CLT Photobiomodulation Science 2 — Questions and Answers
Question 1: Which cellular organelle is the primary chromophore target in photobiomodulation therapy?
- Nucleus
- Mitochondria (Correct answer)
- Endoplasmic reticulum
- Golgi apparatus
Correct answer: Mitochondria
Mitochondria contain cytochrome c oxidase, the primary chromophore that absorbs red and near-infrared light during PBM therapy.
Question 2: The Arndt-Schulz Law as applied to photobiomodulation states that:
- Higher doses always produce better outcomes
- Weak stimuli excite, optimal stimuli promote, and excessive stimuli inhibit biological activity (Correct answer)
- Only continuous wave lasers are therapeutic
- Wavelength is more important than dose
Correct answer: Weak stimuli excite, optimal stimuli promote, and excessive stimuli inhibit biological activity
The Arndt-Schulz Law describes the biphasic dose-response relationship where too little light has no effect and too much light can inhibit or damage tissue.
Question 3: Which of the following best describes the 'optical window' in PBM therapy?
- 600–1100 nm range where light penetrates tissue most effectively (Correct answer)
- 200–400 nm range for surface sterilization
- 1200–1500 nm range for deep heating
- Only the 532 nm green wavelength
Correct answer: 600–1100 nm range where light penetrates tissue most effectively
The therapeutic optical window (600–1100 nm) minimizes absorption by water and hemoglobin, allowing deeper tissue penetration.
Question 4: Retrograde axonal transport of photobiomodulation signals primarily affects which system?
- Cardiovascular system
- Nervous system (Correct answer)
- Immune system
- Endocrine system
Correct answer: Nervous system
PBM light absorbed by peripheral nerve endings can trigger retrograde signals along axons to cell bodies, affecting neurological function.
Question 5: What is the role of nitric oxide (NO) in photobiomodulation mechanisms?
- It absorbs all wavelengths of visible light
- It is displaced from cytochrome c oxidase, restoring mitochondrial function (Correct answer)
- It permanently damages cellular DNA
- It converts ATP to ADP
Correct answer: It is displaced from cytochrome c oxidase, restoring mitochondrial function
In hypoxic or stressed tissue, NO binds and inhibits cytochrome c oxidase; PBM light displaces this NO, restoring normal electron transport.
Question 6: Which parameter describes the total energy delivered to tissue during a PBM treatment?
- Irradiance
- Fluence (energy density) (Correct answer)
- Power density
- Wavelength
Correct answer: Fluence (energy density)
Fluence (J/cm²) is the total energy delivered per unit area and is the key dosimetric parameter for determining therapeutic effect.
Question 7: In the context of PBM, what is the significance of the 'coherence' property of laser light?
- Coherence causes more thermal damage than LEDs
- Coherence allows deeper penetration but loses significance in tissue due to scattering (Correct answer)
- Coherence is the only factor that matters for therapeutic effect
- LEDs are more coherent than lasers
Correct answer: Coherence allows deeper penetration but loses significance in tissue due to scattering
Laser coherence is lost within millimeters of entering tissue due to scattering, so the biological effects of coherent lasers and LEDs at equivalent doses are similar.
CLT Photobiomodulation Science 2
Which cellular organelle is the primary chromophore target in photobiomodulation therapy?