An Evaluation of Pulmonary Atelectasis and its Re-expansion: Hyperpolarized ³He MRI in the Yorkshire Pig

Rationale and Objectives. Atelectasis, the collapse of small airways, is a significant clinical problem. We use hyperpolarized (HP) ³He magnetic resonance imaging (MRI), or HP ³He MRI, to describe atelectasis in the normal Yorkshire pig, the pig with atelectasis, and the pig with re-expansion of atelectasis. We compare HP ³He MRI findings with depictions of atelectasis by proton MRI. Materials and Methods. During end-expiration in the anesthetized and paralyzed Yorkshire pig (n = 6), HP ³He gas produced by the optical pumping spin-exchange method, was delivered via an endotracheal tube. For two separate groups, atelectasis was either induced by Fogarty-catheter occlusion balloon inflation (n = 3), or lateral chest wall administration of sodium hydroxide (NaOH) (n = 3). MRI was performed at time zero, at 5, 9, 13, 15, and 19 minutes after atelectasis production, 30 minutes after balloon deflation, and 10 and 30 minutes after recruitment of atelectatic areas with increased tidal volumes and added positive end-expiratory pressure. High-resolution, cross-sectional MR images were procured, and comparison was made with the traditional proton MRI. Results. Atelectatic areas by HP ³He MRI were easily distinguishable in both subject groups, and correlated with those located by proton MR. HP ³He MR images showed absence of ventilation, whereas proton MR images depicted dense, white areas. Re-expansion of atelectasis was well delineated by HP ³He MRI. Conclusion. HP ³He MRI may overcome many of the shortcomings of other well-established radiographic methods. HP ³He MRI is a novel, informative method for describing atelectasis and its re-expansion.