Department of Medical Physics, University of Wisconsin-Madison, Madison, WI 53705, USA.
Med Phys. 2013 Feb;40(2):021905. doi: 10.1118/1.4773879.
The purpose of this work is to introduce a new device that allows for patient-specific imaging-dose modulation in conventional and cone-beam CT. The device is called a digital beam attenuator (DBA). The DBA modulates an x-ray beam by varying the attenuation of a set of attenuating wedge filters across the fan angle. The ability to modulate the imaging dose across the fan beam represents another stride in the direction of personalized medicine. With the DBA, imaging dose can be tailored for a given patient anatomy, or even tailored to provide signal-to-noise ratio enhancement within a region of interest. This modulation enables decreases in: dose, scatter, detector dynamic range requirements, and noise nonuniformities. In addition to introducing the DBA, the simulation framework used to study the DBA under different configurations is presented. Finally, a detailed study on the choice of the material used to build the DBA is presented.
To change the attenuator thickness, the authors propose to use an overlapping wedge design. In this design, for each wedge pair, one wedge is held stationary and another wedge is moved over the stationary wedge. The composite thickness of the two wedges changes as a function of the amount of overlap between the wedges. To validate the DBA concept and study design changes, a simulation environment was constructed. The environment allows for changes to system geometry, different source spectra, DBA wedge design modifications, and supports both voxelized and analytic phantom models. A study of all the elements from atomic number 1 to 92 were evaluated for use as DBA filter material. The amount of dynamic range and tube loading for each element were calculated for various DBA designs. Tube loading was calculated by comparing the attenuation of the DBA at its minimum attenuation position to a filtered non-DBA acquisition.
The design and parametrization of DBA implemented FFMCT has been introduced. A simulation framework was presented with which DBA-FFMCT, bowtie filter CT acquisitions, and unmodulated CT acquisitions can be simulated. The study on wedge filter design concluded that the ideal filter material should have an atomic number in the range of 21-34. Iron was chosen for an experimental relative-tube-loading measurement and showed that DBA-FFMCT scans could be acquired with negligible increases in tube power demands.
The basic idea of DBA implemented fluence field modulated CT, a simulation framework to verify the concept, and a filter selection study have been presented. The use of a DBA represents another step toward the ultimate in patient specific CT dose delivery as patient dose can be delivered uniquely as a function of view and fan angle using this device.
本工作旨在介绍一种新的设备，该设备可在常规和锥形束 CT 中实现针对患者的成像剂量调制。该设备称为数字射束衰减器（DBA）。DBA 通过在扇形角上改变一组衰减楔形滤波器的衰减来调制 X 射线束。能够在扇形射束上调制成像剂量是朝着个性化医疗方向迈出的又一步。通过 DBA，可以根据特定患者的解剖结构来调整成像剂量，甚至可以调整以在感兴趣区域内提供信噪比增强。这种调制可以降低剂量、散射、探测器动态范围要求和噪声非均匀性。除了介绍 DBA 之外，还提出了用于在不同配置下研究 DBA 的模拟框架。最后，提出了用于构建 DBA 的材料选择的详细研究。
为了改变衰减器的厚度，作者建议使用重叠楔形设计。在该设计中，对于每对楔形，一个楔形保持固定，另一个楔形在固定楔形上移动。两个楔形的复合厚度随楔形之间的重叠量而变化。为了验证 DBA 概念并研究设计更改，构建了一个模拟环境。该环境允许更改系统几何形状、不同的源光谱、DBA 楔形设计修改，并支持体素化和解析体模。评估了从原子序数 1 到 92 的所有元素作为 DBA 滤光片材料的使用情况。计算了各种 DBA 设计的动态范围和管加载量。管加载量通过将 DBA 在其最小衰减位置的衰减与未过滤的非 DBA 采集进行比较来计算。
介绍了 DBA 实施的 FFMCT 的设计和参数化。提出了一个模拟框架，可通过该框架模拟 DBA-FFMCT、蝴蝶结滤光片 CT 采集和未调制 CT 采集。楔形滤光片设计的研究得出的结论是，理想的滤光片材料的原子序数应在 21-34 范围内。选择铁进行相对管负载测量的实验，并表明可以以可忽略不计的管功率需求增加来获取 DBA-FFMCT 扫描。
介绍了 DBA 实施的通量场调制 CT 的基本思想、验证该概念的模拟框架以及滤光片选择研究。使用 DBA 代表了朝着最终的患者特定 CT 剂量输送方向迈出的又一步，因为可以使用该设备根据视图和扇形角独特地输送患者剂量。
