Modeling light transport in tissues is crucial to the
understanding of laser-tissue interactions. A Monte Carlo model of
steady-state light transport in multi-layered tissues (MCML) and a
companion convolution program (CONV) solving responses to a collimated
finite diameter photon beam perpendicularly incident on a multi-layered
tissue has been coded in ANSI Standard C; hence, the program can be
executed on various computers. The program, employing extended
trapezoidal rule for integration, convolves the responses to an
infinitely narrow photon beam computed by MCML. Dynamic data allocation
is used for CONV as well as MCML; therefore, the number of tissue layers
and grid elements of the grid system can be varied at run time. The
program, including the source code, has been in the public domain since
1992 and can be downloaded from here.
As an example of the many applications of the models,
optimal laser light delivery into turbid biological tissues was studied
using Monte Carlo simulations based on the delta-scattering technique.
The goal was to efficiently deliver the maximum amount of optical power
into buried tumors being treated while avoiding potential damage to
normal tissue caused by strong optical power deposition underneath the
tissue surface illuminated by the laser beam. The buried tumors were
considered to have much higher absorption than the surrounding normal
tissue due to selective uptake of absorption-enhancement dye. The power
delivering efficiency to buried tumors was investigated for various
diameters of the laser beam. An optimal beam diameter was estimated to
achieve the maximum product of the power coupling efficiency and the
power delivered to the buried tumor. The distribution of power
deposition was simulated for single beam delivery and multiple beam
delivery as well. The simulated results showed that with an appropriate
dye enhancement and an optimal laser delivery configuration, a high
selectivity for laser treatment of tumor could be achieved.
Selected publications:
L.-H. Wang, "Mechanisms of
ultrasonic modulation of multiply scattered coherent light: a
Monte Carlo model," Optics Letters 26, 1191–1193 (2001). [PDF]
G. Yao, and L.-H. Wang, "Monte
Carlo simulation of optical coherence tomography in homogeneous
turbid media," Physics in Medicine and Biology, 44, 2307-2320
(1999). [PDF]
L.-H. Wang, W. R. Chen, and R.
E. Nordquist, "Optimal beam size for light delivery to
absorption-enhanced tumors buried in biological tissues and
effect of multiple beam delivery: a Monte Carlo study,"
Applied Optics 36, 8286-8291 (1997). [PDF]
L.-H. Wang, S. L. Jacques, and
L.-Q. Zheng, "MCML - Monte Carlo modeling of photon transport in
multi-layered tissues," Computer Methods and Programs in
Biomedicine 47, 131-146 (1995). [PDF]
>>Download software.<<
L.-H. Wang and S. L. Jacques,
"Hybrid model of Monte Carlo simulation diffusion theory for
light reflectance by turbid media," Journal of Optical Society
of America A 10, 1746-1752 (1993). [PDF]
