title: Simulation of heat distribution and thermal damage patterns of diode hair-removal lasers: an applicable method for optimizing treatment parameters.
abstract: OBJECTIVE
  We simulated the heat distribution and thermal damage patterns of diode hair-removal lasers for different spot sizes, pulse durations, and fluences as a guide for optimization.
  
  
  BACKGROUND
  Recently, the concept of thermal damage time as a reference for pulse duration has become a subject of debate.
  
  
  METHODS
  Laser-Induced-Temperature-Calculation-In-Tissue (LITCIT) was used for the simulations. Skin was modeled as two homogenous layers of epidermis/dermis and two coaxial cylinders as the hair shaft/ follicle. Opto-thermal coefficients of the components and the radiant parameters of the laser (diode, 810 nm) were defined.
  
  
  RESULTS
  At constant fluences and pulse durations, the damage occurred deeper when larger spot sizes were used. At constant pulse duration, high fluences caused significant damage to the hair follicle and epidermis. By using longer pulse durations (≤ 400 ms) at constant fluences, there was more effective damage to the hair follicle while sparing the adjacent epidermis and dermis. Because of the time-dependent temperature profiles, an increased pulse duration creates a moderate, gradual rise in the target's temperature. Pulse durations > 400 ms are accompanied by unwanted dermis damage.
  
  
  CONCLUSIONS
  Our results show that using very long pulse durations near the tissue damage time (≤ 400 ms) creates better efficacy in treating unwanted hairs while avoiding unwanted damage.
authors.affiliation: Iranian Center for Medical Lasers, Academic Center for Education, Culture and Research, Tehran.
authors.forename: Leila
authors.initials: L
authors.lastname: Ataie-Fashtami
authors.forename: Afshan
authors.initials: A
authors.lastname: Shirkavand
authors.forename: Saeed
authors.initials: S
authors.lastname: Sarkar
authors.forename: Mohammadreza
authors.initials: M
authors.lastname: Alinaghizadeh
authors.forename: Marjaneh
authors.initials: M
authors.lastname: Hejazi
authors.forename: Mohsen
authors.initials: M
authors.lastname: Fateh
authors.forename: Gholamreza
authors.initials: G
authors.lastname: Esmaeeli Djavid
authors.forename: Nasrin
authors.initials: N
authors.lastname: Zand
authors.forename: Hanieh
authors.initials: H
authors.lastname: Mohammadreza
mesh_terms: D002056:Burns / Q000209:etiology*; D006204:Hair Removal / Q000009:adverse effects* / Q000295:instrumentation* / Q000379:methods; D006358:Hot Temperature; D006801:Humans; D054023:Lasers, Semiconductor / Q000009:adverse effects; D009010:Monte Carlo Method; D013997:Time Factors