ISSN 1004-4140
    CN 11-3017/P

    基于DnCNN-like的方向概率总变差能谱CT重建算法

    DnCNN-like Guided Directional Probabilistic Total Variation Algorithm for Spectral CT Reconstruction

    • 摘要: 能谱CT通过采集多个能量通道的投影数据,显著提升了物质分解能力和临床诊断准确性。然而,在低剂量扫描条件下,光子计数的不足导致重建图像面临严重的量子噪声和条状伪影等挑战。方向概率总变差(dTV-p)正则化通过概率质量函数动态选择参考通道,在多通道重建中表现出色,但其依赖于迭代中间结果构建的参考图像往往包含噪声伪影,限制了最终重建质量。为此,本文提出一种基于DnCNN-like的方向概率总变差能谱CT重建算法(去噪卷积神经网络)。该算法首次将预训练的基于残差学习的DnCNN-like去噪网络嵌入dTV-p正则化框架,在每次迭代中,对依据概率质量函数动态选出的参考图像进行智能增强,从而生成更干净、更准确的方向梯度引导信息。具体而言,算法首先根据各通道信噪比的几何均值构建概率分布,选取参考通道;接着,利用在大规模CT图像数据上预训练的深度残差网络对参考图像进行去噪与结构增强;最后,结合加权最小二乘数据保真项,构建整体优化模型,并采用快速迭代收缩阈值算法(FISTA)实现高效求解。实验结果表明,与传统dTV-p算法相比,所提方法在峰值信噪比(PSNR)、均方根误差(RMSE)、结构相似度指数(SSIM)等定量指标上均有显著提升,尤其在量子噪声抑制和边缘保持方面表现出明显优势。

       

      Abstract: Spectral computed tomography (CT) enhances material decomposition capability and clinical diagnostic accuracy by acquiring projection data from multiple energy channels. However, under low-dose scanning conditions, insufficient photon counting leads to severe quantum noise and streak artifacts in reconstructed images. The directional probabilistic total variation (dTV-p) regularization demonstrates excellent performance in multi-channel reconstruction by dynamically selecting reference channels via a probability mass function. However, its reliance on intermediate iterative results to construct reference images often introduces noise and artifacts, which limits the final reconstruction quality. To address this limitation, in this paper, we have proposed a denoising convolutional neural network (DnCNN)-like oriented probabilistic total variation algorithm for spectral CT reconstruction. For the first time, we integrated a pre-trained residual learning-based DnCNN-like denoising network into the dTV-p regularization framework. During each iteration, the reference image, dynamically selected according to the probability mass function, is intelligently enhanced to generate cleaner and more accurate directional gradient guidance. Specifically, the algorithm first constructs a probability distribution based on the geometric mean of the signal-to-noise ratios across channels to select the reference channel. Then, a deep residual network pre-trained on large-scale CT image datasets is used to denoise and structurally enhance the reference image. Finally, in combination with a weighted least squares data fidelity term, an overall optimization model is formulated and efficiently solved using the fast iterative shrinkage-thresholding algorithm. The experimental results demonstrated that, compared with the traditional dTV-p algorithm, the proposed method achieved significant improvements in quantitative metrics such as peak signal-to-noise ratio, root mean square error, and structural similarity index, revealing pronounced advantages particularly in suppressing quantum noise and preserving edges.

       

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