Efficient object scatter correction algorithm for third and fourth generation CT scanners
Efficient object scatter correction algorithm for third and fourth generation CT scanners
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DOI：
10.1007/s003300050710
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发表时间：
1999-01-01
影响因子：
5.9
通讯作者：
Klingenbeck-Regn, K
中科院分区：
文献类型：
--
作者：
Ohnesorge, B;Flohr, T;Klingenbeck-Regn, K
在对象切片内散射并到达探测器阵列的X射线光子增加了探测到的信号，并产生图像伪影，如大对象中的“杯状”效应和高衰减区域之间的暗带。伪影振幅随扫描体积或切片宽度而增大。在第三代计算机断层摄影（CT）几何结构中，可以通过准直检测器元件来减少对象散射。然而，校正仍然可以改善图像质量。对于第四代CT几何结构，只有较差的抗散射准直是可能的，并且需要数值校正。本文提出了一种可参数化的第三代和第四代CT几何校正算法。该方法需要较低的计算工作量，并允许灵活的应用程序，以不同的身体部位，通过简单的参数调整。从测量信号中减去的对象散射强度通过加权和窗口化的投影数据与空间不变的“散射卷积函数”的卷积来计算。散射卷积函数近似为所需的扫描器几何形状的笔形波束模拟和测量使用相干和非相干微分散射截面数据。几个例子的幻影和医疗对象扫描第三代和第四代CT系统进行了讨论。在第三代扫描仪中，散射伪影得到有效校正。对于抗散射准直较差的第四代几何结构，对象散射伪影大大减少。
X-ray photons which are scattered inside the object slice and reach the detector array increase the detected signal and produce image artifacts as "cupping" effects in large objects and dark bands between regions of high attenuation. The artifact amplitudes increase with scanned volume or slice width. Object scatter can be reduced in third generation computed tomography (CT) geometry by collimating the detector elements. However, a correction can still improve image quality. For fourth generation CT geometry, only poor anti-scatter collimation is possible and a numeric correction is necessary. This paper presents a correction algorithm which can be parameterized for third and fourth generation CT geometry. The method requires low computational effort and allows flexible application to different body regions by simple parameter adjustments. The object scatter intensity which is subtracted from the measured signal is calculated with convolution of the weighted and windowed projection data with a spatially invariant "scatter convolution function". The scatter convolution function is approximated for the desired scanner geometry form pencil beam simulations and measurements using coherent and incoherent differential scatter cross section data. Several examples of phantom and medical objects scanned with third and fourth generation CT systems are discussed. In third generation scanners, scatter artifacts ar effectively corrected. For fourth generation geometry with poor anti-scatter collimation, object scatter artifacts are strongly reduced.