A novel hardware duo of beam modulation and shielding to reduce scatter acquisition and dose in cone-beam breast CT.
A novel hardware duo of beam modulation and shielding to reduce scatter acquisition and dose in cone-beam breast CT.
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在锥束乳腺CT中，散射光子形成所采集信号的大部分，从而在成像系统的整个频率响应中不利地影响图像质量。先前的模拟研究提供了利用硬件解决方案来防止散射采集的概念证明。在这里，我们报告的设计，实施和表征的辅助装置的注量调制和散射屏蔽，确实导致投影与散射水平降低。设计了一种装置，用于永久安装在现有的锥束CT系统内。该装置由两个主要组件组成：“通量调节器”（FM）和“散射屏蔽”（SS）。组件的设计使它们能够在图像采集期间同步操作，将源X射线转换为移动的窄光束。在投影期间，该窄波束扫过成像系统的整个扇形角覆盖。由于这两个组件是相互依赖的，因此它们的联合实现被描述为设备FM-SS。FM和SS组件均包括金属外壳、传感系统和机器人系统。控制器单元处理它们的相对运动。进行了一系列的比较研究，以评估锥束CT系统在两种“模式”的操作：安装和不安装FM-SS的性能，并比较物理实现与以前模拟的结果。在锥束CT成像系统中使用的探测器的动态范围要求首先被表征，与操作模式无关。然后，我们的特点和比较的空间分辨率的成像系统，和没有，FM-SS。一个物理乳房体模，代表一个平均大小的乳房，开发和成像。然后将使用FM-SS与不使用FM-SS获得的信号电平的实际差异与基于先前报告的模拟的预期电平增益进行比较。在这些初始评估之后，研究了两种操作模式下每个投影中的散射采集。最后，作为FM-SS对平均尺寸乳房辐射剂量影响的初步研究，一系列Monte Carlo模拟与空气比释动能的物理测量相结合，有和没有FM-SS。随着FM-SS的实施，探测器所需的动态范围减少了5.5倍。散射射线的采集大幅减少，减少了5.1倍。随着FM-SS的实施，研究乳腺的沉积剂量减少了27%。所公开的FM-SS在锥束乳房CT系统内的实现导致所采集的投影中的散射分量的减少、对乳房的剂量存款的减少以及对探测器的动态范围的要求的放松。在FM-SS锥束乳腺CT实际临床应用之前，控制或校正图像采集期间发生的患者运动仍然是一个有待解决的开放性问题。
In cone-beam breast CT, scattered photons form a large portion of the acquired signal,adversely impacting image quality throughout the frequency response of the imaging system. Prior simulation studies provided proof of concept for utilization of a hardware solution to prevent scatter acquisition. Here,we report the design, implementation, and characterization of an auxiliary apparatus of fluence modulation and scatter shielding that does indeed lead to projections with a reduced level of scatter. An apparatus was designed for permanent installation within an existing cone-beam CT system. The apparatus is composed of two primary assemblies: a “Fluence Modulator” (FM) and a “Scatter Shield” (SS). The design of the assemblies enables them to operate in synchrony during image acquisition, converting the sourced x-rays into a moving narrow beam. During a projection, this narrow beam sweeps the entire fan angle coverage of the imaging system. As the two assemblies are contingent on one another, their joint implementation is described in the singular as apparatus FM–SS. The FM and the SS assemblies are each comprised a metal housing, a sensory system, and a robotic system. A controller unit handles their relative movements. A series of comparative studies were conducted to evaluate the performance of a cone-beam CT system in two “modes” of operation: with and without FM–SS installed, and to compare the results of physical implementation with those previously simulated. The dynamic range requirements of the utilized detector in the cone-beam CT imaging system were first characterized, independent of the mode of operation. We then characterized and compared the spatial resolution of the imaging system with, and without, FM–SS. A physical breast phantom, representative of an average size breast, was developed and imaged. Actual differences in signal level obtained with, versus without, FM–SS were then compared to the expected level gains based on previously reported simulations. Following these initial assessments, the scatter acquisition in each projection in both modes of operation was investigated. Finally, as an initial study of the impact of FM–SS on radiation dose in an average size breast, a series of Monte Carlo simulations were coupled with physical measurements of air kerma, with and without FM–SS. With implementation of FM-SS, the detector’s required dynamic range was reduced by a factor of 5.5. Substantial reduction in the acquisition of the scattered rays,by a factor of 5.1 was achieved. With the implementation of FM–SS, deposited dose was reduced by 27% in the studied breast. The disclosed implementation of FM–SS, within a cone-beam breast CT system, results in reduction of scatter-components in acquired projections, reduction of dose deposit to the breast, and relaxation of requirements for the detector’s dynamic range. Controlling or correcting for patient motion occurring during image acquisition remains an open problem to be solved prior to practical clinical usage of FM–SS cone-beam breast CT.
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