In vivo NMR of hyperpolarized 3He in the human lung at very low magnetic fields.

We present NMR measurements of the diffusion of hyperpolarized 3He in the human lung performed at fields much lower than those of conventional MRI scanners. The measurements were made on standing subjects using homebuilt apparatus operating at 3mT. O(2)-limited transverse relaxation (T(2) up to 15-35s) could be measured in vivo. Accurate global diffusion measurements have been performed in vivo and in a plastic bag; the average apparent diffusion coefficient (ADC) in vivo was 14.2+/-0.6mm(2)/s, whereas the diffusion coefficient in the bag (3He diluted in N(2)) was 79.5+/-1mm(2)/s. 1D ADC mapping with high SNR ( approximately 200-300) demonstrates the real possibility of performing quality lung imaging at extremely low fields.