Light transport in the human spine for optical bone density assessment: Monte Carlo modeling and validation

Spinal disorders are an increasing global health concern, especially in aging populations. Conventional diagnostic methods rely on ionizing radiation, limiting their suitability for portable or frequent assessments. Near-infrared spectroscopy provides a promising non-invasive alternative for evaluating spinal properties, particularly bone mineral density (BMD). This study explores the feasibility of optical monitoring through Monte Carlo simulations based on the Visible Chinese Human dataset. Photon migration at 660, 808, and 980 nm was quantified and visualized, with 808 nm demonstrating the largest penetration depth of up to 3.5 cm in the spinal region. The optimal source-detector separation was identified as 3.4-3.8 cm. In vivo measurements in human subjects further validated the reliability of the simulation results. The pilot experiment revealed a significant correlation between detected signal and BMD, with lower BMD associated with relatively higher light intensity. These findings highlight the potential of optical techniques for spinal BMD assessment and support the development of portable monitoring systems.