Original Paper ORL 1992;54:259-263
a Second Department of Otorhinolaryngology and b Department of Pathology, University of Vienna, Medical School, Vienna, Austria
Key Words Infrared laser HolmiumiYAG laser Laser surgery Photo ablation Wound healing
Infrared Laser Tissue Ablation: Holmium:YAG Laser Surgery
Abstract The in vivo tissue ablation characteristics of a pulsed holmium: YAG laser (A = 1,980 nm) were studied. The laser energy was coupled onto nylon fibers 400 and 600 pm in core diameter. Laser incisions were made on white rats at dif ferent sites of the tongue and of the mucous membranes of the oral cavity. Power settings of 500 and 1,000 mJ/2.5-ms pulse at 5 pulses/s were used and the tissue responses examined by light microscopy. Wound healing was stud ied over a 6-week period. The results of this study are promising for future application of the holmium:YAG laser in otorhinolaryngology.
Introduction Since the early 1970s several types of surgical lasers have been used in otolaryngology, head and neck surgery, e.g. CO2 laser, argon laser, KTP/532 laser, and Nd:YAG laser. These lasers have been associated with a thermal mechanism of bone and of soft tissue ablation with result ing coagulation, carbonization, and vaporization of vital tissue [1,2], The great advantages of these commonly available sur gical lasers over the scalpel is precise excision and abla tion of tissue in areas where the surgical approach is lim ited. However, thermal effects of laser-tissue interaction may lead to large zones of damage and subsequent scar ring of tissue (with limited hemostasis in the case of the CO 2 laser). Complications of wound healing may occur secondary to thermal injury and tissue necroses beyond the intended area of ablation [3-5], The recently developed high energy pulsed lasers are applied on tissues for extremely short exposure times and achieve densities of energy which lead to photo-ablative
Received: December 23. 1991 Accepted: January 15, 1992
and electromechanical mechanisms of laser-tissue inter action with a minor thermal component [6-8]. The holmium:YAG and erbium:YAG lasers, solid-state crystal lasers operating in infrared wavelengths, have been used so far to ablate ocular structures, bone, and arterioscle rotic tissue [9-13]. However, there has been very little work on the efficacy of the holmiurmYAG laser in ablat ing soft tissue and mucous membranes when operating in infrared wavelengths [14], The present study reports on in vivo tissue effects, ablation efficacy, and fiber conduction properties of pulsed holmium laser radiation on the mucous mem branes of rats.
Materials and Methods Anim al Model
Scientific protocol design, animal welfare and conditions for use of animals were approved by the Institutional Animal Care and Use Committee of the University of Vienna under supervision of the Ministry of Science and Research. After approval 50 white male rats,
Dr. M. Kautzky Second Department of Otorhinolaryngology University of Vienna, Medical School Alserstrasse 4. A -1090 Vienna (Austria)
© 1992 S. Karger AG. Basel 0301-1569/92/0545-0259 $2.75/0
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M. Kautzkya M. Susanib P. Schenka
Laser Light Delivery System
A pulsed holmium:YAG laser was used at a wavelength of 1,890 nm. The 2.5-ms laser pulse was transmitted to the target by nylon fibers 400 and 600 pm in core diameter. The length of the Fibers was 300 cnt. On the sublingual side of the tongue two incisions with a length of 4 mm were made with the help of the two fibers, each 2 mm lateral and in parallel to the midline of the tongue. To insert the laser fiber at the correct distance to achieve photoablation, the distance of the tip of the nylon fiber from the tongue surface was 1 mm and the tip was guided by a mechanism providing a contin uous reproducible laser incision (Stepper motor). The holmium: YAG laser was tested in the following settings: (1) power 500 mJ (at 680 V), repetition rate 2 Hz. pulse duration 2.5 ms; (2) power 1,000 mJ (at 920 V), repetition rate 2 Hz. pulse duration 2.5 ms. Pulse Energy Analysis
The pulse energy delivered from the holmium:YAG laser was measured with a pyroelectric energy detector (Gentcc ED-500, Dal las. Tex.) connected to an oscilloscope (Tcctronix. Vancouver, Cana da) and a thermal power monitor (Gentcc TPM). Histology
The animals were sacrificed by an overdose of Nembutal and the tongues were harvested immediately. For histology the specimens were fixed in 7.5% formalin and processed routinely. Paraffin sec tions. 5 pm thick, were prepared and stained with hcmatoxylineosin. Slides were examined light microscopically and measured by ocular micrometry.
Results Animal Model All rats tolerated the laser procedure without obvious difficulties. Two of the 10 rats of subgroup 1 died in the immediate postoperative period due to an inadvertent anesthetic overdose. No tissue contraction occurred dur ing laser treatment. Inspection of the tongue revealed no visual evidence of thermal injury. Immediately after the end of general anesthesia all rats started feed intake, showing neither difficulties in coordinating the normal function of the upper aerodigestive tract nor evident pain.
260
No other deaths occurred and no adverse effects of the procedure were noted during the follow-up period. Laser Light Delivery System: Pulse Energy Analysis The holmium:YAG laser output in our settings was 500 and 1,000 mJ measured directly at the laser coupler. The pulse energy that was delivered at the tip of the fiber was 400 mJ in a 400-pm laser spot and 950 mJ in a 600pm laser spot at a distance of 1 mm from the fiber tip. The holmium:YAG laser beam also produced an audible crack and a 1-mm long yellow-orange flame at the target site for the 500- and the 950-mJ radiation exposure because of photoacoustic-rclated effects. Histology The histologic specimens showed in all samples no zone of carbonized tissue. The resulting defect in the epi thelium after laser surgery reached the muscle layer in both power settings. Subgroup I. Histologic study revealed tissue defects with clean contours. In the marginal area of the laser tar get zone detachment of the surface epithelial layer was seen. The coagulativc necrosis zone for the 400-mJ inju ries measured 370-580 pm. for the 950-mJ injuries 180920 pm (fig. 1). Subgroup II. The coagulativc necrosis zone extended for the 400 mJ injuries to 3,690 pm, for the 950-mJ inju ries to 4,370 pm, and showed various degrees of leuko cytic infiltration and edema (fig. 2). Subgroup III. There was persistent ulcer formation with proliferation of granulation tissue in the 72-hour specimens of both the 400- and the 950-mJ injuries. Granulation tissue partially filled the ablation site and the adjacent zone of coagulative necrosis (fig. 3). Subgroup IV. Early reepithelization was seen. Under the regenerating epithelium granulation tissue containing inflammatory cells extended towards the underlaying musculature (fig. 4). Subgroup V. Epithelization was complete at both power levels. The zone of previous necrosis was replaced by granulation tissue. The amount of inflammatory cells is small but granulation tissue was still intermingled with some superficial muscle layers (fig. 5).
Kautzkv/Susani/Schcnk
Discussion The holmium:YAG laser has an emission band in the mid infrared portion of the spectrum at 1,980 nm. The energy absorption in water at the holmium laser wave-
Holmium:YAG Laser Surgery1
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4-5 months of age (Sprectalii OFA). were randomly divided into five subgroups of 10. Rats had free-choice food and water bottles avail able and were housed in plastic cages in which the bedding was changed daily. The animals were anesthetized with Nembutal (30 mg/kg weight intraperitoneally) and underwent laser surgery of the tongue under sterile operating room conditions. Ten animals forming group I were sacrificed immediately after laser treatment and the tongues were then resected for histologic examination. Subgroup II was sacrificed at 24 h. subgroup III at 72 h. subgroup IV at 7 days, and subgroup V at 42 days. To prevent nutrition-related wound healing complica tions and also to stimulate real postoperative conditions, the rats were fed solely with 10% glucose solution, vitamins, and amino acid solutions.
1
2
Fig. 1. Histological photomicrograph
( X 40) of acute holmium:YAG laser incision on the sublingual side of a rat tongue, arrow heads indicating the detachment of the sur face epithelium layer in the margin area of the laser target zone. N = Necrosis. Fig. 2. Histological photomicrograph ( X 40) of a laser incision 24 h postoperatively. N = Extended zone of coagulative necrosis; I = inflammatory cells. Bar = 200 pm.
Fig. 3. Histological photomicrograph ( X 40) of a laser incision 72 h postoperatively. Granulation tissue (G) partially filled the ablative site and the adjacent zone of coagulative necrosis (N): I = inflammatory cells. Bar= 200 pm. Fig. 4. Histological photomicrograph ( X 100) of a laser incision 1 week postoperatively. Granulation tissue (G) under the re generating epithelium is seen. Bar= 70 pm.
Fig. 5. Histological photomicrograph ( X 40) of a laser incision 6 weeks postoperatively. Granulation tissue (G) is still inter mingled (dotted line) with some superficial muscle layers (M). Bar = 200 pm.
In comparison the holmium:YAG laser is not ab sorbed by biological tissue as well as the erbium:YAG laser beam and cuts soft tissue less effectively and with greater thermal damage. However, the 1,980-nm wave length of the holmium:YAG laser beam can be efficiently transmitted through nylon optic fibers and quartz fibers [18, 19], The fiber itself has a high reliability against laser-induced and mechanical damage, and energy can be transmitted with little attenuation of laser energy (20% energy loss only). The fiber can be guided easily under the operation microscope or endoscopic control to the target in areas where access is limited. The pulsed delivery of the laser energy provides dimin ished transmission to the tissue surrounding the site of impact, minimizing trauma of soft tissue. To further
261
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length is much higher than that of the Nd-YAG laser wavelength (1.064 nm) [ 15], but is lower than the erbium: YAG laser and the COy laser wavelength. Since more than 70% of biological tissue consists of water, a laser energy at a wavelength that is stronly absorbed by water leads to further decrease of the zone of tissue damage. Incisions with little thermal damage have been demon strated with the 193-nm excimer laser pulses [16] and with the 2,940-nm erbium:YAG pulses, which have proved to have the best ablation characteristics of all infrared lasers [11]. However, limitations exist with regard to suitable fiber-optic delivery systems, especially with the erbium: YAG laser [ 17] as well as low ablation efficacy and opera tion reliability using the UV-excimer laser.
decrease the zone of damage a laser is needed which is operating at sufficiently high irradiance to ablate tissue in a plasma cutting manner with minor thermal compo nents. Tissue ablation by the holmium:YAG is caused by a rapid increase in pressure through the mechanism of heating intracellular liquids until a microexplosion occurs with parts of the cellular elements being ejected as micro scopic particles. This mode of ablation is not unique to 1,980-nm radiation [20-22], Photo ablation is generated if an irradiance in the range between 0.1 and lOJ/cm2 and pulse durations in the range of not more than 3 ps can be achieved. This phe nomenon was first described by Srinivasan [23] in 1986. The major part of the incident energy is consumed in the ablative process and only a small fraction of the energy remains in the tissue as thermal energy. Therefore, abla tion of the exposed mucous membrane can be performed more precisely. In our experimental and clinical settings a laser energy was obtained that fulfilled all precautions not only for photo ablation but also for optical breakdown, which is obtained by an avalanching effect of ionization through free electrons [24] in a plasma state caused by energy concentration above 109J/cm2 in a laser beam with a pulse duration not more than 3 ps. These settings in holmium:YAG laser beams were not reported by other authors. The present study demonstrates the acute and chronic effects of pulsed holmium laser ablation on mu cous membranes in vivo in rats. The small immediate residual thermal damage zone and the absence of char within the range of radiant exposures examined correlate with physical effects as mentioned above. Tissue absorption at the holmium laser emission wave length is intermediate between the relatively weakly ab
sorbed Nd:YAG laser and the more strongly absorbed erbium:YAG and CCH lasers. Therefore, optical phenom ena such as scattering are likely to be more important than at the longer wavelengths, where absorption is the domi nant process. Excellent control of depth of tissue ablation could be achieved with low repetition rates of 2 Hz. Photons leav ing the probe tip were spreading out at rather small diver gent angles. The focal spot 600 pm in diameter results in a tissue defect of 620-690 pm. with clean margins at a dis tance of 1 mm between probe tip and tissue (fig. 1). Hemostasis was achieved coincident with ablation. Mac roscopic wound healing showed no complications and was completed after 3 weeks. At this time it became diffi cult to detect the ablation sites due to primary recpithelization. Histologically wound closure was completed after 4 weeks, showing reepithelization without scar formation. Further investigations of our study group will focus on the ultrastructural changes in biological tissues after holmiunrYAG laser irradiation in contrast to previous in vestigations dealing with the CCK and the helium-neon laser [25], The results of this study suggest the feasibility of using a surgical holmium:YAG laser in laryngeal surgery and in endoscopic sinus surgical procedures.
Acknowledgements The technical assistance of Mrs. M. Peterlik and Mr. H. Gaudek is gratefully acknowledged. We also thank Fa. Dr. Koch GmbH, Vienna, Austria, for support. Research was supported by a grant from the Anton Dreher Gedächtnisschenkung für Medizinische For schung.
References
262
6 Dixon JA, Straight RC. Dayton MT: Free elec tron laser fragmentation of biliary calculi. La sers Surg Med 1987:7:88. 7 Steinert RF, Puliafito CA. Kittrell C: Plasma shielding by Q-switched and mode-locked ncodymium:YAG lasers. Ophthalmology 1983:90: 1003. 8 Trokel SL, Srinivasan R. Braren B: Excimer laser surgery' of the cornea. Am J Ophthalmol 1973:96:710. 9 Gonzalez C, Van De Merwe WP. Smith M, Reinisch L: Comparison of the erbium-yttrium aluminium garnet and carbon dioxide lasers for in vitro bone and cartilage ablation. Laryn goscope 1990:100:14 - 17.
Kautzky/Susani/Schenk
10 Haase KK, Baumbach A, Wchrmann M. Duda S, Cerullo G. Riickle B, Steiger E, Karsch KR: Potential use of holmium lasers for angioplas ty: Evaluation of a new solid-state laser for ablation of atherosclerotic plaque. Lasers Surg Med 1991:11:232-237. 11 Nuss RC. Fabian RL, Rajabrata S, et al: In frared laser bone ablation. Lasers Surg Med 1988:8:381-391. 12 Walsh JT. Deutsch TF: EnYAG laser ablation of tissue: Measurement of ablation rates. La sers Surg Med 1989:9:327-337. 13 Wolbarsht ML. Foulks GN. Esterowitz L, Tran DC. Levin K. Storm M: Corneal surgery with an Er:YAG laser at 2.94 pm; in ARVO Ab stracts. Invest Ophthalmol Vis Sci 1986: 93(suppl).
HolmiunrYAG Laser Surgery'
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1 Boulnois JL: Photophysical processes in recent medical laser developments: A rev iew. Lasers Med Sei 1986: 1. 2 McKenzie AL: How far does thermal damage extend beneath the surface of CO; laser inci sions? Phys Med Biol 1983:28:905-912. 3 Cotton RT, Tewfik TL: Laryngeal stenosis fol lowing carbon dioxide laser in subglottic steno sis. Ann Otol Rhinol Laryngol 1985:94:494— 497. 4 Fried MP: Limitations of laser laryngoscopy. Otolaryngol Clin North Am 1984:17:199-206. 5 Ossoff RH. Hotaling AJ. Karlan MS. et al: CO; laser in otolaryngology-head and neck surgery': A retrospective analysis of complications. La ryngoscope 1983:93:1287-1289.
14 Shapshay SM. Arctz HT, Sctzcr SE: Soft tissue effects of the holmium YSGG laser in the canine trachea. Otolaryngol Head Neck Surg 1990:102:251. 15 Bayly JG. Kartha VB. Stevens WH: The ab sorption spectra of liquid phase IFO. HDO and D ;0 from 0.7 to 10 pm. Infrared Physics 1963:3:211-233. 16 Lane RJ. Linsker R. Wynne JJ: Ultravioletlaser ablation of skin. Arch Dermatol 1985: 121:609-617. 17 Tran DC. Levin KH: Zirconium fluoride fiber requirements for mid-infrared laser surgery ap plications; in Optical Fibres in Medicine. Bel lingham. SPIF.. 1986. vol 713. pp 36-37.
18 Nishioka NS. Domankevitz Y. Flotte TJ. An derson RR: Ablation of rabbit liver, stomach and colon with a pulsed holmium laser. Gastro enterology 1989:96:831-837. 19 Treat MR. Trokel SL. Reynolds RD. DeFilippi VJ. Andrew J. Liu JY. Cohen MG: Preliminary evaluation of a pulsed 2.15-u m laser system for fiberoptic endoscopic surgery'. Lasers Surg Med 1988:8:322-326. 20 Dyer PE. Srinivasan R: Nanosecond photo acoustic studies of ultraviolet laser ablation of organic polymers. Appl Phys Lett 1986:48: 445-447.
21 Pack UC. Zaleckas VJ: Scribing of alumina material by YAG and CO; lasers. Ceramic Bull 1975:54:585-588. 22 Srinivasan R. Dyer PE. Braren B: Far-UV laser abla:ion of cornea: Photoacoustic studies. La sers Surg Med 1987:6:514-519. 23 Srinivasan R: Ablation of polymers and biolog ical tissue by ultraviolet lasers. Science 1986: 234:559-565. 24 Bloembergen N: Laser-induced electric break down in solids. IEEE J Quantum Electronics 1974-.QE-10 3:375. 25 Schenk P. Ehrenberger K: Effect of CO; laser on skin lymphatics. Langenbecks Arch Cltir 1980:350:145-150.
Announcements
3rd Symposium on Cochlear Mechanisms and Otoacoustic Emissions
Winter Meeting of the European Academy of Facial Surgery (The Joseph Society)
December 4-6. 1992. Rome
Flims-Laax. March 7-13, 1993
A distinguished faculty, including several invited speakers, will give lectures on a wide variety of topics on otoacoustic emissions and recent advances in cochlear physiology. Papers on all subjects per taining to acoustic emissions and physiological acoustics are so licited. Abstracts (max. 400 words) should be sent by July 10, 1992, to: Dr. F. Grandori Centre of Systems Theory' (CNR) Department of Biomedical Engineering Polytechnic of Milan via Ponzio 34/5 1-20133 Milan (Italy) Tel.: 39-2-2399.3561 Fax: 39-2-2399.3412
It is planned to publish a selection of the papers in a volume edited by the Scientific Committee (F. Grandori. G. Cianfrone and D.T. Kemp). For any further information also contact:
The International ‘Winter Meeting’ of the European Academy of Facial Surgery (The Joseph Society) will be held in Flims-Laax/Switzcrland (Hotel Laaxerhof, Laax-Murschetg). The topic of the meeting is ‘Functional and Reconstructive Plas tic Surgery in the Head and Neck’. Members and guests are invited to submit ‘free papers’ until November 15, 1992. Further information and details can be obtained, from the course organizers: Prof. Dr. Helmut Jung HNO-Klinik. Krankenhaus Marienhof Rudolf-Virchow-Strasse 7 D-W-5400 Koblenz (FRG)
or Prof. Dr. Claus Walter Klinik am Rosenberg CH-9410 Hcidcn (Switzerland)
The Organizing Secretariat Centro Ricerche e Studi Amplifon via Ripamonti 129 1-20141 Milan (Italy)
263
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Tel.: 39-2-5359361 Fax: 39-2-57400384
a Second Department of Otorhinolaryngology and b Department of Pathology, University of Vienna, Medical School, Vienna, Austria
Key Words Infrared laser HolmiumiYAG laser Laser surgery Photo ablation Wound healing
Infrared Laser Tissue Ablation: Holmium:YAG Laser Surgery
Abstract The in vivo tissue ablation characteristics of a pulsed holmium: YAG laser (A = 1,980 nm) were studied. The laser energy was coupled onto nylon fibers 400 and 600 pm in core diameter. Laser incisions were made on white rats at dif ferent sites of the tongue and of the mucous membranes of the oral cavity. Power settings of 500 and 1,000 mJ/2.5-ms pulse at 5 pulses/s were used and the tissue responses examined by light microscopy. Wound healing was stud ied over a 6-week period. The results of this study are promising for future application of the holmium:YAG laser in otorhinolaryngology.
Introduction Since the early 1970s several types of surgical lasers have been used in otolaryngology, head and neck surgery, e.g. CO2 laser, argon laser, KTP/532 laser, and Nd:YAG laser. These lasers have been associated with a thermal mechanism of bone and of soft tissue ablation with result ing coagulation, carbonization, and vaporization of vital tissue [1,2], The great advantages of these commonly available sur gical lasers over the scalpel is precise excision and abla tion of tissue in areas where the surgical approach is lim ited. However, thermal effects of laser-tissue interaction may lead to large zones of damage and subsequent scar ring of tissue (with limited hemostasis in the case of the CO 2 laser). Complications of wound healing may occur secondary to thermal injury and tissue necroses beyond the intended area of ablation [3-5], The recently developed high energy pulsed lasers are applied on tissues for extremely short exposure times and achieve densities of energy which lead to photo-ablative
Received: December 23. 1991 Accepted: January 15, 1992
and electromechanical mechanisms of laser-tissue inter action with a minor thermal component [6-8]. The holmium:YAG and erbium:YAG lasers, solid-state crystal lasers operating in infrared wavelengths, have been used so far to ablate ocular structures, bone, and arterioscle rotic tissue [9-13]. However, there has been very little work on the efficacy of the holmiurmYAG laser in ablat ing soft tissue and mucous membranes when operating in infrared wavelengths [14], The present study reports on in vivo tissue effects, ablation efficacy, and fiber conduction properties of pulsed holmium laser radiation on the mucous mem branes of rats.
Materials and Methods Anim al Model
Scientific protocol design, animal welfare and conditions for use of animals were approved by the Institutional Animal Care and Use Committee of the University of Vienna under supervision of the Ministry of Science and Research. After approval 50 white male rats,
Dr. M. Kautzky Second Department of Otorhinolaryngology University of Vienna, Medical School Alserstrasse 4. A -1090 Vienna (Austria)
© 1992 S. Karger AG. Basel 0301-1569/92/0545-0259 $2.75/0
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 9:50:56 PM
M. Kautzkya M. Susanib P. Schenka
Laser Light Delivery System
A pulsed holmium:YAG laser was used at a wavelength of 1,890 nm. The 2.5-ms laser pulse was transmitted to the target by nylon fibers 400 and 600 pm in core diameter. The length of the Fibers was 300 cnt. On the sublingual side of the tongue two incisions with a length of 4 mm were made with the help of the two fibers, each 2 mm lateral and in parallel to the midline of the tongue. To insert the laser fiber at the correct distance to achieve photoablation, the distance of the tip of the nylon fiber from the tongue surface was 1 mm and the tip was guided by a mechanism providing a contin uous reproducible laser incision (Stepper motor). The holmium: YAG laser was tested in the following settings: (1) power 500 mJ (at 680 V), repetition rate 2 Hz. pulse duration 2.5 ms; (2) power 1,000 mJ (at 920 V), repetition rate 2 Hz. pulse duration 2.5 ms. Pulse Energy Analysis
The pulse energy delivered from the holmium:YAG laser was measured with a pyroelectric energy detector (Gentcc ED-500, Dal las. Tex.) connected to an oscilloscope (Tcctronix. Vancouver, Cana da) and a thermal power monitor (Gentcc TPM). Histology
The animals were sacrificed by an overdose of Nembutal and the tongues were harvested immediately. For histology the specimens were fixed in 7.5% formalin and processed routinely. Paraffin sec tions. 5 pm thick, were prepared and stained with hcmatoxylineosin. Slides were examined light microscopically and measured by ocular micrometry.
Results Animal Model All rats tolerated the laser procedure without obvious difficulties. Two of the 10 rats of subgroup 1 died in the immediate postoperative period due to an inadvertent anesthetic overdose. No tissue contraction occurred dur ing laser treatment. Inspection of the tongue revealed no visual evidence of thermal injury. Immediately after the end of general anesthesia all rats started feed intake, showing neither difficulties in coordinating the normal function of the upper aerodigestive tract nor evident pain.
260
No other deaths occurred and no adverse effects of the procedure were noted during the follow-up period. Laser Light Delivery System: Pulse Energy Analysis The holmium:YAG laser output in our settings was 500 and 1,000 mJ measured directly at the laser coupler. The pulse energy that was delivered at the tip of the fiber was 400 mJ in a 400-pm laser spot and 950 mJ in a 600pm laser spot at a distance of 1 mm from the fiber tip. The holmium:YAG laser beam also produced an audible crack and a 1-mm long yellow-orange flame at the target site for the 500- and the 950-mJ radiation exposure because of photoacoustic-rclated effects. Histology The histologic specimens showed in all samples no zone of carbonized tissue. The resulting defect in the epi thelium after laser surgery reached the muscle layer in both power settings. Subgroup I. Histologic study revealed tissue defects with clean contours. In the marginal area of the laser tar get zone detachment of the surface epithelial layer was seen. The coagulativc necrosis zone for the 400-mJ inju ries measured 370-580 pm. for the 950-mJ injuries 180920 pm (fig. 1). Subgroup II. The coagulativc necrosis zone extended for the 400 mJ injuries to 3,690 pm, for the 950-mJ inju ries to 4,370 pm, and showed various degrees of leuko cytic infiltration and edema (fig. 2). Subgroup III. There was persistent ulcer formation with proliferation of granulation tissue in the 72-hour specimens of both the 400- and the 950-mJ injuries. Granulation tissue partially filled the ablation site and the adjacent zone of coagulative necrosis (fig. 3). Subgroup IV. Early reepithelization was seen. Under the regenerating epithelium granulation tissue containing inflammatory cells extended towards the underlaying musculature (fig. 4). Subgroup V. Epithelization was complete at both power levels. The zone of previous necrosis was replaced by granulation tissue. The amount of inflammatory cells is small but granulation tissue was still intermingled with some superficial muscle layers (fig. 5).
Kautzkv/Susani/Schcnk
Discussion The holmium:YAG laser has an emission band in the mid infrared portion of the spectrum at 1,980 nm. The energy absorption in water at the holmium laser wave-
Holmium:YAG Laser Surgery1
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4-5 months of age (Sprectalii OFA). were randomly divided into five subgroups of 10. Rats had free-choice food and water bottles avail able and were housed in plastic cages in which the bedding was changed daily. The animals were anesthetized with Nembutal (30 mg/kg weight intraperitoneally) and underwent laser surgery of the tongue under sterile operating room conditions. Ten animals forming group I were sacrificed immediately after laser treatment and the tongues were then resected for histologic examination. Subgroup II was sacrificed at 24 h. subgroup III at 72 h. subgroup IV at 7 days, and subgroup V at 42 days. To prevent nutrition-related wound healing complica tions and also to stimulate real postoperative conditions, the rats were fed solely with 10% glucose solution, vitamins, and amino acid solutions.
1
2
Fig. 1. Histological photomicrograph
( X 40) of acute holmium:YAG laser incision on the sublingual side of a rat tongue, arrow heads indicating the detachment of the sur face epithelium layer in the margin area of the laser target zone. N = Necrosis. Fig. 2. Histological photomicrograph ( X 40) of a laser incision 24 h postoperatively. N = Extended zone of coagulative necrosis; I = inflammatory cells. Bar = 200 pm.
Fig. 3. Histological photomicrograph ( X 40) of a laser incision 72 h postoperatively. Granulation tissue (G) partially filled the ablative site and the adjacent zone of coagulative necrosis (N): I = inflammatory cells. Bar= 200 pm. Fig. 4. Histological photomicrograph ( X 100) of a laser incision 1 week postoperatively. Granulation tissue (G) under the re generating epithelium is seen. Bar= 70 pm.
Fig. 5. Histological photomicrograph ( X 40) of a laser incision 6 weeks postoperatively. Granulation tissue (G) is still inter mingled (dotted line) with some superficial muscle layers (M). Bar = 200 pm.
In comparison the holmium:YAG laser is not ab sorbed by biological tissue as well as the erbium:YAG laser beam and cuts soft tissue less effectively and with greater thermal damage. However, the 1,980-nm wave length of the holmium:YAG laser beam can be efficiently transmitted through nylon optic fibers and quartz fibers [18, 19], The fiber itself has a high reliability against laser-induced and mechanical damage, and energy can be transmitted with little attenuation of laser energy (20% energy loss only). The fiber can be guided easily under the operation microscope or endoscopic control to the target in areas where access is limited. The pulsed delivery of the laser energy provides dimin ished transmission to the tissue surrounding the site of impact, minimizing trauma of soft tissue. To further
261
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length is much higher than that of the Nd-YAG laser wavelength (1.064 nm) [ 15], but is lower than the erbium: YAG laser and the COy laser wavelength. Since more than 70% of biological tissue consists of water, a laser energy at a wavelength that is stronly absorbed by water leads to further decrease of the zone of tissue damage. Incisions with little thermal damage have been demon strated with the 193-nm excimer laser pulses [16] and with the 2,940-nm erbium:YAG pulses, which have proved to have the best ablation characteristics of all infrared lasers [11]. However, limitations exist with regard to suitable fiber-optic delivery systems, especially with the erbium: YAG laser [ 17] as well as low ablation efficacy and opera tion reliability using the UV-excimer laser.
decrease the zone of damage a laser is needed which is operating at sufficiently high irradiance to ablate tissue in a plasma cutting manner with minor thermal compo nents. Tissue ablation by the holmium:YAG is caused by a rapid increase in pressure through the mechanism of heating intracellular liquids until a microexplosion occurs with parts of the cellular elements being ejected as micro scopic particles. This mode of ablation is not unique to 1,980-nm radiation [20-22], Photo ablation is generated if an irradiance in the range between 0.1 and lOJ/cm2 and pulse durations in the range of not more than 3 ps can be achieved. This phe nomenon was first described by Srinivasan [23] in 1986. The major part of the incident energy is consumed in the ablative process and only a small fraction of the energy remains in the tissue as thermal energy. Therefore, abla tion of the exposed mucous membrane can be performed more precisely. In our experimental and clinical settings a laser energy was obtained that fulfilled all precautions not only for photo ablation but also for optical breakdown, which is obtained by an avalanching effect of ionization through free electrons [24] in a plasma state caused by energy concentration above 109J/cm2 in a laser beam with a pulse duration not more than 3 ps. These settings in holmium:YAG laser beams were not reported by other authors. The present study demonstrates the acute and chronic effects of pulsed holmium laser ablation on mu cous membranes in vivo in rats. The small immediate residual thermal damage zone and the absence of char within the range of radiant exposures examined correlate with physical effects as mentioned above. Tissue absorption at the holmium laser emission wave length is intermediate between the relatively weakly ab
sorbed Nd:YAG laser and the more strongly absorbed erbium:YAG and CCH lasers. Therefore, optical phenom ena such as scattering are likely to be more important than at the longer wavelengths, where absorption is the domi nant process. Excellent control of depth of tissue ablation could be achieved with low repetition rates of 2 Hz. Photons leav ing the probe tip were spreading out at rather small diver gent angles. The focal spot 600 pm in diameter results in a tissue defect of 620-690 pm. with clean margins at a dis tance of 1 mm between probe tip and tissue (fig. 1). Hemostasis was achieved coincident with ablation. Mac roscopic wound healing showed no complications and was completed after 3 weeks. At this time it became diffi cult to detect the ablation sites due to primary recpithelization. Histologically wound closure was completed after 4 weeks, showing reepithelization without scar formation. Further investigations of our study group will focus on the ultrastructural changes in biological tissues after holmiunrYAG laser irradiation in contrast to previous in vestigations dealing with the CCK and the helium-neon laser [25], The results of this study suggest the feasibility of using a surgical holmium:YAG laser in laryngeal surgery and in endoscopic sinus surgical procedures.
Acknowledgements The technical assistance of Mrs. M. Peterlik and Mr. H. Gaudek is gratefully acknowledged. We also thank Fa. Dr. Koch GmbH, Vienna, Austria, for support. Research was supported by a grant from the Anton Dreher Gedächtnisschenkung für Medizinische For schung.
References
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6 Dixon JA, Straight RC. Dayton MT: Free elec tron laser fragmentation of biliary calculi. La sers Surg Med 1987:7:88. 7 Steinert RF, Puliafito CA. Kittrell C: Plasma shielding by Q-switched and mode-locked ncodymium:YAG lasers. Ophthalmology 1983:90: 1003. 8 Trokel SL, Srinivasan R. Braren B: Excimer laser surgery' of the cornea. Am J Ophthalmol 1973:96:710. 9 Gonzalez C, Van De Merwe WP. Smith M, Reinisch L: Comparison of the erbium-yttrium aluminium garnet and carbon dioxide lasers for in vitro bone and cartilage ablation. Laryn goscope 1990:100:14 - 17.
Kautzky/Susani/Schenk
10 Haase KK, Baumbach A, Wchrmann M. Duda S, Cerullo G. Riickle B, Steiger E, Karsch KR: Potential use of holmium lasers for angioplas ty: Evaluation of a new solid-state laser for ablation of atherosclerotic plaque. Lasers Surg Med 1991:11:232-237. 11 Nuss RC. Fabian RL, Rajabrata S, et al: In frared laser bone ablation. Lasers Surg Med 1988:8:381-391. 12 Walsh JT. Deutsch TF: EnYAG laser ablation of tissue: Measurement of ablation rates. La sers Surg Med 1989:9:327-337. 13 Wolbarsht ML. Foulks GN. Esterowitz L, Tran DC. Levin K. Storm M: Corneal surgery with an Er:YAG laser at 2.94 pm; in ARVO Ab stracts. Invest Ophthalmol Vis Sci 1986: 93(suppl).
HolmiunrYAG Laser Surgery'
Downloaded by: Univ. of California Santa Barbara 128.111.121.42 - 3/5/2018 9:50:56 PM
1 Boulnois JL: Photophysical processes in recent medical laser developments: A rev iew. Lasers Med Sei 1986: 1. 2 McKenzie AL: How far does thermal damage extend beneath the surface of CO; laser inci sions? Phys Med Biol 1983:28:905-912. 3 Cotton RT, Tewfik TL: Laryngeal stenosis fol lowing carbon dioxide laser in subglottic steno sis. Ann Otol Rhinol Laryngol 1985:94:494— 497. 4 Fried MP: Limitations of laser laryngoscopy. Otolaryngol Clin North Am 1984:17:199-206. 5 Ossoff RH. Hotaling AJ. Karlan MS. et al: CO; laser in otolaryngology-head and neck surgery': A retrospective analysis of complications. La ryngoscope 1983:93:1287-1289.
14 Shapshay SM. Arctz HT, Sctzcr SE: Soft tissue effects of the holmium YSGG laser in the canine trachea. Otolaryngol Head Neck Surg 1990:102:251. 15 Bayly JG. Kartha VB. Stevens WH: The ab sorption spectra of liquid phase IFO. HDO and D ;0 from 0.7 to 10 pm. Infrared Physics 1963:3:211-233. 16 Lane RJ. Linsker R. Wynne JJ: Ultravioletlaser ablation of skin. Arch Dermatol 1985: 121:609-617. 17 Tran DC. Levin KH: Zirconium fluoride fiber requirements for mid-infrared laser surgery ap plications; in Optical Fibres in Medicine. Bel lingham. SPIF.. 1986. vol 713. pp 36-37.
18 Nishioka NS. Domankevitz Y. Flotte TJ. An derson RR: Ablation of rabbit liver, stomach and colon with a pulsed holmium laser. Gastro enterology 1989:96:831-837. 19 Treat MR. Trokel SL. Reynolds RD. DeFilippi VJ. Andrew J. Liu JY. Cohen MG: Preliminary evaluation of a pulsed 2.15-u m laser system for fiberoptic endoscopic surgery'. Lasers Surg Med 1988:8:322-326. 20 Dyer PE. Srinivasan R: Nanosecond photo acoustic studies of ultraviolet laser ablation of organic polymers. Appl Phys Lett 1986:48: 445-447.
21 Pack UC. Zaleckas VJ: Scribing of alumina material by YAG and CO; lasers. Ceramic Bull 1975:54:585-588. 22 Srinivasan R. Dyer PE. Braren B: Far-UV laser abla:ion of cornea: Photoacoustic studies. La sers Surg Med 1987:6:514-519. 23 Srinivasan R: Ablation of polymers and biolog ical tissue by ultraviolet lasers. Science 1986: 234:559-565. 24 Bloembergen N: Laser-induced electric break down in solids. IEEE J Quantum Electronics 1974-.QE-10 3:375. 25 Schenk P. Ehrenberger K: Effect of CO; laser on skin lymphatics. Langenbecks Arch Cltir 1980:350:145-150.
Announcements
3rd Symposium on Cochlear Mechanisms and Otoacoustic Emissions
Winter Meeting of the European Academy of Facial Surgery (The Joseph Society)
December 4-6. 1992. Rome
Flims-Laax. March 7-13, 1993
A distinguished faculty, including several invited speakers, will give lectures on a wide variety of topics on otoacoustic emissions and recent advances in cochlear physiology. Papers on all subjects per taining to acoustic emissions and physiological acoustics are so licited. Abstracts (max. 400 words) should be sent by July 10, 1992, to: Dr. F. Grandori Centre of Systems Theory' (CNR) Department of Biomedical Engineering Polytechnic of Milan via Ponzio 34/5 1-20133 Milan (Italy) Tel.: 39-2-2399.3561 Fax: 39-2-2399.3412
It is planned to publish a selection of the papers in a volume edited by the Scientific Committee (F. Grandori. G. Cianfrone and D.T. Kemp). For any further information also contact:
The International ‘Winter Meeting’ of the European Academy of Facial Surgery (The Joseph Society) will be held in Flims-Laax/Switzcrland (Hotel Laaxerhof, Laax-Murschetg). The topic of the meeting is ‘Functional and Reconstructive Plas tic Surgery in the Head and Neck’. Members and guests are invited to submit ‘free papers’ until November 15, 1992. Further information and details can be obtained, from the course organizers: Prof. Dr. Helmut Jung HNO-Klinik. Krankenhaus Marienhof Rudolf-Virchow-Strasse 7 D-W-5400 Koblenz (FRG)
or Prof. Dr. Claus Walter Klinik am Rosenberg CH-9410 Hcidcn (Switzerland)
The Organizing Secretariat Centro Ricerche e Studi Amplifon via Ripamonti 129 1-20141 Milan (Italy)
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Tel.: 39-2-5359361 Fax: 39-2-57400384
