Laser Treatment of Vascular Lesions
137 pages
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137 pages
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Description

Today, nearly 60 years after the invention of the first medical laser, multiple laser and light systems exist and are applied in various medical specialties such as dermatology, ophthalmology, and urology. This volume - the first in the series Aesthetic Dermatology - focuses on the laser treatment of cutaneous lesions with a vascular target. Each chapter describes a particular laser or light modality and its specific application to a variety of both vascular and nonvascular lesions. Renowned specialists in laser medicine have contributed their expertise, incorporating current evidence-based literature and their own personal treatment recommendations, as well as pearls and perils. The purpose of this book is to explore the options and parameters available to treat cutaneous lesions traditionally responsive to vascular laser therapy and to expand the application to further lesion treatments. Readers who wish to broaden their knowledge and further hone their skills in treating cutaneous vascular lesions with lasers will find this publication a valuable and comprehensive review.

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Date de parution 18 février 2014
Nombre de lectures 0
EAN13 9783318023138
Langue English
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Laser Treatment of Vascular Lesions
Aesthetic Dermatology
Vol. 1
Series Editor
David J. Goldberg New York, N.Y.
Laser Treatment of Vascular Lesions
Volume Editors
Susan Bard New York, N.Y.
David J. Goldberg New York, N.Y.
44 figures in color and 8 tables, 2014
_______________________ Dr. Susan Bard Skin Laser and Surgery Specialists of New York and New Jersey, Hackensack, N.J., Director of Laser and Aesthetic Medicine, Vanguard Dermatology, New York, N.Y. Clinical Instructor of Dermatology, Mount Sinai School of Medicine New York, N.Y.
_______________________ Dr. David J. Goldberg Director, Skin Laser and Surgery Specialists of New York and New Jersey, Hackensack, N.J. Chief of Dermatology, Hackensack University Medical Center, Hackensack, N.J. Clinical Professor of Dermatology, Director, Laser Research, Mount Sinai School of Medicine, New York, N.Y. Clinical Professor of Dermatology, Chief, Dermatologic Surgery, UMDNJ - New Jersey Medical School, Newark, N.J. Adjunct Professor of Law, Fordham Law School New York, N.Y.

This book was generously supported by
Library of Congress Cataloging-in-Publication Data
Laser treatment of vascular lesions / volume editors, Susan Bard, David J. Goldberg.
p. ; cm. –– (Aesthetic dermatology ; vol. 1)
Includes bibliographical references and indexes.
ISBN 978-3-318-02312-1 (hard cover: alk. paper) –– ISBN 978-3-318-02313-8 (electronic version)
I. Bard, Susan (Skin laser and surgery specialist), editor of compilation. II. Goldberg, David J. (Dermatologist), editor of compilation. III. Series: Aesthetic dermatology (Series) ; v. 1.
[DNLM: 1. Laser Therapy––methods. 2. Skin Diseases, Vascular––therapy. 3. Cosmetic Techniques. 4. Lasers. WO 511]
RL120.L37
617.4’770598––dc23
2013044287
Bibliographic Indices. This publication is listed in bibliographic services, including Current Contents ® .
Disclaimer. The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publisher and the editor(s). The appearance of advertisements in the book is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
Drug Dosage. The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any change in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
© Copyright 2014 by S. Karger AG, P.O. Box, CH-4009 Basel (Switzerland)
www.karger.com
Printed in Germany on acid-free and non-aging paper (ISO 9706) by Kraft Druck GmbH, Ettlingen
ISSN 2235-8609
e-ISSN 2235-8595
ISBN 978-3-318-02312-1
e-ISBN 978-3-318-02313-8
Contents
Foreword
Goldberg, D.J. (New York, N.Y.)
Preface
Bard, S. (New York, N.Y.)
Laser History, Physics, and Safety
Bard, S. (New York, N.Y.)
Argon, Krypton, and Copper Lasers
Styperek, A.R. (Miami, Fla.)
Pulsed Dye Laser
Waibel, J.S. (Miami, Fla.)
Potassium-Titanyl-Phosphate (KTP) Laser
Green, J.B. (Miami, Fla./Coral Gables, Fla.); Serowka, K. (Irvine, Calif.); Saedi, N. (Philadelphia, Pa.); Kaufman, J. (Miami, Fla./Coral Gables, Fla.)
Alexandrite and Diode Lasers
Nouri, K.; Savas, J.A.; Ledon, J.; Franca, K.; Chacon, A.; Nouri, K. (Miami, Fla.)
Nd:YAG Laser
Kaufman, J. (Miami, Fla./Coral Gables, Fla.)
Intense Pulsed Light
Chen, A.F.; Weiss, E. (Hollywood, Fla.)
Complications of Vascular Laser Treatment
Grunebaum, L.D.; Bartlett, K. (Miami, Fla.)
Author Index
Subject Index
Foreword
Aesthetic dermatology has been transformed over the past two decades. What was initially an arena that had collagen injections, aggressive peels, and argon and carbon dioxide lasers has now evolved into a field that contains a large variety of energy-based devices, injectables, and a wide variety of nonenergy-based topical treatments.
Energy-based devices now include lasers, broadband light sources, radiofrequency technologies, and ultrasound and microwave devices. These devices are now being used on and off the face. They are used to tighten, resurface, and remodel skin. Available devices treat unwanted vascular lesions, abnormal pigmentation, acne, and hyperhidrosis. While early devices took up an entire room, the newer machines are smaller than a suitcase. Some of the devices are now being paired with topical agents to optimize results, and there will be more with time.
Injectables include botulinum toxins, a wide array of dermal fillers, and the soon to arrive fat-melting injections. Indications for treatment have also expanded with time. Each year, there are newer agents.
In the past, there have been entire textbooks on the subject of lasers and energy-based devices, and entire books on aesthetic and cosmetic dermatology. Many of these have been well written - some even by me! The reality, though, is that the field has now become so vast that no one book can give the reader the full breadth of aesthetic medicine. Furthermore, since the field is constantly changing, there is a need for an ongoing updated series of books that covers the ever-changing field of aesthetic dermatology.
Aesthetic Dermatology will answer those needs. Aesthetic Dermatology does not represent one textbook or even a small series of textbooks. Instead, Aesthetic Dermatology will represent an ongoing, multiyear series of textbooks that will cover, and expand, all aspects of aesthetic dermatology.
One to two textbooks, on a variety of topics, will be published each and every year. The first volume is Laser Treatment of Vascular Lesions , the second will be Cosmetic Radiofrequency , and the third will be Photodynamic Therapy . Many more will follow. Enjoy!
David J. Goldberg , New York, N.Y.
Preface
Medical uses of light can be traced back as early as 4000 BC to the ancient Egyptians who utilized psoralen-containing plants in conjunction with sunlight to treat vitiligo. Nearly 60 years after the invention of the first medical laser in the mid-20th century, the field of laser and light medicine has grown vastly and is utilized by a multitude of medical specialties such as dermatology, ophthalmology, and urology. Today, we are fortunate enough to have multiple laser and light systems that target various tissue structures with an array of medical and cosmetic indications.
This book, the first in the Aesthetic Medicine series, will focus on the laser treatment of cutaneous lesions with a vascular target. Each chapter focuses on a particular laser or light modality and its specific application to a variety of both vascular and nonvascular lesions. Renowned specialists in laser medicine have lent their expertise throughout the book. Each section incorporates the current evidence-based literature along with the authors’ personal treatment recommendations, as well as pearls and perils.
As each author in the book has skillfully demonstrated, laser medicine is as much an art as it is a science - there is no cookbook approach. The purpose of this book is to explore the options and parameters available to treat lesions traditionally responsive to vascular laser therapy as well as to expand the application of these lasers to a growing list of nontraditional lesions. Our goal is to allow readers to broaden their knowledge and further hone their skills in the laser treatment of cutaneous vascular lesions.
Susan Bard , New York, N.Y.
Bard S, Goldberg DJ (eds): Laser Treatment of Vascular Lesions. Aesthet Dermatol. Basel, Karger, 2014, vol 1, pp 1-17 (DOI: 10.1159/000355038)
______________________
Laser History, Physics, and Safety
Susan Bard a - c
a Skin Laser and Surgery Specialists of New York and New Jersey, Hackensack, N.J., and b Laser and Aesthetic Medicine, Vanguard Dermatology, and c Mount Sinai School of Medicine, New York, N.Y., USA
______________________
Abstract
Electromagnetic radiation from various sources is used to treat a variety of medical conditions in a multitude of specialties, including dermatology, ophthalmology, urology, otolaryngology, as well as others. Medical uses of light can be traced back thousands of years, and the use of light to treat a variety of skin disorders has continued throughout history. It was Albert Einstein who developed the concepts which ultimately laid the foundation for the development of the laser. Understanding fundamental atomic structure is essential in understanding how laser light is created and its unique characteristics. Over the past few decades, lasers have revolutionized how we treat a variety of skin and other medical conditions. In addition to their great benefit, however, these powerful devices have the potential to pose significant hazard to the patient and operator, making safety a crucial aspect of proper laser operation.
© 2014 S. Karger AG, Basel
Brief Laser History
It was Albert Einstein who developed the concept of light travelling in waves of particles known as photons and of ‘stimulated emission’ [ 1 ], ultimately laying the foundation for the development of the LASER (acronym for light amplification by stimulated emission of radiation, coined by Gordon Gould).
The precursor to the laser was the MASER (microwave amplification by stimulated emission of radiation). The first maser was created by Charles Townes in 1954 [ 2 ] and further improved upon by James Gordon and Herbert Zeiger. The initial maser, however, was incapable of continuous output until Nikolai Basov and Alexander Prokhorov in Moscow created a new system that could release stimulated emission of excited atoms without falling to the ground state, thus maintaining continuous output. In 1964, Basov, Prokhorov, and Townes shared the Nobel Prize in physics for their fundamental work in the development of maser principles. Shortly after the development of the maser, scientists explored the possibility of stimulated emission in other regions of the electromagnetic spectrum, such as the optical and infrared regions. In 1958, Arthur Schawlow and Charles Townes proposed the first optical maser which was later renamed ‘laser’ [ 3 ].
In 1960, Maiman [ 4 ] created the first functional ruby laser excited by a xenon flash lamp. This laser, however, was only capable of pulsed operation, until shortly thereafter Peter Sorokin and Mirek Stevenson developed the first laser capable of continuous output. This uninterrupted beam was very effective in destroying the desired target tissue, but also exposed the surrounding tissue to prolonged periods of laser energy, resulting in excessive collateral damage leading to hypertrophic scarring and pigmentary changes. Mechanical shutters were then introduced to interrupt the laser beam, creating quasi-continuous lasers attempting to minimize adverse effects. In 1961, the technique of quality switching or ‘Q-switching’ was introduced by Fred McClung and Robert Hellwarth [ 5 , 6 ] . This technique allowed for shortening of the pulse width to nanoseconds using an electro-optical shutter. The development of other lasers such as the argon, CO 2 , Nd:YAG, pulsed dye, diode, and excimer lasers rapidly followed. In 1983, Rox Anderson and John Parrish [ 7 ] proposed the theory of selective thermolysis, revolutionizing cutaneous laser surgery. With careful manipulation of wavelength and pulse duration in relation to target relaxation time, lasers could now selectively target and destroy specific structures without damaging the surrounding tissues. This is crucial in the targeted laser treatment of vascular lesions.
Medical uses of light can be traced back to as early as 4000 BC when the ancient Egyptians recorded using sunlight coupled with a topical photosensitizer, such as parsley or other psoralen-containing plants, to aid in the repigmentation of vitiligo. The use of light to treat a variety of skin disorders has continued throughout history. In 19th century Europe, sunlight was used as a treatment for cutaneous tuberculosis, and UV light has been used from the early 1900s until the present day, with and without tar, as an effective treatment for psoriasis. Not surprisingly, dermatologists and ophthalmologists were the first to entertain the therapeutic possibilities of masers and lasers. Shortly after Maiman’s creation of the first ruby laser, ophthalmologists began experimenting with the laser for photocoagulation of various retinal lesions [ 8 ]. In 1961, Leon Goldman, Chairman of the Department of Dermatology at the University of Cincinnati, founded the first biomedical laser laboratory. There he studied and described the selective destruction of pigmented structures in the skin, such as hair follicles, by the ruby laser [ 9 ] . He also published on the potential treatment of nevi, melanomas, and tattoos utilizing the ruby laser, as well as the treatment of vascular lesions using the argon and Nd:YAG lasers [ 10 ] . Given his vast contributions to the field of laser medicine, Goldman is honored by the American Society for Laser Medicine and Surgery as the ‘father of lasers in medicine in the United States’ [ 11 ].

Fig. 1. The electromagnetic spectrum.
Basic Laser Physics
Properties of Light
All forms of energy are represented in the electromagnetic spectrum, which ranges from the short wavelengths of X-rays and gamma-rays to the long wavelengths of microwaves and radiowaves ( fig. 1 ). Light is electromagnetic radiation composed of waves and energy packets known as photons and is in the visible wavelength region from 400 to 700 nm of the electromagnetic spectrum. Wavelength is determined by the distance between two successive troughs or crests of these waves. For the visible portion of the electromagnetic spectrum, the wavelength determines the color of the laser light. Frequency is determined by the number of wave crests or troughs that pass a given point in 1 s. The wavelength and frequency of light are inversely related to one another, obeying the equation c = λ · v in which c = 299,792,485 ms -1 , representing the speed of light in a vacuum. Therefore, shorter wavelengths of light have higher frequencies and more energetic photons than longer wavelengths of light, which have lower frequencies and less energetic photons.
For many years electromagnetic radiation from various sources has been used to treat a variety of medical conditions in a multitude of specialties, including dermatology, ophthalmology, urology, otolaryngology, as well as others. Currently, most lasers with medical applications generate light in the visible, infrared, or ultraviolet spectrum. Laser light within the visible spectrum creates a colored beam depending on the wavelength emitted. For example, the 532-nm KTP laser will produce a green beam while the 694-nm ruby laser will produce a red beam. Lasers that produce light outside of the visible spectrum (mid-infrared, infrared, or ultraviolet), such as Nd:YAG or CO 2 lasers, will produce an invisible beam.
Unlike lasers, intense pulsed light devices are high-intensity broad-band light devices producing light consisting of many wavelengths, ranging from 500 to 1,300 nm. Therefore, these devices are usually equipped with cutoff filters in order to limit the emitted wavelengths to a narrower range to more precisely target a desired chromo-phore. Vascular lesions can best be targeted using filters emitting wavelength ranges of 500-670 or 870-1,400 nm corresponding to peaks of absorption on the absorption spectrum for oxyhemoglobin. Given the wide range of wavelengths that can be emitted by these devices, they are very versatile and can be employed in the treatment of a variety of targets such as vascular lesions, pigmented lesions, and hair. It can also increase efficiency by targeting multiple chromophores at once, for example one can simultaneously target both pigmented and vascular lesions associated with photoaging. However, when intentionally targeting just one chromophore, care must be taken that the other competing chromophore does not decrease the efficacy of the treatment of the intended target. Yet another benefit of intense pulsed light is the large spot size, allowing large areas to be treated more quickly. This is especially beneficial when intense pulsed light is used for hair removal.
Spontaneous and Stimulated Emissions
Understanding fundamental atomic structure is essential to understanding how laser light is created. According to Niels Bohr’s atomic model, all atoms are composed of a central nucleus surrounded by electrons that occupy fixed energy levels or orbitals, giving the atom a stable configuration. Electrons can only jump from one orbit to another, and in doing so can emit or absorb energy. When an atom spontaneously absorbs a photon of light, the outer orbital electrons briefly move to a higher energy orbit. This is an unstable configuration and the atom rapidly and spontaneously releases a photon of light in order to return the electrons to their original stable lower energy orbital configuration. As the atom decays, the photon of energy emitted equals the difference in energy between the two orbits. Normally, spontaneous absorption and release of light occurs in a disorganized fashion, in all directions, producing incoherent light, unlike stimulated emissions.
In order for stimulated emissions to occur, a previously excited electron needs to absorb another photon of energy, which leads to emission of both photons upon returning to the ground state. The released photons will contain the exact same energy, frequency, and direction, and can stimulate emission of further photons. The increasing stimulation of photons will lead to a population of atoms in which there is a larger proportion of atoms in the excited versus the resting state. This is referred to as population inversion and is integral for the generation of laser light.
This synchronized photon release occurring with stimulated emission is responsible for the three unique characteristics of laser light, and it is these characteristics that differentiate it from other nonlaser light sources. These three main features are monochromaticity, coherence, and collimation. Monochromaticity refers to the fact that laser light is composed of a single wavelength or color, unlike white light which is composed of a spectrum of wavelengths. This can be best exhibited by shining white light through a prism which produces a spectrum of colors. In contrast, when shining a laser light through a prism, only a single color, corresponding to the wavelength of the laser light, will be produced. Coherence refers to the fact that the light waves generated travel in phase with one another in regard to time and space. Collimation means that the transmission of light occurs in parallel fashion without significant divergence, even over long distances. This produces a narrow beam diameter, which does not change with changes in distance, allowing laser light to maintain its energy even over long distances.

Fig. 2. Chromophore absorption curve.
Chromophores
The skin contains several chromophores, both endogenous and exogenous, that are able to absorb certain wavelengths of light. The three main endogenous chromo-phores in the skin are melanin, oxyhemoglobin, and water, and they are often targeted by a variety of lasers. Other endogenous chromophores are proteins and lipids. Each of these chromophores has an absorption spectrum with peaks at different wavelengths. The decision of which wavelength laser to utilize in the treatment of a particular lesion is based on these curves and peaks. The absorption spectrum form oxyhemoglobin ranges mostly from 400 to 600 nm with peaks at 418, 548, and 577 nm that can be specifically targeted in order to decrease absorption by competing chromophores ( fig. 2 ). In contrast, the absorption curve for melanin is a subtly decreasing line ranging from 400 to 750 nm with no peaks. Water exhibits a gently increasing absorption curve ranging from 900 to 1,400 nm in the infrared portion of the electromagnetic spectrum. Tattoo pigment is the most common exogenous chromophore in the skin, with corresponding wavelengths depending on the color of the tattoo ink.
In choosing the most optimal wavelength at which to treat a lesion, one must take into consideration not only the absorption peaks of the target, but the location of the targeted structure in the skin as well. It is important to keep in mind that shorter wavelengths penetrate the skin more superficially while longer wavelengths have a greater depth of penetration. For example, while the absorption for melanin is greatest at shorter wavelengths, a laser at a shorter wavelength will be unable to penetrate to the dermis to reach its target, and treatment will likely be ineffective at that setting. As mentioned above, the absorption peaks for oxyhemoglobin range mostly between 400 and 600 nm; however, deeper vessels cannot be adequately targeted at these wavelengths, necessitating treatment with wavelengths capable of attaining a greater depth of penetration such as those emitted by the alexandrite, diode, and Nd:YAG lasers.

Fig. 3. Laser and tissue interactions.
Laser Light Interaction with Tissue
Laser light can be absorbed, reflected, scattered, or transmitted upon interaction with the skin ( fig. 3 ). A combination of these interactions typically occurs at any one time, the net effect of which affects laser impact and can vary based on the laser [ 12 ]. According to the Grotthus-Draper law, in order for laser energy to produce any biological effect in the skin, it must be absorbed. Absorption is the transformation of radiant light energy to a different form of energy, typically heat. It is only the light that is absorbed that is able to produce the desired effect in tissue. Light-absorbing targets in tissue are known as chromophores. Three main chromophores exist in skin: melanin, hemoglobin (or oxyhemoglobin), and water. The interaction of laser light with tissue is generally a function of the wavelength of the laser and whether it corresponds to the specific absorption spectrum of the targeted chromophore. Additionally, appropriate laser wavelength selection must also take into account the depth of the target structure in the tissue as longer wavelengths tend to have a greater depth of penetration. At wavelengths below 300 nm, there is strong absorption by protein, melanin, urocanic acid, and DNA. At wavelengths above 1,300 nm, penetration is shallow due to the absorption of light by water, the dominant chromophore at this end of the spectrum [ 13 ].
If the light is reflected from the surface of the skin, transmitted completely through the skin or scattered, no biologic effect will be produced. Most reflection occurs at the level of the stratum corneum, requiring the use of protective eye shields when operating lasers. Drier, scalier skin tends to exhibit a greater degree of reflection. The level of reflection can be minimized to approximately 4-6% by applying a thin layer of clear oil or gel and ensuring that the laser beam is perpendicular with the skin surface [ 14 ].
Once it has penetrated the stratum corneum, it is possible for laser light to scatter in the dermis due to the presence of collagen fibers. This occurs mostly with shorter wavelengths as the level of scatter is inversely proportional to the wavelength of incident light. Less scatter and deeper penetration with decreased energy loss occurs with a wider laser beam diameter [ 15 ] . Finally, any light that has not been reflected, absorbed, or scattered will be transmitted to deeper structures in the skin.
Light Tissue Effects
Laser tissue effects are dependent on the laser’s parameters as well as the properties of the target tissue. Different effects can be achieved with manipulation of the laser’s power, spot size, and pulse duration. Perhaps the most important criterion influencing the effect achieved is exposure time, which ultimately determines the temperature reached in the tissue [ 16 ] . Once absorbed, laser light can have photothermal, photochemical, or photomechanical effects on tissue [ 17 ] . Photothermal effects, the primary mechanisms by which lasers affect the skin, are due to conversion of the absorbed energy into heat. This is a two-step process in which a molecule absorbs a photon and is excited with subsequent deactivation while exciting a neighboring molecule by colliding with it, causing a rise in tissue temperature. Various photothermal effects can occur depending on the temperature reached such as coagulation, vaporization, carbonization, and melting. For example, a mere 5 ° C increase in tissue temperature can cause tissue injury, which can lead to inflammation and subsequent tissue repair. At 60 ° C, tissue coagulation occurs with DNA and protein denaturation. At 100 ° C, ablative effects are achieved due to vaporization of intercellular water.
Photomechanical destruction of the tissue occurs when high laser energies are absorbed at a short pulse duration, causing rapid thermal expansion of the targeted chromophore. This in turn results in breakage of intermolecular bonds, leading to the creation of ions and the generation of plasma. These ions rapidly expand, creating shockwaves, fragmenting the surrounding tissue. This effect is especially important in the treatment of pigmented lesions and tattoos with Q-switched lasers as well as vascular lesions treated with PDL at purpuric settings.
Photochemical effects occur when laser light is absorbed by either endogenous or exogenous light-absorbing chromophores in the tissue, leading to the formation of cytotoxic reactants, such as reactive oxygen species, causing irreversible oxidation of cellular structures. This reaction is the most important laser effect in photodynamic therapy and is also responsible for the photosensitivity encountered with various porphyrias. Long pulse durations with low irradiances are typically utilized to achieve this reaction. Wavelengths in the visible spectrum are classically used due to their high penetration. Red light with its wavelength at 620 nm and 1- to 3-mm depth of penetration is most effective [ 18 ] . Aminolevulinic acid and methyl aminolevulinate are the two most commonly used exogenous photosensitizing agents utilized in photodynamic therapy. Any laser-emitting light in the visible spectrum (400-800 nm) can be used to activate these sensitizers. Polychromatic light sources are often used in photodynamic therapy as well, allowing for the use of different photosensitizers with different absorption maximums. In vivo studies using a photosensitizer and pulsed dye laser have reported that photodynamic therapy leads to coagulation, vasoconstriction, angiostasis, and hemorrhage [ 19 ].
The ultimate effect of laser light on tissue depends on the energy density, which is the temperature reached in the target chromophore, and pulse width, which is the time spent at that temperature. Additionally, the laser effect on tissue is also affected by the conduction of this heat to surrounding tissues.
Basic Laser Design
All lasers are composed of the same four basic components: the laser medium, the optical cavity, the power supply, and the delivery system [ 20 ] . Lasers are typically named after their medium, which can be a solid, liquid, or gas. It is the lasing media that determines the wavelength emitted by the laser. Solid laser media typically consist of a glass or crystalline host material which is doped with neodymium, chromium, erbium, or ytterbium. Examples of commonly used lasers which utilize a solid medium include ruby, alexandrite, erbium, diode, and Nd:YAG lasers. Liquid media typically consists of an organic dye such as rhodamine doped into a liquid crystal. Dyes can usually be used for a much wider range of wavelengths than solid or gas media, making them ideal for tunable lasers. The pulsed dye laser, used extensively in the treatment of vascular lesions, is a prime example of a liquid medium containing laser. Gas media is usually composed of gaseous elements and compounds such as helium, neon, argon, xenon, krypton, fluorine, or carbon dioxide. Examples of commonly used gas medium lasers include CO 2 and excimer lasers.
The optical cavity or resonator surrounds the laser medium and contains the amplification process. It contains two mirrors that are parallel to each other. One mirror is fully reflective, while the other is only partially reflective. It is in this chamber that the emitted photons of light reflect back and forth from one mirrored end of the chamber to the other repeatedly until a sufficient intensity has been reached and the photons are allowed to escape through a small hole in the partially reflective mirror to the delivery system, which typically consists of fiber optic cables or an articulating arm with mirrored joints.
The power supply or pump excites the atoms and creates population inversion. The pump can be powered by electricity, radio-frequency enhancement, light, chemical reactions, and mechanical power. Electricity is used to pump most gas lasers while radiofrequency enhancement is used mostly for sealed-tube CO 2 lasers. Light originating from another laser or a flashlamp is used to pump dye lasers.
Basic Laser Properties and Principles
Wavelength refers to the distance between two peaks or troughs of the light waves emitted by a specific laser. It is measured in nanometers. Energy refers to the photon delivered by a single laser pulse and is measured in watt seconds or joules.

Energy = power (W) × time (s)

Fluence measures energy density. It is the amount of energy delivered in a single pulse per area and is measured in joules per centimeter squared (J/cm 2 ). It takes into account the power delivered, time of delivery, and the impact of the spot size.

From this calculation, it can be appreciated that spot size and fluence are inversely related. Therefore, increasing the spot size will decrease fluence and vice versa. Power is the amount of energy released by the laser per unit of time. It is measured in joules per second (J/s) or watts (W).
Irradiance measures power density, characterizing the intensity of a laser beam. It is measured in watts per centimeter squared (W/cm 2 ). It is calculated using the following formula:

The area can be calculated by multiplying the square of the radius of the spot size by π. Therefore, according to the above equation, doubling the power will double the power density, while doubling the spot size will decrease the power density by the inverse of the square of the change in radius. Halving the spot size will have the opposite effect, increasing the irradiance. For example, decreasing the spot size by 50% will increase the irradiance by fourfold.
Pulse width or pulse duration is the actual time over which energy is delivered, typically lasting nanoseconds (ns), milliseconds (ms), or seconds (s). Frequency describes the rate at which pulses are delivered and is measured in hertz (Hz), which is a measure of pulses per second.
Spot size is a measure of the diameter of the laser beam usually described in millimeters (mm). It is a crucial parameter that can greatly influence the depth of laser penetration and scatter, irrespective of wavelength, and directly influences the fluence and irradiance of the laser beam. If the exposure time is kept constant, the relationship between irradiance and depth of injury is linear, as the spot size is varied. Consequently, spot size selection cannot be based simply on the size of the area to be targeted. Generally, smaller spot sizes allow for greater beam scatter, thereby decreasing the depth of penetration. Larger spot sizes allow for less scatter and a greater depth of penetration [ 21 ] . However, when dealing with very small spot sizes in the micrometer range as with fractional resurfacing, penetration does not appear to be inhibited and the beam can penetrate very deep with little damage to the epidermis.
Laser light can be delivered in two different manners. It can be delivered in a continuous wave with a low-power constant light beam over an uninterrupted time period, most commonly seen with gaseous lasers such as the CO 2 laser. These lasers lead to bulk heating and nonselective tissue damage. Quasi-continuous wave lasers have a mechanical shutter which can truncate continuous beams into pulses lasting from 1 ms to 1 s. These, however, are not considered true pulsed lasers. Some of the first lasers utilized in the treatment of vascular lesions were continuous and quasi-continuous, such as the argon, copper vapor/bromide, and krypton lasers. Laser light can also be delivered in pulsed waves lasting for nanoseconds (short pulse) or milliseconds (long pulse). Truly pulsed lasers deliver high-power ultrashort pulsed waves of energy and are followed by a lag phase before another pulse can be generated. They are mostly solid state lasers such as the Nd:YAG laser. Altering the pulse duration allows for the treatment of a variety of vascular lesions to various clinical endpoints. Lengthening of the pulse duration can allow for effective treatment while decreasing the risk of subsequent purpura, a common, often undesirable, effect of laser treatment of vascular lesions. Targeting of specific tissues by a laser, known as selective photothermolysis, is only possible with pulsed lasers which can deliver energy for a period of time shorter than the thermal relaxation time of the targeted tissue, thus preventing damage to surrounding tissues. The theory of selective photothermolysis is discussed in greater detail later in this chapter.
As the laser beam passes through the epidermis to its target in the dermis or subcutaneous tissue, it is possible for the epidermis to be damaged during this process. In order to prevent excess heating and damage of the epidermis, it must be cooled to avoid potential adverse reactions such as postinflammatory hyperpigmentation. It can also reduce pain and edema. Cooling can occur prior to, during, or after laser delivery. This is referred to as precooling, parallel cooling and postcooling, respectively. Common methods of cooling include cryogen spray (often times built into the laser handpiece), air cooling, contact cooling (often times via cooled sapphire tips), or ice packs. Achieving a proper balance, when cooling, is crucial. One must take caution not to overcool the skin as it may decrease the efficacy of laser treatment or lead to burns or postinflammatory hyperpigmentation itself.
The intensity of a laser light beam can be distributed in different patterns across the beam known as the transverse electromagnetic mode (TEM). The most ideal scenario is that in which the power is distributed evenly across the entire areas of the beam. However, that is usually not the case. Most medical lasers produce a beam with a gaussian profile which is referred to as the fundamental mode or TEM 00 . In this profile the majority of the power (approx. 86% [ 12 ]) is concentrated in the center. From the center the intensity tapers off in a bell-shaped distribution. This pattern of distribution requires the pulses to be overlapped to a degree in an attempt to achieve a more uniform energy distribution throughout the tissue. Higher order modes such as TEM 01 and TEM 10 are doughnut or target shaped in which the intensity is greatest at the beam’s edge with a cool spot in the center of the beam. These modes deliver a more uniform beam intensity and should never be overlapped.
Theory of Selective Thermolysis
As mentioned earlier, the theory of selective thermolysis, originally proposed by Anderson and Parrish in 1983 [ 7 ], states that laser energy is absorbed by a specific chromophore causing its destruction without damaging the surrounding tissue. In order for this to occur, the laser wavelength must correspond to the absorption spectrum of that particular chromophore. Additionally, in order to prevent damage to surrounding structures, the pulse width of the laser beam needs to be shorter than the thermal relaxation time of the targeted structure. When pulse width is less than the thermal relaxation time, the heat generated within the target does not flow out of the structure until it becomes fully damaged. Thermal relaxation time is the time it takes for 63% of the peak heat absorbed by the target chromophore to dissipate. The time it takes for this to occur is directly related to the area of the targeted chromophore. Smaller structures tend to cool faster than larger ones; hence, larger chromophores will have a longer thermal relaxation time. Thus, pulse width selection needs to be based, in part, on the size of the target chromophore.
The treated target for destruction and the targeted chromophore are often the same structure. A classic example of this is tattoo or pigmented lesion destruction, where the targeted chromophore - the pigment - is located within the targeted structure itself. However, when the target absorption is nonuniform, with part of the target exhibiting weak or no absorption while another part exhibits significant absorption, the weakly absorbing part of the target has to be damaged by heat diffusion from the strongly absorbing part. In order for this to occur, the pulse width must be greater than the thermal relaxation time of the targeted chromophore. This concept proposed by Altshuler et al. [ 22 ] in 2001 is referred to as the extended theory of selective photothermolysis. A good example of such a target is the hair follicle in which the hair shaft and matrical cells in the bulb are highly pigmented, strongly absorbing laser energy, while the bulge, the area in which the follicle stem cells are located, is not pigmented and does not absorb laser energy. In order to achieve permanent follicle destruction, rather than mere epilation, it is necessary to destroy the bulge. Since the bulge area itself does not contain sufficient target chromophore to absorb adequate laser energy to allow for its destruction, sufficient heat from the nearby hair shaft and bulb needs to be transferred to it for permanent hair destruction to occur [ 23 ] . A similar phenomenon is seen with the treatment of vascular lesions in which a wavelength near the maximum hemoglobin absorption is utilized. Laser energy is absorbed by the hemoglobin in the blood and then diffuses to the vessel wall pleading to coagulation and permanent closure of the vessel [ 24 ].
Laser Safety
Over the past few decades, lasers have revolutionized how we treat a variety of skin and other medical conditions. However, in addition to their great benefit, these powerful devices have the potential to pose significant hazard to the patient and operator. Therefore, safety is one of the most important aspects of proper laser operation. Laser hazards are typically divided into two categories: beam hazards and nonbeam hazards. Beam hazards refer to injuries that may occur due to interaction with the beam itself, such as ocular or skin injury. Nonbeam hazards include plume, chemical, electrical, or fire hazards [ 17 ].
Given these potential hazards, it is imperative for the laser operator to understand the risks and how to best mitigate them in order to ensure the safest possible operation of the laser. It is crucial for the operator to be properly trained and familiar with the indications and characteristics of each device. Ideally, the door of the laser operating room should have a sign indicating the laser being used, its wavelength, and energy. Additionally, if possible, the door should be locked to avoid accidental entrance by anyone not donning appropriate personal protective equipment.
Ocular and Dental Hazards
The greatest risk when operating a laser is that of eye injury. Laser pulse durations are typically in the millisecond or nanosecond range, much quicker than the blink reflex which takes a tenth of a second, and the eye cannot be protected adequately by the eyelids in that situation. Additionally, lasers that do not operate in the visible spectrum do not emit light that can trigger a blink reflex at all [ 25 ] . The type of ocular damage that can be sustained depends on the laser wavelength being utilized. Lasers emitting light in the ultraviolet or infrared portions of the electromagnetic spectrum, such as the CO 2 laser, are absorbed by the anterior portion of the eye, namely the cornea and lens which have a very high aqueous composition. It is this water that absorbs the laser energy resulting in thermal injury to the tissue [ 26 ] . Lasers which emit wavelengths in the visible portion of the electromagnetic spectrum, many of which are often utilized in the treatment of vascular lesions, penetrate deeper to the posterior portion of the eye, damaging the retina and vascular choroid [ 27 ] . Injury to the retina is mainly due to the absorption of visible and near-infrared laser energy by melanin and to a lesser extent, hemoglobin. Effects of optical radiation damage to the retina may be inconsequential if it occurs at the periphery or may lead to significant visual impairment if it occurs near the fovea. The greater the number of damaged foveal photoreceptors, the greater the impairment. Some lasers can cause damage to both the anterior and posterior portion of the eye, such as the 1,320- and 1,064-nm Nd:YAG lasers which are often utilized in the treatment of vascular lesions, and can damage the lens and retina. Similarly, the 755-nm alexandrite laser and the 810-nm diode laser, also used in the treatment of vascular lesions, can damage both the lens and retina. The potential ocular hazards are even greater with Q-switched lasers as retinal damage can occur through both thermal and photoacoustic mechanisms, which may ultimately cause perforation [ 28 ] . It is important to note that ocular injury can occur not only from direct exposure to the laser beam, but also from any light scattered off of reflective surfaces such as glass, polished metal, or plastic surfaces.
Therefore, it is imperative for the laser operator and anyone else in the room to wear protective goggles while the laser is in operation. Protective laser glasses are typically composed of coated glass or polymeric plastics, each with its advantages and disadvantages. Glass eyewear tends to be heavy and the protective coating can get scratched, compromising the protection they afford. Plastic goggles are more lightweight than glass and absorb rather than reflect laser light, unlike coated glass goggles. However, plastic goggles have a greater tendency to crack and may even melt. Each set of goggles has a specific wavelength (or range of wavelengths) of rejection which should match the emission spectrum of the specific laser in use. In addition to ensuring that the laser operator and all staff in the room are wearing goggles, the patient must be fitted with minigoggles or corneal shields as well. Corneal shields are most appropriate when laser treatment is being performed near the immediate vicinity of the orbit. Heat-proof stainless steel eye shields which reflect light are preferred over plastic shields that could potentially heat up and melt [ 29 ] . Since they are placed directly on the cornea, anesthetic drops need to be utilized prior to the insertion of corneal shields. If the laser procedure is being performed on the lower face or elsewhere on the body, minigoggles that fit over the eyelids and protect the entire periorbital area are preferred.
Dental enamel, too, needs to be protected from laser light. Protection can be best achieved by keeping the mouth closed or by using a protective mouth piece. Enamel is particularly vulnerable to ultraviolet light such as that emitted by excimer lasers as well as infrared light emitted from CO 2 and Er:YAG lasers. At high fluences, laser light can lead to melting of the enamel, while at lower fluences cracking, charring, and discoloration are more common [ 30 ] . Diode and Nd:YAG lasers are often used in modern dentistry, and to date there have been no reports of any dental hazards from those lasers or any other lasers used in the treatment of vascular lesions. Nonetheless, simple precautions, such as keeping the mouth closed, should be taken to protect the teeth during treatment.
Fire and Electrical Hazards
Most of the medical lasers used today do not carry the same risk of combustion as some older devices; however, a small risk still exists. It is advisable to keep any flammable materials such as gauze, towels, or drapes away from the procedure field. It is also advisable to remove any potentially flammable agents from or near the area being treated, such as cosmetics or hair spray. Additionally, it is recommended that the patient’s hair be secured back from the field and caution be taken when treating hair-bearing areas as hair could potentially ignite causing burns. Alcohol or other flammable agents should never be used to prepare an area prior to laser treatment. Instead, the area and all instruments should be prepped with saline [ 31 ] . In addition to the above precautions, a fire extinguisher should also be readily available in the event of an electrical fire stemming from the equipment.
Plume and Splatter Hazards
Similar to electrosurgery, when tissue is treated with a laser, the target cells can be vaporized and their contents aerosolized, potentially leading to exposure to the laser-generated air contaminants in the resulting plume for the laser operator, other members of the healthcare team, and the patient. It has been estimated that nearly half a million healthcare workers are exposed to laser-generated air contaminants or electrosurgical smoke yearly [ 32 ] . The quantity and nature of the aerosolized matter is dependent on the tissue being treated, the laser employed, and its irradiance. Nearly 150 chemicals have been identified in laser plumes including carbon monoxide, hydrogen cyanide, ammonia, formaldehyde, acrolein, toluene, benzene, ethanol, isopropanol, formaldehyde, and many others [ 33 ] . Numerous studies have been conducted to determine the potential health effects associated with exposure to laser plumes. Many of these released agents have been found to be cytotoxic, clastogenic, genotoxic, and mutagenic [ 34 , 35 ] . In one study, the mutagenic potency observed was comparable to that of cigarette smoke, and it was found that irradiation of 1 g of tissue with a CO 2 laser had the same hazard potential as smoking three unfiltered cigarettes [ 36 ] . Additionally, substances found in laser plumes have been shown to be respiratory irritants which could lead to acute and chronic pulmonary and bronchiolar inflammation. Animals exposed to CO 2 and Nd:YAG laser plumes were found to develop interstitial pneumonia, bronchiolitis, and emphysema, with impaired mucocilliary clearance, transient hypoxia, and increases in inflammatory cells in the lung parenchyma, similar to what is observed after long-term inhalation of other particulates. Additionally, upon the initiation of unfiltered plume exposure, experimental animals immediately became sluggish and discontinued active movement [ 37 , 38 ]. To date, only one epidemiological investigation has been conducted examining the health effects of surgical plume exposure on healthcare workers. Specifically, it assessed lung cancer risk in operating room nurses, but concluded there was no increase in lung cancer related to plume exposure [ 39 ].
The laser plume also includes particulate matter that has been shown to include viable viruses and bacteria. It is believed that laser plumes may have even greater infectious potential than electrosurgical smoke. The first evidence of the presence of viable cellular matter within the laser plume was reported in 1967 by Hoye et al. [ 40 ] after experiments using an excimer laser. In 1988, Garden et al. [ 41 ] were the first to demonstrate the presence of intact viral DNA in a laser plume. Intact human papillomavirus DNA has been isolated from the laser plume of a CO 2 laser used for the treatment of a variety of verruca [ 42 ] . Likewise, human immunodeficiency virus DNA, capable of infection, has also been isolated from laser plumes [ 43 ] . There have been several studies investing the infectious contents of lasers plumes. These studies mainly involved the use of the CO 2 laser and had mixed results. To date, no epidemiologic studies have been conducted to assess the infection rate of medical staff exposed to a laser plume.
Airborne particle deposition and their resulting health effects are directly related to particle size. Smaller-sized particles travel farther relative to larger-sized particles. Several studies have indicated particle size ranging from 0.1 to 27 μm in diameter can be found in laser plumes. Given these findings, it is important to employ methods to effectively mitigate potential plume hazards by utilizing smoke evacuators and laser masks. Dilution ventilation is considered insufficient to effectively control the surgical smoke generated, thus requiring the use of a ventilation system. The most effective portable smoke evacuation system is a triple-filter system equipped with a prefilter designed to capture large particulate matter, a charcoal filter, and an ultralow particulate air filter. Ultralow particulate air filters are capable of capturing 0.01-μm particles at an efficiency rating of 99.9999%, while high-efficiency particulate air filters only capture particles 0.3 μm or larger with an efficiency of 99.97%. The smoke evacuator nozzle inlet must be within 1 cm of the surgical site to effectively remove the plume. The effectiveness is reduced from 99 to 50% when the distance from the laser site is increased from 1 to 2 cm [ 44 ].
Standard surgical masks only filter particles 5 μm in size or larger, providing inadequate protection against exposure to laser-generated air contaminants since approximately 77% of the particles in laser plumes are 1.1 μm or smaller. High-filtration laser masks that filter particles greater than 0.1 μm should be employed.
Q-switched lasers present a particular challenge. When treating tattoos or benign pigmented lesions with a Q-switched laser, the impact of the pulses can disrupt the surface of the skin. These impulses create an explosion of blood and skin fragments flying away from the treatment site at a very high speed. Studies have noted considerable amount of splatter of tissue in all directions in the air as far away as 6-8 feet from the laser impact site [ 40 ] . The speed of these particles is so fast that they escape capture by a smoke evacuator. In these instances, splatter shields or collecting cones have been recommended to contain these particles at the skin surface and most manufacturers now supply these along with their device. Laser treatment through a transparent membrane, such as hydrogel surgical dressing, has also been recommended [ 45 ]. Proper personal protective equipment should also be worn by the laser operator and assisting staff in order to prevent contamination by splattered materials. These include, but are not limited to, appropriate goggles, gloves, gowns, and laser masks.
Despite all this, smoke evacuation devices are not routinely used. A recent Web-based survey among operating room nurses assessing the frequency of smoke evacuator and laser mask use during laser procedures revealed that the frequency of smoke evacuator use was largely dependent on the procedure being performed. Eighty-three percent stated that they use smoke evacuators ‘always or often’ during laser treatment of condyloma. Similarly, 75% responded that they ‘always or often’ use smoke evacuators during dysplasia laser ablation. Less than 14% reported that that they ‘never or seldom’ use a smoke evacuator for either of those instances. On the contrary, greater than 70% admitted that they ‘never or seldom’ use smoke evacuators during endos-copy, bronchoscopy, laparoscopy/arthroscopy, and laser-assisted in situ keratomileusis (LASIK), and less than 20% ‘always or often’ use evacuators during those procedures. Overall, the study found that smoke evacuators or other forms of respiratory protections were used by less than half of the facilities represented by the survey respondents for most laser procedures [ 46 ] . Another survey from the UK revealed that only 3% of surgeons used smoke evacuators regularly, although a vast majority felt that inadequate precautions are taken to protect staff and patients from surgical smoke [ 47 ] . This discordance is believed to be due to the resistance of health care organizations, surgeons, and perioperative personnel, attributed to the lack of knowledge about the potential health hazards associated with exposure to laser plumes, as well as desensitization to the offensive odor that accompanies laser procedures. Additionally, although OSHA does regulate many of the substances found within surgical plumes, it does not specifically require the use of smoke evacuation or filtering systems during laser surgical or electrosurgical procedures.
The vast majority of studies documenting the potential airborne hazards of lasers were conducted using ablative lasers, mostly CO 2 and erbium lasers, with only a few studies documenting the airborne effects of Nd:YAG and excimer lasers. To date, there have been no studies on the potential adverse effects of laser plumes created by any other lasers typically utilized in the treatment of vascular lesions. Nonetheless, basic caution and protective equipment is still advised.
References
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Susan Bard Vanguard Dermatology 161 Avenue of the Americas suite 1304 New York, NY 10013 (USA) E- Mail susanbardmd@gmail.com
Bard S, Goldberg DJ (eds): Laser Treatment of Vascular Lesions. Aesthet Dermatol. Basel, Karger, 2014, vol 1, pp 18-39 (DOI: 10.1159/000355044)
______________________
Argon, Krypton, and Copper Lasers
Andrew R. Styperek
Department of Dermatology, Miller School of Medicine, University of Miami, Miami, Fla., USA
______________________
Abstract
The treatment of vascular lesions was among the first uses for lasers, and the argon, krypton, and copper vapor lasers were chosen for this task due to their relative specificity for the hemoglobin absorption spectrum. Despite their relative specificity, the primary mechanism of these lasers was photothermal, which causes thermal injury and coagulation. By leveraging thermal injury to coagulate vascular lesions, the laser surgeon’s skill in handling a laser and patient selection was critical for ensuring excellent therapeutic results and avoiding potentially significant side effects, such as scarring. Despite the risks of scarring, aesthetic outcomes could be quite good - especially when compared to other contemporary modalities, such as surgical excision. However, once the theory of selective photothermolysis was elucidated, use of these lasers diminished as safer methods of treating vascular lesions were developed.
© 2014 S. Karger AG, Basel
One of the first uses identified for lasers was treating vascular lesions. The earliest lasers applied were the: argon (488, 514 nm), argon-pumped tunable dye (488-638 nm), copper vapor and copper bromide (511, 578 nm), KTP (potassium-titanyl-phosphate; 532 nm), and krypton (568 nm) lasers. Although designed to correspond with the hemoglobin absorption spectrum, the continuous or quasi-continuous wave beams functioned by inducing thermal damage to the surrounding structures, which often caused scarring and dyschromia. The key problem, a mismatch between laser pulse duration and target tissue thermal relaxation time, was effectively resolved once the principles of selective thermolysis were elucidated and the laser pulse duration was tuned to match the thermal relaxation time of the targeted tissue.
Laser Thermal Effects
While the argon, krypton, and copper lasers were chosen for their relative specificity in excitation of hemoglobin, thereby efficiently transferring the energy of the laser to the target chromophore [ 1 ], their primary mechanism of action was delivery of thermal energy to the lesion.
The thermal effect of lasers is mediated by the absorption of laser light energy and represents the primary method by which the clinical effects of the laser are achieved and results in conversion of the absorbed energy into heat. While the thermal mechanism of lasers has been reviewed earlier, it is important to highlight how the photothermal effects of photocoagulation occur, as this is of primary importance in vascular lesions.
The extent of thermal injury with a laser is proportional to the magnitude and duration of a temperature increase because heat increases the rate at which molecules denature. This effect is demonstrated by the Arrhenius model mathematically, with the rate of denaturation exponentially related to temperature [ 2 ] . Cells respond to heat injury by altering protein levels, upregulating expression of heat shock proteins, which confer mild resistance to thermal injury [ 3 ] . One example of the clinical response to mild heat injury is erythema ab igne, which involves exposure to heat below 45 ° C (113°F) and the appearance of reticulated erythema and hyperpigmentation.
When tissue is heated with lethal doses of energy to above 60 ° C (the melting transition point of fibrillar type I collagen), coagulation occurs with DNA and protein denaturation, resulting in loss of function via unfolding and coagulation of macromolecules. Thermal coagulation yields cell necrosis and, if widespread, a burn.

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