Technical note: comparing coherent and incoherent scatter effects for cone-beam CT
Technical note: comparing coherent and incoherent scatter effects for cone-beam CT
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DOI：
10.1088/0031-9155/53/10/n02
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发表时间：
2008-05-21
影响因子：
3.5
通讯作者：
Kalender, Willi A.
中科院分区：
文献类型：
--
作者：
Kyriakou, Yiannis;Meyer, Michael;Kalender, Willi A.
在平面探测器 CT (FD-CT) 扫描仪中，散射的强度和分布越来越受到人们的关注。通常假设散射是一种以非相干散射（康普顿效应）为主的偏移分布。根据 FD-CT 中使用的采集参数计算相干和非相干散射。混合方法优化了散射模拟的性能：快速准确的单散射强度分析计算与多散射的粗略蒙特卡罗 (MC) 估计相结合，以减少总体计算费用，同时确保可接受的信号质量。该模拟包允许分离相干和非相干单散射。对于直径从 40 毫米到 320 毫米不等的圆柱形水模型和各种 z 准直，对单次散射与总散射的比率进行了研究。计算了直径为 160 mm 和 320 mm、能量从 40 keV 到 120 keV 变化的体模的散射强度分布（包括相干单次散射、非相干单次散射和总散射）。此外，体素模型是根据临床头部和胸部 CT 数据集生成的，并用于散射模拟，以证明相干和不相干单散射对 2D 投影的影响。即使对于大型人体模型和大测量范围，单次散射也决定了总散射的很大一部分。对于大多数模拟情况，相干散射在总散射分布中占主导地位，即使对于 120 keV 也是如此。康普顿效应似乎对空间分布的影响较小，但在总体规模上占主导地位。
The intensity and distribution of scatter is of growing interest in the case of flat-detector CT (FD-CT) scanners. It is generally assumed that scatter is an offset distribution dominated by incoherent scatter (Compton effect). Coherent and incoherent scatter were computed with respect to acquisition parameters used in FD-CT. A hybrid method optimized the performance of the scatter simulation: a fast and exact analytical calculation of the single-scatter intensity combined with a coarse Monte Carlo (MC) estimate of multiple scatter to reduce overall computational expenses, while assuring an acceptable signal quality. The simulation package allowed for the separation of both coherent and incoherent single scatter. For cylindrical water phantoms varying from 40 mm to 320 mm diameter and for various z-collimations an investigation of the ratio of single-to-total scatter was performed. The intensity distribution of scatter (including coherent single scatter, incoherent single scatter and total scatter) was computed for phantoms of 160 mm and 320 mm diameter and energies varying from 40 keV to 120 keV. Additionally, voxel phantoms were generated from clinical head and thorax CT datasets and were employed in scatter simulations to demonstrate the effect of coherent and incoherent single scatter on the 2D projections. Single scatter determines a significant fraction of total scatter even for large body-sized phantoms and large field of measurement. Coherent scatter dominates the distribution of total scatter for most of the simulated cases, even for 120 keV. The Compton effect appeared to be less influential with respect to spatial distribution but dominated the overall magnitude.