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 (<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, τ′_rep, which represents the time required for HP ¹²⁹Xe magnetization to be replenished approximately 63% 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.