Safety and feasibility of near‐infrared fluorescence imaging with inhaled indocyanine green to assess the pulmonary parenchyma in six normal dogs

OBJECTIVE: To assess the safety and feasibility of near-infrared fluorescence (NIRF) imaging with inhaled indocyanine green (ICG) to visualize normal pulmonary parenchyma in dogs, report clinically useful information regarding dosage and timing of administration, and to evaluate effects on pulmonary function and tissue histology. STUDY DESIGN: Preclinical exploratory study. ANIMALS: Six purpose-bred dogs. METHODS: Dogs undergoing thoracoscopy were randomly assigned to receive inhaled ICG at 0.1, 0.5, or 1.0 mg/kg. Subjective fluorescence was recorded, images were saved to analyze quantitative fluorescence, and a lung biopsy was obtained. Clinical assessment of respiratory function was performed for 14 days. Peripheral lung biopsies were repeated 6 months later. RESULTS: Inhalation of ICG resulted in real-time NIRF of pulmonary parenchyma in all dogs. Administration time ranged from 1 to 10 min and mean time to first fluorescence was 1.5 min. Peak subjective fluorescence was strong in dogs receiving 0.5 and 1.0 mg/kg, and moderate in dogs receiving 0.1 mg/kg. Peak quantitative fluorescence was positively correlated with dose, with a three-fold and 10-fold increase above baseline 20 min after administration of 0.5 and 1.0 mg/kg doses, respectively. No histologic abnormalities or clinical evidence of respiratory compromise following inhalation of ICG were observed. CONCLUSION: Inhaled ICG provided rapid intraoperative fluorescence of normal pulmonary parenchyma, was clinically feasible, and was safe in normal dogs at 0.1-1.0 mg/kg. CLINICAL SIGNIFICANCE: Inhaled ICG produced rapid pulmonary fluorescence without detectable adverse effects, supporting further investigation of its effectiveness to identify pulmonary lesions in dogs.