Hyperpolarized Kr MRI of lungs

Hyperpolarized (hp) Kr (spin I = 9/2) is a promising gas-phase contrast agent that displays sensitivity to the surface chemistry, surface-to-volume ratio, and surface temperature of the surrounding environment. This proof-of-principle study demonstrates the feasibility of ex vivo hp Kr magnetic resonance imaging (MRI) of lungs using natural abundance krypton gas (11.5% Kr) and excised, but otherwise intact, rat lungs located within a custom designed ventilation chamber. Experiments comparing the Kr MR signal intensity from lungs to that arising from a balloon with no internal structure inflated to the same volume with krypton gas mixture suggest that most of the observed signal originated from the alveoli and not merely the conducting airways. The Kr longitudinal relaxation times in the rat lungs ranged from 0.7 to 3.7 s but were reproducible for a given lung. Although the source of these variations was not explored in this work, hp Kr T1 differences may ultimately lead to a novel form of MRI contrast in lungs. The currently obtained 1200-fold signal enhancement for hp Kr at 9.4 T field strength is found to be 180 times below the theoretical upper limit. 2008 Elsevier Inc. All rights reserved.