Novel uses of ultrasound in various lung diseases

Abstract

Conventional ultrasound (CUS) has been used in the chest to visualize pleural and pericardial fluid collections, diaphragm motion, and blood flow through the heart for anatomic definition and determining pressure gradients across valves. CUS is NOT suitable for imaging lung parenchyma, because of ultrasound multiple scattering (USMS) from millions of air-filled alveoli providing air-tissue interfaces. We used USMS to characterize lung tissue. We measured scattered mean free path (SMFP), the average distance between two scattering events, related to the amount of air present in lung parenchyma, and backscatter frequency shift (BFS), a measure of ultrasound attenuation. Using a rat bleomycin pulmonary fibrosis model, we showed that SMFP was longer in 18 rat lungs with pulmonary fibrosis, compared to 6 normals, and correlated with severity of lung fibrosis assessed by ex vivo CT scan and inflation-fixed histology. SMFP was significantly longer in 6 rat lungs made edematous by ischemia-reperfusion injury with significantly lower BFS. These data support using USMS to characterize severity of pulmonary fibrosis and pulmonary edema due to heart failure, and pneumonia and congestion in humans. In seven large animal lungs, determining the absence of USMS allows localization of pulmonary nodules for minimally invasive surgery. USMS provides many clinical opportunities.