3D Hyperpolarized 129Xe MRI of Mouse Lung at Low Xenon Concentration using a Continuous Flow-type Hyperpolarizing System: Feasibility for Quantitative Measurement of Regional Ventilation

Abstract

We investigated the feasibility of 3D hyperpolarized (HP) (129)Xe magnetic resonance (MR) imaging at an extremely low concentration of HP (129)Xe supplied from a continuous flow-type hyperpolarizing (CF-HP) system and established a standard procedure for measuring regional lung ventilation of small animals, such as the mouse, as a baseline for further studies. We performed 3D HP (129)Xe MR imaging of the lungs of 2 healthy and 2 emphysematous mice that were spontaneously breathing diluted HP (129)Xe (<1%). From the three 3D MR images acquired by varying the flip angle of the radiofrequency (RF) pulse, we calculated the time constant of regional recovery, tau'(rep), which represents the time required for HP (129)Xe magnetization to be replenished approximately 63% after destruction of hyperpolarization by RF saturation pulse. After calculating the tau'(rep) maps, we examined the validity of our method. We used diluted xenon from the CF-HP system to acquire 3D HP (129)Xe MR images of the mouse lung that were undiminished under spontaneous respiration. The averaged tau'(rep) values were longer for the emphysematous lungs than for the healthy lungs, which reflected ventilation defects in the emphysematous lung. This procedure permitted us to estimate the regional lung ventilation for any arbitrarily set slice, and it will provide a standard for measuring regional lung ventilation as a baseline for further studies.