Develop an algorithm to estimate the cortical thickness map

From the given raw weighted image you need to measure cortical thickness map. It is the thickness of the gray matter of the brain at every point and it is the distance between the white matter and the pial surface. The output should be a python script with a 3D volume where every pixel not in gray matter is assigned a value ZERO and for every pixel in the gray matter is assigned the thickness value of the cortex at that point.
Input data sets will be given. you need to use nibabel libraries to load image.
Note: The entire project must be done in python using numpy libraries.