Hyperpolarized 83Kr MRI of lungs

Hyperpolarized (hp) ⁸³Kr (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 ⁸³Kr magnetic resonance imaging (MRI) of lungs using natural abundance krypton gas (11.5% ⁸³Kr) and excised, but otherwise intact, rat lungs located within a custom designed ventilation chamber. Experiments comparing the ⁸³Kr 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 ⁸³Kr 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 ⁸³Kr T₁ differences may ultimately lead to a novel form of MRI contrast in lungs. The currently obtained 1200-fold signal enhancement for hp ⁸³Kr at 9.4 T field strength is found to be 180 times below the theoretical upper limit.