Ch 136 Bolognia Principles Of Laser-Skin Interactions

Front 1

LASER

Back 1

light amplification by stimulated emission of radiation

Front 2

4 essential components of lasers

Back 2

1. gas, liquid, or solid medium can be excited to generate laser light by stimulate emission
2. source of energy to excite medium (pumping system)
3. mirros at ends of laser forming optical cavity that surrounds medium and comfines amplification process
4. Delivery system

Front 3

Population inversion

Back 3

50% of atmos within laser medium are excited by energy source, photons more likely to encouter excited atom --> stimulated emission

Front 4

Laser light properties

Back 4

monochromicity
coherence
collimation
high intensity

Front 5

Laser light continuous vs pulsed wave light

Back 5

continuous: constant beam, Argon, limited peak power
pulsing laser: high peak powers, q-switched

Front 6

Q switched

Back 6

very sourt pulses at high peak power
Q = quality factor of energy storage in lasing medium changed suddenly to produce short intense burst of light
repetition expressed in Hz

Front 7

Quasicontinuous lasers

Back 7

lasers wmit rapid train of low energy pulses surgically like continuous wave lasers

Front 8

Dermatologic Q-switched lasers
pulses?
fluence?
used for?

Back 8

pulses of 10 - 100 ns
fluence 2 - 10 j/cm2
short high power pulses for tattoss and pigmented lesions

Front 9

Laser light interacts w skin in 4 ways

Back 9

1. relfection 4-7%
2. scattering
3. transmission
4. absorption

Front 10

reflection indices of air and stratum corneum

Back 10

air = o
sc = 1.45

Fresnel reflectance: relfectance to the angle of incidence (least reflectanc with perpendiular incident light) and plan of polarization as well as skin

Front 11

chromophore

Back 11

electronic excitement of chromophore by absorption of photon
UV light electronic excitement
Infrared vibrational excitement

Front 12

Infrared absorption

Back 12

vibrational excitement C2 UV absoprtion electronic excitement

Front 13

Chromophores skin

Back 13

water, Hb, melanin

Front 14

Hemoblobin absoprtion

Back 14

blood oxyhemoblobin reduced hemoblobin absorption strong bands in UV blue grena and yellow

Front 15

Scattering of light

Back 15

dermis

Front 16

Below 300 nm wavelength absorption?

Back 16

urocanic acid and DNA

Front 17

> 1300 nm absorption

Back 17

pentration decreases because increase absorption by water

Front 18

most deeply penetrating wavelengths

Back 18

650 to 1200 nm and near-IR

Front 19

least penetrating wavelengths

Back 19

far UV and far IR

Front 20

Heat shock response

Back 20

exposed to high temperatures cells
inhibition of normal protein syntehsis and induction of synthesis of heat shock proteins (HSPs) some resistnace to thermal injury

Front 21

Elastin heat stable

Back 21

yes

Front 22

Type I collagen
melting transition?

Back 22

MC collagen subtype dermis
sharp melting transtion to fibrillar form 60 to 70 C (140 to 160 F)

Front 23

collimated

Back 23

in phase and parallel

Front 24

gas lasers

Back 24

Argon
CO2
Copper vapor
Helium-neon
Krypton
Xenon Chloride (excmer)

Front 25

Liquid lasers

Back 25

Rhodamine dye dissoved in organic solvent

Front 26

crystal lasers

Back 26

alexandrite
Erbium-doped yttrium aluminum garnet (YAG)
Holmium-doped YAG
Neodymium-doped YAG
Potassium titanyl phosphate
Ruby

Front 27

Semiconductor laser

Back 27

Diode (aluminum gallium arsenide)

Front 28

Solid Lasers

Back 28

1. Crystal
2. Semiconductor

Front 29

Selected photothermolysis

Back 29

selected heating of targets in thedermis

Front 30

goal to keep skin temperature below

Back 30

60 to 70 C (140 to 160 F)

Front 31

laser power

Back 31

rate of energy delivery

Front 32

Longer exposed to laser energy

Back 32

more thermal energy to neighboring tissues
limit exposure time for gluence then laser power (rate of energy delivery) increase

Front 33

heat transfer in tissue

Back 33

conduction
thermal relaxation

Front 34

thermal relaxation

Back 34

conduction

Front 35

tissue relaxation time

Back 35

tissue to lose 50% of heat

Front 36

clean ablation

Back 36

heat faster than heat is conducted to surrounding tissues

Front 37

pulse duration longer than thermal relaxation time

Back 37

damage to tissue

Front 38

TRT

Back 38

size and shape
object 1/2 size cool in 1/4 time

Front 39

TRT

Back 39

in seconds in approimately = to square of the target dimension in millimeters

Front 40

TRT shapes

Back 40

spheres cool faster than cylinders
planes cool slow

Front 41

tattoo ink particle
diameter
TRT
laser pulse duration

Back 41

diameter 0.1 um
TRT 10 ns
PULSE DURATION 10 ns

Front 42

Melanosome
diameter
TRT
laser pulse duration

Back 42

diameter 0.5 um
TRT 250 ns
Laser pulse duration 10 - 100 ns

Front 43

PWS vessels
diameter
TRT
laser pulse duration

Back 43

diameter 30 - 100 um
TRT 1 - 10 ms
Laser pulse duration 0.4 - 20 ms

Front 44

Terminal hair follicle
diameter
TRT
laser pulse duration

Back 44

diameter 300 um
TRT 100 ms
Laser pulse duration 3 - 100 ms

Front 45

Leg Vein

Back 45

diameter 1 mm
TRT 1 s
Laser pulse duration 0.1 s

Front 46

viable light

Back 46

400 - 700 nm

Front 47

red light

Back 47

700 nm

Front 48

optimal pulse duration

Back 48

TRT

Front 49

Energy

Back 49

fundamental unit of work
Joules

Front 50

Power

Back 50

rate at which energy is delivered
Watts

Front 51

Fluence

Back 51

amount of energy per unit of area
J/CM2

Front 52

Irradiance

Back 52

power delivered per unit area
W/cm2

Front 53

pulse duration (pusle width)

Back 53

laser exposure duration
seconds

Front 54

spot size

Back 54

diameter of the laser beam on skin surface
mm

Front 55

Pulsed laser

Back 55

photomechanical effects
sudden heating sudden theraml expansion
acoustic and/or shock waves
rupture or increase permeabiltiy of cell membranes'cavitation
temperature and pressure evaporation of water leads to the appearnce expasnion and vilent collapse of vapor bublles, vessel ruptures emitting pusles , 20 ms

Front 56

pusle laser < 20 ms

Back 56

cavitation