Correction Constant is necessary for the use of OCT in Airways – The OCT Air study

The current methods used for diagnosing and assessing airway abnormalities, including a Computed Tomography (CT)-scan and Diagnostic Dynamic Bronchoscopies, have several limitations, which create a demand for an alternative measuring method that is objectively quantifiable and able to obtain dynamic cross-sectional images of the airway. The catheter-based method Optical Coherence Tomography (OCT) obtains dynamic cross-sectional images by using light close to the infrared range. The method is already implemented within the medical fields of cardiology and ophthalmology, where application of the method has shown to improve procedural outcome. The method has been pilot tested in the airway, where the implementation shows promising results. However, to interpretate OCT data correctly, it is necessary to calculate a correction constant that should be applied, when obtaining data in the airway. The aim with this study is to calculate a correction constant for the use of OCT in airways based on an in vitro model and a porcine model. It was done by performing OCT scans on 3D-printed phantoms based on CT-scans of porcine airways. In total three phantoms and corresponding 12 airway segments were included. The phantoms were OCT scanned both in air and iodine contrast. Corresponding segments were compared and matched on frame level using anatomical landmarks. On average, the estimated median ratio of <bold>lumen areas</bold> measured by OCT in contrast is 1.69 (IQR: 1.66 - 1.72) times larger compared to those measured in air. For <bold>lumen diameters</bold> the median ratio is 1.3 (IQR: 1.29 - 1.31) (contrast/air). The application of this correction constant is crucial for the precise interpretation of data derived from OCT in airways.