Laser Interactions with Biological Tissues: Part 1

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12 Questions

What are the two essential elements that determine the interaction of lasers with biological tissues?

Wavelength and power density

Which of the following is NOT one of the factors under control of the clinician in laser-tissue interaction?

Absorption curves

What are chromophores in the context of laser-tissue interactions?

Tissue elements with high absorption coefficients for certain wavelengths

Which of the following is NOT a basic type of laser-tissue interaction?

Penetration

What are the three types of tissue effects resulting from laser irradiation mentioned in the text?

Photo-thermal, photo-chemical, scattering

Which factor is dependent on the optical characteristics of the particular target tissue in laser interactions?

Extent of interaction

What is the main purpose of photo-thermal interactions in medical applications?

Removal of tissue by vaporization and super heating of tissue fluids

What is the thermal effect on tissue at a temperature range of 70-90 degrees Celsius?

Protein denaturation

What is the purpose of carbon arcing in photo-thermal interactions?

To act as a heat sink causing excessive heat generation

Which type of laser is predominantly used for photo-thermal interactions in medical treatments?

CO2 laser

What is the main effect of photochemical low-level laser therapy (LLLT) on tissues?

Tissue fluorescence stimulation

What are the key factors required for correct ablation in photoablation during medical procedures?

Short wavelengths and cooling of target area

Study Notes

Laser Interactions with Biological Tissues

  • The interaction between laser and matter is determined by the wavelength, power density, and temporal characteristics of the beam, as well as the optical characteristics of the target tissue.

Factors Affecting Laser Interaction

  • The extent of interaction depends on two factors: the specific wavelength of the laser and the optical characteristics of the target tissue.
  • Clinician-controlled factors include power density, total energy, rate and duration of exposure, and mode of delivery (continuous vs. pulsed, contact vs. non-contact).

Types of Laser Interactions

  • 4 basic types of laser interactions:
    • Reflection
    • Transmitted
    • Absorbed
    • Penetrate and scatter

Chromophores and Absorption

  • Chromophores are tissue elements that show high coefficients of absorption for a particular wavelength.
  • Examples of chromophores include melanin pigments and hemoglobin, which interact with 488nm and 514nm luminous radiation.

Laser Interactions and Tissue Effects

  • 3 types of laser interactions:
    • Photo-chemical interactions (biostimulation, photodynamic therapy, tissue fluorescence)
    • Photo-thermal interactions (photo ablation, photo pyrolysis, thermal relaxation time)
    • Photo-mechanical interactions (photo disruption, acoustic shock waves)

Photo-Thermal Interactions

  • CO2 laser is mainly used for photo-thermal interactions, absorbed to a depth of 100 micro meters.
  • Thermal effects of laser irradiation:
    • 42-45°C: Hyperthermia
    • Above 65°C: Desiccation, protein denaturation
    • 70-90°C: Tissue welding
    • Above 100°C: Vaporization
    • Above 200°C: Carbonization and charring

Photo-Mechanical Interactions

  • Photoablation requires 3 co-factors: appropriate wavelength, presence of endogenous and exogenous molecular targets, and correct ablation techniques.

This quiz covers the essential elements that determine the interaction between lasers and biological tissues, including wavelength, power density, and temporal characteristics. It also explores factors influencing the extent of interaction, such as specific laser wavelength and optical characteristics of target tissues.

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