Characterization of fractional photothermolysis and visualization of microthermal zone with optical coherence tomography

In this study, an optical coherence tomography (OCT) system is implemented for the noninvasive characterization of photothermolysis in human skin induced by ablative fractional lasers (AFLs) and non-ablative fractional lasers (NAFLs). With OCT imaging, microthermal zones (MZTs) induced by fractional lasers can be noninvasively visualized, and the size of induced MZTs can be quantitatively evaluated. According to the OCT results, the center region of the induced MZT corresponds to weaker backscattered intensity after the AFL exposure as a result of tissue volatilization by photon energy. In contrast, after the NAFL exposure, the skin tissue is damaged and coagulated but not volatilized, which causes the backscattered intensity of the induced MZT enhanced in the OCT image. To further identify the photothermolysis induced by AFLs or NAFLs, the backscattered intensities of MZTs are compared with those of the untreated tissue from the OCT results. The statistical result shows a clear difference in scattering properties of photothermolysis induced by AFLs and NAFLs. Finally, the induced photodamage at various depths can also be quantitatively evaluated, enabling an investigation of the relationship between the photodamage and the depth.