100 Questions About Photorejuvenation – Waiting for Your Questions! (Series)

What are the adjustable parameters of intense pulsed light (IPL)?
The adjustable parameters of IPL (via software) include:
Number of sub-pulses, pulse width, pulse delay time, total energy density, sub-pulse energy density (in AOPT mode), and cooling (on/off).

Concept and adjustment principles of pulse width
The full name of pulse width is pulse duration.
Unlike lasers, light is widely used in medical fields but is usually low-intensity and has no pulse width. However, intense pulsed light is high-intensity light emitted in pulses.
Pulses are emitted intermittently, as opposed to continuous emission (e.g., continuous-wave CO₂ lasers). Therefore, IPL also requires setting a pulse width, which is more important than energy density.

Source: Practical Introduction to Laser in Aesthetic Dermatology*
Different brands of IPL devices have different pulse width ranges:
– The most widely used M22 has an adjustable pulse width range of 3ms-20ms. The maximum total pulse width for single, double, and triple pulses is 20ms.
– Alma’s DPL fixed-point mode offers three pulse width options: 10ms, 12ms, and 15ms.
– BB Light’s sub-pulses can be intelligently increased up to 10, with a maximum total pulse width of 200ms-1000ms.

Key introduction to M22’s pulse width adjustment:
Since single pulses are rarely used today, when setting 2-3 sub-pulses, the adjustable range of sub-pulse width is usually 3ms-8ms.

Principles and tips for adjusting pulse width**:
Pulse width refers to the duration of the pulse, i.e., the time IPL acts on the skin.
– Generally, a narrower pulse width exerts a stronger effect on the epidermis, while a wider pulse width has a weaker effect.
– A stronger epidermal effect increases the risk of skin burns due to heat production from melanin absorbing light.
– Additionally, pulse width is closely related to peak power:
Peak power = Energy density / Pulse width
Peak power represents the speed at which target chromophores absorb light and generate heat. Faster heat generation leads to more heat accumulation, increasing the risk of high temperatures and skin burns.

Therefore, when adjusting parameters, do not simultaneously increase energy density and shorten pulse width.
For skin rejuvenation (mainly targeting water absorption), sufficient heating time for dermal tissue is required, so a wider pulse width is usually used.

Significance and setting principles of sub-pulses
Not only IPL but also many lasers have sub-pulse modes (e.g., the PTP mode of Q-switched lasers, which sets 3 sub-pulses).

The significance of multiple sub-pulses is to make treatment gentler and avoid adverse reactions:
– Single pulse: Strongest effect
– Double pulses: Relatively gentle
– Triple pulses: Gentlest

Multiple pulses (especially triple pulses) are suitable for skin maintenance, while double or even single pulses are used for treating skin issues (since triple pulses are too gentle).
In addition to distributing total energy across multiple sub-pulses, sufficient cooling is provided during pulse intervals to protect the epidermis and reduce burn risks.
Significance and adjustment principles of pulse delay time
Pulse delay time exists with sub-pulses, referring to the skin cooling period between pulses.
– Adjustable range: 5ms-150ms
– Common range: 20-60ms (20-40ms is most frequently used)

Adjustment considerations:
– For treating epidermal spots or closing blood vessels: Avoid complete cooling of target tissues, so the delay time should not be too long.
– The delay time should not be shorter than 10ms (the thermal relaxation time of the epidermis is approximately 10ms), otherwise, burns are highly likely.

Factors affecting pulse delay time:
Number of sub-pulses, skin tone depth, energy density, and pulse width.

In summary, IPL exerts its effects through photothermal action. Thus, target tissues should not be completely cooled, but burns must be avoided—this is achieved by setting an appropriate pulse delay time (cooling time) to moderately lower skin temperature.

Cooling switch and adjustment
– On the M22: Cooling only has on/off options.
– Cooling is usually enabled (required for most treatments).
– Cooling can be disabled only when using gentle parameters for redness reduction (not blood vessel closure). The purpose is to avoid vasoconstriction caused by low temperatures, which may affect redness reduction efficacy.
– However, this scenario is rare: High energy density requires cooling to protect the epidermis.

– On Alma’s DPL: Cooling can be set to 50%, 75%, or 100%.
– Adjustments are based on skin tone depth, energy level, and skin redness/swelling.
– 75% is the most commonly used setting. 100% cooling is overly strong but can be used when other parameters are high.

Concept and adjustment principles of energy density
The “energy” commonly referred to is actually “energy density,” with the unit J/cm² (energy per unit area).
Energy density is the most important parameter for both lasers and IPL.

– For the M22:
– In standard OPT mode, total energy density is evenly distributed among sub-pulses. For example, a total energy density of 15J/cm² with 3 sub-pulses means each sub-pulse has 5J/cm².
– AOPT mode is activated when total energy density ≥15J/cm², allowing independent adjustment of sub-pulse energy distribution. This technical upgrade enables more precise parameter settings but requires higher expertise from physicians.
– Advantage of AOPT mode: At the same energy density, it causes milder epidermal reactions and a lower burn risk compared to standard OPT mode.

Factors affecting energy density settings:
Primarily the skin issue being treated and skin tone.

– For Alma’s DPL:
– Adjustable energy density ranges:
– 500-600nm handpiece: 5-15 J/cm²
– 550-650nm handpiece: 5-14 J/cm²
– Note: DPL’s energy density for treating the same skin issues is significantly lower than M22’s. As a narrowband IPL, it delivers photon energy within a 100nm range, resulting in more concentrated energy—achieving the same efficacy as long-pass filters at lower energy densities.

Similarly, the M22’s dual-wave filter blocks intermediate wavelengths, concentrating photon energy in a narrower range for stronger skin effects. Lower energy density should be used with dual-wave filters to avoid overexposure.

Overall parameter setting principles
It is important to distinguish between “gentle” and “aggressive” parameter combinations:
For very gentle treatments: Combine multiple gentle parameters.
To enhance efficacy: Avoid simultaneously increasing all parameters. Instead, personalize settings based on skin issues to maximize results while preventing burns.

Gentle parameter settings:
Multiple sub-pulses, cooling enabled (or high cooling level), wide pulse width, long delay time (cooling time), low total energy density, and low sub-pulse energy density.

Aggressive parameter settings:
Single pulse, low cooling level, narrow pulse width, short delay time (cooling time), high total energy density, and high sub-pulse energy density.

Critical reminder:
You can simultaneously lower all parameters, but never simultaneously increase all parameters.

Factors affecting IPL penetration depth
For IPL to act on target tissues, it must reach their depth—easy for the epidermis but influenced by multiple factors for the dermis.

Primary factor: Wavelength
Longer wavelengths penetrate deeper; shorter wavelengths penetrate shallower.

Skin tone (critical for dermal-targeted treatments like redness reduction or rejuvenation):
Light must pass through the epidermis to reach the dermis. Epidermal melanin absorbs大量 light, reducing energy reaching the dermis and affecting penetration depth.
To maximize rejuvenation efficacy (targeting water in the dermis):
Consider light absorption by epidermal melanin and hemoglobin in blood vessels. A heavy-pressure technique is recommended for optimal rejuvenation.