Imaging the lungs in asthmatic patients by using hyperpolarized helium-3 magnetic resonance: Assessment of response to methacholine and exercise challenge

Background: Imaging of gas distribution in the lungs of patients with asthma has been restricted because of the lack of a suitable gaseous contrast agent. Hyperpolarized helium-3 (HHe3) provides a new technique for magnetic resonance imaging of lung diseases. Objective: We sought to investigate the use of HHe3 gas to image the lungs of patients with moderate or severe asthma and to assess changes in gas distribution after methacholine and exercise challenge. Methods: Magnetic resonance imaging was performed in asthmatic patients immediately after inhalation of HHe3 gas. In addition, images were obtained before and after methacholine challenge and a standard exercise test. Results: Areas of the lung with no signal or sharply reduced HHe3 signal (ventilation defects) are common in patients with asthma, and the number of defects was inversely related to the percent predicted FEV1 (r = 0.71, P < .002). After methacholine challenge (n = 3), the number of defects increased. Similarly, imaging of the lungs after exercise (n = 6) showed increased ventilation defects in parallel with decreases in FEV1. The increase in defects after challenge in these 9 asthmatic patients was significant both for the number (P < .02) and extent (P < .02) of the defects. The variability and speed of changes in ventilation and the complete lack of signal in many areas is in keeping with a model in which the defects result from airway closure. Conclusion: HHe3 magnetic resonance provides a new technique for imaging the distribution of inhaled air in the lungs. The technique is suitable for following responses to treatment of asthma and changes after methacholine or exercise challenge.