Effect of shaped filter design on dose and image quality in breast CT
Effect of shaped filter design on dose and image quality in breast CT
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DOI：
10.1088/0031-9155/58/12/4205
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发表时间：
2013-06-21
影响因子：
3.5
通讯作者：
Kalender, Willi A.
中科院分区：
文献类型：
--
作者：
Lueck, Ferdinand;Kolditz, Daniel;Kalender, Willi A.
本研究的目的是探讨专门为乳腺计算机断层扫描（CT）扫描仪设计的形状滤光片对剂量和图像质量的影响。采用两种不同的设计方法对扇形方向的滤波器形状和材料进行优化，一种是针对CT图像中均匀的噪声分布，另一种是针对乳房内均匀的剂量分布。为了满足上述标准，对每个滤罩直径迭代确定了最佳滤罩厚度作为扇角的函数。研究了不同的过滤材料（铝、铜、碳、聚四氟乙烯）和直径在80-180毫米之间的胸膜。基于射线追踪方法的CT模拟获得的重建图像中的噪声均匀性，以及通过蒙特卡罗软件工具计算的乳腺剂量，被用作优点值。此外，还评估了ct值的均匀性、锥方向的噪声分布、从中心到外围的空间分辨率和剂量加权的噪比（CNRD）。此外，还研究了形状滤波器对散射的抑制作用。由于在临床CT系统中只有几个或一个滤波器是实用的，因此我们也研究了一个形状滤波器对不同乳房直径的影响。在这种情况下，滤波器，设计为最大的乳房直径，模拟在可变源到过滤器的距离取决于乳房直径。采用以均匀噪声分布为目标的滤波器设计方法，以铝为滤材获得了最佳的设计效果。噪声均匀性从20%下降到5%，所有乳房直径的剂量减少了约30-40%。锥形滤波器对噪声的锥向均匀性、ct值均匀性、空间分辨率和cndn均无明显影响。然而，观察到CNRD略有改善。此外，散射降低了约20-30%，散射分布更加均匀，从而减少了拔罐伪影。在不同的源-滤波器距离下使用一个形状滤波器的模拟结果表明，所有乳房直径的噪声分布几乎均匀，剂量减少幅度相当。综上所述，通过为乳腺CT设计的形状滤光片，可以在不影响图像质量的情况下实现显著的剂量降低。一个形状的过滤器设计为最大的乳房直径使用可变的源到过滤器的距离似乎是乳房CT的最佳解决方案。
The purpose of this study was to investigate the effect of shaped filters specifically designed for dedicated breast computed tomography (CT) scanners on dose and image quality. Optimization of filter shape and material in fan direction was performed using two different design methods, one aiming at homogeneous noise distributions in the CT images and the other aiming at a uniform dose distribution in the breast. The optimal filter thickness as a function of fan angle was determined iteratively to fulfil the above mentioned criteria for each breast diameter. Different filter materials (aluminium, copper, carbon, polytetrafluoroethylene) and breast phantoms with diameters between 80-180 mm were investigated. Noise uniformity in the reconstructed images, obtained from CT simulations based on ray-tracing methods, and dose in the breast, calculated with a Monte Carlo software tool, were used as figure of merit. Furthermore, CT-value homogeneity, the distribution of noise in cone direction, spatial resolution from centre to periphery and the contrast-to-noise ratio weighted by dose (CNRD) were evaluated. In addition, the decrease of scatter due to shaped filters was investigated. Since only few or one filter are practical in clinical CT systems, the effects of one shaped filter for different breast diameters were also investigated. In this case the filter, designed for the largest breast diameter, was simulated at variable source-to-filter distances depending on breast diameter. With the filter design method aiming at uniform noise distribution best results were obtained for aluminium as the filtermaterial. Noise uniformity improved from 20% down to 5% and dose was reduced by about 30-40% for all breast diameters. No decrease of noise uniformity in cone direction, CT-value homogeneity, spatial resolution and theCNRDwas detected with the shaped filter. However, a small improvement of CNRD was observed. Furthermore, a scatter reduction of about 20-30% and a more homogeneous scatter distribution were reached which led to reduced cupping artefacts. The simulations with one shaped filter at variable source-to-filter distance resulted in nearly homogeneous noise distributions and comparable dose reduction for all breast diameters. In conclusion, by means of shaped filters designed for breast CT, significant dose reduction can be achieved at unimpaired image quality. One shaped filter designed for the largest breast diameter used with variable source-to-filter distance appears to be the best solution for breast CT.