N-Net: A novel dense fully convolutional neural network for thyroid nodule segmentation

Abstract

Medical image segmentation is an essential component of computer-aided diagnosis (CAD) systems. Thyroid nodule segmentation using ultrasound images is a necessary step for the early diagnosis of thyroid diseases. An encoder-decoder based deep convolutional neural network (DCNN), like U-Net architecture and its variants, has been extensively used to deal with medical image segmentation tasks. In this article, we propose a novel N-shape dense fully convolutional neural network for medical image segmentation, referred to as N-Net. The proposed framework is composed of three major components: a multi-scale input layer, an attention guidance module, and an innovative stackable dilated convolution (SDC) block. First, we apply the multi-scale input layer to construct an image pyramid, which achieves multi-level receiver field sizes and obtains rich feature representation. After that, the U-shape convolutional network is employed as the backbone structure. Moreover, we use the attention guidance module to filter the features before several skip connections, which can transfer structural information from previous feature maps to the following layers. This module can also remove noise and reduce the negative impact of the background. Finally, we propose a stackable dilated convolution (SDC) block, which is able to capture deep semantic features that may be lost in bilinear upsampling. We have evaluated the proposed N-Net framework on a thyroid nodule ultrasound image dataset (called the TNUI-2021 dataset) and the DDTI publicly available dataset. The experimental results show that our N-Net model outperforms several state-of-the-art methods in the thyroid nodule segmentation tasks.

Segmentation of thyroid glands and nodules in ultrasound images using the improved U-Net architecture

“…ResDUnet combined residual shortcut connections and dilated convolution on the basis of U-Net, and obtained a nodule dice coefficient of 82.0% on the authors’ private dataset [ 48 ]. Nie et al [ 49 ] designed N-Net by introducing multi-scale input layer, attention guidance module and stackable dilated convolution block into U-Net. Their method obtained 92.0% nodule dice coefficient on TNUI-2021 and 93.7% on DDTI.…”