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What is the minimal clinically important difference for helium-3 magnetic resonance imaging ventilation defects?

Pulmonary magnetic resonance imaging (MRI) using inhaled polarised gases provides a way to directly visualise and sensitively measure lung ventilation abnormalities or ventilation defects [1]; the burden in individual patients may be directly quantified as the percent ventilation volume [2], ventilation defect volume (VDV) [3] or ventilation defect percent (VDP) [4], which is VDV normalised to the total lung volume. In patients with asthma, MRI ventilation defects worsen during methacholine [5] and exercise challenge [5, 6], and respond to bronchodilation [5, 6]. However, it is still unknown if quantitative changes in MRI ventilation abnormalities directly reflect changes in patient-related outcomes like symptoms; this is important when considering MRI for clinical and research studies in asthma patients, which require an understanding of the minimal clinically important difference (MCID). In asthmatics, the estimated MCID for 3He MRI ventilation defect volume is 110 mL and that for ventilation defect percentage is 2%, which are similar to FEV1, suggesting that these biomarkers are suitable for use in clinical trials http://ow.ly/yQ8K30jAFnX