NOTE: This project is no longer actively maintained.
gradunwarp is a Python/Numpy package used to unwarp the distorted volumes (due to the gradient field іnhomogenities). Currently, it can unwarp Siemens data (and GE support very soon).
- Python (>2.7)
- Numpy (preferably, the latest)
- Scipy (preferably, the latest)
- Numpy devel package (to compile external modules written in C)
- nibabel (latest trunk, which has the MGH support)
requirements for nibabel.
- PyDICOM 0.9.5 or greater (for DICOM support)
- nose 0.11 or greater (to run the tests)
- sphinx (to build the documentation)
The installation of these in Ubuntu is as simple as
sudo apt-get install python-numpy sudo apt-get install python-scipy
For convenience both the gradunwarp and nibabel tarballs can be downloaded from
They are extracted and the following step is the same for gradunwarp and nibabel installation. First, change to the respective directory. Then,
sudo python setup.py install
Note: It is possible that you don’t have superuser permissions. In that
case, you can use the
--prefix switch of setup.py install.
python setup.py install --prefix=/home/foo/
In that case, make sure your
/home/foo/bin and make sure the
gradient_unwarp.py infile outfile manufacturer -g <coefficient file> [optional arguments]
gradient_unwarp.py sonata.mgh testoutson.mgh siemens -g coeff_Sonata.grad --fovmin -.15 --fovmax .15 --numpoints 40 gradient_unwarp.py avanto.mgh testoutava.mgh siemens -g coeff_AS05.grad -n
The input file (in Nifti or MGH formats) followed by the output file name (which has the Nifti or MGH extensions — .nii/.nii.gz/.mgh/.mgz) followed by the vendor name.
-c <coef_file> -g <grad_file>
The coefficient file (which is acquired from the vendor) is specified
-g option, to be used with files of type
Or it can be specified using a
-c in the case you have the
These two options are mutually exclusive.
-n : If you want to suppress the jacobian intensity correction -w : if the volume is to be warped rather than unwarped --fovmin <fovmin> : a float argument which specifies the minimum extent of the grid where spherical harmonics are evaluated. (in meters). Default is -.3 --fovmax <fovmax> : a float argument which specifies the maximum extent of the grid where spherical harmonics are evaluated. (in meters). Default is .3 --numpoints <numpoints> : an int argument which specifies the number of points in the grid. (in each direction). Default is 60 --interp_order <order of interpolation> : takes values from 1 to 4. 1 means the interpolation is going to be linear which is a faster method but not as good as higher order interpolations. --help : display help
gradunwarp tends to use quite a bit of memory because of the intense spherical harmonics calculation and interpolations performed multiple times. For instance, it uses almost 85% memory of a 2GB memory 2.2GHz DualCore system to perform unwarping of a 256^3 volume with 40^3 spherical harmonics grid. (It typically takes 4 to 5 minutes for the entire unwarping)
- Use lower resolution volumes if possible
- Run gradunwarp in a computer with more memory
- Use —numpoints to reduce the grid size. —fovmin and —fovmax can be used to move the grid close to your data extents.
- Use non-compressed source volumes. i.e. .mgh and .nii instead of .mgz/.nii.gz
- Recent versions of Python, numpy and scipy
- support for GE processing (near future)
- better support for high res volumes (process it slice-by-slice?)
- report statistics
- explore removal of Numpy-devel dependency if the speedup is not that significant
- slice by slice processing
- x-y flip bug fix
- force 32-bit output in 64-bit systems
gradunwarp is licensed under the terms of the MIT license. Please see the COPYING file in the distribution. gradunwarp also bundles Nibabel (http://nipy.org/nibabel ) which is licensed under the MIT license as well.
- Jon Polimeni - gradunwarp follows his original MATLAB code
- Karl Helmer - Project Incharge
- Nibabel team