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

通过测量脉冲光透过人和动物骨骼样品的时间点扩散函数，我们估算了骨组织在765 nm处的折合散射系数(μS)和吸收系数(μS)。为了估计这些参数，我们发展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，借助于散射介质中光子迁移的蒙特卡罗模拟(蒙特卡罗查找表法，MC-LUT法)。在45例猪、牛股骨和胫骨标本中，骨密度与μS‘呈正相关(y=3.18x+0.96r^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0.52g/cm2增加到1.52g/cm 2时，μS的变化范围为1.34~5.57/mm)，这表明应该考虑μS的如此大的变化，以便为基于近红外的血红蛋白(Hb)氧合监测和光学计算机断层扫描建立更稳健和准确的算法。骨密度与μ的密切相关也提示了皮秒时间分辨光谱分析无创性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.