I. Introduction
Brain tumor is a disease with high morbidity, among which glioma occupies the first place within the intracranial tumors and seriously impacts human life safety. Preemptive and proactive treatments can be delivered to realize personalized, pervasive, and patient-centralized healthcare [1]. Magnetic Resonance Imaging (MRI) can provide physicians with comprehensive information about brain tumors by obtaining high-resolution, high soft-tissue contrast information of the patient's brain without damage [2]. Since MRI is generally a 3D image with high processing cost and complexity, considerable differences between patients, and unclear boundaries of tumors, the manual segmentation workload is significant and unreasonable. Deep learning (DCNN) can extract features of the input information autonomously from a large amount of data and does not require a priori knowledge, a quality that precisely meets the requirements for automatic segmentation of MRI images. Havaei M et al. [3] demonstrated the validity of deep learning models in MRI brain tumor segmentation in 2017. As medical treatment advances, DCNN-like methods are required to extract more detailed and precise information from the tumor image. The emergence of the fully connected network (FCN) has quickly become the baseline network in image segmentation [4]. FCN implements end-to-end training to complete semantic segmentation of images by performing pixel-level classification. U-Net [5] is a popular network for FCN in image segmentation. However, there are still problems with the U-Net-based image segmentation of brain tumors. The convolutional neural network cannot obtain long-range semantic information of the image. Pure convolutional networks cannot learn the subtle features of tumor images, resulting in poor segmentation accuracy. The networks with high segmentation accuracy are often accompanied by more complex network architectures and slow inference.