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

Abstract

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

Initial feasibility and challenges of hyperpolarized 129Xe MRI in neonates with bronchopulmonary dysplasia

“…A home-built 129 Xe/ 1 H switched-frequency high-pass birdcage coil (Figure 1B) was used to image both nuclei rapidly without altering the subject's position. 22,23 In between 1 H and 129 Xe scans, the transmit/receive frequency of the coil was switched by adding/removing capacitor banks via pushing/pulling of mechanical rods on the coil and switching the BNC cables from one TR switch to the other. This was done while the subject was in the scanner bore and took between 30 s and 1 min.…”

“…MRI was performed on a multi‐nuclear 1.5T neonatal‐sized MRI system 20,21 (originally an orthopedic scanner from ONI Medical Systems; currently GE Healthcare HDx) (Figure 1A). A home‐built 129 Xe/ 1 H switched‐frequency high‐pass birdcage coil (Figure 1B) was used to image both nuclei rapidly without altering the subject's position 22,23 . In between 1 H and 129 Xe scans, the transmit/receive frequency of the coil was switched by adding/removing capacitor banks via pushing/pulling of mechanical rods on the coil and switching the BNC cables from one TR switch to the other.…”

Scalable and modular 8‐channel transmit and 8‐channel flexible receive coil array for 19F MRI of large animals

“…Various multinuclear coils have been designed for preclinical studies on small animals 7 . A double‐tuned birdcage coil can be realized using either a trap circuit 8,9 or a PIN diode, 10 and mechanical actuators were proposed to avoid losses from the PIN diode 11 . To construct multinuclear birdcage coils, alternating rungs were individually tuned to two different frequencies, 12,13 or the end rings were designed as four‐ring birdcage coils 14 .…”

“…7 A double-tuned birdcage coil can be realized using either a trap circuit 8,9 or a PIN diode, 10 and mechanical actuators were proposed to avoid losses from the PIN diode. 11 To construct multinuclear birdcage coils, alternating rungs were individually tuned to two different frequencies, 12,13 or the end rings were designed as four-ring birdcage coils. 14 However, double-tuned birdcage coils are difficult to realize when the two resonance frequencies are very close.…”