DefED-Net: Deformable Encoder-Decoder Network for Liver and Liver Tumor Segmentation

Deep convolutional neural networks have been widely used for medical image segmentation due to their superiority in feature learning. Although these networks are successful for simple object segmentation tasks, they suffer from two problems for liver and liver tumor segmentation in CT images. One is that convolutional kernels of fixed geometrical structure are unmatched with livers and liver tumors of irregular shapes. The other is that pooling and strided convolutional operations easily lead to the loss of spatial contextual information of images. To address these issues, we propose a deformable encoder-decoder network (DefED-Net) for liver and liver tumor segmentation. The proposed network makes two contributions: 1) the deformable convolution is used to enhance the feature representation capability of DefED-Net, which can help the network to learn convolution kernels with adaptive spatial structuring information and 2) we design a ladder-atrous-spatial-pyramid-pooling (Ladder-ASPP) module using multiscale dilation rate (Ladder-ASPP) and apply the module to learn better context information than the atrous spatial pyramid pooling for CT image segmentation. The proposed DefED-Net is evaluated on two public benchmark datasets, the LiTS, and the 3DIRCADb. Experiments demonstrate that the DefED-Net has better capability of feature representation as well as provides higher accuracy on liver and liver tumor segmentation than state-of-the-art networks. The available code of DefED-Net we propose can be found from https://github.com/SUST-reynole/DefED-Net.