Probing Lung Microstructure with Gradient Echo Plural Contrast Imaging

Introduction The in vivo lung morphometry technique, relying on measuring Brownian motion of inhaled hyperpolarized gas in lung airspaces, makes it possible to obtain in vivo information on lung microstructure at the alveolar level [1-3]. This communication presents a theoretical background and experimental method for a new approach to study lung microstructure, that is based on T2*-relaxation properties of hyperpolarized gas in lung airspaces. T2* relaxation depends on tissue-specific mesoscopic magnetic field inhomogeneities induced by the susceptibility differences between lung tissue (alveolar septa, blood vessels) and lung airspaces. Based on Monte-Carlo computer simulations of diffusion of He atoms in the acinar airway tree, we derive analytical expressions relating the time-dependent MR signal to the geometrical parameters of acinar airways and blood vessel network and test our theory on healthy volunteers using in vivo data obtained with a multi-gradient echo sequence. Theory The MR signal time dependence can be presented in the form 0 ( ) exp( ( )) ( ) S t S t F t = ⋅ −Γ ⋅ , where ( ) F t describes the effects of signal decay