Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, USA.
Department of Orthopaedic Surgery, Johns Hopkins Medical Institutions, Baltimore, MD, USA.
Med Phys. 2020 Mar;47(3):958-974. doi: 10.1002/mp.13983. Epub 2020 Jan 6.
To characterize the radiation dose and three-dimensional (3D) imaging performance of a recently developed mobile, isocentric C-arm equipped with a flat-panel detector (FPD) for intraoperative cone-beam computed tomography (CBCT) (Cios Spin 3D, Siemens Healthineers) and to identify potential improvements in 3D imaging protocols for pertinent imaging tasks.
The C-arm features a 30 × 30 cm FPD and isocentric gantry with computer-controlled motorization of rotation (0-195°), angulation (±220°), and height (0-45 cm). Geometric calibration was assessed in terms of 9 degrees of freedom of the x-ray source and detector in CBCT scans, and the reproducibility of geometric calibration was evaluated. Standard and custom scan protocols were evaluated, with variation in the number of projections (100-400) and mAs per view (0.05-1.65 mAs). Image reconstruction was based on 3D filtered backprojection using "smooth," "normal," and "sharp" reconstruction filters as well as a custom, two-dimensional 2D isotropic filter. Imaging performance was evaluated in terms of uniformity, gray value correspondence with Hounsfield units (HU), contrast, noise (noise-power spectrum, NPS), spatial resolution (modulation transfer function, MTF), and noise-equivalent quanta (NEQ). Performance tradeoffs among protocols were visualized in anthropomorphic phantoms for various anatomical sites and imaging tasks.
Geometric calibration showed a high degree of reproducibility despite ~19 mm gantry flex over a nominal semicircular orbit. The dose for a CBCT scan varied from ~0.8-4.7 mGy for head protocols to ~6-38 mGy for body protocols. The MTF was consistent with sub-mm spatial resolution, with f (frequency at which MTF = 10%) equal to 0.64 mm , 1.0 mm , and 1.5 mm for smooth, standard, and sharp filters respectively. Implementation of a custom 2D isotropic filter improved CNR ~ 50-60% for both head and body protocols and provided more isotropic resolution and noise characteristics. The NPS and NEQ quantified the 3D noise performance and provided a guide to protocol selection, confirmed in images of anthropomorphic phantoms. Alternative scan protocols were identified according to body site and task - for example, lower-dose body protocols (<3 mGy) sufficient for visualization of bone structures.
The studies provided objective assessment of the dose and 3D imaging performance of a new C-arm, offering an important basis for clinical deployment and a benchmark for quality assurance. Modifications to standard 3D imaging protocols were identified that may improve performance or reduce radiation dose for pertinent imaging tasks.
描述一种新型的、配备平板探测器（FPD）的移动等中心 C 臂机（Cios Spin 3D，西门子医疗）的辐射剂量和三维（3D）成像性能，并确定在相关成像任务中改进 3D 成像方案的潜在方法。
C 臂机的 FPD 尺寸为 30×30cm，等中心旋转机架可通过计算机控制进行旋转（0-195°）、倾斜（±220°）和高度调节（0-45cm）。在 CBCT 扫描中评估了 X 射线源和探测器的 9 个自由度的几何校准，并评估了几何校准的可重复性。评估了标准和定制扫描方案，其中方案的差异在于投影数量（100-400）和每个视图的毫安秒（0.05-1.65mAs）。图像重建基于 3D 滤波反投影，使用“平滑”、“正常”和“锐利”重建滤波器以及定制的二维各向同性滤波器。根据均匀性、与亨氏单位（HU）的灰度值对应关系、对比度、噪声（噪声功率谱，NPS）、空间分辨率（调制传递函数，MTF）和噪声等效量子（NEQ）来评估成像性能。在各种解剖部位和成像任务的人体模型中可视化了方案之间的性能权衡。
尽管在标称的半圆形轨道上存在约 19mm 的机架弯曲，但几何校准显示出高度的可重复性。CBCT 扫描的剂量范围为头部方案约 0.8-4.7mGy，到身体方案约 6-38mGy。MTF 与亚毫米空间分辨率一致，平滑、标准和锐利滤波器的频率分别为 0.64mm、1.0mm 和 1.5mm。实施定制的二维各向同性滤波器可分别提高头部和身体方案约 50-60%的 CNR，并提供更各向同性的分辨率和噪声特性。NPS 和 NEQ 量化了 3D 噪声性能，并为协议选择提供了指导，在人体模型的图像中得到了证实。根据身体部位和任务确定了替代扫描方案，例如，用于可视化骨结构的低剂量身体方案（<3mGy）。
本研究客观评估了新型 C 臂的剂量和 3D 成像性能，为临床应用提供了重要依据，并为质量保证提供了基准。确定了标准 3D 成像方案的修改方法，这些方法可能会提高相关成像任务的性能或降低辐射剂量。
