Thank you guys for your excellent comments. For 1, I still do not understand the physiological basis of the Interpolation function. I want to know the relationship between image data and diffusivity. For 2, I am almost okay. For 3, the basis of feeding 798 and 654 into the reaction diffusion equation is still beyond me. I need to be able to explain the mathematics of the codes!

@b3m2a1, done! Your contribution is still an excellent one. Thanks!

@b3m2a1, thank you for the important information!

Thanks m_goldberg. I have now included the code and would be very happy to have your opinion once again.

Thanks rhermans for the encouragement. I have made modifications to my question and I am sorry for the ambiguities in the earlier form of the question.

Done! Thanks once again.