KEYWORDS: Bone, Data modeling, Computed tomography, Signal to noise ratio, Signal attenuation, Model-based design, Image processing, Signal processing, Performance modeling, Medical imaging
Dual-energy computed tomography (DECT) imaging plays an important role in clinical diagnosis applications due to its material decomposition capability. However, in the cases of low-dose DECT imaging and ill-conditioned issue, the direct decomposed material images from DECT images would suffer from severe noise-induced artifacts, leading to low quality and accuracy. In this paper, we propose a self-supervised Nonlocal Spectral Similarity-induced Decomposition Network (NSSD-Net) to produce decomposed material images with high quality and accuracy in the low-dose DECT imaging. Specifically, we first build the model-driven iterative decomposition model and optimize the objective function by the iterative shrinkage-thresholding algorithm (ISTA) with the convolutional neural network. Considering the intrinsic characteristics information (i.e., structural similarity and spectral correlation) underlying DECT images, which can be used as the prior information to improve the accuracy of the decomposed material images, we construct the nonlocal spectral similarity-based cost function by using the prior information and incorporating it into the iterative decomposition network to guarantee stability. The proposed NSSD-Net method was validated and evaluated with real clinical data. Experimental results showed that the presented NSSD-Net method outperforms the other competing methods in terms of noise-induced artifacts reduction and decomposition accuracy.
Low-dose computed tomography (LDCT) examinations are of essential usages in clinical applications due to the lower radiation-associated cancer risks in CT imaging. Reductions in radiation dose can produce severe noise and artifacts that can affect the diagnostic accuracy of radiologists. Although deep learning networks have been widely proposed, most of these networks rely on a large number of annotated CT image pairs (LDCT images/high-dose CT (HDCT) images). Moreover, it is challenging for these networks to cope with the growing amount of CT images, especially large amount of medium-dose CT (MDCT) images that are easily to collect and have lower radiation dose than the HDCT images and higher radiation dose than the LDCT images. Therefore, in this work, we propose a progressive transfer-learning network (PETNet) for low-dose CT image reconstruction with limited annotated CT data and abundant corrupted CT data. The presented PETNet consists of two phases. In the first phase, a network is trained on a large amount of LDCT/MDCT image pairs, similar to the Noise2Noise network that has shown potential in yielding promising results with corrupted data for network training. It should be noted that this network would inevitably introduce undesired bias in the results due to the complex noise distribution in CT images. Then, in the second phase, we combined the pre-trained network and another simple network to construct the presented PETNet. In particular, the parameters of the pre-trained network are frozen and transferred directly to the presented PETNet, and the presented PETNet is trained on a small amount of LDCT/HDCT image pairs. Experimental results on Mayo clinic data demonstrate the superiority of the presented PETNet method both qualitatively and quantitatively compared with the network trained on LDCT/HDCT images pairs, and Noise2Noise method trained on LDCT/MDCT image pairs.
Fully supervised deep learning (DL) methods have been widely used in low-dose CT (LDCT) imaging field and can usually achieve high accuracy results. These methods require a large labeled training set which consists of pairs of LDCT images as well as their corresponding high-dose CT (HDCT) ones. They successfully learn intermediate concept of features describing important components in CT images, such as noise distribution, and structure details, which is important to capture dependencies from LDCT image to HDCT ones. However, it should be noted that it is quite time-consuming and costly to obtain such a large of labeled CT images especially the HDCT images are limited in clinics. In comparison, lots of unlabeled LDCT images are usually easily accessible and massive critical information latent in the unlabeled LDCT can be leveraged to further boost restoration performance. Therefore, in this work, we present a semi-supervised noise distribution learning network to suppress noise-induced artifacts in the LDCT images. For simplicity, the presented network in termed as "SNDL-Net". The presented SNDL-Net consists of two sub-networks, i.e., supervised network, and unsupervised network. In the supervised network, the LDCT/HDCT image pairs are used for network training. And the unsupervised network considers the complex noise distribution in the LDCT images, and model the noise with a Gaussian mixture framework, then learns the proper gradient of LDCT images in a purely unsupervised manner. Similar with the supervised network training, the gradient information in a large of unlabeled LDCT images can be used for unsupervised network training. Moreover, to learn the noise distribution accurately, the discrepancy between the learned noise distribution in the supervised network and learned noise distribution in the unsupervised network can be modeled by a Kullback-Leibler (KL) divergence. Experiments on the Mayo clinic dataset verify the method is effective in low-dose CT image restoration with only a small amount of labeled data compared to previous supervised deep learning methods.
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