An application of cascaded 3D fully convolutional networks for medical image segmentation

TL;DR

This paper introduces a cascaded 3D fully convolutional network approach for medical image segmentation, significantly improving accuracy on challenging organs like the pancreas by focusing on coarse-to-fine segmentation, and demonstrating state-of-the-art results.

Contribution

The work presents a novel two-stage cascaded 3D FCN method that enhances segmentation accuracy across multiple organs without handcrafted features or class-specific models.

Findings

Achieved highest Dice score of 82.2% on pancreas segmentation.

Outperformed 2D FCN methods on small organs and vessels.

Validated robustness across datasets from different hospitals.

Abstract

Recent advances in 3D fully convolutional networks (FCN) have made it feasible to produce dense voxel-wise predictions of volumetric images. In this work, we show that a multi-class 3D FCN trained on manually labeled CT scans of several anatomical structures (ranging from the large organs to thin vessels) can achieve competitive segmentation results, while avoiding the need for handcrafting features or training class-specific models. To this end, we propose a two-stage, coarse-to-fine approach that will first use a 3D FCN to roughly define a candidate region, which will then be used as input to a second 3D FCN. This reduces the number of voxels the second FCN has to classify to ~10% and allows it to focus on more detailed segmentation of the organs and vessels. We utilize training and validation sets consisting of 331 clinical CT images and test our models on a completely unseen data collection acquired at a different hospital that includes 150 CT scans, targeting three anatomical organs (liver, spleen, and pancreas). In challenging organs such as the pancreas, our cascaded approach improves the mean Dice score from 68.5 to 82.2%, achieving the highest reported average score on this dataset. We compare with a 2D FCN method on a separate dataset of 240 CT scans with 18 classes and achieve a significantly higher performance in small organs and vessels. Furthermore, we explore fine-tuning our models to different datasets. Our experiments illustrate the promise and robustness of current 3D FCN based semantic segmentation of medical images, achieving state-of-the-art results. Our code and trained models are available for download: https://github.com/holgerroth/3Dunet_abdomen_cascade.