Noninvasive qualification and quantification of bone mineral density and bone quality in vitro by means of picosecond time-resolved spectroscopy

通过测量脉冲光通过分离的人骨和动物骨样品的时间点扩展函数，我们估计了在765 nm处骨组织的降低散射系数（μs’）和吸收系数（μs）。为了估计这些参数，我们开发了一种新的方法来量化相对较小的光散射和吸收材料的光学常数，通过蒙特卡罗模拟散射介质中的光子迁移（蒙特卡罗查找表法，MC-LUT法）。在45个猪、牛大腿和胫骨标本中，骨密度（BMD）与μs′呈密切相关（y = 3.18x + 0.96, r^2 = 0.953）。与骨密度变化相关的μs‘也有相当大的变化（当骨密度从0.52 g/cm^2增加到1.52 g/cm^2时，μs’的变化范围从1.34到5.57/mm），这表明为了建立基于nil的血红蛋白（Hb）氧合监测和光学计算机断层扫描更健壮和准确的算法，应该考虑μs'的这种大变化。骨密度与μs之间的密切相关也提示了体内皮秒时间分辨光谱法无创测定骨密度的可行性。

By measuring temporal point-spread function of pulsed light transmitted through isolated human and animal bone samples, we estimated reduced scattering coefficient (μs') and absorption coefficient (μs) of bone tissues at 765 nm. To estimate these parameters, we developed a novel method for quantification of optical constants of relatively small light-scattering and absorbing materials by means of Monte Carlo simulation of photon migration within scattering media (Monte Carlo look-up table method, MC-LUT method). Among 45 samples prepared from pig and cow thigh and shinbones, a tight correlation between bone mineral density (BMD) and μs' (y = 3.18x + 0.96, r^2 = 0.953) was found. There were also considerable variations in μs' associated with changes in BMD (μs' ranged from 1.34 to 5.57/mm when BMD increased from 0.52 up to 1.52 g/cm^2), indicating that such large variations in μs' should be taken into account in order to establish more robust and accurate algorithms for NIR-based hemoglobin (Hb) oxygenation monitoring and optical computed tomography. The tight correlation between BMD and μs' also suggested the feasibility of noninvasive determination of BMD by means of in vivo picosecond time-resolved spectroscopy.