Vetter J R, Holden J E
Department of Medical Physics, University of Wisconsin, Madison 53706.
Med Phys. 1988 Sep-Oct;15(5):726-31. doi: 10.1118/1.596187.
Both beam hardening and the detection of scattered radiation cause nonlinearity errors in x-ray computed tomography (CT), leading to artifacts and CT number inaccuracies. Dual-energy measurements can be used to correct beam hardening effects to a high degree of accuracy. However, in the imaging of thick body sections the transmitted intensity of the primary beam is low, making scatter the most significant cause of CT number inaccuracy. Furthermore, the scatter-to-primary ratio is energy dependent, causing a shift in the apparent effective atomic number of the absorbing material. We have measured scatter under a variety of conditions on a third generation CT scanner with dual-energy capability in order to determine its effect on the accuracy of quantitative measurements. The effects of off focus radiation, detector cross-talk, and detector dark current were also accounted for in the analysis of the measured scatter data. Our results indicate that on this well collimated system, an accurate correction for scatter can be made based on the detected intensity in projections.
束硬化和散射辐射的检测都会导致X射线计算机断层扫描（CT）中的非线性误差，从而产生伪影并导致CT数值不准确。双能测量可用于高度精确地校正束硬化效应。然而，在厚体部成像中，原发射线的透射强度较低，使得散射成为CT数值不准确的最主要原因。此外，散射与原发射线的比率与能量有关，会导致吸收材料的表观有效原子序数发生偏移。我们在一台具有双能功能的第三代CT扫描仪上，在各种条件下测量了散射，以确定其对定量测量准确性的影响。在对测量的散射数据进行分析时，还考虑了离焦辐射、探测器串扰和探测器暗电流的影响。我们的结果表明，在这个准直良好的系统上，可以根据投影中的检测强度对散射进行精确校正。
