Function iqsm 

pub fn iqsm(
    phase_rad: &[f64],
    mask: &[u8],
    grid: &Grid,
    te: f64,
    b0: f64,
    phase_sign: f64,
    eroded_rad: i32,
    model_onnx: &[u8],
) -> Result<Vec<f64>, OnnxError>

Run iQSM on a single echo of wrapped phase.

• phase_rad — wrapped phase (radians), column-major (nx,ny,nz).
• mask — binary brain mask (same layout).
• te — echo time in seconds; b0 — field strength in Tesla.
• phase_sign — sign convention (-1 matches the authors’ default).
• eroded_rad — mask erosion radius in voxels (3 matches the default; 0 disables).
• model_onnx — bytes of the exported iqsm.onnx.

Returns susceptibility (ppm), masked, in the same layout.