Department of Radiology, Boston Children's Hospital, Harvard Medical School, Boston, MA, 02115, USA.
National Institute of Advanced Industrial Science and Technology, Tokyo, Japan.
Med Phys. 2021 Jul;48(7):3595-3613. doi: 10.1002/mp.14941. Epub 2021 Jun 23.
For single-source helical Computed Tomography (CT), both Filtered-Back Projection (FBP) and statistical iterative reconstruction have been investigated. However, for dual-source CT with flying focal spot (DS-FFS CT), a statistical iterative reconstruction that accurately models the scanner geometry and acquisition physics remains unknown to researchers. Therefore, our purpose is to present a novel physics-based iterative reconstruction method for DS-FFS CT and assess its image quality.
Our algorithm uses precise physics models to reconstruct from the native cone-beam geometry and interleaved dual-source helical trajectory of a DS-FFS CT. To do so, we construct a noise physics model to represent data acquisition noise and a prior image model to represent image noise and texture. In addition, we design forward system models to compute the locations of deflected focal spots, the dimension, and sensitivity of voxels and detector units, as well as the length of intersection between x-rays and voxels. The forward system models further represent the coordinated movement between the dual sources by computing their x-ray coverage gaps and overlaps at an arbitrary helical pitch. With the above models, we reconstruct images by an advanced Consensus Equilibrium (CE) numerical method to compute the maximum a posteriori estimate to a joint optimization problem that simultaneously fits all models.
We compared our reconstruction with Siemens ADMIRE, which is the clinical standard hybrid iterative reconstruction (IR) method for DS-FFS CT, in terms of spatial resolution, noise profile, and image artifacts through both phantoms and clinical scan datasets. Experiments show that our reconstruction has a higher spatial resolution, with a Task-Based Modulation Transfer Function (MTF ) consistently higher than the clinical standard hybrid IR. In addition, our reconstruction shows a reduced magnitude of image undersampling artifacts than the clinical standard.
By modeling a precise geometry and avoiding data rebinning or interpolation, our physics-based reconstruction achieves a higher spatial resolution and fewer image artifacts with smaller magnitude than the clinical standard hybrid IR.
对于单源螺旋 Computed Tomography（CT），已经研究了 Filtered-Back Projection（FBP）和统计迭代重建。然而，对于具有飞行焦点（DS-FFS CT）的双源 CT，一种能够准确模拟扫描仪几何形状和采集物理特性的统计迭代重建方法，研究人员仍不了解。因此，我们的目的是为 DS-FFS CT 提出一种新的基于物理的迭代重建方法，并评估其图像质量。
我们的算法使用精确的物理模型从 DS-FFS CT 的原始锥形束几何形状和交错的双源螺旋轨迹中进行重建。为此，我们构建了一个噪声物理模型来表示数据采集噪声，以及一个先验图像模型来表示图像噪声和纹理。此外，我们设计了正向系统模型来计算偏转焦点的位置、体素和探测器单元的尺寸和灵敏度，以及 X 射线与体素的交点长度。正向系统模型还通过计算双源在任意螺旋螺距下的 X 射线覆盖间隙和重叠，来表示双源之间的协调运动。通过上述模型，我们通过先进的共识平衡（CE）数值方法进行重建，以计算联合优化问题的最大后验估计，该问题同时拟合所有模型。
我们通过体模和临床扫描数据集，从空间分辨率、噪声分布和图像伪影等方面，将我们的重建与西门子 ADMIRE 进行了比较，后者是 DS-FFS CT 的临床标准混合迭代重建（IR）方法。实验表明，我们的重建具有更高的空间分辨率，基于任务的调制传递函数（MTF）始终高于临床标准混合 IR。此外，我们的重建显示出比临床标准更小幅度的图像欠采样伪影。
通过对精确的几何形状进行建模并避免数据重排或插值，我们的基于物理的重建方法比临床标准混合 IR 具有更高的空间分辨率和更少的图像伪影，且幅度更小。
