CLT Photobiomodulation Science 3 — Questions and Answers
Question 1: Which reactive oxygen species (ROS) produced during PBM acts as a secondary messenger at low levels?
- Hydroxyl radical only
- Superoxide and hydrogen peroxide (Correct answer)
- Ozone
- Carbon monoxide
Correct answer: Superoxide and hydrogen peroxide
Low-level superoxide and hydrogen peroxide generated during PBM act as secondary messengers that activate transcription factors like NF-κB.
Question 2: The process by which PBM activates gene expression through transcription factors is called:
- Photolysis
- Photomodulation of signal transduction (Correct answer)
- Photosensitization
- Photoablation
Correct answer: Photomodulation of signal transduction
PBM stimulates signaling cascades that activate transcription factors (NF-κB, AP-1, HIF-1α), leading to altered gene expression and cellular responses.
Question 3: At which approximate tissue depth does 810 nm near-infrared light lose approximately 50% of its intensity?
- 0.1–0.5 mm
- 1–5 mm (Correct answer)
- 10–20 mm
- 50–100 mm
Correct answer: 1–5 mm
Near-infrared light at 810 nm typically loses about half its intensity within the first few millimeters of tissue, though deeper structures still receive therapeutic doses.
Question 4: Which mechanism explains PBM's ability to reduce inflammation through mast cell modulation?
- PBM destroys mast cells with thermal energy
- PBM stabilizes mast cell membranes, reducing degranulation and histamine release (Correct answer)
- PBM causes mast cells to produce more inflammatory cytokines
- PBM has no effect on mast cells
Correct answer: PBM stabilizes mast cell membranes, reducing degranulation and histamine release
PBM can photobiomodulate mast cells by stabilizing their membranes, decreasing degranulation and the subsequent release of pro-inflammatory histamine.
Question 5: What is the primary difference between Class 3B and Class 4 therapeutic lasers in PBM?
- Class 3B uses ultraviolet light; Class 4 uses infrared only
- Class 4 lasers have power output above 500 mW and pose greater thermal risks (Correct answer)
- Class 3B lasers cannot penetrate skin
- Class 4 lasers are non-coherent
Correct answer: Class 4 lasers have power output above 500 mW and pose greater thermal risks
Class 4 lasers exceed 500 mW output, enabling faster treatment and deeper penetration but also carrying greater risk of thermal injury compared to Class 3B.
Question 6: Which physiological effect of PBM on microcirculation contributes to tissue healing?
- Vasoconstriction reducing blood flow to damaged tissue
- Vasodilation via NO release, increasing perfusion and oxygen delivery (Correct answer)
- Coagulation of capillary beds
- Reduction of lymphatic drainage
Correct answer: Vasodilation via NO release, increasing perfusion and oxygen delivery
PBM-induced NO release causes local vasodilation, improving microcirculation and delivering more oxygen and nutrients to healing tissue.
Question 7: Which of the following best describes the concept of 'fluence rate' in PBM dosimetry?
- Total joules delivered in one session
- Power per unit area (irradiance) measured in W/cm² (Correct answer)
- Number of treatment sessions per week
- Pulse frequency in Hz
Correct answer: Power per unit area (irradiance) measured in W/cm²
Fluence rate (irradiance) is the power delivered per unit area (W/cm²) and determines how quickly energy is deposited in tissue during PBM treatment.
CLT Photobiomodulation Science 3
Which reactive oxygen species (ROS) produced during PBM acts as a secondary messenger at low levels?