Kyriakou Yiannis, Kalender Willi A
Institute of Medical Physics, University of Erlangen-Nuremberg, Henkestrasse 91, 91052 Erlangen, Germany.
Phys Med. 2007 Mar;23(1):3-15. doi: 10.1016/j.ejmp.2006.12.004. Epub 2007 Mar 28.
In modern X-ray computed tomography (CT) a trend to increased volume coverage by using multi-row detectors is apparent. Flat-panel detector CT (FPD-CT) systems provide an even larger field of measurement which, however, results in an increased scatter fraction. We investigated the scatter intensities registered in the case of FPD-CT. A hybrid model for the simulation of scatter combining deterministic and Monte Carlo methods was used for the scatter calculations. The influence of imaging parameters on the registered scatter intensity was examined both in single projections and reconstructed images. Scatter-to-primary ratios (SPRs) are given for various values of object thickness, field size, object-to-detector distance, incident energy and projection angle. For the simulations, homogeneous water phantoms and realistic patient data sets were used to produce scatter data representative for clinical situations. The SPR increases with object size, collimation and z-extent resulting in SPR>>1 and respective scatter artifacts in the reconstructed images. In contrary, the scatter intensity decreases non-linearly with the object-to-detector distance. The angular and spatial distributions of scatter form a flat function as compared to the distribution of the primary signal. Single scatter appears to determine the distribution and magnitude of the total-scatter intensity at the detector.
在现代X射线计算机断层扫描（CT）中，使用多排探测器增加容积覆盖范围的趋势很明显。平板探测器CT（FPD-CT）系统提供了更大的测量视野，然而，这会导致散射分数增加。我们研究了FPD-CT情况下记录的散射强度。使用一种结合确定性方法和蒙特卡罗方法的混合散射模拟模型进行散射计算。在单投影和重建图像中都研究了成像参数对记录的散射强度的影响。给出了不同物体厚度、视野大小、物体到探测器距离、入射能量和投影角度下的散射与原发射线比（SPR）。为了进行模拟，使用均匀水模体和真实患者数据集来生成代表临床情况的散射数据。SPR随物体尺寸、准直和z轴范围增加，导致SPR>>1，并在重建图像中产生相应的散射伪影。相反，散射强度随物体到探测器的距离呈非线性下降。与原发射线信号的分布相比，散射的角度和空间分布形成一个平坦的函数。单次散射似乎决定了探测器处总散射强度的分布和大小。
