Comparison of magnetic resonance imaging of inhaled SF6 with respiratory gas analysis

Magnetic resonance imaging of inhaled fluorinated inert gases (19F-MRI) such as sulfur hexafluoride (SF6) allows for analysis of ventilated air spaces. In this study, the possibility of using this technique to image lung function was assessed. For this, 19F-MRI of inhaled SF6 was compared with respiratory gas analysis, which is a global but reliable measure of alveolar gas fraction. Five anesthetized pigs underwent multiple-breath wash-in procedures with a gas mixture of 70% SF6 and 30% oxygen. Two-dimensional 19F-MRI and end-expiratory gas fraction analysis were performed after 4 to 24 inhaled breaths. Signal intensity of 19F-MRI and end-expiratory SF6 fraction were evaluated with respect to linear correlation and reproducibility. Time constants were estimated by both MRI and respiratory gas analysis data and compared for agreement. A good linear correlation between signal intensity and end-expiratory gas fraction was found (correlation coefficient 0.99±0.01). The data were reproducible (standard error of signal intensity 8% vs. that of gas fraction 5%) and the comparison of time constants yielded a sufficient agreement. According to the good linear correlation and the acceptable reproducibility, we suggest the 19F-MRI to be a valuable tool for quantification of intrapulmonary SF6 and hence lung function.