Generating Noble-Gas Diffusion Maps at Very Short Time Scales

observed, and D ∆ is the (time-dependent) diffusion coefficient measured at this diffusion time. Short-time-scale measurements of hyperpolarized He diffusion in the human lung typically use diffusion times between 1 and 2 ms. At this time scale, the He diffusion coefficient in normal lung airspaces is approximately 0.2 cm/s. Thus these measurements probe a length scale of approximately 350-500 microns, which is substantially larger than a normal alveolus. In order to probe sub-alveolar length scales, diffusion times less than a millisecond must be used. However, it is difficult to make accurate diffusion measurements at sub-millisecond time scales using conventional pulse-sequence techniques.