Segmentation and Identification of Vertebrae in CT Scans using CNN, k-means Clustering and k-NN

If you use this code for your research, please cite our paper:

@Article{informatics8020040,
AUTHOR = {Altini, Nicola and De Giosa, Giuseppe and Fragasso, Nicola and Coscia, Claudia and Sibilano, Elena and Prencipe, Berardino and Hussain, Sardar Mehboob and Brunetti, Antonio and Buongiorno, Domenico and Guerriero, Andrea and Tatò, Ilaria Sabina and Brunetti, Gioacchino and Triggiani, Vito and Bevilacqua, Vitoantonio},
TITLE = {Segmentation and Identification of Vertebrae in CT Scans Using CNN, k-Means Clustering and k-NN},
JOURNAL = {Informatics},
VOLUME = {8},
YEAR = {2021},
NUMBER = {2},
ARTICLE-NUMBER = {40},
URL = {https://www.mdpi.com/2227-9709/8/2/40},
ISSN = {2227-9709},
DOI = {10.3390/informatics8020040}
}

Graphical Abstract:

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Materials

Dataset can be downloaded for free at this URL.

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Configuration and pre-processing

Configure the file config/paths.py according to paths in your computer. Kindly note that base_dataset_dir should be an absolute path which points to the directory which contains the subfolders with images and labels for training and validating the algorithms present in this repository.

In order to perform pre-processing, execute the following scripts in the given order.

1. Perform Train / Test split:

python run/task0/split.py --original-training-images=OTI --original-training-labels=OTL \ 
                          --original-validation-images=OVI --original-validation-labels=OVL

Where:

• OTI is the path with the CT scan from the original dataset (downloaded from VerSe challenge, see link above);
• OTL is the path with the labels related to the original dataset;
• OVI is the path where test images will be put;
• OVL is the path where test labels will be put.

2. Cropping the splitted datasets:

python run/task0/crop_mask.py --original-training-images=OTI --original-training-labels=OTL \ 
                              --original-validation-images=OVI --original-validation-labels=OVL

Where the arguments are the same of 1).

3. Pre-processing the cropped datasets (see also Payer et al. pre-processing):

python run/task0/pre_processing.py

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Binary Segmentation

In order to perform this stage, 3D V-Net has been exploited. The followed workflow for binary segmentation is depicted in the following figure:

Training

To perform the training, the syntax is as follows:

python run/task1/train.py --epochs=NUM_EPOCHS --batch=BATCH_SIZE --workers=NUM_WORKERS \
                          --lr=LR --val_epochs=VAL_EPOCHS

Where:

• NUM_EPOCHS is the number of epochs for which training the CNN (we often used 500 or 1000 in our experiments);
• BATCH_SIZE is the batch size (we often used 8 in our experiments, in order to benefit from BatchNormalization layers);
• NUM_WORKERS is the number of workers in the data loading (see PyTorch documentation);
• LR is the learning rate,
• VAL_EPOCHS is the number of epochs after which performing validation during training (a checkpoint model is also saved every VAL_EPOCHS epochs).

Inference

To perform the inference, the syntax is as follows:

python run/task1/segm_bin.py --path_image_in=PATH_IMAGE_IN --path_mask_out=PATH_MASK_OUT

Where:

• PATH_IMAGE_IN is the folder with input images;
• PATH_MASK_OUT is the folder where to write output masks.

An example inference result is depicted in the following figure:

Metrics Calculation

In order to calculate binary segmentation metrics, the syntax is as follows:

python run/task1/metrics.py

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Multiclass Segmentation

The followed workflow for multiclass segmentation is depicted in the following figure:

To perform the Multiclass Segmentation (can be performed only on binary segmentation output), the syntax is as follows:

python run/task2/multiclass_segmentation.py --input-path=INPUT_PATH \
                                            --gt-path=GT_PATH \
                                            --output-path=OUTPUT_PATH \
                                            --use-inertia-tensor=INERTIA \
                                            --no-metrics=NOM

Where:

• INPUT_PATH is the path to the folder containing the binary spine masks obtained in previous steps (or binary spine ground truth).
• GT_PATH is the path to the folder containing ground truth labels.
• OUTPUT_PATH is the path where to write the output multiclass masks.
• INERTIA can be either 0 or 1 depending or not if you want to include inertia tensor in the feature set for discrminating between bodies and arches (useful for scoliosis cases); default is 0.
• NOM can be either 0 or 1 depending or not if you want to skip the calculation of multi-Hausdorff distance and multi-ASSD for the vertebrae labelling (it can be very computationally expensive with this implementation); default is 1.

Figures highlighting the different steps involved in this stage follows:

• Morphology

• Connected Components

• Clustering and arch/body coupling

• Centroids computation

• Mesh reconstruction

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Visualization of the Predictions

The base_dataset_dir folder also contains the outputs folders:

• predTr contains the binary segmentation predictions performed on training set;
• predTs contains the binary segmentation predictions performed on testing set;
• predMulticlass contains the multiclass segmentation predictions and the JSON files containing the centroids' positions.

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