Biomedical Optics 4 MCQ
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Questions and Answers

What is the primary active medium used in Nd:YAG lasers?

  • Carbon dioxide gas
  • Gallium nitride
  • Dye solution
  • Yttrium-aluminum-garnet crystal (correct)

In which clinical application is the ArF excimer laser primarily utilized?

  • Tumor ablation
  • Pain management therapy
  • Laser eye surgery (LASIK) (correct)
  • Dental procedures

What feature characterizes the laser diodes mentioned in the content?

  • They emit continuous waves exclusively.
  • They utilize a resonant cavity to form the laser. (correct)
  • They require cryogenic temperatures to function.
  • They operate only at UV wavelengths.

What is the range of power output displayed by clinical Nd:YAG lasers?

<p>10-50W (C)</p> Signup and view all the answers

What is a significant property of pulsed excimer lasers?

<p>They produce pulses of approximately 10 ns. (D)</p> Signup and view all the answers

Which wavelength is associated with the ArF excimer laser?

<p>193 nm (C)</p> Signup and view all the answers

How is the energy emission characterized in pulsed Nd:YAG lasers?

<p>They can generate pulses ranging from tens to several hundred mJ. (A)</p> Signup and view all the answers

What aspect of ArF excimer laser function allows for photoablation without thermal damage?

<p>Short wavelength (B)</p> Signup and view all the answers

Which laser is known for its application in treating vascular lesions?

<p>Pulsed dye laser (A)</p> Signup and view all the answers

What type of bonds are formed between the Ar and K atoms in an ArF excimer laser?

<p>Ionic bonds (A)</p> Signup and view all the answers

What is a primary characteristic of the Diode laser?

<p>Used primarily for laser hair removal (B)</p> Signup and view all the answers

What type of light does the Argon laser emit?

<p>Blue-green light (A)</p> Signup and view all the answers

What clinical applications are associated with diode lasers mentioned in the content?

<p>Optical imaging and photodynamic therapy (A)</p> Signup and view all the answers

Which laser is most suitable for skin resurfacing procedures?

<p>Er: YAG laser (A)</p> Signup and view all the answers

The wavelength of the Alexandrite laser is closest to which of the following?

<p>755 nm (B)</p> Signup and view all the answers

Which of the following lasers is specifically indicated for the management of vitiligo?

<p>He-Ne laser (A)</p> Signup and view all the answers

Which laser type is primarily absorbed by melanin and used for hair reduction?

<p>Ruby laser (A)</p> Signup and view all the answers

What is the primary application of the Nd:YAG laser?

<p>Photocoagulation treatments (C)</p> Signup and view all the answers

Which wavelength range corresponds to the Ruby laser?

<p>694 nm (B)</p> Signup and view all the answers

Which laser has the highest wavelength mentioned in the provided content?

<p>Nd:YAG laser (B)</p> Signup and view all the answers

What primarily enables optical fibres to transmit light effectively over long distances?

<p>Total internal reflection within the core (D)</p> Signup and view all the answers

What is the significance of the numerical aperture in optical fibres?

<p>It governs the maximum acceptance angle and controls light divergence. (D)</p> Signup and view all the answers

Which of the following types of fibres typically has a core diameter ranging from 8-10 µm?

<p>Single-mode fibre (D)</p> Signup and view all the answers

In clinical applications involving light for therapeutic purposes, what is typically unnecessary beyond dosimetry or calibration?

<p>Detection of the light itself (B)</p> Signup and view all the answers

What characteristic of the core medium is crucial for maintaining total internal reflection?

<p>Its refractive index must be slightly higher than that of the cladding. (B)</p> Signup and view all the answers

What is a potential application for light in medical settings?

<p>To destroy tumours or reshape the cornea (D)</p> Signup and view all the answers

What is the primary application of the COâ‚‚ laser with a wavelength of 10,600 nm?

<p>Deep laser resurfacing (A)</p> Signup and view all the answers

Which wavelength range of red to near infrared light is most effective for treating aging skin?

<p>650-1000 nm (D)</p> Signup and view all the answers

What is a significant advantage of using optical fibers in light therapy?

<p>Allows for precise delivery of light (B)</p> Signup and view all the answers

Which application is associated with blue to green light in the range of 495-570 nm?

<p>Kill bacteria and control acne (A)</p> Signup and view all the answers

What therapeutic effect is achieved through light in the 570-600 nm range?

<p>Detoxification and sensory nervous system stimulation (A)</p> Signup and view all the answers

Which of the following wavelengths is associated with the treatment of psoriasis, dermatitis, and vitiligo?

<p>380-495 nm (C)</p> Signup and view all the answers

Which of the following wavelengths has low penetration into tissue?

<p>495-570 nm (D)</p> Signup and view all the answers

What is the main effect of using light in the range of 600-650 nm?

<p>Stimulates collagen production (B)</p> Signup and view all the answers

What characteristic of light allows it to be effectively used in photobiomodulation therapy?

<p>Its coupling into optical fibers (C)</p> Signup and view all the answers

Which property is NOT associated with the LED light in the 650-1000 nm range?

<p>Killing bacteria (D)</p> Signup and view all the answers

What primarily causes the intensity of a light beam to decay exponentially when traveling through a scattering medium?

<p>Elastic scattering of photons (D)</p> Signup and view all the answers

Which characteristic distinguishes lasers from light-emitting diodes (LEDs)?

<p>Lasers provide a narrowband output much more than LEDs. (B)</p> Signup and view all the answers

What role does nitrogen (Nâ‚‚) play in the carbon dioxide laser?

<p>It enhances laser efficiency. (B)</p> Signup and view all the answers

What is the primary mechanism through which superluminescent diodes (SLDs) generate light?

<p>Stimulated emission during electron-hole recombination. (D)</p> Signup and view all the answers

What is a common application of carbon dioxide lasers due to their strong absorption by water?

<p>Laser scalpels and skin resurfacing (D)</p> Signup and view all the answers

What is the main difference between LEDs and superluminescent diodes in terms of light emission?

<p>SLDs generate light with amplified stimulated emission, unlike LEDs. (A)</p> Signup and view all the answers

In terms of light wave behavior, what does transport theory primarily describe?

<p>Statistical mechanics of particle passage through scattering media. (A)</p> Signup and view all the answers

Why are carbon dioxide lasers often utilized for medical procedures involving tissue?

<p>They efficiently vaporize tissue constituents with high water content. (A)</p> Signup and view all the answers

Which feature differentiates incoherent light sources from coherent light sources?

<p>Coherent sources have predictable phase relations between light waves. (D)</p> Signup and view all the answers

Flashcards

Coefficient Scattering

The process where light is scattered out of a beam as it passes through a medium, resulting in a decrease in beam intensity.

Transport Theory

A scientific field that studies the movement of particles (photons, neutrons, etc.) through a scattering medium, focusing on the statistical behavior of large particle populations.

Light Emitting Diodes (LEDs)

Solid-state devices that convert electrical energy into light energy. They operate by electron-hole recombination across a p-n junction.

Superluminescent Diodes (SLDs)

LEDs that emit broadband light at high power levels by stimulating emission of light as it passes through the device.

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Lasers

Devices that produce coherent light by stimulated emission. Lasers emit light at a specific wavelength and are highly focused.

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Carbon Dioxide Laser

A type of laser that operates on vibrational levels of the CO2 molecule, emitting infrared light. This light is highly absorbed by water and used for tissue vaporization.

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CO2 Laser in Medicine

Medical application of carbon dioxide lasers for vaporizing tissue, primarily used in surgical procedures and skin resurfacing.

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Laser Skin Resurfacing

The process of using lasers to remove the outer layers of skin, stimulating collagen production and improving skin texture.

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Nd:YAG Laser

A type of laser that uses an yttrium-aluminum-garnett crystal (YAG) doped with neodymium Nd3+ ions as the active medium. It operates on a four-level system, capable of generating pulses of tens to a few hundred millijoules.

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Excimer Laser

A type of laser that utilizes a gas mixture to produce UV wavelengths. The active medium is a gas of diatomic molecules that are bound only in an excited state, emitting light when returning to the ground state.

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Diode Laser

A type of laser that is a semiconductor laser with a resonant cavity, operating similarly to superluminescent diodes but with a much higher output power.

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ArF Excimer Laser

A type of laser used to reshape corneal tissue in laser vision correction (LASIK). Its short wavelength allows for precise ablation without causing significant thermal damage.

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Posterior Capsulotomy

A medical application of Nd:YAG lasers, where pulses are used to disrupt the posterior capsule of the eye, restoring vision after cataract surgery.

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Photoacoustic Imaging

A medical application of Nd:YAG lasers that utilizes the laser's ability to generate heat and sound waves for imaging, revealing tissue structures.

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Coagulation

A medical application of Nd:YAG lasers where the laser's heat is used to seal blood vessels and stop bleeding.

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Medical Lasers

The application of lasers in medicine, focusing on their use for precise tissue manipulation and therapeutic purposes.

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Power of Clinical Systems

The power consumption of clinical lasers, usually ranging from 10 to 50 watts.

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Argon Laser

This laser emits blue-green light, strongly absorbed by hemoglobin and water. It's not often used in aesthetics or dermatology.

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Pulsed Dye Laser

This laser emits yellow light, absorbed by hemoglobin. It's commonly used to treat vascular lesions like spider veins.

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Ruby Laser

This laser uses a red beam, absorbed by melanin in skin and hair. It's primarily used for hair removal and treating pigmented lesions like freckles.

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Alexandrite Laser

This laser emits a deep red light, absorbed by melanin. It penetrates deeper into the skin, making it effective for hair reduction.

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He-Ne Laser

This laser emits a red light and is used in treating vitiligo, nerve injury repair and wound healing.

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Photocoagulation

The use of light energy to heat and destroy tissue, often applied in treating vascular lesions, hair removal, and skin conditions.

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Total Internal Reflection

A phenomenon where light rays traveling in a denser medium hit the boundary with a less dense medium at an angle greater than the critical angle, causing the light to bounce back internally.

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Step-index fiber

A type of optical fiber where the core has a uniform refractive index, allowing light to travel in straight lines.

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Numerical Aperture (NA)

A measure of a fiber's ability to accept and guide light. It is determined by the refractive indices of the core and cladding.

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Photodiode

A device that converts light energy into electrical energy. They are commonly used in imaging and sensing applications.

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Acceptance angle

The angle at which light enters a fiber optic cable. A higher acceptance angle allows more light to enter the fiber.

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Divergence angle

The angle at which light exits a fiber optic cable. It is determined by the numerical aperture of the fiber.

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Scattering

The process where light is scattered out of a beam as it passes through a medium, resulting in a decrease in beam intensity.

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Optical Fibres for Light Delivery

A significant advantage of using light, especially laser light, over other wavelengths of radiation is that it can be coupled into optical fibres.

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Precise Light Delivery

Optical fibres can be used to deliver light easily and precisely to where it needs to be.

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Study Notes

Coefficient Scattering

  • Consider a collimated light beam traveling in the z-direction through a thin, non-absorbing medium that scatters light elastically.
  • As the beam passes through the medium, some light scatters out of the beam in different directions.
  • The intensity of the beam decreases exponentially; exp(-μsz).
  • The probability that a photon is scattered while traveling a short distance between z and z + dz is μsz.

Tissue Propagation Light

  • Transport theory is the statistical mechanics area that describes the passage of particles (neutrons, photons, molecules) through a scattering medium.
  • It is only possible to give some statistics about a large population of particles.

Light Detectors and Sources

  • Incoherent Light Sources: Light Emitting Diodes (LEDs) and Superluminescent Diodes (SLDs).
  • Lasers (coherent light sources).

Light Emitting Diodes: Superluminescent & Emitting Light

  • LEDs are semiconductors (p-n junctions) that emit light when electrons and holes recombine at the junction.
  • LEDs are not narrowband sources like lasers but have a peak wavelength (wide bandwidth).
  • LEDs are cheap, very reliable and can be modulated at high frequencies.

SLED (or Diode SLED)

  • These are high power sources of broadband light.
  • They generate light at p-n junctions, as LEDs do, though with additional amplification due to stimulated emission.

Lasers: Medical Laser CO2

  • Carbon dioxide laser (λ = 10.6 µm).
  • Laser levels are vibrational levels of the CO2 molecule, although the active medium also contains He and N2 to improve efficiency.
  • IR light is strongly absorbed by water, useful for vaporizing tissue (e.g., laser scalpels and resurfacing).
  • Power of clinical systems typically range from 10-50W.

Lasers: Medical Laser Nd:YAG

  • Nd:YAG laser (λ = 1064 nm).
  • A four-level solid-state laser using an yttrium-aluminum-garnet (YAG) crystal doped with neodymium Nd3+ ions.
  • Pulsed Nd:YAG lasers generate pulses of tens to hundreds of millijoules (mJ).
  • Clinically used for photodisruption in posterior capsulotomy, photoacoustic imaging, and coagulation.

Lasers: Medical Laser ArF excimer

  • ArF excimer laser (λ = 193 nm).
  • Excimer lasers are gas lasers that emit UV wavelengths. 'Excimer' is a contraction of excited-dimer.
  • The active medium is a gas of diatomic molecules that are bound only in an excited state; returning to the ground state causes atoms to separate.
  • Molecule in ground state is empty.
  • Pulsed excimer lasers typically produce ~10ns pulses with 0.2-1 J energy.
  • Clinically used in corrective laser eye surgery (LASIK).

Lasers: Medical Diode Laser

  • Laser diodes (λ = 650-2000 nm) are semiconductor lasers with operation similar to superluminescent diodes but use a resonant cavity to form the laser.
  • Feature advantages include compactness, low cost, and long lifespan.
  • Available in a wide range of red-NIR wavelengths with output power as high as 50 W for NIR diode arrays.
  • Clinical applications include NIR spectroscopy, optical imaging, photodynamic therapy, and photocoagulation.

Optics Fibre

  • Light, particularly laser light, has a significant advantage in its use with optical fibers.
  • Laser light can easily be coupled into optical fibers allowing precise delivery to the desired location.

Photodiodes

  • Photodiodes are particularly convenient in endoscopy and minimally invasive surgery where surgical tools need to fit into small holes.
  • Optical fibers utilize total internal reflection to trap light beams; allowing for transmission over long distances, even into hard-to-reach areas.
  • Step-index fibers have a core medium where light travels, and a cladding medium surrounding the core. The core's refractive index is slightly higher than the cladding's.
  • Numerical aperture (NA) governs the maximum acceptance angle and the divergence angle of the light beam as it leaves the fiber.

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