S. J. Kadlecek, K. Emami, M. C. Fischer, M. Ishii, J. Yu, J. M. Woodburn, M. NikKhah, V. Vahdat, D. A. Lipson, J. E. Baumgardner and R. R. Rizi

Traditional magnetic resonance imaging (MRI) uses the NMR signal from protons to obtain images in the human body. The technique enables detailed imaging of brain and soft tissue, but lung MRI is inferior to that of most other tissues because of respiratory movement, the low density of protons in lung tissue, and large air–tissue interface susceptibility gradients. Helium-3 (³He) is a non-radioactive, stable isotope of helium that is used as an exogenous MRI airway contrast agent to overcome these difficulties. When specially prepared through a process known as ‘hyperpolarization’, inhaled ³He gas provides a strong MR signal and enables the acquisition of exquisite images of gas distribution and flow. The technique of ³He MR imaging has advanced considerably during the past several years and is now used regularly in a research setting to obtain high resolution images of lungs, sinuses, and other cavities. While the structural information obtained through these studies is undoubtedly of significant value, the ultimate quantitative assessment of lung function demands functional and metabolic information as well.

The goal of this review is to survey techniques capable of producing the desired physiological information from a series of polarized gas MR images. To this end, Section 2 introduces salient requirements of an ideal radiological method for quantitative assessment of lung function. In this section, we will clarify the benefits of polarized gas MRI through a comparison with other existing modalities. Section 3 summarizes optical pumping methods for the generation of hyperpolarization and the technical aspects of gas delivery and storage. Section 4 details how ³He MRI can be used to obtain both structural and functional information in normal and pathological lungs. Here, we explain methods for obtaining clinically useful regional maps of lung ventilation, perfusion, ventilation to perfusion ratio, lung compliance, alveolar oxygen tension and uptake rate, and the apparent diffusion coefficient. Each of these subsections is concluded with a discussion of the respective technique from a clinical perspective. Section 5 contains a summary and final remarks.

Progress in Nuclear Magnetic Resonance Spectroscopy 47(3-4):187-212, 2005