Spatially resolved assessment of serotonin-induced bronchoconstrictive responses in the rat lung using 3He ventilation MRI under spontaneous breathing conditions

The effect on lung ventilation of bronchoconstriction induced by serotonin (intravenous injection of 50 microg/kg of serotonin) was imaged using a hyperpolarized (3)He MR ventilation protocol in spontaneously breathing rats. Lung function maps assessing airflow obstruction, a key feature in clinical pneumology, were derived from dynamic image series acquired after inhalation of (3)He gas. Dynamic ventilation (3)He MR images spanning a respiratory cycle were obtained using a retrospective cine image reconstruction procedure. Two parameters, defined as signal amplitude and maximum signal decay rate, were derived from the time course of the MR signal for each pixel. These parameters were averaged over regions of interest placed in the lower part of the right and left lungs and submitted to statistical analysis. A homogeneous and significant decrease of signal amplitude and maximum signal decay rate after serotonin injection was observed for each rat on the parametric color maps. The data indicate that dynamic ventilation HP (3)He MRI can be used to assess, in a spatially resolved manner, the ventilation function of spontaneously breathing rats and the effects of agents eliciting short-lasting bronchoconstriction.