Pulsed CO₂ laser tissue ablation: Effect of tissue type and pulse duration on thermal damage

Abstract

Tissue removal by infrared lasers is accompanied by thermal damage to nonablated tissue. The extent of thermal damage can be controlled by a choice of laser wavelength, irradiance, and exposure duration. The effect of exposure duration has been studied in vivo by using CO2 lasers with pulse widths that vary from 2 microseconds to 50 msec. Pulse widths of 50 msec, typical of a shuttered, continuous-wave CO2 laser, produce damage regions 750 micron wide in normal guinea pig skin; the use of a 2-microseconds-long pulse reduced this damage zone to as little as 50 micron. Using 2-microseconds-long pulses, in vitro studies showed that the minimum zone of thermal damage varied significantly with tissue type. The thermal denaturation of these tissues has been studied and correlated with damage. The effect of denaturation temperature and pulse duration on the width of the damage zone is explained by a simple model.

Effects of overlap and pass number in CO2 laser skin resurfacing: A study of residual thermal damage, cell death, and wound healing

“…Most resurfacing CO 2 lasers operate at fluences just at or above threshold, so that only a fraction of the energy is used for ablation; the majority is invested in heating of tissue water. This heat diffuses radially and forms concentric reproducible temperature zones that extend from the hot surface to the cooler periphery [16][17][18]. Thus, nonablative models can be used to characterize CO 2 LSR heating for typical fluences.…”

Wound healing and collagen thermal damage in 7.5-?sec pulsed CO2 laser skin incisions

“…Walsh et al showed that CO 2 laser with short pulse structures cause less thermal damage than those created by a continuous wave (CW) laser [12], and this has been confirmed by others [6,[13][14]. These studies have identified the importance of the pulse length in relation to the thermal relaxation time, a time constant that is the amount of time required for thermal energy to diffuse to surrounding tissues, thus heating and injuring them.…”

“…These studies have identified the importance of the pulse length in relation to the thermal relaxation time, a time constant that is the amount of time required for thermal energy to diffuse to surrounding tissues, thus heating and injuring them. This time has been estimated by several models as ranging from 7 to 700 sec [12,[15][16]. Thus, a pulse duration shorter than this should show less thermal damage because the laser energy is delivered so quickly that it cannot diffuse to surrounding tissues.…”

Permanent and transient changes in the reflectance of CO2 laser-irradiated dental hard tissues at λ = 9.3, 9.6, 10.3, and 10.6 μm and at fluences of 1–20 J/cm2

“…CO 2 lasers can also be used to ablate carious tissue and have the potential for use for cavity preparations [8,9]. Featherstone and coworkers [3,5,10] studied the effects of low-energy pulsed CO 2 laser radiation on human dental enamel and dentin for laser wavelengths between 9.3 and 10.6 m. Scanning electron microscopy (SEM) studies [4] showed that the surface effects were highly wavelength dependent in this region and that 9.3 m and 9.6 m wavelengths were more efficient at modifying the surface of enamel than the longer CO 2 wavelengths.…”