Creating an inhomogeneous medium: inhomogeneous.m

This example demonstrates how define inhomogeneous optical properties

xsize =  10;	% width of the region [mm]
ysize =  10;	% height of the region [mm]
dh = 1;         % discretisation size [mm]
vmcmesh = createRectangularMesh(xsize, ysize, dh);

Give varying optical parameters

% Set constant background coefficients

vmcmedium.absorption_coefficient = 0.01;     % absorption coefficient [1/mm]
vmcmedium.scattering_coefficient = 1.0;      % scattering coefficient [1/mm]
vmcmedium.scattering_anisotropy = 0.9;       % anisotropy parameter g of
                                             % the Heneye-Greenstein scattering
                                             % phase function [unitless]
vmcmedium.refractive_index = 1.3;            % refractive index [unitless]

% Resize the fields in vmcmedium so that they match the number of elements in the mesh
vmcmedium = createMedium(vmcmesh,vmcmedium);

% Select elements from the mesh
radius = 2.5;                 % [mm]
centercoord = [0.0  0.0];     % [mm]
elements_of_the_circle = findElements(vmcmesh, 'circle', centercoord, radius);

% Assign a unique absorption coefficient to the selected elements
vmcmedium.absorption_coefficient(elements_of_the_circle) = 0.25;

Plot the parameter distribution

The resulting absorption coefficient distribution is shown in the figure below. Shown is also the circle that was used to select the elements.

Note that some triangles intersect the circle, resulting in a poor representation of the circular shape. The representation can be improved by a better mesh or by incresing the discretisation size.

Create a light source

vmcboundary.lightsource(4:7) = {'cosinic'};

Run the Monte Carlo simulation

solution = ValoMC(vmcmesh, vmcmedium, vmcboundary);

                 ValoMC-2D
--------------------------------------------
  Version:  v1.0b-118-g853f111
  Revision: 131
  OpenMP enabled                     
  Using 16 threads
--------------------------------------------
Initializing MC2D...
Computing... 
...done

Done

Plot the solution

Note how the area with the higher absorption coefficient affects the fluence distribution (c.f. 'Simple Example')