Optical-thermal model verification by high-speed optical coherence tomography

Optical-thermal models that can accurately predict temperature rise and damage in blood vessels and surrounding tissue may be used to improve the treatment of vascular disorders. Verification of these models has been hampered by the lack of time- and depth-resolved experimental data. In vitro and in vivo studies were performed to visualize laser irradiation of blood in cuvettes or cutaneous (hamster dorsal skin flap) blood vessels. Two optical coherence tomography systems, one operating at 400 a-scans per second and the other at 4-30 frames per second, were used. For the in vitro study, a frequency doubled Nd:YAG laser was used (532 nm, 10 ms pulse duration, 2 mm spot size, 10 J/cm2 radiant exposure). In vivo, an Argon laser was employed (all lines, 0.1-2.0 s pulse duration, 0.1-1.0 mm spot size, 100- 400 mW power. Video microscopy images were compared to predictions of temperature rise and damage using Monte Carlo and finite difference techniques. In general, predicted damage agreed with actual blood, blood vessel, and surrounding tissue coagulation seen in images. However, limitations of current optical-thermal models were identified, such as the inability to model the dynamic changes in blood optical properties and vessel diameters that were seen in the optical coherence tomography images.