A novel switched frequency 3He/1H high-pass birdcage coil for imaging at 1.5 tesla

The ability to produce hyperpolarized noble gases ³He and ¹²⁹Xe has opened up exciting possibilities for pulmonary magnetic resonance imaging (MRI). We have recently built a hyperpolarizer with the goal of using hyperpolarized ³He gas for MRI in neonatal lungs in a dedicated small foot-print 1.5 T MR scanner developed at our institution and sited in our Neonatal Intensive Care Unit. Although hyperpolarized gas imaging can provide unique insights into lung ventilation, acinar microstructure, and gas-exchange dynamics, there is an undiminished need for ¹H MRI of the lung to provide anatomic references, B₁ and B₀ maps, and ¹H images of lung parenchyma. To address this need, we designed, built and tested a novel radiofrequency body coil that provides a high-pass birdcage coil that can be used for both ³He and ¹H frequencies (48.65 and 63.86 MHz, respectively, at 1.5 T). To switch between frequencies, the birdcage coil has a large mechanical actuator that simultaneously changes the capacitance between every rung of the birdcage. Advantages of this coil design include: 1) quadrature excitation and reception at the ³He and ¹H frequencies, 2) identical B₁ field maps for ³He and ¹H imaging, 3) excellent signal-to-noise ratio and B₁ homogeneity at both frequencies, and 4) rapid (10–20 s) switching times between ³He and ¹H operation. This report provides details of the coil's design and fabrication. Images of hyperpolarized ³He and ¹H in phantoms and ex vivo rabbit lungs demonstrate the image quality obtained with the coil. © 2015 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 45B: 174–182, 2015