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

Purpose: We investigated the feasibility of 3D hyperpolarized (HP) 129Xe magnetic resonance (MR) imaging at an extremely low concentration of HP 129Xe 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. Materials and Methods: We performed 3D HP 129Xe MR imaging of the lungs of 2 healthy and 2 emphysematous mice that were spontaneously breathing diluted HP 129Xe (<1z). 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, τ'rep which represents the time required for HP 129Xe magnetization to be replenished approximately 63z after destruction of hyperpolarization by RF saturation pulse. After calculating the τ'rep maps, we examined the validity of our method. Results:We used diluted xenon from the CF-HP system to acquire 3D HP 129Xe MR images of the mouse lung that were undiminished under spontaneous respiration. The averaged τ'rep values were longer for the emphysematous lungs than for the healthy lungs, which reflected ventilation defects in the emphysematous lung. Conclusions: 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.