NeuroImaging in PyTorch

NITorch is a library written in PyTorch aimed at medical image processing and analysis, with a focus on neuroimaging.

It is a versatile package that implements low-level tools and high-level algorithms for deep learning and optimization-based algorithms. It implements low level differentiable functions, layers, backbones, optimizers, but also high level algorithms for registration and inverse problems as well as a set of command line utilities for manipulating medical images.

Much of the current implementation targets image registration tasks, and many differentiable transformation models are implemented (classic and Lie-encoded affine matrices, B-spline-encoded deformation fields, dense deformation fields, stationary velocity fields, geodesic shooting). All of these models can be used as layers in neural networks, and we showcase them by reimplementing popular registration networks such as VoxelMorph. We also provide generic augmentation layers and easy-to-use and highly-parameterized backbone models (U-Nets, ResNets, etc.).

We also provide optimization-based registration tools that can be easily applied from the command line, as well as algorithms and utilities for solving inverse problems in Magnetic Resonance Imaging.

Quick start

Clone and install nitorch

pip install git+https://github.com/balbasty/nitorch

# Or, alternatively
git clone git@github.com:balbasty/nitorch.git
pip install ./nitorch

However, this only installs the core dependencies (torch and numpy). If you wish to automatically install dependencies used by, e.g., readers and writers, plotters and/or dataset loaders, you can specify the extra tags io, plot, data. Alternatively, the tag all combines all of these dependencies.

pip install git+https://github.com/balbasty/nitorch#egg=nitorch[all]

# Or, alternatively
git clone git@github.com:balbasty/nitorch.git
pip install -e "./nitorch[all]"

You may then start using NITorch in a Python program:

import nitorch as ni
# my cool script

Or use high-level tools from the command line:

nitorch --help

Demo code

The demo folder contains various Jupyter notebooks that showcase some of NITorch's funtionality. Just follow the instructions in the notebook to get started, or follow the links below to run an installation-free copy instantly in Google Colab:

• Affine Registration
  
• Spatial Tools
  

Compiling C++/CUDA extensions

By default, a pure PyTorch implementation is used. However, we also provide a version of our image resampling tools written in C++/CUDA, which provide a x10 speedup over the default version. Because it requires a specific compilation environment, this is for advanced users only.

Note that these extensions are built against PyTorch and therefore pin the installation to the specific PyTorch version used for compilation. To force pip to use a specific version of PyTorch, it is advised to install it beforehand and call pip install with the option --no-build-isolation.

0. (If GPU support needed) Install cuda

   • You need the driver and the toolkit (compiler, headers and libraries).
   • Follow instructions from the nvidia website based on your OS and the cuda version supported by your device.
   • See also: section Troubleshooting.

1. Install NITorch with compilation enabled:

   
   git clone git@github.com:balbasty/nitorch.git
   cd nitorch
   NI_COMPILED_BACKEND="C" pip install .

Or, alternatively (the version used is an arbitrary example)

pip install torch==1.9.0+cu111 NI_COMPILED_BACKEND="C" pip install --no-build-isolation .

## Compiling your own wheel

1. Build a wheel file
```{bash}
git clone git@github.com:balbasty/nitorch.git
cd nitorch
./setup.py bdist_wheel
# or alternatively
# NI_COMPILED_BACKEND="C" ./setup.py bdist_wheel

This will create a wheel file in a dist/ directory:

.
├── dist
│   ├── nitorch-[*].whl

2. Install wheel file using pip

   pip install nitorch-[*].whl

Note that when NI_COMPILED_BACKEND="C" is used, NITorch becomes specific to an OS, a Python version and (if CUDA is enabled) a CUDA version. Since we link against libtorch, it is also specific to a PyTorch version You must therefore be careful about what packages are present in your environment.

Troubleshooting

CUDA

• Different versions of the CUDA toolkit support different compute capability versions (see: https://en.wikipedia.org/wiki/CUDA#GPUs_supported). You should install a version of the toolkit that is compatible with the
  compute capability of your device.
• The toolkit installer allows both the driver and the toolkit (compiler, headers, libraries) to be installed. The driver needs admin priviledges to be installed, but the toolkit does not. Here's a way to install the toolkit without admin priviledges (copied from here):

  ./cuda_<VERSION>_linux.run --silent --toolkit --toolkitpath=<INSTALLPATH> --defaultroot=<INSTALLPATH>

• If your CUDA toolkit is installed in a non-standard location (i.e., different from /usr/local/cuda), use the environement variable CUDA_HOME to help the setup script locate it:

  CUDA_HOME=<PATH_TO_CUDA> ./setup.py install

  However, note that nvcc should call the correct nvidia compiler. Therefore, setup your path accordingly:

  export PATH="$CUDA_HOME/bin:$PATH"

• The nvidia compiler (nvcc) calls a host compiler (gcc, clang, ...). If you wish to use a non-standard host compiler (e.g., you are using gcc-8 instead of the native gcc), things might be trickier. A solution could be to alias nvcc so that it uses the -ccbin option by default. In your ~/.bashrc, add:

  alias nvcc='nvcc -ccbin <PATH_TO_GCC_BIN>'

Authors

NITorch has been mostly written by Yael Balbastre and Mikael Brudfors, while post-docs in John Ashburner's group at the FIL (or Wellcome Centre for Human Neuroimaging as it is officially known). It is therefore conceptually related to SPM.

All contributions are welcome (though no nicely drafted guidelines exist, we'll try to get better).

License

NITorch is released under the MIT license.