A new architecture combining convolutional and transformer-based networks for automatic 3D multi-organ segmentation on CT images.

Abstract

Deep learning-based networks have become increasingly popular in the field of medical image segmentation. The purpose of this research was to develop and optimize a new architecture for automatic segmentation of the prostate gland and normal organs in the pelvic, thoracic, and upper gastro-intestinal (GI) regions. We developed an architecture which combines a shifted-window (Swin) transformer with a convolutional U-Net. The network includes a parallel encoder, a cross-fusion block, and a CNN-based decoder to extract local and global information and merge related features on the same scale. A skip connection is applied between the cross-fusion block and decoder to integrate low-level semantic features. Attention gates (AGs) are integrated within the CNN to suppress features in image background regions. Our network is termed "SwinAttUNet." We optimized the architecture for automatic image segmentation. Training datasets consisted of planning-CT datasets from 300 prostate cancer patients from an institutional database and 100 CT datasets from a publicly available dataset (CT-ORG). Images were linearly interpolated and resampled to a spatial resolution of (1.0×1.0×1.5) mm3 . A volume patch (192×192×96) was used for training and inference, and the dataset was split into training (75%), validation (10%), and test (15%) cohorts. Data augmentation transforms were applied consisting of random flip, rotation, and intensity scaling. The loss function comprised Dice and cross-entropy equally weighted and summed. We evaluated Dice coefficients (DSC), 95th percentile Hausdorff Distances (HD95), and Average Surface Distances (ASD) between results of our network and ground truth data. SwinAttUNet, DSC values were 86.54±1.21, 94.15±1.17, and 87.15±1.68% and HD95 values were 5.06±1.42, 3.16±0.93, and 5.54±1.63mm for the prostate, bladder, and rectum, respectively. Respective ASD values were 1.45±0.57, 0.82±0.12, and 1.42±0.38mm. For the lung, liver, kidneys and pelvic bones, respective DSC values were: 97.90±0.80, 96.16±0.76, 93.74±2.25, and 89.31±3.87%. Respective HD95 values were: 5.13±4.11, 2.73±1.19, 2.29±1.47, and 5.31±1.25mm. Respective ASD values were: 1.88±1.45, 1.78±1.21, 0.71±0.43, and 1.21±1.11mm. Our network outperformed several existing deep learning approaches using only attention-based convolutional or Transformer-based feature strategies, as detailed in the results section. We have demonstrated that our new architecture combining Transformer- and convolution-based features is able to better learn the local and global context for automatic segmentation of multi-organ, CT-based anatomy.