Vascular response to laser photothermolysis as a function of pulse duration, vessel type, and diameter: Implications for port wine stain laser therapy

Autor: Lars O. Svaasand, J. Stuart Nelson, Danielle Cao, Marie J. Hammer-Wilson, Sol Kimel
Rok vydání: 2002
Předmět:
Zdroj: Lasers in Surgery and Medicine. 30:160-169
ISSN: 1096-9101
0196-8092
Popis: Background and Objective Treatment of port wine stains (PWS) by photothermolysis can be improved by optimizing laser parameters on an individual patient basis. We have studied the critical role of pulse duration (tp) on the treatment efficacy. Study Design/Materials and Methods The V-beam laser (Candela) allowed changing tp over user-specified discrete values between 1.5 and 40 milliseconds by delivering a series of 100 microsecond spikes. For the 1.5 and 3 millisecond pulses, three spikes were observed at intervals tp/2 and for tp ≥ 6 milliseconds, four spikes separated by tp/3. The ScleroPlus laser (Candela) has a smooth output over its fixed 1.5 milliseconds duration. Blood vessels in the chick chorioallantoic membrane (CAM) were irradiated at fixed wavelength (595 nm), spot size (7 mm), radiant exposure (15 Jcm−2), and at variable tp. The CAM contains an extensive microvascular network ranging from capillaries with diameter D 0.05). Conclusions The difference between initial arteriole and venule damage could be explained by the threefold higher absorption coefficient at 595 nm in (oxygen-poor!) arterioles. In human patients, PWS consist of ectatic venules (characterized by higher absorption), so that these considerations favor the use of 595-nm irradiation for laser photothermolysis. For optimal treatment of PWS it is proposed that tp be between 0.1 and 1.5 milliseconds. This is based on a modified relaxation time τd′, defined as the time required for heat conduction into the full thickness of the vessel wall, which is assumed to have a thickness ΔD ≈ 0.1D. The corresponding τd′ will be a factor of about six smaller than given in the literature. For vessels with D between 30 and 300 μm, τd′ ranges from 0.1 to 1.5 milliseconds. Lasers Surg. Med. 30:160–169, 2002. © 2002 Wiley-Liss, Inc.
Databáze: OpenAIRE
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