A Constant-Volume Ventilator and Gas Recapture System for Hyperpolarized Gas MRI of Mouse and Rat Lungs
J Nouls, M Fanarjian, L Hedlund
Concepts in Magnetic Resonance Part B: Magnetic Resonance Engineering, 39B(2): 78-88, 2011 PMCID: PMC3103138
We present a ventilator that enables high-resolution proton and hyperpolarized gas magnetic resonance 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 1H, 3He and 129Xe. The ventilator is designed to deliver a constant tidal volume regardless of changing airway resistance, which we demonstrate with 3He MR images acquired during severe broncho-constriction. While the images reveal clear airway narrowing, the 3He signal intensity remained within ±10% baseline. Finally, given the paucity of 3He and and high cost of enriched 129Xe, the ventilator has been designed to enable recapture of these rare gases and we demonstrate a compact system to compress and store them for subsequent for 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.
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Ventilator Schematics - Illustrate the plumbing of the ventilator and the electrical connections of the valves.
Power Distribution Schematics - A supplementary schematic describes the wiring of the electronics powering the valves.
Parts List - Lists the ventilator parts, manufacturers, suppliers and websites useful to place an order.
Labview VI - Code used at our lab to set the breathing cycle, as well as the MR triggers. It is a little bit of a legacy piece of code that has been changed by many students, is imperfect, but works well enough. It is configured for a data input/output board PCI-6602 (National Instruments, Austin, TX).
Known Issues - Issues with Labview Code
Supplemental high-resolution pictures - These pictures illustrate the animal set-up, the electronics distributing power to the valves, the computer interfaces and the location of the ventilator next to the magnet.
All work was performed at the Duke Center for In Vivo Microscopy, an NIH/NCRR national Biomedical Technology Research Center (P41 RR005959), with additional support from NCI (R01_CA_14282). We thank Sally Zimney for editorial work.