Response of Lightly and Highly Pigmented Porcine Skin (Sus scrofa ...

3219 users shared this document! click

33 Journal of the American Association for Laboratory Animal Science
Copyright 2006
by the American Association for Laboratory Animal Science Vol 45, No 3 May 2006 Received: 26 Oct 2005. Revision requested: 6 Dec 2005. Accepted: 6 Dec 2005. 1 Walter Reed Army Medical Center, Washington, DC; 2 Colorado State University, Depart- ment of Environmental and Radiological Health Sciences, Fort Collins, Colorado. * Corresponding author. Email: Thomas.E.Johnson@ColoState.EDU Response of Lightly and Highly Pigmented Porcine Skin (Sus scrofa domestica) to Single 3.8- m Laser Radiation Pulses Laser technology has advanced rapidly since the 1st laser was produced in 1960. Initially a large nonportable device,
lasers are now available that are smaller than a pen. Their uses
are increasing, and applications in the medical, industrial and
military communities continue to expand. The use of lasers in
the infrared region also is expanding, as manufacturers tout
these devices as being eye-safe. However, the lasers are not
necessarily eye-safe but, more accurately, are retina-safe, be-
cause infrared light at wavelengths greater than 1.4 m does
not reach the retina and is fully absorbed in the cornea. 17 The maximum permissible exposure to the eye allowed with infra-
red lasers is signi cantly higher than that with visible lasers,
because the cornea and lens cannot focus and thus concentrate
infrared laser light. 1 These factors, combined with advances in technology, make infrared lasers attractive for high-energy
applications. There are 5 basic types of lasers commonly used today: 1) crystal and glass lasers; 2) gas lasers; 3) excimer lasers; 4)
semiconductor lasers; and 5) chemical lasers. A deuterium uoride gas laser was used for all exposures in the current study. With the many types and uses of lasers, it is important
that they are operated safely. The American National Standards
Institute Z136 series is generally accepted as the authority for
laser safety guidelines. These guidelines are generally set such
that the safe exposure levels are below the level at which gross
minimal tissue changes are observed. 1 Injury thresholds for ocular lesions from 3.8- m lasers have been determined for a
variety of pulse durations, but only a few studies have been
performed at 3.8 m, and no studies have been performed that Anthony C Bostick, 1 Deidre E Stoffregen, 1 and Thomas E Johnson 2,* The purpose of this study was to determine the effect of melanin on skin response to single 3.8- m, 8- s laser pulses and the difference in lesion formation thresholds. Our hypothesis was that pigmentation would play a signi cant role in skin energy
absorption at 3.8 m. Previous studies comparing pigmented and lightly pigmented porcine skin with human skin found
that compared with Yorkshire pigs, Yucatan minipigs were a superior model for laser skin exposure because of their higher
pigmentation levels. In the current study, 10 pigs under general anesthesia were exposed to 3.8- m laser pulses ranging from
0.01 J/cm 2 to 93 J/cm 2 . Gross examinations and skin biopsies were done 24 h after laser exposure, and histologic examinations were conducted on these tissue samples. The 24-h effective dose (ED 50 ) was determined to be 4.5 J/cm 2 for Yucatan mini-pigs and 2.6 J/cm 2 for Yorkshire pigs. As deposited energy was increased, the lesion presentation progressed from desiccation of the super cial layer of epidermis (4 J/cm 2 ) to desiccation with in ammatory centers (14 J/cm 2 ), and nally to replacement of in ammatory areas with an epidermal ulcerated central area ( 21 J/cm 2 ). Therefore we found no statistical difference between the 24-h ED 50 of the 2 breeds of pigs, nor was there any difference in histologic presentation at 24 h postexposure. Abbreviations: ED 50 , the dose required to elicit visible gross morphologic changes in the skin 50% of the time at a given combination of exposure parameters examine the effect of pigmentation on skin reaction thresholds
at 3.8 m. 19 In this study, the effective dose (ED 50 ) is the dose required to elicit visible gross morphologic changes in the skin
50% of the time for a given combination of exposure parameters.
The ED 50 data for exposure of skin and cornea with 3.8 m are listed in Table 1 for comparison. 4,19 Although some studies examine the threshold for corneal injury in the infrared region, few available skin studies examine
the thresholds for minimal gross morphologic changes used to
set skin infrared laser exposure standards speci cally at 3.8 m.
Of those infrared skin studies in the literature, only a few 12,15 speci cally address how the threshold for gross morphologic
changes is impacted by pigmentation, and then only at 1.3 and
1.54 m. 15 No studies of 3.8- m irradiation examine pigmenta- tion effects on skin. Earlier studies 5 demonstrate the skin of Yucatan minipigs is a better model for human skin than that of
Yorkshire pigs because the melanin distribution for human skin
samples was closer to that in Yucatan minipigs than Yorkshire
pigs. Prior studies also showed that the skin thickness in the
tested areas of skin was consistent and that Yucatan minipig
skin was, on average, slightly thicker than Yorkshire pig skin. 5,10 Further, Yucatan minipigs also lack much of the hair seen in
Yorkshires, making minipig skin closer anatomically to that
of humans. 14 Our hypothesis was that melanin would have a measurable effect on the ED 50 and energy absorption in the skin. It typi- cally is assumed that water absorption is primarily responsible
for infrared photon absorption in tissue. Thus, the need for a
study comparing the effects of melanin on the changes evoked
in skin by an infrared laser may not immediately be apparent.
Melanin is not expected to provide signi cant contributions
to photon absorption in the infrared region, but there is not
enough information on whether or how absorption charac- Pages 33-37 34 Vol 45, No 3
Journal of the American Association for Laboratory Animal Science
May 2006 teristics change upon irradiation. Studies performed at 2.79 3 and 2.94 16 m have shown that incident radiant exposures can cause temperature rises that reduce the absorption coef cient
of tissue in the infrared, especially in the 3- m region. Incident
exposures required to initiate the changes in absorption coef -
cient are on the order of 0.05 to 1.5 J/cm 2 for 2.79 m and as low as 0.02 J/cm 2 for 2.94 m. 18 These values are from the heating of tissue resulting in the weakening of hydrogen bonds. 18 Similar studies in infrared for melanin could not be found. The current
study addresses whether melanin is a factor in the absorption of
photons at 3.8 m (which it was not), in addition to determining
an ED 50 for skin at this wavelength. The 24-h ED 50 was 4.5 J/cm 2 for Yucatan minipigs and 2.6 J/cm 2 for Yorkshire pigs. Materials and Methods Animals. A total of 10 female pigs5 Yucatan minipigs (Sinclair Research, Auxvasse, MO), ranging in age from 4 to 6
mo and weighing between 16 and 20 kg, and 5 Yorkshire pigs
(Archer Farms, Belcamp, MD), ranging in age from 4 to 6 mo
and weighing between 20 and 26 kgwere used in this study.
All pigs were maintained at a temperature range between 17.8
to 28 C, a relative humidity of 30% to 70%, and a 12:12-h light:
dark cycle. Yucatan minipigs were fed Mini-Swine Diet 8753
(Harlan Teklad, Madison, WI), whereas Yorkshire pigs were fed
Pig/Sow Grower (Harlan Teklad, Madison WI); all had access
to water ad libitum. All research was conducted in compliance
with the Animal Welfare Act and other federal statutes and regu-
lations relating to animals and experiments involving animals
and adheres to the principles stated in the Guide for the Care and
Use of Laboratory Animals. 13 The protocol was approved by the institutional animal care and use committee and performed in
a facility fully accredited by the Association for the Assessment
and Accreditation of Laboratory Animal Care, International. Ketamine (20 mg/kg, Ketaset, Fort Dodge Laboratories, Fort Dodge, IA) and xylazine (2 mg/kg, Vedco, St Joseph, MO) were
administered IM for induction of anesthesia. After intubation,
all animals were maintained under general anesthesia using
iso urane gas (Abbott Laboratories, North Chicago, IL) at a
rate of 1% to 1.5%, and the oxygen ow rate set at 22.0 ml/kg/
min. During laser exposure, Yucatan minipigs were given a
maintenance drip of 0.9% sodium chloride (Baxter Healthcare,
Deer eld, IL) at 5 to 10 ml/kg hourly. Anesthesia was veri ed
via toe-pinch response. All animals were monitored during gen-
eral anesthesia via rectal thermometer (Temp Plus 2080, IVAC,
San Diego, CA), re ectance pulse oximeter (Vet Ox SDI 4402,
Heska, Fort Collins, CO), and an electrically shielded electrocar-
diograph (PowerLab model PTB301, AD Instruments, Colorado
Springs, CO). Body temperature was maintained in the normal
range during anesthesia by using a heated pad or light source
or both. Analgesia was administered (buprenorphine, 0.005 to
0.01 mg/kg intramuscularly, Reckitt and Colman Pharmaceu-
ticals, Richmond, VA) prior to recovery, and as needed upon
evaluation every 8 to 12 h. Laser. A single 8- s pulse at 3.8 m from a deuterium uoride laser was used for each exposure. A square focal spot with a top hat energy pro le of approximately 4 cm 2 was used. The exact spot size was calculated daily prior to exposure and
veri ed postexposure. Beam energy and pulse duration were
sampled for each exposure. Energy densities ranged from 0.76
to 92.3 J/cm 2 in Yucatan minipigs and from 0.01 to 86.6 J/cm 2 in the Yorkshire pigs. Identical exposure ranges were not possible
due to limited ability to adjust the output of the laser. Procedure. Hair on the ank and thoracic regions was clipped prior to exposure. Animals were irradiated on both sides be-
tween the shoulder and ank from approximately 4 cm from
the dorsal aspect of the animal to approximately 8 cm from the
ventral aspect of the animal. Representative laser-exposed areas were biopsied at 24 h postexposure for histopathologic evaluation. Biopsies were
preserved in 10% formalin, stained with hematoxylin and
eosin, blocked in paraf n and cut to 5 m thickness. Slides
stained with hematoxylin and eosin were used to determine
the extent of epidermal lesions and to characterize the type of
tissue and cellular damage induced by the laser exposure. In
addition, structural damage in the various epidermal layers
(strata corneum, lucidum, granulosum, spinosum, and basale),
basal membrane, and dermal layer were examined. Fontana
and Masson trichrome stains were used to further characterize
the tissue damage at the basal and dermal layers, as done in an
earlier laser study. 15 Suture(s) were placed and topical antibiot- ics were administered at each biopsy site. Determination of the
presence of skin lesions was performed at the same time. Skin lesions, recorded by 3 independent graders, were deter- mined by using a single-blind process. The 24-h lesion data were
evaluated using SAS probit analysis (version 6.4, SAS Institute,
Cary, NC) to obtain ED 50 information at the 95% ducial limits, with P 0.005. 2,6 No treatment was required or provided for any of the laser-exposed areas. Results Gross lesion. The 24-h ED 50 was 4.5 J/cm 2 (95% ducial limits, 2.2 and 6.2 J/cm 2 ) for Yucatan minipigs and 2.6 J/cm 2 (95% ducial limits, 2.5 and 3.2 J/cm 2 ) for Yorkshire pigs. Each breed developed bright, erythematous lesions immediately
when exposed at or above the ED 50 , although the erythema in the Yucatan minipig lesions were more dif cult to visualize due
to pigmentation (Figure 1). A total of 57 sites were exposed on
Yucatan minipigs and 56 on Yorkshire pigs; gross lesions pre-
sented for 88% of the Yucatan minipig exposures and 90% of
Yorkshire pig exposures. At the 24-h ED 50 , there was a visible area of slight epidermal erythema with apparent desiccation and
concomitant separation of the super cial layer of the epidermis
in Yucatan minipigs. The area of erythema at the epidermal skin
layer was more prominent in the Yorkshire pig at its 24 h ED 50 (Figure 1 D, E). The loss of super cial epidermis in Yorkshire
pigs began at approximately 6 J/cm 2 and progressed to more extensive removal at approximately 8 J/cm 2 (Figure 1 F, H). Yucatan minipigs showed generalized diffuse areas of erythema
and slight desiccation of the epidermis, with no evidence of
epidermal loss until approximately 14 J/cm 2 (Figure 1 I, H). Table 1. Summary of dermal and corneal studies using laser wavelengths of approximately 3.8 m Pulse duration (s) Model ED 50 (J/cm 2 ) Spot size Reference 8 10 -6 Yorkshire pig skin 2.6 400 mm 2 (square) 19 1.25 10 -1 Rhesus cornea 4.61 0.95 mm 2 (1/e; circular) 4 5 10 -1 Rhesus cornea 7.09 0.95 mm 2 (1/e; circular) 4 1 10 -7 Rhesus cornea 0.377 0.95 mm 2 (1/e; circular) 4 1/e is equal to the area over which 63.2% of the total radiant energy is distributed. 35 At energy levels near 25 J/cm 2 and 24 h postexposure, the desiccation of the super cial epidermis had disappeared and
was replaced by erythematous epidermal tissue in Yucatan
minipigs. Lesions appeared to be in deeper layers of the epi-
dermis than those seen at lower energies, and swelling was
more extensive. Dry exudates or secretions in the center of
the lesion with erythematous tissue at the border began to
form an energy level of approximately 28 J/cm 2 (Figure 2 A). At approximately 38 J/cm 2 and 24 h postexposure, the center of the lesion presented as red erythematous tissue. The lesion
centers may have been deeper at this energy, with dry exudate
restricted to the outside border of the central lesion (Figure 2 B).
At approximately 40 J/cm 2 and 24 h postexposure, red swollen epidermis was not apparent; instead slight swelling appeared
around the central lesion (Figure 2 C). In Yucatan minipigs, the
skin lesions appearing after exposure to 55 J/cm 2 or more all had slightly red and swollen borders with dry exudates in the
center of the lesion (Figure 2 D, E); lesions varied in character at
24 h postexposure to energy levels lower than 55 J/cm 2 . Similar gross anatomic epidermal changes were apparent in Yorkshire
pigs as the exposure intensity of the 3.8- m laser increased. Histology. A total of 20 full-thickness skin samples collected 24 h postexposure from Yucatan mini-pigs and Yorkshire pigs
exposed to laser pulses of various intensities were submitted
for histopathologic examination. Skin sections were evaluated
for severity and depth of degeneration, necrosis, edema, in am-
mation, and vascular changes. In general, the histologies of
the 2 breeds were similar for a given radiant energy. Common epidermal changes ranged from multifocal random hydropic
degeneration to partial- or full-thickness epidermal coagula-
tive or lytic necrosis with neutrophilic in ltrates, epidermal
pustules, or rare vesicles (Figure 3). Degenerative and necrotic
epidermal changes generally ranged from minimal to mild at
the lower pulse intensities to severe at the higher intensities.
Hydropic degeneration occurred most often in the stratum
spinosum and stratum basale, to a lesser extent in the stratum
granulosum, and rarely in the stratum corneum (Figure 3 A).
Dermal changes were con ned to the super cial dermis and
included multifocal perivascular mixed in ammation, pre-
dominantly neutrophilic in ammation, perivascular edema,
and congestion. In more severely affected areas, in ammatory
cells often extended into and separated collagen bundles. The
dermal lesions evident in skin exposed to pulses greater than the
ED 50 for each pig strain were generally more severe than those at lower intensities, with the higher intensities characterized
by hemorrhage and lytic necrosis with numerous degenerate
neutrophils within necrotic foci (Figure 3 B, C). The subcutis
also was evaluated for lesions secondary to laser exposure, but
no histologic changes were present in either Yorkshire pigs or
Yucatan minipigs after exposure to pulses of 86.6 J/cm 2 or less. The presentation of the histology was consistent with the gross
presentation of the lesions. This laser caused no grossly visible hemorrhage; histologic evidence of hemorrhage was seen rarely at the ED 50 from the tissue that was submitted from Yorkshire pigs, and none was
found at the 24-h ED 50 of Yucatan minipigs. A tissue biopsy Figure 1. Major changes in gross lesions at 24 h postexposure in Yucatan minipigs (A, C, E, G, I) and Yorkshire pigs (B, D, F, H, J) at increasing uence (in J/cm 2 ). The darker appearance of Yorkshire skin was in uenced by lighting, in some instances. (D, E) Near the ED 50 , note the differ- ent uences required. (F, G) Removal of the super cial layer of the epidermis in Yorkshire pigs only (black arrow). (H, I) Removal of super cial
epidermis in Yucatan minipigs and Yorkshire pigs. At 8.1 J/cm 2 , the deeper skin layer begins to be affected in Yorkshire pigs (white arrow). Figure 2. Gross epidermal damage in Yucatan minipigs, showing variations in response at 24 h postexposure to increasing radiant energy (in
J/cm) at levels signi cantly greater than the ED 50 . Arrows indicate locations of punch biopsies in B, C, and D. Skin response to 3.8- m laser irradiation 36 Vol 45, No 3
Journal of the American Association for Laboratory Animal Science
May 2006 of the site indicated minimal to mild amounts of hemorrhage
at various energy levels in both the epidermis and super cial
dermis. Perivascular hemorrhage was seen microscopically
within the super cial dermis. Histologic results suggest that there were no differences between the 2 breeds in lesion formation, a conclusion that is
supported by the similarities in histologic presentation in the
current study as well as by the depth of damage measurements
done in earlier studies. 15,19 Because the stratum corneum re- mained in place for many of the exposures immediately above
the ED 50 , we suspect that it may be transparent to or at least have a limited ability to absorb 3.8- m photons. Discussion In this study we found that the ED 50 for Yucatan minipigs was not statistically different at the 95% level from that of Yorkshire
pigs. In addition, the ED 50 results may have been even closer because identifying the reddening in the epidermis was criti-
cal to determining the ED 50 , and the high pigmentation of the Yorkshire pig may have masked some reddening. This nding
was supported by the comparable histologic lesions between
the 2 breeds at different energy levels. Note that the statistical
technique used (probit analysis) does not require that all the
exposures be exactly at the ED 50 or even equally distributed around it, thus minimizing the number of animals required for
a study of this type. In both breeds, the lesion process clearly re ected the in- creasing radiant energy until 55 J/cm 2 , after which no further changes were noted (up to the maximum of 93 J/cm 2 ). The appearance of gross lesions, from reddening and whitening of
the epidermis to the removal of super cial epidermis, occurred
at lower exposures in Yorkshire pigs than in Yucatan minipigs,
but this difference was minor. It was initially postulated that pigmentation might play a signi cant role in the absorption of 3.8- m laser light and
subsequent lesion development, 15,19 but our ndings did not support this theory. Several things other than absorption of
3.8- m light in water might contribute to lesion development
in the skin, but again, it appears that water absorption is the
overriding factor, not pigmentation. If the skin were to absorb
3.8- m light identically to water, the absorption coef cient of
3.8- m photons would be 132 cm -1 , 7 and 63% of the energy would be deposited in the upper 76 m of tissue; the basal
layer, where dermal chromophores are found, is at a depth of
68 m in Yucatan minipigs. 5 Therefore, the in uence of dermal chormophores is expected to be minimal if the tissue absorbs
3.8- m light in a manner similar to that of water. The ability to
discern slight changes also might in uence the identi cation of
lesions in highly pigmented skin, but this bias was not apparent
in light of the statistically identical results obtained. Further
studies are needed to fully characterize how each of these factors
speci cally in uence lesion development, if at all. Further analysis is underway to more completely characterize the extent and nature of the lesions created by this laser. The
determination of the ED 50 did not require histologic examination of the tissues. Histologic sections did con rm that the 2 breeds
responded almost identically to the laser, and these slides will
be used for future studies to ascertain an experimental 3.8- m
absorption coef cient for skin. No noticeable lesions occurred in the subcutaneous layers of either the Yucatan mini-pig or the Yorkshire pig, and no notice-
able differences in the lesions were observed in the vasculatures
of the dermis. Biopsies were taken at just above the ED 50 in both the Yucatan mini-pigs and Yorkshire pigs. Gross lesions were Figure 3. Photomicrographs of cross sections of laser-induced skin le-
sions from Yorkshire pigs at 2.9 J/cm 2 and and Yucatan minipigs at 7.44 J/cm 2 . Hematoxylin and eosin stain; magni cation, 20. (A) Yorkshire pigs: epidermal changes consist of hydropic degeneration primarily in
the stratum basale and stratum spinosum (1), with ulceration and ne-
crosis extending into the super cial dermis. (B) Yorkshire pig: epidermal
vesicle (1); partial- to full-thickness epidermal necrosis (2); and dermal
necrosis (3). (C) Yucatan minipig: partial to complete epidermal necrosis
(1); white aggregates of necrotic neutrophils (2); and dermal necrosis
and perivascular in ltrates (3). 37 observed at lower energies in the Yorkshire when compared
to that of the Yucatan mini-pigs, but histological observations
indicated lesions were present at much lower energy level than
seen grossly. For example, in the Yucatan mini-pig, the ED 50 at 24 h for gross lesions was seen at 4.5 J/cm 2 but histological lesions were seen as early as 2.27 J/cm 2 . No biopsies were avail- able for the Yorkshire below the ED 50 , but a similar situation is expected. The similarities and differences between the 2 pig breeds we evaluated and humans have been addressed in a number of
previous research studies. 8,9,11,14,15,19 Compared with Yorkshire pigs, Yucatan minipigs are believed to be a more ideal model
for human dermatologic studies in light of a number of factors
pointed out in other published papers. 5,8,9,15 In addition, Yucatan minipigs have a heterogeneity otherwise seen only in primates
and humans: 2 morphologically distinct populations of basal
keratinocytes (serrated and nonserrated). 9 The smaller size of Yucatan minipigs is another excellent reason to use it rather
than Yorkshire pigs. In the present study, both breeds appeared
to respond similarly to the laser, so these other factors should
be considered. One of the problems with this study was that identical radiant energies could not be obtained from exposure to exposure. This
drawback was a limitation of the ability of the laser and did not
affect the overall results of the study. Another limitation was
that a biopsy was not taken for every exposure. We therefore conclude that the 24 h ED 50 was statistically the same for Yucatan minipigs and Yorkshire pigs. The selection
of either of these breeds to model 3.8- m single-pulse laser
exposure appears to be appropriate. This study showed that
pigmentation did not play the expected signi cant role in skin
energy absorption at 3.8 m. Acknowledgments The opinions or assertions contained herein are the private ones of the authors and are not to be construed as of cial or re ecting the views
of Colorado State University, the United States Department of Defense,
United States Army, or the Uniformed Services University of the Health
Sciences. We would like to thank Don Randolph, Golda Winston, and
Trida Winston for their assistance in tissue exposure and collection.
We would also like to thank Larry Buelow and Aimee Buelow for their
assistance in the preparation of this manuscript. References 1. ANSI Standard Z136.1. 2000. American national safety standard for safe use of lasers. Orlando (FL): Laser Institute of America. 2. Bliss CI. 1935. The calculation of the dosage mortality curve from small numbers. Quart J Pharmacol 11:192216. 3. Cummings JP, Walsh JT. 1988. Erbium laser ablation: the effect of dynamic optical properties. Appl Phys Lett 62:19881990. 4. Dunsky IL, Egbert DE. 1973. Corneal damage thresholds for hy- drogen uoride and deuterium uoride chemical lasers. Brooks
City Base (TX): USAF School of Aerospace Medicine, Aerospace
Medical Division. 5. Eggleston TA, Roach WP, Mitchell M, Smith K, Oler D, Johnson TE. 2000. Comparison of in vivo skin models for near infrared laser
exposure. Comp Med 50:391397. 6. Finney DJ. 1971. Probit analysis. 3rd ed. Cambridge: Cambridge University Press. 7. Hale GM, Query MR. 1973. Constants of water in the 200 nm to 200 m wavelength region. Appl Optics 12:555563 8. ICRP. 1991. The biological basis for dose limitation in the skin. A report of a task group of committee 1 of the international commis-
sion on radiological protection. Ann ICRP 22(2):1104. 9. Lavker RM, Dong G, Zheng PS, Murphy GF. 1991. Hairless mi- cropig skin. A novel model for studies of cutaneous biology. Am
J Pathol 138:687697. 10. Meyer W, Schwarz R, Neurand K. 1978. The skin of domestic mammals as a model for the human skin, with special reference
to the domestic pig. Curr Probl Dermatol 7:3952. 11. Montagna W, Yun JS. 1964. The skin of the domestic pig. J Invest Dermatol 42:1121. 12. Montes CI, Cain CP, Schuster KJ, Stockton K, Thomas JJ, Egg- leston TA, Roach WP. 2003. Measured skin damage thresholds for
1314-nm laser exposures. Proc SPIE 4953:117123. 13. National Research Council. 1996. Guide for the care and use of laboratory animals. Washington (DC): National Academy Press. 14. Panepinto LM, Phillips RW. 1986. The Yucatan miniature pig: characterization and utilization in biomedical research. Lab Anim
Sci 36:344347. 15. Rico PJ, Roach WP, Mitchell MA, Johnson TE. 2000. ED50 Deter- mination and histological characterization of porcine (Sus scrofa
domestica) dermal lesions produced by 1540 nm laser radiation
pulses. Comp Med 50:633638. 16. Shori RK, Walston AA, Stafsudd OM, Fried D, Walsh JT. 2001. Quanti cation and modeling of the dynamic changes in the ab-
sorption coef cient of water at 2.94 m. IEEE J Sel Top Quantum
Electron 7:959970. 17. Sliney D, Wolbasrcht ML. 1980. Safety with lasers and other optical sources: a comprehensive handbook. New York: Plenum Press. 18. Vogel A, Venugopalan V. 2003. Mechanisms of pulsed laser abla- tion of biological tissues. Chem Rev 103:577644. 19. Williams PCM, Winston GCH, Randolph DQ, Neal TA, Eurell TE, Johnson TE. 2004. Comparison of experimental models for
predicting laser tissue interaction from 3.8 micron lasers. Proc
SPIE 5312:334340. Skin response to 3.8- m laser irradiation

Comments