Bronchial Physiological Saline Injection to Visualize Peripheral Pulmonary Lesions in Ultrathin Bronchoscopy

<b>Background:</b> During bronchial lavage, the lumen can be viewed better by injecting physiological saline into the bronchus. This study aimed to investigate the effect of injecting physiological saline into the bronchus while directly observing the bronchial lumen with peripheral pulmonary lesions using an ultrathin bronchoscope. <b>Methods:</b> We evaluated changes in the depth of field and signal-to-noise ratio due to saline immersion in bronchoscopic images captured with line patterns. We injected physiological saline through the working channel into the bronchial lumen and directly observed the lesions (mainly in cases of suspected peripheral lung cancer) in 38 patients using white-light and narrow-band imaging. Ultrathin bronchoscopic findings and histopathological diagnoses were analyzed. <b>Results:</b> Saline immersion extended the range of subject distance within the depth of the field with an improved signal-to-noise ratio. Saline immersion elevated the signal-to-noise ratio and increased the highest signal-to-noise ratio in the white-light images from 3.12 dB to 3.77 dB (1.21-fold). Under narrow-band imaging, saline immersion also increased the highest signal-to-noise ratio from 5.18 dB to 6.44 dB (1.24-fold). We were able to directly observe the bronchial lumen of the peripheral lesions in 30/38 cases (78.9%). Three (60%) of the five squamous cell carcinomas were of the epithelial type, and 12 (92%) of the 13 adenocarcinomas, including peripheral pulmonary lesions, were of the subepithelial type, similar to central lesions. <b>Conclusions:</b> Injecting saline into the peripheral bronchus is useful for direct bronchoscopic evaluation of peripheral lesions.