Malcova LLC, Baltimore, MD, 21211, USA.
Med Phys. 2020 Apr;47(4):1590-1608. doi: 10.1002/mp.14026. Epub 2020 Feb 10.
To introduce an auxiliary apparatus of fluence modulation and scatter shielding for dedicated breast computed tomography (bCT) and the corresponding patient-specific method of image acquisition.
The apparatus is composed of two assemblies, referred to herein as the "Dynamic Fluence Gate" (FG) and "Scatter Shield" (SS), that work in synchrony to form a narrow beam sweeping the entire fan angle coverage of the imaging system during a projection. The apparatus, as a whole, is referred to as FG-SS. FG and SS are pre-patient and post-patient units, respectively. Each is composed of a rotating drum, on top of which are installed two sheets of high x-ray attenuating material, a sensory system, and the constituent robotics. The sheets of each unit are positioned such that an opening - a window Fluence Modulation and Scatter Shielding is formed between them. The rotations of the drums and positioning of the sheets are synchronized and adjusted such that a line of sight is created between the source, FG window, the breast, and the SS window. With line of sight achieved, the narrow beam transitions from the source to the detector. The fluence of the narrow beam during a projection depends on the size, shape, and positioning of the breast. The FG-SS method of imaging is discussed mathematically and demonstrated using computer simulations. A series of Monte Carlo simulations are conducted to evaluate the performance of the system as relates to its impact on the imager's dynamic range, dose distribution to the breast, noise inhomogeneity in reconstructed images, and scatter buildup in projections within small, medium, and large breasts composed of homogeneous medium breast tissue.
Implementation of FG-SS results in near scatter-free projections, reduction in both dose and the required dynamic range of the imager, and equalization of the quantum noise distribution in the reconstructed image. Using the disclosed design, the dynamic range was reduced by factors ranging from 1.6 to 5.5 across the range of breast sizes studied. A reduction in the acquisition of the scattered rays, varying between the factors of 6.1 (in the small breast) and 9.8 (in that large breast) was achieved and consequently, shading artifacts were suppressed. Noise in the CT image was equalized by reducing the overall spatial variation from 29% to <5% in small breast and from 45% to 14% in the large breast. An overall reduction in deposited dose to the breast was achieved - between 26% and 39% depending on the breast size.
Utilization of the FG-SS apparatus and technique was demonstrated via simulations to result in: significant reductions in dose to the breast, reductions in scatter uptake in projections, reduced required dynamic range of the imager, and homogenizing of quantum noise throughout the reconstructed image.
介绍一种用于专用乳腺计算机断层扫描（bCT）的调制剂量和散射屏蔽辅助装置及其相应的患者专用图像采集方法。
该设备由两个组件组成，这里分别称为“动态剂量门控”（FG）和“散射屏蔽”（SS），它们协同工作，在投影期间形成一个窄束，扫过成像系统的整个扇形角度覆盖范围。整个设备称为 FG-SS。FG 和 SS 分别是患者前和患者后的组件。每个组件由一个旋转滚筒组成，滚筒顶部安装有两张高 X 射线衰减材料、一个感应系统和组成机器人。每个单元的片材的位置使得在它们之间形成一个开口-一个窗口剂量调制和散射屏蔽。滚筒的旋转和片材的定位是同步和调整的，以便在源、FG 窗口、乳房和 SS 窗口之间创建视线。视线实现后，窄束从源传输到探测器。在投影期间，窄束的剂量取决于乳房的大小、形状和位置。FG-SS 成像方法从数学上进行了讨论，并通过计算机模拟进行了演示。进行了一系列蒙特卡罗模拟，以评估系统的性能与其对成像仪动态范围、乳房剂量分布、重建图像中的噪声不均匀性以及小、中、大乳房内散射积聚的影响之间的关系。这些乳房由均匀介质组成。
实施 FG-SS 导致近无散射的投影，剂量和成像仪所需动态范围降低，以及重建图像中量子噪声分布的均衡。使用所公开的设计，在所研究的乳房尺寸范围内，动态范围降低了 1.6 至 5.5 倍。散射射线的采集减少了 6.1（在小乳房中）至 9.8（在大乳房中）的倍数，因此抑制了阴影伪影。通过减少小乳房中总空间变化从 29%到<5%和大乳房中从 45%到 14%，CT 图像中的噪声得到均衡。乳房的剂量沉积总量减少-根据乳房的大小，范围在 26%至 39%之间。
通过模拟证明，使用 FG-SS 设备和技术可显著降低乳房剂量、降低投影中的散射摄取量、降低成像仪所需的动态范围，并使重建图像中的量子噪声均匀化。
