fit_harmonics_grids

Fit spherical harmonic coefficients to deformation grids.

fit_harmonics_grids <grid1> <mask1> [<grid2> <mask2> ...] <output.par> [options]

DESCRIPTION

fit_harmonics_grids fits spherical harmonic basis functions to one or more deformation grid volumes to produce a compact parametric model of the distortion field. Each deformation grid must be paired with a corresponding mask that defines the fitting region.

Spherical harmonics provide a smooth, global basis that is well-suited for modelling slowly varying geometric distortions such as those caused by gradient non-linearity in MRI scanners. The fitted coefficients are saved to a parameter file that can later be evaluated on an arbitrary grid using param2grid.

Multiple grid/mask pairs allow joint fitting across different acquisitions or phantom positions.

OPTIONS

--verbose

Print progress information during processing.

--clobber

Overwrite the output file if it already exists.

--order n

Maximum order of the spherical harmonic expansion.

--skip n

Skip every n-th voxel during fitting to reduce computation time.

--limit val

Exclude voxels with displacement magnitude above this threshold.

--par file

Initialize fitting from an existing parameter file.

EXAMPLES

# Fit spherical harmonics to a single grid/mask pair
fit_harmonics_grids grid.mnc mask.mnc output.par --order 10

# Joint fit across multiple acquisitions
fit_harmonics_grids grid1.mnc mask1.mnc grid2.mnc mask2.mnc \
    output.par --order 12

# Fit with voxel skipping and displacement limit
fit_harmonics_grids grid.mnc mask.mnc output.par \
    --order 8 --skip 2 --limit 10.0

AUTHOR

Vladimir S. Fonov - McConnell Brain Imaging Centre, Montreal Neurological Institute.

COPYRIGHTS

Copyright © 2009-2024 by Vladimir S. Fonov

SEE ALSO

fit_harmonics_grids_diff , fit_harmonics_grids_regularize , param2grid