Hyperpolarized helium-3 MRI (³He MRI) provides detailed visualization of low- (hypo- and non-) ventilated lung. Physiological measures of gas mixing may be assessed by multiple breath nitrogen washout (MBNW) and of airway closure by forced oscillation technique (FOT). We hypothesize that in patients with asthma, areas of low-ventilated lung on ³He MRI are the result of airway closure. Ten control subjects, ten asthma subjects with normal spirometry (non-obstructed), and ten asthmatic subjects with reduced baseline lung function (obstructed) attended two testing sessions. On visit one, baseline plethysmography was performed followed by spirometry, MBNW and FOT assessment pre- and post-methacholine challenge. On visit two, ³He MRI scans were conducted pre- and post-methacholine challenge. Post methacholine the volume of low ventilated lung increased from 8.3% to 13.8% in the non-obstructed group (p = 0.012) and from 13.0% to 23.1% in the obstructed group (p=0.001). In all groups, the volume of low ventilation from ³He MRI correlated with a marker of airway closure in obstructive subjects, Xrs (6Hz) and the marker of ventilation heterogeneity Scond with r² values of 0.61 and 0.56 respectively. The change in Xrs (6Hz) correlated well (r² = 0.45), while the change in Scond was largely independent of, the change in low ventilation volume (r²=0.13). The only significant predictor of low ventilation volume from the multi-variate analysis was Xrs (6Hz). This is consistent with the concept that regions of poor or absent ventilation seen on ³He MRI are primarily the result of airway closure.

中文翻译：

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气道关闭是超极化氦3 MRI肺部扫描所见的低通气的主要生理机制

超极化氦气3 MRI（³ He MRI）可对低通气（低通气和不通气）的肺进行详细的可视化显示。气体混合的生理指标可通过多次呼吸氮冲洗（MBNW）进行评估，气道闭合可通过强制振荡技术（FOT）进行评估。我们假设在哮喘患者中，³ He MRI上低通气的肺区域是气道关闭的结果。十名对照受试者，十名肺活量正常的哮喘受试者（未阻塞）和十名基线肺功能降低的哮喘受试者（阻塞）参加了两次测试。第一次访视时，先进行基线体积描记，然后进行肺活量测定，MBNW和FOT评估美沙胆碱激发前后。参观第二，^三对其进行MRI扫描，然后进行美甲胆碱激发。乙酰甲胆碱治疗后，非阻塞组低通气肺的体积从8.3％增加到13.8％（p = 0.012），阻塞组从13.0％增加到23.1％（p = 0.001）。在所有组中，来自³ He MRI的低通气量与阻塞性受试者气道闭合标志Xrs（6Hz）和通气异质性Scond标志相关，r ²值分别为0.61和0.56。Xrs（6Hz）的变化具有良好的相关性（r ² = 0.45），而Scond的变化很大程度上与低通风量的变化（r ²= 0.13）。多元分析中唯一通气量低的重要预测指标是Xrs（6Hz）。这与以下概念一致：在³ He MRI上看到的通气不良或缺乏通气的区域主要是气道关闭的结果。