Toward the guidance of transbronchial biopsy: identifying pulmonary nodules with optical coherence tomography

Abstract

Background: Solitary pulmonary nodules (SPNs) frequently require transbronchial needle aspiration (TBNA) or biopsy to determine malignant potential, but have variable diagnostic yields. Confirming needle placement within SPNs during TBNA could significantly increase diagnostic yield. Optical coherence tomography (OCT) provides nondestructive, high-resolution, microstructural imaging with potential to distinguish SPN from parenchyma. We have developed needle-based OCT probes compatible with TBNA. Before OCT can play any significant role in guiding clinical TBNA, OCT interpretation criteria for differentiating SPN from lung parenchyma must be developed and validated.

Methods: OCT of SPN and parenchyma was performed on 111 ex vivo resection specimens. OCT criteria for parenchyma and SPN were developed and validated in a blinded assessment. Six blinded readers (two pulmonologists, two pathologists, and two OCT experts) were trained on imaging criteria in a 15-min training session prior to interpreting the validation data set.

Results: OCT of lung parenchyma displayed evenly spaced signal-void alveolar spaces, signal-intense backreflections at tissue-air interfaces, or both. SPNs lacked both of these imaging features. Independent validation of OCT criteria by the six blinded readers demonstrated sensitivity and specificity of 95.4% and 98.2%, respectively.

Conclusions: We have developed and validated OCT criteria for lung parenchyma and SPN with sensitivity and specificity > 95% in this ex vivo study. We anticipate that OCT could be a useful complementary imaging modality to confirm needle placement during TBNA to potentially increase diagnostic yield.

Figure 1.

Training images. Ex vivo optical coherence tomography (OCT) images of uninflated lung parenchyma and solitary pulmonary nodule (SPN). A, OCT image of uninflated lung parenchyma obtained with a benchtop OCT system. The OCT imaging features of lung parenchyma are present, such as evenly spaced, signal-void alveolar spaces (regions in red boxes), some of which are larger in diameter when emphysematous change is present (region in blue box). Evenly spaced, signal-intense backreflections can be seen both in inflated and uninflated alveoli (green arrows). B, OCT image of a lung nodule obtained with a benchtop OCT system. OCT interpretation criteria for SPNs include the lack of both evenly spaced, signal-void alveolar spaces and signal-intense backreflections. Scale bars: 2 mm.

Figure 2.

Ex vivo, transpleural, needle-based OCT image of inflated lung parenchyma and SPN. A, OCT longitudinal image of lung parenchyma away from pulmonary nodule, longitudinal section. B, Corresponding histology of lung parenchyma (hematoxylin and eosin). C, OCT longitudinal image of transition between SPN (adenocarcinoma, left of left line) and hemorrhagic parenchyma (right of right line). D, Corresponding histology demonstrating the transition between SPN (adenocarcinoma, left of left line) and hemorrhagic parenchyma (right of right line) (hematoxylin and eosin). Scale bars: 4 mm. E, Cross-sectional OCT image of lung parenchyma. F, Cross-sectional OCT image of pulmonary nodule (tick marks: 500 μm). See Figure 1 legend for expansion of abbreviations.