Download - 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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Oxy-hemoglobinDeoxy-hemoglobinWater
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Wavelength (nm)
Optical Window
He-
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Ti:
Sap
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Dio
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Nd
:YA
G
Ho
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Er:
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Melanin
Bio-Medical Optics Lab., Yonsei University
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
Bio-Medical Optics Lab., Yonsei University
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)
Bio-Medical Optics Lab., Yonsei University
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)
Bio-Medical Optics Lab., Yonsei University
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)
Bio-Medical Optics Lab., Yonsei University
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
Bio-Medical Optics Lab., Yonsei University
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)
Bio-Medical Optics Lab., Yonsei University
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
Bio-Medical Optics Lab., Yonsei University
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
Bio-Medical Optics Lab., Yonsei University
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)
Bio-Medical Optics Lab., Yonsei University
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
Bio-Medical Optics Lab., Yonsei University
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
Bio-Medical Optics Lab., Yonsei University
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.