Input: Anisotropic diffused volume data.
   Output: Visualization result of biomedical volume data.
1 for each voxel p(x,y,z)  do
2   chose adjacent voxels in the region space ;
3   calculate the intensity median of ;
4   calculate the variance of ;
5   set the value of estimation radius ;
6   if   then
7    p is marked as an inner voxel;
8    ;
9   else
10     is considered to be the boundary voxel;
11    use the second order Runge-Kutta method to search FL and FH value of ;
12 end
13 end
14 compute the depth information for each voxel;
15 construct the depth LH histogram and design the transfer function;
16 visualize the volume data according to the transfer function;
Algorithm 1: Region space guided visualization.