Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland 21202, USA.
Med Phys. 2011 Aug;38(8):4563-74. doi: 10.1118/1.3597566.
A flat-panel detector based mobile isocentric C-arm for cone-beam CT (CBCT) has been developed to allow intraoperative 3D imaging with sub-millimeter spatial resolution and soft-tissue visibility. Image quality and radiation dose were evaluated in spinal surgery, commonly relying on lower-performance image intensifier based mobile C-arms. Scan protocols were developed for task-specific imaging at minimum dose, in-room exposure was evaluated, and integration of the imaging system with a surgical guidance system was demonstrated in preclinical studies of minimally invasive spine surgery.
Radiation dose was assessed as a function of kilovolt (peak) (80-120 kVp) and milliampere second using thoracic and lumbar spine dosimetry phantoms. In-room radiation exposure was measured throughout the operating room for various CBCT scan protocols. Image quality was assessed using tissue-equivalent inserts in chest and abdomen phantoms to evaluate bone and soft-tissue contrast-to-noise ratio as a function of dose, and task-specific protocols (i.e., visualization of bone or soft-tissues) were defined. Results were applied in preclinical studies using a cadaveric torso simulating minimally invasive, transpedicular surgery.
Task-specific CBCT protocols identified include: thoracic bone visualization (100 kVp; 60 mAs; 1.8 mGy); lumbar bone visualization (100 kVp; 130 mAs; 3.2 mGy); thoracic soft-tissue visualization (100 kVp; 230 mAs; 4.3 mGy); and lumbar soft-tissue visualization (120 kVp; 460 mAs; 10.6 mGy)--each at (0.3 x 0.3 x 0.9 mm3) voxel size. Alternative lower-dose, lower-resolution soft-tissue visualization protocols were identified (100 kVp; 230 mAs; 5.1 mGy) for the lumbar region at (0.3 x 0.3 x 1.5 mm3) voxel size. Half-scan orbit of the C-arm (x-ray tube traversing under the table) was dosimetrically advantageous (prepatient attenuation) with a nonuniform dose distribution (-2 x higher at the entrance side than at isocenter, and -3-4 lower at the exit side). The in-room dose (microsievert) per unit scan dose (milligray) ranged from -21 microSv/mGy on average at tableside to -0.1 microSv/mGy at 2.0 m distance to isocenter. All protocols involve surgical staff stepping behind a shield wall for each CBCT scan, therefore imparting -zero dose to staff. Protocol implementation in preclinical cadaveric studies demonstrate integration of the C-arm with a navigation system for spine surgery guidance-specifically, minimally invasive vertebroplasty in which the system provided accurate guidance and visualization of needle placement and bone cement distribution. Cumulative dose including multiple intraoperative scans was -11.5 mGy for CBCT-guided thoracic vertebroplasty and -23.2 mGy for lumbar vertebroplasty, with dose to staff at tableside reduced to -1 min of fluoroscopy time (-4(0-60 microSv), compared to 5-11 min for the conventional approach.
Intraoperative CBCT using a high-performance mobile C-arm prototype demonstrates image quality suitable to guidance of spine surgery, with task-specific protocols providing an important basis for minimizing radiation dose, while maintaining image quality sufficient for surgical guidance. Images demonstrate a significant advance in spatial resolution and soft-tissue visibility, and CBCT guidance offers the potential to reduce fluoroscopy reliance, reducing cumulative dose to patient and staff. Integration with a surgical guidance system demonstrates precise tracking and visualization in up-to-date images (alleviating reliance on preoperative images only), including detection of errors or suboptimal surgical outcomes in the operating room.
开发了一种基于平板探测器的移动等中心 C 臂锥形束 CT（CBCT）系统，以实现具有亚毫米空间分辨率和软组织可见度的术中 3D 成像。在通常依赖于性能较低的基于影像增强器的移动 C 臂的脊柱手术中，评估了图像质量和辐射剂量。开发了特定任务的成像扫描协议，以最小剂量进行，评估了室内辐射暴露，并在微创脊柱手术的临床前研究中展示了成像系统与手术引导系统的集成。
使用胸部和腰椎剂量体模评估千伏（峰值）（80-120 kVp）和毫安秒的辐射剂量。在各种 CBCT 扫描协议中，测量整个手术室的室内辐射暴露。使用胸部和腹部体模中的组织等效插件评估骨和软组织的对比噪声比，以评估剂量的函数，以及定义特定任务的协议（即，骨或软组织的可视化）。结果应用于使用模拟微创经皮手术的尸体躯干进行的临床前研究。
确定的特定任务的 CBCT 协议包括：胸部骨骼可视化（100 kVp；60 mAs；1.8 mGy）；腰椎骨骼可视化（100 kVp；130 mAs；3.2 mGy）；胸部软组织可视化（100 kVp；230 mAs；4.3 mGy）；和腰椎软组织可视化（120 kVp；460 mAs；10.6 mGy） - 每个协议的体素尺寸均为（0.3 x 0.3 x 0.9 mm3）。为腰椎区域确定了替代的低剂量、低分辨率软组织可视化协议（100 kVp；230 mAs；5.1 mGy），体素尺寸为（0.3 x 0.3 x 1.5 mm3）。C 臂的半扫描轨道（x 射线管在桌子下穿过）在剂量学上具有优势（患者前衰减），具有不均匀的剂量分布（入口侧比等中心侧高 2 倍，出口侧低 3-4 倍）。每个扫描剂量的室内剂量（微西弗）与单位扫描剂量（毫格雷）的比值范围为从桌子旁的平均 21 微西弗/毫格雷到距等中心 2.0 米处的 0.1 微西弗/毫格雷。所有协议都涉及手术人员在每次 CBCT 扫描时站在屏蔽墙后面，因此对工作人员没有造成任何剂量。在临床前尸体研究中实施协议表明，C 臂与脊柱手术引导的导航系统集成，特别是微创椎体成形术，该系统提供了准确的引导和对针放置和骨水泥分布的可视化。包括多次术中扫描在内的累积剂量对于 CBCT 引导的胸椎椎体成形术为 11.5 mGy，对于腰椎椎体成形术为 23.2 mGy，将手术台旁的工作人员的剂量降低至 1 分钟的透视时间（4（0-60 微西弗），与传统方法的 5-11 分钟相比。
使用高性能移动 C 臂原型进行术中 CBCT 显示出适合脊柱手术引导的图像质量，特定任务的协议为最小化辐射剂量提供了重要依据，同时保持足以进行手术引导的图像质量。图像显示出在空间分辨率和软组织可见度方面的显著进步，并且 CBCT 引导有可能减少对透视的依赖，降低患者和工作人员的累积剂量。与手术引导系统的集成显示了最新图像中的精确跟踪和可视化（减轻了仅依赖术前图像的负担），包括在手术室中检测到错误或不理想的手术结果。
