Quantitative measurements of regional lung ventilation using helium-3 MRI in a methacholine-induced bronchoconstriction model.
PURPOSE: To demonstrate ventilation changes in an animal model of methacholine-induced bronchoconstriction using hyperpolarized (HP) helium-3 (He-3) MRI. MATERIALS AND METHODS: Bronchoconstriction was induced in 11 healthy rats using an intravenous injection of methacholine. The He-3 was laser-polarized using a custom-built system. MRI studies were performed on a 2-Tesla bore magnet. Coronal dynamic ventilation images were obtained using a single inhalation of the laser-polarized He-3 gas before and after methacholine injection. Ventilation image series were processed on a pixel-by-pixel basis to generate three regional ventilation parameters: gas flow rate, filling time, and maximum gas volume. Student's paired t-test was used for analysis. RESULTS: Ventilation image series with a temporal resolution of 5 msec were obtained before and after methacholine challenge. Quantitative regional gas dynamic information demonstrated statistically significant differences between the baseline and constricted states. Following methacholine injection, the mean flow values were significantly lower for the right lung (RL) (P = 0.006) and left lung (LL) (P = 0.024), while the mean filling time was found to be greater (RL: P = 0.08, LL: P = 0.021). Gas volume values at maximum inspiration were found to be significantly lower after methacholine (RL: P = 0.002; LL: P = 0.036). CONCLUSION: He-3 MRI demonstrated and quantified regional ventilation changes in bronchoconstriction conditions in rats.