Bronchoscopy is the preferred diagnostic technique to evaluate lung nodules that are suspicious for lung cancer. Conventional bronchoscopy has a low complication rate but is limited to central lesions and has a low diagnostic yield (15%-31%). CT-guided transthoracic needle biopsy (TTNB) has a high diagnostic yield (67-97%) but is limited to peripheral lesions and has a high complication rate.
Recent advances in (1) bronchoscopy navigation techniques and (2) intra-operative imaging have enabled physicians to safely navigate within the lung and sample lung lesions with increasing accuracy. These techniques guide the bronchoscopist by creating a virtual pathway to a target lesion, but limitations in the accuracy remain.
Navigational techniques enable the creation of a three-dimensional (3D) virtual map of the airways from a pre-procedural ‘planning’ CT scan. Planning CTs are typically acquired at full inspiration breath hold to acquire a robust accurate three-dimensional mapping of the bronchial tree. A major limitation to all current guided bronchoscopy systems is the reliance on this static pre-procedural ‘planning’ CT scan. Changes in lung anatomy between the planning CT and time of procedure can lead to a discrepancy between the expected and actual location of the lesion. This is known as “CT-to-body divergence” (CTBD). CTBD increases risk and decreases the diagnostic yield and has been reported in up to 30% of navigation bronchoscopy cases.
Given the need for accurate imaging and guidance to enhance the diagnostic yield further, intra-procedural cone-beam CT (CBCT) has emerged as a method to provide intra-procedural 3D imaging that can improve all phases of bronchoscopy; navigation, targeting and tissue acquisition. Intra-operative CBCT has similar spatial resolution as diagnostic Multi-Slice CT (MSCT) but suffers from reduced contrast resolution and non-calibrated gray scale values, limiting the use of a standardized ‘lung window’ as is used with MSCT and introducing inaccuracies in image registration results when used for navigation. Additionally, CBCT is inherently more susceptible to several types of image artifacts relative to MSCT, primarily resulting from increased scatter radiation with flat panel detectors, a significant issue in the presence of bronchoscopy and biopsy surgical tools which cause streak artifacts in CBCT images. Due to the long acquisition time (>60s), CBCT is particularly susceptible to image blurring due to motion artifacts from both breathing and cardiac motion. Improved algorithms to model and compensate for motion are required to enhance the diagnostic yield of intra-operative image guided peripheral bronchoscopy.