ABSTRACT Background Thermal energy‐based technologies are widely used for noninvasive body contouring; however, quantitative characterization of fascia‐level heat propagation in body tissues during multi‐wavelength diode laser irradiation remains limited. Objective To assess fascia‐level temperature kinetics and regional differences in deep‐plane heating during stacking delivery of a multi‐wavelength diode laser (Fortra, Classys Inc., Korea) in human cadaver tissues. Methods Three fresh‐frozen human cadavers underwent laser irradiation at the abdomen, anterior thigh, and lateral upper arm. Subcutaneous fat thickness was measured by ultrasonography. A single thermocouple was inserted to the muscle fascial plane to record fascia‐level temperature over time, and infrared thermography of the exposed measurement field was performed after tissue exposure to identify the local thermographic peak. Deep fascial arrival time, peak fascial temperature, exposed‐field thermographic peak temperature, and fascia‐level cumulative equivalent minutes at 43°C (CEM43) were evaluated. Regional comparisons were descriptive, with exploratory nonparametric testing. Results Heat reached the muscle fascia fastest in the anterior thigh (4.9 ± 0.4 s), followed by the lateral upper arm (5.3 ± 0.5 s), and slowest in the abdomen (6.6 ± 0.6 s). These values represent mean ± SD of cadaver‐level means. Regional differences in fascial arrival time were exploratory but reached significance (Friedman test, p = 0.049). Exposed‐field thermographic peak temperatures were highest in the anterior thigh (70°C–72°C), followed by the lateral upper arm (68°C–71°C), and lowest in the abdomen (65°C–68°C). Conclusions Under non‐perfused ex vivo conditions, fascia‐level thermal behavior during multi‐wavelength diode laser irradiation varied by anatomical region. Greater subcutaneous fat thickness was associated with slower fascial heat arrival, but did not fully explain regional variation. These findings are descriptive and do not establish volumetric heat distribution, histologic injury, or in vivo safety thresholds.
Yi et al. (2026) studied this question.