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A Review of Different Lasers in Endonasal Surgery: Ar-, KTP-, Dye-, Diode-, Nd-, Ho- and CO2-Laser
Med. Laser Appl. 17: 190–200 (2002) © Urban & Fischer Verlag http://www.urbanfischer.de/journals/lasermed
A Review of Different Lasers in Endonasal Surgery: Ar-, KTP-, Dye-, Diode-, Nd-, Ho- and CO2-Laser JÜRGEN EICHLER1 and ODAIR GONC¸ALVES2 1 2
Technische Fachhochschule Berlin, University of Applied Sciences, Berlin, Germany and Universidade Federal do Rio de Janeiro, Instituto de Física, Rio de Janeiro, Brazil
Submitted: January 2002 · Accepted: May 2002
Summary Background and Objective: Endonasal laser surgery is presently performed by seven different laser types with wavelength ranging from about 500 nm to 10.600 nm. It is the purpose of this study to review the clinical applications and to discuss the advantages and problems of each specific laser. Materials and Methods: The interaction of laser radiation and tissue is compared for different laser systems. Clinical applications of endonasal laser surgery are reviewed. Results and Discussions: Absorption and scattering of radiation in tissue depend on the wavelength of the radiation. This has a considerable influence on the radiation field and the temperature distribution during surgery. Different coagulation and evaporation zones arise for each laser system. The study shows that all of these lasers yield good clinical results. This is probably due to the fact that the surgeons properly adapt the power density and the movement of the beam over the tissue.
Key words Endonasal surgery, turbinates, laser coagulation, laser evaporation, argon-laser, KTP-laser, dye-laser, diode-laser, Nd-laser, Ho-laser, CO2-laser
Introduction The first application of endonasal laser surgery was performed in 1977 (34). The principal use was the treatment of nasal turbinates in the case of vasomotor rhinitis. It was found that the main advantage was the strongly reduced bleeding of the mucosa. In the last 20 years a variety of laser methods have been developed in the upper airway region, which are summarized in the following: – surgery of hypertrophied inferior turbinates in the case of various types of rhinitis, – prevention of epistaxis in hereditary haermorrhagic telangiectasia (Osler-Weber-Rendu disease),
– – – – – – – – – – – –
laser assisted polypectomy, tonsil laser surgery, treatment of diseases of the paranasal sinuses, laser surgery of benign and malignant nasal tumors, vaporization of papilloma, correction of septal spurs or dislocations, vaporization of synechia, hemophilia treatment, opening of the naso-lacrymal duct in dacryocystorhinostomy, laser treatment of snorring and sleep apnea by uvolopalatoplasty, opening of the choane in choanal atresia, cancer treatment by photodynamical therapy. 1615-1615/02/17/03-190 $ 15.00/0
A Review of Different Lasers in Endonasal Surgery
In the beginning the Ar-laser was used for endonasal laser surgery. However, since then, a variety of laser types have been introduced for surgery in the nose, which are listed in order of increasing wavelength: – Argon-laser at wavelength of 488 nm (blue) and 514 nm (green), – KTP- or frequency doubled Nd-laser at 532 nm (green), – dye-laser (yellow and red), – diode-laser at about 800 to 1000 nm (near infrared), – Nd-laser at 1.06 µm (near infrared), – Ho-laser at 2.1 µm (near infrared), – CO2-laser at 10.6 µm (mid infrared). It is a difficult task for a surgeon to decide which laser he should choose for a specific application. Each laser type has different properties for coagulation, cutting and evaporating of tissue. In addition, the construction of the beam guide system and the power density are quite different for each laser. Handpieces, endoscopes or operation microscopes can be used in the nasal cavity. Contact and noncontact methods are possible and the movement of the beam on the tissue may be slow or fast. Also an interstitial technique can be used. Some lasers have continuous operation and others are pulsed. In this paper some technical parameters of these lasers and the biophysical interaction between radiation and tissue are discussed. In addition, the literature concerning endonasal surgery using the various lasers is discussed.
Interaction of laser radiation and tissue Tissue optics The laser beam entering the tissue is subjected to absorption and scattering. The absorption coefficient µ a is defined as the probability (per unit length) for absorption of a photon in tissue. In a similar way the scattering coefficient µ s is the probability (per unit length) for scattering of a photon. The angular distribution of scattered radiation is described by the anisotropy factor g (61, 79). For g = 0 we have isotropic scattering in all directions and for g = 1 scattering in the forward direction only. These basic optical coefficients µ a, µ s, and g depend on the wave-
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length of the laser radiation and on the type of tissue. Until now these coefficients were not measured for endonasal tissue. However, data for other tissues were published. Liver tissue has been studied most extensively and we can take these data as a first approximation for nasal tissue (Table 1) (61). Tissue optics is simple in the case of strong absorption. According to table 1 this is the case for the Holmium- and CO2-laser. For these lasers the scattering coefficient µ s is much smaller than the absorption coefficient µ a. The radiation distribution is determined by µ a only showing an exponential decay in the depth x of the tissue. The following relation is valid: Fluence rate ~exp(µ a x) in W/cm–2 (Fig. 1). The depth of penetration of the radiation is given by δ = 1/µ a (This is the 37%-value (= 1/e) in Fig. 1). The values for the Holmium- and CO2-laser are δ = 0.2 and 0.01 mm. The radiation is absorbed mainly at the surface and the absorber is cell water. For medium and low absorption tissue optics is complicated because of scattering. The radiation distribution consists of the direct and scattered radiation. The scattered radiation may be spread over large areas in the tissue, including regions which are not directly irradiated. There is no simple and exact method to predict this distribution in tissue during laser application. However, the diffusion theory yields approximate results. In this theory the effective attenuation coefficient µ eff is introduced. (This coefficient is given by µ eff = [3 µ a (µ a + µ s (1–g))]1/2 (61, 79).) In this theory the radiation distribution shows also an exponential decay: Fluence rate ~ exp(µ eff x) in W/cm–2. The depth of penetration in this case is given by δ = 1/ µ eff (Fig. 1). Lasers with medium absorption are the Ar- and KTP-laser. The values for the depth of penetration δ are for both lasers about 0.4 mm (table 1). Low absorption takes place for the diode- and Ndlaser with δ = 3 and 5 mm. In Table 1, the technical and optical characteristics of different lasers used for endoansal surgery are summarized. The dye-laser is not included because it was used only in few cases. The wavelengths range from the visible spectrum (blue and green) to the near and mid infrared (500 to 10,000 nm). We may distinguish between radiation with strong (CO2-, Holmium-laser), medium (Argon-, KTP-laser), and low (diode-, Ndlaser) absorption in tissue. The CO2- and Holmiumlaser radiate in the infrared spectrum and the absorber in tissue is water. The Argon- and KTP-laser produce
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blue and green radiation, which is highly absorbed by red pigments (haemoglobin). This has special effects on the macro- and microcirculation of tissue. For the diode- and Nd-laser, absorption is low and no special chromophores are responsible for absorption. The radiation belongs to the near infrared region. Scattering in the tissue results in back-scattering or reflection of radiation (2). Table 1 shows the backscattered amount of the laser power. For strong and medium absorption the backscattered fraction of the incoming radiation is between 3 and 10%. For low absorption 25 to 55% of the radiation is reflected back. This fraction is lost during clinical application. Due to absorption of radiation the temperature in the tissue rises, resulting in coagulation, evaporation, and carbonization. During these processes the optical properties of tissue change. The depth of penetration of the radiation is smaller in coagulated tissue (Table 1). The laser may be applied in the contact or noncontact mode. Especially for the diode- and Nd-laser, large differences exist in endonasal applications. In the contact mode the power density is much higher, resulting in fast coagulation and carbonization of the surface. The carbonized layer has a higher absorption
coefficient than the normal tissue. Thus, the depth of penetration is low and scattering is reduced.
Coagulation and evaporation The dimension of the coagulated volume depends on the depth of penetration and on the backscattering of the radiation. The general behaviour is shown in Fig. 2, where the coagulated volume is plotted versus the irradiation time (for a laser power of about 8 W). The data points are measurements on muscle tissue in vitro using the Nd- and Ar-laser. The curves for the other laser types are estimations. According to absorption and scattering the volume of coagulation varies for the different laser types. The largest volume is achieved by the CO2-laser and the smallest by the Nd-laser probably due to back-scattering and heat conduction. Fig. 2 is valid for a low laser power and a short irradiation time. Evaporation of tissue was avoided. Absorption and scattering coefficients in tissue change with the temperature. Similar results are obtained for the evaporated volume during laser surgery (at 8 W). Fig. 3 shows the
Table 1. Properties of different laser systems for endonasal surgery (61). Ar-laser
KTP-laser
Diode-laser
Nd-laser
Ho-laser
CO2-laser
Technical properties: Type Continuous/pulsed Mean power Wavelength Colour
gas (ions) continuous 3–10 W 488/514 nm blue, blue-green
solid state pulsed/quasic. about 10 W 532 nm green
semicond. continuous about 30 W 800/900 nm near infrared
solide state continuous about 50 W 1.06 µm near infrared
solide state pulsed/quasic. about 20 W 2.1 µm near infrared
gas (molec.) pulsed/cont. about 20 W 10.6 µm mid infrared
Optical properties: Absorption Absorber Scattering Backscattering, Reflection Beam guide system
medium haemoglobin low 10% quartz fiber
medium haemoglobin low 10% quartz fiber
low cell material medium/strong 25% quartz fiber
low water strong 55% quartz fiber
strong water negligible 5% fiber
very strong water negligible 3% hollow ceramic rotating mirror
Optical constants: Depth of pentration δ Depth of pentration coagulated Absorption coefficient µ a Absorption coefficient coagulated Scattering coefficient µ s Scattering coefficient coagulated Anisotropy factor g Anisotropy factor coagulated
0.44/0.44 mm 0.13/0.14 mm 0.84/0.90 mm–1 1.5/1.3 mm–1 9.6/9.0 mm–1 60/64 mm–1 0.87/0.88 0.83/0.85
0.39 mm 0.15 mm 1.0 mm–1 1.5 mm–1 8.8 mm–1 57 mm–1 0.88 0.85
2.9/3.5 mm 0.86/1.35 mm 0.08/0.06 mm–1 0.10/0.06 mm–1 5.7/5.1 mm–1 39/35 mm–1 0.92/0.93 0.89/0.91
4.6 mm 3.1 0.020 mm–1 0.014 mm–1 4.4 mm–1 31 mm–1 0.93 0.92
0.2 mm 0.15 mm 2.3 mm–1 2.7 mm–1 2.3 mm–1 17 mm–1 0.79 0.90
0.01 mm 0.01 mm 100 mm–1 100 mm–1
A Review of Different Lasers in Endonasal Surgery
Fig. 1. Flux rate in tisse during laser irradiation versus the depth in tissue for the Ar-, KTP (frequeny doubled Nd)-, diode-, Nd-, Ho-, and CO2laser. The depth of penetration δ is given by the 37%-flux value.
Fig. 2. Volume of coagulation as a function of irradiation time in muscle tissue (in vitro, cow, 8 W, beam diameter 6 mm) for 6 lasers (points: measurements, lines: schematic estimated values). The power density is low and the time of irradiation is short and evaporation doesn’t occur.
Fig. 3. Evaporated mass as a function of irradiation time in muscle tissue (in vitro, cow, 8 W, beam diameter 6 mm) for 6 lasers (points: measurements, lines: schematic, estimated values).
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evaporated mass versus irradiation time for different lasers. For the CO2- and Nd-laser measurements in muscle tissue were performed which are plotted as data points. The curves for the other lasers are estimations. The efficiency for evaporation of tissue is nearly three times larger for the CO2-laser as for the Nd-laser.
Lasers in endonasal surgery Argon-laser The Argon-laser was very successful in ENT, especially for surgery of the nasal turbinates (35). Intravital microscopical studies determined that blood vessels shrank allready at the beginning of laser irradiation (33). This was attributed to the absorption bands of haemoglobin at wavelengths of about 560 nm and 580 nm, which are in the blue-green region of the spectrum. Further research is necessary to determine whether or not vessel shrinking occurs in the same manner for other laser types due to the temperature rise in tissue. Extensive histological studies were performed on healing the of the mucosa after surgery with the Argon-laser. The results are very satisfactory, showing a reepithelisiation after several months (36, 12). Thus, the scientific basis for application of this laser is very solid. Argon-lasers of about 10 W or lower were used. For application in the nasal cavity the bare fiber or a special end piece are applied. The end piece consists of a movable quartz tube of about 6 mm diameter which protects the fiber. A dielectric mirror at the tip of the tube reflects the laser beam by 90°. The main obstacles for a widespread use of the Argon-laser in medicine are the cost of the laser tube and the need for a high current power supply and water flow for cooling. When radiation from the Argon-laser enters tissue, the main interaction is absorption. Scattering is less important. The back-scattered intensity for tissue is about 10%. The intensity distribution of the radiation in tissue is approximately exponential. The depth of penetration given by the 37%-value is about 0.4 mm (Table 1 and Fig. 1). Thus, the production of heat due to absorption is mainly concentrated in this layer. However, heat is transfered to deeper layers by heat conduction.
The volume of coagulation versus irradiation time is shown in Fig. 2 for a laser power of 8 W. In the experiments the intensity was so low that evaporation of tissue was avoided. Fig. 3 shows the evaporated mass as a function of irradiation time (for a higher power density but for the same laser power). The evaporated region is surrounded by a coagulation zone. Its thickness depends on the depth of penetration and on other parameters. The application of the Argon-laser in endonasal surgery can be summarized by the following characteristics: radiation in the blue-green, power of about 10 W or less, direct production of heat in the surface layer of about 0.4 mm, low scattering in tissue, medium sized coagulation zone around evaporated regions, and slow motion of the laser beam on tissue. During coagulation, the depth of penetration is reduced from 0.4 to about 0.1 mm (Table 1). Due to the high costs the argon laser was less used in the last year. The main application is the surgery of the lower turbinates (35). Strip-like laser lesions with a length of several cm are produced. The evaporation zone with a depth of several mm is surround by a coagulation zone. The procedure for the treatment of epistaxis in the case of hereditary haemorrhagic telangiectasia (80, 32, 16, 19) is different. This is described in section 2.6.
Frequency doubled Nd-laser (KTP) The wavelength (532 nm, green) of this laser is similar to that of the Argon-laser, but it is nearer to the absorption band of haemoglobin. Thus, the depth of penetration is slightly smaller but also about 0.4 mm (Table 1). The KTP-laser is pulsed at about 1 kHz, while the Argon-laser operates continuously. During the short laser pulse the power is in the kW-range. Due to the high frequency repetition rate, the physician has the impression of quasicontinous operation. Theoretically, this kind of operation results in higher surface temperatures and less heat conduction in the case of evaporation. However, the characteristics of surgery with this laser should be comparable to those of the Argon-laser. Surgeons who used both lasers report about slight differences during surgery. A comparison of wound healing of KTP- and Ar-laser lesions was performed in Ref. (24).
A Review of Different Lasers in Endonasal Surgery
A typical laser for nasal surgery has a power of about 8 W. The main clinical applications of the KTPlaser are surgery of the lower turbinates. It can be used in superficial contact with the surface of the turbinate. A “checker board” is created by laser photocoagulations from posterior to anterior and then from superior to inferior (39, 40). Excellent results in over 1000 patients were obtained. Other applications are the treatment of epistaxis in the case of hereditary haemorrhagic telangiectasia (80, 70), uvopaletoplasty (18), sinus surgery (38) and dacryocystorhinostomy (37, 59, 4).
Diode-laser Semiconductor or diode-lasers play an important role in medicine, because in future manufacturing cost will be very low. The near infrared radiation of about 800 to 940 nm has a penetration depth in tissue of 3 to 4 mm (Fig. 1 and Table 1) which is slightly smaller than that of the Nd-laser. The general behaviour of laser-tissue interaction is similar to that of the Ndlaser. However, absorption of the diode-laser radiation is larger and scattering is lower. According to Table 1 a backscattering coefficient of 25% occurs. Due to the optical properties of tissue the laser power for a given application must be larger than that used with an Argon- or KTP-laser. A power of about 10 to 20 W is required for endonasal surgery in the noncontact application. A similar value holds for the Ndlaser. Due to the larger penetration depth and the strong scattering in tissue, larger coagulation zones can be obtained in comparison with the Argon- or KTP-laser. The general characteristics of surgery with the diode-laser should be comparable to those of the Ndlaser, which will be discussed in the next section. Only few comparisons between these laser types has been made so far (65). The diode- and Nd-laser are frequently used in the contact mode. Because normal fiber material breaks easily in the contact mode (due to thermal effects), special sapphire tips have been developed for this purpose. Due to the high power density at the tip, the tissue coagulates immediately. The optical parameters change, resulting in higher absorption. In addition the divergence of the radiation from the tip is high, favoring surface effects. Thus, in the contact mode the
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diode- and Nd-laser radiation behaves like radiation with high absorption. Bloodless cutting of tissue can be obtained in this case. So far, the main application of the diode-laser was surgery of the nasal turbinates in the contact (65) and noncontact (22) mode. In the first case the laser power was about 3 to 5 W and in the second case 10 W (total energy 5 kJ).
Nd-laser The Nd-laser, together with the CO2-, diode- and Argon-laser, is one of the most important lasers in medicine. The radiation has a large depth of penetration in tissue (about 5 mm, Table 1 and Fig. 1). Thus, deep coagulation zones can be produced. However, this occurs principally for static conditions at long irradiation time and low power. For high power densities and short times the depth of coagulation is of the order of 1 mm (69). To obtain surface effects the laser beam (with high power) has to be moved quickly over the tissue. Also, in the contact mode, superficial coagulation regions can be achieved. According to Table 1 about 55% of the laser energy is backscattered. As in the case of the diode-laser this loss has to be compensated by a higher laser power. The volume of coagulation and evaporation at a given laser power is small in comparison with the other lasers (Fig. 2 and 3). However, this is not a problem, since higher power up to 20 W can easily be applied. The region of evaporated tissue is surrounded by a relatively thick zone of coagulation. The Nd-laser is used in different ways in the nasal cavity, e.g. in combination with flexible endoscopes (21) or other fiber systems (73). Frequently the contact method is used (58, 52, 53). Also interstitial application is possible (78). No difference in the quality of nasal surgery were observed using the CO2- and Nd-laser (30, 3). However, if the laser beam is not properly handed, the large depth of penetration can result in damage to the nose, e. g. septum perforations. Excellent results have been obtained in applying this laser to endonasal surgery. The large differences in absorption and scattering between the Argon- and Nd-laser are probably compensated for by the surgeon by using a different laser power and different movement of the laser beam over the tissue. The Nd-laser, as used in endonasal surgery, can be characterized by
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the following: radiation in the near infrared, power of about 20 W, direct production of heat in a surface layer up to 5 mm, high scattering in tissue, large coagulation zone around evaporated tissue, and quicker motion of the laser beam (at high power) on tissue results in surface effects. In the contact mode this laser can create also surface effects and cut of tissue. The Nd-laser has been applied mainly for surgery of the lower turbinates (21, 73, 58, 53, 78, 30, 3, 81, 42, 20, 23, 28, 31). A comparison between laser surgery and other methods was published in Ref. 45. Other applications are hereditary haemorrhagic telangiectasia (82, 70, 19, 29, 47), polytectomy (52, 83, 9), uvopalatoplasty (14), dacryocystothinostomy (62, 63, 57). This laser was the most widely used laser in endonasal surgery, because of the good technical design. At the moment is substituted by the diodelaser, which is cheaper. We will show in an example how lasers with different properties can be used successfully for the same medical treatment. The Ar-laser has a low depth of penetration in tissue. Thus, telangiectasia are carefully coagulated with a defocused laser beam first in the periphery in circular movements. Then the center is treated. The procedure with the Nd-laser is different. The depth of penetration is larger and the whole area is irradiated by arbitrary beam movements. Both methods with different lasers yield very similar medical results.
Ho-laser The radiation of the Ho-laser is absorbed mainly in tissue water in a surface layer with a thickness of a few tenths of a millimeter (Table 1, Fig.1). Scattering of radiation in tissue is negligible and the backscattering coefficient is only about 5%. To obtain deep coagulation zones heat conduction from the hot surface into the tissue has to take place. Due to the strong absorption and the quasicontinuous operation, tissue can easily be evaporated. The focused radiation is well-suited for cutting of tissue. A typical Ho-laser for endonasal surgery has a mean power of 2 to 8 W with pulses of about 0.5 J at a repetition frequency of about 10 Hz. Due to the relatively high pulse energy a splattering of tissue fragments occur, which can be dangerous in the use with its surrounding tissue f.e. the erbita. This effect could
be reduced using smaller pulse energy at higher repetition rate. However, such lasers are not available currently. The interaction of laser radiation and tissue is comparable with the one of the CO2-laser, which will be discussed in the following section. However, some differences exist. Due to the reduced absorption the hemostatic action of the Ho radiation is superior to that of the CO2-laser. Other differences arises due to the low pulse frequency and high pulse energy of the Ho-laser. The Ho-laser radiation can be transported via optical fibers, which is not the case for the CO2laser. In the presence of liquids like blood the high pulse power at the fiber output splits the liquid and produces a vapour bubble through which the energy is transmitted to the target tissue. Therefore, it is not necessary to have a totally bloodless field for tissue effects. With the Ho-laser interesting results have been obtained in endonasal surgery (13). The main applications are surgery of the sinus (8, 68), turbinates and polyps (54), osteotomy (26), dacryocystorhinostomy (71, 48, 75) and correction of choanal atresia (55). High energy applications should be avoided, due to splattering tissues, while working near the scull base and the eye.
CO2-laser The mid infrared radiation of the CO2-laser is effectively absorbed by tissue water and it has a penetration depth of only 0.02 mm (Table 1, Fig. 1). Due to the high absorption, scattering is completely negligible. Thus, during laser surgery high surface temperatures arise and the tissue can effectively be evaporated, as in the case of the Ho-laser (Fig. 3). Initially the coagulation zone is very thin. However, large volumes can be coagulated through heat conduction into deeper tissue regions. To achieve large coagulation regions, a relatively low laser power and long radiation times must be applied. It is also possible to use a larger power by moving the beam quickly. CO2-lasers are well developed instruments and with the use of flexible hollow ceramic tubes they can be applied in the nasal cavity. For application to the nasal turbinates, a 90° mirror at the end tip of the beam guide system is useful. While all other laser types discussed in this paper can be used with flexible
A Review of Different Lasers in Endonasal Surgery
endoscopes, this is still not possible with the CO2laser. However, rotating mirror beam guide systems are available, and they can be combined with an operation microscope for application in the nasal cavity. In this case the optical quality of the laser beam is very good. Due to the small depth of penetration, the CO2- and the Ho-laser can also be used to cut or drill bones and cartilage. There are, for example, applications in ear surgery. The use of the CO2-laser in endonasal surgery is summarized by the following characteristics: radiation in the mid infrared, power about 10 W, strong absorption of energy in a 0.02 mm-surface layer, no scattering in tissue, effective evaporation of tissue, usually thin coagulation zones around evaporated tissue, and quick motion of the laser beam for higher laser powers. The main application of the CO2-laser in endonasal surgery is the treatment of the lower turbinates (6, 43, 7, 27, 64, 46, 50, 10, 66, 72, 49, 7, 25, 76, 56, 67). A comparison of the CO2-laser with other lasers for the application was studied in Ref. (44, 3). Other important application are uvopalatoplasty (11, 74) and choanal atrasia (60). Some surgical techniques on the turbinates using the CO2-laser are different from techniques using other lasers. Some surgeons evaporate the whole tissue surface (10).
Dye-laser The dye-laser operates mainly in the yellow and red part of the spectrum. Up to now only few applications of the dye-laser were reported in endonasal surgery: photodynamic cancer therapy (51) and treatment of haernorrhagic telangiectasia (5, 17, 15). If progress can be made in photodynamic therapy, this laser type may be introduced more widely in ENT. For other endonasal laser application this laser system is too expensive.
Discussion Endonasal laser surgery presently is performed with at least seven different laser types. Sucessfull results in clinical trials were reported in all of these cases. Thus, it is not possible to conclude which of these
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lasers is best suited to a specific application. From a theoretical point of view the lasers can be combined into three groups. a) Lasers with low depth of penetration in tissue (CO2- and Ho-laser) yield high surface temperatures and they are good for evaporation and cutting of tissue. They can also be used for cutting bone and cartilage. b) Lasers with medium depth of penetration are the Argon-laser and KTP-laser (frequency doubled Nd-laser). The radiation is effectively absorbed by red pigments such as blood. Thus, they seem to be well suited for endonasal surgery. c) Lasers with a large depth of penetration of several mm (Nd- and diode-laser) produce deep coagulation zones and evaporation is less effective. However cutting of tissue is also possible in the contact mode. Further investigation is required to determine if these theoretical considerations have practical consequences. At present, it is not possible to prove if any of these lasers has any advantages over the others. This is due to the fact that the various lasers are applied using different laser power, power densities and techniques for the movement of the beam on the tissue.
j j j j j j j
Verschiedene Laser in der endonasalen Chirurgie: Ar-, KTP-, Farbstoff-, Dioden-, Nd-, Ho- und CO2-Laser
Einleitung: Endonasale Laserchirurgie wird gegenwärtig im Spektralbereich zwischen 500 nm und 10600 nm mit sieben verschiedenen Lasertypen durchgeführt. In dieser Arbeit werden die klinischen Anwendungen zusammengefasst und die Vorteile und Probleme von jedem Lasertyp diskutiert. Material und Methoden: Die Wechselwirkung von Laserstrahlung und Gewebe wird für die verschiedenen Lasersysteme miteinander verglichen. Es wird ein Überblick über die Literatur zur klinischen Anwendung der endonasalen Laserchirurgie gegeben. Ergebnisse und Diskussion: Absorption und Streuung von Laserstrahlung im Gewebe hängen von der Wellenlänge ab. Dieses hat einen beträchtlichen Einfluss auf die Verteilung der Strahlung und Temperatur während der Laserchirurgie. Die Koagulations- und Verdampfungszonen sind für die verschiedenen Lasersystem unterschiedlich. Die Literatur zeigt, dass alle Lasersysteme gute klinische Ergebnisse liefern. Dies liegt vermutlich daran, dass die Ärzte die Leistungsdichte und die Strahlbewegung über dem Gewebe jeweils geeignet anpassen.
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Schlüsselwörter Endonasale Chirurgie, Nasenmuscheln, Laser Koagulation, Laser Verdampfung, Argonlaser, KTP-Laser, Farbstofflaser, Diodenlaser, Nd-Laser, Ho-Laser, CO2-Laser
Anmerkung der Herausgeber In dieser Arbeit ist unter der Bezeichnung Nd-Laser das üblicherweise mit Nd:YAG-Laser bezeichnete Lasersystem zu verstehen.
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16. HAYE R, AUSTAD J: Hereditary hemorrhagic teleangiectasia argon laser. Rhinology. 29: 5 (1991) 17. HAYE R, AUSTAD J: Hereditary haemorrhagic teleangiectasia: unsuccessful treatment with the flash lamp-pulsed dye-laser. Rhinolgy 30: 135 (1992) 18. IKEDA K, OSHIMA T, TANNO N, OGURA M, SHIMOMURA A, SUZUKI H, TAKASAKA T: Laser assisted uvopalatoplasty for habitual snorring without sleep apnea: outcome and complications. Journal of Oto-Rhino-Laryngology and its Related Specialities 59: 45 (1997) 19. ILLUM P, BJERRING P: Hereditary hemorrhagic telangiectasia treated by laser surgery. Rhinology 26: 19 (1988) 20. ITO H, BABA S, SUZUKI M, MAMIYA S, TAKAGI I, KIM Y, KITAO S: Severe perennial allergic rhinitis treated with Nd:YAG laser. Acta Oto-Laryngologica. Supplement 525: 14 (1996) 21. JAKOBOWICZ M, FRECHE C, DELACOUR JF, DURAND JP: A new endonasal therapy; the endoscopic YAG laser (in french). Annales D Oto-Laryngologie et de Chirurgie Cervico-Faciale. 107: 21 (1990) 22. JANDA P, SROKA R, TAUBER S, BAUMGARTNER R, GREVERS G, LEUNIG A: Diode laser treatment of hyperplastic inferior nasal turbinates. Lasers in Surg. Med. 27: 129–139 (2000) 23. JOVANOVIC S, DOKIC D: Nd:YAG laser surgery in treatment of allergic rhinitis. Laryng-, Rhino-, Otologie 74: 419 (1995) 24. Kass EG, Massaro BM, Komorowski RA, Toohill RJ: Wound healing of KTP and argon laser lesions in the canine nasal cavity. Otolaryngology and Head and Neck Surgery 108: 283 (1993) 25. KATZ S, SCHMELZER B, VIDTS G: Treatment of the obstructed nose by CO2-laser reduction of the inferior turbinates. Techniques and results. Am. J. Rhinology 14: 51–55 (2000) 26. KAUTZKY M, SUSANI M, LEUKAUF M, SCHENK P: Ho:YAG and Er:YAG infrared laser osteotomy (in German). Langenbecks Archiv fuer Chirurgie 377: 300 (1992) 27. KAWAMURA S, FUKUTAKE T, KUBO N, YAMASHITA T, KAMAZUWA T: Subjective results of laser surgery for allergic rhinitis. Acta Otolaryngologica Suppl. 500: 109 (1993) 28. KIRSCHNER RA, MCDONNEL BC, BRODKIN AC: Nd:YAG laser turbinectomy. Laser in Surgery and Medicine 8: 195 (1988) 29. KLUGER PB, SHAPSHAY SM, HYBELS RL, BOHIGIAN RK: Nd:YAG laser intranasal photocoagulation in heridatary hemorrhagic telangiectasia: an update report. Laryngoscope 97: 1397 (1987) 30. LACHIVER X: CO2 or YAG lasers for nasal obstructions. 1st International Congress of Endonasal Laser Surgery, Cologne (1996) 31. LAGERHOLM S, HARSTEN G, ENGARD P, OLSSEN B: Laserturbinectomy: long term results. J. of Laryng. and Otol. 13: 529–531 (1999) 32. LENNOX PA, HARRIES M, LUND VJ, HOWARD DJ: A retrospective study of the role of the argon laser in the management of epistaxis secondary to hereditary haemorrhagic telangiectasia. Journal of Laryngology and Otology. 111: 43 (1997) 33. LENZ H, EICHLER J: The effect of the argon laser on the vessels, the macro- and mircocirculation of the mucosa of the hamster cheek-pouch. An intravitalmicroscopic study (in German), Laryngolgogie. Rhinologie, Ototologie 54: 612 (1975)
A Review of Different Lasers in Endonasal Surgery 34. LENZ H, EICHLER J, SCHÄFER G, SALK J: Parameters for argon laser surgery of the lower human turbinate. Acta Otolaryngolica 83: 360–365 (1977) 35. LENZ H: 8 years laser surgery of the inferior turbinates in vasomotor rhinopathy in the form of laser strip corbonization (in German). HNO 33: 422 (1985) 36. LENZ H, PREUßLER H: Histologic changes in the epithelium of the respiratory mucosa of the lower turbinates following argon laser strip carbonization in vasomotor rhinitis (in German). Laryngologie. Rhinologie. Otolologie 65: 438 (1986) 37. LEVIN PS, STORMO-GISPSON DJ: Endocanalicular laser-assisted dacrycystorhinostomy. An anatomy study. Archives of Ophthalmology 110: 1488 (1992) 38. LEVINE HL: Endoscopy and the KTP/532 laser for nasal sinus disease. Annals of Otol. Rhinol. and Laryng. 98: 46 (1989) 39. LEVINE HL: Laser and endoscopic rhinologic surgery, Otolaryngologic Clinics of North America 22: 739 (1989)
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47. METHA AC, LIVINGSTON DR, LEVINE HL: Fiberoptic bronchoscope and Nd:YAG laser in treatment of severe epistaxis from nasal hereditary hemorrhagic telangectasia and hemangioma. Chest 91: 791 (1987) 48. Metson R, Woog JJ, Puliafito CC: Endoscopic laser dacryocystorhinostomy. Laryngoscope 104: 269 (1994) 49. MITTELMAN H: CO2 laser turbinectorniers for chronic, obstructive rhinitis. Lasers in Surgery and Medicine 2: 29 (1982) 50. MLADINA R, RISAVI R, SUBARIC M: CO2 laser anterior turbinectomy in the treatment of non-allergic vasomotor rhinopathia. A prospective study upon 78 patients. Rhinology 29: 267 (1991) 51. OFNER JG, BARTL B, KOENIG S, THURNFART WF: Photodynamic therapy in selected cases at the ENT clinic, Innsbruck: case reports. J of Photochemistry and Photobiology. B, Biology 36: 185 (1996) 52. OHYAMA M: Laser polypectomy. Rhinology. Supplement 8: 35 (1989) 53. OLTHOFF A, MARTIN A, LIEBMANN F: Nd-YAG laser treatment of the lower turbinates with contact in hyperreflectic and allergic rhinopathy. Laryng-, Rhino-, Otology 78: 240–243 (1999) 54. OSWAL VH, BINGHAM BJ: A pilot study of the Ho:YAG laser in nasal turbinate and tonsil surgery. J of Clinical Laser Medicine and Surgery 10: 11 (1992) 55. Panwar SS, Martin FW: Trans-nasal endocopic Ho:YAG laser correction of choanal atresia. J of Laryngology and Ototlogy 110: 429 (1996) 56. PAPADAKIS G, SKOULAKIS C, NIKOLIDAKIS A, VILEGRATIS G, BIZAKIS J, HELIDONIS G: Swiftlaser inferior turbinoplasty. Am. J. Rhinol. 13: 479–482 (1999) 57. PIATON JM, LIMON S, OUNNAS N, KELLER P: Transcanalicular endodacryocystorhinostomy using Nd:YAG laser. Journal Francais D Ophthalmologie 17: 555 (1994) 58. PLOUZHNIKOV MS: Contact laser surgery in ENT. 1 st International Congress of Endonasal Laser Surgery, Germany, Cologne (1996) 59. REIFLER DM: Results of endoscopic KTP laser-assisted dacrycystorhinostomy. Ophthalmic Plastic and Reconstructive Surgery 9: 231 (1993) 60. ROELLY P, ROGER G, BELLITY A, GARABEDIAN EN: Choanal atrasia: managemant and surgical treatmant. Study of 50 cases. Annales de Pediatrie 39: 479 (1992) 61. ROGGAN A: Dosimetrie thermischer Gewebeeigenschaften in der Medizin. Fortschritte der Lasermedizin 16, ISBN 3-60951290-3, ecomed (1997) 62. ROSEN N, BARAK A, ROSNER M: Trancanalicular laser-assisted dacryocystrhinostomy. Ophthalmic Surgery and Lasers 28: 723 (1997) 63. SAINT BLANCAT P, RISSE JF, KLOSSEK JM, FONTANEL JP: Dacryocystorhinostomy using Nd:YAG laser by the intracanicular approach. Revue de Laryngologie Ototlogie Rhinologie 117: 373 (1996) 64. SAITO S: CO2 laser vaporization of nasal mucosa in patients with allergic rhinitis. Otolaryngolgogy – Head and Neck Surgery 65: 871 (1993) 65. SCHERER M, REICHERT K, SCHILDHAUER S: Laser surgery of the middle nasal meatus in recurrent sinusitis. Laryng-, Rhino-, Otology 78: 50–53 (1999) 66. SELKIN SG: Pitfalls in intranasal laser surgery and how to avoid them. Archives of Otolayngology and Head and Neck Surgery 112: 285 (1986)
67. SCHMELZER B, KATZ S, VIDTS G: Long-term efficacy of our surgical approach to turbinate hypertrophy. Am. J. Rhinol. 13: 357–361 (1999) 68. SHAPSHAY SM, REBEIZ EE, PANKRATOV MM: Ho;YAG laserassisted endoscopic sinus surgery: clinical experience. Laryngoscope 102: 1177 (1992) 69. SICKLINGER A, LENZ H, EICHLER J: In vitro experiments in Nd:YAG laser surgery on the lower turbinates. Laryngo-Rhino-Otol 79: 536–542 (2000) 70. SIEGEL MB, KEANE WM, ATKINS JF, ROSEN MR: Control of epistaxis in patients with hereditary hemorrhagic telangiectasia. Otolarayngology and Head and Neck Surgery. 105: 675 (1991) 71. SILKISS RZ, AXELROD RN, LWACH AG, VASSILIADIS A, HENNINGS DR: Transcanalicular YAG-dacryocystorhinostomy. Ophthalmic Surgery 23: 351 (1992) 72. SIMPSON GT, SHAPSHAY SM, VAUGHAN CW: Rhinologic laser surgery. Otolaryngologic Clinics of North America 16: 829 (1983) 73. SROKA R, RÖSLER P, JONDA P, GREVES G, LEUNIG A: Endonalsal laser surgery with a new fiber guidance instrument. Laryngoscope 110: 332–334 (2000) 74. SULSENTI G, PALMA P: Carbon dioxide laser uvulopalatopharyngoplasty. Part I. Surgical technique. Acta Otorhinolaryngologica Italica 13: 53 (1993) 75. SZUBIN L, PAPAGEORGE A, SACKS E: Endonasal laser-assisted dacryocysto-rhinostomy. American J. of Rhinology 13: 371–374 (1999) 76. TANIGAWA T, YASHIKI T, HAYASHI K, SATO T: Carbon dioxide laser vaporization for turbinate: optimal conditions and indications. Auris, Nasus, Larynx 27: 137–140 (2000) 77. TESTA B, MESOLELLA M, SQUEGLIA C, TESTA D, MOTTA G: Carbon dioxyde laser turbinate surgery for chronic obstructive rhinitis. Lasers in Surg. Med. 27: 49–54 (2000) 78. VAGNETTTI A, GOBBI E, ALGIERI GM, D´AMBROSSO L: Wedge turbinectomy: a new combined photocoagulative Nd:YAG laser technique. Laryngoscope 110: 1034–1036 (2000) 79. WELCH AJ, V. GEMERT M: Optical-thermal response of laserirradiated tissue, Plenum Press, New York and London (1995) 80. WERNER JA, GEISTHOFF UW LIPPERT BM, RUDERTH: Treatment of recurre epistaxis in Rendu-Osler-Weber disease (in German). HNO 45: 673 (1977) 81. WERNER JA, LIPPERT BM: Nd:YAG laser light-induced reduction of the nasal turbinates. Laryngo-, Rhino-, Otologie 75: 523 (1996) 82. WERNER JA, LIPPERT BM, GEISTHOFF UW, RUDERT H: Nd:YAG laser therapy of recurrent epistaxis in hereditary hemorrhagic telangiectasia (in German). Laryngo-, Rhino-, Otologie 76: 495 (1997) 83. ZHANG BQ: Comparison of results of laser and routine surgery therapy in treatment of nasal polyps. Chinese Medical Journal 106: 707 (1993)
Correspondence address: Prof. Dr. Jürgen Eichler, Technische Fachhochschule Berlin/University of Applied Sciences, FB II, Seestraße 64, D-13347 Berlin, Germany Tel.: ++49-30-45 043 917; Fax: ++49-30-45 043 959; e-mail: [email protected]
A Review of Different Lasers in Endonasal Surgery: Ar-, KTP-, Dye-, Diode-, Nd-, Ho- and CO2-Laser JÜRGEN EICHLER1 and ODAIR GONC¸ALVES2 1 2
Technische Fachhochschule Berlin, University of Applied Sciences, Berlin, Germany and Universidade Federal do Rio de Janeiro, Instituto de Física, Rio de Janeiro, Brazil
Submitted: January 2002 · Accepted: May 2002
Summary Background and Objective: Endonasal laser surgery is presently performed by seven different laser types with wavelength ranging from about 500 nm to 10.600 nm. It is the purpose of this study to review the clinical applications and to discuss the advantages and problems of each specific laser. Materials and Methods: The interaction of laser radiation and tissue is compared for different laser systems. Clinical applications of endonasal laser surgery are reviewed. Results and Discussions: Absorption and scattering of radiation in tissue depend on the wavelength of the radiation. This has a considerable influence on the radiation field and the temperature distribution during surgery. Different coagulation and evaporation zones arise for each laser system. The study shows that all of these lasers yield good clinical results. This is probably due to the fact that the surgeons properly adapt the power density and the movement of the beam over the tissue.
Key words Endonasal surgery, turbinates, laser coagulation, laser evaporation, argon-laser, KTP-laser, dye-laser, diode-laser, Nd-laser, Ho-laser, CO2-laser
Introduction The first application of endonasal laser surgery was performed in 1977 (34). The principal use was the treatment of nasal turbinates in the case of vasomotor rhinitis. It was found that the main advantage was the strongly reduced bleeding of the mucosa. In the last 20 years a variety of laser methods have been developed in the upper airway region, which are summarized in the following: – surgery of hypertrophied inferior turbinates in the case of various types of rhinitis, – prevention of epistaxis in hereditary haermorrhagic telangiectasia (Osler-Weber-Rendu disease),
– – – – – – – – – – – –
laser assisted polypectomy, tonsil laser surgery, treatment of diseases of the paranasal sinuses, laser surgery of benign and malignant nasal tumors, vaporization of papilloma, correction of septal spurs or dislocations, vaporization of synechia, hemophilia treatment, opening of the naso-lacrymal duct in dacryocystorhinostomy, laser treatment of snorring and sleep apnea by uvolopalatoplasty, opening of the choane in choanal atresia, cancer treatment by photodynamical therapy. 1615-1615/02/17/03-190 $ 15.00/0
A Review of Different Lasers in Endonasal Surgery
In the beginning the Ar-laser was used for endonasal laser surgery. However, since then, a variety of laser types have been introduced for surgery in the nose, which are listed in order of increasing wavelength: – Argon-laser at wavelength of 488 nm (blue) and 514 nm (green), – KTP- or frequency doubled Nd-laser at 532 nm (green), – dye-laser (yellow and red), – diode-laser at about 800 to 1000 nm (near infrared), – Nd-laser at 1.06 µm (near infrared), – Ho-laser at 2.1 µm (near infrared), – CO2-laser at 10.6 µm (mid infrared). It is a difficult task for a surgeon to decide which laser he should choose for a specific application. Each laser type has different properties for coagulation, cutting and evaporating of tissue. In addition, the construction of the beam guide system and the power density are quite different for each laser. Handpieces, endoscopes or operation microscopes can be used in the nasal cavity. Contact and noncontact methods are possible and the movement of the beam on the tissue may be slow or fast. Also an interstitial technique can be used. Some lasers have continuous operation and others are pulsed. In this paper some technical parameters of these lasers and the biophysical interaction between radiation and tissue are discussed. In addition, the literature concerning endonasal surgery using the various lasers is discussed.
Interaction of laser radiation and tissue Tissue optics The laser beam entering the tissue is subjected to absorption and scattering. The absorption coefficient µ a is defined as the probability (per unit length) for absorption of a photon in tissue. In a similar way the scattering coefficient µ s is the probability (per unit length) for scattering of a photon. The angular distribution of scattered radiation is described by the anisotropy factor g (61, 79). For g = 0 we have isotropic scattering in all directions and for g = 1 scattering in the forward direction only. These basic optical coefficients µ a, µ s, and g depend on the wave-
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length of the laser radiation and on the type of tissue. Until now these coefficients were not measured for endonasal tissue. However, data for other tissues were published. Liver tissue has been studied most extensively and we can take these data as a first approximation for nasal tissue (Table 1) (61). Tissue optics is simple in the case of strong absorption. According to table 1 this is the case for the Holmium- and CO2-laser. For these lasers the scattering coefficient µ s is much smaller than the absorption coefficient µ a. The radiation distribution is determined by µ a only showing an exponential decay in the depth x of the tissue. The following relation is valid: Fluence rate ~exp(µ a x) in W/cm–2 (Fig. 1). The depth of penetration of the radiation is given by δ = 1/µ a (This is the 37%-value (= 1/e) in Fig. 1). The values for the Holmium- and CO2-laser are δ = 0.2 and 0.01 mm. The radiation is absorbed mainly at the surface and the absorber is cell water. For medium and low absorption tissue optics is complicated because of scattering. The radiation distribution consists of the direct and scattered radiation. The scattered radiation may be spread over large areas in the tissue, including regions which are not directly irradiated. There is no simple and exact method to predict this distribution in tissue during laser application. However, the diffusion theory yields approximate results. In this theory the effective attenuation coefficient µ eff is introduced. (This coefficient is given by µ eff = [3 µ a (µ a + µ s (1–g))]1/2 (61, 79).) In this theory the radiation distribution shows also an exponential decay: Fluence rate ~ exp(µ eff x) in W/cm–2. The depth of penetration in this case is given by δ = 1/ µ eff (Fig. 1). Lasers with medium absorption are the Ar- and KTP-laser. The values for the depth of penetration δ are for both lasers about 0.4 mm (table 1). Low absorption takes place for the diode- and Ndlaser with δ = 3 and 5 mm. In Table 1, the technical and optical characteristics of different lasers used for endoansal surgery are summarized. The dye-laser is not included because it was used only in few cases. The wavelengths range from the visible spectrum (blue and green) to the near and mid infrared (500 to 10,000 nm). We may distinguish between radiation with strong (CO2-, Holmium-laser), medium (Argon-, KTP-laser), and low (diode-, Ndlaser) absorption in tissue. The CO2- and Holmiumlaser radiate in the infrared spectrum and the absorber in tissue is water. The Argon- and KTP-laser produce
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blue and green radiation, which is highly absorbed by red pigments (haemoglobin). This has special effects on the macro- and microcirculation of tissue. For the diode- and Nd-laser, absorption is low and no special chromophores are responsible for absorption. The radiation belongs to the near infrared region. Scattering in the tissue results in back-scattering or reflection of radiation (2). Table 1 shows the backscattered amount of the laser power. For strong and medium absorption the backscattered fraction of the incoming radiation is between 3 and 10%. For low absorption 25 to 55% of the radiation is reflected back. This fraction is lost during clinical application. Due to absorption of radiation the temperature in the tissue rises, resulting in coagulation, evaporation, and carbonization. During these processes the optical properties of tissue change. The depth of penetration of the radiation is smaller in coagulated tissue (Table 1). The laser may be applied in the contact or noncontact mode. Especially for the diode- and Nd-laser, large differences exist in endonasal applications. In the contact mode the power density is much higher, resulting in fast coagulation and carbonization of the surface. The carbonized layer has a higher absorption
coefficient than the normal tissue. Thus, the depth of penetration is low and scattering is reduced.
Coagulation and evaporation The dimension of the coagulated volume depends on the depth of penetration and on the backscattering of the radiation. The general behaviour is shown in Fig. 2, where the coagulated volume is plotted versus the irradiation time (for a laser power of about 8 W). The data points are measurements on muscle tissue in vitro using the Nd- and Ar-laser. The curves for the other laser types are estimations. According to absorption and scattering the volume of coagulation varies for the different laser types. The largest volume is achieved by the CO2-laser and the smallest by the Nd-laser probably due to back-scattering and heat conduction. Fig. 2 is valid for a low laser power and a short irradiation time. Evaporation of tissue was avoided. Absorption and scattering coefficients in tissue change with the temperature. Similar results are obtained for the evaporated volume during laser surgery (at 8 W). Fig. 3 shows the
Table 1. Properties of different laser systems for endonasal surgery (61). Ar-laser
KTP-laser
Diode-laser
Nd-laser
Ho-laser
CO2-laser
Technical properties: Type Continuous/pulsed Mean power Wavelength Colour
gas (ions) continuous 3–10 W 488/514 nm blue, blue-green
solid state pulsed/quasic. about 10 W 532 nm green
semicond. continuous about 30 W 800/900 nm near infrared
solide state continuous about 50 W 1.06 µm near infrared
solide state pulsed/quasic. about 20 W 2.1 µm near infrared
gas (molec.) pulsed/cont. about 20 W 10.6 µm mid infrared
Optical properties: Absorption Absorber Scattering Backscattering, Reflection Beam guide system
medium haemoglobin low 10% quartz fiber
medium haemoglobin low 10% quartz fiber
low cell material medium/strong 25% quartz fiber
low water strong 55% quartz fiber
strong water negligible 5% fiber
very strong water negligible 3% hollow ceramic rotating mirror
Optical constants: Depth of pentration δ Depth of pentration coagulated Absorption coefficient µ a Absorption coefficient coagulated Scattering coefficient µ s Scattering coefficient coagulated Anisotropy factor g Anisotropy factor coagulated
0.44/0.44 mm 0.13/0.14 mm 0.84/0.90 mm–1 1.5/1.3 mm–1 9.6/9.0 mm–1 60/64 mm–1 0.87/0.88 0.83/0.85
0.39 mm 0.15 mm 1.0 mm–1 1.5 mm–1 8.8 mm–1 57 mm–1 0.88 0.85
2.9/3.5 mm 0.86/1.35 mm 0.08/0.06 mm–1 0.10/0.06 mm–1 5.7/5.1 mm–1 39/35 mm–1 0.92/0.93 0.89/0.91
4.6 mm 3.1 0.020 mm–1 0.014 mm–1 4.4 mm–1 31 mm–1 0.93 0.92
0.2 mm 0.15 mm 2.3 mm–1 2.7 mm–1 2.3 mm–1 17 mm–1 0.79 0.90
0.01 mm 0.01 mm 100 mm–1 100 mm–1
A Review of Different Lasers in Endonasal Surgery
Fig. 1. Flux rate in tisse during laser irradiation versus the depth in tissue for the Ar-, KTP (frequeny doubled Nd)-, diode-, Nd-, Ho-, and CO2laser. The depth of penetration δ is given by the 37%-flux value.
Fig. 2. Volume of coagulation as a function of irradiation time in muscle tissue (in vitro, cow, 8 W, beam diameter 6 mm) for 6 lasers (points: measurements, lines: schematic estimated values). The power density is low and the time of irradiation is short and evaporation doesn’t occur.
Fig. 3. Evaporated mass as a function of irradiation time in muscle tissue (in vitro, cow, 8 W, beam diameter 6 mm) for 6 lasers (points: measurements, lines: schematic, estimated values).
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evaporated mass versus irradiation time for different lasers. For the CO2- and Nd-laser measurements in muscle tissue were performed which are plotted as data points. The curves for the other lasers are estimations. The efficiency for evaporation of tissue is nearly three times larger for the CO2-laser as for the Nd-laser.
Lasers in endonasal surgery Argon-laser The Argon-laser was very successful in ENT, especially for surgery of the nasal turbinates (35). Intravital microscopical studies determined that blood vessels shrank allready at the beginning of laser irradiation (33). This was attributed to the absorption bands of haemoglobin at wavelengths of about 560 nm and 580 nm, which are in the blue-green region of the spectrum. Further research is necessary to determine whether or not vessel shrinking occurs in the same manner for other laser types due to the temperature rise in tissue. Extensive histological studies were performed on healing the of the mucosa after surgery with the Argon-laser. The results are very satisfactory, showing a reepithelisiation after several months (36, 12). Thus, the scientific basis for application of this laser is very solid. Argon-lasers of about 10 W or lower were used. For application in the nasal cavity the bare fiber or a special end piece are applied. The end piece consists of a movable quartz tube of about 6 mm diameter which protects the fiber. A dielectric mirror at the tip of the tube reflects the laser beam by 90°. The main obstacles for a widespread use of the Argon-laser in medicine are the cost of the laser tube and the need for a high current power supply and water flow for cooling. When radiation from the Argon-laser enters tissue, the main interaction is absorption. Scattering is less important. The back-scattered intensity for tissue is about 10%. The intensity distribution of the radiation in tissue is approximately exponential. The depth of penetration given by the 37%-value is about 0.4 mm (Table 1 and Fig. 1). Thus, the production of heat due to absorption is mainly concentrated in this layer. However, heat is transfered to deeper layers by heat conduction.
The volume of coagulation versus irradiation time is shown in Fig. 2 for a laser power of 8 W. In the experiments the intensity was so low that evaporation of tissue was avoided. Fig. 3 shows the evaporated mass as a function of irradiation time (for a higher power density but for the same laser power). The evaporated region is surrounded by a coagulation zone. Its thickness depends on the depth of penetration and on other parameters. The application of the Argon-laser in endonasal surgery can be summarized by the following characteristics: radiation in the blue-green, power of about 10 W or less, direct production of heat in the surface layer of about 0.4 mm, low scattering in tissue, medium sized coagulation zone around evaporated regions, and slow motion of the laser beam on tissue. During coagulation, the depth of penetration is reduced from 0.4 to about 0.1 mm (Table 1). Due to the high costs the argon laser was less used in the last year. The main application is the surgery of the lower turbinates (35). Strip-like laser lesions with a length of several cm are produced. The evaporation zone with a depth of several mm is surround by a coagulation zone. The procedure for the treatment of epistaxis in the case of hereditary haemorrhagic telangiectasia (80, 32, 16, 19) is different. This is described in section 2.6.
Frequency doubled Nd-laser (KTP) The wavelength (532 nm, green) of this laser is similar to that of the Argon-laser, but it is nearer to the absorption band of haemoglobin. Thus, the depth of penetration is slightly smaller but also about 0.4 mm (Table 1). The KTP-laser is pulsed at about 1 kHz, while the Argon-laser operates continuously. During the short laser pulse the power is in the kW-range. Due to the high frequency repetition rate, the physician has the impression of quasicontinous operation. Theoretically, this kind of operation results in higher surface temperatures and less heat conduction in the case of evaporation. However, the characteristics of surgery with this laser should be comparable to those of the Argon-laser. Surgeons who used both lasers report about slight differences during surgery. A comparison of wound healing of KTP- and Ar-laser lesions was performed in Ref. (24).
A Review of Different Lasers in Endonasal Surgery
A typical laser for nasal surgery has a power of about 8 W. The main clinical applications of the KTPlaser are surgery of the lower turbinates. It can be used in superficial contact with the surface of the turbinate. A “checker board” is created by laser photocoagulations from posterior to anterior and then from superior to inferior (39, 40). Excellent results in over 1000 patients were obtained. Other applications are the treatment of epistaxis in the case of hereditary haemorrhagic telangiectasia (80, 70), uvopaletoplasty (18), sinus surgery (38) and dacryocystorhinostomy (37, 59, 4).
Diode-laser Semiconductor or diode-lasers play an important role in medicine, because in future manufacturing cost will be very low. The near infrared radiation of about 800 to 940 nm has a penetration depth in tissue of 3 to 4 mm (Fig. 1 and Table 1) which is slightly smaller than that of the Nd-laser. The general behaviour of laser-tissue interaction is similar to that of the Ndlaser. However, absorption of the diode-laser radiation is larger and scattering is lower. According to Table 1 a backscattering coefficient of 25% occurs. Due to the optical properties of tissue the laser power for a given application must be larger than that used with an Argon- or KTP-laser. A power of about 10 to 20 W is required for endonasal surgery in the noncontact application. A similar value holds for the Ndlaser. Due to the larger penetration depth and the strong scattering in tissue, larger coagulation zones can be obtained in comparison with the Argon- or KTP-laser. The general characteristics of surgery with the diode-laser should be comparable to those of the Ndlaser, which will be discussed in the next section. Only few comparisons between these laser types has been made so far (65). The diode- and Nd-laser are frequently used in the contact mode. Because normal fiber material breaks easily in the contact mode (due to thermal effects), special sapphire tips have been developed for this purpose. Due to the high power density at the tip, the tissue coagulates immediately. The optical parameters change, resulting in higher absorption. In addition the divergence of the radiation from the tip is high, favoring surface effects. Thus, in the contact mode the
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diode- and Nd-laser radiation behaves like radiation with high absorption. Bloodless cutting of tissue can be obtained in this case. So far, the main application of the diode-laser was surgery of the nasal turbinates in the contact (65) and noncontact (22) mode. In the first case the laser power was about 3 to 5 W and in the second case 10 W (total energy 5 kJ).
Nd-laser The Nd-laser, together with the CO2-, diode- and Argon-laser, is one of the most important lasers in medicine. The radiation has a large depth of penetration in tissue (about 5 mm, Table 1 and Fig. 1). Thus, deep coagulation zones can be produced. However, this occurs principally for static conditions at long irradiation time and low power. For high power densities and short times the depth of coagulation is of the order of 1 mm (69). To obtain surface effects the laser beam (with high power) has to be moved quickly over the tissue. Also, in the contact mode, superficial coagulation regions can be achieved. According to Table 1 about 55% of the laser energy is backscattered. As in the case of the diode-laser this loss has to be compensated by a higher laser power. The volume of coagulation and evaporation at a given laser power is small in comparison with the other lasers (Fig. 2 and 3). However, this is not a problem, since higher power up to 20 W can easily be applied. The region of evaporated tissue is surrounded by a relatively thick zone of coagulation. The Nd-laser is used in different ways in the nasal cavity, e.g. in combination with flexible endoscopes (21) or other fiber systems (73). Frequently the contact method is used (58, 52, 53). Also interstitial application is possible (78). No difference in the quality of nasal surgery were observed using the CO2- and Nd-laser (30, 3). However, if the laser beam is not properly handed, the large depth of penetration can result in damage to the nose, e. g. septum perforations. Excellent results have been obtained in applying this laser to endonasal surgery. The large differences in absorption and scattering between the Argon- and Nd-laser are probably compensated for by the surgeon by using a different laser power and different movement of the laser beam over the tissue. The Nd-laser, as used in endonasal surgery, can be characterized by
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the following: radiation in the near infrared, power of about 20 W, direct production of heat in a surface layer up to 5 mm, high scattering in tissue, large coagulation zone around evaporated tissue, and quicker motion of the laser beam (at high power) on tissue results in surface effects. In the contact mode this laser can create also surface effects and cut of tissue. The Nd-laser has been applied mainly for surgery of the lower turbinates (21, 73, 58, 53, 78, 30, 3, 81, 42, 20, 23, 28, 31). A comparison between laser surgery and other methods was published in Ref. 45. Other applications are hereditary haemorrhagic telangiectasia (82, 70, 19, 29, 47), polytectomy (52, 83, 9), uvopalatoplasty (14), dacryocystothinostomy (62, 63, 57). This laser was the most widely used laser in endonasal surgery, because of the good technical design. At the moment is substituted by the diodelaser, which is cheaper. We will show in an example how lasers with different properties can be used successfully for the same medical treatment. The Ar-laser has a low depth of penetration in tissue. Thus, telangiectasia are carefully coagulated with a defocused laser beam first in the periphery in circular movements. Then the center is treated. The procedure with the Nd-laser is different. The depth of penetration is larger and the whole area is irradiated by arbitrary beam movements. Both methods with different lasers yield very similar medical results.
Ho-laser The radiation of the Ho-laser is absorbed mainly in tissue water in a surface layer with a thickness of a few tenths of a millimeter (Table 1, Fig.1). Scattering of radiation in tissue is negligible and the backscattering coefficient is only about 5%. To obtain deep coagulation zones heat conduction from the hot surface into the tissue has to take place. Due to the strong absorption and the quasicontinuous operation, tissue can easily be evaporated. The focused radiation is well-suited for cutting of tissue. A typical Ho-laser for endonasal surgery has a mean power of 2 to 8 W with pulses of about 0.5 J at a repetition frequency of about 10 Hz. Due to the relatively high pulse energy a splattering of tissue fragments occur, which can be dangerous in the use with its surrounding tissue f.e. the erbita. This effect could
be reduced using smaller pulse energy at higher repetition rate. However, such lasers are not available currently. The interaction of laser radiation and tissue is comparable with the one of the CO2-laser, which will be discussed in the following section. However, some differences exist. Due to the reduced absorption the hemostatic action of the Ho radiation is superior to that of the CO2-laser. Other differences arises due to the low pulse frequency and high pulse energy of the Ho-laser. The Ho-laser radiation can be transported via optical fibers, which is not the case for the CO2laser. In the presence of liquids like blood the high pulse power at the fiber output splits the liquid and produces a vapour bubble through which the energy is transmitted to the target tissue. Therefore, it is not necessary to have a totally bloodless field for tissue effects. With the Ho-laser interesting results have been obtained in endonasal surgery (13). The main applications are surgery of the sinus (8, 68), turbinates and polyps (54), osteotomy (26), dacryocystorhinostomy (71, 48, 75) and correction of choanal atresia (55). High energy applications should be avoided, due to splattering tissues, while working near the scull base and the eye.
CO2-laser The mid infrared radiation of the CO2-laser is effectively absorbed by tissue water and it has a penetration depth of only 0.02 mm (Table 1, Fig. 1). Due to the high absorption, scattering is completely negligible. Thus, during laser surgery high surface temperatures arise and the tissue can effectively be evaporated, as in the case of the Ho-laser (Fig. 3). Initially the coagulation zone is very thin. However, large volumes can be coagulated through heat conduction into deeper tissue regions. To achieve large coagulation regions, a relatively low laser power and long radiation times must be applied. It is also possible to use a larger power by moving the beam quickly. CO2-lasers are well developed instruments and with the use of flexible hollow ceramic tubes they can be applied in the nasal cavity. For application to the nasal turbinates, a 90° mirror at the end tip of the beam guide system is useful. While all other laser types discussed in this paper can be used with flexible
A Review of Different Lasers in Endonasal Surgery
endoscopes, this is still not possible with the CO2laser. However, rotating mirror beam guide systems are available, and they can be combined with an operation microscope for application in the nasal cavity. In this case the optical quality of the laser beam is very good. Due to the small depth of penetration, the CO2- and the Ho-laser can also be used to cut or drill bones and cartilage. There are, for example, applications in ear surgery. The use of the CO2-laser in endonasal surgery is summarized by the following characteristics: radiation in the mid infrared, power about 10 W, strong absorption of energy in a 0.02 mm-surface layer, no scattering in tissue, effective evaporation of tissue, usually thin coagulation zones around evaporated tissue, and quick motion of the laser beam for higher laser powers. The main application of the CO2-laser in endonasal surgery is the treatment of the lower turbinates (6, 43, 7, 27, 64, 46, 50, 10, 66, 72, 49, 7, 25, 76, 56, 67). A comparison of the CO2-laser with other lasers for the application was studied in Ref. (44, 3). Other important application are uvopalatoplasty (11, 74) and choanal atrasia (60). Some surgical techniques on the turbinates using the CO2-laser are different from techniques using other lasers. Some surgeons evaporate the whole tissue surface (10).
Dye-laser The dye-laser operates mainly in the yellow and red part of the spectrum. Up to now only few applications of the dye-laser were reported in endonasal surgery: photodynamic cancer therapy (51) and treatment of haernorrhagic telangiectasia (5, 17, 15). If progress can be made in photodynamic therapy, this laser type may be introduced more widely in ENT. For other endonasal laser application this laser system is too expensive.
Discussion Endonasal laser surgery presently is performed with at least seven different laser types. Sucessfull results in clinical trials were reported in all of these cases. Thus, it is not possible to conclude which of these
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lasers is best suited to a specific application. From a theoretical point of view the lasers can be combined into three groups. a) Lasers with low depth of penetration in tissue (CO2- and Ho-laser) yield high surface temperatures and they are good for evaporation and cutting of tissue. They can also be used for cutting bone and cartilage. b) Lasers with medium depth of penetration are the Argon-laser and KTP-laser (frequency doubled Nd-laser). The radiation is effectively absorbed by red pigments such as blood. Thus, they seem to be well suited for endonasal surgery. c) Lasers with a large depth of penetration of several mm (Nd- and diode-laser) produce deep coagulation zones and evaporation is less effective. However cutting of tissue is also possible in the contact mode. Further investigation is required to determine if these theoretical considerations have practical consequences. At present, it is not possible to prove if any of these lasers has any advantages over the others. This is due to the fact that the various lasers are applied using different laser power, power densities and techniques for the movement of the beam on the tissue.
j j j j j j j
Verschiedene Laser in der endonasalen Chirurgie: Ar-, KTP-, Farbstoff-, Dioden-, Nd-, Ho- und CO2-Laser
Einleitung: Endonasale Laserchirurgie wird gegenwärtig im Spektralbereich zwischen 500 nm und 10600 nm mit sieben verschiedenen Lasertypen durchgeführt. In dieser Arbeit werden die klinischen Anwendungen zusammengefasst und die Vorteile und Probleme von jedem Lasertyp diskutiert. Material und Methoden: Die Wechselwirkung von Laserstrahlung und Gewebe wird für die verschiedenen Lasersysteme miteinander verglichen. Es wird ein Überblick über die Literatur zur klinischen Anwendung der endonasalen Laserchirurgie gegeben. Ergebnisse und Diskussion: Absorption und Streuung von Laserstrahlung im Gewebe hängen von der Wellenlänge ab. Dieses hat einen beträchtlichen Einfluss auf die Verteilung der Strahlung und Temperatur während der Laserchirurgie. Die Koagulations- und Verdampfungszonen sind für die verschiedenen Lasersystem unterschiedlich. Die Literatur zeigt, dass alle Lasersysteme gute klinische Ergebnisse liefern. Dies liegt vermutlich daran, dass die Ärzte die Leistungsdichte und die Strahlbewegung über dem Gewebe jeweils geeignet anpassen.
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Schlüsselwörter Endonasale Chirurgie, Nasenmuscheln, Laser Koagulation, Laser Verdampfung, Argonlaser, KTP-Laser, Farbstofflaser, Diodenlaser, Nd-Laser, Ho-Laser, CO2-Laser
Anmerkung der Herausgeber In dieser Arbeit ist unter der Bezeichnung Nd-Laser das üblicherweise mit Nd:YAG-Laser bezeichnete Lasersystem zu verstehen.
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Correspondence address: Prof. Dr. Jürgen Eichler, Technische Fachhochschule Berlin/University of Applied Sciences, FB II, Seestraße 64, D-13347 Berlin, Germany Tel.: ++49-30-45 043 917; Fax: ++49-30-45 043 959; e-mail: [email protected]