A minimal Monte Carlo program for simulating steady-state light distributions in tissues.

Monte Carlo programming code is available from various sources, and there are many books on the subject. This article is intended to conveniently and quickly enable the student to begin using the Monte Carlo method to model photon transport. Further reading is recommended for the serious student.

A simple program called "mc321.c" is listed here for compilation by the student. It is written in ANSI Standard C and should compile on any platform. Students will need a C compiler on their own computer.

The following pages discuss the various sections of "mc321.c":

• Example figure produced by the program
• Introduction to the basic program
• Header statements
• Definitions of variables and arrays
• User settings for optical properties, etc.
• Launching photon
• Moving a photon through tissue
  • Photon hops to new position where photon-tissue interaction occurs
  • Photon drops some photon weight in local bin arrays due to absorption
  • Photon spins into new trajectory due to scattering
  • Terminating a photon by "roulette" method
• Save bin arrays as output file for graphical plotting

Students are encouraged to modify the program. Some example modifications are listed:

• Launching a collimated narrow beam of photons
• Launching a collimated finite-diameter beam Launching a

This minimal program as written does NOT consider an air/tissue surface or other mismatched boundaries. The program models an infinite unbounded medium with absorption and scattering properties.

The "mc321.c" program was used in writing the published report: S. L. Jacques: "Light distributions from point, line, and plane sources for photochemical reactions and fluorescence in turbid biological tissues," Photochem. Photobiol. 67:23-32, 1998.