Derbyshire G J, Bogen D K, Unger M
Department of Bioengineering, University of Pennsylvania, Philadelphia 19104.
Lasers Surg Med. 1990;10(1):28-34. doi: 10.1002/lsm.1900100108.
Light in the visible and near-infrared region is diffusely scattered in tissues by macromolecules. It was therefore hypothesized that tissue coagulation caused by high-power continuous wave laser irradiation might significantly alter tissue optical properties, resulting in a redistribution of laser energy during the laser ablation process. Infrared transmittance studies confirmed the hypothesis by demonstrating an irreversible decrease in light transmittance (45%) during heating of a 0.75 mm thick slice of tissue. Absorption and scattering coefficients were then determined from transmittance and reflectance measurements on thin slices of raw and coagulated myocardium irradiated with a Nd:YAG laser (1.06 microns). The scattering coefficient was found to increase fourfold (0.427 mm-1----1.74 mm-1) during tissue coagulation, while the absorption coefficient remained relatively unchanged (0.044 mm-1----0.051 mm-1). Calculations indicate that the coagulation-induced changes in tissue optical properties substantially increase surface back-scattering and reduce tissue penetration.
可见光和近红外区域的光在组织中会被大分子漫散射。因此，有人推测高功率连续波激光照射引起的组织凝固可能会显著改变组织的光学特性，从而在激光消融过程中导致激光能量重新分布。红外透射率研究通过证明在加热0.75毫米厚的组织切片过程中光透射率出现不可逆下降（45%）证实了这一推测。然后，根据对用钕：钇铝石榴石激光（1.06微米）照射的未凝固和凝固心肌薄片的透射率和反射率测量结果，确定吸收系数和散射系数。发现在组织凝固过程中散射系数增加了四倍（从0.427毫米-1增加到1.74毫米-1），而吸收系数相对保持不变（从0.044毫米-1变为0.051毫米-1）。计算表明，凝固引起的组织光学特性变化会大幅增加表面后向散射并减少组织穿透深度。
