Siemens Healthcare GmbH, Forchheim, Germany.
Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München, Garching, Germany.
Med Phys. 2021 Jul;48(7):3479-3499. doi: 10.1002/mp.14879. Epub 2021 Jun 2.
In this work, we explore the potential of region-of-interest (ROI) imaging in x-ray computed tomography (CT). Using two dynamic beam attenuator (DBA) concepts for fluence field modulation (FFM) previously developed, we investigate and evaluate the potential dose savings in comparison with current FFM technology.
ROI imaging is a special application of FFM where the bulk of x-ray radiation is propagated toward a certain anatomical target (ROI), specified by the imaging task, while the surrounding tissue is spared from radiation. We introduce a criterion suitable to quantitatively describe the balance between image quality inside an ROI and total radiation dose with respect to a given ROI imaging task. It accounts for the mean image variance at the ROI and the effective patient dose calculated from Monte Carlo simulations. The criterion is further used to compile task-specific DBA trajectories determining the primary x-ray fluence, and eventually used for comparing different FFM techniques, namely the sheet-based dynamic beam attenuator (sbDBA), the z-aligned sbDBA (z-sbDBA), and an adjustable static operation mode of the z-sbDBA. Furthermore, two static bowtie filters and the influence of tube current modulation (TCM) are included in the comparison.
Our findings demonstrate by simulations that the presented trajectory optimization method determines reasonable DBA trajectories. The influence of TCM is strongly depending on the imaging task. The narrow bowtie filter allows for dose reductions of about 10% compared to the regular bowtie filter in the considered ROI imaging tasks. The DBAs are shown to realize substantially larger dose reductions. In our cardiac imaging scenario, the DBAs can reduce the effective dose by about 30% (z-sbDBA) or 60% (sbDBA). We can further verify that the noise characteristics are not adversely affected by the DBAs.
Our research demonstrates that ROI imaging using the presented DBA concepts is a promising technique toward a more patient- and task-specific CT imaging requiring lower radiation dose. Both the sbDBA and the z-sbDBA are potential technical solutions for realizing ROI imaging in x-ray CT.
在这项工作中，我们探索了感兴趣区域（ROI）成像在 X 射线计算机断层扫描（CT）中的潜力。使用之前开发的两种用于强度调制（FFM）的动态束衰减器（DBA）概念，我们研究并评估了与当前 FFM 技术相比的潜在剂量节省。
ROI 成像是 FFM 的一种特殊应用，其中大部分 X 射线辐射传播到特定的解剖目标（ROI），这是由成像任务指定的，而周围的组织则免受辐射。我们引入了一个合适的标准，用于定量描述 ROI 内的图像质量与特定 ROI 成像任务的总辐射剂量之间的平衡。它考虑了 ROI 处的平均图像方差和从蒙特卡罗模拟计算出的有效患者剂量。该标准进一步用于编译特定任务的 DBA 轨迹，确定初始 X 射线强度，并最终用于比较不同的 FFM 技术，即基于薄片的动态束衰减器（sbDBA）、与 Z 轴对齐的 sbDBA（z-sbDBA）以及 z-sbDBA 的可调静态操作模式。此外，还包括两个静态蝴蝶结滤波器和管电流调制（TCM）的影响。
我们的研究结果通过模拟表明，所提出的轨迹优化方法确定了合理的 DBA 轨迹。TCM 的影响强烈依赖于成像任务。在考虑的 ROI 成像任务中，窄蝴蝶结滤波器与常规蝴蝶结滤波器相比可减少约 10%的剂量。DBA 被证明可以实现更大幅度的剂量减少。在我们的心脏成像场景中，DBA 可以将有效剂量降低约 30%（z-sbDBA）或 60%（sbDBA）。我们还可以进一步验证，DBA 不会对噪声特性产生不利影响。
我们的研究表明，使用所提出的 DBA 概念进行 ROI 成像，是朝着更具患者和任务特异性的 CT 成像发展的一种有前途的技术，这种技术需要更低的辐射剂量。sbDBA 和 z-sbDBA 都是在 X 射线 CT 中实现 ROI 成像的潜在技术解决方案。
