Design and evaluation of a low field system for hyperpolarized 3-He gas imaging of neonatal lungs

3-Helium can be optically pumped with laser light to produce exceptionally high nuclear polarization, which is independent of field strength. This increased polarization can allow imaging at low and ultra low field strengths, while still obtaining high signal-to-noise ratio. Low field magnets can be built for a fraction of the cost of high field clinical scanners and feature greatly reduced susceptibility artifact and less RF power requirement than higher field systems. Further advantage can be achieved by combination of hyperpolarized gas with parallel imaging methods. A particularly promising target for 3-He imaging is the premature neonatal lung, where new ways to visualize impaired lung development would be very useful clinically. Overall safety is much improved operating at ultra low fields and there is good compatibility with standard neonatal physiological monitoring equipment. A six coil, open access resistive magnet operating at fields up to 0.015 T with unforced air cooling and sized to allow imaging of the neonatal lungs has been designed and built. A multi-channel broadband spectrometer and software system has also been designed, constructed, and interfaced to the magnet. Both proton and hyperpolarized helium images have been acquired from test objects using the same four channel radiofrequency coil array, operating at a frequency of 450 kHz, by adjusting the magnetic field. The system is now in final preparation for studies of neonatal lungs in the Neonatal Intensive Care Unit. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 31B: 209–217, 2007