Source code of VSRC

Introduction

The source code includes training and inference procedures for a semi-supervised medical image segmentation method with Voxel Stability and Reliability Constraints (VSRC).

Semi-supervised learning is becoming an effective solution in medical image segmentation because annotations are costly and tedious to acquire. Methods based on the teacher-student model use consistency regularization and uncertainty estimation and have shown good potential in dealing with limited annotated data. Nevertheless, the existing teacher-student model is seriously limited by the exponential moving average algorithm, which leads to the optimization trap. Moreover, the classic uncertainty estimation method calculates the global uncertainty for images but does not consider local region-level uncertainty, which is unsuitable for medical images with blurry regions. Here, the Voxel Stability and Reliability Constraint (VSRC) model is proposed to address these issues. Specifically, the Voxel Stability Constraint (VSC) strategy is introduced to optimize parameters and exchange effective knowledge between two independent initialized models, which can break through the performance bottleneck and avoid model collapse. Moreover, a new uncertainty estimation strategy, the Voxel Reliability Constraint (VRC), is proposed for use in our semi-supervised model to consider the uncertainty at the local region level. We further extend our model to auxiliary tasks and propose a task-level consistency regularization with uncertainty estimation. Extensive experiments on two 3D medical image datasets demonstrate that our method outperforms other state-of-the-art semi-supervised medical image segmentation methods under limited supervision.

This method has been submitted to the IEEE Journal of Biomedical and Health Informatics with title "Semi-Supervised Medical Image Segmentation with Voxel Stability and Reliability Constraints" (JBHI-03096-2022).

Requirements

• Python 3.7+ (Python 2 is not supported)
• PyTorch 1.7+
• CUDA 9.0+

Note: It is recommended to install Python and the necessary environment via Anaconda.

Directory structure

• trainer includes base_trainer.py which provides the basic training and validation process of the model.

• datasets is used to store training and test sets.

• data_loaders is used to store data loaders for different datasets. To use your own dataset, write the corresponding Python scripts and add the basic information in data_loaders/__init__.py.

• data_augmentation contains the scripts of pre-processing and data augmentation functions for datasets.

• models is used to store models or networks for semi-supervised medical image segmentation. Note that, if you want to use your own network, write an appropriate class being derived from the class BaseModel defined in models/BaseModelClass.py and add the basic information in models/__init__.py.

• losses3D stores the scripts of loss functions designed for VSRC.

• utils contains the scripts of some tool functions.

• visual3D is used to store the codes for inference and visualization of the test set. For using your own dataset, please add the basic information in visual3D/viz.py.

• works is the directory used to store model checkpoints. You can change parameters args.l_save and args.r_save in train_vsrc.py to modify the default storage directory.

• runs is used to store log information recorded by tensorboard during runtime.

Usage

Step 1. Create a virtual environment and activate it in Anaconda

conda create -n vsrc python=3.7 -y
conda activate vsrc

Step 2. Install PyTorch and torchvision following the official instructions

conda install pytorch=1.7 torchvision cudatoolkit=10.0 -c pytorch

Step 3. Install other dependencies

pip install -r requirements.txt

Step 4. Prepare datasets

• Download the Atrial Segmentation Challenge dataset (LA2018), follow the data preparation instructions of UA-MT to convert medical images into h5 files and get the training and test sets. Taking the dataset LA2018 as an example, the prepared data looks as follows:

    datasets/
        ├── LA2018
            ├── train
            │    ├── IMAGE_ID_1
            │    │      └── la_mri.h5
            │    ├── IMAGE_ID_2
            │    │      └── la_mri.h5
            │    └── ...
            └── val
                 ├── IMAGE_ID_3
                 │      └── la_mri.h5
                 ├── IMAGE_ID_4
                 │      └── la_mri.h5
                 └── ...

• Similarly, you can follow the data preparation steps above for your own datasets. We provide the code to convert medical images to h5 files in utils/nrrd2h5.py (refer to UA-MT). Once the data is prepared (converted to h5 files and divided into training and test sets), write a data loader in Python, place it in the subdirectory data_loaders and add the basic information of the dataset in data_loaders/__init__.py. The corresponding source code for the dataset LA2018 is provided in the subdirectory data_loaders for reference.

Step 5. Train and test by running train_vsrc.py

• Train the model on the specified dataset. The optional parameter --pretrained provides the ability to load pre-trained models.

python train_vsrc.py -d <DATASET_NAME> -p <PATCH_SIZE> --train

• Test and inference. Modify the codes in visual3D/viz.py for your own dataset.

python train_vsrc.py -d <DATASET_NAME> -p <PATCH_SIZE> --test --save_viz -tp <TEST_CKPT_PATH> 

DATASET_NAME is a string that specifies what dataset should be trained on, e.g. LA2018. PATCH_SIZE is used to specify the patch size used for data training, e.g. 112 112 80 which means the patch size $112\times 112\times 80$. TEST_CKPT_PATH is used to specify the path where the model will be loaded during the test phase.

For example, you can run following scripts to train and test VSRC on the LA2018 dataset:

python train_vsrc.py -d LA2018 -p 112 112 80 --train
python train_vsrc.py -d LA2018 -p 112 112 80 --test -save_viz -tp ./works/DualModel/test_checkpoint/sdf_VNet_LA2018_20.pth 

Our pre-trained models for the LA2018 dataset under 20% and 10% supervision are provided in the model directory works/DualModel/test_checkpoint.

Acknowledgement

• Some of the source code is referenced from UA-MT and DTC.
• More semi-supervised learning approaches for comparison can be found in SSL4MIS. We appreciate that Dr. Xiangde Luo provides an efficient code base.