Review: FDG PET assesses lung inflammation during acute lung injury
FDG PET may be a valuable noninvasive method for gaining comprehensive understanding of the mechanisms of acute lung injury (ALI) and acute respiratory distress syndrome, as well as for the evaluation of therapeutic interventions, according to a review published in this month's American Journal of Roentgenology.

Lung inflammation is a key feature of ALI. Pulmonary FDG kinetics are altered during experimental and human ALI and are associated with regional lung dysfunction, histologic abnormalities, and prognosis, according to Marcos Francisco Vidal Melo, PhD, MD, associate professor of anesthesia at Massachusetts General Hospital in Boston, and colleagues.

Neutrophils, monocytes, macrophages, lymphocytes and lung parenchymal cells are involved in the uptake of FDG during ALI and acute respiratory distress syndrome in animal models, according to the review.

The simplest methods of quantifying pulmonary FDG are based on static indices such as the standardized uptake value, noted the authors. However, specific models for studying pulmonary FDG kinetics, particularly in conditions of ALI, are required because compared with solid organs, the lung has greater air content, lower basal glucose consumption, a larger perfusion to tissue ratio and a larger parenchymal edema and flooding to tissue ratio during organ injury, wrote Melo and colleagues.

FDG PET also facilitates early visualization of lung infection, subacute and chronic lung inflammatory diseases, ALI and endotoxemia in various experimental and clinical situations, noted the authors. Among the animal models, a rabbit model has been used to study Streptococcus pneumoniae pneumonia, pulmonary fibrosis and a sheep model for studying smoke inhalation, ventilator-induced lung injury and endotoxemia.

In the acutely inflamed lung, FDG PET facilitates noninvasive assessment of regional lung neutrophil infiltration, and activation and this has led to considerable improvement in the experimental and clinical pathophysiologic investigation of ALI and acute respiratory distress syndrome, the researchers wrote.

The results of animal studies suggest that the use of lung-specific compartmental models may improve quantification of the FDG signal in ALI and acute respiratory distress syndrome. Further research is needed to explore the biologic correlates of FDG uptake, and better understanding of such mechanisms is required before FDG PET can be used as a decision-making tool in the treatment of patients with ALI and acute respiratory distress syndrome, concluded Melo and colleagues.