Abstract：
BACKGROUND: Cone-beam CT (CBCT) has been extensively employed in industrial and medical applications, such as image-guided radiotherapy and diagnostic imaging, with a growing demand for quantitative imaging using CBCT. However, conventional CBCT can be easily compromised by scatter and beam hardening artifacts, and the entanglement of scatter and spectral effects introduces additional complexity.
OBJECTIVE: The intertwined scatter and spectral effects within CBCT pose significant challenges to the quantitative performance of spectral imaging. In this work, we present the first attempt to develop a stationary spectral modulator with flying focal spot (SMFFS) technology as a promising, low-cost approach to accurately solving the x-ray scattering problem and physically enabling spectral imaging in a unified framework, and with no significant misalignment in data sampling of spectral projections.
METHODS: To deal with the intertwined scatter-spectral challenge, we propose a novel scatter-decoupled material decomposition (SDMD) method for SMFFS, which consists of four steps in total, including (1) spatial resolution-preserved and noise-suppressed multi-energy \"residual\" projection generation free from scatter, based on a hypothesis of scatter similarity; (2) first-pass material decomposition from the generated multi-energy residual projections in non-penumbra regions, with a structure similarity constraint to overcome the increased noise and penumbra effect; (3) scatter estimation for complete data; and (4) second-pass material decomposition for complete data by using a multi-material spectral correction method. Monte Carlo simulations of a pure-water cylinder phantom with different focal spot deflections are conducted to validate the scatter similarity hypothesis. Both numerical simulations using a clinical abdominal CT dataset, and physics experiments on a tabletop CBCT system using a Gammex multi-energy CT phantom and an anthropomorphic chest phantom, are carried out to demonstrate the feasibility of CBCT spectral imaging with SMFFS and our proposed SDMD method.
RESULTS: Monte Carlo simulations show that focal spot deflections within a range of 2 mm share quite similar scatter distributions overall. Numerical simulations demonstrate that SMFFS with SDMD method can achieve better material decomposition and CT number accuracy with fewer artifacts. In physics experiments, for the Gammex phantom, the average error of the mean values ( E RMSE ROI $E^{\\text{ROI}}_{\\text{RMSE}}$ ) in selected regions of interest (ROIs) of virtual monochromatic image (VMI) at 70 keV is 8 HU in SMFFS cone-beam (CB) scan, and 19 and 210 HU in sequential 80/120 kVp (dual kVp, DKV) CB scan with and without scatter correction, respectively. For the chest phantom, the E RMSE ROI $E^{\\text{ROI}}_{\\text{RMSE}}$ in selected ROIs of VMIs is 12 HU for SMFFS CB scan, and 15 and 438 HU for sequential 80/140 kVp CB scan with and without scatter correction, respectively. Also, the non-uniformity among selected regions of the chest phantom is 14 HU for SMFFS CB scan, and 59 and 184 HU for the DKV CB scan with and without a traditional scatter correction method, respectively.
CONCLUSIONS: We propose a SDMD method for CBCT with SMFFS. Our preliminary results show that SMFFS can enable spectral imaging with simultaneous scatter correction for CBCT and effectively improve its quantitative imaging performance.
OBJECTIVE: The intertwined scatter and spectral effects within CBCT pose significant challenges to the quantitative performance of spectral imaging. In this work, we present the first attempt to develop a stationary spectral modulator with flying focal spot (SMFFS) technology as a promising, low-cost approach to accurately solving the x-ray scattering problem and physically enabling spectral imaging in a unified framework, and with no significant misalignment in data sampling of spectral projections.
METHODS: To deal with the intertwined scatter-spectral challenge, we propose a novel scatter-decoupled material decomposition (SDMD) method for SMFFS, which consists of four steps in total, including (1) spatial resolution-preserved and noise-suppressed multi-energy \"residual\" projection generation free from scatter, based on a hypothesis of scatter similarity; (2) first-pass material decomposition from the generated multi-energy residual projections in non-penumbra regions, with a structure similarity constraint to overcome the increased noise and penumbra effect; (3) scatter estimation for complete data; and (4) second-pass material decomposition for complete data by using a multi-material spectral correction method. Monte Carlo simulations of a pure-water cylinder phantom with different focal spot deflections are conducted to validate the scatter similarity hypothesis. Both numerical simulations using a clinical abdominal CT dataset, and physics experiments on a tabletop CBCT system using a Gammex multi-energy CT phantom and an anthropomorphic chest phantom, are carried out to demonstrate the feasibility of CBCT spectral imaging with SMFFS and our proposed SDMD method.
RESULTS: Monte Carlo simulations show that focal spot deflections within a range of 2 mm share quite similar scatter distributions overall. Numerical simulations demonstrate that SMFFS with SDMD method can achieve better material decomposition and CT number accuracy with fewer artifacts. In physics experiments, for the Gammex phantom, the average error of the mean values ( E RMSE ROI $E^{\\text{ROI}}_{\\text{RMSE}}$ ) in selected regions of interest (ROIs) of virtual monochromatic image (VMI) at 70 keV is 8 HU in SMFFS cone-beam (CB) scan, and 19 and 210 HU in sequential 80/120 kVp (dual kVp, DKV) CB scan with and without scatter correction, respectively. For the chest phantom, the E RMSE ROI $E^{\\text{ROI}}_{\\text{RMSE}}$ in selected ROIs of VMIs is 12 HU for SMFFS CB scan, and 15 and 438 HU for sequential 80/140 kVp CB scan with and without scatter correction, respectively. Also, the non-uniformity among selected regions of the chest phantom is 14 HU for SMFFS CB scan, and 59 and 184 HU for the DKV CB scan with and without a traditional scatter correction method, respectively.
CONCLUSIONS: We propose a SDMD method for CBCT with SMFFS. Our preliminary results show that SMFFS can enable spectral imaging with simultaneous scatter correction for CBCT and effectively improve its quantitative imaging performance.
摘要：
背景：锥束CT（CBCT）已广泛用于工业和医疗应用，如图像引导放射治疗和诊断成像，随着对使用CBCT的定量成像的需求不断增长。然而,传统的CBCT很容易受到散射和光束硬化伪影的影响，散射和光谱效应的纠缠引入了额外的复杂性。
目的：CBCT内交织的散射和光谱效应对光谱成像的定量性能提出了重大挑战。在这项工作中,我们提出了首次尝试开发具有飞行焦斑（SMFFS）技术的固定光谱调制器，低成本的方法来准确地解决x射线散射问题和物理实现光谱成像在一个统一的框架，在光谱投影的数据采样中没有明显的偏差。
方法：为了应对交织在一起的散射光谱挑战，我们提出了一种新的用于SMFFS的散射-解耦材料分解（SDMD）方法，总共由四个步骤组成，包括(1)空间分辨率保持和噪声抑制的多能量“残差”投影生成无散射，基于散射相似性的假设；（2）从非半影区域中生成的多能量残差投影进行第一遍材料分解，具有结构相似性约束，以克服增加的噪声和半影效应；（3）对完整数据进行散射估计；以及（4）通过使用多材料光谱校正方法对完整数据进行二次材料分解。对具有不同焦斑偏转的纯水圆柱体模进行了蒙特卡罗模拟，以验证散射相似性假设。两种数值模拟都使用临床腹部CT数据集，以及使用Gammex多能量CT体模和拟人化胸部体模在桌面CBCT系统上进行的物理实验，进行了验证，以证明使用SMFFS和我们提出的SDMD方法进行CBCT光谱成像的可行性。
结果：蒙特卡罗模拟表明，2mm范围内的焦斑偏转总体上具有非常相似的散射分布。数值模拟表明，SDMD方法的SMFFS可以获得更好的材料分解和CT数精度，同时伪影更少。在物理实验中,为了Gammex幻影,在SMFFS锥束(CB)扫描中,在70keV的虚拟单色图像(VMI)的选定感兴趣区域(ROI)的平均值(ERMSEROI$E^{\text{ROI}}_{\\\text{RMSE}}$)的平均误差为8HU,以及19和210HU的顺序80/120kVp(双kVp，有和没有散射校正的DKV)CB扫描,分别。对于胸部幻影来说，对于SMFFSCB扫描，VMI的选定ROI中的ERMSEROI$E^{\\text{ROI}}_{\\text{RMSE}}$为12HU，以及15和438HU，用于有和没有散射校正的连续80/140kVpCB扫描，分别。此外，对于SMFFSCB扫描，胸部模型的选定区域之间的不均匀性为14HU，59和184HU用于DKVCB扫描，有和没有传统的散射校正方法，分别。
结论：我们提出了一种使用SMFFS的CBCT的SDMD方法。我们的初步结果表明，SMFFS可以实现光谱成像与CBCT的同时散射校正，并有效地提高其定量成像性能。
目的：CBCT内交织的散射和光谱效应对光谱成像的定量性能提出了重大挑战。在这项工作中,我们提出了首次尝试开发具有飞行焦斑（SMFFS）技术的固定光谱调制器，低成本的方法来准确地解决x射线散射问题和物理实现光谱成像在一个统一的框架，在光谱投影的数据采样中没有明显的偏差。
方法：为了应对交织在一起的散射光谱挑战，我们提出了一种新的用于SMFFS的散射-解耦材料分解（SDMD）方法，总共由四个步骤组成，包括(1)空间分辨率保持和噪声抑制的多能量“残差”投影生成无散射，基于散射相似性的假设；（2）从非半影区域中生成的多能量残差投影进行第一遍材料分解，具有结构相似性约束，以克服增加的噪声和半影效应；（3）对完整数据进行散射估计；以及（4）通过使用多材料光谱校正方法对完整数据进行二次材料分解。对具有不同焦斑偏转的纯水圆柱体模进行了蒙特卡罗模拟，以验证散射相似性假设。两种数值模拟都使用临床腹部CT数据集，以及使用Gammex多能量CT体模和拟人化胸部体模在桌面CBCT系统上进行的物理实验，进行了验证，以证明使用SMFFS和我们提出的SDMD方法进行CBCT光谱成像的可行性。
结果：蒙特卡罗模拟表明，2mm范围内的焦斑偏转总体上具有非常相似的散射分布。数值模拟表明，SDMD方法的SMFFS可以获得更好的材料分解和CT数精度，同时伪影更少。在物理实验中,为了Gammex幻影,在SMFFS锥束(CB)扫描中,在70keV的虚拟单色图像(VMI)的选定感兴趣区域(ROI)的平均值(ERMSEROI$E^{\text{ROI}}_{\\\text{RMSE}}$)的平均误差为8HU,以及19和210HU的顺序80/120kVp(双kVp，有和没有散射校正的DKV)CB扫描,分别。对于胸部幻影来说，对于SMFFSCB扫描，VMI的选定ROI中的ERMSEROI$E^{\\text{ROI}}_{\\text{RMSE}}$为12HU，以及15和438HU，用于有和没有散射校正的连续80/140kVpCB扫描，分别。此外，对于SMFFSCB扫描，胸部模型的选定区域之间的不均匀性为14HU，59和184HU用于DKVCB扫描，有和没有传统的散射校正方法，分别。
结论：我们提出了一种使用SMFFS的CBCT的SDMD方法。我们的初步结果表明，SMFFS可以实现光谱成像与CBCT的同时散射校正，并有效地提高其定量成像性能。
