OPTICAL-ABSORPTION OF BLOOD DEPENDS ON TEMPERATURE DURING A 0.5 MS LASER-PULSE AT 586 NM

Optical properties are important parameters in port wine stain laser t reatment models. In this study we investigated whether changes in bloo d optical properties occur during a 0.5 ms laser pulse, Blood from thr ee volunteers was irradiated in vitro with laser pulses (radiant expos ure 2-12 J cm(-2), wavelength 586 nm, pulse length 0.5 ms). Reflection and transmission coefficients, measured using double integrating sphe res, decreased slightly during the first part of the pulse. At 2.9 J c m(-2) radiant exposure, the reflectance increased, independent of tota l radiant exposure of the pulse, This was-caused by blood coagulation, A second sudden increase in reflection and a significant increase in transmission occurred near 6.3 9 cm(-2) and was accompanied by a ''pop ping'' sound, indicating rapid expansion of bubbles due to blood vapor ization. A multilayered model of blood was used to fit calculated tran smission coefficient curves to the measurements and determine temperat ure-dependent optical blood absorption, Heat diffusion was shown to be of minor importance, A 2.5-fold increase in absorption for temperatur es increasing from 20 to 100 degrees C, accurately describes transmiss ion coefficients measured up to 2.9 J cm(-2).