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MGH Wellman Center for Photomedicine Laser Safety

MGH Wellman Center for Photomedicine Laser Safety. A laser can project more energy at a single wavelength within a narrow beam than can be obtained from more powerful conventional light sources. Electromagnetic Waves.

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MGH Wellman Center for Photomedicine Laser Safety

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  1. MGH Wellman Center for PhotomedicineLaser Safety • A laser can project more energy at a single wavelength within a narrow beam than can be obtained from more powerful conventional light sources

  2. Electromagnetic Waves Light is a small segment of the electromagnetic spectrum that extends from radio waves to g-rays. The only difference among the different waves is the wavelength (frequency).

  3. Electromagnetic Waves (Light) Transport Energy • Radiant power or Radiant flux: • Total power emitted in the form of radiation (Watt) • Irradiance: • Power carried per unit area (W/cm2) • Radiant exposure: • Energy delivered per unit area (Joule/cm2)

  4. LASER • Light Amplification by Stimulated Emission of Radiation • Differences between lasers and conventional light sources: • LaserConventional sources • Monochromatic Many wavelengths • Collimated Emitted in many directions • Coherent Incoherent

  5. Cross Section of a Common Laser Ruby Laser

  6. Lasers vs. Conventional Light Sources LED (Light Emitting Diode) Nd:YAG Laser Source: Google

  7. Lasers vs. Conventional Light Sources laser source A collimated beam can be focused to a small spot on the retina Conventional light source ( a Apparent visual angle info.tuwien.ac.at/iflt/safety/section1/s1_body.htm

  8. Light-Tissue InteractionsTissue Absorbers

  9. Light-Tissue InteractionsSelective Photothermolysis • Medical procedures can only be initiated by absorption of light • Effects can be controlled by choosing the appropriate wavelength

  10. Widely-Used LasersWavelength of Operation Source: Shore Laser Center

  11. Standards for Safe Use of Lasers Federal and State Agencies • Federal: • OSHA • FDA (Center for Devices and Radiological Health) • The Commonwealthof Massachusetts: • Department of Public Health

  12. Laser Beam Hazards • Eye hazard • Skin hazard

  13. Laser Hazard ClassificationAccessible Emission Limit (AEL) • Lasers and laser systems are classified on the basis of the laser radiation accessible outside the laser during the intended use • and to which the human eye or skin is possible to be exposed

  14. Laser Hazard Classification • Class 1 laser: • Low power; Considered safe • Class 2 laser: • Eye protection afforded by the eye blink response • Class 3 laser: • Medium power; Hazard to the eye from direct exposure • Class 4 laser: • High power; Hazard to the eye and skin from direct and reflected exposure; Fire hazard

  15. Beam HazardsEye Hazard • Cornea/lens hazard: 290-400 nm and 1400-10,600 nm • Retinal hazard region: 400 - 1400nm • Eye entering the eye is focused. The irradiance on the retina can be increased as much as 100,000 • One central fovea laser hit can cause blindness

  16. Eye Injury Nd:YAG (1064 nm) - Permanent damage Individual saw a white flash, heard a click, then immediately a dark spot in visual field (www.ucl.ac.uk/uro-neph/ppt/lm221102.ppt)

  17. How do you know if you have an eye injury? • Exposure to infrared high-power laser causes a burning pain to the cornea or sclera • Exposure to visible lasers causes a bright color flash of the emitted wavelength and an after image of a complementary color • Exposure to short pulsed infrared lasers may go undetected or may cause a popping sound followed by visual disorientation

  18. Beam HazardsSkin Hazard • Visible and infrared high-power lasers can cause permanent skin damage or damage to underlying organs • Examples of skin response to laser exposure: • Mild to severe reddening • Blisters and charring • De-pigmentation • Ulceration • Scarring

  19. Maximum Permissible ExposureMPE • Irradiance (Radiant Exposure) to which a person can be exposed without hazard to eye or skin • MPE values may cause discomfort

  20. Maximum Permissible Exposure • The MPE depends on the following parameters: • Laser wavelength • Duration of exposure • The MPE for eye exposure is much lower than the MPE for skin

  21. Warning SignsExample: Class 2 Laser

  22. Warning SignsExample: Class 4 Laser

  23. Protective EyewearGoggles

  24. Protective Eyewear

  25. Protective Eyewear • The protection wavelength(s) and the corresponding attenuation are scribed on the eyewear • The attenuation is given in Optical Density (OD). An OD of 4 means that the irradiance of the beam passing through the eyewear is attenuated by 10,000 times

  26. Non-Beam Hazards • Fire: • Ignition of materials can occur from direct or intense reflected or scattered beams • Electrical: • Most deaths caused by lasers are caused by electrocution. Laser capacitors can retain high energy charges even when the power is off

  27. Non-Beam Hazards • Laser-generated airborne contaminants: • Chemical fumes, aerosols of biological contaminants including viable viruses and other biohazards can and do exist in the laser plume • Chemical: • Laser dyes, solvents and gases used may be toxic, explosive or carcinogens

  28. Credentialing ProcedureCertification to Operate a Particular Type of Laser • It is the policy of the Massachusetts General Hospital that all medical staff utilizing a laser for any procedure must be credentialed. The credentialing process must be followed for each type (wavelength) of laser for which privileges are requested

  29. Credentialing ProcedureCertification to Operate a Particular Type of Laser • Attendance at an approved didactic course • Supervised operation with the particular laser in at least 3 patients. • For new or experimental lasers, the laser manufacturer can provide hands-on instruction • Application for laser credentials to Laser Safety Committee • A baseline fundoscopic eye examination that notes apparent pre-existing abnormalities is recommended

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