Nelson Geoff, Wu Meng, Hinkel Cameron, Krishna Ganesh, Funk Tobias, Rosenberg Jarrett, Fahrig Rebecca
Department of Radiology, Stanford University, Stanford, California 94305.
Palo Alto Medical Foundation, Department of Medicine, University of California San Francisco, San Francisco, California 94143.
Med Phys. 2016 Dec;43(12):6282. doi: 10.1118/1.4966025.
Electromagnetic navigation bronchoscopy (ENB) provides improved targeting accuracy during transbronchial biopsies of suspicious nodules. The greatest weakness of ENB-based guidance is the registration divergence that exists between the planning CT, acquired days or weeks before the intervention, and the patient on the table on the day of the intervention. Augmenting ENB guidance with real-time tomosynthesis imaging during the intervention could mitigate the divergence and further improve the yield of ENB-guided transbronchial biopsies. The real-time tomosynthesis prototype, the scanning-beam digital x-ray (SBDX) system, does not currently display images reconstructed by the iterative algorithm that was developed for this lung imaging application. A protocol using fiducial markers was therefore implemented to permit evaluation of potential improvements that would be provided by the SBDX system in a clinical setting.
Ten 7 mm lesions (5 per side) were injected into the periphery of each of four preserved pig lungs. The lungs were then placed in a vacuum chamber that permitted simulation of realistic motion and deformation due to breathing. Standard clinical CT scans of the pig lung phantoms were acquired and reconstructed with isotropic resolution of 0.625 mm. Standard ENB-guided biopsy procedures including target identification, path planning, CT-to-lung registration and navigation to the lesion were carried out, and a fiducial marker was placed at the location at which a biopsy would have been acquired. The channel-to-target distance provided by the ENB system prior to fiducial placement was noted. The lung phantoms were then imaged using the SBDX system, and using high-resolution conebeam CT. The distance between the fiducial marker tip and the lesion was measured in SBDX images and in the gold-standard conebeam-CT images. The channel-to-target divergence predicted by the ENB system and measured in the SBDX images was compared to the gold standard to determine if improved targeting accuracy could be achieved using SBDX image guidance.
As expected, the ENB system showed poorer targeting accuracy for small peripheral nodules. Only 20 nodules of the 40 injected could be adequately reached using ENB guidance alone. The SBDX system was capable of visualizing these small lesions, and measured fiducial-to-target distances on SBDX agreed well with measurements in gold-standard conebeam-CT images (p = 0.0001). The correlation between gold-standard conebeam-CT distances and predicted fiducial-to-target distances provided by the ENB system was poor (p = 0.72), primarily due to inaccurate ENB CT-to-body registration and movement due to breathing.
The SBDX system permits visualization of small lung nodules, as well as accurate measurement of channel-to-target distances. Combined use of ENB with SBDX real-time image guidance could improve accuracy and yield of biopsies, particularly of those lesions located in the periphery of the lung.
电磁导航支气管镜检查（ENB）在对可疑结节进行经支气管活检时可提高靶向准确性。基于ENB的引导最大的弱点是在干预前数天或数周获取的计划CT与干预当天手术台上的患者之间存在配准偏差。在干预过程中使用实时断层合成成像增强ENB引导可减轻这种偏差，并进一步提高ENB引导的经支气管活检的成功率。实时断层合成原型，即扫描束数字X射线（SBDX）系统，目前未显示通过为这种肺部成像应用开发的迭代算法重建的图像。因此实施了一种使用基准标记的方案，以评估SBDX系统在临床环境中可能提供的潜在改进。
在四个保存的猪肺的每个肺的周边注入10个7毫米的病变（每侧5个）。然后将肺放置在真空室中，该真空室允许模拟由于呼吸引起的真实运动和变形。获取猪肺模型的标准临床CT扫描，并以0.625毫米的各向同性分辨率重建。进行标准的ENB引导活检程序，包括目标识别、路径规划、CT到肺的配准以及向病变的导航，并在将进行活检的位置放置一个基准标记。记录在放置基准标记之前ENB系统提供的通道到目标的距离。然后使用SBDX系统以及高分辨率锥形束CT对肺模型进行成像。在SBDX图像和金标准锥形束CT图像中测量基准标记尖端与病变之间的距离。将ENB系统预测并在SBDX图像中测量的通道到目标的偏差与金标准进行比较，以确定使用SBDX图像引导是否可以提高靶向准确性。
正如预期的那样，ENB系统对小的周边结节显示出较差的靶向准确性。仅使用ENB引导只能充分到达40个注入结节中的20个。SBDX系统能够可视化这些小病变，并且在SBDX上测量的基准到目标的距离与金标准锥形束CT图像中的测量结果非常吻合（p = 0.0001）。金标准锥形束CT距离与ENB系统提供的预测基准到目标的距离之间的相关性较差（p = 0.72），主要是由于ENB CT到身体的配准不准确以及呼吸引起的运动。
SBDX系统允许可视化小的肺结节，并能准确测量通道到目标的距离。将ENB与SBDX实时图像引导结合使用可以提高活检的准确性和成功率，特别是对于那些位于肺周边的病变。
