We explore the use of Monte-Carlo based optical modeling to predict light propagation, sensitivity, and optical interrogation volume (photon hitting density) of a miniature tissue-implantable optical sensor system. There are a limited number of Monte Carlo tools available that allow for the direct import of 3D models of complex optoelectronic systems. We therefore investigate the use of TracePro, a commercial Monte Carlo-based ray-tracing software package, to guide the design of a needle-injectable optical sensor designed for tumor monitoring. We first validated the use of TracePro to model light propagation in multiple scattering tissue by modeling simple infinite geometry systems and comparing light propagation to the known analytical diffusion approximation solutions. We also analyzed ray-tracing history (i.e., photon paths) and observed agreement to analytical models of the optical interrogation volume, varying by an average of 12% across source-detector separations ranging from 5 to 15mm. Finally, we describe how this approach was used to analyze and guide the design of the implantable optical sensor for tumor monitoring. Overall, TracePro provides a straightforward, easy-to-use, and accurate approach to importing and analyzing complex diffuse optical sensing systems.
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