Center for In Vivo Microscopy, Department of Radiology, Duke University, Durham, NC, United States of America.
Department of Radiation Oncology, Duke University, Durham, NC, United States of America.
PLoS One. 2019 Sep 19;14(9):e0218417. doi: 10.1371/journal.pone.0218417. eCollection 2019.
The maturation of photon-counting detector (PCD) technology promises to enhance routine CT imaging applications with high-fidelity spectral information. In this paper, we demonstrate the power of this synergy and our complementary reconstruction techniques, performing 4D, cardiac PCD-CT data acquisition and reconstruction in a mouse model of atherosclerosis, including calcified plaque. Specifically, in vivo cardiac micro-CT scans were performed in four ApoE knockout mice, following their development of calcified plaques. The scans were performed with a prototype PCD (DECTRIS, Ltd.) with 4 energy thresholds. Projections were sampled every 10 ms with a 10 ms exposure, allowing the reconstruction of 10 cardiac phases at each of 4 energies (40 total 3D volumes per mouse scan). Reconstruction was performed iteratively using the split Bregman method with constraints on spectral rank and spatio-temporal gradient sparsity. The reconstructed images represent the first in vivo, 4D PCD-CT data in a mouse model of atherosclerosis. Robust regularization during iterative reconstruction yields high-fidelity results: an 8-fold reduction in noise standard deviation for the highest energy threshold (relative to unregularized algebraic reconstruction), while absolute spectral bias measurements remain below 13 Hounsfield units across all energy thresholds and scans. Qualitatively, image domain material decomposition results show clear separation of iodinated contrast and soft tissue from calcified plaque in the in vivo data. Quantitatively, spatial, spectral, and temporal fidelity are verified through a water phantom scan and a realistic MOBY phantom simulation experiment: spatial resolution is robustly preserved by iterative reconstruction (10% MTF: 2.8-3.0 lp/mm), left-ventricle, cardiac functional metrics can be measured from iodine map segmentations with ~1% error, and small calcifications (615 μm) can be detected during slow moving phases of the cardiac cycle. Given these preliminary results, we believe that PCD technology will enhance dynamic CT imaging applications with high-fidelity spectral and material information.
光子计数探测器（PCD）技术的成熟有望通过高保真的光谱信息来增强常规 CT 成像应用。在本文中，我们展示了这种协同作用的威力以及我们互补的重建技术，在动脉粥样硬化的小鼠模型中进行了 4D、心脏 PCD-CT 数据采集和重建，包括钙化斑块。具体来说，对四只载脂蛋白 E 基因敲除（ApoE KO）小鼠进行了体内心脏微 CT 扫描，以观察其钙化斑块的发展情况。使用具有 4 个能量阈值的原型 PCD（DECTRIS，Ltd.）进行了扫描。每次曝光 10 毫秒时采集投影，每次曝光可以在 4 种能量（每只小鼠扫描 40 个总 3D 容积）下重建 10 个心脏相位。使用分裂布格曼（split Bregman）方法进行迭代重建，同时对光谱秩和时空梯度稀疏性进行约束。重建图像代表了第一个在动脉粥样硬化的小鼠模型中进行的体内 4D PCD-CT 数据。迭代重建过程中的稳健正则化可产生高保真的结果：对于最高能量阈值（相对于未正则化的代数重建），噪声标准差降低了 8 倍，而在所有能量阈值和扫描中，绝对光谱偏差测量值仍低于 13 个亨氏单位。定性地，在体数据的图像域材料分解结果显示，碘造影剂和软组织与钙化斑块之间有明显的分离。定量地，通过水模扫描和现实的 MOBY 体模模拟实验验证了空间、光谱和时间保真度：迭代重建可稳健地保持空间分辨率（10% MTF：2.8-3.0 lp/mm），可以从碘图分割中测量左心室、心脏功能指标，误差约为 1%，并且可以在心脏周期的缓慢运动阶段检测到小钙化（615μm）。鉴于这些初步结果，我们相信 PCD 技术将通过高保真的光谱和材料信息来增强动态 CT 成像应用。
