Lasers for Medical Applications Flashcards

Flashcards for review of laser applications in medicine.

Laser Interaction with Tissue

The application of the laser in medical treatment is based on the interaction of laser radiation with biological tissue.

Photochemotherapy Origins

The Egyptians and Indians treated skin diseases such as vitiligo or leukoderma with sun radiation, which evolved into a method called photochemotherapy.

First Use of Focused Sunlight on Retina

In 1949, G. Meyer-Schwickerath focused sunlight onto patients’ retinas to treat melanomas for the first time.

First Generation of Laser Radiation

Theodore Maiman generated red ruby laser radiation for the first time in May 1960.

First Use of Laser for Skin Disease

In 1961, Leon Goldman was the first researcher to use laser radiation to treat a human skin disease when he treated a skin melanoma.

First Study on Laser Radiation Effects on Skin

In 1963, Goldman and his co-workers published the first study on the effects of laser radiation on the skin, describing the selective destruction of skin pigmented structures.

First Tumor Removal with Laser Radiation

In 1966, Goldman supervised the first operation in which laser radiation was used to remove a tumor without causing bleeding.

Factors Influencing Laser-Tissue Interactions

Factors to consider regarding laser-tissue interactions: laser radiation, irradiated tissues, and mutual interaction processes.

Laser Wavelength and Penetration Depth

Moderate wavelengths (600–1100 nm) typically penetrate deeper into biological tissue, compared to very short or very long wavelengths.

Power

Total energy delivered per second, measured in Watts (W).

Power Density (Irradiance)

Concentration of power over a given area, measured in W/cm²; Increased thermal effects.

Energy

Total amount of energy delivered, measured in Joules (J).

Energy Density (Fluence)

Energy per unit area, measured in J/cm²; Critical in photochemical and ablative effects.

Pulse Duration

Determines the type of interaction: Long pulse → thermal diffusion; Short pulse → photomechanical or ablative effects; Ultrafast pulses (femtosecond) → minimal heat damage.

Chromophore

Molecule or part of a molecule in tissue that absorbs light at specific wavelengths.

Photothermal

Heating, coagulation, vaporization

Photomechanical

Shock waves and cavitation bubbles

Photochemical

Laser activates photosensitive agents in tissue

Photoablative

Direct tissue removal by breaking molecular bonds.

Key Laser Characteristic: Wavelength

Wavelength determines tissue penetration and chromophore absorption

Key Laser Characteristic: Power and Energy

Power (W) is energy per unit time; Energy (J) is total energy delivered

Key Laser Characteristic: Pulse Duration

Continuous vs pulsed; influences thermal confinement

Key Laser Characteristic: Spot Size

Affects fluence and precision

Key Laser Characteristic: Fluence (J/cm)

Energy per unit area; key to interaction mechanism

Key Laser Characteristic: Repetition Rate

Number of pulses per second (Hz)

Laser Sources

Classified into: Gas lasers, Solid-state lasers, and Diode lasers

Common Gas Lasers

CO₂, Argon, Helium-Neon (He-Ne)

Common Solid-State Lasers Doping Ions

Nd³⁺, Er³⁺, Ho³⁺

Diode Lasers

Semiconductor-based laser that converts electrical energy directly into light using p-n junctions.