Hyperpolarized 129 Xenon MRI of the Lung

Pulmonary imaging is the least evolved branch of proton MRI, primarily due to the low volume fraction of tissue in the lung; only ~20% of the volume contains tissue or blood while the remainder is filled with air. By comparison, most of the volume in other organs is hydrogen. Another source of the inherently weak MR signal in the lungs is the extremely large area of the tissue-gas interface. The 3 ppm difference in magnetic susceptibility between tissue and air causes an alteration of the local magnetic field resulting in very short signal coherence times. Despite having limited SNR, several promising techniques have been developed (Edelman et al. 1996; Mai et al. 2001; Hatabu et al. 2001; Jakob et al. 2004; Detre et al. 1994; Hopkins and Prisk 2010; Deimling et al. 2008; Bauman et al. 2009). These techniques work better at low magnetic fields (such as 1.5 T) because of the air/tissue susceptibility issue. This may be problematic for the future as the overall drive for clinical imaging is in the direction of higher field strengths. In preclinical small animal imaging, Kuethe et al. (2007) used 1.89 T field strength system to produce lung images approaching the quality of CT.