title: Comparison of human skin opto-thermal response to near-infrared and visible laser irradiations: a theoretical investigation.
abstract: Near-infrared wavelengths are absorbed less by epidermal melanin, and penetrate deeper into human skin dermis and blood than visible wavelengths. Therefore, laser irradiation using near-infrared wavelengths may improve the therapeutic outcome of cutaneous hyper-vascular malformations in moderately to heavily pigmented skin patients and those with large-sized blood vessels or blood vessels extending deeply into the skin. A mathematical model composed of a Monte Carlo algorithm to estimate the distribution of absorbed light, numerical solution of a bio-heat diffusion equation to calculate the transient temperature distribution, and a damage integral based on an empirical Arrhenius relationship to quantify the tissue damage was utilized to investigate the optothermal response of human skin to near-infrared and visible laser irradiations in conjunction with cryogen spray cooling. In addition, the thermal effects of a single continuous laser pulse and micropulse-composed laser pulse profiles were compared. Simulation results indicated that a 940 nm wavelength induces improved therapeutic outcome compared with a 585 and 595 nm wavelengths for the treatment of patients with large-sized blood vessels and moderately to heavily pigmented skin. On the other hand, a 585 nm wavelength shows the best efficacy in treating small-sized blood vessels, as characterized by the largest laser-induced blood vessel damage depth compared with 595 and 940 nm wavelengths. Dermal blood content has a considerable effect on the threshold incident dosage for epidermal damage, while the effect of blood vessel size is minimal. For the same macropulse duration and incident dosage, a micropulse-composed pulse profile results in higher peak temperature at the basal layer of skin epidermis than an ideal single continuous pulse profile.
authors.affiliation: Department of Bioengineering, Rice University, Houston, TX 77251, USA.
authors.forename: Tianhong
authors.initials: T
authors.lastname: Dai
authors.forename: Brian M
authors.initials: BM
authors.lastname: Pikkula
authors.forename: Lihong V
authors.initials: LV
authors.lastname: Wang
authors.forename: Bahman
authors.initials: B
authors.lastname: Anvari
mesh_terms: D001831:Body Temperature / Q000528:radiation effects; D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D007259:Infrared Rays / Q000627:therapeutic use*; D017075:Laser Coagulation / Q000379:methods*; D053685:Laser Therapy; D008954:Models, Biological; D011879:Radiotherapy Dosage; D012867:Skin / Q000098:blood supply / Q000528:radiation effects*; D012871:Skin Diseases / Q000503:physiopathology / Q000601:surgery*; D013684:Telangiectasis / Q000503:physiopathology / Q000601:surgery*; D013813:Therapy, Computer-Assisted / Q000379:methods; D016896:Treatment Outcome