TRT: Thermal Relaxation Time
What is TRT?
Thermal Relaxation Time (TRT) is an important concept in laser treatments that ensures both safety and effectiveness. It refers to the time it takes for a target in the skin—such as a hair follicle, blood vessel, or pigment spot—to cool down to half of the heat absorbed from a laser. For optimal results, the laser pulse is set to be equal to or shorter than the target’s TRT, allowing the energy to stay concentrated and destroy the target without affecting surrounding tissue. If the pulse is too long, heat can spread and damage nearby skin; if it’s too short, the target may not receive enough energy for effective treatment. By carefully matching laser settings to TRT, clinicians can safely treat concerns like unwanted hair, pigmentation, and vascular lesions with precision and minimal side effects. TRT is dependent on the indication and the energy/parameters of the laser. Apolomed devices are suited to calculate and adjust the TRT automatically, leaving no wasted energy nor uncontrollable risks on the patient’s skin.
|
Target / Indication |
Typical Size |
Approx. TRT |
Laser Considerations |
|
Epidermis (melanin) |
20–100 µm |
1–10 ms |
Used in hair removal, pigment lesions. Pulse duration < TRT (e.g. 1–10 ms). |
|
Hair follicle (terminal hair) |
200–300 µm |
40–100 ms |
Long-pulsed lasers (e.g. 755, 810, 1064 nm) with 20–100 ms pulse width. |
|
Superficial pigmented lesions (lentigines, freckles) |
10–100 µm |
0.1–10 ms |
Q-switched / picosecond lasers with ns–ps pulses. |
|
Tattoo pigment particles |
0.1–10 µm |
10–1000 ns |
Q-switched (ns) or picosecond lasers (ps). |
|
Small blood vessels (telangiectasia) |
30–100 µm |
1–10 ms |
Pulse duration 1–10 ms (e.g. 532, 595 nm lasers). |
|
Large blood vessels (reticular veins) |
200–500 µm |
20–100 ms |
Pulse duration 20–100 ms (e.g. 1064 nm Nd:YAG). |
|
Collagen (for remodeling) |
10–100 µm |
~1–10 ms |
Fractional lasers, mid-IR wavelengths (Er:YAG, CO₂). |
|
Sebaceous glands (acne) |
300–500 µm |
100–200 ms |
Long-pulsed IR lasers (1320–1540 nm). |
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