Investigation of hyperpolarized 3He magnetic resonance imaging utility in examining human airway diameter behavior in asthma through comparison with high-resolution computed tomography

Rationale and Objectives. Application of a previously developed model-based algorithm on hyperpolarized (Hp) He-3 magnetic resonance (MR) dynamic projection images of phantoms was extended to investigate the utility of Hp He-3 MR imaging (MRI) in quantifying airway caliber changes associated with asthma. Materials and Methods. Airways of seven volunteers were imaged and measured using Hp He-3 MRI and multidetector-row computed tomography (MDCT) before and after a methacholine (MCh) challenge. MDCT data were obtained at functional residual capacity and 1 L above functional residual capacity. Results. Comparison of the resultant data showed that Hp He-3 MRI did not match MDCT in measuring the ratios of airway calibers before and after the MCh challenge in 37% to 43% of the airways from the first six generations at the two lung volumes tested. However, MDCT did yield the observation that 49% to 69% of these airways displayed bronchodilation following MCh challenge. Conclusion. The current implementation of Hp He-3 MRI did not match the MCh-induced postchallenge-to-prechallenge airway caliber ratios as measured with MDCT. Elevated parenchymal tethering due to bronchoconstriction-induced hyperinflation was proposed as a possible explanation for this airway dilation.