Function create_sphere_mask 

pub fn create_sphere_mask(
    grid: &Grid,
    center_x: f64,
    center_y: f64,
    center_z: f64,
    radius: f64,
) -> Vec<u8> 

Create a binary sphere mask on a 3D volume

Generates a mask where voxels within the specified radius of the center are set to 1, and all others are 0. Uses Fortran (column-major) ordering to match NIfTI convention: index = x + ynx + znx*ny.

Arguments

• grid - Volume grid (dimensions and voxel sizes)
• center_x, center_y, center_z - Sphere center in voxel coordinates
• radius - Sphere radius in voxels

Returns

Flattened binary mask of length nxnynz