Wavelength-dependent threshold fluences for melanosome disruption to evaluate the treatment of pigmented lesions with 532-, 730-, 755-, 785-, and 1064-nm picosecond lasers

Yu Shimojo; Takahiro Nishimura; Daisuke Tsuruta; Toshiyuki Ozawa; Henry Hin Lee Chan; Taro Kono

doi:10.1002/lsm.23773

Wavelength-dependent threshold fluences for melanosome disruption to evaluate the treatment of pigmented lesions with 532-, 730-, 755-, 785-, and 1064-nm picosecond lasers

Lasers Surg Med. 2024 Apr;56(4):404-418. doi: 10.1002/lsm.23773. Epub 2024 Mar 4.

Authors

Yu Shimojo^{1

2

3}, Takahiro Nishimura², Daisuke Tsuruta¹, Toshiyuki Ozawa¹, Henry Hin Lee Chan⁴, Taro Kono⁵

Affiliations

¹ Graduate School of Medicine, Osaka Metropolitan University, Osaka, Japan.
² Graduate School of Engineering, Osaka University, Osaka, Japan.
³ Research Fellow of Japan Society for the Promotion of Science, Tokyo, Japan.
⁴ Department of Medicine, Division of Dermatology, The University of Hong Kong, Hong Kong SAR, China.
⁵ Department of Plastic Surgery, School of Medicine, Tokai University, Kanagawa, Japan.

PMID: 38436524
DOI: 10.1002/lsm.23773

Abstract

Background and objectives: A threshold fluence for melanosome disruption has the potential to provide a robust numerical indicator for establishing clinical endpoints for pigmented lesion treatment using a picosecond laser. Although the thresholds for a 755-nm picosecond laser were previously reported, the wavelength dependence has not been investigated. In this study, wavelength-dependent threshold fluences for melanosome disruption were determined. Using a mathematical model based on the thresholds, irradiation parameters for 532-, 730-, 755-, 785-, and 1064-nm picosecond laser treatments were evaluated quantitatively.

Study design/materials and methods: A suspension of melanosomes extracted from porcine eyes was irradiated using picosecond lasers with varying fluence. The mean particle size of the irradiated melanosomes was measured by dynamic light scattering, and their disruption was observed by scanning electron microscopy to determine the disruption thresholds. A mathematical model was developed, combined with the threshold obtained and Monte Carlo light transport to calculate irradiation parameters required to disrupt melanosomes within the skin tissue.

Results: The threshold fluences were determined to be 0.95, 2.25, 2.75, and 6.50 J/cm² for 532-, 730-, 785-, and 1064-nm picosecond lasers, respectively. The numerical results quantitatively revealed the relationship between irradiation wavelength, incident fluence, and spot size required to disrupt melanosomes distributed at different depths in the skin tissue. The calculated irradiation parameters were consistent with clinical parameters that showed high efficacy with a low incidence of complications.

Conclusion: The wavelength-dependent thresholds for melanosome disruption were determined. The results of the evaluation of irradiation parameters from the threshold-based analysis provided numerical indicators for setting the clinical endpoints for 532-, 730-, 755-, 785-, and 1064-nm picosecond lasers.

Keywords: 1064 nm; 532 nm; 730 nm; 755 nm; 785 nm; clinical endpoint; melanosome disruption; picosecond laser; pigmented lesion; threshold fluence.

MeSH terms

Animals
Lasers
Lasers, Solid-State* / therapeutic use
Melanosomes* / radiation effects
Skin / radiation effects
Swine
Treatment Outcome