A Constant-Volume Ventilator and Gas Recapture System for Hyperpolarized Gas MRI of Mouse and Rat Lungs.

We present a ventilator that enables high-resolution proton and hyperpolarized gas MR imaging of mice and rats. The design differs from previous approaches by eliminating the need for a custom pneumatic valve located near the trachea. This permits the system to be constructed from off-the-shelf components and reduces dead volumes sufficiently to make HP gas MRI feasible in the mouse. The constant-volume ventilator routinely ventilates mice and rats for period of time up to 6 hrs and maintains reproducible tidal volumes over extended image acquisition periods, as we demonstrate with high-resolution 3D lung images in the mouse using H-1, He-3 and Xe-129. The ventilator is designed to deliver a constant tidal volume regardless of changes in airway resistance, which we demonstrate with 3 He MR images acquired during severe broncho-constriction. While the images reveal clear airway narrowing, the He-3 signal intensity remained within +/- 10% of baseline level. Finally, given the paucity of He-3 and the high cost of enriched Xe-129, the ventilator has been designed to enable the recapture of these rare gases and we demonstrate a compact system to compress and store them for subsequent reprocessing. We expect that this constant-volume ventilator will be readily reproducible by other laboratories, which we facilitate by providing extensive parts lists, detailed wiring diagrams and complete plumbing schematics. (C) 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 39B: 78-88, 2011