lasers e laser like devices 1.pdf

REVIEW ARTICLE

Lasers and laser-like devices: Part one

Nicholas Stewart,1 Adrian C Lim,2 Patricia M Lowe3 and Greg Goodman4

1Concord Repatriation and General Hospital, 2Department of Dermatology, Royal North Shore Hospital,3Clinical Senior Lecturer, Sydney Medical School (Central), University of Sydney, Sydney, New South Wales,

and 4Dermatology Institute of Victoria, Melbourne, Victoria, Australia

ABSTRACT

Lasers have been used in dermatology for nearly 50years. Through their selective targeting of skinchromophores they have become the preferred treat-ment for many skin conditions, including vascularmalformations, photorejuvenation and acne scars.The technology and design of lasers continue toevolve, allowing greater control of laser parametersand resulting in increased safety and efficacy forpatients. Innovations have allowed the range of con-ditions and the skin types amenable to treatment, inboth general and cosmetic dermatology, to expandover the last decade. Integrated skin cooling and laserbeam fractionation, for example, have improvedsafety, patient tolerance and decreased downtime.Furthermore, the availability and affordability ofquality devices continues to increase, allowing clini-cians not only to access laser therapies more readilybut also to develop their personal experience in thisfield. As a result, most Australian dermatologists nowhave access to laser therapies, either in their ownpractice or within referable proximity, and practicalknowledge of these technologies is increasinglyrequired and expected by patients. Non-laser energydevices utilising intense pulsed light, plasma, radiof-requency, ultrasound and cryolipolysis contribute tothe modern laser practitioners armamentarium andwill also be discussed.

Key words: cryolipolysis, energy devices, history,intense pulsed light, laser, plasma, radiofrequency,regulation, tissue optics, ultrasound.

INTRODUCTION

This two-part review aims to refresh the reader to the roleof lasers in procedural and cosmetic dermatology. Part one

begins with a background history of lasers followed by adiscussion of relevant laser physics and tissue optics. Aworking knowledge of tissue targets and lighttissue inter-actions is essential to use of the correct laser for the job andto interpret clinical laser parameters. The different lasertypes, which are classified according to their tissue targetand/or tissue interaction as vascular, pigment and resurfac-ing lasers are discussed. The review includes new lasertechnologies that have gained general acceptance. Sometechnologies and devices showing early promise have notlived up to expectations and will not be discussed. Theintended and deleterious effects of laser treatment will alsobe highlighted in broad terms. The role of some non-lasertechnologies such as intense pulsed light (IPL), plasma,radiofrequency (RF), ultrasound and cryolipolysis will beincluded to broaden the readers understanding of the cur-rently available therapeutic options. Finally in Part one wediscuss several issues arising as a result of current state andfederal regulations on the training and safe use of laser andother cosmetic technologies.In the second part of this review, we discuss the use of

lasers and related technologies in the treatment of specificdisease groups and the likely outcomes. We highlightcertain pitfalls of laser therapy based on a review of theliterature and the personal experience of the lead authors.Finally, we discuss the role of lasers in combination withother physical and pharmacological treatments and high-light their use in difficult Fitzpatrick skin types.

Correspondence: Dr Nicholas Stewart, Concord Repatriation andGeneral Hospital, PO BOX 316, Rozelle, Sydney, NSW 2039,Australia. Email: [email protected] Stewart, MBBS. Adrian C Lim, FACD. Patricia M Lowe,

FACD. Greg Goodman, FACD.Submitted 12 December 2012; accepted 15 January 2013.

Abbreviations:

ALA aminolevulinic acidHIFU High-intensity focused ultrasoundIPL intense pulsed lightKTP potassium titanyl phosphateMTZ microthermal zonesNd neodymiumPDL pulsed dye laserRF radiofrequencyTRT thermal relaxation timeYAG yttrium aluminium garnetYSGG yttrium scandium gallium garnet

[Correction added on 18 June 2013, after first online publication:potassium titanyl phosphate in the Abbreviations list waschanged to pulsed dye laser.]

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Australasian Journal of Dermatology (2013) 54, 173183 doi: 10.1111/ajd.12034

2013 The AuthorsAustralasian Journal of Dermatology 2013 The Australasian College of Dermatologists

A BRIEF HISTORY OF LASERS

The theory of stimulating radiant energy was published byAlbert Einstein in 1916 and followed on from the earlierwork of Rutherford describing the atom in 1911 and thetheory of quanta release from excited substances publishedby Niels Bohr in 1913 (Table 1).1,2 These foundationsenabled the subsequent technical development of the rubylaser by Theodore M Maiman at the Hughes CorporationResearch Laboratories in Malibu, California, in 1960.1,2

Gordon Gould coined the acronym laser that derives fromthe term, light amplification by stimulated emission ofradiation. After a long patent fight, Gould holds the patentfor optical light lasers, while Maiman holds the patent forthe ruby laser. In 1961 the first biological application oflaser technology was published in Science on the use oflasers in retinal photocoagulation.3 Leon Goldman is cred-ited with the first documented use of lasers in dermatologyand is considered one of the founding fathers of the use oflasers in medicine.1 In 1963 he described the selectivedestruction of pigmented structures of the skin, includinghair follicles, with the 694 nm pulsed ruby laser.4 He pub-lished extensively on the use of this laser in the treatment ofnaevi, tattoos and even melanoma.4,5 He performed studieson vascular malformations using the argon laser and in1973 published work on the use of the neodymium: yttriumaluminium garnet (Nd:YAG) laser in the treatment of angi-omas.6 Goldman was also the first to analyse naevi and

melanomas with monocular epiluminescence and inventedthe portable dermatoscope in the 1950s. His pioneeringwork on lasers was subsequently expanded in the early1980s by Anderson and Parrish, who developed the theory ofselective photothermolysis,7 largely reviving the interest inQ-switched lasers for the treatment of unwanted tattoopigment and hair.1 Anderson also helped introduce theconcept of fractional laser technology and, more recently,cryolipolysis.8,9

While the continuous wave lasers (carbon dioxide:Nd:YAG and argon) began to be developed in the1960s, thecarbon dioxide laser did not reach the height of its popular-ity in dermatology practice until the early to mid-1990s,when it was used primarily as an ablative tool to resurfacethe skin and stimulate collagen remodelling.1,2,10 However,the significant postoperative downtime, discomfort andcomplications eventually limited its use in cutaneoussurgery.1113

Most devices, including the carbon dioxide laser, could bepulsed; with normal pulsing giving way to progressivelyshorter and shorter pulsing (superpulsing and ultrapulsingin the case of the carbon dioxide). This meant the laserenergy could be delivered in short (multiple) bursts ratherthan in a continuous wave, thus reducing collateral tissueheating and damage that could potentially cause burning,scarring and dyspigmentation. High energy, extremely shortpulsing was epitomised by the advent of Q-switched lasers(see below). Technological advances continued with theintroduction of fractional lasers in 2004, which led to aconceptual shift in skin resurfacing.1114 This new technol-ogy provided results approaching those achieved by tradi-tional carbon dioxide lasers, except with significantlyreduced morbidity and complications.1114 A summary of keylaser milestones can be found in Table 1.

BASIC PHYSICS OF LASERS

An understanding of the nomenclature (Table 2) and basicphysics associated with electromagnetic radiation is neces-sary for the practitioner to understand how lasers work andhow they interact with the skin. This will help the practi-tioner to apply the appropriate laser to the condition requir-ing treatment and provide a framework for understandinghow laser parameters can be varied according to skin char-acteristics and treatment end-points.15,16

Within the optical cavity of a laser resides the gainmedium of the particular substance that gives the laser itsunique characteristics (e.g. carbon dioxide for the carbondioxide laser). The atoms of the gain medium are excitedby an external power source in a process called pumping.The absorption of this pumped energy converts electronsfrom low-energy to high-energy orbital shells. When theseexcited atoms receive further energy from incident photonsthey subsequently release not only the energy stored fromthe initial pumping but also the incident photons as theelectrons return to a lower energy, resting orbit (Fig. 1). Thetwo photons released from one atom go on to energisetwo other atoms, resulting in the rapid multiplication ofphotons. This stimulated emission of photons forms the

Table 1 Key laser milestones

Date Milestones

1900 Plank describes light as a form of electromagneticradiation

1911 Rutherford describes the atom1913 Bohr publishes theory of quanta release from

excited substances1916 Einstein publishes theory of stimulating radiant

energy1947 Lamb and Rutherford demonstrates stimulated

emission1951 Leon Goldman analyses naevi and melanomas using

monocular epiluminescence1958 Leon Goldman invents the first potable

dermatoscope1959 Gould coins laser acronym1960 Maiman develops the ruby laser1961 Science publishes first biological application of lasers

(retinal photocoagulation)1963 Goldman publishes first laser application in

dermatology (ruby laser on pigmented skin lesionsand hair follicles)

1964 Carbon dioxide laser introduced19641973 Goldman publishes on use of the argon laser and

the neodymium: yttrium aluminium garnet laseron vascular lesions

1980s Anderson and Parrish introduces the theory ofselective photothermolysis

1996 Erbium (erbium: yttrium aluminium garnet) laserintroduced

2004 Anderson and Manstein introduce fractionalphotothermolysis

174 N Stewart et al.


principle behind light amplification. The emitted photonsare reflected by mirrors at either end of the optical cavityand released periodically via the output coupler at a time ofthe operators choosing (Fig. 2). This radiant energy isthen delivered to a handpiece by either mirrors or a fibreoptic cable. The light produced is collimated, coherent andmonochromatic.The laser beam may be administered as a continuous

stream of energy, pulsed (measured in milliseconds) withthe aid of a mechanical shutter or Q-switched with the useof an electro-optical switch. The latter allows the produc-tion of nanosecond pulses with extremely high peak power.Finally, the spot size or beam diameter can be manipulatedto allow the energy to be delivered over different surfaceareas. The energy in the laser beam is constant, so thatchanging the spot size will determine the surface area overwhich this energy is delivered and has consequences for thefluence and energy density of the irradiated area. Inessence, if the number of joules in a laser beam remainsconstant and the operator decreases the spot size thebeams energy is all delivered in a smaller area, thusincreasing the fluence. The relationship between beamdiameter and fluence varies according to the inverse squarelaw, with small changes in spot size resulting in muchlarger changes in fluence.17 However, a smaller spot sizeallows proportionally more heat energy to diffuse to theadjacent tissue than a larger spot size where heat is bettercontained within the treatment field. Therefore in clinicalpractice, whenever the spot size is decreased, there shouldbe a compensatory increase in fluence to maintain efficacy.Conversely, when the spot size is increased, the fluence

should be reduced to prevent overheating and burning thetissue.Incident radiation produced by lasers destroys chromo-

phores by transferring energy as heat, known as photother-molytic and/or photomechanical reactions. The principle ofselective photothermolysis states that the physical proper-ties of the incident radiation (such as its wavelength,fluence and pulse width) can be manipulated to allowthe selective destruction of a target chromophore, whilesparing, or relatively sparing, the surrounding structures.7,13

To achieve this, there must not only be a difference in theabsorption spectra of the target chromophore and its sur-roundings (the larger the difference the better) but the irra-diated area must also be allowed to dissipate heat betweenpulses to reduce collateral damage. If these conditions aremet, heat can be selectively generated in a target, therebycausing its selective destruction. The thermal relaxationtime (TRT), which is variably defined as the time taken fora target chromophore to lose between 5063 per cent16,18 ofthe generated heat to surrounding tissue, is an arbitraryway of describing the thermal properties of a particulartarget. TRT are tissue-specific and chromophore-specificand vary according to the size of the target (Table 3).17 Thelaser pulse duration/width is often selected to match theTRT of the target (e.g. a longer pulse duration is used forlarger blood vessels). In clinical practice, longer pulseduration/width is safer for dark skin even though shorterpulse durations may be more effective. The pulse durationcan also be varied proportionally to correspond with capil-lary diameters in the treatment of telangiectases.Finally, in practical applications there may be a difference

between the chromophore that absorbs the incomingphoton (the absorber chromophore) and the intended target(the target chromophore). This can be illustrated by theprocess of laser depilation, where permanent hair removalis achieved when energy absorbed by melanin in the hairshaft (the absorber chromophore), is transferred to anddestroys hair stem cells and blood vessels (the targetchromophores) in the isthmus/papilla.16

TISSUE OPTICS

Light behaviour follows both wave and particulate (orphoton) characteristics. Quantum mechanics attempts to

Incident photon

e-

e-

Figure 1 An excited atom receives energy from an incident photonand subsequently releases two photons, known as the stimulatedemission of photons.

Table 2 Nomenclature (international system of units)

Joules Unit of energy (J)

Fluence Joules per unit area (J/m2).Power Joules per unit time (J/s also known as a Watt). Also called energy density or exposure dose.Irradiance Power per unit area (W/m2). Also known as power density.Chromophore Molecule that absorbs a particular wavelength of light.Cooling Protecting the superficial layers of skin from collateral thermal damage. It is achieved by cold air convection, contact

cooling or cryogen spray (dynamic) cooling. (Celsius, C)Pulse duration The length of time over which laser energy is delivered to the tissue. Also known as pulse width. Measured in

milliseconds (ms), microseconds (ms), nanoseconds (ns).Collimation The production of photons that are parallel to each other. Divergence over distance is negligible (i.e. < 1 milliradian).Monochromatic The production of photons with identical wavelengths.Coherence The production of photons that are in phase with each other, both temporally and spatially.

Lasers in dermatology 175


describe this duality. Before light interacts with tissue itswave characteristics predominate. Once interacting withstructures, including our tissues, the particulate character-istics are more evident. When incident light waves strike asurface such as the skin, there are a limited number ofpossible outcomes. The photons may be reflected off thesurface or be scattered or absorbed as they interact with thetissue, or they may be transmitted through the skin com-pletely unhindered. Their trajectory and pathway is deter-mined by the manner in which they are applied (e.g. theangle of incidence) and by the physical properties of theparticular skin on which they make contact. The latterforms the basis for our discussion on tissue optics and high-lights the four main targets of laser energy: water, melanin,haemoglobin and exogenous pigments.1519

Short wavelengths of light are strongly scattered by theskin, while long wavelengths tend to penetrate moredeeply.15,16 The optical window of skin is the range of wave-lengths that maximally penetrate living tissue, extend-ing from 620 to 1200 nm.15 Below 620 nm, haemoglobinand melanin are largely responsible for absorbing lightenergy, while wavelengths above 1200 nm are predomi-nantly absorbed by water in the epidermis and superficialdermis (Fig. 3). The latter is exploited by the long wave-length erbium (Er), carbon dioxide and YSGG lasers, whichcause vaporisation and varying degrees of bulk-heating ofthe skin layers.1,11,20,21 Their role in skin resurfacing is dis-cussed below.Haemoglobin is one of the most commonly selected skin

chromophores and has several absorption peaks that are

specifically targeted by the wavelengths of the vascularlasers18,22 (i.e. Nd:YAG potassium titanyl phosphate (KTP)532 nm, pulsed dye laser (PDL) 585 nm and 595 nm andNd:YAG 1064 nm) (Fig. 3). This relationship confirms theimportance of the theory of selective photothermolysis,demonstrating that lasers with a wavelength close to theabsorption peak of their target chromophore will usuallymaximise the difference between energy absorbed by thetarget and surrounding structures.Utilising laser wavelengths to destroy exogenous pig-

ments, such as tattoo ink, relies on similar principles. Indi-vidual tattoo inks produce their colour in situ as a result oftheir unique and preferential absorption within the visualspectrum. Knowledge of these wavelengths can thereforebe utilised by a laser practitioner engaged in their removal.Endogenous chromophores (i.e. skin colour), among otherfactors, need to be considered when utilising lasers for thispurpose. A detailed discussion of this area is provided inPart two of this review.

TYPES OF LASERS

Vascular lasers

Vascular lesions have been some of the most frequentlytreated skin conditions since the advent of lasers. In Aus-tralia vascular lasers are the workhorse of many modernlaser-equipped clinics. The PDL has a wavelength ofbetween 585595 nm and is used to treat superficial bloodvessels, as these wavelengths coincide with the absorptionpeaks of oxyhaemoglobin. In reality, the haemoglobinabsorption spectra is greater at 585 nm than at 595 nm butthe latter is now favoured because the longer 595 nm wave-length penetrates the skin further and is more effective atclearing blood vessels.18 Many dermatologists are familiarwith the purpura-inducing effects of the PDL in the treat-ment of capillary malformations. New PDL platforms canminimise clinically significant purpura by increasing thepulse width/duration or dwell time of the delivered energy.Generally, the smaller the pulse duration, the more explo-sively energy is delivered and the more likely it is to inducepurpura. The classic short pulse duration (0.451.5ms) thatruptures fine-calibre vessels is still the most effective pulseduration for treating capillary malformations, with purpura

Table 3 Thermal relaxation times of common skin structuresand targets

Size(um)

Thermalrelaxation times

Tattoo particles 0.54 10 nsMelanosomes 0.51 I msBlood vessel 50 1 msBlood vessel 100 5 msBlood vessel 200 20 msHair follicle 200 20100 msEpidermis 310 ms

PowerSource

Photons Photons

Partially reflectivemirror

Laser beam

Optical cavitycontaining thegain medium(solid, liquid,or gas)

Fully reflectivemirror

Figure 2 The external power sourceexcites the gain medium and stimulatesthe emission of photons. The photonsenergise surrounding atoms to releasemore photons, which are reflectedbetween two mirrors at either end of theoptical cavity. A laser beam is releasedwhen the output coupler is opened.



as the expected therapeutic end-point. Longer pulse dura-tions ( 6 ms) coagulate vessels, do not produce purpuraand are generally preferred by patients (minimal down-time) despite a reduction of efficacy when compared topurpura-inducing parameters. Sub-purpuric parametersare consequently favoured for the treatment of diffuse ery-thema and more superficial telangiectases.The Nd:YAG laser has a wavelength of 1064 nm, which

can also be used in the treatment of vascular lesions.20,22

This longer wavelength corresponds to the optical windowthat enables deeper penetration into the dermis to targetlarger vessels and is less likely to produce bleeding.22

However, it is not as strongly absorbed by haemoglobin,thus allowing melanin and water to act as competingchromophores. This can cause bulk-heating of tissues,potentially resulting in burns and scarring.23 It is generallyused for treating larger diameter vessels, such as coarsecapillaries and facial venules, as well as bluish vascularlesions such as venous lakes24 and thickened areas in

port wine stains (vascular malformations). However, the1064 nm laser can have its wavelength halved to 532 nm bypassing the beam through a KTP crystal.20 This is a verypopular vascular wavelength for the treatment of finersuperficial facial capillaries as it closely matches a haemo-globin absorption peak and has an excellent safety profile.

Pigment lasers

The major endogenous pigment of clinical importance ismelanin, whereas tattoo ink (amateur, professional or trau-matic) is the most commonly targeted exogenous pigment.Unlike haemoglobin, melanin does not have any appreci-able absorption peak, instead it increasingly absorbs shorterwavelengths of light below about 1000 nm (Fig. 3). There-fore, a multitude of laser wavelengths can be used to targetmelanin, although none is entirely specific for this chromo-phore: 532 nm Nd:YAG KTP, 595 nm PDL, 694 nm ruby,755 nm alexandrite and 10640 nm Nd:YAG. Despite this,

X-rayscosmic rays

UV Visible Infrared

UV

300 400 500 600 700 800 900 1000 2000 3000 10 000 nm1500

Visible Infrared

X-rayscosmic rays

Deoxyhaemoglobin

Oxyhaemoglobin

Melanin Water

MicrowavesTV/radio waves

MicrowavesTV/radio wavesOptical window (620 1200nm)

Argon(510)

KTP(532)

PDL(595)

Ruby(694)

Alexandrite(755)

Diode(810)

Nd: YAG(1064)

Er: YAG(2940)

CO2(10 600)

Figure 3 Absorption coefficient versus wavelength. Skin chromophores include oxyhaemoglobin, deoxyhaemoglobin, melanin and water.Laser wavelengths are compared with chromophore absorption peaks (or troughs). The optical window refers to the spectrum of wave-lengths that deeply penetrate the skin, corresponding to alexandrite, diode and neodymium (Nd): yttrium aluminium garnet (YAG) lasers.



selective photothermolysis is still achievable with the cor-rect choice of laser and machine settings.19,25 Superficial(epidermal) pigment is encountered in solar lentigines,ephelides, caf-au-lait macules and seborrhoeic keratoses,whereas deep (dermal) pigment is a feature of melanocyticnaevi, blue naevi, naevi of Ota and Ito, drug-induced hyper-pigmentation, Beckers naevi, naevus spilus and tattoos.20,25

Superficial pigment is best treated with short wavelengthlasers, whereas deeper (dermal) pigment responds better tolong wavelengths with a greater penetration. Dark-skinnedpatients are more safely treated with long wavelengthlasers, in an attempt to prevent the superficial uptake oflaser energy and potential dyspigmentation.The non-ablative continuous wave lasers (e.g. 488 nm/

512 nm argon, 511 nm copper vapour, 520 nm krypton,532 nm Nd:YAG-KTP) were originally used to treat pig-mented lesions, but their pulse durations far exceeded theTRT of melanosomes (~1ms) and often led to scarring andtextual irregularities from excessive collateral tissue dam-age.20,23,25 Consequently, continuous wave lasers are nolonger routinely used for pigmentary disorders. Lasers suchas the 532 nm Nd:YAG KTP can also be classified as quasi-continuous pulses result from the intermittent shutteringof the continuous laser beam and these remain popular fortreating pigmented lesions, in addition to their primary roleas a vascular laser.Q-switched laser systems can lighten or eradicate both

superficial and deep pigment, including tattoo ink, and arethe mainstay, but not the panacea, of modern anti-pigmenttreatment. They produce high-energy nanosecond pulses inthe green to near infrared spectrum (5321064 nm) thatselectively target melanin or ink and are less likely to causeadverse effects.20 The wavelengths of the Q-switched ruby(694 nm), alexandrite (755 nm) and Nd:YAG-KTP (532 nm)lasers are the most commonly used, with the latter alsofavoured for red, orange and yellow tattoo pigments.20,25 Theoriginal Q-switched Nd:YAGs long wavelength (1064 nm)allows targeting of deeper dermal pigment, such as thatfound in melanocytic naevi and blue or black tattoos.20,25

Adverse effects include tissue splatter, punctate bleeding,

oedema, pruritus, vesiculation/blistering, purpura, post-inflammatory hypopigmentation or hyperpigmentation,scarring, permanent hair loss and systemic allergic or local-ised granulomatous reactions to disrupted tattoo ink parti-cles.20,25 The incidence and severity of some of these sideeffects is increased in dark skinned individuals owing toincreased absorption by surrounding melanin.23

All Q-switched lasers have long-pulsed counterparts thatoperate with reduced anti-pigment efficacy because themilliseconds pulse width cannot adequately and safelytarget small diameter melanosomes or ink particles. Com-peting chromophores within skin structures, such as capil-laries, also assume greater relevance with long pulse widthlasers. For example, the 595 nm PDL preferentially targetsblood vessels but will target skin pigment when the treatedskin is compressed with a clear lens to blanch the underly-ing blood vessels along with its competing chromophore(haemoglobin). In practice, long pulse lasers can targetlarger structures such as clusters of lentiginous melano-cytes or pigmented hair shafts, and can be useful for treat-ing superficial epidermal pigmentation (e.g. ephelides andlentigines) and for hair removal. Superficial lentigines andfreckles respond well to long pulsed 532 KTP and intensepulsed light (IPL), and may be preferred to Q-switchedlasers to minimise the risk of post-inflammatory hyperpig-mentation in Asian skin.

Ablative resurfacing lasers

Ablative lasers are generally used to resurface and rejuve-nate the skin by treating rhytides, dyspigmentation (in fairskin) and scars. The continuous carbon dioxide laser, intro-duced in 1964, emits a beam of far infrared radiation at10 600 nm, mainly targeting water.11,14,19,21 This technologyis occasionally still used as a relatively bloodless skin inci-sion tool, but for resurfacing purposes has given way topulsed carbon dioxide laser technology.21 Ablation, definedas rapid cellular heating and instant tissue vaporisation,11

denudes 2060 mm of the skin surface20 (Fig. 4). Underneaththis ablated layer lies a 200300-mm zone of collateral

Epidermis

Ablativeresurfacing

Non-ablativefractional resurfacing

Ablative fractionalresurfacing

Dermis

Figure 4 Ablative resurfacing (CO2, erbium: yttrium aluminium garnet [Er:YAG]) versus non-ablative fractional resurfacing (erbium[Er:glass) versus ablative fractional resurfacing (CO2, Er:YAG, Er: yttrium scandium gallium garnet [YSGG]).



thermomechanical damage as a result of sub-ablative flu-ences.11 The tissue coagulation and protein denaturation inthis area gives rise to two unexpected yet beneficial out-comes. The first is haemostasis, which occurs almostinstantly, and the second is skin tightening, which resultsfrom the healing and remodelling of damaged proteins.11,21

The latter may take up to several months to achieve itsmaximal effect, but the resulting improvement in rhytidesand scarring is clinically significant.21,26 In the mid-1990sthis technology offered an exciting alternative to the prob-lematic treatment modalities available to resurface skin,which included deep chemical peels and wire brush ordiamond dermabrasion.26 However, the pulsed carbondioxide lasers were not without their own potential risks,including infection, pain, prolonged erythema (sometimes> 6 months), milia, scarring, permanent late hypopigmen-tation and cosmetically unacceptable demarcation linesbetween treated and non-treated skin.11,14,21,23,26

As a result, in 1996 the erbium: yttrium aluminium garnet(Er:YAG) laser was introduced. This laser operates at awavelength of 2940 nm and is absorbed by water 1016-foldmore than with a carbon dioxide laser.1,11,21 The effect of thisis a more superficial ablation, which not only reduceshealing time but also markedly increases patients toler-ance.11,20,21 Significant downsides of superficial ablation arereduced haemostasis and loss of adequate collateral heatingof the underlying dermis. The latter corresponds to a reduc-tion in tissue remodelling and the beneficial skin tighteningphase that is seen with a carbon dioxide laser.11,14,20,21 High-energy Er:YAG lasers could be boosted to produce clinicalresults equivalent to those of the carbon dioxide laser butthis would occur at the cost of reduced recovery times andpossibly result in long-term complications.20,27 Conversely,the carbon dioxide laser could be highly pulsed to reduceresidual thermal heating (i.e. making it more like erbium)and thus reduce the recognised side-effects of the originalconfiguration, albeit with a corresponding reduction in effi-cacy.2,20,27 A third ablative laser, the erbium-doped yttriumscandium gallium garnet (YSGG) (Er:YSGG), which oper-ates at a wavelength of 2790 nm, has been specificallydesigned to occupy the middle ground between the carbondioxide and Er:YAG lasers, and has shown early promise.28

The initial excitement surrounding the ablative laserswas largely dampened by their unacceptable downtime andtroublesome side-effects.11,21,26,27 By the end of the 1990sthere was a move towards minimally invasive and lowdowntime procedures, giving rise to a generation of non-ablative resurfacing lasers.

Non-ablative resurfacing lasers

By definition, non-ablative resurfacing lasers aim to sparethe epidermis either relatively or absolutely, while stillallowing bulk heating and denaturation of the dermal pro-teins.11,14,20,29 This would, in theory, allow for the beneficialeffects of tissue remodelling and skin tightening, as seenwith the ablative lasers, yet with decreased recovery timeand lower risk of scarring, dyspigmentation and infec-tion.11,20 In essence, lasers seeking coloured dermal targets

such as haemoglobin and deeper melanin are non-ablativelasers, but in current nomenclature non-ablative lasers arethose that target dermal water while sparing the sametarget, water, in the epidermis. Usually this is done bycooling the epidermis and keeping this layer at a tempera-ture that is non-destructive, yet allowing the dermis toreach an injurious temperature stimulating dermal remod-elling.20 To get this balance right is very difficult and hard toachieve in reality. Lasers in the infrared 1320 to 1540 nmrange, along with other modalities such as RF, focusedultrasound and IPL, have all been trialled as non-ablativeresurfacing therapies.11,20,21,27 Although these wavelengthsare much better tolerated than their fully ablative counter-parts,11 the clinical results achieved are often subtle, leavingpatients and practitioners underwhelmed.11,14,19,21 In addi-tion, it was observed that the results differed betweenindividuals, multiple treatments were necessary, and main-tenance with repeat treatments was sometimes required.21

In practice, the results achieved with these laser deviceswere so disappointing that they are no longer routinelyoffered to patients.

Fractionated lasers

The enthusiasm for both ablative and non-ablative resur-facing lasers had largely diminished by the turn of 2000. Itwas not until the advent of fractionated devices that interestin this area was rekindled. Fractionated lasers first madean appearance in 2004 (Fraxel, 1550 nm; Solta Medical,Hayward, CA) and represented the dawn of a new era in theapplication of laser technologies in dermatology.1113,19,29

These devices rely on high-fluence irradiation to form mul-tiple, discrete vertical cylinders of thermal damage withcompletely spared intervening areas. These microthermalzones (MTZ) measure up to 1.5 mm in depth and 100400mm in width and there may be up to 6400 treatment zonesper cm2.1114,21 The MTZ are separated by uninvolved tissue(accounting for up to 7585 per cent of the treated surfacearea), which act as a reservoir for tissue regeneration byproviding nutritional support and an intact microstructurefor keratinocyte and fibroblast migration.8,1114 The densitywith which MTZ are created is determined by the machinesettings and the number of passes chosen by the opera-tor.12,21 Fractionated lasers can be either non-ablative(i.e. leaving a histologically and functionally intact stra-tum corneum) or ablative (i.e. full-thickness destruction)(Fig. 4). Generally speaking, the fractional ablative devicesare more effective but tend to have longer recovery timethan the fractional non-ablative devices.14 Non-ablativedevices (Nd:YAG, Er: glass, Er: fibre and Er: thallium) havewavelengths of between 13201927 nm, while the ablatives(Er:YAG, Er:YSGG and carbon dioxide) have longer wave-lengths between 2940 and 10 600 nm.11,21

The most widely known and extensively evaluated frac-tionated laser, the 1550 nm erbium-glass laser (e.g. Fraxelre:store 1550 nm [Solta Medical, Hayward, CA, USA]), typi-cally produces erythema and oedema lasting 2 to 3 dayspost-procedure.1113 However, this non-ablative laser usuallyrequires multiple sessions ( 3) and may only show modest



improvements in rhytides and skin tightening when com-pared with the continuous carbon dioxide laser.21 Despitethis, results show a noticeable improvement over the earliernon-fractionated, non-ablative lasers and the popularity ofthe Fraxel re:store and several other devices (including the1440 nm Affirm [Cynosure, Westford, MA] and the 1440 nmStarLux unit [Palomar Medical Technologies, Burlington,MA, USA]) increased dramatically.11,21 A new platform(Fraxel Dual) combines a deeply penetrating 1550 nmerbium laser with a more superficial 1927 nm thuliumhandpiece in a single unit.29 The erbium laser stimulatesdermal collagen remodelling, while the 1927 nm thuliumbetter addresses dyspigmentation.29 The thulium laser hasalso shown early promise in the treatment of actinic kera-toses30 and actinic cheilitis and is discussed in more detail inPart two.The non-ablative fractionated devices progressed to

ablative fractionated versions of Erb:YAG (2940 nm: Pro-Fractional [Sciton, Palo Alto, CA, USA] and carbon dioxide(10,600 nm: carbon dioxide Fraxel re:pair [Solta Medical],AcuPulse/UltraPulse [Lumenis, San Jose, CA, USA]) toproduce results approaching those seen with the non-fractional ablative carbon dioxide laser.11,21 In addition, theside-effect profile of these lasers was greatly improved com-pared to their non-fractional counterparts, with pin-pointbleeding generally lasting less than 24 h and severe ery-thema lasting only 1 week.31 Aggressive use of these laserscan produce prolonged erythema but only a minority ofpatients are affected and the erythema is usually less severethan that seen with the non-fractional ablative devices.11,26

Given their favourable efficacy to adverse effect profile, theablative fractionated lasers are now considered by manyto be the gold standard in skin resurfacing.11,13,26,31 The

common indications for treatment with ablative fraction-ated laser include photoaging, dyspigmentation, acne scarrevision and superficial/deep rhytides.1114,21,31 Worldwide,over 15 manufacturers currently market fractionateddevices, both ablative and non-ablative.11

NON-LASER MODALITIES

While this review focuses primarily on lasers, we includenoteworthy non-laser devices in order to provide the readerwith a comprehensive review of therapeutic energy devicesavailable in dermatology practice.

Intense-pulsed light

IPL is the name given to filtered flash lamp devices thatemit non-coherent polychromatic radiation (4201300 nm)(Fig. 5), generally with a pulse duration of between2200 ms.15,32,33 Although IPL is not a laser (i.e. it is non-collimated, non-coherent and polychromatic), it is oftenreferred to as a laser by patients. As with lasers, IPL deviceshave been used to treat vascular lesions (especially super-ficial telangiectasias), dyschromia, unwanted hair, acne andsebaceous hyperplasia.15,21,3234 This impressive diversity canbe attributed, at least in part, to the use of selective filtersthat narrow the spectrum of wavelengths emitted from thedevice. High cut-off filters allow the emission of longerwavelengths, which reduce relative absorption by melanin,protecting darker skin types and relatively increasing non-specific absorption by water.15,32,34 Although there has beendiscussion of potential dermal heating and subsequent

Light device Wave form Spectrum

Laser

IPL Filter

Coherent and collimated

Non-coherent and non-collimated

Monochromatic

polychromatic

Figure 5 The features of laser and intense pulsed light. Laser light is defined by the cohesive, collimated and monochromatic photonsproduced.



collagen remodelling,21,3234 IPL is primarily indicated fortargeting melanin and haemoglobin and works best fortreating colour (red, brown) rather than texture. Appropri-ate filters (560590 nm) selectively emit light that corre-spond to the absorption peaks of haemoglobin, thustargeting vascular structures in a manner analogous to thetheory of selective photothermolysis.32,34 Potential adverseeffects include purpura, swelling, blistering, unintentionalphotoepilation (e.g. of the eyebrows), burns or scarring(especially if used aggressively or without considerationof skin type) demarcation lines (between treated anduntreated skin) and post-inflammatory dyspigmentation.32,34

In practice, IPL is used for confluent networks of tel-angiectasia, lentigines and poikiloderma and is a usefuladjunct to vascular lasers. It is well suited to field treatmentof the face and off-face areas such as the chest and limbswhere large areas can be covered by the large footprint (1 3 cm). In the setting of photodamage, aminolevulinic acidcan be added to pretreat the skin for 3060 min (short-contact photodynamic IPL) to enhance efficacy, as well as tophotodynamically reduce actinically induced dysplasticfield change.21,34

Radiofrequency

RF devices are non-ablative. They volumetrically heat thedermis and sub-dermal tissue when the applied electricalfield interacts with the tissues natural electrical resistancein accordance with Ohms law.21,35 The heat producedinduces collagen contraction and remodelling, resulting inthe desired clinical end-point of skin tightening. Increasedlocalised blood flow and improved lipolysis is thought toaccount for the beneficial effects seen in the treatment ofcellulite.35 The epidermis is spared from thermal damage bycontact cooling.35 The procedure produces significant dis-comfort and is time-consuming and the results, at least ofthe original system (ThermaCool, 2002 [Solta Medical]),were somewhat unimpressive and inconsistent.36 However,advances in hand piece design together with the use ofbipolar (and tri-polar or multipolar) RF appear to have mod-estly increased efficacy, while multiple passes at lower set-tings have increased patients tolerance.35 The adverseeffect profile of RF is favourable, with transient erythemaand oedema commonly occurring but blistering, scarringand contour changes seen only with aggressive treat-ment.21,35 Overall, the efficacy of this non-ablative techniqueremains modest when used as a monotherapy. RF can beused in combination with other modalities such as IPL,ultrasound and laser to produce more significant clinicalimprovements.35

Plasma

Plasma skin resurfacing uses ionised nitrogen gas to deliverheat energy directly to the skin. Unlike lasers or IPLsources, it is not a chromophore-dependent treatment. Itdoes not vaporise tissue but leaves a layer of intact,although denatured, epidermis that acts as a natural dress-ing, favouring accelerated wound healing. Histology on

plasma resurfacing patients suggests continued collagenproduction, the reduction of elastosis and progressive skinrejuvenation beyond 1 year after treatment.37

An interesting variation of plasma skin resurfacinginvolves delivery of this technology in a microplasma RFdevice via an array of closely applied micro-perforations inthe skin. Hand pieces either consist of a special skin rolleror have a stamping design, appearing to combine fractionalresurfacing in this technology.38 These plasma technologiesare particularly useful in the treatment of periocular andfacial static rhytides and for the adjunctive treatment ofpost-acne scarring.37,38

Ultrasound

High-intensity focused ultrasound (HIFU) was firstapproved for eyebrow lifting in America in 2009, and hassubsequently been trialled in other body regions for thetreatment of skin and tissue laxity.38 These devices useultrasonic energy to achieve precise microcoagulationzones (i.e. coagulative necrosis) deep in the dermis, subcu-taneous adipose tissue and superficial aponeurotic sys-tem.39,40 During the months following treatment, repair ofthe deep tissue damage leads to contraction and tissueremodelling, resulting in the desired aesthetic effect ofreduced skin laxity.39,40 The superficial dermis and collateraltissues are spared, which not only limits scarring and down-time but potentially permits HIFU to be used in Asian skinand other challenging skin types.39 However, as with the useof RF, inter-individual variation in response to HIFU treat-ment is significant.39 A study of patients treated with HIFUto the lower face and neck demonstrated no recordableresponse in up to 20 per cent of people,41 a level many wouldconsider unacceptable in private practice.

Cryolipolysis

Cryolipolysis, first described in 2008, is a process of cold-induced, non-invasive, selective destruction of subcutane-ous fat.9 It has applications for sculpting subcutaneoustissue and in the treatment of cellulite. Cooling applicatorsapplied to the skin surface extract heat at a set rate (mW/cm2) until a target temperature is reached (e.g. -7 to 1C)for a pre-determined time period.42 The low temperatureinduces a lobular panniculitis and thickening of the inter-lobular fibrous septae over several months after a singletreatment, resulting in apoptosis of adipocytes and anincrease in the collagen: adipose tissue ratio.9 Clinically,this manifests as a reduction in the thickness of the subcu-taneous fat layer. There is no clinical or histological evi-dence of damage to the overlying epidermis or dermis,including the adnexal structures,42 which seemingly limitslocal side-effects to discomfort and transient erythema atthe time of treatment.9,42 In addition, no deleterious effectson serum lipid levels or liver function tests have been dem-onstrated after serial measurements (over months) acrossmultiple studies.9,4244 Cryolipolysis may therefore offer asafe, efficacious and non-invasive alternative to surgicalliposuction for the removal of small to moderate amounts of



subcutaneous fat and cellulite.9,42 The role of lasers as anadjunct to surgical liposuction is also promising45 and willbe included in the second part of this review.In summary, the role of non-laser modalities, especially

RF, plasma, ultrasound and cryolipolysis in cosmetic der-matology is still evolving and it is likely to be some timebefore their contribution to clinical practice can be fullyascertained.

LASER USE AND REGULATIONS IN AUSTRALIA

Laser and IPL devices are used by a variety of practitionersacross Australia to treat a host of medical and cosmeticconcerns. Generally speaking, beauticians and cosmeticclinics with access to these technologies are more likely tobe involved in treating minor complaints (such as theremoval of unwanted hair), whereas more involved treat-ments, such as treating vascular malformations, correctingscars and managing a range of pigment disorders, areusually referred to cosmetic physicians, dermatologists andplastic surgeons.However, there has been ongoing concern amongst many

medically qualified laser practitioners over the regulationand safety of lasers and IPL use in Australia. Currently, nonational guidelines are in place to dictate the level of train-ing or accreditation an individual must possess to beallowed to offer these therapies to the public. In essence, inmost Australian states and in the Northern Territory, thefield is largely unregulated any individual with the meansand inclination can obtain a laser and/or IPL device andbegin practicing. The Therapeutic Goods Administrationregisters laser and IPL devices when they are imported fortherapeutic purposes. Hair removal is not considered atherapeutic purpose and therefore these machines do notneed to be registered despite the potential for seriousadverse effects. This is reflected by reports in the popularmedia on thermal injuries sustained by individuals under-going treatment by practitioners with no formal medicaltraining.4648 There is also an Australian support group forindividuals adversely affected by IPL and laser treatments,which can be found online.49

The Australian Radiation Protection and Nuclear SafetyAgency, the Federal Government body responsible for regu-lating laser and IPL devices, has so far been unable toprovide leadership on this issue. Consequently, the stategovernments of Queensland and Western Australia have setup their own laser authorities, namely QLD RadiationHealth and the Radiological Council of WA. These govern-ment bodies require any potential practitioner to attendradiation safety courses and to obtain a radiation/lasersafety officers certificate before being allowed to offer treat-ments to the public. In a report commissioned in 1999 by theNew South Wales state government similar concerns wereraised about the safety of lasers and the need for regulationsin the local industry. Unfortunately, most of the initiativesrecommended have yet to be implemented.With the variation of both regulations and mandatory

training requirements across the country, it would appearthat the onus of responsibility lies largely with the con-

sumer. It is imperative that they possess the requisiteknowledge and broad understanding of the nature of thetreatment they are about to undertake and the risksinvolved. It may also be prudent for prospective clients toenquire about the level of training their operator hasreceived, as suggested by a recent consumer review.50

CONCLUSION

Lasers have had a significant impact on the treatment ofcutaneous conditions over the last 50 years. New laser tech-nologies, such as fractionation, along with the developmentof other non-laser treatments, have expanded the treatmentoptions available to rejuvenate ageing skin, while estab-lished lasers continue to gain popularity in the treatment ofvascular lesions and the removal of hair and tattoos. Aslaser and IPL devices have become increasingly availableand affordable, and as they are being delivered by a range ofpractitioners with varying experience and training, theneed for government legislation on safety and training inthis field has assumed greater significance.In the second part of this review, we build on the founda-

tions of laser theory and technology to focus on laser treat-ment of discrete clinical entities. We provide the readerwith a concise description of the pathology of specificlesions and a justification of treatment options as they relateto the physical properties of individual lesions and the spe-cific laser devices utilised. We review the currently avail-able literature and utilise the experience of the lead authorsto explain and guide proposed treatments to maximise effi-cacy and avoid common pitfalls.

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