Diffusion MRI Gradient Development Scheme

Hi all,

I was going through one of the tutorial in DIPY. Th tutorial talks about how the gradient schemes are developed. The link to the tutorial is: https://dipy.org/documentation/1.3.0./examples_built/gradients_spheres/#example-gradients-spheres

I have some queries. Why do we take a sphere and consider the concept of electrostatic repulsion to develop a MRI acquisition scheme for dMRI images.