the visible fluorescence photography.
30. On the other hand, measurement results on Pinacyanol iodide
which is a cyanine base dye, like ICG, are as follows. As seen from
the absorption spectrum in FIG. 7, the maximum absorption
wavelength of the dye was about 600 nm on condition that the dye
was dissolved in an aqueous solution. Measuring an excitation
spectrum, however, as shown in FIG. 8, the maximum excitation
wavelength was about 325 nm close to the maximum absorption
wavelength in a near-ultraviolet region of the dye, then the dye
showed the fluorescence spectrum with the maximum fluorescent
intensity wavelength of about 652 nm (see FIG. 9). Although the dye
was excited by the exciting light of a wavelength of about 600 nm
which was the maximum absorption wavelength of the dye, the
fluorescence of about 652 nm was extremely weak. This demonstrates
that the maximum excitation wavelength with respect to the cyanine
base dye did not always correspond to the maximum absorption
wavelength.
31. Next, measurements were made on the maximum wavelengths of
fluorescence and respective fluorescent intensity on condition that
the exciting light was set to be of wavelengths of 735 nm, 780 nm,
and 790 nm respectively. The measurements were conducted at 30
sec., 60 sec., 2 min., 3 min., and 5 min. after injection of ICG
into a blood sample. FIG. 2 shows the results of those
measurements. For any of the excitation wavelengths, the maximum
fluorescence wavelength was in a range of 820 to 840 nm. There were
not seen remarkable differences among the maximum fluorescence
wavelengths due to the difference in excitation wavelength. On the
other hand, the fluorescent intensity was the highest when the
excitation wavelength was 735 nm. This fluorescent intensity was
two times or more as high as in the case where the excitation
wavelength was 780 nm or 790 nm.
32. From the above results, it was proven that in the infrared
fluorescence photography using ICG the use of excitation
wavelengths of about 735 nm could provide better excitation
efficiency than the use of excitation wavelengths of about 780-805
nm.
33. FIG. 3 is a graph showing a fluorescence spectrum obtained by
measurements on the fluorescent intensity of fluorescence emitted
from the serum injected with ICG on condition that the excitation
wavelength was about 735 nm. As seen from this graph, the
fluorescent intensity gradually increased from about 780 nm in a
shorter wavelength region than about 800 nm and peaked in a range
of about 830 nm to 840 nm. The fluorescent intensity could be
measured up to near 900 nm. In this way, since the fluorescent
intensity started to increase in the shorter wavelength region than
about 800 nm, a photographed image of higher luminance can be more
efficiently obtained if the fluorescence photography is carried out
with the fluorescence of wavelengths of about 800 nm or more.
34. Thus, the apparatus for the infrared fluorescence photography
using ICG is constructed as follows in order to achieve the
fluorescence photography capable of producing photographed images
of higher luminance.
35. In a case of using filters, to prevent the influence of false
fluorescence by exciting light according to excitation wavelengths,
an exciter filter used for giving exciting light is designed to
have the property of restricting (transmitting) the wavelengths of
the exciting light to about 780 nm or less, as shown in FIG. 4. For
instance, the property is determined so that the transmittance is
5% or less for the light of wavelengths of about 700 nm or less,
50% or more (preferably, 70% or more) for the light of wavelengths
of about 720-770 nm, and 1% or less for the light of wavelengths of
about 780 nm. A barrier filter used for selectively transmitting
(filtering) infrared fluorescence is designed to have the property
of cutting the light of wavelengths of about 780 nm or less, while
transmitting the light of wavelengths of more than about 780 nm.
For instance, the property is determined so that the transmittance
is 1% or less for the light of wavelengths of about 780 nm or less,
50% or more (preferably, 70% or more) for the light of wavelengths
of about 800-860 nm, up to 900 nm in a longer wavelength region as
well, and 5% or less for the light of wavelengths of about 930 nm
or more.
36. For the purpose of preventing the influence of false
fluorescence, it is preferable that the overlapped region of
transmittance wavelengths between the exciter filter and the
barrier filter is as small as possible and, preferably, the maximum
transmittance in the overlapped region is 0.5% or less. If it is
hard to produce filters with so sharp transmittance that the
transmittance wavelength regions of both filters are less
overlapped, an exciter filter that transmits 50% or more of
wavelengths of at least about 720-750 nm is used. Thus, even when
the barrier filter is constructed to transmit light of wavelengths
including about 800 nm, there is a sufficient margin. This can
increase ease of filter construction.
37. In the case where a laser source which is an efficient light
source capable of emitting light of a single wavelength is used as
an exciting light source, a laser source capable of emitting
near-infrared laser light with the peak wavelength in a range of
about 725 nm to 745 nm is used. For instance, a semiconductor laser
source (laser diode) may be used. This semiconductor laser source
emits a laser beam of a predetermined wavelength region having a
slight width, though 10 nm or less in multimode oscillation. In
this case, therefore, the barrier filter may further have a margin
with respect to a cutting limit in lower wavelengths. For example,
the barrier filter may be designed to have the property of cutting
most of light with wavelengths of about 760 nm or less, while
transmitting light with wavelengths of more than about 760 nm. This
filter can transmit most of infrared fluorescence emitted from the
fundus (the choroidal veins) while sufficiently preventing the
influence of false fluorescence.
38. Next, explanation is made on a structural example of the fundus
photographing device in the present embodiment according to the
invention, referring to FIG. 5. Numeral 1 is an illumination
optical system constructed of a semiconductor laser source 2 which
is an exciting light source, a collimator lens 3, a ring slit plate
4, a mirror 5, relay lenses 6 and 7, and a perforated mirror 8. The
semiconductor laser source 2 emits a laser beam of a single
wavelength with a peak of about 735 nm.
39. Numeral 10 is a photographing optical system constructed of an
objective lens 11, a photographing stop 12, a barrier filter 13, a
focusing lens 14, an imaging lens 15, a mirror 16, a field lens 17,
a mirror 18, a relay lens 19, and a CCD camera 20 having the
sensitivity to infrared region. The CCD camera 20 is connected to a
monitor 21 for displaying a fundus image photographed by the camera
20 and also an image storage section 22 such as a magneto-optic
disk and the like.
40. The barrier filter 13 in the present embodiment has the
property of transmitting wavelengths of about 780-900 nm, while
cutting wavelengths of less than about 780 nm. Preferably, it has
the property of transmitting 50% or more (more preferably, 70% or
more) of the wavelengths of about 800-860 nm (see the transmittance
property of the barrier filter in FIG. 4). As mentioned above, the
exciting light is a laser beam of a single wavelength of about 735
nm. In terms of the lower cutting limit, therefore, the barrier
filter 13 may be designed to have the property of cutting light of
wavelengths of about 760 nm or less and transmitting more than
about 760 nm. This also makes it possible to adequately prevent the
influence of false fluorescence.
41. The infrared exciting light from the semiconductor laser source
2 passes through the collimator lens 3, a ring slit of the plate 4,
the mirror 5, the relay lenses 6 and 7, and then is reflected by a
reflection plane of the perforated mirror a toward the objective
lens 11. Thus the exciting light passes through the objective lens
11 and illuminates the fundus of an examinee's eye E.
42. The fundus in which ICG has been intravenously injected in
advance is illuminated with the infrared exciting light emitted
from the semiconductor laser source 2. When thus excited, the ICG
injected into the choroidal veins emits fluorescence. In the
present embodiment, the exciting light used for exciting the ICG is
the laser beam having the peak wavelength of about 735 nm. As a
result, the ICG emits the fluorescence of higher luminance than in
the case where the exciting light having the peak wavelength in the
range of about 780 nm to 800 nm is used. Since the laser beam of a
single wavelength is used as the exciting light, excitation
efficiency can be enhanced by illumination of a low light amount as
compared with the case where an exciter filter is used.
43. The fluorescence emitted from the fundus (the choroidal veins)
passes through the objective lens 11, an aperture of the perforated
mirror 8, the photographing stop 12, the barrier filter 13, the
focusing lens 14, the imaging lens 15, the mirror 16, the field
lens 17, the mirror 18, and the relay lens 19, and then is focused
on the CCD camera 20 to form a fundus image. The barrier filter 13
allows filtering (transmitting) of the fluorescence of not only the
peak wavelengths of 830-840 nm but also shorter wavelengths than
about 800 nm (about 780-800 nm) which is a rising edge for the
peak, whereby faint infrared fluorescence can be easily captured.
The barrier filter 13 sufficiently cuts the wavelengths of the
exciting light, thus enabling prevention of the influence of false
fluorescence. The fundus image photographed by the CCD camera 20 is
displayed in the monitor 21. The photographed image is properly
stored in the image storage section 22.
44. By the use of the laser beam of wavelengths efficient for
excitation and the use of the above structured barrier filter, even
the fluorescence of very low luminance at the early stage of ICG
injection as compared with the conventional case can be captured by
the CCD camera 20. This makes it possible to provide more detailed
information for diagnosis of choroidal circulation. The intensity
of the whole fluorescence emitted from the fundus increases, so
that the choroidal circulation dynamics from the early to the late
stage of ICG injection can be obtained as high-contrast images.
45. As means for filtering infrared fluorescence for photography,
there may be arranged the barrier filter 13 in the optical path of
the photographing optical system or the CCD camera 20.
Alternatively, a prism and the like may be used to separate the
infrared fluorescence, which is then introduced as photographing
luminous flux.
46. In the above embodiment, the laser beam of a single wavelength
is used as the exciting light. An alternative design is, as shown
in FIG. 6, the use of a light source 30 such as a xenon lamp and an
exciter filter 31 to restrict (transmit) excitation wavelengths. In
this case, the exciter filter 31 and the barrier filter 13 have the
wavelength properties of the filter structures mentioned above (see
FIG. 4).
47. By the use of the exciter filter 31 and the barrier filter 13
with the above properties, like the above embodiment, fluorescence
of higher luminance than in the conventional case can be obtained
while preventing the influence of false fluorescence. In the case
where the exciter filter 31 is designed to transmit light of
wavelengths restricted to about 720-750 nm, it can prevent the
influence of false fluorescence with sufficient margin even if the
barrier filter 13 is designed to allow the transmittance to
wavelengths including about 800 nm. Thus, manufacture of the two
filters can be facilitated.
48. As mentioned above, the fundus photographing device according
to the invention enables infrared fluorescence photography of high
luminance while preventing the influence of false fluorescence.
Accordingly, the fluorescence can be captured at the early stage of
injection of the fluorescent agent into the choroidal veins,
thereby enabling more detailed diagnosis of choroidal circulation
dynamics.
49. The foregoing description of the preferred embodiment of the
invention has been presented for purposes of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise form disclosed, and modifications and
variations are possible in light of the above teachings or may be
acquired from practice of the invention. The embodiment chosen and
described in order to explain the principles of the invention and
its practical application to enable one skilled in the art to
utilize the invention in various embodiments and with various
modifications as are suited to the particular use contemplated. It
is intended that the scope of the invention be defined by the
claims appended hereto.
* * * * *