Course 111 - Diagnostic Imaging II - 1.1.1-1.1.4 - Lasers

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83 Terms

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Speed (Light)

3×108 m/s or 186,000 mi/s

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Wavelength

Distance between two successive light waves

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Shorter wavelengths have ___ energy, while longer wavelengths have ___.

More, less

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Frequency

How many waves pass a given point in one second

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Amplitude

Height of a wave

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Absorption

Caused by impurities or loss

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Specular reflection

Angle of incidence is equal to the angle of reflection

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Diffuse reflection

Angle of reflection is random

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Scattering (diffused)

Caused by impurites

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Refraction

Bending of a wave when it enters a medium where its speed is different

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Transmittance

The fraction of radiant energy that passes through a substance

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Flat mirror

A mirror where angle of incidence is equal to the angle of reflection

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Concave mirror

Light is directed/concentrated to a single point or focal spot

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Convex mirror

Dispersion of light in an outward direction

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Fiber Optic cable has three main parts:

  • Core

  • Cladding

  • Buffering coating

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How to repair fiber optic cables

  • Cut

  • Polish and reconnect

  • Test

  • Check for black dots

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Five parts of an optical microscopes:

  • Lenses

  • Focus adjustments

  • Support and alignment

  • Specimen control

  • Illumination

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Brightfield

Uses transmitted light to observe targets at high magnification

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Phase-Contrast

Modified brightfield microscope that uses additional lenses and angles to vary the light density on the specimen

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Darkfield

Microscope that uses a special condenser lens with an opaque disc so that direct rays of light don’t enter the objective lens

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Binocular stereoscopic

Allows easy observation of 3D objects at low magnification

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Differential interference contrast

Provides better image than phase-contrast. Measures dry weight, thickness and water content of the specimen

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Ultraviolet

This microscope illuminates the specimen using ultraviolet rays from a mercury or iodine-quartz lamp

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Fluorescence

Uses mercury or xenon lamps to produce ultraviolet light

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Two uses of microscopes in medicine

  • Surgery

  • Tests/treatment

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Laser

Light Amplification by the Stimulated Emission of Raditation

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Lasers produce photons of electromagnetic energy that can be…

Within, above, or below the range of visible light

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Laser light contains three qualities:

  • Monochromatic

  • Collimated

  • Coherent

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Monochromatic

Single, very precise, frequency which gives a specific color

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Collimated

Tight, narrow beam that needs to be maintained over a long distance

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Coherent

Waves of light are in phase

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Spontaneous Emission

Emission of light induced by an external energy source

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Stimulated Emission

Emission of light after population inversion of the medium has been achieved by the spontaneously emitted photons

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Light

Type of electromagnetic radiation

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Visible light

~400 nm to 700 nm on the electromagnetic spectrum

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Ocular Focus Region

Human eye can focus light onto retina from 400 nm all the way up to 1,400 nm

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Infrared and ultraviolet light are..

Outside of the visible spectrum

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White light contains…

All the colors of the electromagnetic spectrum

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Amplification

Taking small electronic signal and increasing it enough to have useful output

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SE

Stimulated Emission is a process that starts with spontaneous emission

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Spontaneous Emission

electron in an excited state (higher energy level) naturally falls down to a lower energy level on its own, without any external influence. When it does this, it releases a photon (light).

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Stimulate Emission

electron in an excited state falls to a lower energy level because it is stimulated by an incoming photon (light)

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Optical Resonator

A container that has an inner mirror-like finish to keep photons inside with Totally Reflective (TR) rear mirror and a Partially Reflective (PR) front mirror.

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Population inversion

A state at which most of the atoms in the container have been stimulated

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What is needed create laser light?

  • Same wavelength

  • Same energy source that excited them

  • Same amplitude and wavelength

  • In phase

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Totally Reflective (TR) rear mirror

100% reflective

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Partially Reflective (PR) front mirror

Typically 80-95% reflective

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Radiation

Refers to all of the electromagnetic spectrum

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Types of Surgical Laser Systems

  • Gas

  • Solid State

  • Dye

  • Diode

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Coherence

Light waves that are monochromatic and in phase

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Photothermolysis

Heat damage by use of electromagnetic waves produced by lasers

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Thermal relaxation time

Cooling rate of an object, meant to minimize damage to the surrounding tissue not targeted by the laser

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Four types of surgical laser system run off:

  • Continuous wave (CW)

  • Long-pulse

  • Short-pulse

  • Q-switch

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Delivery devices include:

  • Fiber optic cables

  • Articulate arms

  • Specialty glass components

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CO2 lasers

Referred as “Surgical laser” that achieves both cutting and hemostasis photothermally, operating at 10,600 nm infrared light CW

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Argon lasers

  • Blue-green light @ 488 nm and 514 nm

  • Significant non-selective heating

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Excimer laser

  • disrupts the molecular bonds of surface tissue, causing ablation rather than burning or cutting

  • Argon: Fluorine laser @ 192 nm

  • Used in PRK and LASIK

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YAG (Yttrium-aluminum-garnet)

Uses rare earth metals as lasing medium and operate in all types of modes

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Nd:YAG lasers

  • 1064 nm (sometimes 946 nm, 1120 nm, 1320 nm, & 1440 nm)

  • Used for black tattoo ink and hair removal

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KTP lasers

  • Brilliant green light @ 532 nm

  • CW to cut tissue

  • Pulsed for vascular lesions

  • Q-switched for red/orange tattoo removal

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Er:YAG lasers

  • 2940 nm

  • Ablate tissue for cosmetic laser resurfacing

  • Benefits include: short downtime, less invasive, & minimal thermal injury

  • Also effective in tooth decay removal

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Ho:YAG lasers

  • 2070 nm

  • Ablate bone and cartilage

    • Lithotripsy

    • ENT

    • Prostate

    • Orthopedics

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Ruby lasers

  • Red @ 694 nm

  • Extensively used in tattoo and hair removal

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Alexandrite lasers

  • Chromium-doped solid-state laser

  • Hair removal for light/olive colored skin

  • Causes burns towards darker skin colored individuals

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Pulsed Dye or Rhodamine Dye lasers

  • Yellow @ 577-585 nm

  • Peak absorption of hemoglobin in blood

  • Causing unsightly purpura (black and blue marks)

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Diode lasers

  • "Injection Laser” or “Injection Laser Diode”

  • Often used in dentistry

  • 500-900 °C

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Laser systems are either:

  • Mounted to wheeled carts

  • Sit on top of a countertop

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Laser safety classifications

Levels 1, 2, 3, & 4

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Class 2 lasers

  • Limited to 1 mW

  • Less than 250 ms of exposure is not hazardous

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Class 3R lasers

  • Limited to 5 mW in CW

  • Momentary unintentional exposure is not considered hazardous

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Class 3B lasers

  • Can cause eye and tissue damage

  • Equipped with a key switch and a safety interlock

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Class 4 lasers

  • Pulsed or CW

  • reflected or diffused reflected beams are hazardous

  • Greater than 0.5 W

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Medical laser safety classification

Class 4 lasers

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Nominal ocular hazard distance

Distance from source which intensity of energy per surface unit becomes lower than Maximum Permissible Exposure on cornea or skin

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Nominal ocular hazard area

Depends on the area around the laser and refers to all space around the laser

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Class 3B and 4 lasers have five main safety features:

  • Key switch

  • safety interlock dongle

  • power indicator

  • aperture shutter

  • emission delay

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Safe use regulations adopted by CDRH

  • ANSI Z136.1 - American National Standards for the Safe Use of Lasers

  • ANSI Z136.3 - American National Standards for the Safe Use of Lasers in Health Care

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Laser Safety Officer’s responsibilities:

  • Evaluation of Class 3B and 4 laser system

  • Recommend PPE or screens

  • Enforcing procedures to limit personnel exposure

  • Conduct operational checks

  • Comply with prescribed safety procedures

  • Maintain records required by government regulations

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Posted warning signs must include:

  • Type of laser

  • Wavelength

  • Maximum output

  • Pulse duration (if applicable)

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Cataracts (clouding of the eye lens)

Lens of eye can absorb the NEAR ultraviolet radiation (315-400 nm)

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Cornea absorbs ___ and ___ waves which can cause severe pain, conjunctivitis and/or corneal damage

Far ultraviolet (180-315 nm), Far infrared (1,400-100,000 nm)

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Safety glasses/goggles must have the correct…

Optical Density (OD) and wavelength

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How to assure maximum flow rate of the smoke evacuator?

  • Within 5 cm of the treatment site

  • Change filters regularly