In customary implementation of three-dimensional (3D) Monte Carlo (MC) numerical model of light transport in
heterogeneous biological structures, the volume of interest is divided into voxels by a rectangular spatial grid. Each
voxel is assumed to have homogeneous optical properties and curved boundaries between neighboring tissues inevitably
become serrated. This raises some concerns over realism of the modeling results, especially with regard to reflection and
refraction on such boundaries.
In order to investigate the above concern, we have implemented an augmented 3D MC code, where tissue boundaries
(e.g., blood vessel walls) are defined by analytical functions and thus maintain their shape regardless of grid
discretization. Results of the customary and augmented model are compared for a few characteristic test geometries,
mimicking a cutaneous blood vessel irradiated with a 532 nm laser beam of finite diameter.
Our analysis shows that at specific locations inside the vessel, the amount of deposited laser energy can vary between the
two models by up to 10%. Even physically relevant integral quantities, such as linear density of the energy absorbed by
the vessel, can differ by as much as 30%. Moreover, the values obtained with the customary model vary strongly with
discretization step and don’t disappear with ever finer discretization. Meanwhile, our augmented model shows no such
behavior, indicating that the customary approach suffers from inherent inaccuracies arising from physically flawed
treatment of tissue boundaries.