Design of a Quadrature 1H/31P Coil Using Bent Dipole Antenna and Four-Channel Loop at 3T MRI

Abstract

MRI using nuclei other than protons is of clinical interest due to the important role of these nuclei in cellular processes. Phosphorous-31 (P), for example, plays an important role in energy metabolism. However, measurement of P can be challenging, as the receive signal is weak compared with that of proton (H). Consequently, it is often necessary to integrate H elements for localizations and B shimming in RF coils intended for P measurements. Good decoupling between theH and the P elements is therefore essential. In this paper, bent dipole antennas tuned toH were integrated with a four channel P loop coil array, in a manner providing strong geometric decoupling between dipoles and loops. As the physical length of a resonant dipole antenna is too long at 3T, the dipole antennas were bent around the load. The loss ofP elements due to the presence of the dipole antennas was evaluated by measuring scattering parameters and comparing the SNR of P spectra with and without the presence of the dipole antennas. The performance of the bent dipole antenna was evaluated by simulation and sensitivity measurement. The Q-factors and the SNR of the four-loop array were reduced by less than 5% when the bent dipole antennas were introduced. The measured sensitivity of the bent dipole was higher (15%) than that of dual-tuned birdcage. The combined bent dipole and loop array is therefore a promising design forH/P applications at 3T.

MR‐Nucleomics: The study of pathological cellular processes with multinuclear magnetic resonance spectroscopy and imaging in vivo

“…128,129 Bent dipole antennas tuned to 1 H were integrated with a four-channel 31 P loop coil array, providing 15% higher signal than that of a dual-tuned birdcage. 130 For a 31 P study of the brain at 7 T, an eight-channel multitransmit proton head coil was embedded with a 31 P resonator for transmission, and a seven-channel array coil was designed for 31 P acquisition. 131 A recent study demonstrated the feasibility of using an endorectal 13 C coil for the acquisition of both the hyperpolarized 13 C signal and the 23 Na signal, made possible by the relatively limited resonance difference between the two nuclei at 3.0 T. 132 Despite the expected SNR degradation, this method yielded no significant difference in sodium concentration quantification compared with a dedicated 23 Na coil, potentially implying a cost-efficient solution to clinical translation for MN MRI.…”

“…For instance, a double‐tuned multichannel bilateral RF coil for 1 H/ 23 Na was built to provide sufficient SNR in less than 10 min in breast sodium imaging, while a double‐tuned nested birdcage coil was also reported to detect sodium signal over a large homogeneous volume 128,129 . Bent dipole antennas tuned to 1 H were integrated with a four‐channel 31 P loop coil array, providing 15% higher signal than that of a dual‐tuned birdcage 130 . For a 31 P study of the brain at 7 T, an eight‐channel multitransmit proton head coil was embedded with a 31 P resonator for transmission, and a seven‐channel array coil was designed for 31 P acquisition 131 .…”

A Review of Non-1H RF Receive Arrays in Magnetic Resonance Imaging and Spectroscopy

“…If array coil operation at both frequencies is desired, geometric decoupling [4] , [21] , [22] , [52] can be used to minimize mutual inductance between array elements. This strategy is especially convenient for high-field designs utilizing the complimentary field patterns of dipole and loop elements to innately decouple the two element types [53] , [54] and has been used for both increasing 1 H sensitivity [55] – [58] and as a method of forming double-tuned arrays [59] , [60] .…”

A Monopole and Dipole Hybrid Antenna Array for Human Brain Imaging at 10.5 Tesla

“…For optimal use of dipoles in whole brain imaging and to achieve higher B 1 + efficiency (defined as the B 1 amplitude per unit square root of total power), classical straight dipole antenna arrays can be modified to better follow the contours and shape of the human head. To achieve this, bent/folded dipole antenna arrays have been previously presented and evaluated [ 17 ]–[ 20 ]. In a typical bent dipole antenna array design, one leg of the individual dipole antenna element is bent inwards which effectively results in higher conductor density at the top of the brain [ Fig.…”