Function gaussian_smooth_3d 

pub fn gaussian_smooth_3d(
    data: &[f64],
    sigma: [f64; 3],
    mask: Option<&[u8]>,
    weight: Option<&mut [f64]>,
    nbox: usize,
    nx: usize,
    ny: usize,
    nz: usize,
) -> Vec<f64>

3D Gaussian smoothing using box filter approximation

This matches MriResearchTools.jl’s gaussiansmooth3d function.

Parameters:

• data: input 3D data (will be copied)
• sigma: sigma values for each dimension [sx, sy, sz]
• mask: optional mask (None = no masking)
• weight: optional weights (None = no weighting)
• nbox: number of box filter passes (default 3, or 4 with mask)
• nx, ny, nz: dimensions