Comparison of Wavelength-Dependent Penetration Depth of 532 nm and 660 nm Lasers in Different Tissue Types

The depth of laser light penetration into tissue is a critical factor in determining the effectiveness of photodynamic therapy (PDT). However, the optimal laser light penetration depth necessary for achieving maximum therapeutic outcomes in PDT remains unclear. This study aimed to assess the effectiveness of laser light penetration depth at two specific wavelengths, 532 nm and 660 mm.

Chicken and beef of different thicknesses (1, 3, 5, 10, and 20 mm ± 0.2 mm) were used as in vitro tissue models. The samples were subjected to irradiation by a low-level laser diode of 532 and 660 nm in continuous mode for 10 minutes. with power densities of 167 and 142 J/cm2, respectively. Laser light transmission through the tissue was measured using a power meter.

For beef samples, the 660 nm wavelength achieved a maximum transmission intensity of 30.7% at 1 cm thickness, while the 532 nm laser had a transmission intensity of 6.5%. Similarly, in chicken breast samples, the maximum transmission occurred at 1 cm thickness with 68.1% for the 660 nm wavelength and 18.2% for the 532 nm laser.

Results consistently demonstrated a significant correlation (P < 0.05) between tissue thickness and laser light penetration. Thicker tissues exhibited faster declines in light transmission intensity compared to thinner tissues within 10 minutes. These findings highlight the importance of further research to enhance light delivery in thicker tissues and improve the efficacy of PDT in various medical conditions.