Analysis of hyperpolarized 129Xe dynamics in mouse lungs under spontaneous respiration for separate determination of lung functional parameters and relaxation time.

Magnetic resonance spectroscopy (MRS) was used to investigate the dynamics of hyperpolarized (HP) 129Xe respiration in the chests of mice under spontaneous respiration. The washout curve was analyzed using Kety's exchange model of inert gases, and the 3 factors that affect the slope of the washout curve, i.e., the RF flip angle, respiratory parameters, and apparent relaxation time (which comprises terms including the relaxation time in alveoli, T1air, and perfusion), were determined separately. Flip angle was determined precisely using the dual flip angle method, and ventilation volume was determined using SF6 gas at thermal equilibrium. Furthermore, an attempt was made to separate out the terms of T1air and perfusion from the apparent relaxation time after exploiting the ventilation model of lungs in steady state. Values of relaxation time T1air=30.5 s and perfusion term lambdaQ/VA=0.016 s-1 were obtained, supporting the applicability of the ventilation model proposed.