Учебники / Lasers in Otorhinolaryngology Huttenbrink

of two sessions under general endotracheal anesthesia during a two-day hospital stay. Cutaneous FPDL therapy requires an average of five sessions and can be performed on an ambulatory basis.

Alternative laser systems for the treatment of vascular lesions include the copper-vapor laser for superficial lesions and the diode laser for deep, extensive tumors [11, 15, 41, 42]. Various authors have described the possible use of argon and KTP laser systems, but their indications are usually limited to small, circumscribed, superficial vascular lesions. The low penetration depth (1–3.6 mm) and relatively high risk of scarring limit the therapeutic results that can be achieved with these systems [10, 32, 43–45].

The CO2 laser is used almost exclusively for the ablation of subglottic, symptomatic vascular lesions [10, 46]. One drawback of this system is the risk of circumferential subglottic scarring, prompting some authors to recommend the systemic administration of interferon alpha or corticosteroids as an alternative therapy [10, 46]. Excision or vaporization of (sub)cutaneous vascular lesions with the CO2 laser has not been described as advantageous over conventional surgical methods [15, 27, 32]. This laser has a limited penetration depth, depending on the applied energy density (0.3–6 mm), and can cause thermal skin injuries [32].

should not be a problem if the treatment is carefully administered. The pulsed dye laser is an excellent tool for progressive, disseminated telangiectasias and for vascular dilatations in connective tissue diseases. In most cases this laser is not tolerated in the facial region, however, where post-therapeutic purpuric macules can develop (see Dye Laser). The long-pulse frequency-doubled Nd:YAG laser is a very good alternative. Swelling may persist for up to 3 days after treatment. Excessive light exposure should be avoided before and after each treatment session.

T Benign Tumors and Epidermal or

Organoid Nevi

Neurofibromas

The CO2 laser can be used in the CW mode for the excision or vaporization of multiple neurofibromas. Recurrence can be prevented by opening the epidermis, expressing the neurofibroma in a “buttonhole” fashion, and completely removing it or vaporizing its deepest portion. The lesion will heal with scarring, depending on the size of the defect. The erbium:YAG laser can also be used for facial lesions.

Lymphangiomas

Lymphangiomas are classified as a vascular malformation. They frequently coexist with hemangiomas and are treatable with the CO2 laser [27, 32]. The laser can be used to vaporize lymphangiomas and their mixed forms and can also seal their lymphatic channels. Nd:YAG and argon lasers are also available for the treatment of lymphangiomas [27, 47, 48]. As a rule, however, lymphangiomas are considerably less responsive to laser therapy than hemangiomas.

Lip Angiomas

Lip angiomas can be treated with semiselective coagulating lasers or with the long-pulse frequency-doubled Nd:YAG laser. Nodules larger than 5 mm require multiple treatments. Swelling and crusting may occur. Scarring is rare.

Rhinophyma

Large exophytic nodules are removed with the CO2 laser applied in the CW mode using a focused beam. The general shape of the nose in rhinophyma can be sculpted with a defocused beam, and a pulsed beam can be used in peripheral areas. The laser treatment of rhinophyma is more time-consuming than dermaplaning with a scalpel.

Xanthelasmas, Syringomas, Seborrheic

Keratosis

These lesions can be removed with ablating lasers (pulsed CO2 laser and erbium:YAG laser) or with an argon laser in one or more sittings. The pulsed dye laser can be used on shallow xanthelasmas. Transient or occasionally permanent hypopigmentation can occur, especially when the area around the eyes is pigmented.

Osler Disease

The argon, diode or CW Nd:YAG laser can be used to treat angiomatous nodules on the mucosa, depending on the size of the lesions. Cutaneous angiomas can be treated with the argon laser, pulsed dye laser, or long-pulse frequencydoubled Nd:YAG laser. The lesions may be incompletely removed despite repeated treatments, and recurrences are possible.

Cysts

Cysts in steatocystoma multiplex, mucous cysts, and mucoid dorsal cysts can be opened at their center with a focused CO2 laser beam, the cyst contents expressed, and the cyst wall ablated with a defocused beam. The erbium:YAG laser can also be used.

All lasers with a semiselective action can be used in the treatment of primary and secondary telangiectasias. Scars

Verrucous epidermal nevi are the most common type. Besides cosmetic problems, these lesions cause itching as well as fetor and infections involving the body folds. Soft

Benign Lentigines

Lentigines can occur on the skin and mucous membranes or as solar lentigines. Their superficial location makes them easily accessible to laser therapy. Q-switched devices as well as ablative and semiselective coagulating lasers can be used.

Café-Au-Lait Spots

Lasers are less successful in the removal of café-au-lait spots. Ablative lasers are not recommended due to the po-

Decorative Tattoos

Decorative tattoos done by amateurs are usually applied with needles using India ink, ordinary ink, or soot. Professional tattoos are applied with tattooing machines, which use high-density pigments. Metal salt-based pigments were once commonly used. Modern tattooists use industry manufactured organic pigments, and iron-containing pigments are used for cosmetic tattooing. Professional tattoos are more difficult and time-consuming to remove than amateur tattoos. A Q-switched ruby laser, alexandrite laser, Nd:YAG laser, or pigment dye laser may be effective, depending on the color of the tattoo (see under Laser Types).

Fig. 7.7 a Traumatic tattooing of the nose and upper lip. b Appearance after four treatments with the Q-switched ruby laser.

A test patch should be tried for cosmetic tattoos, since irreversible color changes may occur.

Traumatic Tattoos

Dirt, paint, or other particle driven into the skin by a traumatizing force can be removed with a Q-switched laser with varying degrees of efficacy, depending on the location of the pigment (Fig. 7.7 a, b). A test patch should be treated first, especially on skin that has been tattooed by a pyrotechnic injury.

Dyschromias

Pigmented areas caused by an amalgam, amiodarone, iron, or minocycline can be lightened with the Q-switched ruby laser or Nd:YAG laser.

T Premalignant Lesions, Semimalignant

and Malignant Tumors

Laser therapy for malignant tumors is not an established part of dermatologic treatment. Operative surgery is always the treatment of first choice. “Blind” methods that do

not allow for precise histologic control of margins should be used only in exceptional situations. These include palliative indications, inoperability, and multiple tumors.

Premalignant Lesions

Actinic Cheilitis

Actinic cheilitis is an obligate premalignant lesion encountered in older individuals. Early lesions can be removed with the CO2 laser (CW, pulsed) or erbium:YAG laser following histologic confirmation [51]. It takes 2–3 weeks for the treated area to reepithelialize. The reported recurrence rate is 2 %. More pronounced lesions should be referred for operative treatment.

Actinic Keratosis

This premalignant lesion is caused by the proliferation of atypical keratinocytes. Malignant transformation to squamous cell carcinoma occurs in 10–20 % of cases after a course of years or decades. A number of conservative and operative treatment options are available. The keratotic lesions can be removed with the erbium:YAG laser or pulsed CO2 laser. As with other treatment methods, recurrence is possible and regular follow-ups should be scheduled.

Lentigo Maligna

See the following section.

Basal Cell Carcinoma, Spindle Cell Carcinoma,

Malignant Melanoma

Reports on the laser treatment of these entities have been published [2]. However, we do not feel that laser therapy is justified. Laser use may be considered in selected cases strictly for the palliative treatment of multiple cutaneous metastases from melanoma.

T Esthetic Uses of Lasers

Photoepilation

Long-term epilation is usually desired for cosmetic and cultural reasons. Medical causes of hypertrichosis include polycystic ovaries, adrenocortical hyperplasia, and side effects of drug (e. g., minoxidil, cyclosporin A). Long-term epilation is also desirable in transsexual patients, hairbearing skin grafts, and for ingrowing hairs. A number of light and laser systems are currently available for photoepilation, including the long-pulse alexandrite laser, ruby laser, Nd:YAG laser, diode laser, and high-energy flashlamps (Ellipse, EpiLight, Photoderm) [2].

The efficacy of treatment depends on physical factors (wavelength, pulse duration, energy density) and biologi-

cal factors (hair growth cycle, hair color, target structure). Wavelengths in the range of 700–1000 nm are ideal. Light at this wavelength has a high penetration depth and is preferentially absorbed by melanin (eumelanin). The pulse duration is geared toward the size of the hair follicle, which releases the absorbed energy to its surroundings less efficiently than the small epidermal cells and therefore is preferentially damaged. Because of the high energy density, continuous skin cooling is necessary to protect the epidermis. Energy density appears to be important for good longterm response.

The depth of the follicle varies with the body region and the phase of the hair cycle. Only the actively growing and pigmented hair follicle in the early anagen phase is responsive to laser therapy. Response consists of miniaturization of the follicles, with a corresponding decrease of hair density and pigmentation.

The advantage of laser therapy is that it can be applied easily over a large area. Dark, thick hairs are easy to remove, unlike light, thin hairs. The incidence of side effects is considerably lower in light-skinned patients [52]. Three to eight sessions scheduled at approximately 4–6-week intervals are usually necessary to achieve significant hair reduction (Fig. 7.8 a, b). This is followed by two or three maintenance treatments per year. Currently, permanent, complete epilation cannot be achieved.

Photoepilation is not a painless procedure. Effective surface cooling should be provided to reduce pain. EMLA cream can be applied for topical anesthesia. To avoid pigmentary changes, the skin should not be tanned. Excessive light exposure should be avoided for up to 8 weeks after treatment (see Ruby Laser).

Fig. 7.8 a Hypertrichosis of the upper lip. b Appearance after four treatments with the long-pulse ruby laser.

Ablative Skin Resurfacing

The pulsed CO2 and erbium:YAG lasers are established tools for this indication. Usually they are used with special scanner applicators for large-area skin resurfacing in older patients with elastotic or actinic skin damage and wrinkles and for the smoothing of acne scars [53]. The laser beam vaporizes the aged, sun-damaged epidermal layer while tightening the underlying corium. The thermal damage to the corium is desired to induce superficial fibrosis. Besides an immediately visible shrinkage effect on collagen fibers, new collagen formation occurs at the histologic level [54]. The result is a cosmetically desirable skin-smoothing effect. The less damaging erbium:YAG laser is used to treat problem areas like the periorbital, perioral, and cervical regions and the dorsum of the hand.

Patient selection is essential for a good response. Laser therapy is appropriate for superficial actinic facial wrinkles, radial lip lines, infraorbital wrinkles, crow’s feet, and sleep lines. Caution is advised in patients with a dark skin type (Fitzpatrick type III or IV) or suntanned skin due to the risk of hyperand hypopigmentation. Ablative skin resurfacing is contraindicated in patients who have received systemic isotretinoin therapy during the past 6 months and in patients who have plastic or Gortex implants. The

complication rate is increased in patients who have had prior facial cosmetic surgery (facelift, blepharoplasty, chemical peel) and in cases prone to postinflammatory hyperpigmentation and keloid formation.

Concomitant reactions, side effects: Treatment is followed by significant exudation, swelling, crusting, and an unpleasant burning sensation.

The most common side effect is prolonged erythema lasting up to 8 months or longer. Other side effects are itching for up to 3 weeks; infections, especially with herpes virus (7.4 %); irritative dermatitis (5–10 %); postinflammatory hyperpigmentation (CO2 laser: 2.8–83 %, erbium:YAG laser: 3.4–24 %); hypopigmentation (CO2 laser: 1–19.2 %, erbium:YAG laser: 4 %); irreversible loss of melanocytes (5– 16 %); and scarring (>1–3.8 %) [1, 2, 53].

Acne Scars

Deep acne scars can be corrected with the CO2 laser, shallow scars with the erbium:YAG laser. Acne scars generally require two or three treatments spaced 6 months apart. The smoothing effect will increase somewhat over the next 12 months.

Nonablative Skin Resurfacing

Skin rejuvenation by tightening the skin without damaging the epidermis (“subsurfacing”) has been a subject of intense research for several years [55]. Various flashlamp and laser systems have been used such as the pulsed dye laser (585 nm), Q-switched Nd:YAG laser (1064/532 nm), longpulse Nd:YAG laser (1320 nm), diode laser (1450 nm), erbuim:glass laser (1540 nm), and high-energy flashlamp (IPL technology, 500–1200 nm).

Histologic studies have demonstrated new collagen formation and fibroblast proliferation. To date, however, reported results of nonablative skin resurfacing have not been encouraging enough to justify the use of this cost-intensive procedure. Ablative skin resurfacing is still considered the gold standard for the treatment of age-related skin changes.

T Photodynamic Therapy

Photodynamic therapy (PDT) is used in dermatology to induce immune-modulating effects in inflammatory and malignant skin lesions. It is still classified as an experimental therapy.

Systemic PDT is used to treat large or multiple basal cell carcinomas or early spindle-cell carcinomas in cases where the tumors are deemed to be inoperable. The photosensitizing agent (Photofrin, 2 mg/kg bodyweight i.v.) is administered 24–48 hours before the lesion is exposed to red light. The same regimen is used for Kaposi sarcomas of the skin. Good results can be achieved with indocyanine green followed by irradiation with the diode laser (805 nm) [56].

Topical PDT with 5-aminolevulinic acid (ALA) and exposure to a noncoherent light source is suitable for superficial lesions such as actinic keratosis, Bowen disease, and superficial basal cell carcinoma. The demonstration of immunemodulating effects is opening up new applications for topical PDT such as the treatment of warts, alopecia, and other dermatoses. Studies are currently under way on the efficacy of systemic PDT in the treatment of psoriasis. We should know in the next few years whether systemic PDT will become an effective alternative to PUVA therapy.

T References

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3Gambilchler T, Avermaete A, Wilmert M, Altmeyer P, Hoffmann K. Generalized essential teleangiectasia successfully treated with high-energy, long-pulse, frequency-doubled Nd:YAG laser. Dermatol Surg 2001; 27: 355–357

4Alster Ts, Bryan H, Williams CM. Long-pulsed Nd:YAG laser-as- sisted hair removal in pigmented skin: a clinical and histological evaluation. Arch Dermatol 2001; 137: 885–889

5Wimmershoff MB, Wenig M, Hohenleutner U, Landthaler M. Die Behandlung von Feuermalen mit dem blitzlampengepumpten gepulsten Farbstofflaser. Hautarzt 2001; 52: 1011–1015

6Michel S, Landthaler M, Hohenleutner U. Recurrence of portwine stains after treatment with the flashlamp-pumped dye laser. Br J Dermatol 2000; 143: 1230–1234

7Strempel H, Klein G. Behandlung von therapieresistenten Feuermalen mit einem Langpuls-Farbstofflaser. Z Hautkr 2000;

75: 129–131

8Böhm M, Berlien H-P, Müller G, Philip C, Scholz C, Waldschmidt J. Technik und Klinik der Therapie oberflächlicher und tiefer Hämangiome mit verschiedenen Lasersystemen im Kindesalter. Lasermedizin 1990; 5: 45–51

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10Drolet BA, Esterly NB, Frieden IJ. Hemangiomas in children. NEJMAG 1999; 341: 173–181

11Werner Ja, Lippert BM, Gottschlich S, Folz BJ, Fleiner B, Hoeft S, Rudert H. Ultrasound-guided interstitial Nd:YAG laser treatment of voluminous hemangiomas and vascular malformations in 92 patients. Laryngoscope 1998; 108: 463–470

12Cremer HJ. Gefäßanomalien im Bereich der Haut. Monatsschr Kinderheilkd 1998; 146: 622–638

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By virtue of its physical nature, laser light application in otolaryngology has gone far beyond the “laser scalpel.” The laser is also an optical measuring instrument that has become an indispensable tool in modern middle ear and inner ear research. The laser beam is unique in its ability to measure vibrational displacements as small as a few nanometers in the middle ear and cochlea without touching the object being measured.

This chapter reviews the principal laser measurement technologies that have been used in modern otologic research. It includes detailed applications and new experimental results of laser interferometry in the middle and inner ear. Taking the middle ear as an example, it shows how laser measurements can provide an image of the vibrational pattern of the healthy tympanic membrane–os- sicular chain complex in various frequency ranges. Experiments in temporal bone specimens demonstrate how lasers are used to perfect the design of middle ear implants. Initial clinical studies describe the use of laser interferometry for measuring the vibrational properties of the ossicular chain in patients. One day this method will be a useful adjunct to audiologic testing and supply additional information on the function of the middle ear behind an intact tympanic membrane. Laser interferometry can be used in inner ear research to analyze basilar membrane vibrations and study the micromechanics of the organ of Corti. As an example, it is shown how this method can measure vibrations of the basilar membrane down to the cellular level. The results can advance the design of existing cochlear models and improve our understanding of the cochlear amplifier.

T Introduction

The otolaryngologist is familiar with the laser as a precision surgical instrument that divides tissue structures without contact. But lasers can do more than cut. The physical properties of laser light offer additional advantages. This chapter deals with the capabilities of the laser as a noncontact measuring instrument. It reviews common applications that have helped improve our understanding of middle and inner ear functions in recent years. Particular attention is given to middle ear mechanics, for which the author presents original experimental results. Laser scanning microscopy, a method with new capabilities for tissue structural analysis, comes under microscopy and is beyond the scope of the present chapter.

For a better understanding of laser measurement technology, the chapter begins with a review of the physical properties of laser light that form the basis for its use as an optimal measuring instrument.

h… Planck action quantum (natural constant) f… Frequency

Fig. 8.1 Production of laser light by stimulated emission. The stimulated atoms have identical structures and constitute the laser medium (e.g., CO2 gas) (after Spengler, 2002 [2]).

ser light are derived from the nature of light. Light has properties of both a wave and a particle (wave–particle duality). While the wave theory describes all phenomena related to the propagation of light, the quantum theory explains the energy transformation occurring in the production and extinction of light at the atomic level [1]. Atoms have the unique ability to absorb, store, and release energy in discrete quantities. When an atom absorbs energy, an electron is raised to an orbit that is more distant from the nucleus (quantum leap). When the atom releases energy, the electron returns to a lower level while a discrete amount of energy is released. Energy is absorbed and released in the form of quanta (photons), and this process can occur spontaneously.

Energy release can also be induced by an extrinsic force (stimulated emission). This principle is applied in the production of laser light. A photon generated by spontaneous emission encounters other atoms, where it triggers the emission of more photons. This is the basic process by which electromagnetic radiation is produced. In contrast to the visible light from an incandescent bulb, the propagation of this radiation is controlled by a resonator in such a way that the light rays travel in a single direction (Fig. 8.1, resonator not shown).

A special feature of lasers is that all emitted laser light has the same frequency and wavelength (monochromatism). While ordinary light propagates in all spatial directions, the laser light rays are “bundled” into an approximately parallel path (collimation). And finally, all the wave trains in laser light have a definite phase relationship to one an-

Coherence, monochromatism, collimation

Laser light is produced by the artificial amplification of light by stimulated emission. The physical properties of la-

Fig. 8.2 Techniques of laser measurement and analysis in otologic research based on the physical properties of laser light.

Since the early days of middle and inner ear research, efforts have been made to measure vibrational processes and document them in the form of images. Optical methods are ideal for detecting these vibrational amplitudes, which measure only a few nanometers, because generally they are noncontact techniques, i. e., they work without placing any mechanical stresses on the structures being examined.

Laser Interferometry

The principle of laser interferometry is based on the Doppler effect. When coherent laser light strikes a moving object (e. g., a vibrating tympanic membrane) and is reflected back, the frequency of the reflected beam is shifted relative to the frequency of the incident beam (the Doppler shift, Fig. 8.3). This frequency shift (fd) is proportional to the velocity v of the moving object, as defined by the equation:

fd = 2v/λ

where λ is the wavelength of the laser light and v is the velocity of the moving object.

Thus the frequency shift is a measurable quantity corresponding to the vibrational speed (velocity) of the object, and the amplitude of the vibration can be calculated from the integral of the velocity. Due to the high frequency of laser light (4.7 × 1014 Hz), it is not possible to measure the frequency shift directly. Instead, the reflected beam is combined with a superimposed reference beam. A photodetector then measures the differences that occur in the laser light intensity when the object and reference beams are combined (interference).

These conditions are difficult to fulfill in measurements of biological structures. The pulse and respiration transmit synchronous movements to the ear which are several orders of magnitude greater than the vibrational amplitudes to be measured. Generally the reflectivity (e. g., of the tympanic membrane) is extremely poor when compared with smooth artificial surfaces. Most of the laser light passes through the tympanic membrane and is not reflected [3]. Additional losses result from diffuse reflection due to surface roughness. An obliquely incident laser beam further reduces the intensity of the light returning to the detector (Fig. 8.4).

One way to minimize reflection problems is by using reflectors. In the earliest laser measurements in otology, small reflective targets were glued to the tympanic membrane to increase its reflectivity (Fig. 8.5) [4]. In experiments on temporal bone specimens, this resulted in relatively high sensitivity for displacements up to 100 pm, so that vibrations could be measured using acoustic stimuli of only 60 dB SPL (sound pressure level) at low frequencies. In live animals, the sensitivity was considerably lower (1 nm corresponding to 80 dB SPL) despite the use of reflectors due to greater mechanical artifacts, caused mainly by respiration. To reduce these artifacts, the animal’s head had to be immobilized with cortical bone screws. The high laboratory costs of this procedure, plus the susceptibility of the Michelson interferometer to mechanical artifacts, limited the use of the instrument to a few experimental animals.

Reference beam

Prism

Moving object (velocity v)

Object beam

Fig. 8.3 Principle of an interferometer (Michelson type). The laser light reflected from a moving object is combined with a reference beam.

Fig. 8.4 The sensitivity of the laser interferometer also depends on the reflectivity (f) of the object under study. With an object like the tympanic membrane, which reflects diffusely and has high through-trans- mission (T), the sensitivity is poor and varies with the angle of the laser beam.