Zeng H, MacAulay C, McLean D I, Palcic B, Lui H
Cancer Imaging Department, British Columbia Cancer Research Centre, Vancouver, Canada.
Photochem Photobiol. 1998 Aug;68(2):227-36.
To study the temporal dynamics of human skin autofluorescence photobleaching, we measured the autofluorescence spectral changes of skin in vivo during continuous exposure to 442 nm (He-Cd) laser light. Integral intensities were calculated for various spectral wavelength bands and plotted as a function of time. Mathematical analysis of the time function revealed a double-exponential photobleaching process: I(t) = a exp (-t/tau 1) + b exp(-t/tau 2) + c, in which tau 1 and tau 2 differed by an order of magnitude. A hypothesis for the mechanism of the double-exponential photobleaching dynamics was proposed and evaluated using Monte Carlo modeling of light propagation in the skin and autofluorescence escape from skin. By combining the fluorophore microdistributions, Monte Carlo simulation results and the variation in fluorescence decrease parameters (a, b, c, tau 1, tau 2) with increasing exposure intensities a biophysical explanation for the double-exponential photobleaching function was elucidated. The fast decrease term corresponds to laser-induced photobleaching in the stratum corneum, while the slow decrease term represents fluorophore changes in the dermis. The measured autofluorescence photobleaching dynamics can be used to determine the fractional contributions of different skin layers to the total autofluorescence signal measured in vivo.
为了研究人体皮肤自发荧光光漂白的时间动态变化，我们在连续暴露于442nm（氦镉）激光的过程中，测量了活体皮肤的自发荧光光谱变化。计算了各个光谱波段的积分强度，并将其绘制为时间的函数。对时间函数的数学分析揭示了一个双指数光漂白过程：I(t)=a exp(-t/τ1)+b exp(-t/τ2)+c，其中τ1和τ2相差一个数量级。我们提出了双指数光漂白动力学机制的假设，并通过对皮肤中光传播和自发荧光从皮肤逸出的蒙特卡罗建模进行了评估。通过结合荧光团的微观分布、蒙特卡罗模拟结果以及随着暴露强度增加荧光下降参数（a、b、c、τ1、τ2）的变化，阐明了双指数光漂白函数的生物物理学解释。快速下降项对应于角质层中激光诱导的光漂白，而缓慢下降项代表真皮中荧光团的变化。所测量的自发荧光光漂白动力学可用于确定不同皮肤层对活体测量的总自发荧光信号的分数贡献。
