CLT Laser Treatment Parameters & Dosage 2 — Questions and Answers
Question 1: Which parameter describes the total energy delivered per unit area during a laser treatment session?
- Peak power
- Fluence (J/cm²) (Correct answer)
- Average irradiance
- Pulse repetition rate
Correct answer: Fluence (J/cm²)
Fluence, measured in J/cm², represents the total energy delivered per unit area and is the primary dosage metric in laser therapy.
Question 2: When treating a darker Fitzpatrick skin type (V-VI) with a laser, the therapist should generally:
- Increase fluence to compensate for melanin absorption
- Decrease fluence and increase spot size
- Maintain standard fluence and shorten pulse duration
- Reduce fluence and use longer pulse durations (Correct answer)
Correct answer: Reduce fluence and use longer pulse durations
Darker skin types have more epidermal melanin, requiring lower fluence and longer pulses to reduce the risk of thermal damage and dyspigmentation.
Question 3: The concept of 'thermal relaxation time' (TRT) is most relevant when selecting:
- Treatment wavelength
- Pulse duration (Correct answer)
- Spot size diameter
- Beam divergence angle
Correct answer: Pulse duration
Pulse duration should be shorter than or equal to the TRT of the target to confine thermal damage to the target and spare surrounding tissue.
Question 4: A laser device has an output power of 2 W and the operator uses a spot size with an area of 1 cm². What is the irradiance?
- 0.5 W/cm²
- 1 W/cm²
- 2 W/cm² (Correct answer)
- 4 W/cm²
Correct answer: 2 W/cm²
Irradiance (power density) = Power ÷ Area = 2 W ÷ 1 cm² = 2 W/cm².
Question 5: In photobiomodulation (low-level laser therapy), the Arndt-Schulz law suggests that:
- Higher doses always produce superior biological effects
- Very low and very high doses are stimulatory while medium doses are inhibitory
- Optimal therapeutic doses lie within a specific dose window; too low or too high reduces efficacy (Correct answer)
- Dose has no significant effect on cellular response
Correct answer: Optimal therapeutic doses lie within a specific dose window; too low or too high reduces efficacy
The Arndt-Schulz law applied to LLLT indicates a biphasic dose-response where a therapeutic window exists; doses below or above this window are less effective.
Question 6: Which of the following BEST defines 'duty cycle' in pulsed laser operation?
- The ratio of on-time to the total period (on + off time) (Correct answer)
- The peak power divided by average power
- The number of pulses emitted per second
- The total treatment time per session
Correct answer: The ratio of on-time to the total period (on + off time)
Duty cycle is the proportion of time the laser is actively emitting (on-time / total period), expressed as a percentage.
Question 7: A therapist doubles the spot size diameter while keeping all other parameters constant. How does this affect the irradiance?
- Irradiance doubles
- Irradiance is reduced by half
- Irradiance is reduced to one-quarter (Correct answer)
- Irradiance remains unchanged
Correct answer: Irradiance is reduced to one-quarter
Spot area scales with the square of the radius; doubling diameter quadruples the area, so the same power is spread over four times the area, reducing irradiance to 1/4.
CLT Laser Treatment Parameters & Dosage 2
Which parameter describes the total energy delivered per unit area during a laser treatment session?