  Biological tissues are complex structures composed of many elements which
make light-based tissue diagnostics challenging. Over the past decades, Monte
Carlo technique has been used as a fundamental and versatile approach toward
modeling photon-tissue interactions. This report first describes a MC
simulation of steady-state light transport in an absorbing and diffusing
multi-layered structure. Further, a parallel processing solution is implemented
to reduce execution time and memory requirements. Then, the nonparametric phase
function, which is a discretized version of the phase function, has been
discussed where the integration of the phase function is a numerical process,
instead of an analytical operation. Finally, to simulate more realistic
structures of biological systems, simulations are modified to incorporate
objects of various shapes (sphere, ellipsoid, or cylinder) with a
refractive-index mismatched boundary. The output files mainly contain 2D
reflection matrix, 2D transmission matrix, and 3D absorption matrix.
