bio-medical optics lab., yonsei university

1Bio-Medical Optics Lab., Yonsei University

치료기기학 - 레이저치료 강의노트 III

Medical Lasers

Fall Semester 2004

Bio-Medical Optics Lab., Yonsei University

Absorption Spectra of Tissue Chromophores

Absorption Spectra of Tissue Chromophores

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0.01

1

100

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1000 104

Oxy-hemoglobinDeoxy-hemoglobinWater

Ab

sorp

tio

n C

oef

fici

ent

(1/c

m)

Wavelength (nm)

Optical Window

He-

Ne

Ti:

Sap

ph

ire

Dio

de

Nd

:YA

G

Ho

:YA

G

Er:

YA

G

CO

2

Melanin


CO2 LaserCO2 Laser

Wavelength: 10,600 nm or 10.6 m (most commonly used, mid infrared)Laser medium: CO2 gas (mixed with nitrogen and helium)Excitation: Electrical arc through the gasCharacteristics

Very efficient lasing (10 – 20% of electrical power is converted to the emitted power. Others normally falls into 1 – 2%) No optical fiber delivery – An articulated arm is used for delivery or hollow core fiber delivery Invisible to the naked eye Normally used along with He-Ne laser (red) Can harm cornea seriously Need to wear normal glass or plastic eyeware


CO2 Laser (continued)CO2 Laser (continued)

Applications: numerous, one of the main workhorses20W CW: Applications in vaporization of tissuesPulsed, 500W peak power, 20 – 40W average power: adjusted to appropriate level, it can be used for both vaporization and cutting of tissues without charringSkin resurfacing (pulsed, superpulsed)


Nd:YAG LaserNd:YAG LaserWavelength: 1064 nm or 1.064 m (most common)Laser medium: Nd ions dispersed in a crystal of yttrium-aluminum-garnet (YAG)Excitation:

Lamp pumped: old technologyDiode laser pumped: new technology (very durable, compact and energy efficient but expensive)

Applications: numerous, one of the main workhorses

100 W CW for surgery (e.g. prostate)Coagulation and vaporization of tumors (breast cancer, liver cancer, etc)Q-switched Nd:YAG laser (10 – 30 ns pulse duration)

Can cause retinal injury (goggle needed)


Argon-ion laserArgon-ion laser

Wavelength: 488 nm (blue), 514.5 nm (green)Laser medium: Argon gas at about 1 torr of pressureExcitation: ElectricalOutput: CW mode, power range typically in the range of 100 mW to 20WApplications

Most important medical uses in ophthalmology (retinal detachment)Light sources for bioimagingRaman spectroscopyPumping other lasers

Can cause retinal injury (goggle needed)


Diode Lasers (Semiconductor Lasers)

Diode Lasers (Semiconductor Lasers)

Wavelength: From 400 nm to 1900 nm (dependent on the laser medium)Laser medium:

GaN ~400 nm: 5 mW, 200 mWAlGaAs ~800 nm (near IR): 5 mW, 50 mW, 4 WInGaAs ~670 nm (red): 5 mW, 40 mW, 400 mW ~635 nm (bright red): 5 mW

Excitation: ElectricalCharacteristics

Interface between the active layer and air works as cavity mirrorExtremely high efficiency in light generationExtremely small size (300 m x 100m x 100m)

ApplicationsAiming beamLow level laser therapy: pain relief, wound healingOphthalmology


High Power Diode LaserHigh Power Diode Laser

Diode bars containing many emitters: ~800 nm, 1 – 20WApplications

Cutting of tissue, hair removalOptical pumping of Nd:YAG laser (more efficient and compact)Heat treatment of tissues (BPH treatment etc)


Dye lasers (Liquid laser)Dye lasers (Liquid laser)

Wavelength: Continuously tunable from 400 nm to 900 nm with the change of dyeLaser medium: Fluorescent dyes dissolved in solventsExcitation

Pulsed dye laser: Flash lamp, KTP laser, excimer laserCW dye laser: Ar-ion laser

ApplicationsPhotodynamic therapyDermatologyOphthalmologyVascular disorders, selective target damages of blood vessels or pigment cells


Er:YAG and Ho:YAG lasersEr:YAG and Ho:YAG lasers

Er:YAG (Solid state laser, pulsed)Wavelength : 2.94 mmExcitation : Lamps or diodesUses articulated arm or special fibers such as sapphire crystal fibersWater absorption band : Relatively low collateral damage, may be used for microsurgeryApplications

Ablation of bone and tooth Microscopic surgery

Ho:YAG (Solid state laser, pulsed)Wavelength : 2.1 mmLess absorbed but can be delivered by regular fused silica fibersStrongly absorbed by waterApplications

Surgical cutting of bone and soft tissues


Excimer lasersExcimer lasersWavelength (gas laser, strong UV source)

ArF: 193 nmKrF: 249 nmXeCl: 308 nmXeF: 351 nm

Laser medium: Excited dimer gasCharacteristics

Strongly absorbed in tissues, especially in proteins, nucleic acids, etc…Photothermal ablation? or photochemical? (Leaves low collateral damage : cold laser)Up to 300 Hz or so

ApplicationsOphthalmology (LASIK, LASEK), microsurgery

ProblemsCorrosive and toxic gas, extremely expensive, dangerous UV emission (carcinogeniity problem)


Ti:Sapphire LaserTi:Sapphire Laser

Wavelength: Tunable between 690 and 1000 nmLaser medium: Ti3+ ions in a sapphire solid host (Al2O3)

Excitation: Optical, using an argon laser or a frequency-doubled Nd:YAG laserOutput: CW, nanoseconds and femtoseconds pulses, power typically in hundreds of milliwatts rangeApplications

Multiphoton microscopyMultiphoton photodynamic therapyTissue ablation


Free Electron LaserFree Electron Laser

Lasing methodFree electrons pass through an array of permanent magnetsElectrons modulated emits light

Wavelength (totally tunable)

By changing magnet array, light from extreme UV to millimeter wavelength can be obtained continuously

CharacteristicsStill building sizeNeed a team of scientist to operate

ApplicationsPotential use for many types of diagnosis and therapies


Other lasersOther lasers

KTP laserFrequency-doubled Nd:YAG laser using a nonlinear crystal, KTPWavelength: 1064 nm/2 = 532 nm (green)Applications

CW KTP: Ophthalmic Q-switched KTP (nanosecond pulses): tattoo removal, port wine stain removal

Alexandrite laserWavelength: 700 nm – 820 nm (tunable)Excitation: Flashlamps, diodesCost effectiveApplications

hair removal etc.

bio-medical optics lab., yonsei university

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