U.S. patent number 5,701,902 [Application Number 08/306,118] was granted by the patent office on 1997-12-30 for spectroscopic burn injury evaluation apparatus and method.
This patent grant is currently assigned to Cedars-Sinai Medical Center. Invention is credited to Jean-Michel I. Maarek, Sandor G. Vari.
United States Patent |
5,701,902 |
Vari , et al. |
December 30, 1997 |
**Please see images for:
( Certificate of Correction ) ** |
Spectroscopic burn injury evaluation apparatus and method
Abstract
A burn evaluation apparatus and related method, that allows a
surgeon to make a quick evaluation of the extent and depth of a
skin burn injury by employing induced ultraviolet or blue light
fluorescence spectroscopy and visible and infrared reflectance
spectroscopy. The apparatus monitors the condition of the
structural and metabolic constituents in the injured skin. The
apparatus includes a plurality of light sources, a sensor, a
microprocessor, and several optical fiber bundles. The light
sources emit excitation light at predetermined wavelengths, and
when each is activated, the sensor measures the amount return light
received within several wavelength bands of interest. A side fiber
bundle spaced about a centimeter from a main fiber bundle assists
in detecting tissue water below the burn area. By optically
evaluating the skin at the burn site, the apparatus prevents the
unnecessary removal of viable skin that will heal spontaneously
within a few weeks, thereby reducing the amount of skin that must
be surgically grafted.
Inventors: |
Vari; Sandor G. (Woodland
Hills, CA), Maarek; Jean-Michel I. (Rancho Palos Verdes,
CA) |
Assignee: |
Cedars-Sinai Medical Center
(Los Angeles, CA)
|
Family
ID: |
23183899 |
Appl.
No.: |
08/306,118 |
Filed: |
September 14, 1994 |
Current U.S.
Class: |
600/473;
600/476 |
Current CPC
Class: |
A61B
5/0059 (20130101); A61B 5/0071 (20130101); A61B
5/0075 (20130101); A61B 5/445 (20130101) |
Current International
Class: |
A61B
5/00 (20060101); A61B 5/103 (20060101); A61B
005/00 () |
Field of
Search: |
;128/633,634,664,665 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2 539 613 |
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Jul 1984 |
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FR |
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227 044 A1 |
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Sep 1985 |
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DE |
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227044 |
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Sep 1985 |
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DE |
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37 18202 C1 |
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Nov 1988 |
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DE |
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40 31 320 A1 |
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Apr 1992 |
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DE |
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2 254 417 |
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Oct 1992 |
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GB |
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WO 90/10219 |
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Sep 1990 |
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WO |
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WO 90/13091 |
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Nov 1990 |
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WO |
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WO 91/12766 |
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Sep 1991 |
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WO |
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WO93/01745 |
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Feb 1993 |
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WO |
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Other References
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No. 1, Jan. 1993, pp. 139-141. .
Trop et al., "Core Body Temperature Responses Immediately After
Cutaneous Thermal Injury in Rats," J. of Burn Care & Rehab.,
vol. 13, No. 6, Dec. 1992, pp. 632-638. .
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Skin by .sup.31P-NMR in Vivo," J. of Trauma, vol. 33, No. 6, Dec.
1992, pp. 828-834. .
Ryan et al., "Increased Gut Permeability Early After Burns
Correlates with the Extent of Burn Injury," Critical Care Medicine,
vol. 20, No. 11, Nov. 1992, pp. 1508-1512. .
Tomera et al., "Mod. of Calcium Flux of Twitch Skeletal Muscle in
Mice Subj. to 20% Body Surface Area Burn," J. Burn Care &
Rehab., vol. 15, No. 5, Oct. 1992, pp. 546-555. .
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Critical Care Medicine, vol. 20, No. 9, Sep. 1992, pp. 1284-1288.
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Biswas, D.R., "Optical Fiber Coatings for Biomedical Applications,"
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Green et al., "Burn Depth Estimation Using Indocyanine Green
Fluorescence," Arch Dermatol, vol. 128, Jan. 1992, pp. 43-49. .
Bassnett et al., "Intracellular pH Measurement Using Single
Excitation-Dual Emission Fluorescence Ratios," American Journal of
Physiology, 1990, pp. C171-C178. .
Mendelson et al., "Blood Glucose Measurement by Multiple Attenuated
Total Reflection & Infrared Absorption Spectroscopy," IEEE
Trans. on Biomedical Engr., vol. 37, No. 5, May 1990, pp. 458-464.
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Pini et al., "Laser Dentistry: Root Canal Diagnostic Technique
Based on Ultraviolet-Induced Fluorescence Spectroscopy," Lasers in
Surgery & Medicine, vol. 9, 1989, pp. 358-361. .
Afromowitz et al., "Multispectral Imaging of Burn Wounds: A New
Clinical Instrument for Evaluating Burn Depth," IEEE Trans. on
Biomedical Engr., vol. 35, No. 10, Oct. 1988, pp. 842-849. .
Afromowitz et al., "Clinical Evaluation of Burn Injuries Using an
Optical Reflectance Technique," IEEE Trans. on Biomedical Engr.,
vol. 34, No. 2, Feb. 1987, pp. 114-127. .
Moneta et al., "Infrared Fluorescence Videomicroscopy of Skin
Capillaries with Indocyanine Green," Int. J. Microcirc. Clin. Exp.,
pp. 25-34, 1987. .
Gatti et al., "Evaluation of the Burn Wound with Perfusion
Fluorometry," Journal of Trauma, vol. 23, No. 3, Mar. 1983, pp.
202-206. .
"Substance Identification Neural Network," Physical Optical Corp.
product information, Date: unknown. .
Andersson et al., "Remote Sample Characterization Based on
Fluorescence Monitoring," Appl. Phys., vol. B44, No. 1, Sep. 1987,
pp. 20-28, Berlin, W. Germany. .
Heimbach et al., "Burn Depth Estimation--Man or Machine," Journal
of Trauma, vol. 24, No. 5, 1984, pp. 373-378. .
Anselmo et al., "Infrared Photography as a Diagnostic Tool for the
Burn Wound," Proceedings of the Society of Photo-Optical
Instrumentation Engineers, vol. 40, Aug. 1973, pp. 181-188. .
Anselmo et al., "Multispectral Photographic Analysis," Annals of
Biomedical Engineering, vol. 5, No. 2, Jun. 1977, pp. 179-193.
.
Anselmo et al., "Diagnosis of Cutaneous Thermal Burn Injuries by
Multispectral Imaging Analysis," Jet Propulsion Laboratory
Publication 79-34, Sep. 1978, pp. i-8-2. .
Katsura et al., "Untraviolet Absorption of Human Teeth as Revealed
by Microphotometry," ACTA Histochem Cytochem, vol. 7, No. 4, 1974,
pp. 328-333. .
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Teeth," ACTA Histochem, Cytochem, vol. 7, No. 4, 1984, pp.
334-341..
|
Primary Examiner: Smith; Ruth S.
Attorney, Agent or Firm: Pretty, Schroeder &
Poplawski
Claims
I claim:
1. Apparatus for evaluating the condition of burned skin at the
site of the burn injury to the skin, comprising:
a plurality of light sources, each emitting excitation light having
a predetermined wavelength, that is directed at the burn site to
produce return light, wherein at least one light source is
characterized by a wavelength of sufficient energy to cause
fluorescence of certain chemical constituents of the skin and the
return light includes fluorescent light produced by constituents
present within the skin;
a sensor, responsive to the return light corresponding to each
light source, that monitors the return light and generates a
plurality of electrical signals based on the intensity of return
light within predetermined wavelength bands; and
a processor associated with the sensor, that processes the
plurality of electrical signals and determines the condition of the
skin at the site of the burn injury.
2. Apparatus for evaluating a burn injury to skin as defined in
claim 1, wherein the plurality of light sources include a first
light source that emits narrow band excitation light having a
wavelength between 300 nanometers and 480 nanometers.
3. Apparatus for evaluating a burn injury to skin as defined in
claim 2, wherein the plurality of light sources includes a first
light source that emits excitation light having a wavelength of 405
nanometers, a second light source that emits excitation light
having a wavelength of 452 nanometers, a third light source that
emits excitation light having a wavelength of 775 nanometers, a
fourth light source that emits excitation light having a wavelength
of 810 nanometers, a fifth light source that emits excitation light
having a wavelength of 904 nanometers, and a sixth light source
that emits excitation light having a wavelength of 980
nanometers.
4. Apparatus for evaluating a burn injury to skin as defined in
claim 3, wherein each of the plurality of light sources includes a
diode laser that generates the respective excitation light.
5. Apparatus for evaluating a burn injury to skin as defined in
claim 3, wherein the plurality of light sources include a first
light source producing light within a first wavelength band between
450 to 460 nanometers, a second light source producing light within
a second wavelength band between 480 and 490 nanometers, a third
light source producing light within a third wavelength band between
520 and 530 nanometers, a fourth light source producing light
within a fourth wavelength band between 550 and 560 nanometers, a
fifth light source producing light within a fifth wavelength band
between 770 and 780 nanometers, a sixth light source producing
light within a sixth wavelength band between 805 and 815
nanometers, a seventh light source producing light within a seventh
wavelength band between 900 and 910 nanometers, and an eighth light
source producing light within an eighth wavelength band between 970
and 990 nanometers.
6. Apparatus for evaluating a burn injury to skin as defined in
claim 1, further comprising:
a first optical fiber bundle that includes
a plurality of excitation optical fibers, each excitation optical
fiber associated with a respective light source to transmit
excitation light from the light source to the site of the burn
injury; and
one or more return optical fibers that transmit the return light
from the site of the burn injury to the sensor.
7. Apparatus for evaluating a burn injury to skin as defined in
claim 6, further comprising a second optical fiber bundle of one or
more optical fibers that collect return light, the second bundle
being located at a distance of approximately one centimeter from
the first optical fiber bundle, during the evaluation of the burn
injury.
8. Apparatus for evaluating a skin burn injury as defined in claim
1, wherein:
the plurality of light sources includes:
a first light source that emits excitation light having a
wavelength not greater than about 480 nanometers to cause
fluorescence of certain metabolic and structural constituents in
the skin, and
a second light source that emits excitation light having a
wavelength of at least about 772 nanometers to illuminate the
hemoglobin at the burn injury site;
the return light includes light reflected by the hemoglobin present
in the skin; and
the processor determines the potential viability of the skin at the
site of the burn injury.
9. Apparatus for evaluating a skin burn injury as defined in claim
8, further comprising a display that provides an image that
indicates the potential viability of the skin at the site of the
burn injury.
10. Apparatus for evaluating a skin burn injury as defined in claim
8, wherein the plurality of light sources further includes a third
light source having a wavelength of at least 980 nanometers to
illuminate the water content of the skin and the return light
includes light reflected by water present within the skin.
11. Apparatus for evaluating a skin burn injury as defined in claim
1, wherein:
the plurality of light sources includes a light source that emits,
at a first location, excitation light having a wavelength of about
980 nanometers;
the sensor further monitors the return light at a second location
situated approximately one centimeter from the first location and
generates a first electrical signal based on the intensity of
return light within a relatively based on the intensity of return
light within a relatively narrow wavelength band centered at about
980 nanometers; and
the processor further processes the first electrical signal to
evaluate the water content of the skin and tissues below the site
of the burn injury.
12. Apparatus for evaluating a skin burn injury as defined in claim
1, wherein:
the sensor includes an optical probe for monitoring the reflectance
of infrared light from below a surface of the skin at the site of
the burn injury, the optical probe comprising:
a main optical fiber bundle that directs infrared light toward the
surface, and
a side optical fiber bundle that is located approximately one
centimeter from the main fiber bundle and that collects infrared
light reflected from below the surface.
13. Apparatus for evaluating a skin burn injury as defined in claim
1, wherein:
the processor provides a database that associates, for a particular
skin type, the fluorescence and spectroscopic characteristics of
different degrees of burn injury occurring to the skin of the
particular skin type; and the processor determines the condition of
the skin at the site of the burn injury by
determining the fluorescence and spectroscopic characteristics of
the injured individual's normal skin,
comparing the fluorescence and spectroscopic characteristics of the
injured individual's normal skin with the fluorescence and
spectroscopic characteristics of normal skin for the particular
skin types in the database and selecting the closest match between
the individual's skin type and the skin types provided in the
database,
obtaining from the database, information regarding the fluorescence
and spectroscopic characteristics associated with different degrees
of burn injury for the selected skin type for use in evaluating the
degree of the individual's burn injury;
determining the fluorescence and spectroscopic characteristics of
the injured individual's burned skin;
comparing the information obtained from the database for the
selected skin type with the characteristics of the injured
individual's burned skin to estimate the degree of burn injury of
the burned skin; and
indicating the estimated degree of burn injury of the injured
individual's burned skin.
14. Apparatus for evaluating a skin burn injury as defined in claim
1, wherein:
the plurality of light sources includes:
a first light source that emits excitation light having a
wavelength between 300 and 480 nanometers to cause fluorescence of
certain metabolic and structural constituents in the skin, and
a second light source that emits excitation light having a
wavelength at about 775, 810 or 904 nanometers to illuminate the
hemoglobin at the burn injury site;
the return light includes light reflected by the hemoglobin present
in the skin; and
the processor determines the potential viability of the skin at the
site of the burn injury.
15. Apparatus for evaluating a skin burn injury as defined in claim
14, wherein the plurality of light sources further includes a third
light source having a wavelength of about 980 nanometers to
illuminate the water content of the skin and the return light
includes light reflected by water present within the skin.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to the evaluation of burn injuries
and, more particularly, to apparatus, and related methods, that
evaluate a burn injury using ultraviolet or visible light
fluorescence spectroscopy and infrared absorption spectroscopy of
skin tissue at the site of the burn injury.
As shown in FIG. 1, the skin 2 is composed of a thin outer layer 4
(the epidermis) and a thicker inner layer 6 (the dermis). Beneath
the dermis is subcutaneous tissue 8, which contains mostly fat, and
eventually the muscle fascia 10 and muscle 12. The epidermis forms
a tough, waterproof protective coating having tough dead cells on
its outside surface that are continually worn away and having
living cells on its inner most parts that replace the worn away
dead cells. The dermis is living tissue that includes blood vessels
14, nerves 16, sweat glands 18, and hair follicles 20.
Heating of the skin 2, however brief, can cause damage to the cells
of its living tissue. Such damage typically is referred to as a
burn. Generally, burns can be categorized into degrees that
indicate the depth of the burn injury. First degree burns cause
reddening of the skin and affect only the epidermis 4. Such burns
heal quickly, but the damaged skin may peel away after a day or
two. A "sunburn" is an example of a first degree burn. A second
degree burn damages the skin more deeply, extending into the dermis
6 and usually causes blisters. However, some of the dermis is left
to recover. A third degree burn destroys the full thickness of the
dermis and, if the burn is very deep, muscles 12 and bones may be
exposed.
Experience has shown that second degree superficial dermal (or
partial-thickness) burns will normally heal spontaneously within
two weeks with minimal scarring, whereas second degree deep dermal
and third degree (or full-thickness) burns usually results in
necrotic skin and the resulting wound heals very slowly. Prompt
surgical removal of full-thickness burned skin down to the muscle
fascia 10 with immediate wound closure using grafts of healthy skin
2 decreases mortality and shortens the hospital stay.
To conserve surface and subjacent skin 2 during surgery, areas of
skin that normally will heal spontaneously should be differentiated
from areas of skin having more severe burns which will not heal
within two weeks and, therefore, require surgical excision and
grafting. However, slight changes in burn depth, on the order of
fractions of a millimeter, can mean the difference between a burn
that will heal spontaneously and a burn that must undergo
grafting.
One critical condition that divides necrotic tissue from viable
tissue is the circulation of blood through the burn site. Vascular
stasis is a condition that typically is an early indicator of
eventual tissue necrosis. Clinical criteria utilized to distinguish
burn depth, including sensitivity to pin-prick, visual appearance,
and viable cutaneous circulation, generally do not reliably
identify zones of viable tissue. In addition, techniques such as
passive infrared thermography, false-positive images, and
high-frequency ultrasound have proven ineffective in assisting
surgeons in estimating the depth of burn damage. Without reliable
means for evaluating the extent of a burn injury, it is often
necessary for the surgeon to excise the entire area of burned skin
2 and subcutaneous tissue 8 down to muscle fascia 10. Such a
procedure may sacrifice significant amounts of viable skin.
More successful techniques have been attempted that use fluorescent
drugs, such as indocyanine green and fluorescein, applied
intravenously and detected with a fiber-optic instrument. However,
the fluorescent drugs are slow to reach the burn site and may
linger at the burn site, limiting the frequency of testing. Optical
reflectance techniques that measure the ratio of reflected green
and red light to infrared light using a fiber-optic instrument have
had a measure of success in differentiating between full-thickness
and partial-thickness burns. However, this technique has required
bulky and complex optical instruments and has not been widely
adopted clinically.
From the discussion above, it should be apparent that there is a
need for a burn detection apparatus and method that rapidly
evaluates the extent of a skin burn injury in a reliable and
cost-effective manner. The present invention addresses this
need.
SUMMARY OF THE INVENTION
The present invention is embodied in a burn classification
apparatus, and related method, that employs induced fluorescence
spectroscopy and infrared reflectance spectroscopy to monitor the
condition of the injured skin. The apparatus assists the surgeon in
evaluating the viability of the skin tissue at the site of a burn
injury and potentially reduces the occurrence of unnecessary skin
grafts.
The apparatus includes a plurality of light sources, a sensor, and
a processor. Each light source is adapted to emit excitation light,
having a predetermined wavelength, that is directed at the burn
site to produce return light. At least one light source of the
apparatus is characterized by a wavelength of sufficient energy to
cause fluorescence of certain chemical constituents in the skin.
The return light includes some of the fluorescent light produced by
constituents present within the skin. The sensor, responsive to the
return light corresponding to each light source, monitors the
return light and generates a plurality of electrical signals based
on the intensity of return light within predetermined wavelength
bands. The processor is associated with the sensor and processes
the plurality of electrical signals so as to determine the
condition of the skin at the site of the burn injury.
In a more detailed feature of the invention, the plurality of light
sources include a first light source that emits narrow band
excitation light having a wavelength between 300 nanometers and 480
nanometers. More specifically, the plurality of light sources
includes a first light source that emits excitation light having a
wavelength of 405 nanometers, a second light source that emits
excitation light having a wavelength of 452 nanometers, a third
light source that emits excitation light having a wavelength of 775
nanometers, a fourth light source that emits excitation light
having a wavelength of 810 nanometers, a fifth light source that
emits excitation light having a wavelength of 904 nanometers, and a
sixth light source that emits excitation light having a wavelength
of 980 nanometers. Further, each of the plurality of light sources
includes a diode laser that generates the respective excitation
light.
In another more detailed feature of the invention, the
predetermined wavelength bands include a first wavelength band
between 450 and 460 nanometers, a second wavelength band between
480 and 490 nanometers, a third wavelength band between 520 and 530
nanometers, a fourth wavelength band between 550 and 560
nanometers, a fifth wavelength band between 770 and 780 nanometers,
a sixth wavelength band between 805 and 815 nanometers, a seventh
wavelength band between 900 and 910 nanometers, and an eight
wavelength band between 970 and 990 nanometers. The wavelength
bands are selected based on the wavelength of the respective
excitation wavelengths and are selected in accordance with the
selected excitation wavelengths.
In yet another more detailed feature of the invention, the
apparatus includes a first optical fiber bundle that has a
plurality of excitation optical fibers. The excitation optical
fibers are associated with the plurality of light sources in order
to transmit excitation light from the respective light source to
the site of the burn injury. The first optical fiber bundle also
has one or more return optical fibers that transmit the return
light from the site of the burn injury to the sensor. Further, the
apparatus can include a second optical fiber bundle of one or more
optical fibers located at a distance of approximately one
centimeter from the first optical fiber bundle during the
evaluation of the burn injury. The second optical fiber bundle
collects return light to evaluate tissue water below the skin.
Other features and advantages of the present invention should
become apparent from the following description of the preferred
embodiment, taken in conjunction with the accompanying drawings,
which illustrate, by way of example, the principles of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a cross-section of human skin.
FIG. 2 is a block diagram of a burn evaluation apparatus embodying
the present invention.
FIG. 3 is a graph prospectively representing the intensity of
fluorescence verses wavelength for normal skin induced to fluoresce
by laser light having a wavelength of about 405 nanometers.
FIG. 4 is a is a graph of the intensity of fluorescence verses
wavelength for collagen powder induced to fluoresce by laser light
having a wavelength of about 442 nanometers.
FIG. 5 is a graph of the intensity of fluorescence verses
wavelength for elastin powder induced to fluoresce by laser light
having a wavelength of about 442 nanometers.
FIG. 6 is a graph of the intensity of fluorescence verses
wavelength for NADH powder induced to fluoresce by laser light
having a wavelength of about 442 nanometers.
FIG. 7 is a graph of the intensity of fluorescence verses
wavelength for FAD powder induced to fluoresce by laser light
having a wavelength of about 442 nanometers.
FIG. 8 is a graph prospectively representing the intensity of
fluorescence verses wavelength for skin, having a partial thickness
burn with vasodilation, induced to fluoresce by laser light having
a wavelength of about 405 nanometers.
FIG. 9 is a graph prospectively representing intensity of
fluorescence verses wavelength for skin, having a partial thickness
burn with vascular stasis, induced to fluoresce by laser light
having a wavelength of about 405 nanometers.
FIG. 10 is a graph prospectively representing intensity of
fluorescence verses wavelength for skin having a full-thickness
burn induced to fluoresce by laser light having a wavelength of
about 405 nanometers.
FIG. 11 is a graph indicating the absorption spectra of Hemoglobin
(Hb), oxygenated hemoglobin (HbO.sub.z), and water (H.sub.2 O).
FIG. 12 is a graph prospectively representing relative amounts of
oxygenated hemoglobin and reduced hemoglobin verses time for a
partial-thickness skin burn with vasodilation.
FIG. 13 is a graph prospectively representing relative mounts of
oxygenated hemoglobin and reduced hemoglobin verses time for a
partial-thickness skin burn with vascular stasis.
FIG. 14 is a flowchart indicating a method to be implemented by the
burn evaluation apparatus of FIG. 2.
FIG. 15 is a graph prospectively representing intensity of
fluorescence verses wavelength for normal skin (FIG. 3) overlaid by
four predetermined wavelength bands.
FIG. 16 is a schematic diagram of the concept of a neural
network.
FIG. 17 is a block diagram of spectral signal processing algorithms
for the neural network of FIG. 16.
FIG. 18 is a block diagram of an alternative embodiment of a burn
classification apparatus of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in the exemplary drawings, the present invention is
embodied in a burn evaluation apparatus 30, and related method,
that allows a surgeon to make a quick evaluation of the extent and
depth of a burn injury to the skin. More specifically, the burn
classification apparatus employs induced ultraviolet or blue light
fluorescence spectroscopy and infrared (IR) reflectance
spectroscopy to monitor the condition of the structural and
metabolic compounds in the injured skin allowing evaluation of the
potential viability of the skin at the burn site. The apparatus
helps prevent the unnecessary removal of viable skin that will heal
spontaneously within a few weeks, thereby reducing the amount of
skin that must be surgically grafted.
With reference now to FIG. 2, the apparatus 30 of the present
invention is shown to include a plurality of light sources 32-42, a
sensor 44, and a processor 46. In addition, optical fiber bundles
48-54 assist in directing excitation light from the light sources
to the burn site on the skin 2 and return light from burn site to
the sensor 44.
The plurality of light sources 32-42 consist of six-diode lasers,
each producing excitation light at a predetermined wavelength. The
first light source 32 emits narrow-band excitation light having a
wavelength of approximately 405 nanometers produced by frequency
doubling light from a diode laser having a wavelength of
approximately 810 nanometers. The second light source 34 emits
narrow-band excitation light having a wavelength of about 452
nanometers produced by frequency doubling light from a diode laser
having a wavelength of about 904 nanometers. The wavelengths of the
excitation light from the first and second light sources are chosen
to induce a fluorescence response in the skin's metabolic and
structural compounds, discussed in more detail below. The third,
fourth, and fifth light sources 36-40 emit near-infrared (NIR)
light at the wavelengths of 775 nanometers, 810 nanometer, and 904
nanometers, respectively, which are useful in detecting content of
and state of hemoglobin in the skin. The sixth light source emits
infrared light having a wavelength of approximately 980 nanometers
that is used to evaluate the skin's tissue water content.
The sensor 44 includes a wavelength division multiplexer (WDM) 56
covering a wavelength spectrum from about 400 nanometers to about
1000 nanometers. The WDM images detected signals onto a linear 512
pixel charge-coupled device (CCD) array. The light exposure (light
intensity x exposure time) for each pixel of the CCD array is
digitized on a linear scale. The CCD array is cooled with a TE
cooler or with liquid nitrogen to minimize background noise.
Additionally, since the background noise signals are almost
uniformly distributed across the array, the average noise signal
may be subtracted from the signal from each detector element of the
array. A suitable CCD array is the CCD-512TKB thermoelectrically
cooled CCD detector available from EG&G Princeton Applied
Research of Princeton, N.J. The sensor provides the digitized
signals from the CCD detector elements to the processor 46.
Preferably, the processor 46 is a microcomputer that performs the
control and calculation functions of the present invention. The
processor typically includes a color display 58 and a keyboard 60.
A color display is advantageous for providing the surgeon with
color-coded images of the analysis results. The processor 46 is
programmed to control the sequencing and operation of the light
sources 32-42 and the sensor 44 and stores the resulting
signals.
The excitation light and return light are conveniently directed
between the surface of the skin 2, the light sources, and the
sensor by the optical fiber bundles 48-54. The main fiber bundle 50
is made of 200 to 400 individual optical fibers, each having a
diameter of about 32 micrometers to 50 micrometers. The individual
optical fibers are separated into 7 or 8 bundles of 30 to 50
optical fibers each bundle. Optical fibers from each light source
form an excitation fiber bundle 48 that merges with the main fiber
bundle. The remainder of the optical fibers (those not associated
with a light source) form the detection fiber bundle 52 that
directs the return light from the surface of the skin 2 to the
sensor 44. The optical fibers from the excitation fiber bundle are
randomly dispersed in the main fiber bundle to provide a uniform
mix of excitation and detection fibers at the skin's surface. In
addition to the main fiber bundle, a side fiber bundle 54 is
provided at a distance of approximately 1 cm from the main fiber
bundle 50. The side fiber bundle monitors deep reflectance (0.5
centimeters to 1 centimeter) of light from below the skin's
surface. The side fiber bundle is used in conjunction with the 980
nanometer light source to monitor the amount of tissue water below
the skin. A lens or lens system (such as a confocal lens
configuration) may be included at the end of the fiber-optic
bundles so that the bundles can operate as a non-contact probe.
The burn evaluation apparatus of the present invention takes
advantage of the fact that the normal spectroscopic response of
certain structural and metabolic constituents in the skin 2 are
altered by a burn injury. More specifically, normal skin has a
unimodal fluorescence response curve when induced to fluoresce by
light having a wavelength of about 405 nanometers, reflected in the
prospectively representative curve shown in FIG. 3. The curve is
produced by induced fluorescence in certain naturally occurring
fluorescent chemical compounds in the skin, namely, elastin,
collagen, NADH, and FAD. The elastin and collagen relate to the
structural condition of the skin and the NADH and FAD relate to the
metabolic condition of the skin. As can be seen in FIGS. 4-7, each
of these constituents contribute in varying amounts to the
fluorescence spectrum measured in the skin. (It is noted that FIGS.
4-7 were produced using excitation light having a wavelength of
about 442 nanometers. These curves would shift toward shorter
wavelengths in response to excitation light having a wavelength of
405 nanometers.)
However, after a superficial dermal burn, the blood vessels 14
dilate to promote healing, increasing the amount of hemoglobin in
the area of the burn site. Since hemoglobin absorbs light having a
wavelength between about 400 nanometers and about 500 nanometers,
the fluorescence spectrum curve from skin 2 having a superficial
dermal burn has a bimodal profile as shown in FIG. 8. After
sufficient dermal heating, the blood vessels may be damaged
resulting in vascular stasis. In this condition, the hemoglobin
circulates poorly and any oxygenated hemoglobin tends to be
eventually reduced. As shown in FIG. 9, the fluorescence spectrum
curve has a more pronounced bimodal profile when vascular stasis
occurs in the skin. In a full-thickness burn, the elastin,
collagen, and other constituents of the skin have been severely
altered or damaged and the profile of the fluorescence spectrum
curve returns to a structureless unimodal shape as shown in FIG.
10. The surgeon often will not be confused by this profile since
visual inspection will quickly reveal that the skin is not
normal.
Although the bimodal curve for a burn with vascular stasis (FIG. 9)
has more pronounced dip than the bimodal curve for a burn with
vasodilation (FIG. 10), further confirmation of the condition of
the skin at the burn site is evidenced by NIR absorption analysis
of the hemoglobin present. As shown in FIG. 11, hemoglobin (Hb) and
oxygenated hemoglobin (HbO.sub.2) have distinct absorption (and
reflection) profiles. Further, as shown by FIGS. 12 and 13, the
total hemoglobin present in a burn site with vasodilation (FIG. 12)
typically will be higher than the total hemoglobin present in a
burn site with vascular stasis (FIG. 13). By measuring the
reflectance of excitation light at the respective wavelengths of
775 nanometers, 810 nanometers, and 904 nanometers, the total
amount of hemoglobin and relative amounts of oxygenated hemoglobin
and reduced hemoglobin can be determined.
A further indication of the extent of burn injury is given by the
water content of the skin 2 and the tissues below the skin. The
water reflectance is measured using the light source providing
light having a wavelength of 980 nanometers. At this wavelength,
the absorption curve of water experiences a small peak (FIG. 11).
The water content of the skin is monitored using the main fiber
bundle 50 and the water content of the tissues below the skin are
measured using the side fiber bundle 54. The side fiber bundle
collects IR light emitted by the main fiber bundle and reflected by
water in the tissues below the skin.
The operation of the apparatus 30 is described with additional
reference to FIGS. 14 and 15. The spectroscopic measurements
preformed in evaluating skin burn injuries are largely influenced
by the skin's melanin content, age, bodily location, etc.
Therefore, before the apparatus evaluates the burned skin 2, the
apparatus is "calibrated" by performing measurements on a similar
area of normal unburned skin of the same individual. For example,
if the individual is burned on the left shoulder, then the normal
skin measurement would be performed on a similar location of the
right shoulder. The measurement sequence for normal skin is similar
to the measurement sequence for the evaluation of the burned skin,
discussed below. The calibration measurements are compared against
data in a database of normal skin measurements and a closest match
is found. Each skin type in the database also includes associated
empirical data relating to different degrees of burns for that skin
type. Thus, by matching the normal unburned skin of the individual
with a skin type in the database, the apparatus has available
information regarding the spectroscopic characteristics of
different degrees of burn injury to that skin type and,
accordingly, is better able to evaluate the burn injury using the
data from the database. Each burn injury evaluation provides
further data that can be used to increase the number of skin
measurements available in the database for performing the
"calibration." Initially, the database may be derived from
information in the published literature.
After the matching of the individuals normal skin 2 with the skin
types in the database, the apparatus 30 is ready for evaluation of
the burn injury. A probe, consisting of the main and side optical
fiber bundles 50 and 54, is placed on the skin's surface in the
area of the burn injury. The processor 46 activates the first laser
32, causing it to emit a pulse of excitation light having a
wavelength of 405 nanometers, and enables the sensor 44 to receive
any return light generated during a predetermined time interval.
The excitation light is directed through the excitation fiber
bundle 48 and the main fiber bundle to the site of the burn injury.
Return light from the excited skin is collected from the burn site
by the main fiber bundle and further directed to the sensor by the
detection fiber-optic bundle 52. The sensor is activated to receive
any return light only during the predetermined time interval. The
return light received during the predetermined time interval
presumably results from fluorescence induced by the 405 nanometer
excitation light.
As discussed above, the sensor generates digitized signals
representing the collected return light. The processor preferably,
but not necessarily, selects four wavelength bands from the
received digitized signals as shown in the prospectively
representative graph of FIG. 15. The four wavelength bands each
have a width of 10 nanometers and are centered around 455
nanometers, 485 nanometers, 525 nanometers, and 555 nanometers. For
each of these wavelength bands, the area under the curve is
computed, which represents the intensity of return light received
in these wavelength bands.
The computer calculates two intensity ratios R.sub.1 and R.sub.2
from the area calculations of the four wavelength bands using the
following formulas:
and
where:
I.sub.1, I.sub.2, I.sub.3, and I.sub.4 are the intensity of return
light measured in the four wavelength bands centered about 455
nanometers, 485 nanometers, 525 nanometers, and 555 nanometers,
respectively. The values of these ratios R.sub.1 and R.sub.2 are
used as indicators of the grade of thermal skin damage and are
indicative of the contributions of elastin and collagen, and to a
lesser extent, NADH and FAD, to the fluorescent spectra of the skin
2 when excited by light having a wavelength of 405 nanometers.
Continuing the evaluation, the processor 46 then activates the
second laser 34, causing it to emit a pulse of excitation light
having a wavelength of 452 nanometers, and enables the sensor 44 to
receive return light. At this excitation wavelength, the processor
selects four wavelength bands and again calculates two intensity
ratios. The selected wavelength bands are shifted toward a longer
wavelength (not shown) when compared to the previously selected
wavelength bands (FIG. 15) as a result of using excitation light
having a longer wavelength (452 nanometers). At this wavelength,
the calculated intensity ratio are indicative of the contributions
of NADH and FAD and, to a lesser extent elastin and collagen, to
the fluorescent spectra of the skin.
The processor 46 then evaluates the NIR absorption (or reflectance)
of the skin 2 by sequentially activating the next three lasers
36-40. For each wavelength, the processor enables the sensor 44 to
receive the return light and monitors the reflected light having
same wavelength as the selected laser. From the signals provided by
the sensor, the processor computes the intensity of return light
within a wavelength band centered about the wavelength of the
respective light source. The processor then computes the logarithm
of the measured intensity after each laser is activated. Using
these computed values, the values measure for the healthy skin, and
the empirical information from the database, oxygenated hemoglobin,
reduced hemoglobin, and total hemoglobin content in the skin is
determined by matrix inversion. Alternatively, a nonlinear
optimization algorithm is used to minimize the quadratic error
between observed and measured reflection (or absorption) levels.
Both approaches utilize a empirically derived or known extinction
coefficient for the compound of interest.
Finally, the sixth laser 42 is activated causing it to emit a pulse
of excitation light having a wavelength of about 980 nanometers.
The light received by the side fiber bundle 54 is monitored and the
processor 46 calculates the return light received in a wavelength
band centered about 980 nanometers. The side fiber is used to gain
information about the tissue water content below the skin. By
spacing the side fiber bundle about 1 centimeter from the main
fiber bundle 50, reflected light from the first 0.5 centimeters
below the skin's surface is avoided. Additionally, the tissue water
of the skin can be monitored by performing this measurement using
the main fiber bundle 50.
The values determined in the above evaluation of skin 2 damage for
the investigated site is then provided to the surgeon and compared
with the database of values experimentally obtained from different
cases of thermal skin damage. The calculated values are displayed
on the color display 58, as well as any graphs as desired by the
surgeon. The time to complete the sequence can take only a few
seconds allowing for almost immediate evaluation of the burn injury
at the location of the probe. The surgeon can then probe other
areas of the burned skin to evaluate the extent of the burn area.
Further, the measurements can be stored in the processor 46 for
comparison with later measurements to provide the surgeon with
trend data that would further enable the surgeon to assess the
viability of the burned skin.
In an alternative embodiment of the invention, the processor 46 may
include an artificial neural network 62 as shown in FIGS. 16-17.
The artificial neural network consists of layers of interconnected
processors (neurons) 64. The spectral data from the processor 46 is
input at input neuron layer 66. Preferably, each of the wavelength
bands discussed above is divided into 10 smaller bands or windows.
The input neuron layer has sufficient inputs to receive the data
for each of the wavelengths of interest. The neural network
performs a nonlinear transformation on the input data, using the
hidden neuron layer 68, and produces its result at the output
neuron layer 70'. Neural network has great flexibility in that it
can be taught to transform the spectral data (input neuron layer)
into an output (output neuron layer) that automatically and
uniquely identifies the condition of a burn injury with extremely
high sensitivity high speed (a fraction of a second for identifying
one spectrum), and high reliability (confidence level being
indicated by the neural network output) (FIG. 7). The software
implementing the neuron network is preferably, but not necessarily,
the substance identification "Neural Network" software package from
Physical Optics Corporation of Torrance, Calif. The neural network
operations and decision making may be performed on an IBM
compatible personal computer.
In an alternative embodiment of the present invention, the
plurality of light sources 32-42 are replaced by an arc lamp 72,
filter wheel 74, and lens 76 as shown in FIG. 18. It will be
readily recognized by one skilled in the art that the apparatus of
the present invention can utilize a large variety of excitation
wavelengths and monitored wavelength bands to evaluate a burn
injury. The apparatus need not be limited to only six excitation
wavelengths or any specific number of monitored wavelength
bands.
Although the foregoing discloses preferred embodiments of the
present invention, it is understood that those skilled in the art
may make various changes to the preferred embodiment shown without
departing from the scope of the invention. The invention is defined
only by the following claims.
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