Quantitative measurement of regional lung ventilation using ³He MRI

A new strategy for a quantitative measurement of regional pulmonary ventilation using hyperpolarized helium-3 (3He) MRI has been developed. The method employs the build-up of the signal intensity after a variable number of (3)He breaths. A mathematical model of the signal dynamics is presented, from which the local ventilation, defined as the fraction of gas exchanged per breath within a given volume, is calculated. The model was used to create ventilation maps of coronal slices of guinea pig lungs. Ventilation values very close to 1 were found in the trachea and the major airways. In the lung parenchyma, regions adjacent to the hilum showed values of 0.6-0.8, whereas 0.2-0.4 was measured in peripheral regions. Monte Carlo simulations were used to investigate the accuracy of the method and its limitations. The simulations revealed that, at presently attainable signal-to-noise ratios, the ventilation parameter can be determined with a relative uncertainty of <5% over a wide range of values.