Automated classification of cervical lymph-node-level from ultrasound using Depthwise Separable Convolutional Swin Transformer.

There are few studies on cervical ultrasound lymph-node-level classification which is very important for qualitative diagnosis and surgical treatment of diseases. Currently, ultrasound examination relies on the subjective experience of physicians to judge the level of the cervical lymph nodes, which is easily misclassified. Unlike other automated diagnostic tasks, lymph-node-level classification needs to focus on global structural information. Besides, there is a large range of sternocleidomastoid muscles in levels II, III and IV, which leads to small inter-class differences in these levels, so it also needs to focus on key local areas to extract strong distinguishable features. In this paper, we propose the Depthwise Separable Convolutional Swin Transformer, introducing the deepwise separable convolution branch into the self-attention mechanism to capture discriminative local features. Meanwhile, to address the problem of data imbalance, a new loss function is proposed to improve the performance of the classification network. In addition, for the ultrasound data collected by different devices, low contrast and blurring problems of ultrasound imaging, a unified pre-processing algorithm is designed. The model was validated on 1146 cases of cervical ultrasound lymph node collected from the Sixth People's Hospital of Shanghai. The average accuracy precision, sensitivity, specificity, and F1 value of the model for the valid dataset after five-fold cross-validation were 80.65%, 80.68%, 78.73%, 95.99% and 79.42%, respectively. It has been verified by visualization methods that the Region of Interest (ROI) of the model is similar or consistent with the observed region of the experts.