Glover G H
Med Phys. 1982 Nov-Dec;9(6):860-7. doi: 10.1118/1.595197.
Compton scatter of x-ray quanta is the dominant attenuation mechanism in medical diagnostic imaging. In this paper, it is shown that the scatter-to-primary ratio determines the nature and intensity of scatter artifacts in computed tomography (CT) reconstructions and that this ratio, while significantly lower than in radiographic and fluoroscopic examinations, can still be significant in CT. It is found that high spatial-frequency artifacts can arise even though the detected scatter intensity has little or no high-frequency modulation. Reconstructions from x-ray data are presented which show "cupping" as well as dark streaks connecting high-attenuation regions. Correction of the data from measurements of scatter eliminates these artifacts. It is, moreover, observed that the intensity of the artifacts is often diminished when a beam-shaping attenuator is employed. Calculations of scatter intensity are developed from a model which includes single-event and two-event scatter. This analysis is in good agreement with measurements on round water phantoms. Extension to other detector geometries shows, not unexpectedly, that detectors with poorer collimation yield larger scatter artifacts.
X射线量子的康普顿散射是医学诊断成像中的主要衰减机制。本文表明，散射与原发射线之比决定了计算机断层扫描（CT）重建中散射伪影的性质和强度，并且该比值虽然远低于射线照相和荧光透视检查中的比值，但在CT中仍可能很显著。研究发现，即使检测到的散射强度几乎没有高频调制或根本没有高频调制，也可能出现高空间频率伪影。给出了从X射线数据重建的结果，这些结果显示出“杯状”以及连接高衰减区域的暗条纹。对散射测量数据进行校正可消除这些伪影。此外，观察到当使用光束整形衰减器时，伪影的强度通常会减弱。基于包括单事件散射和双事件散射的模型进行了散射强度计算。该分析与圆形水模体的测量结果高度吻合。不出所料，将其扩展到其他探测器几何形状表明，准直性较差的探测器会产生更大的散射伪影。
