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