Abstract 591: Sensitive and Quantitative Assessment of Pulmonary Inflammation by 19F MRI in vivo
Introduction: Emulsified perfluorocarbons (PFCs) are preferentially phagocytized by monocytes/macrophages and are readily detected by 19F MRI. This study tests the hypothesis that PFCs can be used to quantitate pulmonary inflammation by 19F MRI by tracking of infiltrating PFC-loaded monocytes.
Methods: Pneumonia was induced in mice by intratracheal instillation of LPS followed by iv injection of PFCs (10% 15C5). Respiratory-gated 1H and 19F MR images were obtained at 9.4 T 24 & 48 hrs after LPS.
Results: Anatomically matching example images are shown in the top row of the Figure⇓. 1H MRI provided no evidence of lung injury 24 hrs post-LPS (0.15 μg/g BW), while the concurrent 19F image - after merging with the 1H image - clearly shows PFC accumulation in both pulmonary lobes (n=6). Imaging at 48 hrs post-LPS revealed signal in 1H images at the same location as the 24 hr 19F signals. Thus, progressive pneumonia was first predicted by 19F MRI early after PFC administration. Without LPS, at no time were 19F signals observed within the lung (bottom row, n=6). Histology and FACS confirmed the presence of infiltrating PFC-loaded monocytes/macrophages at 24 hrs post-LPS. Additional experiments with graded doses of LPS (0 –1.5 μg/g BW, n=6 each) demonstrated that 19F signal intensity was strongly correlated with both LPS dose and the induced tissue damage determined from lung dry/wet weight ratios. In separate studies, PFCs and 19F MRI were also used to assess dexamethasone therapy after LPS-induced pneumonia.
Conclusion: PFCs can be used for quantitative molecular imaging of macrophage infiltration with 19F MRI in vivo, which detects pulmonary inflammation with greater sensitivity than 1H MRI.