This repository contains the uncertainty analysis and GCN refinement used in our work "Uncertainty-based Graph Convolutional Networks for Organ Segmentation Refinement".

Organ segmentation in CT volumes is an important pre-processing step in many computer assisted intervention and diagnosis methods. In recent years, convolutional neural networks have dominated the state of the art in this task. However, since this problem presents a challenging environment due to high variability in the organ’s shape and similarity between tissues, the generation of false negative and false positive regions in the output segmentation is a common issue. Recent works have shown that the uncertainty analysis of the model can provide us with useful information about potential errors in the segmentation. In this context, we proposed a segmentation refinement method based on uncertainty analysis and graph convolutional networks. We employ the uncertainty levels of the convolutional network in a particular input volume to formulate a semi-supervised graph learning problem that is solved by training a graph convolutional network.

The code was tested with python3 and CUDA 9.2. using the Pytorch library. To run the code, clone the repository

$ git clone https://github.com/rodsom22/gcn_refinement.git

and install the required packages:

$ cd gcn_refinement
$ pip install -r requirements.txt

Download the model and samples and place it into the source/models folder (sample from the pancreas NIH dataset). Then, run the example code

$ cd source
$ python main.py

The process will output a set of files in the source/models folder (you can change by editing the source/path_config.py file) . The .npy files are for internal use. It also outputs the following Nifti files for visualization:

• volume.nii.gz - The input volume.
• reference.nii.gz - The ground truth reference.
• cnn_prediction.nii.gz - The initial CNN prediction.
• cnn_expectation..nii.gz - CNN expectation.
• cnn_entropy.nii.gz - Obtained CNN entropy
• binary_cnn_entropy.nii.gz - Binarized entropy
• gcn_prediction.nii.gz - GCN refinement.
• crf_prediction.nii.gz - CRF Refinement.

If this work is useful for your research, please cite our paper:

@conference{soberanismukul2020refinement,
	    Author = {Roger D. Soberanis-Mukul and Nassir Navab and Shadi Albarqouni},
	    Booktitle = {MIDL},
	    Title = {Uncertainty-based Graph Convolutional Networks for Organ Segmentation Refinement},
            Year = {2020}
}

Our GCN is based on the GCN implementation by @tkipf.

We use the CRF implementation of @lucasb-eyer. Please refer to this repository to install pydensecrf.