Slagowski Jordan M, Dunkerley David A P, Hatt Charles R, Speidel Michael A
Dept. of Medical Physics, University of Wisconsin, Madison, WI, USA.
Dept. of Biomedical Engineering, University of Wisconsin, Madison, WI, USA.
Proc SPIE Int Soc Opt Eng. 2016 Feb 27;9783. doi: 10.1117/12.2216565. Epub 2016 Mar 22.
Accurate and artifact free reconstruction of tomographic images requires precise knowledge of the imaging system geometry. This work proposes a novel projection matrix (P-matrix) based calibration method to enable C-arm inverse geometry CT (IGCT). The method is evaluated for scanning-beam digital x-ray (SBDX), a C-arm mounted inverse geometry fluoroscopic technology. A helical configuration of fiducials is imaged at each gantry angle in a rotational acquisition. For each gantry angle, digital tomosynthesis is performed at multiple planes and a composite image analogous to a cone-beam projection is generated from the plane stack. The geometry of the C-arm, source array, and detector array is determined at each angle by constructing a parameterized 3D-to-2D projection matrix that minimizes the sum-of-squared deviations between measured and projected fiducial coordinates. Simulations were used to evaluate calibration performance with translations and rotations of the source and detector. In a geometry with 1 mm translation of the central ray relative to the axis-of-rotation and 1 degree yaw of the detector and source arrays, the maximum error in the recovered translational parameters was 0.4 mm and maximum error in the rotation parameter was 0.02 degrees. The relative root-mean-square error in a reconstruction of a numerical thorax phantom was 0.4% using the calibration method, versus 7.7% without calibration. Changes in source-detector-distance were the most challenging to estimate. Reconstruction of experimental SBDX data using the proposed method eliminated double contour artifacts present in a non-calibrated reconstruction. The proposed IGCT geometric calibration method reduces image artifacts when uncertainties exist in system geometry.
断层图像的准确且无伪影重建需要精确了解成像系统的几何结构。这项工作提出了一种基于新型投影矩阵（P矩阵）的校准方法，以实现C型臂逆几何CT（IGCT）。该方法针对扫描束数字X射线（SBDX）进行了评估，SBDX是一种安装在C型臂上的逆几何荧光透视技术。在旋转采集中，在每个机架角度对螺旋配置的基准标记进行成像。对于每个机架角度，在多个平面上进行数字断层合成，并从平面堆栈生成类似于锥束投影的合成图像。通过构建参数化的3D到2D投影矩阵来确定每个角度的C型臂、源阵列和探测器阵列的几何结构，该矩阵可使测量的和投影的基准坐标之间的平方偏差之和最小化。使用模拟来评估源和探测器平移和旋转时的校准性能。在中心射线相对于旋转轴平移1毫米且探测器和源阵列偏航1度的几何结构中，恢复的平移参数的最大误差为0.4毫米，旋转参数的最大误差为0.02度。使用校准方法重建数字胸部模型时的相对均方根误差为0.4%，未校准时为7.7%。源 - 探测器距离的变化是最难估计的。使用所提出的方法重建实验性SBDX数据消除了未校准重建中存在的双轮廓伪影。当系统几何结构存在不确定性时，所提出的IGCT几何校准方法可减少图像伪影。
