Optical Absorption of Blood Depends on Temperature during a 0.5 ms Laser Pulse at 586 nm |
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Authors: | Wim Verkruysse Annika M K Nilsson Thomas E Milner Johan F Beek Gerald W Lucassen Martin J C van Gemert |
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Institution: | Laser Centre, Academic Medical Centre at the University of Amsterdam, The Netherlands;Department of Physics, Lund Institute of Technology, Lund, Sweden;Beckman Laser Institute and Medical Clinic, University of California Irvine, Irvine, CA, USA;Philips Research Laboratories, Eindhoven, The Netherlands |
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Abstract: | Optical properties are important parameters in port wine stain laser treatment models. In this study we investigated whether changes in blood optical properties occur during a 0.5 ms laser pulse. Blood from three volunteers was irradiated in vitro with laser pulses (radiant exposure 2–12 J cm?2, wavelength 586 nm, pulse length 0.5 ms). Reflection and transmission coefficients, measured using double integrating spheres, decreased slightly during the first part of the pulse. At 2.9 J cm?2 radiant exposure, the reflectance increased, independent of total 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 J cm–2 and was accompanied by a "popping" sound, indicating rapid expansion of bubbles due to blood vaporization. A multilayered model of blood was used to fit calculated transmission coefficient curves to the measurements and determine temperature-dependent optical blood absorption. Heat diffusion was shown to be of minor importance. A 2.5-fold increase in absorption for temperatures increasing from 20 to 100°C, accurately describes transmission coefficients measured up to 2.9 J cm?2. |
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