基于卷积神经网络的时频域CT重建算法

针对采用时域滤波器解析重建后图像存在伪影和图像细节丢失等问题，提出了一种基于卷积神经网络（CNN）的时频域计算机断层扫描（CT）重建算法。首先，在频域中构建了基于卷积神经网络的滤波器网络，实现投影数据的频域滤波；其次，利用反投影操作算子对频域滤波后结果进行域转换得到重建图像；接着，在图像域构建网络对来自反投影层的图像进行处理；最后，在采用最小均方误差损失函数基础上引入多尺度结构相似度损失函数组成复合损失函数，减轻神经网络对结果图像的模糊效应，保留重建图像细节。图像域网络和投影域滤波网络联合作用，最终得到重建结果。在临床数据集上验证了所提算法的有效性，相较于滤波反投影（FBP）算法、全变分（TV）算法及图像域残差编解码CNN（RED-CNN）算法，当投影数目分别为180和90时，所提算法重建结果图像信噪比（PSNR）和结构相似度（SSIM）最高，且归一化均方根误差（NMSE）最小；当投影数目为360时，所提算法仅次于TV算法。实验结果表明，所提算法可以提高CT图像重建图像质量，是一种可行且有效的方法。

Time-frequency domain CT reconstruction algorithm based on convolutional neural network

Concerning the problems of artifacts and loss of image details in the analytically reconstructed image by time-domain filters， a new time-frequency domain Computed Tomography （CT） reconstruction algorithm based on Convolutional Neural Network （CNN） was proposed. Firstly， a filter network based on a convolutional neural network was constructed in the frequency domain to achieve the frequency-domain filtering of the projection data. Secondly， the back-projection operator was used to perform domain conversion on the frequency-domain filtered result to obtain a reconstructed image. A network was constructed in the image domain to process the image from the back-projection layer. Finally， a multi-scale structural similarity loss function was introduced on the basis of the minimum mean square error loss function to form a composite loss function， which reduced the blur effect of the neural network on the result image and preserved the details of the reconstructed image. The image domain network and the projection domain filter network worked together to finally get the reconstructed result. The effectiveness of the proposed algorithm was verified on the clinical dataset. Compared with the Filtered Back Projection （FBP） algorithm， the Total Variation （TV） algorithm and the image domain Residual Encoder-Decoder CNN （RED-CNN） algorithm， when the number of projections is respectively 180 and 90， the proposed algorithm achieved the reconstructed result image with highest Peak Signal-to-Noise Ratio （PSNR） and Structural Similarity （SSIM）， and the least Normalized Mean Square Error （NMSE）.When the number of projections is 360，the proposed algorithm is second only to TV algorithm. The experimental results show that the proposed algorithm can improve the reconstructed image quality of CT image， and it is feasible and effective.