U.S. patent number 5,074,306 [Application Number 07/483,907] was granted by the patent office on 1991-12-24 for measurement of burn depth in skin.
This patent grant is currently assigned to The General Hospital Corporation. Invention is credited to Richard R. Anderson, Howard A. Green, John A. Parrish.
United States Patent |
5,074,306 |
Green , et al. |
December 24, 1991 |
**Please see images for:
( Certificate of Correction ) ** |
Measurement of burn depth in skin
Abstract
A method for distinguishing between a full thickness and a
partial thickness skin burn in a patient having a skin burn. The
methods includes administering a fluorescent compound, which is
excited by infrared light, to the patient to cause the compound to
enter one or more capillaries below and adjacent the skin burn. The
compound is then excited with infrared light, and the amount of
fluorescence of the compound caused by the infrared light detected
at the skin burn and at unburned skin adjacent the skin burn. The
ratio of fluorescence detected at the skin burn and at the unburned
skin is an indication of the thickness of the skin burn, e.g., a
ratio of less than 0.4 indicates a full thickness skin burn.
Inventors: |
Green; Howard A. (West Roxbury,
MA), Parrish; John A. (Boston, MA), Anderson; Richard
R. (Boston, MA) |
Assignee: |
The General Hospital
Corporation (Boston, MA)
|
Family
ID: |
23921979 |
Appl.
No.: |
07/483,907 |
Filed: |
February 22, 1990 |
Current U.S.
Class: |
600/317 |
Current CPC
Class: |
A61B
5/445 (20130101); A61B 5/0071 (20130101); A61B
18/20 (20130101); A61F 2/105 (20130101) |
Current International
Class: |
A61B
18/20 (20060101); A61B 5/103 (20060101); A61F
2/10 (20060101); A61B 005/00 () |
Field of
Search: |
;128/633,664,665
;606/9 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Black et al., The Journal of Burn Care Rehabilitation "Burn Death
Evaluation with Fluorometry: is it really definitive?" (Abstract),
vol. 7, No. 4, pp. 313-317 (Jul.-Aug.). .
Gregory S. Van Liew, Martin A. Afromowitz, "Clinical Evaluation of
Burn Injuries using an Optical Relectance Technique", IEEE Trans.
On Biomedical Engineering, vol. BME-34, No. 2, (Feb. 1987), pp.
114-127. .
Martin A. Afromowitz, et al. "Multipectral Imaging of Burn Wounds:
A New Clinical Instrument for Evaluating Burn Depth", IEEE Trans.
Biomed. Eng., vol. 35, No. 10, (Oct. 1988) pp. 842-850. .
John E. Gatti, M.D. et al., "Evaluation of the Burn Wound with
Perfusion Fluorometry", The Journal of Trauma, vol. 23, No. 3, pp.
202-206, (Sep. 9-11, 1982). .
Diversatronics, Inc., "A Breakthrough for Monitoring Nutritive
Blood Flow", pp. 1-4. .
Howard A. Green, M.D., "Dual Wavelength Excitation of Indocyanine
Green Fluorescence to Determine Burn Depth", American Burn Assn.
Conference Abstract, Mar. 27-30, 1990. .
G. Moneta et al., "Infrared Fluorescence Videomicroscopy of Skin
Capillaries with Indocyanine Green", Int. J. Microcirc: Clin. Exp.
6:25-34 (1987), pp. 25-34. .
Flower, R. W., et al., "Indocyanine Green Dye Fluorescence and
Infrared Absorption Choroidal Angiography Performed Simultaneously
with Fluorescein Angiography", Johns Hopkins Medical Journal 138,
pp. 33-42, (1976). .
Howard A. Green, M.D., et al., "Mid-Dermal Wound Healing: A
Comparison Between Excision with a Dermatome and Pulsed Carbon
Dioxide (CO.sub.2) Laser", Pub. American Burn Assocation Meeting,
Abstract, Mar . 27-30, 1990. .
Howard A. Green, M.D., et al., "Pulsed Carbon Dioxide (CO.sub.2)
Laser Ablation of Burn Eschar: In Vitro and In Vivo Analysis", Pub.
American Burn Assocation, Abstract, Mar. 27-30, 1990. .
Green et al., The Journal of Investigative Dermatology, vol. 92,
No. 3, Mar. 1989, "Skin Graft Take and Healing After CO.sub.2 and
193 nm Excimer Laser Ablation of Graft Beds". .
Abergel et al., "Aging Hands: A Technique of Hand Rejuvenation by
Laser Resurfacing and Autologous Fat Transfer", J. Dermatol Surg.,
Jul. 1989, pp. 725-728. .
Abergel et al., "Laser Abrasion for Cosmetic and Medical Treatment
of Facial Actinic Damage", vol. 43, Jun. 1989, pp. 583-587. .
Walsh et al., "Pulsed CO.sub.2 Laser Tissue Ablation: Effect of
Tissue Type and Pulse Duration on Thermal Damage", 1988 Alan R.
Liss, Inc., pp. 109-118, Lasers in Surgery and Medicine 8:108-118.
.
Ben-Baruch et al., "Comparison of Wound Healing Between Chopped
Mode-Superpulse Mode CO.sub.2 Laser and Steel Knife Incision",
Lasers in Surgery and Medicine 8:596-599 (1988). .
Lanzafame et al., "Comparison of Continuous-Wave, Chop-Wave, and
Super Pulse Laser Wounds", Laser in Surgery and Medicine 8:119-124
(1988). .
Fleming et al., "Skin-edge Necrosis in Irradiated Tissue after
Carbon Dioxide Laser Excision of Tumor", Lasers in Medical Science
(1986), pp. 264-265, (Apr. 29, 1986). .
Badawy et al., "Comparative study of continuous and pulsed CO.sub.2
laser on tissue healing and fertility outcome in tubal
anastomosis", vol. 47, No. 5, May 1987. .
Baggish et al., "Comparison of electronically superpulsed and
continuous-wave CO.sub.2 laser on the rat uterine horn*", vol. 45,
No. 1, (1986)..
|
Primary Examiner: Cohen; Lee S.
Assistant Examiner: Pfaffle; K. M.
Attorney, Agent or Firm: Fish & Richardson
Claims
We claim:
1. A method for determining the thickness of a skin burn in a a
patient, comprising the steps of:
administering a first fluorescent compound, which is excitable by
infrared light, to said patient to cause said administered compound
to enter one or more capillaries below and adjacent the skin
burn;
exciting said administered compound with infrared light; and
detecting the amount of fluorescence of said excited compound
caused by said infrared light at the skin burn and at unburned skin
adjacent the skin burn; and calculating a ratio of the amount of
fluorescence detected at the skin burn to the amount of
fluorescence detected at the unburned skin as an indication of the
thickness of the skin burn.
2. The method of claim 1, further comprising a step of detecting
the amount of fluorescence caused by said infrared light at the
skin burn and at the unburned skin adjacent the skin burn prior to
administering said first fluorescent compound, and subtracting
these levels of fluorescence from those levels of fluorescence
detected after administering said fluorescent compound and prior to
said step of calculating the ratio of the levels of fluorescence of
said compound.
3. The method of claim 1 or claim 2, wherein a ratio of less than
0.4 indicates a full thickness skin burn.
4. The method of claim 1 or 2, further comprising a step of
administering a second fluorescent compound, which may be the same
as said first fluorescent compound, which is excitable by
ultraviolet light, to said patient to cause said second fluorescent
compound to enter one or more capillaries below and adjacent the
skin burn;
exciting said second fluorescent compound with ultraviolet light;
and
detecting the amount of fluorescence of said second fluorescent
compound caused by said ultraviolet light at the skin burn and at
unburned skin adjacent the skin burn; and calculating a ratio of
the amount of detected fluorescence of said second compound at the
skin burn to the amount of fluorescence detected at the unburned
skin as an indication of the depth of the skin burn.
5. The method of claim 4 wherein said first fluorescent compound is
indocyanine green.
6. The method of claim 5 wherein the ratio of the amount of
detected fluorescence of said first fluorescent compound to the
amount of detected second fluorescent compound in response to said
infrared and ultraviolet light, respectively, is indicative of the
depth of the skin burn.
7. The method of claim 4 wherein said first fluorescent compound is
indocyanine green, and said second fluorescent compound is
fluorescein.
8. The method of claim 7 wherein the ratio of the amount of
detected fluorescence of said first fluorescent compound to the
amount of detected second fluorescent compound in response to said
infrared and ultraviolet light, respectively, is indicative of the
depth of the skin burn.
9. The method of claim 7, wherein the step of detecting further
comprises a step of measuring the amount of said first fluorescent
compound and said second fluorescent compound with a dual
wavelength fluorescence video imaging processing system.
10. The method of claim 1 or 2 wherein said first fluorescent
compound is indocyanine green.
11. The method of claim 10, wherein the step of detecting further
comprises a step of measuring the amount of said first fluorescent
compound and said second fluorescent compound with a dual
wavelength fluorescence video imaging processing system.
12. The method of claim 1, further comprising a step of removing
the tissue from the skin burn after the step of detecting the
amount of fluorescence, and further comprising a step of detecting
the amount of fluorescence after said tissue removal.
13. The method of claim 12 wherein said step of tissue removal
comprises excising the skin burn tissue with a pulsed CO.sub.2
laser.
14. The method of claim 2, further comprising a step of removing
the tissue from the skin burn after said calculating step and a
step of detecting the amount of said fluorescence caused by said
infrared light at the skin burn after said step of tissue removal.
Description
BACKGROUND OF THE INVENTION
This invention relates to methods and apparatus for determination
of burn depth in skin, and for removing burnt skin.
Afromowitz et al., (BME-34 IEEE Transactions on Biomedical
Engineering 114, 1987; Afromowitz et al., 35 IEEE Transactions on
Biomedical Engineering 842, 1988) describe a real-time video
imaging system for analysis of debrided burn wounds on the third
day after burning. The relative diffuse reflectivity of the burn
wound is measured in the red, green, and near infrared wavelength
bands; these measurements are used to determine the probability of
tissue healing.
Gatti et al., (23 J. Trauma 202, 1983) describe use of sodium
fluorescein to determine the depth of a burn. The rate of
fluorescein uptake and burn wound fluorescence is compared to that
of normal unburned skin. Their results suggest that no distinction
can be made between superficial and deep partial thickness
burns.
Diversatronics (Advertisement) describes the fiberoptic perfusion
fluorometer used by Gatti et al., supra.
SUMMARY OF THE INVENTION
The present invention features a method by which burn depth in skin
can be assessed at an early time after burning. This method allows
differentiation of burns which will not heal completely within two
weeks (full thickness or deep dermal burns), and thus will need
excision and grafting therapy, from burns which will heal in two
weeks (partial thickness burns), and therefore, do not need to be
surgically excised and grafted. The method allows accurate
prediction of burn depth within a few hours after a burn. The
method is thus useful for guiding a surgeon or laser in debriding
burn eschar and necrotic tissue.
Unlike prior methods, the resolution of the method of this
invention is sufficient to allow debridement of eschar to within a
few microns of viable tissue below the burned tissue. Simultaneous
use of this method with a pulsed CO.sub.2 laser allows precise
removal of the eschar with a minimum amount of blood loss to the
patient. Prior methods for intraoperative detection of viable
tissue necessitated removal of eschar until bleeding occurred. Such
bleeding is detrimental to a patient, especially when that patient
has a significant percentage of skin burn.
In a first aspect, the invention features a method for determining
the thickness of a skin burn, and thus distinguishing between a
full thickness and a partial thickness skin burn in a patient. The
method includes administering a fluorescent compound, which is
excitable by infrared light (ranging from 700-12,000 nm, preferably
700-1500 nm), to the patient to cause the compound to enter one or
more capillaries below and adjacent the skin burn. The compound is
then excited with infrared light, and the amount of fluorescence of
the compound caused by the infrared light detected at the skin burn
and at unburned skin adjacent the skin burn. The ratio of
fluorescence detected at the skin burn and at the unburned skin is
an indication of the thickness of the skin burn, e.g., a ratio of
greater than 0.4, preferably more than 1.0 or 2.0, indicates a full
thickness skin burn.
In preferred embodiments, the method also includes detecting the
amount of fluorescence caused by the infrared light at the skin
burn and at the unburned skin adjacent the skin burn prior to
administering the fluorescent compound. These levels of
fluorescence are then subtracted from those levels of fluorescence
detected after administering the fluorescent compound, prior to
calculating the ratio of the levels of fluorescence of the
compound.
In other preferred embodiments, the method also includes
administering a second fluorescent compound, which may be the same
as the above fluorescent compound, which is excitable by
ultraviolet light (ranging from 200-400 nm), to the patient to
cause the second fluorescent compound to enter one or more
capillaries below and adjacent the skin burn. This second
fluorescent compound is then excited with ultraviolet light, and
the amount of fluorescence of the second fluorescence compound
caused by the ultraviolet light detected at the skin burn and at
unburned skin adjacent the skin burn. The ratio of fluorescence of
the compound at the skin burn and at the unburned skin is an
indication of the depth of the skin burn.
In the more preferred embodiments, the fluorescent compounds emit
light in the infrared region when excited; both fluorescent
compounds are indocyanine green, or the fluorescent compound is
indocyanine green, and the second fluorescent compound is
fluorescein; the ratio of fluorescence of the fluorescent compound
and the second fluorescent compound in response to the infrared and
ultraviolet light, respectively, is indicative of the depth of the
skin burn; the amount of fluorescent compound is measured with a
dual wavelength fluorescent video imaging processing system; and
the skin burn tissue is removed after detecting the amount of
fluorescence, and the amount of fluorescence then again detected
after such removal; even more preferably the removal involves
excising the skin burn tissue with a pulsed CO.sub.2 laser.
The use of a fluorescent dye which is excited by infrared light is
significantly advantageous over use of a dye excited only by
ultraviolet light. Infrared light is minimally interfered with by
the major skin and burn chromophores (blood, melanin, and
carotenoids). Thus, the overlying skin or burn eschar is almost
transparent to such light; and the depth of penetration of infrared
light in burn eschar is significantly greater than that of
ultraviolet light. Similarly, use of a dye which fluoresces in the
infrared region allows minimal interference by the major skin and
burn chromophores with detection of such fluorescence. Thus, such a
dye allows deeper penetration and more accurate detection of viable
tissue. When such a fluorescent compound is used in combination
with a compound which fluoresces in response to ultraviolet light,
especially when it fluoresces in the infrared region, the
simultaneous excitation with infrared and ultraviolet light allows
viable tissue to be measured at two depths. This dual wavelength
excitation allows a surgeon with a knife or a laser to remove
necrotic tissue from the burn surface and assess the remaining
tissue circulation at both shallow (100 microns) and deep (1.2 mm)
distances below the cutting surface. This allows a surgeon to cease
removal of overlying necrotic tissue just prior to reaching viable
or regenerating skin. Thus, conservative eschar removal with
preservation of underlying vital tissue is achieved.
Indocyanine green is a preferred embodiment of the invention since
it has the ideal properties of fluorescing in the infrared region
in response to both ultraviolet and infrared exciting light
wavelengths. Thus, this single dye can be used to assess burn depth
with two types of light. Supplementation of the use of indocyanine
green with sodium fluorescein allows even greater accuracy in
assessing the depth of burn tissue.
This early differentiation of full from partial thickness burns
enables a burn surgeon (or even a laser guided by the video image
produced by the above method) to diagnose and therefore perform
early excision grafting of full thickness burns. This decreases
morbidity and mortality.
In a second aspect, the invention features a method for precise
ablative excision of burnt tissue. The method involves providing a
pulsed CO.sub.2 laser with a pulse width of less than 200 msec and
a repetition rate of delivery of fewer than 50 (preferably fewer
than 40) pulses per second to one spot; and causing laser light
from the pulsed CO.sub.2 laser to contact, and thus excise, the
burnt tissue.
In preferred embodiments, the pulsed laser light is provided with a
radiant exposure of between 5.0 and 19 joules/cm.sup.2, and at
least 0.5 cm.sup.2, preferably 1 cm.sup.2, of burnt tissue is
excised.
Applicants have discovered that a pulsed CO.sub.2 laser, with the
above pulse specifications, is an ideal tool for removal of eschar
from skin burns. Use of a short pulse of laser energy allows
removal of tissue efficiently and precisely with limited concurrent
thermal damage to underlying tissue. The residual zone of thermal
damage of the pulsed CO.sub.2 laser does not inhibit split
thickness graft take or healing. With visual feedback, laser
ablation can be stopped within a few microns of viable underlying
muscle fascia. When this procedure is combined with the above burn
depth imaging device the burn eschar can be removed with great
accuracy without damaging underlying viable tissue. Such excision
is far superior to use of mechanical tools, or other medical
lasers.
The above laser is ideal for excisions, that is, the removal of at
least 0.5 cm.sup.2 of tissue. The laser is ideal because it causes
hemostasis; it guickly and efficiently removes dead skin, while
leaving viable remaining tissue intact; and it allows precise
control of the depth of excisions.
Other features and advantages of the invention will be apparent
from the following description of the preferred embodiments, and
from the claims.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The drawings will first briefly be described.
DRAWINGS
FIG. 1 is a diagrammatic representation of a dual wavelength
infrared fluorescence video imaging system;
FIG. 2 is a circuit diagram of an image processing system;
FIGS. 3a, b and c are photographs of images obtained with an image
processing system;
FIG. 4 is a diagrammatic representation of an indocyanine green
fluorimeter; and
FIGS. 5 and 6 are graphical representations of fluorescence ratios
with infrared and ultraviolet light, respectively.
STRUCTURE
Video Imaging System
Referring to Figs. 1 and 2, there is shown in diagrammatic form the
general structure of an image processing system for use in the
method of this invention. Video imaging system 10 is provided with
an excitation light source 12 chosen from continuous wave xenon or
mercury lamps (ILC Technology) or a pulsed xenon lamp (EG&G
Industries). In one embodiment, the light source is an
International Light Corporation Ceermax Xenon Lamp CX300 UV which
provides broad spectrum excitation radiation to fluoresce the
target and its vital dye either in the UV, visible, or infrared
(IR) spectrum. The light from this source is caused to pass through
excitation filters 14. These filters select excitation radiation
wavelengths for fluorescence image capture and quantification
analysis via the CCD or ICCD camera and major computer system.
These are interchangeable variable filters for exciting both
fluorescein and indocyanine green dyes in the visible, ultraviolet
and infrared regions of the light spectrum. For example, a narrow
band interference filter at either 805 or 380 nanometers (Esco
Industries), a long pass 710 nanometers filter or short pass 450
nanometers filter (Corion, Inc.), or an 850 nanometers narrow band
interference filter (Esco Industries) may be used. The band width
of these excitations filters may vary from 5 to 40 nanometers, with
the optimal center band excitation wavelengths being chosen as
follows: fluorescein excitation: 490 nanometers; indocyanine green
(UV excitation): 400 nanometers; and indocyanine green (infrared
excitation): 780 nanometers. The filtered light may also be
delivered as a beam or through a fiber 16, for example, a
bifurcated round bundled silica fiber (Fiberguide Industries) to a
target 18, for example, burned or unburned skin.
The fluorescent radiation of the target is detected by a camera 20,
which is an image intensified CCD camera (ICCD) manufactured by
Clifftondale Electronics, Inc., Model #FT450 with 100 times more
sensitivity than the CCD camera, customized for gain control. This
camera captures selected fluorescing photons. Each pixel or photon
capturing detector in the camera stores the emission photon energy,
and converts it to electrical current of a corresponding intensity.
Prior to detection by the camera, the light is caused to pass
through barrier filters 22 which are interchangeable variable
emission filters designed to select the fluorescing radiation from
the tissue, caused by fluorescence of indocyanine green or
fluorescein dyes, in the visible and infrared regions of the
spectrum. Band widths of these barrier filters may vary from 5 to
40 nanometers with optimal center band emission barrier filter
wavelengths as follows: fluorescein fluorescence: 550 nanometers,
indocyanine green fluorescence (uv excitation): 840 nanometers, and
indocyanine green fluorescence (infrared excitation): 850
nanometers. Other filters from other filter manufacturers, for
example, Melles Griot, Schott, and Omega Corporations, may be used.
For example, the Esco #5-92-8400 (840 nm) is used for infrared
fluorescence from either UV or IR excitation of indocyanine green
in target skin; Corlon S-10-560S is used for visible fluorescence
from fluorescein.
The light detected by the camera is intensified by an image
intensifier 24. Information from the image intensifier is passed to
various electronic components including a major computer 28, and a
monitor 38, for analysis by standard technique.
Computer 28 is a Unitech Thinkmate 386-based IBM compatible with an
80 megabit hard drive, a data translation video frame grabber board
(#2862-60) which converts the electrical output from the video
camera to a digital signal which can be used by the computer; and
Imagepro II (Media Cybernetics Co.), a standard image processing
software adapted for use in this application. This is a
comprehensive image processing software package designed for
microcomputers. Image Pro II clarifies images, removes haze,
improves contrast, outlines edges, zooms in to study detail, and
changes light intensity to help read information hidden to the
human eye; it also performs analysis and enhancement functions,
including filtering operations to detect edges and outlines,
contrast management, and pixel replacement to change contrast and
brightness, histogram sliding and stretching, equalization,
contouring, and thresholding of images and false coloring. This
program is useful to identify and quantify fluorescing intensities
of images within and around burned or damaged skin. Once
quantified, fluorescing intensity values below a predetermined
threshold value is set to represent areas which have deep burns,
and values above a certain threshold represents shallow burns or
unburned tissue. Thus, the computer is designed for quantitative
image analysis, densitometry, image segments, digital substraction
imagine, area measurements, and false coloring. An optical storage
device is also provided; this is a write once read many times
computer hardware optical disc storage system capable of storing
large quantities of data on a library with 940 megabits of memory.
This is useful because each processed image consumes about 250 K of
memory in the computer.
A color monitor 36 (e.g., a Sony PVM 1271Q) is used to display the
output of computer 28. Output from the image intensifier and camera
20 is monitored with monitor 38, e.g., a black and white Panasonic
TR-930 which allows the operator to visually observe and monitor
the fluorescence which the camera captures before processing in the
computer. Information is passed from monitor to computer via black
and white (B&W) signal cable. Hard copy from computer 28 is
obtained using a laser printer 40 (Hewlett Packard Laser Jet Series
II). A third monitor 42 is also provided, e.g., an NEC multisync
3-D color monitor to visually access the computer and software
information and data. Color monitor 36 (Sony 8VM 1271Q) allows the
user to observe pre processed and processed images in color. It is
capable of receiving, via red green-blue-primary color cables,
images processed from the computer, and capable of sending color
signals to a video printer (44, Sony) via R.sub.-- G.sub.-- B
primary color cables for color hard paper copies of the images. It
is also capable of transferring images to a video cassette recorder
(46, VCR) from the video printer via light analog input and output
cables (LAI). This allows recording, via NTSC cable (standard Video
Cable), the entire imaging process and data translation process on
videotape.
Indocyanine Green Fluorimeter
Referring to FIG. 4, there is shown a basic system useful for
collecting rat burn data to show that full from partial thickness
burns can be distinguished on the basis of their fluorescence
intensity after UV and IR excitation of intravenously administered
indocyanine green.
A light source 50, is the same as that described above, using a
handmade water container 52 which filters out infrared radiation
above 2 microns wavelength. This prevents heat denaturation and
overload of equipment. Filters 54 are the same as described for the
above video imaging device. Bifurcated fiber 56 is provided to take
filtered excitation radiation from source 50 and transmit it to a
target 58, and to take the fluorescing radiation response from the
target tissue and deliver it to a detector via a barrier filter 60,
similar to that described above. A photomultiplier tube 62
(Hamamatsu #R829) is provided to detect, amplify, and quantify the
photons fluorescing from the tissue target. A lock in amplifier 64
(Stanford Research Systems Dual Channel Lock In Amplifier #SR510)
includes an electronic filter to eliminate background static
(electrical noise) from the system, and amplify the signal from the
photomultiplier tube for guantification of the fluorescence
signal.
METHODS
The above described dual wavelength fluorescence fluorimeter and
fluorescent videoimaging system are used generally as follows: A
fluorescing vital dye excited by infrared light is injected into a
mammal, and allowed to perfuse through viable skin via patent
viable cutaneous circulation. The dye is then excited with either
short or long wavelength radiation. The fluorescence of the vital
dye is quantified either through fiberoptics and a photomultiplier
tube (in the case of the fluorimeter), or via a videocamera and
image processing computer (in the case of the videoimaging
device).
We have found that the quantified fluorescence intensity is
directly related to the cutaneous blood volume, and thus viablility
of the observed tissue (skin). The intensity is inversely related
to the thickness of the overlying burnt or necrotic tissue. The
stronger or more intense the fluorescence, the more blood in the
tissue, the thinner the burn, and the less the tissue is injured.
The weaker or less intense the fluorescence, the less blood in the
tissue, and the more tissue that is injured or burned. Since
ultraviolet excitation excites vital dye near the surface of the
skin, and infrared light excites vital dyes deeper in the tissue,
various tissue depths can be examined for viability.
The recorded and quantified fluorescence of the target or burned
tissue perfused with dye, is corrected for any autofluorescence of
the tissue (from endogenous chromophores), by subtracting the
fluorescence of target which occurs before injection of dye.
Corrected burned or target tissue fluorescence values are then
compared to normal tissue as fluorescence ratio's (FR). This
fluorescence ratio relates to the relative blood volume, and
thickness of the necrotic tissue in the target area, and is
calculated as burn tissue fluorescence intensity (post dye minus
pre dye injection) divided by normal tissue fluorescence intensity
(post dye minus pre dye injection).
EXAMPLE 1
Indocyanine Green
Indocyanine green is injected intravenously into the patient to be
analyzed. The dye enters the blood system and passes within
capillaries which are adjacent and beneath the area of skin burn.
The dye will not significantly pass into capillaries which are
damaged by the burn. Prior to injection of this dye, one of the
above described devices is used to determine natural or background
fluorescence of the skin in the burnt area and in the adjacent
unburnt skin. After injection, fluorescence is again detected, and
the background level of fluorescence subtracted from that in the
presence of the fluorescent dye. The ratio of fluorescence in the
area of skin burn to unburnt skin is determined. Similarly, the
ratio of fluorescence after excitation with ultraviolet or infrared
light is determined.
EXAMPLE 2
Fiberoptic System
Referring to FIGS. 5 and 6, male hairless fuzzy rats (6-11 weeks
old, weighing at least 250 grams) were selected for burns.
Anesthesia was by use of inhaled anhydrous ether and intramuscular
ketamine and xylazine prior to burning and injection of the
indocyanbine green. The burns were induced with heated brass blocks
heated to 100.degree. C. in boiling water and applied to the skin
for either 20 seconds for the full thickness burn, or 2 seconds for
the partial thickness burn. The full thickness burn was placed on
the right paraspinal area at least 3 cm cephalad to the partial
thickness burn which was induced on the contralateral side. Normal
unburned skin at the same level and on the contralateral side to
the burn was used for controls. On day zero identical full and
partial thickness burns were induced on the backs of 24 rats. Four
rats were selected from this group on days 0, 1, 2, 3, 7 and 14
post burn for fluorescence studies.
In this rat model, the above fiberoptic system, with the particular
characteristics described below, was used to determine the FR on
certain days post burn wound induction. The fiberoptic fluorimeter
is designed to emit two wavelengths and quantify indocyanine green
infrared tissue fluorescence. Excitation light was produced by an
ILC Technology R300-3 Xenon Lamp. Narrow band excitation filters
interposed between the lamp and the bifurcated fiberoptic bundle
(Fiberguide Industries) delivered the desired wavelength of light
to the skin, (369 nm DF 39 Omega Optical Inc., or 780 nm DF 20 ESCO
Industries). Light produced by fluorescence passed from the
vasculature in the skin or eschar, through the fiberoptic fiber
towards barrier filters (840 nm DF 20 Omega Optics, 850 nm DF 20
ESCO Industries) permitting transmission of near infrared IG
fluorescent light while blocking light of lower or higher
wavelengths. The intensity of the fluorescence was detected in the
photomultiplier tube, and quantified through the lock in
amplifier.
Background fluorescence readings were performed on burned and
normal skin prior to injection of indocyanine green (10 mg/kg).
Injections were performed under anesthesia, via the femoral vein.
Indocyanine green infrared fluorescence intensity was quantified
during one hour after injection and at 24 hours after intravenous
bolus of indocyanine green. Immediately after the 24 hour post
injection fluorescence assessment, the rates were sacrificed, and
tissue from the burned sites sent for histopathyology. The
intensity of indocyanine green infrared fluorescence for both burn
areas and their contralateral normal skin was evaluated on Days 0,
1, 2, 3, 7 and 14 post burn induction. Four previously noninjected
burned rats were taken out of the original group of 24 and studied
on each of these days. Fluorescence intensity for each type of burn
were expressed as a ratio of burned to normal skin after
subtracting out pre-indocyanine green background fluorescence
values.
Certain FRs were found to represent either full or partial
thickness wounds, as shown in the Figures. The graphs shown in
FIGS. 5 and 6 represent some of the data collected from burned rats
using this system. The first graph (FIG 5) is an example of
infrared excitation of FT (full thickness) and PT (partial
thickness) burns and the corresponding fluorescence ratios of the
burned tissue to normal tissue. Whether excited by shallow
penetrating UV or deep penetrating IR radiation, the full and
partial thickness burns were distinguishable by their fluorescence
ratios on days 0, 1, 2, 3, 7, and 14 post burn wound induction
after injection of 10 mg/kg indocyanine green.
The fluorescence of indocyanine green in normal skin, partial
thickness burns, and full thickness burns after excitation with
ultraviolet light (369 nm, which fluoresces at 840 nm), and after
excitation with infrared light (780 nm, which fluoresces at 850
nm), was determined on the aforementioned days post burn. Full
thickness burns had a fluorescence intensity not significantly
greater than that of normal skin lacking fluorescent dyes
incorporated into capillaries. Partial thickness burns had a
fluorescence intensity 2-3 fold greater than that of the background
level, with both ultraviolet and infrared radiation.
EXAMPLE 3
Video Imaging
The following algorithm is applicable when indocyanine green is
used as the vital fluorescing dye in the video imaging device
(where +represents degrees of IR fluorescence intensity, with
++++being the highest, ---represents nil IR fluorescence):
______________________________________ superficial deep full normal
dermal dermal thickness skin burn burn burn
______________________________________ UV excitation: ++++ +++-
+--- ---- IR excitation: ++++ ++++ ++-- ----
______________________________________
Referring to FIGS. 3a, b, and c, using video imaging system 10
described above, the 3 images shown in the figures were obtained
with burns created as described in Example 2. Areas of full
thickness burns (e.g., area 50) had little or no fluorescence
compared to areas of unburned tissue (e.g., area 52). In each of
these figures between 5 and 10 milligrams per kilogram of
indocyanine green was injected, as described above, and
fluorescence detected in the infrared range after excitation with
infrared light. FIG. 3a shows the image a few hours after burning,
whereas FIGS. 3b and 3c show the image 1 and 2 days, respectively,
after burning. These data demonstrate that a full thickness burn
can be detected within a few hours after burning. This allows
immediate removal of the burned tissue and grafting of the burnt
area, to provide rapid recovery of the burn area.
The video imaging technique can be used prior to removal of eschar,
at the same time as removal of eschar, or after removal of eschar.
Thus, it allows continuous monitoring of burn depth and the amount
of eschar still to be removed. This permits a surgeon to excise
eschar until only a few micron thickness remains, without damaging
underlying viable tissue.
Eschar Removal
We have found that removal of burn eschar is readily achieved with
a pulsed CO.sub.2 laser. A conventional pulsed CO.sub.2 laser is
provided with a pulse width of less than 200 microseconds,
preferably between 100 to 200 microseconds; at a fluence between
5.0 and 19 joules/cm.sup.2 ; and at a repetition rate of delivery
to one spot of tissue not greater than 50 pulses per second. Such a
laser limits the zone of thermal damage to less than 150 microns in
tissue subjacent to that excised, and allows removal of tissue from
the surface of skin burns precisely, with an accuracy of tens of
microns. The tissue is removed efficiently and blood loss prevented
by hemostasis. Normal healing of the tissue, and normal skin graft
take, is achieved. Burn tissue is excised by surface removal of an
area exceeding about 0.5 cm.sup.2. A tangential type of excision is
used to remove the surface tissue, and to conserve viable
structures.
EXAMPLE 4
Pulsed CO.sub.2 Laser
Freshly excised burned (48 hour) and unburned swine skin was
exposed to a pulsed CO.sub.2 laser having parameters set as
described above. The threshold radiant exposure per pulse for
ablation in normal skin and eschar was 1.9 to 3.2 joules per
centimeter square and 2.5 to 3.5 joules per centimeter square
respectively. The operating radiant exposures for most efficient
ablation was between 5.0 and 19 joules per centimeter square. At
these fluences with a spot size of 1.9 mm, 0.00015 grams of tissue
were ablated per pulse. Radiant exposures above 19 joules per
centimeter square produced plasma, which decreased the efficiency
of laser ablation. The heats of ablation for normal and burned skin
was 2706 and 2416 joules per cubic centimeter of tissue ablated,
respectively.
A mechanically scanned pulsed CO.sub.2 laser was used for in vivo
surface eschar excision. The laser performed bloodless excisions of
48 hour old full thickness burns on the backs of male hairless
rats. Only visual feedback was needed to allow laser ablation to be
stopped within microns of the viable underlying muscle fascia.
In partial thickness of laser excisions, the laser created a
thermal damage of 85 microns over the fascia. Polymorphonuclear
leucocytes and foreign body giant cells removed the denatured
collagen within the laser created zone of thermal damage through
day 7 post excision. By day 7, epithelial coverage of the laser
created wounds was not significantly different from dermatome
created wounds. Dermal collagen reformation was more vigorous in
the healing laser created wounds on days 7, through 28. By day 35
post excision the two excisional modalities demonstrated no
difference in the thickness of the new granulating dermis. At 42
days the two wounds were virtually indistinguishable
histopathologically. There was no significant difference in area of
the two wounds over 42 days.
The above video imaging system and pulsed CO.sub.2 laser are useful
in other applications. For example, the above video imaging system
in combination with an infrared excited dye, e.g., indocyanine
green, can be used to predict the viability of arterialized flaps,
determine the degree of peripheral vascular disease, and delineate
the margins of necrotic tissues and infarcted organs. The pulsed
CO.sub.2 laser described above is also useful for removal of the
dye associated with a tattoo in the mid dermis or higher regions of
the skin; for precise diepithelialization; for cosmetic surgery,
for example, breast reconstructions; for surface surgery, for
example, removal of moles and skin cancers; for internal organ
removal, for example, conization; and for removal of cervical
intraepithelial neoplasia.
Other embodiments are within the following claims.
* * * * *