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Laser

đź’ˇ
Light Amplification by Stimmulated Emmission of Radiation
 
Definition
  • A single wavelength qualified as monochromatic
  • Coherence: temporal and spatial synchronization of the beam
  • Collimation: parallel orientation of the beam
  • Chromophores are the targets of the laser light
    • Achieved by adjusting the: wavelength, pulse duration, spot size, fluence corresponding to the energy per surface area
    • Oxyhemoglobin
    • Melanin
    • Water
    • Artificial pigments (tattoos)
 
Operating modes
  • Continuous mode
    • O modo contĂ­nuo Ă© usado quando o dano secundário Ă© desejado, por exemplo ablação de Bowen
  • Pulse mode
    • O facto de ser pulsado permite que o cromĂłforo (ex. a água) arrefeça e volte a temperatura habitual do tecido evitando o dano secundário.
  • Laser beam splitting | fractionation
    • Involved delivering the laser energy in a dotted pattern
    • This results in either coagulation or ablation of wells surrounded by intact tissue
    • Healing process only in treated microzones
    • Shorter healingReduced side effects
    • Greater effectiveness of treatment because possibility of reaching greater depths
    • Main indications
      • Skin rejuvenation
      • Hypo or hypertrophic scars
      • Stretch marks
 
Mechanism of action
  • Photothermal action
    • Conversion of light into heat with diffusion by conduction
    • Main application: vascular or hair removal
    • Thermal effects: protein denaturation, coagulation necrosis (50-90ÂşC for a period around 1 second) and vaporization (>100ÂşC for a few microseconds to a few tenths of a second)
    • Depend on the thermal relaxation time of the target - time required for the maximum temperature reached at the center of the target to decrease by 50%
    • If the emission duration is less than the thermal relaxation time, this is referred as selective photothermolysis
      • This concept is mainly used in ablative lasers, whose main target is water.
  • Photomechanical effect
    • Sudden change in the target volume, causing thermoelastic waves with subsequent mechanical rupture
    • Induced by pulses so short that the heat generated at the target does not have time to diffuse
    • Triggered or Q-switched lasers allow working with pulse durations on the order of nanoseconds (10^[-9]s)
    • The new generation of lasers in picoseconds (10^[-12]s) resulting in an even more pronounced photomechanical effect
  • Photoablative effect
    • Mechanical disintegration by vaporization of tissues with a high water content (epidermis, dermis)
  • Photochemical action
    • Used in dynamic phototherapy with the administration of a photosensitizer that accumulates in the target and then absorbs light, tiggering prodution of oxygen radicals
 
Main lasers used in dermatology
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Pulsed lamps (IPL and OPL)
  • Intense Pulsed Light (IPL) lamps and their more recent evolution Optimized Pulsed Light (OPL) lamps are similar to lasers
  • Unlike lasers, these lamps emit light that is neither coherent nor monochromatic
  • On the contrary, their spectrum is very broad and filters must be used to make their action more specific on hemoglobin, melanin or water
  • Also, they are in contact with the skin via an optical system
 
Indicações
  • Dermabrasion - ultrapulsed CO2, erbium:YAG
  • Vascular: pulsed dye, Nd:YAG/KTP
    • The absorption spectrum of oxyhemoglobin ranges from 490 to 600nm, with three peaks: 418, 542 and 577nm. Only the last two are useful to lasers due to the depth of penetration required for the wave length to be effective
    • Pulsed dye lasers (PDL) emit in the yellow orange spectrum between 585 and 600nm
      • Multiple generations differ in their pulse duration, ranging from 0,45 to 40ms
      • Very short pulse (i.e. 0,45ms) - well below the thermal relaxation time of small caliber superficial vessels (1-10ms) will lead to rapid thermal damage with vessel rupture and subsequenmt purpura (selective photothermolysis
      • Pulse duration greater than 1,5ms prevents post-procedural purpura thanks to more gradual heating of the target (selective photocoagulation)
      • Longer pulse durations also allow target vessels to be treated
    • Nd:YAG laser | KTP laser
      • Emits at 532nm
      • Pulse duration of 2-50ms reduce risk of purpura
      • Penetration dept is reduced due to the shorter wavelength compared to those used with pulsed dye lasers
      • This disadvantage compensated by much larger spot sizes than before (up to 12mm)
      • Increased risk of pigmentation disorders due to absorption by melanin, specially in dark skin types
    • Argon, krypton, copper vapor lasers → historic
    • Near-infrared lasers
      • Emit wavelenghts between 755 and 1200nm
      • Include alexandrite laser (755nm), long-pulse Nd:YAG laser (1064nm) and laser diodes (800-980nm)
      • These wavelengths, which are higher than the selective absorption peaks of oxyhemoglobin are much penetrating and can be used to treat larger caliber vessels
      • Pulse durations used are in the range of 10 to 100ms
      • Higher fluences are required due to the relatively low absorption of near infrared laser light by oxyhemoglobin, thereby increasing the risk of scarring
      • The good absorption of these wavelenths by deoxyhemoglobin allows for the effective treatment of the vascular lesions that are primarily venous in nature
    • Pulsed filtered lamps (IPL or OPL) can be used for vascular lesions, with a bandwidth between 515 and 1200nm
    • Indications
      • Flat angioma
      • Telangiectasias
      • Erythrosis (associated with skin aging)
      • Angiokeratomas (variable response)
  • Pigmentation: alexandrite, ruby, QS Nd:YAG
    • These lasers target either the melanin contained in melanosomes or the mineral or organic pigments used in tattoos
    • Ruby laser (694nm)
    • Alexandrite (755nm)
    • Nd:YAG (1064 and 532nm)
    • These lasers operate in triggered pulse mode (known as Q-Switched) with extremely short pulse durations, ranging from nanoseconds to tens of nanoseconds.
      • These durations are close to the thermal relaxation time of melanosomes and allow for faster and more complete removal than with lasers operating in miliseconds, which remove pigment minly through themal effects.
      • In the case of tattoos, the Q-switched laser results in a quasi-selective essentially mechanical photothermolysis of the pigments, with fragmentation of the pigments and secondary elimination by phagocytosis, followed by transport and storage in the lymph nodes
    • Indications
      • Benign melanocytic lesions
        • CafĂ©-au-lait spots, Becker nevus → may reccur
        • Best indications: solar lentigines, ephelides
        • Doesn’t allow histologic control
        • Ota and Ito nevus
      • Tattos
        • Q-switched lasers are the gold standard
        • New generation of lasers called picosecond lasers
  • Ablative lasers
    • Lasers whose wavelength is mainly absorbed by water
      • CO2 lasers (10.600nm)
      • Erbium-YAG (2.940nm)
      • Erbium-YSGG (2.790nm)
    • Main effects are based onn the vaporization of epidermal and dermal tissue and coagulation that varies in intensity depending on the wavelengths used
    • Main indications
      • Wrinkles
      • Scars
      • Benign raised skin lesions: warts, seborrheic keratoses, xanthelasma, syringomas
    • Continuous CO2 laser
      • Radiation absorbed by intra and extracellular water and causes non-selective vaporization through a thermal effect
      • Its long pulse duration leads to tissue loss with coagulation necrosis of the margins
      • Vaporization causes emission of potentially toxic and infectious fumes (HPV) → need protection and fume extractor
      • Perform under local, regional or systemic anesthesia
      • Focused mode: incisions to be made with almost no bleeding, thanks to its hemostatic effect on the small vessels at the edges
      • Wider beam of defused mode → most used, allows tissue to be vaporized over a larger area
    • Pulsed CO2 lasers and erbium-YAG lasers
      • Short pulse durations of around 0,5 to 1ms enable pulse or ultra-pulsed CO2 lasers to significatly reduce collateral thermal damage
      • Pulse duration of erbium-YAG lasers ranges from 0,2 to 0,8ms
        • When the pulse duration is short, the ablative effect is purely mechanical, with no residual coagulation
        • However, increasing the pulse duration adds a thermal effect allowing the erbium laser to mimic a CO2 laser
        • Compared to CO2 laser, erbium YAG laser has the disadvantage of causing annowying pin-point cappillary bleeding during treatment, as well as projections from which it is necessary to protect oneself. On the other hand post operative erythema is shorter in duration
        • Erbium YAG has less effect on collagen regeneration and therefore skin tightening
      • Both lasers cause a loss of epidermal substance with moderate damage to the superficial dermis. This is followed by secondary collagen synthesis with a rejuvenating effect
      • Indications
        • Shallow wrinkles, particularly around the mouth and eyes
        • Sun damage
        • Certain shallow atrophic scars
        • Certain thin hypertrophic lesions (verrucous nevi, seborrheic keratoses, facial angiofibromas, rhinophyma)
      • Risk of scarring is not negligible, particularly in dark skin types
      • Perioperative follow-up
        • Anti-herpetic virostatic prophylaxis
        • Post operative dressings
  • Hair removal
    • Main goal is to achieve permanent hair removal through thermal effects
    • Main wavelengths are those absorbed by melanin
      • Alexandrite (755nm)
      • Diode (810nm)
      • Nd:YAG (1064nm)
      • IPL
      • Q-switched lasers (Nd:YAG or ruby) act only by mechanical effect, very popular in Asia, however, they only provide a temporary heir removal effect lasting 3 to 4 months
    • The available cromophore is therefore the melanin present in the shaft but also, and above all, in the hair bulb
    • Indications
      • Hirsutism
      • Hypertrichosis
    • Contraindications
      • White, blod or red hair
      • Tanned skin (prefer lasers with longer wave length Nd:YAG, which can penetrate deeper and avoid superficial melanin)
    • Duration of treatment
      • = hair cycle in order to target all hairs in the anagen phase
      • Varies from 12 to 18 months depending on the areas to be treated
      • Sessions scheduled every 4 weeks to 3 months
  • Acne
    • Inflammatory acne is also a potential target
    • Wavelengths inthe visible spectrum will mainly act on propionibacterium acnes
    • Mid-infrared wavelengths (1450nm) target the sebaceous glands and cause them to shrink under the effect of heat
    • Photodynamic therapy with the application of 5-ALA and the use of visible light or more recently the application of gold particles that specifically absorb an 800nm laser can thermally destroy the sebaceous glands
  • Excimer laser and lamp
    • Emits ingle wavelength of 308nm
    • Allows high doses to be delivered in highly targeted manner
    • Indications: psoriasis, vitiligo, hypochromic scars
  • Radiofrequencies
    • Emit an electrical current of variable frequency rather than light
    • Also play a role because their thermal effect on the dermis can be similar to that of ablative or non-ablative lasers
    • Used mainly to treat acne scars and wrinkles
    • Used in interventional radiology for the desctructive treatment of liver and lung metastased from melanoma
 
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Lasers a ter: Must have non ablative fractional laser and PDL
 
Alternativas para começar sem grande investimento:
  • TermocautĂ©rio
  • Radiofrequency scalpel
  • CO2 laser
  • EletrocautĂ©rio
 
 
Hair reduction laser
Fisiopatologia
  • Laser sĂł apanha os pĂŞlos em anagĂ©nese. PĂŞlos em telogĂ©nese nĂŁo, daĂ­ ser necessário várias sessões
  • PĂŞlo escuro - usar laser que target melanina
  • PĂŞlo claro - laser que target hemoglobina
Onde fazer
  • ClĂ­nica do pĂŞlo
  • Lasers curso - luĂ­s leite
História física e exame objetivo prévio
  • Detailed history: menstrual, endocrine, medication, infection (HSV), endocrine
  • Physical exam: hair distribution & thickness; Fitzpatrick skin type to select appropriate laser & settings
  • Scar history: inquire about tendencies for keloid and hypertrophic scarring
  • Psychosocial assessment
  • Medication: identify use of photosensitizing drugs, certain antibiotics, isotretinoin, or hormonal therapies that may affect outcome
Guidelines of care for laser and IPL hair reduction
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  • Pre treatment instructions
    • Sun exposure
    • Heir removal methods should be stopped
    • Skin products: discontinue 7 days before (retinoids, peels)
    • Clean the treatment area
Type of laser of hair removal
  • Ruby 694nm
  • Alexandrite 755nm
  • Diode laser 810nm
  • Nd:YAG laser
  • IPL 400-1400nm - energy base device just for skin type I and II because very superficial
Laser CO2
Por definição o laser CO2 é ablativo
Fraccionado é quando se faz numa área em que deixa espaços poupados
Podemos querer querer ser mais ou menos seletivos
O laser vai aquecer seletivamente um cromoforo. No comprimento de onda usado é a água que aquece e provoca dano. O facto de ser pulsado permite que a água arrefeça e volte a temperatura habitual do tecido evitando o dano secundário.
O modo contínuo é usado quando o dano secundário é desejado, por exemplo ablação de Bowen
Para cicatrizes de acne
  • Power 8W
  • Micro spacing 500
Antes do laser
  • Lambdalina
  • Bloqueio regional
ApĂłs o laser fazer
  • Fucidine + Betametasona na primeira semana
  • Se muito hemorrágico pode se por dermovate que tem efeito vasoconstritor
  • Depois fazer quinostasa intercalado com Ketrel
  • Lavagem com cyteal
Ablação de CBC superficial ou queilite actinica - usar ponta com laser contínuo e fazer 2 aplicações perto seguida de 1 longe para a cicatriz contrair
  • Queilite actinica - 3W
Laser PDL
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ApĂłs o laser basta cicabio
Pode se fazer na mucosa
Nos membros inferiores nĂŁo tem uma resposta tĂŁo boa
Fazer EMLA ou lamdalina 30 min antes
Ex fluĂŞncia 6-8,5 J pulso 2,5ms spot 5mm
TĂ©cnica para manchas de vinho do Porto: usar Imiquimod 3-4 dias depois (nĂŁo antes porque causa Ăşlcera)
Accure
laser acne - comprimento de onda de 1726 nm a absorção do sebo é maior que a água ideal para acne. accure
It’s a different medium than co2 hence different length
4 sessions for acne 6 weeks apart
Device 100.000
Laser Q-Switch
Indicações:
  • Melasma
Máquina:
  • Q-Plus Evo
Efeitos secundários
  • Hiperpigmentação pĂłs inflamatĂłria
    • Melanose dos sulcos palmares - maior risco de hiperpigmentação pĂłs inflamatĂłria (artigo australiano?)
Parâmetros:
 
 
 
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