Laser Tissue Interaction (2) 6f6y20

L A S E R

ight mplification by the timulated mission of adiation

L stands for Light

• many colors • doesn't come in a narrow beam • can‘t be focused to as a small spot • can’t be as intense as a laser without expending tremendous amounts of energy.

• one color • thin beam • can be focused to a tiny spot. • can be made very intense / not intense at all

A in laser stands for amplification  A very bright intense beam of light can be created.  The laser may be activated by a few photons, but then many,

many more are generated.  The initial light is amplified to make a very bright compact beam.

S in laser stands for stimulated. Stimulated → the photons are amplified by stimulating an atom to release more photons The atom is stimulated by another photon to release its photon.

• Emission → giving off of photons. • The excited atom emits a photon when another photon comes by. • In 1917, Einstein → Stimulated Emission.

Radiation → bad reputation. For lasers→ radiation refers to the photons which are being emitted.

Monochromatic Collimation Coherence

 Continues wave

: emisi terus menerus.

 Shuttering

: mekanisme “buka tutup”

 Pulsed/superpulsed

waktu.  Q-Switched

: sejumlah emisi intensitas tinggi dengan interval

: energi dikumpulkan di “optic cavity” sebelum diemisikan

BEAM TYPE Power (W) 100

Time ( sec ) Continuous Wave

BEAM TYPE Power (W) 100

Time ( sec ) Shuttered Continuous Wave

BEAM TYPE Power (W) 1000

Time ( msec ) Pulsed

BEAM TYPE Power (W) 2000

Time ( msec ) Superpulsed

BEAM TYPE Power (W) 1 x 106

Time ( nsec ) Q-Switched

TISSUE OPTICS TYPICAL CHROMOPHORE BIOLOGIC EFFECT SELECTIVE PHOTOTHERMOLYSIS PARAMETERS OF LASER LIGHT

● REFLECTION ● ABSORPTION ● SCATTERING ● TRANSMISSION

● REFLECTION - about 4-6% of light reflected

● ABSORPTION The transformation of radiant energy to another form of energy ( usually heat) by interacting with matter the most important step to achieve any reaction Grothus Draper Law (No Absorption No Effect) result : thermal or non-thermal reaction based on the beer’s law, 90% of lights is absorbed in epidermis

● SCATTERING Imprecise absorption of laser energy by a biologic system resulting in a diffuse effect on tissue mainly forward in direction may result in light ing back through the medium (backscattering) wavelength 600 – 1200 nm = optical windows → low scattering

● TRANSMISSION The age of laser energy through a biologic tissue without producing any effect wavelength < 300nm-400nm penetrating < 0,1 mm wavelength 600-1200nm penetrating deeper with less scattering

Tissue/Cell content : 70 - 80 % are water CO2 Laser irradiation --> immediately * Absorb by water in the cell * Convert to Heat --> vapor * Build up intracellular pressure * Cell Explosion

Explosion ->Evaporation/ablation Depth of Penetration : Pulse CO2 Laser --> 50 - 100 micron Ebrium YAG Laser --> 10 - 30 micron LSR requirement : * High Power Density * Short Irradiation Time --->Shorter than “ Thermal Relaxation Time”

Light-tissue interactions can be broken down into : The transport of light in tissue Absorption of light and heat generation in tissue Localized temperature elevation in the target tissue Diffusion away from the target

Hemoglobin and oxy-hemoglobin Melanin, Melanosome Collagen Water Tatto Ink

Absorption of Chromophoresgraph

● Photothermal ▪ Thermal injury to cells ▪ Coagulation ▪ Vaporization ● Photo Chemical ▪ Photodynamic reactions ● Photostimulation ● Photomechanical

• Tissue interactions →Transformation of Light Energy into Thermal Energy. • Effect : destroy pathologic tissue --> Coagulate, Vaporize, Ablate, Cut. • “ THERMAL EFFECT “.

• 1967 : Endre Mester -- Carcinogenic Effect ---> observered hair growth after laser irradiation in depilated mice. • He named it LASER BIOSTIMULATION • “ NON - THERMAL EFFECT “ • Low Power Laser Irradiation

Thermal Injury to cells ● < 43º C : the skin remain unharmed ● 43 - 50º C : tissue necrosis (after several minutes) ● 45º C : fibroblast die after about 20 minutes ● 70 - 100º C : irreversible thermal damage

Collagen Reaction to Temperature Elevation - Less than 40o C : no effect - 40o – 53o C : Protein Denaturation - 55o – 60o C : Protein Degradation - 63o – 90o C : Protein Coagulation.

Coagulation ● Maybe reversible or irreversible ● ≥ 61 – 63º C : ▫ reversible non-lethal thermal damage = collagen shrinkage ● 61- 71º C : ▪ The goal of laser resurfacing ▪ Achieve the desired shrinkage of collagen without completely denaturating collagen

Vaporization ● 70 - 100º C : irreversible thermal damage and denaturation → tissue necrosis ● 100º C : vaporization ● 100 - 120º C : fluctuation between vaporization and charring ● 120 - 200º C : charring occurs

"photo“ "thermo“ "lysis“

→ light → heat → destruction.

Selective photothermolysis therefore refers to the precise targeting of a structure or tissue using a specific wavelength of light with the intention of absorbing light into that target area alone. The energy directed into the target area produces sufficient heat to damage the target while allowing the surrounding area to remain relatively untouched.

♣ ♣ ♣ ♣ ♣ ♣

WAVELENGTH PULSED DURATION ENERGY FLUENCE IRRADIANCE SPOT SIZE TISSUE COOLING

WAVELENGTH ● Spesific wavelength → will be absorbed by specific chromophore If more than 1 chromophore → absorption will be divided → competitive absorption ● Wavelength should be near the max. absorption of target chromophore & minimum competitive from other chromophore

PULSE DURATION Pulse Duration or pulse width is the amount of time it takes to deliver the energy. The pulse duration must be shorter than the thermal relaxation time of the target. If the pulse duration is longer than the thermal relaxation time, the surrounding tissue receives thermal damage.

THERMAL RELAXATION TIME (TRT) = waktu yang dibutuhkan untuk jaringan yang dilaser kehilangan 50 % dari panasnya melalui difusi. Besaran waktu : 100 mikro detik hingga 10 millidetik.

ENERGY FLUENCE ● The energy delivered per unit area ● As it increases the destructive force increases ● For most pulsed lasers ENERGY FLUENCE = Laser power output x pulse duration Laser beam cross-sectional area ENERGY FLUENCE = Joules = Watts x sec cm² cm²

IRRADIANCE ● The rate of energy delivery per unit area to an object = Power Density ● Generally used when referring to continuous wave laser, ec. CO2 Laser IRRADIANCE =

______Laser power output____ = Watts Laser beam cross-sectional area cm²

WATTS = Joules Sec

SPOT SIZE Defined as the width of the laser beam. Spot size determines the area to be treated. Lasers vary widely on the spot sizes available for use. Spot sizes determine the depth of penetration. The larger the spot size of the laser beam, the more fluence must be used to achieve the same result. Lasers have limits as to the amount of energy that can be used with the larger spot sizes. Another advantage of the larger spot size is the ability to treat larger areas of the body very quickly.

TISSUE COOLING ● Cooling Method ▪ Cold air cooling ▪ cooling ▪ Dynamic cooling

■ The Role of Cooling Reduce discomfort during treatment, protect epidermis and collateral dermal damage, allow using higher fluence and reducing number of treatments

TERMINOLOGI POWER = ukuran kemampuan kerja yang diukur dalam Joule/detik = Watt. POWER DENSITY = besar daya yang disampaikan per satuan luas yang diukur dalam Watt/cm2 ENERGY = kapasitas kerja diukur dalam JOULE / watt x waktu

FLUENCE = total energi yang disampaikan per-unit luas = Joule/cm2 SPOT SIZE = besar bercak laser pada target diukur diameternya namun dalam perhitungan dalam satuan luas (mm2) PULSE ENERGY = energi dari satu pulsa dari SuperPulse atau UltraPulse -- mjoule -> pulsa sangat pendek, Peak Power tinggi