Pulmonary ventilation imaged by magnetic resonance: at the doorstep of clinical application

Over the past few years, magnetic resonance imaging (MRI) has emerged as an important instrument for functional ventilation imaging. The aim of this r eview is to summarize established clinical methods and emerging techniques for research and clinical arenas. Before the advent of MRI, chest radiography and computed tomography (CT) do minated morphological lung imaging, while functional ventilation imaging wa s accomplished with scintigraphy. Initially, MRI was not used for morpholog ical lung imaging often, due to technical and physical limitations. However , recent developments have considerably improved anatomical MRI, as well as advanced new techniques in functional ventilation imaging, such as inhaled contrast aerosols, oxygen, hyperpolarized noble gases (Helium-3, Xenon-129 ), and fluorinated cases (sulphur-hexafluoride). Straightforward images dem onstrating homogeneity of ventilation and determining ventilated lung volum es can be obtained. Furthermore, new image-derived functional parameters ar e measurable, such as airspace size, regional oxygen partial pressure, and analysis of ventilation distribution and ventilation/perfusion ratios. There are several advantages to using MRI: lack of radiation, high spatial and temporal resolution and a broad range of functional information. The MR I technique applied in patients with chronic obstructive pulmonary disease, emphysema, cystic fibrosis, asthma, and bronchiolitis obliterans, may yiel d a higher sensitivity in the detection of ventilation defects than ventila tion scintigraphy, CT or standard pulmonary function tests. The next step will be to define the threshold between physiological variati on and pathological defects. Using complementary strategies, radiologists w ill have the tools to characterize the impairment of lung function and to i mprove specificity.