Anatomical mapping of transdermal laser irradiation over the carotid and radial arteries: a cadaveric study on light penetration and dosimetry

Abstract Objective This study aimed to map the dispersion of transdermal red-light laser irradiation in anatomical structures adjacent to the common carotid artery (CCA) and radial artery (RA). Using a cadaveric model, the investigation quantifies light attenuation and estimates the effective dosage reaching these clinically relevant vascular targets and surrounding neurovascular tissues. Methods A detailed dissection was performed on a male cadaveric specimen at the University of São Paulo, Brazil. A 660 nm continuous-wave laser with an output power of 100 mW was used, resulting in a surface irradiance of 200 mW/cm 2 over a 0.5 cm 2 area. The active laser tip was positioned perpendicularly over the CCA and RA regions for a 60-second exposure to visualize and document light dispersion. The Beer-Lambert law was applied to calculate the percentage of initial light intensity reaching each artery, using an effective tissue attenuation coefficient (μ_eff) of 0.5 mm⁻ 1 . Results Visual analysis confirmed that laser irradiation extended beyond the target arteries, illuminating significant adjacent structures. At the neck, the vagus nerve, internal jugular vein, and sternocleidomastoid muscle were irradiated. At the wrist, the median nerve and pronator quadratus muscle were affected. Dosimetric calculations revealed a substantial difference in light penetration: approximately 28.65% of the surface light intensity reached the RA (at a depth of 2.5 mm), while only 0.0045% reached the CCA (at a depth of 20 mm). The estimated irradiance at the RA was 57.30 mW/cm 2 , a therapeutically relevant dose, whereas the irradiance at the CCA was negligible (0.0091 mW/cm 2 ). Conclusion This anatomical and dosimetric analysis demonstrates that the RA is a far more efficient and predictable site for transdermal laser therapy aiming for systemic vascular effects compared to the CCA, due to its superficial location. The study highlights that transdermal laser application is not target-specific, resulting in the concomitant irradiation of multiple neurovascular and muscular structures. This expanded regional photobiomodulation should be considered when interpreting clinical outcomes and designing therapeutic protocols. These findings provide a critical anatomical and physical basis for future research in systemic photobiomodulation.