A Window on the Lung: Molecular Imaging as a Tool to Dissect Pathophysiologic Mechanisms of Acute Lung Disease

Figure 3

[¹³N]nitrogen (¹³N₂) positron emission tomography images from a sheep with lavage-induced lung injury. A bolus of ¹³N₂ in saline solution was infused intravenously over 3 seconds at the beginning of a 60-second apnea. The distribution of ¹³N₂ during early apnea (between 5 and 10 seconds) reflects regional perfusion (peak apnea image). The distribution of ¹³N₂ at the end of apnea (between 40 and 60 seconds) is proportional to perfusion only to aerated alveolar units, which retain ¹³N₂ during apnea (end-apnea image). The decrease in tracer activity between peak and end-apnea images in the dorsal, dependent lung (arrowheads) reflects the presence of shunt in this part of the lung because alveoli that are perfused but not aerated do not retain ¹³N₂ during apnea. Modified from Musch et al (Reference [12]).