Cone-beam CT in lung biopsy: a clinical practice review on lessons learned and future perspectives

Abstract

Pulmonary nodules with intermediate to high risk of malignancy should preferably be diagnosed with image guide minimally invasive diagnostics before treatment. Several technological innovations have been developed to endobronchially navigate to these lesions and obtain tissue for diagnosis. This review addresses these technological advancements in navigation bronchoscopy in three basic steps: navigation, position confirmation and acquisition, with a specific focus on cone-beam computed tomography (CBCT). For navigation purposes ultrathin bronchoscopy combined with virtual bronchoscopy navigation, electromagnetic navigation and robotic assisted bronchoscopy all achieve good results as a navigation guidance tool, but cannot confirm location or guide biopsy positioning. Diagnostic yield has seen improvement by combining these techniques with a secondary imaging tool like radial endobronchial ultrasound (rEBUS) and fluoroscopy. For confirmation of lesion access, rEBUS provides local detailed ultrasound-imaging and can be used to confirm lesion access in combination with fluoroscopy, measure nodule-contact area length and determine catheter position for sampling. CBCT is the only technology that can provide precise 3D positioning confirmation. When focusing on tissue acquisition, there is often more than 10% difference between reaching the target and getting a diagnosis. This discrepancy is multifactorial and caused by breathing movements, small samples sizes, instrument tip displacements by tool rigidity and tumour inhomogeneity. Yield can be improved by targeting fluorodeoxyglucose (FDG)-avid regions, immediate feedback of rapid onsite evaluation, choosing sampling tools with different passive stiffnesses, by increasing the number biopsies taken and (future) catheter modifications like (robotic assisted-) active steering. CBCT with augmented fluoroscopy (CBCT-AF) based navigation bronchoscopy combines navigation guidance with 3D-image confirmation of instrument-in-lesion positioning in one device. CBCT-AF allows for overlaying the lesion and navigation pathway and the possibility to outline trans-parenchymal pathways. It can help guide and verify sampling in 3D in near real-time. Disadvantages are the learning curve, the inherent use of radiation and limited availability/access to hybrid theatres. A mobile C-arm can provide 3D imaging, but lower image quality due to lower power and lower contrast-to-noise ratio is a limiting factor. In conclusion, a multi-modality approach in experienced hands seems the best option for achieving a diagnostic accuracy >85%. Either adequate case selection or detailed 3D imaging are essential to obtain high accuracy. For current and future transbronchial treatments, high-resolution (CBCT) 3D-imaging is essential.

Keywords: Pulmonary nodules; cone-beam computed tomography (CBCT); early stage; lung cancer; navigation bronchoscopy.

Figure 1

Example of rEBUS miniprobe imaging of a peripheral pulmonary nodule with a central position of the probe, and a vessel structure which was found to be pulsating on live imaging in the left upper quadrant. rEBUS, radial endobronchial ultrasound.

Figure 2

CBCT images with augmented fluoroscopy. The left panel shows a coronal reconstruction of a CBCT image with a segmented nodule in the left upper lobe, a (purple) marker is placed to correlate the catheter position during breath-hold for the CT acquisition with real-time augmented fluoroscopy. The right-hand panel shows augmented fluoroscopy image of the nodule in the left upper lobe. The slight real-time displacement of the catheter compared to the marker in breath-hold position can be seen in this overlay. This is explained by breathing (CBCT acquired in breath-hold and AF performed under continuous breathing) and the stress imposed on lung tissue by the catheter and sampling tools. CBCT, cone-beam computed tomography; AF, augmented fluoroscopy.

Figure 3

CBCT based navigation bronchoscopy (see Appendix 1 for details). These images are published with the patient's/participant’s consent. CBCT, cone-beam computed tomography.