Introduction: Proton (¹H ) magnetic resonance imaging (MRI) can be utilized to quantify pulmonary edema in endotoxin-induced pulmonary inflammation and hyperpolarized (HP) ³He MRI can assess pulmonary ventilation. Neither of the methods has been applied to assess the impact of a drug on endotoxin-induced pulmonary inflammation in vivo. The aim of the current study was to evaluate the capability of ¹H and HP ³He MRI to assess the effects of a glucocorticoid on endotoxin-induced pulmonary inflammation in vivo.
Materials and methods: Mice were exposed to an aerosol of either saline or endotoxin (5 mg/ml) for 10 min. Half of the endotoxin-exposed mice were pretreated with a glucocorticoid (budesonide 3 mg/kg; 2 times/day) and the other half with vehicle p.o. The first budesonide treatment was administered 1 h prior to the aerosol inhalation. Forty-eight hours after the aerosol exposure, the mice were anaesthetized for subsequent imaging. Hyperpolarized ³He was administered and axial MR images of the lungs obtained. Matching ¹H MR images were then acquired. The mice were sacrificed and broncho-alveolar lavage (BAL) samples were harvested to determine total and cell differential counts.
Results: The lesion volume on both ¹H and ³He MRI, were markedly increased by endotoxin exposure (P<0.001). Budesonide strongly reduced lesion volume (P<0.001). The BAL cell count correlated strongly with both (3)He (P<0.001; r = 0.96) and ¹H lesion volumes (P<0.001; r = 0.97).
Conclusions: Hyperpolarized ³He MRI and ¹H MRI clearly visualized the preventative effect of budesonide on the impact of endotoxin on pulmonary ventilation and edema, respectively. The fact that ventilation defects on ³He MRI corresponded to findings from conventional ¹H MRI, as well as to counts of BAL inflammatory cells suggests that these imaging techniques constitute promising tools for non-invasive monitoring of pulmonary inflammation in vivo.