Expiratory lung MRI: a simple, sensitive method to quantify and visualise regional gas trapping in cystic fibrosis

Computed tomography is the gold standard for visually assessing gas trapping, a hallmark of early lung disease in people with cystic fibrosis (pwCF), but its use is limited in children. Lung proton magnetic resonance imaging (¹H-MRI) offers a simple, non-ionising alternative. This work aimed to use breath-hold ¹H-MRI to visualise and quantify gas trapping in pwCF.

24 normal controls (9 adults, 15 children) and 27 pwCF underwent breath-hold ¹H-MRI at residual volume (RV) and total lung capacity (TLC). For each participant, a threshold was defined from the TLC image and applied to the RV image to quantify low-signal areas, presumed to be gas trapping, as a gas trapping volume (GTV). An upper limit of normal (ULN) was defined based on the normal distribution of GTV, and GTV was compared to spirometry, body plethysmography, multiple breath washout and ¹²⁹Xe Ventilation MRI.

Gas trapping was visualised in pwCF as regions of low signal intensity on RV images. Healthy volunteers had a median GTV of 2.93% (0.32-14.37%). PwCF had a GTV of 21.80% (2.04-82.68%) and FEV₁ z-scores of -1.14 (-5.43, 2.17), with 14 having normal FEV₁. The ULN of GTV was 7.01%; 9/14 pwCF with normal spirometry exceeded this. In pwCF, GTV is strongly correlated with FEV₁ z-scores, ¹²⁹Xe-MRI ventilation defect percentage, and gas trapping measured by body plethysmography (RV/TLC%).

Using a standard, easily implementable breath-hold ¹H-MRI protocol, gas trapping in CF can be clearly visualised and quantified. Preliminary evidence shows lung function impairment in pwCF who have normal FEV₁.