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

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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.